DE102010041084A1 - Electrolysis cell for the production of aluminum - Google Patents

Abstract

The invention relates to an electrolysis cell for extracting aluminum from its oxide, comprising a cathode (1) and a circumferential side wall (1a), the side wall (1a) being provided with a number of through openings (1aa) which open outwards into a Overflow pan (10) open. Furthermore, the invention relates to a method for obtaining aluminum from its oxide by melt flow electrolysis using such an electrolysis cell. A continuous and even discharge of the liquid aluminum is guaranteed.

Description

The invention relates to an electrolytic cell for the production of aluminum by fused-salt electrolysis. Furthermore, the invention relates to a process for the production of aluminum by fused-salt electrolysis.

For the industrial extraction of aluminum from its oxide is currently the so-called "Hall-Héroult process" used. This is an electrolysis process in which aluminum oxide (Al ₂ O ₃ ) is dissolved in molten cryolite (Na ₃ [AlF ₆ ]) and the mixture thus produced serves as a liquid electrolyte in an electrolysis cell. The basic structure of such an electrolytic cell for carrying out the Hall-Héroult process is schematically in the 1a to 1c shown, where 1a shows a cross section through a conventional cell while 1b is a side view of the cell from the outside. 1c shows a perspective view of an electrolytic cell.

Under the reference 1 a cathode is shown, which may be constructed, for example, graphite, anthracite or a mixture thereof. Alternatively, graphitized coke-based cathodes can also be used. The cathode 1 is generally in a mount 2 embedded steel and / or refractory material or the like. The cathode can be constructed in one piece as well as from individual cathode blocks. reference numeral 20 denotes the side walls of the electrolytic cell, which together with the cathode form a trough. This tub can also be considered as an inner lining of the enclosure. The side walls can be constructed both in one piece and from individual blocks.

Across the length of the cell is into the cathode 1 a number of power supply bars 3 introduced, wherein in the cross-sectional view of 1a only a single power supply bar 3 can be seen. In 1c It can be seen that each cathode block, for example, two power supply bars can be provided. The power supply bars serve to supply the cell with the electricity needed for the electrolysis process. The cathode 1 opposite there are several cuboidal anodes 4 , where in 1a two anodes 4 are shown. 1c shows a more detailed arrangement of the anodes in an electrolytic cell. In carrying out the process is by applying a voltage between the cathode 1 and the anodes 4 reduces the dissolved in cryolite aluminum oxide to aluminum, wherein the aluminum cations to the molten aluminum - electrochemically seen the actual cathode - move to pick up electrons there. Because of the higher density aluminum accumulates 5 in the liquid phase below the molten mixture 6 made of aluminum oxide and cryolite. The oxygen ions are reduced at the anode to oxygen, which reacts with the carbon of the anodes.

With the reference numerals 7 and 8th are schematically the negative and positive poles of a voltage source for providing the voltage required in the electrolysis process, the value between, for example, about 3.5 and 5 V, characterized.

As in the side view of 1b can be seen, the enclosure points 2 and thus the entire electrolytic cell conventionally has an elongated shape, with numerous power supply bars 3 perpendicular through the side walls of the enclosure 2 are guided. Typically, the longitudinal extent of currently deployed cells is between about 8 and 15 meters, while the width dimension is about 3 to 4 meters. A cathode like this one in here 1a is shown, for example, in the EP 1845174 disclosed.

The high binding energy between aluminum and oxygen as well as heat and resistance losses require a high energy requirement in the production of aluminum via fused-salt electrolysis. The associated energy costs represent a large part of the process costs. Reducing these costs is one of the essential tasks to be accomplished in the field of fused-salt electrolysis. An essential factor in terms of energy efficiency of a fused-salt electrolysis cell is the necessary distance between anode and cathode, more precisely the distance between the anode and molten aluminum. The larger it must be chosen, the higher the specific energy requirement of the electrolysis cell.

The necessary distance between anode and cathode is mainly determined by the magnetic field induced by the extremely high currents of up to approx. 500 kA, the electromagnetic interactions and the resulting wave movements and bulges of the liquid aluminum. In fact, as explained above, the active cathode during electrolysis is the liquid aluminum. Here, however, the cathode is always called a solid plate forming a bottom plate.

Usually, the resulting liquid aluminum is vacuumed off discontinuously, for example once a day. For this purpose, during the process on the top of the electrolyte, ie the mixture of cryolite and alumina, forming crust must be broken to get to the aluminum. Between two Such discharges of aluminum increases the level of the same in the cathode basin. Generally, with an application of aluminum, about 10-20% of the existing liquid aluminum is removed, while the remainder remains in the cathode basin. On average, the filling height with aluminum is about 15-50 cm. Due to the forces exerted on the aluminum by electromagnetic interaction, bulges and waves are formed in the molten aluminum. This implies that the anodes must be spaced further from the surface of the liquid aluminum to avoid shorting than would be the case without undulations. For this reason, it would be desirable if the bulge and wave motion of the molten aluminum melt could be kept as low as possible throughout. In addition, the discontinuous extraction of aluminum represents a significant disturbance of the electrical and thermal equilibrium of the electrolysis cell.

It is therefore an object of the invention to provide an electrolytic cell for recovering aluminum, with which the level of the aluminum melt can be kept constant and stabilized. Furthermore, it is an object of the invention to provide a fused-salt electrolysis process in which a high energy efficiency can be achieved.

This object is achieved by an electrolytic cell having the features of claim 1 and by a method according to claim 11. Preferred embodiments are specified in the respective subclaims.

An electrolytic cell for recovering aluminum from its oxide in accordance with embodiments of the invention has a cathode and a circumferential sidewall, the sidewall being provided with a number of through-holes which open out into an overflow trough.

For the purposes of the invention, the term "cathode" is understood in general terms. It may be z. B. - but not exclusively - to act a so-called cathode bottom, which is composed of a plurality of cathode blocks, so that the core aspects of the invention are realized in the electrolysis cell according to the invention with a cathode bottom as a whole. The term cathode, however, is also intended to refer to the substructures forming such a cathode bottom in the sense of cathode blocks. All the features which may contribute to the invention in connection with a "cathode" do so in the same way in connection with a "cathode block" or "cathode blocks", without this having to be explicitly explained below.

When using an electrolytic cell according to the invention for the production of aluminum by fused-salt electrolysis, it is possible to remove the resulting aluminum continuously, so that the aluminum level in the actual electrolysis cell itself can always be kept at a constant level. Through the passage openings, the reflection of the flowing aluminum on the side walls of the electrolytic cell is advantageously reduced. As a result, the aforementioned wave formations can be reduced, which is why the anode or the anodes of the electrolytic cell can be brought close to the aluminum surface without the risk of a short circuit. However, this also means that the distance between the anode (s) and the cathode can be reduced and thus the specific energy requirement for the fused-salt electrolysis process can be reduced compared to the prior art. The continuous discharge of the aluminum formed stabilizes the operating behavior of the cell, since the conditions within the cell do not change or hardly change over time.

Advantageously, in one embodiment of the electrolytic cell according to the invention, a collecting channel is arranged on the outer circumference of the overflow trough such that liquid (ie in particular liquid aluminum) passing over the upper edge of an outer edge of the overflow trough flows into the collecting trough. Such an embodiment facilitates a continuous discharge of the liquid aluminum formed in the fused-salt electrolysis.

The aluminum which accumulates above the cathode during the process enters the overflow trough in this embodiment via the passage openings formed in the circumferential side wall. The level of liquid aluminum which forms in this way has the same or almost the same height in the overflow trough and in the basin of the electrolysis cell. If further aluminum forms in the electrolysis cell during molten-salt electrolysis, the level rises in the cathode basin and in the overflow trough. If it reaches the upper edge of the outer edge of the overflow trough, so flows in a further increase in the level of aluminum over the edge out into the gutter and can be removed from there. In this way, the aluminum level within the cathode bowl never rises above a certain level dictated by the height of the top edge of the outer edge of the sump.

At least some of the passage openings in the circumferential side wall of the electrolysis cell, in particular all passage openings, may advantageously be formed at the same height above the cathode. This facilitates a uniform Outflow of liquid aluminum into the drip pan.

It has also proven to be particularly favorable when the cathode is horizontal. In this way, in carrying out the above-mentioned fused-salt electrolysis, the level of the resulting aluminum at any point within the basin is at least nearly the same, and thus uniform process conditions can be maintained over the entire area of the cathode.

The overflow trough according to an embodiment of the invention on outer walls, which are provided with a thermal insulation. This thermal insulation performs the function of preventing too rapid cooling of the molten aluminum. In order to maintain the effect of keeping the aluminum level constant by means of an overflow construction, which can be achieved with the electrolysis cell according to the embodiments of the invention, it is necessary for the aluminum to remain in its liquid state until it has been removed from the overflow trough or from the collecting trough is. However, this requires a sufficiently high temperature outside the cathode basin. The insulation of the overflow trough and optionally also of the gutter helps to minimize the unnecessary heat losses on those components.

In a further advantageous embodiment of the electrolytic cell, the passage openings are formed equidistant from each other in the circumferential side wall. In this way, the outflow of liquid aluminum, d. H. the aluminum melt, largely uniform and uniform, with the formation of turbulence and waves within the cathode basin during outflow is largely excluded. For the same reason, it is favorable not to keep the number of through holes too small. In particular, a number of about 2 to 5 through holes per m length of the side wall has been found to be particularly suitable.

As for the size and shape of the through holes, they may have, for example, a diameter between 3 and 15 cm, if their cross section is circular, which is advantageous in view of the flow conditions. If a cross-sectional shape other than a circular one is selected, the equivalent diameter can be appropriately designed in consideration of the above values. By "equivalent diameter" is meant any dimension of the cross-section that results in a cross-sectional area corresponding to a circular area of that diameter. It can also be a rectangular cross section advantageous, wherein a width of the cross section may be greater than its height.

According to one embodiment of the invention, the circumferential outer wall of the cathode is arranged rotationally symmetrical about a central pillar. In this case, the outer wall in plan view may have a circular shape or a regular polygonal shape. In this context, "rotationally symmetrical" is understood to mean any shape that can be made to coincide with the original shape when rotated about the center with a rotation angle of less than 360 °. Examples of such outer wall profiles may also be regular polygons. The rotational symmetry causes a uniform outflow of the molten aluminum over the entire area of the basin of the trough-shaped cathode.

The above-mentioned central column may be tapered downwardly radially outwardly. This is particularly advantageous with regard to the filling of the cathode basin, as will be discussed in more detail later.

With regard to a versatility of the possible use of the electrolytic cell, it is advantageous if the lateral outer wall of the overflow pan is adjustable in height. Since the height of the lateral outer wall, that is the height of the upper edge of the outer edge over the passage openings determines the height of the aluminum level within the cathode basin, the aluminum level level can be varied quickly and easily as required with a height-adjustable lateral outer wall. For the adjustment of the height of the side wall may be provided a mechanical or motorized adjustment.

A process for the continuous recovery of aluminum from its oxide by fused-salt electrolysis, in which the electrolysis cell according to the invention can be used, comprises discharging the aluminum resulting from the fused-salt electrolysis from a collecting trough, which is fed from an overflow of an overflow trough, which passes through through-holes with the interior an electrolytic cell used in fused-salt electrolysis is below the level of aluminum produced in the cathode basin.

Since the aluminum thus flows from the side of the electrolysis cell, it can flow continuously and evenly into the overflow trough, whereby the level of liquid aluminum in the cathode tank is kept constant constantly. As already mentioned, thus movements of the liquid or melt can be largely avoided, so that the surface of the molten Aluminum remains calm in the basin of the cathode and for this reason, the anodes can be guided close to the level of the liquid aluminum, without a short circuit between anodes and cathodes on the aluminum is to be feared. Thus, the energy efficiency of the aluminum manufacturing process can be significantly increased. In addition, a more stable operation is ensured due to the continuous discharge.

In order to ensure the smoothest possible removal of the liquid aluminum, it is advantageous if the melt electrolysis is carried out above a temperature of about 750 ° C, in particular between 930 and 1000 ° C. A lower temperature limit of 750 ° C ensures that the aluminum melt is still sufficiently liquid outside the tank of the electrolysis cell to flow over the edge of the overflow trough into the gutter and can be discharged from there. Under suitable conditions, according to which the heat loss in the outer parts overflow trough and gutter is kept low, it is avoided to fall below the above-mentioned lower temperature limit. However, since such a method is already carried out for technical reasons, advantageously far above the aluminum melting point sufficient flowability of the aluminum is guaranteed without additional measures in general.

The invention will now be explained in more detail with reference to the accompanying drawings with reference to a non-limiting embodiment. In the drawing show:

1a an electrolytic cell for the extraction of aluminum from alumina according to the prior art in cross section;

1b the electrolytic cell of 1a in a longitudinal view from the outside;

1c an electrolytic cell for the extraction of aluminum from aluminum oxide according to the prior art in a perspective view, partially cut;

2a a cross-sectional view of a section of an electrolytic cell according to an embodiment of the invention;

2 B a plan view of the electrolytic cell of 2a ; and

3 an arrangement of anodes corresponding to the cathode form according to 2a and 2 B are adjusted.

In the figures, like reference numerals are used to indicate the same or corresponding elements in the various. Mark representations.

Regarding 2a an electrolytic cell according to a first embodiment is shown in cross section, which is suitable for use in the production of aluminum from alumina according to the previously described Hall-Héroult method. The electrolysis cell comprises a cathode 1 and a circumferential sidewall 1a , which with passage openings 1aa is provided. The side wall 1a limited together with the cathode 1 the basin 1c , which gives the electrolysis cell the pan shape. At the bottom of the cathode 1 are several connections 1d existing, which the connection with pins 3 serve, which in the present example arranged vertically and with a common busbar 3a are connected.

In the center of the basin 1c is a central pillar 1e formed, which, as in 2a can be seen, having a tip, that runs downwards towards the outside. This shape supports the introduction of the mixture 6 of alumina and optionally cryolite and / or aluminum fluoride, thus the liquid electrolyte in the basin 1c the electrolysis cell. In this case, the chamfer acts outward in terms of a desired reduction of wave movements of the liquid aluminum during filling of the electrolytic cell in the context of fused-salt electrolysis. In the figure, different levels of substances involved in the process are shown: the bottom line shows the level of liquid aluminum 5 at the area of the cathode 1 accumulates. The mixture 6 is located above the aluminum 5 and gets up through a crust 6a from solidified melt 6 limited, which forms in the course of the procedure.

In the cover 9 are the anodes 4 recorded, which for the melt flow electrolysis process as the opposite pole for the cathode 1 serve. As can be seen in the figure, the anodes are 4 so far into the basin 1c The electrolysis cell lowered so that it is close to the level of aluminum from the upper side 5 come close. This is possible because the electrolysis cell is an electrolytic cell according to an embodiment of the invention adjacent to the circumferential sidewall 1a an overflow pan 10 has, the lateral outer wall 10a upwards through the upper edge of an outer edge 10b and down through a lower outer wall 10c is limited. At the lateral outer wall 10a is a gutter 11 attached or integrally formed with this.

When carrying out the fused-salt electrolysis according to the known Hall-Héroult process arises at the cathode 1 from the liquid electrolyte liquid aluminum 5 located in the area of the cathode 1 settles. Because the cathode basin 1c over the passage openings 1aa in the sidewall 1a the electrolysis cell below a desired target level for the aluminum 5 In connection with increasing aluminum formation, the level in the overflow trough also increases 10 , Is that in the 2a level reached, according to the level of aluminum 5 at the height of the upper edge of the outer edge 10b the overflow tub 10 stands, in the further process aluminum flows 5 over the outer edge 10b into the gutter 11 from where it can be removed by conventional means.

As a result of this construction, the level of aluminum 5 both within the overflow trough 10 as well as in the pelvis 1c the cathode 1 to a desired nominal level, determined by the height of the upper edge of the outer edge 10b the overflow trough is defined limited. In order to be able to vary the desired level comfortably, it is favorable, the lateral outer wall 10a the overflow tub 10 in terms of their height above the lower outer wall 10c adjustable to perform. This can be done, for example, by a retractable wall construction (not shown). Furthermore, it is favorable in terms of process management, heat losses of the molten aluminum 5 in the area of the overflow trough 10 and the gutter 11 To minimize this, to prevent the melt from starting to solidify before leaving the gutter 11 was deducted. This can be achieved, for example, by a thermal insulation of the outer walls (not shown in the figures) 10a . 10c the overflow trough and optionally also the gutter 11 be realized. In the same sense, constructive measures aiming at the surface of the aluminum also have an effect 5 inside the overflow pan 10 to stick as small as possible. It is therefore convenient to the overflow tray 10 with a small width b, for example between about 50 mm and 100 mm.

With now reference to 2 B is a plan view of the electrolytic cell of 2a shown. It can be seen that the side wall 1a the electrolysis cell here has a rotational symmetry. The shape of the base of the cathode 1 corresponds to a star with truncated points. It should be noted that this form is not mandatory and that, for example, a conventional rectangular basin 1c or another basin shape for the electrolysis cell according to the invention is possible.

The top view of 2 B further shows the central pillar 1e , which has the shape of a regular hexagon here. Dashed lines are the connections 1d (here six pieces) for the in 2a shown as power supply devices formed pins 3 to recognize which perpendicular to the image plane in the cathode 1 lead. The connections 1d represent in the embodiment shown a radial center around which respective bulges of the side wall 1a run.

As also indicated by dashed lines, the basin can 1c the electrolysis cell into individual sections 1f or sectors, which can be considered as communicating sub-cells of an electrolytic cell. Since the dashed lines represent no true barriers, but only virtual limits of clarification of the position of the cuts 1f or sectors has been in the figure, only a single section 1f defined in its limits by these lines.

Outside the side wall 1a the electrolysis cell is the lateral outer wall 10a the overflow tub 10 to see which is continuous in the case shown and with respect to their outline shape of the outline of the side wall 1a the cathode 1 equivalent. The passage openings 1aa as well as the gutter 11 are in the 2 B not shown.

Regarding 3 is an array of anodes 4 shown in plan view, which are designed as part of the in the 2a and 2 B shown section of an electrolytic cell to act as a total electrolytic cell.

The bases 4a the anodes 4 In plan view here are the shape of elongated, inwardly tapering hexagons (here six pieces), which are arranged in a star shape around a common center Z around. This corresponds to the shape or the number of anodes 4 the shape or number of cuts 1f or sectors of the cathode 1 of the 2a and 2 B , However, it should be noted that the size of the cuts 1f not that of the associated anodes 4 equivalent. Rather, the base of the anodes 4 which in the plan view of 3 is visible, smaller than that of the associated section 1f so that the anodes 4 during operation of the electrolysis cell in the basin 1c the cathode 1 can be lowered into it.

With the cathode unit according to the invention and the method according to the invention, the energy efficiency of an electrolytic cell for fused-salt electrolysis for the production of aluminum can be improved due to the fact that anodes and cathodes can be brought together more closely, since due to the continuous removal of the aluminum produced, a low filling level thereof in the cathode basin and / or or a largely free from wave motion Surface can be achieved. The level of the filling level can be kept at least largely at a desired position within the cathode basin, so that no additional tracking is required in addition to a tracking of the anodes due to their consumption in the course of the process. Overall, such a high quality of the aluminum produced and an optimized temperature control can be achieved.

As far as the materials for cathode and anode are concerned, all materials known and suitable to the person skilled in the art for the electrolysis of aluminum from its oxide can be used. Suitable materials are for example in the DE 10261745 the content of which is hereby incorporated by reference.

LIST OF REFERENCE NUMBERS

1

cathode

1a

Side wall

1aa

Through opening

1c

(Cathode) pool

1d

connections

1e

central pillar

1f

section

2

mount

3

(power supply) pin

3a

conductor rail

4

anode

4a

Floor space

5

aluminum

6

Mixture (alumina, cryolite)

6a

Crust of solidified melt 6

7

negative pole voltage source

8th

positive pole voltage source

9

cover

10

Overflow trough

10a

lateral outer wall

10b

outer edge

10c

lower outer wall

11

collecting channel

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1845174 [0006]
• DE 10261745 [0048]

Claims (15)

Electrolysis cell for recovering aluminum from its oxide, comprising a cathode ( 1 ) and a circumferential side wall ( 1a ), characterized in that the side wall ( 1a ) with a number of through openings ( 1aa ), which outwardly into an overflow trough ( 10 ). Electrolysis cell according to claim 1, characterized in that a gutter ( 11 ) on the outer circumference of the overflow trough ( 10 ) is mounted so that over an outer edge ( 10b ) of the overflow trough ( 10 ) passing liquid aluminum into the gutter ( 11 ) flows. Electrolysis cell according to claim 1 or 2, characterized in that at least some of the passage openings ( 1aa ) in the circumferential side wall ( 1a ) at the same height above the cathode ( 1 ) are formed. Electrolysis cell according to one or more of the preceding claims, characterized in that the cathode ( 1 ) runs horizontally. Electrolysis cell according to one or more of the preceding claims, characterized in that the overflow trough ( 10 ) Outer walls ( 10a . 10c ), which are provided with a thermal insulation. Electrolysis cell according to one or more of the preceding claims, characterized in that the passage openings ( 1aa ) equidistant to each other in the circumferential side wall ( 1a ) are formed. Electrolysis cell according to one or more of the preceding claims, characterized in that the passage openings ( 1aa ) each have a diameter between 3 and 15 cm. Electrolysis cell according to one or more of the preceding claims, characterized in that the peripheral side wall ( 1a ) rotationally symmetrical about a central column ( 1e ) is arranged. Electrolysis cell according to one or more of the preceding claims, characterized in that the central column ( 1e ) is beveled radially outwardly downwards. Electrolysis cell according to one or more of the preceding claims, characterized in that at least one outer wall ( 10a ) of the overflow trough ( 10 ) is adjustable in height. Process for the continuous recovery of aluminum from its oxide by fused-salt electrolysis, characterized in that the resulting aluminum from a gutter ( 11 ) is discharged, which from an overflow of an overflow trough ( 10 ) is fed through through holes ( 1aa ) is in communication with the interior of an electrolytic cell used in fused-salt electrolysis below the level of aluminum produced in the electrolytic cell. A method according to claim 11, characterized in that the fused-salt electrolysis is carried out at a temperature above 750 ° C, in particular between 930 and 1000 ° C. A method according to claim 11 or 12, characterized in that the electrolyte required for the fused-salt electrolysis and / or alumina is supplied continuously from a center of the electrolysis cell. Method according to one or more of claims 11 to 13, characterized in that the center in the central column ( 1e ) is arranged. Method according to one or more of claims 11 to 14, characterized in that it is carried out with an electrolytic cell according to one or more of claims 1 to 10.

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