United States ;
Environmental Protection
Agency
Office of Solid Waste
and Emergency Response
(5102G)
EPA542-B-97-007
September 1997
-------
-------
INNOVATIVE SITE
REMEDIATION TECHNOLOGY:
DESIGN AND APPLICATION
STABILIZATION/
SOLIDIFICATION
One of a Seven-Volume Series
Prepared by WASTECH®, a multiorganization cooperative project managed
by the American Academy of Environmental Engineers® with grant assistance
from the U.S. Environmental Protection Agency, the U.S. Department of
Defense, and the U.S. Department of Energy.
The following organizations participated in the preparation and review of
this volume:
Air & Waste Management
Association
P.O. Box 2861
Pittsburgh, PA 15230
American Academy of
Environmental Engineers®
130 Holiday Court, Suite 100
Annapolis, MD 21401
American Institute of
Chemical Engineers
345 East 47th Street
New York, NY 10017
IASCEI
y«y American Society of
>^>. Civil Engineers
345 East 47th Street
New York, NY 10017
W American Society of
J® Mechanical Engineers
345 East 47th Street
New York, NY 10017
Hazardous Waste Action
Coalition
1015 15th Street, N.W., Suite 802
Washington, D.C. 20005
> Soil Science Society
of America
677 South Segoe Road
Madison, WI 53711 .
•_ Water Environment
' Federation
601 Wythe Street
Alexandria, VA 22314
Monograph Principal Authors:
Paul D. Ealb, Chair Bhavesh R. Patel
Jesse R. Conner Joseph M. Perez, Jr.
John L. Mayberry, P.E. Russell L. Treat
Series Editor
William C. Anderson, P.E., DEE
-------
Library of Congress Cataloging in Publication Data
Innovative site remediation technology: design and application.
p. cm. •
"Principle authors: Leo Weitzman, Irvin A. Jefcoat, Byurig R. Kim"—V.2, p. iii.
"Prepared by WASTECH."
Includes bibliographic references.
Contents: ~[2] Chemical treatment ' • .
1. Soil remediation—Technological innovations. 2. Hazardous waste site remediation--
Technological innovations. I. Weitzman, Leo. II. Jefcoat, Irvin A. (Iryin Ally) HI. Kim, B.R.
IV. WASTECH (Project)
TD878.I55 1997
628.5'5--dc21 97-14812 :
CIP '
ISBN 1-883767-17-2 (v. 1) ISBN 1-883767-21-0 (v. 5)
ISBN l-883767-18rO (v. 2) ISBN 1-883767-22-9 (v. 6)
ISBN 1-883767-19-9 (v. 3) ISBN 1-883767-23-7 (v. 7)
ISBN 1-883767-20-2 (v. 4)
Copyright 1997 by American Academy of Environmental Engineers. All Rights Reserved.
Printed in the United States of America. Except as permitted under the United States
Copyright Act of 1976, no part of this publication may be reproduced or distributed in any
form or means, or stored in a database or retrieval system, without the prior written
permission of me American Academy of Environmental Engineers. ,
.The material presented in this publication has been prepared in accordance with
generally recognized engineering .principles and practices and is for general informa-
tion only. This information should not be used without first securing competent advice
with respect to its suitability for any general or specific application.
The contents of this publication are not intended to be and should not be construed as a
standard of the American Academy of Environmental Engineers or of any of the associated
organizations mentioned in this publication and are not intended for use as a reference in
purchase specifications, contracts, regulations, statutes, or any other legal document.
No reference made in this publication to any specific method, product, process, or
service constitutes or implies an endorsement, recommendation, or warranty thereof by the
American Academy of Environmental Engineers or any such associated organization.
Neither the American Academy of Environmental Engineers nor any of such associated
organizations or authors makes any representation or warranty of any kind, whether
express or implied, concerning the accuracy, suitability, or utility of any information
published herein and neither the American Academy of Environmental Engineers nor any
such associated organization or author shall be responsible for any errors, omissions, or
damages arising out of use of this information.
Printed in the United States of America.
WASTECH and the American Academy of Environmental Engineers are trademarks of the American
Academy of Environmental Engineers registered with the U.S. Patent and Trademark Office.
Cover design by William C. Anderson. Cover photos depict remediation of the Scovill Brass Factory,
Waterbury, Connecticut, recipient of the 1997 Excellence in Environmental Engineering Grand Prize
award for Operations/Management.
-------
CONTRIBUTORS
PRINCIPAL AUTHORS
Paul D. Kalb, Task Group Chair
Brookhaven National Laboratory
Jesse R. Conner Bhavesh R. Patel
Conner Technologies, Inc. U.S. Department of Energy
John L. Mayberry, P.E. Joseph M. Perez, Jr.
SAIC . Battelle Pacific Northwest
Russell L. Treat
MACTEC
The authors gratefully acknowledge David Eaton and Margaret Knecht,
Lockheed Martin Idaho Technologies, for their assistance in reviewing and editing
sections in this monograph on regulatory issues.
REVIEWERS
The panel that reviewed the monograph under the auspices of the Project
Steering Committee was composed of:
Joseph F. Lagnese, Jr., P.E., DEE, Chair Roger Olsen, Ph.D.
Allison Park, Pennsylvania Camp Dresser and McKee
Ed Barth, P.E. . TimOppelt
National Risk Management National Risk Management
• Research Laboratory Research Laboratory
USEPA ' _ USEPA
T. Michael Gilliam, P.E. William C. Webster
Oak Ridge National Laboratory Webster and Associates
-------
STEERING COMMITTEE
This monograph was prepared under the supervision of the WASTECH® Steering
Committee. The manuscript for the monograph was written by a task group of experts
in chemical treatment and was, in turn, subjected to two peer reviews. One review was
conducted under the auspices of the Steering Committee and the second by professional
and technical organizations having substantial interest in the subject.
Frederick G. Pohland, Ph.D., P.E., DEE Chair
Weidlein Professor of Environmental
Engineering . ,
University of Pittsburgh
Richard A. Conway, P.E., DEE, Vice Chair
Senior Corporate Fellow
Union Carbide Corporation
William C. Anderson, P.E., DEE
Project Manager
Executive Director -
American Academy of Environmental
Engineers
Colonel Frederick Boecher
U.S. Army Environmental Center
• Representing American Society of Civil
Engineers
Clyde J. Dial, P.E., DEE
Manager, Cincinnati Office
SAIC
Representing American Academy of
. Environmental Engineers
Timothy B. Holbrook, P.E.
Engineering Manager
Camp Dresser & McKee, Incorporated
Representing Air & Waste Management
Association
Joseph F. Lagnese, Jr., P.E., DEE
Private Consultant
Representing Water Environment Federation
Peter. B. Lederman, Ph.D., P.E., DEE, P.P.'
Center for Env. Engineering & Science
New Jersey Institute of Technology
Representing American Institute of Chemical
Engineers
George O'Connor, Ph.D.
University of Florida
Representing Soil Science Society of America
George Pierce, Ph.D.
Manager, Bioremediation Technology Dev. •
American Cyanamid Company
Representing the Society of Industrial
Microbiology
Peter W. Tunnicliffe, P.E., DEE
Senior Vice President
Camp Dresser & McKee, Incorporated'
Representing Hazardous Waste Action
Coalition ;
Charles O. Velzy, P.E., DEE
Private Consultant
Representing, American Society of
Mechanical Engineers
Calvin H. Ward, Ph.D.
Foyt Family Chair of Engineering
Rice University
At-large representative
Walter J. Weber, Jr., Ph.D.i P.E., DEE
Gordon Fair and Earnest Boyce Distinguished
Professor •
University of Michigan
Representing Hazardous Waste Research Centers
FEDERAL REPRESENTATION
Walter W. Kovalick, Jr., Ph.D.
Director, Technology Innovation Office
•U.S. Environmental Protection Agency
George Kamp
Cape Martin Energy Systems
U.S. Department of Energy
Jeffrey Marqusee
Office of the Under Secretary of Defense
U.S: Department of Defense
Timothy Oppelt
Director, Risk Reductipn Engineering
Laboratory
U.S. Environmental Protection Agency
iv
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REVIEWING ORGANIZATIONS
The following organizations contributed to the monograph's review and acceptance
by the professional community. The review process employed by each organiza-
tion is described in its acceptance statement. Individual reviewers are, or are not,
listed according to the instructions of each organization.
Air & Waste Management
Association
The Air & Waste Management
Association is a nonprofit technical and
educational organization with more than
14,000 members in more than fifty
countries. Founded in 1907, the
Association provides a neutral forum
where all viewpoints of an environmen-
tal management issue (technical,
scientific, economic, social, political,
and public health) receive equal
consideration.'
Qualified reviewers were recruited
from the-Waste Group of the Technical
Council. It was determined that the
monograph is technically sound and
publication is endorsed.
The reviewers were:
Terry Alexander, P.E., DEE, CIH
University of Michigan
Tim Holbrook, P.E., DEE
• Camp Dresser & McKee
Charles Wilk .
Portland Cement Association
American Institute of
. Chemical Engineers
The Environmental Division of the
American Institute of Chemical Engineers.
has enlisted its members to review the
monograph. Based on that review the .
Environmental Division endorses the
publication of the monograph.
American Society of Civil
Engineers
The American Society of Civil .
Engineers, established in 1852, is the
premier civil engineering association in
the world with 124,000 members.
Qualified reviewers were recruited from
its Environmental Engineering Division.
ASCE has reviewed this manual and
believes that significant information of
value is provided. Many of the issues
.addressed, and the resulting conclu-
sions, have been evaluated based on
satisfying current regulatory require- .
ments. However, the long-term stability
of solidified soils containing high levels
of organics, and potential limitations
and deficiencies of current, testing
methods, must be evaluated in more
detail as these technologies are imple-
mented and monitored.
The reviewers included:
Richard Reis, P.E.
Fluor Daniel GTI
Seattle, WA
G. Fred Lee, Ph.D., P.E., DEE
G. Fred Lee & Associates
El Macero, CA
American Society of
Mechanical Engineers
Founded in 1880, the American
Society of Mechanical Engineers
(ASME) is a nonprofit educational
and technical organization, having at
the date of publication of this docu-
ment approximately 116,400 members,
including 19,200 students. Members
-------
work in industry, government,
academia, and consulting. The Society
has thirty-seven technical divisions,
four institutes, and three interdiscipli-
nary programs which conduct more than
thirty national and international
conferences each year.
This document was reviewed by
volunteer members of the Research
Committee on Industrial and Municipal
Waste, each with technical expertise
and interest in the field covered by the
document. Although, as indicated on
the reverse of the tide page of this
document, neither ASME nor any of its
Divisions of Committees endorses or •
recommends, or makes'any representa-
tion or warranty with respect to, this
document, those Divisions and Commit-
tees which conducted a review believe,
based upon such review, that this
document and findings expressed are
technically sound.
Hazardous Waste Action
Coalition
The Hazardous Waste Action
. Coalition (HWAC) is the premier
business trade group serving and
representing the leading engineering
and science firms in the environmental
management and remediation industry.
HWAC's mission is to serve and
promote the interests of engineering and
science firms practicing in multi-media
environment management and
remediation. Qualified reviewers were
recruited from HWAC's Technical
Practices Committee. HWAC is
pleased to endorse the monograph as
technically sound.
The lead reviewer was:
James D. Knauss, Ph.D.
President, Shield Environmental
Lexington, KY
Soil Science Society of
America
The Soil Science Society of America,
headquartered in Madison, Wisconsin,
is home to more than 5,300 profession-
als dedicated to the advancement of soil
science. Established in 1936, SSSA has
members in more than 100 countries.
The Society is composed of eleven
divisions, covering subjects from the
basic sciences of physics and chemistry
through soils in relation to crop
production, environmental quality,
ecosystem sustainability, waste
management and recycling,
bioremediation, and wise land use.
Members of SSSA have reviewed the
monograph and have determined that it
is acceptable for publication.
The lead reviewer was:
Chet Francis
Oak Ridge National Laboratory
Water Environment
Federation
The Water Environment Federa-
tion is a nonprofit, educational „
organization composed of member
and affiliated associations throughput
the world. Since 1928, the Federation
has irepresented water quality
specialists including engineers,
scientists, government officials,
industrial and municipal treatment
plant operators, chemists, students,
academic and equipment manufac-
turers, and distributors.
Qualified reviewers were
recruited from the Federation's
Hazardous Wastes Committee and
from the general membership. It has
been determined that the document is
technically sound and publication is
endorsed.
The lead reviewer was:
Robert C. Williams, P.E., DEE
vi
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ACKNOWLEDGMENTS
The WASTEOH® project was conducted under a cooperative agreement
between the American Academy of Environmental Engineers® and the Office
of Solid Waste and Emergency Response, U.S. Environmental Protection
Agency. The substantial assistance of the staff of the Technology Innovation
Office was invaluable.
Financial support was provided by the ~G.S. Environmental Protection
Agency, Department of Defense, Department of Energy, and the American
Academy of Environmental Engineers®,
This multiprganization effort involving a large number of diverse profes-
sionals and substantial effort in coordinating meetings, facilitating communica-
tions, and editing and preparing multiple drafts was made possible by a
dedicated staff provided by the American Academy of Environmental Engi-
neers® consisting of:
William C. Anderson, P.E., DEE
Project Manager & Editor
John M. Buterbaugh
Assistant Project Manager & Managing Editor
Karen Tiemens.
Editor
Catherine L. Schultz
Yolanda Y. Moulden
Project Staff Production
• . ' • J. Sammi Olmo
. I. Patricia Violette
Project Staff Assistants
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TABLE OF CONTENTS
Contributors iii
Acknowledgments yii
List of Tables xvii
Ust of Figures " xix
1.0 INTRODUCTION 1.1
1.1 Stabilization/Solidification 1.1
1.2 Development of the Monograph 1.2
1.2.1 Background 1.2
1.2.2 Process 1.4
1.3 Purpose 1.4
1.4 Objectives .1.5
1.5 Scope 1.5
1.6 Limitations 1.6
1.7 Organization 1.6
2.0 APPLICATION CONCEPTS 2.1
2.1 Aqueous Stabilization/Solidification. 2.3
2.1.1 Scientific Principles 2.3
2.1.1.1 Stabilization 2.3
2.1.1.2 Cementitious Stabilization/Solidification 2.7
2.1.1.3 In Situ Stabilization and Stabilization/Solidification 2.9
2.1.2 Potential Applications 2.12
2.1.2.1 Stabilization . 2.12
2.1.2.2 Cementitious Stabilization/Solidification 2.12
2.1.2.3 In Situ Stabilization and
.Stabilization/Solidification - 2.14
2.1.3 Treatment Trains 2.14
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Table of Contents
2.2 Polymer Stabilization/Solidification
2.2.1 Scientific Principles
2.2.1.1 Polyethylene
2.2.1.2 Sulfur Polymer Cement
2.2.1.3 Thermosetting Polymers
2.2.2 Potential Applications
2.2.3 Treatment Trains
2.3 Vitrification
2.3.1 Scientific Principles
2.3.1.1 Ex-Situ Melters
2.3.1.2 In Situ Vitrification
2.3.2 Potential Applications
2.3.2.1 Ex-Situ Melters
2.3.2.2 In Situ Vitrification
2.3.3 Treatment Trains
i . .
2.3.3.1 Ex-Situ Melters
2.3.3.2 In Situ Vitrification
3.0 DESIGN DEVELOPMENT
. 3.1 Aqueous Stabilization/Solidification
3.1.1 Remediation Goals
3.1.1.1 Stabilization
3.1.1.2 Cementitious Solidification/Stabilization
3.1.1.3 In Situ Stabilization and
Stabilization/Solidification
3.1.2 Design Basis
3.1.3 Design and Equipment Selection
3.1.4 Process Modifications
3.1.5 Pretreatment Processes
3.1.6 Posttreatment Processes
I
3.1.7 Process Instrumentation and Controls
2.15
1 2.15
2.16
2.17
2.18
2.19
2.22
2.23
2.23
2.23
2.25
2.28
2.31
2.36
2.36
2.38
3.1
3.4
3.4
"3.4
3.9
3.13
3.13
3.16
3.16
3,17
3.18
3.18
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Table of Contents
3.1.8 Safety Issues 3.19
3.1.9 Specification Development 3.19
3.1.10 CostData 3.20
, 3.1,11 Design Validation 3.23
3.1.12 Permitting Requirements 3.23
3.1.13 Performance Measures 3.24
3.1.14 Design Checklist 3.24
3.1.14.lEx-Situ Aqueous Stabilization/Solidification 3.24
3.1.14.2 In Situ Aqueous Stabilization/Solidification 3.25
3.2 Polymer Stabilization/Solidification 3.26
3.2.1 Remediation Goals 3.26
3.2.2 Design Basis • 3.28
3.2.2.1 Polyethylene Encapsulation 3.28
3.2.2.2 Sulfur Polymer Cement Encapsulation 3.29
3.2.2.3 In Situ Polymer.Stabih'zation/Solidification 3.30
3.2.3 Design and Equipment Selection 3.30
3.2.3.1 Polyethylene Encapsulation 3.31
3.2.3.2 Sulfur Polymer Cement Encapsulation 3.45
3.2.3.3 In Situ Polymer Stabilization/Solidification - 3,46
3.2.4 Process Modifications • 3,50
3.2.4.1 Polyethylene Encapsulation 3.50
1 3.2.4.2 Sulfur Polymer Cement Encapsulation 3..51
3.2:4.3 In Situ Polymer Stabilization/Solidification 3..51
3.2.5 Pretreatment Processes 3,52
3.2.5.1 Polyethylene Encapsulation 3.52
3.2.5.2 Sulfur Polymer Cement Encapsulation 3.54
3.2.6 Posttreatment Processes 3.55
3.2.7 Process Instrumentation and Controls 3.55
3.2.7.1 Polyethylene Encapsulation . 3.55
3.2.7.2 Sulfur Polymer Cement Encapsulation 3.57
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Table pf Contents
3.2.7.3 In Situ Polymer Stabilization/Solidification 3.58
3.2.8 Safety Issues 3.58
3.2.8.1 Polyethylene Encapsulation 3.58
3.2.8.2 Sulfur Polymer Cement Encapsulation 3.58
I ;
3.2.8.3 In Situ Polymer Stabilization/Solidification 3.59
3.2.9 Specification Development! . 3.59
3.2.9.1 Polyethylene Encapsulation 3.59
3.2.9.2 Sulfur Polymer Cement Encapsulation 3.60
3.2:9.3 In Situ Polymer Stabilization/Solidification 3,60
3.2.10 Cost Data , 3.61
3.2.10.1 Polyethylene Encapsulation • 3.61
3.2.10.2 Sulfur Polymer Cement Encapsulation 3.62
,3.2.10.3 In Situ Polymer Stabilization/Solidification 3.62
3.2.11 Design Validation 3,62
•
3.2.12 Permitting Requirements 3.63
3.2.13 Performance Measures 3.64
3.2.14 Design Checklist 3.70
3.2.14.1 Ex-Situ Polymer Stabilization/Solidification 3.70
3.2.14.2 In Situ Polymer Stabilization/Solidification 3.70
3.3 Vitrification ' 3.71
' !
3.3.1 Remediation Goals 3.71
3.3.1.1 Ex-Situ Melters 3.71
3.3.1.2 In Situ Vitrification • 3.72
3.3.2 Design Basis 3.74
3.3.2.1 Ex-Situ Melters 3.74
3.3.2.2 In Situ Vitrification 3.81
3.3.3 Design and Equipment Selection 3.82
• 3.3.3.1 Ex-Situ Melters 3.82
3.3.3.2 In Situ Vitrification 3.86
3.3.4 Process Modifications 3.88
xii
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Table of Contents
3.3.4.1 Ex-Situ Melters . 3.88
3.3.4.2 In Situ Vitrification 3.89
3.3r5 Pretreatment Processes 3.90
3.3.5.1 Ex-Situ Melters 3.90
3.3.5.2 In Situ Vitrification 3.92
3.3.6 Posttreatment Processes 3.93
33.6.1 Ex-Situ Melters 3.93
3.3.6.2 In Situ Vitrification " 3.95
3.3.7 Process Instrumentation and Controls f 3.96
3.3.7.1 Ex-Situ Melters 3.96
3.3.7.2 In Situ Vitrification 3.97
3.3.8 Safety Issues , 3.98
3.3.8.1 Ex-Situ Melters . 3.98
3.3.8.2 In Situ Vitrification • 3.99
3.3.9 Specification Development" . 3.99
3.3.9.1 Ex-Situ Melters . 3.99
3.3.9.2 In Situ Vitrification 3.100
3.3.10 Cost Data . 3.100
3.3.10.1 Ex-Situ Melters 3.100
3.3.10.2 In Situ Vitrification 3.101
3.3.11 Design Validation 3.103
3.3.11.1 Ex-Situ Melters . , . 3.103
,3.3.11.2 In Situ Vitrification 3.103
3.3.12 Permitting Requirements ' 3.104
3.3.12.1 Ex-Situ Melters . 3.104
3.3.12.2 In Situ Vitrification . 3.104
3.3.13 Performance Measures 3.105
3.3.13.1 Ex-Situ Melters 3.105
3.3.13.2 In Situ Vitrification 3.105
3.3.14 Design Checklist 3.106
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Table of Contents
3.3.14.1 Ex-Situ Melters 3.106
3.3.14.2 In Situ Vitrification 3.107
4.0 IMPLEMENTATION AND OPERATION 4.1
4.1 Aqueous Stabilization/Solidification 4-1
4.1.1 Implementation 4.1
4.1.2 Start-up Procedures ^-2
4.1.3 Operations Practices 4.2
4.1.4 Operations Monitoring 4.2
4.1.5 Quality Assurance/Quality Control 4.4
4.2 Polymer Stabilization/Solidification 4.5
4.2.1 Implementation 4.5
4.2.2 Startup Procedures 4.6
4.2.3 Operations Practices ^ 4.8
4.2.3.1 Polyethylene Encapsulation 4.8
4.2.3.2 Sulfur Polymer Cement Encapsulation 4.9
4.2.3.3 In Situ Polymer Stabilization/Solidification 4.10
4.2.4 Operations Monitoring 4.10
4,2.5 Quality Assurance/Quality Control 4.11
4.3 Vitrification 4.12
i
4.3.1 Implementation 4.12
4.3.1.1 Ex-Situ Melters |4.12
4.3.1.2 In Situ Vitrification 4.14
! !
4.3.2 Start-up Procedures 4.14
4.3.2.1 Ex-Situ Melters 4.14
4.3.2.2 In Situ Vitrification 4.18
4.3.3 Operation Practices 4.18
4.3.3.1 Ex-Situ Melters 4.18
4.3.3.2 In Situ Vitrification 4.22
; 4.3.4 Operations Monitoring 4.23
4.3.4.1 Ex-Situ Melters , • 4.23
xiv
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. Table of Contents
4.3.4.2 In Situ Vitrification 4.23
4.3.5 Quality Assurance/Quality Control 4.24
• 4.3.5.1 Ex-Situ Melters 4.24
4.3.5.2 In Situ Vitrification 4.24
5.0 CASE HISTORIES 5.1
5.1 Aqueous Stabilization/Solidification 5.1
5,2 Polymer Stabilization/Solidification . 5.2
5.2.1 Polyethylene Microencapsulation Using Single-Screw
Extrusion . , 5.2
5.2.2 Polyethylene Macroencapsulation 5.3
5.2.3 Sulfur Polymer Encapsulation 5.7
5.3 Vitrification ' 5.7
5.3.1 Ex-Situ Melters 5.7
5.3.2 In Situ Vitrification 5.12
APPENDIX A: List of References A.1
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LIST OF TABLES
Table Title Page
2.1 Approximate Solubility of Elements in Silicate Glasses 2.28
2.2 Hazardous Organic Chemical Destruction and Removal
Effectiveness Using In Situ Vitrification ;. 2.34
3.1 Immobilization of Organic Constituents Using Rubber
Paniculate — Volatile Organics 3.5
3.2 Immobilization of Organic Constituents Using Rubber
Paniculate — Semivolatile Organics" 3.6
3.3 Immobilization of Organic Constituents Using
• Modified Rubber Paniculate, KAX-100™ — Volatile and
Semivolatile Organics 3.7
3:4 Organic Leaching from ProFix-Treated Waste 3.10
3.5 Metal Leaching from ProFix-Treated Waste .3.10
3.6 Effect of Various Additives on Technetium 3.12
3.7 Leaching of Treated, Bichromate-Contaminated Soil 3.14
3.8 Data Input and Considerations for S/S Process Design 3.15
3.9 Reagent Costs . . 3.20
3.10 A Typical Example of Aqueous, Ex-Situ S/S Remediation
Costs in 1990 with On-Site Landfill 3.21
3.11 Fifth Level Work Breakdown Structure Cost Elements for
Aqueous S/S 3.22
3.12 Typical Capital Cost Data and Estimated Energy
Requirements for Production-Scale Polyethylene
Encapsulation Process Equipment 3.61
3.13 Typical Durability and Leaching Data for Polyethylene
Microencapsulated Final Waste Forms Containing 60%
Simulated Nitrate Salt Waste by Weight 3.65
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List 01
Table . liflg
3.14 Typical ANS 16.1 Leach Test Data as a Function of
Waste Loading for Microencapsulated Final Waste
Forms Containing Simulated Nitrate Salt Waste 3.65
3.15 Compressive Strength Data for Sulfur Polymer/Ash Waste
Forms Following NRC Performance Testing 3.66
! ' I
3.16 ANS 16.1 Leach Data for Sulfur. Polymer Final Waste Forms
Containing Incinerator Ash ' 3.66
3.17 Typical Toxicity Characteristic Leaching Procedure Data for
Polyethylene Microencapsulatecl Waste . 3.68
3.18 US EPA'sTCLP Performance 3.69
3.19 Properties of Common Melter Refractory Materials 3.76
3.20 Summary of ISV Costs 3.102
4.1 Summary of Standard Methods and Procedures 4.3
4.2 Typical Aqueous S/S> Performance Benchmarks 4.4
4.3 •". Performance Standards and Performance Achieved in an
Actual Aqueous S/S Project 4.5
| . .1
5.1 Production-Scale Process Data for Polyethylene
Microencapsulation of Nitrate Salt Wastes Using a
Single-Screw Extrusion Process 5.5
5.2 Phase I Test Matrices 5.10
5.3 Phase II Test Matrices 5.11
5.4 Evaluation Criteria for the Gepsafe In Situ Vitrification
Process ' 5.14
xviii
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LIST OF FIGURES
s !
Figure . Title Page
2.1 Schematic Diagram of MecTool™ for Solidification and
Stabilization of Contaminated Soils/Sludges • 2.10
2.2 The MecTool™ System in Operation 2.11
2.3 Ex-Situ Vitrification Block-Flow Diagram 2.37
2.4 In Situ Vitrification System 2.39
3.1 Comparison of TCA Results for Carbon vs. Rubber
Particulate 3.8
3.2 . Comparison of TCA% Reduction for Carbon vs. Rubber
Particulate .3.9
3.3 Schematic of Typical Plastics Extruder 3.32
3.4 Various Screw Types Available for Single-Screw Extruders 3.35
3.5 Types of Screw Configurations for Twin-Screw Extruders 3.37
3.6 Schematic of a Typical Thermokinetic Mixer • 3.40
3.7 Photograph of a Typical Bench-Scale Sample of Lead Wool
Macroencapsulated in Polyethylene 3.43
3.8 Process-Flow Diagram for Sulfur Polymer Cement 3.45
3.9 Holo-Flite Mixer " 3.47
3.10 Porcupine Processer 3.48
.3.11 Porcupine Processer Paddles 3.49
3.12 " Subsurface Barrier Installation by Permeation Grouting 3.49
3.13 Conventional Column Jet Grouting 3.50
3.14 Flow Diagram for RVR-200 Vacuum Dryer 3.53
3.15 Particle-Size Distribution of Nitrate Salt Surrogate
Following Pretreatment 3.54
-------
LIST or figures
Figure Title
3.16 Transient Infrared Spectroscopy (TIRS) On-Line Monitoring
' System Developed by Ames Laboratory for the Polyethylene
Encapsulation Process 3.56
3.17 TIRS Monitor Plotted vs. Actual Waste Loading 3.57
' . ' ' ' ' !
3.18 Compressive Strength of Polymer Soil Grouts After
Resistance Testing 3.67
3.19 Cogema Induction Melter Schematic 3.79.
3.20 Stir-Melter, Inc. Agitated Melter Schematic 3.84
3.21 Schematic Layout of Vortec Corporation's Cyclone Melting
System 3.85
5.1 Schematic Diagram of the Integrated Polyethylene
Encapsulation Process 5.3
5.2 Full-Scale Polyethylene Encapsulation Facility 5.4
! I •
5.3 Single-Screw Extruder for Polyethylene Macroencapsulation 5.6
5.4 Macroencapsulated Waste Form 5.6
5.5 B&W Pilot Cyclone Test Facility 5.9
xx
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Chapter 1
INTRODUCTION
This monograph, covering the design, applications, and implementation
of Stabilization/Solidification, is one of a series of seven on innovative site
and waste remediation technologies. This series of seven monographs by the
American Academy of Environmental Engineers® was preceded by eight
volumes published in .1994 and 1995 covering the description, evaluation,
and limitations of the processes. The entire project is the culmination of a
multiorganization effort involving more than 100 experts. It provides the
experienced, practicing professional guidance on the innovative processes
considered ready for full-scale application. Other monographs in this design
and application series and the companion series address bioremediation;
chemical treatment; liquid extraction: soil washing, soil flushing, and sol-
vent/chemical extraction; thermal desorption; thermal destruction; and vapor
extraction and air sparging.
7.7 Stabilization/Solidification
Stabilization and Solidification are generic names applied to a. wide range
of discrete technologies. These technologies, i.e., Stabilization and Solidifi-
cation, are closely related in that both use chemical, physical, and/or thermal
processes to reduce potential adverse impacts on the environment from the
disposal of radioactive, hazardous, and mixed waste. But, they are distinct
technologies.
Stabilization refers to techniques that reduce the hazard potential of a
waste by converting the contaminants into less soluble, mobile, or toxic
forms. The physical nature and handling characteristics of the waste are not
necessarily changed by stabilization.
-------
Solidification refers to techniques that encapsulate the waste, forming a
solid material. The product of solidification, often known as the waste form,
may be a monolithic block, a clay-like material, a granular paniculate, or
some other physical form commonly considered "solid." Solidification as
applied to fine waste particles is termed microencapsulation and that which
applies to a large block or container of wastes is termed macroencapsulation.
Solidification can be accomplished by a chemical reaction between the waste
and solidifying reagents or by mechanical processes. Contaminant migra-
tion is often restricted by decreasing the surface area exposed to leaching
and/or by coating the wastes with low-permeability materials.
I • ., ...:''• I '
Each of the proven innovative technologies which are included within the
general categories of stabilization and solidification are discussed in this
monograph.
They can be grouped into three broad categories: (1) aqueous stabilization/
solidification, (2) polymer stabilization/solidification, and (3) vitrification.
7.2 Development of the Monograph
1.2.1 Background
Acting upon its commitment to develop innovative treatment technologies
for the remediation of hazardous waste sites and contaminated soils and
groundwater, the U.S. Environmental Protection Agency (US EPA) estab-
lished the Technology Innovation Office (TIO) in the Office of Solid Waste
and Emergency Response in March, 1990. The mission assigned TIO. was to
foster greater use of innovative technologies.
In October of that same year, TIO, in conjunction with the National
Advisory Council on Environmental Policy and Technology (NACEPT),
convened a workshop for representatives of consulting engineering
firms, professional societies, research organizations, and state agencies
involved in remediation. The workshop focused on defining the barriers
that were impeding the application of innovative technologies in site
remediation projects. One of the major impediments identified was the
1,2
-------
Chapter 1
lack of reliable data on the performance, design parameters, and costs of
innovative processes.
. The need for reliable information led TIO to approach the American
Academy of Environmental Engineers®. The Academy is a long-standing,
multidisciplinary environmental engineering professional society with
wide-ranging affiliations with the remediation and waste treatment profes-
sional communities. By June, 1991, an agreement in principle (later formal-
ized as a Cooperative Agreement) was reached providing for the Academy to
manage a proje'ct to develop monographs describing the state of available
innovative remediation technologies. Financial support was provided by the
US EPA, U.S. Department of Defense (DoD), U.S. Department of Energy
(DOE), and the Academy. The goal of both TIO and the Academy was to
develop monographs providing reliable data that would be broadly recog-
nized and accepted by the professional community, thereby eliminating or at
least minimizing this impediment to the use of innovative technologies.
The Academy's strategy for achieving the goal was founded on a
multiorganization effort, WASTECH® (pronounced Waste Tech), which
joined in partnership the Air and Waste Management Association, the Ameri-
can Institute of Chemical Engineers, the American Society of Civil Engi-
neers, the American Society of Mechanical Engineers, the Hazardous Waste
Action Coalition, the Society for Industrial Microbiology, the Soil Science
Society of America, and the Water Environment Federation, together with
the Academy, US EPA, DoD, and DOE. A Steering Committee composed of
highly'respected representatives of these organizations having expertise in
remediation technology formulated the specific project objectives and pro-
cess for developing the monographs (see page iv for a listing of Steering
Committee members). '
By the end of 1991, the Steering Committee had organized the Project.
Preparation of the initial monographs began in earnest in January, 1992, and
the original eight monographs were published during the period of Novem-
ber, 1993, through April, 1995. In Spring of 1995, based upon the receptiv-
ity of the industry and others of the original monographs, it was determined
that a companion set, emphazing the design and applications of the technolo-
gies, should be prepared as well. Task Groups were identified during the
latter months of 1995 and work commenced on this second series.
-------
iniroaucTion
.1.2.2 Process
For each of the series, the Steering Committee decided upon the technolo-
gies, or technological areas, to be covered by each monograph, the mono-
graphs' general scope, and the process for their development and appointed a
task group composed of five or more experts to write a manuscript for each
monograph. The task groups were appointed with a view to balancing the
interests of. the groups principally concerned with the application of innova-
tive site and waste remediation technologies — industry, consulting engi-
neers, research, academe, and government.
The Steering Committee called upon the task groups to examine and analyze
all pertinent information available, within the Project's financial and tune con-
straints. This included, but was not limited to, the comprehensive data on
remediation technologies compiled by US EPA, the store of information pos-
sessed by the task groups' members, that of other experts willing to voluntarily
contribute their knowledge, and information supplied by process vendors.
To develop broad, consensus-based monographs, the Steering Committee
prescribed a twofold peer review of the first drafts. One review was conducted
by the Steering Committee itself, employing panels consisting of two members
of the Committee supplemented by at least four other experts (See Reviewers,
page iii, for the panel that reviewed this monograph). Simultaneous with the
Steering Committee's review, each of the professional and technical organiza-
tions represented in the Project reviewed those monographs addressing tech-
nologies in which it has substantial interest-and competence.
Comments resulting from both reviews were considered by the Task
Group, appropriate adjustments were made, and a second draft published.
The second draft was accepted by the Steering Committee and participating
organizations. The statements of the organizations that formally reviewed
this monograph, are presented under Reviewing Organizations on page v.
1.3 Purpose
The purpose of this monograph is to further the use of innovative stabili-
zation/solidification site remediation and waste processing technologies,
that is, technologies not commonly applied, where their use can provide
1.4
-------
Chapter 1
better, more cost-effective performance than conventional methods. To this
end, the monograph documents the current state of stabilization/solidifica-.
tion technology. .-•'-.
7.4 Objectives
The monograph's principal objective is to furnish guidance for experi-
enced, practicing professionals and project managers charged with site
remediation responsibility. The monograph, and its companion monograph,
are intended, therefore, not to be prescriptive, but supportive. It is intended
to aid experienced professionals hi applying their judgment in deciding
whether and how to apply the technologies addressed under the particular
circumstances confronted.
In addition, the monograph is intended to inform regulatory agency per-
sonnel and the public about the conditions under which the processes it ad-
dresses are potentially applicable.
7.5 Scope
The monograph addresses innovative stabilization/solidification technolo-
gies that have been sufficiently developed so that they can be used in
full-scale applications. It addresses all aspects of the technologies for which
sufficient data were available to the Stabilization/Solidification Task Group
to briefly review the technologies and discuss their design and applications.
Actual case studies were reviewed and included, as appropriate.
The monograph's primary focus is site remediation and waste treatment
To the extent the information provided can also be applied elsewhere, it will
provide the profession and users this additional benefit.
Application of site remediation and waste treatment technology is
site-specific and involves consideration of a number of matters besides alter-
native technologies. Among them are the following that are addressed only
-------
Introduction
to the extent that they are essential to understand the applications and limita-
tions of the technologies described:
• • site investigations and assessments;
• planning, management, specifications, and procurement;
' • J
• cost-benefit analyses; .
• regulatory requirements; and
• community acceptance of the technology.
1.6 Limitations
r '
The information presented in this monograph has been prepared in accor-
dance with generally recognized engineering principles and practices and is
for general information only. This information should not be used without
first securing competent advice with respect to its suitability for any general
or specific application.
. Readers are cautioned that the information presented is that which was
generally available during the period when the monograph was prepared.
Development of innovative site remediation and waste treatment technolo-
gies is ongoing. Accordingly, postpublication information may amplify,
alter, or render obsolete the information about the processes addressed.
This monograph is not intended to be and should not be construed as a
standard of any of the organizations associated with the WASTECH® Project;
nor does reference in this publication to any specific method, product, pro-
cess, or service constitute or imply an endorsement, recommendation, or -
warranty thereof.
7.7 Organization
I !
This monograph and others in the series are organized under a similar
outline intended to facilitate cross reference among them and comparison of
the technologies they address.
1.6
-------
Chapter 1
Chapter 2, Application Concepts, summarizes the scientific basis, poten-
tial applications, and key requirements for each stabilization/solidification
technology addressed. Design Development, Chapter 3, provides essential
information for those contemplating use of the technologies discussed.
Chapter 4, Implementation and Operation, focuses on the procedures com-
monly used to implement stabilization/solidification technologies and key
facets of their operation. An evaluation of Case Histories for each technol-
ogy is provided in Chapter 5.
-------
-------
Chapter 2
APPLICATION CONCEPTS
Scientific principles, potential applications, and various treatment train
configurations for aqueous, polymer, and vitrification Stabilization/Solidifi-
cation (S/S) processes are briefly reviewed in this chapter. Additional back-
ground information on these technologies can be found in the companion
monograph, Innovative Site Remediation Technology: Stabilization/Solidifi-
cation (Colombo et al. 1994) and in the references cited throughout this
monograph* Prior to selection of technology(ies) for implementing restora-
tion and waste management operations, site remediation managers and engi-
neers are encouraged to conduct a comprehensive evaluation of potential
processes. This evaluation should address issues of applicability, maturity,
availability, cost-effectiveness, reliability, ease of operation, performance,
health and safety, regulatory compliance, and public acceptance. In addition,
laboratory-scale feasibility and/or treatability studies should be conducted
prior to full-scale implementation to verify the appropriateness of the
technology(ies) selected. .
A frequent criticism of hazardous waste treatment operations is that the
affected public has little, if any, input into the decisions that ultimately im-
pact them directly; namely site and technology selection, operation, and
monitoring. Design engineers and project managers need to take community
interests into account and include their input in planning and oversight ac-
tivities. This may require additional time and resources devoted to educating
the public on the issues, options, risks, and costs. However, the importance
of well-conceived and well-executed public involvement cannot be overem-
phasized for the successful siting, construction, and operation of most site
remediation projects.
Several of the terms used throughout this monograph, although com-
monly used in reference to waste treatment and environmental restoration
activities, are key to the information in this monograph and are, therefore,
reviewed here.
-------
Application Concepts
Stabilization — Techniques that reduce the hazard potential of a
waste by converting the contaminants into less soluble, mobile,
or toxic forms. The physical nature and handling characteristics
of the waste are not necessarily changed by stabilization.
Solidification — Techniques that encapsulate the waste, forming
a solid material. The product of solidification, often known as
the waste form, may be a monolithic block, a clay-like material, a
granular particulate, or some other physical form commonly
considered "solid." Solidification applied to fine waste particles
is termed microencapsulation and that which applies to a large
block or container of wastes is termed macroencapsulation. So-
lidification can be accomplished by a chemical reaction between
the waste and solidifying reagents, or by mechanical processes.
Contaminant migration is often restricted by decreasing the sur-
face area exposed to leaching and/or by coating the wastes with a
low-permeability material.
Ex-Situ Treatment — The treatment of waste materials in an en-
gineered processing system following removal from their original
location. Wastes treated by an ex-situ method are usually dis-
posed at a solid waste landfill, licensed Resource Conservation
and Recovery Act (RCRA) hazardous waste landfill, radipactive
of mixed waste disposal facility.
In Situ Treatment —- The processing of waste materials at the
location where they currently reside, i.e., without removal from '
the ground, tank, settling pond, etc. Wastes treated in situ are
usually left in place for final disposal.
Microencapsulation -r- Thorough and homogeneous mixing of
small waste particles with a liquid binder which then solidifies to
form a solid, monolithic final waste form. Individual waste par-
ticles are coated and surrounded by the solidified binder to pro-
vide mechanical integrity and act as a barrier against leaching of
contaminants.
Macroencapsulation — Compactly packaging large pieces of
waste not suitable for processing by microencapsulation (e.g.,
debris, large pieces of solid metal) and surrounding the package
with a layer of clean binder. The binder forms a "cocoon"
2.2
-------
Chapter 2
around the waste, provides structural support, and helps prevent
migration of contaminants.
2.7 Aqueous Stabilization/Solidification
2.1.1 Scientific Principles
The earliest and by far most commonly used S/S technologies are referred
to as "aqueous S/S" in this monograph because the chemical reactions occur
only in the presence of water. They are commonly referred to as Stabiliza-
tion/Solidification in other literature. This technology is further subdivided
into two process types: stabilization alone and cementitious S/S. For envi-
ronmental restoration applications, the aqueous S/S process can be con-
ducted either ex-situ or in situ. .
In aqueous systems, stabilization and solidification-usually occur simulta-
neously, hence the customary term, stabih'zation/sdlidification. However,
there are many instances in which stabilization is performed without solidi-
fying. The distinction is quite important technically and commercially hi
remediation as will be discussed later. While stabilization requires chemi-
cals to convert contaminants into less soluble, mobile, or toxic forms, the
cementitious binder in S/S processes usually supplies the required reactants
for stabilization. Also, since solidification does hot occur in waste treated
through stabilization alone, the physical properties of the treated waste are
not altered significantly. For this reason, the use of stabilization alone is
limited to those wastes for which physical encapsulation is not requited. On
the other hand, stabilization is often easier to achieve than solidification,
especially for in situ treatment.
2.1.1.1 Stabilization
, Stabilization chemistry is similar to wastewater treatment but the waste to
be treated is usually soil, sludge, or similar material. Stabilization processes
can treat wastes containing metals (and occasionally, other inorganic species
such as cyanides) or organic contaminants, and often both hi the same waste.
The chemistry involved is very different for.the two contaminant types, and
will be discussed separately. -
-------
Application Concepts
Stabilization of Metals and Inorganic Contaminants. Technical descrip-
tions of various reactions that can be used to stabilize metals are given by
Conner (1990), Conner (1997), and Wilson and Clarke (1994). The prin-
ciples of these techniques are well-known, and are usually associated with
cementitious S/S. Examples of some of the more important metal stabiliza-
tion reactions are:
• pH control;
• oxidation/reduction potential (ORP) control; and
• speciation by chemical reaction, including:
• carbonate precipitation,
• sulfide precipitation,
• i , • "' "
• silicate precipitation,
• ion-specific precipitation,
• complexation,
• adsorption, ,
• chemisorption,
• passivation,
• ion exchange,
• diadochy (crystal lattice substitution),
• reprecipitation, and
• coprecipitation.
'!
In addition to metals, other inorganic species amenable to stabilization
(Conner 1990) are cyanides, sulfides, and fluoride. Traditionally, these spe-
cies were destroyed or immobilized in a pretreatment operation, but often
treatment can be accomplished simultaneously with metal and/or organic
stabilization and even with S/S.
While a number of chemicals can be used for speciation of metals (e.g.,
carbonates, sulfides, etc.), only a few have been developed as discrete, inno-
vative systems. One reason is that the regulations and testing requirements
affecting metal stabilization have not significantly changed in recent years
(refer to proposed changes in Chapter 3), so there has been little need for
2.4
-------
ChbpterS
improvement or change in conventional technology. Innovative stabilization
processes covered in this monograph are the ProFix™ and phosphate sys-
tems. Both of these processes can be used in the S/S modes as well. Phos-
phate treatment is discussed below, and ProFix™ is described is Section
2.1.1.2 under cementitious S/S.
Phosphate treatment^ as described in the companion monograph (Co-
lombo et al. 1994), involves adding chemical compounds containing phos-
phate, which form complexes with the metal species present in the matrix.
The phosphate-metal complexes have low solubility and immobilize the
metals over a wide pH range. Alkali can also be added for pH control
(Eighmy et al. 1991) to treat metals such as cadmium. The phosphate treat-
ment process was developed primarily for stabilization of lead. Also, phos-
phates have historically been used in wastewater treatment and as additives
in stabilization (Krueger, Chowdhury, and Warner 1991) because of the low
solubility of the resulting reaction products (Jowett and Price 1932). For
waste stabilization, phosphates have been used primarily for materials, such
as contaminated soils and incinerator ashes, which retain their particulate
nature after treatment. Phosphates can be used in conjunction with
cementitious materials to improve the physical characteristics of the treated
waste, if desired, in which case the process is usually considered to be a
cementitious S/S process with phosphate as an additive.
. Immobilization of Organic Contaminants. The immobilization, or
stabilization, of low levels pf hazardous organic compounds in soils,
sludges, debris, and other wastes has recently received increasing atten-
tion. Newly adopted rules and testing protocols (refer to Chapter 3)
have made the development of innovative stabilization techniques neces-
sary. Previously, the use of additives, such as activated carbon in S/S
systems to immobilize organic constituents, was based on meeting the
requirements of the Toxicity Characteristic Leaching Procedure (TCLP)
test method (US EPA 1986a). However, with the more recent Total Con-
stituent Analysis (TCA) test method, such additives are often not very
effective (Lear and Conner 1991). As a result, a number of other reagent
additives have been developed or adapted from other technologies to
meet the new requirements. Furthermore, the high alkalinity associated
with S/S binders can hinder immobilization of organics, making stabili-
zation alone a more attractive alternative than S/S for these wastes. In-
novative processes or reagents for stabilization of organics include:
-------
Application Concepts
Rubber Paniculate. Conner and Smith (1993) described the ,
results of this new process. The stabilization agent was a
specially-prepared, finely-ground rubber material called
KAX-50™. This material was found to be very effective with
semivolatile and nonvolatile organics; pesticides, herbicides, and
polychlorinated biphenyls (PCBs); and certain volatile organics
and organometallic compounds. Mixed with other additives in a
proprietary formulation, KAX-100™, rubber particulate per-
formed well on nearly all hazardous organics tested to date —-
about 60 compounds. In fact, it was the only compound tested
that was effective for practical use in reducing total levels of
organics across a broad range, as measured by the TCA method.
Organo-Clays. These processes are discussed in the companion
monograph (Colombo et al. 1994) under "Sorption and Surfac-
tant Processes." They are still innovative largely because they are
now being used in the new regulatory context mentioned previ-
ously. Organo-clays are formed by substituting quaternary am-
monium ions for group LA and DA metal ions in clays', increasing
the organophilic property of the clay. This substitution can also
increase the interplanar distance between alumina and silica lay-
ers, allowing organic compounds to intercalate themselves be-
tween the layers. Both of these mechanisms result in stronger
bonding of organic molecules to the clay substrate. Several com-
panies, including Silicate Technology Corporation (STC), Inter-
national Waste Technologies (1WT), Hazcon, and Soliditech,
have provided full-scale services using organo-clays.
Other Sorbents. A number of other sorbents can be, and have been,
used to immobilize organics in specific remediation projects. They
include rice hull ash, coal, and petroleum coke. However, none of
these technologies has sufficiently advanced to a full-scale applica-
tion, and therefore they are not covered in this monograph.
• ' . i
Surfactants. The use of surfactants for stabilization stems from
the ability of the surfactant molecule to attract and hold organic
contaminants at one end, while the other end is attached to an
immobile, solid substrate surface such as soil or cementitious
material. An example of such a process, demonstrated at
field-scale, is described in Section 4.1 of the companion mono-
graph (Colombo et'al. 1994).
2.6
-------
Chapters
2.1.1.2 Gementitious Stabilization/Solidification
.Cementitious S/S technologies use inorganic reagents to react with certain
.waste components; they also react among themselves to form chemically and
mechanically stable solids. Cementitious binders and other additives react in
a controlled manner to produce a solid matrix. The matrix itself often is, or
becomes, a pseudo-mineral. This type of structure is stable and has a rigid,
friable structure similar to many soils and rocks. Many inorganic stabiliza-
tion systems require promoters that are described as "inorganic polymers."
In one sense, all Cementitious systems could be characterized in this way, but
within the narrow definition of polymers, i.e., monomers that react to form
larger molecules by a chemical polymerization process, the setting of Port-
land cement does not qualify as polymerization. Various vendors market
variations of the system to address specific wastes or disposal scenarios.
Vendors often describe a modification or additive as "innovative," but unless
there is a significant difference in the S/S mechanism or in the way that it is
applied to waste treatment, it is not covered here. For example, the addition
of a simple fixative, such as sulfide ion to immobilize mercury is not consid-
ered innovative. On the other hand, the use of a conventional stabilization
agent, such as soluble silicate, in a 'different way to treat a specific waste
type might be innovative.
Different processes exhibit different setting and curing reactions. Most of
the commercial, Cementitious S/S systems, however, solidify by similar reac-
tions which have been thoroughly studied in connection with Portland ce-
ment technology used in concrete (Conner 1990). While the pozzolanic
reactions of the processes using fly ash and kiln dusts are not identical to
those of Portland cement, the general reactions are similar. Sufficient water
must be provided to support the hydration reaction of these chemical sys-
tems. Conventional inorganic chemical processes that have been used com-
mercially are shown below. The most important systems currently on the
market are marked with an asterisk:
• Portland cement-based (major ingredient is cement)*;
• Portland .cement/lime;
• Portland cement/clay;
• Portland cement/fly ash*;
• Portland cement/soluble silicate*;
-------
Application Concepts
• lime/fly ash*;
• cement or lime kiln dust*; and .
• slag. .
Cementitious processes that are deemed innovative due to either their
chemistry or the way in which they are used, are described below.
ProFix™ (EnviroGuard, Inc., Houston, Texas). This product is based on
rice hull ash, an amorphous, biogenetic silica (Durham and Henderson
1984). Because of its sorptive and alkali-reactive nature, rice hull ash has
some unusual properties. Its sorptive nature is well-known, but its ability to
react with alkalies to form soluble silicates is of primary interest here. Un-
der alkaline conditions, the amorphous silica reacts slowly to produce
soluble silicates, which can then react with toxic metal ions to form
low-solubility metal silicates. The scientific basis for this process is covered
in some detail in the companion monograph (Colombo et al. 1994). The
process has patents and patents-applied-for in many countries (Conner and
Reberl992).
Cement-Slag Processes. Slag has been incorporated into a number of
stabilization processes, along with other reagents, especially at or near slag
producers such as steel mills. As with other waste product reagents (fly ash,
kiln dusts), slag usage is often not documented in the literature or promoted
specifically as a commercial S/S process. It is used in a proprietary manner
by waste generators and industries. Vitreous blast furnace slag is produced
when molten slag from an iron-producing blast furnace is cooled quickly to
minimize crystallization. Granulation, the most common process, produces
a product known as "granulated blast furnace slag." Other processes such as
pelletization, are also used. Blast furnace slag is a blend of amorphous sili-
cates and alumini silicates of calcium and other bases. The vitrified slag
must be ground to cement fineness. Because of the presence of ferrous iron
and reduced sulfur compounds, the slag may act as a reducing agent for
metal species that are less mobile in the reduced oxidation state, such as
chromium. Note that slowly-cooled, crystalline slag (e.g., air-cooled slag,
foamed slag) does not exhibit hydraulic cementing reactions.
2.8
-------
Chapter 2
2.1.1.3. In Situ Stabilization and Stabilization/Solidification
For in situ application, S/S binders and additives are introduced into the
contaminated medium (usually sludge or soil) using commonly-available,
large-scale excavation, tilling, or drilling equipment specially modified for
S/S chemical addition. In situ and ex-situ S/S delivery systems each have
advantages and disadvantages. Ex-situ systems provide better control of
reagent addition and mixing, at least as of this tune, and quality control sam-
pling is easier. It is usually more practical for projects with shallow waste
depths and where site access for large equipment is limited. For obvious
reasons, ex-situ equipment and methods are used at central waste treatment
locations, such as RCRA Subtitle G Treatment, Storage, and Disposal Facili-
ties (TSDFs) and are now considered conventional. Large-scale remedial
projects at great depth are more amenable to in situ operation, and in these
instances, the cost is usually lower. In situ methods were probably the first
to be used for remedial projects, long before RCRA, Land Disposal Restric-
tions (LDRs), Superfund, and the other legislative and regulatory drivers that
created the hazardous waste industry. The methods used were rather crude,
mostly mixing the binders with contaminated media using the standard back-
hoe excavation bucket. With time, various devices for injecting S/S reagents
and mixing them into the waste were substituted for the bucket, but the op-
eration remained basically the same.
A recent technique using modified, massive earth drilling and foundation
construction equipment has been introduced to allow well-controlled reagent
'injection and mixing even at great depth. While such mechanical systems .
are not new, and were suggested for this application long ago (Conner 1990),
they have only recently been applied to actual full-scale remediation
projects, and are deemed innovative. One such system is shown in sche-
matic in Figure 2.1 and in actual operation in Figure 2.2. A slurry of the S/S
reagents is pumped through a drilling assembly consisting of a vertical, hol-
low bar called a "kelly bar" and a set of hollow auger blades, into the soil or
sludge as the assembly is rotated down through it. High torque (with forces
up to 41,500 kg • m) is available to produce a well-mixed, treated waste at
depths up to 30 m (100 ft) or more. The resulting treated column may reach
a diameter up to 4.3 m (14 ft). Subsequent columns are positioned to even-
tually cover the entire volume of waste to be treated.
-------
Application Concepts
Figure 2.1
Schematic Diagram of MecTool™ for Solidification
and Stabilization of Contaminated Soils/Sludges
Reproduced courtesy of Millgard Environmental Corp.
A major advantage of this in situ method is its ability to easily and effec-
tively control both volatile and paniculate emissions from the site using a
hood or shroud over the drilling assembly and the column being stabilized.
The control of volatile organic compound (VOC) emissions has become a
major issue in remedial work. This is much more difficult at a remedial site
than at TSDFs and vastly more expensive. Control of VOCs will likely drive
the physical technology toward in situ treatment with equipment that easily
collects and treats emissions.
2.10
-------
Chapter 2
In addition to just S/S processing, in situ methods are available for se-
quential treatment operations, e.g., pretreatment to oxidize or reduce a con-
stituent followed by solidification. One such multi-step operation that is
especially amenable to the drilling type of in situ treatment is stripping vola-
tile organics from the waste prior to metal stabilization. With ex-situ treat-
ment, two different treatment systems must be mobilized to the site and op-
erated; with in situ treatment, the same basic equipment does both more
cost-effectively.
Figure 2.2
The MecTool™ System in Operation
Reproduced courtesy of Millgard Environmental Corp.
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Application concepts
2.1.2 Potential Applications
2.1.2.1 Stabilization
Soluble silicates or phosphates are used for metal stabilization applica-
tions only, not for organic contaminants. In some cases, they can be com-
bined with the various organic immobilization reagents for combined treat-
ment of metals and organics. Care must be taken to ensure combinations of
reagents to be used are compatible in the concentration range. Soluble sili-
cate processes, such as ProFix™, can treat a wide range of metals, while
phosphates are generally more narrowly used, primarily for lead stabiliza-
tion. Phosphate treatment produces lead reaction products that are stable
and have very low solubility over a wide pH range, making them suitable
where the waste form might be exposed to acidic leaching conditions.
Rubber particulate and organo-clays are applicable only for immobiliza-
tion of organic contaminants and are not normally used for wastes contain- :
ing metals unless combined with soluble silicates, phosphates, pH control
agents, or other metal stabilization reagents. They can also be used in con-
junction with other additives. For example, a mixture of rubber particulate
and activated carbon might be useful where a wide range of constituents are
present or where both TCA and f CLP tests are to be used to evaluate effec-
tiveness. In general, these additives do not interfere with the reactions that
occur in cementitious systems and can be mixed in nearly any proportion
with cementitious and pozzolanic binders, if specific physical properties are
required in the final waste form or if metal stabilization is necessary. The
pH of the system can affect the efficiency of the sorbent; this should be as-
certained in prior treatability studies for each application.
I ! " i
2.1.2.2 Cementitious Stabilisation/Solidification
Many of the various conventional cementitious systems, including addi-
tives, are patented or are covered by patents applied for, but most of the ge-
neric system types are believed to be in the public domain, at lea' foe
U.S. and Canada (Conner 1990). These processes have been useu ^uinmer-
cially for solidification of water-based waste liquids, sludges, filter cakes,
and contaminated soils. A large body of technical information on
2,12
-------
Chapter 2
teachability, physical properties, and general stability is available. Treatabil-
ity studies for the particular waste and remedial scenarios being considered
are essential for all S/S projects.
For the most part, potential applications are merely extensions of the
conventional, well-proven processes that have been used for more than two
decades on hazardous and nonhazardous .wastes. These extended applica-
tions or improvements include decreasing teachability by chemical reaction
or rhicroencapsulation, reducing permeability, and improving physical dura-
bility. In addition, physical properties have been improved for easier trans-
port and disposal at landfills. Specific process examples are ProFix™ and
. Cement Slag, detailed below. ,
ProFix™. This process was designed for two waste treatment applications:
• where physical sorption is required to take up the excess water in
low-solids waste, while producing a hardened product by chemi-
cal reaction, a requirement under the 1985 Land Disposal Re-
strictions (US EPA 1986b); and
• where slightly soluble metal compounds are present in the waste,
and could continue to dissolve over time or diffuse out from po-
rous particles. In this case, the advantage is that the slow, con-
tinuous generation of soluble silicate provides a reserve capacity
that can re-speciate the dissolving metal as "silicates."
The ProFix™ process, because of its high sorptive capacity, porous struc-
ture, and high surface area, can also be applied to immobilize organics.
Some ash also has sufficient carbon content — up to 5%. — to potentially
act in a fashion similar to activated carbon.
Cement-Slag. These processes are especially applicable for remediating
primary metal refining wastes when practiced at the slag producer's site,
where the slag is available at little or no cost, or even with a credit for waste
disposal. One form of this process developed by Oak Ridge National Labo-
ratory (ORNL) was designed to immobilize technetium and nitrates. The
ORNL demonstrated processes would be applicable to both Tc+7 and Cr*6
treatment, based on its ability to reduce the oxidation number.
-------
2.1.2.3 In Situ Stabilization and Stabilization/Solidification
Auger-type S/S systems are especially useful in two scenarios:
• where VOCs and odors must be controlled; and
• where the waste to be treated is quite deep, particularly more
than 7.6 m (25 ft), the practical limit of backhoe-based systems.
They also allow better spatial control of mixing since both hori-
zontal (surface) location and vertical position are known pre-
cisely at all times. Reagent introduction and mixing are more
uniform than with the more subjective, operator-dependent con-
trol in backhpe systems. Finally, auger-type systems are more
efficient in sequential treatment operations, such as VOC removal
followed by S/S.
! 'I I
2.1.3 Treatment Trains
1 !
Stabilization or S/S is frequently the only treatment process used in a
particular remedial project. Other site activities in the remediation project
include site preparation, monitoring, final grading, and cover. In addition,
the site might require cutoff walls, liners, leachate collection systems, and
other means to limit incursion of rain, surface and groundwater into the site
and the egress of leachate from the site. In the case of ex-situ stabilization or
S/S, excavation and replacement of treated waste is normally required, and a
pretreatment step in the form of waste particle size reduction might be nec-
essary. With in situ stabilization, these latter activities are usually neither
required nor feasible, although sometimes in situ stabilization or S/S is fol-
lowed by excavation and removal to another landfill location.
• '1
Other than the general site operations described above, S/S products
rarely undergo posttreatment of any sort. However, stabilization is some-
times used as a pretreatment step for subsequent solidification of the waste,
if the original waste is not a solid or if the final waste form must have spe-
cific physical properties.
2.14
-------
Chapter 2
2.2 Polymer Stabilization/Solidification
2.2.1 Scientific Principles ,
Polymer S/S technologies process waste at relatively low temperatures by
combining or surrounding wastes with liquid polymers. Cooling or curing
of the polymer then produces a solidified final waste form product. Al-
though polymer processes are primarily used to solidify waste, when com-
bined with additives, they can be considered S/S technologies. These tech-
nologies are grouped together based on a fundamental similarity in the mo-
lecular structure of polymers, which are made of large molecules formed
from the union of simple molecules (monomers).
In many respects, however, the stabih'zation/solidification technologies in
this category are more divergent than similar. .For example, polymer encap-
sulation or solidification encompasses a wide range of potential binder mate-
rials and several treatment concepts. The binders can be either organic (e.g.,
polyethylene, vinyl ester-styrene) or inorganic (e.g., sulfur polymer). They
can be either thermoplastic or thermosetting. Depending on the nature of the
waste, polymers can be applied for either microencapsulation or
. macroencapsulation. Stabilization/solidification can be accomplished
ex-situ or in situ.
Polymers can be grouped in two distinct categories, i.e., thermoplastic
and thermosetting, based on the means requked for processing:
Thermoplastic binders are materials with a linear molecular
structure that repeatedly melt to a flowable state when heated and
then harden to a solid when cooled. Polyethylene, sulfur poly-
mer, and bitumen are thermoplastic materials used for waste
treatment. Since bitumen is a commercially-available, conven-
tional technology and was covered in detail in the companion
monograph (Colombo et al. 1994) it is not included in this vol-
ume. Thermoplastics, when used for microencapsulation, are
melted, mixed together with waste, and allowed to cool into a
monolithic solid waste form in which small waste particles are
interspersed within the polymer matrix. For macroencapsulation,
the molten thermoplastic is poured into a waste container in
which large pieces of waste material have been suspended or
-------
i ' • " ' • •• J
supported. Upon cooling, the thermoplastic forms a solid poly-
mer layer surrounding the waste.
Thermosetting binders are materials that require the combination
of several liquid ingredients (e.g., monomer, catalyst, promoter)
to polymerize and harden to a solid and which cannot be reversed
,to a flowable state without destroying the original characteristics.
Vinyl ester-styrene, polyester-styrene, and epoxies are examples
of thermosetting resins that have been used for waste treatment.
Thermosetting resins can be used for micrdencapsulation and
macroencapsulation of waste, as well as for in situ S/S. Since
thermosetting polymer processes have been commercially avail-
able for more than 20 years, only novel applications of thermo-
setting polymer technology, such as in situ stabilization, are cov-
ered herein.
2.2.1.1 Polyethylene
• ' ' i. -
Polyethylene is an inert crystalline-amorphous thermoplastic material
with a relatively low melting temperature. It is produced through polymer-
ization of ethylene gas and the structure of the plastic can be varied to create
diverse products with different properties. For example, high-density poly-
ethylene (HOPE) is formed of long polymer chains with relatively little
branching, allowing the polymer layers to be closely packed. Typical HOPE
densities range between 0.941 and 0.959 g/cm3 (58.7 and 59.9 lb/ft3).
Low-density polyethylene (LDPE) is produced by inducing a higher degree
of chain branching, which keeps the layers further apart. The branches in
LDPE occur at a frequency of 10 to 20 per 1,000 carbon atoms, creating a
relatively open structure. Typical LDPE densities range between 0.910 and
0.925 g/cm3 (56.8 and 57.7 lb/ft3). Low density polyethylene has a lower
melt temperature (120°C [248°F]) and melt viscosity than high-density poly-
ethylene (180°C [356°F]), and is easier to process for waste encapsulation
applications. Polymer melt viscosity is inversely proportional to molecular
weight and is characterized in terms of the melt index, which describes the
flow of molten polymer under standard conditions specified by the American
Society for Testing and Materials (ASTM 1990). Low-density polyethylene
is commercially available with melt indices ranging from 1 to 55 g/10 min.
2.16
-------
Chapter 2
While polyethylene is a relatively new engineering material, extensive
testing to establish long-term durability of LDPE for use in encapsulating
waste has been conducted (Kalb, Heiser, and Colombo 1993). Since there
are no proven test methods to evaluate long-term durability of any material,
the approach taken was to examine potential degradation mechanisms using
accepted (e.g., ASTM), short-term tests. Polyethylene resists a wide range
of chemicals and solvents, thermal cycling, saturated conditions, and micro-
bial attack. If polyethylene is exposed to radiation doses up to 108rad,
cross-linking of polymer chains increases and imparts greater mechanical
strength and lower leachability.
2.2.1.2 Sulfur Polymer Cement
Sulfur polymer cement (SPC), also known as sulfur polymer, was developed
by the U.S. Bureau of Mines (USBM) in an attempt to create new,
. commercially-viable construction applications for sulfur produced during the
refining of petroleum and in the cleanup of SO2 stack gases. It was initially
used to treat radioactive, hazardous, and mixed wastes by Brookhaven National
Laboratory (Kalb and Colombo 1985a) and has subsequently been investigated
by the Commission of the European Communities (Van Dalen and Rijpkema
1989), Idaho National Engineering Laboratory (INEL)(Darnell 1991); and Oak
Ridge National Laboratory (ORNL)(Mattus and Mattus 1994). It is produced
by combining elemental sulfur with readily available and relatively inexpensive
chemical modifiers which significantly improve product durability. Elemental
sulfur is reacted with 5% (by weight) dicyclopentadiene, which suppresses the
solid phase transition in the unmodified material responsible for lowering den-
sity and creating an unstable solid. Sulfur polymer cement is manufactured
commercially under license from the USBM, and is marketed under the trade
name Chement 2000 (Martin Resources, Odessa, Texas).
Despite its name, SPC is a thermoplastic material, .not a hydraulic cement.
It has a relatively low melting point of 120°C (248°F) and melt viscosity of
about 25 centipoise (0.0168 Ib/ft-sec), and thus can be processed easily with
a simple, heated, stirred mixer. Compared with hydraulic Portland cements,
sulfur polymer, cement has a number of advantages. The compressive and
tensile strengths of SPC can be twice those of comparable Portland con-
cretes. Full strength is reached in a matter of hours rather than several
weeks. Concretes prepared using SPC are extremely resistant to most acids
and salts. Sulfates, for example, which are known to attack some hydraulic
-------
Application Concepts
cements, have little or no effect on the integrity of sulfur polymer cement.
Sulfur polymer waste forms exposed tp gamma radiation doses up to 108 rad,
did not reveal any statistically significant changes in mechanical integrity
(Kalbetal. 1991; Van Dalen and Rijpkema 1989).
2.2.1.3 Thermosetting Polymers
Thermosetting polymers are formed by the polymerization of an unsatur-
ated monomer (e.g., methacrylates), typically by a chain reaction. The reac-
tion is initiated by a chemical catalyst, such as benzoyl peroxide, which is
decomposed by thermal energy or the action of a chemical promoter, such as
dimethyl toluidine. The decomposition breaks O-O bonds, forming free •
radicals which have unpaired, highly reactive electrons. The free radicals, in
turn, break the double bonds of the monomer and add to it. This process is
exothermic and continues rapidly, as more and more monomers add to the
chain. The reaction finally terminates when the monomer is consumed or
chains meet end-to-end. It can be controlled by temperature (increased tem-
perature accelerates the chain reaction), promoter-catalyst combinations and
concentrations, and the presence of admixtures (or waste materials) that can
retard or accelerate the set. The gel time is defined as the period during
which the resin viscosity increases rapidly and finally can no longer be
poured or worked. The gel time can be varied by the manufacturer of the
resin or catalyst-promoter.
i • ' • • I
Thermosetting resins have undergone extensive durability and perfor-
mance testing for both ex-situ and in situ waste treatment applications.
Since they are typically low in viscosity (3 to 300 centipoise [2 • 10'3 to
2.02 • 10"1 lb/ft-sec]), they are readily adaptable to in situ injection in soil
(Heiser, Colombo, and Clinton 1992). When combined with waste aggre-
gates to form a polymer concrete, they have excellent mechanical strength
(48.3 MPa [7,000 psi] or greater, depending on the type of soil aggregate).
In situ polymer concretes formed from contaminated soils are highly resis-
tant to aggressive chemicals (acidic and alkaline environments), thermal and
wet-dry cycling, microbial degradation, and radiation doses to 108 rad. Low
hydraulic conductivity (<2 • 10'11 cm/sec [<7.9 • 10-12 in./sec]) and leach-
ability have been demonstrated (Heiser and Milian 1994). A disadvantage
of thermosetting polymers is that, unlike thermoplastic polymers, once po-
lymerized they cannot be re-worked. •
2.18
-------
Chapter 2
2.2.2 Potential Applications
Broad application to diverse waste streams is one of the primary advan-
tages of polymer S/S processes. Polymer S/S technologies can be used in
place of conventional cement grout S/S for production of final waste forms
with improved durability and leaching performance. High waste loadings
can result hi fewer waste forms for storage, transportation, and disposal,
providing savings in life-cycle costs compared with conventional technolo-
gies (Kalb and Colombo 1985b; Kalb, Heiser, and Colombo 1991a). These
technologies can be applied for waste management operations to treat aque-
ous concentrates, sludges, incinerator ash, ion exchange resins", secondary
wastes from offgas treatment, and failed conventional concrete waste foirms,
as well as environmental remediation applications, including direct treatment
of soils, sludges, and debris, and indirect treatment of soil washing and other
volume-reduction process residuals.
Application and selection of any S/S technology is based on consideration
of a number of factors, such as waste characteristics, waste volumes, treat-
ment and disposal costs, and regulatory requirements. For polymer encapsu-
lation technologies, specific issues that impact selection of the type of poly-
mer (organic vs. inorganic, thermoplastic vs. thermosetting) and the method
of treatment (microencapsulation vs. macroehcapsulation, in situ vs. ex-situ)
are dicussed in this section. These include chemical and physical properties
of the waste, ultimate disposition of the treated waste, disposal site waste
acceptance criteria, final waste form performance criteria, capital and operat-
ing costs, availability of materials, ease of processing, and reliability. These
issues are described below.
" ' •;• • Chemical Properties of the Waste. Thermosetting polymers re-
quire a chemical polymerization reaction to form a solid product;
interactions with constituents found in the waste can impede
formation of free radicals and adversely impact the solidification
process. For example, wastes that contain reducing agents (e.g.,
. reduced metals such as iron), complexing agents (e.g., EDTA) or
sorbents (e.g., carbon filter media) can interfere with the effec-
tiveness of the catalyst to initiate and complete polymerization.
Thermoplastic polymers do not rely on chemical reactions to
form a solid final waste form product, and solidification is as-
sured on cooling. However, thermoplastic polymers cool to a
solid when exposed to a large thermal mass (e.g., soil) and
-------
Appiiccmon uoncepis
therefore are less suitable for in situ applications where thorough
penetration is required.
Physical Properties of the Waste. Particle size and distribution,
density, and moisture content of the waste can impact polymer
S/S processes. In general, wastes that consist of small particles
are treated more effectively by microencapsulation. The smaller
the waste particles, the greater the ratio of polymer/waste surface
area, resulting in improved teachability characteristics. However,
microencapsulation of extremely fine particles (e.g., <50 pm),
especially those with densities <1.0 g/cm3, may be limited for
some viscous thermoplastic binders. Likewise, particles >3 mm
(0.118 in.) are more effectively processed following size reduc-
tion. Large particles that are considered debris (>60 mm [2.4
in.]) are more effectively treated by macroencapsulation. Ther-
moplastic processes operate at temperatures in the range of 120
to 180'C (248 to 35£>°F), so that moisture contained in the waste
is volatilized. In most cases, it is advantageous to pre- treat the
waste to remove residual moisture. However, small quantities of
moisture (e.g., <2% by weight) can be removed during process-
ing. Although most hazardous metals and radioactive contami-
nants are not volatile at thermoplastic processing temperatures,
some highly volatile species (e.g., mercury) might need to be
captured in the offgas or auxiliary treatment. For wastes contain-
ing significant concentrations of VOCs (>5% by weight), re-
moval and destruction of the organics are recommended prior to
treatment by polymer encapsulation. Some thermdsetting resins
can tolerate significant levels of moisture by forming a
high-shear emulsion of the waste within the polymer prior to
.solidification. Since the process temperature is maintained below
100°C, small droplets of the moisture are trapped within the final
waste form.
Requirements for Disposal, Waste Acceptance, and Final Waste
Form Performance. Final waste form performance requirements
are dictated by the properties of the waste itself (e.g., radioactive,
hazardous, mixed), levels of contaminants, where the waste was
generated (government or commercial site), and where the
treated waste will ultimately be disposed. Waste form perfor-
mance criteria issued by the Nuclear Regulatory Commission,
2.20
-------
Chapters
: U.S. Environmental Protection Agency (US EPA), U.S. Depart-
ment of Energy (DOE), and the States, as well as waste accep-
tance criteria issued by individual disposal sites must be consid-
ered. Waste form performance issues that can influence selection
of polymer encapsulation technologies, in particular, include
mechanical integrity, durability, teachability, biostability, and
radiation stability.
Cost. The cost of polymer materials varies widely, from a low of
about $0.26/kg ($0.12/lb) for sulfur polymer to a high of more
than $14.33/kg ($6.50/lb) for polysiloxanes and some epoxies.
Cost comparisons are further complicated by variations in waste
loading efficiencies which affect the number of drums processed
for disposal, shipping costs, disposal costs, and processing costs:
Therefore, it is particularly important to evaluate fully the
cost-effectiveness of specific polymer encapsulation technologies
under consideration. •
Availability. Most polymers that have been considered or used
for waste encapsulation are commercially available. Some poly-
mers, however, are not widely used for other applications and/or
are produced by a limited number of suppliers (e.g., sulfur poly- •
mer). At any given time, these materials might be in short sup-
ply, especially without advance notification to the manufacturer.
The demand for some polymers used for waste encapsulation
could exceed the current rates of production for conventional
applications, and could create viable new markets. However,
polymer manufacturers should easily be able to meet any in-
creased market demands.
Simplicity of Process. Polymer processes vary in complexity
from relatively simple thermoplastic materials requiring heating/
mechanical batch mixing (e.g., sulfur polymer) to more compli-
cated thermosetting polymers that require precise addition of
catalyst and promoters to initiate chemical polymerization. Poly-
mer processing is done at ambient temperatures (thermosetting
polymers) or at slightly elevated temperatures (150°C [302°F] for
LDPE), reducing or eliminating the need for complex offgas
collection and secondary waste treatment, an advantage com-
pared with higher temperature vitrification processes.
-------
I •. , • '
• Reliability. Although polymers are relatively new engineering
materials, polymer processes in general, and thermoplastic pro-
cesses in particular, have proven reliable in other applications in
over 50 years of development, thermoplastics are routinely used
for packaging, piping, mechanical parts, etc., providing a large
base of experience and high level of process reliability.
• Re-Work Capability. Thermoplastic polymers possess a unique
advantage in that they can be readily reprocessed, if necessary, by
simply remelting and reforming the waste form. In a similar
fashion, processing can be restarted following unplanned shut-
downs, by simply reheating materials to a molten state. This
unique property of thermoplastic resins also allows the use of
recycled plastics from either industrial or post-consumer sources.
2.2.3 Treatment Trains
'! I '
Thermoplastic polymer S/S processing is achieved by heating the poly-
mer binder to the melting temperature, adding the waste material, and mix-
ing to a homogeneous condition. Depending on the type of polymer;, the
treatment train may consist of simple, heated batch mixers (e.g., double
planetary mixers), extruders (single-screw or twin-screw), and
thermokinetic mixers. Thermosetting polymers are processed by adding a
small quantity of catalyst and promoter to the thermosetting monomer, add-
ing the waste material, mixing to form a homogeneous blend and allowing
time for the polymerization reaction to occur. For in situ applications, low
viscpsity thermosetting monomers are used. These materials are applied by
either flooding the waste (e.g., soil) by a technique known as permeation
grouting or by injecting the monomer into the waste under pressure by a
technique known as jet grouting.
* I1 ' ' . I "
- Particle size, density, and moisture content of the waste limit the use of
some polymer technologies. These limitations can usually be ameliorated,
however, by implementing appropriate pretreatment technologies, such as
drying, emulsifying, size reduction, or agglomeration. In other cases, the
polymer processing equipment itself can be modified to improve
processibility and final waste form performance.
2.22
-------
Chapter 2
2.3 Vitrification
2.3.1 Scientific Principles
Vitrification is the class of stabilization and solidification technologies
that expose the waste stream to high temperatures (i.e., >1,000°C [1,830°F])
to achieve the treatment objective. In doing so, organic contaminants and
combustible materials are pyrolized or combusted. Combustion can occur
upon first entering the melter, within the feed pile, in the plenum space, or in
the afterburner. Inorganic metals and oxides are converted into a glass, crys-
talline, and/or slag product. In an oxidizing environment, the waste compo-
nents are converted to oxides, react together, and form the vitreous prodoct.
Decomposition products evolving from the process include water and oxides
of carbon, nitrogen, and sulfur, if present in the waste stream. In addition,
particulates and semivolatiles might also be generated. The behavior and
fate of a majority of the semivolatile metals, such as lead, nickel, antimony,
etc., have been compiled by the US EPA (1992a). The processing condi-
tions and final product vary greatly depending on the wastes treated and the
final product property requirements.
What generally, differentiates the vitrification technologies is the method
by which the. thermal energy is provided. The primary heating methods used
include plasma heating, direct electric heating, fossil fuel combustion, induc-
tion, and microwave heating. Technologies based on these heating methods
are discussed here, with the exception of plasma heating which has not ma-
tured to the point that sufficient information is available to include in this
monograph. However, plasma based technologies, including DC and AC
graphite arc and traditional plasma torch, are expected to emerge in the next
few years. Similar to aqueous S/S and polymer S/S, vitrification can be
applied either ex-situ,or in situ.
2.3,1.1 Ex-Situ Melters
Electric Melters. Electric or joule-heated melters produce a glass or vit-
reous product. The composition and cooling history of the product upon
discharge determine whether the product will have a vitreous or crystalline
nature. Crystalline phases do not usually degrade the leach resistance of the
waste form. As described by Colombo et al. (1994), the glass components
fall into three categories: glass formers, stabilizers, and fluxes. Glass former
-------
oxides (principally oxides of silicon, aluminum, phosphate, and lead) form
the skeleton or glass network. Stabilizers, such as transition metal oxides
and alkaline and rare earth oxides, affect the durability, electrical conductiv-
ity, and viscosity properties of the glass. The fluxes, principally alkali metal
oxides have a very strong affect on the durability, electrical conductivity, and
viscosity properties of the glass. Between room temperature and approxi-
mately 500°C (932°F), glass, is not electrically conductive. However, above
500°C (932°F), the glass structure begins to "relax," and the ionic species,
i.e., the alkali irietals, become mobile. In the presence of an alternating elec-
tric current field, the ionic species will generate heat according.to Joule's
Law,P = PR. I
Combustion Melters. Combustion melters can produce a vitreous, crys-
talline, or slag product depending on the design of the melter. Combustion
melters for stabilization arid solidification of waste streams are; either based
on commercial glass melter designs, kiln furnace designs, or adaptation of
systems originally designed as furnaces for heat generation. T^e latter are
emphasized in this monograph because of their emerging technology status.
Combustion melters burn a fossil fuel such as natural gas, pulyerized coal, or
fuel oil, over the top of the waste and product materials. Thermal energy is
transferred primarily through radiant heat transfer. Waste glass is typically
very dark which results hi all radiant heat energy being adsorbpd within the
first few millimeters of the molten glass surface. Therefore, to; be efficient, it
is necessary to either maintain a relatively thin waste and glass product layer
or actively mix the process to facilitate natural conductive and;Convective
heat transfer. Because joule heating is not used, the electrical conductivity
of the glass is not important. As a result, combustion melters allow some-
what more freedom in defining the glass composition, although the alkali
oxide content strongly influences the viscosity of the molten glass and resis-
tance to leaching, i.e., chemical durability. •
•i ' i i
Induction Melters. Induction melters are similar to electric melters in
that heating is achieved by joule-heating the glass, although the methods
differ. In an electric melter, the electric potential is applied across the glass.
In induction melting, a magnetic field potential is applied across the glass.
The variation in magnetic field causes a change in magnetic flux passing
through the glass according to Lenz's Law. Lenz's Law, restated to apply to
this case, states that when an electromotive force is induced within molten
glass by any change in the relation between the molten glass and the mag-
netic field, the direction of the electromotive force produces a current which
i . ' !
' '
1 2.24
-------
Chapter 2
has a magnetic! field that opposes the change. These eddy or induced cur-
rents are converted to heat through the joule-heating effect. A thorough
discussion of the application of induction heating for industrial uses is given
by Orfeuil (1087). As is true for electric melters, heat transfer occurs prima-
rily through natural convection and conduction from the molten pool to the
waste material unless active mixing of some means is employed.
Microwave Melters. In microwave melting, a container, conveyor, or
furnace holding the waste is connected to a microwave generator via a wave
guide. The microwaves are transported down the guide and enter the pro-
cessing chamber where the microwaves couple to the waste and product.
The melting process is achieved through three primary mechanisms:
• frictional heat caused by the vigorous vibration of dipolar mol-
ecu
es due to oscillation of the electromagnetic field;
• frioional heat caused by the vigorous vibration of magnetic materi-
als due to oscillation of the magnetic component of the field; and
• generation of heat by electrically-conductive materials due to the
current generated by the electrical component of the field.
Standard sysjtems sold within the U.S. Use 915 or 2,45,0 MHz microwave
energy. The penetration, or effective heating depth, of the microwaves varies
depending on the material being treated. Generally, microwaves will penetrate
5 to 10 cm (1.9J to 3.94 in.) through materials having a high water content and
on the order of tens of centimeters for other materials (Orfeuil 1987).
! - . .
2.3.1.2 In Situ Vitrification
Both in situ iand ex-situ electricity-based vitrification share the same fun-
damental scientific basis; i.e., electricity is passed through molten
silica-based media at levels that generate sufficient heat (joule heating) to
melt adjacent media. The resulting glass and crystalline product incorpo-
rates nonvolatile and noncombustible waste species in a highly durable waste
form. For in situ vitrification, volatile and combustible organic waste spe-
cies are pyrolyzed and/or vaporized below grade. Pyrolysis products oxidize
at the melt surface. The gaseous products .of these reactions are directed to
an offgas treatment system for additional polishing, removal, or destructive
treatment to meet air emission requirements. An ex-situ glass melter allows
greater flexibility in, controlling additives to the melt to control primary pa-
rameters, including electrical conductivity, melting temperature, viscosity of
-------
Appiicunoii i*.uf iirefjia
the hot glass, and quality of the resulting glass product than is possible with
in situ vitrification.
In situ vitrification (ISV) has several important advantages compared to
ex-situ vitrification processes, including the following:
• ISV can operate at higher temperatures (1,600° to 2,000°C
[2,900° to 3,600°F]) than melters (1,100° to 1,400°C [2,000° '
to 2,550°F]). To provide for an acceptable life expectancy for
an ex-situ melter's refractory lining, chemical fluxes must be
added to the media processed in melters so as to lower the
melt temperature. Even then, melters must be periodically
shut down and relined. ISV is free of this limitation since it
does not use a refractory lining. This normally allows ISV to
be applied to soil and other earthen media without the addi-
tion of costly fluxes.
• The higher operating temperature of ISV processing produces a
higher quality product compared to the typical ex-situ melter
product, in terms of chemical leach resistance and weatherability.
• ISV processing results, in greater net volume reduction since
: additives generally are not necessary.
: • No corrosion of refractory bricks occurs due to contact of the bricks
with unoxidized metals because IS V uses the surrounding soil for
containment of the melted waste-soil mixture instead of bricks. •
. 1 ' ! , I ' .
• ISV is capable of treating most materials without pretreatment, and
without the need for size reduction to allow feeding to the melt. t
• Because of the greater depth at which elemental metals are incor-
porated into the melt (up to 20 feet), ISV retains a higher fraction
of metals than melters and other vitrification processes which use
much shallower bed depths and typically treat contaminants at
the surface of the melt. Melting at the surface results in higher
losses of metals to ttie pffgas (e.g., plasma melting loses most of
the metals).
• ISV processing produces a monolithic waste form that has less
surface area for weathering or chemical leaching exposure than
melter products.
2.26
-------
Chapter 2,
• The on-site and in situ nature of IS V processing improves occu-
pational, public, and environmental safety compared to melter
processing, which requires significantly more handling and trans-
port of contaminated media.
Hie IS V technology can be applied in four basic configurations, including:
• in situ — the contaminated materials are treated where they pres-
ently exist in the ground;
• staged in situ — contaminated materials are partially or com-
pletely consolidated or relocated to treatment cells for treatment
above, below, or partially below grade;
• stationary batch —: materials are melted in one location, the vitri-
fied product is removed after treatment, and the cycle is repeated
over and over; and
• stationary continuous — wherein processing is performed in one
location with materials being continuously fed to the melting
zone and treated molten material being continuously removed.
It should be noted that the first two configurations listed above involve
leaving the melts in place and moving the equipment between melts to treat
large areas. The latter two configurations involve moving the materials to be
treated and removing the vitrified product while leaving the equipment in a
stationary processing location.
In situ vitrification melts media that are contaminated with, or are in close
proximity to, waste materials that must be destroyed or immobilized. The
media and/or waste must have sufficient alkali content (1.4 to -15%) to en-
sure the proper balance between electrical conductivity and melting tempera-
ture. Too much alkali (>15%) increases the electrical conductivity to the
point that insufficient heat would be developed when operating at the electric
current limit of the equipment. Too little alkali can result in undesirable,
high melt temperatures or insufficient electrical conductivity. Most natural,
earthen materials contain sufficient quantities of alkali to allow efficient IS V
processing. The rare cases of low alkali content or insufficient soil can be
overcome by injecting an alkali-bearing solution into the soil or by simply
mixing additional soil or chemicals into the media.
-------
Application concepts
2.3.2 Potential Applications
Vitrification technologies are attractive because they process a variety of
waste types and combinations of wastes. In addition, nearly every element
in the periodic table is soluble to some extent in glass. Table 2.1 identifies
the relative solubilities of many of the elements in silica-based glasses
(US EPA 1992a). By choosing an appropriate glass system — silica, alu-
mina, phosphate, or lead-based glasses — waste loadings can be maximized,
thereby reducing the final product volume tiiiat requires disposal. Because
vitrification technologies can simultaneously accommodate a large number
of elements, it also provides the flexibility for treating multiple or poorly
characterized waste streams. Depending on the vitrification technology,
metals, combustibles, organics, and inorganics can be processed to varying
degrees. In general, waste streams that are essentially organic liquid waste
are more efficiently treated using standard incinerator technology; rather
than vitrification technologies. Also, of the listed metals, mercury cannot be
processed by any of the vitrification technologies due to its relatively low
vaporization temperature. Mercury will be essentially completely volatilized
from the waste material and discharged to the offgas treatment train. Wastes
containing the remaining listed metals can be treated by one or more of the
vitrification technologies with varying degrees of efficiency.
Table 2.1
Approximate Solubility of Elements in Silicate Glasses
LessthanO.1% (by weight) " Ag| Ar, Au,Br,H,He,Hg,I,Ki,N,Ne,Pd,Pt,Rh,Rn,Ru,Xe
Between 1 and 3% (by weight) ' As, C, Cl, Cr, S, Sb, Se, Sn, Tc, Te
... | '• '
Between 3 and 5% (by weight) Bi, Co, Cu, Mn, Mo, Ni, Ti
I
Between 5 and 15% (by weight) Ce, F, Gd, La, Nd, Pr, Th, B, Ge
Between 15 and 25% (by weight) Al, B, Ba, Ca, Cs, Fe, Fr, K, Li, Mg, Na, Ra, Rb, Sr, U, Zn
Greater than 25% (by weight) Si,P,Pb
Adapted from US EPA 1992a
2.28
-------
Chapter 2
2.3.2.1 Ex-Situ Melters ;
Electric Melters. Soils containing organics, pesticides, combustibles,
heavy metals, and radioactive contaminants are all amenable to treatment by
electric melter technology. As soils differ hi alkali content and many con-
taminated soil areas also contain past evaporation and retention pond materi-
als that are high in clays, it is necessary to obtain representative samples for
analysis to determine the relative concentrations of the primary glass-making
compounds. Large rocks must be crushed or removed from the process
stream if uncontaminated. Refractory organic contaminants might require
secondary thermal combustion units in the air pollution control train to
achieve the destruction and removal efficiency required to meet the facility
discharge requirements.
Electric melters have been proposed for treating buried waste; however,
the waste would have to be more thoroughly characterized and sorted than
would be required for other vitrification processes. Buried wastes consist-
ing predominantly of combustible materials, such as paper and plastics, can
be processed. However, the process would not be as efficient as combustion
or plasma vitrification systems. Buried wastes that are high in metals would
require removal of the metals. Because of the rate of oxidation of metals in
the glass, only trace, finely-divided metals content should be considered.
Methods have been proposed to either oxidize the metal during processing to
bring it into the glass or allow a metal phase to collect hi the melter that
could be dVained from the melter as a separate product. However, neither of
these have been demonstrated. Therefore, electric melters have limited ap-
plication for this waste type.
Electric melters are applicable to process and industrial waste streams.
Electric melters can process wastes in dry, slurry, or liquid form. Generally,
waste streams high in inorganic salts and oxides would be most amenable to
treatment by electric melters. The volume of glass product depends on
whether the targeted waste stream contains a large percentage of the glass
formers, stabilizers, and fluxes required to achieve the final glass composi-
tion. In addition, pretreatment of the waste stream might be required to
make it competitive with applicable nonthermal treatment options. For ex-
ample, dilute streams should be concentrated as much as possible to mini-
mize the water load. This will make the process more efficient and also
reduce the fraction of entrainment into the offgas treatment train that would
be generated by active boiling.
-------
Application concepts
1 i i . .
The efficiency of the vitrification is unaffected by the isoiopic nature of
radioactive waste constituents. Within the U.S., radioactive jwastes include
contaminated soils, buried wastes, process wastes streams, and wastes result-
ing from building and equipment demolition and decontamination. The
electric melter was developed specifically to treat DOE defense high-level
wastes (Chapman and McElroy 1989). Radioactive wastes will, in general,
have the same compatibility for electric melter processing as the waste types
described above.' There are some radioactive isotopes — tritium, carbon-14,
and isotopes of iodine — that will not be immobilized due to their gaseous
state at processing temperatures. If the concentration of these isotopes ex-
ceeds stack release limits, they must be removed prior to vitrification or
captured by offgas treatment equipment and disposed as a secondary Waste.
Combustion Melters. Combustion melters are similar to electric melters in
I , | • : p» in : :
their applicability to contaminated soil. However, combustion jmelters expose
the waste to higher instantaneous temperatures, leading to a lower retention of
many alkali metals and heavy metals, such as lead, zinc, and cadmium. How-
ever, depending on the metals concentration, ultimate retention should be pos-
sible by recycling the metals back from the offgas treatment train.
i • ' . ' ' (,. > > - ^ pilui' , I'll, r.n^piri;!!!!'1;1!!!!!1! ;«'"
Combustion melters are similar to electric melters in their applicability to
buried waste with some clarifications. Combustion melters should be more
applicable to buried wastes containing predominantly combustible materials.
However, combustion melters place maximum size restrictions on the feed
stream materials. Depending on the process, it might be necessary to crush,
shred, pulverize, or slurry the materials for delivery to the melter. Liarge
items, such as drums, equipment components, etc., would be excluded.
Combustion melters typically do not have a significant glass! accumulation
capacity; resulting in a short residence time within the-melter. Therefore,
they would be preferred over other ex-situ vitrification processes if the waste
has a high concentration of ferrous and nonferrous metals. These metals
would be incorporated in the glass as metal inclusions and should have little
effect on the final glass properties.
Combustion melters are similar to electric melters in their applicability to
process and industrial waste streams with some clarifications. Predomi-
nantly organic liquid wastes are compatible with combustion' melters. Com-
bustion melters expose the waste to higher instantaneous temperatures lead-
ing to a lower retention of many alkali metals and heavy metals, such as
lead, zinc, and cadmium. Ultimate retention should be possible by recycling
the metals from the offgas-treatment train. - I
i • , I , . ' | v: •.-;••
2.30
-------
Chapter 2
Combustion melters are similar to electric melters in their applicability to
radioactive waste. Process wastes that are primarily salt solutions are more
difficult to process because of excess volatility of the alkali metals and heavy
metals. Ultimate retention should be possible by recycling the metals back
from the offgas treatment train.
Other Melters. Induction and microwave melters are similar to electric
melters in theii: applicability to contaminated soils, buried waste, process and
industrial waste, and radioactive waste. A benefit of microwave melters is that
they can process a wide range of waste compositions, since the electric conduc-
tivity of the waste is not important. However, because microwave melters do
not have a large glass holding capacity, the incoming waste must be more ho-
mogeneous to .assure an acceptable glass product. Induction melters can oper-
ate at temperatures as high as 2,800°C (5,070°F); making them very applicable
to waste strearhs primarily consisting of metallic waste (i.e., buried waste).
2,3.2.2 In Situ Vitrification
Contaminated Earthen Media (Soil, Sediment, Tailings). The IS V tech-
nology applies to contaminated earthen media containing highly variable
amounts of saiid, silt, and clay. Even rocky soils can be melted by the pro-
cess (Thompson, Bates, and Hansen 1992).
The IS V process is tolerant of multiple small voids in the soil of up to
0.07 m3 (2.5 ft3) each. Until further research resolves questions regarding
the effects of Voids, larger voids should be collapsed or filled to preclude the
possibility of generating large bubbles hi the melt. Large bubbles, When
released at the molten surface, can cause excessive agitation of molten glass
and release of! heat inside the hood.
I . .
In situ vitrification is generally applicable to most soils, regardless of mois-
ture content. Soils and sludge ranging from 4 to 70% moisture (by weigh/:)
have been successfully vitrified (Thompson, Bates, and Hansen 1992). Geosafe
Corporation,- th'e sole U.S. licensee for the ISV technology, states that saturated
soils and slurries can be successfully vitrified. The amount of water associated
with silty soils;or non-swelling clays is important when determining the eco-
nomic feasibility of ISV in those applications. The technology, however, might
not be economically feasible in soils that lie within a permeable aquifer (i.e., .
with a hydraulic conductivity of greater than 1CH cm/sec), unless combined with'
a groundwater [diversion or pumping technique to limit the rate of water re-
charge to the treatment zone.
-------
Appncanon ooncepis
i
Because most soils and sludges are naturally composed of glass-forming
materials, such as silica, they can generally be processed by ISV without
modification. A total alkali content (i.e., combined Na^O, Li2O, and Kf)
content) of 2 to 5% is desirable, however. Alkaline oxides carry the electri-
cal current between electrode pairs when soil is in the molten state. Weath-
ered soils with less than 1.4% (by weight) alkaline oxides require addition
and mixing of alkaline materials to lower the melting temperature and raise
electrical conductivity (Buelt et al. 1987). Excessive amounts of alkali can
pose processing problems by lowering the electrical resistance, which re-
duces the melt temperature, thereby impacting the quantity of vitrified prod-
uct obtained.
The ISV process has been demonstrated at depths of up to 5.8 m (19 ft) in
relatively homogeneous soils. The achievable depth, however, can be lim-
ited under certain heterogeneous conditions, such as the presence of a rock
or gravel layer, which inhibits melting, or if a soil layer with a significantly
higher melting temperature than the overlying material exists. Melting
depths of 4.3 m (14 ft) and 5.2 m (17 ft) have been attained when rock layers
existed at those depths. The relative density of the soils to be processed also
influences the achievable melt depth. Higher-density soils require more time
and energy to be processed due to their higher bulk heat capacities (Thomp-
son, Bates, and Hansen 1992). The vitrification process eliminates the po-
rosity of the soil, thereby increasing its density by 33% to 100% in the vitri-
fied form, according to Geosafe Corporation.
ISV is highly effective at immobilizing heavy metals and other inorganic
contaminants in buried waste. The majority (70 to 99.9% by weight) of
heavy metals, such as arsenic, lead, cadmium, barium, and chromium, are
retained and immobilized in the vitrified product (Thompson, Bates, and
Hansen 1992). The retention efficiency of metals depends on:
• vapor pressure;
• solubility in the molten media; and
• depth of melt.
Metals evolved from the melt are collected by the offgas system and ei-
ther recycled to future melts or disposed separately. Nitrate salts are decom-
posed by the process, releasing NOx to the offgas system. Mercury may, be
removed and collected by the offgas system for reuse or disposal.
2.32
-------
Chapter 2
The high processing temperature (up to 2,000"C [3,630°F]) of ISV de-
stroys hazardous organic chemicals by pyrolysis. See Table 2.2 for data v'.
from the ISV demonstration at the Wasatch Chemical Superfund Site in Salt
Lake City, Utah. Organic concentrations of up to approximately 10% by
weight in the soil can be processed with the current technology. (The limit is
based on the ISV system's ability to accommodate the heat loadings result-
ing from the exothermic oxidation of the pyrolysis products. The limit also
depends oh the distribution and heating value of organics in the soil.) The
small amount of organic contaminants not destroyed by the process (between
0.01 and 1% by weight) is removed from the soil through diffusion, thermal
convection, and the negative pressure induced in the offgas hood and is pro-
cessed by the offgas treatment system." In situ vitrification should not be
applied to unexploded ordnance or highly reactive materials, since little
theoretical or experimental work has been directed toward these types of
materials. However, ISV has been successfully tested and proven safe and
effective on explosives-contaminated soils from the Mead Nebraska Ord-
nance Plant (Cambell, Schultz, and Cichelli 1994). Empirical data show that
VOCs such as carbon tetraehloride and trichloroethylene can be effectively
.removed by ISV by a combination of pyrolysis, oxidation, and offgas treat-
ment (Shade et al. 1991). These data indicate that about 97% of these VOCs
are destroyed, about 3% are captured by the offgas system, and less thain
0.1% remain in the soil surrounding the glass melt.
With recent improvements in the electrode-feed system, which permits
electrodes to be inserted as the soil is melted downward, high scrap-metal i
concentrations can be processed by ISV. Vitrification of up to 37% of el-
emental metals in soils has been demonstrated. The metal melts, and be-
cause of its higher density, forms a molten pool at the bottom of the pool of
molten soil. The molten metal layer can create electrical short circuits be-
tween the electrodes, but by retracting the electrodes a few centimeters
above the molten metal, short circuits can be overcome.
High concentrations of concrete, asphalt, rubble, rock, scrap metal, plas-
tics, wood, tires, and other debris (up to 50% by weight) can generally be
processed by ISV if all other operational constraints are met (Thompson,
Bates, and Hansen 1992). Monolithic debris and other structures that might
impede the release of water vapor from beneath the molten soil to the soil's
surface should only be vitrified when sufficient analysis of the effects of the
debris shows ISV to be safe and efficient.
-------
Application v^unuupis
Table 2.2
Hazardous Organic Chemical Destruction ana
Removal Effectiveness Using In Situ Vitrification
Pre- and Post-ISV Contaminated Soil and Adjacent Surroundine Soil Levels with Cleanuo Criteria
Indicator Chemical
TCDDDioxin
2,4-D .
2,4,5-T
4,4-DDD
4,4-DDE
4,4-DDT
Total Chlordanes
Heptachlor
Hexachlorobenzene
Pentachlorophenol
Trichloroethene
Tetrachloroethene
Pretreatment
(ppb)
11
34,793
1,137
52
3,600
1,090
535,000 •
137.5
17,000
272,918
36,875
<100
Stack
Indicator Chemical
.TCDDDioxin
2,4-D
2,4.5-T
4,4-DDD
4,4-DDE
4/t-DDT
Total Chlordanes
Heptachlor
Hexachlorobenzene
Pentachlorophenol
Tetrachloroethene
HCL
Posttreatment
(ppb)
£0.12*
£20"
<'l4'"
ND
ND
ND
S80
ND
ND**
£ 10.3
(non-TCLP)
' 'ND
ND
Emission Perfori
Surrounding Soil
(ppb)
£0.0045
ND
ND
ND
£2.4
ND
£83.4
• ND
ND
£1.2
ND
ND
nance Data
Regulatory Limit
! (ppb)
. 20, < 1CTCLP)*"
' NA
• NA
! 28,000
; 19,000
: 19,000
:. 7,000
"1
2,000
; 7,000 . '
< 10 (TCLP)"
I
103,000 '
; 22,000
Emission Values nb/hrV
' Runl
<2.46E-9*
<3.09-E-6
!<6.19E-7
<6.19E-8
<6.19E-8
<6.19E-8
<6.19E-8
<6.19E-8
<6.19E-8
< 1.24E-6
NA
<0.05
Run 2
.
<2.;09E-9
< 1J35E-4
<2.70E-5 .
<2.09-E-6
<2.09E-6
<2,09E-6
< 1.05E-6
i
< 1.05E-6
-------
Chapter 2:
Although field data for vitrifying buried combustible materials are lim-
ited, ISY has been used successfully to process more than 80 buried creosote
timbers, each measuring 3.6 m (11.8 ft) long by 15 cm (5.9 in.) square, in a
single, large-scale setting (Luey et al. 1992). Based on the heat-removal
capabilities of existing ISV equipment, combustible inclusions of up to 10%
(by weight) can be processed.
The ISV process is not applicable to sealed containers, including empty
tanks, 208 L (55 gal) drums, and 3.8 L (1 gal) paint cans containing liquids
because of the potential for disruption of the melt due to the release of pres-
surized gases when these containers are breached. Similar concerns exist for
pockets of liquids. For many landfills, corrosion can degrade sealed contain-
ers, largely eliminating the potential for transient releases of trapped gas
related to source liquids. The potential for melt disturbance due to rapid de-
pressurization of sealed containers of liquids can be alleviated using dy-
namic disruption and compaction.
ISV is capable of treating underground pipelines, cribs, and drain fields.
Tanks (including residual wastes) can be treated in place after precondition-
ing (e.g., filling with earthen material to remove voids and grouting to pre-
vent rapid conversion of liquids to .the gaseous state). Building demolition
debris (e.g., concrete and steel), if backfilled with soil, can be directly
treated by ISV.
Geosafe, together with its Japanese partner, ISV Japan Limited, is treating
.industrial wastes in a stationary-batch ISV system. The ISV and joule-
heated melter technologies have been adapted by Battelle Pacific Northwest
National Laboratory to treat newly-generated process and industrial, wastes,
including municipal wastes. The adapted technology, called Terra Vit, uses
inexpensive refractories and construction techniques. The Terra Vit system,
which is constructed below or at the ground surface, greatly reduces the
large capital investment associated with standard melter systems. Molten
glass and molten metal (if created in the vitrification system) can be sepa-
rately recovered and cast into engineered shapes for various uses. Terra Vit
technology is currently being licensed by Geosafe.
The ISV process has been proven effective for treating soils and buried
wastes contaminated with radionuclides, including transuranic materials and
fission" products. Criticality limits of approximately 30 kg (66 Ib) of pluto-
nium per setting have been established for vitrifying soils containing transu-
ranic materials (Thompson, Bates, and Hansen 1992). Thus, soils
-------
contaminated with thousands of nCi/g of ixansuranics can be treated safely
with ISV. When high concentrations of 137Cs exist (i.e., when several curies
are present at a single setting), special measures must be taken to collect and
remove the small percentage (<3% by weight) of cesium that volatilizes to -
avoid undesirable levels of worker exposure to ionizing radiation.
In situ vitrification is effective for treating mixed wastes. Vitrification
processes in general have advantages for such waste because of their ability
to simultaneously destroy organics and immobilize inorganics/radionuclides.
i
. " i • i " • ' ' ' ., r
2.3.3 Treatment Trains
' i
2.3.3.1 Ex-Situ Melters
Vitrification process equipment provides final and total treatment of a
targeted waste stream. The treatment procesis can be transportable, field
erectable, or a fixed facility. A ex-situ vitrification block-flow diagram is
provided in Figure 2.3. The waste stream to be treated is delivered to a stag-
ing area and is analyzed to determine composition and consistency, if not
previously analyzed. This information is used to determine if glass forming
additives are needed. The types and amounts of glass forming additives
depend on the waste stream — they might not be required at all or they
might account for a majority of the final vitrified product.
Pretreatment of the waste occurs next. Large objects are removed to be
handled separately or size reduced. Dry feedstocks could then be crushed,
shredded, or pulverized as required depending on the melter process. Any
required glass forming additives can be addecl to the feedstream at this time.
The glass formers are stored in large bins from which they can be metered to
the melter or to a blend tank to be mixed with the waste. If the feedstock is a
dilute slurry, dewatering can be performed at this time if determined to be
economically favorable. Glass former additives can be blended with the
aqueous feedstream or added to the melter as a separate stream. Usually, if
the glass formers are added to the liquid stream, less water can be removed
prior to blending than would be necessary if the glass formers were added
separately. Finally, any recycle streams originating from the offgas treat-
ment equipment are usually blended with the waste rather than being fed to
the melter as a separate stream.
2.36
-------
Chapter 2
Figure 2.3
Ex-Situ Vitrification Block-Flow Diagram
Waste Receipt
Waste Preparation (Sorting,
Blending, and Feeding)
Glass Additives
Power Supply or
Fbssile Fuel
Vitrification Unit
Offgas Treatment
Glass Receiving
and Packaging
The feed stream can be introduced into a melter in many ways. For elec-
tric and microwave melters, the material is dropped directly on top of the
glass batch. Therefore, the feed can be augured, pumped, pneumatically
transferred, or introduced into the melter in combustible containers. Com-
bustion melters must be fed pneumatically, or the feed is sprayed into the
primary melting chamber as a slurry. Little or no evidence supports liquid
feeding of induction melters. Therefore, at this time it is assumed that dry
feeding is the primary feeding method for these systems.
The size and complexity of the offgas treatment train depends on the
waste stream and on the melter type. Combustion melters.produce the larg-
est, noncondensable offgas volume because of the combustion gases and
excess air normally used to assure complete combustion. The air pollution
control industry provides a wide variety of technologies to treat offgases
discharged from thermal treatment systems. The waste stream characteris-
tics and treatment requirements-will define the best combination of equip-
ment. The reader is encouraged to refer to available air pollution control
(APC) publications and literature; as well as contacting APC vendors to
identify available options. In general, treatment equipment may be required
to treat the following offgas constituents: .
-------
Application Concepts
steam;
acid gases, e.g., HCl,
halogens;
HF;
• NOX; ' . ; • • • * • ; .
» hydrocarbons;
• J . . : ' ' i' '
• particulate "dust";
!
• gas-phase radionuclides; and
• soluble and insoluble aerosols.
The glass product can be handled in many ways. The product can be cast
into containers forming monoliths, air- or water- quenched forming a cullet
or type of aggregate, processed through mechanical handling machines to
make shapes of uniform size, or cast into molds and heat treated to make
products that can be marketed if determined to be nonhazardous.
•• '! •
2.3.3.2 In Situ Vitrification
The ISV treatment system consists of an electric power transformer and
cabling, an offgas collection hood, a process control system, and an offgas treat-
ment system (Figure 2.4)., The transformer provides two-phase alternating
current to the graphite electrodes at the appropriate voltage and current. The
offgas hood collects emissions escaping from the treatment zone and provides
physical support for the electrodes. The hood is a dome-shaped structure that
completely covers the area to be treated. A slight negative pressure is main-
tained in the offgas hood to contain gases, which are piped to the offgas treat-
ment system. The entire ISV system is monitored from a process control room
where electrode power consumption, offgas temperature, hood vacuum, and
other system parameters are monitored and controlled.
Several modular unit treatment processes comprise the typical offgas
treatment train. The train can include a quencher, scrubber, mist eliminator,
heater, filter, activated carbon, and a thermal oxidizer. The choice of treat-
ment units depends on the contaminants and concentrations present at the
site. A large-scale offgas treatment system used by Geosafe Corporation
was designed to ensure that process air emissions are in compliance with
regulatory permit limits. Gases are drawn through the system by an
2.38
-------
Chapter 2
52 mVmin (1,800 scfm) blower. Automatic valving allows ambient air to
enter the hood so that a negative pressure (vacuum) of -1.3 to -5.1 cm
(-0.5 to -2.0 in.) of water is maintained. As the rate of gases evolved-
from the treatment zone changes, the valving controls the amount of
ambient air drawn into the system to maintain a relatively constant,
negative pressure. Potentially contaminated gases are thus prevented
from leaking from the hood.
Figure 2.4
In Situ Vitrification System
Backup Offgas System
Reproduced courtesy of Geosafe Corp.
Typically, the volume of gases entering the treatment system consists of
greater than 99% ambient air and less than 1% gases evolved from the treat-
ment zone. This ratio varies depending on the soil and contaminants being
treated. The dilution effect of ambient air and high combustion efficiency
typically results in low levels of hazardous gases within the hood enclosure.
-------
Application Concepts
The offgases enter the treatment system at temperatures ranging from
about 100 to 40Q°C-(212 to 752°F). The offgas.es are first quenched to about
80°C (176°F) and then scrubbed in a high efficiency, dual-stage venturi
scrubber. A typical scrubber removes 97% of paniculate matter with diam-
eters greater than 0.5 \un (0.02 mils).
The quencher and scrubber perform the majority of the offgas cleanup
task. Condensable materials condense as mists in the quencher. Most mists
and solid particulates are then removed from the offgas by the scrubber. An
impingement-type mist eliminator usually follows the scrubber .to remove
water droplets. The offgas stream is then heated to raise its temperature
above the dew point before it passes through a high efficiency particulate air
(HEPA) filter and activated carbon filter(s) or thermal oxidizer. Dew-point
control prevents "wetting" and blinding the HEPA filter, which removes
99.97% of particulate matter with diameters of 0.3 urn (0.01 mils) or greater.
The gases may finally be passed through activated carbon or a thermal
oxidizer to remove or destroy any organics that escaped the quencher and
.scrubber. The activated carbon or thermal oxidation systems can be de-
signed to remove at least 99.9% of organics in the offgas. Two options exist
for treating the scrubber solution:
'
• • return it to the site for retreatment by IS V; or
• provide additional treatment (e.g., solidification) in accordance
with disposal requirements.
• • ! ' . ' • . •!'•'•
The method of additional treatment depends on the type and concentra-
tions of contaminants collected in the scrubber solution.
2.40
-------
Chapters
DESIGN DEVELOPMENT
This chapter provides information essential for the engineering design
and implementation of Stabilization/Solidification (S/S) treatment technolo-
gies. Each of the major categories of S/S technologies are discussed in turn;
first, Aqueous S/S, followed by Polymer S/S, and Vitrification with ex-situ
and in situ applications of each. For each of these categories and the various
modifications, information is provided on the process capability, basis of
design, equipment design and selection, process modifications, associated
pre- and posttreatment processes, process controls and instrumentation,
safety matters, unique factors to be addressed in specification preparation,
cost data, design validation, permitting requirements, and performance mea-
sures. Each section concludes with a design checklist.
While critical design issues are addressed, this information is intended
only as a first step in the engineering implementation process. The reader is
encouraged to review the references cited and contact developers and ven-
dors of these innovative technologies. In addition, treatability studies to
ensure the applicability of the selected technology for the specific waste
stream are recommended and pilot-scale testing is useful in cases where little
prior engineering experience exists. For in situ technologies, performance
assessment modeling will assist engineers and project managers in evaluat-
ing potential behavior of contaminants following treatment.
Technology-specific safety issues are discussed in this chapter. A ge-
neric safety issue that should be addressed for any treatment technology is
the need for an emergency contingency plan. This plan describes how to
recognize emergency or critical situations and who, when, and how facility
personnel, local agencies, and the community will be notified during such
events. Generally, contingency plans cover routine operation and mainte-
nance inspections, emergency operations, preparedness and prevention re-
quirements, and evacuation procedures. Good communications with local
emergency personnel and training are critical to effective implementation of
contingency plans.
-------
Design Development
Although a comprehensive review of regulations governing S/S waste treat-
ment is beyond the scope of this book, key regulatory changes that have been
implemented or proposed are reviewed here to provide perspective on technol-
ogy implementation issues. Federally-mandated cleanup standards under the
Resource Conservation and Recovery Act (RCRA), Comprehensive Environ-
mental Response, Compensation, and Liability Act (CERCLA, commonly
known as the Superfund Act), and other legislation provide the impetus and
technical guidance for waste treatment and environmental restoration.
U.S. regulatory standards for treating hazardous and mixed wastes, how-
ever, are continuing to change, requiring waste generators and treatment
vendors to continually monitor the regulations and confirm that treatment
technologies meet existing and proposed criteria. In some cases, changing
regulations require new treatment options be developed, tested, and imple-
mented. A dynamic regulatory climate can thus provide the catalyst for
technology development.
i i , . i .
The Hazardous and Solid Waste Amendments (HS WA) to the RCRA,
largely prohibit the land disposal of untreated hazardous wastes that do not
meet treatment standards established by US EPA under section 3004(m).
Once a hazardous waste is prohibited, the statute provides only two options
for legal land disposal: (1) meet the treatment standard for the waste prior to
land disposal, (2) or dispose of the waste in a land disposal facility that has
been found to satisfy the statutory no migration rule. A no migration facility
is one from which there will be no migration of hazardous constituents for as
long as the waste remains hazardous.
US EPA has established treatment standards as specified technologies, as
constituent concentration levels in treatment residuals for Listed and Toxic-
ity Characteristic (TC) waste defined in 40 CFR 261.3, or both. When treat-
ment standards are set as levels, the regulated community may use any tech-
nology not otherwise prohibited (such as impermissible dilution) to treat me
waste. Treatment standards werp initially based on the levels achievable by
the Best Demonstrated Available Technology (BOAT) for treating the waste.
For treatment of hazardous debris defined in 40 CFR 268.45, a series of
alternative treatment standards to remove, destroy, or immobilize contamina-
tion are required.
| , |
US EPA has continued to amend the lists of hazardous wastes and con-
stituents that must be treated and the standards that they must meet for land
disposal. On August 18,1992, a "debris" rule (US EPA 1992b) was issued
3.2
-------
Chapter 3
that established alternative treatment standards for hazardous debris. On May
24,1993, the "Emergency Rule" was issued that required certain ignitable or
corrosive characteristic wastes to be treated to meet more stringent treatment
standards for all hazardous constituents reasonably expected in the waste, mot
just constituents that initially exceeded the 40 CFR 261 levels for characteristic
hazardous waste. On September 19,1994, and April 8,1996, the Phase n and
ffl Land Disposal Restrictions (LDR) rules (US EPA 1994b; US EPA 199(5)
broadened these additional requirements by establishing "Universal Treatment
- Standards" for most characteristic (other than TC metals) wastes that had
concentration-based treatment standards. For the applicable wastes, these rules
identified more than 200 "Underlying Hazardous Constituents" (i.e., hazardous
constituents not present at the point of generation in amounts that exceed the 40
CFR 261 toxicity characteristic levels) that are now subject to LDR.
The Toxicity Characteristic Leaching Procedure (TCLP) is used to idenr
tify toxicity characteristic wastes. However, except for TC metals, the Uni-
versal Treatment Standards require Total Constituent Analysis (TCA) rather
than TCLP to be used to demonstrate the required constituent level for the
treated, waste.
US EPA has also proposed risk-based levels at which wastes are no longer
considered hazardous for purposes of RCRA subtitle C. In the Hazardous
Waste Identification Rule (HWIR)(US EPA 1995d), US EPA proposed such
risk-based levels for the majority of hazardous constituents found in listed
hazardous wastes. Wastes meeting these risk-based levels before or after
treatment could be disposed in facilities not subject to RCRA hazardous
waste management requirements. US EPA was required to finalize the
HWIR exit levels by December 15, 1996. US EPA additionally proposed to
allow the exit levels for some constituents to serve as alternative, risk-based
LDR treatment standards satisfying the "minimize threat5' standard of sec-
tion 3004(m) of RCRA. Where these risk-based levels are higher (less re-
strictive) than current treatment standards, based upon BOAT, they will effec-
tively supersede current standards. - -
Cleanup standards for environmental media contaminated with hazardous
substances at CERCLA sites are generally based on site-specific risk calcu-
lations to meet an acceptable level of risk rather than technology-based per-
formance levels. The risk is dependent on rates of release, routes of expo-
sure, the expected future use of the property or medium, and the specific
-------
Design Development
Record of Decision for the site, RCRA LDR treatment standards are also
applicable if hazardous substances removed from the CERCLA site are also
RCRA hazardous wastes. Hazardous waste treated and left at the CERCLA
site may, or may not, also be subjected to RCRA LDR treatment standards,
as determined in the Record of Decision, depending on the specific treatment
method and its location at the site.
3.7 Aqueous Stabilization/Solidification
3.1.1 Remediation Goals
3.1.1.1 Stabilization
Phosphate Processes, The primary operating advantages of phosphate
processes are low-waste volume increase, low cost compared to
cement-based processes, and ease of application. Their primary environ-
mental advantage is in the reported low leachability of lead compounds over
a wide pH range. In the process's basic form, a solution of phosphoric acid
or phosphate salt is mixed with the waste by spraying or combining in a
mixer. No other physical or chemical operations are required.
Phosphate treatment is best exemplified through commercial application
at a number of municipal waste-tb-energy incinerators using the WES-PHix®
process (O'Hara and Surgi 1988). These installations are totally enclosed,
in-line systems that are claimed to reduce leaching of lead and cadmium to
well below the TC requirements, thereby eliminating the need for RCRA
permits. The system can be used with or without the addition of lime to
adjust the pH, depending on ash characteristics. Phosphoric acid or any
convenient source of water soluble phosphate can be used, at ratios of about
1 to 8% KyPC^ based on weight of the ash. This process has reportedly been
used to treat more than 2,700,000 tonne (3,000,000 ton) of ash and other
particulate material as of 1993. In this application, the phosphate process is
considered conventional; however, application to remedial work is in the
developing stages. A remedial project that reported treating 11,800 tonne
.(13,000 ton) of lead slag (WMX Technologies 1993) is an example of the
adaptation of phosphate treatment. .
3.4
-------
Chapters
. Rubber Particulate. A major research effort at Chemical Waste Manage-
ment (Conner and Lear 1991) used natural soil spiked with 50 hazardous
organic compounds to test the efficacy of various additives for stabilizing
organics. Spiking levels ranged from 5 to 2,400 mg/kg, with total organic
levels between 0.5 and 1.0% by weight. Twelve different cement-based
stabilization formulations were tested. Each formulation contained 15% by
weight cement and 8% by weight additive to the weight of the waste. All
untreated and treated samples were characterized by TCA and TCLP for all
231 RCRA constituents (US EPA l994b). Summaries of the TCA results for
rubber particulate are given in Tables 3.1-3.3. The results are stated both in
absolute terms, with comparison to the US EPA Universal Treatment Stan-
dard (UTS), and in percent reduction factors as defined by US EPA. Abso-
lute numbers are important for judging how well a process meets regulatory
requirements and numerical treatability objectives. Percent reduction is also
provided because it is a much easier number to assimilate than comparing
raw data, because the degree of reduction is a method of setting treatability
objectives in remedial work, and because it is the best way to document
efficiency of the treatment process. Test results adapted from Conner and
Smith (1993) are given in Tables 3.1 and 3.2 for volatile and semivolatile
organics, respectively. Table 3.3 shows the results of testing a new variation
of rubber particulate, KAX-100™, obtained from the vendor (Environmental
Technologies Alternatives 1995).
Table 3.1
Immobilization of Organic Constituents Using
Rubber Particulate — Volatile Organics
Compound
Benzene
2-Butanone
Carbon Disulfide
1,2-Dichloroethane
Methanol
USEPA
Hazardous
Waste Code
D018
D035-
D028
Universal
Treatment
Standard
(mg/kg)
10.00
36.00 '
4.81
6.00
0.75
TCA Before
Treatment
(mg/kg)
200
640
640
270
1219
TCA After
Treatment
(mg/kg)
. <10
<50
<200
<100
444
" \«
Reduction
92
88
53
44
45
-------
Design Development
Table 3.2
Immobilization of Organic Constituents Using
Rubber Particulate — Semivolatile Organics
Compound
Bis(2-EthylhexyliPhthalate
Cresol
1,2-Dichlorobenzene
1,4-Dichlorobenzene
2,4-Dinitiotoluene
Hexachlorobenzene
Hexachloioethane
Lindane (gamma -BHC)
Methoxychlor
Nitrobenzene
Pentachlorophenol
'Pyridine
2,4,5-TrichIorophenol
2,4,6-Trichlorophcnol
Fhthalic Anhydride (as acid)
USEPA
Hazardous
Waste Code
D023-6
D027 .
D030
D032
D034
D013
D014
D036
D037
D038
D041
D043
Universal
Treatment
Standard
(mg/kg)
28
32
6.0
6.0
140
10
30
0.066
n
0.18
14
7.4
16'
' 7.4
7.4
28
TCA Before
Treatment
(mg/kg)
150
<9.9
160
147
226
143
114
124
59.5
166
233
1900
200
178
<30
TCA After
Treatment
(rag/kg)
<0.99
<0.99
5.64
6.03
<0.99
6.96
6.45
<5.0
<'5;0
3.66
0.60
<0.99
<4.8
<0.99
<3.0
%
Reduction
99
85 ( •' '
\
94
93
99
| '•
92
91
94
87
96
I
99
99
96
99
' 85
J •,
KAX-50™ rubber paniculate TCA reductions are compared against acti-
vated carbon and the EPA UTS in Figure 3.1 for several hazardous organic
constituents. Figure 3.2 shows the percent reductions in TCA test results for
the two addifives on the same constituents; tllese values have been corrected
to account for dilution by the additives and the cement binder, so that they
represent the real reduction in mobility. Reductions in TCA ranged up to
99%, indicating the immobilization of low-level organics by stabilization is
feasible. While the exact binding mechanisms are not yet known, it is evi-
dent that many organic constituents are so strongly held that even the organic
solvents used for the extraction step in TCA testing cannot remove them.
3.6
-------
Chapter 3
Table 3.3
Immobilization of Organic Constituents Using Modified Rubber
Particulate, KAX-100™ — Volatile and Semivolatile Organics
Compound
Benzene
N-Butanol
Carbon Disulfide
Chloroform
Cyclohexanone
1,2-DichIoroe thane
Ethyl Acetate
Iso-Butyl Alcohol
Methylene Chloride
1,1,1-Trichloroe thane
Trichloroethylene
1,1,2-Trichloro-
1,2,2-Trifluoroethanc
Bis(2-Ethylhexyl)Phthalate
Cresol
1 ,2-DichIorobenzene
1,4-Dichlorobenzene
2,4-Dinitrotoluene
Hexachlorobenzene
Hexachloroethane
Lindane (gamma-BHC)
Methoxychlor
Nitrobenzene
Pentachloro'pheno!
Pyridine •
2,4,5-Trichlorophenol
2,4,6-TrichIorophenol .
PhtHalic Anhydride (as acid)
USEPA
Hazardous
Waste Code
D018
D022
D028
0040
. ' D023-6
D027
D030
D032
D034
D013
DOW
D036
D037
D038 '
D041
D043
Universal
Treatment
Standard
(mg/kg)
10
2.6
4.81
. &0
0.75 '
6.0
33
170
30
. 6.0
6.0
30
28.
3.2
6.0
6.0
140
10
30
0.066
. 0.18
14
7.4
16
•7.4
7.4 •
28
TCA
Before
Treatment
(mg/fcg)
418
3350
83 , .
431
536
654
258
2100
62
550
881
9.1
150
<9.9
160
147
226
143
. 114
124
59.5
166
233
1900
200
178
<30
TCA After
Treatment
(mg/kg)
<30
<5.0
. <0.25 :
<10
<5.0
<0.25
<0.25 '
<5.0
<0.25
-------
Design Development
Figure 3.1
Comparison of TCA Results for Carbon vs. Rubber Pdrticuiate
150
I
100
50
Acetone Bis(2-Ethylhexyl)Phthalate 1,2-Dichloroethane Methylene Chloride
i Constituent
•• Carbon
E53UTS .
•" KAX
Source: Environmental Technologies Alternatives 1994a
However, no "magic bullet" exists in stabilization. Most of the additives
described by Conner and Lear (1991) are useful with specific contaminants
in specific test methods, and none work best for all. Carbon is effective
overall for reduction in TCLP teachability but not for reduction in TCA.
Paniculate rubber is not as effective in TCLP reduction, but is the only addi-
tive that was broadly useful for TCA reduction, especially for the
low-volatility compounds. Organo-clays are effective with specific contami-
nants, and so were other additives tested but not described here.
One surprising result of the above and other recent experimen >rk
(Spence et al. 1990) is that VOCs are not necessarily lost through volatiliza-
tion during S/S, as was previously thought (Weitzman, Hamel, and Cadmus
1987). Reductions in TCA levels suggest that VOCs sorbed onto or associ-
ated with soil particles might be less susceptible than expected to volatiliza-
tion during stabilization, at least in these slow exothermic reactions, i.e.,
3.8
-------
Chapters
cement-based systems under relatively static air flow conditions. Some
additives, such as rubber paniculate, have been shown in independent studies
(Environmental Technologies Alternatives 1994b), to substantially reduce
the evaporation rate of VOCs so that air pollution is minimized. The addi-
tives also reduce the flash point of the system, thus providing an additional
safety factor in treatment and disposal. This property of the additive is ex-
pected to be of increasing importance when new air pollution control re-
quirements for treatment units come into effect.
Figure 3.2
Comparison of TCA% Reduction Results for Carbon vs. Rubber Particulate
100
so
f.
40
20
Acetone Bis(2-Ethylhexyl)PhlhaIate 1,2-DichIoroethane Methylene Chloride
Constituent
•• Caifaon
•BKAX
Source: Environmental Technologies Alternatives 1994a
3.1.1.2 Cementitious Solidification/Stabilization
ProFix™. The PrqFix process has been commercially applied primarily as
a combined fixation agent and filter aid. It is a process employing rice hull
ash as the primary agent. However, the vendor has described the results of
-------
Design Development
Table 3.4
Organic Leaching from PioFix-Treated Waste
TCLP Leachate (mg/L)
Constituent ' Raw Sludge Treated Sludge
Methylene Chloride 20.0 <0.25
Chloroform 20.0 2.0
. i •'. ••. I
Trichloroethane 2.4 ' ; . 0.56
Toluene 2.1 0.80
Methanol "22.0 5.0
Benzene 30.0 0.76
Table 3.5
Metal Leaching from ProFix-Treated Waste
''\ " • TCLP Leachate (mg/L)
Constituent Raw Sludge . Treated Sludge
Lead 3.97 0.24
Chromium ' 7.1 0.05
Cadmium . 34.8 0.07
Copper 23.5 ' 0.43
Zinc 158.0 • 0.27
Nickel 32.1 ' . 0.18 .
several uses as a stabilization system (Tables 3.4 and 3.5). Data cited in the
patent (Conner 1992) illustrate the hardening reactions that occur. When a
mixture of water and rice hull ash was mixed with sodium hydroxide, no
hardening of the paste was observed after 7 days. When calcium chloride
was added to the mixture, it hardened in 7 days to >50 kPa (7 psi) bearing
strength, and after five months was hard while the sample without the cal-
cium chloride remained a paste! The addition of rice hull ash to a high pH
calcium sludge resulted in a very hard product (>430 kPa [62 psi] bearing
strength) after 12 days, but no measurable strength in one day. This is
3.10
-------
Chapter 3
compared to a- sample treated with sodium silicate solution where the
strength of 160 kPa (24 psi) was reached after one day, but only 170 kPa (25
psi) after 12 days, with no additional hardening thereafter. The continued
hardening demonstrated by the use of rice hull ash appears to support the
chemical theory of this process. The possible advantages of in situ genera-
tion of soluble silicate have'not been fully explored. Such development
should concentrate on the development of long-term properties, i.e., after
long curing periods or in long-term leaching procedures, since that is where
the advantages will likely lie. ,
Cement-Slag. The combination of Portland cement and slag for ordinary
S/S is not necessarily innovative, but its use for reduction and subsequent
stabilization of high-valence species is unusual and deserves inclusion here.
Oak Ridge National Laboratory (ORNL) tested various mixtures of slags
in combination with Portland cement and fly ash for the S/S of radioactive
wastes containing technetium and nitrates (Gilliam, Dole, and McDaniel
1986). Technetium ("Tc) is more mobile hi the higher valence state, Tct7, ,
than in the +4 oxidation state. Therefore, reduction of Tc+7 to To"4 is desir-
able in a stabilization process. This can be accomplished by a variety of
common reducing agents, such as FeSO4 or Na2S, but it was believed that
blast furnace slag, because of the presence of ferrous iron and sulfur, might
accomplish the same purpose at lower cost. The purpose of this project was
to test that hypothesis. The waste used in thet)RNL test project originated
from the treatment of an aqueous effluent, or "raffinate," from uranium re-
covery at the Portsmouth Gaseous Diffusion Plant in Portsmouth, Ohio. The
baseline stabilization composition used in the test program was:
• 38.3% waste sludge,
• 11.7% water,
• 25.0% Type I-DHLA Portland cement, and
. • 25.0% fly ash, ASTM Class F.
This mixture yielded treated waste that leached below US EPA primary
drinking water standards in the Extraction Procedure Toxicity (EPT) test,
and resulted in Leachability Index (LI) values of about 6 when subjected to
the ANSI 16.1 Leach Test (ANSI 1986). The filtrate was used for testing
the various "fixatives" — blast furnace slag, iron filings, FeSO4, and Na^S,
since it had similar concentrations of Tc and nitrate. The fixative results
compared to the treated waste without additives are shown in Table 3.6.
-------
Design Development
Table 3.6
Effect of Various Additives on Technetium
i Grout Composition (% by weight)
Constituent Added to Grout 1
Raw Waste
Water
Cement
Flyash
Iron Filings
FeSO4
NajS
Slag
• 13.9
36.1
25.0
25.0.
ANSI/ANS 16.1
2
13.9
36.1
23.2
23.2
3.7
3
" 113.9
36.1
24.0 '
24.0
2.0
4
13.9
36.1
24.6
. 24.6
0.9
5
30.0
20.0
24.6
24.6
0.9
6
40.0*
0.0
20.0
20.0
20.0
teachability Index. (30-day cure) .
99Tc
7.7
8.1
93
10.0
9.4
10.5
•Flltrat6
The results clearly demonstrate that adding blast furnace slag improves
retention of Tc. Six different slag sources were tested, and all gave similar
results. The £eSO4 and Na2S additives gave results similar to those of the
slag. Since the LI values are the negative logilrithm of the effective diffusion
coefficient, the slag additive improved Tc retention by almost three orders of
magnitude over the standard cement/fly ash formulation, and by 0.5 to 2.4
orders over the values obtained with other additives. Other data, not shown
here, indicated improved nitrate retention also, although only by 1.4 orders
of magnitude. The Tc results are largely attributed to reduction of Tc from
the +7,to the +4 valence state, reduced porosity and increased tortuosity.
The latter effect unproved nitrate retention.
" '!•'''!'•
The treatment of Cr*6 with slag and cement was reported by Rysman de
Lockerente (1979), but no teachability data were given. In 1991, Earth et
al. (1995) conducted a laboratory treatability study on a sodium dichromate-
contaminated soil using three reducing agents to reduce the Cr*6 to levels
3.12
-------
Chapters
that could be stabilized to within US EPA TCLR limits. -Results of the treat-
ability study are summarized in Table 3.7. The agents were sodium
metabisulfite and ferrous sulfate, both standard chromium reducing agents,
and blast furnace slag. When the reducing agents were used alone, neither
sodium metabisulfite nor slag met the requirement, but ferrous sulfate did.
However, when the agents were combined with cement in a complete S/S
process, both slag and ferrous sulfate gave nearly the same acceptable re-
sults. These results clearly show that slag is most effective for chromium
reduction in soils when used in combination with Portland cement.
The slag process has been applied only to metal-bearing wastes; however,
the processes should have general applicability except where reductive prop-
erties would be undesirable, such as in the treatment of certain arsenic-
contaminated wastes. Broader testing of blast furnace slag, both as a pri-
mary stabilizator and as an additive, would be beneficial. Slag is inexpen-
sive and available in most industrial locations. The cost-effectiveness of slag
processes decrease as the distance from the source to the site increases, due
to economic competition from locally-obtained waste materials, such as fly
ash, kiln dust, etc. ' •
3.1.1.3 In Situ Stabilization and Stabilization/Solidification
Aqger-type in situ systems for full-scale projects are new, and process
and mechanical improvements are still being developed (Millgard and
Kappler 1992). One of the first demonstrations of this technology was in
1988 using the Geo-Con system at a US EPA Superfund Innovative Tech-
nology Evaluation (SITE) project in Florida (US EPA 1991c). A small
number of full-scale projects have taken place since 1988. Morse and Den-
nis (1994) described one project in which 1,800 overlapping 2.4 m (8 ft)
diameter holes were drilled to stabilize organic contaminated soils with a
10% addition of Portland cement. The stabilized soil had an unconfined
, compressive strength of 414 kPa (60 psi), permeability of 1 • 10'5 cm/sec,
and leached less than 10 mg/L of polyaromatic hydrocarbons (PAHs).
3.1.2 Design Basis
The information necessary to design an aqueous S/S remediation process
or project is basically the same for all aqueous S/S processes. A summary of
the important design considerations and necessary data is given in Table 3.8
(Conner 1990; US EPA 1989a).
-------
CO
Table 3.7
. Leaching of Treated, Dichromate-Contaminated Soil
Concentration of Cr** and Total Chromium in TCLP Leachates From Treated Soil (mg/L)
... Reducing Agent Alone Reducing Agent + Cement (Binder/Soil Ratio 0.2)
J>peot sample Cr« % Reduction Total Cr %Reduction Cr* % Reduction' Total Cr % Reduction
Untreated Soil 38.0 _ 38.5 _ 9.65 74 93 76
Na2S205 Treated Soil 20.5 46 20.0 48 11.0 70 9.5 75 _
FeS04 Treated Soil 3.65 90 33 U5 97 U0 97
Slag Treated Soil 30.0 21 v 28.5 ZOS 94 l.g 95 ' .
'Parcent leaching reduction is calculated on the basis of chromium leaching from the untraatad raw son samples.
^ ,
s
tn
; !
-------
Chapters
.__• Table 3.8 :
Data Input and Considerations for S/S Process Design
Type of Information
Regulating Body
Regulatory Framework
Waste Characteristics
Required Stabilized Waste Properties
-
Site Characteristics
Operational and Economic Factors
Test Methods
-
CD Consent Decree
CFR Coda of Federal Regulations
FR Federal Register
FS Feasibility Study
RI Remedial Investigation
ROD Record 'of Decision
RWP . Remediation Work Plan
IB Treatabllity Study
Specific Information
US EPA Region
State
CERCLA
RCRA
State Laws
Private
Landbans
Universal Treatment Standards
Site-Specific
Metal Content
Metal Spoliation
Organic Content
Ignitability
Corrosivity
Reactivity
Radioactivity
Physical Characteristics
General Chemical Characteristics
Strength
Permeability
Leachability
Durability . .
Transportability
Water Table
Climate
Location, Depth and Extent of Waste
Soil/Geologic Characteristics
Presence of Debris
. Site layout
Logistics '
Utilities
Availability and Cost of Reagents
Quality and Consistence of Reagents
Pretreatment Requirements
• Materials Handling
Volume and Weight Increase
Future Land Use
Physical
Strength
Permeability
'Durability
Chemical
Leachability
Source
CD
Permit or CD
FR
CFR
RI
FS
ROD
RI
FS
TS
RWP
Pilot Study
FS
TS . . '
RWP
RI
FS
ROD
RWP
Site Walk
PDot Study
RI
FS
ROD.
RWP
Pilot Study
FS
ROD
CD
TS
RWP
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Design Development
In the case of auger-type, in situ stabilization, some additional informa-
tion is required since the reagent is normally injected in the waste as a slurry,
not in dry form. In this application, it is necessary to test the formulation to
determine if it can bemixed arid delivered hydraulically within the
timeframe and with the type of pumping ami injection equipment to be used.
Some commonly used S/S reagents, e.g., kiln dusts and quick lime, usually
react with-water too rapidly to be used in the auger-type system. This limita-
tion should be addressed in the laboratory treatability study so that it does
not affect the engineering design considerations.
i . ' , j - - . ! . . . ].:.
3.1.3 Design and Equipment Selection
, r. i .. . i .
All aqueous S/S processes have the same basic elements (Conner 1990)
when used in remediation projects, with certain variations for in situ designs.
The scale-up of aqueous S/S systems from bench-scale to field-scale implemen-
tation is usually quite straightforward and is well' defined. Pilot studies are
usually not required in ex-situ treatment except to assess operational problems.
A pilot test should always be conducted for in situ S/S applications.
'• ' :'. . ',;". . I ' ' • i •
3.1.4 Process Modifications
] . •! ' i
Aqueous S/S processes and systems are generally quite flexible and can
be easily modified to accommodate atypical site conditions, waste composi-
tion, reagent variations, and other variables. They can also be adjusted for
reasonable changes of scale, either larger or smaller. However, large
changes in scale may necessitate a review of the best reagent delivery sys-
tem. For example, going from a 10,000 m3 (13,080 yd3) project to one of
100,000 m3 (130,800 yd3) may justify switching from an ex-situ to an in situ
method because at large-scale, iii situ may be less expensive.
The laboratory treatability study and pilot phases, if conducted, of a
remediation project should always include a sensitivity analysis of the ef-
fects of changes in waste composition. Wide variations in water content will
usually necessitate a change in reagent/waste ratio to maintain consistent
final product quality. Variations in metals concentration, particularly in met-
als speciation, will often require a change in formulation to meet leachability
•standards. In addition, various compounds including chlorides, fluorides,
sulfates, phosphates, zinc, lead phenols, and many organic compounds can
interfere with cement hydration reactions and impede curing of the solidified
product. Variations in organic content can affect both leachability, and the
! 3.16 ! " ' '
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Chapters
immediate and final physical properties of the treated waste. Careful review
of the Remedial Investigation and Feasibility Study (RI/FS) and various
treatability studies can point out potential problems from waste composition
variations, and.preclude surprises later on.
3.1.5 Pretreatment Processes ,
Pretreatment processes that have sometimes been necessary prior to aque-
ous stabilization or S/S are listed below.
• Cyanide destruction
• Metal chelate destruction
• Cr46 and Tc+7 reduction
• As+3 oxidation
• Removal of volatile organics by steam or hot air stripping, or
thermal desorption
• High-level organic removal by soil washing, solvent extraction
• Destruction of organics by high temperature incineration
• Biological destruction of organics
• Debris size reduction or removal
• Size reduction of certain hard, porous materials
Treatment of inorganics by stabilization or S/S can require additional
processing steps. These operations, whether classified as pretreatment,
step-wise stabilization or S/S, or cotreatment, can be done with conventional
technology, although improved innovative technology might also be avail-
able. High levels of organic contaminants of concern, are usually removed
or destroyed in a separate pretreatment operation.
Cyanides, chelates, and metals pre- or cotreatment with S/S have been
used conventionally at RCRA Treatment, Storage and Disposal Facilities
(TSDFs) since the LDRs went into effect in 1988 and earlier at some other
central treatment operations (Conner 1990).. Cyanide destruction is typically
done with alkaline chlorination for amenable cyanides (Conner 1990) or
with more powerful oxidants for the more refractory cyanides and for metal
chelates (Diel, Kuchynka, and Borchert 1995). Chromium reduction along
with S/S was described by Conner (1990; 1991), arsenic oxidation by Lear
-------
uesigr i, ueveiopi i i«i 11
and Conner (1992), and technetium reduction by Gilliam, Dole, and
McDaniel (1986).
" , ' i ' ' ' " " • , .1
Organics can be removed or destroyed in situ by steam or hot-air sparging,
chemical oxidation (Siegrist et at 1992) or soil flushing (US EPA 1988; US,
EPA 199lb). Likewise prganics can be removed or destroyed ex-situ with ther-
mal desorption (Lighty et al. 1993) or incineration (Magee et al. 1994). Cya-
nide destruction and metal reduction/oxidation should be feasible in situ and
ex-situ, but, no full-scale treatment results have been reported. -
Debris, a frequent problem in remedial projects, can be handled in two
ways: (1) removal-by screening or other physical methods, or (2) by grind-
ing, shredding, or similar size reduction techniques. The primary require-
ment for debris pretreatment stems from limitations on the size or type of
debris that the S/S mixing method can accommodate. If the material is po-
rous and contains hazardous constituents that slowly diffuse out to the par-
ticle surfaces after S/S has been completed, size reduction might be neces-
sary (Wilson and Clarke 1994). An example is hexavalent chromium in
certain waste refractories. By decreasing the diffusion path length and in-
creasing the surface area, particle size reduction allows the stabilization
reactions to go to completion during the mixing stage.
3.1.6 Posttreatment Processes
; ' . .. • ;- '.;!•_ ' • ; j1 . , , • ; , :'.-]. ,;'
Wastes successfully treated by aqueous S/S processes do not normally
require any posttreatment. These wastes are usually disposed by landfilling,
or in the case of in situ treatment they are left in place. The landfill design
and/or closure plan and post-closure monitoring address possible releases to
the environment or dangers to human health. The only posttreatment control
required in some instances is to limit particiulate and VOC air emissions and
odor until the waste is landfilled and/or covered.
3.1.7 Process Instrumentation and Controls
Since the final properties of aqueous S/S products are usually not devel-
oped in the process system itself, monitoring these properties in real time is
not possible. Quality control is exercised by relating the S/S formulation to
the waste properties in the laboratory treatability and pilot studies, and sub-
sequently controlling the reagent and water addition during full-scale pro-
cessing. Instrumentation is primarily for the purpose of controlling waste,
3.18
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Chapters
reagent, and water feed rates. The instrumentation and controls used during
ex-sitii processing are standard in chemical processing and concrete formula-
tion. Most waste properties cannot be measured in real time, but some can
be and are used to "fingerprint" the incoming waste to detect gross varia-
tions. These include continuous pH, water content, and density measure-
ments. If a proper sensitivity analysis was performed in the treatability and
pilot studies, variations in these properties can often be used to change rer
agent and water feed rates hi real time, even in continuous' systems. At least
one such system successfully used a computerized control system for a con-
tinuous S/S plant (Bounini 1990). '
For in situ, auger-type systems, such fingerprinting is not feasible. How-
ever, reagent and water feeds can be controlled accurately.
3.1.8 Safety Issues •
. Three kinds of safety concerns exist when using aqueous S/S — those
associated with the waste, the reagents, and the equipment. All three should
be covered in the project health and safety plan. Concerns with the waste
have usually been thoroughly determined and accounted for during the
Rl/FS, project design, and implementation planning. Most of the reagents
used are not toxic-or hazardous in and of themselves, but can pose hazards
' when reacting with water and/or the waste; some regents do require special
handling for safety reasons. These hazards fall mostly into three categories:
inhalation of fine particulates, heat generated by exothermic reactions, and
evolution of gases. In some situations, sufficient heat may be generated to
cause burns and even pose fire and explosion hazards. Ammonia is the gas
most likely to be generated by reaction with the alkaline reagents commonly
used in aqueous S/S. These potential hazards must be addressed hi the
health and safety plan by providing proper ventilation, personal protective
equipment, and personnel training.
3.1,9 Specification Development
Most specifications used to procure vendors, equipment, and facilities in
aqueous S/S projects are similar to those used in chemical processing and
construction, modified to meet the needs of the project. The only unusual
requirements pertain to reagent quality, since some of the reagents used are
themselves waste products, e.g., kiln dust and fly ash. The quality of Port-
land cement and lime is well-defined by the ASTM and government
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Design Development
specifications. Kiln dust and hy ash are best defined by. the content of
free CaO, since that is the principal reactive ingredient; wide variations
in quality occur with these reagents. Other additives are usually com-
mercially-available chemicals and other products, the quality of which is
controlled by the supplier.
3.1.10 Cost Data
„ i . , , , , , i , , | , „:,':,,'' • '' i"- •
All of the aqueous processes described, with the exception of phosphate
and organic stabilization, use reagents that are conventional and commer-
cially available in North America in most locations at competitive prices.
Phosphate processes most frequently use phosphoric acid, and can often use
the cheaper agricultural grade Grgahic stabilization processes may use
virgin or recycled carbon, rubber particulate, organo-clays, or more exotic
additives. The latter additives are nearly an order of magnitude more costly
than the basic binders, but are normally usecl at much smaller concentrations.
Typical delivered prices for reagents are shown in Table 3.9.
'
Reagent
Table 3.9
teagerit Costs
1996 Price ($/ton)
Portland Cement
Blast Furnace Slag
Quicklime (untreated)
Rice Hull Ash
Phosphoric Acid
Activated Catbon (virgin)
Activated Carbon (recycled)
Rubber Particulate
Organo-Clays
Fly Ash
Cement Kiln Dust
10-20
50-90
about 400
300"-600
1000
500
300-400
500-1,000
15-40
20-40
3.20
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Chapters
Except for a few phosphate process cases, all of the wet processes use
much the same equipment and processing techniques; the primary difference
is between in situ and ex-situ delivery systems. Therefore, variations in the
commercial cost of aqueous S/S for different processes is determined prima-
rily by reagent costs for each delivery method and can be easily assessed and
compared on this basis. In the case of the phosphate process, the application
technique can sometimes be simple spray application of the phosphoric acid
or phosphate solution while the waste is moving through a conveying sys-
tem. In this instance, the processing cost is substantially less.
Since aqueous S/S is, in general, a proven commercial technology (or
group of technologies), the overall costs are well-established. For example,
costs are shown in Table 3.10 for one S/S.scenario (Conner 1992) involving
a large-scale remediation of a low-hazard, lead-contaminated soil at a "dry"
site in an industrial plant property. Of the total price for the remediation cost
of about $83/tonne ($75/ton), $55/tonne ($50/tori) is for the stabilization
Table 3.10
. A Typical Example of Aqueous, Ex-Situ S/S
Remediation Costs in 1990 with On-Site Landfill*
Cost Item •. Case "A"
Waste Type ' . So3
Contaminant/Level Lead/400 mg/kg
Waste Quantity . . 50,000 yd3
Transportation —
Mobilization/Demobilization $25,000
Treatabflity Study and QA/QC $30,000
Excavation . - .. $250,000
Stabilization $2,500,000
Landfill • $1,000,000
Total Cost $3,805,000
Approximate Total Cost per yd3 . $76
•These costs do not include typical oversight and monitoring.
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Design Development
operation. Of this $55/tonne ($50/ton), the typical reagent cost for a
cement-based process would be about $22/tonne ($20/ton), or about 40% of
the overall stabilization cost. This ratio is common for conventional pro-
cesses on large-scale projects.
' ; , , . "•] .' '."''!" ' '" , " "'M
The US EPA has pubh'shed a guide for documenting remediation costs for
various technologies (US EPA 1995a) which provides different levels of cost
categorization. For portable treatment units typically used in remediation,
the fifth level standardized work breakdown structure (WBS) applicable to
aqueous S/S is given in Table 3.11. Comparison of Tables 3.10 and 3.11
indicates that some items in the US EPA WBS are usually combined in pub-
lished S/S cost breakdowns. Also, the US EPA format does not specifically
include QA/QC costs, which are included in Table 3,10.
• j '.• .•)..„• ,• • . | •
For in situ S/S (and stabilization alone), solids preparation and handling
(WBS activity -01) is not required. The other activities are similar, but the
costs may be different, especially in the operation phase.
Table 3.11
Rfth. Leve| Work Breakdown Structure Cost Elements for Aqueous S/S
Interagency
WBS #33 XX XX 01-
Case "A"
01 Solids Preparation and Handling — Includes loading/unloading, screening, grinding,
' ; " pulverizing, mixing, moisture control, and placement/disposal.
04 Pads/Foundations/Spill Control — Includes materials and construction of facilities.
05 Mobilization/Setup — Includes activities needed to prepare for startup.
I - ' '• •'
06 Startup/Testing/Permits — Includes activities needed to begin operation.
f
07 Training — Includes training needed to operate equipment.
08 Operation (Short-term — Up to 3 years) — Includes bulk chemicals/raw materials,
fuel and utility usage, and maintenance and repair.
09 Operation (Long-term — Over 3 years) — Includes bulk chemicals/raw materials,
fuel and utility usage, and maintenance and repair.
10 ' Cost of Ownership — includes amortization, leasing, profit, and other fees not
addressed elsewhere.
11 Dismantling — Includes activities needed prior to demobilization.
12 Demobilization — Includes removal of unit.
3.22
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Chapters
3.1.11 Design Validation ....-._
The physical/mechanical design of the aqueous S/S system is essentially
the same for all of the individual technologies, varying primarily in whether
the process is operated in situ or ex-situ. Because this design is well proven
in many commercial applications, and scale-up and other variables are well
established, validation is normally not required. The only mechanical design
considerations for individual projects are the choice of type, size, and robust-
ness-of material handling equipment, particularly the mixer. These choices
are almost always among standard, off-the shelf equipment. The proper
application of the particular chemistry involved, however, must be validated
for the waste type and operating scenario under consideration. Chemical.
' design validation is done through bench- and pilot-scale testing on actual
waste materials. In the pilot phase, either scaled-down or full-scale commer-
cial equipment may be used. In the case of ex-situ S/S, the pilot phase is
often omitted, but pilot testing should never be neglected when in situ treat-
ment is to be done because of the greater uncertainties encountered in the
latter type of operation. A number of laboratories, consulting and engineer-
ing firms, and S/S vendors are available for evaluating various aqueous S/S
technologies and for choosing the best physical/mechanical design for the
operating system.
3.1.12 Permitting Requirements
The types of information required by regulatory agencies to gain approval
for aqueous S/S remediation projects were discussed in Section 3.1.2 and
listed in Table.3.8. Generally, this information is available from the combi-
nation of RI/FS, Record of Decision (ROD), Consent Decree, treatability
study, and pilot study. In addition, the regulatory agencies will require a
specific project work plan, health and safety plan, quality assurance project
plan (QAPP), and financial and liability information. Depending on the
project, the agency may also require closure and post-closure maintenance
and monitoring plans.
The primary purpose of these requirements is to ensure that the
project will be carried out as planned, that the treated waste will meet
the performance specifications, and that human health and the environ-
ment will not be unacceptably affected. Once the plan is approved, sjpe-
cific environmental permits may be required, depending on the state in
which the project is located. These permits are typically issued by the
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Design Development
I . i i _ i1
state and/or local environmental regulatory agencies. They can include
air permits, groundwater treatment permits, hazardous waste treatment •
and disposal permits, and/or building/zoning permits. Each project is
site-specific.
* . " . ' ' ' . . • '' ' 'i! "''
3.1.13 Performance Measures
There are two aspects of performance: process performance and product
performance. The latter subject is covered in Section 4.1.5, Quality Assur-
ance/Quality Control (QA/QC). Process controls, of course, ultimately af-
fect product QA/QC, but the methods and parameters are different. The .
controls used in aqueous S/S processes were discussed in Section 3.1.7.
i . ' ti | .
3.1.14 Design Checklist
3.1.14.1 Ex-Situ Aqueous Stabilization/Solidification
I ... •. I • . . , i :
1. Characterize the waste stream to determine the following pa-
rameters: homogeneity; presence of debris; moisture content;
particle size; pH; total alkalinity/acidity; reactivity, especially at
high pH; and major constituent composition (metals and organ-
ics, including nonhazardous organics, such as oil and grease).
2. Determine if pretreatment of waste is required. Examples are
chromium and techriicium reduction, particle size reduction,
screening, ptl neutralization, and dewatering.
3. Determine the product property requirements.
4. Complete a proper treatability study.
,;, ::, , I1 , " „ ! :.,':
5. Determine if there is any anticipated end use of the product or
the site. Petermihe final disposition.
' ;' '••. •••!'•' |. • •; ' •'. :•, i ':
6. Ascertain if there are regulatory requirements, such as permits,
etc. and initiate the permitting process.
7. Evaluate site conditions, such as working space, access for
equipment and reagent delivery, weather, groundwater infiltra-
tion, soil type and conditions, and underground utilities.
8. Determine if emission controls are required for volatile organ-
. ics, NH3, sulfur oxides, etc.
3,24
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Chapters
- ' 9. Determine the throughput requirements. - - --••
10. Complete pilot study, if necessary.
11. Prepare a QA/QC (QAPP) for acceptance by the regulatory
agencies.
3.1.14.2 In Situ Aqueous Stabilization/Solidification
1. Characterize the waste site/stream to determine the following
parameters: homogeneity; presence of debris; moisture content;
particle size; pH; total alkalinity/acidity; reactivity, especially at
high pH; and major constituent composition (metals and organ-
ics, including nonhazardous organics, such as oil and grease).
2. Determine if pretreatment of the waste is required. Examples
are chromium and technicium reduction and VOC stripping.
3. Determine the product property requirements, such as strength,
permeability, teachability, durability, and total constituent
analysis (organics).
4. Complete in situ treatability study.
5. Determine if there is any anticipated end use of the product or
. . the site.
6. Ascertain if there are regulatory requirements, such as permits,
etc. and initiate the permitting process.
7. Evaluate site conditions for working space; weather; access for
equipment and reagent delivery; groundwater infiltration; soil
type and conditions; soil bearing strength (for support of heavy
equipment); presence of debris; presence of "hot spots"; site-
geology; and underground utilities.
8. Determine if emission controls are required for volatile organ-
ics, NH3, sulfur oxides, etc. If so, select a proper size Air Pollu-
tion Control system.
• 9. Determine treatment rate requirements.
10. Complete pilot study. .
111 Prepare a QA/QC (QAAP) for acceptance by the regulatory
agencies.
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Design Development
3.2 Polymer Stabilization/Solidification
3.2.1 Remediation Goals
. i i. |- i ,
When applied in ex-situ S/S, polymer technologies can provide improved
mechanical integrity, durability, and leachability in the treated waste com-
.pared with conventional S/S technologies (Neilson and Colombo 1982).
Likewise, in situ applications of polymer S/S for treatment of buried waste
and contaminated soils improve performance of the stabilized product
(Heiser 1995). Difficulties in processing "problem" wastes with conven-
tional hydraulic cement grout and widespread failures of hydraulic cement
waste form products have been well documented (Neilson et.al. 1983; Place
1990; NRC 1991a; Lomenick 1992). In addition, conventional, hydraulic-
cement grout waste forms are relatively porous and therefore have relatively
high leach rates, especially for some contaminants, such as cesium, that are
not well-bound chermcaliy (Colombo and Neilson 1979).
.;, ' "...i , ,,"'' '.. " s1 •'.' I I1::'..; .' ,1 ,.••,. , ' '"' I .
In contrast, compatibility in processing a wide range of wastes and dura-
bility under anticipated disposal conditions has been established for several
polymer binders. The ability to withstand degradation from saturated soil
conditions, freeze-thaw cycling, microbial degradation, and high radiation
environments, has been confirmed for polyethylene (Kalb, Heiser, and Co-
lombo 1991a), vinyl ester-styrene (Dow Chemical Co. 1978), other thermo-
setting polymers (Heiser and Milian 1994), and sulfur polymer (Kalb et al.
1991). Leaching rates for waste that is microencapsulated in polymer waste
forms vary according to the type of polymer, the characteristics of the waste
(e.g., solubility, particle .size), and the quantity of waste encapsulated (waste .
loading). Typically, polymer leaching rates are about two orders of magni-
tude lower than those of conventional cement grout waste forms with equiva-
lent or lower waste loadings. For example, polyethylene encapsulation of
nitrate salt wastes, which are highly soluble and thus, susceptible to leach-
ing, reduced long-term leachability by a factor of 75 compared with conven-
tional cement grout (Fuhrmann and Kalb 1993).
Since no chemical reactions are required to solidify the final waste
form and solidification is assured on cooling, thermoplastic polymer
processes are inherently more reliable than conventional hydraulic ce-
ment grout systems. Regulatory acceptance of ex-situ polymer S/S tech-
nologies is being established. For example, the Nuclear Regulatory
3.26
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Chapters
Commission (NRC) has approved a topical report on the use of vinyl
ester-styrene for solidifying commercial low-level radioactive waste
streams (Dow Chemical Co. 1978). Other polymers, including polyeth-
ylene and sulfur polymer, have passed required test criteria for NRC
approval, but have yet to be submitted by a commercial vendor for for-
mal licensing. The US EPA has identified polymer macroencapsulatiion
of radioactive lead solids as the recommended BOAT (US EPA 1989c).
Considering that polymer S/S is a simple technology that is easily un-
derstood, widespread support from the public is anticipated.
Following successful technology development at Brookhaven National
Laboratory and Rocky Flats Environmental Technology Site, polymer
macroencapsulation of radioactive lead has been commercialized by
Envirocare of Utah, Inc. Under a contract with the DOE, Envirocare, the
only commercial, licensed mixed waste disposal facility in the U.S., is com-
pleting the treatment and disposal of 227,000 kg (500,000 lb) of mixed waste
lead shipped from various sites throughout the DOE complex. In addition to
radioactive lead, Envirocare is planning to treat mixed waste debris by polymer
macroencapsulation and a range of mixed waste solids (e.g., salt and ash) by
polymer microcapsulation. The State of Utah Department of Environmental
Quality has issued an operating permit for the macroencapsulation process and
is currently reviewing Envirocare's permit modification request to commercial-
ize microencapsulation.
Application of thermosetting polymers for in situ treatment of buried
waste (e.g., drums and debris) is currently under development in a collabora-
tion between Idaho National Engineering Laboratory, Brookhaven National
Laboratory, and Sandia National Laboratory (Heiser 1995). The objective of
this effort is to stabilize buried waste and reduce dispersion during planned
removal actions. Other potential applications of in situ polymer S/S are
treatment of contaminated soils and allowing the stabilized product to be left
in place. In a related effort that investigated the use of polymers for in situ
barrier walls around contaminated sites and leaking tanks, extensive data on
performance of polymer grout/soil combinations indicate that this technique
can result hi a stable, durable product. Testing of polymer grout/soil combi-
nations has included hydraulic conductivity; compressive strength; flexural
strength; splitting tensile strength; water immersion; acid, alkaline, and sol-
vent resistance; wet-dry cycling; chloride diffusivity; thermal cycling; and
irradiation stability (Heiser and Milian 1994).
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Design Development
• Regulatory issues associated with in situ injection of polymers in relation
to in situ polymer barriers was also investigated (Siskind and Heiser 1993).
The US EPA indicated that injection of polymers was essentially a construc-
tion operation and did not envision any regulatory problems as long as the
final product is inert. For in. situ S/S applications, further performance test-
ing, such as leaching, of the final products v/ould be required to ensure com-
pliance with federal, state, and local environmental regulations.
1 '! ' '
3.2.2 Design Basis
' • '• ' | r • ! .
As with other potential treatment technologies, polymer processes require
thorough characterization of the waste to enable technically-sound and
cost-effective selection of a polymer S/S system. Waste properties, includ-
ing types and concentrations of contaminants, chemical constituents, mois-
ture content, and particle size, are important'.' Location and condition of the
waste materials (e.g., contaminated soil vs. storage of sludge in buried
drums), as well as the total volume requiring treatment, play a significant
role in technology selection. Treatability studies which determine compat-
ibility of the waste and treatment systems, examine integrity and durability
of the final waste forms, and demonstrate compliance with applicable regula-
tory performance criteria are also key elements in the selection and design of
polymer systems. Specific design issues for each polymer technology are
discussed below.
3.2.2.1 Polyethylene Encapsulation
Since polyethylene can be used for either microencapsulation or
macroencapsulation, waste characterization data, such as particle size and con-
taminants, are needed to determine which technology approach will be used.
For mixed waste debris or contaminated solids with particles >60 mm (2.4 in.),
macroencapsulation can be used for cost-effective treatment, according to US
EPA regulations (US EPA 1992b). For aqueous solutions/dissolved solids,
sludges, resins, ash, and other wastes with relatively small particle size, polyeth-
ylene microencapsulation provides improved performance in the areas of me-
chanical integrity, durability, and teachability (Kalb and Colombo 1997). Since
polyethylene melts at 120"C (248SF), residual moisture driven off during pro-
cessing can cause'the formation of voids due to gaseous entrapment within the
melt. Therefore, moisture content can impact selection of optimal processing .
technology and/or the need for pretreatment to remove residual moisture.
3.28
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Chapters
Likewise, if significant concentrations (e.g., >1 % by weight) of volatile organ-
ics are present in the waste, they can be liberated during processing. In such
cases, the waste will require thermal treatment to destroy the organic constitu-
ents (thermal destruction) or capture of the organics in the offgas (thermal des-
orption) for further treatment.
3.2.2.2 Sulfur Polymer Cement Encapsulation
Because sulfur polymer cement (SPC) is a thermoplastic process and does
not require a chemical reaction for solidification, it is also applicable for the
treatment of a wide variety of wastes. It has been shown to be effective for
incinerator ash, aqueous concentrates (sulfate, bprate, and chloride salts),
sludge, and debris (Kalb and Colombo 1985a; Kalb, Heiser, and Colombo
1991b; Van Dalen and Rijpkema 1989; Darnell 1991). It is not recom-
mended for treatment of ion exchange resin wastes, because it is unable to
withstand swelling stresses that occur when resins are rehydrated. It is also
•unsuitable for nitrate wastes, because of potential dangerous reactions between
sulfur, nitrate, and trace organics (Kalb and Colombo 1985a). Strong alkali
(over 10%), strong oxidizing agents, aromatic or chlorinated hydrocarbons,
oxygenated solvents, carbon disulfide, bromoform, and other sulfur-dissolving
solvents might also have a deleterious effect on SPC waste forms. Additional
durability testing is recommended if these conditions are expected.
There are few data available on the long-term durability of SPC, hence
short-term tests have been used to project durability. The current test meth-
ods for biodegradation, ASTM G-21 and G-22, are not sufficient for sulfur
final waste forms, and the main concerns about SPC durability are biodegra-
dation and the ability of bacteria to oxidize elemental sulfur to sulfate over a
broad pH range (Mattus and Mattus 1994).
• Sulfur polymer cement can be used in microencapsulation or
macroencapsulation applications, hence the need to determine the waste
particle size, Its low melt viscosity makes it potentially well-suited for
macroencapsulation of debris waste, but this application has not been dem-
onstrated. As with other thermoplastic technologies, SPC is processed at
temperatures above the vaporization temperature of water, so that pretreat-
ment to drive off excess residual moisture is recommended. However, since
it is a batch process, it is more .tolerant of moisture contained in the waste
than is the polyethylene process. Small quantities of residual moisture are ,
easily driven off during batch mixing. Re-melt capability allows the final
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Design Development
• J
waste form to be easily remediated if unforeseen degradation occurs or if
more stringent future disposal requirements dictate.
3.2.2.3 In Situ Polymer Stabilization/Solidification
Concentration and density of contaminants in soils are significant issues
when considering this remediation alternative. For soils in which contaminants
are highly concentrated and/or localized to a small discrete area, in situ injection
of polymers for stabilization might be feasible. However, high concentrations
of contaminants in soils could exceed the capabilities of in situ polymer S/S
techniques to reduce contaminant migration to acceptable levels.
Performance assessment (PA) modeling of the site (under baseline condi-
tions prior to treatment and following polymer S/S) is useful in predicting
the potential success of in situ processes. In order to conduct credible PA
modeling, however, site-specific data on soil characteristics such as hydrau-
lic flow and the sorption coefficient, Kd, are required'. These data are gener-
ated through field measurements and bench-scale testing using actual soil
and grounciwater samples, respectively. To accurately predict teachability
reduction following polymer S/S, bench-scale and/or field testing of poly-
merized soils to determine permeabilities and leach rates, are required. In
situ polymer S/S might not be effective for soils contaminated with high
concentrations of organics, so extensive analyses of constituents, including
organics, inorganics, and radionuclides, are needed. Considering the rela-
tively high cost of thermosetting polymer materials, large volumes of con-
taminated soils might not be cost-effectively treated by in situ injection.
Therefore, field monitoring data on the concentration and geographical den-
sity of contaminants are required.
3.2.3 Design and Equipment Selection
Design and selection of processing equipment for polymer S/S depend on
the type of polymer (e.g., thermoplastic polymer such as polyethylene or ther-
mosetting polymer such as polyester styrene j and the manner in which the final
waste form will be produced (ex-situ vs. hi situ, microencapsulation vs.
macroencapsulation). In most cases, these technologies can be implemented
using readily available, "off-the-shelf" components, thereby lowering capital
costs and reducing time required' for implementation. Engineering require-
ments are primarily in the areas of sizing, specifying, configuring, and modify-
ing equipment to assemble components into an integrated processing system.
3.30
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Chapters
Details on system design and equipment selection are available in the literature
for some technologies (Patel, Lageraaen, and Kalb 1995), but as with other
emerging technologies, the engineer must often rely on prior knowledge and
engineering principles to adapt the necessary equipment required to fully inte-
grate the process. The following sections summarize available design and
equipment selection data, to provide a general background for engineers and
site administrators. As with other technologies, final equipment selection must
also account for waste- and site-specific conditions.
3.2.3.1 Polyethylene Encapsulation
. MICROENCAPSULATION. Microencapsulation of waste in polyeth-
ylene involves processing the thermoplastic binder and waste materials into a
waste form product by heating and mixing both materials into a homoge-
neous molten mixture. Cooling of the melt creates a solid monolithic final
waste form in which contaminants have been completely surrounded by a poly-
mer matrix. Heating and mixing requirements for successful microencapsula-
tion of waste in polyethylene can be met using proven technologies available in
various types of commercial equipment. Processing techniques for thermoplas-
tic materials, including polyethylene, are well-established within the plastics
industry. Extruders and mixers are available in a broad range of designs for the
manufacture of consumer and commercial products as well as for compounding
applications. Compounding (mixing additives, such as stabilizers and/or
colorants, with polymers) is analogous to microencapsulation of waste in ther-
moplastic polymers. The majority of commercial polymer processing has his-
torically been accomplished by extrusion, a process that has been used success-
fully for over 60 years. In the extrusion process, materials are heated to a mol-
ten state, mixed, forced through a die under pressure into a mold, and allowed
to cool, forming a solid product. Various types of extruders are available (e.g.,
single-screw, twin-screw) and each can be custom engineered by varying design
parameters, such as barrel diameter, length/diameter ratio, screw design, heating
and cooling systems, etc. In addition, numerous alternative techniques, such as
continuous, batch, and thermokinetic mixers, thin film evaporators, and
screwless extruders have been used to process polymers. Each of these devices
is reviewed here, with an emphasis on those systems most applicable for mi-
croencapsulation of waste.
Extruders — General. Screw extruders operate by converting a flow of
thermoplastic material and additives into a well-mixed continuous melt
stream. Extruder design, as shown in Figure 3.3, consists of a rotating
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Design Development
0>
O
O
V)
3.32
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Chapters
screw(s) within a barrel, forming a channel between the root of the screw
and the interior barrel surface. Material residing within this channel is
mixed, melted, and conveyed by helical flights on the rotating screw.
The process can be divided into three zones common to all screw configu-
rations. Beginning at the feed hopper, thermoplastic resins (in the form of .
beads, pellets, or powder) are fed directly into the feed throat. Additives,
including waste to be encapsulated, can be fed with the polymer or intro-
duced upstream by a "crammer" feeder. This feed zone contains deep chan-
nels and long screw flights that initiate the process by filling the channel,
building a pressure gradient, and conveying the unmelted ingredients
through the barrel. Next, the material enters the transition zone where exter-
nal thermal energy combines with frictional heat to melt the polymer. Exter-
nal heat is usually provided by a series of electric resistance heaters. Cool-
ing, necessitated by the buildup of frictional heat, is provided by cooling fans
or by circulating liquid coolant. The temperature is precisely controlled by
solid-state proportional-integral-derivative controllers. The reduced channel
volume in the transition zone compresses the unmelted material, eliminates air
pockets, and further increases the pressure. -The ingredients are mixed and
plasticized by the intense shear generated by the motion of the screw. Some ,
extruders have a venting zone about two-thirds of the way down the barrel. An
increase hi channel volume induces a pressure drop, enabling vacuum to be
applied at the vent to remove volatiles remaining in the melt. Finally, a sharp
decrease in the channel volume of the metering or pumping zone (located at the
end of the screw) further compresses the melt and increases the melt pressure in
order to pump me material through an output die. Extruder output dies are
designed to meet final product configuration requirements, but for the produc-
tion of final waste forms, complex die configurations are not required.
The motion of the screw advances the material throughout the process and
applies necessary shear forces to blend the polymer and additive. Screw
extruders have limited ability to remove residual moisture or other volatile
gases in excess of 5% (by weight) of the feed material, even when equipped
with vacuum venting. Volatile gases that remain trapped within the melt
cause foaming, undesirable voids, and reduction in final waste form density.
This reduces process efficiency, degrades mechanical integrity, and increases
teachability of the final waste form product. Pretreatment processes dis-
cussed in Section 3.2.5 (e.g., drying), might be used to make particular waste
streams more amenable to extrusion processing.
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Design Development
Screw extruders are primarily classified by the number of screws they
contain. The two most common screw extruders, single-screw and
twin-screw, have been used for waste encapsulation and are discussed here.
Other variations include two-stage compounding extruders, reciprocating-
screw kneader, and concentric-screw extruders.
Single-Screw Extruders. Single-screw extruders are well-proven in the
plastics industry for processing virgin and recycled thermoplastic polymers.
They have also been used for certain compounding applications such as the
mixing of fillers, colorants, and additives with a wide variety of thermoplas-
tics. This broad applicability is achieved with various screw designs. The
choice of screw type depends largely on the physical properties (liquid/solid
compatibility, bulk density, specific gravity, etc.) of the materials being pro-
cessed, as well as the level of mixing and process rates desired. Basic screw
designs include feed, transition, and metering sections with uniform screw
flights. Advancements in screw configuration have led to the incorporation
of second flights, interrupted flights, high-shear barriers, and various types
of mixing sections to improve performance! Every screw design, however, is
a compromise between productivity, melt temperature, degree of mixing, and
output uniformity. Examples, of some generic, single-screw types are shown
in Figure 3.4.
....( r :• • .
The basic metering screw in a standard single-screw design encompasses
the three zones described above. It is routinely used for the extrusion of
polyvinyl chloride compounds, fiber, and other fillers and has sufficient
mixing capabilities for many applications. Mixing, however, can be im-
proved by the Maddock mixing screw that uses a close-clearance mixing
section to deliver added shear. Higher melt temperatures normally associ-
ated with increased shear are controlled by placing the mixing section in an
area of the barrel subject to heating and cooling. This is readily accom-
plished since most extruders are equipped with temperature controllers along
the entire length of the barrel. An alternative mixing mechanism is provided
by the/wz mixing screw which contains multiple rows of pins that break
channel circulatory flow patterns to enhance blending without significantly
increasing shear. The barrier screw design improves melting by separating
melt and solids channels with offset barrier flights. This results in increased
output and/or reduced melt temperatures and improved pressure stability. •
The Maddock mixing section can also be integrated with the barrier mixing
screw. Another design option is the two-stage venting screw. In this option,
3.34
-------
ChaptorS
Figure 3.4
Various Screw Types Available for Single-Screw Extruders
-Feed
Transition
Metering
Feed
Basic Metering Screw
Transition Metering
•Maddock Mixing Screw
Feed Transition Metering
Pin Mixing Screw
Feed Trans. Meter' Vent
Meter
Two-Stage Venting Screw
Feed Barrier
Metering'
Barrier-Maddock Mixing Screw
Reproduced courtesy of Davis-Standard Corp.
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Design Development
a feed, transition, and metering section in the first stage dumps into a
deep-channel area followed by a recompression and pumping zone within
the second stage. Volatile gases can be vented through vent ports within the
let-down section. Additional variables that control product quality are screw
flight pitch angles, length-to-diameter ratio, and operational controls. Fur-
thermore, barrel designs can be modified to include grooved or tapered sec-
tions,to enhance throughput.
Years of proven application within industry make single-screw extruders a
dependable technology that yields advantages in its simplicity, operating
ease, low maintenance, and great versatility at lower operating costs when
compared to other competing processes. An integrated, full-scale polyethyl-
ene encapsulation process based on single-screw extrusion has been success-
fully demonstrated (see description in Chapter 5).
Waste particle size can limit the use of single-screw extruders. De-
velopment work at Brookhaven National Laboratory has indicated that
single-screw processing can successfully microencapsulate waste mate-
rials with mean particle sizes ranging from 50 to 3,000 jJm (2 to 118
mils). Smaller mean particle sizes are difficult to mix with viscous ther-
moplastics and larger particle sizes require size reduction prior to feed-
ing. Recent advances in screw designs, sophisticated control systems,
and modified feed mechanisms have minimized limitations associated
with single-screw extrusion. New developments linking single-screw
extrusion with pretreatment by thermokinetic mixing promise to reduce
or eliminate particle size constraints, while improving overall mixing.
Twin-Screw Extruders. Twin-screw extruders, designed with two screws
placed side-by-side, have proven versatile for handling difficult compounding
jobs, such as glass-fiber, high-loading fillers and heterogeneous plastics. Screw
arrangement can be tailored to meet distinct processing requirements, allowing
unproved control of critical operating parameters, such as residence time, de-
. gree of shearing, and processing temperature. In addition, intermeshing screw
flights deliver a unique forced-conveying or pumping property that broadens the
conveying capabilities of this type of extruder. As a result, the twin-screw ex-
truder can function like a positive screw-type pump to handle difficult-to-feed
materials. Options in screw configuration can further expand versatility through
the addition of intense mixing and shearing elements, venting zones, or a vari-
ety of process-specific devices. As shown in Figure 3.5, twin-screws are nor-
mally categorized as either co-rotating or counter-rotating, with further
3.36
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Chapters
classification of intermeshing and non-intermeshing designs. A new line of
reversible intermeshing twhi-screw machines can operate in both co-rotating
and counter-rotating modes.
Figure 3.5
Types of Screw Configurations for Twin-Screw Extruders
Co-rotating
Counter-rotating
Nonintermeshing
Partially
Intermeshing
Fully .
Intermeshing
Source: Frados 1985
Co-rotating screws are commonly used in processing nylon, thermoplastic
polyester, and polypropylene. In this configuration, two screws rotate in trie
same direction, deflecting the ingredients on a figure eight pattern around
both screws resulting in an excellent exchange of material! At the same
time, small uniform clearances be.tween intermeshing screw flights yield a
unifonn residence time for each melt particle while also helping to eliminate
dead spots. Co-rotating screws, however, are limited to conveying material
-------
Design Development
through drag flow mechanics, Whereas the counter-rotating intermeshing
design operates as a positive-screw type pump, thereby broadening its range.
of application. A counter-rotating intermeshing arrangement can also pro-
vide greater control of mixing, shearing, and conveying properties by regu-
lating the amount of clearance between the screws. For example, narrowing
the gap generates higher shear as material is forced through a smaller open-
ing but lowers output with, less area for longitudinal transport.
Non-intermeshing counter-rotating screws are open both lengthwise and
crosswise to promote generous mixing of material between screws, as well
. as conveying material at higher outputs. However, this "open" design limits
the control over and degree of shearing the screw can impart.
Twin-screw extruders were originally adapted for waste encapsulation
using bitumen in the mid-1970s (Werner and Pfleiderer Corp. 1976). A
production-scale process was installed to process low-level radioactive waste
generated at the Pallisades Nuclear Power Plant in Michigan. More recently,
development efforts at Rocky Flats Plant have successfully used twin-screw
extrusion for microencapsulating wastes in polyethylene. The process has
been demonstrated at laboratory-scale for both surrogate and actual mixed
wastes (Faucette et al. 1994). Some advantages claimed over single-screw
extruders include greater versatility for compounding "difficult-to-mix"
materials and better control of shear and temperature parameters. In addi-
tion, the gear-pump effect makes it possible to accept difficult-to-feed mate-
rial as well as allowing for multiple downstream feed zones which can elimi-
nate the need for pre-blending. Material pretreatment requirements are simi-
lar to those of single-screw extruders, but due to improved dispersive mixing
in twin-screw extruders, a broader particle size range may be tolerated. Dis-
advantages of twin-screw extruders compared with single-screw are higher
capital costs and higher operating costs (due to more frequent and costly
maintenance requirements) and more complicated operations.
Thermokinetic Mixers. The major difference between thermokinetic
mixers and extruders is that they operate in batch mode, instead of continu-
ous processing, and do not require any external heaters. Heat to melt the
thermoplastic polymer is supplied' by frictfonal energy developed during
high speed, high shear mixing. By processing in a batch mode,
thermokinetic mixers can thoroughly mix to a degree unattainable in the
continuous screw designs. Although some differences exist, the
thermokinetic mixer operation begins with measured quantities of polymer
and additives being fed through the top of the machine into a mixing
.•.! . ;••• • • ."i ^:"' '. , ] • , "i ••
3.38
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Chapters
chamber where blades of various designs and arrangements rotate at high
speeds producing the desired modes of mixing, fluxing, and shearing. Once
the material reaches a predetermined parameter (temperature, energy, or
residence time) which occurs rapidly (15 to 30 seconds), it is discharged as a
molten mass through a gate at the bottom of the machine. At this point, the
process cycle is, complete and the mixer can be charged with another batch.
Material impingement against the blades and chamber wall thoroughly
mixes and disperses the ingredients. Mixer operation variables that can be
controlled are limited to blade or rotor speed, residence time, and indirectly,
degree of heating/cooling. In tests sponsored by one manufacturer, the de-
gree of mixing was found to be superior to both single- and twin-screw mix-
ers (Kalb 1995a).
These high-intensity fluxing mixers operate with a powerful drive and are
distinguished by a,single rotor mounted with staggered blades placed at
various angles. A typical thermokinetic mixer is shown in Figure 3.6. Re-
volving at .high speeds (blade tip speeds up to 45 m/sec [148 ft/sec]), the
rotor produces a fast-paced mixing action that causes a rapid temperature
rise as intense shearing converts mechanical energy to heat. The combina-
tion of shorter production cycles and the lack of external heating helps re-
duce overall operational costs for a variety of thermoplastic processing ap-
plications. These mixers are also more flexible than extruders in processing
blends of thermoplastic polymers, especially co-mingled recycled polymers.
Other advantages include simplified operations, low maintenance costs, and
high filler loading capacities (high waste loading capacity). High-intensity
mixers can process a wide range and combination of ingredients, from pli-
able to extremely rigid materials, without changes to machine parts as might
be required for screw extruders. Such versatility can reduce down time and
simplify encapsulation processing requirements when several plastic/waste
combinations are treated. Batch processing allows each particle to receive
the same amount of work, improving control of residence time, temperature,
and product uniformity, while simplified feeding increases the range of poly-
mers and additives that can be compounded. High-shear mixers can process
materials containing up to 50% (by weight) moisture, reducing or eliminat-
ing material pretreatment requirements. The extremely high blade speeds ,
and rapid cycle times of high-shear mixers used because of batch charging
and discharging can adversely affect productivity and batch-to-batch product
consistency, as well as cause greater difficulty in precisely controlling melt-
ing and mixing.
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Design Development
Figure 3.6
Schematic of atypical Thermokinetic Mixer
Integrated
Screw Feed
Mixing,.
Chamber
Drive
Adjustable
Temperature
Control Panel
Signal to Discharge Door
Source: Frados 1985
Currently, Brookhayen National Laboratory is working with EcoLex, Inc.
(Jacksonville, Florida) to combine the advantages of thermokinetic mixing and
single-screw extrusion in one cost-effective process. The thermokinetic mixer
is used to remove residual moisture, reduce the size, premix, and melt the waste
and thermoplastic polymer binder materials. The homogeneously-mixed, mol-
ten mixture is then fed to a single-screw extruder which continues to mix the
materials and converts the process from batch to continuous operation. The
combined process promises improvements in product performance and consis-
tency, while providing increased processing flexibility for microencapsulation
and macroencapsulation in one integrated system.
Other Processing Techniques. Other processing techniques for heating
and mixing both polymer and waste are vertical, thin-film evaporators and
screwless extruders, A thin-film evaporator is a drying device that takes
3.40
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Chapters
advantage of an enlarged surface-to-volume ratio for quick and efficient
heating and vaporization. Waste material and thermoplastic resins are fed at
the top of the evaporator, spread into a thin layer, and conveyed through the
device by gravity flow. Externally-applied heat simultaneously dewaters the
waste and melts the polymer while material flow creates limited mixing for
microencapsulation. The endproduct is a molten mixture that exits continu-
ously out the bottom of the thin^film evaporator. This unique processing
scheme takes advantage of waste pretreatment (drying) technology to melt
and mix for polymer encapsulation. As a result, die need for waste
pre-processing can be either reduced or eliminated. However, feed materials
must be free-flowing; pretreatment in the form of grinding or reduction is
requked for large, bulky materials. Thin-film evaporators are also limited by
high viscosity melts that occur with many thermoplastics and at high waste
loadings resulting in disrupted gravity conveyance and material discharge
problems. Despite using low molecular weight and low viscosity wax, tests
conducted by Rocky Flats Plant indicate a limited maximum waste loading
of 40% (by weight)(Faucette et al. 1994) compared to maximum waste load-
ings of 70% (by weight) using extrusion for selected wastes (Kalb, Heiser,
and Colombo 199la).
Screwless extrusion devices, including disk-type extruders, gear pumps,
planetary-gear extruders, roller extruders, and ram extruders, have been in
existence for years. Many of these devices were designed to meet unique
requirements of specific processing applications and, therefore, lack the
versatility and productivity found in conventional screw designs. To date,
none have been used for waste encapsulation applications.
MACROENCAPSULATION. Macroencapsulation is advantageous
when treating waste consisting of large or abrasive particles not suitable for
processing through the extruder. The waste can contain large metal parts or
fragments (e.g., contaminated equipment, drums, lead turnings), dry radio-
active waste (e.g., trash, gloves, bottles), debris (e.g., decommissioning and
demolition waste), or previously treated waste/waste form products (e.g.,
filters, degraded grout). The waste to be macroencapsulated is packaged in
a porous structure or cage, placed in a drum with a slightly larger diameter,
and the voids.are filled with polymer. Numerous polymers, including poly-
ethylene, epoxies or other thermosetting resins,, and sulfur polymer, can be
used to surround the waste and fill the voids.. Single-screw extruders are
ideal for polyethylene macroencapsulation applications, since they provide the
most economical source of continuous molten plastic output. Mechanical
-------
Design Development
rotation of the drum during processing prevents, localized buildup of poly-
mer and provides even filling of the annqlus surrounding the waste. Figure
3.7 is a photograph of a bench-scale test sample that contains dry active.
waste macroencapsulated in polyethylene, The DOE has supported com-
mercialization of polyethylene macroencapsulation, currently being imple-
. mented at Envirocare, Inc. (Salt Lake City, UT). Under DOE sponsorship,
up to 227,000 kg (500,000 lb) of radibactively-contaminated lead is being
treated by polyethylene macroencapsulation and disposed at Envirocare.
One disadvantage of using polyethylene for macroencapsulation is its
inability to completely fill internal void spaces between the waste particles.
Due to its high melt viscosity and the high thermal mass of the waste mate-
rial to be macroencapsulated, polyethylenei may cool and solidify before
fully penetrating the wasted Although polyethylene macroencapsulation of
lead is identified by 'the US EPA as a BOAT, me need for complete penetra-
tion of voids is not clearly defined from a regulatory perspective. Lower
melt viscosity thermoplastics, such as sulfur polymer, might provide better
penetration, but would still tend to solidify on contact with a large thermal
mass. Preheating the waste would improve penetration of the polymer, but
requires additional energy and an additional process step. Thermosetting
resins, such as polyester styrene or epoxies, can be used to "flood" the con-
tainer and better penetrate the voids. Vacuum or pressure can also be applied
to enhance or accelerate penetration. "A vacuum enhanced delivery system
for thermosetting resins was demonstrated for macroencapsulating com-
pacted dry active waste at Brookhaven National Laboratory (Franz, Heiser,
and Colombo 1987). A gravity-fed delivery process for macroencapsulation
using epoxy resins was developed by Rocky Flats Plant (Faucett et al. 1995).
. UNIT SIZING. Unit sizing and design of processing equipment for
polyethylene encapsulation of waste depends on:
• the type and volume of waste to be processed;
• operational considerations such as available space, staffing for
operations and maintenance, need for remote handling,- and stor-
age capacity; and
; "• , ' . ': ' . I ' '. I. ,' " • ;.'•' ••••'. I.-;
• evaluation of capital and operating costs to provide an optimal
balance in cost-effective operational efficiency.
Versatility to accommodate a broad range of wastes and intra-waste vari-
ability is an important design consideration.. For example, significant
" : ' » l' ' ', '' I, •'',''' " ' 1 1, :"
3.42
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Chapters
.Figure 3.7
Photograph of a Typical Bench-Scale Sample of
Lead Wool Macroencapsulated in Polyethylene
Source: Kalbetal. 199Sa
-------
Design Development
savings and process simplicity can be achieved if a single process is de-
signed to Handle both aqueous liquids and dry incinerator ash residues (mi-
croencapsulation), as well as miscellaneous debris and lead scraps
. (macroencapsulation). Extruders and mixing equipment described are com-
mercially available in a wide range of sizes with potential output ratings
ranging from several Ib/hr to many ton/hi.
Space requirements can range from small bench-top units to large skids -
requiring several hundred square feet. The Brookhaven National Laboratory
production-scale treatment system (rated at 900 kg/hr [2,000 Ib/hr]) is con-
figured as a fixed-base system and occupies approximately 28 m2 (300 ft2).
During the design phase, all components of a fully-integrated system must
be considered. (Capacities and physical space "requirements for all ancillary
equipment, such as pretreatment systems, materials handling systems, feed-
ers, processing equipment, arid monitoring and process control systems,
. must be compatible.
."1 • ... • J ' •.'. .}.. . •-..: ,... .• i .
The need for remote handling and processing of waste materials provides
an additional challenge for system designers. However, materials handling
systems for waste and binder materials and remote drum handling equipment
are readily available and have been used in the commercial nuclear power
industry for many years. Process monitoring and control equipment can
easily be installed away from processing areas to minimize operator expo-
sure to radioactive and hazardous materials.
Polymer encapsulation processes are amenable to fixed-base or mobile
skid-mounted configurations. For mobile units, separate components (e.g.,
pretreatment, extruder, material handling, process control) could be mounted
in modules that are easily assembled and disassembled for shipping.
Unit sizing for macroencapsulation depends on the size of debris being
treated and the volume of waste. As discussed previously, extruders are
readily available in numerous sizes with output rates ranging from 9 kg/hr
(20 Ib/hr) to several tons/hr. Prototypical 208 L (55 gal) drums of debris
have been successfully processed to date. A typical production-scale 11.4
cm (4.5 in.;) single-screw extruder, rated at 900 kg/hr (2,000 Ib/hr), can pro-
cess a 208 Ldrum of macroencapsulated waste in about 18 minutes.
Envirocare has installed a 11.4 cm single-screw extruder, as described, at
their facility in Clive, Utah, to process DOE mixed waste lead and debris.
3.44
!U nil,tmi; :ii i nil.!;..!, :„. a1!:! an:, '.tniiaaiii iiiiiiiiiii^ "Mian i
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Chapters
3.2.3.2 Sulfur Polymer Cement Encapsulation
A major advantage of SPC is the simple design required for stabilizing
waste. A process-flow diagram for SPC is shown in Figure 3.8. A discus-
sion of the equipment required and its operation is provided below.
Figure 3.8
Process-Flow Diagram for Sulfur Polymer Cement
Applicable Generic Wastes
Incinerator Ash
(Ry/Hearth)
Dry Solids
Wet Solids (Sludges)
• Aqueous Concentrates
Dual
Planetary
Orbital
Mixer
I
Offgas
Treatment
(Baghouse)
Final Waste Form
. Feeding the waste and SPC into the mixer must be done precisely in order
to ensure proper waste loading. Brookhaven National Laboratory has shown.
that either volumetric or loss-in-weight feeding (Kalb 1995b) effectively ,
control material flow rates. The same type of feeders can be used to feed
additives, if necessary.
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Design Development
' . - ' : •„! '•• I ' •'•..•'• • . ..;.•-- -)•«... '.
Bench-scale development work at Brookhaven National Laboratory was
conducted using several types of heated batch mixers including low- and
high-shear blade mixers and double planetary orbital mixers. The latter
provides a highly-efficient mixing pattern at relatively low mixing speeds,
thus reducing air and gas entrainment in the molten mixture. Heating can be
achieved by thermocouple-controlled electric resistance band heaters, steam,
orhot oil circulation heaters'(j^bjpi Colombo 1985a; Kalb, Reiser, and
Colombo l991b; Adams and Kalb 1996). .
Two types of production-scale mixers have been evaluated by Idaho Na-
tional Engineering Laboratory (Darnell 1993). One is a Holo-Flite mixer
produced by Denver Equipment Company. The other is a Porcupine Proces-
sor. Both mixers use hot oil as the heating agent. They pump the oil through
the hollow shafts, flights, and external jacket. Both can be easily modified
to extend the heated jackets to heat the shafts. This will allow the re-melting
of solidified waste product without damaging the mixer (Darnell 1993).
The Holo-Flite mixer is shown in Figure 3.9 and has a dual shaft with 18
cm (7 in.) diameter flights. Each of the shafts is approximately 4.0 m (13 ft)
long. This horizontal mixer can place heat within 5.1 cm (2 in.) of every
waste particle, thus preventing hot spots and allowing remelt after shutdown.
As a closed system, the mixer is designed to confine dust and gases by oper-
ating at a negative differential pressure (Darnell 1993). The Porcupine Pro-
cessor, 'as shown in Figure 3.10, has a single shaft with 30 cm (12 in.)
flights. The shaft is approximately 1.8m (6 ft) long. Instead of having a
continuous screw, this processor has hollow paddles shaped like beaver tails
(Figure 3.li). Scientific Ecology Group, Oak Ridge, Tennessee, has con-
ducted pilot-scale testing of SPC encapsulation for mixed waste fly ash us-
ing a steam-heated, high-shear mixer. They have reported successful results
for processing batches of approximately 1,360 kg (1.5 ton).
': • "' . .... | ^, ^ ' - i
Some mixers allow processing under negative pressure conditions. Oper-
ating under vacuum reduces the necessary processing temperature and facili-
tates capture of any offgases that are generated.
3.2.3.3 In Situ Polymer Stabilization/Solidification
A number of technologies that have been used to place conventional grout
walls and curtains can be.used with in situ polymer S/S. These include deep
soil mixing, jet grouting, and permeation grouting. Other methods, such as
excavation or trenching and displacement/replacement techniques, involve
-------
Chapter 3
Figure 3.9
Holo-Flite Mixer
Heated
Contaminated
SPC Fines
Weir
Offgas
Source: Darnell 1993
removal of the soil, treatment, and replacement in the ground. Strictly
speaking, such technologies are ex-situ. Deep soil mixing relies on a verti-
cal auger to bore a large diameter hole in the soil and mix the soil with the
polymer, which is injected under low pressure (-2.1 MPa [~300 psi]). Jet
•grouting uses a rotating pipe that is drilled into the soil. The polymer is
injected through a small orifice (.1 mm [39 mil] diameter) at high pressure
(-34 MPa [-5,000 psi]) as the pipe is gradually withdrawn from the soil.
Penetration is typically 1.5 to 2.0 m (4.9 to 6.6 ft) in diameter. A recent
modification to jet grouting, known as "super jet-grouting" uses very high
pressures (up to 170 MPa [25,000 psi]) to hydrofracture and inject the
grout. This technique might be useful in treating sites where buried waste
in the form of drums and containers needs to be breached for complete
treatment. Permeation grouting injects low viscosity materials through a
series of injection wells at low pressure (-0.69 MPa to 1.38 MPa [-rlOO to
-------
Design Development
"iiMiS'
Figure 3.10
Porcupine Processor
I? "i .:,, '•> ,i! . .,
Product
Inlet '
Porcupine Agitator
Breaker Bars'
Stuffing Box
'Opposing breaker bars, on opposite wall of vessel, not shown.
Source: Darnell 1993
200 psi]) and relies on permeation through the soil for penetration. A recent
evaluation of these methods for use with emplacement of barrier walls
(McLaughlin et al. 1992) recommended peimeation grouting and jet grout-
ing as the most effective methods for placing polymer barriers. These tech-
niques are illustrated in" Figures 3.12 and 3.13. Permeation grouting is sus-
ceptible to hydrofracturing and short-circuiting which make it difficult to
control the flow of grout. Deep soil mixing is effective for contaminated
soils, but.might not be applicable for buried waste; penetration of the augers
might be hindered by the waste.
!
3.48
J. I!"!1*1 i ''tL. ,!*';: '•. ' iSiisi:t '!-: i llftiTl.' ", 'n!'ii; ':':S „'!::„I
-------
Chapter 3
Figure 3.11
Porcupine Processer Paddies.
Distribution Tube
Paddle
Annulus
Source: Darnell 1993
Figure 3.12
Subsurface Barrier Installation by Permeation Grouting
Source: Heiser and Milian 1994
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Design Development
Figure 3.13
Conventional Column Jet Grouting
Source: Helser and Milian 1994
To select the most appropriate in situ teclmology, the following factors
must be considered: the placement effectiveness, site soil conditions, pres-
ence of buried waste (other than soil), volume of soil to be treated; and eco-
nomic feasibility! It is also important to remember that treatment of waste
contaminated soil is different than placing a barrier when extrapolating bar-
rier placement data.
3.2.4 Process Modifications
3.2.4.1 Polyethylene Encapsulation
• ! , i ' ' ' i .'
A major advantage of polyethylene S/S is that it does not require a chemi-
cal reaction to solidify and therefore, is not usually affected by changes in
waste chemistry over tune. Varying the type of waste to be processed or the
physical characteristics of a given waste stream might require modifications
in pretreatment requirements, waste loading specifications, polymer type,
feed mechanism, feed rates, process rates, or zone temperatures. When
!' ' . '
'! ''3.50'
-------
Chapter 3
variations in waste types and/or conditions are anticipated, the system .should
be designed for maximum flexibility. In some cases, modifications in the ex-
truder screw design might provide optimal processing results. For example, one
or more alternative screw designs should be kept on hand in case they are
needed. Many varieties of polymers with a wide range of melt temperatures,
' melt viscosities, and mechanical properties are available both as virgin materials
and as recycled feedstock. Varying the type(s) of polymers or the mix ratio of
several feedstock polymers can dramatically affect processability and final
product performance. While the extrusion process is generally forgiving, vary-
ing waste loading specifications, feed rates, and zone temperatures is usually
required to optimally process a given waste stream. Additives might be incor-
porated to reduce leachability of contaminants. Several materials such as so-
dium sulfide and sodium hydroxide have been used to reduce solubility of toxic
metals and hence reduce leachability of the encapsulated final waste forms.
3.2.4.2. Sulfur Polymer Cement Encapsulation
Depending on the type of waste and its chemical and physical characteristics,.
process modifications might be required. For example, additives to enhance
mechanical integrity (e.g., glass fibers) can successfully mitigate the expansive
forces of soluble salts that can cause cracking when the waste form is exposed
to saturated conditions. Brookhaven National Laboratory added 0.5% (by
weight) of glass fibers into SPC for ash wastes that were high in chloride sails
to eliminate cracking attributable to immersion in water (Kalb, Heiser, and
Colombo 199 Ib). High concentrations of toxic heavy metals can cause the
encapsulated waste to fail US EPA TCLP concentration limits. Additives have
also been shown to decrease leachability of toxic metals when excessive con-
centrations of. metals are present in the waste. Brookhaven National Laboratory
has reported that the addition of sodium sulfide when mixed with the waste and
SPC can effectively stabilize the toxic metals. The sodium sulfide reacts with
metal salts to form a low solubility metal sulfide within the microencapsulated
waste form.. A ratio of 0.175:1, sodium sulfide to fly ash was reported as an
effective ratio to enable the treated ash waste (which contained 7% [by weight]
soluble lead salts) to pass the TCLP (Kalb et al. 1991).
3.2.4.3 In Situ Polymer Stabilization/Solidification
In situ applications are, by definition, more diverse than ex-situ. There-
fore, site-specific conditions including soil characteristics (composition,
-------
't it''" '"i1; w "'I",,,
Design Development
| , .. . ' , , , ; ...
particle size, permeability, moisture content), volume, arid remediation re-
quirements, will foster a need for process modifications from one application
to anbther. In some cases, the type of polymer will need to be varied based
. on cost, viscosity, chemical compatibility, etc. In other cases, the placement
technology will require tailoring to the specific conditions of the site. For
example, if me site contains a high concentration of low permeability clays,
a placement technique that provides more active mixing (e.g., deep soil au-
guring) rather than one that relies on permeation through the soil, would be
preferred. Once a given technique aiid material are selected, modifications
can still be made to improve system performance. For example, quantities
of catalyst and promoter can be varied depending on requirements of the
soil. Lower concentrations of catalyst and promoter may decrease peak
exotherfnie> temperatures (reducing"volatility)", but will also decelerate setting
arid curing times. Grouting pressures and drilling rates can also be adjusted
to compensate for varying site conditions. Higher pressures generally result
in increased penetration and may provide improved homogeneity of the
Waste-binder mixture.
. •• ' .1, ' U '. ; • ,", ,, ',','" <',' >, :.'.|. . ii." . ••-. I '. , ,!i: " . -. ' 0 ',' , ii •» ' I,,, i;-l' i'
3.2.5 Pretreatment Processes
3.2.5.] Polyethylene Encapsulation
To be efficiently processed by polyethylene extrusion, waste materials
must be dry and meet acceptable particle size specifications. If as-generated
waste does not meet these processing requirements, pretreatment processes,
including drying and size reduction, is needed. Waste to be encapsulated in
polyethylene should not contain more than 1 to 2% (by weight) moisture.
Various commercial drying mechanisms including spray dryers, fluidized
bed dryers, thin-film evaporators-, and vacuum dryers, have been investigated
for use with polyethylene-based systems. Vacuum drying was selected at
Broqkhaven National Laboratory because of its ability to meet both moisture
and minimum particle size requirements. The commercially available
RVR-200 Vacuum dryer, supplied by MMT of Tennessee, consists of a
horizontally-mounted stirred mixer, steam generator, condensate recovery
skid, and chiller (Figure 3.14). It can dry up to 760 L/day (200 gal/day), but
larger systems are available with outputs up to 3,030 L/day (800 gal/day).
The dryer is controlled and monitored remotely and includes closed circuit
video for observing the condition of the mixture.
3.52
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Chapter 3
Figure 3.14
. Flow Diagram for RVR-200 Vacuum Dryer
Rinse
Water Slurry
Condensate
Return
Reproduced courtesy of MMT of Tennessee (1997)
Particle size .requirements vary according to the type of processor se-
lected. In general, the smaller the particle size, the more effective the mi-
croencapsulation of waste particles, and the lower the leachability of the
final waste form. Therefore, for particles >3 mm (0.12 in.), performance is
improved by size reduction prior to extrusion. The Brookhaven National
Laboratory pretreatment system includes an in-line comminutator at the
dryer discharge. It consists of a series of rotating knife blades that break up
particles and force them through a mesh screen. A typical resulting
particle-size distribution is shown in Figure 3.15.
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Design Development
1,
' ''*•"••. • ! ! ''Figure3.15 '
Particle-Size Distribution of Nitrate Salt Surrogate Following Pretreatment
'' | . . , i' , , , I'1' '' ,''||jii || l| "' , , i ' I < I < , ll, I ,,,!
40
30
20
10
250 300 425 500 600 710 1000 1400 1700 2000 2380
i '
, ,. : . ; , , :", Particle Size (urn) ; '
Thermpkinetic mixers are currently being tested to pretreat wastes with low-
to moderate- moisture content. The advantages of this approach are lower enr
ergy requirements for drying, lower capital costs, and enhanced homogeneity of
waste and binder. However, wastes with high moisture content reduce available
frictional hpat energy and inhibit the mixer's ability to drive off moisture. These
wastes require more conventional dryer pretreatment.
•' : • ' "- ;.•'] ;.' V I'' ••••-•• i "
3.2.5.2 Sulfur Polymer Cement Encapsulation
As with polyethylene.encapsulation, smaller waste particles allow more
effective micrpencapsulation of the waste and minimize leachability. Pre-
treatment size reduction with a shredder or a crusher may be required to
achieve this small particle size. Unlike LDPE, however, SPC has no limit on
minimum particle size, since it is a low viscosity material and is processed
by batch mixing.
Sulfur polymer cenient is also incompatible with water in the waste.
Moisture that is volatilized during processing can become entrained, lower-
ing the product density and mechanical integrity, and increasing porosity and
leachability. Therefore, all waste should bis dried prior to stabilization (<1%
moisture). If wastes are heated and held at the process temperature prior to
3.54
-------
Chapters
mixing with sulfur polymer, residual moisture is liberated, and the waste/
binder mixture remains in a flowable state for a longer period of time
(Mayberry.etal. 1993). Since SPC is compatible with a wider range of ac-
ceptable particle sizes than is LDPE, the choice of dryer for pretreatment is
less critical. .
3.2.6 Posftreatment Processes
Since polymer encapsulation processes operate at relatively low tempera-
tures, most contaminants (e.g., radionuclides, such as Cs, Sr, Co, and toxic
metals, such as Pb, Cr, Cd) are not volatilized during processing, minimizing
offgas posttreatment requirements. However, highly volatile metals, such as
Hg, as well as sound health and safety engineering practices, require the use
of offgas collection and ventilation systems for extruders, dryers, or other
process equipment that generate gaseous or particulate effluents. For
streams containing small quantities of volatile organics, carbon traps can be
used to absorb organic vapors prior to discharge.
The final waste form geometry can be determined to meet the needs of the
;particular application. For example, final waste form products can be pro-
duced as standard cylindrical or cubical monoliths mat require less room for
storage. Leaching of the microencapsulated final waste form can be de-
creased further by surrounding the waste form with a clean layer of plastic
(double encapsulated). This can accomplished by co-extrusion or a plastic
liner. Alternatively, encapsulated wastes can be pelletized and stored in
secondary containers or encapsulated within a larger waste form.
3.2.7 Process Instrumentation and Controls
3.2.7.1 Polyethylene Encapsulation
Ames Laboratory has developed an on-line monitoring system for the
polyethylene encapsulation process (Wright et al. 1994). Based on Transient
Infrared Spectroscopy (TBR.S), the system enhances quality assurance/quality
control (QA/QC) of the process by assuring that the preset mixture ratio is
being delivered and preserved throughout the process. The Ames monitor is
shown in Figure 3.16. The computerized monitor compares real-time pro- .
cess spectra with previously stored calibration data to produce instantaneous
and time-averaged waste loading data. Calibration data showing predicted
-------
Ill 111 I1
111
Design Development
waste loading using the TlRS monitor plotted against actual waste loading
(Figure 3.17) demonstrate the accuracy of the monitor. Information is also
stored for a permanent QA record of the processing run.
in i Siffli:: i.
1 i: hiiiiii.
Figure 3. II6
Transient infrared Spectroscopy (TlRS) On-Une Monitoring System Developed
bv Ames Laboratory for the Polvethvlene Encapsulation Process
The full-scale polyethylene encapsulation facility at Brookhaven National
Laboratory includes instrumentation and process monitoring modules that
can be remotely located from the processing equipment to reduce operator
exposure to radiation and hazardous materials. The extruder module in-
cludes screw speed control, solid state monitoring, and control of heating
3.56
-------
Chapters
and cooling in five separate barrel and two die zones, and digital and analog
process indicators for melt temperature, melt pressure, screw speed, and
current draw. The integrated process control unit is operated on a personal
computer using a customized program written for WindowsIM-based control
software. The controller receives a weight signal.from a solid state drum
scale, integrates the information into a process rate and operates the feeder
master control unit to keep pace with the process. Thus, as the extruder
screw speed is increased, the output increases and the feeder rates are in--
creased proportionally to maintain the process rate (Kalb et al. 1995b).
65
60
55
50
4S
40
35
30
25
Figure 3.17
TIRS Monitor Plotted vs. Actual Waste Loading
25 . 30 35 40 45 50
Actual Waste Loading
55
60
65
Source: Kalb and Lageraaen 1994
3.2.7.2 Sulfur Polymer Cement Encapsulation
Sulfur polymer is processed by stirred batch heaters, which are relatively
simple mixing systems. Parameters to be monitored are melt temperature,
system vacuum, and mixer speed. A closed circuit video monitor allows the
operator to observe the condition of the mixture.
-------
it.. •:
Design Development
I'it' .<
3273 In Situ Polymer Stabilization/Solidification
1 •,, : ... , • j i • , .• , ,
Combining the catalyst arid promoter with the monomer is best accom-
plished by mixing the proper ratio of each component with half the mono-
merancl then pumping the two mixtures simultaneously through twin grout
nozzles. Flow rates of each mixture must, therefore, be carefully controlled
and monitored to assure that the proper ratios of components are delivered
and mixed with the waste. Grouting pressure controls the extent of radial
penetration, and drill speed regulates how quickly the column can be placed.
Each of these parameters requires operator attention to ensure proper instal-
lation of rne in situ polymer column.
i.. " i. • . • • • i
3.2.8 Safety Issues
3.2.8.1 Polyethylene Encapsulation
Worker exposure to radioactive and hazardous materials during pro-
cessing and maintenance operations is an. important safety issue for any
treatment system. Because of relatively simple and reliable operation,
polymer processing equipment generally requires less maintenance than
other types of S/S systems. For example, extruders can be readily
purged and cleaned by processing polymer that contains no waste or by
using specially-developed, purging compounds. In the event of an un-
planned shutdown, polymer solidified within the extruder can be easily
re-melted enabling the operator to rapidly resume processing. Remote
.handling, monitoring, and process controls also minimize exposure to
hazards. Standard OSttA safety practices for operating equipment at
elevated temperatures (e.g!, heat shields, protective clothing) ensure safe
operation of polymer processing equipment.
• : :. • j • ; • • • i-
3.2.8.2 Sulfur Polymer Cement Encapsulation
Airborne SPC dust can be mildly explosive so safety precautions must be
exercised The ILS. Department of transportation does not consider SPC to
be flammable. When exposed to a direct flame, SPC will burn, but will self
extinguish when the flame is removed (Mayberry et al. 1993). SPC will
emit hydrogen sulfide gas, sulfur dioxide gas, and volatile organic sulfur
compounds if SPC is melted above 160°C (320°F). These gases are both
poisonous and flammable (Mattus and Mattus 1994); therefore, precautions
must be observed to avoid overheating SPC.
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Chapters
The flash point of SPC as determined by the Cleveland Open Gup
method is 177°C (351°F), and the auto-ignition temperature is 232 to
254°C (450 to 489°F).
3.2.8.3 In Situ Polymer Stabilization/Solidification
Polymerization reactions are exothermic and, depending on the types and
quantities of catalyst and promoter used, can be difficult to control. How-
ever, if monomers are stored without added catalyst or promoter, and the
combining of the catalyzed and promoted monomers takes place at the time
of placement in the ground, few difficulties have been experienced. Thermal
energy can also act in a similar manner as chemical promoters, so materials
• should be stored in a cool area prior to use.
3.2.9 Specification Development
3.2.9.1 Polyethylene Encapsulation
In addition to the typical engineering requirements, specification should
take into account materials of construction, power requirements, and the
integration of ancillary components. Many waste streams are either acidic or
alkaline and can be highly corrosive. Process components that come hi di-
r,ect contact with corrosive materials should be of appropriate corrosion-
resistant alloys. Specification of each of the requked auxiliary components
.should be coordinated with the overall system requirements. For example,
pretreatment equipment must complement final waste form processing in
terms of production rates, product specifications (e.g., moisture content,
particle size), and physical layout. Handling systems must be able to supply
materials in either batch or continuous mode, as appropriate, at required
production rates. All equipment must meet appropriate engineering stan-
dards for safety. Vendors with experience in producing equipment for
nuclear and hazardous materials should be able to demonstrate compliance
with appropriate certification standards (e.g., American National Standards
Institute [ANSI]). Thermoplastic polymers are available in a wide range of
densities, melt temperatures, melt viscosities, and as either virgin or recycled
feedstock. Therefore, the type of polymer should be selected according to
the type of waste being treated and feedstock specifications written into the
waste treatment plan and operating procedures.
-------
Design Development
3.2.9.2 Sulfur Polymer Cement Encapsulation
!. ! '.. , ,. ,| .,'. . '-,-' .v ••
" In choosing an appropriate mixing system, the engineer must consider
which method of thermal input will be used (e.g., steam, hot water, oil, or
electric resistance heating) and which type of mixing blade design is opti-
mal. The latter choice should consider the nature of the waste stream that is
anticipated. For dry powders with small particles, slow-speed orbital or
paddle mixers might be ideal. For wastes with larger particle size and/or
greater density, high shear mixing might be preferable. Prior to selecting
the'mixer design, bench-scale vendor testing to confirm applicability is
often required. Offgas treatment should include a carbon trap to reduce
noxious (but harmless) odors that are associated with molten sulfur. To ,
expedite batch processing, the SPC encapsulation process can be designed
with a secondary heating tank to pre-melt the binder and introduce it in
liquid form into the mixing vessel. Likewise, if the waste is preheated prior
to charging into the mixer, overall process time is reduced and mixing can
be unproved Engineering design specification requirements are similar to
other polymer encapsulation technologies, such as polyethylene, in that the
system must be able to withstand corrosive conditions and meet industry
certification standards.
., ..'•Tl':;-:i! *('\: '•'"• ""'-'; '• : •.! ''';:?.:* • i ; :•'•• •' ' - ' • '••'•'.. -, f [Sit '!•-
3.2.9.3In Situ Polymer StdtDilization/isolidiflcation
The key factors hi selecting monomers, catalysts, promoters, and addi-
tives, if required, are the type and properties of the soil being remediated
(e.g., particle size, permeability, chemical composition) and the contami-
nants of concern. Key engineering properties of the polymer matrix, such as
viscosity, setting time, and peak exotherms, can be tailored according to the
specific soil and contaminant conditions present. For example, the choice of
catalyst and promoter and specification of mixing ratios can affect how
quickly polymerization occurs. Setting and curing times must be tailored to
ensure rapid solidification without interfering with on-going drilling and
emplacement operations. Polymer/soil mixing ratios are predetermined from
laboratory-scale testing to optimize performance of the solidified product
(e.g., leaching), while providing cost-effective treatment (e.g., minimizing
the quantity of polymers added). Design specifications for emplacement
equipment must consider issues of pumping and delivery pressure, nozzle
design, penetration, maintenance/cleaning, etc.
3.60
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Chapter 3
3.2.10 Cost Data
3.2.10,1 Polyethylene Encapsulation
In general, capital and operating costs for polyethylene encapsulation sys-
tems are moderate to higher than those of conventional hydraulic cement grout
processes but lower than high temperature vitrification systems. The cost'of
polyethylene feedstock varies between $0.09 to $1.32/kg ($0.45 to $0.60/lb)
depending on the type of polymer and the quantity purchased. Use of recycled
polymer feedstock might reduce material costs in the future, but the availability
of well-characterized recycled polymers is currently limited. Material binder
costs can be estimated considering that microencapsulation waste loadings
typically range from 50-70% (by weight). Typical capital costs and estimated
energy requirements for production-scale process equipment are summarized in
Table 3.12. Several equipment options are presented for comparison. It should
be noted, however, that the total cost of treatment is often influenced most by
storage, transportation, and disposal costs, which, in turn, are directly related to
final waste form volumes produced.
Table 3.12
.Typical Capital Cost Data and Estimated Energy Requirements for
Production-Scale Polyethylene Encapsulation Process Equipment0
Component
Single Screw Extruder
Twin Screw Extruder
Thermokinetic Mixer
Vacuum-Dryer
Material Handling System
Feeder System
Process Control System
Estimated Capital Cost
•($)
200,000
450,000
150,000
550,000
30,000
35,000
15,000
Estimated Energy Requirements
(KW)
50
100
40
7b
c ' .
c
c
•Based on unit sizing with approximate total output of 2,000 Ib/hr
"Per pound of salt produced ~
"Negligibla
-------
Si . V
Design Development
3.2.10.2 Sulfur Polymer Cement Encapsulation
• Since processing is carried out using simple stirred metiers, capital and oper-
ating costs for sulfur polymer encapsulation are slightly lower than for higher
viscosity thermosetting polymers. Production-scale mixers can cost between
$100,000 to $150,000, while pretreatment and feeder equipment are similar in
cost to those described hi Table 112. The cost of the SPC raw material is cur-
rently about $0.26/kg ($0.12/lb), slightly higher than conventional hydraulic
cements. SPC binder costs can be estimated based on typical waste loadings
ranging from 40 to 60% (by weighf). However, the cost of the material is just
one factor in determining the life cycle cost of treatment and disposal. All as-
pects of the cost formula, such as pretreatment requirements, energy, operation
and maintenance, and waste form storage/transportation/disposal costs must be
considered. Because SPC encapsulation can, in some cases, reduce final waste
form volumes by a, factor of up to 3 times as compared with Portland cement
concrete, Spfi should prove cost-effective compared with conventional hydrau-
. lie cement technologies.
3.2.10.3 In Situ Polymer Stabilization/Solidification
Capital costs for in situ polymer S/S processing equipment range
from around $550,000 to $2,000,000 for a typical jet grouting rig. Ap-
proximately 200 kW of energy is required to operate drilling and high
pressure pumping equipment. Material costs for thermosetting polymers
'are relatively high and can range from around $1.74/kg ($0.79/lb) for
polystyrene and some acrylics to more than $14.33/kg ($6.50/lb) for
pdlysiloxanes and some epoxies.
3.2.11 Design Validation
! , , ".. '. ,1," • • : . \ ••. • • ,. . ",. .• ,!::,.; ,
As with other S/S technologies, the appropriateness of specific engineer-
ing system design should be evaluated for each new polymer S/S applica-
tion, typically" this is done through pilot- or full-scale testing using surro-
gate waste materials. Testing can be accomplished by technology develop-
ers, but is most effective if conducted by or in conjunction with commercial
vendors that plan to market the technology. If competing designs or pro-
cesses are being considered for a particular remediation project, treatability
and pilot-scale testing of each system is recommended to provide sufficient
3.62
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Chapter 3
data to make an informed evaluation. Peer review of polymer S/S technolo-
gies have been conducted by tapping expertise within DOE, the regulatory
community (US EPA and NRQ, academia, and the commercial sector.
3.2.12 Permitting Requirements
Treatability studies for characteristic hazardous and mixed wastes are re-
quired to demonstrate compliance with RCRA by 40 CFR 261 as administered
under the US EPA or authorized state agencies with jurisdiction over environ-
mental issues. Treatability studies must include the TCLP test. US EPA re-
cently proposed significantly reducing the allowable concentrations of toxic
metals in TCLP leaching (US EPA 1995b). Small-scale treatability studies
(treatment of <10,000 kg/yr [22,000 lb/yr]) can be conducted without special
permits as long as the appropriate authority (state agency or US EPA) is notified
at least 45 days prior to initiating the study. For larger quantities, a RCRA Re- ,
search, Development, and Demonstration (RD&D) treatment permit is required.
For some listed waste streams, US EPA has established technology-based stan-
dards, eliminating the requirement for treatability studies.
For commercial radioactive or mixed wastes, treatment must meet perfor-
mance based standards defined in 10 CFR 61 by the NRC (NRC 1983). The
NRC requires the waste generator or treatment vendor to prepare a topical
report that documents results of specific final waste form performance tests
for stability and leaching characteristics under a variety of simulated dis-
posal scenarios (NRC 199 la). The stability and performance tests include
compressive strength, water immersion, thermal cycling, biodegradation,
radiation stability, and teachability. Topical reports submitted to NRC are
reviewed, and if deemed acceptable, the technology is licensed for commer-
cial treatment.
The DOE's disposal requirement is based on a risk-based performance
assessment analysis for a specific disposal site (DOE Order 5820.2A). Un-
der current law, DOE must comply with disposal requirements established
by US EPA, but is exempt from NRC requirements. However, some DOE
sites are using NRC's test protocol because DOE has not defined specific
testing requirements to support DOE Order 5820.2A (Mayberry et al. 1993).
Individual disposal sites or states can impose their own waste acceptance.
criteria (WAC) for DOE low-level radioactive wastes. Currently, most site
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Design Development
' i' ^ •• ,i" hr '' i ' ' ' „" , '•' .'j'l ii i'1 I) .y1;',,, ' ''' ' , , " i ' ' " ', ", i , ,i
WACs are less stringent than NRC performance criteria. For example, typi-
cally they require no free water or they impose maximum radioactive con-
centrations. As states and regional state compacts (groups of states agreeing
to cooperate in the siting of new disposal facilities) continue to construct
new facilitieSj more rigorous standards might be adopted.
Regulatory issues associated with the use of polymers for in situ barrier
materials have been investigated (Siskind and Heiser 1993). They concluded
that since polymers have been used extensively in the construction industry
in full compliance with applicable health, safety,'and environmental regula-
tions, no difficulties are anticipated for their use as in situ barriers. The
same sel of regulations, with the possible exception of the Safe Drinking
Water Act, should pertain to polymer injection used in road construction,
subsurface barriers, or S/S of contaminated soils; Of course, the perfor-
mance of the remediated site must be in accord with all pertinent environ-
mental regulations.
"•' ',.' "V,!' '•;*-'.'•• ' •':. j'Vl;;' ,,Vi",„; •• ':'.",' '' : -:';":!":' :••.•
3.2.13 Performance Measures
Performance is measured in terms of both processing efficiency and the
final waste form's ability to retain contaminants over time. As with other
S/S technologies, processing efficiencies are expressed as the quantity-of
waste that can be effectively encapsulated per unit volume, while ;still main-
taining adequate performance^ i.e., ability to meet regulatory and disposal
site acceptance criteria. In order to make comparisons on a equivalent basis,
these data are usually presented in terms of dry weight percent of Waste.
Polyethylene encapsulation has been successfully demonstrated at waste
loadings from 30 to 70% .(by weight) dry waste, depending on the type of
waste, levels of contaminants, and the performance standards required.
Mechanical integrity, durability, and leaching characteristics are the criti-
cal performance measures of potential final waste form behavior under
long-term storage and disposal conditions. Low-level radioactive and mixed
wastes generated in the. commercial sector are subject to NRC licensing
requirements for treatment and disposal described in Section 3.2.12. The
NRC has established minimum waste form performance requirements for
durability and leaching in support of 10 CFR 61.
Typical performance test data for polyethylene encapsulated waste forms
are presented in Tables 3.13 and 3.14. The results of compression strength
tests for SPC are listed in Table 3.15. Sulfur polymer cement provided a
3.64
- i-i"
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Chapter 3
Table 3.13
Typical Durability and Leaching Data for Polyethylene
Microencapsulated Final Waste Forms Containing 60%
Simulated Nitrate Salt Waste by Weight
Final Waste Form Performance
Compressive Strength
Water Immersion
Thermal Stability
Biodegradation
Radiation Stability
Radionuclide Leachability
Test Protocol
ASTM D-695
90-day; ASTM -695
30 cycles, -40+60'C,
ASTM D-695
ASTM 021, 022;
ASTM D-695
10s rad; ASTM D- 695
ANS 16.1
Results
. 2,200 psi
,2,310psi
I,930psi
1,460 psi*
2,420 psi '
9
Minimum Standards
for NRC Licensing
60 psi
60 psi
60 psi
60 psi
60 psi
Leach Index £ 6.0
•Apparent loss In strength following'biodegradatlon was attributed to test protocol rather than structural properties of the
waste forms!
Adapted from Kalb, Reiser, and Colombo 1991 a; Franz, Kaiser, and Colombo 1987 -
Table 3.14
Typical ANS 16.1 Leach Test Data as a Function of
Waste Loading for Microencapsulated Final Waste
Forms Containing Simulated Nitrate Salt Waste
Waste Loading
(% by weight)
30
50
60
70
Cumulative Fraction Leached
0.9
63
.15
73.4
Leachability Index*
uli
9.7
9
7.8
•Conducted as per procedures outlined In ANS 16.1 Standard Leach Test Method. Minimum Leach Index
recommended by NRC Is 6.0.
' Adapted from Kalb, Heiser, and Colombo 1991 a
-------
Design Development
if: .
| Table 3.15
Compressive Strength Data for Sulfur Polymer/Ash
Waste Forms Following NRC Performance Testing
Test Protocol
Compressive Strength8*
Compressive Strength 4,250 psi
Water Immersion 3,870 psi
Thermal Cycling; 3,870 psi
Bipdegradation 2,620 psi
Radiation Stability 1,950 psi
-Data for waste forms containing 30% ash by weight. Biodegradatlon and Radiation Stability tasting conducted oh neat
sulfur polymer specimens (no waste).
'Minimum comprassive strength recommended by NRC Is 500 psi. .
Source: Kalb, Helser, and Colombo 1991b
:,. •'•,-'.' i Table 3.16
ANS 16.1 Leach Data for Sulfur Polymer Final
Waste Forms Containing Incinerator Ash
Ash Waste Loading
(% by weight)
20
40.
Co-60 Leachability Index*
' ' 14 •
14.6
Cs-137 LeachabiUty Index*
' •' ' 11.2'- [
' 11.1 'i:"" ' '
•Conducted as por procedures outlined in ANS 16.1 Standard Leach Test Method. Minimum Leach Index
recommended by NRC Is 6.0.
Source: Kalb and Colombo 1984
compression strength performance of at least four times the minimum NRC
requirements of 3.4 MPa (500 psi) on all tests. Table 3.16 illustrates the
leach performance data for the ANS 16.1 leach test recommended by NRC
(ANSI/AN& 1986; NRC 199ia). the SPC teachability indices are four to
eight orders of magnitude lower than those required by NRC. The perfor-
mance and durability of in situ polymer concrete solidification for.treatment
3.66
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Chapter 3
of buried wastes at Idaho National Engineering Laboratory are currently
under investigation. Preliminary data for in situ stabilized soils shown in
Figure 3.18, indicate excellent integrity and durability of treated surrogate
soil waste samples.
Figure 3.18
Compressive Strength of Polymer Soil Grouts After Resistance Testing
Untreated Water
Base
Solvent
Wet-Dry
Source: Reiser 1995
For hazardous and mixed wastes, US EPA's TCLP criteria apply. The test
was designed for a traditional hydraulic cement S/S process and requires size
reduction of the monolith to pieces that can pass through a 9.5 mm (370 mil)
sieve. Furthermore, the test is biased toward alkaline pH-based systems,
since solubility of most metals is limited under high pH conditions. Given
size reduction requirements and leachate pH conditions, processes that rely
primarily on microencapsulation are at a distinct disadvantage by compari-
son. Nevertheless, all potential S/S technologies must meet 40 CFR 261
TCLP leaching protocol. Typical TCLP leaching data for polyethylene en-
capsulated waste, compared with untreated baseline data, are presented in
-------
Design Development
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3.68
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Chapters
Table 3.17. Table 3.18 provides performance data from the TCLP for
SPC-encapsulated waste. The Idaho National Engineering Laboratory fly
ash (untreated) leachate concentrations were well above the TCLP-allowed
concentrations. Leachability of the fly ash solidified with .SPC was consid-
erably lower, but was still above the allowable concentration levels. The
addition of small amounts of spdium sulfide with SPC encapsulation re-
duced TCLP teachability of the SPC solidified fly ash below allowable con-
centrations. The sodium sulfide reacts with the metals salts to form metal
sulfides that have low solubility within the solidified matrix (Kalb, Heiser,
and Colombo 1991b).
Table 3.18
USEPA's TCLP Performance
. Results from US EPA Toxicity Characterization Leaching Procedure
for MEL Incinerator Fly Ash Encapsulated in Sulfur Polymer Cement
Sample Tested
(by weight) •
•Idaho National Engineering
Laboratory Fly Ash
55% Ash
45% SPC .
• 40% Ash
60% SPC
40% Ash
'53% SPC
43% Ash
50% SPC
Concentrations of Criteria Metals (mg/L)
Cd Pb
85.0 ' 46.0
27.5 17.6
13.6 . 12.0
0.1 1.0
02 15 '
US EPA Allowable Limit 1.0 5.0
Source:. Kalb, Heiser, and Colombo 1991b,
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Design Development
3.2.14 Design Checklist
< - 1,1
3.2.141 Ex-Situ Polymer Stabilization/Solidification
1. Characterize the waste stream to determine moisture content,
particle size, radioactive and hazardous contaminant concentra-
tions, and volatile organic concentration.
2. Determine waste pretreatment requirements (e.g., drying, size
reduction).
- 3. Determine the waste constituentts(e.g., mercury or volatile organ-
ics) that have the potential to be volatilized either during pretreat-
ment or encapsulation processing^ Develop an offgas. system
capable of capturing potentially volatile species.
4: Optimize polymer use based on waste characteristics, volume to
be treated, performance goals, and costs. Consider substitution
of recycled polymers for virgin materials.
5. Size system components to satisfy anticipated production re-
quirements for treating as-generated waste as well as reducing
the volume of stored inventories. Assess cost-effectiveness of
using multiple parallel processing systems or a larger single unit.
6. Define the final waste form product performance criteria. Perform
sufficient testing to confirm product durability and performance.
! | ' ;•!
7. Define operating parameters to ensure cost-effective operation.
8. Develop process QA/QC (QAPP) and confirm through adequate
pilot-and fuU-scale testing and implementation of advanced
monitoring techniques.
3.2.14.2 In Situ Polymer Stabilization/Solidification
•,'.' 1. Characterize soil in terms of porosity, particle-size distribution,
and contaminant concentrations.
2. Determine the waste constituents^lg., mercury or volatile organ-
ics) that have the potential to be volatilized either during pretreat-
ment or 'encapsulation processing. Develop an offgas system
capable of capturing potentially volatile species.
..'!'." ; ' ; ' i. '
3.70
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Chapter 3
3. Optimize the type of monomer based on the characteristics of the
, soil and waste, volume to be treated, performance goals, and
economic considerations.
4. Select the catalyst and promoter based on compatibility with
monomer and soil/waste characteristics. Conduct both bench-
and pilot-scale testing to prove reliability of each.
5. Develop ratios of monomer, catalyst, and promoter based on
consideration of processing (e.g., setting time) and cost.
6. .Design system to avoid mixing components within delivery
pumps, piping, nozzles, and other equipment which would be
damaged by inadvertent setting of the polymer.
7. Optimize emplacement design to minimize waste of materials
and ensure adequate coverage and resulting solidification of the
contaminated soil.
8. Define operating parameters to ensure cost-effective operation.
9. Conduct test bores in situ to confirm material compatibility and
QA/QC of the emplacement system.
3.3 Vitrification
3.3.1 Remediation Goals
3.3.1.1 Ex-Situ Melters
Vitrification technologies have the potential to be widely applied to haz-
ardous and radioactive waste treatment. As an emerging technology, avail-
able performance data are largely based on pilot-scale demonstrations. A
majority of demonstration and testing results have been funded by federal
government agencies such as DOE, DoD, and US EPA. Demonstration tests
have evaluated the technology for treating many types of wastes, such as
soils contaminated with heavy metals and organics, asbestos-containing
waste, industrial fly ashes and furnace dusts, sludges, and solids contami-
nated with radioactive or heavy metals.
-------
Design Development
Hi,,«
The application of vitrification to high-level radioactive waste has been
accepted worldwide as the preferred treatment option. Facilities hi France,
Russia, and Belgium have been operating since the late 1970's. Plants in the
U.S. and Japan became operational in 1996 and 1997. These plants are ex-
pected to operate anywhere from 3 years to 30 years, depending on the spe-
cific mission at the respective sites. Microwave melting of mixed wastes has
been demonstrated at the DOE facilities in Oak Ridge, Tennessee, and
Rocky Flats, Colorado. However, large-scale production has not yet been
implemented by the DOE.
Vitrification has been defined by the US EPA to be the BOAT for
cadmium-bearing wastes.
: • '! •' •<• ° .; ;' •; | , . M •' ' ;"•>'
•3.3.1.2 In Situ Vitrification
In situ vitrification (ISV) is a versatile remediation technology that is
capable of converting contaminated soil, buried waste, radioactive
waste, and industrial and municipal, waste to a solid waste form that
satisfies waste disposal and site closure requirements. Offgas monitor-
ing conducted during several major demonstrations has shown ISV to be
effective in retaining, destroying, and/or removing contaminants to lev-
els that satisfy permitted discharge limits.
"'j11 •"; i| ', • •;," '"•: "| ' •,. i,' ',||" , , j |, "°,||j||,;' ' ' N ""i|:' h"; j',:,;j||,i''' •; 'ihi ', j >), • vi,|i ;, , • ,,11 ii'i;, i,;i ' ,l!,iij|ljl|ii |i, , ,;„'„ , • „ J ; J rCi,,,, • y .'
At the Parsons Chemical Works, Inc., site in Grand Ledge, Michigan,
for example, ISV was used to treat contaminated soil containing pesti-
cides, mercury, and low levels of dioxins and furans (US EPA 1995c).
The work was conducted in association with US EPA's SITE Program.
The results showed that the vitrified waste met US EPA Region V
cleanup criteria and that air emissions were below regulatory limits. A
thermal oxidizer was used in the offgas train to destroy an odiferoiis
(sulfur-related) nonhazardous offgas that hacl created public concern!
Scrubber water from offgas treatment required secondary treatment.
The work on the SITE Program test cell was completed in 10 days with
only minor operational problems. Duriirig this time, approximately 540
tonne (60.6 ton) of contaminated soil were vitrified.
At a Toxic Substances Control Act (TSCA) demonstration project site,
ISV was used to remediate 2,800 tonne (3,100 ton) of soil contaminated with
varying PCB concentrations up to 17,000 mg/C (Thompson, McEfroy, ana1
- Timmerman 1995). Some of the demonstration cells contained significant
amounts of debris, including ruptured drums, asphalt, concrete, protective
3.72
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Chapters
clothing, and other wastes. Dynamic compaction (see Section 3.3.5.2) elimi-
nated major voids and breached drums containing water to prevent disrup-
tion of the melts. The results indicated that (1) 99.76% of the PCBs were
destroyed by the melt; and (2) 99.98% of the entrained PCBs were removed
by the offgas treatment system. Scrubber solutions containing PCBs were
treated and disposed at a permitted TCD facility.
Geosafe Corporation recently applied the ISV technology to treat wastes
at the Wasatch Chemical Superfund Site in Salt Lake City, Utah. Approxi-
mately 5,400 tonne (6,000 ton) of soil and debris contaminated with dioxin,
pentachlorophenol, herbicides, pesticides, and other sernivolatile organic
compounds and VOCs were treated. Large'amounts of debris, including
scrap metal, plastic, wood, and clay pipe, were present within the treatment
volume. The project was successfully completed in November, 1995.
Samples of vitrified product, adjacent soil, and offgases indicated
non-detectable levels of the contaminants of concern (see Table 2.2 in Sec-
tion 2.3.2.2). A notable feature of this project involved the treatment of 650
gallons of oil contaminated with 11 mg/L dioxin. .The oil was mixed with
soil and then staged within the treatment zone. This was the first large-scale
treatment of dioxin-contaminated waste within the U.S. using a
non-incineration technology. The technology is not considered to be an.
incinerator, even though an afterburner was-used for final destruction of
organics. This is because greater than 99% of the organics are destroyed by
pyrolysis rather than by oxidation.
At Oak Ridge National Laboratory, a pilot-scale test was conducted on a
simulated waste trench containing small quantities of 137Cs and '"Sr (Carter,
Koegler, and Bates 1988). The results of the test indicated that the durability
of the glass waste form was similar to or better than glasses formulated for
high-level radioactive wastes. However, a higher-than-expected quantity of
I37Cs was deposited on the walls of the offgas containment hood-. High ra-
dioactive doses to personnel were projected at the observed deposition lev-
els. Further testing is now underway at Oak Ridge National Laboratory to
explore methods of safely using ISV when 137Cs and 90Sr are present. The
testing includes use of a prefilter to remove 137Cs before it enters the offgas
treatment system. Preliminary results indicate that retention of !37Cs in the
melt was very high (99.9987%) and that 78.6% of the volatile 137Cs was
retained by the prefilter. The remainder of the volatile 137Cs was found be- .
tween the prefilter and the final filter.
-------
Design Development
3.3.2 Design Basis
'•'" " •" ,.. -, j ! i , i,M,:: i -,!•.- ; : •> ••. ; . • ", !'»»>:_' '•
To apply vitrification technologies, whether ex-situ or in situ, many of the
same issues must be considered: waste composition and characteristics, re-
sulting glass composition, degree of heterogeneity, offgas treatment require-
ments, and required production rate. Ex-situ treatment applications must
also consider the volume of waste to be treated against the required treat-
ment period. Additional considerations for ISV include certain site condi-
tions, such as the depth of waste and host soil characteristics. Specific de-
sign issues for vitrification technology options are discussed in the following
subsections. -
; , ,, ,i- !,,•„, i - i' . ,• ii j, , ' i,"11!, • r i •. ! ' ,', i1 , ':,. ,1 ,„ i,,1
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3.3.2.1 Ex-Situ Melters ' "'
Electric Melters. Electric melter systems produce a glass product any-
where between 0.45 kg/hr (1 Ib/hr) to 180 tonne/day (200 ton/day); with
commercial glass melters representing the high end of the production rate
spectrum. These melters are designed according to the required production
rate, the composition and characteristics of the material to be processed,
product requirements, and required operating life. Many of the waste
streams under consideration for vitrification have never been processed be-
fore. For this reason, it is necessary "to evaluate the factors discussed below.
Waste characterization" should be completed first to allow initial glass
development to be performed. This will also identify the relative concentra-
tions of "troublesome" components that have limited solubility in glasses.
These include sulfur, the halides, phosphate, and carbon. The initial glass.
work can be done with surrogates and will identify the glass system, e.g.,
sodium-aluminum-silicate, calcium-alumiQum-silicate, borosilicate, or phos-
phate, that will provide the necessary product performance and best accom-
modate the troublesome components. Any glass-forming additives required
to achieve a processable and high quality glass will be determined at this
time. An estimate of the waste loading that can be achieved in the glass will
also be made, often using laboratory- or bench-scale testing. Generally,
higher waste loadings can be achieved with glasses with higher processing
temperatures, such as wastes containing a high proportion of transition group
oxides and refractory oxides like silicon, alumina, and zirconium.
Waste characterization is also important to estimate the degree of compo-
sitional consistency within the waste volume. It is preferable to establish a
single glass composition and a fixed-glass former composition. When the
3.74
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'•• Chapters
composition is fairly consistent, the initial waste characterization and pro-
cess sampling can be minimized. The size and complexity of the glass com-
positional field needed to ensure acceptable glass composition across the
range of waste variability can also be minimized. Finally, the physical con-
dition of the waste, such as water content, particle size, and viscosity (if a
slurry); can be determined.
Once a glass composition is defined, melter construction materials should
be evaluated. The nominal compositions and relevant property data of sev-
eral refractories commonly used in electric melters are presented in Table
3.19. The glass industry predominantly uses an alumina-zirconia-silica
(AZS) refractory in contact with the glass, because it will not color the glass
as it slowly corrodes. Large commercial furnaces can be operated for up to
two years before the wall refractories must be replaced. However, more
frequent rebricking in areas of high glass flow, such as discharge throats, is
required: Durability is improved through refractories that contain a high
fraction of chromium oxide. The slow corrosion of these refractories results
in small quantities of chrome oxide going into the melt. This has no effect
on glass properties. Chrome oxide refractories are widely used in melters
treating hazardous and radioactive wastes. Where insufficient experience
exists, refractory vendors should be consulted to identify candidate refracto-
ries followed by laboratory corrosion testing to select preferred refractories.
. Refractories which back up the glass contact refractory are selected for
both chemical durability and insulative properties. The degree of heat loss
that can be tolerated should be based on two factors. First, the glass tem-
perature at the refractory wall should be high enough (above the liquidus
temperature) to avoid crystal formation. The second factor is cost. Higher
capital costs for initial melter fabrication reduces energy costs and outer
shell water cooling costs during operation.
Refractories in the melter lid will be exposed to high temperatures during
idling, extreme thermal cycling when feeding is started and stopped, and
corrosive offgas constituents such as acid gases, salts, and feed and glass
splatter. The selection of suitable lid refractories is based on the expected
process conditions and required service life. Typically, high alumina
castable refractories, firebrick, and insulating board are used.
Selecting the appropriate electrode material is also crucial. Graphite, tin
oxide, and molybdenum metal are standard glass industry electrode materi-
als that have been adopted for use in radioactive and hazardous waste
-------
Design Development
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-------
Chapters
vitrification. Inconel-690 (INCO Alloys International, Huntington, West
Virginia), a nickel alloy material, has been successfully used in
high-level radioactive waste melters operated below 1,200°0 (2,200°F).
A chrome oxide ceramic has been evaluated recently for use in radioac-
tive waste processing at temperatures up to 1,550°C (2,800°F) (Lamar,
Cooper, and Freeman 1995). Inconel-690, as well as graphite and mo-
lybdenum have been used in electric melters that have been demon-
strated for hazardous waste vitrification. Significant studies have been
performed in the past two years to assess candidate electrode materials
(Freeman, Sundaram, and Lamar 1995; Sundaram, Freeman, and Lamar
1995). The best electrode material is highly dependent on the glass
composition and oxidation conditions that exist during processing..
The initial process testing can be performed with small engineering-scale
equipment, typically about one-tenth scale. The test objective is to assess
the basic processability of the feedstock. Chief measurements are process-
ing rate, determination of any secondary phase formation, accumulation of
unmelted phase deposition of hard-to-melt components, offgas composition,
and extent of paniculate, volatiles, arid aerosol loss from the melter. The test
duration should be long enough to ensure that the system has achieved
steady-state operation and that the glass inventory in the melter has been
.turned over at least three times. This will result in the melter inventory, as
well as the product glass, being approximately 97% derived from the feed-
stock and the remainder being the initial start-up glass composition. Testing
determines whether the basic process as defined will provide acceptable
treatment results. A pilot-scale system (one-fourth to one-third scale) is
usually required to predict full-scale production rates and to obtain accurate
offgas data. This is critical if the melter does not rely on mechanical or other
means of agitating the glass batch.
Combustion Melters. Many of the design basis requirements for the
electric melter are also requirements for combustion melters. These include
waste characterization and analyses and laboratory glass development.
Waste characterization and-assessment of waste homogeneity are important
because of the small glass holdup or inventory associated with combustion
melters. With a small inventory, it is more important that the instantaneous
feed composition closely approximate the target or nominal composition.
Otherwise, glass quality could vary significantly. Troublesome components
include sulfur, halides, and metals having low vaporization temperatures,
such as arsenic, cadmium, and lead. The chief issue is to determine the
-------
Design Development
fractional loss during processing of these components and the ability to re-
cycle them back to the process for ultimate retention in the glass.
Refractories in combustion melters must withstand not only glass corro-
sion, but aiso high erosion, significant thermal cycling, arid gas phase acid
attack. Rerractory selection depends on the combustion melter type. Some
melters rely on refractories for thermal insulation in the combustion zone,
while others use a cold-wall design and allow for higher energy losses. An
added trade-off is the balance between refractory costs versus more frequent
shutdowns for replacement of less durable refractories.
. , „" , illjl!1; ,',•:'! '";,' "j „ ,l," ,!'' '|N! ' ''. ;i ':» F j! I! ..'Illrji1 "li, i'\ ; ",;,':'ill/ :!; .i'!'!;:1 /'' M VI ."I Cil1' "HI* I!' :, I1'!' *', ' "„'«' 'i, » 111, K'.
Combustion melters are noted for high production rates in relatively com-
pact units. Therefore, testing can be performed at pilot-scale in reasonably
small equipment. Process testing objectives are to establish production rate
and obtain product quality data under varying conditions in order to define
optimum operating conditions. Test parameters include feed particle size,
feed composition variability, feed injection rate, fueiyair mixture, production
rate, material losses versus combustion/melting chamber temperature, and
chamber gas flow patterns. Because combustion melters can attain
steady-state conditions in a matter of a couple of hours, many tests can be
conducted in a short time.
Induction Melters. Many of the design basis requirements for the electric
melter are also requirements for induction melters. These include waste
characterization and analyses, and laboratory glass development. Waste
characterization and assessment of waste homogeneity are important due to
the smaller glass holdup or inventory associated with induction melters.
Those components that cause problems for electric melters also present
problems for induction melters.
•.. . .;. , •,: "„, ;,;,'" v ', ••, •• ,,;',•: ' •,;'„;;", ;,,;.:;„,.;" "., |. .," ;', ,."', ,'",'": •. " ' ".'"', ."i- , "'
Induction melters are constructed without refractories. Rather, a seg-
mented \yall constructed of water cooling channels forms the melter
vessel. A schematic of an induction melter designed by Cogema is
shown in Figure 3.19. the cold wall results in a 2 to"5 mm (80 to 200
mil) layer of glass being frozen at the wall. This protects the wall from
glass corrosion. However, significant heat losses can occur, requiring
significantly higher energy input than would an insulated melter. Above
the melt line, the metal is exposed to corrosive offgases which can con-
dense onto the cool surfaces. It is necessary, therefore, to consider this
1 , .' • ''••>' > •:,! ,1" - • '••''••: L - 1 '.!' < ''T. 1 M" " . ' ' II •'.<.. ' " ' .• ••'.;• '. • Id
phenomenon during materials evaluations.
3.78
-------
Chapters
Figure 3.19
Cogema Induction Melter Schematic
Sectorized Crucible
Cooling Water
Casting Nozzle
Reproduced courtesy of C.EA—Cold Crucible Melter (1997)
-------
Design Development
, !, ' |
Presently, the largest high-temperature induction melter tested for treating
hazardous or radioactive wastes has a melt surface diameter of 1 m (3.3 ft).
The majority of testing and development lias been performed in units rang-
ing in diameter from 27 cm (l6.6 in.) to 5$ cm (21.7 in.). Initial process
testing should be performed in such units. The primary test objectives are to
determine process rate, effect of agitation on process rate, thermal efficiency,
losses to the offgas due to entrainment or volatility, process,characteristics,
and rate as a function of feed characteristics. Regarding the latter objective,
presently only dry feeding into induction melters is performed. Liquid feed-
ing has not been established as a routine or recommended option. Therefore,
feed materials should be relatively dry and reduced in particle size to opti-
mize reaction and melting.
Microwave Melters. Microwave melting can be performed with less
waste stream characterization compared to the other melters, since a hetero-
geneous^ waste stream cafl also> be treated. However, because only the top 5
to 10 cm (2 to 5 in.) of material is in a molten state during processing, the
heterogeneous characteristics of the feed are maintained in the final glass
monolith. Requirements for a high quality product might impose additional
characterization, blending, and sampling requirements.
Troublesome components that restrict the effectiveness of the microwave
melter include strictly organic wastes and high metals content. Organics are
substantially volatilized. High metals content can lead to localized arcing
which reduces efficiency and, if next to the container wall, could melt a hole
in the container. Significant concentrations of salts, halides, and high vola-
tility metals, such as mercury, can be treated but could lead to poor quality
products or high offgas losses. .
• ' ' ' . '", " i '„ "','! .'in', """., .,,'' "] ' ! " ' "'"' ".' ""i.: ' MM' ,'i i : ,'! ' ' ' „: f i:' '. :!,!'!„ =-
3.80
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Chapter 31
3.3.2.2 In Situ Vitrification
Each application of the technology requires sufficient knowledge of site
conditions to support design of an effective system. The overall oxide com-
position of the test'soil and waste determines key melting properties, such
as fusion and melting temperatures, and melt viscosity. Soil to be treated
must contain sufficient quantities of conductive alkalis (K, Li, and Na) to
carry the current within the molten mass. Additionally, the soil should con-
tain acceptable amounts of glass formers, for example, silica. Most soils
worldwide have an acceptable composition for ISV treatment. Geosafe
Corporation determines the oxides present in the soil prior to treatment. A
computer-based model then determines the suitability of the site for vitrifi-
cation. The model can also identify solids and wastes that require modifica-
tion before treatment (US EPA 1994a).
The type of contamination present on-site affects the design of the
offgas treatment system more than it affects the design of the rest of the
ISV system. For this reason, the offgas treatment system is modular in
configuration, allowing treatment of the offgases to be tailored to
site-specific conditions.
The limited ability of the current offgas equipment to remove heat
dictates that the organic content of the treatment media be less than 7 to
10% (by weight) thereby allowing for adequate offgas quenching tem-
peratures. Very high metals content (estimated >50% by weight) and
inorganic debris (estimated >75% by weight) may be treated by ISV as
long as the arrangement of such materials within the soil matrix allows
satisfactory performance.
Previous experience has indicated that safe, effective treatment cannot be
assured if large voids and/or pockets of liquids in sealed containers exist
beneath the soil surface. The gases released can cause excessive bubbling of
molten material, resulting in a potential safety hazard. For this reason, suffi-
cient site characterization is recommended prior to treatment if buried drums
exist or are suspected to exist beneath the soil surface. Uncontairied com-
bustible materials generally do not cause processing difficulties since they
decompose relatively slowly as the melt front approaches. Full-scale dem-
onstrations have been successfully conducted on sites containing significant
quantities of combustibles, such as wooden timbers, automobile tires, per-
sonal protective equipment, and plastic sheeting.
-------
-.,.,,
Design Development
The presence of large amounts of water in the medium requiring treat-
ment can hinder the rate of IS V, since electrical energy is initially used to
vaporize this water instead of melting the contaminated soil. The resulting
water vapors must also be handled by the offgas treatment system. Treat-
ment times are thus prolonged and costs increased when excess water is
present. If ISV will be performed at depths below the water table, and the
hydraulic conductivity of the surrounding media exceeds 4 • 1(H cm/sec, it
might be economically advantageous to use some means of dewatering or
limiting the water recharge rate.
The maximum acceptable treatment depth with the current equipment is
6.1 m (20 ft) Below Ground Surface (BGS); however, full-scale tests at
Geosafe's testing facilities in Richland, Washington, have demonstrated that
existing large-scale equipment can successfully melt to a depth of approxi-
mately 6.7 m (22 ft) BGS. Melts at the Parsons site typically reached depths
of 4.6 to 5.8 m (15 to 19 ft) BGS.
Site conditions should also be evaluated for the soil's ability to support a
forklift and a 125-ton crane used for changing containment hood positions.
Gravel, timbers, or other material can be used when the load-bearing charac-
teristics of the soil are not adequate. Sufficient space for maneuvering the
crane and positioning equipment is also required.
3.3.3 Design and Equipment Selection
Ex-situ and in situ melters can generally be considered as single unit
systems and, therefore, are fairly simple in design compared to more
mechanically complex, S/S processes. The electric melters are designed
around standard 480V/60Hz/30 power sources. Depending on the melter
and its design, the process engineer specifies transformers and power
controllers to obtain the voltage, current, power, and phase required for
the system. The following subsections describe additional information
needed to design the technology.
3.3.3,1 Ex-Sifu Meltqrs ; . '...j
Electric Melters. Sizing of electric melters which do not use agitation is
based on glass surface area. This value is strongly affected by the waste stream
being treated. High-level radioactive waste slurry containing about 50% (by
weight) solids can be processed at about'960 kg/m2-day (200 Ib/ft2-day). Dry
solids, such as soils, can be processed at rates 50 to 100% higher. Production
; ''; ' ;,;,,, , ,,, ;";' ,3.82
-------
. Chapters
rate also depends on the individual waste constituents. For instance, high con-
centrations of nitrates, carbonates, or organic materials generate large quantities
of decomposition gases which can interfere with the melting process by inhibit-
ing heat transfer. Therefore, it is important to obtain sufficient pilot plant data
to support melter sizing. .
Commercially-available melter systems have incorporated active mixing
using mechanical or pneumatic (i.e., gas bubblers) means. These systems,
such as the Stir-Melter® system shown in Figure 3.20, negate some of the
effect composition has on melter sizing. Stir-Melter, Inc. has stated that they
can process equivalent rates in melters just 10 to 15% of the size of
unagitated melters. However, verification testing is still necessary to prop-
erly size and specify a unit. Numerical modeling is typically used to specify
refractory thicknesses and placement to meet thermal and mechanical stress
requirements. These models can also analyze electric potential fields and
steady-state convection flow fields as functions of electrode placement,
power levels, temperature, and glass properties (e.g., viscosity and electrical
conductivity)(Eyler et al. 1991).
Power, voltage, and. amperage requirements depend on melter size, glass .
properties, and melter geometry. As a rule of thumb, it is assumed that
roughly one kilowatt-hour of power will be required for every kilogram of
glass produced. This assumes little or no usable heat content exists in the
waste stream. Glass resistivity combined with melter dimensions will estab-
lish the electrical resistance by the following relationship:
R = e(l/A) . (3.1)
where: R = electrical resistance across electrodes in ohms;
e = resistivity of the glass in ohms/cm;
1 = distance between electrodes in cm; and
A = area perpendicular to electrodes in cm2.
The minimum electrode surface area is defined by the maximum current flux
recommended to prevent "destructive heating" of the glass at the electrode-glass
interface (Yellow Book). It has been recommended that current fluxes be main-
tained less than 2 amp/cm2 (13 amp/hi.2) to prevent significant electrode con-
sumption rates. Transformers, power supplies, and controllers designed to
. operate at low voltage (e.g., 100 to 200 V) and high amperage (e.g., 1,000 to
3,000 amp) are more economical. Therefore, melter geometry and glass resis-
tivity should be optimized according to these parameters.
-------
Design Development
Figure 3.20
Stir-Melter, Inc. Agitated Melter Schematic
Feed
Impeller Shaft
Electric Head
Space Heaters
Insulation
.'Teapot Spout"
Reproduced courtesy of Sllr-Malter, Inc.
Combustion Metiers, No significant information has been identified in
the literature to describe in detail the design process for sizing combustion
melters. It is assumed that proprietary engineering and empirical data re-
sides with the developers of the technology to support scale-up calculations.
In general, melter size is a function of the residence time required to heat,
react, and melt the waste stream. Two combustion melter systems, the
Vortec cyclone melting system shownln Figure 3.21, and the Babcock
Wilcox cyclone furnace (Czuczwa et al. 1993) have been subjected to a sig-
nificant number of tests to demonstrate their processes in waste treatment.
3.84
-------
Figure 3.21
Schematic Layout of Vortec Corporation's Cyclone Melting System
Waste
Material .
CRV
Combustor
Fu
el
r
Preheated1
Air
Recuperator
1-
1*
Separator/Reservoir
L-,
tGas
ibber
Baghouse or
Precipitator
O
-Air
Air FD Fan
o
v_^.
ID Fan
Stack
Glass
eprotiuced courtesy of Vortec Corp.
O
Q^
f
Co
-------
Design Development
, v : ';;,,,|' ! , | - .
Both systems were originally developed as compact, high-efficiency thermal
combustion units for supplying heat to boilers or processes. As such, signifi-
cant expertise in radiant and connective heat transfer analysis and modeling
should exist This understanding, combined with pilot-plant tests, would be
used to design melters for waste treatment.
'; " ' • " "| " " ; „ , ,; ••:[•:•':; : "' . il "'[
The selection of fuel source — natural gas, coal, or fuel oil — determines
design of the fuel and combustion air supplies. 'No strong emphasis has been
placed on one fuel source over another. For this reason, economics may be
the major factor. However, the presence of inert substances hi coal, particu-
larly heavy metals and suif^"must1bVcohsid^re3'tb''e'nsure"that offgas treat-
ment and glass product quality are not affected to an unacceptable degree.
Induction and Microwave Melters. Because of the compact size of in-
duction and microwave melters, design and equipment selection issues are
few. The key parameters are the characteristics and composition of the
waste material. Equipment suppliers will most likely perform testing in
smaller units and use these results to specify the commercial unit. Because
these units process less than 100 kg/hr (220 Ib/hr) they are most applicable
to limited waste volumes or in cases for which multiple process lines could
be used. Induction meUers are only now being built and tested with melters
up to 1 m (3,3 ft) inside diameter. As melters increase in diameter, it is
necessary to employ lower frequency ranges so that penetration into the
bulk of the glass occurs. Dryer or calcination furnaces should be considered
as a process step prior to the induction melter when treating liquid Waste
streams. For solid waste streams, calcination should be considered as a
process-boosting step. Microwave melters can accept wet waste streams
, and even slurries. However, overall microwave production rates can be.
enhanced by dewatering and drying.
3.3.3.2 In Situ Vitrification '] j
A predictive model of the IS V process has been developed at Battelle
Pacific Northwest National Laboratory to assist engineers and researchers
with the application of ISV at different sites (US EPA 1992a). The model,
configured on a personal computer, predicts vitrification time, melt depth
and width, and electrical consumption. Predictions are based on data inputs
of electric operating parameters, soil parameters, and molten-glass character-
istics. The model's predictions are useful for planning operations, cost esti-
mating, and defining melt locations.- The depth and width predictions, for
3.86
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Chapter^
example, can be used to locate the melts to help ensure that the entire con-
taminated region is treated and that adjacent structures are not damaged by
ISV treatment. The model has been used to predict melt time, melt shape,
and energy consumption; the model has accurately, predicted monolith
shapes of a large-scale ISV melt.
Luey et-al. (1992) also reported that the important modeling parameters
appear to be scale, power level, power-to-surface area ratio (governed by
power level and/or electrode spacing), and, to a lesser degree, electrode
.diameter-to-spacing ratio. As the scale increases, the percentage of bottom
heat transfer and relative 'downward growth decreases. Increasing the power
supplied to the electrodes tends to produce a hotter melt region, higher flow
speeds, promotes mixing, and consequently enhances the' percentage of total
heat loss passing through the bottom and the sides of the vitreous zone.
Power supplied to the system (typically about 4 MW for a large-scale
unit) is limited by current and yoltage limits imposed on the equipment.
Approximately 700 to 1,000 kWh are consumed for each ton of soil
vitrified. The system requires 12.5 or 13.8 kV, three-phase electricity.
Electrode diameter (typically 30 cm [11.8 in.] for a large-scale unit)
must be sized for the power level to prevent excessive electrode tem-
perature and oxidation. Electrode spacing depends on the electrical
conductivity of the melt and other factors, and typically varies between
3,4 and 4.6 m (11 and 15 ft), depending on site-specific conditions. A
3,5 m (11.5 ft) spacing was recommended for a proposed large-scale test
at the Idaho National Engineering Laboratory. The gas containment
hood is designed to contain potential bubbling of molten glass and to
direct, offgases to the offgas treatment system. Seals are created be-
tween the hood and the surface soils, and the hood and electrodes, to
restrict air in-leakage to about 99% of the total gas collected at a nega-
tive pressure of about 1.3 cm (0.5 in.) water.
Offgas is drawn from the containment hood at about 200°C (392°F) and is
usually cooled in a quencher. The quenched offgas usually is then scrubbed
in one or more scrubbers to remove particulates and some gases. The design
of the offgas treatment system depends largely on the contaminants expected
in the offgas and their concentrations. Geosafe's large-scale unit can process
1,800 scfm (51 mVmih) resulting in CO emissions below 0.5 g/hr (0.001 lb/
hr), NOx emissions below 500 g/hr (1 Ib/hr), and particulates below 9 g/hr
(0.02 Ib/hr). The thermal oxidizer consumes about 880 kW of natural gas
-------
Design'Development
when in use. The on-line efficiency of the overall system is 83 to 90%, ac-
cording to Geosafe.
The time to mobilize or demobilize the equipment at a site is two to three
weeks. A. typical melting time is 10 days when processing 3.5 to 5.5 torine/
hr (4 to 6 ton/hr). The time required to move a containment hood and con-
nect electrodes at a new setting is about two days. Using two hoods,
Geosafe has been able to perform the power-down/power-up transition.be-
tween melts in less than 12 hours.
3.3.4 Process Modifications
3.3.4.i:E><-sifu Meifers'; ^ ^': \ J;J ; '^'', "^\, ,;,,,' ,';'"';';",:';;
Most potential modifications are driven by the desire to increase effi-
ciency and production rate, or accommodate materials not generally thought
to be processable. Electric melter technology is based on the processing of
inorganic materials, i.e., glass making materials, such as silica, boric oxide,
lead oxide, sodium carbonate, calciunj silicate, etc. Process modifications
would necessarily extend this basic" application to the complex physical and
chemical characteristics of hazardous and radioactive wastes. The following
M,;vMI-,,"" I",1:;'; :j,-- :,< »••' •; i- -i • M "i, ": ••&.::. ii'/.-iSi1 f x-'-yi, .:•'••: •. i:-:;i,;i,;, -. • *>.i?.'.,w. *;.\.;i : -:
design or operational modifications can be considered for ex-situ melters:
• increase processing temperature to achieve higher waste loadings
and higher production rates. Higher cost and consumption rate
r of electrode materials can occur; as well as an increase in the rate
of volatility of halides, alkalies, high vapor pressure metals, etc.;
i I in | ii ' iii
• add supplemental heating in the plenum space of a melter to
: boost production rate and maintain space temperature above
1,000°C (1,800°F) to assure cprnbustion of organics. Gas, elec-
tric, or plasma heating have been demonstrated;
• increase plenum space volume to accommodate wastes with a
high organics content and promote pyrolysis, combustion, and
decomposition of organics;
• incorporate mechanical, gas sparging, or other means of mixing
, the glass to increase heat transfer to the waste, thereby increasing
the production rate and reducing the relative size of the melter;
'.I.1 • .' • I '.,'" .' •'. *•:<•!.i...' .in..' . .in-...3 .. . |
3.88
-------
Chapter 3
• introduce oxygen or air jets into the plenum space to aid in oxi- ;
dizing organics (assuming the air is mixed with the gases con-
taining the organics at sufficient temperatures; a separate after-
burner might be the best choice);
• introduce oxygen or air jets into the melt to aid hi oxidizing met-
als; and
• for wastes containing high concentrations of metals, a melter ;
should be designed to accumulate and drain a molten metal
stream separate from the glass stream. For electric melters, this
affects electrode design and placement, and refractory linings
should be replaced with a cold wall design. For induction :
melters, multiple zone heating would need to be designed to
account for the difference between glass and metal induction
properties.
3.3.4.2 In Situ Vitrification • • -
Applications involving buried waste might result in variable offgas evolu-
tion rates and excessively high offgas heat loadings if a high fraction of com-
bustible materials are present. Such applications might require precondition-
ing of the wastes, prior to ISV processing, to avoid or minimize these effects.
Site conditions that may warrant preconditioning include: :
• lack of necessary chemicals in the soil to ensure uniform melting
and attainment of a suitable vitrified product;
• excessive void spaces;
• excessive liquid quantities or liquids in sealed containers;
• excessive heat generation related to the oxidation of the products
of pyrolysis of waste components; and
• significant uncertainty regarding the materials and conditions
present. Such conditions may render the direct application of
ISV more challenging for a variety of technical, economic, and
safety reasons.
In most cases, engineering means are available to effectively deal with
these concerns. The primary engineering means include:
-------
I ni111
,"•„ ,,'i'f 'I ' i'u;" I "I
Design Development
• adding soil with appropriate chemical additives on the surface
above the waste materials;
• modifying the chemistry of the contaminated media by injecting
soil or chemicals into the volume to be treated;
• densifying the waste site using dynamic compaction (see Section
.3.3.5.2);
'""'" rupturing sealed containers using dynamic disruption (see Sec-
Jion 3.3.5.2); ' ' ' ' '^'
• renidving liquids using thermally-assisted vacuum extraction;
t -,il " !!• ':!,•]! i st'i1! [ iii,'!?1,,' >>..'.•], .;!!!(, T,ii",:'i Si"!; I'."" » '"'"''i"!: ."'I • >:''.: : : I'"si
filling voids by injecting solids; and
,IJ' "I li "'lit 'V" I'1 ,r I'",,!',
'I' '!!, I,!!,'!! i!,,i lll'l1!'
,1 '
• excavating arid removing unacceptable materials such as explo-
sives, and then re-staging the wastes in a manner acceptable for
ISV processing.
" , •"' ./",..; I':1 : : • , ','.';, :'. ",;. ;'(;,".; AS ',,;,;;,,'',; |, •; i <::;' ,: .:,: •••,.,.• . . _: v1.' , i!;1,,!
The processing rate can be increased using multiple ISV units or a
second offgas containment hood. The use of a second hood enables the
.hood and electrodes to be installed at a new setting while ISV is being
completed at a current setting. Battelle has also studied the feasibility
of significantly larger units as a mean's "of increasing processing rates
and concluded that units two to three times the size of the present unit
can be built and operated (US EPA 1995c).
3.3.5 Prefreatment Processes
3.3.5.1 Ex-Situ Melters
Industrially-supplied equipment should satisfy the handling, preparation,
and feeding of materials to the rrielter for most applications. For liquid or
slurry systems, properties requiring definition include composition (to assess
corrosion potential and material hardness requirements), percent dissolved
and undissolved solids, particle-size distribution, viscosity of the mixture,
.and requirements for homogeneity. Selection of equipment for size reduc-
tion and conveyance or pumping should be based on capacity requirements!
and physical and chemical properties of the feedstock.
3.90
-------
Chapters
When the waste material is received at the processing facility, a "macro" -
batch should be characterized to determine the amount of glass or chemical
additives. To assure the sample is representative, mixing equipment should
be used to dry or wet blend the material. Size reduction or classification
equipment should also be used at this point if the waste stream contains
rocks or other foreign matter. The material should be crushed or sorted and
the foreign material and large rocks removed and discarded or treated sepa-
rately. Size reduction is also necessary to increase the surface area of the
material so that it will react and melt more quickly in the melter.
Thermal treatment systems, such as melters, are not efficient evaporators.
If a waste stream has a significant free water content, the cost benefits of
installing a dewatering or evaporation unit prior to the melter unit should be
analyzed. Equipment options to consider include mechanical dewatering,
thermal drying, microwave drying, and calcination spray or rotary furnaces.
Costs for the added equipment would be weighed against the benefits of a
smaller melter unit and reduced energy costs, since thermal efficiency should
be higher in an evaporator. The complexity or selection of offgas treatment
equipment in the absence of a large water load should also be considered.
As was stated in Section 3.3.3.1, induction melters require removal of free
water. Radioactive production units have been designed to couple the dryer
or calcination units directly to the melter. A similar design configuration
might be optimal for hazardous waste treatment applications.
Prior to feeding a melter, any necessary glass or chemical additives (as
determined by the waste characterization) should be blended with me waste
stream. These additives would be stored in large bins from which the re-
quired amount can be automatically transferred to a blending bin and then
blended with the waste. Pre-blending is an important step when using a
melter that does not have a means to mix the material once it has been fed.
If pre-blending does not occur, the waste and the additives can separate and
impede the melting fate.
Finally, solid waste and bulk chemical streams can generate appreciable
amounts of suspendable solids. Liquid wastes can contain low vapor pres-
sure orgahics that must be excluded from entering the workspace environ-
ment. The design engineer has to consider these aspects and identify appro-
priate ventilation, filtration, and treatment systems.
-------
Design Development
3.3.5.2Jn Situ Vitrification
• in sornVcases.* is necessary to add chemicals or soil of specific oxide
composition to the treatment zone to obtain the desired properties of the melt
and vitrified product. Materials can be added on top.of the materials to be
treated In such cases, the melt is initiated in the added soil layer, and the
desired composition is attained when the target contaminated matenal melts
and mixes with the molten surface material.
It is possible to overcome deficiencies in chemical composition by inject-
ing the required materials directly into the volume to be treated (Luey et al.
1992) This option might be preferred if large voids exist. The matenals to
bte added should, in general, have a significantly lower melting point than the
waste medium to be treated. .
Large void" volumes are of concern in IS V applications because they hold
the potential to drain off a significant quantity of the melt, resulting in the
loss of electrical continuity between electrodes. Moreover, release of the gas
present in large voids can cause undesirable melt disturbances when the gas
rises through the melt. In such cases, compaction can reduce the size or
'I™ V "j - i INUI.
eliminate large voids.
Dynamic compaction is a proven method of densifying soils. This
method involves dropping very large weights from heights of about 15.3 m
(50 ft) onto the surface of the treatment zone, thereby compacting it. An-
other method, known as dynamic disruption, involves vibrating a vertically
oriented I-beam or similar structural member from the surface down through
the treatment zone on a spaced grid to ensure that the affected area has been
conditioned. Typically, dynamic1 disruption creates a 0.9 to 1.5 m (3 to 5 ft)
radius of influence. Materials present within the radius of influence are
- shaken, compacted, and disrupted. Sealed containers within the treatment
zone are damaged and lose their sealing integrity.
High concentrations of organics(>10% by weight) can generate heat
loads that exceed the ability of the offgas treatment system to adequately
quench"the olfgas temperature: An excessive heat load could cause the
equipment to malfunction or otherwise not meet performance specifications.
Excessive heat loads can also cause overheating and damage the offgas col-
lection hood and treatment equipment, although refinements in the hood
design and operating procedures in the past several years have reduced the
potential for damage.
KSIiifi I ..i1,! iii" i 3 92
""
-------
.Chapters
The primary method of controlling the rate that heat is generated by the
oxidation of pyrolysis products involves controlling the power applied to the
electrodes, which in turn, affects the rate of melting and the corresponding
rate of melt movement through the soil and combustible waste. For buried
waste applications in which significant void volumes exist, the site should be
compacted, or the voids should be filled by injection of solids to ensure
proper control of melting rates.
Another method of controlling the rate of heat generation is to mix soil
that is highly contaminated with organics with soil with low organic concen-
trations. Clean soil can be added if needed to attain acceptable organic con-
centrations..
If a site cannot be made acceptable for IS V processing using the
pre-conditioning options presented above, then re-staging the buried wastes
for treatment should be evaluated. Re-staging wastes for treatment consists
of the following steps: ,
• excavation;
• removal of unacceptable materials or conditions, if any;
• crushing, grinding, or shredding oversize materials, as necessary,
to improve ISV processing; and
• placement of the remaining materials within the soil in an accept-
able manner for ISV processing.
Such re-staging is advisable when the site characterization information is
inadequate to support decisions regarding pre-conditioning options. Re-
staging can also be required if potentially explosive materials (e.g.,
imexploded ordnance, pressurized gases, combustible materials present with
oxidizers, etc.) exist within the site.
3.3.6 Posttreatment Processes
3.3.6.1 Ex-Situ Melters , .
The glass or glass and crystalline product of vitrification can be either
cast into monoliths using containers such as 208 L (55 gal) carbon steel
drums or converted to a cullet and handled as a bulk material. One of the
primary benefits of thermal stabilization/solidification treatment is that the
product has very good durability. If necessary, the glass composition can be
-------
11
Design Development
"!:,1!, ii'hllllSil,
designed to ensure that the product will pass the TCLP test. Its subsequent
disposal or use depends on the original waste stream and US EPA regula-
tions governing the waste stream. 'Handling the product as a cullet elimi-
nates the cost for the drums. To produce a cullet, the molten stream can be
either poured into a water trough or it can be poured through water-cooled
rollers or similar devices designed to form small glass pieces.
The offgas stream treatment requirements depend greatly on the waste
stream. Typically, five components of the offgas stream must be considered.
They are moisture, paniculate, soluble gases, noncondensable gases, and
non-combusted organics.
J . . •", '„' .;• • • j '• ' : I •(
'• ; Moisture can be condensed from the .offgas stream or passed
though the treatment train and allowed to go out the stack. If
condensing the water is required, quench spray systems such as
venturi scrubbers are typically used. If the water does not need
to be condensed, the engineer must pay attention to ensure that
me offgas stream temperature remains above the dew point
throughout the treatment train to prevent condensation. If con-
< densatiqn and recovery are necessary, paniculate matter and
condensable and soluble gases such as HC1, and some fraction of
nbricondensable gases, such as SOx or NO2, are also co-recovered
along with the water.
• Paniculate matter entering the offgas stream can constitute 0.1%
or moreof the material being;fed'to the melter. It will include
", , JI i' ' HIT • ,:•„"". |l , ' 'i,, '""! M lOi:,! III!!! HEW S *-* ,, h
gross paniculate with particle diameters greater than 10 pm. It
will also include submicrbn material that has volatilized from the
glass surface and recondensed in the offgas stream. Both wet and
dry paniculate scrubbers are commercially-available to remove
particulates. Common dry removal processes include fabric fil-
lers, e.g., baghouses, electrostatic precipitators, and cyclone sepa-
rators. Wet scrubbing devices include venturi and free-jet scrub-
bers and wet electrostatic precipitators. If necessary, polishing
scrubbers can be placed downstream of such devices to capture
" airy submicrpn particles that escaped the primary scrubber.
These devices include high-effidiency fiberglass filters arid
High-Efficiency Paniculate Air'(JHEPA) scrubbers.
3.94
-------
Chapters
• Water soluble gases are predominantly halide acid gases. There
are many commercially-available treatment methods that can be
applied to halide acids.
• KOX and SOx are typically the primary noncondensable gases
produced from waste processing when nitrate and sulfate con-
taining wastes are processed. Both of these are partially water
soluble. Wet and dry scrubbing technology exist for SOx recov-
ery. NOx scrubbing can be performed wet or with selective cata-
lytic conversion to nitrogen and oxygen.
• Organics can be effectively oxidized if held at a sufficiently high ,
temperature in an oxidizing environment. Typically, a secondary
combustion chamber is used. However, due to the cost of actiT
vated carbon, it is not normally employed unless the gas volume
and temperature are both low.
It should be remembered that besides the individual constituents in the ]
offgas stream, the composite composition and the absolute concentrations of
the constituents hi the stream are of equal importance. This-affects both, the
sequencing of treatment devices and the selection of the devices themselves.
3.3.6.2 In Situ Vitrification - !
The major process residual of ISV operations is the vitrifield waste mono-
lith. The glass and crystalline vitrified ISV product has been shown to be
highly durable and resistant to leaching (Luey et al. 1992). It is possible that
areas that have not been adequately melted between melt settings might be \
revealed during quality assurance evaluations of the monoliths. Core drilling
of the monolith can be used to verify waste treatment depths and product
consistency. Unmelted areas can be retreated using ISV and, where appro-
priate, alkalis and glass formers can be injected to facilitate melting.
A number of secondary process waste streams are generated by the ISV
technology. These include air emissions, scrubber slurry, decontamination
liquid, spent carbon filters, spent scrub solution bag filters, spent HEPA
filters, used hood panels, and discarded personal protective equipment (US
EPA 1994a). The amount of scrubber slurry and filter waste generated de-
pends on the nature of the contaminated media before treatment. High par-
ticulate loadings in the offgas and high soil moisture contents can increase
the quantities of these wastes. The number of used hood panels to be
-------
I I
1
Design Development
disposed depends on the corrosiveness of the offgases generated[during treat-
in^ (as well as the corrosion-resistance of the hood panels) and the tem-
perature and duration of treatment (US EPA 1994a).
Some process residuals (ei/^'i^'soiutlpnb^filto^^HEPA
filters and discarded personal protective equipment) can be disposed by
' vitrifying In subsequenttSV settings to reduce the amount of these wastes
mat require disposal oftsite. Geosafe vitrified all process residuals in subse-
quent settings at the Wasatch Site. Scrubber slurry generated during treat-
ment may require special handling, depending upon the types and level of
contaminants removedi in;ffie scrubber (US EPA 1994a).
'" Typical treatment processes for scrubber slurry include activated carbon
adsorption, neutralization, precipitation, coagulation, flocculation, and ion
exchange. Granular activated carbon filters can be regenerated and reused.
Metal HEPA filters, if used, can also be cleaned and reused.
3.3.7 Process Instrumentation and Controls
3.3.7.1 Ex-Situ Melters
Electric Melters. Electric melters are controlled by adjusting electrode
power based on temperature measurements of the melter tank. The glass can
be measured directly using thermocouples placed in the glass, electrodes, or
refractory. Based on these readings, the electrode power can be adjusted
accordingly. The temperature is also measured in the glass discharge area,
the plenum space, cooling water or air circuits, and in strategic areas within
the refractory, if desired. Electrical measurements include electrode amper-
age, resistance, voltage, and power; similar measurements are taken for any
resistance heaters used in the glass discharge area or plenum space.
' Pressure values are "measured In ffipleiuim spa& arid pressure and flow
data are measured throughout the offgas treatment line. It is typical that a
slight negative pressure (e.g., 5 to 13 cm [2 to 5 in.] water), be maintained in
the melter plenum space to prevent bffgases from leaking out of flanges into
the general work area. Pressure and flow readings in the offgas treatment
line between equipment pieces are used to verify steady-state operation and
identify equipment or line sections that are developing a blockage.
Process flow rates of the feed to the melter arid glass product are used to
measure production rate stability. Visual oSservation of the feed pile on the
O QA
II Illllll I I I I II I 111 I lull I I' VJ'71J
Inn || l||li|lll I n I ||i I in 11 n I n I illiiili in li ||||||||||||||||||||| in iiigniiiggipi I iiiiiinl|g| iiigii ^^i II n I ill n I I ilgn ill n ll mil III II II I II ill
-------
Chapters
glass surface, either through a view port or camera is still a key means to
evaluate processing efficiency and whether the.melter is being overfed or
underfed. As experience with a particular waste stream is gained, production
efficiency can be inferred by plenum temperature and pressure readings, and
glass temperature, power, current, and resistance readings. Flow rates of the
cooling services are also required to ensure they are maintained at set values.
All of these data can be collected using computer interface equipment for
subsequent inspection, data archival, or for feedback control.
Combustion Metiers. This process requires measurements similar to
electric melters. Noticeable exceptions are the measurement of fuel flow
rate to,the process, combustion air temperature and flow, oxygen concentra-
tion in the exit gas stream, and temperature in the combustion chamber.
Induction Melters. Induction melters are very similar to electric melters.
Unique instrumentation includes induction power generator readings instead
of electrode readings, and coil water flow and temperature and cold-wall
cooling circuit flow rates and temperature.
Microwave Melters. Microwave melters are the least complex of all the
melters. Monitoring and control mechanisms are limited to the microwave
generator power level, microwave leakage detection, generator cooling water :
flow rate and temperature, and container and product temperatures, which
are monitored using thermocouples or pyrometers.
3.3.7.2 In Situ Vitrification . ;
The ISV process instrumentation and control system includes ap-
proximately 50 separate instruments used for tracking temperature, pres-
sure, amperage, voltage, flows, gas concentrations, and other param-
eters. The system automatically logs all parameters and provides visual
displays of data trends. Operators evaluate trend data against operating
limits established in the permit and work plan as the primary basis for
ISV process control decisions.
The ISV system is manually controlled by operators with the exception of ,
two control valves that control the flow of air into the hood and the offgas
system to maintain adequate negative pressure in the offgas hood. Auto-
matic systems are used for certain important functions. For example, in the ,
event of power outage, the system automatically starts a diesel generator that
powers a backup offgas treatment system. The cost of ISV is minimized by
-------
I1 '• ' , '''iii,. ,'• '1(1; J; «• :,'••' , •„" .|i; «' -i ">;«;>''
Design Development
; '• .i •:::,:.:;,' , , •, ' :., ,: , . ,; •„•:;, ;:;:";; ; ••- rjr1 ..;•.,:;j, '. •". '-.:; . .•, .iT ' ;..'..;','i .a. '.,
" operating as close to design and permit limits as possible. Manual control of
the system allows for fine-tuning to optimize process performance.
3.3.8 Safety Issues
•.'.'!•' i • . i
3.3,8.1 Ex-Situ Melters ;'"''. '..
,. ,i|i< ii i1 •• i,,. H : . i1, „ a , ,i,' , i .' , •i,,i|;il.1,,|i,i,irtll',,!«i,,'ii|i» i,,,!!11 i;f iiiiih I'j'i fp :," I1:.'":,,1,1 .„• "i % •;: "•» ,', ''HI ii1"'W1:, '", •
AJ1 ex-situ melter types have safety requirements because of the use of
high voltage or current arid high temperatures! Electrical components should
be specified, designed, and installed according to National Safety Code
specifications. Safety requirements should include:
• using enclosures with positive-closure latches for exposed elec-
: trical sources, such as bus bar connections, fuses, and power
supply wire connections;
• implementing a lock-and-tag procedure to isolate energy sources
i and protect workers;
• using personal safety equipment, such as rubber mats and
rubber-lined gloves when inspecting or troubleshooting energized
- ;•; systems; • • ' . . '
• using water cooling, insulation, or screening on hot surfaces to
prevent contact;
• using Personal protective clothing such as high-temperature
clothing, face shields, and insulated gloves for use when sam-
pling the molten glass stream, probing the melter tank, or han-
dling the hot product; and
• observing OSHA and National Industrial & Occupational Safety
' • & Health (NIOSH) requirements governing industrial plant
worker safety.
Combustion melters will use either natural gas, fuel oil, or coal. There
are special handling, monitoring, and storage requirements for safety using
these fuels. Microwave melters must be monitored for microwave leakage
during operation with a hand-held detection device.
If the normal ventilation system fails due to mechanical or operational
reasons, the hazardous gases, superheated gas, and steam generated during
processing must be discharged through an emergency vent outside the
-------
Chapters
building. Otherwise, the melter would pressurize and a large amount of
.glass could be discharged or the gases would leak into the workers' area
from flanges or fittings.
If a waste stream being treated is a designated CERCLA or RCRA waste, the
operating personnel must receive 40 hours of Hazardous Waste Health and
Safety Training and 72 hours of supervised on-the-job training to comply with
US EPA and OSHA requirements, along with 8 hours of refresher training.
3.3.8.2 In Situ Vitrification
The design of the IS V system is based on OSHA, the National Electric
Code, and other applicable safety standards. An external water spray system
installed outside the offgas hood ensures that the hood does not overheat if
excessive bubbling of glass occurs. This condition can expose the hood to
high radiant heat or high gas temperature if high fractions of combustible
materials are being processed. Fencing and other physical barriers are in-
stalled to prevent trespassing. Administrative controls and training are used
to ensure operator safety. For example, power to the electrodes must be
disengaged and locked out when it is necessary to perform work on the
offgas hood.
All components are connected to a common electrical grounding grid
consisting of six-foot long copper rods driven into the ground and electri-
cally connected. Personnel who require access to the site must complete 40
hours of Hazardous Waste Health and Safety Training and subsequent re-
fresher training.
3.3.9 Specification Development
3.3,9.1 Ex-Situ Melters
Melter equipment components are used routinely by industry, and are
currently designed to meet rugged industrial standards. Manufacturers and .
suppliers of refractories, electrical transformers, power controllers, and solid
and bulk handling equipment should be contacted early in the design process
to discuss the application to identify any special requirements. For instance,
refractories can be produced with a lower volume fraction of voids or cut
and finished with different surface smoothness criteria than are standard.
However, additional delivery time and costs are likely to be incurred.
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1 :• li!" i; I. I'll! • I,
.Design Development
I "i : i
Depending on the waste stream["and location, specifications might need to
be includeS to protect electronic or electrical.' equipment from significant
dust loadings in the air. Also, given trial the equipment might process a vari-
ety of different waste streams, a robust design that can be easily disas-.
sembled'and reassembled following inspection and repair should be an ob-
jective of the process design engineer.
All equipment must meet applicable safety and performance standards to
mitigate the electrical,, mechanical, and thermal hazards associated with the
ISV system and the chemical, physical, and radiological hazards associated
with the hazardous waste site. The ISV design specifications' must be based
on limits defined in the operating permit and conditions of the site. Key
conditions include organic content, rnetal content, void sizes, moisture con-
tent, electrical conductivity, and depth of contaminated media. The types
and concentrations of contaminants present impact the type of offgas system
that must be used. For example, a site containing only heavy metal contami-
nants would not require thermal oxidation of the offgas, although scrubbing,
gas filtration, and/or other treatment units may be required to ensure compli-
ance with permit conditions.
Geosafe Corporation and ISV Japan, Ltd. are the only licensed vendors of
ISV, and the two entities are business partners^ Geosafe^ scope is world-
wide, whereas ISV Japan operates only within the boundaries of Japan. .
3.3.10 Cost Data
3,3.10.1 px-Situ
There are no known operating commercial treatment plants that have
, published reliable cost data. The following information is based on
studies, US EPA SITE demonstrations, or vendor literature. A possible
application of electric melter technology to treat contaminated soils,
sludges, and debris was evaluated by Koegler et al. (1989). Capital cost
for a 180 tonne/day (200 ton/day) melter, power supplies, feed handling,
offgas treatment equipment, and glass handling equipment was esti-
mated to be $5.5 million. Facility design, construction, and equipment
installation were approximately twice the capital equipment cost. For
this application, electric power cost, was 60/kWh and comprised 57% of
i
1 iii
3.100
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Chapter 3
the total estimated operating cost of $60 million. 'Labor cost was only
7% of the operating costs.
Chapman (1991) estimated that municipal waste incinerator bottom ash
could be processed at 45 tonne/day (50 ton/day) in an electric melter for
approximately $88/tonne ($80/ton) of ash. However, these numbers have not
been validated. In early 1996, GTS Duratek Corporation completed con-
struction of a vitrification facility to treat 2.54 ML (0.67 Mgal) of mixed
radioactive waste for a fixed price of $13.4 million.- Costs include design,
construction, operation, radiological health and safety, and decontamination
and decommissioning of nine storage tanks. The vitrification process will
operate in 1996 to process the wastes and produce approximately 1.1 Mkg
(2.4 Mlb) of glass product at a rate of 300 kg/hr (660 Ib/hr).
Combustion melter operation and maintenance costs based on- US EPA
SITE demonstrations of the Vortec Corporation's combustion melter are $39
to $44/tonne ($35 to $40/ton) for contaminated soils (Shearer et al. 1992);
The company estimates capital costs for a 23 tonne/day (25 ton/day) unit to
treat hazardous waste dusts produced from arc furnaces and smelting pro-
cesses, fly ash, and soils contaminated with heavy metals would be on the
order of $3.5 million to $4 million in 1991 (Hnat et al. 1991). Capital costs
included the costs for feed handling equipment, offgas treatment, glass prod- :
uct handling, and process instrumentation and control. Annual operation and
maintenance costs were estimated to be $375,000 to $500,000.
No microwave metiers .are known to be in commercial operation treating
hazardous waste. However, the capital costs for a 60 kW microwave genera-
tor, wave guide, tuner, and cavity enclosure are estimated to cost approxi-
mately $1 million.
3.3.10.2 In Situ Vitrification
The typical cost of ISV is about $440/tonne ($400/ton) of nonradioactive
material treated according to Geosafe Corporation literature. The US EPA
performed an economic analysis of ISV at a site with conditions similar to
those at the Parsons Chemical Works, Inc. Superfund Site where staging was
required (US EPA 1995c). The estimated cost of ISV was $470/tonne ($430/!
ton). This cost is likely higher than would be expected for the typical ISV
site where staging of the contaminated soil into separate cells would not be
required. The US EPA (1995c) defined ISV costs according to the 12
-------
Design Development
it, :,,!,'l!!" .I1!' , ''!, il",'
i' }^: i til"1' 7,'*
Jilil,1') ' f
'• i,,,;ir • •,, is
•1 II
.
II 1 h III II
I
.1 , ( 1 1
Table 3.20
'Summary of ISV Costs
i
.:,,', ; Cost Category
1. Site and Facility Preparation
2. Permitting arid Regulatory Requirements
'',:'. :i, . " '•'! "I1!1"1 il ";: M"1 •.. » ,;, J1. ,1. 'I*,1' 'it i1 • " r
;; 3. , Equipment
4. Start-up and Fixed
5. Labor , ' !
6. Consumables and Supplies
7. .Utilities'1
8. Effluent Treatment and Disposal
9. Residuals and Waste Shipping/Handling
10. Analytical Services
1 " i;i, if!'" " I i!'!'"'i ,r: v llii;:,,1 ", i mi ' ''i"!!!"1'1!111! in , ' :"i"r ' i i\ • , ","' t
11. Facility Modifications and Maintenance
1Z Site Demobilization
13. Long-Term Monitoring
Nl not Included In cost analysis
Adapted from US EPA 1 995c
i ' ''T .. 1 i »
" I , , , '»
* Total Costs (%) ,
•'• 2 '
"I. | '• •;•;: ''*' , ',.,,;''! ;.•' •.' !„ .'i "T;., ,j,. 1 - ''ifi I1' ' • 1'
• " ' ' 17
" 19 '
8 , ,
„.• i i • „ ,,."" '.'"if • : - , • ' ' i ,"", iMliplPti' i'"
" '" "'""• ' 22
0
"••.'''.• 3
2 i
"i'1"":'"''""1"" •' "':' "' "11 "' :';i"" "'
" : 2
" •" ' ' " ' ' ; 1 '
NI
, ',", :, ' :. , '
, ,. , . ;
:;;;: •; r ,,, . , j
categories shown in Table 3.20. Each of the cost categories that represents
more than 5% of the total costs is discussed below.
• Equipment costs are dominated by amortization of the major ISV
equipment costs ($4 millibn per ISV system)^
1 '.'''i1' •' „ 'i| ' !'• ' ,n i ''t » ' •' M' i i '. ,' ' '''' 'Wir't''!''!'!!!''!!:!! '"'" '*"! '"!'""l:lllli 'SI Hhii1!11':'.!!1! 'In, ', ! ' J ,''',''' h/.i1: • / '"' ' , • S,i 'iv'iili'i'PiiPI*", ' '"i
• Start-up and fixed costs are dominated by insurance, taxes, and
•'' "•'"''• contingency costs.
• • Labor costs incurred during meiting represent about one-half the
j i"' I," i'l',111"1!1' '. •'!.'• ': '•.",• Ill" "PI'- '"""' " i ''t" '.'K I. .1 "" " II. .', ' "S" 1..1: '!'
- total labor cost.
•; Electrodes represent the highest consumables cost.
••( ..... 11 ,\ ..... •l:/!l!i!!Lll,v Ci
"The cost of electricity is 99% of the utilities cost and about 20%
of the total treatment cost.
•3.102
-------
Chapter 3
• Maintenance and replacement of hood panels are the most expen-
sive facility modification and maintenance activities. (Note that
hood panel replacement was a requirement at the Parsons site due
to conditions there; however, the need has been much less at
other sites). Typically, only a few hood panels require replace-
ment per job at a cost of several hundred dollars each.
3.3.11 Design Validation
3.3.11.1 Ex-Situ Melters
Any and all of the ex-situ melters might be applicable to a specific waste
stream. Further complicating the decision-making process is the fact that
many options exist for each melter type. Therefore, it is important that an
objective evaluation method be developed for selecting a system. An assess-
ment could be done as part of a vendor proposal review or as a means to
identify and then procure a system. All significant technical, regulatory, and
institutional requirements should be identified and assigned weighting fac-
tors. The requirements should be further divided into two groups; those
which are absolute and the requirements that can be met to varying degrees.
Experts that cover the field of application can then be asked to assess each
requirement and provide a score to indicate how well each technology or
vendor met the requirement. A tally of the scores would indicate which
system best meets the requirements of the application. A broad base of tech-
nical expertise'exists within the personnel of government, industry, and engi-
neering consulting firms who could perform these peer review activities.
3.3.11.2 In Situ Vitrification
The number of individuals qualified to contribute effectively to value
engineering and peer review of IS V options is relatively limited. Most of the
experts in ISV technology are employees of Battelle Pacific Northwest Na-
tional Laboratory and Geosafe Corporation. This technology has been ap-
plied by Battelle at Oak Ridge National Laboratory and Idaho National En-
gineering Laboratory. The greatest opportunity for increasing the robustness
of the technology is in developing methods for increasing the depth and
shape of the melt. Geosafe Corporation may offer certifications and guaran*
tees that ISV will accomplish design objectives at a price that is commensu-
rate with the risks.
-------
1 111
Design Development
3.3.12 Permitting Requirements
I I I I | I 1,1 i',"'v\jji"j': i'lj i:,i|,i
3.3.12.1 Ex-Situ Melters _
General permitting requirements are well described in Section 3.2.12.
Additional regulatory issues associated with ex-situ melters pertain to the
treatment and discharge of secondary waste streams. Federal, state, county,
and local requirements must be met for the degree of offgas and wastewater
cleanup prior to discharge to the environment or municipal treatment system.
In many cases, treatment technology must Use or be equivalent to BOAT
identified by me US EPA to gam regulatory approval. Additionally, process
performance data will be required. Data obtained from demonstration tests
performed in pilot-scale equipment should be sufficient to gain approval to
construct" the process and reach agreement on the testing required for the
plant once constructed. Work plans can then be prepared detailing the test-
ing to be perfbrmeci to validate that the pilot-plant data can be duplicated by
the full-scale plant. Following plant testing, permitting of the plant would
occur and commercial operations could begin.
3.3.12.2 In Situ Vitrification
The application of ISV to hazardous wastes requires permits or approvals
in accordance with federal, state, and local requirements. For example, a
TSCA Demonstration Permit was required for demonstrating ISV at a
PCB-confaminated private site in US EPA Region X. Geosafe now has a
national. TSCA permit for treatment of PCB-contaminated media anywhere
in the u!S^ Federal and state permits required at the Parsons Site included a
National Pollutant Discharge Elimination System (NPDES) permit to dis-
chargei diverted[ groundwater to a nearby waterway. A Michigan State air
permit was also required (US EPA l994a). The US EPA and state-approved
work plans constitute permits for projects governed by CERCLA/Superfund
Amendments and Reauthorization Act (SARA) and RCRA/Hazardous and
Solid Waste Amendments (HS WA) regulations.
• A hazardous waste treatment permit is required when using ISV to
process newly-generate"d industrial wastes, f ne local air quality control
region may also restrict the quantities of air emissions, as well as the
types of equipment and fuels that may be used. Local agencies com-
monly require'an excavation permit when the waste is to be dug up and
staged prior to ISV. Other local permits may be required to ensure safe
3.104
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Chapter 3
operation of a treatment facility and to control discharges of water to a
sanitary sewer. Local permits at the Parsons Site were granted by the"
Department of Building and Safety and by the local fire department (US
EPA 1995c). A permit to transport ISV systems across state lines is
required because one of the mobile units is overweight.
3.3.13 Performance Measures
3.3.13.1 Ex-Situ Melters
Production rate, reliability, and product quality are the main performance
measures. Steady-state production rate is the single most important measure
of process performance. This measure determines the economics of the
system since it affects energy efficiency, materials consumption, labor costs,
and capital cost recovery. The production rate must meet original design
expectations and should be maximized to the extent possible. Reliability '..
refers to the on-line factor of the system and the replacement or repair fre-
quency of the subcomponents. As the operating time approaches and is
maintained near 100%, the cost per kilogram of waste treated is reduced.
Minimizing repair and replacement frequency improves the on-line factor
and further reduces operating and maintenance costs. Product quality can be
achieved through proper operation of the process coupled to proper feed
stream characterization and batching with any glass or chemical additives.
Product characterization to determine chemical durability and co'mposition
analysis should be performed at a frequency determined necessary for main-
taining the processes within required operating parameters.
3.3.13.2 In Situ Vitrification .
Implementability, effectiveness, and cost of the ISV process should be
. evaluated to support decisions regarding its application at a specific site-
Key parameters required to assess implementability include:
• mobilization and demobilization time;
• total operating efficiency;
• equipment corrosion and failure rates;
• power and chemical consumption, and;
• rate of secondary waste generation.
-------
III " .
VI!*
'
lil'ii, ' " ', I if'.
Key parameters requked to measure the effectiveness of the application
include:
I !!f •.,_»)•:;:•' '' !"•„•:•
• • theimocouple temperature readings and geophysical measure-
ments, where applicable, to verify that the target volume has been
•l '''"coiilample analysis to i establish pre-ISV conditions and to verify
" "vitrified product quality;
. • temperature and pressure drop data in the hood and offgas treat-
ment train; and
analyses of samples collected at the offgas treatment system
stack before, during, arid following operations.
'
The latter two parametric sets are requked to measure effectiveness of the
offgas treatment system and compliance with permit conditions.
. .•• . •-.»'"i ,• .. •. ii i i ii .''nil
!:''.", ' ' "<.: i !" • • T, < 'h i i i I ii i
3.3.14 Design Checklist
3.3.14.1 Ex-Situ Melters
. The following key factors should be confirmed to ensure that the design
has been properly developed. 'Depending on the nielter type being consid-
ered, some of the factors may not be applicable.
1, Sufficiently characterize"me; waste stream to determine level of
homogeneity, corrosiveness, major constituent compositions,
primary offgas elements, metals content, and organic content.
II' | I I I I III I I | I I I " '.,'',' l||i l!» ,,|,il' ' 1 IP
• 2. Define the type of waste pretreatmerit, such as blending, crush-
ing, sifting, sorting, and/or dewatering required.
3. Determine if any major or minor waste components will be lost
from the melter during processing, such as mercury, or have
significant volatility, such as lead, cadmium, and halides.
ii,;1'' " ' *"t..(fi , i .',. • ' "i'-ii'ii'i.!, i'" j ,*>", "i:". is;1, ."Pi"" I),!1,1,','("i"!,. i ."'r1 i, mi,1 as •" • -ji..t>'fH
4. Define the requked processing period or rate requked.
5. Determine the final product property requkements and if there
are any anticipated product uses.
6. Identify operating permit requkements.
3.106
-------
Chapter 3
1 , 7. Conduct laboratory studies of waste samples to determine how
the waste should be pretreated or if glass or chemical additives
need to be added to the waste to achieve an acceptable product.
8. Ascertain if the glass will have acceptable conductivity and
viscosity properties at the planned operating temperatures.
9. Determine if the glass is compatible with the materials of con-
struction to be used in the melter.
10. Determine if a secondary combustion chamber is required to
treat organics, if present.
11. Configure the offgas system to maximize the recycle of second-
ary wastes back to the melter without allowing the buildup of
any constituents not compatible with vitrification.
12. Determine if the melter is compatible with the required mode of,
operation, e.g., continuous, intermittent, or batch.
3.3.14.2 In Situ Vitrification - • :
The design phase must determine that conditions are acceptable for vitri-
fication in each melt setting or staged cell.
1. Determine if the waste medium requires compaction to elimi-
nate voids and to destroy the integrity of sealed containers of
liquids.
2. Ascertain if the waste medium contains at least 1.4% alkaline
oxides and if sufficient silica is present to form a durable glass.
3. Determine the organic content of the waste medium. It should
be less than 10% by weight.
4. Determine the elemental metals content of the waste medium.
It should be less than 37% by weight.
5. Determine the -fraction of inorganic debris in the waste medium.
. It should be less than 50% by weight.
6. If the she is below the water table, determine if the rate of re-
charge is acceptable or can be controlled.
7. Determine the depth of material to be vitrified. It should be less
than 6.1m (20 ft).
-------
• „!'„!!!!", Ilili. 'il'ill 'I'll
• 1'
8. Determine the content of silt and non-swelling clay in the site
. soils. These fractions should be small enough to ensure safe
release of water vapor.
9. Determine if soils at the site can support the crane required for
moving the offgas hood.
10. Determine if sufficient space is available at the site to set up and
move all required ISV equipment
11. Employ site modeling to establish appropriate" site arrangement,
melting characteristics, electrode spacing, and oxide composi-
.;,' tipn of the vitrified medium. ' ^ _
12. Estimate the composition of gases released[from the melt, or
nieasure them using treatability testing.
13. Estabh'sh offgas emissions limits.
'. lll"}| '!: . IS "ri, ! "''f' I!'1 ! '"!!! : '' • ! I;"1: "
14. Size the offgas blower to contain the air leakage and all gases
released from the melt'anpTprbyide a negative pressure of 1.3
cm (0.5 in.) water in the offgas hood. The blower should be
controllable so that these objectives can be satisfied.
15. Design the offgas treatment system to meet emissions limits at
the peak offgas flow rates and provide adequate public health
protection.
16. Design the site to ensure adequate run-on/runoff control and
safe worker ingress and egress.
3.108
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Chapter 4
IMPLEMENTATION AND OPERATION
The information in preceding chapters constitutes the basis for selecting
appropriate technologies and initiating engineering design. Each of the tech-
nologies covered in this monograph has matured to the point of potential or
actual commercial implementation. Current implementation status, as well
as issues associated with process startup and full-scale operation are re-
viewed in this chapter. Operational aspects of monitoring and QA/QC are
also covered. Each of the major categories of Stabilization/Solidification
(S/S) technologies are discussed in turn; first, Aqueous S/S, followed by
Polymer S/S, and Vitrification with ex-situ and in situ applications of each.
4.7 Aqueous Stabilization/Solidification
4.1.1 Implementation
Aqueous S/S processes have been implemented at thousands of remedial
sites around the world. Phosphates and organo-clays have recently been.
used for stabilization alone or for cementitious S/S at a number of sites, and
rubber particulate has been used in at least one TSDF, but not yet in a
full-scale commercial operation. Cement-slag processes have occasionally
been used commercially for chromium reduction; most of these uses have
been in proprietary systems and formulations.. The ProFix™ process has
been used as a combined fixation agent and filter aid. In situ S/S, using
auger systems, is now a standard commercial operation, with successful
projects numbering in the dozens.
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,17 . IIT'SII'F1 Iti'in!!
"I,
4.1.2 Start-up Procedures
. , ' i -
Fox, most remediation projects, startup of innovative aqueous S/S pro-
cesses fo1uows*&as conventional S/S processes. Equip-
ment is installed andi, tested, component-by-component, for operation. Test
tuns in^be done at startup, b^ is started
with any problems worked out along the way. This is possible for ex-situ
processes because of the vast experience available and the operational simi-
larity of all the exTsitu systems. ?
Auger-type in situ treatment usually requires a"pilot-scale test because the
quality and "uniformity' of the waste to be treated is seldom known with any
degree of certainty. Frequently, it is necessary to modify the working "tool"
to achieve proper drilling rates and uniformity of mixing. Modification of
injection arrangements might also be required. The presence of debris can
be the major working impediment in the systems. These modifications and
," adjustments are done on an experiential basis by operators skilled in this
technology and are generally held as proprietary information.
'•• : ' ' "" '• :>;''"" V'1 ' ': : '" ;;;":: I'; :;'" '' ' '. ';'"': •":•. 1:'T;
4.1.3 Operations Practices
'' " „ : : " ' '• i . i . i ' , . . ' i '[ '
Operations practices in innovative aqueous S/S projects are taken directly
from long-established practices in conventional S/S, since the only opera-
tional difference is the use of different reagents. The one exception is
auger-type in situ projects. Even these are based on decades of experience in
constructing foundations and cutoff walls. Therefore, the reader is referred
to standard handbooks and case histories of conventional S/S operations for
more details.
•;"'« R5?
4.1.4 Operations Monitoring
Table 3.8 lists some of the test methods used to monitor process param-
eters in an aqueous S/S system. Continuous monitoring is required for feed
rates of waste, reagents, and water. Mixer speed is usually fixed and re-
quires only periodic monitoring to ensure that excessive buildup does not
occur in the mixer. Overall system parameters include waste input and out-
put rates and tests of incoming waste and treated product for the appropriate
parameters (Table 3.8), as well as solids content.
4.2
-------
Table 4.1
Summary of Standard Methods and Procedures
Parameter
Total Solids/Moisture Content
Bulk Density
Free Liquid
Penetration Resistance -
Unconfined Compressive Strength
• Permeability .
PH
Temperature Rise
Binder and Additive Mix Ratios
Color Change
Total Constituent Analyses
Leachability
TCLP
Units
%
g/cm3;Ib/ft3
pass/fail
psi -
psi
cm/s
pH units
•c-
ratio
color
mg/kg
mg/L
Method
EPA 160.1; ASTM D2216-80
EPA SW846, Method 9095
ASTM C-403-80
ASTM D-1633-84; D-2166-85;
C-109-86
EPA SW846, Method 9100
EPA SW846
EPA, SW846 Methods, other
methods as appropriate (see
Table Zl)
SW846-1311, followed by
appropriate analytical method
Method Title
Water (Moisture) Content of Soil,
Rock, and Soil-Aggregate
Mixtures
Apparent Bulk Density
Measurement
Paint Filter Test
Penetration Resistance
Compressive Strength of Molded
Soil-Cement Cylinders/of
Cohesive Soil
Permeability
pH
Temperature Rise for Pozzolanic
Stabilization Agents
Stabilization Formulation Method
' Stabilization Formulation Method
Analytical Methods
Toxicity Characteristic Leaching
Procedure
Method Type Reference
Drying ASTM
Gravimetric/Volumetric
Filter SW846
Pressure " ASTM
Compressive Strength ASTM
Hydraulic Conductivity SW846
pH. SW846
Temperature
Gravimetric
Visual
Total Analysis SW846
Leaching 40 CFR Part 268,
Appendix I
9
a
¥
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4.1.5 Quality Assurance/Quality Control
Product QA/QC in wet stabilization involves any or all of the parameters
listed in Table 4.1 along with brief descriptions and references. Data quality
objectives are determined by standard US EPA practices which apply to
, aqueous S/S and need not be discussed further here. Methods for sampling,
storage! handling, chain-of-custody, and analysis/testing are also standard
US EPA and ASTM methods and practices. A good general description of
QA/QC requirements is given in the US EPA handbook, Preparing Perfect
-Project Plans (US EPA 1989b).
No overall performance standards exist for remedial projects because
each project's requirements are set by site-specific regulatory, environmen-
tal, operational, and future use considerations. However, certain benchmarks
• are fairly common in aqueous S/S; a listing of these is given in Table 4.2.
An example of standards for one project, as well as the performance
achieved in the project, are given in Table 4.3.
ii,. '„„ i:,, :n r ,:iT
4.2
.
typical Aqueous S/S Performance Benchmarks
.",'...: Parameter
Performance Standard
Unconfmed Compressive Strength
Permeability
Modified ANS 16.1 Leachability
Stipsi
1 • 10'6 cm/sec ,
RCfRA foidcity Characteristic Standard for Metals
Leachability Index = S 12
•! These parameters can vary greatly depending on the end use for the project site or final disposition of the waste
products.
4.4
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Chapter 4
<• Table 4.3
Performance Standards and Performance
Achieved in an Actual Aqueous S/S Project
Parameter
Standard
Performance Achieved
. Lead Concentration in Waste
Lead teachability of Raw Waste
BindenSoil Ratio
Water Addition Ratio
Weight Increase
Volume Increase
Strength (Penetrometer) 2000 psi
Unconfined Compressive Strength 2000 psi
' Permeability • !()•* cm/sec
TCLP Leaching 5.0 mg/L
EFT Leaching 5.0 mg/L
Modified TCLP Leaching
Modified ANS 16.1 Leaching !> 12
(Full-Term Test)*'
Diffusion Coefficient . S10'12
50,343 ing/kg
EPT-35.8 mg/L; TCLP-355 mg/L
0.4:1, or 40%
0.23:1, qr23%
40% without water., 63% with water addition
37% including water addition,
18% due to chemical additives
> 9,000 psi
11,720 psi
. 7.3-lO'6 cm/sec
0.62 mg/L for lead
0.35 mg/L for lead
< 0.04 mg/L after filtration
13.8
< 10-'4 for all intervals except the initial washoff
•Leach Index as defined In ANS 16.1 (ANSI/ANS 1986)
4.2 Polymer Stabilization/Solidification
4.2.1 Implementation
Research, development, testing, and demonstration of polyethylene en-
capsulation has been supported by the DOE at Brookhaven National Labora-
tory over the last twelve years and at the Rocky Flats Plant over the last four
years. Several private sector vendors have expressed interest in commercial-
izing the technology. For example, Brookhaven National Laboratory com-
pleted a Cooperative-Research and Development Agreement (CRADA) with
-------
; MMT of; f ennessee and negotiated agreements with several other companies.
Recently, DOE, contracted with.Enviroc^eof 1Mb, Inc., to commercialize
polyethylene macroencapsulation. Thek contract calls for processing up to
• 226,800 kg (500,000 Ib) of DOE mixed waste lead in exchange for develop-
ment incentives (see Section 5.2.2). Brookhaven National Laboratory has
provided technical assistance to Envkocare in thek implementation effort.
Sujfur polymer encapsulation development has also been supported by
DOE at Brookhaven National Laboratory for about 11 years. A process
appu'cation patent for the technology Is pending: The Idaho National Engi-
neering Laboratory has conducted bench- and pilot-scale testing of sulfur
polymer encapsulation over the past five years. More recently, the process
has received attention at Oak Ridge National Laboratory and other national
laboratories. Currently, Brookhaven National Laboratory is engaged in a
CRADA with Scientific Ecology Group, Oak Ridge, Tennessee, for the com-
meircial dernonstration and application of the SPC encapsulation process and
other companies have signed Research and Development license agreements
with Brookhayen National Laboratory. The Scientific Ecology Group has
used me process to stabilize and sofidify^m
tor fly ash from their commercially-licensed volume reduction facility.
In/situ polymer S/S has been under development at Brookhaven National
Laboratory for about four years. Recently, collaborative projects to develop,
test, arid demonstrate this^technolpgy have been launched with Sandia Na-
tional Laboratory, Idaho National Engineering Laboratory, and Hanford. A
small field test of in situ S/S was recently demonstrated at Idaho National
Engineering Laboratory (Loomis, Thompson, and Heiser 1995). An acrylic
polymer was used to stabilize a pit of buried waste that consisted of drums,
metals, rags, and paper. The polymer was delivered via jet grouting at -34.5
MPa (5,000 psl). Excavation of the demonstration site proved the waste was
successfully stabilized. Examination of cored samples indicated homoge-
neous rnixing, absence of voids, and a monolithic solid structure. Additional
testing work to characterize cored samples is planned. Several companies
have expressed interest in commercializing in situ polymer S/S, but no com-
panies have implemented this technology to date.
4.2.2 Startup Procedures
^ ' ' / "^ ; ; . -,l ; | I ; |i1 ;
As with any new treatment technology, startup of a full-scale polyethyl-
ene encapsulation process requires integration and "cold" (i.e.,
4.6
-------
Chapter 4
non-radioactive and nonhazardous) testing of all system components (e.g.,
pretreatment, materials handling, metering, extrusion, process control).
Non-radioactive and nonhazardous surrogate waste materials should be used
in testing individual components and overall system operation.
Following installation of dryer pretreatment equipment, all liquid lines \
(especially high pressure steam) should be examined for leaks. Initial dryer .
operational checks should be conducted using clean water. Pre-operational
checkout of the material handling system should include inspection of
vacuum pumps, lines, and gate valves prior to transferring actual materials.
Metering equipment should be calibrated on a volume and/or mass basis.
Extruder installation requires equipment leveling and bore-scoping of the
barrel for proper alignment. Following installation of electrical wiring, shaft
rotation should be checked to ensure proper motor polarity. The protective ;
corrosion coating applied to the barrel and screw should be removed with a
light solvent. Initial extruder operation should be conducted using 100%
polyethylene until troubleshooting is completed. Process control equipment
should be tested and optimized to maintain proper feeding rates within de-
fined operating parameters. On-line monitoring equipment should be cali-
brated at several known waste loadings and various process rates within
prescribed operating specifications. Following installation and pre-opera-
tional checks of each subsystem, confirmation testing of the integrated pro-
cess is recommended.
Sulfur polymer cement encapsulation equipment should be thoroughly
tested using "cold" surrogate materials prior to hot testing. All steam, hot
water, or oil circulation lines should be checked to ensure leak-proof opera-.
tion. Thermocouples should be calibrated and inspected for proper function-
ing. Successful operation of vacuum and venting systems, as well as process
valves, should be verified. Mixer interlocks and other safety-related systems
should be checked.
For in situ polymer S/S, the selected resin should be compatible with the
waste types and geochemistry of the site. Selection can be accomplished by
consulting polymer manufacturers. The shelf lives of the monomer, cata-
lyst, and promoter should be noted. The manufacturer can provide data on
shelf lives for the resins and for the pre-promoted and pre-catalyzed mixes.
If the shelf life is long enough, the resin mixes can be delivered to the site
pre-mixed by the manufacturer. If the'shelf life is only days for the pre-mix,
then the catalyst and/or the promoter might have to be mixed on-site.
-------
II I I|~H01 I Id IIVJISWl I VJI I*-* '
In most cases, it is wise to hire experienced contractors and use their
equipment. Select a contractor who has previous experience in polymer
grouting and, in particular, two-part delivery using dual wall drill stems. To
protect the equipment/the polymerization reaction should only occur after
the grout leaves the drill stem. For this reason, the dual wall drill stem is
used to deliver the resin in two parts: (1) one part containing the resin
charged with catalyst and (2) me other containing the resin pre-mixed with
the promoter. Mixing and pumping of the resins can be done with conven-
tional equipment, so long as the compatibility of the parts (e.g., seals, dia-
phragms, etc.) is ensured. The resin manufacturer should have a full listing
of compatible materials and pumps/mixers.
; im " ; I IP II I I I "I: ;"'", i' ir:i :i':. ";/' it '?:•] '^
4.2.3 Operations Practices
4.2.3.1 Polyethylene Encapsulation
Operation of the polyethylene process is designed to minimize on-line
operator adjustments. Overall process rate depends on screw speed, which is
directly controlled by the operator by adjusting the speed dashpot. While
observing extruder output rate, the operator gradually increases screw speed
'until the desired output is attained. Feeder controls are automatically ad-
justed at the pre-set ratios to match the demand. Alternatively, this operation
can be tied into the process control system by means of a solid-state speed
controller and appropriate modifications to the process control software. In
' this way, process rate can be ^Ie:^^e^ for even greater automated control.
, As discussed in Section 3.2.4, a specific temperature profile can be set by
adjusting barrel and die zone temperature controllers. Optimal temperature
conditions wiU depend on the typ"e of polymer (melt temperature, melt vis-
cosity) or polymer blend (including the presence of recycled polymers),
' waste type, and waste loading. In general, temperatures are maintained at
! minimal levels to ensure adequate melting while minimizing offgas poten-
tial. Higher temperatures can be useti to reduce melt viscosity, enhancing
mixing and optimizing wasteloading potential. Usually, a gradually
"stepped" temperature profile is used in which the temperature in each zone
along the length of the extruder Isi increased from the previous zone. This
ensures gradual heating of the polymer throughout the barrel. The tempera-
ture is kept lower in the feed zone to maintain the factional forces needed to
convey the mixture forward.
4.8
'I,
-------
Chapter 4
Process startup should always be conducted without waste (100% poly-
mer) and at moderate speed (e.g., 25% of maximum speed) until steady-
state operation is confirmed. After the process is operating smoothly, (he
waste feed is introduced gradually (e.g., increments of 10% by weight)
while the operator confirms proper feeding and continued steady-state flow
at the extruder feed throat, inspection port, and output. Changing the waste
loading from 0% (by weight) directly to the final waste loading (e.g., 60%
by weight) can cause the waste feed controller to overshoot the target feed
irate, resulting in a temporary condition in which maximum processing lim-
its are exceeded. If this occurs, the extruder can become plugged with
waste, necessitating system shutdown and purging. Once the target waste
loading is achieved, the screw speed is gradually increased to maximum
output (determined empirically based on the type of waste and polymer,
waste loading, etc.).
Routine maintenance is conducted according to equipment manufacturer's
recommendations. Depending on the chemical and physical properties of
the wastes being processed, periodic inspection of equipment directly in
contact with waste (dryer vessel, hoppers, extruder barrel, and screw) should
be conducted to monitor corrosion and/or excessive wear. Extruder screws
are removed using a hydraulic jack to push the screw from the barrel, while
supporting and guiding the screw with an overhead crane.
Standard OSHA safety practices should be followed for operation of
equipment at elevated temperatures and pressures. The extruder control
module can be equipped with temperature, pressure, and current load alarms
and automatic shutdown capability in the event of a process excursion. In
the rare event of an over-pressurization of the extruder barrel that goes un-
corrected, a rupture disk provides emergency pressure relief. As in any pro-
cess for hazardous or radioactive materials, appropriate ventilation and fire
protection systems are recommended.
4.2.3.2 Sulfur Polymer Cement Encapsulation
Sulfur polymer cement encapsulation processing is a batch process and, .
as such, is somewhat forgiving in terms of the actual steps of operation.
However, depending on the type and nature of the waste to be processed,
order of addition for the waste, binder, and additives, as well as the form of
SPC charged to the mixture, can affect processing success. For example, for
wastes considered difficult to handle and mix, preheating the waste mixture
-------
II ll ill
and pre-meltirig the SPC before combining and mixing, expedite the mixing
process. Slowly adding waste to molten SPC or vice-versa might help avoid
a rapid decrease in the temperature of the mix and premature "freezing" of
the molten mixture. Small amounts of sulfur that volatilize during process-
ing can cool rapidly in ventilation lines, so care should be taken to inspect
and clean lines as necessary.
4.2.3.3 In Situ Polymer Sfabiiiizafion/Solidification
Grout injection holes should be carefully planned prior to operation to ensure
complete coverage of the contaminated site. Estimates of grout requirements
must be made based on existing site void volume. Since ratios of monomer to
catalyst and monomer to promoter are critical to successful S/S, flow rates
should be calibrated. This can be accomplished using other fluids of similar
viscosiiy/density (e.g., water). Test drilling-under similar soil conditions should
be conducted to optimize drilling parameters, including vertical step (with-
drawal) rate, rotations/step, jet orifice diameter, arid polymer grout pressures.
Optimizing these parameters maximizes grout coverage and minimizes the
'volume of spoils (rejected grout/soil mixture). The grout injection sequence
• should be planned so as to minimize cross-talk (breakthrough of one hole to
adjacent areas) and placement and setup time. Typically, injection holes are
drilled in an alternating sequence. On completion of drilling operations, all
resin delivery lines/pumps should be purged and flushed with appropriate sol-
vents (e.g., detergent solutions and/or diesel fuel).
4.2.4 Operations Monitoring
1 : • •} . • 'i ' ''.•'' l *
: As discussed in Section 3.2.7, process parameters, including heating and
die zone temperature profiles, melt temperature, melt pressure, vacuum,
scireW speed, and current loacC are 'continually monitored through the ex-
truder control module Overall system parameters including output rate,
polyethylene and waste feed rates, and waste/binder ratios, are monitored by
a computerized process control system. Actual waste loading is monitored
by the on-line Transient Infrared Spectroscopy (TIRS) monitor.
i i • .'j ^MJ ' n M i, |ijj|i,in i, iiii'ijh' ^ /Bijl'i fr .ihji/i ^juji, j i i.< ,i, „ ll*,,,, ;j;j;«nj •: u^ .yi,;, . |ii,|n,.||. n i|| *,i i ;•, •
The temperatures of the mixture and heat transfer medium are monitored
constantly. In addition, the operator should track vacuum level, mixing
speed, and motor load. A closed-circuit video camera allows the operator to
observe the mixing vessel at all times.
I, • Kill! i,, , :"\ ', '! ' I
:::S' ,'r '."-". - ;, ' .; •• , • 4.10
-------
Chapter 4
If in situ S/S is conducted in an enclosed area (e.g., tent), monitoring of
potentially hazardous constituents and/or nuisance odors emanating from
either the soil contaminants or the grout materials might be required. Injec-
tion flow meters should be checked on a regular basis to verify proper flow
and correct mixing ratios. Flow meter measurements can be checked by ,
monitoring the decrease in storage tank volumes over time. i
4.2.5 Quality Assurance/Quality Control
For any S/S process, QA/QC activities are conducted for the process and
the final waste form product. To ensure the polyethylene encapsulation sys-
tem is operating within previously-defined processing specifications leading
to successful final waste forms, each of the key process parameters described
in Section 4.2.4 are monitored. Waste loading, one of the most critical pa-
rameters, is monitored in real-time to provide an on-line evaluation of QA/
QC. Since the polyethylene encapsulation process is not affected by changes
in waste chemistry, variations in the waste chemical composition do not
impact processing QA/QC. Melt viscosity can be confirmed for known
polymers or determined for polymer blends using a melt indexer and appro-
priate ASTM standard test methods. :
Final waste form QA/QC can be monitored by evaluating grab samples
taken periodically from the output stream and core samples taken from final
waste forms at pre-determined intervals. Grab samples confirm output rates ;
and homogeneous mixing (by measuring product density). The latter is
measured for small grab samples (<5 g) using a pycnometer. Final waste
form properties discussed in Section 3.2.13 should be confirmed on a regular
basis by conducting the appropriate standard tests (ASTM, Nuclear Regula- .
tory Commission (NRC), US EPA, American Nuclear Society, etc.) on
cored, full-scale samples and comparing the data with previously-generated,
. bench-scale data.
Process QA/QC for SPC involves monitoring key parameters (e.g., tem-
perature, mixing speed) as discussed in Section 4.2.4. Periodic observation
of the mixing process confirms successful operation. Material specifications
confirming that SPC meets applicable ASTM standards should be provided
by the manufacturer. Confirmation of final waste form properties should be
conducted on a regular basis by taking a grab sample of each batch pro-
cessed. Approximately two representative 1 L samples of the molten SPC/
waste mixture should be collected and saved for archival purposes. One
-------
I I I..:' ,
:| ' ', "l!' 11 S it:* KiSi ! " .'"'Hi. ' •«" ; 7 .'
A ii' ,. '' „
]'- Hnll r-'M-i I
" *.UPi ' .I'T-ii!!'!
sample should be used for mandatory QA/QC testing of product density.
This information verifies proper waste loading and homogeneous mixing.
The second set of grab samples can be re-melted and cast into suitable
""bench-scale" test specmiens^ as necessary, for periodic confirmation of waste
form performance. Testing should include compressive strength and appli-
cable leachability tests.
•' ., ' i. •• ' !" '"i1 " ' ; ' ' . ;
For in situ polymer S/S, QA/QC confirmation involves monitoring
and recording injection pressures and flow rates, as well as drilling
speed and depth. Samples of trie catalyzed and promoted monomers
should be taken for archival purposes. Following completion of one
"hole" or section, the soil/polymer mix should be sampled for archiving
prior to solidification. Once in situ polymer S/S is completed, represen-
tative samples of the solidified sml can be cored for confirmation and
performance testing, including compressive strength and leachability.
Depth of penetration can be monitored directly for deep soil mixing and
jet grouting based on how deeply the auger or drill is extended. For
permeation"grouting) indirect confirmation techniques, such as
ground-penetrating radar or acoustical sensors, are required.
4.3 Vitrification
'' .!';•:' • Iv ' '" • .•.• •„"' i""i,S!'!.' 'i'JI iii M ' ! ,i* Jii i''!»!ii ,i.|!' .11 ',,&' "'I''.'':'"I. ' ii :. I'1.'1"' '"-,,*' I''«!'"! ' 'i.1 .fif'!! : >il .,,: ;,",,.ii.
[••••; .. i'1 • '.;,!«'„'.
4.3.1 Implementation
'' 'If' '"' ", "I''|'!F"
4.3.1.1 Ex-Situ Melters
•Vitrification technology has been extensively developed and demonstrated
by the US EPA* DoD, and DOE. This has resulted in the establishment of a
significant technology application arid adaptation expertise within many of
the government research laboratories. Private companies, such as Geosafe
Corporation and Vortec Corporation are aggressively pursuing contracts to
apply government-developed and government-funded technologies. Still
other technologies, such as the Babcock and Wilcox cyclone furnace, have
'been developed solely by industry without government support. As a result,
ex-situ vitrification technologies are available from many different sources.
4,12
-------
Chapter 4
As a generalization, most any site can be remediated using any of the
ex-situ melter technologies, with the possible exception of microwave melt-
ing. However, there are certain wastes for which melter technologies are
best suited. It is important that the engineer responsible for implementing
the ex-situ melter technology understands the relative strengths and weak-
nesses of the technologies considered. Most vitrification technologies are
not offered as turnkey operations — nor are they offered by companies that
would provide operations as a part of the contract — rather, they are pro-
cured using the conventional design-build-operate method, if a turnkey
operation is required, it should be expected that many melter vendors would
team with consulting engineering companies, or remediation companies that
could provide the necessary skills. It is also important to remember that
vitrification technologies have not yet been demonstrated for many of the
potential applications. This dearth of data limits vendor claims regarding
process effectiveness and leaves uncertainty about design, construction, and
operation costs. As a result, the construction contract bid and award process
should require demonstration tests of the waste stream at the vendor's feicil-
ity to verify process and product claims by the vendor.
The preferred contract terms would provide payment to the remediation
company based on treating all the waste within a specified period of time.
Such a lump sum contract has been awarded to GTS Duratek by the DOE to
treat radioactive solid and liquid waste at the Savannah River Site in Aiken,
South Carolina. In this case, the waste volume, composition, and physical
and chemical properties are well-documented. GTS Duratek is in the pro-
cess of designing and constructing the vitrification facility, including tank
sluicing, feed preparation, and offgas treatment processes.
If the waste is poorly characterized or heterogeneous, it might be heces-
saty to negotiate a contract in which unit price payment is based on the vol-
ume or mass of waste treated. The DOE is in the process of attempting to
apply this strategy at the Hanford Site in Richland, Washington. In this case,
a down-selection process is used to select vendors to specify, design, con-
struct, and operate vitrification facilities to treat low-level and high-level '
radioactive tank waste. These vendors will not be paid until they begin to
process the waste and produce a glass product.
-------
Ill1 I'll III
III I I I 111"!
null:: ,! i*;- i ; ;'i up
, il.,
4.3.1.2 In Situ Vitrification
The rights to ISV technology are owned by the U.S. government under
the DOE and by Geosafe Corporation, a company formed by the inventor
(Battelle Pacific Northwest National 'LaboratbiyTto commercialize the tech-
nology. Battelle Pacific Northwest National Laboratory is continuing to
develop the technology for applications at federal sites. To date, Battelle
Pacific Northwest National Laboratory has assisted in ISV demonstrations at
several DOE sites, including Hanford (Luey et al. 1992), Oak Ridge Na-
tional Laboratory (Spalding et al. 1992), and Idaho National Engineering
Laboratory (Callow et al. 1991). Battelle continues to offer ISV treatabffity
testing and demonstration services at federal facilities.
Currently, Geosafe Corporation is the exclusive worldwide licensee for
ISV in applications outside the federal government. In 1995, Geosafe li-
censed,ISV-Japan Limited for applications of ISV within Japan. ISV-Japan
is a joint venture between Geosafe and five leading Japanese companies
(Thompson, McElroy, and Timmerman 1995).
To use ISV1 to remediate a commercial waste site, it is necessary to either
obtain a license or contract the services of a licensee. The technology is
available for use by anyone who plans to remediate a federal waste site. The
ISV services of both Battelle Pacific Northwest National Laboratory and
Geosafe Corporation are available through a variety of contractual mecha-
nisms. The '"testing "and demonstration" services provided by Battelle Pacific
cost-plus-fixed-fee/unit price contract due to the" high level of uncertainties
associated with this type of wor£ Geosafe Corporation can enter into
full-service, turnkey, and design-build-operate contracts under virtually any
type of compensation method.
I;;:;;:,;,
4.3.2 Start-up Procedures
4.3.2.1 Ex^Sjtu Melters t ,.,......,-.,]
Electric Xtelters. Melters containing castable and/or fused-cast refractories
are started gradually to allow the castable refractory to cure arid the fused-cast
refractory to heat up without fracturing. Prior to this, a glass cullet or frit
should be placed in the melter furnace to serve as the start-up charge. The heat
source is supplied by electric or gas heaters suspended in the furnace.
4.14
-------
Chapter 4
. Refractory manufacturers publish temperature ramp and hold point data for
each refractory. Once the furnace refractories have been cured, the electrical
continuity between the electric wire connections penetrating the melter shell
and the melter shell should be measured to ensure that the electric isolation
designed into the system is intact. Once completed, the rest of the bake-out
. cycle can be completed. During the bake-out period, it is wise to circulate a
small amount of air through the furnace plenum space to facilitate.removing the
water vapor released from the castable refractory.
The furnace temperature is steadily increased until the minimum tempera-
ture required for electrical conduction through the glass is achieved. With
the electrode transformer set at the maximum voltage, a low amperage cur-
rent is conducted through the glass. Once conduction is achieved, the am-.
perage rate should be increased very slowly. Otherwise, the glass will be
overheated along a very small cross-section and furnace damage could re-
. suit. As the voltage drops between the electrodes, the transformer taps •
should be adjusted to keep the voltage within the upper quartile of the tap
settings; this minimizes phase instabilities in the electrical supply.
Once the furnace is idling near its operating temperature, electrical isola-"
tion between the electrical connections and the shell should again be
checked. All bolts and fasteners securing the various components should be
checked and tightened to compensate for the thermal expansion that oc-
curred during the startup. At this time, the "air tightness" of the melter can
be checked to determine the amount of in-leakage that occurs when the
offgas system is in service. If excessive, operators should check all gaskets
and tighten all flanges and pipe connections. Some in-leakage can be toler-
ated, but it should not be excessive. At this time, offgas process equipment,
e.g., pumps, valves, and filter blowback systems, and instrumentation, e.g.,
flow, temperature, liquid level, and pressure monitors, should be checked for
proper functioning and operation. The following start-up items should be
completed next:
• add remaining glass charge to bring melter level to its full
inventory;
• determine that all cooling jackets and channels are performing
properly; ,
• observe electrode power, voltage, and amperage to verify proper
operation;
-------
I I
t'
. verify controller performance by entering set point changes and
observing responses;
'.•" ::•;!"'" '.'.. / • ••• .;::»;' " ;•*.. i;.111 ,:.:.•:•. -.'-a: •.; '. : .'..: v;.-... -„;: • •. .-,. , • ., i;:™;
. test glass discharge system to verify leak tightness and glass pour
.;..; , ";: . •; v , control; . • ,
• connect feeding system to the melter and prepare for test feeding;
. feed melter at 25% capacity to verify feed and offgas system
performance is within expected operating ranges; and
• gradually'increase feedingirate toachieve maximum designed
i,_ . ' ,' ' surface coverage. '
Be aware that large elecMc melters might require one or more days to
achieve steady-state mixing patterns? Therefore^ do riot increase the feed
rate more than a few percent per hour until the maximum coverage is
reached! This can take a matter of days! If the glass is actively mixed, this
I I „. »i i,; f " . • ' PI, 'I'lwn:, Bfjii i ' •"!:".Hi!,.,'1" . 'niif «' ,li'Kj,:1:,i,,,11 mi1 1,i:i:!T.,i!,|1 i,|!,'i .!'«n iP1 Milii'Ji.'.yii11 i * ,111111 ,'i: r,i ,,i 'nn, 'U1!1 !:»•;. f"« ''""
cautionary note does not apply. At the end of the acceptance testing phase,
the glass tank should be probed to verify that there are no regions in which
the glass Reels'' sigmficantly more viscous or that crystalline phases are
accumulating. If crystalline phases areTpreserit; the probe will feel like it is
pushing through a sandy or silty layer. If such viscous or crystalline regions
are observed, the melter insulation is either too low in that area, or, if mul-
tiple electrode pairs are used, the electrode power was riot sufficient to prop-
erly heat the area.
', The glass product composition should be analyzed for the entire duration
of the acceptance test to verify proper mixing of the glass tank. If no agita-
tion is used, the change in glass composition shbuH approximate the theo-
retical well-mixed tank model described as:
if;,;- ' :"". :',: "' ^":;,'; "' :, " \, *.[ "... C / Co = 1 - e^'^ '' "' ' ' (^D'
jf*i;.; - •";;•' '.i' " ' ";: '-'ti " ••''",',• ,; .;' ,fi ', , . I. , i 1
where: C = the concentration of tracer in the discharged glass;
C = the concentration of tracer in the feed entering the melter;
n , / „ , ,,, p , n •. . , . „„
t'" = '•' time;
v ~ the glass feed rate to the melter; and
• ™" : • " \ •• V = the melter tank'voi'
stagnalt zbribS within the melter or if poor jni^fng results in a plug flow effect.
4,16
I
i i,
I, i |j ii • i'."ii i~;i ..i
-------
Chapter* 4
Once the melter has gone through initial startup and checkout, it can be
idled at a temperature less than the operating temperature but above the :
liquidus temperature of the glass. Prior to the start of routine feeding, the
glass temperature should be increased to the operating temperature; instru-
mentation readings should be checked to verify that operating parameters are
within limits and that the instrumentation, is functioning. The offgas ventila^-
tion should be started and adjusted to achieve the proper negative pressure
within the melter plenum, and the glass discharge area temperature should be
. increased to the operating temperature. Then, waste feeding can be initiated.
Combustion Melters. A benefit of a combustion melter is the fact that
they can be idled in a cold state and attain operating temperatures within a
matter of hours. Depending on the furnace design, initial startup following
installation includes the curing or drying of the refractory lining. This would
be similar to the process described for electric melters. Initial startup will
cover the applicable items described above, e.g., leak tightness, secondary
heaters, glass discharge, ventilation control, etc. Additionally, the combus-
tion melter fuel system and combustion air supply and preheater must be
inspected to verify leak tightness. Optimal efficient operation of a combus- :
tion melter relies on "tuning" the fuel, primary, and secondary air param-
eters. If the furnace unit or the waste stream are significantly different than ,
past experience, testing is required to optimize the set points. Routine op-
eration is straightforward and follows the start-up sequence described for .
electric melters.
Induction Melters. Induction melters follow a simplified version of the
electric melter startup. Lacking refractory in the melter tank simplifies the
initial startup. A glass charge is placed in the melter, and start-up heaters
heat the charge. At a certain temperature, the glass couples to the induced
current and the start-up heaters can be removed. Once operating tempera-
ture is achieved, the power should be turned off to allow close inspection of
the induction coils and cooling circuits to verify that none have warped and
that water is flowing through each one. Following'this step, the glass dis-
charge system can be tested to verify proper operation. Several tank vol-
umes of test feed material should then be processed to verify proper tank
operation as was described for the electric melter. Routine operation also
duplicates the electric melter start-up sequence.
Microwave Melters. No special start-up activities are required for micro-
waive melters. Once construction is complete and electrical and control
-------
systems have been checked, the microwave generator and furnace can be
started. At startup, staff should inspect the microwave generator, wave
guide, tuner, and furnace for any microwave leakage with hand-held detec-
tors. Initial process tests would then be conducted to determine optimal
power input rates and feed rates.
4.3.2.^"Ih"Sfit-u'yiifr)flcati6n
Startup of the IS V process begins with insertion of four graphite elec-
trodes about one foot into the ground in a square array at the required spac-
ing. Shallow trenches are dug between each of the electrodes. The trenches
are subsequently filled with a mixture of glass frit and graphite powder to
provide Mghly conducive curfHfpams. The offgas hood is installed over
: the electrodes and men: sealed to both the ground and the electrodes to limit
ingress of air when the hood is operated under negative pressure. The hood
is connected to the offgas treatment system, and all electrical, instrumenta:
tion, and control circuits are completed.
'.'": Operational and."management oversight checklists are completed before
power is applied to theTsystenL Pre-start-up checks include bumping motors
to ensure operation and proper rotational direction and calibrating instru-
ments where necessary; The offgas system is started first and, when proper
; performance has been verified, power is applied to the electrodes. Electrode
power is gradually increased to the limits of the equipment and the regula-
tory permit until steady-state power input is reached after about 24 hours.
* |
4.3.3 Operation Practices
!: ," M I i 111 I 1 In
4.3.3.1 Ex-Situ Melters
Electric Melters. At steady-state operation, electric melters are extremely
" stable,and easy to operak:'7GenenSly, the glass temperature is maintained
within an operating range by a controller that"automatically adjusts the elec-
trode current based 'on a temperatofe feedback signal. The temperature can
• be measured directly with thermocouples or. a pyrometer, or, the temperature
catt be inferred by measuring refractory wall temperatures. The latter two
cases are attractive because ihey preclude the need for maintaining a set of
thermocouples in a thermowell within the glass. However, sufficient experi-
ence should be acquired correlating glass temperature measurements to py-
rometer or refractory, and periodic'tank probes with a thermocouple should
4.18
-------
Chapter 4
be performed. Alternatively, if the waste stream and resulting glass compo-
sition are consistent over time, the electrode power can be controlled-by
maintaining constant power or current between electrodes; or the calculated
resistance between the electrodes can be used as a control parameter. This
control measure is possible because glass resistivity is inversely proportional
to glass temperature. Therefore, very reliable temperature control can be
maintained without intrusive temperature measurements.
Secondary heaters can be controlled using continuous or periodic tem-
perature measurements in the heated zone. Plenum space pressure, feed and
offgas line flows and pressures are measured and controlled by standard
industrial devices. Level sensors, such as bubblers, have been used to moni-
tor glass level in the melt tank; however, they are prone to rapid erosion and
must be frequently replaced.
The primary control parameter for electric melters is the feed rate: The
feed rate can be steadily increased until the glass surface is nearly covered
by the cold cap — the optimal situation. The melting and spreading proper-
ties of the feed stream determine whether optimal coverage can be achieved,
and periodic visual observation is the best means to monitor processing con-
ditions as a function of feed rate and coverage. Processing stability can also
be tracked by monitoring the. plenum space temperature and offgas composi-
tion if an offgas product, such as NO^, is generated.
Process upsets result if overfeeding occurs, cooling water enters the
melter, or if ventilation is interrupted. When a melter is overfed, the cold
cap can form a rigid bridge between opposite walls of the melter. As feeding
continues, the feed accumulates on top of the cold cap. At the same time,
the cold cap material contacting the molten pool melts, creating a vapor
space between the bridged cap and the glass pool. When this happens, heat
transfer to the cold cap drops significantly, and the feed accumulation rate
increases. As this occurs, the plenum space temperature drops quickly. If
the glass temperature is maintained using temperature or resistance feed-
back, the electrode power drops in response to the drop in heat transfer to the
cold cap. If a constant current or power input is used for electrode power,
the glass temperature increases. If a slurry is being fed to the melter and a
crack forms in the bridge allowing slurry to pour onto the glass surface, a
steam surge occurs which could pressurize the melter. This pressure cao
blow out gaskets, and a glass surge into the overflow could occur, damaging
heaters or plugging the discharge area. In an extreme case, the melter itself
-------
'
could be damaged. Partly to preclude such an occurrence, melters have an
emergency or secondary vent line that would open automatically if the ple-
num pressure increases above a set point. 'When overfeeding or bridging is
, observed, the feed stream should be stopped and restarted only after the cold
cap has returned to a normal state.
I *••:••!, • i',.'^ MM ll
. if cooling water were to enter the melter due to a leaking cooling line,
steam surges can occur, which disrupt normal operation. Usually the pres-
sure of water supply lines that could fail and leak water into a melter are set
at only a few pounds pressure to avoid the situation whereby a water jet
could be forced into the glass pool and create a vigorous steam surge. The
only response is to stop the water leak and allow the melter to vent until it
has boiled off all of the steam.
The loss of offgas ventilation can result from a failed valve, tripped
blower, or a plug in the offgas line between the melter and first scrubber.
The first two events would happen without warning. If this occurs, melter
feeding should stop and the emergency or secondary vent opened to allow
the accumulated feed to react "and melt into the glass pool. A plugged offgas
line can normally be observed by noting clianges in the relative pressure in
the offgas line. However, significant changes might not be observed until
the blockage is nearly complete. When it is apparent that a blockage is oc-
curring, the feed to the melter should be stopped and the plug located and
removed., ' , , i _ • . , ','„,•
-J" : '.. •:::;- J ;: •• -";' ^' " :• Combustion-Metiers. High process rates and short retention times char-
acterize me combustion melter; ^
The primary control parameters are feed rate^ thermal load, primary and
secondary combustion air flow rate, and temperature. The process is prima-
rily controlled by steadily increasing the feed, fuel, and combustion air rates
until the maximum.rate is.reached, at which an acceptable glass product is
produced For feed streams containing high concentrations of alkali" metals,
an upper temperature limit could be based on minimizing vaporization
losses. For feed material^tiiatj's pneumatic'aUy conveyed into me furnace, the
1 - *''?''!: " ' air pressure and flow rate" can be a'o^
sion of the material into the furnace. '"Process "control consists of monitoring
furnace chamber and exit temperatures and the glass product consistency.
On-line offgas analyses of oxygen, Ktcf, and nitrogen also indicate whether
the process is operating optimally over time.
4.20
-------
Chapter 4
No significant upset conditions have been identified for combustion
melters. Assuming stable air and fuel supplies and reliable feeding systems,
no major events could be considered upset conditions. Feed line blockages
are readily observed from feed flow rate measurements. If they do occur, the
fuel and combustion air are simply reduced until the feed system is restored.
Should either the fuel or combustion air flows become unstable, the system
can be quickly shut down and the problem corrected.
Induction Melters. Induction melter systems behave similarly to electric
melters. Although induction melters are considerably smaller, their through-
put is greater on a glass surface area basis. Therefore, they can change oper-
ating behavior more quickly (e.g., cold cap coverage or average bulk glass
temperature). As a result, reliable process monitoring and operator surveil-
lance become more important. The temperature df the glass can be mea- '
sured with thermocouples or pyrometers. Cold cap size should be observed
through a view port. Upset conditions are similar to those described for
electric melters. .
Microwave Melters. As a batch melting process, microwave melters are
simple to operate. Melt rate is controlled by the microwave power level and
the feed rate into the container. The batch fill rate is controlled based on
visual observations, process knowledge, and thermocouple or pyrometer ;
measurements. For maximum processing rates, power levels should be
maintained as high as possible while still maintaining even heating through-
out the melting zone.
, A potential upset is an event described as "thermal runaway" (White,
Peterson, and Johnson 1986). Thermal runaway occurs when the local heat-
ing rate in the material exceeds the rate at which heat diffuses through the
material. These hot spots subsequently absorb more energy than the sur- :
rounding material because microwave absorption increases with temperature
in most materials. Thermal runaway can be prevented by:
• carefully controlling the microwave power while continuously
monitoring the temperature of the material; and
• providing a uniform microwave illumination of the process
material.
-------
!"' "I! „«'« , ' . ' ' •!>
"'l I ' nll'l!'!1,,
if; II :
4.3i3.2 In Situ Vitrification
Performance costs are minimized when the ISV system is operated at the
maximum power levels that still conform to all design and permit limits.
This speeds the rate of remediation, resulting in lower personnel costs and
lower heat losses to the offgas system. Several factors limit the ability to
attain maxmium power levels, including combustion of pyrolysis products in
the pflgas hood, which might cause excessive offgas temperatures. In this
case, power to the electrodes should be reduced to slow the generation of
pyrolysis products.
A high water table can also limit performance by requiring higher energy
input to evaporate the excess water. This limitation can be minimized at
some sites that are amenable to draining or lowering the water table, and
thereby reduce energy demands. Limits imposed on emissions of constitu-
ents of concern in the offgas also impede optimal performance if the offgas
system is not adequately designed to remove or destroy the concentration of
hazardous offgas constituents produced at maximum power levels.
Potential process upsets include the formation of a.hot cap within the
hood, pressurization of the hood due to excessive gas generation rates, and
excessive agitation of the molten glass inside the hood. The appropriate
response to each of these upset conditions is to curtail or reduce power to the
electrodes. Emergency power cutoff switches ensure rapid response, if nec-
essary. The offgas system is left funning in an emergency to ensure continu-
ing treatment of hazardous oWgases for an adequate time after power to the
electrodes is curtailed. A diesel-powered backup offgas treatment system is
USed hi case of power outage. ;
i"1''!. "",'•" ' '-HI '"' ' I I! I1'1,,'"'M!'!, ' , ' ! " III!1", !' U "!„ 'I'1" "I i l|"i',,H II1 :,'Ml, '"' , ,i I ,,,'l''i|" 'SIN,!;,,: ' ' i, i 1" III,, n I!1 , • V ' , , '",„,!!! ,l| I/IPI ""Ill,1" I,,,
The most significant routine ISV maintenance activity is adding sections
of new graphite to the top of the graphite electrodes to increase the length of
the electrodes as the melt depth increases. Electrode-to-power cable connec-
tions and electrode-to-offgas hood seals also require maintenance. Adding
electrode sections and other forms of maintenance requiring access to the
offgas hood are accomplished after power to the electrodes is cut off.
i i i i •• ' i ill in
4.22
-------
Chapter 4
4.3.4 Operations Monitoring
4.3.4.1 Ex-Situ Melters
All ex-situ melters rely on monitoring and controlling:
• feed rate and distribution;
• energy input; and
• temperature.
If each of these variables is adequately monitored, the process can operate
optimally — a state best achieved by directly measuring, rather than infer-
ring by indirect measurement, each variable. Process optimization assumes
that the combination of waste, glass, and chemical additives has been care-
fully determined to optimize (1) reaction and melting of the batch, and (2)
glass processing properties, such as viscosity, electrical conductivity (when
important), and phase stability. The critical importance of this initial work
cannot be too strongly stressed. In addition to these key variables, process
parameters that should be routinely measured to allow the process engineer
to "see the whole picture" include plenum and offgas system temperatures
and pressures, feed, glass product and offgas composition, and energy supply
measurements. Key parameters should be .displayed and logged continu-
ously in a graphic format to allow historical trending analyses.
4.3.4.2 In Situ Vitrification
Approximately 50 system parameters are monitored during IS V opera-
tions. Alarm levels and responses are established for each of the parameters.
Visual alarm indicators are color-coded to aid in defining the appropriate
response. Trends in parametric data are monitored to aid in fine-tuning elec-
trode power levels. Offgas sampling and analyses are also conducted to
verify that emissions of specific constituents of concern are within accept-
able limits. A limited set of offgas data is logged on a continuous basis as an
indication of the effectiveness of the overall system in destroying or remov-
ing organics. Typical offgas parameters 'that are continuously rrtonitored are
levels of carbon dioxide, carbon monoxide, oxygen, and total hydrocarbons.
-------
•Ill II III ill I
i n in nil i ill I
4.3.5 Quality Assurance/Quality Control
4.3.5.1 Ex-Situ Melters
Quality assurance is applicable to three areas of ex-situ melter operation;
• accuracy and precision of measuring instrumentation;
' • " "•"'"'" ';' :: <« •<" '•'' " "''- • " ' !"; '• »J!• ' - '".'~' ' '"'''•:" • "i • '• '""• "'•' • ' '•• ' • "-•' • '''•• <
• sample analyses; and
• procedure and documentation control.
The .level 'of.accuracy" and precision and the frequency of calibration
for each instrument should be defined by t&e"intended use of the data.
Critical operating parameters should be measured by instrumentation
calibrated according to industry standards and procedures. Accuracy
and precision should be within 1 to 2% of the true measurement. Cali-
bration should be performed at least annually. Samples should be ana-
• lyzed using approved procedures, calibrated 'instruments, and chemical
standards traceable to national standards. Laboratory performance
should also be monitored using statistical control charting techniques to
'monitor""short-term^^on^-tem^oiaio^eiio^' Maintaining a vis-
ible procedure and document control process demonstrates that opera-
tions, operator training, and roles, responsibilities, authorities, and ac-
countabilities are clearly defined and communicated. Certain sampling
and analysis procedures must be traceable to US EPA protocols. For
instance, laboratory physical and chemical methods should follow
guidelines in US EPA manual SW-846 (40 CFR 60). Offgas aerosol and
particulate sampling should follow US EPA Method 5 (US EPA 1986a).
• • ' ' " ;; 3';; i j •'•""; ' '•; ' ;;•• ' ^.-' -\''l~
4.3.5.2 In Sttu Vtfrlflcortion
Data necessary to meet QA/QC and data quality objectives often include
gas sampling data, scrubber solution analyses, glass sample leaching results,
and glass monolith coring/excavationi observations. Gas, glass, and scrubber
solutions are sampled and analyzed in accordance with established US EPA
protocols. Coring in the overlap area between melt settings and excavation
at the edge of the remediated site verifies completeness of the melt overlap
and that melting depth and width objectives Have been met.
4.24
-------
Chapters
CASE HISTORIES
This chapter presents an evaluation of case histories deemed pertinent for
each of the innovative stabilization/solidification technologies addressed in
this monograph.
5. J Aqueous Stabilization/Solidification
Pilot- and full-scale projects have been completed using several of the
innovative aqueous S/S and stabilization processes described. Most S/S
applications, however, have relied on conventional equipment designs and
operational methods (US EPA 1986b; US EPA 1989c), and so the value of
case histories is primarily in the technical results and properties of the
treated wastes, which have already been described in this monograph.
There is one area, however, where case histories are especially in-
structive — auger-type, in situ stabilization and solidification. A small
number of pilot- and full-scale projects have been completed using this
system (US EPA 1991c; Morse and Dennis 1994). One of special inter-
est is a demonstration project conducted on mixed waste (radioactive
and RCRA hazardous) at the DOE Gaseous Diffusion Plant at Ports-
mouth, Ohio, in 1992 (Benda 1992). This site had soils contaminated
with VOCs and low levels of uranium. A full-scale demonstration was
performed by Millgard Environmental Gorporatipn for Rust Remedial
Services Inc: (then Chemical Waste Management, Inc., ENRAC Group),
under the supervision of Martin Marietta Energy Systems.
The project included a number of discrete in situ operations — VOC de-
struction, VOC removal, and stabilization using the MecTool® auger system
described hi Section 2.1.1.3. Tests were conducted within a 10 m (33 ft) by
29 m (95 ft) area of the contaminated site. Twelve soil columns were treated
-------
in situ to depths of 4.6 m (15 ft) and one column to a depth of 6.7 m (22
ft). The treatment process took from one to four hours per column, de-
pending on the treatment used. Initial VOC concentrations in the soil
ranged from 300 to 1,800 mg/L. Each treatment was successful and
conferred specific advantages.
The main contamination was trichloroethylene (TCE) in concentrations up to
100 mg/L, with other halocarbons present, along with trace- to low-levels of
lead, chromium, uranium 235, and technicium 99 (Siegrist et al. 1993). While
there were considerable variations in strength due to non-uniform mixing, so-
"lidification was rapidly accomplished and acceptably low TCLP leaching levels
of all of ''file target contaminants'were; attained.
5.2 Polymer Stabilization/Solidification
5.2.1 Polyethylene MicroencapsulaHon Using Single-Screw
Extrusion
'• "; '• '• '• •«•>'' • '*«<• •'"" •' ' •'* •." ' f'• *••• •'• '"• )•••<•••*••'•" ••• .'•'• . - .«•'•>:'(. =
i§'ingifr-'screw''extrusion for polyethylene microencapsulation of radioac-
tive, hazardous^ and mixed waste has successfully progressed from ;
bench-scale process^ developmenTtEougE A
production-scale technology demonstration, sponsored by the of DOE's
Office of Technology Development, was conducted at the Brookhaven Na-
tional Laboratory's'Polymer'Encapsulation Demonstration and Test Facility
(Kalb and Lageraaen 1994,1996; Kalb et al. 199Sb).
The demonstration included all facets of an integrated process necessary
to process waste under actual plant conditions. A schematic of the process
components is shown in Figure 5.1 and a photo of the facility is shown in
Figure 5.2. An aqueous salt waste surrogate containing 35% (by weight)
dissolved solids was pretreated to dryness using an indirectly-heated, stirred
vaciiuta'dryer arid particle size reduction system capable of processing 757
L/day (200 gal/day). The pretreatment system was discussed in Section
3.2 5 Pretreated waste and polymer materials were remotely transferred to
storage hoppers by a HEPA-filtered pneumatic transfer system.
Production-scale loss-in-weight feeders metered waste to the extruder.
ii ii i
5.2
-------
Chapter 5
Figures.!
Schematic Diagram of the Integrated Polyethylene Encapsulation Process
Single-Screw Extruder.
Process Control Loop
These feeders are capable of extremely precise metering, with accuracies
typically around ±0.5%. A 11.4 cm (4.5 in.) single-screw, vented extruder
with a .maximum output rating of 907 kg/hr (2,000 Ib/hr) was used for pro-
cessing. Extruder output rates were monitored, and data were fed to a com-
puterized process control system that automatically coordinated feeder input
rates with extrusion output. A real-time, on-line monitor, developed by
Ames Laboratory determined actual waste loadings of the product as it
exited the extruder. Process monitoring and instrumentation is described in
Section 3.2.7. Typical production-scale processing data for polyethylene
microencapsulation using a single-screw extrusion process are provided in
Table 5.1. , '
5.2.2 Polyethylene Macroencapsulation
Envirocare of Utah has been engaged by DOE to commercialize polyeth-
ylene macroencapsulation and treat up to 226,800 kg (500,000 Ib) of mixed
waste lead currently stored throughout the DOE complex. Envirocare is a
NRC-licensed disposal facility, for naturally-occurring radioactive materials
-------
r 1
Figure 5.2
Full-Scale Polyethylene Encapsulation Facility
Ol
-------
Chapters
Table 5.1
Production-Scale Process Data for Polyethylene Microencapsulation
of Nitrate Salt Wastes Using a Single-Screw Extrusion Process0 :
Parameter
Data
•
Heat Zone Temperature Settings:
Zonel:
Zone 2:
Zone 3:
Zone 4:
Zone 5:
280'F
285.T '
295T
. 325T :
350T
Vacuum Pump:
Maximum Screw Speed:
Maximum Output Rate:
Waste Loading Range:
ISmmHg
SOrpm
S.4kg/min
. 30,40, SO, 60% (by weight)
Drum Fill Times (55 gallon drum;
60% (by weight) waste loading):
SOrpm
SOrpm
3.5kg/min
5.4 kg/min
SOmin
50 rain
•Data from BNU Production-Scale Polyethylene Encapsulation Technology Demonstration
Source: Kalb and'Lageraaen 1994
and low-level radioactive wastes. It is the only licensed disposal facility in
the U.S. for mixed radioactive/RCRA hazardous wastes. Envirocare con- [
ducted a technology demonstration of the polyethylene macroencapsul ation
process on November 28,1995, for members of DOE and the local commu-
nity. Both nonradioactive and radioactive lead brick samples were success-
fully treated. The lead bricks were packaged in steel cages and suspended in
five-gallon metal buckets. A 11.4 cm (4.5 in.) Davis-Standard single-screw
plastics extruder was used to extrude clean plastic around the lead to form a :
layer >5.1 cm (2 in.) on all sides. A schematic of the macroencapsulatlon
process is shown in Figure 5.3 along with a schematic of the waste form in
Figure 5.4.
-------
case Histories
. Figure 5.3
Single-Screw Extruder for Polyethylene Macroencapsulation
Virgin or Recycled Resin
Molten Polymer
|ZoneS| |Zone4||Zone3| |Zone2J |Zonel|
Independent Temperature
Die Zone Control for All Zones .
Waste Container
with Radioactive
Solids or Debris
Figure 54
Macroencapsulated Waste Form
Polyethylene Layer
Waste Cage
Radioactive Waste Solids
5.6
-------
Chapter 5
5.2.3 Sulfur Polymer Encapsulation '
Idaho National Engineering Laboratory has conducted several pilot-scale
tests of sulfur polymer cement (SPC) encapsulation of ash and debris waste (see
Section 3.2.3.4). Scientific Ecology Group is using SPC encapsulation to treat
incinerator ash residues resulting from their commercially-licensed radioactive
waste volume-reduction incinerator facility. Because of the large concentration
of contaminants, the ash residues contain significant concentrations of toxic
metals in addition to radionuclides.
Scientific Ecology Group modified a high-shear mixing vessel, which is
heated by steam for the process. Typically, about 900 kg (2,000 Ib) of SPC
is heated and melted and approximately 340 kg (750 Ib) of incinerator fly
ash is added and mixed to form a homogeneous mixture for a waste loading
of about 28% (by weight). Currently, Scientific Ecology Group is working
with Brookhaven National Laboratory as part of a Cooperative Research and
Development Agreement to optimize and demonstrate process applicability
to other waste streams.
5.3 Vitrification
5.3.1 Ex-Situ Melters
Babcock & Wilcox (B&W) participated in a US EPA SITE soil treatment
demonstration of the B&W cyclone vitrification furnace (Czuczwa et al.
1993). The pilot cyclone furnace was operated between 1990 and 1992 to
treat wet and dry contaminated soils (i.e., synthetic soil matrix). The syn-
thetic soil matrix (SSM) was combined with known quantities of heavy met-
als, organic contaminants, and nonradioactive isotopes of strontium, bis-
muth, and zirconium. The goals of the testing were as follows:
• determine SSM properties;
• establish cyclone operability with dry soil processing (e.g., feed-
ing, melting behavior, operational data);
• determine slag leachabiliry and volume reduction;
-------
case MisTones
• determine preliminary heavy metals mass balance for the cyclone
treatment process;
• design a wet soil feed system and atomizer; and
• establish cyclone opefability with wet soil processing.
, „ ,n , T ,, T iSi n,n,,, , h, .1. , ...,„ .,,,,„,, "iiiii I'M ,, , ,.,, • ,.,,|M« !!'!',!' I'!'„!'''!„ , ; "!'S ' ,' , '!',:,'• ", ',' I,,1, ." 'I
The pilot cyclone test facility is slibwn in Figure 5.5. The furnace is a 6
MBtu/hr pilot cyclone furnace, which is water-cooled and simulates the
geometry of B&W's front-wall fired, cyclone coal-fired boilers. The furnace
is fired by a single^ scaled-down version of a commercial coal combustion
cyclone furnace^ Both the primary and secondary air were heated to ap-
proximately 437°C (820°F). For the SITE demonstration, natural gas and
preheated primary combustion air entered tangentially into the cyclone
burner. In dry soil processing, preheated secondary air, the soil matrix, and a
portion of the natural gas entered underneath the secondary air and parallel
to the cyclone barrel axis. For wet soil processing, an atomizer sprayed the
soil paste directly into the furnace.
Testing was conducted in two phases. In Phase I, dry SSM was processed
- and in Phase BE, wet SSM was processed. Test conditions are shown in Tables
5.2 and 5l3T" The B&W system is capable of processing different waste streams
under; varyrng conditions of fuel tj^~water1:onteh1i'Md feed rate. The soil
matrix was spiked with 7,000 mg/L lead, 1,000 mg/L cadmium, and 1,500 mg/
L chromium; Spiked SSM samples were submitted wet and dry for TCLP
testing to verify that the starting soil failed the TCLR The leachability of the
lead averaged 81 mg/L; cadmium, 40 mg/L; and chromium, 2.8 mg/L. With the
exception of chromium, the spiked solid exceeded US EPA limits for lead (5
mg/L) and cadmium (1 mg/L). Based on feed and product sample composition
analyses, test results showed 95 to 97% of the noncondensable portion of the
feed was incorporated within the slag product. At processing rates of 23 to 68
kg/hr (50 to 150 Ib/hr) dry feed and 45 to 136 kg/hr (100 to 300 Ib/hr) wet feed,
the heavy metals were retained within the release limits defined under the US
EPA TCLP leaching protocol.
During Phase I testing, the cyclone operation remained very stable. Soil
input was increased from 21 to 64 kg/hr (46 to 141 Ib/hr) with test durations
of 3 to 6 hr. The slag tapped well, and no buildup of deposits was observed
in the furnace. For Phase II tests, the cyclone was operated at a nominal
load of 5 MBtu/hr and 1^ excess pxygen. The SSM input varied between
45 and 13^ kg/hr (100 and 300 fb'/hr). Cyclone operation was characterized
5.8
-------
Chapter 5
SSM Feed System
SSM
Sampling
Location
. Slag and
Quench
Water.
Sampling
Location
Figure 5.5
B&W Pilot Cyclone Test Facility
Stack Particulate
'Sampling Location
Continuous Emissions
Monitor (CEM)
Sampling Location
Scrubber (Not in Use)
Furnace
Stack
Slater (Not in Use)
Natural Gas Injectors
111
Combustion Air
Natural Gas
i Soil Injector
\Cyclc
SlagTrapv m >SIagSpout NCyclone Barrel
-Slag Quenching lank
Reproduced courtesy of Babcock Wilcox (1997)
-------
Case Histories
S, , Bill,':'1,,!!!1'1!,, i. • ,in, i!,!i' ', ' „ W"1 "I1, • ,'!„!. . -i; Wilt,! „ !"IF"
niJ'lllliBlliill'iL I'll i,1 if1:,;,! , . ,,'H !li,i<: :"' ,, »' '"I \ !' ill'I < Wll,
lifii
Table 5.2
Phase I Test Matrices
Test
, Cyclone
Load
(MBtu/br)
SSM Feed Rate
(Ib/hr)
Stack % Slag Fly Ash/
Excess Temperature Slag
Oxygen CF) (%)
Preliminary Vitrification Tests (Dry,
10/25/90
10/26790
10/26/90
10/26/90
4.8
4.6
4.9
4.7
50
100
150
200
1.1
0.8
0.5
0.7
Clean Soil)
2340
2430 ' <5*
2370
2380
Primary and
Secondary Air
Temperature
CF)
813
821
824
823
! Heavy Metals Tests (Dry, Spiked Soil)
11/01/90
11/15/90"
11/16/90
11/19/90
4.6
4.7
4S
4.6
100
46
141
94
0.7
05
0.7
0.9
2350
2400 7.5 "*
2375 5.9*",
2390 5.8-
830 '.
817
.826
•Amount of the SSM leaving the furnace as ash, preliminary estimate.
"Tests used for f CUP and heavy metals mass balance.
•"Includes estimate pf amount of paniculate deposited In the convection pass.
- -» •"-,' • -i' •'. i • i i
Source: Czuczwkaetal. 1993
as relatively smooth. It was noted during testing that SSM particles smaller
than about 1 cm (0 4 in.) could be expected to melt. Larger particles stay in
the cyclone until they melt or are carried out by the slag and are encapsu-
lated upon cooling. Unless crushing equipment precludes the presence of
large particles, the extent of encapsulated particles which can be tolerated
essentially determines the maximum processing rate of the melter unit.
Fluxing agents that cause the soil to melt and flow at lower temperatures
could result in decreased metals volatility." To evaluate this possibility, borax
(sodium borate decahydratej was added to the SSM (10% by weight > 3uring
one of the Phase n tests. After borax was added, the cyclone load could be
reduced to 4.1 MBtu/hr without any problem with slag discharge. With the
5.10
-------
Chapter 5
added borax, the slag temperature was reduced from 1,332°C (2,430°F) at an
SSM feed rate of 91 kg/hr (200 Ib/hr) to 1,271°C (2,320°F). NOx levels
decreased 20%. Fly ash production increased slightly by 3.5% of the input *
SSM, presumably due to vaporization of sodium and boron. :
Table 5.3
Phase II Test Matrices
. Primary and
. Cyclone Stack % Slag Fly Ash/ , Secondary Air
Load SSM Feed Rate Excess Temperature Slag Temperature
Test
(MBtu/hr)
(Ib/hr)
Oxygen
OF)
(*)
•Atomizer air 90 to 130 Ib/hr, 15 to 100 pslg static pressure.
"Atomizer air flow rates of 128 to 134 Ib/hr were used.
—10% Borax was added to the SSM.
Sourca: Czuczwka et al. 1993
OF)
Preliminary Vitrification Tests (Wet, Clean SoH) *
8/20/91
8/21/91
8/27/91
. 8/27/91
8/28/91
8/28/91
8/29/91
. • 9/03/91
5.1
53
5.0
4.9
4.9
4.9
4.9
5.1
100
100
100
150
200
300
300
300
. 0.77
0.76
0.62
0.56
0.58
0.53
0.56
0.47
2455
2420
2370
2410
2370
2390
2405
1.77
2.01
1.73
0.4
' 1.91
1.49 :
1.89
1.94
814
794
814
814
810 :
813
810
807
Heavy Metals Tests (Wet, Spiked Soil)**
9/09/91
9/09/91
.9/10/91
9/10/91
9/11/91
4.8
4.9 -
49
4.9
4.1*"
200
200
100
300
200
12
1.0
0.6
0.7
4.7
2430
2420
2470
2400
2320
2.32
2.63
3.53
823
825
813
822
810
-------
I III II I I 11 II I I Ill
uase Histories
Testing results indicated that the process would be well-suited for the
treatment of low volatility contaminants, such as many radionuclides. At
. least 95 to 97% of the input SSM was incorporated into the slag. The heavy
metals partitioned between the vitrified slag and the stack fly ash. The cap-
ture of heavy metals in the vitrified slag from all tests ranged from 8 to 17%
(by weight) for cadmium, 24 to 35% (by weight) for lead and 80 to 95% (by
weight) for chromium. The capture of heavy metals in the slag increased
with increasing feed rate and with decreasing metal volatility. Stable cy-
" clone operation was achieved 'during Both phasesi'6f testing. Concentrations
of CO and NOX in the offgas werewithin acceptable ranges. Soil volumes
,. were reduced between 25and 35%> (dry[basis) through vitrification.
As a result of the SITE demonstration, several recommendations for
technology application were made. It is betieved that the combustion
melting technology is best suited for treating soils contaminated by or-
ganics and either very high or very low volatility heavy metals. The
high Seat release rates and turb'ulence make the cyclone vitrification
process well-suited for organics destruction. Vitrification of very
high-volatility•'metals orradibriucHdes could tend to concentrate those
elements in the relatively small fly ash stream, from which they could be
recovered^ Vitrification of very low-volatility metals or radionuclides
would tend to concentrate those elements in a nonleachable waste form.
For intermediate volatility metals or radionuclides, recycling the fly ash
to the melter is expected to be the best option.
'. , ••: ' , : ' • " i • ;ii;"_ '•;] "_;_:; , • • • "I;,,,', ,,".;;;; , ;,; ' ;"', ,,"„ ;•" .. j1;1"
" " '•'..', ."V "'". '. '.'. '" "•• ' — • -.""»-•"..";" . 'I'"'.' '.'•'"'' •'»••• ' •"",.'" ".• '-™,.i,,; i",Z
5.3.2 In Situ Vitrification
The findings associated with a demonstration of the Geosafe Corporation
(Geosafe 1993) in situ vitrificatibn (ISV) prbcess under the US EPA SITE
Program in conjunction with remediation activities associated with an US
EPA Region V removal action. The technology was assessed for its ability .
to reduce pesticides (specifically chlordane, dieldrin, and 4,4'-DDT) and
mercury to below Region V-mandated limits. It was evaluated against the
nine criteria for decision-making in the Superfund Feasibility Study process.
Table 5.4 presents the results of this evaluation.
As part of the Region V removal action, Geosafe performed a total of
eight melts that covered nine pre-staged treatment cells at the Parsons
Chemical Works, Inc. site located in Grand Ledge, Michigan. The SITE
i
5.12
-------
Chapter 5
Program studied one of these treatment settings (Cell 8) in detail to deter-
mine the technology's ability to meet the Region V removal criteria and to .
obtain cost and performance data on the technology.
Results for the treated soil are based on postteeatment sampling just below
the surface of the melt alone. Complete posttreatment sampling of the solidi-
fied melt could not be safely performed until at least one year after treatment, at
which time sampling of the melt core will take place. Because the technology
is already being used in commercial applications, a report (Geosafe 1995) has
been published prior to obtaining treated soil samples from the center of the
study area. In this manner, the community is provided with the information
currently available regarding the operability and effectiveness of the technology.
Results of the posttreatment soil samples collected from the core of Cell 8 will
be reported at a later date in a published addendum.
Conclusions Based on Critical Objectives. The studies conducted by the
SITE Program suggest the following conclusions regarding the technology's
performance at the Parsons' site based on the critical objectives stated for thfe
demonstration.
• The treated soil met the US EPA Region V cleanup criteria for .; .
the target pesticides and mercury. Dieldrin and 4,4'-DDT were
reduced to levels below their analytical reporting detection limits
(<16 fJg/kg) in the treated soil. Chlordane was below its detec-
' tion limit (80 |jg/kg) before treatment commenced. Mercury, :
analyzed by standard SW-846 Method 7471 procedures, was
below the specified cleanup level before treatment began, averag-
ing 3,800 Hg/kg. It was reduced by volatilization to an average of
less than 33 pg/kg in the treated soil.
• Stack gas samples were collected during the demonstration to
characterize process emissions. No target pesticides were de-'
tected in the stack gas samples. During the demonstration, mer- <
cury emissions averaged 5.4 • 104 ug/hr (1.2 • 1(H Ib/hr). The •.
emissions were below the regulatory requirement of 2.7 • 105 jjg/
hr (5.93 • 10"4 Ib/hr) at all times. Other metal emissions in the
stack gas (particularly arsenic, chromium, and lead) were of
regulatory concern during process operations, but were found to
be in compliance with Michigan's applicable or relevant and.
appropriate requirements (ARARs).
-------
Sli::,
Table 5.4
Evaluation Criteria for the Geosafe In Situ Vitrification Process
a>
I
Overall Protection of Human
Health and the Environment
Compliance with ARARs
Long-Term Effectiveness
and Performance
Short-Term Effectiveness
Provides both short- and long-term
protection by destroying organic material.
Developer also claims the technology can
pi treat radioactive compounds.
•^ Remediation can be performed in situ,
thereby reducing the need for
excavation.
- — Offgas treatment system reduces
airborne emissions. System is flexible
and can be adapted for a variety of
contaminant types and site conditions.
Technology can simultaneously treat a
n mixture of waste types. Technology is
1 applicable to combustible materials, but
the concentration of such materials in the
' treatment zone must be carefully
: controlled and treatment prudently
planned.
Requires compliance with RCRA
treatment, storage, and land disposal
regulations (for a hazardous waste).
Successfully treated waste may be
delisted or handled as nonhazardous
waste.
Operation of on-site treatment unit may
require compliance with location-specific
applicable or relevant appropriate
requirements (ARARs).
Emission control may be needed to •
ensure compliance with air quality
standards depending upon local ARARs
and test soil components.
Scrubber water will likely require
secondary treatment before discharging
to publicity owned treatment works
(POTW) or surface bodies. Disposal
requires compliance with Clean Water
Act regulations.
Effectively destroys organic
contamination and immobilizes inorganic
material. Developer also claims the
technology can treat radioactive
compounds.
Reduces the likelihood of contaminants
leaching from treated soil. ISV glass is
thought to have a stability similar to
volcanic obsidian which is estimated to
remain physically and chemically stable
for thousands to millions of years.
Allows potential reuse of property after
treatment.
Treatment of a site using ISV destroys
organic compounds and immobilizes
inorganic contaminants.
Vitrification of a single treatment setting
may be completed in approximately ten
days. This treatment time may vary
depending on-site-specific conditions.
Presents potential short-term chemical
exposure risks to workers operating
process equipment. High voltage and
high temperatures require appropriate
safety precautions.
Some short-term risks associated with air
emissions are dependent upon test
material composition and offgas
treatment system design.
Staging, if required, involves excavation
and construction of treatment areas.
A potential for fugitive emissions and
exposure exists during excavation and
construction.
-------
Reduction of Toxicity, Mobility,
or Volume through Treatment
Significantly reduces toxicity
and mobility of soil contaminants
through treatment.
Volume reductions of 20 to 50%
are typical after treatment
Some inorganic contaminants,
especially volatile metals, may
be removed by the vitrification
process, and require subsequent
treatment by the offgas
Some treatment residues may
themselves be treated during
the next vitrification setting.
Residues from the final setting,
including expended or
contaminated processing
equipment, may require special
disposal requirements.
Implementability
Equipment is mobile and can be
brought to a site using conventional
shipping methods. Weight restrictions
on tractors/trailers may vary from
state to state.
Support equipment includes earth
moving equipment for staging '
treantient areas (if required) and
covering treated areas with clean soil.
A crane is required for offgas
containment hood placement and
movement
Chemical characterization of
contaminated soil is required for
proper offgas treatment system
design.
A suitable source of electric power is
required to utilize this technology.
Cost
The cost for treatment .
when the soil is staged
into 15 ft deep cells is ,
approximately $770/yd3
($430/ton).
Treatment is most
economical when treating
large sites to the
maximum depth.
Electrical power is
generally the most
significant cost associated
withlSV. Other factors •'
(in order of significance)
include labor costs,
startup and fixed costs,
facilities modifications
and maintenance costs.
Community Acceptance
Technology is generally
accepted by the public
because it provides a
permanent solution and
because it is performed in
Potential reuse of land
after treatment provides
an attractive alternative
to property owners.
A public nuisance could
be created if odorous
emissions from the soil
constituents are not
properly controlled by the
offgas system.
State Acceptance
State ARARs may be
more stringent than
federal regulations.
State acceptance of the
depending upon ARARs. .
The ISV system
(especially the offgas
treatment portion) is
somewhat modular, such
that it may be modified to
meet state-specific
criteria.
' Volume of scrubber water
generated is highly dependent
upon soil moisture content
sites which contain organic content
greater than 7 to 10% (by weight),
metals content in excess of 25% (by
weight), and inorganic contaminants
greater than 20% (by volume). Sites
with buried drums may only be treated
if drums are not intact or sealed.
Moisture content of the
medium being treated
directly influences the
cost of treatment since
electric energy must be
used to vaporize water
before soil melting occurs.
Sites that require staging'
and extensive site
preparation will have
higher overall costs.
Q
Tf
Ol
-------
"", iv iii ' '"iiiA mi1 iir
I I
case Histories
• Emissions of total hydrocarbons (as propane) and carbon monox-.
ide are regulated at 100. ppjriv and 50 ppmv, respectively.
TJirqughout the demonstration, vapor emissions of these gases
; (measured downstream from the thermal oxidizer) were well
i > below the regulatory guidelines^ Total hydrocarbon and CO
emissions both averaged below 10 ppmv. ,
exclusions Based on Secondary Objectives. The studies conducted by
the SITE Program suggest the following conclusions regarding the
^' based on the secondary objec-
Ill 1P|1 III
1I||I|I1II|I|I( I Kill III II
tives stated for the demonstration.
" i !,.- jl\ '"if1,:: ..... ij,,';iiif I.**!1 fli;;flR|ff)}rRiV 'i-'af ..... i'llJiilililiiiii'liil'l!.!- ..... MJddf.'iivJ.1:,' „ ..... I1.* •;' i Li"1',', o " "' !l * ...... V'"*"' * ''' ......... ' .....
. The technology successfully treated the soil m Cell 8, completing
me test cell melt in ten days with only minor operational prob-
lems. During this time, approximately 252 m3 (330 yd3) (ap-
proximately 546 tonne [600 ton]) of contaminated soil were vitri-
fied, accordmg to Geosafe melt summaries. Approri^
MWhr (i.OSOMBtu) of energy was applied to the total soil vol-
umB melted (estimated to be 367 m3 [480 yd3]) during vitrifica-
tion of Cell 8; power applied to the actual contaminated soil
volume co"Jd™j^ because clean fill
"aijd surrpunding uncontaminated soil were vitrified as part of
each melt. Based on the total soil treated in Cell 8, the energy
consumption was approximately 6.72 MWhr/ton (2.5 Bra/ton).
System operation was occasionally interrupted briefly for routine
maintenance such i as elertrode segment addition and adjustment.
. The solid, vitrified material collected was subjected to TCLP
".' analysis for me target pesticides and m Test results indi-
cated that ^ no target pesticides were detected in the posttreatment
leachate. Chlqrdane was not detected in either the pre- or post-
treatment leachate, so no definitive conclusions can be drawn
about the technology's impact on the leachability of this com-
pound based on this demonstration. Levels of leachable mercury
in both pre- and posttreatment soil leachates were well below the
regulatory limit of 200 fig/L (40 CFR §261 .24). Several other
metals were also found to have passed the TCLP leaching test.
. "' ' H I " . ' . ' 1
• Scrubber water generated during the demonstration contained
volatile prganics, partially-oxidized semivolatile organics (pheno-
. • ; • lies), mercury, arid other metals, 'the scrubber water underwent
5.16
-------
Chapter 5
secondary treatment before ultimate disposal, and data suggest
that secondary treatment of this waste stream will probably be
required in most cases.
• Pretreatment soil dry density averaged 1.8 tonne/m3 (1.5 ton/yd3),
while posttreatment soil dry density averaged 2.5 tonne/m3 (2.1
ton/yd3). Accordingly, a volume reduction of approximately 30%
was observed for the test soil on a dry basis.
• The cost for treatment when the soil is staged into nine cells is
approximately $815/tonne ($740/ton) or $l,300/yd3 for 1.5 m (5
ft) deep cells, $474/tonne ($430/ton) or $770/yd3 for 4.6 m (15 ft)
deep cells (like those at the Parsons' site), and $407/tpnne ($3707
ton) or $660/yd3 for 6.1 m (20 ft) deep cells. The costs presented
are calculated based on the number of cubic yards of contami-
nated soil treated. Because clean fill and surrounding uncon-
taminated soil are treated as part of each melt, the total amount
of material treated is greater than the amount of contaminated
soil treated. Costs per cubic yard based on total soil treated
would, therefore, be lower than the costs per cubic yard based on
contaminated soil treated presented in this report.
• Treatment is most economical when treating large cells to the
maximum depth. The primary cost categories include utilities,
labor, start-up, and fixed costs.
The site studied during this demonstration was Geosafe's first large-scale
commercial project. Valuable lessons learned at this site have been put into
practice in subsequent applications.
-------
J11.HP
ii,1,! ili;
: t> '*' .'"i" i, • 1 iiiSF
Vi'i i iii'iii;;1'
II II I
•I ,[,• nr: .if JUS :
-------
.Appendix A
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-------
ll 1111
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Carter JO S S. Koegler, and S.O. Bates! 1988. Process Performance of the Pilot-Scale In Situ
Vacation ofr Simulated Waste Disposal Site at the Oak Ridge National Laboratory. PNL-6531
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Chap ' y-. 23: 223-232. Cincinnati, OH: American Ceramic Society.
c. .
vS high-level waste. High Level Radioactive Waste and Spent Fuel Management Vol. II. New
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Colombo, P. and R.M.Neilson. 1979. Propenies of Radioactive Wastes and ^te Contain^, First
Topical Report. BNL:NUREG-50957. Upton, NY: Brookhaven National Laboratory. August.
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SJS&j^^ .^"^j^.^r^^±!l!l .
Environmental Engineers.
Conner, J.R. 199>. Chemical Fixation and Sotidi^ationcf Hazardous mstes. New York: Van
Nostrand Reinhold ." _ . ' ..... ; ^ ...... _ ....... ( ............ ..... ................... i'_ ...................... .
Conner'' 'JFiyi/'TreatmentofDWinorgS
" Annual Meeting of the American Ceramics Society. Cincinnati, OH. April 29.
Conner^;R:. J9!2; %eroleofl^ Proc-
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A.2
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" ''''
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t
I | I
A.4
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Appendix
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ipiiiiiiliiiiiiiiiiiiii 111 in i i i i in
I HI1
A.6
In
Hi i
n i||ili|li( (nil P I"
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Appendix A
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Fed. Reg. 60,66344. December 21.
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Lib I Ul
"mini n
jinn j,' . i 'Null1
1«"!,'!''"P 'liull1!*;
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-;1 (eds.). Philadelphia, PA: American Society for Testing and Materials.
ill
i ini|iiiiii|i i IN r in Hi1
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Ill 111 III
Ill I i inn
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THE WASTECH® MONOGRAPH SEKItS QKMA5t II/UIM
INNOVATIVE SITE REMEDIATION TECHNOLOGY:
DESIGN AND APPLICATION
1 " '""--f't'.":'.". •'•' •: .'•' : ' '
' ' ' ' ' ' i
seven-book series focusing on the design and application of innovative site remediation
nologies follows an earlier series (Phase I, 1994-1995) which cover the process descriptions,
uations, and limitations of these same technologies. The success of that series of publications
;ested that this Phase H series be developed for practitioners in need of design information
applications, including case studies.
I * I II lllll inn' i1!111':" II'!'' i1 '.If:,H1;!1; ' . ,',M.iV , ,"' , ."in' i' r, :MI;"I; ,< y '",, invviplllli
STECH® is a multiorganization effort which joins in partnership the Air and Waste Manage-
t Association, the American Institute of Chemical Engineers, the American Society of Civil
ineers, the American Society of Mechanical Engineers, the Hazardous Waste Action
lition, the Society for Industrial Microbiology, the Soil Science Society of America, and
Water Environment Federation, together with the American Academy of Environmental
ineers, the U.S. Envkonmental Protection Agency, the U.S. Department of Defense, and the
. Department of Energy.
leering Committee qomposed of highly respected members of each participating organization
! expertise in remediation technology formulated and guided both phases, with project
(agement and support provided by the Academy. Each monograph was prepared by a Task
up of recognized experts. The manuscripts were subjected to extensive peer reviews prior to
licatipn. This Design and Application Series includes:
1 - Bioremediafion
;ipal authors: R. Ryan Dupont, Ph JO., Chair, '
i State University; Clifford J. Bruell, Ph.D.,
'ersity of Massachusetts; Douglas C. Downey,
cms Engineering Science; Scott G. Hiding,
PA; Michael C. Marley, Ph.D., Environgen, Inc.;
ert D. Morris, Ph.D., Eckenfelder, Inc.; Bruce
tz, USEPA.
2 - Chemical Treatment
ripal authors: Leo Weitzman, Ph.D., LVW
Kiiates, Chair, Irvin A. Jefcoat, Ph.D., University
labama; Byung R. Kim, Ph.D., Ford Research
natory.
3 - Liquid Extraction Technologies:
Washing/Soli Flushing/Solvent Chemical
cipal authors: Michael J. Mann, P.E., DEE,
rnative Remedial Technologies, Inc., Chair,
lord J. Ayen, Ph.D., Waste Management Inc.;
ne G. Everett, Ph.D., Geraghty & Miller, Inc.;
cGombert H, P.E., LIFCO; Mark Meckes,
!PA; Chester R. McKee, Ph.D., In-Situ, Inc.;
>ard P. Traver, PJE., Bergmann USA; Phillip D.
ling, Jr., P.E., Ei'L DuPont Co. Inc.; Shai-Chih
f, Ph.D., In-Situ, Inc.
4 - Stabilization/Solidification
cipal authors: Paul pi kaib, Brooidiaven National
jratory, Chair, Jesse R. Conner, Conner Technolo-
, Inc.; John L. Mayberry, PJE,, SAIC; Bhavesh R,
il, U.S. Department of Energy; Joseph M. Perez, Jr.,
elle Pacific Northwest; RnsseU L. Treat, MACTEC
Vol 5 - Thermal Desorption
Principal authors: William L. Troxler, P.E., Focus
Environmental Inc., Chair; Edward S. Alperin, IT
Corporation; Paul R:de Percin, USEPA; Joseph H.
Button, P.E., Canonie Environmental Services, Inc.;
JoAnn S. Lighty, Ph.D., University of Utah; Carl R.
Palmer, P.E., Rust R'emedial Services, Inc.
Vol 6-Thermal Destruction
Principal authors: Francis W. Holm, Ph.D., SAIC, Chair,
Carl R. Cooley, Department of Energy; James J.
Cudahy, P.E., Focus Enwonmental Inc.; Clyde R.
Dempsey, PJE., USEPA; John P. Longwell, Sc.D.,
Massachusetts Insititute of Technology; Richard S.
Magee, Sc.D., P.E., DEE, New Jersey Institute of
Technology; Walter G. May, ScJX, University of Illinois.
Vol 7 - Vapor Extraction and Air Sparging
Principal authors: Timothy B. Holbrook, P.E., Camp
Dresser & McKee, Chair, David H. Bass, Sc.D.,
Groundwater Technology, Inc.; Paul M. Boersma,
CH2M Hill; Dominic C. DiGuilio, University of
Arizona; John J. Eisenbeis, Ph.D., Camp Dresser &
McKee; Nefl J. Hutzler, Ph.D., Michigan Technologi-
cal University; Eric P. Roberts, P.E., ICF Kaiser
Engineers, Inc.
The monographs for both the Phase I and Phase II
series,may be purchased from the American Academy
of Environmental Engineers9,130 Holiday Court, Suite
100, Annapolis, MD, 21401; Phone: 410-266-3390,
Fax: 410-266-7653,.E-mail: aaee@ea.net
F !
1 ,' '-' . . i
^0.5. GOVERNMENT PRINTING OFFICE: 1997 -521-960/90319
"'• • ::i i"-|,:-i::;
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