Kinetics of Na- and K- uranyl arsenate dissolution.

We integrated aqueous chemistry analyses with geochemical modeling to determine the kinetics of the dissolution of Na and K uranyl arsenate solids (UAs) at acidic pH. Improving our understanding of how UAs dissolve is essential to predict transport of U and As, such as in acid mine drainage. At pH 2, NaH(UO)(AsO)(HO) (NaUAs) and KH(UO)(AsO)(HO) (KUAs) both dissolve with a rate constant of 3.2 × 10 mol m s, which is faster than analogous uranyl phosphate solids. At pH 3, NaUAs (6.3 × 10 mol m s) and KUAs (2.0 × 10 mol m s) 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, which may be integrated into reactive transport models for risk assessment and remediation of U and As contaminated waters.