Immobilization of alkali, alkaline-earth and rare-earth elements by crystalline zirconium phosphate HZr₂(PO₄)₃

Abstract

The immobilization of alkali metal elements (M^I = Li, Na, K, Rb, Cs), alkaline-earth metal elements (M^II = Mg, Ca, Sr, Ba) and rare-earth metal elements (M^III = La, Nd, Sm, Gd, Dy, Ho, Er, Yb) in crystalline zirconium phosphate HZr₂(PO₄)₃ was performed by mixing each of the nitrate salts [M^INO₃, M^II(NO₃)₂ and M^III(NO₃)₃] with the HZr₂(PO₄)₃ powders followed by a thermal treatment at 700°C for 5 h. The leaching test of these immobilized products, M^IZr₂(PO₄)₃, M^IIZr₄(PO₄)₆ and M^IIIZr₆(PO₄)₉, were carried out at 160°C for 24 h in 1 mol·dm⁻³-HCl using an autoclave. The leaching rate of M^I, M^II and M^III showed a tendency to decrease with an increase in the ionic radius of M^I, M^II and M^III, respectively, regardless of the valence of the immobilized metal elements.