Foundamental Study On Pollution-Free Double-Layered Pellet Roasting Of Sulfur&Arsenic-Bearing Gold Concentrates

Refractory gold ore reserves account for60percent of the world’s gold reserves at present, however, gold production from refractory ore account for only6%of total gold production due to the low utilization rate. How to improve the production of refractory gold ores is an important direction of the gold extraction in the future. Among refractory gold ores, sulfur and arsenic containing gold ores account for more than1/3. Pyrite and arsenopyrite are the main gold-bearing minerals in these gold ores, and gold is encapsulated in metal sulfide with the form of advanced micro device so that direct cyanide leaching of gold appears very poor. A variety of pretreatment methods have been used to deal with such refractory gold ores, but the most effective one is traditional roasting. However, there exists a serious problem of environmental pollution. Subsequent proposed solidification roasting also takes many disadvantages.Double-layered pellet roast was proposed in order to solve shortcomings of conventional roasting. The study focused on sulfur and arsenic containing gold ore, adopted briquetting and pelletization methods to form double-layered pellets, mainly investigated removal and solidification of arsenic and sulfur and used XRD to work out the phase changes of product.Pyrite and arsenopyrite could experience oxidative decomposition path besides decomposition themselves. It seems likely that they rely mainly on the oxidative decomposition reaction in the presence of oxygen. Sulfides have corresponding sulfide ignition temperature-the minimum temperature oxidation reaction heated spontaneously needs. When sulfides once reach their ignition temperature, the process of oxidative decomposition could be accelerated.In the process of oxidative roasting, owing to burn and being burnt (the sintering) must be under control, so are the emergence of the ferric arsenate, and ferrous sulfate and so on. However, in this trial, ferric arsenate and sulfate iron have no conditions in the formation of dynamics. These ΔGθ of sulfur and arsenic volatiles reacting to hydrated lime are negative, indicating that the solidification reaction may occur in the roasting process under the ideal thermodynamic conditions.From the roasting experiment on double-layered pellets formed by briquetting, at low temperature, removal and solidification of sulfur and arsenic were in chemical reaction control. As temperature rose, chemical reaction rate were accelerated. Additionally there may occur partial melting at700℃. The mass of package layer affected the process of transferring heat and materials. With the increasement of the roasting time, the removal and solidification rate of sulfur and arsenic got higher, but the desulfurization process was significantly slower than the removal rate of arsenic. The optimum roasting parameters:at temperature of600℃, in package mass of6g for3h, the removal and solidification rate of arsenic can reached95.91%and98.95%, while the rate came to97.19%and97.90%for sulfur. Moreover, pyrite and arsenopyrite were transformed to hematite and magnetite and product of solidification of sulfur and arsenic mainly consisted of calcium sulfate, calcium arsenate and calcium sulfite.From the roasting experiment on double-layered pellets formed by pelletization, as the temperature increased, the removal and solidification rate of sulfur and arsenic became larger. But it was much low compared to the desulfurization rate of double-layered pellet formed by briquetting in the same temperature conditions. The phenomenon occurred mainly because the package layer was so tight that there existed more resistance for02entrance. With the extension of the time, the removal and solidification rate of sulfur and arsenic increased which was similar to the law of double-layered pellets formed by briquetting under time conditions. The optimum roasting parameters:at temperature of600℃for3h, the removal and solidification rate of arsenic can reached89.49%and94.74%, while the rate came to86.47%and98.29%for sulfur. We also believed that the sintering phenomenon was possibly related with FeS; In addition, sulfur and arsenic compound was confirmed by XRD analysis of the volatile matter produced in the process of roasting.