PNNL

Abstract

The radioactive iodine-129 (129I) is a contaminant of concern at radiological waste disposal and nuclear power production sites where it can incidently be released into 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 layered double hydroxides (LDHs) materials comprised of MgFe or CoCr with variable M2+:M3+ molar ratio for their affinity for the environmentally-relevant anions of iodine including iodide (I-) and iodate (IO3-). Both materials were prepared by simple precipitation method, calcined and structurally characterized before and after uptake of I- or IO3- to elucidate mechanism of their sequestration. Uncalcined MgFe material demonstrated overall poor selectivity but high affinity for iodide which significantly increased with Mg:Fe moar ratio and upon calcination due to elimination of the parent anions followed by reconstruction of the original LDH structure. High sorption capacity of MgFe for iodide at about 2.5 mmol g-1 suggests its applicability for immobilization of 129I. On the other hands, uncalcined CoCr material exhibited high selectivity, affinity, and capacity (about 2 mmol g-1) for IO3- indicating its utility for both treatment of groundwater and sequestration of 129I. Calcination of CoCr resulted in irreversible degradation of the LDH structure due to formation on the Co2CrO4 spinel. Overall this study provides mechanistic insights into understanding and prediction of behaviour of the LDH materials for design of remedial option for 129I.