Method for converting quartz and mica impurities in sandy kaolin and synthesizing 4A zeolite

Abstract

The invention discloses a method for converting quartz and mica impurities in sandy kaolin and synthesizing 4A zeolite, which comprises the following steps: uniformly mixing the sandy kaolin, sodium carbonate and aluminum hydroxide, wrapping with carbon paper, and heating in an ultrafast high-temperature furnace at 1100-1400 DEG C for 20 seconds to obtain a precursor; grinding the precursor into fine powder, and adding a proper amount of 0.01 mol / L NaOH solution to obtain a colloidal product; stirring the colloidal product at 80 DEG C for 4 hours, transferring the colloidal product to a reaction kettle, putting the reaction kettle into a drying oven, and performing hydrothermal treatment at 80-100 DEG C for 5-10 hours to obtain a crystallized product; and centrifuging the crystallized product at 5000 revolutions per minute for 1 minute, washing with distilled water for 3-4 times, and drying at 110 DEG C for 24 hours to obtain the 4A zeolite. According to the present invention, the precursor is rapidly generated under the action of sodium carbonate mainly for the sandy kaolin with characteristics of high quartz and mica impurity content, and the 4A zeolite with high purity can be synthesized after the hydrothermal treatment, such that the reaction energy consumption is reduced, the NaOH consumption is substantially reduced, and the green 4A zeolite synthesis method is superior to the traditional high temperature calcination method and the alkali fusion method in the green 4A zeolite synthesis aspect.

Description

Technical Field

[0001] The present invention relates to the technical field of porous material synthesis, and in particular to a method for transforming quartz and mica impurities in sandy kaolin and synthesizing 4A zeolite by using a Joule heat melting method. 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 system. The center of the unit cell is a diameter of The hole is formed by connecting an 8-membered ring and 6 similar holes. The diameter of the free hole formed by the 8-membered ring structure is Therefore, it is called 4A zeolite. 4A zeolite has excellent selective adsorption, high adsorption capacity, ion exchange performance, thermal stability and environmental safety performance. It is widely used in many fields such as detergents, sewage treatment, gas separation, industrial catalysis, etc.

[0003] The current mature industrial process for synthesizing 4A zeolite primarily utilizes the water glass method, which relies on high-purity chemical raw materials such as sodium silicate and sodium aluminate, resulting in high costs and significant resource consumption. Synthesizing 4A zeolite from natural minerals or industrial solid waste offers significant economic and environmental advantages. Its raw materials can be sourced from a wide range of sources, such as kaolin, fly ash, coal gangue, and bentonite. Kaolin, with a Si / Al ratio similar to that of zeolite 4A and abundant reserves in my country, is an ideal raw material for synthesizing 4A zeolite.

[0004] Kaolin in my country is primarily classified by type into coal-based kaolin and sandy kaolin. Coal-based kaolin is generally characterized by a high kaolinite content. The primary difficulty in synthesizing 4A zeolite lies in removing impurities such as C, Fe, and Ti. Sandy kaolin, on the other hand, generally has lower Fe and Ti contents but higher concentrations of gangue minerals such as quartz and mica. These gangue minerals are difficult to completely remove using traditional beneficiation methods, resulting in the synthetic 4A zeolite often containing impurities such as quartz and mica.

[0005] The traditional method of synthesizing 4A zeolite by calcining kaolin. The general preparation method is refined kaolin → calcination → metakaolin → synthesis crystallization → filtration → water washing → drying → packaging the finished product. The final 4A zeolite product has the advantages of high whiteness, fine particle size, good dispersibility, large exchange capacity, and good adsorption performance. In addition, the synthesis reaction process is simple, the quality is reliable, and the 4A zeolite product is cheap and has good economic benefits. However, for sandy kaolin containing quartz and mica, these impurities are difficult to effectively transform within the calcination temperature range of metakaolin (600-900°C), and ultimately still exist as a stable impurity phase during the crystallization process.

[0006] In response to this, another method for synthesizing 4A zeolite using kaolin alkali fusion was invented. This method is characterized by calcining kaolin and sodium hydroxide together. Under the action of sodium hydroxide, the kaolinite, quartz, and mica in the kaolin react to form sodium silicate and sodium aluminate. Further hydrothermal crystallization is carried out to produce high-purity 4A zeolite, while the impurity phase is converted and utilized under the action of strong alkali. However, this method requires the use of a large amount of strong alkali during the calcination stage, which not only increases production costs but also has poor safety. In addition, the alkaline vapor generated during the calcination process causes corrosion to the equipment, significantly reducing its service life.

[0007] In addition, both high-temperature calcination and alkali fusion methods generally use muffle furnaces for calcination. The disadvantages of this calcination method are slow heating and cooling rates and long holding times. The calcination temperature mainly comes from the holding process, and the heat during the heating and cooling processes cannot be effectively utilized, greatly increasing the energy consumption of the kaolin synthesis 4A zeolite reaction. The advantage of Joule heating is that the heating and cooling rates are extremely fast (~105℃ / s and ~104℃ / s, respectively), and the temperature control can be customized. It has the advantages of high efficiency, energy saving, environmental protection, and controllability. It has been widely used in ceramic synthesis, flash graphene synthesis, high-entropy oxide preparation, lithium-ion battery recycling, and plastic degradation. Summary of the Invention

[0008] Purpose of the invention: To address the problems existing in the current technology for synthesizing 4A zeolite, the present invention provides a method for synthesizing 4A zeolite by converting quartz and mica impurities using sandy kaolin as raw material through a Joule heat alkali fusion method. After uniformly mixing sandy kaolin, anhydrous sodium carbonate, and aluminum hydroxide, the raw materials are converted into a precursor for 4A zeolite synthesis under the action of Joule heat. After the precursor is aged, it is hydrothermally treated in an alkali solution with a pH between 11 and 13 to obtain the final 4A zeolite product. This method greatly reduces the amount of sodium hydroxide used, reduces the discharge of waste alkali solution, improves the safety of the alkali fusion process, and greatly reduces the energy consumption of calcination, thereby achieving low-cost and green preparation of 4A zeolite, which is economical and environmentally friendly.

[0009] Technical solution: Sandy kaolin, anhydrous sodium carbonate, and aluminum hydroxide are mixed evenly, then wrapped in carbon paper and heated in an ultrafast high-temperature furnace at 1100-1400°C for 20 seconds to obtain a 4A zeolite precursor. The precursor is then ground into a fine powder and mixed with an appropriate amount of 0.01 mol / L NaOH solution to obtain a colloidal product. The colloidal product is stirred continuously at 80°C for 4 hours. The reaction product is transferred to a polytetrafluoroethylene bottle and placed in a reactor. It is hydrothermally crystallized in an oven at 80°C-100°C for 5-10 hours to obtain a crystallized product. The crystallized product is centrifuged at 5000 rpm for 1 minute and then washed with distilled water 3-4 times until the solution is neutral after the final wash. Finally, it is dried at 110°C for 24 hours to obtain 4A zeolite. The present invention mainly targets low-grade kaolin raw materials with high quartz and mica impurity content, rapidly generates a 4A zeolite precursor under the action of sodium carbonate, and can synthesize high-purity 4A zeolite after hydrothermal treatment.

[0010] Beneficial effects: The synthesis principle of the present invention is as follows:

[0011] Sandy kaolin, anhydrous sodium carbonate and aluminum hydroxide are evenly mixed and react under the action of Joule heat to form sodium aluminosilicate and potassium feldspar (when containing mica) precursors. Therefore, compared with the high-temperature calcination method, in addition to kaolinite, the quartz and mica impurities in the kaolin are activated, and the Si and Al components in the impurities are effectively utilized. Finally, under the action of 0.01 mol / L NaOH solution, the activated sodium aluminosilicate component is dissolved to form a gel and converted into zeolite nuclei. During the hydrothermal process, the zeolite nuclei continuously absorb the sodium aluminosilicate component to grow into larger-sized 4A zeolite crystals.

[0012] Compared with the prior art, the present invention has the following advantages:

[0013] 1) The alkali fusion process is safe and efficient. Using Na2CO3 instead of the hazardous chemical NaOH can effectively activate kaolinite, quartz, and mica impurities in kaolin, converting them into active precursors for zeolite synthesis.

[0014] 2) Reaction energy consumption is reduced. Using Joule heat instead of traditional high-temperature calcination method greatly shortens the reaction time of precursor preparation, thereby greatly reducing the energy consumption required for kaolin activation;

[0015] 3) Full utilization of impurities: The Si and Al components in quartz in kaolin and muscovite are fully integrated into the zeolite framework, improving resource utilization efficiency;

[0016] 4) High purity of the synthesized product. This method significantly reduces the impurity content, resulting in the synthesis of 4A zeolite with high crystallinity, a single composition, and low impurity content. This innovative method provides a green and efficient way to utilize low-grade kaolin. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 XRD pattern and SEM photo of the precursor prepared using sandy kaolin as raw material in embodiment 1;

[0018] Figure 2 XRD pattern and SEM photo of 4A zeolite synthesized using sandy kaolin as raw material in embodiment 1; DETAILED DESCRIPTION

[0019] The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0020] Example 1

[0021] 5g of sandy kaolin, 5g of anhydrous sodium carbonate and 0.5g of aluminum hydroxide were mixed evenly, placed in carbon paper in batches, and then placed in an ultra-fast high-temperature furnace for heating at a temperature of 1300°C, a heating time of 20s, and a heating rate of 10 5 ℃ / s, cooling time is 5s, to obtain a precursor. The precursor is then crushed and added to an appropriate amount of 0.01mol / L NaOH solution with a solid-liquid mass ratio of 1:25. It is stirred evenly to form a colloid, which is then transferred to a polytetrafluoroethylene-lined reactor and hydroheated in a 90℃ oven for 10h. It is then cooled and the product is centrifuged and washed to obtain 4A zeolite.

[0022] The XRD patterns and SEM images of the precursor and the synthesized 4A zeolite prepared in this embodiment are shown in FIG. Figure 1 and Figure 2 As shown in the figure, after Joule heating, the sandy kaolin reacts with anhydrous sodium carbonate and aluminum hydroxide to form sodium aluminosilicate and potassium feldspar. The zeolite obtained after hydrothermal treatment is a highly crystalline 4A zeolite with a typical cubic zeolite morphology and uniform distribution without the presence of impurity phases.

[0023] Example 2

[0024] 5g of sandy kaolin and 0.5g of aluminum hydroxide are mixed evenly without adding anhydrous sodium carbonate. They are placed in carbon paper in batches and then placed in an ultrafast high-temperature furnace for heat treatment at a heating temperature of 1300°C for 20s. After the precursor is crushed, it is added to an appropriate amount of 2mol / L NaOH solution with a solid-liquid mass ratio of 1:25, stirred evenly into a colloid, and then transferred to a polytetrafluoroethylene-lined reactor, hydroheated in a 90°C oven for 10h, cooled, and centrifuged to obtain a product. Compared with Implementation Option 1, the quartz impurity phase appears in this implementation option, and 4A zeolite is not synthesized. The main synthesized phase is zeolite P.

[0025] Example 3

[0026] 5g of sandy kaolin and 0.5g of aluminum hydroxide are mixed evenly without adding anhydrous sodium carbonate. They are placed in carbon paper in batches and then placed in an ultrafast high-temperature furnace for heat treatment at a temperature of 800°C for 20s to obtain a precursor. The precursor is added to an appropriate amount of 2mol / L NaOH solution and mixed with a solid-liquid mass ratio of 1:25. It is stirred evenly into a colloid and then transferred to a polytetrafluoroethylene-lined reactor. It is hydroheated in a 90°C oven for 10h and then cooled. The product is centrifuged and washed to obtain a product. Compared with Embodiment 2, this embodiment generates a 4A zeolite product. However, due to the lack of anhydrous sodium carbonate, quartz and mica impurity phases appear.

[0027] Example 4

[0028] 5g of sandy kaolin and 2.5g of anhydrous sodium carbonate were mixed evenly without adding aluminum hydroxide, and placed in carbon paper in batches. Then, they were placed in an ultra-fast high-temperature furnace for heating at a temperature of 1200°C, a heating time of 20s, and a heating rate of 10 5 ℃ / s, cooling time is 5s, to obtain a precursor. Then, after the precursor is crushed, it is added to an appropriate amount of 0.1mol / L NaOH solution and mixed with a solid-liquid mass ratio of 1:20, stirred evenly into a colloid, and then transferred to a polytetrafluoroethylene-lined reactor, hydroheated in a 100℃ oven for 10h, and then cooled. The product is centrifuged and washed to obtain 4A zeolite. Compared with Implementation Option 1, the crystallinity of the synthesized 4A zeolite in this implementation option is significantly reduced, and a zeolite 13X phase appears, and quartz impurities are also present.

[0029] Example 5

[0030] 5g of sandy kaolin, 7.5g of anhydrous sodium carbonate and 1.5g of aluminum hydroxide were mixed evenly, placed in carbon paper in batches, and then placed in an ultrafast high-temperature furnace for heat treatment at a heating temperature of 1400°C for 20s. After the precursor was crushed, an appropriate amount of 0.1mol / L NaOH solution was added and mixed with a solid-liquid mass ratio of 1:30. It was stirred evenly into a colloid and then transferred to a polytetrafluoroethylene-lined reactor. It was hydroheated in an 80°C oven for 15h, cooled, and the product was centrifuged and washed to obtain 4A zeolite. Compared with Implementation Option 2, the quartz impurity phase disappears in this implementation option, but sodalite impurities appear, and the crystallinity of 4A zeolite is significantly reduced compared to Implementation Option 1.

[0031] From the above comparative implementation scheme, it can be seen that after the addition of appropriate amounts of anhydrous sodium carbonate and aluminum hydroxide, the sandy kaolin can react rapidly under the action of Joule heat to obtain an activated precursor, the quartz and mica impurity phases disappear, and high-purity 4A zeolite is generated after hydrothermal crystallization. This also proves the applicability of the present invention for synthesizing 4A zeolite from kaolin containing difficult-to-treat impurities such as quartz and mica.

[0032] 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 converting quartz and mica impurities in sandy kaolin and synthesizing 4A zeolite, characterized by comprising the following steps: Sandy kaolin, anhydrous sodium carbonate, and aluminum hydroxide were mixed uniformly, wrapped in carbon paper, and heated in an ultrafast high-temperature furnace at 1000-1400°C for 20 seconds to obtain a 4A zeolite precursor. The precursor was then ground into a fine powder and mixed with an appropriate amount of 0.01 mol / L NaOH solution to obtain a colloidal product. After continuously stirring the colloidal product at 80°C for 4 hours, the reaction product was transferred to a polytetrafluoroethylene bottle and placed in a reactor, and then placed in an oven at 80°C to 100°C for hydrothermal crystallization for 5 to 10 hours to obtain a crystallized product; The crystallized product was centrifuged at 5000 rpm for 1 minute, washed with distilled water, and repeated 3 to 4 times until the solution was neutral after the last washing. Finally, it was dried at 110° C. for 24 hours to obtain the 4A zeolite product.

2. The method for synthesizing 4A zeolite by Joule heat melting of sandy kaolin as claimed in claim 1, characterized in that The kaolin is a typical domestic sandy kaolin containing impurities such as quartz and mica, and its chemical composition is: SiO2 content is 55-60wt%, Al2O3 content is 35-42wt%, Fe2O3 content is <1.2wt%, TiO2 content is <0.7wt%, and the total content of other impurities is 0.3wt% to 0.5wt%; the average particle size of the kaolin after crushing is less than 100μm; the anhydrous sodium carbonate and aluminum hydroxide are powdered.

3. The method for synthesizing 4A zeolite by Joule heat melting of sandy kaolin as claimed in claim 1, characterized in that The ratio of the sandy kaolin, anhydrous sodium carbonate and aluminum hydroxide described in step (1) is: 1: (0.8-1.2): (0.1-0.2).

4. The method for synthesizing 4A zeolite by Joule heat melting of sandy kaolin as claimed in claim 1, characterized in that The ultrafast high temperature furnace used in step (1) has a heating rate of 10 5 ℃ / s, cooling rate is ~10 4 ℃ / s, output voltage <40V, current <200A.

Images