Abstract:
A method for electrochemical modification of liquid streams employing an electrolytic cell which utilizes an oxidation site defined by an anode, an anode compartment comprising liquid electrolyte anolyte where oxidation is effected, a cathode compartment comprising liquid electrolyte catholyte where reduction is effected, a cathode comprising conducting cathode particulates forming a cathode particulates bed and a current feeder device in at least intermittent contact with said cathode particulates where the cathode particulates are in motion and the particulates motion is substantially independent of bulk electrolyte flow, a separator which confines the cathode particulates to the cathode compartment, constrains electrolyte flow through the cathode particulates bed and permits ionic conduction of current between the anode and cathode, a cathode particulates conveyance system that manipulates cathode particulates motion. A separate system circulates the liquid undergoing modification through the electrolytic cell. An unidirectional current driving system drives unidirectional electric current supported by the liquid streams from the anode through the anolyte and the separator and into the catholyte and to the cathode particulates and to the current feeder device during the contact between the cathode particulates and the current feeder device.

Description:
RELATED APPLICATIONS 
     This application is a divisional application of the U.S. patent application Ser. No. 11/623,658 filed on 16 Jan. 2007, now U.S. Pat. No. 7,967,967 which is incorporated here by reference in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
     Parts of this invention were conceptualized developed and reduced to practice using US government funding under National Institutes of Health (NIH) Small Business Innovation Research (SBIR) grant 1 R43 ES013622-01A1. The US government has certain rights in this invention. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to an apparatus and a method for modification of liquid streams which contain organic and/or inorganic impurities. More precisely, the invention is concerned with an electrolytic cell technology with potentials to achieve reduction of contaminants commonly found in liquid waste streams and economically feasible extraction of selected dissolved contaminants for commercial applications. 
     BACKGROUND OF THE INVENTION 
     Contamination of liquid streams with various organic and inorganic pollutants is a serious environmental problem affecting the quality of the global environment and represents a significant threat to human health and safety. Substantial heavy metal contamination of aquatic environments arises from commercial mining and metal extraction processes, surfaces modification and protection processes, or communal and industrial waste sites resulting from a variety of active or defunct industrial fabrication and manufacturing activities. Similarly, significant organic water pollutants, like aliphatic, aromatic, or halogenated hydrocarbons and phenols, are frequently associated with oil, gas, and coal exploration, extraction and refining, chemical industry, or large-scale farming and food processing. 
     In addition to potential for significant environmental damage, polluted liquid streams represent sources of desirable raw materials like heavy metals and metal oxides. For example, the Berkeley Mine Pit in Butte, Mont. alone represents an estimated 30 billion gallons of acid mine drainage which contains ˜180 ppm of copper along with other metals and thus could yield up to 22,000 tons of pure copper by use of a small treatment facility. 
     The prevailing method of removal of heavy metal ions from liquid solutions is chemical precipitation. This process is burdened by complexity, high cost, clear preference for extremely large facilities and high-volume operations, and little selectivity towards targeting and separating specific metallic pollutants. One fundamental disadvantage is the resulting byproduct of considerable volumes of heavy sludge which is toxic due to contamination with a mixture of toxic heavy metals. The sludge mandates further processing and costly long term disposal as a highly toxic waste. Many similar disadvantages burden alternative heavy ion removal methods that may incorporate: filtration, ion exchange, foam generation and separation, reverse osmosis, or combinations of listed processes. 
     Modification of polluted liquid streams can be accomplished efficiently using electrochemical processes. Electrochemical methods of reduction of metal ions or oxidation of organic pollutants do not suffer from described disadvantages of complexity, strong preference for large scale operations, or toxic byproducts. Advanced electrochemical methods like Moving Bed Electrode (MBE) electrolytic technology in various forms is relatively efficient even in the cases of comparatively low contaminant concentrations of about 1000 ppm. 
     Liquid stream modification using a Spouted Electrode Technology (SET) variant of the moving bed cell is well-known to prior art. U.S. Pat. No. 4,272,333 to Scot et al. discloses a method of moving bed electrolysis where motion of a particulate bed electrode; imposed by the circulation of electrolyte, prevents electrode particulates aggregation and maintains at least intermittent contacts between the moving particulates bed electrode and current feeder. Scot et al. report copper, zinc, cobalt, and manganese ions reduction from electrolytes with varying pH values. 
     U.S. Pat. No. 5,565,107 to Campen et al. discloses a process of electrochemical purification of “streams which contain organic and/or inorganic impurities”. The disclosed process utilizes a reactor with “a water-containing reaction zone which comprises providing a packed bed of activated carbon, applying an electrochemical potential across said packed bed and simultaneously feeding a reactant selected from the group consisting of ozone and hydrogen to said packed bed.” 
     Efficient electrowinning of zinc in an electrowinning cell using “moving” or “moving packed bed” SET electrode is disclosed in the U.S. Pat. No. 5,635,051 to Salas-Morales et al. from predominantly acidic electrolytes. Related U.S. Pat. No. 5,958,210 to Siu et al. discloses electrowinning of zinc in an SET electrowinning cell from alkaline electrolytes. Both patents also disclose an industrial scale eight-draft-tubes parallel electrowinning cell structure shown in side elevation in corresponding  FIG. 2 . 
     Spiegel et al. in the U.S. Pat. No. 6,298,996 report purification of metal and toxic organic compounds from polluted aqueous waste streams using “an advanced electrolytic cell technology employing a dynamic spouted electrode” SET device. Spiegel et al. also disclose a four-independent-cells device in which electrolyte is pumped in a parallel manner into the cells and returned to the reservoir. 
     A simplified schematic side view cross-section of a SET cell of prior art is given in  FIG. 1 . A typical SET cell consists of one or more anodes  10  coupled to one or more high surface area cathodes  20  in the form of spouted particulates bed, separated by a distance. Catholyte flow  30 , driven by an external catholyte pumping station  40 , is directed through the high surface cathode  20  to achieve vigorous particulates bed convection needed for high degree of electrode utilization. Unidirectional current is fed into the cell via anode current feed  50 (+) and out via cathode current feeder device  90  and cathode current feed  50 (−). The cell illustrated in the  FIG. 1 . is a simple planar configuration comprising cathode cell chamber  60  and anode cell chamber  70  separated by a separator (porous membrane)  80  which directs bulk electrolyte flow  30  while maintaining intimate electrochemical contact by ion transport (selective and/or non-selective) between the separated cathode  20  and anode  10 . Depending upon the state of control valve system  85  the cell can operate in a batch mode processing the fluid contained in the reservoir  97 , or in a flow-through mode modifying liquid streams delivered by external pipelines  95 . A mode of operation created by any combination of the flow-trough and batch modes can be achieved if desired in accordance with application specific requirements and circumstances. 
     An important common feature of the prior art SET devices and processes is the fact that actuation of the electrode bed is achieved by vigorous circulation of electrolytes generally achieved by strong pumping action of various external pumping systems. This feature, clearly motivated by simplicity of the mechanical design, is inherently suboptimal because the achievement of optimal liquid stream flow rate is sacrificed to the requirement for vigorous spouted bed mixing and circulation. The systems of the prior art frequently comprise relatively powerful pumping stations, like one denoted by the reference numeral  10  (corresponding reference numeral 31 in the U.S. Pat. Nos. 5,635,051 and 5,958,210). 
     In addition to higher capital cost and higher energy consumption, pumping stations scaled up to sufficiently mix and circulate particulates beds in SET cells additionally burden the overall efficiency of the liquid stream modification processes by limiting the reactor residence time of treated liquid stream volumes. The devices and methods in accordance with the present invention are designed to essentially decouple the fluid flow and motions of the SET. This novel characteristic of the devices designed in accordance with the present invention allows for independent optimization of the SET motions necessary for improved overall efficiency of the liquid stream modification processes and efficient electrolysis, prevention of particulates aggregation, and dendrite formation, and treated fluid circulation optimized for sufficient reactor resident time necessary for efficient liquid stream treatment even in cases of streams comprising sub 100 ppm concentrations of treatment target materials. 
     SUMMARY OF THE INVENTION 
     The present invention considers an apparatus and a method for electrochemical modification of liquid streams employing an electrolytic cell which comprises a cathode comprising conducting cathode particulates forming a cathode particulates bed, and a current feeder device in at least intermittent contact with the cathode particulates. The cathode particulates are in motion and the particulates motion is substantially independent of bulk electrolyte flow. A separator confines the cathode particulates to the cathode compartment, constrains bulk electrolyte flow through the particulate cathode bed and permits ionic conduction of current between the anode and cathode. A separate cathode particulates conveyance system drives and manipulates cathode particulates motion. 
     The method of present invention includes: circulating liquid stream undergoing modification through said electrolytic cell, activating cathode particulates conveyance system to form the moving cathode particulates bed immersed in the catholyte and transporting the cathode particles bed substantially independently from catholyte circulation, bringing cathode particulates bed in at least intermittent contact with the current feeder device, energizing the system for conducting unidirectional electric current to drive current supported by the liquid streams from the anode through the anolyte and the separator and into the catholyte and to the cathode particulates and to the current feeder device during the contact between the cathode particulates and the current feeder device and sustaining the achieved current conduction long enough to electrochemically react at least detectable quantities of targeted constituents of liquid streams undergoing modifications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 . is a schematic cross-sectional side view of a spouted electrolytic technology (SET) moving bed cell in accordance with prior art. 
         FIG. 2 . is a schematic cross-sectional side view of a moving bed electrolytic cell in accordance with the present invention. 
         FIG. 3 . is a schematic cross-sectional front view comparing the electrolyte flow and cathode particulates convection of an electrolytic cell in accordance with prior art and an electrolytic cell in accordance with the present invention. 
         FIG. 4 . is a schematic cross-sectional top view of a cylindrical electrolytic cell in accordance with an embodiment of the present invention. 
         FIG. 5 . is a schematic cross-sectional side view of an electrolytic cell with a mechanical cathode particulates conveyance system comprising a screw type conveyor in accordance with the preferred embodiment of the present invention. 
         FIG. 6 . is a schematic cross-sectional side view of an electrolytic cell with a mechanical cathode particulates conveyance system in accordance with a different embodiment of the present invention. 
         FIG. 7 . is a schematic cross-sectional side and top views of an cathode halfcell with a magnetic cathode particulates conveyance system in accordance with an additional embodiment of the present invention. 
         FIG. 8 . is a schematic cross-sectional side view of an electrolytic cell with systems for removal of products of electrochemical reactions in accordance with the present invention. 
         FIG. 9 . is a graphic representation of unidirectional current profiles schematic in accordance with the present invention. 
         FIG. 10 . is a graphic representation of copper concentration versus time during the batch operation of the proffered embodiment cell. 
     
    
    
     Like reference numerals identify like parts throughout the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     A simplified schematic side view cross-section of the electrolytic cell of in accordance with current invention is given in  FIG. 2 . The principle difference of the cell depicted in  FIG. 2  is the addition of a separate cathode particulates conveyance system  100  that manipulates cathode particulates motion substantially independently from the catholyte flow  30 . In contrast with the prior art pumping systems similar to one depicted in  FIG. 1 , the external catholyte pumping station  110  of current invention in  FIG. 2  needs only provide relatively slow catholyte flow  30  and can be readily adjusted and directed throughout the cathode particles bed for easy process optimization without significantly altering the particles bed motion. The pumping station  110  of current invention requires relatively lower pumping capacity resulting in smaller size, lower cost, and, most importantly, lower electric energy consumption and the ability to readily manipulate and control the catholyte flow rate and pattern with the moving cathode particles bed. 
     The principle difference in the catholyte flow  30  and cathode particulates convection  120  between the prior art cells with spouting tubes  300 (“draft tube 16” in U.S. Pat. Nos. 5,635,051 and 5,958,210) and the electrolytic cell with a separate cathode particulates conveyance system  100  of current invention is given schematically in  FIG. 3   a  and  FIG. 3   b . While the spouting tube  300  of a prior art cell induces vigorous catholyte flow  30 , causing circulation of excessive volumes of catholyte in order to indirectly produce sufficient cathode particulates convection  120 , the particulates conveyance system transfer momentum predominantly directly to the cathode particulates, contributing only marginally to the catholyte flow  30 . The opportunity for independent optimization of the catholyte flow  30  and catholyte ions resident time leads to the extension of the parameter space of efficient and economically feasible operations of cells in accordance with the present invention to the concentration ranges well below 100 ppm of target ion concentrations. 
     A variety of electroactive solutions comprising solvent, electrolyte, and possibly supporting electrolytes meeting chemical and electrochemical potential window stability criteria will work with the present technology. The anolyte and catholyte can be the same or different depending on the targeted application. Specifically, initial demonstrative work for reducing the technology to practice employed a single shared electrolyte for anolyte and catholyte. A synthetic acid mine drainage solution was prepared using water as the solvent as this represents the most common solvent. 
     The ionically conducting species of the electrolyte were provided by added ionizing compounds which dissolved in the solvent. While a plethora of suitably soluble, conductive, and electrochemically stable compounds exist, initial work utilized copper sulfate pentahydrate. Here the sulfate anion was stable in the electrochemical potential window of interest and the cupric ion provided the target species for electrochemical reduction at the cathode. Water oxidation to generate oxygen was targeted at the anode as the complimentary oxidation reaction to the targeted reduction process. 
     Several supporting electrolytes were also added to better mimic the composition of acid mine drainage. Sulfuric acid was added to lower the solution pH while sodium sulfate was added to increase the sulfate concentration to levels typical of actual acid mine drainage. As the sulfate and sodium are inactive in the potential window of interest, they act simply as supporting electrolytes. Similarly, while protons can be reduced to hydrogen at the cathode, except under mass transfer limitations, cupric ion reduction will dominate and the dissolved protons will effectively serve as supporting electrolyte ions. 
     An embodiment of electrolytic cells in accordance with the present invention possessing cylindrical symmetry is shown in  FIG. 4 . The cells in  FIG. 4  comprise anode  10  and cathode  20  in the form of coaxial cylinders. In  FIG. 4   a  cylindrical spouted bed cathode  20  encompasses the cathode particulates conveyance system  100 , while both are encompassed by the separator  80  and cylindrical anode  10 . In the highest cylindrical symmetry configuration, the cathode particulates conveyance system  100 , the cathode current feeder device  90 , the spouted bed cathode  20 , the separator  90 , and the anode  10  comprise a system of cylindrical tubes filled by the electrolyte. 
     In  FIG. 4   b  the cylindrical anode  10  in the form of conductive rod is encompassed by the separator  80  and spouted bed cathode  20  sharing a common vertical axis of cylindrical symmetry. The cathode particulates conveyance system  100  is distributed throughout the cathode particles bed in order to provide substantially uniform actuation of the cathode bed particulates. It is obvious to the practitioners of the art of electrochemistry that systems with somewhat different geometries that preserve similar topology as the cells given schematically in  FIG. 2  and  FIG. 4  represent an apparatus in accordance with the present invention and will function in the manner in accordance with the claims of the present application. 
     It is frequently desirable, for an efficient and consistent function of an electrolytic cell, that anode  10  does not lose electrode material to the oxidation reaction on anode surfaces inseparable from the proper function of any electrolytic cell. Anodes which substantially preserve their original shape and relationship with the other components of electrolytic cells are known in the art to be geometrically stable. 
     Many geometrically stable anodes comprising platinized titanium, niobium coated copper, and oxide coated conductive substrate or combination of this and other refractory materials are known to the practitioners. The anodes can incorporate relatively smooth active surfaces, or porous surfaces that benefit from the additional surface area introduced by the added pores. 
     In addition, the anode materials comprising lead and lead alloys can be consider geometrically stabile over the electrochemical-process-relevant periods of time in spite the fact that the anode surfaces exhibit very gradual corrosion. The corrosion process of the lead comprising anode surfaces is especially slow and relatively uniform in processes related to electrochemical modifications of liquid streams containing the target materials at dilute concentrations. For the purpose of the present invention the anodes comprising lead and lead alloys are included in the set of geometrically stabile anodes. 
     Commercially available anodes like the Eltech Systems Corporation EC-600 dimensionally stable anode (DSA) comprised of tantalum doped iridium oxide coatings on titanium substrates and optimized for oxygen generation were successfully tested during the development of methods and apparatus of the present invention. 
     Separators  80  perform confinement of the cathode particulates to the cathode compartment and constrain of electrolyte flow through the cathode particulates bed. The separator  80  is in form of membrane, diaphragm, or other permeable mechanical barrier material that permits ionic conduction of current between the anode and the cathode. The preferred separator materials do not participate in electrochemical reactions of the cell, but the listed separator functions can be in principle performed by separators constructed from materials that support the ionic current conduction by ion-exchange reactions on the separator surfaces. The cells with particulates motion substantially independent of bulk electrolyte flow, utilizing ion-exchange separator membranes are recognized as specific embodiments of the current invention. 
     Separators  80  with surfaces that define planes are depicted in  FIG. 2 , while separators  80  with cylindrically-symmetric surfaces that define tubes are depicted in  FIG. 4 . Because of the influence of gravity on the cathode particulates convection, the preferred orientation of separator surfaces that define the plane is with the plane parallel to the vertical axis, while the preferred orientation of the cylindrically-symmetric separator surfaces is with the cylindrical axis parallel to the vertical axis. It is recognized that any non-horizontal orientation, with the separator surfaces planes and/or cylindrical axis form non-zero angles with horizontal planes, will function in accordance with the present invention. 
     The preferred cathode particulates conveyance system  100  that manipulates cathode particulates motion is a mechanical system in the general form of a screw type conveyor  500 (“Archimedes screw”) shown schematically in  FIG. 5 . The cathode particulates convection is achieved by a direct action on the cathode particulates by a helicoidal surface that rotates in preferred sense  510  around the axis  520  powered by an external driver. The diameter of the system, the helicoil pitch and flute to flute separation, rotational velocity, and the driving power should be designed for an operation optimal for the particular application. The preferred speed of rotation for the test device used for the development of this invention is in the range from 10 RPM to 500 RPM. 
     A different embodiment of the cathode particulates conveyance system  100  is shown in cross-sections in  FIG. 6 . where the mechanical cathode particulates conveyance system comprises a moving bucket  620  type conveyor  600 . The moving bucket  620  type conveyor  600  comprises a belt  650  guided and actuated to circulate by the actuators  640 . The belt carries buckets  620  positioned periodically along the belt. The circulation of the belt and the direct action of the buckets upon the cathode particulates causes desired cathode particulates convection  120 . Positioning of the particulates guide  630  in the proximity of the locus of separation of cathode particulates from the conveyer  600  facilitates the efficiency of the cathode particle convection. 
     A different variation on the moving bucket type mechanical conveyer  600  is a moving belt  650  type conveyer where bucket  620  are omitted and the momentum is predominantly transferred to the cathode particulates by frictional forces between the belt  650  and the particulates. 
     In the embodiment when at least a fraction of the cathode particulates comprise at least a portion of their mass in the form of ferromagnetic material, significant interaction between the cathode particulates and the cathode particulates conveyance system  100  can be achieved when at least one permanent magnet is attached to the conveyer belt  650  in such manner that significant portion of the magnetic field penetrates the cathode chamber  60 . In this embodiment, the particles guide  630  needs to be positioned in the proximity of the conveyer at a preferable clearance smaller than the particulates&#39; diameter in order to achieve efficient separation of magnetized particulates from the proximal permanent magnet. 
     A variation of this embodiment where the conveyer belt material comprises permanently magnetized portions to produce the cathode chamber penetrating magnetic field is recognized to be in the scope of the present invention. It is also recognized that many mechanical and magnetic cathode particulates conveyance systems can operate with synergy. Combinations of mechanical cathode particulates conveyance subsystems and magnetic cathode particulates conveyance systems can be desirable to drive sufficient cathode particulates conveyance either in modular liquid streams modification operations or as parts and subsystems of integrated electrolytic cells. 
     A different embodiment utilizing magnetic interaction between the cathode particulates and the cathode particulates conveyance system uses traveling magnetic fields. Sources magnetic fields comprise coils with loops of electric conductors each arranged to generate magnetic fields symmetric with respect to prospective horizontal planes of symmetry when loops of electrical conductors are energized by at least one external source of electric current. This external source of electric current flowing through electromagnets&#39; loops of electric conductors is generally independent and separate from the system for conducting unidirectional electric current supported by the liquid streams from the anode through the anolyte and the separator and into the catholyte and to the cathode particulates and to the current feeder device during the contact between the cathode particulates and the current feeder device. 
     A schematic rendering of the embodiment shown in  FIG. 7  utilizes spouting tube  300  and a set of electromagnets  700  with coils  710 , ferromagnetic core  720 , and ferromagnetic pole pieces  730 . When energized by the external source of electric current modulated in time to create magnetic pulses traveling with a velocity  740  with non-zero vertical component. The magnetic pulse is formed by combined time-variable magnetic fields produced by the coils. The fields are characterized by a volume of high magnetic induction B 750 that continuously transfers toward the upper end of the cathode compartment  60  for the duration of the magnetic pulse. 
     The cathode particulates are chosen to have at least partially conductive surfaces necessary to achieve at least intermittent contact between particulates and the current feeder device. When the traveling magnetic inductance  750  intersects the surfaces of the proximal cathode particulates it induces eddy currents in the particulates that interacts repulsively with the magnetic inductance  750 . Consequently, an upward traveling pulse of the magnetic inductance  750  acts as a piston transferring generally upward momentum to the cathode particulates. 
     The cathode particulates support unidirectional electric current flowing through the electrolytic cell. Consequently, the cathode particulates must comprise electrically conductive or semiconductive materials consisting elements, metals, alloys, compounds, ceramics, organic polymers, and inorganic polymers or combinations thereof. The electrolytic cell in accordance with the present invention utilizes plurality of particulates interacting with exposed surfaces of the current feeder device  90 . This allows for broad ranges of particulate sizes ranging generally from 0.1 mm to 10 mm of length in the characteristic dimension (possible characteristic dimensions include but are not limited to radius, diameter, ellipsoid axis, cylindrical radius and axis). 
     The resistivity of the current carrying component of particulates suitable for practical utility can range from about 1 nano ohm centimeters to about 20,000 nano ohm centimeters. The cathode particulates can comprise common metals such as copper, aluminum, lead, nickel, iron, mild steel, stainless steel, zinc, titanium, silver, gold, platinum, palladium, tin, tungsten, carbon, and its mixtures and combinations. Less common materials for the cathode particles such as conducting polymers, ceramics, semiconductors, and combinations of suitable substrate materials exhibiting appropriate conductivity would also work with the present invention. 
     Products of electrochemical reactions associated with the proper function of an electrolytic cell may accumulate in the cell and interfere with long term cell functionality. Also, products of electrochemical reactions may be of commercial interest as produced or represent raw materials for further processing. The controlled accumulation of products of electrochemical reactions can occur as an attachment and deposition on the cathode particulates, a sedimented material concentrated at lower parts of the cell chambers, or as incremental rise of concentration of materials dissolved in the electrolyte or the presence of suspended product particulates. 
       FIG. 8  depicts several devices for controlled removal of products of electrochemical reactions from the cell. Products of electrochemical reactions associated to the cathode particulates can be separated by extracting at least a portion of cathode particulates using separating pipeline  800  controlled by removal valve system  810 . The replacement of the cathode particulates is achieved via replacement valve system  820  from the reservoir of fresh cathode particulates  830 . 
     The separating pipeline  800  can be used to extract and separate sedimented products from the electrolyte and cathode particulates. The products of electrochemical reactions dissolved in the electrolyte can be removed using external pipeline  95  from the reservoir  97 . 
     Processes of controlled removal of products of electrochemical reactions can be performed continuously during the operation of the electrolytic cell as customary in the art of electrochemical disinfection or pollution removal, or using batch process as customary in art of electrowinning of metals. Both modes of operation are in accordance with the present invention. 
     The direct current of constant intensity during the conduction like the current profile  900  graphed in  FIG. 9  is frequently the preferred choice of current profile because of stability and simplicity of operation and associated equipment. Other unidirectional current sources producing periodic current profiles like profiles  920  and  930  also can be used in a device in accordance with this invention. The current profiles with time dependences like  920  and  930  may provide advantages for specific targeted applications such as selective product or product morphology control. Aperiodic unidirectional currents like profile  910  in  FIG. 9  are frequently associated with programmable current sources operating under control of digital controllers. 
     DESCRIPTION OF PREFERRED EMBODIMENT 
     A brief overview of the proffered embodiment of the technology is included here. Over the course of relevant research a number of additional embodiments were conceived and explored. It is noted that this represents demonstration of technology function in the particular application and consequently is not optimal for many possible applications of the present invention. 
     A bench-scale version of the electrochemical apparatus was constructed and demonstrated. Here a simplified two-chamber cell is described although stacked cell operation works also. Mirror image anode and cathode cell bodies were constructed from polycarbonate sheets to which acrylic strips were welded to create the recesses of the cell chambers (Colorado Plastic Products Inc.). The cell chambers were sized to create an 8 inch by 10 inch active zone. The anode chamber active zone was inch deep while the cathode chamber active zone was 1.5 inches deep and could contain about 2000 mL of cathode particles bed. When the anode and cathode cell bodies were clamped together while facing each other and sandwiching sealing foam strips and the separator membrane, a completed electrolytic cell was formed. Electrolyte inlet and outlet ports were created as needed and were liquid tight electrical feedthroughs using common polypropylene compression fittings (Cole Parmer). Two 4 inch×14 inch EC-600 (Eltech Systems Corporation) anodes were mounted side by side in the anode chamber to create the anode. Spacers were added on both anode sides to ensure free electrolyte access to the anode. The anodes extended out the top of the cell allowing simple dry clamp type electrical contacts to be utilized. Two 4 inch×10 inch×0.0625 inch 316 stainless steel plates (McMaster Carr) were mounted at the back of the cathode chamber to act as current distributors which define the active area of the cell. Two ¼ inch dia. 316 stainless steel rods were mounted to each plate and passed through liquid tight feedthroughs to provide external electrical contact points suitable for simple dry clamp type electrical contacts to be utilized. Cut 302/304 stainless steel wire (2 mm as cut, Pellets LLC) were used as the cathode particles bed. Standard 1 inch dia.×13 inch Wood augers (Hickory Tools, Home Depot) were mounted in the cathode chamber to effect cathode particles bed churning. The augers were coated with polyurethane to prevent corrosion in the synthetic acid mine drainage used for the electrowinning tests. Extenders were added to the augers so that they protruded out the top of the cell and gear and belt drive so that they could be easily rotated by a single external motor. A small variable speed DC gearmotor (2709K16, McMaster Carr) and a variable DC power supply (Extech 382213, Grainger) were used to rotate the augers and control the rotation speed (operated in controlled voltage mode at 24 volts). A microporous ultra high weight polyethylene membrane extending beyond the edges of the cell chambers (Gray Daramic-0.0097 inch thick, Polypore International Inc.) was used to separate of the anode and cathode chambers when they were clamped together. The edges of the anode and cathode chamber were lined with a continuous layer of ⅛ inch thick closed cell polyvinyl chloride foam (McMaster Carr) to create a gasket type seal when the cell bodies were clamped together. 
     The electrochemical cell was operated in a batch mode utilizing a recirculating system for the electrolytes. For this demonstrative work the electrolyte was shared so that both the anolyte and catholyte circulation were taken from and returned to the same single reservoir. A 10 L volume of the standard solution was utilized for the batch operation. The majority of the electrolyte was circulated through the cathode chamber using a larger peristaltic pump (Model 7533-80 with a 7036-30 pump head, Barnant). A small portion of the electrolyte leaked into the anolyte chamber and was recirculated using simple gravity feed. Similarly a portion of the electrolyte was circulated through a 1 cm path length flow-through spectroscopic cell using a small peristaltic pump (model 900-1445, Barnant) to allow near real-time monitoring of the solution copper concentration. Filtering was used to remove any powder product generated which would impair the spectroscopic measurement. The pumps were powered and their speed controlled using variable DC power supplies (Extech 382213, Grainger) operating in the controlled voltage mode at 24 volts unless otherwise noted. All electrolyte circulation plumbing was either silicone, neoprene, polypropylene, or PVC while reservoirs were Nalgene®—all of which are stable to the solution employed. The electrolyte temperature was measured using a Teflon coated thermocouple (CASS-18G-12-PFA, Omega) while the pH was measured using a gel filled double junction pH electrode (PHE-1411, Omega) and a signal pre-amp (PHTX-21, Omega). Selected operation and performance parameters were monitored and digitally recorded each 10 seconds on a laptop computer using a analog to digital conversion data acquisition unit with multiple channels (HP 34970A data acquisition unit with a 34901A multiplexer module) and appropriate software (HP 34970A Data Logger 3). The copper concentration within the electrolyte was measured spectroscopically at 840 nm using a Spectrophotometer 20+ (22348-108, VWR. The analog output of the spectrophotometer was recorded and converted to copper concentration using a calibration curve prepared using copper standards prepared with a 0.1 M sodium sulfate and 0.05 M sulfuric acid background. The electrolytic cell was energized with a high current variable DC power supply (Model XFR12-100, Xantrex) operated in the controlled current mode. The cell was operated at a current of 20 A. 
     The technology was successfully demonstrated for the improved electrowinning of copper from synthetic acid mine drainage. The synthetic acid mine drainage comprised an aqueous solution to which compounds were added to provide the proper pH, target electroactive species, and background ions to explore the chemistry of interest. Specifically the standard solution employed was prepared by adding 249.5 g of copper sulfate pentahydrate, 142.1 g of sodium sulfate, and 500 mL of 1.0 M sulfuric acid to 9.5 L of water. This generated a synthetic acid mine drainage solution containing roughly 2000 ppm of cupric ions, 0.182 M sulfate and 0.1 M sodium ions and provided 0.1 M of protons. Although the nominal pH of 0.1 M sulfuric acid is pH=1.0, buffering due to the excess sulfate in the solution yields a pH of ˜1.6. 
     A stock solution with initial concentration slightly lower than the desired 2000 ppm copper starting point, and roughly 6.5 L of electrolyte was used. The salient operating parameters are tabulated in Table 1 while the observed performance is summarized in  FIG. 10 . The slope of the line in  FIG. 10  indicates the copper removal rate. This data illustrates that the apparatus works consistently down to very low concentrations, lower than 100 ppm. 
     
       
         
               
             
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Electrolytic Apparatus Operating Conditions 
               
             
          
           
               
                   
                 Parameter 
                 Value(s) 
               
               
                   
                   
               
               
                   
                 Cell Power 
                 Current: 20 Amp 
               
               
                   
                   
                 Potential: 3.4-3.7 V 
               
               
                   
                 Catholyte Pump 
                 Current: 1.3 Amp 
               
               
                   
                   
                 Potential: 24 V 
               
               
                   
                 Auger Drive Unit 
                 Current: 0.45 Amp 
               
               
                   
                   
                 Potential: 24 V 
               
               
                   
                 Copper Monitor Pump 
                 Current: 0.9 Amp 
               
               
                   
                   
                 Potential: 7 V 
               
               
                   
                 Elcctrolyte Volume 
                 6.5 L 
               
               
                   
                 Initial Copper Concentration 
                 1609 ppm 
               
               
                   
                 Final Copper Concentration 
                 38 ppm 
               
               
                   
                 Treatment Time 
                 3600 sec 
               
             
          
           
               
                   
                 Electrolyte pH 
                 Initial: 1.6 
                 Final: 1.5 
               
               
                   
                 Electrolyte Temperature 
                 Initial: 21° C. 
                 Final: 25° C.