ALCOA-process

Both the Toth and Alcoa processes provide aluminum chloride for subsequent reduction to aluminum. Pilot-plant tests of these processes have shown difficulties exist in producing aluminum chloride of the purity needed. In the Toth process for the production of aluminum chloride, kaolin [1332-58-7] clay is used as the source of alumina (5). The clay is mixed with sulfur and carbon, and the mixture is ground together, pelletized, and calcined at 700°C. The calcined mixture is chlorinated at 800°C and gaseous aluminum chloride is evolved. The clay used contains considerable amounts of silica, titania, and iron oxides, which chlorinate and must be separated. Silicon tetrachloride and titanium tetrachloride are separated by distillation. Resublimation of aluminum chloride is requited to reduce contamination from iron chloride. 

A consolidated picture of the different processes for the production of aluminum is shown in Figure 6.25. There are altogether four processes (i) Alcan process (ii) Toth process (iii) Alcoa process and (iv) Bayer process. 

Figure 6.25 Flowsheets for Al extraction stream 1 Bayer process, 2 Alcoa process, 3 Toth process, 4 Alcan process.

The only reasonably successful advance in this sense is the Alcoa process, based on the electrolysis of aluminium trichloride in a 2-15 per cent concentration at 700°C in a 3 2 mixture of molten sodium chloride and potassium chloride using carbon electrodes. Aluminium oxide is previously converted into aluminium chloride using chlorine from electrolysis. The reactions are thus... 

Development work on the Alcoa process encountered several difficulties, notably in the chlorination step, and the project has been abandoned. 

Affinity of a reaction, A — The decrease in - Gibbs Alcoa process/Alcoa electrolyzer — This is a process energy on going from the reactants to the products of to manufacture metallic aluminum by electrolysis of... 

Al-manufacture from AICI3 by the Alcoa process is currently unimporttmt. 

Anhydrous aluminum chloride is currently mainly manufactured by chlorination of liquid aluminum in ceramic-lined reaction vessels at 600 to 750°C, gaseous aluminum chloride being fed into condensation chambers. The reductive chlorination of aluminum oxide in the presence of coal (e.g. in the Alcoa process, see Section 3.2.3.2) is also operated industrially. Hydrated aluminum chloride is manufactured by reacting aluminum hydroxide with hydrochloric acid or hydrogen chloride. 

Alcoa process. A more efficient method of producing aluminum from bauxite that requires one-third less electric power than the Hall process. Alumina is reacted with chlorine, the resulting aluminum chloride yielding the metal and chlorine on electrolysis. No fluorine is required in the process. Prototype plants are under development. 

Few data are available on current efficiency in aluminum chloride electrolysis. The CE in the Alcoa process is assumed to be 90% [259]. A major part of the losses are due to current bypassing the bipolar electrodes [261], Losses due to reoxidation, i.e., the reverse of reaction (100) should then be low. Gas bubbles and metal droplets do not seem to react spontaneously upon contact in the melt. 

The production of metallic aluminum by electrochemical decomposition of AICI3 (ALCOA-process) has not yet reached industrial scale. 

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