Recovery of nickel and cobalt from ferronickel alloy by hydrochloric acid leaching and continuous counter-current solvent extraction

Ferronickel, also called Class II nickel, is the intermediate product obtained by pyrometallurgical processing of nickel laterites, used in austenitic stainless steel. This ferronickel alloy could become a potential alternative feedstock for cobalt and nickel, and would thus increase the supply highly demanded battery-grade metals. This study presents a hydrometallurgical approach via oxidative hydrochloric acid leaching and solvent extraction to recover cobalt and nickel from ferronickel. Prior to solvent extraction, oxidation of iron(II) to iron(III) using an excess of hydrogen peroxide was essential for the efficient extraction of iron(III) by undiluted tri- n -butyl phosphate (TBP). Solvent extraction was optimized through bench-scale experiments and validated in lab-scale counter-current mixer-settlers. This resulted in an iron(III) and excess HCl removal of 99% and 94%, respectively, using five-stage counter-current extraction, while maintaining negligible co-extraction of nickel and cobalt. Hydrochloric acid was recovered quantitatively via a four-stage counter-current stripping process, for potential reuse in leaching.