Stoichiometry of the Nickel Complex Formed with LIX 63 Hydroxyoxime under Acidic Chloride Conditions

ABSTRACT The extraction of nickel by LIX® 63 hydroxyoxime (‘hydroxyoxime’) under acidic (10–100 g/L hydrochloric acid) chloride conditions was investigated with the intent of determining the stoichiometry of the resulting complex in solution. Maximum loading and continuous variation tests indicate that nickel is extracted as a cationic salt with chloride counter-ions, the resulting complex exhibiting octahedral coordination with 1:3:2 nickel:hydroxyoxime:chloride stoichiometry. This species is also observed to readily form under mildly acidic (pH 1–4) chloride conditions, with the extent of formation being independent of pH. Nickel extraction kinetics were moderately fast, equilibrium being reached in 10 minutes. The behaviour of this system helps to provide clarity in relation to complex stoichiometry and the role of different ligands in synergistic systems utilising LIX 63 and an organic acid such as Versatic 10, opening up the possibility of nickel extraction from acidic chloride media using LIX 63.