A composite catalyst of tin disulfide supported phosphotungstic acid, its preparation method and application

Abstract

An embodiment of the present invention discloses a composite catalyst of tin disulfide supported phosphotungstic acid, and a preparation method and application thereof. The method includes: mixing tin disulfide, a silane coupling agent and an organic solvent, carrying out a grafting reaction under an inert atmosphere, and filtering to obtain modified tin disulfide; mixing the modified tin disulfide, phosphotungstic acid and water, carrying out an impregnation reaction, filtering and then drying to obtain the composite catalyst of tin disulfide supported phosphotungstic acid. The composite catalyst provided by the present invention can efficiently promote the hydrolysis of lithium hexafluorophosphate and the photocatalytic degradation of organic substances, thereby realizing the purification of lithium hexafluorophosphate wastewater and having good application prospects.

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 composite catalyst of tin disulfide supported phosphotungstic acid, a preparation method thereof, and an application thereof.

[0008] To achieve the above object, an embodiment of the present invention provides the following technical solutions:

[0009] According to the first aspect of the embodiments of the present invention, the present invention provides a preparation method of a composite catalyst of tin disulfide supported phosphotungstic acid, and the method includes the following steps:

[0010] (1) Mix tin disulfide, a silane coupling agent, and an organic solvent, carry out a grafting reaction under an inert atmosphere, and filter to obtain modified tin disulfide;

[0011] (2) Mix the modified tin disulfide, phosphotungstic acid, and water, carry out an impregnation reaction, filter and then dry to obtain the composite catalyst of tin disulfide supported phosphotungstic acid.

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

[0013] The mass ratio of the tin disulfide to the 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 the tin disulfide is 100 - 200 mL:1 g;

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

[0017] The conditions for the grafting reaction are: reflux for 18 - 24 h.

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

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

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

[0021] According to the third aspect of the embodiments of the present invention, the present invention provides the application of the composite catalyst of tin disulfide supported phosphotungstic acid described above in the treatment of lithium hexafluorophosphate wastewater.

[0022] According to the fourth aspect of the embodiments of the present invention, the present invention provides a treatment method for lithium hexafluorophosphate wastewater, and the method includes the following steps:

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

[0024] (2) Add the stannous disulfide supported phosphotungstic acid composite catalyst as described above to the acidified wastewater in step (1), stir to obtain catalytic hydrolysis wastewater;

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

[0026] (4) Add defluorination and dephosphorization reagents to the photocatalytic wastewater in step (3), stir, perform solid - liquid separation, and discharge the qualified water.

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

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

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

[0030] Phosphotungstic acid is a class of polynuclear compounds containing oxygen bridges and having dual functions of acid - base and redox. The unique hexagonal cage - like structure and "pseudo - liquid - phase behavior" of phosphotungstic acid endow it with stronger acidity and a certain pore structure, which can be applied to acid - catalyzed reactions. However, phosphotungstic acid has disadvantages such as a small specific surface area and being easily soluble in the reaction system, resulting in reduced catalyst activity and difficult separation and recovery. In the present invention, phosphotungstic acid is loaded on a carrier to increase the specific surface area of phosphotungstic acid, enhance the acid - catalytic activity, and also facilitate recycling and reuse.

[0031] In addition, phosphotungstic acid has a certain photocatalytic activity. Under visible - light excitation, its aqueous solution undergoes the transition of O→M (oxygen - bridge jumps to metal) metal ligands, generating strongly oxidizing ·OH, forming hole centers and electron - trapping centers, which can react non - selectively with organic substances and decompose the organic substances into water and carbon dioxide.

[0032] Tin disulfide is an n-type semiconductor with a narrower bandgap than metal oxides such as titanium dioxide, better response to visible light, easier electron transition under visible light irradiation, and good photocatalytic activity. When tin disulfide absorbs light energy to generate electron-hole pairs, electron transition will occur, and electrons reach the conduction band position of tin disulfide, and then reduction reaction occurs, while the remaining h + will be used for the oxidation reaction.

[0033] The present invention discovers that by organically combining phosphotungstic acid and tin disulfide, phosphotungstic acid can accept the photo-generated electrons of tin disulfide, form a trapping center to transfer electrons, increase the carrier diffusion length, effectively extend the lifetimes of holes and electrons, inhibit the recombination of electrons and holes, and is more conducive to generating strongly oxidizing ·OH. Therefore, phosphotungstic acid and tin disulfide play a synergistic effect, have more excellent photocatalytic performance, can decompose organic substances into carbon dioxide and water in a short time, reduce the COD content of wastewater, and ensure the up-to-standard discharge of wastewater.

[0034] The composite catalyst provided by the present invention can efficiently promote the hydrolysis of lithium hexafluorophosphate and the photocatalytic degradation of organic substances, thereby realizing the 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, utilizes the "pseudo-liquid phase" characteristic of heteropolyacid, increases the contact between H + on the heteropolyacid and fluoride ions, and promotes the hydrolysis reaction of lithium hexafluorophosphate.

[0037] (2) The present invention loads phosphotungstic acid on the tin disulfide carrier, and the prepared catalyst can efficiently promote the hydrolysis of hexafluorophosphate ions, and at the same time can also promote the digestion of organic substances in wastewater, realizing the up-to-standard discharge of wastewater.

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

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary, and for those of ordinary skill in the art, without creative efforts, other implementation drawings can also be obtained according to the provided drawings.

[0040] Figure 1 It is the process flow diagram of the lithium hexafluorophosphate wastewater treatment provided by the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0041] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

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

[0043] (1) Catalytic hydrolysis of lithium hexafluorophosphate

[0044] Adjust the pH value of the lithium hexafluorophosphate wastewater to 1 - 2 with concentrated sulfuric acid to increase the concentration of free H + in the system and inhibit the formation of lithium fluoride precipitation. Then add a catalyst to the obtained acidified wastewater, and the dosage of the catalyst is 20 - 30 g / L. Stir at a temperature of 20 - 40 °C for 0.5 - 1.5 h. Among them, the catalyst is a composite catalyst of phosphotungstic acid supported on tin disulfide, and its preparation includes the following steps:

[0045] S1. Preparation of tin disulfide: Tin disulfide can be prepared by hydrothermal synthesis. Transfer a total mass of 0.5 - 1.5 g of SnCl4·5H2O and SC(NH2)2 with a mass ratio of 1:1 into a beaker successively, add 30 - 60 mL of deionized water and stir for 20 - 30 min until completely dissolved. Transfer the mixed solution into the inner liner of a 100 mL hydrothermal reaction kettle; seal the reaction kettle and heat it to 150 - 250 °C, and keep it for 8 - 12 h; after the reaction is completed, take it out of the reaction kettle and cool it naturally to room temperature, and wash it with deionized water and absolute ethanol; place the solid phase in a vacuum drying oven at 40 - 80 °C and dry it for 8 - 16 h to obtain tin disulfide, grind it, and pass it through a 100 - 200 - mesh sieve for use.

[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) to a three - necked flask, add 100 - 200 mL of anhydrous toluene to the flask, reflux for 18 - 24 h under an inert (such as helium, argon or neon) atmosphere, filter, wash three times with toluene and absolute 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 1 g of phosphotungstic acid and place it in a beaker. Add 150 - 250 mL of deionized water and stir for 10 - 20 min. Then, add the modified tin disulfide prepared in step S2 according to the mass ratio of 0.75 - 1.5:1, and stir in a constant temperature water bath at 60 - 80 °C for 4 - 8 h. Filter, and place the obtained solid phase in a constant temperature drying oven at 60 - 80 °C for 8 - 12 h to obtain the tin disulfide supported phosphotungstic acid composite catalyst.

[0048] The hydrolysis reaction of lithium hexafluorophosphate is as follows:

[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 derived from lithium hexafluorophosphate combine with the H of phosphotungstic acid at the pseudo - liquid phase interface of phosphotungstic acid to form HF, and the lithium ions derived from lithium hexafluorophosphate are released and exist in the solution in the free state of Li + under acidic conditions. The generated POF3 continues to undergo hydrolysis reaction on the catalyst reaction interface to generate H(PO2F2), H2(PO3F), etc., and finally exists in the solution in the form of PO4 + . A large amount of free H 3- generated in the solution is supplemented to phosphotungstic acid. +

[0054] (2) Photocatalytic decomposition of organic substances

[0055] The wastewater after acid hydrolysis enters the photocatalytic unit. Under the irradiation of a visible light source (wavelength 420 - 700 nm), adjust the power to 300 - 500 W and irradiate for 0.5 - 1.5 h. Organic substances such as dimethyl carbonate and ethyl methyl carbonate, which are used as lithium salt solvents in the wastewater, can efficiently decompose the organic substances into carbon dioxide and water under the photocatalytic activity of the above - mentioned catalyst, reduce the COD content of the wastewater, and ensure the up - to - standard discharge of the wastewater.

[0056] (3) Recycling of the catalyst

[0057] Separate the catalyst from the wastewater through a solid - liquid separation device (filtration or centrifugation), recycle the catalyst, and the wastewater enters the next unit.

[0058] (4) Precipitation for fluoride and phosphorus removal

[0059] The wastewater that has undergone acid-catalyzed hydrolysis and photocatalytic decomposition is subjected to precipitation for fluoride and phosphorus removal. The fluoride and phosphorus removal reagent used is a mixture composed of calcium hydroxide and calcium chloride at a molar ratio of 1:1 to 1.2, with a total calcium-to-fluoride ratio of 0.7 to 0.9. Stir for 20 to 30 minutes at a temperature of 20 to 35 °C for precipitation of fluoride and phosphorus removal. It is found that using the above fluoride and phosphorus removal reagent has a better effect on fluoride and phosphorus removal and also has the advantage of low cost.

[0060] Example 1

[0061] This example provides a composite catalyst of tin disulfide supported phosphotungstic acid, and its preparation method includes the following steps:

[0062] (1) Preparation of tin disulfide: Transfer 0.75 g of SnCl4·5H2O and 0.75 g of SC(NH2)2 into a beaker successively, add 45 mL of deionized water and stir for 20 minutes until completely dissolved. Then transfer the mixed solution into the inner lining of a 100 mL hydrothermal reaction kettle; seal the reaction kettle and heat it to 200 °C, and maintain for 8 h; after the reaction is completed, take it out of the reaction kettle and cool it naturally to room temperature, and wash it three times with deionized water and absolute ethanol; place the solid phase in a vacuum drying oven at 60 °C and dry it for 12 h to obtain tin disulfide, grind it, and pass through a 200-mesh sieve for use.

[0063] (2) Mix 1 g of the tin disulfide prepared in step (1) and 2 g of aminopropyltriethoxysilane, and add them together into a three-necked flask. Add 150 mL of absolute toluene to the flask, and reflux and react for 24 h under a nitrogen atmosphere. Filter, wash it three times with toluene and absolute ethanol, and dry it 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 minutes, then add 1 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 place the obtained solid phase in a constant temperature drying oven at 60 °C and dry it for 12 h to obtain a composite catalyst of tin disulfide supported phosphotungstic acid.

[0065] Example 2

[0066] This example provides a composite catalyst of tin disulfide supported phosphotungstic acid, and its preparation method includes the following steps:

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

[0068] (2) Mix 1 g of tin disulfide prepared in step (1) with 2 g of n-octyltrimethoxysilane, add them together into a three-necked flask, add 150 mL of anhydrous toluene to the flask, reflux and react for 24 h under a nitrogen atmosphere, filter, wash three times with toluene and anhydrous ethanol, and dry 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 the modified tin disulfide prepared in step (2), stir in a constant temperature water bath at 65 °C for 6 h, filter, and place the obtained solid phase in a constant temperature drying oven at 60 °C to dry for 12 h to obtain a tin disulfide supported phosphotungstic acid composite catalyst.

[0070] Example 3

[0071] This example provides a tin disulfide supported phosphotungstic acid composite catalyst, and its preparation method includes the following steps:

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

[0073] (2) Mix 1 g of tin disulfide prepared in step (1) with 2 g of aminopropyltriethoxysilane, add them together into a three-necked flask, add 150 mL of anhydrous toluene to the flask, reflux and react for 24 h under a nitrogen atmosphere, filter, wash three times with toluene and anhydrous ethanol, and dry 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 place the obtained solid phase in a constant temperature drying oven at 60 °C to dry 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 difference in its preparation method from that of Example 1 is only that step (2) is not carried out. That is, the tin disulfide prepared in step (1) is directly impregnated and reacted with phosphotungstic acid.

[0077] Comparative Example 2

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

[0079] Comparative Example 3

[0080] This comparative example provides a composite catalyst, and the difference in its preparation method from that of Example 1 is only that in step (3), phosphotungstic acid is replaced with an equal amount of silicotungstic acid.

[0081] Example 4

[0082] Performance detection

[0083] The specific surface area of the sample was detected using a specific surface area and pore size analyzer. For the sample in the gas system, physical adsorption occurs on the surface of the substance (the surface area of the outside of the particles and the internal through-holes) at low temperature. 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—the total volume of the adsorbed gas when the equilibrium pressure is P; V m —the volume of gas required to cover the first full layer on the catalyst surface; P—the pressure of the adsorbed gas at equilibrium at the adsorption temperature; P s —saturated vapor pressure; C—a constant related to the adsorption.

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

[0087] Table 1

[0088]

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

[0090] Example 5

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

[0092] 98% concentrated sulfuric acid was added to the wastewater to adjust the pH value to 2, the catalyst was added at 20 g / L, and a 500 W xenon light source (wavelength 600 nm) was used to irradiate for 1 h at room temperature. After the reaction ended, a small amount of the solution was taken to measure the phosphorus and COD concentrations, and the hydrolysis rate of lithium hexafluorophosphate and the COD degradation rate were calculated. The wastewater after hydrolysis and photocatalysis was subjected to precipitation for defluorination and dephosphorization. According to the molar ratio of calcium hydroxide to calcium chloride of 1:1 and the total calcium-fluorine molar ratio of 0.8, it was stirred at 25 °C for 30 min for precipitation for defluorination and dephosphorization, and the defluorination rate and dephosphorization rate were calculated.

[0093] The hydrolysis rate (D) of lithium hexafluorophosphate is obtained by measurement using an inductively coupled plasma mass spectrometer (ICP) and an ammonium molybdate spectrophotometer. The total phosphorus concentration in the solution measured by ICP is denoted as P 总 (ppm), and the total phosphorus concentration P 水 (ppm) that has been hydrolyzed in the solution is measured by the ammonium molybdate spectrophotometer method.

[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 denoted as C 初 (ppm), and the COD concentration of the water sample after photocatalysis is denoted as C 终 (ppm).

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

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

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

[0099] The phosphorus concentration in the water sample is measured using ICP. The original water sample is denoted as P 初 (ppm), and after phosphorus precipitation removal, it is denoted 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 in 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 in the examples of the present invention can effectively hydrolyze lithium hexafluorophosphate, while removing COD from the wastewater and achieving the discharge standard of the wastewater.

[0105] Example 6

[0106] During the production of lithium hexafluorophosphate by a certain manufacturer through the solvent method, the wastewater generated has a total chemical oxygen demand (COD) of 1635 ppm, total phosphorus (TP) of 459 ppm, total fluorine (TF) of 325 ppm, and total nitrogen (TN) of 257 ppm.

[0107] Add 98% concentrated sulfuric acid to the wastewater to adjust the pH value to 1.5, add the catalyst at a dosage of 30 g / L, and use a 400 W xenon light source (wavelength 650 nm) to irradiate for 1.5 h at room temperature. After the reaction, take a small amount of the solution to measure the phosphorus and COD concentrations, and calculate the hydrolysis rate of lithium hexafluorophosphate and the COD degradation rate. For the wastewater after hydrolysis and photocatalysis, carry out precipitation to remove fluorine and phosphorus. According to the molar ratio of calcium hydroxide to calcium chloride of 1:1 and the total calcium-fluorine molar ratio of 0.9, stir at 30 °C for 30 min for precipitation 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 in 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 in the examples of the present invention can effectively hydrolyze lithium hexafluorophosphate, while removing COD from the wastewater and achieving the discharge standard of the wastewater.

[0112] Although the present invention has been described in detail above with general descriptions and specific examples, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A method for treating lithium hexafluorophosphate wastewater, characterized in that, The method includes the following steps: (1) Adjust the pH value of the lithium hexafluorophosphate wastewater to 1-2 with concentrated sulfuric acid to obtain acidified wastewater; (2) Add 20-30 g / L of stannous sulfide supported phosphotungstic acid composite catalyst to the acidified wastewater in step (1), stir at 20-40 °C for 0.5-1.5 h to obtain catalytic hydrolysis wastewater; (3) After irradiating the catalytic hydrolysis wastewater in step (2) with a visible light source, perform solid-liquid separation to obtain photocatalytic wastewater; (4) Add a defluorination and dephosphorization reagent to the photocatalytic wastewater in step (3), stir, perform solid-liquid separation, and discharge the qualified water; The preparation method of the stannous sulfide supported phosphotungstic acid composite catalyst includes the following steps: (1) Mix stannous sulfide, a silane coupling agent, and an organic solvent, carry out a grafting reaction under an inert atmosphere, and filter to obtain modified stannous sulfide; (2) Mix the modified stannous sulfide, phosphotungstic acid, and water, carry out an impregnation reaction, filter and dry to obtain the stannous sulfide supported phosphotungstic acid composite catalyst.

2. The treatment method of lithium hexafluorophosphate wastewater according to claim 1, wherein In step (1) of the preparation method of the stannous sulfide supported phosphotungstic acid composite catalyst, the silane coupling agent is aminopropyltriethoxysilane, n-octyltrimethoxysilane; the mass ratio of stannous sulfide to the silane coupling agent is 1:1.5-2.5; the organic solvent is toluene; the volume-mass ratio of the organic solvent to stannous sulfide is 100-200 mL:1 g; the inert atmosphere is helium, argon or neon; the conditions of the grafting reaction are: reflux for 18-24 h.

3. The method for treating lithium hexafluorophosphate wastewater according to claim 1, wherein In step (2) of the preparation method of the stannous sulfide supported phosphotungstic acid composite catalyst, the mass ratio of the modified stannous sulfide 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: stir at 60-80 °C for 4-8 h.

4. The treatment method of lithium hexafluorophosphate wastewater according to claim 1, 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 irradiation time is 0.5-1.5 h.

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

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