RU2331721C2 - Electrolysis method and electrolytic agent used therein - Google Patents

Abstract

FIELD: electrics.

SUBSTANCE: invention relates to electrolysis method and to electrolytic agent used to extract metal from water solution. Method includes the stage dealing with current of non-uniform density generation along collecting surface so that sections with high current density could be generated together with low current density sections in alternating manner. Difference between high density sections and low density sections is sufficient to cause metal deposition concentrating in high density sections to facilitate non-uniform metal deposition on surface. Electrolytic agent contains cathode with collecting surface where metal is deposited during water solution electrolysis. Electric field of cathode collecting surface is not uniform. It has sections of strong electric field alternating with weak electric field sections due to creation of ordered set of alternating ridges and hollows. Ridges form strong electric field sections while hollows form weak electric field sections.

EFFECT: facilitation of metal deposition removal.

29 cl, 17 dwg

Description

FIELD OF THE INVENTION

The present invention relates generally to an electrolysis method for extracting metals from an aqueous solution and to an improved cathode for use in such a method. The main use of the invention disclosed herein is associated with the extraction of copper, however, the invention also finds application in the electrochemical extraction of other metals such as nickel, lead, zinc, etc.

State of the art

In the field of hydrometallurgy, methods are known for leaching base metals from ores and concentrates, followed by recovery of the base metal in electrolyzers. One example of such a method is disclosed in Australian Patent Application No. 42999/93 (669906). This method is multi-stage and gives a stream of a saturated solution after leaching of the mineral in a chloride medium. The stream of saturated solution is subjected to electrolysis in the electrolysis cell to extract metal from the solution, which is deposited on the cathode of the electrolyzer. At high current densities, high-purity dendritic copper forms on the cathode. In the past, it was necessary to periodically remove the cathodes to clean the plates from metal deposits in order to maintain the current output in the cell.

The optimization of the electrochemical extraction operation depends on the purity of the saturated solution stream and the general parameters of the electrolyzer, such as current density, purification cycle, electrolyzer configuration and degree (intensity) of mixing. In accordance with the foregoing, the aim of the present invention is to increase the efficiency of the operation of electrochemical extraction. In particular, the goal is to create an electrolysis method and an electrolytic cell design that is better able to control the current density over the cathode deposition surface in order to facilitate both the formation and removal of the metal deposit.

Disclosure of invention

In a first aspect of the present invention, there is provided an electrolysis method for recovering metal from an aqueous solution, wherein during electrolysis, dissolved metal is precipitated on the cathode deposition surface, the method comprising the step of creating an uneven current density over the deposition surface so as to form high current density regions interleaved sections of low current density, while the difference between sections of high current density and low current density is sufficient to It is necessary to cause the concentration of metal deposition in areas of high current density to promote uneven deposition of metal over the deposition surface.

In the context of the invention, the deposition surface may have an integral structure (monolithic structure) or, alternatively, may be made of separate elements that can be spaced from each other or in direct contact with each other.

Creating a non-uniform current density over the deposition surface provides a mechanism by which the deposition of metal on a given surface can be controlled. In particular, this allows the concentration of metal deposition to be concentrated in certain areas (i.e., areas of high current density) in order to facilitate uneven deposition over the surface. Uneven deposition of the metal is advantageous because it is easier to remove from the cathode, which contributes to the process of metal extraction.

Preferably, metal deposition is highly concentrated in high current density regions, such that metal deposition over the deposition surface is virtually intermittent. During operation of the electrolyzer, the concentration of the metal deposit in the areas of high current density is preferably more than 80%, and more preferably more than 95%.

Preferably, the areas of high current density and low current density are elongated along the surface in one direction and alternate on the surface in the opposite direction. With this design, the metal is deposited in the form of a sequence of generally linear stripes, which is ideal for removal using a cleaning action, which will be described in more detail below.

Preferably, the electrolysis method causes an uneven current density over the deposition surface by providing a cathode that, when the cell is operated, creates an inhomogeneous electric field with areas of a strong electric field and a weak electric field. With this design, areas of a strong electric field create areas of high current density, and areas of a weak electric field create areas of low current density.

An inhomogeneous electric field can be created by numerous mechanisms, including surface geometry, and by changing the electrical resistance between the cathode and anode along the deposition surface, or by combining both of these mechanisms.

The geometry of the surface affects the electric field and is associated with the curvature of the surface. Electric fields are always perpendicular to the surface and therefore sharp edges or peaks on the deposition surface create areas of a stronger electric field compared to areas of a flat surface or troughs. The electrical resistance can vary due to the use of different materials along the deposition surface (for example, supplying sections with insulating material) or due to a change in the current path length between the cathode and anode.

In a preferred embodiment, an inhomogeneous electric field is induced on the deposition surface due to the geometry of the surface and, in particular, due to the formation of a sequence of ridges and depressions alternating on the surface. Due to this geometry, during operation of the electrolyzer, the electric field along the ridges is stronger than along the troughs. In addition, the current path length on the ridges is shorter than on the troughs, which creates a situation in which there is less resistance on the ridges compared to the troughs.

The change in current density over the deposition surface may be such that there is a sharp separation between the areas of high current density and low current density, or, alternatively, there may be a more gradual (smooth) transition between areas of high current density and low current density.

Applicant has found that creating a gradual transition between the areas of highest and lowest current density still provides good deposition profiles in order to promote substantially intermittent growth over the deposition surface. In particular, the applicant has found that the use of a cathode, which includes a deposition surface with ridges and depressions and in which there are no abrupt transitions between ridges and depressions so that a more gradual change occurs between the highest current density and the lowest current density, provides high working characteristics. This design causes secondary effects that contribute to the concentration of metal deposition on the ridges, as described in more detail below, and also provides easier metal removal, since it allows easier access to the entire deposition surface, as opposed to a sharp transition between the ridge and the cavity, which can create areas that are difficult to approach.

In a preferred embodiment, in which the electrolyzer is designed to separate copper from an aqueous solution, the current density in the areas of high current density is in the range from 500 to 2500 A / m ² , and more preferably is 1000 A / m ² . The current density in the areas of low current density is preferably in the range from 0 to 1250 A / m ² , and more preferably from 0 to 500 A / m ² .

In the case of a gradual transition between the sections of the highest current density and the lowest current density, the separation between the sections of "high current density" and "low current density" is somewhat arbitrary. With this design, the transition region can be considered as a section of moderate (average) current, which, in turn, is located between adjacent sections of "high current density" and sections of "low current density".

Preferably, the method further includes the step of removing the deposited metal from the deposition surface by conducting the element on the surface.

Preferably, in the design where the high current density and low current density sections are elongated along the surface in one direction and alternate on the surface in the opposite direction, the element is moved in the direction in which the high and low current density sections are stretched.

Preferably, the deposited metal is removed by the element while maintaining an electric current in the aqueous solution. In this case, the process can be substantially continuous.

In yet another aspect, the present invention relates to an electrolytic cell for electrochemical extraction of metal from an aqueous solution containing a cathode, which includes a deposition surface onto which the metal is deposited during electrolysis of the aqueous solution, and during operation of the electrolyzer, the deposition surface has an inhomogeneous electric field, so that there are sections of a strong electric field interspersed with sections of a weak electric field, and the difference between the sections of a strong electric field and the God electric field is sufficient to cause the concentration of metal deposition in areas of strong electrical field to promote non-uniform deposition of metal on the surface.

Preferably, the areas of strong electric field and weak electric field are elongated along the surface in one direction and alternate on the surface in the opposite direction. In a particularly preferred embodiment, the deposition surface of the cathode contains a set of alternating ridges and depressions, while the ridges form areas of a strong electric field, and depressions form areas of a weak electric field.

Profiling the deposition surface to produce a set of alternating ridges and depressions provides a significant advantage in contributing to the substantially intermittent deposition of metal at the cathode. Such profiling usually promotes the deposition of metal in the form of dendrite growth on each of the ridges. The resulting dendrites provide the advantage of easy removal (as described below). Such a profile not only provides a suitable uneven current density at the beginning of operation of the electrolyzer for concentrating metal deposition on ridges in the form of dendrites, but also helps to maintain intermittent growth as the process continues. It should be understood that, as soon as the metal is deposited on the deposition surface, the deposited metal forms a continuation of the deposition surface. The advantage of using a structure with ridges and depressions is that, as the crests grow, dendrites tend to “obscure” the depressions, which further prevents the deposition of metal in the depressions. In addition, the aqueous solution tends to stagnate in the depressions, which further prevents the deposition of metal in the depressions. In tests conducted by the applicant using a profile of alternating ridges and depressions, more than 98.8% of the metal was deposited on the ridges of the deposition surface.

Although the beneficial effects of using ridges and troughs can be achieved with a variety of profiles, applicants have found that good results are achieved by a periodic profile in which the surfaces between the top of the ridge and the base of the trough are substantially linear and have an internal angle of approximately 60 ° between adjacent surfaces . In addition, the pitch between adjacent ridges is preferably of the order of 10–40 mm, more preferably 15–25 mm, and the depth between the ridge and depression is of the order of 8–32 mm, and is preferably in the range of 12–20 mm. It has been found that a deposition surface with these characteristics gives substantially discontinuous metal deposits. An additional advantage is that this profile allows you to clean the surface, essentially, without creating "hot spots" in current density, which would lead to contamination of metal deposits. If the current density in some place is too high, then as the deposition proceeds, this leads to concentration polarization (which takes place around the growing sediment). If this phenomenon occurs, then a relatively large amount of impurity inclusions can appear in the deposited metal (for example, in copper). Therefore, it is important to control the current density at a given location. An advantage of the aforementioned profile is that the high current density portions on which the metal is deposited continue to occupy a significant portion of the total cathode area (i.e., approximately 25-35% of the total deposition surface area). With this design, the current can be maintained at a substantially constant value regardless of whether the surface is clean of metal precipitation or precipitation has already occurred. As such, there is no need to increase the current when starting (turning on) the electrolyzer, since the profile itself is not inclined to create strong "hot spots" in current density, which are likely to cause problems at the beginning of metal deposition.

In a particularly preferred embodiment, the cathode includes a sheet with at least one main surface that forms a deposition surface of the cathode, the sheet being preformed to give it alternating ridges and depressions. Therefore, the sheet may define a corrugated profile. This pre-molding operation is preferably achieved by folding (folding) the sheet, but it can be performed in any other suitable way, such as stamping, milling, crimping, casting, or combinations thereof.

In a particularly preferred embodiment, the sheet is made of titanium or similar material resistant to oxidation. Although other oxidation-resistant materials such as platinum, stainless steel, and corrosion-resistant metal alloys can be used, titanium is most preferred because of its high oxidation resistance and its ability to resist the formation of metallurgical bonds with metals such as copper , and due to its relative availability.

An additional advantage of using a corrugated profile is that it helps to maintain dimensional stability of the sheet. This design can help overcome the disadvantages of prior art designs in which sheet cathodes tend to bend and deform. In addition, when the metal is deposited on the sheet in the form of growing dendrites or crystallites, the dimensional stability of the sheet allows the use of stripping methods to easily remove sediment from the sheet. Applicants have found that titanium sheets with a thickness of the order of 1.6 mm provide sufficient dimensional stability for this method.

Preferably, the sheet is adapted to be attached during operation to the conductive top beam. This upper beam during operation serves as a support for the cathode and brings electrons to it.

In one embodiment, opposing major surfaces of the folded sheet are used as deposition surfaces during cathode operation.

In an alternative embodiment, the cathode is made in the form of a composite structure and further comprises a conductive element that extends (stretched) along the sheet. The conductive element is electrically connected to the sheet so as to supply the deposition surface with electrons during electrolysis during operation. One of the advantages of using a conductive element that extends along the sheet is that it minimizes the ohmic voltage drop that occurs when electrons are fed from only one edge of the sheet. A second advantage of using a conductive element is that it can be of sufficient size to stiffen the sheet so as to further maintain the dimensional stability of the cathode. Therefore, with the composite structure, thinner sheet structures for the deposition surface (s) can be used.

In a preferred embodiment of this latter construction, the cathode comprises a second sheet that is connected to the first sheet and which has a main surface that forms a second cathode deposition surface, the second sheet being preformed to give it alternating ridges and depressions along this deposition surface. Preferably, the second sheet is connected to the first sheet of the cathode so as to form a plurality of cavities that are elongated in the direction of alternating ridges and depressions. At least some of these cavities are arranged to accommodate a cathode conductive element therein.

In a preferred embodiment, the stripping device is arranged to conduct along the deposition surface of the cathode in order to remove the deposited material from the deposition surface. In a particularly preferred embodiment, in which the cathode comprises a profile of ridges and depressions, the stripping device comprises a plurality of protrusions that are adapted to fit into the depressions of the deposition surface. In a preferred embodiment, these protrusions are made of ceramic material, but they can be made of any other corrosion-resistant material.

In a preferred embodiment, the protrusions are movable between the first and second positions and are arranged to surface along any of these positions. In the first position, the element is in contact with or in close proximity to the deposition surface, so that it removes substantially all of the deposited material from this surface. In the second position, the element is preferably spaced from the deposition surface and configured to remove the deposited material that protrudes a predetermined distance from the deposition surface.

In yet another aspect, the present invention relates to a cathode for use in any of the above embodiments of a method or cell.

In yet another aspect, the present invention relates to a cleaning system for use in any of the above cell options.

In yet another aspect, the present invention relates to a cathode for use in an electrolytic cell for electrochemical extraction of metal from an aqueous solution containing a deposition surface with a plurality of ridges interspersed with a plurality of depressions, the cathode profile being intended to cause the deposition of metal on the ridges to concentrate during the operation of the cell to facilitate uneven metal deposition on this surface.

Brief Description of the Drawings

Although there are various variations that may fall within the scope of the present invention, the following, by way of example only, describes preferred embodiments of the invention with reference to the accompanying drawings, in which:

Figure 1 is a generalized block diagram of the processing and extraction of copper;

Figure 2 is a view in section of an electrolytic cell in accordance with one embodiment of the invention with sets of scrapers of the electrolytic cell in the closed position;

Figure 3 is a side view in section of the electrolyzer of Figure 2;

Figure 4 is a sectional view of the cell of Figure 2 with scrapers in the open position;

Figure 5 is a partial view of the lever mechanism assembly in the cell of Figure 2;

Fig.6 is a perspective view with a local section of the electrolyzer of Fig.2;

7 is an enlarged schematic view of the scrapers located in the open position on top of the cathode plates;

Fig is an enlarged local view of the scrapers in the closed position;

Fig.9 is a front view of the cathode panel used in the electrolyzer of Fig.2;

Figure 10 is an end view of the panel of Figure 9;

11 is a schematic perspective view of a scraper meshed with the cathode in the electrolyzer of FIG. 2;

Fig is a view in section along the line XII-XII in Fig.11;

Fig.13 is a local view of the design of the blade of the scrapers used in the electrolyzer of Fig.2;

Fig and 15 are variants of the design of the blade depicted in Fig;

FIG. 16 is a schematic perspective view of an alternative construction of a cathode for use in the cell of FIG. 2; and

Fig.17 is a view in section along the line XVII-XVII of the cathode of Fig.16.

Embodiments of the invention

Figure 1 schematically shows a complex process 100, including leaching and electrochemical extraction 104 of metal. In a preferred embodiment of this process, the crushed copper sulfide 106 is fed into a multi-stage countercurrent leaching process in which the metals are brought into solution by oxidation with a leach agent. In a preferred embodiment, the leachant contains a complex halide substance that is formed on the anode in a subsequent electrolysis step and fed back to the leach step as part of the recycled electrolyte 108.

Dissolved metals in the desired oxidation state are removed from the leaching process at various stages in the leachate. The leachate is passed through a filtration step 110 to remove unwanted solid particles such as sulfur and iron oxide (III). The leachate is then fed to purification step 112 to remove metals that could otherwise contaminate subsequent electrolysis (such as silver and mercury). Polluting metals may be precipitated as metal oxide or carbonate.

Then, the purified leachate is fed to the electrolysis stage 104, which can be implemented in many groups of electrolytic cells (electrolytic cells) connected in series and / or in parallel. In each group, it is possible to obtain a different metal, while metallic copper is usually electrochemically extracted in the electrolyzers of the first group, and metals such as zinc, lead and nickel are extracted in electrolyzers of subsequent or parallel groups. The electrolysis process is usually carried out so that a strongly oxidizing leach (such as a complex halide substance) is obtained at the anode. Then the spent electrolyte (anolyte) is returned (recycled) to the leaching stage with the strongly oxidizing leach contained in it, which is involved in further countercurrent leaching. Therefore, the process can be carried out continuously.

The present invention relates to the optimization of electrochemical extraction of metals and relates to significant structural improvements in the electrolysis process, including improved design and geometric shape of the cathode.

Turning now to FIGS. 2-5, the electrolyzer 10 for use in the process 100 contains a series of cathode plates 11 that are located in the electrolysis bath 50 with the anodes 12 in the spaces between them. The electrolyte supplied to the electrolyzer provides the flow of electric current between the anodes and cathodes. The outer surfaces 13, 14 of the respective cathodes form a deposition surface in the cell, on which the recoverable metal is deposited during operation of the cell 10. As described in more detail below, the cathode plates are made of a generally corrugated profile with alternating ridges and depressions in order to influence the deposition mode of the metal on the respective deposition surfaces 13 and 14.

The cell 10 contains a cleaning system 15, which contains many scraper sets 16, designed to enter with the pairing between the respective cathodes and anodes, while the scrapers 17 of the corresponding scraper sets 16 are designed to move on the deposition surfaces 13 and 14 of the respective cathodes 11 in order to remove precipitation of metal from these surfaces. The scrapers 17 are arranged to strip the respective deposition surfaces 13 and 14 at predetermined intervals so as to cause the separated metal to fall to the bottom of the cell 10, where it moves to the conveyor 18 to be removed from the cell.

To achieve this cleaning action, two fundamental movements are provided in the cleaning system 15, the first being a vertical movement that allows the scraper sets 16 to move between the top and bottom of the respective cathodes 11, and the second allows the scrapers 17 of each set 16 to be moved from the open position ( most clearly shown in Fig.7) in the closed position (most clearly shown in Fig.8).

Scraper kits 16 are mounted on a frame 32, which is fixed at its upper end to four support posts 19, 20, 21 and 22. Each of these posts contains a helical groove 23 that interacts with a worm wheel 24 connected to the frame 32. Thus, frame 32 moves relative to the uprights. The electric motor 25, mounted on the transverse beam 26, is designed to drive the worm wheels 24 to ensure vertical movement of the scraper sets relative to the deposition surfaces 13 and 14. During this operation, the scrapers are capable of moving between the lower position shown in FIG. 2 and the upper position shown in FIG. 4.

The frame 32 serves as a support for the lever mechanism 27, which, in turn, is connected to the scraper sets 16. The lever mechanism 27 contains a pair of connecting plates 28 on each side of the scraper sets 16, which are connected to the corresponding connecting rods 29. The link 30 is pivotally connected to the corresponding pairs of connecting plates 28 by means of rotary axes 31. The link arms 40 extend from the link 30 to the scraper sets 16 to provide support for each end of the scraper sets. The connecting rods 29 are adapted for vertical movement by means of the second drive 41. In the depicted embodiment, the second drive is made in the form of worm wheels that interact with helical grooves made on the respective connecting rods. The worm wheels rotate and cause the connecting rods 29 to rotate to bring these rods into vertical motion relative to the frame 32, which, in turn, drives the link 30 to move the scrapers between their open and closed positions. The second drive can be damped to prevent pinching and jamming of the scrapers at the cathode. Cushioning can be provided with a spring clutch or by using a pneumatic cylinder instead of a worm wheel.

As best shown in FIG. 6, each cathode line in the cell 10 is made of a plurality of cathode plates 11, which are connected to the upper beam 34 so that the individual plates are suspended in the bath 50. The upper beam 34 is conductive and connected to a power source for supply electrons to the cathode.

Typically, an electrolyte has high corrosivity due to a characteristic 5 molar or higher concentration of alkali or alkaline earth metal halides. To enable parts to work in this environment, the cleaning system 15 is made of a corrosion-resistant material, which is preferably titanium. Other suitable materials include platinum, stainless steel, corrosion-resistant metal alloys (e.g. Hastalloy C 22), or even some plastics. In addition, titanium is most preferred for the cathode because of its excellent corrosion resistance and its ability to withstand the formation of metallurgical bonds with a metal such as copper, and because of its relative availability (and therefore cost-effective). The resistance of titanium to the formation of metallurgical bonds improves the ability of the plates to strip using the above-described stripping system.

Figures 9 and 10 illustrate the construction of individual cathode plates 11. In the illustrated embodiment, the cathode plate 11 is made of a titanium sheet with a thickness that is preferably about 1.6 mm. The applicant has determined that sheets of this thickness give the cathode plate the necessary rigidity to prevent warping during operation. The titanium sheet is folded to form a generally corrugated profile so as to provide alternating depressions and ridges 35, 36 on each deposition surface 13, 14, respectively. These folds extend along the entire length of the cathode from its upper edge 37 to the lower edge 38, respectively.

In the depicted embodiment, the distance between adjacent ridges 36 is 20 mm, and the depth between the top of the ridges 36 and the bottom of the troughs 35 is approximately 16 mm. The surfaces 43 of the walls formed on the corrugated sheet are generally linear and have an internal angle at the top of the ridges and the bottom of the troughs at approximately 60 °.

The main purpose of giving folds to the cathode is to influence the current density on the deposition surfaces 13, 14 during operation of the electrolyzer. In particular, folds on the deposition surface cause an uneven electric field on this surface during operation of the cell.

The corrugated deposition surface on the cathode creates high current density bands along the cathode ridges due to the corresponding strong electric field in these areas and relatively low current densities in the valleys. This causes concentrated metal deposition in high current density areas and contributes to uneven surface deposition, so that the vast majority of the deposition occurs in the region 35 of the ridges of the deposition surface. The creation of substantially intermittent deposition improves the ability to remove the extracted metal from the cathode using the wiper system 15.

The deposition surface profile with depressions and ridges causes an uneven electric field due to two mechanisms. Firstly, due to the geometry of the profile, the electric field will be stronger on the ridges than in the troughs, due to the curvature of this surface. In general, electric field lines are always perpendicular to the surface. Therefore, on each ridge there will be a concentration of the field along these points. Secondly, the path of electric current on ridges is shorter than the path of electric current on cavities. As a result, there is less resistance on ridges than in troughs.

In addition, the use of a corrugated profile at the cathode allows more precise control at the main deposition sites (i.e. along ridges). If the current density in some place is too high, then this leads to concentration polarization (which takes place around the growing precipitate) as the deposition proceeds. If this phenomenon occurs, then a relatively large amount of impurity inclusions can appear in the deposited metal (for example, in copper). With a corrugated profile, the main deposition sites account for approximately 25-35% of the total cathode surface area. Depending on the mass transfer, ideally, the current on the deposition surface should be about 1000 A / m ² or less. As dendrites grow on this surface, the actual surface area of the deposition increases, as the metal is deposited on the previously deposited metal. If the initial deposition sites on the cathode are too small, then there is a tendency for the current density at this location to become too high after dendrites are removed from the cathode. By tests carried out by the applicant using a corrugated profile, it was found that the current density at the deposition sites both at the beginning of the operation of the electrolyzer and after the dendrites increased, can be maintained near 1000 A / m ² in order to ensure high quality of the deposited metal . As such, there is no need to change the current during the process.

An additional advantage of using a corrugated profile at the cathode is that it increases the rigidity of the cathode plate, since the corrugated profile is inherently stiffer than a flat plate along the direction of ridges and depressions. In addition, the corrugated profile is ideally suited for cleaning using the blade cleaning system described in more detail below.

As can be seen from 11-15, the scrapers 17 contain fingers 39, which are fixed between a pair of strips 42. In the depicted embodiment, each of the individual fingers is made of ceramic material, and the strips are made of titanium. Each of the fingers is mounted along the strip 42 with such a step that the scrapers 17 generally coincide in shape with the corrugated cathode plate 11, with the individual fingers entering the depressions 35 of the deposition surface and extend over the respective ridges 36.

As best shown in FIG. 12, the stripping system 15 is structurally designed so that when the scraper sets 16 are in their closed position, the scrapers 17 are at an angle to the cathode plate 11 and therefore the individual fingers 39 are in a lagging position ( behind) relative to the line of movement of the scraper 17 down the cathode plate 11. This design is preferable because it does not allow jamming of fingers in the hollows, which could happen if fingers 39 were in the leading position relative to respect to the direction of motion of the scraper down the cathode plate.

As described above, due to the configuration of the cathode plates 11, the metal extracted from the cell is concentrated on the ridges of the respective deposition surfaces of the cell. Essentially, when the scraper 17 is moved along the deposition surface, the material separated from the ridges tends to move to adjacent depressions of the deposition surface. This leads to the accumulation in the hollows of the metal, which tends to envelop the fingers 39 and thereby protect the ceramic fingers 39 from wear. In addition, there is an increase in the friction force as the mass of material moves down the deposition surface, which helps to remove the material, since the material is scraped off the surface under the action of this friction force. The fingers 39 need not be in direct contact with the deposition surface in order to ensure proper cleaning of the surface.

Another advantage of this design of the cleaning system 15 is that it provides different degrees of cleaning of the cathodes. In particular, as described above, the scrapers 17 can be configured to remove the bulk of the deposited material from the deposition surfaces by dragging along these surfaces when they are in their closed position. Scrapers can also be moved along the draft when they are in their open position. This case is not used to completely clean the deposition surface, but in order to ensure the absence of extended dendritic growths on the part of the deposition surface, which otherwise could grow to such an extent that they come into contact with the anode and, thereby, cause a short circuit of the electrolyzer . In addition, this case makes it possible for more consistent growth along the cathode ridges, which helps to control the current density along the deposition surface.

Figures 14 and 15 illustrate some modifications to the design of the scrapers 17. Similarly to the design of Figure 13, each of the scrapers 17 contains ceramic fingers 39. However, instead of using the design with the strips 42, as shown in Figure 13, the fingers 39 are interconnected by an inner connecting rod 44. In the embodiment of FIG. 14, the rod 44 is made with a square cross section, and the connecting rod in FIG. 15 is made of two cylindrical rods 45.

Turning now to FIGS. 16 and 17, an alternative cathode construction is shown there. In this embodiment, the cathode is made in the form of a composite structure in which the outer deposition surfaces 13, 14 are formed by separate sheets that are bonded to each other along their respective side edges 60, 61 and which can, if necessary, be bonded to each other at intermediate sections 62.

In this embodiment, the plurality of conductive rods 63 forms part of the structure and extends downward from the upper beam 34, while the conductive rods are also usually made of titanium (or titanium-coated copper rods to further increase conductivity). The conductive rods usually extend over the entire length of the plates 13, 14 through each of the channels formed between the plates, and are attached to them. This design provides an improved electron distribution throughout the assembly and thereby minimizes the ohmic voltage drop that can occur when electrons are brought to only one edge of the sheet. In addition, it was found that the composite structure, including the location of the conductive rods in the channels, increases the dimensional stability of the sheet, so that thin plate structures (for example, thinner than 1 mm) or, alternatively, wide plate structures can be used as the cathode. In other respects, the cathode operating principles of FIGS. 16 and 17 are described above.

Although the invention has been described with several preferred embodiments, it should be understood that there are many other embodiments of the present invention.

Claims (29)

1. The electrolysis method for extracting metal from an aqueous solution, according to which during electrolysis, the dissolved metal is precipitated on the deposition surface of the cathode, which includes the step of creating an uneven current density on the deposition surface in such a way as to form sections of a high current density alternated with sections of a low current density the difference between the areas of high current density and low current density is sufficient to cause the concentration of metal deposition on ASTK high current density to promote non-uniform deposition of metal on the deposition surface. 2. The method according to claim 1, in which the sections of high current density and low current density are elongated along said surface in one direction and alternate on the surface in the opposite direction. 3. The method according to claim 1 or 2, which is designed to extract copper from an aqueous solution, and the current density in areas of high current density is in the range of 500-2500 A / m ² , and more preferably is 1000 A / m ² . 4. The method according to claim 1 or 2, which is designed to extract copper from an aqueous solution, and the current density in areas of low current density is in the range of 0-1250 A / m ² , and more preferably 0-500 A / m ² . 5. The method according to claim 1 or 2, further comprising the step of removing the deposited metal from the deposition surface by holding the element along said surface. 6. The method according to claim 5, in which the sections of high current density and low current density are elongated along the surface in one direction and alternate on the surface in the opposite direction, and the element is moved in the direction in which stretched sections of high and low current density. 7. The method according to claim 5, in which the deposited metal is removed by said element while maintaining an electric current in an aqueous solution. 8. The method according to claim 5, in which the element is movable between the first and second positions and is configured to conduct deposition on the surface in any of the first and second positions. 9. The method according to claim 8, in which, when in its first position, the element is in contact with the deposition surface or in close proximity to it so that it removes essentially all of the deposited material from this surface. 10. The method according to claim 7 or 8, in which, when in its second position, the element is spaced from the deposition surface and configured to engage and remove the deposited material, which protrudes a predetermined distance from the deposition surface. 11. An electrolytic cell for electrochemical extraction of metal from an aqueous solution, comprising a cathode, which includes a deposition surface onto which metal is deposited during electrolysis of an aqueous solution, wherein, during operation of the electrolyzer, the deposition surface has an inhomogeneous electric field having regions of a strong electric field interspersed with regions a weak electric field, and the difference between the areas of a strong electric field and a weak electric field is sufficient to cause depositing metal concentration be in areas of strong electrical field to promote non-uniform deposition of metal on said surface. 12. The cell according to claim 11, in which sections of a strong electric field and a weak electric field are elongated along the surface in one direction and alternate on the surface in the opposite direction. 13. The cell according to claim 11 or 12, in which the deposition surface of the cathode contains an ordered set of alternating ridges and depressions, while the ridges form sections of a strong electric field, and depressions form sections of a weak electric field. 14. The electrolyzer according to item 13, in which the cathode contains a sheet with at least one main surface that forms the deposition surface of the cathode, the sheet is preformed to give it alternating ridges and depressions. 15. The electrolyzer according to 14, in which the sheet has opposite main surfaces, each of which forms a deposition surface of the cathode. 16. The electrolyzer according to claim 15, wherein the sheet is folded to form depressions and ridges on opposite deposition surfaces, the ridges on one deposition surface being directly opposite depressions on the opposite deposition surface and vice versa. 17. The electrolyzer according to 14, in which the sheet has a generally uniform thickness. 18. The electrolyzer according to any one of paragraphs.14-17, in which the sheet is made of titanium. 19. The cell of claim 14, further comprising at least one conductive element that extends along said sheet, wherein the conductive element is electrically connected to said sheet so as to supply the deposition surface with electrons during electrolysis during operation. 20. The electrolyzer according to claim 19, in which the conductive element is of sufficient size to impart rigidity to the sheet. 21. The cell of claim 19 or 20, wherein the cathode comprises a second sheet that is connected to said first sheet and which has a main surface that forms a second cathode deposition surface, wherein the second sheet is preformed to give it said alternating ridges and depressions along said deposition surface. 22. The cell of claim 21, wherein the second sheet is connected to said first cathode sheet so as to form a plurality of cavities that are elongated in the direction of alternating ridges and depressions, the cavities being configured to accommodate a cathode conductive element therein. 23. The electrolyzer according to any one of paragraphs.11, 12, 14 to 17, 19, 20 and 22, further comprising a cleaning device that is configured to conduct cathode deposition on said surface in order to remove deposited material from this deposition surface. 24. The cell according to item 23, in which the deposition surface of the cathode contains an ordered set of alternating ridges and depressions, the ridges form sections of a strong electric field, and the depressions form sections of a weak electric field, and the stripping device contains many protrusions that are suitable for placement into the corresponding depressions of the deposition surface. 25. A cathode for use in an electrolytic cell for electrochemical extraction of metal from an aqueous solution having a deposition surface with an ordered set of alternating ridges and depressions. 26. The mechanism for removing metal deposited on the deposition surface of the cathode of claim 25, comprising a plurality of elements configured to protrude into and move along respective depressions in order to remove deposited metal from ridges and depressions. 27. The mechanism of claim 26, wherein the elements have a shape generally corresponding to depressions. 28. The mechanism according to p. 26 or 27, in which the elements are made of ceramic material. 29. The mechanism according to p. 26 or 27, in which the elements are made with the possibility of articulated movement between the first position in which the elements protrude into the depressions, and the second position in which the elements do not protrude in this way.

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