Lanthanide/actinide ion-exchange and structural investigations of the layered phosphatoantimonic acid, H3Sb3P2O14·ZH2O

The ion-exchange behaviour of the lamellar phosphatoantimonate phases, A3Sb3P2O14·ZH2O (A = H, K; Z = 5, 6) in acidic media has been explored for several trivalent lanthanides (La3+, Eu3+ and Pr3+) and the actinide 241Am3+. The protonated phase displayed high levels of uptake for each of these cations in mildly acidic media (<2 M HNO3) and was also shown to be tolerant of moderate levels of potassium cations. The La3+ ↔ 3H3O+ 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 La3+ at one or both of the unique ion-exchange sites of the {Sb3P2O14}∞ framework were experienced due to complications arising from the presence of intercalated water. This study has demonstrated that the exchange of La3+ leads to a proportion of the ion-exchange sites about some of the PO4 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.