Method for producing copper ingot

Abstract

To provide a method for obtaining a copper ingot from cutting chips in which aluminum wires are mixed in copper wires.SOLUTION: A method for producing a copper ingot according to the present invention includes an oxidation step of preheating cutting chips of a copper wire in which an aluminum wire is mixed at a first temperature at which the aluminum wire does not melt to oxidize the aluminum wire, a melting step of heating the cutting chips after the oxidation step at a second temperature at which the copper wire melts to obtain molten copper, and a solidification step of cooling the molten copper to obtain a copper ingot. In the oxidation step, for example, dispersion such as stirring of the cutting chips after the preheating may be performed in parallel with or alternately with the preheating. The cutting chips are obtained from, for example, a wire harness. The aluminum wire in the cutting chips is contained in an amount of, for example, 3 to 50 mass% with respect to the total amount of the aluminum wire and the copper wire.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for obtaining copper ingots from copper wire cutting waste. [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 factors such as the increase in electric vehicles, and its recycling is becoming increasingly important. For this reason, various methods for recovering or recycling (refining) copper from recovered copper scrap have been proposed, and for example, the following patent documents contain related disclosures: [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2012-87376 [Patent Document 2] Patent Publication No. 2016-180164 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Documents 1 and 2 describe the recycling of copper wires (or electric wires). In Patent Document 1, waste copper wires are heated and melted in a shaft furnace. In Patent Document 2, crushed electric wire chips are put into an aqueous solution of ferric sulfate and stirred for six hours to dissolve them.

[0005] None of the patent documents anticipates the possibility that aluminum wires, which will increase in number in the future, will be mixed in with the copper wire scraps, and naturally, there is no description or suggestion regarding this point.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a method for recovering copper in a lump form even from cutting scraps of copper wires containing aluminum wires. [Means for solving the problem]

[0007] As a result of intensive research, the inventors have newly discovered that high-purity copper ingots can be recovered from cutting scraps containing aluminum wire by preheating the wire so that the wire is oxidized without melting it. By expanding on this finding, the present invention, which will be described below, has been completed.

[0008] <<Method for manufacturing copper ingots>> (1) The present invention is a method for producing copper ingots, comprising an oxidation step in which cutting chips of copper wire mixed with aluminum wire are preheated at a first temperature at which the aluminum wire does not melt, thereby oxidizing the aluminum wire; a melting step in which the cutting chips after the oxidation step are heated at a second temperature at which the copper wire melts, thereby obtaining molten copper; and a solidification step in which the molten copper is cooled to obtain a copper ingot.

[0009] (2) According to the copper ingot manufacturing method (also referred to as the "recovery method") of the present invention, copper ingots can be efficiently obtained from copper wire cutting waste. The reasons for this are currently thought to be as follows.

[0010] Even if scraps of copper wire mixed with aluminum wire (also called "copper nuggets") are simply heated (called "main heating") to a second temperature (for example, above the copper melting point) at which the copper wire melts, it is not easy to obtain an ingot in which the copper wire has melted and solidified.

[0011] On the other hand, prior to melting the copper wire, the aluminum wire is heated (called "preheating") at a first temperature (for example, below the melting point of aluminum) at which it does not melt, to fully oxidize the aluminum wire (fine pieces). When this preheated copper nugget is heated (called "main heating") to a second temperature (for example, above the melting point of copper) at which the copper wire melts, a high-purity copper ingot is obtained. The mechanism behind this is presumed to be as follows.

[0012] When a copper nugget containing an aluminum wire is rapidly heated to the second temperature, the aluminum wire, which has a lower melting point than the copper wire, melts during the process. The molten aluminum spreads over the surface of the copper wire (flakes), coating the copper wire. When aluminum in this state (e.g., layered or film-like) is oxidized, the surface of the copper wire is surrounded (covered) by an aluminum oxide layer, resulting in a composite wire (flake) with a core (copper wire)-shell (aluminum layer) structure. Because aluminum oxide, a ceramic, has a much higher melting point than copper and excellent insulating properties, the copper wire is thermally protected by the aluminum oxide. Thus, simply heating a copper nugget containing an aluminum wire to the second temperature likely would have resulted in the copper wire retaining its original shape and no copper ingot being obtained from the cutting waste. Furthermore, the molten aluminum that spreads over the surface of the copper wire can react with oxygen near the surface of the copper wire to form aluminum oxide, even when heated in a non-oxidizing atmosphere.

[0013] However, when the aluminum wire is preheated at a first temperature that does not melt it, as in the present invention, the aluminum wire, which is more easily oxidized than copper wire, becomes mostly aluminum oxide. Even if the preheated cutting chips are heated to a second temperature, almost no aluminum liquid phase is produced, and the above-mentioned core-shell structure composite wire is hardly produced. Therefore, it is thought that the main heating makes it possible to melt the copper wire, and the resulting molten copper (copper liquid phase) is cooled and solidified to obtain a copper ingot.

[0014] Salvaged Materials The present invention may be understood as a recovered copper material (copper ingot, etc.) obtained by the above-described method.

[0015] "others" (1) In this specification, "copper (wire)" or "aluminum (wire)" does not limit the specific composition of the components. It may be a pure metal (wire) or an alloy (copper alloy, aluminum alloy) containing other components (including impurity elements).

[0016] The origin (source) of the copper or aluminum wire does not matter, but for conductors that require high electrical conductivity, pure copper or pure aluminum with a purity of 98% by mass or more, 99% by mass or more, or 99.5% by mass or more is usually used.

[0017] Also, aluminum oxide, which is produced when aluminum wire is oxidized, does not have a specific composition or structure. Although it depends on the heating conditions (including atmospheric conditions), the main component of aluminum oxide is usually considered to be alumina (Al2O3).

[0018] (2) The oxidation process (preheating) and the melting process (main heating) should be at least conceptually separate. Cooling may be interposed when transitioning from the oxidation process to the melting process, or each process may be performed continuously without cooling. It is preferable to perform a process in which the aluminum wire is oxidized almost entirely without melting it. By adjusting and combining the heating rate and atmosphere, the oxidation process and melting process can be performed according to various heat patterns.

[0019] (3) 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]

[0020] [Figure 1] 1 is a photograph showing the appearance of cutting chips of Sample 1 and the state after heating and cooling. [Figure 2] 10 is a photograph showing the appearance of cutting chips of sample C1 and the state after heating and cooling. [Figure 3] 10 is a photograph showing the appearance of cutting chips of sample C2 and the state after heating and cooling. DETAILED DESCRIPTION OF THE INVENTION

[0021] 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.

[0022] 《Cutting waste》 Cutting waste (copper nuggets) consists of granular or powdery pieces cut from scrap (waste) wire (copper wire, aluminum wire).

[0023] 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.

[0024] The source of the wire (scrap) is not important, but examples include wire harnesses, coils (windings) of armatures (motors, etc.), household electric wires, etc. Regardless of the type and degree of sorting, the cutting waste may contain elements other than Cu and Al (C, O, Si, Al, Mg, Fe, etc.) and scraps (coating scraps, residue, etc.).

[0025] The main component of the cutting waste (50 mass % or more, 65 mass % or more, or even 80 mass % or more of the total) is copper wire (fine pieces). Even if the cutting waste is sorted in advance, it is difficult to avoid the inclusion of aluminum wire, so the aluminum wire may be contained in an amount of, for example, 3 to 50 mass % or 5 to 30 mass % of the total of aluminum wire and copper wire.

[0026] 《Oxidation process》 In the oxidation process, the cutting chips are preheated to a first temperature at which the aluminum wire does not melt, thereby oxidizing the aluminum wire. The first temperature may be lower than the melting point of aluminum (wire). Even if the first temperature is low, oxidation of the aluminum wire will proceed, but a long treatment time will be required. The first temperature may reach, for example, 450 to 650°C, 500 to 630°C, or 550 to 615°C. Preheating may be performed by holding the maximum preheating temperature (first temperature) for a predetermined time, or by heating while continuously increasing the temperature to the maximum temperature. To ensure oxidation of the aluminum wire, a predetermined time may be ensured in a high temperature range where oxidation is promoted (for example, from the maximum temperature -100°C to the maximum temperature). The rate of temperature increase to the desired temperature is not important, but in a low temperature range (for example, less than the maximum temperature -100°C), heating may be performed slowly at a small temperature increase.

[0027] In the oxidation step, the heating may be stopped (by allowing the material to cool naturally or by starting forced cooling) after the material is maintained at a desired first temperature (within the temperature range) for a predetermined time. After the oxidation step, the material may be heated to a second temperature and then subjected to a melting step in which the material is heated.

[0028] The oxidation step (preheating) is performed, for example, in an oxidizing atmosphere (such as air). The treatment time is appropriately adjusted taking into consideration the treatment amount (amount of cutting waste, amount of aluminum), the first temperature reached, the rate of temperature rise, and the oxidizing atmosphere (oxygen concentration, etc.). The treatment time from the start of heating to the end of heating (start of cooling) is, for example, 5 to 120 minutes, 10 to 60 minutes, or 15 to 30 minutes.

[0029] Since the aluminum wire is dispersed in the cutting chips, it is advisable to disperse (process) the cutting chips by crushing or stirring them after preheating (after reaching the desired temperature) depending on the processing amount (amount of cutting chips), etc. Preheating and dispersion may be performed in parallel (for example, heating while stirring) or alternately (for example, heating → crushing / mixing → heating → crushing / mixing). This promotes the oxidation of the aluminum wire.

[0030] <Melting process> In the melting process, the cutting chips after the oxidation process are heated to a second temperature at which the copper wire melts to form molten copper. The second temperature may be equal to or higher than the melting point of copper (wire). A higher second temperature leads to increased input energy and equipment costs. Therefore, the second temperature is, for example, 1085 to 1250°C, 1090 to 1150°C, or 1095 to 1125°C. The heating may be continued for a predetermined time within such a temperature range, or may be terminated (cooling may begin) after the second temperature reaches a desired temperature. Such heating may be repeated depending on the melting of the cutting chips.

[0031] The time required for the melting step is adjusted appropriately taking into consideration the processing amount (amount of cutting waste, amount of aluminum radiation) and the heating method, and is preferably 30 to 120 minutes, 40 to 90 minutes, or 50 to 75 minutes, for example.

[0032] The melting step (main heating) may be carried out in any atmosphere, including an oxidizing atmosphere such as air, or a non-oxidizing atmosphere such as an inert gas (Ar, N2, etc.) atmosphere or a vacuum atmosphere.

[0033] The aluminum oxide mixed in the molten copper may be separated from the molten copper by floating, coagulation, etc. Such separation is achieved, for example, by stirring the molten copper (including the semi-solidified state and the slurry state) during the melting process.

[0034] 《Coagulation process》 In the solidification process, the liquid phase material (including a solid-liquid coexistence state / simply referred to as "molten copper") obtained in the melting process is cooled to form a copper ingot. The copper ingot may have aluminum oxide, copper oxide, etc. attached to its upper surface or periphery. Cooling may be natural cooling or forced cooling. The cooling atmosphere may be either an oxidizing or non-oxidizing atmosphere. The copper lump obtained from the copper nugget is reused, for example, as a copper source. The copper lump may be used for any purpose, for example, as a raw material for various copper-based components (not limited to wire rods) or as a source of alloy elements. [Example]

[0035] The present invention will be described in more detail based on this specific example.

[0036] [Sample preparation] <Sample 1> (1) Cutting waste Discarded wire harnesses (scrap) were crushed to rice-grain size using a crusher, and then coated materials were removed using a magnetic separator, a vibrating sieve, and a wet specific gravity separator to obtain cutting chips (copper nuggets: wire diameter 0.2-0.4 mm, length 1-5 mm). Measurement using an X-ray fluorescence elemental analyzer revealed that the cutting chips consisted of Cu and Al, with Al accounting for 13.4 mass% of the total (Cu + Al).

[0037] (2) Oxidation The cutting chips (120 g) were placed in a graphite crucible, as shown in Figure 1. The cutting chips in the crucible were treated in the atmosphere according to the following heating pattern.

[0038] First, the temperature inside the heating furnace containing the crucible was raised from room temperature to 600°C at a rate of approximately 15°C / min (first preheating). After reaching 600°C, the cutting chips inside the crucible were removed from the heating furnace and manually stirred with a graphite rod for approximately 1 minute (first dispersion).

[0039] The crucible was returned to the heating furnace and heated to 600°C. This took approximately 20 minutes (second preheating). After the temperature reached 600°C, the crucible was removed from the heating furnace and the cutting chips in the crucible were manually stirred with a graphite rod for approximately 1 minute (second dispersion).

[0040] (3) Melting The crucible containing the chips after the oxidation process was returned to the heating furnace and heated to 1100°C (main heating). This took about 60 minutes. The chips became molten (slurry-like) as a result of the main heating.

[0041] While the crucible was kept at 1100°C in the heating furnace, the mixture was manually stirred for about 1 minute using a graphite rod, causing the aluminum oxide, which has a low specific gravity, to float (separate) onto the molten copper.

[0042] (4) Coagulation The crucible was removed from the heating furnace and allowed to cool naturally. This resulted in the molten material in the crucible solidifying into an ingot. The appearance of the resulting ingot and its cross section are shown in Figure 1.

[0043] <Sample C1> The graphite crucible containing the same cutting chips (120 g) as those in Sample 1 was heated in a heating furnace from room temperature to 1200°C at a rate of approximately 20°C / min. The inside of the heating furnace was a vacuum atmosphere (absolute pressure: 10 -1 The pressure was set at 100 Pa or less. After that, the chips were allowed to cool to room temperature in the vacuum atmosphere. The appearance of the chips before and after heating is shown in Figure 2.

[0044] <Sample C2> Cutting chips (60 g) consisting of pure copper wire were separately prepared. This cutting chip was subjected to the same heat treatment as sample C2. The appearance of the cutting chip before and after heating is shown in Figure 3.

[0045] [Sample evaluation] First, as can be seen from Figure 3 (sample C2), when the cutting chips consisted only of pure copper wire, they were entirely melted by heating above the Cu melting point, and a copper ingot with a glossy surface was obtained.

[0046] Next, as can be seen from Figure 2 (sample C1), the cutting scraps containing aluminum wire did not melt like sample C2, even when heated in the same way. In the case of sample C1, although the surface turned slightly whitish, the copper wire fragments remained, maintaining their original shape. In other words, the cutting scraps became a calcined body (sintered body) in which the copper wire fragments were bonded together via the aluminum, and no copper ingot was obtained.

[0047] On the other hand, as can be seen from Figure 1 (Sample 1), when the cutting chips, which were made by almost completely oxidizing the aluminum wire in advance, were heated above the melting point of the copper wire, the shape of the copper wire (flakes) disappeared and they became molten and solidified into an ingot.

[0048] The outer surface of the ingot was black, but the cut surface exhibited the luster characteristic of high-purity copper. In other words, by processing like Sample 1, a copper ingot could be obtained even from a copper nugget containing aluminum wires.

[0049] The black areas formed on the outer surface of the copper ingot were oxides of Al and Cu. The oxides were aggregated on the surface of the copper ingot, and were not dispersed or mixed in the copper ingot. In other words, it was found that copper nuggets with separated oxides were obtained.

[0050] One of the reasons for obtaining such copper ingots is thought to be the influence of the stirring performed during the melting process. Immediately after melting began, the molten copper (liquid phase) contained aluminum oxides and was in a highly viscous state, but the stirring caused the oxides, which have a low specific gravity, to float near the surface of the molten metal and agglomerate, which is thought to have led to the separation of the copper nuggets from the oxides.

[0051] Thus, it was confirmed that the present invention makes it possible to produce a copper ingot from a copper nugget containing an aluminum wire.

Claims

1. an oxidation step of preheating scraps of copper wires containing aluminum wires at a first temperature at which the aluminum wires do not melt, thereby oxidizing the aluminum wires; a melting step of heating the cutting chips after the oxidation step at a second temperature at which the copper wire melts to obtain the molten copper; a solidification step of cooling the molten copper to obtain a copper ingot; A method for manufacturing copper ingots comprising:

2. The method for producing copper ingots according to claim 1 , wherein the oxidation step includes dispersing cutting chips after the preheating step.

3. The method for producing copper ingots according to claim 2, wherein the oxidation step comprises performing the preheating and the dispersion in parallel or alternately.

4. A method for producing copper ingots as described in claim 1, wherein the first temperature reached is 450 to 650°C.

5. The method for producing copper ingots according to claim 1 , wherein the melting step includes separating aluminum oxide mixed in the molten copper.

6. A method for producing copper ingots as described in claim 1, wherein the second temperature reached is 1085 to 1250°C.

7. 2. The method for producing copper ingots according to claim 1, wherein the aluminum wire is contained in an amount of 3 to 50 mass% of the total of the aluminum wire and the copper wire.

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

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