Fluorine-removing agent for fluorine-containing wastewater treatment and preparation method thereof

Abstract

The application provides a defluorination agent for fluorine-containing wastewater treatment and a preparation method thereof, and belongs to the technical field of wastewater treatment. The defluorination agent takes modified hydroxyapatite as a carrier, loads magnesium oxide-aluminum oxide-lanthanum oxide composite metal oxide, and is surface-modified through a silane coupling agent, and the mass percentage of each component is as follows: modified hydroxyapatite 60-75%, magnesium oxide 8-15%, aluminum oxide 5-10%, lanthanum oxide 3-8%, and silane coupling agent 2-5%. The preparation method comprises the steps of carrier modification, composite metal oxide loading, surface modification, and drying and calcination. The defluorination agent has a large adsorption capacity for fluorine ions, the maximum adsorption capacity can reach 86.2 mg / g, the adsorption rate is fast, the fluorine removal rate can reach more than 95% within 30 min, the pH range is wide, the defluorination agent can stably play a role in the pH range of 3-10, and the fluorine ion concentration in the treated wastewater can be reduced to below 1 mg / L. Meanwhile, the defluorination agent has a simple preparation process, controllable cost, and is convenient for industrialized production, can be widely applied to the deep treatment of fluorine-containing wastewater in the electroplating, metallurgy, and chemical industries.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically a defluorinating agent for treating fluoride-containing wastewater and its preparation method. Background Technology

[0002] Fluorine is widely present in nature, and large amounts of fluoride-containing wastewater are generated during industrial production processes such as electroplating, metallurgy, chemical engineering, and semiconductor manufacturing. Direct discharge of fluoride ions from this wastewater can severely pollute soil and water bodies, harming the ecological environment. Furthermore, excessive fluoride ions can affect human bone and teeth health, causing diseases such as dental fluorosis and skeletal fluorosis. Therefore, the treatment of fluoride-containing wastewater has become an important issue in the field of environmental protection.

[0003] Currently, the main methods for treating fluoride-containing wastewater include chemical precipitation, adsorption, membrane separation, and ion exchange. Chemical precipitation is simple to operate and low in cost, but its treatment effect is limited; the fluoride ion concentration in the effluent is difficult to reduce to below 1 mg / L, requiring further advanced treatment processes. Membrane separation and ion exchange offer good treatment results, but the membrane modules and ion exchange resins are expensive, prone to fouling and clogging, and have high maintenance costs, limiting their large-scale application. Adsorption, due to the wide variety of adsorbents, ease of operation, and stable treatment effect, has become one of the mainstream methods for advanced treatment of fluoride-containing wastewater; the performance of the adsorbent directly determines the treatment effect. Existing adsorbents mainly include aluminum-based, iron-based, calcium-based adsorbents, and natural mineral-modified adsorbents. Aluminum-based adsorbents have high adsorption capacity but a narrow applicable pH range, typically 4-6, and are prone to producing residual aluminum ions after adsorption. Calcium-based adsorbents are low in cost but have slow adsorption rates and limited adsorption capacity. Natural mineral-modified adsorbents, such as hydroxyapatite and zeolite, are environmentally friendly, but the original minerals have low adsorption activity, requiring modification to improve their adsorption performance. Furthermore, single metal oxide adsorbents often suffer from poor adsorption selectivity and agglomeration, affecting adsorption efficiency and service life. Therefore, developing a defluorinating agent with high adsorption capacity, fast adsorption rate, wide applicability, and strong stability is of significant practical importance. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned problems in existing technologies by proposing a defluoridating agent for treating fluoride-containing wastewater and its preparation method. The technical problem to be solved by this invention is that existing defluoridating agents have problems such as limited adsorption capacity, narrow applicable pH range, and slow adsorption rate.

[0005] The objective of this invention can be achieved through the following technical solutions: A defluoridating agent for treating fluoride-containing wastewater and its preparation method, comprising a synergistic system of carrier modification + composite metal oxide loading + surface modification; Furthermore, modified hydroxyapatite, as a carrier, can increase the number of hydroxyl groups and specific surface area on its surface through nitric acid acidification, thereby enhancing the carrier's loading capacity and adsorption activity for metal ions. Furthermore, in the composite metal oxides magnesium oxide, aluminum oxide, and lanthanum oxide, magnesium oxide and aluminum oxide have strong chemical adsorption effects on fluoride ions, while lanthanum oxide can enhance the selectivity of the adsorbent for fluoride ions through the special electronic structure of rare earth elements. The synergistic effect of the three can significantly improve the adsorption capacity. Furthermore, surface modification of silane coupling agents can improve the surface hydrophilicity and hydrophobicity of adsorbents, reduce aggregation during adsorption, and further enhance adsorption rate and stability. Preferably, the mass percentage of each component is optimized and determined, with modified hydroxyapatite accounting for 60%-75%. If the percentage is too low, the support of the carrier will be insufficient, which will easily lead to the shedding of metal oxides; if the percentage is too high, the number of adsorption active sites will be reduced. Magnesium oxide accounts for 8%-15%, aluminum oxide accounts for 5%-10%, and lanthanum oxide accounts for 3%-8%. Since rare earth elements are expensive, controlling them within this range can balance adsorption performance and production costs. Silane coupling agent accounts for 2%-5%. Excessive addition will cover the active sites and reduce the adsorption effect.

[0006] Furthermore, the acidification temperature and time must be strictly controlled to avoid over-acidification that could damage the hydroxyapatite structure. Furthermore, in the loading reaction, the dropping rate of ammonia and pH adjustment are crucial. Slow dropping allows metal ions to precipitate evenly on the carrier surface, and pH control at 8-9 ensures complete precipitation of metal ions. Furthermore, the calcination process employs programmed temperature increase, which avoids the collapse of the adsorbent structure caused by a sudden temperature rise, effectively improving its mechanical strength and stability.

[0007] Compared with the prior art, the defluoridating agent for treating fluoride-containing wastewater and its preparation method of the present invention have the following advantages: 1. Excellent adsorption performance: The synergistic effect of composite metal oxide and modified carrier enables the defluorinating agent to adsorb up to 86.2 mg / g of fluoride ions, which is much higher than the 30-50 mg / g of traditional aluminum-based adsorbents; more than 95% fluoride removal rate can be achieved within 30 minutes, and the concentration of fluoride ions in the treated wastewater is ≤1 mg / L, which can meet the first-level discharge standard of ≤10 mg / L of fluoride ions in the integrated wastewater discharge standard, and is also suitable for the deep treatment needs of sensitive areas; 2. Wide range of applications: This defluorinating agent can maintain stable adsorption performance in the pH range of 3-10, eliminating the need for complex acid-base adjustments to fluoride-containing wastewater and significantly reducing treatment costs. 3. High stability: The surface modification of silane coupling agent reduces adsorbent aggregation and metal ion detachment. After 5 adsorption-desorption cycles, the adsorption capacity can still maintain more than 85% of the initial value, resulting in a longer service life. 4. Simple preparation process: The required raw materials are readily available, the reaction conditions are mild, no high temperature and high pressure environment is required, the steps are easy to control, and it is suitable for large-scale industrial production. 5. Environmentally friendly: The main components of the adsorbent are modified natural mineral products and metal oxides, which will not produce secondary pollution. Moreover, after adsorption saturation, it can be regenerated by roasting, effectively reducing the pressure of solid waste treatment. Attached Figure Description

[0008] Figure 1 This is a flowchart illustrating the preparation process of a defluorinating agent for treating fluoride-containing wastewater and its preparation method, according to the present invention. Detailed Implementation

[0009] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments. Example 1

[0010] A defluorinating agent for treating fluoride-containing wastewater, comprising the following components by mass percentage: 65% modified hydroxyapatite, 12% magnesium oxide, 8% aluminum oxide, 5% lanthanum oxide, and 4% γ-aminopropyltriethoxysilane KH55O. The preparation method includes the following steps: 1. Preparation of modified hydroxyapatite: Weigh 100g of hydroxyapatite powder, add it to 500mL of 0.8mol / L nitric acid solution, stir and acidify at 50℃ for 3h, filter, wash with deionized water until the pH of the filtrate is 7, and then dry at 90℃ for 7h to obtain modified hydroxyapatite. 2. Preparation of composite metal salt solution: Weigh 12g magnesium chloride, 8g aluminum chloride, and 5g lanthanum chloride, add 200mL of deionized water and stir until completely dissolved to obtain a composite metal salt solution with a total metal ion concentration of 0.7mol / L. 3. Loading reaction: 65g of the modified hydroxyapatite prepared in step 1 was added to the composite metal salt solution with a solid-liquid ratio of 1:15g / mL. The mixture was stirred at 60℃ for 5h. During the reaction, 25% ammonia was added dropwise at a rate of 1.5mL / min to adjust the pH of the system to 8.5. 4. Surface modification: Add 4g of γ-aminopropyltriethoxysilane KH550 to the above system and continue to stir the reaction at 60℃ for 2.5h; 5. Post-processing: After filtration, the filter cake is washed 4 times with deionized water, dried at 110℃ for 10h, then heated to 350℃ at a rate of 5℃ / min and calcined at a constant temperature for 2.5h. After cooling, it is pulverized and passed through a 200-mesh sieve to obtain the defluorinating agent product. Performance test: 100 mL of simulated fluoride-containing wastewater with an initial fluoride ion concentration of 100 mg / L was taken, pH was adjusted to 6, 0.5 g of the above-mentioned defluorinating agent was added, and the mixture was stirred and adsorbed at 25 °C for 30 min. After standing and filtration, the fluoride ion concentration of the filtrate was measured to be 0.8 mg / L, and the fluoride removal rate was 99.2%. After 5 adsorption-desorption cycles, the fluoride removal rate remained at 91.5%. Example 2

[0011] A defluorinating agent for treating fluoride-containing wastewater, comprising the following components by mass percentage: 70% modified hydroxyapatite, 10% magnesium oxide, 7% aluminum oxide, 3% lanthanum oxide, and γ-glycidyl etheroxypropyltrimethoxysilane KH56O2. The preparation method is basically the same as in Example 1, except that the following parameters are adjusted: in step 1, the nitric acid concentration is 1.0 mol / L, the acidification temperature is 60℃, and the acidification time is 2h; in step 3, the solid-liquid ratio is 1:12 g / mL, and the pH is adjusted to 8; in step 5, the calcination temperature is 320℃, and the calcination time is 3h. Performance test: When 1.0g of defluoridating agent was added to simulated fluoride-containing wastewater with an initial fluoride ion concentration of 150mg / L and pH=8, after 60min of adsorption, the fluoride ion concentration in the filtrate was 1.2mg / L, and the fluoride removal rate was 99.2%; the maximum adsorption capacity was calculated to be 86.2mg / g.

[0012] Comparative Example 1 Using hydroxyapatite that has not undergone nitric acid acidification as a carrier, and with other components and preparation processes consistent with Example 1, a defluorinating agent was prepared. Performance testing: When treating simulated fluoride-containing wastewater as in Example 1, the fluoride removal rate was 82.3% after 30 minutes of adsorption, and decreased to 75.1% after 5 cycles. This result indicates that carrier modification significantly improves adsorption performance and stability. Comparative Example 2 A defluorinating agent was prepared by loading only magnesium oxide, with other components and preparation process consistent with Example 1. Performance test: When treating simulated fluoride-containing wastewater as in Example 1, the fluoride removal rate was 78.5% after 30 minutes of adsorption, and the maximum adsorption capacity was 45.3 mg / g, which was much lower than that in Example 1, proving that the synergistic effect of the composite metal oxide can significantly improve the adsorption capacity.

[0013] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A defluoridating agent for treating fluoride-containing wastewater, characterized in that, It includes 60%-75% modified hydroxyapatite, 8%-15% magnesium oxide, 5%-10% aluminum oxide, 3%-8% lanthanum oxide, and 2%-5% silane coupling agent; the modified hydroxyapatite is hydroxyapatite acidified with nitric acid at a temperature of 40-60℃ for 2-4 hours and with a nitric acid concentration of 0.5-1.0 mol / L.

2. The defluoridating agent for treating fluoride-containing wastewater according to claim 1, characterized in that, The silane coupling agent is γ-aminopropyltriethoxysilane KH550 or γ-glycidoxypropyltrimethoxysilane KH560.

3. A method for preparing the defluoridating agent for treating fluoride-containing wastewater as described in claim 1, characterized in that, Includes the following steps: Preparation of S1 modified hydroxyapatite: Hydroxyapatite powder is added to nitric acid solution and stirred and acidified at 40-60℃ for 2-4h. Then, it is filtered and washed until the filtrate is neutral, and then dried at 80-100℃ for 6-8h to obtain modified hydroxyapatite. Preparation of S2 composite metal salt solution: Weigh magnesium chloride, aluminum chloride and lanthanum chloride according to the proportion, add deionized water and stir until completely dissolved to obtain composite metal salt solution, wherein the total concentration of metal ions is 0.5-1.0 mol / L; S3 loading reaction: The modified hydroxyapatite prepared in S1 was added to the composite metal salt solution with a solid-liquid ratio of 1:10-1:20 g / mL. The mixture was stirred at 50-70℃ for 4-6 h. During the reaction, the pH of the system was adjusted to 8-9 with ammonia water to precipitate the metal ions and load them onto the carrier surface. S4 Surface Modification: Add a measured amount of silane coupling agent to the reaction system of S3, and continue to stir the reaction at 50-70℃ for 2-3 hours to complete the surface modification; S5 post-treatment: Filter the mixture after reaction, wash the filter cake with deionized water 3-5 times, dry it at 100-120℃ for 8-12h, then calcine it at 300-400℃ for 2-3h, cool it to room temperature, and then crush it through a 200-mesh sieve to obtain a defluorinating agent for fluoride-containing wastewater treatment.

4. The preparation method according to claim 3, characterized in that, The mass concentration of ammonia in S3 is 25%-28%, and the dropping rate is 1-2 mL / min.

5. The preparation method according to claim 3, characterized in that, The S5 roasting process uses programmed heating at a rate of 5℃ / min, and is then kept at a constant temperature after reaching the target temperature.

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