Metal remover

Abstract

One object is to provide a metal remover used when removing Mg from an aluminum alloy melt whose raw material is scrap or the like. The present invention provides a metal remover for forming a molten salt layer that absorbs Mg from an aluminum alloy melt. The metal remover contains: a specific metal element, which is one or more of Cu, Zn or Mn; a specific halogen element, which is one or more of Cl or Br; and Mg. The metal remover may also contain: a base halide, which serves as a base material for the molten salt layer; and a specific metal halide, which is a compound of a specific metal element and a specific halogen element. The specific metal element is one or more of Cu, Zn or Mn, and the specific halogen element is one or more of Cl or Br. When the molten salt layer formed using the metal remover contacts an aluminum alloy melt containing Mg, Mg is absorbed from the aluminum alloy melt side to the molten salt layer side and is effectively removed.

Description

Technical Field

[0001] The invention relates to a method for removing Mg from an aluminum alloy melt and related technologies. Background Art

[0002] As environmental awareness increases, lightweight aluminum parts are being used in a variety of fields. By using recycled scrap instead of virgin aluminum, energy consumption and environmental load can be reduced, promoting the use of aluminum parts.

[0003] However, when the scrap is melted, various elements other than Al tend to dissolve in the molten metal. In order to prepare a melt having a desired composition, it is necessary to remove the superfluous or excess elements from the molten metal after the scrap (also referred to as "Al alloy melt") is melted. It is necessary to remove the superfluous or excess elements from the raw material molten metal (also referred to as "molten Al alloy") obtained by melting the scrap. As an example, there is a description of Mg removal in the following literature.

[0004] Reference List

[0005] Patent Literature

[0006] Patent document 1: US4097270B

[0007] Patent Document 2: JP2007-154268A

[0008] Patent Document 3: JP2008-50637A

[0009] Patent Document 4: JP2011-168830A

[0010] Non-patent literature

[0011] Non-patent document 1: Journal of Japan Institute of Light Metals, Vol. 33 (1983), pp. 243-248

[0012] Non-patent document 2: Journal of the Japan Institute of Light Metals, Vol. 54 (2004), pp. 75-81 Summary of the invention

[0013] Technical issues

[0014] Patent Document 1 describes a method (a metal oxide method) in which an Al alloy melt containing Mg is reacted with silicon dioxide (SiO 2 ) (2Mg+SiO 2 →2MgO+Si) to remove Mg as MgO.

[0015] Patent Document 2 proposes a method in which particles containing aluminum borate (9Al2O3.2B2O3) are added to an Al alloy melt containing Mg so that Mg adheres to the particles and Mg is removed as a reaction product (MgAl2O4).

[0016] Patent Document 3 and Patent Document 4 propose a method in which powdered battery residues obtained by baking used dry batteries are added to a molten Al alloy containing Mg to remove Mg. The main components of the battery residues are ZnO and MnO2, and Mg is removed as a reaction product of these oxides with Mg (MgO, MgMn2O4 or MgMnO3). The chloride contained in the battery residues enhances the wettability of these oxides with the molten Al alloy and promotes the generation of reaction products. However, it should be noted that the battery residues of alkaline dry batteries have a lower chloride content than the battery residues of manganese dry batteries. In this regard, Patent Document 4 proposes adding a mixed salt of KCl and NaCl to the molten Al alloy to supplement the chloride.

[0017] The chlorine method and the flux method are described in Non-Patent Document 1 and Non-Patent Document 2. In the chlorine method, a gas such as chlorine, hexachloroethane or carbon tetrachloride blown into an Al alloy melt is reacted with Mg (Mg+Cl2→MgCl2), and Mg is removed as MgCl2.

[0018] In the flux method (a metal halide method), a flux (such as AlF3, NaAlF4 or K3AlF6) added to a molten Al alloy is reacted with Mg (e.g., 3Mg+2AlF3→3MgF2+2Al), and Mg is removed as MgF2. In order to improve the wettability of the flux with the molten Al alloy, chlorides or the like may be added.

[0019] The common point of the above methods is that Mg is removed as an oxide (such as MgO) or a halide (such as MgCl2 or MgF2) produced by a chemical reaction in an Al alloy melt. In such methods, the substances and reaction products used for Mg removal may easily remain in the Al alloy melt as inclusions. In addition, in conventional methods, Al captured in by-products such as scum (mainly Al2O3) and AlCl3 may be lost, and a large amount of waste is generated in addition to oxides and halides of Mg. In addition, in the chlorine method and the flux method, AlCl3 with a high vapor pressure and the exothermic components in the flux become smoke, so facilities that ensure safety and working environment are required.

[0020] The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method of removing Mg from an aluminum alloy melt and related technologies using a scheme different from the conventional scheme.

[0021] Solutions to the problem

[0022] As a result of intensive research conducted to achieve the above-mentioned purpose, the inventors of the present invention succeeded in removing Mg by bringing an Al alloy melt into contact with a molten salt layer formed on the surface of the aluminum alloy melt and absorbing Mg into the molten salt layer. After developing this result, the inventors of the present invention completed the present invention, which is described below.

[0023] <<Metal Removal Method>>

[0024] (1) The present invention provides a metal removal method, comprising a treatment step of forming a molten salt layer in contact with an Al alloy melt containing Mg, the molten salt layer covering at least a portion of the surface of the Al alloy melt. The molten salt layer contains a specific halogen element and a specific metal element, the specific halogen element is one or more of Cl or Br, and the specific metal element is one or more of Cu, Zn or Mn. The metal removal method also includes removing Mg by absorbing Mg from the Al alloy melt to the molten salt layer side.

[0025] (2) In the metal removal method of the present invention (also referred to as "Mg removal method" or simply "removal method"), Mg contained in the aluminum alloy melt (also referred to as "Al alloy melt") is removed by being absorbed to the molten salt layer side via the contact interface between the Al alloy melt and the molten salt layer. According to this method, the loss and waste of Al are reduced, and Mg can be removed efficiently or at low cost. In addition, since chlorine gas or the like is not used or generated, deterioration of the working environment can be avoided.

[0026] The removal method of the present invention is not limited to the regeneration of aluminum scrap, and can be used for the preparation of various Al alloy melts. In addition, the use of the removal method of the present invention makes it possible to obtain a regenerated Al alloy with a desired composition in a short time and efficiently from cheap scrap such as cheap scrap with a high Mg content. Therefore, the metal removal method of the present invention also relates to a "method for producing a regenerated Al alloy". The regenerated Al alloy after Mg removal can be used as a solidified material (such as an ingot) or a molten metal (including a semi-molten state).

[0027] <<Metal Recovery Methods>>

[0028] The present invention also relates to a method for recovering a specific metal element used in the above-mentioned removal method. That is, the present invention can also provide a metal recovery method, including a treatment step of forming a molten salt layer in contact with an Al alloy melt containing Mg, wherein the molten salt layer covers at least a portion of the surface of the Al alloy melt. The molten salt layer contains a specific halogen element and a specific metal element, wherein the specific halogen element is one or more of Cl or Br, and the specific metal element is one or more of Cu, Zn or Mn. The metal recovery method also includes arranging a conductor at least near the contact interface between the aluminum-based molten metal and the molten salt layer to deposit and recover the specific metal element on the conductor. The conductor bridges the aluminum alloy melt with the molten salt layer.

[0029] According to the metal recovery method of the present invention (also referred to as "recovery method"), the specific metal element used for Mg removal can be effectively recovered. By reusing the recovered specific metal element, the amount of waste formed due to Mg removal can be reduced. In addition, it is also possible to recover expensive specific metal elements (pure metals) while using cheap specific metal element compounds (such as oxides) for Mg removal. Therefore, the recovery method of the present invention can help reduce the cost of Mg removal as a whole.

[0030] <<Metal Remover>>

[0031] The present invention also relates to a metal removing agent for forming (or preparing) the above-mentioned molten salt layer. This will be described in detail below.

[0032] (1) The present invention may also provide a metal remover for forming a molten salt layer that absorbs Mg from an Al alloy melt. The metal remover contains: a specific metal element that is one or more of Cu, Zn, or Mn; a specific halogen element that is one or more of Cl or Br; and Mg.

[0033] In the metal remover (also referred to as "Mg remover" or simply "remover"), all or part of the specific metal element and Mg may be present, for example, in the form of oxides and / or halides. In this case, the oxide of Mg (MgO) may be a reaction product of an oxide of a specific metal element (M) (specific metal oxide: MO) and a magnesium halide (MgX2).

[0034] In the remover, the amount of the specific metal element in molar amount may be the same as the amount of Mg, or may be greater than or less than the amount of Mg. When the amount of the specific metal element in molar amount is greater than the amount of Mg, at least a portion of the specific metal element may be an oxide. When the amount of the specific metal element in molar amount is less than the amount of Mg, the specific metal element as a whole may be a halide. The remover may also contain a base halide serving as a substrate of the molten salt layer.

[0035] (2) The present invention can also provide a metal remover for forming a molten salt layer that absorbs Mg from an Al alloy melt. The metal remover contains: a base halide that serves as a base material of the molten salt layer; and a specific metal halide that is a compound of a specific metal element and a specific halogen element. The specific metal element is one or more of Cu, Zn, or Mn, and the specific halogen element is one or more of Cl or Br.

[0036] (3) By using any of these removers, a molten salt layer required for the above-mentioned method of removing Mg and recovering a specific metal element can be effectively formed. However, it should be noted that it is not necessary to form a molten salt layer using only the remover. Depending on the situation of implementing the removal method or the recovery method, specific metal oxides, magnesium halides, specific metal halides, basic halides, etc. can be appropriately supplemented or used in combination.

[0037] The form of the remover can be any one of for example block form, powdered form, layered form and other similar forms. Under the form of the remover, the composition (such as specific metal oxide, magnesium halide, specific metal halide and basic halide) may not be uniformly mixed. In this specification, each material constituting the remover or the effective material in the implementation of the removal method and the recovery method is referred to as "removal material". "Removal agent" is a mixture or composition by preparing, blending or preparing such a material (simple substance, compound etc.) or carrying out other similar procedures to obtain.

[0038] <<Others>>

[0039] (1) Unless otherwise specified, the concentrations and compositions mentioned in this specification are expressed by the mass ratio (mass %) of an object (such as a molten metal or a composition) relative to the whole. The mass % is appropriately expressed simply by "%".

[0040] (2) The Al alloy melt or molten salt layer as mentioned in this specification includes a solid-liquid coexistence state (semi-molten state). The Al alloy melt contains Al as a main component (the Al content exceeds 50 atomic % in one embodiment, is 70 atomic % or more in another embodiment, or is 85 atomic % or more in another embodiment, relative to the molten metal as a whole), and the specific composition is not limited, provided that it contains Mg. The amount of Mg in the raw material molten metal (Al-based molten metal before Mg is removed) is not limited, but is generally about 10 mass % or less in one embodiment, or about 5 mass % or less in another embodiment, relative to the molten metal as a whole.

[0041] (3) Unless otherwise specified, the numerical range "x to y" mentioned in this specification includes a lower limit x and an upper limit y. Any numerical value included in the various numerical values ​​or numerical ranges described in this specification can be selected or extracted as a new lower limit or upper limit, and thus any numerical range, such as "a to b", can be newly provided using such a new lower limit or upper limit. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] [ Figure 1A ] Figure 1A is the standard formation free energy diagram of metal oxides and metal chlorides at 660°C.

[0043] [ Figure 1B ] Figure 1B is the standard formation free energy diagram of metal oxides and metal bromides at 660°C.

[0044] [ Figure 2A ] Figure 2A This is a model diagram showing the mechanism by which Mg is absorbed from the Al-based molten metal into the molten salt layer.

[0045] [ Figure 2B ] Figure 2B is a model diagram showing the mechanism by which a specific metal element (eg, Cu) is deposited on a conductor.

[0046] [ Figure 3A ] Figure 3A is a set of schematic diagrams illustrating the Mg removal step using a molten salt layer containing CuCl2 and photographs showing solidified materials (solidified salt and Al alloy).

[0047] [ Figure 3B ] Figure 3B It is a graph showing the relationship between the Mg concentration, the Cu concentration or the Mg removal efficiency and the CuCl 2 amount.

[0048] [ Figure 4A ] Figure 4Ais a set of schematic diagrams illustrating a Mg removal step using a molten salt layer containing MgCl2 and CuO, and photographs showing the solidified material.

[0049] [ Figure 4B ] Figure 4B It is a graph showing the relationship between the Mg concentration or the Cu concentration and the CuO amount.

[0050] [ Figure 4C ] Figure 4C is a set of photographs showing the effect of MgCl2 and CuO on solidifying materials.

[0051] [ Figure 5 ] Figure 5 It is a graph showing the relationship between the Mg concentration, the Cu concentration or the Mg removal efficiency, and the amount of ZnO or CuO.

[0052] [ Fig. 6A ] Fig. 6A is a set of schematic diagrams showing the Mg removal step by insertion of a graphite rod or strong stirring.

[0053] [ Figure 6B ] Figure 6B It is a graph showing the relationship between the Mg concentration, the Cu concentration or the Mg removal efficiency and the insertion of the graphite rod or the strong stirring.

[0054] [ Figure 6C ] Figure 6C This is a photograph showing the appearance of the graphite rod after the Mg removal step (Cu recovery step).

[0055] [ Fig. 7A ] Fig. 7A is a set of schematic diagrams showing the preparation steps of the Mg removing agent.

[0056] [ Figure 7B ] Figure 7B is a set of photographs showing the relationship between the amount of MgCl2 and CuO and the appearance of the solidified mixed salt.

[0057] [ Fig. 8A ] Fig. 8A is the standard formation free energy diagram of metal fluorides at 660°C.

[0058] [ Figure 8B ] Figure 8B is the standard formation free energy diagram of metal iodides at 660°C. DETAILED DESCRIPTION

[0059] One or more features freely selected from this specification may be added to the above-mentioned features of the present invention. The contents described in this specification may be features about the product (eg, recycled Al alloy (molten metal)) even if they represent features on the method.

[0060] <<Principle of Mg removal>>

[0061] It is considered that the principle of removing Mg from the Al alloy melt by the removal method of the present invention is as follows.

[0062] (1) Redox reaction (electrochemical reaction)

[0063] Mg in the Al alloy melt is oxidized to Mg as follows 2+ and dissolves in the molten salt layer from the contact interface (molten metal surface of the Al-based molten metal).

[0064] Anodic reaction: Mg → Mg 2+ + 2e － (10a)

[0065] On the other hand, divalent metal ions (M = one or more of Cu, Zn, Mn) of specific metal elements in the molten salt layer (M 2+ ) are reduced as follows and precipitate in the molten salt layer (including near the contact interface with the Al-based molten metal).

[0066] Cathodic reaction: M 2+ + 2e － → M (10b)

[0067] (2) Magnesium halide

[0068] Specific halogen elements (X = Cl and / or Br) exist in the molten salt layer as monovalent halogen ions (X - ), and thus the above redox reaction is expressed as follows.

[0069] MX2 + Mg → M + MgX2 (11)

[0070] Here, the standard formation free energies (also simply referred to as "free energies") of halides (chlorides and bromides) of various metal elements are as shown in Figure 1A or Figure 1B (collectively referred to as "Figure 1" in these figures). Figure 1 also shows the free energies of oxides of various metal elements. The free energies shown in Figure 1 depend on Knacke O., Kubaschwski O., Hesselmann K., "Thermochemical Properties of Inorganic Substances" (1991), SPRlNGER-VERLAG. This also applies to Fig. 8A and Figure 8B(These figures are collectively referred to as "FIG. 8"), which will be described later. FIG. 1 and FIG. 8 show the free energies at 660°C. The trend (magnitude relationship) of the free energies at least from 660°C to 800°C is the same as the trend of the free energies shown in FIG. 1 and FIG. 8.

[0071] As is apparent from FIG1 , each of the halides (specific metal halides) composed of a specific metal element (M) and a specific halogen element has a greater free energy than magnesium halide. Therefore, the equation (11) or equation (10a) / (10b) proceeds in a stable direction where the free energy difference is negative (ΔG < 0), that is, from the left to the right. Therefore, Mg as Mg 2+ It is absorbed into the molten salt layer and removed from the Al alloy melt. In this reaction, the specific metal element constituting the specific metal halide (MX2) as the Mg removing material is precipitated as a simple substance (M) and can be recovered, for example, by the above-mentioned method.

[0072] (3) Magnesium oxide

[0073] It is also possible to add an oxide of a specific metal element (specific metal oxide) to the molten salt layer as a Mg removing material to remove Mg from the Al alloy melt. In this case, the specific metal oxide (MO) is preferably added to the molten salt layer containing Mg (Mg 2+ ) and certain halogen elements (X - ) in a molten salt layer.

[0074] MO+MgX2→MX2+MgO ​​(12)

[0075] As is apparent from FIG1 , a particular metal oxide (MO) has a greater free energy than a particular metal halide (MX2). In contrast, magnesium oxide (MgO) has a smaller free energy than magnesium halide (MgX2) (see Figure 1A The enlarged part). Therefore, Equation (12) proceeds in the stable direction where the free energy difference is negative (ΔG < 0), that is, from the left to the right. In particular, MgO has a smaller free energy than MgX2 and is stable in the molten salt layer, so it does not return to MgX2. Therefore, Mg in the molten salt layer 2+ It is consumed (removed) as MgO.

[0076] On the other hand, MX2 generated along the formula (12) acts as a Mg removing material as shown in the formula (11), and makes the Mg absorbed from the Al alloy melt into the molten salt layer 2+ This MgX2 further reacts with MO as shown in formula (12) and becomes MgO.

[0077] Through such a cycle, the Mg in the molten salt layer 2+The concentration does not change, and the molten salt layer containing MgX2 can be used almost permanently, and the Mg absorbed from the Al-based molten metal is only in an amount corresponding to the MO amount (molar amount). 2+ Removed as MgO. Figure 2A The case where Mg is removed in this manner is schematically shown as an example of the case where M=Cu.

[0078] Therefore, the use of a specific metal oxide that is cheaper than a specific metal halide enables the removal of Mg at low cost. In addition, the use of a specific metal oxide enables more reliable removal of Mg because the Mg in the Al alloy melt is absorbed into the molten salt layer as stable MgO.

[0079] (4) Conductor

[0080] Mg in the Al-based molten metal is removed by the anode reaction represented by the previously described formula (10a) and the cathode reaction represented by the previously described formula (10b). Here, when a conductor is provided to bridge the Al alloy melt with the molten salt layer, this is a structure similar to a battery (galvanic cell) in which the Al-based molten metal side is the anode (electrode) side and the molten salt layer side is the cathode (electrode) side. Therefore, the specific metal element is concentrated and deposited on the surface of the conductor located on the molten salt layer side, and can be effectively recovered. In addition, the deposited specific metal element is avoided from mixing into the Al alloy melt side. In addition, the conductor can promote the electrochemical reaction represented by formula (10a) and formula (10b) to improve the deposition rate of the specific metal element and the removal rate of Mg.

[0081] exist Figure 2B Schematically shows a case where a specific metal element is deposited on a conductor while removing Mg in this way as an example of the case where M=Cu. Figure 2B The case where the conductor is an electrode rod is shown, but the conductor may be in other forms. For example, the conductor may be composed of an electrode disposed in the Al alloy melt, an electrode disposed in the molten salt layer, and a conductor (such as a wire) electrically connecting the two electrodes. In addition, the container body that holds the Al alloy melt and the molten salt layer may also serve as a conductor. For example, the container body itself may be made of a conductive material (such as a metal), or a conductive material disposed at least on the inner wall of the container body near the melt surface (near the contact interface) may be used as a conductor.

[0082] Preferably, the conductor is made of a conductive material such as graphite or metal. Preferably, at least the conductive portion in contact with the Al-based molten metal is insoluble in the Al alloy melt.

[0083] <<Specified Metal Elements>>

[0084] Based on the free energy of metal halides shown in Figure 1, the specific metal element (M) may not be Cu, Zn or Mn. That is, even when the specific metal element is Ti, Al, Si, Fe, Ni, etc., the electrochemical reaction shown by formula (11) can be performed.

[0085] However, it should be noted that the dissolution reaction of the metal oxide (MO) represented by formula (12) is also considered to be carried out in the molten salt layer, and the specific metal element (M) is preferably one or more of Cu, Zn or Mn. This can be understood from the free energy of the metal oxide shown in Figure 1. In particular, when the specific metal element is Cu, the free energy of copper halide is correspondingly smaller than the free energy of copper oxide, and the reaction represented by formula (12) is easy to be carried out in the molten salt layer.

[0086] The free energy of the metal oxide shown in Fig. 1 is intended for CuO, ZnO, MnO, etc. Therefore, the specific metal oxide is preferably one or more of CuO, ZnO, or MnO.

[0087] <<Specified Halogen Elements>>

[0088] In addition to Cl or Br, F and I can also be used as halogen elements (X). Fig. 8A As shown in , the free energy of MgF2 is very small, and MgF2 is stable. Therefore, when X=F, the reaction represented by formula (12) is unlikely to proceed in the molten salt layer.

[0089] On the contrary, Figure 8B As shown in , the free energy of the iodide of the specific metal element is large, and the difference between the free energy and the free energy of the specific metal oxide is small. Therefore, when X=I, the reaction represented by formula (12) does not necessarily proceed stably in the molten salt layer. Considering such a situation, the specific halogen element (X) is preferably Cl and / or Br.

[0090] <<Base material / base halide of molten salt layer>>

[0091] The molten salt layer preferably has a substrate such as a stable metal halide. For example, as shown in FIG1, the substrate (basic halide) of the molten salt layer is preferably a magnesium halide or a halide of a metal element (Ca, Na, Li, Sr, K, Cs, Ba, etc.) having a free energy less than that of the magnesium halide. In particular, halides of Na and / or K are inexpensive and stable, and are therefore suitable as basic halides. In addition, the basic halide is preferably composed of a specific halogen element. The larger the contact area between the Al alloy melt and the molten salt, the more improved the reaction efficiency, but the molten salt layer does not necessarily cover the entire surface of the molten metal.

[0092] <<Processing steps / removal steps>>

[0093] The treatment step is to form a molten salt layer that contacts the surface of the Al alloy melt and covers at least a portion of the melt surface. By maintaining the molten salt layer prepared or maintained to have a desired composition and the Al alloy melt in direct contact with each other, Mg is absorbed into the molten salt layer from the Al-based molten metal and removed (removal step).

[0094] When the Mg removal material (MX2, MO) is fully present in the molten salt layer, the Mg concentration in the Al-based molten metal can be reduced as the holding time increases. However, it should be noted that an excessively long holding time is unrealistic. Therefore, the holding time is preferably, for example, 1 minute to 180 minutes in one embodiment, or 15 minutes to 90 minutes in another embodiment. In addition, each process (step) is not limited to intermittent, and can be performed continuously.

[0095] Preferably, the molten salt layer covers the entire surface of the Al alloy melt and has an amount (thickness) that enables sufficient Mg to be absorbed from the Al alloy melt. For example, the thickness of the molten salt layer is preferably 3 mm or more.

[0096] The molten salt layer is prepared, for example, as follows. First, a basic molten salt layer in which a basic halide (base material) is dissolved is formed on an Al alloy melt. Due to the difference in density, the basic molten salt layer is located on the upper layer side of the Al alloy melt. Then, an Mg removing material (such as a specific metal halide, a magnesium halide or a specific metal oxide) is added to the basic molten salt layer to prepare a molten salt layer containing desired substances (such as elements and ions).

[0097] Considering the concentration of Mg contained in the Al alloy melt, the processing amount of the Al-based molten metal, etc., it is preferred to temporarily, intermittently or continuously supply the Mg removing material to the molten salt layer. When the conductor is arranged between the Al alloy melt and the molten salt layer (at least near the contact interface), it is preferred to supply the Mg removing material around (near) the conductor. This enables the recovery of specific halogen elements and the removal of Mg to be carried out more effectively.

[0098] Example

[0099] The molten salt layer is brought into contact with an Al alloy melt containing Mg. Each solidified material (Al alloy, solidified salt) after the contact is observed, and the Mg concentration in each Al alloy is measured. The present invention will be described in more detail based on such specific examples.

[0100] <<Experimental Overview>>

[0101] (1) Al alloy melt

[0102] An Al alloy having a composition of Al-0.87%Mg or Al-0.7%Mg was prepared as an Al alloy melt (raw material molten metal) to be the object of removing Mg. The Mg concentration is the mass ratio of Mg to the entire melt. Commercially available pure Al and pure Mg were used as metal raw materials to become the Al alloy melt. The amount of Al-based molten metal used for each sample was 80g.

[0103] (2) Molten salt

[0104] The following halides and oxides were prepared as raw materials of the molten salt. Commercially available reagents were used for all the raw materials.

[0105] Basic halide: NaCl and KCl (mixed salt with a molar ratio of 1:1)

[0106] Specific metal halides: CuCl2

[0107] Specific metal oxides: CuO (copper (II) oxide) or ZnO (zinc oxide)

[0108] The amount of base halide used for each sample was 29.6 g.

[0109] (3) Melting

[0110] The Al alloy melt and the molten salt layer were prepared by heating each raw material in a Tammann tube (SSA-H-T6 purchased from Nikkato Corporation) as a crucible. The heating was performed using an electric furnace (cylindrical furnace) accommodating a Tammann tube (inner diameter: φ34 mm, outer diameter: φ40 mm, height: 150 mm). The temperature during melting was set to 700° C. or 750° C., and the temperature during holding was set to 700° C., 720° C., or 730° C.

[0111] (4) Analysis / Observation

[0112] The analysis / observation was performed using a disk-shaped solidified material obtained by injecting an Al alloy melt and a molten salt into a cylindrical mold (stainless steel mold for analysis) and then naturally cooling and solidifying in air. In this embodiment, for the purpose of explanation, the solidified material of each Al alloy melt is referred to as "Al alloy", and the solidified material of each molten salt is referred to as "solidified salt".

[0113] The chemical composition (Mg concentration, Cu concentration) of the Al alloy was analyzed by fluorescent X-ray spectroscopy. The composition (concentration) of the Al alloy is the mass ratio relative to the entire Al alloy. The appearance of the Al alloy was visually observed. The color of the solidified salt was visually observed.

[0114] <<Example 1>>

[0115] Each molten salt layer was obtained by adding a specific metal halide (Mg removing material) to a base molten salt (layer) composed of a base halide, and the Mg removal efficiency of the molten salt layer was investigated as follows.

[0116] (1) Processing

[0117] First, a weighed metal raw material (Al-0.87% Mg: 80 g) and a weighed base halide (mixed salt of NaCl and KCl: 29.6 g) were placed in a crucible (Tammann tube) and heated at a set temperature of 750° C. Thus, an Al alloy melt and a base molten salt layer were formed, as shown in FIG. Figure 3A As shown in . Due to the difference in density (specific gravity), the Al alloy melt and the base molten salt layer are divided into two layers, and the low-density base molten salt layer is located on the upper layer side of the Al alloy melt and covers the entire surface of the Al alloy melt.

[0118] Then, 0.5 g or 2 g of CuCl2 was added to the base molten salt layer to prepare a molten salt layer. After the addition, the temperature of the crucible was set to 730°C, and the crucible was kept for 30 minutes. The obtained Al alloy melt and molten salt layer were solidified in a mold for analysis, respectively, to obtain an Al alloy and a solidified salt.

[0119] (2) Evaluation

[0120] The coagulation salt after the treatment step is white. The coagulation salt is believed to be a mixed salt of MgCl2, KCl and NaCl.

[0121] Figure 3B Mg concentration and Cu concentration in each Al alloy are shown in FIG. The actual measured value of Mg concentration is almost lower than the calculated value (stoichiometry) obtained from the addition amount of CuCl2. Therefore, it has been confirmed that in the case of this embodiment, the Mg removal efficiency is almost 100%.

[0122] The calculated value of Mg concentration is obtained based on the molar ratio determined by formula (11). The Mg removal efficiency (%) is the ratio of the decrease in Mg concentration (ΔD) obtained from the actual measured value to the decrease in Mg concentration (ΔD0) obtained from the calculated value (100×ΔD / ΔD0). In the following examples, the calculated value of the concentration and the method for calculating the Mg removal efficiency are the same.

[0123] In each case, the Cu concentration in the Al alloy was 0.05% or less. From this fact, it was found that the Cu (specific metal element) contained in the Mg-removing material was hardly mixed into the Al alloy melt and remained in the molten salt layer (including near the boundary with the Al alloy melt (near the contact interface)).

[0124] <<Example 2>>

[0125] Each molten salt layer was obtained by adding magnesium halide and a specific metal oxide (Mg removing material) to a base molten salt layer composed of a base halide, and the Mg removal efficiency of the molten salt layer was investigated as follows.

[0126] (1) Processing

[0127] First, a weighed metal raw material (Al-0.7% Mg: 80 g) and a weighed base halide (mixed salt of NaCl and KCl: 29.6 g) were placed in a crucible (Tammann tube) and heated at a set temperature of 750° C. Thus, a base molten salt layer in contact with the Al alloy melt was formed, as shown in FIG. Figure 4A This procedure is the same as in Example 1.

[0128] Then, 0.43 g (0.0045 mol) of MgCl 2 was added onto the base molten salt layer, and the crucible was maintained at a set temperature of 730° C. for 10 minutes.

[0129] Then, CuO was further added to the base molten salt layer maintained at the same temperature (730°C). At this time, the amount of CuO added and the holding time were varied. During each holding time, three times (initial, intermediate and late) of slight stirring were performed, and the degree of slight stirring was to rotate the crucible for about 3 seconds.

[0130] In this way, the Al alloy and the solidified salt were obtained from the Al alloy melt and the molten salt layer prepared by variously changing the amount of CuO and the holding time.

[0131] (2) Evaluation

[0132] Figure 4B The Mg concentration and Cu concentration in each Al alloy are summarized and shown in FIG. Figure 4B It is obvious that the Mg concentration in the Al alloy decreases with the increase in the amount of CuO added to the base molten salt layer. However, as the amount of CuO increases, it takes longer to reduce the Mg concentration. It is believed that the reason why the actual measured value of the Mg concentration is higher than the calculated value is that CuO is consumed by some unexpected reaction products (Al2O3, MgAl2O4).

[0133] Also in the present embodiment, the Cu concentration in the Al alloy was 0.05% or less in each case. That is, it has been confirmed that Cu contained in the Mg-removed material is hardly mixed into the Al alloy melt and remains in the molten salt layer.

[0134] (3) Effect of MgCl2

[0135] For sample A obtained by adding 0.43 g of MgCl and 2.0 g of CuO to the base molten salt layer and setting the holding time to 10 minutes, sample B obtained by adding only MgCl, and sample C obtained by adding only CuO, the appearance when observing the solidified salt (the supernatant portion of the molten salt), the Al alloy, and the bottom of the crucible is summarized as follows: Figure 4C middle.

[0136] The solidified salt of sample A is gray or black. This is because Mg absorbed from the Al alloy melt is removed as MgO (black) and remains in the molten salt layer.

[0137] Cu (red) precipitated on the Al alloy is observed. Cu has a higher density and a higher melting point than the Al alloy. However, it is believed that Cu is not mixed into the Al alloy melt because Cu is finely precipitated near the contact interface between the molten salt layer and the Al alloy melt.

[0138] The solidified salt of sample B was almost white. No precipitation of Cu or the like was observed on the Al alloy. Thus, it has been confirmed that if CuO as a Mg removing material is not added, the reaction represented by formula (12) does not proceed and Mg is not removed.

[0139] Even when MgCl2 was not added as in sample C, discoloration of the solidified salt and Cu precipitation on the Al alloy were observed. However, the extent was small compared to sample A, and a large amount of unreacted CuO remained at the bottom of the crucible. Thus, it was found that when MgCl2 was added to the molten salt layer in advance, the reaction represented by formula (12) was promoted and Mg was effectively removed.

[0140] <<Example 3>>

[0141] (1) Processing

[0142] The CuO used in Example 2 was changed to ZnO, and the same treatment as in Example 2 was performed. At this time, Al-0.7%Mg molten metal (80 g) was used as the Al alloy melt. The temperature during melting and holding was set to 700°C. The holding time after adding ZnO was 30 minutes. The other conditions were the same as those in Example 2.

[0143] (2) Evaluation

[0144] The Mg concentration and Zn concentration in each Al alloy obtained from the Al-based molten metal in contact with the molten salt layer to which ZnO was added were measured. The results are shown in Figure 5 middle. Figure 5 The Mg concentration and the Cu concentration in each Al alloy of Example 2 using CuO are also shown.

[0145] As from Figure 5 Obviously, when ZnO is used, Mg can also be removed from the Al-based molten metal. However, the Mg removal efficiency is lower than that when CuO is used. This is believed to be because Figure 1A As shown in , the free energy difference between the oxide and chloride of Zn is smaller than that between the oxide and chloride of Cu, and the progress of formula (12) is moderate.

[0146] In addition, the Zn concentration when ZnO is used is higher than the Cu concentration when CuO is used. It is believed that since the melting point of Zn (about 420°C) is lower than the melting point of Cu (about 1084°C), part of the Zn precipitated in the molten salt layer (see formula (11)) is mixed into the Al alloy melt.

[0147] <<Example 4>>

[0148] (1) Processing

[0149] In the same manner as in Example 2, 0.43 g of MgCl2 was added to the base molten salt layer at a set temperature of 750°C and maintained for 10 minutes, and then 2 g of CuO was further added. Fig. 6A As shown in , a graphite rod (conductor) was inserted into the crucible and maintained at a set temperature of 730° C. for 30 minutes.

[0150] As a comparative example, Fig. 6A As shown in, the following samples were also prepared, for which, after adding CuO, the molten salt layer and the Al alloy melt were strongly stirred with a protective tube (made of ceramic) instead of inserting a graphite rod. Strong stirring was performed after adding CuO, after 10 minutes, after 20 minutes, and after 30 minutes.

[0151] (2) Evaluation

[0152] The Mg concentration and Cu concentration in the Al alloy obtained from the Al-based molten metal after each treatment were measured. The results are shown in Figure 6B In. Figure 6B It is obvious that the insertion of graphite rods improves the Mg removal efficiency and reduces the Cu concentration. This is not only obvious compared with the case of strong stirring, but also with Figure 4B and Figure 5 This is also obvious compared with the case shown in . This is considered to be because the reaction of formula (11) mainly occurs on the graphite rod (conductor), and oxidation of Al near the contact interface between the Al alloy melt and the molten salt layer is suppressed.

[0153] It was also confirmed that strong stirring during the treatment tended to increase the Mg concentration and Cu concentration because the Mg (Mg 2+, MgO) and precipitated Cu are easily mixed into the Al alloy melt.

[0154] Figure 6C The graphite rod is taken out from the Al alloy melt and the molten salt layer 30 minutes after the addition of CuO. Figure 6C It is obvious that a large amount of Cu is deposited on the molten salt layer side, especially in its lower part (the upper part just above the boundary with the Al alloy melt). It has been found that when a graphite rod (conductor) is used during the Mg removal step, the areas where the cathode reaction and the anode reaction occur are separated (controlled), and the recovery step of the specific metal element (Cu) becomes more efficient. When the graphite rod is taken out, the Cu located at the bottom of the molten salt layer is attached. Figure 6C Cu on the Al alloy melt side of the graphite rod shown in FIG.

[0155] <<Example 5>>

[0156] The base halide (NaCl + KCl), magnesium halide (MgCl2) and specific metal oxide (CuO) are blended to produce each of the various mixed salts (solid / Mg remover) for preparing the molten salt layer. This will be described in detail. Unless otherwise specified, each mixed salt is produced in the same manner as the solidification salt of the molten salt layer described in Example 2.

[0157] (1) Processing

[0158] like Fig. 7A As shown in , a weighed mixed salt of NaCl and KCl (29.6 g) is put into a crucible (Tammann tube as described above) and heated at a set temperature of 750° C. MgCl 2 and / or CuO are added to the base molten salt layer thus obtained.

[0159] The addition amount of MgCl2 is 0g (not added) or 0.43g (0.0045mol). The addition amount of CuO is any one of 0g (not added), 0.05g, 0.1g and 0.36g (0.0045mol). Addition of CuO is performed after adding MgCl2 and holding for 10 minutes. After adding CuO, further hold for 10 minutes. In each case, the set temperature during holding is 720°C. Thus, a variety of molten salts are prepared. Each molten salt is fully stirred and injected into a mold for analysis, and solidified by natural cooling in the air. Figure 7B The appearance of each disc-shaped mixed salt is summarized and shown in FIG.

[0160] (2) Evaluation

[0161] from Figure 7BThe following facts were found from the colors of each mixed salt shown in . First, the mixed salt (#10) of MgCl2: 0.43g and CuO: 0g (not added) is white. As the amount of CuO added increases, the mixed salts (#11 to #13) change from gray to black. The black color is attributed to MgO.

[0162] Then, the mixed salt (#20) of MgCl2: 0 g (no addition) and CuO: 0.36 g was also substantially colorless and transparent. The pale yellow color seen in the mixed salt is partially attributed to the CuO formed by the dissolution of a very small amount of CuO. 2+ At this time, most of the CuO adheres to the inner wall surface of the crucible. The mixed salt (#13) with a molar ratio of MgCl2 and CuO of 1:1 is black.

[0163] As is apparent from comparing the mixed salt without added MgCl2 (#20) with the other mixed salts, it was found that Mg 2+ The presence of increases the amount of dissolved CuO. That is, the reaction represented by formula (12) is promoted. Therefore, the mixed salt obtained by adding magnesium halide and a specific metal oxide is effective as a Mg remover (metal remover).

[0164] When the specific metal oxide is less than Mg in stoichiometric proportion 2+ (magnesium halide), the mixed salt (metal removing agent) obtained as described above is basically composed of a base halide, a magnesium halide, a specific metal halide and magnesium oxide. As described in Example 1, the specific metal halide (CuCl2) contributes to Mg removal. When Mg is further removed from the Al alloy melt, it is preferred to supply a specific metal oxide (such as CuO) to the molten salt layer formed by using the metal removing agent as needed.

[0165] As described above, according to the metal removal method of the present invention, Mg can be effectively removed from the Al alloy melt. In addition, according to the metal recovery method of the present invention, a specific metal element used when removing Mg can be effectively recovered. In addition, the use of the metal removal agent of the present invention enables the efficient formation of a molten salt layer used when removing Mg.

Claims

1. A metal remover for forming a molten salt layer for absorbing Mg from an aluminum alloy melt, The metal removing agent comprises: A specific metal element, wherein the specific metal element is Cu; Specific halogen elements, which are one or more of Cl or Br; and Mg, Wherein all or part of the specific metal element exists in the form of an oxide, and wherein all or part of the Mg exists in the form of a halide MgX2, wherein X is Cl or Br. 2 . The metal removing agent according to claim 1 , comprising at least one of an oxide of the specific metal element and an oxide of Mg. 3 . The metal removing agent according to claim 1 , further comprising a base halide serving as a base material of the molten salt layer. The metal removing agent according to claim 3 , wherein the base halide is a halide of Na and / or K.

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