RU2374362C2 - High-resistant running non-coal anodes for electrolytic receiving of aluminium - Google Patents

Abstract

FIELD: metallurgy. ^ SUBSTANCE: electrolytic cell for electrolytic receiving of aluminium from alumina dissolved in fluoride-bearing molten electrolyte, contains non-coal anode on metallic basis, allowing electroconductive metallic surface. This anode structure contains external part with electrochemical active anode surface on which during electrolysis it is anode extracted oxygen and which is suspended in electrolyte, in essence, parallel to directed to it anode. Anode structure allows one or more running openings passing from active anode surface through this metallic structure, herewith running opening (s) are implemented with ability of direction of electrolyte circulation driven into motion by fast escape of anode extracted oxygen. External part of anode contains layer which contains mainly cobaltous oxide CoO. ^ EFFECT: increasing of resistance increasing of anode against corrosion. ^ 51 cl, 16 dwg, 17 ex

Description

Field of Invention

This invention relates to the use in a molten electrolyte for the electrolytic production of aluminum of a non-carbon anode having an active flow structure with increased stability.

State of the art

Use of non-carbon anodes, i.e. anodes that are not made of carbon as such, such as graphite, coke, etc., but which possibly contain carbon in some chemical compound for the production of aluminum in electrolysis cells, should radically improve the process of aluminum production by reducing pollution and cost aluminum production.

The development of non-carbon anode materials, in particular metals, has led to the creation of new forms of anodes that are better suited to the mechanisms of fluid movement in the electrolyzer and electromagnetic effects than traditional solid carbon anode blocks.

Several designs that provide the release of oxygen anodes for electrolytic cells for the electrolytic production of aluminum were proposed in the following documents. US patent No. 4681671 (Duruz) discloses vertical anode plates or blades operating in low-temperature electrolytic cells for the electrolytic production of aluminum. US Patent No. 5,310,476 (Sekhar / de Nora) discloses anodes providing oxygen evolution, consisting of pairs of anode plates assembled as a roof. US patent No. 5362366 (de Nora / Sekhar) describes non-consumable forms of anodes, including pairs of anode plates assembled in the form of a roof. U.S. Patent No. 5,368,702 (de Nora) discloses vertical tubular or truncated cone-shaped anodes for oxygen evolution in multimonopoly aluminum electrolyzers. US patent No. 5683559 (de Nora) describes an electrolytic cell for the electrolytic production of aluminum with oxygen generation curved anode plates, which are arranged in the form of a roof facing the corresponding cathodes. US Pat. No. 5,725,744 (de Nora / Duruz) discloses oxygen anode vertical anode plates, preferably porous or mesh, with a multimonopol electrolysis device for electrolytic aluminum electrolysis cells operating at low temperature. WO 00/40781, WO 00/40782 and WO 03/006716 (all de Nora) disclose anodes for the production of aluminum with a series of parallel, elongated anode elements that are electrochemically active with respect to oxygen oxidation.

Dissolving alumina starting material requires a highly aggressive fluoride-based electrolyte such as cryolite. Various modified electrolytes have been proposed in order to improve the operation of the electrolyzer and to reduce the wear of the non-carbon anode on a metal base, in particular caused by corrosion by the action of the electrolyte.

WO 00/06804 (Crottaz / Duruz) suggests that a nickel-iron anode can be used in an electrolyte at a temperature of from 820 to 870 ° C, containing from 23 to 26.5 wt.% AlF ₃ , from 3 to 5 wt. % Al ₂ About ₃ , from 1 to 2 wt.% LiF and from 1 to 2 wt.% MgF ₂ . All US patents Nos. 5006209 and 5284562 (both Back / Brooks), 6258247 and 6379512 (both Brown / Brooks / Frizzle / Juric), 6419813 (Brown / Brooks / Frizzle) and 6436272 (Brown / Frizzle) disclose the use of nickel-copper iron anodes in an electrolyte for aluminum production at 660-800 ° C, containing 6-26 wt.% NaF, 7-33 wt.% KF, 1-6 wt.% LiF and 60-65 wt.% AlF ₃ . The electrolyte may contain Al ₂ O ₃ in an amount up to 30 wt.%, In particular from 5 to 10 or 15 wt.%, Most of which is in the form of suspended particles and some of which is dissolved in the electrolyte, i.e. typically 1 to 4 wt.% dissolved Al ₂ O ₃ . In US patent No. 6258247, 6379512, 6419813 and 6436272 such an electrolyte is mentioned as suitable for use at temperatures up to 900 ° C. In US Pat. Nos. 6,258,247 and 6,379,512, the electrolyte further comprises from 0.004 to 0.2% by weight of transition metal additives in order to facilitate alumina dissolution and improve cathode performance. US patent No. 5725744 (de Nora / Duruz) discloses an electrolytic cell for the production of aluminum, having anodes made of nickel, iron and / or copper, in an electrolyte at a temperature of from 680 to 880 ° C, containing 42-63 wt.% AlF ₃ , up to 48 wt.% NaF, up to 48 wt.% LiF and from 1 to 5 wt.% Al ₂ O ₃ . MgF ₂ , KF and CaF _{2 are} also referred to as possible components of an electrolyte bath. WO 2004/035871 (de Nora / Nguyen / Duruz) discloses a metal-based anode containing at least one of nickel, cobalt and iron. The anode is used for the electrolytic production of aluminum in a fluoride-containing molten electrolyte, consisting of: from 5 to 14 wt.% Dissolved alumina; from 35 to 45 wt.% aluminum fluoride; from 30 to 45 wt.% sodium fluoride; from 5 to 20 wt.% potassium fluoride; from 0 to 5 wt.% calcium fluoride; and from 0 to 5 wt.% additional components.

The materials having the highest oxidation stability are metal oxides, which are all to some extent soluble in cryolite. Oxides are also poorly conducting electricity, therefore, to avoid significant ohmic losses and high voltages on the cell, the use of non-conducting or poorly conducting oxides in the manufacture of anodes should be minimal. When possible, a well-conductive material should be used to make the core of the anode, while the surface of the anode is preferably made of oxide having high electrocatalytic activity. Several attempts have been made in order to develop non-carbon anodes for electrolytic cells for the production of aluminum, resistant to chemical aggressive effects of the electrolyte bath and the environment of the cell and having an electrochemically active surface designed to oxidize oxygen ions to atomic and molecular gaseous oxygen and having a low dissolution rate . Many patents have been filed for non-carbon anodes, but not one of them has yet found commercial application, including for economic reasons.

US patent No. 4614569 (Duruz / Derivaz / Debely / Adorian) describes metal anodes for the electrolytic production of aluminum, coated with a protective coating of cerium oxyfluoride formed in situ in the cell or pre-applied, and this coating is maintained during electrolysis by adding small amounts of cerium compounds in the molten cryolite electrolyte, so as to protect the surface of the anode from the aggressive effects of the electrolyte. Several patents disclose the use of an electrically conductive metal core of the anode with an oxide-based active outer part, in particular, US Pat. , 6113758 (de Nora / Duruz) and 6248227 (de Nora / Duruz), 6361681 (de Nora / Duruz), 6365018 (de Nora), 6372099 (Duruz / de Nora), 6379526 (Duruz / de Nora), 6413406 (de Nora), 6425992 (de Nora), 6436274 (de Nora / Duruz), 6521116 (Duruz / de Nora / Crottaz), 6521115 (Duruz / de Nora / Crottaz), 6533909 (Duruz / de Nora), 6562224 (Crottaz / Duruz ), as well as PCT publications WO 00/40783 (de Nora / Duruz), WO 01/42534 (de Nora / Duruz), WO 01/42535 (Duruz / de Nora), WO 01/42536 (Nguyen / Duruz / de Nora ), WO 02/070786 (Nguyen / de Nora), WO 02/083990 (de Nora / Nguyen), WO 02/083991 (Nguyen / de Nora), WO 03/014420 (Nguyen / Duruz / de Nora), WO 03/078695 (Nguyen / de Nora), WO 03/087435 (Nguyen / de Nora).

US patent No. 4374050 (Ray) discloses numerous polyoxide compositions for electrodes. Such compositions include, but are not limited to, iron and cobalt oxides. These oxide compositions can be used as plating on a metal layer of nickel, nickel-chromium, steel, copper, cobalt or molybdenum. US patent No. 4142005 (Cadwell / Hazelrigg) discloses an anode having a substrate made of titanium, tantalum, tungsten, zirconium, molybdenum, niobium, hafnium or vanadium. This substrate is coated with cobalt oxide Co ₃ O ₄ .

U.S. Patent Nos. 6103090 (de Nora), 6361681 (de Nora / Duruz), 6365018 (de Nora), 6379526 (de Nora / Duruz), 6413406 (de Nora) and 6425992 (de Nora), and WO 04/018731 (Nguyen / de Nora) disclose anode substrates which contain at least one of chromium, cobalt, hafnium, iron, molybdenum, nickel, copper, niobium, platinum, silicon, tantalum, titanium, tungsten, vanadium, yttrium and zirconium and which coated with at least one of cobalt, copper, chromium, manganese, nickel and zinc ferrites. WO 01/42535 (Duruz / de Nora) and WO 02/097167 (Nguyen / de Nora) disclose anodes for the electrolytic production of aluminum, made of iron alloys with an oxidized surface, which contain at least one of nickel and cobalt. US patent No. 6638412 (de Nora / Duruz) discloses the use of anodes made of an alloy containing a transition metal having an integral oxide layer with it, this alloy containing at least one of iron, nickel and cobalt.

Non-carbon anodes are still not used commercially and in industry, and there is still a need for metal-based anode material and a suitable anode shape that can be used in the electrolytic production of aluminum.

SUMMARY OF THE INVENTION

The present invention generally relates to the electrolytic production of aluminum with metal-based anodes having a shape to facilitate electrolyte circulation and having an electrochemically active outer part that has increased resistance to corrosion by the highly aggressive circulating electrolyte and / or to oxidation released on the anode (anode) oxygen, and this increased stability is provided through a layer that contains mainly cobalt oxide CoO.

In particular, the invention relates to an electrolytic cell for electrolytically producing aluminum from alumina dissolved in a fluoride-containing molten electrolyte. The electrolyzer contains at least one non-carbon metal-based anode having an electrically conductive metal structure, which contains an outer part with an electrochemically active anode surface on which oxygen is generated anode anode, and which is suspended in the electrolyte substantially parallel to the cathode facing it. This metal structure has one or more flow holes extending from the active anode surface through this metal structure, and the flow hole (s) are made (s) with the possibility of directing the circulation of the electrolyte, driven by the rapid release of oxygen anode. The outer part of the anode contains the aforementioned layer, which mainly contains cobalt oxide CoO, in order to increase the stability of the anode.

In other words, the invention relates to an electrolytic cell having an anode that has a shape that promotes the circulation of the electrolyte, and that has an electrochemically active outer part that is resistant to circulating electrolyte and / or anode released oxygen due to the presence of a layer made predominantly of a special forms of cobalt oxide, i.e. CoO.

There are several forms of stoichiometric and non-stoichiometric cobalt oxides, which are based on:

- CoO, which contains Co (II) and which forms mainly at temperatures above 920 ° C in air;

- Co ₂ O ₃ , which contains Co (III) and which forms at temperatures up to 895 ° C, and at higher temperatures begins to decompose to CoO;

- Co ₃ O ₄ , which contains Co (II) and Co (III) and which is formed at temperatures between 300 and 900 ° C.

It was found that, unlike Co ₂ O ₃ , which is unstable, and Co ₃ O ₄ , which slightly slows down the diffusion of oxygen, CoO forms a well-conducting electrochemically active material for the oxidation of oxygen ions and for slowing down the diffusion of oxygen. Thus, this material forms a limiting barrier against oxidation of the anode cobalt metal underlying it.

The specified CoO-containing layer of the anode may be a layer made of sintered particles, in particular, sintered particles of CoO. Alternatively, the CoO-containing layer may be an integral ("integral") oxide layer on the Co-containing metal layer or the core of the anode. Tests have shown that the integral oxide layers have a higher density than the sintered layers, and are thus preferred for inhibiting oxygen diffusion.

When CoO must be formed by oxidizing cobalt metal, steps must be taken to carry out a treatment that will actually result in the formation of CoO. It was found that the use of Co ₂ O ₃ or Co ₃ O ₄ in a known electrolyte for the electrolytic production of aluminum does not lead to a suitable conversion of these forms of cobalt oxide into CoO. Therefore, it is important to provide the anode with this CoO layer before the anode is used in the electrolyte to electrolytically produce aluminum.

The formation of CoO on cobalt metal is preferably controlled so as to obtain a coherent and substantially crack free oxide layer. However, not every treatment of cobalt metal at temperatures above 895 ° C or 900 ° C in an oxygen-containing atmosphere will result in an optimally coherent and substantially crack-free CoO layer that offers better electrochemical properties than Co ₂ O ₃ / Co ₃ O ₄ .

For example, if the processing temperature of metallic cobalt to form CoO by oxidizing metallic cobalt in air increases at an insufficient rate, for example, less than 200 ° C / h, then a thick oxide layer rich in Co ₃ O ₄ and glassy Co ₂ forms on the surface of cobalt metal About ₃ . Such a layer does not allow the optimal formation of a CoO layer by conversion at a temperature above 895 ° C from Co ₂ O ₃ and Co ₃ O ₄ into CoO. In fact, the CoO layer resulting from such a conversion is not preferred, but still useful, despite the increased porosity, and may be cracked. Therefore, the required temperature for oxidation in air, i.e. above 900 ° C, usually at least 920 ° C, or preferably above 940 ° C, should be achieved quickly enough, for example, at a rate of temperature increase of at least 300 ° C or 600 ° C per hour, in order to obtain the optimum CoO layer. Cobalt metal can also be placed in a furnace that is preheated to a desired temperature above 900 ° C.

Similarly, if after the formation of a CoO layer, the anode is not used immediately for the electrolytic production of aluminum, but is allowed to cool, this cooling should be carried out quickly enough, for example, by placing the anode in air at room temperature to avoid significant formation of Co ₃ O ₄ , which can occur during cooling, for example in a furnace that is turned off.

An anode with a CoO layer obtained by slow heating of cobalt metal in an oxidizing environment will not have optimal properties, but still provides better results during operation of the cell than an anode having a Co ₂ O ₃ —Co ₃ O ₄ layer, and therefore also represents an improved anode for the electrolytic production of aluminum according to the invention.

Said anode structure may be perforated. For example, the anode structure may take any of the forms disclosed in the aforementioned WO 00/40781, WO 00/40782 and WO 03/006716. For example, the anode structure contains a number of parallel anode elements, in particular horizontal anode elements having electrochemically active surfaces in a generally coplanar arrangement to form said active anode surface, these anode elements being separated from each other, forming elongated flow openings (openings) for circulation electrolyte, driven by the rapid release of anodic oxygen. Typically, these anode elements are blades, rods, rods, or wires. The active anode surface may be substantially horizontal, substantially vertical or inclined with respect to the horizontal, for example, as disclosed in WO 00/40782 or WO 03/023092 (both de Nora).

In one embodiment, said molten electrolyte is at a temperature below 950 ° C, in particular in the range from 910 to 940 ° C, and consists of:

- from 6.5 to 11 wt.% dissolved alumina, in particular, from 7 to 10 wt.%;

- from 35 to 44 wt.% aluminum fluoride, in particular, from 36 to 42 wt.% aluminum fluoride, for example, from 36 to 38 wt.%;

- from 38 to 46 wt.% sodium fluoride, in particular, from 39 to 43 wt.%;

- from 2 to 15 wt.% potassium fluoride, in particular, from 3 to 10 wt.% potassium fluoride, for example, from 5 to 7 wt.%;

- from 0 to 5 wt.% calcium fluoride, in particular, from 2 to 4 wt.% calcium fluoride; and

- from 0 to 5 wt.% in the sum of one or more additional components, in particular up to 3 wt.%.

The presence in the electrolyte of potassium fluoride in the above amount gives two effects. On the one hand, it leads to a decrease in the operating temperature up to several tens of degrees without increasing the aluminum fluoride content in the electrolyte or even when it is reduced compared to standard electrolytes operating at about 950 ° C, with an aluminum fluoride content of about 45 wt.%. On the other hand, it maintains the high solubility of alumina in the electrolyte, i.e. up to a value above about 8 or 9 wt.%, even though the temperature of the electrolyte is reduced compared to the traditional temperature.

Therefore, in contrast to the low-temperature electrolytes known in the art, which carry large amounts of undissolved alumina in particulate form, a large amount of alumina is in dissolved form in the aforementioned electrolyte.

Without reference to any theory, it is assumed that the combination of a high concentration of dissolved alumina in the electrolyte and a limited concentration of aluminum fluoride leads mainly to the formation of (oxyfluoride) poor aluminum fluoride ions ([Al ₂ O ₂ F ₄ ] ^2- ) near the anode instead of ( acidic) fluorine-rich aluminum oxyfluoride ions ([Al ₂ OF ₆ ] ^2- ). In contrast to acidic fluorine-rich aluminum oxyfluoride ions, the main fluorine-poor aluminum oxyfluoride ions do not significantly dissolve the CoO anode and do not significantly passivate or corrode metallic cobalt. The mass ratio of dissolved alumina / aluminum fluoride in the electrolyte should be above 1/7, and often above 1/6 or even above 1/5, in order to obtain a favorable ratio of fluorine-poor aluminum oxyfluoride ions and fluorine-rich aluminum oxyfluoride ions.

It follows that the use of the above-described electrolyte with metal-based anodes that contain CoO slows down their dissolution, passivation and corrosion. Moreover, a high concentration of alumina dissolved in the electrolyte further reduces the dissolution of oxides from the anode, in particular CoO.

The electrolyte may consist of: from 7 to 10 wt.% Dissolved alumina; from 36 to 42 wt.% aluminum fluoride, in particular from 36 to 38 wt.%; from 39 to 43 wt.% sodium fluoride; from 3 to 10 wt.% potassium fluoride, for example, from 5 to 7 wt.%; from 2 to 4 wt.% calcium fluoride; and from 0 to 3 wt.% in the sum of one or more additional components. This corresponds to a molten electrolyte based on cryolite (Na ₃ AlF ₆ ) containing an excess of aluminum fluoride (AlF ₃ ), which is in the range from about 8 to 15 wt.% Electrolyte, in particular from about 8 to 10 wt.%, And additives, which may include potassium fluoride and calcium fluoride in the above amounts.

The electrolyte may contain at least one fluoride selected from magnesium fluoride, lithium fluoride, cesium fluoride, rubidium fluoride, strontium fluoride, barium fluoride and cerium fluoride as additional component (s).

Advantageously, the electrolyte contains alumina in a concentration near saturation on the active anode surface.

In order to maintain the alumina concentration above a predetermined threshold in the above range during normal electrolysis, the electrolyzer is preferably equipped with means for monitoring and adjusting the alumina content in the electrolyte.

The CoO-containing layer of the anode can be integral with the core made of cobalt or cobalt alloy. Such an anode core may be made of the same materials as the Co-containing alloys described below. Advantageously, the cobalt-containing core of the anode can be cast.

Alternatively, the anode comprises an electrically conductive substrate that is coated with an applied electrochemically active coating that includes a CoO-containing layer.

The CoO-containing layer may be a layer of sintered particles. In particular, a CoO-containing layer can be formed by applying a layer of powder CoO to the anode and sintering. For example, the CoO-containing layer is applied in the form of a suspension, in particular a colloidal and / or polymer suspension, and then subjected to heat treatment. Good results were obtained by suspending powdered metal cobalt or CoO, optionally with additives such as Ta, in an aqueous solution containing at least one of ethylene glycol, hexanol, polyvinyl alcohol, polyvinyl acetate, polyacrylic acid, hydroxypropyl methylcellulose and ammonium polymethacrylate, and mixtures thereof followed by application to the anode, for example, staining or immersion, and heat treatment.

The CoO-containing layer can be integral with the oxide layer on the deposited Co-containing metal coating layer.

A CoO-containing layer can be formed by applying a Co-containing metal layer to the anode and subjecting the metal layer to oxidation to form a CoO-containing layer on the metal layer, the CoO-containing layer being integral with the metal layer.

Conveniently, the oxidation treatment could be performed in an oxygen-containing atmosphere, such as air. This treatment can also be performed in an atmosphere that is oxygen rich or consists essentially of pure oxygen.

It is also contemplated to perform this oxidation treatment by other means, for example, electrolytically. However, it was found that the complete formation of a single layer of CoO cannot be achieved in situ during the electrolytic production of aluminum under normal conditions of operation of the electrolyzer. In other words, when such an anode is intended for use in an electrolytic cell for the electrolytic production of aluminum with a non-carbon anode operating under ordinary conditions, the anode should always be placed in the electrolyzer with a pre-formed integral oxide layer containing predominantly CoO.

Since the conversion of Co (III) to Co (II) occurs at a temperature of about 895 ° C, the oxidation treatment must be performed above this temperature. Typically, the oxidation treatment is carried out at a treatment temperature above 895 ° C or 920 ° C, preferably above 940 ° C, in particular within the range of 950 ° C to 1050 ° C. The co-containing metal layer can be heated from room temperature to this processing temperature at a rate of at least 300 ° C / hour, in particular at least 450 ° C / hour, or placed in an environment, in particular in a furnace, which preheated to the indicated temperature. The oxidation treatment at this processing temperature can be carried out for more than 8 or 12 hours, in particular from 16 to 48 hours. More specifically, when the oxygen content in the oxidizing atmosphere increases, the processing time can be reduced to less than 8 hours, for example up to 4 hours.

The co-containing metal layer may be further oxidized during use. However, the basic formation of CoO is preferably achieved before use and in a controlled manner for the reasons explained above.

A method of forming a CoO-containing layer on a Co-containing metal layer can be used to form a CoO-containing layer on the previously mentioned Co-containing core of the anode.

The co-containing metal layer may contain alloying metals to further reduce oxygen diffusion and / or corrosion through the metal layer.

In one embodiment, the anode comprises an oxygen barrier layer between the CoO-containing layer and the electrically conductive substrate. The oxygen barrier layer may contain at least one metal selected from nickel, copper, tungsten, molybdenum, tantalum, niobium and chromium, or their oxide, for example, alloyed with cobalt, such as a cobalt alloy containing tungsten, molybdenum, tantalum and / or niobium, in particular, an alloy containing at least one of nickel, tungsten, molybdenum, tantalum and niobium in a total amount of from 5 to 30 wt.%, such as from 10 to 20 wt.%; and one (one) or more additional elements and compounds in a total amount up to 5 wt.%, such as from 0.01 to 4 wt.%, with the rest being cobalt. These additional elements may contain at least one of aluminum, silicon and manganese.

Typically, the oxygen barrier layer and the CoO-containing layer form by oxidizing the surface of the deposited layer of the aforementioned cobalt alloy, which contains nickel, tungsten, molybdenum, tantalum and / or niobium. The resulting CoO-containing layer is predominantly made of CoO and is integral with the non-oxidized portion of the cobalt metal alloy, which forms an oxygen-barrier layer.

When the CoO layer is integral with the cobalt alloy, nickel, if present, should be contained in the alloy in an amount up to 20 wt.%, In particular from 5 to 15 wt.%. Such an amount of nickel in the alloy leads to the formation of a small amount of nickel oxide NiO in the integral oxide layer in approximately the same ratio to cobalt as in the metal part, i.e. from 5 to 15 or 20 wt.%. It was found that the presence of a small amount of nickel oxide stabilizes cobalt oxide CoO and for a long time slows down the formation of Co ₂ O ₃ or Co ₃ O ₄ . However, when the nickel / cobalt weight ratio exceeds 0.15 or 0.2, the useful chemical and electrochemical properties of cobalt oxide CoO tend to disappear. Therefore, the nickel content should not exceed this limit.

Alternatively, an oxygen barrier layer, for example made of the aforementioned cobalt alloy, which contains nickel, tungsten, molybdenum, tantalum and / or niobium, may be coated with a coated CoO layer or its precursor, as discussed above. In this case, the oxygen barrier layer may be a deposited layer or it may be integral with the electrically conductive substrate.

In another embodiment, the Co-containing metal layer consists essentially of cobalt, typically contains cobalt in an amount of at least 95 wt.%, In particular more than 97 wt.% Or 99 wt.%.

Optionally, the Co-containing metal layer contains at least one additive selected from silicon, nickel, manganese, niobium, tantalum and aluminum in a total amount of from 0.1 to 2 wt.%.

Such a Co-containing layer can be applied to the oxygen barrier layer, which is integral with or deposited on the electrically conductive substrate of the flow-through anode structure.

The electrically conductive substrate may contain at least one metal selected from chromium, cobalt, hafnium, iron, molybdenum, nickel, copper, platinum, silicon, titanium, tungsten, molybdenum, tantalum, niobium, vanadium, yttrium and zirconium, or their compounds, in particular oxide, or combinations thereof. For example, the electrically conductive substrate may have an outer part made of cobalt or an alloy containing predominantly cobalt, which is coated. For example, this cobalt alloy contains nickel, tungsten, molybdenum, tantalum and / or niobium, in particular, it contains: nickel, tungsten, molybdenum, tantalum and / or niobium in a total amount of from 5 to 30 wt.%, For example, from 10 up to 20 wt.%; and one (one) or more additional elements and / or compounds in a total amount of up to 5 wt.%, the rest is cobalt. These additional elements may contain at least one of aluminum, silicon and manganese. The electrically conductive substrate or its outer part may comprise at least one oxidation resistant metal or consist essentially of at least one oxidation resistant metal, in particular one or more metals selected from nickel, tungsten, molybdenum, cobalt, chromium and niobium, and, for example, contain less than 1, 5 or 10 wt.% in the sum of other metals and metal compounds, in particular oxides. Alternatively, the electrically conductive substrate may be made of an alloy of nickel, iron and copper, in particular an alloy containing: from 65 to 85 wt.% Nickel; from 5 to 25 wt.% iron; from 1 to 20 wt.% copper; and from 0 to 10 wt.% additional components. For example, an alloy contains about: 75% by weight nickel; 15 wt.% Iron; and 10 wt.% copper.

Advantageously, the CoO-containing anode layer, in particular when the CoO layer is integral with the deposited Co-containing metal layer or anode body, has an open porosity of less than 12%, such as, for example, less than 7%.

The CoO-containing anode layer may have porosity with an average pore size of less than 7 microns, in particular less than 4 microns. It is preferable to provide a substantially crack-free CoO-containing layer in order to effectively protect the metal outer portion of the anode that is coated with this CoO-containing layer.

Typically, the CoO-containing layer contains cobalt oxide CoO in an amount of at least 80 wt.%, In particular more than 90 wt.% Or 95 wt.% Or 98 wt.%.

Advantageously, the CoO-containing layer is substantially free of Co ₂ O ₃ cobalt oxide and substantially free of Co ₃ O ₄ and preferably contains less than 3 or 1.5% of these forms of cobalt oxide.

The CoO-containing layer may be electrochemically active with respect to the oxidation of oxygen ions during use, in which case this layer is uncoated or coated with an electrolyte-permeable layer.

Alternatively, the CoO-containing layer may be coated with a deposited protective layer, in particular an applied oxide layer, such as a layer containing cobalt and / or iron oxide, for example cobalt ferrite. The applied protective layer may contain a pre-formed and / or locally deposited cerium compound, in particular cerium oxyfluoride, as, for example, disclosed in the aforementioned US Pat. oxygen and is uncoated or in turn is coated with a layer permeable to electrolyte.

The electrochemically active surface of the anode may contain at least one additive, in particular at least one additive selected from metals iridium, palladium, platinum, rhodium, ruthenium, silicon, tungsten, molybdenum, tantalum, niobium, tin or zinc, mischmetal and metals a number of lanthanides, in the form of metals and compounds, in particular oxides, and mixtures thereof. Additive (s) may / may be present on the surface of the anode in a total amount of from 0.1 to 5 wt.%, In particular, from 1 to 4 wt.%.

Such an additive may be an electrocatalyst to favor the oxidation of oxygen ions on the electrochemically active surface of the anode and / or may help slow the diffusion of oxygen ions into the anode.

The additive can be added to the precursor material, which is applied to form an active surface, or it can already be applied to the active surface in the form of a thin film, for example, by plasma spraying or applying a suspension, and incorporated into this surface by heat treatment.

The cell may have a cathode that has an aluminum wettable surface, in particular a horizontal or inclined drained surface. This surface can be formed by a wettable aluminum material that contains refractory boride and / or an oxide wetting aid. Examples of such materials are disclosed in WO 01/42168, WO 01/42531, WO 02/070783, WO 02/096830 and WO 02/096831 (all in the name of MOLTECH).

The anode can be suspended in the electrolyte by means of a rod, in particular, a rod having an outer part containing a layer that contains mainly cobalt oxide CoO.

Another aspect of the invention relates to a method for the electrolytic production of aluminum in such an electrolyzer as described above. The method includes electrolysis of dissolved alumina to produce oxygen at the anode and aluminum at the cathode and feeding alumina to the electrolyte to maintain dissolved alumina in it from 6.5 to 11 wt.%, In particular from 7 to 10 wt.%.

Oxygen ions can be oxidized on the CoO-containing layer of the anode, which mainly contains cobalt oxide CoO, and / or, if present, on the active layer deposited on the CoO layer of the anode, the CoO layer slowing down the oxidation and / or corrosion of the metal outer part of the anode .

The invention also relates to a metal-based non-carbon anode for the electrolytic production of aluminum from alumina dissolved in a fluoride-containing molten electrolyte. This anode contains an electrically conductive metal structure that contains an outer part with an electrochemically active anode surface on which oxygen is anode released and which, during use, is suspended in the electrolyte substantially parallel to the cathode facing it. This metal structure has one or more flow openings extending from the active anode surface through the metal structure. This (and) flow-through (s) hole (s) is made (s) with the possibility of directing during use the circulation of the electrolyte, set in motion by the rapid release of anodically released oxygen. The outer part of the anode contains the aforementioned layer, which mainly contains cobalt oxide CoO to increase the stability of the anode. This anode may have any of the above features of the anode or a combination thereof.

Brief Description of the Drawings

The invention will now be described with reference to schematic drawings in which:

FIG. 1a and 1b show, respectively, a side view and a top view of the anode according to the invention;

FIG. 2a and 2b show, respectively, a side view and a top view of another anode according to the invention;

FIG. 3, 4, 5 and 6 show side views of variants of the anode shown in FIGS. 1a and 1b;

FIG. 7 and 8 show cross-sections of several parts of the anode elements according to the invention;

Fig.9 shows an electrolytic cell for the electrolytic production of aluminum, working with the anodes according to the invention, equipped with guiding electrolyte elements;

FIG. 10, 11 and 12 are enlarged views of parts of variants of electrolyte guiding elements shown in FIG. 9, FIG. 10, illustrating the operation of the electrolyzer;

13 is a cross section of another anode according to the invention with electrolyte guiding elements, of which only one is shown;

Fig. 14 shows a top view of a half assembly of several electrolyte guiding elements similar to that shown in Fig. 13;

Fig is a top view of the anode shown in Fig, with half the assembly of the guiding electrolyte elements, which is shown in Fig; and

Fig.16 is a top view of a variant of the anode of Fig.15.

Detailed description

Figa and 1b schematically show the anode 10 of the electrolytic cell for the electrolytic production of aluminum according to the invention.

The anode 10 comprises a vertical current lead 11 for connecting the anode to the positive busbar, a cross member 12 and a pair of transverse connecting elements 13 for connecting a number of anode elements 15.

The anode elements 15 have an electrochemically active lower surface 16, where oxygen is generated anode anode during the operation of the cell. The anode elements 15 are in the form of parallel rods in a coplanar arrangement, laterally separated by inter-element gaps 17. The inter-element gaps 17 constitute flow openings for the circulation of the electrolyte and the release of the anode released gas released on the electrochemically active surfaces 16.

The anode elements 15 are connected in the transverse direction by a pair of transverse connecting elements 13, which in turn are connected together by a cross member 12 on which a vertical current lead 11 is mounted. The current lead 11, the cross member 12, the transverse connecting elements 13 and the anode elements 15 are mechanically connected together by welding, rivets or other means.

In accordance with the invention, the electrochemically active surface 16 of the anode elements 15 is formed by the outer part, which contains a layer containing mainly CoO. This CoO layer may form an electrochemically active surface 16 and be directly exposed to the electrolyte during use, or the CoO layer may be coated with an additional layer, for example, a layer containing predominantly a cerium compound such as cerium oxyfluoride.

The cross member 12 and the transverse connecting elements 13 are made and placed on top of the anode elements 15 so as to ensure a substantially uniform distribution of current through the anode elements 15 to their electrochemically active surfaces 16. The current lead 11, the cross member 12 and the transverse connecting elements 13 need not be electrochemically active, and their surface can be passivated by exposure to an electrolyte. However, they must conduct electricity well to avoid unnecessary voltage drops, and should not dissolve significantly in the electrolyte. Electrochemically inactive conductive elements (11, 12, 13) can have an outer part with a protective layer containing mainly CoO.

Figa and 2b schematically show a variant of the anode 10 shown in Figa and 1b.

Instead of having transverse connecting elements 13, a cross member 12, and a current lead 11 for mechanically and electrically connecting the anode elements 15 to a positive busbar, as illustrated in FIG. 1a and 1b, the anode 10 shown in FIG. 2a and 2b, has a pair of cast or profiled support elements 14 that perform the same function. Each cast support element 14 comprises a lower horizontally extending leg 14a for electrically and mechanically connecting the anode elements 15, a rod 14b for connecting the anode 10 to the positive busbar, and a pair of side reinforcing flanges 14c between the horizontally extending leg 14a and the rod 14b.

Anode elements 15 can be attached by tight fit or welding to a horizontal foot 14a. Alternatively, the shape of the anode elements 15 and the corresponding receiving grooves in the paw 14a may be such that only longitudinal movements of the anode elements are possible. For example, the anode elements 15 and the paw 14a can be connected via dovetail connections.

FIG. 3-6 show a series of anodes 10 according to the invention, which are similar to the anode 10 shown in FIG. 1a and 1b. However, the cross sections of the anode elements 15 of the anodes 10 shown in FIG. 3-6 differ from the circular cross section of the anode elements 15 shown in FIG. 1a and 1b.

The anode elements 15 of the anode shown in FIG. 3 have, in cross section, a generally semicircular upper part and a flat base that forms the electrochemically active surface 16 of each anode element 15.

FIG. 4 illustrates bar-shaped anode elements 15 that have a cross section of a generally bell-shaped or pear-shaped shape. The electrochemically active surface 16 of such anode elements 10 is placed along the base of this bell-shaped or pear-shaped shape.

The anode elements 15 shown in FIG. 5 are rods having a generally rectangular cross section. The electrochemically active surface 16 is placed along the lower narrow side of the bar.

FIG. 6 and 7 show an anode 10 having prefabricated, multi-piece anode elements 15 comprising a first element 15b supporting an electrochemically active second element 15a. The electrochemically active element 15a has an electrochemically active surface 16 and is connected along its entire length to the electrically conductive supporting element 15b via an intermediate connecting element 15c, such as, for example, a flange.

Fig. 7 shows an enlarged view of the assembled anode element 15 of Fig. 6, containing a generally cylindrical electrochemically active element 15a with an electrochemically active surface 16, a generally cylindrical electrically conductive support element 15b and an intermediate connecting element or flange 15c, electrically and mechanically connecting the supporting element 15b with an electrochemically active element 15a. Alternatively, the connecting element 15c may be a protrusion of either the electrochemically active element 15a or the supporting element 15b, as shown in Fig. 8.

The intermediate connecting element 15c shown in FIG. 7 can be connected to the electrochemically active element 15a and to the supporting element 15b by means of a tight fit or welding. However, these parts can be mechanically connected by providing a suitable geometry of the connecting elements 15c and the corresponding receiving grooves of the electrochemically active element 15a and the supporting element 15b, for example, with dovetail connections.

According to the invention, the electrochemically active element 15a shown in FIG. 7 and 8, has an outer part, which contains a layer containing predominantly CoO. As mentioned above, this CoO layer can form an electrochemically active surface 16 and be directly exposed to the electrolyte during use, or the CoO layer can be coated with an additional layer, for example, a layer containing mainly a cerium compound, such as cerium oxyfluoride.

The support member 15b shown in FIGS. 7 and 8 and the connecting member 15c shown in FIG. 7 are preferably highly conductive and may contain a metal core, for example, nickel, coated with a layer of oxidized cobalt (having a CoO based surface).

FIG. 9 shows an electrolytic cell for electrolytically producing aluminum according to the invention, having a series of generally horizontal anodes 10, which are similar to those shown in FIG. 1a and 1b immersed in the electrolyte 30. The anodes 10 face the horizontal cathode bottom 20 of the cell connected to the negative busbar by conductive rods 21. The cathode bottom 20 of the cell is made of a conductive material such as graphite or other carbon material coated with a wettable aluminum refractory a cathode coating 22, on which aluminum 35 is obtained and from which it flows or on which it forms a shallow (shallow) bath, a deep bath or a stabilized bath. The obtained molten aluminum 35 is separated from the anodes 10 facing it by an interpolar gap.

The pairs of anodes 10 are connected to the positive busbar through a primary vertical current lead 11 'and a horizontal current distributor 11 "connected at both ends with a perforated anode 10 through a secondary vertical current distributor 11".

The secondary vertical current distributor 11 ″ is mounted on the anode structure 12, 13, 15 on the cross member 12, which in turn is connected to a pair of transverse connecting elements 13 for connecting a series of anode elements 15. Current leads 11 ′, 11 ″ and 11 ″, cross member 12 , transverse connecting elements 13 and anode elements 15 are mechanically fastened together by welding, rivets or other means.

The anode elements 15 have an electrochemically active lower surface 16, on which oxygen is anode emitted during operation of the electrolyzer. The anode elements 15 are made in the form of parallel rods in a “perforated” coplanar arrangement, separated laterally from each other by inter-element gaps 17. The inter-cell gaps 17 form flow openings for circulation of the electrolyte and the release of anode released gas from electrochemically active surfaces 16.

The cross member 12 and the transverse connecting elements 13 provide a substantially uniform distribution of current across the anode elements 15 to their electrochemically active surfaces 16. The current lead 11, the cross member 12 and the transverse connecting elements 13 need not be electrochemically active, and their surface can be passivated by the action of an electrolyte. However, they must conduct electricity well in order to avoid unnecessary voltage drops, and should not substantially dissolve in the molten electrolyte.

In accordance with the invention, the active surface 16 of the anode elements 15 can be made based on CoO.

This CoO-based surface can extend over all the immersed parts 11 ″, 12, 13, 15 of the anode 10, in particular along the immersed portion of the secondary vertical current distributor 11 ″, which is preferably coated with a CoO-based layer, at least up to 10 cm above the surface of the electrolyte 30.

The anodes 10 are additionally equipped with means for increasing the dissolution of the supplied alumina in the form of electrolyte guiding elements 5 formed from parallel, separated from each other inclined deflectors 5 located above and adjacent to the perforated anode structure 12, 13, 15. The deflectors 5 provide upper downward converging surfaces 6 and lower upward converging surfaces 7, which reflect gaseous oxygen, which is produced on the anode under the electrochemically active surface 16 of the anode elements 15 and the cat the ore exits between the inter-element gaps 17 through the perforated anode structure 12, 13, 15. The oxygen released above the deflectors 5 stimulates the dissolution of the alumina supplied to the electrolyte 30 above the downwardly facing surfaces 6. Further details of such deflectors are disclosed in the aforementioned WO 00/40781 and WO 00/40782.

The aluminum-wettable cathode coating 22 of the electrolyzer shown in FIG. 9 can advantageously be a suspension refractory carbide coating which is disclosed in WO 01/42534 (de Nora / Durus), WO 01/42531 (Nguyen / Durus / de Nora ) and WO 02/096831 (Nguyen / de Nora).

During operation of the electrolyzer, the alumina is fed into the electrolyte 30 along the entire length of the deflectors 5 and the metal anode structure 12, 13, 15. The supplied alumina dissolves and is distributed from the lower end of the converging surfaces 6 into the interpolar gap through the gap elements 17 and around the edges of the metal anode structure 12, 13, 15, i.e. between adjacent pairs of anodes 10 or between peripheral anodes 10 and side walls 25. When electric current is passed between the anodes 10 and the cathode bottom 20 of the electrolyzer facing them, oxygen is released on the electrochemically active anode surfaces 16, and aluminum is produced, which combines with the molten cathode aluminum 35. Oxygen released on the active surfaces 16 exits through the inter-element gaps 17 and is reflected by the upwardly facing surfaces 7 of the deflectors 5. Oxygen exits from the uppermost x ends up converging surfaces 7 enhancing dissolution of alumina fed above the downward converging surfaces 6.

Electrolytic cells for the electrolytic production of aluminum, partially shown in FIG. 10, 11 and 12, are similar to the electrolytic cell for the electrolytic production of aluminum, shown in Fig.9.

In figure 10, the guide elements are inclined deflectors 5, as shown in figure 9. In this example, the uppermost end of each deflector 5 is placed just above the middle of the height between the surface of the electrolyte 30 and the transverse connecting elements 13.

Also shown in FIG. 10, electrolyte circulation 31 is generated by a gas outlet that is released from the active surfaces 16 of the anode elements 15 between the gap elements 17 and which is reflected by the upwardly facing surfaces 7 of the deflectors 5, restricting the gas and electrolyte flow between their uppermost edges. From the uppermost edges of the deflectors 5, the anode-released gas exits to the surface of the electrolyte 30, while the circulation of the electrolyte 31 flows downward along the converging surfaces 6 through the gap elements and around the edges of the metal anode structure 12, 13, 15, to compensate for the vacuum created by the anode-released gas under the active surfaces 17 of the anode elements 15. The circulation 31 of the electrolyte draws down into the pole gap the dissolving alumina particles 32, which are fed over the converging surface mi 6.

11 shows a portion of an electrolytic cell for the electrolytic production of aluminum with deflectors 5 acting as electrolyte guiding elements similar to those shown in the electrolytic cell of FIG. 9, but whose surfaces converge only partially. The lower sections 4 of the deflectors 5 are vertical and parallel to each other, while their upper sections have upward and downward converging surfaces 6, 7. The uppermost ends of the deflectors 5 are located below the surface of the electrolyte 30, but close to it, to increase turbulence on the surface of the electrolyte, caused by the release of anodic gas.

Fig. 12 shows a variant of the deflectors shown in Fig. 11, in which parallel vertical sections 4 are placed above the converging surfaces 6, 7.

By directing and forcing the anodically released oxygen to move to the surface of the electrolyte 30 using deflectors or other restrictive means, as shown in FIGS. 11 and 12, oxygen is released so close to the surface as to create turbulence over the downwardly facing surfaces 6, thereby stimulating the dissolution of the alumina supplied from above.

It is understood that the electrolyte-limiting elements 5 shown in FIGS. 9, 10, 11 and 12 can either be elongated deflectors or, instead, can consist of a series of vertical “exhaust” openings of funnels of round or polygonal cross section, for example, as described below.

13 and 15 illustrate the anode 10 ′ having a circular base (sole), wherein the anode 10 ′ is shown in cross section in FIG. 13 and from above in FIG. 15. On the right side in FIGS. 13 and 15, the anode 10 ′ is shown with electrolyte guiding elements 5 ′. The electrolyte guiding elements 5 ′ shown in FIG. 15 are shown separately in FIG. 14.

The anode 10 ′ shown in FIGS. 13 and 15 has several concentric circular anode elements 15. These anode elements 15 are laterally separated by inter-element gaps 17 and connected together by radial connecting elements in the form of flanges 13 that are connected to the outer ring 13 '. The outer ring 13 'extends vertically upward from the outermost anode elements 15, as shown in Fig. 13, forming with the radial flanges 13 the wheel-shaped structure 13, 13' shown in Fig. 15, which attaches the anode elements 15 to the central anode current lead 11.

As shown in FIG. 13, the innermost circular anode element 15 is partially integrated with the current lead 11, with channels 18 extending between the innermost circular anode element 15 and the current lead 11 so as to allow oxygen produced below under the central current lead 11 to escape.

Each electrolyte guide element 5 'has a generally funnel shape having a wide bottom hole 9 for receiving anodically produced oxygen and a narrow upper hole 8 where oxygen is released, thereby dissolving the alumina fed over the electrolyte guide element 5'. The inner surface 7 of the electrolyte guiding element 5 'is positioned to channel and stimulate an upward flow of electrolyte driven by anodically produced oxygen. The outer surface 6 of the electrolyte-guiding element 5 ′ is positioned to stimulate the dissolution of the alumina fed from above and to direct the alumina-rich electrolyte down into the interpolar gap, the electrolyte flowing mainly around the perforated structure.

As shown in FIGS. 14 and 15, the electrolyte guiding elements 5 ′ are in a circular arrangement, with only half of this arrangement shown. The electrolyte guiding elements 5 ′ are laterally attached to each other by fastening devices 3 and arranged to be held on top of the anode elements 15, these fastening devices 3 being placed, for example, on the flanges 13, as shown in FIG. 15, or fixed as it is required. Each electrolyte guide element 5 'is placed in a circular sector formed by two adjacent radial flanges 13 and an arc of the outer ring 13', as shown in Fig. 15.

The assembly of the electrolyte guiding elements 5 'and the anode 10' may be solid. This gives the advantage of eliminating mechanical joints and the risk of changes in the properties of materials guiding the electrolyte elements 5 'or anode 10' during welding.

Anodes 10 'and electrolyte guiding elements 5' can be made of the same materials, in particular, they can be made of a metal body having an outer part with a layer containing mainly CoO.

FIG. 16 illustrates a square anode 10 ′ as an embodiment of the circular anode 10 ′ in FIGS. 13 and 15. The anode 10 ′ of FIG. 16 has generally rectangular concentric parallel anode elements 15 with rounded corners. The anode 10 'shown in Fig. 16 may be equipped with electrolyte guiding elements similar to those shown in Figs. 13-15, but in a corresponding rectangular arrangement.

The anodes 10 ′ of FIGS. 13 and 16 can be made by casting a metal or alloy. Typically, the anode substrate, for example, consisting mainly of nickel, may be cast to form the inside of the anode, which is then coated as described above, forming the outside of the anode having a layer that consists predominantly of CoO. Alternatively, the cobalt or cobalt alloy may be cast to form the inside of the anode, which is then oxidized as described above, forming the outside with a layer that consists predominantly of CoO. It is also contemplated to pour cobalt or cobalt alloy around an anode core or anode skeleton having a composition other than cast cobalt or cobalt alloy, such as iron or steel. The electrolyte guiding elements 5 'can be made in the same way and from the same or different materials.

Useful variations of this anode structure are disclosed in the aforementioned WO 00/40782. Additional suitable anode designs are disclosed in WO 99/027064 (de Nora / Duruz), WO 01/31088, WO 03/006716 and WO 03/023092 and US Pat. No. 5,368,702 (all de Nora).

The fabrication and behavior in the electrolytic cell for the electrolytic production of aluminum of a cobalt oxide-containing material used to make the anode of the present invention will be further described in the following examples.

Comparative Example 1

A cylindrical metal cobalt sample was oxidized to form a coherent cobalt oxide layer that did not contain predominantly CoO. The cobalt samples contained a total of not more than 1 wt.% Additives and impurities and had a diameter of 1.94 cm and a height of 3 cm

The oxidation was carried out by placing a cobalt sample in a furnace in air and increasing the temperature from room temperature to 850 ° C at a rate of 120 ° C / hour.

After 24 hours at 850 ° C, the oxidized cobalt sample was allowed to cool to room temperature and examined.

A cobalt sample was coated with a grayish scale having a thickness of about 300 microns. This scale consisted of: an inner layer 80 microns thick, which had a porosity of 5% with pores that were 2-5 microns in size; and an outer layer with a thickness of 220 microns, having an open porosity of 20% with pores that were 10-20 microns in size. The outer oxide layer consisted of a mixture of essentially Co ₂ O ₃ and Co ₃ O ₄ . The denser inner oxide layer consisted of CoO.

As shown in Comparative Examples 2 and 3, such oxidized cobalt provides poor results when used as an anode material in an electrolytic cell for the electrolytic production of aluminum.

Example 1a

A cobalt sample that can be used to make the anode according to the invention was obtained in the same manner as in Comparative Example 1, except that this sample was oxidized in a furnace heated from room temperature to 950 ° C (instead of 850 ° C ) at the same speed (120 ° C / hour).

After 24 hours at 950 ° C, the oxidized cobalt sample was allowed to cool to room temperature and examined.

The cobalt sample was coated with a black glassy scale having a thickness of about 350 microns (instead of 300 microns). This scale had a continuous structure (instead of a layered structure) with an open porosity of 10% (instead of 20%) and pores that were 5 microns in size. The outer oxide layer consisted of CoO obtained above 895 ° C as a result of the conversion into CoO of those Co ₃ O ₄ and glassy Co ₂ O ₃ that formed below this temperature and by oxidation of the metal outer part of the sample (below under cobalt oxide) directly to CoO . Porosity was associated with a phase change during the conversion of Co ₂ O ₃ and Co ₃ O ₄ into CoO.

Such a material can be used to make an anode for the electrolytic production of aluminum according to the invention. However, the density of the CoO layer and the characteristics of this material can be further improved, as shown in examples 1c and 1d.

Generally speaking, in order to ensure the proper conversion of cobalt oxide and the growth of CoO from the metal outer part of the substrate, it is important to leave the sample long enough at temperatures above 895 ° C. The duration of the heat treatment will depend on the oxygen content in the oxidizing atmosphere, the temperature of the heat treatment, the desired amount of CoO and the amount of Co ₂ O ₃ and Co ₃ O ₄ to be converted to CoO.

Example 1b

Example 1a was repeated with a similar cylindrical sample of metallic cobalt. The furnace in which the sample was oxidized was heated to a temperature of 1050 ° C (instead of 950 ° C) at the same speed (120 ° C / h).

After 24 hours at 1050 ° C, the oxidized cobalt sample was allowed to cool to room temperature and examined.

A cobalt sample was coated with a black crystallized scale having a thickness of about 400 microns (instead of 350 microns). This scale had a continuous structure with an open porosity of 20% (instead of 10%) and pores that were 5 microns in size. The outer oxide layer consisted of CoO obtained above 895 ° C, as in Example 1a.

Such oxidized cobalt is comparable to the oxidized cobalt from Example 1a and can likewise be used as an anode material for the production of aluminum in accordance with the present invention.

Generally speaking, in order to ensure the proper conversion of cobalt oxide and the growth of CoO from the metal outer part of the substrate, it is important to leave the sample long enough at temperatures above 895 ° C. The duration of the heat treatment at temperatures above 895 ° C will depend on the oxygen content in the oxidizing atmosphere, the temperature of the heat treatment, the desired amount of CoO and the amount of Co ₂ O ₃ and Co ₃ O ₄ (obtained below 895 ° C), which should be converted to CoO .

Example 1c (improved material)

Example 1a was repeated with a similar cylindrical sample of metallic cobalt. The furnace in which the sample was oxidized was heated to the same temperature (950 ° C) at a speed of 360 ° C / hour (instead of 120 ° C / hour).

After 24 hours at 950 ° C, the oxidized cobalt sample was allowed to cool to room temperature and examined.

The cobalt sample was coated with a dark gray, substantially non-glassy, scale having a thickness of about 350 microns. This scale had a continuous structure with an open porosity of less than 5% (instead of 10%), and the pores were 5 microns in size.

The outer oxide layer consisted of CoO, which was formed directly from cobalt metal at a temperature above 895 ° C, which was reached after about 2.5 hours, and to a limited extent as a result of the conversion of the previously formed Co ₂ O ₃ and Co ₃ O ₄ . It followed that there was less porosity caused by the conversion of Co ₂ O ₃ and Co ₃ O ₄ into CoO than in Example 1a.

Such a sample of oxidized cobalt had a significantly higher density than the samples from Examples 1a and 1b, and essentially had no cracks. This oxidized cobalt is a preferred material for the manufacture of an improved anode for the electrolytic production of aluminum, intended for use in the electrolyzer according to the invention.

Example 1d (improved material)

Example 1c was repeated with a similar cylindrical sample of metallic cobalt. The furnace in which the sample was oxidized was heated to the same temperature (1050 ° C) at a speed of 600 ° C / hour (instead of 120 ° C / hour in Example 1a and 1b and 360 ° C / hour in Example 1c).

After 18 hours at 1050 ° C, the oxidized cobalt sample was allowed to cool to room temperature and examined.

The cobalt sample was coated with a dark gray, substantially non-glassy, scale having a thickness of about 300 microns (instead of 400 microns in Example 1b and 350 microns in Example 1c). This scale had a continuous structure with no cracked open porosity of less than 5% (instead of 20% in Example 1b), and the pores had a size of less than 2 microns (instead of 5 microns in Example 1b and in Example 1c).

The outer oxide layer consisted of CoO, which was formed directly from cobalt metal at a temperature above 895 ° C, which was reached after about 1.5 hours, and to a very small extent as a result of the conversion of the previously formed Co ₂ O ₃ and Co ₃ O ₄ . From this it followed that there was a significantly lower porosity caused by the conversion of Co ₂ O ₃ and Co ₃ O ₄ into CoO than in Example 1b and Example 1c.

Such a sample of oxidized cobalt had a significantly higher density than the samples in Examples 1a and 1b, and essentially had no cracks. This oxidized cobalt is a preferred material for the manufacture of an improved anode for the electrolytic production of aluminum, intended for use in the electrolyzer according to the invention.

Comparative Example 2 (overvoltage test)

An anode made of cobalt metal oxidized under the conditions of Comparative Example 1 was tested in an electrolytic cell for the electrolytic production of aluminum.

The electrolyte of such an electrolyzer was at a temperature of 925 ° C and consisted of 11 wt.% AlF ₃ , 4 wt.% CaF ₂ , 7 wt.% KF and 9.6 wt.% Al ₂ O ₃ , the rest was cryolite Na ₃ AlF ₆ .

The anode was placed in the electrolyte of the electrolyzer at a distance of 4 cm from the cathode facing it. An electrolysis current of 7.3 A was passed from the anode to the cathode at an anode current density of 0.8 A / cm ² .

The electrolysis current was varied between 4 and 10 A, and the corresponding voltage across the electrolyzer was measured in order to evaluate the overvoltage of oxygen at the anode.

When extrapolating the electrolyzer potential to zero electrolysis current, it was found that the oxygen overvoltage at the anode was 0.88 V.

Example 2 (overvoltage test)

The test was performed under the conditions of Comparative Example 2 with two anodes made of cobalt metal, oxidized under the conditions of Example 1c and 1d, respectively, in electrolyzers according to the invention using the same electrolyte as in Comparative Example 2. Estimated oxygen overvoltage for these anodes was 0.22 V and 0.21 V, respectively, i.e. about 75% lower than in Comparative Example 2.

From this it follows that the use of metallic cobalt coated with an integral layer of CoO instead of Co ₂ O ₃ and Co ₃ O ₄ as the anode material for the electrolytic production of aluminum in the electrolyzer according to the invention leads to significant energy savings.

Comparative Example 3 (electrolytic production of aluminum)

Another anode made of cobalt metal oxidized under the conditions of Comparative Example 1, i.e. resulting in a coherent surface layer of Co ₂ O ₃ and Co ₃ O ₄ , was tested in an electrolytic cell for electrolytic aluminum production. The electrolyte of such an electrolyzer was at a temperature of 925 ° C and had the same composition as in Comparative Example 2. A nominal electrolysis current of 7.3 A was passed from the anode to the cathode at an anode current density of 0.8 A / cm ² .

The voltage at the electrolyzer at start-up was above 20 V and dropped to 5.6 V after about 30 seconds. During the initial 5 hours, the voltage across the cell fluctuated around 5.6 V between 4.8 and 6.4 V with short peaks above 8 V. After this initial period, the voltage across the cell stabilized at 4.0-4.2 V.

Throughout the electrolysis, fresh alumina was supplied to the electrolyte in order to compensate for the alumina already subjected to electrolysis.

After 100 hours of electrolysis, the anode was removed from the electrolyzer, allowed it to cool to room temperature and examined.

The diameter of the anode increased from 1.94 to 1.97 cm. The metal part of the anode was highly oxidized. The thickness of the one-piece scale has increased from 350 microns to about 1.1-1.5 mm. Scale consisted of: an outer layer 300-400 microns thick, containing pores with a size of 30-50 microns and having cracks; the inner layer is 1-1.1 mm thick, which was formed during electrolysis. The inner layer was porous and contained electrolyte under the cracks of the outer layer.

Example 3 (electrolytic production of aluminum)

An anode made of cobalt metal oxidized under the conditions of Example 1c, i.e. resulting in a coherent surface layer of CoO, was tested in an electrolytic cell for electrolytic aluminum production under the conditions of Comparative Example 3. A nominal electrolysis current of 7.3 A was passed from the anode to the cathode at an anode current density

0.8 A / cm ² .

At start-up, the voltage across the electrolyzer was 4.1 V and monotonically decreased to 3.7-3.8 V after 30 minutes (instead of 4-4.2 in Comparative Example 3). The voltage across the cell stabilized at this level throughout the test without significant fluctuations, in contrast to Comparative Example 3.

After 100 hours of electrolysis, the anode was removed from the electrolyzer, allowed it to cool to room temperature and examined.

The outer diameter of the anode did not change during electrolysis and remained equal to 1.94 cm. The inner part of cobalt metal below the scale decreased slightly from 1.85 to 1.78 cm. The thickness of the cobalt oxide scale increased from 0.3 to 0.7 -0.8 mm (instead of 1-1.1 mm in Comparative Example 3) and consisted of: a non-porous outer layer 300-400 microns thick; and a 400 micron porous inner layer that was formed during electrolysis. This growth of internal oxide (thickness 400 microns per 100 hours) was much less than the growth observed in Comparative Example 3 (thickness 1-1.1 mm per 100 hours).

It follows that the integral surface layer of the CoO anode slows down the diffusion of oxygen and the oxidation of the underlying metallic cobalt as compared with the integral surface layer of the Co ₂ O ₃ and Co ₃ O ₄ anode in Comparative Example 3.

Example 4 (Options)

The anode material of Examples 1a-1d, 2, and 3 can be coated after the formation of a single layer CoO layer by an applied suspension layer, in particular, containing CoFe ₂ O ₄ particles in an iron hydroxide colloid, followed by drying at 250 ° C to form a protective layer on a component of a single layer of CoO.

Example 5

A coated anode for use in the electrolytic cell according to the invention was made by coating a cobalt metal substrate with an electrochemically deposited active coating containing an outer layer of CoO and an inner layer of tantalum and cobalt oxides.

Such a coating was formed by applying cobalt and tantalum using electrodeposition. More specifically, tantalum was dispersed in the form of physical inclusions in electrolytic cobalt deposits.

The electrolyte for electrodeposition had a pH of from 3.0 to 3.5 and contained:

- 400 g / l CoSO ₄ · 7H ₂ O;

- 40 g / l H ₃ BO ₃ ;

- 40 g / l KCl; and

- 7-10 g / l of Ta particles.

Tantalum particles were less than 10 microns in size and were dispersed in an electrolyte for electrodeposition.

Electrodeposition on a cobalt substrate was performed at a current density of 35 mA / cm ² , which led to the formation of a cobalt deposit containing Ta inclusions, the deposit growing on the substrate at a speed of 45 microns per hour.

After deposition reached a total thickness of 250-300 microns, electrodeposition was interrupted. The deposition contained 9-15 wt.% Ta, which corresponds to a volume fraction of 4-7 vol.%.

In order to form a coating, the substrate with its deposition was subjected to oxidation treatment at a temperature of 950 ° C. The substrate with its deposition was brought from room temperature to a temperature of 950 ° C at a speed of 450-500 ° C / hour in an oven to optimize the formation of CoO instead of Co ₂ O ₃ or Co ₃ O ₄ .

After 8 hours at 950 ° C, the substrate and the coating that was formed by oxidation of the deposit were removed from the oven and allowed to cool to room temperature. The coating had an outer oxide layer of CoO on an inner oxide layer of Co-Ta oxides, in particular CoTaO ₄ , which grew from deposition. The innermost part of the deposition remained unoxidized, so that the Co-Ta oxide layer was integral with the remaining metallic Co-Ta deposition. The Co-Ta oxide layer and the CoO layer had a total thickness of about 200 microns on the remaining metallic Co-Ta.

As demonstrated in Example 6, this outer layer of CoO can act as an electrochemically active anode surface. The inner layer of Co-Ta oxides slows down the diffusion of oxygen to the cobalt metal substrate.

Example 6

The coated anode was made of a cobalt substrate coated with a Co-Ta coating, as in Example 5, and was used in an electrolytic cell for the electrolytic production of aluminum according to the invention.

Such an anode was suspended in the electrolyte of the electrolyzer at a distance of 4 cm from the cathode facing it. The electrolyte contained 11 wt.% AlF ₃ , 4 wt.% CaF ₂ , 7 wt.% KF and 9.6 wt.% Al ₂ O ₃ , the rest was Na ₃ AlF ₆ . The electrolyte was at a temperature of 925 ° C.

An electrolysis current was passed from the anode to the cathode at an anode current density of 0.8 A / cm ² . The voltage across the cell remained remarkably stable at 3.6 V throughout the entire electrolysis.

After 150 hours of electrolysis, the anode was removed from the electrolyzer. On visual inspection, no significant change in the size of the anode was observed.

Example 7

Example 5 was repeated by applying a Co-Ta coating on an anode substrate made of a metal alloy containing 75 wt.% Ni, 15 wt.% Fe and 10 wt.% Cu.

The anode was tested in the same manner as in Example 6, at an anode current density of 0.8 A / cm ² . At start-up, the voltage across the electrolyzer was 4.2 V and decreased within the first 24 hours to 3.7 V, and after that it remained stable.

After 120 hours of electrolysis, the anode from the cell was removed. Upon visual inspection of the anode, no signs of passivation of the nickel-rich substrate were observed, and no significant change in the size of the anode was observed.

Example 8

Examples 5 to 7 can be repeated when replacing tantalum with niobium.

Example 9

Another anode for use in the electrolyzer according to the invention was made by coating Co-W on an anode substrate made of a metal alloy containing 75 wt.% Ni, 15 wt.% Fe and 10 wt.% Cu.

The coating was formed by applying cobalt and tungsten using electrodeposition. The electrolyte for electrodeposition contained:

- 100 g / l CoCl ₂ · 6H ₂ O;

- 45 g / l Na ₂ WO ₄ · 2H ₂ O;

- 400 g / l KNaC ₄ H ₄ O ₆ · 4H ₂ O; and

- 50 g / l NH ₄ Cl.

In addition, NH ₄ OH was added to this electrolyte so that the electrolyte reached a pH of 8.5-8.7.

Electrodeposition on the Ni-Fe-Cu substrate was performed at a temperature of 82-90 ° C and a current density of 50 mA / cm ² , which led to the deposition of cobalt-tungsten alloy on the substrate, and the deposition grew at a rate of 35-40 microns per hour at a cathode current output of approximately 90%.

After deposition reached a total thickness of approximately 250 microns, electrodeposition was interrupted. The deposited cobalt alloy contained 20-25 wt.% Tungsten.

In order to form a coating, the substrate with its deposition was subjected to oxidation treatment at a temperature of 950 ° C. The substrate with its deposition was brought from room temperature to 950 ° C at a rate of 450-500 ° C / hour in an oven in order to optimize the formation of CoO instead of Co ₂ O ₃ or Co ₃ O ₄ .

After 8 hours at 950 ° C, the substrate and the coating that was formed by oxidation of the deposit were removed from the oven and allowed to cool to room temperature. The coating contained cobalt monoxide and tungsten oxide on its surface.

The structure of the coating after oxidation was denser and more coherent than that of the coating obtained by oxidizing the electrodeposited Ta-Co layer, as disclosed in Example 1.

As demonstrated in Example 10, this coating can act as an electrochemically active anode surface. The presence of tungsten slows the diffusion of oxygen to the cobalt metal substrate.

Example 10

The anode was fabricated as in Example 9, and was used in an electrolytic cell to electrolytically produce aluminum according to the invention.

Such an anode was suspended in the electrolyte of the electrolyzer at a distance of 4 cm from the cathode facing it. The electrolyte contained 11 wt.% AlF ₃ , 4 wt.% CaF ₂ , 7 wt.% KF and 9.6 wt.% Al ₂ O ₃ , the rest was Na ₃ AlF ₆ . The electrolyte was at a temperature of 925 ° C.

An electrolysis current was passed from the anode to the cathode at an anode current density of 0.8 A / cm ² . The voltage across the electrolyzer remained stable at 3.5-3.7 V throughout the electrolysis. After 100 hours of electrolysis, the anode was removed from the cell. On visual inspection, no change in the size of the anode was observed.

Example 11

Examples 9 and 10 can be repeated with an anode support made of cobalt, nickel or an alloy of 92 wt.% Nickel and 8 wt.% Copper.

Comparative tests show that the use of a metal-based anode in a traditional cryolite-based electrolyte at 960 ° C with an electrochemically active outer part containing a layer that contains predominantly cobalt oxide CoO leads to accelerated oxidation of the anode and dissolution of the oxides from this anode in the electrolyte , in particular, CoO. Moreover, the use of such an anode in an electrolyte at 910 ° -940 ° C without potassium fluoride leads to corrosion or passivation of the anode.

These Examples demonstrate that a material having an outer part with a layer that contains predominantly cobalt oxide CoO, as described above, provides increased stability during use in an electrolytic cell for the electrolytic production of aluminum and is therefore suitable for protecting anodes having a flow structure that undergoes the influence of molten electrolyte on a fluoride basis, which becomes more aggressive with respect to the anodes when it is circulated through these anodes.

Claims (51)

1. An electrolyzer for the electrolytic production of aluminum from alumina dissolved in a fluoride-containing molten electrolyte, containing at least one non-carbon metal-based anode, having an electrically conductive metal structure, which contains an outer part with an electrochemically active anode surface, on which oxygen is released during electrolysis , and which is suspended in the electrolyte, essentially parallel to the cathode facing it, and the metal structure mentioned has one or more flow holes extending from the active anode surface through this metal structure, said flow passage hole (s) being made (s) with the possibility of directing the circulation of the electrolyte, driven by the rapid release of anodically released oxygen, said outer part of the anode contains a layer that contains predominantly cobalt oxide CoO. 2. The cell of claim 1, wherein the anode structure is a perforated structure. 3. The cell according to claim 2, in which the anode structure contains a series of parallel anode elements, in particular horizontal anode elements having electrochemically active surfaces in a generally coplanar arrangement to form said active anode surface, these anode elements being separated from each other with the formation of elongated flow holes for the circulation of the electrolyte, driven by the rapid release of anodic oxygen. 4. The cell according to claim 3, in which the anode elements are blades, rods, rods or wires. 5. The cell of claim 1, wherein the active anode surface is substantially horizontal. 6. The cell of claim 1, wherein the active anode surface is substantially vertical or inclined relative to the horizontal. 7. The electrolyzer according to claim 1, in which the molten electrolyte is at a temperature below 950 ° C, in particular in the range from 910 to 940 ° C, and consists of
from 6.5 to 11 wt.% dissolved alumina, in particular from 7 to 10 wt.%;
from 35 to 44 wt.% aluminum fluoride, in particular from 36 to 42 wt.% aluminum fluoride, for example, from 36 to 38 wt.%;
from 38 to 46 wt.% sodium fluoride, in particular from 39 to 43 wt.%;
from 2 to 15 wt.% potassium fluoride, in particular from 3 to 10 wt.% potassium fluoride, for example, from 5 to 7 wt.%;
from 0 to 5 wt.% calcium fluoride, in particular from 2 to 4 wt.% calcium fluoride; and
from 0 to 5 wt.% in the sum of one or more additional components, in particular up to 3 wt.%. 8. The electrolyzer according to claim 7, in which the electrolyte as an additional component (s) contains at least one fluoride selected from magnesium fluoride, lithium fluoride, cesium fluoride, rubidium fluoride, strontium fluoride, barium fluoride and cerium fluoride . 9. The electrolyzer according to claim 1, in which the electrolyte contains alumina in a concentration near saturation on the active anode surface. 10. The cell of claim 1, wherein said CoO-containing layer is integral with the core made of cobalt or cobalt alloy. 11. The electrolyzer according to claim 1, in which the anode contains an electrically conductive substrate, which is coated with an applied electrochemically active coating, which contains said CoO-containing layer. 12. The electrolyzer according to claim 11, in which the CoO-containing layer is a layer of sintered particles. 13. The electrolyzer according to claim 11, in which the CoO-containing layer is an integral oxide layer on the deposited Co-containing metal layer of this coating. 14. The electrolyzer according to claim 11, which contains an oxygen barrier layer between the CoO-containing layer and the electrically conductive substrate. 15. The cell of claim 14, wherein the oxygen barrier layer comprises at least one metal selected from nickel, copper, tungsten, molybdenum, tantalum, niobium, and chromium, or an oxide thereof. 16. The cell of claim 15, wherein the oxygen barrier layer further comprises cobalt. 17. The electrolyzer according to clause 16, in which the oxygen-barrier layer is a cobalt alloy containing at least one metal selected from nickel, tungsten, molybdenum, tantalum and niobium. 18. The electrolyzer according to 17, in which this cobalt alloy contains
at least one of nickel, tungsten, molybdenum, tantalum and niobium in a total amount of from 5 to 30 wt.%, in particular 10-20 wt.%; and
one (but) or more additional elements and compounds in a total amount of up to 5 wt.%,
the rest is cobalt. 19. The cell of claim 18, comprising as said additional elements at least one of aluminum, silicon and manganese. 20. The cell of claim 14, wherein the CoO-containing layer is integral with the oxygen barrier layer. 21. The cell of claim 14, wherein the oxygen barrier layer is integral with the electrically conductive substrate. 22. The cell of claim 14, wherein the oxygen barrier layer and the CoO containing layer or their precursors are separate deposited layers. 23. The cell of claim 13, wherein the Co-containing metal layer contains cobalt in an amount of at least 95 wt.%, In particular more than 97 wt.% Or 99 wt.%. 24. The cell of claim 13, wherein the Co-containing metal layer contains at least one additive selected from silicon, manganese, nickel, niobium, tantalum and aluminum, in a total amount of from 0.1 to 2 wt.%. 25. The electrolyzer of claim 11, in which the electrically conductive substrate contains at least one metal selected from chromium, cobalt, hafnium, iron, nickel, copper, platinum, silicon, tungsten, molybdenum, tantalum, niobium, titanium, tungsten, vanadium , yttrium and zirconium, or a compound thereof, in particular an oxide, or a combination thereof. 26. The electrolytic cell according A.25, in which the electrically conductive substrate has an outer part made of cobalt or a cobalt-rich alloy, on which said coating is applied. 27. The electrolyzer according to claim 26, wherein the outer part is made of a cobalt-rich alloy containing at least one of nickel, tungsten, molybdenum, tantalum and niobium, said cobalt alloy containing, in particular
at least one of nickel, tungsten, molybdenum, tantalum and niobium in a total amount of from 5 to 30 wt.%, in particular 10-20 wt.%; and
one (but) or more additional elements and compounds in a total amount of up to 5 wt.%,
the rest is cobalt. 28. The electrolyzer according to claim 11, in which the electrically conductive substrate contains one or more or consists essentially of one or more oxidation-resistant metals. 29. The electrolyzer of claim 28, wherein said one or more oxidation-resistant metals is selected (s) from nickel, cobalt, chromium and niobium. 30. The electrolytic cell according A.25, in which the electrically conductive substrate is an alloy of Nickel, iron and copper, in particular an alloy containing from 65 to 85 wt.% Nickel; from 5 to 25 wt.% iron; from 1 to 20 wt.% copper; and from 0 to 10 wt.% additional components. 31. The electrolyzer of claim 10, in which the core is made of the same material as the oxygen barrier layer according to any one of paragraphs.16 to 19; Co-containing metal layer according to item 23 or 24; or cobalt-rich alloy according to claim 27. 32. The electrolyzer according to claim 1, in which the CoO-containing layer has an open porosity of up to 12%, in particular up to 7%. 33. The electrolyzer according to claim 1, in which the CoO-containing layer has a porosity with an average pore size of less than 7 microns, in particular less than 4 microns. 34. The electrolyzer according to claim 1, in which the CoO-containing layer contains cobalt oxide CoO in an amount of at least 80 wt.%, In particular more than 90 wt.% Or 95 wt.%. 35. The electrolyzer according to claim 1, in which the CoO-containing layer is essentially free of Co ₂ O ₃ and essentially free of Co ₃ O ₄ . 36. The electrolyzer according to claim 1, in which the CoO-containing layer is electrochemically active with respect to the oxidation of oxygen ions and uncoated or coated with a layer permeable to electrolyte. 37. The electrolyzer according to claim 1, in which the CoO-containing layer is coated with a deposited protective layer, in particular a deposited oxide layer. 38. The electrolyzer according to clause 37, in which the applied protective layer contains cobalt oxide. 39. The electrolyzer according to clause 37, in which the applied protective layer contains iron oxide. 40. The electrolyzer according to § 39, in which the applied protective layer contains oxides of cobalt and iron, in particular cobalt ferrite. 41. The electrolyzer according to clause 37, in which the applied protective layer contains a compound of cerium, in particular cerium oxyfluoride. 42. The electrolyzer according to clause 37, in which the applied protective layer is electrochemically active with respect to the oxidation of oxygen ions and uncoated or coated with a layer permeable to electrolyte. 43. The electrolyzer according to claim 1, which has an electrochemically active surface that contains at least one additive, in particular at least one additive selected from metals iridium, palladium, platinum, rhodium, ruthenium, silicon, tungsten, molybdenum, tantalum , niobium, tin or zinc, mischmetal, metals of a number of lanthanides, in the form of metals and compounds, in particular oxides, and mixtures thereof. 44. The electrolyzer according to item 43, in which the electrochemically active surface is made of an active material containing this (s) additive (s) in a total amount of from 0.1 to 5 wt.%, In particular from 1 to 4 wt.%. 45. The electrolyzer according to claim 1, containing a cathode, which has a wettable surface of aluminum, in particular a horizontal or inclined drained surface. 46. The electrolyzer according to item 45, in which the cathode has a wettable aluminum coating, which contains refractory boride and / or promotes wetting with aluminum oxide. 47. The electrolyzer according to claim 1, in which the anode is suspended in an electrolyte on a rod, in particular a rod having an outer part containing a layer that contains mainly cobalt oxide CoO. 48. A method for producing aluminum in an electrolytic cell according to any one of claims 1 to 47, comprising transmitting an electric current through said or each active anode structure to its active anode surfaces in the form of an electronic current and through the electrolyte to the cathode in the form of an ion current, whereby carry out the electrolysis of dissolved alumina to produce aluminum at the cathode (s) and oxygen on the active anode (s) surface (s), which is discharged through said flow openings. 49. The method according to p, in which oxygen ions are oxidized on the anode layer, which contains mainly cobalt oxide CoO. 50. The method according to p, in which oxygen ions are oxidized on the active layer deposited on the anode layer, which contains mainly cobalt oxide CoO. 51. A non-metallic metal-based anode for the electrolytic production of aluminum from alumina dissolved in a fluoride-containing molten electrolyte, containing an electrically conductive metal structure that contains an outer part with an electrochemically active anode surface on which oxygen is anode released, and which is suspended in the electrolyte during use by essentially parallel to the cathode facing it, and said metal structure has one or more flow openings, rubbing from the active anode surface through this metal structure, the aforementioned flow-through hole (s) being made (s) with the possibility of directing during use the circulation of the electrolyte, driven by the rapid release of anode released oxygen, while the outer part the anode contains a layer that contains predominantly cobalt oxide CoO.

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