Removal of Radioactive Iodine Species by using Layered Double Hydroxides under Aqueous Condition

Abstract

To improve our understanding of management for radioactive iodine waste generated by operation of nuclear power plants (NPPs), or severe accidents at them, layered double hydroxides (LDHs) synthesized using different metal cations (divalent Sn2+, Ca2+, Mg2+, Co2+; trivalent Fe3+, Cr3+) with and without calcination were tested to evaluate the efficiency (%) with which they remove iodide (I^-) and iodate (IO_3^-) from solution. Calcination at high temperature (500 °C) increased the compactness and decreased the stability of LDHs by evaporating water molecules and volatilizing anions from its inter-layers. Calcined MgFe_Cl_C_21 LDHs that contained Mg2+ and Fe3+ in M2+ : M3+ concentration ratio of 2:1 achieved the highest I^- removal (89.2 %) and non-calcined CoCr_Cl_NC_41 LDHs that contained Co2+ and Cr3+ in M2+ : M3+ concentration ratio of 4:1 showed the highest IO_3^- removal (97.0 %). The results suggest that the memory effect of LDHs and smaller ionic radii of I^- (206 pm) than IO_3^- (> 270 pm) are important for I^- removal using calcined LDHs. However, IO_3^- removal was most effective with non-calcined LDHs because of strong anion exchange capacity with Cl^-.