Cobalt/nickel purification by solvent extraction with ionic liquids in millifluidic reactors: From single-channel to numbered-up configuration with solvent recycle

This work describes the continuous separation of cobalt and nickel by solvent extraction in a numbered-up millifluidic system (1 mm ID) using Cyphos IL 101 (C101) as extractant, which is recycled. A dilution of 50 vol% C101 in p-cymene was chosen as the optimal trade-off between extraction performance and hydrodynamic properties of the solvent. The effects of channel length (20-100 cm), flow rate (1-2.5 mL min-1) and temperature (20-70 degrees C) were investigated on the extraction, scrubbing and stripping performance in a single-channel system. Subsequently, the developed manifold structure (five parallel reactors) was benchmarked against the single-channel system, which displayed a maldistribution of only 1% and performed equally well as the single-channel system. Then, a continuous separation process of one extraction and two countercurrent stripping stages was executed for 6 h with the proven manifold. A cobalt and nickel purity of, respectively, 99.7 and 97.7 % were achieved at a rate of 5 mL min-1. Stable slug flow was observed in the entire system throughout the operating period.