The treatment of concentrated acidic and alkaline-cyanide electroplating wastes by innovative methods to neutralize and precipitate the cyanides and recover the metal content are discussed. Large quantities of cyanides, plus significant tonnages of useful metals, such as silver, nickel, and copper, are customarily discarded and contribute to stream and ground water pollution. The addition of an acid waste to an alkaline-cyanide waste was investigated as a means of neutralizing both materials while alleviating pollution from these sources. At a final solution ph value near 6.5, Metals and cyanides in both wastes were precipitated almost completely. The filtrate from this step was relatively harmless compared to the original waste and had a free 0.08 Ppm. The metal cyanide precipitate contained significant amounts of copper and nickel, which were separated and recovered by additional processing. Valuable metals were also recovered from the acid waste by selective precipitation of the metal hydroxides and by a combination of selective precipitation and electrolysis.
Ch. in Env. Mgmt.; Science and Politics. Allyn and Bacon, Inc., Boston, PP. 175-178