GB2051862A - Electrolytic reclamation of precious metals - Google Patents

Abstract

Apparatus for the electrolytic reclamation of precious metals, especially of silver, from aqueous precious-metal salt solutions, comprises an electrolytic vessel 1 which has at the top an inlet 10 and at the bottom an outlet 11 for the precious-metal salt solution to be electrolyzed, and wherein are vertically and concentrically disposed in spaced relationship a cylindrical anode 15 and a cathode 16 with a motor driven stripping equipment 20 concentric to the anode and arranged to rotate in the space between anode and cathode, and with a filter 6 for collecting the separated precious metal entrained by the electrolyte flow. The filter 6 is situated in a filtering vessel disposed next to the electrolytic vessel. The electrolyte vessel is provided with a pressure limiter or with a breather 14. A rotatable slide plate 23 is preferably provided near the bottom of the electrolytic vessel to travel with slight clearance across the outlet opening located in the bottom, and is preferably rigidly connected with the stripping equipment. Preferably the inlet 12 to and the outlet 13 from the filtering vessel are located at the top, the outlet being screened by a filter bag 25 spread out by means of a spreading-out device consisting of several rods 26 encircled by a helical spring 27 and the inlet being outside of the filter bag. <IMAGE>

Description

SPECIFICATION Apparatus for the electrolytic reclamation of precious metals This invention relates to apparatus for the electrolytic reclamation of precious metals.

There has hitherto been proposed apparatus for the purpose aforesaid which comprises essentially an electrolytic vessel through which, in operation, a precious-metal salt solution flows from the top downwards and in which as cathode a ring of rods is arranged in a circle concentric to the anode.

Between the anode and the cathode rods rotates a turbine wheel driven through reaction of the flow in the electrolytic vessel. The turbine wheel is connected with stripping equipment which consists of several vertically extending arms provided with bristles. The precious metal powder deposited on the cathode rods is stripped off by the bristles and carried downwardly with the flow, where it is trapped directly below the electrodes by a filter also arranged in the electrolytic vessel.

As soon as the filter, a bag, is fully ioaded, the electrolytic vessel is opened from above and the electrodes, the stripping equipment and the turbine wheel thereof are lifted out; the filter is then exposed and can be removed.

This hitherto-proposed apparatus has several disadvantages. On the one hand the emptying of the filter is irksome and time-consuming as, for that purpose, the assembly disposed above the filter and comprising electrodes, stripping equipment and turbine wheel, must be dismantled, cleaned, and on assemblage be resealed. Moreover, the numerous cathode rods must be placed in position individually, secured, and be connected with one another through a ring conduit for coupling up electrically. Finally, there is the danger of operating troubles through gap bridging of the deposited precious metal between cathode and anode.As the stripping equipment is driven by the flow of the precious-metal salt solution in the electrolytic vessel, this flow may not be too quick for the achievement of as complete a separation as possible, and it is possible that the stripping equipment will stop because of the frictional resistance or is caught on depositions of precious metal without stripping these off.

The object of the present invention is so to develop said hitherto-proposed apparatus that it is reliable in operation and easier to manipulate.

According to the present invention, we provide apparatus for the electrolytic reclamation of precious metals, especially of silver, from aqueous precious-metal salt solutions, comprising an electrolytic vessel which is provided with a pressure limiter or with a breather and has at the top an inlet and at the bottom an outlet for a precious-metal salt solution to be electrolyzed, and wherein are concentrically and vertically disposed a cylindrical anode and a cathode spaced therefrom and consisting of a cage, gauze, net, screen or the like element provided with perforations, stripping equipment concentric with the anode, a prime mover for driving the stripping equipment to rotate in the space between the anode and the cathode, and a filtering vessel disposed next to the electrolytic vessel, and having therein a filter for collectiny the separated precious metal entrained by the electrolyte flow.

As the filth is located in a filtering vessel outside of the electrolytic vessel, the filter is easily accessible and the electrolytic vessel itself need not be opened for clearing out the filter. This is of particular significance as the solutions, from which precious metals are reclaimed, are frequently highly toxic. Contrary to the opinion expressed in Federal German Offenlegungsschrift No.

25 43 600, it has been shown that the powdery precious metals can be discharged very well by the liquid flow out of the electrolytic vessel into a separate filter.

Furthermore, the cathode arrangement is considerably simplified. The number and size of the perforations in the cathode should be so selected that the cathode surface is as small as possible and consequently the current density which can be achieved is as high as possible.

As the stripping equipment is driven by a prime mover, it is ensured that no short-circuiting bridges are set up between cathode and anode since the rotation of the stripping equipment is effected independently of the speed of flow in the electrolytic vessel. Consequently the rotation can also be effected considerably more quickly than in the case of the previously-proposed apparatus.

The turbulence of the liquid in the electrolytic vessel brought about by the quicker rotation is sufficient to strip the separated precious metal powder from the cathode without there being required for this purpose bristles or the like which brush over the cathode and bring about a progressive attrition thereof.

The pressure limiter or breather increases the operating reliability of the apparatus as it permits the controlled escape of the gas mixture formed during the electrolytic process.

A rotatable slide plate is preferably provided near the bottom of the electrolytic vessel and can travel with slight clearance across the outlet opening located in the bottom. The slide plate assists the flushing out of the separated precious metal powder which has fallen from the cathode, as it sweeps it into the outlet opening in the bottom of the electrolytic vessel.

Preferably the slide plate is rigidly connected with the stripping equipment and therefore does not require a separate drive.

Preferably also, the inlet to and the outlet from the filtering vessel are located at the top, the outlet being screened by a filter bag spread out by means of a spreading-out device, and the inlet being outside of the filter bag. This feature makes it possible, without particularly stressing the filter bag, to have a large filtering volume with a relatively small filter bag.

An apparatus for the reclamation of silver is represented diagrammatically and by way of example in the accompanying drawings, wherein: Fig. 1 shows a general view of the apparatus; Fig. 2 shows the electrolytic vessel in vertical section through the longitudinal axis; and Fig. 3 shows the filtering vessel in vertical section through the longitudinal axis.

Referring now to the drawings, there stands upright on a stationary base 1, within which is located a pump for feeding a silver salt solution, a cylindrical electrolytic vessel 2 whereof the bottom 3, peripheral wall 4 and cover 5 are of plastics material. Next to the electrolytic vessel 2 there is attached to the base 1 a filtering vessel 6 the peripheral wall 7 of which is of transparent plastics materiai, so that visual inspection of the separated quantity of silver is possible. The inlet 10 and the outlet 11 for the silver salt solution are, respectively, at the top and bottom of the electrolytic vessel 1, whereas in the case of the filtering vessel 6 both the inlet 12 and the outlet 13 are at the top.On the electrolytic vessel 2 there is, moreover, for reasons of safety, a vent valve 1 4 through which the gas mixture formed during the electrolysis can escape. Within the electrolytic vessel 2 is disposed a cylindrical anode 15, for example of expanded metal form, preferably of platinum-plate titanium. The anode 1 5 is concentrically surrounded by a cathode 1 6 of refined steel in the form of a grid or cage. The connection contacts 1 7 of the cathode 1 6 and anode 1 5 are arranged on the cover 5 and simultaneously serve for attachment Qf the cathode 16 and anode 1 5 to the cover 9.

A shaft 1 8 rotatably supported through the cover 5 of the electrolytic vessel 2, supports at its lower end at least two horizontal supporting arms 19 arranged axially symmetrically and from which stirrers 20 extend vertically upwards into the space between cathode 1 6 and anode 1 5. The shaft 18 is driven by a small electric motor 21 attached on to the cover 5.

The inlet 10 in the cover 5 discharges into the space between anode 15 and cathode 16. The outlet 11 is located in the bottom 3 and has the form of a radially-extending duct which is open to the interior of the electrolytic vessel 2 through a slot 22. The silver powder which has fallen from the cathode 1 6 is washed into this slot 15, the flushing out being accelerated by a slide plate 23 which is fastened to one of the supporting arms 19, extends in the radial direction, and rotates with the shaft 1 8. The lower edge of the slide plate 23 has only a slight clearance from the bottom 3 of the electrolytic vessel 2.

The stirrers 20 rotating between the cathode 1 6 and anode 1 5 prevent the formulation of shortcircuiting bridges between cathode and anode.

The turbulence of the silver salt solution caused by the stirrers 20 ieads moreover to a partial detachment from the cathode 1 6 of the silver powder which thereupon sinks on to the bottom 3.

The liquid laden with silver powder leaves the electrolytic vessel 2 through the outlet 11 and is conveyed upwards through a conduit 24 to the inlet 12 at the side in the cover 9 of the filtering vessel 6. The outlet 1 3 from the filtering vessel is located centrally of the cover 9. The outlet 1 3 is screened by a filter bag 25 which is turned inside out over a spreading device. The spreading device consists of several rods 26 disposed in a circle and attached to the cover 9, the rods 26 being encircled by a helical spring 27. The edge of the filter bag 26 is turned inside out over a stub 28 of the cover 9 and is there clamped by an elastic ring 29, the outlet 13 passing through the stub 28. The silver powder is consequently held back outside the filter bag 25 and collects in the vessel formed by the bottom 7 and peripheral wall 8. To remove the silver powder, disconnection Is effected of the strap 30 which connects the cover 9 with the lower part 7, 8 of the filtering vessel securely and, because of an O-ring 31 in the cover, in a sealed manner. The lower part formed by the bottom 7 and peripheral wall 8 can then be withdrawn downwardly and emptied. Moreover, the filter bag 25, while accessible, may also be cleaned and, if necessary, replaced.

Claims (5)

1. Apparatus for the electrolytic reclamation of precious metals, especially of silver, from aqueous precious-metal salt solutions, comprising an electrolytic vessel which is provided with a pressure limiter or with a breather and has at the top an inlet and at the bottom an outlet for a precious-metal salt solution to be electrolyzed, and wherein are concentrically and vertically disposed a cylindrical anode and cathode spaced therefrom and consisting of a cage, gauze, net, screen or the like element provided with perforations, stripping equipment concentric with the anode, a prime mover for driving the stripping equipment to rotate in the space between the anode and the cathode, and a filtering vessel disposed next to the electrolytic vessel, and having therein a filter for collecting the separated precious metal entrained by the electrolyte flow.

2. Apparatus according to claim 1, in which a rotatable slide plate is provided near the bottom of the electrolytic vessel and can travel with slight clearance across theoutlet opening located in the bottom.

3. Apparatus according to claim 2, in which the slide plate is rigidly connected with the stripping equipment.

4. Apparatus according to any one of the preceding claims, in which an inlet to and an outlet from the filtering vessel are located at the top, the outlet being screened by a filter bag spread out by means of a spreading-out device, and the inlet being outside of the filter bag.

5. Apparatus for the electrolytic reclamation of precious metals, especially of silver, substantially as hereinbefore described with reference to the accompanying drawings.