CH647267A5 - Device for electrolytic rueckgewinnen of precious metals. - Google Patents

Description

647267

PATENT CLAIMS

1. Device for the electrolytic recovery of precious metals, in particular silver, from aqueous precious metal salt solutions,

a) with a vertically arranged cylindrical anode,

b) with a cathode arranged concentrically and at a distance from the anode in an electrolysis vessel which has an inlet at the top and an outlet opening for the solution at the bottom,

c) with a stripping device which is arranged concentrically to the anode in the space between the anode and cathode, and d) with a filter for collecting the deposited noble metal carried by the electrolyte flow,

characterized in that e) the filter (25) is located in a filtering vessel (6) arranged next to the electrolysis vessel (2),

0 the cathode (16) is a body provided with openings,

g) the stripping device (18-21) is motor-driven, and h) the electrolysis vessel (2) is provided with a pressure limiter or with a venting device (14).

2. Device according to claim 1, characterized in that on the bottom (3) of the electrolysis vessel (2) a rotatable slide (23) is provided which can be moved at a short distance over the outlet opening (22) located in the bottom (3).

3. Device according to claim 2, characterized in that the slide (23) is rigidly connected to the stripping device (18-21).

4. Device according to one of the preceding claims, characterized in that the inlet (12) and the outlet (13) of the filtering vessel (6) are arranged at the top, the outlet (13) by means of a clamping device (26 -29) stretched filter bag (25) is shielded and the inlet (12) is outside the filter bag (25).

The innovation is based on a device according to the preamble of claim 1. Such a device is known from DE-OS 2 543 600. It is a device that i.w. comprises an electrolysis vessel through which the noble metal salt solution flows from top to bottom, in which a ring of rods is arranged as the cathode on a circle concentric with the anode. Between the anode and the cathode rods, driven by the action of the flow in the electrolysis vessel on a turbine wheel connected to the stripping device, rotates a stripping device which consists of several arms which run vertically and are provided with bristles. The precious metal powder deposited on the cathode rods is stripped off by the bristles and carried downward with the flow, where it is collected directly under the electrodes by a filter which is still arranged in the electrolysis vessel. As soon as the filter, a bag, is fully loaded, the electrolysis vessel is opened at the top and the electrodes, the scraper and its turbine wheel are lifted out; the filter is then exposed and can be removed.

The known device has several disadvantages. On the one hand, emptying the filter is tedious and time-consuming, because the insert lying over the filter also helps

Electrodes, scraper device and turbine wheel must be removed, cleaned and resealed during assembly. Furthermore, the numerous cathode rods have to be individually aligned, fastened and connected to one another for electrical connection by a ring line. Finally, there is a risk of malfunctions due to the bridging of the deposited precious metal between the cathode and the anode. Since the stripper is driven by the flow of the precious metal salt solution in the electrolysis vessel, this flow must not be too fast to achieve the most complete separation possible, it is possible that the stripper will stop due to frictional resistance or get stuck on precious metal deposits without stripping it.

It is the object of the present innovation to further develop the device mentioned at the outset in such a way that it is more reliable in operation and easier to use.

This object is achieved by a device with the features specified in claim 1. Characteristic (e) ensures that the filter is easily accessible and that the electrolysis vessel itself does not have to be opened to empty the filter. This is particularly important because the solutions from which precious metals are recovered are often highly toxic. Contrary to the opinion expressed in DE-OS 2 543 600, it has been shown that the powdery noble metals can very well be discharged from the electrolysis vessel into a separate filter by the liquid flow.

The feature (f) simplifies the removal of the cathode considerably. The number and extent of the openings in the cathode should be selected so that the cathode area is as small as possible, and consequently the achievable current density is as large as possible. The cathode can have the shape of a cage and consist of a perforated plate, a metallic net or grid or the like.

The feature (g) ensures that there are no short-circuit bridges between the cathode and the anode, because the rotation of the stripping device takes place independently of the flow speed in the electrolysis vessel. Therefore, the rotation can also take place considerably faster than in the previously known device. The swirling of the liquid in the electrolysis vessel caused by the faster rotation is sufficient to detach the deposited precious metal powder from the cathode without bristles or the like. a gradual wear subject to scraper blades that strip along the cathode.

The feature (h) increases the operational safety of the device because it allows the controlled escape of the gas mixture formed during the electrolysis process.

Advantageous further developments of the innovation are the subject of the dependent claims. The slide provided according to claim 2 supports the flushing out of the deposited and dropped from the cathode precious metal powder by sweeping it into the outlet opening at the bottom of the electrolysis vessel.

When configured according to claim 3, the slide does not require a separate drive.

The design according to claim 4 enables a large filter volume with a relatively small filter bag without a particular load on the filter bag.

In the accompanying drawings, a device for recovering silver is shown schematically.

FIG. 1 shows an overall view of the device,

Figure 2 shows the electrolyzer in vertical section through the longitudinal axis and

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Figure 3 shows the filter vessel in vertical section through the longitudinal axis.

On a base 1, in which there is a pump for conveying the silver salt solution, there is a cylindrical electrolysis vessel 2, the bottom 3, jacket 4 and lid 5 of which are made of plastic. In addition to the electrolysis vessel 2, a filter vessel 6 is attached to the base 1 in a suspended construction, the jacket 7 of which is made of transparent plastic, so that a visual inspection of the amount of silver deposited is possible.

The inlet 10 for the silver salt solution is located at the top and the outlet 11 at the bottom of the electrolysing vessel 1, while both the inlet 12 and the outlet 13 are located at the top of the filter vessel 6. On the electrolysis vessel 2 there is also for safety a vent valve 14 through which the gas mixture formed during the electrolysis can escape.

In the electrolyser 2 there is a cylindrical anode 15 e.g. in the form of expanded metal, preferably made of platinized titanium. The anode 15 is concentrically surrounded by a stainless steel cathode 16 in the form of a grid or cage. The connection contacts 17 of the cathode 16 and anode 15 are arranged on the cover 5 and at the same time serve to fasten the cathode 16 and anode 15 to the cover 9.

An axis 18, which is rotatably guided through the cover 5 of the electrolysis vessel 2, carries at its lower end at least two axially symmetrically arranged horizontal support arms 19, from which agitator arms 20 extend vertically upwards into the space between cathode 16 and anode 15. The axis 18 is driven by a small electric motor 21 fastened on the cover 5.

The inlet 10 in the lid 5 opens into the space between the anode 15 and the cathode 16. The outlet 11 is located in the bottom 3 and has the shape of a radially extending channel which is open through a slot 22 to the inside of the electrolysis vessel 2. The silver powder dropped from the cathode 16 is flushed into this slot 22, the flushing out being promoted by a slide 23 which is fastened to one of the support arms 19, extends in the radial direction and rotates with the axis 18. The lower edge of the slide 23 is only a short distance from the bottom 3 of the electrolysis vessel 2.

The stirring arms 20 rotating between the cathode 16 and the anode 15 prevent the formation of short-circuit bridges io between the cathode and the anode. The swirling of the silver salt solution caused by the stirring arms 20 also leads to a partial detachment of the silver powder from the cathode 16, which then sinks to the bottom 3.

The liquid loaded with silver powder leaves the electrolysis vessel 2 through the outlet 11 and is conveyed through a pipe 24 upwards to the inlet 12 laterally in the lid 9 of the filter vessel 6. In the middle of the lid 9, the outlet 13 of the filter vessel 6 is conveyed. In the middle of the lid 9 there is the outlet 20 of the filter vessel. It is shielded by a filter bag 25, which is placed over a clamping device. The clamping device consists of several rods 26 arranged in a circle and fastened to the cover 9, which are surrounded by a helical spring 27. The edge of the filter bag 25 is placed over a nozzle 28 of the cover 9 through which the outlet 13 passes and is clamped there by an elastic ring 29.

The silver powder is therefore retained outside the filter bag 25 and collects in the vessel formed by the bottom 30 and the jacket 8. To remove the silver powder, the bracket 30 is loosened, which firmly connects the lid 9 and, owing to an O-ring 31 in the lid 9, tightly connects it to the lower part 7, 8 of the filtering vessel. The lower part formed by the bottom 7 and the jacket 8 can then be pulled off and emptied downwards as a unit 35. Furthermore, the filter bag 25 can also be cleaned and replaced if necessary.

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3 sheets of drawings