Immobilization of strontium by crystalline zirconium phosphate

Mixtures of HZr2(PO4)3 with varying amounts of Sr(NO3)2 were thermally treated at 600–1200 °C in order to investigate the immobilization of radioactive Sr. When the Sr(NO3)2 / HZr2(PO4)3=0.2 mixture was thermally treated at 700 °C, the main product was postulated to be SrZr4(PO4)6 from the XRD results. The Sr(NO3)2/HZr2(PO4)3=0.2 immobilized product thermally treated at 700 °C containing the maximum amount of immobilized Sr (a 0.2 molar ratio of Sr(NO3)2/HZr2(PO4)3 equates to approximately 4 wt.% of Sr) had minimal Sr leaching rates in several solvents at 160 °C in an autoclave. The leaching rate of Sr ion from that product was <10−6, 1.3×10−4, 1.4×10−4, 1.1×10−3, 2.0×10−3, 8.8×10−3 and <10−6 g m−2 day−1 in deionized water, sea water, 0.1 mol l−1- HCl, 0.5 mol l−1- HCl, 1 mol l−1- HCl, 1.5 mol l−1- HCl and 1 mol l−1- NH3 in an autoclave at 160 °C, respectively, indicating that HZr2(PO4)3 reacts with Sr(NO3)2 to give a stable Sr-immobilized product.