Roasting pretreatment of poly-metallic and complex gold concentrate to extract gold, silver and copper

Gold, silver and copper were extracted from poly-metallic and complex gold concentrate by roasting-acid leaching-cyanide method. The effects of roasting atmosphere, roasting temperature, roasting time, and sodium hydroxide dosage on the extracting rate of gold, silver and copper were investigated. Experimental results showed that the roasting atmosphere was the key factor to impact the extraction rate of gold, silver and copper. The extraction rate of gold, silver and copper was improved significantly when roasting pre-treatment was performed in oxygen-rich atmosphere. And the optimal conditions were further determined as follows: rich oxygen, roasting temperature of 903 K, roasting time of 3 h, sodium hydroxide dosage of 4 g, liquid to solid ratio of 4:1 in acid leach, sulfuric acid concentration of 1 mol·L-1, reaction temperature of 363 K, reaction time of 3 h, liquid to solid ratio of 4:1 in cyanide leach, pH value of 10.5, sodium cyanide concentration of 4‰, reaction time of 72 h. Under above-mentioned conditions, the extracting rate of gold, silver and copper were 94.55%, 83.25%, 94.75%, respectively. Silver chemical phase analysis showed that adding sodium hydroxide during roasting pretreatment could obviously reduce the amount of silver encapsulated in silicates. The analysis of thermodynamics calculation data showed that sodium hydroxide played an important role in reducing the generation of zinc ferrite, copper ferrite, positive zinc silicate, positive lead silicate, lead silicate which wrapped around gold and silver during roasting pretreatment. The relationship diagram between oxygen partial pressure and sulfur dioxide partial pressure revealed that the higher the oxygen pressure was, the larger the stable area of sulfation roasting was, the easier the sulfation roasting was, and the higher the extracting rate of gold, silver and copper was.