Tin disulfide supported phosphotungstic acid composite catalyst as well as preparation method and application thereof

Abstract

The embodiment of the invention discloses a tin disulfide supported phosphotungstic acid composite catalyst as well as a preparation method and application thereof. The method comprises the following steps: mixing tin disulfide, a silane coupling agent and an organic solvent, carrying out a grafting reaction in an inert atmosphere, and filtering to obtain modified tin disulfide; and mixing the modified tin disulfide, phosphotungstic acid and water, carrying out impregnation reaction, filtering, and drying to obtain the tin disulfide loaded phosphotungstic acid composite catalyst. The composite catalyst provided by the invention can efficiently promote hydrolysis of lithium hexafluorophosphate and photocatalytic degradation of organic matters, so that lithium hexafluorophosphate wastewater purification is realized, and the composite catalyst has a relatively good application prospect.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of wastewater treatment, and specifically to a tin disulfide-loaded phosphotungstic acid composite catalyst and a preparation method and application thereof. Background Art

[0002] The new energy industry has driven the rapid development of the lithium battery industry. As one of the four major materials of lithium batteries, lithium battery electrolyte is a carrier of ion transmission in lithium batteries, and plays a role in conducting lithium ions between the positive and negative electrodes. Lithium hexafluorophosphate (LiPF6) electrolyte has the advantages of good ionic conductivity, good electrochemical stability, safety and environmental protection, and is currently the most widely used lithium ion electrolyte. There are usually three methods for the industrial preparation of lithium hexafluorophosphate: wet method, dry method, and solvent method. Among them, the production of lithium hexafluorophosphate by solvent method causes a high content of organic matter in the wastewater, and the hexafluorophosphate and other fluorophosphates contained in the wastewater are difficult to remove. Direct discharge is likely to cause eutrophication and other pollution of water bodies.

[0003] The hydrolysis process of LiPF6 in this type of wastewater is relatively complicated, and the degree of hydrolysis is difficult to control. LiPF6 is easily hydrolyzed to form LiF, POF3, HF and other substances. In conventional treatment, the hydrolysis is incomplete. After conventional fluorine and phosphorus removal treatment, some lithium hexafluorophosphate is still hydrolyzed, causing the concentration of fluorine and phosphorus ions to rise again, making it difficult to meet the discharge standards.

[0004] CN113716731A discloses a calcium treatment process for lithium hexafluorophosphate industrial wastewater, wherein alkaline substances such as calcium hydroxide and flocculants are added to lithium hexafluorophosphate wastewater to remove fluorine and phosphorus by precipitation. The method is simple to operate and can quickly remove fluorine and phosphorus, but the precipitation method itself is difficult to achieve deep fluorine removal, and the hydrolysis of residual hexafluorophosphate will cause the recovery of fluoride ions and phosphates.

[0005] CN110921899A discloses a method for treating wastewater of lithium hexafluorophosphate and low-fluorine lithium phosphate compounds, wherein after adding alkali, calcium-containing compounds and flocculants, the precipitate is separated, and then hydrochloric acid is added, and then alkali, dephosphorizing agent and flocculants are added successively after passing through a fixed bed catalytic filler. The catalytic filler is a mixture of iron, carbon and titanium oxide, wherein the carbon has a low mechanical strength, and the particles are easily broken and lost, making it difficult to recycle.

[0006] CN115784539A uses a supported catalyst loaded with silicotungstic acid and tin tetrachloride for acid hydrolysis, then uses calcium hydroxide precipitation to remove fluorine and adjusts the pH to remove calcium, and then uses resin for adsorption to achieve Li recovery. The acid hydrolysis is carried out at 80-95°C, which consumes a lot of energy. Summary of the invention

[0007] To this end, an embodiment of the present invention provides a tin disulfide-supported phosphotungstic acid composite catalyst and a preparation method and application thereof.

[0008] In order to achieve the above purpose, the embodiment of the present invention provides the following technical solutions:

[0009] According to a first aspect of an embodiment of the present invention, the present invention provides a method for preparing a tin disulfide-supported phosphotungstic acid composite catalyst, the method comprising the following steps:

[0010] (1) mixing tin disulfide, a silane coupling agent and an organic solvent, carrying out a grafting reaction under an inert atmosphere, filtering, and obtaining modified tin disulfide;

[0011] (2) The modified tin disulfide, phosphotungstic acid and water are mixed, and an impregnation reaction is carried out. After filtering, the mixture is dried to obtain the tin disulfide-supported phosphotungstic acid composite catalyst.

[0012] Furthermore, in step (1), the silane coupling agent is aminopropyltriethoxysilane or n-octyltrimethoxysilane;

[0013] The mass ratio of tin disulfide to silane coupling agent is 1:1.5-2.5;

[0014] The organic solvent is toluene;

[0015] The volume mass ratio of the organic solvent to tin disulfide is 100-200 mL:1 g;

[0016] The inert atmosphere is helium, argon or neon;

[0017] The grafting reaction conditions are: reflux for 18 to 24 hours.

[0018] Furthermore, in step (2), the mass ratio of the modified tin disulfide to phosphotungstic acid is 0.75-1.5:1, and the volume mass ratio of water to phosphotungstic acid is 150-250 mL:1 g;

[0019] The conditions of the impregnation reaction are: stirring at 60-80° C. for 4-8 hours.

[0020] According to a second aspect of an embodiment of the present invention, the present invention provides a tin disulfide-supported phosphotungstic acid composite catalyst, which is prepared by the method described in any one of the above items.

[0021] According to a third aspect of an embodiment of the present invention, the present invention provides use of the tin disulfide-supported phosphotungstic acid composite catalyst as described above in the treatment of lithium hexafluorophosphate wastewater.

[0022] According to a fourth aspect of an embodiment of the present invention, the present invention provides a method for treating lithium hexafluorophosphate wastewater, the method comprising the following steps:

[0023] (1) Using concentrated sulfuric acid to adjust the pH value of lithium hexafluorophosphate wastewater to 1-2 to obtain acidified wastewater;

[0024] (2) adding the tin disulfide-supported phosphotungstic acid composite catalyst as described above to the acidified wastewater of step (1), stirring, and obtaining catalytic hydrolysis wastewater;

[0025] (3) After the catalytic hydrolysis wastewater in step (2) is irradiated with a visible light source, solid-liquid separation is performed to obtain liquid-phase photocatalytic wastewater;

[0026] (4) Adding defluorination and dephosphorization reagents to the photocatalytic wastewater in step (3), stirring, solid-liquid separation, and discharging the water that meets the standards.

[0027] Furthermore, in step (2), the dosage of the tin disulfide-supported phosphotungstic acid composite catalyst is 20-30 g / L; the stirring temperature is 20-40° C., and the stirring time is 0.5-1.5 h.

[0028] Furthermore, in step (3), the wavelength of the visible light source is 420-700 nm, the power is 300-500 W, and the illumination time is 0.5-1.5 h.

[0029] Furthermore, in step (4), the defluorination and dephosphorization reagent is composed of calcium hydroxide and calcium chloride in a molar ratio of 1:1-1.2, and the total calcium-fluorine ratio is 0.7-0.9; the stirring temperature is 20-35°C, and the stirring time is 20-30 min.

[0030] Phosphotungstic acid is a type of polynuclear compound containing oxygen bridges and having dual functions of acid-base and redox. The unique hexagonal cage structure and "pseudo-liquid phase behavior" of phosphotungstic acid make it have stronger acidity and certain pore structure, and can be used in acid-catalyzed reactions. However, phosphotungstic acid has the disadvantages of small specific surface area and easy solubility in the reaction system, resulting in reduced catalyst activity and difficulty in separation and recovery. The present invention loads phosphotungstic acid on a carrier, increases the specific surface area of ​​phosphotungstic acid, enhances acid catalytic activity, and is also easy to recycle and reuse.

[0031] In addition, phosphotungstic acid has certain photocatalytic activity. When its aqueous solution is excited by visible light, the metal ligand transition O→M (oxygen bridge transition to metal) occurs, producing ·OH with strong oxidizing properties, forming hole centers and electron capture centers, which can react non-selectively with organic matter and decompose the organic matter into water and carbon dioxide.

[0032] Tin disulfide is an n-type semiconductor with a narrower band gap than metal oxides such as titanium dioxide. It responds better to visible light and is more likely to undergo electron transitions under visible light irradiation, and has good photocatalytic activity. When tin disulfide absorbs light energy to the point where it can generate electron-hole pairs, electron transitions will occur, and the electrons will reach the conduction band position of tin disulfide, and then undergo a reduction reaction, while the remaining h + Will be used for oxidation reactions.

[0033] The present invention finds that by organically combining phosphotungstic acid and tin disulfide, phosphotungstic acid can accept photogenerated electrons of tin disulfide to form a capture center transfer electron, increase the carrier diffusion length, effectively extend the hole and electron life, inhibit electron-hole recombination, and be more conducive to the generation of strong oxidizing ·OH. Therefore, phosphotungstic acid and tin disulfide play a synergistic role, have better photocatalytic performance, can decompose organic matter into carbon dioxide and water in a short time, reduce the COD content of wastewater, and ensure that wastewater meets the discharge standards.

[0034] The composite catalyst provided by the present invention can effectively promote the hydrolysis of lithium hexafluorophosphate and the photocatalytic degradation of organic matter, thereby achieving purification of lithium hexafluorophosphate wastewater.

[0035] The embodiments of the present invention have the following advantages:

[0036] (1) The present invention uses phosphotungstic acid with stronger acidity and utilizes the characteristics of the "pseudo-liquid phase" of heteropolyacid to increase the H + Contact with fluoride ions promotes the hydrolysis reaction of lithium hexafluorophosphate.

[0037] (2) In the present invention, phosphotungstic acid is loaded on a tin disulfide carrier, and the prepared catalyst can efficiently promote the hydrolysis of hexafluorophosphate, and at the same time can also promote the digestion of organic matter in wastewater, thereby achieving wastewater discharge that meets the standards.

[0038] (3) The present invention uses a grafting method to load tungsten phosphate, which is not easy to fall off and has a high catalyst reuse rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0040] Figure 1 This is a process flow chart of lithium hexafluorophosphate wastewater treatment provided by the present invention. DETAILED DESCRIPTION

[0041] The following is a description of the implementation of the present invention by specific embodiments. People familiar with the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] See also Figure 1 The present invention provides a method for treating lithium hexafluorophosphate wastewater, which mainly comprises the following steps:

[0043] (1) Lithium hexafluorophosphate catalytic hydrolysis

[0044] The pH value of lithium hexafluorophosphate wastewater was adjusted to 1-2 using concentrated sulfuric acid to increase the free H + The concentration of lithium fluoride is suppressed to form a precipitate. Then, a catalyst is added to the obtained acidified wastewater, the amount of the catalyst added is 20-30 g / L, and the mixture is stirred at a temperature of 20-40°C for 0.5-1.5 hours. The catalyst is a tin disulfide-supported phosphotungstic acid composite catalyst, and its preparation includes the following steps:

[0045] S1. Preparation of tin disulfide: Tin disulfide can be prepared by hydrothermal synthesis. Transfer 0.5-1.5g of SnCl4·5H2O and SC(NH2)2 with a mass ratio of 1:1 into a beaker, add 30-60mL of deionized water and stir for 20-30min to dissolve completely, transfer the mixture to the lining of a 100mL hydrothermal reactor; seal the reactor and heat to 150-250℃ for 8-12h; after the reaction is completed, take it out of the reactor and cool it naturally to room temperature, wash it with deionized water and anhydrous ethanol; dry the solid phase in a vacuum drying oven at 40-80℃ for 8-16h to obtain tin disulfide, grind it, pass it through a 100-200 mesh sieve, and set it aside.

[0046] S2. Add 1 g of tin disulfide prepared in step S1 and 1.5-2.5 g of a silane coupling agent (aminopropyltriethoxysilane or n-octyltrimethoxysilane) into a three-necked flask, add 100-200 mL of anhydrous toluene into the flask, reflux for 18-24 h under an inert atmosphere (such as helium, argon or neon), filter, wash three times with toluene and anhydrous ethanol, and dry in a constant temperature drying oven at 80-100° C. for 8-12 h to obtain modified tin disulfide.

[0047] S3, weigh 1g of phosphotungstic acid and place it in a beaker, add 150-250mL of deionized water, stir for 10-20min, add the modified tin disulfide prepared in step S2 at a mass ratio of 0.75-1.5:1, stir in a constant temperature water bath at 60-80°C for 4-8h, filter, and dry the obtained solid phase in a constant temperature drying oven at 60-80°C for 8-12h to obtain a tin disulfide-supported phosphotungstic acid composite catalyst.

[0048] The hydrolysis reaction of lithium hexafluorophosphate is:

[0049] LiPF6 + H2O = POF3↑+ 2HF + LiF↓

[0050] POF3 + H2O = H(PO2F2) + HF

[0051] H(PO2F2) + H2O = H2(PO3F) + HF

[0052] H2(PO3F) + H2O = H3PO4 + HF

[0053] The fluoride ions from lithium hexafluorophosphate interact with the H + Combined with HF, the lithium ions from lithium hexafluorophosphate are released and react with free Li + The POF3 generated continues to undergo hydrolysis reaction on the catalyst reaction interface to generate H(PO2F2), H2(PO3F), etc., and finally PO4 3- The solution contains a large amount of free H + Supplement to phosphotungstic acid.

[0054] (2) Photocatalytic decomposition of organic matter

[0055] The acidified and hydrolyzed wastewater enters the photocatalytic unit and is irradiated with a visible light source (wavelength 420-700nm) at a power of 300-500W for 0.5-1.5h. Under the photocatalytic activity of the above catalyst, organic substances such as dimethyl carbonate and ethyl methyl carbonate contained in the wastewater, which are lithium salt solvents, can be efficiently decomposed into carbon dioxide and water, reducing the COD content of the wastewater and ensuring that the wastewater meets the discharge standards.

[0056] (3) Catalyst recycling

[0057] The catalyst is separated from the wastewater through solid-liquid separation equipment (filtration or centrifugation), the catalyst is reused, and the wastewater enters the next unit.

[0058] (4) Fluoride and phosphorus removal by precipitation

[0059] The wastewater after acid catalytic hydrolysis and photocatalytic decomposition is subjected to precipitation for fluorine and phosphorus removal. The fluorine and phosphorus removal reagent used is a mixture of calcium hydroxide and calcium chloride in a molar ratio of 1:1~1.2, with a total calcium-fluorine ratio of 0.7~0.9. It is stirred at a temperature of 20~35°C for 20~30min to precipitate for fluorine and phosphorus removal. The study found that the use of the above fluorine and phosphorus removal reagent has a better fluorine and phosphorus removal effect and also has the advantage of low cost.

[0060] Example 1

[0061] This embodiment provides a tin disulfide-supported phosphotungstic acid composite catalyst, and the preparation method thereof comprises the following steps:

[0062] (1) Preparation of tin disulfide: 0.75 g SnCl4·5H2O and 0.75 g SC(NH2)2 were transferred into a beaker, 45 mL deionized water was added and stirred for 20 min to dissolve completely, and then the mixture was transferred to the inner lining of a 100 mL hydrothermal reactor; the reactor was sealed and heated to 200 °C for 8 h; after the reaction was completed, the reactor was taken out and naturally cooled to room temperature, and washed three times with deionized water and anhydrous ethanol; the solid phase was placed in a vacuum drying oven at 60 °C and dried for 12 h to obtain tin disulfide, which was ground and passed through a 200-mesh sieve for standby use.

[0063] (2) 1 g of tin disulfide prepared in step (1) and 2 g of aminopropyltriethoxysilane were mixed and added to a three-necked flask. 150 mL of anhydrous toluene was added to the flask. The mixture was refluxed under a nitrogen atmosphere for 24 h. The mixture was filtered, washed three times with toluene and anhydrous ethanol, and dried in a constant temperature drying oven at 100 ° C for 12 h to obtain modified tin disulfide.

[0064] (3) Weigh 1 g of phosphotungstic acid and place it in a beaker, add 200 mL of deionized water, stir for 20 min, then add 1 g of modified tin disulfide prepared in step (2), stir in a constant temperature water bath at 65 ° C for 6 h, filter, and dry the resulting solid phase in a constant temperature drying oven at 60 ° C for 12 h to obtain a tin disulfide-supported phosphotungstic acid composite catalyst.

[0065] Example 2

[0066] This embodiment provides a tin disulfide-supported phosphotungstic acid composite catalyst, and the preparation method thereof comprises the following steps:

[0067] (1) Preparation of tin disulfide: same as in Example 1.

[0068] (2) 1 g of tin disulfide prepared in step (1) and 2 g of n-octyltrimethoxysilane were mixed and added to a three-necked flask. 150 mL of anhydrous toluene was added to the flask. The mixture was refluxed under a nitrogen atmosphere for 24 h. The mixture was filtered, washed three times with toluene and anhydrous ethanol, and dried in a constant temperature drying oven at 100 ° C for 12 h to obtain modified tin disulfide.

[0069] (3) Weigh 1 g of phosphotungstic acid and place it in a beaker, add 200 mL of deionized water, stir for 20 min, then add 1 g of modified tin disulfide prepared in step (2), stir in a constant temperature water bath at 65 ° C for 6 h, filter, and dry the resulting solid phase in a constant temperature drying oven at 60 ° C for 12 h to obtain a tin disulfide-supported phosphotungstic acid composite catalyst.

[0070] Example 3

[0071] This embodiment provides a tin disulfide-supported phosphotungstic acid composite catalyst, and the preparation method thereof comprises the following steps:

[0072] (1) Preparation of tin disulfide carrier: same as in Example 1.

[0073] (2) 1 g of tin disulfide prepared in step (1) and 2 g of aminopropyltriethoxysilane were mixed and added to a three-necked flask. 150 mL of anhydrous toluene was added to the flask. The mixture was refluxed under a nitrogen atmosphere for 24 h. The mixture was filtered, washed three times with toluene and anhydrous ethanol, and dried in a constant temperature drying oven at 100 ° C for 12 h to obtain modified tin disulfide.

[0074] (3) Weigh 1 g of phosphotungstic acid and place it in a beaker, add 200 mL of deionized water, stir for 20 min, then add 1.5 g of the modified tin disulfide prepared in step (2), stir in a constant temperature water bath at 65 ° C for 6 h, filter, and dry the resulting solid phase in a constant temperature drying oven at 60 ° C for 12 h to obtain a tin disulfide-supported phosphotungstic acid composite catalyst.

[0075] Comparative Example 1

[0076] This comparative example provides a composite catalyst, and the preparation method thereof is different from that of Example 1 only in that step (2) is not performed, that is, the tin disulfide prepared in step (1) is directly impregnated with tungsten phosphate.

[0077] Comparative Example 2

[0078] This comparative example provides a composite catalyst, and the preparation method thereof is different from that of Example 1 only in that tin disulfide is replaced with an equal amount of nano-sized titanium dioxide (synthesized by a solid phase method, with a particle size of 10-50 nm).

[0079] Comparative Example 3

[0080] This comparative example provides a composite catalyst, the preparation method of which is different from that of Example 1 only in that, in step (3), tungsten phosphate is replaced by an equal amount of silicotungstic acid.

[0081] Example 4

[0082] Performance Testing

[0083] The specific surface area of ​​the sample is tested using a specific surface area and pore size analyzer. The sample in the gas system will undergo physical adsorption on its surface (surface area of ​​the outside of the particles and the internal through-holes) at low temperatures. When the adsorption reaches equilibrium, the equilibrium adsorption pressure and the amount of adsorbed gas are measured according to the BET equation:

[0084]

[0085] V—Total volume of adsorbed gas when equilibrium pressure is P; V m —The volume of gas required to fully cover the catalyst surface with the first layer; P—The pressure of the adsorbed gas at equilibrium at the adsorption temperature; P s —Saturated vapor pressure; C—a constant related to adsorption.

[0086] The sample monolayer adsorption amount was calculated, and the specific surface area of ​​the sample was calculated. The test results are shown in Table 1.

[0087] Table 1

[0088]

[0089] The results show that the tin disulfide-supported phosphotungstic acid composite catalyst provided in the embodiment of the present invention has a higher specific surface area.

[0090] Example 5

[0091] The wastewater generated by a manufacturer during the production of lithium hexafluorophosphate through the solvent method had a total chemical oxygen demand COD = 389ppm, total phosphorus TP = 127ppm, and total fluorine TF = 46ppm.

[0092] Add 98% concentrated sulfuric acid to the wastewater to adjust the pH value to 2, add a catalyst at 20g / L, and use a 500W xenon lamp light source (wavelength 600nm) to irradiate at room temperature for 1h. After the reaction is completed, take a small amount of solution to measure the phosphorus and COD concentrations, and calculate the hydrolysis rate of lithium hexafluorophosphate and the COD degradation rate. The wastewater after hydrolysis and photocatalysis is precipitated for fluorine and phosphorus removal. According to the molar ratio of calcium hydroxide and calcium chloride of 1:1 and the total calcium-fluorine molar ratio of 0.8, stir at 25℃ for 30min, precipitate for fluorine and phosphorus removal, and calculate the fluorine removal rate and phosphorus removal rate.

[0093] The hydrolysis rate (D) of lithium hexafluorophosphate was measured by inductively coupled plasma mass spectrometry (ICP) and ammonium molybdate spectrophotometer. The total phosphorus concentration in the solution measured by ICP was recorded as P. 总 (ppm), using ammonium molybdate spectrophotometer to measure the total phosphorus concentration P in the solution after hydrolysis 水 (ppm).

[0094] D = P 水 / P 总 ×100%

[0095] The COD concentration in the solution is measured using a rapid digestion instrument. The COD concentration of the original water sample is recorded as C 初 (ppm), the COD concentration of the water sample after photocatalysis is recorded as C 终 (ppm).

[0096] COD degradation rate = (C 初 -C 终 ) / C 初 ×100%

[0097] The fluoride concentration in the water sample was measured using the fluoride ion electrode method, and the original water sample was recorded as F 初 (ppm), after precipitation and removal of fluorine, recorded as F 终 (ppm).

[0098] Fluoride removal rate = (F 初 -F 终 ) / F 初 ×100%

[0099] ICP was used to measure the phosphorus concentration in water samples, and the original water sample was recorded as P 初 (ppm), after phosphorus removal by precipitation, recorded as P 终 (ppm).

[0100] Phosphorus removal rate = (P 初 -P 终 ) / P 初 ×100%

[0101] The hydrolysis catalytic effect and COD degradation effect of the catalysts of Examples 1-3 and Comparative Examples 1-3 are shown in Table 2.

[0102] Table 2

[0103]

[0104] The results show that the catalyst provided by the embodiment of the present invention can effectively hydrolyze lithium hexafluorophosphate and remove COD in the wastewater, thereby achieving wastewater discharge that meets the standards.

[0105] Example 6

[0106] The wastewater generated by a manufacturer during the production of lithium hexafluorophosphate by the solvent method had a total chemical oxygen demand COD = 1635ppm, total phosphorus TP = 459ppm, total fluorine TF = 325ppm, and total nitrogen TN = 257ppm.

[0107] Add 98% concentrated sulfuric acid to the wastewater to adjust the pH value to 1.5, add 30g / L catalyst, and use a 400W xenon lamp light source (wavelength 650nm) to irradiate at room temperature for 1.5h. After the reaction, take a small amount of solution to measure the phosphorus and COD concentrations, and calculate the hydrolysis rate of lithium hexafluorophosphate and the COD degradation rate. The wastewater after hydrolysis and photocatalysis is precipitated to remove fluorine and phosphorus. According to the molar ratio of calcium hydroxide and calcium chloride of 1:1 and the total calcium-fluorine molar ratio of 0.9, stir at 30℃ for 30min, precipitate to remove fluorine and phosphorus, and calculate the fluorine removal rate and phosphorus removal rate.

[0108] The hydrolysis catalytic effect and COD degradation effect of the catalysts of Examples 1-3 and Comparative Examples 1-3 are shown in Table 3.

[0109] Table 3

[0110]

[0111] The results show that the catalyst provided by the embodiment of the present invention can effectively hydrolyze lithium hexafluorophosphate and remove COD in the wastewater, thereby achieving wastewater discharge that meets the standards.

[0112] Although the present invention has been described in detail above by general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A method for preparing a tin disulfide-supported phosphotungstic acid composite catalyst, characterized in that: The method comprises the following steps: (1) mixing tin disulfide, a silane coupling agent and an organic solvent, carrying out a grafting reaction under an inert atmosphere, filtering, and obtaining modified tin disulfide; (2) The modified tin disulfide, phosphotungstic acid and water are mixed, and an impregnation reaction is carried out. After filtering, the mixture is dried to obtain the tin disulfide-supported phosphotungstic acid composite catalyst.

2. The method for preparing the tin disulfide-supported phosphotungstic acid composite catalyst according to claim 1, characterized in that: In step (1), The silane coupling agent is aminopropyltriethoxysilane or n-octyltrimethoxysilane; The mass ratio of tin disulfide to silane coupling agent is 1:1.5-2.5; The organic solvent is toluene; The volume mass ratio of the organic solvent to tin disulfide is 100-200 mL:1 g; The inert atmosphere is helium, argon or neon; The grafting reaction conditions are: reflux for 18 to 24 hours.

3. The method for preparing the tin disulfide-supported phosphotungstic acid composite catalyst according to claim 1, characterized in that: In step (2), The mass ratio of the modified tin disulfide to phosphotungstic acid is 0.75-1.5:1, and the volume mass ratio of water to phosphotungstic acid is 150-250 mL:1 g; The conditions of the impregnation reaction are: stirring at 60-80° C. for 4-8 hours.

4. A tin disulfide-supported phosphotungstic acid composite catalyst, characterized in that: The method is prepared by the method according to any one of claims 1 to 3.

5. Use of the tin disulfide-supported phosphotungstic acid composite catalyst according to claim 4 in the treatment of lithium hexafluorophosphate wastewater.

6. A method for treating lithium hexafluorophosphate wastewater, characterized in that: The method comprises the following steps: (1) Using concentrated sulfuric acid to adjust the pH value of lithium hexafluorophosphate wastewater to 1-2 to obtain acidified wastewater; (2) adding the tin disulfide-supported phosphotungstic acid composite catalyst as described in claim 4 to the acidified wastewater of step (1), stirring, and obtaining catalytic hydrolysis wastewater; (3) After the catalytic hydrolysis wastewater in step (2) is irradiated with a visible light source, solid-liquid separation is performed to obtain photocatalytic wastewater; (4) Adding defluorination and dephosphorization reagents to the photocatalytic wastewater in step (3), stirring, solid-liquid separation, and discharging the water that meets the standards.

7. The method for treating lithium hexafluorophosphate wastewater according to claim 6, characterized in that: In step (2), the dosage of the tin disulfide-supported phosphotungstic acid composite catalyst is 20-30 g / L; the stirring temperature is 20-40° C., and the stirring time is 0.5-1.5 h.

8. The method for treating lithium hexafluorophosphate wastewater according to claim 6, characterized in that: In step (3), the wavelength of the visible light source is 420-700 nm, the power is 300-500 W, and the illumination time is 0.5-1.5 h.

9. The method for treating lithium hexafluorophosphate wastewater according to claim 6, characterized in that: In step (4), the defluorination and dephosphorization reagent is composed of calcium hydroxide and calcium chloride in a molar ratio of 1:1-1.2, and the total calcium-fluorine ratio is 0.7-0.9; the stirring temperature is 20-35°C, and the stirring time is 20-30 minutes.

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