Development and Testing of a Silver Chloride-Impregnated Activated Carbon for Aqueous Removal and Sequestration of Iodide

Abstract

Silver impregnated activated carbon (SIAC) can effectively remove iodide from water and sequester it in the form of AgI(s). Given the extremely insoluble nature of AgI(s), the spent SIAC can be safely disposed of in land burial facilities. However, when the molar ratio of silver to iodide is greater than one, which is typical for waters contaminated with iodide, unreacted silver on the SIAC leached into solution with decreasing pH. To minimize silver leaching, a silver chloride impregnated activated carbon (SIAC-Cl) was produced from a SIAC. Scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and X-Ray Diffraction (XRD) analyses confirmed the presence of silver chloride on the SIAC-Cl. Batch isotherm experiments conducted at pH 5, 7 and 8 showed that the iodide uptakes of SIAC-Cl and SIAC were similar and independent of pH. SEM/EDX and XRD analyses after reaction with iodide indicated that chloride was exchanged with iodide to form AgI(s) on the SIAC-Cl. Batch leaching experiments demonstrated that leaching of silver from SIAC-Cl under acidic conditions was significantly lower than from SIAC. The performance of SIAC and SIAC-Cl for practical applications was evaluated by conducting column experiments using a radioactively contaminated groundwater that included 129I. SIAC and SIAC-Cl showed similar degrees of iodide uptake. However, a significant degree of silver leaching, about 50% of the total silver, occurred from the SIAC during the course of the column experiments, whereas silver leaching from SIAC-Cl was remarkably low (only 6% of the total silver). SIAC-Cl appears to be a suitable getter material to remove and sequester iodide from contaminated waste streams.