Abstract
The present paper describes detailed kinetics investigations on some selected chlorine-solid reactions through thermogravimetric measurements. The solids studied in this article include chemical pure oxides and sulfides as well as their natural bearing materials. The chlorinating agents employed are gaseous mixtures of Cl 2 +N 2 (chlorination), Cl 2 +O 2 (oxychlorination), and Cl 2 +CO (carbochlorination). Results are presented as effects of various parameters on the reaction rate of these solids with these chlorinating agents. It was observed that the reactivity of these solids towards different chlorinating agents varied widely. Sulfides could be chlorinated at room temperature, while carbochlorination of chromium (III) oxide was possible only above 500 °C. The variation of the chlorination rate of these complex materials with respect to gas velocity, composition and temperature enabled us to focus some light on the plausible reaction mechanisms and stoichiometries. The obtained results were used for selective removal of iron from chromite concentrates, extraction of valuable metals from sulfide materials, purification of MgO samples, etc.
Highlights
It is well known that chlorine possesses a high reactivity towards different substances at low temperatures
The methodology adopted for the kinetics studies of various solid samples with different chlorinating gaseous mixtures consists in the following: 1. thermogravimetric analysis (TGA) using nonisothermal conditions, 2. batch-boat experiments and analysis of the solid products (SEM, microprobe, X-ray diffraction (XRD), chemical analysis, etc.), 3. comparison of the reaction rate with that of volatilization of the reaction products, 4. determination of adequate gaseous mixture flow rate, 5. effect of the reactive gases proportions on the reaction rate, 6. determination of the apparent reaction orders with respect to the reactive gases, 7. evaluation of the apparent activation energy of the reaction, 8. mathematical data processing in order to define the geometry of the reaction interface
This study shows that the oxychlorination of chromite proceeds in two stages characterized by different reactivities of chromite towards chlorinating medium such as oxychlorination (Cl +O)
Summary
It is well known that chlorine possesses a high reactivity towards different substances at low temperatures. Many metal chlorides and/or oxychlorides have low boiling points and have appreciably different vapor pressures at a particular temperature. These aspects led the “chlorine technique” as the subject of much attention in areas like mineral beneficiation, metal extraction and waste treatment. The present paper mainly focuses on the kinetics aspects of chlorine-solids reactions approached through thermogravimetric measurements. Higher selectivity of the chlorination methods by SOME KINETICS ASPECTS OF CHLORINE-SOLIDS REACTIONS ALGUNOS ASPECTOS CINÉTICOS DE LAS REACCIONES DE SÓLIDOS CON CLORO employing different chlorinating medium such as oxychlorination (Cl +O ) or carbochlorination (Cl +CO) is discussed. Paragraphs depict some examples where detailed kinetic studies were made
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