Low leachability phosphate lattices for fixation of select metal ions

The feasibility of using phosphate compounds to fix ions of different sizes and charge such as Sr2+, Ba2+, Pb2+, Fe3+, Cr3+, Zr4+, Sm3+, Eu3+, and Gd3+ is investigated. Two structure types of phosphate compounds, viz., NZP (NaZr2P3O12) and eulytine, are considered. The compounds of formula AM3+ZrP3O12 (A = Sr, Ba, and Pb; M3+ = Cr and Fe) [NZP] are studied with respect to the incorporation of ions such as Fe3+, Cr3+, and Zr4+. The compounds of the formula M3LnP3O12 (M = Sr and Ba; Ln = Sm, Eu, and Gd) [eulytine] are studied with respect to the encapsulation of rare earth ions. Chemical durability tests indicate that the leach rates of various ions from the NZP structure type compounds are of the order of 10−4 gm−2d−1, and of the order of 10−3 gm−2d−1 from compounds with eulytine structure.