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77 TREATMENT PROCESSES AND ECONOMIC EVALUATION OF CARBONATE REDUCTION AND CYANIDE REMOVAL FROM AN ELECTROPLATING SOLUTION C. Peter Varuntanya, Project Manager Kathleen M. Lagnese, Project Engineer Chester Environmental Pittsburgh, Pennsylvania 15244 INTRODUCTION In the electrogalvanizing process, cyanide contained in the zinc cyanide plating bath breaks down to form carbonate which eventually supersaturates the plating solution. This supersaturated carbonate solution interferes with the plating process and reduces the production efficiency of the electrogalvanizing line. In order to reduce the concentration of carbonates that tend to accumulate in the plating bath solution, two separate treatment processes are currently employed at the subject facility which produces electrogalvanized strip steel. One system involves chilling the solution to 58 — 60°F for one to two days to precipitate the carbonate as sodium carbonate crystals. The crystals, which contain cyanide within or on the crystalline structure, are collected in baskets at the base of the chiller. Following the treatment, the baskets are removed and the crystals are stored temporarily in drums prior to off-site disposal as a hazardous waste. The liquid is recycled to the plating baths. Because the capacity of the chiller system is limited, another separate treatment system was installed to treat additional plating bath. This system uses lime to precipitate carbonate as calcium carbonate. Following precipitation, the solution is pumped through a filter press for dewatering. The filter cake, which also contains cyanide, is collected in roll-off boxes and sent off-site for treatment and disposal as a hazardous waste. The filtrate is recycled to the plating baths. The current cost for disposal varies depending on the cyanide content of these two solid wastes. A study was conducted to identify alternative methods to minimize the disposal costs. In addition, any wastewater generated by the proposed treatment methods was required to meet the pre-treatment standards for discharge to the Publicly Owned Treatment Works (POTW), after combining with the other wastewaters currently discharged from the electrogalvanizing line. The existing pre-treatment for the electrogalvanizing line discharge is listed in Table I. As shown, the requirements include a total cyanide limit of 1 mg/L. LABORATORY TREATABILITY STUDIES Laboratory treatability studies were performed in two phases. The Phase 1 studies focused on treating aqueous solutions of the sodium carbonate crystals to reduce the concentration of cyanide to an acceptable level for discharge to the POTW. In Phase 2 studies, alternative methods to minimize cyanide concentrations in the calcium carbonate filter cakes generated by the existing lime treatment system were performed. Based on the results of treatability studies, two alternative treatment schemes were developed. The results of the treatability studies are presented below. Phase 1: Treatment of Sodium Carbonate Crystals Waste Characterization Samples from three separate batches of the sodium carbonate crystals generated by the existing chilling system at the facility were collected and analyzed for total solids, total cyanide, total iron, and total zinc. The results of the initial analyses are provided in Table II. The cyanide concentrations in the three samples ranged from 5,040 to 41,000 mg/L. The disparity between the cyanide concentrations in these samples indicates that the quality of the sodium carbonate crystals is highly variable. 48th Purdue Industrial Waste Conference Proceedings, 1993 Lewis Publishers, Chelsea, Michigan 48118. Printed in U.S.A. 763
Object Description
Purdue Identification Number | ETRIWC199377 |
Title | Treatment processes and economic evaluation of carbonate reduction and cyanide removal from an electroplating solution |
Author |
Varuntanya, C. Peter Lagnese, Kathleen M. |
Date of Original | 1993 |
Conference Title | Proceedings of the 48th Industrial Waste Conference |
Conference Front Matter (copy and paste) | http://earchives.lib.purdue.edu/u?/engext,21159 |
Extent of Original | p. 763-776 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital object copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Date Digitized | 2009-11-10 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Resolution | 300 ppi |
Color Depth | 8 bit |
Description
Title | page 763 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital object copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Transcript | 77 TREATMENT PROCESSES AND ECONOMIC EVALUATION OF CARBONATE REDUCTION AND CYANIDE REMOVAL FROM AN ELECTROPLATING SOLUTION C. Peter Varuntanya, Project Manager Kathleen M. Lagnese, Project Engineer Chester Environmental Pittsburgh, Pennsylvania 15244 INTRODUCTION In the electrogalvanizing process, cyanide contained in the zinc cyanide plating bath breaks down to form carbonate which eventually supersaturates the plating solution. This supersaturated carbonate solution interferes with the plating process and reduces the production efficiency of the electrogalvanizing line. In order to reduce the concentration of carbonates that tend to accumulate in the plating bath solution, two separate treatment processes are currently employed at the subject facility which produces electrogalvanized strip steel. One system involves chilling the solution to 58 — 60°F for one to two days to precipitate the carbonate as sodium carbonate crystals. The crystals, which contain cyanide within or on the crystalline structure, are collected in baskets at the base of the chiller. Following the treatment, the baskets are removed and the crystals are stored temporarily in drums prior to off-site disposal as a hazardous waste. The liquid is recycled to the plating baths. Because the capacity of the chiller system is limited, another separate treatment system was installed to treat additional plating bath. This system uses lime to precipitate carbonate as calcium carbonate. Following precipitation, the solution is pumped through a filter press for dewatering. The filter cake, which also contains cyanide, is collected in roll-off boxes and sent off-site for treatment and disposal as a hazardous waste. The filtrate is recycled to the plating baths. The current cost for disposal varies depending on the cyanide content of these two solid wastes. A study was conducted to identify alternative methods to minimize the disposal costs. In addition, any wastewater generated by the proposed treatment methods was required to meet the pre-treatment standards for discharge to the Publicly Owned Treatment Works (POTW), after combining with the other wastewaters currently discharged from the electrogalvanizing line. The existing pre-treatment for the electrogalvanizing line discharge is listed in Table I. As shown, the requirements include a total cyanide limit of 1 mg/L. LABORATORY TREATABILITY STUDIES Laboratory treatability studies were performed in two phases. The Phase 1 studies focused on treating aqueous solutions of the sodium carbonate crystals to reduce the concentration of cyanide to an acceptable level for discharge to the POTW. In Phase 2 studies, alternative methods to minimize cyanide concentrations in the calcium carbonate filter cakes generated by the existing lime treatment system were performed. Based on the results of treatability studies, two alternative treatment schemes were developed. The results of the treatability studies are presented below. Phase 1: Treatment of Sodium Carbonate Crystals Waste Characterization Samples from three separate batches of the sodium carbonate crystals generated by the existing chilling system at the facility were collected and analyzed for total solids, total cyanide, total iron, and total zinc. The results of the initial analyses are provided in Table II. The cyanide concentrations in the three samples ranged from 5,040 to 41,000 mg/L. The disparity between the cyanide concentrations in these samples indicates that the quality of the sodium carbonate crystals is highly variable. 48th Purdue Industrial Waste Conference Proceedings, 1993 Lewis Publishers, Chelsea, Michigan 48118. Printed in U.S.A. 763 |
Resolution | 300 ppi |
Color Depth | 8 bit |
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