See more from this Session: Chemistry of Metal(loids) and Trace Elements in Soils
Antimony (Sb) is a co-contaminant with lead (Pb) in shooting range soils at DoD installations throughout the United States. The in-situ immobilization of Pb in shooting range soils may be accomplished through the application of phosphate (PO4). However, the impact of this treatment on the mobility and bioaccessibility of Sb is unknown. In soil, Sb commonly exists in the Sb(V) oxidation state as the hydroxyanion Sb(OH)6–, which is derived through the dissociation of a antimonic acid (Sb(OH)50, a weak acid). The objectives of this research were to elucidate the mechanisms and thermodynamics of Sb(V) adsorption by the hydrous Al hydroxide gibbsite, as a function of ionic environment, pH, temperature, and the competitive effects of PO4 and SO4. The adsorption of Sb(V) by gibbsite is pH-dependent. Maximum retention occurs in the pH 3 to 4 range, and decreases to a minimum in the pH 8 to 9 range. Adsorption is also independent of ionic strength when solution pH is < 7. However, at pH values > 7, Sb(V) adsorption increases with increasing ionic strength. The adsorption edge data were employed to develop a chemical model of Sb(V) adsorption using the constant capacitance surface complexation model. The data were satisfactorily described by imposing the ≡AlOSb(OH)40 and ≡AlOSb(OH)5– surface species. The chemical modeling activity will result in mechanistic parameters that describe Sb(V) retention and that are transferable; they can be used to predict Sb(V) fate and behavior in any soil environment (given that soil chemical information are available).