Method for recovering fluorine-silicon resources in phosphorus-containing acidic wastewater

Abstract

The invention relates to the technical field of wastewater treatment, in particular to a method for recycling fluorine-silicon resources in phosphorus-containing acidic wastewater. According to the method, fluorine and silicon in the phosphorus-containing acidic wastewater are firstly removed from the wastewater by utilizing a coagulation coupling chemical precipitation method, and then waste residues are treated, so that fluorine and silicon resources are respectively recovered. By coupling a coagulation method with a chemical precipitation method, the removal rate of silicon in the acidic wastewater can be 80% or above, and the removal rate of fluorine can be 90% or above; and the calcium fluoride with the purity of 78% or above can be obtained by purifying the precipitate. The pH value of the treated acidic wastewater is basically unchanged, the loss rate of phosphorus is 0-10%, the treatment effect is good, the investment is low, the operation is simple, the implementation is easy, and the application range is wide.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a method for recovering fluorine and silicon resources in phosphoric acid-containing wastewater. Background Art

[0002] Fluorine exists mainly in the form of fluorite and associated phosphate rock in the natural environment. As of 2009, the world's basic fluorite reserves reached 470 million tons, and the proven recoverable reserves were 230 million tons (calculated as 100% CaF2). Currently, the fluorite resources in the United States, Japan and Western Europe, which are the main fluorite consumption areas, have been exhausted. The current situation of fluorite mines in my country is that there are few rich ores, many poor ores, and many difficult ores to be processed, while there are few easy ores to be processed. At the same time, my country's recoverable fluorite reserves are less than 1 / 10 of the world's total, but its output accounts for about 60% of the world's total output. The problem of over-exploitation is very serious.

[0003] In the production of wet phosphoric acid, the by-product phosphogypsum is generally filtered and separated by a wet slag discharge method, and then sent to the slurry tank for re-slurry; finally, it is transported to the phosphogypsum slag yard for storage through a pipeline. After static sedimentation, most of the soluble phosphorus elements, soluble fluoride ions, and soluble silicon elements mixed in the phosphogypsum dissolve in water, forming acidic wastewater containing a large amount of phosphorus, fluorine, and silicon. In the process of reuse as process water, phosphorus can be reused in the production of wet phosphoric acid, while fluorine and silicon will increase the burden of purifying wet phosphoric acid products. At the same time, continuous circulation will cause the fluorine and silicon content in the slag yard return water to continue to increase. When the solubility of calcium fluoride and calcium fluorosilicate (magnesium, potassium, etc.) is exceeded, fluoride ions will be deposited on the pipe wall in the form of pipe scale such as calcium fluoride and calcium fluorosilicate (magnesium, potassium, etc.), which will hinder fluid transportation and indirectly cause the waste of fluorine resources in phosphate resources. In the semiconductor industry, wet etching is often used in the preparation of photovoltaic materials and chips. Wet etching is a relatively simple and low-cost method that uses an etchant to react with a thin film to remove the part that needs to be etched. It can usually be used at room temperature. Fluorosilicic acid is a commonly used etchant for silicon dioxide, and phosphoric acid is a commonly used etchant for silicon nitride. The wet etching process will inevitably produce acidic wastewater containing phosphorus, fluorine and silicon in production. If it is not treated, there is a potential risk of environmental pollution; if fluorine and silicon are not recovered, there is also a waste of fluorine and silicon resources.

[0004] There are many methods for treating fluorine-containing and silicon-containing wastewater at home and abroad, such as chemical precipitation, coagulation and sedimentation, adsorption, reverse osmosis, ion exchange, electrodialysis, and electrocoagulation. As traditional water treatment methods, chemical precipitation and coagulation and sedimentation are the most common fluorine removal chemical reagents Ca(OH)2 / CaO / CaCO3, and silicon removal reagents include sodium hydroxide / sodium carbonate, aluminum sulfate, etc. Common flocculants are divided into two categories: aluminum salts and iron salts; common coagulants are polyacrylamide (PAM) and polyaluminum chloride (PAC). Through chemical reaction and coagulation and sedimentation, fluorine and silicon are separated in the form of CaF2, CaSiF6, silicate, etc. The disadvantage is that a large amount of sludge will be produced, which makes subsequent treatment more difficult. Fluorine-containing filter residues are treated as waste residues, resulting in a great waste of resources. In addition to relatively cheap adsorbents such as traditional activated carbon and molecular sieves, various new adsorbents are also being synthesized and applied. The biggest problem with the adsorption method is that it is easy to adsorb but difficult to desorb. Therefore, it is usually only suitable for the treatment of wastewater or drinking water with low fluorine and silicon content. In addition, the cost of adsorption, especially the cost of new synthetic adsorbents, may not be cost-effective for the treatment of industrial wastewater. Membrane separation technology has a wide range of applications in separation, concentration and extraction. Among the treatment of fluorine-containing and silicon-containing wastewater, the most studied are reverse osmosis and electrodialysis membrane separation. From the existing research, high energy consumption, harsh operating conditions, high membrane cost, easy pollution and other problems limit the application of this technology in high-fluorine industrial wastewater. The principle of electrodialysis is to use the selective permeability of ion exchange membranes to make anions and cations in water migrate in a directional manner under the action of an external DC electric field. Ion exchange membranes are formed by ion exchange resins, so electrodialysis is actually another application form of ion exchange resin method. Electrodialysis has many applications in seawater desalination, but its selectivity is low for the treatment of high-fluorine and silicon wastewater. As a combination of electrolysis and flocculation, the application of electrocoagulation in wastewater defluorination mainly uses aluminum or iron electrodes under the action of a DC electric field to hydrolyze the dissolved aluminum ions or iron ions in water to form hydroxides of different forms to adsorb fluorine and silicon in water. The electrocoagulation method is simple and safe to operate, but it has high energy consumption; when the fluorine concentration is high, the electrode is easily passivated and new aluminum or iron ions will be introduced.

[0005] When treating fluorine-containing wastewater, the above methods are mostly based on the perspective of meeting industrial wastewater discharge standards. Therefore, the pH value of the wastewater after treatment is generally between 7 and 9, the loss rates of phosphorus, fluorine and silicon are very high, and the recovery rate of the treated waste residue is not high. Summary of the invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a method for effectively recovering fluorine and silicon resources in phosphoric acid-containing wastewater with low cost and simple process under the premise of very small loss of phosphorus resources.

[0007] The present invention provides a method for recovering fluorine and silicon resources in phosphoric acid-containing wastewater, comprising the following steps:

[0008] A) using a coagulant to remove silicon from the acidic wastewater to obtain primary treated water and coagulation precipitate;

[0009] B) washing the coagulated precipitate to obtain a silica gel product;

[0010] Defluoridating the primary treated water with a precipitant to obtain secondary treated water and crude calcium fluoride;

[0011] C) purifying the crude calcium fluoride to obtain a calcium fluoride product.

[0012] Preferably, in step A), the acidic wastewater has a phosphorus content of more than 3000 mg / L, a fluorine content of more than 500 mg / L, a silicon content of more than 200 mg / L, and a pH value of 1-4.

[0013] Preferably, in step A), the coagulant includes one or two of polyaluminium chloride, polyaluminium sulfate, polyferric chloride, polyferric sulfate, polyacrylamide, potassium aluminium sulfate dodecahydrate, ferric sulfate, ferric chloride and ammonium ferrous sulfate;

[0014] In the acidic wastewater, the dosage of the coagulant is 0.2-5 g / L.

[0015] Preferably, in step A), the desiliconization treatment comprises:

[0016] After the coagulant and the acidic wastewater are stirred and mixed, they are allowed to settle and then the solid and liquid are separated;

[0017] The stirring and mixing temperature is 0-50°C, the speed is 100-500r / min, and the time is 5-30min;

[0018] The static sedimentation time is 10 to 30 minutes;

[0019] In the primary treated water, the silicon removal rate is above 70%.

[0020] Preferably, in step B), the cleaning agent used for washing comprises sodium hydroxide solution and / or sodium carbonate solution;

[0021] In the coagulation precipitate, the dosage of the cleaning agent is 0.1 to 10 g / g;

[0022] The washing is carried out under stirring conditions; the stirring speed is 100-500 rpm. The washing temperature is 0-50° C. and the washing time is 10-60 min.

[0023] Preferably, in step B), the precipitant comprises one or two of CaCO3, Ca(OH)2, CaO, CaCl2, calcium citrate, calcium oxalate and calcium lactate;

[0024] In the primary treated water, the dosage of the precipitant is 1-10 g / L.

[0025] Preferably, in step B), the defluorination treatment comprises:

[0026] The precipitant is stirred and mixed with the primary treated water, and after standing and settling, the solid and liquid are separated;

[0027] The stirring and mixing is performed at a speed of 100 to 500 rpm, a temperature of 0 to 50° C., and a time of 10 to 120 min;

[0028] The static sedimentation time is 0.2 to 72 hours.

[0029] Preferably, in step B), in the secondary treated water, the loss rate of phosphorus is below 5%, the total recovery rate of fluorine is above 70%, and the total removal rate of silicon is above 80%.

[0030] Preferably, in step C), the purification reagent used in the purification treatment is one or two of pure water, tap water, the secondary treated water, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, fluorosilicic acid, citric acid, lactic acid and ascorbic acid;

[0031] The usage ratio of the crude calcium fluoride to the purification reagent is 1-50 g / L.

[0032] Preferably, in step C), the purification process comprises:

[0033] The crude calcium fluoride is mixed with the purification reagent and then the solid and liquid are separated;

[0034] The stirring and mixing is performed at a rotation speed of 100 to 500 rpm and for a time of 5 to 120 minutes.

[0035] The present invention provides a method for recovering fluorine and silicon resources in phosphoric acid-containing wastewater, comprising the following steps: A) using a coagulant to remove silicon from the acidic wastewater to obtain primary treated water and a coagulated precipitate; B) washing the coagulated precipitate to obtain a silica gel product; using a precipitant to remove fluorine from the primary treated water to obtain secondary treated water and a crude calcium fluoride product; C) purifying the crude calcium fluoride product to obtain a calcium fluoride product. The present invention utilizes a coagulation-coupled chemical precipitation method to first remove fluorine and silicon from the phosphoric acid-containing wastewater, and then treats the waste residue to recover fluorine and silicon resources respectively. By coupling the coagulation method with the chemical precipitation method, the removal rate of silicon in the acidic wastewater can be above 80%, and the removal rate of fluorine can be above 90%; by purifying the precipitate, calcium fluoride with a purity of above 78% can be obtained. The pH value of the acidic wastewater treated by the present invention remains acidic, and the loss rate of phosphorus is between 0 and 10%. The treatment effect is good, the investment is small, the operation is simple, the implementation is easy, and the application range is wide. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A process flow chart for recovering fluorine and silicon resources from phosphoric acid-containing wastewater provided in one embodiment of the present invention. DETAILED DESCRIPTION

[0037] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The present invention provides a method for recovering fluorine and silicon resources in phosphoric acid-containing wastewater, comprising the following steps:

[0039] A) using a coagulant to remove silicon from the acidic wastewater to obtain primary treated water and coagulation precipitate;

[0040] B) washing the coagulated precipitate to obtain a silica gel product;

[0041] Defluoridating the primary treated water with a precipitant to obtain secondary treated water and crude calcium fluoride;

[0042] C) purifying the crude calcium fluoride to obtain a calcium fluoride product.

[0043] In step A):

[0044] The acidic wastewater is treated for silicon removal using a coagulant to obtain primary treated water and coagulated precipitate.

[0045] In certain embodiments of the present invention, the acidic wastewater comes from phosphorus chemical enterprises that produce phosphate fertilizers, phosphoric acid, phosphates, etc., or phosphate ore beneficiation enterprises, or new energy enterprises, or photovoltaic materials, chip preparation and processing enterprises. The phosphorus content in the acidic wastewater is above 3000 mg / L, the fluorine content is above 500 mg / L, the silicon content is above 200 mg / L, and the pH value is 1-4.

[0046] In certain embodiments of the present invention, the coagulant is one or two of polyaluminium chloride (PAC), polyaluminium sulfate, polyferric chloride, polyferric sulfate, polyacrylamide (PAM), potassium aluminium sulfate dodecahydrate, ferric sulfate, ferric chloride and ammonium ferrous sulfate. In the acidic wastewater, the amount of the coagulant is 0.2 to 5 g / L, such as 0.2 g / L and 4 g / L.

[0047] In certain embodiments of the present invention, the desiliconization process comprises:

[0048] The coagulant and acidic wastewater are stirred and mixed, left to settle, and then the solid and liquid are separated.

[0049] The stirring and mixing is performed at a temperature of 0 to 50° C., such as 25° C., a rotation speed of 100 to 500 r / min, such as 150 r / min, and a time of 5 to 30 min, such as 5 min. The stirring and mixing is performed in a coagulation treatment tank.

[0050] The static sedimentation time is 10 to 30 minutes. The static sedimentation is carried out in the first sedimentation tank.

[0051] The pH value of the obtained primary treated water is substantially the same as that of the acidic wastewater, and the silicon removal rate is above 70%.

[0052] The solid-liquid separation method is filtration.

[0053] In step B):

[0054] Washing the coagulated precipitate to obtain a silica gel product;

[0055] The primary treated water is subjected to defluorination treatment using a precipitant to obtain secondary treated water and crude calcium fluoride.

[0056] In certain embodiments of the present invention, the cleaning agent used in the washing includes sodium hydroxide solution and / or sodium carbonate solution. The concentration of the sodium hydroxide solution is 0.08-1 mol / L, such as 0.1 mol / L and 1 mol / L. In the coagulated precipitate, the dosage of the cleaning agent is 0.1-10 g / g, such as 0.4 g / g and 10 g / g. The washing is carried out under stirring. The stirring speed is 100-500 rpm. The temperature of the washing is 0-50°C and the time is 10-60 min.

[0057] After washing, silica gel products and washing water are obtained. The washing water is treated with lime, quicklime, etc. and then discharged.

[0058] In certain embodiments of the present invention, the precipitant is one or two of an organic calcium salt and an inorganic calcium salt; specifically one or two of CaCO3, Ca(OH)2, CaO, CaCl2, calcium citrate, calcium oxalate and calcium lactate. In the primary treated water, the dosage of the precipitant is 1 to 10 g / L, such as 5 g / L.

[0059] In certain embodiments of the present invention, the defluorination treatment comprises:

[0060] The precipitant is stirred and mixed with the primary treated water, and after being allowed to settle, the solid and liquid are separated.

[0061] The stirring and mixing is performed at a speed of 100 to 500 rpm, such as 150 r / min, a temperature of 0 to 50° C., such as 25° C., and a time of 10 to 120 min, such as 90 min. The stirring and mixing is performed in a chemical precipitation tank.

[0062] The static sedimentation time is 0.2 to 72 hours, such as 72 hours or 48 hours. The static sedimentation is carried out in the second sedimentation tank.

[0063] The solid-liquid separation method is filtration.

[0064] In step C):

[0065] The crude calcium fluoride is purified to obtain a calcium fluoride product.

[0066] In certain embodiments of the present invention, the purification agent used in the purification treatment is one or two of pure water, tap water, the secondary treated water, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, fluorosilicic acid, citric acid, lactic acid and ascorbic acid. The dosage ratio of the crude calcium fluoride to the purification agent is 1 to 50 g / L, such as 50 g / L, 10 g / L.

[0067] In certain embodiments of the present invention, the purification process comprises:

[0068] The crude calcium fluoride is stirred and mixed with the purification reagent, and then the solid and liquid are separated.

[0069] The stirring and mixing is performed at a rotation speed of 100 to 500 rpm, such as 200 r / min, and the stirring and mixing time is 5 to 120 min, such as 5 min.

[0070] After the solid-liquid separation, the method further comprises: drying.

[0071] The purity of the calcium fluoride product is above 78%.

[0072] Figure 1 A process flow chart for recovering fluorine and silicon resources from phosphoric acid-containing wastewater provided in one embodiment of the present invention.

[0073] Compared with the original acidic wastewater, the acidic wastewater treated by the present invention (i.e., secondary treated water) still has an acidic pH value, a phosphorus loss rate of less than 5%, a total fluorine removal rate of more than 90%, and a total silicon removal rate of more than 80%.

[0074] The recovery method provided by the invention has good treatment effect, low investment, simple operation, easy implementation and wide application range.

[0075] The present invention has no particular limitation on the sources of the raw materials used above, and they can be generally commercially available.

[0076] In order to further illustrate the present invention, a method for recovering fluorine and silicon resources in phosphoric acid-containing wastewater provided by the present invention is described in detail below in conjunction with embodiments, but it should not be construed as limiting the scope of protection of the present invention.

[0077] Example 1

[0078] Method for recovering fluorine and silicon resources from phosphoric acid wastewater:

[0079] 1) Take 1L of acidic wastewater with a pH value of 2.35, a fluorine content of 2202mg / L, a phosphorus content of 7810mg / L, and a silicon content of 663mg / L, add 100mL of PAM with a mass concentration of 2‰ prepared in advance (the amount of coagulant PAM in the acidic wastewater is 0.2g / L), stir and mix at room temperature (25°C) and 150r / min for 5min, let it stand for 30min, and filter to obtain primary treated water and coagulated precipitate. In the primary treated water, the fluorine content is 1781mg / L, the phosphorus content is 7125mg / L, and the silicon content is 180mg / L.

[0080] 2) Add 0.1 mol / L NaOH solution as a cleaning agent to the coagulated precipitate (in the coagulated precipitate, the amount of the cleaning agent added is 0.4 g / g) to obtain a sodium silicate solution (silica gel product) with a silicon content of 432 mg / L.

[0081] CaCl2 was added as a precipitant in the primary treated water (the dosage of the precipitant in the primary treated water was 5 g / L), stirred for 1.5 h under a mechanical stirring blade at room temperature (25°C) and a speed of 150 r / min, and then filtered after standing for 3 days to obtain secondary treated water and 4.51 g of fluorine-containing precipitate (crude calcium fluoride). The F content in the secondary treated water was 87.7 mg / L, the P content was 5818 mg / L, and the Si content was 102 mg / L. In the fluorine-containing precipitate, the mass content of CaF2 was 51.5%, and the mass content of P was 6.9%.

[0082] 3) Add 90 mL of hydrochloric acid with a mass concentration of 3% as a purification agent to the fluorine-containing precipitate (the ratio of the crude calcium fluoride to the purification agent is 50 g / L), stir at a speed of 200 r / min and for 5 min, respectively, filter, and obtain 2.83 g of precipitate. The mass content of calcium fluoride in the precipitate is 78.3%, and the filtrate (wash water) is recovered and mixed into the secondary treated water to obtain produced water, wherein the P content is 7419 g / L, the F content is 71 mg / L, the Si content is 113 mg / L, and the pH is 2.77; after calculation, the fluorine removal rate is 97%, the silicon removal rate is 83%, and the phosphorus loss rate is 5%.

[0083] Example 2

[0084] Method for recovering fluorine and silicon resources from phosphoric acid wastewater:

[0085] 1) Take 1L of acidic wastewater with a pH value of 2.35, a fluorine content of 2202mg / L, a phosphorus content of 7810mg / L, and a silicon content of 663mg / L, add 80mL of PAM with a mass concentration of 5‰ prepared in advance (in the acidic wastewater, the amount of coagulant PAM is 4g / L), stir and mix at room temperature (25°C) and 150r / min for 5min, let it stand for 30min, filter, and obtain primary treated water and coagulated precipitate. In the primary treated water, the fluorine content is 1792mg / L, the phosphorus content is 7229mg / L, and the silicon content is 304mg / L.

[0086] 2) 10 mL of 1 mol / L NaOH solution was added to the coagulated precipitate as a cleaning agent (in the coagulated precipitate, the amount of the cleaning agent added was 10 g / g) to obtain a sodium silicate solution (silica gel product) having a silicon content of 316 mg / L.

[0087] CaO was added as a precipitant in the primary treated water (the dosage of the precipitant in the primary treated water was 5 g / L), stirred for 1.5 hours under a mechanical stirring blade at room temperature (25°C) and a speed of 150 r / min, and then filtered after standing for 2 days to obtain secondary treated water and 5.53 g of fluorine-containing precipitate (crude calcium fluoride). The F content in the secondary treated water was 58 mg / L, the P content was 5397 mg / L, and the Si content was 165.4 mg / L. In the fluorine-containing precipitate, the mass content of CaF2 was 50.5%, and the mass content of P was 8.1%.

[0088] 3) Add 75 mL of hydrochloric acid with a mass concentration of 2% as a purification agent to the fluorine-containing precipitate (the ratio of the crude calcium fluoride to the purification agent is 10 g / L), stir at a speed of 200 r / min and for 5 min, respectively, filter, and obtain 3.15 g of precipitate. The mass content of calcium fluoride in the precipitate is 83.9%, and the filtrate (wash water) is recovered and mixed into the secondary treated water to obtain produced water, wherein the P content is 7130 g / L, the F content is 136 mg / L, the Si content is 130 mg / L, and the pH is 2.98; after calculation, the fluorine removal rate is 94%, the silicon removal rate is 80%, and the phosphorus loss rate is 9%.

[0089] The description of the above embodiments is only used to help understand the method of the present invention and its core idea. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features disclosed herein.

Claims

1. A method for recovering fluorine and silicon resources from phosphoric acid-containing wastewater, comprising the following steps: A) using a coagulant to remove silicon from the acidic wastewater to obtain primary treated water and coagulation precipitate; B) washing the coagulated precipitate to obtain a silica gel product; Defluoridating the primary treated water with a precipitant to obtain secondary treated water and crude calcium fluoride; C) purifying the crude calcium fluoride to obtain a calcium fluoride product.

2. The recycling method according to claim 1, characterized in that: In step A), the acidic wastewater has a phosphorus content of more than 3000 mg / L, a fluorine content of more than 500 mg / L, a silicon content of more than 200 mg / L, and a pH value of 1-4.

3. The recycling method according to claim 1, characterized in that: In step A), the coagulant includes one or two of polyaluminium chloride, polyaluminium sulfate, polyferric chloride, polyferric sulfate, polyacrylamide, potassium aluminium sulfate dodecahydrate, ferric sulfate, ferric chloride and ammonium ferrous sulfate; In the acidic wastewater, the dosage of the coagulant is 0.2-5 g / L.

4. The recycling method according to claim 1, characterized in that: In step A), the desiliconization treatment comprises: After the coagulant and the acidic wastewater are stirred and mixed, they are allowed to settle and then the solid and liquid are separated; The stirring and mixing temperature is 0-50°C, the speed is 100-500r / min, and the time is 5-30min; The static sedimentation time is 10 to 30 minutes; In the primary treated water, the silicon removal rate is above 70%.

5. The recycling method according to claim 1, characterized in that: In step B), the cleaning agent used for washing includes sodium hydroxide solution and / or sodium carbonate solution; In the coagulation precipitate, the dosage of the cleaning agent is 0.1 to 10 g / g; The washing is carried out under stirring conditions; the stirring speed is 100-500 rpm; the washing temperature is 0-50° C., and the washing time is 10-60 min.

6. The recycling method according to claim 1, characterized in that: In step B), the precipitant includes one or two of CaCO3, Ca(OH)2, CaO, CaCl2, calcium citrate, calcium oxalate and calcium lactate; In the primary treated water, the dosage of the precipitant is 1-10 g / L.

7. The recycling method according to claim 1, characterized in that: In step B), the defluorination treatment comprises: The precipitant is stirred and mixed with the primary treated water, and after standing and settling, the solid and liquid are separated; The stirring and mixing is performed at a speed of 100 to 500 rpm, a temperature of 0 to 50° C., and a time of 10 to 120 min; The static sedimentation time is 0.2 to 72 hours.

8. The recycling method according to claim 1, characterized in that: In step B), in the secondary treated water, the loss rate of phosphorus is below 5%, the total recovery rate of fluorine is above 70%, and the total removal rate of silicon is above 80%.

9. The recycling method according to claim 1, characterized in that: In step C), the purification reagent used in the purification treatment is one or two of pure water, tap water, the secondary treated water, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, fluorosilicic acid, citric acid, lactic acid and ascorbic acid; The usage ratio of the crude calcium fluoride to the purification reagent is 1-50 g / L.

10. The recycling method according to claim 1, characterized in that: In step C), the purification process comprises: The crude calcium fluoride is mixed with the purification reagent and then the solid and liquid are separated; The stirring and mixing is performed at a rotation speed of 100 to 500 rpm and for a time of 5 to 120 minutes.

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