The Influence of Temperature On the Adsorption of Antimonate by Soil Minerals.

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. Antimony adsorption edge studies indicate that Sb(V) is retained by outer-sphere complexation in neutral to alkaline systems, and inner-sphere complexation in acidic, by aluminol functional groups on gibbsite and kaolinite. However, the retention of Sb(V) by goethite appears to occur by inner-sphere mechanism throughout a broad pH range. The objectives of this research were to further elucidate the mechanisms of Sb(V) retention by examining the influence of temperature on Sb(V) adsorption by gibbsite, kaolinite, and goethite. Adsorption isotherm studies were conducted under four different temperature regimes at pH 5 and 8. The isotherms were quantified using the Langmuir adsorption isotherm model to obtain a Henry’s Law constant of adsorption. The van’t Hoff equation was then employed to compute the enthalpy of adsorption. Adsorption of Sb(V) was found to be pH dependent; greater adsorption was observed in the acidic systems. Antimony adsorption by gibbsite was not strongly influenced by temperature. The enthalpy of adsorption ranged between -5 and -11 kJ/mol, suggesting that the mechanism of Sb(V) adsorption contained outer-sphere complexation character in both the pH 5 and 8 systems.