Recovery and kinetics of gold and iron from cyanide tailings by one-step chlorination–reduction roasting

Abstract

The experiment on recovery of gold and iron by one-step chlorination-reduction roasting in the muffle furnace was conducted using cyanide tailings from a gold smelting enterprises (Henan Province, China) as research object. The effects of the dosage of calcium chloride, dosage of bituminous coal, roasting temperature, roasting time, and other factors on the high-temperature chlorination efficiency of gold were studied. The effects of iron reduction were also investigated. X-ray diffraction analysis on the roasting products was carried out. Results showed that the high-temperature chlorination efficiency of gold increased with the rising of calcium chloride dosage. The high-temperature chlorination efficiency of iron also increased, leading to iron loss. The concentration of CO and CO2 produced by bituminous coal increased in roasting atmosphere, leading to the decrease of chlorine gas concentration. Thus, the high-temperature chlorination efficiency of gold decreased. During the roasting process, the reduction process of iron oxide is Fe2O3 → Fe3O4 → FexO → Fe, and the wustite can easily react with the silicon dioxide to form iron silicate in the weak reduction atmosphere. Under the condition of calcium chloride dosage of 6%, bituminous coal dosage of 22%, roasting temperature of 1200 °C, and roasting time of 1.5 h, the technical indices of gold high-temperature chlorination efficiency of 83.1%, iron grade of 92.0%, and iron recovery of 84.9% were obtained. The relationship between the high-temperature chlorination efficiency of gold and roasting temperature was established. The high-temperature chlorination reaction of gold was controlled by the interfacial chemical reaction. The apparent activation energy of the high-temperature chlorination of gold is calculated to be E = 20.3 kJ/mol.