US2122876A - Electrolytic apparatus - Google Patents

Description

y ,193,s. 7 w. H.'-B.TNER 2,122,816

ELECTROLYTIC APPARATUS Filed Feb. 14, 193.5 2 Sheets-Sheet l INVENTOR I William 5.317110 MLS K ATTCiiNEY July 5, 1938. w. H. BITNER ELECTROLYTIC APPARATUS Filed Feb. 14, 1955 2 Sheets-Sheet 2 FIZDOFLIDO TTORNEY INVENTOR William 11 iii/10' Patented July 5, 1938 UNITED STATES PATENT OFFICE ELECTROLYTIC APPARATUS Application February 14, 1935, Serial No. 6,426

4 Claims.

In the electrometallurgy of zinc, it is the general practice to produce a solution of zinc sulphate which is used as the electrolyte for the electrodeposition of the zinc, the zinc sulphate 5 used as the electrolyte being obtained from zinc ores, concentrates or by-products by the suitable leaching thereof, usually'followin'g a roasting operation in which the zinciferous material is converted into a form suitable for eflicient solution in a suitable solvent.

In general, two types of operations are employed for the electrolysis of zinc sulphate. One of these procedures involves the use of a zinc sulphate solution of low acid concentration, wherein 16 low current densities are employed, and the other procedure involves the use of high acid concentrations, with high current densities. Each of these procedures requires its own particular type of electrolytic equipment, and when consideration is 20 given to the erection of a plant for the production of electrolytic zinc, it is customary to choose between one of these two processes and to construct a plant along the existing standardized lines.

It will be recalled that the principal natural sources of zinc are sulphide ores and concentrates, and these materials are attacked only with difliculty by the usual concentrations of sulphuric acid. The materials are therefore roasted to convert the sulphides into oxides, which are soluble in the sulphuric, acid or sulphate solutions employed for the leaching operations. The conditions under which roasting is carried on also control to some extent the solubility of iron, copper,

and cadmium in the leaching solution.

In operating with low acid concentrations, roasting is primarily the most important step in the process, as the possible recovery of zinc is entirely dependent upon the degree of perfection of the roast, when dilute sulphuric acid leaching is employed. In the low acid process, the preparation of relatively pure zinc sulphate solution and leaching with sulphuric acid of from 10 to 15% are essential steps. Not only zinc, but many other 5 metals, if present in the concentrate, are dissolved by sulphuric acid, and most of the metals other than zinc must be removed from solution to insure successful electrolysis. This division of the process is a combination of several steps, leaching to dissolve zinc, separation of solution from insoluble residue, the purification of the solution,

- and the clarification of the solution. This is in actuality the second most important step in the process, as, given perfect roasting,the recovery of zinc is dependent upon proper leaching and filtration, and the electrolysis of zinc sulphate solution is dependent upon proper purification of solution. Other factors influencing the electrolysis are temperature of electrolyte, current density, ratio of zinc to acid in the electrolyte, period of deposition, and purity of electrodes. The electrodes used in accordance with standard practice are lead anodes and aluminum cathodes. The electrolyte, which is neutral or slightly acid, is fed to the cells and for each unit of zinc deposited approximately one and one-half units of acid are regenerated. All zinc in solution is not deposited, usually not more than and the spent electrolyte, containing approximately 25% of the zinc, is returned to the leaching stage of the operation.

Since zinc sulphide is practically insoluble in dilute sulphuric acid at ordinary leaching temperatures, the above-mentioned roasting operation is carried out for conversion of the sulphide into oxide, and sulphate, the former being readily soluble in dilute sulphuric acid, and zinc sulphate is water soluble. During the roasting, however, other products are formed, one of which is zinc ferrite, produced by the combination of zinc oxide and iron oxide and which is insoluble in cold, dilute sulphuric acid, representsthe chief source of loss of zinc in this low acid process, and the formation of this compound can be prevented only by the careful control of roasting conditions; as a matter of fact, no roasting conditions have been thus far devised whereby no ferrite is formed when iron is present in the material to be roasted.

The increasing complexity of operations required in a low acid electrolytic zinc plant shows the importance of the necessity of a pure solution on the one hand, and the difliculty of reconciling this condition with that of a high extraction of zinc.

This fact, together with the inactivity of zinc ferrite towards the solvent used, were factors in investigations leading to commercial development of the electrolysis of high acid zinc sulphate solutions with high current densities. It was found,

in this connection, that if the cathodic current density and the free acid in the electrolyte were simultaneously raised to very high values, especially in the presence of colloids, zinc deposits of good quality were obtained; and certain advantages of such mode of procedure became apparent. For example, the use of return electrolyte carrying, for example, 28% of free acid instead of 10%, would reduce to one-fourth the solution to be neutralized, filtered, etc. for a given output of zinc. Similarly, the use of a current density of, o

for example, amps. per square foot enables a very substantial reduction of the cathode area and cell capacity. Using strong acid solutions, the difficulties encountered'by the presence of zinc ferrite are overcome, this material being soluble in sulphuric acid of relatively high concentration.

However, these requirements are to some extent, at least, antagonistic, for if the residue going out of the plant has been treated with a solvent suificiently active to make a high extraction of the zinc values, other constituents of the ore must have been taken into solution and must be eliminated before the solution can be used for electrolysis; and in this connection, it may be noted that there is probably no other electrolytic process operating on a large scale requiring the same degree of purity of solution as do the electrolytic zinc processes.

Consequently, the most economical procedure for operating an electrolytic zinc plant is dependent upon a balance between extraction of the metals contained in the ore and the cost of purification together with the efficiency of electrolysis. In connection with the present operations, it has been found that the quantity of impurities dissolved is a function of the acid concentration, so' that an ideal acid concentration exists for an ideally roasted ore or mixture of ores possessing definite metallurgical characteristics such for example, as solubility, and chemical and mineralogical composition. Furthermore, this ideal acid concentration will vary not only with the various mixtures of different ores, but with various roasting procedures of the same ore; and the effects of impurities to a large extent are based on cyclic operations which can only be definitely determined by the actual operation of an electrolytic zinc plant.

In general, it has been found that the use of strong acid solutions for leaching provides certain advantages, among which may be mentioned .(1) permitting the treatment of zinc ferrite, which is ordinarily an obstacle in the treatment of ferruginous concentrates with weak acid solutions; (2) increasing the percentage extractions of zinc, cadmium, and copper, and reducing the amount of zinc in the residue; (3) bringing about the solution (and subsequent precipitation) of a large quantity of iron in the leach, which helps purify the solution for arsenic, antimony and germanium; (4) improving filtration and permitting the treatment of ores containing soluble silicates; (5) by reducing the quantity of pulp to be agitated and filtered, and the volume of solution to be stored and purified.

In these processes, manganese is precipitated throughout the electrolyte, this precipitation arising as a result of the formation at the anode of permanganic acid, which reacts with ,manganese sulphate in the solution to precipitate manganese dioxide. Each of these two methods of operation outlined above has its advantages, and each has its own type of equipment and installation; and the choice betweenthe processes hinges on the extraction desired and the metallurgical characteristics of the ores to be treated.

In view of these facts, in the design of a plant for the electrometallurgy of zinc it is most desirable that the cell room equipment be of sufficient flexibility of operation to enable either process to be carried out, selectively, with the same equipment, it beingrecalled that heretofore, as was previously mentioned above, each process utilized its own type of equipment which is not interchangeable.

With the above considerations ,in mind, it will become apparent that a cell room installation which can be arranged to operate so as to produce acid concentrations over a wide range without material alteration of equipment would give a great amount of flexibility, and would enable the economic selective practicing of either process as desired.

The present invention has for one of its 0bjectsthe arrangement of an installation which will possess the above-indicatedflexibility of operation, and which will enable a quick conversion from one type of operation to the other without involving any material amount of labor or cost.

A further object of the invention is to provide an apparatus in which the cells may be expeditiously cleaned.

Other objects of the invention will become apparent as the description proceeds, the features of novelty being set out in the appended claims.

Before proceeding with a detailed description of the improved apparatus of the present invention, it is thought to be desirable to review, for explanatory purposes, a typical cell-room installation embracing the flexibility obtained by the present construction.

In such installation, the cell room consists of 216 cells, which are arranged in two units of 96 cells. Each unit is. divided'into four banks of 24 cells each, an extra bank of 24 cells being provided so that one bank may be cut out of the circuit at all times for cleaning and repairing. The cells in each unit are connected in series to a 10,000 ampere D. C. power source, with provision provided for cutting out one bank and inserting the spare bank. The load on each circuit is relatively constant at 3,300 k. w. h. D. C. except for the short period when the cells would be cut in or out of the circuit. Every two days a bank is cut out and the previously cleaned one is inserted. There being nine banks, a cycle of 18 days is maintained, i. e., each cell is cleaned once in 18 days.

Above each row or bank of cells there is provided a feed launder of suitable dimensions, which delivers solution to one end of the cells through suitable downpipes of hard rubber, or

other material unaffected by the electrolyte. The

solution overflows the opposite end of the cells through similar pipes to a sump launder located directly beneath. The intake of the overflow pipe is preferably bailied so as to retain the froth which forms on the top of the cells, which re tention is desirable, as the froth holds down acid spray. The sumps for the cells are made of suflicient cross-section to allow for settling of manganese dioxide. The sumps overflow into launders which discharge over a removable weir into a connecting sump. Located alongside the center of each connecting sump is a pump feed box into which solution flows over a weir gate.

For reference, the cell banks are numbered from A to J across the width of the cell room, the extra bank being cut out for maintenance. A-B, C-D, F-G, and HJ cell sumps are connected in groups of two tofour circulating pumps, this giving four individual electrolyte circulating systems. By inserting two simple lead-covered wood gates, one in a bank feed launder and the other in the corresponding cell sump overflow launder, any bank of cells may be'cut out for cleaning, the sump may be inspected, and the manganese sludge flushed to a slurry tank and pumped to I Fig. 1.

ing.

. vation' above that of the cell banks.

Fig. 3 is an elevation of the left hand end of the installation as viewed in Fig. l, the view being taken on the line 33 of Fig. 1, looking in the direction of the arrows.

Fig. 4 is a vertical section taken on the line 4-4 of Fig. 1, the view showing in detail the construction and mounting-of the control gates or weirs.

Referring more particularly to the drawings, it will be seen that the illustrated installation comprises a plurality of banks of cells, indicated, respectively, as A, B, C, D, E, F, G, Hand J. Each bank of cells is shown as comprising, four blocks of six cells each, the cells of the left hand pair of blocks being spaced from the right hand pair, the arrangement of the cells being as stated above, i. e., the'cells are arranged, for example. in two units of 96 cells, each unit being divided into four banks of 24 cells each, an extra bank of 24 cells being provided so that one bank may be cut out of .he circuit at all times for cleaning and repair- I'hecells themselves are designated by the reference characters l A, IB, IC, etc., corresponding to the respective cell banks.

Beneath each bank of cells A, B, C, etc., there is a sump, the sumps being designated respectively as 3A, 3B, 30, etc., corresponding to the cell bank beneath which the respective sumps are located. Each of these sumps is identical in construction and receives electrolyte overflowing from or launder I3 extending across the entire cell installation, from which trough or launder I3 the electrolyte is returned to the respective cell banks by means of pumps ISA, I53, I50, ISD and 'I5E,

there being in general one pump for each pair of cell banks, these pumps being independently operable. Each of the pumps operates through p pes I I and I9, which are connected, respectively, to the intake and outlet of the pumps, the pumps acting to withdraw electrolyte from the launder l3 and to return the electrolyte to a header trough or launder 2|, which also extends all the way across the cells and which is mounted at an ele- In order to allow settling of any entrained solids from the electrolyte, there is provided a plurality'of feed boxes, designated as 23A, 23B, 23C, 23D for receiving the immediate discharge from the pumps, the electrolyte overflowing from these feed boxes into the feed launder 2| through overflow passag'es 25. From the header launder, electrolyte passes to the respective cell banks by way of the feed troughs or launders 21A, 21B, 210, etc., there being one of these launders extending over .the entire length of each cell bank, electrolyte being supplied to the individual cells by the feed pipes .29 which discharge from the respective launders,

there being one of these feed. pipes provided for .each cell. Flow of electrolyte from the header extra cell bank, previously referred to herein, enabling one bank of cells tobe cut out of the circuit at all times for cleaning and repairing.

The degree of acidity of the electrolyte being circulated through the cells is controlled by-the circulation of the electrolyte through the return launder I3 and the header launder 2|. For controlling this circulation, a pump I5A, etc., and a feed box 23A, etc., are provided for each pair of cell banks as aforesaid, with the exception that the middle cell bank E is supplied with electrolyte delivered from the feed box 230, which receives electrolyte from a pair of pumps I50 and I 5D, which deliver electrolyte through branch pipes ISA and I9B which lead from the pumps I50 and I5D to the feed pipe I9 for this particular feed box 230.

For the further control of the electrolyte, both the return launder I3 and header launder 2| are provided with a plurality of overflow gates or weirs, of identical construction, those in the return launder being indicated on Fig. ,1 as 33A, 33B, 33C and 33D, while those in the header launder 2| are designated as 34A, 34B, 34C and 34D. These gates are made of lead-coated wood, hard rubber or any other material which resists the corrosive action of the electrolyte, and their 2 construction and mounting is illustrated in Fig.

launders.

Referring to Fig. 4, it will be seen that the launder receiving the gates or weirs, for example the return launder I3, is provided at selected points along its length with suitable co-operating frames 35, 31, placed within the launder and defining between them'a slot 36, of suitable width,

for example, 2 inches, into which slot is received one of the gates or weirs 33, which is made up of a plurality of separate sections 39, M, 43, which are separable, and separately removable, so that the amount of overflow of electrolyte over the gate or weir is controlled by the number of these sections which are inserted at a given time. The function of these gates will become apparent as the description proceeds.

Inoperating the system of the present invention, if it is desirable to increase the acid concentration of the electrolyte, and consequently, the current density, transversely across the cell room, pregnant electrolyte is added to the system at any desired point, for example at either end of the return launder I3, as indicated for instance by arrow 45, and spent electrolyte is withdrawn from the other end of the return launder, as indicated by arrow 41. The same efiect, of course, canbe accomplishedby adding the pregnant solution to one end of the header launder 2| and the spent electrolyte is withdrawn from the opposite end of the header launder; or it may be removed anywhere in the corresponding pumping system, as for example, at I5E.

and mounting of each gate is identical in both header launder 2 I Now, for simplicity of illustration, suppose cell bank Ehas been cut out of the circuit for maintenance purposes. In such instance the plug valve 3IE in the header launder I3 is closed, and gates 33B and 33C in the return launder are inserted.

The pumps 15A, I5B, I5C, l5D and I5E collect the solution from the return launder l3 and deliver the solution through a corresponding feed box to each pumps corresponding section of the This header launder, like the return launder, comprises the usual U-type launder which is divided, as indicated above, into sections by the gates 34A, 34B, 34C and 34D. Actually, since the construction of these gates consists only of two-inch boards, which may be lead covered, such gates are placed between each of the feed launders 21A, etc. For the purpose of the present illustration, cell bank E being cut out, the boards forming gate 340 are removed from the header launder 2i and the pump I5C is out of service. Consequently, the header launder 2| is divided into four sections, separated by gates 34A, 34B and 34D. Correspondingly, the return launder is divided into three sections separated by gates 33A, 33B and 33D, gate 330 in this illustration being removed. In this connection, it may be noted that a gate of similar construction to the above may be inserted in each sumpoverflow H for use when the corresponding cell bank is removed from service. One of these gates is illustrated at [2.

In the particular illustration being considered, the gate I2 is inserted in the sump overflow of cell-bank E. It is to be noted, although this gate I is of the same construction as the other gates, that when used to cut a sump out of service, enough boards are inserted to fill the height of the overflow, while the gates in the header launder 2|" and the return launder l3 do not competely obstruct the passage of solution, allowing it to overflow as, over a weir.

The gates when inserted as explainedabove, allow the overflow of solution across the cells in the direction away from the point of admission of the pregnant solution. The pump |5A pumps from the portion of the return launder l3 corresponding to the cell banks A and B, a volume of solution approximately ten times the volume oi. pregnant solution admitted at the arrow 45 into the return launder l3.

Metal is electrodeposited in the cells, which increases the acid concentration of the electrolyte. In these banks A and B, current density is relatively lower than the current density maintained in the cell banks H and J. A volume of solution overflows the gate 34A, which volume corresponds to the volume of solution admitted to the system at 45. The pump I5B circulates electrolyte from its section of thereturn launder l3 to its corresponding section in the header launder 2| which delivers solution to the feed launders 21C and 21D of the cell-banks C and D.

Corresponding to the volume of solution overflowing gate 34A, solution overflows gate 343, which allows still more highly acid solution to enter the third section of the circulating system.

similar to pumps I5A and I5B, pump l5D circulates solution from its corresponding section of the return launder l3 to its corresponding section of the header launder 2|, which supplies solution to cell banks F and G. Likewise pump I5E circulates solution from its corresponding section of the return launder to its corresponding section of the feed launder, which feeds cell banks H and J. The quantity of solution overflowing gate MD is withdrawn from the system as indicated by the arrow 41.

By progressively decreasing the number of cathodes which decreases the cathode area in cell-bank pairs A-B, C-D, F--G, and H-J, the cathode current density is progressively increased so that at the high acid section of the installation, good current eificiencies are maintalned; also, at the low acid section of the installation where the conductivity of the electrolyte is relatively lower, eificient precipitation of the metal is also accomplished. Furthermore, the use of relatively high acid concentrations throughout the entire cell room, which increases maintenance costs, is avoided, being limited to a definite area of the installation. At the same time high acid concentrations suitable for leaching purposes are produced.

In a similar manner, any one of the cell-banks may be removed from service by appropriate manipulation or positioning of the various gates and valves.

It will be seen from the above considerations that the apparatus of the present invention is capable of producing high acid concentrations in the sp'entelectrolyte while electrolyzirg the major portion of the electrolyte at low acid concentrations; also it will be understood that the system of the present invention is not limited in any sense to only one spare cell bank, as any number thereof may be provided as may be thought desirable for any given installation, and any one or more of the cell banks can be cut out of service for maintenance purposes, the spare bank or banks enabling normal operations to continue during the lapse of time that the said banks are out of service. The electrical connections to the cells have not been shown, as various ways of connecting the cells will be obvious to one skilled in this art, whereby selected banks can be readily cut out of the circui; and the spare banks cut in; and the exact nature of the electrical connections is largely dependent upon the size of a specific installation and the disposition of the cells in the cell room of the plant.

It may be pointed out at this point that another advantage of this arrangement is accomplishable. That is, if it is desired to circulate the electrolyte as a whole, as is common practice in the high acid, high current density electrolytic zinc process, this can be accomplished by simply removing-the gates from the header and return launder. Pregnant solution is then admitted in batches into the system, the acid concontration is allowed to buildup to a predetermined point, whence a bath of the circulating electrolyte is withdrawn and replaced by the pregnant solution.

By reference to the drawings, it will be seen that extending transversely of the installation and positioned beneath the sumps 3A, 3B, etc., is a sludge tank 5| which is adapted to receive manganese sludge collected in the sumps from the cells. Each sump is provided with a valve 53, in a discharge pipe 54, which discharges into a common flush launder 55, which in turn discharges into the sludge tank 5|. From the tank 5| the collected sludge is pumped, by pump 56, as a slurry and isreturned to the leach department of the plant. The pump 55' withdraws the sludge through pipe 51, which is provided with a plurality of branch pipes 58, 59, 60, which being provided with control valves 58a, 59a, Ella, respectively. The pump 56 discharges through pipe BI to the leach department of the plant.

Although the installation herein illustrated'and described has been set forth with particular refcrence to the electrodepositlon of zinc and the handling of zinc electrolytes, for example, zinc sulphate solution, the system is adapted for handling materials other than zinc electrolytes, for instance for the electrodepositlon of copper or cadmium.

It will be apparent of course that the invention is not limited to the precise details herein illustrated and described, but that variations and departures from the specifically illustrated form the banks for supplying electrolyte thereto, a second common launder for the banks for receiving electrolyzed electrolyte therefrom, a sump beneath each cell bank for receiving electrolyte discharged from the cells, overflow launders connecting the sumps with the return launder, feed launders connecting the header launder to the cell banks for delivering electrolyte to the cell banks from the header launder, adjustable means in the launders for controlling flow of electrolyte through the launders and dividing the launders into sections corresponding to predetermined -cell banks, and pumps arranged to'pumpelectrolyte from the return launder to theheader. laurider, each of the said pumps operating to deliver electrolyte from one section of the return launder to a corresponding section of the header launder.

2. Electrolytic apparatus comprising a plurality of cell banks, a common header launder for the banks for supplying electrolyte thereto, a second common launder for collecting electrolyzed electrolyte from the cell banks, a sump beneath each cell bank for receiving electrolyte discharged from the cells, overflow launders connecting the sumps with the return launder, feed launders connecting the header launder to the cell banks for delivering electrolyte to the cell banks from the header launder, adjustable means in the launders for controlling fiow of electrolyte through the launders and dividing the laundersinto sections corresponding to predetermined cell banks, pumps arranged to pump electrolyte from the return launder to the header launder, and valve means associated with the header launder for cutting off circulation of electrolyte to any of the cell banks as selected.

3. Electrolytic apparatus comprising a plurality of cell banks, a common header launder for the banks for supplying electrolyte thereto, a second common launder .for collecting electrolyzed electrolyte from the cell banks, a sump beneath each cell bank for receiving electrolyte discharged from the cells, overflow launders conbanks, pumps arranged to pump electrolyte from thereturn launder to the header launder, valve means associated with the header launder for cutting off circulation of electrolyte to any of the cell banks as selected, and feed'boxes intermediate the pumps and header launder for permitting sediment in the electrolyte to settle before the electrolyte passes into the header launder from the pumps.

4. A process for the electrodepositlon of ,zinc which comprises providing electrolyte comprising zincsulphatein acid solution in a plurality of cell banks, each celLbank comprising a plurality of individual cells, maintaining electrolyte at different acid concentrations in different cell banks, controlling the flow of electrolyte in such manner that electrolyte of the same acid concentration is fed from a common source to each of the individual cells in any specified cell bank, feeding a low acid solution pregnant with zinc sulphate into the circulatory system of the cell bank operating at the lowest acid concentration, withdrawing high acid, spent electrolyte from the circulatory system of the cell bank operating at the highest acid concentration, and permitting flow of electrolyte from circulatory systems of lower acid concentration to circulatory systems of higher acid concentration in amount approximately equal to the low acid solution pregnant with zinc sulphate introduced.

WILLIAM H. BI'I'NER.

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