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 Mg included in the Al-based molten metal is set to be 0.2 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

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

Background Art

[0002] With the increasing awareness of environmental protection, the construction of a recycling-based society is being pursued. As part of this, the recycling of metal resources is being promoted. As an example, descriptions related to methods for recovering Cu can be found in the following documents.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent Document 1 uses a graphite rod (electrode) that bridges the contact interface between an Al-based molten metal (Al-0.7% Mg), a molten salt layer (NaCl + KCl + MgCl2) provided thereon, and deposits Cu from copper oxide (CuO) added to the molten salt layer onto the graphite rod for recovery.

[0005] Incidentally, when a (pure) copper piece is added to the molten salt layer instead of the copper oxide, the copper piece will float and disperse in the molten salt layer, settle at 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 its form. In such cases, efficient recovery of Cu is difficult.

[0006] The present invention has been made in view of such circumstances, and an object thereof is to provide a new method for recovering copper from recycled raw materials and the like.

Means for Solving the Problems

[0007] The inventors diligently researched the problem and discovered that the recovery efficiency of Cu changes significantly depending on the Mg concentration of the Al-based molten metal. By further developing this finding, the inventors completed the present invention described below.

[0008] 《Cu Recovery Method》 The present invention is a method for recovering copper, comprising a processing step of adding a recycled raw material containing a mixture of Al substrates and Cu substrates to a molten salt formed on an Al-based molten metal, and recovering copper by dissolving it into the Al-based molten metal while reducing the amount of Mg to 0.2% by mass or less relative to the entire Al-based molten metal.

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

[0010] Al alloy / Method of manufacturing it The present invention can also be understood as an Al alloy containing Cu (including molten metal) or a method for producing the same. The Cu incorporated into the Al-based molten metal can be separated as metallic copper (elemental), for example, by electrolysis. However, Cu is also a typical alloying element of Al alloys. For this reason, the Al-based molten metal containing Cu (Al-based molten metal after the processing step) may be used as a (recycled) Al alloy (ingot, molten metal, etc.) or as a raw material.

[0011] "others" (1) Unless otherwise specified, the concentration and composition referred to herein are the mass ratio (indicated as "%") to the total amount of the substance (molten metal, base material, etc.).

[0012] (2) The term "Al-based molten metal" as used herein does not specify any particular composition other than Mg, as long as Al is the main component (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 also be in a solid-liquid coexistence state (semi-molten state).

[0013] (3) Unless otherwise specified, "x~y" in this specification includes the lower limit x and the upper limit y. Any numerical value included in the various numerical values ​​or ranges of numerical values ​​described in this specification may be used to create a new lower limit or upper limit, such as a range "a~b". [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram showing the steps involved in recovering copper from recycled raw materials. [Figure 2] This graph shows the relationship between the Mg concentration in the molten aluminum and the Cu concentration recovered in the molten aluminum. [Modes for carrying out the invention]

[0015] One or more components, arbitrarily selected from this specification, may be added to the components of the present invention described above. The contents described herein may be methodological components or components relating to materials (e.g., recycled aluminum alloy (molten metal)).

[0016] 《Recycled raw materials》 The recycled material consists of a mixture of at least Al (alkaline alloy) and Cu (copper) substrates. The recycled material consists of, for example, shredded pieces (such as paper scraps). The form (shape and size) of the pieces is not specified, but the maximum length of a single piece is, for example, about 0.1 to 30 mm or 1 to 15 mm.

[0017] Such recycled materials are supplied from sources such as discarded heat exchangers and electronic / electrical equipment. Specifically, Al substrates (pieces) are obtained from, for example, the heat exchanger body consisting of tubes and fins, electronic circuit boards, and heat sinks. Cu substrates (pieces) are supplied from sources such as the piping of heat exchangers and the film-like or wire-like wiring (conductors) provided on circuit boards.

[0018] The composition of the Al substrate or Cu substrate pieces is not limited. The Al substrate may be a pure Al material or an Al alloy material. Also, the Cu substrate may be a pure Cu material or a Cu alloy material. However, when the Mg content in the whole recycled raw material is 0.2 mass% (simply referred to as “%”) or less, 0.15% or less, and further 0.1% or less, the recovery of Cu can be stably and efficiently carried out.

[0019] 《Molten Al Bath》 The molten Al bath preferably has a Mg concentration of 0.2% or less, less than 0.2%, 0.18% or less, 0.15% or less, 0.1% or less, 0.05% or less at least before the treatment process (before adding and charging the recycled raw material, etc.). The lower limit value of the Mg concentration is not limited, but if we have to say, Mg may be 0.01% or more, 0.03% or more. In this specification, the molten Al bath before the start of the treatment process (before adding the recycled raw material) is appropriately referred to as the “molten bath before treatment”.

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

[0021] The component composition of the molten Al bath may vary depending on the type and amount of the recycled raw material added during the treatment process, the time of the treatment process, etc., but it is preferable that the Mg concentration is maintained within the above-mentioned range. However, if the Mg content in the recycled raw material (especially the Mg concentration in the Al substrate) is sufficiently small (for example, 0.2% or less, and further 0.1% or less), the Mg concentration of the molten Al bath is also maintained low during the treatment process, and the recovery of Cu by the molten Al bath can be stably and efficiently carried out.

[0022] 《Molten Salt》 The molten salt may be made of, for example, stable metal halides (especially chlorides and / or bromides) as raw materials. The metal elements constituting the halides are, for example, one or more of Ca, Na, Li, Sr, K, Mg, Cs, Ba, etc. Halides of Na and / or K are inexpensive and stable and are 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. By adjusting the composition (adjustment of components) of the molten salt, it is possible to adjust the melting temperature, density, etc. At a minimum, the molten salt should have a lower density (specific gravity) than the Al-based molten metal. Note that the molten salt may be a single layer or multiple layers.

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

[0025] Processing steps The processing step involves adding or introducing the recycled material to the molten salt (layer) covering the surface of the Al-based molten metal (molten metal before processing). The recycled material may be added continuously or intermittently. The processing step may be carried out while stirring the Al-based molten metal and / or the molten salt, or it may be carried out while standing still. The processing time (the time from adding the recycled material to removing the Al-based molten metal) is, for example, 1 to 180 minutes or even 10 to 90 minutes.

[0026] The Al-based molten metal after the processing step (referred to as "processed molten metal" as appropriate) may be removed intermittently or continuously. The processed molten metal may be used as is, or it may be used after its composition has been adjusted, or it may be used after solidification. [Examples]

[0027] As a concrete example of the present invention, we conducted the following experiment assuming a scenario in which Cu is recovered from shredded pieces of a heat exchanger equipped with fins and tubes made of pure Al and piping made of pure Cu. This clarified the relationship between the Mg concentration in the Al-based molten metal and the Cu concentration recovered in that 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 Four types of Al-based molten metal (pre-treatment molten metal) with different Mg concentrations were prepared. The specific compositions of each molten metal were pure Al (0% Mg), Al-0.2% Mg, Al-0.4% Mg, and Al-0.6% Mg. The Mg concentration is the mass ratio of Mg to the total molten metal. Commercially available pure Al and pure Mg (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 dissolve it. In this way, 50g each of Al-based molten metal with different Mg concentrations was prepared.

[0029] (2) Molten salt A mixed salt (100g) of sodium chloride (44g) and potassium chloride (56g) was placed in an alumina crucible (B3, manufactured by Nikkatoh Co., Ltd.) and heated in a furnace to 720°C (melting temperature) until completely dissolved. Thus, a molten salt (100g) 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 molten aluminum 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-layer processing bath was formed in the alumina crucible, with the molten aluminum (lower layer) on top of the molten salt (upper layer).

[0031] (4) Recycled raw materials Ten grams of shredded material (piece material) was prepared, which contained a mixture of pure aluminum pieces (al-based / approximately 1-10 mm square) and pure copper pieces (copper-based / approximately 1-10 mm square). These shredded pieces were actual waste fragments, and the proportion (mass percentage) of copper pieces was approximately 9-12%.

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

[0033] Observation of the treatment bath revealed that some of the recycled material was finely dispersed in the molten salt, while the remainder 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 process). Specifically, this was done by gently tilting the alumina crucible to drain only the upper layer of molten salt.

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

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

[0037] "evaluation" As is clear from Figure 2, it was found that the lower the Mg concentration of the Al-based molten metal before processing, the higher the Cu concentration incorporated from the recycled raw material. This trend was particularly pronounced when the Mg concentration was 0.2% by mass or less.

[0038] From the above, it has been confirmed that the present invention allows for the efficient recovery of Cu contained in recycled raw materials by incorporating it into the Al-based molten metal.

Claims

1. The process includes adding a recycled raw material containing a mixture of Al and Cu base materials to a molten salt formed on an Al-based molten metal. A method for recovering Cu by dissolving it into the Al-based molten metal, wherein the amount of Mg is 0.2% by mass or less relative to the entire Al-based molten metal.

2. The Cu recovery method according to claim 1, wherein the recycled raw material has an Mg content of 0.2% by mass or less relative to its total volume.

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

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

5. A method for recovering Cu according to any one of claims 1 to 4, wherein the Al-based molten metal after the above processing step is used as a recycled Al alloy.

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