AU2007249133A1

AU2007249133A1 - Method of countermeasure against interruption of electric power in electrolytic refining of copper

Info

Publication number: AU2007249133A1
Application number: AU2007249133A
Authority: AU
Inventors: Tomonari Goda; Shigeru Sasaki; Kazuaki Takebayashi
Original assignee: Nippon Mining and Metals Co Ltd; Nippon Mining Co Ltd
Current assignee: JX Nippon Mining and Metals Corp
Priority date: 2007-03-29
Filing date: 2007-12-19
Publication date: 2008-10-16
Anticipated expiration: 2027-12-19
Also published as: JP4343969B2; CN101275241A; CN101275241B; CL2007003862A1; JP2008248273A; AU2007249133B2

Description

Australian Patents Act 1990 Regulation 3.2 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention Title Method of countermeasure against interruption of electric power in electrolytic refining of copper The following statement is a full description of this invention, including the best method of performing it known to me/us:- P/00/011 5102

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BACKGROUND OF INVENTION 1. Field of Invention Cc The present invention relates to a method for electrolytic refining of copper, particularly to a countermeasure method against interruption of electric power in electrolytic copper-refining which employs a permanent cathode (hereinafter referred to 10 as 2. Background of Invention The present applicant had produced in NIKKO SMELTING REFINING CO., LTD. HITACHI REFINERERY (herein after referred to as "Hitachi Refinery") electrolytic copper by means of a conventional method using starting sheets. However, it was difficult to simultaneously attain high productivity and excellent qualities by the conventional method. Under these circumstances, the present applicant introduced the electrolytic method using a PC, to overcome the difficulties and also to drastically improve the suspension property of a cathode plate.

After introduction of the PC method, current efficiency was enhanced from the conventional one, approximately 94%, to 98%. The electrolysis capacity was increased from 182,000 tons/year to 210,000 tons/year, as well.

Hitachi Refinery, where the PC method was first introduced in Japan, has continued with almost trouble free operation. The PC method carried out in the Hitachi Refinery is ISA (Isa process) type, in which masking material (wax) is not used.

An edge-strip protector consisting of resinous material is formed on lateral sides of a cathode plate, provided with a V-shaped grooves on the bottom. The edge strip protector and the V-shaped groove contribute to effective peeling of the electrolytically deposited copper from the cathode.

Current is conducted through three rectifiers of 37kA/150V, 37kAJ90V and 37kAI30V of the Hitachi Refeinery to 644 electrolytic cells, in each of which 56 cathodes are mounted. Thus, one characteristic feature of an electrolytic refining plant of copper is large scale production of metal in a number of electrolytic cells, to which a large current is conducted.

Japanese Unexamined Patent Publication (kokai) 2006-265699 discloses an improved adhesion between the edge strip and a cathode plate employed in the PC method. However, this publication does not mention any countermeasure against a power cut in an electrolytic refining plant of copper.

DISCLOSURE OF INVENTION Since the electric transformer of an electrolytic copper-refining plant is maintained annually, electric power is cut off approximately once annually. The interruption lasts for 8 tol2 hours. In addition, interruption of electric power for approximately 8 hours may be carried out several times a year for construction of conductors and conduits and also for maintaining the electrolytic cells.

Referring to Fig. 1, is illustrated a cathode plate 1 provided with a V-shaped groove la on the bottom. When current conduction is resumed after an interruption of Oelectric power supply, the electrolytically deposited copper 3 is laminated on electrolytic copper 2, which has been deposited on a cathode plate 1 before electricity was cut off, as shown in Fig. 1. Fig. 2 illustrates a case where the interruption of electric power does not occur, while Fig. 3 illustrates a case where the interruption of electric power has occurred. Both figures show a lower part of an electrolytically deposited and then peeled copper sheet. In Fig. 2, a crack 2a is formed on the electrolytically deposited copper 2, at a position corresponding to the V-shaped groove la (Fig. Therefore, the c'.ctrolytically deposited copper 2 can be cracked and divided into two halves, the center of which is positioned at the V-shaped groove la. In Fig.3, the copper 3 that is electrolytically deposited after resumption of flow of current (hereinafter referred to as second electrolytic copper) is in the form of film and is deposited on the copper 2 that was electrolytically deposited before the electric power interruption (hereinafter referred to as the first electrolytic copper). When the electrolytically deposited copper is peeled, although the first and second electrolytic coppers 2 and 3, respectively, are bent as a whole, the second electrolytic copper 3 in the form of film is peeled from the first electrolytic copper 2 in the vicinity of the V-shaped groove la. The second electrolytic copper 3 merely peels but does not crack. It is, therefore, extremely difficult to divide the electrolytically deposited copper into two halves. The peeling of electrolytically deposited copper incurs reduction in productivity of electrolytic refining plant.

The interruption of electric power, such as that of an annual one, is planned in advance in an electrolytic copper-refining plant that uses the permanent cathode (PC).

When current flow is resumed after the interruption of electric power, copper is electrolytically deposited in the form film on the copper deposited before the interruption of electric power.

It is an object of the present invention to eliminate as much as possible the difficulty in peeling due to the deposition of the electrolytic copper in the form of film after the interruption of electric power.

In accordance with the objects of the present invention, there is provided an electrolytic refining method of copper by means of the PC method, characterized in that, when the interruption of electric power is planned, the stationary current, which has been conducted to electrolytic cells through a main rectifier permanently installed in an Melectrolytic refining plant to electrolytic cell, is moderately decreased, and, subsequently, low current is conducted to the electrolytic cell, from an auxiliary rectifier additionally installed in the electrolytic refining plant until the interruption of electric power is (-i S 10 restored. The low-current conduction until the restoration of electric-power

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Ointerruption is hereinafter referred to as the preliminary current conduction. The (-i present invention is, hereinafter, described in detail.

DESCRIPTION OF PREFERRED EMBODIMENTS Electrolytic refining of copper is carried out at a current density in the range of from approximately 250 to 320 A/m 2 of a cathode surface. This is the stationary current conduction. When electric power is interrupted, since the current density of the electrolytic cells abruptly decreases to zero, the electrolytic copper (the first electrolytic copper) is then exposed to the sulfuric acid-based electrolyte for 8 to 12 hours. When the stationary current conduction is resumed, the electrolytic copper (the second electrolytic copper) deposits and is laminated on the first electrolytic copper.

Observation of the cross sectional structure of the laminated first and second electrolytic coppers reveals a streaked pattern, formed along the interface of the first and second electrolytic coppers, which pattern is produced as a result of interruption of electric power. The streaks become more distinct when the power outage is continued for longer time. It has been found that, when crystal growth resumed after the interruption of electric power, the grown crystals are inhomogeneous so that the streak-like flaws are formed.

Incidentally, in the case of unexpected or accidental interruption of electric power, it can be restored after approximately 4 hours at the longest. Peeling of electrolytic copper is not particularly hindered in this case.

The present inventors propose to operate an auxiliary rectifier 12 (Fig. 4) through an auxiliary power source, which is embodied for example as a power generator (not shown). The "low current" herein indicates a current density, at which virtually no electrolytic deposition occurs. The low current is preliminarily conducted from the auxiliary rectifier 2 preferably at a current density of from 10 to 40 Aim 2 However, surprisingly, such low current conduction is effective for resuming a homogenous crystal growth while preventing essentially formation of streak-like defects. When the supply of electric power is resumed, the main rectifier 13 is operated, and crystal growth occurs in such a manner that streak-like defects become less apparent.

When electric power is planned to be temporarily interrupted in an electrolytic plant, the current density must be moderately decreased by means of a controller M (Fig. 4) directly before the electric power is cut off. The current density is decreased from a stationary level to a preliminary level. In the present invention, "moderately" means that the speed of change in current density by means of the controller 15 is i 10 essentially slower than that of abrupt decrease to zero due to the interruption of electric

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Spower. In addition, "moderate" change is as slow as possible as the electric techniques can permit to control. Practically, it is preferred that the stationary current density be decreased to the preliminary current density for approximately two hours. After restoration of electric power, the electrodes are examined for such parameters as to the inter-distance and the like, following which the current density is restored to the stationary level. The restoration time is not particularly limited, but is preferably approximately two hours. Production of electrolytic copper is then started.

The following are some embodiments of the present invention.

A method according to claim 1, wherein the current density of preliminary current conduction is from approximately 10 to 40A/m 2 A method according to claim 1 or mentioned above, wherein the preliminary current conduction is carried out for 8 to 12 hours.

A method according to according to claim 1, item or mentioned above, wherein the current density is decreased from that of the stationary current conduction to the preliminary current conduction for approximately 1 to 3 hours.

A method according to claim 1, item or wherein the electrolyte is circulated during the preliminary current conduction.

The present invention attains the following advantages.

According to the present invention, it is possible to avoid the problem of electrolytic copper being difficult to peel from the cathode after interruption of electric power in an electrolytic copper refining plant. The advantages of the present invention are further described in terms of the actual operating results of the Hitachi Refinery.

Nevertheless, it is quite evident that if the present invention is implemented in any other electrolytic plants, the advantages of the present invention will be attained.

Productivity When electrolytic copper is deposited in the form of film, the peeling of electrolytic copper plate necessitates twice to five times longer than that required for (,i normal peeling of the electrolytic copper without film. Such problems can be avoided or mitigated by the present invention.

Qualities of copper starting plate Deposition of electrolytic copper in the form of film can be suppressed.

Appearance of electrolytic copper is acceptable.

BRIEF DESCRIPTION OF DRAWINGS Fig.1 schematically illustrates production of a starting sheet. Electric power S 10 is interrupted so that different copper layers grow before and after the interruption.

OFig. 2 illustrates that the starting sheet is peeled from a mother plate.

Fig.3 illustrates a similar situation of peeling as shown in Fig. 2, except that electric power is interrupted.

Fig. 4 is a schematic drawing of an electrolytic plant provided with a permanently installed rectifier and an additionally installed auxiliary rectifier.

Fig. 5 shows the metal structure of copper in Comparative Example.

Fig. 6 is a graph showing the change in electric current in Example.

Fig. 7 shows the metal structure of copper in Example.

EXAMPLE

Comparative Example In electrolytic refining of copper in the Hitachi Refinery provided with three rectifiers mentioned above, 12 -hour power cut off was planned and was actually carried out. The electrolytically deposited copper plates were allowed to be exposed in the electrolyte without circulation. After restoration of electric-power, stationary current conduction was again started. Therefore, the stationary current conduction was carried out twice. The metal structure of cross section of an electrolytic copper sheet is shown in Fig. 5. Defects in the form of streaks were formed at the interface of electrolytic copper layers deposited before and after the power cut off.

Example An auxiliary rectifier was installed in the Hitachi Refinery. A 12-hour power cut off was planned and carried out as in Comparative Example. The density of current from the main rectifiers was decreased as shown in Fig. 6. The actual interruption time of electric power was 10 hours. The preliminary current conduction was carried out at 10A/m 2 for 10 hours. Before and after the conduction of the preliminary current, switching off of the rectifiers and changing of the current density were carried out. The metal structure of the resultant electrolytic copper is shown in Fig. 7. The streak-like defects are considerably less apparent in the present invention than those produced in the comparative method.

INDUSTRIAL APPLICABIITY SSince the supply and demand of copper have been stringent recently, the enhanced productivity achieved by the present invention is advantageous for the copper smelting industry. When economic situations change so that supply and demand r- 10 requirements for copper become easier to meet, maintenance of electrolytic plants can be thoroughly carried out. The present invention is also advantageous for such a situation.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims

2. A method according to claim 1, wherein the current density of preliminary current conduction is from approximately 10 to 40A/m 2 10 3. A method according to claim 1 or 2, wherein the preliminary current conduction is carried out for 8 to 12 hours.
4. A method according to according to any one of claims 1 through 3, wherein the current density is decreased from that of the stationary current conduction to the preliminary current conduction for approximately 1 to 3 hours.
5. A method according to any one of claim 1 through 4, wherein the electrolyte is circulated during the preliminary current conduction.