CA1103205A - Insoluble anode for the electrowinning of copper - Google Patents
Insoluble anode for the electrowinning of copperInfo
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- CA1103205A CA1103205A CA347,765A CA347765A CA1103205A CA 1103205 A CA1103205 A CA 1103205A CA 347765 A CA347765 A CA 347765A CA 1103205 A CA1103205 A CA 1103205A
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Abstract
ABSTRACT
An insoluble anode for use in the electro-winning of copper, the anode being formed by casting molten lead alloy preferably including approximately 0.01-01% by weight calcium as an alloying agent in a suitable mold necessary flow of the molten alloy being minimized within the mold, the temperature of the molten alloy and the temperature of the mold being selected to minimize the time necessary for solidification of the molten alloy within the mold, the lead alloy anode preferably being removed from the mold substantially as soon as it is mechanically self-supporting and rapidly cooling the anode in an unstressed configuration to freeze its grain structure and develop dimensional stability. The anode has a substantially flat configuration with an effective surface even on either side of at least approximately 5 square feet and is characterized by the uniform precipitate distribution illustrated in Fig. 7 and the surface finish illustrated in Fig. 9.
An insoluble anode for use in the electro-winning of copper, the anode being formed by casting molten lead alloy preferably including approximately 0.01-01% by weight calcium as an alloying agent in a suitable mold necessary flow of the molten alloy being minimized within the mold, the temperature of the molten alloy and the temperature of the mold being selected to minimize the time necessary for solidification of the molten alloy within the mold, the lead alloy anode preferably being removed from the mold substantially as soon as it is mechanically self-supporting and rapidly cooling the anode in an unstressed configuration to freeze its grain structure and develop dimensional stability. The anode has a substantially flat configuration with an effective surface even on either side of at least approximately 5 square feet and is characterized by the uniform precipitate distribution illustrated in Fig. 7 and the surface finish illustrated in Fig. 9.
Description
The present invention relates to an insoluble anode for use in the electrowinning of copper.
This appllcation is a divisional application of Canadian Patent Application Serial No. 239,754, filed November 17, 1975.
The Electrowin_ing Process:
A brief descript-Lon of t'he electrowinning process for the recovery of copper is set forth below to permit a better understanding of the present invention.
Generally, a solution of concentrated copper in sulfuric acid is formed, usually by leaching of copper ore.
An acid concentration in the range of 100-200 gms. per liter of sulfuric acîd is generally necessary in order to place sufficient copper in solution. A corresponding copper concentration may be in the range of approximately 30-50 gms. per liter for a pregnant electrolyte to be introduced into the electrowinning process.
The copper-laden solution is then introduced into one or more electrolytic cells each containing a series of anodes and cathodes.
Within the electrolytic cells 9 the anodes are sub-.
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stantially insoluble wi-th an electrical potential impressed between the anodes and cathodes -tending to cause migration of copper from -the electrolyte toward the cathode with metallic copper being deposited or built up on each of the cathodes.
Fresh electroly-te is constantly supplied to the cells. Sul-furic acid solution is recycled from the cells for the leach-ing or solution of additional copper which is then again in-troduced into the electrowinning cells.
The cathodes containing the build-up of metallic copper are periodically removed from the cells and replaced by fresh electrodes or starter sheets to permit continued de-position. The cathodes removed from the cells contain rela-tively pure copper, for example in the range of 99~ purity.
A portion of the copper resulting from the electrowinning process is accordingly used directly in copper consuming ap-plications. However, since many applications require copper of even higher purity, it is also common to further refine copper obtained from the electrowinning process by conven-tional electro-refining techniques.
Insoluble Anodes Used In Electrowinning:
The theoretically insoluble anodes are a particular source of concern within the electrowinning process and have been the object of substantial developmen-t efforts throughout the relatively long history of the electrowinning process.
Problems arising in connection with the anodes tend to de-velop because of the infeasibility of providing a completely insoluble anode which is still capable of adequa-te electrical performance within the cell. It has been commonly found tha-t material from the anode tends to become dissolved in small quantities within the electrolyte with a portion of the dis-~r ~ 2 .: .
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solved anode maLerial being collected or trapped upon thecathode together with metallic copper.
For some time, insoluble anodes used in the elec-trowinning of copper have been formed Erom lead or lead al-loys. Relatively limited amoun-ts of lead have been found within the copper deposit on the ca1:hodes. However, in many copper consumin~ applications, the acceptable limits for lead as an impurity are very low, commonly in the range of 10-20 parts per million. Much of the effort directed toward devel-opment of improved anodes has therefor concerned techniquesfor making lead or lead alloy anodes having high hardness and resistance to corrosion or exfolia-tion while also maintaining adequate mechanical and dimensional stability in the anodes to permit their continued use in electrowinning cells over substantial periods of time.
In the recent past t the most common lead alloy em-; ployed in electrowinning anodes was one containing substan-tial quantities of antimony, for example, 5-15~ Sb by wèight.
In addition to such binary alloys, ternary and quaternary -~
alloys including lead and antimony have also been commonly employed with the additional alloying agents being selected -~ from a broad group including arsenic, bismuth, tin, cadmium, thallium, tellurium, mercury, cobalt, barium, strontium, selenium, tantalum, smooth platinum, etc. More recently, lead-silver alloys have been investigated, particularly those in ternary form including a third alloy such as arsenic or bismuth.
Generally, anodes formed from lead alone do not have sufficient hardness or resistance to corrosion or exfol-iation to permit their use in electrowinning because of ex-. ~ .
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cessive lead migratioll with -the lead being deposited or entrapped upon the cathocles together with metallic copper.
The various alloying agents ten~ to increasc hardness and corrosion resistance while also con-tributing to rnechanical and dimensional stability, all of -these being particular:Ly desirable characteristics for insoluble anodes in the electro-winning process.
Calcium is an addi-tiona:L material of particular interest within such lead alloys. Although calcium may be employed wi-th binary, -ternary or even quaternary alloys in widely varying amounts, the most useful concentrations for calcium in such alloys are believed to be within the range of 0.01 to 0.1% by weight.
The attractive corrosion resistance and superior mechanical properties of lead alloys which contain calcium have been known for many years as is demonstrated to some degree by the use of calcium alloys in the manufacture of battery grids. However, it is to be particularly noted that manufacturing techniques and operating performance require-ments for battery grids are different from the requirementsfor insoluble anodes such as are employed in the electrowin-ning process. Experience in the battery field may be taken - to reinforce the conclusion that lead-calcium alloys are more difficult to cast or otherwise form into a usable configura-tion.
This appl~cation describes one or more casting tech-niques, which either alone or in combination, permit the casting of a lead-calcium anode having grea-tly superior properties of cor-rosion resistance and mechanical and dimensional stabili-ty, parti-: , ,. ....
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cular]y for use in electrowinning processes. ~lowever, it is emphasiY.ed that the casting techniques are not limited merely to lead-calcium al]oys employed in lnsoluble anodes for use in the copper e]ectrowining process. On the other hand, because of the particular efEec-tiveness of these techniques for forming such anocles, the preferred embodiment and examples as described below, are directed in large part towards lead-calcium alloys.
It is also noted at this point that the techniques and apparatus described are also specifically applicable to more complex lead-calcium alloys, for example ternary alloys which include silver or tin, for example, as well as calcium.
It was indicated above that the purpose of employ-ing lead alloys is to improve resistance to corrosion or ex-foliation as well as to enhance both dimensional and mechan-ical stability. These requirements are relatively complex for insolubie anodes of the type employed within the electro-winning process. ~o provide additional background in this connection, it is noted that the "insoluble" or "inert'' anodes are immersed in sulfuric acid solution contained by electrowinning cells. Wi-thin the electrolytic process or under generally similar conditions commonly employed to sta-bilize or precondition the anode surface, lead within the anode tends to react with the sulfuric acid and also with air bubbles generated by electrolysis upon the surface of the anode. Interaction of these materials under electrolytic or similar stabilizing conditions tends to cause forma-tion of a film upon the lead or lead alloy anode. The film principally consists of lead dioxide (PbO2) which acts as a semiconductor, thus enabl.ing electrical conductance throu~h -the anode and particularly enhancin~ i-ts corros:ion resis-tance. Lead oxide (PbO) and lead sulfate (PbSO~) are also present during various s-tages of the film formation and are characterized as being generally poor conductors.
It is theorized that the phenomenon of initial film formation and subsequent film reforma-tion is important in maintaining the corrosion resistance o:E the anode. In any event, it has been found that the chemical and physical characteristics of the anode are important factors affec-ting formation of the above noted film and accordingly are important in achieving maximum corrosion resistance of the anode.
Important Characteristics For Insoluble Anodes:
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In addition, certain chemical and physical charac-teristics of the anode are also important in determining its mechanical and dimensional stability as was suggested above.
These chemical and physical properties of the anode, which may affect corrosion resistance and/or mechanical and dimen-- 20 sional stability are summarized below.
Initially, chemical composition of the anode is of critical importance as suggested by the preceding discussion of the various lead alloys which have been developed. For example, it was clearly indicated above that certain lead alloys, particularly those including calcium as well as other binary, ternary and quaternary alloys, contribute both to the corrosion resistance of the anode as well as i-ts mechanical strength and dimensional stability. It is also believed ; importan-t to maintain in uncombined form the basic lead com-ponent except for the presence of precipitates formed with ~1~.,;~
s~ -6-3~i and between -the various alloyinq ayen-ts. ~or example, in a lead-calci~m alloy, a precipi-ta-te oE lead calcium (Pb Ca3) is believed to be an importan-t fac-tor contributing to -the improved characteris-tics of anodes formed from such alloys.
In respect to one aspect of the presen-t invention, it is theorized tha-t other compound forma-tions of lead, in particular, wi-thin the anode, may be undesirable. In this regard it is particularly believed that the combination of lead with oxygen to form either lead oxide or lead dioxide within the anode may undesirably interfere with subse~uent formation of a stabilizing or conditioned film, as noted above.
Uniform precipitate distribution is an additional desirable characteristic to be considered in connection with alloy composition of the type discussed immediately above.
Particularly with alloy compositions such as lead-calcium it is believed that precipitate formation and uniform distribu-tion of the precipitate throughout a matrix of lead contri-butes particularly to corrosion resistance and the related characteristic of surface hardness.
The characteristics of high density and low poro-sity are believed to be interconnected and jointly contribute again to the characteristics of corrosion resistance and surface hardness for the anode. These characteristics may also effect in part mechanical and dimensional stability of the anode.
Grain size is another characteristic which is believed to provicle an important contribu-tion to both corrosion resistance and mechanical charac-teristics such as ha~dness.
Generally, it is believed that for a non-ferrous metal such :;;- ~ , '' ' ' as lead, i-t is desirable to malntcLin a relatively large or coarse grain size. Here again, -the charactcris-tic of coarse or large grain size is particularly important for the lead ma-trix in an alloy such as lead~calcium. I-t is assurned tha-t relatively large or coarse grain size in such an alloy con-tributes both -to film formation, as discussed above, and possibly also ~o uniEorm precipitate distribution. This supposition again illustrates that the many characteristics discussed herein are interrelated or interdependent upon each other.
Finally, it is believed desirable to form a surface upon the anode which may be characterized as uniform, continuous or generally smooth. It is believed that the nature of the initial surface formed upon the anode is of substantial importance. It is again theorized that the surface characteristics contribute importantly to proper film forma-tion, as discussed above. Possibly, the combined characteris-tics of a smooth surface and relatively large grain size tend to promote development of a uniform film upon an anode which importantly minimizes corrosion within the electrolytic bath. It will be noted below that in conjunction with the present invention, anodes formed according to the procedure described below tend to have the appearance of being "rolled"
- or "galvanized." In any event, the surface characteristics of the anode formed accoxding to the present invention are believed to contribu-te importantly to its value within an electrowinning process.
In summary, the preceding comments have been directed to~ard a discussion of basic anode characteristics including 30 good resistance to corrosion or exfoliation, mechan- ~
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z~s ical stability or "strength", dimensional stabllity and relative hardness, both on the anode surface and within the anode interior. In this connection, it is important to note that as material is eventually lost from the anode, those portions originally within the anode interior then form its surface.
In addition, the preceding discussion emphasized the characteristics of chemical composition, uniform precipitate distribution, high density and low porosity, large or coarse grain size and initial surface characteristics of the anode.
This discussion of anode characteristics is set forth above in some detail in order to emphasize advantages of the present invention. With the e~ception of chemical composition, the other basic anode characteristicsdiscussed above are believed to be primarily dependent upon the method of casting or forming the anode, either alone or in conjunction with the ` chemical composition.
Objects of the_I_vention A basic object of the present invention is ~o provide a novel and particularly useful insoluble lead alloy anode of a type useful in electrowinning processes ~; for metals such as copper, the anode preferably lncluding calcium as an alloying agentO
It is a more specific and related object of the invention to provide such a lead alloy anode, including calcium as one of the alloying agents, wherein the anode is characterized by maximum density, minimum porosity, uniform precipitate distribution and further by a uniformly smooth and hard anode surface.
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~ s an even further part.i.cularity, it is an object to provide such a lead alloy anode havinc3 a calciurn content within the approxlmate range of 0.01 to 0.1% by wei~ht.
Within the process for produc:ing an anode of the -type descrlbed above, a nurnber o~ process objects or elements have been determined as being of interrela-ted importance.
However, it is believed that no-t all of these objects must necessarily be employed together in order to produce a novel insoluble anode. These process objects are set forth immediately be:Low.
Summary of the Inven-t.ion ._ __ __ __ This invention relates to an insoluble anode for .
use in the electrowinning of copper, -the anode having a substantially flat configuration with an effective surface area on either side thereof of at least approxima-tely 5 square feet, the anode being formed by a casting process from a lead : alloy including approximately 0.01-0.1~ by weight calcium the anode being further characteri~ed by substantially a maximum density and minimum porosity, a uni~orm precipitate distribution of PbCa3 in a lead matrix, the surface of the : anode being continuous and smooth and further characterized as having a galvanized or rolled appearance.
The method of producin~ the anode contemplates limiting the amount of time during which the lead alloy remains in a molten state after being introduced into a suitable mold. This time limit is preferably achieved through selectively controlling the temperature of the molten alloy in a melting pot :.
or furnace and in a ladle prior to introduction to the mold. Additionally, the temperature of the mold is ~:
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also controlled within selected limits at least upon commencement of pouring the lead alloy into the mold.
This feature is believed to contribute to both chemical and physical characteristics of the anode. In addition, it is thereby possible to remove the anode from the mold within a relatively short time, for example within two to three minutes, in order to facilitate further treatment of the anode and to achieve operating economy within the casting operation.
-It is particularly contemplated that the anode be suspended in a vertical condition immediately after being removed from the mold. The vertically suspended anode is then rapidly cooled. This step is believed to "freeze" the grain size and precipitate distribution throughout the anode and particularly adjacent its surface while also contributing to di=enslo=al and/or mechl:nlcal s~ability.
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~32~i ~ n additiona:L elemen-t o:E the casting method contemplates limiting the amount o.E :E:Low for the molten lead alloy wit~in the mold. Thi.s i.s believed to contribu-te -to the achievement maximum densi-ty and minimum porosi-ty for the anocle while also con-tributing to -the :Eo.rma-tion of a smooth or continuous surface. M.inimum flow of the molten alloy wi-thin the mold is achieved by preferably disposing the mold in a vertical position with the top o:E the mold cavity being completely open to receive molten lead alloy along its length. The molten lead alloy is then "streamed"
into the mold along the length of -the molcl cavi-ty wi-th the amount of lead alloy being introcluced into each portion of the mold in proportion to the volume of the mold cavity.
: In this manner/ all portions of the mold tend to be filled in approxima-tely the same amount of time with minimum flow of the alloy being necessary within the mold to achieve complete filling of the mold cavity. The alloy material thereby enters into continuous and intimate contact with all surfaces of the mold cavity. In addition to con-tributing toward the development of maximum density and minimum porosity, minimum flow in the mold is also believed to contribute toward other chemical and physical features of the finished anode such as, for example, uniform precipitate distribution particularly adjacent the anode surfaces, as well as the 25 surface finish itself. ~.
It is another particular element of the casting method to preven-t access of oxygen -32q~
to the molten lead alloy, particularly for an alloy includincJ calclum as an alloying agent, or even after the molten lead alloy solidifies within the mold -to form an insoluble anode. I'his step is believed impor-tant both to regu:Late chemical composition of the lead alloy within the finished anode and also to limit the loss oE calcium from a lead alloy including calcium as an alloying agent.
Additional elemen-ts of the method are also directed -towards main-taining the calcium conten-t of such a lead alloy, for example by the imposi-tion of an electrical potential, preferably a low DC voltage, upon the molten lead alloy within the furnace or mel-ting pot.
Finally, i-t is also an element of the method -to select a lead alloy including calcium as an alloying agent.
Calcium may be present within -the lead alloy to form a binary alloy and other alloying agents may also be added to provide either a terna~y or quaternary alloy, for example, from which an insoluble anode may be produced within the scope of the present invention.
Calcium is particularly selec-ted as a preferred alloying agent within the lead alloy because of its tendency to-increase alloy hardness, improve corrosion resistance and enhance mechanical or dimensional strength. The calcium ; alloying agent may be present in a relatively wide range of 0.01 -to 0.1% by weight. It is further noted -that calcium is a particularly desirable alloying agent for lead alloy anodes because of i-ts -tendency -to reac-t wi-th sulfuric acid and produce salts of low solubili-ty. This characteris-tic is believed to greatly con-tribute toward the forma-tion of pro-tective, compact or thick films of a type par-ticularly sui-table `~ csm/`~
for minimizing corrosion resistance of -the anode under elec-trolytic condi-tions such as those encountered in an elec-trowinnin~ process.
- Adcli-tional objec-ts and advantages oE -the presen-t inven~ion are made apparent in the following description having reference to the accompanying drawings.
Desc lpt~
To facilitate unders-tanding of the invention, casting apparatus of -the type employed to produce such an insoluble anode is illu~trated in Fig. 1 which is a side view in elevation of apparatus including a mold, a ladle, and a furnace or mel-ting pot.
Fig. 2 is an additional view taken from the rlght side of Fig. 1, to particularly illustrate the configuration and arrangement of an internal cavity within the mold.
Fig. 3 is a view of an insoluble anode produced by the method of the presen-t invention.
Fig. 4 is a fragmentary view taken along section -~
line IY-IV in Fig. 3.
Fig. 5 is a detailed, isometric view of the ladle - for the casting apparatus of Fig. 1 to illustrate a preferred ~
configuration therefor. ~-Fig. 6 illustrates ano-ther preferred configuration of the ladle.
Figs. 7 and 8 are photomicrographs, at different degrees of magnification, of a typical insoluble anode produced from a lead alloy including calcium as an alloying agen-t.
i~ig. 9 illustra~es the su:rEace f:inish o~ a lead alloy ~nocle procluced by the method o:~ -the present invention.
D sc ri~t_on or t.he Pre_erred l,mbocllmen_ As noted above, the present inven-tion is directed towarcl an anode having a p:referred compositic-n as well as other characteristic features. In view o:E -the rela-tively large number of fea-tures invo:Lved ~or the insoluble anode the following descrip-tion includes fixst a discussion of suitable alloys for use in such an insolub:Le anode followed by a description of the anode configura-tion, a description oE
the casting apparatus, a descrip-tion of the casting process followed by a number of specific examples setting forth various anodes produced by the present method with pertinent method parameters for each example.
Suitable Alloy Compositions:
As indicated above, the present invention is particularly directed toward lead alloys including calcium as an alloying ayent. However, the invention is not intended .~-to be limited to lead alloys including calcium as a single :20 alloying agent or even to alloys necessarily including calcium.
For example, a lead alloy including calcium as an alloying agent might also include one or more other alloying agents such as silver or tin. Accordingly, a lead alloy of the type contemplated by the present invention could be, for example, .
a binary, ternary or quaternary alloy.
Furthermore, it is generally accepted thak lead alloys including calcium as an alloying agent are particularly difficult to form or cast. This even further indicates the .~.
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value and novelty of the present inven-tion in providing a me-thod for successfully casting such ma-terials. ~lowever, the success of the present invention in providing cas-t lead alloys inclucling calcium also indica-tes i-ts value in cas-ting other ma-terials particularly other generally similar lead alloys, such as those including, for example, silver or tin, with -the present inven-tion not necessarily being limi-ted to the additional~inclusion of calcium.
Moreover, alloying agents such as calcium have a tendency to evaporate or otherwise be lost Erom -the alloy when i-t is in molten condition. Accordingly, the composition of the alloy as originally produced may vary from the alloy composition within a finished anode.
Generally, one preferred composition for the lead alloy anode includes calcium as an alloying agent either alone or in combination with other alloying agents. More particularly, it is con-templated that a lead alloy anode with calcium as an alloying agent include calcium within the proximate range of 0.01 to 0.1% by weight. An even more limited concentration for calcium,within the range of approximately of 0.02 to 0.07% by weight, is believed to be of particular importance.
One typical composition for a lead calcium alloy to be employed within the present method, for example as ~- 25 an alloy ingot, inclucles approximately 0.0~-0.06~ by weight calcium, the remainder essentially pure lead except for normal impurities. In view of the tendency for calcium to be lost from the alloy, it is accordingly possible that an alloy ingot to be employed within the presen-t casting method may include calcium above 0.1%.
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~ s a Eurther exclmple oE the application for -the method of -the present inven-tion, it is also belicved appli-cable -to leacl-an-timony alloys including antimony as an alloying agent within the approxima-te range of 5-15% by weight. One typical composition for such an alloy is set forth below:
Pure, soft lead 90% by wg-t.
Pure, antimony 10~ by wgt.
Maximum impurity content: Ag-0.0004% by wgt.
Cu-0.0009~ by wgt.
Zn-0.0005% by wgt.
As-0.0003~ by WCJt.
Fe-0.0002~ by wgt.
Bi-0.00014~ by wgt. .-Many additional alloy compositions may also be employed in conjunction with the method of the present invention. Such alloys may include alloying agents of the type summarized above. It is believed that silver and tin have particular value as alloying agents either alone, in combina-tion with each othert and/or in com~ination with calcium,for example.
Insoluble Anode Configuration:
- As indicated above, the present invention is par-ticularly direc-ted -toward techniques for casting an insoluble anode of a type used in an electrowinning process such as for the recovery of copper. A typical configuration for such an insoluble anode is illustrated in Fig. 3. Referrïng to Fig.
3, it may be seen that the anode is relatively large, for example having overall dimensions of approximately 48" x 36", ; a thickness of about 1/2 inch, with an eEEective surface area on either side of approximately 8-9 sq. :Et. The effective .
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area of the anode is inclica-ted at 11 and includes a generally continuous rectancJular portion which is immersed wi.-thin an electrolyte solu-tion for an electrowinning pxocess. The effectlve portion 11 of the anode may be either continuous or perfora-ted as i.llustrated :Eor a portion of the anode at lla.
Insoluble anodes are commonly formed wit.h such perforations in order to reduce the weigh-t of the anode and to increase its effective surface.
Each insoluble anode inclucles a rela-tively heavy copper bar or conductor 12 which ex-tends transversely beyond the edges of -the anode. The extended ends of the copper bar 12 may be conventionally disposed on paralle]. spaced apart supports (not shown) for suspending the anode within the electrolyte solution. The copper bar 12 also provides a conductor path and accordingly must be in intimate conductive relation with the anode 11. For that purpose, it may be seen that the lead alloy encompasses the copper bar and has a relatively increased thickness (indicated at 13 in Fig. 4) to provide proper support upon the copper bar. A window, or opening 14, is commonly formed along a central portion of the anode adjacent the copper bar mainly for the purpose of reducing weight of the anode. Accordingly, the weight of the anode is supported by a s-trip of lead alloy which extends upwardly along either side of the anode for engagement with the 25 copper bar 12. These strips are indicated a-t 16. The overall thickness of the anode is increased to approximately 1 in.
where the anode surrounds the copper support bar.
It is preferable to form or cast the anodes in substantially the shape indicated in the drawings in order to conserve the lead alloy and to minimize further finishing ~3Z(~
work. The copper suppor-t bar 12 is initially arranged within the base oE -the mold prior -to introduction of the lead alloy and thus ~ecomes an intimate por-t:ion of the cas-t anode.
C3~ ~ bus The castin~J appara-tus employed in practice of the method of the present lnvention is of a generally conven-tional type found in many foundry operations. The casting apparatus does not form a particularly importan-t elemen-t of the -present invention excep-t to enable practice of the preferred method as described below, with one e~ception as to specific cons,ruction of the ladle. Accordingly, the casting apparatus is only indicated generally in Figs. 1 and 2 and includes a conventional furnace or melting pot 21, a ladle 22 and a mold 23 forming an internal cavity as indicated at 24 in Fig. 2.
The furnace is of a general type sui-ted for the heating of a lead alloy to molten condition in a temperature range generally 700-800F. The capacity of the furnaee is selected to greatly exceed the volume of the mold eavity 24 so that the lead alloy may be maintained in a molten condi-; tion within the furnaee after each pour without an interval -being required for reheating. Preferably, the capacity of the furnace is selected so that only about 5% of its eontent is required to fill the mold cavity. Accordingly, additional lead alloy ingo-ts may be added to the furnace after each pour with the molten alloy in the furnace then being immediately ready to commence pouring a new anode.
The combination of the configuration of the ladle 22 and the orientation for the mold 23 are important to the present invention. The importance of those two elemen-ts is ' . -19-. . ~ , .
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summarized immedia-tely below and is desc~ibed in grea-ter - detail below in terlns of the pref~rred process or rnethod~
Initially, the mold 23 is preferably forrned by separate mold sections 26 and 27 which divide around the periphery oE -the mold cavi-ty in order to permi-t rapid removal of the anode. :[n addi-tion, the mold is arrangecl with the cavity 24 in vertical alignmen-t to facilitate a preferred method of filling the mold cavi-ty as described in greater detail below. The mold sections 26 and 27 are also preferably formed to provide a top opening 28 along the entire transverse dimension of the cavity 2~ in order to permit simultaneous fillinq along the length of the anode as is also described in greater detail below.
In conjunction with the fea-tures of the mold as described above, the ladle 22 is preferably formed as a cylinder which is closed at each end and has approximately a quadrant of its cylindrical surface removed (at 29) in order to permit filling of the ladle from the furnace.
The ladle 22 includes gating in the form of perfor-ations or apertures 31 extending completely along the trans-verse length of the cylindrical ladle, -the leng-th of the ladle generally conforming with the length of the mold cavity 2~.
The angular location of the gating upon the cylindrical ladle is selected so that, with the ladle in the position illustrated in-Fig. 1, the ladle may be filled with molten alloy from the furnace. The cylindrical ladle is then rapidly rotated to bring the gating apertures 31 into alignment with the .
opening 29, the molten lead alloy from -the ladle streaming downwardly to simultaneously fill all portions of the mold along its length. As may be seen in Figs. 5 and 6, the .
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apertures are configured or arrangecl to permit increased flow into selected portions oE the mo:ld. Referrlny again -to Fig. 3, it may be seen that the copper bar 12 is ini-tially disposed in a hase portion of the molcl cavity 24 so that the anode is actually formed in inverse or upside-down relation within the mold. Relatively larger amoun-ts of lead alloy are then required adjacent the ends of the mold cavity 2~ to initially fill the enlarged por-tions 13 oE the mold cavity which form the sections surrounding the copper bar 12. The window 1~ formed along the central portion of -the anode fur-ther minimizes the amount of lead alloy required along the center of the mold cavity. Accordingly, the gating apertures 31 may be of a larger size adjacent the ends of the mold cavity as is illustrated in the embodiment of Fig. 5. Alterna-tively, the gating may include a larger number of openings or slots 31' of longer length may be provided adjacent the longitudinal ends of the mold cavity as illustrated in the embodiment of Fig. 6.
The ladle of Fig. 6 is employed for filling a mold cavity having no structure to impede or interfere with the streaming of molten alloy toward the bottom of the cavity.
Such a mold configuration is employed to form an insoluble anode of continuous cross-sections. The ladle of Fig. 5 is employed to fill a mold configured to form a perfora-ted anode.
For this purpose, one of the mold sec-tions may be formed - with a large number of lugs arranged in vertical rows. The luys, as indicated at 32 in Fig. 2, are arranged substan tially across the effec-tive area and extend outwardly to abou-t with the other mold section. The gating apertures in the ladle of Fig. 5 are disposed a3ong its length to conform ` -21-. . .
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This appllcation is a divisional application of Canadian Patent Application Serial No. 239,754, filed November 17, 1975.
The Electrowin_ing Process:
A brief descript-Lon of t'he electrowinning process for the recovery of copper is set forth below to permit a better understanding of the present invention.
Generally, a solution of concentrated copper in sulfuric acid is formed, usually by leaching of copper ore.
An acid concentration in the range of 100-200 gms. per liter of sulfuric acîd is generally necessary in order to place sufficient copper in solution. A corresponding copper concentration may be in the range of approximately 30-50 gms. per liter for a pregnant electrolyte to be introduced into the electrowinning process.
The copper-laden solution is then introduced into one or more electrolytic cells each containing a series of anodes and cathodes.
Within the electrolytic cells 9 the anodes are sub-.
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stantially insoluble wi-th an electrical potential impressed between the anodes and cathodes -tending to cause migration of copper from -the electrolyte toward the cathode with metallic copper being deposited or built up on each of the cathodes.
Fresh electroly-te is constantly supplied to the cells. Sul-furic acid solution is recycled from the cells for the leach-ing or solution of additional copper which is then again in-troduced into the electrowinning cells.
The cathodes containing the build-up of metallic copper are periodically removed from the cells and replaced by fresh electrodes or starter sheets to permit continued de-position. The cathodes removed from the cells contain rela-tively pure copper, for example in the range of 99~ purity.
A portion of the copper resulting from the electrowinning process is accordingly used directly in copper consuming ap-plications. However, since many applications require copper of even higher purity, it is also common to further refine copper obtained from the electrowinning process by conven-tional electro-refining techniques.
Insoluble Anodes Used In Electrowinning:
The theoretically insoluble anodes are a particular source of concern within the electrowinning process and have been the object of substantial developmen-t efforts throughout the relatively long history of the electrowinning process.
Problems arising in connection with the anodes tend to de-velop because of the infeasibility of providing a completely insoluble anode which is still capable of adequa-te electrical performance within the cell. It has been commonly found tha-t material from the anode tends to become dissolved in small quantities within the electrolyte with a portion of the dis-~r ~ 2 .: .
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solved anode maLerial being collected or trapped upon thecathode together with metallic copper.
For some time, insoluble anodes used in the elec-trowinning of copper have been formed Erom lead or lead al-loys. Relatively limited amoun-ts of lead have been found within the copper deposit on the ca1:hodes. However, in many copper consumin~ applications, the acceptable limits for lead as an impurity are very low, commonly in the range of 10-20 parts per million. Much of the effort directed toward devel-opment of improved anodes has therefor concerned techniquesfor making lead or lead alloy anodes having high hardness and resistance to corrosion or exfolia-tion while also maintaining adequate mechanical and dimensional stability in the anodes to permit their continued use in electrowinning cells over substantial periods of time.
In the recent past t the most common lead alloy em-; ployed in electrowinning anodes was one containing substan-tial quantities of antimony, for example, 5-15~ Sb by wèight.
In addition to such binary alloys, ternary and quaternary -~
alloys including lead and antimony have also been commonly employed with the additional alloying agents being selected -~ from a broad group including arsenic, bismuth, tin, cadmium, thallium, tellurium, mercury, cobalt, barium, strontium, selenium, tantalum, smooth platinum, etc. More recently, lead-silver alloys have been investigated, particularly those in ternary form including a third alloy such as arsenic or bismuth.
Generally, anodes formed from lead alone do not have sufficient hardness or resistance to corrosion or exfol-iation to permit their use in electrowinning because of ex-. ~ .
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cessive lead migratioll with -the lead being deposited or entrapped upon the cathocles together with metallic copper.
The various alloying agents ten~ to increasc hardness and corrosion resistance while also con-tributing to rnechanical and dimensional stability, all of -these being particular:Ly desirable characteristics for insoluble anodes in the electro-winning process.
Calcium is an addi-tiona:L material of particular interest within such lead alloys. Although calcium may be employed wi-th binary, -ternary or even quaternary alloys in widely varying amounts, the most useful concentrations for calcium in such alloys are believed to be within the range of 0.01 to 0.1% by weight.
The attractive corrosion resistance and superior mechanical properties of lead alloys which contain calcium have been known for many years as is demonstrated to some degree by the use of calcium alloys in the manufacture of battery grids. However, it is to be particularly noted that manufacturing techniques and operating performance require-ments for battery grids are different from the requirementsfor insoluble anodes such as are employed in the electrowin-ning process. Experience in the battery field may be taken - to reinforce the conclusion that lead-calcium alloys are more difficult to cast or otherwise form into a usable configura-tion.
This appl~cation describes one or more casting tech-niques, which either alone or in combination, permit the casting of a lead-calcium anode having grea-tly superior properties of cor-rosion resistance and mechanical and dimensional stabili-ty, parti-: , ,. ....
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cular]y for use in electrowinning processes. ~lowever, it is emphasiY.ed that the casting techniques are not limited merely to lead-calcium al]oys employed in lnsoluble anodes for use in the copper e]ectrowining process. On the other hand, because of the particular efEec-tiveness of these techniques for forming such anocles, the preferred embodiment and examples as described below, are directed in large part towards lead-calcium alloys.
It is also noted at this point that the techniques and apparatus described are also specifically applicable to more complex lead-calcium alloys, for example ternary alloys which include silver or tin, for example, as well as calcium.
It was indicated above that the purpose of employ-ing lead alloys is to improve resistance to corrosion or ex-foliation as well as to enhance both dimensional and mechan-ical stability. These requirements are relatively complex for insolubie anodes of the type employed within the electro-winning process. ~o provide additional background in this connection, it is noted that the "insoluble" or "inert'' anodes are immersed in sulfuric acid solution contained by electrowinning cells. Wi-thin the electrolytic process or under generally similar conditions commonly employed to sta-bilize or precondition the anode surface, lead within the anode tends to react with the sulfuric acid and also with air bubbles generated by electrolysis upon the surface of the anode. Interaction of these materials under electrolytic or similar stabilizing conditions tends to cause forma-tion of a film upon the lead or lead alloy anode. The film principally consists of lead dioxide (PbO2) which acts as a semiconductor, thus enabl.ing electrical conductance throu~h -the anode and particularly enhancin~ i-ts corros:ion resis-tance. Lead oxide (PbO) and lead sulfate (PbSO~) are also present during various s-tages of the film formation and are characterized as being generally poor conductors.
It is theorized that the phenomenon of initial film formation and subsequent film reforma-tion is important in maintaining the corrosion resistance o:E the anode. In any event, it has been found that the chemical and physical characteristics of the anode are important factors affec-ting formation of the above noted film and accordingly are important in achieving maximum corrosion resistance of the anode.
Important Characteristics For Insoluble Anodes:
.
In addition, certain chemical and physical charac-teristics of the anode are also important in determining its mechanical and dimensional stability as was suggested above.
These chemical and physical properties of the anode, which may affect corrosion resistance and/or mechanical and dimen-- 20 sional stability are summarized below.
Initially, chemical composition of the anode is of critical importance as suggested by the preceding discussion of the various lead alloys which have been developed. For example, it was clearly indicated above that certain lead alloys, particularly those including calcium as well as other binary, ternary and quaternary alloys, contribute both to the corrosion resistance of the anode as well as i-ts mechanical strength and dimensional stability. It is also believed ; importan-t to maintain in uncombined form the basic lead com-ponent except for the presence of precipitates formed with ~1~.,;~
s~ -6-3~i and between -the various alloyinq ayen-ts. ~or example, in a lead-calci~m alloy, a precipi-ta-te oE lead calcium (Pb Ca3) is believed to be an importan-t fac-tor contributing to -the improved characteris-tics of anodes formed from such alloys.
In respect to one aspect of the presen-t invention, it is theorized tha-t other compound forma-tions of lead, in particular, wi-thin the anode, may be undesirable. In this regard it is particularly believed that the combination of lead with oxygen to form either lead oxide or lead dioxide within the anode may undesirably interfere with subse~uent formation of a stabilizing or conditioned film, as noted above.
Uniform precipitate distribution is an additional desirable characteristic to be considered in connection with alloy composition of the type discussed immediately above.
Particularly with alloy compositions such as lead-calcium it is believed that precipitate formation and uniform distribu-tion of the precipitate throughout a matrix of lead contri-butes particularly to corrosion resistance and the related characteristic of surface hardness.
The characteristics of high density and low poro-sity are believed to be interconnected and jointly contribute again to the characteristics of corrosion resistance and surface hardness for the anode. These characteristics may also effect in part mechanical and dimensional stability of the anode.
Grain size is another characteristic which is believed to provicle an important contribu-tion to both corrosion resistance and mechanical charac-teristics such as ha~dness.
Generally, it is believed that for a non-ferrous metal such :;;- ~ , '' ' ' as lead, i-t is desirable to malntcLin a relatively large or coarse grain size. Here again, -the charactcris-tic of coarse or large grain size is particularly important for the lead ma-trix in an alloy such as lead~calcium. I-t is assurned tha-t relatively large or coarse grain size in such an alloy con-tributes both -to film formation, as discussed above, and possibly also ~o uniEorm precipitate distribution. This supposition again illustrates that the many characteristics discussed herein are interrelated or interdependent upon each other.
Finally, it is believed desirable to form a surface upon the anode which may be characterized as uniform, continuous or generally smooth. It is believed that the nature of the initial surface formed upon the anode is of substantial importance. It is again theorized that the surface characteristics contribute importantly to proper film forma-tion, as discussed above. Possibly, the combined characteris-tics of a smooth surface and relatively large grain size tend to promote development of a uniform film upon an anode which importantly minimizes corrosion within the electrolytic bath. It will be noted below that in conjunction with the present invention, anodes formed according to the procedure described below tend to have the appearance of being "rolled"
- or "galvanized." In any event, the surface characteristics of the anode formed accoxding to the present invention are believed to contribu-te importantly to its value within an electrowinning process.
In summary, the preceding comments have been directed to~ard a discussion of basic anode characteristics including 30 good resistance to corrosion or exfoliation, mechan- ~
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z~s ical stability or "strength", dimensional stabllity and relative hardness, both on the anode surface and within the anode interior. In this connection, it is important to note that as material is eventually lost from the anode, those portions originally within the anode interior then form its surface.
In addition, the preceding discussion emphasized the characteristics of chemical composition, uniform precipitate distribution, high density and low porosity, large or coarse grain size and initial surface characteristics of the anode.
This discussion of anode characteristics is set forth above in some detail in order to emphasize advantages of the present invention. With the e~ception of chemical composition, the other basic anode characteristicsdiscussed above are believed to be primarily dependent upon the method of casting or forming the anode, either alone or in conjunction with the ` chemical composition.
Objects of the_I_vention A basic object of the present invention is ~o provide a novel and particularly useful insoluble lead alloy anode of a type useful in electrowinning processes ~; for metals such as copper, the anode preferably lncluding calcium as an alloying agentO
It is a more specific and related object of the invention to provide such a lead alloy anode, including calcium as one of the alloying agents, wherein the anode is characterized by maximum density, minimum porosity, uniform precipitate distribution and further by a uniformly smooth and hard anode surface.
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~ s an even further part.i.cularity, it is an object to provide such a lead alloy anode havinc3 a calciurn content within the approxlmate range of 0.01 to 0.1% by wei~ht.
Within the process for produc:ing an anode of the -type descrlbed above, a nurnber o~ process objects or elements have been determined as being of interrela-ted importance.
However, it is believed that no-t all of these objects must necessarily be employed together in order to produce a novel insoluble anode. These process objects are set forth immediately be:Low.
Summary of the Inven-t.ion ._ __ __ __ This invention relates to an insoluble anode for .
use in the electrowinning of copper, -the anode having a substantially flat configuration with an effective surface area on either side thereof of at least approxima-tely 5 square feet, the anode being formed by a casting process from a lead : alloy including approximately 0.01-0.1~ by weight calcium the anode being further characteri~ed by substantially a maximum density and minimum porosity, a uni~orm precipitate distribution of PbCa3 in a lead matrix, the surface of the : anode being continuous and smooth and further characterized as having a galvanized or rolled appearance.
The method of producin~ the anode contemplates limiting the amount of time during which the lead alloy remains in a molten state after being introduced into a suitable mold. This time limit is preferably achieved through selectively controlling the temperature of the molten alloy in a melting pot :.
or furnace and in a ladle prior to introduction to the mold. Additionally, the temperature of the mold is ~:
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also controlled within selected limits at least upon commencement of pouring the lead alloy into the mold.
This feature is believed to contribute to both chemical and physical characteristics of the anode. In addition, it is thereby possible to remove the anode from the mold within a relatively short time, for example within two to three minutes, in order to facilitate further treatment of the anode and to achieve operating economy within the casting operation.
-It is particularly contemplated that the anode be suspended in a vertical condition immediately after being removed from the mold. The vertically suspended anode is then rapidly cooled. This step is believed to "freeze" the grain size and precipitate distribution throughout the anode and particularly adjacent its surface while also contributing to di=enslo=al and/or mechl:nlcal s~ability.
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~32~i ~ n additiona:L elemen-t o:E the casting method contemplates limiting the amount o.E :E:Low for the molten lead alloy wit~in the mold. Thi.s i.s believed to contribu-te -to the achievement maximum densi-ty and minimum porosi-ty for the anocle while also con-tributing to -the :Eo.rma-tion of a smooth or continuous surface. M.inimum flow of the molten alloy wi-thin the mold is achieved by preferably disposing the mold in a vertical position with the top o:E the mold cavity being completely open to receive molten lead alloy along its length. The molten lead alloy is then "streamed"
into the mold along the length of -the molcl cavi-ty wi-th the amount of lead alloy being introcluced into each portion of the mold in proportion to the volume of the mold cavity.
: In this manner/ all portions of the mold tend to be filled in approxima-tely the same amount of time with minimum flow of the alloy being necessary within the mold to achieve complete filling of the mold cavity. The alloy material thereby enters into continuous and intimate contact with all surfaces of the mold cavity. In addition to con-tributing toward the development of maximum density and minimum porosity, minimum flow in the mold is also believed to contribute toward other chemical and physical features of the finished anode such as, for example, uniform precipitate distribution particularly adjacent the anode surfaces, as well as the 25 surface finish itself. ~.
It is another particular element of the casting method to preven-t access of oxygen -32q~
to the molten lead alloy, particularly for an alloy includincJ calclum as an alloying agent, or even after the molten lead alloy solidifies within the mold -to form an insoluble anode. I'his step is believed impor-tant both to regu:Late chemical composition of the lead alloy within the finished anode and also to limit the loss oE calcium from a lead alloy including calcium as an alloying agent.
Additional elemen-ts of the method are also directed -towards main-taining the calcium conten-t of such a lead alloy, for example by the imposi-tion of an electrical potential, preferably a low DC voltage, upon the molten lead alloy within the furnace or mel-ting pot.
Finally, i-t is also an element of the method -to select a lead alloy including calcium as an alloying agent.
Calcium may be present within -the lead alloy to form a binary alloy and other alloying agents may also be added to provide either a terna~y or quaternary alloy, for example, from which an insoluble anode may be produced within the scope of the present invention.
Calcium is particularly selec-ted as a preferred alloying agent within the lead alloy because of its tendency to-increase alloy hardness, improve corrosion resistance and enhance mechanical or dimensional strength. The calcium ; alloying agent may be present in a relatively wide range of 0.01 -to 0.1% by weight. It is further noted -that calcium is a particularly desirable alloying agent for lead alloy anodes because of i-ts -tendency -to reac-t wi-th sulfuric acid and produce salts of low solubili-ty. This characteris-tic is believed to greatly con-tribute toward the forma-tion of pro-tective, compact or thick films of a type par-ticularly sui-table `~ csm/`~
for minimizing corrosion resistance of -the anode under elec-trolytic condi-tions such as those encountered in an elec-trowinnin~ process.
- Adcli-tional objec-ts and advantages oE -the presen-t inven~ion are made apparent in the following description having reference to the accompanying drawings.
Desc lpt~
To facilitate unders-tanding of the invention, casting apparatus of -the type employed to produce such an insoluble anode is illu~trated in Fig. 1 which is a side view in elevation of apparatus including a mold, a ladle, and a furnace or mel-ting pot.
Fig. 2 is an additional view taken from the rlght side of Fig. 1, to particularly illustrate the configuration and arrangement of an internal cavity within the mold.
Fig. 3 is a view of an insoluble anode produced by the method of the presen-t invention.
Fig. 4 is a fragmentary view taken along section -~
line IY-IV in Fig. 3.
Fig. 5 is a detailed, isometric view of the ladle - for the casting apparatus of Fig. 1 to illustrate a preferred ~
configuration therefor. ~-Fig. 6 illustrates ano-ther preferred configuration of the ladle.
Figs. 7 and 8 are photomicrographs, at different degrees of magnification, of a typical insoluble anode produced from a lead alloy including calcium as an alloying agen-t.
i~ig. 9 illustra~es the su:rEace f:inish o~ a lead alloy ~nocle procluced by the method o:~ -the present invention.
D sc ri~t_on or t.he Pre_erred l,mbocllmen_ As noted above, the present inven-tion is directed towarcl an anode having a p:referred compositic-n as well as other characteristic features. In view o:E -the rela-tively large number of fea-tures invo:Lved ~or the insoluble anode the following descrip-tion includes fixst a discussion of suitable alloys for use in such an insolub:Le anode followed by a description of the anode configura-tion, a description oE
the casting apparatus, a descrip-tion of the casting process followed by a number of specific examples setting forth various anodes produced by the present method with pertinent method parameters for each example.
Suitable Alloy Compositions:
As indicated above, the present invention is particularly directed toward lead alloys including calcium as an alloying ayent. However, the invention is not intended .~-to be limited to lead alloys including calcium as a single :20 alloying agent or even to alloys necessarily including calcium.
For example, a lead alloy including calcium as an alloying agent might also include one or more other alloying agents such as silver or tin. Accordingly, a lead alloy of the type contemplated by the present invention could be, for example, .
a binary, ternary or quaternary alloy.
Furthermore, it is generally accepted thak lead alloys including calcium as an alloying agent are particularly difficult to form or cast. This even further indicates the .~.
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value and novelty of the present inven-tion in providing a me-thod for successfully casting such ma-terials. ~lowever, the success of the present invention in providing cas-t lead alloys inclucling calcium also indica-tes i-ts value in cas-ting other ma-terials particularly other generally similar lead alloys, such as those including, for example, silver or tin, with -the present inven-tion not necessarily being limi-ted to the additional~inclusion of calcium.
Moreover, alloying agents such as calcium have a tendency to evaporate or otherwise be lost Erom -the alloy when i-t is in molten condition. Accordingly, the composition of the alloy as originally produced may vary from the alloy composition within a finished anode.
Generally, one preferred composition for the lead alloy anode includes calcium as an alloying agent either alone or in combination with other alloying agents. More particularly, it is con-templated that a lead alloy anode with calcium as an alloying agent include calcium within the proximate range of 0.01 to 0.1% by weight. An even more limited concentration for calcium,within the range of approximately of 0.02 to 0.07% by weight, is believed to be of particular importance.
One typical composition for a lead calcium alloy to be employed within the present method, for example as ~- 25 an alloy ingot, inclucles approximately 0.0~-0.06~ by weight calcium, the remainder essentially pure lead except for normal impurities. In view of the tendency for calcium to be lost from the alloy, it is accordingly possible that an alloy ingot to be employed within the presen-t casting method may include calcium above 0.1%.
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~ s a Eurther exclmple oE the application for -the method of -the present inven-tion, it is also belicved appli-cable -to leacl-an-timony alloys including antimony as an alloying agent within the approxima-te range of 5-15% by weight. One typical composition for such an alloy is set forth below:
Pure, soft lead 90% by wg-t.
Pure, antimony 10~ by wgt.
Maximum impurity content: Ag-0.0004% by wgt.
Cu-0.0009~ by wgt.
Zn-0.0005% by wgt.
As-0.0003~ by WCJt.
Fe-0.0002~ by wgt.
Bi-0.00014~ by wgt. .-Many additional alloy compositions may also be employed in conjunction with the method of the present invention. Such alloys may include alloying agents of the type summarized above. It is believed that silver and tin have particular value as alloying agents either alone, in combina-tion with each othert and/or in com~ination with calcium,for example.
Insoluble Anode Configuration:
- As indicated above, the present invention is par-ticularly direc-ted -toward techniques for casting an insoluble anode of a type used in an electrowinning process such as for the recovery of copper. A typical configuration for such an insoluble anode is illustrated in Fig. 3. Referrïng to Fig.
3, it may be seen that the anode is relatively large, for example having overall dimensions of approximately 48" x 36", ; a thickness of about 1/2 inch, with an eEEective surface area on either side of approximately 8-9 sq. :Et. The effective .
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area of the anode is inclica-ted at 11 and includes a generally continuous rectancJular portion which is immersed wi.-thin an electrolyte solu-tion for an electrowinning pxocess. The effectlve portion 11 of the anode may be either continuous or perfora-ted as i.llustrated :Eor a portion of the anode at lla.
Insoluble anodes are commonly formed wit.h such perforations in order to reduce the weigh-t of the anode and to increase its effective surface.
Each insoluble anode inclucles a rela-tively heavy copper bar or conductor 12 which ex-tends transversely beyond the edges of -the anode. The extended ends of the copper bar 12 may be conventionally disposed on paralle]. spaced apart supports (not shown) for suspending the anode within the electrolyte solution. The copper bar 12 also provides a conductor path and accordingly must be in intimate conductive relation with the anode 11. For that purpose, it may be seen that the lead alloy encompasses the copper bar and has a relatively increased thickness (indicated at 13 in Fig. 4) to provide proper support upon the copper bar. A window, or opening 14, is commonly formed along a central portion of the anode adjacent the copper bar mainly for the purpose of reducing weight of the anode. Accordingly, the weight of the anode is supported by a s-trip of lead alloy which extends upwardly along either side of the anode for engagement with the 25 copper bar 12. These strips are indicated a-t 16. The overall thickness of the anode is increased to approximately 1 in.
where the anode surrounds the copper support bar.
It is preferable to form or cast the anodes in substantially the shape indicated in the drawings in order to conserve the lead alloy and to minimize further finishing ~3Z(~
work. The copper suppor-t bar 12 is initially arranged within the base oE -the mold prior -to introduction of the lead alloy and thus ~ecomes an intimate por-t:ion of the cas-t anode.
C3~ ~ bus The castin~J appara-tus employed in practice of the method of the present lnvention is of a generally conven-tional type found in many foundry operations. The casting apparatus does not form a particularly importan-t elemen-t of the -present invention excep-t to enable practice of the preferred method as described below, with one e~ception as to specific cons,ruction of the ladle. Accordingly, the casting apparatus is only indicated generally in Figs. 1 and 2 and includes a conventional furnace or melting pot 21, a ladle 22 and a mold 23 forming an internal cavity as indicated at 24 in Fig. 2.
The furnace is of a general type sui-ted for the heating of a lead alloy to molten condition in a temperature range generally 700-800F. The capacity of the furnaee is selected to greatly exceed the volume of the mold eavity 24 so that the lead alloy may be maintained in a molten condi-; tion within the furnaee after each pour without an interval -being required for reheating. Preferably, the capacity of the furnace is selected so that only about 5% of its eontent is required to fill the mold cavity. Accordingly, additional lead alloy ingo-ts may be added to the furnace after each pour with the molten alloy in the furnace then being immediately ready to commence pouring a new anode.
The combination of the configuration of the ladle 22 and the orientation for the mold 23 are important to the present invention. The importance of those two elemen-ts is ' . -19-. . ~ , .
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summarized immedia-tely below and is desc~ibed in grea-ter - detail below in terlns of the pref~rred process or rnethod~
Initially, the mold 23 is preferably forrned by separate mold sections 26 and 27 which divide around the periphery oE -the mold cavi-ty in order to permi-t rapid removal of the anode. :[n addi-tion, the mold is arrangecl with the cavity 24 in vertical alignmen-t to facilitate a preferred method of filling the mold cavi-ty as described in greater detail below. The mold sections 26 and 27 are also preferably formed to provide a top opening 28 along the entire transverse dimension of the cavity 2~ in order to permit simultaneous fillinq along the length of the anode as is also described in greater detail below.
In conjunction with the fea-tures of the mold as described above, the ladle 22 is preferably formed as a cylinder which is closed at each end and has approximately a quadrant of its cylindrical surface removed (at 29) in order to permit filling of the ladle from the furnace.
The ladle 22 includes gating in the form of perfor-ations or apertures 31 extending completely along the trans-verse length of the cylindrical ladle, -the leng-th of the ladle generally conforming with the length of the mold cavity 2~.
The angular location of the gating upon the cylindrical ladle is selected so that, with the ladle in the position illustrated in-Fig. 1, the ladle may be filled with molten alloy from the furnace. The cylindrical ladle is then rapidly rotated to bring the gating apertures 31 into alignment with the .
opening 29, the molten lead alloy from -the ladle streaming downwardly to simultaneously fill all portions of the mold along its length. As may be seen in Figs. 5 and 6, the .
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apertures are configured or arrangecl to permit increased flow into selected portions oE the mo:ld. Referrlny again -to Fig. 3, it may be seen that the copper bar 12 is ini-tially disposed in a hase portion of the molcl cavity 24 so that the anode is actually formed in inverse or upside-down relation within the mold. Relatively larger amoun-ts of lead alloy are then required adjacent the ends of the mold cavity 2~ to initially fill the enlarged por-tions 13 oE the mold cavity which form the sections surrounding the copper bar 12. The window 1~ formed along the central portion of -the anode fur-ther minimizes the amount of lead alloy required along the center of the mold cavity. Accordingly, the gating apertures 31 may be of a larger size adjacent the ends of the mold cavity as is illustrated in the embodiment of Fig. 5. Alterna-tively, the gating may include a larger number of openings or slots 31' of longer length may be provided adjacent the longitudinal ends of the mold cavity as illustrated in the embodiment of Fig. 6.
The ladle of Fig. 6 is employed for filling a mold cavity having no structure to impede or interfere with the streaming of molten alloy toward the bottom of the cavity.
Such a mold configuration is employed to form an insoluble anode of continuous cross-sections. The ladle of Fig. 5 is employed to fill a mold configured to form a perfora-ted anode.
For this purpose, one of the mold sec-tions may be formed - with a large number of lugs arranged in vertical rows. The luys, as indicated at 32 in Fig. 2, are arranged substan tially across the effec-tive area and extend outwardly to abou-t with the other mold section. The gating apertures in the ladle of Fig. 5 are disposed a3ong its length to conform ` -21-. . .
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with the spaces between the lugs. q~hus, moLten alloy may pass in con-tinuous strealns toward -the bottom of -the mold cavity in accordance wi.th a basic object of the present invention.
soth of these embodiments have the purpose of enab:Ling -the mold cavity to be comple-tely ancl uni.formly filled with the lead alloy entering into close intimate con-tact with all surface portions of -the cavity while requiring minimum flow of the molten lead alloy. This feature of the invention is initially believed to contribute importan-tly to maximum clensity for the anode. In addition, the minimiza-tion of molten flow wi-thin the mold cavity permits -the anode to be solidified more rapidly, an additional important objective of the method of the present invention as described below.
With the arrangement described above, it is possible that lead exiting through the apertures 31 of the ladle may initially tend to contact a lateral surface of the rnold cavity during rotation of the ladle to place the gating in register with -the mold cavity. Even this amount of contact between the molten alloy and -the cavity surfaces could be minimized or substantially eliminated, for example, by the arrangement of a stationary gating member direc-tly beneath the ladle. Through the use of such an element, molten lead alloy from the ladle would tend to be prevented from passing through the gating of the ladle into the mold cavity until -the gating apertuxes 31 are directly above the mold cavity.
The casting apparatus necessary for -the method of the presen-t invention may include cextain supplemental compo-nents, particularly such as -tempexature sensors, in order to :
facilitate proper contxol of the casting process. However, such sensors are believed to be sufficiently conventional ,.
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Wit}lill the casting art that they need not be illustrated herein. In addit:ion, the present inven-tlon particularly contemplates means for selectively coolincJ the mold sections 21 and 22. This cooling means, which is also no-t illustrated, could comprise condui-t m~ans integrally Eormed within the mold sec-tions or could merely comprise separate means such as a nozzle arrangement Eor spraying a fluid or liquid upon -the surfaces of the mold.
Method of Casting:
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Novelty of the presen-t invention is believed to priMarily reside wi-thin -the me-thod of cas-ting as desGribed immediately below. The use of various alloy agents has long been recognized as providing a means for achieving desired charac-teristics in resul-tant castings. In particular, it has long been recognized that lead alloys, especially those including calcium as an alloying agent, are capable of contri-buting subs-tan-tially to desired chemical and physical charac~
teristics. Accordingly, the present inven-tion is believed to be of substantial importance since it provides a method of casting which is believed to approach maximum utilization of tne performance capabilities for-alloying agents such as calcium.
As was indicated above, the cas-ting method of the present invention includes a number of important elemen-ts.
Initially, it has been found impor-tant -to regulate tempera-ture or temperature differential throughout much of thecasting process. In addition, and/or simultaneously, another importan-t feature has been the minimization of necessary molten flow within the mold before solidifica-tion. Addi-tional impor-tan-t elements of the presen-t process include the preferred :
exclusion of ox~gen from -the alloy whi.le it .is in a rnolten state an~ the selection of the alloy m~-terial, particularly -the selection o:~ leacl alloys with calcium as an alloying agent. However, it is once again stressed that the method of the presen-t invention is not lim:i-ted -to lead alloys necessarily including calcium as an alloying agent. Further, it is possible tha-t the casting method oE the present invention may be applied to other non-ferrous metals as well as lead.
In describing -the various elemen-ts o:E the present casting method, it is noted that -the selection of alloy composition is discussed above and will be illust:rated in even greater detail within the specific examp:les set forth below.
The various specific steps within the casting method or process are described in sequential order below.
15 Initially, a selected alloy composition is intro-duced into the furnace and heated to a molten condition. As indicated above, a substantlal excess of molten alloy is preferably maintained within the furnace in order to facilitate continuous casting. For example, where each insoluble anode may weigh, for example, in the range of 150 lbs., the total amount of molten lead alloy within the furnace is maintained a-t approximately twenty times that amount. Accordingly, the total amount o~ molten lead alloy within the furnace may approximate 3000 lbs. Thus,~approximateIy 150 lbs. of lead alloy, for example, in the form of ingots, may be added to the furnace after each anode is poured. The figures set forth ; immediately above are primarily for purposes of example and .
; illustrate the proportions necessary to permit generally continuous casting.
The temperature of molten lead alloy is also closely c ~2~-; ~ . ' ': . ~:
32~
controlled within the furllace. Althou~h optimu~l values may be estab:Lished ~or -temperature of the molten alloy within the furnace, those values tend ~o vary depending upon various external factors such as ambient temperature, humidity, e-tc.
Accordirlgly, .i-t .is to be understood that the discussion of tempera-ture limi-ts Eor the present cas-tiny me-thod es-tablish approximate values or ran~es. It is to be further understood that these approximate values or ranges may be varied within the scope of the present i.nven-tion depending upon factors such as those set forth above and upon add:itional factors such as selection of the par-ticul.ar alloy composit.ion, size of the anode or casting, etc.
The molten lead alloy within the furnace is . maintained at a minimum of about 50F above its melting point ~ 15 in order to assist in minimizing the time during which the alloy remains molten within the mold. The various types of alloy composition considered at this time exhibit a range of .
` melting points within the approximate range of 500-625F.
The temperature of the molten lead alloy within the furnace is more particularly maintained at a temperature differential of approximately 50-100F above the melting point. For the lead alloys under exemplary consideration, the temperature within the furnace may thus vary from approximately 550F
~ to approximately 725F.
:~ 25 As was also indicated above, it is desirable to prevent or minimize oxidation o~ the molten a:Lloy. The excess quantity of alloy maintained in a molten state within the furnace assists towards this end since the exposed surface area for the molten lead alloy within the furnace necessarily becomes of lesser significance. In addition, it g .- ~, . , ~
has been found that oxygen contact with the surface of -the molten ]ead alloy may ~e further limited by Eloa-ting charcoal upon the surface oE the moltell a]loy Or by maintaininy a blanket of a relatively heavy, inert gas such as argon above the mol~en lead alloy within the furnace. It is also noted tha-t such steps are believed -to Eurther minimize the loss of calcium from lead al:Loys where calcium is an alloying agent~
It has further been found tha-t, when calcium is employed as an alloying agent in combination with lead, the calcium conten-t can be Eurther stabilized by impressing an electrical po-tential across the molten alloy in the ~urnace.
For example, a relatively low direc-t current voltage of approximately 6V may be applied across the molten alloy by creating a potential between the furnace and a separate elec-trode (not shown) which is floated on the molten alloy.
In order to commence a cycle for formlng an anodeof the type illustrated in Fig. 3, a suitable amount of molten lead alloy is transferred from the furnace to the cylindrical ladle. The ladle is maintained in the upright position illustrated ln Fig. 1 so that the alloy lnitially remains completely within the ladle.
It is of course desirable to maintain the alloy temperature within the range discussed above and accordingly it may be necessary to initially preheat the ladle so that it does not cause excessive lowering of the temperature for the molten alloy. However, during a continuous casting process where the ladle is rapidly being filled with molten lead alloy which is then poured into the mold, the temperature of the ladle tends to remain s-tabilized and does not in-terfere with proper maintenance of the molten alloy temperature.
~ -26 IJI orcler to further prevent excessive contac-t of o~ygen wi-tl~ the molten alloy, it is conternplated -that the alloy be preferably blanketed against contact with the air in the same manner described above for -the Eurn~ce.
Prior to th~ step of pouring molten alloy into the mold, -the -temperature of the molcl is established at a selec-ted differential benea-th the tempera-ture maintained for the molten alloy within both the furnace and the ladle. For example, i-t is ~enerally preferred -that -the initial tempera-ture of the mold be approximately 200-250F lower than the molten alloy temperature. Accordingly, it is generally desirable to maintain the mold surfaces within a temperature range of approximately 400-500F. Maintenance of the mold temperature is particularly subject to variation depending upon ambient conditions. It has been found through experimentation that an experienced operator can closely ascertaln and control the desired temperature of the mold through observation of the alloy when it is in contact with the mold. For example, ; the optimum temperature differential may be determined by such an experienced operator through observation of the rate of shrinkage, the rate of solidification and the amount of "drag," etc. as the molten alloy commences to solidify within the mold. The term "drag," as used above, refers to the rate of movement for the molten alloy relative to the . -surfaces of the mold. As is clearly observed, such movement is limited by -the casting me-thod described a~ove.
The mold is also arranged in the vertical position illustrated in Fig. l with the mold sections being closed toge-ther to form the mold cavity which is open along its top.
The lad].e is then rapidly rotated so tha-t the perforations are ' ~3;2t3~ii placed i.n recJiste.L- or vertical alignmen-t wi-th -the mold cavity.
The mol.ten alloy :is thell perm:itted to "stream" in-to the mold cavity and -to illcrementally fill the mold wi-th llmi-ted MoVement of the mol-ten a]loy. A t:ime period of approximately 20-30 sec. may be required for fil:ling of the mold for an insoluble anode. Duri~y that time, the mol-ten alloy commences solidification because of -the temperature dif:Eerential for the mold sur~aces. Under certain conditions, i-t may be necessary to further cool the ou-tside of the mold even during the pouring s-tage, for example, when the ambient tempera-ture is relatively high. Once the mold is filled wi-th molten alloy, it is allowed to remain within the mold for approximately 1-2 min. As soon as the molten alloy is sufficiently solidified within the mold to permit it to become mechanically self- ~.
supporting, the mold is opened up by separation of the mold sections 21 and 22. . .
Before proceeding to describe treatment of the anode ~: after its removal from the mold, it is noted that further : -cooling of the mold may be necessary during the time period that the molten alloy is solidifying following the pouring step. Cooling of the mold may preferably be accomplished by ~ :
merely spraying its external surfaces with a mixture of air and water.
It may also be desirable to further limit contact of the alloy with oxygen during filling of the mold. Accord-ingly, it is also contemplated that the heated mold may be.
initially filled with a heavy, inert gas such as argon. As the molten alloy is then poured into the mold cavity, the . argon is displaced from the mold and in no way interferes with the casting operation.
with the spaces between the lugs. q~hus, moLten alloy may pass in con-tinuous strealns toward -the bottom of -the mold cavity in accordance wi.th a basic object of the present invention.
soth of these embodiments have the purpose of enab:Ling -the mold cavity to be comple-tely ancl uni.formly filled with the lead alloy entering into close intimate con-tact with all surface portions of -the cavity while requiring minimum flow of the molten lead alloy. This feature of the invention is initially believed to contribute importan-tly to maximum clensity for the anode. In addition, the minimiza-tion of molten flow wi-thin the mold cavity permits -the anode to be solidified more rapidly, an additional important objective of the method of the present invention as described below.
With the arrangement described above, it is possible that lead exiting through the apertures 31 of the ladle may initially tend to contact a lateral surface of the rnold cavity during rotation of the ladle to place the gating in register with -the mold cavity. Even this amount of contact between the molten alloy and -the cavity surfaces could be minimized or substantially eliminated, for example, by the arrangement of a stationary gating member direc-tly beneath the ladle. Through the use of such an element, molten lead alloy from the ladle would tend to be prevented from passing through the gating of the ladle into the mold cavity until -the gating apertuxes 31 are directly above the mold cavity.
The casting apparatus necessary for -the method of the presen-t invention may include cextain supplemental compo-nents, particularly such as -tempexature sensors, in order to :
facilitate proper contxol of the casting process. However, such sensors are believed to be sufficiently conventional ,.
~, , ~ , - .' ' . . - . ' - . .
: . .
~)3~
Wit}lill the casting art that they need not be illustrated herein. In addit:ion, the present inven-tlon particularly contemplates means for selectively coolincJ the mold sections 21 and 22. This cooling means, which is also no-t illustrated, could comprise condui-t m~ans integrally Eormed within the mold sec-tions or could merely comprise separate means such as a nozzle arrangement Eor spraying a fluid or liquid upon -the surfaces of the mold.
Method of Casting:
.. . .
Novelty of the presen-t invention is believed to priMarily reside wi-thin -the me-thod of cas-ting as desGribed immediately below. The use of various alloy agents has long been recognized as providing a means for achieving desired charac-teristics in resul-tant castings. In particular, it has long been recognized that lead alloys, especially those including calcium as an alloying agent, are capable of contri-buting subs-tan-tially to desired chemical and physical charac~
teristics. Accordingly, the present inven-tion is believed to be of substantial importance since it provides a method of casting which is believed to approach maximum utilization of tne performance capabilities for-alloying agents such as calcium.
As was indicated above, the cas-ting method of the present invention includes a number of important elemen-ts.
Initially, it has been found impor-tant -to regulate tempera-ture or temperature differential throughout much of thecasting process. In addition, and/or simultaneously, another importan-t feature has been the minimization of necessary molten flow within the mold before solidifica-tion. Addi-tional impor-tan-t elements of the presen-t process include the preferred :
exclusion of ox~gen from -the alloy whi.le it .is in a rnolten state an~ the selection of the alloy m~-terial, particularly -the selection o:~ leacl alloys with calcium as an alloying agent. However, it is once again stressed that the method of the presen-t invention is not lim:i-ted -to lead alloys necessarily including calcium as an alloying agent. Further, it is possible tha-t the casting method oE the present invention may be applied to other non-ferrous metals as well as lead.
In describing -the various elemen-ts o:E the present casting method, it is noted that -the selection of alloy composition is discussed above and will be illust:rated in even greater detail within the specific examp:les set forth below.
The various specific steps within the casting method or process are described in sequential order below.
15 Initially, a selected alloy composition is intro-duced into the furnace and heated to a molten condition. As indicated above, a substantlal excess of molten alloy is preferably maintained within the furnace in order to facilitate continuous casting. For example, where each insoluble anode may weigh, for example, in the range of 150 lbs., the total amount of molten lead alloy within the furnace is maintained a-t approximately twenty times that amount. Accordingly, the total amount o~ molten lead alloy within the furnace may approximate 3000 lbs. Thus,~approximateIy 150 lbs. of lead alloy, for example, in the form of ingots, may be added to the furnace after each anode is poured. The figures set forth ; immediately above are primarily for purposes of example and .
; illustrate the proportions necessary to permit generally continuous casting.
The temperature of molten lead alloy is also closely c ~2~-; ~ . ' ': . ~:
32~
controlled within the furllace. Althou~h optimu~l values may be estab:Lished ~or -temperature of the molten alloy within the furnace, those values tend ~o vary depending upon various external factors such as ambient temperature, humidity, e-tc.
Accordirlgly, .i-t .is to be understood that the discussion of tempera-ture limi-ts Eor the present cas-tiny me-thod es-tablish approximate values or ran~es. It is to be further understood that these approximate values or ranges may be varied within the scope of the present i.nven-tion depending upon factors such as those set forth above and upon add:itional factors such as selection of the par-ticul.ar alloy composit.ion, size of the anode or casting, etc.
The molten lead alloy within the furnace is . maintained at a minimum of about 50F above its melting point ~ 15 in order to assist in minimizing the time during which the alloy remains molten within the mold. The various types of alloy composition considered at this time exhibit a range of .
` melting points within the approximate range of 500-625F.
The temperature of the molten lead alloy within the furnace is more particularly maintained at a temperature differential of approximately 50-100F above the melting point. For the lead alloys under exemplary consideration, the temperature within the furnace may thus vary from approximately 550F
~ to approximately 725F.
:~ 25 As was also indicated above, it is desirable to prevent or minimize oxidation o~ the molten a:Lloy. The excess quantity of alloy maintained in a molten state within the furnace assists towards this end since the exposed surface area for the molten lead alloy within the furnace necessarily becomes of lesser significance. In addition, it g .- ~, . , ~
has been found that oxygen contact with the surface of -the molten ]ead alloy may ~e further limited by Eloa-ting charcoal upon the surface oE the moltell a]loy Or by maintaininy a blanket of a relatively heavy, inert gas such as argon above the mol~en lead alloy within the furnace. It is also noted tha-t such steps are believed -to Eurther minimize the loss of calcium from lead al:Loys where calcium is an alloying agent~
It has further been found tha-t, when calcium is employed as an alloying agent in combination with lead, the calcium conten-t can be Eurther stabilized by impressing an electrical po-tential across the molten alloy in the ~urnace.
For example, a relatively low direc-t current voltage of approximately 6V may be applied across the molten alloy by creating a potential between the furnace and a separate elec-trode (not shown) which is floated on the molten alloy.
In order to commence a cycle for formlng an anodeof the type illustrated in Fig. 3, a suitable amount of molten lead alloy is transferred from the furnace to the cylindrical ladle. The ladle is maintained in the upright position illustrated ln Fig. 1 so that the alloy lnitially remains completely within the ladle.
It is of course desirable to maintain the alloy temperature within the range discussed above and accordingly it may be necessary to initially preheat the ladle so that it does not cause excessive lowering of the temperature for the molten alloy. However, during a continuous casting process where the ladle is rapidly being filled with molten lead alloy which is then poured into the mold, the temperature of the ladle tends to remain s-tabilized and does not in-terfere with proper maintenance of the molten alloy temperature.
~ -26 IJI orcler to further prevent excessive contac-t of o~ygen wi-tl~ the molten alloy, it is conternplated -that the alloy be preferably blanketed against contact with the air in the same manner described above for -the Eurn~ce.
Prior to th~ step of pouring molten alloy into the mold, -the -temperature of the molcl is established at a selec-ted differential benea-th the tempera-ture maintained for the molten alloy within both the furnace and the ladle. For example, i-t is ~enerally preferred -that -the initial tempera-ture of the mold be approximately 200-250F lower than the molten alloy temperature. Accordingly, it is generally desirable to maintain the mold surfaces within a temperature range of approximately 400-500F. Maintenance of the mold temperature is particularly subject to variation depending upon ambient conditions. It has been found through experimentation that an experienced operator can closely ascertaln and control the desired temperature of the mold through observation of the alloy when it is in contact with the mold. For example, ; the optimum temperature differential may be determined by such an experienced operator through observation of the rate of shrinkage, the rate of solidification and the amount of "drag," etc. as the molten alloy commences to solidify within the mold. The term "drag," as used above, refers to the rate of movement for the molten alloy relative to the . -surfaces of the mold. As is clearly observed, such movement is limited by -the casting me-thod described a~ove.
The mold is also arranged in the vertical position illustrated in Fig. l with the mold sections being closed toge-ther to form the mold cavity which is open along its top.
The lad].e is then rapidly rotated so tha-t the perforations are ' ~3;2t3~ii placed i.n recJiste.L- or vertical alignmen-t wi-th -the mold cavity.
The mol.ten alloy :is thell perm:itted to "stream" in-to the mold cavity and -to illcrementally fill the mold wi-th llmi-ted MoVement of the mol-ten a]loy. A t:ime period of approximately 20-30 sec. may be required for fil:ling of the mold for an insoluble anode. Duri~y that time, the mol-ten alloy commences solidification because of -the temperature dif:Eerential for the mold sur~aces. Under certain conditions, i-t may be necessary to further cool the ou-tside of the mold even during the pouring s-tage, for example, when the ambient tempera-ture is relatively high. Once the mold is filled wi-th molten alloy, it is allowed to remain within the mold for approximately 1-2 min. As soon as the molten alloy is sufficiently solidified within the mold to permit it to become mechanically self- ~.
supporting, the mold is opened up by separation of the mold sections 21 and 22. . .
Before proceeding to describe treatment of the anode ~: after its removal from the mold, it is noted that further : -cooling of the mold may be necessary during the time period that the molten alloy is solidifying following the pouring step. Cooling of the mold may preferably be accomplished by ~ :
merely spraying its external surfaces with a mixture of air and water.
It may also be desirable to further limit contact of the alloy with oxygen during filling of the mold. Accord-ingly, it is also contemplated that the heated mold may be.
initially filled with a heavy, inert gas such as argon. As the molten alloy is then poured into the mold cavity, the . argon is displaced from the mold and in no way interferes with the casting operation.
3;2~S
When -the anocle is removed Erom -the mold, it i5 still at a re]atively hiqll tempera-tllre, posc;ibly :in the range of 500~. It h~s been Eound ~hat the conEigura-tion oE -the anode is relatively important from this time until the anode tem-perat~lre is at a relative:Ly low tempera-ture, possib:Ly 200F, at which temperature ~he anode -tends to become stable. The anode -tends to exhibit a "dimensional memory" whereby upon beiny Ereely suspended, it will tend to return to the shape in which it was config-lrecl during the final stages of cooling of such a lower temperature. Accordingly, the anode is preferably maintclined in a straight configuration and further cooled, for example, by spraying with an air-water mix-ture until it reaches the low temperature noted above. ~lterna-tively and preferably, the anode is suspended in a vertical position during this cooling step after its removal from the mold. For example, the anode may be readily suspended by the copper hanger bar during this step. With the anode being suspended in a vertical position, substantially no dimensional stresses are developed in the anode. Thus, after it is cooled, it tends to maintain its straight alignment or shape.
This of course is importan-t with-in the elec-trowinning bath to maintain a uniform gap between the anodes and cathodes and thereby enhance electrolytic action within the process.
It may be noted that, within the preceding method description, substantial importance is placed upon maintaining tempera-ture limits during certain stages of the anode forma-tion. It is believed apparen-t tha-t these temperature controls are primarily directed toward achieving complete filling of the mold cavity while limiting the amount of time within which the lead alloy remains molten after it enters the mold.
~i~c -29-,.. . . .
z~s After -the ano~le solidiLies and is removecl from the mold, rapi~l coolil~q of the a~ode is important both for the purpose of limiting further grain chancJe as we:Ll as to enhancc dimen-sional stability as described :immediately above.
Speci~ic Examples:
____ _ _ The followincJ specific examples are intended to set for-th exemplary limi-ts for various alloy composi-tions together with the correspondiny process parameters under which each of the alloy composition is formed in-to an :insoluble anode.
Example No. 1:
An anode of the size described above and having a configura-tion as illustrated in Fig. 3 (wi-thout perforations) was formed according -to the preceding method description using a ladle wi-th a gating arrangement illustrated in Fig. 5.
The lead alloy was selected as representative of a binary alloy including 0.01-0.1% by wgt. calcium, being I obtained in alloyed form as ingots containing 0.04-0.06 wgt.
-~ percent calcium,the remainder essentially lead except for normaI impurities of the type and amount specified above.
This specific alloy, having a melting poin-t of approximately 621.5F and a theoretical density of 11.34 grams/cc, is a commercial lead alloy obtained from St. Joe Minerals Corporation.
The alloy was heated in a gas-fired open furnace to a temperature range of ~75-700F and maintainea a-t that approximate temperature during a rela-tively shor-t dwell time (up to approximately 30 seconds) in -the ladle. The ladle was not heated be-tween pouring cycles bu-t was main-tained at a high temperature because of the shor-t time duration (approx-ima-tely 2 1/2-3 minutes) for each cycle.
.~
2~
~rhc mold, formed oE steel, was ma.inta:ined at a preheated or precooled -t:emperature of approximately ~00F
prior to pouring of the mol-ten al:Loy. No release agen-t or other coating ma-terial was employed in the mold cavi-ty.
~he mold was filled, over a time period of approxi-mately 20-30 seconds, according to the method described above.
The mold was then allowed to stand :Eor approximately one minute while being sprayed with a water-air mixture to maintain its relatively low temperature (at leas-t at its outer surfaces1.
The mold was then opened and the anode removed.
The bottom of the anode, which was arranged adjacent the opening 28 of the mold (see Fig. 2) could then be trimmed if desired. However, as soon -thereafter as practicable, the anode was suspended in vertical alignment by the copper hanger bar and sprayed for approximately one-half minute on each side with an air-water mixture or until its temperature was lowered to the approximate range of 200-250F. .
The anode then exhibited a precipitate distribution and grain structure as illustrated in Figs. 7 and 8 with the anode surface having a "galvanized" or "rolled" appearance as illustrated in Fig. 9. :
The anode surface was not treated or conditioned, beyond the steps described immediately above, prior to preparation of the photograph in Fig. 9.
The anode was also not etched prior to the photo-micrographs cf Figs. 7 and 8, at 200x and 800x magnification respec-tively. However, to better illustrate both grain structure and precipitate distribution, the anode surface was polished with a commercial diamond powder. It is believed .
32~
that the polishlng powder picked up fine calcium particles from -the precipita-tes which in turn caused very fine scra-tches on the anode surface. Such a scratch is par-ticularly no-ted commencing midway along the leEt side of Fig. 8 and extending upwardly ancl rightwardly to approximately the center of -the photomicrograph. Such scratches are not to be confused with observable grain boundaries which are presen-t to only a minimum degree in anodes prepared by the method of the present invention. An observable grain boundary may be detected in the highly magnified surface of Fig. 8, noting the short and Eine dark line in the upper right corner.
The finished anode was found to have an average densi-ty of 11.214 grams/cc and a calcium content of 0.028% by wgt. calcium.
The grain structure and precipitate distribu-tion illustrated by Figs. 7 and 8 and the surface finish illus-trated by Fig. 9, although specifie to the binary anode deseribed immediately above, are believed applieable to a wide range of lead alloy compositions, particularly those including calcium as an alloying agent in the approximate range of 0.01-0.1~ by wgt.
Example No. 2:
This example rela-tes to an anode and method of preparation differing from the limi-ts of Example No. 1 as indieated below.
The alloy for Example No. 2 was selee-ted to include approximately eigh-t percent by weight of anti~ony, the remainder essentially lead except for normal impurities such as (in terms of percen-t by weight) silver-0.000~%, copper-0.0009%, zinc-0.0005%, arsenie-0.0003%, iron-0.0002% and bismuth-0.00014%.
.. ,~, .~
.. ~. .
;' ' '. ' ' 2~ii The above alloy has a meltincJ point of approximately 520F ancl a theoretical density of 10.7~ grams/cc. Such an alloy is hea-tecl to an approximate molten -tempera-ture of 600Or~' according to the present invention and thereafter processed as described above for Example No. 1.
The anode produced according to this ~xample No. 2 would exhibit many of the advantages set Eor-th above.
However, it was indica-ted above that certain characteristics are particularly due to -the inclusion of calcium as an alloying agent. Accordingly, even through the anode produced according to Example No. 2 does not prove to have equal characteristics as for an anode including calcium,Example No. 2 does illustra-te applicability to a broad range of alloys.
Example No. 3:
This example relates to an anode prepared according to the preceding method based on an alloy including approxi-mately 1.5% by wgt. silver, 1.0~ by wgt. tin, balance essen-tially lead except for normal impurities.
This alloy has a melting point of approximately 589F and a theoretical density of approximately 11.26 grams/cc.
Here again, the method of preparation differs from that described above for Example No. 1 only in the following respects.
The alloy is heated to a molten temperature of approximately 650~F and thereafter treated as described above for Example No. 1.
The anode of Example No. 3 is intended to particu-larly demonstrate applicability of the present method to more 30 complex alloys, such as the ternary composition described above. ~;
- , . .
,
When -the anocle is removed Erom -the mold, it i5 still at a re]atively hiqll tempera-tllre, posc;ibly :in the range of 500~. It h~s been Eound ~hat the conEigura-tion oE -the anode is relatively important from this time until the anode tem-perat~lre is at a relative:Ly low tempera-ture, possib:Ly 200F, at which temperature ~he anode -tends to become stable. The anode -tends to exhibit a "dimensional memory" whereby upon beiny Ereely suspended, it will tend to return to the shape in which it was config-lrecl during the final stages of cooling of such a lower temperature. Accordingly, the anode is preferably maintclined in a straight configuration and further cooled, for example, by spraying with an air-water mix-ture until it reaches the low temperature noted above. ~lterna-tively and preferably, the anode is suspended in a vertical position during this cooling step after its removal from the mold. For example, the anode may be readily suspended by the copper hanger bar during this step. With the anode being suspended in a vertical position, substantially no dimensional stresses are developed in the anode. Thus, after it is cooled, it tends to maintain its straight alignment or shape.
This of course is importan-t with-in the elec-trowinning bath to maintain a uniform gap between the anodes and cathodes and thereby enhance electrolytic action within the process.
It may be noted that, within the preceding method description, substantial importance is placed upon maintaining tempera-ture limits during certain stages of the anode forma-tion. It is believed apparen-t tha-t these temperature controls are primarily directed toward achieving complete filling of the mold cavity while limiting the amount of time within which the lead alloy remains molten after it enters the mold.
~i~c -29-,.. . . .
z~s After -the ano~le solidiLies and is removecl from the mold, rapi~l coolil~q of the a~ode is important both for the purpose of limiting further grain chancJe as we:Ll as to enhancc dimen-sional stability as described :immediately above.
Speci~ic Examples:
____ _ _ The followincJ specific examples are intended to set for-th exemplary limi-ts for various alloy composi-tions together with the correspondiny process parameters under which each of the alloy composition is formed in-to an :insoluble anode.
Example No. 1:
An anode of the size described above and having a configura-tion as illustrated in Fig. 3 (wi-thout perforations) was formed according -to the preceding method description using a ladle wi-th a gating arrangement illustrated in Fig. 5.
The lead alloy was selected as representative of a binary alloy including 0.01-0.1% by wgt. calcium, being I obtained in alloyed form as ingots containing 0.04-0.06 wgt.
-~ percent calcium,the remainder essentially lead except for normaI impurities of the type and amount specified above.
This specific alloy, having a melting poin-t of approximately 621.5F and a theoretical density of 11.34 grams/cc, is a commercial lead alloy obtained from St. Joe Minerals Corporation.
The alloy was heated in a gas-fired open furnace to a temperature range of ~75-700F and maintainea a-t that approximate temperature during a rela-tively shor-t dwell time (up to approximately 30 seconds) in -the ladle. The ladle was not heated be-tween pouring cycles bu-t was main-tained at a high temperature because of the shor-t time duration (approx-ima-tely 2 1/2-3 minutes) for each cycle.
.~
2~
~rhc mold, formed oE steel, was ma.inta:ined at a preheated or precooled -t:emperature of approximately ~00F
prior to pouring of the mol-ten al:Loy. No release agen-t or other coating ma-terial was employed in the mold cavi-ty.
~he mold was filled, over a time period of approxi-mately 20-30 seconds, according to the method described above.
The mold was then allowed to stand :Eor approximately one minute while being sprayed with a water-air mixture to maintain its relatively low temperature (at leas-t at its outer surfaces1.
The mold was then opened and the anode removed.
The bottom of the anode, which was arranged adjacent the opening 28 of the mold (see Fig. 2) could then be trimmed if desired. However, as soon -thereafter as practicable, the anode was suspended in vertical alignment by the copper hanger bar and sprayed for approximately one-half minute on each side with an air-water mixture or until its temperature was lowered to the approximate range of 200-250F. .
The anode then exhibited a precipitate distribution and grain structure as illustrated in Figs. 7 and 8 with the anode surface having a "galvanized" or "rolled" appearance as illustrated in Fig. 9. :
The anode surface was not treated or conditioned, beyond the steps described immediately above, prior to preparation of the photograph in Fig. 9.
The anode was also not etched prior to the photo-micrographs cf Figs. 7 and 8, at 200x and 800x magnification respec-tively. However, to better illustrate both grain structure and precipitate distribution, the anode surface was polished with a commercial diamond powder. It is believed .
32~
that the polishlng powder picked up fine calcium particles from -the precipita-tes which in turn caused very fine scra-tches on the anode surface. Such a scratch is par-ticularly no-ted commencing midway along the leEt side of Fig. 8 and extending upwardly ancl rightwardly to approximately the center of -the photomicrograph. Such scratches are not to be confused with observable grain boundaries which are presen-t to only a minimum degree in anodes prepared by the method of the present invention. An observable grain boundary may be detected in the highly magnified surface of Fig. 8, noting the short and Eine dark line in the upper right corner.
The finished anode was found to have an average densi-ty of 11.214 grams/cc and a calcium content of 0.028% by wgt. calcium.
The grain structure and precipitate distribu-tion illustrated by Figs. 7 and 8 and the surface finish illus-trated by Fig. 9, although specifie to the binary anode deseribed immediately above, are believed applieable to a wide range of lead alloy compositions, particularly those including calcium as an alloying agent in the approximate range of 0.01-0.1~ by wgt.
Example No. 2:
This example rela-tes to an anode and method of preparation differing from the limi-ts of Example No. 1 as indieated below.
The alloy for Example No. 2 was selee-ted to include approximately eigh-t percent by weight of anti~ony, the remainder essentially lead except for normal impurities such as (in terms of percen-t by weight) silver-0.000~%, copper-0.0009%, zinc-0.0005%, arsenie-0.0003%, iron-0.0002% and bismuth-0.00014%.
.. ,~, .~
.. ~. .
;' ' '. ' ' 2~ii The above alloy has a meltincJ point of approximately 520F ancl a theoretical density of 10.7~ grams/cc. Such an alloy is hea-tecl to an approximate molten -tempera-ture of 600Or~' according to the present invention and thereafter processed as described above for Example No. 1.
The anode produced according to this ~xample No. 2 would exhibit many of the advantages set Eor-th above.
However, it was indica-ted above that certain characteristics are particularly due to -the inclusion of calcium as an alloying agent. Accordingly, even through the anode produced according to Example No. 2 does not prove to have equal characteristics as for an anode including calcium,Example No. 2 does illustra-te applicability to a broad range of alloys.
Example No. 3:
This example relates to an anode prepared according to the preceding method based on an alloy including approxi-mately 1.5% by wgt. silver, 1.0~ by wgt. tin, balance essen-tially lead except for normal impurities.
This alloy has a melting point of approximately 589F and a theoretical density of approximately 11.26 grams/cc.
Here again, the method of preparation differs from that described above for Example No. 1 only in the following respects.
The alloy is heated to a molten temperature of approximately 650~F and thereafter treated as described above for Example No. 1.
The anode of Example No. 3 is intended to particu-larly demonstrate applicability of the present method to more 30 complex alloys, such as the ternary composition described above. ~;
- , . .
,
Claims (2)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An insoluble anode for use in the electro-winning of copper, the anode having a substantially flat configuration with an effective surface area on either side thereof of at least approximately 5 square feet, the anode being formed by a casting process from a lead alloy including approximately 0.01-0.1% by weight calcium, the anode being further characterized by substantially minimum porosity, a uniform precipitate distribution of PbCa3 in a lead matrix, the surface of the anode being continuous and smooth and further characterized by having a galvanized or rolled appearance.
2. An insoluble anode for use in the electro-winning of copper, the anode having a substantially flat configuration with an effective area on either side thereof of at least approximately 5 square feet, the anode being formed in a casting process by introduction of a molten lead alloy into a suitable mold, the finished anode having a composition including approximately 0.02-0.07% by weight calcium, the balance essentially pure lead except for normal impurities, the resultant anode being characterized by substantially minimum porosity and having a typical uniform precipitate distribution of PbCa3 in a lead matrix as illustrated in Fig. 7, the surface of the anode having a galvanized or rolled appearance as illustrated in Fig. 9.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA347,765A CA1103205A (en) | 1974-11-22 | 1980-03-17 | Insoluble anode for the electrowinning of copper |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US526,161 | 1974-11-22 | ||
| US05/526,161 US4050961A (en) | 1974-11-22 | 1974-11-22 | Method for casting anodes |
| CA239,754A CA1074527A (en) | 1974-11-22 | 1975-11-17 | Method and apparatus for casting anodes |
| CA347,765A CA1103205A (en) | 1974-11-22 | 1980-03-17 | Insoluble anode for the electrowinning of copper |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1103205A true CA1103205A (en) | 1981-06-16 |
Family
ID=27164198
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA347,765A Expired CA1103205A (en) | 1974-11-22 | 1980-03-17 | Insoluble anode for the electrowinning of copper |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1103205A (en) |
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4966235A (en) * | 1988-07-14 | 1990-10-30 | Canadian Occidental Petroleum Ltd. | In situ application of high temperature resistant surfactants to produce water continuous emulsions for improved crude recovery |
| US4978365A (en) * | 1986-11-24 | 1990-12-18 | Canadian Occidental Petroleum Ltd. | Preparation of improved stable crude oil transport emulsions |
| US4983319A (en) * | 1986-11-24 | 1991-01-08 | Canadian Occidental Petroleum Ltd. | Preparation of low-viscosity improved stable crude oil transport emulsions |
| US5000872A (en) * | 1987-10-27 | 1991-03-19 | Canadian Occidental Petroleum, Ltd. | Surfactant requirements for the low-shear formation of water continuous emulsions from heavy crude oil |
| US5083613A (en) * | 1989-02-14 | 1992-01-28 | Canadian Occidental Petroleum, Ltd. | Process for producing bitumen |
| US5156652A (en) * | 1986-12-05 | 1992-10-20 | Canadian Occidental Petroleum Ltd. | Low-temperature pipeline emulsion transportation enhancement |
| US5263848A (en) * | 1986-11-24 | 1993-11-23 | Canadian Occidental Petroleum, Ltd. | Preparation of oil-in-aqueous phase emulsion and removing contaminants by burning |
| CN113913870A (en) * | 2021-11-03 | 2022-01-11 | 昆明冶金研究院有限公司 | Anode plate for low-deformation high-electric-efficiency zinc electrolysis and preparation method thereof |
-
1980
- 1980-03-17 CA CA347,765A patent/CA1103205A/en not_active Expired
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4978365A (en) * | 1986-11-24 | 1990-12-18 | Canadian Occidental Petroleum Ltd. | Preparation of improved stable crude oil transport emulsions |
| US4983319A (en) * | 1986-11-24 | 1991-01-08 | Canadian Occidental Petroleum Ltd. | Preparation of low-viscosity improved stable crude oil transport emulsions |
| US5263848A (en) * | 1986-11-24 | 1993-11-23 | Canadian Occidental Petroleum, Ltd. | Preparation of oil-in-aqueous phase emulsion and removing contaminants by burning |
| US5156652A (en) * | 1986-12-05 | 1992-10-20 | Canadian Occidental Petroleum Ltd. | Low-temperature pipeline emulsion transportation enhancement |
| US5000872A (en) * | 1987-10-27 | 1991-03-19 | Canadian Occidental Petroleum, Ltd. | Surfactant requirements for the low-shear formation of water continuous emulsions from heavy crude oil |
| US4966235A (en) * | 1988-07-14 | 1990-10-30 | Canadian Occidental Petroleum Ltd. | In situ application of high temperature resistant surfactants to produce water continuous emulsions for improved crude recovery |
| US5083613A (en) * | 1989-02-14 | 1992-01-28 | Canadian Occidental Petroleum, Ltd. | Process for producing bitumen |
| CN113913870A (en) * | 2021-11-03 | 2022-01-11 | 昆明冶金研究院有限公司 | Anode plate for low-deformation high-electric-efficiency zinc electrolysis and preparation method thereof |
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