Masayasu Kawahara

Effect of Dense Layer Formation on Dissolution Rate of MgO-C Refractory in Molten Slag

The corrosion test for magnesia-carbon refractory, MgO-C, with dense layer has been carried out by a rotating cylinder method at 1673 K. The specimen, which was a cylinder of 25 mm diameter and 25mm height, was rotated in molten slag at 50 rpm. The chemical composition of slag was CaO-SiO2-FeO-MgO-CaF2. The corrosion rate was determined by the variation of radius of the cylindrical specimen against corrosion time. The decrease of radius was obtained by a calculation of dissolved MgO into the slag. In addition, the diameter of the specimen was measured with a slide calipers after the corrosion test. The cylindrical specimen was heated to form a dense layer before the corrosion test. The corrosion rate of the MgO-C refractory with dense layer was slower than that of the MgO-C refractory without dense layer. The oxidized layer, where the dense layer formed, dissolved at much the same rate as the MgO brick. The dense layer probably obstructed contact between slag and carbon in the matrix, and then oxidation of C by slag did not take place. Formation of the dense layer was effective to inhibit corrosion of MgO-C refractory by molten slag.

The Oxidation Rate of a Magnesia-Carbon Refractory under Low Oxygen Partial Pressures

The oxidation rate of resin-bonded magnesia-carbon refractory, MgO-C, containing 5 mass % carbon, was measured continuously with a thermobalance in the temperature range from 1273 to 1823 K in N 2 -O 2 and Ar-O 2 mixed gases with 2.1 X 10 4 and 3.7 X 10 2 Pa of oxygen partial pressure, pO 2 , respectively. The effect of the oxygen concentration in the atmospheric gas on the oxidation rate for the MgO-C refractory has been investigated. The value of the effective diffusion coefficient D e of O 2 , which diffuses through the porous decarburized layer, decreased abruptly when the oxidation temperature went up to 1823 K under 2.1 X 10 4 Pa of pO 2 in N 2 -O 2 . When the value of pO 2 in the atmospheric gas was 3.7 X 10 2 Pa, the abrupt decrease of D e occurred at a lower oxidation temperature of 1673 K. At low pO 2 , a dense layer, probably MgO, formed near the surface of the refractory. It was speculated that the recession speed of the graphite phase was slower due to the formation of this dense phase.

Dilute sulphuric-acid leaching of garnierite ore after magnetic-roasting the ore mixed with iron powder

Abstract In order to investigate sulphuric-acid leaching of garnierite ore rich in magnesia, an attempt was made to selectively extract nickel using the dilute sulphuric acid leaching method after magnetic-roasting the ore mixed with iron powder. In addition, a study was made of the effects of various factors in this process on the extraction percentages of various components. The selective extraction of nickel by dilute sulphuric acid leaching has been made possible by mixing about 5% iron powder with the garnierite and subsequently carrying out magnetic roasting at 1000°C in a water vapor atmosphere for more than 30 min. In order to raise the nickel extraction percentage while keeping low those of magnesia and iron it is advisable to lower the concentration of sulphuric acid (about 1/50), and raise the extraction temperature (about 95°C). When the leaching temperature is comparatively low (about 50°C), a weak agitation exercises more effective influence on the selective extraction of nickel. Under optimum conditions, the extraction percentages of nickel, magnesia and iron are more than 98%, less than 5%, and less than 3%, respectively.

Corrosion Mechanism of Refractory Immersed in Molten Slag

Researchers have reported that the dissolution rate of solid matters in liquids was usually controlled by diffusion of solute through the boundary layer. The authors have founded that the movement of the bubbles through the boundary layer has rapidly increased the corrosion rate, and the existence of chromium oxide suspension in the boundary layer has increased the resistance to corrosion. 5, 6 Recently, the development of new corrosion-resistant materials has been desired. In the present study, we present the deep understanding about the mechanism of corrosion under three conditions of the boundary layer. EXPERIMENT

Oxidation rate of magnesia-carbon refractory with aluminum additive

An effect of addition of 2 mass % aluminum powder on the oxidation rate of magnesia-carbon refractory, MgO-C, containing 5 mass % carbon has been investigated by measuring weight change with a thermobalance for the cubic specimens in the temperature range from 1073 to 1823 K in air. The oxidation rate of carbon was measured by analyzing the residual carbon in the specimens at some oxidation time. The variations of the weight with oxidation time at temperatures from 1273 to 1673 K showed the similar tendency. The oxidation rate of carbon in the MgO-C refractory with 2 mass % of aluminum additive was a little smaller than that of the MgO-C refractory with no additives. When the oxidation temperature increased to 1823 K, the weight change became very small. It was suggested that the gaps between MgO grains in the thin oxidation layer were bridged by MgO·Al2O3, which was identified by a X-ray diffraction method.

The Masking of Cobalt by Sulfite Ion in Solvent Extraction.

After leaching cobalt crusts in an ammoniacal solution using sulfur dioxide gas as a reductant, the extraction of cobalt was held down in the solvent extraction process. The effects of sulfite ion on cobalt were studied by using nitroso R salt which forms a complex with cobalt. As a result, formation of cobalt complex salt was negligible in the solution of ammonium sulfite and sodium sulfite. It is supposed that sulfite ion acts as a masking reagent for cobalt.Solvent extraction of cobalt and nickel was carried out using LIX84-I as an extractant for the solution of ammonium sulfite. The effects of the ammonium sulfite concentration and retention time on the extraction of cobalt were investigated. Cobalt (10 ppm) was not extracted from the ammonium sulfite solution of concentration more than 0.5 M and the pH over 10.5. In the same condition, nickel (10 ppm) was extracted completely. Same studies were carried out by using PC-88A and D2EHPA, but superior separation of cobalt and nickel was not attained.An EDTA titration was carried out by addition of sodium sulfite or ammonium sulfite to the solution including cobalt and nickel. As a result, only nickel was titrated quantitatively inthe mixed solution containing up to 1 mg (20 ppm) of cobalt