Sorption of trivalent metal ion on fibrous cerium(IV) hydrogenphosphate

Thermodynamics of trivalent metal ions/hydrogen ions exchange on a fibrous cerium(IV) hydrogenphosphate have been investigated by the micro-amount uptake. Selectivities for trivalent metal ions increase in the order; La3+ < Y3+ < Eu3+ much-lt Sc3+. The standard enthalpy change and entropy change of the ion exchange reaction increase in the order of Eu3+ < La3+ < Y3+ < Sc3+ and Eu3+ < Sc3+ < La3+ < Y3+, respectively. An enthalpy-entropy compensation relation holds except for Sc3+ ion. X-ray diffractometry and thermal analyses were also conducted the ion-exchanger phase for the macro-amount uptake. The maximal interlayer spacings were observed around the metal loading of 0.5 mmol/g and the weight loss for the adsorbed and interlayer water at the low metal loading increased in the order; Sc3+ < La3+ < Eu3+ < Y3+. In the case of scandium ion, the formation of insoluble scandium phosphate was confirmed by the DTA peak at 255 C and characteristic peaks to Sc(PO4) · 2H2O in the XRD pattern