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Could cadmium contamination be due to airborne zinc breaking down in rinse water




Q. I work for a company involved with various surface treatments, including cadmium plating, thermal zinc spraying and anodizing. In the process of treating waste anodize rinse water we have discovered that after treatment (using sodium bisulphate and sulfuric acid to reduce the chromate from hexavalent to trivalent) we have slight cadmium contamination. We know that this is not due to the plating as this runs on a separate waste stream, and I have eliminated the chemicals used in treatment as being the cause. I am interested to know anyones views on the possibility that airborne zinc(from thermal spraying) could be contaminating the rinse water at some stage in the process and breaking down to produce cadmium? any help would be greatly appreciated.

Stuart Haynes
Technician - Stalybridge, Cheshire, England
2004


A. Cadmium is found with zinc, so it is possible. Try analysing the zinc to see what levels of cadmium are present. I believe there was prosecution against a zinc plating company in Kent who were done for discharging cadmium into the water stream, without them knowing it. Furthermore, they did not know they were handling cadmium because it was a trace element in their zinc sources and had not been mentioned before an overzealous Environmental Protection Officer found it by analysis.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK


A. Stuart, NO. Zinc will not breakdown to give cadmium. But it could be there as an impurity. Have you checked your water supply, It is well known that the level of cadmium in tap water is above the discharge consent in some areas.

Steve Kelson
hard chrome plater- Cheshire, UK




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