Kinetics of reduction of iron oxide with carbon monoxide and hydrogen

Abstract

Case I n s t i t u t e of Technology, Cleveland, O h i o This investigation was undertaken to determine the rate controlling step i n the reduction of iron oxides with hydrogen and carbon monoxide. For the reduction of porous hemotite pellets, and bars it was found that the reduction rate is controlled by the counterdiffusion of reactant gas and product gas between the reaction zone and the main gas stream.The reduction specimens were spheres ranging i n size from 1.5-to 4.4-cm. diameter and 5.1-by 7.6-cm. bars either 0.69 or 1.24 cm. thick. They were prepared from electrolytic iron powder, partially oxidized i n a rotary kiln. The final oxidation of the specimens to hematite was accomplished by firing them a t 1,149OC. i n an oxidizing atmosphere. The bulk density was 3.5 g./cc. The specific surface area was 0.08 sq.m./g. and the void faction was 0.31. The oxide specimens were reduced i n streams of pure hydrogen or carbon monoxide a t temperatures between 700' and 1,200OC. The reduction was followed by measuring the sample weight during the reaction. Reduction rates were studied a t system pressures of 1 and 2 at. The samples reduced step by step, to magnetite, t o wiistite, and finally to iron. A shell of reduction, clearly visible i n sections of partially reduced specimens, moved concentrically into the core of the samples. Ahead of the receding interface the specimens were known to be pervious to the reactant gases. This led to the conclusion that the gas composition a t the interface was in equilibrium with the oxide phases present.Except for the removal of the last portions of oxygen a t the lower reduction temperatures, the course of the reduction followed Fick's first law of diffusion. Values of the diffusion coefficients, determined from the experimental data, were i n close agreement with values predicted from empirical equations. Varying the total pressure of the system hod no effect on the rate of reduction, which i s consistent with the equations developed from Fick's law for the diffusion-cantrolled reaction under investigation.It is speculated that the retarding of the reduction reaction a t the lower reduction temperatures is due t o the entrapment of oxide inside shells of iron, which are impervious to the reducing gas. Reduction of the trapped oxide then proceeds by solid state diffusion in a manner proposed by Edstrom (6).

Direct fabrication of high-performance high speed steel products enhanced by LaB 6

“…Vigorous carbon-oxygen reactions facilitate the formation of highly active reduced powders [35] and lay a foundation for complete densification and material purification.…”

“…Elemental powders (Fe and Co), other than chemically stable carbides, suffer high sensitivity to oxidation [30][31][32][33][34]. Regarding that the oxygen dissociation pressure (P O2 ) of CO is lower than those of the oxides of Fe and Co [35] above 600℃, which are the main oxygen donors, the redox reactions between carbon and oxides can thermodynamically occur. Actually, the evolved gas generated from the reduction of oxides by active carbon in the compacts sintered above ~760℃ under vacuum has been approved to mainly encompass carbon monoxide [36] based on an overall reaction [35]:…”

Carbon Co-Deposition During Gas Reduction of Water-Atomized Fe-Cr-Mo Powder

“…(13), y is the carbon content of the reduced sample and x is the CH 4 gas flow rate. Using this expression, the amount of carbon can be carefully controlled so as to minimize the cost and time of processing.…”

“…The reduction of Fe oxides in a reducing gas environment has been widely studied due to its economic and industrial importance, with a number of studies looking at the kinetics of reduction with H 2 [8][9][10][11][12][13][14], CO [13][14][15][16] and CH 4 [17][18][19][20] gas. In a previous study, we briefly discussed the reduction of Fe-based oxides in an environment of H 2 , CO and CH 4 [21], and so the present study specifically focuses on the reduction of Cr-based oxides using CH 4 gas and the carbon that is co-deposited during reduction.…”

Catalyzing Carbothermic Reduction of Siderite Ore with High Content of Phosphorus by Adding Sodium Carbonate

“…[4][5][6][7] Much work has been done on the carbothermic reduction of hematite with sodium carbonate used as an additive, and experimental results indicate the carbothermic reduction of hematite can be reinforced by adding Na2O and the mass and heat transfer during the reducing reaction can be optimized by CO2. [8][9][10][11] However, not much work has been done on the reinforcement of the reduction of siderite, mainly because of the low grade of raw ore and the complicated phase change of siderite. 12,13) Consequently, the exploration and utilization of the siderite ore with high phosphorus content becomes a challenging task.…”