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

Abstract

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.

Biological and environmental interactions of emerging two-dimensional nanomaterials

“…351 WS 2 has been reported to behave similarly as MoS 2 in terms of environmental stability and bio-oxidation. 352 Beyond oxidative dissolution, other phase changes in TMDs are conversion from the semiconducting 2H phase to the metallic 1T form induced by alkali metal intercalation. 188 …”

The preferential oxidation of orthorhombic sulfur during batch culture

“…The production of elemental sulfur during the bio-mining of mineral sulfides is now well known and mechanisms for the oxidation process and the catalytic roles played by the acidophilic iron and sulfur oxidising cells have been described (Rohwerder et al 2003;Schippers andSand 1999, Schippers et al 1996). Also described has been the control that the solid-state characteristics of the solid mineral phase exert on the mechanism of dissolution and the products that accumulate (Tributsch, 1981a;1981b, 2001). In the 'thiosulfate' and the 'polysulfide' mechanisms described by Schippers and Sand (1999), elemental sulfur is formed from the disproportionation of thiosulfate (S 2 O 3 2-) and the partial oxidation of sulfide (S 2-) respectively (Rohwerder et al 2003).…”

Bacterial Leaching of Metal Sulfides Proceeds by Two Indirect Mechanisms via Thiosulfate or via Polysulfides and Sulfur

“…Consequently, these metal sulfides are degradable only by an oxidizing attack, e.g., by iron(III) ions. None of these compounds is soluble in acid (proton attack) (21,25,26). Furthermore, both metal sulfides consist of pairs of sulfur atoms.…”