Ion exchange properties of zirconium phosphate phosphite with alkaline earth metal ions.

ABSTRACT The ion exchange properties of zirconium phosphate phosphite, a layered compound with asymmetrical layers, towards alkaline earth cations were investigated and compared with those of a-zirconium hydrogenphosphate. It was found that these cations were easily taken up in the phosphate regionsof_ a-Zr(HPO4)0 7(HPO3),.O.5H2O whereas only Ca2+ and Sr2+ are directly exchanged from a-Zr(HP04)2.H2O. The ion exchange mechanism involves a single pnase transition and the solubility of the exchanging cations in the already formed phases. A wide solubility range was found for barium exchange. The interlayer distances and water content of the exchanged forms of zirconium phosphate-phosphite and those of the corresponding phases of zirconium phosphate were compared and discussed on the basis of the structural features of the two hosts. Zirconium phosphate-phosphite has a relatively low ion exchange capacity (2.5 meq/g) compared to that of the zirconium phosphate (6.64 meq/g)but it is a more facile exchanger for large and hydrated cations.