Selective Metal Recovery from Jarosite Residue by Leaching with Acid-Equilibrated Ionic Liquids and Precipitation-Stripping

The recovery of valuable metals from industrial process residues is complex because those metals are often present in very low concentrations and locked in complex matrices. Hence it is important to develop a process that selectively recovers the metal(s) of interest, while the undesired metals remain in the solid residue. Conventional pyrometallurgical and hydrometallurgical routes suffer from high cost and poor selectivity. In this work, a solvometallurgical approach was investigated for the selective leaching of lead and zinc from iron-rich jarosite of the zinc industry. Solvometallurgy uses organic solvents rather than water in order to reduce energy, acid, and water consumption and to improve selectivity and reactivity. The screening of different solvometallurgical lixiviants showed that the presence of chloride anions in the lixiviant was crucial for the leaching of lead. The ionic liquids Aliquat 336 ([A336]­[Cl]) and Cyphos IL 101 ([C101]­[Cl]), after equilibration with HCl, leached more lead and zinc compared to the other lixiviants. [A336]­[Cl] and [C101]­[Cl] equilibrated with 0.5 mol L–1 HCl, were selected for the optimization study because of their higher selectivity toward lead and zinc and lower codissolution of iron, compared to the same ionic liquids equilibrated with a higher concentration of HCl. At optimized leaching conditions, 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 2:1 and 1:2, in the leachate, respectively. The dissolved metals were recovered by selective precipitation-stripping with an aqueous ammonia solution. Finally, the corresponding flowsheets were developed for the recovery of zinc and lead for both [A336]­[Cl] and [C101]­[Cl]