Mutual separation of nickel and cobalt by gradient multistage extraction

According to the known solvent extraction behavior of nickel, cobalt and iron in TBP-HCl or TOPO-HCl system, a new method for the mutual separation of the above three ions using a counter-current extractor with a train of eight or six stages was presented. All tubs being filled up with the organic solution as the stationary phase, 1620 portions of aqueous solutions with varying hydrochloric acid concentration are crammed as the mobile phase. The sample solutions flowed out are aqueous solutions of nickel, cobalt or iron in various acidities. Nickel is concentrated in the beginning few fractions. Cobalt flows out in intermediate fractions, and iron last. Starting from 5ml of 8N hydrochloric acid sample solutions containing 3.0 g nickel chloride and 0.03 g cobalt chloride, the decontamination factor of cobalt for 98% recovery of nickel is attained to 2×103. When the starting solution is saturated with nickel chloride, separation becomes difficult with increasing concentration of cobalt chloride. Therefore, it is considered that this separation method is most suitable for the purification of nickel chloride in order to eliminate the impurities of cobalt and iron.