Behavior of Antimony(V) during the Transformation\nof Ferrihydrite and Its Environmental Implications

Abstract

In\nthis study, we investigated the behavior of Sb­(V) during the\ntransformation of poorly crystalline Fe­(III) oxyhydroxides (two-line\nferrihydrite) with various Sb/Fe molar ratios at pH 6.0. Both XRD\nand Fe EXAFS analyses confirmed that goethite and hematite are the\nprimary transformation products of the ferrihydrite in the presence\nof Sb­(V). The crystallization kinetics showed that the transformation\nrate with Sb­(V) was approximately the same as that of the control\n(without Sb­(V)), which indicates that the presence of Sb­(V) does not\ninfluence the transformation rate to a noticeable extent. Throughout\nthe transformation, Sb­(V) dominantly partitioned in the solid phase\nand no desorption of Sb­(V) was observed. Furthermore, Sb EXAFS analyses\nsuggested that Sb­(V) in the solid phase is structurally incorporated\ninto crystalline goethite and/or hematite generated by the ferrihydrite\ntransformation. Hence, Sb­(V) transfers into the thermodynamically\nstable solids from the metastable ferrihydrite with aging, indicating\na rigid immobilization of Sb­(V). These findings are valuable for making\npredictions on the long-term fate of Sb associated with ferrihydrite\nin natural environments.