The oxidation and self‐heating of metal sulphides as an electrochemical corrosion phenomenon

Sixteen metal sulphides with widely differing solid state, chemical and electrochemical properties have been investigated with respect to their suitabilityasanenergy source for Thiobucillus ferrooxiduns. The most critical rate-determining parameter for bacterial oxidation (in the absence of any electron acceptors, e.g. Fe3+) was the solubility product of the sulphide. Deviations from the systematic dependence are, however, observed when a large concentration of the holes are present in the semiconducting sulphide (p-type conduction), or when holes are generated through electron extraction from the sulphide surface (e.g. by Fe3+). The experimental results are consistent with a mechanism in which Th. ferrooxiduns utilises H+ and Fe3+ as catalytic agents which break surface bonds by chemical and electrochemical mechanisms, respectively. They are subsequently recycled while the bacterium oxidises the generated surface products, -SHS-and SO, etc., to sulphate. On the basis of the derived mechanism it should be possible to estimate and predict the suitability of sulphides for bacterial oxidation and to analyse the influence of crystalline quality and impurities, as well as the composition of the solution, on the rate of oxidation.

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Semiconductor‐electrochemical aspects of bacterial leaching. I. Oxidation of metal sulphides with large energy gaps

Tributsch

Bennett

1981

J. Chem. Technol. Biotechnol.

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Thiobacillus ferrooxidans has been cultivated successfully on synthetic metal sulphides with large energy gaps (CdS, ZnS) as the only energy source for many culture generations during a period of 4 years. The results obtained, which were quantitatively evaluated by calculations of electron transfer probabilities, show that a direct electron transfer from the metal sulphide valence band to the bacterial metabolic system (hole injection into the valence band of the sulphide) has to be excluded as the cause for the enhanced oxidative dissolution for energetic reasons. A detailed analysis of the dynamics of the metal sulphide aqueous electrolyte interface reveals that protons are involved in the mechanism on which bacterial activity is based. By reacting chemically with the metal sulphide surface they break chemical bonds and shift electronic states energetically into the forbidden energy gap to produce surface states which can be chemically described as −SH∂ groups. These control the rate of dissolution of the metal sulphide and are removed by bacterial activity. In this way the proton is recycled and its action can be considered catalytic. For sulphides in which the valence band of the semiconductor is derived from metal orbitals instead of from sulphur orbitals, this mechanism is bound to fail. MoS2 and WS2 are discussed as examples of such metal sulphides which are not a suitable energy source for bacteria. Some kinetic aspects of the bacterial surface reaction are discussed.

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The oxidation and self‐heating of metal sulphides as an electrochemical corrosion phenomenon

Cited by 20 publications

References 9 publications

Semiconductor-electrochemical aspects of bacterial leaching. I. Oxidation of metal sulphides with large energy gaps

Semiconductor-electrochemical aspects of bacterial leaching. I. Oxidation of metal sulphides with large energy gaps

Semiconductor-electrochemical aspects of bacterial leaching. Part 2. Survey of rate-controlling sulphide properties

Semiconductor‐electrochemical aspects of bacterial leaching. I. Oxidation of metal sulphides with large energy gaps

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