TY - JOUR

T1 - Pentavalent U Reactivity Impacts U Isotopic Fractionation during Reduction by Magnetite

AU - Pan, Zezhen

AU - Loreggian, Luca

AU - Roebbert, Yvonne

AU - Bartova, Barbora

AU - Hunault, Myrtille O.J.Y.

AU - Weyer, Stefan

AU - Bernier-Latmani, Rizlan

N1 - Funding Information: The work at Fudan received supports from the National Natural Science Foundation of China (42107228) and the Shanghai Pujiang Program (21PJ1401000), and the work at EPFL was supported by Swiss National Science Foundation Grant 200021E-164209 and European Research Council Consolidator Grant 725675 (UNEARTH).

PY - 2024/4/16

Y1 - 2024/4/16

N2 - Meaningful interpretation of U isotope measurements relies on unraveling the impact of reduction mechanisms on the isotopic fractionation. Here, the isotope fractionation of hexavalent U [U(VI)] was investigated during its reductive mineralization by magnetite to intermediate pentavalent U [U(V)] and ultimately tetravalent U [U(IV)]. As the reaction proceeded, the remaining aqueous phase U [containing U(VI) and U(V)] systematically carried light isotopes, whereas in the bicarbonate-extracted solution [containing U(VI) and U(V)], the δ238U values varied, especially when C/C0 approached 0. This variation was interpreted as reflecting the variable relative contribution of unreduced U(VI) (δ238U < 0‰) and bicarbonate-extractable U(V) (δ238U > 0‰). The solid remaining after bicarbonate extraction included unextractable U(V) and U(IV), for which the δ238U values consistently followed the same trend that started at 0.3-0.5‰ and decreased to ∼0‰. The impact of PIPES buffer on isotopic fractionation was attributed to the variable abundance of U(V) in the aqueous phase. A few extremely heavy bicarbonate-extracted δ238U values were due to mass-dependent fractionation resulting from several hypothesized mechanisms. The results suggest the preferential accumulation of the heavy isotope in the reduced species and the significant influence of U(V) on the overall isotopic fractionation, providing insight into the U isotope fractionation behavior during its abiotic reduction process.

AB - Meaningful interpretation of U isotope measurements relies on unraveling the impact of reduction mechanisms on the isotopic fractionation. Here, the isotope fractionation of hexavalent U [U(VI)] was investigated during its reductive mineralization by magnetite to intermediate pentavalent U [U(V)] and ultimately tetravalent U [U(IV)]. As the reaction proceeded, the remaining aqueous phase U [containing U(VI) and U(V)] systematically carried light isotopes, whereas in the bicarbonate-extracted solution [containing U(VI) and U(V)], the δ238U values varied, especially when C/C0 approached 0. This variation was interpreted as reflecting the variable relative contribution of unreduced U(VI) (δ238U < 0‰) and bicarbonate-extractable U(V) (δ238U > 0‰). The solid remaining after bicarbonate extraction included unextractable U(V) and U(IV), for which the δ238U values consistently followed the same trend that started at 0.3-0.5‰ and decreased to ∼0‰. The impact of PIPES buffer on isotopic fractionation was attributed to the variable abundance of U(V) in the aqueous phase. A few extremely heavy bicarbonate-extracted δ238U values were due to mass-dependent fractionation resulting from several hypothesized mechanisms. The results suggest the preferential accumulation of the heavy isotope in the reduced species and the significant influence of U(V) on the overall isotopic fractionation, providing insight into the U isotope fractionation behavior during its abiotic reduction process.

KW - isotope fractionation

KW - pentavalent uranium

KW - redox tracer

KW - uranium remediation

UR - http://www.scopus.com/inward/record.url?scp=85189910080&partnerID=8YFLogxK

U2 - 10.1021/acs.est.3c10324

DO - 10.1021/acs.est.3c10324

M3 - Article

C2 - 38573735

AN - SCOPUS:85189910080

VL - 58

SP - 6595

EP - 6604

JO - Environmental Science and Technology

JF - Environmental Science and Technology

SN - 0013-936X

IS - 15

ER -