US2231030A - Process of reducing aluminum sulphate to metallic aluminum - Google Patents

Description

Fb. 11, 1941. s w SQQFIELD ETAL 2,231,030

PROCESS OF REDUCING ALUMINUM SULPHATE TO METALLIC ALUMINUM Filed April 24, 1937 5 Sheets-Sheet l fivvewroms fia. fiHE WWAN 14 5601 7540 Jamv 6. .494 P05, 05Gb BY file mm w 660mm A0 Ml.

Feb. 11, 1941.

S. 'W. SCOFIELD ETAL PROCESS OF REDUCING ALUMINUM SULPHATE T0 METALLIC ALUMINUM Filed April 24, 1937 5 SheetsSheet 2 I BY JHERMAN w 5cm:

J D ADM! ATTORNE'KS Feb. 11, 1941. 2,231,030

PROCESS OF REDUCING ALUMINUM SULPHATE TO METALLIC ALUMINUM s. w. SCOFIELD HAL Filed April 24, 1937 5 Sheets-Sheet 5 JOHN 5. AA Rue" DEC/D W J 40 m.

WQQMJ/ 1941- s. w. SCOFIELD ETAL 24,231,030

PROCESS OF REDUCING ALUMINUM SULPHATE TO METALLIC ALUMINUM fleets-Sheet 4 NM f JOHN 5'. LA Rz/EMcb 8) SHERMAN W.

JCOF/ELD 14 MIN.

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1941- s. w. SCOF'IELD EI'AL 2,231,030

PROCESS OF REDUCING ALUMINUM SULPHATE T0 METALLIC ALUMINUM Filed April 24, 1957 5 Sheets-Sheet 5 5I/EGI'14N W fcoF/flo JOHN 5. LA RUE DEC'D BY g IERyN wf scor lfi/owmw A TTOR/VEVS.

Patented Feb. 11, 1941 UNITED STATES PATENT OFFICE PROCESS OF REDUCING ALUMINUM SUL- PHATE TO' METALLIC ALUMINUM Application April 24, 1937, Serial No. 138,852

2 Claims.

The invention relates to apparatus for, and a process of, reducing aluminum sulphate to metallic aluminum. Particularly, the invention relates to apparatus and a process for obtaining metallic aluminum electrochemically from alu-. minum sulphate. The claims of this application are limited to the improvements in processes of reducing aluminum sulphate to metallic aluminum.

The annexed drawings and the following description set forth in detail certain means and steps respectively illustrating and carrying out the invention, the disclosed means and steps, however, constituting, respectively, but a few of the various forms in which the principle of the said invention may be embodied and but one of the various methods by which it may be worked.

In said annexed drawings:

Figure 1 represents a central, vertical, longitudinal section of one form of the improved apparatus;

Figure 2 represents a plan view of a modified form;

Figure 3 represents a side elevation, taken from u the plane indicated by the line l3, Figure 2;

- Figure 4 represents a fragmentary vertical section, taken from the plane indicated by the line 4-4, Figure 2; and

Figure 5 represents a fragmentary central, verso tical, longitudinal section of a second modification.

Referring to the annexed drawings in which the same parts are indicated by the same respective numbers in the several views, a cast iron 85 box I, Figure 1, is provided with a carbon shell 2 and serves as a furnace in which the improved process is worked. Dipping into the box I are a plurality of carbon electrodes 3 depending by copper supports 4 from a copper rod 6 connected to an electric generator (not shown). The rod 6 can be automatically lowered as desired by means of apparatus 5 which indicates any conventional form of apparatus for accomplishing this purpose. Intermediate the walls of the furnace l 5 and the carbon shell 2 is a lining of highly conductive material, for instance, a copper plate I,

also connected bya conductor 8 to the generator. The copper plate I is a liner for the furnace I and the carbon shell 2 is a liner for the copper plate I.

50 Means are provided for heating furnace I exteriorly and, although these means may be any one of several convenient forms of heating apparatus, for purposes of illustration, a gas burner 9 is shown. Cryolite (NaaAlFs) is indicated by the ordinal I0 and a layer of deposited aluminum by the ordinal II. An outlet I2 controlled by a valve I2 serves as means by which the aluminum may be periodically drawn on from the bottom of the furnace I. The furnace I is closed by a cover 29 perforated to permit passage and adjustment 5 of the electrodes 3 therethrough and properly insulated therefrom. Intersecting the cover 29 is a conduit member 21 which leads to a sulphur dioxide storage tank 28.

- Referring now in detail to the process by means 10 (A12(SO4) 3.181120) are introduced uniformly and the heat greatly increased, this increase of heat being preferably obtained by using the auxiliary exterior heating 3; means 9. The molten mass gives off steam from the water of crystallization in the aluminum sulphate and sulphur dioxide ($02) which is stored in the tank 28, aluminum oxideWAhOa) being formed. 30

The aluminum oxide is immediately acted upon electrochemically by the current and the cryolite, and is decomposed into aluminum and oxygen, the molten aluminum, being heavier than the cryolite, sinking to the bottom of the furnace I, and the oxygen going to the anodes 3, and in part escaping and in part uniting with the carbon. The cryolite always remains unchanged as a compound, serving merely as a transferer of the metallic aluminum or plus ion, the aluminum of the aluminum oxide which is eventually posited in the lower part of the furnace I having first deposed the aluminum of the cryolite. The whole process is a continuous one, after the proper heat is established by the current, fresh charges of 5 aluminum sulphate being supplied regularly to the furnace I and the metallic aluminum being drawn ofl periodically through the discharge conduit I2.

The carbon electrodes 3 are decomposed by the oxygen from the aluminum oxide and also gradually impaired by the heat, so that they are automatically lowered by the device 5, in order to hold the electrodes to arc. In order that the contents of the furnace I may be uniformly heated and to obviate the formation of central zones where a deleterious crust would be formed, the furnace I is set quite deeply into a well [5 formed in a masonry furnace support I4.

The use of the auxiliary heating means 9 is not necessary to the success of the Process, but it is preferred to utilize the same as an aid to the reduction of the aluminum oxide, since the latter operation for its success would require a greater current than is necessary for reducing the aluminum sulphate to aluminum oxide. Also, preferably, although not necessarily, a plurality of carbon blocks l3 mounted upon the floor of the furnace l and respectively adjacent the electrodes 3 are utilized.

The aluminum sulphate crystals utilized are preferably obtained by processes of separating potash feldspar into its constituents, such as described and claimed in Letters Patent Nos 1,483,627; 1,494,029; 1,503,603; and 1,563,875. Other mineral silicates for obtaining the aluminum sulphate crystals may be utilized, such as alunite, leucite, orthoclase, clays, microcline, cericite and cyanite. The sulphur dioxide obtained as a by-product in the process can be utilized for the manufacture of sulphuric acid.

In the form of furnace shown in Figures 2, 3, and 4, the electrodes 30 intersect the cast iron furnace 3i laterally and are preferably arranged in sets of 3 units each, the central unit of which is designated by the ordinal 30, and is positioned intermediate an oppositely disposed pair of carbon blocks 32 to which the other two electrodes 30 of the set are directly opposed. These electrodes 30 and 33' are connected by branch conductors 33 to the main conductor 34 and are adjustable of said conductor 34 whereby the electrodes 30 and 33' are capable of adjustment toward and from the carbon blocks 32. In order that screws 2| which hold the conductors 33 rigid relative to the conductor 34, after the desired adjustment of the electrodes 33 and 30 has been made, may not be quickly destroyed by the great heat to which they would normally be subjected, enlarged holes 25 are formed in conductor 34, in which the branch conductors 33 play, and insulating clamps 20 are mounted, within the holes 25, upon both sides of the branch conductors 33, the conductor 34 being tapped to receive the screws 2 I, for rigidly holding the branch conductors 33 and hence the electrodes 30 and 30'. In this form of construction the carbon blocks 32 intersect the -'opposite side wall of the furnace casing 3i and in them are embedded branch conductors l8 connected to a main conductor IS. The electrodes 30-30 and the carbon blocks 32 are respectively supported in nonconductive bearings 16 and H. The copper lining 35 has a carbon lining 36.

In the form of construction shown in Figures 2, 3, and 4, whenever it is desired to adjust the electrodes 30-30 to arc, the central electrode 30' is utilized as a pilot or trial electrode and shoved in toward the oppositely opposed pair of carbon blocks 32, as shown in the upper set of electrodes, Figure 4, until the arc is established. Then the electrode 30' is pulled back to a point just short of where the arc would be broken and the companion electrodes 30 shoved in to this point, as illustrated with the lower set of electrodes 3030', Figure 4. The electrodes may then be left in this position during the operation, the arcing taking place between the electrodes 30--30, according to the vagaries of the current and the physical condition of the several electrodes and carbon blocks, or the pilot or trial electrode 30' may be entirely withdrawn and the companion electrodes 30 left in such an adjustable position as seems proper and best for the desired arcing, as illustrated in the intermediate set of electrodes, Figure 4.

In the form of furnace shown in Figure 5, the difficulty and inconvenience attendant upon the effervescing of the aluminum sulphate when it is first heated are obviated. This effervescence is caused by the great aflinity that aluminum has for oxygen. The aluminum sulphate when subjected to heat becomes a sponge-like substance and the air supplying the oxygen causes the aluminum sulphate to shoot into the air like feathers. Thus, a comparatively small amount of aluminum sulphate when first heated will fill a comparatively large chamber and, until it has finished effervescing and been cooled, it occupies a comparatively large space. Therefore, a furnace 22 has been formed with an auxiliary compartment 26 water cooled by jacket 31. The main chamber 22 and the compartment 26 are connected by means of an upwardly inclined passage 23 and a lower horizontal passage 24. When the aluminum sulphate is first heated in the chamber 22, it passes during its effervescent stage through conduit 23 to the compartment 26 where it completes its effervescence and is cooled. The resultant products of these eifervescing and cooling stages collect upon the bottom of the compartment 2B and return or are returned to the chamber 22 through the medium of the passage 24. In the chamber 22 they are, of course, subjected to the further treatments above described, with reference to the furnaces shown in Figures 1, 2, 3 and 4, and reduced successively to aluminum oxide and metallic aluminum.

What is claimed is:

1. In a continuous process of reducing aluminum sulphate to metallic aluminum, the steps which consist, in heating cryolite NasAlFe in a receptacle until it is melted; periodically charging into the melted cryolite aluminum sulphate crystals A12(SO4)3-18H2O, the heat being greatly increased and the mixture of cryolite and sulphate being subjected to the action of an electric current; and periodically withdrawing metallic aluminum from the floor of the receptacle.

2. In a continuous process of reducing aluminum sulphate to metallic aluminum, the steps which consist, in periodically charging aluminum sulphate crystals A12(SO4)3*18H2O into a bath of molten cryolite NaaAlFs; and subjecting the mixture of aluminum sulphate and cryolite to the action of an electric current and maintaining the mass in a molten condition, removing the evolved sulphur dioxide S02, and periodically withdrawing metallic aluminum from the bath.

SHERMAN W. SCOFIELD. SHERMAN W. SCOFIELD, Administrator of the Estate of John B. La Rue,

Deceased.

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