CA1068641A - Method and apparatus for the electrodeposition of metal - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

In an electrodeposition cell, high quality metal such as copper is produced on a non-retentive cathode blank at a high current density. A predetermined close cathode-anode spacing and a gas bubble tube for continuously agitating the electrolyte across the face of the cathode enable effective use of high current densities to electrowin or electrorefine a metal such as copper. The apparatus includes means for spacing anodes apart from cathodes at a predetermined close distance, optimally less than one inch face to face. Bubble tubes are inserted in cathode-anode pairs and are supported by bubble tube support members.
An anode for electrowinning includes a non-conductive exten-tion on its base and non-conductive convection baffles at opposite edges of its faces. Baffles and an extension prevent unwanted electro-deposition on specific areas of the cathode. Baffles, close spacing, and bubble tubes cause the desired convection of electrolyte throughout the cell.
In an electrorefining cell, convection baffles are positioned on vertical support members within the tank.

Description

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The present invention relates to method for the electro-deposition of mekal, more particularly of copper. The method and - apparatus of the present invention are use~ul in both electro-winning and electrorefining~
In th~ present invention a high current den~ity may be employed to deposit metal on a cathode. In connection with the ~oregoin~, the term l'current densityl~ is the ratio of current in amperes to the area of cathode in square feet and is expre~sed in ASF unitsO
The current density normally employed in prior art electrowinning pro~eqses is approximately 21 ASF. Of course, it is well known in this art that an increasa in current density de-crease$ the time required for a given amount of copper deposition.
The main obskacle preventing those skilled in the art ~rom in-creasing tha Trrent density appears to have been the lack o~ a suitable ~onvection system for the electrolyte. The method and apparatus o~ the present invention provides a convection system which permits the curren~ density in an electrolytic deposition proce~Q to be increa~ed, while at the same time minimizing the incremental consumption of electrical power.
-~ A major benefit to be derived from tha application of the method and apparatus of this in~ent~on is the elimination of - electrical shorts due to contac~ between anodes and cathodes.
This baneficial feature greatly reduces the amount o~ "sy~tems work~ required in commercial practice to locate and correct ele-ctrical short~.
At the outset it is emphasized that gas agitation in an electrolytic process for recovering metal is not novel. I~deed, it was known heretofore, in the alectrolytic deposition o~ coppar from acid solutions, to continuously agitate the electrolyte, ,

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:, , : , . ' ~,' 6~364~L -particularly across the face of the anodes. ~gitation was pro-vided by a mixture of sulfur dioxide gas and steam. The purpose of the steam was to insure the correct temperature conditions.
The pipes through which the mixture of steam and sulfur dioxide was carried contain perforations or nozzles arranged at such ; angles that the escaping gas and steam will tend to impinge angularly upon the faces of the anodes, so that the electrolyte will be continuously circulated and maximum agitation will occur across the anode faces. The use of a mixture of steam and a gas to provide agitatlon in an electrolyte cell for the deposition of copper was also known.
By and large, however, the prior art methods for aqitating the electrolyte have not provided a sufficient amount of convection of the electrolyte which would enable a significant increase in the current density with an atten-dant production of high quality copper or other metals.
Moreover, the prior art agitation methods have not been applica-.. ..
ble to electrorefining, because of the resulting suspension ofanode slimes and the consequent deterioration of deposit 2Q quality.
In the prior art processes which employ non-retentive cathode blanks, the edges of the cathode blanks are masked with non-conducting or insulating material to prevent the metal being deposited on each face of the cathode from joining, which would make removal of the deposit from the cathode difficult.
An important side benefi~ of the convection system of thé
present invention, at least in the preferred forms, is that insulating edging does not have to be positioned on the edges of a non-retentive cathode in order to prevent the edges of 30 the deposit on each face from joining. ;
Other important benefits of the present invention, 1 at least in the preferred forms, include guidance of the cathodes into correct position and prevention

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. of electrical contacts between anodes and cathodes, once positioned in the cell. ~: -According to one aspect of the present invention, ~ .
;; there is provided an electrodeposition cell comprising: .
anodes for submergence in an electrolyte; non-conductive anode bottom extensions positioned beneath the anodes;
non-conductive convection edge baffles positioned adjacen.t to opposite edges of the anode faces and extending toward ; the cathode faces; cathodes, spaced from said anodes, the . 10 submerged length of the cathodes being equal to or greater ; than the submerged length of the anodes and anode bottom extensions, the cathodes being wider than the anodes so .
that the edges of the cathodes extend outwardly from the~.
convection baffles; means for maintaining close spacing between anode-cathode faces; and, bubble tubes having orifices for generating sheets of relatively small rapidly ascending bubbles of gas that result in agitation of the electrolyte over the cathode faces, the portion of said buble tube having the orifices being positioned beween the 20 non-conductive anode extensions and the cathode face; said baffles Eorming enclosures between cathode and anode faces ~
which minimize lateral spreading and contraction of the . ..
sheet of bubbles and prevent deposition of metal at the edges of cathodes extending beyond the baffles, said anode bottom extensions preventing deposition of metal at the bottom of the cathode face, said means for maintaining close spacing, said bubble tubes, and said baffles pro-viding an electrolyte convection system which enables the -efficient use of high current densities in an electro-deposition process with an attendant production of high quality metal which can be easily stripped from the ~æ-. . . . . . .

0~8641 : cathodes.
According to another apsect of the present invention there is provided a method of performing electrodeposition ~
at a high ratio of current density to metal ion concentra- .
.:
; tion in a cell which includes anodes, cathodes and an :
electrolyte with an attendant production of high quality metal which can be easily stripped from the cathodes com-prising the following steps: positioning non-conductive :~
. convection edge baffles adjacent to opposite edges of the anode faces so as to extend toward the cathode faces; . ;.
positioning non-conductive anode bottom extensions beneath the anodesi providing cathodes that are wider than the . anodes so that the edges of the cathodes extend outwardly `:. from the convection edge baffles; submerging the cathodes so that the submerged lengths of the cathodes are equal to or greater than the submerged lengths of the anodes .-;
and the anode bottom extensions; positioning bubble tubes -having orifices between the non-conductive anode exten-. sions and the cathode faces; spacing opposed anode and 20 cathode faces apart from each other at a distance of about 1-1/4 inches or less; and, electrodepositing metal on the : :
., cathodes while generating a sheet of gas bubbles from the bubble tubes through the electrolyte between opposed anode-cathode faces to produce agitation of the electro-lyte over the cathode faces as metal is being deposited ;:
thereon and maintaining said convection edge baffles : during electrodeposition to form enclosures between cathode and anode faces to minimize lateral spreading and :
contraction of the sheet of bubbles and prevent deposition of metal at the edges of the cathode extending beyond the ` baffles, and maintaining the position of said anode bottom ~

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~ extensions during electrodeposition to prevent deposition of metal at the bottom of the cathode face.
According to another aspect of the invention there is provided an electrowinning cell comprising: insoluble anodes for submergence in an electrolyte; non-conductive anode bottom extensions attached to the bottom of the :
anodes; non-conductive convection, edge baffles attached to opposite edges of the anode faces and extending toward the cathode faces; cathodes, spaced from said anodes, the ~ ~.
submerged length of the cathodes being equal to or greater than the submerged length of the anodes and anode bottom extensions, the cathodes being wider than the anodes so . that the edges of the cathodes extend outwardly from the ;
convection baffles; means for maintaining close spacing ;
between anode~cathode faces; and, bubble tubes having orifices for generating sheets of relatively small rapidly ; :
ascending bubbles of gas that result in agitation of the electrolyte over the cathode faces, the portions of said bubble tubes having the orifices being positioned between 20 the non-conductive anode extensions and the cathode faces so that each sheet of bubbles sweep across a cathode face, said baffles forming enclosures between cathode and anode faces which minimize lateral spreading and contraction of the sheet of bubbles and prevent deposition of metal at edges of cathodes extending beyond the baffles, said anode bottom extensions preventing deposition of metal at the bottom of the cathode face, said means for maintaining close spacing, said bubble tubes, and said baffles pro-viding an electrolyte convection system which enables the efficient use of high current densities in an electro-deposition process with an attendant production of high ~.

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~ quality metal which can be easily stripped from the cathodes.
According to yet another aspect of the invention there .
is provided a method of electrowinning a metal at a bigh ratio of current density to metal ion concentration in a cell which includes insoluble anodes, cathodes and an electrolyte with an attendant production of high quality metal which can be easily stripped from the cathodes com-.~ prising the following steps: attaching non-conductive 10 convection edge baffles to opposite edges of the anode .
- faces so as to extend toward the cathode faces; attaching ~ non-conductive anode bottom extensions beneath the anodes;
providing cathodes that are wider than the anodes so that . :
the edges of the cathodes extend outwardly from the convection edge baffles; submerging the cathodes so that ' the submerged lengths of the cathodes are equal to or `
greater than the submerged lengths of the anodes and the :;:
anode bottom extensions; positioning bubble tubes having ~;
1 orifices between the non-conductive anode extensions and 20 the cathode faces; spacing opposed anode and cathode faces .
apart from each other at a distance of about 1-1/4 inches .
or less; and, electrodepositing metal on the cathodes while generating a sheet of gas bubbles from the bubble tubes through the electrolyte between opposed anode- .
. cathode faces to produce agitation of the electrolyte over :; the cathode faces as metal is being deposited thereon and maintaining said convection edge baffles during electro deposition to form enclosures between cathode and anode faces to minimize lateral spreading and contraction of the .
sheet of bubbles and prevent deposition of metal at the edges of the cathodes extending beyond the baffles, and :
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- maintaining the position of said anode bottom extensions during electrodeposition to prevent deposition of metal at the bottom of the cathode faces.
Accordingly, it is an advantage of the present inven-tion, at least in preferred forms, that it can provide an electrodeposition method and apparatus which enable the electrodeposition of metal at current densities which are high in relation to the metal concentration, while producing metal of acceptable purity and mechanical integrity.
, Another advantage of the present invention, at least in the preferred forms, is that it can provide a novel method and apparatus for effecting vigorous electrolyte convection in an electrodeposition process.
A further advantage of the present invention, at least J
'`1` in the preferred forms, is that it can provide an improved method and apparatus for electrorefining copper. `
A still further advantage of the present invention, at least in the prefered forms, is that it can provide an 20 improved method and apparatus for electrowinning copper.
Additional objects and advantages of the invention will become readily apparent from the following descrip-.- . . . .
tion of preferred embodiments of the invention.
The convection system of this invention ususally includes a combination of convection baffles and cathode guides affixed to the anodes, or positioned in the~tank, . a predetermined close cathode-~,:
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', ' '' ': '' ' ", ' . ' ' ' ' ~ . "' 686~1 anode spacing, and a gas agitation bubble-producing means po-sitioned below and between the faces of the cathode and anode.
As a result, current density can be significantly increased while enabling lower power consumption with an attendant pro-duction of high quality metal. Since it is preferred ~o utilize a non-retentive cathode, starting sheets are unnecessary with the present invention. Significant economic advantages ; of the present invention àre that it minimizes plant size, systems work, power consumption and metal inventories. `
In order that the invention may be more fully under-stood, the preferred embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:
Fig. 1 is a view of a prior art non-retentive cathode blank with an insulating edging applied thereto;
; Fig. 2 is a perspective view of a non-retentive cathode blank having a layer of copper applied to both faces;
Fig. 3 is a sectional view taken along line 3-3 of Fig. 2; ~ ;
Fig. 4 is a perspective view of a non-retentive cathode and bubble tubes for forming a fluidized sheet of gas bubbles adjacent to both faces of the cathode;
Fig. 5 is an exploded perspective view of the cathode , -;
clamips of Fig. 4, which are required only at very high current densities;
Fig. 6 is a perspective view of a portion of a cell showing ;
an insoluble anode with insulating bottom extension and edge convection baffles;
Fig. 7 is an exploded perspective view of an anode clamp particularly adopted for use with cast soluble anodes in very high curreht density electrorefining;
Fig. 8 is a sectional view taken along line 8-8 of Fig. 6; -~
Fig. 9 is a sectional view taken along line 9-9 of Fig. 6;

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1~)68641 Fig~ 10 is a perspective view of bubble tubes in a ~ bubble ~ube support~member.
The present invention provides a method and apparatus for depositing superior quality cathode metal ~rom all conven-tional elactrolytes, including those having a high concentration `
of sulfuric acid. The apparatus may be used in conjunction with several anode ma~erials. By way of example, a lead-antimony anode is acceptable in the apparatus of the present invention. The cathode may be a starter sheet or a non retentive cathode blank formed of a material such as stainless steel or titanium.
Although the present invention can be practiced with a starter shaet as a cathode, in one important embodiment of this invention, an e~ongate non-retentive cathode blank is used. At this point, it should be noted that non-retentive blanks have been employ~d in the prior art. However~ a problem associated with the prior art use of these cathode blanks is that the edges have to be masked with an insulating material, to prevent the metal which deposits on each face from joining and thereby making removal of the metal dsposited difficult.
Referring to the drawings, Fig. 1 shows a prior art ;.
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non-retentive cathode blank 10 submerged in electrolyte 12. For clarit~, the anodes and other structure normally associated wQth cathodic dspositlon are not sh~wn in Fig. 1. When non-retentive cathodes are employed9 the metal deposited thereon is removed a~ter electrodeposition is complete. In order to~permit such removal it is lmportant that the layer o~ metal deposited on the two faces of the cathode do not join ~ach other in the vicinity of the side edges. To prevent joining of the metal layers 1~ and 15 on the side edg~s, insulating edging 16 is applied to the edges of the cathode blank 10. As a result of providing the cathode blank 10 with edging 16, ~here i5 no metal depo~ition on the cathode in the area of the blank covered by the edging. Aft~r the removal of the edging, a cathode containing two layer~ of deposited me-tal is produced. (See ~igs. 2 and 3).
By employing the apparatus o~ the present invention, no edging îs required on the cathode; however, two sheets of metal ; similar to those shown in Figs. 2 and 3 are, nevertheless, pr~
duced-on the faces of the cathode blank. In the electro~inning embodiment of the present invention, electrodepo~ition on the edges of the cathode blank beneath the surfa~e of the ~lectrolyte i~ ~-prevented by a combination of insulated convection ba~fleæ 1~ lo~
ca~ed on the side edges of the insoluble anode and an insulated .
bottom extension 20 affixed to the bottom of the anode. The sub- ~:
merged length of the cathode blank is conveniently made equal to or somewhat greater than the submerged l~ngth of anode and its bottom extension, as illustrated in Fig. 9.
In electrore~ining, the anode extension is posi~ioned on the bottom of the tank, with the anode positioned above it. The sids baffles ln an electrorefining cell ma~ be positi~ned on a support member and af~ixed in the ccll in relationship to the '~'' , ' .. .. ; ' , ' , ' ' . . ,, ., '., ., , ', .. ' , .~ I ! .. . ..

` ~ 364~

soluble anode. Side baffles lB and bottom extension 20 for in-solubl~ anodeX are best shown in Fig~ 6 and 9. Details o~ how side ba~les 1~ and bottom e~tension 20 prevent the deposition of copper on th~ edg~s o~ the cathode and also prevent undeQired de-flection o~ the ascending gas bubbles are ampli~ied at a more ap-propriate point in the speci~ication.
Fig. 4 includes a perspective view of a non-retentive cathode blank 22, which is usable in accordance with the present invention. It i~ advantageou~ to form cathode 22 ~rom Type 316 ~tainless steel having a standard 2B rolled finish. When this material i~ employed~ no pre-treatmen~ or brea~-ln period is nece~
s~ary for the ca~hode blank 22. Furthermore, it is easy to strip deposits from this cathode blank manuall~. Inde~d, the deposits release easily ~rom the cathode blanks 22 once the upper edges o~
the deposit are loosen~d. Deposits can also ba detached by ~lexing the cathode~. It should be noted, however, that other materials can be employed in fabricating cathode blanks 22. For example, titanium blanks have been employed to advantage in the process of the present invention. Sheets of other conducting 20 materials may be employed a~ cathode blanks, as appropriate to the nature of the metal to be deposited and the eomposition of ; -- the electrol~te~ ;
, When the current carrying capacity of the contact between conventional triangular bar current conductor and elec~rode ; ~uspension bar is to be exceeded, it has been ~ound effective to decrease the contact resistance by mean~ o~ a very high current density contact clamp such as i~ illustrated in Figs. 4, 5 and 7. ~;
Cathode suspension bar 24 is shown in Fig. 4 clamped at one end;
depending upon the magnitude o~ the current donsity emplo~ed and the mode o~ conducting current between adjacent cells, the number `

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of contact clampæ required per el~ctrode may be variously zero, one or two.
A sandwich arrangement similar to that illustrated i~
Figs~ 1, 2 and 4 is often used to suspend insoluble anodes. The second common su~pension means for an inæoluble anode consists of two integrally cast vcrical lugs 26 envelopin~ section~ of a rec-tangular suspension bar, which i~ usually of copper. (See Figs~
6 and ~)~ The sandwich construction is preferred in the practice of this invention becauseit permi~s a closer approach of the anode face relative to the ~ace of the cathode. In either ca~e, contact clamps of the design detailsd in Figo 5 may be used with insoluble anodes, if desired.
Soluble anodes employed in electrorefining are typi- ~ -cally cas~ with outwardly directed lugs, or ears of nonrectangular ~ -, . ... . .
cros~-section. The contact clamp detailed in Fig. 7 was desi~ned ~or use in very high current density electrorefining by the method ` of the pres~nt invention. In general, contact clamps are super- ~ ;
fluous at curren~ densities of about 60 ASF or below; their use is strongly indicated at current densities of abo~t 100 ASF and above.
Clamps used in production could be alternatively weight-activated cam type or of other suitable design not requiring manual fastening.
-Fig. 6 shows a peræpective vie~ of an an~de 30 which 'i5 used in the present invention. Anode 30 is typically for~ed of a lead-antimony alloy. At this point, h~wever, it is emphasized that the material from which the anodes are formed, fQrms no part -~o~ the present invention. In the slectrowinning embodiment, anodes may be fashioned o~ any material of suitabla electrochemical and mechanical properties. It is, of course, preferable for the most e~fective use o~ the invention that the anodes be rigid and of uniform croæs-section. As is shown in Figs. 6 and ~, anode 30 .:

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10686~1 includes a plurality of holes 32. The square perforations are a design feature ~ a good quality inæoluble anode, employed in con-ventional copper electrowinning, but afford no special advantages in the practice of gac agitation.
A signiPicant feature of the anodes used in the present invention is the attachment of baffles 1~ and extensions 20 there-to. Both baffles 1~ and extension 20 are electrically insulating or non-conductive. They may be formed o~ any electrically non-conductive material wh~h is relatively stable in the electrolyte environment. Ex~ensions and baffles have been fabricated from a polyvinyl chloride polymer, which has been found better suited to this u~e than other insulating materials of construction, ~uch as polyeth~lene) polypropylene and fiberglass-reinforced epoxy board.
A8 i3 shown in Fig. 9, edge baffles 1~ form narrow passageways through which the ends of cathode blanks ~2 project.
It is apparent to those ~killed in the art that there will be no deposition o~ metal on the faces of the elongate cathode blan~s for more than a short distance below the bottoms ~f the anodes. Furthermore, there will be no deposition on the faces of the cathode blanks at the area of the cathode fac~s which extend outwardly from the edges of baffles 1~, due to the additional electrical resistance introduced. The convection baffles 1~, thus, also function~ a~ electrolytic current shields. Accordingly, with the arrangement of extensions 20 and baffles 1~ on the anode or with the equivalent arrangement in the electrorerining embodiment, a sheet of copper is formed on each face of the cathod~ similar to those shown in Figs. 2 and 3, but without the use of insulating i~
edging. Confinement of tAe deposit spread to within the borders of the cathode faces has distinct advantages in that a. it elimi-: , .
nates time-consuming maintenance and rsplacement o~ in~ulat~ng . . .:
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- edging, b. facilitates removal of deposits from the cathode blanks and c. eliminates a source of contamination, namely the nodulose bead of deposit which typically orms along an edge strip. A further useful feature of the edge ba~fles of :. :
the present invention is that, with the anodes in place in the cell, the cathodes are thereby yuided accurately into correct position relative to anodes and bubble tubes.
With the soluble anodes employed in electrorefining, it is generally not expedient to affix the convection baffles thereto. In that case, equally good results are obtained by positioning the side baffles in support members placed along ~ -the appropriate walls of the electrorefining cell. It is especially noteworthy that by using the technique and apparatus of the present invention, copper electrorefining was conducted at current densities as high as 210 ASF (i.e., ten times norm~
without causing passi~ation of the anodes. Passi~ation of the soluble anodes in conventional practice normally precludes ` - electrorefining at high current densities.
As has been stated above, important features in the process and apparatus which enable efficient high current density operation are the reduced electrode spacing and a , novel conyection system. Movement of the electrolyte in the system of the present invention is powered by gas agitation.
Gas agitation is an old technique in the electrodeposition art. In the present invention, the convection system includes a fluidized sheet of relatively small, rapidly ascending gas bubbles that, together with the turbulence théy create, result in vigorous mixing at the cathode surface, where mixing is .
most needed. The convection system insures optimum deposition conditions so that the cathode is smooth and free of voids throughout all stages of its growth.

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The gas agitation provides sufficient convection to prevent suspended particulates from lodging on ~he ~aces of the ; cathodes. Furthermore, the convection system avoids obstructions to electrolyte flow across the faces of the cathode and eliminates physical discontinuitie~ of the cathod~ surface such as edg~g and loop~ which cause entrapment and accretion of solids. These faatures are particularly advantageous in the case of electro-re~ining, where large quantities of anode slimes are generated in the cell. It has be~n found ~hat 9 contrary to the ~eaching of th0 prior art, the anode slimes can be disturbed to an appreciable degree without lncurring enhanced incorporation of impurities into the cathode deposits. ~owever, in order for this result to be achieved, the convection mu~t be exceptionally vigorous and physi-cal ob~tructions avoided, as is the case with the present invention.
Similarly, in electrowinning, th~ present invention prevents in-corporation of particulate impurities ~uch as are derived from eor-rosion or erosion of the insoluble anodes. Thus, for example, electrowon copper o~ exceptional purity has been produced while employing conventional laad or lead alloy anodes in eleetrolyte~
whlch are corrosive to the~e anode material~.
The small bubble~ 50 are propelled into the electrolyte 12 from bubbl~ tubes 52 located beneath the electrodes 30 and 22 ; . .
in the tanks. The air flow through the bubble tubes need not be ~, . . .
large. For a 3/~ inch O.D~ stainle~s bubble tubs with 2o/laooths inch wall thicknes~, ~ suitable orifice diameter is 6/lOOOth inch (6 mils) at an orifice spacing of 1/2 inch. However, a less suit~
.. . .. -able bubbler configuration may be employed if the desired improve-ment in current denslty And deposit quality i8 not as ~great. ;~
The most ~uitable con~iguration o~ the bubbler com~
30 prises a rigid tube with closely spac~d (l/2" apart) round holes ~ -. ' ' ' , ' "' ', ''' ' " ' ' ' ' '~ ' ' ' ' i' ;''' ' ' ~

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~` of diameter iR the range o~ 5-7 mils. It has been found that bubble tubes having smaller diameter holes, e.g., 4 mils are not o more efficient and are, moreover, more difficult to manufacture.
It h~s also been found that bubble tubes with larger holes, e.g., ~ mils~ expel an unneces~arily large volume o~ gas, or a compara-ble volume at'a lower bubble velocity. If one bubble t~be 52 is provided per cathode, as is shown in Fig. 9, an e~fective air flow is in the range o~ 3-4 SCFH per foot o~ cathode width or, for ~ull-~ize cathodes, about 1.5 - 2.0 SCFH air per square foot of cathode.
This flow volum~ is equivalent to the rate of oxygen generation at an insoluble anode at an anodic current don ity of 135 to 1~0 ASF.
It has been found that it is not ~o much the volume Or air expelled as the total bubble-tube/electrode configuratio~ that determines ~he ef~ectivenes~ of gas agitation. Lack of appreciation of this concept has probably retarded the more widespread application of gas a~itation in largo scale electrodeposition.
Although nitrogen has been used as the gas ~or agita-tion~ air is pr~ferred for reasons o~ economy whenever the ingress `~ of atmospheric oxygen can be tolerated. When properly applied, ~ -air agitation becomes more, rather ~han less effective with de-., ~ . .
creasing electrode face to face separation, in contrast to other conve¢tion *echniques known and practiced in the art.
TQ prevent the orifices from becoming crusted over with solidified solutes,~the incoming air is presaturated with water vapor at a temperature close to that o~ the electrol~te. When this is done~ the bubble tubes can be operated indefinitely with-out plugg-ing of the orifices.
The invention finally provide~ that the electrode ; separation be a~ its practical minimum given the ~ize of the elec-~ 30 trode supporting means and the clearance required for inserting ~ '~ ` ' " ' .

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and withdrawing the cathodes. Together wnth the gas agitation the reduced spacing provides ths means of minimizing power consum-ption in the electrowinning or electrorefining process. The re-duced spacing i~ maintained by a bottom raek 54 which is secur~d togethcr by cross-member~ 5~. Leg~ 60 attached to cross-members 5~ support bottom rack 54 off the cell bottom. It will be clear that sufficient space must be provided at the sides and bottom of the cell to permit the electrolyte to circuIate and to allow the slimes, if any, t~ settle out.
- 10 The bottom edges of the cathodes 22 are positioned in the electrowinning ta~k by the bubble tube support members 56 and are guided into position by the anode edge baffles 1~. The anode and baffleq also serve to conrine the bubble rlow to the volume o~
electrolyte immediately adjacent to the cathode faces, thereby ef-~ecting the neceqsary concentration depolarization and uniform mass transport of metal ions to the cathod~s. The separaticn be-tween the cathode blank or starter sheet and the insulating edge i baffle is on the order of between about 1/16th to about l/~th inch.
; The gas agitation method of the present invention also ;~
has favorable consequences for the anode reaction. In particular in the eIectrorefining embodiment, not onl~ is anode passivation fully forestalled~ but the soluble anodes are caused to corrode uniformly, thereby allowing a reduction in the amount of anode scrap. Improved efficiency is derived by substitution o~ ~oluble ,~
anodes having regular crosæ-section for the s~ewhat irregular anodes cast by custom~rr means.
The anode bottom extension 20, also ~n insulat~r, functions to confine the bubble flow in the low~r regions and to ~-position the anode 30. The anode 30 is also maintainsd in poæi-tion by the bottom rack 5~. The bubbler i-tself is held in .. . . . .. ... . . .

~L06l36~
position below and adjacent t~the cathode surface by the bubbler support member 56. With soluble anodes, it is generally not prac-tical to secure an insulating ex~ension ~o the anode bottom. In that event, the anode bottom may be inserted in-to the bottom rack, for ~hich purpose the vertical members 54 are covered with insul-ating material. Alternatively, the insulating barriers 20 may be positioned in bottom rack 5~ so that their upper edges are brough-t into contact with or in proximity to the bottoms of the soluble anodes~
The principal incentive for electrowinning or electro-refining at high current density is th~ attendant reduction in ` plant ~ize, metal inventory, and labor requirements. Further ad-vantage is gained by elimination of several o~ the normal proces- !
sing steps, including starter sheet production and short clearing.
In order to take full advantage of electrodeposition at high cur- ~ ;
rent density, however, the process must (1) ~ake place at currents which are much less ~han the limiting current density and (2) minimi~e the power consumption. The present invention presents a combination of factors which together accomplish these conditions by reducing the spacing ~ the electrodes and providing an agitation system which assures an adequate supply of metal ions to all parts l o~ the cathode surface. The agitation has the additional benefit - of mixing the electrolyte bath sufficiently to make it dif~icult ~or suspended particulate impurities to attach themselves to the faces of the cathode, thereby resulting in higher quality deposits.
Fine oxygen bubbles are formed at the insoluble anode during the electrowinning process. These ~ine bubbles reduce the concentration potential at the anode but are inadequate in pro-viding mixing at the opposing cathode, even ~ith ~lose spacing of electrodes. The reason is that their small size causes them to . ... ' ' .` ' ' ,;
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/
~j86 drif-t ineffectively. Therefor~, alternativa agitation at the cathode is necessary, especially at high current densities, to bring about sufficient depolari~ation at the cathode. It has been ; found that gas agitation has the desirable characteristic in this invention of increasing the cathodic dépolarization as the elect-rode spacing is decreased, at lea~t wqthin appropriate limits.
With closely spaced commercial size electrodes, gas agitation ~ay be the only e~ficient means Or providing adequately good mass tran~port conditiens over the entire ~aces of the cathodes in high current density operation. -~ The gas agitation system of the present 1nvention in-; duces an appreciable flow of electrolyte and maintains uniformity electrolyte composition throughout an electrolytic cell of reasonable size. Indeed, the electrol~te composition is subs~an-, tially the same, both within the cell and in the over~low.
The preferred configuration for the con~ection system is best shown in Fig. ~, where the bottom raek 5~, tha anode 30 and its bottom extension 20 and the anode edge baf~le~ l~, to~
gether with the elongated cathode blank 22, form an enclosure which minimizes th~ lateral spreading or contraction of the sheet of bubbles. Other con~iguration~ of supporting members in the tank may be used to confine the bubble ~low; however, i~ has been round that the above configuration is mo3t effective and ~onvsnient in allowing ease of loading and unloading of cathodes and virtual elimination of shorts due to misalignment or warping and b~wing.
Of cour3e, oth~r deslgns in bubbler tubes ara possible, For example, gas bubbles may be pre-mixed into recirculating elec~
trolyte and the mixture o~ bubble$ and electrolyts i~troduced i~to ~ ;
the tank through a source located at the same apProximate position as air bubbler tube 52 shown i-n the drawing. In thi~ case, the .' .
' , ' .

` ~06~3641 dimen~io~s of the bubbler may vary and the hole ~ze be enlargcd to permit th~ passag~ of the correct volume of recirculated elec-trolyte and ~olume of entrained ga~.
The essential criterion ror the gas agitation generator is that it introduce s~all bubbles from a line immediately adjacent to the cath~de face to form a sheet of rapidly ascending bubbles that co~tinue in a direction immediately adjacent to the cathode sur~ace until reaching the electrolyte surface, The present in vention ha~ been applied to relatively pure electr~lytes, such as are produced b~ liquid io~ exchange extraction or are empl~yed in starter ~heet produ~tion, and to relatively impure ~lectrolytes .. such as con3titute electrorefining purge streams or as are pro-duced by various processes of ore leaching.
~, Th~ utility of the present invention becomes more mani-.~ ~est when dealing with impure electrolyto~ from which pure metal `, canno~ normally be r~covered at a low ratio of metal concentration -, to current density~ In normal copper electrowinning from vat leach soluti~n9 for example, the lower limit for acc~ptable de-posits is r0ached at a ratio ~f about 1.5 (grams Cu per liter/ASF) : 20 because of the increa~e in the ele¢trolyte visc03ity and the con~ - sequ~nt de~rsa~e in the mass transport coefricient o~ cupric ions occasioned by the presence of extraneou~ solute~ at appreciable concentration.
.
Features Or th~ prese~t in~entio~ (reduced electrode .
spa~ing9 vigorous ~nd uaiform electrolyte agitation) allow the . .;
electrowinning process to be carried out economicall~ at high cur-~ rent density which is still sub~tantially below the limiting cur-; rent density under the given mass transport condltions. The re- -. sult is very acceptable. Dense and coherent cathode products are `` 30 obtained at ratios as low as 0.2 to 0.3 (g/l Cu/ASFJ, whatever the ~. . . .

~. . : . . , ; , , ~ .

--` 106~643L
.

electroly~e compo3ition. Further, the elimination o~ starting sheet~ and parting agents, through the use Or non-retentive cath-ode blanks, and the control of current density distribution so as to obviate the need for blank edging has resulted in deposits o~ exceptional purity in all of their parts, including the edge i regions. In particular, lead and sulfur impurities were held to a9 low as 0.1 ppm and le~s than 2,0 ppm, respectively. ~-The ~ollowing examples may more clearly point out the extreme conditions of electrolyte impuri~y and low ~etal ion con-centration under which high current density electrowii~ning may beemplo~ed using the present inventionO
The numerical results for Examples 1 through 4 are given in Table I. ;;

(Typical high aoid, high current density electrowinning) i The eathode-anode spacing was fixed at about 1.26 -~
inches. The copper and acid concentration3 shown in Table I are tho~a in the cell9 not in the feed to the cell. The suspended matter ~as hold at a minimum with continuous recirculation and ~iltration. The agitation was accomplished with tha apparatus as -shown in the drawings and with 3/~ inch O.D. stainless ~teel bub-bler tubes with 0.020 inch wall thickness and 6 mil orifices at 1/2 inch intervalsO ~ir was presaturated with water by sparging the air through heated water and supplied at about 1.0 SCFH per square foot of cathode. A copper starting sheet was u~ed as the .. .. . .
cathode in this trial, and a co~mercial lead/antimony anode was used.
The re~ults as ~hown in Table I indicate a good deposit at 97% current efficiency even though copper concentration to cur-30 rent den~ity ratio wa~ approximately 0.7, a condition about twice -: ' ..~...

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as s~ere as in commercial copper electrowinning. Impurities levels were very low~ The high current efficiency attained in this trial is typical of that obtained in the following examples~
~; EX~MPLE 2 ; (Ef~ect of liquid ion exchangc contaminants) The electrolyke was deliberately saturated with a liquid ion exchange reagent and kerosene to simulate the contaminants which may enter the ~l~ctrowinning tank from a prior procèss of liquid ion exchange. Furthermore, the contaminated ele~trolyte was~not filtered, so as to avoid removal of entrained organic phase. The data from Table I indicates that the prese~ce of the organic contaminants did not affect th~ results previously obtained.
,. . .
Copper concentration was here redu~ed to 29.5 g/l and current den-sity remained at about 60 ASF. Electrolyte conductivity measured (for most high acid tests) about 0~54 mho/cm.
.

(Extreme current dsnsity~
Det0rmination o~ the limit of current~d~nsity to produce .
; an acceptable quality cathode was accomplis~ using non-retentive Type 316 stainless steel cathodes in an elactrolyte of intermediate ~-~
i . . .
copper concen~rativn~ The copper sh~ets were deposited to starter sheet thickn~s at a current density of 141 ASF ln about 200 minutes.
The deposits were ductile, although coarse-grained, and some areas had higher s:ulfur le~els than previously found. The cell voltage and power con5umption were reasonable for thi~ current denxlty, and the air agitation from the bubbler tube was increased to only 1.3 SCFH/sq. ft. of cathode surfaceO
. ~ .
~` EXAMPLE 4 (Porous (Air Roll) Bubbl r) ~ ` ``
. . .
Typical conditions of high current density (E~ample 3) .":^` .~ '' ;. . ...

, , - ~ -. .: . .

~- ~06~36~

were maintained while usin~ a porou~ tube in place of the bubbler tube under eac.h cathode. Excessive mîs~ing occurred at the electro~ :~
lyte surface, and lead and sulfur impurities were highsr than Ex- ~:
ample 3, The sw~ep pattern of the bubble stream was clearly visible on the deposit, resulting in non-uni~ormity of the cathode ; deposit, The stripping of the ca~hode deposit from the Type 316 ; stainless steel cathode blank was difficult due to ~he poor mechan~
ical integrity of the deposit. :
TABLE I
` ~xample 1 2 3 4 :
~; Current density ~ASF) 59 60 141 139 Electrode spacing (inches) 1.26 1,06 1~04 0.75 Cu concentration ~
: (g/l) ~2 g/l 29.5 32 32 ~ :
Acid concentration : (g/l) 159 ~/1 172 171 171 Temperature 1~0 142 142 139 . Steady voltage ,. (V) 2.3 2~3 2.~ 2.5 ; Power consumption : (kwh/lb. Cu) 0.91 0.~9 1.~7 0.97 `:' Cathode current ' (effici~ncy (%) 97 97 100 100 .-~' ImPurities ' ~ ' Lead (ppm) 0.59 -7 0-7 1.1, 2.1 `q 30 Sul~ur (ppm) ~3 <2.5 4.32 7.22 : .
Sli~es (mg/l) 009 ~.5 13 35 .,. . ~.. .
' -2~

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Example 5 (Vat Leach Electroly~e) The favorable results of the ~oregoing examples were obtained by electrowinning from a relatively pure electrolyte such a~ that referred to as liquid ion exchan~e strip concentrate. In the leaching of ores, many extraneous solutes are ex~racted into the leach solution in addition to the desired metal values. Often, these extraneous solutes, including aluminum, magnesium and iron, are presenk in sufficient quantities to so degrade mass transport -conditions that deposits o~ good quality are not obtained by direct electrowinning, Further, if reducible solutes such as ferric ion - appear in the electrolyte in appreciabl~ concentration, the current ef~iciency of metal deposition is decreased markedly.
By employing the methods and apparatus of the pre~ent invention, it has been poæ3ible to electrowin~pure copper o~ ac-ceptable m~chanical integrity from impure vat leach electrolytes. -~
Furthermore, the ratio of metal concentration to current density ~' employed wa- many times smallar than in convention 1 practice, which genarally produces an inferior product. By so operating, it ~-was possible to take advantage Or the improvement of curre~t e~-ficiency with increa~ing current d~nsi~y a~ rev~aled in the data o~ Table II. The solutions ~mployed in the~e instanceæ had alumi-num, iron and magne~iu~ eaGh in the range of 10-20 g/l.
- ~:

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; Table II
Examples 1 2 3 ~ 5 6 . :
. Current density ; (ASF) 20 30 40 30 ~0 60 Electrode ~pacing (inches) 2.3 2,3 2.3 1.05 1~23 1.23 :~
Cu concentration (g/l) 20 20 20 10.3 10.4 10.6 Acid concentration (g/l) 49 49 ~9 63 64 63 ~ :
Temperature (F) 140 125 140 1~ 139 141 ::`
Cell voltage (V) 2.7 3.2 3~ 2.4 2~9 4.
Power consumPtion . ~Kwh/lb Cu~ 1.64 1.~5 2.07 1.44 1057 1.~2 Mechanical integrity good good fair good fair poor :~
Current e~ficiency (o/o) 62 66 7 64 71 ~5 ~ :
Although the previous examples deal with electro~ ing, the pre~ent gas agitation s~tem has been extensively tested under el~ctrorefin1ng condition~. Dense and mechani~ally sound copper depo~its of high purity and superior appearance have been produced - .
to starter sheet thickness on non-retentive blanks and also on ~.
copper blank~ tr~ated ~ith a release agent. Heavier depo~its o~
ex~ellent quality and appearance, so~e up to 175 lbs. in weight per side, ha~e been produced on ~tarter sheets and on stainless .
; steel and titanium blanks, as well as on other cathodic substrate~
Anede passivation did not occur even at current dens~tie~ a~ high a~ 300 ASF, and the daposits ~ere unc~ntaminated by suspended anode slimes~ _ ... ' ~ -: .
. .

~ `
10~;~36~

By using the sy tem of the present invention9 full size deposits w~re obtained which were ~qual or ~uperior to typi-cal electrorefined copper in terms of lead, sulfur, oxygen and other impuritie~. Cathode current efficiencies greater than 95%
were obtained routin~ly when th~ electrolyte did not ~ontain large amounts o~ reduc~ble impuritie~. There are many ad~antage~ d~rived from ~ollowing the teachings ~f the present in~ention. One ad-vanta~e i5 that high acid electrolytes can be tr~ated more effect~ ;
irely with the pre3ent invention. In co~nection witb~ point, ~ ~ it is well known in this art that conventional lead and lead alloy ; anodes ~orrode in high acid electrolytes (that is, electrolytes containing more than 100 g/l H2S04). While the corrosio~ of con-ventional lead or le~d alloy anode~ is not prevented, the present invention avoids the incorporation into the electrowo~ deposits of corro~ion products of the insoluble anodes. Thus, although the invention is not limited to high acid electrolytes or anodes con-taining lead, particular advantage i~ derived from practicing the invention in this type of enviro~ment.
Another advantage derived from following the teachings o~ the present in~ntion is that ele~trolyte~ containing 1Q~ amounts -~o~ copper can bq~economîcally treated. In connect~on with this point, the ratio o~ current density in amps per square foot to copper concentration in ~rams per liter can be as great as 5 in the present system, a~ compared to ,5 in conventional commer~ial practice.
Although lead-antimony anode~ have been di~cl~sed, it is apparent to those skilled in this art that anode~ o~ any suit-abl~ material can be employed. By way of example and not by way of limitation, other anodes that are u~eable in the present in-vention include lead or lead alloy anodes, ti~anium coated with -2~r :, . . , ~ , ~(~686~ -precious metal oxides, or graphite. Indeed, for the electro-winning ambodiment of thc prei3ent invention any insoluble or "dimensionally stable" anode can be used~ Of course, in electro-refining, soluble anodes of the m~tal to be refined are used~
; Although non~retentive cathode blanks are preferred, any cathodic sub~trate can ba employed i~ the present invention, i~cluding ~arter sheets such as copper starter sheets and blank~
coat~d with release agents.
One of the mo~t signi~ioant advan~ag~s o~ the present system is that high current density can be effectively employed ~hile still obtalning a high quality produ~t. Indeed, ex~ellent -re3ults are obtainable in the present invention with current den-sity as high as 300 ASF, depending upon the temperature and the eomposition of the electrolyte. In connection with the term high current density, a current density of around 40 ASF would be con-sidered high by those skilled in this art; thus, the invention can ba used to great advantage with current d~nsities between 40-300 ASF ~ith normal metal concentration in the electrolyte.
A~other significant advantage of the system o~ the present invention is that the face to face separation of the~node-- cathode can be decreai3ed to a value which is limited only by the dimensions of the supporting means9 In c~nnection with ~hii3 point, it is well known that to keep power costs at a minimum, the re-sistance in the ~11 should be decreased. Thr~e wars to accomplish the foregoing are to increase the temperature, increase the con~
centration of conducting solutes in the electrolyte a~d reduce the ~pacing between electrode~. Hows~er, in prior art proces~es, reduced spacing creates other serious problems, particularly by restricting convection~ With a properly deqigned gas agitation 3ystem, in distinction to the prior art, the ~maller the spacing between opposing cathode and anode ~aces, the better is the -2~
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:: :^ 106864~L

; convection. A~ ~as stated above, the reduction in spacing is limited by the suspension means; thus, as a practieal matter, the ~pacing cannot usually be made les~ ~han about ~.50 inch. In con-ventional practice, the face to face cathode-anode separation is usually nok le~ than 1.25 inch.
Of course, as is apparent to ~hose skilled in the art, the invention is not restricted to the electrodeposition o~ copper.
Indeed, the process and apparatu~ can be employed to great ad-vantage ~or treating any metal which is normally electr~deposited from aqueous solutions. Such metalq include nickel, zinc and lead~

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Claims (24)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An electrodeposition cell comprising: anodes for submergence in an electrolyte; non-conductive anode bottom extensions positioned beneath the anodes; non-conductive convection edge baffles positioned adjacent to opposite edges of the anode faces and extending toward the cathode faces; cathodes, spaced from said anodes, the submerged length of the cathodes being equal to or greater than the submerged length of the anodes and anode bottom extensions, the cathodes being wider than the anodes so that the edges of the cathodes extend outwardly from the convection baffles; means for maintaining close spacing between anode-cathode faces; and, bubble tubes having orifices for generating sheets of relatively small rapidly ascending bubbles of gas that result in agitation of the electrolyte over the cathode faces, the portions of said bubble tubes having the orifices being positioned between the non-conductive anode extensions and the cathode faces; said baffles forming enclosures between cathode and anode faces which minimize lateral spreading and contraction of the sheet of bubbles and prevent deposition of metal at the edges of cathodes extending beyond the baffles, said anode bottom extensions preventing deposition of metal at the bottom of the cathode face, said means for maintaining close spacing, said bubble tubes, and said baffles providing an electrolyte convection system which enables the efficient use of high current densities in an electrodeposition process with an attendant production of high quality metal which can be easily stripped from the cathodes.

2. The cell as set forth in claim 1 wherein the orifices on said bubble tubes are 5-7 mils in dia-meter.

3. The cell as set forth in claim 2 wherein the means for maintaining close spacing includes:
a bottom rack member positioned in the cell which fixes the position of the bottoms of the anodes in relation to the cathodes; and, bubble tube supporting members which are connected to said bottom rack, said bubble tube sup-porting members supporting said bubble tubes, fixing the position of the bottoms of the said cathodes in relation-ship to said anodes, fixing the position of each bubble tube so that a sheet of bubbles from each bubble tube sweeps across a single cathode face and suspends the bubble tubes from the bottom of the cell to permit cir-culation of the electrolyte.

4. The cell as set forth in claim 3 wherein said bottom rack is inclusive of vertical members which posi-tion the bottom of the anodes in relationship to the cathodes and which confine the flow of bubbles from said bubble tubes.

5. The cell as set forth in claim 4 wherein said orifices lie in a line and are spaced apart a distance of about one-half inch.

6. The cell as set forth in claim 5 wherein said cathodes are non-retentive cathodes.

7. An electrowinning cell comprising: insoluble anodes for submergence in an electrolyte; non-conductive anode bottom extensions attached to the bottom of the anodes; non-conductive convection, edge baffles attached to opposite edges of the anode faces and extending toward the cathode faces; cathodes, spaced from said anodes, the sub-merged length of the cathodes being equal to or greater than the submerged length of the anodes and anode bottom extensions, the cathodes being wider than the anodes so that the edges of the cathodes extend outwardly from the convection baffles;
means for maintaining close spacing between anode-cathode faces; and, bubble tubes having orifices for generating sheets of relatively small rapidly ascending bubbles of gas that result in agitation of the electrolyte over the cathode faces; the portions of said bubble tubes having the orifices being positioned between the non-conductive anode extensions and the cathode faces so that each sheet of bubbles sweep across a cathode face; said baffles forming enclosures between cathode and anode faces which minimize lateral spreading and contraction of the sheet of bubbles and prevent deposition of metal at edges of cathodes extending beyond the baffles, said anode bottom extensions preventing deposition of metal at the bottom of the cathode face, said means for maintaining close spacing, said bubble tubes, and said baffles providing an electrolyte convection system which enables the efficient use of high current densities in an electrodeposition process with an attendant production of high quality metal which can be easily stripped from the cathodes.

8. The cell as set forth in claim 7 wherein the orifices on said bubble tubes are 5-7 mils in diameter.

9. The cell as set forth in claim 8 wherein the means for maintaining close spacing includes: a bottom rack member positioned in the cell which fixes the position of the bottoms of the anodes in relation to the cathodes; and, bubble tube supporting member which are connected to said bottom rack, said bubble tube supporting members supporting said bubble tubes, fixing the position of the bottoms of the said cathodes in relationship to said anodes, fixing the position of each bubble tube so that a sheet of bubbles from each bubble tube sweeps across a single cathode face and suspends the bubble tubes from the bottom of the cell to permit circulation of the electrolyte.

10. The cell as set forth in claim 9 wherein said orifices lie in a line and are spaced apart a distance of about one-half inch.

11. The cell as set forth in claim 10 wherein said cathodes are non-retentive cathodes.

12. The cell as set forth in claim 11 wherein the convection baffles are spaced apart from the cathodes a distance in the range of one-sixteenth to one-eighth inch.

13. The cell as set forth in claim 9 wherein said bottom rack is inclusive of vertical members which position the bottom of the anodes in relationship to the cathodes and which confine the flow of bubbles from said bubble tube.

14. A method of performing electrodeposition at a high ratio of current density to metal ion concentration in a cell which includes anodes, cathodes and an electrolyte with an attendant production of high quality metal which can be easily stripped from the cathodes comprising the following steps: positioning non-conductive convection edge baffles adjacent to opposite edges of the anode faces so as to extend toward the cathode faces; positioning non-conductive anode bottom extensions beneath the anodes; providing cathodes that are wider than the anodes so that the edges of the cathodes extend outwardly from the convection edge baffles; submerging the cathodes so that the submerged lengths of the cathodes are equal to or greater than the submerged lengths of the anodes and the anode bottom ex-tensions; positioning bubble tubes having orifices between the non-conductive anode extensions and the cathode faces;
spacing opposed anode and cathode faces apart from each other at a distance of about 1-1/4 inches or less; and, electrodepositing metal on the cathodes while generating a sheet of gas bubbles from the bubble tubes through the electrolyte between opposed anode-cathode faces to produce agitation of the electrolyte over the cathode faces as metal is being deposited thereon and maintaining said convection edge baffles during electrodeposition to form enclosures between cathode and anode faces to minimize lateral spreading and contraction of the sheet of bubbles and prevent deposition of metal at the edges of the cathodes extending beyond the baffles, and maintaining the position of said anode bottom extensions during electrodeposition to prevent deposition of metal at the bottom of the cathode faces.

15. The method as set forth in claim 14 wherein the sheet of air bubbles is saturated with water vapor and generated through a perforated bubble tube.

16. The method as set forth in claim 14 wherein the convection edge baffles are attached to the walls of the cell.

17. The method as set forth in claim 14 wherein the convection edge baffles are positioned on vertical support members on the walls of the cell.

18. A method of electrowinning a metal at a high ratio of current density to metal ion concentration in a cell which includes insoluble anodes, cathodes and an electrolyte with an attendant production of high quality metal which can be easily stripped from the cathodes com-prising the following steps: attaching non-conductive convection edge baffles to opposite edges of the anode faces so as to extend toward the cathode faces; attaching non-conductive anode bottom extensions beneath the anodes;
providing cathodes that are wider than the anodes so that the edges of the cathodes extend outwardly from the convection edge baffles; submerging the cathodes so that the submerged lengths of the cathodes are equal to or greater than the submerged lengths of the anodes and the anode bottom extensions; positioning bubble tubes having orifices between the non-conductive anode extensions and the cathode faces;
spacing opposed anode and cathode faces apart from each other at a distance of about 1-1/4 inches or less; and, electrodepositing metal on the cathodes while generating a sheet of gas bubbles from the bubble tubes through the electrolyte between opposed anode-cathode faces to produce agitation of the electrolyte over the cathode faces as metal is being deposited thereon and maintaining said convection edge baffles during electrodeposition to form enclosures between cathode and anode faces to minimize lateral spreading and contraction of the sheet of bubbles and prevent deposition of metal at the edges of the cathodes extending beyond the baffles, and maintaining the position of said anode bottom extensions during electrodeposition to prevent deposition of metal at the bottom of the cathode faces.

19. The method as set forth in claim 18 wherein the electrodepositing is performed at a current density in the range of 40-300 ASF.

20. The method as set forth in claim 19 wherein the opposed anode and cathode faces are spaced apart a distance of less than 1 inch from each other.

21. The method as set forth in claim 20 wherein copper is electrodeposited on the cathode.

22. The method as set forth in claim 18 wherein a non-retentive cathode is provided.

23. The method as set forth in claim 22 wherein copper is electrodeposited on the cathode.

24. The method as set forth in claim 19 wherein copper is electrodeposited on the cathode.