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Surface chemistry of disordered mackinawite (FeS) |
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| Authors: | Marië tte Wolthers,Laurent Charlet,David Rickard |
| Affiliation: | 1 Department of Earth Sciences - Geochemistry, Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands 2 Laboratoire de Géophysique Interne et Tectonophysique, Université Grenoble I, Grenoble, France 3 University of Professional Education Leiden, Leiden, The Netherlands 4 School of Earth, Ocean and Planetary Sciences, Cardiff University, Cardiff, Wales UK |
| Abstract: | Disordered mackinawite, FeS, is the first formed iron sulfide in ambient sulfidic environments and has a highly reactive surface. In this study, the solubility and surface chemistry of FeS is described. Its solubility in the neutral pH range can be described by Ksapp = {Fe2+} · {H2S(aq)} · {H+}−2 = 10+4.87±0.27. Acid-base titrations show that the point of zero charge (PZC) of disordered mackinawite lies at pH ∼7.5. The hydrated disordered mackinawite surface can be best described by strongly acidic mono-coordinated and weakly acidic tricoordinated sulfurs. The mono-coordinated sulfur site determines the acid-base properties at pH < PZC and has a concentration of 1.2 × 10−3 mol/g FeS. At higher pH, the tricoordinated sulfur, which has a concentration of 1.2 × 10−3 mol/g FeS, determines surface charge changes. Total site density is 4 sites nm−2. The acid-base titration data are used to develop a surface complexation model for the surface chemistry of FeS. |
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