Method for preparing NaP type molecular sieve by using calcined coal series kaolin

Abstract

The invention belongs to the field of coal solid waste resource utilization, and relates to a method for preparing a NaP type molecular sieve by utilizing kaolinite rock type coal gangue. The method comprises the following steps: 1) crushing and grinding blocky kaolinite rock type coal gangue into powder; 2) roasting and activating the coal gangue powder to obtain metakaolin; 3) mixing and stirring metakaolin, sodium hydroxide, a silicon source and deionized water to obtain an initial solution; 4) standing and aging the initial solution to obtain a precursor solution; 5) performing dynamic hydrothermal crystallization treatment on the precursor solution to obtain crystals; and 6) washing, neutralizing, centrifuging and drying the crystal to obtain the NaP type molecular sieve. The kaolinite rock type coal gangue is used as a raw material to replace a traditional chemical raw material required by molecular sieve synthesis, and resource utilization of aluminosilicate solid waste is promoted. According to the method, seed crystals or guiding agents are not required to be added in the molecular sieve crystallization process, and special crystallization methods such as microwaves and ultrasound are also not required, so that the process is simple, the cost is low, and the method is environment-friendly.

Description

Technical Field

[0001] The invention belongs to the field of resource utilization of coal solid waste and relates to a method for preparing a NaP type molecular sieve by utilizing kaolinite type coal gangue. Background Art

[0002] As the main energy source in my country, coal is an important support for the development of the national economy. In the process of coal mining and washing, coal seam interlayers and roof and floor plates are usually discarded as coal gangue, which has become one of the largest industrial solid wastes in my country. The large accumulation of coal gangue not only occupies land resources, but also the harmful elements contained in it will be leached out after long-term rain erosion, causing soil and groundwater pollution. The resource attributes of coal gangue have not received due attention for a long time, especially interlayer coal gangue, most of which are a high-quality coal-bearing kaolinite resource, with a kaolinite grade of more than 90%, which is the best alternative resource for traditional soft kaolin. The mineral composition characteristics dominated by kaolinite give coal gangue natural silicon and aluminum source properties.

[0003] NaP molecular sieve is an important inorganic micro-mesoporous material and a synthetic zeolite molecular sieve. Its crystal chemical formula can be expressed as Na6Al6Si 10 O 32 ·12H2O. In the crystal structure, silicon ions and aluminum ions are connected by oxygen atoms, and sodium ions neutralize the negative charge in the framework. As a micro-mesoporous material, P-type molecular sieve has a small pore radius and excellent adsorption and ion exchange properties. It has broad application prospects in the adsorption and separation of small molecular gases or liquid molecules and the removal of heavy metals in wastewater. In addition, P-type molecular sieve has a strong affinity for Ga 2+ and Mg 2+ It has an outstanding adsorption effect (cation exchange), and its adsorption performance is significantly better than that of 4A molecular sieve, so it also has great potential in softening hard water. Using kaolinite coal gangue as raw material to synthesize P-type molecular sieve can not only expand the source of raw materials for P-type molecular sieve and reduce the synthesis cost, but also realize the resource utilization of coal solid waste, and promote my country's green economic development model and ecological civilization construction.

[0004] In summary, the comprehensive utilization of solid wastes such as coal gangue is an inevitable choice for adhering to the path of resource-saving and environmentally friendly society, conforms to the concept of ecological civilization construction, and is the general trend.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing NaP type molecular sieve using coal gangue. The preparation method uses the natural silicon source and aluminum source of the coal gangue itself to prepare the NaP molecular sieve. The method is simple and efficient, and is a high value-added comprehensive utilization technology of coal solid waste, which has important social and environmental benefits.

[0007] The present invention adopts the following technical solution:

[0008] A method for preparing NaP type molecular sieve by calcining coal-based kaolin, the method comprising the following steps:

[0009] 1) Grinding: crush the blocky coal gangue and grind it into powder (200 mesh);

[0010] 2) Activation: calcining and activating the coal gangue powder to obtain metakaolin;

[0011] 3) Material addition: the metakaolin, sodium hydroxide, silicon source and deionized water are mixed and stirred for 1 hour to obtain an initial solution;

[0012] 4) Aging: Aging the initial solution to obtain a precursor solution;

[0013] 5) Crystallization: subjecting the precursor solution to dynamic hydrothermal crystallization to obtain crystals;

[0014] 6) Extraction: washing, neutralizing, centrifuging and drying the crystals to obtain NaP type molecular sieve.

[0015] Wherein, in step 1), the massive coal gangue is:

[0016] a) A massive coal gangue, the main mineral component of which is kaolinite; in fact, it is a coal-bearing kaolinite, which can be called kaolinite-type coal gangue.

[0017] Optionally, in the above method, the calcination activation conditions in step 2) include: in an air atmosphere, a calcination temperature of 750-850° C., and a calcination time of 2-4 hours.

[0018] Optionally, in the above method, the molar ratio of the metakaolin, the sodium hydroxide, the silicon source and the deionized water in step 3) is: Al2O3:Na2O:SiO2:H2O=1:3~8.4:2.5~7:192~504.

[0019] Optionally, in the above method, the static aging conditions in step 4) include: an aging temperature of 30 to 70° C. and an aging time of 0 to 5 hours.

[0020] Optionally, in the above method, the dynamic hydrothermal crystallization treatment conditions in step 5) include: a dynamic rotating shaft speed of 10 to 20 rpm, a crystallization temperature of 90 to 130° C., and a crystallization time of 4 to 28 h.

[0021] Preferably, in the above method, the rate of the calcination activation heating in step 2) is 10°C / min.

[0022] In the present invention, the silicon source in step 3) includes but is not limited to water glass, silica sol and other substances that can provide a stable active silicon source.

[0023] The present invention provides a NaP type molecular sieve, wherein the NaP type molecular sieve is prepared by the present invention.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] (1) The present invention provides a method for synthesizing NaP molecular sieve by using coal gangue instead of chemical raw materials, which is green and environmentally friendly;

[0026] (2) The NaP-type molecular sieve synthesized by the present invention has a single crystal phase and high crystallinity.

[0027] (3) The crystallization process of the present invention is simple, the process is easy to control, the cost is low, and the environmental pollution is small.

[0028] The invention improves the technical level of resource utilization of coal gangue and is a high value-added comprehensive utilization technology of coal solid waste. The synthesized NaP type molecular sieve has good adsorption for heavy metals in soil and calcium and magnesium ions in mine water, which can achieve waste treatment with waste and has high social and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The X-ray diffraction (XRD) diagram of the NaP molecular sieve prepared in each example.

[0030] Figure 2 This is a scanning electron microscope (SEM) image of the NaP molecular sieve prepared in Example 1;

[0031] Figure 3 This is the infrared spectrum (FTIR) of the NaP molecular sieve prepared in Example 2;

[0032] Figure 4 X-ray diffraction (XRD) patterns of NaP molecular sieves synthesized under different n(Na2O / SiO2) conditions. DETAILED DESCRIPTION

[0033] The following is a specific embodiment of the present invention, and the embodiments described are intended to further describe the present invention, rather than to limit the present invention. The described examples are part of the examples of this application, rather than all the examples. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of this application.

[0034] A method for preparing NaP type molecular sieve by calcining coal-based kaolin comprises the following steps:

[0035] (1) Grinding: crushing and grinding kaolinite gangue into powder; in a preferred embodiment, the powder is selected to be below 200 mesh.

[0036] (2) Activation: The ground coal gangue powder is activated and roasted at 750-900°C to obtain metakaolin; in the best embodiment, the coal gangue powder is roasted for 2-3 hours at a temperature of 800-850°C. The main mineral component of coal gangue is kaolinite. If it is directly used without activation, its silicon and aluminum activity is low. The activity of metakaolinite after roasting is high.

[0037] (3) Material addition: The calcined high-alkaline ore was stirred and mixed with sodium hydroxide, silicon source and deionized water for 1 hour to obtain an initial solution. In the optimal embodiment, the molar ratio of each substance is: Al2O3:Na2O:SiO2:H2O=1:4.8~5.6:4~7:192~336; stirring is performed to fully dissolve and mix the components. Too much water will lead to a decrease in the material concentration of the system, slow down the crystallization rate and reduce the crystallinity. Increasing the alkali content in the system within a certain range is beneficial to promote the depolymerization and condensation of aluminosilicates, accelerate the nucleation rate of molecular sieves and improve the crystallinity, but too much alkali will cause the molecular sieve to dissolve at a higher hydrothermal temperature, resulting in a decrease in crystallinity.

[0038] (4) Aging: The initial liquid is allowed to stand for aging treatment to obtain a precursor solution. In the optimal embodiment, the aging time is 2 hours and the aging temperature is 30°C. Sufficient aging time is beneficial to increase the aluminosilicate ions in the reaction system and enhance the crystallinity, while too long aging time will cause the dissolved silicon and aluminum to polymerize, thereby affecting the crystallinity.

[0039] (5) Crystallization: The precursor solution is placed in a reactor for dynamic hydrothermal crystallization to obtain crystals. Hydrothermal crystallization can be performed using equipment commonly used in the art, such as a stainless steel reactor lined with polytetrafluoroethylene; in the optimal embodiment, the crystallization temperature is 110-120°C and the crystallization time is 8-24 hours; the crystallization process is a process in which the crystals grow and gradually grow. If the crystallization temperature is too low, the crystal growth rate will be too slow or even unable to crystallize. However, if the crystallization temperature is too high, the crystals will dissolve, the crystallinity will decrease, and even crystal transformation will occur; appropriately extending the crystallization time is conducive to the uniform growth of the molecular sieve, but too long a crystallization time will increase energy consumption.

[0040] (6) Extraction: The crystals are washed, neutralized, centrifuged and dried to obtain a NaP type molecular sieve.

[0041] In some embodiments, the element components of the coal gangue are as shown in Table 1 (in mass fraction):

[0042]

[0043] Table 1

[0044] In some embodiments, the silicon source is water glass (Na2O·3SiO2) with a purity of AR and a modulus of 2.8 to 3.0.

[0045] Example 1

[0046] (1) Grinding: Take an appropriate amount of the coal gangue block rock sample shown in Table 1, grind it in a ball mill, and sieve it to 200 mesh to obtain coal gangue powder;

[0047] (2) Activation: Put the coal gangue powder into a crucible and heat it to 800°C in a muffle furnace at a heating rate of 10°C / min to obtain metakaolin;

[0048] (3) Material addition: Mix and stir the high-temperature tertiary territorial water, silicon source, sodium hydroxide and deionized water in a certain ratio to obtain an initial solution, the molar ratio of which is: Al2O3:Na2O:SiO2:H2O=1:4.8:4:192;

[0049] (4) Aging: The gel was aged at 30°C for 2 h to obtain a precursor solution;

[0050] (5) Crystallization: All the materials of the precursor solution are placed in a reactor lined with polytetrafluoroethylene, and the reactor is then placed in a magnetic stirring oil bath pot. Dynamic crystallization is carried out at 110° C. for 8 h, with the rotating shaft speed being 15 rpm to obtain a crystallized product;

[0051] (6) Extraction: Deionized water was added to the crystallized product and centrifuged. This process was repeated until the system became neutral. The product was then dried at 60° C. for 6 h to obtain NaP molecular sieve.

[0052] The SEM of the NaP molecular sieve prepared in this example is as follows Figure 2 As shown in FIG. 1 , it can be seen from the scanning electron microscope photograph that the NaP molecular sieve grains are approximately spherical, and there are a large number of microcrystalline particles (100-200 nm) on the surface.

[0053] Example 2

[0054] The method is the same as in Example 1, except that:

[0055] (1) Material addition: Mix and stir the high-temperature tertiary terroir, silicon source, sodium hydroxide and deionized water in a certain ratio to obtain a gel, wherein the molar ratio is: Al2O3:Na2O:SiO2:H2O=1:8.4:7:504;

[0056] (2) Aging: The gel was aged at 60°C for 2 h to obtain a precursor solution;

[0057] (3) Crystallization: All the materials of the precursor solution are placed in a reactor lined with polytetrafluoroethylene, and the reactor is then placed in a magnetic stirring oil bath pot. Dynamic crystallization is carried out at 100° C. for 8 h, with the rotating shaft speed being 20 rpm to obtain a crystallized product;

[0058] The infrared spectrum (FTIR) of the NaP molecular sieve prepared in this example is as follows Figure 3 As shown, it can be seen that at 3464cm -1 and 1647cm -1 The OH stretching vibration and HOH bond angle bending vibration absorption peaks are attributed to the adsorbed water of NaP molecular sieve. -1 The absorption peak at 743 cm is the asymmetric stretching vibration absorption peak of Si-O or Al-O in the crystal structure of NaP molecular sieve, while at 743 cm -1 and 677cm -1 The absorption peak at 607cm is caused by the symmetrical stretching vibration of Si-O or Al-O. -1 The absorption peak at 435cm is due to the vibration of the double ring structure inside the NaP molecular sieve. -1 The absorption peak at is attributed to the bending vibration peak of Si-O or Al-O bond. It can be seen that the molecular sieve prepared in this example is a NaP type molecular sieve.

[0059] Example 3

[0060] The method is the same as in Example 1, except that:

[0061] (1) Material addition: Mix and stir the high-temperature tertiary terroir, silicon source, sodium hydroxide and deionized water in a certain ratio to obtain a gel, wherein the molar ratio is: Al2O3:Na2O:SiO2:H2O=1:7:5:420;

[0062] (2) Aging: The gel was aged at 60°C for 3 h to obtain a precursor solution;

[0063] (3) Crystallization: Place all the precursor liquid materials in a reactor lined with polytetrafluoroethylene, then place the reactor in a magnetic stirring oil bath, and perform dynamic crystallization at 100° C. for 8 h with a rotating shaft speed of 15 rpm to obtain a crystallized product;

[0064] Example 4

[0065] The method is the same as in Example 1, except that:

[0066] (1) Activation: Put the coal gangue powder into a crucible and heat it to 850°C in a muffle furnace at a heating rate of 10°C / min to obtain metakaolin;

[0067] (2) Aging: The gel was aged at 50°C for 2 h to obtain a precursor solution;

[0068] (3) Crystallization: Place all the precursor liquid materials in a reactor lined with polytetrafluoroethylene, then place the reactor in a magnetic stirring oil bath, and perform dynamic crystallization at 100° C. for 24 h with a rotating shaft speed of 20 rpm to obtain a crystallized product.

[0069] Example 5

[0070] The method is the same as in Example 1, except that:

[0071] (1) Crystallization: All the materials of the precursor solution are placed in a reactor lined with polytetrafluoroethylene, and then the reactor is placed in a magnetic stirring oil bath pot. Dynamic crystallization is carried out at 110° C. for 18 h with a rotating shaft speed of 20 rpm to obtain a crystallized product.

[0072] Test Example 1

[0073] This test example investigates the effects of process parameters in the synthesis of NaP molecular sieve on the preparation of NaP molecular sieve.

[0074] 1. Influence of feed sodium-silicon ratio n (Na2O / SiO2)

[0075] The process is similar to that of Example 1, except that in the process of preparing the gel, the alkalinity is controlled by changing the amount of sodium hydroxide added, and the alkalinity of the added materials, i.e., n(Na2O / SiO2), is 0.6, 0.8, 1.0, 1.2, 1.4, and 1.6, respectively. The materials are stirred and mixed at the stated ratio to investigate the effects of different alkalinities on the preparation of NaP molecular sieves.

[0076] XRD patterns of NaP molecular sieves synthesized with different n(Na2O / SiO2) Figure 4 As shown: when n(Na2O / SiO2)=0.6, the physical phase of NaP molecular sieve is not detected, and the alkalinity is too low, resulting in no crystallization reaction and the formation of amorphous material; when n(Na2O / SiO2)=0.8~1.6, pure phase NaP molecular sieve is synthesized. As the amount of sodium hydroxide added increases, the alkalinity of the initial liquid material also increases, which accelerates the depolymerization of the initial aluminosilicate, and also promotes the formation of NaP molecular sieve crystal nuclei, accelerates the crystal growth rate, and improves the crystallinity of the molecular sieve. When n(Na2O / SiO2)=1~1.2, the crystallinity of the product reaches the highest, and then the alkalinity continues to increase, the peak intensity of the NaP molecular sieve weakens, and the crystallinity decreases. The possible reason is that the alkalinity is too high, causing some crystals to dissolve at high temperature, or crystal transformation occurs, resulting in a decrease in crystallinity. Therefore, the optimal n(Na2O / SiO2) of the present invention is 1~1.2.

Claims

1. A method for preparing NaP molecular sieve using kaolinite-type coal gangue, the preparation method comprising the following steps: 1) Grinding: crushing the blocky coal gangue and grinding it into powder; 2) Activation: calcining and activating the coal gangue powder to obtain metakaolin; 3) Material addition: the metakaolin, sodium hydroxide, silicon source and deionized water are mixed and stirred at a certain molar ratio for 1 hour to obtain an initial solution; 4) Aging: placing the initial solution in a static state for aging to obtain a precursor solution; 5) Crystallization: subjecting the precursor solution to dynamic hydrothermal crystallization to obtain crystals; 6) Extraction: washing, neutralizing, centrifuging and drying the crystals to obtain NaP type molecular sieves. Wherein, in step 1), the massive coal gangue is: a) A massive coal gangue, the main mineral component of which is kaolinite, is actually a coal-bearing kaolinite, which can be called kaolinite-type coal gangue.

2. The method according to claim 1, characterized in that In step 2), the calcination activation conditions include: in an air atmosphere, a calcination temperature of 750-900° C., and a calcination time of 2-4 hours.

3. The method according to claim 1, characterized in that In step 3), the molar ratio of the metakaolin, the sodium hydroxide, the silicon source and the deionized water is: Al2O3:Na2O:SiO2:H2O=1:3-8.4:2.5-7:192-504.

4. The method according to claim 1, characterized in that: In step 4), the static aging conditions and treatment conditions include: aging temperature of 30 to 70° C., and aging time of 0 to 5 hours.

5. The method according to claim 1, characterized in that In step 5), the dynamic hydrothermal crystallization treatment conditions include: the dynamic rotating shaft speed is 10 to 20 rpm, the crystallization temperature is 90 to 130° C., and the crystallization time is 4 to 28 h.

6. The method according to claim 1, characterized in that In step 1), the powder is ground to 200 mesh.

7. The method according to claim 2, characterized in that The rate of the calcination activation heating is 10°C / min.

8. The silicon source according to claim 3, characterized in that: Including but not limited to water glass, silica sol and other substances that can provide a stable active silicon source.

9. A NaP type molecular sieve, characterized in that: The NaP type molecular sieve is prepared by the method described in any one of claims 1 to 9.

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