Sulfidization of As(V)-containing schwertmannite and its impact on arsenic mobilization

•Incorporated As(V) inhibits the nucleation of schwertmannite.•Reactivity follows the order of Sch-free > Sch-As(V) > Sch*-As(V).•Re-adsorption of As(V) is more significant in the Sch-As(V) system.•Insignificant re-adsorption of As(V) is in the Sch*-As(V) system.•Transformation process cannot cause significant mobilization of incorporated As(V).

Fe (oxyhydr)oxides have been extensively studied due to their strong potential to immobilize arsenic. However, the reactivity of Fe (oxyhydr)oxides with adsorbed or structurally-incorporated As(V) is poorly understood. In this study, As(V)-free, -adsorbed [Sch*-As(V)] and structurally-incorporated schwertmannites [Sch-As(V)] were prepared, and their reactivity was compared during S(—II)-mediated dissolution. Our results show that development of schwertmannite is significantly inhibited as As(V) is incorporated into the structure of Fe (oxyhydr)oxide, and it can be gradually transformed to amorphous ferric arsenate with increasing As:Fe ratios. The reactivity of the three schwertmannites depends on whether As(V) is adsorbed or structurally incorporated and follows the order of Sch-free > Sch-As(V) > Sch*-As(V), as indicated by Fe(II)HCl [HCl extractable Fe(II)], although the specific surface area of Sch-As(V) is higher than those of Sch-free and Sch*-As(V). As(V) influences the maximal release of Fe(II)diss from Sch-As(V) and Sch*-As(V), and Fe(II)diss increases with higher S(− II) and lower As:Fe ratios. Differences in As(V) release can also be observed between Sch*-As(V) and Sch-As(V) during dissolution. As(V) releases from both Sch*-As(V) and Sch-As(V) with time, and re-adsorption of aqueous As(V) is only observed in the Sch-As(V) system. During the catalytic transformation of As(V)-containing schwertmannites by the adsorbed Fe(II), secondary minerals such as magnetite and/or goethite, detected in the Sch-As(V) and Sch*-As(V) systems, contribute to the immobilization of the released As(V).