EPA-660/2-73-023
December 1973
Environmental Protection Technology Series
Regeneration of Ghromated Aluminum
Deoxidizers
«c
55
o
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C. 20460
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
H. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
degradation from point and non-point sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards.
EPA REVIEW NOTICE
This report has been reviewed by the Office of Research and
Development, EPA, and approved for publication. Approval does
not signify that the contents necessarily reflect the views
and policies of the Environmental Protection Agency, nor does
mention of trade names or commercial products constitute
endorsement or recommendation for use.
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $1.95
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REPORT NO. EPA-660/2-73-023
December 1973
REGENERATION OF CHROMATED
ALUMINUM DEOXIDIZERS
Phase I Report
By
Harry C. Hicks, Senior Research Engineer
Robert A. Jarmuth, Project Director
Project 12070 HEK
Program Element 1B2036
Project Officer
Dr. Hugh B. Durham
Heavy Industrial Sources Branch
Grosse He, Michigan 48138
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
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ABSTRACT
Large quantities of chromium compounds are disposed of annually through discard of spent
aluminum deoxidizer solutions. Regeneration, rather than discard, of these concentrated
solutions is a significant contribution to antipollution efforts.
The regeneration concept involves oxidation of trivalent (depleted) chromium to hexavalent
(active) chromium at an electrode of a dc rectifier. This step requires that an electrical
circuit be maintained within the solution, yet movement of dissolved metals must be
restricted to specific areas. Infinite lifespan of the solution also implies separation and
removal of aluminum and other metals that are dissolved in the deoxidizing process.
Technical activities of the project involve:
• Testing, evaluation, and development of diaphragm and electrode materials of
regeneration
• Development of design information for separation and removal equipment
Performance activities of the project involve:
• Pilot scale-up and demonstrations to verify the dependability of evolved technical
information
• Evaluation of the regeneration process economics
The objectives of the program were met and it is concluded that the concept of regenerating
chromated aluminum deoxidizers is a feasible and practical method for significantly
reducing the quantity of discarded toxic chromium compounds and conserving chromium
metal resources.
This report, which has been assigned Boeing document number D6-22251-8 for internal use,
was submitted in fulfillment of phase I, project number 12070 HEK, between the
Environmental Protection Agency and the Boeing Commercial Airplane Company.
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CONTENTS
Page
ABSTRACT ii
FIGURES iv
TABLES v
ACKNOWLEDGMENTS vi
SECTION I-CONCLUSIONS 1
SECTION II-RECOMMENDATIONS 3
SECTION III-INTRODUCTION 5
SECTION IV-TECHNICAL DISCUSSION 9
Diaphragm Evaluation 9
Electrode Evaluation 20
Laboratory Determination of Operating Parameters 27
Pilot Plant Assembly and Operation 46
Commercial Products Evaluation 60
Product Demonstration 68
Economic Evaluation of Regeneration 81
SECTION V-BIBLIOGRAPHY 87
SECTION VI-LIST OF INVENTIONS 89
SECTION VII-GLOSSARY 91
SECTION VIII-APPENDIX 93
111
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FIGURES
No. Page
1 Diaphragm Test Cell 10
2 Diaphragm Test Cell Schematic 11
3 Asbestos Diaphragm 13
4 Constant-Temperature Bath and Rectifier 15
5 Hydraulic Press 17
6 Diaphragm Test Cell Electrical Resistance 19
7 Electrode Evaluation Schematic 21
8 Electrode Chemical Resistance Test 23
9 H-Cell Cross Section 24
10 H-Cell - 25
11 Anode Current Efficiency Test 26
12 Potentiostat Electrodes 28
13 Potentiostat and Accessories for Polarization Curves 29
14 Polarization Curve—Nickel 30
15 Polarization Curve-Stainless Steel 31
16 Polarization Curve—Copper 32
17 Polarization Curve—Lead 33
18 Polarization Curve—Duriron 34
19 Laboratory Metal Removal Evaluation 37
20 Solids Separation Cooling Rate Tests 40
21 Aluminum Sulfate Separation System Schematic 42
22 Display of Centrifuge Experimental Results 43
23 Setup for Laboratory-Developed Solids Separator 44
24 Pilot Plant Facility 47
25 227- liter Pilot Regeneration Tank and Accessories 48
26 pH Titration Curves for Sulfuric Acid Plus Aluminum Sulfate 50
27 227-liter Pilot Tank Continuous Regeneration Analyses 51
28 Test Stand for Diaphragm Porosity Evaluation 53
29 227-liter Pilot Tank Continuous Regeneration—Sulfuric-Dichromate
Deoxidizer 55
30 Precision Laboratory Balance 57
31 227-liter Pilot TankEtch Rates-Continuous Regeneration 58
32 2-liter Cell for Commercial Products Regeneration Evaluation 61
33 Regeneration of Nitric Acid Based Proprietary Deoxidizer 62
34 Regeneration of Amchem 6-16(HNO3) 64
35 Regeneration of Smutgo 4 (HNO3) 65
36 Regeneration of Amchem 6-16 (H2SO4) 66
37 Diaphragm Cell for Preproduction Tank 69
38 Regeneration in Preproduction Tank 70
39 Drum Filter Installed at Preproduction Tank '. 72
40 Details of Drum Filter System 73
41 Scraper Discharge on 20- by 12-in. (50.8- by 30.5-cm) Drum Filter .... 74
42 Drum Filter Evaluation-Drum Speed Calibration 75
43 Drum Filter Evaluation—Drum Speed Versus Output 76
44 Drum Filter Evaluation—Drum Speed Versus Cake Moisture and Chromium . 77
45 Electrolytic Regeneration Preproduction Tank 80
iv
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TABLES
No, Page
1 Membrane Chemical Resistance 12
2 Membrane Electrical Conductivity 14
3 Electrode Evaluation Cell Analyses 20
4 Electrode Polarization 35
5 H-Cell Mass Transfer Data 36
6 Ion Exchange Evaluation 38
7 Laboratory Crystallizer Evaluation 45
8 Diaphragm Porosity 52
9 Drum Filter Evaluation 59
10 Drum Filter Capacity 59
11 Electrical Efficiency 79
12 Regeneration Process Economics 81
13 Capital Equipment Costs 83
14 Regeneration Costs Per Unit Area 84
15 Waste Load Per Unit Area 85
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ACKNOWLEDGMENTS
The support of Equipment Engineering, Quality Control, Planning, Operations, and
Manufacturing Research and Development of the Boeing Commercial Airplane Company is
gratefully acknowledged.
Mr. John Prysi of Ametek Corporation and Mr. Hugh Evans, representing the Leon J.
Barrett Company, provided valuable technical information.
VI
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SECTION I
CONCLUSIONS
Regeneration of chromated aluminum deoxidizers is feasible, practical, and economical.
Electrolytic reoxidation of chromium plus removal of dissolved metals is more efficient in
the conventional dichromate-sulfuric deoxidizer than in proprietary deoxidizers and can
result in a cost savings to the operator.
The useful life of proprietary chromated deoxidizers can be appreciably extended by
electrolytic reoxidation of the chromium, thereby minimizing disposal of concentrated
chromates. Removal of dissolved metals in some of these deoxidizers requires additional
investigation to resolve residual technical problems.
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SECTION II
RECOMMENDATIONS
During the progress of this project, a chemically inert, electrically conductive diaphragm was
developed to isolate chromate ions. Development of fabrication techniques and service life
were not within the scope of this program and were not optimized. Therefore, it is
recommended that further work be done to improve this diaphragm in terms of lower
fabrication cost and longer service life.
It is also recommended that the process for regeneration of dichromate-sulfuric deoxidizers
as described in this report be encouraged for use by heavy industrial metal finishers.
It is further recommended that electrolytic reoxidation be implemented for proprietary
deoxidizers wherever economically and/or environmentally feasible.
Because simple crystallization is not practical for some deoxidizers, it is suggested that other
techniques for removing dissolved metals, such as reverse osmosis or precipitation, be
evaluated.
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SECTION III
INTRODUCTION
BACKGROUND
Chromium-containing chemical compounds have long been recognized as a major contrib-
utor to water pollution problems because of the high toxicity of chromium's ionic forms
and the prevalence of chromium in a wide variety of industrial processes. Approximately
10% of the total U.S. chromium consumption is in the chemical industries (in excess of
50,000 tons annually). Nearly one-third of this is used for paint pigments and hence can be
considered as nonpolluting, as are the metallurgical and refractory uses.
Metal surface treatments and corrosion control measures also use a large quantity of
chromium, estimated at 30,000 tons annually. In this metal-finishing industry, chromated
processing solutions are used extensively to treat aluminum surfaces during various
operations such as anodizing, conversion coatings, prepaint preparation, welding, and
adhesive bonding. A specific process commonly referred to as deoxidizing of aluminum (a
part of a cleaning cycle) is of special interest. Chromated aluminum deoxidizing solutions
have a relatively high concentration of chromium in the hexavalent state, and this chromium
is used up in three ways: (1) a minute amount remains on the surface of the aluminum as a
complex chemical conversion coating; (2) a somewhat larger amount is lost by drag-out into
rinse waters; and (3) high concentrations are lost when the processing solution is discarded
for various nonfunctional reasons. It is predicted that for many technical and economic
reasons, chromated aluminum deoxidizers will continue to be used.
The loss described in item 3 is the problem to which the efforts of this project were
directed. A concept for a regeneration process was devised to extend the useful life of the
chromated deoxidizes. The advantages of the regeneration process described in this report
are:
• Environmental
• Major reduction in the quantity of chromium-containing effluent
• Conservation of chromium resources
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• Industrial
• Reduction in the requirements of treatment plants
• Increased production through reduced downtime
• Lower processing costs
Reduction of chemical additions
Reduction of quality control costs
Elimination of dumping and recharging costs
• Increased process reliability
Preliminary research work has proved that it is feasible to regenerate spent deoxidizer
solutions rather than discard them. Thus it is possible, by applying chemical engineering
technology, to maintain the acceptable performance of chromium-containing solutions
indefinitely. By making this technology available to all metal finishers, a significant
contribution to antipollution efforts can be made.
SCOPE
The engineering techniques developed in this project involve regeneration of active
chromium compounds by electrolysis plus removal of undesirable metals by crystallization
and separation. A deoxidizer consisting of sulfuric acid and sodium dichromate was selected
for this investigation for two reasons: (l)the initial composition is known exactly, and
(2) the workload and performance of this solution within the facilities of the project
contractor are critical and precisely controlled.
PROJECT OBJECTIVES
The objectives of this work are to develop equipment information and establish the
operating conditions for the continuous regeneration of a sodium dichromate-sulfuric acid
aluminum deoxidizer solution and evaluate this technology for other commercially available
chromated aluminum deoxidizers. Successful regeneration can be realized by: (1) electro-
chemical oxidation of trivalent chromium to hexavalent chromium, (2) removal of dissolved
aluminum and trace metals, and (3) addition of chemicals to keep the solution within
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required limits. The following are specific tasks to be accomplished during this project:
• Determine electrochemical characteristics of the materials selected.
• Acquire additional laboratory experimental data for the oxidation of chromium
and the removal of dissolved metals.
• Construct a pilot plant regeneration system and operate to Verify previous data.
• Evaluate use of regeneration equipment on proprietary aluminum deoxidizers.
• Scale up a process to simulate production installation.
• Provide a technical report of the project.
TECHNICAL APPROACH
A previous research and development program demonstrated the feasibility of electrolytic
oxidation of trivalent chromium to the hexavalent state, together with precipitation of
dissolved aluminum as aluminum sulfate. Work was done in a divided tank, with anode and
cathode chambers separated by a porous ceramic membrane. The porous ceramic worked
well in the laboratory, but it is undesirable for large-scale industrial use because of fragility,
short life, and high cost.
Initial tests in this new program were made on a laboratory scale to obtain data on alternate
diaphragm material, electrode performance, current efficiency versus current density, mass
transport, and solids separation. The data obtained allowed a 227-liter sodium dichromate-
sulfuric acid (Na2Cr2O<7-HSO4) regeneration system to be assembled and tested.
Dissolved aluminum can be crystallized as aluminum sulfate [A^CSO^.-ISH^O] and
removed. Trace metals, principally copper, zinc, magnesium, iron, and manganese, which are
found in the aluminum alloys being treated, slowly accumulate in solution and methods for
their removal were tested. The pilot system was operated until it was shown that oxidation
and metal removal can be regulated to maintain the solution within desired functional
limits.
Another phase of this work tested the regeneration techniques and equipment on three
proprietary chromated aluminum deoxidizers. Finally, 2200 liters of Na2Cr2Oy-H2SO4
deoxidizer was operated for production verification. Regeneration equipment for this unit
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was designed, installed, and operated under simulated production conditions and quality
assurance surveillance.
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SECTION IV
TECHNICAL DISCUSSION
i
The program consists of seven tasks, as detailed in the following sections.
TASK I-DIAPHRAGM EVALUATION
Testing of materials was conducted to obtain a membrane that is resistant to ^2^20-7-
H2SO4 solution and will permit adequate ion transport to maintain electrolysis rates at
lowest power (IR) drop through solution. Dacron, polyester, polypropylene, Dynel, and
acid-washed long fiber asbestos (supported by a polypropylene screen) were tested. The
test assembly is illustrated in figure 1. Schematic arrangement was according to figure 2.
Samples of commercially available synthetic fibers were procured as follows:
Woven polypropylene Two samples
Woven Dynel Two samples
Nonwoven polypropylene felt One sample
Nonwoven Dacron felt One sample
Nonwoven polyester Two samples
Material Preparation
The selected materials were prepared in the following manner:
• Asbestos
The asbestos diaphragm was prepared by pouring a weighed slurry of acid-washed
asbestos fiber onto a polypropylene screen fastened to a vacuum box. Water was
drawn off with vacuum and the asbestos membrane was removed from the
supporting screen.
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PLAN
Pt-Pt
CATHODE
(M^\I^>^%<^^^<^^^||
PLEXIGLASS
CELL-
Pt-Pt ANODE
MEMBRANE IN
LIQUID TIGHT
HOLDER
SIDE ELEVATION
ELECTRICAL SCHEMATIC
Figure 2. Diaphragm test cell schematic
11
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Synthetic fibrous materials
These materials were washed and dried to remove sizing and lubricants used in
manufacture.
Asbestos was investigated and set aside because of inherent difficulties in obtaining
acceptable diaphragm shapes without the incorporation of soluble binder material with the
asbestos fibers (see fig. 3). Further investigation of this material will be conducted only if
alternate materials prove to be unsatisfactory. It is apparent that uniformity and consistent
permeability can be more easily obtained with off-the-shelf synthetic fiber material.
Membrane Testing
Samples of the synthetic fibers were soaked in a sodium dichromate-sulfuric acid deoxidizer
solution (Na2Cr2O"7-H2SO4) for 240 hr at 82° C. Weight loss, dimensional changes, and
solution concentration changes were determined. Results are shown in table 1. During the
progress of the test, a supplier of synthetic fibers furnished a sample of another material,
Orion felt, for evaluation. This sample was exposed to the sulfuric acid-sodium dichromate
deoxidizer solution at 71°C. Severe degradation of the fiber occurred after 3 weeks of
exposure. The Orion material is therefore judged to be unsatisfactory.
Table 1. MEMBRANE CHEMICAL RESISTANCE
Sample
no.
1
2
3
4
5
6
7
Control
Description
Woven polypropylene
Woven Dynel
Woven polypropylene
Woven Dynel
Polypropylene felt
Dacron felt
Polyester film
Material change
Weight loss,
%
3.5
2.4
12.0
4.1
2.1
3.5
0.7
-
Dimension loss,
%
0
0
0
0
0
0
0
-
Solution change
Hexavalent
chrome loss,
%
73
40
99
65
99
94
7
-
Sulfuric acid
loss, %
12
5.5
18
10
15
13
2
-
12
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Figure 3. Asbestos diaphragm
13
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Samples of the polypropylene felt, Dacron felt, and polyester material were installed in the
diaphragm test cell. The test cell was contained in a constant-temperature bath (fig. 4) while
electrical readings were determined. Electrical conductivity data were collected by filling
one side of the cell with Na2Cr20-7^2804 deoxidizer. The other side of the cell was filled
with sulfuric acid only. Electrode plates with platinum black were inserted, and voltage
readings were made at several amperage levels at steady-state conditions. Data are presented
in table 2.
Table 2. MEMBRANE ELECTRICAL CONDUCTIVITY
Current,
amp
Increasing
<
amperage
Decreasing
amperage
'1.0
2.0
3.0
4.0
,5.0
'4.0
3.0
2.0
k 1.0
Potential, V
Polypropylene
(1-3cfm)a
1.6
1.9
2.1
2.3
2.5
2.3
2.1
1.9
1.6
Dacron
(17cfm)a
Dichromate
bleed-through;
test
discontinued
Polyester
(6 layer)
1.7
2.0
2.3
2.6
3.0
2.6
2.4
2.1
1.75
Polyester*3
(12 layer)
2.3
3.0
3.6
4.4
5.0
4.4
3.7
3.0
2.3
Polyesterb
(15 layer)
2.6
3.6
4.75
6.2
8.5
5.8
4.6
3.5
2.6
Vendor's permeability data
Pressure-temperature laminate
It was observed very early that all materials under evaluation were much too porous to
prevent diffusion of the dichromate ion into clear sulfuric acid. The least permeable
material, rated by its vendor at 1 to 3 cfm (air) by ASTM test method D737, allowed too
much diffusion. Since the polyester material is the most chemically resistant (reference
table 1), efforts were made to decrease its permeability by laminating techniques. This
laminated polyester was the diaphragm material used for continuing process development.
Throughout the remainder of the project, the designation J5D will refer to a diaphragm
consisting of multiple layers of this Dupont 2024 Reemay nonwoven polyester.
In addition to the above tests, a J5D diaphragm and a single layer of the J5D laminate were
subjected to 3 months' continuous exposure to the dichromate-sulfuric deoxidizer at 71°C.
Small particles of fiber flaked off and some swelling occurred with the laminate. Otherwise,
the polyester appeared unaffected. This qualitative test was sufficiently encouraging to
warrant continuing development and testing of the J5D diaphragm.
14
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A quantity of 15- by 20-cm J5D diaphragms were fabricated in the hydraulic press
illustrated in figure 5 and were subjected to testing in the diaphragm test cell.
Test Procedure—Membranes were tested according to the following procedure:
1) Coat platinum electrodes with platinum black and insert in cell. Place cell in 71° C
constant-temperature bath.
2) Fill cell with ^C^O-y-r^SC^ solution.
3) Insert membrane in holder and immerse in beaker filled with Na2Cr2O-y-H2SO4
solution maintained at 71° C. Soak for 1 hr.
4) Remove membrane and holder, shake off excess solution, and insert in test cell.
Allow to reach thermal equilibrium at 71° C.
5) Adjust solution to level.
6) Turn on direct current power supply and increase to predetermined level as
indicated on ammeter.
7) Run cell for 5 min, adjusting to maintain constant amperage.
8) Read potential, E, between electrodes with voltmeter.
Discussion—The potential, E, obtained from item 8 above will be directly proportional to
the resistance of the membrane to ion passage. EC is the total potential across the cell and
can be separated into:
EP = Er + Na + Nr + IR
C 1 ct v
where:
Er = algebraic sum of the reversible potentials of anode and cathode
Na and NC = polarization of anode and cathode, respectively
IR = voltage drop due to resistance of solution
16
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Under carefully controlled test conditions, Er + NC can be kept approximately constant.
The use of platinum-black electrodes helps to keep Na and NC at a low value and therefore
make IR a higher percentage of EC. Thus, Er + NC = K.
The IR drop through the solution can be expressed as:
I ; therefore,
EC-K_
I =Rm
Voltage and current data were collected in the diaphragm test cell to determine the
electrical resistance of the fabricated J5D diaphragm. Figure 6 illustrates the collected data.
Data from this test established the linear relationship between voltage and current. Thus the
values for Kj and K^ in the equation EC = Kj + K^ + IRm can be eliminated algebraically.
The resistance due to the diaphragm system is calculated directly. This resistance is 0.61
ohm for 135.5 sq cm of J5D through the range of 1.0 to 5.0 amp. This is equivalent to a
maximum current density of 3.69 amp/sq dm through the diaphragm and up to 1.72 amp/sq
dm on the electrodes. A regeneration current up to 2.5 amp/1 can be used in the anode and
cathode chambers.
Since the chemical resistance and electrical performance of the J5D diaphragm proved to be
satisfactory, a preliminary functional test was desirable to predict the capability of the
diaphragm to maintain separation of ions under operating loads for a longer period of time
18
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6r-
15-LAYER POLYESTER
5 -
4 -
to
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O
GALVANIC
CELL
VOLTAGE
12-LAYER POLYESTER
6-LAYER POLYESTER
3 -
POLYPROPYLENE FELT
(2 LAYERS)
X REVERSED POLARITY
1
2
3
AMPS
4
5
6
Figure 6. Diaphragm test cell electrical resistance
than had been used previously. Therefore, the diaphragm test cell was set up with a J5D
diaphragm, sulfuric-dichromate deoxidizer in the anode chamber, and sulfuric acid only in
the cathode chamber. The cell was operated for 4 hr at 4.0 amp and 4.5 V.
The chemical analyses are given in table 3. A small but proportional increase in
concentration occurred due to water evaporation during the test. No visual degradation of
solutions or diaphragm occurred. Analyses for trivalent chromium verify that regeneration
did occur. The results of this test encouraged continued use of the J5D diaphragm. All other
diaphragm materials tested had less chemical resistance and allowed bleed-through of
dichromate ion, and consequently were rejected from further consideration.
19
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Table 3. ELECTRODE EVALUATION CELL ANAL YSES
Test
no.
J5D-1
J5D-2
J5D-3
J5D-4
Chamber
description
Cathode
at
start
Cathode
at
finish
Anode
at
start
Anode
at
finish
Analyses, gm/l
Sulfuric
acid
39.3
40.0
40.8
41.6
Active
chromate
None
None
4.6
4.6
Total
chromate
None
0.01
4.6
4.6
Trivalent
chrome
None
None
0.028a
0.01 7a
aReduction of trivalent chromium in the anode chamber indicates an expected regeneration
of chromium.
TASK II-ELECTRODE EVALUATION
Anode Material Selection
Ample references can be found in the literature that metallic lead (Pb) anodes give the
1-3 ^
highest current efficiency for the oxidation of Cr J to C^Oy . Tests were made on
Pb-7%Sn and Pb-6%Sb to obtain the material that gives the best compromise of current
efficiency and resistance to attack by the solution.
1) Determine stability of Pb, Pb-7%Sn, and Pb-6%Sb in Na2Cr2O7-H2SO4 solution
by electrolysis at maximum amperage for 400 hr.
2) Determine current efficiency of Pb, Pb-7%Sn. and Pb-6%Sb anodes in Na2Cr2O-y-
H2SO4 solution for the reaction 2Cr+3 + 7H2O = Cr2O7'2 + 14H+ + 6e.
• Connect annodes in series to obtain some value of amperes. A schematic
diagram of the test cell is shown in figure 7.
• Electrolyze for a total of 400 hr in ^2^207-112804 solution using a 2-hr
on/2-hr off cycle. Test in a 227-liter solution to minimize effects of
concentration changes.
20
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TEST ELECTRODES
(5 PAIRS)
SOLUTION RESERVOIR
PLEXIGLASS
SEPARATOR
(6 PLACES)'
Figure 7. Electrode evaluation schematic
• Evaluate test by:
Weight change
Appearance (scale, cracking, etc.)
Cathode Material Selection
9 _i_
The major cathode reaction is the reduction of H"^ to H (i.e., 2H + 2e = H^). Reduction of
9 I T
^r2^7 to Cr and deposition of dissolved metals are also possible. Cathodes of low
hydrogen overpotential are desired to operate the cell with the lowest power cost.
1) Determine stability of cathodes in
as for anodes.
solution. Use same evaluation scheme
21
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2) Determine polarization curves for Ni, Pb, Cu, CRES, and Duriron cathode
material in H^SC^ solution. Use Anatrol model 4200 research potentiostat for
determinations.
Electrode Chemical Resistance
Seven materials were arranged in a 227-liter tank of sulfuric-dichromate deoxidizer, as
illustrated in figure 8. The materials were positioned so that only lead (Pb) and lead alloys
were anodic, and the other metals were cathodic. Such an arrangement provided a
possibility for anodic discrimination between commercially pure lead (Pb), lead-tin (Pb-Sn),
and lead-antimony (Pb-Sb) materials in addition to evaluation of cathodic materials.
A dc rectifier was set up to impose 30 amp on the circuit with an instrument to register
operating time. A time controller to provide a 2-hr on/2-hr off cycle was used. The total test
time was 400 hr. At the end of this time the setup was disassembled and the electrode
materials were examined.
Upon examination of the anode materials, no differences could be detected among the
various lead alloys. For cathode materials, the copper and the nickel were completely
dissolved. The Duriron was slightly etched. No effect could be seen on the stainless steel
(AISI 316) or the lead.
Electrode Current Efficiency
The H-cell (figs. 9 and 10) was set up with sulfuric-dichromate in the anode chamber,
sulfuric acid only in the cathode chamber, and a J5D diaphragm between the chambers. A
quantity of trivalent chromium (as chromous sulfate) was added to the anode chamber for
regeneration. Conditions of the test (current and time) were set to introduce slightly more
than enough current to theoretically regenerate 1 gm of trivalent chromium to hexavalent
chromium. The anode chamber was sampled every 15 min and analyzed for hexavalent and
trivalent chromium.
Although analyses for the different valences of chromium are difficult, the collected data
correlated quite well. The results are illustrated in figure 11. There appears to be a very
slight advantage in selecting the Pb-7%Sn alloy for the anode material because the rate of
regeneration (slope of curve) is steeper at low trivalent chromium content.
22
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^ ' \
Figure 8. Electrode chemical resistance test
23
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Pt-Pt
CATHODE
CATHODE
COMPARTMENT
ANODE
COMPARTMENT
•DRAINS
Figure 9. H-cell cross section
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100% Pb
Pb7Sn
Pb6Sb
Figure 11. Anode current efficiency test
26
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During the test run, a small leak developed around the gasket area of the H-cell. The cathode
chamber was analyzed for total chromium at the end of each run. Calculations verified that
this leak contributed less than 1% error to the test.
Since the electrolytic regeneration is nonlinear, efficiencies must be calculated for specific
test conditions. For this test run, the regeneration efficiency is calculated on the basis of
total weight of trivalent chrome oxidized to hexavalent chrome for a period of 93 min.
Electrode efficiencies are calculated at: pure Pb, 38%; Pb-6%Sb, 38%; Pb-7%Sn, 45%.
Polarization of Cathode Materials
Electrodes of nickel, stainless steel, copper, lead, and Duriron (see fig. 12) were made for
the Anatrol potentiostat. The setup for these tests is illustrated in figure 13. Polarization
curves obtained from the potentiostat are shown in figures 14 through 18. Data
extrapolated from these curves are given in table 4.
Since both nickel and copper dissolved during the 400-hr chemical resistance test, it is
unwise to consider these materials as cathode candidates. In terms of energy consumption,
stainless steel is the most desirable cathode material, followed by lead and Duriron.
Electrode selection is stated in the summary for this section.
TASK III-LABORATORY DETERMINATION OF OPERATING PARAMETERS
The purpose of task III was to determine conditions that allow system operation to
maintain the ^2^207-112804 solution within process limits.
Mass Transport Through J5D Diaphragm
The procedure for the mass transport test was as follows:
1) Identify ion species involved in transport of amperage through cell. A schematic
of the H-cell used in transport tests is shown in figure 9.
2) Estimate changes to be expected in anode and cathode compartments because of
ion transport.
3) Estimate changes to be expected in solution through removal of H+ (as FU) and
SO4'2 as A12(SO4)3-18H2O.
27
-------
Figure 12. Potentiostat electrodes
28
-------
c
.o
o
Q.
.8
O
a
.8
00
V^
s
.§>
k.
29
-------
VOLTS
04 03 02 0.1 0 0.1 0.2 0.3
III! Ill
/ s^-
0.4
4.0 3.0 2.0
CATHODIC
I III
1.0 0 10 2.0 3.0 4.0
MILLIAMPS ANODIC
Figure 14. Polarization curve—nickel
30
-------
1.5
0.3
CATHODIC
ANODIC
MILLIAMPS
Figure 15. Polarization curve—stainless steel
31
-------
VOLTS
0.4 0.3 0.2 0.1 0 0.1
till
I
/ ^
1 ^^
02
0.4
I
VOLTS
AMPERES
4.0
1
3.0
1
2.0
1
1.0 (
1
3 1.0
1
2.0
1
3.0
I
4.0
CATHODIC
ANODIC
MILLIAMPS
Figure 16. Polarization curve—copper
32
-------
2.0
1.5
I.O
0.5
I
VOLTS
0 0.5
1.0
1.5
2.0
• VOLTS
AMPERES
I
4.0
1
3.0
— r
2.0
1.0 C
) 1.0
2.0
1
3.0
I
4.0
CATHODIC
MIL LI AM PS
ANODIC
Figure 17. Polarization curve—lead
33
-------
VOLTS
4.0
3.0
CATHODIC
1.0
0 1.0
MILLIAMPS
I
2.0
I
3.0
T
4.0
ANODIC
Figure 18. Polarization curve—Duriron
34
-------
Table 4. ELECTRODE POLARIZA TION
Metal
Nickel
Copper
Duriron
Lead
Stainless
Hydrogen
overvoltage,
V
0.31
0.26
0.60
0.79
0.25
Decomposition
potential,
V
0.56
0.63
0.61
1.19
0.74
Test electrode
Current3
-
-
3.8
1.4
l.b
Current
density
-
-
0.0796
0.0280
0.0323
Power0
-
-
0.048
0.033
0.024
Milliamps at decomposition potential
Amps per square decimeter at decomposition potential
cWatts per square decimeter at decomposition potential
The H-cell was set up with a J5D diaphragm, sulfuric-dichromate deoxidizer in the anode
chamber, and sulfuric acid only in the cathode chamber. In addition, metal ion
contaminants equivalent to a worked production bath were introduced into the anode
(deoxidizer) chamber.
Data in table 5 indicate that the J5D diaphragm effectively inhibits transport of the major
metal ion components (chromium and aluminum) of the used deoxidizer solution. The data
also indicate that the minor constituents of copper, iron, zinc, magnesium, and manganese
can be expected to pass through the diaphragm to some degree. It can be expected that
sulfuric acid will be driven from the cathode chamber into the anode chamber. Copper,
iron,and zinc should appear in a deposit on the cathode.
Removal of Dissolved Metals
The test procedure for the removal of dissolved metals was as follows:
1) Operate test cell and determine extent to which dissolved metals can be removed.
Fill cell with a solution containing known amounts of Al, Cu, Zn, Fe, Mg,
and Mn.
2) Inspect for electrodeposition on cathode surface.
35
-------
Table 5. H-CELL MASS TRANSFER DA TA
Sample
HA 1
HA-2
HC-3
HC-4
CF-1
Description
Anode chamber.
start
Anode chamber.
finish
Cathode chamber,
start
Cathode chamber,
finish
Filtered crystals of
aluminum sulfate
H2S04
gm 'I
254
278
287
310
Cr*6
Active,
gm i
983
1035
None
None
Total,
gm !
1035
10 95
None
None
Cr*-*.
gm.'l
05
OC
None
None
Al,
ppm
20,800
22,000
None
17
Cu,
ppm
380
392
0 15
065
Fe,
ppm
830
840
070
1 70
Zn
Ppm
326
324
1 72
248
Mg,
Ppm
92
99
1 47
1 58
Mn
ppm
4 75
525
065
1 00
Cr = 0 84% by weight (2 4% as NajC^O^HjO!
3) Inspect for precipitation on cathode surface. Removal of H+ in vicinity of
cathode as H2(g) causes pH to increase. Precipitation of basic salts of dissolved
metals can result from process.
4) Estimate material loss if cathode compartment is periodically dumped.
Preliminary work on a beaker scale was performed by dissolving aluminum sulfate
[A^CSO^-lSI-^O] in a heated dichromate-sulfuric deoxidizer solution. Subsequent
cooling produced insoluble solids ready for separation. The color of the crystals indicated
the presence of chromium salts. A chemical laboratory analysis verified the residual
chromium to be 0.84% by weight (sample CF-1, table 5).
Varying concentrations were used to establish a working range of dissolved aluminum that
would lend itself well to cooling and filtration. It became apparent that a difficult
crystallization and crystal separation problem existed. A concentration of aluminum sulfate
below 290 gm/1 requires excessive cooling capacity to produce the crystals. At a
concentration of 315 gm/1, the entire volume of solution becomes a solid, immovable mass
impossible to pump through a filter system. Normal quantities of minor metal constituents
were added with no apparent effect on crystallization results.
Therefore, several steps were taken to reassess the details. Laboratory assemblies were made
as illustrated in figure 19.
36
-------
ITEM 3
CRYSTALLIZATION
AND SEPARATION
ITEM 2
DEEP TANK AND FILTER
CAKE EVALUATION
Figure 19. Laboratory metal removal evaluation
37
-------
Item 1 was assembled to evaluate a backup system of ion exchange for removal of dissolved
aluminum because ion-exchange beds have been successfully used to remove dissolved
aluminum from chromic acid anodizing solutions. A quantity of the sulfuric-dichromate
deoxidizer was passed through the regenerated bed. Results of before and after analyses are
given in table 6.
Table 6. ION EXCHANGE EVALUA TION
(grams/liter)
Description
Beginning deoxidizer
Deoxidizer through
ion exchange
Sulfuric
acid
273
260
Active
dichromate
30.3
29.0
Trivalent
chrome
0.825
1.20
Aluminum
sulfate
173
107
From the information shown in table 6, it is apparent that development of ion exchange for
recovery of dissolved metals in the strong deoxidizer would involve considerable
development work. Less than half the aluminum is removed in one pass, yet the trivalent
chromium content is greatly increased. This indicates degradation and consequent short life
expectancy of the resin unless the oxidation potential of the deoxidizer is reduced. Further
ion exchange development was withheld.
Item 2 (fig. 19) was assembled for two purposes. It was apparent that suction would be
required to separate the mother liquor from the crystallized aluminum sulfate. For design
purposes it is necessary to predict the maximum allowable cake thickness and the degree of
vacuum required. As a result of testing, an unbroken cake of crystals 15 cm thick without
the aid of a filter taxes the capability of a mechanical vacuum pump by requiring more than
700 mm of vacuum. Conversely, the mother liquor can be evacuated adequately through a
125-mm cake with less than 125 mm of vacuum.
The second test purpose of the item 2 assembly was to apply the deoxidizer solids
separation problem to equivalent plating shop practices. In industrial plating shops, a
common problem is the removal of carbonates from cyanide plating solutions. One
procedure practiced in many areas is to transfer the problem solution to a spare tank, allow
the temperature to drop, let the resultant crystals of carbonates settle out, and decant the
supernatant liquid back to the plating tank. This same procedure was duplicated in item 2
on a small scale with the sulfuric-dichromate deoxidizer. Results indicate that aluminum
sulfate crystals form at an extremely slow rate when slow cooling is used. Also, the
aluminum sulfate crystals settle very slowly; a week or more is required for partial settling
38
-------
even with vigorous stirring after crystallization. And, finally, the mother liquor cannot be
removed effectively from the top of a settling because of the slow settling rate. Nor can the
liquor be drawn by vacuum from the chamber bottom because of the thick bed of crystals.
Therefore, this procedure was abandoned.
Item 3 (fig. 19) was assembled to gain more accurate information on the apparent problem
areas of crystallization and filtration. The capacity of this setup was 7.5 liters. A heat
exchanger coil of small diameter stainless steel tubing was assembled for immersion in the
chamber. This provided capability for cyclic dissolving and crystallizing.
A single layer of the polyester diaphragm material was installed in the Buchner funnel to
simulate a single-plate filter. A water aspirator provided suction. Later, a valve was installed
between the Buchner funnel and the suction chamber. Figure 20 is a typical set of cooling
curves collected from this setup.
Results of many test runs verified that:
• The workable concentration of dissolved aluminum sulfate is very narrow and lies
between 290 and 315 gm/1.
• It is impractical to suction the mother liquor through a thick layer of crystals. As
much as two-thirds of the liquid can be held by the crystal mass even after
prolonged suction.
• It is impossible to adjust operating conditions to bring down a partial quantity of
the crystals at any one cycle. The point at which small quantities of aluminum
sulfate will crystallize requires refrigeration equipment for cooling. Extremes of
refrigeration and reheating impose an economic burden on the process.
• A single layer of the polyester diaphragm material has adequate retention to hold
the crystals. The flow resistance of the single layer is very low.
• Thick cakes of the crystals have a tendency to channel and reduce the
effectiveness of suction.
• Fast cooling promotes fast crystal formation. A 10-min cooling rate from 71° to
18° C is desirable.
39
-------
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-------
• Agitation aids crystal formation and cooling rate.
• At 315 gm/1 of aluminum sulfate, the cooled and crystallized solution is an
immovable mass.
• Aluminum sulfate crystals cling to a chilled surface if the deoxidizer is sprayed or
flowed over the cold surface. However, these crystals still retain a large volume of
the mother liquor and must be evacuated.
The above results provided information for preliminary design of separation equipment for
the 2200-liter preproduction tank.
Crystallizer Equipment Evaluation
A totally automated, completely continuous system was evaluated (see fig. 21). System
sizing data were based on typical workload information for a full-production deoxidizer
tank scaled down to the 2200-liter pilot tank size. Cost estimates for such a system
indicated that continuous separation systems for a 2200-liter installation would be in excess
of $4000, which was judged to be an excessive expenditure for job shop operations.
Centrifuge Evaluation
Centrifuging is a potentially effective means of removing the dissolved metals after their
concentrations have increased sufficiently to allow crystallization. Therefore, the following
evaluation was carried out.
A sulfuric-dichromate deoxidizer solution with 300 gm/1 of dissolved aluminum sulfate was
allowed to crystallize. A sample of this beginning solution is illustrated in item 1 of figure
22. A quantity of this solution (plus crystals) was processed through a commercial-size
centrifuge that had both batch- and continuous-type separation capabilities.
During batch operations, only about 40% of the crystals were retained in the centrifuge
bowl, while 60% passed through with the effluent (item 2 of fig. 22). Additional operations
indicated that batch-type separation furnished crystals with less retained liquid than those
obtained from continuous-separation operations (item 3 versus item 4 of fig. 22).
Compacting the crystals by spinning (without adding additional solution) provided
somewhat drier but still unacceptable crystals (item 5 of fig. 22).
41
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A recirculating concept was then tried. Adequate dryness and solids removal were achieved
by five passes of the deoxidizer volume through the centrifuge. Thus, centrifuging is
technically a workable method for solids removal. However, selection of separation
equipment depends not only on technical capability but also on economics, as noted later in
the economics evaluation section.
Filtration Evaluation
Investigation and evaluation of conventional solids separation techniques indicated that a
specialized type of filtration would most nearly satisfy the requirements of this project. A
conventional cartridge-type plastics filter was tried out. The cartridges plugged up quickly,
the volume of crystals limited the capacity of the filter, and the retained moisture in the
crystals was very high.
Consequently, additional effort was made to adapt a laboratory-developed system for this
need. The laboratory setup is illustrated in figure 23. Test data for design purposes are given
in table 7. Test run 1 was made with water only and without circulation to establish basic
operating data. Test run 2 was made with circulating water to establish equipment heating
capabilities and ambient heat losses. To establish combined heating and cooling capabilities,
test runs 3 and 4 were again made with water only. Test run 5 was made with a
sulfuric-dichromate deoxidizer to determine solids separation capacity. As indicated in
table 7, several test temperature plateaus were used within each test run to evaluate
variations in operating conditions.
Previously evaluated systems have not provided as efficient a bulk removal as this separation
system.
HEAT
EXCHANGER
-1
RETURN TO
PROCESS TANK
CRYSTAL
DISCHARGE
Figure 23. Setup for laboratory-developed solids separator
44
-------
Table 7. LABORATORY CRYSTALLIZER EVALUATION
Items
Volume, ml
Heat exch inlet temp, °C
Reservoir temp, °C
Crystal zone temp, °C
Chill water outlet temp, °C
Deoxidizer flow, ml/min
Belt speed, cm/min
Bulk removal, kg/hr
Liquid in bulk, %
Crystallize temp, °C
Test run no.
1
7000
45-54-66
39-49-55
2
7000
53-66
52
51
—
500
21
3
7000
53-66
50
42
25
520
23
4
7000
53-70
50-52
37-88
19.5
520
27
5
7000
45-90
45-52
45-36
24-19
520
23
395
48
39
The following summarizes technical data for operation of the 227-liter pilot tank:
1 ) Deoxidizing reaction :
2A1 + Na2Cr2O7-2H20 + 7H2SO4 + 9H2O^A12(SO4)3-18H2O + Cr2(SO4)3
+ Na2SO4
2) Regeneration reaction:
Cr2(SO4)3 + Na2SO4 + 7H2O 6 FaradayS)
4H2SO4
3) Chemical and electrical consumption (227 liters):
• 315 gm/1 A12(SO4)3-18H2O O 95 kg crystals O 7.7 kg aluminum
• Dissolving 7.7 kg of aluminum requires 42.6 kg Na2Cr2Oy-2H2O
• Regenerating 42.6 kg Na2Cr2O7-2H2O requires 23,000 amp-hr
• 23,000 amp-hr -=- 7 hr/day -'- 20 days/month -=- 3 months = 54.6 amp
-or-
23,000 amp-hr -r 24 hr/day -=- 30 days/month -=- 3 months = 10.6 amp
45
-------
4) Current densities at 45% regeneration efficiency:
Component One-shift operation Three-shift operation
20-by 41-cm diaphragm 7.53 amp/sq dm 1.45amp/sqdm
25-by 61-cm electrode 3.87 amp/sq dm 0.764 amp/sq dm
227-liter deoxidizer 0.69 amp/liter 0.11 amp/liter
5) Comparative costs for a suitable cathode configuration:
100% lead $0.379/sq dm
Pb-6%Sb alloy $0.468/sq dm
Pb-7%Sn alloy $ 1.88/sq dm
Type 316 stainless steel $0.917/sq dm
Duriron (includes junction) $2.78/sq dm
Copper and nickel were not priced due to total destruction of these metals in the
sulfuric-dichromate deoxidizer. When this cost information is compared with electrical
consumption and efficiency data collected from the potentiostat and the H-cell, the lowest
priced material, 100% lead, is the logical choice for both the anode and cathode.
TASK IV-PILOT PLANT ASSEMBLY AND OPERATION
The pilot plant facility is illustrated in figure 24. The 227-liter tank was charged up and put
into operation (see fig. 25), and 37 sq dm of aluminum were exposed to the solution. From
10 to 30 amp of dc current were imposed across the electrodes. In this way, aluminum
dissolution and continuous regeneration were accomplished simultaneously.
Cathode chamber problems arose during the shakedown period. Chemical analyses of the
tank and chamber solutions verified that an unexpectedly high mass transfer of components
occurred between the chambers.
Although fabrication of the small (15- by 20-cm) polyester diaphragm developed early in
the program presented no problems, equivalent low permeability in a 30- by 50-cm size was
not achieved.
46
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In the chamber itself, electrolytic corrosion of 18-8 stainless steel fastener was severe. Loss
of sealing pressure occurred within a few days. Total fastener failure followed within a week
or two, depending on fastener location.
The cathode chamber was redesigned and rebuilt. Several small diaphragms were used
instead of one larger size. Titanium fasteners replaced those of stainless steel.
The pilot plant tank was recharged. Solution-operating conditions were:
Sodium dichromate 31 to 37 gm/i as N^C^Oy^F^O
Sulfuric acid 290 to 310 gm/1 as H2SO4
Temperature 62° to 71° C
Metal removal rate 0.00006 to 0.00016 cm/surface/hr
The rebuilt diaphragm cell was operated in the tank using various configurations of
laminated polyester diaphragms. The diaphragm cell solution was sulfuric acid at 290 to 310
gm/1. Titanium fasteners performed satisfactorily. Commercial-grade lead in sheet form was
used as electrode material. A dc current was imposed across the electrodes with the anode in
the tank solution and the cathode in the diaphragm cell solution.
Operational performance was recorded by daily analyses for sulfuric acid, sodium
dichromate, and aluminum sulfate. Hexavalent chromium was determined by conventional
titration with a standardized thiosulfate solution. A specialized titrimetric method for
determination of sulfuric acid and aluminum sulfate was developed to satisfy the frequency
and accuracy needs of this project. The method involves titration with standardized sodium
hydroxide solution to specific pH values. The calibration curves for the pH values are
illustrated in figure 26.
Typical data for 2 months of operation are shown in figure 27. The early work, such as that
of period A, consisted of batch-type operations. The hexavalent chromium and sulfuric acid
were depleted rapidly by immersing a large area of aluminum alloy in the tank. The sheet of
aluminum was then removed from the tank and the resultant trivalent chromium was
electrolytically regenerated. This sequence was repeated several times.
After period A, effort was spent in determining equilibrium conditions of deoxidizing plus
electrolytic regeneration and migration of chemicals through the diaphragm. Sufficient data
and operating experience were gained so that only a short period of simultaneous
deoxidizing and electrolytic regeneration was necessary. The data are illustrated in period B
of figure 27.
49
-------
E E
O) O)
in CM
CM •*
o
en
_ _
O Q. O.
992
ouo
o
oo
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r-.
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I
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«- o o> oo iv
in
CO
CM «-
50
-------
TIME PERIOD "A"
TIME PERIOD "B'
CELL RECHARGED
HEXAVALENTCHROME
SULFURIC ACID
o
I-
<
cc
V——
O
o
ALUMINUM SULFATE
MAY
JUNE
TANK
CELL
Figure 27. 227-liter pilot tank continuous regeneration analyses
51
-------
It can be seen from the graphs of figure 27 that metal salts migrated into the diaphragm cell
and sulfuric acid passed into the tank volume. Since the volume of the cell constitutes only
about 4.5% of the total process volume, a small migration of chemicals through the
diaphragm produces large concentration changes in the cell. These changes affect the
regeneration efficiency and chemical concentration control. Therefore, effort was under-
taken to reduce the porosity of the diaphragm.
A 130-cm water column test stand (fig. 28) was built to provide a porosity evaluation
capability. A constant hydrostatic head is maintained over the diaphragm and the rate of
water passing through the diaphragm as a result of this head is measured in milliliters per
square centimeter per hour. Testing with this equipment indicated that porosity can be
reduced by: (1) increasing the number of layers of polyester material, (2) increasing the
pressure at which the layers are laminated, and (3) increasing the time at pressure. Exposure
tests also indicate that excessive temperatures (such as 200° C) for a period of time tend to
deteriorate the fabric. No specific time/temperature relationship has been established,
however. Porosity as measured on this test stand was reduced from 220 to 2.3-4.6
ml/sq cm/hr.
Table 8 illustrates test data accumulated on the porosity test stand.
Table 8. DIAPHRA GM POROSITY
Diaphragm
no.
Diaphragm
code
Layers
Pressure,
kg/sq cm
Temp,
°C
Time,
hr
Porosity,
ml/sq cm/hr
62 sq cm
1
2
3
4
5
J5D-20STM-3
13Jun-20-10/400
13Jun-20-15/400
16 Jun-20-45/300
19 Jun-20-4/300
20
20
20
20
20
140
280
280
280
280
150
205
205
150
150
0.2
0.2
0.25
0.75
4.0
220
164
370
18
2
97 sq cm
6
7
8
9
10
11
12
13
14
J5D-20-1-22
J5D-20-1-25
J5D-20-1-21
J5D-20-1-25a
(repressed)
J5D-30-1-9
2J5D-30
3J5D-20
J5D-60
J5D-60-2
20
20
20
20
30
60
60
60
60
280
280
280
280
280
280
280
280
280
150
150
150
150
150
150
150
150
150
3.0
4.0
5.0
3.0
7.0
3.0
3.2
9.0
5.7
50
25
17
7
5
0
2.5
2.3
-
52
-------
Figure 28. Test stand for diaphragm porosity evaluation
53
-------
Diaphragm numbers 10, 11, 13, and 14 were selected for service testing in the 227-liter pilot
tank. The tank was again recharged and, as before, operational performance of the
deoxidizer regeneration was monitored by daily chemical analyses. Acceptable deoxidizing
performance was judged by determining: (l)etch rates on 2024 bare and 2024 clad
aluminum alloys, and (2) uniformity of etch on large areas (such as 10 to 20 sq dm) of
alloys 2024 bare, 2024 clad, and 7075 bare.
Dissolved aluminum buildup for the 227-liter pilot tank was scaled down from existing
production tank records. Continuous suspension of 372 sq cm of aluminum in 227 liters is
equivalent to 200% of the normal cyclical load of a production tank. Therefore, this is the
magnitude of the load imposed on the pilot tank.
A chart of daily analyses is given in figure 29. An explanation of the individual analyses is as
follows:
1) Total chrome (tank)—This analysis is performed periodically to monitor the
material balance of the system.
2) Active chrome (tank)—This analysis measures the chromium ion that is available
for deoxidizing.
3) Total chrome (cell)—If chromium migrates through the diaphragm, it will exist
only in the trivalent stage during regeneration because of the strong reducing
conditions at the cathode. Therefore, this analysis evaluates the functional
capability of the diaphragm.
4) Sulfuric acid (tank)-Additions of sulfuric acid are required to replace the acid
used to form aluminum sulfate.
5) Sulfuric acid (cell)—Acid in the cell provides electrical conductivity in the cell
solution. Migration into the tank through the diaphragm is expected and,
therefore, additions will be required.
6) Aluminum sulfate (tank)—Analysis information provides rate and quantity of
dissolved metal for eventual removal by crystallization. During pilot testing this
analysis also measures the accelerated age of the test solution.
7) Aluminum sulfate (cell)—The regeneration current will drive some aluminum
through the diaphragm into the cathode area.
54
-------
Cell'
Tank — • — • —
10 15 20 25
AUGUST
5 10 15 20 25
SEPTEMBER
Figure 29. 227-liter pilot tank continuous regeneration—sulfuric-dichromate deoxidizer
55
-------
The upper zone of figure 29 indicates the ability of the electrical system to maintain a
relatively constant concentration of hexavalent chromium at 85% to 90% of the initial
charge. During this test period, an area of 280 to 880 sq cm of aluminum alloy 7075 was
immersed continuously. Rectifier settings were varied from 15 to 30 amp.
The middle zone of the chart illustrates the stability of the sulfuric acid in the tank and its
instability in the cell. The acid in the cell was allowed to fluctuate from 225 to 375 gm/1
with no detectable effect on the total system. Near the end of the test, the sulfuric acid in
the cell was allowed to drop to a very low value (90 gm/1). No ill effects were noted other
than a slight rise in voltage required at the rectifier (9!4 versus 11 !4 V).
The lower zone of the chart records the deliberate buildup of aluminum in the tank and its
migration into the cell. Note that in the best case (August 9 through 31), chromium in the
cell increased from 0 to 18 gm/1 while aluminum sulfate increased from 0 to 61 gm/1.
The first low-porosity diaphragm (J5D-30-1-9) was tested from July 10 through 24 without
imposing electrical current. Diffusion of chromium ions occurred quickly and the diaphragm
was replaced. The second low-porosity diaphragm (2J5D-30) was laminated from two
previously pressed 30-layer sections that had shown some promise in preliminary evaluation.
However, delamination and structural degradation occurred after 4 days of regeneration.
Two 60-layered diaphragms (J5D-60 and J5D-60-2) performed quite well. The indication is
that pressure time during diaphragm fabrication is important to the functional life.
Precise determination of aluminum etch rate plus visual inspection of large areas of
deoxidized aluminum surfaces are used to evaluate the deoxidizer performance. Etch rates
are determined by weight losses per unit of time measured on a precision laboratory balance
(fig. 30). Values from 0.00093 gm/sq cm/hr at 60°C to 0.0045 gm/sq cm/hr at 71° C are
considered normal.
Data from the etch rate determinations are shown in figure 31. The fluctuations in the early
stages are typical of a fresh solution. For visual evaluation of deoxidizer solutions, large
areas of aluminum alloys 2024 bare, 2024 clad, and 7075 bare were deoxidized for 20 min,
which is twice the normal process time. The presence of pits or preferential attack in any
area would be objectionable. No such defects were noted either at low- or high-aluminum
content. All surfaces retained the normal, frosted appearance.
Conclusions to be drawn from this pilot test are:
• Continuous electrolytic regeneration of trivalent chromium to hexavalent
chromium is not detrimental to the deoxidizing capability of the sulfuric-
dichromate solution.
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The concentration of hexavalent chromium can be maintained at 85% to 90% of
the total chromium concentration in the deoxidizer solution.
• Chromium compounds can be retained in the oxidizing chamber of the
regeneration system with a polyester diaphragm when porosity is less than 2.3
ml/sq cm/hr at 130 cm hydrostatic head.
Previous laboratory work established that a drum-type separation system is best for removal
of solids from the deoxidizer solution. Additional testing has been accomplished to more
accurately define size and rate requirements of equipment necessary for the 2200-liter pilot
tank. A summary of these data are contained in table 9.
Table 9. DRUM FIL TER EVALUA TION
Items
Drum speed, rpm
Filter time, sec
Dewater time, sec
Water in cake, %
Cr in dry cake, %
Test no
1
1/4
88
96
45.2
2.4
2
1/4
88
96
41.5
2.1
3
1/6
132
144
45.1
2.6
4
1/6
90
180
43.8
1 4
5
1/4
88
96
4B.7
2.2
6
1/6
132
144
43.8
4.5
7
1/6
132
144
41.2
4.6
A commercially available drum filter was identified by using the data from table 9. A 20- by
12-in. drum filter (50.8-cm diameter by 30.5-cm width) was the smallest marketed filter
that could be located. The published characteristics of this filter were used to calculate
capacities for aluminum sulfate separation and are presented in table 10.
Table 10. DRUM FILTER CAPACITY
Test no
Items
Pumping capacity,
liters/sq dm/hr
Solids output.
dry gm/sq dm/hr
1
15.5
352
2
14.7
366
3
3.5
156
4
2.8
151
5
4 1
259
6
1.9
142
7
1.7
142
The data in table 10 are applicable to the 2200-liter pilot tank operation. When capacities
are compared with deoxidizer solution characteristics, the 20- by 12-in. filter would have
such overcapacity that only intermittent or semi-automated solids separation would be
required in conjunction with the continuous electrolytic regeneration for this operational
volume.
59
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TASK V-COMMERCIAL PRODUCTS EVALUATION
Amchem 6-16, a commercial deoxidizer produced by Amchem Products, Inc., received
benchtop evaluation. This proprietary product can be mixed with either sulfuric acid or
nitric acid according to the user's choice. A supply was made up using sulfuric acid
according to the following analysis:
Hexavalent chromium 24 gm/1 as ^2^207-2^0
Sulfuric acid 68 gm/1
This solution was depleted by dissolving aluminum until the following analysis was reached:
Hexavalent chromium 12 gm/1 as Na2Cr2O-7-2H2O
Sulfuric acid 53 gm/1
Aluminum 48 gm/1 as A12(SO4) -18H2O
Two liters were regenerated at 5 amp in the benchtop cell illustrated in figure 32. After 4 hr
the hexavalent chromium rose to 16 gm/1. After 5 hr the hexavalent chromium rose to 18.3
gm/1, or about 75% regenerated. Before-and-after weighing of the lead electrodes showed no
loss in weight by either electrode. This information indicates that Amchem 6-16, using
sulfuric acid, is suitable for further regeneration evaluation. Since this product gives the user
the choice of either sulfuric or nitric acid as the makeup acid component, continuing work
requires that regeneration in the nitric acid phase also be investigated.
A partially depleted solution of Amchem 6-16, using nitric acid for makeup, was transferred
to the 227-liter pilot tank. Benchtop work indicated that this formulation will dissolve both
lead and lead alloys by simple immersion and by electrolytic action. This work also
illustrated that 316 stainless steel was severely eroded when used as an anode. However,
Duriron withstood the anodic erosion. Therefore, Duriron anodes were assembled for the
227-liter volume. Stainless steel was used for the cathode in the diaphragm cell. Diaphragms
as fabricated in previous work were used for this test.
No regeneration of trivalent chromium to hexavalent chromium occurred after 1440 amp-hr
were passed through the solution. The Duriron anodes were replaced with conventional
precious metal plating electrodes of platinized titanium mesh overplated with platinum
black to reduce hydrogen overvoltage. No regeneration of trivalent chromium occurred in
3840 amp-hr. Analytical progress results of this test are illustrated in figure 33.
60
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Figure 33. Regeneration of nitric-acid-based proprietary deoxidizer
62
-------
At this time, further work on proprietary deoxidizers was augmented by the use of the
2-liter diaphragm cell. Regeneration operating conditions were varied as to time,
temperature, concentration, and current densities. During this period, the proprietary
deoxidizers evaluated were Amchem 6-16 and Smutgo 4 (manufactured by Turco Products,
Inc.)- Both used nitric acid as the makeup acid. Amchem 6-16 with sulfuric acid, instead of
nitric, was also evaluated.
Work during this period indicated that efficient regeneration of all three materials can be
accomplished if the temperature is raised to 65° C or higher, and the total chromium in
terms of sodium dichromate (I^C^Oy^^O) is 22.5 gm/'l or higher. This higher
chromium content presents no problem industrially since hexavalent chromium is added as a
solution maintenance material in normal usage. However, the elevated temperature
requirement makes the regeneration process somewhat less flexible. The users of these dilute
deoxidizers have the choice of using an elevated-temperature batch treatment for
regeneration or investing in heating plus cooling capacity for a continuous-loop
regeneration.
Each of three proprietary deoxidizers was cycled through three accelerated depletions and
regenerations to verify the concept of batch regeneration at elevated temperature. Where
necessary, the total chromium content was raised above 22.5 gm/1 before the first depletion
stage. During normal usage, all deoxidizers based on nitric acid require periodic adjustment
of etch rate by the addition of a fluoride compound. This was done by additions of
hydrofluoric acid. Etch rates were determined and adjusted prior to the depletion steps to
ensure an optimum reduction rate of the chromium. Accelerated depletion was accom-
plished by immersing bare aluminum plates (alloy 2024) in the deoxidizer so that at least
4.91 sq dm/1 were exposed. Hexavalent chromium content was monitored until the
deoxidizer was depleted to approximately 75% of its starting concentration. The used
deoxidizer was then transferred to a regeneration cell and the temperature raised above
65°C. Electrical current of 9.2 to 13.0 amp/1 was imposed from a dc power supply. As
regeneration proceeded, the hexavalent chromium content usually leveled off at 85% of its
original makeup. At this time, regeneration was stopped, the solution cooled, the etch rate
was readjusted, ^nd the depletion step was repeated.
The results of these experiments are illustrated in figures 34, 35, and 36. The active
chromium content, dc power supply output, and temperature are tracked for each
proprietary deoxidizer for three full cycles of depletion plus regeneration. Active chromium
is expressed as grams per liter of ^20207-2^0 and aluminum content is expressed as
grams per liter of A1(NO3) -9H2O or A12(SO4) -18H2O.
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Information from observations and from data during this evaluation is summarized as
follows:
1) Regeneration can be accomplished to 85% of the total chromium content
provided this total exceeds 22.5 gm/1 of Na2Cr2Oy-2H2O and the temperature
during regeneration is 65°C or higher.
2) Electrical conductivity of the solution increases with increased temperature.
3) Increasing quantities of dissolved aluminum appear to inhibit the maximum level
of regeneration.
4) Smutgo 4 (HNOg) responded better to regeneration than the other two
proprietary deoxidizers. This may be due to its inherently higher chromium
content. No attempt was made to evaluate the other deoxidizers by adding more
chromium.
5) Regeneration efficiency of these dilute deoxidizers is in the range of 10% as
calculated from the ampere-hour data.
6) Electrode material is a problem for deoxidizers containing nitrate and/or fluoride
ions. Platinum gauze proved to be satisfactory in the test cell.
A much less expensive arrangement of stainless steel plated with gold performed
satisfactorily for about 30 min before the coating flaked off. (This was a
preliminary, nonprogrammed test to seek a direction of effort since platinized
titanium anodes failed in test due to severe erosion.)
7) As the concentration of copper builds up in the deoxidizer due to dissolving
copper-bearing aluminum alloys, the copper ions migrate through the diaphragm
and deposit on the cathode. The deposition of copper on the cathode is beneficial
because it reduces the formation of copper smut on critical aluminum surfaces
during deoxidizing.
8) Satisfactory deoxidizing of an aluminum surface continues even after the third
regeneration as long as the deoxidizer etch rate is adjusted—a normal production
practice.
67
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A literature search revealed very little information about solubilities of aluminum nitrate or
aluminum fluoride formulations, particularly in the presence of chromium and fluoride
compounds. Therefore, a preliminary investigation was made to determine the amount of
aluminum nitrate required to saturate Amchem 6-16 (HNO^). It was found that 840 gm of
-9H2O dissolved in a liter of the deoxidizer. In a representative tank line for
precleaning prior to anodizing, 840 gm/1 of dissolved AKNOg) -9H2O represents 4 to 5
years of production. This high solubility indicates that it is impractical to use simple
ambient temperature crystallization for removal as was done in the previous work of this
program. The deoxidizer is quite viscous at high salt content, and the capability of the
deoxidizer to perform its normal function is questionable. A different approach to dissolved
metals removal is needed, but additional work was not done along this line. However, early
in the program it was shown that an ion-exchange resin was rapidly degraded by a
deoxidizer.
TASK VI-PRODUCTION DEMONSTRATION
For this phase of the work, a 2200-liter preproduction tank was charged with a
sulfuric-dichromate deoxidizer. A cathode cell of plexiglass was fabricated to contain seven
1 5- by 20-cm J5D diaphragms of 60 layers each (fig. 37).
The tank was filled with a partially depleted solution of sulfuric acid-sodium dichromate
deoxidizer. The analysis of this solution was as follows:
H2SO4 266 gm/1
Na2Cr2O7-2H2O 15.5 gm/1
Cu 5.9 ppm
Zn 7.7 ppm
Fe 20.2 ppm
Mn 2.4 ppm
Mg 3.75 ppm
The solution was depleted until the hexavalent chromium was near zero. Electrolytic
regeneration was initiated and progress was monitored by daily analyses, as illustrated in
figure 38.
As can be seen from the upper section of the figure, regeneration leveled off at 15 to 30
gm/1 of active (hexavalent) chromium. Since the regenerated concentration was well below
the available amount that could be generated, this became an area of concern.
68
-------
69
-------
45
30
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The solution was cooled, pumped into a spare tank, and allowed to settle. The original tank
was cleaned out and inspected. This examination provided the explanation for the low
efficiency of regeneration. The tank lining is composed of carbon brick. In the areas of the
electrical flux paths between anode and cathode, each brick became a dipole, i.e., one end
of each brick is anodic, the other end is cathodic. The dipole phenomenon is confirmed by
the fact that the anodic end of each brick was severely eroded. For further confirmation,
the filter cake was analyzed at 3.2% insoluble solids, which were carbonlike in appearance.
Thus, much of the regenerating current was wasted.
To correct the problem, the sensitive areas of the tank lining were insulated with 0.25-in.
(0.635-cm) thick rigid plastic. It is recommended that carbon brick not be used as a tank
lining material when electrolytic regeneration is planned.
The cooled and settled deoxidizer solution was decanted into the original tank, and the
solids removal evaluation was continued.
An Ametek, Inc., 20- by 12-in. (50.8- by 30.5-cm) drum filter system was installed at the
2200-liter tank. The equipment assembly is shown in figure 39. String discharge was selected
for the first trial. In this discharge system, polypropylene string loops are spaced on 0.5-in.
(1.27-cm) centers around the drum surface and over idling rollers. The cake is formed on the
drum, lifted off by the strings, and discharged over an idling roller, as illustrated in
figure 40.
A severe drop in filter output, traceable to plugged cloth on the filter, emphasized the
carbon contamination problem. As the carbon filled the pores of the filter cloth, the cake
became increasingly thinner and wetter, and would no longer lift off the drum for
discharging. This zero output occurred within 1 hr of startup. In addition, the strings
showed a tendency to climb on top of the cake after a few drum revolutions, which also
reduced cake liftoff. As a remedy, after the deoxidizer solution was decanted, the string
discharge was replaced with a scraper discharge. This discharge method proved to be
satisfactory and was used for the remainder of the test period (see fig. 41).
The aluminum content of the deoxidizer was raised to 330 gm/1 (expressed as
^2(864) -18H2O). Batch- and continuous-type runs were made for salts removal. Three
different types of cloth were tried on the drum, and drum speeds were varied within the
range of the equipment. The drum speed dial control setting was calibrated (fig. 42) for
accurate determination of drum rpm.
71
-------
72
-------
FILTER DRUM
STRINGS
IDLING ROLLER
Figure 40. Details of drum filter system
The following information was obtained from the drum filter evaluation:
1) Crystallized aluminum sulfate can be removed effectively from the deoxidizer
solution with a drum filter.
2) The rate of removal is dependent upon the drum speed (fig. 43). Optimum
removal rate is over a broad range of drum speeds. This flexibility is advantageous
for industrial applications.
3) Moisture retained by the cake can be held at 30% to 40%. The least amount of
retained moisture can be achieved by adjusting operating conditions for minimum
practical cake thickness and maximum drum vacuum. Visual observations indicate
that the amount of retained moisture varies with the crystal size. However, no
attempt was made to investigate this aspect.
4) The amount of chromium lost by the solids removal technique can be held at less
than 4% and is related to the amount of moisture retained in the cake. The
relationships between drum speed, retained moisture, and retained chromium are
illustrated in figure 44.
73
-------
Figure 41. Scraper discharge on 20- by 12-in. (50.8- by 30.5-cm) drum filter
74
-------
a.
oc
10
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.09
0.08
0.07
I I I
234
DIAL SETTING
Figure 42. Drum filter evaluation—drum speed calibration
75
-------
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13.5
s.
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Q_
9.0
4.5
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
DRUM SPEED, rpm
Figure 43. Drum filter evaluation—drum speed versus output
76
-------
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30
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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
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Figure 44. Drum filter evaluation-drum speed versus cake moisture and chromium
5) Crystallized aluminum sulfate can be removed either by batch operation or by
continuous operation of the drum filter. The removal capacity of the smallest
available commercial drum filter is such that batch operations are desirable for all
except very large tank volumes.
6) Coarse weaves of olefin, polypropylene, or polyester woven fabrics are satisfac-
tory for the drum filter cake retaining cloth.
A summary of the drum filter evaluation is as follows:
Equipment
Effective drum area
Maximum removal rate
20- by 12-in. (50.8- by 30.5-cm)
drum filter with scraper
3677 sq cm
15 kg/hr wet cake
77
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Moisture in cake 35% by weight
Chromium in dried cake 1.85% by weight
Equivalent aluminum metal
removed from deoxidizer 0.80 kg/hr
This last value of 0.80 kg/hr equilibrates to a range of 172 to 460 sq m/hr of deoxidized
aluminum parts depending on the effective etch rate of the deoxidizer at time of processing.
The calculation is based on the usual immersion time of 10 mm/cycle.
The inclusion of residual chromium in the dried salts indicates that consideration should be
given to the loss of chromium in the filter cake. In the chemical reaction that takes place
during deoxidizing, 1 kg of aluminum reduces 3.49 kg of chromium from hexavalent to
trivalent. Therefore, at the maximum rate of removal during which 0.797 kg of dissolved
aluminum is removed from the deoxidizer per hour, 0.18 kg of chromium is also removed.
Thus, 6.5% of the total chromium metal required for deoxidizing will be carried out in the
cake.
The impact of the regeneration process is more simply made by saying that a process that
formerly consumed 3 kg of chromium per unit of time will now consume slightly less than
0.4 kg in the same unit of time.
In the continuing work of production demonstration, maintenance problems on the
2200-liter preproduction tank severely hampered the accumulation of continuous regenera-
tion data progress. Failures of the tank level control system made it necessary to replace the
deoxidizer solution several times. DC power supply problems delayed data accumulation.
The tank lining continued to deteriorate the solution.
This last item, when finally identified, was measured quantitatively for rate of chromium
reduction and was used to advantage for calculating rates of regeneration as well as
regeneration system loading. The quantitative data were collected by eliminating all other
variables and tracking hexavalent chromium content as a function of time.
In the final simulated production run with the 2200-liter tank, the chromium reduction
loading was equivalent to 5 sq cm of aluminum per liter suspended in the solution
continuously. This is equivalent to almost three times the normal loading in a typical
production sulfuric-dichromate deoxidizer tank line.
The dc power supply was set at 225 amp. The electrical load in the tank volume was 0.1
amp/1 and 6.6 amp/1 in the diaphragm cell. This vigorous electrical activity promoted
78
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migration of sulfuric acid from the cell into the tank. Consequently, all acid additions were
made in the cell. The quantity of acid added over an extended period of time approximated
the quantity of acid required for chemical reaction in dissolving the aluminum.
The actual amperage produced by the dc power supply fluctuated with the acid
concentration of the cell. Therefore, an ampere-hour meter was included in the equipment
setup and ampere-hours were recorded.
Performance of the regeneration was monitored by analyses for active chromium reported as
Na7Cr2O7-2H2O. Figure 45 illustrates the active chromium monitoring analyses. The
intermittent graph lines illustrate regeneration attempts during and between equipment
failure periods. The final confirming regeneration run is graphed for the period April 3 to
13. The period from April 13 through 19 is a reconfirmation test of the quantitative effect
of the deteriorating tank lining.
Table 11 illustrates reduction of data that establish the electrical efficiency of a sulfuric
dichromate deoxidizer.
Table 11. ELECTRICAL EFFICIENCY
Date,
1973
22Feb
20 Mar
22 Mar
28 & 29 Mar
4& 5 Apr
6 - 9 Apr
10- 12 Apr
13 Apr
Regenerated
chromium,
kg metal
2.15
1.86
2.65
3.68
2.09
6.09
4.83
1.01
Current required,
amp-hr
3,320
2,880
4,090
5,670
3,227
9,400
7,450
1,920
Current used,
amp-hr
4,280
3,310
4,670
6,185
3,884
10,878
10,413
2,440
Efficiency,
%
78
87
88
91
83
86
72
79
Average: 83
The polyester diaphragm assembly in the 2200-liter pilot tank performed satisfactorily for
approximately 5 months in the sulfuric-dichromate deoxidizer, which was held from 60° to
71° C most of the time. The electrical load through the diaphragm was low ranging, from 0
to 10 amp/sq dm. During the final confirmation run, the electrical load on the diaphragm
system increased to 30-36 amp/sq dm. Near the end of this final run, chromium migrated
heavily into the cathode chamber. This migration is considered to be caused by a diaphragm
79
-------
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failure. Electrical current density thus appears to be a factor in the service life of the
diaphragm.
This concludes the technical work and data collection requirements of the program.
TASK VH-ECONOMIC EVALUATION OF REGENERATION
The following baseline costs have been used for economic evaluation of the regeneration
process. For application of this information to specific installations, local costs in each area
should be determined for each plant and the values proportioned accordingly. Quantities
shown in table 12 are expressed in British rather than metric system units because of
common industry usage at the present time.
Table 12. REGENERA TION PROCESS ECONOMICS
Baseline period
Cost item 2nd Quarter 1973
Equipment amortization 10 years
Electrical cost 13tf per 100,000 BTU
Water cost (purchase) 10tf per 100 cubic feet
Water cost (dispose) 10# per 100 cubic feet
Na2Cr207-2H20 (tech) $30.95 per cwt
H2S04 (tech), 66° Be $5.15 per cwt
Chromated salts disposal (1% as Cr+6) $ 3.62 per cwt
Deoxidizer disposal 12^ per gallon
100 A, 30 V rectifier, installed $500
1,000 A, 30 V rectifier, installed $5,000
20- by 12-in. drum filter, installed $11,044
12-by6-in. drum filter, installed $7,000
12-by5-in. centrifuge, installed $5,475
Regeneration accessories, 600 gallons (2,200 liters)
(cathode chamber, electrodes, level control, diaphragms) $660
Regeneration accessories, 6,000 gallons (22,000 liters)
(cathode chamber, electrodes, level control, diaphragms) $1,195
In assessing the impact of regeneration of chromated aluminum deoxidizers, a departure
from product weight reporting is necessary. Metal-finishing processes are unique in that they
are surface related and not proportional to pounds of product throughput. Therefore, in
relating costs and production rates, this task will state values based on areas (such as square
decimeters) of aluminum processed.
81
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Effect on Waste Volume and Characteristics
Implementation of this regeneration process will reduce the sporadicity of plant waste
effluent that is normally due to periodic dumping of concentrated solutions. As a result of
regeneration, it is reasonable to assume that the chromated deoxidizer need never be
changed, or at the most—in the case of some proprietary formulations—changed only every
4 or more years. Thus, the total amount of plant effluint containing chromium compounds
can be greatly reduced, and the effluent is expected to be more uniform in concentration
and character per unit of time.
Effect of Reuse
The added benefits of regeneration are immediately obvious:
• Capital investment in waste treatment facilities can be lower because it is no
longer necessary to size the facility to handle the periodic heavy overloads.
• This same waste facility can be more easily automated because of the lack of
annual surges of high concentrates.
During the period of testing and production simulation in this regeneration program, no
detrimental effects caused by continual reuse of the chromium compounds could be
detected on the deoxidized surfaces. Thus, continual regeneration of chromated aluminum
deoxidizers will contribute to preservation of chromium resources.
Effectiveness of Treatment
The electrolytic section of regeneration is a wholly self-contained system since the
reoxidation of the chromium occurs within or adjacent to the aluminum processing tank.
When dissolved aluminum concentration reaches the point at w'lich separation procedures
should be implemented (estimated at 1 year), the waste product (salts of various metals) is
sufficiently dry to be used as a chrome-bearing, solid fill material. Under the most effective
conditions encountered in this program, chromium metal constituted about 1% of the dried
salts weight. In very large installations, metals recovery operations may be considered.
Capital Costs
Capital costs are based on regeneration equipment sized to meet the workload throughput
of a deoxidizer tank that has been monitored for several years. Workload information has
been extrapolated to other tank sizes proportionally to tank volumes, as shown in table 13.
82
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Table 13. CAPITAL EQUIPMENT COSTS
2,200-liter (600-gal.) deoxidizer tank
Rectifier (100 A, 30 V), installed
Centrifuge (12- by 5-in.), installed
Regeneration accessories, installed
Total capital
$ 500.00
5,475.00
660.00
$ 6,635.00
22,000-liter (6,000-gal.) deoxidizer tank
Rectifier (1,000 A, 30 V), installed
Drum filter (20- by 12-in.), installed
Regeneration accessories, installed
Total capital
$ 5,000.00
1 1 ,004.00
1,195.00
$17,239.00
Maintenance
Maintenance costs for the types of equipment described in this report are generally low
compared with those for other chemical processing facilities. Maintenance of a centrifuge is
usually considered as being higher than that for other types of separation equipment. The
diaphragm cost as stated in this report is abnormally high because the diaphragm is in the
early stages of development. A 15- by 20-cm unit cost is estimated at $30 and presently has
a maximum of 6 months' service life.
Yearly maintenance cost for the 2200-liter regeneration equipment is estimated at $620.
Yearly maintenance cost for a 22,000-liter system is estimated at $1380.
Operating Costs, Regeneration Versus Nonregeneration
2200-liter Deoxidizer-During the first year, electrical cost for the rectifier is $6.39 per
month. After dissolved metals separation is implemented, add: 1) $4.73 per month for
electricity for centrifuge, 2) $10.54 for cooling to crystallize, 3) $4.38 for reheating, and
4) $3.34 per month for disposal of removed solids. Total operating costs under full
regeneration conditions are $29.28 per month.
This figure is contrasted to nonregenerated deoxidizer costs of: 1) $23.65 per month for
addition of chemicals, 2) $6.00 per month for prorated dumping charge, and 3) $14.15 per
month for prorated new solution makeup charge. Total nonregeneration cost is $43.80 per
month.
83
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22,000-liter Deoxidizer—During the first year, electrical cost for the rectifier is $63.90 per
month. After dissolved metals separation is implemented, add: 1) $13.77 per month for
drum filter electrical cost, 2) $21.08 for cooling to crystallize, 3) $8.55 for reheating, and
4) $38.67 per month for disposal of removed solids. Total operating costs under full
regeneration conditions are $145.97 per month.
This figure is contrasted to nonregenerated deoxidize5- costs of: 1) $93.29 per month for
addition of chemicals, 2) $60.00 per month for prorated dumping charge, and 3) $141.50
per month for prorated new solution makeup charge. Total nonregenerated cost is $249.79
per month.
In summary, regeneration operating costs can be related to the area of aluminum processed
according to table 14.
Table 14. REGENERATION COSTS PER UNIT AREA
Item
Electrolytic
only,
4 per sq dma
Total
regeneration,
tf per sq dma
2,200-liter tank volume
Capital
Maintenance
Operating
-0.0115
-
+0.1035
+0.0920
-0.1531
-0.0014
+0.0402
-0.1143
22,000-liter tank volume
Capital
Maintenance
Operating
-0.0115
-
+0.0639
+0.0524
-0.0398
-0.0003
+0.0412
+0.0011
a+ indicates a cost savings;-indicates a cost
No calculation relating regeneration of deoxidizers to product value increase has been
attempted because of the wide variations encountered when attempting to relate product
value to product surface area. It is well to note, however, that this cost analysis indicates
that regeneration of chromated aluminum deoxidizers can be cost effective.
84
-------
Waste Load—The waste load is calculated in terms of grams of chromium metal in plant
waste effluent per square decimeter of aluminum processed, as shown in table 15.
Table 15. WASTE LOAD PER UN IT ARE A
Tank volume,
liters
2,200
22,000
Nonregenerated waste,
gm Cr/sq dm/month
0.0660
0.0660
Regenerated waste,
gm Cr/sq dm/month
0.00041
0.00053
Note: These values do not include chromium lost by dragout.
85
-------
-------
SECTION V
BIBLIOGRAPHY
1. Hempel, C. A., Rare Metals Handbook, Second Edition, Reinhold Publishing Company.
2. Continuous Regeneration of Aluminum Deoxidizer, Manufacturing Development
Report 6-92013, The Boeing Company.
3. Continuous Regeneration of Aluminum Deoxidizer, Service Request/Program Authori-
zation 692-038, The Boeing Company.
4. Gross and Hickling, J. Chem. Soc., 235, 1937.
5. Hickling and Richards, ibid, 256, 1940.
6. Glasstone, An Introduction to Electrochemistry, van Nostrand, p. 107-128, 1956.
7. Potter, Electrochemistry, Cleaver-Hume, London, p. 31-100, 1961.
8. Metals Handbook, Eighth Edition, American Society for Metals.
9. Bulletin 172 CL-FL, the Leon J. Barrett Company, Worcester, Mass.
10. Bulletins, the Duriron Company, Inc., Dayton, Ohio.
11. Solubilities of Inorganic and Metal Organic Compounds, Fourth Edition, American
Chemical Society.
12. Bulletin S-4, E. 1. Du Pont de Nemours & Co., Inc., Wilmington, Delaware.
13. Purchas, Derek B., Industrial Filtration of Liquids, Second Edition, Leonard Hill
Books.
14. Bulletin A135A, Ametek, Inc., East Moline, Illinois.
15. Drawing 9665-2900, Ametek, Inc., East Moline, Illinois.
16. Bulletins, Troy Mills, Inc., New York, New York.
87
-------
17. Form 19, Chicopee Mills, Inc., Milltown, New Jersey.
18. Bulletin JPB 3/21/68, Diamond Shamrock Corp., Cleveland, Ohio.
19 Seegmiller, R. and Lamb, V. A., Re-Oxidation of Trivalent Chromium in Chromic Acid
Plating Baths, National Bureau of Standards, Washington, D.C.
20. Telex 920407, Dennison Manufacturing Company, Renton, Washington.
88
-------
SECTION VI
LIST OF INVENTIONS
Ion Selective Membrane, Boeing patent disclosure 71-0238, EPA case no. WQO-70-73 (c).
89
-------
-------
SECTION VII
GLOSSARY
r Trivalent oxidation state of chromium
Cr ,Cr+" Hexavalent oxidation state of chromium (also expressed as G^O-y )
E,V Potential, volts
Ec Total potential measured between anode and cathode
E- Reversible electrode potential
(g) Gas
I or A Current, amperes
Ieff Current efficiency
i Current density, amperes per square foot
Na Anode polarization, volts
NC Cathode polarization, volts
R Resistance, ohms
Rjfl Membrane resistance
Rs Solution resistance
Dichromate sulfuric An aluminum deoxidizer whose makeup chemistry consists of only the
r\
dichromate (C^Oy'^) ion plus sulfuric acid
91
-------
-------
SECTION VIII
APPENDIX
93
-------
-------
TASK I
DIAPHRAGM EVALUATION
DATA SHEETS
95
-------
LABORATORY REPORT
«.
Purpose __lS!L__ Model _ Oat* _ 1 0-6-71
To: H- Hicl« _ Org'n. 7-7310 porf No. __
$„!,:, ct. Regeneration of Chromates _
Environmental Protection Agency, Water Quality Office __ Reinip. Rum. _
Purchase Order R.R Dote Rec'd Quon Ate. R«j.
Material Filter Media Evaluation Spec. BAC 5765, Solution 10
[*] Chen.. Lob. Job !270 r-| Sonic Q M«»- Lob Q Mechanical
Q X-Roy L] Mog/Penetront___J Q 12070 HEK
Reference: C.C. to:
Boeing Program Authorization No. 632-083
Work Order No. 5-66967-7322-632083
Phase I: Diaphragm Evaluation
Sample 1 Polypropylene Polymax B, style 222-00900, by National Filter
Media Company
Sample 2 Dynel style 182-003-00, by National Filter Media Company
SampleS Polypropylene Polymax B, style 222-001-00, by National Filter
Media Company
Sample 4 Dynel style 182-004-00, by National Filter Media Company
Sample 5 100% Polypropylene, item 342-1903, Troy Mills, Inc.
Sampled 100% Dacron, item S-4, Troy Mills, Inc.
Sample? Filter paper, 6-pt SC, Dennison Mfg. Company
Above 7 samples were immersed 240 hours at 82 C in a covered 100-ml aliquot of
BAC 5765, solution 10.
Results are tabulated on attachment
Prepared by Approved by Ora'n. R-6725
Leo Hagen M. Minak
96
-------
DIAPHRAGM EXPOSURE TEST (START- STOP)
Material
Sample 1 -
Polypropylene
Sample 2-
Dynel
Sample 3-
Polypropylene
Sample 4-
Dynel
Sample 5-
Polypropylene
Sample 6-
Dacron
Sample 7—
6-ptSC
Control 1
Control 2
Weight
gm
6.172
-5.952
0.220
7.254
-7.080
0.174
6.859
-6.030
0.829
7.546
-7.237
0.309
8.551
-8.341
0.210
9.255
-8.935
0.320
1.029
-0.959
0.070
0
0
%
loss
3.5
2.4
12
4.1
2.1
3.5
0.7
Diameter
cm
13.6
-13.6
13.8
-13.8
13.6
-13.6
13.8
-13.8
13.4
-13.2
13.4
-13.4
13.7
-13.7
%
loss
0
0
0
0
0
0
0
Na2Cr207 • 2H20
gm/l
3C.4
-9.8
26.6
36.4
.-21.7
14.7
36.4
-0.4
36.0
36.4
-12.8
23.6
36.4
-0.2
36.2
36.4
-2.2
34.2
36.4
-33.8
2.6
36.4
36.4
Solution
color
Yellow
Brown
Green
Green
Blue
Green
Brown
Brown
Brown
%
loss
73
40
99
65
99
94
7
H2S04
gm/l
280
-248
32
280
-265
15
280
-230
50
280
-251
29
280
-238
42
280
-242
38
280
-274
6
280
280
%
loss
12
5.5
18
10
15
13
2
97
-------
J5D LAMINATED DIAPHRAGM THICKNESS- 15 LAYERS
THICKNESS, cm
SECTION I | SECTION II
SECTION III
SECTION IV
30cm
51 cm
LAMINATION SEQUENCE
ELAPSED TIME, MIN.
CONDITION
0
9
11
42
58
62
51 TONS APPLIED, HEAT TURNED ON
BOTTOM PLATEN AT 149° C
TOP PLATEN AT 149° C
HEAT OFF, COOLING AIR ON, 46 TONS
PLATENS AT 93° C, RELIEVED PRESSURE
REMOVED DIAPHRAGM
98
-------
J5D LAMINATED DIAPHRAGM THICKNESS-20 LA YERS
THICKNESS, cm
30cm
51cm
LAMINATION SEQUENCE
ELAPSED TIME, MIN.
CONDITION
0
9
11
42
58
62
51 TONS APPLIED, HEAT TURNED ON
BOTTOM PLATEN AT M9° C
TOP PLATEN AT 149° C
HEAT OFF, COOLING AIR ON
PLATENS AT 93° C, RELIEVED PRESSURE
REMOVED DIAPHRAGM
99
-------
DIAPHRAGM ELECTRICAL RESISTANCE-POL YESTER, 6-PTSC (SIX LA YERSf
Amperes
Volts
Observations
Run 1
Increasing
amperage
Decreasing
amperage
1.0
2.0
3.0
4.0
5.0
4.0
3.0
2.0
1.0
1.7
2.0
2.3
2.6
3.0
2.6
2.4
2.1
1.75
Gassing at both electrodes at all conditions.
Dichromate bleeds thru diaphragm into
h^SO^ Dichromate reduced (visually) in
cathode chamber.
Run 1-1 b
Increasing
amperage
Decreasing
amperage
1.0
2.0
3.0
4.0
5.0
4.0
3.0
2.0
1.0
1.8
2.1
2.5
2.75
3.0
2.75
2.5
2.1
1.8
Gassing at both electrodes at all conditions.
Extended time necessary to reach first
steady state after polarity reversed.
Dichromate in h^SC^ appears (visually)
to be reoxidized.
aDennison Company
bElectrodes worked at 4.0 amp for 15 min after first run. Polarity at
electrodes reversed and test repeated for second run.
DIAPHRAGM ELECTRICAL RESISTANCE-100% POL YPROPYLENE (TWO LA YERS)3
Amperes
Volts
Observations
Run 2
Increasing
amperage
Decreasing ,
amperage
1.0
2.0
3.0
4.0
5.0
4.0
3.0
2.0
1.0
1.6
1.9
2.1
2.3
2.5
2.3
2.1
1.9
1.6
Some bleed-thru of dichromate
chamber.
Test temperature: 67°C
into cathode
aTroy Mills, 100% Polypropylene, No. 342-1903
100
-------
DIAPHRAGM ELECTRICAL RESISTANCE-100% POL YESTER*
Amperes
Volts
Observations
Run 3, 15-layer laminate
Increasing
amperage
Decreasing
amperage
1.0
2.0
3.0
4.0
5.0
4.0
3.0
2.0
1.0
2.6
3.6
4.75
6.2
8.5
5.8
4.6
3.5
2.6
Required about 1 5 min of soak time to wet
thru the diaphragm and establish conductivity.
Diaphragm stopped dichromate bleed-thru.
Temperature: 69° C.
Run 4, 12-layer laminate
Increasing
amperage
Decreasing
amperage
1.0
2.0
3.0
4.0
5.0
4.0
3.0
2.0
1.0
2.3
3.0
3.6
4.4
5.0
4.4
3.7
3.0
2.3
Bleed-thru of dischromate observed after test
run.
Temperature: 69° C.
aDennison Company, No. 024
101
-------
DIAPHRAGM ELECTRICAL RESISTANCE-100% POL YESTER (15-LA YER LAMINATE)''
Amperes
Volts
Observations
Run 5
Increasing
amperage
Decreasing
amperage
1.0
2.0
3.0
4.0
5.0
4.0
3.0
2.0
1.0
2.60
3.48
4.32
5.12-5.10
5.86-5.88
5.05
4.23
3.43
2.58
Preconditioned by holding at 4 amp for
15 min. Stabilized for 5 min at each
setting. Temperature: 66° C.
Run 6
4.0
5.0
4.97
5.68
Second conditioning by holding at 4 amp
for 15 min.
Run 7
/1.0
Increasing 1 2.0
amperage \ 3.0
1 4.0
V5.0
4.0
2.43
3.12
3.76
4.40
5.00
4.36
Third conditioning by holding at '4 amp for
15 min. Resistance continues to drop.
Temperature: 66° C.
Run 8
Increasing
amperage
Decreasing
amperage
1.0
2.0
3.0
4.0
5.0
4.0
3.0
2.0
1.0
2.41
3.04
3.66
4.25
4.85
4.25
3.65
3.04
2.41
After four
preconditioning periods of 4 amp
for 15 min each, diaphragm is now considered
stabilized
aDuPont Reemay, No. 2024
102
-------
TASK II
ELECTRODE EVALUATION
DATA SHEETS
103
-------
PO TENTIOSTA T PROBE DA TA
Identification
Number
D-1
D-2
C-3
C-4
P-5
P-6
N-7
N-8
S-9
S-10
Description
Duriron AS1 101-7
Duriron AS1 101-7
Copper, commercial
Copper, commercial
Lead, commercial
Lead, commercial
Nickel, commercial
Nickel, commercial
31 6 Stainless steel
31 6 Stainless steel
Diameter,
cm
0.947
0.934
0.955
0.955
0.955
0.953
0.951
0.957
0.958
0.953
Length,
cm
1.268
1.234
1.272
1.298
1.300
1.288
1.289
1.294
1.288
1.265
Exposed
Area, cm
4.83
...
4.89
...
...
4.93
...
...
-
4.86
104
-------
ANODE CURRENT EFFICIENCY DATA
Time,
min
Volume,
ml
Cr"1"6, gm/l
Active
Total
Corrected Cr+6, total gm
Active
Total
Corrected Cr+3,
total gm
Lead Anode (commercially pure)
Start
15
35
45
60
75
90
105
500
490
470
460
450
440
430
420
11.8
11.8
11.8
11.8
11.8
11.9
11.8
11.8
14.2
14.1
14.0
13.95
13.8
13.9
13.7
13.6
5.93
5.81
5.58
5.45
5.34
5.19
5.10
4.98
7.10
6.91
6.60
6.42
6.21
6.11
5.87
5.71
1.17
1.10
1.02
0.97
0.87
0.92
0.77
0.73
Tin-lead anode (7% Sn-93% Pb)
Start
15
30
45
60
75
90
105
510
500
490
480
470
460
440
430
34.4
34.1
34.2
34.6
34.6
34.2
34.2
34.2
41.6
40.4
40.6
40.6
40.4
40.0
39.65
39.4
6.13
5.95
5.85
5.80
5.68
5.50
5.38
5.26
7.42
7.07
6.97
6.83
6.65
6.44
6.24
6.04
1.29
1.12
1.12
1.03
0.97
0.94
0.86
0.78
Antimony-lead anode (6% Sb-94% Pb)
Start
15
35
45
60
75
90
105
510
500
490
480
470
460
450
440
34.4
34.4
34.6
34.6
34.6
34.4
34.2
33.8
41.1
40.8
41.2
40.8
40.6
39.9
39.3
39.1
6.13
6.01
5.93
5.80
5.68
5.53
5.38
5.20
7.33
7.14
7.06
6.85
6.68
6.42
6.18
6.02
1.20
1.13
1.13
1.05
1.00
0.89
0.80
0.82
105
-------
-------
TASK III
OPERATING PARAMETERS
DATA SHEETS
107
-------
H-CELL OPERATION FOR MASS TRANSFER DATA
Time
10:05
10:10
10:20
10:30
11:25
1:20
2:05
Temperature,
°C
32
49
57
66
70
70
70
Amperes
0
1.5
1.5
1.5
1.5
1.5
1.5
Volts
23
12.5
10.75
9.5
8
8.5
8.5
H-CELL ANALYSES
Sample
no.
HA-1
HA-2
HA-3
HA-4
Description
Anode
chamber
start
Anode
chamber
end
Cathode
chamber
start
Cathode
chamber
end
H2S04,
gm/l
254
278
287
310
Hexavalent
chromium,
gm/l
Active
9.83
10.4
None
None
Total
10.4
10.9
None
None
Cr+3,
gm/l
0.52
0.60
None
None
Al,
ppm
20,800
22,000
None
17
Cu,
ppm
380
392
0.15
0.65
Fe,
ppm
830
840
0.70
1.70
Zn,
ppm
326
324
1.72
2.48
Mg,
ppm
9.2
9.9
1.47
1.58
Mn,
ppm
4.75
5.25
0.65
1.00
108
-------
LABORATORY REPORT „.
R-672551 1450
Purpose.
Model.
Dot. 11-1171
Ta- H. Hicks
Subject: Tank 6, Dept. 6-7310, Regeneration of Chromium
. Org'n. 6-7310 Port No. M/S 92-06
Source Renton MR&D Lab
gx] Chen.. Lob. 1305
Q X-Roy
Rein ip. Req._
Purtha** QrdW
Material
R.R. Dote R«c'd. Quan. Aer.
Spec. BAC 5765, Solution 10
Rej.
Sonic
Q Met. Lab
Q Mechanical .
Mag/Penetrant
Reference:
12070 HEK project
C.C. to:
Sample pulled 11 -02-71. Results are as follows:
Sample
J5D2
J5D3
J5D4
Tank no. 6
Sample
J5D1
J5D2
J5D3
J5D4
Tank no. 6
Na2Cr207 • 2H20,
gm/l
34.2
Omitted
34.2
32.0
H2S04,
gm/l
295
306
300
312
287
Total chrome,
gm/l
34.8
0.3
34.6
33.0
A chrome,
gm/l
0.6
Omitted
0.4
1.0
Cr ,
gm/l
0.2
0.1
0.1
0.3
Prepared by.
. Approved by_
.Org'n..
109
-------
LABORATORY REPORT *>. m^i-iao
Purpose Model Dote 1-20-72
To: H. Hicks Org'n. 6-7310 Port No. M/S 92-06
- .. Solutions X-l and X-2
Sub|ect:
^e. Renton MR&D Lab R.inlp. R.q._
Purchase Order R.R Dote Rec'd Quon Ace. Rej.
Material Spec. BAG 5765, Solution 10
n Chem. Lob __ Q Sonic _Q Met. Lab Q Mechanical
Q X-Roy I I Mog/Penetront Q
Reference: C.C. to:
R-6725-51-1500
Analyses on 12/2, 12/3, and 12/6 show the following results:
X-l 273 gm/1 HS
X-2 260 gm/1 H2
X-l 30 gm/1 Na2
X-2 29 gm/1 Na-
X-l 0.8 gm/1 Cr
X-2 1.2 gm/1 Cr
Analyses 1-19-72
Aluminum in X-l =13,900 ppm
Aluminum in X-2 = 8,600 ppm
Prepared by Approved by Qrg'n. R-6725
Leo Hagen M. Minsk
110
-------
ALUMINUM SULFATE CRYSTAL FORMATION - TEST 1
Aluminum
sulfate
gm/l
150
150
165
165
165
180
180
195
195
210
210
225
225
Cooling rate,
min from 82°
to 38°C
1.
1.
5
5
Observation
temperature,
°C
32
27
32
27
22
43
22
38
21
38
21
38
21
Observed
crystals
None
None
11
-------
ALUMINUMSULFATECRYSTAL FORMATION- TEST2
Aluminum
sulfate,
gm/l
150
150
150
165
165
165
180
180
180
225
225
Temperature
drop,°C
66-38
38-23
23-23
66-38
38-23
23-23
66-38
38-23
23-23
66-38
38-23
Elapsed time for
temperature
drop,min
1.5
5
5
1.25
5
5
2
5
5
1.5
8
Observed
crystals
None
Nc
>ne
112
-------
LABORATORY-SIZE CRYSTALLIZER COOLING RATE- RUNS 1-6
Low Agitation
Time
Temperature,
°C
Run 1
9:31
32
33
34
35
36
37
3&
39
40
78
64
54
43
37
31
27
23.5
21.5
19.5
Run 2
10:10
11
12
13
14
70.5
58
47
38
31
Run 3
10:30
31
32
33
34
35
34
29
26
23
21
19
High Agitation
Time
Temperature,
°C
Run 4
1:15
16
17
18
19
20
21
22
23
Time,
min
Start
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
79
59
48
39
32
28
25
22
20
Temperature, °C
Run 5
65
50
40
32
26.5
22.5
20
17.5
Run 6
67
53
43
36
30.5
26
22.5
19.5
18.5
16.5
113
-------
LABORATORY-SIZE CRYSTALLIZER COOLING RATE- RUNS 7-9
Time,
min
Start
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Run 7
(311 gm/l
alum sulfate
84.5
72
62
54
46.5
41
36.5
32
29
Run 8
(297 gm/l
alum sulfate)
42.5
39.5
36
33
30
27.5
25.5
23.5
22
Run 9
(304 gm/l
alum sulfate)
89
77.5
68.5
60.5
54.5
48.5
44
40
36.5
Agitator on
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
10.5
11.0
11.5
12.0
26
23.5
21
19.53
18
21.5
21
20
19a
33
30.5
28
26
24
22.7
21.5
20
19a
18.5
17.5
17
16.5
15.5
15
14.5
Crystallization occurs
114
-------
LABORATORY-SIZE CRYSTALLIZER COOLING RATE- RUNS 10 & 11
Time, min
Start
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
6.0
7.0
8.0
9.0
9.5
10.0
18.0
19.0
Temperature, °C
Run 10
(289 gm/l
alum sulfate)
43
39.5
32
28
28.5
23.5
22
20.5
19
Cooling water and stirrer off
19
Air agitator on
18.5
18a
17
Run 11
(289 gm/l
alum sulfate
with vigorous agitation)
45
39
32
27
22.5
19.5
17.5
16
15
14
13a
Crystallization occurs
115
-------
LABORATORY-SIZE CRYSTALLIZER -ALUMINUM SULFATE REMOVAL EQUIPMENT
(Water Used in Solution Chamber)
Item
Reservoir Volume, ml
Heat exchanger inlet temp °C
Reservoir temp, °C
Upper chamber temp, °C
Chilled water outlet temp, °C
Chilled solution flow, ml/min
Belt speed, cm/min
Solids removed total, kg/hr
Crystallize temp, °C
Test Run
1a
7000
45-54-66
39-49-55
2b
7000
53-66
52
51
500
20.8
3C
7000
53-66
50
42
25
520
22.9
4C
7000
53-70
50-52
37-38
19.5
520
26.7
5C
7000
45-90
45-52
45-36
24-19
520
22.9
393
39
a Circulating pump not operating
Circulating pump operating
c Circulating pump operating, cooling water used
116
-------
Purpose.
H. Hicks
LABORATORY REPORT HO.
Model P— 2-2-72
. Or*. 6-7310 P8ft No M/S 92-06
Subject:.
Source _
Analysis
R&D BAG 5765, Solution 10
Purchase Order
Material Cr-1 and Cr-2
R.R DateRec'd..
Reinsp. Rea,._
.Quon Aee._
.Rej.
n Chem. tab. Apfospace Q Sonic
[3 X-Ray Q Moa/P«netront_
Met. Lab..
Mechanical.
-D.
Reference:
C.C. to:
Analysis of Al (SO) -18H 0 on R&D tank:
& 4 o f*
Cr-l = 2.3% by weight
Cr-2= 2.5% by weight
Prepared by.
AO 2I47A
Leo Hag en
.Approved by.
M. Minsk
v R-6725
117
-------
LABORA TORY-BUIL T BEL TED DRUM PRODUCT ANAL YSIS
Assay of solids removed by belt (not dried)
Solution
Aluminum sulfate
Sulfuric acid
Sodium dichromate
Water
Weight, gm
19.6
12.7
11.2
5.2
% of total
40.2
26.1
23.0
10.7
Weight analysis of solids removed by belt
Item
Weight, gm
Liquid loss
Gross weight
Tare weight
Net solids
Gross weight
Vacuum dried weight
Weight loss
Vacuum dried weight
Alcohol washed weight
27.3433
12.7837
14.5596
27.3433
20.3119
7.0314
20.3119
17.8355
2.4764
48.3%
17.0%
65.3% total
118
-------
DATA
LABORATORY TEST DATA FOR CENTRIFUGE OPERATING CONDITIONS
D°F
Type Liquid: acid-water pH: acid Process Temp: Ambient SOther
Type Solids: crystals Quantity Material Received: ipprox. 9.5 liters
Remarks: See second sheet for material preparation procedure.
Procedure: Samples taken before processing, after one pass, three passes, five passes and sludge
samples before and after compaction.
MACHINE(S) USED
[x] 125-F Barrett clarifuge
Q 125-F with accelerator
[x] Lab centrifuge (test tube)
Flow Rate: 4 gpm
TEST RESULTS
Sample
no.
1
2
3
4
5b
5a
Sampling
done
As received
1 pass
3 passes
5 passes
Sludge
Sludge
Solids in
10-ml sample.
ml
5.1
0.9
0.04
0
% of solids
by volume
51
9
0.4
0
Remarks
Before compaction
After compaction
%
Moisture
29
23
%
Cr03
0.4
0.45
NOTE: Samples are spun at maximum speed in lab centrifuge for 1 minute unless otherwise noted.
*Solids are [x] Scoopable \^\ Screwable Q Undeterminable (explain below)
[x] Not Q Not D Other
Scoopable Screwable
REMARKS: *Solids are scoopable before the 5-minute compaction and not scoopable thereafter.
CONCLUSIONS & RECOMMENDATIONS: The clarifuge does an excellent job of recovering all crystals
from this chemical solution.
We have found the weight of the compacted crystals to be 1.5 kg/I, which means the customer could
acquire his 9 kg of crystals in two batches. The solids are easily removed from the bowl by hand and
whatever crystals or liquid that remain can easily be flushed from the clarifuge since the solution is
water soluble.
This solution had no effect on the CRES clarifuge or its hoses.
19
-------
LABORATORY TEST DATA FOR CENTRIFUGE OPERATING CONDITIONS (Concluded)
MATERIAL PREPARATION PROCEDURE
The necessary ingredients were mixed and dissolved at the temperature of 71° C
for 5 minutes. The container was then allowed to cool to ambient temperature
for 2 hours before processing.
The batch as we mixed it: Aluminum sulfate 2.24kg
Sodium dichromate 0.21 kg
Sulfuric acid 2.21 liters
Water 4.88 liters
The weight of 1 gallon of compacted crystals:
500 ml of compacted crystals = 1.625 Ib
1000 ml= 1.057qt
946 ml = 1 qt
3784 ml = 1 gal.
Crystals weigh 12.298 Ib/gal. or 1.47 kg/I
120
-------
TB. H. Hicks
LABORATORY REPOI
Model
Oro'n. 6-7310 ?„, No.
RT NO. R-6725-51-1580B
D«,. 04-14-72
M/S 92-06
Q
Research Laboratory
R.R. Dote R.rM.
Spec.
^fn'if [ | Met. 1 ot>
Mog/Panetrant Q
Reinip. R^V
Ouan. Aee. Rej.
BAC 5765. Sol. #10
.f~"l M«fhanieal
Reference: C.C. to:
Environmental Protection Agency
5-66967-7322-632083
ANALYSIS
Total Na2Cr20? x 2H20
Active Na2Cr207 x 2H20
Chromium (trivalent)
Aluminum
ANALYSIS
Total Na2Cr20? x 2H20
Active Na2Cr207 x 2H20
Chromium (trivalent)
Al umi num
CELL
04-05-72
221 gm/1
4.1 gm/1
0 gm/1
1.5 gm/1
35 gm/1
TANK
04-05-72
270 gm/1
31 gm/1
24 gm/1
2.6 gm/1
102 gm/1
CELL
04-06-72
223 gm/1
5.7 gm/1
0 gm/1
2.0 gm/1
55 gm/1
TANK
04-06-72
275 gm/1
30 gm/1
25 gm/1
2 gm/1
100 gm/1
Prepored by _
Leo Hagen
_ Approved by_
M. Minsk
. Org'n..
R-6725
121
-------
LABORATORY REPORT «..
Purpose.
To:
Model.
Dat. 05-05-72
H. Hicks
. OroV 6-7310 P8rf No. M/S 92-06
Subject:
Source_
Analysis of Chromium Regeneration Tank
Pilot Tank 6-7310 Research Lab.
Purchase Order
R.R..
.Dote Rec'd..
Reinsp. Req._
-Qoon Ace._
.Rej.
u_ . . 12070 HEK Project
Motenal
Spec. BAG 5765, Sol. #10
G Chem. Lob.
G X.Roy
Met- Lab. .
_G Mechanical.
. Q Mag/Penetront.
-a.
Reference:
C.C. to:
Environmental Protection Agency
5-66967-7322-632083
ANALYSIS
CELL
04-07-72
CELL
04-10-72
CELL
04-11-72
H2S04 gm/1
Total gm/1
Active gm/1
270
26
5.0
331
39.2
2.5
331
37
11
Aluminum Metal gm/1
Chromium +++
gm/1
ANALYSIS
H2S04
Na2Cr207 x 2H20 Total gm/1
Na2Cr207 x 2H20 Active gm/1
Aluminum Metal gm/1
Chromium (trivalent) gm/1
2,0
7.4
TANK
04-07-72
344
36
26
3.6
3.5
4.5
7.6
TANK
04-10-72
336
36
12
4.5
8.5
4.5
9.0
TANK
04-11-72
321
36
6.5
4.5
10.2
Prepored by_
Leo Hagen
. Approved by_
M. Minsk
. Org'n.,
R-6725
122
-------
LABORATORY REPORT «.. R-6725-5i-i6io
Model
Dot. 05-05-72
TB. H. Hicks
s.,H.,,. Analysis of
s»u,.. p^ot Tank
Pgrchaf* Qrdar
12070 HEK
G Cham, l.nh.
Q X.Ray
0,BV 6-7310 Por,
Chrome Regeneration Tank
6-7310 Research Lab.
R.R. Dote R«c'd.
Project
Q Sonic . QJ Mat. 1 oh.
Q Mog/P«ie»«m» Q
,No M/S 92-06
R«in«p. R«a.
Ouon. , Acc. Rej.
w BAC 5765, Sol. #10
[ I Mechanical
)
Reference: C.C. to:
Environmental Protection Agency
5-66967-7322-632083
ANALYSIS
H2S04 gm/1
Na,Cr,07 x 2H,0
CELL
05-03-72
270
27
TANK
05-03-72
319
36
Total gm/1
Active gm/1
Aluminum
gm/Liter
Chromium (trivalent)
gm/1
34
9
24
34
1.5
Prepared by Approved by Org'n.
Leo Hagen M. Minsk
AO 2M7A
R-6275
123
-------
REMOVAL OF ALUMINUM SULFATE CRYSTALS WITH SOCK-TYPE FILTER
Sock type
Polypropylene fiber
with Dynel core
Gross
weight.
gm
1048.4
Tare
weight
gm
132.4
Net
weight
gm
916.0
Dried
weight.
gm
614.1
Crystal
weight
loss, gm
434.3
Crystal
%
liquid
47.5
DRUM FILTER OPERATING CONDITIONS- TESTS 1-6
Dressed Buchner Type Filter Cloth, 97 sq cm
Laboratory Test
Item
Sample, volume cc
Vacuum, cm Hg
Filtering time, sec
Initial dewatering rinse, sec
Time before cracking , sec
Discharge from cloth
Cake thickness, cm
Clarity of filtrate
Wet weight of cake, gm
Dry weight of cake, gm
h^O removed, gm
H2O in cake %
Rate, kg/cmVhr
Volume, ml filtrate/sq cm/hr
Removal rate (dry cake), gm/l
Chrome in cake (CrC^), %
Comments and Observations
1
Not valid
due to
vacuum
leak.
2
200
66-71
180
180
3
300
66-71
405
405
4
100
66-71
45
45
5
200
66-71
50
100
6
200
66-71
215
215
No cracking observed in any test run
Clean in all cases
0.32
0.95
0.16
0.16
Filtrate became progressively cloudy
19.1
11.6
7.5
39.2
2.5
43
56
0.95
31.0
24.8
6.2
20.0
2.4
29
83
0.88
9.2
5.3
3.9
42.4
4.6
85
53
0.99
10.1
5.9
4.2
41.5
2.3
77
56
0.90
Drying
period
double
that of
test 4
had no
effect.
0.24
18.0
11.3
7.3
39.1
2.1
36
56
0.93
124
-------
DRUM FILTER OPERATING CONDITIONS- TESTS 1a-7a
Item
Submergence, %
Rpm
Filtering time, sec
Initial dewatering time, sec
Time before cracking, sec
Discharge from cloth
Cake thickness, cm
Clarity of Filtrate
Filtrate volume, cc
Wet weight of cake, gm
Dry weight of cake, gm
h^O removed, gm
H20 in cake, %
Rate, kg/sq dm/rev
Rate, kg/sq dm/hr
Volume, ml filtrate/sq cm/hr
Removal rate (dry cake), gm/l
Chrome in cake (CrOg), %
Comments and Observations
Laboratory Test
1a
37.5
1/4
88
96
None
Clean
0.48
Sparkling
1600
66.7
36.6
30.1
45.2
0.23
3.5
156
23
2.4
String
discharge
ok
2a
37.5
1/4
88
96
None
Clean
0.48
Sparkling
1500
65.3
38.2
27.1
41.5
0.25
3.5
145
26
2.1
String
discharge
ok
3a
37.5
1/6
132
144
None
Clean
0.32
Clear but
precipita-
ting
540
43.7
24.0
19.7
45.1
0.15
1.5
35
44
2.6
String
discharge
ok
4a
37.5
1/6
90
180
None
Clean
0.32
Clear but
precipita-
ting
430
42.2
23.7
18.5
43.8
0.15
1.5
28
53
1.4
String
discharge
ok
5a
37.5
1/4
88
96
None
Clean
0.32
Clear but
precipita-
ting
435
49.0
26.6
22.4
45.1
0.17
2.6
42
62
2.2
String
discharge
limit seems
to have
been
reached
6a
37.5
1/6
132
144
None
Clean
0.16
290
31.1
22.0
17.1
43.8
0.14
1.4
19
75
4.5
Too thin
for
strings-
try
roller
7a
37.5
1/6
132
144
None
Clean
0.16
265
36.9
21.7
15.2
41.2
0.14
0.14
17
83
4.6
Carbon
steel
roll
125
-------
LABORATORY REPORT *». 2-4861-0002-354
Purpose Mod.) Dot. Oct. 18. 1972
To: Leo Hagen M/S 93-54 Org-n R-6725 Port No
S^ect: Analysis of Solution #10 BAG 5765 ___
Source Reinip. Req.
Purchase Order
Material
1 | Ch«m. 1 ah.
n X.Roy
R.R. Dote RecM. Quan. Ace.
Spec.
[2) Sonic Q M«t. 1 ah. Q Mechanical
i 1 Mog/Penetront | |
Rej.
Reference: C.C. to •
H. Hicks 7-3141
The submitted Solution #10 samples for iron, copper, zinc, magnesium, and manganese,
were analyzed by atomic absorption techniques. Aluminum was requested on two samples
and was determined wet chemically.
JOB #180 10-5-72 Job #185 10-16-72
Jil OOT 1 T_ « L JiO^-TT
Fe 322 ppm
Cu 920 ppm
Zn 186 ppm
Mg 572 ppm
Mn 34 ppm
Al 21 gm/1
Job #185 Sample #3 - Sludge scraped from cathode of tank
cu = 53.06% Mu = 0.002%
Fe = 0.034% Mg = 0.055%
Zn = 0.20% Al = 2.8%
#1 227-1 Tank
268 ppm
74 ppm
164 ppm
56 ppm
26.5 ppm
#2 Cell (from Tank}
304 ppm
0.93 ppm
198 ppm
69 ppm
32 ppm
Prepared by . _ . Approved by . Org'n. ^__
Bruce Smith S. D. Urban
126
-------
TASK IV
PILOT PLANT OPERATION
DATA SHEETS
127
-------
DIAPHRA GM H YDROSTA TIC POROSITY
Identification3
J5D-20 STM-3
J5D-20 STM-2
J5D-30 STM-4
(after service)
13Jun EX-20
13Jun-20-15M400°
13Jun-20-15M400°
16Jun-20-45M300°
19Jun-20-4H300°
J5D-20-1-21
J5D-20-1-22
J5D-20-1-25
J5D-20-1-21a
J5D-20-1-25a
J5D-20-1-22a
J5D-20-1-25a
J5D-30-1-9
J5D-30-1-24 (spec)
2J5D-30
3J5D-20
J5D-30-1-7Nov
J5D-30-1-16 Nov
J5D-20-1-19Nov
First water drops,
cm
_
97
41
74
30
53
79
> 127
> 127
122
> 127
> 127
> 127
127
64
> 127
31
30
68
30
Volume,
ml/10 min
2276
390
225
1900
1690
3838
182
21
280
810
396
91
58
120
108
81
565
0
260
236
Porosity,
ml HjO/hr/sq cm
559
96
55
467
415
941
45
5
44)
128 / '
63
14
9
19
17
13
28
0
6
12
7
356
Remarks
Pressure failure in hydraulic
press; forming time at pres-
'sure is unknown.
Two used 30-layer
diaphragms.
Three used 20-layer
diaphragms.
Identification code:
J5D - 20 - 1 - 21
t t t t
Material Number of Daily Day of the
cloth layers series month
or
16 June - 20 - 45M - 300°
t t t t
Date Layers Pressure Temperature
128
-------
R!
5
^
Q,
DC
i
ii
II
Uj I
Uj
-i
O
o
Uj
^1
Uj
g
I
f:
8
I/)
If:
C
CD
fU
o
k analysis
i-
Remarks
m sulfate
Alummu
c acid
D
3
to
O)
O
.C
to
o
\-
m sulfate
nuiujr
<
TJ
CJ
CD
O
5
in
chrome
>
d
0)
CM
*-.
0)
E
01
I
"E
0)
E
"E
b
"E
O)
b
"E
01
_
O
D
OJ
F
H
QJ
(0
Q
r- CM
— CD tri
__ E co co
"^ DlCD CO
01 1^ O O
C> rv^ _
J*p S f I
CD >r ^ ^ _ -D
OOOOOO OoOOOJ
'-'-COQ.fXQ. H Q_ Q_ Q_ _ 1
in in
o CD' o •* r- CD m in
o^--cocna> ^^c»oo
2*~*-CMCNCMCNCMCO <^ *— t-
129
-------
CONTINUOUS (ELECTROLYTIC) REGENERATION TANK AND CELL ANALYSES
MA Y-JUNE 1972
227-Liter Pilot Tank, Sulfuric-Dichromate Deoxidizer
1972
Date
May
1
2
3
4
5
8
9
10
11
15
16
17
18
19
22
23
24
25
26
30
31
Sample
size,
ml
2.5
2.5
2.0
2.0
Chamber
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Active Cr+G
ml
9.0
0
10.7
0
11.3
0
12.5
0
13.1
0
15.7
0
12.8
0
13.3
0
13.5
0
13.5
0
13.4
0
13.3
0
9.7
0
10.1
0
11.2
1.8
12.0
0
12.3
0
12.7
0
12.7
0
12.3
0
12.4
0
qm/l
18
0
22
0
23
0
25
0
26
0
31
0
32
0
33
0
34
0
34
0
33
0
33
0
24
0
25
0
28
5
3
0
31
0
32
0
32
0
31
0
31
0
H2S04 (pH 3.5)
(a) ml
17.4
14.5
17-6
14.6
17.8
14.9
17.6
14.3
17.2
14.3
17.6
14.5
13.7
10.9
13.7
10.9
13.7
19.9
13.5
10.2
13.75
10.2
13.5
9.9
12.8
9.8
12.7
9.7
12.8
9.5
12.5
8.9
12.8
9.2
12.9
9.4
12.7
9.6
12.2
8.55
12.5
10.4
grr'l
341
284
344
286
348
292
353
287
345
287
345
290
344
274
344
274
344
274
339
257
345
257
339
249
321
246
318
243
321
241
314
224
321
231
323
236
318
236
305
215
313
261
Aluminum (pH 1 1.3)
(b) ml
24.1
19.1
24.0
19.3
24.1
20.3
23.5
19.8
22.2
20.0
22.9
21.9
18.1
17.2
18.2
17.6
19.6
17.0
18.3
18.0
18.9
18.2
18.5
17.8
18.8
18.2
18.4
16.8
18.4
17.2
18.1
17.9
17.8
18.1
18.3
19.0
17.9
19.4
17.1
18.5
17.9
19.9
b-a-blank)
ml
4.6
2.5
4.3
2.6
4.1
2.3
3.8
3.4
2.9
3.6
3.2
4.3
2.7
4.6
218
5.0
4.2
5.2
3.1
6.1
3.45
6.3
3.3
6.2
4.3
6.7
4.0
7.2
3.9
5.9
3.9
6.3
3.3
7.2
3.7
7.9
3.5
8.1
3.2
8.25
3.7
7.8
gm/l
144
78
135
82
131
72
119
107
91
113
101
135
106
180
110
196
131
203
122
239
135
247
129
243
168
262
157
281
153
231
153
246
129
281
145
309
137
317
125
323
145
305
Total Cr,
gm/l
36
27
36
34
45
22
130
-------
CONTINUOUS (ELECTROLYTIC) REGENERATION TANK AND CELL ANALYSES
MA Y-JUNE 1972 (Concluded)
227-Liter Pilot Tank, Sulfuric-Dichromate Deoxidizer
1972
Date
Jun
1
2
5
6
7
8
9
12
7 :00 a.m.
12
12 : 30p.m.
12
1 :30 p.ra
13
14
16
19
25
26
27
Sample
size,
ml
2.0
2.0
Chamber
Tank
Cell
Tank
Cell
Tank
Cell
Cellc
Tank
Cell
Celld
Tank
Cell
Celld
Tank
Cell
Celld
Tank
Cell
Tank
Cell
2nd Tank
Cell
3rd Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Cell
Tank
Tank
Tank
Active Cr+6
ml
12.8
0
12.5
0
12.5
0
0.5
12.5
0
213
12.8
0
5.8
12.4
0
7.2
10.8
0
9.1
0
8.8
0
0
0
8.4
0
8.2
0
8.8
0
9.7
0
11.0
11.0
14.1
gm/l
32
0
31
0
31
0
1
31
0
6
32
0
14
31
0
18
27
0
23
0
22
0
0
0
21
0
20
0
22
0
24
0
27
27
35
H2SO4 (pH 3.5)
(a) ml
12.5
10.1
12.4
9.95
12.0
8.6
11.1
12.5
11.3
1.9
12.8
11.5
5.5
12.6
11.5
6.9
11.9
11.2
10.9
11.0
11.3
11.5
12.3
0
12.0
11.5
11.5
11.3
11.7
9.5
12.2
9.5
10.55
10.5
12.3
gm/l
318
253
316
254
305
219
282
304
289
49
312
294
141
305
294
176
305
287
279
281
289
294
314
0
307
294
295
290
299
243
313
243
270
270
315
Aluminum (pH 1 1.3)
(b) ml
17.5
19.8
17.3
19.8
16.7
9.4
13.2
17.6
13.4
3.4
17.9
14.4
8.1
17.4
14.7
10.1
16.9
14.8
16.2
16.3
16.8
16.8
18.0
0
17.5
17.2
17.2
17.9
18.1
17.2
19.7
19.8
12.25
(b-a-blank
ml
313
8.0
3.2
8.15
3.0
9.1
0.4
3.4
0.4
0.0
3.4
1.2
0.9
3.1
1.5
1.5
3.3
1.9
3.6
3.6
3.8
3.6
4.0
0
3.8
4.0
4.0
4.9
317
6.0
5.6
8.6
gm/l
129
313
128
324
119
362
16
131
16
0
131
49
37
119
61
61
134
77
146
146
154
146
162
0
154
163
163
199
150
244
227
349
Total Cr,
gm/l
aFirst titration
Second titration
"Refilled
Special test
131
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135
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CONTINUOUS (ELECTROL YTIC) REGENERATION CELL ANAL YSES
NOVEMBER 1972
227-liter Pilot Tank, Sulfuric-Dichromate Deoxidizer
1972
Date
Nov
10
11
12
13
14
15
16
17
18
19
20
21
H2S04,
gm/l
177
297
279
312
308
288
310
310
Total chrome,
gm/l
5
8
11
Additions
130ml H2S04
100ml H2S04
136
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137
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m /surf/hr
Etch rate
gm/sq cm/hr
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139
-------
-------
TASK V
COMMERCIAL PRODUCTS EVALUATION
DATA SHEETS
141
-------
pH CURVE FOR AMCHEM 6-16 (HNO3) WITH Al (N03)3 -9H20 AT308gm/At
ml
pH
pH standard at 4.01
0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
11.5
11.6
11.7
11.8
11.9
12.0
12.1
12.2
12.3
12.4
12.5
12.7
12.8
12.9
13.0
13.1
13.5
14.0
15.0
16.0
17.0
1.83
1.85
1.88
1.91
1.98
2.04
2.13
2.21
2.33
2.49
2.80
3.05
3.15
3.20
3.30
3.38
3.42
3.47
3.49
3.51
3.54
3.56
3.61
3.63
3.64
3.66
3.67
3.69
3.70
3.75
3.78
3.80
ml
18.0
19.0
20.0
21.0
22.0
23.0
24.0
25.0
26.0
27.0
28.3
29.0
30.0
31.0
32.0
33.0
34.0
35.0
36.0
37.0
38.0
39.0
40.0
pH
3.81
3.83
3.85
3.86
3.88
3.89
3.90
3.91
3.93
3.94
3.96
3.99
4.00
4.02
4.05
4.09
4.10
4.05
4.20
4.28
4.40
4.61
5.19
pH standard at 10.00
40.0
41.0
42.0
42.1
42.2
42.3
42.4
42.5
6.00
67.0
7.26
7.30
7.36
7.41
7.50
7.58
ml
42.6
42.7
42.8
42.9
32.0
43.1
43.2
43.3
43.4
43.5
43.6
43.7
43.8
43.9
44.0
44.1
44.2
44.3
44.45
44.6
44.7
44.8
44.9
45.0
45 1
45.2
45.3
45.4
45.5
45.6
45.7
45.8
45.9
pH
7.63
7.70
7.76
7.82
7.90
7.99
8.04
8.10
8.17
8.24
8.30
8.38
8.44
8.51
8.60
8.70
8.82
8.88
8.96
9.01
9.08
9.15
9.22
9.28
9.33
9.39
9.42
9.47
9.50
9.54
9.60
9.61
9.67
ml
46.0
46.1
46.2
46.5
47.0
47.5
47.0
49.0
50.0
51.0
52.0
53.0
54.0
55.0
56.0
57.0
57.1
57.2
57.3
57.4
57.5
57.6
57.7
57.8
57.9
58.0
58.2
58.3
58.4
58.5
59.0
60.0
61.0
pH
9.70
9.72
9.75
9.83
9.95
10.03
10.11
10.20
10.31
10.42
10.50
10.55
10.61
10.68
10.72
10.56
10.90
10.93
10.95
10.84
10.91
10.99
11.03
11.08
11.11
11.14
11.18
11.20
11.21
11.23
11.38
11.55
11.66
aThese values doubtful; pH meter was unstable.
142
-------
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TASK VI
PRODUCTION DEMONSTRATION
DATA SHEETS
149
-------
CALIBRATION OF VARIABLE-SPEED DRIVE ON DRUM FILTER
Dial reading
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16.5
15.5
14.5
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LABORATORY REPORT
*>.
Purpose _ Model _ . Dat, January 16, 1973
To: H. Hicks _ Qrg'n. 6-7310 Port No. M/S 92-06 _ _
Sublet: Regeneration of Deoxidizer _ _
Source Auburn - 600 Gallon Tank __ Rein«p. Req._^ _
Purchase Order R.R Date Ree'd Quart. Ace. Rej._
Mat.no! 12070 HEK . Spec. BAG 5765 Sol. #10
[3 Chero. Lob. Q Sonic Q Met. Lab. . .Q Mechanical
3 X-Roy [J Mag/Penetrant [j
Reference: C.C. to
EPA 5-66967-7322-632083
Run #1 (01-04-73) Moisture 0.6%
Total Chrome *
Run #2 (01-04-73) Moisture 0.5%
Total Chrome *
Run #3 (12-18-72) Moisture 44.1%
Total Chrome *
Run #5 (01-02-73) Moisture 36.7%
Total Chrome 0.8%
Run #6 (01-02-73) Moisture 37.6%
Total Chrome 0.8%
Run #8 (01-02-73) Moisture 36.6%
Total Chrome 0.8%
*Total Chrome to be done by Atomic Absorption or Equivalent
Prepored by Approved by Org'n. R-6725
Leo Hagen M. Minsk
AD 2847*
153
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CONTINUOUS REGENERATION TANK AND CELL ANALYSES— 2200-LITER
PREPRODUCTION TANK
Sulfuric- Dichroma te Deoxidizer
1972
Date
Jul
12
Sept
25
Oct
30
31
Nov
3
6
7
9
10
12
13a
14
15
16
17
20
21
22
28
29
30
Dec
1
5
6
7
8
9
10
Total
chrome,
gm/l
63.0
Tank analysis
Active
chrome,
gm/l
4.31
2.07
0.12
0.065
1.4
1.0
1.5
2.5
4.1
6.7
7.2
7.7
8.2
9.3
13.6
14.9
15.5
16.1
16.7
17.6
19.5
19.3
18.0
17.9
Sulfuric
acid,
gm/l
39.6
35.4
2.3
1.97
281
284
Aluminum
sulfate,
gm/l
295
295
Cell analysis
Sulfuric
acid,
gm/l
233
122
315
297
344
173
122
311
278
217
161
111
251
226
247
277
264
352
284
293
Remarks
362 kg aluminum sulfate added
91 kg aluminum sulfate added
36 kg aluminum sulfate
removed with drum filter
30.6 kg aluminum sulfate
removed with drum filter
aMinor element analysis (ppm):
Cu = 5.9 Mn = 2.4
Zn = 7.7 Mg = 3.8
Fe = 20.2
154
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158
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COMPARISON OF MINOR ELEMENT CONTENT - 22,000 -liter PREPRODUCTION
SOLUTION
Element
Fe
Cu
Mn
Mg
Zn
November 13, 1972
ppm
20.2
5.9
2.4
3.8
7.7
% of Total
50
15
6
9
19
December 18, 1972
ppm
805
685
210
245
40
% of Total
40
34
11
12
2
February 22, 1973
ppm
195
93
6
35
105
% of Total
45
21
14
18
24
CONTINUOUS (ELECTROL YTIC) REGENERA TION TANK ANAL YSES - MARCH 1973
Su If uric- Dichroma te Deoxidizer
1973
Date
Mar
7
7
8
Exposed
material
None3
PVCand
PVDC
Carbon
brick
(plus
mortar)c
Deoxidizer
temp, °C
28.3
34.0
61.1
91.5
96
98
Time
9:15
10:15
11:00
12:00
12:40
1:45
2:45
8:00
9:15
10:10
11:00
12:00
1:15
6:45
12:30
12:30
7:30
Elapsed
time, hr
Start
1.0
2.0
3.0
4.5
5.5
Start
1.25
2.2
3.0
4.0
5.25
22.75
28.50
Start
19.0
Power supply
V
6.2
6.2
6.2
6.2
12.0
11.0
14.0
NA
NA
NA
NA
amp
5.0
5.0
5.0
5.0
15.0
15.0
30.0
NA
NA
NA
NA
Tank analysis
Active chrome
ml
7.1
7.1
7.7
7.9
9.5
13.8
7.2
6.9
6.9
7.1
6.8
6.8
6.6
6.4
6.4
6.4
gm/l
17.7
17.7
19.2
19.7
23.6
34.4
17.9
17.2
17.2
17.7
17.0
17.0
16.7
15.2
15.2
15.2
Nitric acid
ml
7.1
7.0
6.7
6.9
6.7
6.7
6.3
6.2
6.2
0.2
gm/l
17.7
17.4
16.7
17.2
16.7
16.7
15.8
15.5
15.5
0.5
aSolution regeneration verification data
^"otal surface area = 9 sq dm/I; temperature varied from 78° - 108° C
cOne large piece and two small pieces
159
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REDUCTION OF HEX A VALE NT CHROMIUM BY TANK LINING MA TERIAL
Time
7:45
8:15
8:45
9:45
10:45
11:45
12:45
Elapsed
Time, min
Start
0.5
1.0
2.0
3.0
4.0
5.0
Titration,
ml
11.7
11.6
11.6
11:45
11.45
11.50
11.5
Sodium Dichromate,
gm/l
230
228
228
225
225
226
226
160
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SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
I, Report NG,
w
REGENERATION OF CHROMATED ALUMINUM DEOXIDIZERS
5. Repcrl Oate
Organization
Hicks, H. C. and Jarmuth, R. A.
The Boeing Commercial Airplane Company
P. 0. Box 3707
Seattle, Washington 98124
12, Sj,~--no; Organization
12070 HEX
AI. at Report ^jic
ivnea Covered
Environmental Protection Agency report number,
HPA-660/2-73-023, December 1973.
In the metal finishing industry highly concentrated hexavalent chromium solutions are
used extensively to deoxidize aluminum surfaces prior to anodizing, conversion
coatings, prepaint preparation, welding and adhesive bonding. A regeneration process
was conceived and tested to reduce the frequency of discarding the spent chromated
deoxidizers. The engineering techniques developed in this project involve
reoxidation of trivalent chromium to the hexavalent state by electrolysis thru a
diaphragm plus removal of undesirable dissolved metals by crystallization and
separation. Results of the accomplished work establish that regeneration of chromated
aluminum deoxidizers is feasible, practical and economical.
* Chromate recycle, *Regeneration, *Electrolytic reoxidation, *Water pollution control,
*Toxic metal control, Crystallization, Drum filtration, Centrifugation, Permeable
diaphragms, pH titrimetry.
*Aluminum deoxidizer reuse, *Chromated deoxidizers, *Chromium reoxidation, Chemical
cleaning, Aluminum etching, Aluminum cleaning, Pre-cleaning, Acid etching, Metal
cleaning, Chromium resources conservation, Regeneration of chromium solutions,
Hexavalent chromium, Trivalent chromium, Dissolved metals removal, Diffusion
diaphragm, Metal finishing waste treatment.
19 %,,umy Class,
("Repo/t!
'. . Sjcuriu ^
(I'aje)
21. No, of
Fag"
. J , I'nce
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U* DEPARTMENT OF THE INTERIOR
WASHINGTON. D.C. 2024O
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