This study investigates physical and chemical sorption mechanisms of U and As onto natural limestone by integrating laboratory experiments, aqueous chemistry, microscopy, and spectroscopy. Recent studies found elevated concentrations of U and As in water sources affected by mining, posing potential health hazards to Native American communities. Limited research has evaluated sorption of co-occurring U and As using naturally occurring materials such as limestone which is abundant in the Southwestern US. Initial experiments assessed the reactivity of 1 mM of As and U with soluble CO32- and Ca2+at pH 3 and 7. Changes on the concentration of U and As depended on the pH, presence of CO32- and Ca2+, and interaction between U and As. Main findings showed that at pH 3, As and U concentration decreased to &lt;0.15 mM when both metals were present in the system. At pH 7, the presence of CO32- limited the reactivity of U and As. Soluble U and As concentration decreased to &lt;0.05 mM - when both metals were present in the system in absence of CO32-. Nevertheless, CO32- increased their solubility to ≈0.45 mM. Future experiments will also evaluate the reactivity of low concentrations U and As in presence of soluble CO32-and Ca2+, sorption of U and As using natural limestone, and conduct synchrotron-based spectroscopy analyses to identify solid chemical changes. Results from this study indicate that the dissolution of Ca2+ and CO32- from limestone and the co-precipitation U with As affect metal solubility. These findings have relevant implications for site remediation.

Physical and chemical mechanisms of uranium (U) and arsenic (As) sorption onto limestone

256th National Meeting (2018)

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