COMPARISON OF INDUSTRIAL CYANIDE DESTRUCTION PROCESSES

摘要

Tighter regulatory requirements and the implementation of the International Cyanide ManagementrnCode has seen an increase in recent years in the implementation of cyanide destruction processes atrngold operations to reduce the residual weak acid dissociable (WAD) cyanide being discharged intornthe tailings storage facility (TSF). Fundamental investigations of the three commonly used cyaniderndestruction processes (SO_2/air, H_2O_2 and Caro’s acid) have been undertaken to better understandrnthe mechanisms of these processes and the reactions involved in treating cyanidation tails from thernprocessing of complex ores, particularly those ores containing sulfide minerals. Initial investigationsrnhave found that all three processes oxidise WAD cyanide species to cyanate, which will more slowlyrnundergo hydrolysis to carbonate and ammonia. The Caro’s acid system kinetics is very fast and thisrnsystem can also further oxidise cyanate under acidic conditions.rnThe potential of these processes to also oxidise other species generated during the cyanidation ofrncomplex ores, such as thiocyanate and thiosulfate, influences the residual environmental risk of therntailings being discharged into the TSF. Caro’s acid was the only oxidant that oxidised thiocyanate,rnwhilst Caro’s acid and H_2O_2 both rapidly oxidise thiosulfate. Thus, when these species are present thernoxidant consumption for the Caro’s acid and H_2O_2 systems can be much higher than that requiredrnto oxidise only the WAD cyanide. However, this is offset by the reduced environmental risk of therntailings discharged into the TSF. Cyanate and thiocyanate pose some environmental and toxicologicalrnconcerns, however the extent of these concerns needs further quantification.