PREPARATION, CHARACTERIZATION OF CRYSTALLINE ZIRCONIUM-PHOSPHATES ANDSTUDY ON THEIR ACID STABILITY AND ION-EXCHANGE BEHAVIOR WITH URANYL IONS

Two kinds of crystalline zirconium phosphate, alpha- and gamma-ZrP wer e prepared by direct method, and characterized by means of X-ray powde r diffractometry, thermogravimetric analysis and pH titration. The tot al exchange capacity of alpha-ZrP and gamma-ZrP for Na+ ions determine d by pH titration was 8.80 mmol/(gZr(HPO4)(2) . 6H(2)O) and 3.80 mmol/ (g NH4ZrH(PO4)(2) . H2O), respectively. The thermodynamic equilibrium constant of exchange reactions <(HH)over bar>/UO22+ on alpha-ZrP and < (HNH4)over bar>/UO22+ on gamma-ZrP at 25.0 degrees C is 2.5 and 1.1, r espectively. Although UO22+ in solution is more preferred by alpha-ZrP than by gamma-ZrP, the selectivity of alpha-ZrP for UO22+ decreases w ith decreasing pH value while less effect of pH oil the amount of UO22 + ions exchanged to gamma-ZrP has been found. It is also interesting t o find out that both H+ and NH4+ ions in gamma-ZrP can be replaced by UO22+ ions existed in concentrated solution.