Kinetics of reduction of synthetic chromite with carbon.

Abstract

SynopsisSynthetic Chromite was prepared and reduction studies were carried out with di fferent amounts of carbon in the mixture in the temperature range 1150-'1300 °C. Partially reduced material was analysed by X-ray di , f f'ractometry which indicated the presence of Fe, Cr203, unreduced chromite, Cr304 and residual graphite. An analysis of the results on the basis of quasi steady state equation for diffusion control through product layer, phase boundary reaction and unsteady state diffusion of oxygen, reveal, that the process can best be described by diffusion control of oxygen towards the surface of individual particles with fast reaction at the surface. Activation energies for this djffusion process was estimated to be about 57 kcalimol. This does not change with the carbon content in the initial reduction stage (upto 25 %), investigated in this work.

Kinetics of the formation reaction of manganese carbide under various gases

“…Next, the activation energy was evaluated in the temperature range of 1373-1573 K, with a value of 299.27 kJ/mol being obtained for the formation reaction of Mn 7 C 3 in the present work. This value is nearly equal to that of activation energy for the carbide formation reaction of the metal oxide such as Mn oxide and Cr oxide, which are from 217 to 310 kJ/mol [10,11,13,14]. It has been known that the carbide formation reaction by CO and carbon or carbide are controlled by Boudouard's reaction and interfacial chemical reaction or solid state diffusion of carbon, respectively [10][11][12][13][14]20,21].…”

“…Furthermore, several studies have reported the rate determining step of the carbothermic reduction of metallic oxide [7,8,[12][13][14][15][16][17][18][19]. In the reduction of a metallic oxide by carbon, it is assumed that the overall rate can be controlled by the gasification of graphite at temperatures up to 1273 K [7,[12][13][14]. At higher temperatures, this reaction proceeds quite rapidly, which may lead to the case of a diffusion-controlled reaction [15,16].…”

“…However, knowledge of the effect of the CO partial pressure on the formation reaction of manganese carbide is not sufficient for fully understanding the carbothermic reaction, even though it constitutes a very important factor in determining the formation reaction of manganese carbide. Furthermore, several studies have reported the rate determining step of the carbothermic reduction of metallic oxide [7,8,[12][13][14][15][16][17][18][19]. In the reduction of a metallic oxide by carbon, it is assumed that the overall rate can be controlled by the gasification of graphite at temperatures up to 1273 K [7,[12][13][14].…”

The recovery of platinum group metals from low-grade concentrates to an iron alloy using silicon carbide as reductant

“…Murti et al [10] studied the reduction of synthetic chromite by carbon at 1423 to 1573 K. In this study it was concluded that reduction was controlled by diffusion of oxygen in the chromite. The same authors studied the reduction of chromite ore at 1513 to 1583 K. In this case, the reduction process was found to be controlled by the diffusion of oxygen in the ore to the gas/solid interface.…”

“…Various possible mechanisms controlling the rate of reaction have been discussed in literature [8][9][10][11].…”