A method for removing fluoride ions from wastewater

Abstract

The present invention discloses a method for removing fluoride ions from wastewater, which comprises the following steps: Step 1: Based on 100% of the total volume of the stirring barrel, 30-50% of white sand is added, then fluoride-containing wastewater is added, first stirring is performed, then sodium aluminate solution is added, the pH of the mixed solution is adjusted to >11, stirring, and stratification is performed to obtain the first mixed solution on the upper layer; Step 2: Based on 100% of the total volume of the stirring barrel, 30-50% of white sand is added, then the first mixed solution is added, stirring, sulfuric acid is added to adjust the pH value to 6.5-7.5, stratification is performed to obtain the second mixed solution on the upper layer; Step 3: The second mixed solution is added to a stirrer, then expanded graphite is added, a mixed gas of oxygen, carbon dioxide and argon is introduced, mechanical stirring is performed at a speed of 200-300r / min, ultrasonic oscillation is performed at the same time, then yttrium hydroxide and ferric chloride are added, the reaction is performed for 5-8h, stratification is performed, and wastewater after fluoride ions are removed is obtained. The method provided by the present invention does not produce excess precipitates, and reduces processing costs.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a method for removing fluoride ions in wastewater. Background Art

[0002] Fluorine is one of the essential trace elements for the human body. The appropriate fluorine concentration in drinking water is 0.5-1 mg / L. When the fluorine content in drinking water is insufficient, it is easy to suffer from dental caries; but if you drink water with a fluorine concentration higher than 1 mg / L for a long time, it will cause dental fluorosis; long-term drinking of water with a fluorine concentration of 3-6 mg / L will cause fluorosis. In industry, wastewater discharged from fluorine-containing ore mining, metal smelting, aluminum processing, coke, glass and ceramic manufacturing, semiconductors, electroplating, fertilizers, pesticides and other industries often contains high concentrations of fluoride, causing environmental pollution. Therefore, how to remove fluoride ions in water and reduce fluorine pollution is one of the problems that must be solved by fluorine-related industries.

[0003] There are many methods for treating fluoride-containing wastewater in the prior art. At present, the most widely used treatment processes in engineering are chemical precipitation, flocculation precipitation, adsorption, etc. Among them, the most commonly used is the traditional lime precipitation process, that is, by adding Ca(OH)2 or a mixture of Ca(OH)2 and CaCl2 to produce CaF2 precipitation that is insoluble in water, and then forming fluoride precipitation and separating the solid precipitate to remove fluoride. The disadvantage of this process is that the generated CaF2 precipitation will be wrapped on the surface of Ca(OH)2 particles, which reduces the utilization efficiency of calcium salts, the rate of precipitation formation is slow, and the sedimentation characteristics of the precipitation are poor. At this time, if excessive lime is further added, the corresponding chemical agent cost will increase, and the calcium concentration, pH value and sludge volume in the effluent will also increase; and the removal of fluoride ions is not thorough, and it cannot meet environmental protection standards. It is usually only applicable to the defluorination of wastewater with a fluoride concentration of more than 20 mg / L, and there is a fluoride treatment limit. Moreover, the calcium chloride decomposed after adding quicklime has a great impact on the biochemical system (bacteria), the salt content is too high, and the sludge in the front-end system increases. This is unacceptable to many sewage treatment plants and the treatment cost is also very high.

[0004] In summary, after extensive searching by the applicant, it is found that at least one of the current methods for removing fluoride ions from wastewater in this field produces excess precipitates, increases treatment costs, and the fluoride ion concentration limit after treatment is not low enough, and cannot simultaneously treat high-concentration fluoride-containing wastewater and low-concentration fluoride-containing wastewater. Therefore, it is necessary to develop or improve a method for removing fluoride ions from wastewater. Summary of the invention

[0005] Based on this, in order to solve the problem that the current method for removing fluoride ions from wastewater produces excess sediment, increases treatment costs, and the fluoride ion concentration limit after treatment is not low enough, and high-concentration fluoride-containing wastewater and low-concentration fluoride-containing wastewater cannot be treated at the same time, the present invention provides a method for removing fluoride ions from wastewater, and the specific technical scheme is as follows:

[0006] A method for removing fluoride ions in wastewater, comprising the following steps:

[0007] Step 1: Based on 100% of the total volume of the mixing barrel, add 30-50% of white sand, then add fluorine-containing wastewater, perform a first stirring at a speed of >50 r / min, then add sodium aluminate solution, adjust the first pH of the mixed solution to >11, perform a second stirring at a speed of >50 r / min, and stand for stratification to obtain a first mixed solution in the upper layer;

[0008] Step 2: Based on 100% of the total volume of the mixing barrel, add 30-50% of white sand, then add the first mixed solution, perform a third stirring at a speed of >50 r / min, then add sulfuric acid to adjust the second pH value to 6.5-7.5, stand for stratification, and obtain a second mixed solution on the upper layer;

[0009] Step 3: Add the second mixed liquid into a stirrer, then add expanded graphite, introduce a mixed gas of oxygen, carbon dioxide and argon, mechanically stir at a speed of 200 to 300 r / min, and ultrasonically oscillate at the same time, then add yttrium hydroxide and ferric chloride, react for 5 to 8 hours, stand and separate, and obtain wastewater after removing fluoride ions.

[0010] Furthermore, the frequency of the ultrasonic oscillation is 25-35 KHz.

[0011] Furthermore, the first stirring speed is 60-80 r / min;

[0012] The first stirring time is 5 to 8 hours.

[0013] Furthermore, the second stirring speed is 70-90 r / min;

[0014] The second stirring time is 3 to 10 minutes.

[0015] Furthermore, the speed of the third stirring is 55-75 r / min;

[0016] The third stirring time is 5 to 8 hours.

[0017] Furthermore, the pH value of the fluorine-containing wastewater is 1 to 6;

[0018] The concentration of fluoride ions in the fluoride-containing wastewater is 1 to 2000 mg / L.

[0019] Furthermore, the expansion ratio of the expanded graphite is 220-230 mm / g.

[0020] Furthermore, the volume ratio of oxygen, carbon dioxide and argon in the mixed gas is 1:5-7:8-10.

[0021] Furthermore, the mass ratio of the yttrium hydroxide to the ferric chloride is 1:7-9.

[0022] Further, the first pH value is 11.2 to 14.0;

[0023] The second pH value is 6.8-7.2.

[0024] The method for removing fluoride ions from wastewater provided by the above technical solution uses white sand in step one and step two, and uses expanded graphite, yttrium hydroxide and ferric chloride in step three, and is supplemented by mechanical stirring and ultrasonic oscillation at the same time, and a mixed gas of oxygen, carbon dioxide and argon is introduced at the same time, which can remove fluoride-containing wastewater with a large concentration span, that is, it can simultaneously treat high-concentration fluoride-containing wastewater and low-concentration fluoride-containing wastewater. The specific embodiment shows that from 102.32 to 1652.97 mg / L, no excess precipitate will be generated, no additional large processing cost will be increased, and the fluoride ion concentration limit after treatment is low, specifically as low as 1.01 mg / L. The method for removing fluoride ions from wastewater provided by the technical solution has a stable fluoride ion removal rate of more than 99%. DETAILED DESCRIPTION

[0025] 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 its embodiments. It should be understood that the specific implementation methods described herein are only used to explain the present invention and do not limit the protection scope of the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0027] A method for removing fluoride ions from wastewater in one embodiment of the present invention comprises the following steps:

[0028] Step 1: Based on 100% of the total volume of the mixing barrel, add 30-50% of white sand, then add fluorine-containing wastewater, perform a first stirring at a speed of >50 r / min, then add sodium aluminate solution, adjust the first pH of the mixed solution to >11, perform a second stirring at a speed of >50 r / min, and stand for stratification to obtain a first mixed solution in the upper layer;

[0029] Step 2: Based on 100% of the total volume of the mixing barrel, add 30-50% of white sand, then add the first mixed solution, perform a third stirring at a speed of >50 r / min, then add sulfuric acid to adjust the second pH value to 6.5-7.5, stand for stratification, and obtain a second mixed solution on the upper layer;

[0030] Step 3: Add the second mixed liquid into a stirrer, then add expanded graphite, introduce a mixed gas of oxygen, carbon dioxide and argon, mechanically stir at a speed of 200 to 300 r / min, and ultrasonically oscillate at the same time, then add yttrium hydroxide and ferric chloride, react for 5 to 8 hours, stand and separate, and obtain wastewater after removing fluoride ions.

[0031] Preferably, based on 100% of the total volume of the stirring barrel, 35-45% of white sand is added, and then fluorine-containing wastewater is added, and a first stirring is performed at a speed of >50 r / min, and then a sodium aluminate solution is added, and a first pH of the mixed solution is adjusted to >11, and a second stirring is performed at a speed of >50 r / min, and the mixture is allowed to stand for stratification to obtain a first mixed solution in an upper layer;

[0032] Step 2: Based on 100% of the total volume of the mixing barrel, add 35-45% of white sand, then add the first mixed solution, perform a third stirring at a speed of >50 r / min, then add sulfuric acid to adjust the second pH value to 6.5-7.5, stand for stratification, and obtain a second mixed solution on the upper layer;

[0033] Step 3: Add the second mixed liquid into a stirrer, then add expanded graphite, introduce a mixed gas of oxygen, carbon dioxide and argon, mechanically stir at a speed of 200 to 300 r / min, and ultrasonically oscillate at the same time, then add yttrium hydroxide and ferric chloride, react for 5 to 8 hours, stand and separate, and obtain wastewater after removing fluoride ions.

[0034] Further preferably, based on 100% of the total volume of the stirring barrel, 40% of white sand is added, and then fluorine-containing wastewater is added, and a first stirring is performed at a speed of >50 r / min, and then a sodium aluminate solution is added, and the first pH of the mixed solution is adjusted to >11, and a second stirring is performed at a speed of >50 r / min, and the mixture is allowed to stand for stratification to obtain a first mixed solution in an upper layer;

[0035] Step 2: Based on 100% of the total volume of the mixing barrel, add 40% of white sand, then add the first mixed solution, perform a third stirring at a speed of >50 r / min, then add sulfuric acid to adjust the second pH value to 6.5-7.5, stand for stratification, and obtain a second mixed solution on the upper layer;

[0036] Step 3: Add the second mixed liquid into a stirrer, then add expanded graphite, introduce a mixed gas of oxygen, carbon dioxide and argon, mechanically stir at a speed of 200 to 300 r / min, and ultrasonically oscillate at the same time, then add yttrium hydroxide and ferric chloride, react for 5 to 8 hours, stand and separate, and obtain wastewater after removing fluoride ions.

[0037] In one embodiment, the frequency of the ultrasonic oscillation is 25 to 35 KHz. Preferably, the frequency of the ultrasonic oscillation is 25 to 33 KHz. Further preferably, the frequency of the ultrasonic oscillation is 28 to 33 KHz.

[0038] In one embodiment, the first stirring speed is 60-80 r / min;

[0039] The first stirring time is 5 to 8 hours.

[0040] Preferably, the first stirring speed is 65-75 r / min;

[0041] The first stirring time is 5 to 8 hours.

[0042] Further preferably, the first stirring speed is 70r / min;

[0043] The first stirring time is 5 to 8 hours.

[0044] In one embodiment, the second stirring speed is 70-90 r / min;

[0045] The second stirring time is 3 to 10 minutes.

[0046] Preferably, the second stirring speed is 75-85 r / min;

[0047] The second stirring time is 3 to 10 minutes.

[0048] Further preferably, the second stirring speed is 80r / min;

[0049] The second stirring time is 3 to 10 minutes.

[0050] In one embodiment, the speed of the third stirring is 55-75 r / min;

[0051] The third stirring time is 5 to 8 hours.

[0052] Preferably, the speed of the third stirring is 60-70 r / min;

[0053] The third stirring time is 5 to 8 hours.

[0054] Further preferably, the speed of the third stirring is 65r / min;

[0055] The third stirring time is 5 to 8 hours.

[0056] In one embodiment, the pH value of the fluorine-containing wastewater is 1 to 6;

[0057] The concentration of fluoride ions in the fluoride-containing wastewater is 1 to 2000 mg / L.

[0058] Preferably, the pH value of the fluorine-containing wastewater is 1 to 5;

[0059] The concentration of fluoride ions in the fluoride-containing wastewater is 1 to 2000 mg / L.

[0060] Further preferably, the pH value of the fluorine-containing wastewater is 1.5 to 4.5;

[0061] The concentration of fluoride ions in the fluoride-containing wastewater is 1 to 2000 mg / L.

[0062] In one embodiment, the expansion ratio of the expanded graphite is 220-230 mm / g. Preferably, the expansion ratio of the expanded graphite is 222-230 mm / g. More preferably, the expansion ratio of the expanded graphite is 222-228 mm / g.

[0063] In one embodiment, the volume ratio of oxygen, carbon dioxide and argon in the mixed gas is 1:5-7:8-10. Preferably, the volume ratio of oxygen, carbon dioxide and argon in the mixed gas is 1:6:8-10. More preferably, the volume ratio of oxygen, carbon dioxide and argon in the mixed gas is 1:6:9.

[0064] In one embodiment, the mass ratio of yttrium hydroxide to ferric chloride is 1:7 to 9. Preferably, the mass ratio of yttrium hydroxide to ferric chloride is 1:8 to 9. More preferably, the mass ratio of yttrium hydroxide to ferric chloride is 1:8.

[0065] In one embodiment, the first pH value is 11.2 to 14.0;

[0066] The second pH value is 6.8-7.2.

[0067] Preferably, the first pH value is 11.2 to 13.8;

[0068] The second pH value is 6.8-7.2.

[0069] Further preferably, the first pH value is 11.2 to 13.5;

[0070] The second pH value is 6.8-7.2.

[0071] The embodiments of the present invention will be described in detail below with reference to specific examples.

[0072] Embodiment 1:

[0073] Based on 100% of the total volume of the stirring barrel, 40% of white sand was added, and then 379.41 mg / L of fluoride-containing wastewater with a pH of 3.55 was added, and stirred at a speed of 70 r / min for 6 hours, and then sodium aluminate solution was added to adjust the first pH of the mixed solution to 12.2, and stirred at a speed of 80 r / min for 5 minutes, and allowed to stand for stratification to obtain the first mixed solution on the upper layer; based on 100% of the total volume of the stirring barrel, 40% of white sand was added, and then the above-mentioned first mixed solution was added, and stirred at a speed of 65 r / min for 6 hours, Then add 98wt% sulfuric acid to adjust the second pH value to 7.10, stand and separate, obtain the second mixed solution in the upper layer, add the second mixed solution to the stirrer, then add expanded graphite with an expansion ratio of 225mm / g, pass a mixed gas of oxygen, carbon dioxide and argon with a volume ratio of 1:6:9, stir mechanically at a speed of 250r / min, and ultrasonically oscillate at a frequency of 33KHz, then add yttrium hydroxide and ferric chloride with a mass ratio of 1:8, react for 7h, stand and separate, and obtain wastewater after fluoride ion removal. The fluoride ion concentration of the wastewater after treatment is tested to be 1.21mg / L, and the removal rate is calculated to be 99.68%.

[0074] Embodiment 2:

[0075] Based on 100% of the total volume of the stirring barrel, 40% of white sand was added, and then 102.32 mg / L fluorine-containing wastewater with a pH of 3.11 was added, and stirred at a speed of 70 r / min for 6 hours, and then sodium aluminate solution was added to adjust the first pH of the mixed solution to 12.2, and stirred at a speed of 80 r / min for 5 minutes, and allowed to stand for stratification to obtain the first mixed solution on the upper layer; based on 100% of the total volume of the stirring barrel, 40% of white sand was added, and then the above-mentioned first mixed solution was added, and stirred at a speed of 65 r / min for 6 hours, Then add 98wt% sulfuric acid to adjust the second pH value to 7.10, stand and separate, obtain the second mixed solution in the upper layer, add the second mixed solution to the stirrer, then add expanded graphite with an expansion ratio of 225mm / g, pass a mixed gas of oxygen, carbon dioxide and argon with a volume ratio of 1:6:9, mechanically stir at a speed of 250r / min, and ultrasonically oscillate at a frequency of 33KHz, then add yttrium hydroxide and ferric chloride with a mass ratio of 1:8, react for 7h, stand and separate, and obtain wastewater after fluoride ion removal. The fluoride ion concentration of the wastewater after treatment is tested to be 1.01mg / L, and the removal rate is calculated to be 99.01%.

[0076] Embodiment 3:

[0077] Based on 100% of the total volume of the stirring barrel, 40% of white sand was added, and then 282.81 mg / L of fluoride-containing wastewater with a pH of 3.45 was added, and stirred at a speed of 70 r / min for 6 hours, and then sodium aluminate solution was added to adjust the first pH of the mixed solution to 12.2, and stirred at a speed of 80 r / min for 5 minutes, and allowed to stand for stratification to obtain the first mixed solution on the upper layer; based on 100% of the total volume of the stirring barrel, 40% of white sand was added, and then the above-mentioned first mixed solution was added, and stirred at a speed of 65 r / min for 6 hours, Then add 98wt% sulfuric acid to adjust the second pH value to 7.03, stand and separate to obtain the second mixed solution on the upper layer, add the second mixed solution to the stirrer, then add expanded graphite with an expansion ratio of 225mm / g, pass a mixed gas of oxygen, carbon dioxide and argon with a volume ratio of 1:6:9, mechanically stir at a speed of 250r / min, and ultrasonically oscillate at a frequency of 33KHz, then add yttrium hydroxide and ferric chloride with a mass ratio of 1:8, react for 7h, stand and separate to obtain wastewater after fluoride ions are removed. The fluoride ion concentration of the wastewater after the test treatment is 1.33mg / L, and the removal rate is calculated to be 99.53%.

[0078] Embodiment 4:

[0079] Based on 100% of the total volume of the stirring barrel, 40% of white sand was added, and then 968.96 mg / L fluorine-containing wastewater with a pH of 4.35 was added, stirred at a speed of 70 r / min for 6 hours, and then sodium aluminate solution was added to adjust the first pH of the mixed solution to 12.2, stirred at a speed of 80 r / min for 5 minutes, and allowed to stand for stratification to obtain the first mixed solution on the upper layer; based on 100% of the total volume of the stirring barrel, 40% of white sand was added, and then the above-mentioned first mixed solution was added, stirred at a speed of 65 r / min for 6 hours, and then 98wt% sulfuric acid was added to adjust the second pH value to 7.10, let stand and separate into layers to obtain the second mixed solution in the upper layer, add the second mixed solution into the stirrer, then add expanded graphite with an expansion ratio of 225 mm / g, introduce a mixed gas of oxygen, carbon dioxide and argon with a volume ratio of 1:6:9, stir mechanically at a speed of 250 r / min, and ultrasonically oscillate at a frequency of 33 kHz, then add yttrium hydroxide and ferric chloride with a mass ratio of 1:8, react for 7 hours, let stand and separate into layers to obtain wastewater after fluoride ions are removed. The fluoride ion concentration of the wastewater after treatment is tested to be 6.20 mg / L, and the removal rate is calculated to be 99.36%.

[0080] Embodiment 5:

[0081] Based on 100% of the total volume of the mixing barrel, 40% of white sand was added, and then 1652.97 mg / L of fluoride-containing wastewater with a pH of 5.12 was added, and stirred at a speed of 70 r / min for 6 hours, and then sodium aluminate solution was added to adjust the first pH of the mixed solution to 12.2, and stirred at a speed of 80 r / min for 5 minutes, and allowed to stand for stratification to obtain the first mixed solution on the upper layer; based on 100% of the total volume of the mixing barrel, 40% of white sand was added, and then the above-mentioned first mixed solution was added, and stirred at a speed of 65 r / min for 6 hours , then add 98wt% sulfuric acid to adjust the second pH value to 7.10, stand and separate, obtain the second mixed solution on the upper layer, add the second mixed solution to the stirrer, then add expanded graphite with an expansion ratio of 225mm / g, pass a mixed gas of oxygen, carbon dioxide and argon with a volume ratio of 1:6:9, stir mechanically at a speed of 250r / min, and oscillate ultrasonically at a frequency of 33KHz, then add yttrium hydroxide and ferric chloride with a mass ratio of 1:8, react for 7h, stand and separate, and obtain wastewater after fluoride ion removal. The fluoride ion concentration of the wastewater after treatment is tested to be 15.37mg / L, and the removal rate is calculated to be 99.07%.

[0082] Comparative Example 1:

[0083] The other parts are the same as Example 1, except that the white sand is replaced by yellow sand. The fluoride ion concentration of the wastewater after the test is 118.19 mg / L, and the removal rate is calculated to be 68.85%.

[0084] Comparative Example 2:

[0085] The other parts are the same as Example 1, except that the white sand is replaced with diatomaceous earth. It is found that a large amount of excess sediment is generated, which requires additional removal work and has high processing costs.

[0086] Comparative Example 3:

[0087] The other parts are the same as Example 1, except that the step "mechanical stirring at a speed of 250 r / min and ultrasonic oscillation at a frequency of 33 kHz" is replaced by "mechanical stirring at a speed of 250 r / min," and the fluoride ion concentration of the wastewater after testing is 186.48 mg / L, and the removal rate is calculated to be 50.85%.

[0088] Comparative Example 4:

[0089] The other parts are the same as Example 1, except that the step "mechanical stirring at a speed of 250 r / min and ultrasonic oscillation at a frequency of 33 kHz" is replaced by "ultrasonic oscillation at a frequency of 33 kHz", and the fluoride ion concentration of the wastewater after testing is 181.62 mg / L, and the removal rate is calculated to be 52.13%.

[0090] Comparative Example 5:

[0091] The other parts are the same as Example 1, except that yttrium hydroxide is not added. The fluoride ion concentration of the wastewater after the test is 245.78 mg / L, and the calculated removal rate is 35.22%.

[0092] Comparative Example 6:

[0093] The other parts are the same as Example 1, except that "adding yttrium hydroxide and ferric chloride in a mass ratio of 1:8" is replaced by "adding yttrium hydroxide and ferric chloride in a mass ratio of 1:20", and the fluoride ion concentration of the wastewater after testing is 193.65 mg / L, and the removal rate is calculated to be 48.96%.

[0094] Comparative Example 7:

[0095] The other parts are the same as Example 1, except that "adding yttrium hydroxide and ferric chloride in a mass ratio of 1:8" is replaced by "adding yttrium hydroxide and ferric chloride in a mass ratio of 1:1". The fluoride ion concentration of the wastewater after testing is 161.89 mg / L, and the removal rate is calculated to be 57.33%.

[0096] Comparative Example 8:

[0097] The other parts are the same as Example 1, except that the step of "introducing a mixed gas of oxygen, carbon dioxide and argon in a volume ratio of 1:6:9" is not included. The fluoride ion concentration of the wastewater after testing is 258.91 mg / L, and the removal rate is calculated to be 31.76%.

[0098] It can be seen from the data of Examples 1 to 5 and Comparative Examples 1 to 8 that the method for removing fluoride ions from wastewater provided by the present invention uses white sand in step 1 and step 2, and uses expanded graphite, yttrium hydroxide and ferric chloride in step 3, and is assisted by mechanical stirring and ultrasonic oscillation at the same time, and a mixture of oxygen, carbon dioxide and argon is introduced at the same time. It can remove fluoride-containing wastewater with a large concentration span, from 102.32 to 1652.97 mg / L, without producing excess precipitates, and without increasing additional large processing costs. The advantage of the low limit of fluoride ion concentration after treatment is specifically as low as 1.01 mg / L. The method for removing fluoride ions from wastewater provided by the technical solution has a stable fluoride ion removal rate of more than 99%. The method for removing fluoride ions from wastewater provided by the present invention is simple and easy to operate, and does not pollute the environment.

[0099] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0100] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for removing fluoride ions from wastewater, characterized in that: It includes the following steps: Step 1: Based on 100% of the total volume of the mixing barrel, add 30-50% of white sand, then add fluorine-containing wastewater, perform a first stirring at a speed of >50 r / min, then add sodium aluminate solution, adjust the first pH of the mixed solution to >11, perform a second stirring at a speed of >50 r / min, and stand for stratification to obtain a first mixed solution in the upper layer; Step 2: Based on 100% of the total volume of the mixing barrel, add 30-50% of white sand, then add the first mixed solution, perform a third stirring at a speed of >50 r / min, then add sulfuric acid to adjust the second pH value to 6.5-7.5, stand for stratification, and obtain a second mixed solution on the upper layer; Step 3: adding the second mixed liquid to a stirrer, then adding expanded graphite, introducing a mixed gas of oxygen, carbon dioxide and argon, mechanically stirring at a speed of 200 to 300 r / min, and ultrasonically oscillating at the same time, then adding yttrium hydroxide and ferric chloride, reacting for 5 to 8 hours, standing and stratifying, and obtaining wastewater after the fluoride ions are removed; The volume ratio of oxygen, carbon dioxide and argon in the mixed gas is 1:5-7:8-10; The frequency of the ultrasonic oscillation is 25 to 35 KHz; The mass ratio of the yttrium hydroxide to the ferric chloride is 1:7-9.

2. The method according to claim 1, characterized in that The first stirring speed is 60-80 r / min; The first stirring time is 5 to 8 hours.

3. The method according to claim 1, characterized in that The speed of the second stirring is 70-90 r / min; The second stirring time is 3 to 10 minutes.

4. The method according to claim 1, characterized in that: The speed of the third stirring is 55-75 r / min; The third stirring time is 5 to 8 hours.

5. The method according to claim 1, characterized in that The pH value of the fluorine-containing wastewater is 1 to 6; The concentration of fluoride ions in the fluoride-containing wastewater is 1 to 2000 mg / L.

6. The method according to claim 1, characterized in that The expansion ratio of the expanded graphite is 220-230 mm / g.

7. The method according to claim 1, characterized in that The first pH value is 11.2 to 14.0; The second pH value is 6.8-7.2.