Competitive sorption of arsenic and antimony onto synthetic ferrous sulfide

The competitive sorption of arsenite, As(III), and antimonite, Sb(III) on mackinawite (FeS) was investigated, so as to better understand the influence between As(III) and Sb(III) in anaerobic water, soil, or sediment systems rich in FeS.

FeS was synthesized and As(III) and Sb(III) were simultaneously or sequentially added into the FeS suspensions, so as to simulate the competitive sorption of As(III) and Sb(III) on the surface of FeS particles when As(III) and Sb(III) were parallelly sorbed or As(III) sorption was priorly aged.

It was found that As(III) uptake by FeS could be significantly inhibited by Sb(III) at pH 7.0. When As(III) (initial concentration: 1 mg L⁻¹) and Sb(III) were simultaneously added into FeS suspensions at pH 7.0, the presence of Sb(III) reduced the As(III) uptake by FeS from 51.8% (no Sb(III) added) to 22.7% (1 mg L⁻¹ Sb(III) added) and to 6.9% (5 mg L⁻¹ Sb(III) added), respectively. In contrast, As(III) uptake by FeS was only slightly inhibited at pH 5.5 and not inhibited at pH 9.0. It was postulated that the competitive sorption of As(III) and Sb(III) was primarily associated with the binding of As(III) and Sb(III) to FeS at the sulfur sites and the different chalcophility of Sb(III) and As(III) led to the significant replacement of As(III) by Sb(III) at pH 7.0. It was also found that aging of As(III) sorption significantly reduced the amount of As(III) that was outcompeted by Sb(III).

This study revealed the competitive sorption of As(III) and Sb(III) on FeS particles, and implicated the importance of competitive sorption in evaluating the mobilization or immobilization of arsenic or antimony in iron- and sulfur-rich anaerobic lake sediments or soils.