The ion-exchange behavior of the ammonium ion on crystalline zirconium phosphate (c-ZrP) was studied by pH titration and X-ray powder diffraction. The ion-exchange capacity of c-ZrP was 4.4 meq/g in an acidic solution and 6.6 meq/g in an alkaline solution. At an exchange of 66% the Zr(NH4PO4)1.33(HPO4)0.67·H2O phase was present and at an exchange of 100% Zr(NH4PO4)2·H2O phase was present. The forward and backward titration curves exhibited a hysteresis loop. This results from the presence of the different phases in the titration of each direction. Through the ion-exchange cycle, the crystallinity of c-ZrP was maintained.
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