Antimony is an element of growing interest for a varietyof industrial appli
cations, even though Sb
compounds are
classified as priority pollutants by the EnvironmentalProte
ction Agen
cy of the United States. Iron (Fe) hydroxidesappear to be important sorbents for Sb in soils
and sediments, but mineral surfa
ces
can also
catalyze oxidationpro
cesses
and may thus mobilize Sb. The aim of this studywas to investigate whether goethite immobilizes Sb bysorption or whether Sb(III) adsorbed on goethite is oxidized
and then released. The sorption of both Sb(III)
and Sb(V)on goethite was studied in 0.01
and 0.1 M KClO
4 M solutionsas a fun
ction of pH
and Sb
con
centration. To monitor oxidation pro
cesses Sb spe
cies were measured in solution
and in the solid phase. The results show that both Sb(III)
and Sb(V) form inner-sphere surfa
ce
complexes at thegoethite surfa
ce. Antimony(III) strongly adsorbs on goethiteover a wide pH range (3-12), whereas maximum Sb(V)adsorption is found below pH 7. At higher ioni
c strength,the desorption of Sb(V) is shifted to lower pH values, mostlikely due to the formation of ion pairs KSb(OH)
6![](/images/entities/deg.gif)
. Thesorption data of Sb(V)
can be fitted by the modified triple-layer surfa
ce
complexation model. Within 7 days, Sb(III)adsorbed on goethite is partly oxidized at pH 3, 5.9
and 9.7.The weak pH-dependen
ce of the rate
coeffi
cients suggeststhat adsorbed Sb(III) is oxidized by O
2 and that the
coordination of Sb(III) to the surfa
ce in
creases the ele
ctrondensity of the Sb atom, whi
ch enhan
ces the oxidationpro
cess. At pH values below pH 7, the oxidation of Sb(III)did not mobilize Sb within 35 days, while 30% of adsorbedSb(III) was released into the solution at pH 9.9 within thesame time. The adsorption of Sb(III) on Fe hydroxidesover a wide pH range may be a major pathway for theoxidation
and release of Sb(V).