Coated metal anode for the electrolytic recovery of metals

Abstract

A coated metal anode for the electrolytic recovery of metals is disclosed, whereby the working surface of this anode is represented by rods 4 which are arranged in a plane in spaced, parallel relationship to each other and which are electrically connected to a current supply rail 3.

To provide a coated metal anode of the identified type, which ensures an operation with acceptable current density and which permits with a simple constructive assembly an energy saving deposit of metal with high purity on the oppositely disposed cathode, the total surface F_A of the rods 4 and the surface F_p assumed by the total arrangement of the rods 4 fulfills the relationship 6≧F_A :F_p ≧2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION OF THE INVENTION

As shown by FIG. 1, a cell tank represented only schematically is indicated with 1. On bearing blocks 2 at the opening edge of the cell tank 1, a current supply rail 3 is positioned, which is connected via a contact rail 5 to the source of current. The current rail 3 bears a series of rods 4, which represents the working surface of the anode. The rods with the length L_S have a rectangular cross-section with the width B and the depth T. In this respect, the rods are orientated such that their depth T extends perpendicular to the arrangement plane of FIG. 1. The surface assumed by the rods is defined by the length of the rods L_S and by the distance L_G of the outer sides of the two outer rods of the anode structure. The rods 4 are arranged with a clear distance A to each other.

The electrical and mechanical connection of the current supply rail, comprised e.g. of copper, with the rods 4, comprised e.g. of coated titanium, is best shown by FIG. 3. According to same, the current supply rails 3 and the rods 4 are arranged in a plane such that the upper end faces of the rods 4 border against the lower surface of the current supply rail 3. The connection of the current supply rail 3 with the rods 4 takes place via two connecting strips 6 arranged on both sides of the current supply rail and parallel thereto, whereby said strips 6 can also be of coated titanium. The connecting strips 6 are secured by means of screws 7a and nuts 7b to the current supply rail 3. The connection of the rods 4 with the connecting strips 6 takes place by welding spots 8. For the further stiffening of the anode structure, a plurality of crossbars 9, which are also of coated titanium, are connected to the rods 4 by spot welding. In this respect, the successive crossbars 9 are arranged alternatively on the one or the other side of the arrangement plane of the rods 4.

With the described construction, the rods 4 have a length L_S of 1170 mm, whereas their width B is 2 mm and their depth T 12 mm. The clear distance A between two adjacent rods 4 is 8 mm. The entire length L_G of the anode structure is 852 mm. 82 rods are provided.

The described anode is designed for a current of 600 A corresponding with an anode-side current density of 355 A/m² (F_p). With a current of 600 A, merely an IR drop of about 100 mV occurs in the anode.

The anode construction is stiff and robust. This results not only from the described connection of the rods 4 with the current supply rail 3 by means of the connecting strips 6 and from the spot welding of the rods with these connecting strips 6, but also from the additional arrangement of the crossbars 9, which have a diameter of 4 mm in the embodiment. In this manner, each lamella-like rod 4 is held by seven welding spots.

The anode is simple in construction, relatively inexpensive to produce on account of the smallest possible amount of material, and has a very large geometrical surface. Without the current supply rail 3, it weighs about 12 kg. The total surface of the rods F_A, to which the coating is applied, is about 3 m², inclusive of the contacts. The working surface of the anode, i.e. that which immerses in the electrolyte, is about 2.4 m², which provides at 600 A a D_A value (anodic current density) of about 250 A/m² (F_A). The actual physical anode current density which results from the extremely large BET surface of the coating amounts to only a few 5%o of the D_A value. Therefrom, and from the catalytic effectivity of the active components of the coating, a constant, low oxygen voltage results at the anode according to the invention for a long period of operation.

The coating of the anode surface which projects from the bath serves for the protection against corrosion of the component parts of the anode consisting of titanium.

The relatively small current load of the current supply rail 3 consisting of copper of about 0.8 A/mm² with a current of 600 A at the anode permits the provision of nine bores 3a in the current supply rail 3 over a length L_G of 852 mm. Each bore 6a in the connecting strip 6 has a partial current of about 33 A. On account of this small partial current in the contact zones and the good contact coating, the voltage drop in these regions remains constant for long periods of operation.

It should be understood that other modifications and variations are possible without departing from the spirit of this invention, accordingly the scope of the invention is limited only by the claims which follow. We claim

Claims

1. A coated metal anode for the electrolytic recovery of metals, the working surface of which is represented by rods which are arranged in a plane in spaced, parallel relationship to each other, and which are electrically connected to a current supply rail, wherein:

said rods lie in a plane with the current supply rail, so as to create a substantially planar rectangular, surface of the anode;

said rods being arranged in such a manner that a larger portion of the area of said rods extends perpendicular to the arrangement plane assumed by said rods than is congruent with said plane; and

said rods are connected to said current supply rail at one end face; and

both the electrical and mechanical connection of each rod with said current supply rail takes place by means of at least one connecting strip extending parallel to said rod; and wherein

one marginal region of said connecting strip is connected with said current supply rail and another marginal region is connected with said rods.

2. The anode according to claim 1, wherein said rods have a substantially rectangular cross-section and are arranged in such a manner that the larger stretch of the cross-section of said rods extends perpendicular to the arrangement plane assumed by said rods.

3. The anode according to claim 2, wherein the ratio of the short side of the rectangular cross-section of said rods to the long side thereof is .Badd.1:2 to 1:10.

4. The anode according to claim 3, wherein the width of said (B) of said rods, measured parallel to the arrangement plane, is about 0.5 mm to about 2.5 mm and wherein the depth (T) of said rods, measured perpendicular to the anode plane, is about 5 mm to 25 mm.

5. The anode according to claim 2 wherein the ratio of the width of one of each of said rods to the middle distance between two adjacent rods is between 1:4 to 1:6.

6. The anode according to claim 2 wherein the clear distance (A) between two adjacent rods is ≧2 mm.

7. The anode according to claims 1 or 2 wherein as to each rod, two connecting strips are connected one along each side of the current supply rail and rod.

8. The anode according to claim 7 wherein each connecting strip is secured to said current supply rail by screw connections.

9. The anode according to claim 8, wherein the contact area between said connecting strip or strips and said current supply rail is selected to be so large that the reduction of the contact area caused by the bores of said screw connection have no substantial effect on the current density or current load, respectively, in said contact area.

10. The anode according to claims 1 or 2 wherein said rods are secured to said connecting strips by means of spot-welding.

11. The anode according to claims 1 or 2 wherein said rods are connected with each other by a plurality of crossbars.

12. The anode according to claim 11, wherein the successive crossbars are arranged alternatively on the one and on the other side of said rods.

13. The anode according to claim 12 wherein said crossbar is secured to said rods by spot-welding.

14. The anode according to claims 1 or 2 wherein the bores of said rods is formed of valve metal, especially titanium, whereas the coating is formed of platinum metal and/or platinum metal oxide and/or an electrically conductive, non-stoichiometric oxide and/or a base metal and/or its oxide and/or mixtures of the above substances.

15. The anode according to claims 1 or 2 wherein the total surface of all the rods F_A and the planar rectangular surface F_P assumed by the total arrangement of the rods fulfills the relationship 6≧F_A :F_P ≧2.