DK163310B - ELECTRODS, ELECTROCHEMICAL AND BIPOLAR CELLS CONTAINING SUCH ELECTRODS AND PROCEDURES FOR THE PRODUCTION OF SUCH ELECTRODS - Google Patents

Abstract

The invention includes electrodes having a plurality of fibers wherein an essentially continuous metallic coating of high bond strength extends over at least a portion of each fiber, and wherein the fibers provide a large surface area. The electrodes of the invention have an efficient electrical connection at their terminals comprising fiber/metal matrices which provide the desired connections to the terminals without damage to the fibers. The fiber metal matrices also provide excellent electrical contact between all of the fibers, and inhibit wicking of the electrolyte or process stream into the electrical connections. Where the fibers are coated along a substantial portion of their length, they also have a high electrical conductivity. The invention further includes electro-chemical cells, and processes for forming and utilizing the electrodes and cells.

Description

in

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The present invention relates to electrodes, electrochemical and bipolar cells containing such electrodes and a method for producing such electrodes.

The efficiency of electrochemical processes, such as electrolysis, electroplating, electro-extraction, electro-organic synthesis and waste recovery, depends to a large extent on the surface area of the electrode. Electrodes have been constructed with ribs or folds to increase the surface area. Sandblasting has also been used to round up the electrode surface, thereby providing a larger surface area. These known methods have been found to have limited efficiency in increasing the surface area.

Recently, carbon fibers for electrodes providing 15 large surface areas have been described in U.S. Patent Nos. 4,046,663, 4,108,754 and 4,108,757. The electrodes comprise a plurality of carbon fibers generally arranged parallel to each other and attached at one end to an electrical connection. Although these electrodes may have large surface areas, they provide relatively poor electrical connections. In particular, a large number of carbon fibers are always broken when a cable of such fibers is attached to an electrical connection. This breakage of fibers adversely affects the electrical efficiency of the cable. In addition, the mechanical connection of carbon fibers causes an undesirably high electrical resistance to the connection.

Consequently, the theoretical efficiencies of the electrodes cannot be achieved due to the mechanically destructive and ineffective electrical connections.

The electrodes disclosed in U.S. Pat.

4,046,663, 4,046,664, 4,108,754 and 4,108,757 also act as a wick that sucks electrolyte up into the region of the terminal block. As the electrolyte evaporates, a residual salt remains, affecting the electrical connection. The salt-35 bearings thermally shield the pole clamp, causing heat build-up, increased resistance, and possibly polarity.

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2 clamp failure due to conduction. Although the wall effect and fiber damage could be controlled, there would be little electrical connection to the fibers in the center of the bundle.

Several attempts have been made to place metallic coatings on the carbon fibers so that cables of the plated carbon fibers can be used more effectively as electrodes in various electrochemical processes. In most cases, the plating applied to these carbon fibers has been discontinuous, brittle and expensive to apply. For example, U.S. Patent No. 4,132,828 describes vacuum deposition of nickel on carbon fibers. However, the coating described in this patent is not in continuous contact with the carbon fibers and will easily crack and fall off the fibers if twisted.

15 So-called nickel baths have also been used for plating carbon fibers. However, this plating process is slow, costly to implement, and in turn causes low discontinuous coatings.

In summary, the prior art electrodes 20 have consisted of carbon fibers or metal coated fibers with poor quality metal coatings. These metal coatings have typically been thick and have a uniform thickness. Furthermore, they have not adhered well to the fiber core. The carbon fibers have been subject to breakage during the installation of the terminal connection.

Furthermore, due to the relatively low conductivity of the carbon fibers, the fibers located within the fiber bundle and therefore not in direct contact with the terminal connection did not participate equally in the electrode function.

The use of metal-coated fibers of the prior art has also not alleviated the disadvantages associated with the use of carbon fibers.

Since the metal coatings have not been uniform, they have typically been applied as thick coatings. This has reduced the surface area of the electrode, since fewer 35 fibers can be used per day. elektrodevolumenenhed. The adhesion of the coatings has also been unsatisfactory, and

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3, overcoating / fiber separation, especially during the attachment of the terminal connection. This has resulted in a pole clamp in contact with non-coated carbon fibers and thus again the problems associated with the use of non-coated fibers.

It is the object of the invention to overcome said disadvantages of the prior art.

The invention thus relates to an electrode comprising a plurality of adjacent continuous fibers, each fiber having a thin, firmly adhered metal coating thereon, which electrode is characterized in that ends of the metal-coated fibers have a connection piece and that a electrically conductive metal extends between the ends of the fibers and connects them to each other and to the connector to provide a coherent metal matrix providing an effective electrical connection between the metal-coated fibers and the connector.

The invention also relates to an electrochemical cell comprising at least one pair of electrodes, the electrodes in each pair having opposite electrical charges, and at least one of the electrodes in each pair comprising a plurality of adjacent continuous fibers, each fiber having a thin, solid adhesive metal coating thereon, said electrochemical cell being characterized in that the ends of the fibers of said at least one electrode containing fibers are close to each other and said electrode comprises a metal coating of each fiber of said fibers. said ends extending along each fiber, a connection piece at said metal-coated ends of the fibers, and an electrically conductive metal extending between the metal coatings at the ends of the fibers and connecting them to each other and to said connection piece for providing of a coherent metal matrix providing an efficient electrical connection between the metal-coated fibers and the connecting piece.

The invention further relates to a bipolar electrochemical

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A cell, said bipolar electrochemical cell, comprising a two-chamber container for accommodating various electrolyte solutions, one chamber containing an active anode and a passive cathode, and the other 5 chamber containing an active cathode and a passive anode, wherein the active electrodes are connected to a power source, and the passive electrodes are electrically connected to each other and wherein the passive anode and passive cathode consist of fiber-containing electrodes according to claim 1, wherein the first electrolyte solution will be reduced and the second electrolyte solution will be oxidized when the first and second electrolyte solution are placed in the first and second chambers.

Finally, the invention also relates to a method for producing a fibrous electrode according to claim 1, characterized in that by providing a continuous length of a plurality of core fibers, plating at least one end of each core fiber with a substantially uniform, metal adherent coating, places an electrical connector in contact with the metal-coated ends of the core fibers, and joins the metal-coated ends and the electrical connector with an electrically conductive metal extending between the metal-coated fiber ends to form a coherent fiber / metal matrix that provides an efficient electrical connection.

The electrode of the present invention contains a plurality of fibers, each fiber having a metallic coating which adheres thereto. The coating is preferably continuous and is bonded so well that if the metal-coated fiber is bent, the coating may break but will not peel off. The fibers for the electrodes of the invention 35 may be semi-metallic, such as carbon and silicon carbide fibers, or non-conductive, such as polyamide, polyester and / or aramid fibers.

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When the fibers are semi-metallic, such as carbon or silicon carbide, the metal coating can be electrolytically applied by the method described in DK Patent Application No. 1206/83 (corresponding to DK Patent No. 158,159). The fiber coating described in this application is continuous and has improved bonding and flexibility characteristics. As a result, it is possible to mold fibers coated by the method of this application into shapes useful for electrodes which were considered unattainable with known metal-coated carbon or silicon carbide fibers.

In a preferred method of making the metal-coated carbon or silicon carbide fibers, the following steps will be used: a) providing a continuous length of a plurality of the electrically conductive core fibers, b) continuously immersing at least a portion of the the length of said fibers in a solution capable of electrolytically depositing at least one metal, and c) providing an amount of electricity while applying an external voltage between the fibers and an electrode immersed in the solution, which voltage is above the one normally required to induce deposition of metal, thereby reducing (i) the metal on the surface of the fibers, (ii) the metal forming germs in a substantially uniform manner on the surface of the fibers, and (iii) providing the substantially uniform, solid adhesive layer of metal on the core.

The fibers formed by the method described will have a bond strength between metal and core sufficient to allow the coating to bend but not peel when bending the fiber. Furthermore, the bond strength of preferred fibers is more than sufficient for knots to be bonded to the fibers without substantial, i.e. more than 5% by volume separation and peeling of the coating.

* When the fibers are non-conductive, such as polyamide, polyester and / or aramides, they are first made conductive by providing an extremely thin metallic intermediate layer such as

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6 described in DK patent application 3070/84 and then electrolytically coated with a metallic layer as described in DK patent application 1206/83.

Whether the core fibers are semi-metallic or non-metallic, the electrode of the invention is formed from fibers which are metal coated near the electrode's connection to a power source. The metal coating on the fibers allows the connection to the power source to be formed by such methods as soldering, so as to form a continuous fiber / metal matrix adjacent to the electrical connection, avoiding mechanical connections such as shrinkage which damages the fibers and reduces the efficiency of the electrode.

In addition, with the brazed connection and the consequent continuous fiber / metal matrix, the wall effect which has been common with known mechanical compounds and which rapidly deteriorates the quality of the electrical connection is avoided. In addition, the brazed compound and the resulting continuous fiber / metal matrix encapsulate all the fibers in metal, resulting in a low contact resistance, even to the center of a mass of 100,000 fibers.

The present electrode can be formed by plating only the portion of a fiber rope which is near the electrical connection. The electrode may also be formed by a fiber rope which is completely metal coated and which is then freed of part of the metal coating prior to use as an electrode. In most electrochemical applications, the electrode having only plating near the electrical connection will preferably act as an anode.

The present invention further comprises an arrangement of fibers, each fiber of the arrangement being continuously coated with metal throughout its length. These coated fibers provide a large surface with high electrical conductivity. They are electrically connected to a power source by e.g. soldering to form a contiguous carbon / metal matrix near the electrical connection. As explained above, this continuous

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7 honest matrix damage to the fibers, and wall action is substantially prevented. The electrode formed by plating the entire length of each fiber is typically used as a cathode.

5 Due to the improved coating of the fibers, as described above and in DK patent application no.

1206/83 and 3070/84, it is possible to mold the present fiber electrode into various useful forms which have not been available so far. Specifically, a metal-coated fiber rope can be wound around a flow support with little or no possibility of the metal coating breaking away from the fibers. Other plated electrode shapes include woven mats that can be supported in planar form or can be wrapped around a flow support, and knitted tubular designs that can be placed around a cylindrical flow support.

Due to the flexibility of the present electrodes, several unique cell structures and processes are made possible. For example, anodes and cathodes mounted about flow supports may be alternately placed in one or more cells. The electrolyte can then be passed through the cells in such a way as to ensure maximum contact with the carbon fibers. In one embodiment, each cell may contain an anode on a flow support and a cathode on a flow support. Each such cell can be separated by a non-conductive barrier, each barrier having electrolyte access paths in the form of one or more holes. In order to achieve the desired flow pattern, the access paths in the barriers will be located alternately in a corner at the bottom or in an opposite corner at the top. Holes so positioned in the barriers,. will help achieve maximum contact between the electrolyte and the electrodes.

In another embodiment of the construction described above, each cell may contain several fibrous anodes and cathodes wrapped around flow substrates.

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8

Several of such multi-electrode cells can be arranged in series with the connections between the cells designed to ensure maximum contact between the electrolyte and the electrodes. As noted above, this electrolyte flow pattern can be obtained by alternately placing the holes in the barriers between the cells in the upper and lower corners of the barriers.

Other embodiments of electrochemical cells are possible. For example, porous metal sheets can be used as 10 cathodes and arranged alternately with the anodes described above. In yet another embodiment, a discretionary cell may be provided using a small anode, such as a platinum wire, together with a large-area metal-plated fiber cathode for depositing certain metals on the cathode while leaving other metals in solution. To ensure optimum electrolyte contact with the electrodes in the discretionary cell described above, the metal-plated fiber cathode can be formed into a cylindrical shape with the cylinder located concentrically around the anode. The cylindrical fiber cathode can be formed either by helical winding of a fiber rope around a porous cylindrical shape or by knitting a tubular structure of the metal-plated fiber. A bipolar cell of the invention which can be used for oxidation / reduction reactions comprises alternately placing 25 anodes and cathodes in a cell containing both solutions, wherein one of the interconnected electrodes of the present invention is disposed in one solution. while the second cell is placed in the second solution.

In each of the embodiments described, the electrodes of the invention provide large surface areas, effective electrical connections and high bond strength between the core fibers and the metal coatings thereon.

In the following, the invention is described in detail with reference to the accompanying drawing which illustrates illustrative embodiments of the invention.

island

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FIG. 1 is a partial cross-sectional elevational view of an electrode of the present invention containing a rope of partially plated fibers and a coherent fiber / metal matrix at the pole terminal; FIG. 1a shows an enlarged cross-section of the electrode 5 shown in FIG. 1 taken along the line 1a-1a; FIG. 1b shows an enlarged cross section of the electrode shown in FIG. 1 taken along line lb-lb; FIG. 1c shows an enlarged cross-section of the electrode 1Q shown in FIG. 1 taken along line lc-lc; FIG. 1d shows an enlarged cross-section of the electrode shown in FIG. 1 taken along the line ld-ld; FIG. 2 shows an enlarged vertical view, partly in cross-section, of a single fiber in the electrode shown in FIG. 1, FIG. 3 shows a vertical view, partly in cross section, 10 of the electrode shown in FIG. 1 used in conjunction with a protective tube; FIG. 4 shows a vertical view, partly in cross-section, of another electrode according to the invention containing a rope of completely plated fibers; FIG. 4a shows an enlarged cross-section of the electrode shown in FIG. 4 taken along the line 4a-4a; FIG. 4b shows an enlarged cross-section of the electrode shown in FIG. 4 taken along line 4b-4b; FIG. 4c shows an enlarged cross-section of the electrode shown in FIG. 4 taken along line 4c-4c; FIG. 5 shows an enlarged vertical view, partly in cross-section, of a single fiber in the electrode shown in FIG. 4, FIG. 6 shows a vertical view, partly in cross-section, of the electrode shown in FIG. 4 used in conjunction with a protective tube; FIG. 7 is a "broken up" perspective view of another embodiment of the electrode of the present invention in which the rope of fibers is wound around a flow support;

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10 o FIG. 8 is a vertical sectional view of the electrode shown in FIG. 7, FIG. 9 shows a side view, partly in cross-section, of the electrode shown in FIG. 7, 5 FIG. 10 is a side view, partly in cross-section, of an electrochemical cell according to the invention containing the electrode shown in FIG. 7-9, FIG. 11 is a perspective view of the part panels used in the electrochemical cell shown in FIG. 10, 10 FIG. 12 is a perspective view of the flow distance portion located between the electrodes shown in FIG. 10, FIG. Figure 13 is a schematic diagram of an electrochemical system containing an electrochemical cell according to the invention; 14 is a horizontal view of the electrochemical cell shown in FIG. 13, FIG. 15 is a vertical cross section of the electrochemical cell shown in FIG. 14 taken along line 15-15, FIG. 16 shows a cross section of the electrochemical cell shown in FIG. 14 taken along line 16-16; FIG. Figure 17 is a vertical sectional view, partly in cross-section, of a discretionary electrochemical cell of the invention; 18 is a perspective view of the cell 25 shown in FIG. 17, FIG. 19 is a vertical sectional view, partly in cross-section, of an electrochemical cell according to the invention containing a porous plate electrode; FIG. 20 is a perspective view of the porous plate electrode of the cell shown in FIG. 19, FIG. Fig. 21 is a vertical sectional view, partly in cross-section, of a bipolar electrochemical cell of the invention; 22 shows a perspective view of the partition and the active electrodes in the cell shown in FIG. 21st

The electrode of the present invention is generally designated by the number 10 in FIG. 1, la, lb, lc, ld

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11 and 2. The electrode 10 is formed from a plurality of fibers 12 each containing a central fiber 13, preferably carbon, e.g. 7-13 µm thick, and a thin concentric continuous layer 14 of nickel or other plating metal, e.g. ca. 0, -5 µm thick. The plated fibers 12 are formed into a rope 15 which is a generally parallel arrangement of several plated fibers, e.g. ca. 40,000-50,000 fibers, the rope typically having a diameter of approx. 3.2 mm. A rope 15 of the desired length is located in an electrical connection piece 16 such that the clamping arms 17 of the electrical connection piece 16 grip about one end of the rope 15. Specifically, the arms 17 of the electrical connection piece 16 grip the rope 15. with sufficient force for the rope 15 to be loosely retained, yet 15 ensure that the plated fibers 12 are not damaged. This force exerted by the clamping arms 17 of the rope 15 is substantially less than the force that would normally be used if this mechanical connection were essential to the conduction of electricity.

When the rope 15 has been retained by the electrical connector 16, the combination of the connector 16 and the rope 15 is immersed in a molten metal bath such as solder with approx. 60% tin and approx. 40% remain. The solder 18 is absorbed in the region between the electrical connector 16 and the plated fibers 12 and between the fibers to form what is essentially a carbon / metal matrix at the end of the electrode 10, thereby defining an effective electrically conductive connection. between the rope 15 and the connecting piece 16. The desired aspiration between the plated fibers 12 can take place in a few seconds, typically approx. 10 seconds.

The metal plating 14 on the portion of each fiber 13 that is not near the connector 16 is then removed, e.g. by soaking in a nitric acid bath. More specifically, the plating 14 is removed leaving a short 35 piece of plating 14 extending away from the solder 18. Preferably, the plating 14 extends between 0

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12 1.3 and 5.1 cm away from the solder 18, as shown by the distance x in FIG. 2. Thus, as illustrated in FIG. 1a, the upper part of the electrode 10 defines a continuous carbon / metal matrix comprising the carbon fibers 12, the plating 5, the solder 18 and the arms 17 of the connector 16. A little from the connector 16, as shown in FIG. 1b, the continuous carbon / metal matrix comprises the carbon fibers 13, the plating 14 and the solder 18. Further away from the connector 16, as shown in FIG. 1c, the electrode 10 comprises the carbon fibers 13 and the plating 14, but not solder 18. This solderless plating provides a stepped current resistance which is smoothed from the terminal block 16 to the free fiber 13. In this way, a current gradient is provided which prevents the formation of a solder. area with a strong current that would be attacked more rapidly by any electrolyte in contact therewith. Finally, as shown in FIG.

Id, the fibers 13 are loosely arranged in the rope 15 in the remainder of the electrode without plating, and the electrolyte, generally designated by arrows 19, can flow freely between the fibers 13 20 and obtain maximum contact therewith. The carbon fibers are graphite and generally free of amorphous carbon.

In FIG. 3, the electrode 10 is used in conjunction with a non-conductive protective tube 20 formed of plastic or other inert material. The tube 20 loosely fits over the electrode 10 and generally extends from the connector 16 to a point on the electrode 10 which will be located several inches below the surface of the electrolyte with which the electrode 10 is used. The protective tube 20 reflects the fact that the most aggressive harmful electrolyte reactions take place in the region immediately below the surface of the electrolyte. Thus, the protective tube 20 minimizes the deleterious effects in this critical area of the electrolyte. To further minimize the transition effects between the electrolyte and electrode 10, the protective tube 20 35 is provided with a plurality of small holes 21 at the end of the protective tube 20 which is farthest from the electric 0.

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13 connecting piece 16 so as to effectively create a transition zone with a current gradient that minimizes an area of excessive current and electrolyte attack.

Another electrode 22 of the invention is illustrated in FIG. 4, 4a, 4b, 4c and 5. The electrode 22 resembles in its construction the electrode 10 described above, except that the electrode 22 comprises plating 14 which is located continuously throughout the length of each fiber 13.

Thus, as illustrated in FIG. 4a, the portion of the electrode 22 near the connector 16 defines a continuous carbon / metal matrix comprising carbon fibers 13, metal plating 14, solder 18 and arms 17 of the connector 16. At a location on the electrode 22 at a short distance from the connector. 16, the contiguous 15 carbon / metal matrix comprises carbon fibers 13, metal plating 14 and solder 18 as shown in FIG. 4b. Further away from the connector 16 and extending to the opposite end of the electrode 22, the fibers 13 each have metal plating 14, but, as shown by arrows 19, the electrolyte can flow freely 20 through the electrode 22. These metal plated fibers have a high electrical conductivity.

FIG. 6 illustrates the electrode 22 used in conjunction with the protective tube 20 which, as stated above, minimizes the detrimental effects of the electrolyte at the boundary between the electrolyte and the environment. In most electrochemical applications, the electrodes shown in FIG. 4-6 as cathodes.

FIG. 7-9 show a generally planar electrode 30 embraced by the present invention. The electrode 30 is formed by an elongated rope 32 wrapped around a generally rectangular inert flow support 34 and held in place on the support 34 by an inert screen 36. The rope 32 can either be freed for most of the plating as shown in FIG. . 1-3 or be fully plated as shown in FIG. 4-6. All electrodes 30, whether used as anodes or cathodes, comprise a metal 0

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14 plated region 38. This metal plated region 38 allows the application of solder 40 to attach the electrical connector 42 to the rope 32 and thus to form a continuous carbon / metal matrix. As explained above, the metal-plated region 38 preferably extends beyond the boundaries of the brazed region 40, and on certain electrodes, it will extend throughout the length of the rope 32. The electrode 30 further comprises a protective tube 44 which typically extends from a location above the interface between the air and the electrolyte to a location preferably 7.5-10 cm down in the electrolyte. Although the protective tube 44 may end over the flow support 34, it preferably extends into an area up to the flow support 34 to facilitate the mounting of the rope 32 to the support 34. As illustrated most clearly in FIG. 7, the flow support 34 has several openings 48 and may contain an elongate cut portion or groove 46 in which the tube 44 is located. The rope 32 can then be threaded through an opening in the flow support 34 and wound around the support 34 in a continuous manner. Although in FIG. 8 shows a single rope 32 terminated at each end, several ropes and terminations may be used in the practice of the invention. The rope 32 is held in place on the support 34 and is protected from damage to the screen 36, which is folded around the combination of flow support 34 and rope 32. The screen 36, which may be made of polyamide or fiberglass, also prevents loose fibers from one electrode in contact with another electrode.

When the electrode 30 is used as a cathode, the entire rope 32 is typically maintained in its plated state. With the preferred plating, as described above, the plating will remain intact on the fibers of the rope 32 despite the many sharp bends formed in the rope 32 during the formation of the electrode 30.

0

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When the electrode 30 is used as an anode, the plating is typically removed from the rope 32 throughout its length except for the areas near the solder connection 40 between the rope 32 and the electrical connector 42. This removal of plating from the rope 32 can be performed either before or after the mounting of the rope 32. the rope 32 on the flow support 34.

In the illustrative embodiments shown in FIG. 1-9, the fibers 12 forming the core of the electrodes 10 or 30 are of carbon. In addition, the fibers 12 may be formed of other semi-metallic fibers such as silicon carbide or of non-metallic fibers such as polyamides, polyesters and / or aramides and the like, which are made electrically conductive with a thin intermetallic layer of silver, copper, nickel and the like. .

The metal coating 14 may be formed from a wide variety of metals including nickel, copper, silver, lead, zinc, plate group metals and other metals depending on the application. The metal coating may also be a multilayer coating, e.g. an inner layer of nickel and an outer layer of silver.

As to the matrix, the term solder as used in the present specification includes alloys such as tin and lead or copper and silver, as well as pure metals, e.g. copper. The solder matrix creates an electrical bridge between the walls of the terminal block and each fiber 12.

The length of the rope of fibers 12 will depend on the width and length that the electrode 10 or 30 must have, and it can be wound as shown in FIG. 7-9 or weaved or knitted. Illustratively, ropes with a length from a few inches to over 12 m have been used with satisfactory results in the practice of the invention.

One of the particular features of the present invention is the large surface area made possible by the electrodes in a small volume of solution, causing

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16 provides a low current density and at the same time provides a high total current for the Faraday equivalents. Illustratively, a 7 µ fiber giving a coated fiber of 8 µ after stain in a rope of 40,000 fibers gives an area of 101.6 cm per square meter.

5 cm length of the rope.

Furthermore, the resistance of the electroplated fibers is so low that the potential of the rope is substantially uniform, even at a substantial distance from the terminal blocks.

The electrodes of the invention can be used for the removal and recovery of soluble metals in dilute solutions, such as plating process streams, hydrometallurgical mining processes, mining waste streams, and wherever metals are present in dilute solutions such as photographic and catalytic processes. As described above, the electrodes of the present invention have large effective areas. As a result, efficient recovery streams and discretionary voltages can be obtained for selectively recycling metals and removing impurities. Furthermore, the electrodes can be used in bipolar cell systems for efficient oxidation and reduction in separate chambers to recover solutes and carry out organic electrochemical processes.

In the following embodiments, electrochemical cells and processes using electrodes 25 of the present invention are described.

A typical use of the electrodes 30 described above is shown in FIG. 10, illustrating a tank 52 used for an electrochemical process, such as removal or recovery of metals from an electrolyte 54. The electrodes used as anodes are designated 30A, while the electrodes used as cathodes are designated 30C. The anodes 30A and the cathodes 30C are arranged alternately in the tank 52, with flow-through spacers 56 located between adjacent anodes 30A and cathodes 30C. The tank 52 contains a plurality of cells, each cell containing an anode 30A, a flow spacer panel 56 and a cathode 30C.

0

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The anodes 30A and the cathodes 30C are electrically connected to a power source 58 by means of standard connections as shown in FIG. 10. The voltage difference provided by the power source is a function of the current / voltage-5 relationship for the electrolytic solutions used.

The preferred voltage will correspond to the correct "knee" on the power / voltage curve of the particular metal to be removed or recovered.

Each cell in the tank 52 is defined by a pair of 10 dividing panels 60 as shown in FIG. Each panel 60 is formed of an inert transparent material such as polyethylmethacrylate and contains a plurality of holes 62 near a corner of panel 60 and illustratively arranged in a vertical row. Preferably, the total area of the holes 15 62 is approx. 50% larger than the area of the outlet conduit 66. The holes 62 can be approx. 15.9 mm in diameter and spaced approx. 12.7 mm. The holes 62 are provided to allow the electrolyte 54 to flow from one cell to the next cell in the tank 52. The panels 60 are particularly rotated 180 ° in the plane of the panel 60. As a result, one panel 60 will have holes 62 in a bottom corner, while the adjacent panel 60 will have the holes located in the opposite top corner.

During operation, electrolyte 54 is introduced into tank 25 52 through an inlet conduit 64 located near the upper edge of tank 52. Electrolyte 54 first enters a collection area 55 before passing through holes 62 in first dividing panel 60. This construction secures the desired flow pattern of electrolyte 54 into and through 30 of the first cell. The collection area 55 also acts smoothly on flow variations and collects precipitates which may be present in the electrolyte 54. Finally, the electrolyte 54 runs out of the tank 52 through the outlet conduit 66. The location of the holes 62 in the panels 60 throughout the tank 52 causes the electrolyte 54 alternately flows up and down and across from one cell to the next. This

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The general flow pattern of the electrolyte 54 through the tank 52, illustrated graphically by arrows 68, causes the electrolyte to cascade in length and width relative to the tank 52, thus maximizing the residence time of the tank 52 and the contact time with the electrodes 30, thereby the removal or recycling of metals from the solution is optimized. Thus, the construction of the anodes 30A and the cathodes 30C as described above provides an extremely large surface area, while the construction of the tank ensures maximum contact between the electrolyte 54 and the anodes 30A and the cathodes 30C.

The metal to be recovered or removed is deposited on cathode 30C. Therefore, it is periodically necessary to remove the cathodes 30C from the cell to recover the metal.

Typically, this recovery of recovered metal from cathode 30C can be accomplished by digestion, pyrometallurgy, or by making the cathode anodic in a concentration cell.

The electrochemical and structural principles described above can be incorporated into a system as shown in FIG. 13, for processing a process stream using an electrochemical cell shown in detail in FIG. 14 and 16. In this system, the process stream is pumped to a storage tank 70 and then fed to the multi-celled tank 72. The process stream is freed of metal in the tank 72 and 25 discharged through a conduit 98 to a collection container 97.

The effluent in the collection vessel 97 is pumped by a pump 99 to a neutralization tank 100 containing lime, where it is neutralized and then discharged as wastewater via a conduit 101.

In FIG. 14-16, the process stream containing a dilute acidic solution of a metal, e.g. nickel, tin, lead, copper, etc., through an inlet conduit 76 to a collection vessel 78. The illustrated tank 72 is rectangular and a dividing panel 80 extends in width thereof at one end thereof to form a chamber serving as collecting container 78. The dividing panel 80 between collecting containers 19 0

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the holder 78 and a first cell 82a in the tank 72 contain a channel 84 which allows the process stream 74 to flow to the upper portion of the region 86 to control flow variations. More specifically, the range 86 to 5 is the control of flow variations defined by an overflow panel 88 extending transversely at one end above the level of the process flow 74 in the first cell 82a to a point at a certain distance from the bottom wall 90 of the bath 72. a bottom channel 91 is formed through which the process stream flows into the first cell 82a. The first cell 82a is provided with an alternating and repeated arrangement comprising an anode 30a, a flow-through spacer 56, a cathode 30c and a second flow-through spacer 56. This arrangement is repeated so that each cell 82a to 82d contains several alternating anodes 30a and cathodes 30c As shown in FIG. 15, the anodes 30a and the cathodes 30c are held at a certain distance from the bottom wall 90 and are supported by portions 93 so that sediment can be collected. As shown in FIG. 13, the anodes and cathodes 20 are connected to a variable power source by means of standard connections such as common bus rails. For the sake of clarity, the electrical connectors are not shown in FIG. 14-16. As already described, the voltage for operation of the system is chosen such that the recovery or removal of metals from electrolyte 54 is optimized.

Cells 82a to 82d extend over tank 72 parallel to collection vessel 78 and are separated from each other by dividing panels 94. Each dividing panel contains one or more holes 96 located in a corner of dividing panel 94. As described above, dividing panels 94 are rotated 180 ° in their plane alternately, so that the holes 96 alternate in the opposite top and bottom corners. Thus, the dividing panel 94 between cells 82a and 82b has the holes 96 located in the corner farthest from the bottom wall 92 and the overflow panel 88. It follows that the dividing panel 94 between cells 82b and 82c is located in the corner closest to the bottom wall 0.

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20 92 and the overflow panel 88. This particular construction ensures an end-to-end flow of process flow in each of cells 82a to 82d together with a top-to-bottom or bottom-to-top flow pattern. As described above, this flow pattern optimizes the residence time of the process flow in the tank 72 while minimizing channel formation. Finally, the process stream 74 is removed from the bath 72 through the outlet conduit 98 located near the bottom wall 92 of the bath 72.

10 The electrochemical cells and processes shown in FIG. 10-12 and 13-16, are suitable for removal and recycling of metals, including semi-precious and precious metals, from process streams or waste streams to less than approx. 1.0 ppm. For example, the system shown in FIG. 13-16, 15 is used to remove approx. 50% of the nickel in a process stream containing 30 ppm of nickel at a rate of 18.9 liters / min. runs into an 189 liter multi-cell tank 72. For removal of additional nickel, the process can be repeated until the nickel content is reduced to 20 a level satisfactory for discharge. This can be done by recirculating the process flow from line 98 to line 76 via line 103 before finally flowing to the neutralizer.

The cells described can also be used to dissociate the solution to make soluble salts, e.g.

municipal wastewater, insoluble, so that they can be filtered from the effluent.

Furthermore, the present electrodes can be used in a discretionary cell, as shown in FIG. 17 and 18, where the voltage is set to a particular, precisely selected level so that a desired metal is deposited on the cathode, while metals higher in the electromotive range remain in solution. In order to carry out this discretionary deposition, it is necessary to use a cathode 35 with a large surface area. This is achieved in a small volume and with a small amount of electrolyte by means of the 0

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21 discretionary cell 100 shown in FIG. 17 and 18, and uses a carbon fiber cathode 102 with a thin single-wire anode 104, such as platinum. Electrolyte 106 is fed into the discretionary cell 100 through an inlet line 108 located approximately centrally in the discretionary cell 100. The inlet line 108 is mounted in a deflection sleeve 110 and includes a plurality of holes 111 which cause the electrolyte 106 to disperse uniformly in the cell 100. The single wire anode 104 is wound helically around the inlet line 108. The cathode 102 is located concentrically around but at some distance from the anode 104. Due to this construction, the electrolyte 106 running out of the inlet line 108 is caused to flow past the anode 104 and through the cathode 102 so as to obtain the desired deposition of metals on the cathode 102.

The cathode 102 used in the discretionary cell 100 is a nickel plated carbon fiber electrode. The concentric mounting of the cathode 102 around the anode 104 is accomplished by uniform winding of the cathode 102 around a generally cylindrical flow support or plastic grating 112. The flow substrate 112 may e.g. formed by a solid but flexible plastic screen, bent and fastened in a cylindrical shape. The cathode 102 is held on the support 112 by a porous outer shield 114.

The flow properties of the support 112 and the shield 114 allow the electrolyte 106 to flow easily through the cathode 102 and come into contact with the many nickel-plated carbon fibers contained in the cathode 102.

Although the cathode 102 is shown to be uniformly wound around the lattice 112, it will be understood that the cathode 102 may be knitted to a cylindrical base or woven into a mat which will then be wrapped around the lattice 112 or other structural flow support. An outlet conduit 116 for removing electrolyte 106 from discretionary cell 100 is also provided. Typically, discretionary cell 100 defines

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0 22 ket system in which the outlet 116 and the inlet 108 are in connection with a common source of electrolyte solution from which metal will be removed. The discretionary cell 100 can be constructed with any size. For example, cell 100 may be a small unit mounted over a larger container containing the electrolyte solution. In a typical application, a cathode 102 of a rope of 40,000 nickel plated fibers is formed into a cylinder as shown in FIG. 17 having a diameter of approx. 10.2 cm and a length of approx.

30.5 cm. This cathode 102 provides a surface area of approx.

2 9.29 m and can be mounted in a discretionary cell with a volume of less than 3.79 liters. Alternatively, much larger tanks can be constructed. As described above, after a suitable amount of metal in electrolyte 106 has been deposited on cathode 102, the removal and / or replacement of cathode 102 is temporarily stopped so that the metal deposited thereon can be appropriately removed when the metal is a pollution, or is recovered when the metal has value.

In FIG. 19 and 20, the electrochemical cell comprises a tank 122 which is substantially identical to the tank 52 shown in FIG. 10. The tank 122 contains a plurality of dividing plates 124, each containing a plurality of apertures 126 through which the electrolyte 128 can pass. As described, the holes 126 are located near a corner of the panel 124, and the panels 124 are alternately rotated 180 ° in their plane to provide the desired up-and-down and side-to-side flow pattern of the electrolyte through and across. of the tank 122.

As described above, panels 124 separate the different cells from one another, cell 130 containing an anode 132 and cathode 134 separated by a flow spacer 136. The anode 132 comprises a carbon fiber rope 138 wrapped around a flow support. Specifically, the carbon fiber rope 138 in each anode 132 is formed by a plurality of carbon fibers having 0

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23 each are metal plated near the electrical connection but are non-plated or freed of plating farther from the electrical connection. Thus, each anode 132 has substantially the same configuration as the anode 30a described above.

As shown in FIG. 20, the cathodes 134 are flow-through or porous metal plates containing a plurality of apertures 142. In this embodiment, the plate 134 is stainless steel. The flow-through spacers 136, 10 located between each anode 132 and cathode 134 are substantially identical to the flow-through spacers 56 already described.

Illustratively, the cell of this embodiment of the invention can be used for the removal and recovery of cyanide and other alkaline electrolytes containing metals such as silver, copper, zinc, cadmium and tin.

Another embodiment of the invention particularly useful in electro-organic chemistry and synthesis and in the treatment of organic residues is illustrated in FIG. 21 and 22. In FIG. 21, the cell comprises a tank 150 divided by a porous membrane 152 into two chambers for two separate electrolyte solutions 154 and 156. The cell also contains an anode 158 and a cathode 160 which are substantially identical to the anodes 30A already described and cathodes 30C. Anode 158 and cathode 160 are passive electrodes that are electrically connected to each other at a point 164 but are not electrically connected to an external power source, thereby becoming bipolar. The anode 158 and cathode 160 are preferably separated from each other by the porous membrane so that the anode 158 is in the chamber containing the electrolyte 154 and the cathode is in the chamber containing the electrolyte 156. The membrane 152 comprises a hollow support 161 around which is attached a porous portion 162, e.g. of canvas.

As shown, membrane 152 is filled with solution 165 which may be neutral. The active electrodes for the cell are a plate cathode 166 in the electrolyte 154 and a plate anode 168 in the electrode 24

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the trolyte 156. As mentioned, the electrolyte solutions 154 and 156 are different, one being acidic and the other basic. The solution 154 is oxidized at the anode 158, while the solution 156 is reduced at the cathode 160 without polarization of the fiber electrodes. In practice, the porous membrane 152 need not be ion selective. Consequently, the membrane 152 is relatively inexpensive and does not require high electrical energy.

The bipolar cell is particularly well suited for use where the anolyte and catholyte must be kept separate, where the oxidation or reduction on either side of the cell may be ionic or where a polarized electrode is desired.

15 20 25 30 35

Claims (5)

An electrode (10; 22) comprising a plurality of adjacent continuous fibers (12), each fiber (12) having a thin, firmly adhered metal coating 5 (14) therein, characterized in that ends of the metal-coated fibers (12) have a connector (16) and an electrically conductive metal (18) extends between the ends of the fibers (12) and connects them to each other and to the connector (16) to provide a coherent metal matrix, providing an effective electrical connection between the metal-coated fibers (12) and the connector (16). An electrochemical cell comprising at least one pair of electrodes, wherein the electrodes (30a, 30c; 102, 104; 132, 134; 15 158, 160; 166, 168) in each pair have opposite electrical charges, and at least one of the electrodes in each pairs comprise a plurality of adjacent continuous fibers (12), each fiber having a thin, fixed adhesive metal coating (14) thereon, characterized in that the 20 ends of the fibers (12) in said at least one electrode The fibers which contain fibers are close together and said electrode comprises a metal coating on each fiber (12) at said ends extending along each fiber (12), a connection piece at said metal coated ends of the fibers, and an electrically conductive metal (18) extending between the metal coatings at the ends of the fibers and connecting them to each other and to said connector to provide a coherent metal matrix providing an effective electrical connection between the metal coated fibers and the connector. Electrochemical cell according to claim 2, characterized in that one of the electrodes (134) is a metal plate with a plurality of openings (142) therethrough. 4, Bipolar electrochemical cell, characterized in that it comprises a container (15a) with two chambers for accommodating different electrolyte solutions, wherein the one chamber contains an active anode (168) and a passive cathode (160). ), and the second chamber contains an active cathode (166) and a passive anode (158), wherein the active electrodes are connected to a power source and the passive electrodes are electrically connected to each other and wherein the passive anode and passive cathode (158,160) consists of fibrous electrodes according to claim 1, wherein the first electrolyte solution will be reduced and the second electrolyte solution will be oxidized when the first and second electrolyte solution are placed in the first and second chambers. Process for producing a fibrous electrode according to claim 1, characterized in that a continuous length of a plurality of core fibers (13) is provided, plating at least one end of each core fiber with a substantially uniform, solid metal adhesive coating (14) places an electrical connector in contact with the metal-coated ends of the core fibers (13), and 20 joins the metal-coated ends and the electrical connector with an electrically conductive metal (18) extending between the metal-coated fiber ends (12) to form a coherent fiber / metal matrix providing an efficient electrical connection.