| This research is concerned with the roles of interfacial electrical and organic phase aggregation phenomena in metal solvent extraction rate processes. Both hexane and toluene droplets were found to be negatively charged at pH > 3, with the absolute EM increasing with pH. LIX63 had no significant effect on the EM of hexane droplets, whereas the addition of HDNNS or HDEHP enhanced the negative charge at the organic/water interface. LIX63 (i.e., H(,2)L) was found to lower the EM of HDNNS-hexane droplets, an additive effect in EM was seen in HDNNS + HDEHP systems, while the presence of Aliquat 336 in HDNNS solution reversed the interfacial charge from negative to positive. Charge reversals were generally observed within the pH 9-11 range for Ni(II)- and Co(II)-containing systems, and within a wide range of pH (3-11) for Fe(III).;The hydrodynamics of various HDNNS-LIX63-hexane solutions and the rate of Ni(II) extraction from an acidic solution by HDNNS and LIX63-HDNNS mixtures were studied with the rising drop technique. The rate process was described by a mechanism incorporating simultaneous molecular diffusion and chemical reaction within an interfacial organic film. The extraction rate was found to be half order with respect to Ni('2+), zeroth order and inverse first order with respect to H('+) at high and low pH, respectively, while it is first order with respect to HDNNS for the pure HDNNS system. The total flux of nickel into a LIX63-HDNNS-hexane solution is mainly contributed by the pure HDNNS micelles and the active mixed micelles (i.e. (HD)(,m)(.);The bulk phase speciation of HDNNS and LIX63-HDNNS solutions has been analyzed by postulating the existence of various aggregates (HD(.)H(,2)L, (HD)(,m), HD)(,m)(.)H(,2)L, (HD)(,m)(.)2H(,2)L, (HD)(,m)(.)3H(,2)L) and by making use of the reported Ni(II) and Co(II) extraction data. This analysis showed that HDNNS aggregates through a monomer-micelle equilibrium process and that as the total HDNNS concentration is increased, the aggregates in the LIX63-HDNNS mixtures form in the sequence: HD(.)H(,2)L (--->) (HD)(,m)(.)3H(,2)L (--->) (HD)(,m)(.)2H(,2)L (--->) (HD)(,m)(.)H(,2)L (--->) (HD)(,m). |
