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

Abstract

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 K_F 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 K_F 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.