Bacteria oxidize ferrous ions to ferric ions in the bulk solution, and the ferric ions oxidize the sulfur moiety. Bacteria attached to the mineral surface oxidize ferrous ions to ferric ions within a biofilm comprised AZD1208 research buy of bacteria and extracellular polymeric material (EPS), and the ferric ions generated within this layer oxidize the sulfur. Bacteria attached to the surface of the mineral oxidize the sulfur directly, without any requirement for ferric or ferrous ions is considered as the direct contact mechanism.

While the evidence and signals of a direct electron transport through catalyzing by enzymes and some other organelles of the cell, between the metal sulfide and the attached cell has not been found up to now. The terms, contact leaching and non-contact leaching have been proposed for bioleaching by attached and planktonic cells, respectively. The oxidation of the acid-insoluble metal sulfide (e.g., pyrite, tungstenite, molybdenite,) and acid soluble metal sulfide (e.g., chalcopyrite, pyrrhotite, and sphalerite) can be categorized into two pathways, the thiosulphate intermediate pathway

and polysulphide intermediate pathway [11] and [84]. Pyrite (FeS2) is composed of a ferrous (Fe2+) ion and S2−2 ion with the Fe/S ratio of 1:2. Deviations (<1%) from this stoichiometric relationship have been densely reported [72]. Pyrite oxidation is essentially important

in flotation and leaching mineral ores or deposits selleck compound [85] and biogeochemical cycling of Fe ions and S ions in the ecology of Fe- and S-oxidizing bacteria [86] through the production of sulfuric acid as a result of oxidation [87]. Oxidation of pyrite surfaces may occur upon exposure to atmospheric O2 and water [85] and the oxidized layer can hinder against further oxidation and further control the subsequent processes on aqueous phase oxidation [88]. Singer et al. described the aqueous oxidation of pyrite with stoichiometric chemical reactions and the Eqs. (1), (2) and (3) are listed as followed [89], equation(1) FeS2+72O2(aq)+H2O→Fe2++2SO42−+2H+ equation(2) Fe2++14(aq)+H+→Fe3++12H2O Alanine-glyoxylate transaminase equation(3) FeS2+14Fe3++8H2O→15Fe2++2SO42−+16H+O2 molecule and Fe3+ ions have been recognized as the two most important oxidants for pyrite oxidation. Moses et al. proposed that oxidation rates of pyrite in the saturated Fe3+ solution were two orders of magnitude higher than that due to dissolved oxygen (DO) at the condition of low pH [86] and [90]. The sulfur of pyrite is oxidized to the soluble sulfur intermediates after the initial attack of the oxidizing agent, ferric (Fe3+). The bonds between S2−2 and Fe2+ are cleaved, and hydrated ferrous iron ions and thiosulfate [91] and [92] are formed, then the soluble thiosulfate intermediate is oxidized to tetrathionate [93].