Activity coefficients of NiO and CoO in CaO–Al₂O₃–SiO₂ slag and their application to the recycling of Ni–Co–Fe-based end-of-life superalloys via remelting

Abstract

To design optimal pyrometallurgical processes for nickel and cobalt recycling, and more particularly for the end-of-life process of Ni–Co–Fe-based end-of-life (EoL) superalloys, knowledge of their activity coefficients in slags is essential. In this study, the activity coefficients of NiO and CoO in CaO–Al₂O₃–SiO₂ slag, a candidate slag used for the EoL superalloy remelting process, were measured using gas/slag/metal equilibrium experiments. These activity coefficients were then used to consider the recycling efficiency of nickel and cobalt by remelting EoL superalloys using CaO–Al₂O₃–SiO₂ slag. The activity coefficients of NiO and CoO in CaO–Al₂O₃–SiO₂ slag both show a positive deviation from Raoult’s law, with values that vary from 1 to 5 depending on the change in basicity. The activity coefficients of NiO and CoO peak in the slag with a composition near B = (%CaO)/(%SiO₂) = 1, where B is the basicity. We observed that controlling the slag composition at approximately B = 1 effectively reduces the cobalt and nickel oxidation losses and promotes the oxidation removal of iron during the remelting process of EoL superalloys.

Keywords

recycling / nickel / cobalt / end-of-life / superalloys / activity coefficients / remelting / slag

References

[1] Reck B.K., Graedel T.E. Challenges in metal recycling. Science, 2012, 337(6095): 690.

[2] Reck B.K., Müller D.B., Rostkowski K., Graedel T.E. Anthropogenic nickel cycle: Insights into use, trade, and recycling. Environ. Sci. Technol., 2008, 42(9): 3394.

[3] Harper E.M., Kavlak G., Graedel T.E. Tracking the metal of the goblins: cobalt’s cycle of use. Environ. Sci. Technol., 2012, 46(2): 1079.

[4] Norgate T.E., Jahanshahi S., Rankin W.J. Assessing the environmental impact of metal production processes. J. Cleaner Prod., 2007, 15(8-9): 838.

[5] Norgate T., Jahanshahi S. Assessing the energy and greenhouse gas footprints of nickel laterite process. Miner. Eng., 2011, 24(7): 698.

[6] Eckelman M.J. Facility-level energy and greenhouse gas life-cycle assessment of the global nickel industry. Resour. Conserv. Recycl., 2010, 54(4): 256.

[7] Mudd G.M. The Environmental sustainability of mining in Australia: key mega-trends and looming constraints. Resour. Policy, 2010, 35(2): 98.

[8] Wahll M.J., Maykuth D.J., Hucek H.J. Handbook of Superalloys, International Alloy Compositions and Designations Series, 1979, Columbus, Battelle Press, 1.

[9] Stoloff N.S., Handbook A.S.M. Volume 1: Properties and Selection: Irons, Steels, and High-performance Alloys (06181), 1990 10 OH, ASM International Handbook Committee, Materials Park, 950.

[10] W. Boesch, Superalloys, Supercomposites and Superceramics, Edited by J.K. Tien and T. Caulfield, Academic Press, Boston, 1989, p.3.

[11] Schlatter R. Melting and refining technology of high-temperature steels and superalloys: a review of recent process developments. Superalloys 1972, 1972, New York, John Wiley, A1.

[12] deBarbadillo J.J. Nickel-base superalloys; physical metallurgy of recycling. Metall. Trans. A, 1983, 14(2): 329.

[13] Srivastava R.R., Kim M., Lee J., Jha M.K., Kim B.S. Resource recycling of superalloys and hydrometallurgical challenges. J. Mater. Sci., 2014, 49(14): 4671.

[14] Crundwell F., Moats M., Ramachandran V., Robinson T., Davenport W.G. Extractive Metallurgy of Nickel, Cobalt and Platinum Group Metals, 2011, Oxford OX5 1GB, UK, Elsevier, 215.

[15] Shen H., Forssberg E. An overview of recovery of metals from slags. Waste Manage., 2003, 23(10): 933.

[16] Gorai B., Jana R.K., Premchand Characteristics and utilisation of copper slag-a review. Resour. Conserv. Recycl., 2003, 39(4): 299.

[17] Lu X., Matsubae K., Nakajima K., Nakamura S., Nagasaka T. Thermodynamic considerations of contamination by alloying elements of remelted end-of-life nickel- and cobalt-based superalloys. Metall. Mater. Trans. B, 2016, 47(3): 1785.

[18] Henao H.M., Hino M., Itagaki K. Phase equilibrium between Ni–S melt and FeO_x–SiO₂ or FeO_x–CaO based slag under controlled partial pressures. Mater. Trans., 2002, 43(9): 2219.

[19] Takeda Y., Ishiwata S., Yazawa A. Distribution equilibrium of minor elements between liquid copper and calcium ferrite slag. Trans. Jpn. Inst. Met., 1983, 24(7): 518.

[20] Reddy R.G., Acholonu C.C. Distribution of nickel between copper-nickel and alumina saturated iron silicate slags. Metall. Trans. B, 1984, 15(1): 33.

[21] Pagador R.U., Hino M., Itagaki K. Phase equilibrium between FeO_x–MgO–SiO₂ or FeO_x–CaO–MgO–SiO₂ slag and nickel alloy. J. Min. Mater. Process. Inst. Jpn., 1998, 114(2): 127.

[22] Henao H.M., Hino M., Itagaki K. Distribution of Ni, Cr, Mn, Co and Cu between Fe–Ni alloy and FeO_x–MgO–SiO₂ base slags. Mater. Trans., 2001, 42(9): 1959.

[23] Li G.Q., Tsukihashi F. Distribution equilibria of Fe, Co and Ni between MgO-saturated FeO_x–MgO–SiO₂ slag and Ni alloy. ISIJ Int., 2001, 41(11): 1303.

[24] Cho S.W., Suito H. Magnesium deoxidation and nitritogen distribution in liquid nickel equilibrated with CaO–Al₂O₃–MgO slags. ISIJ Int., 1994, 34(9): 746.

[25] Henao H.M., Hino M., Itagaki K. Phase equilibrium between Ni–S melt and CaO–Al₂O₃ based slag in CO–CO₂–SO₂ gas mixtures at 1773 K. Mater. Trans., 2002, 43(11): 2873.

[26] Henao H.M., Itagaki K. Phase equilibrium and distribution of minor elements between Ni–S melt and Al₂O₃–CaO–MgO slag at 1873 K. Metall. Mater. Trans. B, 2004, 35(6): 1041.

[27] Wang S.S., Kurtis A.J., Toguri J.M. Distribution of copper–nickel and copper–cobalt between copper–nickel and copper–cobalt alloys and silica saturated fayalite slags. Can. Metall. Q., 1973, 12(4): 383.

[28] Wang S.S., Santander N.H., Toguri J.M. The solubility of nickel and cobalt in iron silicate slags. Metall. Trans., 1974, 5, 261.

[29] Grimsey E.J., Toguri J.M. Cobalt in silica saturated fayalite slags. Can. Metall. Q., 1988, 74(4): 331.

[30] Katyal A., Jeffes J.H.E. Activities of cobalt and copper oxides in silicate and ferrite slags. 3rd International Conference on Molten Slags and Flues, 1989, London, Institute of metals, 46.

[31] Grimsey E.J., Liu X.L. The activity coefficient of cobalt oxide in silica-saturated iron silicate slags. Metall. Mater. Trans. B, 1995, 26(2): 229.

[32] Teague K.C., Swinbourne D.R., Jahanshahi S. A thermodynamic study on cobalt containing calcium ferrite and calcium iron silicate slags at 1573 K. Metall. Mater. Trans. B, 2001, 32(1): 47.

[33] Chen C., Zhang L., Jahanshahi S. Review and thermodynamic modelling of CoO in iron silicate-based slags and calcium ferrite-based slags. VII International Conference on Molten Slags Fluxes and Salts, 2004, Johannesburg, The South African Institute of Mining and Metallurgy, 509.

[34] Derin B., Yücel O. The distribution of cobalt between Co–Cu alloys and Al₂O₃–FeO–Fe₂O₃–SiO₂ slags. Scand. J. Metall., 2002, 31(1): 12.

[35] Pagador R.U., Hino M., Itagaki K. Distribution of minor elements between MgO saturated FeO_x–MgO–SiO₂ or FeO_x–CaO–MgO–SiO₂ slag and nickel alloy. Mater. Trans. JIM, 1999, 40(3): 225.

[36] Kitamura S., Kuriyama H., Maruoka N., Yamaguchi K., Hasegawa A. Distribution of cobalt between MgO-saturated FeO_x–MgO–CaO–SiO₂ slag and Fe–Cu–Co molten alloy. Mater. Trans., 2008, 49(11): 2636.

[37] Barin I. Thermochemical Data of Pure Substances, 1993 2 Weinheim, VCH Verlagsgesellschaft mbH, 271.

[38] O’Neill H.S., Berry A.J. Activity coefficients at low dilution of CrO, NiO and CoO in melts in the system CaO–MgO–Al₂O₃–SiO₂ at 1400°C: using the thermodynamic behavior of transition metal oxides in silicate melts to probe their structure. Chem. Geol., 2006, 231, 77.

[39] O’Neill H.S., Eggins S.M. The effect of melt composition on trace element partitioning: an experimental investigation of the activity coefficients of FeO, NiO, CoO, MoO₂ and MoO₃ in silicate melts. Chem. Geol., 2002, 186(1-2): 151.

[40] Lukas H., Fries S.G., Sundman B. Computational Thermodynamics: the Calphad Method, 2007, New York, USA, Cambridge University Press

[41] Hillert M. Phase Equilibria, Phase Diagrams and Phase Transformations: Their Thermodynamic Basis, 2007 2 Cambridge, UK, Cambridge University Press

[42] an Mey S. Thermodynamic re-evaluation of the Cu–Ni system. Calphad, 1992, 16(3): 255.

[43] Kubišta J., Vřešťál J. Thermodynamics of the liquid Co–Cu system and calculation of phase diagram. J. Phase Equilib., 2000, 21(2): 125.

[44] Taniguchi Y., Morita K., Sano N. Activities of FeO in CaO–Al₂O₃–SiO₂–FeO and CaO–Al₂O₃–CaFe₂–FeO slags. ISIJ Int., 1997, 37(10): 956.

[45] Ogura T., Fujiwara R., Mochizuki R., Kawamoto Y., Oishi T., Iwase M. Activity determinator for the automatic measurements of the chemical potentials of FeO in metallurgical slags. Metall. Trans. B, 1992, 23(4): 459.

[46] Banya S., Hino M. Calculation of activities of the constituents in Fe_tO–(CaO+MgO)–(SiO₂+P₂O₅) slags by regular solution model. Tetsu-to-Hagane, 1987, 73(3): 74.

[47] O’Neill H.S.C. Free energies of formation of NiO, CoO, Ni₂SiO₄, and Co₂SiO₄. Am. Mineral., 1987, 72, 280.

[48] Mao H., Hillert M., Selleby M., Sundman B. Thermodynamic assessment of the CaO–Al₂O₃–SiO₂ system. J. Am. Ceram. Soc., 2006, 89(1): 298.

[49] Guillermet A.F. Assessing the thermodynamics of the Fe–Co–Ni system using a calphad predictive technique. Calphad, 1989, 13(1): 1.

[50] Guillermet A.F. Assessment of the thermodynamic properties of the Ni–Co system. Z. Metallkd., 1987, 78(9): 639.

[51] Ohnuma I., Enoki H., Ikeda O., Kainuma R., Ohtani H., Sundman B., Ishida K. Phase equilibria in the Fe–Co binary system. Acta Mater., 2002, 50(2): 379.

[52] Cacciamani G., Dinsdale A., Palumbo M., Pasturel A. The Fe–Ni system: thermodynamic modelling assisted by atomistic calculations. Intermetallics, 2010, 18(6): 1148.

[53] Dinsdale A.T. SGTE data for pure elements. Calphad, 1991, 15(4): 317.