The reduction of MoO 2 powder by hydrogen is one of the most important steps for manufacturing ferromolybdenum alloy and molybdenum powder. The results of experiments on the kinetics of this reaction are presented in this paper. The experiments were carried out under nonisothermal condition in hydrogen atmosphere using TGA equipment. The nonisothermal experiments were carried out at various linear heating rates up to 1273 K. It was found that the reduction reaction is very fast under the whole heating rate until the reduction ratio of MoO 2 approaches to about 0.92. The reduction ratio of MoO 2 was about 0.98 after finishing the reduction reaction at a heating rate of 4 K/min. Kinetics of the reaction was analyzed from the dynamic TGA data by means of Coats and Redfern equation. The nucleation and growth model yielded a satisfactory fit to these experimental data.

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Molybdenite concentrate is the major mineral for the molybdenum industry. The industrial processing of molybdenite concentrate is first to convert to technical grade molybdenum trioxide by its oxidative roasting, followed by its purification by distillation or its ammonia leaching. In the present research, detailed experimental results for the oxidative roasting of low grade Mongolian molybdenite concentrate are presented. The experiments were carried out in the temperature range of 778 to 838 K under air atmosphere by using a thermogravimetric analysis technique. The particle size of the molybdenite concentrate was varied between 53 and 103 mm. As an example of the oxidative roasting of low grade Mongolian molybdenite concentrate, more than 95% of 53 mm particle size molybdenite was converted to molybdenum trioxide in 40 min at 823 K. The Jander equation was found to be useful in describing the rates of the oxidative roasting, which had an activation energy of 215.0 to 259.3 kJ/mol (51.4 to 62.0 kcal/mol) for various sizes, such as 53 mm, 67 mm and 103 mm.

As copper concentrates are progressively becoming more complex and low in grades, it is meaningful to remove sulfur from complex copper concentrates for smelting them by a carbon reduction process. In the present work, a kinetic study on the oxidative roasting of complex copper concentrate was experimentally investigated under nonisothermal condition in air using TGA equipment. Nonisothermal experiments were carried out at various linear heating rates up to 1123 K. Intermediates formed in each stage of the oxidative roasting of the complex copper concentrate were identified. After the first weight loss step, sulfate compounds were mainly formed in the second stage, and about 55% of sulfur contained in the concentrate was removed. In the third stage, the sulfur removal reaction was carried out, the rest of sulfur was nearly removed in this stage. Kinetics of the third stage were analyzed from the dynamic TGA data by means of Coats and Redfern equation. The nucleation and growth model yielded a satisfactory fit to these experimental data.

It is very important to remove sulfur from complex copper concentrates for smelting them by a carbon reduction process since copper concentrates are progressively becoming complex and low grade. The carbon reduction process largely consists of the oxidation process of complex copper concentrate and smelting process of the oxidized concentrate. In the present work, the kinetics study has been performed on a complex copper concentrate to understand the oxidation process over a temperature range of 998 to 1073 K and an oxygen partial pressure range of 15.20 to 50.66 kPa using a thermogravimetric method. It was found that the oxidation rate was very fast under the whole temperature range and almost 95% of sulfur contained in the concentrate was removed after 15 min at 1073 K under an oxygen partial pressure of 21.28 kPa. Sulfur removal ratio as a function of time has been analyzed by using a shrinking-core model and the effect of oxygen partial pressure has been elucidated.