Modified kaolinite, method for preparing the same, and application thereof to removal of fluoride

Abstract

The application discloses modified kaolinite, a preparation method thereof and application of the modified kaolinite in fluoride removal. The modified kaolinite is obtained by mixing and calcining kaolinite after carboxyl treatment. The modified kaolinite can be added into a strong-acid fluorine-containing sulfate solution for adsorption, and the modified kaolinite can preferentially act on fluoride in the solution and weakly act on sulfate ions, so that selective removal of the fluoride is realized. The modified kaolinite is suitable for removal of the fluoride in a strong-acid sulfate system such as electrolytic zinc, and has the characteristics of simple process and strong adaptability.

Description

Technical Field

[0001] This invention belongs to the technical field of fluoride solution treatment and inorganic non-metallic mineral material application, specifically involving modified kaolinite and its preparation method and its application in removing fluorides. Background Technology

[0002] In industrial processes such as hydrometallurgy and zinc electrolysis, large quantities of strongly acidic sulfate solutions are often generated or used. These solutions typically feature high sulfuric acid concentrations, high ionic strength, and complex systems, and are often accompanied by the introduction of a certain amount of fluoride. Sources of fluoride include leaching from fluorine-containing minerals in raw ores, entrainment by process acids, and equipment corrosion. In strongly acidic sulfate systems, the presence of fluoride can adversely affect the production process and equipment operation, such as exacerbating equipment corrosion, affecting the stability of the electrolysis process, and reducing product quality. Therefore, effectively removing fluoride from the solution without disrupting the basic composition of the sulfate system is a pressing technical problem that needs to be solved in relevant industrial fields.

[0003] Existing methods for treating fluoride-containing solutions mainly include chemical precipitation, ion exchange, and adsorption. However, these methods all have limitations in strongly acidic systems with high sulfate concentrations. For example, chemical precipitation often requires the introduction of large amounts of external reagents, easily leading to secondary precipitation and solid waste. Ion exchange resins are prone to performance degradation under strong acid and high ionic strength environments. Some adsorbent materials lack stability under strong acid conditions or simultaneously exhibit strong activity towards sulfate ions, making selective removal of fluorides difficult.

[0004] Kaolinite, a common layered aluminosilicate mineral, is widely available and inexpensive. Existing research indicates that modification treatment can improve its surface structure and reactivity to some extent, making it potentially valuable for adsorption and separation. However, in strongly acidic, high-sulfate systems, achieving effective and selective removal of fluorides while maintaining material structural stability remains a challenge, lacking mature and reliable technical solutions. Summary of the Invention

[0005] To address the problems mentioned in the background section, the present invention aims to provide a modified kaolinite, its preparation method, and its application in fluoride removal. This modified kaolinite has a simple preparation process, good material stability, and can achieve selective fluoride removal in a high sulfate environment, thus possessing significant engineering application value.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing modified kaolinite includes the following steps: Kaolinite was carboxylated to obtain carboxylated kaolinite; The modified kaolinite was obtained by calcining the carboxylated kaolinite and lanthanum MOF.

[0007] As a further improvement of the present invention, the mass ratio of carboxylated kaolinite to lanthanum MOF is 10:1~2.

[0008] As a further improvement of the present invention, the calcination temperature is 200~800℃.

[0009] As a further improvement of the present invention, the calcination time is 1 to 5 hours.

[0010] As a further improvement of the present invention, the calcination is carried out in an air atmosphere.

[0011] As a further improvement of the present invention, the calcination process includes: First, raise the temperature to 280-300℃ at a rate of 6-10℃ / min, and hold for 20-30 minutes. Then increase the temperature to 550-600℃ at a rate of 3-5℃ / min and hold for 60-120 minutes; Finally, increase the temperature to 650-700℃ at a rate of 2-4℃ / min and hold for 30-60 minutes.

[0012] As a further improvement of the present invention, the carboxylation treatment uses sodium chloroacetate.

[0013] As a further improvement of the present invention, the mass ratio of kaolinite to sodium chloroacetate in the carboxylation treatment is 10:1~2.

[0014] As a further improvement of the present invention, the temperature of the carboxylation treatment is 60~80°C.

[0015] As a further improvement of the present invention, the carboxylation treatment time is 1-5 hours.

[0016] As a further improvement of the present invention, the preparation method of the modified kaolinite includes the following steps: Kaolinite was dispersed in NaOH solution, and sodium chloroacetate was added to react and carboxylated kaolinite was obtained. Carboxylated kaolinite and lanthanum MOF were mixed and calcined at a temperature of 500-600℃ for 2-4 hours to obtain modified kaolinite.

[0017] As a further improvement of the present invention, the concentration of the NaOH solution is 0.4~0.6 mol / L.

[0018] As a further improvement of the present invention, the particle size D50 of the kaolinite is 2~5μm, preferably 2.5~3.5μm.

[0019] As a further improvement of the present invention, the kaolinite has a particle size D90 of 8~25μm, preferably 8.5~11.5μm.

[0020] As a further improvement of the present invention, the raw materials for preparing the lanthanum MOF include 2-aminoterephthalic acid and a lanthanum source.

[0021] As a further improvement of the present invention, the molar ratio of 2-aminoterephthalic acid to lanthanum source is 1:0.9~1.2.

[0022] As a further improvement of the present invention, the lanthanum source is selected from at least one of lanthanum nitrate, lanthanum chloride, and lanthanum sulfate.

[0023] As a further improvement of the present invention, the lanthanum MOF is prepared by the following method: 2-Aminoterephthalic acid and lanthanum nitrate were dissolved in DMF and placed in a high-pressure reactor. The mixture was reacted at 110-150°C for 12-36 h to obtain lanthanum MOF.

[0024] This invention achieves functional modification of kaolinite through carboxylation, lanthanum MOF composite, and calcination. First, kaolinite undergoes carboxymethylation with sodium chloroacetate under alkaline conditions, introducing carboxyl functional groups. This carboxylation process not only increases the negative charge density and hydrophilicity of kaolinite but also provides anchoring sites for subsequent lanthanum MOF loading. Subsequently, the carboxylated kaolinite is mixed with lanthanum MOF and calcined. During heating, the organic ligands of the lanthanum MOF gradually oxidize and decompose, and the kaolinite undergoes dehydroxylation, transforming into amorphous metakaolinite. This preparation method preserves the layered structure of kaolinite while increasing the active sites and pore structure of the material, thus improving its adsorption performance.

[0025] Modified kaolinite is obtained by any of the preparation methods described above.

[0026] The preparation method described in any of the above methods enables the application of modified kaolinite for fluoride removal.

[0027] As a further improvement of the present invention, the fluoride includes fluoride in a fluorinated sulfate solution.

[0028] As a further improvement of the present invention, the fluoride concentration in the fluorinated sulfate solution is 80~130 mg / L, preferably 90~110 mg / L.

[0029] As a further improvement of the present invention, the amount of modified kaolinite added is 15~25g / L.

[0030] As a further improvement of the present invention, the fluorinated sulfate solution is a strongly acidic solution.

[0031] As a further improvement of the present invention, the fluorinated sulfate solution is a solution produced or used during the electrolysis of zinc.

[0032] As a further improvement of the present invention, the concentration of sulfate ions in the fluorinated sulfate solution is higher than the concentration of the fluoride.

[0033] As a further improvement of the present invention, the modified kaolinite removes fluorides by adsorption.

[0034] As a further improvement of the present invention, the adsorption time is 0.5h to 2h.

[0035] As a further improvement of the present invention, the modified kaolinite is removed by solid-liquid separation after adsorption.

[0036] As a further improvement of the present invention, the application includes: The modified kaolinite was added to a fluoride sulfate solution, and adsorption was carried out by stirring and shaking. After adsorption is complete, the solution is filtered to obtain a fluorinated sulfate solution with fluoride removed.

[0037] Compared with the prior art, the technical solution of the present invention can bring the following beneficial technical effects: The modified kaolinite adsorbent provided by this invention is suitable for strongly acidic, high-concentration sulfate solution systems, achieving fluoride removal while maintaining material structural stability during adsorption. In high sulfate environments, the modified kaolinite exhibits good selective removal of fluorides and a weak effect on sulfate ions, which is beneficial for maintaining the original sulfate system composition of the solution. The modified kaolinite preparation method provided by this invention is simple, the kaolinite raw material used is widely available and inexpensive, and the calcination process is mature, making it suitable for industrial-scale application. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, and not all embodiments.

[0039] Therefore, the following detailed description of embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0040] The materials and instruments used in the following examples are all commercially available.

[0041] In some embodiments of the present invention, the application includes contacting modified kaolinite with a fluoride sulfate solution to selectively remove fluorides from the solution.

[0042] In some embodiments of the present invention, the fluorinated sulfate solution is a solution produced or used during the electrolysis of zinc.

[0043] In some embodiments of the present invention, the concentration of sulfate ions in the fluorinated sulfate solution is higher than the concentration of fluoride.

[0044] In some embodiments of the present invention, the fluorinated sulfate solution is strongly acidic, with a pH value <3.

[0045] In some embodiments of the present invention, the fluoride in the fluorinated sulfate solution is mainly in the form of HF.

[0046] In some embodiments of the present invention, the amount of modified kaolinite added is 15 g / L to 25 g / L.

[0047] In some embodiments of the present invention, the fluoride concentration in the fluorinated sulfate solution is 90~110 mg / L.

[0048] In some embodiments of the present invention, the modified kaolinite removes fluorides by adsorption.

[0049] In some embodiments of the present invention, the adsorption time is 0.5h to 2h.

[0050] In some embodiments of the present invention, the modified kaolinite is separated by solid-liquid separation after adsorption is completed.

[0051] In some embodiments of the present invention, the modified kaolinite is reusable.

[0052] In some embodiments of the present invention, the modified kaolinite is subjected to adsorption treatment followed by desorption treatment.

[0053] In some embodiments of the present invention, the desorption treatment uses a 0.1M NaOH solution.

[0054] The fluorinated sulfate solution used in this embodiment of the invention is a strongly acidic sulfate fluorinated electrolyte, derived from the zinc sulfate electrolyte in the hydrometallurgical zinc smelting process of a smelter in Hunan Province, wherein the fluoride concentration is 100 mg / L (as expressed in F). - (Calculated), the sulfate ion concentration is 180 g / L, and the pH value is 1.6.

[0055] Example 1 This embodiment provides a method for preparing modified kaolinite, including the following steps: S1. Crush and sieve the natural kaolinite raw material to obtain kaolinite particles with a particle size of D50=3μm and D90=10μm. S2. Disperse kaolinite particles in a 0.5 mol / L NaOH solution at a solid-liquid ratio of 1g:10mL, add sodium chloroacetate at 15% of the mass of kaolinite, and stir the reaction at 70℃ for 3h. After the reaction was complete, the pH was adjusted to 4.5 with hydrochloric acid, the insoluble matter was washed until neutral, and dried at 80°C for 12 h to obtain carboxylated kaolinite; S3. Dissolve 2-aminoterephthalic acid and lanthanum nitrate in DMF at a molar ratio of 1:1 (solid-liquid ratio of 1g:50mL) and sonicate for 20min. Transfer the solution to a polytetrafluoroethylene-lined stainless steel high-pressure reactor and react at 130℃ for 24h. After natural cooling, take the insoluble matter and wash it three times each with DMF and ethanol, and dry it at 60℃ for 12h to obtain lanthanum MOF. S4. Mix carboxylated kaolin and lanthanum MOF at a mass ratio of 5:1 and calcine them in air at a temperature of 600℃ for 2 hours. Modified kaolinite was obtained after cooling.

[0056] This embodiment also provides an application of modified kaolinite in the selective removal of fluorides in strongly acidic fluoride-containing sulfate solutions, specifically including the following steps: Modified kaolinite was added to a fluorinated sulfate solution at a solid-liquid ratio of 25 g / L, and stirred and vibrated at 200 rpm at 25°C. After 1 hour of adsorption, solid-liquid separation was performed by vacuum filtration to obtain the treated solution.

[0057] After adsorption, the fluoride removal rate of the fluoride-containing sulfate solution was 94.5%, and the sulfate ion removal rate was 2.8%.

[0058] Example 2 The difference between this embodiment and Embodiment 1 is that: In the preparation process of modified kaolinite: In step S1, the particle size of the kaolinite particles is adjusted to: D50=5μm, D90=25μm; In step S4, the calcination temperature is adjusted to 500℃ and the calcination time is adjusted to 3h.

[0059] After adsorption, the fluoride removal rate of the fluoride-containing sulfate solution was 89.2%, and the sulfate ion removal rate was 3.5%.

[0060] Example 3 The difference between this embodiment and Embodiment 1 is that: Adjustments to the calcination procedure in step S4: First, raise the temperature to 280℃ at a rate of 8℃ / min and hold for 20 minutes; Then increase the temperature to 550℃ at a rate of 4℃ / min and hold for 60 minutes; Finally, increase the temperature to 650℃ at a rate of 3℃ / min and hold for 30 minutes.

[0061] After adsorption, the fluoride removal rate of the fluoride-containing sulfate solution was 96.8%, and the sulfate ion removal rate was 1.9%.

[0062] Example 4 The difference between this embodiment and Embodiment 1 is that: In step S2, the amount of sodium chloroacetate was adjusted to 20% of the mass of kaolinite, and the reaction time was adjusted to 4 hours. In step S4, the mass ratio of carboxylated kaolinite to lanthanum MOF is adjusted to 10:1.

[0063] After adsorption, the fluoride removal rate of the fluoride-containing sulfate solution was 92.3%, and the sulfate ion removal rate was 2.2%.

[0064] Examples 5-7 The modified kaolinite obtained in Examples 1, 3 and 4 were respectively added to a fluorinated sulfate solution at a solid-liquid ratio of 25 g / L and stirred and vibrated at 200 rpm at 25°C. After 1 hour of adsorption, solid-liquid separation was performed by vacuum filtration to obtain the treated solution and adsorbent.

[0065] The adsorbent was cleaned and defluorinated (soaked in 0.1M NaOH solution for 2 hours), and then added to a fluoride sulfate solution for adsorption.

[0066] The same batch of modified kaolinite was used to perform five adsorption-elution cycles using the same procedure.

[0067] The second adsorption is recorded as the first cycle. The fluoride removal rates of the modified kaolinite obtained in Examples 1, 3, and 4 during the first to fifth cycles are shown in Table 1.

[0068] Table 1

[0069] Comparative Example 1 The difference between this comparative example and Example 1 is as follows: Excluding step S2, the carboxylated kaolinite in step S4 is replaced with the kaolinite particles obtained in step S1.

[0070] After adsorption, the fluoride removal rate of the fluoride-containing sulfate solution was 81.2%, and the sulfate ion removal rate was 4.5%.

[0071] Comparative Example 2 The difference between this comparative example and Example 1 is as follows: Lanthanum MOF is not added in step S4.

[0072] After adsorption, the fluoride removal rate of the fluoride-containing sulfate solution was 76.5%, and the sulfate ion removal rate was 3.2%.

[0073] Comparative Example 3 This comparative example uses commercially available γ-type activated alumina as the adsorbent material, with a particle size of 1~2 mm and a specific surface area of ​​300 m². 2 / g, aluminum oxide content ≥92%.

[0074] Adsorption conditions: solid-liquid ratio 2 g / L, temperature 25℃, stirring speed 200 rpm, adsorption time 2 h.

[0075] After adsorption, the fluoride removal rate of the fluoride-containing sulfate solution was 75.5%, and the sulfate ion removal rate was 12.5%.

[0076] The results showed that the modified kaolinite prepared by carboxylation, MOF composite, and calcination exhibited significantly better adsorption performance for fluorides in fluoride-containing sulfate solutions than the adsorbents in Comparative Examples 1-3, demonstrating excellent adsorption selectivity and cycling stability. The gradient calcination process in Example 3 facilitated the formation of a hierarchical porous structure and stable active sites, resulting in optimal recyclability.

[0077] This invention achieves high adsorption performance modification of kaolinite through carboxylation, MOF composite formation, and calcination. The resulting modified kaolinite can effectively remove fluorides in strong acid systems with high sulfate and high ionic strength, while having minimal impact on sulfate ions, thus meeting the requirements of relevant industrial processes for solution composition stability.

[0078] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A method for preparing modified kaolinite, characterized in that, Includes the following steps: Kaolinite was carboxylated to obtain carboxylated kaolinite; The modified kaolinite was obtained by calcining the carboxylated kaolinite and lanthanum MOF.

2. The preparation method according to claim 1, characterized in that, The mass ratio of carboxylated kaolinite to lanthanum MOF is 10:1~2; And / or, the calcination temperature is 200~800℃; And / or, the calcination time is 1 to 5 hours.

3. The preparation method according to claim 1, characterized in that, The carboxylation treatment uses sodium chloroacetate.

4. The preparation method according to claim 3, characterized in that, In the carboxylation treatment, the mass ratio of kaolinite to sodium chloroacetate is 10:1~2; And / or, the carboxylation treatment is performed at a temperature of 60~80°C; And / or, the carboxylation treatment time is 1~5h.

5. The preparation method according to claim 1, characterized in that, The raw materials for preparing the lanthanum MOF include 2-aminoterephthalic acid and a lanthanum source.

6. The preparation method according to claim 5, characterized in that, The molar ratio of 2-aminoterephthalic acid to lanthanum source is 1:0.9~1.2; And / or, the lanthanum source is selected from at least one of lanthanum nitrate, lanthanum chloride, and lanthanum sulfate.

7. Modified kaolinite is obtained by the preparation method according to any one of claims 1 to 6.

8. The application of modified kaolinite for fluoride removal obtained by the preparation method according to any one of claims 1 to 6.

9. The application according to claim 8, characterized in that, The fluoride includes fluorides in fluorinated sulfate solutions.

10. The application according to claim 9, characterized in that, The concentration of fluoride in the fluoride-containing sulfate solution is 80~130 mg / L; And / or, the amount of modified kaolinite added is 15~25g / L.

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