DE2013470A1 - Process for cleaning molten metals or alloys - Google Patents

Description

PATENT LAWYERS 2013470 Dipi.-chem. Dr, D. Thomsen Dipi.-ing. H. Tiedtke
Dipichem G. Buehling MUNICH 2
VAL 33
TEL 0811/220804
CABLES: THOPATENT
TELEX: FOLQT Dipi-ing. W.Weinkauff FRANKFURT (MAIN) 50
FUCHSHOHI. 71
TEL. 0611/514666

Reply requested to: Please reply to:

8000 Munich 2 March 20, 1970 case 14930 / T 3546

Alloys and Chemicals Corporation Cleveland / USA

Process for cleaning molten metals or

Alloys.

The invention relates to a method for Chlorination of molten aluminum; In particular, it relates to a process for the chlorination of aluminum, where a reactive chlorine-containing vapor is not used as the sole source of chlorine.

Although the invention also relates both to the chlorination of molten aluminum as the chlorination of the molten aluminum alloy, which consist, by weight, mainly of aluminum, it is for convenience described sake below with reference to the chlorination of molten aluminum itself to remove impurities, if on the other hand, there is no contradiction in the context. The meaning of the expression "impurities" comes from the following

Mündlldi · Agreements, InibetonOaM ArS Hlnon, bJdür »TT Poor confirmation

from the description; In general it denotes undesirable components, usually metallic components, albeit in a different context as components an alloy can be viewed. For example, magnesium is the most common impurity after this Procedure is removed.

It is also apparent / that according to the invention, both the removal of impurities and the Reduction of the content of impurities is achieved.

The term "reactive chlorine-containing steam (such as it is used below) refers to both gaseous chlorine and other gaseous chlorine compounds under Inclusion of chlorinated hydrocarbons. All of the above Percentages given in connection are - unless otherwise indicated - based on weight.

Metallic aluminum used technically is either raw aluminum from bauxite melts (known as primary aluminum) or metallic aluminum obtained through scrap recovery from many Sources (known as secondary aluminum).

In any case, the metal must be used before it can be used for manufacture

treatment purposes can be refined. at Primary metal, the product of an electrolytic melt, can contain magnesium and sometimes sodium. With secondary metal, the main problem is unwanted metal, the was referred to above as an impurity, particularly magnesium. These either have to be completely removed or at least removed sufficiently that no more than a predetermined amount remains in the metal.

One method used to remove contaminants, useful with both primary and secondary aluminum, is to treat molten metallic aluminum with a reactive chlorine-containing vapor, generally free gaseous chlorine. Following this process, the contaminant metals are removed. For example, metallic sodium and magnesium converted into chlorides, which - if necessary - can be removed as slag at the end of the process.

In this known method, gaseous Chlorine is simply introduced into the molten metal with a suitable lance while it is in a suitable 'Oven is kept. Although this simple method has advantages, it has the disadvantage that the degree the use of chlorine is low. When the removal of

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Indeed, if magnesium to a low level (e.g., below 0.1%) is desired, it is generally common to use a 200% excess of chlorine; that is, the amount used is three times as large as required. However, the reaction between molten aluminum and gaseous chlorine to form AlCl is extremely fast. This AlCl ₃ has a boiling point of around 185 ° C at normal pressure and therefore evaporates immediately from the metal. In this way, not only is chlorine lost, but significant amounts of aluminum are also lost. In addition, AlCl. Vapor hydrolyzes in contact with atmospheric water to form fumes of gaseous hydrogen chloride and aluminum oxide dust. The alumina dust can be microscopic with a particle size of 2 microns or smaller.

One proposal to overcome the smoke problem is directed to the chlorination process under one To carry out the fluid cover. In this advanced Form of the process, gaseous chlorine or another suitable reactive chlorine-containing steam, such as trichlorethylene, is used as the source of chlorine. As a result of the presence of the flux, no aluminum chloride formed evaporates, but is retained in the flux. this is achieved by using a material as a flux with a content of chlorides or fluorides of the alkali

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or alkaline earth metals (i.e., the metals of Group Ia and Ha of the periodic table) or used by ammonium The requirements that this flux must meet, are:

1. There must be at the temperature at which the chlorination is performed (generally in the range of 700 ° to 750 ⁰ C), be sufficiently fluid

2. it should itself at least the greater part of what may be formed during the chlorination

Absorb aluminum chloride and

3. there should be no contaminating metals, i.e. undesirable components, in the aluminum from the river *, funds can be entered.

According to the invention it was found that by the use of a flux which is itself a chlorinating agent, e.g., a substantial amount of aluminum chloride, contains, a substantial part, or in some cases that all of the chlorine required for the reaction can be supplied and that the smoking problem mentioned above can be overcome by either the flux core all aluminum chloride is absorbed which is caused by the presence of any reactive chlorine-containing employed Steam forms, or by even the need for one Use of added reactive chlorine-containing steam

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is avoided.

According to the invention there is provided a method of removing contaminants by chlorinating molten aluminum or a molten aluminum alloy consisting predominantly of aluminum by weight, the molten aluminum having a Flux layer, which contains at least a part of the amount of chloricrgent required to react with the impurities, is covered under such conditions that the flux does not become thermally too Smoke decomposes.

Although the flux may provide all of the chlorinating agent (thereby making it possible to regulate the removal of contaminants by using a predetermined amount of the chlorinating agent in the flux), an alternative embodiment of the invention provides such a method in which at least a portion of the amount of chlorinating agent required to react with the impurities through Introduction of a reactive chlorine-containing vapor into the molten aluminum is provided.

In this case, you can regulate the distance of the impurities are caused by a predetermined

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Amount of reactive chlorine-containing vapor is introduced into the molten aluminum, the supply of this Steam is interrupted and the implementation between the Fluid middle layer and the molten aluminum continues. This is explained in more detail below.

Usually the flux layer is melted and contains an aluminum chloride double salt.

A number of such double salts are known to Ea, for example the following

Double salt - melting point (C)

NaAlCl ₄ 154

KAlCl ₄ 245

142

'2AlCl ₃ 301

NH ₄ AlCl ₄ 227

(Literature: W. Schmidt, USA Patent 3 240 590)

The double salt Na ₃ AlCl ₆ can also be used. However, the alkaline earth double chlorides appear to be both somewhat less reactive and less stable than the alkali double chlorides; furthermore, the ammonium double salt is somewhat less stable; therefore, it is preferred to use a flux composed primarily of the alkali metal chlorides

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although all of the foregoing types of materials are useful. Mixtures of these alkali metal chlorides can be used may be used as exemplified in the table below (percentages are by weight expressed).

aAlCl ₄ KAlCl ₄ LiAlCl ₄ Melting point % % % ° c - 35 65 120 - 50 50 132 33.3 33.3 33.4 115 25th 50 25th 156 65 35 - 135 50 50 180

Literaturt W. Schmidt and J.W. Carson, Canadian patent 813 276.

However, these alkali metal double salts and their mixtures have extremely low melting points and therefore some "stiffening" of the flux may be desirable. This can be achieved in a number of ways. For example, can be made a melt of the double salt NaAlCl ₄ stiffer by the addition of sodium chloride: The addition of only 5 wt .-% sodium chloride increases the melting point of 158 ⁰ C to about 600 C. In the same way, the addition of 2% cryolite, Ha ₃ AlF ₆ , about the same effect.

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From the above it can be seen that the interference even small amounts of aluminum chloride in fluxes based on KCl and NaCl have a fundamental influence has the melting point. When the chlorination of aluminum expires, it can be assumed that as a result of the lowering of the double salt content of the flux melt ' point increases and liquidity decreases. In practice if this is generally not the case: E.g. with the Chlorination of aluminum with a content of magnesium per 2 moles of aluminum chloride, which from the flux to the metal are removed, 3 moles of magnesium chloride from the metal are added to the flux. While. Magnesium chloride itself has a high Melting point (712 ° C), it forms both Eutectica with KCl as well as with NaCl:

KCl NaCl MgCl ₂ Melting point 60% - 40% 425 - 48% 52% 450 14% 12% 74% 420

It can thus be seen that the removal of Alumi ^ nium chloride in such cases does not significantly affect the

Affected fluid liquidity. Other systems also often show the formation of such eutectica.

These double salt fluxes can act on several Way to be made. The easiest way

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consists in melting the two salts together in a suitable crucible; for the Arbeltswelse regarding NaAlCl, In Example 1, details are given that are typical. Alternatively, the flux can be used in an indirect way getting produced. In particular, it has been found above that gaseous chlorine and aluminum react very rapidly to form aluminum chloride and that a suitable flux absorbs the aluminum chloride. Therefore For example, a reactive flux can be prepared by simply chlorinating molten aluminum covered with an existing flux not containing aluminum chloride until the aluminum chloride content in such a flux increases to the desired level Has. A typical procedure is described in Example 2.

Contact between the metal and the flux can be achieved in a number of ways. A simple one Form of the chlorination process is to use a roughly cube-shaped furnace and chlorine directly in introduce the molten metal through lances that are inserted into the. Metal through suitable openings in the Bring the walls down above the molten metal. While this process can be operated more effectively, by simply providing a molten flux blanket, this simple operation does not do particularly well

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-U-

apply to the method according to the invention? that is special this is the case when no gaseous chlorine is used at all. It is difficult to stir the metal

to achieve that is sufficient to achieve a suitably rapid reaction between flux and metal. ,

It should also be noted that this way of working not in the case of an immediately "gas heated" (i.e. heated by natural gas, town gas, evaporating oil, etc.) furnace or a gas-heated reverberation furnace can be used. One object of the method according to the invention is therein, the smoking problems associated with the known method to reduce $ if there is a "gas-heated" If the furnace is used by simply adding a flux to the furnace heart, there is no decrease in smoke. the Temperatures in such "gas-heated" ovens. In particular in the combustion chamber, are so high that thermal decomposition of the flux is unavoidable. Considerable amounts of smoke result from this decomposition.

However, when a modified® furnace shape is used, sufficient contact between the molten flux and the metal can be achieved, as further described in Example 3. This furnace shape is also suitable for the embodiment of the invention,

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in which both a chlorine-containing flux and gaseous chlorine are used, as described in Example 4. If done in this way, it offers new method according to the invention over the known method the advantage / that the feed rate of the gaseous Chlorine in the chlorination chamber generally does not match the rate of contaminant removal; the gas flow rate is essentially constant during the The content of impurities follows an exponential curve that goes infinitely towards a magnesium content of O at the point in time. However, once the desired amount of chlorine (with a small excess for dissolved hydrogen) has been added, the gas flow must be stopped. Analysis shows that the impurities are removed continues until the flux does not contain reactive chlorine. In this way, this embodiment of the invention offers a second advantage; the chlorination process is made adjustable; the removal of impurities down to a predetermined value (not completely) is practical, at least in a batch process.

As will be further described in Example 8 below, it is not difficult to obtain by a simple experiment determine how much magnesium has been removed from the metal by each contact with the metal and flux. So (provided that care is taken to keep the flux

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composition acceptably constant) a certain Adjustment of the degree of magnesium removal possible. It clearly follows that if there is a good contact between metal and flux is achieved, almost complete removal of contaminants is possible. One try has shown that this process, in addition to removing magnesium, contains a metal with low hydrogen, sodium and oxide content (as aluminum oxide) provides. .

A simple cascade system can be provided, to operate a continuous process, provided that steps are provided to control the chloride content of the flux at a suitable level. This can be achieved in different ways: E.g. by Add aluminum chloride or pass the exhausted flux through a slag chlorination process. The usage of these double salt containing materials provides an excellent flux for the recovery of slag: After This technique allows cheap metal to be used as the source of aluminum chloride, thereby eliminating all of the metal recovery is improved. While the flow of metal through such a system must be continuous, the flow of flux must be not be: Therefore, a batch replacement is possible. Such a procedure is described in Example 5.

In the following examples of the procedure, 109808/1198

Reference is made to the figures of the drawings, wherein

Fig. 1 is a plan view of a furnace,

the explanation of the procedure according to
of the invention is useful.

Fig. 2 is a vertical cross section taken along line 2-2 of Fig. 1;

Fig. 3 is a front view of the furnace of Fig. 1;

Fig. 4 is a vertical cross section of a second furnace useful for explaining the modification of the method according to the invention
is useful, and

FIG. 5 is a cross section taken along line 5-5 of FIG. 4.

The drawings are to explain the

Process according to the invention useful, although the illustrated ovens are not the subject of the invention. Accordingly, various details of execution, such as the
the loading door operating device, not shown. In particular, the details of the refractory lining and the gas heating burners are not shown; both are common in metallurgical practice.

It is also understood that the melting part of the furnace shown in the figures of the drawings

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does not have to be heated inside with natural gas burners, as described in the following examples. It can any convenient source of heating; either directly or indirectly, such as electricity.

example I.

Production of the double salt * NaCLAlCl ₃ . materials

It is of paramount importance that both components are dry; if either of them is not dry wet alumina is formed in the flux, which is undesirable. Sodium chloride is generally dry; however, when it is caked, it can be easily powdered and heated all in one Oven dried at about 120 ° C. Xm case of aluminum chloride Water causes hydrolysis with the formation of aluminum oxide and HCl. Hydrolysis can occur, though Aluminum chloride not properly sealed during storage will. Purification is best achieved by distillation.

method

It was the two dry salts in a 109808/1198

The weight ratio of 3 parts of sodium chloride and 7 parts of aluminum chloride was mixed and placed in a bottom-heated crucible which was kept at an internal temperature of 300 ° C. A liquid swamp was formed very quickly. Further mixture was added to this sump at a rate such that the liquid state was entirely maintained.

Further sodium chloride can be added to the double salt of Example 1. Additional sodium chloride does not dissolve, but remains suspended in the liquid, which makes it less liquid. However, sodium chloride need not be added at the point where the flux becomes too stiff. As a guideline, the melting point of the flux should not exceed about 675 ° C.

Example 2
Indirect production of a reactive flux.

To 1000 kg of molten aluminum was added 1900 kg of a flux of the following composition in a crucible kept at 710 ° to 730 ° C.

Material parts by weight

NaCl 50 KCl 45 Cryolite 5

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When the flux melted it became gaseous Chlorine introduced into the metal and most of it converted to aluminum chloride. After a period of 3 hours a total of 2960 kg of chlorine was in the Metal initiated. The flux obtained in this way had the following composition:

NaCl: 950 kg KCl s 855 kg Cryolite: 95 kg AlCU ι - 3710 kg

which corresponds to a flux containing about 3142 kg NaAlCl ₄

and contains 2,091 KAlCl _{4. '}

Examples 3 and 4

In both examples, the one shown in FIGS Oven 10 shown to 3 is used.

It generally comprised: a storage vessel to hold a known amount of molten aluminum and to keep it molten; means for introducing metal into the vessel; a generally closed chamber (but communicating with the storage vessel below the level of the molten aluminum) for separating a portion of the metal to a location where a

■ 109808/1198

A layer of flux can be kept on this part; a conveyor, e.g. a pump line from a Forehearth to introduce molten metal from the storage vessel into the chamber. If necessary, can one or more gas lances are provided in the chamber, which end below the metal level.

The furnace 10 consists of a heating chamber 12 which heats the inside with natural gas burners (not shown) and accordingly has chimneys 14. He's also with Doors 16 provided for access. There are two chambers 18 and 20 on each side of the heating chamber 12 Chamber 18 is connected to the heating chamber 12 through the two openings 22. The openings 22 are simple openings in the partition wall 24 and have such a height that they are covered by the residue (heel), which remains in the oven after it has been deducted. In operation, metal to be melted is added to the chamber 18 and melted by thermal circulation of the molten metal.

The chamber 20 is divided into two sub-chambers 21 and 23 by the wall 26, which rises to the full height of the chamber. Although a flow of metal is possible between the heating chamber and each sub-chamber 21 and 23 of this chamber through the openings 28 in the partition wall 30

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no flow between the sub-chambers 21 and 23 possible. A smoke hood 32 is arranged above the lower chamber 21, which is provided with lance openings 34 and a gas vent 36. The sub-chamber 21 is a chlorination chamber.

In the lower chamber 23, a pump 38 is mounted on a support (not shown), the metal from the Sub-chamber 23 into sub-chamber 21 via the partition 26 promotes. The delivery pipe 40 of the pump 32 ends above the flux layer 42. In this way everything has to be done Metal flowing from sub-chamber 23 into the chlorination chamber 21 is promoted, pass the flux layer. Furthermore, due to the presence of the pump, the flow take place through the openings 28 in the indicated directions.

The values of Examples 3 and 4 are given below:

Example 3 Example 4

used metal aluminum aluminum

(purely electro- (purely electro-

lytic) lytic) Oven batch (no residue) 19 500 kg 19 500 kg added magnesium 20 kg
«0.11% Mg 100 kg
= 0.51% Mg Flux: basic mass NaCl: 50 NaCl i 50 (Parts by weight) KCl: 45 KCl: 45 Na ₃ AlF ₆ : 5 Na ₃ AlF ₆ : 5 "AlCl -" content at the beginning (wt .-%) 13.6% 2.4% ** - ~ - -
approximate weight of the
Flux 1 0 9 8-0 8/1 19 B 700 kg 910 kg

added chlorine

Pump flow rate (approx.) Reaction time

Duration of the chlorine addition (min.)

Magnesium content of the withdrawn metal (% by weight)

"AlCl ₃ " content at the end (% by weight)

Example 3 Example 4

nothing 343 kg 680 kg / min. 680 kg / min.

120 min.
nothing

0.06%
2.8%

165 min.

120 minutes after switching on the pump

0.17t 0.2%

Example 5 Continuous chlorination process

In the apparatus shown in Figures 4 and 5, a continuous chlorination process be performed. The incoming metal, which may be solid or molten, becomes the bath 50 of the heating chamber 52 used. The purpose of this chamber is to melt it for solid metal and to melt it for molten metal Metal to adjust its temperature to the range of 710 ° to 750 ° C. desired for chlorination. The metal leaves the chamber and comes into the forehearth 54, where all slag can be removed. The metal is removed from the forehearth 54 fed into the chlorination chamber 58 by the pump 56. The delivery pipe 59 of the pump ends above the level of the flux. In addition to the contact of metal and flux, the use of pump 56 ensures constant flow conditions by the chlorinator, even if

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201.3 ATQ

the supply to bath 50 is irregular, e.g. Emptying a pan.

The chlorination chamber is provided with an exhaust system 60, by means of which one or more lances 62 can be inserted through openings in the exhaust 60.

As shown in Figure 5, the chamber is divided into two longitudinal sections by the partition wall 64; on one side is the chlorination chamber 66, while the other side 68 as a collecting container serves. During the chlorination increases as a result of the formation of magnesium chloride slow the raw amount of the flux present / even if all the chlorine is supplied by the flux will. It is not advisable to increase the flux strength as this will affect the metal level in the chlorination system. Accordingly, the excess flux is allowed to flow through the partition wall 64 into the collecting container 68. By doing a simple siphon (not shown) is provided, this collecting container is self-emptying, whereby a new one Charging the flux with aluminum chloride is possible. The recycled flux is simple Way through a suitable opening (not shown) in the Smoke vent 60 poured in.

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The chlorinated metal exits chamber 58 through a pair of weirs 70 and 72 which hold back slag and other insoluble material and flux. It can then immediately be put to the intended use / e.g. a casting device for ingots.

In the following example, molten metal was placed in a bath 50 from a pan, the prepared Metal directly from an extrusion bolt caster was fed.

Metal feed rate: 8,000 kg / h

Composition of the insert: aluminum with 1.7%

magnesium

Composition of production: aluminum with less

than 0.1% Mg

Temperature of the used

Metal: 680 ° to 700 ° C

Chlorination temperature: 710 ° to 730 ° C

Composition of the flux at the beginning (parts by weight):

NaCl 50 _{} melting point}

^{KC1 45} J 66O ° C Na ₃ AlF ₆ 5j

to which 12.7% AlCl ₃ (obtained by chlorination over molten metal) had been added.

Flux thickness during operation: 15 to 20 cm Chlorine flux rate: 40 kg / h

Flux weight increase: 51 kg / h.

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Excess flux was removed from the collection container 68 removed via a siphon, reloaded with aluminum chloride and returned to the chlorination device. During the return of the flux to the chlorinator, the metal supply can be maintained - especially if steps are provided to introduce fresh flux into the chlorinator at the level of the metal / flux interface, thereby depleted Flux is dispensed into the collecting container 68. It is necessary to turn off the chlorine supply to the chlorinator while the flux is being supplied or is withdrawn from it in order to avoid smoke formation.

The following examples were run on a laboratory scale to demonstrate the removal of magnesium from To demonstrate aluminum by simply bringing it into contact; In a cascade, molten metal was mixed with a brought into contact generally covering flux layer.

Example 6

There were 200 g of an aluminum alloy with a Content of 20% magnesium with a flux made of

Potassium chloride 100 g

Sodium chloride 400 g aluminum chloride 200 g

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brought into contact. The aluminum chloride was probably a mixture of the two double salts NaAlCl and Ca (AlCl ₄ ) j. After stirring for 15 minutes, analysis indicated that the aluminum contained only 3.3% magnesium.

Example 7

There were 2714 g of an alloy with a content of 0.56% magnesium with a flux

Sodium chloride 150 g (40%)

Potassium chloride 150 g (40%)

Magnesium chloride 75 g (20%)

Aluminum chloride 60 g

brought into contact. The aluminum chloride was most likely a mixture of KAlCl. and NaAlCl ₄ . After contact with stirring for 15 minutes , the magnesium content of the metal was below 0.01%.

Example 8

A series of tests were conducted to determine the effectiveness of magnesium removal by a flux containing aluminum chloride. For this purpose, molten aluminum was conveyed by a pump through an open trough, which ended after about 60 cm, over the flux center , lobe rf area and through the flux into a bath

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dropped from molten metal under the flux. The pump flow rate in each case was 1500 kg / h (nominal) and the flux thickness was about 25 cm. The initial one The magnesium content of the metal was less in both the pump feed and the bath under the flux than 0.1%

Flux: NaCl

KCl

MgCl ₂

AlCl ₃

Metal:% Mg used, withdrawn% Mg mid-flow temperature

example
8Λ
23.1 example
8B
22.3 Example 1
■ ac
22.3 23.0 22.5 23.1 46.5 45.9 47.0 7.4 9.3 7.6 0.06 0.30 0.46 0.02 0.08 0.15 710 to
74O ° C 710,.
74O ° C 710 to
740OC

The metal samples given above were: used: Sampling directly from the pump flow deducted: sampling after the pump flow the

Flux layer passed.

So it is possible when passing in the form of a simple cascade of a flux layer about 25 cm thick, remove up to 0.3% magnesium per pass without a more perfect contact is evidently attempted.

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Claims (12)

Claims 1. Chlorination process to remove impurities from molten aluminum or from a molten aluminum alloy / which contains predominantly aluminum by weight, characterized in that one the molten aluminum with a flux layer which contains at least part of the amount of chlorinating agent required to react with the impurities, covers under conditions where. 'the flux does not thermally decompose to smoke. 2. The method according to claim 1, characterized in that the removal of the impurities by using a predetermined amount of the chlorinating agent regulated in the flux layer. 3. The method according to claim 1, characterized in that at least part of the reaction with the amount of chlorinating agent required for the impurities by introducing a reactive chlorine-containing vapor into which provides for molten aluminum. 4. The method according to claim 3, characterized in that the removal of the impurities by introducing a predetermined amount of the reactive chlorine-containing 109808/1198 Steam in the molten aluminum regulates the supply of the steam is interrupted and the reaction between the flux middle layer and the molten aluminum continues. 5. The method according to any one of the preceding claims »characterized in that a flux layer containing an aluminum chloride double salt is used. 6. The method according to claim 5, characterized in that a flux layer is used which.ein Double salt between aluminum chloride and an alkali metal chloride, alkaline earth chloride or ammonium chloride, e.g. a Double salt of (1) NaCl and AlCl ₃ , (2) KCl and AlCl ₃ , (3) LiCl and AlCl ₃ or mixtures thereof. 7. The method according to any one of the preceding claims, characterized in that a flux containing Na ₃ AlCl ₆ , NaAlCl, KAlCl ₄ , LiAlCl ₄ , MgCl ₂ .2AlCl ₃ or NH ₄ AlCl _{4 is} used. 8. The method according to any one of the preceding claims, characterized in that molten aluminum with a content of magnesium and / or water ^: 109808/1198 substance and / or sodium used as impurities. 9. The method according to any one of the preceding claims, characterized in that the flux with a content of sodium chloride and / or cryolite for Used to increase its melting point. 10. The method according to any one of the preceding claims, characterized in that one works at a metal temperature of 710 ° to 750 ° C. 11. The method according to one of the preceding claims, characterized in that it is carried out in batches. 12. The method according to any one of the preceding claims, characterized in that it is carried out continuously. 109808/1 1 98 Blank page