Dross processing method

Abstract

To provide a dross processing method that can efficiently recover Al (alloy) from aluminum-based dross.SOLUTION: A dross processing method comprises a supply step for introducing, into a molten salt reservoir, dross produced on an Al-based molten metal, where a metal component and a non-metal component included in the dross are separated in the molten salt. The method may further comprise at least a recovery step for extracting the metal component. The molten salt is prepared, e.g., by melting a chloride, and the temperature thereof is configured to be greater than or equal to the melting point of the metal component. The dross is added to the molten salt reservoir, e.g., in a granular form. The dross is produced, e.g., in a process for manufacturing a recycled Al base metal from scrap of an Al base material. The present invention makes it possible to efficiently recover the metal component from which the non-metal component and impurity elements have been separated and removed.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for treating aluminum-based dross. [Background technology]

[0002] Aluminum smelting involves huge energy consumption and carbon dioxide (CO2) emissions, so from the perspective of reducing the environmental burden and building a recycling-oriented society, it is important to recover and effectively utilize aluminum from aluminum-based dross (simply referred to as "dross") that is generated during the production process of (recycled) ingots, etc.

[0003] Many proposals have been made regarding methods for treating such dross, and for example, there are related disclosures in the following patent documents. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 6-100956 [Patent Document 2] Patent Publication No. 9-310129 [Patent Document 3] Patent Publication No. 2002-322519 [Patent Document 4] Patent Publication No. 2020-142190 [Patent Document 5] Patent Publication No. 2006-312766 [Patent Document 6] Patent Publication No. 2015-83711 Summary of the Invention [Problem to be solved by the invention]

[0005] In the high-temperature heat treatment methods described in Patent Document 1 and Patent Document 2, a large amount of Al is lost due to oxidation. In the hydrothermal treatment method or wet treatment method described in Patent Document 3 or Patent Document 4, only the ammonia generated when aluminum nitride (AlN) contained in the dross reacts with water is treated. In other words, Al cannot be effectively recovered from the dross.

[0006] Patent Document 5 relates to an ash squeezing method (apparatus) for recovering Al by mechanically stirring and squeezing heated dross. Patent Document 6 proposes a flux that serves as a heat generating agent for the dross to be ash squeezed. In such conventional ash squeezing, the dross is heated to a high temperature in the air, resulting in a large loss of Al due to oxidation.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a new method for treating dross that differs from conventional methods. [Means for solving the problem]

[0008] As a result of intensive research into solving this problem, the inventors have discovered that by pouring the dross into molten salt, it is possible to efficiently separate the metal and non-metallic components contained in the dross. By expanding on this finding, the inventors have completed the present invention, which will be described below.

[0009] <How to dispose of dross> (1) The present invention relates to a method for treating dross, which includes, for example, a step of feeding dross generated on an Al-based molten metal into a molten salt reservoir, and separates non-metallic and metallic components contained in the dross in the molten salt.

[0010] (2) According to the present invention, it is possible to efficiently recover metals contained in dross. The mechanism behind this is thought to be as follows.

[0011] When the dross comes into contact with the molten salt, the non-metallic components are taken up by the molten salt, and the non-metallic components are separated from the metallic components. The metallic components separated from the non-metallic components are dispersed in the molten salt, and then usually move (settle) downward (for example, to the bottom of the container) due to the difference in specific gravity with the molten salt, and may aggregate.

[0012] This metal content is in a refined state in which non-metallic content has been removed, and is also in a state in which it is shielded from the outside world (e.g., the atmosphere) by the molten salt, suppressing oxidation, nitridation, etc. Therefore, according to the present invention, Al can be efficiently recovered in a high-quality state from the dross that is the raw material, while suppressing Al loss and ammonia generation, etc.

[0013] <<Aluminum substrate / its manufacturing method>> The present invention can also be understood as an Al substrate made of a metal component obtained by treating dross, or a manufacturing method thereof. The Al substrate is a liquid phase (molten metal) or solid phase (cast ingot (base metal), member, etc.) made of pure Al or an Al alloy.

[0014] "others" Unless otherwise specified, "x to y" in this specification includes a lower limit of x and an upper limit of y. Any numerical value included in the various numerical values ​​or numerical ranges described in this specification may be used as a new lower limit or upper limit to create a new range such as "a to b." [Brief description of the drawings]

[0015] [Figure 1] This is an X-ray diffraction pattern obtained by analyzing dross (an example). [Diagram 2] This is an X-ray diffraction pattern obtained by analyzing the chloride obtained after processing the dross. [Diagram 3] FIG. 2 is a schematic diagram illustrating a process of treating dross. [Figure 4] 1 is an example of a compositional analysis of dross and chlorides and metal nuggets obtained after processing the dross. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The above-mentioned components of the present invention may be supplemented with one or more components selected from the present specification. The contents described in the present specification may be either method-related components or product-related components (e.g., Al substrate).

[0017] Dross Dross is a by-product produced during the slag removal process (including slag removal process) that reduces or removes impurities and unnecessary component elements contained in the Al-based molten metal. Dross may be produced during smelting, refining, or preparation of an Al-based molten metal of a desired composition.

[0018] Dross contains metals (MP: Metal Products) as well as various non-metallics (NMP: Non-Metal Products). The non-metallics are mainly composed of compounds. The compounds include oxides and nitrides of Al, as well as compounds of impurity elements and alloy elements contained in the raw materials to be dissolved, and compounds of components contained in the flux and gas used in the slag removal process. Specifically, the compounds include oxides of Si, Fe, Mg, Cu, Mn, Zn, etc. (composite oxides (including, for example, Al2O3MgO (spinel)), etc.), nitrides, chlorides (halides, carbonates, sulfates, etc.), intermetallic compounds, etc.). The oxides of Fe may be FeO, Fe3O4, Fe2O3, or spinel type (FeAl2O4, etc.).

[0019] The metal component mainly composed of Al may be pure Al or an Al alloy, and there is no restriction on the form (shape, size). The metal component in the dross is usually covered entirely or partially on its outer surface with a non-metallic component.

[0020] The dross may be in a solid or fluid state. For example, the dross may be in a solid-liquid coexistence state immediately after being taken out of the crucible of the Al-based molten metal, or may be in a solid state after being cooled and solidified.

[0021] Molten Salt The molten salt is prepared, for example, by dissolving a stable metal halide (particularly, a chloride and / or a bromide). The metal element constituting the halide is, for example, one or more of Ca, Na, Li, Sr, K, Mg, Cs, Ba, etc. The halides of Na and / or K (particularly, chlorides) are inexpensive and stable, and are suitable for the molten salt. Naturally, the composition of the molten salt varies from the initial value as the dross treatment progresses. For example, even if the molten salt is prepared by dissolving only chlorides (NaCl, KCl, etc.), it may contain halogen elements other than Cl (F, etc.) due to the components contained in the dross (residual components of the flux, etc.).

[0022] The molten salt may be a mixed salt containing multiple types of metal halides (e.g., NaCl and KCl). The melting temperature, density, etc. may be adjusted by blending the molten salt (adjusting the components). If the molten salt has a lower density (specific gravity) than the metal content (mainly Al), the metal content can be allowed to settle and be recovered. The molten salt is not limited to a single layer, and may be a multi-layer.

[0023] The molten salt is sufficient if it can separate the metal and non-metallic components contained in the dross. Therefore, the molten salt may be below the melting point of the metal (mainly Al). However, if the molten salt is at or above the melting point, the metal components are more likely to dissolve, aggregate, and integrate, improving the recovery of the metal components.

[0024] The amount of molten salt may be adjusted depending on the amount of dross to be processed. For example, the molten salt reservoir may have a depth (layer thickness) that allows the supplied dross to be immersed. The layer thickness may be, for example, 5 to 100 mm, or 15 to 50 mm.

[0025] 《Al-based molten metal》 The Al-based molten metal that produces dross can be obtained, for example, by melting metal or scrap (waste material), etc. If the dross produced during the refining of the recycled Al-based molten metal produced by melting scrap is treated, the Al resource can be used more effectively (improving the recovery rate).

[0026] Processing method (1) Supply process The form in which the dross is introduced into the molten salt reservoir is not important. The dross may be supplied (added, charged, etc.) to the molten salt reservoir continuously or intermittently.

[0027] When granulated dross is poured or scattered into molten salt, the reaction with the molten salt is promoted and the metal recovery efficiency is improved. Granular dross can be obtained, for example, by crushing or pulverizing lumpy (solid) dross to a desired size. The particle size is, for example, 50 mm or less, 25 mm or less, or 10 mm or less. There is no restriction on the lower limit, but it may be, for example, 1 mm or more or 5 mm or more. The particle size (particle size) referred to here is specified, for example, by the sieve size (size of the mesh openings).

[0028] (2) Recovery process The form in which the metal is recovered is not important. The metal may be recovered continuously or intermittently. For example, the molten metal (treated molten metal) may be continuously removed from the bottom of the molten salt reservoir. The metal may be cooled and solidified together with the molten salt and recovered by removing the solid salt (by washing with water, etc.). The recovered metal may be used for casting as it is, or may be used as an Al base metal (raw material). EXAMPLES

[0029] The present invention will be described in more detail with reference to a specific example in which a metal component (Al-based alloy) is recovered from dross generated in the manufacturing process of Al-based recycled ingot.

[0030] Dross (1) Test material Scrap (raw material) of aluminum-based components was melted and the slag was removed. The dross formed on the recycled aluminum-based molten metal was removed from the crucible and cooled in a dross cooler. The solid dross was further crushed and classified into granules. The granular dross was used as the test material. The maximum grain length was 5 mm or less (grain length: about 1 to 5 mm).

[0031] (2) Observation and analysis The test material (granular dross) was analyzed using an X-ray diffractometer (EMPYREAN manufactured by Malvern PANalytical Co., Ltd.) and the obtained diffraction pattern is shown in Figure 1.

[0032] The diffraction pattern revealed that the dross surface was covered with at least non-metallic components such as aluminum nitride (AlN), aluminum oxide (Al2O3), spinel (MgAl2O4), silicon (Si), and iron oxide (FeO). X-ray diffraction (XRD) can only analyze substances present on the surface of the object being measured. For this reason, it is believed that diffraction peaks indicating metallic components such as Al or Al alloys did not appear in Figure 1.

[0033] The elements contained in the test materials were analyzed using an X-ray fluorescence analyzer (JSX-1000S manufactured by JEOL Ltd.). The results are shown in Table 1 of FIG. 4. In this example, the concentration of each element is shown as a mass percentage (mass%) relative to the total (same below).

[0034] As is clear from Table 1, the majority of the test material (approximately 3 / 4) consists of Al, and it was found that it contains a fair amount of alloy elements (Si, Mg, Cu, Mn, Zn, Ti, etc.) and impurity elements (Fe, etc.) that are thought to be derived from the raw material scrap. In addition, component elements (Na, K, Ca, Cl, S, etc.) that are thought to be derived from the flux used in the slag treatment were also detected. The range of elements measured by fluorescent X-ray analysis is 11 Na~ 92 For this reason, 7N, 8O, etc. are not included in the analysis results in Table 1.

[0035] From the analysis results in Figure 1 and Table 1 (Figure 4), it is inferred that the metallic components (pure Al or Al alloy), which make up the majority of the dross, were almost entirely covered by non-metallic components.

[0036] Molten Salt Pool 2000 g of mixed chloride (KCl-44% by mass NaCl) was heated and melted in a graphite crucible to prepare a molten salt bath (800° C.).

[0037] Dross Processing (1) Supply process 1000g of the test material (dross) was added to the molten salt reservoir (feeding process), and the behavior afterwards was observed. The non-metallic components on the surface of the granular dross dispersed first into the molten salt and separated from the metallic components (separation process). The granular metallic components that emerged dissolved a little later, becoming spherical in the molten salt due to surface tension. The spherical metallic components further gradually integrated in the molten salt, settling and piling up at the bottom of the crucible. This series of events is shown diagrammatically in Figure 3.

[0038] (2) Recovery process The entire crucible, with the two layers separated into a molten salt layer containing non-metallic components and a metal layer below it, was cooled. The metal layer solidified into a metal lump, and the molten salt solidified into chlorides were then separately collected (recovery process).

[0039] The amount of metal mass (Al-based alloy) after removing the chlorides adhering to the surface by washing with water was 650g. In other words, 65% of the dross was recovered as metal.

[0040] (3)Analysis The composition of the recovered metal ingot was analyzed by spark discharge optical emission spectroscopy. The results are shown in Table 2 in Figure 4. As is clear from Table 2, the composition of the metal ingot was close to that of aluminum alloy for die casting (ADC12). This is thought to reflect the alloy composition of the scrap (raw material for recycled Al-based alloy) used to generate the dross.

[0041] In addition, as is clear from a comparison of Tables 1 and 2, the Fe concentration in the metal ingot was significantly lower than that in the dross. In other words, it was found that the above-mentioned dross treatment can produce a refined Al alloy ingot that is almost free of the Fe (or iron oxide) contained in the dross.

[0042] Furthermore, the recovered chlorides were analyzed using the above-mentioned X-ray diffractometer, and the resulting diffraction pattern is shown in FIG.

[0043] In the diffraction pattern, in addition to the peaks of sodium chloride (NaCl) and potassium chloride (KCl), which are the raw materials of the molten salt, peaks indicating at least aluminum nitride (AlN), aluminum oxide (Al2O3), and spinel (MgAl2O4) were observed. It was also confirmed that such non-metallic components (mainly compounds) were captured in the chloride after treatment. If the chloride after treatment is washed with water, it is possible to recover such non-metallic components.

[0044] The elements contained in the chloride after the treatment were analyzed using the X-ray fluorescence analyzer described above. The results are shown in Table 3 of Figure 4. As is clear from Table 3, the chloride contained more than 10 mass% Fe in addition to Cl, K, and Na, which are the raw materials of the molten salt. This shows once again that the molten salt takes in Fe, resulting in a refined metal lump with a low Fe concentration.

[0045] Comparative Example A comparative experiment was also conducted to recover metals from dross (ash) by squeezing the metals.

[0046] The above-mentioned test material (dross): 914 g was placed in a graphite crucible and heated to 800 ° C in the atmosphere. At this time, the metal content molten in the crucible was integrated while being stirred with a graphite rod. During stirring with the graphite rod, the dross generated heat in the crucible. This is thought to be due to the heat of oxidation of the molten metal content (Al).

[0047] The molten metal was poured into an analytical mold and cooled to solidify. The metal ingot thus obtained was 500 g (recovery rate: 54.7%).

[0048] The metal lump was also analyzed by the spark discharge optical emission spectroscopy described above. The results are shown in Table 4 in Figure 4. As is clear from Table 4, the composition of the metal lump was also close to the alloy composition (ADC12) of the scrap. However, as is clear from a comparison of Tables 2 and 4, the Fe concentration in the metal lump was as high as 2.1 mass%. In other words, it was found that with conventional ash squeezing, the Fe (or iron oxide) contained in the dross also dissolves into the metal lump, and almost no Fe is removed.

[0049] From the above, it was confirmed that the processing method of the present invention makes it possible to efficiently recover metals from dross from which non-metallic components (Al2O3, AlN, MgAl2O4, FeO, etc.) and impurity elements have been removed.

Claims

1. A supply step of feeding dross generated on the Al-based molten metal into a molten salt reservoir is provided, The method for treating dross comprises separating non-metallic and metallic components contained in the dross in the molten salt.

2. The method for treating dross according to claim 1 , wherein the molten salt is prepared by dissolving a chloride.

3. The method for treating dross according to claim 1 , wherein the molten salt is heated to a temperature equal to or higher than the melting point of the metal component.

4. The method for treating dross according to claim 1, wherein the dross is in a granular form.

5. The non-metallic components include oxides and / or nitrides; The method for treating dross according to claim 1 , wherein the metal content includes an Al alloy.

6. 2. The method for treating dross according to claim 1, wherein the Al-based molten metal is a recycled Al-based molten metal prepared by melting scrap.

7. The method for treating dross according to any one of claims 1 to 6, further comprising a recovery step of extracting the metal components and / or the non-metal components.

8. The method for treating dross according to claim 7, wherein an Al-based alloy is obtained from the metal content.

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