The results indicated that the sulfidation degree of lead and zinc reached 98% and 95%, respectively. 26 investigated the recovery of lead and zinc from low-grade Pb-Zn oxide ore by sulfidation roasting and flotation process. Sulfidation roasting is more beneficial for the formation and growth of sulfide crystals and thus shows better results for the recovery of nonferrous metals by flotation. At present, many sulfidation methods have been proposed to convert various oxidized materials, including sulfidation with Na 2S 16, 17, mechanochemical sulfidation 18, 19, hydrothermal sulfidation 20, 21, 22, 23 and sulfidation roasting 24, 25. As a result, the aim to recover metals by flotation and reduce the pollution of heavy metals can be achieved theoretically. In this process, metal oxides and oxidized compounds are converted into sulfides, which have a good floatability and are relatively insoluble in aqueous solutions 15. Sulfidation has recently received much attention as a possible generic technology for the recovery of valuable metals from low-grade oxide ores or wastes. Despite many achievements made, these technologies have still not been widely applied for mass production due to the presence of some technical and economical drawbacks. For catering to the sustainable development of nonferrous industry, a number of hydrometallurgical 5, 6, 7, 8, pyrometallurgical 9, 10 and their combined processes 11, 12, 13, 14 have been performed to exploit low-grade oxide ores and recycle valuable metals from smelting wastes. Since the heavy metals in wastes are rarely in sulfides but are in oxides and oxidized compounds, which are more soluble in water than their sulfide counterparts, the concerns are not only the waste of metal resources but environmental threats 3, 4. In the past decades, most users preferred stockpiling or landfilling to recycling the wastes because of lack of economic and legislative driving forces. With the ceaseless exploitation of metal resources, high-grade ores are exhausted day by day, and correspondingly, millions of tons of smelting wastes containing plenty of heavy metals are generated every year in the world 2.
Most of nonferrous metals, such as Cu, Pb and Zn, are primarily recovered from sulfide ores with beneficiation followed by metallurgical process 1. The oxidation of synthetic Zn 1− xFe xS is easier than marmatite in air. Hydroxyl easily absorbs on the surface of iron-bearing zinc sulfide (Zn 1− xFe xS). The surfaces of marmatite and synthetic zinc sulfides contain high oxygen due to oxidation and oxygen adsorption. The addition of carbon can not only enhance the sulfidation but increase sulfur utilization rate and eliminate the generation of SO 2. Fe 2O 3 captured the sulfur in the initial sulfidation process as iron sulfides, which then acted as the sulfurizing agent in the late period, thus reducing sulfur escape at high temperatures. The results indicate that increasing temperature and adding iron oxide can not only improve the sulfidation of ZnO but also promote the formation and growth of ZnS crystals. The thermodynamic analysis, sulfidation behavior of zinc, phase transformations, morphology changes, and surface properties were investigated by HSC 5.0 combined with FactSage 7.0, ICP, XRD, optical microscopy coupled with SEM-EDS, and XPS.
The mechanism of ZnO sulfidation with sulfur and iron oxide at high temperatures was studied.