EP2183409B1 - Method for operating copper electrolysis cells - Google Patents

Abstract

In a method for operating copper electrolysis cells which comprise a plurality of anode and cathode plates positioned perpendicularly and parallel to each other, an electrolyte inlet on the longitudinal side and an electrolyte outlet, the electrolyte flows in through the electrolyte inlet horizontally and parallel to the electrodes in each electrode gap at the level of the lower third of the electrodes at a rate of 0.3 to 1.0 m/s, wherein the cathode plates are in a fixed position with respect to the inlet direction. Thus, an optimum flow control of the electrolyte is achieved with respect to the electrodes, which results in an increase in the limiting current density.

Description

The invention relates to a method for operating copper electrolysis cells, which comprise a plurality of vertically and mutually parallel anode and cathode plates, a longitudinal electrolyte inlet and an electrolyte effluent, and a novel copper electrolysis cell.

• Anode:
  
          Cu →7 Cu²⁺ + 2 e^-
  
  
• Kathode:
  
          Cu²⁺ + 2 e^- → Cu
  
  

In principle, in a copper electrolysis anodic copper in the form of copper (II) ions is brought into solution, which is deposited at the cathode back to metallic copper.

• Anode:
  
  Cu → 7 Cu ²⁺ + 2 e ^-
  
  
• Cathode:
  
  Cu ²⁺ + 2 e ^- → Cu
  
  

The amount of metallic copper can be determined by Faraday's law (Equation 1): $$\mathrm{m}\mathrm{=}\frac{\mathrm{M}\mathrm{\cdot }\mathrm{i}\mathrm{\cdot }\mathrm{A}\mathrm{\cdot }\mathrm{t}}{\mathrm{z}\mathrm{\cdot }\mathrm{F}}$$

Here, m is the mass of copper produced in g, M the molar mass of copper in g / mol, i the current density in A / m ² , A the electrode surface in m ² , t the time in s, z the valence of the reaction ions involved and F the Faraday constant in As / mol. If one now wants to increase the amount of produced copper for a given plant size (A), one can only increase the current density i.

The currently technically feasible current densities are, for example, in a copper refining electrolysis at a maximum of 350 A / m ² . This value results from the fact that in a technical electrolysis cell only about 30-40% of the theoretical limiting current density can be driven. This theoretical _limiting current density i _limit (equation 2) is a function of the copper ion concentration in the electrolyte (c °) and the diffusion layer thickness δ _N at the electrode. N, the number of ions involved in the process, F, the Faraday constant and D, the diffusion coefficient, are constant. $${\mathrm{i}}_{\mathrm{border}}\mathrm{=}\mathrm{n}\mathrm{\cdot }\mathrm{F}\mathrm{\cdot }\mathrm{D}\mathrm{\cdot }\frac{{\mathrm{<figure-callout\; id="0"\; label="c"\; filenames="imgf0001.png"\; state="\{\{state\}\}">c</figure-callout>}}^{\mathrm{0}}}{{\mathrm{\delta }}_{\mathrm{N}}}$$

The calculation of the theoretical current density results in today's designs, values of about 1000 A / m ² and therefore technical current densities of 350 A / m ² maximum.

At higher current densities, dendrite formation and, ultimately, electrical short circuits between the anode and the cathode occur, which reduces the efficiency of deposition of cathode copper and the cathode quality as well. In order to set a much higher current density, the limiting current density must be increased. This is possible essentially only by reducing the nemstschen diffusion layer thickness. This reduction can be achieved by a higher relative movement between the electrolyte and the electrode.

The types of refining electrolysis cells used today are distinguished by the fact that the electrolyte is fed in on the front side and removed again on the opposite end side. The main flow therefore takes place between the cell wall and the electrodes or the cell bottom and the lower edges of the electrodes. This externally applied flow (also called forced convection) has little effect on the flow conditions between the electrodes. The flow between the electrodes is determined by the natural convection that results from the density difference of the electrolyte in front of the cathodes (lighter electrolyte due to depletion of copper ions) and before the anodes (heavier electrolyte due to the accumulation of copper ions).

In addition to electrolysis cells with cross-flow principle, therefore, cells have also been proposed in which the electrolyte flows mainly parallel to the surfaces of the electrodes.

So-called channel cells have been developed, in which a parallel flow is applied at a relatively high speed, wherein to ensure a uniform flow distribution over the entire channel cross-section in the electrolyte feed section in front of the electrode groups sieve flow-through structures are required.

Also known are parallel flow cells with double-walled partitions, which closes a wall with the upper edge of the bath, but does not reach to the bathroom floor, while the other wall starts at the bathroom floor, but does not reach to the top. In another known electrolysis bath ( DD 87 665 ) are arranged double- or multi-walled partitions with openings distributed over the entire width, which are located on one side at the level of the cathode lower edge and / or slightly upwards and on the other side in the amount of the electrolyte level and / or slightly downwards.

Furthermore, containers for electrolytic metal extraction are known in which, to achieve a parallel flow, the electrolyte inlet and outlet into or out of the electrode space is effected by perforated plates arranged parallel to the longitudinal walls.

In another cell construction, a parallel partition with openings for the passage of electrolyte into the electrode space is arranged only on one longitudinal wall. The passage openings are distributed over the entire electrode height and are aligned with the electrode interstices.

In order to achieve a parallel flow further Leiteinbauten have been proposed on the longitudinal walls of the cell through which the electrolyte is directed serpentine manner around the electrodes.

A relatively simple means of achieving parallel flow in conventional electrolysis cells is the provision of tubular electrolyte supply and drainage devices which direct the electrolyte in opposite directions between the bath longitudinal walls and the electrode side edges in the two free spaces. Due to the larger cathode width, a jam of the electrolyte occurs in front of the cathode side edges, as a result of which the latter partially flows into the respective electrode gap.

Also known is an electrolytic bath, in which the parallel flow is achieved by an inlet of the electrolyte from the bath floor. Here are the electrolyte inlet openings under the anodes and are directed vertically upwards.

In the DD 109 031 an electrolysis cell is described with longitudinal electrolyte inlet, in which on one or both longitudinal sides extending over the entire length of the bath extending to just below the cathode lower edge, down and closed at the sides, above the electrolyte level open electrolyte inlet box is attached to the the electrodes facing horizontal and parallel to the electrodes aligned through openings, which in the region of the lower cathode edges over a extend certain area of the cathode spaces. According to one embodiment, the cross-sectional area of all the passage openings is smaller than the open horizontal cross-sectional area at the top of the electrolyte inlet box in order to achieve a slight overpressure.

However, the above-mentioned parallel current cells have numerous disadvantages, which is why they could not prevail over the cross-flow cells so far.

Thus, the channel cell requires a large pump capacity to achieve the high flow rates. To separate the entrained anode sludge continuous electrolyte filtration is required.

Likewise, due to the risk of fluidization of anode sludge electrolyte inlet openings in the bathroom floor are not suitable.

Even in parallel flow cells with simple dividing walls, considerable flow branches can still occur despite lower flow velocities. The arrangement of the electrolyte drain or inlet on the bath floor also entails the risk of fluidization of anode sludge and thus the deterioration of the cathode quality. Such a risk also exists in the arrangement of double-walled partition walls, one of which does not extend to the bathroom floor. In addition, unfavorable conditions for the mixing of bath and fresh electrolyte arise. Another disadvantage is the burden of such double-walled partitions. Thus, these walls must be made particularly stable for receiving the anode loads, but this is associated with significant material problems.

In the parallel flow baths with double- or multi-walled partitions improved flow conditions are achieved by the arrangement of row-shaped openings at the level of the cathode lower edge and slightly above and in the amount of electrolyte level and slightly below, but there are the same material problems as above. In the double- or multi-walled partitions also areas with little electrolyte movement are present, in which it can lead to encrustations.

Of the known parallel flow cells with separate Elektrolytzu- and the equipped with perforated plates container can not be used, since the desired parallel flow due to the density differences between the bath electrolyte and the warmer Feed electrolyte can not realize and the conditions for a sufficient sedimentation of anode sludge are not given.

In the proposed electrolytic bath with only one perforated partition on the electrolyte inlet side, the flow conditions are not satisfactory for the same reasons. Due to the relatively strong self-contained partition, the bath width increases considerably, which is associated with a larger footprint.

The use of Leiteinbauten as a flow straightener and the arrangement of appropriately shaped partitions is associated with a very large material and manufacturing effort. In addition, the hanging of these baths with the electrodes requires great care, since the desired electrolyte circulation is guaranteed only if the required geometric conditions are precisely met.

The present invention aims to avoid the above-mentioned disadvantages and problems of the prior art and has as its object to provide a method for operating (conventional) copper electrolysis cells and a copper electrolysis cell with which higher current densities and thus higher current yields than in State of the art are possible, the cathode quality, for example but not affected by fluidization of the anode sludge, disturbance of anode sludge deposition, or poor inhibitor distribution. Likewise, extensive changes to and complex installations in the cell should be avoided.

This object is achieved in a first aspect in a method of the type mentioned above in that the electrolyte via the electrolyte inlet horizontally and parallel to the electrodes in each electrode gap at the level of the lower third of the electrodes at a speed of 0.3 to 1, 0 m / s is flowed, wherein the cathode plates are arranged stationary relative to the inflow direction.

In this way, an optimization of the flow guidance in the electrolysis cell based on a maximum relative movement of electrolyte to the electrode is achieved, which advantageously in a reduction of the hydrodynamic boundary layer, a homogenization of the concentration and temperature of the electrolyte, a better distribution of the inhibitors and especially an increase in the limiting current density results.

Due to the natural convection in the vicinity of the cathode, an upward movement takes place between anode and cathode, and a downward movement of the electrolyte near the anode. There is a velocity distribution between the electrodes as in Fig. 1 shown. The higher electrolyte velocity in the immediate vicinity of the cathode surface leads to an improved deposition of copper at the cathode, while the reduced velocity at the anode surface at the same time favors the sinking of the anode sludge.

In a preferred embodiment, the electrolyte is flowed into the cell at a rate of 0.3 to 0.6 m / s.

A further improvement of the method is possible if the electrolyte is not applied as usual and applied in the examples on the front side of the cell but longitudinally drained.

In particular, the method according to the invention has the additional advantage that it can be carried out even with existing electrolysis cells without great effort with few changes to the existing facilities.

According to another aspect of the invention, there is provided a copper electrolytic cell comprising a plurality of vertically and parallelly disposed anode and cathode plates, a longitudinal electrolyte inlet, and an electrolyte drain, characterized in that the electrolyte inlet is located on a longitudinal wall thereof Cell which extends into the region of the electrode lower edge and comprises a closed feed box which can be attached to the end faces of the cell and can be connected to an electrolyte source and means for stationary arrangement of each cathode plate and in the lower third of the electrode height extending and respectively corresponding to the electrode gap Regions with at least one opening, in particular nozzle, for the directed supply of electrolyte is provided.

Preferably, the means for the fixed arrangement of the cathode plates are designed as means for vertical guidance.

According to a preferred embodiment, the means for vertical guidance are formed as circular discs or wheels, wherein the cathode plates are each centered between two adjacently arranged and spaced discs or wheels.

According to a possible embodiment of the electrolytic cell, the electrolyte drain is arranged on the front side. However, it can also advantageously be arranged longitudinally.

The electrolyte feed box used in the cell according to the invention can also be used advantageously in already existing conventional electrolysis cells.

The invention will be explained in more detail with reference to examples and the drawing.

Fig. 2 shows a schematic representation of a copper electrolysis cell according to the present invention, in which, for reasons of better visibility of the inventive electrolyte feed box in relation to the electrolytic cell itself has been highlighted graphically. The closed inlet box 1 extends along a side wall 3 of the bath 2 and is attached to the end walls 4 of the bath 2 fastened in the cell, wherein the Einhängvorrichtungen 5 simultaneously serve the supply and discharge of the electrolyte in the actual feed box. At the end of a suspension device 5, the inlet box 1 with an electrolyte source, for example via a flange 6, connectable.

The inlet box 1 is arranged so deep in the cell that it extends into the region of the electrode lower edge. In the lower region of the inlet box 1, facing the electrodes, openings, in particular nozzles 7, are arranged, wherein at least one opening is located in each region corresponding to the electrode gap and extending over the lower third of the electrode height ( Fig. 3 ). Through these openings, the electrolyte is flowed into the cell in the lower area of the electrode gap at a speed of 0.3 to 1.0 m / s in order to achieve the advantageous flow guidance mentioned above. However, since this effect is achieved only with a defined and actually maintained arrangement of the electrodes with respect to the direction of flow, which is difficult to accomplish when mounting the electrodes in the bath, it is essential to arrange the cathode plates with respect to the inflow direction in a fixed manner. For this purpose, means for the stationary arrangement of each cathode plate are provided in the electrolytic cell, more precisely at the inlet box 1.

At the in Fig. 3 In the embodiment shown, the fixed arrangement is achieved by means for the vertical guidance of the cathode plates, which are formed as circular disks or wheels 8, wherein the cathode plates 9 are respectively centered between two adjacently arranged and spaced disks or wheels ( Fig. 4 ). The skilled person, however, numerous other embodiments are known or easy to find due to his expertise.

Examples:

For the following examples, a conventional industrial copper electrolysis cell was equipped with an electrolyte inlet according to the invention, comprising a feed box as described above.

Example 1:

In an industrial electrolysis cell copper sheets were produced with an inflow rate of 0.75 m / s and a current density of 407 A / m ² . The cathodic current efficiency during the whole anode travel was more than 97%.

Example 2:

In an industrial electrolysis cell copper sheets were produced with an inflow rate of 1.0 m / s and a current density of 498 A / m ² . The cathodic current efficiency during the whole anode travel was more than 93%.

Example 3:

In an industrial electrolysis cell copper sheets were produced with an inflow rate of 0.5 m / s and a current density of 498 A / m ² . The cathodic current efficiency during the whole anode travel was more than 98%.

Example 4:

In an industrial electrolysis cell copper sheets were produced with an inflow rate of 0.67 m / s and a current density of 543 A / m ² . The cathodic current efficiency was more than 95% throughout the anode travel.

Table 1 gives the operating conditions and results of further experiments. Table 1 Experiment No. i Q v η 1 trip η 2 trip in A / m ² in l / min in m / s in % in % 1 407 75 0.75 93.92 95.01 2 407 75 0.5 97.24 98,15 3 407 75 0.5 99.46 98.35 4 407 75 0.5 97.49 96.27 4a 407 75 0.5 92.1 93.77 5 498 150 1 98.99 93.47 6 498 75 0.5 99.55 99.28 7 498 100 0.67 99.53 99.13 8th 543 100 0.67 98.18 97.59

Claims (9)

1. A method for operating electrolytic cells of copper, comprising a plurality of anode and cathode plates arranged vertically and in parallel to each other, a longitudinal electrolyte feed and an electrolyte discharge, characterized in that the electrolyte is fed via the electrolyte feed horizontally and in parallel to the electrodes into each interstice between the electrodes, each at the height of the lower third of the electrodes, with a rate of 0.3 to 1.0 m/s, wherein the cathode plates are arranged in a stationary way with reference to the feed direction.
2. The method according to claim 1, characterized in that the electrolyte is fed into the cell with a rate of 0.3 to 0.6 m/s.
3. The method according to claim 1 or 2, characterized in that the electrolyte is run off in a longitudinal direction.
4. An electrolytic cell of copper, comprising a plurality of anode and cathode plates arranged vertically and in parallel to each other, a longitudinal electrolyte feed and an electrolyte discharge, characterized in that the electrolyte feed comprises a closed feed box extending alongside the longitudinal wall of the cell as far as the region of the bottom edge of the electrode, which feed box may be mounted at the front faces of the cells and attached to an electrolyte source and which is provided with means for the stationary arrangement of each cathode plate as well as with at least one opening, in particular a nozzle, for the oriented feed of electrolyte, with the opening being provided in the regions extending across the lower third of the electrode height and corresponding to each electrode interstice.
5. The electrolytic cell of copper according to claim 4, characterized in that the means for the stationary arrangement of the cathode plates are formed as means for vertical guidance.
6. The electrolytic cell of copper according to claim 5, characterized in that the means for vertical guidance are formed by circular discs or wheels, wherein each cathode plate is centered between two discs or wheels, respectively, which are arranged adjacently and spaced apart from each other.
7. The electrolytic cell of copper according to any of claims 4 to 6, characterized in that the electrolyte discharge is arranged at the front face.
8. The electrolytic cell of copper according to any of claims 4 to 6, characterized in that the electrolyte discharge is arranged longitudinally.
9. An electrolyte feed box for an electrolytic cell of copper, with the feed box being closed and extending alongside the longitudinal wall of the cell as far as the region of the bottom edge of the electrode, characterized in that it may be mounted at the front faces of the cell and attached to an electrolyte source and that it is provided with means for the stationary arrangement of each cathode plate as well as with at least one opening, in particular a nozzle, for the oriented feed of electrolyte, with the opening being provided in the regions extending across the lower third of the electrode height and corresponding to each electrode interstice.

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