Simultaneous Solvent Extraction of Co and Ni from Copper Raffinate Waste Solution

The extraction and stripping of Co, Ni, Mn, and Mg ions from raffinate solution of the Sarcheshmeh copper complex containing Cu (0.14 g/L), Ni (0.15 g/L), Co (0.06 g/L), Fe (10.72 g/L), Zn (2.4 g/L), Mn (4.83 g/L), and Mg (8 g/L) was comprehensively studied using D2EHPA and LIX 984 extractants. To design the solvent extraction experiments, the response surface method (RSM) was employed. The optimal and most efficient conditions and extraction rates of nickel and cobalt were considered for the application of a central composite design (CCD). The design of experiments (DOE) was carried out using three operating variables: the equilibrium pH of the solution (4–6), extractant concentration (10–20%), and aqueous-to-organic phase ratio (1–3). The results indicated that the highest extraction of Co and Ni occurred within 5 min at a mixing speed of 500 r/min and 40 °C. The results showed that the equilibrium pH of the aqueous solution had a greater influence on nickel and cobalt extraction than the other parameters. According to the research results, 99% of cobalt and 94% of nickel were extracted simultaneously under optimum conditions of pH = 6, [LIX984N] = 10%, and A/O = 3. In the stripping stage, 95% of nickel ions were recovered in one step using 1 M sulfuric acid, and 80% of cobalt ions were recovered in three steps using 5 M hydrochloric acid. Finally, 98% of Zn, 99% of Co, and 94% of Ni were extracted in two stages with D2EHPA and LIX984N extractants.