Sorption behavior of Ga(III) and In(III) into a microcapsule containing long-chain alkylphosphonic acid monoester

Abstract

The sorption behavior of gallium and indium into a microcapsule containing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester is investigated. The effects of pH and metal concentration on sorption rate are investigated to estimate the sorption mechanism. The initial sorption rates are compared to the corresponding initial extraction rates measured for the solvent extraction system. The initial sorption rate varied with pH and metal concentration, following the solvent extraction system. Furthermore, the rate-determining step was evaluated from the activation energy. The activation energy of sorption is obtained as 48.9 kJ/mol for gallium and 30.7 kJ/mol for indium. These values indicate that both chemical reaction and diffusion processes affect the rate-determining step. These results suggest that metal sorption proceeds following sequential processes: diffusion of metal ions through aqueous film, complex formation on the surface of microcapsule, and diffusion of metal complexes through the pores. That is, the global sorption rates were controlled by both complex-formation reaction and intraparticle diffusion.