Hydrogen Reduction of Cassiterite Concentrate and Possibilities for Sustainable Tin Extraction

Abstract Hydrometallurgical extraction of metals is generally considered eco-friendly compared to pyrometallurgical routes due to lesser energy requirements and the absence of hazardous gaseous emissions. Nonetheless, the leaching of SnO 2 (Sn 4+ ) is challenging, considering that cassiterite has been found to be rather resistant to chemicals. Theoretically, it would be easier to dissolve tin in acid if it is first converted to SnO (Sn 2+ ) by controlled reduction. Moreover, hydrogen, when produced through the use of renewable energy sources, is a favored reductant for metal oxides due to the resulting low CO 2 emission footprint compared to the use of carbonaceous alternatives. The concept of partial hydrogen reduction followed by hydrometallurgical treatment with regard to cassiterite concentrate was explored in this research. Literature review and FactSage™ modeling indicated that tin monoxide (SnO) is most stable in the slag phase. In addition, numerical modeling was used to assess maximum gas flow injection during experimentation without excessive splashing. Experiments were carried out in this regard to achieve SnO in the slag by varying reductant amounts at different temperatures. Slags generated from these reduction experiments exhibited different performances during acid leaching. Modeling values showed reasonable agreement with experimental observations. Reduction with 1.5 g H 2 /100 g of a tin concentrate provided a leachable slag (also with regard to Sn) without producing a metal phase. On the other hand, reduction of the same tin concentrate with 3 g H 2 /100 g of concentrate at 1300 °C yielded 50.4% Sn recovery (> 80% of the equilibrium value) in the metallic phase as a nugget with 99.60 wt% purity. However, ca. 12.51 wt% Sn was measured in a glassy slag phase from which complete dissolution of tin occurred in an acidic solution. Several process routes, including one-stage hydrogen reduction of cassiterite concentrate to produce raw tin, were explored based on achieved results to propose sustainable extraction methods for tin concentrates. Graphical Abstract