Separation of iron(iii), zinc(ii) and lead(ii) from a choline chloride–ethylene glycol deep eutectic solvent by solvent extraction

Abstract

Deep eutectic solvents (DESs) were used as alternatives to the aqueous phase in solvent extraction of iron(III), zinc(II) and lead(II). The selective extraction of iron(III) and zinc(II) was studied from a feed of ethaline (1 : 2 molar ratio of choline chloride : ethylene glycol) and lactiline (1 : 2 molar ratio of choline chloride : lactic acid), with the former DES being more selective. A commercial mixture of trialkylphosphine oxides (Cyanex 923, C923) diluted in an aliphatic diluent selectively extracted iron(III) from a feed containing also zinc(II) and lead(II). The subsequent separation of zinc(II) from lead(II) was carried out using the basic extractant Aliquat 336 (A336). The equilibration time and the extractant concentration were optimized for both systems. Iron(III) and zinc(II) were stripped using 1.2 mol L⁻¹ oxalic acid and 0.5 mol L⁻¹ aqueous ammonia, respectively. An efficient solvometallurgical flowsheet is proposed for the separation and recovery of iron(III), lead(II) and zinc(II) from ethaline using commercial extractants. Moreover, the process was upscaled in a countercurrent mixer-settler set-up resulting in successful separation and purification.