Methanesulfonic acid: a sustainable acidic solvent for recovering metals from the jarosite residue of the zinc industry

Abstract

Methanesulfonic acid (MSA) is a green acid with a remarkably high solubility for several speciality and base metals including lead, making it an interesting leaching agent for metals. MSA is safer and less toxic than the mineral acids (HCl, H₂SO₄, HNO₃) currently employed for leaching metals from primary and secondary sources. In this study, MSA was tested for the leaching of lead and zinc from the iron-rich jarosite residue of the zinc industry. The leaching of lead, zinc and iron increased as a function of the MSA concentration in water up to 90 vol% MSA. Higher MSA concentrations resulted in precipitate formation due to the limited solubility of the iron and zinc methanesulfonate salts in water-lean MSA. Leaching with pure MSA resulted in a pregnant leach solution (PLS) comprising most of the lead and zinc, and a precipitate comprising the majority of the iron and a fraction of the zinc originally present in the jarosite. The optimization of the leaching conditions showed that increasing the liquid-to-solid ratio or temperature increased the leaching efficiencies of the metals, especially of lead. The leaching under optimized conditions was successfully performed on a larger scale using a temperature-controlled batch leaching reactor. The metal/iron mass ratio increased from 1/4 for Pb/Fe, and from 1/7 for Zn/Fe in the initial jarosite, to over 2.66/1 and 1/2, in the PLS, respectively. The remaining MSA in the PLS was recovered by vacuum distillation and successfully reused for three leaching cycles.