A method for preparing nano-aluminum oxide from industrial-grade aluminum hydroxide

Abstract

The invention discloses a method for preparing nano-scale alumina from industrial-grade aluminum hydroxide. The invention adopts industrial-grade aluminum hydroxide as a raw material to prepare nano-scale alumina. The industrial-grade aluminum hydroxide is purified by removing impurities, removing silicon, and performing supercritical de-alkali using an ionic liquid to remove soluble alkali metals. The aluminum hydroxide obtained after purification is used to prepare an alumina product with high yield and quality. The preparation method of the invention can use low-grade aluminum hydroxide with low purity as a raw material to obtain a high-quality nano-scale alumina product, which has good application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum oxide preparation, and in particular to a method for preparing nano-scale aluminum oxide from industrial-grade aluminum hydroxide. Background Art

[0002] Alumina is an industrial raw material. Nano-alumina is high in purity, low in impurities, and widely used in various industries, including optoelectronics, information technology, and healthcare. Among the methods for preparing nano-alumina, there are methods such as organoaluminum alkoxide hydrolysis, ammonium aluminum carbonate crystallization and thermal decomposition, ammonium aluminum sulfate crystallization and thermal decomposition, and hydrothermal synthesis. The organoaluminum alkoxide hydrolysis method has harsh reaction conditions and is difficult to produce; the crystallization and thermal decomposition method has the problem of difficult impurity removal and is prone to pollution; and the hydrothermal synthesis method has relatively harsh reaction conditions and also produces hydrogen during the reaction, which is prone to explosion and difficult to achieve industrial production.

[0003] In the prior art, CN117142502A discloses a method for preparing nano-alumina and nano-alumina. By thermal decomposition of ammonium aluminum carbonate, nano-alumina has a spherical structure and a non-porous feature. In addition, the nano-alumina has a uniform particle size, a small specific surface area, a high product quality, a relatively simple process, and a reaction mother liquor that can be recycled. However, impurities such as K, Ca, and halogens are still present, requiring a high purity of the raw materials. Industrial aluminum hydroxide is a cheap raw material suitable for preparing aluminum oxide. However, it contains a large number of impurities, such as sodium, silicon, and calcium, which can affect the purity and quality of aluminum oxide when used for aluminum oxide preparation. In particular, during the decomposition process of sodium aluminate solution, aluminum hydroxide crystals contain a portion of crystallized alkali and have attached alkali on the surface. Traditional washing methods can significantly reduce the attached alkali, but the crystallized alkali in the aluminum hydroxide crystals is difficult to remove. Moreover, the level of soluble alkali content (such as sodium and potassium) in aluminum hydroxide determines the quality of the aluminum hydroxide product.

[0004] In the prior art, nano-alumina is rarely prepared using industrial-grade aluminum hydroxide. Therefore, a method for preparing nano-alumina with a simple process and high purity and low impurities is needed. Summary of the Invention

[0005] The present invention claims protection for a method for preparing nano-sized aluminum oxide from industrial-grade aluminum hydroxide, the technical solution adopted is:

[0006] A method for preparing nano-alumina from industrial-grade aluminum hydroxide, the specific preparation method is:

[0007] Step 1: Add industrial-grade aluminum hydroxide powder to sodium hydroxide solution, stir and react, and then filter to obtain a primary mother liquor. In step 1, impurities such as Fe in the industrial-grade aluminum hydroxide react with the alkali to form a precipitate, while the aluminum hydroxide reacts with the alkali to form soluble sodium aluminate, which is further separated and purified by filtration.

[0008] Step 2: adding lime water to the primary mother liquor, filtering the solid precipitate after the reaction is completed to obtain a secondary filtrate; lime water can react with Si in the sodium aluminate solution to form calcium silicate precipitate, thereby removing silicon impurities in the mother liquor;

[0009] Step 3: The secondary filtrate is placed in a supercritical device, carbon dioxide is injected, and then pressurized and heated. The reaction is stirred under supercritical conditions for 3-6 hours, cooled to expel the carbon dioxide, and filtered to separate the tertiary filtrate. The supercritical carbon dioxide acts as both a solvent and a reactant, and reacts with the acidic environment provided by the subcritical water to react with the base to produce sodium carbonate, removing lattice base and residual alkaline calcium, magnesium, lithium and other trace impurities.

[0010] Step 4: Add active seed crystals to the three filtrates, crystallize, and filter to obtain a solid aluminum hydroxide product; add the aluminum hydroxide solid product to an Al-containing ionic liquid, stir and mix for 1-2 hours, filter, wash with water, and dry to obtain purified aluminum hydroxide; the ionic liquid can dissolve sodium and potassium ions, and subsequent separation is also very simple and efficient;

[0011] Step 5: calcining the purified aluminum hydroxide to obtain nano-aluminum oxide.

[0012] Furthermore, in step 1, the mass concentration of the sodium hydroxide solution is 30-60%, the mass ratio of sodium hydroxide to industrial-grade aluminum hydroxide is 1:1.2-1.6; and the reaction time is 1-2 hours;

[0013] Furthermore, in step 2, the amount of the clarified lime water added is calculated based on the solid content of calcium hydroxide, and the amount of calcium hydroxide added is 0.05-1% of the mass of the industrial-grade aluminum hydroxide powder in step 1;

[0014] Furthermore, in step 3, the supercritical state parameters are set to a temperature of 60-90°C and a pressure of 20-30 MPa. By controlling the pressure and temperature, the aluminate can be adjusted to be converted into aluminum hydroxide and the pH after the reaction can be maintained between 8-9.

[0015] Furthermore, the Al-containing ionic liquid in step 4 is an ionic liquid containing aluminum chloride, and the preparation method of the Al-containing ionic liquid is: stirring anhydrous aluminum chloride and trimethylamine hydrochloride at 30-35° C. for 4-5 hours to obtain the Al-containing ionic liquid;

[0016] Furthermore, the mass ratio of the anhydrous aluminum chloride to trimethylamine hydrochloride is 2.6-2.9:1;

[0017] Furthermore, the calcination condition in step five is heating at 900-1000° C. for 2-4 hours to obtain high-purity nano-alumina.

[0018] Technical Effects

[0019] The present invention uses industrial-grade aluminum hydroxide as a raw material to prepare nano-alumina, which can effectively remove impurities in the raw material and obtain high-purity, high-quality aluminum oxide. The preparation method of the present invention uses aluminum hydroxide of low purity as a raw material, removes Fe, Si, Ca, Na, etc. in sequence, and particularly adopts supercritical carbon dioxide and subcritical water comprehensive treatment for the solution mainly composed of sodium aluminate. The acidic environment provided by the supercritical carbon dioxide and subcritical water can simultaneously remove the alkali and lattice base on the surface of the sodium aluminate, and simultaneously convert the trace amounts of Li, Mg, Ca, etc. into lithium carbonate, magnesium carbonate, and calcium carbonate precipitation. The supercritical treatment conditions of the present invention are easier to control in the process of converting the aluminate into aluminum hydroxide. At the same time, the present invention adopts an Al-containing ionic liquid for Na and K ions that are difficult to remove. The configuration is simple and the processing is convenient. The ionic liquid used can effectively dissolve Na and K so as to separate them from the aluminum hydroxide, and can avoid the problems of high energy consumption and dissolution loss of aluminum hydroxide in the traditional evaporation and concentration process. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Attachment Figure 1 SEM image of the nano-alumina prepared in Example 1;

[0021] Attachment Figure 2 Characterization spectrum of the nano-alumina prepared in Example 1. DETAILED DESCRIPTION

[0022] The present invention will be further described below with reference to specific embodiments.

[0023] Example 1

[0024] Take 20g of industrial-grade aluminum hydroxide powder and add it to 40g of sodium hydroxide solution with a mass fraction of 40%, stir and react, filter after completion to obtain a primary mother liquor; add clarified lime water to the primary mother liquor, the amount of calcium hydroxide added is 1% of the mass of the industrial-grade aluminum hydroxide powder, and filter the solid precipitate to obtain a secondary filtrate after the reaction is completed, thereby removing silicon impurities in the mother liquor; connect the secondary filtrate to a supercritical carbon dioxide device, set the parameters to 65°C, the pressure to 28MPa, and the processing time to 4h, cool and discharge carbon dioxide, filter and separate to obtain a tertiary filtrate with a pH of 8.2; add active aluminum hydroxide seed crystals to the tertiary filtrate, crystallize, and filter to obtain an aluminum hydroxide solid product; add an Al-containing ionic liquid to the aluminum hydroxide solid product, stir for 2h, filter, and then filter and wash with 85°C hot water. After completion, dry to obtain purified aluminum hydroxide, and heat the obtained purified aluminum hydroxide in a muffle furnace at 1000°C for 3h to calcine to obtain nano-alumina (see Figure 1-2 The yield is 99%. The preparation method of the ionic liquid is as follows: 65g of anhydrous aluminum chloride and 25g of trimethylamine hydrochloride are weighed and mixed in a flask, and stirred at 30°C for 4h to obtain an Al-containing ionic liquid.

[0025] Example 2

[0026] 20g of industrial-grade aluminum hydroxide powder is added to 40g of a 40% sodium hydroxide solution, stirred, and filtered after the reaction completes to obtain a primary mother liquor. Clear lime water is added to the primary mother liquor, with the amount of calcium hydroxide added being 0.2% of the industrial-grade aluminum hydroxide powder. After the reaction completes, the solid precipitate is filtered to obtain a secondary filtrate, thereby removing silicon impurities from the mother liquor. The secondary filtrate is adjusted to pH 8 by adding hydrochloric acid, and then activated aluminum hydroxide seeds are added for crystallization and filtration to obtain a solid aluminum hydroxide product. The solid aluminum hydroxide product is added to an Al-containing ionic liquid, stirred for 2 hours, washed, filtered, and then filtered and washed with 85°C hot water. After washing, it is dried to obtain purified aluminum hydroxide. The ionic liquid is prepared by weighing 65g of anhydrous aluminum trichloride and 25g of trimethylamine hydrochloride in a flask, stirring at 30°C for 4 hours to obtain the Al-containing ionic liquid. The purified aluminum hydroxide is calcined in a muffle furnace at 1000°C for 3 hours to obtain nano-alumina. The yield is 98.2%.

[0027] Example 3

[0028] 20g of industrial-grade aluminum hydroxide powder is added to 40g of a 40% sodium hydroxide solution by mass. The mixture is stirred and filtered after the reaction completes to obtain a primary mother liquor. Clarified lime water is added to the primary mother liquor, with the amount of calcium hydroxide added being 1% of the industrial-grade aluminum hydroxide powder. After the reaction completes, the solid precipitate is filtered to obtain a secondary filtrate, thereby removing silicon impurities from the mother liquor. The secondary filtrate is connected to a supercritical carbon dioxide apparatus at 65°C, a pressure of 22 MPa, and a treatment time of 4 hours. The carbon dioxide is then cooled and removed. The filtrate is then filtered to obtain a tertiary filtrate with a pH of 9. Active aluminum hydroxide seed crystals are added to the tertiary filtrate, crystallized, and filtered to obtain a solid aluminum hydroxide product. The product is then filtered and washed with 85°C hot water and dried to obtain purified aluminum hydroxide. The purified aluminum hydroxide is then calcined in a muffle furnace at 1000°C for 3 hours to obtain nano-alumina. The yield is 99%.

[0029] Example 4

[0030] 20g of industrial-grade aluminum hydroxide powder is added to 40g of a 40% sodium hydroxide solution, stirred, and filtered after the reaction to obtain a primary mother liquor. Limewater (0.5% of the amount of calcium hydroxide added to the industrial-grade aluminum hydroxide powder) is added to the primary mother liquor. After the reaction, the solid precipitate is filtered to obtain a secondary filtrate, thereby removing silicon impurities from the mother liquor. The secondary filtrate is adjusted to pH 8.5 by adding hydrochloric acid, and then activated aluminum hydroxide seed crystals are added to crystallize and filter to obtain a solid aluminum hydroxide product. The precipitate of the aluminum hydroxide solid product is filtered and washed with 85°C hot water. After washing, it is dried to obtain purified aluminum hydroxide. The purified aluminum hydroxide is calcined in a muffle furnace at 1000°C for 3 hours to obtain nano-alumina. The yield is 95%.

[0031] Tables 1 and 2 show the partial impurity test results of the industrial-grade aluminum hydroxide raw materials and the obtained aluminum oxide products in Examples 1-4.

[0032] Table 1 Component content of industrial grade aluminum hydroxide before purification

[0033]

[0034] Table 2 Component content of nano-alumina

[0035] Sample name Si (ppm) Fe (ppm) Na (ppm) K (ppm) Mg (ppm) Example 1 18 5 5 5 Not detected Example 2 25 37 12 11 12 Example 3 17 8 248 53 Not detected Example 4 22 26 313 42 10

[0036] As can be seen from the above examples, there are large differences in the yield and purity of aluminum hydroxide between supercritical carbon dioxide treatment and traditional acid treatment and seed crystal preparation aluminum hydroxide methods, and as can be seen from the comparison of sodium content, supercritical carbon dioxide and ionic liquids containing Al can remove the vast majority of sodium, iron, and potassium, while only ionic liquids containing Al or supercritical carbon dioxide can not reduce the sodium content to below 10ppm, and the same is true for potassium content. Mainly due to the loss of a portion of Al in traditional acid treatment, and the inability to remove lattice alkali, resulting in a high final Na content, and supercritical treatment can make full use of its solubility to take away lattice alkali, and also further reduces impurities such as Fe and Mg, thereby ensuring the yield and purity of aluminum oxide. Similarly, ionic liquid washing can fully take away the soluble alkaline metals of solid residues, and ionic liquids containing Al do not cause the dissolution and loss of Al in the solid, thereby ensuring the yield of the product while removing impurities. It can be seen from this that the preparation method in the present invention can use aluminum hydroxide with low purity as raw material, and the impurity removal process is simple, while reducing Al loss, and is suitable as a preparation method for high-purity aluminum oxide.

Claims

1. A method for preparing nano-aluminum oxide from industrial-grade aluminum hydroxide, characterized in that: The specific preparation steps are: Step 1: Add industrial grade aluminum hydroxide powder to sodium hydroxide solution, stir and react, filter to obtain the primary mother liquor; Step 2: adding lime water to the primary mother liquor, and filtering the solid precipitate after the reaction is completed to obtain a secondary filtrate; Step 3: Place the secondary filtrate in a supercritical device, inject carbon dioxide, then pressurize and heat, stir and react for 3-6 hours under supercritical conditions, cool and discharge carbon dioxide, and filter and separate to obtain a tertiary filtrate; Step 4: adding active seed crystals to the three filtrates, crystallizing, filtering, and obtaining a solid aluminum hydroxide product; adding the aluminum hydroxide solid product to an Al-containing ionic liquid, stirring and mixing for 1-2 hours, filtering, washing with water, and drying to obtain purified aluminum hydroxide; the Al-containing ionic liquid in step 4 is an ionic liquid containing aluminum chloride, and the preparation method of the Al-containing ionic liquid is: stirring anhydrous aluminum trichloride and trimethylamine hydrochloride at 30-35° C. for 4-5 hours to obtain an Al-containing ionic liquid; Step 5: Calcine the purified aluminum hydroxide to obtain nano-aluminum oxide.

2. A method for preparing nano-aluminum oxide from industrial-grade aluminum hydroxide according to claim 1, characterized in that: In the step 1, the mass concentration of the sodium hydroxide solution is 30-60%, the mass ratio of sodium hydroxide to industrial-grade aluminum hydroxide is 1:1.2-1.6; and the reaction time is 1-2 hours.

3. A method for preparing nano-aluminum oxide from industrial-grade aluminum hydroxide according to claim 1, characterized in that: The amount of lime water added is calculated based on the solid content of calcium hydroxide, and the amount of calcium hydroxide added is 0.05-1% of the mass of the industrial-grade aluminum hydroxide powder in step 1.

4. A method for preparing nano-aluminum oxide from industrial-grade aluminum hydroxide according to claim 1, characterized in that: In the step 3, the parameters of the supercritical state are setting the temperature to 60-90° C. and the pressure to 20-30 MPa.

5. A method for preparing nano-sized aluminum oxide from industrial-grade aluminum hydroxide according to claim 1, characterized in that: The mass ratio of the anhydrous aluminum chloride to trimethylamine hydrochloride is 2.6-2.9:

1.

6. A method for preparing nano-aluminum oxide from industrial-grade aluminum hydroxide according to claim 1, characterized in that: The calcination condition in step five is heating at 900-1000° C. for 2-4 hours to obtain nano-aluminum oxide.

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