EP0487881B1 - Process and apparatus for the electrolytic recovery of metals from a solution containing metal-ions and electrode for carrying out said process - Google Patents

Abstract

For the electrolytic extraction of metal from a solution containing metal ions and situated in a first cell, metal is cathodically deposited by means of an anode on an electrically conductive endless band immersed partially into the solution, and is redissolved anodically in the electrolyte of an adjacent second cell by partial immersion of the circulating endless band; the metal dissolved in the second cell is again deposited in high purity on a cathode.

Description

The invention relates to a method for the electrolytic removal of metal from a solution containing metal ions, an anode connected to the positive pole of a voltage source being immersed in the solution in a first cell and metal being deposited from the solution on one electrode, this electrode in a second a cell containing liquid electrolyte is transferred and the deposited metal is again released from the electrode into the electrolyte and deposited again from the electrolyte on a counterelectrode, and the metal-free electrode is then transferred from the second cell back into the first cell, and a device and an electrode for performing the method.

DE-A-22 32 903 discloses a process for the electrolytic refining of copper from its salt solutions contaminated with other metal ions using titanium electrodes as electrolyte sheets; the titanium electrodes are used as cathodes in a first solution and, after the copper has been deposited, are fed to a second bath with pure electrolyte, where the previously deposited copper is 100% detached again, the titanium electrode being connected anodically. Titanium is used as the material for the switchable electrode. After the anodic removal of the copper, the electrode can be used again without intermediate treatment in the first bath, in which it is connected cathodically; the titanium electrode behaves like a copper anode with anodic switching, as long as copper adheres to the titanium anode; the after the dissolution of the Passivation of titanium that occurs in copper then becomes noticeable through a sharp drop in current or rise in voltage. Even if this spontaneous drop in current and voltage increase can be used well for automatic monitoring of the electrolysis process, the possibility of largely automated operation is largely restricted, since the switch-off process of the cathodically switched titanium electrode is not so easy to monitor; Automatic operation is problematic in that special handling tools are required to convert the titanium plate into the respective solution.

Another process for the electrorefining of a metal from the group of copper, zinc, nickel, lead or manganese using a titanium electrode as the cathode is known from GB-A-13 45 411. The removed metal is removed from the titanium electrode by mechanical stripping. In one embodiment, the electrical series connection of several copper refining cells is described, all of which are traversed by the same current; different cathode current densities can be achieved depending on the size of the cathode surfaces immersed in the electrolyte.

Furthermore, EP-A-0 049 172 discloses a process for obtaining a noble metal on its solution by adsorbing a dissolved compound of the noble metal on activated carbon, the activated carbon being in the form of a body comprising fibers of activated carbon; the fiber-containing body can be used as an electrically conductive circulating endless belt in an electrochemical process for the depletion of metal in solutions and for the regeneration of electrolyte belts; the endless belt working in continuous operation is connected as an anode in an electrochemical cell.

Furthermore, WO-A-90/03456 discloses a device for the electrolytic regeneration of metal, in particular silver, from the photographic development process, the metal being deposited on the cathodically connected endless belt and mechanically stripped off the belt outside the solution.

Starting from DE-A-22 32 903, the invention has for its object to provide an automatic process for the electrolytic refining of metals from a solution containing metal ions, the transport of the electrode provided with the deposited metal takes place automatically in a further solution and a respective attitude to Optimization of the process parameters is possible. Furthermore, a device and an electrode for carrying out the method are to be created, wherein in particular an optimal use of energy is also to be achieved.

The object is achieved with respect to the method in that an electrically conductive first endless belt is used as the electrode, which is circulated between the first and the second cell, partly immersed in the solution and the electrolyte, and in that the belt in the first cell is operated cathodically and anodically in the second cell, a counter electrode being connected as the cathode to the negative pole of the voltage source.

With regard to the device, the object is achieved in that the electrode is an electrically conductive first endless band, which is partially immersed in the solution and the electrolyte, the first endless band being connected cathodically in the first cell and anodically in the second cell and a counter electrode is designed as a cathode, which is connected to the negative pole of the voltage source and that the device has a guide device with deflection and / or drive rollers for guiding the first endless belt, the drive roller and some deflection rollers outside the solution and the Electrolytes are arranged.

With regard to the electrode, the object is achieved in that it consists of a flexible endless belt, at least whose outwardly facing surface is electrically conductive and that it has at least two deflection and / or drive rollers which are arranged one above the other, at a distance from one another are, wherein at least an upper roller abuts the inner surface of the endless belt and a lower roller abuts the electrically conductive surface of the belt.

The endless belt preferably consists of a film made of electrically conductive material; however, it is also possible to use an endless belt in the form of a network or a chain. Metal from the platinum metal group or valve metal or a valve metal base alloy is preferably used as the material for the band; However, it is also possible to use electrically conductive plastic or plastic with electrically conductive fillers in contact with one another as the material for the band. The endless band thus forms a bipolar flexible electrode.

Advantageous refinements of the method are specified in claims 2 to 4, advantageous refinements of the device in claims 6 to 9, further refinements of the electrode in claims 11 to 17.

A major advantage of the invention is that the endless belt effects both the electrical connection between the individual cells and the mass transfer of the deposited metal into the next cell.

The advantages achievable with the invention are furthermore to be seen in the fact that a very high level of purity in the refining process is possible through serial operation of any number of electrolysis cells of the same structure, depending on the application, a cascade cell operation with electrolyte recycling or different electrolyte compositions in the individual cells is possible, so that desired deposition morphologies can be generated in each case. A major advantage of cascade cell operation is the extremely low consumption of chemicals and thus the extremely low pollution of the environment.

Another advantage can be seen in the fact that the series connection of a large number of cells enables the metal recovery electrolysis and the refining electrolysis to be combined in a single, continuous process, so that labor-intensive and energy-intensive individual steps in the process can be avoided.

Figur 1

zeigt im Längsschnitt eine mit zwei Zellen ausgestattete Vorrichtung,

Figur 2

eine Vorrichtung zur Raffinationselektrolyse, wobei das Ausgangsmaterial in Granalienform in einem Anodenkorb untergebracht ist,

Figur 3

zeigt im Längsschnitt eine mit drei Zellen ausgestattete Vorrichtung, wobei die Gegenelektrode der zweiten Zelle als umlaufendes Endlosband ausgebildet ist,

Figur 4

eine Vorrichtung mit drei Zellen, in der auch die Gegenelektrode der dritten Zelle als Endlos-Band ausgebildet ist, wobei das abgeschiedene Metall außerhalb des Elektrolyten mechanisch entfernt wird,

Figuren 5 und 6

zeigen weitere Ausführungsformen zur Führung des Endlosbandes.

The subject matter of the invention is explained in more detail below with reference to FIGS. 1 to 6.

Figure 1

shows in longitudinal section a device equipped with two cells,

Figure 2

a device for refining electrolysis, the starting material being accommodated in granule form in an anode basket,

Figure 3

shows in longitudinal section a device equipped with three cells, the counter electrode of the second cell being designed as a continuous endless belt,

Figure 4

a device with three cells, in which the counterelectrode of the third cell is also designed as an endless band, the deposited metal being mechanically removed outside the electrolyte,

Figures 5 and 6

show further embodiments for guiding the endless belt.

According to FIG. 1, the trough 1 consists of two trough regions 2, 3 which are separated from one another by an intermediate wall 4. The level 5 of the solution 5 located in the trough regions 2, 3 and the electrolyte 6 are numbered by the level symbols 5 ', 6'. In solution 5 of the trough area 2 there is an anode 7 which is connected to the positive pole 8 of a voltage source 9. Furthermore, a partial section 10 ′ of a flexible belt 10 guided over drive or deflection rollers 11, 12, 13, 14, 15, 16, 17, 18 is immersed in the solution 5, the deflection rollers being arranged in predetermined positions relative to the trough. Drive and deflection roller 11 is connected to a drive motor, not shown here for the sake of a better overview, which forces the flexible belt 10 to rotate. With its other subsection 10 ″, strip 10 dips into the electrolyte 6 of the trough area 3. The band 10 consists of a metal foil with a thickness in the range of 50 to 100 μm, preferably of a titanium foil. However, it is also possible to use a net made of a platinum group metal or a band made of electrically conductive plastic or a band made of interlinked electrically conductive plastic bodies as the endless band. In practice, in addition to a titanium foil, the use of a platinum mesh has proven to be particularly useful. The U-shaped bent ends of the sections 10 'and 10' 'of the flexible band are each guided over the deflection rollers 17, 18 arranged in the bottom area of the trough areas 2, 3; all axes of the deflection rollers 11 to 18 run horizontally.

During operation of the arrangement, section 10 'of the flexible strip 10 functions as a cathode and section 10' 'as an anode; there is also a cathode 19 in the electrolyte 6 of the trough region 3, which is connected to the negative terminal 20 of the voltage source 9.

In a practical embodiment, a contaminated copper extraction solution containing 200 g / l sulfuric acid and 45 g / l copper is used in trough area 2, the anode 7 being an insoluble electrode which produces oxygen. In trough area 3 there is an aqueous electrolyte containing 200 g / l sulfuric acid with 45 g / l copper. A steel sheet serves as cathode 19.

During operation of the arrangement according to FIG. 1, the flexible strip is put into circulation at a strip circulation speed of approx. 0.2 m / min at a current density of 150 A / m at 60 ° C., the portion 10 ′ acting as cathode of the strip continuously passed through solution 5 copper. The flexible belt 10, which is guided in the electrolyte 6 of the trough area 3 as a result of the belt transport via deflection rollers, now acts as an anode with its copper-coated area 10 ″, the copper previously deposited in solution 5 now being dissolved again in the trough area 3, and the section 10 '' is now operated as an anode. The dissolved copper is then deposited on the cathode 19. Since both trough regions 2, 3 acting as electrolysis cells form a single electrolyzer with cells connected in series, the amount of copper deposited on the steel sheet corresponds exactly to the same amount that was previously deposited on the section 10 ′ of the flexible strip 10 in the trough region 2 would have. In practice, a continuous belt transport is preferably carried out. However, it is also possible to transport the strip in sections, so that sections act step by step as cathode and anode.

The analyzes of the copper deposited on section 10 'of the endless belt 10 and the cathode 19 are listed in the table below: Metal deposited on section 10 ' Metal deposited on cathode 19 CU 99.5% 99.99% Pb 800 ppm <5 ppm Zn 15 ppm <5 ppm Ni 600 ppm <5 ppm Fe 300 ppm <5 ppm Ag 450 ppm <5 ppm

Figure 2 shows a modification of the device shown in Figure 1, wherein anode 7 from an electrically conductive, electrolyte-resistant anode basket basket 7 ', which contains the starting material 7 "in granular form. According to FIG. 2, the starting material is deposited on the part 10' of the flexible belt which acts as a cathode and, after a transport movement of the flexible belt 10, is transferred into the trough region 3, where that previously deposited material is dissolved and deposited on cathode 19.

An exemplary embodiment for silver refining electrolysis in a device with anode basket 7 according to FIG. 2 is given below:

The solution in the trough areas 2 and 3 consists of HNO₃ (nitric acid with a pH of 3), which contains 50g / 1 silver, 5g / l NaNO₃ (sodium nitrate).

Composition of the silver materials used and extracted:

Example of Ag refining

Granules in anode basket 7 Deposition on subsection 10 ' Deposition on cathode 19 Ag 88% 98% 99.99% Cu 9% 1% <50 ppm Pb 1.5% 0.2% <10 ppm Au 0.5% Balance Pd, Sn, Ni, Zn Au, Pd, Ni, Zn

Another embodiment is shown in FIG. 3, the trough 21 being divided into three trough regions 22, 23, 24. Partition walls 4 are arranged between the trough regions. The basic mode of operation of the first cell 22 formed in trough 21 with solution 25 corresponds to the embodiment explained with reference to FIGS. 1 and 2. In the trough area 23, on the other hand, partial section 10 ″ serves as an anode in the electrolyte 26 present there, the previously deposited metal content being dissolved in the electrolyte 26 and being deposited on the partial area 30 ′ of a further flexible strip 30 acting as a cathode. The flexible strip 30 corresponds in structure and mode of operation to that already Band 10 described with reference to FIGS. 1 and 2, drive and deflection rollers or guides also corresponding to the known embodiment. The flexible band 30 thus acts in the trough area 23 with its section 30 'as a cathode, while in the adjacent trough area 24 with its partial section 30''acts as an anode, the previously deposited metal being dissolved again and on the cathode 19 is deposited.

During operation of the embodiment shown in FIG. 3, the solution 25 and the electrolytes 26 and 27 likewise consist of an electrolyte made of sulfuric acid and copper dissolved therein, as described with reference to FIG. A copper sheet according to FIG. 1 or an anode basket for raw granules according to FIG. 2 again serves as the anode. A steel cathode, as described with reference to FIGS. The belt transport of the flexible belts 10 and 30 can take place continuously or in cycles; it is possible to provide a coupling between the drives of the belt transports for the flexible belts 10 and 30. Such an arrangement is particularly suitable for combining extraction electrolysis in the trough region 22 and refining electrolysis in the trough regions 23 and 24.

It is of course possible to increase the fineness (deposition of 99.999% Cu based on a material of the purity specified in the table above) of the refining electrolysis to provide further trough areas which are connected in accordance with the areas 23, 24.

According to FIG. 4, the device known from FIG. 3 is provided in its third cell 27 instead of a plate-shaped counterelectrode with a circumferential, electrically conductive endless band 31 as the cathode; the endless belt 31 is connected via a current collector 32 and line 33 to the negative pole 20 of the DC voltage source 9; the section 30 ″ dipping into the trough area 24 acts as an anode, as already explained with reference to FIG. 3, the metal previously deposited in the trough area 23 on the section 30 ′ now being brought into solution in the electrolyte 27; after deposition of the metal on the cathodically connected endless belt 31, the belt runs through mechanical separator 34 for removing the deposited metal from the belt. The endless belt 31 passes in the separating device 34, viewed in the direction of rotation, through a drying device in which the deposited metal is dried and a stripping device in which the dried metal is separated from the belt by means of rotating brushes and scrapers.

Further options for guiding the endless belt 10, 30 are explained in more detail with reference to FIGS. 5 and 6.

Figure 5 shows a guide of the endless belt 10,30 in the simplest possible form.

According to this figure, the endless belt is guided by two deflection rollers of different diameters 14 ', 11, which are arranged one above the other and at a distance from one another; the upper roller is designed as a drive and deflection roller 14 'and lies on the inner surface of the endless belt, it has a larger diameter than the lower deflection roller 11, which on the outer surface of the endless belt 10.30 is present.

The endless belt forms on both sides of the rollers 14 ', 11 flanking, depending loops which are provided for immersion in the solution or the electrolyte.

According to FIG. 6, it is also possible to provide a large number of small deflecting rollers instead of a single large upper roller, similar to that of FIG. 1, two additional deflecting rollers 12 'and 16' being arranged according to FIG rest the other deflection rollers 12, 13, 14, 15, 16 on the inner surface of the endless belt; roller 14 is provided as a deflection and drive roller; The lower deflection roller 11, which lies against the outer surface of the endless belt 10, 30, is arranged at a distance below this roller. The flanking loops of the endless belt 10, 30 intended for immersion in the solution or the electrolyte are formed on both sides of the roller 11, the two lower loop ends each having a further deflection roller 17, 18 to stabilize the belt movement. Such Embodiment is particularly suitable for a positive transmission of the driving force from the drive roller to the endless belt.

However, it is also possible to provide the lower deflection roller 11 instead of the roller 14 as the drive roller; such an embodiment allows a greater frictional connection between the drive roller and the endless belt.

Claims (17)

1. A method for the electroyltic discharge of metal from a solution containing metal ions, in which in a first cell (22) an anode (7), connected with the positive pole (8) of a voltage source (9) is immersed into the solution (5,25) and metal is separated out from the solution on an electrode, this electrode is transferred into a second cell (23) containing a fluid electrolyte (6,26) and the separated metal is delivered again from the electrode into the electrolyte and is deposited again out of the electrolyte on a counter-electrode (19,30') and in which thereafter the electrode which is freed from the metal is transferred from the second cell again into the first cell, characterised in that an electrically conducting first endless Dand (10) is used as electrode, which is drought into circulation between the first and the second cell partially immersed into the solution (5,25) and the electrolyte (6,26) and that in the first cell the and is operated cathodically and in the second cell anodically, in which a counter-electrode (19,31) is connected as cathode with the negative pole (20) of the voltage source (9).
2. A method according to Claim 1, characterised in that a third cell (24) with electrolyte (27) is arranged after the second cell (23) and that a second, electrically conducting endless band (30) is brought into circulation partially immersed into the electrolytes (26,27) of the second and third cell between these cells, in which the second endless Dand (30) is operated cathodically in the second cell (23) and anodically in the third cell (24) and in which the metal is separated on a counter-electrode (19,31) in the third cell.
3. A method according to Claim 1 or 2, characterised in that the metal separated on the counter-electrode (19,31) is removed mechanically outside the electrolyte.
4. A method according to one of Claims 1 to 3, characterised in that as counter-electrode an electrically conducting circulating endless band (31) is used.
5. A device for the electrolytic discharge of metals from a solution containing metal ions, in which a first cell (22) containing the solution (5,25) has an anode (7) connected with the positive pole (8) of a voltage source (9) and has an electrode for the separation of metal, which to transfer the metal separated on it is able to be transferred into a second cell (23) containing a counter-electrode (19,30') and an electrolyte (6,26), characterised in that the electrode is an electrically conducting first endless band (10), which is immersed partially into the solution (5,25) and the electrolyte (6,26), in which the first endless band (10) is connected cathodically in the first cell and anodically in the second cell, and a counter-electrode is constructed as cathode (19,31), which is connected with the negative pole (20) of the voltage source (9) and that the device has a guiding device with guise- and/or drive rollers (11;12'; 12 to 18; 16'; 14') to guide the first endless band (10), in which the drive roller and some guide rollers are arranged outside the solution and the electrolyte.
6. A device according to Claim 5, characterised in that a third cell (24) with electrolyte is arranged after the second cell (23) and that a second electrically conducting endless Dand (30) is provided, immersed partially into the electrolytes (26,27) of the second and third cell, in which the second endless band is connected cathodically in the second cell and anodically in the third cell and in which in the third cell a counter-electrode is arranged.
7. A device according to Claim 6, characterised in that the counter-electrode is an electrically conducting circulating endless band (31).
8. A device according to one of Claims 5 to 7, characterised in that at least one of the two electrodes (7,19) in the region of its active electrode surface directed towards the counter-electrode is provided with a shielding device of electrically insulating material hindering the ion flow, which device covers parts of the electrode surface.
9. A device according to one of Claims 5 to 7, characterised in that the two partial sections (10',10",30',30") of the band (10,30) have different lengths.
10. An electrode for the electrolytic separation of metal from a solution containing metal ions and for the redissolving of the separated metal again, characterised in that it consists of a flexible endless band (10,30), at least the outwardly facing surface of which is electrically conducting and that it has at least two guide rollers (11,14;14'), which are arranged one over the other at a distance from each other, in which at least an upper roller (12',12 to 16;16',14') lies against the inner surface of the endless band and a lower roller (11) lies against the electrically conducting surface of the band (10,30).
11. An electrode according to Claim 10, characterised in that for deflecting the endless band, several rollers (12';12,13,14,15,16;16') are arranged adjacent to each other at a distance from each other.
12. An electrode according to one of Claims 10 or 11, characterised in that to guide the band (10,30) at least two further inner guide rollers (17,18) are provided underneath the lower roller (11).
13. An electrode according to Claim 12, characterised in that the endless band (10,30) consists entirely of electrically conducting material.
14. An electrode according to one of the preceding Claims 10 to 13, characterised in that the endless band (10,30) is formed from a foil, a net or a chain.
15. An electrode according to Claim 14, characterised in that the endless band (10,30) is formed from electrically conductive plastic or of a plastic containing electrically conductive filler bodies.
16. An electrode according to Claim 14, characterised in that the endless band (10,30) consists of a valve metal or a valve metal base alloy.
17. An electrode according to Claim 14, characterise in that the endless band consists of at least one metal of the platinum metal group.

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