Reactions of dense MgO with calcium ferrite-based slags at 1573 K
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RODUCTION
THE MgO-based refractories are widely used in ferrous and nonferrous metal smelting industries. In the coppermaking process, magnesia-chrome or chrome-magnesia refractories are extensively used to line the furnace.[1] Refractory wear due to slag attack is a major concern for many metallurgical processes. The cost of replacing the refractory and the disruption to the plant operation could be substantial. Minimizing refractory wear therefore is highly desirable. Calcium ferrite–based slags (CaO-FeO-Fe2O3) were first used industrially in the Mitsubishi (Tokyo) copper converting process, in place of the traditional iron silicate–based slags (FeO-Fe2O3-SiO2).[2,3] Compared to iron silicate slags, calcium ferrite slags have the advantages of lower viscosity, lower copper loss to slag, and higher magnetite solubility. However, because of its high basicity and low viscosity, the calcium ferrite slag is much more aggressive to the magnesiachrome refractories than the iron silicate slag.[4] Considerable research[5–8] has been conducted on the wear of magnesiachrome refractory in iron silicate slags. The dissolution of MgO into the iron silicate slag and the slag penetration and reaction with refractory components leading to spalling were shown to be major wear mechanisms.[5–8] However, work on refractory wear in calcium ferrite slags was rarely reported, especially under the conditions corresponding to the copper converting process. Allen et al.[9] studied the reactions between MgO and calcium ferrite slags from 1573 to 1773 K in air, and found magnesioferrite and magnesiowustite layers formed at the slag-refractory interface. Similar findings have been made by Sato et al.[10] at 1513 K and Yamaguchi et al.[4] at 1573 K in air. The solubility of MgO in copper-containing calcium ferrite slags was studied by S. YAN, formerly Postgraduate Student, G.K. Williams Cooperative Research Centre for Extractive Metallurgy, is Research Scientist, Comalco Research and Technical Support, Comalco Aluminum Limited, Thomastown, Victoria 3074, Australia. S. SUN, Senior Principal Research Scientist, and S. JAHANSHAHI, Program Manager–High Temperature Processing, are with the Division of Minerals, CSIRO, Clayton South, Victoria 3169, Australia. Contact e-mail: [email protected] Manuscript submitted August 14, 2002. METALLURGICAL AND MATERIALS TRANSACTIONS B
Yazawa and Takeda[11] and Sato et al.[10] Yazawa and Takeda showed that MgO solubility was about 2 to 3 wt pct and increased slightly with increasing oxygen potential at 1573 K. Sato et al., however, reported that the MgO solubility in similar slags was as high as 5 to 6 wt pct, and decreased markedly with increasing oxygen potential. As MgO is a dominant component in the commercial magnesia-chrome refractory, the behavior of MgO in calcium ferrite slags is of critical importance for the wear of commercial refractories. The solubility of MgO in the melt relates to the driving force for chemical dissolution. Phase transformations may result in chemical and structural damages withi
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