Competitive Adsorption of Antimonate, Phosphate, and Sulfate On Gibbsite.

Antimony (Sb) is a growing concern for many DoD installations, as well as private shooting range facilities, and is found in the soil as a result of the weathering of lead bullet fragments.  In the soil environment, Sb is found in the Sb(V) oxidation state, existing as the hydroxyanion Sb(OH)₆^-. While in recent years phosphate (PO₄) has been increasingly used to immobilize lead in situ, little is known about the effects of its application on Sb(V) bioaccessibility and mobility.  The objectives of this research were to elucidate the mechanisms of Sb(V) adsorption to gibbsite (Al(OH)₃) as a function of ionic strength and pH, and to ascertain the competitive effects of PO₄  and sulfate (SO₄) on Sb(V) retention. Adsorption of Sb(V) was found to be pH and ionic strength dependent, with maximum adsorption at pH ~3-4 and in low ionic strength systems.  The order in which Sb(V) and PO₄ (or SO₄) were introduced to the gibbsite surface influenced the amount of Sb(V) retained. When PO₄ (or SO₄) was introduced to the system either prior to simultaneously with Sb(V), the amount of Sb(V) adsorbed was reduced. However, the addition of Sb(V) prior to PO₄ (or SO₄) had little effect on Sb(V) retention. This information is important in helping predict the fate and transport of Sb(V) in contaminated soils in the presence of commonly found anions.