Preparation method and application of kaolinite-based adsorbent for adsorbing ammonia nitrogen

Abstract

The invention discloses a preparation method and application of a kaolinite-based adsorbent for adsorbing ammonia nitrogen, and the preparation method comprises the following steps: roasting kaolinite raw powder in an air atmosphere of a muffle furnace at 750-800 DEG C for 3-3.5 h, adding the roasted product into 2 mol / L hydrochloric acid according to a solid-to-liquid ratio of 1: 40, stirring at 80 DEG C for 1-1.5 h, and carrying out solid-liquid separation to obtain the kaolinite-based adsorbent for adsorbing ammonia nitrogen. The invention relates to the technical field of water treatment.The kaolinite-based adsorbent is obtained by adding a sample into a 0.1 mol / L NaOH and KOH mixed solution to be stirred at the normal temperature for 1.5-2 h.The kaolinite-based adsorbent is obtained through the specific sequence that roasting is conducted firstly, then acid modification is conducted, then alkali treatment is conducted at the specific temperature, and the kaolinite-based adsorbent is applied in the adsorption environment with the pH being 8-10. According to the present invention, the porous kaolinite structure formed by acid etching and the Na-A type zeolite phase in the adsorbent can be promoted to produce the synergistic effect, such that the rich ion exchange sites are provided, the developed pore structure is provided so as to substantially improve the ammonia nitrogen adsorption capacity and the ammonia nitrogen adsorption efficiency, the zeta potential of the adsorbent is-20--30 mA, the system is relatively stable, and the adsorption efficiency is substantially improved; the ammonia nitrogen adsorption capability is further improved.

Description

Technical Field

[0001] This invention relates to the field of mineral material preparation technology, specifically to a method for preparing and applying a kaolinite-based adsorbent for adsorbing ammonia nitrogen. Background Technology

[0002] Ammonia nitrogen is a common organic nitrogen pollutant in water bodies, mainly originating from industrial, agricultural, and domestic wastewater. Untreated ammonia nitrogen can lead to eutrophication, disrupt the balance of aquatic ecosystems, and pose a potential threat to human health. Currently, methods for removing ammonia nitrogen from water primarily include chemical precipitation, membrane separation, biological methods, and adsorption.

[0003] Adsorption is widely used due to its simplicity and effectiveness. Commonly used adsorbents include zeolite, bentonite, fly ash, and activated carbon. However, these traditional adsorbents have many limitations: for example, natural zeolite has limited adsorption capacity and a short lifespan, and often contains a large number of impurities, resulting in low ion exchange and adsorption performance; the pretreatment process for fly ash is complex and prone to secondary pollution; the modification of activated carbon usually involves complex steps, such as surface oxidation, reduction, metal loading, and acid / alkali solution treatment, which are costly and cumbersome.

[0004] Weathered kaolin is a widely distributed and abundant resource that is inexpensive and readily available. After recovering its sand and gravel aggregates, low-iron kaolin is used as a ceramic raw material, while high-iron (Fe2O3>1.5%) kaolin is mostly used as an ingredient or for general solid waste landfill. This patent obtains kaolinite from high-iron kaolin through simple iron removal and graded purification, and then uses kaolinite to prepare a kaolinite-based adsorbent, which shows a good purification effect on medium-to-high concentration ammonia nitrogen wastewater. Summary of the Invention

[0005] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a method for preparing and applying a kaolinite-based adsorbent for adsorbing ammonia nitrogen, which solves the problems of limited adsorption capacity and high cost of existing traditional adsorbents.

[0006] (II) Technical Solution To achieve the above objectives, the present invention provides a method for preparing a kaolinite-based adsorbent for adsorbing ammonia nitrogen, comprising the following steps: S1. Calcination and activation: Kaolinite powder is calcined in an air atmosphere in a muffle furnace at 750℃-800℃ for 3-3.5h to obtain the calcined product; S2. Acid modification treatment: The calcined product is added to 2 mol / L hydrochloric acid at a solid-liquid ratio of 1:40, and stirred in a magnetic stirrer at 80℃ for 1-1.5 hours at a speed of 120 rpm. The acid-treated product is then subjected to solid-liquid separation, washed, and dried to obtain the modified product. S3. Post-treatment: Add the modified product to 0.1 mol / L NaOH and KOH and stir at room temperature for 1.5-2 hours. The mass ratio of NaOH to KOH in the mixture is 8:2. Wash and dry the obtained solid product to obtain the kaolinite-based adsorbent.

[0007] In some embodiments, in step S1, the heating rate of the calcination is 3-10 °C / min.

[0008] In some embodiments, the heating rate of the calcination is 5°C / min.

[0009] In some embodiments, in step S2, the stirring time of the stirrer is 1.2 hours.

[0010] Furthermore, this invention also claims the application of a kaolinite-based adsorbent prepared according to any one of the above-described methods in the adsorption and removal of ammonia nitrogen in water, particularly suitable for treating medium- to high-concentration ammonia nitrogen wastewater. Under suitable adsorption conditions (e.g., pH=10, adsorbent dosage 15g / L), the original ammonia nitrogen concentration is 40-60mg / L, and after purification by the kaolinite-based adsorbent, the ammonia nitrogen removal rate can reach 80.76%-84.35%.

[0011] (III) Beneficial Effects The beneficial effects of this invention are: 1. This invention uses natural kaolinite as raw material, which is widely available and inexpensive. The entire preparation process involves only two main steps: roasting and acid treatment. It is simple to operate, requires no complex equipment or expensive reagents, and is suitable for large-scale production.

[0012] 2. After modification using the specific process of this invention, the adsorption capacity of kaolinite for ammonia nitrogen achieves a qualitative leap. Experiments show that the adsorption rate of unmodified kaolinite for ammonia nitrogen is only 3.78%, while after modification using the method of this invention, its adsorption rate can be rapidly increased to 80.76%. This is attributed to the appropriate calcination temperature and suitable hydrochloric acid etching time. Calcination causes the kaolinite skeleton to collapse, increasing its activity while maintaining its lamellar structure. Suitable acid etching produces suitable amorphous cementitious materials and zeolite products, while retaining some kaolinite as a carrier, allowing it to exert a synergistic effect. This not only forms abundant pores and a larger specific surface area but also significantly increases the active sites available for ammonia nitrogen binding, thus significantly improving the adsorption performance of ammonia nitrogen.

[0013] 3. This invention prepares a kaolinite-based adsorbent with a Na-A type zeolite phase, an amorphous cementing material, and a porous kaolinite structure formed by acid etching through a specific sequence of "calcination followed by acid modification" under alkaline conditions containing sodium and potassium. The three products produce a synergistic effect. This composite structure not only provides widely dispersed and abundant ion exchange sites, but also has a well-developed pore structure and capacity. The application under alkaline conditions further enhances this effect, and the adsorbent has a zeta potential of -20 mA to -30 mA. The system is relatively stable, which greatly improves the adsorption capacity and efficiency of ammonia nitrogen.

[0014] 4. The acid used in the modification process can be recycled, and kaolinite itself is non-toxic and harmless, avoiding the secondary pollution problems that may be caused by adsorbents such as fly ash. It is a green and environmentally friendly wastewater treatment material. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of SEM analysis according to the present invention; Where Y is the SEM of kaolinite raw material, M is the SEM of intermediate product after calcination and acid modification, and K is the SEM of the prepared adsorbent.

[0016] Figure 2 This is a schematic diagram of XRD analysis according to the present invention; Wherein, Y is the XRD of kaolinite raw material; M is the XRD of intermediate product of kaolinite after roasting and acid modification, in which part of the kaolinite is converted into metakaolinite; K is the XRD of the prepared adsorbent product, which consists of kaolinite, part of amorphous cementing material and part of Na-A zeolite.

[0017] Figure 3 This is a schematic diagram of the FT-IR analysis of the present invention; Wherein, Y is the infrared spectrum of raw kaolinite powder, M is the infrared spectrum of intermediate kaolinite products after calcination and acid modification, and K is the infrared spectrum of the prepared adsorbent product. Detailed Implementation

[0018] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] Preparation of a kaolinite-based adsorbent and testing of its ammonia nitrogen adsorption performance.

[0020] Calcination and activation: Weigh a certain amount of kaolinite powder and place it in a muffle furnace. Proceed to 800℃ at a heating rate of 5℃ / min and maintain this temperature for 3 hours for calcination. Then stop heating and allow the material in the furnace to cool naturally to room temperature to obtain the calcined product.

[0021] Acid modification treatment: The above calcined product was transferred to a three-necked flask, and a 2 mol / L hydrochloric acid solution was added at a solid-liquid mass-to-volume ratio of 1:40 g / mL. The three-necked flask was placed on a constant temperature heating magnetic stirrer, and the reaction was carried out at a constant temperature of 80℃ and a speed of 120 rpm for 1 hour. The acid-treated product was then subjected to solid-liquid separation, washed, and dried to obtain the modified product. Post-processing: The modified product was added to 0.1 mol / L NaOH and KOH and stirred at room temperature for 1.5-2 hours. The mass ratio of NaOH to KOH in the mixture was 8:2. The resulting solid product was centrifuged, and the supernatant was discarded. The solid product was washed repeatedly with distilled water at least 3 times until the washing liquid was nearly neutral. The washed solid was dried in an oven at 80°C to constant weight, ground, and sieved to obtain the modified kaolinite-based adsorbent of this invention, denoted as sample MK.

[0022] Ammonia nitrogen adsorption performance test: Prepare a simulated ammonia nitrogen wastewater of a certain concentration. Take 100 mL of this wastewater into an Erlenmeyer flask, adjust its pH to 10 with NaOH solution, weigh 1.5 g (the dosage is 15 g / L), add the prepared sample MK to the Erlenmeyer flask, place the Erlenmeyer flask in a constant temperature shaker, and shake at a certain speed for 360 minutes at 25℃. After shaking, take a sample, filter, and determine the concentration of residual ammonia nitrogen in the filtrate using Nessler's reagent spectrophotometry, and calculate the ammonia nitrogen removal rate.

[0023] Table 1 shows the adsorption rate of this product at different pH conditions with a dosage of 10 g / L.

[0024] Table 1: Table 2 shows the adsorption rate of this product under different dosage conditions at pH=10.

[0025] Table 2: As shown in Tables 1 and 2, the adsorption rate of this product can be maximized under the conditions of pH=10 and dosage of 15g / L.

[0026] Comparative Example To demonstrate the modification effect, untreated kaolinite powder was used to conduct an ammonia nitrogen adsorption experiment under the same adsorption conditions as in Example 1, namely pH=10 and dosage of 15g / L.

[0027] Table 3 below shows the ammonia nitrogen adsorption experiment. In the table, 0 represents raw kaolinite powder, and 1, 2, 3, 4, and 5 represent the adsorption of ammonia nitrogen by kaolinite adsorbent at different initial concentrations of ammonia nitrogen under the conditions of 15 g / L dosage, pH=10.

[0028] Table 3: Test results show that the ammonia nitrogen removal rate of raw kaolinite powder is only 2.40%, which indicates that unmodified kaolinite has very few surface active sites and almost no adsorption capacity for ammonia nitrogen.

[0029] Effect Analysis As can be seen from the comparison between Example 1 and Comparative Example 1, the "calcination + acid modification" process provided by the present invention can greatly improve the adsorption performance of kaolinite for ammonia nitrogen. Under the optimized process parameters, the adsorption performance reaches the best. This is mainly because, under these optimized conditions, the acid etching effect and the material structure optimization reach the best balance: calcination removes impurities and activates the structure, while moderate acid etching dissolves some aluminum oxides and forms a porous structure with a suitable pore size distribution and a large specific surface area, exposing a large number of Si-OH active groups. In addition, under alkaline conditions containing sodium and potassium, the silicon-aluminum components in the material are partially converted into Na-A type zeolite and amorphous cementitious materials. Their adsorption and the physical adsorption of porous kaolinite produce a compound and synergistic effect, jointly contributing to the efficient ammonia nitrogen removal capacity. Moreover, the application under alkaline conditions further enhances this effect. At the same time, Tables 1 and 2 show that by adjusting the process within a certain parameter range, a significantly better adsorption effect than that of unmodified kaolinite can still be obtained, proving the wide applicability and stability of the technical solution of the present invention.

[0030] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0031] In the description of this specification, the terms "one embodiment," "some embodiments," "embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0032] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a kaolinite-based adsorbent for adsorbing ammonia nitrogen, characterized in that, Includes the following steps: S1. Calcination and activation: Kaolinite powder is calcined in an air atmosphere in a muffle furnace at 750℃-800℃ for 3-3.5h to obtain the calcined product; S2. Acid modification treatment: The calcined product is added to 2 mol / L hydrochloric acid at a solid-liquid ratio of 1:40, and stirred in a magnetic stirrer at 80℃ for 1-1.5 hours at a speed of 120 rpm. The acid-treated product is then subjected to solid-liquid separation, washed, and dried to obtain the modified product. S3. Post-treatment: Add the modified product to 0.1 mol / L NaOH and KOH and stir at room temperature for 1.5-2 hours. The mass ratio of NaOH to KOH in the mixture is 8:

2. Wash and dry the obtained solid product to obtain the kaolinite-based adsorbent.

2. The method for preparing the kaolinite-based adsorbent for adsorbing ammonia nitrogen according to claim 1, characterized in that, In step S1, the heating rate of the calcination is 3-10℃ / min.

3. The method for preparing the kaolinite-based adsorbent for adsorbing ammonia nitrogen according to claim 2, characterized in that, The heating rate for roasting is 5°C / min.

4. The method for preparing the kaolinite-based adsorbent for adsorbing ammonia nitrogen according to claim 1, characterized in that, In step S2, the stirring time of the stirrer is 1.2 hours.

5. The application of a kaolinite-based adsorbent obtained by the preparation method of the kaolinite-based adsorbent for adsorbing ammonia nitrogen as described in any one of claims 1-4 in the adsorption of ammonia nitrogen.

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