The Adsorption of Antimonate by Goethite.

Antimony (Sb) comprises approximately 2 to 5 % of lead ammunition. The presence of Sb in shooting range soils is of concern to Department of Defense installations, as well as to civilian facilities. Antimony is found in the environment in the Sb(V) oxidative state as the monovalent antimonate hydroxyanion. It is an acceptable practice to use phosphate to immobilize and remediate Pb contaminated soils in-situ. However, the impact of phosphate on the retention of Sb(V) by soil minerals was not been well-described. The objectives of this research were to elucidate the kinetics and mechanisms of Sb(V) adsorption on goethite as a function of pH and ionic strength along with competitive effects of the common soil ligands, phosphate and sulfate.  Adsorption of Sb(V) was found to be pH dependent, increasing with decreasing pH to an adsorption maximum in the pH 4 to 5 range. Antimony adsorption was independent of ionic strength. The order in which Sb(V) and  phosphate were introduced to the mineral surface influenced the amount of Sb(V) retained.  When phosphate was added either before or at the same time as Sb(V), the amount of Sb(V) retained was significantly reduced when compared to the single ligand Sb(V) system. This effect was minimized when Sb(V) was introduced to the mineral surface prior to phosphate. Antimony had a small impact on the adsorption of phosphate, reducing phosphate retention primarily in acidic systems. The presence of sulfate had no impact on Sb(V) retention regardless of the order of ligand introduction. This information can be used to predict the fate and behavior of Sb(V) in the soil environment and the impact of phosphate and sulfate on Sb(V) retention and bioaccessibility.