New heterogeneous synthesis of mixed Ti-Ca-Mg phosphates as efficient sorbents of 137Cs, 90Sr and 60Co radionuclides

Abstract

Abstract New heterogeneous synthesis of mixed Ti-Ca-Mg phosphates was developed and investigated using DTA-TG, XRD, FT-IR and SEM-EDX techniques. The route of synthesis is based on the heterogeneous interaction between aqueous solution of titanyl-diammonium sulfate and solid precursor as phosphated dolomite Ca0.7Mg0.3HPO4·2H2O (PD-1) and Ca2.65Mg3(NH4)1.3(PO4)4(CO3)0.3·6H2O (PD-2) composition. It has been shown that interaction of PD-1 with titanium solution is accompanied by successive dissolution of magnesium hydrogen phosphate and calcium hydrogen phosphate followed by titanium phosphate precipitation. For PD-2 solid precursor, the interaction proceeds by heterogeneous exchange reaction simultaneously with tertiary calcium, magnesium phosphates and magnesium-ammonium phosphate. It has been shown that when PD-1 is used, the final solid has surface area of 220–230 m2·g-1, total pore volume of 0.32–0.37 cm3·g−1 and average pore diameter of 5.7–6.7 nm. The solid obtained from PD-2 has lower surface properties such as 140–144 m2 g-1 for surface area and 0.27–0.34 cm3 g−1 for total pore volume. It has been shown that the samples of Ca-Mg-Ti phosphates effectively removed 137Cs, 90Sr and 60Co radionuclides at pH 5.0 (Kd 10−3–10−5 cm3 g−1) that could be used for one-stage purification of liquid radioactive wastes with complex radionuclide composition.