Facilitated Liquid-Liquid Extraction and Stripping of Nickel and Cadmium from Aqueous Solutions by Ionic Liquid

Application of an ionic liquid (4-Methyl-2-pentanone) carrier on liquid-liquid extraction of nickel and cadmium from aqueous solutions is reported. 4-Methyl-2-pentanone was found to dissolve in octanol (as diluent) and was capable of extracting both nickel and cadmium ions, however in terms of extraction efficiency, 4-Methyl-2-pentanone has higher capability for nickel extraction in compare to cadmium. The effects of feed phase pH, carrier concentration, mixing time, stripping phase pH and inert salt concentration on extraction of nickel and cadmium were analyzed using factorial design for screening experiment and face centered composite design of experiments for optimization. The results of liquid-liquid extraction process led to removal of 91% of nickel ions and 32% of cadmium from mixed Ni-Cd aqueous feed phase with carrier concentration of 250 mM, feed phase pH of 4, mixing time of 5 minutes and 1.5 M of sodium sulphate as inert salt. In stripping phase, both nickel and cadmium were highly stripped while stripping phase pH was set at alkaline range of 10-11. The effect of feed phase pH on distribution ratio (Feed/Org) for both metals was investigated and the results revealed that one nickel ion is extracted into the organic phase by an average 3.2 of 4-Methyl-2-pentanone molecules to form nickel-4-Methyl-2-pentanone complex, while for cadmium extraction, the carrier molecules involved in metal-carrier complexation is equal to 2.