Thermodynamics and mechanisms of silver tailings roasting processes

To separate and extract all the useful components of tailings, taking silver tailings as the object, the thermodynamics of silver tailings during the roasting processes was investigated, and the phases transformation mechanism of major minerals were obtained. Based on the mineralogy characteristics of silver tailings, the standard Gibbs free energy changes for the chemical reactions in the roasting processes were calculated; the thermal chemical behaviors and the mineral phases transformation were investigated using TG/DTG-DSC and XRD; and the microstructure changes with chemical composition of microregions were characterized through SEM-EDS. The thermochemical reaction characteristics for the roasting activation of tailings and sodium carbonate at different temperatures were as follows: at 450–650 °C, the ankerite, siderite and sulfide in tailings were oxidized and decomposed, while the crystal transformation of quartz and chlorite occurred; at 650–750 °C, quartz, muscovite and chlorite decomposed to form soluble sodium silicate, sodium aluminum silicate, diopside, sodium ferrite and copper ferrite etc; at 750–800 °C, due to the increase in products with low melting point, the roasted samples melted. During the roasting processes, the surface of minerals depressed and the structures were destroyed. These results can provide a theoretical foundation for thoroughly resource utilization of tailings.