Preparation method of specific integration precipitant and application thereof in defluorination of waste acid

Abstract

This invention relates to the field of industrial wastewater treatment technology, and discloses a method for preparing a specific integrated precipitant and its application in the defluorination of wastewater. The invention first dissolves gluconic acid, aluminum sulfate, and zirconium oxychloride in water to obtain a metal complex precursor solution. This metal complex precursor solution is then added dropwise to a chitosan solution to obtain a specific integrated precipitant. The obtained specific integrated precipitant is added to fluoride-containing wastewater and stirred for a primary removal reaction. Subsequently, zirconium fluoride seed crystals are added and stirred for a secondary seeding enhancement reaction, ultimately achieving the defluorination purpose. In this invention, the gluconic acid-metal complex and chitosan form a composite metal salt polymer gel with a specific three-dimensional network structure through hydrogen bonding and coordination. The active metal centers in this gel network, upon encountering F… ‑ At that time, it can efficiently and selectively capture F ‑ This process forms "metal-organic framework-fluorine" composite precipitate microcrystals. The defluorination method described in this invention does not cause secondary environmental pollution and achieves a defluorination rate as high as 96%.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, specifically to a method for preparing a specific integrated precipitant and its application in the defluorination of wastewater. Background Technology

[0002] Industries such as non-ferrous metal smelting, titanium dioxide production, and fluorochemicals generate large quantities of complex, highly acidic (usually sulfuric acid systems) waste acid rich in chloride ions. The presence of fluoride ions not only severely corrodes production equipment and affects product quality, but also causes serious environmental pollution when discharged with wastewater. Currently, fluoride removal from waste acid mainly employs lime neutralization, adsorption, and evaporation concentration methods. However, these methods have significant drawbacks: lime neutralization produces large amounts of calcium salt sludge with extremely high water content, where calcium fluoride precipitation is incomplete and easily forms colloids, resulting in low chloride ion removal rates and difficult sludge disposal; adsorption methods experience a sharp decline in adsorption capacity in highly acidic, high-salinity waste acid, making regeneration difficult and costly; and evaporation concentration methods are extremely energy-intensive, and the resulting concentrated waste salt is hazardous waste, leading to high disposal costs.

[0003] Therefore, existing technologies have defects and shortcomings, and need further improvement and development. Summary of the Invention

[0004] In view of the shortcomings of the prior art, one of the objectives of this invention is to provide a method for preparing a specific integrative precipitant, which has the advantage of selectively precipitating fluoride ions. The specific steps of the method are as follows: A mixed solution was obtained by adding gluconic acid solution to water. Aluminum sulfate and zirconium oxychloride were mixed evenly and then added to the mixed solution and stirred until a clear and transparent metal complex precursor solution was obtained. Chitosan was added to water to fully swell and disperse evenly to obtain a structure directing agent solution. The metal complex precursor solution was added dropwise to the structure directing agent solution. After the metal complex precursor solution was added, it was aged at a constant temperature under stirring to obtain a specific integration precipitant.

[0005] Preferably, the mass ratio of gluconic acid solution, aluminum sulfate, zirconium oxychloride and chitosan is (8~10):(3~5):(1.5~2.5):(0.8~1.2), wherein the mass percentage concentration of gluconic acid solution is 50%.

[0006] Preferably, the preparation temperature of the metal complex precursor solution is 50℃~60℃.

[0007] Preferably, the preparation temperature of the structure-directing agent solution is 60℃~70℃.

[0008] Preferably, the dropping rate of the metal complex precursor solution is 1 to 2 drops / second.

[0009] Preferably, the constant temperature ripening conditions are 80℃~90℃ for 2h~4h.

[0010] The second objective of this invention is to provide an application of a specific integrated precipitant in the defluorination of waste acid, the specific steps of which are as follows: (1) Add a specific integrated precipitant to the fluorine-containing acidic wastewater and stir to carry out a primary removal reaction.

[0011] (2) After the primary removal reaction is completed, zirconium fluoride seed crystals are added and stirring is continued to carry out secondary seed enhancement to achieve the removal of fluorine.

[0012] Preferably, the method for calculating the amount of specific integrated precipitant added in step (1) is as follows: the total molar amount of active metal centers in the specific integrated precipitant is 0.5 to 2.0 times the total molar amount of fluoride ions in the wastewater.

[0013] Preferably, in step (2), the amount of zirconium fluoride seed crystals added is 0.1% to 0.5% of the total mass of the waste acid wastewater and the specific integrated precipitant.

[0014] Preferably, the preparation method of the zirconium fluoride seed crystal is as follows: ZrOCl2·8H2O is dissolved in water to obtain a zirconium oxychloride solution. A 20% hydrofluoric acid solution is added dropwise to the zirconium oxychloride solution. After the addition is complete, a constant temperature stirring reaction is carried out. After the constant temperature stirring reaction is completed, the mixture is naturally cooled to room temperature. Anhydrous ethanol is added under stirring conditions to precipitate a white precipitate. When the white precipitate no longer precipitates, the addition of anhydrous ethanol is stopped. The mixture is allowed to stand. After standing, the precipitate is separated, washed, and dried to obtain the zirconium fluoride seed crystal.

[0015] Preferably, the method for calculating the amount of hydrofluoric acid solution added is as follows: based on the molar ratio of fluorine in the hydrofluoric acid solution to zirconium in the zirconium oxychloride solution being 1.2:1, the dropping rate of the hydrofluoric acid solution is 1~2 / second.

[0016] Preferably, the constant temperature stirring reaction conditions are 58~62℃ for 1.5h~2h.

[0017] Preferably, the settling time is 11h to 12h.

[0018] Preferably, the washing method is to wash three times in sequence with deionized water and anhydrous ethanol.

[0019] Preferably, the primary removal reaction and the secondary seeding strengthening are carried out at 50℃~80℃; the stirring speed is 250rpm~400rpm, wherein the stirring time for the primary removal reaction is 1.5h~2.0h, and the stirring time for the secondary seeding strengthening is 15min~30min.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) In this invention, gluconic acid, as a "metal active center protector," and the synergistic coordination ability of multiple hydroxyl and carboxyl groups in the "crosslinking bridging ligand" molecule, with Al 3+ and Zr 4+ The formation of a stable five-membered ring chelate structure effectively inhibits the premature hydrolysis of metal ions under acidic conditions, enabling them to maintain high reactivity in subsequent cross-linking reactions with chitosan structure-directing agents.

[0021] (2) In the metal complex precursor solution of this invention, the gluconic acid-metal complex acts as a "metal-organic coordination unit." Through hydrogen bonding and coordination with the amino (-NH2) and hydroxyl (-OH) groups on the chitosan molecular chain via its uncoordinated hydroxyl groups, a composite metal salt polymer gel with a specific three-dimensional network structure is induced. The active metal center (Al) in this gel network 3+ and Zr 4+ When encountering F - At that time, F can be efficiently and selectively captured through ligand exchange reactions. - This forms a "metal-organic framework-fluorine" composite precipitate microcrystal.

[0022] (3) The three-dimensional network gel structure formed by the gluconic acid-metal complex and chitosan through hydrogen bonding and coordination in this invention endows the precipitant with excellent sedimentation performance. Compared with the amorphous fine precipitates produced by traditional chemical precipitation methods, the "metal-organic framework-fluorine" composite precipitate generated by the reaction of the precipitant with fluoride ions in this invention has a larger microcrystal size and a denser structure, which significantly improves the solid-liquid separation efficiency and reduces the difficulty and cost of subsequent filtration treatment.

[0023] (4) This invention achieves a 96% fluoride removal rate from waste acid by specifically integrating the synergistic effect between the precipitant and zirconium fluoride seed crystals, without generating pollutants throughout the process. This invention uses zirconium fluoride as a seed crystal for secondary seed enhancement, which has excellent lattice matching with the aluminum / zirconium fluoride precipitate generated in the primary removal reaction, effectively inducing secondary nucleation and growth of the precipitate on the seed crystal surface. Experimental data show that the D of the precipitate after seed enhancement... 50 The particle size increased from approximately 8.5 μm after primary removal to 35.2 μm, representing a fourfold increase and significantly improving the filtration and dewatering performance of the precipitate.

[0024] (5) The specific integrated precipitant and its defluorination method described in this invention can still maintain excellent defluorination performance in complex acidic wastewater systems with strong acidity (sulfuric acid system) and high salinity. Experimental results show that under harsh conditions with sulfuric acid concentration as high as 25~42 g / L and fluoride ion concentration of 1.7~2.1 g / L, the fluoride ion removal rate after two-stage treatment can reach more than 96%, breaking through the technical bottleneck of the traditional adsorption method where the adsorption capacity drops sharply under strong acid conditions. Attached Figure Description

[0025] Figure 1 This is a particle size distribution diagram of the precipitate product after the first-stage removal reaction in Application Example 1.

[0026] Figure 2 This is a particle size distribution diagram of the precipitate product after the secondary seed enhancement reaction in Example 1.

[0027] Figure 3 The precipitate product after the first-stage removal reaction and the precipitate product after the second-stage seed enhancement reaction in Application Example 1 are D. 50 Compare. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1 A method for preparing a specific integrative precipitant, the specific steps of which are as follows: (1) Add 120 mL of deionized water and 27.0 g of 50% gluconic acid solution to a 250 mL three-necked flask, place it in a constant temperature water bath, control the temperature at 50 °C, and stir until completely dissolved. Under the conditions of constant temperature at 50 °C and stirring speed at 300 rpm, add 12.0 g of pre-mixed aluminum sulfate and 6.0 g of zirconium oxychloride to the above system in batches within 40 min. After the addition is completed, continue to stir the reaction at constant temperature for 1.5 h to obtain a clear and transparent metal complex precursor solution.

[0030] (2) Add 135 mL of deionized water and 3.0 g of chitosan to a 500 mL three-necked flask, adjust the stirring speed to 400 rpm, heat to 60 °C at a heating rate of 2 °C / min, and stir at a constant temperature until fully swollen and evenly dispersed for about 1.5 h to obtain a uniform and stable chitosan solution as a structure directing agent.

[0031] (3) Under the conditions of 60℃ and 300rpm stirring speed, the metal complex precursor liquid was slowly added to the structure guiding agent at a rate of 2 drops / second. After the addition was completed, the system temperature was raised to 80℃, the stirring speed was adjusted to 200rpm, and the mixture was kept at a constant temperature for 3h. During this period, the mixture gradually turned into a uniform semi-transparent amber viscous gel. Heating and stirring were stopped, and the system was naturally cooled to room temperature to obtain the specific integration precipitant.

[0032] Example 2 (1) Add 180 mL of deionized water and 40.5 g of 50% gluconic acid solution to a 500 mL three-necked flask, place it in a constant temperature water bath, control the temperature at 50 °C, and stir until completely dissolved. Under constant temperature of 50 °C and stirring speed of 300 rpm, add 18.0 g of pre-mixed aluminum sulfate and 9.0 g of zirconium oxychloride to the above system in batches within 40 min. After the addition is completed, continue to stir the reaction at constant temperature for 1.5 h to obtain a clear and transparent metal complex precursor solution.

[0033] (2) Add 135 mL of deionized water and 4.5 g of chitosan to a 500 mL three-necked flask, adjust the stirring speed to 400 rpm, heat to 60 °C at a heating rate of 2 °C / min, and stir at a constant temperature until fully swollen and evenly dispersed for about 1.5 h to obtain a uniform and stable chitosan solution as a structure directing agent.

[0034] (3) Under the conditions of 60℃ and 300rpm stirring speed, the metal complex precursor liquid was slowly added to the structure guiding agent at a rate of 1 drop / second. After the addition was completed, the system temperature was raised to 80℃, the stirring speed was adjusted to 200rpm, and the mixture was kept at a constant temperature for 3h. During this period, the mixture gradually turned into a uniform semi-transparent amber viscous gel. Heating and stirring were stopped, and the system was naturally cooled to room temperature to obtain the specific integration precipitant.

[0035] Example 3 (1) Add 600 mL of deionized water and 135 g of 50% gluconic acid solution to a 2 L reactor, control the temperature at 50 °C, and stir until completely dissolved. Under constant temperature of 50 °C and stirring speed of 300 rpm, add 60 g of pre-mixed aluminum sulfate and 30 g of zirconium oxychloride to the above system in batches within 40 min. After the addition is completed, continue to stir the reaction at constant temperature for 1.5 h to obtain a clear and transparent metal complex precursor solution.

[0036] (2) Add 675 mL of deionized water and 15 g of chitosan to a 2 L reactor, adjust the stirring speed to 400 rpm, heat to 60 °C at a heating rate of 2 °C / min, and stir at a constant temperature until fully swollen and evenly dispersed for 1.5 h to obtain a uniform and stable chitosan solution as a structure directing agent.

[0037] (3) Under the conditions of 60℃ and 300rpm stirring speed, the metal complex precursor liquid was slowly added to the structure guiding agent at a rate of 2 drops / second. After the addition was completed, the system temperature was raised to 80℃, the stirring speed was adjusted to 200rpm, and the mixture was kept at a constant temperature for 3h. During this period, the mixture gradually turned into a uniform semi-transparent amber viscous gel. Heating and stirring were stopped, and the system was naturally cooled to room temperature to obtain the specific integration precipitant.

[0038] Example 4 This embodiment provides a method for preparing zirconium fluoride seed crystals, the specific steps of which are as follows: (1) Add 100 mL of deionized water to a 250 mL three-necked flask, place it in a constant temperature water bath and control the temperature at 60 °C, weigh 20.0 g of zirconium oxychloride (ZrOCl2·8H2O) and add it to the water, stir until completely dissolved to obtain a zirconium oxychloride solution.

[0039] (2) Slowly add a 20% hydrofluoric acid solution to the above zirconium oxychloride solution, controlling the adding speed to 1 drop / second. The amount of hydrofluoric acid solution added is calculated as follows: the molar ratio of fluorine in the hydrofluoric acid solution to zirconium in the zirconium oxychloride solution is 1.2:1. After the addition is completed, continue to stir the reaction at a constant temperature for 2.0h.

[0040] (3) After the reaction system is naturally cooled to room temperature, 30 mL of anhydrous ethanol is slowly added under stirring. A white crystalline precipitate is formed and allowed to stand for 12 h.

[0041] (4) The precipitate was separated by vacuum filtration and washed three times with deionized water and anhydrous ethanol. The washed product was placed in a vacuum drying oven and dried at 80°C for 6 hours. After grinding, zirconium fluoride seed crystals were obtained.

[0042] Application Example 1 The wastewater used in this application example comes from a copper smelting enterprise. The sulfuric acid concentration in the wastewater is 39.69 g / L and the fluoride ion concentration is 1.71 g / L. The zirconium fluoride seed crystals used are those prepared in Example 4.

[0043] The application of a specific integrated precipitant in the defluorination of waste acid, the specific steps of which are described below: (1) Take 100 mL of waste acid water and measure the total molar amount of active metal centers in the specific integrated precipitant (Al). 3+ With Zr 4+ The total molar amount of fluoride ions in the waste acid was 1.5 times the theoretical requirement. The specific integrated precipitant prepared in Example 1 was added, and the primary removal reaction was carried out by magnetic stirring at 60°C and 300 rpm for 1.5 h.

[0044] (2) Subsequently, 0.3% of the total mass of the waste acid wastewater and the specific integrated precipitant was added to the reaction system, and the mixture was stirred for 20 minutes to carry out secondary seed enhancement, so as to finally remove fluoride from the waste acid wastewater.

[0045] After the reaction was completed, the concentration of residual fluoride ions was determined using the standard addition method of ion electrode. The results showed that the concentration of residual fluoride ions after the first-stage removal reaction was 253 mg / L, and the fluoride ion removal rate was 85.2%. After the second-stage seed enhancement, the concentration of residual fluoride ions was further reduced to 63 mg / L, and the fluoride ion removal rate was increased to 96.3%, which meets the currently recognized requirements for waste acid treatment.

[0046] To verify the seed-induced crystallization effect, particle size analysis was performed on the precipitates before and after secondary seed strengthening. The results are as follows: Figure 1 As shown, the results indicate that the precipitate after the primary removal reaction is amorphous or fine granular with uneven particle size distribution (D). 50 The initial particle size was approximately 8.5 μm; however, after adding zirconium fluoride seeds and stirring for 20 min, the precipitate particles significantly increased in size, exhibiting a regular crystal morphology and a more concentrated particle size distribution (D). 50 (Growing to 35.2 μm), confirming the seed-induced crystal growth effect.

[0047] Application Example 2 The wastewater used in this application example comes from a lead-zinc smelter. The sulfuric acid concentration in the wastewater is 25.3 g / L and the fluoride ion concentration is 2.05 g / L. The zirconium fluoride seed crystals used are those prepared in Example 4.

[0048] The application of a specific integrated precipitant in the defluorination of waste acid, the specific steps of which are described below: (1) Take 200 mL of waste acid water and measure the total molar amount of active metal centers in the specific integrated precipitant (Al). 3+ With Zr 4+ The total molar amount of fluoride ions in the waste acid was 1.2 times the theoretical requirement. The specific integrated precipitant prepared in Example 2 was added, and the primary removal reaction was carried out by magnetic stirring at 70°C and 400 rpm for 2.0 h.

[0049] (2) Subsequently, 0.2% of the total mass of the waste acid wastewater and the specific integrated precipitant was added to the reaction system, and the mixture was stirred for 25 minutes to carry out secondary seed enhancement, so as to finally remove fluoride from the waste acid wastewater.

[0050] After the reaction was completed, the concentration of residual fluoride ions was determined using the standard addition method of ion electrode. The results showed that the concentration of residual fluoride ions after the first-stage removal reaction was 267 mg / L, and the fluoride ion removal rate was 87.2%. After the second-stage seed enhancement, the concentration of residual fluoride ions was further reduced to 69 mg / L, and the fluoride ion removal rate was increased to 96.6%, which meets the currently recognized requirements for waste acid treatment.

[0051] Application Example 3 The wastewater used in this application example comes from a copper smelting enterprise. The sulfuric acid concentration in the wastewater is 42.1 g / L and the fluoride ion concentration is 1.88 g / L. The zirconium fluoride seed crystals used are those prepared in Example 4.

[0052] The application of a specific integrated precipitant in the defluorination of waste acid, the specific steps of which are described below: (1) Take 2L of waste acid wastewater and measure it according to the total molar amount of active metal centers in the specific integrated precipitant (Al 3+ With Zr 4+ The total molar amount of fluoride ions in the waste acid was 1.5 times the theoretical requirement. The specific integrated precipitant prepared in Example 3 was added, and the primary removal reaction was carried out by magnetic stirring at 65°C and 250 rpm for 1.5 h.

[0053] (2) Subsequently, 0.4% of the total mass of the waste acid wastewater and the specific integrated precipitant was added to the reaction system, and the mixture was stirred for 30 minutes to carry out secondary seed enhancement, so as to finally remove fluoride from the waste acid wastewater.

[0054] After the reaction was completed, the concentration of residual fluoride ions was determined using the standard addition method of ion electrode. The results showed that the concentration of residual fluoride ions after the first-stage removal reaction was 205 mg / L, and the fluoride ion removal rate was 89.1%. After the second-stage seed enhancement, the concentration of residual fluoride ions was further reduced to 66 mg / L, and the fluoride ion removal rate was increased to 96.5%, which meets the currently recognized requirements for waste acid treatment.

[0055] Comparative Example 1 In comparison, this comparative example uses calcium fluoride seeds (not zirconium fluoride fluoride of the present invention) for secondary seed strengthening. The wastewater used in this comparative example comes from a copper smelting enterprise, and the concentration of sulfuric acid in the wastewater is 39.69 g / L and the concentration of fluoride ions is 1.71 g / L. The specific steps are as follows: (1) Take 100 mL of waste acid water and measure the total molar amount of active metal centers in the specific integrated precipitant (Al). 3+ With Zr 4+The total molar amount of fluoride ions in the waste acid was 1.5 times the theoretical requirement. The specific integrated precipitant prepared in Example 1 was added, and the primary removal reaction was carried out by magnetic stirring at 60°C and 300 rpm for 1.5 h.

[0056] (2) Subsequently, calcium fluoride seed crystals accounting for 0.3% of the total mass of the waste acid wastewater and the specific integrated precipitant were added to the reaction system, and the mixture was stirred for 20 minutes to carry out secondary seed enhancement, so as to finally remove fluoride from the waste acid wastewater.

[0057] After the reaction was completed, the concentration of residual fluoride ions was determined using the standard addition method of ion electrode. The results showed that the concentration of residual fluoride ions after the first-stage removal reaction was 253 mg / L, and the fluoride ion removal rate was 85.2%. After the second-stage seed enhancement, the concentration of residual fluoride ions was further reduced to 63 mg / L, and the fluoride ion removal rate was increased to 96.3%, which meets the currently recognized requirements for waste acid treatment.

[0058] The test results showed that the residual fluoride ion concentration was 184 mg / L and the fluoride ion removal rate was 89.2%, which was lower than the 96.3% removal rate in Example 1. This indicates that the lattice matching degree between the calcium fluoride seed crystals and the aluminum / zirconium fluoride precipitate products generated by the specific integrated precipitant of the present invention is limited, and the induced crystallization effect is not as good as that of the zirconium fluoride seed crystals of the present invention.

[0059] Comparative Example 2 In comparison, this comparative example differs from Example 1 in that sodium gluconate is replaced with a precipitant prepared from citric acid.

[0060] The precipitant prepared in this comparative example was used to remove fluoride from acidic wastewater (the same as in Application Example 1) according to the method of Application Example 1. The results are shown in Table 1. The defluorination effect was significantly reduced after gluconic acid was replaced with citric acid.

[0061] Comparative Example 3 In comparison, this comparative example differs from Example 1 in that sodium gluconate is replaced with a precipitant prepared from tartaric acid.

[0062] The precipitant prepared in this comparative example was used to remove fluoride from wastewater (the same wastewater as in Application Example 1) according to the method of Application Example 1. The results are shown in Table 1. The defluorination effect was significantly reduced after gluconic acid was replaced with tartaric acid.

[0063] Comparative Example 4 In comparison, this comparative example differs from Example 1 in that sodium gluconate is replaced with a precipitant prepared from ethylenediaminetetraacetic acid (EDTA).

[0064] The precipitant prepared in this comparative example was used to remove fluoride from acidic wastewater (the same as in Application Example 1) according to the method of Application Example 1. The results are shown in Table 1. The defluorination effect was significantly reduced after gluconic acid was replaced with EDTA.

[0065] Table 1 As can be seen from the results in Table 1, gluconic acid is not a simple complexing agent in the system of this invention. Its specific molecular structure (polyhydroxy α-hydroxy acid) endows the precipitant with optimal metal ion protection, cross-linked gel network formation ability, and subsequent fluoride ion capture efficiency. Although citric acid and tartaric acid are both hydroxycarboxylic acid complexing agents, their coordination structures and stability constants are different, making it impossible to achieve a synergistic cross-linking effect with chitosan. While EDTA has strong complexing ability, its high stability hinders the effective competitive replacement of metal ions by fluoride ions, resulting in a significant decrease in the removal rate. This comparison fully demonstrates the non-obviousness of the selection of gluconic acid in this invention and the unexpected technical effects it brings.

[0066] Through experimental research, this invention has discovered that gluconic acid does not act as a "complexing agent" to deactivate metal ions in the system of this invention, but rather plays a dual key role as a "metal active site protector" and a "cross-linking bridging ligand": On the one hand, in the preparation stage of the metal complexing precursor solution, gluconic acid, through the synergistic coordination of its carboxyl group and multiple hydroxyl groups with Al... 3+ Zr 4+ A stable five-membered ring chelate structure is formed, temporarily "protecting" the metal ion from premature hydrolysis under acidic conditions. However, this protection is moderate and reversible—gluconic acid and Al... 3+ The complexation stability constant (log β) is moderate (approximately 3.16), sufficient to suppress the hydrolysis of metal ions during the preparation stage, yet not so stable as to hinder subsequent ligand exchange reactions. Furthermore, after the formation of the gluconic acid-metal complex, the remaining uncoordinated hydroxyl groups on its molecule retain their activity. These hydroxyl groups can crosslink with the amino (-NH2) and hydroxyl (-OH) groups on the chitosan molecular chain through hydrogen bonding and coordination, making the gluconic acid-metal complex act as a "bridging ligand" connecting the metal ions to the chitosan backbone, inducing the formation of a composite metal salt polymer gel with a specific three-dimensional network structure. It is this organic unity of "protection" and "bridging" functions that makes the active metal center (Al) in this invention... 3+ and Zr 4+ ) able to encounter F later - At that time, F is efficiently released and selectively captured through ligand exchange reactions. -This forms a "metal-organic framework-fluorine" composite precipitate microcrystal. However, in existing technologies, when gluconic acid is used only as a common complexing agent, its function is to "deactivate" metal ions rather than "protect and then activate" them. The two technologies are fundamentally different in terms of their technical approach and mechanism of action.

[0067] Comparative Example 5 To verify the superiority of the precipitant formed by gluconic acid, aluminum sulfate, zirconium oxychloride, and chitosan through a specific preparation process compared to the simple mixing of the components, this comparative example was set up. The same raw materials as in Example 1 were taken, namely 27.0 g of gluconic acid solution, 12.0 g of aluminum sulfate, 6.0 g of zirconium oxychloride, and 3.0 g of chitosan, and directly added to 135 mL of deionized water (without stepwise dissolution, preparation of metal complex precursor solution, dropwise addition, or isothermal aging treatment). The mixture was simply mechanically stirred at 60°C for 1.5 h to obtain a mixed suspension.

[0068] Following the method described in Example 1, the mixed suspension was added to 100 mL of the same acidic wastewater (sulfuric acid concentration 39.69 g / L, fluoride ion concentration 1.71 g / L). The mixture was stirred at 60°C and 300 rpm for 1.5 h for a first-stage reaction. Subsequently, 0.3% (by mass) of zirconium fluoride seed crystals (based on the total mass of the acidic wastewater and the mixed suspension) was added, and stirring was continued for 20 min for a second-stage intensification. After the first-stage removal, the residual fluoride ion concentration was 408 mg / L, with a removal rate of only 76.1%. After the second-stage intensification, the residual fluoride ion concentration was 186 mg / L, with a removal rate of only 89.1%, significantly lower than the 96.3% in Example 1. Particle size analysis of the precipitate was performed, and its D... 50 It is only 10.8 μm, which is significantly smaller than the 35.2 μm after seeding in Example 1.

[0069] The above results demonstrate that, without the specific process of this invention, gluconic acid, aluminum sulfate, zirconium oxychloride, and chitosan cannot form a three-dimensional network gel structure with specific capture capabilities, and the active metal centers cannot be effectively loaded and maintain high reactivity. The simply mixed components are unable to exert a synergistic effect in capturing fluoride ions in polluted acid, and may even lose some activity due to premature hydrolysis of the metal ions. This comparative example fully demonstrates the indispensability of the specific preparation process in this invention, and the unexpected synergistic effect that the components can achieve through this process.

[0070] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a specific integrative precipitant, characterized in that: The method specifically includes the following steps: A mixed solution was obtained by adding gluconic acid solution to water. Aluminum sulfate and zirconium oxychloride were mixed evenly and then added to the mixed solution and stirred until a clear and transparent metal complex precursor solution was obtained. Chitosan was added to water to fully swell and disperse evenly to obtain a structure directing agent solution. The metal complex precursor liquid was added dropwise to the structure-directing agent solution. After the metal complex precursor liquid was added, it was aged at a constant temperature under stirring to obtain a specific integrative precipitant.

2. The method for preparing the specific integrative precipitant according to claim 1, characterized in that: The mass ratio of gluconic acid solution, aluminum sulfate, zirconium oxychloride and chitosan is (8~10):(3~5):(1.5~2.5):(0.8~1.2), wherein the mass percentage concentration of gluconic acid solution is 50%.

3. The method for preparing the specific integrative precipitant according to claim 1, characterized in that: The preparation temperature of the metal complex precursor solution is 50℃~60℃; the preparation temperature of the structure directing agent solution is 60℃~70℃; the dropping rate of the metal complex precursor solution is 1~2 drops / second. The constant temperature ripening conditions are 80℃~90℃ for 2~4 hours.

4. The application of the specific integrated precipitant prepared by the method of claim 1 in the defluorination of waste acid, characterized in that: The specific steps of the application are as follows: (1) Add a specific integrated precipitant to the fluorine-containing acidic wastewater and stir to carry out a primary removal reaction; (2) After the primary removal reaction is completed, zirconium fluoride seed crystals are added and stirring is continued to carry out secondary seed enhancement to achieve the removal of fluorine.

5. The application according to claim 4, characterized in that: The calculation method for the amount of specific integration precipitant added in step (1) is as follows: the total molar amount of active metal centers in the specific integration precipitant is 0.5 to 2.0 times the total molar amount of fluoride ions in the wastewater.

6. The application according to claim 4, characterized in that: In step (2), the amount of zirconium fluoride seed crystals added is 0.1% to 0.5% of the total mass of the waste acid wastewater and the specific integrated precipitant. The preparation method of the zirconium fluoride seed crystals is as follows: ZrOCl2·8H2O was dissolved in water to obtain a zirconium oxychloride solution. A 20% hydrofluoric acid solution was added dropwise to the zirconium oxychloride solution. After the addition was complete, the mixture was stirred at a constant temperature. After the stirring reaction was completed, the mixture was allowed to cool naturally to room temperature. Anhydrous ethanol was added under stirring conditions to precipitate a white precipitate. Once the white precipitate stopped precipitating, the addition of anhydrous ethanol was stopped. The mixture was allowed to stand. After standing, the precipitate was separated, washed, and dried to obtain zirconium fluoride seed crystals.

7. The application according to claim 6, characterized in that: The method for calculating the amount of hydrofluoric acid solution to be added is as follows: based on the molar ratio of fluorine in the hydrofluoric acid solution to zirconium in the zirconium oxychloride solution being 1.2:1, the dropping rate of the hydrofluoric acid solution is 1~2 / second.

8. The application according to claim 6, characterized in that: The constant temperature stirring reaction conditions are 58~62℃ for 1.5h~2h.

9. The application according to claim 6, characterized in that: The settling time is 11-12 hours.

10. The application according to claim 4, characterized in that: The primary removal reaction and the secondary seeding strengthening were carried out at 50℃~80℃; the stirring time for the primary removal reaction was 1.5h~2.0h, and the stirring time for the secondary seeding strengthening was 15min~30min.

Images