Fluorine ion crystallization recovery method based on PCR (Polymerase Chain Reaction) pellet reactor

Abstract

The invention relates to the technical field of environmental engineering, in particular to a fluorine ion crystallization recovery method based on a PCR (polymerase chain reaction) pellet reactor, which comprises the following steps: (1) measuring and recording the concentration of fluorine ions in wastewater to be treated, and adding a calcium salt agent and a special seed crystal according to the concentration of the fluorine ions in the wastewater to be treated; (2) adding a calcium salt agent and a special seed crystal, uniformly stirring and mixing, and adjusting the pH value of the wastewater to 6.0-7.5; (3) controlling the reaction time to be 10-30 minutes; (4) recycling fluorine-containing pellet crystals after the wastewater treatment is completed; the invention provides a fluorine ion crystallization recovery method based on a PCR (polymerase chain reaction) pellet reactor, which comprises the following steps: adding a calcium-containing composite chemical agent and a seed crystal into fluorine-containing wastewater to induce fluorine element crystallization to form microcrystals, and crystallizing layer by layer to form a fluorite-like layer as time goes on so as to realize recovery and reutilization of fluorine resources.

Description

Technical Field

[0001] The invention relates to the technical field of environmental engineering and chemical engineering, and in particular to a fluoride ion crystal recovery method based on a PCR pellet reactor. Background Art

[0002] Fluoride-containing wastewater mainly comes from chemical manufacturing industries such as electrolytic aluminum, glass etching, and fluorine chemicals. Fluoride-containing wastewater not only has a great impact on the environment, but also can cause chronic inflammation of the upper respiratory tract, damage to bones and teeth after entering the human body. Such as dental fluorosis, skeletal fluorosis, kidney, liver and brain damage. The discharge of fluoride-containing wastewater in my country is about 1 billion tons / year. The treatment and control of fluoride-containing wastewater is crucial to protecting human health and the ecological environment. On the other hand, my country's fluorite (a natural ore with calcium fluoride as the main component) mineral reserves are insufficient, and more than 60% of fluorite ore needs to be imported. Fluorite has been listed as a national strategic resource.

[0003] Traditional chemical defluorination and de-hardening is to convert fluorine calcium plasma into chemical precipitation such as calcium fluoride with the help of chemical agents and flocculants, but the process often produces amorphous precipitation, disorderly particles, loose structure, containing a large amount of water and impurities, large volume, complex process including coagulation, precipitation, clarification process, high operating cost, difficult to achieve 1.0 emission standards, no economic value for recycling precipitation, etc. In addition, if RO membrane or resin is used for defluorination, the effect is not ideal, and clogging and stability are difficult to solve.

[0004] In response to the challenges of severe fluorine pollution and insufficient fluorite reserves, we have developed a pellet technology based on PCR (Pelletized Crystal Reactor) to solve the fluorine pollution problem. At the same time, it realizes the recovery and efficient resource utilization of high-purity calcium fluoride (artificial fluorite), and solves the problem of insufficient fluorite reserves and reliance on imports. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a fluoride ion crystallization recovery method based on a PCR pellet reactor.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A fluoride ion crystallization recovery method based on a PCR pellet reactor comprises the following steps:

[0008] (1) Measure and record the concentration of fluoride ions in the wastewater to be treated, and then add calcium salt reagents and special crystal seeds according to the concentration of fluoride ions in the wastewater to be treated;

[0009] (2) After adding calcium salt reagents and special crystal seeds, stir and mix them evenly, and then adjust the pH value of the wastewater to 6.0-7.5;

[0010] (3) The reaction time is controlled within 10-30 minutes;

[0011] (4) After the wastewater treatment is completed, the fluorine-containing pellet crystals are recovered.

[0012] As a further technical solution, the calcium salt agent is prepared by mixing calcium hydroxide, calcium chloride and calcium sulfate;

[0013] Among them, the mixing mass ratio of calcium hydroxide, calcium chloride and calcium sulfate is 3-4:100-120:15-18.

[0014] As a further technical solution, when adding materials, the molar ratio of calcium ions in the calcium salt agent to fluoride ions in the wastewater to be treated is 1:2.

[0015] As a further technical solution, the amount of special seed crystals added is 1 / 5-1 / 6 of the effective volume of the PCR pellet reactor.

[0016] As a further technical solution, the special seed crystal is made of quartz sand, tourmaline powder, dolomite powder and fluorite powder.

[0017] As a further technical solution, the mixing mass ratio of the quartz sand, tourmaline powder, dolomite powder and fluorite powder is 80:1:2:1.

[0018] As a further technical solution, the method for preparing the special seed crystal is:

[0019] Quartz sand, tourmaline powder, dolomite powder and fluorite powder are mixed with chitosan bonding solution as a binder, and then vacuum dried to obtain;

[0020] The mixing ratio of quartz sand and chitosan bonding solution is 30-35g:100mL.

[0021] As a further technical solution, the chitosan bonding solution preparation method is:

[0022] Dissolve 5 g of chitosan in 1% acetic acid solution to obtain a 5% (w / v) preliminary chitosan solution;

[0023] Weigh dopamine, prepare an alkaline aqueous solution, add dopamine to the alkaline aqueous solution, stir and mix for 20 minutes to obtain a dispersion, and keep it warm in an ice bath for later use;

[0024] The preliminary chitosan solution and the dispersion were mixed in a mass ratio of 5:1 to obtain a chitosan bonding solution.

[0025] As a further technical solution, the alkaline aqueous solution is a sodium hydroxide solution, and the pH value of the sodium hydroxide solution is 11;

[0026] The dopamine and alkaline aqueous solution are mixed in a mass ratio of 10 g:180 mL.

[0027] As a further technical solution, the vacuum drying temperature is 50° C. and the time is 20 hours.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention provides a fluoride ion crystallization recovery method based on a PCR pellet reactor, wherein calcium-containing composite chemical agents and crystal seeds are added to fluoride-containing wastewater to induce crystallization of fluorine element to form microcrystals. Based on experimental results, calcium fluoride forms fine microcrystals in the wastewater, and large particles added to the bottom of the fluidized bed through the PCR pellet technology induce crystal seeds, and the fine microcrystals are maintained in a fluidized state, promoting the adsorption of microcrystals on the surface of the crystal seeds through electrostatic interaction force and Brownian motion. As time goes by, fluorite-like layers are crystallized layer by layer to achieve the recovery and reuse of fluorine resources.

[0030] The core of the method of the present invention is to combine the chemical reaction precipitation method with the generalized nucleation-growth-aggregation theory to adjust the pH value of the wastewater, control the appropriate supersaturation, inhibit homogeneous nucleation, promote the combination of fluoride ions and calcium ions to form calcium fluoride crystals, and induce large-particle crystal seeds to accelerate their precipitation process through intermolecular interaction forces such as electrostatic interaction forces. The recovered calcium fluoride can be used as an industrial raw material, avoiding the waste and pollution of fluorine element.

[0031] The technical solution of the present invention is mainly formed by combining the chemical reaction precipitation method with the seed induction method. Among them, the chemical reaction precipitation method: adding calcium salt agents (such as calcium hydroxide, calcium chloride, calcium sulfate) to the wastewater, through chemical reaction, fluoride ions and calcium ions are combined to generate calcium fluoride microcrystals. The reaction formula is as follows:

[0032] Ca 2+ +2F-=CaF2

[0033] After the calcium fluoride microcrystals are generated by the reaction, the pH of the wastewater is controlled between 6.0-7.5, the strength of hydrogen proton ions is weakened, the reaction balance is adjusted, and the concentration of fluoride ions in the system is reduced. In addition, according to the double layer theory of colloidal systems and the thermodynamics of precipitation reactions, the potential of the fixed layer and the diffusion layer (zeta potential) will be affected by the pH value of the system. Therefore, in a room temperature water system, reducing the ionic strength can effectively reduce the zeta potential. The repulsive force between precipitates is weakened, which is conducive to the agglomeration of precipitates.

[0034] Seed induction method: By adding specially prepared seeds (such as tiny particles made of quartz sand, tourmaline powder, dolomite powder, fluorite powder, etc. as the main ingredients) into the wastewater, the nucleation and crystallization process of calcium fluoride is accelerated.

[0035] The formation of precipitation is a complex process, usually involving two key stages: nucleation and growth. In a supersaturated solution, the nucleation stage includes one-step nucleation and two-step nucleation. One-step nucleation can occur homogeneously in a pure solution without foreign particles, requiring a higher supersaturation. In addition, foreign particles can reduce the supersaturation required for nucleation. The two-step nucleation system does not directly form the most stable phase, but first forms the closest metastable phase. This metastable phase acts as a precursor and is eventually transformed into the target crystal. This occurs in the presence of existing seeds, and the process is caused by fluid shear force or contact between seeds.

[0036] However, in the industrial crystallization process, the occurrence of one-step nucleation can be effectively suppressed and the orderly growth of crystals can be promoted by finely controlling the supersaturation of the reaction in a fluidized bed and promoting the fluidization effect. Introducing an appropriate amount of seed crystals during the precipitation process can not only reduce the supersaturation and suppress one-step nucleation, but also provide more secondary nucleation sites and increase the contact area for crystal growth, thereby promoting the crystallization and growth of small particle precipitation. The entire process system needs to overcome an initial free energy barrier, and then a shallow minimum (saddle point) appears on the free energy curve. It further overcomes an energy barrier to transform into the final crystalline state, and the overall energy required is less than one-step nucleation. After the nucleus is formed, it will grow in the supersaturated solution through diffusion and surface reaction processes. These processes consist of the migration of solutes from the solution to the crystal surface and the embedding of solutes on the crystal surface.

[0037] In the PCR pellet reactor, chemical reaction precipitation method and seed induction method are used to reduce fluoride ion concentration, reduce zeta potential, promote secondary nucleation and inhibit primary nucleation, agglomeration of small particles, adsorption of small particles on seeds, adsorption and agglomeration between seeds, and finally realize the preparation of artificial fluorite and fluoride ion recovery, and finally recover artificial fluorite. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0039] Figure 1 The diagram is the mechanism of particle precipitation growth;

[0040] Figure 2 This is the relationship diagram of the Zeta (ζ) potential of the seed surface under different environmental pH. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. 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.

[0042] A fluoride ion crystallization recovery method based on a PCR pellet reactor comprises the following steps:

[0043] (1) Measure and record the concentration of fluoride ions in the wastewater to be treated, and then add calcium salt reagents and special crystal seeds according to the concentration of fluoride ions in the wastewater to be treated;

[0044] (2) After adding calcium salt reagents and special crystal seeds, stir and mix them evenly, and then adjust the pH value of the wastewater to 6.0-7.5;

[0045] (3) The reaction time is controlled within 10-30 minutes;

[0046] (4) After the wastewater treatment is completed, the fluorine-containing pellet crystals are recovered.

[0047] Calcium salt agents are made by mixing calcium hydroxide, calcium chloride, and calcium sulfate;

[0048] Among them, the mixing mass ratio of calcium hydroxide, calcium chloride and calcium sulfate is 3-4:100-120:15-18.

[0049] When adding materials, the molar ratio of calcium ions in the calcium salt agent to fluoride ions in the wastewater to be treated is 1:2.

[0050] The amount of special seed crystals added is 1 / 5-1 / 6 of the effective volume of the PCR pellet reactor.

[0051] Special seed crystals are made of quartz sand, tourmaline powder, dolomite powder and fluorite powder.

[0052] The mixing mass ratio of quartz sand, tourmaline powder, dolomite powder and fluorite powder is 80:1:2:1.

[0053] The method for preparing special seed crystals is:

[0054] Quartz sand, tourmaline powder, dolomite powder and fluorite powder are mixed with chitosan bonding solution as a binder, and then vacuum dried to obtain;

[0055] The mixing ratio of quartz sand and chitosan bonding solution is 30-35g:100mL.

[0056] The preparation method of chitosan bonding solution is as follows:

[0057] Dissolve 5 g of chitosan in 1% acetic acid solution to obtain a 5% (w / v) preliminary chitosan solution;

[0058] Weigh dopamine, prepare an alkaline aqueous solution, add dopamine to the alkaline aqueous solution, stir and mix for 20 minutes to obtain a dispersion, and keep it warm in an ice bath for later use;

[0059] The preliminary chitosan solution and the dispersion were mixed in a mass ratio of 5:1 to obtain a chitosan bonding solution.

[0060] The alkaline aqueous solution is a sodium hydroxide solution, and the pH value of the sodium hydroxide solution is 11;

[0061] The dopamine and alkaline aqueous solution are mixed in a mass ratio of 10 g:180 mL.

[0062] The vacuum drying temperature was 50°C and the time was 20 hours.

[0063] In order to further improve the treatment effect of wastewater and improve the recovery of fluoride ions, after the treatment in step (4) of the present invention, the treated wastewater is passed through a secondary PCR pellet crystallization reactor, and 1 / 5-1 / 6 of the volume of the effective volume of the reactor is added with special crystal seeds, sodium dihydrogen phosphate and calcium salt agents. The PCR pellet crystallization reaction is carried out for 20 minutes, and then the fluorine-containing pellet crystals are recovered.

[0064] The mechanism of particle precipitation growth includes the following three main modes: A. Agglomeration of small particles; B. Adsorption of small particles on seed crystals; C. Adsorption and agglomeration of seed crystals, such as Figure 1 shown.

[0065] The following are specific embodiments:

[0066] Example 1

[0067] A fluoride ion crystallization recovery method based on a PCR pellet reactor comprises the following steps:

[0068] (1) Measure and record the concentration of fluoride ions in the wastewater to be treated, and then add calcium salt reagents and special crystal seeds according to the concentration of fluoride ions in the wastewater to be treated;

[0069] (2) After adding calcium salt reagents and special crystal seeds, stir and mix them evenly, and then adjust the pH value of the wastewater to 6.0;

[0070] (3) The reaction time is controlled within 10 minutes;

[0071] (4) After the wastewater treatment is completed, the fluorine-containing pellet crystals are recovered.

[0072] Calcium salt agents are made by mixing calcium hydroxide, calcium chloride, and calcium sulfate;

[0073] Among them, the mixing mass ratio of calcium hydroxide, calcium chloride and calcium sulfate is 3:100:15.

[0074] When adding materials, the molar ratio of calcium ions in the calcium salt agent to fluoride ions in the wastewater to be treated is 1:2.

[0075] The amount of special seed crystals added is 1 / 6 of the effective volume of the PCR pellet reactor.

[0076] Special seed crystals are made of quartz sand, tourmaline powder, dolomite powder and fluorite powder.

[0077] The mixing mass ratio of quartz sand, tourmaline powder, dolomite powder and fluorite powder is 80:1:2:1.

[0078] The method for preparing special seed crystals is:

[0079] Quartz sand, tourmaline powder, dolomite powder and fluorite powder are mixed with chitosan bonding solution as a binder, and then vacuum dried to obtain;

[0080] The mixing ratio of quartz sand and chitosan bonding solution is 30g:100mL.

[0081] The preparation method of chitosan bonding solution is as follows:

[0082] Dissolve 5 g of chitosan in 1% acetic acid solution to obtain a 5% (w / v) preliminary chitosan solution;

[0083] Weigh dopamine, prepare an alkaline aqueous solution, add dopamine to the alkaline aqueous solution, stir and mix for 20 minutes to obtain a dispersion, and keep it warm in an ice bath for later use;

[0084] The preliminary chitosan solution and the dispersion were mixed in a mass ratio of 5:1 to obtain a chitosan bonding solution.

[0085] The alkaline aqueous solution is a sodium hydroxide solution, and the pH value of the sodium hydroxide solution is 11;

[0086] The dopamine and alkaline aqueous solution are mixed in a mass ratio of 10 g:180 mL.

[0087] The vacuum drying temperature was 50°C and the time was 20 hours.

[0088] Example 2

[0089] A fluoride ion crystallization recovery method based on a PCR pellet reactor comprises the following steps:

[0090] (1) Measure and record the concentration of fluoride ions in the wastewater to be treated, and then add calcium salt reagents and special crystal seeds according to the concentration of fluoride ions in the wastewater to be treated;

[0091] (2) After adding calcium salt reagents and special crystal seeds, stir and mix them evenly, and then adjust the pH value of the wastewater to 6.6;

[0092] (3) The reaction time is controlled within 15 minutes;

[0093] (4) After the wastewater treatment is completed, the fluorine-containing pellet crystals are recovered.

[0094] Calcium salt agents are made by mixing calcium hydroxide, calcium chloride, and calcium sulfate;

[0095] Among them, the mixing mass ratio of calcium hydroxide, calcium chloride and calcium sulfate is 3.2:110:16.

[0096] When adding materials, the molar ratio of calcium ions in the calcium salt agent to fluoride ions in the wastewater to be treated is 1:2.

[0097] The amount of special seed crystals added is 1 / 5 of the effective volume of the PCR pellet reactor.

[0098] Special seed crystals are made of quartz sand, tourmaline powder, dolomite powder and fluorite powder.

[0099] The mixing mass ratio of quartz sand, tourmaline powder, dolomite powder and fluorite powder is 80:1:2:1.

[0100] The method for preparing special seed crystals is:

[0101] Quartz sand, tourmaline powder, dolomite powder and fluorite powder are mixed with chitosan bonding solution as a binder, and then vacuum dried to obtain;

[0102] The mixing ratio of quartz sand and chitosan bonding solution is 35g:100mL.

[0103] The preparation method of chitosan bonding solution is as follows:

[0104] Dissolve 5 g of chitosan in 1% acetic acid solution to obtain a 5% (w / v) preliminary chitosan solution;

[0105] Weigh dopamine, prepare an alkaline aqueous solution, add dopamine to the alkaline aqueous solution, stir and mix for 20 minutes to obtain a dispersion, and keep it warm in an ice bath for later use;

[0106] The preliminary chitosan solution and the dispersion were mixed in a mass ratio of 5:1 to obtain a chitosan bonding solution.

[0107] The alkaline aqueous solution is a sodium hydroxide solution, and the pH value of the sodium hydroxide solution is 11;

[0108] The dopamine and alkaline aqueous solution are mixed in a mass ratio of 10 g:180 mL.

[0109] The vacuum drying temperature was 50°C and the time was 20 hours.

[0110] Example 3

[0111] A fluoride ion crystallization recovery method based on a PCR pellet reactor comprises the following steps:

[0112] (1) Measure and record the concentration of fluoride ions in the wastewater to be treated, and then add calcium salt reagents and special crystal seeds according to the concentration of fluoride ions in the wastewater to be treated;

[0113] (2) After adding calcium salt reagents and special seed crystals, stir and mix them evenly, and then adjust the pH value of the wastewater to 6.8;

[0114] (3) The reaction time is controlled within 20 minutes;

[0115] (4) After the wastewater treatment is completed, the fluorine-containing pellet crystals are recovered;

[0116] (5) The treated wastewater is then passed through a secondary PCR pellet crystallization reactor, and 1 / 5 of the volume of the reactor's effective volume of special seed crystals, sodium dihydrogen phosphate and calcium salt reagents are added. The PCR pellet crystallization reaction is performed for 20 minutes, and then the fluorine-containing pellet crystals are recovered;

[0117] The amount of sodium dihydrogen phosphate added is 50% of the mass of the calcium salt agent, and the molar ratio of calcium in the calcium salt agent to fluoride ions in the treated wastewater is 1:2.

[0118] Calcium salt agents are made by mixing calcium hydroxide, calcium chloride, and calcium sulfate;

[0119] Among them, the mixing mass ratio of calcium hydroxide, calcium chloride and calcium sulfate is 4:115:16.

[0120] When adding materials, the molar ratio of calcium ions in the calcium salt agent to fluoride ions in the wastewater to be treated is 1:2.

[0121] The amount of special seed crystals added is 1 / 6 of the effective volume of the PCR pellet reactor.

[0122] Special seed crystals are made of quartz sand, tourmaline powder, dolomite powder and fluorite powder.

[0123] The mixing mass ratio of quartz sand, tourmaline powder, dolomite powder and fluorite powder is 80:1:2:1.

[0124] The method for preparing special seed crystals is:

[0125] Quartz sand, tourmaline powder, dolomite powder and fluorite powder are mixed with chitosan bonding solution as a binder, and then vacuum dried to obtain;

[0126] The mixing ratio of quartz sand and chitosan bonding solution is 35g:100mL.

[0127] The preparation method of chitosan bonding solution is as follows:

[0128] Dissolve 5 g of chitosan in 1% acetic acid solution to obtain a 5% (w / v) preliminary chitosan solution;

[0129] Weigh dopamine, prepare an alkaline aqueous solution, add dopamine to the alkaline aqueous solution, stir and mix for 20 minutes to obtain a dispersion, and keep it warm in an ice bath for later use;

[0130] The preliminary chitosan solution and the dispersion were mixed in a mass ratio of 5:1 to obtain a chitosan bonding solution.

[0131] The alkaline aqueous solution is a sodium hydroxide solution, and the pH value of the sodium hydroxide solution is 11;

[0132] The dopamine and alkaline aqueous solution are mixed in a mass ratio of 10 g:180 mL.

[0133] The vacuum drying temperature was 50°C and the time was 20 hours.

[0134] Comparative Example 1: This comparative example is basically the same as Example 1, except that no calcium salt agent is added.

[0135] Comparative Example 2: This comparative example is basically the same as Example 1, except that no special seed crystals are added.

[0136] Based on Example 1, the surface Zeta potential of the seed crystals at different pH values ​​was tested.

[0137] The characterization of the Zeta (ζ) potential of the seed surface includes the following steps:

[0138] Dynamic light scattering (DLS) was used to analyze the surface zeta potential of the seed crystals under different environmental pH values. Phosphate buffer solutions of pH = 2, pH = 4, pH = 6, pH = 7, pH = 8, pH = 10, and pH = 12 were prepared respectively, 10 mg of the ground seed crystal powder was weighed, and 1 mL of phosphate buffer solutions of pH = 2, pH = 4, pH = 6, pH = 7, pH = 8, pH = 10, and pH = 12 were added respectively. After standing at room temperature for 1 day, after the suspension was stable, 750 uL of the solution was taken for detection on the machine to measure the surface zeta potential.

[0139] like Figure 2 As shown in the figure, the zeta potential on the surface of the seed crystal decreases with the increase of pH. When pH ≥ 6, the zeta potential on the surface of the seed crystal is stable at around -20 mV. The above data show that when pH ≥ 6, the zeta potential on the surface of the seed crystal is effectively reduced, indicating that pH ≥ 6 in the environment can effectively promote two-step nucleation and inhibit one-step nucleation.

[0140] Photovoltaic panel wastewater was used as a sample and treated using the example and comparative example methods respectively:

[0141] Among them, the fluoride ion concentration of photovoltaic panel wastewater is 1000mg / L, and the water volume is 5000m 3 / d, pH value is 5.0;

[0142] Detect and treat the fluoride ion concentration in the photovoltaic panel wastewater, and calculate the weight of fluoride-containing pellets recovered every day (dry weight):

[0143] Table 1

[0144]

[0145] It can be seen from Table 1 that the method of the present invention can significantly reduce the fluoride ion concentration of photovoltaic panel wastewater after treatment, and can recover more fluorine-containing pellets.

[0146] The chip wastewater was used as a sample and treated by the method of Example 3;

[0147] The fluoride ion concentration of chip wastewater is 300mg / L, and the water volume is 3000m 3 / d, pH value is 2.0, after the treatment of the previous steps (1)-(4), the fluoride ion concentration of the wastewater is 4.5 mg / L, and more than 1.9 tons of fluoride-containing pellets are recovered every day. After the treatment of step (5), the fluoride ion concentration of the wastewater after treatment is 0.5 mg / L, and more than 400 kg of fluoride-containing pellets are recovered every day.

[0148] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A fluoride ion crystallization recovery method based on a PCR pellet reactor, characterized in that: The following steps are involved: (1) measuring and recording the concentration of fluoride ions in the wastewater to be treated, and then adding calcium salt reagents and special crystal seeds according to the concentration of fluoride ions in the wastewater to be treated; (2) After adding calcium salt reagents and special crystal seeds, stir and mix them evenly, and then adjust the pH value of the wastewater to 6.0-7.5; (3) The reaction time is controlled within 10-30 minutes; (4) After the wastewater treatment is completed, the fluorine-containing pellet crystals are recovered.

2. The method for recovering fluoride ions by crystallization based on a PCR pellet reactor according to claim 1, characterized in that: The calcium salt agent is prepared by mixing calcium hydroxide, calcium chloride and calcium sulfate; Among them, the mixing mass ratio of calcium hydroxide, calcium chloride and calcium sulfate is 3-4:100-120:15-18.

3. The method for recovering fluoride ions by crystallization based on a PCR pellet reactor according to claim 2, characterized in that: When adding materials, the molar ratio of calcium ions in the calcium salt agent to fluoride ions in the wastewater to be treated is 1:

2.

4. The method for recovering fluoride ions by crystallization based on a PCR pellet reactor according to claim 1, characterized in that: The amount of special seed crystals added is 1 / 5-1 / 6 of the effective volume of the PCR pellet reactor.

5. The method for recovering fluoride ions by crystallization based on a PCR pellet reactor according to claim 4, characterized in that: The special seed crystal is made of quartz sand, tourmaline powder, dolomite powder and fluorite powder.

6. The method for recovering fluoride ions by crystallization based on a PCR pellet reactor according to claim 5, characterized in that: The mixing mass ratio of the quartz sand, tourmaline powder, dolomite powder and fluorite powder is 80:1:2:

1.

7. The method for recovering fluoride ions by crystallization based on a PCR pellet reactor according to claim 6, characterized in that: The method for preparing the special seed crystal is as follows: Quartz sand, tourmaline powder, dolomite powder and fluorite powder are mixed with chitosan bonding solution as a binder, and then vacuum dried to obtain; The mixing ratio of quartz sand and chitosan bonding solution is 30-35g:100mL.

8. The method for recovering fluoride ions by crystallization based on a PCR pellet reactor according to claim 7, characterized in that: The chitosan bonding solution preparation method is: Dissolve 5 g of chitosan in 1% acetic acid solution to obtain a 5% (w / v) preliminary chitosan solution; Weigh dopamine, prepare an alkaline aqueous solution, add dopamine to the alkaline aqueous solution, stir and mix for 20 minutes to obtain a dispersion, and keep it warm in an ice bath for later use; The preliminary chitosan solution and the dispersion were mixed in a mass ratio of 5:1 to obtain a chitosan bonding solution.

9. The method for recovering fluoride ions by crystallization based on a PCR pellet reactor according to claim 8, characterized in that: The alkaline aqueous solution is a sodium hydroxide solution, and the pH value of the sodium hydroxide solution is 11; The dopamine and alkaline aqueous solution are mixed in a mass ratio of 10 g:180 mL.

10. The method for recovering fluoride ions by crystallization based on a PCR pellet reactor according to claim 6, characterized in that: The vacuum drying temperature is 50° C. and the time is 20 hours.

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