Method for producing potassium nitrate for strengthening glass from fluorine-containing potassium hydroxide wastewater

Abstract

This invention relates to a method for producing potassium nitrate for tempered glass from fluoride-containing potassium hydroxide wastewater. The method includes the following steps: (1) adding nitric acid-containing wastewater to the fluoride-containing potassium hydroxide wastewater for neutralization reaction to obtain a first feed solution containing potassium nitrate; (2) adding lime to the first feed solution obtained in step (1) for defluorination reaction, and then performing a first solid-liquid separation to obtain a first filtrate; (3) adjusting the pH value of the first filtrate obtained in step (2), then adding potassium carbonate for calcium removal reaction, and then performing a second solid-liquid separation to obtain a second filtrate; (4) sequentially evaporating and concentrating the second filtrate obtained in step (3), cooling and crystallizing, and performing a third solid-liquid separation to obtain potassium nitrate product. The method provided by this invention can prepare potassium nitrate product in conjunction with nitric acid-containing wastewater while ensuring deep defluorination. The obtained potassium nitrate product can effectively guarantee product quality when used in tempered glass.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, specifically to a method for producing potassium nitrate for tempered glass from fluoride-containing potassium hydroxide wastewater. Background Technology

[0002] Fluorosulfonic acid cation exchange resins are widely used in chemical catalysis, industrial water softening, and material purification. Their production inevitably generates large amounts of fluoride-containing potassium hydroxide wastewater. This wastewater is highly alkaline, high in fluoride, and high in potassium, with fluoride ion concentrations reaching 500-5000 ppm and potassium ion concentrations reaching 4-6 mol / L, accompanied by organic impurities such as sulfonic acid resin fragments. If it cannot be treated to render it harmless, it will lead to soil and water pollution, damage the ecological environment, and result in the loss of potassium resources.

[0003] Potassium nitrate is the core functional raw material for chemically strengthened glass. Chemically strengthened glass is widely used in mobile phone touchscreens, automotive tempered glass, and aerospace specialty glass. It works by melting at high temperatures and exchanging ions with sodium ions on the glass surface to form a dense compressive stress strengthening layer, significantly improving the glass's impact resistance, bending resistance, and abrasion resistance. Compared to ordinary industrial-grade potassium nitrate, potassium nitrate for strengthened glass has stringent quality requirements regarding particle size and specific surface area. Potassium nitrate products with suitable particle size and specific surface area ensure a more uniform melting rate, resulting in more complete ion exchange on the glass surface and a continuous and stable stress layer, which is crucial for ensuring the quality of strengthened glass.

[0004] Currently, the main treatment processes for fluoride-containing potassium hydroxide wastewater employ traditional, simple neutralization and lime defluorination methods. These methods lack refinement, resulting in low-quality and low-yield potassium nitrate, failing to meet the production requirements for potassium nitrate specifically for tempered glass. Specifically, during lime defluorination, the generated calcium fluoride crystals are small, colloidal, and flocculent, making deep defluorination difficult, ultimately ending up in the final product. Traditional crystallization processes cannot achieve precise crystal grain control, failing to yield potassium nitrate products suitable for tempered glass. Furthermore, the treatment process for fluoride-containing potassium hydroxide wastewater is complex, costly, and results in low product added value.

[0005] Therefore, how to achieve the resource utilization of fluoride-containing potassium hydroxide wastewater and generate potassium nitrate products is a technical problem that needs to be solved. Summary of the Invention

[0006] To address the above problems, the present invention aims to provide a method for producing potassium nitrate for tempered glass from fluoride-containing potassium hydroxide wastewater. Compared with the prior art, the method provided by the present invention can prepare potassium nitrate products in conjunction with nitric acid-containing wastewater while ensuring deep defluorination. The resulting potassium nitrate products can effectively guarantee product quality when used in tempered glass.

[0007] To achieve this objective, the present invention employs the following technical solution: This invention provides a method for producing potassium nitrate for tempered glass from fluoride-containing potassium hydroxide wastewater, the method comprising the following steps: (1) Add nitric acid-containing wastewater to fluorine-containing potassium hydroxide wastewater for neutralization reaction to obtain the first solution containing potassium nitrate; (2) Add lime to the first liquid obtained in step (1) to carry out a defluorination reaction, and then carry out the first solid-liquid separation to obtain the first filtrate; (3) Adjust the pH of the first filtrate obtained in step (2), then add potassium carbonate to carry out calcium removal reaction, and then carry out the second solid-liquid separation to obtain the second filtrate; (4) The second filtrate obtained in step (3) is subjected to evaporation and concentration, cooling and crystallization and third solid-liquid separation in sequence to obtain potassium nitrate product.

[0008] In this invention, two wastewater streams, fluoride-containing potassium hydroxide wastewater and nitric acid wastewater, are mixed for a neutralization reaction. Excess fluoride ions are removed by adding lime, and excess calcium ions are removed by adjusting the pH value and adding potassium carbonate. This process yields potassium nitrate with high purity in the liquid phase. Finally, potassium nitrate product is obtained through evaporation, concentration, cooling, and crystallization.

[0009] In this invention, the nitric acid-containing wastewater may also contain potassium, and the mass concentration of potassium nitrate is 10-30% according to the mass ratio.

[0010] In this invention, the condensate produced by evaporation and concentration can be filtered and reused.

[0011] Preferably, in step (1), the fluoride-containing potassium hydroxide wastewater contains F - The concentration is 500~5000ppm, for example, it can be 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 1500ppm, 2000ppm, 2500ppm, 3000ppm, 3500ppm, 4000ppm, 4500ppm, or 5000ppm; OH - The concentration is 4~6 mol / L, for example, it can be 4 mol / L, 4.2 mol / L, 4.4 mol / L, 4.6 mol / L, 4.8 mol / L, 5 mol / L, 5.2 mol / L, 5.4 mol / L, 5.6 mol / L, 5.8 mol / L, or 6 mol / L; K +The concentration is 4~6 mol / L, for example, it can be 4 mol / L, 4.2 mol / L, 4.4 mol / L, 4.6 mol / L, 4.8 mol / L, 5 mol / L, 5.2 mol / L, 5.4 mol / L, 5.6 mol / L, 5.8 mol / L or 6 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0012] Preferably, the H in the nitric acid-containing wastewater + The concentration is 4~6 mol / L, for example, it can be 4 mol / L, 4.2 mol / L, 4.4 mol / L, 4.6 mol / L, 4.8 mol / L, 5 mol / L, 5.2 mol / L, 5.4 mol / L, 5.6 mol / L, 5.8 mol / L, or 6 mol / L; NO3 - The concentration is 4~6 mol / L, for example, it can be 4 mol / L, 4.2 mol / L, 4.4 mol / L, 4.6 mol / L, 4.8 mol / L, 5 mol / L, 5.2 mol / L, 5.4 mol / L, 5.6 mol / L, 5.8 mol / L or 6 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0013] Preferably, the endpoint pH value of the neutralization reaction in step (1) is 6 to 8, for example, it can be 6, 6.2, 6.4, 6.6, 6.8, 7, 7.2, 7.4, 7.6, 7.8 or 8, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0014] Preferably, the temperature of the neutralization reaction is 60~80℃, for example, it can be 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, 72℃, 74℃, 76℃, 78℃ or 80℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0015] Preferably, the neutralization reaction time is 20-30 min, for example, 20 min, 22 min, 24 min, 26 min, 28 min or 30 min, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] Preferably, stirring is performed during the neutralization reaction.

[0017] Preferably, the stirring rate in the neutralization reaction is 50~100 r / min, for example, it can be 50 r / min, 60 r / min, 70 r / min, 80 r / min, 90 r / min or 100 r / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] Preferably, the Ca contained in the lime during the defluorination reaction in step (2) is... 2+ With the F contained in the first liquid - The molar ratio is (1~1.5):2, for example, it can be 1:2, 1.1:2, 1.2:2, 1.3:2, 1.4:2 or 1.5:2, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] In this invention, lime is used for the defluorination reaction, which reduces the fluoride ion content in the first feed solution and precipitates calcium fluoride. This invention controls the Ca content of the lime in the defluorination reaction. 2+ With the F contained in the first liquid - The molar ratio of these components can further ensure the deep removal of fluoride ions and improve the purity of the product.

[0020] Preferably, the endpoint pH value of the defluorination reaction is 6 to 9, for example, it can be 6, 6.2, 6.4, 6.6, 6.8, 7, 7.2, 7.4, 7.6, 7.8, 8, 8.2, 8.4, 8.6, 8.8 or 9, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Preferably, the temperature of the defluorination reaction is 50~90℃, for example, it can be 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃ or 90℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] Preferably, the defluorination reaction time is 10 to 30 minutes, for example, 10 minutes, 12 minutes, 15 minutes, 18 minutes, 20 minutes, 22 minutes, 25 minutes, 28 minutes or 30 minutes, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, stirring is performed during the defluorination reaction.

[0024] Preferably, the stirring rate in the defluorination reaction is 50~100 r / min, for example, it can be 50 r / min, 60 r / min, 70 r / min, 80 r / min, 90 r / min or 100 r / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the first solid-liquid separation method in step (2) includes pressure filtration.

[0026] Preferably, the pH adjuster used in step (3) includes nitric acid.

[0027] Preferably, the endpoint pH value for pH adjustment is 5 to 8, for example, it can be 5, 5.2, 5.4, 5.6, 5.8, 6, 6.2, 6.3, 6.6, 6.8, 7, 7.2, 7.4, 7.6, 7.8 or 8, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] In this invention, pH adjustment can further ensure the deep removal of calcium ions in the calcium removal reaction, and the addition of acid can emulsify and destabilize the small amount of organic matter in the wastewater, reducing its impact on the purity and morphology of subsequent products.

[0029] Preferably, the potassium carbonate in step (3) is added in the form of a solution.

[0030] Preferably, the mass concentration of potassium carbonate is 1% to 5%, for example, it can be 1%, 2%, 3%, 4% or 5%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] In this invention, the CO3 content in potassium carbonate is controlled. 2- With Ca in the first filtrate 2+ The molar ratio is 1:1.

[0032] In this invention, the addition of potassium carbonate can further remove excess calcium ions, reduce the subsequent calcium removal load, and ensure the purity of the product.

[0033] Preferably, the temperature of the calcium removal reaction is 30~50℃, for example, it can be 30℃, 32℃, 34℃, 36℃, 38℃, 40℃, 42℃, 44℃, 46℃, 48℃ or 50℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0034] Preferably, the time for the calcium removal reaction is 10 to 30 minutes, for example, 10 minutes, 12 minutes, 14 minutes, 16 minutes, 18 minutes, 20 minutes, 22 minutes, 24 minutes, 26 minutes, 28 minutes or 30 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, stirring is performed during the calcium removal reaction.

[0036] Preferably, the stirring rate during the calcium removal reaction is 20-50 r / min, for example, it can be 20 r / min, 22 r / min, 24 r / min, 26 r / min, 28 r / min, 30 r / min, 32 r / min, 34 r / min, 36 r / min, 38 r / min, 40 r / min, 42 r / min, 44 r / min, 46 r / min, 48 r / min or 50 r / min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0037] Preferably, the second solid-liquid separation method includes pressure filtration.

[0038] Preferably, the Ca in the second filtrate 2+ or F - The concentrations of each are individually ≤5ppm, for example, 5ppm, 4ppm, 3ppm, 2ppm or 1ppm, but not limited to the listed values. Other unlisted values ​​within the range also apply.

[0039] Preferably, the evaporation concentration in step (4) includes a first concentration and a second concentration performed sequentially.

[0040] Preferably, the first concentration is carried out in a stirred MVR evaporator.

[0041] Preferably, the temperature of the first concentration is 130~140℃, for example, it can be 130℃, 132℃, 134℃, 136℃, 138℃ or 140℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0042] Preferably, the pressure of the first concentration is 0.1~0.12MPa, for example, it can be 0.1MPa, 0.11MPa or 0.12MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] Preferably, the mass concentration of potassium nitrate at the first concentration endpoint is 30% to 50%, for example, it can be 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48% or 50%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0044] Preferably, the concentrated solution obtained from the first concentration contains Ca 2+ or F - The concentrations of each are individually ≤1 ppm, for example, 1 ppm, 0.9 ppm, 0.8 ppm, 0.7 ppm, 0.6 ppm or 0.5 ppm, but are not limited to the listed values. Other unlisted values ​​within the range also apply.

[0045] Preferably, the second concentration is carried out in a single-effect evaporator.

[0046] Preferably, the temperature of the second concentration is 80~120℃, for example, it can be 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃ or 120℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0047] Preferably, the second concentration is carried out under vacuum conditions.

[0048] Preferably, the vacuum degree of the second concentration is 0.02~0.05MPa, for example, it can be 0.02MPa, 0.03MPa, 0.04MPa or 0.05MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] Preferably, the mass concentration of potassium nitrate at the second concentration endpoint is 40% to 55%, for example, it can be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54% or 55%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0050] Preferably, the cooling crystallization rate is 5~8℃ / min, for example, it can be 5℃ / min, 6℃ / min, 7℃ / min or 8℃ / min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0051] In this invention, the operations of evaporation concentration and cooling crystallization are combined to promote the formation of potassium nitrate crystal nuclei and to continuously deposit them on the surface of the nuclei, thereby controlling the crystal size and specific surface area so that the finished product meets the requirements for use in tempered glass.

[0052] Preferably, the third solid-liquid separation method in step (4) includes centrifugation.

[0053] Preferably, the purity of the potassium nitrate product in step (4) is ≥99.99%.

[0054] Preferably, the average particle size of the potassium nitrate product is 0.1~0.5mm, for example, it can be 0.1mm, 0.2mm, 0.3mm, 0.4mm or 0.5mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0055] In this invention, the average particle size of potassium nitrate products is specifically controlled within a certain range, which can further ensure its application effect in tempered glass. When the average particle size is too small, it will lead to a deterioration in the surface quality of the glass, and when the average particle size is too large, it will lead to a deterioration in the transparency of the glass.

[0056] Preferably, the specific surface area of ​​the potassium nitrate product is 1~5m². 2 / g, for example, could be 1m 2 / g、2m 2 / g、3m 2 / g、4m 2 / g or 5m 2 / g, but not limited to the listed values, other unlisted values ​​within the range also apply.

[0057] In this invention, the specific surface area of ​​potassium nitrate products is controlled within a specific range, which can further ensure its application effect in tempered glass. When the specific surface area is too small, the compressive stress of the glass will decrease, and when the specific surface area is too large, the strength of the glass will decrease.

[0058] As a preferred embodiment of the present invention, the method includes the following steps: (1) Add nitric acid wastewater to potassium hydroxide wastewater containing fluoride and carry out neutralization reaction for 20-30 minutes at a temperature of 60-80℃ and a stirring rate of 50-100r / min. The final pH value is 6-8, and the first solution containing potassium nitrate is obtained. (2) Add lime to the first liquid obtained in step (1), and carry out a defluorination reaction for 10-30 minutes at a temperature of 50-90℃ and a stirring rate of 50-100 r / min. The final pH value is 6-9, and the Ca content of the lime is reduced. 2+ With the F contained in the first liquid - The molar ratio of the two components is (1~1.5):2, and then pressure filtration is performed to obtain the first filtrate; (3) Add nitric acid to the first filtrate obtained in step (2) to adjust the pH value to 5-8. Then add a potassium carbonate solution with a mass concentration of 1%-5% and carry out a calcium removal reaction for 10-30 minutes at a temperature of 30-50℃ and a stirring rate of 20-50 r / min. After that, filter by pressure to obtain a second filtrate. The second filtrate contains Ca 2+ or F - The concentrations of each are individually ≤5 ppm; (4) The second filtrate obtained in step (3) is first concentrated in a stirred MVR evaporator at a temperature of 130~140℃ and a pressure of 0.1~0.12MPa. At the end of the first concentration, the mass concentration of potassium nitrate is 30%~50%, and the mass concentration of Ca is... 2+ or F - The concentrations of each component are independently ≤1ppm. Then, a second concentration is carried out in a single-effect evaporator with a vacuum degree of 0.02~0.05MPa and a temperature of 80~120℃. At the end of the second concentration, the mass concentration of potassium nitrate is 40%~55%. After that, the product is cooled and crystallized at a rate of 5~8℃ / min, and then centrifuged to obtain the potassium nitrate product.

[0059] Compared with the prior art, the present invention has the following beneficial effects: (1) The method provided by the present invention utilizes two wastewater streams, fluoride-containing potassium hydroxide wastewater and nitric acid wastewater, to carry out a neutralization reaction. Excess fluoride ions are removed by adding lime, and excess calcium ions are removed by adjusting the pH value and adding potassium carbonate. This allows potassium nitrate with high purity to be obtained in the liquid phase. Finally, potassium nitrate product is obtained by means of evaporation concentration, cooling crystallization and other methods.

[0060] (2) The potassium nitrate product obtained by the method provided by the present invention has a suitable particle size and specific surface area, which can ensure a more uniform melting rate, more sufficient ion exchange on the glass surface, and continuous and stable stress layer, which is beneficial to the application in the field of glass strengthening.

[0061] (3) The method provided by the present invention realizes the synergistic treatment of two wastewater streams, namely fluoride-containing potassium hydroxide wastewater and nitric acid-containing wastewater, with low emissions and low hazardous waste generation, resulting in cleaner and more environmentally friendly production. Attached Figure Description

[0062] Figure 1 This is a flowchart of the method provided in Example 1. Detailed Implementation

[0063] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0064] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0065] In the following examples and comparative examples, the F in the fluoride-containing potassium hydroxide wastewater - The concentration was 4000 ppm, OH - The concentration is 5 mol / L, K + The concentration of H in the nitric acid-containing wastewater is 5 mol / L. + The concentration of NO3 is 5 mol / L. - The concentration is 5 mol / L.

[0066] Example 1 This embodiment provides a method for producing potassium nitrate for tempered glass from fluoride-containing potassium hydroxide wastewater, such as... Figure 1 As shown, the method includes the following steps: (1) Add nitric acid wastewater to potassium hydroxide wastewater containing fluoride and carry out neutralization reaction for 25 min at a temperature of 70℃ and a stirring rate of 75r / min. The final pH value is 7, and the first liquid containing potassium nitrate is obtained. (2) Add lime to the first liquid obtained in step (1), and carry out the defluorination reaction for 20 minutes at a temperature of 70℃ and a stirring rate of 75r / min. The final pH value is 8, and the Ca content of the lime is reduced. 2+ With the F contained in the first liquid - The molar ratio of the components is 1.2:2, and then pressure filtration is performed to obtain the first filtrate; (3) Add nitric acid to the first filtrate obtained in step (2) to adjust the pH value. The final pH value is 6. Then add a 3% potassium carbonate solution to control the CO3 content in the potassium carbonate. 2- With Ca in the first filtrate 2+ The molar ratio of the two components was 1:1. The calcium removal reaction was carried out for 20 minutes at a temperature of 40℃ and a stirring rate of 35r / min. After that, the mixture was filtered to obtain the second filtrate. (4) The second filtrate obtained in step (3) is first concentrated in a stirred MVR evaporator at a temperature of 135°C and a pressure of 0.11 MPa. At the end of the first concentration, the mass concentration of potassium nitrate is 40%. Then, it is concentrated in a single-effect evaporator at a vacuum of 0.03 MPa and a temperature of 100°C. At the end of the second concentration, the mass concentration of potassium nitrate is 50%. Then, it is cooled and crystallized at a rate of 6°C / min. Then, it is centrifuged to obtain the potassium nitrate product.

[0067] Example 2 This embodiment provides a method for producing potassium nitrate for tempered glass from fluoride-containing potassium hydroxide wastewater, the method comprising the following steps: (1) Add nitric acid wastewater to potassium hydroxide wastewater containing fluoride and carry out neutralization reaction for 30 min at a temperature of 80℃ and a stirring rate of 50 r / min. The final pH value is 7, and the first solution containing potassium nitrate is obtained. (2) Add lime to the first liquid obtained in step (1), and carry out a defluorination reaction for 10 min at a temperature of 50℃ and a stirring rate of 100 r / min. The final pH value is 6.5, and the Ca content of the lime is reduced. 2+ With the F contained in the first liquid - The molar ratio of the components is 1.2:2, and then pressure filtration is performed to obtain the first filtrate; (3) Add nitric acid to the first filtrate obtained in step (2) to adjust the pH value. The final pH value is 5. Then add a 1% potassium carbonate solution to control the CO3 content in the potassium carbonate. 2- With Ca in the first filtrate 2+ The molar ratio of the two components was 1:1. The calcium removal reaction was carried out at a temperature of 50℃ and a stirring rate of 20r / min for 30min, followed by pressure filtration to obtain the second filtrate. (4) The second filtrate obtained in step (3) is first concentrated in a stirred MVR evaporator at a temperature of 130°C and a pressure of 0.1 MPa. At the end of the first concentration, the mass concentration of potassium nitrate is 30%. Then, it is concentrated in a single-effect evaporator at a vacuum of 0.05 MPa and a temperature of 80°C. At the end of the second concentration, the mass concentration of potassium nitrate is 40%. After that, it is cooled and crystallized at a rate of 8°C / min. Then, it is centrifuged to obtain the potassium nitrate product.

[0068] Example 3 This embodiment provides a method for producing potassium nitrate for tempered glass from fluoride-containing potassium hydroxide wastewater, the method comprising the following steps: (1) Add nitric acid wastewater to potassium hydroxide wastewater containing fluoride and carry out neutralization reaction for 20 min at a temperature of 60℃ and a stirring rate of 100r / min. The final pH value is 7, and the first liquid containing potassium nitrate is obtained. (2) Add lime to the first liquid obtained in step (1), and carry out a defluorination reaction for 30 minutes at a temperature of 90℃ and a stirring rate of 50r / min. The final pH value is 8.5, and the Ca content of the lime is [not specified]. 2+ With the F contained in the first liquid - The molar ratio of the components is 1.5:2, and then pressure filtration is performed to obtain the first filtrate; (3) Add nitric acid to the first filtrate obtained in step (2) to adjust the pH value to 7.5. Then add a 5% potassium carbonate solution to control the CO3 content in the potassium carbonate. 2- With Ca in the first filtrate 2+ The molar ratio of the two components was 1:1. The calcium removal reaction was carried out for 10 minutes at a temperature of 30℃ and a stirring rate of 50 r / min. After that, the mixture was filtered to obtain the second filtrate. (4) The second filtrate obtained in step (3) is first concentrated in a stirred MVR evaporator at a temperature of 140°C and a pressure of 0.12 MPa. At the end of the first concentration, the mass concentration of potassium nitrate is 50%. Then, it is concentrated in a single-effect evaporator at a vacuum of 0.02 MPa and a temperature of 120°C. At the end of the second concentration, the mass concentration of potassium nitrate is 55%. Then, it is cooled and crystallized at a rate of 5°C / min. Then, it is centrifuged to obtain the potassium nitrate product.

[0069] Example 4 This embodiment provides a method for producing potassium nitrate for tempered glass from fluoride-containing potassium hydroxide wastewater. The difference between this method and that of Example 1 lies only in the amount of Ca contained in the lime during the defluorination reaction in step (2). 2+ With the F contained in the first liquid - The molar ratio is 0.8:2.

[0070] Example 5 This embodiment provides a method for producing potassium nitrate for tempered glass from fluoride-containing potassium hydroxide wastewater. The only difference from Embodiment 1 is that the final pH value of the pH adjustment in step (3) is 4.

[0071] Example 6 This embodiment provides a method for producing potassium nitrate for tempered glass from fluorine-containing potassium hydroxide wastewater. The only difference from Embodiment 1 is that the evaporation and concentration in step (4) is only the first concentration, that is, the second filtrate is concentrated in a stirred MVR evaporator until the mass concentration of potassium nitrate is 50% at the endpoint, and then cooled and crystallized.

[0072] Example 7 This embodiment provides a method for producing potassium nitrate for tempered glass from fluoride-containing potassium hydroxide wastewater. The only difference from Embodiment 1 is that the evaporation and concentration in step (4) is only a second concentration, that is, the second filtrate is concentrated in a single-effect evaporator until the mass concentration of potassium nitrate is 50% at the endpoint.

[0073] Example 8 This embodiment provides a method for producing potassium nitrate for tempered glass from fluorine-containing potassium hydroxide wastewater. The only difference from Example 1 is that the cooling crystallization rate in step (4) is 4°C / min.

[0074] Example 9 This embodiment provides a method for producing potassium nitrate for tempered glass from fluorine-containing potassium hydroxide wastewater. The only difference from Example 1 is that the cooling crystallization rate in step (4) is 10°C / min.

[0075] Comparative Example 1 This comparative example provides a method for producing potassium nitrate for tempered glass from fluoride-containing potassium hydroxide wastewater. The only difference from Example 1 is that pH adjustment is not performed in step (3), and the calcium removal reaction is carried out directly.

[0076] Comparative Example 2 This comparative example provides a method for producing potassium nitrate for tempered glass from fluoride-containing potassium hydroxide wastewater. The only difference from Example 1 is that pH adjustment and calcium removal reaction are not performed, and the first filtrate is directly subjected to step (4).

[0077] Results Test

purity

[0078] Average particle size The potassium nitrate products obtained in the above examples and comparative examples were tested using laser particle size analysis, and the results are shown in Table 1.

[0079] Specific surface area The potassium nitrate products obtained in the above examples and comparative examples were tested using the BET method, and the results are shown in Table 1.

[0080] Table 1 The following points can be observed from Table 1: (1) As can be seen from the data in Examples 1-3, under preferred conditions, the method provided by the present invention can achieve a potassium nitrate purity of over 99.5%, an average particle size of potassium nitrate of less than 0.35 mm, and a specific surface area of ​​3.0 m². 2 / g or more.

[0081] (2) As can be seen from the data of Examples 1 and 4-5, 8-9, the present invention further optimizes and controls the Ca content of lime in the defluorination reaction. 2+ With the F contained in the first liquid - The range of parameters such as the molar ratio, the endpoint pH value for pH adjustment, and the rate of cooling crystallization can further improve the purity of potassium nitrate, reduce the average particle size, and increase the specific surface area to better meet the requirements for use in tempered glass.

[0082] (3) As can be seen from the data of Examples 1 and 6-7, the present invention can further improve the purity of potassium nitrate, reduce the average particle size, and increase the specific surface area by using a combination of first concentration and second concentration operations, making it more in line with the requirements for use in tempered glass.

[0083] (4) As can be seen from the comparison between Example 1 and Comparative Examples 1-2, the present invention can significantly improve the purity and specific surface area of ​​potassium nitrate and control the average particle size to a small size through a combination of neutralization reaction, defluorination reaction, pH adjustment, calcium removal reaction, evaporation concentration and cooling crystallization.

[0084] In summary, the method provided by this invention can, while ensuring deep defluorination, synergistically prepare potassium nitrate products from nitric acid-containing wastewater. The resulting potassium nitrate products, when used to strengthen glass, effectively guarantee product quality. The above descriptions are merely specific embodiments of this invention, but the scope of protection of this invention is not limited thereto. Those skilled in the art should understand that any variations or substitutions easily conceived by those skilled in the art within the technical scope disclosed in this invention fall within the scope of protection and disclosure of this invention.

Claims

1. A method for producing potassium nitrate for tempered glass from fluoride-containing potassium hydroxide wastewater, characterized in that, The method includes the following steps: (1) Add nitric acid-containing wastewater to fluorine-containing potassium hydroxide wastewater for neutralization reaction to obtain the first solution containing potassium nitrate; (2) Add lime to the first liquid obtained in step (1) to carry out a defluorination reaction, and then carry out the first solid-liquid separation to obtain the first filtrate; (3) Adjust the pH of the first filtrate obtained in step (2), then add potassium carbonate to carry out calcium removal reaction, and then carry out the second solid-liquid separation to obtain the second filtrate; (4) The second filtrate obtained in step (3) is subjected to evaporation and concentration, cooling and crystallization and third solid-liquid separation in sequence to obtain potassium nitrate product.

2. The method according to claim 1, characterized in that, Step (1) The fluoride-containing potassium hydroxide wastewater contains F - The concentration is 500~5000ppm, OH - The concentration is 4~6 mol / L, K + The concentration is 4~6 mol / L; Preferably, the H in the nitric acid-containing wastewater + The concentration of NO3 is 4~6 mol / L. - The concentration is 4~6 mol / L.

3. The method according to claim 1 or 2, characterized in that, The endpoint pH value of the neutralization reaction described in step (1) is 6-8; Preferably, the temperature of the neutralization reaction is 60~80℃; Preferably, the neutralization reaction takes 20-30 minutes; Preferably, stirring is performed during the neutralization reaction; Preferably, the stirring rate during the neutralization reaction is 50~100 r / min.

4. The method according to any one of claims 1 to 3, characterized in that, In step (2), the calcium contained in the lime during the defluorination reaction... 2+ With the F contained in the first liquid - The molar ratio is (1~1.5):2; Preferably, the endpoint pH value of the defluorination reaction is 6-9; Preferably, the temperature of the defluorination reaction is 50~90℃; Preferably, the defluorination reaction takes 10-30 minutes; Preferably, stirring is performed during the defluorination reaction; Preferably, the stirring rate during the defluorination reaction is 50~100 r / min.

5. The method according to any one of claims 1 to 4, characterized in that, Step (2) The first solid-liquid separation method includes pressure filtration.

6. The method according to any one of claims 1 to 5, characterized in that, The pH adjuster used in step (3) includes nitric acid; Preferably, the endpoint pH value of the pH adjustment is 5 to 8.

7. The method according to any one of claims 1 to 6, characterized in that, In step (3), the potassium carbonate is added in the form of a solution; Preferably, the mass concentration of potassium carbonate is 1% to 5%; Preferably, the temperature of the calcium removal reaction is 30~50℃; Preferably, the calcium removal reaction takes 10-30 minutes; Preferably, stirring is performed during the calcium removal reaction; Preferably, the stirring rate during the calcium removal reaction is 20~50 r / min; Preferably, the second solid-liquid separation method includes pressure filtration; Preferably, the Ca in the second filtrate 2+ or F - The concentrations of each are independently ≤5ppm.

8. The method according to any one of claims 1 to 7, characterized in that, Step (4) of the evaporation and concentration includes a first concentration and a second concentration performed sequentially; Preferably, the first concentration is carried out in a stirred MVR evaporator; Preferably, the temperature of the first concentration is 130~140℃; Preferably, the pressure of the first concentration is 0.1~0.12 MPa; Preferably, the mass concentration of potassium nitrate at the first concentration endpoint is 30%~50%; Preferably, the concentrated solution obtained from the first concentration contains Ca 2+ or F - The concentrations of each are independently ≤1 ppm; Preferably, the second concentration is carried out in a single-effect evaporator; Preferably, the temperature for the second concentration is 80~120℃; Preferably, the second concentration is carried out under vacuum conditions; Preferably, the vacuum degree of the second concentration is 0.02~0.05MPa; Preferably, the mass concentration of potassium nitrate at the second concentration endpoint is 40%~55%; Preferably, the cooling crystallization rate is 5~8℃ / min.

9. The method according to any one of claims 1 to 8, characterized in that, The third solid-liquid separation method in step (4) includes centrifugation.

10. The method according to any one of claims 1 to 9, characterized in that, The purity of the potassium nitrate product in step (4) is ≥99.99%; Preferably, the average particle size of the potassium nitrate product is 0.1~0.5 mm; Preferably, the specific surface area of ​​the potassium nitrate product is 1~5m². 2 / g.

Images