Catalytic oxidation of thiocyanates

Abstract

The current liquid waste neutralization technology in the hydrometallurgical processing of gold concentrates includes thiocyanate oxidation with calcium hypochlorite, which is carried out after the separation of cyanides and heavy metals as precipitates of complex compounds. Here, we consider the possibility of replacing calcium hypochlorite with hydrogen peroxide, an environmentally friendly oxidizer. Hydrogen peroxide is superior to calcium hypochlorite because the latter needs pretreatment before use and, in addition, thiocyanate and cyanide oxidation with calcium hypochlorite can release toxic compounds of chlorine and yields large amounts of gypsum waste. The objects of this study are model thiocyanate solutions, as well as real solutions from the neutralization department of a hydrometallurgical refinery (Kholbinskii mine, OAO Buryatzoloto) after acidification and cyanide removal by stripping. The oxidative destruction of thiocyanates with hydrogen peroxide in the model and real solutions was studied in the presence of iron ions. Hydrogen peroxide offers promise as an environmentally appropriate and sufficiently efficient oxidizer for neutralization of liquid waste from the hydrometallurgical processing of gold concentrates.