Method for preparing nanoscale aluminum oxide from industrial-grade aluminum hydroxide

Abstract

The invention discloses a method for preparing nanoscale aluminum oxide from industrial-grade aluminum hydroxide, which adopts industrial-grade aluminum hydroxide as a raw material to prepare nanoscale aluminum oxide, and comprises the following steps: removing impurities from industrial-grade aluminum hydroxide alkali liquor, removing silicon, performing supercritical alkali removal, removing soluble alkali metal by ionic liquid and the like. According to the present invention, the industrial grade aluminum hydroxide is purified, the yield and the quality of the aluminum oxide product prepared from the purified aluminum hydroxide are high, the low-grade aluminum hydroxide with the low purity can be used as the raw material through the preparation method so as to obtain the high-quality nano-scale aluminum oxide product, and the good application prospect is provided.

Description

Technical Field

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

[0002] Alumina is an industrial raw material. Nano-alumina has high purity, few impurities, and is widely used. It can be used as coatings, ceramic materials, catalysts or catalyst carriers, etc., and is applied to optoelectronic information, medical and other industries. Among the preparation methods of nano-alumina, there are methods such as organic aluminum alkoxide hydrolysis, ammonium aluminum carbonate crystallization pyrolysis, ammonium aluminum sulfate crystallization pyrolysis, and hydrothermal synthesis. The organic aluminum alkoxide hydrolysis method has harsh reaction conditions and high production difficulty; the crystallization pyrolysis method has the problem of difficult impurities to remove and there will be more pollution; the hydrothermal synthesis method has harsh reaction conditions, and hydrogen will be produced 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 aluminum oxide and nano aluminum oxide. Through the thermal decomposition method of ammonium aluminum carbonate, the nano aluminum oxide has a spherical structure and has a non-porous feature. In addition, the particle size of the nano aluminum oxide is uniform, the specific surface area is small, the product quality is high, the process is relatively simple, the reaction mother solution can be recycled, and there are still impurities such as K, Ca, and halogen, and the purity of the raw material is required to be high. The industrial aluminum hydroxide raw material is cheap and is suitable for preparing aluminum oxide. However, it contains more impurities, such as sodium, silicon, calcium and other impurities, which will affect the purity and quality of aluminum oxide when used for aluminum oxide preparation. Especially in the decomposition process of sodium aluminate solution, aluminum hydroxide crystals contain a part of crystallized alkali and have attached alkali on the surface. The traditional washing method can greatly reduce the attached alkali, but the crystallized alkali in the aluminum hydroxide crystals is difficult to remove. And the level of the soluble alkali content (sodium, potassium, etc.) in aluminum hydroxide determines the quality of the aluminum hydroxide product.

[0004] In the prior art, nano-alumina is rarely prepared by using industrial-grade aluminum hydroxide. Therefore, a preparation method of nano-alumina with high purity and few impurities is needed, which has a simple process. Summary of the invention

[0005] The present invention claims a method for preparing nano-alumina from industrial-grade aluminum hydroxide, and 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 filter after the reaction is completed to obtain a primary mother liquor; in step 1, impurities such as Fe in the industrial-grade aluminum hydroxide react with alkali to form a precipitate, while aluminum hydroxide reacts with 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 generate calcium silicate precipitate, thereby removing silicon impurities in the mother liquor;

[0009] Step 3: placing the secondary filtrate in a supercritical device, injecting carbon dioxide and then pressurizing and heating it, stirring and reacting it for 3-6 hours under a supercritical state, cooling and discharging the carbon dioxide, filtering and separating to obtain a tertiary filtrate; carbon dioxide in a supercritical state acts as both a solvent and a reactant, and reacts with the acidic environment provided by water in a subcritical state to react with the base to generate sodium carbonate, remove lattice bases and residual alkaline calcium, magnesium, lithium and other trace impurities;

[0010] Step 4: Add active seed crystals to the three filtrates, crystallize, filter, and obtain aluminum hydroxide solid product; add the aluminum hydroxide solid product to the 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 the subsequent separation is also very simple and efficient;

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

[0012] Furthermore, 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; 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 parameters of the supercritical state are to set the temperature to 60-90°C and the pressure to 20-30MPa, and the conversion of aluminate into aluminum hydroxide can be adjusted by controlling the pressure and temperature 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] Further, the mass ratio of the anhydrous aluminum chloride to trimethylamine hydrochloride is 2.6-2.9:1;

[0017] Furthermore, the calcination condition of step five is heating at 900-1000° C. for 2-4 hours to obtain high-purity nano-scale 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 aluminum oxide with high purity and good quality. The preparation method of the present invention uses aluminum hydroxide with low purity as a raw material, removes Fe, Si, Ca, Na, etc. in sequence, and especially uses supercritical carbon dioxide and subcritical water to treat the solution mainly composed of sodium aluminate. The acidic environment provided by the present invention can simultaneously remove the alkali and lattice alkali on the surface of sodium aluminate, and simultaneously generate lithium carbonate, magnesium carbonate, and calcium carbonate precipitation from trace amounts of Li, Mg, Ca, etc., and the supercritical treatment conditions of the present invention are easier to control in the process of converting aluminate into aluminum hydroxide. At the same time, the present invention adopts an ionic liquid containing Al for Na and K ions that are difficult to remove, which is not only simple in configuration and convenient in processing, but also can effectively dissolve Na and K to separate them from 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] Attached Figure 1 SEM image of the nano-alumina prepared in Example 1;

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

[0022] The present invention is further described below in conjunction with 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, and 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 after the reaction to obtain a secondary filtrate, 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, pH=8.2; add active aluminum hydroxide seeds to the tertiary filtrate, crystallize, filter, and obtain an aluminum hydroxide solid product; add an Al-containing ionic liquid to the aluminum hydroxide solid product, stir for 2h, filter after washing, and then filter and wash with 85°C hot water. After completion, dry to obtain purified aluminum hydroxide, heat the purified aluminum hydroxide obtained at 1000°C in a muffle furnace 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: 65 g of anhydrous aluminum chloride and 25 g of trimethylamine hydrochloride are weighed and mixed in a flask, and then stirred at 30° C. for 4 hours to obtain an Al-containing ionic liquid.

[0025] Example 2

[0026] 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 filter after the reaction is completed to obtain a primary mother liquor; add clear lime water to the primary mother liquor, and the amount of calcium hydroxide added is 0.2% of the industrial-grade aluminum hydroxide powder. After the reaction is completed, filter the solid precipitate to obtain a secondary filtrate, thereby removing silicon impurities in the mother liquor; add hydrochloric acid to the secondary filtrate to adjust the pH to 8, then add active aluminum hydroxide seeds, crystallize, filter, and obtain aluminum hydroxide solid product; add aluminum hydroxide solid product to Al-containing ionic liquid, stir for 2h, filter after washing, and then filter and wash with 85℃ hot water. After washing, dry to obtain purified aluminum hydroxide. The preparation method of the ionic liquid: weigh 65g of anhydrous aluminum chloride and 25g of trimethylamine hydrochloride in a flask, mix them, and stir at 30℃ for 4h to obtain an Al-containing ionic liquid. The purified aluminum hydroxide obtained is heated at 1000℃ in a muffle furnace for 3h to calcine to obtain nano-alumina. The yield is 98.2%.

[0027] Example 3

[0028] 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, and obtain the primary mother liquor; add clear lime water to the primary mother liquor, and the amount of calcium hydroxide added is 1% of the industrial-grade aluminum hydroxide powder. After the reaction is completed, filter the solid precipitate to obtain the secondary filtrate, thereby removing the silicon impurities in the mother liquor; connect the secondary filtrate to the supercritical carbon dioxide equipment, set the parameters to 65°C, the pressure to 22MPa, and the processing time to 4h, cool and discharge carbon dioxide, filter and separate to obtain the tertiary filtrate, the filtrate pH = 9; add active aluminum hydroxide seeds to the tertiary filtrate, crystallize, filter, and obtain aluminum hydroxide solid product; then filter and wash it with 85°C hot water, and after completion, dry it to obtain purified aluminum hydroxide. The purified aluminum hydroxide obtained is heated at 1000°C in a muffle furnace for 3h to calcine to obtain nano-alumina. The yield is 99%.

[0029] Example 4

[0030] 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, and obtain primary mother liquor; add lime water to the primary mother liquor, and the amount of calcium hydroxide added is 0.5% of the industrial-grade aluminum hydroxide powder. After the reaction is completed, filter the solid precipitate to obtain secondary filtrate, thereby removing silicon impurities in the mother liquor; add hydrochloric acid to the secondary filtrate to adjust the pH to 8.5, then add active aluminum hydroxide seeds, crystallize, filter, and obtain aluminum hydroxide solid product; filter and wash the precipitate of the aluminum hydroxide solid product with 85℃ hot water, and after washing, dry to obtain purified aluminum hydroxide, and heat the purified aluminum hydroxide in a muffle furnace at 1000℃ for 3h to calcine 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 of 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 preparation of aluminum hydroxide, and it can be seen from the comparison of sodium content that supercritical carbon dioxide and ionic liquid containing Al can remove most of sodium, iron, and potassium, and only ionic liquid containing Al or supercritical carbon dioxide can not reduce the sodium content to less than 10ppm, and the potassium content is the same. Mainly due to the loss of a part of Al in traditional acid treatment, and the lattice alkali cannot be removed, 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 reduce impurities such as Fe and Mg, 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 liquid containing Al does not cause the dissolution and loss of Al in the solid, 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 a 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-alumina 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 filter after the reaction is completed to obtain a primary mother solution; 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: placing the secondary filtrate in a supercritical device, injecting carbon dioxide and then pressurizing and heating it, stirring and reacting it for 3-6 hours under a supercritical state, cooling and discharging carbon dioxide, and filtering and separating to obtain a tertiary filtrate; Step 4: adding active seed crystals to the filtrate of the three times, crystallizing, filtering, and obtaining a solid aluminum hydroxide product; adding the solid aluminum hydroxide 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; Step 5: calcining the purified aluminum hydroxide to obtain nano-aluminum oxide.

2. A method for preparing nano-alumina from industrial-grade aluminum hydroxide as claimed in 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-alumina from industrial-grade aluminum hydroxide as claimed in claim 1, characterized in that: 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 one.

4. A method for preparing nano-alumina from industrial-grade aluminum hydroxide as claimed in 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-alumina from industrial-grade aluminum hydroxide as claimed in claim 1, characterized in that: The mass ratio of the anhydrous aluminum chloride to trimethylammonium hydrochloride is 2.6-2.9:

1.

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

7. A method for preparing nano-alumina from industrial-grade aluminum hydroxide as claimed in claim 1, characterized in that: The Al-containing ionic liquid in step 4 is an ionic liquid containing aluminum chloride. The preparation method of the Al-containing ionic liquid is as follows: stirring anhydrous aluminum chloride and trimethylamine hydrochloride at 30-35° C. for 4-5 hours to obtain the Al-containing ionic liquid.

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