Cu recovery method

Abstract

To provide a method capable of efficiently recovering Cu from a recycled raw material such as scraps.SOLUTION: A Cu recovery method includes a treatment process of putting a recycled raw material with an Al base material and a Cu base material mixed together into a molten salt formed on an Al-based molten metal. If Ca included in the Al-based molten metal is set to be 0.3 mass% or less, Cu can be efficiently molten into the Al-based molten metal and recovered. The recycled raw material is, for instance, composed of piece materials obtained by cutting a heat-exchanger, etc. A mixed salt of sodium chloride and potassium chloride may be used for the molten salt, for instance. The Cu may be precipitated and recovered from the Al-based molten metal after the treatment process, or the Al-based molten metal may be used as it is for a recycled Al alloy or a raw material thereof.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for recovering copper (Cu) from recycled raw materials. [Background technology]

[0002] As environmental awareness increases, efforts are being made to build a recycling-oriented society. As part of this, the reuse (recycling) of metal resources is being promoted. As an example, the following document describes a method for recovering Cu. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-110026 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 describes an Al-based molten metal (Al-0.7%Mg) and a molten salt layer (NaCl+KCl+MgCl) placed on top of it. 2 The copper oxide (CuO) added to the molten salt layer is precipitated on the graphite rod and recovered by using a graphite rod (electrode) that bridges the contact interface between the two.

[0005] Incidentally, if (pure) copper pieces are added to the molten salt layer instead of the copper oxide, the copper pieces will float and disperse in the molten salt layer, sink to the bottom of the Al-based molten metal, or precipitate near the interface between the molten salt and the Al-based molten metal, depending on their morphology. In such cases, it is difficult to efficiently recover Cu.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a new method for recovering copper from recycled raw materials. [Means for solving the problem]

[0007] As a result of intensive research into solving this problem, the inventors have discovered that the efficiency of Cu recovery varies greatly depending on the Ca concentration in the Al-based molten metal. By expanding on this finding, the inventors have completed the present invention, which will be described below.

[0008] <Cu recovery method> The present invention provides a Cu recovery method that includes a process of placing a recycled raw material containing a mixture of Al and Cu base materials into a molten salt formed on an Al-based molten metal, reducing Ca to 0.3 mass% or less with respect to the entire Al-based molten metal, and dissolving Cu into the Al-based molten metal to recover it.

[0009] According to the present invention, Cu can be efficiently recovered by incorporating it into an Al-based molten metal from recycled raw materials containing a mixture of Al-based and Cu-based materials.

[0010] <Aluminum alloy / its manufacturing method> The present invention can also be understood as an Al alloy (including molten metal) containing Cu or a manufacturing method thereof. Cu incorporated in the Al-based molten metal can be separated as metallic copper (single element) by, for example, electrolytic deposition. However, Cu is also a representative alloying element of Al alloys. For this reason, the Al-based molten metal that has incorporated Cu (the Al-based molten metal after the treatment process) may be used as a (recycled) Al alloy (ingot, molten metal, etc.) or a raw material thereof.

[0011] "others" (1) Unless otherwise specified, concentrations and compositions in this specification are mass percentages (denoted as "%" as appropriate) relative to the entire object (molten metal, base material, etc.).

[0012] (2) In this specification, the Al-based molten metal may have any specific composition other than Ca, as long as it is mainly composed of Al (more than 50%). The Al-based molten metal may be substantially pure Al molten metal (Al: 98% or more, or even 99% or more). The Al-based molten metal may be in a solid-liquid coexistence state (semi-molten state).

[0013] (3) Unless otherwise specified, "x to y" in this specification includes a lower limit of x and an upper limit of 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 to create a new range such as "a to b." [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a schematic diagram showing each step of recovering Cu from recycled raw materials. [Diagram 2] 1 is a graph showing the relationship between the Ca concentration in an Al-based molten metal and the Cu concentration recovered in the Al-based molten metal. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The above-mentioned 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 components related to a method or a product (e.g., recycled Al alloy (molten metal)).

[0016] 《Recycled raw materials》 The recycled raw material is a mixture of at least an Al base material and a Cu base material. The recycled raw material is, for example, a piece of material that has been cut (such as a shredder piece). The form (shape and size) of the piece of material does not matter, but the maximum length of the piece is, for example, about 0.1 to 30 mm, or 1 to 15 mm.

[0017] Such recycled raw materials are supplied from, for example, discarded heat exchangers, electronic and electrical equipment, etc. Specifically, Al base materials (pieces) are obtained from, for example, heat exchanger bodies consisting of tubes and fins, electronic substrates, and heat sinks, etc. Cu base materials (pieces) are supplied from, for example, heat exchanger piping, film-like or wire-like wiring (conductors) provided on substrates, etc.

[0018] The composition of the Al substrate and the Cu substrate pieces does not matter. The Al substrate may be a pure Al material or an Al alloy material. The Cu substrate may be a pure Cu material or a Cu alloy material. However, when the Ca content of the recycled raw material is 0.3 mass% (simply referred to as "%) or less, 0.2% or less, or even 0.1% or less, Cu can be recovered stably and efficiently.

[0019] 《Al-based molten metal》 The Al-based molten metal may have a Ca concentration of 0.3% or less, less than 0.3%, 0.25% or less, 0.2% or less, 0.15% or less, 0.1% or less, 0.05% or less, or 0.03% or less at least before the treatment process (before the recycled raw materials are added or charged). There is no lower limit for the Ca concentration, but if necessary, the Ca concentration may be 0.005% or more, or 0.01% or more. In this specification, the Al-based molten metal before the start of the treatment process (before the recycled raw materials are added) is referred to as the "molten metal before treatment" as appropriate.

[0020] The molten metal before treatment may be a pure Al molten metal (which may contain unavoidable impurities), or may contain one or more alloying elements (other than Ca) that do not inhibit the recovery of Cu (incorporation into the molten metal).

[0021] The component composition of the Al-based molten metal may vary depending on the type and amount of the recycled raw material added during the treatment process, the treatment time, etc., but it is preferable that the Ca concentration be maintained within the above-mentioned range. However, if the Ca content in the recycled raw material (particularly the Ca concentration in the Al base material) is sufficiently small (for example, 0.3% or less, 0.2% or less, or even 0.1% or less), the Ca concentration of the Al-based molten metal will be maintained low during the treatment process, and Cu can be recovered stably and efficiently using the Al-based molten metal.

[0022] Molten Salt The molten salt may be made from, for example, a stable metal halide (particularly, chloride and / or bromide) as a raw material. The metal element constituting the halide may be, for example, one or more of Ca, Na, Li, Sr, K, Mg, Cs, Ba, etc. The halide of Na and / or K is inexpensive and stable, and is suitable for the molten salt.

[0023] The molten salt may be a mixed salt containing multiple types of metal halides. A typical example is a mixed salt of NaCl and KCl. The melting temperature, density, etc. can be adjusted by blending the molten salt (adjusting the components). It is preferable that the molten salt has at least a lower density (specific gravity) than the Al-based molten metal. The molten salt is not limited to a single layer, and may be a multi-layer.

[0024] The temperature of the molten salt should be at least equal to or higher than the melting temperature of the Al substrate (piece). The molten salt should have a sufficient thickness (for example, a layer thickness of 3 mm or more, or even 10 mm or more) to immerse the recycled raw material.

[0025] Processing Steps The treatment step is carried out by adding or pouring the recycled raw material into the molten salt (layer) covering the surface of the Al-based molten metal (molten metal before treatment). The recycled raw material may be added continuously or intermittently. The treatment step may be carried out while stirring the Al-based molten metal and / or the molten salt, or may be carried out while the Al-based molten metal is left to stand. The treatment time (the time from adding the recycled raw material to taking out the Al-based molten metal) is, for example, 1 to 180 minutes, or further 10 to 90 minutes.

[0026] The removal of the Al-based molten metal after the treatment step (properly referred to as the "treated molten metal") may be intermittent or continuous. The treated molten metal may be used as it is, may be used after its composition is adjusted, or may be used after being solidified. EXAMPLES

[0027] As a specific example of the present invention, the following experiment was carried out assuming a case where Cu was recovered from shredded pieces of a heat exchanger having fins and tubes made of pure Al and piping made of pure Cu. This clarified the relationship between the Ca concentration in the Al-based molten metal and the Cu concentration recovered in the Al-based molten metal. The present invention will be described in more detail based on this specific example.

[0028] "experiment" (1) Al-based molten metal Seven types of Al-based molten metals (molten metal before treatment) with different Ca concentrations were prepared. The specific compositions of each molten metal were pure Al (Ca 0%), Al-0.05%Ca, Al-0.08%Ca, Al-0.1%Ca, Al-0.2%Ca, Al-0.3%Ca, and Al-0.5%Ca. The Ca concentration is the mass ratio of Ca to the entire molten metal. Commercially available pure Al and pure Ca (reagent) were used as raw materials for the molten metal. Each weighed raw material was placed in a graphite crucible (manufactured by TYK Corporation) and heated in a furnace to 720°C (melting temperature) to completely melt it. In this way, 50g of Al-based molten metals with different Ca concentrations were prepared.

[0029] (2) Molten salt A mixed salt (100 g) of sodium chloride (44 g) and potassium chloride (56 g) was placed in an alumina crucible (Nikkato Corporation B3) and heated to 720°C (melting temperature) in a furnace until it was completely melted. Thus, a molten salt (100 g) consisting of the mixed salt was prepared. The molar ratio of NaCl to KCl in the molten salt was approximately 1.

[0030] (3) Treatment bath The Al-based molten metal in the graphite crucible was gently poured into the molten salt in the alumina crucible. Due to the difference in specific gravity between the two, a two-layered treatment bath was formed in the alumina crucible, with the molten salt (upper layer) on top of the Al-based molten metal (lower layer).

[0031] (4) Recycled raw materials 10 g of shredded pieces (piece material) containing a mixture of pure Al pieces (Al base material / approximately 1-10 mm square) and pure Cu pieces (Cu base material / approximately 1-10 mm square) were prepared. These shredded pieces were actual waste fragments, and the Cu fraction (mass ratio) was approximately 9-12%.

[0032] (5) Treatment process As shown in Figure 1, first, the recycled raw material was slowly and gradually added to the treatment bath held at 720°C. It was left to stand for 30 minutes without stirring.

[0033] Observation of the treatment bath revealed that a portion of the recycled raw material was finely dispersed in the molten salt, while the remainder was dissolved in the Al-based molten metal.

[0034] Next, only the molten salt containing fine dispersed particles was removed from the treatment bath (molten salt removal step). Specifically, the alumina crucible was gently tilted to pour out only the upper layer of molten salt.

[0035] Furthermore, the Al-based molten metal (treated molten metal) remaining at the bottom of the alumina crucible was poured into a mold (stainless steel analytical mold) and allowed to solidify by natural cooling in the air. Thus, an ingot was obtained in which the Al-based molten metal after the treatment process had solidified.

[0036] "analysis" The Cu concentration in each ingot was analyzed by X-ray fluorescence spectroscopy (XRF). Figure 2 shows the relationship between the Ca concentration in the molten metal before treatment and the Cu concentration in the ingot that solidified from the molten metal after treatment.

[0037] "evaluation" As is clear from Figure 2, the lower the Ca concentration of the Al-based molten metal before treatment, the higher the Cu concentration absorbed from the recycled raw material. This tendency was remarkable when the Ca concentration was 0.3 mass% or less, or even 0.25% or less.

[0038] From the above, it was confirmed that according to the present invention, Cu contained in the recycled raw material is incorporated into the Al-based molten metal and efficiently recovered.

Claims

1. The method includes a process of inserting a mixed recycled raw material containing an Al base material and a Cu base material into a molten salt formed on an Al-based molten metal, The Cu recovery method comprises adjusting the Ca content to 0.3 mass % or less relative to the entire Al-based molten metal, and dissolving Cu in the Al-based molten metal to recover it.

2. The Cu recovery method according to claim 1 , wherein the recycled raw material has a Ca content of 0.3 mass % or less relative to the total amount of the recycled raw material.

3. The Cu recovery method according to claim 1 , wherein the recycled raw material is made of cut pieces of material.

4. The Cu recovery method according to claim 1 , wherein the molten salt comprises a mixed salt.

5. The Cu recovery method according to any one of claims 1 to 4, wherein the Al-based molten metal after the treatment step is utilized as a recycled Al alloy.

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