DE2318857A1 - METHOD FOR ELECTROLYTIC METAL EXTRACTION AND ELECTROLYSIS CELL USED FOR IT - Google Patents

Description

Process for electrolytic metal extraction and therefor ■ Electrolysis cell used

The invention relates to a method for the extraction of metals, in particular aluminum and magnesium, by Electrolysis of their respective metal halides, preferably the chlorides, which in alkali halide melts, preferably alkali chloride melts are included; the invention also relates to the electrolytic cells used in this process.

Cells of the type in question are not limited to the extraction of aluminum and magnesium, but can be used in any system where the metal obtained is heavier than the electrolyte and in the liquid phase from the respective molten,

Dr Ha / Mk _3Ο ββ43 / 0938

Halide used as a solvent (preferably chloride) accrues - e.g. lead, bismuth, zinc, cerium, gallium.

In one embodiment, the invention comprises a system for recovering aluminum or magnesium from their respective halides, with molten metal collecting at the bottom of the electrolytic cell, as in conventional reduction, but with the movable pool of molten metal not necessarily serving as a cathode, which metal is deposited or _: through which current is discharged from the cell. Rather, metal is preferably deposited here on non-consuming electrodes, which are inclined at a relatively small angle of, for example, 5 to 30 ° to the vertical and approximately parallel to the opposite electrodes get lost. Electrode sheets of this type, which do not need to be used up, can be connected alternately to the positive and negative pole of the energy source and thus form a system of parallel electrodes.

According to another embodiment of the invention, need only the end links of a system of parallel "sheets to be connected to the energy source and -those- in between The metal sheets located then function as bipolar electrodes.

It is not necessary and even undesirable that electric current flows through the metal pool accumulated at the bottom of the cell, except for a small fraction.

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An essential feature of the invention is the creation of ways to facilitate the Escape of gas, e.g. chlorine, from the spaces between the electrodes during the electrolysis by means of a suitable gas separation chamber so that the gas is prevented from contacting metal near the cathode surface "to react back".

The invention comprises a method for the electrowinning of metals in molten halide systems wherein metal is deposited on one electrode of a pair of spaced apart electrodes with the opposing surfaces of the electrodes inclined at an angle of between 5 and 30 degrees from vertical run and wherein gas released in the spaces between the electrodes is discharged upwards into a gas separation chamber arranged above this space.

Preferably, the cathode surface on which the Metal is deposited at a positive angle to the vertical and that spaced therefrom Anode surface inclined at a similar negative angle to the vertical. The electrodes are preferred planar, do not need to be and are closely spaced from each other. The one another opposite sides of the electrodes are preferably at an angle of 7 to 20 ° to the vertical inclined.

The surface of the melt and the depth of the liquid electrolyte in the gas separation chamber are preferably sufficient off to gas from the electrolyte into the gas separation chamber

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at about the same speed with which it is generated in the space between the electrodes, to let out. .

In particular, the invention in one of its embodiments relates to a cell structure that "largely takes advantage of compactness by using a system of closely spaced located planar electrodes inclined at relatively small angles (e.g. 5b, is 30 °) to the vertical is made possible, with these cells at high current densities, e.g. above 1 ampere / cm and preferably not operated below 1.5 amps / cm. The distance between electrodes (A.C.D.) is preferably less than 5 cm and suitably between 3.5 and 4.3 cm. In each case the angle at which the Electrodes are inclined with the usual operating parameters; for example, it is expected that the inclination. angle for higher current densities and for smaller electrode spacings (A.CD.'s) are larger. The invention enables thus achieving significant advantages in terms of operating and construction costs.

In the case of aluminum, the size of the reduction cell can be reduced to such an extent that the need for Steel and refractory material about 1/4 as for usual Cells of the same production capacity and the required floor space can be reduced to 1/5 will. Typical cell dimensions for possible electrode configurations, which are determined by calculations the test results obtained in the examples are given in the table below:

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Tabel

Cell type and
Capacity' number of
Electrodes Working
depth d.
Electrodes
(cm) Length of
cell
(cm) Width of
Cell (cm) height of
Cell (cm) surface
(rr?) floor
area
(m ^§ ) 1
¹ OI .Monopolar
150,000 amps 3 91.4 15.2 19.5 12.7 11.7 4.18 I. O Monopolar
150,000 amps 2 91 »4 24.4 11.4 12.7 ■ 15.8 4.9 co
OO
Jp-
to Monopolar
150,000 amps 4th 61.0 18.5 17.5 10.2 13.7 4.65 Ό938 Bipolar
37,500 amps 2. 61.0 34.3 10.2 10.2 14.9 5.0 Bipolar
25,000 amps 3 61.0 22.9 14.0 10.2 ai, 4 - 4.65

Annotation; Bipolar cells have similar production capacities as monopolar cells,
however, work with lower cell currents.

Because of the simplified design and greatly reduced The size of the cells according to the invention can be calculated so that the investment costs are reduced to about 1/4 of the usual Cells are degraded at 150,000 amps accumulating can and that the total cost of the electrolysis system can be reduced to about 1/4 that of a conventional system.

In the manufacture of magnesium, the cost of low-density electrolyte cells can be avoided in the same way by a factor of 2 to 3 compared with cells used in conventional methods or compared with magnesium cells of the Hall type, which electrolysis with use comparable low density, be reduced. ■

A significant advantage when operating the with vertical dry electrode operating cells according to the invention is generally that there are no restrictions on cell current or current density; such Constraints always stick to normal cells working with liquid cathodes due to the high currents caused magnetic stirring effect. The one on the elimination of the liquid cathode and on the improved cell geometry According to the invention to be attributed removal of this restriction means that now cells with a Capacity of several hundred thousand amps can be built. In addition, the electrode gap values become stable maintained without the electrodes being adjusted or the level of the accumulated at the bottom of the cell Metal pools needs to be regulated.

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Because of the stability of the gap between the electrodes and the lack of turbulence due to magnetic agitation the invention enables the operation of inclined cathode chloride reduction cells at substantially electrode spacing smaller than is practicable in normal cells. Because a considerable proportion the energy consumed in common electrolysis cells is dissipated as heat (due to resistance effects), The new electrode geometry according to the invention enables not only savings in electrical energy but also a simplification of the problem of heat dissipation from large cells.

It has been found that an important condition for the successful operation of cells with tightly packed inclined electrodes with high current density in them exists, a suitably constructed gas separation chamber to create- "models. of obtained by the anode reaction Gas-liquid flow patterns have shown that a sufficient depth of liquid electrolyte and sufficient liquid-gas interface above the Cathode must be present so that a complete gas separation from the electrolyte at approximately the same rate, with which the gas is generated in the anode reaction is possible. The gas pumping effect der .Anode reaction generated in the vicinity of the interface between melt / gas eddies. If the speed the gas evolution from the melt because of a fail sufficient free surface is too small, gas that has not escaped can continue to circulate in the vortex pattern, where it accumulates and causes the formation of a layer of foam, the thickness of which increases until it extends into the area between the electrodes.

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In addition, if the rate of gas evolution, with in other words the current density in a cell with ge. the given electrode spacing increases, a point is reached which gas is carried along by the melt returning to the electrode space.

The electrode spacing, i.e. the space between Electrodes (A.C.D.) possesses an additional important Effect because the melt returns to the space between the electrodes after the gas has been pumped up to the surface can interact with the ascending stream of gas and liquid. As a result, gas is deflected from the upward current and directed back down into the electrode gap. For a given rate of gas evolution, i.e. current density, an increase in A «eliminates C.D. this effect. For a given total rate of gas evolution there is therefore an optimal A.C.D., which is the best compromise between avoiding gas recirculation and increasing the cell voltage of the increasing current path. For current densities close to 1.5 amps / cm and using electrodes with one has work steps of up to about 60 cm, which are inclined at an angle of 10 ° to the vertical get an A.C, D. of about 3.8 cm has proven to be about optimal.

These are two critical sizes of the gas separation chamber

Width of the surface of the melt (i.e. the surface

between the liquid electrolyte and gas) in the

Gas separation chamber and the depth of the liquid electrolyte in

the gas separation chamber above the cathode. These two

Large ones are shown in Fig. 1 of the drawing as S or «, D,

30 9843 / 0-9 3 8

In Fig. 1, 1 denotes the anode, 2 the cathode, 5 the liquid electrolyte in the gas separation chamber Above the cathode 2, 8a shows the mirror of the static melt, S shows the width of the surface of the melt, D the depth of the electrolyte in the gas separation chamber above the cathode, L the length of the Cathode and M den A.C, D. (the space between Electrodes). -

This model study says that for electrodes that are inclined at an angle of 7 to 15 ° to the vertical are abundant or minimum values for S using the empirically derived formula:

ς ο _v L " C _ 1.5 LC (Formula A) S = 8 χ ^ χ Y ₇₅ - χ - ^ - = -3JP

can be obtained, where S has the dimension inches, C is the numerical value of the current density in amps / cm, L is the numerical value of the cathode length in inches, and M is the numerical value of the electrode spacing (A.C.D.) in inches. The width of the surface of the melt and the depth of the liquid electrolyte in the gas separation chamber are -preferably not less than twice the electrode gap and are preferably not less than about 10 cm (4 inch). Preferably S is no greater than D.

The use of vertical electrodes. In cells for the

Production of both aluminum and magnesium results in, for example, already known from US-PS2 512 157. The cell described therein is limited to the purification of impure solid Ai _for i _n i _{uman0 (s} in chloride electrolyte by deposition of solid aluninium on Aluminiumkatoden However. Since There is no provision for adequate

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Gas discharge taken from the space between the electrodes If this cell is used for the electrowinning of aluminum, the power output would be low. Previous methods of extracting aluminum such as those disclosed in U.S. Patents 2,959,533 and 3,382,166 and 3,352,767 described, working with a varibal A.C.D. and therefore do not see sufficient. Gas separation before. In these patents, atch is the usual use Cryolite-AlpO- ^ - electrolyte described, including - the consumed carbon anodes, which in one

such a system are indispensable. ■ ■

In the case of magnesium, the usual electrolytic cells used to reduce magnesium chloride are used \ vertical anodes in connection with very dense electrolytes, i.e. with electrolytes that are heavier than what is produced molten magnesium, which is why intricate cathode structures to collect the molten magnesium at the Surface of the melt are required. Although today ■ Low density chloride electrolytes that collect of magnesium on the cell floor are known to are the current ones using such electrolysis Cells are built quite differently than those according to the invention Cells.

In U.S. Patents 2,468,022 and 2,696,688 there is a magnesium cell described with bipolar electrodes of a very complex design, the vertical electrodes used, but deviates from the present invention in many essential points. The ones there too; solving Tasks consist of the construction of the electrolysis

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To simplify space, an improved gas seal to give and increase the capacity of the cells by adding a larger number of electrodes than in the usual Device are provided. These tasks are, however solved only at the expense of an extensive complication of the entire cell structure. So is a separate one Feed room with two or three compartments together with a molten salt distribution system required, either from a storage space above the center of the cell or from a row of in the walls of the cell housed distribution ducts is required. There is also a pump for molten salt to circulate the electrolyte needed.

The cell described in the foregoing U.S. Patents is based on the forced circulation of melt to remove magnesium from the gap between the electrodes in cells in which melts with a higher density than magnesium are used. In these cells the molten metal flows to the surface. The cell is said to operate at 0.43 to 0.45 amps / cm is typical of common practice. However, the current output should be about 75? 6 and it should be noted that no actual operating conditions are described, this low power output is not surprising since the construction of the cell appears extremely unsuitable for a safe separation of chlorine from magnesium. Considerable gas pockets between the electrodes must occur, since not only do the electrodes have no inclination at all, but also the gap between the electrodes is narrow up to and beyond the surface of the melt.

309843/0938

The cell described does not even come close to being compact and performance of the cell of the invention, namely because of the use of low current densities and in particular because of the lack of means for adequate chlorine separation, which leads to the low power output. Further make the cost of the additional components required largely negate the claimed benefit that more electrodes with smaller A.C.D. in the electrolysis room than to be housed in a normal facility.

U.S. Patent 3,396,094 discloses the lengths that one must achieve the current output in conventional cells by modifying the method of accumulation of magnesium on the surface of the melt. U.S. Patent 3,418,223 shows the wasted space within a cell that results from the use of a two-piece cathode to collect metal on the surface the melt results and it also shows the structural complexity of the typical chlorine collection chamber. In both cells described above can only an incomplete separation of chlorine from the melt can be expected, since sufficient free Surface for gas separation is missing.

An essential feature of an embodiment of the invention consists in that the cathode surface is at a positive angle of e.g. +5 to 30 ° to the vertical is inclined and a parallel or nearly parallel planar anode which is at a negative angle of is inclined, for example, -5 to 30 ° to the vertical, opposite. In other words, it is important for this embodiment of the invention that the work surface

309843/0938

the cathode is arranged so that its surface is light looks up and that the corresponding surface of the anode looks slightly down.

The gap between the electrodes is preferably less than about 5 cm and expediently between about 3 and 4.6 cm (1.2 and 1.8 inches). As discussed in detail above, an examination of the path of circulation of the melt leads to the assumption of a preferred distance anode - cathode '

of about 3.8 cm (1.5 inches) at current densities of 1.5

2 2

Amps / cm to 2.0 amps / cm.

Other important parameters in the construction of the gas separation chamber are the depth of the electrolyte above the cathode and the Width or the surface area of the electrolyte in the gas separation chamber. It was found that a gas separation chamber, that of the anode shoulder about 10 to 12.5 cm (4 to 5 inches) back across the space: between the electrodes and over the tip of the cathode is sufficient for twelve inch cathodes (30.5 cm). For other values of the cell parameters is the above formula A within the specified range of the electrode inclinations applicable. ·

The very sizeable and somewhat surprisingly cheap one Effect of the inventive electrode arrangement is demonstrated by a comparison of FIGS. 2 and 3 of the drawing, which the operation of a less favorable or explain a more favorable cell configuration.

In Figs. 2 and 3, 1 denotes the anode with active anode surfaces 1a, 2 denotes the cathodes with active ones

309843/0 93 8-

Cathode surfaces 2a, with 8 the electrolyte, with 8a the surface of the electrolyte and with 10 the gap between the electrodes designated.

A shows the area of strong gas formation and B shows areas less strong gas formation. In Fig. 3, 9 denotes the gas separation chamber immediately above the Cathode 2.:

In Figs. 2 and 3, the inclination of the active electrode surfaces was about 10 degrees from normal and the electrode spacing (A.C.D.) was about 3.8 cm (1.5 inches). In

In Fig. 2, the current density was 1 ampere / cm and in Fig. 3

it was 2 amps / cm. In Figure 2, the depth of static electrolyte above the working surface was Cathode within electrode gap about 5 cm (2 inches); in Figure 3 the depth of the electrolyte at rest was about 10 cm (4 inches) above the working surface of the cathode within the gas separation chamber. The width of the Electrolyte surface area was 3.8 cm (1.5 inches) in Figure 2 and about 10 cm (4 inches) in Figure 3.

As can be seen, one of those shown in FIG Conditions a lot of gas is retained between the electrodes, even at a fairly low current density

p "

of 1 amp / cm. Operation under these conditions resulted in a reverse reaction of about 30% of the product, in other words a current output of 10% or less.

Fig. 3 illustrates the effect you get when using a Cell and a gas separation chamber according to an embodiment

309 8 4 37 09 38.

form of the invention achieved in the electrolysis. Operation with improved gas separation under the conditions shown in FIG. 3 conditions shown increased the power output to about 90%. A feature of the embodiment shown in FIG of the invention, compared with the cell structure shown in Fig. 2 is that the width and the depth of the gas separation chamber 9 immediately above the working surface of the cathode 2a is sufficient to ensure that (a) that in the electrode gap 10 gas formed during the electrolysis largely discharged from this space 10 into the gas separation chamber 9 and that (b) this gas is largely freed in the gas separation chamber 9 from the electrolyte. Preferably the width and / or depth of the gas separation chamber 9 are at least twice the electrode spacing (A-C.D.) The cell arrangement described above greatly reduces the reverse reaction that would otherwise occur between the gas and the metal in the vicinity of the cathode surface 2a (see Fig.2) would occur and thus increases the current output of the cell significantly.

Fig. 4 shows a schematic side elevation of one form of a cell according to the invention with a plurality of electrodes. The overall dimensions of the cell are preferably those given in Table 1. 1 denotes the graphite anodes, their electrolytically active surfaces 1a inclined at a negative angle of about 10 ° to the vertical are; these anodes have paragraphs 4 to form a gas outlet chamber 5, the dimensions of which are preferred correspond to formula A and which have a reasonable speed the gas development from the surface 8a of the melt guaranteed. 2 denotes the cathodes that for the production of aluminum from graphite and for the production

30984 3/0928

of magnesium can consist of hollow steel structures or compact steel sheets; 2a are the cathode surfaces, which are inclined at a positive angle of approximately 10 ° to the vertical and approximately parallel to; the anode surfaces 1a run and 3 means the steel container lined with refractory material. 8 is the electrolyte and 6 are the electrical power connections for the anodes. Connections for the cathodes are not shown; these can optionally be applied directly to the container 3. It should be noted that in each cell type, the anode (s) must be positioned vertically or almost vertically to adjust or re-adjust the A.CD. are adjustable.

Fig. 5 shows a schematic side elevation of a more compact one Electrode arrangement, namely the one using bipolar electrodes Arrangement. The reference symbols used do not denote the same parts as in FIG. 4. 1 is the graphite anode whose working surfaces 1a according to FIG. of the invention, 2 are the bipolar electrodes with working surfaces 2a; these electrodes 2 can be made from consist of monolithic graphite blocks resting at their ends on the insulating walls of the cell. 3 denotes the collector cathodes, which in the case of magnesium are made of steel, but in the case of aluminum are made of graphite and 3a means the work surfaces the cathodes 3. With 4 is the outer steel container lined with refractory material and with 5 is the Designates gas outlet chamber, which is preferably dimensioned according to formula A. "The insulating lower supports 6 for the bipolar electrodes 2 serve as brakes for reducing leakage current.

30 9843/0938

Example 1 -. -

An experiment was carried out in a single inclined electrode cell of the general type shown in FIG Form driven. The effective electrode area

2 "

was about 1,000 cm. The electrolyte composition was 21% MgCl ₂ - 75% KCl - 4% LiCl and a total cell current of 400 amps was applied at a temperature of 850 ° C. The anode / cathode incline was 9 from vertical, which is within the recommended range for effective operation. The other parameters were chosen so that some of the less favorable conditions for gassing could be tested. The use of a melt depth of only 3.8 cm above the cathode together with a current density of only 0.36 amperes / cm turned out to be the worst. Under these conditions, a considerable reverse reaction was to be foreseen, since chlorine flows back into the space between the electrodes.

During a 61-minute operation, 404 g of Cl generated and consumed 543 g of MgClp.

The power output was 75%

Example 2-Magnesium

An experiment was carried out using a cell with a single anode and with the general design shown in FIG.

3098 43/09 3 8

ρ
area of about 1000 cm.

The electrolyte composition was = 21% MgClp, 75% K Cl and 4% LiCl.

The anode / cathode inclination was 9 ° to the vertical and was within the recommended range for effective operation. The cathode length L was 30.5 cm, S and D were each 10 cm. The operating temperature was 850 ° C, the current density was 0.64 amps / cm and a total cell current of 700 amps was during the Maintain 60 minutes of operation.

801 g CIp were generated and 1077 g MgClp were consumed, so that the power output was 88%.

Example 3-Magnesium

A second experiment was carried out in the same cell as in Example 2 using a 22% MgClp, 29% KCl and 50% LiCl existing electrolyte driven. The operating conditions were chosen so that resulted in an optimal combination of cell parameters.

The current density was increased to 1.5 amps / cm and the cell was provided with a melting depth of 10 cm the cathode operated at a temperature of 85 ° C. L was 30.5 cm and S and D were each 10 cm. During the 45-minute operation, a steady Cell current of 1650 amps used *

1477 g of Cl ₂ were recovered and 1981 g of MgCl ₂ were consumed so that the current output was 90%.

30 9843/0938

7318857

j Example 4 - aluminum.

An experiment was carried out in the cell of the general design shown in Fig. 3 using a melt which on average consisted of 10% Al Cl, 45/0 Na Cl and 45% K Cl. The dimensions of the cell were those given in example 3. the temperature was 73O ⁰ C. During the 1-hour operation of the cell, the cell current was 1400 amperes.

1857 g of CIp were recovered and 2323 g of Al Cl- * became consumed.

The average power output was thus 89%.

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Claims (28)

Claims' 1. Process for the electrowinning of metals molten halide systems, characterized in that metal on one of a pair in an approximately parallel spaced electrodes is deposited, with the opposing surfaces ^ - of the electrodes are inclined at an angle between 5 and 30 to the vertical, and that in the electrode gap released gas is discharged upwards into a gas separation chamber, which is located above the space between the electrodes located * 2. The method according to claim 1, characterized in that the cathode surface on which the metal is deposited at a positive angle to the vertical and that the anode surface located therefrom inclined at an equal negative angle to the vertical is. 3. The method according to claim 1 or 2, characterized in that the electrodes are planar and no consumption anodes and are closely spaced from each other. 4. The method according to any one of claims 1 to 3, characterized characterized in that the opposing electrode surfaces are at an angle between 7 and Are inclined by 20 ° to the vertical. 30 9843/09 38 5. The method according to any one of claims 1 to 4, characterized in that that the surface of the melt and the depth of the liquid "electrolyte in the gas separation chamber to discharge gas from the electrolyte into the gas separation chamber at approximately the same speed that the gas is generated in the electrode gap are sufficient. 6. The method according to any one of claims 1 to 5, characterized characterized in that the width of the surface of the melt in the gas separation chamber is not less than LG 3M where (1) the electrodes are at an angle between 7 u: are inclined between 7 and 15 ° to the vertical (2) C is the current density in amperes / cm (3) L is the cathode length in inches and ' (4) M is the electrode gap in inches. 7. The method according to any one of claims 1 to 5, characterized characterized in that the width of the surface the melt and the depth of the liquid electrolyte in the * gas separation chamber are each not less than that Be twice the electrode spacing. 8. The method according to "one of claims 1 to 5, characterized in that the width of the surface of the melt 309843/0938 and the depth of the liquid electrolyte in the gas outlet separation chamber should not be less than 10 cm each. 9. The method according to any one of claims 1 to 8, characterized in that that a pool of molten metal is formed under the electrodes, but not as Cathode is used on which metal is deposited. 10. The method according to any one of claims 1 to 9, characterized in, that deposited as metal aluminum or magnesium will.. IT. Method according to one of Claims 1 to 10, characterized in that
characterized in that the metal is deposited by electrolysis of its halides contained in an alkali halide melt. 12. The method according to any one of claims 1 to 11, characterized in that that the metal is deposited on the cathodes of a plurality of pairs of electrodes arranged in parallel. _. · 13. The method according to any one of claims ί to 12, characterized characterized in that the electrolysis occurs at a current density 2
of not less than 1 ampere / cm. 14. The method according to any one of claims 1 to 13 »thereby characterized in that the electrode spacing is less than 5 cm. ' 15. The method according to claim 14 _5, characterized in that the electrode spacing is between about 3 _s 0 and 4.6 cm. 309843/0938 16. An electrolytic cell for recovering metal from molten halide systems, comprising a pair approximately parallel, at a distance "located and at an angle between 5 and 30 ° to the vertical inclined electrodes and one over the gap between the electrodes arranged gas separation chamber, into which gas is discharged from the electrode gap upwards. 17. Electrolysis cell according to claim 16, characterized in that that the cathode surface is at a positive angle to the vertical and the anode surface is inclined at an approximately equal negative angle to the vertical. 18. Electrolysis cell according to claim 16 or 1? » through this characterized in that the electrodes are planar and not consuming anodes and are closely spaced from one another to have. 19. Electrolytic cell according to one of claims 16 to 18, characterized in that the electrodes are inclined at an angle between 7 and 20 ° to the vertical are. 20. Electrolysis cell according to one of claims 16 to 19, , characterized in that the surface of the melt and the depth of the liquid electrolyte in the gas separation chamber is sufficient to remove the gas from the electrolyte at about the same speed as it is is generated in the electrode gap, can exit into the gas separation chamber. 309843/0938 21. Electrolytic cell according to one of claims 16 to 20, characterized in that the width of the surface of the melt in the gas separation chamber is not less as LC is, where (1) the electrodes are inclined at an angle between 7 and 15 ° to the vertical (2) C is the current density in amperes / cm (3) L is the cathode length in inches and, (4) M is the electrode gap in inches. 22. Electrolytic cell according to one of claims 16 to 20, characterized in that the width of the surface the melt and the depth of the liquid electrolyte in the gas separation chamber each time not less than twice the distance between the electrodes. 23. Electrolytic cell according to one of claims 16 to 20, characterized in that the width of the surface the melt and the depth of the liquid electrolyte in the gas separation chamber are each not less than about 10 cm. 24. Electrolytic cell according to one of claims 16 to 23, characterized in that the electrode spacing is less than about 5 cm. 30 9843/0938 25 · Electrolysis cell after. Claim 24, characterized in that that the electrode spacing is between about 3.0 and 4.6 cm. 26. Electrolytic cell according to one of claims 16 to 25, characterized by several arranged in parallel Pairs of electrodes. 27. Electrolysis cell according to one of claims 16 to 26, characterized in that a pool of molten metal is formed under the electrodes, which however does not serve as a cathode on which metal is deposited. 28. Electrolytic cell according to one of claims 16 to 27, characterized in that the electrolysis at a Current density of not less than 1 amp / cm is carried out will. 303843/0938