Chlorination of alumina in kaolinitic clay
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I.
INTRODUCTION
DURINGthe
past two decades, a number of processes have been devised to replace the Bayer/Hall-Hrroult aluminum manufacturing process. Among them, the production of aluminum metal by the electrolysis of chloride salt melts promises significant energy and cost savings over the conventional Hall process. This explains the great research interest in developing a combined chlorination/electrowinning route to aluminum. One possible technique is to produce aluminum chloride from the pure oxide product from a conventional Bayer
A1203 + 3 CO + 3 C12 ~ 2 A1C13 + 3 CO2 Fe203 + 3 CO + 3 C12 ~ 2 FeCI3 + 3 CO2 SiO2 + 2 CO + 2 C12 ~--- SIC14 + 2 CO2 TiO2 + 2 CO + 2 C12 TiCI4 + 2 CO2 2 A1203 + 3 SiCI4 ~- 4 A1C13 + 3 SiO2 H20 + C12 + CO 2 HCI + CO2 C12 + CO ~--- COClz plant. A lot of work was carried out on the pretreatment and the chlorination of alumina. The influence of parameters such as the type of chlorination media, partial pressure of the gaseous components, particle shape and size distribution, and the reactor design on the kinetics of the reaction were determined in the temperature region between 700 and 1300 K. ~-6 Great efforts have been made, however, to replace the bauxitic raw material with domestic aluminum resources such as clays. The direct recovery of aluminum chloride from clays, however, is much more complex, not only because of the other components present in these raw materials, but also because of the low reaction rates achieved in the direct chlorination. The separation of the volatile chlorides of A1, Fe, Si, and Ti was not considered in the present study. Some factors affecting the chlorination kinetics of kaolinitic clay were reported by Landsberg7,s and Milne. 9 Taking into account their results, the optimum conditions were determined for high aluminum chlorination rates while minimizing silicon conversion. Data are presented here B. GROB is Engineer, Mettler Company, Instrument Division, 8606 Greifensee, Switzerland. W. RICHARZ is Professor, Department of Industrial and Engineering Chemistry, Swiss Federal Institute of Technology, 8092 Zurich, Switzerland. Manuscript submitted November 7, 1983. METALLURGICALTRANSACTIONS B
showing the influence of the pretreating method, NaC1 addition, and the partial pressure of SIC14.
II.
THERMODYNAMICS
In the present work, an equimolar mixture of C12 and CO was used as the chlorination medium. Using tabulated enthalpy and free energy data, ~~ the equilibria of the following reactions were calculated in the temperature range between 300 and 1300 K: AGr~9o0
A/-/~,~
(kJ/fc)
(kJ/fc)
-299 -499 -200 -284 + 0.8 -206 + 13.4
-352 -552 -314 -386 +242 -223 -108
[1] [2] [3] [4] [5] [6] [7]
As an example, enthalpy and free energy data for the overall formula conversion (fc) at 900 K are given here. From thermodynamic considerations we can conclude that iron oxide is more susceptible to chlorination than alumina and titania which is similar to alumina. Thus, because the electrolysis stage requires a highly purified A1C13 feed, an adequate separation
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