STUDIES ON THE USE OF ALGINATE GEL POLYMERS AS SELECTIVE ADSORBENTS OF RARE EARTH ELEMENTS FROM AQUEOUS SOLUTIONS

Rare earth elements (REEs) have unique physicochemical properties that make them essential elements in many high-tech components. In general, the abundance of REEs produced by aqueous extraction processes is low. Additionally, most samples contain elements that interfere with the determination of REEs, so that separation and pre-concentration steps are often necessary. A number of techniques based on ion-exchange resins and solvent extraction have been studied and proposed. In the present work, the feasibility of using alginate gel for REE recovery and separation was examined. Alginic acid is a linear copolymer consisting of D-mannuronic and L-guluronic acids that forms hydrogels with many divalent cations, including Ca(II), Ba(II), Sr(II), Cu(II), Pb(II) and others. In our experiments, the gel beads were formed by dropping 2% sodium alginate directly into aqueous solutions of REEs with various mixtures of divalent cations. Modifications of solid alginate beads made by dosing with compounds capable of generating specific REE-binding ligands were also tested. We examined how specific REEs were selectively sequestered within alginate gel via gel polymerization and by further diffusion and potential displacement reactions. The data are discussed relative to improvements in the analytical quantification of low level REEs and with regard to potential applications of this technique for fast and complete recovery of REE from complex matrices.