Identification of surface species that inhibit and passivate thiosulfate leaching of gold

Effect of Pyrite on Thiosulfate Leaching of Gold and the Role of Ammonium Alcohol Polyvinyl Phosphate (AAPP)

“…[55,56]. The higher energy peak may have originated from S 2 2− in disulfides such as CuS 2 or FeS 2 [57], of which FeS 2 may be pyrite fines adsorbed on the gold surface whilst CuS 2 may occur as an ammonia copper(I) polysulfide [21]. Obviously, the intensity and area of peak in the presence of pyrite was much stronger and larger than that in the presence of quartz, indicating that the increased quantity of sulfur element on gold surfaces.…”

“…However, copper(II), together with the oxygen in the leach liquors, can also catalyze the degradation of thiosulfate, resulting in a high consumption of thiosulfate during gold leaching. The thiosulfate degradation not only leads to higher reagent cost, but also results in the generation of copper sulfide and sulfur layers which can passivate gold and hinder the leaching rate [19][20][21][22]. So the successful application of the thiosulfate leaching technology is obviously restricted by the high thiosulfate consumption and the gold surface passivation.…”

Anode current on gold in mixed thiosulfate-sulfite electrolytes

“…Tetrathionate may be transformed on the gold electrode into sulfate and elemental sulfur in the series of chemical rearrangement reactions with higher polythionates [23,24]. Overall reaction is usually written as…”

“…Under certain conditions, elemental sulfur forms a passive polysulfide layer on gold [22][23][24][25], which prevents the current from passing though the electrode -solution interface. The polysulfide layer on gold can be formed not only by electrochemical oxidation of thiosulfate but also by its long-lasting exposure to these solutions.…”

Electrochemical methods to measure gold leaching current in an alkaline thiosulfate solution

“…This decrease is the result of the formation of a passive layer on the gold surface, produced by the decomposition of thiosulfate, preventing further dissolution of gold. Previous studies have shown that this passive layer is composed of surface sulfur species that are the result of gold interaction with thiosulfate and that these sulfur species are different from the electrochemical oxidation of thiosulfate products [4,5].…”