An exploration into the sulphide precipitation method and its effect on metal sulphide removal

In hydrometallurgical processes, the use of metal sulphide instead of hydroxide precipitation has gained prominence in recent decades. The arguments for its preferential use are based on the high degree of metal removal at relatively low pH values; the sparingly soluble nature of sulphide precipitates; favourable dewatering characteristics and the stability of the metal sulphides formed. However, when choosing a metal sulphide precipitation route, various difficulties are encountered, two of which are described in the current work.The first issue is that these metal sulphide precipitation processes, dominated by low solubilities and high supersaturation levels, favour the formation of fine particles due to the dominant mechanisms of homogeneous nucleation, aggregation and attrition.The second issue is that, in areas of high local sulphide concentration, the excess sulphide can lead to the formation of aqueous polysulphide complexes, which consume the sulphide reagent and compromise the metal removal.