Sorption of rare-earth ions on biopolymer gel beads of alginic acid

Abstract

Gel beads of alginic acid were used as a biopolymer sorbent for collecting the rare earths, La(III), Nd(III), Sm(III), Dy(III) and Yb(III), from aqueous solutions. The sorption equilibria of the dissolved rare earths were studied in the absence or presence of lactic acid as a complexing agent. In the absence of lactic acid, some experiments were done to determine the distribution equilibrium constants for the trivalent rare-earth ions and the maximum sorption capacity of the gel beads, and there were slight differences in the values of distribution equilibrium constants among the rare earths. In the presence of lactic acid, the measured distribution ratios of the five rare earths were consistent with predictions made assuming that the sorption takes place by ion-exchange reactions of the trivalent rare-earth ion and the divalent rare-earth-lactate complex. The distribution equilibrium constants for the cationic complex of individual rare earths were determined by comparing the experimental data with the theoretical predictions. The quantitative information on the sorption equilibria suggests that an effective separation of rare earths is caused by the combined use of alginic acid gels and lactic acid.