Impact of Antimony(V) Adsorption On Surface Charge.

Antimony (Sb) is a toxin that can be found in high concentrations in the soil due to anthropogenic sources. Antimony exists in soil as Sb(V) in the monovalent antimonate hydroxyanion. The adsorption mechanisms of Sb(V) are not well-understood. The objective of this study is to further elucidate Sb(V) adsorption mechanisms by examining the impact of adsorbed Sb(V) on the surface charging characteristics of gibbsite, birnessite, and kaolinite. Proton adsorption isotherms were employed to examine the net proton surface charge density as a function of pH and ionic strength, and in the presence or absence of adsorbed Sb(V), phosphate, or sulfate. Results show an increase in negative surface charge on the gibbsite and kaolinite with decreasing pH for all three ligands. The findings suggest an outer-sphere adsorption mechanism for Sb(V) and sulfate in neutral to alkaline systems, and inner-sphere in acidic. The findings are also consistent with those of Sb(V) adsorption edge studies. The adsorption of Sb(V) and sulfate by birnessite had no impact of surface charge throughout the pH range studied, indicating outer-sphere complexation mechanisms.