Composite metal phosphates for selective adsorption and immobilization of cesium, strontium, and cobalt radionuclides in ceramic matrices

Zr–Ca–Mg composite phosphates of various chemical compositions were prepared by facile heterogeneous synthesis and their adsorption properties towards 137Cs, 85,90Sr, 60Co radionuclides were studied. The obtained composites showed a high efficiency for 137Cs, 85,90Sr, and 60Co adsorption (Kd > 104 mL/g) from model 0.1M NaNO3 aqueous solution. A sharp decrease in adsorption properties was found against 0.01M CaCl2 and seawater background, due to a decrease in the adsorbents selectivity. Zr–Ca–Mg phosphates exhibited high efficiency of radionuclides immobilization during metal ions leaching in water (desorption efficiency ∼10%). At the same time, the desorption rate of radionuclides in seawater solutions increased by 4–8 times. Calcination of saturated adsorbents at 1000 °C led significantly to increase in the efficiency of radionuclides immobilization. Thus, the activity of 60Со and 85Sr radionuclides in seawater solutions after exposure for 28 days did not exceed the lower detection limit, and the desorption efficiency of 137Cs was less than 4%. This was due to the formation of mixed Cо0.5Zr0.5(PO4), SrZr4(PO4)6 phosphates, characterized by high efficiency of radionuclides immobilization. The obtained Zr–Ca–Mg composite phosphates are promising materials for the adsorption and immobilization of 137Cs, 85,90Sr, and 60Co radionuclides.