Michaël Descostes | PubMed Health

PubMed2006

Troilite oxidation by hydrogen peroxide.

The kinetics and mechanism of troilite oxidation by H(2)O(2) was studied at temperatures of 25 and 45 degrees C. Solutions within the range 0.1-0.85 mol L(-1) H(2)O(2) in HClO(4) (0.01-0.1 mol L(-1)) were used as dissolution media. The experimental amount of dissolved iron was plotted versus t(n), with n ranging from 0.25 to 1.55. The theoretical interpretation of this dependence suggests that the troilite oxidation involves several processes: Both experimental results and theoretical considerations illustrate the importance of temperature, pH, and [H(2)O(2)] for the kinetics and mechanisms of troilite oxidation. The amounts of dissolved iron strongly increase with temperature and [H(+)], whereas an increase of H(2)O(2) concentration seems to reduce the troilite oxidation. The reaction orders with respect to [H(+)] are variable, pointing out notable modifications of reaction mechanism with experimental conditions. The estimated value E(a)=25.4+/-0.9 k J mol(-1) ([H(2)O(2)]=0.4 mol L(-1) and pH 1) points to dissolution kinetics controlled by a mix regime of surface reaction and diffusion.

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PubMed2005

Anoxic dissolution of troilite in acidic media.

The anoxic dissolution of troilite (FeS) in acidic medium has been investigated at 50 degrees C using batch dissolution experiments. Two different progress variables were followed during solid dissolution, i.e., the amounts of dissolved iron (nFe) and formed hydrogen sulfide (n(H(2)S)). The experimental studies performed at hydrogen ion concentrations ([H+]) ranging from 0.04 to 0.2 mol L(-1) showed that anoxic dissolution of troilite is dependent on [H+]. The cumulative release of both Fe and H2S could be described by a diffusion-like rate law, with rate constants for Fe (k(p)(Fe) always greater than for H2S (k(p)(H2S). The surplus of dissolved iron over formed hydrogen sulfide was quantified by the n(Fe):n(H2S) ratio, and ranged from 1.21 to 1.46, higher than the specific n(Fe):n(H2S) ratio of troilite bulk, i.e., 1. Rate constants are linearly related to the pH with a slope of 0.66 +/- 0.23 (n(Fe)) or 0.63 +/- 0.13 (n(H2S)). The obtained results suggest that troilite anoxic dissolution is a process controlled by the diffusion of the reaction products across an obstructive layer, sulfur-rich layer (SRL), having a thickness that increases during reaction progress. The accumulation of H2S between the surface and the SRL, eventually leads to the mechanical destruction of this outer layer, a process that results an increased flux of reaction products.

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