Abstract
In recent years, recovery and separation of metal using solvent impregnated resins and microcapsules have been as an alternative technique to solvent extraction. It is easy to make them have great selectivity between metals because selection of extractant is possible.
In this work, a study on the sorption behavior of gallium and indium into a microcapsule containing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester is investigated. The sorption rates are measured under various experimental conditions. The effects of pH and metal concentration on the sorption rate are examined to estimate the sorption mechanism. The initial sorption rates are compared with the initial extraction rates measured for the corresponding solvent extraction system. It is clarified that the initial sorption rate varies with pH and the metal concentration following the same manner as that for the solvent extraction system.
The sorption of the metals into a microcapsule is considered to proceed as follows. The metal ions firstly diffuse through the liquid film around the microcapsule. The metal ions diffusing through the liquid film react with the extractant on the surface of the microcapsule. The metal-extractant complexes formed diffuse through the pore in the microcapsule.
The rate-determining step is evaluated from the activation energy estimated experimentally. As the results, it is found that both the complexation reaction and the intraparticle diffusion control the overall sorption rates.
