Dross processing method

Abstract

Provided is a dross processing method that can efficiently recover Al (alloy) from an aluminum-based dross. The present invention is a dross processing method comprising a supply step for introducing, into a molten salt reservoir, dross that was produced on an Al-based molten metal, wherein 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, for example, 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 in, for example, a granular form. The dross is produced, for example, 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.

Description

How to dispose of dross

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

[0002] Aluminum smelting consumes a huge amount of energy and produces carbon dioxide (CO ２ ), it is important from the perspective of reducing the environmental load and building a recycling-oriented society to recover and effectively utilize aluminum from aluminum-based dross (simply referred to as "dross") that is generated during the manufacturing 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.

[0004] JP 6-100956, JP 9-310129, JP 2002-322519, JP 2020-142190, JP 2006-312766, JP 2015-83711

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

[0006] Patent Document 5 relates to an ash squeezing method (apparatus) for recovering aluminum 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 squeezing. In such conventional ash squeezing, the dross is heated to a high temperature in the atmosphere, resulting in a large loss of aluminum due to oxidation.

[0007] The present invention has been made in view of the above circumstances, and aims to provide a new method for treating dross that is different from conventional methods.

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

[0009] <<Dross Treatment Method>> (1) The present invention provides a dross treatment method, for example, comprising a supply step of pouring dross generated on an Al-based molten alloy into a molten salt reservoir, and separating 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 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 vessel) and aggregate due to the difference in specific gravity with the molten salt.

[0012] The metal components are in a refined state in which non-metallic components have been removed, and are shielded from the outside world (e.g., the atmosphere) by the molten salt, thereby suppressing oxidation, nitridation, etc. Therefore, according to the present invention, Al can be efficiently recovered in a high-quality state from the dross used as a raw material, while suppressing Al loss and ammonia generation, etc.

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

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

[0015] 1 is an X-ray diffraction pattern obtained by analyzing dross (an example); 2 is an X-ray diffraction pattern obtained by analyzing chlorides obtained after treating the dross; 3 is a schematic diagram illustrating the dross treatment process; 4 is an example of a component analysis of dross, chlorides obtained after treating the dross, and metal ingots.

[0016] The above-described 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 components related to a method or a product (e.g., an Al substrate).

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

[0018] Dross contains metal components (MP: Metal Products) as well as various non-metallic components (NMP: Non-Metal Products). The non-metallic components 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, oxides of Si, Fe, Mg, Cu, Mn, Zn, etc. (composite oxides (e.g., Al ２ O ３ MgO (spinel), etc.), nitrides, chlorides (halides, carbonates, sulfates, etc.), intermetallic compounds, etc. Oxides of Fe include FeO, Fe ３ O ４ , Fe ２ O ３ In addition to the above, spinel type (FeAl ２ O ４ etc.) etc. may also be used.

[0019] The metal component containing Al as a main component may be pure Al or an Al alloy, and may be in any form (shape, size, etc.). The metal component in the dross is usually covered, in whole or in part, with a non-metallic component.

[0020] For example, the dross may be in a solid-liquid coexisting state immediately after being removed from a crucible containing the Al-based molten metal, or may be in a solid state obtained by cooling and solidifying the dross.

[0021] Molten Salt Molten salt is prepared, for example, by dissolving a stable metal halide (particularly, chloride and / or bromide). The metal element constituting the halide is, for example, one or more of Ca, Na, Li, Sr, K, Mg, Cs, Ba, etc. Na and / or K halides (particularly, chlorides) are inexpensive and stable, making them suitable for molten salts. Naturally, the component 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 (e.g., F) due to components contained in the dross (e.g., residual components of the flux).

[0022] The molten salt may be a mixed salt containing a mixture of multiple metal halides (for example, 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 recovered by settling. The molten salt is not limited to a single layer, and may be a multi-layer.

[0023] The molten salt is sufficient as long as 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 components (mainly Al). However, if the molten salt is at or above the melting point, the metal components are more likely to dissolve, aggregate, integrate, etc., and the recovery thereof is improved.

[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) sufficient to immerse the supplied dross. The layer thickness may be, for example, 5 to 100 mm or 15 to 50 mm.

[0025] <<Al-based molten metal>> An Al-based molten metal that generates dross can be obtained, for example, by melting metal, scrap (waste material), etc. If the dross generated during the refining of recycled Al-based molten metal obtained by melting scrap is treated, more effective utilization of Al resources (improvement of recovery rate) can be achieved.

[0026] <<Treatment Method>> (1) Supply Step The form of feeding the dross into the molten salt reservoir is not limited. The dross may be fed (added, poured, etc.) into the molten salt reservoir continuously or intermittently.

[0027] Adding or scattering granulated dross to molten salt promotes reaction with the molten salt and improves the efficiency of metal recovery. 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 mesh openings).

[0028] (2) Recovery Step The recovery form of the metal component is not limited. The metal component may be recovered continuously or intermittently. For example, the molten metal component (treated molten metal) may be continuously removed from the bottom of the molten salt reservoir. Alternatively, the metal component cooled and solidified together with the molten salt may be recovered by removing the solid salt (by washing with water, etc.). The recovered metal component may be used for casting as is, or may be used as an Al-based alloy (raw material).

[0029] The present invention will be described in more detail based on a specific example in which metal components (Al-based alloys) are recovered from dross generated in the manufacturing process of Al-based recycled ingots.

[0030] <Dross> (1) Test Material Scrap (raw material) of an Al-based component was melted and subjected to a slag removal process. The dross formed on the recycled Al-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 particle length was 5 mm or less (grain length: approximately 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). The obtained diffraction pattern is shown in Figure 1.

[0032] From the diffraction pattern, the dross surface is composed of at least aluminum nitride (AlN), aluminum oxide (Al ２ O ３ ), spinel (MgAl ２ O ４It was found that the sample was covered with non-metallic components such as silicon (Si) and iron oxide (FeO). X-ray diffraction (XRD) can only analyze substances present on the surface of the object being measured. This is thought to be why 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 Figure 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 removal process were also detected. The range of elements measured by fluorescent X-ray analysis is １１ Na~ ９２ U. Therefore, ７ N. ８ O et al. 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 metal components (pure Al or Al alloy) that make up the majority of the dross were almost entirely covered by non-metallic components.

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

[0037] Dross Processing (1) Supply Process 1,000 g of test material (dross) was added to the molten salt reservoir (supply process), and the subsequent behavior 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 and became spherical due to surface tension in the molten salt. The spherical metallic components then gradually coalesced 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 step The entire crucible, in which the molten salt layer containing non-metallic components was separated into two layers, the molten salt layer containing non-metallic components and the metal layer below it, was cooled. The metal mass solidified from the metal layer and the chloride solidified from the molten salt were separately recovered (recovery step).

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

[0040] (3) Analysis The chemical composition of the recovered metal ingots was analyzed by spark discharge optical emission spectroscopy. The results are shown in Table 2 of Figure 4. As is clear from Table 2, the chemical composition of the metal ingots 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] Furthermore, as is clear from a comparison of Tables 1 and 2, the Fe concentration in the metal ingot was significantly lower than the Fe concentration in the dross. In other words, it was found that the above-described 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 chloride was analyzed using the above-mentioned X-ray diffractometer, and the resulting diffraction pattern is shown in FIG.

[0043] The diffraction pattern shows that in addition to sodium chloride (NaCl) and potassium chloride (KCl), which are the raw materials of the molten salt, at least aluminum nitride (AlN), aluminum oxide (Al ２ O ３ ) and spinel (MgAl ２ O ４ ) was 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 treated chloride 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 10 mass% or more of Fe in addition to Cl, K, and Na, which are the raw materials for the molten salt. This demonstrates once again that the molten salt can take in Fe, thereby producing a refined metal ingot with a low Fe concentration.

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

[0046] 914 g of the above-mentioned test material (dross) was placed in a graphite crucible and heated to 800°C in the atmosphere. During this process, the molten metal components in the crucible were stirred with a graphite rod to be integrated. 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 component (Al).

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

[0048] The metal ingot was also analyzed by the spark discharge optical emission spectroscopy described above. The results are shown in Table 4 of Figure 4. As is clear from Table 4, the elemental composition of the metal ingot 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 ingot was as high as 2.1 mass%. In other words, it was found that with conventional ash extraction, the Fe (or iron oxide) contained in the dross also dissolves into the metal ingot, and almost no Fe is removed.

[0049] From the above, according to the treatment method of the present invention, the non-metallic content (Al ２ O ３ , AlN, MgAl ２ O ４ It was confirmed that metal components from which impurity elements (e.g., FeO) and other impurities have been removed can be efficiently recovered from the dross.

Claims

1. A method for treating dross comprising a step of feeding dross generated on an Al-based molten alloy into a molten salt reservoir, and separating the 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. A method for treating dross as described in claim 1, wherein the molten salt is heated to a temperature equal to or higher than the melting point of the metal.

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

5. The method for treating dross according to claim 1, wherein the non-metallic components include oxides and / or nitrides, and the metallic components include Al alloys.

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