Recovery of high-purity cobalt oxalate from acidic effluents with solvent extraction technology

• Solvent extraction effectively recovers cobalt from acidic effluents. • The reusability of the proposed organic solution warrants minimizing solvent waste. • High cobalt extraction efficiency (94.1%) significantly reduces effluent toxicity. • Valorization of recovered 99.3% pure cobalt oxalate supports circular resource use. The precipitation of cobalt using oxalic acid (H 2 C 2 O 4 ) is widely regarded as a cost-effective method for cobalt recovery from hydrometallurgical solutions. However, a significant fraction of cobalt, oxalic acid, and mineral acids remain dissolved after the precipitation, posing environmental and resource efficiency challenges. Solvent extraction offers an effective treatment process to recover cobalt as a valuable residual component from such a precipitation mother liquor. The synthetic aqueous solutions contained 1.7–6.8mol L −1 HCl, 1.05 ± 0.05 g L −1 Co, and 10.20 ± 0.82 g L −1 H 2 C 2 O 4 , simulating supernatant waste liquors in this study. Batch extraction experiments were performed using trioctylamine (TOA), methyltrioctylammonium chloride (Aliquat 336), and Tridodecyl amine (Alamine 304–1) as amine reagents, all diluted in Exxsol D80. The effects of chloride concentration, concentration of reagents and modifiers, mixing time, and temperature were investigated. As a result, TOA reagent in a mixture of 1-decanol and Exxsol D80 was evaluated as the promising organic system for separation of cobalt. Also, the loading isotherm predicted that 94.1% of cobalt was extracted with four countercurrent stages at T = 45 ± 2 ℃, organic-to-aqueous volumetric ratio (O/A) 2:5, and c (HCl) a = 6.8mol L −1 . Moreover, the stripping isotherm indicated that almost 100% of cobalt was stripped at an O/A ratio of 2:1 using 0.2mol L −1 HCl. Bench-scale validation in industrial-type mixer-settler confirmed process stability over three extraction-stripping cycles, maintaining cobalt recovery efficiencies between 90.3 and 99.4%. The recovered cobalt was subsequently precipitated as cobalt oxalate at a 99.3 wt% relative purity.