Nanostructured MgFe and CoCr layered double hydroxides for removal and sequestration of iodine anions

Abstract

Radioactive iodine-129 (129I) is a contaminant of concern at radiological waste disposal and nuclear power production sites where it can incidentally be released into the environment and migrate to groundwater. Development of remediation options for 129I is hindered by its complex and mobile redox speciation. In this work, we systematically evaluated nanostructured layered double hydroxide (LDH) materials comprised of MgFe or CoCr with variable M2+:M3+ molar ratios for their affinity for the environmentally-relevant anions of iodine including iodide (I−) and iodate (IO3−). Uncalcined MgFe material demonstrated overall poor selectivity, however, affinity for I− significantly increased with increasing Mg:Fe molar ratio and upon calcination due to elimination of the parent anions followed by reconstruction of the original LDH structure, assuming physisorption. Specific surface area of calcined MgFe before and after I− sorption showed 44.3 and 13.2 m2 g−1, respectively, indicating significant decrease by reconstruction effect. In addition, high sorption capacity of calcined MgFe for I− at about 2.5 mmol g−1 suggests its applicability for immobilization of 129I. On the other hand, uncalcined CoCr material exhibited high selectivity, affinity, and capacity (about 2 mmol g−1) for IO3− indicating chemisorption and its utility for treatments of 129I in groundwater. There was a minor specific surface area variation of uncalcined CoCr before and after IO3− sorption by ion exchange (53.2 and 64.0 m2 g−1, respectively). Overall this study provides mechanistic insights into understanding and prediction of behavior of the LDH materials as efficient sorbent for design of remedial option for 129I.