Study On Novel Technology For Pretreatment Of Sulfur&Arsenic-bearing Gold Concentrates By Pollution-free Double-layered Pellets Roasting

With the rapid development of gold industry, refractory gold ores are becoming more and more important resources for gold production. Among several types of refractory gold ores, sulfur&arsenic-bearing gold ores act as the most typical ones. Double-layered pellet (DLP) roasting is a novel pretreatment method for sulfur&arsenic-bearing gold concentrates. The DLP includes a core of gold concentrate and a coating layer of solidifying agent, which aims at completely absorbing SO2and As2O3generated during roasting process to realize pollution-free roasting. The gold calcine cores are effectively separated from the coating layer residues of sulfate and arsenate by a proper separation method to improve gold leaching. With gold concentrate in Hunan Province as raw material of research subject, preparation process, roasting process and mechanism of DLPs were studied.The preparation of DLPs is a fundamental step which is required to produce DLPs with favorable mechanical strength and thermal stability enough to endure following processes such as transportation, drying and roasting. Investigations have been carried out to exam the affecting factors and conditions on preparation and properties of DLPs. The results showed that moisture content has significant influence on DLPs preparation. With the increase of moisture content in the range of no more than9.8%, the drop resistance and compressive strength of green DLPs were raised accordingly and the pelletizing dynamics was improved. The optimum conditions were determined as moisture content9.8%, coating time14min-16min, drying temperature<80℃and a drying blowing velocity<1.2m·s-1.The result of roasting shows that favorable removal and solidifying rates of both arsenic and sulfur were obtained by DLP preparation. When the DLPs roasted at the condition of solidifying agent dosage2.1times mass of concentrate cores, roasting temperature600℃, roasting time3h, the removal rate of arsenic and sulfur were95.91%and97.19%, and the solidifying rate of arsenic and sulfur reached98.95%and97.90%, respectively. X-ray diffraction phase analysis indicates that the sequence of transformation of sulfur and arsenic minerals is FeSâ†'Fe3O4â†'Fe2O3. Solidifying agent of Ca(OH)2is partly reacted into CaCO3and partly decomposed into CaO. Therefore, except Ca(OH)2, both CaCO3and CaO also act as solidifying agent absorbing SO2and As2O3into Ca3(As04)2and CaSO4.