Leaching kinetics and mechanisms of surface reactions during cyanidation of gold in the presence of pyrite or stibnite

This paper quantifies the detrimental effects of pyrite and stibnite on gold leaching kinetics. Means to reduce the effect of these minerals by the addition of lead nitrate and oxygen are presented. A significant retarding effect was observed when the pyrite concentration was 20%. A pretreatment with lead nitrate reduced the extent of gold surface coating by Ag, Fe and S. Stibnite, at a concentration as low as 20 ppm, significantly affected the gold leaching kinetics through forming a passivating film of Sb(V) oxide, possibly Sb2O5, on the surface of gold particles. The most practical way to alleviate the effect of stibnite is to leach the materials at a moderate pH (pH 10) with the addition of lead nitrate. A low temperature reduced the efficiency of lead nitrate to counteract the effect of stibnite. An increase of dissolved oxygen is not favorable to alleviate the coating of Sb compounds on gold.