COMPETITIVE SORPTION OF ALKALI-METAL AND ALKALINE-EARTH-METAL CATIONS BY CARBOXYLIC-ACID RESINS CONTAINING ACYCLIC OR CYCLIC POLYETHER UNITS

Sorption of Na+, K+, Mg2+, and Ca2+ from aqueous solutions by the polymethacrylic acid resin Amberlite CG-50 and by three carboxylic acids resins that contain acyclic or cyclic polyether units has been investigated. Compared with CG-50, for which the competitive sorption selectivity is Ca2+ > Mg2+ >> Na+, K+, the sorption selectivity order remains the same with the acyclic polyether carboxylic acid resin and one of the crown ether carboxylic acid resins, but the Ca2+/Mg2+ sorption selectivity increases substantially. On the other hand, for a crown ether carboxylic acid resin in which the ion-exchange site is positioned over the polyether ring, sorption of the monovalent cation that best fits the crown ether cavity becomes comparable with Ca2+ sorption. Thus the incorporation of polyether units into carboxylic acid resins and the position of the ion-exchange site with respect to a crown ether unit are shown to exert an appreciable influence upon the competitive sorption of alkali-metal and alkaline-earth-metal cations.