I. Gaballah

Kinetics of reduction of iron oxides by H2: Part II. Low temperature reduction of magnetite

This study deals with the reduction of Fe3O4 by H2 in the temperature range of 210–950 °C. Two samples of Fe3O4 produced at 600 and 1200 °C, designated as Fe3O4(600) and Fe3O4(1200), have been used as starting material. Reduction of Fe3O4(600) by H2 is characterized by an apparent activation energy ‘Ea’ of 200, 71 and 44 kJ/mol at T 390 °C, respectively. The important change of Ea at 250 °C could be attributed to the removal of hydroxyl group and/or point defects of magnetite. This is confirmed during the reduction of Fe3O4(1200). While transition at T ≈ 390 °C is probably due to sintering of the reaction products as revealed by SEM. In situ X-rays diffraction reduction experiments confirm the formation of stoichiometric FeO between 390 and 570 °C. At higher temperatures, non-stoichiometric wustite is the intermediate product of the reduction of Fe3O4 to Fe. The physical and chemical modifications of the reduction products at about 400 °C, had been confirmed by the reduction of Fe3O4(600) by CO and that of Fe3O4(1200) by H2. A minimum reaction rate had been observed during the reduction of Fe3O4(1200) at about 760 °C. Mathematical modeling of experimental data suggests that the reaction rate is controlled by diffusion and SEM observations confirm the sintering of the reaction products. Finally, one may underline that the rate of reduction of Fe3O4 with H2 is systematically higher than that obtained by CO in the explored temperature range.

Recovery of Co, Ni, Mo, and V from unroasted spent hydrorefining catalysts by selective chlorination

Spent hydrorefining catalysts may contain 4 to 6 pct of CoO and/or NiO, 8 to 16 pct of MoO3, and up to 10 pct of V2O5, generally supported by alumina. They also contain up to 25 pct of carbon, hydrocarbons, and sulfur. Selective chlorination of raw, unroasted samples with Cl2 + air, Cl2 + N2, and Cl2 + CO + N2 gas mixtures have been investigated for the recovery of valuable elements. The fastest chlorination kinetics are obtained using the Cl2 + CO + N2 gas mixture, followed by Cl2 + N2. The best selective chlorination of spent hydrorefining catalysts is obtained using a Cl2 + air gas mixture. At temperatures lower than 600 °C, it is possible to recover more than 90 pct of the Ni and Co, about 99 pct of the Mo, and up to 75 pct of the V compounds. Cobalt and Nickel chlorides are extracted from the chlorination residues by their dissolution with water. Molybdenum and Vanadium chlorides and/or oxychlorides are recovered by selective condensation from the vapor phase. The chlorination of the catalyst support, A12O3, can be limited to less than about 6 pct. A flow sheet is proposed.

Kinetics of Chlorination and Carbochlorination of Molybdenum Trioxide

Kinetics of chlorination of MoO3 with Cl2-air, Cl2-N2, and Cl2-CO-N2 gas mixtures have been studied by nonisothermal and isothermal thermogravimetric measurements, between ambient temperature and 900 °C. Between 500 °C and 700 °C, the chlorination reaction of MoO3 with Cl2-N2 gas mixture has an apparent activation energy of about 165 kJ/mole, reflecting that a chemical reaction is the rate-controlling step. The reaction order with respect to Cl2 partial pressure is about 0.75. The apparent activation energy for carbochlorination with Cl2-CO-N2 gas mixture is about 83 kJ/mole, between 400 °C and 650 °C. The carbochlorination of MoO3 was controlled by the chemical reaction, probably affected by the pore diffusion regime. The maximum reaction rate is obtained by using a Cl2-CO-N2 gas mixture, having a Cl2/CO volume ratio equal to about 1. The total apparent reaction order with respect to Cl2 + CO in Cl2-CO-N2 gas mixture is about 1.5 for a Cl2/CO ratio equal to 1.

Kinetics of chlorination and carbochlorination of vanadium pentoxide

Kinetics of chlorination of V2O5 with Cl2-air, C12-N2, and C12-CO-N2 gas mixtures have been studied by nonisothermal and isothermal thermogravimetric measurements. In the temperature range of 500 °C to 570 °C, the chlorination of V2O5 with C12-N2 gas mixture is characterized by an apparent activation energy of about 235 kJ/mole. This could be attributed to chemical reaction. Between 570°C and 650 °C, the apparent activation energy is equal to 77 kJ/mole, indicating that the overall reaction rate is controlled by chemical reaction and pore diffusion. The reaction order with respect to chlorine is 0.78. The apparent activation energy of the carbochlorination of V2O5 by C12-CO-N2 gas mixture is about 100 kJ/mole in the temperature range of 400 °C to 620 °C. In this case, the chemical reaction is the limiting step. At temperatures higher than 620 °C, an anomaly is observed in the Arrhenius plot, probably due to thermal decomposition of COC12 formedin situ and/or transformation of the vanadium oxide physical state. The maximum reaction rate is obtained by using a C12-CO-N2 gas mixture having a C12/CO volume ratio equal to about 1.

A low temperature chlorination-volatilization process for the treatment of chalcopyrite concentrates

Abstract Chlorination of two chalcopyrite concentrates with Cl 2 +N 2 was investigated under isothermal conditions in the temperature range of 20–750°C using boat experiments. The effects of gas flow rate, chlorine content of the gas mixture and residence time on the reaction rate were also investigated. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and chemical analysis are used for the physico-chemical characterization of the reaction products. The chlorination of chalcopyrite concentrates started at room temperature generating chlorides of Cu, Pb, Zn, Fe, and S. The reaction of chlorine with sulfides is almost complete at about 300°C and the overall reaction is exothermic. At this temperature, the valuable metal chlorides were concentrated in the chlorination residues, while those of iron and sulfur were volatilized. A flow sheet is proposed for the selective chlorination of chalcopyrite concentrates at low temperatures. Such flow sheet could be considered as an attractive route for the sulfide concentrates’ treatment without SO x emissions. It could be also regarded as energy saving with respect to the classical pyrometallurgical routes.

Kinetics of oxychlorination of chromite: Part II. Effect of reactive gases

Abstract The effects of Cl2/O2 ratio, P(Cl2+O2), PCl2, and PO2 on the oxychlorination rate of the chromite mineral were determined between 750 and 1000°C using isothermal TGA measurements. The effect of the gases’ composition on the oxychlorination rate of chromite were compared with those resulting from the oxychlorination of simple oxides of the chromite (Cr2O3, Fe2O3 and MgO). The apparent reaction orders with respect to Cl2+O2, Cl2, and O2 for the chromite oxychlorination at 750°C were about 0.94, 1.24, and −0.30, respectively. At 1000°C, apparent reaction orders with respect to the reactive gases changed significantly as the reaction progressed. Boat experiments were carried out to oxychlorinate a chromite concentrate between 600 and 1000°C. The reaction products were analyzed by SEM, XRD and chemical analysis. The oxychlorination of a chromite concentrate at about 800°C led to the partial elimination of iron increasing the Cr/Fe ratio in the treated concentrate. A part of chromium was also oxychlorinated and it was recovered as chromium oxychloride (CrO2Cl2).

Reactions of wüstite and hematite with different chlorinating agents

Chlorination of wustite (Fe(1−x)O) and hematite (Fe2O3) with Cl2 + CO and Cl2 + N2 was studied by thermogravimetric analysis using non-isothermal conditions up to about 1000°C. The wustite started to react with the carbochlorinating gas mixtures at low temperatures producing FeCl3 and Fe2O3 as final reaction products. The presence of carbon monoxide, during non-isothermal tests, enhanced the chlorination of wustite at temperatures higher than 550°C when the produced hematite started to react with carbochlorinating gas mixture. The separate treatment of the two oxides under isothermal conditions in Cl2 + CO for 2 h led to their full reaction at about 550°C. An apparent activation energy of about 53 kJ/mol was obtained for the carbochlorination of hematite between 350°C and 550°C. Reaction of wustite with FeCl3 was also studied by thermogravimetric analysis using non-isothermal conditions. Higher oxides of iron and ferrous chloride were the main reaction products at 600°C, even in the presence of carbon monoxide.

Use of chlorination for chromite upgrading

The chlorination of a chromite concentrate was studied between 600 and 1000°C. The reaction products were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and chemical analyses. Chlorination of a chromite concentrate at about 700°C allowed the extraction of about 50% of the iron, thus doubling the Cr/Fe ratio in the treated concentrate. Aluminum chloride was tested as a chlorinating agent in the presence of a reducing atmosphere. The effect of temperature on the kinetics of chromite chlorination was studied between 900 and 1040°C using thermogravimetric analysis (TGA). Temperature effects changed significantly with reaction extent. The initial stage of the chlorination was characterized by an apparent activation energy of about 112 kJ/mol, while a value of about of 269 kJ/mol was found for reaction extents greater than 0.4.

Thermal treatment of complex sulfide ores in N2 and H2 Atmospheres: A new approach for the extraction of their valuable elements

The thermal treatment of natural sulfidic minerals such as sphalerite, galena, chalcopyrite, and pyrite in an N2 or H2 atmosphere was studied to examine the nature of reactions taking place. Such treatments have the potential of avoiding sulfur dioxide production which is associated with the roasting of complex sulfide ores (CSOs). The thermal treatment of CSO concentrates at temperatures less than 1000 °C in a nitrogen atmosphere leads to the decomposition of the pyritic matrix to pyrrhotite and the volatilization of sulfur, galena, and some of the CSOs’ trace elements. Treating the CSO in a reducing atmosphere converted sphalerite to zinc and produced a solid containing Cuo, Feo, and silicoaluminates. Selective dissolution of copper may be achieved by a hydrometallurgical process. Hydrogen sulfide could be reacted with pyrrhotite to form pyrite and hydrogen. A flow sheet is proposed.

Kinetics of chlorination and carbochlorination of lead sulfate

The kinetics of chlorination and carbochlorination of PbSO4 with Cl2 + N2 and Cl2 + CO + N2 gas mixtures has been studied using thermogravimetric measurements in the range 700–900°C. The chlorination reaction rate of PbSO4 with Cl2 + N2 increases with rise in the chlorine content in the gas mixture. The reaction order is about 0.66 with respect to chlorine. The chlorination rate of PbSO4 is controlled by a chemical reaction mechanism with an apparent activation energy of about 174 kJ/mol. In the same temperature range, the apparent activation energy of the carbochlorination of lead sulfate by Cl2 + CO + N2 gas mixture is about 114 kJ/mol. The reaction order is about 0.72 with respect to Cl2 + CO. The maximum reaction rate is obtained by using a carbochlorinating gas mixture having a Cl2(Cl2 + CO) ratio equal to about 0.6.