Phase transformation of Sn in tin-bearing iron concentrates by roasting with FeS2 in CO-CO2 mixed gases and its effects on Sn separation

A novel method to separate Sn and obtain qualified iron concentrates with low sulfur content from tin-bearing iron concentrates is proposed in the present paper. Combining the results of thermodynamic analysis, chemical analysis, and XRD, EPMA and XPS analyses, it can be concluded that the tin volatilization is restricted in the presence of iron-containing phases through the formation of Fe-Sn spinel or Fe-Sn alloy. The Fe-Sn spinel is formed through the replacement of Fe2+ in Fe3O4 by Sn2+, and the formation of Fe-Sn alloy is accelerated at higher CO contents. The pyrrhotite (Fe(1-x)S) and troilite(FeS) which derive from the FeS2 self-decomposition could be oxidized to FeO and SO2 by CO2, causing the sulfur contents in roasted residues to decrease with the increase of the CO2 content in CO-CO2 mixed gases. Under the optimum parameters of roasting temperature of 1473 K, CO content of 28.0 vol%, pyrite-to-cassiterite ratio of 90% and roasting time of 60 min, the tin content in the tin-bearing iron concentrate is decreased from 0.56% to 0.0028%, while the sulfur residual content is only 0.072%.