The vapor-liquid equilibria of the Aluminum chloride-Ferric chloride system
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Communications The Vapor-Liquid Equilibria of t h e A l u m i n u m Chloride-Ferric Chloride S y s t e m H. C. KO, A. LANDSBERG, and JACK L. HENRY Iron is a constituent in most aluminum resource materials and must be separated at some point in the processing of these materials for aluminum recovery. Separation occurs in the Bayer process in the production of reduction-grade alumina from bauxite for the Hall-Heroult cell because iron oxide is insoluble in the caustic leach solution. If the anhydrous chloride reduction route is someday used to produce aluminum on a commercial scale, either an alumina source free o f iron will be chlorinated or a separation of iron and aluminum chlorides must be made. There has been much speculation in this latter case as to whether purification by distillation is possible. 1,2,3 Mass spectrometric data indicate the existence o f mixed aluminum chloride-iron chloride molecules with vapor pressure h i g h enough to negate distillation as a means to separate these two chlorides.4-8 However, these mass spectrometric data are, of necessity, measured at very low pressures and must be related to practical pressures through extrapolation. In order to avoid such indirect determinations, work was undertaken at the Albany Research Center o f the United States Bureau o f Mines to measure the vapor-liquid equilibria in the aluminum chloride-iron chloride system at realistic pressures. The equilibrium diagram constructed from these data can then be used to evaluate the possibility o f using distillation for separating iron chloride from aluminum chloride. This work is part of a larger effort to study the carbochlorination o f domestic clay as a means to produce anhydrous aluminum chloride for reduction in the more energyefficient chloride cell. The apparatus, consisting of a borosilicate glass equilibrium vessel and chlorination chamber, is illustrated in Figure 1. The chlorination tube, which is partially shown in Figure 1, was 21 c m long. The inlet end o f the chlorination tube was connected to a ball joint and a three-way stopcock which allowed for gas-flow and evacuation o f the whole apparatus. Predetermined weights o f aluminum turnings and electrolytic iron were loaded into a 10-cm-long alumina boat and put in the center of the chlorination tube. This tube was wrapped in heating tape capable of maintaining the reaction temperature at about 340 °C. Before chlorination began, the whole apparatus was flushed with nitrogen gas. The temperature was raised to 340 °C before chlorine gas was introduced. Both gases were passed through simultaneously in the direction o fthe arrows at about 100 ml/min each. In about five hours the chlorination was complete and the chlorine was turned off, but nitrogen continued to pass through the vessel. Once the H. C. KO, Research Chemist, A. LANDSBERG, Chemical Engineer, and JACK L. HENRY, Research Supervisor, are all at Albany Research Center, United States Bureau of Mines, P. O. Box 70, Albany, OR 97321. M~anus~ipt submitted December 7, t ~ 2 .
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