US1935245A - Process for the reduction of alkaline earth metals and the production of alloys of aluminium - Google Patents

Description

Nov. 14, G; N KIRSEBOM i PROCESS FOR THE REDUCTION OF ALKALINE EARTH METALS AND THE PRODUCTION OF ALLOYS OF ALUMINIUM Filed July 2, 1952 www md5/e faam a5 /Z a6.

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Patented Nov. 14, 1933 UNITED STATES PATENT OFFICE Gustaf Newton Kirsebom, slo, Norway,V assignor to Calloy Limited, London, England, a joint-stock company of England Application July 2, 1932, Serial No. 620,574, and in Norway January 23, 1932 23 Claims.

This invention relates to a method or process for the production of aluminium alloys by reducing a compound or compounds of the alkaline earth metals in a bath of molten aluminium; and

further relates to. thel treatment of the dross,

Which forms in theheatng chamber while carrying out said process, for the recovery of the metal or metals therefrom.

The method or .process for the production of aluminium alloys, according to the present invention, is carried out by introducing into a bath of molten aluminium a compound or compounds of the alkaline earth metals while vin other than powder form-for example in pieces grains or l5` lumps having the size of 1 or 2 mm. up to 100 mm. or more-to reduce said compound or compounds and thereby alloy said alkaline earth metal orA metals with the aluminium.

In carrying out the said process or method according to the present invention, it will be found that all the alkaline earth metal produced during the process does not alloy with the `aluminium but on the contrary a considerable amount of the alkaline earth metal is left in the crucible ormelting pot, or other heating chamber containing the heated charge, in the form of infusible dross; such dross sometimes y running higher in the alkaline earth metal than the proportion in the aluminium alloy; and it is an object of the present invention to treat this dross for recovery or utilization of the metal or metals therein. f

The present invention comprises certain other features and certain modications all of which will be fully described and set forth hereinafter.

Any known or suitable type of heating chamber such as a pot furnace or crucible (all of which will hereinafter be referred to as the heating vchamber) may be used; and the temperature to be employed would be between the melting point of aluminium (viz. 650 C.) and the vaporizing point of aluminium (about 1600 C.), the working range in operation being say between 700 C. and 1500 C.

The temperature is selected according to the compound or compounds to be reduced and the metal or metals to be alloyed with the aluminium and the amount (percentage) of such metal or metals which it is desired to alloy with a given amount of aluminium.

I employ the compound or compounds of the alkaline earth metal in other than powder form (i. e. any size above 12-mesh to the inch may be employed) namely I employ the said compound 55 or compounds in pieces grains, or lumps', of a size minium of any given weight will be calculated or 'under great evolutions of heat.

or sizes ranging between 1 or 2 mm. up to 100 mm.

or more; and I prepare said-pieces'grains.or

lumps by crushing or grinding or in any other suitable way.

The amount or proportion of the compound or compounds in such pieces grains or lumps (either in mixed sizes, or graded approximately or as nearly as desired to any particular size or sizes) to be added to a charge or bath of molten aluregulated according to the amount of such compound or compounds which will have to be re- I duced in order to (a) allow for the metal which will become dross during the process and (b) provide the required percentage of the alkaline earth metal or metals which it is desired to alloy with the aluminium.

Having determined the temperature to be employed and the percentage of the alkaline earth 7 metal or metals which it is desired to bepresent in alloy with the aluminium (in the aluminium alloy tobe produced) the amount of the compound or compounds, in pieces grains or lumps, is then computed and fed to the'bath of molten aluminium; for instance .if the aluminium alloy is to contain ten percent of an alkaline earth metal in such alloy then such an amount of the compound is fed to the bath of molten aluminium as will produce about 20% of the reduced metal, half of which latter (or thereabouts) will becomey dross in the heating chambers and the other half (or thereabouts) become alloyed with the aluminium to this produce the required ten percent of the alkaline earth metal in alloy with the aluminium.

My process for producing alkaline earth metal alloys with aluminium will now be further d escribed as follows In carrying out the process with calcium oxide; the pieces grains or lumps of calcium oxide are placed on top of a bath of molten aluminium at the required temperature whereupon the pieces grains or lumps of calcium oxide will gradually sink into the molten aluminium and the calcium 'oxide Will be reduced by the aluminium and result in the formation of a calcium-aluminium 'alloy and aluminium oxide; the reaction being as follows:-

The above reaction is essentially different from that which takes place in a process Well known as the Goldschmidt Thermit process in which metal oxides are treated with aluminium powder Now I have found that the above calcium oxide aluminium reaction does not take place if the calcium oxide is placed on top of the heated bath of aluminium in a finely divided state i. e. in powder form. On the other hand I have found that a very satisfactory result is obained by placing upon the top of the bath of molten aluminium calcium oxide in pieces grains or lumps of the size or sizes above referred to. I have found that the grains or pieces of calcium oxide sink into the molten aluminium and then react therewith (in contradistinction to the powder which does not sink into the aluminium) and I have succeeded in this way in obtaining an aluminium alloy containing up to 10% Ca. l

In carrying out the present invention with calcium oxide for instance the following procedure may be adopted:-

Aluminium metal is first melted in preferably a crucible furnace and then heated till the temperature has reached about or between 1000-1200 C. Ordinary burnt lime (as low in iron as possible) is then added to the top of the bath of molten aluminium in pieces ranging ordinarily from a few millimeters diameter to a walnut size. As the operation proceeds, the pieces of lime gradually sink into the molten aluminium bath;

whereas if the pieces are too small, e. g. if lime powder be used same will not sink down into the molten aluminium but will float on the top and even after hours contact little or no calcium would be found in the metal.

The accompanying drawing illustrates a flow sheet of a suitable plant for carrying out the process according to my present invention with calcium oxide; or with any other compound or compounds of the alkaline earth metals.

After several hours of contact the pieces grains or lumps of calcium oxide will have been dissipated and the alloy is discharged having reached the desired percentage el g. around 10% Ca. About fifty percent of the metals is however left in the heating chamber in the form of infusible dross of aluminium calcium alloy and usually running even higher in calcium than the molten aluminium itself.

I have found that an economic way of treating this dross is by smelting it down under a covering of common salt in aifurnace at about 1000 C.

I have found that the calcium-aluminium alloy dross will react directly with the sodium chloride under the reactions:

Thus the aluminium is recovered from this dross as substantially pure metal free from calcium. The calcium in the dross reacts with the sodium chloride under release of sodium. This sodium will at this temperature partly be used up in reducing some of the oxidized aluminium and partly be oxidized directly to NazO.

A good deal of this NazO fumes off on top of the bath and may be recovered in a fume bag. Some of it may be traced in the secondary dross formed in the salt melt. This secondary' dross will consist largely of sodium and calcium chlorides with insoluble particles of aluminium oxide, lime, etc. It may-be treated wih a caustic soda solution for the recovery of the contained aluminium, and this caustic solution may be produced by wetting the fume of sodium oxide obtained during the salt reaction.

According to a further feature of this invention,

, dross containing 44% Sr., which decomposed wa- I have found that if, instead of adding only calcium oxide I also' add magnesium oxide in pieces grain or lump formas aforesaid, I obtain both calcium and magnesium in the metal. During the salt treatment of the dross the magnesium will however not react with the sodium chloride and it is thus possible if required to remove the calcium from the dross of calcium magnesium aluminium by melting it together with salt.

Furthermore I have found that the secondary dross will contain nitrides (probably of calcium). These nitrides can be discerned as small yellow particles scattered in the mass. On wetting some of the dross with Water and heating the mass, large volume of ammonia will be given off and can be collected. It is therefore possible to obtain nitrogen from the air by this process in the form of ammonia, which may be collected.

By subsiituting barium oxide for lime, I have obtained a metal containing ,15% Ba. and a metallic dross, which was found to decompose water` and contain 21% metallic barium.

By substituting strontium oxide for lime, I obtained a metal containing 22% Sr. and a metallic ter violenly.

Similarly a. beryllium-aluminium alloy can be obtained, e. g. containing 0.2% Be.

Also in these cases the dross may be treated with salt recovering the aluminium in metallic form and barium chloride, or strontium chloride or beryllium chloride, and ammonia as by-products.

It is also possible to treat the dross by other fluxes, such as for example cryallite. The dross may then be added to a cryallite molten bath and the pure aluminium recovered, while the oxidized aluminium dissolved in the bath may be recovered by electrolysis.

By adding calcined magnesite in the form of pieces, grains or lumps toI the aluminium I have obtained a Mg-Al-alloy containing up to 1.5% Mg.

Also I have found that when calcium-aluminium alloy is treated with molten Mg-chloride the Mg will enter the metal and the calcium forms a chloride.

I have also found that when calcium-aluminium alloy dross is melted together with salt in the presence of magnesium oxide (calcined magnesite) some magnesium will enter into the aluminium.

I have also found'that the presence of calcium 130 oxide beside magnesium oxide favours the preferential entrance of magnesium into aluminium; and I therefore propose to use dolomites or burnt dolomites, which will give a calcium-magnesium aluminium alloy which may then be converted l into a Mg-Al-alloy by eliminating the Ca either with salt or MgCl2;

It is also possible to introduce the alkaline earth metal compound as a carbonate, which will ultimately form an oxide before it reacts with the 146 aluminium; and also any other alkaline earth metals compound, which is capable of being broken up and delivering the oxide at the temperature of the aluminium bath, may be used.

What I claim is:-

1. A process for the manufacture of alkaline earth alloys of aluminium which comprises the steps of heating in a molten bath of aluminium, below the surface thereofVan oxygen-containing compound, other than a sulphate, of the alkaline 150 earth metal, whereby a molten alloy and an infusible alloy dross containing alumina are formed, and thereafter separating the molten portion from the infusible dross.

2. A process foi the manufacture of alkaline earth alloys of aluminium which comprises the steps 'of heating, in a molten bath of aluminium, an oxygen-containing compound other than a sulphate of the alkaline earth metal in solid pieces of sufiicient size to overcome the surface tension of molten aluminium and thereby sink below the surface of the bath, whereby a molten alloy and an infusible alloy dross containing alumina are formed, and thereafter separating the molten portion from the infusible dross.

3. A process for the manufacture of alkaline earth alloys of aluminium which comprises the steps of vheating in a molten bath of aluminium below the surface thereof, an oxide or carbonate of the alkaline earth metal whereby a. molten alloy and an infusiblef alloy dross containing alumina are formed, and thereafter separating the molten portion from the infusible dross.

4. A process for the manufacture of alkaline earth alloys of aluminium which comprises the steps of heating in a molten bath of aluminium an oxide or carbonate of the alkaline earth metal, in solid pieces of sumcient size to overcome the surface tensionof molten aluminium and therebysink below the surface of the bath, whereby a molten alloy and an infusible alloy dross containing alumina are formed, and thereafter vseparating the molten portion from the infusible dross. y

5. A process for the manufacture of alkaline earth alloys of aluminium which comprises the steps of heating in a molten bath of aluminium, below the surface thereof, a silicate of the alkaline earth metal, whereby a molten alloy and an infusible alloy dross containing alumina are formed, and thereafter separating the molten portion from the infusible dross.

6. A process for the manufacture of alkaline earth alloys of aluminiumwhich comprises the steps of heating in a molten bath of aluminium a silicate of the alkaline earth metal, in solid piecesvof sumcient size to overcome the surface tension of molten aluminium, whereby a molten alloy and an infusible alloy'dross containing alumina are formed, and thereafter separating the molten portion from Ythe infusible dross.

7. A process for the manufacture of alkaline earth alloys of aluminium which comprises the steps of heating in a molten lbath of aluminium, below the surface thereof, an oxygen-containing compound, other than a sulphate, of the alkaline earth metal, whereby a molten alloy and an infusible alloy dross containing alumina are formed, thereafter separating the molten pory tion from the infusible dross, and the further step of recovering-valuable constituents from the infusible dross.

8. A process for themanufacture of alkaline earth alloys of aluminium which comprises in combination the steps oi heating in a molten bath of aluminium, below the surface thereof, an oxygen-containing compound, other than a sulphate, of the alkaline earth metal, whereby a molten alloy and an infusible alloy dross containing alumina are formed, thereafter separating the molten portion from the infusible dross,

recovering aluminium from the infusible dross` bymelting the latter with a reagent capable of forming a, salt' with the alkaline earth constituent of the alloy therein, whereby a metallic layer and a secondary dross are formed, and. separating the metallic layer.

9. A process for the manufacture of alkalin earthealloys of aluminium which comprises in combination the steps. of heating in a molten bath of aluminium, below the surfacev thereof, an oxide or carbonate of the alkaline earth metal whereby a molten alloy and an infusible valloy dross containing alumina are formed, thereafter separating the molten portion from the infusible dross, recovering aluminium from the Yinfusible dross by melting the latter with a reagent capable of forming a salt with the alkaline earth constituent ofthe alloy therein, whereby a metallic layer and a secondary dross are formed, and separating the metallic layer.

l0. A process for the manufacture of alkaline earth alloys of aluminium which comprises in combination the steps of heating in a molten bath of aluminium, below the surface thereof, an oxide or carbonate of the alkaline earth metal, whereby a molten alloy and an infusible alloy dross containing alumina are formed, thereafter separating the molten portion from the infusible dross, recovering aluminium from the infusible dross by melting the latter with an alkali-halide, whereby a metallic layer and a secondary dross are formed, and separating the metallic layer.

ll. A process for the manufacture of alkaline earth alloys of aluminium which comprises Ain combination the steps of heating in a molten bath of aluminium, below the surface thereof, an oxide or carbonate of the alkaline earth metal, whereby a molten alloy and an infusible alloy dross containing aluminal are formed, thereafter 110 separating the molten portion from the infusible dross, recovering aluminium from the infusible dross `by melting the latter with sodium chloride, whereby a metallic layer and a secondary dross are formed, and separating the metallic 115 layer.

, 12. A process for the manufacture of alkaline earth alloys of aluminium which comprises in steps of heating in a molten bath of aluminium, an oxygen-containing compound, other than a 120 sulphate, of the alkaline earth metal, in solid pieces of suicient size to overcome the surface tension of molten aluminium and thereby sink below the surface of the bath, whereby a molten alloy and an infusible alloy dross containing alumina are formed, thereafter separating the molten portion from the infusible dross, and the further step of recovering valuableconstituents from the infusible dross.

13.- A process for the manufacture of alkaline earth ,alloys of aluminium which ncomprisesy in combination the steps of heating in a molten bath of aluminium an oxygen-containing compound, other than a sulphate, of the alkaline earth metal, in solid pieces of sufficient size to overcome the surface tension of molten aluminium and thereby sink below the surface of the bath, whereby a molten alloy and an infusible alloy dross containing alumina are formed, thereafter separating the molten portion from the infusible dross, recovering valuminium from the infusible dross by melting the latter with a reagent capable ies ' of forming a salt with the alkaline earth constituent of the alloy therein, whereby a metallic layer and a secondary dross are formed, and separating the metalliclayer.

14. A process for the manufacture of alkaline earth alloys of aluminium which comprises in combination the steps of heatingin a molten ybath of aluminium an oxide or carbonate of the alkaline earth metal, in solid pieces of sufficient size to overcome the surface tension of molten aluminium and thereby sink below the surface of the bath, whereby a molten alloy and an infusible dross containing alumina are formed, thereafter separating the molten portion from the infusible dross, recovering aluminium from the infusible dross by melting the latter with a reagent capable of forming a salt with the alkaline earth constituent of theA alloy therein, whereby a metallic layer and a secondary dross are formed, and separating the metallic layer.

I15. A process for the manufacture of alkaline earth alloys of aluminium which comprises in alkali-halide, whereby a metallic layer and a secondary dross are formed, and separating the metallic layer.

16. A process for the manufacture of alkaline earth alloys of aluminium which comprises in combination the steps of heating in a molten bath of aluminium an oxide or carbonate of the alkaline earth metal, in solid pieces of sufficient size to overcome the surface tension of molten aluminium and thereby sink below the surface of the bath, whereby a molten alloy and an infusible alloy dross containing alumina are formed, thereafter separating the molten portion from the infusible dross, recovering aluminium from the infusible dross by melting the latter with sodium chloride, whereby a metallic layer and a secondary dross are formed, and separating the metallic layer.

17. A process forthe manufacture of alkaline earth alloys of aluminium i which comprises in combination the steps of heating in a molten bath of aluminium an oxide or carbonate of the alkaline earth metal, in solid pieces of 1/2 to 100 m. m. size, whereby a molten alloy and an infusible alloy drosscontaining alumina are formed, thereafter separating the molten portion from the infusible dross, recovering aluminium from the infusible dross by melting the latter with sodium chloride, whereby a metallic layer and a secondi combination the steps of heating in a molten bath of aluminium, below the surface thereof an oxide or carbonate of thealkaline earthvmetal, whereby a molten alloy and an infusible alloy dross containing alumina are formed, thereafter separating'the molten portion from the infusible dross, recovering aluminium from the infusible dross by melting the latter with an alkali-halide, whereby a metallic layer and a secondary dross l are formed, separating the metallic layer, and

recovering alumina and ammonia from the secondary dross by heating the latter with water.

19. A process for the manufacture of alkaline earth alloys of aluminium which comprises in combination the steps of heating in a molten bath of aluminium an oxide or carbonate of the alkaline earth metal, in solid pieces of sufficient size to overcome the surface tension of molten aluminium andl thereby sink below the surface of the bath, whereby a molten alloy and an infusible alloy dross containing alumina are formed, thereafter separating the molten portion from the infusible dross, recovering aluminium from the infusible dross by melting' the latter with an alkali-halide, whereby a metallic layer and a secondary dross are formed, separating the metallic layer, and recovering alumina and ammonia from the secondary dross by heating the latter with water.`

20. A process for the manufacture of a calciumaluminium alloy which comprises the stepsof heating in a molten bath of aluminium, below the surface thereof, calcium oxide or carbonate, whereby a molten calcium-aluminium alloy and an alloy dross containing alumina are formed, and thereafter separating the molten portion from the infusible dross.

v21. A process for the manufacture of a calcium-aluminium alloy which comprises the steps of heating in a molten bath of aluminium calcium oxide or carbonate, in solid pieces of suiiicient size to overcome the surface tension of molten aluminium and thereby sink below the surface of the bath, whereby a molten alloy and an infusible alloy dross containing alumina are formed, and thereafter separating the molten portion from the infusible dross.

22. A process for the manufacture of calciumaluminium alloy which comprises in combination the steps of heating in a molten bath of aluminium calcium oxide or carbonate, in solid pieces of sufficient size to overcome the surface tension of molten aluminium and thereby sink below thesurface of the bath, whereby a molten alloy and an infusible alloy dross containing alumina are formed, thereafter separating the molten portion from the infusible dross, recovering aluminium from the infusible dross by melting the latter with sodium chloride, whereby a metallic layer and a secondary dross are formed, separating the metallic layer, and recovering alumina and ammonia from the secondary dross by heating the latter with water.

23. A process forthe manufacture of a magnesium-aluminium alloy which comprises in combination the steps of heating in a molten bath of aluminium calcium oxide or carbonate in solid pieces of suiiicient size to overcome the surface tension of molten aluminium and thereby sink below the surface of the bath, whereby a molten alloy and an infusible alloy dross containing alumina are oformed, thereafter separating the molten portion from the infusible dross, and treating the molten portion with molten magnesium chloride.'

GUSTAF NEWTON KIRSEBOM.

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