Selection of Solvents and Their Diluents for Solvent Extraction of Metals

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This research is concerned with elucidating the basic concept of selecting the solvents and their diluents for metal extraction with chelating agents, from the view points of kinetics and equilibrium. Metal extraction with microemulsion is also studied for providing alternative separation field for metal extraction. The results obtained are as follows: 1)the reaction between the 1:1 metal complex absorbed on the interface and the solvent dissolved in the aqueous phase determines the rates of metal extraction with chelating agents of commercial use. Three factors,i.e., the partition of the solvent between the aqueous and the organic phases, the adsorption process of the solvent on the interface, and the equilibrium constant of proton dissociation of the solvent are important for the optimal choice of the solvents and diluents. The solvent of commercial use has interfacial activity in nature, and the adsorption process is less important than the other two factors. 2)The chain length of the hydrocarbon group in a chelating agent molecule has an effect on the partition coefficient,which is different from that for acidic organophosphorous compunds. Then, an approach based on quantum chemistry is needed for obtaining the basis of solvent and its diluent selection. 3) It was shown that the metal separation with the aid of microemulsion is feasible. The metal extraction equilibrium for this system is determined by the Coulomb interaction. Thermodynamic analysis was also carried out for controlling the size of the microemulsion droplets with salinity for the aqueous phase. We are now planning the researches on the stability of the organized assemblies composed of amphiphilic agents and the phase diagrams concerned with this assemblies.