Uranium Removal from Ground Water Using Zero Valent Iron Media

Abstract

Removal of uranium from contaminated ground water using zero valent iron is currently under evaluation at several U.S. Department of Energy (DOE) facilities. Uranium removal by zero valent iron may occur via adsorption onto iron corrosion products, and by reduction to less soluble valence states by reactions with elemental iron. This research investigated the effects of water chemistry and surface precipitate buildup on the removal of soluble uranium by zero valent iron. Batch testing was performed to assess solution chemistry effects on uranium adsorption to the potential iron corrosion products, magnetite and a mixed valent amorphous iron oxide. Uranium adsorption to the simulated iron corrosion products was highly dependent on pH, and the concentration and speciation of the background electrolyte solution. Uranium removal via reduction by elemental iron closely approximated pseudo‐first‐order removal kinetics, despite the buildup of up to 40,000 monolayers of precipitated uranium on the iron surfaces. This indicates that the rate of uranium removal is not strongly dependent on the thickness of the adsorbed uranium layer. Short‐term rates of uranium reduction were similar for all solutions tested, but long‐term rates were highly dependent on water chemistry. Compared to deionized water, uranium removal rates were increased in sodium chloride containing solutions and reduced in sodium nitrate solutions. The strong influence of water chemistry on long‐term reduction rates indicates that system design will require extnded testing with the ground water of interest.

Investigating the Mechanism of Uranium Removal by Zerovalent Iron

“…At this pH value (4.2), U(VI) adsorption onto iron oxides is not favorable. [Farrell et al 1999] This result indicates that another process plays an important role in the mechanism of U(VI) removal by ZVI.…”

“…[Burris et al 1995, Kim & Carraway 2000 Significant contaminant sorption in "Pollutant-ZVI-H 2 O"-Systems have been demonstrated and attributed to iron corrosion products or graphitic inclusions in ZVI materials. [Burris et al 1998, Lin & Lo 2005 Furthermore, the role the products of iron corrosion has been mostly investigated on synthetic materials [Farrell et al 1999, Huang et al 2003 or by pretreating ZVI materials by several procedures (e.g. acid-washing or H 2 reduction of ZVI).…”

“…Here, a controversial issue is the uncertainty in removal mechanisms for uranium. [9,[14][15][16][17][18][19] Considering the chemistry of uranium and iron under conditions of natural aqueous systems, it is unlikely that reduction of U(VI) species to less soluble U(IV) species is the main mitigating process. [12,20] In fact, few evidence has been reported for the formation of U(IV) precipitates and the identification of reactions products suffers from strong interference of corrosion products and other inorganic precipitates.…”

The removal of uranium from mining waste water using algal/microbial biomass

“…Uranium can also be adsorbed to inorganic ligands. Zero valent iron immobilizes U(VI) (Farrell et al, 1999;Gu et al, 1998) by the formation of iron hydroxides (ferrihydrite, goethite) (Duff and Amrhein, 1996;Morrison et al, 1995;Wielinga et al, 1999Wielinga et al, , 2000Noubactep et al, 2003).…”

Potential Health Risks from Uranium in Home Well Water: An Investigation by the Apsaalooke (Crow) Tribal Research Group

“…In these conditions, high uranium also corresponded with high TDS levels [68]. These correlations can be explained: in oxic conditions in shallow groundwater and surface water, uranium most commonly exists as U(VI) in the uranyl ion (UO2 2+ ); this ion typically complexes with the ligand carbonate (or phosphate), which greatly increases the solubility of uranium in water [69].…”