SIMPLIFYING CYANIDE TREATMENT THROUGH IN-SITU ELECTROLYTIC CHLORINE GENERATION / REGENERATION: NOT SO SIMPLE

This paper presents results of testing in situgeneration/regeneration of chlorine from chloride at less than stoichiometric concentrations required for oxidation of cyanide. The goals were to provide effective oxidation and minimizing residual total dissolved solids (TDS) addition. Cyanide wastewaters produced in the plating operations are typically treated by conventional caustic chlorination to oxidize the cyanide. This conventional process uses elevated pH (typically pH ≥ 10) to prevent the formation of toxic cyanogen chloride, and a chlorine source for the cyanide oxidation reaction. The conventional processes use chlorine doses in excess of stoichiometric requirements to achieve cyanide oxidation, and this increases TDS in the treated water. The chlorine is reduced to chloride, which, in this in situ electrolytic process can be oxidized in the electrolytic process to chlorine. The cyclical electrolytic generation of chlorine from chloride, oxidation of cyanide by the chlorine with the reformation of chloride, and that reformed chloride being reused to form chlorine again presents an attractive conceptual means of achieving the oxidation of cyanide and minimizing TDS increases. However, the process is complicated by cyanide interaction with the electrodes used in the testing, and that fouling will need to be overcome for the process to be practical