Apparatus for controlling flow in an electrodeposition process

An electrowinning cell, having a tank with an opened upper end defined by a tank edge, electrolyte within the tank and a plurality of flat, metallic electrode plates disposed within the tank in side-by-side, spaced-apart, parallel relationship. Adjacent electrode plates define an electrode gap therebetween. An injector manifold is disposed at the bottom of the tank for feeding electrolyte into the tank at locations below the electrode plates. A collector grid, comprised of a plurality of collectors having ports, define an upper level of electrolyte by collecting the electrolyte from the tank. The ports are disposed in spaced-apart relationship within the open upper end defined by the tank edge. The collector grid and the injector creating a flow of electrolyte upward between the plates as the electrolyte flows from the manifold locations below the plates to the ports.

FIELD OF THE INVENTION

The present invention relates generally to the electrodeposition of metal, and more particularly, to an electrowinning cell and an electrolyte flow system therefor. While the present invention is particularly applicable to an electrowinning process for forming copper, and will be described with reference thereto, the invention also finds advantageous application in electrodepositing other types of metals and metal compounds.

BACKGROUND OF THE INVENTION

It is well known that metal can be extracted from metal ions in an electrolytic solution through an electrowinning process. An electrowinning process utilizes the known technique of plating metal or metal compounds out of an electrolytic solution onto an electrode plate. Modern electrowinning typically occurs in a relatively large, non-conductive tank that contains metal ions dissolved in an electrolytic solution. A plurality of side-by-side, parallel cathode and anode plates are suspended in the electrolytic solution. In a copper electrowinning cell, the cathodes and the anodes are ultimately arranged such that each cathode is disposed between two anodes. The cathodes and anodes are connected to an electrical power source to cause the plating of copper onto the cathode plates.

Electrowinning cells typically include a circulating system that circulates the electrolytic solution from a reservoir to the electrowinning cell and back to the reservoir. Metal ions depleted from the electrolytic solution during the electrodeposition process, are replenished in the reservoir. The replenished (i.e., “fresh”) electrolytic solution is pumped into the electrowinning tank, typically at the bottom thereof. Excess solution in the tank overflows the upper edge of the tank and is collected in a trough. The collected (i.e., “metal depleted”) electrolyte is returned to the reservoir.

This type of arrangement produces a less than desirable flow of the electrolytic solution in the tank. The electrolytic solution typically flows from its point of entry at the bottom of the tank toward the edge of the tank where the solution exits, i.e., overflows, the tank. This produces areas of lower flow between the plates, that is more marked in the middle of the upper region of the tank. The flow of the electrolytic solution is also influenced by gas bubbles that form between the electrode plates during the electrodeposition process, as gas is liberated at the surface of the anode plates. These gas bubbles also tend to direct the electrolytic solution away from the spaces or gaps between the parallel anode and cathode plates toward the sides and edges of the tank. Thus, the replenished, fresh electrolytic solution forced into the tank typically flows toward the edges of the tank where it overflows the tank, rather than into the cathode and anode gaps where the actual electrodeposition occurs and where the replenished electrolytic solution is needed.

The present invention overcomes these and other problems and provides an electrowinning cell and a circulation system therefor, wherein fresh electrolytic solution entering the tank is directed more uniformly between the cathode and the anode plates.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided an electrowinning cell that is comprised of a tank for holding electrolyte. The tank has an opened upper end. A plurality of flat, metallic electrode plates are disposed within the tank in side-by-side, spaced-apart, parallel relationship, the electrode plates defining a gap between adjacent electrode plates. An electrolyte circulation system includes an inlet manifold disposed below the electrode plates, and a plurality of spaced-apart collectors extending across the open upper end of the tank. The collectors extend parallel to the electrode plates. Electrolyte is continuously pumped into the tank through the inlet manifold. The electrolyte pumped into the tank flows upward through the gaps to the collectors, the collectors establishing a level for the electrolyte in the tank.

In accordance with another aspect of the present invention, there is provided an electrowinning cell, having a tank, electrolyte within the tank and a plurality of flat, metallic electrode plates disposed within the tank in side-by-side, spaced-apart, parallel relationship. Adjacent electrode plates define an electrode gap therebetween. An electrolyte feed line is provided for injecting electrolyte into the tank below the lower portions of the electrode plates. An electrolyte collector grid comprised of a plurality of generally parallel collectors that extend across the tank are disposed between the electrode plates and establish a level of electrolyte in the tank by collecting the electrolyte when the electrolyte reaches the level. The collectors are disposed relative to the inlet feed line to collect the electrolyte solution at spaced-apart locations within the tank and to produce a generally vertical flow of electrolyte through the gaps between the electrode plates.

In accordance with another aspect of the present invention, there is provided an electrowinning cell, having a tank having an opened upper end defined by a tank edge, electrolyte within the tank and a plurality of flat, metallic electrode plates disposed within the tank in side-by-side, spaced-apart, parallel relationship. Adjacent electrode plates define an electrode gap therebetween. An injector manifold is disposed at the bottom of the tank for feeding electrolyte into the tank at locations below the electrode plates. An electrolyte collector grid comprised of a plurality of collector ports defines an upper level of the electrolyte by collecting the electrolyte from the tank. The ports are disposed in spaced-apart relationship across the open upper end of the tank. The collector grid and the injector creating a flow of the electrolyte upward between the plates as the solution flows from the manifold locations below the plates to the collector ports.

In accordance with another aspect of the present invention, there is provided a method of electrowinning copper, comprising the steps of:

(a) vertically orienting a cathode plate between two, spaced-apart, vertical anode plates within a tank, the cathode plate and the anode plates being essentially parallel to each other with a uniform gap defined between the cathode plate and each anode plate;

(b) negatively energizing the cathode plate and positively energizing the anode plates; and

(c) causing a vertical, upward flow of electrolyte through the gaps between the cathode plate and the anode plates 1) by forcing electrolyte into the tank below the cathode and anode plates and 2) by collecting the electrolyte with a plurality of collector ports disposed across the tank between the anode plates.

In accordance with another aspect of the present invention, there is provided a method of electrowinning copper as described above, further comprising the step of:

(d) causing the electrolyte to flow through the gaps between the cathode plate and the anode plates at a uniform, average velocity of between 0.50 in./min. and 10.0 in./min.

It is an object of the present invention to provide an electrowinning cell having improved operating characteristics.

It is another object of the present invention to provide an electrowinning cell as described above for electrowinning copper.

Another object of the present invention is to provide an electrowinning cell as described above having improved electrolyte flow between the electrode plates.

It is an object of the present invention to provide an electrolyte circulation system for an electrodeposition cell.

It is another object of the present invention to provide an electrolyte circulation system as described above that produces uniform flow of electrolyte past electrode plates in an electrowinning cell.

A still further object of the present invention is to provide an electrowinning cell and electrolyte circulation system as described above that improves the product quality and productivity of the electrowinning cell.

These and other objects and advantages will become apparent from the following description of a preferred embodiment of the invention taken with the accompanying drawings and the appended claims.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for the purpose of illustrating the preferred embodiment of the invention only, and not for the purpose of limiting same,FIG. 1is a perspective view of an electrowinning cell10for extracting metal from an electrolytic solution containing ions of the metal. (Throughout the specification, the terms “electrolytic solution” and “electrolyte” are used synonymously). The present invention will be described with respect to an electrowinning cell for producing copper, although it will be appreciated that cell10may be also used for forming other metals, such as, by way of example and not limitation, zinc or manganese.

Broadly stated, cell10is comprised of a tank20containing an electrolytic solution12. In the embodiment shown, tank20is generally rectangular in shape and includes vertical side walls22,24, end walls26,28and a bottom wall32. Troughs34,36are formed along the outer, upper edges22a,24aof side walls22,24, respectively, as best seen inFIGS. 1,5and9. Troughs34,36are part of an electrolyte circulation system that shall be described in greater detail below. Tanks of electrowinning cells are typically formed of a corrosion-resistant and acid-resistant material, such as plastic or inert metal. Tank20and troughs34,36are preferably formed of a plastic material. Tank20is dimensioned to receive a plurality of side-by-side, parallel electrodes, designated40,50, in side-by-side, spaced-apart relationship. Electrode40is a cathode plate, and electrode50is an anode plate.

Cathode plate40is generally a flat, rectangular plate having a straight hanger bar42extending along the upper edge thereof. Hanger bar42is preferably welded to cathode plate40as is conventionally known. Hanger bar42has a length greater than the width of tank20, wherein the ends of hanger bar42extend beyond the periphery of tank20, as seen in FIG.1.

Anode plate50, best seen inFIG. 8, is a flat, rectangular plate having a hanger bar52extending along the upper edge thereof. Hanger bar52is dimensioned to extend beyond troughs34,36of tank20, as best seen in FIG.1. Hanger bars42,52are formed of a conductive metal as is conventionally known.

Cathode plates40and anode plates50are dimensioned to be supported within tank20in side-by-side, alternating relationship. To this end, structural supports62,64are disposed outside tank20to support cathode plates40and anode plates50on their respective hanger bars42,52.

Supports62,64are only partially shown in the drawings. In the embodiment shown, supports62,64are conductive rails, i.e., copper bus bars, that in addition to supporting cathode plates40and anode plates50, form conductive pathways to energize cathode plates40and anode plates50, as schematically illustrated inFIGS. 1-5.

As best seen inFIGS. 1 and 3, supports62are dispersed relative to tank20such that cathode plates40are supported within tank20with a lower portion of each cathode plate40disposed within tank20, and with hanger bar42and an upper portion of cathode plate40disposed above the upper edges22a,24aof side walls22,24of tank20. Supports64for anode plates50are disposed relative to tank20such that each anode plate50and its respective hanger bar52, are disposed below upper edges22a,24aof side walls22,24of tank20.

To allow anode plates50to be positioned below upper edges22a,24aof side walls22,24, spaced-apart, vertical slots72are formed in upper edges22a,24aof side walls22,24, as best seen inFIGS. 1 and 2. Slots72are dimensioned to receive anode hanger bars52. The distal ends of hanger bars52extend over troughs34,36when anode plates50are in position within tank20, as best seen in FIG.3. Slots72are dimensioned such that the upper edge of hanger bar52is disposed a predetermined distance below upper edges22a,24aof side walls22,24. In the embodiment shown inFIGS. 1-9, the width of slots72is dimensioned to match closely the width of hanger bar52, such that hanger bar52fits snuggly therein. In an alternate embodiment, a seal76, formed of a resilient, elastomeric material that is chemically inert to electrolyte12, may be provided between hanger bar52and side walls22,24to form a fluid-tight seal therebetween, as illustrated in FIG.12.

In the embodiment shown, cathode plates40and anode plates50are arranged in side-by-side, alternating fashion, wherein a cathode plate40is disposed between two anode plates,50. Guide rails (not shown) are disposed within tank20extending between end walls26,28to receive the lower edges of cathode plates40and anode plates50, respectively. The guide rails are provided to vertically align cathode plates40and anode plates50within tank20. Slotted, vertical guides (not shown) may also be provided along the inner surface of side walls22,24to assist in vertically aligning cathode plates40and anode plates50relative to each other. A generally uniform interelectrode gap88is defined between adjacent cathode plates40and anode plates50.

An electrolyte circulation system90is provided to circulate electrolyte12through tank20. Circulation system90is comprised of a reservoir92and a pump94, that are both schematically illustrated in FIG.3. Reservoir92provides a supply of electrolyte12having metal ions therein for use in electrowinning cell10. Reservoir92is essentially a replenishing tank, wherein spent or metal-ion-depleted electrolyte12is replenished with metal ions. Such a “metal ion replenishing tank” is conventionally known in the art, and therefore shall not be described in detail. Reservoir92provides a source of electrolyte12to pump94via line93. In the embodiment shown, a feed line95from the pump is split into two feed lines95a,95b. Feed lines95a,95bextend through side walls22,24into tank20. Feed lines95a,95beach terminate in a manifold pipe96, best seen in FIG.2. Manifold pipes96are disposed above bottom wall32of tank20and below the lower ends of cathode plates40and anode plates50. Manifold pipes96have downward facing apertures98formed therein, as best seen inFIGS. 2 and 7.

A plurality of electrolyte collectors100extend across the upper end of tank20. In the embodiment shown, collectors100are U-shaped channels that are mounted along the upper edge of hanger bar52. The U-shaped collectors100preferably have a flat, bottom wall102and parallel, upward extending side walls104. Collectors100are preferably formed of a non-conductive, plastic material. Collectors100may be secured to hanger bars52by a number of different fastening means, but in the preferred embodiment, collectors100are secured to hanger bars52with nonmetallic, threaded fasteners112that are threaded into openings in the upper surface of hanger bars52, as best seen in FIG.6.

As best seen inFIG. 5, collectors100are dimensioned such that a portion of the distal ends of each collector100extends beyond side walls22,24of tank20. Collectors100are dimensioned to have a width closely matching the width of the associated anode hanger bar52, such that sides104of collectors100fit snuggly within slot72in side walls22,24of tank20, as best seen inFIG. 6, and form a relatively fluid-tight joint therewith.

A plurality of spaced-apart, aligned apertures106are formed in each side wall104of each U-shaped collector100. In the embodiment shown, apertures106are cylindrical in shape and are disposed about half way up each side wall104of collectors100. Apertures106are aligned in rows, and each row of apertures106is preferably parallel to apertures106in other collectors100to lie in a common plane.

Collectors100are adapted to collect electrolyte12from tank20and to direct electrolyte12to troughs34,36. Each trough34,36contains one or more drainpipes132that are connected to an electrolyte return line134to return electrolyte12to reservoir92.

Referring to the operation of electrowinning cell10, the present invention shall be described with respect to electrowinning copper. Tank20is filled with electrolyte12comprised of sulfuric acid (H2SO4) containing copper ions. Cathode plates40are negatively charged and anode plates50are positively charged to produce an electric field across the interelectrode gaps88defined between adjacent cathode plates40and anode plates50. Pump94causes electrolyte12to be forced into tank20through manifold pipes96. Apertures98in manifold pipes96direct electrolyte12toward the bottom of tank20, as indicated by the arrows in FIG.2. From the bottom of tank20, electrolyte12flows generally vertically through gaps88between cathode plates40and anode plates50.

In accordance with one aspect of the present invention, pump94is preferably operated to create flow of electrolyte12through said electrode gaps88between cathode plates40and anode plates50at a velocity between 0.50 in./min. and 10.0 in./min. In another embodiment, the velocity of electrolyte12through gaps88is between 2 in./min. and 7 in./min. Preferably, the velocity of electrolyte12through gap88is between 4 in./min. and 6 in./min.

The level of electrolyte12in tank20is established by apertures106in collectors100. Because upper edges22a,24aof side walls22,24and upper edges26a,28aof end walls26,28of tank20are above apertures106, once electrolyte12reaches the level of apertures106, electrolyte12flows into U-shaped collectors100and is carried through collectors100to troughs34,36, as illustrated in FIG.9. Electrolyte12in troughs34,36is returned to reservoir92via lines134.

As indicated above, anode hanger bar52and collector100preferably form a tight fit with slots72in side walls22,24to minimize leakage of electrolyte12from tank20through said joints. However, as will be appreciated, minor leakage of electrolyte will not significantly affect the flow of electrolyte12through apertures106of collectors100, and any leakage through side walls22,24will, of course, be collected by troughs34,36and returned to reservoir92via drain pipes132and return lines134. If a fluid-tight joint is desired, a seal76, as shown inFIG. 12, may be employed.

The plurality of collectors100extending across the upper edge of tank20basically forms a grid-like arrangement of apertures106that essentially provide a plurality of outlet ports or drain ports for electrolyte12that span the upper surface of tank20.FIG. 10schematically shows the plurality of apertures106in collectors100and how such apertures106basically provide a grid-like pattern of electrolyte outlet ports across the upper end of tank20. Because the electrolyte outlet ports, i.e., apertures106, are directly above the electrolyte inlet ports, i.e., apertures98in manifold pipes96, electrolyte12is forced into the bottom of tank20and follows a generally vertical flow path upward through gap88between cathode plates40and anode plates50, as indicated by arrows in FIG.7. As a result, there is a continuous flow of new, replenished electrolyte12from reservoir92flowing between cathode plates40and anode plates50, where the electrodeposition process occurs. This type of flow not only provides a metal-ion-rich electrolyte12between cathode plates40and anode plates50, but also assists in forcing away gas bubbles B that are typically formed on the surface of anode plates50during the electrodeposition process.

FIG. 7schematically illustrates cell10in operation. The arrows indicate the direction of flow of electrolyte12. Copper, designated “C” in the Figure, is shown being plated onto cathode plates40. Gas bubbles, designated “B” in the drawing, are illustrated as forming on the surface of anode plates50. Gas bubbles B act as insulators and reduce the electric field potential between cathode plates40and anode plates50. Using the flow of electrolyte12to force away such bubbles B further enhances the electrodeposition process. By providing the electrolyte outlet ports, i.e., apertures106in collectors100between adjacent cathode plates40, spent electrolyte12, i.e., electrolyte having a reduced metal ion concentration as a result of the electrodeposition process, is forced out of tank20into collectors100by fresh electrolyte12being forced up from below.

The present invention thus provides an electrowinning cell10, and an electrolyte circulation system for such cell, that provides more uniform, consistent flow of electrolyte12through gaps88between adjacent cathode plates40and anode plates50. The more uniform, consistent flow of electrolyte facilitates more uniform, consistent metal deposition.

Another advantage of the present invention is that the rate of flow of electrolyte12through gaps88can be controlled. Since the flow through gap88is dependent upon the flow of electrolyte12into tank20by controlling the output of pump94, variable flow rates of electrolyte12can be established in gap88to optimize a desired deposition rate. Typically, most conventional copper electrowinning cells that have side or edge overflow configurations operate at an electrolyte flow rate equivalent to about 1.5 gal./min. through a 1 square foot area. This is equivalent to an average fluid velocity through the unit area of about 0.163 ft./min. (≈0.033 in./sec.). In conventional side or edge draining copper electrowinning cells, increasing the flow rate of the electrolyte does not significantly improve the deposition rate of copper. It is believed that such a configuration produces non-uniform flow rates between electrodes and therefore, limits the operating flow rate of the electrolyte because in some areas of such tanks, particularly at the sides, the flow rates of the electrolyte are higher than areas in the upper center of the tank. Such non-uniform flow rates of the electrolyte between the electrodes also produce a non-uniform deposition of electrodeposited metal.

The present invention provides a more uniform and evenly distributed vertical flow of electrolyte12past cathode and anode plates40,50. Such flow provides better copper deposition rates at conventional flow rates of about 0.05 gal./min./ft.2. Even at higher rates up to about 0.5 gal./min./ft.2, a cell according to the present invention provides increased copper deposition. At flow rates above 0.15 gal./min./ft.2, only slight improvements in copper deposition seem to occur as the flow rate increases.

The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purposes of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. For example, it will be appreciated by those skilled in the art, that other types of collectors100may be used to form spaced-apart electrolyte outlet ports across the upper end of tank20. In this respect,FIG. 11shows a collector100′ having V-shaped notches106′ formed in side walls104′. V-shaped notches106′ define the electrolyte outlet ports for collecting electrolyte12.

Further, the invention has heretofore been described with respect to a copper electrowinning cell, where the copper is deposited onto cathode plates40and collectors100are disposed along the upper edge of anode plates50. In other types of electrowinning cells, such as cells for forming manganese, the metal is electrodeposited onto an anode plate. In such cells, collectors would preferably be disposed along the upper edges of the cathode plates.

It will further be appreciated that collectors100need not be secured to an upper edge of an electrode plate to provide the grid-like array of electrolyte outlet ports across the upper end of the tank.

It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.