Reaction of FeS with Fe(III)-bearing acidic solutions

• Published in: Chemical geology Vol. 334; pp. 131 - 138
• Main Authors: Chiriţă, Paul, Schlegel, Michel L.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 12.12.2012
• Subjects: adsorption; Dissolution; Ferric iron; iron; Iron monosulfide; protons; sulfur; Sulfur rich layer; Sulfur rich layer; Iron monosulfide; Ferric iron; Dissolution
• ISSN: 0009-2541; 1872-6836
• DOI: 10.1016/j.chemgeo.2012.10.015

The reaction of FeS with Fe(III)-bearing acidic solutions (Fe(III)BAS) was probed at 25°C and pH between 2 and 3. Initial dissolved Fe3+ ([Fe3+]init) was varied from 0.1mM to 1mM, and the length of the experiments was 240min. Except for the experiment at initial pH 2, total dissolved iron ([Fe]total) decreased immediately (within 1min) after contact of FeS and Fe(III). Afterwards, [Fe]total increased smoothly. A progressive increase in pH values and an Eh decrease within 240min of reaction time were also observed. The reaction order of FeS dissolution in Fe(III)BAS with respect to [H+] is estimated to 0.65 at initial pH 3.0, and increases up to 1.0 with decreasing initial pH, indicating that [H+] is an important parameter of FeS dissolution in Fe(III)BAS. In contrast, changes in [Fe3+]init have only a limited effect on the rate of FeS dissolution in Fe(III)BAS. Raman spectra of initial and reacted FeS samples reveal the accumulation of α-S8-like material on FeS surface. These results support a mechanism of FeS dissolution in Fe(III)BAS starting with the protonation of mineral surface and Fe3+(aq) adsorption. Adsorbed protons subsequently accelerate Fe2+ release from FeS matrix into solution. The adsorbed Fe3+ may oxidize sulfur moieties and generate insoluble species, presumably polysulfide and elemental sulfur. The subsequent migration of Fe2+ into solution is controlled by the formed sulfur rich layer. [Display omitted] ► The reaction of FeS with Fe3+(aq) was probed at 25°C and pH between 2 and 3 ► The reaction order of FeS oxidation with respect to [H+] ranged between 0.65 and 1.0 ► FeS oxidation starts with the protonation of mineral surface and Fe3+(aq) adsorption