Kinetics and Equilibria of the Interaction of 8-Hydroxyquinoline with Gallium(III) in Water and Sodium Dodecyl Sulfate Solution

The kinetics and equilibria of binding of gallium(III) to the 8-hydroxyquinoline (HQ) have been investigated in water and in the presence of sodium dodecyl sulfate (SDS) micelles. Moreover, the pK_A1 and pK_A2 of HQ and first hydrolysis constant of Ga³⁺ ion have been measured in water and SDS solution. The analysis of the kinetic and thermodynamic behavior reveals that the reactive form of Ga(III) is GaOH²⁺ in both cases. Although in water the only bound form of Ga(III) appears to be the deprotonated complex GaL, evidence for stabilization of the protonated form, GaHL on the micelle surface and stabilization of Ga³⁺ with respect to GaOH²⁺ is provided by the kinetic behavior in SDS. The addition of SDS at concentrations around the critical micellar concentration, results in a large enhancement of the rate of complex formation. The large catalytic effect produced by the SDS micellar solution provides a promising basis for the extraction of gallium from water using the HQ/SDS system. A procedure for gallium(III) extraction and recovery based on ligand modified-micellar enhanced ultrafiltration method, using the HQ/SDS system, is described.