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. 2023 Oct 5:636:121642.
doi: 10.1016/j.chemgeo.2023.121642. Epub 2023 Jul 26.

Kinetics of Na- and K- uranyl arsenate dissolution

Isabel Meza  1   2 , Noah Jemison  1   2 , Jorge Gonzalez-Estrella  3 , Peter C Burns  4 , Virginia Rodriguez  4 , Ginger E Sigmon  4 , Jennifer E S Szymanowski  4 , Abdul-Mehdi S Ali  5 , Kaelin Gagnon  1   2 , José M Cerrato  1   2 , Peter Lichtner  2
Affiliations

Kinetics of Na- and K- uranyl arsenate dissolution

Isabel Meza et al. Chem Geol. .

Abstract

We integrated aqueous chemistry analyses with geochemical modeling to determine the kinetics of the dissolution of Na and K uranyl arsenate solids (UAs(s)) at acidic pH. Improving our understanding of how UAs(s) dissolve is essential to predict transport of U and As, such as in acid mine drainage. At pH 2, Na0.48H0.52(UO2)(AsO4)(H2O)2.5(s) (NaUAs(s)) and K0.9H0.1(UO2)(AsO4)(H2O)2.5(s) (KUAs(s)) both dissolve with a rate constant of 3.2 × 10-7 mol m-2 s-1, which is faster than analogous uranyl phosphate solids. At pH 3, NaUAs(s) (6.3 × 10-8 mol m-2 s-1) and KUAs(s) (2.0 × 10-8 mol m-2 s-1) have smaller rate constants. Steady-state aqueous concentrations of U and As are similarly reached within the first several hours of reaction progress. This study provides dissolution rate constants for UAs(s), which may be integrated into reactive transport models for risk assessment and remediation of U and As contaminated waters.

Keywords: geochemical modeling; rate constants; reaction kinetics; solubility; uranyl arsenate.

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Conflict of interest statement

Declaration of competing interest We have nothing to declare.

Figures

Figure 1.
Figure 1.
A) NaUAs dissolution experiments at pH 1.9 vs modeling with Crunchflow (continuous lines) presenting concentrations of U (open circles), and As (open triangles). B) pH of the NaUAs dissolution experiments vs modeling with Crunchflow in time.
Figure 2.
Figure 2.
A) NaUAs dissolution experiments at pH 3.0 vs modeling with Crunchflow (continuous lines) presenting concentrations of U (open circles), and As (open triangles). B) U/As ratio of the NaUAs experiments vs modeling with Crunchflow in time. C) pH of the NaUAs dissolution experiments vs modeling.
Figure 2.
Figure 2.
A) NaUAs dissolution experiments at pH 3.0 vs modeling with Crunchflow (continuous lines) presenting concentrations of U (open circles), and As (open triangles). B) U/As ratio of the NaUAs experiments vs modeling with Crunchflow in time. C) pH of the NaUAs dissolution experiments vs modeling.
Figure 3.
Figure 3.
A) KUAs dissolution experiments at pH 2.0 vs modeling with Crunchflow (continuous lines) presenting concentrations of U (open circles), and As (open triangles). B) pH of the KUAs dissolution experiments vs modeling with Crunchflow in time.
Figure 4.
Figure 4.
A) KUAs dissolution experiments at pH 3.2 vs modeling with Crunchflow (continuous lines) presenting concentrations of U (open circles), and As (open triangles). B) pH of the KUAs dissolution experiments vs modeling with Crunchflow in time.
See this image and copyright information in PMC

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