スラグ中酸化クロムの固体炭素による還元機構

抄録

In relation to the smelting reduction of chromite ore, the mechanism of reduction of aluminate slags containing about 40% of Cr₂O₃ by graphite has been investigated. The rate of reduction has been determined from the mass loss measured by means of thermogravimetry, and the physical situation of the reduction products formed at the slag-graphite interface has been examined by microscopic observation.
While the layer of the reduction product keeps intimate contact with the graphite, the rate of reduction obeys the parabolic rate equation. The rate constant is not affected by the ratio (%CaO)/(%Al₂O₃), and the activation energy is 229 kJ/mol. The rate is controlled by the diffusion of carbon in the product layer.
When the slag penetrates through cracks in the product and is brought into direct contact with the graphite, the reduction of chromium oxide is accelerated. The rate of reduction is approximately represented by the zeroth-order-type rate equation. The rate is independent of the ratio (%CaO)/(%Al₂O₃). For the slags with (%CaO)/(%Al₂O₃)=0.97 and containing Cr₂O₃ more than about 9%, the rate remains essentially unchanged with increasing initial content of Cr₂O₃. The apparent activation energy is 533 kJ/mol. It is supposed that the rate of reduction is limited by the solubility of chromium in slag.