Uranium Precipitation in a Permeable Reactive Barrier by Progressive Irreversible Dissolution of Zerovalent Iron

Abstract

A permeable reactive barrier (PRB) containing zerovalent iron [Fe(O)] was installed at a former uranium milling site in Monticello, UT. A large-scale column experiment was conducted at the site to test the feasibility of Fe(O) to treat U prior to installing the PRB. Effluents from the field column experiment had pH values near 7.34, moderate decreases in C(IV) and Ca concentrations, and an elevated Fe concentration (27.1 mg/L). In contrast, groundwater exiting the PRB had a pH value of 9.82, decreases in C(IV) and Ca concentrations, and a low concentration of Fe (0.17 mg/L). A geochemical model was used to explain the chemical changes that occurred in both the field column experiment and the PRB. The model simulated the systems by the progressive irreversible dissolution of Fe(O). Modeling results indicated that a longer residence time in the PRB compared with the shorter residence time in the column contributed to the disparate effluent qualities. Prior to modeling, a controlled laboratory column experiment was conducted to help evaluate the dominant chemical mechanisms by which Fe(O) removes U from aqueous solutions. Results of the laboratory column experiment indicated that only a small amount of U could be adsorbed to ferric minerals, and, therefore, this mechanism was not considered in the model.

Recycling of complexometric extractants to remediate a soil contaminated with heavy metals

“…None the less. much of the complexing activity was restored to the extractant solution so that the extract post a second equilibration with the soil 63 particulate was very similar (in both heavy metal distribution and content) to the extract from fresh soil. solution is considered to be promising.…”

Calcite precipitation dominates the electrical signatures of zero valent iron columns under simulated field conditions

“…Although encouraging treatment efficiency has been documented (Gu et al, 1998;Morrison et al, 2001;Su and Puls, 2003), reactions between ZVI and groundwater constituents causing ZVI corrosion and subsequent secondary mineral precipitation contribute to long term performance reduction of ZVI PRBs (Liang et al, 2003;Slater and Binley, 2003;Wilkin et al, 2003;Jin Suk et al, 2009). Carbonate minerals (often precipitated concurrent with iron oxides (Mackenzie et al, 1999;Phillips et al, 2000;Liang et al, 2003)), are known to significantly impact ZVI reactivity and hydraulic efficiency in systems with frequently encountered high carbonate groundwater conditions through surface passivation and pore clogging (Agrawal and Tratnyek, 1996;Phillips et al, 2000;Liang et al, 2003;Slater and Binley, 2003;Wilkin et al, 2003;Jeen et al, 2006;Jeen et al, 2007;Jin Suk et al, 2009).…”

Investigating the Mechanism of Uranium Removal by Zerovalent Iron

“…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.…”

“…[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. [13,19,20] Coprecipitation of U(VI) species by iron corrosion products [amorphous and crystalline iron (oxyhydr)oxide] allows to explain the immobilisation. [20,21] The aim of this paper is to present the experimental procedure which enabled the elucidation of the mechanism of U(VI) removal from aqueous solutions by ZVI.…”