An effective method for recovering ultrafine SnO2, MgSn(OH)6, and Zn from complex iron tailings

The generation of complex tailings from iron mining is continuously increasing, reaching a reserve of 500 million tons. The iron tailings mainly contain 0.10–0.50 wt% ultrafine SnO2 (−9.6 μm, >50 %), acid-solule Sn (MgSn(OH)6) and 0.20–1.50 wt% Zn and are recognized as an important secondary Sn resource. Unfortunately, traditional mineral processing techniques have a low Sn recovery ratio. In this study, a novel method is proposed for effectively recovering Sn and Zn from complex iron tailings through reduction-sulfurization roasting, and their transformation behavior is determined. The results reveal that MgSn(OH)6 is first transformed into MgSnO3 at 1073 K, and SnO2 is reduced to SnO(g) and then sulfurized to SnS(g). COS acts as the main curing agent during the roasting process, which originates from the oxidation of FeS. As the temperature increases from 1173 to 1273 K, part of SnO2 can combine with CaO to form CaSnO3, and the generated CaSnO3 and MgSnO3 are further reduced to Sn(l) and Fe–Sn alloy. Meanwhile, ZnO and ZnS can be efficiently converted to Zn(g). Interestingly, the Fe–Sn alloy cannot be removed due to low Sn activity (a[Sn]). However, the Sn recovery ratio increases to 90 % due to low SnS partial pressure (PSnS) at 1373 K. Under optimal conditions, 90.10 wt% Sn and 94.90 wt% Zn can be extracted in the dust, which can be further processed into higher value-added Sn concentrate. Compared with current beneficiation process, the recovery ratio of SnO2 increased by 20 %. More importantly, MgSn(OH)6 can be efficiently recovered. This is of great significance for sustainable metallurgy of Sn.