JP7689540B2 - Cu recovery method - Google Patents

Description

The present invention relates to a method for recovering copper (Cu) from recycled raw materials.

As environmental awareness grows, 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 contains a description of a method for recovering Cu.

Patent Publication No. 2021-110026

In Patent Document 1, an Al-based molten metal (Al-0.7% Mg) is used, a molten salt layer (NaCl+KCl+MgCl ₂ ) is placed on the Al-based molten metal, and a graphite rod (electrode) bridges the contact interface between the two. Cu is recovered by precipitating it onto the graphite rod from copper oxide (CuO) added to the molten salt layer.

Incidentally, if (pure) copper pieces are added to the molten salt layer instead of the copper oxide, the copper pieces will, depending on their form, either float or 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. In such cases, it is difficult to efficiently recover Cu.

The present invention was made in consideration of these circumstances, and aims to provide a new method for recovering copper from recycled raw materials.

The inventors conducted extensive research to solve this problem and 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, they were able to complete the present invention, which is described below.

<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 an Al base and a Cu base 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.

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

<<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. Therefore, the Al-based molten metal containing Cu (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.

"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.).

(2) As used herein, the Al-based molten metal may have any specific composition other than Ca, so 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).

(3) Unless otherwise specified, "x to y" in this specification includes a lower limit of x and an upper limit of y. Any number 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."

FIG. 2 is a schematic diagram showing each step of recovering Cu from recycled raw materials. 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.

One or more components selected from this specification may be added to the components of the present invention described above. The contents described in this specification may be components related to a method or to an object (e.g., recycled Al alloy (molten metal)).

《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 shredder pieces). 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.

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

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

《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 material is 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 material is added) is appropriately referred to as the "molten metal before treatment".

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

The component composition of the Al-based molten metal may vary depending on the type and amount of 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 recovery using the Al-based molten metal will be stable and efficient.

Molten Salt
The molten salt may be prepared, for example, from a stable metal halide (particularly, chloride and/or bromide). The metal element constituting the halide may be, 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.

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.

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 be thick enough to immerse the recycled raw material (for example, a layer thickness of 3 mm or more, or even 10 mm or more).

Processing Steps
The treatment step is performed 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 performed while stirring the Al-based molten metal and/or the molten salt, or may be performed in a stationary state. The treatment time (the time from adding the recycled raw material to removing the Al-based molten metal) is, for example, 1 to 180 minutes, or further 10 to 90 minutes.

The removal of the Al-based molten metal after the treatment process (referred to as the "treated molten metal") may be intermittent or continuous. The treated molten metal may be used as is, may have its composition adjusted, or may be solidified and used.

As a specific example of the present invention, the following experiment was conducted, assuming a case in which Cu was 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 Ca concentration in the Al-based molten metal and the Cu concentration recovered in the Al-based molten metal. The present invention will be explained in more detail based on this specific example.

"experiment"
(1) Al-based molten metal Seven types of Al-based molten metal (molten metal before treatment) with different Ca concentrations were prepared. The specific compositions of the molten metals 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 the 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 metal with different Ca concentrations was prepared.

(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 to completely melt the salt. Thus, a molten salt (100 g) made of the mixed salt was prepared. The molar ratio of NaCl to KCl in the molten salt was approximately 1.

(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-layer treatment bath was formed in the alumina crucible, with the molten salt (upper layer) formed on the Al-based molten metal (lower layer).

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

(5) Treatment Step As shown in Fig. 1, first, the recycled raw material was slowly and gradually added to the treatment bath maintained at 720°C. The mixture was left to stand for 30 minutes without stirring.

When the treatment bath was observed, 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.

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 pour out only the upper layer of molten salt.

The Al-based molten metal (post-treatment molten metal) remaining at the bottom of the alumina crucible was then poured into a mold (stainless steel analytical mold) and allowed to cool naturally in the air and solidify. In this way, an ingot was obtained in which the Al-based molten metal after the treatment process had solidified.

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

"evaluation"
As is clear from Fig. 2, the lower the Ca concentration of the Al-based molten metal before treatment, the higher the Cu concentration taken in from the recycled raw material. This tendency was remarkable when the Ca concentration was 0.3 mass% or less (less than 0.3 mass%) and further 0.25% or less.

From the above, it has been confirmed that the present invention allows the Cu contained in the recycled raw material to be incorporated into the Al-based molten metal and efficiently recovered.

Claims (5)

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. 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. The Cu recovery method according to claim 1, wherein the recycled raw material consists of cut pieces of material. The Cu recovery method according to claim 1, wherein the molten salt is a mixed salt. A Cu recovery method according to any one of claims 1 to 4, in which the Al-based molten metal after the treatment process is used as recycled Al alloy.

Images