Pyrite surface theory

About three years after Wachtershauser s first publication appeared, an article by Christian de Duve and Stanley Miller was published in the Proceedings of the National Academy of Sciences under the title Two-Dimensional Life the title alluded to the theory of reactions at positively charged pyrite surfaces (de Duve and Miller, 1991). Their criticisms of the chemoautotrophic theory were directed particularly towards certain kinetic and thermodynamic aspects, but also to theoretical statements for which no experimental support was available. 

A lot of work (Opahle et al, 2000 Andrew et al, 2002a,b Muscat et al, 2002 Edelbro et al, 2003) has been performed on bulk and surface properties of FeS2 using various kinds of density functional theory. These works have shown that such methods are capable of producing calculated bulk properties such as lattice constants which agree well with experiment, and has provided a reference for the study of pyrite surfaces. 

Pyrite is not only one of the key compounds in Wachtershauser s theory, but could also have fulfilled an important function for phosphate chemistry in prebiotic syntheses. A group in Rio de Janeiro studied the conditions for phosphate sorption and desorption under conditions which may have been present in the primeval ocean. In particular, the question arises as to the enrichment of free, soluble inorganic phosphate (Pi), which was probably present in low concentrations similar to those of today (10 7-10 8M) (Miller and Keffe, 1995). Experiments show that acid conditions favour sorption at FeS2, while a weakly alkaline milieu works in an opposite manner. Sorption of Pi can be favoured by various factors, such as hydrophobic coating of pyrite with molecules such as acetate, which could have been formed in the vicinity of hydrothermal systems, or the neutralisation of mineral surface charges by Na+ and K+. 

The most controversial and contradicting problem is, perhaps, the natural and collectorless floatability of sulphide minerals. Gaudin (1957) classified the natural hydrophobicity of different minerals according to their crystal structure and showed that most sulphide minerals were naturally hydrophobic to some extent, which had been fiirther proved based on van der Waals theory by Chander (1988, 1999). Lepetic (1974) revealed the natural floatability of chalcopyrite in dry grinding. Finklestein (1975, 1977) demonstrated that orpiment, realgar and molybdenite were naturally floatable, and that pyrite and chalcopyrite had natural floatability at certain conditions due to the formation of surface elemental sulphur. Buckley and Woods (1990,1996) attributed the natural floatability of chalcopyrite... 

Abstract In the light of quantum chemistry, sulphide minerals and the interaction of them with reagents are investigated in this chapter. With the density functional theory pyrite is first researched including its bulk properties about energy band and frontier orbitals and the property of FeS2 (100) surface. 

Density Functional Theory Research on Oxygen Adsorption on Pyrite (100) Surface... 

Sun Wei, Hu Yuehua, Qiu Guanzhou, Qin Wenqing, 2004a. Oxygen adsorption pyrite (100) surface by density functional theory. J. Cent. South Univ. Technol., 11(4) 385 - 390 Sun Wei, Hu Yuehua, Qin Wenqing, 2004b. DFT research on activation of sphalerite. Trans. Nonferrous Met. Soc. China, 14(2) 376-382... 

Semiconductors are considered to be catalytic particles that contributed to the development of primitive metabolism. According to Wahtershauser life could have developed on the surface of iron sulphide minerals (eg mackinawite or pyrrhotite [FeS] or pyrite [FeS2]) [8], The chemoautotrophy theory is based on the reaction between iron sulphide and hydrogen sulphide, which acts as a reducing agent, whereas iron sulphide provides adsorption sites for substrates and acts as a catalyst (equation 10.1) ... 

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