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-----Can we safely leach a former thiocyanate tank with sulfuric acid?
Q. We are leaching a tank that was zinc-nickel . Is it ok to use 10% sulfuric acid to leach the tank? The tank used to contain 10 grams per liter zinc chloride, nickel chloride, and ammonium thiocyanate.
Thomas Christianplating engineer - Sanford, North Carolina
September 15, 2008
A. Thomas,
Yes, as long as all the spent solution is removed from the tank. I would fill the tank 3/4 with water then add the acid slowly while mixing.
process engineer - Malone, New York
A. You need not be anxious. Thiocyanate will not liberate HCN when its solutions are acidified. I routinely do silver metal analysis in plating solutions via thiocyanate titration, in a matrix of about 5 N nitric acid, and no HCN is released even when a large excess of titrant is used.
Thiocyanate will react with chlorine/hypochlorite to form cyanogen chloride, however.
Dave Wichern
Consultant - The Bronx, New York
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