Abstract
Sulfidation is a widely used technology to improve the floatability of oxidized metal minerals or to stabilize the heavy metals in various wastes. The sulfidation mechanism of ZnO with pyrite was detailedly studied by thermodynamic calculation and roasting experiments. The sulfidation behaviors, phase transformations, microscopic morphology and surface properties were investigated by TG-DSC, ICP, XRD, SEM-EDS, and XPS analysis. The results indicate that the nature of the sulfidation is the reaction of ZnO with the gaseous sulfur generated by the decomposition of pyrite. Pyrite instead of sulfur as the sulfidizing agent can not only relieve the volatilization loss of sulfur but also enhance the formation of liquid phase and thus facilitate the growth of ZnS particles. The sulfidation reaction belongs to surface chemical reaction and relates to the migration of oxygen from the inside of ZnO to its surfaces. The presence of carbon not only eliminates the release of SO2, but also decreases the decomposition temperature of pyrite and promotes the sulfidation of ZnO. The addition of Na2CO3 promotes the sulfidation of ZnO at lower temperatures (below 850 °C) and enhances the growth of ZnS particles but has a negative effect on the sulfidation at higher temperatures.
Highlights
Zinc is an important base metal required for various applications and is mainly recovered from primary sulfide ores via flotation and metallurgical processes[1]
Flotation results indicated that the synthetic metal sulfides showed a poor flotation performance a high sulfidation extent and low heavy metal dissolubility could be achieved after mechanochemical or hydrothermal sulfidation
The sulfidation reactions of ZnO with pyrite (FeS2) that probably occurred during the roasting process are represented as follows: 2ZnO + 3FeS2 = 2ZnS + 3FeS + SO2(g)
Summary
Zinc is an important base metal required for various applications and is mainly recovered from primary sulfide ores via flotation and metallurgical processes[1]. The addition of carbon promotes the sulfidation of ZnO and eliminates the generation of SO2.36 For iron phases, conversion to Fe2O3 (Eq 11) and Fe3O4 (Eq 12) has lower ΔG than conversion to FeS at temperature below 200 °C, above which the ΔG for Eq 10 becomes more negative than the others and ZnS, FeS, and CO2 are preferentially generated after ZnO roasted with FeS2.
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