Chapter 7 - Development and Performance of an Iron Oxide/Phosphate Reactive Barrier for the Remediation of Uranium-Contaminated Groundwater

Abstract

This chapter reports on the laboratory and field testing of engineered solid mixtures for use with deep aquifer remediation tool (DART) technology for the removal of groundwater metal contamination resulting from mining and ore processing. In laboratory testing mixtures of pelletized bone charcoal (bone char apatite) and hematite pellets coated with amorphous iron oxide are studied in various ratios in both batch and column experiments, to evaluate the effectiveness of the mixture in removing uranium from groundwater. The variables include phosphate levels in solution and on the iron oxide surface, pellet ratios, and aging of the solids. Laboratory batch experiments indicate phosphorus adsorption by the iron oxide pellets, but there is no apparent increase in uranium removal in mixtures compared to bone char pellets alone. In contrast, column experiments show greater uranium removal by the mixture of materials, possibly as a result of longer aging times and/or higher adsorbed phosphorus concentrations. No evidence of autonite formation is also found. Field tests using DART deployment technology also compares various pellet ratios and includes shallow DART deployment in an unpumped well array in Fry Canyon, Utah, the site of an abandoned uranium upgrader operation, and deep DART emplacement 146 m below land surface during active mining at the Christensen Ranch in situ uranium mine in northeastern Wyoming. An additional field test at Fry Canyon also includes DART testing with zerovalent iron. This study demonstrates that DARTs can effectively remove contaminants. Both laboratory column and the Fry Canyon field results suggest that a mixture of materials can be more effective at contaminant removal than a single reactive barrier material, although efficiencies of removal in the field tests could not be determined accurately due to a lack of knowledge of the input fluxes of U(VI) to the DARTs.