Process for removing fluorine from chlor-alkali brine

Abstract

The application discloses a kind of defluorination process methods of chlor-alkali brine, comprising the following steps: after heating chlor-alkali brine, adjust pH, then add refining agent, stir uniformly, then add sodium carbonate solution, constant temperature treatment, adjust pH again, filter, complete defluorination.The method of the application reduces fluorine ion to below 2mg / L by refining defluorination process of high fluorine-containing industrial waste salt or waste brine, while not introducing other impurities that chlor-alkali industrial brine system cannot handle.Due to the addition of defluorination refining agent and the certain overlapping range of pH control of caustic soda and sodium carbonate refining process commonly used in chlor-alkali primary brine, it can prevent the accumulation of fluorine ion, providing a feasible method for the recycling of fluorine-containing industrial salt.The defluorination process equipment is simple, easy to operate, economical and environmentally friendly, and easy to popularize.

Description

Technical Field

[0001] This invention relates to the field of defluorination technology, specifically to a defluorination process method for chlor-alkali brine. Background Technology

[0002] Fluorine is a naturally occurring chemical element, widely distributed in soil, rocks, plants, air, and water. With the development of the industrial age, the electronics industry and fluorine-containing mining generate large amounts of toxic fluoride-containing wastewater. Examples of industries with fluoride-containing wastewater include: fluorochemical industry, semiconductor industry, aluminum profile production industry, mining and metallurgical industry, steel industry, cement industry, electrolytic aluminum industry, ceramics industry, and pharmaceutical industry.

[0003] The chlor-alkali industry is a salt chemical industry that uses sodium chloride as raw material. It has a large demand for industrial salt with relatively high quality requirements and is also the main process for large-scale utilization of industrial waste salt. However, the composition of industrial waste salt is very complex, making recycling extremely difficult. Among these factors, fluoride ions have a particularly significant impact on the electrolysis system. During electrolysis, fluoride ions exist as hydrofluoric acid in the acidic environment of the electrolytic cell. At cell temperatures of 83–85°C, they can corrode the electrode coating and the titanium substrate of the electrode mesh. Therefore, fluoride-containing industrial salts are generally not suitable for use in the chlor-alkali industry.

[0004] Most existing defluorination processes are alkaline defluorination, adsorption defluorination, and membrane separation defluorination. While these processes can remove fluorides from wastewater, they all leave behind large amounts of precipitates and adsorbents that are difficult to remove. In addition, they consume a lot of energy and are costly, making them unsuitable for defluorination in fluoride-containing industrial salts or brine used in the chlor-alkali industry. Summary of the Invention

[0005] In order to solve the above-mentioned technical problems, the purpose of this invention is to provide a defluorination process for chlor-alkali brine, so as to solve the problems that existing defluorination processes are costly and generate a large amount of difficult-to-remove precipitates and adsorbents when applied to chlor-alkali brine.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0007] A defluorination process for chlor-alkali brine includes the following steps:

[0008] After heating the chlor-alkali brine, the pH is adjusted for the first time. Then, a refining agent is added, stirred evenly, and sodium carbonate solution is added. The mixture is kept at a constant temperature, the pH is adjusted again, and then filtered to complete the defluorination process.

[0009] Furthermore, the sodium chloride mass fraction in the chlor-alkali brine is 5-30%, and the fluoride content is ≤30mg / L.

[0010] Furthermore, if the fluoride content in the chlor-alkali brine is ≥30mg / L, it can be pretreated by lime or limestone precipitation to reduce the fluoride content in the chlor-alkali brine to below 30mg / L before using the above method for defluorination.

[0011] Furthermore, the temperature of the chlor-alkali brine after heating is 55–65°C.

[0012] Further, the first pH adjustment involves adding hydrochloric acid and sodium hydroxide to adjust the pH value to 7-10.

[0013] Furthermore, the mass ratio of the refined preparation to sodium carbonate is 4-6:3-5, and the mass fraction of the sodium carbonate solution is 8-12%.

[0014] Furthermore, the refining agent includes at least one of calcium hydroxide, calcium chloride, magnesium chloride, and aluminum chloride.

[0015] Furthermore, a flocculant is added after the sodium carbonate solution is added.

[0016] Furthermore, the flocculant includes at least one of ferric sulfate, ferric chloride, and polyferric sulfate.

[0017] Furthermore, the isothermal treatment temperature is 55–65°C.

[0018] Furthermore, the pH was adjusted again to bring the pH of the system to 7.1-7.8.

[0019] Furthermore, the filtration device includes one of a plate and frame filter press, an inorganic membrane filter, and an organic membrane filter.

[0020] The present invention has the following beneficial effects:

[0021] The method of this invention reduces the fluoride ion concentration of industrial waste salt or waste brine with high fluoride content to below 2 mg / L through a refining and defluorination process. At the same time, it does not introduce other impurities that cannot be treated by the chlor-alkali industrial brine system. Since the addition of the defluorination refining agent and the pH control of the caustic soda and sodium carbonate refining process commonly used in chlor-alkali primary brine have a certain overlap range, the accumulation of fluoride ions can be prevented. This provides a feasible method for the recycling of fluoride-containing industrial salt. The defluorination process equipment is simple, easy to operate, economical and environmentally friendly, and easy to promote. Attached Figure Description

[0022] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0023] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0024] Example 1:

[0025] A defluorination process for chlor-alkali brine is shown in the process flow diagram below. Figure 1 As shown, it includes the following steps:

[0026] A 100 mL sample of fluoride-containing industrial brine that had been pretreated to remove heavy metal ions was used for the experiment. The fluoride-containing industrial brine contained 141 g / L of sodium chloride and 91 mg / L of fluoride ions.

[0027] (1) First, 0.5g of calcium oxide was added to the 100mL sample. After stirring and reacting for 1h, the precipitate was filtered. The content of fluoride ions in the sample was 21mg / L at this time.

[0028] (2) The sample treated in step (1) was heated to 60°C. The pH of the sample was adjusted to 8 using 0.1 mol / L hydrochloric acid and 0.1 mol / L sodium hydroxide solution. Then, 5 mL of 10% calcium chloride solution was added and stirred thoroughly. Next, 10% sodium carbonate solution and 10 mg of ferric chloride were added as flocculants to adjust the pH of the solution to 7.1. The reaction was continued at 60°C for 1 hour with stirring. Finally, the solution was filtered using an inorganic membrane filter to complete the fluoride removal. The fluoride content in the brine was measured to be 1.76 mg / L, with a fluoride removal rate of 91.62%.

[0029] Example 2:

[0030] A defluorination process for chlor-alkali brine includes the following steps:

[0031] A 100 mL sample of fluoride-containing industrial brine that had been pretreated to remove heavy metal ions was used for the experiment. The fluoride-containing industrial brine contained 128 g / L sodium chloride and 31 mg / L fluoride ions.

[0032] (1) First, 0.5g of calcium oxide was added to the 100mL sample. After stirring and reacting for 1h, the precipitate was filtered. The content of fluoride ions in the sample was 16mg / L at this time.

[0033] (2) The sample treated in step (1) was heated to 60°C. The pH of the sample was adjusted to 8 using 0.1 mol / L hydrochloric acid and 0.1 mol / L sodium hydroxide solution. Then, 5 mL of 10% calcium hydroxide solution was added and stirred thoroughly. Next, 10% sodium carbonate solution was added to adjust the pH to 7.5. The mixture was stirred and reacted at 60°C for 1 hour. Finally, the solution was filtered using an organic membrane filter to complete the fluoride removal. The fluoride content in the brine was measured to be 1.91 mg / L, with a fluoride removal rate of 93.84%.

[0034] Example 3:

[0035] A defluorination process for chlor-alkali brine includes the following steps:

[0036] A 100 mL sample of fluoride-containing industrial brine that had been pretreated to remove heavy metal ions was used for the experiment. The fluoride-containing industrial brine contained 126 g / L sodium chloride and 18 mg / L fluoride ions.

[0037] The sample was heated to 60°C. The pH was adjusted to 8 using 0.1 mol / L hydrochloric acid and 0.1 mol / L sodium hydroxide solution. Then, 5 mL of 10% calcium hydroxide solution was added and stirred thoroughly. Next, 10% sodium carbonate solution was added to adjust the pH to 7.8. The reaction was continued at 60°C with stirring for 1 hour. Finally, the solution was filtered using an organic membrane filter to complete the fluoride removal. The fluoride content in the brine was measured to be 1.56 mg / L, with a fluoride removal rate of 91.33%.

[0038] Comparative Example 1

[0039] A defluorination process for chlor-alkali brine includes the following steps:

[0040] A 100 mL sample of fluoride-containing industrial brine that had been pretreated to remove heavy metal ions was used for the experiment. The fluoride-containing industrial brine contained 141 g / L of sodium chloride and 91 mg / L of fluoride ions.

[0041] The sample was heated to 60°C. The pH was adjusted to 8 using 0.1 mol / L hydrochloric acid and 0.1 mol / L sodium hydroxide solution. Then, 5 mL of 10% calcium hydroxide solution was added and stirred thoroughly. Next, 10% sodium carbonate solution was added to adjust the pH to 7.5. The reaction was continued at 60°C with stirring for 1 hour. Finally, the solution was filtered using an organic membrane filter to complete the fluoride removal. The fluoride content in the brine was measured to be 15.43 mg / L, with a fluoride removal rate of 83.04%.

[0042] Comparative Example 2:

[0043] A defluorination process for chlor-alkali brine includes the following steps:

[0044] A 100 mL sample of fluoride-containing industrial brine that had been pretreated to remove heavy metal ions was used for the experiment. The fluoride-containing industrial brine contained 128 g / L sodium chloride and 31 mg / L fluoride ions.

[0045] 0.5 g of calcium oxide was added to the above-mentioned brine sample, and the pH was adjusted to 13 using sodium hydroxide solution. After stirring and reacting for 1 hour, the precipitate was filtered out, completing the defluorination process. The fluoride content in the brine at this point was measured to be 10.58 mg / L, with a fluoride removal rate of 65.87%.

[0046] Comparative Example 3:

[0047] A defluorination process for chlor-alkali brine includes the following steps:

[0048] A 100 mL sample of fluoride-containing industrial brine that had been pretreated to remove heavy metal ions was used for the experiment. The fluoride-containing industrial brine contained 126 g / L sodium chloride and 18 mg / L fluoride ions.

[0049] The above sample was adjusted to pH 6 at room temperature using 0.1 mol / L hydrochloric acid. Then, 5 mL of 10% calcium hydroxide solution was added and stirred thoroughly. Next, 10% sodium carbonate solution was added to adjust the pH to 9. The reaction was continued at room temperature with stirring for 1 hour. Finally, the solution was filtered using an organic membrane filter to complete the fluoride removal. The fluoride content in the brine was measured to be 7.68 mg / L, with a fluoride removal rate of 57.33%.

[0050] 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 principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A defluorination process for chlor-alkali brine, characterized in that, Includes the following steps: After heating the chlor-alkali brine, the pH is adjusted for the first time, then the refining agent is added, stirred evenly, and then sodium carbonate solution is added. The mixture is kept at a constant temperature, the pH is adjusted again, and then filtered to complete the defluorination process. The first pH adjustment involves adding hydrochloric acid and sodium hydroxide to adjust the pH value to 8. The mass ratio of the refined preparation to the sodium carbonate is 4-6:3-5, and the mass fraction of the sodium carbonate solution is 8-12%. The refining agent includes at least one of calcium hydroxide, calcium chloride, magnesium chloride, and aluminum chloride; The constant temperature treatment is 55~65 ℃, and the pH is adjusted again to make the pH of the system 7.1-7.

8.

2. The defluorination process for chlor-alkali brine according to claim 1, characterized in that, The sodium chloride mass fraction in the chlor-alkali brine is 5-30%, and the fluorine content is ≤30 mg / L.

3. The defluorination process for chlor-alkali brine according to claim 1, characterized in that, The temperature of the chlor-alkali brine after heating is 55~65℃.

4. The defluorination process for chlor-alkali brine according to claim 1, characterized in that, Add flocculant after adding sodium carbonate solution.

5. The defluorination process for chlor-alkali brine according to claim 4, characterized in that, The flocculant includes at least one of ferric sulfate, ferric chloride, and polyferric sulfate.

6. The defluorination process for chlor-alkali brine according to claim 1, characterized in that, The filtration device includes one of a plate and frame filter press, an inorganic membrane filter, and an organic membrane filter.

Images