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

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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.

Original languageEnglish
Pages (from-to)25-36
Number of pages12
JournalInternational Journal of Minerals, Metallurgy and Materials
Volume24
Issue number1
DOIs
Publication statusPublished - 2017 Jan 1

Keywords

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

ASJC Scopus subject areas

  • Mechanics of Materials
  • Mechanical Engineering
  • Geochemistry and Petrology
  • Metals and Alloys
  • Materials Chemistry

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