Purification of nickel from multicomponent aqueous sulfuric solutions by synergistic solvent extraction using Cyanex 272 and Versatic 10

The present study investigated the purification of nickel sulfate by solvent extraction with Cyanex 272 (bis(2,4,4-trimethylpentyl) phosphinic acid) and mixtures of Cyanex 272 with Versatic 10 (neodecanoic acid). Batch scale tests were carried out using a laboratory multicomponent aqueous sulfuric solution with metal ion concentration similar to those typically found in High Pressure Acid Leaching (HPAL) liquors, following the iron removal step (in g.L− 1): [Ca] = 0.50; [Co] = 2.10; [Cu] = 0.25; [Mg] = 3.50; [Mn] = 0.55; [Ni] = 75.0; [Zn] = 0.06. This solution was first placed in contact with organic phases containing only Cyanex 272 (T = 50 °C; A/O ratio = 1). Subsequently, the effect of two operating variables pH of the aqueous solution (1.5 to 7.0) and concentration of Cyanex 272 (5, 10, 15, and 20%v/v) were investigated. It was verified that nickel could be selectively separated from zinc, cobalt, copper, and manganese, at pH = 3.9 and [Cyanex 272] = 20%v/v, but not from calcium and magnesium. Therefore, to purify nickel from such alkaline earth metals, organic phases containing Cyanex 272 (20%v/v) and Versatic 10 (5, 10, and 20%v/v) were then evaluated. Approximately 80% of the nickel could be purified using Cyanex 272 (20%v/v) and Versatic 10 (10%v/v), thus obtaining a clean final solution containing at least 60 g.L− 1 of nickel.