Electrochemical cell and process for manufacturing temperature sensitive solutions

An electrochemical cell for regenerating temperature sensitive solutions is described. In a preferred construction, the cell comprises a central electrode chamber and two counterelectrode chambers. To maintain the temperature of the electrolyte within a desired temperature range, the electrode in the electrode chamber is formed from at least one hollow tube through which a heat exchange medium flows. In a preferred construction, the electrode comprises a plurality of hollow tubes and a plurality of current collectors bonded to the tubes to form a grid-like structure.

This application is related to co-pending U.S. patent application Ser. No., 
539,598, filed on an even date herewith, to Pryor et al. for PROCESS FOR 
CLEANING COPPER BASE MATERIALS AND REGENERATING THE CLEANING SOLUTION. 
This invention relates to an electrochemical cell for regenerating a 
temperature sensitive solution. 
The fundamental cleaning medium used in the copper industry is sulfuric 
acid at a strength from 10 to 15% by volume. The extensive use of sulfuric 
acid is based on the fact that for most brasses and high copper alloys, 
the annealing oxides are readily soluble in mineral acids. This produces 
very rapid oxide removal and the resulting cleaning process is, therefore, 
readily amenable to a short immersion time, continuous operation. 
However, an increasing number of alloys now contain elements which can form 
insoluble, refractory type oxides. For these alloys, alternative cleaning 
procedures have been developed. These alternative cleaning procedures 
generally involve adding an oxidant such as sodium dichromate or hydrogen 
peroxide to the cleaning solution. While sodium dichromate has been used 
effectively for years, its use has been discontinued because of its known 
high toxicity and restrictions on waste treatment and discharge level. The 
use of hydrogen peroxide is limited by its inherent stability problems. 
The decomposition of hydrogen peroxide to water plus oxygen will occur 
during storage but is greatly accelerated by elevated temperatures and/or 
dissolved copper. These factors limit the maximum etching rates that can 
be obtained with hydrogen peroxide. 
In response to these shortcomings and the need for an effective oxidizing 
cleaning solution, attention has turned to persulfate solutions. The use 
of persulfates is attractive for a copper cleaning operation because the 
end products of the reaction of persulfate with copper is sulfuric acid 
and copper sulfate. As such, no special waste water treatment is required. 
Furthermore, the depleted or spent persulfate solution may be regenerated 
and the copper in the depleted solution reclaimed. U.S. Pat. Nos. 
3,475,242 to Radimer, 3,671,344 to Chiang et al. and 4,144,144 to Radimer 
et al. illustrate the use of aqueous persulfate solutions to etch copper. 
The use of electrochemical cells to regenerate spent solutions and to 
reclaim metal values from the solutions are well known in the art. 
Typically, these cells have at least one anode chamber and at least one 
cathode chamber physically separated by a membrane. Depending upon the 
type of solution being regenerated and the chemical reactions sought to be 
produced, the membrane generally comprises either an ion exchange member 
or a microporous separator and the spent solution is used as either the 
anolyte or the catholyte. U.S. Pat. Nos. 2,748,071 to Eisler, 2,865,823 to 
Harris et al., 3,761,369 to Tirrell, 3,764,503 to Lancy et al., 4,051,001 
to Inoue et al. and 4,149,946 to Burke illustrate some of the 
electrochemical cells used to regenerate spent cleaning solutions. 
It has been suggested in the prior art to regenerate persulfate etchants 
using electrochemical cells. In one technique for regenerating a spent 
aqueous ammonium persulfate etchant, the spent etchant is treated to 
remove a substantially persulfate-free mixture containing ammonium sulfate 
and the corresponding metal sulfate. The substantially persulfate-free 
mixture is then transferred to the cathode chamber of an electrochemical 
cell where it is used as the catholyte. The remainder of the spent 
solution is transferred to the anode chamber of the cell where it is used 
as the anolyte. The cathode and anode chambers of the cell are separated 
by a diaphragm which permits at least hydrogen ions to pass freely between 
the anolyte and the catholyte but which prevents any substantial amounts 
of persulfate in the anolyte from mixing with the catholyte. By passing an 
electric current through the anolyte and the catholyte, metal is plated 
out at the cathode and persulfate values are produced at the anode. U.S. 
Pat. No. 3,406,108 to Radimer et al. illustrates this technique for 
regenerating spent persulfate etchants. The primary deficiency of this 
technique is its complexity which renders it commercially unacceptable. 
A second and simpler technique is illustrated in U.S. Pat. No. 3,470,044 to 
Radimer. In this technique, the spent aqueous ammonium persulfate etching 
solution is used as the anolyte of an electrochemical cell. An electrolyte 
such as an acidic sulfate or a bisulfate containing electrolyte is used as 
the catholyte of the cell. The cathode and anode sections of the cell are 
separated by a cation exchange membrane which permits the dissolved metal 
ions to pass from the anolyte into the catholyte but which prevents any 
substantial amount of persulfate in the anolyte from mixing with the 
catholyte. By passing an electric current through the catholyte and the 
anolyte, dissolved metal is removed from the solution at the cathode and 
sulfate values are converted to persulfate values at the anode. 
While simpler, this second technique is believed to be inefficient and 
commercially unacceptable. The production of temperature sensitive, 
oxidizing cleaning solutions such as persulfate etchants often require 
electrolyte temperatures to be maintained within certain critical limits 
during processing. Therefore, an electrochemical cell for regenerating 
such a temperature sensitive solution needs to have some means for 
controlling electrolyte temperature. Furthermore, special anodes are often 
required to improve cell efficiency. For example, a titanium-platinum 
anode such as that illustrated in U.S.S.R. Pat. No. 470,307 to Markov et 
al. may be used to improve current efficiency. Where cooling of the 
electrolyte is required, an internally cooled anode such as that 
illustrated in U.S.S.R. Pat. No. 311,502 to Markov et al. may be used. 
In accordance with the present invention, a relatively simple but yet 
highly efficient electrochemical cell for regenerating temperature 
sensitive solutions is provided. The cell of the present invention may be 
used to regenerate a wide variety of solutions including but not limited 
to persulfuric acid, perchloric acid, perborates, sodium perchlorate, 
hydrogen peroxide, sodium persulfate, ammonium persulfate, potassium 
persulfate, cesium persulfate and rubidium persulfate. 
The electrochemical cell of the present invention has means for controlling 
and maintaining a desired electrolyte temperature, means for providing a 
substantially uniform current distribution across the cell, means for 
separating the anolyte from the catholyte and means for minimizing IR drop 
in the electrolytes. In addition, the cell of the present invention may be 
used for both exothermic systems where cooling is required and endothermic 
systems where heating is required. 
The cell of the present invention comprises at least one chamber containing 
an electrode and at least one chamber containing a counterelectrode. In a 
preferred construction, the cell has a central electrode chamber and two 
counterelectrode chambers, one on each side of the electrode chamber. To 
substantially avoid mixing of the products in the various cell chambers, a 
physical separator is located between each electrode and each 
counterelectrode. The physical separator may be either a diaphragm having 
a relatively fine porosity structure for allowing a restricted bulk flow 
from one chamber to another without any preference to the charge of the 
ions passing therethrough or an ion exchange membrane for permitting only 
the flow of ions of certain preferred charges between the chambers. 
To control the temperature of the electrolytes in the cell within a desired 
range of temperatures, the electrode chamber of the cell is provided with 
means for heating or cooling the electrolyte. The heating/cooling means 
comprises at least one hollow tube through which a suitable heat exchange 
fluid passes. The tube or tubes form part of the electrode structure. Each 
tube is formed from an electrically conductive material which is also 
substantially corrosion resistant in the operating environment. Each tube 
is preferably formed from titanium or one of its alloys. 
To provide the cell with a substantially uniform current distribution, the 
electrode further comprises at least one current collector bonded to each 
heating/cooling tube and at least one electrochemically active portion 
bonded to each tube preferably adjacent each current collector. In a 
preferred electrode construction, a plurality of spaced-apart current 
collectors are bonded to a plurality of heating/cooling tubes to form a 
grid-like structure. Each current collector preferably comprises a pair of 
metal or metal alloy strips contoured to fit about each tube and designed 
to minimize excessive overvoltage drop and power loss across the current 
collector. The size and the spacing of the current collectors depends upon 
the range of current density to be used in the cell and the operating 
electrode surface area. In a preferred construction, the current collector 
strips are formed from titanium or one of its alloys. 
In a preferred construction, a plurality of electrochemically active 
portions are bonded to each tube adjacent to and between the spaced-apart 
current collectors. The electrochemically active portions comprise metal 
or metal alloy members such as metal or metal alloy rings spot welded to 
or inlayed in the heating/cooling tubes. The extent of each 
electrochemically active portion depends upon the current density required 
in the cell. If needed, the electrochemically active portions could cover 
the total electrically conductive area exposed to the electrolyte. In a 
preferred embodiment, the electrochemically active portions are formed 
from bright recrystallized platinum. The use of platinum members is 
particularly advantageous where it is desired to have considerable 
overvoltages for the evolution of oxygen. 
To further provide the cell with a substantially even current distribution, 
each counterelectrode is preferably formed from a metallic mesh-type 
structure. Each mesh-type counterelectrode preferably has an open area 
comprising at least about 50% of its surface area. In a most preferred 
construction, the open area comprises about 50% to about 70% of the 
counterelectrode surface area. This much open area insures good mass 
transport from the surrounding electrolyte to the operating electrode 
surface. 
To minimize IR drop or losses in the electrolyte, particularly those due to 
electrolyte heating, the current path between each electrode and each 
counter-electrode is significantly reduced by using a narrow width cell 
construction having each electrode and counterelectrode in close 
proximity. 
In a preferred cell construction, the chambers are arranged in a 
substantially vertical direction. By arranging the chambers in this 
fashion, the cell of the present invention may utilize bubble lift to 
promote electrolyte movement. The bubbles used to promote electrolyte 
movement are generally gaseous products formed at both the electrode and 
the counterelectrode. 
While the cell of the present invention has wide applicability, it has been 
found to be particularly advantageous to regenerate a spent 
peroxydisulfuric acid solution used to clean copper or copper alloy strip 
material and to reclaim copper values from the spent solution. In such a 
peroxydisulfuric acid regeneration system, the spent solution will be 
transferred to the anode chamber where it will be used as the anolyte. An 
aqueous sulfuric acid solution is preferably used as the catholyte. By 
passing an electric current through the anolyte and the catholyte, copper 
will be deposited on each cathode, in this case the metallic mesh 
counterelectrodes, and persulfate values will be generated at the anode. 
To control and maintain the temperature of the regenerated solution, a 
suitable coolant such as a glycol solution is passed through the anode 
tubes. 
It is an object of the present invention to provide a simple and efficient 
electrochemical cell for producing and/or regenerating temperature 
sensitive solutions. 
It is a further object of the present invention to provide a cell as above 
for reclaiming metal values from the solutions. 
It is yet a further object of the present invention to provide a cell as 
above for regenerating a spent peroxydisulfuric acid solution used to 
clean copper or copper alloy strip material and to reclaim copper from the 
spent solution.

An increasing number of copper alloys now contain elements which form 
insoluble refractory type oxides. As a result, some conventional cleaning 
or etching solutions have had to be replaced by oxidizing cleaning 
solutions such as hydrogen peroxide and ammonium persulfate. The use of 
these oxidizing solutions, however, has created certain additional 
problems. One of these problems has to do with the inherent stability of 
some oxidizing cleaning solutions, e.g. decomposition at elevated 
temperatures. To obviate this problem, it often becomes necessary to 
maintain the temperature of the solution during processing and/or use 
within certain temperature limits. Another problem has to do with the 
reality that it is no longer economically justifiable to immediately 
discard and replace spent solutions. Therefore, it becomes necessary to 
find some mechanism for regenerating the spent solution. 
In accordance with the present invention, an improved electrochemical cell 
for regenerating spent cleaning solutions is provided. The electrochemical 
cell of the present invention has particular utility in regenerating 
temperature sensitive solutions such as oxidizing cleaning solutions. As 
used herein, the term "cleaning solution" is synonymous with the terms 
"pickling solution" and "etchant". 
Referring now to FIG. 1, a system for cleaning metal or metal alloy strip 
such as copper or copper alloy strip is illustrated. The metal or metal 
alloy strip not shown to be cleaned is passed through a cleaning tank 10 
containing a cleaning solution. The type of cleaning solution depends upon 
the material forming the strip to be cleaned and the nature of the 
contaminants to be removed. Depending upon the cleaning solution used, the 
strip may be cleaned either by chemical action alone or by chemical action 
in combination with mechanical action. Any suitable cleaning technique 
known in the art may be used to clean the metal strip. 
Incorporated into the system of FIG. 1 is an electrochemical cell 14 for 
regenerating the cleaning solution after its cleaning power has been 
depleted and its cleaning rate is no longer commercially acceptable. The 
spent solution may be withdrawn from the cleaning tank 10 and transferred 
via flow line 16 and valve 18 to a chamber 12 of the electrochemical cell 
14. As shown in FIG. 2, the chamber 12 has an electrode 48 to be described 
in more detail hereinafter and the spent solution is used as the 
electrolyte in chamber 12. 
The electrochemical cell 14 also has at least one chamber 20 containing a 
counterelectrode 50. In a preferred cell construction, the electrode 
chamber 12 is located in the central portion of the cell and is flanked on 
two sides by counterelectrode chambers 20. A physical separator 22 
separates the electrode chamber 12 from each counterelectrode chamber 20. 
A suitable counterelectrolyte is supplied to and circulated through each 
counterelectrode chamber 20 by a counterelectrolyte circulation loop 24. 
Each counterelectrolyte circulation loop 24 has a pump 26 to circulate the 
counterelectrolyte. Circulating the counterelectrolyte is desirable to 
help the efficiency of the system, particularly the system's cooling 
efficiency. If needed, each loop 24 may also have additional means not 
shown for cooling or heating the counterelectrolyte prior to its entry 
into each counterelectrode chamber 20. For reasons to be discussed 
hereinafter, it is preferred to flow the counterelectrolyte through the 
chamber 20 in the same direction that the electrolyte flows through the 
chamber 12. 
To maintain the temperature of the electrolyte within certain desired 
limits, a heat exchange medium or fluid is circulated through the 
electrode chamber 12. The heat exchange medium may comprise any suitable 
heat exchange fluid known in the art and is circulated through the chamber 
12 by heat exchange loop 28. Heat exchange loop 28 comprises a pump 30 for 
circulating the heat exchange medium, a unit 32 for either cooling or 
heating the heat exchange medium, and at least one hollow fluid conduit 34 
extending through the chamber 12. The heat exchange medium preferably 
flows through the heat exchange loop 28 so that the fluid in each conduit 
34 travels in a direction counter to the flow direction of the electrolyte 
in the chamber 12. 
If adjustments in raw material concentration, solution temperature or other 
parameters are needed prior to solution regeneration, the spent solution 
may be first transferred from the cleaning tank 10 to a reconditioning 
unit 38. To do this, the spent solution is withdrawn from the tank 10 via 
line 17 and valve 36 in lieu of line 16 and valve 18. The reconditioning 
unit 38 may comprise any suitable solution reconditioning means known in 
the art. Of course, the type of reconditioning unit utilized depends upon 
the type of adjustment that needs to be made to the spent solution. For 
example, reconditioning unit 38 may comprise means for heating or cooling 
the spent solution or means for adding one or more raw materials and 
mixing them into the spent solution. After the spent solution has been 
reconditioned, it may be transferred to the chamber 12 via flow line 16. 
After the spent solution has been regenerated in the cell 14, it is 
returned to the cleaning tank 10 through the flow line 40. A valve 42 is 
provided in flow line 40 to permit recirculation of the solution to the 
electrode chamber 12 via flow line 44 if desired or if needed. To 
facilitate circulation of the cleaning solution, a pump 46 may be 
incorporated into the flow line 40. If desired, a storage tank not shown 
for holding the regenerated cleaning solution until it is needed may be 
incorporated into the flow line 40. 
Pumps 26, 30 and 46 may be any suitable pump known in the art. Similarly, 
valves 18, 36 and 42 may be any conventional valve known in the art. 
Referring now to FIGS. 2-4, the electrochemical cell 14 is illustrated in 
more detail. As previously described, the cell 14 preferably has a central 
electrode chamber 12 and two counterelectrode chambers 20. The extent of 
the electrode chamber 12 is defined by the placement of the physical 
separators 22. Preferably, the separators 22 are located in close 
proximity to the electrode 48. The extent of each counterelectrode chamber 
20 is defined by one of the physical separators 22 and a respective cell 
wall 51. The cell walls 51 may be formed from any suitable material known 
in the art. The cell walls may be formed from an electrically 
non-conductive material or from a suitable metallic material. 
The physical separators 22 are used to substantially prevent mixing of the 
products in the electrode and counterelectrode chambers 12 and 20, 
respectively. The physical separators 22 may be mounted in the cell in any 
suitable manner. For example, notches not shown for receiving the 
separators may be cut into each cell wall 53 and suitable packing means 
not shown may be placed around the edges of the separators to form a fluid 
seal between the notches and the respective separators. Each physical 
separator 22 is preferably formed from a material resistant to attack by 
the electrolyte and the counterelectrolyte and may be either a diaphragm 
such as a microporous polyethylene diaphragm or an ion exchange membrane 
such as a Nafion or a cation exchange member. A diaphragm would be used 
where it is desired to have a restricted bulk flow from one chamber to 
another without any preference to the charge of the ions passing through 
it. Preferably, a diaphragm having a fine porosity structure would be 
used. An ion exchange membrane would be used where it is desired to 
substantially prevent any bulk flow but to permit the flow of ions of 
certain preferred charges. If desired, each physical separator could 
comprise either a diaphragm or a membrane and inert plastic meshes. 
The electrode 48 in the chamber 12 is the most complex structure in the 
cell of the present invention because of the variety of roles that it 
plays during cell operation. At a bare minimum, the electrode 48 comprises 
at least one hollow tube or conduit through which the heat exchange medium 
flows, at least one current collector 52 bonded to the at least one tube, 
and at least one electrochemically active portion 54 bonded to the at 
least one tube. In a preferred construction, the electrode 48 comprises a 
grid-like structure formed by a plurality of spaced-apart substantially 
parallel tubes 34, a plurality of spaced-apart substantially parallel 
current collectors 52 arranged substantially transverse to said tubes 34, 
and a plurality of electrochemically active portions 54 located on each 
tube 34 preferably substantially adjacent to and between the location 
where each current collector 52 is bonded to each tube 34. The electrode 
48 may be mounted in the chamber 12 in any suitable manner using any 
suitable means known in the art. 
Each of the tubes 34 is formed from an electrically conductive material 
which is substantially corrosion resistant in the operating environment. 
While any electrically conductive material having suitable corrosion 
resistance characteristics may be used, titanium or one of its alloys is a 
preferred material for the tubes 34. 
It is important to the efficient operation of the cell of the present 
invention to minimize the volume of the electrode chamber 12. It has been 
found that by minimizing the electrode chamber volume it is possible to 
obtain better control of the electrolyte temperature and increase product 
output of the cell. The primary limitation on electrode chamber size is 
the diameter of each tube 34. The diameter of each tube is a function of 
the electrolyte resistance and the operating overvoltage needed to insure 
a substantially even current distribution. It has been found that a 
preferred diameter for the heat exchange tubes is in the range of about 1 
mm. to about 30 mm. and a most preferred diameter is in the range of about 
3 mm. to about 7 mm. 
The wall thickness of the tubes 34 is another important factor in the 
efficient operation of the cell 14. The wall thickness for each tube 
should be such that adequate mechanical stability and good heat conduction 
are provided. It has been found that a wall thickness in the range of 
about 0.2 mm. to about 0.5 mm. should provide the desired effects. 
The current collectors 52 bonded to the tubes 34 preferably each comprise a 
pair of spaced-apart strips 56 of electrically conductive material. While 
the strips 56 may have any desired shape, it is desirable to contour each 
strip 56 to form good contacts with the tubes 34. In the cell of the 
present invention, each strip 56 preferably has a substantially 
semicircular portion 58 where it contacts each tube 34. 
To promote a substantially uniform current distribution throughout the 
cell, the current collectors 52 are substantially uniformly distributed 
over the length of the tubes 34. The number, the spacing and the size of 
the current collectors 52 depend upon the range of current density to be 
used in the cell and the operating electrode surface area. It is desirable 
to design each current collector 52 to minimize the excessive overvoltage 
drop and the resultant power loss across the current collectors. It has 
been found that satisfactory operation of the cell can be obtained by 
spacing the current collectors 52 from about 1 cm. to about 5 cm. apart, 
preferably from about 2 cm. to about 3 cm. apart and by providing each 
strip 56 with a substantially rectangular cross section having a width in 
the range of about 0.5 cm. to about 3 cm. and a thickness in the range of 
about 0.02 cm. to about 0.04 cm. 
While any suitable metal or metal alloy may be used to form the current 
collectors 52, titanium or one of its alloys is a preferred material. The 
material selected for the current collectors 52 should also have good 
corrosion resistance properties. 
The strips 56 may be joined to the tubes 34 in any suitable manner known in 
the art. Preferably, each strip 56 is spot welded to each tube 34. 
The electrochemically active portions 54 are preferably formed by metal 
members bonded to the tubes 34. While any suitable member providing the 
necessary surface area may be used, it is preferred to form the portions 
54 by spot welding a plurality of rings 54 to the tubes 34. In lieu of 
spot welding the rings 54 to the tubes 34, the rings 54 could be inlayed 
into the tubes 34. 
The extent of the portions 54 on each tube 34 and the surface area needed 
for each portion depend upon the current density sought to be used in the 
cell. If needed, the portions 54 could cover the total electrically 
conductive area of the electrode 48 exposed to the electrolyte. It has 
been found that the surface area of each portion 54 should be in the range 
of about 2 cm.sup.2 to about 3.5 cm.sup.2. 
The thickness of the portions 54 should be such that the portions 54 have 
sufficient strength to be durable and economically acceptable. The 
thickness of the portions should preferably be in the range of about 10 
microns to about 50 microns and most preferably in the range of about 15 
microns to about 25 microns. 
While the electrochemically active portions 54 may be formed from any 
suitable metal or metal alloy, it is preferred to form them from platinum 
or one of its alloys because platinum forms oxides which slow down any 
oxygen evolution at the electrode 48 and introduces the overvoltages 
needed for most reactions. In a most preferred construction, the portions 
54 are formed from bright recrystallized platinum. 
It is important to the efficient operation of the cell 14 that the spacing 
between the electrode 48 and each counterelectrode 50 be minimized. By 
minimizing the spacing between the electrode 48 and each counterelectrode 
50, the current paths through the electrolyte and the counterelectrolyte 
are minimized and the I.sup.2 R losses are greatly reduced. Therefore, 
each counterelectrode 50 should be designed to have sufficient stiffness 
that it may be placed in close proximity to the separator 22. Each 
counterelectrode 50 should also be designed to promote substantially even 
current distribution throughout the cell 14. 
In a preferred embodiment, each counterelectrode 50 is formed from a 
metallic mesh type structure having at least about 50% of its surface area 
open. The at least about 50% open area insures good mass transport from 
the surrounding counterelectrolyte and promotes better usage of the 
separator 22 because more of its surface area is exposed to the 
counterelectrolyte. In a most preferred embodiment, the open area is from 
about 50% to about 70% of the counterelectrode surface area. 
Depending upon the metal or metal alloy chosen for each counterelectrode 
and its resilience, each counterelectrode 50 should have a thickness in 
the range of about 0.5 mm. to about 5 mm. and preferably in the range of 
about 0.7 mm. to about 1.5 mm. Preferably, the counterelectrodes are 
formed from copper or one of its alloys. For example, each 
counterelectrode may be a brass screen formed by 0.062" diameter wires and 
having about 64% open area. 
The counterelectrodes 50 may be mounted in the chambers 20 in any suitable 
manner using any suitable means known in the art. However, it is important 
during use of the cell that the counterelectrodes be maintained in 
position and not have hydrostatic pressure from the electrolyte move them 
away from the electrode. If desired, polyvinylchloride standoffs not shown 
may be mounted on the outside wall of each counterelectrode chamber to 
prevent such an occurrence. 
In some systems, each counterelectrode 50 functions as a cathode. In those 
systems, metal from the electrolyte may be deposited on the 
counterelectrodes 50. If needed, removal of the deposited metal may be 
done in either a batchwise or a continuous manner. 
Referring now to FIG. 5, a counterelectrode assembly suitable for use in a 
batchwise removal system is illustrated. The counterelectrode comprises a 
pair of metallic mesh members 60 elastically attached to a current 
collector post 62 by spring current collectors 64. During insertion or 
removal of the counterelectrode assembly, the spring current collectors 
may be held in a retracted position by clamps 66. Clamps 66 may comprise 
any suitable clamping devices known in the art. 
If a continuous removal system is desired, a counterelectrode assembly such 
as that shown in FIG. 6 may be used. In this assembly, the 
counterelectrode is formed from an endless metallic mesh belt 68 rotated 
by drive means 72. Drive means 72 may comprise any suitable drive 
arrangement such as a motor and gear arrangement known in the art. 
Suitable means 70 for removing the deposited metal from the belt 68 may be 
provided adjacent one of the belt surfaces. The metal removing means 70 
may comprise any suitable scrapping or scrubbing device known in the art. 
In operation, the electrode 48 and the counterelectrodes 50 are connected 
to a suitable current source not shown. Preferably, the electrode 48 is 
connected to the curent source via one or more copper busses not shown 
attached to the current collectors 52. The current source may be any 
conventional power supply known in the art. 
In a preferred manner of using the cell 14, the cell is arranged so that 
the electrolyte and the counterelectrolyte both flow substantially 
upwardly. By flowing the electrolyte and counterelectrolyte through the 
cell in such a manner, it is possible to take advantage of any bubble 
lifting effect created in the chambers 12 and 20. The bubble lifting 
effect results from gas bubbles being created at the electrode 48 and the 
counterelectrodes 50. The gas bubbles rise in the chambers 12 and 20 and 
promote movement of the electrolyte and the counterelectrolyte. To achieve 
the benefits of this effect, it is desirable to orient the cell 14 so the 
chambers 12 and 20 have their longitudinal dimensions in a substantially 
vertical plane. 
It has been discovered that the electrochemical cell of the present 
invention has particular utility in regenerating peroxydisulfuric acid and 
persulfate solutions used to clean copper and copper alloy materials. In a 
peroxydisulfuric acid or persulfate solution regeneration system, the 
electrode 48 would be connected as the anode and the counterelectrodes 50 
would be connected as the cathodes. The anode 48 preferably comprise thin 
sheets of platinum foil spot welded to thin titanium tubes. A 
substantially uniform current density can be provided by connecting the 
anode tubes to copper busses with a series of thin titanium strips. Spot 
welding may be used to attach the current collector strips to the anode 
tubes. The cathodes may comprise brass screens formed from 0.062" diameter 
wires having a 64% open area. The physical separators between the anode 48 
and each of the cathodes 50 preferably comprise microporous polyethylene 
diaphragms which act as a diffusion barrier between the anolyte and the 
catholyte but which also allow some interdiffusion between the chambers 12 
and 20. 
The spent peroxydisulfuric acid or persulfate cleaning solution is used as 
the anolyte in the chamber 12. The catholyte may comprise an aqueous 
sulfuric acid solution. To maintain the temperature of the anolyte within 
a desired temperature range, a refrigerated glycol solution may be 
circulated through the tubes 34 to remove heat from the cell. The anolyte 
should be reasonably chilled to prevent decay as the result of increasing 
temperature during the regeneration process. In addition, the heat buildup 
in the anolyte needs to be controlled to favor production of persulfate as 
opposed to production of peroxide. 
By applying an appropriate current to the cell, copper values in the spent 
cleaning solution will be plated out at the cathodes while persulfate 
values are being generated at the anode. The removal of the copper values 
from the spent solution and the production of new persulfate values 
increases the cleaning power of the spent solution and permits it to be 
reused. After a commercially acceptable level of cleaning power has been 
restored to the peroxydisulfuric acid or persulfate solution, the solution 
is withdrawn from the anode chamber and either supplied to a cleaning tank 
for cleaning metal or metal alloy strip or to a storage tank for later 
use. The process for regenerating and/or producing peroxydisulfuric acid 
using sulfuric acid catholyte is more fully described in co-pending U.S. 
patent application Ser. No. 539,598, filed on an even date herewith, to 
Pryor et al. which is hereby incorporated by reference. 
While the electrochemical cell of the present invention has been described 
as having particular utility in regenerating peroxydisulfuric or 
persulfate cleaning solutions, it also may be used to regenerate and/or 
produce other temperature sensitive solutions such as hydrogen peroxide, 
perchloric acid, sodium perchlorate and perborates. 
While the cell has been shown as having a central electrode and a pair of 
counterelectrodes, it may be designed to have more than one electrode and 
more than two counterelectrodes. 
While the counterelectrodes have been described as being formed from 
metallic mesh screens, they may be formed from other types of metallic 
materials having the desired open area. 
The U.S. patents, the U.S. patent application and the foreign patent 
publications set forth in the specification are intended to be 
incorporated by reference herein. 
It is apparent that there has been provided in accordance with this 
invention an electrochemical cell for regenerating temperature sensitive 
solutions which fully satisfies the objects, means, and advantages set 
forth hereinbefore. While the invention has been described in combination 
with specific embodiments thereof, it is evident that many alternatives, 
modifications, and variations will be apparent to those skilled in the art 
in light of the foregoing description. Accordingly, it is intended to 
embrace all such alternatives, modifications, and variations as fall 
within the spirit and broad scope of the appended claims.