Separation of rare metal ions by a column packed with microcapsules containing an extractant

The separation of gallium and indium was investigated using a column in which microcapsules containing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester were packed. First, adsorption isotherms were measured and analyzed according to the Freundlich adsorption isotherm model, from which the saturation capacities and the operation lines were determined. Then, breakthrough curves were measured at several flow rates and pH's of the feed solution. When the flow rate decreased, the adsorption capacity of gallium also decreased, but that of indium did not change. By selecting the appropriate pH, the separation of gallium from indium was achieved. Specifically, it was possible to separate the two metals by selecting the hydrogen-ion concentration in the stripping operation. Even after the fifth cycle of adsorption and stripping, the loss of the extractant, in the microcapsules was only about 0.01%. The theoretical equation for the breakthrough, curve was established. The experimental data were correlated to the lines calculated using the predictive equation.