US3755114A

US3755114A - Decreasing the metallic content of liquids by an electrochemical technique

Info

Publication number: US3755114A
Application number: US00133923A
Authority: US
Inventors: M Tarjanyi; M Strier
Original assignee: Hooker Chemical Corp
Current assignee: Occidental Chemical Corp
Priority date: 1971-04-14
Filing date: 1971-04-14
Publication date: 1973-08-28
Anticipated expiration: 1990-08-28

Abstract

A method for decreasing the metallic content of a solution which comprises passing an electric current through a solution containing metallic material, which solution is contained as the electrolyte in a cell, said cell having at least one positive and one negative electrode, between which the current is passed, and wherein the electrolyte also contains a bed of particles, distributed therein, such that the porosity of the bed is from about 40 to 80%, porosity being defined as

The electrolysis of the electrolyte is continued until the desired reduction in the metallic content thereof is obtained.

Description

United States Patent [1 91 Tarjanyi et al.

[ DECREASING THE METALLIC CONTENT OF LIQUIDS BY AN ELECTROCHEMICAL TECHNIQUE [75] Inventors: Michael Tarjanyi, North Tonawanda; Murray P. Strier, Amherst, both of NY.

[73] Assignee: Hooker Chemical Corporation,

Niagara Falls, N.Y.

[22] Filed: Apr. 14, 1971 [21] Appl. No.: 133,923

[52] US. Cl 204/114, 204/149, 204/D1G. 3 [51] Int. Cl C02b l/82, C02c 5/12 [58] Field of Search 204/86, 97, 91, 149, 204/152, 180 P, 130, 131, 110, 106, 114, 52, 55, 105

[56] References Cited UNlTED STATES PATENTS 543,673 7/1895 Crawford 204/110 X 698,292 4/1902 Kendall 204/1 10 3,457,152 7/1969 Maloney, Jr. et al 204/131 3,616,275 10/1971 Schneider 204/91 X 3,616,276 lO/l97l Schneider 204/91 X 3,616,356 lO/l971 Roy 204/152 FOREIGN PATENTS OR APPLICATIONS 1,500,269 9/1967 France 204/DIG. 1O

1,584,158 12/1969 France 204/D1G. 10

OTHER PUBLICATIONS Le Goff et a1., Applications of Fluidized Beds in Elec- 1 1 Aug. 28, 1973 trochem", lndust. & Engin. Chem, Vol. 61. No. 10, October 1969, pp. 8-17.

Thangappan et a1., Copper Electrforming in Fluidized Bed," Metal Finishing, December 1971, pp. 43-49.

Primary Examiner-John I-l. Mack Assistant Examiner-A. C. Prescott A!torney--Peter F. Casella, Donald C. Studley, Richard P. Mueller and James F. Mudd [57] ABSTRACT volume of particles volume of cell wherein the 100 particles are distributed The electrolysis of the electrolyte is continued until the desired reduction in the metallic content thereof is obtained.

13 Claims, 1 Drawing Figure DECREASING THE METALLIC CONTENT OF LIQUIDS BY AN ELECTROCHEMICAL TECHNIQUE This invention relates to a process for treating solutions which contain metallic materials and more particularly it relates to an improved electrochemical process for decreasing the metalliccontent of a solution.

in various industries, solutions are utilized which contain metallic materials, and the disposal of these poses a significant pollution problem. For example, in the metal plating industries, the plating baths contain copper, zinc and similar metals. Additionally, the effluent from numerous processes, such as chlor-alkali processes, frequently contain mercury or lead/Although heretofore, various chemical techniques have been proposed for the treatment of such metallic containing effluents, these have generally been either inefficient or too expensive or have resulted in the formation of products whose disposal presents as many pollution problems as the metallic materials themselves. Accordingly, there has recently been a great deal of effort expended in the development of new and different processes for the treatment of these metallic containing effluent solutions.

In Belgium patent 739,684, for example, there is described an electrochemical technique wherein a semiconductive bed of solid particles is used to oxidize various substances to non-toxic forms. Another process, utilizing an electrochemical technique, is described in New Scientist June 26, 1969 Page 706. In these and similar processes which have recently been proposed, the electrochemical systems utilized have been found to be both inefficient, and/or uneconomical and require frequent changing of the bedof particles which is utilized. Accordingly, these systems have not met with any appreciable commercial utilization.

It is, therefore, an object of the present invention to provide an improved process for treating solutions containing metallic materials so as to reduce the metallic content of such solutions.

A further object of the present invention is to provide an improved process for reducing the metallic content of a solution by means of an efficient and economical electrochemical treatment.

These and other objects will become apparent to those skilled in the art from the description of the invention which follows,

Pursuant to the above objects, the present invention includes a process for treating a solution containing metallic materials to decrease the metallic content thereof which comprises passing an electric current through the solution which contains the metallic materials, which solution is contained as the electrolyte in solutions may contain varying amounts of the metallic a cell, said cell having at least one positive and one negative electrode, between which the current is passed, and wherein the electrolyte also contains a bed of particles, distributed therein such that the porosity of the bed is from about 40 to 80 percent, porosity defined as solutions containing metallic materials in this manner, it has been found to be possible to reduce the concenvolume of particles volume of cell wherein the X100 particles are distributed cadmium and the like, but also these metals in ionic form, such as Pb, Hg, Hg* and the like. These may be present as various compounds orcomplexes, both organic and inorganic. Additinally, since it is believed that the removal of the metallic materials from the solutions treated by the present process involves reduction, the materials going through various electrochemical reductions and resulting ultimately in the metal itself which is deposited out at the cathode, the solutions treated may also contain various reduced states of the metallic materials as well.

The solutions containing metallic materials which are to be treated in accordance with the present method may come from various sources. Thus, for example, they may be effluent streams from industrial plants which have relatively high concentrations of the metallic materials, as have been indicated heretofore. Additionally, however, the solutions treated may have a relatively low concentration of metallic materials, e.g. one part per million or less, which solutions may come from municipal or other water treating plants. Thus, the method of the present invention may be used not only to reduce the relatively high content of metallic materials in industrial and similar waste streams, but, additionally, may also be used to effect substantially complete removal of relatively small amounts of metallic materials, as a final purification step in the treatment of water intended for human consumption. The solutions treated may also contain various other components, in addition to the metallic materials and may include mixed effluent streams from several different industrial processes. Thus, for example, the solutions may contain, in addition to the metallic materials, various chloride materials, such as chlorinated organics, chlorine, HCl, hypochlorites, hypochlorous acid, as well as, sulfates, fluorides, silicofluorides, phosphates, cyanides, and the like, as are typically present in plating bath and chlor-alkali process effluents. Such solutions are, however, merely exemplary of the effluent solutions which may be treated.

The pH of the solution to be treated may vary over a wide range, being either acidic, neutral or basic, pH values of from about 1 to 14 having been found to be suitable. Desirably, where lead is the metal being removed, the pH is from about 4 to 7, with a pH of from about 6 to 13 being preferred when the metal is mercury. Depending upon the makeup of the metalcontaining solution which is to be treated, adjustment of the pH may be done by the addition of various support electrolytes to the metallic solution. Suitable support electrolytes which may be used'are aqueous solutions of borates, ammonia, sodium chloride, sulfuric acid, calcium chloride, sodium cyanide, chloroacetates, sodium hydroxide, sodium bicarbonate, hydrochloric acid, and the like.

The temperature of the electrolyte, i.e., the solution being treated, may also vary over a wide range, the only criteria being that at the temperature used, the electrolyte remain a liquid. Thus, temperatures within the range of about to 100 Centigrade have been found, generally, to be suitable. For economy in operation, however, it has frequently been found to be preferred to utilize these solutions at ambient temperatures. Similarly, the present process is desirably carried out at atmospheric pressure although either sub or super atmospheric pressures may be employed, if desired. It has been found in some instances, however, that the use of elevated temperatures, e.g., 6075C, may be desirable in effecting a more rapid reduction in the metallic content, depending upon the particular support electrolyte, pH range, type and concentration of metal which are used.

As has been noted hereinabove, the electrolyte, i.e., the solution being treated, is contained, during treat ment, in a suitable electrolytic cell and contains a bed of particles which are distributed in the electrolyte in the cell, such that the porosity of the bed ranges from about 40 to 80 percent, porosity being defined as:

By determining the density of the particles used and weighing them, the term volume of the particles in the above porosity formula may be replaced by the value for the weight of the particles divided by the true density of the particles. The particle density can be measured by filling a one liter container with particles, the weight of which is known. Then, an electrolyte is added to the container to fill the voids between the particles, the amount of electrolyte needed being measured as it is added. The true density of the particles, in grams per cm", is the weight of the particles in grams divided by the true volume of the particles in cm. The true volume of the particles is the bulk volume minus the volume of the voids in the particle bed, the latter being the volume of the electrolyte which is added to the one liter container. Thus, the true volume of the particles in this instance would be 1,000 cubic centimeters minus the volume of the voids, i.e., the volume of electrolyte added to the container.

It will, of course, be apparent that the porosity of the bed of particles maintained in the electrolyte which is being treated in the cell may be varied and that with different types of particles, under the same operating conditions or with similar particles under different operating conditions, changes in the bed porosity will take place. Thus, the true density of the particle will vary depending upon the porosity of the particles themselves, e.g., graphite as compared to glass beads, with similar variations in density being effected by the electrolyte itself because of the differences in the surface tension of various electrolyte solutions. Additionally, since the particles of the bed are generally dispersed or distributed by the flow of the the electrolyte through the cell,

volume of particles volume of cell wherein the X 100 particles are distributed If the same quantity of particles were then distributed by the flow of the electrolyte, such that the volume of the bed now reached two liters, using its same formula, the porosity of the bed is now volume of particles in cc.

1000 cc. )Xloo v0lume of particles in cc.

Clearly, in the second instance, the porosity of the bed has, increased. As has been noted above, the porosity of the bed of particles dispersed in the electrolyte may range from about 40 to percent. In many instances, a preferred range for the bed porosity is from about 55 to 75 percent with a specifically preferred range being from about 60 percent to 70 percent.

The particles employed to form the porous bed in the present process typically are solid, particulate materials that may be conductive, non-conductive or semiconductive. By conductive it is meant that the material of which the particles are made will normally be considered an electron-conducting material. Where they particles are conductive, they may have a metallic surface, either by virtue of the particles themselves being metallic or by being made of non-conductive material on which a metallic surface has been deposited. Typical of the metals which may be employed are the metals of Group VIII of the Periodic Table, such as mthenium and platinum, as well as other conductive elements, such as graphite, copper, silver, zinc, and the like. Additionally, the conductive particles may be electrically conductive metal compounds, such as ferrophosphorus, the carbides, borides or nitrides of various metals such as tantalum, titanium, and zirconium, or they may be various electrically conductive metaloxides, such as lead dioxide, ruthenium dioxide, and the like. Where the particles are non-conductive, they may be made of various materials, such as glass, Teflon coated glass, polystyrene spheres, sand, various plastic spheres and chips, and the like. Exemplary of various semiconductive materials of which the particles may be made are fly ash, oxidized ferrophos, zirconia, alumina, conductive glasses, and the like.

The particles used desirably range in size from about 5 to 5,000 microns, with particle sizes of from about 50 to 2,000 microns being preferred. In many instances, a particularly preferred range of particle sizes has been found to be from about to 800 microns. Although it is not essential to the successful operation of the process of the present invention that all of the particles in the porous bed distributed in the electrolyte have the same size, for the most preferred operation of the process, it has been found to be desirable if the range of particle sizes is maintained as small as is practical.

It has further been found that the density of the particles used should be such, that in conjunction with the size and shape of the particles, it will provide the proper balance between the drag force created by the electrolyte motion and the buoyancy and gravitational forces required to achieve particle dispersion or distribution at the desired bed porosity. Thus, where the particle dispersion is established against or in opposition to the buoyancy force, the particle densities typically may range from about 0.1 (less than the density of the electrolyte) to about 1.0 grams per cc. Where the particle dispersion is achieved against or in opposition to the gravitational force, the particle densities typically may range from about 1.1 to grams per cc and preferably from about 1.5 to 3.5 grams per cc. The most preferred operating conditions have been found to be when the particles are dispersed throughout the electrolyte, within the cell, during the movement of the electrolyte and when the particles are more dense than the electrolyte. r

The electrolytic cell may be of any suitable material and configuration which will permit electrolysis of the metallic containing solution to effect a reduction in its metal content and which will permit retention of the porous bed of particles in the electrolyte, within the cell. Exemplary of suitable materials of construction which may be used for the cell are various plastics, such as the polyacrylates, polymethacrylates, polytetrahaloethylenes, polypropylenes, and the like, rubber, as well as materials conventionally used in the construction of chlor-alkali cells such as concretes. Additionally, the cells may be made of metal, such as iron or steel. In such instances, electrically insulating coatings should be provided on the metal surfaces in the cell interior or electrical insulation provided between the metal of the cell and the electrodes.

The size of the electrolytic cell may also vary widely, depending upon the nature andquantity of the metallic containing solution which is to be treated. Thus, where appreciable quantities are involved, as in the treatment I of industrial wastes or as a part of a water purification system, the cell may be relatively large and include a multiplicity of treating zones, whereas for the treatment of water for individual home use, appreciably smaller units may be utilized, similar in size to conventional soft-water treating units. Additionally, the cell may be of a suitable size so as'to be portable, for use at camp sites, and the like. Typically, the cell will have a suitable inlet and outlet means for introducing and removing the solution to be treated, means for retaining the porous bed of particles dispersed in the electrolyte within the cell, means for supporting at least one positive and one negative electrode in contact with the electrolyte in which the porous bed of particles is distributed and, if desired, a diaphragm disposed-between the positive and negative electrodes.

The electrolytic cell has within it at least one positive and one negative electrode. These are disposed within the cell so as to be in contact with the electrolyte in which is distributed the porous bed of particulate material. These electrodes may be formed of various materials, as are known to those in the art. Typical of suitable electrode materials which may be used are graphite; noble metals and their alloys, such as platnium, iridium, ruthenium dioxide, and the like, both as such and as deposits on a base metal such as titanium, tantalum, and the like; conductive compounds such as lead dioxide, manganese dioxide, and the like; metals, such as cobalt, nickel, copper, tungsten bronzes, and the like; andrefractory metal compounds, such as the nitrides and borides of tantalum, titanium, zirconium, and the like.

6 The positive and negative electrodes will be positioned withinthe electrolytic cell so as to be separated sufficiently to permit the flow of the electrolyte throughthe celland the movement of the particle within the electrolyte. It will be appreciated, of course,

that as the separation between the electrodes is increased the voltage necessary to effect the desired reduction in the metallic impurity content of the electrolyte will also increase. Accordingly, .inm'any instances it has been found to be desirable if the separation between the positive and negative electrode in the cell is from about 0.1 to 5.0 centimeters, with a separation of from about 0.3 to about 3.0 centimeters being preferred and a separation of from about 0.5 to 2.0 centimeters being particularly preferred. Although particu lar reference has been made to an electrolytic cell having one positive and one negative electrode, it will be appreciated that the cell may be provided with a plurality of electrode pairs, in much the same manner that such a plurality of electrodes are normally utilized in various commercial, large scale electrolytic continuous processes.

It will, of course, be appreciated that in addition to the amount of electrode separation, the flow of the electrolyte through the electrode area will also be dependent upon the size and density of the particles which are distributed in the electrolyte to form the porous bed. Typically, this flow, which is described in terms of the linear flow velocity of the electrolyte, will be within the range of from about 0.1 to 1,000 centimeters per second. A preferred electrolyte flow velocity has been found to be from about 0.5 to 100 centimeters per second with a flow velocity of fromabout l to 10 centimeters" per. second being specifically preferred. Under these operating conditions, current densities within the range of about 1.010 500 milliamps per square centimeter have been found to be typical of those which are utilized.

To further illustrate the present invention, reference is made to the accompanying drawing which is a schematic diagram of a system incorporating the electrolytic cell of the invention.

As shown in the drawing, this system includes an electrolytic cell (1) having a fluid inlet (6) and a fluid outlet (9). Within the cell (1) are disposed a positive electrode(2) and a negative electrode (3). Although these electrodes are shown as being separated by a diaphragm (4), in many instances, the use of such a diaphram has not been found to be necessary. Where such a diaphragm is used, e-.g., to control the particles in the anolyte or catholyte compartments, the diaphragm may be formed of various materials, such as-a Teflon coated screen, Fiberglas, asbestos,-porous ceramics and the like. .An electrolyte (8) is provided within the cell, which electrolyte is a solution containing metallic material. A source (5) of this electrolyte is provided, from which the electrolyte may be introduced into the cell through the inlet (6 Distributed within the electrolyte (8) are; particles ,(7), which particles are distributed randomly through the electrolyte, the nature of the distribution depending upon the electrolyte flow, size and lyte sources, cell inlets and outlets may be provided so that the introduction of electrolyte into the anode and cathode compartments of the cell may be separately controlled. The cell is further provided with screens (10) and (11), screen (11) serving to support the particles in the cell and screen (10) serving to maintain the particles within the cell and prevent their discharge through the outlet (9). As the distance between the screens (10) and (11) is changed, the volume of that portion of the cell in which the particles are distributed will likewise vary, thus, varying the porosity of the bed of particles which is maintained within the cell.

While it is not intended to restrict the operability of the present invention by any theory of operation, the use of particles in an electrolytic cell in the manner which has been described, has been found to have the following advantages. in a conventional electrolytic cell, such as a chlor-alkali cell, the amount of electrode surface at which the electrolytic reaction is conducted is dependent upon the surface area of the electrodes. Typically, this surface are will be about 1.3 times l cm. With a typical cell volume of about 305 times cm, the resulting ratio of the electrode area per cell volume is about 0.037 cmlcm". By the use of conductive particles in an electrolytic reaction, as in the process of the present invention, there is a significant increase in the surface area at which the electrolytic reaction may occur. in Chemical and Process Engineering, February i968, page 93, there is described a cell containing an electrolyte having particles therein. It was calculated that the electrolyte containing the particles has an electrode area of about i [,500 cm and that the volume of the cell is about 153 cm. This gives a ratio of electrode area to cell volume of about 75 cmlcm which, clearly, is significantly higher than that of an electrolytic cell having conventional electrodes.

Additionally, it is believed that by the use of the particles in the electrochemical reaction, a mass transport phenomena may be taking place. In this, the contact of metallic materials with the particles and electrodes is dependent upon a number of variables, including the electrolyte flow rate, the particles size, density and type, and the concentration of the metallic material. From a consideration of all of the above variables, it has been found that the one condition which has an effect upon all of them is the porosity of the bed of particles and that this porosity, as defined hereinabove, is the determining factor that makes possible a commercially feasible operation.

In order that those skilled in the art may better understand the present invention and the manner in which it may be practiced, the following specific examples are given. in these examples, unless otherwise indicated, temperatures are in degrees centigrade and parts and percent are by weight. It is to be appreciated, however, that these examples are merely exemplary of the present invention and the manner in which it may be practiced and are not to be taken as a limitation thereof. I

in the following Examples, 1.5 liters of aqueous 0. lNCaCl,, 0.1N NaCl or 0.1N HCl solutions, containing about 500 parts per million lead were used. The solution was circulated through apparatus similar to that shown in the drawing, having an electrode crosssectional area of 450 cm, for l5 minutes to allow for equilibration. A 50 milliliter sample was then with-- drawn and analyzed for pH and lead content. The analyses showed substantially no reduction from theoriginal lead content of about 500 parts per million, indicating little if any absorption on the particles or electrodes in the cell. The solution was then electrolyzed under the conditions indicated in the following table. The electrolyte was then drained from the apparatus and again analyzed for pH and lead content. All lead analy; ses were done by atomic absorption technique. In these Examples, there was no diaphragm used in the cell, the particles were glass beads, having a particles size of 500 microns, the anode was graphite, the cathode was stainless steel and the separationbetween the anode and cathode was 0.7 centimeters. The electrolyte flow rate was adjusted during the electrolysis so as to have a porosity of the bed of glass bead particles of 67 percent. The current density used in all cases was 15 milliamps/cm'. Using this procedure, the following results were obtained:

peated using similar apparatus having an electrode cross-sectional area of cm. From 700-800 milliliters of the electrolyte solution was circulated through the cell. The cathode used was nickel, the anode graphite and the separation between the electrodes was 0.4 cm. The electrolyte flow was adjusted so that the porosity of the bed of the glass bead particles was 65 percent. Using this procedure, the following results were obtained:

Time of Initial Final elec- Pb Pb Ex- Electrolyte Initial Final trolysls, content, content, ample solution p pH minutes p.p.m p.p.m.

5 0.1 N 0801: 5. 10 7.11 60 470 0. 2 6 0.1 N NaCh 5. 05 1. 68 570 9. 6 7 0.1N E01 1.20 0.93 180 5(1) 3.8

The procedure of Examples 5-7 was repeated with the exception that the electrolyte used contained mercury, rather than lead. in Examples 8, 9 and 10, the electrolyte solution was the filtrate obtained by filtering an industrial mercury containing waste effluent slurry through a coarse porosity sintered glass crucible. in the remaining Examples, the electrolyte was obtained by mixing 50 grams of the slurry with 1 liter of a 1.3N Na0Cl solution and filtering the resulting solution through No. 42 Whatman filter paper, the resulting filtrate being used as the electrolyte. The solid resulting from the filtration of the original effluent slurry was found by X-ray analysis to contain Fe, Ca, K, S, and Cl; minor amounts of Ba and Hg; and traces of Ni and Si. The filtrate which was obtained was found to contain, in addition to Hg, Cl and K and traces of Zn and S. Analysis of the filtrate for Hg was done by a modified Dow procedure using a Beckman Mercury Vapor Meter.

The conditions under which these solutions were electrolyzed were as follows:

Example 8 Nickel anode; graphite cathode; 1.0 cm electrode separation; glass bead bed porosity 67 percent; current density 20 milliamps/cm Example 9 Same as Example 8 except the anode was platinum coated titanium and the current density was 50 milliamps/cm Example 10 Graphite anode and cathode; 0.4 cm electrode separation glass bead bed porosity 65 percent; current density milliamps/cm for first 240 minutes and 50 milliamps/cm for last 60 minutes Example 11 Same as Example 10 except current density was 50 milliamps/cm for first 120 minutes and 100 milliamps/cm for last 120 minutes.

Example 12 Same as Example 10 except current density was 50 milliamps/cm for first 60 minutes and 100 milliamps/cm for last 180 minutes and HCl was added to electrolyte to obtain indicated initial pH.

Using this procedure the following results were obtained:

Initial Hg content,

p.p.m.

Time 01 electrolysis, minutes Final Hg content, p.p.m.

I EXAMPLE 13 crons. The anode used was graphite, the cathode nickel, the area of each electrode was 100 cm and the electrode separation was 1.35 cm. After electrolysis for 52 minutes, at a current density of 15 milliamps/cm and a voltage within the range of 2-3 volts, the Cu content was 5 ppm, the solution pH was 13.0 and the cyanide content was 05 ppm. Additionally, the cathode was found to have a characteristic copper coating.

EXAMPLE 14 The procedure of Example 13 was repeated with the exception that the solution treated was the effluent from a cyanide zinc electroplating bath having a pH of 12.54, a cyanide content of 200 ppm and a zinc ion content of 141 ppm. The graphite particles were of a size of 595-840 microns, the flow velocity was 2.0 cm/sec to produce a bed porosity of percent and the electrode separation was 0.4 cm. After electrolysis for 1 10 minutes at 15 milliamps/cm and a voltage of 2-2.8 volts, the pH was 12.8, the zinc ion content was 33 ppm and the cyanide content 0.5 ppm. Additionally, there was a characteristic zinc coating on the cathode.

EXAMPLE 15 The procedure of Example l-4 was repeated with the exception that 3.0 liters of a copper cyanide solution containing 1,353 ppm Cu and 2,000 ppm CN was used. Periodically a 50 ml sample of the solution was withdrawn and analyzed for copper using atomic absorption technique. Using this procedure, the following results were obtained:

Electrolysis Time Cut Concentration (Minutes) (ppm) pH Start 1353 12.8 60 559 12.57 93 12.50 21 12.40 11 12.35 1.8 12.25 210 1.5 12.15 240 1.0 12.20

The procedure of Examples l-4 was repeated using a zinc cyanide plating bath which had been diluted to 16,000 ppm CN, 11,260 ppm zinc and 0.44 N Na0H and a copper cyanide solution which had 16,000 ppm CN", 12,000 ppm copper and 0.5 NKOH. These solutions were electrolyzcd using a current density of 30 milliamps/cm and the following results were obtained:

While there have been described various embodiments of the invention, the compositions and methods described are not intended to be understood as limiting the scope of the invention, as it is realized that changes therewithin are possible and it is further intended that each element recited in any of the following claims is intended to be understood as referring to all equivalent elements for accomplishing substantially the same result in substantially the same or equivalent manner, it

being intended to cover the invention broadly in whatever form its principle may be utilized.

What is claimed is:

l. A method for decreasing the metallic content of a solution which comprises passing an electric current through a solution containing metallic materials selected from mercury, lead cadmium and zinc, which solution is contained as tlie electrolyte in a cell, said cell having at least one positive and one negative electrode between which the current is passed, and wherein the electrolyte also contains a bed of dispersed particles, distributed therein such that the porosity of the bed is from about 40 to 80 percent, porosity being defined as:

volume of particles cathodically reducing the metallic materials to elemental metal until the metallic content is reduced to a desirable level, plating the metal on the cathode, and removing said solution of reduced metallic content from said cell.

2. The method as claimed in claim 1 wherein the electrolyte solution is an aqueous solution.

3. The method as claimed in claim 2 wherein the initial concentration of the metallic material in the electrolyte solution is from about 1 part per million to 10 percent by weight.

4. The method as claimed in claim 1 wherein the particles distributed in the electrolyte solution have a density which is greater than that of the electrolyte.

5. The method as claimed in claim 1 wherein the particles distributed in the electrolyte solution are conductive particles.

6. The method as claimed in claim 5 wherein the particles are graphite.

7. The method as claimed in claim 1 wherein the particles are distributed within the electrolyte by flowing the electrolyte through the electrolytic cell in a direction opposed to the gravitational forces.

8. The method as claimed in claim 7 wherein the electrolyte flow velocity through the cell is from about 0.1 to 1,000 centimeters per second.

9. The method as claimed in claim 1 wherein metal in the electrolyte is lead and the electrolyte solution has a pH of from about 4 to 7.

10. The method as claimed in claim 1 wherein the metal in the electrolyte is mercury and the electrolyte solution has a pH of from about 6 to 13.

11. The method as claimed in claim 1 wherein the porosity of the bed of particles is from about 55 to 75 percent.

12. The method as claimed in claim 11 wherein the porosity of the bed of particles is from about 60 to percent.

13. The method as claimed in claim 1 wherein the separation between the positive and negative electrode within the cell is from about 0.1 to 5.0 centimeters.

Claims

2. The method as claimed in claim 1 wherein the electrolyte solution is an aqueous solution.
3. The method as claimed in claim 2 wherein the initial concentration of the metallic material in the electrolyte solution is from about 1 part per million to 10 percent by weight.
4. The method as claimed in claim 1 wherein the particles distributed in the electrolyte solution have a density which is greater than that of the electrolyte.
5. The method as claimed in claim 1 wherein the particles distributed in the electrolyte solution are conductive particles.
6. The method as claimed in claim 5 wherein the particles are graphite.
7. The method as claimed in claim 1 wherein the particles are distributed within the electrolyte by flowing the electrolyte through the electrolytic cell in a direction opposed to the gravitational forces.
8. The method as claimed in claim 7 wherein the electrolyte flow velocity through the cell is from about 0.1 to 1,000 centimeters per second.
9. The method as claimed in claim 1 wherein metal in the electrolyte is lead and the eLectrolyte solution has a pH of from about 4 to 7.
10. The method as claimed in claim 1 wherein the metal in the electrolyte is mercury and the electrolyte solution has a pH of from about 6 to 13.
11. The method as claimed in claim 1 wherein the porosity of the bed of particles is from about 55 to 75 percent.
12. The method as claimed in claim 11 wherein the porosity of the bed of particles is from about 60 to 70 percent.
13. The method as claimed in claim 1 wherein the separation between the positive and negative electrode within the cell is from about 0.1 to 5.0 centimeters.