Chlorination

Oxidation of cyanide to cyanate occurs in the pH range of 8-9 and requires only minutes (equation 8.3[ 13]). Further oxidation to carbon dioxide and nitrogen is much slower, requiring hours (equation 8.3[14]).

Chlorine is added as gaseous chlorine or as a hypochlo-rite solution. Special equipment is required for safe and efficient addition of chlorine gas. For smaller plants, hypochlorite solution is recommended since metering and handling is simpler and less hazardous. Sludge formation usually accompanies chlorination. The sludge consists of hydroxides of metal ions, always present in plating solution.

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