MECHANISM OF ION-EXCHANGE IN ZIRCONIUM-PHOSPHATES .12. CALORIMETRIC DETERMINATION OF HEATS OF CESIUM ION-HYDROGEN ION-EXCHANGE
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The heats of Cs+-H+ exchange on two samples of zirconium phosphate of different crystallinities have been determined calorimetrically. The reactions are initially exothermic. The nearly amorphous sample attained a maximum value of Hx = -4.5 kcal/mol of exchanger at about 55% of exchange. At higher loadings the reaction became progressively endothermic. The high initial preference of amorphous zirconium phosphate for Cs+ relative to other alkali metal cations stems from the greater exothermicity of the reaction. For the more crystalline exchanger -Hx increased linearly up to 75% of exchange whereupon the reaction became endothermic. This indicates the formation of an exchanged phase with 1.5 mol of Cs+ per formula weight of exchanger. The results of this study are compared to those of a similar one carried out previously for the Na+-H+ system.
