Kinetics of carbide formation from reduced iron in CO-H2-H2S mixtures

Gravimetric measurements were made for the kinetics of the carbide formation from reduced iron by preventing the decomposition of iron carbides and the deposition of carbon by utilizing the effect of sulfur. Particles of a hematite ore were completely reduced in the H-2-H2S mixture and converted to iron carbide in a CO-H-2-H2S-CO2-H2O-Ar or CO-CO2-COS-N-2 mixture at 873 to 1073 K. The carbide formation kinetics was drastically accelerated by the addition of a few percent H-2 to CO and reached the maximum at about 20 pct H-2. From morphology observation, it was assumed that the carburization reaction on the surface of pores in the reduced iron determines the carbide formation kinetics, and the carburization rate, df(theta)/dt, is expressed as the product of a function of carburization rate, g(pi, T), and the relative reaction surface area at the time t, 1 - f(theta). Applying the integrated rate equation, -In (1 - f(theta)) = g(p(i), T)t, to the experimental results, the value of g(pi, T) was obtained. By analyzing the carbide formation rate, it was assumed that the elementary reactions determining the carbide formation rate are CO + H(ad) --> [C] + OH(ad) and OH(ad) + H-2 = H2O + H(ad), except in the low ratio Of pH(2)/Pco, where the rate determining elementary reaction shifts to O(ad) + CO - CO2. The overall rate Eq. [22] has been proposed for the carbide formation from the reduced iron in CO-H-2-H2S-CO2-H2O mixtures.