Method for manufacturing pure copper

Abstract

To provide a method for recovering high-purity copper from copper wire being a scrap.SOLUTION: A method for manufacturing pure copper comprises an electrodeposition step in which a compact formed by compression-molding cutting wastes of copper wires is used as an anode side and the compact is electrified in electrolyte solution to allow copper to be deposited on a body to be deposited on a cathode side. The cutting wastes consist of fine pieces having a wire diameter: 10 to 1000 μm and length: 1 to 100 mm, for example. The cutting wastes are obtained from a wire harness, for example. The compact has relative density of 90% or more which is a ratio of apparent density to copper density, or is obtained by compressing the cutting waste at 400 MPa or more, for example. The electrolyte solution is copper sulfate aqueous solution, for example. The cathode is pure copper, for example. According to the present invention, high-purity copper can be obtained from scrap while suppressing power consumption.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for producing pure copper. [Background technology]

[0002] With the rise of a recycling-oriented society and a recycling-oriented economy, resource recycling has been attracting attention. For example, the use of copper, a main conductive material, is increasing due to the increase in electric vehicles, etc., and the importance of its recycling is increasing. For this reason, various methods have been proposed for recycling (refining) high-purity copper from recovered copper scrap, and for example, the following patent documents contain related descriptions. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2001-181883 [Patent Document 2] Patent Publication No. 2005-42161 [Patent Document 3] Patent Publication No. 2005-42162 [Patent Document 4] Patent Publication No. 2009-35801 [Patent Document 5] Patent Publication No. 2012-87376 [Patent Document 6] Patent Publication No. 2016-180164 [Patent Document 7] Patent Publication No. 2017-203182 [Patent Document 8] Patent Publication No. 2017-203210 [Patent Document 9] Patent Publication No. 2019-157160 Summary of the Invention [Problem to be solved by the invention]

[0004] Of the above documents, Patent Documents 5 and 6 describe the recycling of copper wire (or electric wire). Patent Document 5 describes melting waste copper wire by heating it in a shaft furnace. Patent Document 6 describes dissolving pulverized electric wire chips by adding them to an aqueous ferric sulfate solution and stirring for six hours. These methods involve increased energy consumption and higher costs for facilities and processing.

[0005] Incidentally, in Patent Document 1, the residue used in the electrolytic refining of blister copper is placed in a basket and immersed in an electrolyte to refine copper from the residue. Although this method can be applied to coarse, lumpy residues, it cannot be applied to fine copper wire cutting chips that tend to float in the electrolyte.

[0006] The present invention has been made in view of the above circumstances, and has as its object to provide a method for efficiently recovering copper from copper wire cutting waste. [Means for solving the problem]

[0007] As a result of intensive research, the inventors have succeeded in recovering pure copper by electrodeposition using a compact made by compressing cutting chips as an anode. By expanding on this achievement, the present invention, which will be described below, has been completed.

[0008] <Conductive material> The present invention is a method for producing pure copper, which includes an electrodeposition step in which a compact obtained by compressing copper wire scraps is used as the anode, and current is passed through an electrolyte to deposit copper on a depositing body as the cathode.

[0009] According to the method for producing pure copper (also referred to as the "recovery method") of the present invention, high-purity copper can be obtained from copper wire cutting waste (copper nuggets) while suppressing power consumption.

[0010] 《Recycled copper》 The present invention may also be understood as copper (recycled copper, pure copper) obtained by the above-mentioned production method.

[0011] "others" Unless otherwise specified, "x to y" in this specification includes a lower limit value x and an upper limit value y. Any numerical value included in the various numerical values ​​or numerical ranges described in this specification may be used as a new lower limit or upper limit value to create a new range such as "a to b." Also, "x to y mm" in this specification means x mm to y mm. The same applies to other unit systems. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a schematic diagram showing an electrodeposition step using a compact as an anode. [Figure 2] 1 is a graph showing the change over time in the voltage applied between the electrodes in the electrodeposition step. [Figure 3] 1 is a table showing the composition of cutting waste and electrodeposits. [Figure 4] FIG. 1 is a schematic diagram showing the state in which cutting chips are placed in a basket (anode side) and electrodeposited. DETAILED DESCRIPTION OF THE INVENTION

[0013] The above-described components of the present invention may be supplemented with one or more components selected from the present specification. The contents described in the present specification may be method-related components or product-related components.

[0014] <<Molded body>> The molded body is made by compression molding copper wire scraps. Copper is not only highly conductive but also highly ductile, so the cut (shredded) copper wire (slivers) become closely intertwined with each other through pressure molding, do not easily crumble, and reduce contact resistance between them. Therefore, the molded body of the present invention has excellent shape retention and a low overall apparent electrical conductivity (electrical conductivity).

[0015] The strips have a wire diameter of, for example, 10 to 1000 μm, 50 to 600 μm, or 100 to 400 μm. Their lengths are, for example, 1 to 100 mm, 4 to 50 mm, or 6 to 10 mm. These lengths are determined, for example, as the arithmetic mean value of the measured dimensions of approximately 10 randomly selected strips.

[0016] The compact must have enough shape retention to hold the small pieces without collapsing, and its apparent density (relative density) and compacting pressure are not important. 3 The relative density, which is the ratio of the apparent density of the compact to the total density (approximately), is, for example, 70 to 99%, 80 to 98%, or 90 to 96%. The higher the density of the compact, the more it can suppress the collapse of small pieces and reduce the power required for the electrodeposition step (energy saving).

[0017] The molding pressure for the cutting chips is, for example, 100 to 1000 MPa, 300 to 900 MPa, or 400 to 700 MPa. Excessive molding pressure increases the equipment costs and processing costs.

[0018] 《Cutting waste》 The cutting waste is in the form of granules or powder obtained by cutting copper wire (scrap). The copper wire (scrap) may come from any source, such as wire harnesses, coils (windings) of armatures (motors, etc.), or household electric wires. The copper wire referred to in this specification is not limited to pure copper wire, but may be one recovered from waste. In other words, the copper wire may contain Cu as its main component, and may also contain or adhere a large amount of various elements (C, O, Si, Al, Mg, Fe, etc.) and scraps (coating residue, residue, etc.) other than Cu. Specifically, the Cu content of the copper wire or cutting waste relative to the total amount is preferably 40% by mass or more, 50% by mass or more, or even 60% by mass or more.

[0019] The method of cutting the copper wire is not limited. The cutting chips and the compact may contain foreign matter such as coating material, but the higher the proportion of copper wire, the better. The cutting chips may contain Cu, for example, 40 mass % or more, 50 mass % or more, or even 60 mass % or more relative to the total. The copper wire itself may contain elements other than Cu. Usually, the impurities (Ni, Sn, Pb, etc.) in the copper wire itself are, for example, 5 mass % or less, or even 3 mass % or less relative to the total.

[0020] 《Electrodeposition process》 In the electrodeposition process, the compact acts as the anode and the target body acts as the cathode in an electrolytic solution, and electricity is passed through the compact. 2+ is dissolved, and Cu is precipitated on the surface of the deposition target.

[0021] Any electrolyte (electrolytic bath) may be used, but for example, an aqueous solution of copper sulfate, which is inexpensive and easy to handle, may be used. The electrolyte may contain additives, etc.

[0022] The material and form of the deposition target are not critical as long as Cu can be stably deposited in the electrolytic solution. The deposition target may be a copper substrate, an aluminum substrate, an iron substrate (including stainless steel), a titanium substrate, or the like. If the objective is to recover copper, pure copper (electrolytic copper (tough pitch copper), oxygen-free copper, or deoxidized copper) is usually used as the deposition target. Pure copper may also be recovered from molded bodies (cutting chips) to plate the deposition target (substrate) with copper.

[0023] The copper ion concentration in the electrolytic solution is, for example, 0.1 to 2.5 mol / L or 0.5 to 1.5 mol / L. The temperature of the electrolytic solution is, for example, 5 to 60°C or 10 to 40°C.

[0024] For example, the current density is 1 to 50 A / dm 2 or 5~25A / dm 2 If the current density is too low, the electrodeposition rate will decrease, and the efficiency of refining (recovering) pure copper will fall. If the current density is too high, metals less noble than copper will be more likely to precipitate as impurities, which may increase power consumption. Note that impurities that are likely to be mixed into the deposit (electrodeposit) include metals with an electrode potential close to that of copper (nickel, tin, lead, etc.).

[0025] The purity of the copper recovered in the electrodeposition step is not critical, but it is preferably, for example, 98% or more, 99% or more, or even 99.9% or more. [Example]

[0026] Copper was recovered by electrodeposition from copper wire scraps. The present invention will be described in more detail based on this specific example.

[0027] <<Sample Preparation>> (1) Cutting waste Discarded wire harnesses (scrap) were crushed to the size of rice grains using a crusher, and then iron components and coating materials were removed using a magnetic separator, a vibrating sieve, a wet specific gravity separator, etc. to obtain cutting scraps (copper nuggets: wire diameter φ0.2 to 0.4 mm, length 1 to 5 mm).

[0028] (2) Molded object (anode) The cutting chips were placed in the cavity of a mold and pressed to obtain a rectangular columnar compact (6 mm × 10 mm × 55 mm). The molding pressure was changed for each sample, and Sample 1: 2 t / cm 2 (196MPa), Sample 2: 4t / cm 2 (392 MPa), Sample 3: 8 t / cm 2 The apparent density was also calculated from the dimensions and mass of the compact. The ratio (relative density) to the copper density (true density) was 76% for sample 1, 87% for sample 2, and 92% for sample 3.

[0029] (3) Depositing object (cathode) The deposition target was a strip cut from an oxygen-free copper plate (thickness: 0.3 mm). The area exposed to the electrolyte was limited to 20 mm × 30 mm by masking.

[0030] (4) Electrolyte The electrolyte used was an aqueous solution of copper sulfate [CuSO4: 220 g / L (1.38 mol / L)].

[0031] (5) Electrodeposition process As shown in Figure 1, the compact and the object to be deposited were immersed from above in an electrolyte (1 L) placed in a bath (beaker). A constant current was applied, with the compact as the anode and the object to be deposited as the cathode. The current value was 600 mA (current density: 10 A / dm 2 This current was applied for 10 minutes.

[0032] 《Measurement / Analysis》 (1) Voltage During the above-mentioned current application, the voltage applied between the anode (molded body) and the cathode (substrate to be deposited) was recorded, and a portion of the voltage (for the first 5 minutes) is shown in Figure 2.

[0033] (2) Ingredient composition The chemical composition of the electrodeposit formed on the surface of the substrate was analyzed using an X-ray fluorescence elemental analyzer. Furthermore, the chemical composition of the cutting chips was analyzed using a compact (forming pressure: 392 MPa) of the cutting chips before electrodeposition in the same manner as for the electrodeposits. The results are summarized in Figure 3.

[0034] "evaluation" (1) During the electrodeposition process, the compact did not collapse, and there was almost no floating chips in the electrolyte.

[0035] (2) As is clear from Figure 2, the higher the density of the compact formed under high pressure, the lower the applied voltage required for the electrodeposition process, resulting in greater power savings. However, the density of the compact and the compacting pressure did not have a significant effect on power consumption.

[0036] (3) As can be seen from Figure 3, the Cu content of the cutting chips was approximately 65% ​​by mass. On the other hand, the deposits (electrodeposits) on the deposition target side all had a Cu content of 99.9% by mass (purity: 99.9%), which was sufficiently high purity copper, regardless of the density of the compact.

[0037] (4) For reference, we attempted the electrodeposition process by placing the cuttings directly into a basket made of an insoluble titanium substrate, as shown in Figure 4. However, the small pieces of cuttings passed through the mesh of the basket and floated or settled in the electrolyte, making it impossible to perform the electrodeposition process stably.

[0038] From the above, it was confirmed that according to the present invention, high-purity copper (electrolytic copper) can be recovered from scrap copper wire.

Claims

1. A method for producing pure copper, which includes an electroplating process in which a compact made by compressing copper wire scraps is used as the anode, and electricity is passed through it in an electrolyte to deposit copper on the cathode.

2. 2. The method for producing pure copper according to claim 1, wherein the cutting chips include small pieces having a wire diameter of 10 to 1000 μm and a length of 1 to 100 mm.

3. The method for producing pure copper according to claim 1 or 2, wherein the cutting chips are obtained from wire harnesses.

4. 2. The method for producing pure copper according to claim 1, wherein the compact has a relative density, which is the ratio of the apparent density to the copper density, of 70% or more.

5. The method for producing pure copper according to claim 1 or 4, wherein the compact is obtained by pressing the cutting chips at 400 MPa or more.

6. 2. The method for producing pure copper according to claim 1, wherein the electrolytic solution is an aqueous solution of copper sulfate, and the cathode is made of pure copper.

Images