Study of Chromium Oxide Activities in EAF Slags
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Based on the above results, the activities of bivalent and trivalent chromium oxide in some slags at 1873 K (1600 °C) were measured. The slags were equilibrated with Cu-Cr melts under two oxygen partial pressures (pO2 = 6.9 9 104 and 1.8 9 106 Pa, respectively). The morphology of the quenched slags and the solubility of chromium oxide in the melts were investigated by EPMA, SEM, and XRD. Under both oxygen partial pressures, the slags were saturated by the solid solution MgAl2xCrxO4d. At the low oxygen partial pressure (1.8 9 106 Pa), the content of Cr in the liquid phase varied from 0.4 to 1.6 mass pct with the total Cr content in the slags increasing from 1.3 to 10.8 mass pct. At the high oxygen partial pressure (6.9 9 104 Pa), the content of Cr in the liquid phase decreased to the level of 0.2 to 0.6 mass pct. Both the activities of CrO and Cr2O3 in slag were found to increase approximately linearly with the increase of the total Cr content in slag. While the oxygen partial pressure had minor effect on the activity of Cr2O3 in the slag, it had significant effect on the activity of CrO. DOI: 10.1007/s11663-015-0453-4 Ó The Minerals, Metals & Materials Society and ASM International 2015
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INTRODUCTION
IT is inevitable in the production of high chromium grades steel, e.g., in the EAF process, that chromium gets oxidized and enters the slag. The loss of chromium into the slag is not only a waste of chromium resource, but also a serious environmental issue. According to environmental legislation in some countries, external use of steel slag is restricted primary due to its content of chromium. Reducing the chromium content in the slag is therefore an essential task and a challenge for the metallurgist and chemist. To meet the demand of reducing the loss of chromium into slag, reliable thermodynamic data for chromium oxide activities are necessary. Although a number of studies have been conducted,[1–4] the experimentally
BAIJUN YAN, Professor, is with the State Key Laboratory of Advanced Metallurgy, Department of Physical Chemistry of Metallurgy, University of Science and Technology Beijing, Beijing 100083, P.R. China. FAN LI, Associate Professor, is with the Beijing Key Laboratory for Green Catalysis and Separation, Department of Chemistry and Chemical Engineering, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100124, P.R. China. HUI WANG, Research Professor, is with the China Institute of Mineral Resource, Beijing General Research Institute of Mineral Metallurgy, Beijing 100044, China. DU SICHEN, Professor, is with the Department of Materials Science and Engineering, Royal Institute of Technology, 10044 Stockholm, Sweden. Contact e-mail: [email protected] Manuscript submitted October 30, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
determined data are still too few. The lack of data is mainly due to the difficulties of measurement, especially due to the co-existence of Cr2+ and Cr3+ in the slag and the dependence of their fraction on oxygen p
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