PHASE TRANSFER AND MICELLAR CATALYSIS IN METAL SOLVENT EXTRACTION: A KINETIC MODEL FOR THE LIX63-HDNNS SYSTEM.

In this paper, a preliminary kinetic model is presented which attempts to simulate the effects of the concentrations of the various species on the interfacial flux for the system KNO//3-HNO//3-Ni(NO//3)//2 /LIX63-HDNNS-hexane. A mechanism is proposed for the extraction reaction which draws from the speciation of the organic reagents, incorporates the K** plus -H** plus interchange undergone by HDNNS, and assigns the role of phase transfer catalyst to HDNNS. The pseudo-steady state approach consisting of systematically taking one step as rate-controlling while the other steps are maintained at equilibrium is followed. Four possible rate equations are derived. Kinetic data obtained in a quiescent interface cell using the initial rate technique with HDNNS as the only extractant is used to evaluate the constants in the derived models and to decide which of the models fits the pure system data best. The model found is then used to generate fluxes corresponding to the mixed system, which are compared with experimental data obtained with the rising drop technique.