Selective recovery of Co(II) over Ni(II), Al(III), and Li(I) from ethylene glycol solution by solvent extraction and precipitation

Using “green solvents” like ethylene glycol (EG) to replace water in hydrometallurgical processes is increasingly popular because of its feasibility and environmental friendliness advantages. In this study, the selective recovery behavior of Co(II) over Ni(II), Al(III), and Li(I) from mixed EG and H2O of HCl solution was studied by a combination of solvent extraction and stripping precipitation. The results showed that Co(II) from the EG-H2O solutions was selectively extracted over other metals by ionic liquids, in which ALi-SCN was more efficient than Aliquat 336. The presence of EG offered significant advantages in selectivity and efficiency for Co(II), whereas the effect of HCl concentration in the EG-H2O system was negligible. The selective extraction behavior of ALi-SCN for Co(II) is due to differences in the stability and speciation of metal complexes in the EG-H2O solution. Co(II) from the loaded ALi-SCN was directly precipitated to cobalt oxalate with above 99.9% purity under conditions: 60 min, O/A ratio of 1, and 1:2 of mole ratio of Co(II) to H2C2O4. ALi-SCN solutions after the Co(II) precipitation can be reused several times with selective Co(II) extraction capacity at high performance. Thus, Co(II) recovery from an EG-H2O system through continuous two steps of ALi-SCN extraction and precipitation is feasible.