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65 EVALUATION OF NONCYANIDE METAL STRIPPERS Stuart K. Janikowski, Scientist Peter A. Pryfogle, Senior Scientist Idaho National Engineering Laboratory Idaho Falls, Idaho 83415 INTRODUCTION The cyanide ion has many chemical properties that make it suitable for use in the metal finishing and refurbishing industry. It lowers the reduction potential of many metals' making them more susceptible to oxidation under relatively mild conditions, and hence, enhances metal stripping for commonly plated materials.2 It is a strong chelating agent3 that serves to clean metal surfaces of oxidized species in cleaning and stripping applications, or hold high concentrations of metal ions in electroplating solutions. Cyanide also participates in several reversible electrochemical reactions that make it suitable for electroplating certain metals.2 Because of these characteristics, concentrated cyanide solutions are widely used in the electroplating industry: 1) in cleaning formulations to remove scale, smut, rust, and other surface contaminants before electroplating new parts or refurbishing used parts; 2) in electroplating solutions for zinc, cadmium, copper, silver, and gold; and 3) for plate metal stripping prior to refurbishing used parts.4 In today's atmosphere of worker awareness, environmental concern, and long term liability, the hazards of continued cyanide use are becoming unacceptable. The spent solutions containing cyanide are considered hazardous wastes and are a significant fraction of the total wastes generated at electroplating facilities.5 In most industrial waste treatment plants, isolated transport lines and chemical processing facilities are required to destroy the cyanide prior to metals precipitation and biological degradation of the remaining constituents. If acceptable noncyanide formulations can be substituted for the cyanide solutions, the magnitude of these disadvantages can be greatly diminished. The purpose of the work reported here was to test and evaluate commercially available noncyanide metal stripping products. Three types of tests were conducted in the laboratory to evaluate the stripping performance, basis metal protection, and biodegradability characteristics of the solutions. The tests were conducted using some parameters specific to and reflecting on conditions commonly encountered at U.S. Air Force installations. EXPERIMENTAL Stripping tests were conducted in borosilicate glass reactors roughly 2 1/4 inches in diameter by 8 inches tall. A schematic of the reactor assembly is shown in Figure 1. Metal coupons were suspended from support rods in a nominal volume of 180 mL of the stripper solution made to the manufacturer's specifications. Two coupons were suspended in each of the reactors, one of the test samples and the other a "dummy" coupon of equal surface area. Test samples were either plate or basis metals 1 x 2 x 1/8 or 1/16 inch in size and were sanded to a 120 grit surface. The dummy coupons used opposite the plate and basis metals were stainless steel or passivated stainless steel, respectively. Electrical connections were made between the supports to simulate galvanic effects that would be present under immersion operating conditions in a job shop. Under electrolytic operating conditions, the supports were connected to a d.c. regulated power supply and stainless steel cathodes were used. Agitation of the solution was supplied by air sparge or magnetic stirring, as per the manufacturer's recommendations. The coupons were cleaned6, tared7, and immersed8 in the stripper solution, after which the reactor was immersed in a constant temperature water bath, maintained at the desired temperature, to a height just above the solution level. The operating temperatures were the highest recommended or to a maximum of 130°F. At designated time intervals, the reactors were removed from the bath and the coupons were rinsed with deionized water and immersed in acetone, wiped dry, further dried at 50°C in an oven, and then placed in a desiccator to cool.6 Duplicate tests were run for each sample type. The times ranged from one half to 6 and 1 to 24 hours for the plate and basis metals, respectively. The 44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118. Printed in U.S.A. 609
Object Description
Purdue Identification Number | ETRIWC198965 |
Title | Evaluation of noncyanide metal strippers |
Author |
Janikowsli, Stuart K. Pryfogle, Peter A. |
Date of Original | 1989 |
Conference Title | Proceedings of the 44th Industrial Waste Conference |
Conference Front Matter (copy and paste) | http://e-archives.lib.purdue.edu/u?/engext,40757 |
Extent of Original | p. 609-616 |
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 |
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Description
Title | page 609 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Transcript | 65 EVALUATION OF NONCYANIDE METAL STRIPPERS Stuart K. Janikowski, Scientist Peter A. Pryfogle, Senior Scientist Idaho National Engineering Laboratory Idaho Falls, Idaho 83415 INTRODUCTION The cyanide ion has many chemical properties that make it suitable for use in the metal finishing and refurbishing industry. It lowers the reduction potential of many metals' making them more susceptible to oxidation under relatively mild conditions, and hence, enhances metal stripping for commonly plated materials.2 It is a strong chelating agent3 that serves to clean metal surfaces of oxidized species in cleaning and stripping applications, or hold high concentrations of metal ions in electroplating solutions. Cyanide also participates in several reversible electrochemical reactions that make it suitable for electroplating certain metals.2 Because of these characteristics, concentrated cyanide solutions are widely used in the electroplating industry: 1) in cleaning formulations to remove scale, smut, rust, and other surface contaminants before electroplating new parts or refurbishing used parts; 2) in electroplating solutions for zinc, cadmium, copper, silver, and gold; and 3) for plate metal stripping prior to refurbishing used parts.4 In today's atmosphere of worker awareness, environmental concern, and long term liability, the hazards of continued cyanide use are becoming unacceptable. The spent solutions containing cyanide are considered hazardous wastes and are a significant fraction of the total wastes generated at electroplating facilities.5 In most industrial waste treatment plants, isolated transport lines and chemical processing facilities are required to destroy the cyanide prior to metals precipitation and biological degradation of the remaining constituents. If acceptable noncyanide formulations can be substituted for the cyanide solutions, the magnitude of these disadvantages can be greatly diminished. The purpose of the work reported here was to test and evaluate commercially available noncyanide metal stripping products. Three types of tests were conducted in the laboratory to evaluate the stripping performance, basis metal protection, and biodegradability characteristics of the solutions. The tests were conducted using some parameters specific to and reflecting on conditions commonly encountered at U.S. Air Force installations. EXPERIMENTAL Stripping tests were conducted in borosilicate glass reactors roughly 2 1/4 inches in diameter by 8 inches tall. A schematic of the reactor assembly is shown in Figure 1. Metal coupons were suspended from support rods in a nominal volume of 180 mL of the stripper solution made to the manufacturer's specifications. Two coupons were suspended in each of the reactors, one of the test samples and the other a "dummy" coupon of equal surface area. Test samples were either plate or basis metals 1 x 2 x 1/8 or 1/16 inch in size and were sanded to a 120 grit surface. The dummy coupons used opposite the plate and basis metals were stainless steel or passivated stainless steel, respectively. Electrical connections were made between the supports to simulate galvanic effects that would be present under immersion operating conditions in a job shop. Under electrolytic operating conditions, the supports were connected to a d.c. regulated power supply and stainless steel cathodes were used. Agitation of the solution was supplied by air sparge or magnetic stirring, as per the manufacturer's recommendations. The coupons were cleaned6, tared7, and immersed8 in the stripper solution, after which the reactor was immersed in a constant temperature water bath, maintained at the desired temperature, to a height just above the solution level. The operating temperatures were the highest recommended or to a maximum of 130°F. At designated time intervals, the reactors were removed from the bath and the coupons were rinsed with deionized water and immersed in acetone, wiped dry, further dried at 50°C in an oven, and then placed in a desiccator to cool.6 Duplicate tests were run for each sample type. The times ranged from one half to 6 and 1 to 24 hours for the plate and basis metals, respectively. The 44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118. Printed in U.S.A. 609 |
Resolution | 300 ppi |
Color Depth | 8 bit |
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