The exchange of the cations Ag+, Mg2+, Ca'+, Sr2+ Ba2+, Y:1+, and Th4+ on tantalum arsenate in the H + form was studied. The slow step which determines tde rate of exchange of these ions is diffusion through the particle. T h e diffusion coefficients, energies of activation, and entropies of activation were calculated and were used to determine the theoretical behavior of ion-exchange separations.

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A new inorganic ion exchanger, iron(III) selenite has been synthesized having an Fe:Se ratio of 2:3 and cation exchange capacity of 0.40 meq g−1. It is fairly stable in water and dilute solutions of acids, bases, and salts. Ion distribution studies on twenty one metal ions have been done in water. Iron(III) selenite granules in H+-form have also been used as indicators in the determination of thorium in presence of some rare earth cations using hexacyanoferrate(II) as titrant. On the basis of chemical analysis, pH titrations, thermal and infrared analyses the following scheme for the decomposition of iron(III) selenite has been proposed: 2Fe2O3·3H2SeO3·2H2O\overset140°C→2Fe2O3·3H2SeO3\overset500°C→2Fe2O3.

A new inorganic ion exchanger, cerium(IV) selenite has been synthesized with a cation exchange capacity of 0.98 mequiv g−1. It is fairly stable in water and in dilute solutions of acids, bases and salts. The Kd values for number of metal ions were determined in different solvent systems. The exchanger possesses a high affinity for Hg(II) and hence its separation from certain metal ions have been made.