Aluminum manufacturing method

Abstract

This method for producing aluminum is for obtaining, from an aluminum alloy material, aluminum having higher purity than said aluminum material, the method being characterized by: immersing, in an electrolytic solution 11, a cathode electrode 9 and an anode electrode 7 including an aluminum alloy material containing 0.1-24 mass% of Si; causing a current to flow at a current density of 0.1-25 mA / cm2 on the surface of the anode electrode 7 where the electrolytic solution 11 and the aluminum alloy material come in contact with each other; and depositing aluminum on the cathode electrode.<sp / >

Description

Technical Field

[0001] The present invention relates to a method for producing aluminum capable of obtaining higher purity aluminum from, for example, alloys for castings.

Background Art

[0002] Aluminum, which is widely used, cannot be smelted by a thermal reduction reaction using carbon from ore as a raw material like steel materials. Therefore, generally, in smelting, it is necessary to use electricity, such as the Bayer process or the Hall-Héroult process. For this reason, the production of primary aluminum emits a large amount of carbon dioxide and has a large environmental impact.

[0003] For this reason, it is desirable to recycle used aluminum products. For example, attempts have been made to simply produce high-purity aluminum materials from aluminum alloy scraps (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, even if it is simply called "aluminum", various alloys are used depending on its use. For example, in the case of an aluminum can, an A3000 series (Al-Mn series) drawn material is used. If this is recycled directly into an aluminum can, there is no problem, but when diverted to other alloys, its components may become a problem. In this case, it is necessary to reduce the amount of recycled alloy used and mix it with primary metal above a certain level. For this reason, recycling into the same alloy system as much as possible is efficient.

[0006] However, although the amount of scrap aluminum alloys that have been used in automobile engine parts and the like is large, the amount of their reuse has been decreasing in recent years due to the spread of electric vehicles and the like. For this reason, it has become difficult to reuse them in the same field. In particular, metals in the above fields include many cast products (castings, die-castings), and since they have more alloy components compared to wrought materials, it is difficult to divert them to other fields. For example, the AC2A alloy (JIS) used as a casting material contains 4.0 mass% or more and 6.0 mass% or less of silicon (Si), and the content of Si and the like is extremely high even compared to wrought materials. Therefore, it is extremely difficult to reuse it for other wrought material applications.

[0007] The present invention has been made in view of such problems, and an object thereof is to provide a method for producing aluminum that can be produced as aluminum with a higher purity than the aluminum material by using aluminum ingots, used aluminum alloys, particularly aluminum alloys with a high Si content, as the aluminum material.

Means for Solving the Problems

[0008] In order to achieve the above object, the present invention is a method for producing aluminum for obtaining aluminum with a higher purity than the aluminum material from the aluminum material, comprising: A non-aqueous electrolyte containing a dialkyl sulfone, an aluminum halide, and a nitrogen-containing compound, wherein the amount of the aluminum halide is 1.5 moles or more and 5 moles or less, and the nitrogen-containing compound is 0.05 moles or more and 1.5 moles or less per 10 moles of the dialkyl sulfone, an anode electrode containing an aluminum material containing 0.1 mass% or more and 24 mass% or less of Si, and a cathode electrode soak immersing, The electrolyte temperature is between 80°C and 120°C. a current is passed at a current density of 0.1 mA / cm 2 or more and 25 mA / cm 2 or less on the surface of the anode electrode where the aluminum material and the electrolyte are in contact, and aluminum is deposited on the cathode electrode The nitrogen compound contained is ammonium halide, a hydrogen halide of a primary amine, a hydrogen halide of a secondary amine, a hydrogen halide of a tertiary amine, general formula: R 1 R 2 R 3 R 4 Selected from the group consisting of quaternary ammonium salts represented by N·X, the R 1 ~The aforementioned R 4 are the same or different alkyl groups, and X is a counteranion for the quaternary ammonium cation.It is a method for producing aluminum, characterized by the following.

[0009] The aluminum material of the anode electrode may further contain 0.1% by mass or more and 5% by mass or more of copper (Cu).

[0010] The aluminum material of the anode electrode may further contain 0.15% by mass or more and 1.8% by mass or less of iron (Fe).

[0011] It is desirable to pass an electric current through the anode electrode while stirring the electrolytic solution around the anode electrode.

[0012] It is desirable to make the surface area of the portion of the aluminum material of the anode electrode that contacts the electrolytic solution larger than the surface area of the portion of the cathode electrode that contacts the electrolytic solution.

[0016] While an electric current is flowing through the anode electrode, it is desirable to deposit aluminum on the cathode electrode so that the arithmetic mean height Sa of the anode electrode becomes 2.3 μm or more and 10 μm or less.

[0017] The current density is preferably 0.1 mA / cm 2 [^2] or more and 20 mA / cm 2 [^2] or less. Also, any combination of the above-described characteristic matters can be combined with each other.

Advantages of the Invention

[0018] According to the present invention, it is possible to provide a method for producing aluminum capable of producing higher purity aluminum from used aluminum alloys, particularly aluminum alloys with a high Si content, and other aluminum materials. B

Brief Description of the Drawings

[0019] [Figure 1] Conceptual diagram showing an aluminum production apparatus used in the aluminum production method according to an embodiment of the present invention. [Figure 2A] Scanning electron microscope (SEM) image of a cross-section near the surface of the anode electrode after electrolysis when the current density of the anode electrode is 10 mA / cm². [Figure 2B] SEM image of a cross-section near the surface of the anode electrode after electrolysis when the current density of the anode electrode is 20 mA / cm². [Figure 2C] SEM image of a cross-section near the surface of the anode electrode after electrolysis when the current density of the anode electrode is 40 mA / cm². [Figure 2D] SEM image of a cross-section near the surface of the anode electrode after electrolysis when the current density of the anode electrode is 80 mA / cm². [Figure 3] A diagram showing the correlation between the current density of the anode electrode and the surface roughness of the anode electrode surface. [Figure 4A] SEM image of the electrodeposited film surface on the cathode electrode when high-purity aluminum was used as the anode electrode. [Figure 4B] SEM image of a cross-section of the electrodeposited film deposited on the cathode electrode when high-purity aluminum was used as the anode electrode. [Figure 5A] SEM image of the electrodeposited film surface on the cathode electrode when electrolysis was performed at a high current density using an AC2A alloy as the anode electrode. [Figure 5B] SEM image of a cross-section of the electrodeposited film deposited on the cathode electrode when electrolysis was performed at a high current density using an AC2A alloy as the anode electrode. [Figure 6A] SEM image of the electrodeposited film surface on the cathode electrode when electrolysis was performed at a low current density using an AC2A alloy as the anode electrode. [Figure 6B] SEM image of a cross-section of the electrodeposited film deposited on the cathode electrode when electrolysis was performed at a low current density using an AC2A alloy as the anode electrode. [Figure 7] A diagram showing the impurity concentration of the electrodeposited film deposited at the cathode electrode. [Modes for carrying out the invention]

[0020] According to one embodiment of the present invention, a method for producing high-purity aluminum from an aluminum alloy involves immersing an anode electrode containing an aluminum alloy with 0.1% to 24% by mass of Si and a cathode electrode in an electrolyte, and applying 0.1 mA / cm² to the surface of the anode electrode where the aluminum alloy and the electrolyte are in contact. 2 More than 25mA / cm 2 The method is characterized by applying a current at the following current density to deposit aluminum on the cathode electrode.

[0021] The following describes an aluminum manufacturing method according to one embodiment of the present invention, with reference to the drawings. Figure 1 is a schematic diagram of an aluminum manufacturing apparatus 1 used in the aluminum manufacturing method according to one embodiment of the present invention. The concentrations of each element in the following description can be measured by ICP emission spectrometry.

[0022] The aluminum manufacturing apparatus 1 used in the aluminum manufacturing method of this embodiment comprises an electrolytic cell 3, a DC power supply 5, an anode electrode 7, a cathode electrode 9, and an electrolyte 11, wherein the anode electrode 7 contains an aluminum alloy extracted from scrap or the like. The anode electrode 7 and the cathode electrode 9, on which high-purity aluminum is deposited, are immersed in the electrolyte 11, and a DC voltage is applied between the anode electrode 7 and the cathode electrode 9 by the DC power supply 5. At that time, when a DC voltage is applied between the anode electrode 7 and the cathode electrode 9, the current flowing between the anode electrode 7 and the cathode electrode 9 is controlled, or the surface area of ​​the aluminum alloy in the anode electrode 7 that is in contact with the electrolyte 11 is adjusted so that the current density in the part of the aluminum alloy surface of the anode electrode 7 that is in contact with the electrolyte 11 is within a predetermined range. In this way, by passing a current through the anode electrode 7, an electrodeposited film of high-purity aluminum is deposited on the cathode electrode 9.

[0023] In this specification, the current density at the part of the aluminum alloy surface of the anode electrode that is in contact with the electrolyte is referred to as the "current density of the anode electrode." Furthermore, in this specification, the current density at the part of the aluminum alloy surface of the anode electrode that is in contact with the electrolyte is the value obtained by dividing the current between the anode electrode and the DC power supply by the area of ​​the part of the aluminum alloy surface of the anode electrode that is in contact with the electrolyte.

[0024] An electrolytic cell 3 in the aluminum manufacturing apparatus 1 stores an electrolyte 11 in which aluminum can be dissolved, and an anode electrode 7 and a cathode electrode 9 are immersed in the electrolyte 11. The anode electrode 7 and the cathode electrode 9 are connected via a DC power supply 5. The anode electrode 7 is made of an aluminum alloy with a purity lower than the target purity, and contains Si: 0.1% by mass or more and 24% by mass or less. Furthermore, it may also contain Cu: 0.1% by mass or more and 5% by mass or less, and Fe: 0.15% by mass or more and 1.8% by mass or less. If the above upper limit is exceeded, Si will be a factor that hinders the dissolution of aluminum during electrolysis, slowing down the deposition rate of the desired high-purity aluminum and causing a decrease in throughput. On the other hand, if the above upper limit is exceeded, Cu and Fe will be more likely to dissolve into the electrolyte 11. Therefore, it will become difficult to obtain the desired high-purity aluminum. As for the anode electrode 7, for example, used material of AC2A alloy can be formed into an electrode shape by casting or the like. Furthermore, the anode electrode 7 only needs to contain at least 0.1% by mass or more and 24% by mass of Si, and may also contain elements other than magnesium (Mg) that are nobler than aluminum.

[0025] The cathode electrode 9 is made of aluminum, for example, and can be made of pure aluminum or an aluminum alloy specified in the JIS standard for wrought materials. That is, the cathode electrode 9 has a lower Si and Cu content than the aluminum alloy content contained in the anode electrode 7. By making the cathode electrode 9 out of aluminum, the cathode electrode with the deposited aluminum can be used as high-purity aluminum ingot. Therefore, it is preferable that the cathode electrode 9 is made of aluminum with a purity equal to or higher than the target purity. In addition to aluminum, titanium and stainless steel can also be used as the cathode electrode 9. Since titanium and stainless steel have a dense oxide film on their surface, if aluminum is electrodeposited on the surface using a titanium or stainless steel cathode electrode, the electrodeposited aluminum can be easily peeled off the cathode electrode 9.

[0026] The DC power supply 5 that applies a DC voltage between the anode electrode 7 and the cathode electrode 9 can be any well-known DC power supply device, but it is preferable to have a current control mechanism that controls the output current in order to reduce the amount of impurities that dissolve into the electrolyte 11, as described later. In addition, in order to control the current density of the anode electrode 7, a current detector (not shown) that measures the current flowing between the anode electrode 7 and the DC power supply 5 may be provided near the anode electrode 7. The current density of the anode electrode can be calculated from the surface area of ​​the anode electrode 7 in contact with the electrolyte 11 and the current detected by the current detector. For this reason, it is preferable that the output current of the DC power supply 5 be adjustable by the current control mechanism of the DC power supply 5 so that the current density of the anode electrode is within a predetermined range. In addition, the contact area of ​​the aluminum alloy used for the anode electrode 7 with the electrolyte 11 may be changed according to the current flowing through the anode electrode 7. For example, the current density of the anode electrode may be adjusted by changing the area of ​​the anode electrode exposed from the surface of the electrolyte 11, thereby changing the contact area of ​​the anode electrode 7 with the electrolyte 11.

[0027] The electrolyte 11 into which the anode electrode 7 and cathode electrode 9 are immersed is a non-aqueous (non-aqueous electrolyte) and contains, for example, (1) dialkyl sulfone and (2) aluminum halide. Using this electrolyte 11, high-purity aluminum can be formed on the surface of the cathode electrode 9 at a fast film formation rate. Furthermore, (3) ammonium halide, hydrogen halide of primary amine, hydrogen halide of secondary amine, hydrogen halide of tertiary amine, general formula: R 1 R 2 R 3 R 4 N·X(R 1 ~R 4 It is desirable that the electrolyte 11 contains at least one nitrogen-containing compound selected from the group consisting of quaternary ammonium salts (where is the same or different alkyl group and X represents a counteranion for the quaternary ammonium cation). Compared to electrolytes using ionic liquids, the electrolyte 11 is industrially advantageous in terms of reagent availability and low cost.

[0028] Examples of dialkyl sulfones to be included in the electrolyte 11 above include dimethyl sulfone, diethyl sulfone, dipropyl sulfone, dihexyl sulfone, and methyl ethyl sulfone, which have an alkyl group with 1 to 6 carbon atoms (they may be linear or branched). From the viewpoint of good electrical conductivity and ease of availability, dimethyl sulfone can be preferably used.

[0029] Examples of aluminum halides include aluminum chloride and aluminum bromide. It is preferable that the aluminum halide be anhydrous. Anhydrous aluminum halides do not contain water molecules, which can reduce electrodeposition efficiency, thus preventing a decrease in electrodeposition efficiency.

[0030] Examples of ammonium halides that can be used as nitrogen-containing compounds include ammonium chloride and ammonium bromide. Furthermore, examples of primary to tertiary amines in the hydrogen halides of primary to tertiary amines include alkyl groups with 1 to 6 carbon atoms (either linear or branched), such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, tripropylamine, hexylamine, and methylethylamine. Examples of hydrogen halides include hydrogen chloride and hydrogen bromide. General formula: R 1 R 2 R 3 R 4 N·X(R 1 ~R 4 In quaternary ammonium salts, R is represented as (where is the same or different alkyl group, and X represents the counteranion for the quaternary ammonium cation). 1 ~R 4 Examples of alkyl groups represented by include methyl, ethyl, propyl, and hexyl groups, which have 1 to 6 carbon atoms (they can be linear or branched). X can be a halide ion such as chloride, bromide, or iodide, as well as BF4 - PF6 - Examples include the following. Specific examples of compounds include tetramethylammonium chloride, tetramethylammonium bromide, tetramethylammonium iodide, and tetraethylammonium boron tetrafluoride. As for suitable nitrogen-containing compounds, hydrochlorides of tertiary amines, such as trimethylamine hydrochloride, can be cited because they facilitate the formation of high-purity aluminum at a rapid film formation rate.

[0031] Regarding the blending ratio of dialkylsulfone and aluminum halide, for example, it is desirable that the amount of aluminum halide be between 1.5 moles and 5.0 moles per 10 moles of dialkylsulfone. Furthermore, the upper limit is more desirable in the order of 4.0 moles or less, 3.0 moles or less, and 2.5 moles or less, with 1.5 moles or more and 2.0 moles or less being the most desirable. If the amount of aluminum halide blended is less than 1.5 moles per 10 moles of dialkylsulfone, there is a risk that the formed aluminum will blacken (a phenomenon called burning) and the film formation efficiency will decrease. On the other hand, if the amount of aluminum halide blended exceeds 5.0 moles per 10 moles of dialkylsulfone, the liquid resistance of the electrolyte 11 will become too high, which may cause the electrolyte 11 to generate heat and decompose.

[0032] Furthermore, if the composition ratio of aluminum halide to dialkylsulfone becomes too high, the concentration of aluminum-source ions becomes too high, which can hinder the movement of aluminum ions from the anode electrode. On the other hand, if the composition ratio of aluminum halide to dialkylsulfone becomes too low, the amount of ions contributing to electrical conduction decreases, and the efficiency of electrolysis decreases.

[0033] On the other hand, the nitrogen-containing compound blended with the dialkylsulfone and aluminum halide is preferably in an amount of 0.01 moles to 2.0 moles, and more preferably 0.05 moles to 1.5 moles, per 10 moles of dialkylsulfone. If the amount of nitrogen-containing compound blended is less than 0.01 moles per 10 moles of dialkylsulfone, the effects of blending, namely the improvement of film deposition rate based on the improvement of the electrical conductivity of the electrolyte 11, and the effects of high purity and improved ductility of aluminum, may not be obtained. Furthermore, if the amount of nitrogen-containing compound blended exceeds 2.0 moles per 10 moles of dialkylsulfone, the composition of the electrolyte 11 will change fundamentally, which may prevent aluminum from precipitation.

[0034] The electrolysis of aluminum using the above-described electrolyte 11 is performed, for example, when the temperature of the electrolyte 11 is between 80°C and 120°C, and the applied current density is 0.1 mA / cm². 2 More than 25mA / cm 2 The procedure should be carried out under the following conditions. Note that the applied current density is 0.1 mA / cm². 2 More than 20mA / cm 2 The following conditions are even more preferable. The lower limit of the electrolyte 11 temperature should be determined considering the melting point of the electrolyte 11, preferably 85°C or higher, and more preferably 95°C or higher (if the temperature falls below the melting point of the electrolyte 11, the plating solution will solidify, making plating impossible). If the temperature of the electrolyte 11 is 120°C or lower, the activation of the reaction between aluminum and the electrolyte can be suppressed, making it less likely for many impurities to be incorporated into the aluminum. In order to efficiently obtain a highly pure electrodeposited film of aluminum by electrolysis, it is necessary to efficiently move the ions of the metal to be deposited at the cathode electrode from the anode electrode to the surface of the cathode electrode. Here, increasing the temperature reduces the viscosity of the electrolyte, and as a result, the transport efficiency of the material increases, thus improving electrical conductivity. For this reason, considering electrical conductivity, a higher electrolyte temperature is better. On the other hand, if the electrolyte temperature becomes too high, the surface of the cathode electrode becomes activated, and the deposition of impurities proceeds more easily. This may result in a decrease in purity. For these reasons, the temperature of the electrolyte 11 during electrolysis is preferably 85°C or higher, more preferably 95°C, with an upper limit of 120°C or lower. Furthermore, the anode current density is 0.1 mA / cm². 2 If the above is true, the decrease in film deposition efficiency can be suppressed. On the other hand, 25 mA / cm 2 The following conditions make it easy to achieve the high purity of aluminum described later. More preferably, 20 mA / cm². 2 The following conditions make it easier to achieve higher purity. The electrolyte 11 used is not particularly limited.

[0035] Next, the principle of high-purity aluminum production in the aluminum manufacturing apparatus 1 according to one embodiment of the present invention will be explained using Figure 1. When the anode electrode 7 and the cathode electrode 9 are immersed in the electrolyte and a direct current is passed through them, aluminum loses electrons on the surface of the anode electrode 7 and dissolves into the electrolyte 11 as aluminum ions (A in Figure 1). On the surface of the cathode electrode 9, electrons are supplied to the aluminum ions and deposited as aluminum metal.

[0036] Furthermore, in order to efficiently supply aluminum ions to the cathode electrode 9, it is preferable to agitate the electrolyte 11 while current is flowing through the anode electrode 7. Therefore, it is desirable to provide an outlet for releasing an inert gas such as nitrogen gas at the bottom of the electrolytic cell 3 and release bubbles of the inert gas from this outlet into the electrolyte 11 (cathode electrode 9) (so-called bubbling). The electrolyte 11 is agitated by the generation of convection in the electrolyte 11 in accordance with the flow of bubbles in the electrolyte 11. Alternatively, liquid flow may be provided using a pump or agitator, or the electrodes themselves may be oscillated. In the illustrated example, one anode electrode 7 and one cathode electrode 9 are arranged as a pair, but multiple anode electrodes 7 and cathode electrodes 9 may be arranged alternately.

[0037] Here, the inventors found that (1) when metal ions are eluted from the anode electrode 7, the type of metal ion eluted changes depending on the current density at the anode electrode 7. For example, since Cu has a higher standard electrode potential than aluminum, in equilibrium, aluminum is preferentially ionized at the anode electrode 7. However, in reality, ionization of Cu also proceeds under conditions such as when Cu is solid-dissolved in aluminum, or when the current density exceeds a certain level, resulting in a high concentration of aluminum ions on the surface of the anode electrode 7. In contrast, when the current density at the anode electrode 7 is 25 mA / cm², 2We have found that the leaching of elements nobler than aluminum, such as Cu, can be suppressed by doing the following. Therefore, the aluminum manufacturing apparatus 1 of one embodiment of the present invention uses a DC power supply 5 having a current adjustment mechanism. The current adjustment mechanism of the DC power supply 5 changes the current flowing from the DC power supply 5 to the anode electrode 7, so even if the surface shape of the anode electrode 7 changes and the surface area in contact with the electrolyte 11 changes, it is possible to adjust the current of the anode electrode 7 so that the above current density is achieved.

[0038] Furthermore, the inventors discovered that (2) when aluminum ions are eluted from the anode electrode 7, segregated portions of Cu and Si (crystallized portions of Cu and Si) present in the material constituting the anode electrode 7 can be exposed on the surface of the anode electrode 7 and detached under certain conditions. In this way, they found that high-purity aluminum can be efficiently produced by preventing Cu and Si from eluting into the electrolyte 11 and allowing the crystallized heterogeneous elemental components such as Cu and Si to detach in a solid state on the surface of the anode electrode 7 (Figure 1B). Specifically, they found that when Cu and Si are not completely and uniformly dispersed in the material constituting the anode electrode 7, but rather partially contain Cu phase, Si phase, or intermetallic compound phases containing these (for example, phases with a maximum diameter of 10 μm or more), these phases can be removed from the anode electrode 7 without eluting by setting the current density of the anode electrode 7 below a predetermined level.

[0039] Thus, in order to efficiently remove impurities contained in the aluminum of the anode electrode 7 from the surface of the anode electrode 7 without dissolving them into the electrolyte 11, it is preferable to apply a DC voltage between the anode electrode 7 and the cathode electrode 9 while stirring the electrolyte 11 surrounding the anode electrode 7. For example, instead of or in addition to the bubbling directed toward the cathode electrode 9 as described above, bubbling toward the vicinity of the anode electrode 7 or stirring the electrolyte with a stirring device may be performed, or the anode electrode 7 may be oscillated or rotated. Alternatively, the surface of the anode electrode 7 may be physically rubbed with another insulating material during electrolysis to remove impurities.

[0040] Furthermore, in order to efficiently remove impurities from the anode electrode 7, the impurity phase may be coarsened during the manufacturing of the anode electrode 7 to facilitate its removal. For example, when forming an anode electrode by melting and casting aluminum material such as aluminum alloy or aluminum ingot containing Si or Cu extracted from scrap, reducing the cooling rate after solidification can form a Cu phase, Si phase, or intermetallic compound phase containing these that is 10 μm or larger (even 20 μm or larger).

[0041] Furthermore, in order to reduce the current density of the anode electrode 7, it is desirable to make the surface area of ​​the anode electrode (the area in contact with the electrolyte 11, hereafter the same) sufficiently larger (for example, 1.5 times or more) than the surface area of ​​the part of the cathode electrode 9 that is in contact with the electrolyte 11. As mentioned above, there is an upper limit to the current density of the anode electrode 7, but if the current flowing through the anode electrode 7 is large, the deposition rate of aluminum deposited on the cathode electrode 9 will increase. Therefore, by making the surface area of ​​the part of the anode electrode 7 that is in contact with the aluminum alloy and the electrolyte larger than the surface area of ​​the part of the cathode electrode 9 that is in contact with the electrolyte 11, it is possible to improve the electrodeposition efficiency of high-purity aluminum. Furthermore, the anode electrode 7 in this embodiment may consist of a mesh cage made of a metal material of an element nobler than aluminum, and granular aluminum alloy extracted from scrap, which is contained inside the cage. By using such an anode electrode 7, the current flowing through the anode electrode 7 can be increased while keeping the current density of the anode electrode 7 below the upper limit mentioned above, thereby increasing the deposition rate of aluminum deposited on the cathode electrode 9.

[0042] Furthermore, in the electrolyte 11, impurity particles (sludge) that detach from the anode electrode 7 settle below the anode electrode 7. For this reason, the process may include a step to recover this sludge simultaneously with or after the electrolysis process. For example, the sludge can be recovered by filtering with filter paper, a filter, an anode bag, or a cathode bag, and the electrolyte 11 can be reused. The nominal mesh size of the filter paper, filter, anode bag, or cathode bag used should be between 0.1 μm and 100 μm. The lower limit is preferably 1 μm or more, and if the material is aluminum with increased crystal grain size of the Cu phase, Si phase, or intermetallic compound phase containing these, then 10 μm or more, and more preferably 20 μm or more, is preferable.

[0043] As described above, according to this embodiment, high-purity aluminum with reduced levels of impurity elements, particularly Si and Cu, can be efficiently obtained from aluminum alloys containing large amounts of these elements. For example, the total content of Si, Fe, and Cu in the high-purity aluminum obtained by this embodiment can be 0.1% by mass or less. Furthermore, the amount of CO2 emitted when obtaining 1 kg of high-purity aluminum by electrolysis in this embodiment can be reduced by approximately 45% compared to the amount of CO2 emitted when obtaining 1 kg of new ingot from ore by conventional smelting methods.

[0044] Generally, the three-phase electrolysis method is known for increasing the purity of aluminum. However, since casting alloys, in particular, have a high impurity concentration, attempting to increase the purity of used casting alloy materials using the three-phase electrolysis method is difficult because it becomes impossible to maintain the anode composition. In addition, silicon, a typical alloying element, has a density close to that of aluminum and is lighter than the molten salt used, so silicon is mixed into the refined aluminum, and its separation is difficult.

[0045] In contrast, the aluminum manufacturing method of this embodiment can efficiently remove impurity elements including Si, making it possible to further purify the obtained aluminum using a three-phase electrolysis method. In other words, the aluminum obtained in this embodiment is effective as an aluminum raw material (anode-side raw material) in a three-phase electrolysis method.

[0046] As described above, the aluminum manufacturing method of this embodiment makes it possible to obtain aluminum of higher purity from aluminum alloys and aluminum ingots containing 0.1% to 24% by mass of Si. For this reason, for example, recycled alloys from castings can be purified and repurposed for other uses. In particular, recycled alloys from automobile engine parts and the like that contain a large amount of Cu can be easily repurposed for other uses, making it possible to utilize used alloys more effectively. Furthermore, it becomes possible to produce high-purity aluminum from aluminum ingots. Furthermore, by stirring the liquid near the anode electrode 7, sludge can be efficiently removed from the anode. In addition, by making the surface area of ​​the part of the anode electrode 7 that is in contact with the electrolyte larger than the surface area of ​​the cathode electrode, high-purity aluminum can be efficiently deposited on the cathode while suppressing the current density of the anode.

[0047] Furthermore, by using an electrolyte consisting of dialkyl sulfone, aluminum halide, and nitrogen-containing compounds, it is possible to perform operations at lower temperatures compared to cases where molten salt is used, and handling is also safe and easy. Furthermore, by recovering the sludge that detaches from the anode electrode 7, contamination can be suppressed, and the aluminum alloy can be efficiently purified to a high degree of purity. In this process, the sludge recovery rate can be increased by using filter paper with an appropriate mesh size to collect the sludge. [Examples]

[0048] Using an apparatus with a configuration similar to the aluminum manufacturing apparatus shown in Figure 1, electrolysis of the aluminum alloy used as the anode electrode and deposition of high-purity aluminum onto the cathode electrode were performed. An AC2A aluminum alloy (Si: 4.0% to 6.0% by mass, Cu: 3.0% to 4.5% by mass, Fe: 0.8% by mass or less) was used as the anode electrode. Figures 2A to 2D are SEM images of cross-sections near the anode electrode surface showing the differences in the anode electrode surface after electrolysis when the current density of the anode electrode is varied. In each SEM image, the current density of the anode electrode is 10 mA / cm² in Figure 2A. 2 In Figure 2B, the current is 20 mA / cm². 2 In Figure 2C, the current is 40 mA / cm². 2 In Figure 2D, the rate is 80 mA / cm². 2 The cumulative current flow per unit volume of electrolyte is in the range of 9.2 to 10.6 Ah / L.

[0049] As mentioned above, applying current to the anode electrode causes the aluminum in the base material of the AC2A aluminum alloy to dissolve. Here, the microstructure of the AC2A aluminum alloy at each anode electrode partially contains segregation (crystallized material) of Cu, Si, Fe, etc., and intermetallic compounds (hereinafter simply referred to as impurities). The current density of the anode electrode is 10 mA / cm². 2 (Figure 2A), 20 mA / cm 2 In the case of (Figure 2B), these impurities remain on the surface when aluminum is dissolved. Therefore, as the aluminum dissolution progresses, these impurities will eventually detach from the anode electrode surface and form sludge.

[0050] On the other hand, the current density of the anode electrode is 40 mA / cm². 2 (Figure 2C) and 80 mA / cm 2 In the case of (Figure 2D), the surface of the aluminum and the surface of the impurity almost coincide. This indicates that the impurity is partially eluting along with the aluminum. Similarly, even Cu, which has a higher standard electrode potential compared to aluminum, will ionize along with aluminum when the current density increases.

[0051] Figure 3 shows the results of measuring the surface roughness of the anode electrode surface after electrolysis. Both the arithmetic mean height Sa and the maximum height Sz were measured at a current density of 25 mA / cm² at the anode electrode. 2 The following is true: 10mA / cm 2 and 20mA / cm 2 In this case, the value is relatively high, inversely proportional to the current density of the anode electrode. On the other hand, if the current density is 25 mA / cm² 2 Larger, 40mA / cm 2 , 80mA / cm 2 Therefore, the surface roughness will be a small value. This is because the current density is 25 mA / cm². 2 In the following cases, impurities contained in the aluminum alloy used for the anode electrode remain on the surface of the anode electrode during the process of purifying aluminum. Thus, the current density is 25 mA / cm². 2 By doing the following, the surface roughness (arithmetic mean height Sa and maximum height Sz) of the anode electrode surface can be controlled, and the elution of impurities can be suppressed.

[0052] Furthermore, it is desirable to deposit aluminum on the cathode electrode such that the arithmetic mean height Sa of the anode electrode is 2.3 μm or more and 10 μm or less during electrolysis (any time from the start of electrolysis to the scheduled end time after a predetermined time has elapsed) or at the scheduled end time of electrolysis. For example, while current is flowing through the anode electrode, elements contained in the aluminum alloy are dissolved from the anode electrode into the electrolyte. Therefore, during this time, it is preferable to deposit aluminum on the cathode electrode by controlling the current of the anode electrode or by adjusting the area of ​​the anode electrode exposed from the liquid surface so that the arithmetic mean height Sa of the anode electrode is 2.3 μm or more and 10 μm or less.

[0053] When the arithmetic mean height Sa of the portion of the anode electrode surface where the aluminum alloy contacts the electrolyte is 2.3 μm or greater, the elution of Cu and other elements is reduced. Furthermore, if the arithmetic mean height Sa is 10 μm or less, the concentration of current at the tips of the fine irregularities appearing on the anode electrode surface, which would otherwise increase the anode current density, is suppressed, thus reducing the elution of Cu and other elements. The arithmetic mean height Sa and maximum height Sz were measured using a laser microscope at five locations within a 100 μm × 100 μm area, with n=5 measurements for each location, and the average value was calculated. A laser microscope (Keyence VK-X100) with a pinhole confocal optical system, using a wavelength of 658 nm, a 50x objective lens, a vertical resolution of 5 nm, and a horizontal resolution of 10 nm was used.

[0054] To maintain surface roughness within a predetermined range during electrolysis, electrolysis tests should be conducted beforehand using an anode electrode manufactured with the same composition as the anode electrode actually used (e.g., aluminum alloy or aluminum ingot obtained from scrap), varying the conditions. The electrolysis conditions should then be set using the correlation information between each condition and surface roughness obtained from these tests. For example, by applying a DC voltage between the anode and cathode electrodes in the same electrolyte and varying the current flowing through the anode electrode during electrolysis, and measuring the roughness over time, correlation information between the change in surface roughness over time for each current can be obtained. Furthermore, by changing the current and the surface area of ​​the anode electrode in contact with the electrolyte, correlation information between current density and surface roughness can be obtained. For example, as mentioned above, after a predetermined time has elapsed since the start of electrolysis, coarse impurities remain on the aluminum surface, increasing the surface roughness (Sa,Sz), and thereafter, the detachment and exposure of coarse impurities are repeated. Therefore, it is desirable to maintain this state during electrolysis.

[0055] Such electrolysis conditions are set based on the correlation information described above. Furthermore, if the correlation information determines that the surface roughness at any time between the start of electrolysis and the end of electrolysis, or at the scheduled end time of electrolysis, exceeds the predetermined range, the current density may be reduced before exceeding this range to suppress further increases in surface roughness. In other words, based on the correlation information obtained in advance, the current may be reduced after a predetermined time has elapsed from the start of electrolysis. When setting electrolysis information based on the surface roughness after a predetermined time has elapsed from the start of electrolysis, the correlation information between surface roughness and current density when the current density is changed after a predetermined time has elapsed from the start of electrolysis can also be measured in advance to determine the timing and amount of reduction when changing the current value. Conversely, as electrolysis progresses, the surface roughness increases, effectively increasing the surface area of ​​the anode electrode. For this reason, the current may be increased to take into account the increase in the surface area of ​​the anode electrode and remain within the set current density range. In other words, based on the correlation information described above, the current may be increased after a predetermined time has elapsed from the start of electrolysis.

[0056] Next, the electrodeposited film deposited on the surface of the cathode electrode was observed. Figure 4A is an SEM image of the surface of the electrodeposited film, and Figure 4B is an SEM image of the cross-section of the electrodeposited film. High-purity aluminum (99.99%) was used as the anode electrode, and the anode current density and cathode current density were set to 80 mA / cm². 2 This is the result in that case. By using high-purity aluminum as the anode electrode, impurities are hardly introduced, and a high-purity electrodeposited film can be obtained even at high current densities.

[0057] On the other hand, Figures 5A and 5B show a configuration using AC2A alloy as the anode electrode, with anode current density and cathode current density of 10-80 mA / cm², respectively. 2 These are SEM images of the surface of the electrodeposited film and a cross-section of the electrodeposited film when the current density was changed. An AC2A alloy was used as the anode electrode, and the current density was 40 mA / cm². 2 Beyond a certain point, particles believed to be copper were observed in the cross-section. This indicates that copper ions are being reduced on the cathode electrode surface.

[0058] In contrast, Figure 6A is an SEM image of the surface of the electrodeposited film, and Figure 6B is an SEM image of the cross-section of the electrodeposited film. An AC2A alloy was used as the anode electrode, and the anode current density and cathode current density were set to 10 mA / cm². 2 This is the result when the current density is kept constant. An AC2A alloy was used as the anode electrode, and the current density was 25 mA / cm². 2 In the following cases, no Cu was observed in the cross-section, and an electrodeposited film with a morphology almost identical to that obtained when high-purity aluminum was used as the anode electrode (Figures 4A and 4B) was obtained.

[0059] Figure 7 shows the results of the component analysis of the electrodeposited film, at 10 mA / cm². 2 ~80mA / cm 2 When changed to 10mA / cm² 2 This is the difference under certain conditions. By keeping the current density of the anode electrode below a predetermined level, the impurity concentration of the resulting electrodeposited film could be reduced.

[0060] Furthermore, the impurity concentration of the electrodeposited film was evaluated in more detail by changing the electrolytic conditions. Table 1 shows the various conditions and evaluation results for each example.

[0061] [Table 1]

[0062] The electrolytes used in electrolysis for No. 1 to No. 6 all contain dialkylsulfone, aluminum chloride, and the additives ammonium chloride and tetramethylammonium chloride. The electrolytes used in Examples No. 1 to No. 3 and No. 6 contain 0.2 mol of ammonium chloride and 1.0 mol of tetramethylammonium chloride per 10 mol of dialkylsulfone. On the other hand, the electrolytes used in Examples No. 4 and No. 5 contain 0.1 mol of ammonium chloride and 0.5 mol of tetramethylammonium chloride per 10 mol of dialkylsulfone.

[0063] In the table, the "composition ratio" of the electrolyte is the molar ratio of dialkyl sulfone to aluminum halide (aluminum chloride). Electrical conductivity changes mainly depending on the composition ratio of dialkyl sulfone to aluminum halide and temperature. The current densities of the anode electrodes for each embodiment from No. 1 to No. 6 are as shown in the table, but the current density for No. 6 is 10-80 mA / cm². 2 This is a variation within that range. The impurity concentration in the electrodeposited film was evaluated as follows.

[0064] For Si, concentrations of 50 ppm or less were rated A (excellent), concentrations between 50 ppm and 150 ppm were rated B (good), and concentrations above 150 ppm were rated C (bad). Similarly, for Cu, concentrations of 1000 ppm or less were rated A (excellent), concentrations between 1000 ppm and 1500 ppm were rated B (good), and concentrations above 1500 ppm were rated C (bad). For Fe, concentrations of 100 ppm or less were rated A (excellent), concentrations between 100 ppm and 200 ppm were rated B (good), and concentrations above 200 ppm were rated C (bad). The total impurity concentration of Si + Cu + Fe was rated A (excellent), concentrations between 1000 ppm and 2000 ppm were rated B (good), and concentrations above 2000 ppm were rated C (bad). Note that all impurity content is expressed as a mass ratio.

[0065] Based on the results, focusing solely on Si, all tests passed (rated B or higher). On the other hand, the current density was 80 mA / cm². 2 It reached 25mA / cm². 2 Sample No. 6, which exceeded the limit, had a Si content of 150 ppm or less, resulting in a good evaluation. However, its Cu and Fe content exceeded 1500 ppm and 200 ppm, respectively. As a result, the evaluation of Cu and Fe was unsatisfactory (C grade), and consequently, the total impurity concentration was unsatisfactory. This indicates that the current density has a greater impact on Cu and Fe than on Si.

[0066] Furthermore, it was found that, for the same composition ratio, electrical conductivity tends to increase with increasing temperature.

[0067] Based on the above, examining the results in Table 1, a comparison of No. 1, No. 2, and No. 6 shows that reducing the current density reduces the impurity concentration. Furthermore, a comparison of No. 2 and No. 3, and No. 4 and No. 5, shows that the impurity concentration tends to increase as the temperature becomes too high. Also, a comparison of No. 2 and No. 5, and No. 3 and No. 4, shows that the impurity concentration tends to increase as the composition ratio of aluminum halides becomes too high.

[0068] The electrolyte temperature should be between 80°C and 120°C, but between 85°C and 110°C is more desirable, and between 95°C and 110°C is even more desirable.

[0069] Although embodiments of the present invention have been described above with reference to the attached drawings, the technical scope of the present invention is not limited to the embodiments described above. It is clear to those skilled in the art that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these also naturally fall within the technical scope of the present invention. [Explanation of Symbols]

[0070] 1…Aluminum manufacturing equipment 3......electrolytic cell 5……DC power supply 7………Anode electrode 9... Cathode electrode 11... Electrolyte

Claims

1. A method for producing aluminum from an aluminum material to obtain aluminum of higher purity than the aforementioned aluminum material, A non-aqueous electrolyte containing a dialkyl sulfone, an aluminum halide, and a nitrogen-containing compound, wherein the amount of the aluminum halide is 1.5 moles or more and 5 moles or less, and the nitrogen-containing compound is 0.05 moles or more and 1.5 moles or less per 10 moles of the dialkyl sulfone, The anode electrode and cathode electrode are immersed in an aluminum material containing 0.1% to 24% by mass of Si. The electrolyte temperature is 80°C to 120°C, and the surface of the anode electrode in contact with the aluminum material and the electrolyte is supplied with 0.1 mA / cm². ２ 25mA / cm or more ２ By passing a current at the following current density, aluminum is deposited on the cathode electrode. A method for producing aluminum, characterized in that the contained nitrogen compound is selected from the group consisting of ammonium halides, hydrogen halides of primary amines, hydrogen halides of secondary amines, hydrogen halides of tertiary amines, and quaternary ammonium salts represented by the general formula: R1 R2 R3 R4 N·X, wherein R1 to R4 are the same or different alkyl groups, and X is a counteranion for the quaternary ammonium cation.

2. The method for producing aluminum according to claim 1, characterized in that the aluminum material of the anode electrode further contains 0.1% by mass or more and 5% by mass or less of Cu.

3. The method for producing aluminum according to claim 1, characterized in that the aluminum material of the anode electrode further contains 0.15% by mass or more and 1.8% by mass or less of Fe.

4. The method for producing aluminum according to claim 1, characterized in that an electric current is passed through the anode electrode while stirring the electrolyte around the anode electrode.

5. The method for manufacturing aluminum according to claim 1, characterized in that the surface area of ​​the portion of the anode electrode in contact with the aluminum material and the electrolyte is made larger than the surface area of ​​the portion of the cathode electrode in contact with the electrolyte.

6. The method for producing aluminum according to claim 1, characterized in that, while current is flowing through the anode electrode, aluminum is deposited on the cathode electrode such that the arithmetic mean height Sa of the anode electrode is 2.3 μm or more and 10 μm or less.

7. The current density is 0.1 mA / cm². ２ 20mA / cm or more ２ The method for producing aluminum according to any one of claims 1 to 6, characterized in that it is as follows:

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