Depression of pyrrhotite superstructures in copper flotation: A synchrotron X-ray powder diffraction and DFT study

Abstract

Pyrrhotite naturally occurs in various superstructures including magnetic (4C) and non-magnetic (5C, 6C) types, each with distinct physicochemical properties and flotation behaviors. Challenges in accurately identifying and quantifying these superstructures hinder the optimization of pyrrhotite depression in flotation processes. To address this critical issue, synchrotron X-ray powder diffraction (S-XRPD) with Rietveld refinement was employed to quantify the distribution of superstructures in the feed and flotation concentrates of a copper-gold ore. To elucidate the mechanisms influencing depression, density functional theory (DFT) calculations were conducted to explore the electronic structures and surface reactivity of the pyrrhotite superstructures toward the adsorption of water, oxygen and hydroxyl ions (OH⁻) as dominant species present in the flotation process. S-XRPD analysis revealed that flotation recovery rates of pyrrhotite followed the order of 4C<6C<5C. DFT calculations indicated that the Fe 3d and S 3p orbital band centers exhibited a similar trend relative to the Fermi level with 4C being the closest. The Fe 3d band center suggested that the 4C structure possessed a more reactive surface toward the oxygen reduction reaction, promoting the formation of hydrophilic Fe-OH sites. The S 3p band center order also implied that xanthate on the non-magnetic 5C and 6C surfaces could oxidize to dixanthogen, increasing hydrophobicity and floatability, while 4C formed less hydrophobic metal-xanthate complexes. Adsorption energy and charge transfer analyses of water, hydroxyl ions and molecular oxygen further supported the high reactivity and hydrophilic nature of 4C pyrrhotite. The strong bonding with hydroxyl ions indicated enhanced surface passivation by hydrophilic Fe-OOH complexes, aligning with the experimentally observed flotation order (4C<6C<5C). These findings provide a compelling correlation between experimental flotation results and electronic structure calculations, delivering crucial insights for optimizing flotation processes and improving pyrrhotite depression. This breakthrough opens up new opportunities to enhance the efficiency of flotation processes in the mining industry.

Keywords

Pyrrhotite depression / Synchrotron X-ray powder diffraction analysis / Pyrrhotite superstructures / DFT simulation / Surface reactivity

Acknowledgement

This work was supported by the Australian Research Council Linkage Project (No. LP200200717), co sponsored by Newmont Corporation (United States) and Vega Industries (India); the Pow-der Diffraction Beamline at the Australia’s Nuclear Science and Technology Organisation (No. PDR19870), Australia; the Centre for Microscopy and Microanalysis at the University of Queensland (No. 1366), Australia; and computational resources provided by the University of Queensland Research Computing Centre’s Bunya supercomputer, Australia.

Supplementary material

Supplementary data to this article can be found online at https://doi.org/10.1016/j.ijmst.2025.07.002.

References

[1] Tang XQ, Chen Y. A review of flotation and selective separation of pyrrhotite: a perspective from crystal structures. Int J Min Sci Technol 2022; 32(4):847-63.

[2] Raji F, Kappes R, Peng YJ. Deleterious impacts of triethylenetetramine and sodium metabisulphite on gold flotation during pyrrhotite depression. Miner Eng 2024; 216:108884.

[3] Becker M. The mineralogy and crystallography of pyrrhotite from selected nickel and PGE ore deposits and its effect on flotation performance. Pretoria: University of Pretoria; 2009. Doctoral dissertation.

[4] Rezvani A, Raji F, Liu Q, Peng YJ. Identification and quantification of pyrrhotite superstructures in base metal sulfide ore samples: A critical review. Miner Eng 2024; 218:108975.

[5] Özdeniz AH, Kelebek S. A study of self-heating characteristics of a pyrrhotite-rich sulphide ore stockpile. Int J Min Sci Technol 2013; 23(3):381-6.

[6] Multani RS, Waters KE. A review of the physicochemical properties and flotation of pyrrhotite superstructures (4C-Fe7S8/5C-Fe9S10) in Ni-Cu sulphide mineral processing. Can J Chem Eng 2018; 96(5):1185-206.

[7] Janzen MP, Nicholson RV, Scharer JM. Pyrrhotite reaction kinetics: Reaction rates for oxidation by oxygen, ferric iron, and for nonoxidative dissolution. Geochim Cosmochim Acta 2000; 64(9):1511-22.

[8] Belzile N, Chen YW, Cai MF, Li YR. A review on pyrrhotite oxidation. J Geochem Explor 2004; 84(2):65-76.

[9] Kolahdoozan M. Adsorption and flotation characteristics of hexagonal and monoclinic pyrrhotite. Kingston: Queen’s University; 1996. Doctoral dissertation.

[10] Lawson V, Hill G, Kormos L, Marrs G. The separation of pentlandite from chalcopyrite, pyrrhotite and gangue in nickel projects throughout the world. In:Proceedings of the 12th AusIMM Mill Operators. Townsville: AusIMM; 2014.

[11] Ekmekçi Z, Becker M, Tekes EB, Bradshaw D.The relationship between the electrochemical, mineralogical and flotation characteristics of pyrrhotite samples from different Ni Ores. J Electroanal Chem 2010; 647(2):133-43.

[12] Multani RS, Williams H, Johnson B, Li RH, Waters KE. The effect of superstructure on the zeta potential, xanthate adsorption, and flotation response of pyrrhotite. Colloids Surf A Physicochem Eng Aspects 2018; 551:108-16.

[13] Rezvani A, Raji F, Fan R, Kappes R, Peng YJ. Quantifying pyrrhotite superstructures in copper-gold ore flotation through synchrotron X-ray diffraction analysis. Miner Eng 2024; 216:108894.

[14] Qiu TS, Ding KW, Yan HS, Yang L, Wu H, Zhao GF, Qiu XH. Electrochemistry and DFT study of galvanic interaction on the surface of monoclinic pyrrhotite ( 0 0 and galena (1 0 0). Int J Min Sci Technol 2024; 34(8):1151-62.

[15] Feng Y, Li ZF, Chen JH, Chen Y. Effect of content and spin state of iron on electronic properties and floatability of iron-bearing sphalerite: A DFT+U study. Int J Min Sci Technol 2023; 33(12):1563-71.

[16] Tao HB, Liu SB, Luo JL, Choi P, Liu Q, Xu ZH. Descriptor of catalytic activity of metal sulfides for oxygen reduction reaction: A potential indicator for mineral flotation. J Mater Chem A 2018; 6(20):9650-6.

[17] Powell AV, Vaqueiro P, Knight KS, Chapon LC, Sánchez RD. Structure and magnetism in synthetic pyrrhotite Fe7S8: A powder neutron-diffraction study. Phys Rev B 2004; 70:014415.

[18] Liles DC, de Villiers JPR. Redetermination of the structure of 5C pyrrhotite at low temperature and at room temperature. Am Mineral 2012; 97(2- 3):257-61.

[19] de Villiers JPR, Liles DC. The crystal-structure and vacancy distribution in 6C pyrrhotite. Am Mineral 2010; 95(1):148-52.

[20] Kresse G, Hafner J. Ab initiomolecular-dynamics simulation of the liquid-metal-amorphous-semiconductor transition in germanium. Phys Rev B 1994; 49(20):14251-69.

[21] Wang JJ, Jing GG, Zheng RJ, Huang ZJ, Sun W, Gao ZY. Ethylenediamine tetramethylenephosphonic acid as a selective collector for the improved separation of chalcopyrite against pyrite at low alkalinity. Int J Min Sci Technol 2023; 33(7):873-82.

[22] Perdew JP, Burke K, Ernzerhof M. Generalized gradient approximation made simple. Phys Rev Lett 1996; 77(18):3865-8.

[23] Kresse G, Joubert D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys Rev B 1999; 59(3):1758-75.

[24] Methfessel M, Paxton AT. High-precision sampling for Brillouin-zone integration in metals. Phys Rev B 1989; 40(6):3616-21.

[25] Grimme S, Antony J, Ehrlich S, Krieg H. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J Chem Phys 2010; 132(15):154104.

[26] Chen JH, Xu ZH, Chen Y. Electronic structure and surfaces of sulfide minerals: Density functional theory and applications. Amsterdam: Elsevier; 2020.

[27] ivković A, King HE, Wolthers M, de Leeuw NH. Magnetic structure and exchange interactions in pyrrhotite end member minerals: Hexagonal FeS and monoclinic Fe7S8. J Phys Condens Matter 2021; 33(46):465801.

[28] Qi C, Khalkhali M, Grundy JS, Liu J, Malainey J, Liu QX. Unraveling polymorphic pyrrhotite electrochemical oxidation by underlying electronic structures. J Phys Chem C 2019; 123(43):26442-9.

[29] St JC.The brittle-to-ductile transition in pre-cleaved silicon single crystals. philos Mag A J Theor Exp Appl Phys 1975; 32(6):1193-212.

[30] Becker U, Munz AW, Lennie AR, Thornton G, Vaughan DJ. The atomic and electronic structure of the (001) surface of monoclinic pyrrhotite (Fe7S8) as studied using STM, LEED and quantum mechanical calculations. Surf Sci 1997; 389(1-3):66-87.

[31] Momma K, Izumi F. VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data. J Appl Cryst 2011; 44(6):1272-6.

[32] Wang V, Xu N, Liu JC, Tang G, Geng WT. VASPKIT: A user-friendly interface facilitating high-throughput computing and analysis using VASP code. Comput Phys Commun 2021; 267:108033.

[33] Hanwell MD, Curtis DE, Lonie DC, Vandermeersch T, Zurek E, Hutchison GR. Avogadro: an advanced semantic chemical editor, visualization, and analysis platform. J Cheminform 2012; 4(1):17.

[34] Henkelman G, Arnaldsson A, Jónsson H. A fast and robust algorithm for Bader decomposition of charge density. Comput Mater Sci 2006; 36 (3):354-60.

[35] Rezvani A, Raji F, Liu Q, Peng YJ. Unveiling different pyrrhotite superstructures in copper-gold ore samples: Insights from advanced spectroscopic and microscopic characterization. Miner Eng 2024; 206:108536.

[36] Zhang HL, Wang R, Sun W, Zhu YG, Lin SY, Zhang CY. Progressive hydrophilic processes of the pyrite surface in high-alkaline lime systems. Langmuir 2023; 39(26):9051-9.

[37] Hung A, Yarovsky I, Russo SP. Density-functional theory studies of xanthate adsorption on the pyrite FeS2(110) and (111) surfaces. J Chem Phys 2003; 118 (13):6022-9.

[38] Allison SA, Goold LA, Nicol MJ, Granville A. A determination of the products of reaction betweer various sulfide minerals and aqueous xanthate solution, and a correlation of the products with electrode rest potentials. Metall Trans 1972; 3(10):2613-8.

[39] Khan A, Kelebek S. Electrochemical aspects of pyrrhotite and pentlandite in relation to their flotation with xanthate. Part-I: Cyclic voltammetry and rest potential measurements. J Appl Electrochem 2004; 34(8):849-56.

[40] Musuku B, Dahl O. Impact of recycled process water on electrochemical reactivity of sulphide ore. Minerals 2022; 12(11):1455.

[41] Mphela N. Fundamental studies of the electrochemical and flotation behaviour of pyrrhotite. Pretoria: University of Pretoria; 2010. Doctoral dissertation.

[42] de Lima GF, de Oliveira C, de Abreu HA, Duarte HA. Water adsorption on the reconstructed (001) chalcopyrite surfaces. J Phys Chem C 2011; 115 (21):10709-17.

[43] Waterson CN, Tasker PA, Farinato R, Nagaraj DR, Shackleton N, Morrison CA.A computational and experimental study on the binding of dithio ligands to sperrylite, pentlandite, and platinum. J Phys Chem C 2016; 120(39):22476-88.

[44] Nesbitt HW, Muir IJ. X-ray photoelectron spectroscopic study of a pristine pyrite surface reacted with water vapour and air. Geochim Cosmochim Acta 1994; 58(21):4667-79.

[45] Dos Santos EC, de Mendonça Silva JC, Duarte HA.Pyrite oxidation mechanism by oxygen in aqueous medium. J Phys Chem C 2016; 120(5):2760-8.

[46] Fuerstenau MC, Sabacky BJ. On the natural floatability of sulfides. Int J Miner Process 1981; 8(1):79-84.

[47] Li YQ, Chen JH, Chen Y, Zhao CH, Zhang YB, Ke BL. Interactions of oxygen and water molecules with pyrite surface: A new insight. Langmuir 2018; 34 (5):1941-52.

[48] Heidel C, Tichomirowa M, Junghans M. The influence of pyrite grain size on the final oxygen isotope difference between sulphate and water in aerobic pyrite oxidation experiments. Isot Environ Health Stud 2009; 45(4):321-42.