AU2005202863B2

AU2005202863B2 - Method for producing sheet-form electrolytic copper

Info

Publication number: AU2005202863B2
Application number: AU2005202863A
Authority: AU
Inventors: Hiroo Tsuchiya
Original assignee: Nippon Mining and Metals Co Ltd
Current assignee: Nippon Mining Holdings Inc
Priority date: 2004-09-06
Filing date: 2005-06-29
Publication date: 2006-11-30
Anticipated expiration: 2025-06-29
Also published as: AU2005202863A1

Description

S&FRef: 726238

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: Nippon Mining Metals Co., Ltd., of 10-1, Toranomon 2 chome, Minato-ku, Tokyo, 105-0001, Japan Hiroo Tsuchiya Spruson Ferguson St Martins Tower Level 31 Market Street Sydney NSW 2000 (CCN 3710000177) Method for producing sheet-form electrolytic copper The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845c Method for Producing Sheet-form Electrolytic Copper BACKGROUND OF INVENTION S1. Field of Invention The present invention relates to production of metallic copper, more Sparticularly to an electrowinning method for producing a sheet-form, dense electrolytic \O 00 copper from halide solution.

S2. Description of Related Art The electrowinning method is broadly implemented commercially for Sproducing metallic copper. SX-EW (solution extraction electrowinning method) is a representative method implemented at present for producing metallic copper mainly from oxide ores. The copper solution yielded by the sulfuric acid leaching is purified by various processes to prepare a refined and concentrated copper electrolyte containing sulfuric acid. Instead of the sulfuric acid leach liquor, the halide leach liquor such as a chloride bath has been developed for electrowinning of copper Japanese Patent No.

2,857,830).

The halide leaching is advantageous in the following points.

Sulfide ores, which are poor reactive, can be leached by utilizing elementary chlorine or bromine or its compounds. The elementary chlorine or the like are formed by the anodic oxidation of the electrowinning and is strongly oxidizing.

The leach liquor, which contains halides at a high concentration, enables stable dissolution of mono-valent copper ions. The electrolyzing of the monovalent copper ions can, therefore, be realized. The electric quantity required for the electrolysis of the monovalent copper is as low as a half that of the divalent copperions dissolved in the sulfuric acid bath.

The ionic conductivity and exchange current density are high. The current efficiency, therefore, does not lower seriously at high current density and hence the productivity is high.

However, in the case of electrowinning from the halide solution, the metallic copper electrolytically deposits in the form of a dendritic powder or aggregated coarse grains. In the case of the SX-EX method using the sulfuric-acid bath, the copper electrolytically deposits in the form of a sheet. Such a sheet can be separated from the cathode as a cathodically deposited copper and sold as it is.

The metallic copper deposited from the halide solution involves complicated handling processes, such as in withdrawal from the electrolytic cell,

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washing, casting in the form of a commercial product, and the like. In addition, even if o the washing is repeated, since the copper powder is liable to be oxidized, the properties of Z a product are deteriorated.

00 In order to eliminate the drawbacks involved in the electrowinning from the chloride bath, experiments have been carried out to discover the conditions to obtain Cc smooth electrolytic product in the electrolyzing of the monovalent ions. However, the 00 electrolytic deposits from the halide bath, such as the chloride bath have strong tendency Sto grow dendritically or form a number of nodules, as compared with the case of Selectrolytic deposition from the sulfuric acid electrolyte. Although such additives as glue and gelatin are effective for refining and smoothening the electrolytically deposited product in the sulfuric acid bath, in order to attain similar effects in the case of operation of the halide bath, the additive content must be increased ot as high as a few g/L which lowers the current density. Practical conditions are unknown for extended production of dense and smooth electrolytically deposited copper.

Summary of Invention The present invention relates to an electrowinning method of metallic copper from the halide solution, which is advantageously performed by electrolysis of monovalent ions and the saving of electric power. It is an object of the present invention to improve the electrowinning method in such a manner that dense and sheet-form electrolytic copper is produced at a practical current density. The sheet-form electrolytic copper has improved washing property and handling property such as in withdrawal from an electrolytic cell.

The present inventors discovered that polyethylene glycol (PEG) among various additives is especially effective to suppress the dendritic growth of electrolytic copper and is also effective to densify the structure of electrolytic copper. The present invention is based on this discovery and provides the following methods.

A method for producing dense sheet-form electrolytic copper, wherein the electrowinning of metallic copper from the halide copper-electrolyte is carried out in the halide electrolyte, which contains a polyethylene glycol additive as a smoothening agent, and which is stirred in the vicinity of the cathode, wherein the additive polyethylene glycol has an average molecular weight in the range of from about 600 to about 4,000 and is added at a concentration of about 5mg/L to about 1,000mg/L.

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I A method for producing dense sheet-form electrolytic copper according to (1) o above, wherein the copper-halide electrolyte contains not less than 3 mol/L of alkali metal Z chloride, alkali metal bromide or a mixture of the alkali metal chloride and bromide as a 00 bearing salt, and also dissolves copper in the form of chloride or bromide.

A method for producing dense sheet-form electrolytic copper according to (1) Cc or wherein the additive polyethylene glycol has an average molecular weight in a

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00oO range of from 1,000 to 2,000 and is added at a concentration of 1 Omg/L to A method for producing dense sheet-form copper according to through t wherein gas stirring or mechanical stirring is carried out to stir the halide electrolyte in the vicinity of the cathode surface.

The advantages obtained by the present invention are as follows.

Since the electrolytic copper deposited from the halide solution has dense structure, the collecting of powder is unnecessary, but the electrolytic copper in the form of a sheet is separated from the cathode mother plate.

The electrolytic deposit can be satisfactorily washed to eliminate contamination, while preventing the oxidation on the surface. The qualities of the product are, therefore, improved.

Homogenous electrolytic deposit can be stably obtained ever for a long period of 24 hours or longer.

Preferred embodiments of the present invention are hereinafter described with reference to the drawings, in which a predetermined amount of polyethylene glycol is added into a copper-halide electrolyte.

Brief Description of Drawings Figure 1 illustrates an electrowinning method of copper according to the present invention.

Figure 2 illustrates the results of Example 1 (O10mg/L of added PEG), particularly the appearance of electrolytic copper and SEM image of the cross-section.

Figure 3 illustrates the results of Example 4 (1,000mg/L of added PEG), particularly the appearance of electrolytic copper and SEM image of the cross-section.

Figure 4 illustrates the results of Comparative Example 1 (no addition of PEG), particularly the appearance of electrolytic copper and SEM image of the cross-section.

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C1 Figure 5 illustrates the results of Example 2 (10mg/L of added PEG, but no addition O of stirring) particularly the appearance of electrolytic copper and SEM image of the cross- Z section.

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00 R:\LIB ZZ] 726238cai ms.doc:gym V DESCRIPTION OF PREFERRED EMBODIMENTS ;Referring to Fig. 1, an embodiment of the method according to the present invention is illustrated.

SThe electrolyte used for electrowinning of copper from the halide solution is acidic, particularly pH 1-3 to enable copper leaching and to prevent precipitation of the basic salt and monovalent copper halides. High concentration of halogenated 00 alkali, such as sodium chloride, as the bearing salt, enables to stable dissolution of the monovalent copper halogen-complex in the leached copper-liquor. In order to attain Ssatisfactory high solubility of copper complex ions, the concentration of the bearing salt should be 3mol/L or more, preferably 4mol/L or more and less than the saturation N solubility.

The electrolysis of the monovalent copper is carried out by using a diaphragm electrolysis method, in which the anode and cathode chambers are separated by a filter cloth 2. Referring to Fig. 1, 1 denotes an electrolytic cell, 3 denotes an anode, and 4 denotes a cathode. The liquor directly after the ore leaching contains appreciable amount of divalent copper ions, because the copper ions in such liquor may be oxidized due to air oxidation or the leaching reactions may be insufficient. The divalent copper ions incur undesired consumption of cathode current, which upsets the balance between the cathode and anode reactions during the electrolysis. The liquor directly after the ore leaching is, therefore, preliminarily transferred to a reducing tank, and the metallic copper added in the reducing tank reduces the divalent copper ions to monovalent copper ions. The so-treated liquor is fed to the cathode chamber of the electrolytic cell 1. The polyethylene glycol additive 8 is preliminarily mixed with the fed electrolyte 7 and is then fed into the cathode chamber. Alternatively, the polyethylene glycol additive may be directly fed into the cathode chamber. The additive is stirred and mixed in the cathode chamber.

In order to prevent air oxidation of the catholyte, inert gas such as nitrogen and argon is blown into the catholyte to stir it.

The polyethylene glycol additive used has an average molecular weight, which indicates the polymerization degree, in a range of from 600 to 4,000, preferably from 1,000 to 2,000. When the molecular weight is less than 600, the effect of such a low-molecular weight polymer on densifying the electrolytic deposit is poor and is not practical. On the other hand, when the molecular weight is more than 4,000, although the electrolytically deposited product is generally dense, the deposit is liable to grow in the form of a number of nodules or unevennesses around the edges of the cathode, where the current concentrates. High molecular weight polyethylene glycol is, therefore, inappropriate for continuous operation over a long period of time.

;Appropriate concentration of the additive is dependent upon the electrolytic conditions. Generally, dense electrolytic copper is obtained under the additive concentration in a range of from 5 to 1,000mg/L. Extremely high concentration of the additive is not only ineffective for improving the surface qualities of the electrolytic copper but also incurs such problems as increase of the reagent cost, 0 embrittlement of the electrolytic copper, and accumulation of organic matters in the electrolyte. Practically, satisfactory effects are obtained by the additive in the V) concentration of from 10 to S 10 Productivity is enhanced at higher current density. However, considerably high current density results in non-uniform current distribution on the cathode surface. Effectiveness of the additive for preventing the dendrite formation is, therefore, limited to the current density being kept within an appropriate range. In order to attain the productivity of copper electrolysis in the halide bath comparable with that of the copper electrolysis in the sulfuric bath under 280 to 320A/m 2 of current density, the current density of the monovalent copper electrolysis should be approximately 150A/m 2 Thus, effects of the additive to form satisfactorily dense electrolytic copper are not impaired at a level of the latter current density.

The electrolyte is maintained at a temperature to attain high solubility of the respective components of the electrolyte, including the bearing salt. Desirably, the entire electrolytic cell is warmed in order to implement the electrolysis in a compact cell.

The concentration of the bearing salt and hence the concentration of copper ions can be high enough so that the electrolysis can be carried out in such compact cell. However, when the temperature of the electrolyte is very high, problems may occur in that the grain size of the deposit becomes larger, the abnormal deposition tends to occur, and the additive may decompose. Appropriate temperature of the electrolyte is in a range of from 40 to The catholyte must be stirred by means of for example a stirring plate 6 so as to produce the dense electrolytic copper. When no stirring is carried out, the concentration gradient is formed in the catholyte and seriously impairs the effects of the additive, that is, densification and smoothening of the electrolytic copper. The effects of the additive are attributable to strong adhesion of the polyethylene glycol on the surface of the electrolytic copper. The additive contained in the electrolyte in contact with the cathode surface moves toward the cathode surface and adheres there. As a result, the concentration of the additive in the electrolyte in contact with the cathode surface decreases to form a diffusion layer. Upon formation of the diffusion layer, the

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diffusion becomes the rate-determining step of feeding of the additive toward the ;cathode surface. The additive becomes, then, non-effective for densification and smoothening of the electrolyte copper. Consequently, the catholyte in the vicinity of C the cathode is stirred to eliminate the diffusion layer. Intensity of the stirring should, therefore, be such as to flow the electrolyte in the very vicinity of the cathode surface.

The very vicinity of the cathode surface herein indicates a range of within 1 to 2mm 00 from the cathode surface. Inert gas is sparged into the catholyte to form bubbles in the 0 vicinity of the cathode. The inert gas can maintain the cathode compartment in the inert condition as described above. Alternatively, a direct mechanical stirring may be carried out, such that the electrolyte is circulated by a pump or the electrolyte is caused to flow by means of a stirrer as shown in Fig. 1.

The cathode 4 is made of material, such as titanium, having satisfactory corrosion-resistance against the halide copper-electrolyte. After completing the electrolysis, the electrolytic copper 5 is peeled from the cathode 4. Alternatively, a copper mother plate is used to deposit the electrolytic copper on it as in the case of the production of electrolytic copper using the sulfuric acid bath. The electrolytic copper and the copper mother-plate are cast together in the form of product. The appearance and structure of the electrolytic copper are virtually unaffected by the underlying material except for only during the initial period of electrolytic deposition.

As is described hereinabove, the present invention utilizes the advantages of the monovalent electrolysis, and hence electric-power-saving, and simultaneously produces dense electrolytic copper which has improved handling performance.

EXAMPLES

Example 1 The additive, polyethylene glycol (the average molecular weight 1,000) was added to the halide copper-electrolyte (the concentration of halogenated alkali Metallic copper pieces were added to the so-prepared copper electrolyte, and the copper electrolyte was heated and stirred at 600C. During this process, the electrolyte cell was covered by a top plate which prevented air flow on to the surface of the electrolyte bath. The divalent copper ions were thus preliminarily reduced to monovalent ions. The pH was then adjusted to 1.

An electrolytic cell was provided with a diaphragm made of acid-resistant filter cloth (trade name Tetron). The electrolyte was admitted in the electrolytic cell and was maintained at a temperature of from 57 to 600C. A cathode located in a cathode chamber of the electrolytic cell is a titanium plate having a 100 mm square

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effective surface. An anode located in the anode chamber was an insoluble anode made of a titanium plate, on which an iridium compound is applied and baked. Argon gas was blown upwards from beneath the cathode and the catholyte in the neighborhood of C the cathode was stirred without interruption. Current of 1.5A corresponding to 150A/m 2 of the current density was conducted.

C) The electrolyte, composition of which is shown in Table 1, was continuously fed 00 into the cathode chamber. The copper concentration in the cathode chamber was 0 maintained at approximately 25g/L. Current conduction was carried out for 24 hours.

ln During the current conduction, the monovalent copper ions in the anode chamber were oxidized to divalent ions, and the concentration of the copper ions in the anode chamber was maintained at 25g/L as well. As shown in Fig. 2, the electrolytically deposited copper on the cathode had dense sheet-form structure.

Table 1 Example 1 Comparative Example 1 Electrolyte Fed Electrolyte Electrolyte Fed Electrolyte NaC1 280g/L 280g/L 280g/L 280g/L NaBr 28g/L 28g/L 28g/L 28g/L CuCl 39g/L 117g/L 39g/L 117g/L (Cu 25g/L) (Cu Additive (polyethylene 10mg/L 10mg/L Omg/L Omg/L glycol #1,000) Example 2 In the present example, the concentration of the salts was the same as in Example 1. The additive polyethylene glycol used in the present example had various degrees of polymerization. The concentration of the additive was constant at 10mg/L The electrowinning was carried out for 6 hours under the same current and stirring conditions. As shown in Table 2, the densification effects are recognized at the molecular weight of 600 or greater. The electrolytic copper having improved appearance was obtained, when the average molecular weight is from 1,000 to 2,000.

Table 2 Average Molecular Weight of Appearance and Properties of Electrolytic Copper Polyethylene glycol 300 X Meshwork form as a whole. No densification 600 A Electrolytic deposition in the meshwork form near the cathode edges.

1,000 O Dense and uniform as a whole 1,500 O Dense and uniform as a whole 2,000 O Dense and uniform as a whole 4,0000 O-A Dense as a whole. A considerable number of nodules on the edges.

20,000 A Dense. A number of nodules on the edges are considerable.

Dk: 150A/m 2 60C, 6 hours of the electrolysis. Concentration of the additive Example 3 Example 2 was repeated, except that the additive polyethylene glycol (PEG) used had 1,000 of average molecular weight. The electrowinning was carried out for 6 hours. As shown in Table 3, the concentration of the additive for attaining the densification of the electrolytic deposits is 5 mg/L or more, preferably 10 mg/L or more.

Table 3 Concentration of Additive Appearance and Properties of Electrolytic Copper (PEG #1,000)(mg/L) 2 X Deposition in the form of meshwork O~-AAlmost dense, a considerable number of nodules are formed on the edges.

O Dense and uniform as a whole O Dense and uniform as a whole 1,000 O -A Dense as a whole, somewhat brittle Dk: 150A/m 2 60°C, 6 hours of the electrolysis.

Example 4 In the present examples, the electrowinning was carried out for 24 hours, using the same electrolyte as in Example 1, except that: the average molecular weight of the polyethylene glycol was 1,000; and its concentration was 1,000 mg/L. As shown in Fig. 3, the electrolytic copper obtained in the present example had appearance virtually as dense as in Example 1. However, the electrolytic copper was so hard as a whole. It was, therefore, somewhat difficult to peel the electrolytic copper from the cathode.

'4 Comparative Example 1 ;As shown in Table 1 of Example 1, the additive was not added but the concentration of the other reagents was the same as in Example 1. The electrolytic and stirring conditions were the same as in Example 1. The electrowinning was carried out for 24 hours. As shown in Fig. 4, the electrolytic copper had unevennesses in the form of nodules on the entire surface. Washability of the electrolytic copper was poor.

00 When the electrolytic copper was peeled from the cathode, the copper was easily broken

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into fragments.

Comparative Example 2 C Example 1 was repeated, except that the stirring was not carried out. The electrowinning was carried out for 6 hours. Directly after the electrolytic deposition, the deposition state became non-uniform. Dendritic nodules frequently formed locally on the deposited copper. It turned out that the additive was not effective for densification.

Claims

2. A method for producing dense sheet-form electrolytic copper according to claim 1, wherein the copper-halide electrolyte contains not less than about 3 mol/L of alkali metal chloride, alkali metal bromide or a mixture of the alkali metal chloride and bromide as a bearing salt, and also dissolves copper in the form of chloride or bromide.
3. A method for producing dense sheet-form electrolytic copper according to claim 1 or 2, wherein the additive polyethylene glycol has an average molecular weight in a range of from about 1,000 to about 2,000 and is added at a concentration of about lOmg/L to about
4. A method for producing dense sheet-form copper according to any one of claims 1 to 3, wherein gas stirring or mechanical stirring is carried out to stir the halide electrolyte in the vicinity of the cathode surface. A method for producing dense sheet-form electrolytic copper comprising the steps substantially as hereinbefore described with reference to the accompanying drawings.
6. Dense sheet-form electrolytic copper produced by the method of any one of claims 1 to Dated 31 October, 2006 Nippon Mining Metals Co., Ltd. Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON ri3-\I IU'77T71/:T10