Effect of lattice defects on the electronic structures and floatability of pyrites

Abstract

The electronic structures of three types of lattice defects in pyrites (i.e., As-substituted, Co-substituted, and intercrystalline Au pyrites) were calculated using the density functional theory (DFT). In addition, their band structures, density of states, and difference charge density were studied. The effect of the three types of lattice defects on the pyrite floatability was explored. The calculated results showed that the band-gaps of pyrites with Co-substitution and intercrystalline Au decreased significantly, which favors the oxidation of xanthate to dixanthogen and the adsorption of dixanthogen during pyrite flotation. The stability of the pyrites increased in the following order: As-substituted < perfect < Co-substituted < intercrystalline Au. Therefore, As-substituted pyrite is easier to be depressed by intensive oxidization compared to perfect pyrite in a strongly alkaline medium. However, Co-substituted and intercrystalline Au pyrites are more difficult to be depressed compared to perfect pyrite. The analysis of the Mulliken bond population and the electron density difference indicates that the covalence characteristic of the S-Fe bond is larger compared to the S-S bond in perfect pyrite. In addition, the presence of the three types of lattice defects in the pyrite bulk results in an increase in the covalence level of the S-Fe bond and a decrease in the covalence level of the S-S bond, which affect the natural floatability of the pyrites.

Keywords

pyrites / lattice defects / density functional theory / electronic structure / flotation

References

[1] Luszczkiewicz A., Chmielewski T. Acid treatment of copper sulfide middlings and rougher concentrates in the flotation circuit of carbonate ores. Int. J. Miner. Process., 2008, 88, 45.

[2] Brito S., Abreu E., Brien C., Skinner W. ToF-SIMS as a new method to determine the contact angle of mineral surfaces. Langmuir, 2010, 26, 8122.

[3] Chandra A.P., Gerson A.R. A review of the fundamental studies of the copper activation mechanisms for selective flotation of the sulfide minerals, sphalerite and pyrite. Adv. Colloid Interface Sci., 2009, 145, 97.

[4] Deditius A.P., Utsunomiya S., Renock D., Ewing R.C., Ramana C.V., Becker U., Kesler S.E. A proposed new type of arsenian pyrite: Composition, nanostructure and geological significance. Geochim. Cosmochim. Acta, 2008, 72, 2919.

[5] Deditius A.P., Utsunomiya S., Reich M., Kesler S.E., Ewing R.C., Hough R.M., Walshe J.L. Trace metal nanoparticles in pyrite. Ore Geol. Rev., 2011, 42, 32.

[6] Savage K.S., Tingle T.N., O’Day P.A., Waychunas G.A., Bird D.K. Arsenic speciation in pyrite and secondary weathering phases, Mother Lode Gold District, Tuolumne County, California. Appl. Geochem., 2000, 15, 1219.

[7] Gaskova O.L., Belogub E.V., Makarov D.V. Cobalt behavior during natural and technogenic oxidative leaching of Co-containing pyrites (Letnee chalcopyrite deposit, Southern Urals). Russ. Geol. Geophys., 2010, 51, 176.

[8] Reich M., Kesler S.E., Utsunomiya S., Palenik C.S., Chryssoulis S.L., Ewing R.C. Solubility of gold in arsenian pyrite. Geochim. Cosmochim. Acta, 2005, 69, 2781.

[9] A.P. Deditius, S.E. Kesler, R.C. Ewing, S. Utsunomiya, and J. Walshe, Behaviour of trace elements in arsenian pyrite in ore deposits, [in]_Proceedings of the 10th Biennial SGA Meeting of the Society for Geology Applied to Mineral Deposits, Townsville, 2009, p.710.

[10] Abraitis P. K., Pattrick R.A.D., Vaughan D.J. Variations in the compositional, textural and electrical properties of natural pyrite: a review. Int. J. Miner. Process., 2004, 74, 41.

[11] Li Y.Q., Chen J.H., Chen Y. Electronic structures and flotation behavior of pyrite containing vacancy defects. Acta. Phys. Chim. Sin., 2010, 26, 1435.

[12] Savage K.S., Stefan D., Lehner S.W. Impurities and heterogeneity in pyrite: Influences on electrical properties and oxidation products. Appl. Geochem., 2008, 23, 103.

[13] Lehner S., Savage K., Ciobanu M., Cliffel D.E. The effect of As, Co, and Ni impurities on pyrite oxidation kinetics: an electrochemical study of synthetic pyrite. Geochim. Cosmochim. Acta, 2007, 71, 2491.

[14] Lehner S.W., Savage K.S., Ayers J.C. Vapor growth and characterization of pyrite (FeS₂) doped with Co, Ni, and As: variations in semiconducting properties. J. Cryst. Growth, 2006, 286, 306.

[15] Valdivieso A. L., Escamilla C. O., Song S., Baez I. L., González Martínez I. Adsorption of isopropyl xanthate ions onto arsenopyrite and its effect on flotation. Int. J. Miner. Process., 2003, 69, 175.

[16] Makanza A.T., Vermaak M.K.G., Davidtz J.C. The flotation of auriferous pyrite with a mixture of collectors. Int. J. Miner. Process., 2008, 86, 85.

[17] Chen J.H., Chen Y., Wei Z.W., Liu F.X. Bulk flotation of auriferous pyrite and arsenopyrite by using tertiary dodecyl mercaptan as collector in weak alkaline pulp. Miner. Eng., 2010, 23, 1070.

[18] Blanchard M., Alfredsson M., Brodholt J., Wright K., Catlow C.R.A. Arsenic incorporation into FeS₂ pyrite and its influence on dissolution: a DFT study. Geochim. Cosmochim. Acta, 2007, 71, 624.

[19] Segall M.D., Lindan P.J.D., Probert M.J., Pickard C.J., Hasnip P.J., Clark S.J., Payne M.C. First-principles simulation: ideas, illustrations and the CASTEP code. J. Phys. Condens. Matter, 2002, 14, 2717.

[20] Kresse G., Joubert D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B, 1999, 59, 1758.

[21] Zhang Y.K., Yang W.T. Comment on “generalized gradient approximation made simple”. Phys. Rev. Lett., 1998, 80, 890.

[22] Wu Z.G., Cohen R.E. More accurate generalized gradient approximation for solids. Phys. Rev. B, 2006, 73, 235116.

[23] Perdew J.P., Ruzsinszky A., Csonka G.I., Vydrov O.A., Scuseria G.E., Constantin L.A., Zhou X., Burke K. Restoring the density-gradient expansion for exchange in solids and surfaces. Phys. Rev. Lett., 2009, 102, 039902.

[24] Xiao Q., Qiu G.Z., Hu Y.H., Wang D.Z. Theoretical study on the geometry and the electronic structure of FeS₂ (100) surface. Acta Phys. Sin., 2002, 51, 2137.

[25] von Oertzen G.U., Jones R.T., Gerson A.R. Electronic and optical properties of Fe, Zn and Pb sulfides. Phys. Chem. Miner., 2005, 32, 255-268.

[26] Opahle I., Koepernik K., Eschrig H. Full potential band structure calculation of iron pyrite. Comput. Mater. Sci., 2000, 17, 206.

[27] Valdivieso A.L., López A.A.S., Song S. On the cathodic reaction coupled with the oxidation of xanthates at the pyrite/aqueous solution interface. Int. J. Miner. Process., 2005, 77, 154.

[28] Miller J.D., Du Plessis R., Kotylar D.G., Zhu X., Simmons G.L. The low-potential hydrophobic state of pyrite in amyl xanthate flotation with nitrogen. Int. J. Miner. Process, 2002, 67, 1.

[29] Chen J.H., Feng Q.M., Lu Y.P. Energy band model of electrochemical flotation and its application: II. Energy band model of xanthate interacting with sulphide minerals. Chin. J. Nonferrous Met., 2000, 10, 426.