Effect of Complexing Agents on Extractive Separation of Co(II) and Ni(II) from Acidic Sulfate Solution Using Aliquat 336

Extraction separation of Co2+/Ni2+ from aqueous sulfate solutions with water-soluble complexing agents of ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid (IDA) and citrate using Aliquat 336 in kerosene was experimentally studied at 303 K. Experiments were carried out as a function of initial aqueous pH (2.0-6.0), the concentration ratio of complexing agent to the total metals (0.5-2), the concentration of extractant and stripping acidities. It was shown that the extraction selectivity strongly depended on solution pH and was not completely related to the affinity of any metal with the complexing agents. When a certain level of complexing agent was present, highly effective separation could be achieved at an appropriate pH range (for an equimolar metal solution, e.g., pH 3-4 with EDTA). The application potential of this method was highlighted for the separation of Ni2+ from binary mixtures in the presence of trace amount of Ni2+ due to its high selectivity and the smaller amount of the complexing agents needed.