Method for synthesizing potassium fluosilicate large-particle crystals by using recycled potassium sulfate

Abstract

The invention relates to a method for synthesizing large-particle potassium fluosilicate crystals by using recycled potassium sulfate. The method comprises the following steps: 1, standing fluorine-containing waste liquid, and taking a clear solution; 2, silicon dioxide is added into the clarified solution for pretreatment, free fluorine in the fluorine-containing waste liquid is converted into fluosilicic acid, fluorine complexing liquid is prepared, and the chemical equation is SiO2 + 6HF-> H2SiF6 + 2H2O; step 3, adding the complexing liquid into a potassium hydrogen sulfate solution to synthesize potassium fluosilicate, wherein the chemical equation is H2SiF6 + 2KHSO4 = K2SiF6 + 2H2SO4; 4, carrying out solid-liquid separation on the reacted solution system to obtain potassium fluosilicate mother liquor and solids, washing the solids, and drying the solids in a drying oven at the temperature of 100 DEG C to obtain a potassium fluosilicate product; step 5, neutralizing the sulfuric acid component in the washing water in the step 4 through lime; and 6, collecting the potassium fluosilicate mother liquor in the step 4, and adding a proper amount of potassium sulfate to prepare potassium hydrogen sulfate for recycling when a large amount of sulfuric acid exists in the potassium fluosilicate mother liquor.

Description

Technical Field

[0001] The invention belongs to the field of fluorine-containing waste liquid treatment, and particularly relates to a method for synthesizing large-particle potassium fluorosilicate crystals by recycling potassium sulfate. Background Art

[0002] Fluorine resources are a strategic resource for the country and are widely used in many fields, such as ceramic manufacturing, aluminum and magnesium smelting, and optical glass manufacturing. In the industrial production process, especially in the fluorine chemical industry, tantalum niobium industry, and phosphate fertilizer industry, a large amount of fluorine-containing waste liquid will be generated. Direct discharge will cause environmental pollution. Therefore, proper treatment of fluorine-containing waste liquid is not only for environmental protection, but also an important part of achieving sustainable development. At present, most of the treatment methods for fluorine-containing waste liquid are to add lime for neutralization, and the resulting calcium fluoride has low purity and can only be used in the ceramic industry with low added value. Potassium fluorosilicate, as an important fluoride product, has a wide range of application value. It can be used in many fields such as optical glass manufacturing, and it is also an important raw material for synthesizing other fluorides, with broad market prospects. Therefore, converting fluorine-containing waste liquid into valuable potassium fluorosilicate products promotes the rational use of fluorine resources. Summary of the invention

[0003] In view of the above technical problems, the present invention provides a method for synthesizing large-particle potassium fluorosilicate crystals by recycling potassium sulfate, which is as follows: A method for synthesizing large-particle potassium fluorosilicate crystals by recycling potassium sulfate, Step 1: let the fluorine-containing waste liquid stand and take a clarified solution; Step 2: Add silica to the clarified solution for pretreatment, so that the free fluorine in the fluorine-containing waste liquid is converted into fluorosilicic acid to obtain fluorine liquid. The chemical equation is as follows: SiO2+6HF→H2SiF6+2H2O; Step 3: Add the fluorine solution to the potassium bisulfate solution to synthesize potassium fluorosilicate. The chemical equation is as follows: H2SiF6+2KHSO4=K2SiF6+2H2SO4; Step 4: separating the reaction-completed solution system into a solid-liquid separation to obtain a potassium fluorosilicate mother liquor and a solid, washing the solid and then drying it in an oven at 100° C. to obtain a potassium fluorosilicate product; Step 5: The washing water from step 4 is passed through lime to neutralize the sulfuric acid component therein; Step 6: Collect the potassium fluorosilicate mother liquor in step 4. At this time, there is a large amount of sulfuric acid in the potassium fluorosilicate mother liquor. Add an appropriate amount of potassium sulfate to configure it as potassium hydrogen sulfate for recycling. At this time, there is a large amount of sulfuric acid in the solution and potassium sulfate reacts to form potassium hydrogen sulfate. Potassium sulfate and sulfuric acid are mixed in a certain proportion and heated to a certain temperature, so that potassium sulfate and sulfuric acid can react to form potassium hydrogen sulfate and hydrogen. The reaction equation is: K2SO4+H2SO4→2KHSO4.

[0004] Preferably, the molar ratio of the amount of silicon dioxide added in step 2 to the free fluorine in the solution is 1-2:6, and the mixture is stirred for 24 hours. The amount of silicon dioxide added is 1.0-2 times the theoretical amount, and the mixture is stirred for 24 hours to complete the reaction.

[0005] Preferably, the excess silicon dioxide in step 2 is filtered by a vacuum filtration pump, and the excess residual silicon dioxide is re-used in new fluorine-containing waste liquid.

[0006] Preferably, the silicon concentration in the fluorine solution is controlled to be 10-20 g / L.

[0007] Preferably, the concentration of the potassium bisulfate solution is 200-300 g / L.

[0008] Preferably, the molar ratio of the amount of potassium added in the potassium hydrogen sulfate solution to the total fluorine content in the fluorine solution is 1.0-1.5:3, that is, the amount of potassium added is 1.0-1.5 times the theoretical amount.

[0009] Preferably, the reaction temperature in step 3 is 30-80°C.

[0010] Beneficial effects: (1) This scheme uses industrially recovered potassium sulfate instead of potassium chloride to avoid chloride ion emissions during the production of potassium fluorosilicate.

[0011] (2) This scheme reuses the mother liquor with high sulfuric acid concentration produced after the synthesis of potassium fluorosilicate to increase the solubility of potassium sulfate, thus overcoming the problem of low solubility of potassium sulfate.

[0012] (3) Compared with the existing scheme, this scheme is more environmentally friendly and can synthesize potassium fluorosilicate crystals with high purity and large particle size. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of the process of the embodiment. DETAILED DESCRIPTION

[0014] The present invention will be further described below in conjunction with the embodiments.

[0015] A method for synthesizing large-particle potassium fluorosilicate crystals by recycling potassium sulfate: Step 1: Let the fluorine-containing waste liquid stand and take the clarified solution.

[0016] Step 2: Add silica to the clarified solution for pretreatment, so that the free fluorine in the fluorine-containing waste liquid is converted into fluorosilicic acid to obtain the fluorine liquid. The molar ratio of silica dosage: free fluorine in the solution is 1-2:6, and stir for 24 hours. The silica dosage is 1.0-2 times the theoretical amount, and stir for 24 hours to make the reaction complete. Excess silica is filtered through a vacuum filtration pump, and the excess residual silica is re-added to the new fluorine-containing waste liquid for use. The silicon concentration in the fluorine liquid is controlled to be: 10-20g / L. The chemical equation is as follows: SiO2+6HF→H2SiF6+2H2O.

[0017] Step 3: Add the fluorocarbon solution to the potassium hydrogen sulfate solution to synthesize potassium fluorosilicate, the reaction temperature is: 30-80℃. The concentration of the potassium hydrogen sulfate solution is: 200-300g / L. The molar ratio of the amount of potassium element added in the potassium hydrogen sulfate solution to the total fluorine content in the fluorocarbon solution is 1.0-1.5:3. That is, the amount of potassium element added is 1.0-1.5 times the theoretical amount. The chemical equation is as follows: H2SiF6+2KHSO4=K2SiF6+2H2SO4.

[0018] Step 4: The solution system after the reaction is completed is subjected to solid-liquid separation to obtain potassium fluorosilicate mother liquor and solid, the solid is washed and then placed in an oven at 100° C. to dry to obtain a potassium fluorosilicate product.

[0019] Step 5: The wash water from step 4 is treated with lime to neutralize the sulfuric acid content therein.

[0020] Step 6: Collect the potassium fluorosilicate mother liquor in step 4. At this time, there is a large amount of sulfuric acid in the potassium fluorosilicate mother liquor. Add an appropriate amount of potassium sulfate to configure it as potassium hydrogen sulfate for recycling. At this time, there is a large amount of sulfuric acid in the solution and potassium sulfate reacts to form potassium hydrogen sulfate. Potassium sulfate and sulfuric acid are mixed in a certain proportion and heated to a certain temperature, so that potassium sulfate and sulfuric acid can react to form potassium hydrogen sulfate. The reaction equation is: K2SO4+H2SO4→2KHSO4. Example

[0021] A fluorine-containing waste liquid, in which the F content is 78g / L, the Si content is 6.1g / L, the HF content is 2.55N, and the sulfuric acid content is 6.95N.

[0022] Step 1: Let the fluorine-containing waste liquid stand and take the clarified solution.

[0023] Step 2: Take 1L of the clarified fluorine-containing waste liquid after standing, add 50g of silicon dioxide, and stir at room temperature for 24h to convert the free fluorine in the fluorine-containing waste liquid into fluorosilicic acid to obtain fluorine liquid. After the reaction is completed, filter and enter the next reaction step.

[0024] Step 3: Take 200 mL of the fluorine solution obtained in step 2, add 120 mL of a 300 g / L potassium hydrogen sulfate solution, react at 50°C for 6 hours to synthesize potassium fluorosilicate. After the reaction is completed, let it stand for 4 hours.

[0025] Step 4: After standing, a vacuum filtration pump is used to filter the solid-liquid separation to obtain potassium fluorosilicate mother liquor and solid, wherein the potassium fluorosilicate mother liquor is collected and reused, the filter cake is washed, and placed in an oven at 100°C for drying. The crystals after drying are weighed and calculated to have a yield of 97.5%. The particle size is observed under a microscope to be about 0.5 mm.

[0026] Step 5: The wash water from step 4 is treated with lime to neutralize the sulfuric acid content therein.

[0027] Step 6: Collect the potassium fluorosilicate mother liquor in step 4, and use the mother liquor and the recovered potassium sulfate to configure potassium hydrogen sulfate for recycling. At this time, there is a large amount of sulfuric acid in the potassium fluorosilicate mother liquor, and an appropriate amount of potassium sulfate is added to configure potassium hydrogen sulfate for recycling in step 3. At this time, there is a large amount of sulfuric acid in the solution and potassium sulfate reacts to generate potassium hydrogen sulfate.

[0028] Table 1 Water sample test results (unit: g / L or N) Water Sample Total F Si HF <![CDATA[H2SO4]]> Original solution 78g / L 6.1g / L 2.55N 10.41 Fluorine solution 78g / L 18.0g / L 1.15N 10.40 After treatment 4.78g / L 0.025g / L 0.22N 10.77 Obviously, the above embodiments of the present invention are merely examples for illustrating the present invention, and are not intended to limit the implementation methods of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to exhaust all implementation methods here. However, these obvious changes or modifications derived from the essential spirit of the present invention still fall within the protection scope of the present invention.

Claims

1. A method for synthesizing large-particle potassium fluorosilicate crystals by recycling potassium sulfate, characterized in that: Step 1: let the fluorine-containing waste liquid stand and take a clarified solution; Step 2: Add silica to the clarified solution for pretreatment, so that the free fluorine in the fluorine-containing waste liquid is converted into fluorosilicic acid to obtain fluorine liquid. The chemical equation is as follows: SiO2+6HF→H2SiF6+2H2O; Step 3: Add the fluorine solution to the potassium bisulfate solution to synthesize potassium fluorosilicate. The chemical equation is as follows: H2SiF6+2KHSO4=K2SiF6+2H2SO4; Step 4: separating the reaction-completed solution system into a solid-liquid separation to obtain a potassium fluorosilicate mother liquor and a solid, washing the solid and then drying it in an oven at 100° C. to obtain a potassium fluorosilicate product; Step 5: The washing water from step 4 is passed through lime to neutralize the sulfuric acid component therein; Step 6: Collect the potassium fluorosilicate mother liquor in step 4. At this time, there is a large amount of sulfuric acid in the potassium fluorosilicate mother liquor. Add an appropriate amount of potassium sulfate to prepare potassium bisulfate for recycling.

2. A method for synthesizing large-particle potassium fluorosilicate crystals by recycling potassium sulfate according to claim 1, characterized in that: The molar ratio of silicon dioxide dosage in step 2: free fluorine in the solution is 1-2:6, and stirring is performed for 24 hours.

3. A method for synthesizing large-particle potassium fluorosilicate crystals by recycling potassium sulfate according to claim 1, characterized in that: The excess silicon dioxide in step 2 is filtered out by a vacuum filtration pump, and the excess residual silicon dioxide is re-used in new fluorine-containing waste liquid.

4. A method for synthesizing large-particle potassium fluorosilicate crystals by recycling potassium sulfate according to claim 1, characterized in that: The silicon concentration in the fluorine solution is controlled to be: 10-20g / L.

5. A method for synthesizing large-particle potassium fluorosilicate crystals by recycling potassium sulfate according to claim 1, characterized in that: The concentration of potassium bisulfate solution is 200-300g / L.

6. A method for synthesizing large-particle potassium fluorosilicate crystals by recycling potassium sulfate according to claim 1, characterized in that: The molar ratio of the amount of potassium element added in the potassium hydrogen sulfate solution to the total fluorine content in the complex fluorine solution is 1.0-1.5:

3.

7. The method for synthesizing large-particle potassium fluorosilicate crystals by recycling potassium sulfate according to claim 1, characterized in that: The reaction temperature in step 3 is: 30-80°C.

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