A novel process to effectively extract values from a manganese-bearing Au-Ag ore by pretreatment with iron scrap as reductant

Abstract

A novel process was developed to improve the extraction of valuable metals from a manganese-bearing gold-silver ore. Before cyanidation, a reductive sulfating leaching pretreatment process was adopted to preferentially dissolve manganese from the primary ores, according to mineralogy of the ores and possible leaching thermodynamic calculations of manganese minerals, and iron scrap was firstly introduced as reductant because of its low cost and wide source in China. In pretreatment tests, the effects of iron scrap concentration, sulfuric acid concentration and leaching temperature were studied, and the results indicated that manganese could be rapidly leached out to a complete degree even at room temperature. Then the reduced residue was suggested to the cyanidation process for silver and gold extraction, and the effect of cyanide concentration was also addressed. Based on the above study, pilot tests were finally conducted in Beiya 50 t/d concentrator to correctly evaluate the whole leaching process in the case of continuous production, and the gold and silver extractions in the novel process were up to 92.16 and 82.33%, respectively, corresponding to an increase of 9.08 and 45.97% compared to those in the direct cyanidation process, which are of great implications for future commercial operations of these refractory manganese-bearing gold-silver ores.