FI97305C - Aluminum cathode plate for electrolytic recovery of zinc - Google Patents

Abstract

Aluminium cathode plates for the electrowinning of zinc, which have insulation strips at least at the edges which form two mutually approximately parallel narrow-side surfaces with the electrode surfaces and which have holding devices for the purpose of suspension in the electrolysis bath and for current collection at one narrow-side surface joining said narrow-side surfaces. The insulation strips consist, at least in the parts adjoining the plate, of copolymeric polyolefin and are fused on around the edges formed by the side surfaces with the electrode surfaces. <IMAGE>

Description

97305

Aluminum cathode plate for the electrolytic production of zinc

The invention relates to a cathode plate for the electrolytic production of zinc, comprising a plate consisting of aluminum and an insulating strip made of plastic at least at one edge of the plate, fused around the edge.

Insulation strips are installed on the edge of currently known cathode plates for the electrolytic production of zinc. It is necessary in order to prevent the accumulation of zinc deposited on the cathode surfaces in the direction of the anode plate or electrolyte pool and thus the formation of a short circuit. These insulating strips are either clicked or pressed to the edges of the cathode plate. However, variations are also known in which the insulating strips are screwed on. These insulation strips themselves consist of plastic, rubber or wood. A cathode plate such as that mentioned at the beginning is known from DE-A-3 219 300.

20 Because cathode plates are used immersed in sulfuric acid used as an electrolyte, aluminum is exposed to corrosion. Corrosion occurs above all under the lists. I did so because the acid penetrates between the board and the insulating strips and causes ____ very quickly there; 25 aluminum corrosion. As a result, the cathode plate • «... is taken out of service early because its edges are corroded, the insulating strip loses its grip on the plate and a short circuit between the accumulated zinc and the ano- '·: * dilute plate or electrolyte pool occurs.

*. · * 30 According to the invention, this detrimental effect of corrosion is prevented, so that the insulation strip consists of copoly, ···. of a polyolefin at least in part in contact with the sheet. The pair of copolymeric polyolefin and aluminum has proven to be particularly liquid-resistant against corrosive, sulfuric acid-containing electrolyte. According to a preferred embodiment of the invention, the insulating strip comprises on the plate side a layer consisting of a copolymeric polyolefin and otherwise consisting of ordinary polyolefin. This type of structure is very advantageous for hin-5 nals because less expensive copolymeric polyolefin is needed.

In addition, in one form according to the invention, a design type is designed in such a way that the insulating strip consists entirely of a highly adhesive poly-10 olefin.

In the case of this type of construction, the production can take place at a particularly low cost and simply when the number of plates to be produced is large.

It has been found that the process used for the preparation is carried out according to the invention by extruding the insulating strip and pressing it after extrusion in heat (at a temperature of 100 to 200 ° C, preferably 160 to 180 ° C, for 1 to 5 minutes). against the adhesive surfaces of the cathode plate strip, the plates are cut and then 20 into the narrow side surfaces of the cathode plate which connect; narrow side surfaces with insulating strips,. . ·. welded brackets.

In one form of the invention, the extrusion of the strip then takes place preferably by extruding a highly adhesive copolymeric polyolefin and a normal "" polyolefin together. In this way, it is possible to use less alloy and only the well-adhering polyolefin required on the plate side, which makes the production of the cathode plate according to the invention more advantageous. ίφί; 30 By extruding the profile and then fusing it to the cathode strips, the heat required for extrusion is utilized in the best possible way. The production can take place on a continuous basis, in which case large quantities of such cathode-strips can be produced. After that, they only have to be cut off and the brackets necessary for conducting and suspending the current must be installed.

In one aspect of the invention, it is advantageous to manufacture the cathode plates by forming a layer of adhesive copolymeric polyolefin on the surfaces to be insulated and overlying this layer a part of ordinary polyolefin which forms the actual strips.

Because this highly adherent polyolefin is tightly bound to the cathode plate, the electro-10 lithium cannot penetrate the joint and only needs to push the actual insulating strip warm into place. The adhesion between the polyolefin layer and the insulating strip is sufficient to adhere when the cathode plate is used. This method is economical, especially when only a few cathode plates have to be manufactured, as is often the case with repairs and maintenance of an electrolysis plant.

Copolymeric polyolefins are, within the meaning of the invention, copolymers between olefins and adhesives suitable for metal surfaces. These adhesive additives are generally aliphatic carboxylic acids, for example acrylic acid or its derivatives, and are present in an amount of 1 to 10%. Instead of acrylic acid, esters such as vinyl acetate may also be present. Vinyl acetate can also be used simultaneously with acrylic acid; similarly, other terpolymers are also considered. In addition, polyolefin-based hot-melt adhesives which have sufficient corrosion resistance are suitable.

::: 30 The invention is illustrated by the following drawings; Figure 1 is an overall view of a roof plate according to the invention.

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Figure 2 is an enlarged view of a horizontal section of a detail of a cathode plate according to the invention.

4 97305

Figure 3 shows a detail of a cathode plate according to another invention.

The cathode plate containing the aluminum plate 1 is placed in the electrolyte 2 in the basin 3 on its support 5 placed on the busbars 4 5 and 4 ', and insulating strips 6 and 6' made of polyolefin are attached to both narrow vertical sides.

Figure 2 shows an embodiment of a cathode plate in which an insulating strip consisting exclusively of a highly adhesive copolymeric polyolefin is fused to the side edge of the aluminum plate 1. The insulating strip may be extruded and melted using the heat of extrusion.

Figure 3 shows a layer 7 of adhesive copolymeric polyolefin formed on the aluminum plate 1 of the cathode plate, on which a U-shaped rail 8 forming the body of the insulating strip is pushed. The pushing takes place in heat, preferably using the heat of extrusion.

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Claims (4)

A cathode plate for electrolytic recovery of zinc comprising a plate (1) of aluminum and a plastic insulating strip (6) located at the edges of the plate at least about the edges, characterized in that at least the portion of the insulating strip (6) contained in contact with the plate (1) consists of copolymerized polyolefin. The cathode plate according to claim 1, characterized in that the insulation strip (6) consists of a copolymer polyolefin contact layer (7) and a plain polyolefin layer (8) located on it. Method for making a cathode plaque according to claim 1, characterized in that the insulation strip (6) is extruded in a manner known per se and it is pressed after the extrusion, still in hot condition, against the edges of a cathode plaque band, The strip provided with insulation strips is then cut into cathode plaques, after which welders (5) are welded to one of two: ·. 20 between edges provided with insulation strips. A method for making a cathode plate according to claim 3, characterized in that the extrusion of the insulation strip (6) is effected by coextrusion; ring of copolymeric polyolefin and normal polyolefin. • «• ·« * • «» • «·« · <• «• n · m« 1 • «•« • · • · # »·