Recovery of Co, Ni, and Li from solutions by solvent extraction with β-diketone system

Abstract

A method of recovering cobalt, nickel, and lithium from mixed solutions was proposed based on β-diketone solvent extraction using benzoyltrifluoroacetone (HBTA), trioctylphosphine oxide (TOPO), and green kerosene. The effective metal recovery and separation parameters such as solution pH, saponification degree, extraction time, and phase ratio were evaluated experimentally. The results indicated that cobalt and nickel were recovered through 2-stage cross-current extraction at different phase ratios and that lithium was recovered through three-stage countercurrent extraction. The metal-loaded organic phase was stripped using an inorganic acid solution to obtain cobalt-, nickel-, and lithium-concentrated solutions. The Co/Ni and Ni/Co molar ratios in the cobalt- and nickel-concentrated solutions were 54.4 and 164, respectively, and the lithium concentration reached 1.78 × 104 mg L−1 in the lithium-enriched solution. The extraction mechanism was studied, and the results revealed that Co2+ and Ni2+ were extracted by ion exchange in which two moles of H+ or Na+ had been replaced by divalent metal ions. The Li+ extraction stoichiometry was studied by cultivating single crystals. Because cobalt, nickel, and lithium were recovered by single extraction, no other organic substances were required. This work provides a sustainable, environmentally friendly, and versatile method of recovering valuable metals from spent lithium batteries.