EPA 542-B-94-001
!',d Emergency
&EPA
'Stabilization
-------
INNOVATIVE SITE
REMEDIATION TECHNOLOGY
STABILIZATION/
SOLIDIFICATION
One of an Eight-Volume Series
Edited by
William C. Anderson, P.E., DEE
Executive Director, American Academy of Environmental Engineers
1994
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 Y"V American Society of
Association \/* Civil Engineers
P.O. Box 2861 345 East 47th Street
Pittsburgh, PA 15230 New York, NY 10017
American Academy of vS?*>§J American Society of
Environmental Engineers81 \SD® Mechanical Engineers
130 Holiday Court, Suite 100 345 East 47th Street
Annapolis, MD 21401 New York, NY 10017
American Institute of riifltfll / Hazardous Waste Action
Chemical Engineers £SS Coalition
345 East 47th Street 1015 15th Street, N.W., Suite 802
New York, NY 10017 Washington, D.C. 20005
r Water Environment
Federation
601 Wythe Street
Alexandria, VA 22314
Published under license from the American Academy of Environmental Engineers*.
© Copyright 1994 by the American Academy of Environmental Engineers*.
-------
Library of Congress Cataloging-in-Publication Data
Innovative site remediation technology/ edited by William C. Anderson
166p. 15.24 x 22.86cm.
Includes bibliographic references.
Contents: - [3] Soil Washing/Soil Flushing - [4] Stabilization/solidification
- [6] Themal desorption.
1. Soil remediation. I. Anderson, William, C., 1943-
II. American Academy of Environmental Engineers.
TD878.I55 1994 628.5'5~dc20 93-20786
ISBN 1-883767-03-2 (v. 3)
ISBN 1-883767-04-0 (v. 4)
Copyright 1994 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 the 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
information only. This information should not be used without first securing
competent advice with respect to its suitability for any general or specific applica-
tion.
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 net
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 olF any
kind, whether express or implied, concerning the accuracy, suitability, or utility of
any information published herein and neither the American Academy of Environ-
mental Engineers nor any such associated organization or author shall be responsible
for any errors, omissions, or damages arising out of use of this information.
Book design by Lori Imhoff
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.
-------
CONTRIBUTORS
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 stabilization/solidification 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.
PRINCIPAL AUTHORS
Peter Colombo, Task Group Chair
Manager, Waste Management Research and Development
Brookhaven National Laboratory
Edwin Earth, P.E. Jim Buelt
Environmental Engineer Staff Engineer
Office of Research and Development Batelle Pacific Northwest Laboratory
U.S. Environmental Protection Agency
Paul L. Bishop, Ph.D., P.E., DEE Jesse R. Conner
William Thorns Professor Senior Research Scientist
Department of Civil and Environmental Rust Remedial Services, Inc.
Engineering Clemson Technical Center
University of Cincinnati
REVIEWERS
The panel that reviewed the monograph under the auspices of the Project
Steering Committee was composed of:
Paul L. Busch, Ph.D., P.E., DEE, Chair Roger Olsen, Ph.D.
President Vice President
Malcolm Pirnie, Inc. Camp Dresser and McKee
Bill Batchelor, Professor Ram Ramanujam, P.E.
Department of Civil Engineering Associate Waste Management Engineer
Texas A & M University California EPA/DTSC
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STEERING COMMITTEE
Frederick G. Pohland, Ph.D., P.E., DEE
Chair
Weidlein Professor of Environmental
Engineering
University of Pittsburgh
William C. Anderson, P.E., DEE
Project Manager
Executive Director
American Academy of Environmental
Engineers
Paul L. Busch, Ph.D., P.E., DEE
President and CEO
Malcolm Pirnie, Inc.
Representing, American Academy of
Environmental Engineers
Richard A. Conway, P.E., DEE
Senior Corporate Fellow
Union Carbide Corporation
Chair, Environmental Engineering
Committee
EPA Science Advisory Board
Timothy B. Holbrook, P.E.
District Engineering Manager
Groundwater Technology, Inc.
Representing, Air and Waste Management
Association
Walter W. Kovalick, Jr., Ph.D.
Director, Technology Innovation Office
Office of Solid Waste and Emergency
Response
U.S. Environmental Protection Agency
Joseph F. Lagnese, Jr., P.E., DEE
Private Consultant
Representing, Water Environment
Federation
Peter B. Lederman, PhJX, P.E., DEE, P.P.
Center for Env. Engineering & Science
New Jersey Institute of Technology
Representing, American Institute of
Chemical Engineers
Raymond C. Loehr, Ph.D., P.E., DEE
H.M. Alharthy Centennial Chair and
Professor
Civil Engineering Department
University of Texas
James A. Marsh
Office of Assistant Secretary of Defense
for Environmental Technology
Timothy Oppelt
Director, Risk Reduction Engineering
Laboratory
U.S. Environmental Protection Agency
George Pierce, Ph.D.
Editor in Chief
Journal of Microbiology
Manager, Bioremediation Technology Dev.
American Cyanamid Company
Representing the Society of Industrial
Microbiology
EL Gerard Schwartz, Jr., Ph.D., P.E., DEE
Senior Vice President
Sverdrup
Representing, American Society of Civil
Engineers
Claire H. Sink
Acting Director
Division of Technical Innovation
Office of Technical Integration
Environmental Education Development
U.S. Department of Energy
Peter W. Tunnicliffe, P.E., DEE
Senior Vice President
Camp Dresser & McKee, Incorporated
Representing, Hazardous Wasts Action
Coalition
Charles O. Velzy, P.E., DEE
Private Consultant
Representing, American Society of
Mechanical Engineers
William A. Wallace
Vice President, Hazardous Waste
Management
CH2M Hill
Representing, Hazardous Waste Action
Coalition
Walter J. Weber, Jr., Ph.D., P.E., DEE
Earnest Boyce Distinguished Professor
University of Michigan
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
organization 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.
This worldwide network represents
many disciplines: physical and social
sciences, health and medicine, engineer-
ing, law, and management. The
Association serves its membership by
promoting environmental responsibility
and providing technical and managerial
leadership in the fields of air and waste
management. Dedication to these
objectives enables the Association to
work towards its goal: a cleaner
environment.
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:
James R. Donnelly
Director of Environmental Services and
Technologies
Davy Environmental
Paul Lear
OHM Remediation Services, Corp.
American Institute of
Chemical Engineers
The Environmental Division of the
American Institute of Chemical Engi-
neers 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
Qualified reviewers were recruited
from the Environmental Engineering
Division of ASCE and formed a Sub-
committee on WASTECH®. The mem-
bers of the Subcommittee have re-
viewed the monograph and have deter-
mined that it is acceptable for publica-
tion.
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 document
approximately 116,400 members, in-
cluding 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 confer-
ences 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 title page of this docu-
ment, neither ASME nor any of its
Divisions or 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 docu-
ment and the findings expressed are
technically sound.
Hazardous Waste Action
Coalition
The Hazardous Waste Action Coali-
tion (HWAC) is an association dedi-
cated to promoting an understanding of
the state of the hazardous waste practice
and related business issues. Our mem-
ber firms are engineering and science
firms that employ nearly 75,000 of this
country's engineers, scientists, geolo-
gists, hydrogeologists, toxicologists,
chemists, biologists, and others who
solve hazardous waste problems as a
professional service. HWAC is pleased
to endorse the monograph as technically
sound.
The lead reviewer was:
James D. Knauss, Ph.D.
Hatcher-Sayre, Incorporated
Water Environment
Federation
The Water Environment Federa-
tion is a nonprofit, educational orga-
nization composed of member and
affiliated associations throughout the
world. Since 1928, the Federation
has represented water quality specialists
including engineers, scientists, govern-
ment officials, industrial and municipal
treatment plant operators, chemists,
students, academic and equipment
manufacturers, and distributors.
Qualified reviewers were recruited
from the Federation's Hazardous Wastes
Committee and from the general mem-
bership. A list of their names, titles, and
business affiliations can be found listed
below. It has been determined that the
document is technically sound and
publication is endorsed.
The reviewers were:
William Librizzi
Director of Government l^rograms
OHM Corporation
Linda Roberts Phipps, Ph.D., REM*
Process Chemist
RESOURCE CONSULTANTS, INC.
*WEF lead reviewer
vi
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ACKNOWLEDGMENTS
The WASTECH® 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 U.S. Environmental Protection
Agency, Department of Defense, Department of Energy, and the American
Academy of Environmental Engineers®.
This multiorganization 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:
Paul F. Peters
Assistant Project Manager & Managing Editor
Karen M. Tiemens
Editor
Susan C. Richards
Project Staff Assistant
J. Sammi Olmo
Project Administrative Manager
Yolanda Y. Moulden
Staff Assistant
I. Patricia Violette
Staff Assistant
vii
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TABLE OF CONTENTS
CONTRIBUTORS iii
ACKNOWLEDGMENTS vii
LIST OF TABLES xvi
LIST OF FIGURES xix
1.0 INTRODUCTION 1.1
1.1 Stabilization and Solidification 1.1
1.2 Development of the Monograph 1.2
1.2.1 Background 1.2
1.2.2 Process 1.3
1.3 Purpose 1.4
1.4 Objectives 1.4
1.5 Scope 1.4
1.6 Limitations 1.5
1.7 Organization 1.6
2.0 PROCESS SUMMARY 2.1
2.1 Process Identification and Description 2.1
2.1.1 Sorption and Surfactant Processes 2.1
2.1.2 Emulsified Asphalt 2.2
2.1.3 Bituminization 2.2
2.1.4 Vitrification 2.2
2.1.4.1 Electrical Processes 2.3
ix
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Table of Contents
2.1.4.2 Thermal Processes 2.4
2.1.4.3 Plasma 2.4
2.1.5 Modified Sulfur Cement 2.4
2.1.6 Polyethylene Extrusion Process 2.4
2.1.7 Inorganic, Cementitious Technologies of the Siliceous
Category 2.4
2.1.7.1 Soluble Silicate Processes 2.5
2.1.7.2 Slag Processes 2.5
2.1.7.3 Lime 2.5
2.1.7.4 Inorganic Polymers 2.6
2.1.8 Soluble Phosphates 2.6
2.2 Potential Applications 2.6
2.3 Process Evaluation 2.8
2.3.1 Sorption and Surfactant Processes 2.8
2.3.2 Emulsified Asphalt 2.8
2.3.3 Bituminization 2.8
2.3.4 Vitrification 2.8
2.3.5 Modified Sulfur Cement Process 2.9
2.3.6 Polyethylene Extrusion Process 2.9
2.3.7 Inorganic, Cementitious Technologies of the Siliceous
Category 2.9
2.3.8 Soluble Phosphates 2.10
2.4 Limitations 2.10
2.5 Technology Prognosis 2.10
3.0 PROCESS IDENTIFICATION AND DESCRIPTION 3.1
3.1 Sorption and Surfactant Processes 3.1
3.1.1 Description 3.1
3.1.2 Scientific Basis 3.1
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Table of Contents
3.1.3 Status and Development 3.2
3.1.4 Pretreatment Requirements 3.2
3.1.5 Health and Safety Considerations 3.2
3.1.6 Operational Considerations 3.3
3.2 Emulsified Asphalt 3.3
3.2.1 Description 3.3
3.2.2 Scientific Basis 3.4
3.2.3 Information Necessary to Employ Process 3.5
3.2.4 Operational Considerations 3.5
3.3 Bituminization 3.5
3.3.1 Description 3.5
3.3.2 Operational Considerations 3.6
3.4 Vitrification 3.6
3.4.1 Description 3.6
3.4.2 Scientific Basis 3.8
3.4.3 Technology Variations 3.9
3.4.3.1 Electrical Processes 3.10
3.4.3.2 Thermal Vitrification 3.14
3.4.3.3 Plasma Vitrification 3.15
3.5 Modified Sulfur Cement Process 3.17
3.5.1 Description 3.17
3.5.2 Operational Considerations 3.18
3.5.3 Health and Safety Considerations 3.18
3.6 Polyethylene Extrusion Process 3.18
3.6.1 Description 3.18
3.6.1.1 Polyethylene 3.19
3.6.2 Status of Development 3.22
xi
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Table of Contents
3.6.2.1 Bench-Scale Development 3.22
3.6.2.2 Scaleup Feasibility 3.25
3.7 Inorganic, Cementitious Technologies of the Siliceous
Category 3.28
3.7.1 Description 3.28
3.7.2 Scientific Basis 3.29
3.7.3 Operational Considerations 3.29
3.7.4 Status of Development 3.31
3.7.5 Technology Variations 3.32
3.7.5.1 Soluble Silicate Processes 3.32
3.7.5.2 Slag Processes 3.38
3.7.5.3 Lime 3.42
3.7.5.4 Inorganic Polymers 3.43
3.8 Soluble Phosphates 3.45
3.8.1 Description 3.45
3.8.2 Scientific Basis 3.45
3.8.3 Status of Development 3.50
3.8.4 Operational Considerations 3.51
3.9 Comparative Costs 3.51
4.0 POTENTIAL APPLICATIONS 4.1
4.1 Sorption and Surfactant Processes 4.1
4.2 Emulsified Asphalt 4.3
4.3 Bituminization 4.5
4.4 Vitrification 4.5
4.4.1 Refractory-Lined Melters 4.6
4.4.2 In Situ Vitrification (ISV) 4.7
4.4.3 Thermal Vitrification 4.7
4.4.4 Plasma Vitrification 4.8
xii
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Table of Contents
4.5 Modified Sulfur Cement Process 4.9
4.6 Polyethylene Extrusion Process 4.9
4.7 Inorganic, Cementitious Technologies of the Siliceous
Category 4.10
4.7.1 Soluble Silicate Processes 4.10
4.7.1.1 EnviroGuard/ProTek/ProFix, Houston, Texas 4.10
4.7.1.2 Lopat, Wanamassa, New Jersey 4.11
4.7.1.3 Other Soluble Silicate Processes 4.11
4.7.2 Slag Processes 4.11
4.7.3 Lime 4.12
4.7.4 Inorganic Polymers Category 4.13
4.8 Soluble Phosphates 4.13
5.0 PROCESS EVALUATION 5.1
5.1 Sorption and Surfactant Processes 5.1
5.1.1 Process Performance and Effectiveness 5.1
5.1.2 Types and Amounts of By-products 5.4
5.1.3 Cost Per Unit Volume 5.4
5.2 Emulsified Asphalt 5.5
5.3 Bituminization 5.6
5.4 Vitrification 5.6
5.4.1 Refractory-Lined Melters 5.7
5.4.2 In Situ Vitrification (ISV) 5.7
5.4.3 Thermal Vitrification 5.9
5.4.4 Plasma Vitrification 5.10
5.5 Modified Sulfur Cement Process 5.11
5.5.1 Process Performance and Effectiveness 5.11
5.6 Polyethylene Extrusion Process 5.16
5.6.1 Process Performance and Effectiveness 5.16
xiii
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Table of Contents
5.6.1.1 Economic Feasibility 5.19
5.7 Inorganic, Cementitious Technologies of the Siliceous
Category 5.26
5.7.1 Process Performance and Effectiveness 5.26
5.7.1.1 Soluble Silicate Processes 5.26
5.7.1.2 Slag Processes 5.30
5.7.1.3 Lime 5.32
5.7.1.4 Inorganic Polymers 5.33
5.7.2 Cost Information 5.35
5.8 Soluble Phosphates 5.35
6.0 LIMITATIONS 6.1
6.1 Sorption and Surfactant Processes 6.1
6.1.1 Site Considerations 6.1
6.1.2 Waste Matrix and Risk Considerations 6.1
6.2 Emulsified Asphalt 6.2
6.3 Bituminization 6.2
6.4 Vitrification 6.2
6.4.1 Feed Moisture Content 6.3
6.4.2 Feed Material Composition 6.3
6.4.3 Feed Compatibility 6.4
6.4.4 Combustible Material 6.4
6.4.5 Potential Shorting Caused by Metals 6.4
6.4.6 Cost of Energy 6.5
6.5 Modified Sulfur Cement Process 6.5
6.6 Polyethylene Extrusion Process 6.6
6.7 Inorganic, Cementitious Technologies of the Siliceous
Category 6.6
xiv
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Table of Contents
6.7.1 Soluble Silicate Processes 6.7
6.7.1.1 EnviroGuard/ProTek/ProFix, Houston, Texas 6.7
6.7.1.2 Lopat, Wanamassa, New Jersey 6.7
6.7.1.3 Other Soluble Silicate Processes 6.7
6.7.2 Slag Processes 6.8
6.7.3 Lime 6.8
6.7.4 Inorganic Polymers Category 6.8
6.8 Soluble Phosphates 6.9
7.0 TECHNOLOGY PROGNOSIS 7.1
7.1 Sorption and Surfactant Process Aspects Needing Further
Development and Demonstration 7.1
7.2 Emulsified Asphalt 7.1
7.3 Bituminization 7.2
7.4 Vitrification 7.2
7.5 Modified Sulfur Cement Process 7.2
7.6 Polyethylene Extrusion Process 7.3
7.7 Inorganic, Cementitious Technologies of the Siliceous
Category 7.3
7.7.1 Soluble Silicate Processes 7.3
7.7.1.1 EnviroGuard/ProTek/ProFix, Houston, Texas 7.3
7.7.1.2 Lopat, Wanamassa, New Jersey 7.3
7.7.1.3 Other Soluble Silicate Processes 7.4
7.7.2 Slag Processes 7.4
7.7.3 Lime 7.4
7.7.4 Inorganic Polymers 7.4
7.8 Soluble Phosphates 7.4
APPENDIX A: List Of References A. 1
XV
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LIST OF TABLES
Table Title Page
2.1 Potential applications 2.7
3.1 Influence of constituents on electrical conductivity 3.9
3.2 Properties of low density polyethylene 3.21
3.3 Effect of various chemicals on polyethylene after 3-month
contact 3.23
3.4 Parameter setting and test data for polyethylene
encapsulation production-scale feasibility 3.27
3.5 Solubility of various metal phosphate species 3.46
3.6 Lead solubility equilibria 3.48
3.7 Comparison of two stabilization/solidification scenarios 3.52
4.1 TCLP and organic extraction test data for silicate technology
corporation process for wood preserving contaminated soils 4.2
4.2 TCLP leaching results for Soliditech process ^ 4.3
4.3 Specific stabilization/solidification applications of lime 4.12
5.1 Partitioning coefficients for organic fillers and binders
evaluated for stabilizing dichloromethane 5.2
5.2 Attenuative capacity of various materials for heavy metals 5.3
5.3 Organic extraction test data from Wastech process 5.4
5.4 Cost per unit of sorbent or surfactant stabilization/
solidification processes 5.5
5.5 Contaminant decontamination factor for a slurry fed vertical
melter 5.7
5.6 Normalized elemental and contaminant releases from
ratioactie ISV products 5.8
xvi
-------
List of Tables
Title Page
5.7 TCLP concentrations for metallic phase from one bench-
scale test 5.9
5.8 Elemental composition of INEL incinerator fly ash 5.11
5.9 Results from EPA Extraction Procedure Toxicity Test and
Toxicity Characterization Leaching Procedure for INEL ash
encapsulated in modified sulfur cement 5.15
5.10 Waste form test methods 5.18
5.11 ANS 16.1 leach test data for sodium nitrate in polyethylene
waste forms 5.21
5.12 Compressive yield strength of cored pilot-scale polyethylene
waste forms containing 60 wt% sodium nitrate 5.22
5.13 Self-ignition temperatures of polyethylene with nitrate salt
and salt waste components 5.23
5.14 Results from Extraction Procedure Toxicity Test and Toxicity
Characterization Leaching Procedure for Rocky Flats Plant
nitrate salt encapsulated in polyethylene 5.23
5.15 Assumptions used in the economic analysis of nitrate salt
encapsulation for Rocky Flats Plant 5.24
5.16 Economic analysis for nitrate salt encapsulation at Rocky
Flats Plant 5.24
5.17 Cost breakdown 5.25
5.18 Stabilization of organics in the Profix process 5.27
5.19 Stabilization of metals in the Profix process 5.28
5.20 Summary of test data on LOPAT K-20 Process 5.29
5.21 Effect of various additives on technetium and nitrate
teachability 5.30
xvii
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List of Tables
Table Title Page
5.22 Summary of leaching data - SoliRoc™ Process 5.31
5.23 Leaching of treated, dichromate-contaminated soil-
cement-slag process 5.32
5.24 Summary of treatability studies using the OCR Process 5.33
5.25 Leachate results from geopolymerization of mine tailings 5.34
5.26 Reduction in leaching due to phosphate treatment 5.36
5.27 Comparison of species release for availability leaching
tests on untreated and treated municipal solid waste residues
(mg released/kg dry ash) 5.37
xviii
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LIST OF FIGURES
Figure Title Page
3.1 Simplified diagram of a bituminization plant 3.7
3.2 In situ vitrification 3.13
3.3 Pilot-scale, graphic-electrode DC arc furnace 3.16
3.4 Sectional view of a simplified screw extruder 3.20
3.5 Photograph of laboratory-scale extruder with separate
dynamic feeders for waste and binder 3.24
3.6 Polyethylene encapsulation system process flow diagram 3.27
3.7 Ternary composition diagram for cementitious systems 3.30
3.8 Leachability of metals as a function of soluble silicate
content 3.34
3.9 Flow diagram of SoliRoc™ Process 3.41
3.10 Solubility diagrams for simple mineral phases containing
lead 3.49
3.11 Solubility diagrams for various lead phosphate minerals 3.50
5.1 Bench-scale double planetary mixer for processing modified
sulfur cement waste forms 5.12
5.2 Compressive strength data for INEL incinerator fly ash
encapsulated in modified sulfur cement 5.14
5.3 Comparison of waste loadings of INEL incinerator fly ash in
modified sulfur cement and portland cement. 5.17
5.4 Compressive yield strength of polyethylene waste forms
containing sodium nitrate salt, untreated and after 90 days
in water immersion 5.19
5.5 Comparison of Compressive yield strength vs. Waste form
density for waste forms undergoing ASTM g-21 and g-22
biodegradation testing and control (untreated) samples 5.20
xix
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List of Figures
ire Title Page
5.6 Leaching index determined according to the ANS 16.1 leach
test as a function of sodium nitrate waste loading for
polyethylene waste forms 5.21
5.7 Economic analysis for Rocky Flats Plant nitrate salt
encapsulation 5.25
5.8 Summary of cost breakdown for economic analysis of
nitrate salt waste encapsulation at Rocky Flats Plant using
polyethylene and Savannah River Plant saltstone cemenl;
formulations 5.26
xx
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Chapter 1
INTRODUCTION
This monograph on stabilization and solidification is one of a series of
eight on innovative site and waste remediation technologies that is the cul-
mination of a multiorganization effort involving more than 100 experts over
a two-year period. It provides the experienced, practicing professional guid-
ance on the application of innovative processes considered ready for full-
scale application. Other monographs in this series address bioremediation,
chemical treatment, chemical extraction, soil washing/soil flushing, thermal
desorption, thermal destruction, and vacuum vapor extraction.
7.7 Stabilization and Solidification
Stabilization and Solidification are closely related in that both use chemi-
cal, physical, and thermal processes to detoxify a hazardous waste. But
they are distinct technologies.
Stabilization refers to processes that reduce the risk posed by a waste by
converting the contaminants into a less soluble, mobile, or toxic form. The
physical nature of the waste is not necessarily changed.
Solidification refers to processes that encapsulate the waste in a mono-
lithic solid of high-structural integrity. The encapsulation may be that of
fine waste particles (microencapsulation) or of a large block or container of
wastes (macroencapsulation). Solidification does not necessarily involve a
chemical interaction between the waste and the solidifying reagents, but
may mechanically bind the waste in the monolith. Contaminant migration
is restricted by vastly decreasing the surface area exposed to leaching and/
or by isolating the waste within an impervious capsule.
1.1
-------
Introduction
7.2 Development of the Monograph
1.2.1 Background
Acting upon its commitment to develop innovative treatment technolo-
gies for the remediation of hazardous waste sites and contaminated soils
and groundwater, the U.S. Environmental Protection Agency (USl EPA)
established 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 Ad-
visory Council on Environmental Policy and Technology, convened a work-
shop for representatives of consulting engineering firms, professional soci-
eties, research organizations, and state agencies involved in site
remediation. The workshop focused on defining the barriers that were im-
peding the application of innovative technologies in site remediation
projects. One of the major impediments identified was the lack of reliable
data on the performance, design parameters, and costs of innovatiive pro-
cesses.
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. The Academy would man-
age a project to develop monographs describing the state of available inno-
vative remediation technologies. Financial support would be provided by
the 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
American Institute of Chemical Engineers, the American Society of Civil
Engineers, the American Society of Mechanical Engineers, the Hazardous
1.2
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Chapter 1
Waste Action Coalition, the Society for Industrial Microbiology, and the
Water Environment Federation, together with the Academy, EPA, DOD,
and DOE. A Steering Committee composed of highly respected representa-
tives of these organizations having expertise in remediation technology
formulated the specific project objectives and process 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 monograph began in earnest in January, 1992.
1.2.2 Process
The Steering Committee decided upon the technologies, or technological
areas, to be covered by each monograph, the monographs' 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 innovative site and waste
remediation technologies — industry, consulting engineers, research, aca-
deme, and government (See page iii for a listing of members of the Stabili-
zation/Solidification Task Group).
The Steering Committee called upon the task groups to examine and
analyze all pertinent information available, within the Project's financial
and time constraints. This included, but was not limited to, the comprehen-
sive data base on remediation technologies compiled by US EPA, the store
of information possessed 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 con-
ducted 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). Si-
multaneous with the Steering Committee's review, each of the professional
and technical organizations represented in the Project reviewed those mono-
graphs addressing technologies in which it has substantial interest and com-
petence. Aided by a Symposium sponsored by the Academy in October
1992, persons having interest in the technologies were encouraged to par-
ticipate in the organizations' review.
1.3
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Introduction
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.
7.3 Purpose
The purpose of this monograph is to further the use of innovative stabili-
zation and solidification site remediation and waste-processing technolo-
gies, i.e., technologies not commonly applied, where their use can provide
better, more cost-effective performance than conventional methods. To this
end, the monograph documents the current state of the technology for a
number of innovative stabilization and solidification processes.
14 Objectives
The monograph's principal objective is to furnish guidance for experi-
enced, practicing professionals and users' project managers. The monograph
is intended, therefore, not to be prescriptive, but supportive. It is intended to
aid experienced professionals in 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
addresses are potentially applicable.
7.5 Scope
The monograph addresses innovative stabilization and solidification
technologies that have been sufficiently developed so that they can be used
1.4
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Chapter 1
in full-scale applications. It addresses all such technologies for which suffi-
cient data were available to the Stabilization/Solidification Task Group to
describe and explain the technology and assess its effectiveness, limitations,
and potential applications. Laboratory- and pilot-scale technologies were
addressed, as appropriate.
The monograph's primary focus is site remediation and waste treatment.
To the extent the information provided can also be applied to production
waste streams, it will provide the profession and users this additional ben-
efit. The monograph considers all waste matrices to which stabilization and
solidification processes can be reasonably applied, such as, soils, liquids,
and sludges.
Application of site remediation and waste treatment technology is site-
specific and involves consideration of a number of matters besides alterna-
tive technologies. Among them are the following that are addressed only to
the extent essential to understand the applications and limitations of the
technologies described:
• site investigations and assessments;
• planning, management, specifications, and procurement; and
• regulatory requirements.
1.6 Limitations
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®
1.5
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Introduction
Project; nor does reference in this publication to any specific method, prod-
uct, process, or service constitute or imply an endorsement, recommenda-
tion, or warranty thereof.
7.7 Organization
This monograph and others in the series are organized under a uniform
outline intended to facilitate cross reference among them and comparison
of the technologies they address. Chapter 2.0, Process Summary, provides
an overview of all material presented. Chapter 3.0, Process Identification,
provides comprehensive information on the processes addressed. Each pro-
cess is analyzed in turn. The analysis includes, to the extent information and
data are available, a description of the process (what it does and how it does
it), its scientific basis, status of development, environmental effects, pre-
and posttreatment requirements, health and safety considerations, design
data, operational considerations, and comparative cost data. Also addressed
are process-unique planning and management requirements and process
variations.
Chapter 4.0, Potential Applications, Chapter 5.0, Process Evaluation, and
Chapter 6.0, Limitations, provide syntheses of available information and
informed judgments on the processes. Each of these chapters addresses the
processes in the same order as they are described in Chapter 3.0. Technol-
ogy Prognosis, Chapter 7.0, identifies aspects of each of the processes need-
ing further research and demonstration before full-scale application can be
considered.
1.6
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Chapter 2
PROCESS SUMMARY1
2. ] Process Identification and Description
Innovations in stabilization and solidification technology abound. This
monograph addresses eight distinct innovative processes or groups of pro-
cesses. Most of the innovations are modifications of proven processes and
are directed to encapsulating or immobilizing the harmful constituents and
involve excavation and processing of the waste or contaminated soil.
2.1.1 Sorption and Surfactant Processes
Sorption processes are based on a contaminant being attracted and re-
tained on a sorbent. Interactions between inorganic heavy metals and ion
exchange media, clay, humic material, fly ashes, activated carbon, etc., are
well documented in the waste management literature.
In general, hydrophobic organic material is not compatible with inor-
ganic material such as cement. By substituting quaternary ammonium ions
for group IA and IIA metal ions in clays, however, the interplaner distance
between aluminum and silica can be increased allowing clays to sorb or-
ganic compounds. The resulting clay/organic interactions vary from weak to
strong and are solidified by the addition of cement.
In simple terms, surfactants are manufactured to have different compat-
ibilities on each end of the molecule, allowing waste material to be sorbed
on one end, while the other end is compatible with inorganic cement. Sur-
factants can be used also to disperse organic waste material in an aqueous
phase and then combine with cement for solidification.
1. This chapter is a summary of Chapters 3.0 through 7.0. Sources are cited, where
appropriate, in those chapters — Ed.
2.1
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Process Summary
These processes, typically protected by patents, often combine the use of
both sorbent additives and surfactants. Examples of companies that have
provided field-scale services using these processes include Silicate Technol-
ogy Corporation (STC), International Waste Technologies (IWT), Hazcon,
Soliditech, and Wastech.
2.1.2 Emulsified Asphalt
Asphalt emulsions are very fine droplets of asphalt dispersed in water
that are stabilized by chemical emulsifying agents. Emulsified asphalt is
commercially available either as an anionic or a cationic emulsion. For the
highest efficiency, the most appropriate emulsified asphalt for the waste to
be treated must be selected.
The process involves adding emulsified asphalts having the appropriate
charge to hydrophilic liquid or semiliquid wastes at ambient temperature.
After mixing, the emulsion breaks, the water in the waste is released, and
the organic phase forms a continuous matrix of hydrophobic asphalt around
the waste solids. In some cases, additional neutralizing agents, such as lime
or gypsum, may be required. After given sufficient time to set and cure, the
resulting solid asphalt has the waste uniformly distributed throughout it and
is impermeable to water.
2.1.3 Bituminization
In the bituminization process, wastes are embedded in molten bitumen
and encapsulated when the bitumen cools. The process combines heated
bitumen and a concentrate of the waste material, usually in slurry form, in a
heated extruder containing screws that mix the bitumen and waste. Water is
evaporated from the mixture to about 0.5% moisture. The final product is a
homogenous mixture of extruded solids and bitumen.
2.1.4 Vitrification
Vitrification processes are solidification processes that employ heat to
melt and convert waste materials into glass or other glass and crystalline
products. Waste materials, such as heavy metals and radionuclides, are
actually incorporated into the glass structure which is, generally, a relatively
strong, durable material that is resistant to leaching.
2.2
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Chapter 2
Vitrification involves glass formers, stabilizers, and fluxes. Silica is the
principal glass former and provides the basic matrix of the vitrified product.
In waste management, silicates and borosilicates are used. Fluxes, primarily
sodium oxide that generally exist within the waste material, reduce the
melting temperature and, when molten, increase electrical conductivity,
thereby enhancing process efficiency. Stabilizers are employed to increase the
durability of the glass and to decrease the conductivity of the molten pool.
The high-temperatures employed, 1,200°C or higher, cause the glass
formers, fluxes, stabilizers, and wastes to melt together to form a glass ma-
trix. The high temperatures also destroy any organic constituents with very
few byproducts, which are treated with an offgas treatment system that
generally accompanies vitrification processes. There are three basic tech-
nology variations that differ in the kind of heating employed - electrical
processes, thermal processes, and plasma systems.
2.1.4.1 Electrical Processes
Electrical vitrification processes employ joule heating in which electrical
energy is imparted to glass to create a molten pool. Convective currents,
generated within the molten pool, enhance mixing, creating a more homog-
enous product. Further, cleaning of the process offgases is simpler than it
would be if fossil fuels were used, since no excess air for combustion of
fuels is required.
Electrical processes are generally applied above ground in refractory-
lined or water-cooled melters of either horizontal or vertical design using
electrodes or radiant heating. Waste materials, which can be slurries, wet or
dry solids, or combustible material, are mixed with glass formers and con-
veyed to the molten pool in the melter. Offgases are cleaned and the glass
formed withdrawn continuously or intermittently through a bottom drain or
overflow weir. Processing rates range from 80 to 220 kg/hr (175 to 485 lb/
hr), but may be as high as 3,600 kg/hr (9,900 Ib/hr) for municipal waste
vitrification.
Electrical processes are also applied in situ by inserting 4 graphite elec-
trodes a few centimeters into the contaminated soil, laying on a mixture of
ground glass frit and graphite flakes, and then applying an electrical current.
Once molten, the soil conducts electrical current causing the molten soil to
grow outward and downward. Blocks, up to 12 m (13 yd) on each side, can
be created in this batch-type application. Processing rates range from 2.7 to
4.5 tonne/hr (3 to 5 ton/hr).
2.3
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Process Summary
2.1.4.2 Thermal Processes
Thermal processes require an external heat source, typically fo&sil fuels,
to heat the waste constituents, glass formers, and fluxes via convective and
radiative heat. The typical reactor is a refractory-lined rotary kiln.
2.1.4.3 Plasma
Plasma systems employ temperatures up to 10,000°F, created by an elec-
trical discharge in an arc or torch through a gas. The resulting plasma de-
stroys organic constituents of the waste and liquefies the remainder through
radiative heat transfer. The process is operated on a batch basis and requires
treatment of the offgas. Compared with thermal processes, plasma systems
have much faster rates of heat transfer and can process waste up to 0.45
tonne/hr (0.5 ton/hr).
2.1.5 Modified Sulfur Cement
Modified sulfur cement is a commercially-available thermoplastic mate-
rial. It is easily melted (127° to 149°C (260° to 300T)) and then mixed with
the waste to form a homogenous molten slurry which is discharged to suit-
able containers for cooling, storage, and disposal. A variety of common
mixing devices, such as, paddle mixers and pug mills, can be used. The
relatively low temperatures used limit emissions of sulfur dioxide and hy-
drogen sulfide to allowable threshold values.
2.1.6 Polyethylene Extrusion Process
The polyethylene extrusion process involves the mixing of polyethylene
binders and dry waste materials using a heated cylinder containing a mix-
ing/transport screw. The heated, homogeneous mixture exits the cylinder
through an output die into a mold, where it cools and solidifies.
Polyethylene's properties produce a very stable, solidified product. The
process has been tested on nitrate salt wastes at plant-scale, establishing its
viability, and on various other wastes at the bench- and pilot-scale.
2.1.7 Inorganic, Cementitious Technologies of the Siliceous
Category
Cementitious stabilization is applicable to a wide range of industrial
wastes and results in very stable products. It is a well-established process;
2.4
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Chapter 2
the most common are lime-fly ash and portland cement-sodium silicate
systems. Innovations include modifications of established systems and the
use of other reagents.
2.1.7.1 Soluble Silicate Processes
Soluble silicates are applied either as accelerators or retarders in
cementitious systems to reduce leachability. A variety of conventional pat-
ented processes employ this technology. Innovations in chemistry of the use
soluble silicates include enviroGuard™, enviroGuard Plus™, ProFix™, and
Lopat. There are many other patented processes employing this technology,
although none is commercialized.
2.1.7.2 Slag Processes
Slags, themselves waste products, have been used for several years in
waste treatment. Slags, either alone or with cementitious materials, are
mixed with waste slurries to enhance settling and compaction, after which
the supernatant is drawn off leaving a stable residue. Typically, slag pro-
cesses are applicable to dilute wastes, require large areas for settling and
compaction ponds, and can be conducted over long periods.
The Oak Ridge National Laboratory (ORNL) Process employs blast-
furnace slag in combination with portland cement and fly ash for stabiliza-
tion of radioactive wastes. SoliRoc™ is a complete hazardous waste treat-
ment system that employs a complex pretreatment process using blast-fur-
nace slag, precipitation using process-generated soluble silicates, sludge
dewatering, and solidification with portland cement.
Another innovation employs portland cement and slag to stabilize
hexavalent chromium. Laboratory leachability tests confirm that the Cr**
could be stabilized to within US EPA Toxicity Characteristic Leaching
Procedure (TCLP) limits.
2.1.7.3 Lime
Another process uses lime that has been pretreated with additives caus-
ing it to be hydrophobic. Patented processes offering this technology are
Separation and Recovery Systems (SRS)/EIF and DCR/Boelsing/Sound
Environmental Services, Inc. According to the patent, these processes en-
able lime to sorb organics and encapsulate them within an insoluble calcium
carbonate.
2.5
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Process Summary
2.1.7.4 Inorganic Polymers
In soluble silicate processes, some polymerization may occur. The
"Geopolymer" process, however, appears to form inorganic polymers based
on silicon and aluminum through chemical reaction. The geopolymers act
as binders when mixed with wastes, producing a high-viscosity mixture that
can be molded. After curing, the resulting product is characterized by high-
strength, hardness, and resistance to chemical attack, especially attack by
acids.
2.1.8 Soluble Phosphates
The process involves the addition of various forms of phosphate and
alkali for control of pH as well as for formation of complex metal mol-
ecules of low-solubility to immobilize (insolubilize) the metals over a wide
pH range. Unlike most other stabilization processes, soluble phosphate
processes do not convert the waste into a hardened, monolithic mass.
Rather, the waste remains free-flowing and increases little in volume. Pro-
cess chemistry is detailed in Chapter 3.0.
Soluble phosphates and lime have been used commercially to stabilize
fly ash. Expanding upon this proven data base, Wheelabrator Environmental
Systems developed the patented WES-PHix process for immobilizing lead
and cadmium in other ash residues and waste streams. This totally-enclosed,
in-line system has been permitted by several states. Because it is totally
enclosed, health or safety problems for workers are minimal. The resulting
product, which reduces lead and cadmium leaching below Toxic ity Charac-
teristic Leaching Procedure (TCLP) limits, is in paniculate form. Mix for-
mulations must be determined on a site-specific basis, but any convenient
source of water soluble phosphates may be used. Some guidance on chemi-
cal-waste ratios are provided in Chapter 3.0.
2.2 Potential Applications
Stabilization and solidification processes can be applied to a wide range
of wastes. Since all the processes depend upon chemical and physical reac-
tions of varying complexity between the wastes and the applied fixation
2.6
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Chapter 2
Tdble2.1
Potential Applications
Stabilization/
Solidification
Process
Kinds of Wastes
Sorbents and Oily wastes, industrial sludges and contaminated soils (containing inorganics
Surfactants with low concentrations of organics), acid mine leachate and tailings, and
radioactive liquid scintillation fluids
Emulsified Asphalt Contaminated foundry sands and sand-blasting grit; wastes from paint removal,
metal finishing, and electroplating; petroleum-contaminated soils
Soluble Phosphates Refuse-to-energy plant and medical wastes ash, insulation wastes, metals-
smelting dusts, contaminated soils, and metal-contaminated sludges
Bituminizalion Low- and medium-level radioactive waste solutions, and metal plating sludges
Electrical Process High-level radioactive wastes, municipal solid waste ash, medical wastes, and
Vitrification contaminated soils and sludges
In Situ Vitrification Soils or sludges contaminated with radioactive, metallic, or organic wastes;
particularly suited for large quantities of in-place or stock-piled soils or sludges
Thermal Vitrification Contaminated soils, incinerator fly ash, organic wastes, and nonvolatile metallic
wastes
Plasma Small, concentrated quantities of slurries and contaminated solid materials, such
Vitrification as, metals, glass, and filter elements
Modified Sulfur Predried paniculate wastes, such as, incinerator ash, contaminated soils, sludges.
Cement Process metals, and mill tailings
Polyethylene Primary and secondary waste streams produced by waste management and
Extrusion restoration activities, nitrate salt wastes, sludges, ion-exchange resins,
incinerator ash, and scrubber blow-down solution
Soluble Silicates (Specific process variation dependent) metal-containing wastes, auto shredder
(Patented Processes) fluff, incinerator-bottom ash, and contaminated debris
Soluble Silicates Metal-refining wastes, metal-finishing wastes, and metal-bearing sludges
(Slags)
Soluble Silicates Steel pickle liquor, ferric chloride etching waste, oil waste, hydrocarbon waste,
(Lime) incinerator ash, petroleum sludge, phosphoric acid residue, oily wastes, and tars
Soluble Silicates (Specific process variation dependent) metal-containing wastes, auto shredder
(Inorganic Polymers) fluff, incinerator-bottom ash, and contaminated debris
agents, care is required in order to select the most appropriate process or
system. Table 2.1 lists the most common kinds of wastes to which each
process described in this monograph is applicable.
2.7
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Process Summary
2.3 Process Evaluation
Available performance and cost data for each of the stabilization/solidifi-
cation processes examined in this monograph are compiled and summarized
in Chapter 3.0. These processes depend upon physical and chemical reac-
tions of varying complexity between the wastes and the fixation agents.
Accordingly, performance data provided are limited, for the most part, to
those combinations that have achieved the greatest success.
2.3.1 Sorption and Surfactant Processes
Sorption and surfactant processes have evolved from bench-scale to full-
scale implementation. When the various binders are correctly matched with
waste materials, these processes appear to be able to immobilize many or-
ganic constituents present at low concentrations, at least temporarily. Gen-
erally, inorganic solids (such as pozzolanic material) are weak sorbents for
organic materials. Quaternary ammonium compounds that are added to
clays have been extensively studied for sorbing organics. Available cost
data are site-specific and generally do not permit cost comparison of ven-
dors.
2.3.2 Emulsified Asphalt
The emulsified asphalt process has proven to be effective in solidifying
liquid wastes, reducing solidified waste permeability, and improving the
effectiveness of stabilization/solidification processes using portland cement
and soluble silicates. The cost to treat wastes using this process generally
ranges from $90 to $110/tonne ($80 to $100/ton), but can be as high as
$165/tonne ($150/ton).
2.3.3 Bituminization
Bituminization has proven to be effective in treating low-level radioac-
tive wastes. While radionuclides are effectively controlled, there are no data
for heavy metals or organics.
2.3.4 Vitrification
Each of the vitrification processes reported has been extensively studied.
Generally, all vitrification processes are very effective in treating radwastes,
2.8
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Chapter 2
heavy metals, and in many cases organics, with total destruction and re-
moval efficiencies ranging from 99.99% to 99.99999% (seven nines). Some
metals are volatilized and must be captured with offgas treatment systems.
2.3.5 Modified Sulfur Cement Process
The majority of application studies of the modified sulfur cement process
have focused on incinerator fly ash. Modified sulfur cement alone is a rela-
tively brittle material, but in combination with wastes (values are not highly
dependent on waste loading), its compressive strength is more than doubled.
To meet TCLP criteria, modified sulfur cement may be augmented (sodium
sulfide has proven effective in a mix containing, by weight, 40% waste,
53% modified sulfur cement, and 7% sodium sulfide).
2.3.6 Polyethylene Extrusion Process
Polyethylene waste forms containing various radioactive and hazardous
wastes have been extensively tested. Most of these tests were conducted
with sodium nitrate waste and proved the process can produce a product
that is nonhazardous by all applicable criteria. Polyethylene encapsulation
offers potentially significant cost savings over cement-based encapsulation
when all relevant cost factors are considered.
2.3.7 Inorganic, Cementitious Technologies of the Siliceous
Category
With the exception of geopolymers, these processes are well-established
and employ a range of commercially-available reagents. They have proven
their ability to eliminate the hazardous characteristics of most wastes. How-
ever, it is important to match the particular process to the waste stream. The
cost effectiveness of most of these processes depend entirely upon the re-
agent employed and its availability at a particular site, although a royalty
may be exacted for some of the patented processes, such as Lopat or
EnviroGuard™.
Inorganic geopolymers have not been used commercially for the stabili-
zation of wastes, but reportedly have been used in Europe and Canada for
construction purposes. Tests on various waste streams have established the
effectiveness of such polymers to eliminating hazardous characteristics.
However, geopolymerization takes a relatively long period, up to 21 days.
2.9
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Process Summary
2.3.8 Soluble Phosphates
Evaluation of the WES-PHix process has shown it to be far more effec-
tive than portland cement treatment for control of zinc, copper, cromium,
and lead and similar in performance for control of cadmium. Soluble phos-
phates reduced lead in leachates by a factor of 6 in bottom ash and by a
factor of 900 in leachates from air pollution control residues compared with
treatment by portland cement alone.
2.4 Limitations
While the eight general categories of stabilization/solidification pro-
cesses, and their variations, are distinct in many regards, most have remark-
ably similar limitations. Following is a summary of limitations:
• waste composition - each of the processes is tailored to one
particular kind of waste or to a family of wastes, there is not one
best process for all waste types;
• reagent availability - the cost-effectiveness of those processes
that employ reagents is substantially affected by reagent avail-
ability at the site;
• moisture content - for some processes, there can be too much
moisture in the waste for the process to perform as intended or
to be cost-effective. For others, there can be too little moisture;
and,
• risk of release - for almost all processes, except vitrification,
there remains the risk, to varying degrees, that the stabilized/
solidified waste matrix will break down over time, leading to
release of harmful constituents into the environment.
2.5 Technology Prognosis
Each of the processes have proven their suitability for at least one kind of
waste. Additional research will enable application of each to be expanded to
2.10
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Chapter 2
other wastes. Some of the more promising areas of development or key
information requirements of each process are summarized, below:
• Sorption/Surfactant - development of additional natural or syn-
thetic binders; also needed is information on saturation limits
and the degree of sorption or degradation under realistic disposal
conditions;
• Emulsified Asphalt - development to apply to wastes containing
metals and nonpetroleum organics;
• Bituminization - development of more durable waste/bitumen
mixtures;
• Vitrification - refinement of the technology to spread applica-
tion beyond contaminated soil applications, and improve process
efficiency (e.g., process rate, cost, energy utilization);
• Modified Sulfur Cement - determination of optimum waste
loadings and application to sludges and contaminated soils;
• Polyethylene Extrusion - full-scale demonstration of process
reliability and determination of maximum heavy metals load-
ings;
• Soluble Silicates - more information is needed on each of the
various technologies involved to broaden their application and/
or enhance their performance and reliability; and
• Soluble Phosphates - development to apply to metals-bearing
wastes.
2.11
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Chapter 3
PROCESS IDENTIFICATION AND
DESCRIPTION
3.1 Sorption and Surfactant Processes
3.1.1 Description
Sorption processes are based on a contaminant being attracted to and
retained on a sorbent. Various attraction forces act to partition the contami-
nant out of the aqueous phase and onto the surface of the sorbent. The in-
teraction forces are of various degrees, such as hydrogen bonding, ion
exchange reactions, and may include van der Waals or electrostatic forces.
Surfactants are manufactured so as to have different chemical compat-
ibilities on each end of the molecule. In simple terms, this configuration
allows organic waste material to be sorbed on one end, while the other end
is compatible with water mixed with the inorganic cement.
3.1.2 Scientific Basis
In general, hydrophobic organic material is not compatible with cement.
Therefore, added organic sorbents can combine with organic waste material
before being solidified in cement. For example, quaternary ammonium
ions (R4N+) can be substituted for group IA and IIA metal ions (Li+, Na+,
K+, Mg2+, Ca2+, and Ba2+) yielding clays that have both organic and inor-
ganic reactive properties, enabling the clay to also sorb organic compounds.
These substitutions sterically increase interplanar distance (allowing com-
pound insertion) and create an organic stationary phase with polarity com-
patible with the organic waste. Chemical interactions that range in strength .
3.1
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Process Identification and Description
retain the organic compound near the clay surface. Cement is added for
solidification to reduce available surface area accessible to leaching.
With the use of a surfactant to lower surface tension, organic waste mate-
rial can be dispersed with water in which the continuous phase is aqueous.
This suspension can then be mixed with cement for solidification.
3.1.3 Status and Development
There are several patents registered covering a variety of processes.
Some of them cover a combination of sorbent additives or the use of surfac-
tants for dispersion.
Listed below are some of the commercial vendors who have provided
field-scale services:
• Silicate Technology Corporation (STC);
• International Waste Technologies (IWT);
• Hazcon;
• Soliditech; and
• Wastech.
Stabilization/solidification data relating to some of these vendors' pro-
cesses are provided in Section 4.1.
3.1.4 Pretreotment Requirements
For some processes, pretreatment would include mixing the contaminant
and sorbent before adding cement. As an example, surfactants are first
utilized to emulsify organic waste and then this dispersion is mixed with
cement.
3.1.5 Health and Safety Considerations
Volatile organic compounds that are not instantaneously sorbed might be
released during a mixing operation because of the exothermic cement/water
reaction and increased surface area exposure. Since stabilized organic ma-
terial is normally disposed of in the soil, there will always remain a threat to
groundwater because of possible contaminant diffusion from the: treated
matrix.
3.2
-------
Chapter 3
Some sorbents, such as quaternary ammonium compounds, may have
detrimental environmental effects if released into surface water.
3.1.6 Operational Considerations
The amount of sorption chemicals that is used to stabilize a waste, plus
the amount of cement needed to solidify a waste, compared to the waste
amount is normally referred to as a binder-to-waste ratio. Contaminant
sorption is a function of several factors, such as pH, concentration of con-
taminants, selectivity of sorbent surface, and kind of aqueous disposal envi-
ronment. Bench-scale column release testing is useful in determining the
amount of sorbent needed.
Processing capacity is largely dependent on the time required to get ad-
equate mixing of the sorbent, waste, and cement.
Among the more important operating parameters is the degree of mixing
between the contaminant and sorbent and between the sorbent and cement.
Employing an additional reagent that is natural to a cement-based pro-
cess should increase cost very little relative to cement alone because the
materials are generally available at low cost. Furthermore, sorption may reduce
the amount of cement necessary to minimize leaching. Synthetic compounds,
however, such as quaternary ammonium compounds, are relatively expensive
compared with other natural sorbents, such as sawdust, humic materials, etc.
The designer of an organic sorbent stabilization process must know the
degree of interaction between the contaminants and sorbent under the con-
ditions existing at the time of stabilization/ solidification.
There is practically an unlimited number of variations of sorption pro-
cesses, since each vendor can use more than one sorbent or combination of
sorbents, with or without a surfactant.
3.2 Emulsified Asphalt
3.2.1 Description
Asphalt-based solidification processes have been investigated since the
1950s for encapsulation of nuclear wastes. Little research was done until
3.3
-------
Process Identification and Description
recently, however, on use of asphalt for treatment of hazardous wastes or
contaminated soils.
One promising technology for fixation of hazardous wastes ami contami-
nated soils is based on the use of emulsified asphalt. Asphalt emulsions are
intimate mixtures of asphalt and water. Very fine droplets of asphalt are
dispersed in water to create emulsions. Chemical emulsifying agents, such
as detergents, are then added to make the product stable. They form a pro-
tective film around the emulsified asphalt droplets and carry an electric
charge that causes the droplets to repel one another.
This process operates at ambient temperature, thereby eliminating the
problems associated with hot asphalt mix processes, namely, volatilization
of contaminants and high energy costs. Hydrophilic liquid and semi-liquid
wastes can be treated with emulsified asphalt and, possibly, with other so-
lidification additives, rendering the wastes hydrophobic and impermeable to
water. The process can be used with high-solids wastes, such as sludges,
with contaminated soils, or with contaminated liquids.
3.2.2 Scientific Basis
In emulsified asphalt processes, the waste is mixed with the suspension
of emulsified asphalt particles at ambient temperature in an amount suffi-
cient to react with counter-ions in the waste and coalesce into a hydropho-
bic mass. After mixing, the mixture will destabilize chemically, causing the
asphalt emulsions to "break" and solidify. The water in the waste is re-
leased, forming a biphasic mixture. The organic phase forms a continuous
matrix of hydrophobic asphalt around the waste solids (Conner 1990). The
released water may need further treatment.
The mixture is then allowed sufficient time to set and cure. The resultant
end product is a solid material varying in consistency from a rock-like solid
to a friable material. Addition of the emulsified asphalt to the waste mate-
rial increases the hydrophobicity and decreases the water permeability of
the end product. Thus, the asphalt-treated waste material is no longer ac-
cessible to water-based leachates, and the end product is highly stable and
substantially impervious to aqueous leaching of waste constituents.
3.4
-------
Chapter 3
3.2.3 Information Necessary to Employ Process
The ionic charge of the waste counter-ions is determined empirically by
adding cationic and anionic asphalt emulsions to small samples of waste
and observing which mixtures coalesce. Alternatively, the charge on waste
particles can be determined by using an electrokinetic zeta potential mea-
suring device such as a "Zeta Meter." An appropriate suspension of emulsi-
fied asphalt particles having an opposite particle charge to the ionic charge
of the waste contaminant is then selected.
3.2.4 Operational Considerations
Emulsified asphalt is commercially available either as a cationic or an
anionic emulsion. The asphalt is added to the waste in quantities ranging
from 0.1% to about 40% by weight. After mixing the asphalt emulsion with
the waste material, solidification is promoted by neutralizing the surface
charge on the emulsified asphalt particles with the waste counter-ions. This
reduces the charge repulsion between particles and allows the particles to
coalesce into a hydrophobic mass, leaving higher quality water behind. In
some cases, it may be necessary to add additional neutralizing agents, such
as lime (Ca2+) for neutralizing anionic asphalt emulsions or gypsum (SO42~)
for neutralization of cationic ones. The resulting solid asphalt contains the
waste material uniformly distributed throughout it. The hydrophobic prop-
erties cause it to have very low permeability to water.
3.3 Bituminization
3.3.1 Description
Bitumen, or asphalt, is a relatively leach-resistant, thermoplastic sub-
stance. Contaminated residues can be embedded in molten bitumen which,
when it cools, encapsulates the residues. Heated bitumen is extruded from a
storage tank at approximately 10 to 50 L/hr (2.6 to 13 gal/hr) into an ex-
truder. Simultaneously, the concentrate of contaminated material, usually
in slurry form, is pumped into the extruder. Processing rates as high as 300
kg/hr (660 Ib/hr) are available. Screws inside the extruder mix the material
until it is conveyed to a discharge pipe. Water is evaporated from the mix-
3.5
-------
Process Identification and Description
ture until the residual moisture content is about 0.5% by weight (Simon and
Botzem 1984). The final product, a homogeneous mixture of extruded
solids and bitumen, is then discharged from the extruder into a 55-gallon drum.
The process achieves a volume reduction for slurry materials of about
60%. Generally 1 m3 (1.3 yd3) of concentrated slurry, when mixed with
bitumen, can be converted to about 0.4 m3 (0.5 yd3) of final product. This
value is highly dependent, however, on the kind of waste. Westsik (1984)
reported volume changes, varying with waste stream characteristics; vol-
ume reductions of 2.4:1 of waste:bitumen product were achieved, i.e., the
volume of original waste slurry before treatment was 2.4 times the volume
of the final bitumen product. But in some cases, volume increases of 0.5:1
resulted.
3.3.2 Operational Considerations
Processing rates as high as 300 kg/hr (660 Ib/hr) can be achieved at exist-
ing process scale (Simon and Botzem 1984). The amount of electrical
power required to maintain temperature within the extruder is approxi-
mately 20 kw. A bituminization extruder of this capacity is approximately
6 m (20 ft) in length by 1.5 m (5 ft) in width by 2 m (7 ft) in height. The
overall dimensions of the bituminization plant would be approximately 15
m (50 ft) by 10 m (33 ft) by 4 m (13 ft). Figure 3.1 (on page 3.7) provides a
schematic of a typical bituminization plant.
3.4 Vitrification
3.4.1 Description
Vitrification is a class of thermal treatment processes that convert waste
materials into a glass or glass and crystalline product. Waste materials,
such as heavy metals or radionuclides, are not simply encapsulated, but are
actually incorporated in their oxide form into the structure of the glass prod-
uct. Metallic components that may coexist with the waste materials sepa-
rate into a different phase that can be tapped separately in many vitrification
processes. This process results in a relatively strong and durable material
that is capable of lasting for thousands of years.
3.6
-------
Chapter 3
o
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3.7
-------
Process Identification and Description
3.4.2 Scientific Basis
Vitrification products are commonly composed of oxides that can be
classified into one of three primary groups: (1) glass formers, (2) stabiliz-
ers, and (3) fluxes (Tooley 1974).
For most glasses, the principal glass-former constituent is silicai (SiO2)
(US EPA 1992b). Glass formers provide the basic silicon-oxygen tetrahe-
dron matrix of vitrified products. Other glass formers such as phosphates
and borates exist, but waste remediation technologies are generally limited
to silicate and borosilicate glasses.
Fluxes reduce the melting temperature and viscosity of the oxides within
the glass matrix, as well as increase the electrical conductivity of glasses
when molten. Therefore, fluxes become important to the processibility of
the vitrified product, especially for electrically heated vitrification pro-
cesses. The primary flux constituent is sodium oxide (Na2O), but the flux
can also contain potassium oxide (K^O), lithium oxide, and other alkaline
oxide chemicals. Fluxes can be added in more common chemical forms,
such as soda ash (Na2CO3), and be allowed to decompose to their oxide
form during processing. They can also be added in chemical forms that
include glass formers, such as sodium silicate (Na2SiO3).
Stabilizers are most responsible for increasing the durability and decreas-
ing the electrical conductivity of molten glasses. The primary constituents
of stabilizers are calcium oxides (CaO) and other alkaline earth oxides.
Alumina (A12O3) can also act as a modifier. Stanek (1977) shows the rela-
tive impact of stabilizers on electrical conductivity in relation to other con-
stituents. The relative influence is shown in table 3.1 (on page 3.9).
When heated, the constituents decompose to their oxide form, fuse, and
melt together to form a glass matrix. For example, in a simple system, the
fusion of SiO2 and Na2CO3 occurs when Na2CO, decomposes to form Na2O
and CO2, and Na2O fluxes with SiO2 to form a melt at less than the melting
temperature of SiO2. The sodium interferes with some of the silicon-oxy-
gen-silicon bonds, thus disrupting the polymerization of units of tetrahedral
structure of SiO2 and reducing the melting temperature and viscosity of the
mixture. Similarly, the addition of a stabilizer, such as CaO, can lower the
melting point, yet maintain the durability of the glass (US EPA 1992b).
In most vitrification processes, the glass product can be designed with
specific compositions in order to obtain specific physical and chemical
3.8
-------
Chapter 3
.1
Influence of Constituents on Electrical Conductivity
Greatly Decrease CaO
Slightly Decreased BO
Neutral
Slightly Increased
Greatly Increased
Extremely Increased
Bad
Note: Degree of influence of individual oxides on the electrical conductivity of glass, CaO effecting the most
significant reduction and Na2O, the most significant increase.
(Stanek 1977)
properties. Waste constituents, such as lead or chromium, also enter into
the formation of the glass product. These constituents can act as glass
formers, replacing silica in the structure or acting as stabilizers and fluxes
and interfering with the bonds of silicon and oxygen ions. Consequently,
the waste constituents become part of the glass, making them more resistant
to chemical attack than if they were merely encapsulated within the glass.
The high temperature of the vitrification process also destroys organic
constituents. Most vitrification processes operate at 1,200°C (2,200°F) or
higher, a temperature capable of destroying any organic contaminant. The
organic contaminants decompose into carbon dioxide (CO2), water (H2O),
and hydrogen chloride (HC1) when interacted with oxygen as the gases exit
the vitrification process.
3.4.3 Technology Variations
There are three basic variations in the technology of vitrification pro-
cesses - electrical, thermal, and plasma.
3.9
-------
Process Identification and Description
3.4.3.1 Electrical Processes
Many vitrification processes operate on the principle of joule heating.
Joule heating is the mechanism by which electrical energy is imparted to the
glass to generate heat. Normally, glasses are not electrically conductive,
but when in the molten state, the alkaline elements within the glass ionize
and become mobile, allowing them to transmit an electrical charge. This
electrical charge is usually transmitted in a 60 Hz alternating current. An
electrical voltage is applied to electrodes at either end of the melting cavity.
The joule heating effect causes the alternating current to flow between the
electrodes, thereby generating the heat necessary for continued melting of
material to be vitrified.
As more heat is generated within the molten pool, the molten glass be-
comes less viscous and more electrically conductive. Convective currents
within the molten pool keep the material well mixed. It is this combined
effect of convective flow and joule heating that makes the electrical melting
process so effective.
Electrical processes generally operate at electrical voltages from approxi-
mately 100 volts up to thousands of volts. Consequently, operational proce-
dures and engineering safety features must be designed to avoid the
potential for electrical shock to the operators.
Electrical processes have a distinct advantage in terms of gaseous efflu-
ent generation. Because no fossil fuel is required to generate the heat, the
gases that are generated are limited primarily to water vapor, from the dry-
ing of the waste materials, and decomposition gases, such as CO2, that form
during the vitrification process. Residues from combustion of fossil fuel or
organic contaminants within the waste may also contain gas-forming salt,
Cl, as well as calcium salts from acid-gas scrubbing systems and absorbed
volatile metals. These gases must be collected and sent to an offgas treat-
ment system consisting of wet scrubbers and filters. An induced draft
blower system connected at the tail end of the offgas treatment system
keeps the operating pressure of the vitrification process slightly negative
with respect to atmospheric pressure. Therefore, any gaseous leaks during
processing will be inward, providing greater assurance of protection to
workers and the public during operation.
There are two types of electrical vitrification processes - refractory-lined
melters and in situ vitrification (ISV).
3.10
-------
Chapter 3
Refractory-Lined Melters. In refractory-lined melters, the molten glass
cavity, which processes the waste, is contained within a high temperature
ceramic refractory. Waste constituents, which can be slurries, wet or dry
solids, or combustible material, are first mixed with glass formers and then
conveyed onto the surface of the molten glass. Offgases due to evaporation
of water, chemical decomposition, paniculate entrainment, and combustion
are scrubbed and/or filtered before being released to the atmosphere. The
electrodes, which are commonly flat plates placed at either end of the melt-
ing cavity, or as with electric arc furnaces large diameter rods, keep the
glass pool molten as feed material is introduced to the surface of the melt.
The electrodes are usually composed of a nickel/chromium alloy, but can
also consist of graphite or molybdenum rods. Glass formed during the vitri-
fication process can be withdrawn continuously or through an overflow
weir into the receiving canisters, drums, or glass quenching systems.
When combustible materials are present, additional oxygen or air is in-
troduced into the cavity of the open pool. The feed rate and melter design
can be adjusted to control the residence time for efficient destruction of the
organic contaminants.
Different electric melter designs, primarily the horizontal melter and the
vertical melter, are available. A horizontal glass melter is a relatively long
and shallow chamber. Waste is introduced with the glass formers at one
end of the chamber and the offgases and glass product are removed at the
other. This type of melter is designed to provide long residence time for
destruction of combustible gaseous effluents. The vertical glass melter has
a pooled molten glass chamber that is roughly equal in length and width.
The waste is introduced near the center of the melt.
When waste constituents are vitrified, there is generally a volume reduc-
tion due to the consolidation and densification of the material. For contami-
nated materials that do not require a great deal of additional glass formers,
the volume reduction is generally in the range of 10 to 30%. In the case of
dry combuster ash residue from municipal wastes, the volume reduction
approaches 80%.
Because heat is distributed within the glass melt, electric glass melters
provide the advantage of being able to be scaled to support the design pro-
cess rate. When fed liquids and slurries, vertical glass melters have been
demonstrated at rates of 30 to 100 L/hr/m2 (0.7 to 2.5 gal/hr/ft2) of top sur-
face area (Freeman 1988). The solid material processing rate is 80 to 120
3.11
-------
Process Identification and Description
kg/hr/m2 (16 to 24 lb/hr/ft2) (US EPA 1992b). Therefore, a vertical melter
capable of processing 220 kg/hr (480 Ib/hr) would have to have internal
dimensions roughly 1.4 m (4.5 ft) on a side. Similarly, a horizontal melter
1.2 m (4 ft) wide by 7 m (23 ft) long is sufficient to process dry solids at a
rate of 220 kg/hr (480 Ib/hr) (Freeman 1988). A 2.7 m (8.9 ft) by 1.2 m (3.9
ft) deep, water-cooled electric melter can accommodate a processing rate of
3,600 kg/hr (7,940 Ib/hr) for dry municipal waste incinerator ash.
Operational costs for an electric heated glass melter have been estimated
by Chapman (1991) at $0.06/kg ($53/ton) of dry municipal incinerator ash,
a nonhazardous waste. This estimate is based on a 55 tonne/day (50 ton/
day) melter. This process is quite inexpensive because of reduced energy
requirements; residual carbon present in the ash acts as a supplemental heat
source upon combustion. The estimate takes into account the advantage of
other ongoing operations also, such as offgas treatment associated with the
incinerator. Operational costs for electric, refractory-lined melters are
highly dependent on the kind of waste being vitrified. For example, the
Bureau of Mines estimates costs at $130 to $225/dry tonne ($115 to $205/
dry ton) of nonradioactive, solid waste material. Freeman (1988) estimated the
cost of treating low-level nuclear waste in the range of $0.63 to $1.92/kg
($0.29 to $0.87/lb) of wastes, and Ross and Kindle (1992) estimated the
costs for mixed radioactive waste treatment to be $l,600/m3 ($l,200/yd3).
For chemical hazardous wastes, these costs would probably be drastically
reduced because there would be no need for remote operation features as
there is when vitrifying nuclear waste material. Koegler et al. (1989) esti-
mated the total cost of vitrification of hazardous waste refractory-lined
melters to be $770/tonne ($700/ton), including offgas treatment by wet
scrubbing and filtration.
In Situ Vitrification (ISV). In processes employing refractory-lined
melters, wastes are fed to a molten pool within a refractory-lined cavity;
ISV, treating contaminated soils and sludges in place, eliminates the need
for refractory lining. In situ vitrification is a batch process, whereas those
using refractory-lined melters are continuously-fed processes. To begin the
process, four graphite electrode rods are inserted vertically a few centime-
ters into the surface of the soil. A mixture of ground glass frit and graphite
flakes is laid in an "X" pattern among the four electrodes. Voltage applied
to the electrodes initiates an electrical current within the starter path that
heats the surrounding soil and causes it to melt. Once molten, the soil be-
gins to conduct electrical current and the graphite is consumed by oxidation.
3.12
-------
Chapter 3
The molten soil grows outward and downward until the desired vitrification
depth is obtained (Buelt et al. 1987). Figure 3.2 illustrates the process.
The processing rate for ISV is generally 2.7 to 4.5 tonne/hr (3 to 5 ton/
hr), and the process is capable of producing blocks up to a 910 tonne (1,000
ton) per batch setting. The blocks can measure up to 12 m (39 ft) on each
side. For larger sites, multiple settings would be used, and the blocks would
be fused together.
The maximum demonstrated depth of the process has been 6 m (19 ft),
but with enhanced depth techniques currently under development, the pro-
jected depth is greater than 10 m (33 ft). The depth, however, can be lim-
ited by the presence of heterogeneous conditions, such as layers of rock or
higher melting soil compositions, or high groundwater tables.
As with the refractory-lined melters, the projected volume reduction is
about 30%; that is, the vitrified volume is 70% of the initial volume of the
soil. The subsidence void that is evident on the surface after processing is
simply backfilled with clean soil to restore the site to its original surface
level. The volume reduction for sludges of high combustibility and/or high
Figure 3.2
In Situ Vitrification
During in situ vitrification, the soil melts from the surface to the desired depth, producing a strong, high-integrity residual
that can safely withstand long-term environmental exposure.
3.13
-------
Process Identification and Description
moisture content can be much greater. A volume reduction of more than
3:1 (70%) has been demonstrated with sludges containing 55% water by
weight (Buelt and Freim 1986). When contaminated soils extend into a
permeable aquifer, however, the recharge of moisture to the vicinity of the
melt can prevent melting into the saturated zone. It is projected that
permeabilities greater than 10"5 cm/sec will impede the progress of the melt
into a saturated zone (Buelt et al. 1987).
The ISV technology is presently commercially available for use on con-
taminated soils of virtually all types. The estimated costs of vitrifying con-
taminated soils when translated into 1992 dollars, is approximately $385 to
$495/tonne ($350 to $450/ton) of material, which includes offgas treatment,
energy, labor, materials, and an amortized amount for capital equipment
and equipment mobilization (Buelt et al. 1987).
3.4.3.2 Thermal Vitrification
Unlike electrical vitrification, thermal vitrification uses an external heat
source, such as fossil fuel combustion, to melt the material. The heat is
then transferred by convective and radiative heat transfer to the mixture of
waste constituents, glass formers, and fluxes. Although other types of ther-
mal vitrification exist, such as the cyclone furnace (US EPA 1991), the
primary technique for thermal vitrification is the rotary kiln incinerator (US
EPA 1992b). The rotary kiln is a cylindrical, refractory-lined shell that is
mounted at an incline and rotated slowly to drive the materials through the
incinerator. The rotation also helps improve heat transfer and facilitates
mixing of the materials during the vitrification process. Waste materials
and fuel are injected at the upper end of the rotary kiln. Combustible mate-
rials are oxidized within the combustion chamber. The vitrified ash is with-
drawn from the lower end of the kiln. A typical rotary kiln is operated at
150 tonne/day (165 ton/day) at temperatures of about 1,200°C (2,200°F)
(US EPA 1992b). Rotary kilns with production rates on this order are gen-
erally 60 to 90 m (200 to 300 ft) in length.
The cyclone furnace is emerging as a vitrification process for hazardous
wastes from well-established coal-burning technology (Batdorf, Gillins, and
Anderson 1992). In this process, pulverized solid waste (less than 6 mm
(0.24 in.)), such as soil, is introduced with fossil fuel in a cyclic chamber.
The molten slag that is formed is collected on the walls of the furnace and is
then tapped through a slag spout. Cyclone furnace designs generally
3.14
-------
Chapter 3
quench the molten slag in water, which must then be subsequently treated
periodically. The organic components associated with the feed material,
besides adding to the heating value to support the combustion process, are
destroyed in the one, or as in some designs, two stages in primary and sec-
ondary chambers.
Information on operating costs of thermal vitrifiers is not documented in
available sources.
3.4.3.3 Plasma Vitrification
Plasma systems can be used to incinerate and vitrify contaminated mate-
rials by passing them through a plasma arc or torch that creates extremely
high temperatures for destruction of liquid and solid waste. The high tem-
peratures in the plasma are created by an electrical discharge through a gas.
The resulting plasma destroys the waste through radiant heat transfer. As
with other vitrification processes, the offgas is passed through a treatment
system that can consist of a caustic scrubber to remove acid gases and ash
components, followed by filters. Typical plasma torches and arc melters
have power requirements of about 600 kw, although larger systems with
high-production rates are emerging rapidly (Donaldson, Carpenedo, and
Anderson 1992). This translates to production rates ranging from 4 to 19
kg/min (9 to 42 Ib/min) or up to approximately 0.45 tonne/hr (0.5 ton/hr)
(Pacific Northwest Laboratory 1991).
Basically, two types of plasma vitrification processes are available,
plasma torch, in which waste is passed through two water-cooled, generally
copper electrodes, and plasma arc, in which an electrical arc is passed in the
near vicinity or in contact with a molten slag. One example for the plasma
torch process is the plasma centrifugal furnace (US EPA 1991). Contami-
nated soils enter a sealed, rotating furnace. The centrifugal forces cause the
soils to cling to the sides of the furnace, exposing them to the plasma arc.
Organic contaminants are destroyed at 1,300°C (2,400°F) and the molten
soil at up to 1,600°C (2,900°F). The soil is periodically removed (tapped)
and allowed to cool in the slag chamber. One example of the plasma arc
process is the graphite electrode DC arc furnace (Surma et al. 1993). This
furnace shown in figure 3.3 (on page 3.16), is composed of an insulated
graphite pot, which contains the molten slag, and a hollow graphite elec-
trode above the surface of the molten slag. Offgases are drawn through the
hollow electrode, thus exposing them to maximum temperatures to maxi-
3.15
-------
Process Identification and Description
Figure 3.3
Pilot-Scale, Graphite-Electrode DC Arc Furnace
Electrode housing
Isolation
slide gates
Glass discharge
section
Glass waste
canister
mize organic destruction efficiency. The electrical arc can be established in
the nontransferred mode, in which the electrical arc is created just above the
molten material being treated, or the transferred mode, which establishes
the arc between the electrode and the molten slag itself. The former operat-
ing mode assists in startup of the process, while the latter is used to improve
operating efficiency.
In comparison with thermal vitrification systems that require fossil fuels
for heat generation, the plasma system accomplishes heat transfer much
faster because of the low gas-flow requirements and extremely high tem-
3.16
-------
Chapter 3
peratures of up to 5,500"C (10,000°F) (US EPA 1992b). The plasma pro-
cess allows vitrification to take place in a relatively small piece of equip-
ment. For example, a transportable pilot-scale system designed for
destruction of liquid wastes has been housed in a 14 m (45 ft) trailer.
No operational cost information is available for plasma vitrification sys-
tems in any of the sources cited in the List of References, Appendix A.
3.5 Modified Sulfur Cement Process
3.5.1 Description
Modified sulfur cement was developed by the United States Bureau of
Mines in 1972 as a means of utilizing waste sulfur from flue gas and petro-
leum distillation processes. Previous attempts to use elemental sulfur as a
construction material in the chemical industry (Raymont 1978) failed be-
cause of internal stresses set up by changes in crystalline structure during
cooling. By reacting elemental sulfur with hydrocarbon polymers, the Bu-
reau of Mines developed a product that successfully suppresses the solid
phase transformation, and thus dramatically improves stability of the mate-
rial. A Bureau of Mines formulation that is licensed commercially (Martin
Resources, Inc., Odessa, Texas) was used for this work. The formulation
contains a total of 5% by weight modifiers consisting of equal amounts
dicyclopentadiene (DCPD) and cyclopentadiene (CPD) that react with the
sulfur to form long chain polymers (Sullivan and McBee 1976). It has a
melting point of 119°C (246°F) and a viscosity of approximately 25
centipoise (cp) at 135°C (275°F).
Modified sulfur cement is a thermoplastic material that can be easily
melted, combined with waste components in a homogeneous mixture, and
cooled to form a solid, monolithic waste form. Compared with hydraulic
cements, sulfur cement has several advantages. For example, no chemical
reactions are required for solidification, eliminating the possibility that
elements in the waste can interfere with setting and thereby limit the range
of waste materials that can be successfully encapsulated. Sulfur concrete
compressive and tensile strengths twice those of comparable portland con-
cretes have been achieved, and full strength is attained in several hours
3.17
-------
Process Identification and Description
rather than weeks (Sulfur Institute 1979). Sulfur concretes are resistant to
attack by most acids and salts, e.g., sulfates that can severely degrade hy-
draulic cement, and have little or no effect on the integrity of sulfur cement
(McBee, Sullivan, and Jong 1985).
3.5.2 Operational Considerations
The first application of modified sulfur cement to the solidification of
radioactive and mixed wastes was performed at Brookhaven National Labo-
ratory (Colombo, Kalb, and Fuhrmann 1983). Processing of modified sul-
fur cement and wastes to form a solid, monolithic form requires (1) heating
of the components until the binder has completely melted, (2) mix ing the
constituents into a homogeneous molten slurry, and (3) pouring the mixture
into suitable containers for storage and disposal. These relatively simple
processing requirements can be met by a number of different techniques,
including double planetary mixers, in-drum mixers, pug mills, and in gen-
eral, the same type of equipment used to make hot asphalt mixes.
3.5.3 Health and Safety Considerations
When sulfur cement materials are produced in the recommended mixing
temperature range of 127° to 149°C (260° to 300°F), gaseous emissions of
sulfur dioxide and hydrogen sulfide will not exceed the allowable threshold
limit values and sulfur vapor emissions will be minimized. The threshold
values established for sulfur dioxide are 5 ppm for a short-term exposure
and 2 ppm (time-weighed average concentration) for an 8 hr exposure. The
corresponding values for hydrogen sulfide are 15 and 10 ppm (McBee,
Sullivan, and Fike 1985).
3.6 Polyethylene Extrusion Process
3.6.1 Description
A polyethylene extrusion process for treatment of radioactive, chemical
hazardous, and mixed wastes has been developed at Brookhaven National
Laboratory. The extrusion process for the encapsulation of wastes in poly-
3.18
-------
Chapter 3
ethylene involves the heating, mixing, and extruding of materials in one
basic operation. To more clearly understand this process, it may be broken
down into the following steps (Kalb and Colombo 1984):
• The polyethylene binder and predried waste materials are trans-
ferred from either a single hopper or individual hoppers in which
they are stored to the extruder feed throat. Metering of waste-to-
binder ratios is accomplished at this step;
• The mixture is conveyed through a heated cylinder by the mo-
tion of the rotating screw. The initial portion of the cylinder is
controlled at a temperature below the polyethylene melting point
(120°C (250°F)). This serves to gradually preheat the materials,
but, at the same time, assure proper transport of the mixture;
• As the waste-binder mixture moves forward past the initial pre-
heating zone, it is masticated under pressure due to the compres-
sive effects of a gradual reduction in the channel area between
the screw and cylinder. Screw rotation also assists in the mixing
of the materials to a homogenous state;
• The gradual transfer of thermal energy by the combined effects
of the barrel heaters and frictional heat serves to melt the mix-
ture. The fractional heat input is difficult to control and must be
compensated for by the regulation of the resistance band heaters.
In some cases, it is necessary to remove excessive heat by use of
external blowers or coolers; and
• The melted mixture is forced through an output die into a mold
where it is allowed to cool and solidify.
An extruder consists of four basic components, as depicted in the simpli-
fied schematic diagram in figure 3.4 (on page 3.20). These are (1) a feed
hopper, (2) a rotating auger-like screw, (3) a heated cylinder in which the
screw rotates, and (4) an output die assembly to shape the final product.
3.6.1.1 Polyethylene
Polyediylene is a thermoplastic, organic polymer of paracrystalline struc-
ture formed through the polymerization of ethylene gas. Thermoplastic
polymers consist of branched or linear polymer chains that normally are not
cross-linked. At elevated temperature, thermoplastic polymers change from
3.19
-------
Process Identification and Description
a hard material to a rubbery, flowable liquid. On cooling, the polymers
revert to their original form.
Polyethylene has been commercially produced in the United States for
over 45 years and is the most widely used of all polymers. Current produc-
tion capacity for the ten domestic producers of low density polyethylene
(LDPE) is about 3 x 108 kg/yr (7 x 10" Ib/yr). The market price for LDPE is
approximately $0.84/kg ($0.38Ab) (Theis 1989).
Mechanical and physical properties of LDPE are listed in table 3.2 (on
page 3.21), along with the test methods used to determine them. These data
provide an overview of the strength and durability of this material and back-
ground information concerning potential performance for encapsulation of
various kinds of waste.
Figure 3.4
Sectional View of a Simplified Screw Extruder
KEY
1. Feed material
2. Feed hopper
3. Heating unit
4. Mechanical screw
5. Strainer
6. Extruded product
7. Die
The sketch depicts flow of material from the hopper to the output die, where it is extruded in a molten state'.
3.20
-------
Chapter 3
toble3.2
Properties of Low Density Polyethylene(a)
Property
Brittleness temperature, *C
Burning rale
Crystalline melting point, *C
Deflection temperature, at 66 psi, *C
Density, g/cm2
Elongation, %
Extrusion process temperature, *C
Flexural modulus, at 23'C, 103 psi
Hardness, Shore
Heat capacity, calAVg
Heat resistance, continuous, *C
Impact strength, ft Ib/in of notch
Melt index, g/10 min
Mold (linear)shrinkage, in/in
Molecular weight, weight average
Organic solvents, effect of
Tensile impact strength, ft Wat2
Tensile modulus, 103 psi
Tensile strength, at break, psi
Tensile yield strength, psi
Thermal conductivity. Iff4 cal cm/sec cm2 *C
Thermal expansion, 10"* in/inTC
W^ter absorption, (1/8 in specimen), 24 hi, %
ASTMTest
Method
D746
D635
D648
D792
D638
D790
D2240
D256
D1238
D1822
D638
D638
D638
C177
D696
D790
Results
-80 to -55
very slow
108-126
65-80
0.910-0.925
100-650
121-232
35-48
Shore D 44-50
0.55
82-100
>16 (No break)
0.2-55
0.015-0.050
10" -105
resistant below 60"C
180
25-41
1,200-4,550
1,300-2,100
8
100-220
<0.01
''AdaptedfromTheis 1989 and Bikales 1967
Polyethylene's resistance to aggressive chemicals is a primary reason for
its widespread use in many diverse applications. The key to ensuring long-
term stability of waste forms is the ability of the binder to withstand the
chemical environment, internally, of the waste materials, and externally, of
the disposal site. Protection from a broad range of chemical reagents is
essential because it is difficult to accurately predict the chemical composi-
tion of leachates resulting from varied waste forms in disposal.
At ambient temperatures, polyethylene is insoluble in virtually all or-
ganic solvents and is resistant to many acids and alkaline solutions (Raff
and Allison 1956). Polyethylene is resistant to any concentration of hydro-
3.21
-------
Process Identification and Description
chloric, hydrofluoric, phosphoric, and formic acids, ammonia, potassium
hydroxide, sodium hydroxide, potassium permanganate, and hydrogen per-
oxide. In dilute concentrations (up to 50% by weight), polyethylene is re-
sistant to sulfuric and nitric acids. Exposure to some aliphatic, aromatic,
and chlorinated hydrocarbons can cause swelling, but will not permanently
change the mechanical properties of polyethylene (e.g., strength), because
the original properties reappear upon evaporation of the swelling medium.
In general, LDPE is relatively unaffected by polar solvents, including
alcohols, phenols, esters, and ketones. Table 3.3 (on page 3.23) provides
an overview of polyethylene's compatibility with many chemicals, after
three months' contact.
3.6.2 Status of Development
3.6.2.1 Bench-Scale Development
The feasibility of encapsulating various types of wastes in polyethylene
has been demonstrated for sodium nitrate salts, incinerator fly ash, ion-
exchange resins, and evaporator concentrates from nuclear facilities (Franz
and Colombo 1985).
Formulation development work was conducted using a bench-scale 32
mm (1.25 in.) polyethylene extruder, with a maximum output capacity of
about 16 kg/hr (35 Ib/hr), shown in figure 3.5 (on page 3.24). Envelopes of
potential and optimal operating ranges were defined for critical process
parameters, such as, temperature, pressure, feed rate, extrusion rate, and
solidification kinetics. The effect of other parameters, including polyethyl-
ene flow properties (i.e. melt index), waste-binder mixing techniques, waste
pretreatment requirements, and power requirements were also investigated.
Some of these parameters are reviewed briefly here in order to provide
background for the discussion of scaleup feasibility in Section 3.6.2.2 (Kalb
and Colombo 1984).
Temperature. Temperature is an important parameter because it affects
processibility and product quality. For waste encapsulation, minimal tem-
peratures are preferred in order to reduce potential volatilization of contami-
nants. Typical process temperatures for waste encapsulation ranged
between 125° and 150°C (257° to 300°F).
Pressure. Pressure is a function of many factors, including the kind of
polyethylene used, waste characteristics, and extrusion parameters, such as
3.22
-------
Chapter 3
Table 3.3
Effect of Various Chemicals on Polyethylene after 3-Month Contact (a)
After 24 Hr.
On Removal from Reagent Conditioning at Room Temp.
Tensile
Reagent Change in Wt, % Appearance Strength, psi Elongation, %
Inorganic Acids and Bases
H2SO4, cone.
H2S04, 10%
HO, cone.
HC1, 10%
HNO3, cone.
HNO3, 10%
NaOH, 50%
NH4OH,conc.
+ 0.13
+ 0.04
+ 0.13
+ 0.20
+ 3.02
+ 0.22
+ 0.13
+ 0.31
No change
No change
No change
No change
No change
No change
No change
No change
1458
1370
1406
1442
1093
1387
1432
1378
462
483
258
336
71
325
313
371
Resistance
Rating
-------
Process Identification and Description
Figure 3.5
Photograph of Laboratory-Scale Extruder with Separate Dynamic
Feeders for Waste and Binder
Franz, Heizer, and Colombo 1987
3.24
-------
Chapter 3
screw design, temperature, and rate. Moderate pressures in the range of 1 to
20 MPa (up to several thousand psi) are desirable, because they enhance
mixing and the delivery of mixture to the mold.
Process Rates. Feed and extrusion rates can vary depending on waste
loading and characteristics; they must be coordinated to avoid jamming or
starving. The laboratory-scale extruder was operated with an output rate
between 1 kg/hr (2.2 Ib/hr) and 9 kg/hr (20 Ib/hr).
Melt Index. Melt index, shown among other properties of LDPE in table
3.2 (on page 3.19), is the measure of a material's capacity for flowing at
190°C (374°F). For optimal processing of laboratory-scale waste forms, a
melt index of 55 g/10 min (1.9 oz/10 min) was selected.
Feed Method. When using a stock (static hopper) feed system, density
and particle size differences led to segregation of waste and binder, creating
a heterogeneous mixture. Separate dynamic feeders for waste and binders
were used to overcome these difficulties and provide a means for precisely
controlling waste-binder ratios.
Pretreatment. For optimal extrusion, waste should be dry; granular par-
ticles provide the best flow characteristics.
3.6.2.2 Scaleup Feasibility
When bench-scale formulation and testing for the polyethylene encapsu-
lation of nitrate salt was complete, planning was initiated to demonstrate
this system using production-scale equipment in conjunction with Rocky
Flats Plant (Kalb, Heiser, and Colombo 1992). Estimates of necessary pro-
duction capacity were made based on data from the Rocky Flats Plant. Siz-
ing of extruder equipment varies over a wide range, from bench-scale
equipment with a screw diameter of 19 mm to 32 mm (0.75 to 1.25 in.) to
very large machines with screw diameters up to 152 mm (6 in.) or more.
Typically, laboratory-scale extruders can process around 9 to 14 kg/hr (20
to 30 Ib/hr), while production-scale machines can process hundreds or thou-
sands of kg/hr. For the technology demonstration, a 114 mm (4.5 in.) ex-
truder, with output capacities in the range of 900 kg/hr (2,000 Ib/hr) was
selected. Data on the process parameters generated during bench-scale
investigations were reviewed to develop a set of required design specifica-
tions. A survey of potential vendors was then conducted. Equipment de-
signs were examined in order to assure that processing and monitoring
requirements could be met using conventional, off-the-shelf equipment.
3.25
-------
Process Identification and Description
The production-scale feasibility test was conducted using a 114 mm (4.5
in.) extruder at laboratory facilities provided by Davis-Standard
(Pawcatuck, Conn.), a manufacturer of extruder equipment whose facility is
designed for feasibility testing. It is equipped with state-of-the-art monitor-
ing and control systems for data collection and process control, as well as a
wide selection of extruder and screw designs to accommodate diverse user
needs. Personnel from Brookhaven National Laboratory (BNL) and Rocky
Flats Plant attended the demonstration; the staff at Davis-Standard provided
technical assistance.
Two Accu-Rate (Whitewater, Wis.) Model 610 dry material feeders were
purchased and calibrated prior to the feasibility test in order to maintain an
accurate waste loading of sodium nitrate salt. A slightly more conservative
waste loading of 60% by weight nitrate salt was selected for the scaleup
feasibility test (compared to the maximum loading of 70% by weight) be-
cause of the many variables under consideration. (Optimization of waste
loading under full-scale conditions will be performed as part of the planned
Technology Demonstration.) These feeders are larger versions of the feed-
ers used in bench-scale studies. They were installed above the extruder
feed throat, in place of a standard static feed hopper. Figure 3.6 (on page
3.27) is a simplified process flow diagram of the full-scale polyethylene
encapsulation system.
Initial trials resulted in excessive foaming due to air entrainrnent, caused
by the physical properties of the simulated granular salt waste and length of
the extruder barrel. This problem was remedied quickly by removing the
extruder screw and replacing it with one designed to vent gases midstream.
Process settings similar to those developed at BNL, shown in table 3.4 (on
page 3.27), were successfully duplicated. Maximum output rates; were not
attempted, but an output peak of 1,577 kg/hr (3,477 Ib/hr) was attained at 65
rev/min and steady-state rates in excess of 454 kg/hr (1,000 Ib/hr) were
easily achieved. A 114 L (30 gal) drum of encapsulated sodium nitrate was
filled in about 25 minutes. Only minimal shrinkage was observed upon
cooling, indicating a lack of significant voids in the waste form.
Conclusions resulting from the production-scale feasibility test for the
polyethylene encapsulation of nitrate salt wastes may be summarized, as
follows:
• Polyethylene encapsulation of at least 60% by weight nitrate salt
wastes can be accomplished successfully, using a production-
3.26
-------
Chapter 3
Figure 3.6
Polyethylene Encapsulation System Process Flow Diagram
Dry waste
storage
hopper
Polyethylene
storage
hopper
To HEPA>
filter
Waste
feeder
F^r
)
1,261
r
1 rate: Feed rate:
Dlh/hr 540 Ib/hr
Polyethylene
feeder
A Vent
port
Extruder
Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 p
Vacuum
pump
Output: l,8001h/hr
:300F
Temp: 325 F Temp: 300 F Temp: 300 F
Press: 1,240 psi Press: Opsi Press: 380 psi
Temp: 300 F Temp: 300 F
Press: 2,000 psi Press: 0 psi
Output scale
Table 3.4
Parameter Settings and Test Data for Polyethylene
Encapsulation Production-Scale Feasibility
Melt Temperature, 'C CF) 149 (300)
Melt Pressure, MPa (psi) 2.6 (380)
Max. Screw Speed, RPM 65
Steady-state Output, kg/hr (Ib/hr) >454 (1,000)
Max. Output, kg/hr (Ib/hr) 1,577 (3,477)
Horsepower at Max Output 354
3.27
-------
Process Identification and Description
scale 114 mm (4.5 in.) extruder at steady-state rates of at least
454 kg/hr (1,000 Ib/hr);
Comparison of bench- and production-scale process data con-
firms that process scaleup is feasible and that information gener-
ated during research and development phases of this project can
be applied during the technology demonstration phase;
Quality assurance testing of the 114 L (30 gal) waste form pro-
duced during the full-scale feasibility test demonstrates that a
homogenous waste form with excellent properties can be pro-
duced using off-the-shelf production equipment; and
Close agreement of results from waste form performance tests of
specimens produced using bench- and full-scale systems, indi-
cates the validity and importance of bench-scale research and
development, prior to scaleup and demonstration of new tech-
nologies.
3.7 Inorganic, Cementitious Technologies
of the Siliceous Category
3.7.1 Description
Following are characteristics of inorganic, cementitious stabilization/
solidification systems:
• relatively low cost;
• good, long-term stability, both physical and chemical;
• documented use on a variety of industrial wastes over a period
of at least ten years;
• widespread availability of the chemical ingredients;
• nontoxicity of the chemical ingredients;
• ease of use in processing (processes normally operate at ambient
temperature and pressure and without unique or very sipecial
equipment);
3.28
-------
Chapter 3
• wide range of volume increase;
• inertness to ultraviolet radiation;
• high resistance to biodegradation;
• low water solubility;
• relatively low water permeability; and
• good mechanical and structural characteristics.
3.7.2 Scientific Basis
Setting and curing reactions vary among processes. Most of the com-
mercial, cementitious inorganic stabilization/solidification systems, how-
ever, solidify in highly similar reactions, which have been thoroughly
studied in connection with portland cement technology used in concrete
making. 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 alike. One reason for this is presented in an interesting way by Cote
(1986). The compositions of most of the primary reagents used in inorganic
stabilization/solidification systems were plotted on a ternary diagram using
the three oxide combinations, SiO2, CaO + MgO, and A12O3+ Fe2O3. All of
these reagents have the same active ingredients as far as solidification reac-
tions are concerned; this is illustrated in figure 3.7 (on page 3.30). The
combinations of these five oxides express the essential composition of any
of these materials, even though, in many cases, the actual compounds are
not simple oxides, but more complex silicates and aluminates. It is interest-
ing that all of the reagents, with exception of power-plant fly ash, have their
origin in natural limestone and clay formations, and all are inexpensive
compared to industrial "chemicals."1
3.7.3 Operational Considerations
The cementitious reactions that occur in these processes require the pH
to be above 10. This level is achieved through the dissolution of free lime
from the solid, and continues throughout the setting and curing stages of the
mixture. A "false set" can occur when enough free lime is present initially
1. Reprinted by permission of Chapman & Hall from "Chemical Fixation and Solidifi-
cation of Hazardous Wastes" by Jesse R. Conner. Copyright 1990 by Chapman & Hall.
3.29
-------
Process Identification and Description
Figure 3.7
Ternary Composition Diagram for Cementitious Systems
SiO
CaO
+MgO
AI203
+Fe2O3
Adapted from Conner 1990
to start the reactions, but availability of free lime decreases as the process
proceeds and the reactions stop or slow down. Therefore, any reaction that
competes successfully for the calcium ion may inhibit setting. The
cementitious or pozzolanic reactions also require sufficient free water if
they are to run to completion. Water is used up in the hydration reaction of
these chemical systems. The water content, as measured by total solids
determination, is not necessarily all available for reaction.2
2. Reprinted by permission of Chapman & Hall from "Chemical Fixation and Solidifi-
cation of Hazardous Wastes" by Jesse R. Conner. Copyright 1990 by Chapman & Hall.
3.30
-------
Chapter 3
The inorganic processes include those that use bulking agents, such as
Class F fly ash, and those that do not. A bulking agent, in this context, is an
additive that primarily adds to the total solids and viscosity of the waste,
thus preventing settling out of the suspended waste components before so-
lidification can occur; it may also help produce a solid with better physical
properties. Examples of these two groups of processes are: (1) cement-
based or cement/soluble silicate systems (no bulking agents) and (2) ce-
ment/fly ash, lime/fly ash, cement/clay, or lime/clay (systems with bulking
agents). There are two types of bulking agents: those that are essentially
inert in the system and act as described above and those that also have reac-
tive capacity or exhibit poz/olanic activity. A pozzolan is defined as a
material that does not exhibit cementing ability when used by itself, but
when used in combination with other materials, such as, portland cement
and lime, will interact with these agents resulting in a cementitious reaction.
The most noticeable difference resulting from the use of systems with
and without bulking agents is that systems with bulking agents often yield
lower chemical costs because some of the more expensive cementing mate-
rials are replaced by less expensive waste products such as fly ash. Systems
without bulking agents sometimes yield lower overall costs because of the
lower weight and volume increase associated with them.
3.7.4 Status of Development
Conventional inorganic chemical stabilization/solidification processes
that have been used commercially are listed below. The most important
systems today 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*;
• lime/fly ash*;
• cement or lime kiln dust*; and
• slag.
3.31
-------
Process Identification and Description
Many of the permutations and combinations of these systems, including
those varying as to the kinds of additives used, are patented or are covered
by patent applications, but information about most of the generic systems is
believed to be in the public domain. All of these processes have been used
commercially for solidification of water-based waste liquids, sludges, filter
cakes, and contaminated soils. A large body of technical information about
them concerning teachability, physical properties, and general stability is
available.
In terms of volume of waste treated, the lime-fly ash process has prob-
ably been the most used in the U.S., although it has been very narrowly
applied, primarily to flue-gas desulfurization sludges. For other kinds of
wastes and industrial sludges, the kiln dust and portland cement-based pro-
cesses are the most widely used at the present. In the United States, one of
the most flexible techniques used is the portland cement-sodium silicate
process. This process has been applied to a variety of wastes and a good
technical base, including leaching test information, is available. Another
technique, the portland cement-fly ash process, has been used in Europe and
Canada, but has not been applied extensively in the United States. This
process works well with certain kinds of waste; like the lime-fly ash pro-
cess, it involves large additions of the solidifying agents and, therefore,
results in large volume increases.
3.7.5 Technology Variations
Innovative systems at the present include those using the reagents dis-
cussed in Subsections 3.7.5.1 through 3.7.5.4, below, usually in combina-
tion with conventional cementitious systems, but sometimes alone.
3.7.5.1 Soluble Silicate Processes
Sodium silicates have been used for more than a century in the produc-
tion of commercial products, such as, special cements, coatings, molded
articles, and catalysts. In these mixtures, the soluble silicate is mixed with
cement, lime, slag, or other sources of multivalent metal ions that promote
the gelation and precipitation of silicates. Katsanis, Krumrine, and Falcone
(1982) have shown that the solubility of systems containing multivalent
ions in combination with soluble silicates differs significantly from precipi-
tation of solutions composed of metal salts or silica. The presence of cal-
cium or magnesium ions, even at low concentrations, can reduce the
3.32
-------
Chapter 3
solubility of silica by several orders of magnitude. These results suggest
that soluble silicates reduce the teachability of toxic metal ions by forma-
tion of low-solubility metal oxide/silicates and by encapsulation of metal
ions in a silicate- or metal silicate-gel matrix. This characteristic is one
basis for the use of soluble silicates in stabilization/solidification systems.3
Soluble silicates have been used both as accelerators and as anti-inhibi-
tors for concrete and have the same function in a portland cement-based
stabilization/solidification system. In the precipitant-type retarders, such as
heavy metals, soluble silicate probably works by removing the metal from
solution before it can precipitate on the cement grains. With retarders that
operate by coating the grains, soluble silicate may function as a surfactant,
emulsifying oils and flocculating fine particulates so that they remain sus-
pended in the water phase. In any event, soluble silicate has been useful in
many instances for this purpose, rather than as a fixant or gellant.
The reactions of polyvalent metal salts in solution with soluble silicates
have been studied extensively over many years (Vail 1952; Her 1979).
Nevertheless, the "insoluble" precipitates that result from such interactions
are not usually well characterized, especially in the complex systems repre-
sentative of most wastes. Falcone, Spencer, and Katsanis (1983) explained
the apparent negative effects of soluble silicates on metal leachability expe-
rienced by some other investigators. When an excess of soluble silicate
over available metal ion is present in such a system, the silica species with
adsorbed metal ion may remain suspended, not be filtered in the leaching
protocol, and give the appearance of increased leachability. Also, large
excesses of soluble silicate can so decrease the set time that it is impossible
to obtain a homogeneous mass, and the resulting pore size is much larger.
This counters the reduction in permeability, which is the real benefit of
soluble silicate in systems where the metal has already been precipitated as
another species. Davis et al. (1986) found that "treatment of a waste with
sodium silicate reduced the degree to which leaching acid can penetrate the
waste matrix by a factor of five to seven." The sum result of these effects is
demonstrated graphically in figure 3.8 (on page 3.34). In this system, a
silicate content range of 6% to 10% gives minimum leachability. Interest-
ingly, this is precisely the range which has long been used empirically by
workers in this stabilization/solidification specialty.
3. Reprinted by permission of Chapman & Hall from "Chemical Fixation and Solidifi-
cation of Hazardous Wastes" by Jesse R. Conner. Copyright 1990 by Chapman & Hall.
3.33
-------
Process Identification and Description
Figure 3.8
Leachability of Metals as a Function of Soluble Silicate Content
.11
u
-\—r
—T~
10
12
14
T~
16
18
20
Silicate content (%)
Davis et al. 1986
The current market price of sodium silicate solution, 42° Be (specific
gravity), 3:2 SiO2:Na2O ratio, is about $180/tonne ($165/ton), FOB works
in truck/car load lots. Other ratios are generally more expensive. Potas-
sium silicate solution costs about $510/tonne ($460/ton).
Conventional soluble silicate processes or vendors are listed below:
• Chemfix Technologies, Inc., Kenner, LA (Chemfix™);
• Fujimasu Synthetic Chemical Laboratory Company, Ltd., Japan;
• Kurita Water Industries, Ltd., Japan;
• Nippon Synthetic Chemical Industry, Japan;
• SolidTek, Inc., Atlanta, GA;
• Hitachi, Japan;
3.34
-------
Chapter 3
• Japan Organo Co., Japan;
• PD Pollution Control, England; and
• CGE - SARP, France.
The most confusing aspect of silicate stabilization/solidification technol-
ogy is that a very large number of vendors promote their processes, either
intentionally or unintentionally, as "silicate" within the framework of
soluble silicate systems, when, in fact, they are using other siliceous re-
agents. Clays, cement, slags, and kiln dusts either are or contain silicates,
but not soluble silicates. Users often believe that they are buying or recom-
mending a soluble silicate process when they are actually using one of the
latter reagents. In this monograph, only true soluble silicate processes are
discussed. It is possible that some processes have been missed because the
vendors consider the exact nature of their processes to be proprietary.
Soluble silicate processes that appear innovative, because of either their
chemistry or the way in which they are used, are described below.
EnviroGuard/ProTek/ProFix, Houston, Texas. This company sells a
number of sorbents and formulated chemicals under the name
enviroGuard™ (sorbent), enviroGuard Plus™ (S/S agent), and ProFix™.
All of these products are 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 na-
ture is well known (Durham and Henderson 1984), but its ability to react
with alkalies to form soluble silicates is of primary interest here. Under
alkaline conditions, the amorphous silica reacts slowly to produce soluble
silicates, which can then react with ions of toxic metals to form low-solubil-
ity metal silicates. At the same time, the soluble silicate can react with
available calcium or other polyvalent metal ions to set and harden the sys-
tem in a controlled manner. The advantage of this method over that of most
soluble silicate processes is that the slow, continuous generation of soluble
silicate provides a reserve capacity analogous to the action of buffers in a
pH-control system. As metal hydroxides and other species slowly dissolve
in the alkaline environment of the waste form, they can then become re-speci-
ated as the "silicate." The process is patented in the U.S. and is the subject of
patent applications in many other countries (Conner and Reber 1992)."
4. Reprinted by permission of Chapman & Hall from "Chemical Fixation and Solidifi-
cation of Hazardous Wastes" by Jesse R. Conner. Copyright 1990 by Chapman & Hall.
3.35
-------
Process Identification and Description
A simplified version of the basic chemistry involved in the process is as
follows:
2NaOH + xSiO2 -» Na2O:x(SiO2} + H2O ,„
Na2O:x(SiO2) + Ca(OH}2 -» CaSixO2 + INaOH [2]
In place of calcium, any polyvalent metal species may be substituted,
thence the formation of immobilized metals, since these metals compete
with calcium for the silicate anion. The anion originally associated with the
metal will help determine the reaction rate and, also, the final pH of the
solid. For example, if the hydroxyl ion is dominant, sodium hydroxide will
be continuously reformed to react again with the silica from the rice hull
ash, until the ash is eventually exhausted. On the other hand, if the metal is
in the form of chloride or sulfate, the reaction product will be neutral and
alkalinity of the system will decrease until there is no longer sufficient hy-
droxyl ion to react with the silica. It must be understood, however, that this
is a simplistic view of a very complex system, especially since the: silicates
formed are not exact, stoichiometric compounds.
Lopat, Wanamassa, New Jersey. Lopat has been actively marketing a
process using potassium silicate and setting agents. The process has been
applied in California to reduce lead leaching from automobile shredder
waste. Little independent technical information has been published, al-
though it has been said that the process can immobilize lead, dioxins, and
PCBs (Environmental Science & Technology 1986). The "innovative"
aspect of this process is the use of a liquid potassium silicate solutions
modified with additives, K-20 (U.S. Patent 1987), as a fixative added to the
waste in place of or before conventional stabilization/solidification with
cementitious materials. The additives consist of "a catalytic amount of an
aqueous sodium borate solution and a fixative containing solid calcium
oxide," with or without a fumed silica addition. It is not stated exactly what
function these additives perform in this application.
The concept of permeating soils (soil stabilization) (Joosten 1937) and
other geological structures, and even waste piles (Tyco Laboratories, Inc.
1971), with soluble silicates is not new. These old methods, however, have
not been commercially applied in this way until Lopat began marketing its
potassium silicate formulations for the treatment of auto shredder "fluff,"
the residue remaining after all recyclable materials have been removed from
3.36
-------
Chapter 3
shredded automobiles. This residue is usually classified as hazardous ac-
cording to the California Waste Extraction Test (WET), but usually passes
the US EPA Toxicity Characteristics Leaching Procedure (TCLP) and,
therefore, is not considered to be a hazardous waste elsewhere. The Lopat
process apparently was applied successfully to this waste at low cost, since
physical solidification was not required.
Lopat sells the chemicals and/or licenses the process. Therefore, a num-
ber of other organizations may offer the system under the Lopat name, as
"K-20," or under another name. One of these is described by Trezek (US
EPA 1990a).
Other Soluble Silicate Processes. In addition to the commercial systems
offered by vendors listed above, there are many patents and other technical
literature that describe the use of soluble silicate processes for soil solidifi-
cation, grouting, and various compositions of matter. New stabilization/
solidification companies could arise in this area at any time. Most of the
commercial soluble silicate processes use sodium silicate and portland cei-
ment as the chemical system. Some consider it a portland cement system
with sodium silicate as an additive, while others view it as a soluble silicate
system that uses portland cement as one of a number of possible setting
agents for the soluble silicate. If these processes are being looked upon as
being based on soluble silicates along with a setting agent, then a variety of
setting agents have been enumerated in the technical and patent literature.
The known chemistry of most such systems is discussed in detail in Vail
(1952). Following are some of the systems:
• glycolides;
• glyoxal;
• polyalcohol esters;
• boric - phosphoric acid condensation products;
• sequestered metal ion complexes;
• succinic acid diesters; e.g., dimethyl succinate;
• methyl acetate, methyl propionate, methyl formate mixtures;
• formaldehyde or paraformaldehyde;
• diacetin and triacetin;
• formamide and ethyl acetate;
3.37
-------
Process Identification and Description
• phosphates;
• amides;
• glycerin - glacial acetic acid reaction products;
• chlorides, sulfates and nitrates of aluminum, magnesium, and
iron;
• soluble polyvalent metal compounds in general;
• silicon polyphosphate;
• potassium silicofluoride and sodium silicofluoride acids; and
• mono-, di-, and triacetate acid esters of glycerol.5
Several patented processes in the soluble silicate stabilization/solidifica-
tion area (Conner 1985, 1986a) may become commercially significant,
although they are not yet commercialized. One of these is interesting be-
cause it uses a combination of liquid and dry sodium silicates to solve the
problem of too-rapid setting of soluble silicate systems. In a batch-type
process, which is usually the preferred approach for small quantities of
wastes, the liquid silicate system sets too rapidly. This process uses small
amounts of silicate solution to thicken (but not gel to a nonflowable state)
the waste so that low-solids wastes will not separate before they can set,
along with a powdered sodium silicate and portland cement that react more
slowly to set and harden the mixture without the use of large amounts of
reagents.
3.7.5.2 Slag Processes
One of the earliest uses of slag for waste treatment was in the Calcilox®
Process (Elnagger et al. 1977; Conner 1990). Calcilox® is fundamentally a
settling or compaction process that relies on the addition of a proprietary
ingredient to slowly form a cementitious mass under the overlying water
layer. In normal operation, this process requires the water layer for proper
compaction and reaction, and, in this respect, is much different from other
stabilization/solidification processes. In some ways it is more related to
conventional waste treatment than to stabilization/solidification work. It
has been marketed, however, as a stabilization/solidification process and
5. Reprinted by permission of Chapman & Hall from "Chemical Fixation and Solidifi-
cation of Hazardous Wastes" by Jesse R. Conner. Copyright 1990 by Chapman & Hall.
3.38
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Chapter 3
competes in certain areas with other stabilization/solidification processes.
The proprietary ingredient, Calcilox®, is actually finely ground blast-fur-
nace slag obtained as a waste product from basic steel producing plants.
The process developer, Dravo Lime Co., produces Calcilox® in quantity at a
plant in the Pittsburgh, Pennsylvania area. Calcilox® is typically added in
the amount of about 5 to 10% by weight to the waste (Pojasek 1980). The
composition of the sludge being treated is quite critical, both in solids con-
tent and as to other chemical factors. The process may use other ingredi-
ents, such as, fly ash, kiln dust, lime or portland cement, as well as the
ground slag.6
This process has been used to stabilize flue-gas desulfurization sludges
and coal waste fines in very large projects. The ground slag is mixed with
the dilute waste slurry, which is then allowed to settle and compact in an
impoundment where the supernatant water is drawn off and recycled or
discharged. One such project has been operated at the Bruce Mansfield
power station near Pittsburgh, Penn., since 1975. The capital cost for this
system was more than $70,000,000. The planned capacity was 16,300
tonne (18,000 ton) of sludge per day, at a reported price of $2.75/tonne
($2.50/ton), or a daily cost of approximately $45,000; the project is sched-
uled to run for 30 years before the disposal site is filled. The process has
applications where very large volumes of dilute waste are produced and
where large areas for settling and compaction ponds can be constructed and
operated over long periods.
Slag has probably been incorporated into a number of stabilization pro-
cesses, along with other reagents, especially at or near the slag producers,
such as steel mills. As with other waste product reagents (fly ash and kiln
dusts), slag usage is often not documented in the literature or promoted
specifically as a commercial stabilization/solidification process. It is used
in a proprietary way at waste generators and industries. Because it is a
waste product, and its composition varies considerably from generator to
generator, its utility will also vary. Some of the earliest literature on the use
of slag for hazardous waste treatment goes back to 1956 (Wunderly 1956),
where its use for treatment of waste pickle liquor was described. Quienot
(1978) described a process for using slag in the presence of an alkaline
material and sulfate for solidification. Alkaline slags are known to be reac-
6. Reprinted by permission of Chapman & Hall from "Chemical Fixation and Solidifi-
cation of Hazardous Wastes" by Jesse R. Conner. Copyright 1990 by Chapman & Hall.
3.39
-------
Process Identification and Description
live in the presence of water, or can be made reactive by the addition of
alkalies. This reaction probably involves the formation of soluble silica
species as intermediates, followed by reprecipitation of metal silicates or
calcium and/or aluminum silicates. Alternatively, slag may be maide
strongly acidic to accomplish the same purpose, although the reactions may
be different (Rysman de Lockerente 1976). Slag is often mixed with ce-
ment, fly ash, or kiln dusts to further enhance the properties of the product
(Matsushita 1978). It has reportedly been used commercially in C'anada at
Atlas Steel Company (OWMC 1986) for treatment of waste acid. Slag was
also found to be effective in immobilizing lead (US EPA 1990a).
Blast-furnace slag is produced when the molten slag from an iron-pro-
ducing blast furnace is cooled quickly to minimize crystallization. It is a
blend of amorphous silicates and aluminosilicates of calcium and other
bases. Because of the presence of ferrous iron and reduced sulfur com-
pounds, it may act as a reducing agent for metal species, such as chromium,
that are less mobile in the reduced valence state. It is also reactive with
alkalies and acids, reportedly producing soluble silica species (Ezell and
Suppa 1989).
Oak Ridge National Laboratory (ORNL) Process. The ORNL tested
various mixtures of slags in combination with portland cement and fly ash
for the stabilization of radioactive wastes containing technetium and nitrates
(Gilliam, Dole, and McDaniel 1986). Technetium ("Tc) is more mobile in
the higher valence state, Tc+7, than in the +4 oxidation state. Therefore,
reduction of Tc+7 to Tc*4 is desirable in a stabilization process. This can be
accomplished with 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 results are
given in Table 5.19 (on page 5.28).
SoliRoc™. The SoliRoc™ system is really not a solidification process,
but rather a complete hazardous waste treatment facility and system. While
the SoliRoc™ system uses solidification as the final step, the solidification
part of the process is performed using portland cement. Therefore, in this
respect, it can be viewed as a cement-based process. The process consists
of a fairly complex pretreatment process: generation of soluble silica spe-
cies in situ at low pH, reaction of the soluble silica with metal ions, increas-
ing pH to precipitate the system as a sludge, dewatering the sludge, and,
finally, solidification with portland cement. Because of the overall ap-
3.40
-------
Chapter 3
proach, the process can be viewed as innovative, especially from the U.S.
perspective (it has been available for some time and used commercially in
Europe). Other names associated with the SoliRoc™ process are
Cemstobel, S.A., and Mechim, S.A., of Belgium.
Figure 3.9 shows the process flow for the SoliRoc™ system. The pre-
treatment (Stages 1 and 2) steps are:
• Formation of monosilicic acid by mixing blast-furnace slag with
acidic waste (or acid) at a pH of about 1.5, wherein the silicic
acid formed reacts with polyvalent metal cations; and
• "Polymerization" of the silicates to form a gel at a pH of about 11 to
12.
The resulting metal sludge can then be dewatered and disposed of in the
land, or solidified with cement, lime/slag, or another generic solidification
process. The main claim for the process is that metal silicates so formed are
more insoluble than metal hydroxides, especially under acid leaching condi-
tions. It is also claimed that the process is effective on certain chelated metals.
The first plant using this process was started in France in 1976 by a com-
pany called GEREP, in north Paris. It has a reported annual capacity of
10,000 tonne (11,000 ton) of waste (MECHIM 1975). As of 1984, three
more plants were in operation in Belgium, Italy, and Norway.
Figure 3.9
Flow Diagram of SoliRoc™ Process
Metal bearing wastes-
Silica
reagent-
Acid-
Alkali
t — ^
— >
Production of
monosilicic
acid
Stage 1
Production
of metal
silicates
Stage 2
Polymerization
Stage 3 >
k
F
Reagents-
3.41
-------
Process Identification and Description
Cement-Slag Process. The combination of portland cement and slag for
ordinary stabilization is not considered innovative, but its use for stabiliza-
tion of hexavalent chromium is unusual and deserving of discussion here.
The treatment of Cr4* with slag and cement was reported by Rysman de
Lockerente et al. (1976), but no teachability data were given. A laboratory
treatability study was conducted on a sodium dichromate-contaminated soil,
using three reducing agents to reduce the Cr* to levels that could be stabi-
lized to within US EPA Toxicity Characteristic (TC) limits (US EPA
1990d). The agents were sodium metabisulfite and ferrous sulfate, both
standard chromium reducing agents, and blast-furnace slag. When the re-
ducing agents were used alone, neither sodium metabisulfite nor slag met
the requirement, but ferrous sulfate did. When the reducing agents were
combined with cement in a complete stabilization/solidification process,
however, both slag and ferrous sulfate gave nearly the same acceptable
results.
3.7.5.3 Lime
Processes that use lime, in general, would not be considered innovative,
but one such process, OCR, has been pretreated with additives that cause it
to become hydrophobic. This approach allows the improved treatment of
oily and other high organic content wastes, according to the developers.
The commercial offering of DCR/Boelsing/Sound Environmental Services,
Inc. uses this same basic approach and the Separation and Recovery Sys-
tems (SRS)/EIF approach may be similar. The latter vendor does not dis-
close the exact nature of the lime that "is specially prepared and contains
proprietary chemicals," but the SRS literature refers to some of the same
remedial projects in Europe as does the OCR literature.
The OCR process is based on a patent by Boelsing (1977) that describes
the chemistry of the method. Quicklime (CaO) is treated with a surfactant,
0.001 to 10% of its weight, that delays the reaction between the CaO and
water until the CaO has first interacted with the organic matter in the waste.
Subsequently, the CaO-organic mixture is converted into dispersed
Ca(OH)2 solid that gradually converts to limestone (CaCO3) by reaction
with carbon dioxide from the air. The surfactants employed and disclosed
in the patent include fatty acids, paraffin oil, and aliphatic alcohols. The
theory is that the high specific surface area and internal cavities of the lime
will sorb large amounts of organics when the surfaces have been rendered
3.42
-------
Chapter 3
hydrophobia. Eventually, the water penetrates the hydrophobic surface of
the CaO, reacts with it in an exothermic reaction, and:
"fractures" into powder-like material with particles in the
sub-micron range. The oil which was previously adsorbed on
the calcium oxide particles is now dispersed and irreversibly
bound within the newly formed and highly adsorptive cavi-
ties of the hydrophobized Ca(OH)2 crystals. The finely
dispersed Ca(OH)2 will then slowly react with natural CO2 to
generate CaCO3, while still bound in the original soil
matrix....The formation of insoluble calcium carbonate oc-
curs on all exposed calcium hydroxide surfaces which are
covered by a coherent carbonate crust....The specific surface
area of the CaCO3 decreases to less than 0.5 m2/g as the
porous surfaces are sealed by the insoluble glass-like carbon-
ate. (Payne, McManus, and Boelsing 1991.)
This theory is supported by scanning electron microscope studies re-
ported in the source.
The SRS process is described somewhat differently (SRS 1988a). It uses
a two-step approach. First, a modified lime preparation is mixed with the
waste. About 15 minutes later, a second lime preparation is added to com-
plete the process. Thus, it appears that there is some difference between the
processes, at least in the way that they are applied.
3.7.5.4 Inorganic Polymers
In soluble silicate processes, the silicates generally contain a wide range
of molecular sizes from monomers to colloidal size. Depending on the
actual reactions during stabilization, some polymerization may occur, but
much of the gelling process is simply precipitation of the silicate species
with metal ions. In at least one process, however, "Geopolymer," the pri-
mary reaction mechanism does appear to be the formation of literal inor-
ganic polymers, based on silicon and aluminum, through chemical reaction.
These materials, also called polysialates, were described by Davidovits
(1982) as mineral polymers having "the empirical formula:
Mn [-(Si - O2_ X - A/ - O2 -]n, wH2O [3]
3.43
-------
Process Identification and Description
where z is 1, 2 or 3, M is sodium, or sodium plus potassium, n is the degree
of polycondensation, and w has a value up to about 7. The method for mak-
ing these polymers includes heating an aqueous alkali silico-aluminate mix-
ture having an oxide-mole ratio within certain specific ranges for a time
sufficient to form the polymer." In a later patent, Davidovits and Sawyer
(1985) describe "an early high-strength mineral polymer composition
...formed of a polysialatesiloxo material obtained by adding a reactant mix-
ture consisting of alumino-silicate oxide (Si2O5,Al2O3) with the aluminum
cation in a four-fold coordination, strong alkalies such as sodium hydroxide
and/or potassium hydroxide, water and a sodium/potassium polysilicate
solution; and from 15 to 26 parts, by weight, based on the reactive mixture
of the polysialatesiloxo polymer of ground blast furnace slag."
These compositions were designed to be used as high-strength cements
or molded products for various commercial uses and for construction pur-
poses, especially barrier walls, using grouts composed of geopolymer. The
geopolymer binder was further described as the "result of polycondensation
of a still hypothetical monomer, the orthosialate ion, producing poly(sialate)
(-Si-)-Al-), poly(sialate-siloxo) (-Si—Al-O-Si-O) and poly(sialate-disiloxo)
polysialates Geopolymeric polycondensation has also been discussed as
alkali-activation of silico-aluminates by the U.S. Army Corps of Engi-
neers." (Comrie, Runte, and Davidovits 1988).
The geopolymer system consists of two components: a very fine and dry
powder and a syrupy, highly alkaline liquid (Anonymous 1989). The two
are combined to produce a high viscosity mixture which is then reacted with
the waste. The resulting mixture can be molded. The cured product is char-
acterized by high strength and hardness and ability to resist chemical attack,
especially by acids. The latter property results because, unlike portland
cement, lime does not play a part in the lattice structure of the solid. Haz-
ardous metals are "locked" into the three-dimensional framework of the
geopolymeric matrix (Comrie, Runte, and Davidovits 1988). Therefore, the
ability of a geopolymer to immobilize metals does not rely on the alkalinity
of the system to maintain resistance to leaching, and, thus, the geopolymer
should exhibit exceptional long-term durability even under acidic: environ-
mental conditions. This property should answer many of the commonly
expressed environmental concerns about conventionally stabilised wastes.
3.44
-------
Chapter 3
3.8 Soluble Phosphates
3.8.1 Description
Soluble phosphates and lime have been used commercially to stabilize
fly ash and mixtures containing fly ash resulting from the combustion of
municipal solid waste. It has been postulated that this process may also be
of use in the stabilization of other wastes heavily laden with metals, such as,
medical waste ash, insulation wastes, metals smelting dusts, contaminated
soils and metal contaminated sludges. It is primarily effective against lead
and cadmium, but may be of benefit also in controlling other toxic metals.
The process involves the addition of various forms of phosphate and
alkali for control of pH as well as for formation of complex metal mol-
ecules of low solubility. The intent is to immobilize or insolubilize the
metals in the solid waste over a wide pH range. Unlike most other stabili-
zation/solidification processes, soluble phosphate processes do not convert
the waste into a solid, hardened, monolithic mass. Instead, the treated waste
retains its paniculate nature. It remains free-flowing, and increases little in
volume.
3.8.2 Scientific Basis
The process is based on the conversion of lead or cadmium to metal
phosphates of very low solubility. Table 3.5 (on page 3.46 (Conner 1990))
indicates the solubility of various phosphate species and shows that most
metal phosphates are highly insoluble in water.
Many metals can be precipitated as silicates, sulfides, hydroxides, car-
bonates, etc. The solubilities of these species will depend, to some extent,
on the complexing ion and on pH. Phosphates typically have the ability to
bind with lead and other toxic metals in insoluble complexes over a rela-
tively wide pH range, although they may resolubilize under acidic condi-
tions.
The effect of phosphate addition on precipitation of toxic metals can be
illustrated by examining its influence on speciation of lead. The dissolution
or precipitation of a solid phase can be described by the solubility product,
3.45
-------
Process Identification and Description
fable 3.5
Solubility of Various Metal Phosphate Species(a)
Metal
Ag
Al
Ba
Be
Cd
Ca
Cr*
Co
Cu2*
Fe2+
Fe3*
Pb
Mg
Mn
Hg"
Hg2*
Ni
Sr
Tl
Sn2+
Zn
Solubility
A
A/L
A
W
A
A
300
W
A/L (NH4OH)
A
A
A(HC1)
A/L
0.08
A
200
w
A
A
A
A
5000
A
A/L (NH4OH)
26,000
Note: W = water soluble:
w = slightly water soluble;
A = insoluble in water, soluble in acids;
L = insoluble in water, soluble in alkalies;
numbers are mg/L in water at pH 7.0
(a) Adapted from Conner 1990,64-67.
Ks . The following equation depicts a stoichiometric reaction between a
metal cation, M1™*, and a base salt, Aa~ (Eighmy et al. 199 1).
+mA"~ [4]
3.46
-------
Chapter 3
At equilibrium, the reaction is described by the solubility product for the
solid phase, MaAm:
[4.wr
*• }
~
Because the activity of the solid phase is considered to be unity, equation
[5] can be simplified to:
Many precipitation/dissolution reactions are influenced by participation
of Lewis acid-type salts so that equation [4] becomes:
)H+ <=> Mm+ + mHaA
[7]
which, at equilibrium, is described by the thermodynamic equilibrium con-
stant, K°, so that:
Table 3.6 (on page 3.48) presents thermodynamic equilibrium constants
for many lead solid phases (Lindsay 1979). These are useful in depicting
the pH-dependent relative solubilities of these minerals. The more negative
the log K° value, the more insoluble is the mineral. As can be seen, most
lead phosphates have very low solubilities. These equations can be used to
prepare solubility diagrams for the various lead solid phases, based on solu-
tion pH (see figure 3.10 (on page 3.49)). Lead concentrations below the
indicated solubility isotherm for a given species reflect undersaturation and
potential dissolution of a solid phase in contact with the solution. Concen-
trations above the isotherm reflect supersaturation and precipitation of the
indicated solid phase.
3.47
-------
Process Identification and Description
As shown in figure 3.10 (on page 3.49), Pb5(PO4)3Cl is the most in-
soluble lead mineral that might form. In phosphate stabilization systems, in
which high pH values result from the addition of alkali along with the phos-
phate, PbO and PbSiO, can also be dominant solid phases that are effective
in controlling aqueous lead concentrations, while PbCO3, Pb(OH)2 and
PbSO4 tend towards greater solubility. This suggests that use of phosphate
or silicate would be preferable as chemical treatments that could sequester
and precipitate teachable lead in alkaline wastes.
Santillan-Medrano and Jurinak (1975) studied the solid phases control-
ling soil pore water aqueous lead concentrations. They found that in
noncalcareous soils, the solubility of lead was controlled by Pb(OH)2,
Pb3(PO4)2, Pb4O(PO4)2 and Pb5(PO4)3OH. In calcareous soils, PbCO3 and
Pb5(PO4)3OH were the principal controlling solid phases. The latter would
Table 3.6
Lead Solubility Equilibria'0'
Equilibrium Reaction log K*
General Lead Solid Phase
(1) PbO+2H*<=»Pb2*+H2O 12.8')
8-1'S
4.6:5
(4) PbCO3Cl2+2H\=»2Pb2*4C02(g)+H20+ 2C1 -1.8B
(5) Pb(C03)2(OH)2-t*H*»3Pb2*+2C02(g)+ 4IL.O 17.51
(6)PbS04<=>Pb2*+S042- -7.79
5.94
-27.51
Lead Phosphate Solid Phases
(9) PXHjPO^oPb^^FyO,,- -9.85
(10) Pb(HPO4)+H*«Pb2++H.,PO4- -4.25
(11) Pb3(P04)2+4rr«3Pb2*+2H2P04- -5.26
(12) Pb4O(PO4)2+*H<=>4Pb2t+2H2PO4-+ H2O 2.2*
(13) PbJ(PO4)3OH+7H+<=>5Pb2++3H2PO4-+ HJ3 -4.14
(14) Pb5(P04)3Br4«H+<=>5Pb2++3H2P04-+ Br" -19.49
(15) PbJ(PO4)3a+6H+fc>5Pb2++3H2P04-+ CF -25.05
(16) PbJ(PO4)JF+«ffo5Pb2*+3H2PO4-+ F -12.98
(a) Adapted from Lindsay 1979
3.48
-------
Chapter 3
Figure 3.10
Solubility Diagrams tor Simple Mineral Phases Containing Lead
0.0
2.0 -
4.0 -
6.0 -
10.0 -
12.0 -
14.0 -
16.0
pH
Adapted from Bobowski 1991
be analogous to a phosphate stabilization system in which lime was added
along with the phosphate. These findings are in agreement with the solubil-
ity diagram in figure 3.10.
Figure 3.11 (on page 3.50), a solubility diagram for various lead phos-
phate minerals, (Eighmy et al. 1991), indicates that the addition of soluble
phosphates to a waste containing lead will convert the lead into very in-
soluble species. In most cases, the solubility is below 1 \ 10'6M and may be
as low aslx 10"14M. Figure 3.11 shows also that the immobilization occurs
3.49
-------
Process Identification and Description
Figure 3.11
Solubility Diagrams for Lead Phosphate Minerals
0.0
2.0-
4.0-
6.0-
10.0-
12.0-
14.0-
16.0
Pb5(po4)3a '- %
^ Pb4CKP04)2 x
Pb,(P04)3Br
Pb3(P04).
10
12
14
pH
Adapted from Eighmy at al. 1991,20
over a wide pH range. Only under highly acidic conditions will lead con-
centrations in leachate become important. Adding lime along with the
phosphate helps assure that there is sufficient alkalinity to prevent this from
occurring.
3.8.3 Status of Development
Wheelabrator Environmental Systems Inc. has a patented process (patent
no. 4,737,356; April 12,1988) called the WES-PHix process which uses
soluble phosphate technology for immobilization of lead and cadmium in
3.50
-------
Chapter 3
ash residues and other waste streams. It is a totally enclosed, in-line system
which, it is claimed, reduces leaching of lead and cadmium to below TCLP
limits, eliminating the need for Resource Conservation and Recovery Act
(RCRA) Part B permits. The process, developed in 1985, has been permit-
ted by several state and local regulatory agencies. The WES-PHix process
technology is currently being offered by Wheelabrator to various industries
internationally through site-specific license agreements. Because it is to-
tally enclosed, potential health or safety problems for workers are minimal.
The resulting product is still in particulate form, with little increase in vol-
ume, so final disposal requirements are minor.
3.8.4 Operational Considerations
Mix formulations must be determined for the particular site, although the
patent provides some general guidance. The fly ash to be treated is first
mixed with lime in a ratio of 0.2 parts lime to 5 parts fly ash by weight.
The fly ash-lime mixture is then mixed with bottom ash, generally in the
range of 5 to 20% fly ash by weight. The lime-fly ash-bottom ash mixture
is then treated with water soluble phosphate to complete the immobiliza-
tion. The amount of water soluble phosphate required will depend on such
variables as alkalinity of the solid residue, its buffering capacity, and the
amount of lead and cadmium initially present. Generally, an amount of
water soluble phosphate source equivalent to between 1% and about 8% by
weight of phosphoric acid, HjPO4, based on total solid residue, is sufficient.
Any convenient source of water soluble phosphate may be used. Such
sources can be phosphoric acids, including orthophosphoric acid,
hypophosphoric acid, metaphosphoric acid, and pyrophosphoric acid, as
well as less acidic sources of soluble phosphate such as, monohydrogen
phosphate and dihydrogen phosphate salts, and trisodium phosphate. How-
ever, calcium phosphate cannot be used, as it was found not to bind lead or
cadmium.
3.9 Comparative Costs
All of the processes addressed in this monograph, with the exception of
vitrification and organic polymer technologies, use much the same equip-
3.51
-------
Process Identification and Description
Table 3.7
Comparison of Two Stabilization/Solidification Scenarios
Waste Type
Contaminant/Level
Waste Quantity
Transportation
Mobilization/Demobilization
Treatability Study & QA/QC
Excavation
Stabilization
Landfill
TOTAL COST
TOTAL COST PER YD3
Case "A"
Soil
Lead/400 mg/kg
50,000yd3
$25,000
$30,000
$250,000
$2,500,000
$1,000,000
$3,805,000
$76.10
Case"B"
Sludge
Hex.
Chromium/2,000
mg/kg
1000yd3
$40,000
-
-
$5,000
$150,000*
$100,000
$295,000
$295.00
* Includes state/local disposal tax
ment and processing techniques. Therefore, the differences in the cost of
stabilization/solidification applied through these technologies will depend
principally upon reagent costs and can be projected on this basis. Since
stabilization/solidification embraces proven technologies, its overall costs
are well established. For example, Conner (1992) gives a cost comparison
of two stabilization/solidification scenarios, shown in table 3.7. Case "A"
shows estimated costs for the large-scale remediation through stabilization/
solidification of a low-hazard, lead-contaminated soil at a "dry" industrial
plant site. Case "B" shows estimated costs for the stabilization and disposal
of single truckloads of sludge contaminated with high levels of hesavalent
chromium at a fixed treatment, storage, and disposal facility 200 miles from
the waste site. Of the total price for the remediation (about $83/tonne ($75/
ton)), $55/tonne ($50/ton) is for the stabilization operation itself. Of this
$55, typical reagent cost for a cement-based process would be about $22, or
about 40% of the overall stabilization price. This ratio is common for con-
ventional processes on large-scale jobs.
3.52
-------
Chapter 4
POTENTIAL APPLICATIONS
4.1 Sorption and Surfactant Processes
Wastes amenable to sorption or surfactant processes include, but are not
limited to, the following:
• oily waste;
• industrial sludges contaminated with inorganics and low levels
of organics;
• soil contaminated with inorganics and low levels of organics;
• acid mine leachate and tailings; and
• radioactive liquid scintillation fluids.
Many demonstrations involving sorbents have been performed under
field-scale conditions. The effectiveness of sorbents for stabilizing organic
waste has not been demonstrated with this data; while reduction in leach-
able metals was observed.
The Silicate Technology Corporation (STC) process treated wood preser-
vation-contaminated soils containing pentachlorophenol (PCP) with a total
raw concentration ranging from 2,000 mg/kg to 8,300 mg/kg (US EPA
1992a). The hydraulic conductivity of the treated waste was on the order of
10"7 cm/sec and the unionized compressive strength (UCS) ranged between
1.2 to 5 MPa (170 to 720 psi). Weight loss from thermal cycling and wet/
dry was less than 1%. Volume increase averaged 68%. Table 4.1 (on page
4.2) presents the leaching/extraction data. Concentrations of PCP were
reduced 93 to 97% using an organic extraction test, however, the Toxicity
Characteristics Leaching Procedure (TCLP) data showed an increase in PCP
4.1
-------
Potential Applications
Table 4.1
TCLP and Organic Extraction Test Data for Silicate Technology Corporation
Process for Wood Preserving Contaminated Soils
TCLP Leaching
(mg/1)
Compound
Metals:
Arsenic
Chromium
Copper
Organics:
Pentachloro-
phenol
Raw
1.8
0.13
3.42
1.5
Treated
0.86
0.245
0.090
3.42
Reduction
(Corrected)
91.6
-232
95.4
-302
Orgaic Extraction
(mg/kg)
Raw
NA
NA
NA
2,350
Treated
NA
NA
NA
85.5
Reduction
(Corrected)
ND
ND
ND
93.6
NA = Not Analyzed
ND = Not Determined
Note: % reduction adjusted for binder addition
adapted from US EPA, 1992
in the treated waste. The TCLP leaching values were reduced for arsenic
and copper, but increased for chromium.
The International Waste Technologies (IWT) process and the GEOCON
mixing process were combined for an in situ stabilization demonstration for
treating a polychlorinated biphenyl (PCB) contaminated soil (US EPA
1990b). No overall trend in PCB changes from raw to treated waste were
evident, although certain data point pairs showed differences. Results from
the freeze/thaw test failed an arbitrary limit of less than 5% weight loss. The
UCS averaged 2 MPa (288 psi) and the hydraulic conductivity was 107 cm/sec.
The Soliditech, Inc. process treated contaminated soil, waste filter cake
material, and oily sludge from an oil company site (US EPA I990c). Table
4.2 (on page 4.3) presents the leaching data. The TCLP leaching values for
lead and arsenic decreased 85% to more than 99%; however, TCLP leach-
ing values for barium increased. Polychlorinated biphenyls were not de-
tected in the TCLP extracts of the raw or treated waste. Less than 1%
weight loss after wet/dry and freeze/thaw was noted. The average volume
increase was 22%. Hydraulic conductivity was 17 cm/sec. The UCS ranged
from 2.8 to 6 MPa (390 to 860 psi).
4.2
-------
Chapter 4
Table 4.2
TCLP Leaching Results for Soliditech Process
Compound
Organics:
(ug/L)
Acetone
Toluene
Arochlor 1242
Metals:
(mg/L)
Lead
Barium
Arsenic
Filter Cake
Raw Treated
250
<2.0
<0.42
4.3
1.4
0.5
<210
<2.0
<0.45
<0.20
1.3
<0.20
Cake/Sludge Off Site Area
Raw Treated Raw Treated
1,000
55
<0.43
5.4
2.5
0.28
<820 200
<24 270
-------
Potential Applications
was found to substantially improve the end product by making it highly
hydrophobic and substantially impermeable to water. Furthermore, no su-
pernatant liquid was produced during the solidification process.
Asphalt fixation has also been suggested for wastes produced by paint
removal, metal finishing, electroplating, and allied industries (Kulkarni and
Rosencrance 1983). Microencapsulation with asphalt was found to greatly
reduce leaching of metals and cyanide.
Several vendors are now marketing cold asphalt processes for encapsula-
tion of petroleum-contaminated soils resulting from spills or leaks. In es-
sence, the cold mix asphalt process uses an emulsifier to allow water to be
combined with the asphalt, resulting in a mixture that has a viscosity low
enough to be mixed with aggregate (contaminated soil). This emulsion
keeps the asphalt particles separated from each other by a thin film of water.
When the emulsified asphalt and aggregate have been mixed and placed,
pressure from compaction breaks the water film to allow asphalt particles to
come into contact with each other and the aggregate (Testa and Patton
1991). The resulting material could be used for highway paving, but the
products of treating petroleum-contaminated soils would probably have
lower strength and durability because of the presence of fines. This mate-
rial may be suitable for low-use road base, parking lots, dust abatement,
bank stabilization, storage areas, etc.
Applied Environmental Recycling Systems, Inc., (AERS) Salem, Mass.,
is recycling petroleum-contaminated soils into cold asphalt paving. Recy-
cling is achieved by separating the soil components, crushing large pieces to
a maximum size, recombining the components in proportions suitable for
paving, and mixing the material with specific emulsions and additives. Be-
cause the process is conducted at ambient temperatures, volatilization is not
a concern, and no extra energy is consumed (Anonymous 1990). Applied
Environmental Recycling Systems, Inc., is focusing on petroleum contami-
nants, but the firm also is conducting tests on soils containing hazardous
wastes, such as chlorinated hydrocarbons. The firm has also evaluated the
process for use with foundry slag.
American Reclamation Corporation (AmRec) has a similar emulsified
asphalt process. This process has been used to convert 12,000 tonne
(13,230 ton) of oil-contaminated soil into safe, asphaltic concrete paving at
a site in Worcester, Mass. (Anonymous 1991; Camougis 1990).
4.4
-------
Chapter 4
In a demonstration project for the U.S. Naval Civil Engineering Labora-
tory (NCEL), scientists from Battelle Memorial Institute demonstrated that
contaminated sandblasting grit could be incorporated into a cold asphalt
mix that could be used as a roadbed. A section of road has been laid using
this asphalt and will be monitored for long-term performance (Nehring and
Brauning 1992).
4.3 Bituminization
The bituminization process was developed primarily for low- and me-
dium-level radioactive waste solutions. These solutions include: evapora-
tor concentrates, filter sludges, and ion-exchange resin slurries. No sources
are available on the use of this material for purely hazardous chemical
wastes. The process has been evaluated, however, for mixed radioactive
and hazardous chemical wastes (Simpson, Vidal, and Morris 1988). The
report postulated potential applications of sludges from metal plating opera-
tions, laboratory sink drains, metal preparation cleanup operations, decon-
tamination processes, and mop waters. In this process, the bitumen was
designed to contain contaminants such as nitrates, cyanide, nickel, and cad-
mium, as well as radioactive wastes.
Although not yet widely used on a variety of waste sites, significant field
data has been collected in past demonstrations and tests which are summa-
rized in this section.
4.4 Vitrification
Vitrification systems are generally applicable to contaminated soil, slud-
ges, slurries with radionuclides, heavy metals, and other inorganic contami-
nants, such as nitrates. Vitrification systems are also used to destroy com-
bustible and organic contaminant materials that may coexist with inorganic
contamination. Vitrification processes are generally accompanied by offgas
treatment trains to remove volatile metals, particulates, and organics that
evolve from the process before offgas discharge. In general, vitrification
4.5
-------
Potential Applications
processes are able to handle a wide variety of wastes. The following are
examples (US EPA 1992b):
• radioactive waste and sludges;
• soils and sediments contaminated with radionuclides, heavy
metals and organics;
• incinerator ashes;
• industrial wastes and sludges;
• medical wastes;
• drummed wastes;
• shipboard wastes; and
• asbestos wastes.
Each of the vitrification processes may have special advantages in pro-
cessing a particular waste. The following subsections discuss potential
applications that are best suited to each vitrification process.
4.4.1 Refractory-Lined Melters
Refractory-lined melters are best suited for intermediate quantities of
concentrated contaminants in either solid combustible or liquid slurry form
that either have been previously collected or are currently being generated
or stored. One example of a refractory-lined melter application is a vertical
melter for the treatment of high-level radioactive wastes. This type of
melter has been designed and constructed for operation within the Defense
Waste Processing Facility at DOE's Savannah River Site. The vertical
melter has also been used for several pilot-scale tests with simulated high-
level radioactive wastes (Perez and Nakaoka 1986). Pilot-scale tests of a
horizontal melter for Resource Conservation and Recovery Act (RCRA)
wastes have also been conducted (Peters 1985). Other plans involve using a
vertical melter at DOE's West Valley, New York, site to process high-level
radioactive wastes. Recent efforts include designing a vertical melter for
municipal solid waste incinerator ash applications (Chapman 1991). The
system is also under consideration for processing medical wastes. Use of
an electric arc furnace has been demonstrated for industrial and municipal
waste by the American Society of Mechanical Engineers — Bureau of
Mines in 1992. Seven commercial-sized vitrification plants using a water-
cooled wall design have been built and are operating for municipal waste
4.6
-------
Chapter 4
combustor ash. These systems are being used with ash as well as soils con-
taminated with hexavalent chromium, vanadium pentoxide, and sludge and
industrial ash.
4.4.2 In Situ Vitrification (ISV)
The ISV process is generally suited for treatment of large quantities of
contaminated soils or sludges or for treatment of soils and sludges that have
been staged or stockpiled awaiting treatment. Restaging of contaminated
soils becomes possible when the contamination is spread over a large sur-
face area at shallow (<1 m (3 ft)) depths. Simple excavation techniques and
stockpiling in the center of the site makes for more efficient operation of the
process. Since a single processing unit is capable of treating approximately
23,000 rnVyr (30,000 ydVyr), relatively large quantities of contaminated
soil can be processed. Prudent application of the technology, however, calls
for vitrification of "hot spots" in combination with other restoration tech-
nologies, such as capping, for the less concentrated areas.
To date, the ISV process has been used on three hazardous and/or radio-
active sites, including a transuranic waste site and a hazardous chemical and
radioactive waste site at DOE's Hanford site near Richland, Washington.
The results of these tests have been published (Buelt, Timmerman, and
Westik 1989; Luey et al. 1992). The process has also been demonstrated on
a pilot-scale at a fire training pit at the Arnold Air Force Base in Tennessee
(Timmerman and Peterson 1990). Records of Decision (RODs), supported
by treatability tests, have selected ISV as the preferred treatment method for
six Superfund sites in five states. These sites vary as to contaminants, hav-
ing soils contaminated with PCBs, radium, pesticides, heavy metals, and
radionuclides. At the time of this writing, the ISV process is being applied
at the first of these six sites, the Parson's Chemical Superfund site in Grand
Ledge, Michigan.
4.4.3 Thermal Vitrification
Rotary kiln vitrification, because of its large processing rates of 90
tonne/day (100 ton/day), is best-suited to large quantities of contaminated
soils that can be easily excavated. This technology is also well-suited for
incinerator fly ash. Because of constraints of the rotary kiln, however, par-
ticle size and foreign substances must be carefully controlled. In addition,
because of limited retention data available for the more volatile contami-
4.7
-------
Potential Applications
nants, such as lead, arsenic, and cadmium, it is better suited for organic
contaminants or nonvolatile inorganic contaminants, such as chromium. In
one case, this technology was used upon soils contaminated with a chemical
at a dye plant in Oak Creek, Wisconsin. The soils were found to be con-
taminated with carcinogenic residues and lead. Materials in the amount of
45,000 tonne (50,000 ton) were processed at this site (Sulzer, Albert, and
Palmer 1988). This process has been used much more extensively, how-
ever, for treatment of organic contamination (McGowan and Harmon 1989).
Even though large capacity systems with equivalent soil-processing rates
of 9 tonne/hr (10 ton/hr) have been used for the combustion of coal for
decades, cyclone incinerators are just emerging from development as a
hazardous waste vitrification process (Batdorf, Gillins, and Anderson
1992). Pilot-scale tests have been completed on hazardous dust containing
lead, cadmium, and chromium. Tests have also been performed on liquid
wastes, including wastewaters and carbon tetrachloride. The technology is
currently being investigated as a process option for solidifying the low-level
waste fraction of slurries currently stored at DOE's Hanford, Washington,
installation.
4.4.4 Plasma Vitrification
The plasma processes are best suited for small concentrated quantities of
slurries at relatively low throughput rates (0.45 tonne/hr (0.5 ton/hr)). The
plasma arc is also well-suited to treat solid materials such as metals, glass,
rubber, plastic, and filter elements. Tests with a 600 kw plasma torch have
been completed on soils spiked with 15% oil (US EPA 1992b). These tests
showed air to be the most satisfactory plasma gas over that of argon and
argon/oxygen mixtures. Results showed destruction and removal efficien-
cies of between 99.99% and 99.999%. The plasma centrifugal furnace has
been demonstrated in the US EPA SITE program with 1,800 kg (4,000 Ib)
of waste. The graphite-electrode DC arc furnace has completed a series of
tests on simulated contaminated soil and combustible and metallic waste
material for the DOE's Buried Waste Integrated Demonstration (BWID)
technology development program (Surma et al. 1993).
4.8
-------
Chapter 4
4.5 Modified Sulfur Cement Process
The modified sulfur cement process was developed primarily for
predried or slightly-wetted paniculate wastes, such as, incinerator ash, con-
taminated soils, sludges, metals, and mill tailings (Kalb, Heiser, and
Colombo 1991b). Waste form development and property evaluation studies
have been performed also on the incorporation of evaporator bottoms and
spent ion-exchange resins generated at commercially-operated nuclear fa-
cilities (Kalb and Colombo 1985).
Other applications of modified sulfur cement include barriers, storage
bins, and disposal containers.
4.6 Polyethylene Extrusion Process
The polyethylene extrusion process has potential applications in the en-
capsulation of primary and secondary waste streams produced by waste
management and environmental restoration activities. The process can be
adapted for ex situ waste treatment, and it is conceivable that it can also be
applied to in situ applications, although it has not yet been field-proven.
The following waste stream applications of the technology at DOE sites
and facilities have been identified:
• Rocky Flats - nitrate salt wastes, sludges, ion-exchange resins,
incinerator ash;
• Idaho National Engineering Laboratory - buried wastes, includ-
ing over 2,300 m3 (3,000 yd3) of buried nitrate salt cake, incin-
erator ash, ion-exchange resins;
• Hanford - underground single shell tank wastes, predominately
nitrate salts, sludges and ion-exchange resins;
• Oak Ridge - nitrate salts, sludges, heavy metals; and
• Savannah River - aqueous blow-down scrubber solution.
4.9
-------
Potential Applications
4.7 Inorganic, Cementitious Technologies
of the Siliceous Category
This is the broadest category of stabilization/solidification processes
from the standpoint of existing and potential applications. 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 hazard-
ous and nonhazardous wastes. The basis for such extended applications lies
in the processes' capacities for (1) lowering teachability through chemical
reaction, microencapsulation, reducing permeability, and improving physi-
cal durability, and (2) improving physical properties for better landfills or
beneficial reuse.
4.7.1 Soluble Silicate Processes
The innovative soluble silicate processes are intended to extend applica-
tions primarily by lowering leachability through chemical reaction, micro-
encapsulation, or reducing permeability. They may also, as is the Conner
process (Conner 1985), be directed to solidify low-solids wastes. These
processes apply primarily to metal-containing wastes for which the primary
concern is the toxic metals, as defined by the US EPA.
4.7.1.1 EnviroGuard/ProTek/ProFix, Houston, Texas
This process was designed to be used in two waste treatment applica-
tions:
• where physical sorption is required to take up the excess water
in low-solids wastes, while still producing a hardened product
by chemical reaction, a requirement under the 1985 Land Dis-
posal Restrictions; and
• where partially soluble metal species are present in the: waste,
which could continue to dissolve out over time, or diffuse out
from porous particles. The slow, continuous generation of
soluble silicate provides a reserve capacity that can re-speciate
the dissolving metal as "silicates."
Because of its high sorptive capacity, porous structure, and high surface
area, the process might also be applied to immobilize organics. Some ash
4.10
-------
Chapter 4
also has sufficient carbon content - up to 5% - to potentially act in a fash-
ion similar to activated carbon.
4.7.1.2 Lopat, Wanamassa, New Jersey
The Lopat process has conventional applications, but may be considered
innovative in applications where the liquid soluble silicate is used to di-
rectly treat the waste. This step may be followed by solidification with
conventional cementitious reagents, depending on the requirements of the
project. Innovative use of the Lopat process lies in applications where a
pretreatment with soluble silicate solutions is necessary or is preferable.
This most often occurs where the waste to be treated is not finely divided
and relatively homogeneous, but, instead, is very heterogeneous in physical
form and often in chemical makeup. Such wastes include auto shredder
fluff, incinerator bottom ash, contaminated debris, and some soils. Another
innovative use lies in applications where the treatment chemicals are not
physically-mixed with the waste, but are infiltrated into it. An example is
the stabilization of contaminants in soil by injection or permeation of a fluid
from the surface, without substantially disturbing the soil.
4.7.1.3 Other Soluble Silicate Processes
The authors do not know of applications of the possible soluble silicate
formulations described in Section 3.7.5.1, since they are not presently used
and are not being tested as commercial processes. The Conner process was
designed to be used with low solids wastes where processing with liquid
silicates alone would be too sensitive to mixing time and waste variations.
4.7.2 Slag Processes
Slag processes are especially applicable in remediating wastes from pri-
mary metal refining when practiced at the producer's site where the slag is
available at little or no cost, or even with a credit for waste disposal. The
Oak Ridge National Laboratory (ORNL) process was designed for the im-
mobilization of technetium and nitrates. As it applies to reduction of mo-
bile, higher oxidation states of metals, the demonstrated process would be
applicable to Tc+7 and Cr**.
The same applies to the cement-slag process. In general, slag improves
certain physical properties such as porosity and tortuosity, thereby improv-
ing retention of a number of species. The SoliRoc™ process is a special
4.11
-------
Potential Applications
case, developed especially with strongly acidic, metal-containing waste
solutions in mind (MECHIM 1975). It is most economical in treating this
kind of waste, because the initial step requires acidifying the waste, unless
it is already acidic, to dissolve the metals. Metal finishing, metal surface
treatment, and steel pickling acids are good candidates. Other metal-bear-
ing wastes can be treated - sludges, filter cakes, etc. - but, again, the waste
must be acidified before treatment, requiring an extra step and cost.
4.7.3 Lime
Lime is widely used in the "stabilization" of sewage sludge (Roediger
1987), primarily for odor control and pathogen reduction. Some specific
stabilization/solidification applications of lime are listed in table 4.3.
Table 4.3
Specific Stabilization/Solidification Applications of Lime
PROCESS
Lime
Lime
Lime + Hydrophobizing Agent
Lime + Special Reagent
Lime
Lime + Gypsum
Lime
Lime or Lime/Fly Ash
WASTE
Steel Pickle Liquor
Ferric chloride etching waste
Oily waste
Hydrocarbon waste
Incinerator ash
Petroleum sludge
Phosphoric acid residue
V&rious
REFERENCE
Sandesara 1980
Oberkrom et al. 1985
Boelsing 1977
SRS 1988a&b
Japan Patent 1988
Nippon Mining 11980
Schroeder et al. 1980
DuPont 1986
Adapted from Conner 1990
Lime has been used rather extensively in recent years in remediation
projects, especially in the stabilization/solidification of oily wastes and tars
(DuPont 1986). It is in these applications that the processes described in
this monograph find their primary use, at least, in the sense of innovative
methods.
4.12
-------
Chapter 4
4.7.4 Inorganic Polymers Category
The geopolymer process should, technically, be applicable to all, or al-
most all, of the same kinds of wastes to which cement- or pozzolan-based
stabilization/solidification methods are applicable, and in the same
remediation scenarios.
4.8 Soluble Phosphates
The WES-PHix process was designed specifically for treatment of
lead and cadmium in refuse-to-energy ash, but its use has now been ex-
panded for treatment of medical wastes ash, insulation wastes, metals-
smelting dusts, contaminated soils and metal-contaminated sludges. Based
on the solubility data given in table 3.1 (on page 3.9), the process may also
be suitable for many toxic metals in addition to lead and cadmium.
4.13
-------
-------
Chapter 5
PROCESS EVALUATION
5.1 Sorption and Surfactant Processes
5.1.1 Process Performance and Effectiveness
Sorption and surfactant stabilization/solidification technology has
evolved from bench-scale studies to full-scale implementation. This section
will discuss relevant research. Results of full-scale implementation are
discussed in Section 4.1.
Various binders were evaluated for their ability to sorb dichloromethane
as part of a solidification process for a waste oil (Wolf 1988). Table 5.1 (on
page 5.2) shows that generally the inorganic solids were weak sorbents,
except ground slate (the fly ash was approximately 3% organic carbon).
The organic fillers and binders exhibited very high partition coefficients,
with the exception of coarse-grained coke. Various combinations of these
binders and fillers resulted in the leaching of only a small amount of
dichloromethane into distilled water, even though the solubility of this com-
pound is high.
The attenuative capacity of three materials (kaolin, fly ash, and sawdust)
was investigated in a column testing procedure being utilized in a solidifica-
tion process (Benson 1980). Table 5.2 (on page 5.3) shows the capacities of
these materials as to the various metals being solidified. The sawdust ca-
pacity was believed to have been enhanced due to organic complexation
reactions.
Several studies have reported upon the use of organophilic clays to re-
move organic compounds from water. These clays have been evaluated for
their ability to stabilize a wide variety of soils contaminated with organics.
5.1
-------
Process Evaluation
TableS.l
Partitioning Coefficients for Organic Fillers and Binders Evaluated for
Stabilizing Dichloromethane
Material
Partitioning
Coefficient
Inorganic Fillers:
Quartz 2
Infusorial Silica (0.015 to 0.040mm) 113
(0.040 to 0.063mm) 25
(0.063 to 0.200mm) 23
Ground Slate 5,200
Marl 31
Chalk 33
Clays:
Kaolinite
niite
U lite/Smectite
Melionile
Na-bentonite
Ca-bentonite
Inorganic Binders:
Kiln Cement
Cement
Waste Kiln Dust
Waste Kiln Dust/Fly Ash (50/50)
Coal Fly Ash
Organic Sorbents:
Fine Coke (<2 mm)
(0.20 to 0.63 mm)
(0.63 to 1.0 mm)
(1.0 to 1.5 mm)
Raw Brown Coal
Dry Burning Brown Coal
Brown Coal Dust
88
1,320
990
5
132
68
29
36
75
14,000
6,100
87,000
9,100
6,000
5,100
26,000
37,400
80,000
Adapted from Wolf 1988, Table 3
An evaluation of the organophilic clays conducted with four polyaromatic
compounds, each with a concentration of less than 20 mg/kg, showed sig-
nificant reductions in an organic extraction test (Soundararajan, Barth, and
5.2
-------
Chapter 5
Table 5.2
Attenuative Capacity of Various Materials for Heavy Metals
Metal
Chromium
Copper
Cadmium
Lead
Zinc
Kaolin
(mg/g)
0.69
0.26
0.05
0.28
0.13
Fly Ash
(mg/g)
0.91
0.64
0.22
1.60
0.51
Sawdust
(mg/g)
1.28
0.63
0.11
1.42
0.30
Adapted from Benson 1 980
Gibbons 1990). Furthermore, sorbent effectiveness evaluation techniques
such as fourier transom infrared spectroscopy (FTIR) and differential scan-
ning calometry (DSC), coupled with gas chromatography/mass spectros-
copy (GC/MS), suggested interactions.
In another evaluation of organophilic clays, an organic waste (petroleum,
1% by weight) was stabilized with a combination of activated carbon,
organoclay, and silicate. No compounds could be detected in an organic
extraction test, and FTIR data suggested interactions (Frost and Carandang
1990).
In a study involving 1,000 mg/kg each of phenol, trichlorophenol (TCP),
and PCP, the relative amounts of organoclay, soil, cement, and contaminant
determined the immobilization effectiveness (Sell et al. 1992). The TCP
and PCP appeared to be immobilized according to the Toxicity Characteris-
tic Leaching Procedure (TCLP) test, while the phenol was not as efficiently
bound.
A decreased water extraction efficiency for organic waste up to 12% was
observed when modified clays were added to cement to stabilize liquid
phenol and chlorinated phenols (Montgomery et al. 1988). The stabilization
increased as the degree of chlorination and hydrophobicity increased.
The use of surfactants to act as dispersing agents has been evaluated for a
waste containing organic material. Table 5.3 (on page 5.4) shows a signifi-
cant reduction of organics using an organic extraction test.
5.3
-------
Process Evaluation
Table 5.3
Organic Extraction Test Data from Wastech Process
Organic Extraction (|ig/kg)
Treated
Compound Raw Waste Waste % Reduction
Benzene
Toluene
Trichloroethylene
1,3 Dichlorobenzene
Ethyl Benzene
M/P Xylene
1,2/1,4 Dichlorobenzene
O-Xylene
<2.0 <1.7
28.0 <1.7
1,000.0 4.8
33.0 2.1
24.0 <1.7
12.0 <1.7
3,800.0 68.0
59.0 <1.7
ND
>85
98.9
85.2
83.5
>67
95.8
93.3
ND = Not determined because of small difference.
Note: % reduction adjusted for binder dilution
Adapted from Peacocke 1991,37-66
5.1.2 Types and Amounts of By-products
The DSC, coupled with GC/MS, suggested that the interactions between
the sorbent and contaminant may have produced other compounds after
sorption (Soundararajan, Earth, and Gibbons 1990). Leaching data from
treated waste showed a higher concentration of organic compounds than
was detected in raw waste leachate (US EPA 1990a). It is not known if this
increase was caused by sorbent interaction, the higher pH due to binder
cement, or the conditions of the leaching test. For these reasons, a mass
balance encompassing the air release pathway, binder constituents, binder
dilution, and complete leachate analysis is recommended when evaluating
organic stabilization techniques.
5.1.3 Cost Per Unit Volume
Table 5.4 (on page 5.5) presents a comparison of projected cost per unit
quantity by several vendors that use some type of sorbent in their binders.
Comparisons should not be made among the vendors because of the differ-
ing site conditions and assumptions used in the cost projection. Reagent
costs make these processes slightly more costly than conventional cement
processes.
5.4
-------
Chapter 5
Table 5.4
Cost Per Unit of Sorbent or Surfactant
Stabilization/Solidification Processes
Process Reference
Hazcon
rwr
Soliditech
STC
Cost/Unit
$97.75 to $205.98/ton
$111.50 to $194.45/ton
$152.00/CY
$190.00 to $360.00/CY
Assumptions
300 to 2,300 Ib/min
batch process unit
38,400 tons in-situ
5,000 CY
15,000 CY
Reference
US EPA
1989, Ch.4
US EPA
1990b, Ch.4
US EPA
1990a, Ch.4
US EPA
1992, Ch.4
5.2 Emulsified Asphalt
The emulsified asphalt process has been shown to be effective in solidi-
fying liquid wastes, reducing solidified waste permeability, and improving
the stabilization/solidification of wastes using portland cement and soluble
silicates (Conner 1986b).
Kulkarni and Rosencrance (1983) reported on the use of emulsified as-
phalt in treating electroplating wastes containing Cd2+, Cr3+, Cr6*, Fe2+, Fe3+,
Pb2+, Zn2+, Ni2+, Hg2+, and CN1'. A leaching study was carried out on the
immobilized waste using an acetic acid/sodium acetate leachant buffered at
pH 4.5 and two extractions. Results showed that the metals and cyanide
leached from the fixed samples were very low in concentration; all were
less than 0.5 mg/L and several were below detection limits.
Applied Environmental Recycling Systems, Inc., evaluated the use of a
cold asphalt emulsion process on petroleum-contaminated soils. Using the
Extraction Procedure Toxicity Test (EP Tox), AERS found that levels of
total petroleum hydrocarbons and eight metals were below detection limits,
except for barium, which was present in two samples at levels of less than 2
mg/L (Anonymous 1990).
The AmRec process was evaluated using the EP Tox. No petroleum
hydrocarbons were detected in any extraction liquid (Camougis 1990).
5.5
-------
Process Evaluation
Means, et al., (1991) evaluated the recycling of spent sandblasting grit
into asphalt concrete. They found the product, produced at a spent grit
proportion of about 7 to 10% by weight, to be very stable and suitable for
use for light-traffic roadways.
The cost of operating the cold asphalt emulsion process has been esti-
mated to be about $88 to $110/tonne ($80 to $100/ton) of petroleum-con-
taminated soil; it could go up to $165/tonne ($150/ton) for material with a
high metal content (Anonymous 1990).
The cost of recycling sandblasting grit into asphalt concrete has been
reported to be much lower than the cost of disposal. One study found the
cost of continued disposal in a hazardous waste landfill to be $l,452,000/yr
versus a maximum cost of $220,000/yr for the recycling option, based on an
estimated annual production of 2,000 tonne (2,200 ton) of spent grit ($1107
tonne ($100/ton)) (Means et al. 1991).
5.3 Bituminization
Use of the bituminization process has been limited to the treatment of
low-level radioactive wastes. Westsik (1984) presents an exhaustive ex-
periment and study on the bitumen product in comparison with cement
waste forms. He determined that the teachability of radionuclides from
bitumen is very low with a fractional release rate of less than 10~5 fraction/
day. No data are available, however, for heavy metals or organics. Volatile
and semi-volatile organics would not be expected to be retained, but would
be removed with the water vapor. The water vapor that issues from the
extruder during processing is collected for treatment.
5.4 Vitrification
Tests, demonstrations, and applications of each of these types of vitrifi-
cation processes addressed here have produced a significant amount of data
on the fate of various contaminants. Subsections 5.4.1 through 5,4.4, be-
5.6
-------
Chapter 5
low, present data from a mass balance perspective on the retention or de-
struction of contaminants when treated by the several vitrification processes.
5.4.1 Refractory-Lined Melters
The overall destruction and removal efficiency for refractory-lined
melters ranges from 99.7 to 99.99999% (Pacific Northwest Laboratory
1991).
The retention of inorganic elements within the refractory-lined melter is
highly dependent on the element. Table 5.5 provides some typical decon-
tamination factors within a slurry fed vertical melter (Freeman 1988). The
decontamination factor (DF) is defined as the ratio of the mass of contami-
nant entering the melter to the mass exiting within the offgas stream. A DF
of 100 would be equivalent to a 99% retention of that element. The higher
the DF, the greater the amount of material retained within the glass. The
more volatile elements can be captured by the offgas system, precipitated or
filtered from the scrub solution, and recycled back to the melter.
5.4.2 In Situ Vitrification (ISV)
The ISV process is capable of treating organic contaminants within con-
taminated soils and sludges, as well as inorganic metals and radionuclides.
Table 5.5
Contaminant Decontamination Factor For a Slurry Fed Vertical Melter
Element Average DF
Total
Aluminum
Boron
Cadmium
Chlorine
Cesium
Iron
Lanthanum
Manganese
Sodium
Sulfur
Stroiitium
Tellurium
Zirconium
22,000
100
9.9
2.9
14
1,800
2,100
1,800
300
5.5
1,800
3.0
22,800
5.7
-------
Process Evaluation
The reported destruction efficiency of organics (US EPA 1992b) ranges
from 90% to greater than 99.99% depending on the volatility of the con-
taminant and the configuration within the contaminated soil. For example,
the destruction efficiency of methyl ethyl ketone, a relatively volatile com-
pound, was greater than 99% when contained within a sealed container
(Koegler et al. 1989). Although the process has not yet been adequately
developed for processing sealed containers safely, preliminary tests show
that gases evolving from the sealed container during processing are directed
through the molten glass, allowing higher destruction efficiencies. When
combined with the removal efficiency of the offgas system, the total de-
struction and removal efficiency of organics is greater than 99.99% and can
range as high as 99.99999%.
Pacific Northwest Laboratory reports retention in glass of nonvolatile
metals and radionuclides, such as, chromium, strontium, plutoniurn, and
americium, ranging from 99.99% to 99.999%. The 0.01% to 0.001% by
weight that issues from the molten soil is captured by the offgas treatment
system. For semivolatile metals and radionuclides such as cadmium, lead,
arsenic, tellurium, and cesium, the retention ranges from 50% to 99.9% (US
EPA 1992b). When combined with the offgas treatment system, the reten-
tion can range from 99.99% to 99.99999999% (Buelt and Carter 1986).
Several studies and teachability tests have been performed on the ISV
waste form. For radioactive applications, some of the most relevant studies
are the leachability results from the radioactive demonstrations at Hanford's
116-B-6A site (Luey et al. 1992) and the radioactive test at Oak Ridge Na-
tional Laboratory (Spalding 1992). Table 5.6 summarizes the normalized
release rates for given elements and contaminants.
Table 5.6
Normalized Elemental and Contaminant Releases from
Radioactive ISV Products
Element/Contaminant Normalized release over 28 day period, g/m2
Hanford 116-B-6A Crib ORNL ISV material
Aluminum
Calcium
Potassium
Magnesium
Silicon
Strontium
0.035
0.015
-
0.01
0.04
0.13
003
0.02
0.04
0.05
0.035
-
5.8
-------
Chapter 5
Spalding (1992) also indicates that the fraction of Sr-90 extracted by acid
solutions was reduced by more than two orders of magnitude after treatment
from 0.8 wt % to 0.006 wt %.
When scrap metals exist, it is important to determine the relative durabil-
ity of the metallic phase that forms at the bottom of the vitrified product.
Although no radioactive contaminant information is available, toxicity re-
sults have been reported for heavy metals as shown in table 5.7. These
results provide preliminary indications of the durability of metallic waste
forms that may be counted by this process when scrap metals exist with
radioactive soils.
Table 5.7
TCLP Concentrations for Metallic Phase from one Bench-Scale Test
Contaminant
Arsenic
Barium
Cadmium
Chromium
Silver
Lead
Mercury
Initial cone, in soil (ig/g
4400
4400
4400
270 to 4400
4400
50
46
TCLP cone., metal, mg/L
<5
<1
<1
<0.2 to 2.7
<0.1
<0.1
<0.0001
Allowable cone.
5
100
1
5
5
5
0.2
, mg/L
5.4.3 Thermal Vitrification
The results of using a rotary kiln vitrifier for cleanup of contaminated
soils have been reported (Sulzer, Albert, and Palmer 1988). The processing
rate for this unit is 14 tonne/hr (15 ton/hr) of contaminated soil. At this
process rate, the burner fuel consumption was approximately 1.85 MM Btu/
hr. The operating temperature was generally 980°C (1,800°F), with the
vitrified discharge material at 829°C (1,525°F). At an input concentration
of 400 to 800 ppm of lead in the contaminated soil, the emission rate of lead
at the stack was 0.0998 g/hr (0.00022 Ib/hr). This rate accounts for a mini-
mum removal efficiency of 99.7% from the baghouse filter, meaning that up
to 99.4% of the lead was either retained in the glass or collected in the spray
5.9
-------
Process Evaluation
tower scrub solution, which results in an overall retention of 99.4%. No
information is available, however, on the retention of lead within the glass
product relative to that collected in the spray tower and baghouse filter.
These data are important for a determination whether a meaningful fraction
of lead is retained in the glass as opposed to simply being removed from the
soil and collected within the offgas treatment system.
Preliminary tests with cyclone vitrification tests have shown generally
less effective retention characteristics for semivolatile hazardous constitu-
ents. Even though preliminary tests show 80 to 95 wt% retention of chro-
mium, only 10 to 35 wt% of lead and 8 to 17 wt% of cadmium were
retained in the vitrified slag and were entrained with the offgas after a
single pass (Batdorf, Gillins, and Anderson 1992); much greater retention
values are associated with electrical and plasma vitrification systems. De-
spite these low retention values for semivolatile constituents, preliminary
tests show that the slag passes the TCLP test for metals, and that organic
constituents are generally destroyed to 99.9999 wt% (six nines) efficiency.
5.4.4 Plasma Vitrification
Until recently, no information was available on retention and destruction
efficiencies of plasma systems in treating specific waste contaminants. The
graphite-electrode DC arc furnace tests performed for simulated soil, com-
bustible, and metallic waste material provides data on process performance
(Surma et al. 1993; Wittle et al. 1993). Although specific efficiencies are
not reported, complete pyrolysis of combustible material is indicated. In
these tests, cesium retention was of primary interest, which showed a reten-
tion of between 98.1 wt% and 99.12 wt%. This level of retention compares
well with other vitrification processes. Durability tests with the resultant
slag showed an approximate order of magnitude reduction in teachability
when compared with high-level borosilicate glasses. Leachability tests over
seven days for silicon showed a release rate of 0.030 to 0.080 g/m2 com-
pared to 0.450 g/m2 for typical high-level borosilicate glass. For sodium,
the measured release rate ranged between 0.111 and 0.557 g/m2, compared
to 1.481 g/m2 for high-level borosilicate glass.
5.10
-------
Chapter 5
5.5 Modified Sulfur Cement Process
5.5.1 Process Performance and Effectiveness
Major efforts in the application of modified sulfur cement have been
directed towards the encapsulation of incinerator fly ash containing mixed
wastes generated at the Waste Experimental Reduction Facility (WERF) at
Idaho National Engineering Laboratory (INEL) (Kalb, Heiser, and Colombo
1991b).
The INEL fly ash has a total activity of about 1 to 5 becquerels/gram (40
pCi/g), consisting of mixed fission products (primarily 137Cs) and activation
products (primarily "Co and 125Sb). Elemental analyses of the ash were
performed for 12 elements. Results of these analyses, expressed as percent
by weight of ash, are summarized in table 5.8. Hazardous constituents in-
clude significant concentrations of Pb and Cd. Encapsulation and disposal
of this ash is further complicated by the presence of highly soluble metal
chloride salts (primarily zinc chloride), which create an acidic environment
in the presence of moisture (pH of the ash slurry is approximately 3.8).
This condition can interfere with the solidification reaction of conventional
Table 5.8
Elemental Composition of INEL Incinerator Fly Ash
Element
Zinc
Lead
Sodium
Potassium
Calcium
Copper
Iron
Cadmium
Chromium
Barium
Silver
Nickel
Weight Percentage
36.0
7.5
5.5
2.8
0.8
0.7
0.5
0.2
BDL
BDL
BDL
BDL
BDL—Below detection Units (<0.05 wt%)
5.11
-------
Process Evaluation
solidification materials, such as portland cement. The presence of zinc,
lead, sodium compounds, and chloride compounds has been shown to im-
pede cement hydration or weaken the ultimate mechanical properties of the
waste form by causing cracking or spalling (Conner 1990).
Several mixing systems were investigated for use in encapsulating fly
ash in modified sulfur cement, including high shear stirrers, emulsifiers,
blenders, kneaders, and double planetary orbital mixers. Based on the pro-
cessing requirements for this mixture, a double planetary orbital mixer
equipped with a heat-jacketed container and vacuum capability was chosen
as the most appropriate means of mixing. A laboratory-scale processing
system is shown in figure 5.1.
Formulation and process development work was conducted to determine
the limits and ease of processibility in producing waste forms mat conform
to regulatory criteria. Maximum waste loadings were determined by first
processing at waste loadings above the limits of workability (i.e., extremely
Figure 5.1
Bench-Scale Double Planetary Mixer for Processing Modified
Sulfur Cement Waste Forms
5.12
-------
Chapter 5
dry mixtures that yielded friable products with little structural integrity) and
then adding additional increments of modified sulfur cement until accept-
able workability and product integrity were achieved. Reported waste load-
ings represent percent by weight of dry ash, after all residual moisture has
been removed. Using mis procedure, a maximum waste loading of 55% by
weight INEL incinerator fly ash was determined. Because of its low pH
and high chlorides content, the maximum waste loading using portland
cement achieved at INEL was 16% by weight.
Testing of waste form properties, including unconfined compressive
strength, water immersion, freeze-thaw resistance, and teachability, was
conducted on laboratory-scale specimens to provide information on struc-
tural integrity and potential waste form behavior in a disposal environment.
Compressive strength data for modified sulfur cement waste forms in the
range of 27.6 MPa (4,000 psi) have been reported (Kalb, Heiser, and
Colombo 1991b). Additional testing to demonstrate compliance with U.S.
Nuclear Regulatory Commission (NRC) criteria for low-level waste (water
immersion testing, thermal cycling, and radionuclide teachability) has been
reported previously for similar kinds of wastes (Kalb and Colombo 1985).
The US EPA's initial test criteria for defining characteristic hazardous
waste, those of the EP Tox, were recently superseded by those of the Toxic-
ity Characteristic Leaching Procedure (TCLP). Both tests were conducted
on selected formulations to assess mobility of US EPA characteristic con-
taminants.
Measurement of unconfined compressive strength is a general indication
of a waste form's mechanical integrity and its ability to withstand loading
pressures associated with overburden at a disposal site. Modified sulfur
cement is a relatively brittle material and tends to fail by a shattering frac-
ture under an axial compressive load. Thus, compressive strength testing
was conducted in accordance with the standard method developed for hy-
draulic cements, ASTM C-39, "Compressive Strength of Cylindrical Con-
crete Specimens."
Results from compressive strength testing of waste form specimens con-
taining 40 and 55% by weight INEL fly ash encapsulated in modified sulfur
cement are presented graphically in figure 5.2 (on page 5.14) and are com-
pared with compressive strength data for modified sulfur cement specimens
containing no waste. Mean values for compressive strength were not highly
dependent on waste loading (27.9 MPa (4,053 psi) for 40% by weight ash;
5.13
-------
Process Evaluation
Figure 5.2
Compressive Strength Data for INEL Incinerator Fly Ash
Encapsulated in Modified Sulfur Cement
- 4
40
30
20
10
10 20 30 40 SO 60
Waste loading, wt %
70
80
Data shown are mean values for 3 replicates (5 for 55% samples), with error bars at 95% confidence interval.
28.4 MPa (4,118 psi) for 55% by weight ash), but both waste loadings dis-
played strength more than twice that of the binder material alone (12.4 MPa
(1,800 psi)).
Idaho National Engineering Laboratory ash and samples of encapsulated
ash at several waste loadings were tested using both the EP Tox and the
TCLP. Both procedures specify maximum allowable concentrations of
eight metals (arsenic, barium, cadmium, chromium, lead, mercury, sele-
nium, and silver) and a number of organic compounds. Leachate analyses
were performed by atomic absorption; results are presented in table 5.9 (on
page 5.15) in terms of mg/L (ppm). Although not required by US EPA,
leachate concentration data are also normalized to account for the reduced
mass of fly ash in encapsulated waste forms. The TCLP leachate data from
5.14
-------
Chapter 5
Table 5.9
Results from EPA Extraction Procedure Toxicity Test and Toxicity
Characterization Leaching Procedure for INEL Ash Encapsulated in
Modified Sulfur Cement
Concentrations of Criteria Metals, mg/L (ppm)
-------
Process Evaluation
potential additives were examined, including precipitation agents, adsorption
agents, and ion-exchange resins. Based on the results of scoping experiments
and other considerations (e.g., ease of processing, cost, and availability) sodium
sulfide was selected for use as an additive. Sodium sulfide reacts with the
toxic metal salts to form metal sulfides of extremely low solubility. A ratio
of sodium sulfide to fly ash of 0.175:1 was used based on the results of an
experiment to determine the effectiveness of this additive on Cd mobility
under US EPA TCLP leaching protocol. As seen in table 5.9 (on page 5.15),
TCLP leachate concentrations for Cd and Pb (0.1 and 1.0 mg/L, respectively)
from waste forms containing 40% by weight ash, 53% by weight modified
sulfur cement, and 7% by weight sodium sulfide were well within allowable
concentration limits. Optimization of INEL incinerator fly ash waste load-
ing with added sodium sulfide (while maintaining additive/ash ratio con-
stant) yielded a maximum waste loading of 43% by weight fly ash, 49.5%
by weight modified sulfur cement, and 7.5% by weight sodium sulfide. As
shown in figure 5.3 (on page 5.17), this represents about 2.7 times more
incinerator fly ash per 55-gallon drum than is currently possible using port-
land cement, while still maintaining TCLP teachability below US EPA
concentrations defining characteristic hazardous wastes.
5.6 Polyethylene Extrusion Process
5.6.1 Process Performance and Effectiveness
Polyethylene waste forms containing various forms of radioactive and
hazardous wastes have been subjected to a comprehensive set of perfor-
mance evaluation tests (Kalb 1993). These tests consist of those specified
by the NRC for low-level radioactive waste, the US EPA for hazardous
waste, the U.S. Department of Transportation (DOT) for solid oxidizers,
and other testing to confirm waste-binder compatibility. Because of the
lack of DOE waste form performance criteria, NRC waste form test criteria
were applied. The NRC tests are stipulated in the Technical Position on
Waste Form (US NRC 1991), developed in support of 10 CFR 61 (US NRC
1983). The US EPA testing for characteristic hazardous waste is defined in
40 CFR 261 (US EPA 1986). Waste form performance evaluation tests that
have been conducted are listed in table 5.10 (on page 5.18), along with test
5.16
-------
Chapter 5
Figure 5.3
Comparison of Waste Loadings of INEL Incinerator Fly Ash in
Modified Sulfur Cement and Portland Cement
INEL cement formula BNL MSC* formula
INEL fly ash R55SSSI Cement [ 1 Water
Modified sulfur
Sodium sulfide
•MSC = Modified Sulfur Cement
methods and specifications where applicable. The results of these tests will
be reviewed in the paragraphs immediately following in discussions con-
centrating on data for sodium nitrate waste encapsulated in polyethylene.
Additional details on how the tests were conducted, as well as performance
data for encapsulation of other waste streams in polyethylene (including
sodium sulfate, boric acid, incinerator ash, and ion-exchange resins) can be
found in Kalb and Colombo (1984); Franz and Colombo (1985); Franz,
Heiser, and Colombo (1987); and Heiser, Franz, and Colombo (1989).
Tests were conducted using laboratory-scale waste form specimens 51
mm in diameter x 102 mm in height (2 in. x 4 in.), containing simulated
sodium nitrate salt waste, or actual nitrate salt waste from the Rocky Flats
Plant (RF Plant). In addition, testing was also conducted on sample cores
taken from a pilot-scale (115 L (30 gal)) waste form. The pilot-scale waste
form was produced during scaleup feasibility testing using a production-
5.17
-------
Process Evaluation
Table 5.10
Waste Form Test Methods
Test
Method
TestCriteria*"*
NRC:
Comptessive strength
90-Day Water Immersion
Thermal Cycling
teachability (90 days)
Irradiation -108 rad
Biodegradation
Fungus Attack
Bacteria Attack
EPA:
Hazardous Constituent
teachability
DOT
Solid Oxidizer
ASTMD-695
ASTM B-553
ANS 16.1
Gamma Irradiator
or Equivalent
ASTM G-21
ASTM G-22
TCLP
EP-Tbx
lest for Solid
Oxidizing
Substances
Compressive Strength 2 60 psi
Compressive Strength > 60 psi
Compressive Strength 2 60 psi
teachability Index > 6.0
Compressive Strength > 60 psi
No observed fungal growth
Compressive Strength > 60 psi
No observed bacterial growth
Compressive Strength £ 60 psi
Constituent Dependent
Constituent Dependent
Comparison with reference oxidizers
(a) The minimum strength for generic waste forms specified by NRC is 60 psi. However, maximum practical
Compressive strengths for a given solidification agent are required. Minimum Compressive strength for liydraulfc
cement waste forms is 500 psi.
scale 114 mm (4.5 in.) extruder to encapsulate simulated sodium nitrate salt
waste in polyethylene. Results of bench- and full-scale waste form testing
are given in figures 5.4 (on page 5.19), 5.5 (on page 5.20), and 5.6 (on page
5.21); and tables 5.11 (on page 5.21) and 5.12 (on page 5.22) and tables
5.13 and 5.14 (on page 5.23).
The DOT has recommended a test to quantify hazards associated with
solid oxidizing materials such as nitrates. This method, "Test for Solid
Oxidizing Substances," was published by the Canadian Department of
Transportation of Dangerous Goods (DOT Canada 1987). It supersedes that
previously recommended by DOT, "Methods for Testing for Oxidizers."
The "Test for Solid Oxidizing Substances" was conducted at Brookhaven
National Laboratory (BNL) to determine effects of polyethylene encapsula-
tion on the oxidization potential of RF Plant sodium nitrate salt waste. Re-
sults indicated that the nitrate salt solidified in polyethylene burned
5.18
-------
Chapter 5
significantly slower (by a factor of 8 to 33 times) and less violently than any
of the reference oxidizing materials (ammonium persulfate, potassium per-
chlorate, and potassium bromate). Compared with unsolidified sodium
nitrate salt, the waste form test samples burned about 16 times slower. The
solidified waste burned only about 1.3 times faster than plain polyethylene.
Based on these results, sodium nitrate solidified in polyethylene is not clas-
sified as an oxidizer by the DOT, and, therefore, does not need to meet
regulations for shipping oxidizers.
5.6.1.1 Economic Feasibility
This section discusses the advantages of polyethylene encapsulation of
Rocky Flats nitrate salt waste from the standpoint of increased waste load-
ing per drum, leading to a reduction in the number of processed drums re-
quired for storage, transport, and disposal. To determine net economic
feasibility, savings resulting from this reduction must be balanced with
overall costs, including such factors as differences in the cost of binder
materials. A simple economic analysis was conducted to estimate potential
Figure 5.4
Compressive Yield Strength of Polyethylene Waste Forms Containing
Sodium Nitrate Salt, Untreated and After
-------
Process Evaluation
Figure 5.5
Comparison of Compressive Yield Strength vs. Waste Forms
Undergoing ASTM G-21 and G-22 Biodegradation Testing and Control
(Untreated) Samples
1.6
1.5
1.1
10 11 12 13 14
Compressive yield strength, MPa
—B— Biotest samples 0 Untreated samples
15
16
Test specimens consisted of 60 wt% sodium nitrate in polyethylene, and were cored from a pilot-scale (30 cial) waste form
cost savings from polyethylene encapsulation of nitrate salt waste at the RF
Plant. A more rigorous economic analysis of polyethylene solidification of
commercial reactor waste led to the conclusion that significant cost savings
could be achieved using this technology (Kalb and Colombo 1985).
The analysis compares three alternatives for encapsulation of nitrate salt
waste at the RF Plant:
• polyethylene;
• saltstone, (portland cement formulation using a concentrated
aqueous salt solution) developed at Savannah River Plant (SRP);
and
• West Valley formulation for concentrated nitrate salt encapsula-
tion in cement.
5.20
-------
Chapter 5
The RF Plant has also used a portland cement-based formulation incor-
porating higher salt loadings (Saltcrete) developed there, but because of
catastrophic failures of these waste forms in storage, this formulation was
not considered (Petersen, Johnson, and Peter 1986). Maximum nitrate salt
waste loadings of 13% by weight and 20% by weight in the SRP and West
Figure 5.6
Leaching Index Determined According to the ANS 16.1 Leach Test as a
Function of Sodium Nitrate Waste Loading for Polyethylene Waste Forms
30
50 60
Waste loading, wt%
70
Table 5.11
ANS 16.1 Leach Test Data for Sodium Nitrate in Polyethylene Waste Forms
Weight Percent
NaNO,
30
50
60
70
Cumulative Fraction
Leached
0.9
6.3
15.0
73.4
Leach Rate (s'1)
84x10-'°
6.0 xlO'9
l.lxlO8
1.5 x 10'7
Leacn Index
11.1
9.7
9.0
7.8
5.21
-------
Process Evaluation
Table 5.12
Compressive Yield Strength of Cored Pilot-Scale Polyethylene Waste
Forms Containing 60 wt% Sodium Nitrate
Test Description
Initial
Post Thermal Cycling
Post Irradiation
Post Biodegradation(c|
Compressive Yield Strength, MPa (psi)("-b)
14.2 ±0.3
(2,060 ±45)
13.3 ±0.5
(1,930 ±70)
16.7 ±0.7
(2,420 ±100)
10.1 ±1.8
(1,460 ±255)
(a) Based on 6 replicate specimens.
(b) Error expressed as ± one standard deviation.
(c) Based on 12 replicate specimens.
Valley formulations, respectively, were taken from published literature
(Wilhite 1987; McVay, Stimmel, and Marchetti 1988). Data for polyethyl-
ene waste forms were based on research and development work performed
at BNL (Reiser, Franz, and Colombo 1989).
To simplify economic calculations, an annualized cost economic analysis
(which considers present costs and benefits and neglects potential future
variations) was performed. Some of the economic data were adapted from
previous RF Plant analyses (Petersen, Johnson, and Peter 1986; Petersen,
Johnson, and Swanson 1987) with allowances made for inflation. In addi-
tion, RF Plant data were based on an annual nitrate salt waste production of
800,000 kg/yr (1.76 MM Ib/yr), and these calculations were updated to
reflect a RF Plant production rate of 1.0 MM kg (2.2 MM Ib) per year.
Transportation and disposal costs are based on the assumption that waste
packages will be shipped to the Nevada Test Site for disposal and on RF
Plant data. Equipment costs for all systems were neglected under the as-
sumption that these costs are roughly equivalent. Operating costs; were
assumed to be negligible compared to other costs and were therefore ex-
cluded. Assumptions used in the calculations are summarized in table 5.15
(on page 5.24).
5.22
-------
Chapter 5
Table 5.13
Self-Ignition Temperatures of Polyethylene with Nttrate Salt
and Salt Waste Components(a)
Specimen Specimen Temperature at
Ignition Point, °C ± 5 'C
Polyethylene
Polyethylene/50 wt% NaNO3
Polyethylene/30 wt% NaNO}
Polyethylene/50 wt% NaNO2
Polyethylene/70 wt% NaNO2
Polyethylene/50 wt% SRP Nitrate Salt
426
380
362
360
363
365
Air Temperature at
Ignition Point, 'C ± 5°C
430
381
360
358
359
365
(a) Testing in accordance with ASTM D-1929, 'Standard Method of Test lor Ignition Property of Plastics."
Table 5.14
Results from Extraction Procedure Toxiclty Test (EP Tox) and Toxicity
Characterization Leaching Procedure (TCLP) for Rocky Flats Plant Nitrate
Salt Encapsulated in Polyethylene'05
Concentrations of Criteria Metals, ppm
Sample Tested Chromium Cadmium Lead Barium
RFP Nitrate Salt
60 wt% RFP Salt
in LDPE
60 wt% RFP Salt in LDPE(b)
EPA Allowable Limit
9.0
3.6
0.8
5.0
0.4
0.2
0.1
1.0
0.5
0.3
0.2
5.0
<0.5
<0.5
<0.5
100
(a) Data for TCLP test, except where noted.
(b) Low-density polyethylene
(c) Data for EP Tox test.
Technical data used in the analysis are summarized in table 5.16 (on
page 5.24), and cost breakdowns and results are included in table 5.17 (on
page 5.25). Component and total costs are presented graphically in figure
5.7 (on page 5.25) and the percentages of the total cost for the BNL and
SRP formulations are presented in figure 5.8 (on page 5.26). Taking into
account the increased waste loading capacity and lower transport and dis-
posal costs because of fewer and lighter packages, polyethylene represents a
5.23
-------
Process Evaluation
Table 5.15
Assumptions Used in the Economic Analysis of Nitrate Salt Encapsulation
for Rocky Flats Plant
RFP Nitrate Salt Production: kg/yr 1,000,000
(Ibs/yr) .2,204,000)
Materials Costs: Vkg ($/lb)
Cement 0.22(0.10)
Polyethylene 0.99 (0.45)
1986 Cost Dataw
8.07 x 10s kg/yr
(1.78U06 Ibs/yr)
Labor 295,500
Repair 25,150
Miscellaneous 30,210
Waste Pre-treatment 350,860
Shipping (Wb) 0.047
Disposal ($/lb) 0.016
Drums (Vdrum) 28.700
1.0 x 106 kg/yr
(2.2x1 tf Ibs/yr)
365,784
31,132
37,395
434,311
Escalation @ 5%/yr: 1990$=1986$ (1+0.05)4
Equipment and operating costs not included based on the assumption that:
- equipment costs for all systems are roughly equivalent
- operating costs are negligible compared to other costs
(a) Adjusted from data in reference (Peterson, Johnson, and Peter 1986, Peterson, Johnson, and Swiircon 1987), to
reflect increased salt production
Table 5.16
Economic Analysis for Nitrate Salt Encapsulation at Rocky Flats Plant
Waste Loading (wt% dry salt)
Product Density, g/cm3 (Ib/ft3)
Waste & Binder, kg/drum
(Ibs/drum)
Waste/drum, kg (Ibs)
Binder/drum, kg (Ibs)
Total binder, kg/yr (Ibs/yr)
Drums/yr
Drum wt, kg/yr (Ibs/yr)
Total Shipping wt., kg/yr
(Ibs/yr)
Polyethylene
70
1.67
(104)
329
(725)
230
(508)
99
(218)
428,377
(944,571)
4,343
49,238
(108,571)
1,477,162
(3,257,143)
RFP Cement
13
1.70
(106)
337
(743)
45
(99)
292
(644)
6,515,841
(14,367,429)
22,303
253,144
(557,585)
7,768,260
(17,129,014)
West Valley
Cement
20
1.65
(103)
328
(724)
64
(141)
264
(583)
4,126,333
(9,098,')64)
15,631
176,999
(390,282)
5,302,878
(11,692,846)
5.24
-------
Chapter 5
Table 5.
17
Cost Breakdown(a)
Labor
Repair
Miscellaneous
Portland Cement
Polyethylene
Shipping
Disposal
Drums
Waste Pretreatment
Total
Unit Cost, $/kg salt
(Mb salt)
Polyethylene
444,612
37,841
45,454
—
425,057
186,077
63,345
151,501
527,907
1,881,795
1.88
(0.85)
RFP Cement
444,612
37,841
45,454
1,436,743
...
978,560
333,127
778,055
527,907
4,582,299
4.58
(2.08)
West Valley
Cement
444,612
37,841
45,454
909,856
...
667,998
227,404
544,600
527,907
3,405,673
3.41
(1.55)
(a) Cost data given in 1990$
Figure 5.7
Economic Analysis for Rocky Flats Plant Nitrate Salt Encapsulation
4.6
BNL Polyethylene Saltstone West Valley Cement
Binder fWSJ Shipping FM^J?^ Disposal
Drums Illllll Pretreatment
Labor, Repairs. Misc.
Based on RFP production of 1.0 million kg nitrate salt per year
5.25
-------
Process Evaluation
Figure 5.8
Summary of Cost Breakdown for Economic Analysis for Nitrate Salt
Waste Encapsulation at Rocky Flats Plant Using Polyethylene and
Savannah River Plant Saltstone Cement Formulations
Miscellaneous Repair
2% 2%
Shipping
21%
Polyethylene
23% '
Shipping
10%
Disposal
3% Drums
8%
Miscellaneous 1%
Polyethylene formulation
SRP cement formulation
potential cost savings of about $2.7 million per year over the SRP cement
formulation and $1.5 million over the West Valley cement formulation.
Although these results are approximate and do not reflect rigorous eco-
nomic analysis, they should provide a first order estimation of potential
savings.
5.7 Inorganic, Cementitious Technologies
of the Siliceous Category
5.7.1 Process Performance and Effectiveness
5.7.1.1 Soluble Silicate Processes
The ability of soluble silicates to reduce metal leachability by chemical
means depends on their ability to react with metals to form "silicates,"
5.26
-------
Chapter 5
which are more resistant to leaching, especially to that of acidic leachants.
This can occur in two ways:
• by reaction with metal ions in solution; and
• by respeciation of low-solubility metal compounds already
present in the waste.
The two processes discussed below are aimed primarily at one of these
two different approaches.
EnviroGuard/ProTek/ProFix, Houston, Texas. The ProFix process has
been commercially applied mostly as a combined fixation agent and filter
aid. The results of several uses of the stabilization system per se, however,
are described by the vendor and shown in tables 5.18 and 5.19 (on page 5.28).
Data given in a patent (Conner and Reber 1992) also illustrate the hard-
ening 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
seven days. When calcium chloride was added to the mixture, it hardened
in seven days to >44,000 kg/m2 (>4.5 ton/ft2) bearing strength. After five
months it was rock hard while the sample without the calcium chloride
remained a paste. On an actual high pH calcium sludge, the addition of rice
hull ash resulted in a very hard product >44,000 kg/m2 (>4.5 ton/ft2) bearing
strength, after 12 days, although there was no measurable strength after one
day. In contrast, a sample treated with sodium silicate solution demon-
strated a bearing strength of 16,600 kg/m2 (1.7 ton/ft2) after one day, but
only 17,600 kg/m2 (1.8 ton/ft2) after twelve days, with no additional harden-
Table5.18
Stabilization of Organics in the Prefix Process
Constituent TCLP Leachate (mg/L)
Raw Sludge Treated Sludge
Methylene chloride
Chloroform
Trichloroethane
Toluene
Methanol
Benzene
20.0
20.0
2.4
2.1
22.0
30.0
<0.25
2.0
0.56
0.80
5.0
0.76
5.27
-------
Process Evaluation
ing thereafter. The continued hardening demonstrated by the use of rice
hull ash appears to support the chemical theory of this process.
Table 5.19
Stabilization of Metals in the Prefix Process
Constituent TCLP Leachate (mg/L)
Raw Sludge Treated Sludge
Lead
Chromium
Cadmium
Copper
Zinc
Nickel
3.97
7.1
34.8
23.5
158.0
32.1
0.24
0.05
0.07
0.43
0.27
0.18
Lopat, Wanamassa, New Jersey. Trezek (US EPA 1989b) described the
treatment of auto shredder fluff containing about 200 mg/kg of lead with a
concentrated solution of potassium silicate in water containing 1.2 to 1.9 L
(0.33 to 0.5 gal) of silicate solution per ton of waste. Subsequently, the
waste was treated with 10 to 12% pozzalime (lime kiln dust) and cured until
dry. Leachability of lead was reduced to "acceptable" Cal WET leachable
levels. The leaching levels in the untreated waste ranged from 7.8 to 600
mg/L in the Cal WET test, but <0.5 mg/L in the EP Tox. The treated waste
showed leachable levels from 2.5 mg/L (untreated waste leached 7.8 mg/L)
to 160 mg/L, depending on the treatment conditions. The best results re-
ported were 6.1 mg/L in a waste that leached at the 600 mg/L level un-
treated. Detailed data are given by Trezek (1987) and are summarized in
table 5.20 (on page 5.29) along with treatment results on other wastes. At
current generic market prices, the reagent cost for this application would be
only $4.40 to $5.50/tonne ($4 to $5/ton) of waste treated.
A system installed in 1987 at Hugo Neu-Proler, an auto shredder in Long
Beach, California, reportedly has operated successfully (Corum 1988). The
leachable Cal WET levels were acceptable to California Department of
Health Services (DHS) and the facility was permitted to landfill the treated
5.28
-------
Chapter 5
waste in a nonhazardous landfill. Other auto shredders in California have
reportedly installed similar systems.
The process has also been proposed for use on lead-contaminated soils.
Lead reductions of 63 to 99.97% have been reported at costs ranging from
$22 to $200/tonne ($20 to $180/ton) of waste treated (US EPA 1990a). On
river sediments, samples containing 320 mg/kg arsenic leached 1.0 to 1.5
mg/L as determined by the EP Tox (US EPA 1989b). A summary of other
results reported by the vendor (Trezek 1987) for other wastes treated with
the Lopat process are given in table 5.20 (on page 5.28). These results not
only show the possible advantages of the use of soluble silicates for certain
wastes, but also illustrate the care that must be exercised in their use and the
variations that can occur with different additives. For example, the data on
casting sand show that the use of soluble silicate alone confers no advan-
Table 5.20
Summary of Test Data on LOPAT K-20 Process
Waste
Description
Incinerator ash
II H
..
Baghouse dust
II H
II n
Auto shredder
waste
„ „
Contaminated
soil
Battery slag
Battery case
residue
,, ..
Casting sand
•I ii
ii ii
II H
K-20
gal/ton
1.0
1.0
1.0
1.0
1.0
1.0
0.33
0.33
2.0
1.0
0.6
0.6
1.0
0.0
1.0
1.0
Additive Ratio
Water Pz.Lime Cement Fly ash
gal/ton ton/ton ton/ton ton/ton
90. 0.2
90. 0.2
90. 0.2
114. 0.2
114. 0.2
84.
16.7 0.25 1.7
16.7 0.25
39. 0.2
77. 0.4
28. 0.34
28. 0.34
78. 0.2
78. 0.2
68.
84. 0.2
Leachability (mg/L)
Metal Untreated
Cd
Cu
Pb
Cd
Pb
Pb
Cd
Pb
Cr
Pb
Pb
Pb
Pb
Pb
Pb
Pb
4.3
27.
880.
15.
220.
220.
1.7
600.
9.3
740.
760.
760.
160.
160.
160.
160.
Treated
0.4
38.
5.7
<0.1
4.4
<0.5
<0.2
6.1
4.4
3.7
140.
66.
2.9
1.5
120
19.
Test %
Type Reduction
WET
WET
WET
EPT
EPT
EPT
WET
WET
WET
WET
WET
EPT
WET
WET
WET
WET
91
-
99
>99
98
>99
>88
99
53
99
82
91
98
99
25
88
WET = California Waste Extraction Test
EPT = EW Extraction Procedure Toxidty Test
5.29
-------
Process Evaluation
tage, and at least for lead stabilization, the choice of additive (pozzalime vs.
cement) makes a significant difference.
5.7.1.2 Slag Processes
Oak Ridge National Laboratory (ORNL) Process. The waste used in the
ORNL test project originated in the treatment of an aqueous effluent, or
"raffinate," from uranium recovery 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-II-LA portland cement; and
• 25.0% fly ash, ASTM Class F.
This yielded treated waste that leached below US EPA primary drinking
water standards by the EP Tox, and resulted in Leachability Index (LI) val-
ues of about 6. For testing of the various "fixatives" - blast-furnace slag,
iron filings, FeSO4 and Na2S — the filtrate was used. It had similar concen-
trations of technetium (Tc) and nitrate. The results are shown and com-
pared with the treated waste without additives in table 5.21.
Table 5.21
Effect of Various Additives on Technetium Leachability
Constituent Added to Grout
Grout Composition (Weight %)
2345
Raw Waste
Water
Cement
Fly Ash
Iron Filings
FeS04
NajS
Slag
13.9
36.1
25.0
25.0
13.9
36.1
23.2
23.2
3.7
13.9
36.1
24.0
24.0
2.0
13.9
36.1
24.6
24.6
0.9
30.0
20.0
24.6
24.6
0.9
40.0*
20.0
20.0
20.0
ANSI/ANS 16.1 Leachability Index (30 day cure)
"Tc
7.7
8.1
9.3
10.0
9.4
10.5
Filtrate
5.30
-------
Chapter 5
The results clearly demonstrate the improved retention of Tc and, to a
lesser extent, nitrates, by addition of granulated blast-furnace slag. Six
different slag sources were tested and all gave similar results. The FeSO4
and Na2S additives gave similar results to those of the slag. Since the LI
values are the negative logarithm of the effective diffusion coefficient, the
slag additive improved Tc retention by three to four orders of magnitude
and nitrate retention by more than one order. The Tc results are attributed
largely to reduction of Tc from the +7 to the +4 valence state, accompanied
by a reduction in porosity and an increase in tortuosity in the resulting ma-
trix. The latter effect was responsible for improved nitrate retention.
SoliRoc™ Process. Data available on the SoliRoc™ process in the U.S.
were most recently given by Ezell and Suppa (1989) for wastes from plants
in Ohio, Michigan, and Tennessee. These are summarized in table 5.22.
The advantage of the SoliRoc™ process over that of straight lime treat-
ment is obvious for these waste streams. Increasing the final pH resulted in
little improvement in lime treatment, while the SoliRoc™ product showed
little difference in teachability with final pH, except in the case of nickel.
Table 5.22
Summary of Leaching Data - SoliRoc™ Process
Formulation Final pH EP Toxicity Extraction Results (mg/L)
Cadmium Chromium Nickel Lead
Ohio Waste
Lime
Lime
SoliRoc™
SoliRoc™
Michigan Waste
Lime
Lime
SoliRoc™
SoliRoc™
Tennessee Waste
Lime
Lime
SoliRoc™
SoliRoc™
9.8
12.5
9.5
11.4
10.8
12.5
10.9
12.2
9.0
11.0
8.4
11.0
6.40
5.20
0.15
0.04
0.04
0.03
0.02
0.02
0.40
0.80
0.10
0.12
0.7
0.9
0.2
0.2
11.3
0.2
0.4
0.2
1.4
0.5
0.08
0.41
21.7
8.4
1.5
1.8
62.2
3.9
14.3
0.1
19.0
16.1
10.8
3.1
0.06
0.01
0.03
0.01
0.17
0.07
0.06
0.15
0.29
0.28
0.36
0.50
5.31
-------
Process Evaluation
Cement-Slag Process. Results of the treatability study described previ-
ously are summarized in table 5.23 (US EPA 1990d).
These results clearly show that slag is most effective for chromium re-
duction in soils when used in combination with portland cement. In this
formulation, it produced results similar to those from the standard ferrous
sulfate reduction technique.
Table 5.23
Leaching of Treated, Dichromate-Contaminated Soil -
Cement - Slag Process
Type of
Sample
Untreated
Soil
Trotted fcoil
FeSO, Treated
SoU
Slag Treated
SoU
Concentration of Cr** and Total Chromium in TCLP Leachates From Treated Soil (mg/L)
Reducing Agent Alone
% Total
Cr1* Reduct Cr
38. - 38.5
20.5 46.0 20
3.65 90.35 3.3
30. 21.05 28.5
Reducing Agent + Cement
(Binder/SoU Ratio = 0.2)
% % Total
Reduct. Crrt Reduct.* Cr
9.65 74.5 9.3
48.05 11. 70 9.5
1.15 97. 1.10
2.05 94.5 1.8
%
Reduct.
76
75
97
95.5
"Percent leaching reduction is calculated on the basis of chromium leaching from the untreated raw soil samples.
5.7.1.3 Lime
The first large-scale commercial uses of both the SRS and DCR pro-
cesses were treatment of 41,000 m3 (54,000 yd3) of acid tar sludge/soil at a
chemical plant in Dollbergen, Germany, in 1977, and 9,000 m3 (12,000 yd3)
of contaminated beach sand and debris from the Amoco Cadiz oil tanker
spill at Brest, France, in 1978. Subsequently, these technologies were ap-
plied in projects in Japan, Canada, and elsewhere in Europe. The SRS
states that 380,000 m3 (500,000 yd3) of waste has been treated to date with
5.32
-------
Chapter 5
its process (SRS 1988b). Immobilization data are given for the OCR pro-
cess in table 5.24.
The leachable organics have been substantially immobilized in the stabi-
lized wastes in all cases except chlorobenzene, where the leachable amount
is below detection limits even in the untreated waste. Leachable benzene in
the Marathon sludge is well below the US EPA Toxicity Characteristic limit of
0.5 mg/L, despite very high leachable levels in the untreated waste.
Data provided by SRS (SRS 1988a) are of no use in evaluation, since the
leachable levels for various organic constituents, even in the untreated
waste, are near or below detection limits.
5.7.1.4 Inorganic Polymers
The geopolymer process has not been used commercially for the stabili-
zation of wastes, but reportedly (Conner 1991), it has been used in Europe
and Canada in fabricating construction materials. It has been tested on
various wastes (Davidovits et al. 1990): mine tailings, paint sludge, arsenic-
bearing wastes, and scrap yard waste. The compounds tested for environ-
mental applications have been the sodium- and potassium-poly(sialates),
Table 5.24
Summary of Treatability Studies Using the DCR Process
Project
Marathon tank bottom sludge
(dewatered)
- before DCR treatment
- after DCR treatment
Acid tar contaminated soils
- before DCR treatment
- after DCR treatment
(8 days curing)
Oil exploration and production
sludges
- before DCR treatment
- after DCR treatment
Toxicity Characteristic Limits
(mg/L.)
TPH
(ppm)
Benzene
106 368
<0.01
1.4X105 0.21
0.005
17,700 0.526
<0.004
0.5
TCLP Results (mg/L)
Ethyl- Chloro-
Toluene Benzene Xylenes benzene
1300 334 1830 <0.01
0.30 0.10 0.56 <0.01
1.10 0.38 2.4 <0.01
0.008 0.004 0.023 <0.01
1.69 0.334 0.479 <0.012
<0.004 <0.004 <0.012 <0.012
100
5.33
-------
Process Evaluation
(sodium, potassium)-poly(sialate-siloxo), potassium-poly(sialate-siloxo)
and (calcium, potassium)-poly(sialate-siloxo). Results from the treatment
of various mine tailings are shown in table 5.25. The leaching test used was
Ontario's Regulation 309 method, which is similar to the US EPA EP Tox.
It is apparent from these data that geopolymerization is effective in reduc-
ing the mobility of the very soluble sodium and chloride ions to an unusual
extent, and in other respects, in effectively stabilizing this kind of waste.
These properties take time to develop, as would be expected for a pro-
cess that relies heavily on lattice substitution and/or physical
microencapsulation of the hazardous constituents, i.e., on the development
of a physical structure. Compressive strengths of the geopolymerized tail-
ings were in the range of 14 to 20 MPa (2,000 to 3,000 psi) after 21 days'
curing.
Similar results (Davidovits et al. 1990) are obtained in treating paint
sludge waste, arsenic-bearing mine tailings, and scrap yard wastes, at
geopolymer loadings of 15 to 50% by wet weight of the original waste,
loadings much the same as with cement-based processes. Results in treat-
Table 5.25
Leachate Results from Geopolymerization of Mine Tailings
Waste Type
Potash waste
NaCl + KCI
Uranium waste
226R,
Metal base waste
Iron
Cadmium
Cobalt
Chromium
Copper
Molybdenum
Nickel
Lead
Vanadium
Zinc
Feed
-------
Chapter 5
ing arsenic tailings, which are thought to contain arsenic as a ferric arsenate
compound, showed that the untreated waste released arsenic at the rate of
about 50 mg/kg of waste, while the waste treated at the 10% geopolymer
addition level released only 0.6 mg of arsenic per kg of waste in the Regula-
tion 309 test, a reduction of eighty-fold.
5.7.2 Cost Information
With the exception of the geopolymers, all of the processes described
here use reagents that are conventional and commercially-available in North
America in most or many locations at competitive prices. Typical delivered
prices for reagents are shown below:
REAGENT PRICE
Portland cement 60 - 80
Kiln Dust 20 - 40
Blast furnace slag 10-20
Quicklime (untreated) 50 - 90
Rice hull ash about $400
Sodium silicate solution 165 (FOB manufacturing plant)
Potassium silicate solution 460 (FOB manufacturing plant)
Geopolymers 880-1,100 (FOB manufacturing
plant)
The price of hydrophobized lime in the U.S. has not been determined.
Based on the ingredients, its cost should not be significantly higher than
quicklime, but, as with the Lopat, geopolymer, and EnviroGuard processes,
the applications are covered by patents; hence, the pricing may include
appropriate markups, fees, or royalties.
5.8 Soluble Phosphates
The patent for the WES-PHix process presents process performance
results for stabilization of several different bottom ash-fly ash-flue gas
scrubber product mixtures. A number of leachants, including EP Toxicity
and synthetic acid rain leachants, were used. It was found that the US EPA
limits for Pb were met for untreated wastes only within the pH range 6.7 to
5.35
-------
Process Evaluation
12.0, and, for Cd only at a pH above 7.5. In most cases, the pH of the mix-
tures were below these values so that the wastes would have failed the EP
Tox. Treatment of these wastes with lime and either disodium hydrogen
phosphate (Na2HPO4) or phosphoric acid greatly reduced the amount of lead
and cadmium leaching and extended the range over which they passed the
test to approximately pH 5.0. Table 5.26 shows the results of one such test.
Table 5.26
Reduction in Leaching Due to Phosphate Treatment^5
FGSP*:FlyAsh
%HjPO4
%Na2HPO4
EPToxicityTest
Initial pH
Final pH
Extract, mg/L
Lead
Cadmium
4:1
—
12.62
12.38
5.6
0.014
4:1
4.25
12.70
6.50
0.1
0.036
4:1
—
5.0
12.69
11.62
0.075
0.015
1:1
4.25
6.27
5.11
0.1
0.34
1:1
._
5.0
12.30
5.18
0.24
0.33
3:7
4.25
—
5.50
5.07
0.1
0.19
3:7
...
5.0
11.88
5.10
0.15
0.50
'Flue gas scrubber product.
(a)Adapted from O'Hara and Surgi(1988).
The US EPA (Kosson et al. 1991) conducted a study of leaching of a
wide range of metals from ash following treatment by four processes, in-
cluding soluble phosphates (table 5.27 (on page 5.37)). The Availability
Leach Test results are reported here. This test is used to assess the maxi-
mum amount of specific elements or species that could be released under an
assumed "worst case" environmental scenario. Two serial extractions are
carried out on crushed samples. The pH of the leachant is automatically
controlled to pH 7 during the first extraction and to pH 4 during the second
extraction, using nitric acid. The first and second extracts are combined for
analysis (van der Sloot, Piepers, and Kok 1984). This test generally ex-
tracts all species that are not tightly bound in a mineral or glassy matrix.
Compared with portland cement treatment, the use of WES-PHix was found
5.36
-------
Chapter 5
Table 5.27
Comparison of Species Release for Availability Leaching Tests
on Untreated and Treated Municipal Solid Waste Residues
(mg released/kg dry ash)
Process 1 Process 2
Bottom Ash
Cadmium
Chromium
Copper
Lead
Zinc
8
4
77
130
670
10
10
270
520
7,100
Process 3
16
9
200
360
1,600
Process 4
17
<1
230
350
1,800
Portland
cement
control
18
8
150
180
2,100
Untreated
residue
28
13
360
2,700
2,800
Total
residue
analysis
36
200
2,100
NA
4,800
Air Pollution Control Residue
Cadmium
Chromium
Copper
Lead
Zinc
Combined Ash
Cadmium
Chromium
Copper
Lead
Zinc
220
10
160
1,200
6,700
32
5
240
260
1,700
170
20
280
2,100
11,000
20
16
400
490
2,500
220
17
390
2,300
12,000
20
19
390
1,400
2,000
120
<1
130
4
6,700
26
< 1
240
46
2,200
150
37
520
3,700
16,000
27
6
360
370
2,300
130
6
190
980
7,700
27
3
380
500
2,900
200
41
360
3,000
3,000
36
200
2,100
1,600
4,800
Process 1 - Portland cement and a polymeric additive.
Process 2 - Portland cement and soluble silicates.
Source: (Kosson et al. 1991,127-129).
Process 3 - Quality controlled waste pozzolans.
Process 4 - Soluble phosphate.
to be much more effective for Zn, Cu, Cr, and Pb control and similar for Cd
control. The control of lead with soluble phosphates was found to be six
times more effective than portland cement when treating bottom ash and
900 times more effective when treating air pollution control (APC) resi-
dues. Control of lead was also much better with the soluble phosphate pro-
cess than with either the portland cement plus polymer or the portland
cement plus soluble silicate processes.
5.37
-------
-------
Chapter 6
LIMITATIONS
6.7 Sorption and Surfactant Processes
Reliability of the sorption and surfactant processes for organic waste
cannot be assessed because field-scale monitoring of completed projects is
in its infancy. Remediation personnel need to rely on predictive methodolo-
gies, such as accelerated-aging testing, to determine the long-term effective-
ness of sorption processes.
6.1.1 Site Considerations
Stabilized/solidified material that is disposed of in a nonlined area has
the potential to be contacted with and degraded by groundwater. The
sorbed organics could become mobile if the groundwater contains organic
compounds.
6.1.2 Waste Matrix and Risk Considerations
The effectiveness of all sorbents is limited to the extent that waste mate-
rial is sorbed and controlled in an equilibrium condition. There is always a
risk that the waste may be released, since it continues to reside within the
stabilized/solidified material. The degree of risk depends on the extent
leaching is controlled, which is determined by the extent the material is
bound or dispersed.
6.1
-------
Limitations
6.2 Emulsified Asphalt
The emulsified asphalt process has not yet been evaluated for application
to a wide range of wastes. More research is needed before the long-term
durability of this material can be assessed.
Certain constituents of the waste may interfere with the production of
high-quality asphalt. For example, high-organic content is detrimental to
stability and sulfate may cause swelling upon contact with water.
If the waste materials are hazardous, compliance with transportation and
storage regulations is required. Reuse as pavement material may be problem-
atic.
6.3 Bituminization
The primary limitation of this process results from lack of experience
and data beyond low- and medium-level waste applications. Consequently,
its applicability and limitations in hazardous chemical waste areas are diffi-
cult to determine. As stated before, however, the waste solids being pro-
cessed are generally in a slurry form. Solids content is usually concentrated
to 50% by weight solids, the remainder is moisture. The final product is
composed of approximately 40% solids and 60% bitumen.
6.4 Vitrification
Limitations of vitrification processes have been evaluated and summa-
rized (US EPA 1992b). The following factors may limit the overall effec-
tiveness or cost-effectiveness of vitrification:
• feed moisture content;
• feed material composition;
• feed compatibility;
• combustible material;
6.2
-------
Chapter 6
• potential shorting caused by metals, and
• cost of energy.
6.4.1 Feed Moisture Content
The moisture in the feed increases the amount of energy needed for vitri-
fication. To evaporate a given mass of water generally requires about the
same amount of energy as the vitrification of a given mass of solid materi-
als at 1,200°C (2,200°F) (approximately 0.7 kwh/kg). Nevertheless, mois-
ture limits the application of vitrification only in certain circumstances.
For example, special engineering measures may be needed to apply ISV
to contaminated soil within shallow, permeable aquifers. Although ISV has
been used to process sludges with moisture contents as high as 55% by
weight (Buelt and Freim 1986), the potential for moisture recharge in a
permeable aquifer will prevent the process from proceeding downward.
Calculations show that soil permeabilities greater than 10"* to 10~5 cm/sec
will inhibit downward vitrification (Buelt et al. 1987). Where this occurs,
groundwater diversion or pumping techniques would have to be imple-
mented.
6.4.2 Feed Material Composition
One of the advantages of vitrification processes is that the feed can be
augmented by glass formers, modifiers, or fluxes to achieve optimal product
durability and process performance. Consequently, feed materials for re-
fractory-lined melters, as well as water-cooled melters, thermal vitrification,
and plasma systems can be augmented to eliminate any limitations associ-
ated with the feed materials' composition. For the ISV process, however,
the soil must be amenable to vitrification as it exists. Most soils have the
appropriate processing and product durability characteristics (Buelt et al.
1987). One of the few exceptions occurs in weathered soils that have been
discovered along the eastern seaboard of the United States. The alkaline
content of such soils is lower than the minimum 1.4% by weight require-
ment. In this case, alkaline chemicals, such as soda ash, could be premixed
with the soil by deep soil mixing techniques before vitrification.
6.3
-------
Limitations
6.4.3 Feed Compatibility
Feed compatibility refers to the compatibility of the feed material as to
size and nature of the material being treated. Size is generally dictated by
the feed mechanisms, and for the above ground vitrification processes, the
feed must be pretreated to assure that materials are of a size that can be
handled. The ISV process has been shown, however, to be capable of pro-
cessing large rocks and boulders, large combustible materials, such as tim-
ber, and large chunks of metal. The ISV process is not yet sufficiently de-
veloped to process buried, sealed containers, such as 55-gallon drums.
These items can result in sudden release of offgases, expelling molten soil
into the offgas collection hood and resulting in a loss of offgas containment.
6.4.4 Combustible Material
Combustible material generates gases of decomposition and increases the
thermal heat load of the offgas treatment system. Above-ground melters are
well-suited to handling combustibles because the residence time in the
melters can be controlled by feed rate. The only concern is that the com-
bustibles be compatible with the feed delivery system. Combustible feed is
less frequently processed by refractory-lined melters than by the rotary kiln
vitrification process, because of the combustion capacity of the rotary kiln,
an extension of incineration technology. Limits on combustible feed are
prescribed for ISV in order to avoid excessive heat loads in the hood and
offgas system. Heat from combustion is generated above the molten glass,
where pyrolyzed gases meet oxygen. Much of the heat generated is not
returned to the glass and, therefore, must be removed from the offgas sys-
tem. Current combustible content limits have been established at 7% by
weight maximum in the soil being vitrified (Buelt 1992). The process has
been successfully applied at full scale for combustible wastes, handling
eighty, 3.7-m (12 ft) long, creosoted timbers in a single ISV setting. Gas-
eous effluents were completely contained during this operation., and the
offgas system was effective in handling the increased heat load.
6.4.5 Potential Shorting Caused by Metals
When metals are introduced in a vitrification process, they can form a
dense phase of molten metal at the bottom of the molten glass pool. This
can cause an electrical shorting in some kinds of vitrification processes (or
more rapid corrosion of refractories in others). Vertical refractoiy-lined
6.4
-------
Chapter 6
melters and ISV are most suitable for handling metals. As molten metals
form in a vertical melter, they can be tapped through the bottom drain into
the receiving canister. The ISV technology has recently been upgraded to
allow processing of wastes with high concentrations (up to 25% by weight)
of metals (Buelt 1992). The electrode feeding system of ISV allows the
vertical position to be controlled to avoid electrical shorting. This system
has been effectively demonstrated on a large scale and is ready for field
deployment. Horizontal refractory-lined melters and rotary kiln vitrifica-
tion are less suitable for treating wastes containing metals because of con-
cerns about refractory longevity.
6.4.6 Cost of Energy
Although energy costs are a significant part of the overall operational
cost (i.e., up to 40% of that of ISV), the amount of energy needed to per-
form vitrification is generally overestimated. Energy requirements are gen-
erally 0.6 to 1.0 kwh/kg for electrical vitrification processes, such as ISV
and refractory-lined melters, and up to 1.6 kwh/kg for fossil fuel fired pro-
cesses, such as the rotary kiln (Buelt 1992). A study showed that less en-
ergy is required to vitrify a given volume of contaminated soil by ISV than
to transport it 500 miles or more. Most vitrification processes consume
between 500 and 3,500 kw. This is much less power than a large hotel
would consume. Nevertheless, vitrification does require significant
amounts of electrical energy. If it is not available at the site, it may have to
be provided by portable generators; generator power is usually more expen-
sive than line power.
6.5 Modified Sulfur Cement Process
The modified sulfur cement solidification process has been shown to be
highly reliable (Kalb and Colombo 1985). Following are the primary re-
quirements for processing:
• suitable thermal input to supply latent heat of fission and main-
tain a molten condition; and
• ability to thoroughly mix waste and binder under viscous condi-
tions to form a homogenous mixture.
6.5
-------
Limitations
Generally, the waste should be predried, since sulfur is not compatible
with water. Some moisture, however, can be tolerated; it will subsequently
evaporate under processing temperatures. Since sulfur cement is essentially
inert at temperatures used for processing, no interaction between waste and
binder is anticipated.
6.6 Polyethylene Extrusion Process
The reliability of the Polyethylene Extrusion Process has been demon-
strated through application to waste streams having a broad range of chemi-
cal and physical properties. The inert characteristics of polyethylene and its
compatibility with many kinds of wastes over wide concentrations assures
reliability of performance and predictable end products. The process, how-
ever, requires that the waste be dried, since polyethylene is not compatible
with water or other aqueous solutions. Drying of wastes before, their incor-
poration with polyethylene results in volume reduction, higher waste load-
ings, and a homogenous product. Confirmatory tests (Franz, Heizer, and
Colombo 1987) have shown that no reactions would occur that could ad-
versely affect either the health and safety of workers during processing
operations or compromise the integrity of the end product.
6.7 Inorganic, Cementitious Technologies
of the Siliceous Category
The innovative aspects of these processes are generally limited to spe-
cific applications, discussed in Subsections 6.7.1 through 6.7.4, below. The
reagents used are widely available (except for rice hull ash) at competitive
prices. In general, more independent evaluation is needed to assess the
effectiveness and practicality of these innovations versus the conventional
cementitious, siliceous technologies.
6.6
-------
Chapter 6
6.7.1 Soluble Silicate Processes
Soluble silicate processes are generally not effective in immobilizing
organics and are not marketed for that use. There is little reason to believe
that they, as a group, enter into chemical reactions with organics, as a
group. As with other processes, however, there could be advantageous
reactions with specific hazardous compounds. The main limitation in the
use of soluble silicate processes results from their sensitivity to such opera-
tional factors as order of addition, mixing type, duration and degree, and
quantity added. The latter aspect is discussed in Section 3.7.5.1.
6.7.1.1 EnviroGuard/ProTek/ProFix, Houston, Texas
The ProFix process has limited use in solidification of high-solids con-
tent wastes, such as, sludges, filter cakes, and contaminated soils, since
sorbents are not required or recommended. The chief operational disadvan-
tage lies in the cost of shipping and handling rice hull ash. This material,
while inexpensive at the source, is available in only a few locations and is
expensive to transport because of its low-bulk density, which also requires
that it receive specialized handling at remedial sites in order to avoid dust
problems and to effect proper metering into the treatment system.
6.7.1.2 Lopat, Wanamassa, New Jersey
The Lopat process, in the innovative sense, applies primarily to wastes
that contain soluble toxic metal salts, but are otherwise nonhazardous. Ex-
amples include auto shredder fluff, certain contaminated soils, and various
ashes. In this case, the silicate can react directly with the metal salt, form-
ing relatively immobile metal "silicates." The process can, of course, be
applied, along with cementitious agents, in conventional use treating other
wastes. The innovative aspect of the process, discussed in Section 3.7.5.1,
is limited to certain applications. There appears to be no data available
from independent evaluations of the Lopat process. All available data came
from Lopat itself, its licensees, or customers.
6.7.1.3 Other Soluble Silicate Processes
Except for the Conner process, it appears that the soluble silicate formu-
lations described in Subsection 3.7.5.1, are not currently being used or
tested as commercial processes. In any event, their use would likely be
limited to specific kinds of wastes or site scenarios. The Conner process's
6.7
-------
Limitations
usefulness, in the innovative sense, is limited to low-solids wastes where
processing with liquid silicates alone would be too sensitive to mixing time
and waste variations.
6.7.2 Slag Processes
For remediation projects, as the distance from the source to the site in-
creases, the cost-effectiveness of slag processes decreases because of com-
petition from locally available materials - fly ash, kiln dust, etc. The pro-
cess has been applied only to metal-bearing wastes. Slag should have gen-
eral applicability except where its reductive properties would be undesir-
able, such as in the treatment of certain arsenic-contaminated wastes. The
SoliRoc™ process is highly waste specific. The economics favor highly
acidic wastes where no additional cost for acid is incurred and the waste
must be neutralized before solidification in any event.
6.7.3 Lime
The processes described in this monograph are designed to treat wastes
containing high levels of organics. Lime processes would be considered
innovative in treating metal wastes, but there appears to be no theoretical or
practical advantage in such an application.
6.7.4 Inorganic Polymers Category
There are several limitations attending the geopolymer process. The
most important is cost. Costs for large quantities of the reagents in Europe
are in the range of $800 to $l,000/tonne ($730 to $900/ton). At present,
there is no source of supply in North America. Reagent cost is about $100
to $600/tonne ($90 to $550/ton) of waste treated - typically $100 to $200/
tonne ($90 to $180/ton) of waste for the examples tested. Therefore, at
present, this process would be limited to waste and remediation scenarios
that cannot be handled effectively by other processes (Conner 1991). Addi-
tional use may be expected if the cost of the geopolymers were reduced.
6.8
-------
Chapter 6
6.8 Soluble Phosphates
To date, soluble phosphates have been thoroughly evaluated only for use
with municipal fly ash. Further research is needed to determine whether the
process will be applicable to other wastes. Not all metal phosphates are
insoluble; therefore, application is limited to wastes containing mixtures of
contaminants. Organics would probably not be stabilized by this process.
6.9
-------
-------
Chapter 7
TECHNOLOGY PROGNOSIS
7.1 Sorption and Surfactant Process
Aspects Needing Further Development
and Demonstration
Other natural or synthetic materials that result hi strong interactions with
heavy metals or organics need to be evaluated. The saturation limits of
sorbents need to be evaluated for loading purposes. The degree of sorption
must be assessed under realistic disposal environments, as opposed to regu-
latory bench-scale testing methods.
7.2 Emulsified Asphalt
The future is promising for use of the emulsified asphalt process with
petroleum-contaminated soils, such as those resulting from oil spills. The
product is very similar to commercially-available, low-strength asphaltic
construction materials, and the cost of treatment is relatively low. Use in
treating wastes containing metals or organics, such as chlorinated hydrocar-
bons, however, is problematic, and this application must undergo much
more analysis.
7.1
-------
Technology Prognosis
7.3 Bituminization
In recent years, very little information about bituminization has been
published. Consequently, the prognosis for use of this technology in treat-
ing hazardous chemical waste is quite poor. No data are available on the
durability of bituminized waste forms to use in determining whether use of
the product would be in compliance with US EPA restrictions on leachabil-
ity, such as the Toxicity Characteristic Leaching Procedure.
7.4 Vitrification
Significant programs are continuing the development of the refractory-
lined melter, melters with water-cooled walls, in situ vitrification, and
plasma vitrification, for expanded applications. Several private industrial
firms, government agencies, and national laboratories are developing and
marketing these types of vitrification systems for the treatment of a broad
variety of wastes. Several of these melters are emerging from both foreign
and domestic manufacturing and municipal waste treatment industries for
application to hazardous and radioactive wastes. These relatively new and
emerging technologies hold a great deal of promise in the hazardous waste
treatment field. Application is expected to extend beyond contaminated soil
to drummed waste, tanked waste, and even reactive materials. Rotary kiln
vitrification, on the other hand, is relatively mature and is generally being
pursued only for contaminated soil applications.
7.5 Modified Sulfur Cement Process
The waste loading or packing efficiency of the system is dependent on
the size and electrical capacity of the unit, since the material becomes more
viscous with the addition of waste particulates. A large-scale demonstration
is needed to determine optimum waste loadings. Further work is needed with
sludges, soils, and other waste streams to better evaluate the end products.
7.2
-------
Chapter 7
7.6 Polyethylene Extrusion Process
Although the process has been thoroughly studied and evaluated in the
laboratory, a demonstration is needed to ascertain its reliability under scale-
up conditions. Planning has been initiated to demonstrate this system using
production-scale equipment at Brookhaven National Laboratory.
Additional work is necessary to determine the types and capacities of
dryers suitable for the removal of moisture from aqueous, wet-solid wastes
before processing. Presently, spray-dryers, vacuum-dryers and thin-film
evaporators are being evaluated for a wide variety of wet-solid waste
streams.
Although the waste forms have demonstrated their ability to retain toxic
mixed waste components, studies are needed to determine maximum con-
centrations of heavy metals that can be incorporated into polyethylene in
compliance with regulatory requirements.
7.7 Inorganic, Cementitious Technologies
of the Siliceous Category
7.7.1 Soluble Silicate Processes
7.7.1.1 EnviroGuard/ProTek/ProFix, Houston, Texas
The possible advantages of in situ generation of soluble silicate have not
been fully explored. Work should concentrate on the development of long-
term properties, i.e., long curing periods or long-term leaching procedures,
since that is where the advantages will lie.
7.7.1.2 Lopat, Wanamassa, New Jersey
There is a need for more information on the comparative properties of
different soluble silicates. There are many grades and types of alkali metal
silicates whose differing alkalinities and silica contents may be important.
This approach to stabilization has probably not been optimized overall.
7.3
-------
Technology Prognosis
7.7.1.3 Other Soluble Silicate Processes
There is need for further general work in this area. Various silicate set-
ting agents and other additives may result in improved stabilization meth-
ods. This is important in view of recent, more exacting regulations and
remedial project specifications.
7.7.2 Slag Processes
Broader testing of blast-furnace slag, both as a primary stabilization
agent and as an additive, would be beneficial. Slag is inexpensive and
available in most industrial locations. It should be compared with other
additives, such as fly ash and kiln dusts, in this respect. Like these other
waste materials, the properties are quite variable and slag usage requires
good quality control procedures.
7.7.3 Lime
The processes described have not been directly compared with other
treatment methods, or even to untreated lime, either CaO or Ca(OH)2. Such
a study needs to be done to establish whether the presumed additional cost
of the treated lime is justified.
7.7.4 Inorganic Polymers
Relatively little test information is available on inorganic polymer pro-
cesses. Especially needed are data on difficult-to-treat wastes, such as those
containing significant amounts of organo-metallics, organics, arid radioac-
tive species. In remedial applications where high early strength is needed
and where acid leaching conditions are expected, geopolymer use is a possi-
bility. In these applications, the higher cost of the reagents could be justified.
7.8 Soluble Phosphates
Soluble phosphate treatment of fly ash from municipal solid waste incin-
eration should continue to grow in use. Its use in treating other metals-
bearing wastes, such as metals smelting dusts or contaminated soils, must
be extensively tested and evaluated.
7.4
-------
Appendix A
APPENDIX A
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A.1
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List of References
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A.2
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Appendix A
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A.3
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List of References
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A.10
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THE WASTECH® MONOGRAPH SERIES ON
INNOVATIVE SITE REMEDIATION TECHNOLOGY
WASTECH® is a multiorganization effort which joins in partnership the Air and
Waste Management Association, the American Institute of Chemical Engineers, the
American Society of Civil Engineers, the American Society of Mechanical Engineers,
the Hazardous Waste Action Coalition, the Society for Industrial Microbiology, and the
Water Environment Federation, together with the American Academy of Environmental
Engineers, the U.S. Environmental Protection Agency, the U.S. Department of Defense
and the U.S. Department of Energy.
A Steering Committee composed of highly respected members of each participating
organization with expertise in remediation technology formulated and guided the
project with project management and support provided by the Academy. Each
monograph was prepared by a task group of five or more recognized experts. Their
initial manuscript was subjected to an extensive peer review prior to publication. This
1994 series includes:
Vol 1 - BIOREMEDIATION
The Principal Authors include: Calvin H. Ward,
Ph.D., Chair, Professor & Chair of Environmental
Science & Engineering, Rice University; Raymond C.
Loehr, Ph.D., P.E, DEE, Civil Engineering, University
of Texas; Robert Morris, Ph.D., Technical Director,
Eckenfelder, Inc.; Evan Nyer, Vice President, Techni-
cal Resources, Geraghty & Miller, Inc.; Michael
Piotrowski, Ph.D.; Jim Spain, Chief, Environmental
Biotechnology, AFESCA/RAVC;John Wilson, Ph.D.,
Process & Systems Research Division, U.S. Environ-
mental Protection Agency.
Vol 2 - CHEMICAL TREATMENT
The Principal Authors include: Leo Weitzman,
Ph.D., Chair, President, LVW Associates, Inc.; Kim-
berly Gray, Ph.D., Assistant Professor of Civil Engi-
neering & Geological Sciences; Robert W. Peters,
Ph.D., P.E., DEE, Environmental Systems Engineer,
Argonne National Laboratory; Charles Rogers, Ph.D.,
Senior Research Scientist, USEPA Risk Reduction
Engineering Laboratory; John Verbicky, Ph.D.,
Chemfab Corporation.
Vol 3 - SOIL FLUSHING/SOIL WASHING
The Principal Authors include: Michael J. Mann,
P.E., Chair, President, Alternative Remedial Tech-
nologies, Inc.; Donald Dahlstrom, Ph.D., Department
of Chemical Engineering, University of Utah; Patricia
Esposito, PAK/TEEM, Inc.; Lome Everett, Ph.D.,
Geraghty & Miller, Inc.; Greg Peterson, P.E., Director
of Technology Transfer, CH2M Hill, Inc.; Richard P.
Traver, P.E., General Manager, Bergmann USA.
Vol 4 - SOLIDIFICATION/STABILIZATION
The Principal Authors include: Peter Colombo,
Chair, Manager, Waste Management Research & De-
velopment, Brookhaven National Laboratory; Edward
Barth, P.E., Environmental Engineer, Office of Re-
search & Development, U.S. Environmental Protection
Agency; Paul L. Bishop, Ph.D., P.E., DEE, William
Thorns Professor, Department of Civil & Environmen-
tal Engineering, University of Cincinnati; Jim Buelt,
Staff Engineer, Battelle Pacific Northwest Laboratory;
Jesse R. Connor, Senior Research Scientist, Clemson
Technical Center, Inc.
Vol 5 - SOLVENT/CHEMICAL EXTRACTION
The Principal Authors include: James R. Donnelly,
Chair, Director of Environmental Services &
Technologies, Davy Environmental; Robert C. Ahlert,
Ph.D., P.E., DEE, Distinguished Professor, Rutgers
University; Richard J. Ayen, Ph.D., Director of
Chemical Processing, Chemical Waste Management,
Inc.; Sharon R. Just, Environmental Engineer, Engineering-
Science, Inc.; Mark Meckes, Physical Scientist, USEPA
Risk Reduction Engineering Laboratory.
Vol 6 - THERMAL DESORPTION
The Principal Authors include: JoAnn Lighty, Ph.D.,
Chair, Assistant Professor of Chemical and Fuel Engi-
neering, University of Utah; Martha Choroszy-
Marshall, Program Manager, Thermal Treatment,
CIB A-GEIGY; Michael Cosmos, Project Director, Roy
F. Weston, Inc.; Vic Cnndy, Ph.D., Professor of Me-
chanical Engineering, Louisiana State University.and
Paul De Percin, Chemical Engineer, U.S. Environmen-
tal Protection Agency.
Vol 7 - THERMAL DESTRUCTION
The Principal Authors include: Richard S. Magee,
Sc.D., P.E., DEE, Chair, Executive Director, Hazard-
ous Substance Management Research Center, New Jer-
sey Institute of Technology; James Cudahy, President,
Focus Environmental, Inc.; Clyde R. Dempsey, P.E.,
Chief, Thermal Destruction Branch, Office of Research
and Development, U.S. Environmental Protection
Agency; John R. Ehrenfeld, Ph.D., Senior Research
Associate, Center for Technology, Policy, & Industrial
Development, Program Coordinator, Hazardous Sub-
stances Management, Massachusetts Institute of Tech-
nology; Francis W. Holm, Ph.D., Senior Scientist &
Principal Deputy, Chemical Demihterization Center,
SAIC, Dennis Miller, Ph.D., Science Advisor, U.S.
Department of Energy; Michael Model), Modell De-
velopment Corp.
Vol 8 - VACUUM VAPOR EXTRACTION
Paul Johnson, Ph.D., Chair, Research Engineer,
Shell Development; Arthur Baehr, Ph.D., U.S. Geo-
logical Survey, Water Resources Division; Richard A.
Brown, Ph.D., Vice President, Groundwater Technol-
ogy; Robert Hinchee, Ph.D., Research Leader, Battelle;
George Hoag, Ph.D., Director, University of Connecti-
cut, Environmental Research Institute.
The monographs can be purchased for $49.95 per volume or $349.65 for the entire series (includes shipping
and handling) from the American Academy of Environmental Engineers®, 130 Holiday Court, Suite 100,
Annapolis, MD, 21401; phone 410-266-3311, FAX 410-266-7653. MC & VISA accepted.
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