Method for preparing fluosilicate from acidic fluorine-containing wastewater

Abstract

The invention discloses a method for preparing fluosilicate from acidic fluorine-containing wastewater, and belongs to the technical field of wastewater treatment. The method comprises the following steps: carrying out conversion reaction on the acidic fluorine-containing wastewater and a silicon source to obtain conversion reaction clear liquid; adjusting the concentration of the conversion reaction clear liquid by adopting a synthetic reaction clear liquid to obtain a mixed adjusting liquid; carrying out a synthetic reaction on the mixed adjusting solution and a potassium-sodium precipitant solution, and after the synthetic reaction is completed, carrying out solid-liquid separation to obtain a synthetic reaction clear solution and fluosilicate; part of the synthetic reaction clear liquid is used for concentration adjustment, part of the synthetic reaction clear liquid is used for potassium-sodium precipitant solution preparation, and the rest of the synthetic reaction clear liquid enters a subsequent treatment process. According to the method, the acidic fluorine-containing wastewater is used as a raw material, full resource recycling of fluorine elements in the fluorine-containing wastewater is achieved, the synthesis cost of fluosilicate is reduced, and a fluosilicate product which is large in particle size, uniform in particle size, low in water content, high in purity and qualified in quality can be obtained.

Description

Technical Field

[0001] The invention relates to a method for treating acidic fluorine-containing wastewater, in particular to a method for preparing fluorosilicate from acidic fluorine-containing wastewater, and belongs to the technical field of wastewater treatment and resource utilization. Background Art

[0002] Common fluorosilicates in industry are potassium fluorosilicate (K2SiF6) and sodium fluorosilicate (Na2SiF6). As important fluorine chemical intermediates, they have irreplaceable application value in many industries. Among them, potassium fluorosilicate is not only a key raw material for wood preservatives, special ceramic glazes and optical glass, but also widely used in high-end fields such as aluminum-magnesium alloy refining, welding rod coating preparation and synthetic mica; sodium fluorosilicate, due to its unique chemical properties, occupies an important position in the fields of glass opacifiers, agricultural pesticides, water treatment corrosion inhibitors, rubber vulcanization accelerators, etc., and is also a precursor for the preparation of high-purity sodium fluoride, ammonium fluoride and other electronic-grade chemicals.

[0003] In industrial processes such as semiconductor etching, photovoltaic silicon wafer cutting, phosphate fertilizer production, and metal smelting and processing, a large amount of acidic fluorine-containing wastewater is often produced. If this type of wastewater is discharged directly, it will cause serious fluorine pollution, but because it is rich in recyclable fluorine and silicon resources, it is also regarded as a potential "urban mineral". However, the current methods for preparing fluorosilicates from acidic fluorine-containing wastewater generally have technical bottlenecks such as difficulty in solid-liquid separation after the reaction, low product purity, high water content, poor dehydration performance, and high reagent costs ("Technical Transformation of Sodium Fluorosilicate Production Process", Ma Haisheng, Chemical World, 2019, 60 (11), 829-832). Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for preparing fluorosilicate from acidic fluorine-containing wastewater. The method uses acidic fluorine-containing wastewater as a raw material to achieve full resource recovery of fluorine in the fluorine-containing wastewater, reduce the synthesis cost of fluorosilicate, and can obtain a fluorosilicate product with large particle size, uniform particle size, low water content, high purity and qualified quality, which well solves the problems of difficult solid-liquid separation, low product purity, high water content, poor dehydration performance and high reagent cost in the preparation of fluorosilicate in the prior art.

[0005] In order to achieve the above technical objectives, the present invention provides a method for preparing fluorosilicate from acidic fluorine-containing wastewater, the method comprising the following steps:

[0006] 1) Acidic fluorine-containing wastewater is subjected to a conversion reaction with a silicon source to obtain a conversion reaction clear liquid;

[0007] 2) adjusting the concentration of the conversion reaction supernatant using the synthesis reaction supernatant to obtain a mixed adjustment solution;

[0008] 3) subjecting the mixed regulating liquid to a synthesis reaction with a potassium and sodium precipitant solution, and after the synthesis reaction is completed, separating the solid from the liquid to obtain a synthesis reaction clear liquid and fluorosilicate;

[0009] 4) Part of the synthetic reaction clear liquid is used for concentration adjustment in step 2), part is used for preparation of potassium and sodium precipitant solution in step 3), and the rest enters the subsequent treatment process.

[0010] The method for preparing fluorosilicate from acidic fluorine-containing wastewater of the present invention:

[0011] In step 1), the hydrogen fluoride component in the acidic fluorine-containing wastewater is mainly used to react with the silicon source to obtain a conversion reaction clear liquid containing H2SiF6. The reaction is shown in formula (1):

[0012] SiO2+6HF= H2SiF6+2H2O (1)

[0013] In step 2), the concentration of H2SiF6 in the conversion reaction supernatant is relatively high, which will affect the crystallization of fluorosilicate generated in the subsequent synthesis reaction. The synthesis reaction supernatant produced during the synthesis reaction is recycled to adjust the concentration of H2SiF6 in the conversion reaction supernatant, thereby reducing the supersaturation of the subsequent synthesis reaction and creating reaction conditions for effectively controlling the particle size of the fluorosilicate product.

[0014] In step 3), the synthesis reaction equation is shown in formula (2) or formula (3):

[0015] H2SiF6+2Na + = Na2SiF6+2H + (2)

[0016] H2SiF6+2K + = K2SiF6+2H + (3)

[0017] In step 4), most of the synthesis reaction supernatant is recycled, a part is used to adjust the concentration of the conversion reaction supernatant, a part is used to prepare the potassium and sodium salt precipitant solution, and the remaining part is subjected to subsequent treatment.

[0018] As a preferred solution, the concentration of H2SO4 in the acidic fluorine-containing wastewater is 250-350 g / L, the concentration of HF is 60-100 g / L, the concentration of iron ions is 4000-5000 mg / L, the concentration of aluminum ions is 100-500 mg / L, the concentration of manganese ions is 600-900 mg / L, and the concentration of tungstate ions is 1600-7500 mg / L. Among them, the mass of tungstate ions is measured by the mass of tungsten element. Iron ions, aluminum ions, manganese ions, and tungstate ions in wastewater are easily precipitated together with fluorosilicates in the form of adsorption, coprecipitation, etc. during the synthesis process of fluorosilicates, resulting in an adverse effect on the purity of fluorosilicates, so their concentrations should not be too high.

[0019] As a preferred solution, the silicon source includes at least one of quartz sand, silica gel, and diatomaceous earth. The main component of the preferred silicon source is SiO2, which is easily converted into fluorosilicic acid by reaction with hydrogen fluoride. The particle size of the preferred silicon source is 300-500 mesh, which can ensure a faster conversion reaction speed and will not agglomerate due to too small particle size, affecting the dispersion and conversion reaction effect.

[0020] As a preferred solution, the silicon in the silicon source and the fluorine in the acidic fluorine-containing wastewater are measured in a molar ratio of (1.1-1.5):1. The molar ratio of silicon in the silicon source to fluorine in the acidic fluorine-containing wastewater is controlled within an appropriate range to ensure that HF ​​is fully converted into H2SiF6. If the molar ratio of silicon to fluorine is less than 1.1:1, a mixed solution of H2SiF6 and HF may be formed in the conversion reaction clear liquid, which will result in a lower yield and purity of the final fluorosilicate product, and hydrogen fluoride cannot be fully utilized.

[0021] As a preferred solution, the conditions of the conversion reaction are: temperature of 10°C to 35°C and time of 2 to 4 hours. The conversion reaction can be completed at room temperature without high temperature reaction, and the conversion reaction is a liquid-solid reaction with limited reaction rate. If the time is less than 2 hours, the reaction may not be completely completed.

[0022] As a preferred solution, the volume ratio of the conversion reaction supernatant to the synthesis reaction supernatant is 1:(1-3). When the reaction system just starts, the first synthesis reaction supernatant can be replaced by adding tap water or pure water. Diluting the conversion reaction supernatant to an appropriate concentration range is beneficial to the subsequent fluorosilicate crystallization process, and fluorosilicates with large and uniform particle sizes can be obtained. Controlling the volume ratio of the conversion reaction supernatant to the synthesis reaction supernatant is an important factor in controlling the purity of potassium fluorosilicate. By controlling the appropriate reactant concentration and supersaturation, impurity elements such as iron, aluminum, manganese, and tungsten can be suppressed as much as possible from entering the fluorosilicate product.

[0023] As a preferred solution, the potassium-sodium precipitant solution is prepared by mixing potassium-sodium salt with the synthesis reaction clear solution in a mass ratio of 1:(4-12). Controlling the mass ratio of the synthesis reaction clear solution to potassium-sodium salt creates conditions for controlling the supersaturation of the synthesis reaction.

[0024] As a preferred embodiment, the potassium-sodium salt includes at least one of sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, sodium hydroxide and potassium hydroxide. If potassium fluosilicate product is to be obtained, the potassium-sodium salt is selected from at least one of potassium chloride, potassium sulfate and potassium hydroxide. If sodium fluosilicate product is to be obtained, the potassium-sodium salt is selected from at least one of sodium chloride, sodium sulfate and sodium hydroxide.

[0025] As a preferred solution, the ratio of the mixed regulating liquid to the potassium-sodium precipitant solution is measured according to the molar ratio of silicon in the mixed regulating liquid to sodium and / or potassium in the potassium-sodium precipitant of 1: (1.05-1.20). The potassium-sodium precipitant is controlled to be appropriately excessive to ensure that the fluorosilicic acid is completely converted, which can improve the recovery rate of fluorine.

[0026] As a preferred solution, the conditions of the synthesis reaction are: temperature of 10°C to 35°C, and time of 0.5 to 2 hours. The synthesis reaction conditions mainly control the production and growth of crystal grains. Under the preferred synthesis reaction conditions, it is conducive to obtaining fluorosilicate crystals with large and uniform particle size, low water content and high purity.

[0027] As a preferred scheme, the synthesis reaction is carried out in an induced crystallization tank; the induced crystallization tank has a double-layer structure, the upper layer is a double-layer cylindrical structure, and the lower layer is a conical structure; the double-layer cylindrical structure includes an outer cylinder and a central cylinder, the bottom of the outer cylinder is connected to the conical structure, and the central cylinder is arranged at the center of the outer cylinder; the mixed regulating liquid and the potassium and sodium precipitant solution enter from the top of the central cylinder of the induced crystallization tank, enter the outer cylinder through the bottom of the central cylinder and continuously overflow and discharge, the rising linear velocity of water in the outer cylinder is 0.7 to 1.2 m / h, the hydraulic retention time in the outer cylinder is 2 to 3 hours, and the hydraulic retention time in the inner cylinder is 0.5 to 1.0 h. The double-layer cylindrical structure design on the upper part of the induced crystallization tank makes the reaction liquid flow in a circuitous manner "first from top to bottom, then from bottom to top". The flowing reaction liquid can drive the fluorosilicate nuclei to suspend in the reaction liquid and continue to grow, and greatly prolong the growth time of the fluorosilicate nuclei, which is conducive to obtaining fluorosilicate nuclei with larger particle size. The design of the cone structure at the bottom makes the fluorosilicate crystals grown to an appropriate size in the reaction liquid settle to the cone structure under the action of their own gravity and be discharged in time, ensuring the uniformity of the fluorosilicate grain size. On the basis of the special induced crystallization tank structure design, the setting of the induced crystallization operation parameters is optimized at the same time, which can not only effectively control the process of fluorosilicate grain growth, but also inhibit the adsorption and precipitation of impurity elements such as iron ions, aluminum ions, manganese ions, and tungstate ions. In summary, the present invention utilizes the induced crystallization tank with a special structure and cooperates with appropriate process parameters to obtain fluorosilicate crystals with large particle size, uniform particle size, low water content, and high purity.

[0028] As a preferred solution, the height-to-diameter ratio of the outer cylinder is 0.8:1 to 1:0.8.

[0029] As a preferred solution, the cone angle of the cone structure is 30 to 40 degrees. The bottom of the induced crystallization tank is designed as a cone structure, which can ensure that large-particle fluorosilicate crystals are precipitated at the bottom of the cone structure under the action of gravity, and are easy to discharge later.

[0030] As a preferred solution, the mass concentration of the precipitate in the induced crystallization tank is controlled at 5% to 20%. The precipitate in the induced crystallization tank plays a role in inducing nucleation by seed crystals, and a certain mass concentration needs to be guaranteed. If the mass concentration of the precipitate is higher than 20%, it may cause the dispersion of the precipitate to deteriorate, and the induced crystallization effect to deteriorate. If the mass concentration of the precipitate is lower than 5%, the precipitate is too dispersed and the concentration is insufficient to achieve induced nucleation. Fluorosilicate seeds can be pre-added in the induced crystallization tank, and the seed particle size is 20μm to 100μm. The seeds are potassium fluorosilicate and / or sodium fluorosilicate.

[0031] As a preferred solution, a stirrer is provided in the induced crystallization tank, and the stirrer has 2 to 3 layers of stirring, and each layer is spaced 1 to 1.2 m apart.

[0032] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0033] 1. Fluorosilicate products have high purity, large and uniform particle size, and low water content;

[0034] 2. The reaction conditions are mild, without high temperature and high pressure;

[0035] 3. Use low-cost silicon sources as raw materials to recover valuable fluorine resources in wastewater, with low cost and significant economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0037] Figure 1 The present invention provides a process flow chart for preparing fluorosilicate from acidic fluorine-containing wastewater.

[0038] Figure 2 Schematic diagram of the induced crystallization tank device: wherein 1 is the central cylinder, 2 is the outer cylinder, 3 is the stirring device, 4 is the cone structure, 5 is the sedimentation discharge port, and 6 is the overflow port for the synthesis reaction clear liquid.

[0039] Figure 3 These are SEM images of the fluorosilicate products obtained in Example 1, Comparative Example 1 and Comparative Example 4 of the present invention: wherein (a) is the fluorosilicate product obtained in Example 1, (b) is the fluorosilicate product obtained in Comparative Example 1, and (c) is the fluorosilicate product obtained in Comparative Example 4. DETAILED DESCRIPTION

[0040] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only 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.

[0041] The present invention has no particular limitation on the sources of the above raw materials, which can be commercially available.

[0042] In order to further illustrate the present invention, the method for preparing fluorosilicate from acidic fluorine-containing wastewater provided by the present invention is described in detail in combination with the following examples and comparative examples, but they should not be construed as limiting the scope of protection of the present invention.

[0043] The method for preparing fluorosilicate from acidic fluorine-containing wastewater provided by the present invention:

[0044] The silicon source used is one or more of quartz sand, silica gel, and diatomaceous earth. The main component of the silicon source is SiO2. The silicon source is mixed with HF in the acidic fluorine-containing wastewater for conversion reaction to obtain a conversion reaction clear liquid containing H2SiF6. The reaction is shown in formula (1).

[0045] SiO2+6HF= H2SiF6+2H2O (1)

[0046] The molar ratio of silicon in the silicon source to fluorine in the acidic fluorine-containing wastewater is controlled to (1.1-1.5):1, in order to ensure that HF ​​is fully converted into H2SiF6. If the molar ratio of silicon to fluorine is less than 1.1:1, a mixture of H2SiF6 and HF may be formed in the conversion reaction clear liquid, which will result in a lower yield and purity of the final fluorosilicate product.

[0047] The conversion reaction temperature is controlled to be 10°C to 35°C, and the conversion reaction time is controlled to be 2 to 4 hours. The reaction described in formula (1) is a liquid-solid reaction, and the reaction rate is limited. If the time is less than 2 hours, the reaction may not be completely completed. The present invention can ensure a faster conversion reaction speed by controlling the particle size of the silicon source to be 300 to 500 meshes, without the need for high temperature reaction.

[0048] Step B): Add the synthesis reaction supernatant to the conversion reaction supernatant to adjust and mix.

[0049] The volume ratio of the synthesis reaction supernatant to the conversion reaction supernatant is controlled to be (1-3): 1. The purpose of adjusting the mixture is to further reduce the concentration of H2SiF6 in the adjusted mixture, thereby reducing the supersaturation of the subsequent synthesis reaction and creating reaction conditions for effectively controlling the particle size of the fluorosilicate product.

[0050] If there is no external water source, the volume of the synthesis reaction supernatant should be smaller than the volume of the conversion reaction supernatant, so the volume ratio of the synthesis reaction supernatant to the conversion reaction supernatant is less than 1: 1. Therefore, when the system is started, the volume of the synthesis reaction supernatant can be adjusted by adding tap water or pure water.

[0051] Step C): adding a mixed regulating liquid and a precipitant into an induced crystallization tank to carry out a synthesis reaction, and obtaining a synthesis reaction clear liquid and fluorosilicate after solid-liquid separation.

[0052] The precipitant is prepared from potassium and sodium salts and the clear solution of the synthetic reaction, so no external water source is required. Potassium and sodium salts are one or more of sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, sodium hydroxide, and potassium hydroxide. If the product is potassium fluorosilicate, one or more of potassium chloride, potassium sulfate, and potassium hydroxide should be used. If the product is sodium fluorosilicate, one or more of sodium chloride, sodium sulfate, and sodium hydroxide should be used.

[0053] The mass ratio of the synthetic reaction clear liquid to the potassium and sodium salts is controlled to be (4-12):1, in order to control the appropriate concentration of potassium and sodium salts and create conditions for controlling the supersaturation of the synthetic reaction.

[0054] The synthesis reaction equation is shown in formula (2) or formula (3):

[0055] H2SiF6+2Na + = Na2SiF6+2H + (2)

[0056] H2SiF6+2K + = K2SiF6+2H + (3)

[0057] The molar ratio of potassium or sodium to silicon in the mixed regulating liquid is controlled to be (1.05-1.20):1. An appropriate excess of potassium or sodium can ensure the recovery rate of fluorine.

[0058] The synthesis reaction temperature is controlled at 10°C to 35°C without additional heating, and the synthesis reaction time is controlled at 0.5 to 2 hours, which is beneficial to improving the reaction efficiency and reducing the volume of the inner tube (reaction zone) of the induced crystallization tank.

[0059] The existing technology mainly reacts at high temperature, and as the temperature rises, the solubility of fluorosilicate will increase, which is conducive to promoting the crystal growth of fluorosilicate. The present invention does not need high temperature, because by controlling the reasonable reflux of the synthesis reaction clear liquid and the synthesis reaction conditions, the reaction supersaturation is controlled within a suitable range, and at the same time, relying on induced crystallization, the fine particles are continuously adsorbed and grown on the surface of the seed crystal, and a good induced crystallization effect can be achieved even at room temperature.

[0060] The synthesis reaction needs to be carried out in an induced crystallization tank and the appropriate hydraulic retention time must be controlled.

[0061] The induced crystallization tank has a double-layer structure, the upper layer is a double-layer cylindrical structure, and the lower layer is a conical structure 4; the double-layer cylindrical structure includes an outer cylinder 2 and a central cylinder 1, the outer diameter of the outer cylinder is larger than the outer diameter of the central cylinder, the outer cylinder diameter is about twice the diameter of the inner cylinder, the bottom of the outer cylinder is connected to the conical structure, and the central cylinder is arranged at the center of the outer cylinder; the induced crystallization tank is provided with a stirring device 3, the stirring device has two layers of stirrers, each layer is 1.2m apart, the upper stirrer is in the central cylinder, and the lower stirrer is at the bottom of the conical structure. The upper part of the outer cylinder is provided with a synthesis reaction clear liquid overflow port 6. The bottom of the conical structure is provided with a sedimentation discharge port 5.

[0062] Water for the synthesis reaction enters from the top of the central tube of the induced crystallization tank, enters the outer tube through the bottom of the central tube and is continuously discharged by overflow. The rising linear velocity of water in the outer tube is 0.7-1.2 m / h, the hydraulic retention time in the outer tube is 2-3 h, and the hydraulic retention time in the inner tube is 0.5-1.0 h.

[0063] The mass concentration of the precipitate in the induced crystallization tank is 5% to 20%, and the precipitate discharge port is located at the bottom of the induced crystallization tank and is equipped with a stirring paddle.

[0064] The precipitate in the induced crystallization tank plays a role in inducing nucleation by seed crystals, and a certain mass concentration needs to be maintained. If the mass concentration of the precipitate is higher than 20%, the dispersion of the precipitate may deteriorate, and the induced crystallization effect may deteriorate. If the mass concentration of the precipitate is lower than 5%, the precipitate is too dispersed and the concentration is insufficient to induce nucleation. The precipitate discharge should select the product with the largest particle size, so the discharge port is located at the bottom of the induced crystallization tank. In order to make the precipitate fully play the role of seed crystal inducing nucleation, a stirring paddle should be provided at the precipitate discharge port.

[0065] Step D): A portion of the synthetic reaction supernatant is added to a mixing and regulating tank, and the remaining portion is mixed with a precipitant and recycled. The remaining portion is subjected to subsequent treatment.

[0066] In the following embodiments and comparative examples provided by the present invention, the acidic fluorine-containing wastewater used was taken from a tantalum-niobium smelter in Guangdong, and the concentration of H2SO4 was 250 g / L, the concentration of HF was 60 g / L, the concentration of Fe was 4000 mg / L, the concentration of Al was 200 mg / L, the concentration of Mn was 700 mg / L, and the concentration of W was 2000 mg / L.

[0067] Example 1

[0068] A method for preparing fluorosilicate from acidic fluorine-containing wastewater, the process flow chart is as follows Figure 1 shown.

[0069] Add 2.22 kg of 95% pure silica gel to 10 L of acidic fluorine-containing wastewater, control the conversion reaction temperature to 10 ° C, the silicon-fluorine molar ratio to 1.1:1, the conversion reaction time to 2 hours, and perform the conversion reaction to obtain a conversion reaction clear liquid. This process is a batch process, and should be carried out continuously to ensure that there is enough adjustment mixed liquid for the synthesis reaction.

[0070] Add 30L of synthesis reaction clear liquid to 10L of conversion reaction clear liquid (during the system startup phase, the synthesis reaction clear liquid is not discharged, and tap water is added at the same time) to adjust and mix. This process is a batch process and should be continued to ensure that there is enough adjustment mixture for the synthesis reaction.

[0071] The mixed regulating liquid and precipitant are continuously added to the induced crystallization tank, the mixed regulating liquid flow rate is 10L / h, and the precipitant flow rate is 2.58L / h. The molar ratio of potassium in the precipitant to silicon in the mixed regulating liquid is 1.05:1, the mass of potassium chloride in the precipitant is 2.58kg, the mass concentration of potassium chloride is 25%, the synthesis reaction temperature is 20℃, and the synthesis reaction time is 0.5h. The rising linear velocity of water in the outer cylinder of the induced crystallization tank is 0.7m / h, the hydraulic retention time in the outer cylinder is 2h, and the hydraulic retention time in the inner cylinder is 0.5h. The synthesis reaction in the induced crystallization tank is continuous water inflow and continuous water outflow, and the mass concentration of precipitation in the induced crystallization tank is continuously controlled to be 10%, and the precipitate discharge is discharged from the bottom of the induced crystallization tank.

[0072] After testing, the product was potassium fluorosilicate, and its average particle size was 82.8 μm ( Figure 3 In (a), the particle size conforms to the normal distribution, the purity is 98.5%, and the recovery rate is 94.1%. Its quality meets the first-class requirements of HG / T 4693-2014 "Industrial Potassium Fluorosilicate".

[0073] Example 2

[0074] Add 2.55kg of quartz sand with a purity of 98% to 10L of acidic fluoride-containing wastewater, control the conversion reaction temperature to 20°C, the silicon-fluorine molar ratio to 1.3:1, and the conversion reaction time to 3h to carry out the conversion reaction to obtain a conversion reaction clear liquid. This process is a sequential batch process and should be carried out continuously to ensure that there is enough adjustment mixed liquid for the synthesis reaction.

[0075] Add 10L of synthesis reaction clear liquid to 10L of conversion reaction clear liquid (during the system startup phase, the synthesis reaction clear liquid is not discharged, and tap water is added at the same time) to adjust and mix. This process is a batch process and should be continued to ensure that there is enough adjustment mixture for the synthesis reaction.

[0076] The mixed regulating liquid and precipitant are continuously added to the induced crystallization tank, the mixed regulating liquid flow rate is 10L / h, and the precipitant flow rate is 10.04L / h. The molar ratio of sodium in the precipitant to silicon in the mixed regulating liquid is 1.1:1, the mass of sodium chloride in the precipitant is 2.51kg, the mass concentration of sodium chloride is 12.5%, the synthesis reaction temperature is 10℃, and the synthesis reaction time is 1h. The rising linear velocity of water in the outer cylinder of the induced crystallization tank is 0.9m / h, the hydraulic retention time in the outer cylinder is 2.5h, and the hydraulic retention time in the inner cylinder is 0.5h. The synthesis reaction in the induced crystallization tank is continuous water inflow and continuous water outflow, and the mass concentration of precipitation in the induced crystallization tank is continuously controlled to be 5%, and the precipitate discharge is discharged from the bottom of the induced crystallization tank.

[0077] After testing, the product is sodium fluorosilicate with an average particle size of 96.1 μm, a normal distribution, a purity of 98.8%, and a recovery rate of 73.2%. Its quality meets the first-class requirements of GB / T 23936-2018 "Industrial Sodium Fluorosilicate".

[0078] Example 3

[0079] Add 3.2 kg of 90% pure diatomaceous earth to 10 L of acidic fluoride wastewater, control the conversion reaction temperature to 35 ° C, the silicon-fluorine molar ratio to 1.5:1, the conversion reaction time to 4 hours, and perform the conversion reaction to obtain a conversion reaction clear liquid. This process is a batch process, and should be carried out continuously to ensure that there is enough adjustment mixed liquid for the synthesis reaction.

[0080] Add 20L of synthesis reaction clear liquid to 10L of conversion reaction clear liquid (during the system startup phase, the synthesis reaction clear liquid is not discharged, and tap water is added at the same time) to adjust and mix. This process is a batch process and should be continued to ensure that there is enough adjustment mixture for the synthesis reaction.

[0081] The mixed regulating liquid and precipitant are continuously added to the induced crystallization tank, the mixed regulating liquid flow rate is 10L / h, and the precipitant flow rate is 15.66L / h. The molar ratio of potassium in the precipitant to silicon in the mixed regulating liquid is 1.2:1, the mass of potassium sulfate in the precipitant is 3.92kg, the mass of potassium hydroxide is 0.5kg, the mass concentration of potassium salt (potassium sulfate + potassium hydroxide) is 8.33%, the synthesis reaction temperature is 35℃, and the synthesis reaction time is 2h. The rising linear velocity of water in the outer cylinder of the induced crystallization tank is 0.1.2m / h, the hydraulic retention time in the outer cylinder is 3h, and the hydraulic retention time in the inner cylinder is 1.0h. The synthesis reaction in the induced crystallization tank is continuous water inflow and continuous water outflow, and the mass concentration of precipitation in the induced crystallization tank is continuously controlled to be 20%, and the precipitation discharge is discharged from the bottom of the induced crystallization tank.

[0082] After testing, the product is potassium fluorosilicate, with an average particle size of 76.9μm, a particle size that conforms to normal distribution, a purity of 98.7%, and a recovery rate of 91.0%. Its quality meets the first-class requirements of HG / T 4693-2014 "Industrial Potassium Fluorosilicate".

[0083] Comparative Example 1

[0084] The difference from Example 1 is that the volume ratio of the synthesis reaction supernatant to the conversion reaction supernatant is 0.5:1.

[0085] After testing, the average particle size of potassium fluorosilicate product is 19.8μm ( Figure 3 (b) The smaller the particle size, the more interstitial water there is, the greater the water content is, the moisture content increases significantly, and the dehydration performance decreases significantly.

[0086] Comparative Example 2

[0087] The difference from Example 1 is that during the conversion reaction, the molar ratio of silicon to fluorine is 1:1.

[0088] After testing, the recovery rate of potassium fluorosilicate was 82.3% and the purity was 98.2%. The recovery rate was significantly reduced and the purity did not meet the first-class requirements of HG / T 4693-2014 "Industrial Potassium Fluorosilicate".

[0089] Comparative Example 3

[0090] The difference from Example 1 is that the mass concentration of the precipitate in the induction crystallization tank is 30%.

[0091] After testing, the particle size of potassium fluorosilicate is 61.9μm, but the particle size does not conform to the normal distribution, and there is a clear distinction between coarse particles and fine particles, indicating that the seed crystallization induced crystallization effect is not good, the newly generated particles are finer, and the coarse particles do not effectively induce nucleation.

[0092] Comparative Example 4

[0093] The difference from Example 1 is that no induced crystallization tank is used, and the synthesis reaction is carried out in a conventional stirred reactor.

[0094] After testing, the average particle size of potassium fluorosilicate product is 8.1μm ( Figure 3 In (c), the particle size is significantly reduced and the dehydration performance is significantly reduced.

[0095] It can be seen from Examples 1 to 3 and Comparative Examples 1 to 4 that if the process control conditions of the present invention are not adopted, a fluorosilicate product with large particle size, uniform particle size, low water content, high purity and qualified quality cannot be obtained.

[0096] The above description of the disclosed embodiments enables those skilled in the art to experiment or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing fluorosilicate from acidic fluorine-containing wastewater, characterized in that: The following steps are involved: 1) Acidic fluorine-containing wastewater is subjected to a conversion reaction with a silicon source to obtain a conversion reaction clear liquid; 2) adjusting the concentration of the conversion reaction supernatant using the synthesis reaction supernatant to obtain a mixed adjustment solution; 3) subjecting the mixed regulating liquid to a synthesis reaction with a potassium and sodium precipitant solution, and after the synthesis reaction is completed, separating the solid from the liquid to obtain a synthesis reaction clear liquid and fluorosilicate; 4) Part of the synthetic reaction clear liquid is used for concentration adjustment in step 2), part is used for preparation of potassium and sodium precipitant solution in step 3), and the rest enters the subsequent treatment process.

2. The method for preparing fluorosilicate from acidic fluorine-containing wastewater according to claim 1, characterized in that: The concentration of H2SO4 in the acidic fluoride-containing wastewater is 250-350 g / L, the concentration of HF is 60-100 g / L, the concentration of iron ions is 4000-5000 mg / L, the concentration of aluminum ions is 100-500 mg / L, the concentration of manganese ions is 600-900 mg / L, and the concentration of tungstate ions is 1600-7500 mg / L.

3. The method for preparing fluorosilicate from acidic fluorine-containing wastewater according to claim 1, characterized in that: The silicon source includes at least one of quartz sand, silica gel and diatomaceous earth.

4. The method for preparing fluorosilicate from acidic fluorine-containing wastewater according to claim 1 or 3, characterized in that: The silicon in the silicon source and the fluorine in the acidic fluorine-containing wastewater are measured in a molar ratio of (1.1-1.5):

1.

5. A method for preparing fluorosilicate from acidic fluorine-containing wastewater according to claim 1, 2 or 3, characterized in that: The conditions of the conversion reaction are: temperature of 10°C to 35°C and time of 2 to 4 hours.

6. The method for preparing fluorosilicate from acidic fluorine-containing wastewater according to claim 1 or 2, characterized in that: The volume ratio of the conversion reaction supernatant to the synthesis reaction supernatant is 1:(1-3).

7. The method for preparing fluorosilicate from acidic fluorine-containing wastewater according to claim 1, characterized in that: The potassium-sodium precipitant solution is prepared by mixing potassium-sodium salt and the synthesis reaction clear solution in a mass ratio of 1:(4-12); and / or, The potassium-sodium salt includes at least one of sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, sodium hydroxide and potassium hydroxide.

8. The method for preparing fluorosilicate from acidic fluorine-containing wastewater according to claim 1 or 7, characterized in that: The ratio of the mixed regulating liquid to the potassium-sodium precipitant solution is measured according to the molar ratio of silicon in the mixed regulating liquid to sodium and / or potassium in the potassium-sodium precipitant of 1: (1.05-1.20).

9. The method for preparing fluorosilicate from acidic fluorine-containing wastewater according to claim 1, characterized in that: The conditions of the synthesis reaction are: temperature of 10° C. to 35° C. and time of 0.5 to 2 h.

10. The method for preparing fluorosilicate from acidic fluorine-containing wastewater according to claim 1 or 9, characterized in that: The synthesis reaction is carried out in an induced crystallization tank; the induced crystallization tank has a double-layer structure, the upper layer is a double-layer cylindrical structure, and the lower layer is a conical structure; the double-layer cylindrical structure includes an outer cylinder and a central cylinder, the bottom of the outer cylinder is connected to the conical structure, and the central cylinder is arranged at the center of the outer cylinder; The mixed regulating liquid and the potassium and sodium precipitant solution enter from the top of the central tube of the induced crystallization tank, enter the outer tube through the bottom of the central tube and are continuously discharged by overflow. The rising linear velocity of the water in the outer tube is 0.7-1.2 m / h, the hydraulic retention time in the outer tube is 2-3 h, and the hydraulic retention time in the inner tube is 0.5-1.0 h. and / or, The mass concentration of the precipitate in the induction crystallization tank is controlled at 5% to 20%.

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