Sequential Separation of Cobalt, Copper, and Nickel from Alkaline Glycinate Solutions Using Solvent Extraction

There is a growing need for the sustainable supply of critical battery metals, such as Ni, Co, and Cu. Recently, glycine has been utilized to leach these metals from their host materials. The leached metals could be recovered employing mixed sulphide precipitation; however, the sulphide precipitates require further processing to meet battery-grade standards. This study evaluates the sequential separation of Co, Cu, and Ni from alkaline glycine solutions using solvent extraction. The metals behave quite differently in alkaline glycine solutions due to being present as strongly chelated anionic (Ni and Co) or neutral (Cu) complexes and the organic extractant must therefore compete with the strongly complexing ligand in the leachate. Various parameters impacting the extraction process with LIX 84-IC extractant, including pH, extractant concentration, glycine concentration, temperature, and the organic to aqueous phase ratio, were investigated. Across the studied parameter ranges, the extraction efficiency of Cu remained high, over 95%. Cobalt also showed high extraction efficiency, above 95%, except when glycine concentration increased, reducing the efficiency down to 80%. Interestingly, unlike Cu and Co, Ni only achieved satisfactory extraction efficiency (> 90%) when the time of extraction was increased to 4.0 h, indicating that Ni extraction was kinetically/mass transfer limited. While Cu (100%) and Ni (> 80%) could be stripped from LIX 84-IC using 200 g/L H2SO4, that of Co was near zero. Sequential separation of the three metals was achieved using Cyanex 272 for the selective extraction of Co and LIX 84-IC for the subsequent extraction of Cu and Ni. Being emerged as a "green" lixiviant for extracting metals from various materials in alkaline conditions, glycine effectively reduces the dissolution of gangue minerals, tackling both the economic and environmental challenges associated with traditional high-pressure acid leaching and enhancing the sustainability of this process.