Environment-friendly synthesis method of magnesium-aluminum hydrotalcite

Abstract

The invention relates to an environment-friendly synthesis method of magnesium-aluminum hydrotalcite, and belongs to the technical field of hydrotalcite synthesis. The method comprises the following steps: 1, adding an aluminum source, a magnesium source, sodium carbonate and sodium bicarbonate into pure water or recycled mother liquor; 2, after mixing, carrying out a hydrothermal reaction at a set temperature; thirdly, mother liquor separation is carried out, and filter residues and filtrate are obtained; 4, adding pure water into the filter residue obtained in the previous step, slurrying, carrying out ultrasonic cleaning, filtering and separating the cleaned product, and carrying out spray drying to obtain a magnesium-aluminum hydrotalcite product; and recovering the filtrate in the third step as a recovered mother solution, or introducing carbon dioxide, and concentrating to separate out sodium bicarbonate crystals as a raw material or a byproduct. According to the synthesis method, sodium metaaluminate is used as a raw material, the synthesis cost is low, no other impurity ions are introduced in the reaction, and the product purity is high. The whole preparation process is green and closed-loop, mother liquor can be recycled and reused, a large amount of waste liquor cannot be discharged, the water consumption for one-time cleaning is low, the yield is high, and the concept of green chemistry is met.

Description

Technical Field

[0001] The invention relates to an environmentally friendly synthesis method of magnesium-aluminum hydrotalcite, belonging to the technical field of hydrotalcite synthesis. Background Art

[0002] Hydrotalcite is a type of layered inorganic material with a special structure. It has adjustable composition and unique structure and properties, and is widely used in flame retardancy, catalysis, ion exchange, adsorption separation, medicine and other fields. In particular, the special properties of hydrotalcite materials such as selectivity, infrared absorption, flame retardancy and ion exchange have made it a new type of inorganic functional material that has been used in polymer materials such as PE and PVC, showing its unique performance advantages.

[0003] At present, the preparation methods of hydrotalcite are studied at home and abroad. The main synthesis methods of hydrotalcite are: salt-alkali co-precipitation method, sol-gel method, hydrothermal synthesis method, ion exchange method, roasting composite oxide recovery method, etc. Among them, the salt-alkali co-precipitation method is the most widely studied. Quan Wuling et al. prepared magnesium-aluminum hydrotalcite by co-precipitation and secondary crystallization of magnesium-aluminum soluble salt solution and alkali solution in patent 102203013A. However, this method has the following disadvantages: ① A large amount of salt-containing by-products are produced and a large amount of salt-containing and alkali-containing wastewater needs to be treated, which has great environmental pressure and low product purity; ② Due to the solubility of the raw materials, it is difficult to increase the concentration, and the single-pot output is small, so the production cost is high; ③ During the co-precipitation reaction, it is necessary to pay attention to the pH value and temperature of the reaction at all times. The synthesized hydrotalcite particles are uneven and the particles are obviously agglomerated. The above shortcomings are also the main problems and technical bottlenecks faced by all co-precipitation methods.

[0004] Compared with the coprecipitation method, hydrothermal synthesis technology has become one of the important methods for synthesizing nanomaterials. The synthesized materials generally have the characteristics of regular and uniform morphology, and the reaction process is mild and the conditions are controllable, making it a more stable and environmentally friendly method for synthesizing hydrotalcite. In patent CN107416872A, Wu Shuhang et al. added magnesium hydroxide and aluminum hydroxide to an alkaline catalyst and passed carbon dioxide through a hydrothermal reaction to prepare magnesium aluminum hydrotalcite. This method recovers the filtrate for recycling, but it is necessary to pass carbon dioxide into the reactor at high temperature for many times, and constantly adjust the reaction pressure. The operation is complicated, and the purity of the prepared magnesium aluminum hydrotalcite is low.

[0005] The raw materials of sodium aluminate are easy to obtain, the preparation process is simple, the investment is small, the cost is low, and the product quality is good. In addition, a large amount of sodium aluminate by-product is generated in many industrial production processes and aluminum-containing solid waste treatment processes. Using sodium aluminate as an aluminum source to prepare magnesium-aluminum hydrotalcite can greatly reduce the production cost of magnesium-aluminum hydrotalcite, and can also make full use of the by-products after aluminum-containing solid waste treatment, which has good economic and environmental significance.

[0006] In the prior art, Liu Zhiqi et al. in patent CN113461037A adopted magnesium oxide or hydroxide as magnesium source, aluminum oxide or hydroxide as aluminum source, added carbonate or bicarbonate and a small amount of sodium aluminate as conversion agent solution, and hydrothermally synthesized magnesium aluminum hydrotalcite with small particle size and high purity at 140°C, wherein aluminate accounts for 1 / 11 of carbonate or bicarbonate, and only a small amount of sodium aluminate is used to promote the reaction, and it is not directly used as aluminum source. In addition, the reaction produces a large amount of high-alkali wastewater and the wastewater needs to be washed multiple times for treatment, which is not suitable for the concept of green synthesis. Summary of the invention

[0007] According to the background problem, the problem to be solved by the present invention is:

[0008] Develop a low-cost, green and environmentally friendly method for producing magnesium-aluminum hydrotalcite.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] An environmentally friendly synthesis method of magnesium-aluminum hydrotalcite comprises the following steps:

[0011] S1. Add aluminum source, magnesium source, sodium carbonate and sodium bicarbonate to pure water or recovered mother liquor, and stir and mix at room temperature for 0.5h to obtain a mixed slurry;

[0012] The molar ratio of aluminum source, magnesium source, carbonate and bicarbonate is aluminum source: magnesium source: carbonate: bicarbonate = 1: 1.0-5.0: 1.0-2.0: 1.0-3.0;

[0013] S2, subjecting the mixed slurry stirred in step S1 to a hydrothermal reaction at a set temperature;

[0014] S3, after the reaction in step S2 is completed, mother liquor separation is performed to obtain filter residue and filtrate;

[0015] S4, adding pure water to the filter residue obtained in step S3 to re-slurry, ultrasonic cleaning for 20-60 minutes, filtering and separating the product after cleaning, and spray drying to obtain a magnesium aluminum hydrotalcite product;

[0016] The aluminum source is sodium metaaluminate;

[0017] The filtrate in step S3 is mainly sodium carbonate and sodium bicarbonate alkaline environmental stabilizer, which can be directly recycled to recover the mother liquor; carbon dioxide can also be introduced to condense and precipitate sodium bicarbonate crystals, which can be used as a raw material or as a by-product for other purposes.

[0018] Preferably, in step S1, the magnesium source is any one of magnesium hydroxide and magnesium oxide, or a mixture of the two in any proportion.

[0019] Preferably, in step S1, the molar ratio of carbonate to bicarbonate is 1:1.2-2.5.

[0020] Preferably, in step S2, the hydrothermal reaction time is 2 to 20 hours, and the set temperature of the hydrothermal reaction is 80 to 200°C.

[0021] Preferably, the set temperature of the hydrothermal reaction is 120-140°C.

[0022] Wherein magnesium oxide or magnesium hydroxide is used as the magnesium source of the reaction, and aluminate is used as the aluminum source. No other impurity ions are introduced during the reaction. The filtrate can be recycled or used to produce sodium bicarbonate at low cost during production. The product purity is high and it is more environmentally friendly. As the hydrothermal reaction proceeds, the pH value of the solution gradually increases. The present invention adds sodium carbonate and sodium bicarbonate in proportion to form a sodium carbonate-sodium bicarbonate buffer solution system. The system can provide a stable alkaline environment for the reaction at the beginning of the reaction, avoiding the miscellaneous crystals caused by the increase of the pH value of the system. In addition, aluminate can also be double hydrolyzed with carbonate or bicarbonate to further ensure the alkaline stable environment of the system. Moreover, no other impurity ions are introduced in the reaction, the product purity is high, there is no impurity phase, the morphology is regular, and the particles are uniform and not agglomerated.

[0023] The beneficial effects of the present invention are:

[0024] The synthesis method of the present invention uses sodium aluminate, which is cheap and widely available, as a raw material, has low synthesis cost, does not introduce other impurity ions in the reaction, and has high product purity. The entire preparation process is green closed-loop, no by-products are generated, the mother liquor can be recycled and reused, and a large amount of waste liquid discharge or treatment problems will not be generated. The amount of water used for one washing is small, the yield is high, and it is environmentally friendly and in line with the concept of green chemistry. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 2 are XRD patterns of different embodiments of the present invention.

[0026] Figure 2 is a SEM image of Example 1 of the present invention. DETAILED DESCRIPTION

[0027] Example 1

[0028] Weigh 32.8g of sodium aluminate, 32.3g of magnesium oxide, 42.4g of sodium carbonate, and 50.4g of sodium bicarbonate, add them into 800mL of water, and stir and mix for 0.5h; hydrothermally react at 120°C for 8h; after the reaction is completed, cool to room temperature, and centrifuge to obtain a crude magnesium aluminum hydrotalcite and a filtrate, collect the filtrate for next feeding, add 1000mL of pure water to the crude magnesium aluminum hydrotalcite, stir and re-slurry, ultrasonically wash with a probe-type ultrasonic generator for 30min, centrifuge and filter, and spray dry to obtain the product magnesium aluminum hydrotalcite.

[0029] Example 2

[0030] The difference between this embodiment and embodiment 1 is that the molar ratio of the magnesium source to the aluminum source is 3:1, the reaction temperature is 140° C., and the recovered mother liquor of embodiment 1 is used.

[0031] Weigh 32.8g of sodium aluminate, 48.4g of magnesium oxide, and 50.4g of sodium bicarbonate and add them to the mother liquor recovered in Example 1, add 200ml of pure water, and stir and mix for 0.5h; hydrothermally react at 140°C for 8h; after the reaction is completed, cool to room temperature, centrifuge to obtain a crude magnesium aluminum hydrotalcite and a filtrate, collect the filtrate, pass carbon dioxide, concentrate and crystallize, and obtain a sodium bicarbonate product for standby use. Add pure water to the crude magnesium aluminum hydrotalcite, stir and re-slurry, use a probe-type ultrasonic generator for ultrasonic washing for 20min, centrifuge and filter, and spray dry to obtain the product magnesium aluminum hydrotalcite.

[0032] Example 3

[0033] The difference between this embodiment and embodiment 1 is that the magnesium source is replaced with magnesium hydroxide, and the sodium bicarbonate crystallized in embodiment 2 is used.

[0034] Weigh 32.8g of sodium aluminate, 116.6g of magnesium hydroxide, 42.4g of sodium carbonate, and 33.6g of sodium bicarbonate and add them to the mother liquor recovered in Example 1, stir and mix for 0.5h; hydrothermally react at 80°C for 20h; after the reaction is completed, cool to room temperature, centrifuge to obtain a crude magnesium aluminum hydrotalcite and a filtrate, and collect the filtrate for next use. Add 1000mL of pure water to the crude magnesium aluminum hydrotalcite, stir and re-slurry, ultrasonically wash with an ultrasonic generator for 60min, centrifuge and filter, and spray dry to obtain the product magnesium aluminum hydrotalcite.

[0035] Example 4

[0036] The difference between this embodiment and embodiment 1 is that the ratio of sodium bicarbonate to sodium carbonate is increased.

[0037] Weigh 32.8g of sodium aluminate, 23.3g of magnesium hydroxide, 84.8g of sodium carbonate, and 100.8g of sodium bicarbonate and add them to 1L of water, stir and mix for 0.5h; hydrothermally react at 200℃ for 2h; after the reaction, cool to room temperature, centrifuge to obtain crude magnesium aluminum hydrotalcite and filtrate, and collect the filtrate for next use. Add 1000mL of pure water to the crude magnesium aluminum hydrotalcite, stir and re-slurry, use a probe ultrasonic generator for ultrasonic washing for 30min, centrifuge and filter, and spray dry to obtain the product magnesium aluminum hydrotalcite.

[0038] The products in the above examples 1-4 were subjected to XRD tests respectively. Figure 1As shown in the figure, after comparison with the standard card 89-0460, the prepared sample has typical magnesium aluminum hydrotalcite characteristic diffraction peaks (003), (006) and (009), a stable baseline, strong and sharp characteristic diffraction peaks, and no impurity peaks, indicating that the magnesium aluminum hydrotalcite product has a regular crystal structure, a relatively single crystal phase, and a high purity product. Then, the sample (Example 1) was analyzed by scanning electron microscopy. Figure 2 As shown, the prepared magnesium-aluminum hydrotalcite is in the form of thin flakes, mainly in a hexagonal layered structure, with regular crystal shape, uniform particle size and good dispersibility.

Claims

1. An environmentally friendly synthesis method of magnesium aluminum hydrotalcite, characterized in that: The following steps are involved: S1. Add aluminum source, magnesium source, sodium carbonate and sodium bicarbonate to pure water or recovered mother liquor, and stir and mix at room temperature for 0.5h to obtain a mixed slurry; The molar ratio of aluminum source, magnesium source, carbonate and bicarbonate is aluminum source: magnesium source: carbonate: bicarbonate = 1: 1.0-5.0: 1.0-2.0: 1.0-3.0; S2, subjecting the mixed slurry stirred in step S1 to a hydrothermal reaction at a set temperature; S3, after the reaction in step S2 is completed, mother liquor separation is performed to obtain filter residue and filtrate; S4, adding pure water to the filter residue obtained in step S3 to re-slurry, ultrasonic cleaning for 20-60 minutes, filtering and separating the product after cleaning, and spray drying to obtain a magnesium aluminum hydrotalcite product; The aluminum source is sodium metaaluminate; The filtrate in step S3 is mainly sodium carbonate and sodium bicarbonate alkaline environmental stabilizer, which can be directly recycled to recover the mother liquor; carbon dioxide can also be introduced to condense and precipitate sodium bicarbonate crystals, which can be used as a raw material or as a by-product for other purposes.

2. The environmentally friendly synthesis method of magnesium-aluminum hydrotalcite according to claim 1, characterized in that: In step S1, the magnesium source is any one of magnesium hydroxide and magnesium oxide, or a mixture of the two in any proportion.

3. The environmentally friendly synthesis method of magnesium aluminum hydrotalcite according to claim 1, characterized in that: In step S1, the molar ratio of carbonate to bicarbonate is 1:1.2-2.

5.

4. The environmentally friendly synthesis method of magnesium aluminum hydrotalcite according to claim 1, characterized in that: In step S2, the hydrothermal reaction time is 2 to 20 hours, and the set temperature of the hydrothermal reaction is 80 to 200°C.

5. The environmentally friendly synthesis method of magnesium aluminum hydrotalcite according to claim 4, characterized in that: The set temperature of the hydrothermal reaction is 120-140°C.

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