DE2318857B2 - ELECTROLYSIS CELL FOR THE EXTRACTION OF METALS, IN PARTICULAR ALUMINUM AND MAGNESIUM, FROM MOLTEN HALOGENIDE SYSTEMS - Google Patents

Description

.VU

where C is the current density in amperes / cm ² , L is the effective cathode length in cm and M is the distance between the electrodes in cm, and the width of the surface of the melt is not greater than the depth and width of the liquid electrolyte in the gas separation chamber and depth are each not less than twice the distance between the electrodes.

2. Electrolytic cell according to claim 1, characterized in that the width of the surface of the Melt and the depth of the liquid electrolyte of the gas separation chamber are each not less than

10 cm.

3. Electrolytic cell according to claim 1 or 2, characterized in that it is below the Electrodes has a bath of molten metal, but which does not serve as a cathode, on the the metal is deposited.

4. Electrolytic cell according to one of claims 1 to

3, characterized in that it is operated at a current density of not less than 1 ampere / cm ² .

bO

) The invention relates to an electrolytic cell for extraction of metals, especially aluminum I magnesium, from molten halide systems, the two or more spaced less than 5 cm apart, essentially allelic to each other, opposite to the vertical lines Contains non-consumable electrodes inclined at an angle between 7 and 15 ° the surface of the negative electrode (catho de) at a positive angle with respect to de Vertical is inclined, while the surface of the positive electrode (anode) is under a similar one! negative angle inclined to the vertical

Electrolysis cells for the extraction of metals, especially aluminum and magnesium, sine already known For example, US Pat. No. 25 12 15; a cell for electrolytic cleaning unclean! solid aluminum anodes in a chloride electrolyter described umkathoden under the deposition of solid aluminum on aluminum, in which the electroder are arranged vertically. In U.S. Patents 29 59 533, 33 82 166 and 33 52 767, electrolytic cells are used for the extraction of aluminum using a cryolite / AbOj-ElektroJyten described in dej Consuming carbon anodes are used and the distance between the electrodes is variable. ir de »US Patents 2,468,022 and 2,696,688 is one Electrolysis cell for the production of magnesium be written, the bipolar, vertically arranged electro which has and has a very complicated structure Multi-cell furnace for the electrolytic production of aluminum from alumina described in the bipolar Electrodes are used whose active surface is at an angle of more than 45 ° with respect to the Vertical is inclined. Cells for electrolytic Extraction of metals are also in US Patents 33 96 094 and 34 18 223 and in US Pat US Pat. No. 3,067,124, the latter being an electrolytic cell for the production of aluminum relates, which has two or more electrodes arranged at a distance of less than 5 cm, the are inclined to the vertical at an angle between 7 and 15 ° so that the surface the cathode has a positive angle and the surface of the anode has a similar negative angle with the Form verticals.

However, the electrolytic cells described in the above-mentioned prior publications have the Disadvantage that the chlorine formed during the electrolysis of the halide melt is insufficient Dimensions are separated from the melt, so that considerable gas inclusions between the electrodes occur that allow the operation of these electrolytic cells only at a relatively low current density and limit the achievable current yield.

The object of the invention is to provide an electrolytic cell for the extraction of metals, in particular from Specify aluminum and magnesium from molten halide systems in which the above The disadvantages described do not occur, with the help of which it is possible in particular to prevent the occurrence of undesired gas inclusions in the electrolyte melt, which limit the applicable current density, to prevent and to improve the achievable current yield. It has now been found that this The object can be achieved in that one between the electrodes and above the same one provides gas separation chamber which is connected to the electrode gap and into which the in the gas developed between the electrodes can escape upwards.

The invention relates to an electrolytic cell for the Extraction of metals, in particular aluminum

<nd magnesium, from molten halide systems, which contain two or more electrodes which are less than 5 cm apart, essentially parallel to one another and inclined to the vertical at an angle between 7 and 15 °, which do not consume one another, wherein the surface of the negative electrode (cathode) is inclined at a positive angle with respect to the vertical, while the surface of the positive electrode (anode) is inclined at a similar negative angle with respect to the vertical, and is characterized in that a A gas separation chamber in connection therewith is provided, into which the gas developed in the electrode gap escapes upwards, whereby the size of the surface of the melt in the gas separation chamber and the depth of the liquid electrolyte in the gas separation chamber are coordinated so that the gas from the electrolyte with practically the gl The same speed can be withdrawn into the gas separation chamber as it is formed in the electrode space, the width S of the surface of the melt in the gas separation chamber not less than

LC

3iW

(A / cm ² )

where C is the current density in amperes / cm ² , L is the effective cathode length in cm and M is the distance between the electrodes in cm, and the width of the surface of the melt is not greater than the depth of the liquid electrolyte in the gas separation chamber and width and Depth in each case should not be less than twice the distance between the electrodes.

With the aid of the electrolytic cell of the invention it is possible to do this during the electrolysis of the halide melt resulting halogen and the other evolved gases upwards immediately after their formation dissipate so that no inclusions and vortex patterns arise within the electrolyte melt and the Formation of a foam layer on the electrolyte melt is prevented. This is due to the inclination of the electrodes, which run essentially parallel to one another, at a very specific angle promoted so that it is possible to use the electrolytic cell of the invention with their at a short distance from each other to operate arranged electrodes at a high current density and to achieve a high current yield, as was previously not possible.

Cell type / capacity Number of effective i \\ Electrodes electrodes

¹ 'length

A prerequisite for achieving this advantageous technical effect is that the inclination of the electrodes 7 to 15 ° relative to the vertical is that above the electrode gap and thus in S standing connection a gas separation chamber is provided and that between the different cell dimensions and operating parameters a precisely defined mathematical relationship is maintained.

Particularly advantageous results are obtained if the width of the surface of the melt and the depth of the liquid electrolyte of the gas separation chamber are each not less than 10 cm, if the electrolysis cell has a bath of molten metal below the electrodes, but this does not serve as a cathode, on which the metal is deposited and / or when the electrolytic cell is operated at a current density of not less than 1 ampere / cm ² .

The electrolytic cell of the invention is not limited to the extraction of aluminum and magnesium, but can be used in any system in which the metal obtained is heavier than the electrolyte and in the liquid phase from the respectively molten halide serving as solvent, preferably the chloride, is obtained, for example for the production of lead, bismuth, zinc, cerium and gallium.

The electrolytic cell forming the subject of the invention has a compact structure, the electrodes used therein are preferably flat, parallel to one another and inclined at an angle between 7 and 15 ° with respect to the vertical. It is operated at high current densities, for example at current densities of more than 1 ampere / cm ² , preferably not below 1.5 amperes / cm ² . The distance between the electrodes is less than 5 cm, expediently between 3 and 4.6, preferably between 3.5 and 4.3 cm. The angle of inclination of the electrodes varies depending on the other operating parameters; it becomes larger, for example, with higher current densities and smaller electrode spacings. This makes it possible to manufacture and operate the electrolytic cell of the invention in a technically simple and economical manner.

In the extraction of aluminum, the size

the reduction cell can be reduced so far that the

^{Requires only about 1} A for steel and refractory material

that for common electrolysis cells of the same product

tion capacity is required and the

required floor space can be reduced to 1/5

be like that. Some typical cell dimensions for inven

Correctly applicable electrode configurator

result from the following table.

Monopolar / 3rd
150000

Monopolar / 2nd
150,000

Monopolar / 4th
150,000

Bipolar / 37 500 2
Bipolar / 25,000 3

91.4 91.4 61.0

61.0 61.0

Length of
cell
(cm) Width of
cell
(cm) height of
cell
(cm) surface
(m ² ) floor
area
M. 15.2 19.5 12.7 11.7 4.18 24.4 11.4 12.7 15.8 4.9 18.5 17.5 10.2 13.7 4.65 34.3
22.9 10.2
14.0 10.2
10.2 14.9
11.4 5.0
4.65

Note: Bipolar cells have similar production capacities as non-polar cells, but work with lower! Cell currents.

Because of the simpler structure and smaller size of the electrolytic cell of the invention, the investment cost can be estimated at about Wa that of conventional electrolytic cells with a capacity of 150,000 amperes (A). In connection with the lower operating costs, total costs of the electrolysis cell of the invention thus result, which are also only about Wa of the total costs of comparable conventional systems.

In the production of magnesium, the cost of having electrolytes is of a low density working cells in a corresponding way by a factor of 2 to 3 less than with conventional electrolysis cells for the production of magnesium, for example those of the Hall type, in which electrolytes with a comparably low density can be used.

Another major technical advantage achieved by the electrolytic cell of the invention insists that the previously existing restrictions with regard to the applicable cell current and the applicable current density does not apply, as is the case with conventional working with a liquid cathode Electrolysis cell as a result of the magnetic stirring effect caused by the high cell currents have always passed. The elimination of the liquid cathode and the improved cell geometry in the Electrolytic cell of the invention lead to the fact that now electrolytic cells with a capacity of several hundred thousand amps can be built that the spacing between the electrodes can be kept constant without the electrodes being adjusted or the level of the at the bottom of the Electrolytic cell accumulated metal bath need to be regulated. Since a significant proportion of the in conventional electrolysis cells consumed energy (as a result of resistance effects) in the form of Heat must be dissipated, it is not only possible with the electrolytic cell of the invention, Saving electrical energy, but also the problem of heat dissipation from large cells simplify and solve.

When the electrolytic cell of the invention is operated at current densities of about 1.5 to about 2.0 A / cm ² and when the electrodes have an effective length (working length) of up to about 60 cm and are inclined at an angle of 10 ° to the vertical a distance between the electrodes of about 3.8 cm has proven to be optimal.

Two critical sizes of the gas separation chamber contained in the electrolytic cell of the invention are the width of the surface of the melt (ie the surface between the liquid electrolyte and the gas) in the gas separation chamber (denoted by 5 in FIG. 1 of the accompanying drawings) and the Depth of the liquid electrolyte in the gas separation chamber above the cathode ( designated as D in FIG. 1).

For the electrodes, which are inclined at an angle of 7 to 15 ° to the vertical, the Minimum value for S amounts:

S - S

24

1.5

1.5 A- /

= ^LC r ~ ^A ~ i

3 Λ / L cm ² J

where C is the current density in A / cm ² , L is the effective cathode length in cm and M is the distance between the electrodes in cm. The width of the surface of the melt (S) and the depth of the liquid electrolyte (D) in the gas separation chamber are preferably not less than twice the distance between the electrodes, and it is preferably not less than 10 cm. 5 is preferably not greater than D.

The considerable and surprising technical effect achieved by the present invention results from a comparison between FIGS. Ί and 3 of the accompanying drawings, showing the operation of a less cheap and a cheaper cell

ίο explain baus.

The invention is described in more detail below with reference to the drawings.

The F i g. 1 shows an anode 1, a cathode 2, the liquid electrolyte 5 in the gas separation chamber above the cathode 2, the mirror 8a of the static melt, the width S of the surface of the melt, the depth D of the electrolyte in the gas separation chamber above the cathode, the effective Length L of the cathode and the distance M between the electrodes.

In the F i g. 2 and 3, the number 1 denotes the anode with the effective anode surfaces la, the number 2 the cathode with the effective cathode surfaces 2a, the number 8 the electrolyte, the number 8a the surface of the electrolyte and the number 10 the space between the electrodes. The number 9 designates the gas separation chamber arranged directly above the cathode 2. The letter A shows the area of strong gas formation, while the letter B shows the area of less strong gas formation.

In the F i g. 2 and 3, the inclination of the effective electrode surfaces relative to the vertical is about 10 ° and the distance between the electrodes is about 3.8 cm. The current density in the case of FIG. 2 1 A / cm ² and in the case of FIG. 3 2 A / cm ² . The depth of the static electrolyte above the effective area of the cathode within the space between the electrodes is in the case of FIG. 2 about 5 cm and in the case of FIG. 3 it is about 10 cm (inside the gas separation chamber). The width of the electrolyte surface is 3.8 cm in the case of FIG. 2 and 10 cm in the case of FIG. 3.

Among the in F i g. 2, even with a low current density of only 1 A / cm ^2, a great deal of gas is retained between the electrodes. Operation under these conditions resulted in a reverse reaction of about 30% of the product, ie in other words a current efficiency of only 70% at most.

The F i g. 3 explains an electrolytic cell constructed according to the invention with improved gas separation, when they were operated, the current yield increased to around 90%. The essential feature of this electrolytic cell is that compared to the in

F i g. The electrolytic cell shown in FIG. 2 shows the width and the depth of the melt in the gas separation chamber 9 immediately above the effective area of the cathode 2a are sufficient to ensure that the in the electrode space 10 formed during the electrolysis gas largely into the gas separation chamber 9 is discharged and that this gas within the gas separation chamber 9 largely from the electrolyte is released. The width and depth of the melt in the gas separation chamber are preferably min-

at least twice the distance between the electrodes. This makes it possible to use the related on the F i g. 2 reverse reaction between the gas and the metal! near the cathode burner

before 2a to avoid and the current efficiency of the cell to increase significantly.

4 shows a schematic cross section by an embodiment of an electrolytic cell according to the invention with several electrodes. The dimensions of this electrolytic cell correspond to the values given in the table above. The number 1 denotes the graphite anodes whose electrolytically effective surfaces 1 a at a negative angle are inclined by about 10 ° to the vertical. These anodes have paragraphs 4, the one Form gas outlet chamber 5, the dimensions of which correspond to the general formula given above and an adequate rate of gas evolution from the surface 8a of the melt guaranteed. The number 2 designates the cathodes, which are used for the extraction of aluminum from graphite and for Extraction of magnesium from hollow steel bodies or from compact steel sheets. the Number 2a indicates the cathode surfaces, which are at a positive angle of about 10 ° with respect to the Verticals are inclined and run approximately parallel to the anode surfaces la. The number 3 denotes the steel container lined with a refractory material. The number 8 stands for the electrolyte and the number 6 indicates the electrical power connections for the anodes. The connections for the cathodes are not shown. If necessary, these can be applied directly to the container 3.

5 shows a schematic cross section by a more compact embodiment of the electrolyte cell of the invention with bipolar electrodes. the Numbers indicated have the same meanings as in FIG. 4. The number 1 denotes the Graphite anode, the working surfaces of which are inclined la Numeral 2 denotes bipolar electrodes with the working surfaces 2a, which are made of monolithic graphite blocks may exist, resting at their ends on the insulating walls of the cell. The number 3 denotes collector cathodes, which in the case of the extraction of magnesium from steel, in the case of Extraction of aluminum consist of graphite and the number 3a denotes the working surfaces of the Cathodes 3. The number 4 denotes the outer steel container lined with a refractory material and the number 5 denotes a gas exit chamber, the dimensions of which are those given above correspond to the general formula. The insulating lower supports 6 for the bipolar electrodes 2 are used “Is braking for a reducing leakage current.

The invention is illustrated in more detail by the following examples

Example 1 (extraction of Mg)

In a cell with a single inclined electrode with the one shown in FIG. An experiment was carried out in the structure shown in FIG. The effective electrode area was 1000 cm ² . Electrolyte composition: 21% MgCh - 75% KCl - 4% LiCl. A total cell current of 400 amps at a temperature of 850 ° C was applied. The anode / cathode inclination was 9 ° from the vertical. The other parameters were chosen so that some less favorable gas delivery conditions could also be tested. A melting depth of only 3.8 cm above the cathode together with a current density of only 0.36 amperes / cm ² proved to be the worst. Considerable reverse reaction occurred under these conditions as chlorine flowed back into the electrode space.

During 61 minutes of operation, 404 g Ch is formed and 543 g of MgCh are consumed. The current efficiency was 75%.

Example 2 (extraction of Mg)

Using a single anode cell with the method shown in FIG. 3, with an effective electrode surface of 1000 cm ² , an experiment was carried out.

Electrolyte composition: 21% MgCh, 75% KCI and 4% LiCl.

The anode / cathode inclination was 9 ° from the vertical. The effective cathode length L was 30.5 cm, 5 and D were each 10 cm. The operating temperature was 850 ⁰ C, the current density was 0.64 amps / cm ² and 60 minutes during the operating period a total cell current of 700 amps was maintained.

801 g of Ch were formed and 1077 g of MgCh were consumed, so that the current efficiency is 88% fraud.

Example 3 (extraction of Mg)

In the same cell as in Example 2, using one of 22% MgCh, 29% KCl and 50% LiCl existing electrolytes carried out a second attempt. The operating conditions were like that chosen that an optimal combination of cell parameters resulted.

The current density was 1.5 amp / cm ² increases and the cell was at a melt cm depth of 10 operated to the cathode at a temperature of 850 ⁰ C. L was 30.5 cm and S and D were each 10 cm. A constant cell current of 1650 amps was maintained during the 45 minute operation.

1477 g of Ch were formed and 1981 g of MgCl: were consumed, so that the current efficiency was 90 ° / c fraud.

Example 4

(Extraction of Al)

In the cell with the structure shown in Fig was a test using a melt consisting of 10 ° / AlCb, 45% NaCl and 45% KCl carried out. The dimensions of the cell were the same as in Example 3. The temperature was 730 ° C. During the 1 hour operation of the cell, the cell current was 1400 amperes.

1857 g of Ch were formed and 2323 g of AlC were consumed. The current efficiency was som

89%.

For this there are 4 drawings

Claims (1)

Claims; 1. Electrolysis cell for the extraction of metals, in particular aluminum and magnesium, from molten halide systems, containing two or more at a distance of less than 5 cm from each other, essentially parallel to each other, at an angle between 7 and 15 with respect to the vertical ° inclined, non-consuming electrodes, wherein the surface of the negative electrode (cathode) is inclined at a positive angle to the vertical, while the surface of the positive electrode (anode) is inclined at a similar negative angle to the vertical, characterized in, that a gas separation chamber connected to it is provided above the electrode gap, into which the gas developed in the electrode gap escapes upwards, the size of the surface of the melt in the gas separation chamber and the depth of the liquid electrolyte in the gas separation chamber so deviating from one another are true that the gas can be withdrawn from the electrolyte into the gas separation chamber at practically the same rate as it is formed in the electrode gap, the width of the surface of the melt in the gas separation chamber being no less than