Experimental determination of phase equilibria in CuOx-containing slag systems at 1100 - 1500 °C

Niko Hellstén

Research output: ThesisDoctoral ThesisCollection of Articles


Copper is vital to modern society. However, its production consumes non-renewable resources, generating waste and harmful emissions. Currently, the copper production industry is trying to optimize pyrometallurgical processing to increase resource efficiency. Good control of slag is key in achieving this goal. Prediction and optimization of the slag properties is possible using computational thermodynamics. Nevertheless, creation of reliable thermodynamic models for a multicomponent slag requires experimental phase equilibria and thermodynamic data, especially from its binary and ternary subsystems. Presently, there is a lack of experimental data concerning Al2O3, CuOx, MgO and SiO2 containing subsystems of the slag. In the present work, thermodynamic phase equilibria, and especially the liquidus, of the Cu-O-Al2O3, Cu-O-MgO, Cu-O-Al2O3-MgO and Cu-O-Al2O3-SiO2 systems were studied experimentally in the temperature range of 1100 °C – 1500 °C. The experiments were conducted using a primary-phase quenching method and a spectroscopic analysis of the chemical compositions of the resulting phases. This method produces direct phase equilibria data from the liquid and solid phases. The experimental results of this work were compared with the predicted phase equilibria calculated using MTDATA 6.0 software and Mtox database version 8.2. It was found that 0 – 2 wt% of Al2O3 and MgO dissolved in the liquid oxide phase at the studied temperatures. Moreover, the addition of SiO2 increased the solubility of Al2O3 in the liquid oxide phase by up to 18 wt%. These results indicate that Al2O3, MgO and MgAl2O4 spinel are chemically resistant to a CuOx-rich liquid oxide at the studied conditions. Discrepancies were found between this new liquidus data, previous experimental data, and calculated liquidus by MTDATA and Mtox database. These discrepancies highlight the necessity of this experimental work. These results indicate that earlier descriptions of the studied systems in Mtox database need reassessment. Furthermore, the new experimental phase equilibrium data obtained in this work is of great importance in generating reliable thermodynamic descriptions of copper-making slag, leading to resource-efficient processing. In addition, these data are useful in various other applications, such as superconductors, refractories and glass-ceramics.
Translated title of the contributionCuOx:ia sisältävien kuonasysteemien faasitasapainojen kokeellinen mittaus 1100 – 1500 °C lämpötiloissa
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
  • Jokilaakso, Ari, Supervising Professor
  • Taskinen, Pekka, Thesis Advisor
Print ISBNs978-952-60-8222-6
Electronic ISBNs978-952-60-8223-3
Publication statusPublished - 2018
MoE publication typeG5 Doctoral dissertation (article)


  • slag
  • phase equilibria
  • thermodynamics
  • equilibration and quenching


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