US3384475A - Aluminum refining - Google Patents

Description

May 21, 1968 Filed Sept. 8, 1965 N. W. F. PHILLIPS ETAL ALUMINUM REFINING 2 Sheets-Sheet l CIRCULATOR Some Al Fog SomeAlClm700C lmpure l Al at 675C 24 AICI CONVERTER DECOMPOSER AlCl 38, H

2 Pure Al Al CI 36 |200 c RESIDUE GAS HE AT ER Alcl INVENTORS NORMAN W.E PHILLIPS FREDERICK WILLIAM SOUTHAM BY WS'Mn/a-W ATTORNEY May 21, 1968 Filed Sept. 8, 1965 N. W. F. PHILLIPS ET AL ALUMINUM REFINI NG 2 Sheets-Sheet lmpure Al l /3 AICI3 200 c 44 42 v l SCRUBBER GIRCULATOR fi A'rsn 40B 56 CIRCULATOR AICI3 Some AICI L Alcl impure N \L SomeAl Fogx I saw-e Am 61 o m 5 C --58 /4-- 40A CYCLONE SEPARATOR AICI; l0- 5 34 DECOMPOSER L 38- Pure Al 32 CONVERTER Pure Al 7 6- 36 200C e- I INVENTORS NORMAN W.F. PHILLIPS FREDERICK WILLIAM SOUTHAM laz utaA-cmnw ATTORNEY United States Patent 3,384,475 ALUMINUM REFINING Norman W. F. Phillips and Frederick William Southam,

Arvida, Quebec, Canada, assignors to Aluminium Laboratories Limited, Montreal, Quebec, Canada, a corporation of Canada Filed ept. 8, 1965, Ser. No. 485,862 14 Claims. (Cl. 75-68) This invention relates to improvements in the refining of aluminum metal by the so-called subhalide distillation procedure, and more particularly the present invention is concerned with the problems of scrubbing unwanted constituents from the halide gases employed in the process and with supplying necessary heat to impure aluminum bearing solid materials used in the process.

In particular, the present invention is related to improved procedure and apparatus for carrying out the subhalide distillation process for the refining of aluminum where gaseous normal aluminum halide is employed to convert aluminum metal from an impure body thereof. The conversion is to a gaseous aluminum subhalide which is thereafter decomposed to yield purified metal and a restored quantity of the normal halide.

In the subhalide process for refining or extracting aluminum, the impure material generally consists of alloys of aluminum with other metals or the like, or other compositions or bodies of aluminum and foreign material, usually metallic, all such mixtures, compositions or aggregates being here generically considered as impure aluminum. In a preferred way of carrying out the refining operation, the impure material, in divided solid form, is supplied substantially continuously, e.g. by increments from time to time, into a suitable converter of furnace-like character, where it is heated and where the normal halide of aluminum in gaseous form is passed through it, for example aluminum trichloride (AlCl or aluminum tribromide (AlBr also commonly called respectively aluminum chloride and aluminum bromide. At appropriate temperature, ordinarily in the range of about 1000 C. and upwards, the gaseous halide reacts with the aluminum in the material to produce, in gaseous form, an aluminum subhalide, e.g. monohalide. Thus the conversion reaction, where the treating gas is aluminum trichloride, yields aluminum monochloride, carrying the aluminum in gaseous combined form.

The solid material under treatment is thus progressively depleted of aluminum, e.g. as it moves downward through a converter of vertical type, so that the resulting aluminum-impoverished solids are discharged from a lower part of the converter. The gas withdrawn from the upper part of the conversion chamber contains the aluminum subhalide, usually together with unreacted normal halide, and is advanced to another vessel, which may be called a decomposer, where at suitably lower temperatures the reverse reaction occurs, with the subhalide reverting to aluminum and normal aluminum halide. The metallic aluminum, conveniently in molten state, is there deposited and collected, while the discharged gas now again consists essentially of the normal aluminum halide, e.g. aluminum trichloride.

However, an equilibrium concentration of aluminum subhalide remains in the discharged gas dependent upon the discharge temperature and pressure. For instance, when the chlorides are used, an equilibrium concentration of aluminum monochloride equivalent to approximately four pounds of aluminum per 10,000 pounds of gas remains in the discharged gas it the temperature is 700 C. and the pressure is one atmosphere. Furthermore, this discharge gas contains a certain amount of condensed liquid aluminum in extremely finely divided form such 'ice that it is suspended in the discharge gas and may be said to constitute an aluminum fog. These constituents in the gas discharged from the decomposer have been found to create some serious problems because they cause corrosive attack on the metals used in pipe lines and mechanical gas circulators which are used for additional, handling of the gas. Furthermore, during such additional handling, the aluminum fog tends to condense and settle out and solidify and to thus build up blockages in the apparatus. Furthermore, additional circulation generally results in additional cooling of the gaseous discharge from the decomposer, and this causes further decomposition of the residual equilibrium quantity of subhalide gas to release additional pure aluminum.

Accordingly, one important object of the present in vention is to reduce the temperature of the gas discharged from the decomposer and to remove the aluminum condensate fog and the subhalide from the gas while at the same time avoiding corrosion and blockages due to accumulation of solidified aluminum.

In the practice of theprocess of the present invention, substantial quantities of heat must be supplied to the converter in order to achieve the desired reaction in which the normal aluminum halide is converted, at least in part, to the aluminum subhalide. A large amount of this heat may be supplied by electrical resistance heating, by passing an electric current directly through the impure solid aluminum bearing material within the cohverter. For example, this solid material, in divided or granular form, may be contained in a refractory-lined converter vessel or furnace having internal electrodes at spaced locations and an electric current may be caused to flow between these electrodes. Such converter or furnace may be of an upright shaft type, with embedded annular electrodes at vertically spaced localities along the inner walls and with arrangements for introducing the normal aluminum halide vapor and withdrawing the product gas, for removing spent solid material and for inserting further quantities of unreacted solids. The solid material is conveniently prepared in a granular form, which may range from coarse powder (or fine granules) to relatively large lumps, the extent and character of subdivision being governed by the need for porosity to the gases and for a sufficiently high ratio of the surface area to the volume of the solid to provide an efiicient rate of removal of aluminum. In the operation of such a converter it has been proposed to introduced the unreacted halide gas at one end of the body of divided solid material and to withdraw the subhalide-containing gas from a highly heated zone of the mass, i.e. adjacent the electrode which is furthest from the locality of gas entrance, the principle of such operation being to remove the gas at a zone of maximum heat, for best economy in the separation of aluminum in subhalide form.

The use of electrical resistance heating to supply heat energy for the endothermic reaction in the converter is regarded as avoiding difficulties that would be encountered in certain other ways of furnishing heat. For instance, the nature of the reaction precludes the use of direct firing or other arrangements exposing the material to combustion or combustion products. External heating, meaning any procedure whereby heat is to be conducted through the wall of the converter or other structure from a localized source, appears undesirable for providing the relatively considerable flow of heat energy which the reaction must consume as it progresses. That is to say, with external heating applied to the body of solid fragments, lumps or granules constituting the charge in the reaction zone, for example with heating means around the converter or even with heating elements embedded in or otherwise exposed to the charge, it is difficult to obtain the heat transfer rates necessary for a large power input without causing considerable temperature gradients, and it is correspondingly difiicult to avoid a low thermal etficiency. If there are large temperature variations between dilferent localities of the charge, the special nature of the reaction is such that there will either be places of undesirably low temperature where there is little conversion of aluminum to subhalide (or even redeposit of metal from subhalide produced elsewhere), or if such situation is to be avoided, there will be some places kept at an excessively and thus wastefully high temperature, perhaps even to the point of objectionable melting of the material.

Although internal resistance heating, with electric current supplied in a manner that would be expected to distribute its flow through the charge, should obviate the above difliculties, it has been discovered that in many cases a correspondingly serious problem arises. Specifically it is found that a highly uneven current distribution often occurs, with large temperature differences, of a random and upredictable sort, among various parts of the charge. It has been discovered that these non-uniform current conditions with local overheating and large temperature gradients, arise in bringing cold charge material up to reaction temperature (as must be done continuously, in a continuous operation) and also tend to persist after the material has been brought, generally, to reaction temperatures. The condition of uneven heating may be so severe as to have other adverse effects on the practical accomplishment of the reaction, e.g. in that there may be agglomeration of particles or pieces of the charge due to local fusion.

Accordingly, it is another object of the present invention to provide an efficient method for preheating the solid materials prior to the converter operation in order to avoid the above mentioned difliculties.

Another feature and object of the present invention is to accomplish both of the above mentioned objects by a single addition step. Thus it is an important feature of the present invention that the gaseous discharges from the decomposer are used for the purpose of preheating the solid aluminum bearing materials which are to be reacted upon in the converter, and in the process of accomplishing the preheating function, these gases are scrubbed and cleansed of constituents which are not desired at this stage of the process.

Thus, in carrying out the present invention, the gases discharged from the decomposer are passed through a new charge of the divided solid aluminum bearing material so as to preheat that material before it is subjected to the higher temperature reaction of the converter. Any liquid aluminum fog or residual subhalides remaining in the gaseous discharge from the decomposer and supplied to the charge of solid aluminum bearing material are substantially completely removed, the entrained metallic aluminum being deposited in this new charge of impure aluminum material.

Another object of the present invention is to pro vide apparatus which is particularly useful for carrying out subhalide distillation processes for the recovery of aluminum.

Other objects, advantages and features of the present invention will be apparent from the following description and the accompanying drawings which are as follows:

FIG. 1 is a schematic flow chart of a preferred form of the process of the present invention. This flow chart illustrates the process in part through the use of schematically illustrated system components. Thus, the figure can be considered also as a schematic illustration of apparatus suitable for carrying out the process.

FIG. 2 is a schematic flow chart illustrating a modification of the process illustrated in FIG. 1 and again the process is illustrated partially in terms of schematic apparatus components, and thus, can be taken also to illus- 4 trate apparatus suitable for carrying out this modification of the process.

And FIG. 3 illustrates, in somewhat more detail, an actual structure which may be employed for the scrubber-preheater function in the processes and apparatus of the present invention.

Stated in a more complete form, the improved subhalide distillation process for the recovery of aluminum in accordance with the present invention may be carried out by following the steps of passing a normal halide of aluminum in preheated gaseous form through divided solid impure aluminum bearing material while supplying heat thereto so that at least a portion of the gaseous halide reacts with the aluminum in the material to produce a gaseous aluminum subhalide. The subhalide containing gas is then removed and decomposed at a lower temperature to obtain the reverse reaction in which the subhalide reverts to the normal aluminum halide and releases pure aluminum. Then the decomposed gases are passed through a new charge of the solid impure aluminum bearing material for preheating that material prior to reaction with the preheated normal halide.

In accordance with another feature of this invention, it is contemplated that the new charge of divided solid impure aluminum bearing material is caused either to move continuously or at frequent intervals so that any metallic aluminum which is deposited therein does not cause any substantial blockage or obstruction. This feature may be referred to below as movement at frequent intervals. It will be understood of course, that if the material is actually moving continuously it can certainly be said to be moving at least at frequent intervals.

A more detailed description of a preferred form of the process in accordance with the persent invention is as follows: Normal aluminum chloride (AlCl is preheated in a gaseous state to a temperature of at least 1000 degrees centigrade. The preheated aluminum chloride is then passed through divided solid impure aluminum hearing material while heat is applied to the aluminum hearing material to achieve a temperature in the range from 1200 to 1400 degrees centigrade. At least a portion of the aluminum chloride reacts with the aluminum material to produce a gaseous aluminum monochloride. Monochloride containing gas is then removed from the solid material and cooled to obtain a decomposition reaction in which the aluminum monochloride reverts to the normal aluminum chloride and releases pure aluminum. During this decomposition reaction, the temperature of the remaining gas is reduced to about 700 degrees Centigrade. The decomposed gas is then passed through a new charge of the solid impure aluminum bearing material to reduce the gas temperature to at least as low as 630 degrees centigr'ade while preheating the solid material to a temperature in the order of 675 degrees Centigrade. The preheating step is accomplished while moving the solid aluminum bearing material at frequent intervals so that any metallic aluminum which is deposited in the solid material during the preheating step does not contribute materially to blocking or impairing the flow properties of the solid material. The direction of movement of the divided solid material is generally in a direction opposite to the direction of movement of the decomposed gases therethrough. After passing through the new charge of solid material, the decomposed gases may be recirculated and reheated and reused in the process.

For the purposes of providing a full disclosure of the process of the present invention, the following example typifies the practice of a preferred form of the process of the present invention:

Example I Gaseous aluminum trichloride is heated to 1200 centigrade and passed at a rate of 20,000 pounds per hour through a body of divided solid impure aluminum hearing material. The divided solid impure aluminum bearing material is a crude alloy (such as obtained from a carbothermic reduction of aluminum ore, e.g. bauxite) which is supplied at a rate of 3,860 pounds per four. As the preheated gas is passed through, the divided solid aluminum bearing material is heated to the range from 1200 degrees to 1400 degrees centigrade at substantially atmospheric pressure. A portion of the aluminum chloride then reacts with the solid aluminum material to produce a gaseous aluminum monochloride. The gases containing the monochloride are removed from the divided solid material and substantial amounts of heat are removed therefrom to cause a decomposition reaction in which the aluminum monochloride reverts to normal aluminum chloride and releases pure liquid aluminum at a temperature above 660 C., e.g. 680 C. or higher, and at a rate of about 2000 pounds per hour. The decomposed gases, now at a temperature of approximately 700 degrees centigrade consist almost entirely of the normal aluminum chloride (A101 but a small amount of finely divided molten aluminum is present in suspension (aluminum fog) and an equilibrium concentration of undecomposed aluminum monochloride (AlCl) is also present. These decomposed gases are then passed through a new charge of the divided solid impure aluminum bearing material, thereby preheating the new charge to 675 degrees centigrade while reducing the temperature of the decomposed gases to 630 degrees centigrade. With this operation, as the gases travel through the interstices of the body of particulate charge material, the aluminum fog is thereby removed from the gases and deposited in the new charge where it is available for later recovery in the operation of the process. The reduction in temperature and the passage through the new charge also renders the gas substwtially free of the residual aluminum monochloride.

In a modified form of the process of the present invention, the same process steps as described above are repeated, but after the decomposition step the aluminum fog is mechanically separated from the decomposed gases prior to passing the decomposed gases through the new charge of solid impure aluminum bearing material.

The following example illustrates the practice of this modified form of the invention:

Example [I Gaseous aluminum trichloride is heated to 1200 degrees centigrade and passed at a rate of 20,000 pounds per hour through a body of divided solid impure aluminum bearing material. The divided solid impure aluminum bearing material is a crude alloy (such as obtained from a carbothermic reduction of aluminum ore, e.g. bauxite) which is supplied at a rate of 3860 pounds per hour. As the preheated gas is passed through, the divided solid aluminum bearing material is heated to the range from 1200 degrees to 1400 degrees centigrade at substantially atmospheric pressure. A portion of the aluminum chloride then reacts with the solid aluminum material to produce a gaseous aluminum monochloride. The gases containing the monochloride are removed from the divided solid material and substantial amounts of heat are removed therefrom to cause a decomposition reaction in which the aluminum monochloride reverts to normal aluminum chloride and releases pure liquid aluminum at a temperature above 660 C., e.g. 680 C. or higher, and at a rate of about 2000 pounds per hour. The decomposed gases, now at a temperature of approximately 700 degrees centigrade, consist almost entirely of the normal aluminum chloride (AlCl but a small amount of finely divided molten aluminum is present in suspension (aluminum fog) and an equilibrium concentration of undecomposed aluminum monochloride (AlCl) is also present. The decomposed gases are passed through a mechanical liquid-gas separator to remove the aluminum fog, and then a portion (about 4000 pounds per hour) of the gases which have been cleansed of the aluminum fog is passed through a.

new charge of the divided solid aluminum bearing material, thereby preheating the new charge to approximately 675 degrees centigrade while reducing the temperature of this portion of the decomposed gases to approximately 200 degrees centigrade. The remainder (about 16,000 pounds per hour) of the decomposed gases is reheated for reuse in a repetition of the process.

FIGURE 1 illustrates in schematic diagrammatic form the operation of the first embodiment of the process exemplified by Example I. FIGURE 1 also represents a schematic illustration of a prefer-red apparatus which is adapted for carrying out this process. The FIGURE 1 apparatus includes, a converter 10, which is a vessel for containing the impure solid aluminum bearing material, a gas heater 12, from which heated aluminum trichloride may be supplied to the converter 10, and a decomposer 14, in which the aluminum monochloride is decomposed to yield pure aluminum and aluminum trichloride. A sorubber-preheater 16 is provided which contains a new charge of the impure, aluminum bearing, divided, solid material and through which decomposed gases from decomposer 14 are passed. Thus, the solid material is preheated and the gases are scrubbed free of aluminum fog and residual aluminum monochloride.

An inlet 18 is provided for the introduction of the impure aluminum bearing, divided, solid material. The material then moves through rotating gate devices 20 and 22 to the scrubber-preheater vessel 16. Details of a preferred form of the scrubber-preheater structure are shown and described below in connection with FIGURE 3. The divided solid material passes from the scrubber-preheater 16 through rotating gate devices 24 and 26 into the converter 10. After treatment in the converter 1%, the residual solid material which has been substantially depleted of its aluminum content, passes out of the converter 10 through the rotating gate devices 28 and 30. Each of the pairs of gate devices 20-22, 2426, and 2830, serve as gas locks for the purpose of substantially preventing the passage of gases while providing for a measured flow of the divided solid material.

It is to be seen from the above description that the apparatus including the lock formed by the gate devices 2022, the scrubber-preheater vessel 16, the lock provided by the gate devices 24-26, the converter vessel 10, and the lock provided by the gate devices 28410 defines a path for the conveyance of the divided solid impure aluminum bearing material while it is being processed. The material is conveyed through this path of apparatus in sequence in the order in which the apparatus components are named above.

While the solid materials are in the converter 10, substantial quantities of heat must be supplied to these materials in the presence of the aluminum halide gases in order to achieve the reaction resulting in the formation of the aluminum subhalide which combines the halogen with the aluminum content of the solid material. This heat may be provided by various methods, but the preferred and most satisfactory method which has been found is by electrical resistance heating of the solid material. This may be accomplished simply by providing conductive electrodes exposed to the solid material in spaced positions within the walls of the converter vessel, and a source of electrical energy connected across these electrodes to provide a current between the electrodes through the divided solid material. This method of heating the contents of the converter is schematically illustrated by the presence of an alternating current generator 32 which is connected to supply a current between the two spaced electrodes having external terminals 34 and 36. This method of electrical heating of the converter in a subhalide conversion process for recovery of aluminum is illustrated and described in more detail in US. Patent No. 2,937,082 entitled, Conversion Process for Aluminum Subhalide Distillation," issued May 17, 1960, to A. H. Johnston, and others, and assigned to the same assignee as the present application.

The gas heater 12 may be of conventional construction, and the normal aluminum chloride may be preheated and then supplied to the converter at a temperature in the order of twelve hundred degrees centigrade. After reaction within the converter 10, the gases, including both aluminum monochloride and aluminum trichloride are passed to the decomposer 14. The decomposer 14 may have various conventional constructions, however, it is preferred that it be of the splash type involving the use of mechanical agitators to splash liquid aluminum through the gases. Furthermore, the decomposer must include means for removing substantial quantities of heat in order to successfully accomplish the decomposition reaction to release the pure aluminum. A suitable structure for the decomposer 14 is carried out in accordance with the teachings of US. Patent 2,914,398 entitled, Recovery of Aluminum in Subhalide Distillation, and issued Nov. 24, 1959, to A. H. Johnston and F. W. Southam and assigned to the same assignee as the present application.

The operation of the decomposer 14 results in the delivery of pure liquid aluminum at the outlet 38 and in the delivery of decomposed gases at the gas conduit 40. The conduit 40 is connected to supply the decomposed gases to the scrubber-preheater 16. These decomposed gases consist mainly of the normal aluminum trichloride, but also include some aluminum fog and some aluminum monochloride. After cleaning and cooling in the scrubber-preheater 16, the gases, now almost entirely the normal aluminum chloride, pass out of the scrubberpreheater 16 to the gas conduit 42. This normal aluminum chloride from conduit 42 may be recirculated by means of a conventional circulator apparatus 44 and a return gas conduit 46 which is connected to supply the aluminum chloride to gas heater 12. Thus, the gas may be repeatedly recirculated and reused in the process as illustrated in FIGURE 1.

The preheating of the divided solid material in the scrubber-preheater 16 by means of the decomposed gases may be all the preheating that is necessary for carrying out the process. However, in many cases it may be necessary to supply further preheating to higher temperatures such as by using the teachings of the US. Patent 2,937,082, previously mentioned above.

It may be noted, in passing, that the invention in at least its broader aspects is applicable to systems where the aluminum trichloride is ultimately recirculated to the converter by procedure which partially or wholly comprises absorption or other condensation, and reevaporation, rather than by direct return of the entire i flow in the gaseous state as shown in the drawings.

FIGURE 2 is a schematic diagram illustrating the modified process of the present invention as exemplified,

by Example II. FIGURE 2 also constitutes a schematic representation of a system which is particularly adapted for carrying out this modification of the process. The system of FIGURE 2 is similar in many respects to the system of FIGURE 1, and corresponding components of the system of FIGURE 2 are numbered for identification with the same numbers used for those components in FIGURE 1. The system of FIGURE 2 includes the addition of a mechanical separator 48, for removing entrained material from a gas, which is connected by a means of conduit 40A to receive the decomposed gases discharged from the decomposer 14. Separator 48 may be a cyclone separator of conventional construction which is operable to remove the aluminum fog from the decomposed gases, and the precipitated liquid aluminum from this separation is discharged at the bottom outlet 50 of the separator 48. The decomposed gases, after processing in the separator 48, pass through a circulator 52, which may be of a construction similar to circulator 44. The output at 54, from the circulator 52 is divided, and part of it is supplied through the conduit 408 to the serubber-preheater 16 to accomplish the preheating function of the divided solid material therein. This portion of the decomposed gas is also relieved of any residual aluminum monochloride which remains therein. The other portion of the gas from circulator 52 is returned and recirculated through -a branch conduit 56 to the gas heater 12A. Heater 12A is substantially the same as the gas heater 12 of FIGURE 1, except that it has the additional inlet for the gas conduit 56. The gas from conduit 56 is thus reheated and reused in the operation of this system.

In the embodiment of FIGURE 2, the combined gas pressures created by the circulators 44 and 52 are such that the gas pressure within the top portion of the converter 10 is substantially equal to the gas pressure within the bottom portion of the scrubber-preheater 16. Thus, the gas lock system provided in FIGURE 1 by the gates 24 and 26 between the scrubber-preheater 16 and converter 10 are not required in the embodiment of FIGURE 2, and a straight and substantially unobstructed passage 58 is substituted. This provides an advantageous simplification of the apparatus. It is evident that the passage 58 may be quite short and the two vessels 16 and 10 may be practically combined.

If desired, in the process as represented by either the FIGURE 1 or FIGURE 2 embodiments, a small part of the gas from the conduit 42 may be carried for treatment in an auxiliary absorbing and re-evaporating system whereby contaminating permanent gases (such as hydrogen) can be separated so that the build up of such gases in the main system can be prevented. The re-evaporated normal aluminum halide (that is aluminum trichloride, AlCl may then be returned to the system at conduit 46, and thus to the gas heater 12 or 12A for recirculation. Since such a cleansing system for the recirculated gases is optional in the system of the present invention, for pur poses of clarity, it is not illustrated in the system drawings of either FIGURE 1 or FIGURE 2. However, the provision of such a recirculated gas cleansing systems forms at least a portion of the subject matter described and claimed in a copending patent application Ser. No. 199,934 filed on June 4, 1962, by N. W. F. Phillips and F. W. Southam and assigned to the same assignee as the present application.

FIGURE 3 is a sectional side view illustrating a construction which is suitable for use as the scrubber-preheater 16 in the system of FIGURE 1 or in the system of FIGURE 2. This structure includes an inlet 60 at the top for admitting the divided solid material after passing through the gate devices 20 and 22 shown in FIGURES l and 2. The vessel 16 also includes an outlet 62 at the bottom for conveying the preheated divided solids to the converter 10 in the systems of either FIGURE 1 or FIGURE 2. While the body of solids remains in the scrubber-preheater vessel 16, as indicated at 64, heat is imparted to the solids by the decomposed gases entering at the conduit 40 and leaving at the conduit 42. The walls of the vessel 16 preferably include a steel outer shell 66 with a suitable refractory liner 68 preferably of a heat insulating character. The solids within the vessel 16 are preferably moved continuously, or at least at frequent intervals if the movement is intermittent. This movement of solids through vessel 16 is primarily controlled by a table feeder 70 which is arranged for rotation on a shaft 72 at the bottom of the vessel 16. In order to enhance the operation of the table feeder 70, a plow member 74 is arranged within the vessel 16 and supported at a fixed position above the table feeder 70 and serves to cause the material on the edge of the feeder to flow over the edge in response to rotation thereof. The feeder 70 and the plow 74 may be of conventional construction. Other similar feeder structures, such as a rotary cone feeder, may be employed if desired.

When the scrubber-preheater structure of FIGURE 3 is employed in a system such as that of FIGURE 1, then the rotating gate members 2022 and 24-26 must be operated at a rate of speed which is coordinated with the speed of operation of the table feeder 70. As will be understood, the dimensions of a scrubber-preheater will depend on the capacity of the given monohalide distillation system, and particularly on the quantity of alloy to be fed through it and other conditions of operation. By way of illustration, structure providing internal column dimensions of about 1.5 to 2 feet in diameter and about 4 feet in height is one instance of a device suitable for use in carrying out the above-described examples of the process.

As explained above in the description of Example I, passage of the gas from the decomposer 14 (FIG. 1) through the aluminum-containing alloy in the scrubberpreheater 16 renders the gas substantially free of aluminum monochloride. It' may be explained that the aluminum activity of impure aluminum-bearing material of this nature decreases with temperature, and at about 700 C. is only about 0.25. The significance here of this fact is that because of absorption of aluminum into the alloy material above the melting point of aluminum, the gas which has passed through the bed or column of such alloy (in the scrubber-preheater) is unsaturated with respect to pure aluminum, and therefore will not deposit aluminum on being cooled somewhat further, e.g. upon cooling such as might be caused by heat losses in subsequent circulation or other handling of the gas. Thus in operations such as exemplified in FIG. 1, where the entirety of the aluminum trichloride-containing gas from the decomposer traverses the scrubber-preheater, there is special advantage in the foregoing respects.

It will be understood that the examples hereinabove are illustrative and that the process is subject to modification and variation as circumstances or requirements may dictate in the light of its principles as explained. F r instance, whereas in Example II conditions of operation have been described which involve the discharge of gas from the scrubber-preheater 16 at an outlet temperature of 200 C., other conditions may be employed such as other magnitudes of flow, e.g. larger proportions of the decomposer outlet such as will afford corresponding temperatures of gas outlet from the scrubber-preheater intermediate between 200 C. and say 630 C. In other words, the proportion of the trichloride gas from the decomposer that is utilized in passage through the incoming impure aluminum material may be any selected value, from a rather small proportion as in Example II (or even somewhat less), to the entirety of the gas as in Example I. It will also be appreciated that apparatus embodying two circulators such as indicated at 52 and 44 in FIG. 2 (with the cyclone separator 48, if necessary) may be utilized for flow conditions such as illustrated in Example I (e.g. where all of the trichloride gas is passed through the scrubber-preheater), if it is desired to eliminate the lock between the latter device and the converter, i.e. to permit use of a simple, open passage as shown at 58 in FIG. 2 rather than the gates 24 and 26 in FIG. 1.

While other variations and modifications of the present invention will occur to those who are skilled in the art, it is intended that the following claims shall cover the entire valid scope of this invention and shall include such variations and modifications.

We claim:

1. An improved subhalide distillation process for the recovery of aluminum comprising the steps of passing a normal halide of aluminum in preheated gaseous form through divided solid impure aluminum bearing material while supplying heat thereto so that at least a portion of the gaseous halide reacts with the aluminum in the material to produce a gaseous aluminum subhalide, removing the subhalide containing gas and decomposing it at a lower temperature to obtain the reverse reaction in which the subhalide reverts to the normal aluminum halide and releases pure aluminum, and then passing at least a portion of the decomposed gases through a new charge of the solid impure aluminum bearing material for the preheating thereof prior to reaction with the preheated normal halide.

2. The process of claim 1 in which the normal halide of aluminum is an aluminum trichloride and the subhalide is aluminum monochloride.

3. The process of claim 1 in which the normal halide of aluminum is an aluminum tribromide and the subhalide is aluminum monobromide.

4. An improved subhalide distillation process for the recovery of aluminum comprising the steps of passing a normal halide of aluminum in preheated gaseous form through divided solid impure aluminum bearing material while supplying heat thereto in a temperature range above l,000 C. so that at least a portion of the gaseous halide reacts with the aluminum in the material to produce a gaseous aluminum subhalide, removing the subhalide containing gas and decomposing it while removing heat therefrom to obtain the reverse reaction in which the subhalide reverts to the normal aluminum halide and releases pure aluminum, and then further cooling the decomposed gases by passage through a new charge of the solid impure aluminum bearing material.

5. An improved subhalide distillation process for the recovery of aluminum comprising the steps of passing a normal halide of aluminum in preheated gaseous form through divided solid impure aluminum bearing material while supplying heat thereto so that at least a portion of the gaseous halide reacts with the aluminum in the material to produce a gaseous aluminum subhalide, removing the subhalide containing gas and decomposing it at a lower temperature to obtain the reverse reaction in which the subhalide reverts to the normal aluminum halide and releases pure aluminum, mechanically separating any aluminum fog entrained in the decomposed gases, and then passing a portion of the decomposed gases through a new charge of the solid impure aluminum bearing material for the preheating thereof prior to reaction with the preheated normal halide.

6. An improved subhalide distillation process for the recovery of aluminum comprising the steps of preheating a normal aluminum halide salt in a gaseous state, passing the heated aluminum halide through divided solid impure aluminum bearing material while supplying heat thereto to achieve a reaction in which at least a portion of the aluminum chloride reacts with the solid aluminum material to produce a gaseous aluminum monochloride, removing the monochloride containing gas from the solid material and removing heat therefrom to obtain the reverse reaction in which the aluminum monochloride decomposes to the normal aluminum chloride and releases pure aluminum, passing the decomposed gas through a new charge of the solid impure aluminum bearing material to thereby preheat said solid material while reducing the temperature of said decomposed gases, said last mentioned step being accomplished while moving the solid material at frequent intervals, the direction of movement of said solid material being generally opposite to the direction of movement of the decomposed gases therethrough.

7. An improved subhalide distillation process for the recovery of aluminum comprising the steps of preheating a normal aluminum chloride salt in a gaseous state to a temperature of at least 1,000 degrees C., passing the heated aluminum chloride through divided solid impure aluminum bearing material while supplying heat thereto to achieve a temperature in the range from 1000 to 1400 degrees C. so that at least a portion of the aluminum chloride reacts with the aluminum material to produce a gaseous aluminum monochloride, removing the monochloride containing gas from the solid material and decomposing it while removing heat therefrom to obtain the reverse reaction in which the aluminum monochloride reverts to the normal aluminum chloride and releases pure aluminum while reducing the temperature of the remaining gas to about 700 degrees C., passing the decomposed gas through a new charge of the solid impure aluminum bearing material to thereby preheat said solid material to approximately 675 C. while reducing the temperature of said decomposed gases to at least as low as 630 C., said last mentioned step being accomplished while moving the solid aluminum bearing material at frequent intervals the direction of movement of said solid aluminum bearing material being generally in opposition to the direction of movement of the decomposed gases therethrough, and then recirculating the decomposed gases after passing through the new charge of solid material to repeat the process.

8. In apparatus for subhalide refining of aluminum, in combination, a refining system comprising a preheater arranged to receive aluminum-containing charge material and having gas inlet and outlet means, a converter connected and arranged to receive said charge material after preheating in said prcheater and having gas inlet and outlet means for passage of halide gas to react with aluminum of the charge material at high temperature, a decomposer having gas inlet and outlet means with said gas inlet means connected with the gas outlet of the converter and arranged to receive reacted gas therefrom for depositing pure aluminum metal and discharging halide gas, the gas inlet means of said preheater being connected with the gas outlet means of said decomposer to receive at least a portion of the halide gas discharged therefrom, said preheater being operable to circulate said halide gas through the charge material therein to scrub said halide gas and preheat the charge material.

9. In apparatus for subhalide refining of aluminum, in combination, a refining system comprising a converter arranged to receive aluminum-containing charge material and having gas inlet and outlet means for passage of halide gas to react with aluminum of the charge material at high temperature, a decomposer connected with the gas outlet of the converter and arranged to receive reacted gas therefrom for depositing aluminum metal and discharging halide gas, a scrubber-pre-heater connected to receive halide gas discharged from said decomposer said scrubber-preheater being arranged ahead of said converter in the path of said aluminum-containing charge material and containing a new charge of said material, said scrubber-preheater being operable to circulate said halide gas through said new charge to scrub said halide gas and preheat the new charge.

10. An aluminum recovery system comprising apparatus defining a path for the conveyance of divided solid impure aluminum bearing material, said path defining apparatus including a first gas lock, a scrubber-preheater vessel, a converter vessel, and a second gas lock; said path defining components being connected to receive and convey the divided solids in sequence in the order named; said scrubber-preheater and said converter each having a gas inlet and a gas outlet, a gas heater connected to said gas inlet of said converter to supply preheated aluminum halide gas thereto, and a gas decomposer connected to said gas outlet of said converter to receive and decompose the gas from said converter to thereby obtain pure aluminum and including output connection means to supply at least a portion of the decomposed gases to said scrubber-preheater.

11. An improved system which is particularly adapted for the recovery of aluminum by subhalide distillation comprising apparatus defining a path for the conveyance of divided solid impure aluminum bearing material including a first gas lock, a scrub-berapreheater vessel, a second gas lock, a converter vessel, and a third gas lock; said last named components defining said path being connected to receive and convey the divided solids in sequence in the order named; said scrubber-preheater and said converter each having a gas inlet near the solids outlet end thereof and a gas outlet near the solids inlet end thereof, a gas heater connected to supply preheated aluminum halide gas to said gas inlet of said converter, a gas decomposer connected between the gas outlet of said converter and the gas inlet of said scrubber-preheater to receive and decompose the gas from said converter to thereby obtain pure aluminum and to supply at least a portion of the decomposed gases to said scrubber-preheater and a circulator connected between said gas Outlct of said scrubber-preheater and said gas heater to recirculate the gases discharged from said scrubber-preheater to said gas heater.

12. A subhalide distillation aluminum refining system comprising apparatus defining a path for the conveyance of divided solid impure aluminum bearing material including a first gas lock, a scrubber-preheater vessel, a converter vessel, and a second gas lock; said path defining apparatus being connected to receive and convey the divided solids in sequence in the order named; said scrubber-preheater and said converter each having a gas inlet near the solids outlet end thereof and a gas outlet near the solids inlet end thereof, a gas heater connected to supply preheated aluminum halide gas to said gas inlet of said converter, a gas decomposer connected to said gas outlet of said converter to receive and decompose the gas from said converter to thereby obtain pure aluminu-m, a mechanical liquid-gas separator connected to receive the decomposed gases from said decomposer and operable to remove entrained liquid aluminum therefrom, a connection from said liquid-gas separator to said scrubber-\preheater to convey at least a portion of the decomposed gases to said scrubber-preheater.

13. A system as set forth in claim 12 which includes a circulator connected between said gas outlet of said scrubber-preheater and said gas heater to recirculate at least a portion of the gases discharged from said scrubber-preheater to said gas heater.

14. A system as set forth in claim 13 which includes a second circulator connected from said mechanical liquid-gas separator to said gas heater to recirculate a portion of the gases discharged therefrom directly to said gas heater.

References Cited UNITED STATES PATENTS 2,937,082 5/1960 Johnston et al --68 X 3,078,159 2/1963 Hollingshead et a1. 75-68 X 3,220,165 11/1965 Howie 7568 X 3,336,731 8/1967 Phillips et al 23-93 X 3,343,911 9/1967 Eisenlohr 23-93 3,346,368 10/1967 Braunwarth et al 7568 3,351,461 11/1967 Southam 75-68 HYLAND BIZOT, Primary Examiner. H. W. TARRING, Assistant Examiner.

Claims (2)

1. AN IMPROVED SUBHALIDE DISTILLATION PROCESS FOR THE RECOVERY OF ALUMINUM COMPRISING THE STEPS OF PASSING A NORMAL HALIDE OF ALUMINUM IN PREHEATED GASEOUS FORM THROUGH DIVIDED SOLID IMPURE ALUMINUM BEARING MATERIAL WHILE SUPPLYING HEAT THERETO SO THAT AT LEAST A PORTION OF THE GASEOUS HALIDE REACTS WITH THE ALUMINUM IN THE MATERIAL TO PRODUCE A GASEOUS ALUMINUM SUBHALIDE, REMOVING THE SUBHALIDE CONTAINING GAS AND DECOMPOSING IT AT A LOWER TEMPERATURE TO OBTAIN THE REVERSE REACTION IN WHICH THE SUBHALIDE REVERTS TO THE NORMAL ALUMINUM HALIDE AND RELEASE PURE ALUMINUM, AND HTEN PASSING AT LEAST A PORTION OF THE DECOMPOSED GASES THROUGH A NEW CHARGE OF THE SOLID IMPURE ALUMINUM BEARING MATERIAL FOR THE PREHEATING THEREOF PRIOR TO REACTION WITH THE PREHEATED NORMAL HALIDE.

8. IN APPARATUS FOR SUBHALIDE REFINING OF ALUMINUM, IN COMBINATION, A REFINING SYSTEM COMPRISING A PREHEATER ARRANGED TO RECEIVE ALUMINUM-CONTAINING CHARGE MATERIAL AND HAVING GAS INLET AND OUTLET MEANS, A CONVERTER CONNECTED AND ARRANGED TO RECEIVE SAID CHARGE MATERIAL AFTER PREHEATING IN SAID PREHEATER AND HAVING GAS INLET AND OUTLET MEANS FOR PASSAGE OF HALIDE GAS TO REACT WITH ALUMINUM OF THE CHARGE MATERIAL AT HIGH TEMPERATURE, A DECOMPOSER HAVING GAS INLET AND OUTLET MEANS WITH SAID GAS INLET MEANS CONNECTED WITH THE GAS OUTLET OF THE CONVERTER AND ARRANGED TO RECEIVE REACTED GAS THEREFROM FOR DEPOSITING PURE ALUMINUM METAL AND DISCHARGING HALIDE GAS, THE GAS INLET MEANS OF SAID PREHEATER BEING CONNECTED WITH THE GAS OUTLET MEANS OF SAID DECOMPOSER TO RECEIVE AT LEAST A PORTION OF THE HALIDE GAS DISCHARGED THEREFROM, SAID PREHEATER BEING OPERABLE TO CIRCULATE SAID HALIDE GAS THROUGH THE CHARGE MATERIAL THEREIN TO SCRUB SAID HALIDE GAS AND PREHEAT THE CHARGE MATERIAL.

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