CA1107235A - Treatment of aqueous dispersions - Google Patents
Treatment of aqueous dispersionsInfo
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- CA1107235A CA1107235A CA304,195A CA304195A CA1107235A CA 1107235 A CA1107235 A CA 1107235A CA 304195 A CA304195 A CA 304195A CA 1107235 A CA1107235 A CA 1107235A
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Abstract
ABSTRACT OF THE DISCLOSURE
The zonal concentration of solids in an aqueous dispersion is increased through the use of electro-endosmosis. In the aqueous dispersion, a first cathode means, an anode means, spaced from the first cathode means, a second cathode means, intermediate the first cathode means and the anode means, and means for establishing a direct current electrical potential between the first and second cathode means and the anode means, is provided wherein electroendosmosis may be used to increase the density of solids within aqueous dispersions covering areas greater than twelve meters in diameter.
The zonal concentration of solids in an aqueous dispersion is increased through the use of electro-endosmosis. In the aqueous dispersion, a first cathode means, an anode means, spaced from the first cathode means, a second cathode means, intermediate the first cathode means and the anode means, and means for establishing a direct current electrical potential between the first and second cathode means and the anode means, is provided wherein electroendosmosis may be used to increase the density of solids within aqueous dispersions covering areas greater than twelve meters in diameter.
Description
TREATMENT OF AQUEOUS DISPERSIONS
BACKGROUND OF THE INVENTION
This invention relates to a process for in-creasing the rate of zonal concentration and final density of solids in an aqueous dispersion of such solids and to apparatus for the practice of such process.
In many industrial processes, aqueous dis-persions of solids are obtained as waste streams. For example, washing of ores, scrubbing of gas streams, precipitation of impurities, sewage disposal, etc., often produce waste streams referred to industrially as tailings, mud, etc. Such waste streams often cannot be conveniently disposed of due to materials handling difficulties or ecological or safety considerations.
Therefore, it is a common practice to retain ~uch wastes in large ponds, holding tanks, or other con-tainment means. To the extent the solids in the re-tained dispersions can be zonally concentrated by settling, 10tation, etc., to provide a relatively solids-free aqueous phase which can be sewered or otherwise disposed of following any necessary filtra-tion or purification procedures, space is provided in the containment means for retention of additional waste. However, in the case of many aqueous disper-sions, zonal concentration of the solids by settling takes place at an extremely low rate, if at all. Thus, periodic construction of additional containment means .,, ~,~
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BACKGROUND OF THE INVENTION
This invention relates to a process for in-creasing the rate of zonal concentration and final density of solids in an aqueous dispersion of such solids and to apparatus for the practice of such process.
In many industrial processes, aqueous dis-persions of solids are obtained as waste streams. For example, washing of ores, scrubbing of gas streams, precipitation of impurities, sewage disposal, etc., often produce waste streams referred to industrially as tailings, mud, etc. Such waste streams often cannot be conveniently disposed of due to materials handling difficulties or ecological or safety considerations.
Therefore, it is a common practice to retain ~uch wastes in large ponds, holding tanks, or other con-tainment means. To the extent the solids in the re-tained dispersions can be zonally concentrated by settling, 10tation, etc., to provide a relatively solids-free aqueous phase which can be sewered or otherwise disposed of following any necessary filtra-tion or purification procedures, space is provided in the containment means for retention of additional waste. However, in the case of many aqueous disper-sions, zonal concentration of the solids by settling takes place at an extremely low rate, if at all. Thus, periodic construction of additional containment means .,, ~,~
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-2- C-17-21-3192A
at great difficulty and expense becomes necessary.
Numerous attempts have been made at increasing the rate of zonal concentration of solids in such dispersions.
However, the use of conventional means such as filtra-tion, settling aids, or the like, is frequently physically impossible or prohibitively expensive. It has been found that laboratory techniques for effect-ing zonal concentration of solids in aqueous disper-sions often cannot be successfully applied to large scale industrial waste retention systems. For example, it is known that applying an electrical potential between electrodes placed in an aqueous dispersion will cause migration of water towards the cathode to effect zonal concentration of solids via electro-endosmosis. However, in large systems where the anode and cathode must, as a practical matter, be separated by relatively great distances, large and non-linear voltage drops occur which prevent effective applica-tion of the electroendosmotic technique.
It is thus well recognized that practical means for promoting zonal concentration of solids in aqueous dispersions have long been desired by those skilled in the art.
SUMMARY OF THE INVENTION
.
This invention provides a process for in-creasing the rate of zonal concentration and final density of solids in aqueous dispersions containing such solids and apparatus for use in the process.
The process is suitable for use in large scale dis-persion retentlon systems and involves positioning electrodes in critically spaced relationships as hereinafter defined in aqueous dispersions of the type discussed and applying a direct current electrical potential between the electrodes to effect zonal conc2ntration of solids via electroendosmosis.
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_3_ C-17-21-3192A
DESCRIPTION OF THE PREFE~RED E~ODIMENTS
The process and apparatus of the present invention apply for use on aqueous dispersions con-tained in large (greater than 100 square meter area) impoundments, in which the dispersed particles are characterized by having an electrical charge in re-lation to ground zero. The greatest practical advan-tages of the invention are obtained with systems wherein zonal concentration of solids by natural set-tling does not rapidly occur to a high density.
In the practice of the present invention, electrodes are positioned within the aqueous disper-sion as hereinafter described and a direct current electric potential is applied to effect zonal con-centration of the solids via electroendosmosis. The dispersed particles within the hereinafter described aqueous dispersions may be characterized as having a negative electrical charge in relation to ground zero.
The critical spacing of electrodes required in the present invention is described by reference to the drawings in which Figure I is a schematic top view of an electrode arrangement as employed in previously known electroendosmosis techniques in which a first cathode means 1 and an anode means 3 are disposed in an aqueous dispersion of solids 4. Figure II is a schematic top view of an electrode arrangement used in the practice of the present invention wherein a first cathode means 1, a second cathode means 2, and an anode means 3 are disposed in an aqueous dispersion of solids 4. Figure III is a schematic top view of a more preferred arrangement of electrodes according to the present invention wherein a first cathode means 1, a plurality of second cathode means 2, and a plurality of anode means 3 are disposed in an aqueous dispersion of solids 4.
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It has long been recongnized that an elec-trode arrangement as shown in Figure I can be used to effect migra~ion of water in an aqueous dispersion towards a cathode means 1 so long as the cathode means 1 and anode means 3 are separated by relatively small distance. However, when the distance between the cathode means 1 and anode means 3 is greater than a fewmeters,a large voltage drop occurs in close proximity to the cathode and anodes and a smaller drop per linear meter more distant from the electrodes which prevents effective application of the electro-endosmosis principal. In general, electroendosmosis techniques cannot be practically employed for increas-ing the rate of zonal concentrations in aqueous dis-persions in systems wherein the voltage drop over any5~/O of the linear distance between the cathode and anode is greater than 30% of the total voltage drop between the cathode and anode. Where the 5% rule is violated, large percentages of energy are wasted in the form of heat and the electroendosmosis system ceases to function properly.
In accordance with the present invention, it is unexpectedly found that proper positioning of the second cathode means 2 between the first cathode means 1 and anode means 3 as shown in Figure II will prevent the occurrence of unduly large voltage drops across small linear distances and will allow electro-endosmosis techniques to be used in large impoundments.
In accordance with the present invention, the first cathode means 1 and the anode means 3 are separated by a distance sufficiently great that if the second cathode means 2 were relocated so that the first and second cathode means 1 and 2 were closely adjacent and the same distance from the anode means 3, and if a direct current electric potential sufficient to effect preferential migration of water in the dis-persion toward the cathodes were imposed, the voltage . - :
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drop over any 5% of the linear distance between the cathodes and anodes would be greater than 30V/o of the total voltage drop between the cathodes and anodes.
If the first cathode means 1 is located closer to the anode means 3, the advantage provided by the present in~ention is substantially reduced or eliminated. In the treatment of most aqueous dispersions, the maxi-mum advantages of this invention are obtai.ned wherein the first cathode means 1 is separated from the anode means 3 by a distance of at least about six meters.
In the practice of the present invention, the second cathode means 2 will be positioned closer to the first cathode means 1 than to the anode means 3 and will be disposed on a plane perpendicularly trans-versing the plane between the first cathode means 1and the anode means 3. The anode means 3 and second cathode means 2 each are comprised of a plurality of electrodes which are preferably positioned within the impoundment 4 in the form of two concentric circles about the first cathode means 1. The plurality of anodes comprising the anode means 3 is positioned such that each anode is equally spaced from its adjacent anodes. Similarly, the plurality of cathodes compris-ing the second cathode means 2 is positioned such that each cathode is equally spaced from its adjacent cathodes. The electrodes will be arranged such that a line drawn from the central cathode 1 through a cathode of the second cathode means 2 will bisect the angle formed by lines drawn between the central cathode 1 and alternate pairs of ad;acent anodes of the anode means 3.
Thus, in Figure III the angles 0 are all equal. Each electrode is anchored in its preferred position by a large weight which is attached by a nonconducting nylon rope. The relative spacing of the first cathode means 1, the second cathode means 2, and the anode means 3 will be such that when the potential chosen to effect elec-troendosmotic migration of water towards the first and .lr~723S
-6- C-17-21~3192A
second cathode means 1 and 2 is applied that no 5% of the linear distance between the first and second cathode means 1 and 2 and anode means 3 will exhibit a voltage drop greater than 30% of the total voltage drop between the first cathode means 1 and anode means 3. The opti-mum positioning of the electrodes, particularly the second cathode means 2, for particular aqueous disper-sions and applied electrical potentials can be readily determined by routine testing.
The maximum distance by which the anode means
at great difficulty and expense becomes necessary.
Numerous attempts have been made at increasing the rate of zonal concentration of solids in such dispersions.
However, the use of conventional means such as filtra-tion, settling aids, or the like, is frequently physically impossible or prohibitively expensive. It has been found that laboratory techniques for effect-ing zonal concentration of solids in aqueous disper-sions often cannot be successfully applied to large scale industrial waste retention systems. For example, it is known that applying an electrical potential between electrodes placed in an aqueous dispersion will cause migration of water towards the cathode to effect zonal concentration of solids via electro-endosmosis. However, in large systems where the anode and cathode must, as a practical matter, be separated by relatively great distances, large and non-linear voltage drops occur which prevent effective applica-tion of the electroendosmotic technique.
It is thus well recognized that practical means for promoting zonal concentration of solids in aqueous dispersions have long been desired by those skilled in the art.
SUMMARY OF THE INVENTION
.
This invention provides a process for in-creasing the rate of zonal concentration and final density of solids in aqueous dispersions containing such solids and apparatus for use in the process.
The process is suitable for use in large scale dis-persion retentlon systems and involves positioning electrodes in critically spaced relationships as hereinafter defined in aqueous dispersions of the type discussed and applying a direct current electrical potential between the electrodes to effect zonal conc2ntration of solids via electroendosmosis.
:
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_3_ C-17-21-3192A
DESCRIPTION OF THE PREFE~RED E~ODIMENTS
The process and apparatus of the present invention apply for use on aqueous dispersions con-tained in large (greater than 100 square meter area) impoundments, in which the dispersed particles are characterized by having an electrical charge in re-lation to ground zero. The greatest practical advan-tages of the invention are obtained with systems wherein zonal concentration of solids by natural set-tling does not rapidly occur to a high density.
In the practice of the present invention, electrodes are positioned within the aqueous disper-sion as hereinafter described and a direct current electric potential is applied to effect zonal con-centration of the solids via electroendosmosis. The dispersed particles within the hereinafter described aqueous dispersions may be characterized as having a negative electrical charge in relation to ground zero.
The critical spacing of electrodes required in the present invention is described by reference to the drawings in which Figure I is a schematic top view of an electrode arrangement as employed in previously known electroendosmosis techniques in which a first cathode means 1 and an anode means 3 are disposed in an aqueous dispersion of solids 4. Figure II is a schematic top view of an electrode arrangement used in the practice of the present invention wherein a first cathode means 1, a second cathode means 2, and an anode means 3 are disposed in an aqueous dispersion of solids 4. Figure III is a schematic top view of a more preferred arrangement of electrodes according to the present invention wherein a first cathode means 1, a plurality of second cathode means 2, and a plurality of anode means 3 are disposed in an aqueous dispersion of solids 4.
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It has long been recongnized that an elec-trode arrangement as shown in Figure I can be used to effect migra~ion of water in an aqueous dispersion towards a cathode means 1 so long as the cathode means 1 and anode means 3 are separated by relatively small distance. However, when the distance between the cathode means 1 and anode means 3 is greater than a fewmeters,a large voltage drop occurs in close proximity to the cathode and anodes and a smaller drop per linear meter more distant from the electrodes which prevents effective application of the electro-endosmosis principal. In general, electroendosmosis techniques cannot be practically employed for increas-ing the rate of zonal concentrations in aqueous dis-persions in systems wherein the voltage drop over any5~/O of the linear distance between the cathode and anode is greater than 30% of the total voltage drop between the cathode and anode. Where the 5% rule is violated, large percentages of energy are wasted in the form of heat and the electroendosmosis system ceases to function properly.
In accordance with the present invention, it is unexpectedly found that proper positioning of the second cathode means 2 between the first cathode means 1 and anode means 3 as shown in Figure II will prevent the occurrence of unduly large voltage drops across small linear distances and will allow electro-endosmosis techniques to be used in large impoundments.
In accordance with the present invention, the first cathode means 1 and the anode means 3 are separated by a distance sufficiently great that if the second cathode means 2 were relocated so that the first and second cathode means 1 and 2 were closely adjacent and the same distance from the anode means 3, and if a direct current electric potential sufficient to effect preferential migration of water in the dis-persion toward the cathodes were imposed, the voltage . - :
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drop over any 5% of the linear distance between the cathodes and anodes would be greater than 30V/o of the total voltage drop between the cathodes and anodes.
If the first cathode means 1 is located closer to the anode means 3, the advantage provided by the present in~ention is substantially reduced or eliminated. In the treatment of most aqueous dispersions, the maxi-mum advantages of this invention are obtai.ned wherein the first cathode means 1 is separated from the anode means 3 by a distance of at least about six meters.
In the practice of the present invention, the second cathode means 2 will be positioned closer to the first cathode means 1 than to the anode means 3 and will be disposed on a plane perpendicularly trans-versing the plane between the first cathode means 1and the anode means 3. The anode means 3 and second cathode means 2 each are comprised of a plurality of electrodes which are preferably positioned within the impoundment 4 in the form of two concentric circles about the first cathode means 1. The plurality of anodes comprising the anode means 3 is positioned such that each anode is equally spaced from its adjacent anodes. Similarly, the plurality of cathodes compris-ing the second cathode means 2 is positioned such that each cathode is equally spaced from its adjacent cathodes. The electrodes will be arranged such that a line drawn from the central cathode 1 through a cathode of the second cathode means 2 will bisect the angle formed by lines drawn between the central cathode 1 and alternate pairs of ad;acent anodes of the anode means 3.
Thus, in Figure III the angles 0 are all equal. Each electrode is anchored in its preferred position by a large weight which is attached by a nonconducting nylon rope. The relative spacing of the first cathode means 1, the second cathode means 2, and the anode means 3 will be such that when the potential chosen to effect elec-troendosmotic migration of water towards the first and .lr~723S
-6- C-17-21~3192A
second cathode means 1 and 2 is applied that no 5% of the linear distance between the first and second cathode means 1 and 2 and anode means 3 will exhibit a voltage drop greater than 30% of the total voltage drop between the first cathode means 1 and anode means 3. The opti-mum positioning of the electrodes, particularly the second cathode means 2, for particular aqueous disper-sions and applied electrical potentials can be readily determined by routine testing.
The maximum distance by which the anode means
3 can be spaced from the first cathode means l is limited only by the maximum distance at which required control of voltage drop can be obtained by proper positioning of the second cathode means 2 and, as a more practical matter, the distance at which electro-endosmosis can be induced by application of reasonable electric potentials. As a practical matter, spacings between the first cathode and anode greater than sixty meters will rarely be employed.
It will be recognized by those skilled in the art that the permissible and optimum spacings of elec-trodes will be dependent upon the characteristics of the aqueous dispersion of solids, electrode design, and electric power sources available. However, as previously mentioned, for any given dispersion, elec-trode design, and electric power source permissible and optimum spacings within the limitations above set forth can be readily determined by routine tests.
The materials employed for the cathodes are not critical and any electrically conductive material can be employed. Preferably, the materials employed for cathode construction will be relatively resistant to chemical attack by the constituents of the aqueous dispersion. However, the cathode may be relatively light in weight as they, unlike the anodes, will not be decomposed electrically~ The anodes are pre~erably largely iron. Iron is preferred as an inexpensive metal which is easily decomposed to form iron-oxide.
The design of the individual electrodes must also be considered. It is generally preferred to use elongated electrodes of relatively small cross-sectional area. The electrodes could, for example, be formed from bar stock or I-beams, and railroad rails are par-ticularly well suited. For longer operating times solid rods are preferred over hollow pipe because a greater mass is present for decomposition.
Preferred systems will employ a plurality of second cathodes spaced around a centrally located first cathode and a plurality of anodes spaced around the cathode system as shown in Figure III. Such an arrange-ment permits optimization of electric fields in the system and effectively subjects large areas of the aqueous dispersion to the electroendosmotic effect.
For reasons of safety, it is desirable that the cathodes and anodes be totally submerged in the aqueous dispersion.
The arrangement of electrodes has been dis-cussed relative to systems wherein the electrodes are laterally spaced. However, depending upon the charac-teristics of the aqueous dispersion and the containment means within which it is held, it may in some instances be desirable to employ vertically spaced electrode systems or combinations of vertically and horizontally spaced electrode systems. It is generally desirable that the anodes be disposed at a depth somewhat greater than the depth of the cathodes when water is removed from aqueous dispersions of negatively charged parti-cles in order to promote concentration of the solids towards the bottom of the containment means in which they are confined. An example of vertical spacing has the shape of a pyramid wherein the anodes are positioned at the four corners of the base and the cathodes are located at the apex.
A direct current electrical potential is con-" ~lO~Z35 -8- c-l7-2l-3l92A
nected between the anodes and cathodes. The current and voltage levels are chosen to remove the greatest amount of water from the aqueous dispersion of solids at the least power costs.
Theory dictates that an electrical field with a constant potential gradient should be optimum. How-ever, in large impoundments the desired constant gradi-ent is impossible to achieve and relatively large poten-tial drops are suffered near the cathode and anodes.
To smooth the potential gradient the second cathode means is added between the central cathode and the anodes. It is found that the measured field resist-ance of the aqueous dispersion is much more dependent upon the cathode area than the anode area when an anode rich system is used.
Several factors dictate the need for an anode rich system. One factor is that in the impoundments water moves toward the cathode. It is desirable to move the water toward a central location where it can escape relatively rapidly from the aqueous dispersion and be easily removed from the impoundment. Thus, a greater number of anodes are required surrounding a central cathode system. Additionally, the anodes are consumed electrochemically as predicated by Faraday's law.
(anode) Fe -~ Fe+2 + 2e (cathode) H2O + 2e >o 2 + H2 _ _ Fe + H2O + 2e ~ FeO + H2 + 2e Faraday's law states that one gram equivalent of metal will corrode for each 96,500 ampere-seconds, or, in other words, 56/2 = 28 grams of iron will corrode for each 96,500 ampere-seconds of electricity consumed.
It is, therefore, required that the mass of the anodes be large compared to that of the cathodes. The cathodes do not corrode because they are held at a high negative potential. It is the amperage, not potential, which consumes anodes and by adjusting the surface . :
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-9- c-17-21-3192A
area of the cathodes the field resistance of the aqueous dispersion, and the corresponding amperage-voltage relationship, may be varied over large limits.
In the practice of the present invention various auxiliary techniques can be employed, if desired.
For example, electrolyte can be added to the aqueous dispersion to increase the conductivity thereof or electrode cooling means can be provided to remove excess heat to prevent the complete drying of the material adjacent the anodes.
The drying of the aqueous dispersicn surround-ing the anodes, and the resulting buildup of solids on the anode, is one of the major problems encountered when using the techniques of this invention. To pre-vent the complete drying of the material surroundingthe anode, a gas or liquid may be bubbled through the aqueous dispersion adjacent the anode. A more practical solution requires the periodic reversal of the elec-trical potential between the anodes and cathodes for a short period of time to cause migration of the liquid within the aqueous dispersion toward the anodes in-stead of toward the cathodes. However, reversal of the electrical potential causes rapid disintegration of cathodes which are relatively light in weight compared to the anodes. To prevent disintegration of the cathodes a second anode may advantageously be installed beneath the central cathode. When the polarity of the electrical potential is reversed, the cathodes are electrically removed from the circuit and the second anode is connected in their place so that the second anode disintegrates rather than the cathodes.
This invention may also be utilized when the dispersed particles within the aqueous dispersion are characterized as having a positive electrical charge in relation to ground zero. All parameters of the foregoing disquisition of aqueous dispersions contain-ing negatively charged particles equally apply when , - ~
the particles have a positive charge except that the positions of the anodes and cathodes must be reversed.
To cause migration of water toward a central location, the anodes, rather than cathodes as discussed above, must be located at the center of the electrode system.
Referring to Figure III, in an aqueous dispersion, a first anode means 1 is surrounded by concentric circles of the plurality of anodes forming a second anode means and the plurality of cathodes forming the cathode means 3.
By the use of this invention, water is sepa-rated from the solids and brought to the upper surface of an aqueous dispersion where it may be removed and the solids are more rapidly compacted than by natural settlement. Thus, the volume of aqueous dispersion of solids which can be accepted by the impoundment within any time span is increased over that volume which can be accepted by the impoundment if settling is accom-plished solely by natural means. Similarly, the more rapid settling of the solids caused by this invention more rapidly restores the impoundment to an acceptable habitat for aquatic life.
Workin~ Example An electroendosmosis system as described herein is tested in a large 120 hectare pond. The system consists of 20 stations, each station comprising one central cathode, 4 secondary cathodes and 8 anodes arranged as in Figure III. Each secondary cathode is placed 3 meters from the central cathode and each anode is placed 36 meters from the central cathode. Each cathode is an iron pipe about 5 meters long, submerged such that the tops thereof are about 1 meter below the mudline. Each anode is a railroad rail about 10 meters long, submerged such that the tops thereof are about 3 meters below the mudline.
~ C-17-21-3192A
The pond is a storage pond for aqueous illite clay slime from the benefication of phosphate ore. At star~-up of the electroendosmosis system the mudline in the pond is at an elevation o~ 225 meters above sea level and rising with the addition of further slime at a rate of about 15 centimeters per month.
About 25,000 watts of D.C. electrical power are applied across each station. After 8 months of operation the mudline rises only 30 centimeters. With-out electroendosmosis the rise would be about 120 centi-meters. During operation the temperature of the slime is measured frequently at various locations between the central cathode and the anodes as a measurement of the uniformity of the voltage drop between the cathodes and the anodes. Temperature variations within +5C.
between locations at any given time shows that the voltage drop is substantially linear.
This invention can also be used, for example, in separating water from muds, sludges or slimes result-ing from mining and/or processing of various native,nonorganic or fossilized organic ores such as bauxite, alumina, fluorspar, feldspar, barite, pyrophyllite, talc, ilmenite, andalusite and cyanite; coal; peat;
micas; diatomaceous earths; clays such as kaolin, bentonite, fullers earth, ball clay, fire clay and crushed stone. The invention has further utility in, for example, separating water from sewage and various other muds, sludges or slimes resulting from river dredging, paper manufacture, beet and cane sugar process-ing, phosphate sludges, and the like.
As various changes could be made in themethod and apparatus herein described without depart-ing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.
It will be recognized by those skilled in the art that the permissible and optimum spacings of elec-trodes will be dependent upon the characteristics of the aqueous dispersion of solids, electrode design, and electric power sources available. However, as previously mentioned, for any given dispersion, elec-trode design, and electric power source permissible and optimum spacings within the limitations above set forth can be readily determined by routine tests.
The materials employed for the cathodes are not critical and any electrically conductive material can be employed. Preferably, the materials employed for cathode construction will be relatively resistant to chemical attack by the constituents of the aqueous dispersion. However, the cathode may be relatively light in weight as they, unlike the anodes, will not be decomposed electrically~ The anodes are pre~erably largely iron. Iron is preferred as an inexpensive metal which is easily decomposed to form iron-oxide.
The design of the individual electrodes must also be considered. It is generally preferred to use elongated electrodes of relatively small cross-sectional area. The electrodes could, for example, be formed from bar stock or I-beams, and railroad rails are par-ticularly well suited. For longer operating times solid rods are preferred over hollow pipe because a greater mass is present for decomposition.
Preferred systems will employ a plurality of second cathodes spaced around a centrally located first cathode and a plurality of anodes spaced around the cathode system as shown in Figure III. Such an arrange-ment permits optimization of electric fields in the system and effectively subjects large areas of the aqueous dispersion to the electroendosmotic effect.
For reasons of safety, it is desirable that the cathodes and anodes be totally submerged in the aqueous dispersion.
The arrangement of electrodes has been dis-cussed relative to systems wherein the electrodes are laterally spaced. However, depending upon the charac-teristics of the aqueous dispersion and the containment means within which it is held, it may in some instances be desirable to employ vertically spaced electrode systems or combinations of vertically and horizontally spaced electrode systems. It is generally desirable that the anodes be disposed at a depth somewhat greater than the depth of the cathodes when water is removed from aqueous dispersions of negatively charged parti-cles in order to promote concentration of the solids towards the bottom of the containment means in which they are confined. An example of vertical spacing has the shape of a pyramid wherein the anodes are positioned at the four corners of the base and the cathodes are located at the apex.
A direct current electrical potential is con-" ~lO~Z35 -8- c-l7-2l-3l92A
nected between the anodes and cathodes. The current and voltage levels are chosen to remove the greatest amount of water from the aqueous dispersion of solids at the least power costs.
Theory dictates that an electrical field with a constant potential gradient should be optimum. How-ever, in large impoundments the desired constant gradi-ent is impossible to achieve and relatively large poten-tial drops are suffered near the cathode and anodes.
To smooth the potential gradient the second cathode means is added between the central cathode and the anodes. It is found that the measured field resist-ance of the aqueous dispersion is much more dependent upon the cathode area than the anode area when an anode rich system is used.
Several factors dictate the need for an anode rich system. One factor is that in the impoundments water moves toward the cathode. It is desirable to move the water toward a central location where it can escape relatively rapidly from the aqueous dispersion and be easily removed from the impoundment. Thus, a greater number of anodes are required surrounding a central cathode system. Additionally, the anodes are consumed electrochemically as predicated by Faraday's law.
(anode) Fe -~ Fe+2 + 2e (cathode) H2O + 2e >o 2 + H2 _ _ Fe + H2O + 2e ~ FeO + H2 + 2e Faraday's law states that one gram equivalent of metal will corrode for each 96,500 ampere-seconds, or, in other words, 56/2 = 28 grams of iron will corrode for each 96,500 ampere-seconds of electricity consumed.
It is, therefore, required that the mass of the anodes be large compared to that of the cathodes. The cathodes do not corrode because they are held at a high negative potential. It is the amperage, not potential, which consumes anodes and by adjusting the surface . :
:, ~
17Z3~
-9- c-17-21-3192A
area of the cathodes the field resistance of the aqueous dispersion, and the corresponding amperage-voltage relationship, may be varied over large limits.
In the practice of the present invention various auxiliary techniques can be employed, if desired.
For example, electrolyte can be added to the aqueous dispersion to increase the conductivity thereof or electrode cooling means can be provided to remove excess heat to prevent the complete drying of the material adjacent the anodes.
The drying of the aqueous dispersicn surround-ing the anodes, and the resulting buildup of solids on the anode, is one of the major problems encountered when using the techniques of this invention. To pre-vent the complete drying of the material surroundingthe anode, a gas or liquid may be bubbled through the aqueous dispersion adjacent the anode. A more practical solution requires the periodic reversal of the elec-trical potential between the anodes and cathodes for a short period of time to cause migration of the liquid within the aqueous dispersion toward the anodes in-stead of toward the cathodes. However, reversal of the electrical potential causes rapid disintegration of cathodes which are relatively light in weight compared to the anodes. To prevent disintegration of the cathodes a second anode may advantageously be installed beneath the central cathode. When the polarity of the electrical potential is reversed, the cathodes are electrically removed from the circuit and the second anode is connected in their place so that the second anode disintegrates rather than the cathodes.
This invention may also be utilized when the dispersed particles within the aqueous dispersion are characterized as having a positive electrical charge in relation to ground zero. All parameters of the foregoing disquisition of aqueous dispersions contain-ing negatively charged particles equally apply when , - ~
the particles have a positive charge except that the positions of the anodes and cathodes must be reversed.
To cause migration of water toward a central location, the anodes, rather than cathodes as discussed above, must be located at the center of the electrode system.
Referring to Figure III, in an aqueous dispersion, a first anode means 1 is surrounded by concentric circles of the plurality of anodes forming a second anode means and the plurality of cathodes forming the cathode means 3.
By the use of this invention, water is sepa-rated from the solids and brought to the upper surface of an aqueous dispersion where it may be removed and the solids are more rapidly compacted than by natural settlement. Thus, the volume of aqueous dispersion of solids which can be accepted by the impoundment within any time span is increased over that volume which can be accepted by the impoundment if settling is accom-plished solely by natural means. Similarly, the more rapid settling of the solids caused by this invention more rapidly restores the impoundment to an acceptable habitat for aquatic life.
Workin~ Example An electroendosmosis system as described herein is tested in a large 120 hectare pond. The system consists of 20 stations, each station comprising one central cathode, 4 secondary cathodes and 8 anodes arranged as in Figure III. Each secondary cathode is placed 3 meters from the central cathode and each anode is placed 36 meters from the central cathode. Each cathode is an iron pipe about 5 meters long, submerged such that the tops thereof are about 1 meter below the mudline. Each anode is a railroad rail about 10 meters long, submerged such that the tops thereof are about 3 meters below the mudline.
~ C-17-21-3192A
The pond is a storage pond for aqueous illite clay slime from the benefication of phosphate ore. At star~-up of the electroendosmosis system the mudline in the pond is at an elevation o~ 225 meters above sea level and rising with the addition of further slime at a rate of about 15 centimeters per month.
About 25,000 watts of D.C. electrical power are applied across each station. After 8 months of operation the mudline rises only 30 centimeters. With-out electroendosmosis the rise would be about 120 centi-meters. During operation the temperature of the slime is measured frequently at various locations between the central cathode and the anodes as a measurement of the uniformity of the voltage drop between the cathodes and the anodes. Temperature variations within +5C.
between locations at any given time shows that the voltage drop is substantially linear.
This invention can also be used, for example, in separating water from muds, sludges or slimes result-ing from mining and/or processing of various native,nonorganic or fossilized organic ores such as bauxite, alumina, fluorspar, feldspar, barite, pyrophyllite, talc, ilmenite, andalusite and cyanite; coal; peat;
micas; diatomaceous earths; clays such as kaolin, bentonite, fullers earth, ball clay, fire clay and crushed stone. The invention has further utility in, for example, separating water from sewage and various other muds, sludges or slimes resulting from river dredging, paper manufacture, beet and cane sugar process-ing, phosphate sludges, and the like.
As various changes could be made in themethod and apparatus herein described without depart-ing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.
Claims (24)
1. A process for removing water from an aqueous dispersion of solids which have a negative electrical charge in relation to ground zero via electroendosmosis characterized by:
mounting a first cathode means in said aqueous dispersions, mounting an anode means in said aqueous dis-persion separated from said first cathode means, mounting a second cathode means in said aqueous dispersion intermediate said first cathode means and said anode means and closer to said first cathode means than said anode means, establishing a direct current electrical potential between said first and second cathode means and said anode means wherein the water in said aqueous dispersion of solids is moved toward said first and second cathode means whereby said water may be removed and said solids remain.
mounting a first cathode means in said aqueous dispersions, mounting an anode means in said aqueous dis-persion separated from said first cathode means, mounting a second cathode means in said aqueous dispersion intermediate said first cathode means and said anode means and closer to said first cathode means than said anode means, establishing a direct current electrical potential between said first and second cathode means and said anode means wherein the water in said aqueous dispersion of solids is moved toward said first and second cathode means whereby said water may be removed and said solids remain.
2. The process of Claim 1 characterized by:
mounting said second cathode means inter-mediate said first cathode means and said anode means wherein no five percent (5%) of the linear distance between said first cathode means and said anode means exhibits a voltage drop greater than thirty percent (30%) of the total voltage drop between said first cathode means and said anode means.
mounting said second cathode means inter-mediate said first cathode means and said anode means wherein no five percent (5%) of the linear distance between said first cathode means and said anode means exhibits a voltage drop greater than thirty percent (30%) of the total voltage drop between said first cathode means and said anode means.
3. A process for removing water from an aqueous dispersion of solids which have a positive electrical charge in relation to ground zero via electroendosmosis characterized by:
mounting a first anode means in said aqueous dispersions, mounting a cathode means in said aqueous dispersion separated from said first anode means, mounting a second anode means in said aqueous dispersion intermediate said first anode means and said cathode means and closer to said first anode means than said cathode means, establishing a direct current electrical potential between said first and second anode means and said cathode means wherein the water in said aqueous dispersion of solids is moved toward said first and second anode means whereby said water may be removed and said solids remain.
mounting a first anode means in said aqueous dispersions, mounting a cathode means in said aqueous dispersion separated from said first anode means, mounting a second anode means in said aqueous dispersion intermediate said first anode means and said cathode means and closer to said first anode means than said cathode means, establishing a direct current electrical potential between said first and second anode means and said cathode means wherein the water in said aqueous dispersion of solids is moved toward said first and second anode means whereby said water may be removed and said solids remain.
4. The process of Claim 3 characterized by:
mounting said second anode means intermediate said first anode means and said cathode means wherein no five percent (5%) of the linear distance between said first anode means and said cathode means exhibits a voltage drop greater than thirty percent (30%) of the total voltage drop between said first anode means and said cathode means.
mounting said second anode means intermediate said first anode means and said cathode means wherein no five percent (5%) of the linear distance between said first anode means and said cathode means exhibits a voltage drop greater than thirty percent (30%) of the total voltage drop between said first anode means and said cathode means.
5. A process for increasing the zonal con-centration of solids having a negative electrical potential in relation to ground zero in an aqueous dispersion thereof, said method characterized by:
providing in said dispersion a first cathode means, an anode means spaced from said first cathode means, and a second cathode means disposed in a plane perpendicularly transversing the plane between said first cathode means and said anode means, and closer to said first cathode means than to said anode means, establishing an electrical potential between said anode means and said first and second cathode means sufficient to effect preferential migration of water in said dispersion toward said first and second cathode means, separating said first cathode means and said anode means by a distance such that if said first cathode means and said second cathode means were located at the same distance from said anode means and closely adjacent, that some 5% of the linear distance between said combined first and second cathode means and said anode means would exhibit a voltage drop greater than 30% of the total voltage drop between said first cathode means and said anode means, and disposing said second cathode means in a position such that no 5% of the linear distance between said first cathode means and said anode means exhibits a voltage drop greater than 30% of the total voltage drop between said first cathode means and said anode means.
providing in said dispersion a first cathode means, an anode means spaced from said first cathode means, and a second cathode means disposed in a plane perpendicularly transversing the plane between said first cathode means and said anode means, and closer to said first cathode means than to said anode means, establishing an electrical potential between said anode means and said first and second cathode means sufficient to effect preferential migration of water in said dispersion toward said first and second cathode means, separating said first cathode means and said anode means by a distance such that if said first cathode means and said second cathode means were located at the same distance from said anode means and closely adjacent, that some 5% of the linear distance between said combined first and second cathode means and said anode means would exhibit a voltage drop greater than 30% of the total voltage drop between said first cathode means and said anode means, and disposing said second cathode means in a position such that no 5% of the linear distance between said first cathode means and said anode means exhibits a voltage drop greater than 30% of the total voltage drop between said first cathode means and said anode means.
6. The process of Claim S, characterized by:
separating said first cathode means and said anode means by a distance of at least six meters.
separating said first cathode means and said anode means by a distance of at least six meters.
7. The process of Claim 6, characterized by:
disposing a plurality of second cathode means circumferentially around said first cathode means, and disposing a plurality of anode means circum-ferentially around said first and second cathode means.
disposing a plurality of second cathode means circumferentially around said first cathode means, and disposing a plurality of anode means circum-ferentially around said first and second cathode means.
8. A process for increasing the zonal con-centration of solids having a positive electrical poten-tial in relation to ground zero in an aqueous dispersion thereof, said method characterized by:
providing in said dispersion a first anode means, a cathode means spaced from said first anode means, and a second anode means disposed in a plane perpendicularly transversing the plane between said first anode means and said cathode means, and closer to said first anode means than to said cathode means, establishing an electrical potential between said first and second anode means and said cathode means sufficient to effect preferential migration of water in said dispersion toward said first and second anode means, separating said first anode means and said cathode means by a distance such that if said first anode means and said second anode means were located at the same distance from said cathode means and closely adjacent, that some 5% of the linear distance between said combined first and second anode means and said cathode means would exhibit a voltage drop greater than 30% of the total voltage drop between said first anode means and said cathode means, and disposing said second anode means in a posi-tion such that no 5% of the linear distance between said first anode means and said cathode means exhibits a voltage drop greater than 30% of the total voltage drop between said first anode means and said cathode means.
providing in said dispersion a first anode means, a cathode means spaced from said first anode means, and a second anode means disposed in a plane perpendicularly transversing the plane between said first anode means and said cathode means, and closer to said first anode means than to said cathode means, establishing an electrical potential between said first and second anode means and said cathode means sufficient to effect preferential migration of water in said dispersion toward said first and second anode means, separating said first anode means and said cathode means by a distance such that if said first anode means and said second anode means were located at the same distance from said cathode means and closely adjacent, that some 5% of the linear distance between said combined first and second anode means and said cathode means would exhibit a voltage drop greater than 30% of the total voltage drop between said first anode means and said cathode means, and disposing said second anode means in a posi-tion such that no 5% of the linear distance between said first anode means and said cathode means exhibits a voltage drop greater than 30% of the total voltage drop between said first anode means and said cathode means.
9. The process of Claim 8, characterized by:
separating said first anode means and said cathode means by a distance of at least six meters.
separating said first anode means and said cathode means by a distance of at least six meters.
10. The process of Claim 9, characterized by:
disposing a plurality of second anode means circum-ferentially around said first anode means, and disposing a plurality of cathode means circumferen-tially around said first and second anode means.
disposing a plurality of second anode means circum-ferentially around said first anode means, and disposing a plurality of cathode means circumferen-tially around said first and second anode means.
11. A process for removing water from an aqueous dispersion of solids which have an electrical charge in relation to ground zero via electroendosmosis characterized by:
mounting a first electrode means in said aqueous dispersions, mounting a third electrode means in said aqueous dispersion separated from said first electrode means, mounting a second electrode means in said aqueous dispersion intermediate said first electrode means and said third electrode means and closer to said first electrode means than said third electrode means, establishing a direct current electrical potential between said first and second electrode means and said third electrode means wherein the water in said aqueous dispersion of solids is moved toward said first and second electrode means whereby said water may be removed and said solids remain.
mounting a first electrode means in said aqueous dispersions, mounting a third electrode means in said aqueous dispersion separated from said first electrode means, mounting a second electrode means in said aqueous dispersion intermediate said first electrode means and said third electrode means and closer to said first electrode means than said third electrode means, establishing a direct current electrical potential between said first and second electrode means and said third electrode means wherein the water in said aqueous dispersion of solids is moved toward said first and second electrode means whereby said water may be removed and said solids remain.
12. An apparatus for increasing the rate of zonal concentration and the final density of solids having an electrical potential in relation to ground zero in an aqueous dispersion characterized by:
a first electrode means having the same polarity as said dispersed solids, an electrode means having the opposite polarity from said dispersed solids, separated from said first electrode means, a second electrode means having the same polarity as said dispersed solids, positioned intermediate between said first electrode means and said electrode means of opposite polarity, and means for applying a direct current potential between said first and second electrode means and said electrode means of opposite polarity wherein water is moved toward said first and second electrode means and may be removed from said aqueous dispersion.
a first electrode means having the same polarity as said dispersed solids, an electrode means having the opposite polarity from said dispersed solids, separated from said first electrode means, a second electrode means having the same polarity as said dispersed solids, positioned intermediate between said first electrode means and said electrode means of opposite polarity, and means for applying a direct current potential between said first and second electrode means and said electrode means of opposite polarity wherein water is moved toward said first and second electrode means and may be removed from said aqueous dispersion.
13. An apparatus as in Claim 12 characterized in that said solids have a negative electrical potential, said first and second electrode means are cathode means, and said electrode means of opposite polarity are anode means.
14. An apparatus as in Claim 12 characterized in that said solids have a positive electrical potential, said first and second electrode means are anode means, and said electrode means of opposite polarity is a cathode means.
15. The apparatus of Claim 13 characterized in that:
said second cathode means is positioned intermediate said first cathode means and said anode means such that no five percent (5%) of the linear distance between said first cathode means and said anode means has a voltage drop greater than thirty percent (30%) of the total voltage drop between said first cathode means and said anode means.
said second cathode means is positioned intermediate said first cathode means and said anode means such that no five percent (5%) of the linear distance between said first cathode means and said anode means has a voltage drop greater than thirty percent (30%) of the total voltage drop between said first cathode means and said anode means.
16. The apparatus of Claim 13 characterized in that said second cathode means comprises a plurality of cathodes arranged in a concentric circle about said first cathode means, each of said plurality of cathodes being equally spaced from its adjacent cathodes.
17. The apparatus of Claim 16 characterized in that said anode means comprises a plurality of anodes arranged in a concentric circle about said first and second cathode means, each of said plurality of anodes being equally spaced from its adjacent anodes.
18. The apparatus of Claim 17 characterized in that said plurality of cathodes of said second cathode means and said plurality of anodes of said anode means are arranged such that a line drawn from said first cathode means through one of said plurality of cathodes will bisect the angle formed by lines drawn between the first cathode means and alternate pairs of adjacent anodes of said plurality of anodes.
19. The apparatus of Claim 17 characterized in that each cathode and anode of said first and second cathode means and said anode means comprises an elongated metal rod of a relatively small cross-sectional area.
20. The apparatus of Claim 14 characterized in that:
said second anode means is positioned intermediate said first anode means and said cathode means such that no five percent (5%) of the linear distance between said first anode means and said cathode means has a voltage drop greater than thirty percent (30%) of the total voltage drop between said first anode means and said cathode means.
said second anode means is positioned intermediate said first anode means and said cathode means such that no five percent (5%) of the linear distance between said first anode means and said cathode means has a voltage drop greater than thirty percent (30%) of the total voltage drop between said first anode means and said cathode means.
21. The apparatus of Claim 14 characterized in that said second anode means comprises a plurality of anodes arranged in a concentric circle about said first anode means, each of said plurality of anodes being equally spaced from its adjacent anodes.
22. The apparatus of Claim 21 characterized in that said cathode means comprises a plurality of cathodes arranged in a concentric circle about said first and second anode means, each of said plurality of cathodes being equally spaced from its adjacent cathodes.
23. The apparatus of Claim 22 characterized in that said plurality of anodes of said second anode means and said plurality of cathodes of said cathode means are arranged such that a line drawn from said first anode means through one of said plurality of anodes will bisect the angle formed by lines drawn between the first anode means and alternate pairs of adjacent cathodes of said plurality of cathodes.
24. The apparatus of Claim 22 characterized in that each cathode and anode of said first and second anode means and said cathode means comprises an elongated metal rod of a relatively small cross-sectional area.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA304,195A CA1107235A (en) | 1978-05-26 | 1978-05-26 | Treatment of aqueous dispersions |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA304,195A CA1107235A (en) | 1978-05-26 | 1978-05-26 | Treatment of aqueous dispersions |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1107235A true CA1107235A (en) | 1981-08-18 |
Family
ID=4111554
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA304,195A Expired CA1107235A (en) | 1978-05-26 | 1978-05-26 | Treatment of aqueous dispersions |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1107235A (en) |
-
1978
- 1978-05-26 CA CA304,195A patent/CA1107235A/en not_active Expired
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