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.

The adsorption of scandium from diluted, acidic solutions by a supported ionic liquid phase (SILP) was investigated, as part of a process for recovery of scandium from bauxite residue (red mud). Both dry impregnation and covalent linking were studied for the SILP preparation. The SILP betainium sulfonyl(trifluoromethanesulfonylimide) poly(styrene-co-divinylbenzene) [Hbet–STFSI–PS–DVB] was prepared by covalent linking of the ionic liquid to the resin and this resulted in an adsorbent suitable for scandium recovery. For a chloride feed solution, the effects of pH, contact time, adsorption capacity, desorption, reusability of adsorbent and the influence of Fe(III), Al(III) and Ca(II) on the Sc(III) adsorption were studied. The adsorption of Sc(III) from nitrate and sulfate feed solution under optimal conditions was studied as well. The adsorption kinetics followed a pseudo-second order kinetic model. Equilibrium studies at room temperature showed that the experimental data could be well fitted by the Langmuir isotherm model. The stripping of Sc(III) from the loaded SILP was achieved with 1 M sulfuric acid. The SILP was stable and could be reused for seven adsorption/desorption cycles without significant losses in its adsorption efficiency for Sc(III).