US1996342A - Electrolytic refining and to the casting of anodes and the like - Google Patents

Description

A. G. McGREGOR ELECTROLYTIC REFINING AND TO THE CASTING OF ANODES AND THE LIKE April 2, 1935.

Filed Nov. 1951 4 Sheets-Shee1; 1

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' ELECTROLYTIC REFIN'ING AND TO THE CASlIN G OF ANODES' AND THE LIKE Filed Nov. -6, 19:51 4 Sheets-Sheet 2 'm m 52 2 w 4% il I [fall 'H'ulr 11ml. E

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" April 2, 1935. G MCGREGOR 1,996,342

ELECTROLYTIC REFINING AND TO THE CASTING ANODES AND 'I HE LIKE Filed Nov. 6, 1951 4 Sheets-Sheet 3 A ril 2, 1935. A. GQM GR E GOR 9 ELECTROLYTIC REFINING AND TO THE CASTING OF ANODES AND THE LIKE V Filed Nov. 6, 1931 4- Sheets-Sheet. 4

Patented Apr. 2, 1935 OFFICE 1,996,342 ELECTROLYTIC REFINING AND'TO THE CASTING OF ANODES AND THE LIKE Alexander Grant McGregor, London, England Application November 6', 1931, Serial No. 573,496

In Great Britain November 11, 1930 8 Claims.

This invention comprises improvements in or relating to electrolytic refining and to the casting of anodes and the like; a

One main object of the invention is to provide an improved process of and plant for the electrolytic refining of copper, although the invention is not limited to the electrolytic refining-of copper and most of the features thereof are also applicable to f the electrolytic refining of other metals, for example nickel, in relation to which the invention possesses the same advantages as it possesses in therefining of copper. o

One well known system of electrolytic refining of copper known as the series system is characteras the cathode of the next adjacent anode so that on passing a current through the series of cells from end-to-end the effect is to displace copper from one face of the anodes and deposit it' on the backsof the anodes of the next higher cells in the series. ess iscarried out with thin anode plates so that the deposition may be continued without intermission until the whole of the anode plateshave been electrolytically displaced and are deposited as cathodes, whereupon they are removed from the cells for utilization. It is only practicable to employ thin anodes for this purpose, because if thicker anodes are used and thick deposits are.

made the deposited metal attains an irregular surface, which leads to the building up of trees and sprouts on the deposit which short circuit the electric current or at all events reduce the efficiency- Moreover, in the multiple system of electrolytic copper refining it is necessary to commence operations with a fair spacing between the anode and cathode sheets, which have uneven surfaces, which spacing involves an additional volt- Lo age drop, beyond that attainable if the plates could be spaced more closely together. Further, as thejanodes are corroded away and new thin cathode sheets are substituted for the finished cathodes, (usually three or more crops 'of cathodes 5 are taken 'for each tank'filling of anodes) thea space between anode and cathode centre tocentre remains the same but the space from face to anodeto face of cathode increases with a corresponding voltage drop and loss in efllciency. An-

0 other disadvantage of the multiple system is the great amount of labour required in producing the thin cathode sheets and the subsequent care required with them.

One object of the present invention is' to en-' 5 able stout and relatively easily cast anode plates ized by the fact that one side of the anode acts As ordinarily practised, this proc-' to be employed in the series system of electrolysis.

"According to the present invention in the series system of electrolytic refining of metals (for example copper) anodes are employed of greater thickness than can be efllciently refined by electro-deposition in a single stage and electrolysis is carried out in stages by stripping cathode deposits from the backs of the anodes at the end of one or more stage or stages of deposition andthereafter effecting a further cathode deposit or deposits.

Preferably, after stripping at the end of one stage the anode plates are respaced for the next stage nearer together. By this means the face to face distance between electrodes may be kept. constant throughout the stages of treatment of the anodes, and consequently, notwithstanding the fact that the anodes become progressively thinner, the efliciency of the process is maintained throughout the several stages.

By the process described the anode plates may be cast of such thickness as to render them free from liability to buckling during the casting operation, and thus to ensure an initial true flat surface to the plates, which assists in uniform deposition of metal during electrolysis. Thus, the liability to the formation of trees and to uneven current density is minimized, and the initial spacing between opposed faces of the plates, as compared with the ordinary multiple system, may be reduced. The invention includes plant for the electrolytic refining of metals (for example copper) comprising a plurality of electro-deposition tanks of differing sizes, means for mounting electrodes therein'for series electro-deposition and means for removing electrodes from a larger tank orv tanks, stripping cathode deposits therefrom and re-assembling them at a closer spacing in a smaller tank. Thus, the respaced plates also fit closely in the tanks in which they are located, which is an unnecessary feature of waste of the electro-, lyte to be avoided.

Y The invention includes as a new manner of manufacture, anode plates for electrolytic refining consisting of a flat plate portion and a'plurality of suspension lugs cast solid therewith,- the lugs being thinner than the plate portion, offset so that they stand to one side of the central plane thereof and cast with suspension holes of tapered formation to rovide a knife edge bearing upon a supporting ook.

According to a further feature of the invention in an electrolytic cell for series electrolysis there is provided means for suspension of the anodes in 55 the form of a frame which spans the cell and a plurality of rows of supporting hooks hung upon said frame but insulated therefrom and so shaped and spaced as to be capable of suspending the anodes at an appropriate distance apart. Preferably the end supporting hooks of each frame are provided with electrical connections to fixed insulated downwardly-facing connector elements on each frame and contact members are provided secured to'the sides of the electrolytic cell for co-operation with the connector elements. By this means a frame complete with insulated hooks and anodes hanging therefrom may readily be lifted by suitable tackle out of an electrolytic cell for inspection or changing of the anodes, and on replacement the electrical connections between the connector plate and the spring contact members on the cell walls will automatically be remade.

These and other features of the invention will now be described with reference to one specific embodiment of the invention which is given by way of example.

Referring to the accompanying drawings:-

Figures 1 to 4 are diagrammatic representationsiof anodes at various stages in the process of electrolysis according to the present invention;

-Figure 5 is an elevation of the interior of an electrolytic refining plant according to the present invention;

Figure 6 is a vertical sectional view through an electrolytic cell and part of a second cell;

Figure 7 is a plan of parts of two such cells;

Figure 8 is a section upon the line 88 of Fig. 6, looking in the direction of the arrows;

- Figures 9 and 10 are details of the connections from cell to cell, and

Figure 11 is a detail of an anode-supporting hook.

Referring to Figures 1 to 4, these show four stages of electrolysis according to the present invention, and in Figure 1 a series of anodes I I, 2|, 3| are provided, the initial thickness of which is indicated by the dotted lines in the figure. As electrolysis proceeds copper from the anode I I is deposited on the back of the anode 2I to form the deposit 22 and copper from the anode 2I is deposited on the back of the anode 3| to form the, deposit 32.

When electrolysis has proceeded to the point of depositing about one-quarter of the original thickness of the anodes upon the backs of their fellows, the stage is reached which is represented in the figure. The anodes are then removed from the cells and the deposits 22, 32 and so on are stripped from the backs of the anodes. The anodes are then respaced close together as shown in Figure 2 and a fresh series of deposits 23, 33 is effected. Thereafter, these deposits are stripped, the anodes are again spaced closer toether than before as shown in Figure 3 and a third series of deposits 24, 34 and the like are made.

Finally after the stripping of the deposits 24, 34, the anodes are respaced and inserted in an electrolytic cell for the last time and electrolysis is continued until all of the anodes become redeposited as cathode deposits 25, 35.

Reference to Figure 5 will show the general character of the plant in which the. above op-- 'erations are carried on. The cells I20, I22 which are the largest are provided for receiving the initial widely spaced anodes represented in Figure 1. The anodes are hung in the cells in batches 82 as hereinafter described and a parallel travelling crane IOI is provided for depositing the anodes in the cells and for removing them therefrom.

After removal and stripping of the deposits, the anodes are respaced upon another frame I82 and deposited in smaller cells 220, 222. The third operation, represented in Figure 3, is carried out in still smaller cells 320, 322 and the final operation of Figure 4 in a last series of cells 420, 422. The construction of the cells and of the supporting frames and anodes will now be described with reference to Figures 6 to 11.

Each vat or cell consists of cement walls lined with mastic 8I for the insulation required in the series system of electrolytic refining. Each vat is of such dimensions that the anodes 82 (Figure 8) when vertically supported therein a short distance above the bottom of the vat, reach as far as the surface of the electrolye, only the suspension lugs 83 projecting above the liquid level. The vats may be of considerable size, sufiicient to accommodate say four anodes edge to edge in the length of the vat as shown in Figure 6 with the minimum space between the anodes which can be mechanically arranged for. Thus the space between the anodes and their neighbours at their edges may be as little as one half of an inch and the distance between the edges of the anodes and the sides of the tank may be less than one inch, while a two inch space may suflice between the bottom edges of the anodes and the bottom of the tank, assuming the anodes to be about three feet square and. say, one and one-quarter inches in thickness. About forty anodes are disposed face to face in the width of the tank so as to be in series with one another. Allowing for four such sets of forty anodes edge to edge this makes a total of 160 anodes in one vat.

Above each set of 40 anodes there is disposed a carrying frame 84 which takes the form of two rolled steel joists 85, 88 one above each row of suspension lugs 83 of the anodes below it. The joists are spaced from one another by transverse members 81 and the rigidity of the frame as a whole is secured by cross bracing 88 between the joists.

To the underside of the lower flange of each joist there are bolted a number of supporting hooks 89 for the suspension lugs of the anode plates. The supporting hooks have flange-shaped bases 90 which are insulated from the joists by interposed insulating material 9| (Figure 11) and are drilled to receive securing bolts 92, likewise insulated from the flanges. The anode plates are, therefore, necessarily hung a distance apart from one another which is determined by the spacing of the hooks along the joist.

It will be observed that the anode plates 82 are cast with the lugs 83 projecting upwardly from them with one face of the lugs lying fiush with one face of the anode plates. The lugs are in thickness a little more than one-quarter of the thickness of the anode plates, so that they are ofiset from the centre line of the thickness of the plate. They are cast with tapered holes I83. the smallest diameter of which is in the face of the lug which lies to the right as viewed in Figure 9. Thus, the upper interior periphery of the tapered holes I83 constitutes a suspension edge for the plates. Owing to the fact that the holes I83 in the suspension lugs of the anode plates are tapered and provide a knife-edged bearing on the side of the lug which lies nearest to the central plane of the anode plate, the plates all hang strictly parallel with'one another, and a; nearly vertical as possible throughout their e. 1 Special means for circulating the electrolyte, which are hereinafter described, sufiice to ensure that no electrolyte is trapped between the plates notwithstanding the small clearances provided, and such electrolyte-circulating means constitute a further feature of the present in- .vention.

At one end of the suspension frame for the anode plates is provided a pair of hooks 93, similarly insulated from the steel joists, to support a single cathode sheet 94. The cathode sheet consists of a thin sheet of electrolytic copperpierced with holes near its upper edge and hooked on to hangers which are attached to the pivoted hooks hereinbefore described. It is necessary to effect an electric connection from the cathode sheet supporting hooks 93 at the end of one cell to the first anode supporting hooks 89 of the next cell and this connection is effected as -follows:-

The supporting hooks at the two ends of the joists have interposed between them and the insulating material against which they are clamped, copper connecting pieces95 (Figure 10) which extend laterally, as viewed in plan (Figure 7), to one side of the joists and are bent round so as to overlie the end wall 80 of the cell close to the place wherethe joists 85, 86 bear upon the same. Here there is provided a copper contact member 96 (Figure 9) the connector element bears.

, Thus it will be seen that if the frame 84, 4mm

' all the anode plates 82 and the cathode sheet 94 hanging thereon is lifted by a crane out of the vat, the electric connection of the copper con-- nector elements 96 with thecontact members secured to the sides of the vat is automatically broken,,and on replacement of the frame, with new anodes the connection is automatically re-'- newed without entailing any labour on the part of the operator.

Tapered dowels I are provided in the walls 00 between the vats, which dowels enter holes drilled in the bottom outer flanges of the; steel joists 85, 86 of the anode supporting-frame and these serve to locate the frames accurately relatively to the vats, which is a necessary feature in view of the small clearances allowed. The frames are provided with suitable lifting eyes 91 at the four corners and the travelling crane IOI (Figure .9) which serves a whole section of vats is provided with a double-drum hoisting mechanism comprising a, frame 90 and four cables 99 having four hooks I02 so spaced as readily to fit the eyes 9'! in the anode supporting frames.

A further feature of the electrolytic cell arrangementis that means are provided to completely cover over the surface of the liquid in the cells and thus to reduce the heat losses which otherwise are heavy due to the rapid evaporation which is facilitated by the gassing and bubbling constantly taking place on the surface of the electrolyte. To this end cover-plates I04 are interposed between the undersldes of the steel.

joists and the insulating material 9| which separatesthem from the anode-supporting hooks. The plates are protected from corrosion by a suitable acid resistant paint or enamel. Their width is sufficient to cover the greater part of the space occupied in the cell by the anodes supported by the frame 84 to' which they belong, but oetween the cover-plate I04 of one framework I upon which and the corresponding cover-plate of the next framework an inspection space is provided so that the operator can examine the condition of the plates and if necessary can use instruments to dislodge trees or undesired growths or bodies from between the plates. The inspection openings are covered by hinged doors I (Figure '6) secured to one edge of the cover-plates I04 and broad enough each to overlap the coverplate of the next frame. The doors I05 are provided with lifting handles I06. A door I01 is provided along one edge of the vat to overlap the first cover-plate I 04.

By the arrangements described each vat .is

provided with four frames 'of anodes which are accurately located in it so that the anode plates register with one-another edge to edge, leaving narrow passages between them, for the electrolyte, which extend clear across the tank from one side to the other. At one side the tank is provided with an electrolyte supply channel I00 which runs along the entire length of the side, and may be extended so as to run along the side of a whole battery of electrolyte vats. One

'edge of this channel is formed as a sill I09 over which the electrolyte can fiow in a gentle uniform stream into the vat. the tank there is an overflow sill IIO set at a slightly lower level and thus the electrolyte traverses the tank from side to side ina direc-- tionparallel with the plane of the anodes and encounters no obstructions in its course..

This method of circulation, in contradistinction to the usual method in which the electrolyte passes through the tank from end to end aro'und At the other side of the edges and beneath-the anodes, oflers decided advantages, inasmuch as it enables the clearance around the edges of the anodes to be reduced to a minimum and therefore increases the current emciency of electrolysis carried out on thevseries system, and at the same time it permits unobstructed flow of the-electrolyte and ensures a complete change of electrolyteacross the whole a face of every anode, thus preventing variable density of the electrolyte and discouraging uneven deposition of metal. Moreover, the speed of flow of the electrolyte is rendered even and as slow as possible for a given rate ofchange of electrolyte so that settlement of impurities is not interfered with.

From the overflow sill of one tank the electrolyte drops into a launder I I I which runs along the whole battery of tanks and from the. launder there area series of transfer pipes H2 which extend to the inlet channel at the side of another battery of tanks, set at a slightly lower level.

It will be seen that all the tanks in a given battery such as I20 (Figure 9) are in series with one another and-that electrolyte flows in parallel streams through all the tables in one battery to corresponding tanks in the next battery such as I22. The various batteries are in parallel with each other. By this means the electrical connections are reduced to a minimun and voltage differences betweenadjacent cells are nowhere high.

the back of the adjacent anode, and only the last anode in a given cell being provided with a cathode plate. 7

I claim:

1. In an electrolytic cell for series electrolysis, the combination of an electro-deposition cell, an anode, intermediate electrodes and a cathode therein, means for suspension of the electrodes in the form of a frame which spans the cell, rests on the walls at the sides'thereof and constitutes a unitary removable structure, and a plurality of rows of supporting hooks hung upon said frame but insulated therefrom and so shaped and spaced as to be capable of engaging portions of the electrodes above the liquid level and holding the electrodes at an appropriate distance apart.

2. An electrolytic cell for series electrolysis as claimed in claim 1, wherein end supporting hooks of each frame are provided with electrical connections to downwardly-facing connector-elements on each frame and contact members are provided secured to the sides of the electrolytic cell for cooperation with the connector-elements. 3. 'In an electrolytic cell as claimed in claim 1 the provision upon the electrode suspension frame, interposed between the electrode supporting hooks and the frame, of a cover plate for the cell an that the cover plate is removable from the cell with the frame.

I. An electrolytic cell as claimed in claim 1 wherein a plurality of electrode-suspension frames areprovided for each cell and are disposed in thebellslde by side so that the electrodes of one frame are adjacent to the electrodes of the next frame, edge to edge.

5. An electrolytic cell as claimed in claim 1 wherein a plurality of electrode-suspension frames are provided for each cell and are disposed in the cell side by side so that the electrodes of one frame are adjacent to the electrodes of the next frame edge to edge, and the frames are provided with cover-plates for the cell and with hinged doors upon the cover-plates extending from the cover-plate of one frame to the cover-plate of the next.

6. An electrolytic cell as claimed in claim 1, wherein the electrode supporting frame takes the form of two parallel beams having horizontal lower flanges and the hooks have flanged bases bolted to but electrically insulated from the underside of said flanges.

7. In an electrolytic cell the combination of a plurality of electrode-supporting frames side by side each of which spans the cell and constitutes a unitary removable structure, a plurality of rows of supporting hooks for electrodes thereon so located that electrodes on one frame will be supported in the cell adjacent to the electrodes of the next frame edge to edge, electrodes upon the hooks comprising on each frame an anode at one end of the frame, a cathode at the other end and intermediate electrodes, means for feeding electrolyte to the cell between the edges of the electrodes at one side of the cell, and means for withdrawing electrolyte from between the edges of the electrodes along the opposed side of the cell.

8. In an electrolytic cell as claimed in claim 7, the provision'of locating abutments upon the sides of the cell and of co-operating abutments upon the electrode-supporting frames for the purpose of locating said frames accurately relatively to the sides of said cell.

ALEXANDER GRANT MCGREGOR.

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