KINETICS AND MECHANISM OF COPPER-EXTRACTION WITH DIALKYLPHOSPHORIC ACIDS AND HYDROXYOXIMES STUDIED BY A ROTATING DIFFUSION CELL

A rotating diffusion cell with a porous membrane was used to study the kinetics of liquid/liquid extraction of copper ions using commerciall y important acidic extractants, i.e. dialkylphosphoric acids and hydro xyoximes. The reaction zone is assumed to be situated in a thin zone o f varying thickness within the aqueous diffusion layer but adjacent to the aqueous/organic interface. The kinetic results were modeled by as suming a mixed control regime involving both chemical reaction and dif fusion of reactants and products to and from the reaction zone as cont rolling steps. The ''solubility'' of the extractant in the aqueous pha se, expressed in terms of the extractant distribution coefficient betw een the organic and aqueous phases, was shown to exert a considerable influence on the kinetic performance of the extractants. By the distri bution coefficient being incorporated into the kinetic model, it is no w possible to fully explain the behavior of the extraction rate curve with changing hydrogen ion concentration in the aqueous phase. The thi ckness of the reaction zone for hydroxyoximes is estimated to be of th e order of 1.3 x 10(-3) mu m while for dialkylphosphoric acids it is o f the order of 0.7 mu m.