Ferrihydrite as a powerful scavenger of As: A thermochemical and a field study

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Arsenic is one of the most toxic elements, generally classified as a priority pollutant. Here I propose to investigate the association of As and Fe oxide minerals by experimental and field work. The goal of the work proposed here is to determine 1) the thermochemical properties of As-ferrihydrite (~Fe(OH)3(nAs2O5(mH2O) and scorodite (FeAsO4(2H2O), and 2) the chemical association and oxidation state of As at a selected heavily polluted site Nizny Hrusov, Slovakia. The thermochemical properties of As-ferrihydrite and scorodite will be measured by acid-solution calorimetry. The knowledge of these properties for the selected minerals is important for assessing and predicting the fate of As-ferrihydrite, a common waste-form for immobilization and long-term storage of As. The field site in Nizny Hrusov was selected because our preliminary work points at a massive As contamination, elevated organic carbon content in the water, and bioavailability of As. The chemical association of As (with ferrihydrite versus organic matter) and its oxidation state will be probed by sequential extractions and X-ray absorption spectroscopy, respectively. Understanding the speciation of As will direct the future cleanup effort at this site and other similarly polluted sites.