A treatment agent for acidic fluoride-containing wastewater and a method of using the same

Abstract

A treatment agent for acidic fluorine-containing wastewater and a method for using the same. The treatment agent for acidic fluorine-containing wastewater of the present invention comprises an agent A and an agent B; the agent A comprises carbonate minerals and silicate minerals; the agent B is mainly aluminum salt. The method for using the treatment agent for acidic fluorine-containing wastewater of the present invention comprises the following steps: (1) pretreatment: sedimentation filtration to remove suspended solids; (2) pH adjustment: adding agent A to the acidic fluorine-containing wastewater to make the solution pH 6.5-7.5; (3) coagulation precipitation: adding agent B to the solution, standing and precipitating after reaction, and the supernatant is discharged. The use of the treatment agent for acidic fluorine-containing wastewater of the present invention can effectively improve the acid-base buffering capacity of the water quality, and spontaneously stabilize the pH to 6.5-7.5, with high fluorine removal efficiency. It can also improve the sedimentation efficiency of the fluorine removal alum flower, avoid the use of polyacrylamide, and the treatment process is simple and low-cost.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and in particular relates to a treatment agent for acidic fluorine-containing wastewater and a use method thereof. Background Art

[0002] The development of fluorine chemical industry has brought people high value-added, high-performance fluorine products, but also brought a large number of fluorine-containing pollutants. What needs special attention is the fluorine-containing wastewater. If it is not treated and discharged in excess of the standard, it will accumulate in the soil and groundwater for a long time, posing a serious threat to the environment and human safety.

[0003] Coagulation and sedimentation is a commonly used fluoride removal technology. When a fluoride removal agent with aluminum salt as the main ingredient is used, the aluminum salt will release aluminum ions in the water, and then undergo hydrolysis to produce Al(OH)3 colloid with fluoride removal activity. Under the coagulant effect of polyacrylamide, fluoride ions are removed through various effects such as static electricity, complexation, and ion exchange.

[0004] A Chinese patent entitled "A wastewater defluoridation agent and its preparation and application method" (application number: 202211459290.7) discloses a defluoridation agent composed of aluminum salt, hydrochloric acid, polyferric sulfate, citric acid, silicate, and sodium hydroxide. The agent utilizes the synergistic effect of polyferric sulfate, aluminum flakes, and silicate to improve the defluoridation efficiency.

[0005] The Chinese patent application entitled "A defluoridation agent for acidic high-fluoride wastewater and its use method" (application number: 202310039043.X) has developed a defluoridation agent for high-fluoride wastewater. The defluoridation agent includes agent A (calcium aluminate powder, calcium chloride, ferric chloride, potassium dihydrogen phosphate, magnesium chloride, anionic polyacrylamide) and agent B (aluminum chloride hexahydrate, anionic polyacrylamide, reverse osmosis concentrated water), which can effectively solve the problems of fluoride removal efficiency and slag water separation difficulties.

[0006] However, due to the double hydrolysis characteristics of aluminum ions, when using defluoridation agents with aluminum salts as the main component, the optimal pH for defluoridation is in the range of 6.5~7.5. Therefore, if the water quality does not have a certain acid-base buffering capacity, it is necessary to continuously and accurately control the pH of the solution. In addition, the Al(OH)3 colloid generated by the hydrolysis of aluminum ions is small in size and usually needs to be used in conjunction with polyacrylamide, but this will increase the COD and ammonia nitrogen content of the water, and it still needs to be treated to meet the standards before discharge. Summary of the invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a treatment agent for acidic fluorine-containing wastewater and a method for using the same. The agent of the present invention can improve the sedimentation efficiency of fluorine-removing alum flowers, avoid the use of polyacrylamide, has a simple treatment process and low cost, and has high fluorine removal efficiency.

[0008] The technical solution adopted by the present invention to solve its technical problem is that the treatment agent for acidic fluorine-containing wastewater of the present invention includes agent A and agent B.

[0009] Agent A includes carbonate minerals and silicate minerals. Agent B is mainly aluminum salt. The mass ratio of carbonate minerals to silicate minerals in Agent A is 1~5:1. Studies have shown that the mass ratio of carbonate minerals to silicate minerals in Agent A is 1~5:1, and the effect of pH value regulation is the best. If the ratio is not within the range, it will lead to insufficient release of hydroxide ions by Agent A in water, and the effect of pH value regulation will be poor.

[0010] Preferably, the silicate mineral in agent A includes at least one of serpentine, wollastonite and olivine. The carbonate mineral includes at least one of calcite, magnesite and dolomite.

[0011] Preferably, the aluminum salt in agent B includes at least one of aluminum sulfate, aluminum chloride and aluminum nitrate.

[0012] Agent A is prepared by mixing silicate minerals with carbonate minerals after roasting and grinding and activating them.

[0013] Preferably, the calcination temperature of the silicate mineral in agent A is 300-500°C for 1-2 hours. The grinding and activation methods of the mixed carbonate minerals and silicate minerals include at least one of manual grinding, ball milling, rod milling, etc. Studies have shown that if the calcination temperature is too low or the calcination time is too short, the activation degree of the silicate minerals will be insufficient and the ability to dissolve and release hydroxide ions will be insufficient; but if the calcination temperature is too high or the calcination time is too long, the mineral phase will change, affecting its function of adjusting the pH of the solution.

[0014] The method for using the treatment agent for acidic fluoride-containing wastewater of the present invention comprises the following steps:

[0015] (1) Pretreatment: Remove suspended solids such as sand and gravel from acidic fluoride-containing wastewater through sedimentation and filtration;

[0016] (2) Adjusting pH: adding agent A to the acidic fluoride-containing wastewater pretreated in step (1) to adjust the pH of the solution to 6.5-7.5;

[0017] (3) Coagulation and sedimentation: Add agent B to the solution after pH adjustment in step (2). After the reaction, let it stand and precipitate. The supernatant is the treated acidic fluoride-containing wastewater.

[0018] Preferably, in step (2), the mass ratio of carbonate minerals to silicate minerals in agent A is 1 to 5:1. In step (3), the amount of agent B is calculated according to the Al:F molar ratio of 2 to 4:1; wherein aluminum is the aluminum element contained in the aluminum salt in agent B; and fluorine is the fluorine element in the acidic fluoride-containing wastewater. Studies have shown that excessive aluminum will lead to excessively high content of residual aluminum ions in the treated wastewater, affecting the effluent quality.

[0019] The working principle of the present invention is:

[0020] Although carbonate minerals and silicate minerals are not easily soluble in water, they both have the potential to release hydroxide, and through a slow dissolution and hydrolysis process, they can spontaneously stabilize the pH in the range of 6.5 to 7.5. Among them, carbonates release carbonate ions after dissolving in water, and the carbonate ion hydrolysis equilibrium process produces hydroxide ions, and the surface of silicates is rich in -OH, which will dissolve from the outside to the inside in water and release hydroxide at the same time. The present invention can promote the exposure of more -OH on the surface of silicate minerals and promote the amorphization of the surface of carbonate minerals by roasting silicate minerals and mixing and grinding them with carbonate minerals, thereby stimulating the potential of carbonate minerals and silicate minerals to regulate pH; in addition, after the silicate minerals and carbonate minerals are mixed and ground, the two minerals are more evenly distributed, so that the OH produced by the carbonate minerals - It can migrate more to the surface of silicate minerals, and the alkaline environment further promotes the dissolution process of silicate minerals, achieving a synergistic enhancement of pH control efficiency.

[0021] In addition, due to the OH - Therefore, the aluminum ions dissolved in aluminum salts mainly produce Al(OH)3 colloids at the solid-liquid interface, and divalent ions such as calcium and magnesium are exposed on the surfaces of both minerals. Under the induction of the strong binding ability of calcium and magnesium ions with fluoride ions, fluoride-removing alum flowers will preferentially attach to the mineral particles that are not completely dissolved, thereby significantly improving the efficiency of slag-water separation.

[0022] The beneficial effects of the present invention are:

[0023] 1. The silicate and carbonate in the agent of the present invention can spontaneously regulate the pH of the solution, and also have the ability to buffer the fluctuation of the acidity and alkalinity of the solution, which can provide the optimal solution pH environment for aluminum salt and has high fluoride removal efficiency.

[0024] 2. The agent of the present invention can make the alum flocs produced by the dissolution of aluminum salts adhere to the undissolved mineral particles, thereby increasing the sedimentation power of the alum flocs and achieving a good slag-water separation effect.

[0025] 3. Since the agent of the present invention has excellent fluorine removal performance and can improve the sedimentation power of alum flocs themselves, the use of polyacrylamide can be eliminated, thereby avoiding the secondary pollution of COD and ammonia nitrogen in the water. It is not only more environmentally friendly, but also has a simple process.

[0026] 4. Compared with polyaluminium chloride commonly used for fluoride removal, the agent used in the present invention is cheap and the cost of wastewater treatment is relatively low.

[0027] The treatment agent for acidic fluoride-containing wastewater of the present invention can effectively improve the acid-base buffering capacity of water quality, and spontaneously stabilize the pH to a range of 6.5 to 7.5, with high fluoride removal efficiency. In addition, the agent of the present invention can improve the sedimentation efficiency of fluoride removal alum flowers, avoid the use of polyacrylamide, and the treatment process is simple and low in cost. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with specific embodiments. Example 1

[0029] The treatment agent for acidic fluoride-containing wastewater in this embodiment is composed of agent A (calcite, serpentine) and agent B (aluminum chloride). Among them, agent A is prepared by mixing serpentine with calcite after roasting at 300°C for 2 hours and activating it by ball milling, and the mass ratio of calcite to serpentine is 5:1. During the use of the agent, the wastewater is first filtered by sedimentation to remove suspended solids such as sand and stone; then agent A is added to make the pH of the solution 7.5; then agent B is added to the pH-adjusted solution, and the amount of agent B is calculated according to the Al:F molar ratio of 4:1; the solution of the coagulation reaction is allowed to settle, and the supernatant is the effluent. Example 2

[0030] The treatment agent for acidic fluorine-containing wastewater in this embodiment is composed of agent A (magnesite, wollastonite) and agent B (aluminum nitrate). Among them, agent A is prepared by mixing wollastonite with magnesite after roasting at 500°C for 1 hour and activating it by rod milling, and the mass ratio of magnesite to wollastonite is 1:1. During the use of the agent, the wastewater is first filtered by sedimentation to remove suspended solids such as sand and stone; then agent A is added to make the pH of the solution 6.5; then agent B is added to the pH-adjusted solution, and the amount of agent B is calculated according to the Al:F molar ratio of 2:1; the solution of the coagulation reaction is allowed to settle, and the supernatant is the effluent. Example 3

[0031] The treatment agent for acidic fluorine-containing wastewater in this embodiment is composed of agent A (dolomite, olivine) and agent B (aluminum sulfate). Among them, agent A is prepared by mixing dolomite with olivine after roasting at 400°C for 1.5 hours and activating it by manual grinding, and the mass ratio of dolomite to olivine is 2:1. During the use of the agent, the wastewater is first filtered by sedimentation to remove suspended solids such as sand and stone; then agent A is added to make the solution pH 7; then agent B is added to the solution with adjusted pH, and the amount of agent B is calculated according to the Al:F molar ratio of 3:1; the solution of the coagulation reaction is allowed to settle, and the supernatant is the effluent. Comparative Example

[0032] Compared with Example 1, in the comparative example, the pH of the acidic fluorine-containing wastewater is adjusted to 7.5 by sodium hydroxide, and then a common defluorinating agent and flocculant on the market are added to treat the wastewater. Polyaluminium chloride is selected as the defluorinating agent and polyacrylamide is selected as the flocculant, wherein the amount of polyaluminium chloride is 1-5g / L wastewater, and the amount of polyacrylamide is equivalent to 1‰ of the mass of the wastewater. The amount of the defluorinating agent and flocculant here is equivalent to the treatment agent in Example 1.

[0033] Acidic fluoride wastewater in an industrial park was used as the experimental object. The wastewater was treated with the treatment agent and method described in the embodiment and comparative example, and then the supernatant was filtered through a 0.45 μm membrane to analyze the concentration of fluoride ions and the pH value of the treated water. The treated defluorinated water was allowed to stand and the time for slag-water separation was recorded. The results are shown in Table 1.

[0034] Table 1 Experimental results of treating fluoride-containing water using different defluorination processes

[0035] Test items Raw water Comparative Example Example 1 Example 2 Example 3 Fluoride ion concentration / mg / L 100 10 3 4.5 3.5 pH 3.5 8 7.1 6.7 6.9 Slag-water separation time / min / 15 5.5 7.5 6

[0036] It can be seen from the above table that compared with the treatment effect of the defluorination agent in the comparative example, the defluorination agent prepared by the present invention has excellent defluorination effect, the fluoride ion concentration in the water body after defluorination is significantly lower, and the alum floc sedimentation time is also shorter.

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A treatment agent for acidic fluorine-containing wastewater, characterized in that: The invention is composed of agent A and agent B; agent A is composed of carbonate minerals and silicate minerals; agent B is aluminum salt; the mass ratio of carbonate minerals to silicate minerals in agent A is 1-5:1; the silicate minerals in agent A include at least one of serpentine, wollastonite and olivine; agent A is prepared by mixing silicate minerals with carbonate minerals after roasting, and grinding and activating them; the roasting temperature of the silicate minerals in agent A is 300-500°C, and the time is 1-2h.

2. The treatment agent for acidic fluorine-containing wastewater according to claim 1, characterized in that: The carbonate mineral includes at least one of calcite, magnesite and dolomite.

3. The treatment agent for acidic fluorine-containing wastewater according to claim 1 or 2, characterized in that: The aluminum salt in agent B includes at least one of aluminum sulfate, aluminum chloride, and aluminum nitrate.

4. The treatment agent for acidic fluorine-containing wastewater according to claim 1 or 2, characterized in that: The method of grinding and activating the carbonate minerals and silicate minerals after mixing includes at least one of manual grinding, ball milling and rod milling.

5. The method for using the treatment agent for acidic fluorine-containing wastewater according to any one of claims 1 to 4, characterized in that: The following steps are included: (1) Pretreatment: Remove suspended solids from acidic fluoride-containing wastewater through sedimentation and filtration; (2) Adjusting pH: adding agent A to the acidic fluoride-containing wastewater pretreated in step (1) to adjust the pH of the solution to 6.5-7.5; (3) Coagulation and sedimentation: Add agent B to the solution after pH adjustment in step (2). After the reaction, let it stand and precipitate. The supernatant is the treated acidic fluoride-containing wastewater.

6. The method for using the treatment agent for acidic fluorine-containing wastewater according to claim 5, characterized in that: In step (3), the amount of agent B is calculated according to an Al:F molar ratio of 2 to 4:1; wherein aluminum is the aluminum element contained in the aluminum salt in agent B; and fluorine is the fluorine element in the acidic fluorine-containing wastewater.