Method for preparing high-molecular-ratio cryolite from fluorine-containing wastewater

Abstract

The invention relates to the field of preparation of cryolite from fluorine wastewater, in particular to a method for preparing high-molecular-ratio cryolite from fluorine-containing wastewater. The method for preparing the high-molecular-ratio cryolite from the fluorine-containing wastewater comprises the following steps: preparing a fluorine-containing wastewater clear liquid, preparing an auxiliary solution, adding the auxiliary solution, reacting, drying and crystallizing. According to the method for preparing the high-molecular-ratio cryolite from the fluorine-containing wastewater in the photovoltaic industry, the reaction raw materials aluminum chloride and sodium chloride are easily dissolved in water, the cost is low, the operation is simple, fluorine in the wastewater is easily recycled, and the concentration of the fluorine in the wastewater is reduced.

Description

Technical Field

[0001] The invention relates to the field of preparing cryolite with fluorine wastewater, and in particular to a method for preparing high-molecular-ratio cryolite with fluorine-containing wastewater. Background Art

[0002] Solar energy is the most abundant and widely distributed renewable resource on earth. With the advancement of technology and the reduction of costs, photovoltaic power generation has become the fastest-growing and largest renewable energy in China in recent years after wind power generation. China's photovoltaic industry scale, manufacturing and technology level are ranked first in the world. The production of photovoltaic cells and components in the photovoltaic industry chain is an important part of the realization of crystalline silicon raw materials to photovoltaic products. With the development and growth of the photovoltaic industry, the generation of three wastes has also been accompanied. Among them, the pollution control of high-concentration fluorine-containing wastewater is a persistent problem that the photovoltaic industry needs to solve.

[0003] Fluorine is a trace element necessary for the human body, but long-term excessive intake of high-fluoride water can have serious adverse effects on the gastrointestinal tract, liver, kidneys, nervous system, muscles, reproductive and immune systems, and DNA structure, and even cause bone sclerosis, permanent disability and cancer. In addition to threatening human health, fluorine pollution also has serious harm to the ecological environment. Excessive fluorine content can inhibit soil nitrification and acid phosphatase activity, change the structure and pH of soil protozoan communities, and affect the normal growth of plants.

[0004] The treatment methods for fluorine-containing wastewater mainly include chemical precipitation, coagulation precipitation, adsorption and crystallization. In addition, there are membrane separation, ion exchange and electrocoagulation. At present, domestic photovoltaic cell manufacturers often use chemical precipitation and coagulation precipitation to purify water quality after mixing fluorine-containing wastewater from different sources. The most commonly used precipitant in the chemical precipitation method is calcium salt, such as lime, calcium chloride, calcium carbonate and carbide slag. Calcium salt has a good effect on fluoride removal, but the disadvantage in actual engineering is that calcium fluoride formed by calcium salt and fluorine will be wrapped on the surface of calcium hydroxide, which is not conducive to the complete reaction, resulting in a large amount of calcium salt addition (the amount is often 3 to 4 times the theoretical value), high sludge yield and complex composition, low calcium fluoride content, and low reuse value. In addition, the effluent from the simple chemical precipitation method cannot meet the discharge standards, and generally requires a coagulant for deep fluoride removal. Commonly used inorganic coagulants are iron salts and aluminum salts, and organic flocculants are mostly polyacrylamide (PAM). The disadvantage of using aluminum salts is that it will introduce aluminum elements that are harmful to the human body and cause excessive chloride ions, while iron salts require higher pH conditions to proceed smoothly, resulting in increased water treatment costs.

[0005] In summary, fluoride-containing wastewater from photovoltaic cell production seriously threatens the life safety of humans, animals, and aquatic organisms, and damages the ecological environment. It must be strictly controlled in accordance with national standards before being discharged into the water environment. The current method of combining chemical precipitation and coagulation precipitation for fluoride-containing wastewater produced by photovoltaic cell production enterprises has a high sludge yield and complex composition, low calcium fluoride content, and difficulty in reuse. It still cannot solve the problem of fluoride-containing sludge treatment and disposal, resulting in high operating costs.

[0006] Therefore, it is necessary to provide a new method for preparing high molecular weight cryolite from fluorine-containing wastewater to solve the above technical problems. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a method for preparing high molecular weight cryolite from fluorine-containing wastewater.

[0008] The method for preparing high molecular weight cryolite from fluorine-containing wastewater provided by the present invention comprises the following steps:

[0009] S1. Preparation of fluoride-containing wastewater clear liquid;

[0010] S2, fully mixing aluminum chloride and water to prepare an aluminum chloride solution with a concentration of 10%-20%;

[0011] S3, fully dissolving solid sodium chloride in water to prepare a 20%-30% sodium chloride solution;

[0012] S4, slowly adding sodium aluminosilicate into the hydrofluoric acid waste liquid, stirring the sodium aluminosilicate to completely dissolve, and reacting to form a stable fluorine-aluminum complex;

[0013] S5, slowly dropping the aluminum chloride aqueous solution into the reaction solution in S4, and stirring until fully mixed, reacting to produce aluminum hydroxide, capturing fluoride ions in the fluoride-containing wastewater and forming precipitated particles;

[0014] S6, slowly adding the sodium chloride aqueous solution to the reaction solution in S4 and stirring until fully mixed to promote the precipitation of the particles and form larger and more stable particles;

[0015] S7, filtering and drying the reaction liquid of S6 to obtain high molecular cryolite.

[0016] Preferably, the preparation in step S1 includes:

[0017] 1) Fluoride-containing wastewater with fluoride ≤ 15 mg / L is discharged into the raw water tank and transported to the multi-media filtration unit by a water pump;

[0018] 2) The wastewater passes through the multi-media filtration unit and the precision filtration unit in sequence, and the solid suspended matter concentration SS is ≤ 5mg / L;

[0019] 3) The wastewater is pumped to the pH adjustment tank, and the pH of the wastewater is adjusted to 7-9 by adding sulfuric acid or sodium hydroxide;

[0020] 4) The wastewater is pumped to the ion exchange resin tank for fluoride ion exchange, and the fluoride content is reduced to ≤1mg / L before being discharged;

[0021] 5) After the ion exchange resin reaches the continuous operation limit time, start the resin regeneration system, add alkaline regeneration agent through the dosing pump, and the alkaline regeneration agent waste liquid is transported to the waste liquid storage tank through the pump;

[0022] 6) The waste liquid in the waste liquid storage tank is pumped to the regeneration agent waste liquid treatment system, and then discharged into the sludge filter press unit after passing through the secondary coagulation and sedimentation unit;

[0023] 7) Acid cleaning agent and pure water are added in sequence to clean the resin through the dosing pump, and the resin cleaning wastewater is transported to the waste liquid storage tank through the pump;

[0024] 8) Enter the sludge filter press unit, where the sludge is filtered through a plate and frame filter press to form a sludge cake for external treatment, and the filtrate is transported to the raw water tank through a water pump.

[0025] Preferably, the concentration of hydrofluoric acid in the fluorine-containing wastewater in step S1 is greater than 0.7%.

[0026] Preferably, in steps S4, S5 and S6, the stirring time is 0.5-2h.

[0027] Preferably, in steps S4, S5 and S6, the reaction temperature during stirring is 25°C-85°C.

[0028] Preferably, in steps S4, S5 and S6, the molar ratio of aluminum chloride, sodium chloride and fluorine in hydrofluoric acid wastewater is 1:2.8-3.2:6-6.5.

[0029] Preferably, the temperature of the drying crystallization is 100°C-120°C.

[0030] Compared with the related art, the method for preparing high molecular weight cryolite from fluorine-containing wastewater provided by the present invention has the following beneficial effects:

[0031] The invention discloses a method for preparing high molecular weight cryolite by using fluorine-containing wastewater in the photovoltaic industry. The reaction raw materials aluminum chloride and sodium chloride are easily soluble in water, the cost is low, the operation is simple, the fluorine in the wastewater can be easily recovered and the concentration of fluorine in the wastewater can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a structural schematic diagram of the cryolite preparation process shown in the present invention;

[0033] Figure 2It is a structural schematic diagram of the process for preparing fluorine-containing wastewater shown in the present invention;

[0034] Figure 3 This is an XRD comparison diagram of the homemade cryolite shown in the present invention and a standard card of cryolite with a high molecular weight ratio. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0036] The specific implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0037] Embodiment 1

[0038] See also Figure 1 and Figure 3

[0039] Preparation of Fluoride-containing Wastewater Clear Liquid

[0040] Fluoride-containing wastewater with fluoride ≤15mg / L is discharged into the raw water tank and transported to the multi-media filtration unit by a water pump. The wastewater passes through the multi-media filtration unit and the precision filtration unit in turn. The solid suspended matter concentration SS is ≤5mg / L. The wastewater is transported to the pH adjustment tank by a water pump. The pH of the wastewater is adjusted to 7-9 by adding sulfuric acid or sodium hydroxide. The wastewater is transported to the ion exchange resin tank by a water pump for fluoride ion exchange. The fluoride content is reduced to ≤1mg / L before it is discharged. After the ion exchange resin reaches the continuous operation limit time, the resin regeneration system is started. The system is configured to add an alkaline regeneration agent through a dosing pump, and the waste liquid of the alkaline regeneration agent is transported to a waste liquid storage tank through a pump. The waste liquid in the waste liquid storage tank is transported to a regeneration agent waste liquid treatment system through a pump, and is discharged into a sludge filter press unit after passing through a secondary coagulation and sedimentation unit. Acidic cleaning agent and pure water are sequentially added through a dosing pump to clean the resin, and the resin cleaning wastewater is transported to a waste liquid storage tank through a pump, and enters a sludge filter press unit. The sludge is filtered through a plate and frame filter press to form a sludge cake for external transportation and treatment. The filtrate is transported to a raw water tank through a water pump to obtain fluorine-containing wastewater with a hydrofluoric acid concentration of more than 0.7.

[0041] Preparation of auxiliary solution

[0042] Fully mix aluminum chloride and water to prepare an aluminum chloride solution with a concentration of 10%-20%; fully dissolve solid sodium chloride in water to prepare a sodium chloride solution with a concentration of 20%-30%;

[0043] During the preparation process, attention should be paid to the stirring speed, time, temperature and the method of adding sodium chloride; that is, the stirring speed should not be too fast or too slow. Too fast stirring speed may cause the solution to splash and increase energy consumption; while too slow stirring speed may cause incomplete dissolution of sodium chloride and uneven solution. Generally, medium stirring speed should be selected to ensure that sodium chloride can be dissolved quickly and evenly; the stirring time should be long enough to ensure that sodium chloride is completely dissolved. The stirring time is 15 minutes to 1 hour, and the specific time should be determined according to the amount of sodium chloride and the volume of the solution. Whether sodium chloride is completely dissolved can be judged by observing the clarity of the solution or using tools such as conductivity meters; appropriately increasing the temperature can speed up the dissolution of sodium chloride, but too high a temperature may cause the water in the solution to evaporate too quickly, affecting the concentration of the solution. Generally, sodium chloride can be dissolved at room temperature. If it is necessary to accelerate the dissolution, it can be heated appropriately, but the temperature should be avoided from being too high; during the stirring process, sodium chloride should be added to the water gradually instead of pouring it in all at once. Gradual addition helps to dissolve sodium chloride evenly and prevents local oversaturation from causing crystallization.

[0044] Addition and reaction of auxiliary solutions;

[0045] Slowly add sodium aluminosilicate to the hydrofluoric acid waste liquid, and stir until the sodium aluminosilicate is completely dissolved, and react to form a stable fluorine-aluminum complex; slowly drop the aluminum chloride aqueous solution into the S4 reaction liquid, and stir until fully mixed, react to produce aluminum hydroxide, capture the fluoride ions in the fluoride-containing wastewater and form precipitated particles; slowly drop the sodium chloride aqueous solution into the S4 reaction liquid, and stir until fully mixed, promote the precipitation of particles, and form larger and more stable particles; stirring is required during the addition process, the stirring time is 0.5-2h, and the reaction temperature is 25℃-85℃;

[0046] Drying crystallization

[0047] The temperature of the crystallization process is 100°C-120°C.

[0048] The preparation method of cryolite has multiple advantages, namely:

[0049] 1) Wide treatment range: can recycle hydrofluoric acid wastewater with a hydrofluoric acid concentration of 0.7%;

[0050] 2) The types and quantities of drugs added are small, and the cost of raw materials is low;

[0051] 3) The high molecular weight cryolite produced by the present invention has good stability and is easy to handle;

[0052] 4) The fluoride ion concentration of the present invention and the pH of the final waste liquid are also in the neutral to alkaline range, which meets the national emission standards;

[0053] 5) The prepared high molecular cryolite product meets the requirements of national standards and has high market value.

[0054] Embodiment 2

[0055] Effect of different reaction temperatures on cryolite

[0056] Weigh 20g of sodium aluminosilicate and add it to 200mL of fluoride-containing wastewater, stir at 20℃, 30℃, 40℃ and 50℃ respectively, and set aside after the sodium aluminosilicate is completely dissolved, which is solution 1; take a certain amount of aluminum chloride, add water to dissolve it, and then add it drop by drop to solution 1, which is called solution 2; then weigh a certain amount of sodium chloride, add water to dissolve it, and then add it drop by drop to solution 2, keep stirring at different temperatures for 30min, then stop stirring, and keep warm for 1-2h; finally, filter and dry it to obtain cryolite.

[0057]

[0058] Embodiment 3

[0059] Effects of different fluoride wastewater concentrations on cryolite

[0060] Weigh 20g of sodium aluminosilicate and add it to fluoride-containing wastewater of different concentrations (the fluoride-containing wastewater is diluted 1 times, 2 times, 5 times and 10 times respectively), stir it thoroughly, and set it aside after the sodium aluminosilicate is completely dissolved, which is solution 1; take a certain amount of aluminum chloride, add water to dissolve it, and then add it drop by drop to solution 1, which is called solution 2; then weigh a certain amount of sodium chloride, add water to dissolve it, and then add it drop by drop to solution 2, stop stirring after 30 minutes, and let it stand for 1-2 hours; finally, filter and dry it to obtain cryolite.

[0061]

[0062] Embodiment 4

[0063] Effects of different molar ratios of aluminum chloride, sodium chloride and fluoride in fluoride-containing wastewater on cryolite

[0064] Weigh 20g of sodium aluminosilicate and add it to 200mL of fluoride-containing wastewater. After the sodium aluminosilicate is completely dissolved, set aside to obtain solution 1; take a certain amount of aluminum chloride, add water to dissolve it, and then add it dropwise to solution 1, which is called solution 2; then weigh a certain amount of sodium chloride, add water to dissolve it, and then add it dropwise to solution 2 (the molar ratios of aluminum chloride, sodium chloride and fluoride in fluoride-containing wastewater are 1:3:6, 1:2.8:6, 1:3.2:6.5, and 1:3.2:6, respectively); stop stirring after 30min and let it stand for 1-2h; finally, filter and dry it to obtain cryolite.

[0065]

[0066] The above are only embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing high molecular weight cryolite from fluorine-containing wastewater, characterized in that: The following steps are involved: S1. Preparation of fluoride-containing wastewater clear liquid; S2, fully mixing aluminum chloride and water to prepare an aluminum chloride solution with a concentration of 10%-20%; S3, fully dissolving solid sodium chloride in water to prepare a 20%-30% sodium chloride solution; S4, slowly adding sodium aluminosilicate into the hydrofluoric acid waste liquid, stirring the sodium aluminosilicate to completely dissolve, and reacting to form a stable fluorine-aluminum complex; S5, slowly dropping the aluminum chloride aqueous solution into the reaction solution in S4, and stirring until fully mixed, reacting to produce aluminum hydroxide, capturing fluoride ions in the fluoride-containing wastewater and forming precipitated particles; S6, slowly adding the sodium chloride aqueous solution to the reaction solution in S4 and stirring until fully mixed to promote the precipitation of the particles and form larger and more stable particles; S7, filtering and drying the reaction liquid of S6 to obtain high molecular cryolite.

2. The method for preparing high molecular weight cryolite from fluorine-containing wastewater according to claim 1, characterized in that: The preparation in step S1 includes: 1) Fluoride-containing wastewater with fluoride ≤ 15 mg / L is discharged into the raw water tank and transported to the multi-media filtration unit by a water pump; 2) The wastewater passes through the multi-media filtration unit and the precision filtration unit in sequence, and the solid suspended matter concentration SS is ≤ 5mg / L; 3) The wastewater is pumped to the pH adjustment tank, and the pH of the wastewater is adjusted to 7-9 by adding sulfuric acid or sodium hydroxide; 4) The wastewater is pumped to the ion exchange resin tank for fluoride ion exchange, and the fluoride content is reduced to ≤1mg / L before being discharged; 5) After the ion exchange resin reaches the continuous operation limit time, start the resin regeneration system, add alkaline regeneration agent through the dosing pump, and the alkaline regeneration agent waste liquid is transported to the waste liquid storage tank through the pump; 6) The waste liquid in the waste liquid storage tank is pumped to the regeneration agent waste liquid treatment system, and then discharged into the sludge filter press unit after passing through the secondary coagulation and sedimentation unit; 7) Acid cleaning agent and pure water are added in sequence to clean the resin through the dosing pump, and the resin cleaning wastewater is transported to the waste liquid storage tank through the pump; 8) Enter the sludge filter press unit, where the sludge is filtered through a plate and frame filter press to form a sludge cake for external treatment, and the filtrate is transported to the raw water tank through a water pump.

3. The method for preparing high molecular weight cryolite from fluorine-containing wastewater according to claim 1, characterized in that: The concentration of hydrofluoric acid in the fluorine-containing wastewater in step S1 is greater than 0.7%.

4. The method for preparing high molecular weight cryolite from fluorine-containing wastewater according to claim 1, characterized in that: In steps S4, S5 and S6, the stirring time is 0.5-2h.

5. The method for preparing high molecular weight cryolite from fluorine-containing wastewater according to claim 1, characterized in that: In steps S4, S5 and S6, the reaction temperature during the stirring process is 25°C-85°C.

6. The method for preparing high molecular weight cryolite from fluorine-containing wastewater according to claim 1, characterized in that: In steps S4, S5 and S6, the molar ratio of aluminum chloride, sodium chloride and fluorine in hydrofluoric acid wastewater is 1:2.8-3.2:6-6.

5.

7. The method for preparing high molecular weight cryolite from fluorine-containing wastewater according to claim 1, characterized in that: In step S7, the temperature of drying the crystals is 100°C-120°C.

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