Ferric methanesulfonate as an effective and environmentally sustainable lixiviant for Zn extraction from sphalerite (ZnS)

Abstract

Zinc is currently extracted from sphalerite (ZnS) by either sintering-smelting or roasting-leaching. These high-temperature processes produce environmentally hazardous sulfur dioxide gas. Hence, sustainable zinc extraction calls for direct leaching at low temperatures. Here, we show that ferric methanesulfonate is a high performing lixiviant for this purpose. Using 0.8M ferric methanesulfonate, 99.3% Zn was extracted from 106−150μm sphalerite particles after leaching at 70°C for 96h. Elemental sulfur, rather than sulfur dioxide, was produced as a by-product. When compared to common inorganic lixiviants such as ferric sulfate or ferric chloride, ferric methanesulfonate demonstrates greater extraction efficiency and is less corrosive, less toxic, and does not release harmful gases. Mineralogical, microscopical, and compositional characterization of reaction products confirmed the formation of a core–shell structure consisting of a sphalerite core and a sulfur shell, and the manifestation of a coupled dissolution-reprecipitation mineral replacement mechanism. Efficient zinc extraction was facilitated by the interconnected pores in sulfur, which provided pathways for mass transfer between the lixiviant and sphalerite core. The precipitation of anglesite (PbSO4), which in some instances caused surface passivation through the infilling of sulfur shells, suggests that Pb2+ concentration should be controlled when applying ferric methanesulfonate for Zn extraction.