WO1993020261A1 - Bipolar filter press cell for producing peroxodisulphates - Google Patents

Abstract

A bipolar electrolytic cell designed as a filter press may be used both for producing peroxodisulphuric acid and/or peroxodisulphate and for regenerating etching, mordant and oxidating solutions by a peroxodisulphate recycling process. The basic structure of the bipolar cells is at first explained on the basis of figure. The cathode channels (2) are shaped into the cathode side of the base body (1) of the electrode plates made of impregnated graphite, and the cooling channels (4), which are closed in a pressure-tight manner by sunk-in cover plates (3), are shaped in the anode side of the base body (1) of said electrode plates. The anode insulating plates (5) made of PVC arranged thereon are also sunk-in in the base body and their sides are flush therewith. On the anode insulating plates are located the composite anodes (6) made of titanium foils, upon which are soldered platinum strips by high-temperature isostatic pressing, which take up about 25 % of the titanium surface. On both sides of the back side of the composite anodes are soldered platinum contact strips which lie on the lateral contact surfaces of the base body and which establish an electric contact between the composite electrodes and the base bodies of the electrode plates when they are clamped together. The anode chamber is outwardly delimited by the anode sealing frames (7) which also transmit the compression force to the contacts during clamping, sealing them with respect to the anolyte. Within the anode chamber (8), the spacing strips (9) are arranged in such a way that separate, parallel flow channels result, a platinum strip being located in each anode channel. The ion exchange membranes (10), which are also laterally sealed by the anode sealing frames, are clamped each between two electrodes plates. It has been discovered that it is possible to solve the proposed problem in a surprisingly simple way, and in addition to obtain other positive technical and economic results, by using electrode plates over 1.5 m high, but only 0.2 to 0.5 m wide, together with the combined use of both new and known per se technical means.

Description

Bipolar filter press cell for the production of peroxodisulfates

The invention relates to a bipolar electrolysis cell in filter press type, which can be used both for the production of peroxodisulfuric acid and / or peroxodisulfate, and for the regeneration of etching, pickling and oxidation solutions in peroxodisulfate recycling processes.

The technical status of peroxodisulfate electrolysis is decisively determined by the use of bipolar cells in filter press design (see, for example, DECHEMA monograph vol. 123 VCH publishing company 1991 "Electrochemical Cell Design and Optimization Procedures" pp. 133 to 165), whose bipolar single cells are impregnated from basic bodies Graphite exist on which all important components of the anodic and cathodic half cells including the supply and discharge of the electrolyte solutions are mounted or integrated into them (DD-PS 27 961).

The division of the anode and cathode spaces into parallel flow channels has proven to be particularly favorable, on the one hand to largely avoid undesired backmixing in the anode spaces and on the other hand a gas bubble-related catholyte circulation which has an advantageous effect on the cell voltage via a catholyte back arranged within each individual cell - favor the flow channel (DD-PS 99 548).

However, the use of the buoyancy of the anodic oxygen for hydrodynamic coupling of a large number of individual cells at approximately the same level has also already been proposed (DD-PS 281 095).

Composite anodes made of platinum and a film-forming metal, e.g. Tantalum or titanium, proven. Tantalum foils are preferably used as supports and at the same time current leads to the vertical platinum strip electrodes arranged thereon. The platinum strips are firmly welded to the tantalum foil using a suitable process (resistance welding, laser welding). According to DE-PS 3 823 760, the composite can be brought about particularly advantageously by hot-isostatic pressing of base metal and platinum foil between layers of release agent. The current supply to the individual composite anodes takes place through contacts attached to the side of the tantalum foils.

Microporous, flexible PVC diaphragms with average pore sizes of approx. 1 μm are used as separators for separating the anode and cathode spaces. According to a further proposal, these can also be equipped with ribs for forming the anodic flow channels and for promoting the transport of heat and electricity (DD-PS 141 463).

Anode insulating plates made of a non-electrochemically active material are applied between the base bodies made of impregnated graphite and the composite anodes, through which the contacts between platinum-tantalum electrodes and cathode base bodies are guided or conveyed. PVC-H plates are mainly used as anode insulation plates, which at the same time also delimit the cooling channels incorporated in the base body on the anode side compared to the anode spaces (DD-PS 99 548). It has also already been proposed to produce the anode insulating plates from titanium, in particular from a titanium-palladium alloy (DD-PS 152 266) and to apply the platinum strips there directly to improve the heat transfer. However, it turned out to be problematic to connect the thin platinum strips so firmly and securely to the titanium plate that even after several years of operation there is no excessive corrosion or even detachment of the weld connection.

The inlets and outlets led out of the side of the anode plates serve to feed and discharge the electroysis media, i.e. the catholyte and anolyte solutions as well as the gaseous and dissolved electrolysis products carried along. They are provided with feed and discharge lines for the electrolysis media (hereinafter referred to as outer feed and discharge lines) arranged outside the cell, as far as with the separating devices for separating the gaseous electrolysis products, which are also arranged outside the cell at the outlets (hereinafter referred to as " outer separators "referred) connected.

Although the dimensions of the electrode channels with parallel flow through which are advantageously to be used have already been proposed in DD-PS 99 548 to be 0.5 to 2.0 m, bipolar cells (type EZ II) that have been used on the technical scale to date have been based on this principle of construction. lower electrode heights of only 0.5 m have been claimed to date. In order to achieve a current capacity of 500 to 600 A per bipolar single cell with a minimal voltage drop in the composite anodes with lateral power supply, several of them had to be arranged side by side. This had the disadvantage that part of the available area had to be used for the arrangement of the contacts within the electrode plates and for their secure sealing, combined with a loss of effective electrode area.

In order to achieve sufficiently high current yields with this low electrode height, it was also necessary to allow several such cell sections of the width of the composite anodes to flow through the anolyte one after the other with the interposition of a return flow channel, combined with a further loss of effective electrode area. On the cathode side, this applies equally to the internal backflow channels arranged there.

Overall, this resulted in a loss of available electrode area of about 20%, combined with a reduction in the space-time yield in the same order of magnitude. A further disadvantage was that the contacts and backflow channels arranged within the electrode plates formed the cause for different damage which could not be recognized from the outside, which in extreme cases could lead to failure of the entire filter press cell (eg, leaky contact shielding). An important indicator for the economic use of an electrolysis cell is the area-time yield, which is understood to mean the capacity of the electrolysis cell based on the required base area. Especially when retrofitting electrolysis cells in existing systems, it is crucial to be able to make maximum use of the available, usually limited, space. There has therefore been no lack of attempts to increase the electrolysis capacity to be accommodated per base unit by maintaining the construction principle of the proven EZ II electrolysis cell by increasing the vertical scale and, at the same time, more favorable conditions for achieving higher current yields without the previously required series connection of several cell sections within the bipolar To reach individual cells.

This led to the development and testing of the prototype of a large peroxodisulfate electrosensor (type EZ III) with 2 m high electrode plates with a current load of 1.2 kA. It was then also possible to dispense with the connection of several cell sections in series and the area-time yield could be doubled with comparable specific electrical energy consumption. However, the long-term testing also led to the realization that the performance limits of this design principle or of the building materials and assemblies used in this way had been reached or already exceeded. In particular, the following shortcomings arose:

1. To ensure the mechanical stability of the large-area electrode plates and to accommodate the larger cross-sections for the supply and discharge of the electrolysis media, the base body made of impregnated graphite had to be reinforced. This increased the footprint and partly compensated for the increase in area-time yield achieved by increasing the vertical scale.

2. The weight of a completely assembled bipolar electrode plate increased to approx. 200 kg. The handling of these heavy electrode plates in the manufacture, assembly and repair of the electrolytic cell on site was considerably more difficult and required additional expenditure for the handling technology required.

3. The increase in height by about 3 times also brought about a corresponding increase in the hydrostatic pressure. This led to a significant increase in the damage to the contacts arranged within the electrode plates and also the secure sealing of all other assemblies caused difficulties.

4. The flexible diaphragms made of PVC with a pore size of approx. 1 μm, which have been tried and tested with the EZ II, have been found to be unsuitable here. The higher pressure differences between the electrode spaces, the greater surface pressure within the sealing surfaces, led to losses of peroxodisulfates (too high permeability, stress cracks on the seals) and to an increase in the failure rate. In a relatively short period of time It was therefore necessary to change the diaphragm. The vertical assembly of the heavy, large-area electrode plates to be carried out on site in connection with the very precise positioning of the profiled diaphragms used was only possible with considerable expenditure of time, personnel and costs.

5. The covering of the cooling channels incorporated on the anode side by the PVC anode insulation plates also proved to be a particular weak point. The higher hydrostatic pressure in the cooling channels led to their deformation, combined with problems with the sealing.

To sum up, it remains to be stated that the vertical enlargement of the cell at cell heights over 1 m did not lead to the improvement of the economy in the desired extent with the known technical means, since the increase in the area-time yield only with high technical effort and at the expense of operational safety and freedom from maintenance could be achieved.

However, the increasing use of persulfate recycling processes in environmental technology increases the importance of operational safety and freedom from maintenance, since the mostly small or medium-sized companies often do not have suitable specialist personnel in the field of electrochemical technology. The demand for a further increase in the electrolysis capacity to be accommodated per unit of base area remains burning, as there is usually only little free space available for retrofitting recycling technology in existing systems.

The object of the present invention was therefore to provide, based on the high level of bipolar filter press cells achieved, but avoiding the disadvantages described, such an electrolysis cell which enables a further increase in the area-time yield with high operational reliability and ease of maintenance, and both for the production of peroxodisulfates, as well as for the regeneration of etching, pickling and oxidation solutions in persulfate recycling systems.

This technical problem was solved according to the invention by a bipolar filter press cell, which is characterized by the features mentioned in claims 1 to 10.

It has been found that the use of electrode plates over 1.5 m high but only 0.2 to 0.5 m narrow in connection with the combined use of new, but also known, technical means succeeds in a surprisingly simple manner to solve the task and to achieve further positive technical and economic results.

The electrode plates constructed according to the invention are easy to handle and mount due to their relatively low weight. The large cell heights of up to 2.5 m allow full utilization , ,

the buoyancy of the dispersed gas phase for circulating the electrolyte, without losing usable electrode area for internal backflow channels.

The total electrode height required for high current yields can also be achieved in a simple manner without the previously required series connection of several anode sections. In the case of the narrow electrode plates to be used according to the invention, it was also possible entirely to dispense with the susceptible contacts within the plates. The contacts arranged on both sides in the area of the anode sealing frame are completely sufficient to achieve a negligibly small voltage drop in the current leads even when using composite anodes made of thin metal foils of 20 to 50 μm in thickness.

The use according to the invention of pressure-resistant cooling ducts sealed against the anode compartments and the use of completely liquid-tight ion exchange membranes or of microporous diaphragms with a higher strength and further reduced permeability compared to the PVC diaphragms previously used contribute significantly to the disruption shown - Eliminate and minimize sources of loss in cells more than 1.5 m high.

The pressure-tight sealing of the cooling channels is either achieved according to claims 3 to 5 in that the anode insulating plates are separated from the cooling channels by a rigid intermediate layer made of impregnated graphite or that stronger anode insulating plates made of titanium are used. Pressure-resistant in the sense of the invention is to be understood to mean that a hydrostatic cooling water pressure corresponding to the cell height is withstood without deformation of the anode insulating plate.

The use of the ion exchange membranes which are preferably to be used, in particular those made from sulfonated fluoropolymers, has already been proposed in connection with bipolar persulfate cells, but has hitherto only been used for lower overall heights (EZ II). But even with the at least 1.5 m high electrode plates used according to the invention, the chemical resistance combined with the tightness makes a decisive contribution to significantly improving the performance parameters of the cell and the service life. When using the cells in the context of recycling processes, it is also possible to decouple the cathode process almost completely from the anode process of peroxodisulfate formation, apart from the cation transport, and to use it for specific application for reduction and metal deposition processes.

The composite anodes used according to a further feature of the invention with a platinum coating of 20 to 40% of the surface can be produced in a known manner by resistance welding or laser welding. However, significantly longer service lives are achieved if the platinum foils, preferably in the form of vertical platinum strips, according to claim 9 , ,

can be welded to the base made of titanium or tantalum by hot isostatic pressing, as described in DE-PS 3 823 760.

In contrast to the diagonal flow through the previous wide electrode plates, the narrow and high electrode plates also enable the electrolyte solutions to be distributed more evenly over the individual flow channels, an important prerequisite for achieving high current yields. This is supported by the arrangement according to the invention of the lower inlets for catholyte and anolyte and the upper outlets for the anodic and cathodic electrolysis products one above the other. A particularly advantageous embodiment is present if, according to claim 11, the inlets and outlets for the electrolysis media are led out of the electrode plates on one side and the outlets are connected to a combined outer separating device for the cathodic and anodic electrolysis products. This makes it possible to arrange the electrolysis cell with its outer assemblies in a particularly space-saving and clearly arranged manner and to make the outer return flow line (catholyte circuit) or overflow line (passage of the catholyte into the anolyte supply line) particularly efficient without lengthy line routing.

Therefore, the electrolytic cell according to the present invention is also particularly well suited for recycling processes which have already been proposed and in which metals, such as e.g. Copper, deposited in the form of metal powders and discharged from the cathode spaces by the circulating catholyte stream. For this purpose, according to a further feature of the invention, the cathodic outer separating device is additionally equipped with means for separating these solid particles, as described in DE application, AZ P 41 37 022.8.

The tall and narrow cells also allow the use of lower-strength electrode plates without impairing the mechanical stability of the cell construction. The following table compares the dimensions and the performance data of electrode plates of the comparison cells EZ II and EZ III with those of the cell according to the invention, as described in the exemplary embodiments. Comparison cells cell according to EZ II EZ III invention

Height of the electrode plates

Width of the electrode plates

Thickness of the electrode plates

Weight of an electrode plate

Rated current

Footprint per single cell

Amperage per unit area

Increase in height

Increase d. Amperage per GFE

je GFE zur Steigerung der HöheRatio of climbers, i.e. Flow,

per GFE to increase the height

From this it becomes clear that by reducing the plate thickness in connection with the elimination of the internal contacts and backflow channels compared to the EZ II, the electrolysis capacity to be accommodated per base unit can be increased more than the cell height and thus that which can be seen in the EZ III reverse the negative trend.

The apparent disadvantage of an insufficient individual current capacity of the narrow electrode plates can be compensated for in a simple manner according to a further feature of the invention in that a plurality of electrode segments consisting of at least one bipolar and two monopolar electrode plates are electrically connected in parallel within a clamping frame. If bipolar cells of greater total capacity are required, as are required in particular for the technical production of peroxodisulfate, two of these cell segments with a larger number of bipolar electrode plates can be arranged next to one another within the stenter frame, the entrances and exits in each case to the left or to the right are led out of the end faces of the electrode plates. This technical solution, too, can only be realized in connection with the electrode plates to be used according to the invention, with the one-sided lead-in and outlet for anolyte and catholyte.

Figures 1 and 2 are intended to illustrate the design and functional principle of a preferred embodiment of the bipolar cell according to the invention.

FIG. 1 shows a cross section through two complete bipolar electrode plates, each with a fully assembled and an anodic half cell broken down into the individual assemblies, and the ion exchange membranes arranged thereon. It clarifies the construction principle and shows the position of the most important assemblies in relation to each other in the middle, electrochemically effective area of the cell. The representation of the inlets and outlets for the electrolysis and cooling media has been omitted for better clarity.

This information can be found in FIG. 2, which shows one of the bipolar electrode plates with a view of the cathode side in cooperation with the assemblies attached outside the electrode plates (outer supply lines and outer separating device). The position of the indentations is in the cutouts. and exits to the anode compartments on the back of the electrode plate are shown schematically.

The basic structure of the bipolar cells will first be explained with reference to FIG. 1. In the base body 1 of the electrode plates made of impregnated graphite, the cathode channels 2 are incorporated on the cathode side, and the cooling channels 4, which are sealed pressure-tight by recessed and glued-in cover plates 3, are incorporated on the anode side. The anode insulating plates 5 made of PVC are also embedded in the base body and are flush with the sides. On the anode insulating plates are the composite anodes 6, consisting of titanium foils with platinum strips welded thereon by means of the hot isostatic pressing method, which take up approximately 25% of the titanium surface. Platinum contact strips are welded onto both sides of the back of the composite anodes, which lie on the lateral contact surfaces of the base body and, when they are clamped together, produce the electrical contact between the composite electrodes and the base bodies of the electrode plates. The anode space is delimited from the outside by the anode sealing frame 7. When clamping together, the contact pressure is simultaneously transmitted through them to the contacts and these are sealed off from the anolyte, within the anode spaces 8 the spacer strips 9 are arranged in such a way that they are subdivided into parallel flow channels and there is a platinum strip in each anode channel. The ion exchange membranes 10 are clamped between two electrode plates, also laterally sealed by the anode sealing frame.

The arrangement of the inlets and outlets for the electrolysis media, the flow guidance and the interaction of the cathodic and anodic half cells with the external attachments will be described with reference to FIG. 2. The catholyte is fed to the cathodic half cells via the outer feed line 11 and the inlets 12. Together with the cathodically separated hydrogen, the catholyte leaves the cathode spaces through the outlets 13 and reaches the catholyte segment of the combined outer separating device 14. Here, the hydrogen is separated off and discharged via the gas outlet 15. The catholyte is returned via the outer return flow channel 16 to the feed line and from there into the cathode spaces. In the catholyte circuit thus closed, the inlet 17 on the outer separating device continuously Catholyte (K) added. The volume increase in the catholyte circuit caused thereby and by the electrolysis reaction leads to a continuous overflow of catholyte, which is fed through the overflow line 18, the outer supply line 19 and the inlets 20 to the anodic half cells. The anolyte flows through the anode compartments and, together with the electrolysis products (peroxodisulfate dissolved and oxygen gaseous), reaches the anode segment of the combined external separation device via the outlets 21. The separated oxygen is discharged through the gas outlet 22, while the peroxodisulfate solution (A) leaves the outer separating device at the anolyte outlet 23. Cooling water (KW) is fed through the entrances 24 to the cooling channels (not shown in FIG. 2), which leaves the electrode plates again through the exits 25.

The invention is explained in more detail below with the aid of examples.

example 1

The electrode plates constructed according to FIGS. 1 and 2 were 2 m high and 0.3 m wide. The basic bodies were made of graphite impregnated liquid-tight with phenol-formaldehyde synthetic resin. They had a thickness of 38 mm. On the cathode side, the cathode channels were worked in about 4 mm deep. On the anode side, the built-in cooling channels were sealed off by glued-in plates made of liquid-impregnated graphite. The anodic half cells consisted of the PVC anode insulating plates likewise embedded in the base body, the titanium-platinum composite anodes lying there, the approx. 3 mm thick sealing frame made of soft PVC and the spacer strips also made of PVC. The composite anodes, consisting of a 100 μm thick titanium foil and 25% of the vertical strips of approx. 30 μm thick platinum foil, were produced by hot isostatic pressing according to DE-PS 3 823 760. The contact with the graphite base body was made by contact strips arranged on both sides under the sealing frame. The inlets and outlets for the electrolysis media were led out from one side of the end faces. Ion exchange membranes of the type Nafion ^R 430 were used as separators. When fully assembled, the plate thickness was 41 mm. The weight of a complete electrode plate for 500 A was found to be 35 kg. Based on a single bipolar cell, this results in a current strength of 41.7 kA / m ² per unit area.

Example 2

A regeneration cell suitable for recycling processes using peroxodisulfates consisted of three bipolar electrode plates according to Example 1, two monopolar edge plates with a power supply analogue on the cathode side or anode side and the tensioning frame, the supply and discharge lines for the electrolysis media and a combined external separation device . The total current load was 4 x 500 = 2000 A. Including the required floor space the edge plates, the tensioning device and the external add-on parts result in approx. 0.13 m ² , the current strength per base area unit is 15.4 kA / m ² .

Example 3

The persulfate regeneration cell according to Example 2 with the electrode plates according to Example 1 was used for the regeneration of sodium persulfate pickling solutions in the context of a recycling pickling process as described in DD-PS 21 1 129. The cathodic external separating device was additionally equipped with means for separating the copper particles which separate cathodically and are discharged with the circulating catholyte from the cathode compartments, as described in DE application AZ P 41 37 022.8. The exhausted pickling solution had a cathodic effect after it had been carried out Reduction and decoppering have a content of 200 g / f sulfuric acid and 300 g / I sodium sulfate and a residual copper content of approx. 2 g / I. It was fed into the catholyte circuit of the regeneration cell at a dosage of 30 l / h. After passing through the cathode compartments and separating the hydrogen and the copper particles, the electrolyte passed into and passed through the anode compartments. In addition, a potential-increasing addition of sodium thiocyanate in an amount of 4.5 g / h was metered into the overflow line to the anode chambers as an aqueous solution. Under the influence of the promoting effect of the oxygen formed, the anolyte was promoted from the lower catholyte outlet to the higher anolyte outlet. The emerging regenerated peroxodisulfate solution contained 198 g / l sodium persulfate. The total voltage was 17 V (approx. 4.2 V cell voltage). This results in an hourly formation of 5.94 kg of sodium persulphate and a specific direct current consumption of 1.43 kWh / kg. After 5 hours of operation of the system, a quantity of 284 g of copper powder had deposited in the outer cathodic separating device.

Example 4

For the dimensioning example of an electrolysis cell for the technical production of sodium persulfate, it is assumed that four cell modules connected in parallel, each with 23 bipolar electrode plates according to Example 1 and 2 edge plates, are arranged within a stenter frame. The corresponding external attachments are assigned to each module. Two modules are arranged side by side within the clamping frame, two in a row. With a current load of 0.5 kA per individual cell and 24 individual cells per module, the total current capacity is 48 kA. The current of the electrolyser is 2 kA, the voltage is 100 V. The total footprint including the stenter and the external attachments is approximately 2 m ² and the current per base unit is approximately 24 kA / m ² . If one assumes the same current yield as in Example 3 in the production of persulfate, the result is an hourly sodium peroxodisulfate formation of 143 kg, corresponding to an annual capacity of approximately 1 00 1.

Claims

Claims 1. Bipolar filter press cell for the production of peroxodisulfates or for the regeneration of Etching, pickling and oxidation solutions in peroxodisulfate recycling processes, consisting of clamping frames, monopolar electrode plates with current supply, bipolar electrode plates, flexible separators clamped between the electrode plates, outer supply and discharge lines and outer separating devices for the electrolysis and cooling devices media, the electrode plates having the following features: a) base body (1) made of liquid-impregnated graphite, b) cathode spaces (2) and cooling channels (4) incorporated in the base body, c) anodic half-cells applied to the base body, consisting of anode insulating plates ( 5), anode sealing frame (7) and composite anodes (6) made of platinum with current leads made of titanium or tantalum, which are electrically conductively connected to the base body (1), d) anode (8) and cathode compartments (2) divided into parallel flow channels , e) led out of the base bodies at the end faces n inlets (12, 20, 24) and outlets (13, 21, 25), which are connected to the outer feed lines (11, 19) and outer separating devices (14), characterized by the following features: f) 1.5 to 2.5 m high, but only 0.2 to 0.5 m wide electrode plates are used, g) the cooling channels (4) incorporated in the base body are pressure-tightly sealed against the anode compartments (8), h ) the electrically conductive connections between the base bodies (1 1) and Composite anodes (6) are arranged exclusively on both sides within the sealing surfaces of the anode sealing frame (7), i) ion exchange membranes (10) or microporous are used as separators Plastic sealing frame with an average pore size of <0.2 μm is used, j) the lower inlets for anolyte (20) and catholyte (12) as well as the upper outlets (21, 13) for the anodic and cathodic electrolysis products are arranged one above the other, k) the outlets (13) for the cathodic electrolysis products are via the cathodic outer separating device (14), an outer return flow channel (16) and the outer feed line (1 1) connected to the entrances (12) for the catholyte to form a circulation system, _. _ 2. Electrolytic cell according to claim 1, characterized in that the completely assembled bipolar electrode plates are preferably 30 to 50 mm thick. 3. electrolytic cell according to claims 1 and 2, characterized in that the cooling channels (4) are incorporated on the anode side into the base body (1) and are sealed pressure-resistant by an adhesive cover plate (3) made of impregnated graphite. 4. electrolytic cell according to claims 1 and 2, characterized in that the cooling channels (4) are incorporated on the anode side into the base body (1) and are sealed pressure-resistant by anode insulating plates (5) made of titanium. 5. electrolysis cell according to claims 1 to 4, characterized in that the composite anodes (6) consist of tantalum or titanium foils or plates, the sides of which face the cathode, in some cases 20 to 40% of their surface coated with piatin foils are. 6. electrolytic cell according to claims 1 to 5, characterized in that the Verbund¬ anodes (6) are provided on their back with lateral contacts which are pressed onto the contact surfaces of the base body (1) when clamped together by the anode sealing frame (7) . 7. electrolytic cell according to claims 1 to 6, characterized in that the platinum foils are applied in the form of vertical strips of 2 to 5 mm in width and 20 to 50 microns in thickness and at a distance of 5 to 20 mm on the base of the composite metal. 8. electrolytic cell according to claims 1 to 7, characterized in that the cathodic outer separating device is additionally equipped with means for separating cathodically deposited and with the circulating catholyte discharged metal particles. 9. electrolysis cell according to claims 1 to 8, characterized in that the inlets and outlets (12, 20, 13, 21) for the electrolysis media are carried out from one side of the electrode plates and the outlets 13, 21) with a combined separating device (14) are connected for the cathodic and anodic electrolysis products. 10. Electrolysis cell according to claims 1 to 9, characterized in that two cell segments are arranged next to one another within a stenter frame, the inlets and outlets for the electrolysis media being led out to the left and to the right from the end faces of the electrode plates.