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

• Concentrated solution similar to HPAL liquors was treated by solvent extraction
• Cyanex 272 proved ineffective in separating Ni2 + sulfate from Ca2 + and Mg2 +
• Cyanex 272 + Versatic 10 proved to be suitable at pH = 5.1 using staged operations

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.