(683f) Impact of Solvated Water Layer on Adsorption of Selenium Oxo-Anion on <012> Hematite Surface

Selenium is highly soluble in water as selenate and selenite and is toxic to human and aquatic life even at very low concentration (TWA 0.2 mg/m³). Increased usage of selenium in the electronic and glass industry threatens to further increase the concentrations of these species in our water resources. Adsorption is a promising remediation strategy, particularly in low population densities area and communities with self-run wells, because of its potentially lower cost than the construction of chemical treatment plants. The adsorption of oxo-anions on existing sorbents is , however, not selective; this is exacerbated by the fact that Selenium oxoanions occur at much lower concentrations than similar S ions. This leads to increased financial burden for water treatment. Recent adsorption experiments of selenium oxoanion of different hematite surface found that selenate and selenite have higher selectivity on [012] and [110] hematite facet respectively. Here we use first principle calculations to study the facet dependent behavior of hematite based adsorption. Adsorption energies are calculated for varying oxo-anion configuration including inner and outer sphere complexes on [012] surface. In this work, we delineate the most important effects controlling adsorption, including surface configuration, pH, solvation, etc. We find the solvation configuration directed by the surface controls the adsorption behavior. In addition to shedding light on this particular adsorption species, this work highlights the criticality of correctly considering solvation, and outer sphere adsorption, in first principles analysis of oxoanion adsorption.