Comparative thermogravimetric study of chlorinations of hematite and wustite

Abstract

The reactions of hematite and wustite with C12, COC12, CO + C12 and gaseous CC14 were studied by thermogravimetry, X-ray diffraction and computer-assisted thermodynamic calculations. During the chlorination of hematite, only gaseous products were formed. The apparent activation energies were calculated from the isothermal TG curves. The chlorination of wustite involves the formation and transformation of a series of sofid chloride products. FeCl2(s), FeCla(s ) and FeOCl(s) were found as intermediates during chlorination with CI 2 or CI 2 + CO, while onlyFeClz(s) was detected in reactions with COCI: oe CC14. The chlorinations of the iron oxides with various agents were compared, and the differences in reactivity sequences were established.Chlorination is a useful tool for the processing of low-grade ores and can also be used for the removal of iron from raw materials. Because of its technical importance, the chlorination behaviour of hematite was investigated in some recent publications

Kinetics of hematite chlorination with Cl2 and Cl2+O2: Part I. Chlorination with Cl2

“…It seems that carbon monoxide has little effect on the chlorination of wüstite at low temperatures during non isothermal treatment. Similar results were reported in other investigations [14], [15] An hematite sample was also subjected to non isothermal treatments under conditions identical to those described above for wüstite. Results obtained for the chlorination of wüstite allow to assume Eqs.…”

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

“…Furthermore, the high E in determined in this study agrees with the high values reported by other authors. [1][2][3][4] For instance, Bertoti et al [1] reported a value of E ap affected by mass transport in the temperature range 873 to 1053 K as great as 188 kJ/mol, which is very similar to the value obtained under the mixed regime (that is, 212 kJ/mol).…”

“…The following chemical equations represent the hematite chlorination: [1][2][3][4][5] Reaction [I] occurs with mass loss due to the formation of iron chloride gaseous. Although it has a DG°positive (viz., DG°5 À0.213 T 1 306 kJ/(mol of Cl 2 )) at the temperatures studied in this paper, it occurs completely under a chlorine flow above 873 K. [1][2][3][4][5] Reaction [II] refers to the equilibrium between FeCl 3 (g) and Fe 2 Cl 6 (g), which is about 50 pct molar at 998 K, [8] decreasing the concentration of Fe 2 Cl 6 (g) as the temperature increases. Hematite powder was placed in a semispherical crucible adopting a loose-pocked bed shape with a high porosity.…”

“…[1][2][3][4][5] Bertoti et al [1] proposed that the chlorination rate of Fe 2 O 3 might be influenced by mass transport in the 873 to 1253 K temperature range, even though it occurs with a high apparent activation energy of 188 kJ/mol. Fruehan and Martonik [2] claimed that the reaction rate was controlled by pore diffusion between 1073 and 1273 K and by chlorine diffusion through the gas film boundary layer around the pellet from 1273 to 1473 K. Szekely et al [3] also reported that the chlorination of Fe 2 O 3 was controlled by mass transfer at high temperatures and moderate pellet sizes.…”

Reactions of wüstite and hematite with different chlorinating agents

“…The researchers agreed that, whilst using the same chlorinating reagents, the chlorination of hematite starts at higher temperatures than that of wüstite. The final reaction product was found to be FeCl 3 . The values of the apparent activation energy of hematite chlorination varied from about 6 kJ/mol to 190 kJ/mol depending on the chlorinating agent used and on the temperature range explored (Table II).…”