Electronic structure and flotation behavior of monoclinic and hexagonal pyrrhotite

Abstract

Electronic structures of monoclinic and hexagonal pyrrhotite were studied using density functional theory method, together with their flotation behavior. The main contribution of monoclinic pyrrhotite is mainly from Fe 3d, while that of hexagonal pyrrhotite is from Fe 3d, Fe 3p and S 3s. The hexagonal pyrrhotite is more reactive than monoclinic pyrrhotite because of large density of states near the Fermi level. The hexagonal pyrrhotite shows antiferromagnetism. S—Fe bonds mainly exist in monoclinic pyrrhotite as the covalent bonds, while hexagonal pyrrhotite has no covalency. The main contributions of higest occupied molecular orbital (HOMO) and lowest unoccupied molecular obital (LUMO) for monoclinic pyrrhotite come from S and Fe. The main contribution of HOMO for hexagonal pyrrhotite comes from Fe, while that of LUMO comes from S. The coefficient of Fe atom is much larger than that of S atom of HOMO for hexagonal pyrrhotite, which contributes to the adsorption of CaOH⁺ on the surface of hexagonal pyrrhotite when there is lime. As a result, lime has the inhibitory effect on the floatation of hexagonal pyrrhotite and the coefficient of Fe is very close to that of S for monoclinic pyrrhotite. Therefore, the existence of S prevents the adsorption of CaOH⁺ on the surface of monoclinic pyrrhotite, which leads to less inhibitory effect on the flotation of monoclinic pyrrhotite.

Keywords

monoclinic pyrrhotite / hexagonal pyrrhotite / electronic structure / flotation behavior / density functional theory

References

[1] VaughanD J, CraigJ RMineral chemistry of metal sulphides [M], 1978, Cambridge, UK, Cambridge University. Press: 493

[2] ProfsaiM, DodonayI. Pyrrhotite superstructures: Part I. Fundamentals structures of the NC (N=2, 3, 4 and 5) type [J]. Eur J Mineral, 1990, 2: 525-528

[3] ThomasJ E, SmartR S C, SkinnerW M. Kinetics factors for oxidative and non-oxidative dissolution of iron sulfides [J]. Min Eng, 2000, 10–11: 1149-1159

[4] ThomasJ E, SkinnerW M, St SmartR C. A mechanism to explain sudden changes in rates and products for pyrrhotite dissolution in acide solution, Geochim [J]. Cosmochim Acta, 2001, 65(1): 1-12

[5] JanzenM P, NicholsonR V, ScharerJ M. Pyrrhotite reaction kinetics: Reaction rates for oxidation by oxygen, ferric iron, and for nonoxidative dissolution [J]. Geochim Cosmochim Acta, 2000, 64(9): 1511-1522

[6] OriovaT A, StupnikowV M, KrestanA L. Mechanism of oxidative dissolution of sulphides [J]. Zhurnal Prikladnoi Khimii, 1989, 61: 2172-2177

[7] BeckerU, HunzA W, ThorntonG, VaughanD J. The atomic and electronic structure of the (001) surface of monoclinic pyrrhotite (Fe₇S₈) as studied using STM, LEED and quantum mechanical calculations [J]. Surf Sci, 1997, 389: 66-87

[8] BeckerM, BradshawD, De VilliersJ. The mineralogy of pyrrhotite from Sudbury CCN and Phoenix nickel ores and its effect on flotation performance [J]. Canadian Metallurgical Quarterly, 2011, 50(1): 10-19

[9] HongQ Y, TangY H, WangY H, LiangD Y, YuL X. Investigation on properties and structure of pyrrhotite and the difference of its floatability [J]. Metal Mine, 2011, 40(1): 64-67

[10] KalahdoozanMAdsorption and flotation characteristics of hexagonal and monoclinic pyrrhotite [D], 1996, Brisbane, Australia, Queens University

[11] HeM F, QinW Q, LizW Z, ChenY J, LaiC H. Research on flotation performances of polymorphic pyrrhotite [C]. 24th International Mineral Processing Congress, 2008, Beijing, Science Press: 1153-1160

[12] LawsonV, KerrA N, ShieldsY, WellsP F, XuM, DaiZ. Improving pentlandite pyrrhotite separation at INCO’s Clarabelle Mill [C]. Centenary of Flotation Symposium, 2005, Brisbane, Australia, AusIMM Brisbane: 875-885

[13] WellsP F, KelebekS, BurrowsM J, SuarezD FFinchJ A, RaoS R, HolubecI. Pyrrhotite rejection at Falconbridge’s Strathcona Mill [C]. Processing of Complex Ores: Mineral Processing and the Environment, 1997, Montreal, CIM: 51-62

[14] GersonA, JasieniakM. The effect of surface oxidation on the Cu activation of pentlandite and pyrrhotite [C]. 24th International Mineral Processing Congress, 2008, Beijing, Science Press: 1054-1063

[15] PayneM C, TeterM P, AllanD C, AriasT A, JoannopoulosJ D. Iterative minimization techniques for ab initio total energy calculations: molecular dynamics and conjugate gradients [J]. Reviews of Modern Physics, 1992, 64: 1045-1097

[16] PerdewJ P, WangY. Accurate and simple analytic representation of the electron-gas correlation energy [J]. Phys Rev B, 1992, 45: 13244-13249

[17] VanderbiltD. Soft self-consistent pseudopotentials in a generalized eigenvalue formalism [J]. Phys Rev B, 1990, 41: 7892-7895

[18] WardJ C. The structure and properties of some iron sulphides [J]. Rev Pur Appl Chem, 1970, 20: 175-206