Application of hydrotalcite in soil immobilization of iodate (IO3−)

Radioactive iodine is quite mobile in soil and poses threats to human health and the ecosystem. Many materials, including layered double hydroxides (LDH), have been synthesized to successfully capture iodine from aqueous environments. However, limited information is available on the application of LDH in soil to immobilize iodine species. In the present study, the feasibility of using Mg–Al–NO3 LDH for retention of soil iodate (IO3−) in both batch and column systems was analyzed. The 2 : 1 Mg–Al–NO3 LDH exhibited the greatest removal efficiency of IO3− from aqueous solution, compared with 3 : 1 and 4 : 1 Mg–Al–NO3 LDH. The Mg2–Al–NO3 LDH demonstrated a strong affinity for IO3−, with a high sorption capacity of 149 528 mg kg−1 and a Freundlich affinity constant KF of 21 380 L kg−1. The addition of Mg2–Al–NO3 LDH in soil resulted in significant retention of IO3− in both the batch and column experiments. The affinity parameter KF of soil with the addition of 1.33% Mg2–Al–NO3 LDH was 136 L kg−1, which was 28.6 times higher than soil without LDH added. Moreover, the eluted iodate percentage was only 12.9% in the soil column with the 1.33% Mg2–Al–NO3 LDH addition, whereas almost 43.5% iodate was washed out in the soil column without LDH addition. The results suggested that Mg2–Al–NO3 LDH could effectively immobilize iodate in soil without obvious interference.