Preparation method of high-concentration fluorine-containing wastewater remover

Abstract

The invention relates to the technical field of water treatment, in particular to a preparation method of a high-concentration fluorine-containing wastewater remover, which comprises the following steps: crushing oyster shells which are determined to be qualified in pretreatment based on thermal decomposition temperature to obtain oyster shell powder; determining the strontium-phosphorus molar ratio of strontium carbonate and disodium hydrogen phosphate based on the calcium dissolution rate of the pretreated qualified oyster shell powder, and mixing to form a fluorine-fixing skeleton; determining the adding strategy of calcium hydroxide and aluminum trichloride based on the acid-base buffer index of the fluorine-fixing skeleton to obtain a mixed material; and performing a simulated fluorine fixing performance test on the mixed material, and determining whether a fluorine fixing skeleton structure is complete or not based on a comparison result of the fluorine ion removal rate and a preset fluorine ion removal rate so as to obtain a qualified fluorine-containing wastewater remover finished product. The technical problems of complex process and high cost in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a high-concentration fluoride-containing wastewater removal agent. Background Technology

[0002] High-concentration fluoride-containing wastewater mainly originates from industries such as photovoltaic silicon wafer etching, semiconductor cleaning, fluorochemicals, and aluminum smelting. Due to the extensive use of raw materials like hydrofluoric acid and ammonium fluoride, the fluoride ion concentration in this wastewater is extremely high (e.g., fluorochemical wastewater reaches 1000–5000 mg / L). This type of wastewater is highly acidic, has high salinity, and is biotoxic, often containing heavy metals and organic pollutants. Traditional technologies are difficult to use efficiently for purification. Fluoride pollution is bioaccumulative and has long-distance migration capabilities, entering ecosystems through water bodies and atmospheric deposition, accumulating in benthic organisms, and amplifying through the food chain. Long-term human exposure will lead to skeletal fluorosis, dental fluorosis, and cardiovascular damage, while also destroying aquatic biodiversity.

[0003] Currently, commonly used industrial methods for treating fluoride-containing wastewater include chemical precipitation, coagulation sedimentation, and adsorption. Chemical precipitation involves adding calcium salts (such as lime or calcium chloride) to form calcium fluoride precipitate with fluoride ions. This method can treat wastewater with high fluoride concentrations, uses readily available raw materials, and is cost-effective. However, it suffers from problems such as large sludge production, high sludge moisture content, and poor settling performance due to the small particle size of calcium fluoride. Furthermore, it typically only reduces the fluoride ion concentration to around 15-20 mg / L, making it difficult to meet stringent discharge standards. Coagulation sedimentation uses coagulants such as aluminum and iron salts to remove fluoride ions through flocculation. This method is simple, easy to operate, and suitable for large-scale treatment, but it also produces a large amount of sludge, and many factors affect the fluoride ion removal efficiency. Adsorption utilizes the special affinity of adsorbent materials to remove fluoride ions. While simple, efficient, and economical, it treats small volumes of water, requires pretreatment, and has a limited adsorption capacity.

[0004] Chinese Patent Publication No. CN119912012A discloses a deep defluorination agent and its preparation method. The deep defluorination agent comprises the following raw materials in the following weight ratios: chitosan 2-5 parts; polyaluminum chloride 65-90 parts; magnesium oxide 5-15 parts; titanium dioxide 1-5 parts; manganese oxide 1-5 parts; and lanthanum oxide 1-5 parts. The beneficial effects of this invention are: the defluorination agent obtained by this invention breaks away from the constraints of traditional calcium salts. Based on controlling the compatibility of the raw materials and the synthesis reaction process, key catalysts (such as transition metal oxides like titanium dioxide and manganese dioxide) are introduced through comparative selection. These catalysts not only have catalytic functions for complexation reactions but also enhance the adsorption capacity of the defluorination agent, providing micro-floc growth sites to generate adsorption and encapsulation effects. It can reduce the fluoride ion content of pretreated fluoride-containing wastewater (fluoride ion content below 20 mg / L) to below 2 mg / L, with a fluoride ion removal rate of over 90%.

[0005] Therefore, it can be seen that the aforementioned deep defluorination agent and its preparation method have the following problems: 1. The formula contains rare earth elements such as lanthanum oxide, which are expensive and have an unstable supply.

[0006] 2. It is only applicable to the advanced treatment stage of low-concentration fluoride-containing wastewater, and lacks effective treatment capacity for raw high-concentration fluoride-containing wastewater generated by industries such as photovoltaics and semiconductors. Summary of the Invention

[0007] Therefore, the present invention provides a method for preparing a high-concentration fluoride-containing wastewater removal agent to overcome the problems of complex processes and high costs in the prior art.

[0008] To achieve the above objectives, the present invention provides a method for preparing a high-concentration fluoride-containing wastewater removal agent, comprising: The oyster shells that have passed the pretreatment process, determined based on the thermal decomposition temperature, are pulverized to obtain oyster shell powder. The strontium-phosphorus molar ratio of strontium carbonate and disodium hydrogen phosphate was determined based on the calcium dissolution rate of pretreated qualified oyster shell powder to form a solid fluoride framework. The dosing strategy for calcium hydroxide and aluminum trichloride is determined based on the acid-base buffer index of the solid fluoride framework, so as to obtain a mixture by adding and mixing. The mixture is subjected to solid fluoride performance testing. The integrity of the solid fluoride skeleton structure is determined based on the comparison between the fluoride ion removal rate and the preset fluoride ion removal rate, so as to obtain a qualified finished product of fluoride-containing wastewater removal agent.

[0009] Furthermore, the pretreatment process for the oyster shells includes, Use deionized water to wash oyster shells to remove surface impurities and soluble salts; The raw material powder was obtained by drying at 105℃ to constant weight and then crushing and grinding it to pass through a 150-mesh sieve. The temperature is increased to the preset thermal decomposition temperature range at a rate of 10℃ / min.

[0010] Furthermore, the process of crushing pretreated oyster shells to obtain oyster shell powder based on the thermal decomposition temperature includes, The thermal decomposition temperature is compared with the preset thermal decomposition temperature range; Based on the thermal decomposition temperature being within a preset thermal decomposition temperature range, the pretreated oyster shell powder is determined to be qualified. The oyster shell powder was obtained.

[0011] Furthermore, the process for determining the strontium-phosphorus molar ratio includes, Based on the fact that the calcium dissolution rate is greater than or equal to the preset calcium dissolution rate, the strontium-phosphorus molar ratio is determined using a first functional relationship; The first functional relationship is the product of the benchmark strontium-phosphorus molar ratio and the difference between the first compensation coefficient and the calcium dissolution rate and the preset calcium dissolution rate. The result is used as the strontium-phosphorus molar ratio.

[0012] Furthermore, the process of determining the strontium-phosphorus molar ratio also includes, Based on the fact that the calcium dissolution rate is less than the preset calcium dissolution rate, the strontium-phosphorus molar ratio is determined using a second functional relationship; The second functional relationship is the product of the baseline strontium-phosphorus molar ratio plus the second compensation coefficient and the difference between the preset calcium dissolution rate and the calcium dissolution rate. The result is used as the strontium-phosphorus molar ratio.

[0013] Furthermore, the acid-base buffer index of the solid fluoride skeleton is greater than or equal to the preset acid-base buffer index, and the dosage of calcium hydroxide is determined to be 5% to 15% of the mass percentage of the finished fluoride wastewater removal agent, and the dosage of aluminum trichloride is 15% to 30% of the mass percentage of the finished fluoride wastewater removal agent.

[0014] Furthermore, the acid-base buffer index of the solid fluoride skeleton is less than the preset acid-base buffer index, and the dosage of calcium hydroxide is determined to be 15% to 20% of the mass percentage of the finished fluoride wastewater removal agent, and the dosage of aluminum trichloride is 5% to 15% of the mass percentage of the finished fluoride wastewater removal agent.

[0015] Furthermore, the integrity of the solid fluoride framework structure is determined based on the fluoride ion removal rate being greater than or equal to a preset fluoride ion removal rate.

[0016] Furthermore, the incomplete solid fluoride framework structure is determined based on the fact that the fluoride ion removal rate is less than the preset fluoride ion removal rate.

[0017] Furthermore, it consists of the following components by mass percentage: Oyster shell powder 10%–60%, calcium hydroxide 5%–20%, strontium carbonate 0.5%–2%, disodium hydrogen phosphate 0.5%–3%, aluminum trichloride 5%–30%.

[0018] Compared with existing technologies, the advantages of this invention lie in its ability to achieve efficient and stable preparation of high-concentration fluoride-containing wastewater removal agents by constructing a fully quantitative control system from raw material pretreatment to finished product verification. By strictly controlling the activation quality of oyster shell raw materials based on thermal decomposition temperature and dynamically adjusting the strontium-phosphorus molar ratio through calcium dissolution rate, the precise adaptation of the solid fluoride framework construction is ensured. Furthermore, the addition strategy of calcium hydroxide and aluminum trichloride is optimized based on the acid-base buffer index of the solid fluoride framework, effectively resisting the acidic impact of subsequent processes. Finally, the integrity of the framework structure is directly verified through solid fluoride performance testing, improving the product's defluorination efficiency and providing a reliable guarantee for large-scale industrial production.

[0019] Furthermore, this invention establishes a standardized pretreatment specification for raw material oyster shells by comparing the thermal decomposition temperature with the preset thermal decomposition range. The temperature meets the standard to ensure the formation of a porous activated structure and to provide a stable calcium source, thus ensuring the efficiency and consistency of the subsequent solid fluoride reaction from the source, thereby improving the controllability of the basic raw material quality of the entire preparation system.

[0020] Furthermore, this invention achieves precise matching between the solid fluoride framework formulation and raw material characteristics by constructing a correlation mechanism between calcium dissolution rate and strontium-phosphorus molar ratio. Since the calcium dissolution rate directly reflects the reactivity of oyster shell raw materials, while the strontium-phosphorus molar ratio determines the structural stability of the solid fluoride framework, the strontium-phosphorus molar ratio is determined using either a first functional relationship or a second functional relationship. The first functional relationship calculates a relatively low strontium-phosphorus molar ratio, fully stimulating and utilizing the framework-forming potential of the raw material's own high-quality calcium source, effectively avoiding redundant addition of external reagents. When the raw material activity is insufficient, the second functional relationship initiates a compensation mechanism, calculating a moderately increased strontium-phosphorus molar ratio. By enhancing the structural support of the external strontium-phosphorus components, a stable solid fluoride framework is continuously formed. This achieves an optimal balance between raw material costs and reagent input, providing a reliable technical guarantee for large-scale industrial production.

[0021] Furthermore, this invention establishes a graded and precise acid shock defense system by directly linking the acid-base buffering index of the solid fluoride framework with the dosage strategies of calcium hydroxide and aluminum trichloride. When a high buffering index is detected in the solid fluoride framework, a combination of calcium hydroxide (5%–15%) and aluminum trichloride (15%–30%) is used to maximize the flocculation effect while ensuring system stability. When the buffering index is insufficient, an enhanced protection scheme of calcium hydroxide (15%–20%) and aluminum trichloride (5%–15%) is adopted to offset the risk of acid attack from the source by increasing the alkalinity reserve. This bidirectional adjustment mechanism based on measured buffering capacity achieves a leap from passive response to active defense, avoiding the risk of framework dissolution caused by excessive aluminum trichloride addition in traditional processes, and preventing the sludge increase problem caused by blindly excessive calcium hydroxide, thus ensuring the structural integrity and active site stability of the solid fluoride framework during treatment.

[0022] Furthermore, this invention directly determines the structural integrity of the solid fluoride framework through standardized solid fluoride performance testing, establishing a quality control mechanism oriented towards end-performance. This testing method achieves rapid and objective evaluation of the framework structure by accurately quantifying the fluoride ion removal rate and comparing it with a preset fluoride ion removal rate. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the steps of preparing a high-concentration fluoride-containing wastewater removal agent according to an embodiment of the present invention. Figure 2This is a logic diagram for determining whether the pretreated oyster shell powder is qualified according to an embodiment of the present invention; Figure 3 A logic diagram for determining the strontium-phosphorus molar ratio in an embodiment of the present invention; Figure 4 The logical judgment diagram for determining the integrity of the solid fluorine framework structure in the embodiments of the present invention is shown. Detailed Implementation

[0024] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0025] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0026] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0027] Please see Figure 1 The diagram shown is a flowchart illustrating the steps of preparing a high-concentration fluoride-containing wastewater removal agent according to an embodiment of the present invention.

[0028] The oyster shells that have passed the pretreatment process, determined based on the thermal decomposition temperature, are pulverized to obtain oyster shell powder. The strontium-phosphorus molar ratio of strontium carbonate and disodium hydrogen phosphate was determined based on the calcium dissolution rate of pretreated qualified oyster shell powder to form a solid fluoride framework. The dosing strategy for calcium hydroxide and aluminum trichloride was determined based on the acid-base buffer index of the solid fluoride framework to obtain a mixture. The mixture is subjected to solid fluoride performance testing. The integrity of the solid fluoride skeleton structure is determined based on the comparison between the fluoride ion removal rate and the preset fluoride ion removal rate, so as to obtain a qualified finished product of fluoride-containing wastewater removal agent. Based on the incomplete solid fluoride framework structure, it was determined to increase the calcination temperature of the next batch of pretreated oyster shells.

[0029] Specifically, this invention achieves efficient and stable preparation of high-concentration fluoride-containing wastewater removal agents by constructing a full-process quantitative control system from raw material pretreatment to finished product verification. Based on strict control of the activation quality of oyster shell raw materials at the thermal decomposition temperature, and by dynamically adjusting the strontium-phosphorus molar ratio through the calcium dissolution rate, the precise adaptation of the solid fluoride framework construction is ensured. Furthermore, the addition strategy of calcium hydroxide and aluminum trichloride is optimized according to the acid-base buffer index of the solid fluoride framework, effectively resisting the acidic impact of subsequent processes. Finally, the integrity of the framework structure is directly verified through solid fluoride performance testing, improving the product's defluorination efficiency and providing a reliable guarantee for large-scale industrial production.

[0030] Please see Figure 2 As shown, it is a logic diagram for determining whether pretreated oyster shell powder is qualified according to an embodiment of the present invention.

[0031] Specifically, the process of crushing pretreated oyster shells to obtain oyster shell powder, based on the thermal decomposition temperature, includes the following steps: If the thermal decomposition temperature is within the preset thermal decomposition temperature range, the pretreated oyster shell powder is deemed qualified.

[0032] In this embodiment of the invention, the thermal decomposition temperature is the temperature value corresponding to the peak value of the differential thermogravimetric curve in the thermogravimetric-differential thermal analysis test. The preset thermal decomposition temperature range is [800℃, 900℃], but the above value is not limited to this. Those skilled in the art can also adjust the value according to actual needs.

[0033] In this embodiment of the invention, the oyster shell pretreatment process is as follows: the oyster shells are washed with deionized water to remove surface impurities and soluble salts, then dried at 105°C to constant weight, crushed and ground to pass through a 150-mesh sieve to obtain raw material powder, which is then placed in a thermogravimetric analyzer and heated from room temperature to 900°C at a heating rate of 10°C / min in an air atmosphere. The thermogravimetric curve and the differential thermogravimetric curve are recorded simultaneously. The temperature corresponding to the peak value of the maximum weight loss rate is read from the differential thermogravimetric curve and recorded as the thermal decomposition temperature of this batch of oyster shells.

[0034] Specifically, this invention establishes a standardized pretreatment specification for raw material oyster shells by comparing the thermal decomposition temperature with the preset thermal decomposition range. The temperature meets the standard to ensure the formation of a porous activated structure and to provide a stable calcium source, thus ensuring the efficiency and consistency of the subsequent solid fluoride reaction from the source, thereby improving the controllability of the basic raw material quality of the entire preparation system.

[0035] Please see Figure 3 As shown, it is a logic diagram for determining the strontium-phosphorus molar ratio in an embodiment of the present invention.

[0036] Specifically, the strontium-phosphorus molar ratio of strontium carbonate and disodium hydrogen phosphate was determined based on the calcium dissolution rate of pretreated qualified oyster shell powder, and the mixture was then used to form a solid fluoride framework. If the calcium dissolution rate is greater than or equal to the preset calcium dissolution rate, the strontium-phosphorus molar ratio is determined by the first functional relationship; If the calcium dissolution rate is less than the preset calcium dissolution rate, the strontium-phosphorus molar ratio is determined by the second functional relationship.

[0037] In this embodiment of the invention, the calcium dissolution rate is the mass of calcium ions dissolved from a unit mass of oyster shell powder in an acidic solution with pH=4 within 10 minutes. The preset calcium dissolution rate ranges from [8, 12] mg / (g·10min), preferably set to 10 mg / (g·10min). However, the above value is not limited to this, and those skilled in the art can adjust the value according to actual needs.

[0038] In this embodiment of the invention, the first functional relationship is the product of the benchmark strontium-phosphorus molar ratio minus the product of the first compensation coefficient and the ratio of "the difference between the calcium dissolution rate and the preset calcium dissolution rate" to "the preset calcium dissolution rate", and the result is taken as the strontium-phosphorus molar ratio. The second functional relationship is the product of the benchmark strontium-phosphorus molar ratio and the product of the second compensation coefficient and the ratio of "the difference between the preset calcium dissolution rate and the preset calcium dissolution rate" to "the preset calcium dissolution rate", and the result is taken as the strontium-phosphorus molar ratio.

[0039] In this embodiment of the invention, the range of the reference strontium-phosphorus molar ratio is determined to be [1.0, 1.2] through historical experiments, the range of the first compensation coefficient is [0.1, 0.3], and the range of the second compensation coefficient is [0.3, 0.5]. However, the above values ​​are not limited to these, and those skilled in the art can adjust the values ​​according to actual needs.

[0040] In this embodiment of the invention, oyster shell powder and strontium carbonate and disodium hydrogen phosphate in a determined molar ratio are placed in a three-dimensional motion mixer and mixed at 30 rpm for 40 minutes at room temperature to obtain a homogeneous solid fluorine framework powder.

[0041] Specifically, this invention achieves precise matching between the solid fluoride framework formulation and raw material characteristics by constructing a correlation mechanism between calcium dissolution rate and strontium-phosphorus molar ratio. Since the calcium dissolution rate directly reflects the reactivity of oyster shell raw materials, while the strontium-phosphorus molar ratio determines the structural stability of the solid fluoride framework, the strontium-phosphorus molar ratio is determined using either a first functional relationship or a second functional relationship. The first functional relationship calculates a relatively low strontium-phosphorus molar ratio, fully stimulating and utilizing the framework-forming potential of the raw material's own high-quality calcium source, effectively avoiding redundant addition of external reagents. When the raw material activity is insufficient, the second functional relationship initiates a compensation mechanism, calculating a moderately increased strontium-phosphorus molar ratio. By enhancing the structural support of the external strontium-phosphorus components, a stable solid fluoride framework is continuously formed. This achieves an optimal balance between raw material costs and reagent input, providing a reliable technical guarantee for large-scale industrial production.

[0042] Specifically, the addition strategy of calcium hydroxide and aluminum trichloride is determined based on the acid-base buffer index of the solid fluoride skeleton to obtain a mixture. If the acid-base buffer index of the solid fluoride skeleton is greater than or equal to the preset acid-base buffer index, the dosage of calcium hydroxide is determined to be 5% to 15% by mass, and the dosage of aluminum trichloride is determined to be 15% to 30% by mass. If the acid-base buffer coefficient of the solid fluoride skeleton is less than the preset acid-base buffer coefficient, the dosage of calcium hydroxide is determined to be 15% to 20% by mass, and the dosage of aluminum trichloride is determined to be 5% to 15% by mass.

[0043] In this embodiment of the invention, the acid-base buffer index is the number of moles of hydroxide ions required to raise the pH of an acidic solution with pH=4 to 6 per unit mass of solid fluoride framework powder, determined by acid-base titration. The preset acid-base buffer index ranges from [2.0, 3.0] mmol OH - / g, but the above value is not limited to this, and those skilled in the art can adjust the value according to actual needs.

[0044] In this embodiment of the invention, the mass percentage range of calcium hydroxide and aluminum trichloride is an optimized range determined through experimental verification based on the acid-base buffering characteristics of the solid fluoride framework. When the acid-base buffering index is greater than the preset acid-base buffering index, a scheme of 5%–15% calcium hydroxide and 15%–30% aluminum trichloride is adopted. Under this condition, the solid fluoride framework itself has sufficient buffering capacity, and reducing the amount of calcium hydroxide can reduce sludge production, while maintaining a high amount of aluminum trichloride to ensure flocculation effect. When the acid-base buffering index is less than the preset acid-base buffering index, a scheme of 15%–20% calcium hydroxide and 5%–15% aluminum trichloride is adopted. This compensates for the insufficient buffering capacity of the framework by increasing the amount of calcium hydroxide, and limits the amount of aluminum trichloride to avoid excessive acid intrusion.

[0045] Specifically, this invention establishes a graded and precise acid shock defense system by directly linking the acid-base buffering index of the solid fluoride framework with the dosage strategies of calcium hydroxide and aluminum trichloride. When a high buffering index is detected in the solid fluoride framework, a combination of calcium hydroxide (5%–15%) and aluminum trichloride (15%–30%) is used to maximize the flocculation effect while ensuring system stability. When the buffering index is insufficient, an enhanced protection scheme of calcium hydroxide (15%–20%) and aluminum trichloride (5%–15%) is adopted to offset the risk of acid attack from the source by increasing the alkalinity reserve. This bidirectional adjustment mechanism based on measured buffering capacity achieves a leap from passive response to active defense, avoiding the risk of framework dissolution caused by excessive aluminum trichloride addition in traditional processes, and preventing the sludge increase problem caused by blindly excessive calcium hydroxide, thus ensuring the structural integrity and active site stability of the solid fluoride framework during the treatment process.

[0046] Please see Figure 4 As shown, it is a logic judgment diagram for determining the integrity of the solid fluorine framework structure in an embodiment of the present invention.

[0047] Specifically, the integrity of the solid fluoride skeleton structure is determined based on the comparison between the fluoride ion removal rate and the preset fluoride ion removal rate. If the fluoride ion removal rate is greater than or equal to the preset fluoride ion removal rate, then the solid fluoride skeleton structure is considered intact. If the fluoride ion removal rate is less than the preset fluoride ion removal rate, then the solid fluoride skeleton structure is determined to be incomplete.

[0048] In this embodiment of the invention, the determination process of the solid fluoride performance test is as follows: three portions of the mixture with a mass of 0.500g ± 0.005g are weighed and placed in three 250mL conical flasks as parallel samples. 100.0mL of simulated wastewater with an initial fluoride ion concentration of 20.0mg / L ± 0.5mg / L is added to each conical flask. The mixture is reacted at a constant temperature of 25℃ and shaken at 150r / min for 30min. After the reaction, the supernatant is taken from each conical flask and filtered through a 0.45μm filter membrane. The fluoride ion concentration of the filtrate is measured using the fluoride ion selective electrode method. The fluoride ion removal rate is calculated by the ratio of the difference between the initial fluoride ion concentration and the fluoride ion concentration in the filtrate after the reaction to the initial fluoride ion concentration. The average value is taken as the final fluoride ion removal rate.

[0049] In this embodiment of the invention, the preset fluoride ion removal rate is in the range of [95%, 99%], preferably set to 96%, but the above value is not limited to this, and those skilled in the art can adjust the value according to actual needs.

[0050] In this embodiment of the invention, the solid fluoride framework is the core component responsible for fixing fluoride ions. Its structural integrity is the key dominant factor that determines the final fluoride removal efficiency. Therefore, the fluoride ion removal rate obtained through solid fluoride performance testing can effectively characterize and reflect the structural integrity and reactivity of the solid fluoride framework.

[0051] In this embodiment of the invention, the removal mechanism of the fluoride ion remover is based on pretreated and activated oyster shell powder as the core calcium source. The calcium ions provided by the powder, together with the calcium ions generated from the dissolution of calcium hydroxide, provide a basis for chemical precipitation. The fluoride ions react with fluoride ions to form calcium fluoride precipitate. Furthermore, strontium carbonate and disodium hydrogen phosphate in the composition are mixed at a specific molar ratio to form a stable "strontium-phosphorus" solid fluoride framework. This solid fluoride framework structure can specifically adsorb and fix the fluoride through ion exchange and surface coordination, forming a thermodynamically more stable and less soluble fluoride-like substance. Apatite structures (such as Sr5(PO4)3F) hydrolyze in water after the addition of aluminum trichloride, generating a series of polyaluminum flocculants with polynuclear hydroxyl-bridged structures and amorphous aluminum hydroxide flocs. These positively charged flocs can effectively neutralize and adsorb negatively charged colloidal particles. Through the "adsorption-bridging-trapping" effect, they rapidly aggregate fine CaF2 precipitates, solid fluoride skeleton particles and other suspended pollutants in the water into dense flocs, greatly accelerating the solid-liquid separation process and ensuring clear effluent, thereby achieving deep removal of fluoride ions.

[0052] Specifically, this invention directly determines the structural integrity of the solid fluoride framework through standardized solid fluoride performance testing, establishing a quality control mechanism oriented towards end-performance. This testing method achieves rapid and objective evaluation of the framework structure by accurately quantifying the fluoride ion removal rate and comparing it with a preset fluoride ion removal rate.

[0053] Example 1 Weigh 58.39 g of pretreated oyster shell powder, 2.19 g of strontium carbonate, and 2.92 g of disodium hydrogen phosphate, place them in a three-dimensional motion mixer, and mix at 30 rpm for 40 minutes at room temperature to obtain solid fluorine framework powder. Add 14.60 g of calcium hydroxide to the obtained solid fluoride framework powder and continue mixing for 20 minutes. Then add 21.90 g of aluminum trichloride and mix for another 30 minutes to obtain a mixture.

[0054] Example 2 Weigh 59.70 g of pretreated oyster shell powder, 1.49 g of strontium carbonate, and 1.49 g of disodium hydrogen phosphate, place them in a three-dimensional motion mixer, and mix at 30 rpm for 40 minutes at room temperature to obtain solid fluorine framework powder. Add 14.93 g of calcium hydroxide to the obtained solid fluoride framework powder and continue mixing for 20 minutes. Then add 22.39 g of aluminum trichloride and mix for another 30 minutes to obtain a mixture.

[0055] Example 3 Weigh 55.56 g of pretreated oyster shell powder, 2.78 g of strontium carbonate, and 4.17 g of disodium hydrogen phosphate, place them in a three-dimensional motion mixer, and mix at 30 rpm for 40 minutes at room temperature to obtain solid fluorine framework powder. Add 13.89 g of calcium hydroxide to the obtained solid fluoride framework powder and continue mixing for 20 minutes. Then add 23.61 g of aluminum trichloride and mix for another 30 minutes to obtain a mixture.

[0056] Example 4 Weigh 21.28 g of pretreated oyster shell powder, 1.06 g of strontium carbonate, and 1.06 g of disodium hydrogen phosphate, place them in a three-dimensional motion mixer, and mix at 30 rpm for 40 minutes at room temperature to obtain solid fluorine framework powder. Add 42.55 g of calcium hydroxide to the obtained solid fluoride framework powder and continue mixing for 20 minutes. Then add 34.04 g of aluminum trichloride and mix for another 30 minutes to obtain a mixture.

[0057] Example 5 Weigh 62.50 g of pretreated oyster shell powder, 2.08 g of strontium carbonate, and 3.13 g of disodium hydrogen phosphate, place them in a three-dimensional motion mixer, and mix at 30 rpm for 40 minutes at room temperature to obtain solid fluorine framework powder. Add 5.21 g of calcium hydroxide to the obtained solid fluoride framework powder and continue mixing for 20 minutes. Then add 27.08 g of aluminum trichloride and mix for another 30 minutes to obtain the mixture.

[0058] Example 6 Weigh 47.95 g of pretreated oyster shell powder, 1.64 g of strontium carbonate, and 2.46 g of disodium hydrogen phosphate, place them in a three-dimensional motion mixer, and mix at 30 rpm for 40 minutes at room temperature to obtain solid fluorine framework powder. Add 20.55 g of calcium hydroxide to the obtained solid fluoride framework powder and continue mixing for 20 minutes. Then add 27.40 g of aluminum trichloride and mix for another 30 minutes to obtain a mixture.

[0059] Comparative Example 1 Weigh 66.67 g of calcium hydroxide and 33.33 g of aluminum trichloride, place them in a three-dimensional motion mixer, and mix at 30 rpm for 90 minutes at room temperature to obtain a mixture.

[0060] Comparative Example 2 Weigh 62.50 g of pretreated oyster shell powder and 37.50 g of aluminum trichloride, place them in a three-dimensional motion mixer, and mix at 30 rpm for 90 minutes at room temperature to obtain a mixture.

[0061] Comparative Example 3 Weigh 20.00 g of pretreated qualified oyster shell powder, 50.00 g of calcium hydroxide, and 30.00 g of aluminum trichloride, place them in a three-dimensional motion mixer, and mix at 30 rpm for 90 minutes at room temperature to obtain a mixture.

[0062] Comparative Example 4 Weigh 41.67 g of pretreated oyster shell powder, 33.33 g of calcium hydroxide, and 25.00 g of aluminum trichloride, place them in a three-dimensional motion mixer, and mix at 30 rpm for 90 minutes at room temperature to obtain a mixture.

[0063] Comparative Example 5 Weigh 57.14 g of pretreated oyster shell powder, 21.43 g of calcium hydroxide, and 21.43 g of aluminum trichloride, place them in a three-dimensional motion mixer, and mix at 30 rpm for 90 minutes at room temperature to obtain a mixture.

[0064] Comparative Example 6 Weigh 70.59 g of pretreated oyster shell powder, 11.76 g of calcium hydroxide, and 17.65 g of aluminum trichloride, place them in a three-dimensional motion mixer, and mix at 30 rpm for 90 minutes at room temperature to obtain a mixture.

[0065] Comparative Example 7 Weigh 78.95 g of pretreated oyster shell powder, 5.26 g of calcium hydroxide, and 15.79 g of aluminum trichloride, place them in a three-dimensional motion mixer, and mix at 30 rpm for 90 minutes at room temperature to obtain a mixture.

[0066] Comparative Example 8 Weigh 58.82 g of pretreated oyster shell powder, 14.71 g of calcium hydroxide, and 26.47 g of aluminum trichloride, place them in a three-dimensional motion mixer, and mix at 30 rpm for 90 minutes at room temperature to obtain a mixture.

[0067] Comparative Example 9 Weigh 47.06 g of pretreated qualified oyster shell powder, 35.29 g of calcium hydroxide, and 17.65 g of aluminum trichloride, place them in a three-dimensional motion mixer, and mix at 30 rpm for 90 minutes at room temperature to obtain the fluoride removal agent product.

[0068] Comparative Example 10 Weigh 40.00 g of pretreated qualified oyster shell powder, 40.00 g of calcium hydroxide, and 20.00 g of aluminum trichloride, place them in a three-dimensional motion mixer, and mix at 30 rpm for 90 minutes at room temperature to obtain a mixture.

[0069] Comparative Example 11 Weigh 11.85 g of pretreated oyster shell powder, 2.22 g of strontium carbonate, and 2.96 g of disodium hydrogen phosphate, place them in a three-dimensional motion mixer, and mix at 30 rpm for 40 minutes at room temperature to obtain solid fluorine framework powder. Add 14.81 g of calcium hydroxide to the obtained solid fluoride framework powder and continue mixing for 20 minutes. Then add 68.15 g of aluminum trichloride and mix for another 30 minutes to obtain the mixture.

[0070] Comparative Example 12 Weigh 68.97 g of pretreated oyster shell powder, 1.59 g of strontium carbonate, and 2.12 g of disodium hydrogen phosphate, place them in a three-dimensional motion mixer, and mix at 30 rpm for 40 minutes at room temperature to obtain solid fluorine framework powder. Add 10.34 g of calcium hydroxide to the obtained solid fluoride framework powder and continue mixing for 20 minutes. Then add 16.98 g of aluminum trichloride and mix for another 30 minutes to obtain a mixture.

[0071] Comparative Example 13 Weigh 58.48 g of pretreated oyster shell powder, 2.19 g of strontium carbonate, and 2.92 g of disodium hydrogen phosphate, place them in a three-dimensional motion mixer, and mix at 30 rpm for 40 minutes at room temperature to obtain solid fluorine framework powder. Add 4.38 g of calcium hydroxide to the obtained solid fluoride framework powder and continue mixing for 20 minutes. Then add 32.04 g of aluminum trichloride and mix for another 30 minutes to obtain the mixture.

[0072] Comparative Example 14 Weigh 48.78 g of pretreated oyster shell powder, 1.83 g of strontium carbonate, and 2.44 g of disodium hydrogen phosphate, place them in a three-dimensional motion mixer, and mix at 30 rpm for 40 minutes at room temperature to obtain solid fluorine framework powder. Add 30.49 g of calcium hydroxide to the obtained solid fluoride framework powder and continue mixing for 20 minutes. Then add 16.46 g of aluminum trichloride and mix for another 30 minutes to obtain a mixture.

[0073] Comparative Example 15 Weigh 58.65 g of pretreated oyster shell powder, 0.44 g of strontium carbonate, and 2.92 g of disodium hydrogen phosphate, place them in a three-dimensional motion mixer, and mix at 30 rpm for 40 minutes at room temperature to obtain solid fluorine framework powder. Add 14.66 g of calcium hydroxide to the obtained solid fluoride framework powder and continue mixing for 20 minutes. Then add 23.33 g of aluminum trichloride and mix for another 30 minutes to obtain a mixture.

[0074] Comparative Example 16 Weigh 58.65 g of pretreated oyster shell powder, 2.19 g of strontium carbonate, and 0.44 g of disodium hydrogen phosphate, place them in a three-dimensional motion mixer, and mix at 30 rpm for 40 minutes at room temperature to obtain solid fluorine framework powder. Add 14.66 g of calcium hydroxide to the obtained solid fluoride framework powder and continue mixing for 20 minutes. Then add 24.06 g of aluminum trichloride and mix for another 30 minutes to obtain a mixture.

[0075] Comparative Example 17 Weigh 58.48 g of pretreated oyster shell powder, 2.19 g of strontium carbonate, and 2.92 g of disodium hydrogen phosphate, place them in a three-dimensional motion mixer, and mix at 30 rpm for 40 minutes at room temperature to obtain solid fluorine framework powder. Add 4.38 g of calcium hydroxide to the obtained solid fluoride framework powder and continue mixing for 20 minutes. Then add 32.04 g of aluminum trichloride and mix for another 30 minutes to obtain the mixture.

[0076] Comparative Example 18 Weigh 52.63 g of pretreated oyster shell powder, 1.97 g of strontium carbonate, and 2.63 g of disodium hydrogen phosphate, place them in a three-dimensional motion mixer, and mix at 30 rpm for 40 minutes at room temperature to obtain solid fluorine framework powder. Add 13.16 g of calcium hydroxide to the obtained solid fluoride framework powder and continue mixing for 20 minutes. Then add 29.61 g of aluminum trichloride and mix for another 30 minutes to obtain a mixture.

[0077] 2.00 g of the mixtures prepared in Examples 1-6 and Comparative Examples 1-18 were weighed and added to 500 mL of semiconductor wastewater with a fluoride ion concentration of 478.6 mg / L (the dosage was 4000 mg / L). The mixtures were stirred at 200 rpm for 40 minutes, allowed to stand and settle, and the supernatant was collected. The results of the fluoride concentration and pH value of the water were measured and are shown in Table 1 below.

[0078] Table 1 ; In the above embodiments, oyster shell powder serves as the core calcium source and physical framework, and its content directly affects the sustainability of the reaction and the sludge production. Examples 1-3 and Examples 5-6 (dosage 35%-60%) all achieved an effluent fluoride concentration ≤9.0 mg / L, demonstrating its crucial role in providing a stable calcium source and buffering capacity. However, Comparative Example 11 (8% oyster shell powder dosage) resulted in an effluent fluoride concentration jump to 20.3 mg / L, significantly reducing efficiency. Comparative Example 12 (65% oyster shell powder dosage) retained some effect (13.2 mg / L), but reached the critical point of excessive precipitation and increased cost. Calcium hydroxide, as a core pH regulator, affects the reaction environment in terms of dosage. Examples 1-6 stabilized the pH in the ideal range of 7.0-9.2, ensuring reaction efficiency. However, Comparative Example 13 (3% calcium hydroxide dosage) suffered from insufficient fluoride removal (15.6 mg / L) due to insufficient pH (6.2). mg / L), while Comparative Example 14 (calcium hydroxide dosage 25%) caused adjustment costs and sludge increment issues due to excessively high pH (11.0).

[0079] Strontium carbonate and disodium hydrogen phosphate achieved synergistic effects by constructing a strontium-phosphorus-based fluoride-fixing framework. Example 3 achieved the best fluoride removal effect (7.2 mg / L), while Comparative Example 8 (without Sr-P component) showed a significant decrease in efficiency (12.1 mg / L) under the same conditions, demonstrating the specific capture ability of this framework for fluoride ions. Comparative Examples 15 and 16 (0.3% strontium carbonate and disodium hydrogen phosphate) showed no improvement in effect below this range. The dosage determines the sedimentation and separation efficiency of the fluoride-fixing products. Examples 1-6 (15% aluminum trichloride) performed excellently, while Comparative Example 17 (3% aluminum trichloride) showed a sharp deterioration in efficiency (26.8 mg / L) due to insufficient coagulation. Comparative Example 18 (35% aluminum trichloride) faced practical problems in transportation management and sludge increase.

[0080] Specifically, the scientific nature of this invention is reflected in the functional complementarity and precise synergy of the dosage boundaries of each component. Oyster shells and calcium hydroxide together construct and maintain the alkaline environment and calcium ion concentration required for the reaction. Strontium carbonate and disodium hydrogen phosphate form a stable fluoride-fixing framework at a specific molar ratio, which efficiently fixes fluoride ions through co-precipitation. Aluminum trichloride achieves the capture and sedimentation of fine precipitates through hydrolysis and flocculation. This synergistic formulation system successfully solves the pain points of traditional methods such as low fluoride removal efficiency, large pH fluctuations, and high sludge production, providing a reliable solution for the treatment of high-concentration fluoride-containing wastewater.

[0081] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a high-concentration fluoride-containing wastewater removal agent, characterized in that, include, The oyster shells that have passed the pretreatment process, determined based on the thermal decomposition temperature, are pulverized to obtain oyster shell powder. The strontium-phosphorus molar ratio of strontium carbonate and disodium hydrogen phosphate was determined based on the calcium dissolution rate of pretreated qualified oyster shell powder to form a solid fluoride framework. The dosing strategy for calcium hydroxide and aluminum trichloride is determined based on the acid-base buffer index of the solid fluoride framework, so as to obtain a mixture by adding and mixing. The mixture is subjected to solid fluoride performance testing. The integrity of the solid fluoride skeleton structure is determined based on the comparison between the fluoride ion removal rate and the preset fluoride ion removal rate, so as to obtain a qualified finished product of fluoride-containing wastewater removal agent.

2. The preparation method of the high-concentration fluoride-containing wastewater removal agent according to claim 1, characterized in that, The pretreatment process for the oyster shells includes, Use deionized water to wash oyster shells to remove surface impurities and soluble salts; The raw material powder was obtained by drying at 105℃ to constant weight and then crushing and grinding it to pass through a 150-mesh sieve. The temperature is increased to the preset thermal decomposition temperature range at a rate of 10℃ / min.

3. The method for preparing the high-concentration fluoride-containing wastewater removal agent according to claim 2, characterized in that, The process of crushing pretreated oyster shells (determined based on thermal decomposition temperature) to obtain oyster shell powder includes the following steps: The thermal decomposition temperature is compared with the preset thermal decomposition temperature range; Based on the thermal decomposition temperature being within a preset thermal decomposition temperature range, the pretreated oyster shell powder is determined to be qualified. The oyster shell powder was obtained.

4. The preparation method of the high-concentration fluoride-containing wastewater removal agent according to claim 1, characterized in that, The process for determining the strontium-phosphorus molar ratio includes, Based on the fact that the calcium dissolution rate is greater than or equal to the preset calcium dissolution rate, the strontium-phosphorus molar ratio is determined using a first functional relationship; The first functional relationship is the product of the benchmark strontium-phosphorus molar ratio and the difference between the first compensation coefficient and the calcium dissolution rate and the preset calcium dissolution rate. The result is used as the strontium-phosphorus molar ratio.

5. The method for preparing the high-concentration fluoride-containing wastewater removal agent according to claim 1, characterized in that, The process of determining the strontium-phosphorus molar ratio also includes, Based on the fact that the calcium dissolution rate is less than the preset calcium dissolution rate, the strontium-phosphorus molar ratio is determined using a second functional relationship; The second functional relationship is the product of the baseline strontium-phosphorus molar ratio plus the second compensation coefficient and the difference between the preset calcium dissolution rate and the calcium dissolution rate. The result is used as the strontium-phosphorus molar ratio.

6. The method for preparing the high-concentration fluoride-containing wastewater removal agent according to claim 1, characterized in that, The acid-base buffer index of the solid fluoride skeleton is greater than or equal to the preset acid-base buffer index. The dosage of calcium hydroxide is determined to be 5% to 15% of the mass percentage of the finished fluoride wastewater removal agent, and the dosage of aluminum trichloride is 15% to 30% of the mass percentage of the finished fluoride wastewater removal agent.

7. The method for preparing the high-concentration fluoride-containing wastewater removal agent according to claim 1, characterized in that, The acid-base buffer index of the solid fluoride skeleton is less than the preset acid-base buffer index. The dosage of calcium hydroxide is determined to be 15% to 20% of the mass percentage of the finished fluoride wastewater removal agent, and the dosage of aluminum trichloride is 5% to 15% of the mass percentage of the finished fluoride wastewater removal agent.

8. The method for preparing the high-concentration fluoride-containing wastewater removal agent according to claim 1, characterized in that, The integrity of the solid fluoride framework structure is determined based on the fluoride ion removal rate being greater than or equal to a preset fluoride ion removal rate.

9. The method for preparing the high-concentration fluoride-containing wastewater removal agent according to claim 1, characterized in that, The incomplete solid fluoride framework structure is determined based on the fact that the fluoride ion removal rate is less than the preset fluoride ion removal rate.

10. The high-concentration fluoride-containing wastewater removal agent obtained by the preparation method according to any one of claims 1-9, characterized in that, It consists of the following components by mass percentage: Oyster shell powder 10%–60%, calcium hydroxide 5%–20%, strontium carbonate 0.5%–2%, disodium hydrogen phosphate 0.5%–3%, aluminum trichloride 5%–30%.

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