Single-Stage Extraction and Separation of Co(2+) from Ni(2+) Using Ionic Liquid of [C(4)H(9)NH(3)][Cyanex 272]

The purpose of this study was to optimize the extraction conditions for separating Co(2+) from Ni(2+) using N-butylamine phosphinate ionic liquid of [C(4)H(9)NH(3)][Cyanex 272]. A Box–Behnken design of response surface methodology was used to analyze the effects of the initial pH, extraction time, and extraction temperature on the separation factor of Co(2+) from sulfuric acid solution containing Ni(2+). The concentrations of Co(2+) and Ni(2+) in an aqueous solution were determined using inductively coupled plasma-optical emission spectrometry. The optimized extraction conditions were as follows: an initial pH of 3.7, an extraction time of 55.8 min, and an extraction temperature of 330.4 K. The separation factor of Co(2+) from Ni(2+) under optimized extraction conditions was 66.1, which was very close to the predicted value of 67.2, and the error was 1.7%. The equation for single-stage extraction with high reliability can be used for optimizing the multi-stage extraction process of Co(2+) from Ni(2+). The stoichiometry of chemical reaction for ion-exchange extraction was also investigated using the slope method.