Lanthanide/actinide ion-exchange and structural investigations of the layered phosphatoantimonic acid, H 3Sb 3P 2O 14· ZH 2O

Abstract

The ion-exchange behaviour of the lamellar phosphatoantimonate phases, A 3Sb 3P 2O 14 · ZH 2O (A = H, K; Z = 5, 6) in acidic media has been explored for several trivalent lanthanides (La 3+, Eu 3+ and Pr 3+) and the actinide 241Am 3+. The protonated phase displayed high levels of uptake for each of these cations in mildly acidic media (<2 M HNO 3) and was also shown to be tolerant of moderate levels of potassium cations. The La 3+ ↔ 3H 3O + exchange has been further studied using thermogravimetric, variable temperature X-ray diffraction, FT-IR and 31P MAS NMR. Difficulties in drawing conclusions regarding the siting of La 3+ at one or both of the unique ion-exchange sites of the {Sb 3P 2O 14} ∞ framework were experienced due to complications arising from the presence of intercalated water. This study has demonstrated that the exchange of La 3+ leads to a proportion of the ion-exchange sites about some of the PO 4 tetrahedra being left vacant upon exchange. The utility of the phosphatoantimonate framework for removal of radiogenic lanthanide and americium from acidic media has been demonstrated.