Method and apparatus for capacitive deionization and electrochemical purification and regeneration of electrodes

An electrically regeneratable electrochemical cell (30) for capacitive deionization and electrochemical purification and regeneration of electrodes includes two end plates (31, 32), one at each end of the cell (30). Two end electrodes (35, 36) are arranged one at each end of the cell (30), adjacent to the end plates (31, 32). An insulator layer (33) is interposed between each end plate (31, 32) and the adjacent end electrode (35, 36). Each end electrode (35, 36) includes a single sheet (44) of conductive material having a high specific surface area and sorption capacity. In one embodiment, the sheet (44) of conductive material is formed of carbon aerogel composite. The cell (30) further includes a plurality of generally identical double-sided intermediate electrodes (37-43) that are equidistally separated from each other, between the two end electrodes (35, 36). As the electrolyte enters the cell, it flows through a continuous open serpentine channel (65-71) defined by the electrodes, substantially parallel to the surfaces of the electrodes. By polarizing the cell (30), ions are removed from the electrolyte and are held in the electric double layers formed at the carbon aerogel surfaces of the electrodes. As the cell (30) is saturated with the removed ions, the cell (30) is regenerated electrically, thus significantly minimizing secondary wastes.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an electrochemical separation method and 
apparatus for removing ions, contaminants and impurities from water, 
fluids, and other aqueous process streams, and for placing the removed 
ions back into solution during regeneration. 
2. Background Art 
The separation of ions and impurities from electrolytes has heretofore been 
generally achieved using a variety of conventional processes including: 
ion exchange, reverse osmosis, electrodialysis, electrodeposition, and 
filtering. Other methods have been proposed and address the problems 
associated with the conventional separation processes. However, these 
proposed methods have not been completely satisfactory and have not met 
with universal commercial success or complete acceptance. One such 
proposed ion separation method is a process for desalting water based on 
periodic sorption and desorption of ions on the extensive surface of 
porous carbon electrodes. 
The conventional ion exchange process generates large volumes of corrosive 
secondary wastes that must be treated for disposal through regeneration 
processes. Existing regeneration processes are typically carried out 
following the saturation of columns by ions, by pumping regeneration 
solutions, such as concentrated acids, bases, or salt solutions through 
the columns. These routine maintenance measures produce significant 
secondary wastes, as well as periodic interruptions of the deionization 
process. Secondary wastes resulting from the regeneration of the ion 
exchangers typically include used anion and cation exchange resins, as 
well as contaminated acids, bases and/or salt solutions. 
In some instances, the secondary radioactive wastes are extremely hazardous 
and can cause serious environmental concerns. For instance, during 
plutonium processing, resins and solutions of HNO.sub.3 become 
contaminated with PuO.sub.2.sup.++ and other radioisotopes. Given the 
high and increasing cost of disposal of secondary wastes in mined 
geological repositories, there is tremendous and still unfulfilled need 
for reducing, and in certain applications, eliminating the volume of 
secondary wastes. 
Another example is the use of the ion exchange process for industrial 
purposes, such as in the electroplating and metal finishing industries. A 
major dilemma currently facing the industry relates to the difficulties, 
cost considerations and the environmental consequences for disposing of 
the contaminated rinse solution resulting from the electroplating process. 
A typical treatment method for the contaminated rinse water is the ion 
exchange process. 
Other exemplary processes which further illustrate the problems associated 
with ion exchange include residential water softening and the treatment of 
boiler water for nuclear and fossil-fueled power plants. Such water 
softeners result in a relatively highly concentrated solution of sodium 
chloride in the drinking water produced by the system. Therefore, 
additional desalination devices, such as reverse osmosis filters are 
needed to remove the excess sodium chloride introduced during 
regeneration. 
Therefore, there is still a significant and growing need for a new method 
and apparatus for deionization and subsequent regeneration, which 
significantly reduce, if not entirely eliminate secondary wastes in 
certain applications. The new method and apparatus should enable the 
separation of any inorganic or organic ion or dipole from any ionically 
conducting solvent, which could be water, an organic solvent, or an 
inorganic solvent. For example, it should be possible to use such a 
process to purify organic solvents, such as propylene carbonate, for use 
in lithium batteries and other energy storage devices. Furthermore, it 
should be possible to use such a process to remove organic ions, such as 
formate or acetate from aqueous streams. 
The new method and apparatus should further be adaptable for use in various 
applications, including without limitation, treatment of boiler water in 
nuclear and fossil power plants, production of high-purity water for 
semiconductor processing, removal of toxic and hazardous ions from water 
for agricultural irrigation, and desalination of sea water. 
In the conventional reverse osmosis systems, water is forced through a 
membrane, which acts as a filter for separating the ions and impurities 
from electrolytes. Reverse osmosis systems require significant energy to 
move the water through the membrane. The flux of water through the 
membrane results in a considerable pressure drop across the membrane. This 
pressure drop is responsible for most of the energy consumption by the 
process. The membrane will also degrade with time, requiring the system to 
be shut down for costly and troublesome maintenance. 
Therefore, there is a need for a new method and apparatus for deionization 
and ion regeneration, which substitute for the reverse osmosis systems, 
which do not result in a considerable pressure drop, which do not require 
significant energy expenditure, or interruption of service for replacing 
the membrane(s). 
U.S. Pat. No. 3,883,412 to Jensen describes a method for desalinating 
water. Another ion separation method relating to a process for desalting 
water based on periodic sorption and desorption of ions on the extensive 
surface of porous carbon electrodes is described in the Office of Saline 
Water Research and Development Progress Report No. 516, March 1970, U.S. 
Department of the Interior PB 200 056, entitled "The Electrosorb Process 
for Desalting Water", by Allan M. Johnson et al., ("Department of the 
Interior Report") and further in an article entitled "Desalting by Means 
of Porous Carbon Electrodes" by J. Newman et al., in J. Electrochem. Soc.: 
Electrochemical Technology, March 1971, Pages 510-517, ("Newman Artide"). 
A comparable process is also described in NTIS research and development 
progress report No. OSW-PR-188, by Danny D. Caudle et al., 
"Electrochemical Demineralization of Water with Carbon Electrodes", May, 
1966. 
The Department of the Interior Report and the Newman Article review the 
results of an investigation of electrosorption phenomena for desalting 
with activated carbon electrodes, and discuss the theory of potential 
modulated ion sorption in terms of a capacitance model. This model 
desalination system 10, illustrated in FIG. 1, includes a stack of 
alternating anodes and cathodes which are further shown in FIG. 2, and 
which are formed from beds of carbon powder or particles in contact with 
electrically conducting screens (or sieves). Each cell 12 includes a 
plurality of anode screens 14 interleaved with a plurality of cathode 
screens 16, such that each anode screen 14 is separated from the adjacent 
cathode screen 16 by first and second beds 18, 20, respectively, of 
pretreated carbon powder. These two carbon powder beds 18 and 20 are 
separated by a separator 21, and form the anode and cathode of the cell 
12. In operation raw water is flown along the axial direction of the cells 
12, perpendicularly to the surface of the electrode screens 14, 16, to be 
separated by the system 10 into waste 23 and product 25. 
However, this model system 10 suffers from several disadvantages, 
including: 
1. The carbon powder beds 18 and 20 are used as electrodes and are not 
"immobilized". 
2. Raw water must flow axially through these electrode screens 14 and 16, 
beds of carbon powder 18 and 20, and separators 21, which cause 
significant pressure drop and large energy consumption. 
3. The carbon bed electrodes 18 and 20 are quite thick, and a large 
potential drop is developed across them, which translates into lower 
removal efficiency and higher energy consumption during operation. 
4. Even though the carbon particles "touch", i.e., adjacent particles are 
in contact with each other, they are not intimately and entirely 
electrically connected. Therefore, a substantial electrical resistance is 
developed, and significantly contributes to the process inefficiency. 
Energy is wasted and the electrode surface area is not utilized 
effectively. 
5. The carbon beds 18 and 20 have a relatively low specific surface area. 
6. The carbon powder bed electrodes 18 and 20 degrade rapidly with cycling, 
thus requiring continuous maintenance and skilled supervision. 
7. The model system 10 is designed for one particular application, sea 
water desalination, and does not seem to be adaptable for other 
applications. 
Numerous supercapacitors based on various porous carbon electrodes, 
including carbon aerogel electrodes, have been developed for energy 
storage applications, and are illustrated in the following: 
"Double Layer Electric Capacitor", Nippon Electric Co., Japanese Patent 
application No. 91-303689, 05211111. 
"Electric Double-layer Capacitor", Matsushita Electric Industrial Co., 
Ltd., Japanese Patent application No. 83-89451, 59214215. 
Tabuchi, J., Kibi, Y., Saito, T., Ochi, A., "Electrochemical Properties of 
Activated Carbon/Carbon Composites for Electric Double-layer Capacitor in 
New Sealed Rechargeable Batteries and Supercapacitors", presented at the 
183rd Electrochemical Society meeting, Honolulu, Hawai, May 16-21, 1993. 
"Electrical Double-layer Capacitor, Uses Porous Polarized Electrode 
Consisting of Carbonized Foamed Phenol Resin", Mitsui Petrochem Ind., 
Japanese Patent application No. 3,141,629. 
Delnick, F. M., Ingersoll, D., Firsich, D., "Double-Layer Capacitance of 
Carbon Foam Electrodes", SAND-93-2681, Sandia National Laboratory, 
international seminar report on double layer capacitors and similar energy 
storage systems, 6-8 Dec. 1993. 
Mayer, S. T., Pekala, R. W., Kaschmitter, J. L., "The Aerocapacitor: An 
Electrochemical Double-layer Energy-Storage Device", J. Electrochemical 
Society, vol. 140(2) pages 446-451 (February 1993). 
U.S. Pat. No. 5,260,855 issued to Kaschmitter et al. 
None of these energy storage devices is designed to permit electrolyte flow 
and most require membranes to physically separate the electrodes. Other 
electrode materials have been developed for electrolytic cells, e.g. 
composites of activated carbon powder and an appropriate polymeric binder, 
as described by Wessling et al., in U.S. Pat. No. 4,806,212. Even though 
such materials are made from activated carbon powders with very high 
specific surface areas (600 m.sup.2 /gm), much of the surface is occluded 
by the binder. 
Therefore, there is still a significant unfulfilled need for a new method 
and apparatus for deionization and regeneration, which, in addition to the 
ability to significantly reduce, if not completely eliminate, secondary 
wastes associated with the regeneration of ion exchange columns, do not 
result in a considerable pressure drop of the flowing process stream, and 
do not require significant energy expenditure. Furthermore, each electrode 
used in this apparatus should be made of a structurally stable, porous, 
monolithic solid. Such monolithic electrodes should not become readily 
entrained in, or depleted by the stream of fluid to be processed, and 
should not degrade rapidly with cycling. These electrodes should have a 
very high specific surface area; they should be relatively thin, require 
minimal operation energy, and have a high removal efficiency. The new 
method and apparatus should be highly efficient, and should be adaptable 
for use in a variety of applications, including, but not limited to sea 
water desalination. 
It would be highly desirable to provide a new class of electrosorption 
media that may be less susceptible to poisoning and degradation than 
carbon-based materials, for use in capacitive deionization and 
regeneration methods and apparatus. 
It is likely that continued direct exposure of the electrosorption medium 
to the electrolytes and chemical regenerants could further degrade the 
electrodes. Therefore, there is a need for a new separation process that 
protects the electrosorption medium from the damaging effect of the 
electrolytes and chemical regenerants, and which does not require the use 
of chemical regenerants. 
Ion exchange chromatography is an analytical method which involves the 
separation of ions due to the different affinity of the solute ions for 
the exchanger material. It is a liquid-solid technique in which the ion 
exchanger represents the solid phase. In ion-exchange separation, the 
solid phase or column is usually a packed bed of ion exchanger in finely 
comminuted form; the anion or cation exchanger must be appropriate as the 
solid phase for the sample of interest. The mobile phase is a solvent such 
a water with one or more additives such as buffers, neutral salts or 
organic solvents. 
In ion-exchange chromatography the ion-exchanging suppressor column must be 
periodically regenerated. This is a time-consuming procedure and during 
the time that the stripper column is being regenerated, the apparatus is 
not available for use. To minimize the frequency of regeneration, the 
volume ratios of the suppressor column with respect to the separator 
column should be kept as low as possible, typically at a ratio of 1:1. 
This essentially doubles the cost of the ion-exchange materials required. 
U.S. Pat. No. 4,672,042 to Ross, Jr. et al., describes an exemplary 
ion-chromatography system. Two separate exchange columns, anionic and 
cationic, are required, which increases the cost of the chromatograph, and 
essentially doubles the cost of the ion exchange or packing material 
required. Solid ion exchange column packings are used, which limit the 
applications of the chromatograph and require a significantly higher 
energy to operate compared to a single hollow column. 
Several attempts have been made to select an appropriate ion-exchange 
composition for the solid phase, e.g. U.S. Pat. No. 5,324,752 to Barretto 
et al.; U.S. Pat. No. 4,675,385 to Herring; U.S. Pat. No. 5,294,336 to 
Mizuno et al.; U.S. Pat. No. 4,859,342 to Shirasawa; U.S. Pat. Nos. 
4,952,321 and 4,959,153 to Bradshaw et al. 
However, these devices and methods are specifically designed for particular 
applications, and a single chromatograph cannot be used universally in 
various applications. Additionally, these conventional devices require the 
use of multiple columns. 
Therefore, there is still a significant unfulfilled need for a new and 
versatile chromatograph and method of operation, which uses a single 
column for simultaneous anionic and cationic types chromatography. This 
new chromatograph should control the elution time of the species being 
analyzed, should have reduced overall cost of manufacture, operation and 
maintenance, should use electrical rather than chemical regeneration and 
should use the same column (or stack of cells) for both anions and 
cations. 
SUMMARY OF THE INVENTION 
In one embodiment, the separation process or apparatus is used for the 
deionization of water and the treatment of aqueous wastes, referred to as 
capacitive deionization (CDI). Unlike conventional ion exchange processes, 
no chemicals, whether acids, bases, or salt solutions, are required for 
the regeneration of the system; instead, electricity is used. 
A stream of electrolyte to be processed, which contains various anions and 
cations, electric dipoles, and/or suspended particles is passed through a 
stack of electrochemical capacitive deionization cells. Each of these 
cells includes numerous carbon aerogel electrodes having exceptionally 
high specific surface areas (for example, 400-1000 m.sup.2 /gm). By 
polarizing the cell, non-reducible and non-oxidizable ions are removed 
from the fluid stream electrostatically and held in the electric double 
layers formed at the surfaces of the electrodes. Some metal cations are 
removed by electrodeposition. Electric dipoles also migrate to and are 
trapped at the electrodes. Small suspended particles are removed by 
electrophoresis. Therefore, the fluid stream leaving the cell is purified. 
In the present CDI process, energy is expended using electrostatics to 
remove salt and other impurities from the fluid, and, as a result, is 
orders-of-magnitude more energy efficient than conventional processes. 
Furthermore, the pressure drop in the capacitive deionization cells is 
dictated by channel flow between parallel surfaces of monolithic, 
microporous solids (i.e., the electrodes); hence, it is insignificant 
compared to that needed to force water through the permeable membrane 
required by the reverse osmosis process. 
One feature of the CDI separation system is that no expensive ion exchange 
membranes are required for the separation of the electrodes. All the 
anodes and cathodes of the electrode pairs are connected in parallel. The 
system is modular, and the system capacity can be increased to any desired 
level by expanding the cell(s) to inciude a greater number of electrode 
pairs. 
Some advantages of the present invention include, but are not limited to 
the following: 
1. Unlike conventional processes where water is forced through a membrane 
by pressure gradient, or where fluid is flown through a packed bed, the 
CDI separation methods and systems do not require the electrolyte to flow 
through any porous media such as membranes or packed beds. In the present 
system, electrolyte flows in open channels formed between two adjacent, 
planar electrodes, which are geometrically parallel. Consequently, the 
pressure drop is much lower than conventional processes. The fluid flow 
can be gravity fed through these open channels, or a pump can be used. 
2. The CDI system does not require membranes, which are both troublesome 
and expensive, which rupture if overpressured, which add to the internal 
resistance of the capacitive cell, and which further reduce the system 
energy efficiency. 
3. The electrodes in the CDI system are composed of immobilized sorption 
media, such as monolithic carbon aerogel, which is not subject to 
entrainment in the flowing fluid stream. Thus, material degradation due to 
entrainment and erosion is considerably less than in conventional packed 
carbon columns. 
4. The present systems and methods are inherently and greatly energy 
efficient. For instance, in both evaporation and reverse osmosis 
processes, water is removed from salt, while in the present systems, salt 
is removed from water, thus expending less energy. 
5. The present systems and methods present superior potential distribution 
in the thin sheets of carbon aerogel; most of the carbon aerogel is 
maintained at a potential where electrosorption is very efficient. 
The above and further features and advantages of the present invention are 
realized by a new electrically regeneratable electrochemical cell for 
capacitive deionization and electrochemical purification and regeneration 
of electrodes. The cell includes two end plates, one at each end of the 
cell, as well as two end electrodes that are arranged one at each end of 
the cell, adjacent to the end plates. An insulator layer is interposed 
between each end plate and the adjacent end electrode. 
Each end electrode includes an electrosorption medium having a high 
specific surface area and sorption capacity. In the preferred embodiment, 
the electrosorption medium is formed of carbon aerogel composite. The cell 
further includes one or more intermediate electrodes that are disposed 
between the two end electrodes. As the electrolyte enters the cell, it 
flows through a continuous open serpentine channel defined by the 
electrodes, substantially parallel to the surfaces of the electrodes. By 
polarizing the cell, ions are removed from the electrolyte and are held in 
the electric double layers formed at the carbon aerogel surfaces of the 
electrodes. As the cell is saturated with the removed ions, the cell is 
regenerated electrically, thus significantly minimizing secondary wastes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 3 illustrates an electrochemical cell 30 which generally includes two 
oppositely disposed, spaced-apart end plates 31 and 32, one at each end of 
the cell 30, and two generally identical single-sided end electrodes 35, 
36, one at each end of the cell 30, adjacent to the end plates 31 and 32, 
respectively. An insulator layer 33 is interposed between the end plate 31 
and the end electrode 35. Similarly, an insulator layer 34 is interposed 
between the end plate 32 and the end electrode 36. Each single-sided 
electrode 35, 36 includes a single sheet of carbon aerogel composite 
bonded to one side of a titanium sheet with a conductive epoxy or other 
appropriate bonding material. 
A plurality of generally identical double-sided intermediate electrodes 
37-43 are spaced-apart and equidistally separated from each other, between 
the two end electrodes 35, 36. Each double-sided electrode, i.e., 37, 
includes two sheets of carbon aerogel composite bonded to both sides of a 
titanium sheet with conductive epoxy. While FIG. 3 illustrates only seven 
double sided intermediate electrodes 37-43, a different number of 
intermediate electrodes can alternatively be used. For instance, the 
capacity of the cell 30 can accommodate at least 192 intermediate 
electrodes, such that the total anode (or cathode) surface area is 
approximately 2.7.times.10.sup.8 cm.sup.2. Ultimately, the system could be 
expanded to include an unlimited number of electrode pairs. 
The end electrodes 35, 36 and the intermediate electrodes 37-43 are 
generally similar in design, construction and composition, but each 
intermediate electrode has two sheets of carbon aerogel composite bonded 
to both sides of a titanium sheet with conductive epoxy, whereas each end 
electrode has only one sheet of carbon aerogel composite bonded to one 
side of a titanium sheet with conductive epoxy. Other porous conductive, 
monolithic materials can be used for the carbon aerogel composite. 
FIG. 4A shows end electrode 35, which includes a generally flat, thin 
rectangularly shaped, corrosion resistant, metallic (i.e., titanium) 
sheet, structural support 40. A tab 42A extends integrally from one side 
of the structural support 40, for connection to the appropriate pole of a 
D.C. power source (not shown). A thin sheet 44 of high specific area, 
porous, conductive, monolithic material (i.e., carbon aerogel composite) 
is bonded to the surface of the structural support 40, and can be either a 
cathode or an anode. The structural support 40 further includes a series 
of generally identical apertures 47 for providing a passage to the 
electrolyte, through the end electrode 35. 
Preferably, the thin layer of high specific area material 44 is composed of 
a composite material formed by impregnating a carbon cloth with carbon 
aerogel, wherefore, the thin layer 44 will also be referred to as carbon 
aerogel composite electrode 44. The new use of this carbon aerogel 
composite electrode 44 relies primarily on the unique open-cell 
nanostructure of the carbon aerogel material, including its interconnected 
porosity, ultrafine pore sizes and huge surface area. This carbon aerogel 
composite material is described in more detail in an article entitled 
"Carbon Aerogel Composite Electrodes", by Joseph Wang et al., in Anal. 
Chem. 1993, vol. 65, pages 2300-2303, and in U.S. Pat. No. 5,260,855 by 
James L. Kaschmitter et al. entitled "Supercapacitors Based on Carbon 
Foams". Another method of producing a porous carbon foam is described in 
U.S. Pat. No. 5,358,802 to Mayer et al. 
Carbon aerogels are synthesized by the polycondensation of resorcinol and 
formaldehyde (in a slightly basic medium), followed by supercritical 
drying and pyrolysis (in an inert atmosphere). This fabrication process 
results in unique open-cell carbon foams that have high porosity, high 
surface area (400-1000 m.sup.2 /g), ultrafine cell/pore sizes (less than 
50 nm), and a solid matrix composed of interconnected colloidal-like 
partides or fibrous chains with characteristic diameters of 10 nm. The 
porosity and surface area of aerogels can be controlled over a broad 
range, while the pore size and particle size can be tailored at the 
nanometer scale. The carbon aerogels further offer both low density and 
ultrasmall cell size. 
The use of the carbon aerogel composite electrode 44 presents a significant 
improvement over conventional devices, since in these latter devices only 
part of the specific area is effective for removing ions, and the 
remaining area is not effective because of the potential gradients across 
the electrodes. By using thin sheets of carbon aerogel composite as 
electrodes 44, substantially the entire surface area of these monolithic 
microporous electrodes is effective in the removal of ions, due to the 
desirable potential distribution in the aerogel. 
While the best mode of the present invention utilizes thin sheets of carbon 
aerogel composite as electrodes, beds of carbon aerogel particles can 
alternatively be used to form electrodes. Such beds of carbon aerogel 
particles have much higher specific area and sorption capacity than beds 
of conventional carbon powder, and therefore they are superior electrodes 
for capacitive deionization. 
In FIG. 3, the end electrodes 35, 36 and the adjacent intermediate 
electrodes 37-43 are separated by means of thin sheets of insulating 
material, such as rubber gaskets 50-56. Each gasket has a large, square 
aperture in the center to accommodate adjacent carbon aerogel composite 
electrodes 44. As shown in FIGS. 4A,B the structural support 40 includes a 
plurality of peripheral holes 48. When the cell 30 is to be assembled, the 
peripheral holes 48 are coaligned with corresponding peripheral holes in 
the insulation layers 33, 34 and the rubber gaskets 50-56, and a plurality 
of threaded rods 58, 59 are inserted through these coaligned holes, and 
are tightened by conventional means, such as nuts 60-63. Non-compressible, 
insulating, hollow, cylindrical spacers or compression rings 50A can be 
inserted in the peripheral holes of the rubber gaskets 50-56, and used to 
control the spacing of adjacent electrodes. A plurality of compression 
sleeves 64A, 64B can be added to provide additional force for sealing. 
While only two threaded rods 58, 59 are shown in FIG. 3, in this particular 
example, eight threaded rods are used to tighten the cell 30 to a leak 
proof state. These eight rods are designed to fit through the eight 
peripheral holes 48 in the structural support 40, as well as through the 
corresponding peripheral holes in the rubber gaskets 50-56 fitted with 
hollow-cylindrical spacers 50A (FIG. 4B). 
Once the cell 30 is assembled, a plurality of chambers 65-71 are formed 
between the end and intermediate electrodes 354 These chambers 65-71 are 
adapted to fluidly communicate with each other via a plurality of 
apertures 73-79 in the structural supports of the intermediate electrodes 
37-43, respectively. These apertures 73-79 are not coaligned, and may be 
either holes or slits. They are positioned so that the fluid path 
therethrough, within the chambers 65-71, is forced to flow across all the 
exposed surfaces of the carbon aerogel composite electrodes 44. In FIG. 3, 
the fluid first flows from left-to-right, then from right-to-left, and so 
on. 
In operation, and merely for illustration purposes, the anodes and the 
cathodes of the cell 30 are interleaved in an alternating way. In this 
respect, every other electrode is an anode, starting with the end 
electrode 35, and ending with the intermediate electrode 43, and the 
remaining intermediate electrodes 37, 39, 41, 42 and the end electrode 36 
are cathodes. As such, each pair of adjacent electrodes (anode and 
cathode) forms a separate capacitive deionization/regeneration unit. 
The stream of raw fluid or electrolyte to be processed enters the cell 30 
through a plurality of superposed, coaxially registered, generally 
circularly or rectangularly shaped openings, including an aperture 80 in 
the end plate 31, one or more apertures 82 in the insulation layer 33, and 
the apertures 47 in the end electrode 35. The fluid flows through the 
first chamber 65 as indicated by the arrow A, is substantially parallel to 
the electrode surface. By polarizing the first deionization/regeneration 
unit, ions are removed from the fluid stream electrostatically, and are 
held in the electric double layers formed at the carbon aerogel surfaces 
of the electrodes 35 and 37. This will purify the fluid stream, at least 
partially. 
The fluid stream then flows through the aperture 73 into the next chamber 
as indicated by the arrow B, where additional ions are removed by the 
polarization of the second deionization/regeneration unit 81 formed by the 
intermediate electrodes 37 and 38, thus further purifying the fluid 
stream. The fluid stream continues to travel through the remaining 
deionization-regeneration units, indicated by the arrows C through G, and 
is progressively purified. Thereafter, as indicated by the arrow H, the 
purified fluid stream exits the cell 30 via a plurality of coaxially 
aligned apertures 90, 91, 92 in the end electrode 36, insulator layer 34, 
and the back plate 32, respectively. 
The fluid stream leaving the cell 30 is purified since the contamination 
ions have been removed and collected by the cell 30. One important 
characteristic of the novel configuration of tell 30 is that the fluid 
stream does not flow through the porous electrodes, but rather in an open 
channel, with a relatively low pressure drop, and with minimal energy 
consumption for pumping. The energy expended to operate the cell 30 is 
minimal. In this respect, the fluid stream does not necessarily need to be 
pressurized by a pump to cause it to flow through the cell 30; gravity can 
be used, if desired. 
Also, if the inventive deionization process were used for water 
desalination, the energy expended is that which is necessary to remove 
salt from water, whereas in conventional desalting processes, such as 
evaporation and reverse osmosis, the energy is expended to remove the 
water from salt. As a result, the present process is orders-of-magnitude 
more energy efficient than conventional processes. 
Additionally, the pressure drop in the capacitive deionization cell 30 is 
insignificant compared to that needed for reverse osmosis. Also, contrary 
to conventional deionization processes, the electrodes have a very high 
and immobilized specific surface area and a high removal efficiency, and 
the carbon aerogel particles are not entrained by the fluid stream. 
As the CDI cell 30 is saturated with the removed ions, the capacitive units 
become fully charged, and a sensor (not shown) indicates that such 
condition has been reached, and that the cell 30 is ready for 
regeneration. Contrary to conventional chemical regeneration processes, 
the present regeneration process is carried out electrically, thus 
eliminating the secondary wastes. The regeneration process takes place by 
disconnecting the power supply, by interconnecting the anodes and the 
cathodes, by electrically discharging all electrodes 35-43, and by flowing 
a suitable fluid stream of water or another suitable solution through the 
cell 30, along the same path described above in connection with the 
deionized stream of raw fluid. As a result, the capacitive units are 
discharged through, and release the previously removed ions into the 
flowing fluid stream, until the cell 30 is fully regenerated, at which 
time, the regeneration process is stopped and the deionization process 
restarts. The timing control of the deionization--regeneration process 
could be manual or automated. 
The overall shape and dimensions of the cell 30 are determined by the mode 
of use and application of the CDI systems. In a preferred embodiment, the 
end plates 31 and 32 are identical, rectangularly shaped, and made of 316 
stainless steel or another appropriate corrosion resistant alloy. The end 
plates, unlike the electrodes, are not polarized. However, other shapes 
can be used; e.g., if the cell 30 were cylindrically shaped, the end 
plates 31 and 32 are circular, or if the cell 30 were conically shaped, 
one of the end plates 31, 32 can have a smaller size than the other plate, 
and the size of the electrodes therebetween gradually increases from one 
end plate to the other. 
The insulator layers 33 and 34, as well as 50-56 are preferably made of an 
elastic, compressible, insulating, non-leachable material. For example, 
Teflon, Viton, Neoprene and similar materials are suitable materials for 
specific applications. 
However, other suitable materials can be used. The structural supports 40 
(FIGS. 4A, 4B) of the end electrodes 35, 36 and the intermediate 
electrodes 37-43 are preferably made of titanium, or, alternatively they 
can be selected from a suitable group of materials such as coated, 
corrosion-resistant, iron-chromium-nickel based alloys. Suitable coatings 
include gold, platinum, iridium, platinum-iridium alloys, or other 
corrosion resistant materials. 
In one example, the back plates are similarly sized and rectangularly 
shaped, and have the following dimensions: length 8.38 cm; width 7.87 cm; 
and thickness 0.16 cm. However, other dimensions can alternatively be 
used. The tab 42A, used to make electrical connection with the electrode, 
extends integrally from the structural support 40, and is generally, but 
not necessarily rectangularly shaped. In the above example, the tab 42A 
has the following dimensions: length 1.78 cm; width 2.03 cm; and thickness 
0.16 cm. 
As shown in FIGS. 4A and 4B, the structural support 40 includes a plurality 
of (in this example eight) peripheral holes 48 through which the threaded 
rods 58, 59 pass, for aligning the electrodes 35-43. Several elongated 
apertures 47 are shown co-aligned outside, along, and adjacent to one side 
105 of the sheets of aerogel carbon composite 44. These apertures 47 are 
sized so as to distribute the flow uniformly across the sheet of carbon 
aerogel composite with minimal pressure drop. The number, position and 
size of these apertures 47 can vary with the desired mode of use and 
application of the cell 30. 
The carbon aerogel composite electrode 44 is shown as having a square 
shape, and as being centrally positioned relative to the structural 
support 40. In the present example, the carbon aerogel composite electrode 
44 has a side dimension of 6.86 cm, a projected area of 23.5298 cm.sup.2, 
and a thickness of about 0.0127 cm. The electrode 44 can also be circular, 
rectangular, or triangular. 
While the electrode 44 is preferably made of carbon aerogel composite, any 
monolithic, porous solid that has sufficient electrical conductivity and 
corrosion resistance (chemical stability) to function as an electrode, can 
alternatively be used. Such alternative materials include porous carbon 
electrodes typically used in fuel cells, reticulated vitreous carbon 
foams, porous metallic electrodes made by powder metallurgy, packed 
columns of powder (i.e., packed beds of carbon powder, tungsten carbide 
powder, various conductive oxides including tin oxide and iridium oxide), 
a mixture of these and other materials, electrolcatalysts such as Pt, Ir, 
SnO.sub.2, or porous electrodes, that are made by microfabrication 
techniques, including photolithography, electroforming, physical vapor 
deposition (evaporation, sputtering, etc.) and etching, and conductive 
sponges of any type. 
The electrode 44 could also be fabricated as a packed bed of carbon aerogel 
particles, having significantly higher specific surface area than the 
conventional packed carbon bed described in the Department of Interior 
Report and the Newman Article. This design offers the advantage of greatly 
enhanced capacity for electrosorption of ions, adsorption of organics, and 
capture of fine particles, but would require flow through porous media. 
In the example illustrated in FIG. 3, the chambers 65-71 have a volume of 
about 300 ml, which corresponds to the minimum possible liquid volume 
required for regeneration. In other embodiments, the chambers 65-71 can 
have different volumes, such that the minimum possible liquid required for 
regeneration can be further reduced. 
FIG. 5 illustrates a first embodiment of a capacitive 
deionization--regeneration system 111 which generally includes one or a 
stack of sequential (i.e., serial) electrochemical cells 30 (FIG. 3), an 
electrical circuit 112, and a fluid circuit 114, such that the fluid 
circuit 114 regulates the flow of the fluid stream through the cell 30, 
under the control of the electrical circuit 112. 
Electrical circuit 112 includes a voltage controlled D.C. power supply 117 
which provides a constant D.C. voltage across the adjacent pairs of 
electrodes 35-43 (FIG. 3). A resistive load 120 and a switch 121 are 
connected in parallel, across the positive and negative terminals 122A, 
122B, respectively, of the power supply 117, and are used to discharge, or 
regenerate the single electrochemical cell 30. 
The electrical circuit 112 further includes a control system, as a 
triggering device to initiate regeneration. This control system utilizes 
on-line conductivity cells, ion selective electrodes, pH electrodes, 
polarographic sensors, impedance sensors, optical transmission cells, and 
light scattering sensors. The components that can be triggered by this 
on-line control system include power supplies, valves and pumps. 
A differential amplifier 126 is connected across a shunt resistor 118, and 
is further connected to an analog-to-digital converter 127 and a computer 
128. The shunt resistor 118 is used to measure the current flowing from 
the power supply 117 to the cell 30, for monitoring and control. The 
differential amplifier 126 amplifies the voltage across the shunt resistor 
118 to a level that is monitorable by the analog-to-digital converter 127 
and the computer 128. Another differential amplifier 125 is connected 
across the terminals 122A, 122B of the power supply 117, via the shunt 
resistor 118, and operates as a buffer between the power supply 117 and 
the analog-to-digital converter 127, for protecting the analog-to-digital 
converter 127. 
The differential amplifier 125 is connected across the terminals of the 
cell 30, and serves as a buffer between the cell 30 and the A/D converter 
127. In operation, as the cell 30 is used to deionize the electrolyte, the 
switch 121 is open. In order to start the regeneration process, the power 
supply 117 is turned off, or disconnected, and the switch 121 is closed, 
for providing a path for the discharge current. 
The analog-to-digital converter 127 is connected to the inlet stream of the 
fluid circuit 114, via a plurality of sensors, such as a thermocouple 134, 
a conductivity probe 135, and a pH sensor 136, via respective transducers 
131, 132, 133. The thermocouple 134 enables the monitoring of the 
temperature of the inlet stream, in order to prevent the overheating of 
the electrolyte, and further enables the calibration of the conductivity 
probe 135. Conductivity probe 135 is an on line sensor which monitors the 
conductivity of the inlet stream. The pH sensor measures the pH level of 
the inlet stream. The transducers 131, 132, 133 convert the measurements 
of the thermocouple 134, conductivity probe 135 and pH sensor 136 into 
voltages that are readable by and compatible with the analog-to-digital 
converter 127. A flow rate meter 154 measures the flow rate of the inlet 
stream. 
The fluid circuit 114 includes a feed and recycle tank 150 which contains 
the raw fluid to be processed by the cell 30. The fluid stored in the feed 
and recycle tank 150 can be replaced with a continuous inflow of raw 
fluid. A valve 151 is fluidly connected between the feed and recycle tank 
150 and a pump 152. The speed of the pump 152 is used to control the flow 
rate of the inlet stream to the cell 30. The outlet stream is respectively 
connected, via two valves 156, 157, to a product tank 160 for storing the 
purified fluid, and to the feed and recycle tank 150. Valves 156 and 157 
are used to select the mode of operation: batch mode or complete recycle; 
continuous mode or once through. 
Similarly to the inlet stream, the analog-to-digital converter 127 is also 
connected to the outlet stream of fluid circuit 114, via three transducers 
141, 142, 143, a thermocouple 144, a conductivity probe 145, and a pH 
sensor 146. 
In the continuous mode of operation, the raw fluid or electrolyte to be 
deionized is initially stored in the feed and recycle tank 150, and the 
valve 157 is closed. The pump 152 is activated for pumping the fluid from 
the feed and recycle tank 150 to the cell 30, where the fluid stream is 
deionized and purified. The purified effluent is then routed to the 
product tank 160 via the open valve 156. In certain applications, it would 
be desirable to recycle the fluid stream more than once, in order to 
obtain the desired level of purification, in which case, the valve 156 is 
closed, and the valve 157 is opened, in order to allow the fluid stream to 
be recycled through the cell 30. 
When the cell 30 is saturated, the deionization process is automatically 
interrupted and the regeneration process starts. For this purpose, the 
power supply 117 is disconnected, and a regeneration tank (not shown) is 
fluidly connected to the pump 152 and the cell 30. The regeneration tank 
contains a suitable regeneration solution (only a relatively small amount 
is needed and can have the same composition as the feed stream, for 
instance raw water), or alternatively, pure water can be used. The 
regeneration solution is passed through the cell 30, and the regeneration 
process takes place by placing the removed ions back into the regeneration 
solution. 
In the event the electrodes become saturated with organic contaminants, it 
is possible to clean and regenerate the carbon composite electrode 44, or 
other porous monolithic electrodes by passing solutions of chemically and 
electrochemically regenerated oxidants, including but not limited to 
Ag(II), Co(III), Fe(III), ozone, hydrogen peroxide, and various bleaches, 
through the electrochemical cell 30. 
FIGS. 12 through 14 represent empirical timing charts using the capacitive 
deionization--regeneration system 111 of FIG. 5. 
FIG. 6 includes three superposed timing charts A, B, C, illustrating the 
operation of the capacitive deionization--regeneration system 111 of FIG. 
5, used for the deionization and regeneration of 100 micromhos NaCl 
solution. Chart A represents the conductivity of the electrolyte, and 
includes two curves, one illustrating the inlet stream conductivity and 
the other curve illustrating the outlet stream conductivty. Chart B 
represents the current flowing through the cell 30. Chart C represents the 
voltage across the cell 30. T represents the deionization-regeneration 
cycle. 
FIG. 7 illustrates a second embodiment of the capacitive 
deionization--regeneration system 175 using at least two parallel 
electrochemical cells 30A and 30B, both similar to the cell 30 shown in 
FIG. 3. FIGS. 8A,B,C show an exemplary operation of the capacitive 
deionization system 175 using 100 micromhos NaCl solution. One of the main 
advantages of the system 175 is its ability to maintain a continuous 
deionization and regeneration operation. The system 175 is generally 
similar to the system 111, and uses two cells 30A and 30B, such that when 
one cell 30A or 30B is deionizing the fluid stream, the other cell is 
regenerating, in preparation for the deionization process. Therefore, the 
operation of the system 175 is cyclical and continuous. For each one of 
the cells 30A and 30B, each cycle includes two half cycles. The first half 
cycle is the deionization process, and the second half cycle is the 
regeneration process, such that the cycles of the cells 30A and 30B are 
essentially 180 degrees out of phase. 
The system 175 includes a power supply and switching apparatus 176 
connected across both cells 30A and 30B, for selectively operating these 
cells. While the preferred embodiment of the system 175 includes operating 
one cell for deionizing a fluid stream while the other cell is 
simultaneously being regenerated, both cells 30A and 30B can 
simultaneously perform the same process, i.e., deionization or 
regeneration. 
A controller 178 regulates a plurality of inflow and outflow valves 179, 
180a, 180b, 180c, 181a, 181b, 181c, and 182, for controlling the flow of 
the fluid stream to and from the cells 30A and 30B. An analog-to-digital 
converter 185 converts measurement signals from a plurality of 
conductivity and ion specific sensors 187, 188 disposed along the fluid 
circuit of the system 175, and transmits corresponding digital signals to 
a computer 190, which controls the controller 178, the power supply and 
switching apparatus 176, and thus the overall operation of the system 175. 
While only two sensors 187, 188 are shown, other sensors can also be 
included to provide additional feedback data to the computer 190. 
FIGS. 8A,B,C are three timing charts illustrating the operation of the 
capacitive deionization--regeneration system 175 of FIG. 7. In this case, 
no electrical power released during the regeneration of one cell is used 
by the other cell for deionization. FIG. 8A shows the conductivity 
(micromhos) versus time (seconds), of the effluent fluid streams flowing 
from the cells 30A and 30B. FIG. 8B shows the current (amperes) flowing 
through the cells 30A and 30B. FIG. 8C shows the voltage (volts) applied 
across each cell 30A, 30B. In the case of aqueous (water-based) streams, 
optimum performance is obtained with a voltage pulse having an amplitude 
of 0.6-1.2 volts. Lower voltages diminish the capacity of the electrodes 
while significantly higher voltages cause electrolysis and associated gas 
evolution from the electrodes. The solid lines in FIGS. 8A,B,C, relate to 
the behavior of the cell 30A, while the phantom or broken lines relate to 
the behavior of the cell 30B. 
In FIG. 8C, the solid line illustrates a series of square shaped voltage 
pulses 191, 192, 193 applied across the cell 30A, with a plateau value of 
about 1.2 volts, while the broken line illustrates a series of square 
shaped voltage pulses 194, 195 applied across the cell 30B, also with a 
plateau value of about 1.2 volts. It should however be understood that 
different voltages can be applied. Specifically, in the case of aqueous 
streams, the preferred voltages range between 0.6 and 1.2 volts. The 
voltage pulses applied to cells 30A and 30B are 180 degrees out of phase. 
The voltage pulse 191 in FIG. 8C will cause the cell 30A to progress with 
the deionization process, as illustrated by the current curve 197 in FIG. 
8B, and by the conductivity curve 198 in FIG. 8A. While the voltage pulse 
191 in FIG. 8C is applied across the cell 30A, the anodes and cathodes of 
cell 30B are connected together through an external load, causing cell 30B 
to regenerate, as illustrated by the current curve 199 in FIG. 8B, and by 
the conductivity curve 200 in FIG. 8A. 
Thereafter, the voltage pulse 194 is applied across the cell 30B causing it 
to progress with the deionization process, as illustrated by the current 
curve 201 in FIG. 8B, and by the conductivity curve 202 in FIG. 8A. While 
the pulse 194 is applied across the cell 30B, the anodes and cathodes of 
cell 30A are connected together through an external load, causing cell 30A 
to regenerate, as illustrated by the current curve 203 in FIG. 8B, and by 
the conductivity curve 204 in FIG. 8A. 
The foregoing deionization--regeneration cycle enables the system 175 to 
operate continuously without interruption, since, as one of the cells 30A, 
30B becomes saturated, the other cell is almost or completely regenerated, 
and is ready to proceed with the deionization process. As a result, the 
purified fluid stream at the output of the system 175 is continuous. The 
operation of the system 175 might be particularly attractive in nuclear 
power plants for scavenging contaminants from boiler water. 
To briefly summarize the operation of the system 175, during the 
deionization process, the corresponding cell, either 30A or 30B, 
capacitively charges the electrode pairs forming it, thereby removing ions 
from the fluid stream passing through it. At the beginning of the 
deionization process, the cell has been completely and electrically 
discharged; at the end of the deionization process, the cell has been 
completely and electrically charged. Subsequently, during the regeneration 
process, the corresponding cell, either 30A or 30B, capacitively 
discharges the electrode pairs forming it, thereby placing ions into the 
fluid stream passing through it, greatly increasing the concentration of 
ions in that stream. At the beginning of the regeneration process, the 
cell has been completely and electrically charged; at the end of the 
regeneration process, the cell has been completely and electrically 
discharged. 
FIG. 9 illustrates another characteristic of the present invention, namely 
an enhanced energy efficiency or energy saving mode. In this particular 
mode of operation, a timing chart is used to illustrate the potential 
across each of the cells 30A and 30B, where the solid lines relate to the 
behavior of the cell 30A, while the broken lines relate to the behavior of 
the cell 30B. Starting at time t.sub.0, the cell 30B is fully charged and 
ready to be regenerated, while the cell 30A is fully discharged and ready 
to begin the deionization process. 
While it would be possible to disconnect the cell 30B from the power supply 
176, and to connect the power supply 176 to the cell 30A, it is now 
possible to save energy, and in certain applications, save a significant 
fraction of the energy required to operate the system 175. According to 
the present invention, at time t.sub.0, the cells 30A and 30B can be 
connected, such that cell 30B is discharged through the cell 30A, as 
indicated by the curve 210, causing the cell 30A to be charged, as 
indicated by the curve 211. Electrical energy stored in the cell 30B is 
used to power the cell 30A during deionization in the cell 30A. 
As soon as an equilibrium voltage is reached, i.e., approximately 0.6 volts 
at time t.sub.1, the cell 30A is connected to the power supply 176 so that 
the charging process can be completed, as illustrated by the curve 212. 
Simultaneously, the cell 30B is completely discharged through an external 
load, as indicated by the curve 213. As a result, a significant portion of 
the energy required to charge the cell 30A is generated by the cell 30B, 
with the remaining energy supplied by the power supply 176. 
Thereafter, at time t.sub.2, the cell 30A is fully charged and is ready for 
regeneration, while the cell 30B is completely discharged, and is ready 
for the deionization process. The cells 30A and 30B are then connected, 
such that the cell 30A is discharged through the cell 30B, as illustrated 
by the curve 214, while the cell 30B is charged, as illustrated by the 
curve 215. 
As soon as the equilibrium voltage is reached at time t.sub.3, the cell 30B 
is connected to the power supply 176 so that the charging process can be 
completed, as illustrated by the curve 216, and the cell 30A is allowed to 
completely discharge through an external load, as illustrated by the curve 
217. As a result, a significant portion of the energy required to charge 
the cell 30B is generated by the cell 30A, with the remaining energy 
supplied by the power supply 176. 
FIG. 10 illustrates a third embodiment of a deionization--regeneration 
system 220 which includes a matrix of systems 222, 224, 226 similar to the 
system 175 (FIG. 7), which are connected in series. Each system includes 
at least one pair of cells which are connected and which operate as 
described in relation to the system 175. Thus, the system 222 includes 
cells (1,1) and (1,2); the system 224 includes cells (2,1) and (2,2); and 
the system 226 includes cells (n,l) and (n,2). Each of the systems 222, 
224, 226 includes a power supply and switching system 176A, 176B, 176C, 
which is similar to the power supply and switching system 176 shown in 
FIG. 7. 
In operation, when one cell, i.e., (1,1) of the pair of cells, i.e., 222, 
is performing the deionization process, the other cell, i.e., (1,2), is 
being regenerated. While only three systems 222, 224, 226, each including 
two cells, are shown, a different combination of systems or cells can be 
selected. 
One novel application for the system 220 is the progressive and selective 
deionization and regeneration feature. Different potentials (V.sub.1, 
V.sub.2, V.sub.n) are applied across each system (222, 224, 226, 
respectively) in order to selectively deionize the influent fluid stream, 
by having each system (222, 224, 226) remove different ions from the fluid 
stream. Thus, in this particular example, V.sub.1 &lt;V.sub.2 &lt;V.sub.n, such 
that the system 222 is capable of removing reducible cations such as 
Cu.sup.++ ; the system 224 is capable of removing reducible cations such 
as Pb.sup.++ ; and the system 226 is capable of removing non-reducible and 
non-oxidizable ions such as Na.sup.+, K.sup.+, Cs.sup.+, C.sup.-, or other 
similar ions, which remain in their ionic state. 
FIGS. 11A,B, represent an electrochemical cell 250, and a portion 252 
thereof. The cell 250 can be adapted for use as part of the capacitive 
deionization-regeneration systems 111 and 175 of FIGS. 5 an 7, 
respectively. The cell 250 includes a plurality of electrodes 253, 254 
that are separated by a porous separator or membrane 255. The separator 
255 is sandwiched between two adjacent electrodes 253, 254, and allows an 
open channel to be formed and defined therebetween. The electrodes 253 and 
254 are similar to the electrodes of cells 30, 30A and 30B described 
above. The electrodes 253, 254 and the separator 255 are rolled spirally 
together, so that the electrolyte flows in the open channels formed 
between the electrodes 253, 254, and exits the cell 250 with minimal flow 
resistance. While the cell 250 has been described as including two 
electrodes 253, 254 and one separator 255, additional electrodes and 
separators can be used. 
FIGS. 15 and 16 illustrate another double-sided electrode 300, for use in 
the cells and systems described herein. While a double sided electrode 
will be described in detail for illustration purpose only, a single-sided 
electrode can be designed using the same or similar concepts. 
Electrode 300 has a generally similar function to electrode 35 of FIG. 4A. 
Electrode 300 includes a substantially flat, thin, corrosion resistant, 
rectangularly shaped structural support member 302, which comprises a 
dielectric board, substrate, or sheet 303. In one embodiment, support 
member 302 is fabricated using printed circuit board technology for 
replacing the more expensive metallic (i.e., titanium) structural support 
40 of FIG. 4A. Thus, support member 302 may be a metallized epoxy board 
formed by metallizing at least part of dielectric board 303 with a thin 
metallic layer or film 304. In another embodiment, dielectric board 303 
includes a fiber glass epoxy board. 
Metallic layer 304 may be composed of any suitable metal, such as titanium, 
and can be formed through alternative manufacturing processes, including 
sputtering the metal onto the surface of dielectric board 303 and chemical 
vapor deposition (CVD) of metallic film or layer 304 on the surface of 
dielectric board 303. The opposite side of dielectric board 303 is 
similarly metallized with a metallic layer 306. 
A tab 308 extends integrally from one side of metallic layer 304, for 
connection to one pole of a D.C. power source. If tab 308 lacks structural 
rigidity required for specific applications, dielectric board 302 can be 
extended underneath tab 308 to provide the required mechanical support. 
Another tab 310 similarly extends integrally from the opposite metallic 
layer 306 to the other pole of the D.C. power source. Both tabs 308 and 
310 could also have the same polarity. 
A thin sheet 314 of high specific area, porous, conductive, monolithic 
material (e.g., carbon aerogel composite) is bonded to the surface of 
metallic layer 304. In one embodiment, sheet 314 is glued to metallic 
layer 304 with an electrically conductive epoxy. Conductive sheet 314 is 
substantially similar in composition to sheet 44 in FIG. 4A. Another thin 
conductive sheet 316 has a similar composition to that of conductive sheet 
314, and is bonded to the opposite metallic sheet 306. 
Structural support member 302 further includes a series of generally 
identical apertures 320 for providing a passage to the electrolyte through 
electrode 300, and peripheral holes 322, which are similar to apertures 47 
and peripheral holes 48 in FIG. 4A. 
FIG. 17 shows a cartridge 350 which includes a case 352 and a cell 355 
enclosed therein. Cell 355 includes a plurality of electrodess 357, 358, 
359, disposed in a parallel relationship relative to each other. While 
only three electrodes are shown, a different number of electrodes may be 
selected. 
In one embodiment, the end electrodes 357, 359 are single-sided, while the 
intermediate electrode 358 is double-sided. Electrodes 357, 358, 359 may 
be generally similar in design, construction and composition to electrode 
300 of FIGS. 15 and 16. In another embodiment, electrodes 357, 358, 359 do 
not include a structural support member 302. High specific surface area, 
porous, conductive, monolithic materials may be used alone as electrodes 
and are separated and maintained at a predetermined distance by either 
dielectric spacers or placement grooves in case 352, such that adjacent 
electrodes, e.g., 357, 358 define channels or clearances 360 therebetween. 
In these embodiments, electrodes 357, 358, 359 may form one or more 
integral cells, such as cell 355, that can be removed from, and replaced 
within case 352 to form a cell or cartridge 350. 
In use, cell 355 is secured to, and placed within case 352, and is 
connected to a D.C. power source. A fluid stream is allowed to flow freely 
within channels 360, under the force of gravity, between electrodes 357, 
358, 359, as indicated by the arrows labeled INFLOW and OUTFLOW. The basic 
operation of cartridge 350 has been explained above in relation to cell 
30. A pump (not shown) may also be used. While cell 355 is illustrated as 
having three flat electrodes 357, 358, 359, other electrodes of different 
shapes may be used. For instance electrodes 357, 358, 359 may be 
positioned within case 352 so as to provide a serpentine flow (See FIG. 
3). 
One advantage presented by cartridge 350 is that cell 355, or even the 
entire cartridge 350, can be easily replaced for maintenance or other 
purposes. Additionally, cartridge 350 can be scaled to any desired size. 
Furthermore, the size and weight of cartridge 350 are reduced by 
eliminating the structural support 302 in FIG. 15. 
FIGS. 18, 19 show two other electrodes 400, 401. Electrode 400 generally 
includes a flat, rectangularly shaped, centrally hollow, peripheral 
support member 402. Similarly, electrode 401 generally includes a flat, 
rectangularly shaped, centrally hollow, peripheral support member 404. 
Both electrodes 400, 401 are maintained at a predetermined separation 
distance by means of a dielectric separator 406. While only two electrodes 
400 and 401 may be connected to form a cell, more than two electrodes can 
be combined to form a cell. 
Support members 402, 404 are generally similar in composition and 
construction. Support member 402 is made of conductive material, such as 
titanium, and extends integrally from one of its sides into a tab 409 for 
connection to a pole of a D.C. power source. Support member 402 can be 
formed of a metallized epoxy board. A plurality of peripheral holes 410 
are formed in support member 402 for assembling a cell, as before. 
Electrode 400 further includes a refill cartridge 415 that fits within, and 
fills a central opening surrounded by peripheral support member 402. In 
general, cartridge 415 is rectangularly shaped, but other shapes can be 
used. Cartridge 415 may include a refill member comprised of a porous 
sponge 417 made by powder metallurgy. Sponge 417 can be made of titanium, 
platinum or other suitable metal. In a preferred embodiment, sponge 417 
can be made of reticulated vitreous carbon (RVC) impregnated by 
resorcinal-formaldehyde carbon aerogel. Sponge 417 is coated on its upper 
and lower sides with two thin sheets 419, 420 of high specific area, 
porous, conductive, monolithic material, such as carbon aerogel composite. 
Sponge 417 could also be a packed volume of particulate carbon, carbon 
aerogel, or metal. Buckminster fullerene or "Bucky Balls" may also be used 
to fill the central opening. 
Conductive sheets 419, 420 may be bonded, such as by gluing, to 
substantially the entire surface of the sponge upper and lower sides. 
Conductive sheets 419, 420 are electrically and physically connected to 
support member 402, so as to establish electrical contact with the 
corresponding pole of the D.C. power source. 
Electrode 401 is generally similar in construction and composition to 
electrode 400, and includes a refill cartridge 422 coated with two 
conductive sheets 423, 425. In operation, electrode 400 is connected to 
one pole of the D.C. power source, while electrode 401 is connected to the 
other pole. A fluid stream is allowed to flow, either freely, under the 
force of gravity, or under minimal pressure, through a channel 430 defined 
between electrodes 400, 401, as indicated by the arrows labeled INFLOW and 
OUTFLOW. The basic operation of the cell or cartridge formed of at least 
electrodes 400, 401 has been explained above in relation to cell 30. 
FIG. 20 shows another cartridge or cell 450 which includes at least two 
substantially similar electrodes 452, 454 that are connected to opposite 
poles of a D.C. power source. Electrodes 452, 454 are maintained at a 
predetermined separation distance by a dielectric separator 456. While 
separator 456 is optional, electrodes 452, 454 are not allowed to be 
electrically connected. 
Electrode 452 is porous and generally rectangularly shaped. Electrode 452 
may be made of any spongeous, foamy or porous material, such as a metal 
sponge or reticulated vitreous carbon (RVC) impregnated with carbon 
aerogel or a similar high specific area, conductive, monolithic substance, 
in order to enhance the active surface area of electrode 452. Different 
electrodes may be impregnated with different compounds. 
In use, cell 450 is connected to the D.C. power supply, and a fluid stream 
is allowed to flow, either freely, under the force of gravity, or under 
minimal pressure, through electrodes 452, 454, as indicated by the arrows 
labeled INFLOW, FLOW and OUTFLOW. The basic operation of cell 450 is 
similar to cell 30. The fluid stream flows through the large pores of 
electrodes 452 and 454. Carbon aerogel is used to coat the surfaces of the 
carbon foam. 
Chemical regeneration may include the use of strong acids like HCl, 
HNO.sub.3, H.sub.2 SO.sub.4, HS, so that they dissolve solid metals that 
have become deposited on the surface of the (carbon aerogel) electrode, 
and remove other types of scale formation. Alternatively, chemical 
regeneration could include the use of strong bases capable of dissolving 
various types of scales and impurities in order to regenerate the 
electrodes. 
In one embodiment, a heavy organic solvent is used to dissolve heavy 
organic fouling, followed by a strong chemical oxidant such as ozone, 
hydrogen peroxide, Fenton's reagent, silver (II), cobalt (III), iron 
(III), or peroxydisulfate (S.sub.2 O.sub.8.sup.-2). These oxidants can 
oxidize very thin layers of organic contaminants that have been 
chemisorbed to the surface of the electrode, thereby regenerating the 
electrode. Thus, an important aspect of the present invention is that the 
carbon electrodes are chemically resistant and regenerative. Additionally, 
the periodic reversal of the electrode potential will permit the electrode 
to regenerate very effectively. The regeneration of the electrode will 
prolong the effective life of the electrode and cell, and will lower the 
maintenance and operating cost. Periodic voltage reversal can be done 
while passing feed stream through the cell, or while passing chemical 
regenerant (acid, base, etc.) through the cell. 
According to the present invention, a new class of electrosorption media 
may be used in the present capacitive deionization and regeneration 
systems, cells and methods. These electrosorption media are less 
susceptible to poisoning and degradation than carbon-based materials, 
including carbon aerogel, reticulated vitreous carbon foam and carbon 
powder. They include a number of metallic carbides that can be in the form 
of powders, particles, foams, sponges, or porous solids made by flame 
spraying or powder metallurgy, sputtered thin films, or formed by other 
processes. These carbides include TiC, ZrC, VC, NbC, TaC, UC, MoC, WC, 
MO.sub.2 C, Cr.sub.3 C.sub.2, Ta.sub.2 C, and similar carbides that are 
stable at high temperatures, chemically resistant, and highly conductive 
with a resistivity ranging between about 17 .mu.ohm-cm and 1,200 
.mu.ohm-cm. 
FIG. 21 shows a cell 460 that may be adapted for use in the capacitive 
cells and systems of the present invention. Cell 460 can be used in 
several other applications, such as in electrolyte capacitors for energy 
storage, and for load leveling in electric vehicles. 
Cell 460 is mainly formed of two outer conductive plates 462, 463 connected 
to a D.C. power source. Two beds 465, 466 of a powdered or granular 
electrosorption medium selected from the above group, as well as activated 
carbon powder and various metallic powders, are retained against their 
corresponding plates 465, 466 by means of two porous or conductive 
membranes 468, 469, respectively. 
A channel 470 is formed centrally between membranes 468, 469, to insure a 
free, unobstructed flow of fluid therethrough. The principle of operation 
of cell 460 is similar to that of capacitive deionization cells described 
herein. 
FIG. 22 shows another cell 475 for use in an electrochemically-regenerated 
ion exchange (ERIE). Cell 475 includes two composite electrodes 476, 477 
that define a central channel 478 therebetween. Cell 475 can also be 
modified for use with the capacitive deionization systems and cells 
disclosed herein. For example, the composite electrodes 476, 477 can be 
readily modified for use in cell 30 (FIG. 3). Moreover, while central 
channel 478 is illustrated as a straight planar channel, it may assume 
various shapes and designs, e.g. a serpentine path. 
Electrode 476 is a cathode while electrode 477 is an anode. Electrode 476 
includes an outer conductive plate 480, an electrosorptive bed 482 and a 
polymer coating 483. Conductive plate 480 is connected to the negative 
pole of a D.C. power source. Conductive plate 480 can be replaced by a 
suitable structural support member, e.g. a dielectric board, substrate, or 
sheet. 
Bed 482 is formed of an electrosorption medium and is bonded to plate 480. 
Alternatively, bed 482 may be retained against plate 480 by means of 
coating 483. Bed 482 may be formed of any of the electrosorption media 
described above, including but not limited to high specific area, porous, 
conductive, monolithic material (e.g., carbon aerogel composite), porous 
metal (e.g., titanium or platinum), pack of column powder, reticulated 
vitreous carbon (RVC) impregnated in resorcinal/formaldehyde carbon 
aerogel, metallic carbides that can be in the form of powders, particles, 
foams, sponges, or porous solids (e.g., TiC, ZrC, VC, NbC, TaC, UC, MoC, 
WC, MO.sub.2 C, Cr.sub.3 C.sub.2, Ta.sub.2 C). 
Bed 482 is coated with a suitable cation exchange resin to form coating 
483. For example, bed 482 is dip coated in a solution of Nafion. The 
Nafion solution infiltrates bed 482, and upon drying, it coats the active 
surface area of bed 482. The cation exchange resin may be selected from a 
group of polymers having negatively charged functional groups such as 
sulfonate (--SO.sub.3.sup.-), phosphonate (--PO.sub.3.sup.2-) and/or 
carboxylate (--COO.sup.-). Inorganic cation exchange may also be used. The 
thickness of the coating 483 is determined by the specific application for 
which cell 475 is used. 
Electrode 477 includes an outer conductive plate 485, an electrosorptive 
bed 487 and a polymer coating 489. Conductive plate 485 is connected to 
the negative pole of a D.C. power source, and is generally similar in 
design and construction to conductive plate 480. Bed 487 is also generally 
similar in composition and construction to bed 482. Bed 487 is coated with 
a suitable anion exchange resin to form coating 489. The anion exchange 
resin may be selected from a group of polymers having positively charged 
functional groups such as quaternary (--NR.sub.3), tertiary (--NR.sub.2), 
and/or secondary (--NR) amines. Inorganic anion exchangers may also be 
used. The thickness of the coating 483 is determined by the specific 
application for which cell 475 is used. 
In use, an aqueous solution with mixture of radionuclides, heavy metals and 
inorganic salts is flowed through central channel 478 of cell 475. The 
radionuclides and heavy metals are removed from the flowing stream with 
similar selectivities as conventional ion exchangers. However, unlike 
conventional ion exchange, no chemicals are required for regeneration 
since only electricity is used for the regeneration of cell 475. 
During the polarization of cell 475, protons (H.sup.+) migrate from coating 
483 to the interface 490 between cation exchange resin coating 483 and bed 
482, and are held in the electric double layer formed at interface 490. 
This proton migration frees active sites on coating 483 for adsorbing 
cations in the flowing stream. Cations (M.sup.+ and N.sup.+, e.g. 
Na.sup.+) migrate into cation exchange resin coating 483 and are held at 
active sites therein. Simultaneously, hydroxyl ions (OH.sup.-) migrate 
from coating 489 to the interface 492 between anion exchange resin coating 
489 and bed 487, and are held in the electric double layer formed at 
interface 492. This migration of the hydroxyl ions frees active sites on 
coating 489 for adsorbing anions in the flowing stream. Anions (X.sup.- 
and Y.sup.-, e.g. Cl.sup.-, NO.sub.3.sup.-, SO.sub.4.sup.-2, or 
CO.sub.3.sup.-2) migrate into anion exchange resin coating 489 and are 
held at active sites therein. 
During discharge (i.e., regeneration) of cell 475, such as by shorting 
conductive plates 480 and 485, resin coatings 483 and 489 are regenerated, 
and protons and hydroxyl ions are liberated from interfaces 490 and 492, 
respectively. These protons and hydroxyl ions displace the cations and 
anions (M.sup.+, N.sup.+ and X.sup.-, Y.sup.-) into a regeneration 
solution, such as water having the same composition as the feed stream. 
Therefore, the present ionization and regeneration cell 475 and process of 
use minimize, if not completely eliminate the reliance on chemical 
regenerants. Cell 475 can be used for deionizing boiler water for ships 
and power plants, for fossil-fired and nuclear power plants, for the 
treatment of mixed and hazardous wastes, for domestic and industrial water 
softening, for the analysis and treatment of body fluids including blood 
dialysis, and for several other applications. 
Cell 475 also enables the selective, simultaneous separation of cations and 
ions in a fluid or aqueous solution, with the same selectivity known for 
the ion exchange resin used as a coating. In the present illustration, 
this solution contains anions X.sup.- and Y.sup.-, and cations M.sup.+ 
and N.sup.+. As the solution starts flowing through central channel 478 
certain anions and cations, i.e., X.sup.- and M.sup.+, respectively, 
saturate the proximal segment 494 of electrodes 477 and 476. As the resin 
coatings 489 and 483 in this proximal segment 494 become saturated, the 
remaining anions and cations, i.e., Y.sup.- and N.sup.+ begin to 
saturate the distal segment 495 of electrodes 477 and 476. Ionic 
selectivities of the ion exchange resins, and hence the 
electrochemically-regenerated ion exchange (ERIE) process, are established 
by the relative coulombic attraction between various dissolved ions and 
the oppositely charged functional groups. The force of attraction is 
determined by the size, configuration, and charge of both the ions and the 
functional groups. 
Thus this capacitive deionization system and method present significant 
improvements and advantages over other technologies. For instance, unlike 
ion exchange, no acids, bases, or salt solutions are required for 
regeneration of the system. Regeneration is accomplished by electrically 
discharging the cells. Therefore, no secondary waste is generated. Since 
no membranes or high pressure pumps are required, the present system 
offers operational advantages over electrodialysis and reverse osmosis. It 
is more energy efficient than competing technologies, and is substantially 
more energy efficient than thermal processes. 
The present system can also be used to treat brackish water (800 to 3200 
ppm), which is very important, particularly to coastal communities. 
Competing technologies for the treatment of brackish water are 
electrodialysis and reverse osmosis. These processes consume about 7.7 
Wh/gal and about 5.3 to 8.5 Wh/gal, respectively. The present system is 
much more energy efficient, and may require less than 1 Wh/gal, possibly 
0.2-0.4 Wh/gal, depending upon energy recovery, cell geometry, and 
operation. 
The system eliminates costly and troublesome membranes. A carbon aerogel 
CDI system has additional cost advantages over electrodialysis and reverse 
osmosis since expensive and troublesome membranes are eliminated. 
The system also eliminates wastes from chemical regeneration. A carbon 
aerogel CDI system could be used for home water softening, the treatment 
of hazardous and radioactive wastes, the deionization of boiler water for 
steam and power generation, and the production of ultra pure water for 
manufacturing. Industrial applications of ion exchange may require 100 
pounds of acid for the regeneration of one pound of cation exchange resin, 
or 100 pounds of base for the regeneration of one pound of anion exchange 
resin. The carbon aerogel CDI system uses electrical regeneration, thereby 
eliminating the need for chemical regenerants and the associated wastes. 
The present system is simpler and more energy efficient than continuous 
deionization which requires ion exchange resins, ion exchange membranes, 
and electrodes. A carbon aerogel CDI system requires only carbon aerogel 
electrodes. The polymeric ion exchange media used in Continuous 
Deionization are susceptible to chemical attack during the removal of 
scale and fouling. Carbon aerogel is resistant to chemical attack. 
A carbon aerogel CDI system is superior to beds of activated carbon. 
Another electrochemical process known as Electric Demineralization, 
described in U.S. Pat. No. 3,755,135 to Johnson, uses flow-through packed 
beds of activated carbon as electrodes. However, problems associated with 
the use of such packed beds prevented the development of a viable 
commercial product. These problems included the irreversible loss of 
electrosorption capacity during operation, the relatively low specific 
surface area of the activated carbon appropriate for use in such 
flow-through beds, electric potential drop across beds, hydrodynamic 
pressure drop across beds, bed erosion due to the entrainment of carbon 
powder in the flowing stream, and the need for porous electrode 
separators. For illustration, a carbon aerogel CDI system with monolithic 
carbon aerogel electrodes offers advantages over a CDI system with 
flow-through packed beds of activated carbon. Slight drops in the 
electrosorption capacity of carbon aerogel electrodes are almost fully 
recoverable by periodic potential reversal. Thus, the system capacity can 
be maintained at a high level. Since the specific surface area of carbon 
aerogel (600-1000 m.sup.2 /gm) is significantly greater than that of 
activated carbon powder appropriate for use in a flowthrough packed bed 
(230 m.sup.2 /gm or 200-300 m.sup.2 /gm), a greater quantity of salt can 
be electrosorbed on carbon aerogel than on a comparable mass of activated 
carbon powder A. M. Johnson, J. Newman, J. Electrochem. Soc. 118,3 (1971) 
510-517!. 
It has been experimentally demonstrated that in a CDI process having 384 
pairs of carbon aerogel electrodes (768 individual electrodes) and a total 
activated surface area of 2.4.times.10.sup.6 ft2 (2.2.times.10.sup.9 
cm.sup.2), less potential drop occurs in a thin sheet of carbon aerogel 
than in a relatively deep bed of activated carbon. Consequently, more ions 
can be electrosorbed on a unit of carbon aerogel surface area than on a 
comparable unit of activated carbon surface area. In deep packed beds of 
carbon, the potential can drop to levels where the electrosorption process 
is not very effective. Immobilization of the carbon in the form of aerogel 
has made it possible to construct systems that do not require porous 
membrane separators. Unlike activated carbon powder, monolithic sheets of 
carbon aerogel are not entrained in the flowing fluid stream. Water passes 
through open channels between adjacent anodes and cathodes, experiencing 
only a modest pressure drop of about 30 psi. In contrast, flow through a 
packed bed of activated carbon with comparable surface area experiences a 
significantly greater pressure drop .gtoreq.1000 psi. 
The CDI system has a simple, modular plate-and-frame cell construction. 
Electrochemical cells required for Continuous Deionization and Electric 
Demineralization are complicated by the need for particulate ion exchange 
resin and activated carbon, ion exchange membranes, electrode separators, 
and electrodes. The present CDI system requires simple, double-sided 
planar electrodes. Double-sided electrodes are made by gluing two sheets 
of the carbon aerogel composite to both sides of a titanium plate that 
serves as both a current collector and a structural support. Conductive 
silver epoxy can be used for gluing. In one embodiment, the carbon aerogel 
composite has a very high specific surface area of 2.9-4.9.times.10.sup.6 
ft.sup.2 /lb (600-1000 m.sup.2 /gm). Each sheet is 2.7 in .times.2.7 in 
.times.0.005 in (6.86 cm .times.6.86 cm .times.0.0125 cm) and has a total 
active surface of approximately 3,014 ft.sup.2 (2.8.times.10.sup.6 
cm.sup.2). Two orifices are located along one side of the carbon aerogel 
electrode and admit water to the electrode gap. A pattern of holes are 
located around the perimeter of the titanium plate and accommodate 12 
threaded rods that hold the cell stack together. The assembly of these 
components into a capacitive deionization cell is also very simple. The 
electrodes and headers are aligned by the threaded rods. An electrode 
separation of 0.02 in (0.05 cm) is maintained by cylindrical nylon spacers 
concentric with the threaded rods and a rubber compression seal. Even 
electrodes serve as cathodes while odd electrodes serve as anodes. Since 
the orifices in each electrode alternate from one side of the stack to the 
other, the flow path through the stack is serpentine. An experimental 
capacitive deionization cell configuration includes 384 pairs of carbon 
aerogel electrodes with a total active cathodic (or anodic) surface area 
of approximately 2.4.times.10.sup.6 ft.sup.2 (2.2.times.10.sup.9 
cm.sup.2). However, the system can be expanded to accommodate any desired 
concentration gradient across the stack, as well as any flow rate. 
Scale-up or scale-down for capacity and concentration can be readily 
accomplished. 
The present CDI system uses materials, such as carbon aerogel, that are 
easy to make and commercially available. Monolithic sheets of this 
material can be made by infiltrating a resorcinol-formaldehyde solution 
into a porous carbon paper, curing the wetted paper between glass plates 
in a closed vessel, and then carbonizing in an inert atmosphere. This 
fabrication process results in unique open-cell carbon foams that have 
high porosities, high specific surface areas (600-1000 M.sup.2 /g), 
ultrafine cell and pore sizes (.ltoreq.50 nm), and a solid matrix composed 
of interconnected colloidal-like particles (fibrous chains) with 
characteristic diameters of 10 nm. The porosity and surface area of 
aerogels can be controlled over a broad range, while the pore size and 
particle size can be tailored at the nanometer scale. 
The present capacitive deionization system uses materials, such as carbon 
aerogel, that are resistant to chemical attack. Fouling and scale 
formation are inevitable in process equipment used for desalination. 
Aggressive chemical treatments are required for rejuvenation. Therefore, 
it would be desirable to construct the capacitive deionization system out 
of materials that can withstand such chemical treatments. Carbon aerogel 
is relatively resistant to many of the chemicals now used for scale 
control, such as HCl. Unlike polymeric membranes and resins, it is also 
resistant to dissolution by organic solvents. Oxidants such as chlorine 
attack polyamide reverse osmosis membranes, but do not appear to be a 
significant problem in carbon aerogel systems. Similar problems are 
encountered with electrodialysis and Continuous Deionization. 
The present capacitive deionization system has a fully-automated 
potential-swing operation. The Electric Demineralization process was 
operated in batch mode with no energy recovery. Capacitive deionization 
can, for instance, produce a continuous flow of product water by operating 
two stacks of carbon aerogel electrodes in parallel. One stack purifies 
while the other is electrically regenerated. This mode of operation is 
referred to as "potential swing" and also enables energy recovery. For 
example, energy released during the discharge of one stack of electrodes 
(regeneration) can be used to charge the other stack (deionization). Such 
synchronous operation requires user-friendly automation. 
One exemplary application of the present invention includes the design and 
manufacture of a deionization system for purifying radioactive water. For 
instance, one embodiment of the present system could be used to purify the 
waste water generated from washing fuel assemblies coated with metallic 
sodium residuals. The 500 gallons of waste water currently generated 
during the washing of each assembly include approximately 200 ppm sodium, 
trace quantities of other metals, trace quantities of some non-metal that 
can be removed by filtration, and trace quantities of radioactive 
constituents (primarily fuel cladding corrosion products). Grade B water 
purity would have to be achieved so that water could be recycled; (i.e., 
conductivity less than 20 microsiemens/cm). 
FIG. 23 shows an electrosorptive ion chromatograph (EIC) 500 which can be 
used for analysis, treatment and processing of various fluids and/or 
aqueous solutions containing a variety of anions and cations. A carrier 
tank 510 and a pump 515 for drawing the carrier (e.g., deionized water) 
are connected to chromatograph 500 which includes a column 501, a detector 
or conductivity sensor 511, and a computer system 512. The solution at the 
output of detector 511 is collected in an effluent tank 514. 
Unlike conventional ion chromatography where anions are analyzed with a 
column of anion exchange resin and cations with a column of cation 
exchange resin, EIC 500 can simultaneously analyze both anions and cations 
in a single column 501 that may include one or a series of electrochemical 
cells 502, 504, 506. Column 501 replaces conventional ion exchange columns 
with packing material. Furthermore, the selectivity of EIC 500 can be 
readily changed by altering the potential between the anodes and cells 
502-506, compared with conventional ion chromatographs where selectivity 
is manipulated by changing the columns of ion exchange resin or the 
carrier. 
In use, a sample is injected into a carrier stream from carrier tank 510, 
and passes through the single or series of cells 502-506. Each cell 
generally includes a pair of porous electrodes, i.e., an anode and a 
cathode. These cells have an anode and/or a cathode constructed according 
to the present invention. The electrodes are polarized, and draw ions from 
the flowing stream to the surface of the porous electrodes where they are 
held in the electric double layers. 
Each species of cation and anion has a different affinity for the porous 
electrodes, and has a characteristic elution time in the cells 502-506. 
The elution time can be used as a basis for identifying the ions. A 
conductivity sensor 511 or another type of detector at the output of 
exchange column 501 is used to detect ions as they leave column 501. The 
concentration of the ions is proportional to the area under the 
conductivity-time (concentration-time) peak. FIG. 26 illustrates three 
conductivity-time (concentration-time) peaks for three different ionic 
species A, B, C. 
Computer system 512, with an analog-to-digital converter is connected to 
detector 511 to process data and to generate reports. 
FIGS. 24 and 25 illustrate a single cell 502. In certain applications 
column 501 may include a single long cell. Cell 502 generally includes a 
hollow open ended vessel 520 which allows the sample stream to flow 
therethrough in the direction of the arrows INFLOW, FLOW and OUTFLOW. In 
FIG. 25, vessel 520 has a rectangular cross section; however, the cross 
section of vessel 520 can have other shapes, as shown in FIG. 27. 
A thin sheet 524 of high specific area, porous, conductive, monolithic 
material (e.g., carbon aerogel composite) is bonded to the inner surface 
of one side of cell 502. In one embodiment, sheet 524 is glued to cell 502 
with an electrically conductive epoxy. Conductive sheet 524 is 
substantially similar in composition to sheet 44 shown in FIG. 4A. Sheet 
524 may also be bonded to at least part of the remaining three sides of 
cell 502. Sheet 524 may be coated with a coating (not shown) similar to 
that described in FIG. 22. Sheet 524 is connected to one pole of a D.C. 
power source to form an electrode. Another thin conductive sheet 526 has a 
similar composition to that of conductive sheet 524, and is bonded to the 
opposite, or another side of cell 502. Sheet 526 is connected to the other 
pole of the D.C. power source to form an electrode. 
Vessel 520 and sheets 524, 526 define a central channel 530 within cell 
502, through which the sample stream flows. In one embodiment, channel 530 
is very narrow so as to minimize the amount of the sample needed. In this 
example, channel 530 is straight; however, as shown in FIGS. 28 and 29, 
channel 530 can have other shapes, e.g. a serpentine pathway. 
The general principle of operation of cell 502 has been explained above in 
relation to the capacitive deionization cells and systems. As the sample 
stream, which includes the carrier and the sample to be analyzed or 
processed, passes through the first cell 502, a voltage is applied across 
anode 524 and cathode 526, which causes the various ions in the sample to 
be eluted at different rates. Consequently, the species are separated. 
FIG. 26 shows three species A, B and C. Species C interacts with electrodes 
524, 526 to a greater extent than species A and B, and therefore, species 
C is retarded to a greater extent than species A and B. The extent of 
interaction between the species and electrodes 524, 526 is described in 
terms of an adsorption or electrosorption isotherm and is quantified in 
terms of an equilibrium constant "K" which can be controlled by varying 
the electrode material and the available electrode surface area available 
for adsorbing or interacting with the ions, to control the travel time of 
the species. 
A significant advantage of the present chromatograph 500 is that the 
interaction between the ionic species and the electrodes 524, 526 is an 
electrostatic coulombic attraction rather than a chemical interaction. The 
degree of integration and the elution time can be controlled by simply 
changing the voltage between the anode and the cathode. In conventional 
ion chromatography, columns have to be changed to alter the degree of 
interaction. 
Furthermore, the present chromatograph 500 enables the use of a single 
column 501 for simultaneous anionic and cationic types of chromatography. 
Conventional ion chromatography requires that different columns be used. 
Additionally, this new chromatograph 500 can be used for separating and 
processing biological cells, molecules and other matter without damage 
since the sample stream flows freely along channel 530. Chromatograph 500 
can control the elution time of various species being analyzed, and has a 
reduced overall cost of manufacture, operation and maintenance because of 
the ability to combine and implement the anionic and cationic separation 
processes within a single column 501. 
In another embodiment, the voltage gradient across electrodes 524, 526 is 
varied, so that the voltage is modulated or pulsed or is programmed to a 
desired pattern. As a result, the elution time of the species being 
analyzed can be varied, so as to minimize overlap between the 
conductivity-time graphs of the species. In other words, by varying the 
elution times of the species, the separations between the various peaks on 
detector 511 are increased, thus making it easier to distinguish and 
analyze the species. 
In yet another embodiment, an ion selective electrode is used as part of 
cell 506, in addition to detector 511. This ion selective electrode is 
preferentially sensitive to specific ions, and may be formed of 
electrochemical cells from various forms of polarography, cydic 
voltammetry, X-ray fluorescence, spectroscopy such as UV, visible, 
vibrational, infra-red. 
FIG. 27 is a cross sectional view of cell 502 taken along line 25--25, and 
represents another design of cell 502. In this example, cell 502 is 
generally cylindrically shaped and has a generally circular section. Four 
electrodes 540-543 having similar composition to that of electrodes 524, 
526, are bonded to the inner surface of a vessel 545, and are separated by 
four suitable insulation dividers 546-549. Each of these electrodes 
540-543 is connected to a corresponding pole of the power source. As 
shown, electrodes 540, 541 act as anodes, while electrodes 542, 543 act as 
cathodes. The voltage gradient across one electrode pair (e.g., 540, 542) 
can be different from the voltage gradient across the other electrode pair 
(e.g., 541, 543). A cylindrical geometry would be advantageous for 
applications where high pressure operation is required. 
FIGS. 28 and 29 illustrate a column cell 600 which operates pursuant to the 
same principles as cell 502 but differs with respect to the shape of the 
internal channel. While central channel 530 (FIG. 24) is straight, cell 
600 defines a serpentine channel 601 through which the sample stream 
flows. Channel 601 is made as narrow but as long as possible, providing a 
long flow path in a small space, in order to minimize the amount of sample 
needed. 
Cell 600 generally includes two oppositely disposed, substantially flat 
plates or substrates 603, 605 that are separated by an insulation layer 
606 of a predetermined thickness. The first plate 603 includes a 
serpentine trough 607, and the second plate 605 includes a similar 
serpentine trough 608, such that when both plates 603, 605 are connected 
together, troughs 607, 608 and part of insulation layer 606 form channel 
601, which defines a serpentine pathway. Channel 601 has a single inlet 
610 and a single outlet 611 for the sample stream. 
A thin conductive sheet 616 has a similar composition to that of conductive 
sheet 524 (FIG. 24), and is bonded to the inner surface of trough 607. A 
similar conductive sheet 617 is bonded to the inner surface of trough 608. 
These conductive sheets 616, 617 are connected to the poles of the D.C. 
power supply. 
The teachings described herein, particularly as to the chromatograph 
columns, can also be used to design an electrochemical intensifier or 
concentrator. An electrochemical intensifier is a device used to 
concentrate dilute ionic solutions for subsequent measurement by any of a 
variety of analytical techniques, such as ion chromatography, ion 
selective electrodes, differential pulse polarography. 
An intensifier 650, illustrated in FIG. 30, generally includes a cell 
similar to the cells described above for the chromatographs. The porous 
anodes and cathodes remove ions from a relatively dilute solution 652 
during a capacitive charging phase. Ions are removed from the dilute 
solution under the force of an imposed electric field (cell voltage 
gradient) and held in the double layers formed at the surfaces of the 
electrodes. Subsequently, ions are collected in a more concentrated 
solution 654 during a capacitive discharging or regeneration phase. The 
capacitive charging and discharging phases are as described above in 
relation to the CDI systems, cells and methods. 
The species that are present in the dilute solution at levels below the 
detection limit of a particular analytical technique can be concentrated 
to a level where they become detectable. If the ions are radioactive, they 
can be measured as they accumulate on the porous electrodes. Similarly, 
X-ray fluorescence can be used to monitor heavy metals, or like materials, 
that accumulate on the electrodes. A gamma ray detector 655 may be used to 
monitor the radiation of radioactive material that accumulates on the 
electrodes or in the concentrated solution 654. An analytical or 
measurement instrument 660 is connected to the effluent solution at the 
output of intensifier 650, and is further connected to a computer 665 
which processes the accumulated data and controls the operation of 
intensifier 650, a pump 667 that draws the dilute solution 652 into 
intensifier 650, a valve 668 that controls the flow of the effluent 
solution from intensifier 650 to the analytical instrument 660, and a 
valve 669 that controls the flow of the effluent to a tank 680 for storing 
the solution that has been depleted of ions or deionized by intensifier 
650. 
FIGS. 31, 32 show a single, monolithic, thin film electrode 700 made by 
photolithography. Electrode 700 has a very high specific surface area and 
may replace the various electrodes described above. For example, electrode 
700 may replace electrode 44 (FIG. 4A), electrodes 253, 254 (FIG. 11B), 
electrode 314 (FIG. 15), electrode 357 (FIG. 17), electrodes 419, 420 
(FIG. 19), electrodes 465, 466 (FIG. 21), beds 482, 487 (FIG. 22), sheets 
524, 526 (FIG. 24), electrodes 540-543 (FIG. 27), and sheets 616, 617 
(FIG. 29). 
Electrode 700 is shown as a thin, flat, porous sheet, screen or film 701 
made of any conductive metal, e.g., titanium, copper, platinum, tungsten, 
iridium, nickel or silver. The metal is selected to be corrosion resistant 
to the solution being processed. Using conventional photolithography, an 
array of very fine holes, i.e., 702-705 is formed on one surface of film 
701. While only four holes 702-705 are shown, many more holes may be 
formed across the entire surface of film 701. It would be desirable to 
optimize the number of holes so as to increase the surface area of film 
701. In one example, the diameter of one hole is about 0.1 micron, and 
film 701 will have a density of about 10.sup.10 holes per cm.sup.2. If 
film 701 has a depth of about 25 microns, and holes 702-705 were to 
penetrate through most of the thickness of film 701, the volummetric 
specific surface area of film 701 would be about 64 m.sup.2 /cm.sup.3. If 
the electrode includes a stack of ten (10) films, the volummetric specific 
surface area of the electrode would be about 640 m.sup.2 /cm.sup.3, which 
is comparable to that of a carbon aerogel electrode. 
In an electrode 700 comprised of a single film 701, holes 702-705 may or 
may not extend through film 701. While film 701 is shown as a thin flat 
screen, it can assume various configurations. Holes 702-705 can be 
cylindrical with a circular cross-section, square, or of any desired 
shape. Alternatively, holes 702-705 may be etched interconnected grooves. 
FIG. 33 shows another electrode 715 which includes a stack of generally 
identical films 716-722, that are alternately interleaved with a stack of 
spacers 725-730. Films 716-722 are porous, and have a similar construction 
to film 701 (FIG. 31). In order for the solution to infiltrate through the 
stack of films 716-722, the holes, as illustrated by a single hole 734, 
extend through the entire depth of films 716-722. Spacers 725-730 are thin 
and porous, and can be metallic or nonmetallic. In one embodiment, spacers 
725-730 consist of filter papers. 
It is possible to select the number of films forming electrode 715 such 
that the volummetric specific surface area of electrode 715 approaches 
that of a carbon aerogel electrode, and in certain applications, it is 
possible to replace the carbon aerogel electrode. An additional advantage 
of the present electrode design is that it is now possible to accurately 
regulate the desired volummetric specific area of the electrode, by either 
increasing or decreasing the number of constituent films. The films 
described in FIGS. 31-33 are also referred to as graphic sheets. 
FIG. 34 shows yet another embodiment of an electrode 750 called a tea bag 
electrode. Electrode 750 includes a dosed dielectric porous bag 752 that 
contains and restrains an electrically conductive material 753. Conductive 
material 753 may be any conductive powder, and in particular any one of 
the conductors listed herein, for example carbon aerogel. An electrical 
conductor or wire 754 extends inside bag 752 in contact with conductive 
material 753. When in use, wire 754 is connected to one pole of a D.C. 
power source. 
In use, a single tea bag electrode 750 is dropped in a container 755 
containing a fluid 756 to be processed or analyzed. In this most basic 
example, electrode 750 is positively charged and acts as an anode, while 
container 755 is negatively charged and acts as a cathode. As explained 
above with respect to the various CDI systems and cells, electrode 750 
electrosorbs the anions contained in fluid 756 inside bag 750. 
Once a desired ionic concentration is reached, bag 752 is removed from 
fluid 756 and processed. In one example, the concentrated ions are 
hazardous and bag 752 is disposed of. In another example, the concentrated 
ions captured within bag 752 can be released, analyzed and processed. 
Therefore, electrode 750 can have several uses, including but not limited 
to capacitive deionization and ion concentration. 
Two or more tea bag electrodes of the same polarity can also be used, with 
the container having the opposite polarity. The container can be 
electrically neutral and several tea bag electrodes 750, 760 act as 
anodes, while other tea bag electrodes 762, 764 act as cathodes. In this 
particular illustration the anodes and cathodes are interleaved; however, 
the anodes and cathodes can be placed in a variety of different 
arrangements. For example, the anodes may be arranged along an outer 
circular pattern, while the cathodes may be arranged in a coaxial inner 
circular pattern. In another example, the container may be negatively 
charged, and used as a cathode with the concentric circular patterns 
described in the latter example. Other patterns may also be selected. 
While the number of anodes and cathodes may, in many applications, be the 
same, this equality is not always required. 
FIG. 35 illustrates a pair of tea bag electrodes 750, 762 placed in a fluid 
stream within a vessel or pipe for sampling the fluid stream. This 
sampling can take place periodically, at predetermined or programmed time 
intervals, by the controlled application of a voltage across electrodes 
750, 762. 
FIG. 36 shows an electrodialysis cell 800 which includes a bipolar 
electrode 802 disposed intermediate a cathode 805 and an anode 807. 
Bipolar electrode 802 includes two films, screens, plates, etc. 808, 810 
disposed on either side of a conductive barrier 811. Films 808, 810 can be 
any high specific surface area material, similar to the materials 
described above, for instance, carbon aerogel or porous carbon. Bipolar 
electrode 802 acts as a central divider and defines a cathode compartment 
814 and an anode compartment 815. 
In use, the electrical current flows from anode 807, through anode 
compartment 815, through bipolar electrode 802, through cathode 
compartment 814, toward cathode 805. For illustration purpose only, the 
fluid, solution or electrolyte to be processed by cell 800 is salt or sea 
water (NaCl+H.sub.2 O). The solution flows from cathode compartment 814 to 
anode compartment 815 in the direction of the arrow shown in broken lines. 
Within cathode compartment 814, the electrode reaction at cathode 805 is 
hydrogen (H.sub.2) evolution, while the chloride ions (Cl.sup.-) 
precipitate toward bipolar electrode 802 and are electrosorbed by film 
808. This results in an alkaline solution of sodium hydroxide (NaOH), 
which then flows to anode compartment 807, where the sodium ions 
(Na.sup.+) precipitate toward bipolar electrode 802 and are electrosorbed 
by film 810. The electrode reaction at anode 807 is oxygen (O.sub.2) 
evolution. The effluent solution consists of purified, desalted water 
(H.sub.2 O). 
An important advantage of cell 800 is that the salt, i.e., NaCl, or various 
radioactive salts, can be removed from the solution and immobilized or 
stored within bipolar electrode 802. In one embodiment, bipolar electrode 
802 may be removed and disposed of. In another embodiment, bipolar 
electrode 802 may be removed to a different location and regenerated. In 
yet another embodiment, conductive barrier 811 is removed, and the 
cations, i.e., sodium ions (Na+) and the anions, i.e., chloride ions 
(Cl-), form a salt, i.e., sodium chloride (NaCl), which precipitates on 
the porous films 808, 810, and which is then removed and either disposed 
of, or processed further. 
The forgoing applications may be particularly important in the treatment of 
radioactive wastes. For instance, the radioactive salts, such as CsCl 
(.sup.137 Cs), may be caused to precipitate on carbon aerogel films 808, 
810. The volume of these films 808, 810 can then be significantly reduced 
by crushing them, or by oxidizing the carbon to form carbon dioxide. 
FIG. 37 is a schematic view of a capacitive deionization system 850 
employing a moving electrode 852. The capacitive deionization system 850 
generally includes moving electrode 852 that travels between an anode cell 
853 and a cathode cell 854. Moving electrode 852 includes a conductor 857 
such as a wire, sheet, fluidized beads, which is supported by, and moved 
by a plurality of wheels 858-863. Anode cell 853 includes a container 870, 
that is held at a positive potential relative to conductor 857 of moving 
electrode 852. Cathode cell 854 includes a container 872 that is 
maintained at a negative potential relative to conductor 857. As an 
example, the potential difference between the anode container 870 and the 
moving conductor 857 is about 1.2 volts, while the potential difference 
between the cathode container 872 and the moving conductor 857 is about 
1.2 volts. 
In this particular example, anode cell 853 contains a solution or fluid 880 
to be processed; however, in other applications, the solution may be 
contained in cathode cell 854. 
In operation, the electrical current passes from container 870, through 
fluid 880, to conductor 857. Consequently, the positively charged ions in 
the solution 880 move to conductor 857 and are electrosorbed thereon. 
These ions will be carried along conductor 857 into cathode cell 854, 
where the electrosorbed positive ions are drawn toward the negatively 
charged container 872, and are released from conductor 857 into solution 
881. 
One advantage of CDI system 850 is that the required-actual surface area of 
moving electrode 852 does not need to be relatively high, i.e., not as 
high as that of carbon aerogel. It is possible to increase the surface 
area that solution 880 sees per unit time, by increasing the velocity of 
the moving electrode 852. As a result, it is now possible to perform 
processes such as CDI without a high porosity electrode. 
COMMERCIAL APPLICATIONS 
By using the cells and systems according to the present invention, it is 
possible to remove the following and other impurities and ions from 
fluids, including body fluids, and aqueous streams, and to subsequently 
regenerate the cells: 
1. Non oxidizable organic and inorganic anions. Inorganic anions include: 
OH.sup.-, Cl.sup.-, I.sup.-, F.sup.-, NO.sub.3.sup.-, SO.sub.4.sup.2-, 
HCO.sub.3.sup.-, CO.sub.3.sup.2-, H.sub.2 PO.sup.4-, HPO.sub.4.sup.2-, and 
PO.sub.4.sup.3-, In this case, the operative mechanism is electrostatic 
double layer charging. For this purpose, it would be desirable to maintain 
the terminal potential across the electrodes lower than that required for 
electrolysis of the solvent in order to avoid gas evolution. The optimum 
potential is in the range between 1.0 and 1.2 volts, relative to the 
normal hydrogen electrode (NHE). In general, the recommended range of 
potential for water treatment lies between 0.6 and 1.2 volts. 
2. Non reducible cations, such as Li.sup.+, Na.sup.+, K.sup.+, Cs.sup.+, 
Mg.sup.++, Ca.sup.++. Here too the operative mechanism is electrostatic 
double layer charging. 
3. Reducible cations, such as: Cu.sup.++, Fe.sup.++, Pb.sup.++, Zn.sup.++, 
Cd.sup.++. In this case, the operative mechanism is electrodeposition. 
4. Reducible anions. 
5. Colloidal particles such as bacteria, viruses, oxide particles, dirt, 
dust. In this case, the operative mechanism is electrophoresis. 
6. Chemisorption of organic molecules onto the carbon composite electrode 
44. This adsorption process might be relatively irreversible. Regeneration 
in this case would involve the use of strong oxidants for the purposes of 
destroying the adsorbed organics (i.e., PCB). 
In particular, the present systems and cells enable the electrodeposition 
of any metal, including but not limited to silver, gold, platinum, 
iridium, rhodium, and the removal of contaminants from body fluids, such 
as blood. These contaminants could range from organic and inorganic ions 
to fine particles including viruses. 
The present separation processes and systems have several important 
applications, including: 
1. Removal of various ions from waste water without the generation of acid, 
base, or other similar secondary wastes. This application may be 
especially important in cases involving radionuclides, where the inventive 
capacitive deionization process could be used to remove low-level 
radioactive inorganic materials. 
2. Treatment of boiler water in nudear and fossil power plants. Such 
treatment is essential for the prevention of pitting, stress corrosion 
cracking, and scaling of heat transfer surfaces. Such a process may be 
particularly attractive for nuclear powered ships and submarines where 
electrical power is readily available and where there are space 
limitations, thereby restricting the inventory of chemicals required for 
regeneration of ion exchange resins. 
3. Production of high-purity water for semiconductor processing. In 
addition to removing conductivity without the addition of other chemical 
impurities, the system is capable of removing small suspended solids by 
electrophoresis. Furthermore, the organic impurities chemisorb to the 
carbon. 
4. Electrically-driven water softener for homes. The CDI system would 
soften home drinking water without the introduction of sodium chloride, 
and does not require salt additions for regeneration. 
5. Removal of salt from water for agricultural irrigation. 
6. Desalination of sea water. 
By using the CDI separation systems of the present invention, it is now 
possible to remove organic and inorganic contaminants and impurities from 
liquid streams by the following physiochemical processes: the reversible 
electrostatic removal of organic or inorganic ions from water or any other 
dielectric solvent; the reversible or irreversible removal of any organic 
or inorganic impurity by any other adsorption process, including but not 
limited to underpotential metal deposition, chemisorption, and 
physisorption; the removal of any organic or inorganic impurity by 
electrodeposition, which could involve either electrochemical reduction or 
electrochemical oxidation; and the electrophoretic deposition and 
trappings of small suspended solids, including but not limited to 
colloids, at the surface of the electrodes. Induced electric dipoles will 
be forced to the electrode surfaces by the imposed electric field. 
More specific applications for the CDI system and process include any 
application where the capacitive deionizer is used to assist a gas 
scrubbing column; for example, if CO.sup.2 were removed from a gas stream 
into an aqueous stream, it would convert into HCO.sub.3.sup.- and 
CO.sub.3.sup.2-. These ions could be removed from the scrubbing solution 
by capacitive deionization. Such applications include any large scale 
parallel use of the capacitive deionizer to assist in load leveling 
applications since it is recognized that the present invention can 
simultaneously serve as an energy storage device. Other applications 
include analytical instruments that combine the principles of capacitive 
deionization and ion chromatography, and chromatographic instruments based 
upon ion adsorption on carbon aerogel electrodes, either monolithic or 
powder beds. 
The chromatographs of the present invention have various applications, 
including: 1. Separation and identification of amino acids, peptides, 
proteins, and related compounds. 2. Separation of carbohydrates and 
carbohydrate derivatives. 3. Analysis of various organic acids such as 
aliphatic and aromatic acids. 4. Separation of aliphatic, heterocyclic and 
aromatic amines. 5. Separation of nucleid acid components. 6. Separation 
of nucleosides, nucleotides and bases, such as purine and pyrimidine 
bases, and mono-, di-, and triphosphate nucleotides. 7. Analysis of alkali 
and alkaline earth metals in the complexed and uncomplexed forms. 8. 
Separation of some rare earth elements. 9. Separation of halides, such as 
chloride, bromide and iodide. 10. Separation of phosphorous oxyanions, 
such as complex polyphosphate mixtures, and mixtures containing lower 
phosphorus anions, thiophosphates, imido-phosphates. 11. Separation of AIC 
components from hemoglobin in blood. See U.S. Pat. No. 5,294,336 to Mizuno 
et al. 12. Separation and isolation of human plasma procoaguolant protein 
factor VIII from biological factors. See U.S. Pat. No. 4,675,385 to 
Herring. 13. Analysis of Hemoglobins. See U.S. Pat. No. 5,358,639 to 
Yasuda et al. 14. Isolation of various constituents in blood, including 
but not limited to the HIV virus. 
The intensifier can be used for the analysis of various fluids, including 
blood and other body fluids, and aqueous solutions of organic and 
inorganic salts, e.g. to prove compliance with environmental laws, and for 
the control of plating baths used in the manufacture of printed circuit 
boards. 
The foregoing description of the embodiments of the present invention has 
been presented for purposes of illustration and description. It is not 
intended to be exhaustive or to limit the invention to the precise forms 
described.