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

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.