COUPLED REACTION TRANSPORT MODELING OF A CHEMICAL BARRIER FOR CONTROLLING URANIUM(VI) CONTAMINATION IN GROUNDWATER

Adsorption of uranium onto amorphous ferric oxyhydroxide can be used f or in situ containment of uranium(VI) present in mill tailings and for prevention of potential groundwater contamination. Adsorption of uran ium(VI) is strongly influenced by groundwater chemistry, especially pH and total dissolved carbonate concentration. To evaluate the effectiv eness of adsorption onto amorphous ferric oxyhydroxide as a containmen t barrier, the extent of uranium adsorption was quantified as a functi on of solution chemistry and other adsorption parameters. The adsorpti on model was used within a coupled hydrogeochemical transport model to evaluate the conditions under which amorphous ferric oxyhydroxide can be effective in preventing groundwater contamination. The modeling re sults depicted spatial and temporal evolution of the tailings-groundwa ter system, and permitted delineation of the uranium(VI) plume in grou ndwater under different scenarios. The analysis showed that adsorption of uranium(VI) onto amorphous ferric oxyhydroxide can be an effective mechanism for preventing release of uranium(VI) into groundwater espe cially for neutral-pH mill tailings. It was also found that essentiall y no retardation occurred in tailings with alkaline pore fluids. An ec onomic analysis showed that the amorphous ferric oxyhydroxide treatmen t can be applied to neutral-pH mill tailings in a cost-effective manne r. The results obtained in the study support the conceptual foundation of geochemical engineering in waste management.