SORPTION OF RARE-EARTH IONS ON BIOPOLYMER GEL BEADS OF ALGINIC ACID

Gel beads of alginic acid were used as a biopolymer sorbent for collec ting 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 com plexing agent. In the absence of lactic acid, some experiments were do ne to determine the distribution equilibrium constants for the trivale nt rare-earth ions and the maximum sorption capacity of the gel beads, and there were slight differences in the values of distribution equil ibrium constants among the rare earths. In the presence of lactic acid , the measured distribution ratios of the five rare earths were consis tent with predictions made assuming that the sorption takes place by i on-exchange reactions of the trivalent rare-earth ion and the divalent rare-earth-lactate complex. The distribution equilibrium constants fo r the cationic complex of individual rare earths were determined by co mparing the experimental data with the theoretical predictions. The qu antitative information on the sorption equilibria suggests that an eff ective separation of rare earths is caused by the combined use of algi nic acid gels and lactic acid. (C) 1998 Elsevier Science B.V. All righ ts reserved.