A method for preparing flaky low-sodium alpha-alumina using secondary aluminum dross

Abstract

The application discloses a kind of preparation method for preparing sheet low-sodium alpha-alumina using secondary aluminum ash.The method uses high-temperature sintering method to prepare alumina, and the performance of the product is improved by pickling or water washing.The obtained sheet low-sodium alpha-alumina has the advantages of perfect crystal form development, high purity, low sodium content, high alpha-alumina content, and micro-nano level particle size.The application does not add any morphology inducer, and eliminates the pollution problem caused by ammonia gas generated due to incomplete denitrification of aluminum ash, realizes the removal of harmful elements in aluminum ash, and achieves the purposes of harmless treatment and resource utilization.Also, the application overcomes the shortcomings of high cost, low efficiency, low purity and serious pollution in the prior art for preparing sheet alumina.The prepared sheet low-sodium alpha-alumina has great application potential in high-end automobile polishing, gem processing, high-precision microelectronic processing, cosmetics, functional coating and ceramic toughening, etc.

Description

Technical Field

[0001] This invention belongs to the field of secondary aluminum ash recycling and α-alumina preparation technology, specifically relating to a method for preparing flake-shaped low-sodium α-alumina using secondary aluminum ash. Background Technology

[0002] With the rapid development of my country's economy, the demand for aluminum has continued to increase, making my country the world's largest aluminum producer. As the production scale of metallic aluminum and aluminum alloys in my country continues to expand, the generation of secondary aluminum ash has also shown a sharp upward trend. Secondary aluminum ash is a product of the slag produced in the electrolytic aluminum or casting aluminum production process, which has undergone cooling and processing. It is a recyclable resource, generally producing 30-50 kg of secondary aluminum ash for every ton of aluminum produced. Its main components are Al, Al2O3, Fe, SiO2, nitrides, and metal oxides, with Al and Al2O3 being the most abundant, reaching 10-80 wt%. The main component of secondary aluminum ash is alumina, a stable oxide of aluminum. It is a high-hardness compound with high melting and boiling points. In mining, ceramics, and materials science, it is also known as bauxite. It can be used as an analytical reagent, dehydrator for organic solvents, adsorbent, organic reaction catalyst, abrasive, polishing agent, and refractory material, thus having a wide range of applications.

[0003] Because secondary aluminum ash slag has a high Al2O3 content and is a toxic and hazardous substance, direct disposal would damage the environment. According to the "National Hazardous Waste List" (2016), the following four types of waste slag belong to HW48 non-ferrous metal smelting waste: waste slag generated from the maintenance and disposal of electrolytic cells during aluminum electrolysis, primary smelting slag generated during aluminum pyrometallurgy, salt slag and floating slag generated during aluminum electrolysis, and flammable skimmed slag generated during aluminum pyrometallurgy. Therefore, extracting alumina from secondary aluminum ash slag not only realizes the resource utilization of secondary aluminum ash slag but also promotes environmentally friendly development. However, due to the presence of various impurities in secondary aluminum ash slag, the purity of alumina extracted from it using existing technologies is low. Obtaining high-purity alumina has become a common pursuit for researchers, and it also has extremely high economic and social significance.

[0004] Low-sodium flake α-alumina not only possesses the excellent properties of conventional α-alumina, such as high hardness, high melting point, high temperature resistance, corrosion resistance, and good thermal conductivity, but its special two-dimensional planar structure also gives it special properties such as good adhesion, significant shielding effect, and the ability to reflect light. It has great potential for application in high-end automotive polishing, gemstone processing and high-precision microelectronics processing, cosmetics, functional coatings, and ceramic toughening.

[0005] Therefore, using secondary aluminum ash as raw material to prepare low-sodium flake α-alumina can not only realize the resource utilization of secondary aluminum ash slag, but also be environmentally friendly, and can produce high-quality low-sodium flake α-alumina products, with very good application prospects. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing flake-shaped low-sodium α-alumina using secondary aluminum ash. This method is not only a novel approach to the comprehensive utilization of secondary aluminum ash, but also addresses the pollution problem caused by incomplete denitrification of aluminum ash leading to ammonia production, thus achieving the removal of harmful elements and achieving harmless treatment and resource utilization. Furthermore, this method is a novel method for preparing flake-shaped low-sodium α-alumina. It uses a high-temperature sintering method to prepare alumina, and improves the product's performance through acid washing or water washing. It overcomes the shortcomings of existing technologies in preparing flake-shaped alumina, such as high cost, low efficiency, low purity, and severe pollution. The obtained low-sodium flake-shaped low-sodium α-alumina has advantages such as well-developed crystal structure, high purity, low sodium content, high α-alumina content, and micro / nano-scale particle size. It has great application potential in high-end automotive polishing, gemstone processing, high-precision microelectronics processing, cosmetics, functional coatings, and ceramic toughening.

[0007] A method for preparing flake-shaped low-sodium α-alumina using secondary aluminum ash specifically includes the following steps:

[0008] (1) Crush, grind and sieve the secondary aluminum ash;

[0009] (2) After the aluminum ash from step (1) is crushed and ground, it is mixed evenly with the additive and then calcined; the additive is a mixture including sodium carbonate, oxidant and calcium carbonate; the oxidant includes at least one of sodium nitrate, sodium percarbonate, sodium peroxide and calcium peroxide.

[0010] (3) After the clinker from step (2) is removed and cooled, it is dissolved with dilute alkali or water, and the solid and liquid are separated. The filtrate is crude sodium aluminate solution.

[0011] (4) Add calcium oxide to deeply desiliconize the crude sodium aluminate solution, add aluminum hydroxide seed crystals, crystallize to obtain aluminum hydroxide, filter and then calcine the aluminum hydroxide at high temperature to obtain aluminum oxide.

[0012] (5) The alumina obtained in step (4) is acid-washed and water-washed and then dried to obtain flake-shaped low-sodium α-alumina.

[0013] Step (1) Pass through a 200-mesh sieve.

[0014] In step (2), the amount of sodium carbonate added is 1.4-3 times the amount of alumina in the secondary aluminum ash, the amount of oxidant added is 1.2-2.4 times the amount of aluminum nitride in the secondary aluminum ash, and the amount of calcium carbonate added is 2.6-4.6 times the total amount of fluoride and silicon dioxide in the secondary aluminum ash.

[0015] Step (2) The roasting temperature is 800-1300℃ and the time is 1-5h.

[0016] Step (2) The additive reacts with the metal in the secondary aluminum ash, and the reaction at high temperature yields the corresponding carbonate precipitate.

[0017] The dilute alkaline solution used in step (3) includes sodium carbonate solution or sodium hydroxide solution with a concentration of 1-3 mol / L and a dissolution time of at least 30 min.

[0018] The insoluble filter residue after filtration in step (3) is fluorine-containing residue and is returned to the electrolytic cell for use.

[0019] In step (4), the ratio of calcium oxide to 10-30g / 500g secondary aluminum ash is used, and the amount of aluminum hydroxide seed crystals added is 250-350g / 500g secondary aluminum ash; then aluminum oxide is obtained by high-temperature calcination.

[0020] Step (4) Calcination treatment: the temperature is set to 1000-1400℃, the time is set to 2-5h, and the rate is controlled at 5-10℃ / min.

[0021] Step (3) mainly involves the reaction of alkaline solution with all metals to form a precipitate, which is then separated to obtain a crude sodium aluminate solution. In step (4), the crude sodium aluminate solution is separated and purified, and then seed aluminum hydroxide is added to obtain aluminum hydroxide. After high-temperature calcination, aluminum oxide is obtained.

[0022]

[0023] Step (5) The acid includes one or more of nitric acid, carbonic acid, acetic acid, oxalic acid, hydrochloric acid or citric acid; the acid concentration is controlled within the range of 0.03%-3.0%; the solid content of the slurry is controlled at 20-60% during pickling; the pickling time is controlled at 1-5h; the pH value of the slurry is controlled at 6.0-8.0; after pickling, the slurry is washed with pure water or ultrapure water until neutral, and then dried at a temperature controlled at 60℃-110℃ for at least 6h.

[0024] The flake-shaped low-sodium α-alumina obtained by this invention has a sodium oxide content as low as 0.13% and a particle size of 20-50 micrometers. The flake-shaped low-sodium α-alumina prepared by this invention exhibits good stability, and the preparation process is simple and low-cost, making it suitable for industrial production. By controlling the slurry solid content during the pickling process to 20-60%, this invention can control the slurry density and flowability, facilitating industrial production and sodium oxide removal. By controlling the pH value to around 7.0 during pickling and water washing, the sodium oxide content after pickling can be reduced, avoiding environmental pollution and equipment damage. Compared with existing technologies, this invention does not require the introduction of desodiuming salts or additives; it directly uses pure water or softened water, effectively avoiding pipeline corrosion. The process is simple to operate, low-cost, and suitable for large-scale production. Attached Figure Description

[0025] Figure 1 This is a diagram of secondary aluminum ash raw materials;

[0026] Figure 2 The product prepared by this invention is flake-shaped α-Al2O3;

[0027] Figure 3 This is a SEM image of the original secondary aluminum ash sample;

[0028] Figure 4 This is a SEM image of the sheet-like α-Al2O3 prepared according to the present invention;

[0029] Figure 5 This is the XRD pattern of the original secondary aluminum ash sample;

[0030] Figure 6 This is the XRD pattern of the sheet-like α-Al2O3 prepared according to the present invention. Detailed Implementation

[0031] The following examples are intended to further illustrate the present invention, but not to limit it.

[0032] Example 1

[0033] A method for preparing flake-shaped low-sodium α-alumina using secondary aluminum ash, the specific steps of which are as follows:

[0034] (1) Crush and grind the secondary aluminum ash with a crusher and sieve it (200 mesh, 500g dosage);

[0035] (2) After the aluminum ash from step (1) is crushed and ground, it is mixed evenly with the additives and then calcined (at a temperature of 1200℃ for 3 hours) and the sintering gas is recovered.

[0036] (3) After the clinker from step (2) is taken out and cooled to room temperature, it is dissolved in dilute alkaline solution (1M sodium hydroxide solution) for 1 hour, and the solid and liquid are separated. The filtrate is crude sodium aluminate solution, and the insoluble filter residue is fluorine-containing residue to be returned to the electrolytic cell. The sodium aluminate solution after deep desilication by adding calcium oxide (calcium oxide addition amount 10g) to the crude sodium aluminate solution is decomposed by seed crystal (aluminum hydroxide seed crystal addition amount 200g) to obtain aluminum hydroxide, and then calcined at high temperature (temperature 1400℃, time 5h, heating rate 5℃ / min) to obtain aluminum oxide.

[0037] (4) The alumina product obtained in step (3) is pickled (citric acid) with an acid concentration of 0.03%; the solid content of the slurry is controlled at 40% during pickling; the pickling time is controlled at 2 hours; the pH value of the slurry is controlled at 7.0; the pickled slurry is washed with pure water or ultrapure water (washed until the pH value is 7.0) and dried (the temperature is controlled at 100℃ and the drying time is 6 hours). The sodium oxide content of the flake low-sodium α-alumina obtained after pickling and washing is controlled to be as low as 0.13%.

[0038] Step (2) The additive is a mixture of sodium carbonate, oxidant and calcium carbonate; the oxidant is sodium nitrate, the amount of sodium carbonate added is 2 times the amount of alumina in aluminum ash, the amount of oxidant added is 2.4 times the amount of aluminum nitride in aluminum ash, and the amount of calcium carbonate added is 3 times the total amount of fluoride and silicon dioxide in aluminum ash.

[0039] The secondary aluminum ash used as raw material has the following percentage content as an indicator parameter:

[0040]

[0041] The percentage content of the flake-shaped low-sodium α-alumina obtained by the method of this invention is as follows:

[0042]

[0043] Example 2

[0044] All steps are the same as in Example 1, except that the concentration of citric acid is 1%.

[0045] The percentage content of the flake-shaped low-sodium α-alumina obtained by the method of this invention is as follows:

[0046]

[0047] Example 3

[0048] All steps are the same as in Example 1, except that the concentration of citric acid is 3%.

[0049] The percentage content of the flake-shaped low-sodium α-alumina obtained by the method of this invention is as follows:

[0050]

[0051] Under the same conditions as in Example 1, the present invention found that the type and concentration of acid during pickling have a significant impact on the performance parameters of the final product. The specific comparison results are as follows:

[0052] Different types of acids:

[0053]

[0054] Different citric acid concentrations:

[0055]

Claims

1. A method for preparing flake-shaped low-sodium α-alumina using secondary aluminum ash, characterized in that, Specifically, the steps include the following: (1) Crush and grind the secondary aluminum ash with a crusher and sieve it through a 200-mesh screen. The dosage is 500g. (2) After the aluminum ash from step (1) is crushed and ground, it is mixed evenly with the additives and then calcined at 1200℃ for 3 hours, and the sintering gas is recovered. (3) After taking out the clinker after roasting in step (2), it is cooled to room temperature and dissolved with 1M sodium hydroxide solution for 1 hour. Solid-liquid separation is performed. The filtrate is crude sodium aluminate solution and the insoluble filter residue is fluorine-containing residue to be returned to the electrolytic cell. 10g of calcium oxide is added to the crude sodium aluminate solution. After deep desilication, the sodium aluminate solution is decomposed by adding 200g of aluminum hydroxide seed crystals to obtain aluminum hydroxide. Then, it is calcined at a high temperature of 1400℃ for 5 hours and a heating rate of 5℃ / min to obtain aluminum oxide. (4) The alumina product obtained in step (3) is pickled with citric acid, and the concentration of acid is controlled at 0.03%. The solid content of the slurry is controlled at 40% during pickling. The pickling time is controlled at 2h. The pH value of the slurry is controlled at 7.

0. The pickled slurry is washed with pure water or ultrapure water until the pH value is 7.

0. It is then dried at 100℃ for 6h. The sodium oxide content of the flake low sodium α-alumina obtained after pickling, washing and drying is as low as 0.13%. Step (2) The additive is a mixture of sodium carbonate, oxidant and calcium carbonate; the oxidant is sodium nitrate, the amount of sodium carbonate added is 2 times the amount of alumina in aluminum ash, the amount of oxidant added is 2.4 times the amount of aluminum nitride in aluminum ash, and the amount of calcium carbonate added is 3 times the total amount of fluoride and silicon dioxide in aluminum ash.

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