Pretreatment of refractory gold concentrate calcine using ammonium bifluoride and sulfuric acid solution

Abstract

The secondary encapsulation of gold and silver by silicates and Fe-oxide during the roasting oxidation of refractory gold concentrate significantly influence the gold and silver leaching efficiency. In this study, a pretreatment method of refractory gold concentrate calcine using ammonium bifluoride and sulfuric acid solution is proposed. The effects of the NH4HF2 and H2SO4 concentration, pretreatment temperature, and time on the leaching efficiency of gold and silver were investigated in detail. The optimum conditions were determined to be NH4HF2 concentration of 1.5 mol/L, H2SO4 concentration of 2 mol/L, pretreatment temperature of 40°C, and duration of 90 min. The leaching efficiency of gold and silver reached 97.6 % and 94.8 %, respectively. The pretreatment process of refractory gold concentrate calcine can be expressed with Johnson-Mehl-Avrami (JMA) equation and depends on the diffusion. The pretreated residue was mainly composed of silicates and Fe-oxide minerals. The gold and silver can be exposed to the ore surface by NH4HF2 pretreatment, which helps to improve its cyanide leaching efficiency.