Method for synthesizing magnetic 4A zeolite based on kaolin and red mud raw materials

Abstract

The invention discloses a method for synthesizing magnetic 4A zeolite based on kaolin and red mud raw materials. The method comprises the following steps: (1) preparing metakaolin; the preparation method comprises the following steps: heating kaolin in an ultrafast high-temperature furnace at 700-900 DEG C for 20 seconds to obtain metakaolin; and (2) preparing reduced red mud. Wrapping red mud with double-layer carbon paper, and heating at 1100-1400 DEG C for 20 seconds to obtain reduced red mud; (3) mixing the metakaolin and the reduced red mud in the steps (1) and (2) according to the mass ratio of 5: (1-2); (4) mixing the mixture in the step (3) with NaOH and water according to a mass ratio of 1: 0.5-1.5: 25, and activating at 80 DEG C for 4 hours to obtain a gel product; (5) transferring the gel product in the step (4) into a reaction kettle, and performing hydrothermal treatment at 80-100 DEG C for 10 hours; and (6) centrifuging the crystallized product in the step (5), washing with distilled water for 3-4 times, and drying at 110 DEG C for 24 hours to obtain the magnetic 4A zeolite. According to the method, the red mud is reduced as a magnetic substance by using a carbon heat rapid burning method, so that the use of reducing gases such as hydrogen is avoided, and low-cost and low-energy-consumption green synthesis of the magnetic 4A zeolite is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of porous material preparation, and in particular to a method for synthesizing magnetic 4A zeolite based on kaolin and red mud raw materials. Background Art

[0002] The chemical composition of 4A zeolite is Na 12 ((AlO2) 12 (SiO2) 12 )·27H2O is a porous hydrated alkali metal aluminum silicate with a framework structure. It belongs to the cubic crystal system and is composed of an 8-membered ring and 6 similar cavities. The diameter of the free cavity formed by the 8-membered ring structure is Zeolite 4A exhibits excellent selective adsorption, high adsorption capacity, ion exchange properties, thermal stability, and environmental safety, making it widely used in detergents, wastewater treatment, gas separation, industrial catalysis, and other fields. The synthesis of zeolite 4A from natural minerals or industrial solid waste offers significant economic and environmental advantages. Its synthesis can be made from a wide range of raw materials, including kaolin, fly ash, kaolin, and bentonite.

[0003] my country has abundant reserves of kaolin, which can be divided into hard kaolin, soft kaolin, and sandy kaolin by raw material type. The first two are coal-bearing kaolins, primarily produced in northern coal-producing regions such as Inner Mongolia, Shanxi, and Hebei. my country ranks first in the world in coal-bearing kaolin production. Sandy kaolin is primarily produced in southern regions such as Guangxi, Guangdong, and Fujian. Using kaolin to produce 4A zeolite is an effective means of reducing zeolite production costs and increasing the utilization rate of kaolin. However, the zeolite produced is difficult to recycle and reuse in adsorption applications such as detergents and sewage treatment. Therefore, imparting magnetism to zeolite is an effective way to improve zeolite recovery efficiency.

[0004] Red mud is rich in iron, and the sodium silicon, aluminum and sodium components in red mud can also be used as a source of zeolite 4A. Currently, an important application of red mud is to reduce hematite and other minerals in red mud to magnetite by reduction and combine them with kaolin to synthesize magnetic zeolite. For example: a method for preparing magnetic 4A zeolite using kaolin and red mud as raw materials. The preparation method is to mix kaolin and red mud, calcine them at high temperature under a nitrogen atmosphere, and then introduce H2 for reduction. The resulting product is then hydrothermally crystallized to synthesize magnetic 4A zeolite. The preparation process avoids the preparation of magnetic particles and reduces the subsequent processing process. In addition, it also includes the use of H2 / Ar reducing atmosphere to reduce red mud and mix it with kaolin to prepare magnetic zeolite (Microporous and Mesoporous Materials, 2024, 370, 113069). And by alkali reduction calcination under N2 atmosphere, the red mud, kaolin and NaOH mixture is alkali-melted and reduced, and then the magnetic zeolite is synthesized by hydrothermal crystallization. The obtained magnetic zeolite has superparamagnetism and is easy to magnetically separate (Powder Technology, 2023, 423, 118495). However, in the above-mentioned magnetic zeolite synthesis method, the operational safety of reducing red mud at high temperature using hydrogen or other reducing gases is difficult to guarantee, and the calcination reduction equipment all uses a tubular furnace. The disadvantage of this calcination method is that the heating and cooling speed is slow and the insulation reduction time is long, which makes the synthesis of magnetic 4A zeolite energy consumption large. The advantage of carbon thermal reduction of fast-burned red mud is that it does not require the introduction of reducing gas, and the heating rate is extremely fast, the reduction time is greatly shortened, which ensures the safety of the reduction process and greatly improves the synthesis efficiency of magnetic 4A zeolite. Summary of the Invention

[0005] Purpose of the Invention: To address the challenges currently encountered in synthesizing magnetic 4A zeolite, the present invention provides a method for synthesizing magnetic 4A zeolite using kaolin and red mud as raw materials. Using kaolin and red mud as raw materials, the red mud is reduced via a rapid calcination reduction process and mixed with metakaolin prepared from kaolin. Alkaline heat is then added, followed by hydrothermal treatment to synthesize magnetic 4A zeolite. This method avoids the use of reducing gases such as H2 and N2, significantly improves reduction efficiency, and achieves low-cost, low-energy, and safe synthesis of magnetic 4A zeolite.

[0006] Technical Solution: The present invention provides a method for synthesizing magnetic 4A zeolite using kaolin and red mud as raw materials, characterized by comprising the following steps: ① Heating kaolin in an ultrafast high-temperature furnace at 700-900°C for 20 seconds to obtain metakaolin. ② Wrapping the red mud in reverse with double-layer carbon paper and heating it in an ultrafast high-temperature furnace at 1100-1400°C for 20 seconds to obtain carbon-calcined reduced red mud. ③ Thoroughly mixing the metakaolin obtained in steps ① and ② with the carbon-calcined reduced red mud in a mass ratio of 5:1-2. ④ Mixing the mixture in step ③ with sodium hydroxide and water in a mass ratio of 1:0.5-1.5:25 and activating the mixture at 80°C for 4 hours to obtain a gel precursor. ⑤ Transferring the gel precursor in step ④ to a polytetrafluoroethylene-lined reactor and hydrothermally crystallizing it at 80-100°C for 10 hours. ⑥ Centrifuging and washing the crystallized product obtained in step 5, followed by drying, yields magnetic 4A zeolite.

[0007] Beneficial effects: The synthesis principle of the present invention is as follows:

[0008] Kaolin, heated at 700-900°C for 20 seconds, removes hydroxyl groups and transforms into active metakaolin, which can be used to synthesize magnetic 4A zeolite. Red mud is wrapped in a double layer of carbon paper, shielded from air. The heated carbon paper generates CO at high temperatures, creating a reducing atmosphere within the carbon paper. The CO reduces the iron oxides in the red mud to magnetite. The metakaolin and reduced red mud are then mixed and treated with a sodium hydroxide solution to dissolve the sodium-silicon-aluminum components, forming a gel that transforms into zeolite nuclei. During the hydrothermal process, the zeolite nuclei continuously absorb the sodium-silicon-aluminum components and grow into larger 4A zeolite crystals. Magnetite particles are encapsulated within the zeolite crystals during their growth, imparting magnetic properties to the 4A zeolite.

[0009] Compared with the prior art, the present invention has the following advantages.

[0010] 1) The reduction process is safe and efficient. Using carbon paper instead of hazardous H2 gas allows for safe and efficient reduction of red mud, converting it into a magnetic material for the synthesis of magnetic 4A zeolite.

[0011] 2) Reaction energy consumption is reduced. The use of an ultrafast high-temperature furnace instead of a tubular furnace greatly shortens the reaction time for the preparation of metakaolin and reduced red mud, thereby greatly reducing the energy consumption required for the synthesis of magnetic 4A zeolite.

[0012] 3) Full utilization of components: The iron element in red mud is utilized. At the same time, its sodium silicate and sodium aluminum react at high temperature to form sodium aluminosilicate and sodium aluminate. These components can be used to construct the zeolite framework, thereby improving resource utilization efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1The XRD pattern and appearance of the carbon thermally sintered reduced red mud in embodiment 1;

[0014] Figure 2 The XRD pattern and appearance of the magnetic 4A zeolite in embodiment 1;

[0015] Figure 3 4A zeolite magnetic hysteresis loop and magnetic separation diagram in embodiment 1; DETAILED DESCRIPTION

[0016] The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0017] Example 1

[0018] 10g of kaolin was placed in batches on carbon paper and then placed in an ultrafast high-temperature furnace for heating at 800℃ for 20s at a heating rate of 10 5 ℃ / s, cooling time is 5s, to obtain metakaolin. 2g of red mud was reversely wrapped with double-layer carbon paper in batches, and then heated in an ultra-fast high-temperature furnace at a heating temperature of 1100℃ for a heating time of 20s to obtain carbon-heated rapidly reduced red mud. After metakaolin and carbon-heated rapidly reduced red mud were fully mixed in a ratio of 5:1, the mixture was added to an appropriate amount of NaOH solution, the mass ratio of the mixture, NaOH and water was 1:1:25, stirred evenly into a colloid, and then transferred to a polytetrafluoroethylene-lined reactor, hydroheated in a 90℃ oven for 10h, and then cooled. The product was centrifuged, washed and dried to obtain magnetic 4A zeolite. The hysteresis loops and magnetic separation diagrams of the carbon-heated rapidly reduced red mud and the synthesized magnetic 4A zeolite prepared in this embodiment are shown as follows: Figure 1 and Figure 2 It can be seen that after carbon thermal reduction, the red mud is transformed into a black powder containing magnetite with paramagnetism, and the magnetic 4A zeolite obtained by adding the reduced red mud also has good paramagnetism, which is conducive to magnetic separation.

[0019] Example 2

[0020] 10g of kaolin was placed in batches on carbon paper and then heated in an ultrafast high-temperature furnace at 900°C for 10 seconds. 2g of red mud was wrapped in reverse with double layers of carbon paper in batches and then heated in an ultrafast high-temperature furnace at 1000°C for 20 seconds. After thoroughly mixing the metakaolin and carbon-calcined reduced red mud in a ratio of 5:2, the mixture was added to an appropriate amount of NaOH solution with a mass ratio of 1:1.5:25 between the mixture, NaOH, and water. The mixture was stirred until it formed a colloid and then transferred to a polytetrafluoroethylene-lined reactor. The mixture was hydroheated in a 90°C oven for 10 hours, then cooled, and the product was centrifuged, washed, and dried to obtain magnetic 4A zeolite. Compared with Implementation 1, the magnetism of the reduced red mud in this implementation was significantly reduced, and the saturation magnetic field strength of the synthesized magnetic 4A zeolite was significantly reduced, indicating that the lower carbon-calcined temperature is not conducive to the reduction of red mud.

[0021] Example 3

[0022] 10g of kaolin was placed in carbon paper in batches and then placed in an ultra-fast high-temperature furnace for heating at 900°C for 10s. 4g of red mud was reversely wrapped with double-layer carbon paper in batches and then heated in an ultra-fast high-temperature furnace at 1200°C for 30s. After the metakaolin and carbon-heated reduced red mud were thoroughly mixed in a ratio of 5:2, the mixture was added to an appropriate amount of NaOH solution with a mass ratio of 1:1.5:25 between the mixture, NaOH and water. The mixture was stirred evenly into a colloid and then transferred to a polytetrafluoroethylene-lined reactor. It was hydroheated in a 90°C oven for 10h and then cooled. The product was centrifuged, washed and dried to obtain magnetic 4A zeolite. Compared with Implementation Option 1, the content of reduced red mud added in this implementation option is increased, and the saturation magnetic field strength of the magnetic 4A zeolite is significantly improved.

[0023] Example 4

[0024] 10g of kaolin was placed in batches on carbon paper and then heated in an ultrafast high-temperature furnace at 800°C for 20 seconds. 6g of red mud was wrapped in reverse with double layers of carbon paper in batches and then heated in an ultrafast high-temperature furnace at 1100°C for 20 seconds. After thoroughly mixing metakaolin and carbon-calcined reduced red mud in a ratio of 5:3, the mixture was added to an appropriate amount of NaOH solution with a mass ratio of 1:2:25 between the mixture, NaOH, and water. The mixture was stirred until it formed a colloid and then transferred to a polytetrafluoroethylene-lined reactor. The mixture was hydroheated in a 90°C oven for 10 hours, then cooled, and the product was centrifuged, washed, and dried to obtain magnetic 4A zeolite. Compared with Implementation 2, the addition of reduced red mud in this implementation increased the content of reduced red mud and further enhanced the saturated magnetic field strength of the magnetic 4A zeolite. However, the crystallinity of the 4A zeolite decreased, indicating that excessive red mud addition affects the hydrothermal crystallization of the 4A zeolite. Therefore, adding red mud to meet the requirements for magnetic separation and recovery of the magnetic zeolite is sufficient.

[0025] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made thereto. Therefore, such modifications and improvements, without departing from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A method for synthesizing magnetic 4A zeolite based on kaolin and red mud raw materials, characterized in that The steps include: (1) Kaolin is wrapped with carbon paper and heated in an ultrafast high-temperature furnace at 700-800°C for 20 seconds to obtain metakaolin; (2) The red mud raw material is reversely wrapped with double-layer carbon paper and then placed in an ultra-fast high-temperature furnace and heated at 1100-1400°C for 20 seconds to obtain carbon thermally sintered reduced red mud; (3) After metakaolin and carbon-thermally calcined reduced red mud are fully mixed in a mass ratio of 5:1-2, the mixture is mixed with sodium hydroxide and water in a mass ratio of 1:0.5-1.5:25, and activated at 80°C for 4 hours to obtain a gel precursor; (4) The gel precursor is transferred to a reactor lined with polytetrafluoroethylene and hydrothermally crystallized at 80-100°C for 10 hours. The crystallized product is centrifuged, washed and dried to obtain a magnetic 4A zeolite.

2. The method for synthesizing magnetic 4A zeolite based on kaolin and red mud raw materials as claimed in claim 1, characterized in that The kaolin in step (1) is a clay mineral mainly composed of the kaolinite family. When pure, it is white and delicate in color. When it contains impurities, it may have gray, yellow, brown and other colors. The appearance may be loose soil blocks or dense rock blocks. Its chemical composition is: SiO2 content is 50-55wt%, Al2O3 content is 35-45wt%, Fe2O3 content is <1wt%, TiO2 content is <0.5wt%, and the total content of other impurities is 1wt% to 3wt%. The average particle size of the kaolin raw material is less than 100μm.

3. The method for synthesizing magnetic 4A zeolite based on kaolin and red mud raw materials as claimed in claim 1, characterized in that The red mud described in step (2) is an industrial waste residue generated during the production process of the aluminum industry. It is usually red or brown because it contains oxides such as iron and titanium. Its main mineral components are hematite, sodalite, kaolinite, anatase, etc. Its chemical composition is: SiO2 content is 10-25wt%, Al2O3 content is 10-20wt%, Fe2O3 content is 25-40wt%, TiO2 content is 2-10wt%, Na2O content is 3-10wt%, and the total content of other impurities is 5wt%-10wt%; the average particle size of the red mud raw material is less than 100μm.

4. The method for synthesizing magnetic 4A zeolite based on kaolin and red mud raw materials as claimed in claim 1, characterized in that The carbon paper used has an external dimension of 12cm long * 5cm wide * 0.05cm thick. The purpose of using double layers of carbon paper to reversely wrap the red mud is to isolate the external air atmosphere so that when the red mud is heated in the carbon paper, it is in a reducing atmosphere under the action of carbon.

5. The method for synthesizing magnetic 4A zeolite based on kaolin and red mud raw materials as claimed in claim 1, characterized in that The ultrafast high temperature furnace used in steps (1) and (2) has a heating rate of 10 5 ℃ / s, cooling rate is ~10 4 ℃ / s, output voltage <40V, current <200A.

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