Intrinsic kinetics of the chlorination of hematite powder between 898 and 1023 K

Abstract

The kinetics of the chlorination of hematite powder was investigated between 898 and 1023 K by isothermal thermogravimetry. The influence of the chlorine partial pressure and sample size on the reaction rate was studied between 15 and 70 kPa and between 0.5 and about 50 mg, respectively. The reaction occurs under mixed control; pore diffusion and chemical reaction are the rate-controlling steps. An apparent reaction order of 0.5 with respect to chlorine partial pressure (that implies a zero intrinsic order) and a value of activation energy of 451 kJ/mol were found.

The kinetics and mechanism of selective iron chlorination of an ilmenite ore

“…This is probably an apparent value instead of an intrinsic kinetic value, because it is known that the reactions rate occurring in powder samples may be affected by diffusion through pores. 27 Furthermore, as can be seen in Fig. 4a the reaction rate increases when decreasing the sample mass, which might be indicating that the reaction rate is being influenced by mass…”

Chlorination of Zinc Oxide between 723 and 973 K

“…For this reason, the correlation between the change in the reaction rate and the different partial pressures of chlorine is not evident from these kinds of measurements. A methodology already reported by Pasquevich et al [24] was applied. It consists of varying pCl 2 between 15 and 70 kPa, during the chlorination of the same sample of 40 mg.…”

“…A more detailed explanation of the procedure can be found elsewhere. [24] In Figure 6, the TG curve obtained for 873 K is shown; the different partial pressures used were 16, 34, 45, 55, and 70 kPa. The same type of curve was obtained for 773 K. The rate of reaction (Eq.…”

“…[3] written as R = da/dt = K*(1 -a) 2/3 . This is an approximation that has been already applied in similar systems, [24,25] because the sample is a powder that adopts the crucible shape. The values of the ''apparent rate constant'' (K*), obtained for the different temperatures, are shown in Table II, together with the correlation coefficient of the fittings.…”

“…[26] A possible test involves comparing the values of D Cl 2 and D K ; if the ratio D Cl 2 =D K is small, then ordinary diffusion can be considered as the rate determining step. The value of D Cl 2 was assumed of the order 10 -2 cm 2 s -1 , as estimated by Pasquevich et al [24] for a mixture of Ar-FeCl 3 -Fe 2 Cl 6 -O 2 -Cl 2 , due to the absence of more accurate data. The value of D K calculated according to Eq.…”