Impact of Antimonate On the Charging Characteristics of Metal Oxyhydroxides.

Antimony (Sb) is a toxin and a co-contaminant with lead (Pb) in shooting range soils. Antimony commonly exists in soil as Sb(V) as the antimonate hydroxyanion (Sb(OH)₆^-), which is derived from the hydrolysis of the weak acid, Sb(OH)₅⁰. The adsorption mechanisms of Sb(V) are not known; thus, its fate and behavior in shooting range soils, and its response to in-situ lead immobilization (e.g., by phosphate amendment) have not been well established. Previous studies show that Sb(V) adsorption by hydrous metal oxides is a function of pH and ionic strength. Antimony(V) retention is also reversible in alkaline systems (suggesting anion exchange); however, strongly hysteretic in acidic (suggesting ligand exchange). The objective of this study is to further elucidate Sb(V) adsorption mechanisms by examining the impact adsorbed Sb(V) on the surface charging characteristics of goethite and gibbsite. Potentiometric titrations were employed to examine the net proton charge density as a function of pH and ionic strength, and in the presence or absence of adsorbed Sb(V).