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Prepared by
Tom Lewis, Lewis Engineering Services Glenn Bush, CMP Consultant
FIELD EVALUATION OF CARBON ADSORPTION/ELECTROWINNING
FOR RECOVERY OF CHROMIUM
A Description of Field Tests of the ENVIRO-CLEAN PROCESS for Removing Chromium from Plating Waste Liquid
CMP REPORT NUMBER 90-2
August 1990
Prepared by
Tom Lewis, Lewis Engineering Services Glenn Bush, CMP Consultant
Prepared for
Electric Power Research Institute Center for Materials Production
Carnegie Mellon Research Institute 4400 Fifth Avenue
Pittsburgh, PA 15213-2683
Robert J. Schmitt CMP Project Manager
Legal Notice
This report was prepared by the organizations named below as an account for work sponsored by the Center for Materials Production (CMP). Neither members of CMP, the organizations named below, nor any person acting on their behalf: (a) makes any warranty express or implied, with respect to the use of any information, apparatus, method, o r process disclosed in this report o r that such use may not infringe privately owned rights, or (b) assumes any liabilities with respect to the use of, o r for damages resulting from the use of any information, apparatus, method, o r process disclosed in this report.
Organizations that prepared this report: Torn Lewis, Lewis Engineering Services
Glenn Bush, Consultant
ii
CMP PERSPECTIVE
PROJECT BACKGROUND
Chromium is used in industry for a variety of applications such as electroplating of metal to enhance the appearance of fabricated steel products and to provide corrosion protection during transit and storage of metal products. The applica- tion of chromium to metal either through electroplating or chemical treatments can result in the presence of chromium in rinse waters and process solutions that eventually become a waste discharge. Chromium is on EPA's hazardous materials list and thus presents a problem to dispose of properly. EPA has set acceptance discharge limits at 0.05 mg/l for hexavalent chromium and 1.7 mg/l for total chromium for drinking waters. A number of chromium recovery processes are being marketed to address chromium recovery options. A new process called the ENVIRO-CLEAN process has been developed by Lewis Engineering Services and offers the advantage of recovering the chromium as a salable product. Bench scale studies were conducted at the University of Pittsburgh to determine the feasibility of this novel process. These studies successfully demonstrated the viability of the process, and Lewis Engineering has filed disclosure statements with the U.S. Patent Office. In an effort to scale-up the process, a trial of a small pilot unit was conducted at Jersey Chrome Plating, a hard chromium plating company in Pittsburgh.
PROJECT OBJECTIVE
The purpose of the trial was to 1) demonstrate the process on a larger scale, 2) to evaluate the process in a commercial application, 3 ) to develop engineering data which would facilitate the design of a larger commercial unit and 4) determine electrical power consumption.
iii
PROJECT APPROACH
Funding and mater ia l s u p p o r t f o r t h e t r i a l w a s p r o v i d e d by:
1. Ben F r a n k l i n Technology C e n t e r o f Western P e n n s y l v a n i a 2 . Calgon Carbon C o r p o r a t i o n 3 . E P R I C e n t e r f o r M a t e r i a l s P r o d u c t i o n 4 . E l k e m Metals Company 5 . L e w i s E n g i n e e r i n g Services
I n a d d i t i o n , J e r s e y Chrome P l a t i n g p r o v i d e d t h e i r f a c i l i t i e s as a t es t s i t e f o r t h i s program.
The t e s t u n i t e v a l u a t e d a t J e r s e y Chrome p r i m a r i l y c o n s i s t e d o f f o u r p l e x i g l a s s s t r i p p i n g columns each c o n t a i n i n g a p p r o x i - m a t e l y 15 pounds ( 7 k i l o g r a m s ) o f Calgon F i l t r a s o r b 4 0 0 act ivated ca rbon , a 50 -ga l lon ( 1 9 0 l i t e r s ) p o l y p r o p y l e n e feed
t a n k , t h e n o v e l L e w i s E l e c t r o l y t i c Metal Recovery u n i t and a s s o c i a t e d p i p i n g and i n s t r u m e n t a t i o n .
PROJECT RESULTS
S e v e r a l e x p e r i m e n t a l d i f f i c u l t i e s were e n c o u n t e r e d d u r i n g t he
t r i a l ; however, t h e r e s u l t s o f t h e t e s t i n d i c a t e d tr lat the
ENVIRO-CLEAN PROCESS can be u s e d t o r e c o v e r chromium from a n i n d u s t r i a l wastewater. The g r a n u l a r act ivated ca rbon columns e f f e c t i v e l y removed h e x a v a l e n t chromium from t h e waste water and p roduced an EPA a c c e p t a b l e e f f l u e n t . R e s i d u a l q u a n t i t i e s o f c o p p e r and i r o n w e r e a l s o removed. T h e ca rbon columns w e r e s u c c e s s f u l l y r e g e n e r a t e d and t h e r e s u l t i n g chromium-rich r e g e n e r a t e s o l u t i o n w a s p r o c e s s e d i n t he EMR u n i t . Chromium o x i d e d e p o s i t s w e r e p roduced w i t h a chromium metal y i e l d o f a b o u t 16 -21 g/kWh. On t h e bas i s o f t h i s s t u d y , it i s recommended t h a t a n o t h e r t r i a l be conduc ted and t h a t c e r t a i n improvements d e t e r m i n e d from t h i s e v a l u a t i o n be i n c l u d e d i n t h e ENVIRO-CLEAN PROCESS.
i v
b
ABSTRACT
T h i s s t u d y r e p o r t s on t h e e v a l u a t i o n o f t he ENVIRO-CLEAN
PROCESS f o r r e c o v e r i n g chromium from p r o c e s s i n g waste streams. The ENVIRO-CLEAN PROCESS deve loped by L e w i s
E n g i n e e r i n g Services i n v o l v e s t he a d s o r p t i o n of chromium i n t h e w a s t e stream by act ivated ca rbon f o l l o w e d by r e c o v e r y o f chromium o x i d e from an acid r e g e n e r a n t s o l u t i o n by a n o v e l e l e c t r o w i n n i n g step. A tes t o f a s m a l l p i l o t u n i t w a s conduc ted a t J e r s e y Chrome P l a t i n g i n P i t t s b u r g h i n t h e f a l l o f 1989 . The p u r p o s e o f t h e t r i a l w a s t o 1) d e m o n s t r a t e t h e
p r o c e s s , 2 ) t o e v a l u a t e t h e p r o c e s s i n a commercial a p p l i c a t i o n , 3) t o d e v e l o p e n g i n e e r i n g data which would f a c i l i t a t e t h e d e s i g n o f a la rger commercial t y p e u n i t , and 4 ) t o d e t e r m i n e e lectr ical power consumption.
Al though a number o f e x p e r i m e n t a l d i f f i c u l t i e s w e r e e n c o u n t e r e d d u r i n g t he t r i a l , t he r e s u l t s of t he tes t i n d i c a t e d t h a t t h e ENVIRO-CLEAN PROCESS can be u s e d t o r e c o v e r chromium from i n d u s t r i a l waste water. The act ivated c a r b o n columns e f f e c t i v e l y removed h e x a v a l e n t chromium from the w a s t e w a t e r and produced an EPA a c c e p t a b l e e f f l u e n t . The
act ivated c a r b o n w a s s u c c e s s f u l l y r e g e n e r a t e d and the
r e s u l t i n g chromium-rich r e g e n e r a t e s o l u t i o n w a s p r o c e s s e d t h r o u g h t h e e l e c t r o l y t i c r e c o v e r y u n i t . Chromium o x i d e d e p o s i t s w e r e p roduced w i t h a chromium metal y i e l d o f a b o u t 16-21g/kWh. These d e p o s i t i o n s c o n t a i n e d r e s i d u a l q u a n t i t i e s o f coppe r a n d i r o n .
On the bas i s o f t h i s s t u d y , it i s recommended t h a t a n o t h e r t r i a l be conduc ted on a waste stream c o n t a i n i n g o n l y chromium metal and n o t o t h e r r e s i d u a l metals. This p r o c e s s i s p a r t i c u l a r l y s u i t e d t o r e c o v e r y o f chromium from waste waters from t i n - f r e e steel p r o c e s s i n g l i n e s and chromium chemical
V
t r e a t m e n t p r o c e s s e s on g a l v a n i z i n g and t i n n i n g l i n e s i n t he
s t ee l i n d u s t r y . C e r t a i n improvements i n t h e t h e ENVIRO-CLEAN
PROCESS d e t e r m i n e d from t h i s t r i a l s h o u l d be i n c l u d e d i n t he
n e x t e v a l u a t i o n o f t h i s p r o c e s s .
v i
ACKNOWLEDGMENTS
The authors would like to thank Carol Balliet, President, Ben Franklin Technology Center of Western Pennsylvania; Roger Zanitsch, Senior Vice President, Calgon Carbon Corporation; Alan FitzGibbon, Product Manager, Elkem Metals Company; and James Jersey, President, and the staff of Jersey Chrome Plating Company for their support, cooperation, and energies in aiding this project.
To Robert Schmitt and John Kollar at the Center for Materials Production for their support, direction, and assistance; and also EPRI for providing the means to demonstrate this needed recovery technology.
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CONTENTS
Section
1
Page
1
2
3
4
5
6
7
8
9
1 0
SUMMARY
INTRODUCTION
BACKGROUND
PURPOSE
TEST EQUIPMENT
EXPERIMENTAL PROCEDURES
RESULTS Chromium Removal from Waste Stream by Activated Carbon Acid Stripping and Carbon Regeneration GAC Rinsing and Pretreatment Electrolyte Metal Recovery Solution Additives EMR Solution Reuse Chromium Recovery Power Consumption
CONCLUSIONS
RECOMMENDATIONS
BIBLIOGRAPHY
1-1
2 - 1
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4 - 1
5 -1
6 -1
7 - 1
7 - 1
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7-8
7-15
7-17
7-17
7-18
8 - 1
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10-1
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c
ILLUSTRATIONS
Figure
1 Photograph of Demonstration Unit at Jersey Chrome
2 Schematic Diagram of ENVIRO-CLEAN PROCESS
3 Carbon Removal of Chromium
4 Rinse Water Data Summary
5 Cathode as Removed from Cell
6 Recovered Cathode Deposit
7 Effect of Sodium Sulfite on Product Deposition Rate
Page
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5-3
7-5
7-9
7-12
7-13
7-16
ix
TABLES
Table
1
2
3
4
Summary of GAC Adsorption Data
Activated Carbon Acid Stripping
Summary of Electrolytic Metal Recovery Data
Cathode Deposit Analyses
Page
7-2
7-7
7-10
7-14
X
APPENDIX
Table
A1 Adsorption Removal Data
Page
11-1
A2 Jersey Chrome Rinse Water Characterization 11-3
A3 Water Rinse Data 11-4
A4 Electrolytic Metal Recovery Data 11-5
A5 Summary of Electrolytic Metal Recovery Analysis 11-8
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Section 1
SUMMARY
Chromium is used in industry for a variety of applications such as electroplating of metal to enhance the appearance of fabricated steel products and to provide corrosion protection during transit and storage of metal products. The applica- tion of chromium to metal either through electroplating or chemical treatments can result in the presence of chromium in rinse waters and process solutions that eventually become a waste discharge. Chromium is on EPA's hazardous materials list and thus presents a problem to dispose of properly. EPA has set acceptable discharge limits at 0.05 mg/l for hexavalent chromium and 1.7 mg/l for total chromium for drinking waters.
A number of chromium recovery processes are being marketed to address chromium recovery options. The three leading processes are 1) evaporation, 2) ion exchange, and 3) reverse osmosis. Each of these processes reportedly has disadvantages which have hindered their commercial development. The ENVIRO-CLEAN PROCESS has been developed by Lewis Engineering Services as an alternate recovery process which should overcome the disadvantages of presently available processes. The ENVIRO-CLEAN PROCESS involves the adsorption and concentration of chromium onto a bed of granular activated carbon followed by recovery of the chromium from a sulfuric acid regenerant solution with an innovative Electrolytic Metal Recovery Process (EMR). The EMR unit produces a chromium oxide product through an electrowinning process. The advantages for this process are it produces an EPA quality effluent, no hazardous waste is generated, and a salable by-product is recovered.
Bench scale studies were conducted at the University of Pittsburgh to determine the feasibility of this novel process. These studies successfully demonstrated the
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viability of the process, and Lewis Engineering has filed a patent application with the U.S. Patent Office. In an effort to scale-up the process, a trial of a small pilot unit was conducted at Jersey Chrome Plating, a hard chromium plating company in Pittsburgh. The purpose of the trial was to 1) demonstrate the process on a larger scale, 2) to evaluate the process in a commercial application, 3) to develop engineering data which would facilitate the design of a larger commercial unit and 4) determine electrical power consumption. Funding and material support for the trial was provided by:
1. Ben Franklin Technology Center of Western Pennsylvania 2. Calgon Carbon Corporation 3. EPRI Center for Materials Production 4. Elkem Metals Company 5. Lewis Engineering Services
In addition, Jersey Chrome Plating provided their facilities as a test site for this program.
The test unit evaluated at Jersey Chrome primarily consisted of four plexiglass stripping columns each containing approximately 15 pounds (7 kilograms) of Calgon Filtrasorb 400 activated carbon, a 50-gallon (190 liters) polypropylene feed tank, the novel Lewis Electrolytic Metal Recovery Unit and associated piping and instrumentation. In order to minimize the impact of this pilot evaluation on the normal operation at Jersey Chrome, samples of waste solution were transferred from their waste stream holding tank to the 50 gallon feed tank in the ENVIRO-CLEAN unit.
Although a number of experimental difficulties were encountered during the trial, the results of the program indicated that the ENVIRO-CLEAN PROCESS can be used to recover chromium from an industrial waste water. The granular activated carbon columns effectively removed
1-2
h e x a v a l e n t chromium from t h e waste water and produced an EPA
a c c e p t a b l e e f f l u e n t . R e s i d u a l q u a n t i t i e s of coppe r and i r o n w e r e a l s o removed. The columns w e r e s u c c e s s f u l l y r e g e n e r a t e d and t h e r e s u l t i n g chromium-rich r e g e n e r a t e s o l u t i o n w a s p r o c e s s e d i n t h e EMR u n i t . Chromium o x i d e d e p o s i t s w e r e p roduced w i t h a chromium metal y i e l d o f abou t 16 -21 g/kWh.
These d e p o s i t s c o n t a i n e d r e s i d u a l q u a n t i t i e s of coppe r and i r o n .
On t h e bas i s o f t h e t r i a l , it i s recommended t h a t a n o t h e r scale t r i a l be conduc ted and t h a t c e r t a i n improvements be
i n c l u d e d i n t he ENVIRO-CLEAN PROCESS. These i n c l u d e
1.
2 .
3 .
4 .
5 .
6.
7 .
8 .
Improved column d e s i g n and u s e t o i n c r e a s e chromium l o a d i n g .
Improved column r e g e n e r a t i o n t o i n c r e a s e t he c o n c e n t r a t i o n o f chromium i n t he r e g e n e r a t e . Improved a g i t a t i o n t o i n c r e a s e mass t r a n s p o r t i n t he
E l e c t r o l y t i c Metal Recovery p r o c e s s . A method t o p r e v e n t t r i v a l e n t chromium o x i d a t i o n i n t h e
E l e c t r o l y t i c Metal Recovery p r o c e s s . E v a l u a t i o n o f improved anode-cathode materials. E v a l u a t e t h e effect of r e s i d u a l i m p u r i t i e s on t h e
economic v a l u e o f t h e r ecove red p r o d u c t . Improved sys t em d e s i g n t o i n c o r p o r a t e u s e of t he p r o c e s s r i n s e s . Pe r fo rm an economic a n a l y s i s of t h e p r o c e s s .
1-3
,
Section 2
INTRODUCTION
Environmental regulatory pressures have brought to the forefront the serious problem of hazardous waste generation and disposal. For example, commercial landfill volumes in 1986 totaled 3.5-4.0 million t/y. Roughly 25% of all the materials disposed of in such commercial hazardous waste landfills in 1986 will ultimately be banned from landfills in the future. This will result in approximately 825,000 - 1,000,000 t/y of new hazardous waste demand on alternative disposal or recovery methods (1). These stringent EPA regulations affect the entire industrial community and especially those involved with metal plating or metal finishing. Specifically, chromium which is on EPA's hazardous materials list is one of the more costly metals to treat and dispose of properly. It is listed with the "EPA- Primary Drinking Water Standards" with acceptable discharge limits set at 0.05 mg/l for hexavalent chromium and 1.7 mg/l for total chromium for drinking waters. Such limits reflect EPA health based concerns regarding human toxicity of consumed chromium. Consequently, chromium related industries such as hard chrome plating and tin mill processing are especially hard pressed to find economical solutions to waste treatment and sludge disposal problems. These industries are seeking a strategy to comply with regulatory guidelines and at the same time effectively reduce the cost of the associated waste treatment.
In response to this need, Lewis Engineering Services, a service company, has developed the novel, integrated ENVIRO- CLEAN PROCESS for the reclamation of metals such as chromium from process and waste water streams.
The ENVIRO-CLEAN PROCESS consists of two steps: First the heavy metal influent solution is processed through a granular activated carbon system which removes the heavy
2-1
,
metals and produces an EPA acceptable effluent. The second step recovers the metals from the carbon system using an electrolytic technique. This patent-pending process produces an EPA-acceptable effluent, recovers the heavy metal, and generates no sludge!
Through the assistance of a Ben Franklin Challenge Grant, the process was tested in the laboratory for over a year. On the basis of the favorable results obtained, a decision to proceed with the further development of the process was made. The purpose of this new program was to evaluate the process on a larger scale in an industrial setting. Funding and support for the additional work was provided by:
1. Ben Franklin Technology Center of Western Pennsylvania 2. Calgon Carbon 3. EPRI Center for Materials Production 4. Elkem Metals 5. Lewis Engineering Services
In addition, Jersey Chrome Plating in Lawrenceville, Pa., offered their facilities as a site for this program.
The purpose of this report is to describe the ENVIRO-CLEAN PROCESS and detail the results obtained during this larger scale test program.
2-2
Section 3
BACKGROUND
Present state-of-the-art technology for chromium "clean-upii involves pH adjustment of the waste stream to about 4.5, followed by chemical reduction of hexavalent chromium to trivalent chromium using sulfur dioxide or sodium meta- bisulfite. The trivalent chromium is precipitated using lime and/or sodium hydroxide into a sludge for land disposal at a Superfund site. However, with the imposition of RCRA regulations, chromium-based sludges are considered toxic, and land disposal practices are becoming prohibitively expensive to the industrial client (2). -
A number of recovery processes are being marketed to address chromium recovery options. The three leading processes are (1) evaporation, (2) ion exchange, and (3) reverse osmosis. Each process has disadvantages which have hindered its commercial development. A brief discussion of these options and their disadvantages follows.
EVAPORATION - Recovery is accomplished by boiling off sufficient water from the collected rinse stream to concentrate the stream for return to the operation. This is a very energy-intensive process, and its cost effectiveness is questionable. The cost of evaporator equipment is high and maintenance is required. Also impurity buildup is a major problem, and additional unit processes such as ion exchange or activated carbon may be required to remove other impurities.
ION EXCHANGE - A major drawback of ion exchange is that when the resin is exhausted, its reprocessing generates significant volumes of waste solution which adds to the overall waste treatment loading and complicates the operation of the waste treatment system. Also resin life is very sensitive to high metal concentrations and
3-1
impurity fouling. Ion exchange resins are limited in their ability to recover a wide range of metal species and normally require two separate units - one for cations and one for anions. Each system would have its own regenerating solutions with resulting waste streams.
REVERSE OSMOSIS - The major limitation of commercial reverse osmosis systems is the inability to maintain membrane performance. Fouling and gradual deterioration of membranes can reduce the processing capacity of the unit and require frequent membrane replacements. The recovery solutions must be in a restrictive pH range to ensure reasonable membrane life. Moreover, these membranes are not suitable for treating solutions having high oxidation potentials, or
for concentrating dilute solutions.
The ENVIRO-CLEAN PROCESS was developed as an alternate recovery process which overcomes the disadvantages of the present processes. The ENVIRO-CLEAN PROCESS involves the adsorption and concentration of chromium onto a bed of granular activated carbon followed by recovery of the chromium from the subsequent regenerant with an innovative Electrolytic Metal Recovery (Em) process which produces a chromium oxide product. This process is superior to the existing state of art processes for treating chromium wastes from metal finishers because it produces an EPA quality effluent, no hazardous waste is generated, and a salable by- product is recovered.
ENVIRO-CLEAN PROCESS
In the ENVIRO-CLEAN PROCESS, the waste stream is treated to adjust its pH to within a range of 4-5 to facilitate removal of chromium on the adsorption media. Passing this stream
3-2
.
t h r o u g h t h e activated carbon media p r o d u c e s a n EPA
a c c e p t a b l e e f f l u e n t f o r f i n a l discharge. P e r i o d i c r e g e n e r a t i o n o f t h e a d s o r p t i o n media by a s u l f u r i c acid ( 1 0 % by weight ) s t r i p p i n g s o l u t i o n i s r e q u i r e d t o remove the
chromium from t h e s u r f a c e o f t h e a d s o r p t i o n media which can t h e n be r e u s e d . The s t r i p p i n g s o l u t i o n i s r e t u r n e d t o a separate s t o r a g e t a n k where it can be u s e d t o r e g e n e r a t e o t h e r a d s o r p t i o n u n i t s o r can be s e n t t o t h e E l e c t r o l y t i c Metal Recovery cel l when it i s l o a d e d w i t h chromium. The
s t r i p p i n g s o l u t i o n i s p r o c e s s e d t h r o u g h the EMR ce l l where e l e c t r o w i n n i n g takes place and a chromium o x i d e i s d e p o s i t e d on i n e r t c a t h o d e s . This b lue -g reen powdery d e p o s i t i s e a s i l y removed from the c a t h o d e and i s a n i n e r t by-product . The e l e c t r o l y s i s a l s o r e g e n e r a t e s t h e s t r i p p i n g s o l u t i o n which c a n t h e n be r e u s e d f o r repeated s t r i p p i n g c y c l e s min imiz ing o v e r a l l chemical consumption.
P o t e n t i a l l y v a r i o u s l i q u i d streams s u c h as p i c k l i n g acids, p l a t i n g o p e r a t i o n r i n s e waters, and s p e n t p r i n t e d c i r c u i t b o a r d e t c h i n g s o l u t i o n s c o u l d be t reated by t h i s p r o c e s s . The s y s t e m is n o t i n h i b i t e d by o r g a n i c s , b u t t he s o l u t i o n c h e m i s t r y must be a d j u s t e d and c o n t r o l l e d t o maximize the
metal r e c o v e r y c a p a b i l i t y o f t h e sys tem f o r each p a r t i c u l a r waste stream. The sys t em i s d e s i g n e d t o t r e a t segregated ( s i n g l e metal component) streams b u t c e r t a i n m u l t i - m e t a l streams c a n a l s o be t reated.
L e w i s E n g i n e e r i n g S e r v i c e s h a s conduc ted l a b o r a t o r y tes ts d e t e r m i n i n g t he f e a s i b i l i t y o f chromium r e c o v e r y u t i l i z i n g act ivated c a r b o n as an a d s o r p t i o n media and a n advanced d e s i g n e l e c t r o l y t i c r e c o v e r y module. T h i s research work w a s pe r fo rmed a t t he U n i v e r s i t y of P i t t s b u r g h i n c o n j u n c t i o n w i t h D r . R. Neufe ld and addressed chromium r e c o v e r y from h e x a v a l e n t s o l u t i o n s .
3-3
The preliminary bench studies at the University of Pittsburgh were conducted in three (3) separate phases. Initial experiments solely evaluated removal and recovery of dilute concentrations of hexavalent chromium in aqueous solutions. Separate experiments were then conducted for the removal phase using granular activated carbon (GAC) and concurrently independent tests were conducted determining system parameters for electrolytic metal recovery (EMR) of chromium. After GAC bench mark results were completed, stripping solutions containing concentrated amounts of chromium were evaluated as the feedstock to the EMR system. This last portion of bench work simulated the conceptual design of the system proposed for the present study.
Lewis Engineering Services has filed disclosure statements (3,4) - - to the U.S. Patent Office regarding the process documentation of the EMR unit. A patent application was filed July 28, 1989, detailing the innovative steps into an overall recovery process (5). -
3-4
Section 4
PURPOSE
The primary purposes of this trial were 1) to demonstrate the process on a larger scale, 2) to evaluate treating a chromium rinse water stream, and 3) to develop engineering data which would facilitate the design of larger units. Secondary objectives were to determine electrical power consumption and the effects of solution additives on the recovery process.
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Section 5
TEST EQUIPMENT
The equipment used at the Jersey Chrome trial was assembled from generally available standard items and is shown in Figure 1. A schematic diagram of the test unit i s shown in Figure 2. The sizing of the unit was based on previous laboratory tests, and a description of the pilot plant components is presented below.
Feed System - The feed system consisted of a 50-gallon (190 liters) polypropylene tank, a chemical metering pump, agitator with impeller, and a pH control system. The pH controller included a pH probe, acid or base feed, internal metering pump, and LED read out.
Carbon Column Modules - Four plexiglass columns of 6"
diameter by 6 ' high were skid mounted. These were complete with piping (1/2" OD tubing) and a valving system to operate the system in upflow or downflow modes and accommodate switching the positioning of the columns. Each column was filled with approximately 15 lbs. (7 kilograms) of Calgon Filtrasorb 400 carbon to a height of 55" up the column.
Regeneration Tank - A 50-gallon (190 liters) polypropylene tank was used as a recirculating tank for the acid regeneration of the GAC columns and for the EMR cell. The tank was equipped with a pH controller and a 1.5 gal/min recirculation pump.
EMR Cell
The EMR cell consisted of a custom fabricated polypropylene module (size: 3 ' by 1' wide by 2' deep). The cell included proprietary agitators, anodes, cathodes, and a dc power supply (150 amps (3 10 volts).
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N
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Cathodes - Two types of cathodes were provided; copper and stainless steel. The cathodes were 8" wide by 12" high by 1/4" thick. Cathode surface area was either 2 or 4 ft2.
Anodes - Two types of lead anodes were used; lead-calcium alloy and lead-antimony alloy. The lead-calcium anodes were of a flat plate design and the lead-antimony anodes were of a grid design. The anode sizes were 8" wide by 10" high by 1/4" thick. Anode surface area was either 1.4 or 2.8 ft . 2
Cell Agitators - The EMR unit was designed with special agitators to recirculate the solution in a high velocity, but nonturbulent fashion. The agitators were driven by variable speed 1/4 hp dc motors (0-150 rpm).
5-4
S e c t i o n 6
EXPERIMENTAL PROCEDURES
I n o r d e r t o minimize t h e impact o f t h i s f i e l d e v a l u a t i o n on t h e normal o p e r a t i o n a t J e r s e y Chrome, samples of waste s o l u t i o n w e r e t r a n s f e r r e d from t h e i r waste stream h o l d i n g t a n k t o t h e Feed Tank and t rea ted on a batch basis . Approximate ly 5 0 g a l l o n s (190 l i t e rs ) o f waste stream s o l u t i o n w e r e t a k e n a t one t i m e from J e r s e y Chrome's h o l d i n g t a n k and t r a n s f e r r e d . t o t h e Feed Tank f o r p H a d j u s t m e n t . T h i s feed w a s p H a d j u s t e d t o 4-5 u s i n g c o n c e n t r a t e d c a u s t i c s o d a f l akes .
B e f o r e t h e i n i t i a l r u n on each GAC column, t h e ca rbon i n t h e
column w a s pretreated w i t h a d i l u t e s u l f u r i c acid s o l u t i o n a t p H 1 . 8 and a f l o w r a t e o f 1 gpm ( 3 . 8 L / m ) , t h e n water r i n s e d t o p H 2 . 1 w i t h c i t y water a t a f l o w r a t e o f 1
g a l / m i n . A f t e r c o n d i t i o n i n g of t h e column, t he p H a d j u s t e d w a s t e s o l u t i o n from J e r s e y Chrome w a s pumped from t h e Feed
Tank t h r o u g h a s i n g l e GAC column a t a nominal f l o w ra te o f 1 . 7 ( 6 . 4 L / m ) g a l / m i n . P e r i o d i c samples o f t h e e f f l u e n t
w e r e t a k e n and a n a l y z e d . Each r u n w a s c o n t i n u e d u n t i l "b reak th rough" o f t h e column, as e v i d e n c e d by a f a i n t y e l l o w c o l o r a t i o n o f t he e f f l u e n t , o c c u r r e d . If t h e s o l u t i o n i n t he Feed Tank w a s depleted b e f o r e b r e a k t h r o u g h , t he run w a s i n t e r r u p t e d u n t i l a new batch o f waste stream s o l u t i o n w a s t r a n s f e r r e d t o t h e Feed Tank and p H a d j u s t e d . A f t e r w a r d s
t he r u n w a s c o n t i n u e d u n t i l b r e a k t h r o u g h .
A f t e r a c a r b o n column was e x h a u s t e d , it w a s r e g e n e r a t e d w i t h
a 1 0 % s u l f u r i c acid s o l u t i o n a t a p H o f 1 . 8 . T h i s s o l u t i o n w a s pumped from t h e R e g e n e r a t i o n Tank a t a f low r a t e o f a b o u t 1 g a l / m i n which f l u i d i z e d t h e ca rbon bed t o 5 0 % of i t s o r i g i n a l h e i g h t . This s t r i p p i n g step w a s per formed f o r 1-2
h o u r s . An o v e r n i g h t soak i n t he same s o l u t i o n w a s added
d u r i n g t h e c o u r s e o f t he t es t . A f t e r t h e o v e r n i g h t soak , the acid s t r i p p i n g step would be r e p e a t e d . The r e s u l t i n g
6-1
,
c o n c e n t r a t e d t r i v a l e n t ch romium/su l fu r i c acid s o l u t i o n w a s r e t u r n e d t o t h e Regene ra t ion Tank where it c o u l d be r e u s e d f o r s t r i p p i n g a n o t h e r column o r d i r e c t e d t o t he EMR f o r chromium r e c o v e r y . The column w a s t h e n water washed t w i c e w i t h one s t a n d i n g bed volume o f f resh c i t y w a t e r . The
ca rbon w a s t h e n p r e t r e a t e d w i t h a d i l u t e p H 2 . 1 a c i d s o l u t i o n a t a f low r a t e of 1 0 0 0 ml/min f o r 30 minu tes b e f o r e b e i n g placed back i n service.
The ch romium/su l fu r i c a c i d s o l u t i o n from the a c i d r e g e n e r a t i o n p rocedure w a s t h e n p r o c e s s e d t h r o u g h t h e EMR
u n i t . T h i s s o l u t i o n w a s p H a d j u s t e d t o 2 . 0 - 3 . 5 u s i n g c a u s t i c soda f lakes , and r e c i r c u l a t e d from the Regene ra t ion Tank t h r o u g h t h e EMR u n i t a t a f low r a t e o f 2-3 ga l /min . The EMR u n i t w a s o p e r a t e d a t v a r i o u s power s e t t i n g s r a n g i n g from abou t 6 - 1 0 v o l t s and 20 - 1 4 0 amps. The c a t h o d e s w e r e removed and t h e r ecove red p r o d u c t scraped o f f , a i r d r i e d and t h e n weighed. The we igh t o f t he p r o d u c t w a s r e c o r d e d as w e l l as t he power s e t t i n g s ( v o l t a g e and ampere r e a d i n g s ) and ampere t o t a l i z e r r e a d i n g . T h e e l e c t r o l y z e d s o l u t i o n was r e u s e d f o r t he n e x t ca rbon s t r i p p i n g c y c l e w i t h
the p r o p e r p H v a l u e s and c o n t r o l s .
Also , a d d i t i o n s o f t h i o u r e a , sodium t h i o c y a n a t e and sodium s u l f i t e w e r e made t o t he Regene ra t ion Tank, t o enhance p l a t i n g e f f i c i e n c y . T h e GAC and EMR r u n s w e r e conduc ted i n d e p e n d e n t l y and s e p a r a t e l y as t h e y would be i n a commercial i n s t a l l a t i o n .
The f o l l o w i n g var iables were i n v e s t i g a t e d .
GAC EXPERIMENTS VARIABLES
* E f f l u e n t Q u a l i t y - h e x a v a l e n t chromium < 0 . 1 m g / l and t r i v a l e n t chromium level < 1 . 0 mg/l
6-2
I
* E f f l u e n t Chemis t ry - C r , Fe, Cu, p H , c o n d u c t i v i t y , and s u l f a t e s
* S o l u t i o n Parameters - t e m p e r a t u r e , c o l o r i n d i c a t o r s , suspended s o l i d s
* Media R e g e n e r a t i o n - number of c y c l e s media c a n be
r e g e n e r a t e d and p roduce q u a l i t y e f f l u e n t
* S t r i p p i n g S o l u t i o n Reuse - number o f c y c l e s acid c a n be
r e u s e d a f t e r e l e c t r o l y t i c t r e a t m e n t
* S t r i p p i n g S o l u t i o n Volume - amount o f acid needed t o remove t h e C r from the media
EMR VARIABLES
* E l e c t r o l y t i c O p e r a t i o n - v o l t a g e d r o p a c r o s s cel l , ampere f low, and c a t h o d e l o a d i n g (grams)
* Yield - C r p e r c e n t a g e i n r e c o v e r e d o x i d e compound
* EMR Components - e v a l u a t e t h e ce l l i n t e r n a l s , lead and coppe r c a t h o d e s , mechanica l drives and a g i t a t i o n
* EMR S o l u t i o n Chemis t ry - moni to r p H , % acid, C r
l o a d i n g s (grams/ l i te r ) and a d d i t i o n a g e n t s
* Power Consumption - kWh per l b . o f chromium
* Power S e t t i n g - c u r r e n t d e n s i t i e s (amp/sq. f t . )
6 - 3
,
S e c t i o n 7
RESULTS
T h e f o l l o w i n g are s e p a r a t e d i s c u s s i o n s o f t h e r e s u l t s o b t a i n e d from each u n i t o p e r a t i o n d u r i n g t he f i e l d d e m o n s t r a t i o n s t u d y a t J e r s e y Chrome.
GAC COLUMNS
Chromium Removal from Waste S t r e a m by Activated Carbon
S i x t e e n separate r u n s were conduc ted t o e v a l u a t e t he u s e o f t h e GAC columns t o remove chromium from t h e waste s o l u t i o n s . T h e t a b u l a t e d e x p e r i m e n t a l data t a k e n d u r i n g most o f these r u n s a re l i s t ed i n Table A 1 (Appendix) and t h e o v e r a l l r e s u l t s are summarized i n Table 1.
I t s h o u l d be n o t e d t h a t there were s i g n i f i c a n t d i f f e r e n c e s i n t h e c o m p o s i t i o n o f t h e waste s o l u t i o n s b e i n g treated. One a n a l y s i s t a k e n on J e r s e y Chrome's h o l d i n g t a n k on June 2 0 , 1989, Table A2 (Appendix) , showed a chromium c o n t e n t o f 2 7 0 0 m g / l which w a s t o t a l l y h e x a v a l e n t . Ana lyses o f t h e
s o l u t i o n s b e i n g t reated d u r i n g t he t e s t program varied from 4 4 2 m g / l t o 990 m g / l o f h e x a v a l e n t C r ; 0 . 5 m g / l t o 7 .2 m g / l o f Fe; a n d 5 .1 m g / l t o 13 m g / l o f Cu.
I t w a s o b s e r v e d t h a t the i n i t i a l r u n s on each column e x h i b i t e d low removal c a p a c i t y and high e f f l u e n t p H v a l u e s ( 6 - 9 ) . I t w a s l e a r n e d t h a t F i l t r a s o r b 4 0 0 , a c o a l - b a s e d
p r o d u c t , has a high ash c o n t e n t . This a l k a l i n e ash was leached o f f t h e ca rbon s u r f a c e when t h e h e x a v a l e n t chromium c o n t a c t e d it r e s u l t i n g i n h i g h e f f l u e n t pH and low chromium removal c a p a c i t y . A f t e r 2-3 r u n s t he chromium removal l o a d i n g s i n c r e a s e d , lower e f f l u e n t p H v a l u e s ( 4 - 5 ) w e r e o b t a i n e d and volume t h r o u g h p u t i n c r e a s e d 1 . 7 - 3 . 2 times. T h i s r e s u l t e d from p r o c e s s i n g o f t he ac id ic s o l u t i o n t h r o u g h t h e c a r b o n sys t em which u l t i m a t e l y p r e p a r e d t h e activated c a r b o n s u r f a c e t o maximize chromium removal . T h i s effect is
7-1
RUN t
V a r i a b l e
F e e d C o n c e n t r a t i o n ( m g / l )
pH Influent
pH E f f l u e n t
E f f l u e n t C o n c e n t r a t i o n C r + 6, ( m g / l ) CrTOT, ( m g / l )
V o l u m e T r e a t e d ( l i ters)
A v e r a g e F l o w r a t e ( m l / m i n )
C a r b o n weight per column t , ( g r a m s )
C h r o m i u m Absorbed ( g r a m s )
C a r b o n L o a d i n g (mg CrToT/g c a r b o n )
TABLE 1 ACTIVATED CARBON ADSORPTI~N OF cmomm DATA
2 6 7 8 9 10 11 12 13 14 15 16
450*
4.2
3.2-7.4
0.0-25.0 2.14-25.2
266.5
365
6356 #I
120
18.9
450*
4.3
6.5
18.0 18.0
181.2
386
5675 62
72.5
12.8
450*
4.4
3.5
0.01 1.2
277.6
525
6583 63
111
16.9
442*
4.25
3.1-6.8
.01-68.0 9.8-69.0
325.7
460
6810 62
125
18.4
500
4.1
6.3
8.7 8.8
232.2
400
5448 61
104.5
19.2
500
4.2
5.6
32.0 33.0
305.96
460
5676 t2
137.6
24.2
500
4.2
5.6
--- ---
286.1
464
6356 t3
28.7
20.9
500
4.2
5.0
5.1 8.5
308.8
340
6810 t l
143.1
21.0
470 480 501** 990**
4.2 4.3 4.3** 4.2
3.1-3.6 3.0-3.4 3.6 3.4
.02-5.6 .Ol-10 2.0 1.4 7.5 9.4-11 17 15.6
640.0 186.9 135.9 407.9
510 420 460 502
6356 5902 4994 4994 62 tl t2 t1
191.7 307.2 100.9 130.5
30.2 52.1 20.2 26.1
* A v e r a g e V a l u e ** E s t i m a t e d V a l u e s
' I I 1
i l l u s t r a t e d by t he r e s u l t s o f t h e i n i t i a l r u n s on columns 1,
2, and 3.
The i n i t i a l run , #1, conducted on column #1 e x h i b i t e d v e r y q u i c k b r e a k t h r o u g h . The e f f l u e n t showed y e l l o w c o l o r and pH o f 6 .8 i n less t h a n 2 h o u r s . Approximate ly 60 l i t e r s (15 .9 g a l ) o f r i n s e chromic a c i d had been t rea ted . The feed pH w a s d ropped s l o w l y t o 3.5 b u t t h e e f f l u e n t p H c o n t i n u e d t o i n c r e a s e t o a f i n a l level o f pH 9 . 0 . The r u n w a s t e r m i n a t e d and no f u r t h e r sample a n a l y s i s w a s made.
Column #1 w a s r e g e n e r a t e d and r u n #2 s ta r ted w i t h column #l.
Break th rough o c c u r r e d a f t e r 177 l i t e rs (47 g a l ) w i t h 266.5 l i t e rs (70 .5 ga l ) b e i n g p r o c e s s e d o v e r a l l . T h e e f f l u e n t p H
s t a r t e d a t 2 . 5 and had an end p o i n t o f 7 .5 . Three r u n s were made w i t h t h e feed pH levels a d j u s t e d t o 2 .0 , 2 .5 , and 4 . 0 .
Low p H e f f l u e n t s w e r e n o t e d f o r these r u n s , 3, 4 , and 5, on columns 1 and 2 .
The r e m a i n i n g t e s t r u n s w e r e conduc ted w i t h t h e feed i n t h e
pH r a n g e o f 4.2 - 4 . 5 . The e f f l u e n t from t h e ca rbon sys t em w a s c r y s t a l c lear and water w h i t e . Chromium w a s t h e main metal species p r e s e n t and trace levels o f coppe r and i r o n w e r e a l s o p r e s e n t . I n i t i a l l y , samples of t h e e f f l u e n t w e r e c o l l e c t e d e v e r y hour and a n a l y z e d . These v a l u e s as l i s ted i n GAC r u n s 2, 7, and 8 showed h e x a v a l e n t chromium levels o f 0 . 0 , 0 . 0 1 , and 0 . 0 1 , r e s p e c t i v e l y and t o t a l chromium v a l u e s o f 2 .1 , 1 . 2 , and 9.8, r e s p e c t i v e l y (Table A l ) . The chromium v a l u e s p r e s e n t e d i n Table 1 are e f f l u e n t samples t a k e n a t b r e a k t h r o u g h based on c o l o r i n d i c a t i o n . T h i s e x p l a i n s why t h e y are higher t h a n t h e 0 . 1 o r 1 0 m g / l f o r h e x a v a l e n t o r t o t a l chromium, r e s p e c t i v e l y . T h e e f f l u e n t from t h e ca rbon columns w i l l r e q u i r e p o l i s h i n g t o g u a r a n t e e less t h a n 1 . 7
m g / l t o t a l C r e f f l u e n t q u a l i t y . Removal levels f o r chromium were i n t he 94-99% r a n g e and f o r coppe r and i r o n 97-99% as can be d e t e r m i n e d from Table A l .
7-3
4
Figure 3 shows chromium removal as a function of the volume throughput. Chromium removal was relatively independent of volume treated with the exception of runs 6, 13 and 14. Examination of the data in Table 1 shows a generally increasing carbon loading value for each column as use increased. For example, the sequential values for Column #1 were 18.9, 19.2, 21.0, 52.1, and 26.1 milligrams of chromium per gram of carbon (mgCr/gC). For Column #2 the values were 12.8, 18.4, 24.2, 30.2, and 20.2 mgCr/gC. For Column #3 the values were 16.9 and 20.9 mgCr/gC. These data suggest that the columns had not been completely conditioned, as described before, and that the increasing use of them completed conditioning of the media surface. No explanation for the lower values obtained in runs 15 and 16 can be given. However, the removal values for runs 13 and 14 approximate the range 30-40 mgCr/gC reported in the literature (6). -
Acid Stripping and Carbon Regeneration
The loaded carbon columns were stripped of chromium and regenerated by recirculating a 10% sulfuric acid solution through them while controlling its pH at 1.8. If pH was not controlled it would slowly increase upon contact with the carbon. The color of the acid stripping solution upon exiting the carbon column was violet blue. Initially, the stripping step was performed for 1-2 hours.
It was observed that when the acid solution was left in contact with the carbon overnight, an additional 14% of trivalent chromium could be recovered. Consequently, a soak period and subsequent rinses were added to the stripping procedures.
The carbon adsorption/acid regeneration cycle was performed for most of the sixteen runs. For some runs the stripping
7-4
E 1
.r(
E 0 k
3 cw 0
d 0
r a
8 u
+
0 0 m
0 0 m
0 m m 0 m 4
8 4
0 m
7-5
s o l u t i o n w a s u sed more t h a n one t i m e t o c o n c e n t r a t e t he
amount o f chromium i n t h e s o l u t i o n . S i x d i f f e r e n t s o l u t i o n s w e r e o b t a i n e d by these s t r i p p i n g p r o c e d u r e s . The
e x p e r i m e n t a l data f o r these s t r i p p i n g r u n s are l is ted i n Table 2 . More t h a n 99.7% o f t h e chromium removed from the
columns w a s t r i v a l e n t chromium. Ana lyses o f t h e r e g e n e r a n t f rom GAC r u n s 9, 13, and 1 4 show t h a t coppe r and i r o n w e r e a l s o removed from t h e waste stream by t h e ca rbon columns.
Chromium r e c o v e r y p e r c e n t a g e s achieved by acid s t r i p p i n g t h e
c a r b o n column ranged from 13.5-96.6%.
GAC R i n s i n g and P r e t r e a t m e n t
B e f o r e b e g i n n i n g t h e n e x t chromium removal c y c l e , t h e GAC
had t o be w a t e r r i n s e d and pretreated. I n i t i a l l y , o n l y two w a t e r r i n s e s w e r e u s e d t o c o n s e r v e t h e amount o f r i n s e water needed a f te r s t r i p p i n g t he chromium from the ca rbon . The
two water r i n s e s r e c o v e r e d a n average o f 750 and 370 m g C r / l
r e s p e c t i v e l y w i t h a maximum c o n c e n t r a t i o n o f 900 m g C r / l .
The w a t e r r i n s i n g r e s u l t e d i n two separate s o l u t i o n s o f t r i v a l e n t chromium. Both s o l u t i o n s w e r e v i o l e t i n c o l o r w i t h t h e f irst r i n s e s o l u t i o n b e i n g darker. The pH 6 .8 r i n s e water, e x i t e d t h e c a r b o n column a t pH 2 .1 .
A f t e r water r i n s i n g , a weak acid r i n s e w a s u s e d t o es tabl ish the p r o p e r ac id i c s u r f a c e c o n d i t i o n s on t he ca rbon s u r f a c e . The weak acid r i n s e w a s r e c i r c u l a t e d t h r o u g h t h e ca rbon column a t a f l o w r a t e o f 1 0 0 0 ml/min. T h e p H w a s c o n t r o l l e d between 2 . 1 - 2.5. T h i s r i n s e w a s obse rved as a clear e f f l u e n t a t t h e e n d of t h e r i n s e p e r i o d . The ca rbon column w a s t h e n r e a d y f o r t he n e x t chromium removal c y c l e .
When a c a r b o n column t h a t w a s acid r e g e n e r a t e d , w a t e r r i n s e d , and acid pretreated c o n t a i n e d water o v e r n i g h t , a 1-2 i n c h b l u e - v i o l e t h a z e c o u l d be obse rved i n t h e s o l u t i o n on t h e t o p o f t h e ca rbon bed. T h i s i n d i c a t e d t h a t some
7-6
a c
0 r l o o m w w r J m o m 0 3 o r l m d t - m o m m o t - w o r l o m rl m m m
0 0 3 1 l m m m o w . I I
d o l I N m m m r J w w m o w 0 3 w u ) r l r l r l
0 0 3 1 I r l m m o m o m 1 I N m m o c n o m m 0 3 r J w w m d r(
* I I
A
rl \
Y 8 .
m + & u
A
rl \
Y 8 .
& a, a a 0 L,
4 \
Y 8 .
C 0 & H
X a tn C -4 a a -4 & U v1
A
$ & tn
a a,
0
4
Y
f! 4 5 -4
& c u
7 - 7
1
additional trivalent chromium remained in the column after stripping and pretreating.
This phenomenon was further investigated in GAC runs 11 and 12 by leaving a third water rinse in the column overnight. The chromium concentrations of the three rinses are tabulated in Table A3 (Appendix) and shown in Figure 4 . The chromium concentrations of the first rinse from Runs 11, 12, 13, and 1 6 ranged from about 5 6 0 mg/l to about 770 mg/l. The concentrations for the second rinses from these runs ranged from about 3 5 0 to 550 mg/l. In comparison, the chromium concentrations from the third rinses for Runs 11 and 12 were about 700 and 900 mg/l, respectively.
The hexavalent chromium concentrations in the rinses were very low averaging 0 . 8 mg/l with nine runs at 0.1 mg/l. The trace metals of copper and iron were also present in the rinse solutidns with average concentrations of 3 8 and 3 0 mg/l, respectively.
Electrolytic Metal Recovery
The stripping procedures described above produced six solutions which could be processed in the EMR unit. A total of nine EMR runs were made from five of these solutions. These concentrated trivalent chromium/ sulfuric acid solutions from the acid regeneration procedure were pH adjusted to 2 . 0 - 3 . 5 , and processed in the EMR unit to recover the contained chromium. The EMR unit was operated at various power settings ranging from about 6-10 volts and 2 0 - 1 4 0 amps. Each recovery run lasted about 4 hours. The experimental data from the nine EMR runs are reported in Tables A4 and A5 (Appendix) and summarized in Table 3. During the early runs, it was observed that very little cathode deposit was obtained at less than 7 volts. This observation suggests the existence of a threshold voltage or current density. It was also observed that higher voltages
T 0 T A L
C H R 0 M I U M
M Z G
I L
-
1400 -
1200 -
1000 -
800 -
600 -
400
200 -
0
Figure 4 - Rinse Water Data Summary
Run #11
COLUMN 1 I COLUMN 3
Run #13 Run #16
COLUMN 2 ' COLUMN 1
COLUMNS RINSED I
TABLE 3 SUMMARY OF ELECTROLYTIC METAL RECOVERY DATA
Variable T i m e CrTOT (mg/l) % C r Chromium Average Avg. Deposi t ion Avg. Chromium ( H r s . ) I n i t i a l F i n a l Recovered Recovered, g Current (amp) kwh Rate ( g / h . ) Y i e l d (g/kWh)
EMR RUN #
A
F
G
I
6.5
3.6
1 . 9
2 .6
6 6 1 623 5.7
2050 1650 19.5
1650 1600 3.0
2030"" 1650 10.2
5.3
48.4
6 .1
35 :2
5.0 1 .66
33.0 2.97
40.0 0 .80
30.0 1 .69
0 . 8 1
13.44
3 . 2 1
13.54
6.38*
16.30
7.63
20.83
4 I P 0
*EMR contained on ly 2 cathodes; average recovery ra te calculated assumed 4 cathodes. S t a r t i n g c o n c e n t r a t i o n of s o l u t i o n was 3000 mg/l b u t 35.9 l i t e rs of w a t e r wi th 500 mg/l of C r + 3 was ** added t o f i l l t h e h y d r a u l i c c i r c u i t .
did n o t s i g n i f i c a n t l y i n c r e a s e t h e r a t e of d e p o s i t i o n . T h i s
s u g g e s t s a need f o r g r e a t e r mass t r a n s p o r t t o t h e c a t h o d e . On t h i s bas i s , t h e p r e f e r r e d o p e r a t i n g c o n d i t i o n s f o r t h e
r ema in ing r u n s w e r e about 7 -7 .5 v o l t s and 1 2 0 - 1 4 0 amperes .
I t w a s a l s o obse rved t h a t there was v e r y l i t t l e , i f any, d e p o s i t on t he lower p o r t i o n o f t h e c a t h o d e which e x t e n d e d below t h e anode. Th i s i s a f u r t h e r i n d i c a t i o n t h a t
d e p o s i t i o n d o e s n o t occur a t low c u r r e n t d e n s i t i e s .
The d e p o s i t on t h e c a t h o d e s i n t h e c e l l w a s a l o o s e and powdery form o f chromium o x i d e as shown i n F i g u r e 5. A
t y p i c a l d e p o s i t a f t e r removal from t h e c a t h o d e by s c r a p i n g i s shown i n F i g u r e 6. The w e i g h t s o f t h e c a t h o d e d e p o s i t s w e r e r e c o r d e d f o r each run and on some r u n s t h e w e i g h t s w e r e
r e c o r d e d on an i n d i v i d u a l c a t h o d e bas i s . The r e c o v e r e d p r o d u c t we igh t s ranged from 7 .2 -78 .7 grams. A f t e r weighing, t h e m a t e r i a l from each run w a s s t o r e d i n a common c o n t a i n e r .
Most o f t h e c a t h o d e d e p o s i t s w e r e a b lue -g reen s l a t e c o l o r .
Two d e p o s i t s , however, w e r e g r e e n . A n a l y s i s o f these d i f f e r e n t c o l o r e d r e c o v e r e d p r o d u c t samples are p r e s e n t e d i n Tab le 4 .
The EMR s o l u t i o n s c o n t a i n e d copper and i r o n a f t e r s t r i p p i n g t h e ac t iva ted ca rbon columns. A mass b a l a n c e w a s per formed and based on chromic acid feed c o n c e n t r a t i o n s , t h e
t r i v a l e n t / s u l f u r i c acid s o l u t i o n s f o r t he EMR r u n s c o n t a i n e d o v e r two t i m e s as much copper as removed by t h e ca rbon . I t
a p p e a r s t h a t t he copper c a t h o d e s were etched by t h e EMF. s o l u t i o n and caused t h e h igher copper c o n c e n t r a t i o n s . I r o n c o n c e n t r a t i o n s w e r e a l s o p r e s e n t a t levels higher t h a n feas ib le b a s e d on a mass b a l a n c e . The s o u r c e of t h e i r o n c o n t a m i n a t i o n w a s u n c e r t a i n .
7-11
7-12
7-13
Sample
Blue Color (1)
Blue Color ( 2 )
Green Color
Table 4 - Cathode Deposit (WT % )
Total Chromium Copper Iron Lead
36.7
27.5
1 2 . 6
21.0
13 .7
43.0
8.0 8 .3
5.5 7 .5
12 .4 1 0 . 3
7-14
P
Solution Additives
The EMR solution was oxidized during the runs as evidenced by a greenish-yellow color of the solution. In three of the early runs, sodium sulfite was added to the EMR solution to prevent oxidation of the trivalent chromium. Additions in the range of 10-300 mg/l were made. Large additions reduced the hexavalent chromium as indicated by a change in the solution to a predominantly blue color, but these had a negative effect on the process. After the additions, current flow would remain constant or decrease and the weight of recovered product was insignificant.
This effect was investigated by periodically replacing the cathodes during runs and obtaining product weights for several time intervals throughout the runs. The resulting data for run E with sodium sulfite additions and run F without any additions are shown in Figure 7. For both runs the deposition rate for the first hour of recovery was high. For run E, the average hourly deposition rate for cathodes withdrawn after 2, 3, and 4 hours dropped significantly indicating a marked decrease in deposition rate. For run F, however, the hourly rate remained high for the first three hours and decreased after four hours. As a result of these data the use of sodium sulfite was discontinued.
The effects of two plating additives, sodium thiocyanate and thiourea, were also evaluated. Additions of 10-40 mg/l were made. Sodium thiocyanate was used most of the time. The following observations were made: (1) cathode deposits appeared wetter or shinier and (2) the electrical current reading increased 5-10 amps after a chemical addition was made, and electrical efficiency was increased by 15.9%. The impact of this addition on plating efficiency will require more investigation. Small quantities of the additive were used so this area has promise.
7-15
Figure 7 - Effect of Sodium Sulfite On Product Deposition Rate
7 1 6.7 NO CHEMICAL ADDITION
5.9 EMR - RUN F
4.5 INTERVAL
PRODUCT WEIGHT PER
(GRAMS/HR) 4.6
2.9
T 1 SODIUM SULFITE ADDITION EMR-RUNE
I I 1 1 I 0 ' 1I 2l 3 ' 4l I 5 l
HOURS
7-16
EMR S o l u t i o n Reuse A s described ear l ie r , t he s o l u t i o n would change from b l u e t o g r e e n a f t e r t he f i rs t hour o f o p e r a t i o n and l a t e r t o a g r e e n i s h y e l l o w c o l o r . Ana lyses o f t h e s o l u t i o n s a f t e r t he
n i n e r u n s showed the h e x a v a l e n t chromium c o n c e n t r a t i o n s i n t h e s p e n t s o l u t i o n s r anged from 259-870 m g / l . T h i s w a s 31%
t o 51% o f t h e i n i t i a l t r i v a l e n t chromium c o n c e n t r a t i o n s .
Reuse o f these s p e n t EMR s o l u t i o n s w a s e v a l u a t e d by r e d u c i n g t h e p H t o 1 . 8 and p r o c e s s i n g t h e s o l u t i o n s t h r o u g h e x h a u s t e d c a r b o n columns. There w a s a change i n t he s o l u t i o n c o l o r f rom g r e e n i s h - y e l l o w t o b l u e a f t e r 1-2 h o u r s o f r e c i r c u l a t i o n t h r o u g h t h e ca rbon column. A l s o t h e b l u e c o l o r would i n t e n s i f y a f t e r an o v e r n i g h t soak and s u b s e q u e n t
r e c i r c u l a t i o n . One r u n r e q u i r e d 3 c y c l e s o f s o a k i n g / r e c i r c u l a t i o n t o r e t u r n t h e s o l u t i o n t o a d a r k b l u e c o l o r . A n a l y s e s showed t h a t t h e h e x a v a l e n t chromium p r e s e n t i n t h e s p e n t EMR s o l u t i o n w a s r educed by t he activated c a r b o n w i t h
o v e r 99% r e d u c t i o n e x h i b i t e d f o r t h e three r u n s . S t r i p p i n g
o f t h e column w a s i ncomple t e , and a d d i t i o n a l work i s r e q u i r e d t o e s t a b l i s h p r o c e d u r e s t o r e g e n e r a t e e x h a u s t e d c a r b o n columns w i t h s p e n t EMR s o l u t i o n .
Recovery o f chromium from t h e " r e g e n e r a t e d " EMR s o l u t i o n s appeared t o e q u a l t h a t o f v i r g i n t r i v a l e n t c h r o m i u m / s u l f u r i c
acid s o l u t i o n s . EMR r u n s D, F, and H w e r e made w i t h r e g e n e r a t e d EMR s o l u t i o n s .
Chromium Recovery
S o l u t i o n a n a l y s e s were per formed on f o u r of t h e EMR r u n s t o c a l c u l a t e t h e amount of chromium metal r e c o v e r e d on a mass b a l a n c e basis . These c a l c u l a t i o n s are shown i n Table 3. The c a l c u l a t e d r e c o v e r i e s r a n g e from 5.3 t o 48.4 grams which
c o r r e s p o n d t o r e c o v e r y o f 5 .7 t o 19.5% o f t he chromium c o n t a i n e d i n t h e i n i t i a l EMR s o l u t i o n s .
7-17
The average rate of chromium removal is also shown in Table 3 to normalize the difference in the length of the runs. These values ranged from 0.81 for Run A to 13.54 g/hr for Run I. However, as shown above, the deposition rate decreased with time so the value for Run A is understated. Nevertheless, these calculations show that the deposition rate was higher for those solutions with higher initial chromium concentrations.
The average current for these runs was calculated from the amphere-hour meter readings and the length of the run. These calculations show that the lowest deposition rate was obtained for Run A which also had the lowest current (5 amperes for the given cathodes). The current densities for the other runs were similar. Of those, Runs F and I had similar initial concentrations and similar deposition rates. Run G had a much lower deposition rate and it is proposed that the low rate is the result of the high ratio (40%) of hexavalent chromium to trivalent chromium in the initial solution.
Power Consumption
Table 3 shows the average yield of chromium metal per kWh. These values reflect the trends shown for the deposition rates. The highest yields obtained were 16.3 and 20.8 g/kWh for Runs F and I, respectively. These values represent the average for the length of the run and are understated because, as indicated by Figure 7, the deposition rate decreases with time.
7-18
S e c t i o n 8
CONCLUSIONS
Al though a number o f e x p e r i m e n t a l d i f f i c u l t i e s w e r e e n c o u n t e r e d d u r i n g t h e t r i a l , the r e s u l t s o f t h e program i n d i c a t e d t h a t t h e ENVIRO-CLEAN PROCESS can be used t o
r e c o v e r chromium from an i n d u s t r i a l waste water. The g r a n u l a r a c t i v a t e d ca rbon columns e f f e c t i v e l y removed chromium from t h e waste water . R e s i d u a l q u a n t i t i e s of
coppe r and i r o n were a l s o removed. T h e columns w e r e s u c c e s s f u l l y r e g e n e r a t e d and t h e r e s u l t i n g r e g e n e r a t e s o l u t i o n w a s p r o c e s s e d i n t h e E l e c t r o l y t i c Metal Recovery u n i t . Chromium ox ide d e p o s i t s were produced w i t h a chromium metal y i e l d o f abou t 16 -21 g/kWh. These d e p o s i t s c o n t a i n e d r e s i d u a l q u a n t i t i e s of coppe r and i r o n .
8-1
S e c t i o n 9
RECOMMENDATIONS
On t h e basis o f t h i s program, it i s recommended t h a t t h e
f o l l o w i n g areas be c o n s i d e r e d f o r f u r t h e r s t u d i e s t o d e v e l o p t he ENVIRO-CLEAN PROCESS.
1.
2.
3.
4.
5. 6.
7 .
a .
Improved column d e s i g n and u s e t o i n c r e a s e chromium l o a d i n g .
Improved column r e g e n e r a t i o n t o i n c r e a s e t he c o n c e n t r a t i o n o f chromium i n t h e r e g e n e r a t e . Improved a g i t a t i o n t o i n c r e a s e mass t r a n s p o r t i n t he
E l e c t r o l y t i c Metal Recovery p r o c e s s . P r e v e n t i o n o f t r i v a l e n t chromium o x i d a t i o n i n t he
E l e c t r o l y t i c Metal Recovery p r o c e s s . E v a l u a t i o n o f improved anode-cathode mater ia ls . E v a l u a t i o n of t he effect o f r e s i d u a l i m p u r i t i e s on t h e
economic v a l u e o f t h e r e c o v e r e d p r o d u c t . Improved s y s t e m d e s i g n t o i n c o r p o r a t e u s e o f t h e p r o c e s s r i n s e s . Per form a n economic a n a l y s i s o f the p r o c e s s .
9-1
. I
Section 10
BIBLIOGRAPHY
1.
2 .
3.
4.
5.
6 .
7.
Schofield, W.R. "Incineration: Technology; Marketplace, It
reprint, ITDHW, September 23, 1987.
Nemerow, N. "Industrial Water Pollution: Origins, Characteristics, and Treatment, Addison-Wesley Publishing, Reading, 1978.
EPS of Canada. "Technology Transfer Seminar on Waste Handling, Disposal and Recovery In The Metal Finishing," Industrial Report No. EPS 3-WP-77-3, November 12, 1975, p. 53.
"RECOVERY OF CHROMIUM FROM COOLING TOWER BLOWDOWN STREAMS, Disclosure Statement to U.S. Patent Office, filed March 3, 1987.
"HEAVY METAL RECOVERY FROM WASTEWATER, Disclosure Statement to U.S. Patent Office, filed March 3, 1987.
Lewis, T.A. "Method and Apparatus For Heavy Metal Recovery Process, patent application to U. S. Patent Office, filed July 29, 1989.
Logozzo, A. "Chromium Plating", Metal Finishing Guidebook and Directory, February 20, 1979, p. 188.
10-1
APPENDIX
EXPERIMENTAL DATA
m * rl * N * m * N * rl * N *
In W m
W 43 m
In N In
0 W w
0 0 w
0 W w
w W w
N N W N w
w m m w l - . . . . . mLn
w w . . w m
w m . . r l m
w w e .
r-4 I ' 0
rl I - O
ol-
0 4 3 v) w
* .
0 4 3
0 4 3 0 In
. .
N
N m N
N W . . mu) w I n . . In
d
0
v ) r l r l I . . . 0 0 0
V
I I I l l
I l l
I
I
&
I
I
&
I
m d r l I . . .
w o o V
rl I ' 0 I I I
& .. rl 0 0
0 0 0 cy
. . rl 0 0 0 0
w o o 4 3 w v ) w m w
. e . . 0 0 0 o o o o r l
O O O L n C u 0 N W w rl
. . . . . 0 0
0 4 3 o r l w
. . O N 0 I n m I n 1 cr w
* o r l r l m w O N d I n N v) N W w rl
. . . . . * 0 0 . . *
O N
O d v) w
. . 00430 . . . . 0 0 e . 0
0 4 3 v)rl w
v o m m 4 3 0 w m l n
- o m o m 0 In 0 1
In
v)
W W N
W
l- l- N
d m
W 43 N
In 0 m
m m 43
I
m 43
m 43 I rl rl I 01
m 43 I
m rl I m
0) 43 I
W I m
43 I 21 z
a i N I I
43 . -.
W
11-1
TABLE A1 ADSORPTION REMOVAL DATA (page 2)
V o l u m e TOT -- D a t e L i t e r s CR
HEX CR
F l o w r a t e pH m l / m i n C o l u m n # C o p p e r I r o n RUN #
#12 Feed eff #1
9 -2 0 -- 8 9 500.0
308.8 8.5
340 #1 4.2 5.0
450.0 5.1
#13 Feed eff #1 eff #2
510 4.2 3.1 3.6
9-2 8- 8 9 #2 470.0 7.5
407.9 7.5
460.0 0.02 5.6
6.0 0.6 0.2 0.1 0.1 0.1
#14 Feed (1) Feed (2) eff #1 eff #2 eff #3
420 4.3 4.2 3.3 3.5 3.7
10-2-89 #1 480 -0 480.0 9.4 3.1
640 11.0
360.0 470.0
0.01 0.01 10.7
6.5 7.2 5.3 0.6 0.3 0.2 0.1 0.1 0.1 0.1
#2 #15 Feed (1) Feed (2) eff #1
10-10-89 501.0 622.0
189.6 17.0
460 4.2 4.4 3.6
480.0 600.0 2.0
5.1 0.9 7.7 2.2 1.2 0.2
#16 Feed (1) Feed (2) eff #1
10-12-89 950.0 1026.0
135.9 17.0
502 4.2 4.2 3.4
#1 920.0 1000.0
1.4
12.0 3.0 13.0 2.4 1.5 0.3
* E s t i m a t e d V a l u e s
b
TABLE A2 JERSEY CHROME RINSE WATER CHARACTERIZATION*
Test
PH
Suspended Solids
TOC
COD
Hexavalent Chromium
Trivalent Chromium
Total Chromium
Sulfates
C hl o rides
Iron
Copper
Lead
Sodium
Hardness as CaC03
Result Mq/L
1.6
6
23
455
2700 -
2700
140
Nil
57
25
0.6
30
Nil
* Pittsburgh Applied Research Corporation report of June 20, 1989
11-3
TABLE A3 WATER RINSE DATA
Resu l t s i n mg/l RUN # Date T o t a l C r Hex C r T r i C r pH Copper
Run #11 9-28-89 column #3 r i n s e #1 770 r i n s e #2 550 r i n s e # 3 10-2-89 700
Run #12 column #1 r i n s e #l 9-28-89 640 r i n s e #2 390 r i n s e #3 10-2-89 900
Run #13 column #2 r i n s e #1 10-5-89 720 r i n s e #2 350
.1 769.9 2
.01 549.99 2
.03 699.97 2 - 2 (overn ight soak)
-01 639.99 2 .01 389.99 2.1 -33 899.67 1.9 (overn ight soak)
2.88 717.12 2 - 2 4.22 345.78 2.1
I ron
Run #16 column #1 r i n s e #1 10-18-89 560 1.6 558.4 2.3 36 29 r i n s e #2 390 1.26 388.74 2.2 40 30
Each r i n s e used one bed volume of c l e a n water . The f i r s t and second r i n s e s were g r a v i t y d r a i n w i t h about 15-30 minutes holding t i m e .
-.
I ' i
i
2
TABLE A4 ELECTROLYTIC METAL RECOVERY DATA
Time
EMR A-RUN 9-6-89 11:28 AM 12:oo AM 12:45 AM 1:OO P M 2:30 P M 3:OO P M 5:15 P M 6:OO P M
EMR B-RUN 9-11-89 12:oo AM 12:30 AM 1:OO P M 2:25 P M
2:45 P M 4:OO P M 4:20 P M
EMR C-RUN 9-13-89 12:oo AM 2:OO P M 2:30 P M 3:OO P M 4:OO P M
Solution pH
2.3 2.3 2.3 2.2 3.0 2.6 2.5 2.7
2.2 2.2 2.1 2.5
2.5 2.5 2.5
2.6 2.5 2.5 2.5 2.5
Voltage Amp-Hrs Totalizer Reading Reading Amp-Hrs Comments
7.2 20 7.0 20 7.4 20 7.4 22 9.2 26
10.0 36 10.2 38
10 -21 33
160 pH controlled at 2.3 704 1715 2222 noticed black film on cathode 4240 increased voltage setting 5137 increased voltage setting 9904 increased pH setpoint to 3.1
11614 12 grams of product recovered
10.0 32 2670 pH controlled at 2.3 10.0 31 3637 used NaS03 and NaSCN 10.0 32 4540 made chemical addition 10.1 30 7124 removed set of cathodes, shut down
10.2 29 716 solution turned blue to green 10.3 30 1895 added NaSCN (30 grams) 10.3 30 24.5 NaS03 addition each hour
run, replaced cathodes
20 (12/8) grams of product
10.5 10.2 10.2 10.4 10.0
25 32 32 32 33
137 3468 NO COMMENTS 4758 5566 7436 7.2 grams of product recovered
Time EMR D-RUN 9-20-89 1:30 PM 2:OO PM 2:30 PM 3:OO PM 4:OO PM 4:OO PM
EMR E-RUN 9-21-89 11:oo AM 11:30 AM 12:lO AM 1:OO PM 1:30 PM 2:00 PM 2:30 PM 3:OO PM
EMR F-RUN 9-29-89 11:oo AM 11:30 AM 12:oo AM 1:OO PM 1:30 PM 2:lO PM 2:30 PM
Solution pH
2.2 2.2 2.2 2.2 2.2 2.2
2.0 2.2 2.3 2.1 2.3 2.3 2.3 2.3
2.6 2.4 2.4 2.4 2.4 2.4 2.4
TABLE A4 ELECTROLYTIC METAL RECOVERY DATA (cont'd. page 2)
Vo 1 t age Reading
7.0 7.5 7.0 7.8 7.6 7.8
7.0 7.0 7.0 6.8 6.8 6.8 6.3 6.1
7.4 7.2 7.0 6.8 7.2 7.0 6.5
Amp-Hrs Totalizer Reading Amp-Hrs Comments
104 1030 pH controlled at 2.2 117 3096 solution turned green - - added NaSCN and NaS03 12 6 10306 made NaSCN addition
made NaS03 addition 12 8 17356 138 21369 38.5 grams of product recovered
100 115 122 130 12 9 140 123 122
- 4082 8079 11300 14321 22419 26132 29133
pH controlled at 2.2 NaSCN addition, color green NaS03 addition pH dropped to 1.9 readjusted made chemical additions NaS03 addition reduced volts to 6.3, 120 amps 34.4 grams of product recovered
96 - pH controlled at 2.5 106 3419 solution color blue 116 6640 only one addition made 130 13500 138 17458 139 22520 reduced voltage to 6.5, 128 amps 130 25627 78.7 grams of product recovered
T i m e EMR G-RUN 10-2-89 2:05 PM 2:35 PM 3:15 PM 4:OO PM
EMR H-RUN 10-5-89 9:oo AM 9:55 AM
10:45 AM 11:15 AM 12:oo AM
EMR I-RUN 10- 11- 8 9 12:30 AM 12:45 AM 1:lO PM 1:30 PM 2:oO PM 2:15 PM 3:05 PM
Solu t ion pH
2.5 2.6 2.7 2.7
3.0 3.0 2.9 2.9 2.8
3.3 3.0 2.7 2.6 2.6 2.6 2.6
TABLE A4 ELECTROLYTIC METAL RECOVERY DATA ( con t ' d . page 3)
Vo It age Amp-Hrs T o t a l i z e r Reading Reading Amp-Min Comments
6.0 56 - no pH c o n t r o l and no r e c i r c u l a t i o n 6.0 74 1540 NO COMMENTS 6.0 87 4500 s o l u t i o n green-yellow c o l o r 6.0 88 8000 11.9 grams of product recovered
ph c o n t r o l l e d a t 3 . 0 7.2 75. - 7.0 92 1835 NaSCN add i t ion , c o l o r green 6.8 114 6609 a d j u s t e d v o l t s t o 7.0 7.0 132 10564 pH slowly dropping 6.6 132 16890 18.9 grams of product recovered
7.0 38 7.2 48 7.2 60 7.0 66 7.2 73 8.6 118 8.6 142
- NaSCN add i t ion , s o l c o l o r b l u e 400
1655 2820 i nc reased a g i t a t o r speed 4726 i nc reased v o l t s t o 8.5, 106 amps 7162 added NaSCN (1 gram)
13178 51.9 grams of product recovered
TABLE A5 SUMMARY OF ELECTROLYTIC METAL RECOVERY ANALYSES
EMR RUN # A B C D E F G H I
Variable
661
-- 740
8.6
7.6
1650*
61
24
3000**
98
100
2050
65
43 Iron (mg/l) --
Effluent Concentration C r + 6 , (mg/l) 259 640
1010
1650
61
24
121
3.6
120.35
7.0
2.97
78.7
870
730
1600
78
24
121
1.9
76.3
6.0
0.80
11.9
62 6
1024
1650
113
48
92.6
2.6
77.9
7.7
1.69
51.9
364
623
--
I r o n (mg/l)
System Volume
--
139.9 --
5.4
29.5
10.3
1.64
20.6
-- --
3.7 4.0
101.7 124.1
7.5 6.7
2.78 3.27
38.5 34.4
--
2.5
109.0
6.9
1.95
18.9
4.0
Average amp-hrs 29.9 30.7
10.3 Average Voltage 8.6
Power (kWh) 1.66 1.27
7.2 Product Recovered (grams) 12.0
.-
I N i
The Center for Materials Production is an R&D applications center funded by the Electric Power Research Institute and operated by Carnegie Mellon Research Institute, Carnegie Mellon University.
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