US2294546A - Production of aluminum - Google Patents

Description

Sept. 1, 1942. H. L. GENTIL PRODUCTION OF ALUMINUM Filed June 28, 1940 ,Rrz, a)"

PatenteriSept. 1, 1942 PRODUCTION or ALUMINUM Henri Louis Gentil, Paris, France, assignor to Alloy Processes Limited, London, England, a British company Application June 28, 1940, Serial No. 343,035 In Great Britain June 29, 1939 2 Claims.

The present invention comprises improvements in or relating to the production of aluminum and has for its object to provide a process for the production of aluminum from its ores in metallic form without the employment of electrolytic methods as have been common heretofore.

According to the present invention a process for the reduction of aluminum comprises the steps of first reducing the crude aluminum-bearing material by treatment, in an electric furnace along with other compounds of more readily reducible metals so as to produce an alloy of these other metals with aluminum,'thereafter reducing thepressure of the atmosphere in contact with the molten alloy to an absolute pressure not exceeding 4 mm. of mercury and bringing the temperature of the alloy to a point at which unadded to the charge, preferably with a little quicklime, so that the silicon will reduce the alumina and the aluminum content is increased.

In carrying the invention into effect the alloy produced in the distillation step is preferably introduced into a, separate distillation furnace in to treat in an electric furnace bauxite, clay,

natural silicates of aluminum and generally most aluminous rocks so long as the quantity of aluminum contained in the raw material is sumcient to lead to the production of a metallic alloy containing the aluminum.

The alloy containing the aluminum which is obtained from this furnace may present various compositions in accordance with the minerals which are utilised, but such variations are of little importance, although for convenience it is desirable to seek to obtain the highest possible aluminum content in the alloy. When the ob- Ject of the process is to obtain aluminum by itself, the production of an alloy containing less than 20% of aluminum will hardly lead to a commercial result.

The charge may consist of aluminum-bearing material such as bauxite, clay or aluminumsilicate in admixture with iron oxides, silica and carbon or carbides of heavy metals whereby a ferro-silico-aluminum alloy is produced. The amount of silica may be such that the alloy produced is rich in silicon and after the reduction charge.

molten condition and therein distilled and condensed in a condensing zone within the furnace which is kept at a cooler temperature than the portion of the furnace containing the molten The condensation may be eilected upon water-cooled metal surfaces.

The distillation of'the aluminum may be conducted in the presence of a neutral gas. By "neutral gas is meant in this specification one which does not interfere with the distillation by any reaction with the molten alloy; of the gases available hydrogen argon, and light hydrocarbons such as methane'are suitable.

The accompanying drawing illustrates diagrammatically one way of carrying the invention into effect.

In the drawing Ii represents an electric reduction furnace such as is used for the production of carbide of calcium or ferro-silicon. The furnace is indicated as being heated by three-phase current from mains i2. The charge in the furnace II will on reduction'yield an alloy containing aluminum in a molten condition and the alloy is transferred after the reducing operation, as indicated by line l3, to a volatilisation furnace consisting of a heated chamber it into which the charge is fed and which is supplied with external heat by electrical connections l5 from the mains which operate heaters 2| arranged within the furnace casing it. The furnace casing i6 v is made vacuum-tight and is lined with refrachas taken place a further quantity of alumina is tory material 22, with an inner lining of 00mmdum 23. The heated portion of the furnace is connected by a port 24 with a condensation chamber l1, located within the casing [8 to one side of the chamber i4. Thewhole furnace is kept under vacuum by means of a vacuum pump indicated at [8 and connected to the chamber by the connection I8.

Depending into the condensation chamber I1 there is a water-cooled pipe 25 which is closed at the bottom end. concentrically within it is a water supply pipe 28 which carries cooling water to the bottom of the pipe 25, which water rises around the pipe 28 and is carried away at 21. Upon the pipe 25 are plates 28 which are kept cool by their contact with the pipe. On these plates which are conveniently made of aluminum the aluminum vapours from the bowl 20 condense, and grow in crystalline form downwards. The condensing plates and the cooling means therefor are carried upon a removable lid 29 and when a suflicient weight of aluminum has been condensed in this manner the lid can be removed and replaced with a fresh condensing unit, 1. e. water-cooled plates, after which the action can be further continued.

The furnace is provided with a casting spout 30 for pouring out molten metal which remains after the aluminum has been eliminated therefrom. There is also a drain orifice 3|.

In order to obtain the best aluminum content in the alloy produced the reduction should be conducted at the lowest temperature at which the reaction will take place in order to lead to the least possible loss of aluminum by volatilisation in the furnace ll. Preferably the composition of the charge of the furnaceis adjusted by addin iron or quartzite to the charge so that the alloy produced tends to be aferro-silico-aluminum alloy.

The order of the vacuum desirable in practice is such as to correspond to an absolute pressure of 0.5 to 4 millimetres of mercury. Under these conditions the aluminum distils rapidly at a temperature of about 1220 C. to 1360 C. whereas at higher pressures, that is to say lower vacua, the temperature becomes too high for practical work with a furnace of this type.

Owing to the introduction of the metal into the furnace in a liquid form it is possible to arrange for a vacuum seal on the inlet pipe and for the introduction of the metal as required without breaking the vacuum.

Where the alloy produced in the first furnace.

is, due to the nature of the charge, one which is rich in silicon it is possible to incorporate alumina in it after the alloy has been produced because the alumina is reduced by silicon. The addition of a little quicklime at the moment of the admixture of the alumina facilitates this operation, which can be conducted either in the first furnace for the production of the charge which is tt be distilled or subsequently in the second furnace when the charge therein becomes suilicient- 1y rich in silicon due to the distillation of aluminum out of it. The term metals" is used herein as including silicon.

I claim:

1. A proces for the reduction of aluminum comprising the steps of first reducing in an electrio furnace a charge consisting of an aluminum bearing material in admixture with iron oxide, a reducing agent, silica in such amount that the alloy produced is rich in silicon, adding to the molten alloy thus formed a further quantity oi aluminum bearing material so that the silicon in the alloy will reduce the aluminum bearing material and the aluminum content is thereby increased, and thereafter reducing the pressure 01 the atmosphere in contact with the molten alloy to a degree such that the absolute pressure does not exceed 4 mm. of mercury, and bringing the temperature of the alloy to a point at which the aluminum volatilises therefrom, and condensing the vapors so produced while they are still under the vacuum by leading them into contact with a cooled condensing element.

2. The process of separating metallic aluminum from a bath containing a plurality of molten metals one of which is aluminum, and recovering the same in solid form, which comprises maintaining above the surface of the bath an absolute pressure not exceeding 4 mm. of mercury and maintaining the temperature of the bath at approximately 1220 C. to 1360 C., whereby low temperature vaporization of aluminum from the bath will occur, and causing the low temperature aluminum vapor thus generated, while still under the vacuum, to contact with a member having a surface temperature sufflciently low to cause condensation-of such vapor and its direct transformation into solid form.

HENRI LOUIS GENTIL.

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