Radical-induced selective oxidation and depression of pyrite in copper flotation

Abstract

Selective depression of pyrite remains a major bottleneck in copper flotation, particularly when high-pyrite ores are processed and saline water is used. In such environments, conventional approaches using lime and inert grinding media often fail to discriminate effectively between pyrite and valuable copper minerals due to strong copper activation on pyrite surfaces. This study introduced a novel approach using inorganic radicals generated from peroxymonosulfate (PMS) to selectively oxidize and depress pyrite. Flotation tests with synthetic high-pyrite ore blends showed that PMS significantly reduced pyrite recovery while maintaining or improving chalcopyrite flotation. Ethylenediaminetetraacetic acid (EDTA) extraction confirmed selective oxidation of pyrite, and electron paramagnetic resonance (EPR) spectroscopy identified hydroxyl (•OH) and sulfate (SO₄^•− radicals as the dominant reactive species. Iron ions from grinding media and mineral surfaces were identified as key activators of PMS. A major insight was pyrite’s dual role, acting both as a radical scavenger and an activator, which made it highly reactive and susceptible to radical-induced oxidation. This process converted surface copper–sulfur species into copper hydroxides, effectively suppressing pyrite flotation. While previous studies have applied EPR to detect radicals in simplified activator/precursor systems, this study provides the first direct mechanistic evidence of radical-driven selectivity in flotation by detecting inorganic radicals in a complex flotation slurry, thereby demonstrating their persistence under industrially relevant conditions and establishing a foundation for more effective and targeted flotation strategies.

Keywords

selective flotation / radical oxidation / peroxymonosulfate / pyrite depression / chalcopyrite recovery

References

[1] Neisiani AA, Saneie R, Mohammadzadeh A, Wonyen DG, Chelgani SC. Polysaccharides-based pyrite depressants for green flotation separation: An overview. Int. J. Min. Sci. Technol., 2023, 33101229

[2] Mu YF, Peng YJ, Lauten RA. The depression of pyrite in selective flotation by different reagent systems – A literature review. Miner. Eng., 2016, 96–97: 143

[3] Feng QC, Yang WH, Chang MH, Wen SM, Liu DW, Han G. Advances in depressants for flotation separation of Cu–Fe sulfide minerals at low alkalinity: A critical review. Int. J. Miner. Metall. Mater., 2024, 3111

[4] Agheli S, Hassanzadeh A, Hassas BV, Hasanzadeh M. Effect of pyrite content of feed and configuration of locked particles on rougher flotation of copper in low and high pyritic ore types. Int. J. Min. Sci. Technol., 2018, 282167

[5] Peng YJ, Wang B, Gerson A. The effect of electrochemical potential on the activation of pyrite by copper and lead ions during grinding. Int. J. Miner. Process, 2012, 102–103: 141

[6] Li WQ, Li YB, Wang ZH, Yang X, Chen W. Selective flotation of chalcopyrite from pyrite via seawater oxidation pretreatment. Int. J. Min. Sci. Technol., 2023, 33101289

[7] Huang HJ, Hu YH, Sun W. Activation flotation and mechanism of lime-depressed pyrite with oxalic acid. Int. J. Min. Sci. Technol., 2012, 22163

[8] Li YQ, Chen JH, Kang D, Guo J. Depression of pyrite in alkaline medium and its subsequent activation by copper. Miner. Eng., 2012, 26: 64

[9] Wang C, Wu ZX, Wang TBet al.. Mechanisms of nanobubble-enhanced flotation of galena from pyrite. Int. J. Miner. Metall. Mater., 2025, 324817

[10] Huang G, Grano S. Galvanic interaction of grinding media with pyrite and its effect on floatation. Miner. Eng., 2005, 18121152

[11] Lee RLJ, Peng YJ. Evaluate the depression of high-concentration pyrite in copper flotation by high-chromium grinding media. Miner. Process. Extr. Metall. Rev., 2025, 461153

[12] R.L.J. Lee and Y.J. Peng, Assessing the depression of high-concentration pyrite in copper flotation by high pH, Miner. Eng., 209(2024), art. No. 108651.

[13] R.L.J. Lee, X.M. Chen, and Y.J. Peng, Flotation performance of chalcopyrite in the presence of an elevated pyrite proportion, Miner. Eng., 177(2022), art. No. 107387.

[14] Mu YF, Peng YJ. The effect of saline water on copper activation of pyrite in chalcopyrite flotation. Miner. Eng., 2019, 131: 336

[15] Wang ZJ, Shi Q, Zhang GF, Zhu YX, Li BB. Effect of pyrite content on chalcopyrite flotation under different regrinding conditions. Int. J. Miner. Metall. Mater., 2025, 32149

[16] Y.F. Mu and Y.J. Peng, Maximise pyrite depression in copper ore flotation using high salinity water, Miner. Eng., 196(2023), art. No. 108060.

[17] Lee RLJ, Peng YJ. Selectively oxidizing and depressing high-concentration pyrite in copper flotation. Proceedings of XXXI IMPC-International Mineral Processing Congress, Society for Mining, Metallurgy and Exploration, 20242202

[18] Ghanbari F, Moradi M. Application of peroxymonosulfate and its activation methods for degradation of environmental organic pollutants: Review. Chem. Eng. J., 2017, 310: 41

[19] Wang JL, Wang SZ. Activation of persulfate (PS) and peroxymonosulfate (PMS) and application for the degradation of emerging contaminants. Chem. Eng. J., 2018, 334: 1502

[20] Li HX, He HB, Jiang TNet al.. Preparation of Co/S codoped carbon catalysts for excellent methylene blue degradation. Int. J. Miner. Metall. Mater., 2025, 321169

[21] Lee RLJ, Vaughan J, Oh WD, Peng YJ. Revolutionising gold dissolution via chloride-triggered inorganic radicals from peroxymonosulfate. Miner. Process. Extr. Metall. Rev., 2025, 46: 1

[22] X.D. Duan, S.S. Yang, S. Wacławek, G.D. Fang, R.Y. Xiao, and D.D. Dionysiou, Limitations and prospects of sulfate-radical based advanced oxidation processes, J. Environ. Chem. Eng., 8(2020), No. 4, art. No. 103849.

[23] Oh WD, Dong ZL, Lim TT. Generation of sulfate radical through heterogeneous catalysis for organic contaminants removal: Current development, challenges and prospects. Appl. Catal. B, 2016, 194: 169

[24] X.Y. Liu and J.L. Wang, Selective oxidation of ammonia to dinitrogen gas by facile Co²⁺/PMS/chloridion process through reactive chlorine radicals, Chemosphere, 313(2023), art. No. 137648.

[25] Z. Ding, M.J. Chen, J.Q. Yuan, A.M. Yu, H.X. Dai, and S.J. Bai, Fenton oxidation modification mechanism of pyrite and its response to Cu-S flotation separation: Experiment, DFT, XPS and ToF-SIMS studies, Appl. Surf. Sci., 652(2024), art. No. 159305.

[26] Qiu YH, Huang YP, Wang YL, Liu X, Huang D. Facile synthesis of Cu-doped manganese oxide octahedral molecular sieve for the efficient degradation of sulfamethoxazole via peroxymonosulfate activation. Int. J. Miner. Metall. Mater., 2024, 31122770

[27] Nie WS, Mao QH, Ding YB, Hu Y, Tang HQ. Highly efficient catalysis of chalcopyrite with surface bonded ferrous species for activation of peroxymonosulfate toward degradation of bisphenol A: A mechanism study. J. Hazard. Mater., 2019, 364: 59

[28] Zhou Y, Wang XL, Zhu CYet al.. New insight into the mechanism of peroxymonosulfate activation by sulfur-containing minerals: Role of sulfur conversion in sulfate radical generation. Water Res., 2018, 142: 208

[29] Zou J, Ma J, Chen LWet al.. Rapid acceleration of ferrous iron/peroxymonosulfate oxidation of organic pollutants by promoting Fe(III)/Fe(II) cycle with hydroxylamine. Environ. Sci. Technol., 2013, 472011685

[30] Ji F, Li CL, Wei XY, Yu J. Efficient performance of porous Fe₂O₃ in heterogeneous activation of peroxymonosulfate for decolorization of Rhodamine B. Chem. Eng. J., 2013, 231: 434

[31] Y.F. Mu and Y.J. Peng, The role of sodium metabisulphite in depressing pyrite in chalcopyrite flotation using saline water, Miner. Eng., 142(2019), art. No. 105921.

[32] Roessler MM, Salvadori E. Principles and applications of EPR spectroscopy in the chemical sciences. Chem. Soc. Rev., 2018, 47: 2534

[33] Eaton GR, Eaton SS, Barr DP, Weber RT. Quantitative EPR, 2010, Vienna, Springer Vienna37

[34] X.R. Li, P.W. Yan, L.N. Li, Y. Chen, and Z.L. Chen, Activation of peroxymonosulfate by natural pyrite for effective degradation of 2,4,6-trichlorophenol in water: Efficiency, degradation mechanism and toxicity evaluation, Sep. Purif. Technol., 322(2023), art. No. 124253.

[35] X.L. Wang, Y.Z. Ding, D.D. Dionysiou, et al., Efficient activation of peroxymonosulfate by copper sulfide for diethyl phthalate degradation: Performance, radical generation and mechanism, Sci. Total Environ., 749(2020), art. No. 142387.

[36] Tayebi-Khorami M, Manlapig E, Forbes E, Edraki M, Bradshaw D. Effect of surface oxidation on the flotation response of enargite in a complex ore system. Miner. Eng., 2018, 119: 149

[37] Guo B, Peng YJ, Espinosa-Gomez R. Effects of free cyanide and cuprous cyanide on the flotation of gold and silver bearing pyrite. Miner. Eng., 2015, 71: 194

[38] Miao Y, Ye GK, Zhang GF. Effect of dissolved-oxygen on the flotation behavior of pyrite at high altitude area. Int. J. Miner. Metall. Mater., 2024, 31102148

[39] Xie HY, Chen JL, Zhang P, Gao LK, Liu DW, Chen LZ. Separation of galena and chalcopyrite using the difference in their surface acid corrosion characteristics. Int. J. Miner. Metall. Mater., 2023, 30112157

[40] S.H. Xu, M. Zanin, W. Skinner, and S. Brito e Abreu, Surface chemistry of oxidised pyrite during grinding: EDTA extraction analysis, Miner. Eng., 160(2021), art. No. 106683.

[41] M.A. Cashman, L. Kirschenbaum, J. Holowachuk, and T.B. Boving, Identification of hydroxyl and sulfate free radicals involved in the reaction of 1,4-dioxane with peroxone activated persulfate oxidant, J. Hazard. Mater., 380(2019), art. No. 120875.

[42] Q.H. Gui, L.B. Zhang, S.X. Wang, et al., Study on high-efficiency sulfide removement using sulfate radical-based AOPs and its oxidation mechanism of refractory gold ore, Chem. Eng. J., 494(2024), art. No. 153019.

[43] Zhao TY, Yang SQ, Hu XC, Song WX, Cai JW, Xu Q. Restraining effect of nitrogen on coal oxidation in different stages: Non-isothermal TG-DSC and EPR research. Int. J. Min. Sci. Technol., 2020, 303387

[44] S. Xiao, M. Cheng, H. Zhong, et al., Iron-mediated activation of persulfate and peroxymonosulfate in both homogeneous and heterogeneous ways: A review, Chem. Eng. J., 384(2020), art. No. 123265.

[45] Feijoo S, Yu XB, Kamali M, Appels L, Dewil R. Generation of oxidative radicals by advanced oxidation processes (AOPs) in wastewater treatment: A mechanistic, environmental and economic review. Rev. Environ. Sci. Bio/Technol., 2023, 22: 205

[46] B. Song, Z.T. Zeng, E. Almatrafi, et al., Pyrite-mediated advanced oxidation processes: Applications, mechanisms, and enhancing strategie, Water Res., 211(2022), art. No. 118048.

[47] 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, 337873

[48] S.W. Chee, S.F. Tan, Z. Baraissov, M. Bosman, and U. Mirsaidov, Direct observation of the nanoscale Kirkendall effect during galvanic replacement reactions, Nat. Commun., 8(2017), art. No. 1224.

[49] Zhu HY, Ke BL, Lei L, Feng HY, Wan JH, Shen ZH. Influence of galvanic interaction between the iron grinding medium and chalcopyrite on collectorless flotation behavior of chalcopyrite: Experimental and density functional theory study. Langmuir, 2024, 401462

[50] Y.F. Mu, Y.P. Cheng, and Y.J. Peng, The interaction of grinding media and collector in pyrite flotation at alkaline pH, Miner. Eng., 152(2020), art. No. 106344.

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