Wolthers, M; Charlet, L; van Der Linde, PR; Rickard, D; van Der Weijden, CH; (2005) Surface chemistry of disordered mackinawite (FeS). Geochimica et Cosmochimica Acta , 69 (14) 3469 - 3481. 10.1016/j.gca.2005.01.027.

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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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