Department of Geology , University of Illinois at Urbana-Champaign , 3081 Natural History Building, 1301 W. Green St. , Urbana , Illinois 61801 , United States.
College of Earth, Ocean, and Atmospheric Sciences , Oregon State University , 104 CEOAS Administration Building, 101 SW 26th St. , Corvallis , Oregon 97331 , United States.
Environ Sci Technol. 2018 Mar 20;52(6):3422-3430. doi: 10.1021/acs.est.7b05162. Epub 2018 Mar 1.
Biostimulation to induce reduction of soluble U(VI) to relatively immobile U(IV) is an effective strategy for decreasing aqueous U(VI) concentrations in contaminated groundwater systems. If oxidation of U(IV) occurs following the biostimulation phase, U(VI) concentrations increase, challenging the long-term effectiveness of this technique. However, detecting U(IV) oxidation through dissolved U concentrations alone can prove difficult in locations with few groundwater wells to track the addition of U to a mass of groundwater. We propose the U/U ratio of aqueous U as an independent, reliable tracer of U(IV) remobilization via oxidation or mobilization of colloids. Reduction of U(VI) produces U-enriched U(IV), whereas remobilization of solid U(IV) should not induce isotopic fractionation. The incorporation of remobilized U(IV) with a high U/U ratio into the aqueous U(VI) pool produces an increase in U/U of aqueous U(VI). During several injections of nitrate to induce U(IV) oxidation, U/U consistently increased, suggesting U/U is broadly applicable for detecting mobilization of U(IV).
生物刺激诱导可溶 U(VI)还原为相对不溶的 U(IV)，是降低受污染地下水中水相 U(VI)浓度的有效策略。如果生物刺激阶段后发生 U(IV)氧化，U(VI)浓度会增加，这对该技术的长期有效性构成挑战。然而，在地下水井数量较少的地区，仅通过溶解 U 浓度来检测 U(IV)氧化可能具有挑战性，因为难以追踪 U 向大量地下水的添加。我们提出将水相 U 的 U/U 比值作为通过氧化或胶体迁移再移动 U(IV)的独立、可靠示踪剂。U(VI)的还原会产生富含 U 的 U(IV)，而固态 U(IV)的再移动不应引起同位素分馏。具有高 U/U 比值的再移动 U(IV)与水相 U(VI)池结合，会导致水相 U(VI)的 U/U 比值增加。在几次注入硝酸盐以诱导 U(IV)氧化的过程中，U/U 持续增加，表明 U/U 广泛适用于检测 U(IV)的迁移。
