Electrolytic cell for removal of material from a solution

FIELD OF THE INVENTION

The present invention relates to an electrochemical method and apparatus for recovering materials from solution by electrowinning or electrooxidization.

BACKGROUND OF THE INVENTION

The concept on recovering materials from solutions by electrolysis is not new. Many industries, such as plating processes, mining processes and metal finishing, produce waste product of solutions containing ions of metals, and recovery of these metals are both environmentally and economically beneficial. Waste from solutions with unrecovered metal increases the amount of sludge disposed on land-fields. Many systems of metal recovery currently use a mechanical device such as a blade, to remove deposited material from an electrode. The use of a mechanical device has the disadvantages of increased wear, risk of breakage, and tendency to slow the treating process down.

Our copending U.S. application Ser. No. 10/941,900 describes an improved method for recovering materials. This solution, which employs an electrode rotating at high speed, has proved to be remarkably effective.

SUMMARY OF THE INVENTION

The present invention builds on the success of the invention disclosed in our copending application by improving the throughput. The invention is capabable of either processing a higher volume of material in the same sized cell or alternatively reducing the size of the cell for a given throughput.

According to the present invention there is provided an electrolytic cell for the recovery of material as a powder or flakes from a solution, comprising a cell cavity for containing the solution; a rotatable electrode in the cavity having a pair of opposite electrode faces; counter electrode portions in spaced and opposing relationship with said respective opposite electrode faces of the rotatable electrode to supply a current through solution in the cavity to permit extraction of the material by electrochemical reaction; and a vibrator for directing vibrational energy toward the rotatable electrode to dislodge material extracted as a powder or flakes from the solution by an electrochemical reaction.

In one embodiment the rotatable electrode is a cathode, which is in the form of a double-faced cylinder having internal and external faces. The second electrode portions form part of a common anode and are defined by the inwardly facing surfaces of an annular channel receiving the cylindrical cathode. Alternatively, the second electrode portions could be separate elements facing the opposite faces of the cathode. The rotatable electrode should preferably have a tangential speed in excess of 1 m/s, in which case it is desirable to provide a meniscus breaker to inhibit the rising tendency of liquid in the cell.

The structure of the electrodes can take various forms. In one embodiment, the rotatable electrode is a cylinder, as noted above, but, for example, the rotatable electrode, cathode in the case of electrowinning, could also have a grating or mesh structure, or could be porous so as to have a three dimensional sponge structure.

The apparatus can be used for the recovery of metal from either an aqueous or non-aqueous solution, enabling facile separation of electrochemically deposited metal or metallic compounds from an underlying cathode.

In one embodiment the formation of a powder, or flakes, removed by ultrasonic or other mechanical vibrational energy, occurs on a double-face rotatable electrode. This type of electrode may comprise a hollow disk or cylinder open at both ends to allow the solution to be treated to travel inside and outside the electrode. Hence, a powdery or flaky deposit obtained by electrochemical means can be formed on both surfaces of the double-face rotatable electrode and removed with an ultrasonic or other type of vibrating device either on one or both surfaces of the electrode.

In one embodiment, an internal double-face counter-electrode is placed around the double-face rotatable electrode to permit current flow. Each surface of the double-face rotatable electrode, both inner and outer sections, faces a surface of the double-face counter-electrode. The double-face rotatable electrode is placed in a sandwich-like fashion inside the cell cavity. More than one double-face electrode can be built to fit inside a cell cavity.

The invention provides a type of double-faced rotatable electrode that, for the same throughput, is reduced in size compared with the rotatable electrode disclosed in U.S. application Ser. No. 10/941,900. The size of the present double-face rotatable electrode is reduced at least by half when both sides of its cylindrical surfaces are being used to extract metals or oxidize organics from a solution to be treated.

The double-face counter-electrode can be placed in such a way that both electrode surfaces (anode and cathode) face one another in a parallel fashion. Preferably, the distance between both inner and outer faces is equal in order to achieve symmetry in the assembly, thus providing similar electrochemical conditions for both surfaces of the double-face rotatable electrode. Alternatively, the distance between each pair of electrode and counter-electrode can be adjusted in such a way that a different tangential speed is obtained. Hence, electrochemical properties that link this latter parameter to the reactor efficiency are respected.

In one embodiment, the double-face rotatable electrode forms a cathode, and the double-face counter-electrode forms an anode, wherein metal in the solution is deposited on the cathode as a metal powder or flakes, such that the ultrasonic energy displaces the metal powder from the cathode. In another embodiment, the double-face rotatable electrode forms an anode, and the double-face counter-electrode forms a cathode. This embodiment is suitable for extracting organic waste, which is deposited on the anode.

Since ultrasonic or other vibrating energy is present inside the cell cavity to remove the powdery, or flaky, deposit off the double-face rotatable electrode, a device propagating or generating the energy should be placed toward the outer and/or the inner surfaces of the double-face rotatable electrode. Such device can be placed along the same plane of the counter-electrode location. When non-retractable ultrasonic generators are selected as a powder, or flakes, removal device for a specific electrochemical reaction, at least one generator may be placed on both faces of the double-face rotatable electrode.

Depending upon the size of the cell cavity and the number of double-face rotatable electrodes used, the number and dimensions of the generators can be limited. For a determined electrolytic cell size, the limitation concerns the number of generators that can be placed within the internal holder. The number of ultrasonic generators that can be fitted inside the holder is limited by the size and the number of the transducers placed inside the generators, an thus by the size of the generator housing itself.

In one embodiment the solution to treat is passed along both rotating faces of a double-face rotatable electrode, preferably at the same flow rate on each side. Furthermore, when more than one double-face rotatable disk or cylinder turn together, since they are fixed to the same rotating shaft, each disk or cylinder turns at a different tangential speed for a fixed rotating speed (rpm) since the diameter of each disk or cylinder is different. This property can be especially useful when two or more metals are to be electrowon within the same solution to be treated.

Ultrasonic generators or any other mechanical vibrating device which can be used for the removal of powder, or flakes, can be placed inside the reactor in either a static or dynamic (retractable) manner, facing only the outer or inner face or both faces of the double-face rotatable electrode. When a static arrangement is employed, the double-face rotatable electrode requires at least one device for each face. When a dynamic arrangement is employed, at least one single device can be located toward the inner face only or the outer face only. A sliding mechanism can be used to withdraw it from one face and introduce in front of the other. The thickness of the double-face rotatable electrode can be thin enough to transmit the energetic effect of the vibrating device.

The dynamic arrangement involves a contact between the vibrating device and the rotatable electrode. The device can be located inside a housing and, when needed, a mechanism slides the device toward the electrode and touches it in order to transmit its energy for the time period it takes to remove all the powdery, or flaky, deposit from the two faces of the double-face rotatable electrode.

The sliding mechanism involves any type of actuator, piston, spring, blade, cushion or other similar element that allows a mechanical movement in one or two axes, vertically or horizontally. Hence, the movement provides a retractable motion of the vibrating device that is being used only when needed. Thus, the device does not impede the rotating motion of the rotatable electrode. More than one such device can be placed inside the electrochemical reactor, targeting the removal of the powder, or flakes, from both rotatable electrode surfaces.

The electrolytic cell may further comprise a bin for collecting the material removed from the rotatable electrode, such as powdered or flaky metal from the cathode, or organic waste from the anode.

The electrolytic cell may be equipped with a device that has the property of breaking the liquid rise effect caused by the rotation movement of the rotatable electrode. Such device, referred to as a “meniscus-breaker”, is required when the tangential speed (U) of the electrode is higher than 1 m/sec, which is desirable in order to provide extraction removal of the powder. The order of magnitude of the rising (R) of the liquid level above its nominal value (liquid level when U=0) is given by the following relationship:

R=U²/4g; where g is the acceleration due to gravity.

The geometry and dimensions of the meniscus-breaker are determined from the following consideration: a) evolution of hydrogen, oxygen and other possible gases produced at the electrodes during the electrolysis process, b) liquid section above the meniscus-breaker that has to go down through the center hole of the device for being treated, c) presence of solid particles within that liquid (e.g. metallic powder). Because of these considerations, the bottom section of the meniscus-breaker should have a conical or pyramidal shape while the upper section should have an inverted similar shape on top of the bottom section, given an overall hour-glass shape. The angle present within both sections must be such that the bottom section allows the gases to exit upwardly toward the center hole of the meniscus-breaker (where the shaft of the double-face rotatable electrode goes through) while the upper section allows the liquid charged with the solid particles (mostly metallic) to go back into the cell by gravity. To be efficient, the meniscus-breaker should be located below the nominal level of the liquid into the cell. Its rim (or borders) must closely touch the inner wall of the cell in such a manner that no liquid can go between the wall and the meniscus-breaker.

The present invention makes it possible to substantially reduce, at least by half, the size of the rotatable electrode used and, thus, the size of the electrolytic cell, when both sides of the rotatable electrode are being used. Furthermore, it is also possible to extend the use of both faces of more than one double-face rotatable electrode. Indeed, several disks, or cylinders, can be inserted inside one another, creating an array of electrodes of alternate polarity, turning at different tangential speed and simultaneously working at various current densities.

Since both faces of the double-face rotatable electrode are being used to produce a deposit, an inner surface and an outer surface call out for two or more ultrasonic generators to remove such deposit.

Embodiments of the invention permit the selective purification of concentrated electrolytes from undesired low concentration metallic contaminants present into them. Furthermore, the invention can also be used to destroy organic contaminants present in low concentration in inorganic or organic conductive electrolytes by electrooxidation. The desired electrochemical reaction is achieved depending upon the induced polarity of the double-face rotatable electrode.

In another aspect the invention provides a method for extracting material from a solution comprising providing an electrolytic cell including a rotating electrode having a pair of opposite electrode faces and counter electrode portions in spaced and opposing relationship with said respective opposite electrode faces of the rotating electrode; introducing a solution containing the material into the electrolytic cell; applying a direct current to the solution between the electrodes so that the material becomes deposited on both said opposite faces of the rotating electrode as a powder or flakes by electrochemical reaction; and dislodging the material as a powder or flakes from the rotating electrode with vibrational energy.

Other aspects and advantages of embodiments of the invention will be readily apparent to those ordinarily skilled in the art upon a review of the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described in conjunction with the accompanying drawings, wherein:

FIG. 1 is a high-level illustration of an electrolytic cell in accordance with the teachings of this invention;

FIG. 2 is a schematic cross-section of the cell cavity of the electrolytic cell containing one double-face rotatable electrode;

FIG. 3 shows an example of an internal retractable ultrasonic generator located inside the internal holder and facing the inner surface of the rotatable electrode;

FIG. 4 illustrates the geometric relationship between the internal electrode diameter and the available space location for the ultrasonic generator; and

FIG. 5 illustrates the electrolytic cell of FIG. 1 in an industrial application. This invention will now be described in detail with respect to certain specific representative embodiments thereof, the materials, apparatus and process steps being understood as examples that are intended to be illustrative only. In particular, the invention is not intended to be limited to the methods, materials, conditions, process parameters, apparatus and the like specifically recited herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The apparatus provided by the invention may be used either for electrowinning metals or oxidizing organic compounds. The operation of the apparatus is selectively changed by changing the polarization of a double-face rotatable electrode, as is described below.

Referring to FIG. 1, which in schematic form, is an overall view of an apparatus in accordance with the invention. It comprises an electrolytic cell 10 with a cell housing 12. The cell housing 12 defines a cell cavity 14 containing the electrodes. The shape of the housing 12 is not limited. It may be composed of any suitable material so long as the housing is electrically insulated from the double-face electrodes. Generally, the housing is cylindrical, although other shapes are possible. In this embodiment, it is shown to be funnel-shaped. The cell 10 contains a double-face rotatable electrode, where the powdery or flaky deposit is formed, as will be described in more detail with reference to FIG. 2.

A rectifier 16 provides the necessary current and voltage required between the electrodes to generate the electrochemical reaction in the cell for producing the powdery deposit when the double-face rotatable electrode is polarized cathodically or to oxidize organic contaminants when the double-face rotatable electrode is polarized anodically.

The current is supplied to the electrodes by electrical busbars 26, 28. At least two electrodes, namely a cathode and an anode, are connected to the cathode and anode busbars 26, 28, respectively. The double-face rotatable electrode can be polarized as the cathode or as the anode. The double-face rotatable electrode can also be called the working electrode, and the double-face static electrode is called the counter-electrode.

The housing 12 includes an inlet port 18 and flow passage 20 for feeding the feedstock solution to be treated from a storage tank (not shown) to the cell 10, and an outlet port 22 for removal of the solution, both being effected by a pump 24. When the powder or flakes is being deposited as a result of the electrochemical reaction the solution will be depleted of metal or organic contaminant. The depleted solution is passed through a tank 32 containing a filter 52 (this number refers to FIG. 5) to a wastewater facility, or is being recycled in the originating process. In the case of a solution containing copper, it is found that even during the deposition stage some powder becomes dislodged and is entrained with the depleted solution to the filter 52.

Periodically, during use the current is switched off and ultrasonic energy is applied to the double-face electrode to dislodge the powder or flakes formed thereon. The current may be stopped periodically depending upon the electrowinning cycle for anywhere from a few seconds to several minutes. For instance, the current can be interrupted to activate the ultrasonic generator for 10 seconds every 20 minutes of electrowinning cycle in a process to recover copper. Typically during the dislodgement phase the speed of rotation of the double-face rotatable electrode is reduced at 25% its nominal rotating speed.

When the powder or flakes is being dislodged from the double-face electrode by the application of ultrasonic energy, the dislodged powder is entrained in the liquid flowing through the outlet and subsequently passed through the filter 52 for removal. Since the liquid flowing through the cell in this phase is not depleted, the resulting liquid, after flowing through the tank 32, is switched to a buffer tank (not shown) rather than the wastewater facility. The liquid in the buffer tank can be subsequently returned to the cell for further processing during a subsequent deposition stage.

The cell 10, according to principles of the invention, also includes an ultrasound generator having an oscillator 30 and ultrasound transducers 50 (in FIG. 3) for directing ultrasonic energy at the double-face rotatable electrode during the powder removal phase. Other forms of vibrational energy can also be applied to dislodge the powder or flakes.

The construction of the electrodes will be seen in more detail in FIG. 2, which is an apparatus for the recovery of metals. The double-face rotatable electrode 5 is a distinct discrete component separate from the housing mounted on a drive shaft 1. This type of electrode comprises a hollow disk or cylinder opened from both ends to allow the solution to be treated to travel inside and outside the electrode. In FIG. 2, the double-face rotatable electrode 5 is shown as a hollow cylinder. This electrode has opposite faces 5a, 5b on the inner and outer walls respectively. The double-face rotatable electrode 5 is being made of a suitable conductive material including stainless steel, titanium and its alloy aluminum, or any other conductive material such as graphite.

The counter-electrode 11 is also situated within the cell 10. The material of the counter-electrode 11 is not limited in any particular way and may be selected from any material typically used in the art. Usable materials may include stainless steel, platinized titanium, lead, DSA-type coating or graphite, among others. In this embodiment, the counter-electrode 11 defines an outer annular channel 11c having inner and outer walls providing electrode portions 11a, 11b respectively opposing the electrode faces 5a, 5b of the cathode 5, although it will be appreciated that the electrode portions 5a, 5b could be separate. The annular channel 11c, which in this embodiment provides a double-faced cathode, thus serves to receive the cylindrical anode in a sandwich-like manner.

Thus, it will be seen that the internal double-face anode is placed around the double-face rotatable cathode to permit current flow through the solution. Each surface of the double-face rotatable cathode, both inner and outer sections, faces a surface of the double-face counter-anode. Preferably, the distance between both inner and outer faces is equal in order to achieve symmetry in the assembly, thus providing similar electrochemical conditions for both surfaces of the double-face rotatable electrode. Alternatively, the distance between each pair of electrode and counter-electrode can be adjusted in such a way that a different tangential speed is obtained.

The electrolytic cell 10 has an internal support 9 mounted on legs 42, which hold the internal section of the double-face counter-electrode 11 connected to its external sections 6 and 40. The support 9 can hold several double-face counter-electrodes, up to a number equal to the number of double-face rotatable electrodes. The support 9 also holds the vibrating device(s) 50 such as an ultrasonic generator as shown on FIG. 3, that can be retractable or not, as is described below. The legs are fixed such that the liquid is free to flow toward the cell outlet 22.

The electrolytic cell has a rim 2 that prevents liquid overflow. This rim, or border, can also be used to hold a ventilation dock, and an intlet tubing 20 (from FIG. 5) connected to the tank where the liquid to be treated comes from. A second rim below the previous one supports the meniscus-breaker 27 where the rotating shaft 1 of the double-face rotatable electrode 5 goes through.

The double-face rotatable electrode may be equipped with a cap 4 over and under the top section of the double-face rotatable electrode and a ring 7 at the bottom edge in order to mask areas on the electrode where the electrochemical reaction is not desired and/or to control the electrical field lines present within the electrolyte when a current is being applied between the double-face electrodes, in such a manner that the deposit becomes as much uniform as possible over the double-face rotatable electrode.

The double-face counter-electrode is placed in such a way that both electrode surfaces (anode and cathode) are facing one another in a parallel fashion. Preferably, the distance between both inner and outer faces is equal in order to achieve symmetry in the assembly, thus providing similar electrochemical conditions for both surfaces of the double-face rotatable electrode. Alternatively, the distance between each pair of electrode and counter-electrode can be adjusted in such a way that a different tangential speed is obtained. Hence, electrochemical properties that link this latter parameter to the reactor efficiency are respected.

The shape of each of the double-face electrodes 5 and 11 should all correspond with one another. For example, if the anode is cylindrical, the cathode will be a cylindrical and coaxial with the anode. In the described embodiment, suitable for recovering metals, the electrode 5 is the cathode and the electrode 11 is the anode. The roles can be reversed, for example, for the oxidation of organic material, in which case the electrode 11 would become the cathode and the electrode 5 the anode. In this latter case, the material shall be so selected that it will not dissolve, passivate, anodize or be destroyed by any chemical or electrochemical effect.

There is a relationship between the current density and the liquid flow rate that an electrolytic cell has to treat. The solution to be treated travels along both faces of the, for example, cylindrical section of the double-face rotatable electrode. The liquid flows between the inner and the outer surfaces of the double-face rotatable electrode and the double-face counter-electrode, preferably at the same flow rate. To go inside the double-face rotatable electrode, the liquid goes through opening or apertures on top of it. The opening can be as wide as possible, as long as there are some structural elements that hold the rotating cylindrical section to the central shaft. The opening can be made of several holes, curved or straight slots, of various lengths, diameters and/or geometries, all depending upon the number of double-face rotatable electrodes that are fixed altogether.

Depending upon the size of the cell cavity and the number of double-face rotatable electrodes used, the number and dimensions of the generators can be limited. For a particular electrolytic cell size, the limitation concerns the number of generators that can be placed within the internal holder. The number of ultrasonic generators that can be placed inside the holder is limited by the size and the number of the transducers placed inside the generators, thus, by the size of the generator housing itself.

FIG. 4 illustrates the geometric relationship between the rotatable electrode inner surface REIS and the ultrasonic generator size. With a simplified geometry of generators built with a width that is symmetrical to its depth, it is possible to calculate the number and/or the limiting dimension of the generators that can be placed inside the internal holder (that faces the inner surface of the double-face rotatable electrode), using the following equations:

L²+L²=4r_A²
2L²=4r_A²
2^1/2L=2r_A
Since r_A=r_C−Y, then
L=2(r_C−Y)/2^1/2

The “X” value on FIG. 4 represents the distance between the face of the generator that generates the ultrasounds and the internal counter-electrode radius. The “Y” value corresponds to the distance between the counter-electrode and the rotatable electrode inner surface (REIS). The “L” value is the actual width of the generator and “r_A” is the radius of the counter-electrode.

In order to determine the value X and consequently, the distance “D” between the generator and the REIS, the following equations are being used:

(r_A−X)²=r_A²−(L/2)²
r_A−X=(r_A²−(L/2)²)^1/2
X=r_A−(r_A²−(L/2)²)^1/2
D=Y+(r_A−(r_A²−(L/2)²)^1/2)

This latter value is important since the ultrasonic energy may become weaker as the distance between the generator and the REIS increases. The equation stands for a non-retractable generator. For a retractable generator, the equation shall take under consideration the length of the path that the generator travels before it touches the rotatable electrode. The minimum size of the holder diameter will be increased according to the width of the generator plus the length of the path. Therefore, the dimension of the REIS limits the overall size and number of generators.

Regardless of the target application or operation of the apparatus, the working electrode is the one that rotates. The rotatable electrode is the electrode where the target reaction occurs. The rotatable electrode can therefore be polarized cathodically or anodically.

The source 16 of direct electrical current that is mounted on the electrolytic cell frame 69 is connected between the anode and cathode via leads 26, 28 to allow current to flow. When the double-face rotatable electrode is polarized cathodically, metal ions in solution in the cavity migrate toward the cathode where the metal is deposited. Therefore, the cathode rotates to improve the mass transport and reduce the thickness of the diffusion layer. The cathode is rotated by means such as one rotating shaft which may be made of the same metal as the cathode, through which the electric current is fed and which rotate in two bearings formed in walls of the cell. Rotation of the cathode can be achieved by means of an electric motor (not shown on FIG. 1) through a speed controller (not shown). Although the double-face rotatable electrode 5 is shown to rotate counter-clockwise, the direction of rotation may also be clockwise.

When more than one double-face rotatable electrode 5 is used to treat a certain volume of solution, they can be connected in parallel or in series in order to achieve the desired electrochemical reaction or targeted chemical concentration level. Each double-face rotatable electrode 5 can operate under similar or different operation modes.

When the current flows between the anodically polarized electrode and the cathodically polarized electrode, the current is ideally distributed evenly on both sides of the facing electrodes. For instance, when the double-face rotatable electrode is made a cathode, the current density on both inside and outside surfaces is identical, as well as the anodic current density flowing within all anodes. When more than one double-face rotatable electrode are present, it is possible to electrically isolate one double-face rotatable electrode from one another and connect them to a separate power supply, in such a way that the desired current density, coupled to a desired rotating speed is obtained to electrowin a metal specifically or to oxidize an organic species specifically.

Furthermore, when more than one double-face rotatable disk or cylinder turn together, since they are fixed to the same rotating shaft, each disk or cylinder turns at a different tangential speed for a fixed rotating speed (rpm) since the diameter of each disk or cylinder is different. This property can be especially useful when two or more metals are to be electrowon within the same solution to be treated.

FIG. 3 shows where a device 50 such as an ultrasonic generator may be located. Such device can be retractable (dynamic) or static, being located inside the holder and/or within the double-face rotatable electrode.

When a static fashion is selected, the double-face rotatable electrode requires at least one device for each face.

When a dynamic arrangement is selected, at least one single device can be located toward the inner face only or the outer face only; the thickness of the double-face rotatable electrode can be thin enough to transmit the energetic effect of the vibrating device. The dynamic fashion involves a contact between the vibrating device and the rotatable electrode.

The device can be located inside a housing and when needed, a mechanism slides the device toward the electrode and touches it in order to transmit its energy upon it for the time period it takes to remove all the powdery, or flaky, deposit from the two faces of the double-face rotatable electrode.

The sliding mechanism can be any type of actuator, piston, spring, blade, cushion or other similar element that allows a mechanical movement in one or two axes, vertically or horizontally. Hence, the movement provides a retractable motion of the vibrating device that is being used only when needed, thus, the device does not impede the rotating motion of the rotatable electrode. More than one such device can be placed inside the electrochemical reactor, targeting the removal of the powder, or flakes, from both rotatable electrode surfaces.

There may be as many devices as the available space volume allows. The devices are preferably connected to one another, or alternatively they may be separate. During an electrowinning process, it is preferable to activate the device to remove the powder, or flakes, at the end of the extraction cycle, hence, synchronizing all energetic devices at once. The vibrating device can be located horizontally or vertically with respect to the double-face rotatable electrode. When placed vertically, in a retractable fashion especially, the generator shall touch the rotatable electrode between the ring 7 and the cap 4 for a direct metal-to-metal contact.

It should be understood that the term “ultrasonic” embraces sound vibrations capable of causing a cavitation effect sufficient to dislodge the powder or flakes from the electrode whether strictly beyond the audible range or not. A suitable range is 16 to 40 KHz, with 25 KHz being preferred.

The present invention employs the ultrasonic generator for the removal of deposit from the inner surface of the rotatable electrode, and in addition such a generator can be retractable, hence, physically touching the rotatable electrode when idle. Other type of vibrating devices can also be considered. When physical available spaces between electrodes prevent the insertion of ultrasonic generators, other coating removal methods shall be considered.

The opening of the cap 4 matches the aperture of the double-face rotatable electrode 5. Hence, there is no obstacle for the liquid to flow between the inner face of the double-face rotatable electrode and the internal section of the double-face counter-electrode 11. The form of the opening can be of various geometries such as circles, triangles, etc. The opening is such that depending upon its size, the mechanical constraints of fabrication are at minimum and that service security factors are met.

The bridge between the internal and external double-face counter-electrode sections may be masked and/or perforated; this is especially true if expanded mesh is used as a substrate for a coated material like DSA-type anodes.

One or more bridges can be fixed, as long as the form and, shape or dimensions of the bridges do not interfere with the liquid flow rate within the cell and/or entraps powder or flaky particles. An unlimited number of bridges can be fixed, depending upon the number of counter-electrodes being used or from mechanical considerations (machining, welding, fixing parts). Minimum number of bridges is being determined by the current intensity that travels across the section of the electrode bridge.

The internal holder may have a central hole that guides and secures the shaft position of the rotatable electrode when it turns at a tangential speed higher than 2.0 m/s.

The liquid flow rate across a double-face rotatable electrode may be at least twice the value of a single-face one, because of its double electrode surface area. On the other hand, if the liquid flow rate of a single-face rotatable electrode has to be maintained and a double-face rotatable electrode has to replace the single-face rotatable electrode, the size of the double-face rotatable electrode has to be reduced at least by half to keep the same electrode surface area. Hence, the size of the electrolytic cell is at least half the size of the original one.

FIG. 5 illustrates the electrolytic cell of FIG. 1 in an industrial application. Solution from storage tank 51 is pumped into the cell 10 for processing by means of pump 54. The cell is fitted with an ultrasonic level detector that controls the operation of pumps 24, 54 to maintain the liquid in the cell at the desired level.

The liquid flowing out of the base of the cell 10 flows into the filter housing 32 with the filter 52 for removing powder or flakes entrained in the liquid exiting the cell 10 from the filter housing outlet 71.

The filter 52 can include filter bags arranged such that the liquid flows through their walls and deposits the powder or flakes within the bags for subsequent removal. Any suitable filter technology can be employed for this purpose.

The busbar 26 is electrically connected to the double-face rotatable electrode 5 by means of a brush connector 62 in contact with the shaft 1. The shaft 1 is driven in rotation by a motor 64 and pulley system 66. The shaft rotates in bearings 68.

The electrolytic cell may preferably be equipped with a device 27 referred to as a “meniscus breaker” that eliminates the meniscus rising effect that becomes increasingly important when the tangential speed reaches about 1 m/sec and beyond. The device 27 has a “Chinese hat” shape, that is it is in the form of a disk with a central aperture 27a, the disk having upper and lower surfaces 27b tapering inwardly toward the central aperture 27a. This device prevents the meniscus from rising up the cell while permitting gases formed within the cell to escape.

In operation, a cathode and anode are put into the cell 10. The inlet port is connected to the storage tank holding solution to treat, and the solution is pumped via a pump from the tank into the cell cavity to fill the cavity and close the circuit between the cathode and anode. The vast majority of expected applications are in aqueous media, but in certain cases it could be in non-aqueous solutions or electrolytes (e.g. ethanol, benzoic acid, etc.). Preferably, enough solution is pumped into the cavity to completely submerge both the cathode and the anode. The solution is suitably pumped into the cell cavity. For electrolysis, the total metal concentration of the solution is from 30 to 3000 ppm (mg/L), preferably between 50 to 1000 ppm (mg/L).

The cell can be supplied with any form of electric current, such as direct current, alternating current, pulsed, periodic reverse pulse, etc. The anode and cathode of the electrolytic cell are connected to a rectifier which controls the application of electrical power to the anode and cathode.

The apparatus of this invention can be used to produce metal powders or flakes when the rotatable electrode is cathodically polarized. Powders or flakes may include metals or alloys in pure forms or metallic hydroxides or oxides. The definition of a powder or a flake shall be broad (grain size, shape, metal ceramic, metal, alloys etc.). The formation of a powder or a flake, instead of a compact film of metal or alloy, allows the use of ultrasounds to remove the metal from the cathode (as is described below). For maintenance purposes, gather material samples or for any other reasons, the apparatus is equipped with a rising structure 70 that elevates and lowers the entire rotatable mechanism.

Deposition of metal powder is accomplished by the rigid control of process parameters. The parameters to be controlled include: voltage, current density (pushed toward the limiting current) at the cathode, plating time, cathode rotation speed, electrolytic conditions through proper adjustments of pH, composition, temperature, conductivity, viscosity, concentration, and other parameters to ensure that the metal precipitates on the cathode (being reduced) as a powder or flakes. The voltage and current are selected by fixing the current level across the electrodes at an optimum level for the range of concentrations found in a particular application. The current level has been determined by experimentation. For instance, to produce zinc powder from an electrolyte that contains only 100 ppm of this metal, a disk of a diameter 0.5 meter (two times its width) will turn at 175 rpm with a current density of 60 mA/cm². If the metal concentration is different, electrowinning conditions will be different as well. If the sought metal is copper instead of zinc, present at the same concentration, speed of rotation and applied current will also be different. Electrowinning conditions are determined on a case by case basis.

As noted the metal powder or flakes produced at the cathode may be removed periodically by switching off the current and applying ultrasonic energy. The metal deposit removal period may vary from one electrolyte to another. Preferably, the deposit does not exceed 10% of the distance between anode and cathode. For example, the preferred gap between electrodes is 2 cm, thus, a 0.2 cm thick deposit will be removed by using the ultrasonic device. Powder or flakes removal conditions can vary from one case to another. For instance, powder can be removed as per determined numbers of coulombs or thickness, depending upon powder properties and electrolyte composition or reactor efficiency.

The ultrasonic generator 30 supplies an alternating-current energy at an excitation frequency in an ultrasonic range, for example, from 16 kHz to 40 kHz, 25 kHz being preferred. The ultrasonic electrical energy is converted into ultrasonic mechanical vibrations at a frequency corresponding to the excitation frequency. The mechanical vibrations produced by the transducers 50 are applied directly toward the cathode to cause cavitation at the surface of the cathode. This effect causes the metal powder to be removed from the electrode surface. For example, to remove a zinc powder deposit from the rotatable electrode, 2 to 4 minutes of intense ultrasounds at 25 kHz every 24 hours of deposition is sufficient to loosen the powder or flakes from the rotatable electrode Required ultrasonic energy to dislodge powder or flakes from a known electrode surface area is determined experimentally from solution to solution. For instance, with a copper powder produced at 160 mA/cm2 at a tangential speed of 10.88 m/s, it has been found that 1 watt/cm2 for 10 seconds is enough to remove the powder completely when the tangential speed during the removal has been reduced to 2.72 m/s. The loosened powder or flaky deposit is subsequently collected by the filter 52.

The metal becomes deposited as discrete particles at the cathode and is collected at the bottom of the cell, which is preferably conical or shaped as a funnel having a practical solid angle from 20 to 75 degrees, 45 degrees being preferred, or as a loosely adherent deposit which may be lifted from the cell and washed off the cathode. The metal powder or flakes accumulated at the bottom of the cavity can be removed periodically or continuously through the bottom outlet on removal of a plug or through a valve. A collecting bin is located at the bottom of the cell, and collects the powdered or flaky metal removed from the cathode. The powder or flakes can be collected either by recovering metals from industrial process waters (plating shops, smelters, mining, etc.) and by producing a specific powder from a defined electrolyte. Electrolyte composition can be such that metal powder or flakes can be made of a pure metal or alloys.

The apparatus of this invention may also be used to oxidize organic compounds when the double-face rotatable electrode is anodically polarized. The double-face rotatable electrode is capable of destroying organic contaminants from organic or inorganic electrolytes. If fouling of the double-face rotatable electrode occurs during such application, ultrasonic cleaning is performed using the ultrasonic generators. For example, phenol or creosols can be electrooxidized from 1500 ppb (μg/L) down to 20 ppb (μg/L) using a rotatable electrode and cathode made of stainless steel. The nature of the organic compounds to be destroyed, its concentration, and the material to use as electrodes such as anode and cathode are not limited. The double-face rotatable electrode is most efficient in destroying organic compounds found in low concentrations in organic or aqueous solutions.

For return of the solution once treated either by electrowinning or electrooxidation, the outlet port is connected to the original tank in a closed loop fashion or to another tank for further use or disposal of the solution. When the double-face rotatable electrode works in a way that the treated solution meets disposal rules and regulations (or concentrations required by a specific process EX: 3000 ppm to 1000 ppm of zinc for the chromate bath), the treated solution may go directly into the sewer. Otherwise, the treated solution may be connected to a conventional wastewater system (or returned to the process). The flow rate of the liquid being treated is such that the volume of the liquid that enters the inlet is the same than the one that comes out of the outlet.

It can be seen that the cell can be employed repeatedly with the same anode and cathode.

The method of the present invention may be illustrated in the following examples. These examples are provided for further illustrating the present invention, but are in no way to be taken as limiting.

EXAMPLE 1

If a single-face rotatable electrode is to be design to treat for instance 40 liters/minute of a copper solution at 150 mA/cm², the required surface of the cathode is 19635 cm²and its diameter is 100 cm; keeping the liquid flow rate but doubling the surface area reduces the current by half; since the current density cannot be changed, the surface area can only be kept at its original calculated value by dividing by half the diameter of the rotatable electrode. Hence, the overall size of the electrolytic cell is being reduced by half when the surface area of the rotatable electrode is doubled.

EXAMPLE 2

If two metals such as copper and nickel are to be electrowon at respectively 150 mA/cm²and 50 mA/cm²and tangential speeds of 10.88 and 5.44 m/s, two double-face rotatable electrode mechanically fixed together to the same shaft but electrically isolated from one each other will required a diameter difference of 2:1 and a total applied current difference of 3/2:1.

The invention is more adapted to recover metals from plating processes and mining processes, but can be applied to other types of industries such as metal finishing, metallurgy, pigments and chemical additives. The recovery of metals lowers the amount of generated waste when the apparatus is installed up-stream a wastewater system, thus, reducing the amount of sludge to dispose on land-fields.

Numerous modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

	Number	Date	Country
Parent	10941900	Sep 2004	US
Child	11362233	Feb 2006	US

Electrolytic cell for removal of material from a solution

Information

Publication Number

Date Filed

Date Published

Inventors

Original Assignees

CPC

US Classifications

International Classifications

Abstract

Description

Claims

CROSS-REFERENCE TO RELATED APPLICATION

Continuation in Parts (1)