Contribution of Amorphous Iron Compounds to Adsorptions of Pentavalent Antimony by Soils

Antimony, a known toxic element, is emitted into the environment by industrial processes. The objective of this research was to identify the components adsorbing antimony(V) in soils. Antimony(V) uptake by soil samples and synthesized allophane was measured by the spiking method. The phosphorous sorption coefficient of soil samples was measured and the amorphous index calculated. The antimony(V) adsorptive capacity of various soils, calculated from the uptake, indicated that Andosol soils rich in amorphous components have a high capacity of adsorption. A strong relationship was observed between the amorphous index and antimony(V) adsorptive capacity and also between the Fe/(Al + Fe) ratio and antimony(V) adsorptive capacity of synthesized allophane, thus indicating that the contribution of iron-related surface base groups is higher than the aluminol and silanol groups. Evidence supporting this result was obtained from an extraction experiment in which 34–92% of antimony(V) adsorbed by soil samples was bound to amorphous iron compounds. This research indicates that the adsorption of antimony(V) is closer to that of arsenic(III) than arsenic(V), which is of interest in considering the mobility of antimony in the environment.