Hydrometallurgical recovery of manganese, gold and silver from refractory Au-Ag ore by two-stage reductive acid and cyanidation leaching

Abstract

In this study, a refractory Au-Ag ore from Beiya (Yunnan, China) was characterised and the occurrence states of low-grade gold and silver were clarified. The results revealed that the gold in the ore mainly occurred as visible native gold, which can be leached easily via cyanidation, whereas the visible silver minerals occurred as native silver, acanthite, chlorargyrite, acanthite, pyrargyrite, andorite and polybasite. Nevertheless, most of the silver occured as invisible silver in manganese oxide ore with the form of isomorphs and could not be leached via direct cyanidation. A pretreatment of reductive acid leaching using sodium sulphite as a reductant successfully leached the manganese and liberated the silver, which was very beneficial for the cyanidation of silver. The manganese was enriched in the leaching solution at a concentration of 16.51 g/L with an average leaching percentage of 70.27% after five-stage cyclic reductive acid leaching under optimised conditions of 1.0 mol/L of H2SO4, 20 g/L of Na2SO3, a liquid-solid ratio of 5:1, and stirring speed of 300 r/min at room temperature (28 ± 1 °C) for 1.0 h. We could easily recover 99.90% copper and 99.80% manganese from the leaching solution via iron powder reduction and sodium carbonate precipitation. Following the leaching of manganese, the cyanidation leaching percentages of gold and silver were to 87.37% and 80.19% respectively. In summary, we developed a novel process for the hydrometallurgical recovery of manganese, gold, and silver from refractory Au-Ag ore.