Iron monosulfide (FeS) oxidation by dissolved oxygen: characteristics of the product layer

Abstract

Samples of FeS were oxidized by oxygen-bearing acidic solutions at 25• C and different initial pH values (2.75 ≤ pH ≤ 3.45). The reacted FeS samples were investigated by scanning electron microscopy (SEM), nitrogen adsorption/desorption isotherms measurements, and FT-Raman spectroscopy. A sulfur rich phase (layer) is inferred to be form on reacting FeS surface based on sequential extraction with acidic chromium(II) chloride solutions. The sulfur-rich layer (SRL) formed on oxidized FeS samples is traversed by various mesopores with average pore size <450Å. It is reasonable to assume that the mesopores facilitate the migration of iron and sulfur from FeS structure into solution across SRL. The FT-Raman spectra of oxidized FeS samples show an intense peak at 162 cm −1 , which can be attributed to SRL developed on FeS surface. A model for SRL development on FeS during its oxidation by dissolved oxygen has been proposed from the present results and previous studies.

Influence of 2,2′‐bipyridine on oxidative dissolution of iron monosulfide

“…b), one can see acicular crystals. This morphology is typical of goethite (α‐FeOOH) and lepidocrocite (γ‐FeOOH) . EDX analysis of iron and sulfur (Figs a and b) indicates that the surface of FeS immersed in 1 mM 2,2′‐bipyridine (Fe, 58.72 at.% and S, 41.28 at.%) is poorer in iron than that of initial FeS sample (Fe, 62.43 at.% and S, 37.57 at.%).…”

“…Although iron monosulfides (FeS) are not the most spread iron sulfides, they are important because of their high reactivity . The oxidative dissolution of FeS is controlled by the surface layer resulted from preferential release of iron relative to sulfur from mineral surface . It contains polysulfide species, elemental sulfur, ferrous iron and ferric oxyhydroxides …”

Nano-FeS Inhibits UO2 Reoxidation under Varied Oxic Conditions

“…An oxidized hydrophobic sulfur-rich layer with nanosize pores likely forms on the FeS surface during oxidation, which may facilitate oxygen diffusion or electron transfer to enhance the rate of oxygen removal by FeS. 20 A similar pH-dependent oxidation mechanism has been reported in a batch study of FeS oxidation. 18 Given the longest inhibition of oxidative UO 2 dissolution by FeS occurred at a basic pH, these conditions would be preferred over acidic conditions for prolonging the protective nature of FeS in groundwater.…”

Rapid Mobilization of Noncrystalline U(IV) Coupled with FeS Oxidation

“…After reacting with noncrystalline U­(IV), the >Fe­(III)-S species is reduced and released to the effluent as soluble Fe­(II) (Figure ). The fact that this Fe­(III) species is short-lived and unsustainable over the oxidation of FeS possibly results from (1) the precipitation of less reactive Fe­(III) (hydr)­oxides solids, and (2) the formation of polysulfide and elemental sulfur . Under acidic pH conditions, the slow oxidation of noncrystalline U­(IV) (Figure S5) further implies the complexity of geochemical conditions affecting Fe­(III) speciation.…”

“…The fact that this Fe(III) species is shortlived and unsustainable over the oxidation of FeS possibly results from (1) the precipitation of less reactive Fe(III) (hydr)oxides solids, and (2) the formation of polysulfide and elemental sulfur. 40 Under acidic pH conditions, the slow oxidation of noncrystalline U(IV) ( Figure S5) further implies the complexity of geochemical conditions affecting Fe(III) speciation. One possible explanation is the lack of Fe(III) surface species at a pH of ∼5 owing to the slow oxidation kinetics of dissolved Fe(II).…”