Seed crystal for recycling fluorine ions in fluorine-containing wastewater, preparation method of seed crystal and nucleation granulation process

Abstract

The invention relates to the technical field of wastewater treatment, in particular to a seed crystal for recycling fluorine ions in fluorine-containing wastewater, a preparation method of the seed crystal and a nucleation granulation process, the preparation method is simple, convenient and low in cost, used raw materials are pure, no other pollutants are brought in, and industrial production is facilitated; the prepared seed crystal can strengthen fluorine ion recovery in practical application, so that fluorine ions in a water body selectively approach to the seed crystal to crystallize and grow into large-particle-size crystal grains, and the utilization rate of the seed crystal is increased; meanwhile, the water content of the generated granulation body is reduced, the solid-liquid separation efficiency is improved, and the obtained granulation body is high in purity and free of pollution to recycled water and has certain economic benefits.

Description

Technical Field

[0001] The present disclosure relates to the technical field of wastewater treatment, and in particular to a seed crystal for recovering fluoride ions in fluoride-containing wastewater, a preparation method thereof, and a core crystal granulation process. Background Art

[0002] Fluorine mineral products are widely used in fluorine chemical industry, metallurgy, electronics, electroplating, photovoltaic, new energy and other industries. In the process of processing and utilization, a large amount of fluorine-containing acidic wastewater will be generated, which poses a major potential hazard to the ecological environment and human health. At present, the commonly used defluorination processes for fluorine-containing acidic wastewater include adsorption, ion exchange, chemical precipitation, coagulation and sedimentation, and biological methods. Calcium salt chemical precipitation and coagulation are usually used in industry to treat fluorine-containing wastewater. Its main principle is to convert fluoride ions in wastewater into calcium fluoride crystal precipitation to form fluorine-containing sludge solid waste, so that the discharge of fluorine-containing wastewater meets the first-level standard specified in GB8978-1996 "Comprehensive Sewage Discharge Standard" (F ion content is less than 10 mg / L). However, since calcium fluoride particles are naturally slightly soluble, the high-water content sludge produced by the chemical precipitation and coagulation method must be properly treated to solve the serious problems of low consumption, complex treatment process, and waste of fluorine resources in the current landfill method and comprehensive utilization method.

[0003] In recent years, more and more studies have been conducted on the application of nuclear crystal granulation technology in fluoride-containing wastewater, and certain results have been achieved. This technology effectively reduces the amount of precipitant added and avoids the generation of high-water content sludge, while achieving efficient recovery of fluoride ions in wastewater, creating additional economic benefits for enterprises. The core of this technology lies in the research and development of special crystal seeds. Existing crystal seeds such as garnet and quartz sand have limited ability to recover fluoride resources in wastewater. The granules formed can usually only grow to about 0.8 mm, and the utilization rate of crystal seeds is low, resulting in increased water treatment costs and inconvenience in operation and management.

[0004] In summary, how to provide a fluorine-specific seed crystal that can improve the fluoride ion recovery capacity in wastewater and reduce the cost of water treatment has become a problem that needs to be solved urgently. Summary of the invention

[0005] In order to solve the above technical problems, the present disclosure provides a seed crystal for recovering fluoride ions in fluoride-containing wastewater, a preparation method thereof and a core crystal granulation process. The seed crystal preparation method is simple and not only improves the induction ability of fluoride ions, but also improves the utilization rate of the seed crystal, thereby achieving the purpose of efficient recovery of fluoride ions and reducing treatment costs.

[0006] In a first aspect, the present disclosure provides a method for preparing seed crystals for recovering fluoride ions in fluoride-containing wastewater, the method comprising the following steps:

[0007] The phosphoric acid solution is added to the calcium hydroxide solution for reaction. During the reaction, stirring is continued and the pH value is controlled. After the reaction, solid-liquid separation and drying are performed in sequence to obtain seed crystals for recovering fluoride ions in fluoride-containing wastewater.

[0008] The crystal seeds prepared in the present disclosure belong to the hexagonal crystal system, and the structure contains hydroxide ions, which partially replace the phosphate ions, and the fluoride ions are single negative ions in the aqueous solution, which can form electrostatic attraction or hydration with the calcium ions and hydroxide ions in the crystal lattice of the crystal seeds, thereby strengthening the attachment of fluoride ions to the surface of the special crystal seeds. In addition, the precise control of the lattice stripes on the surface of the crystal seeds reduces the nucleation energy barrier of fluoride ions in fluoride-containing wastewater, strengthens the mass transfer between the crystal seeds and fluoride ions, and can realize the resource recovery and utilization of fluoride ions in high-concentration fluoride-containing wastewater, creating considerable economic benefits for enterprises and achieving the purpose of reducing costs and increasing efficiency in the treatment process of fluoride-containing wastewater.

[0009] The following are preferred technical solutions of the present disclosure, but are not intended to be limitations of the technical solutions provided by the present disclosure. Through the following technical solutions, the technical objectives and beneficial effects of the present disclosure can be better achieved and realized.

[0010] As a preferred technical solution of the present disclosure, the concentration of the phosphoric acid solution is 30-60wt%, such as 30wt%, 40wt%, 50wt% or 60wt%, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0011] As a preferred technical solution of the present disclosure, the calcium hydroxide solution is obtained by reacting calcium oxide with water;

[0012] The mass ratio of calcium oxide to water is (30-60):1, such as 30:1, 40:1, 50:1 or 60:1, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0013] In the present disclosure, appropriate raw material concentration helps to ensure the quality and performance of the obtained seed crystals.

[0014] As a preferred technical solution of the present disclosure, the phosphoric acid solution is added dropwise to the calcium hydroxide solution at a speed of 3-5 seconds / drop, for example, 3 seconds / drop, 4 seconds / drop or 5 seconds / drop, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0015] In the disclosed seeds, the dropping speed should not be too fast, otherwise it will lead to excessively high concentration in the local area, uneven reaction, and failure to obtain high-quality seed crystals.

[0016] As a preferred technical solution of the present disclosure, during the reaction, the pH is controlled to be 6-10, such as 6, 7, 8, 9 or 10, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0017] As a preferred technical solution of the present disclosure, the reaction temperature is 45-60°C, such as 45°C, 50°C, 55°C or 60°C, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0018] Preferably, the reaction time is 150-250 min, such as 150 min, 180 min, 200 min, 220 min or 250 min, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0019] As a preferred technical solution of the present disclosure, after the solid-liquid separation, the molar ratio of Ca to P in the obtained solid is (1-5):1, for example 1:1, 2:1, 3:1, 4:1 or 5:1, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0020] In the present disclosure, a reasonable molar ratio of Ca to P in the obtained solid is beneficial to improving the performance of the seed crystal. If the Ca content is too high, the lattice structure of the synthesized seed crystal will collapse, increasing the nucleation resistance; if the P content is too high, while causing lattice structure defects, a large amount of P will be released into the water body, causing secondary water pollution.

[0021] As a preferred technical solution of the present disclosure, the drying temperature is 100-110°C, for example, 100°C, 102°C, 104°C, 106°C, 108°C or 110°C, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0022] Preferably, the drying is followed by crushing.

[0023] Preferably, after the crushing, the average particle size of the seed crystals used to recover fluoride ions in fluoride-containing wastewater is 0.25-0.36 mm, such as 0.25 mm, 0.30 mm, 0.32 mm or 0.36 mm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0024] In a second aspect, the present disclosure provides a seed crystal for recovering fluoride ions in fluoride-containing wastewater as described in the first aspect.

[0025] In a third aspect, the present disclosure provides a core crystal granulation process, wherein the core crystal granulation process is carried out using the seed crystals for recovering fluoride ions in fluoride-containing wastewater prepared by the preparation method described in the first aspect or using the seed crystals for recovering fluoride ions in fluoride-containing wastewater described in the second aspect;

[0026] The core crystal granulation process comprises:

[0027] (1) filling the seed crystals for recovering fluoride ions from fluoride-containing wastewater into a nuclear crystal granulation reactor;

[0028] (2) Fluorine-containing wastewater and a crystal-inducing agent are introduced from the lower part of the nuclear crystal granulation reactor to make the seed crystals fluidized and react, and the regenerated water obtained after the reaction flows out from the upper part of the nuclear crystal granulation reactor; the granulated body obtained after the reaction is discharged from the bottom of the nuclear crystal granulation reactor.

[0029] In the core crystal granulation process, fluorine-containing wastewater is introduced into the core crystal granulation reactor to make the fluorine seed crystals in a fluidized state, and the fluorine ions in the water body reach supersaturation under the induction of the seed crystals and the driving of the crystal inducing agent, thereby forming local supersaturation within the confinement of the seed crystal surface, so that the fluorine ions nucleate and grow on the surface of the fluorine-specific seed crystal in the form of calcium fluoride, thereby obtaining granules with low water content and large particle size while purifying the fluorine-containing wastewater.

[0030] As a preferred technical solution of the present invention, the filling height of the seed crystals for recovering fluoride ions in fluoride-containing wastewater in step (1) is 15-25% of the height of the nuclear crystal granulation reactor, for example, 15%, 18%, 20%, 23% or 25%, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0031] As a preferred technical solution of the present invention, the concentration of fluoride ions in the fluoride-containing wastewater in step (2) does not exceed 4000 mg / L, for example 500 mg / L, 800 mg / L, 1000 mg / L, 1500 mg / L, 2000 mg / L, 2500 mg / L, 3000 mg / L, 3500 mg / L or 4000 mg / L, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0032] As a preferred technical solution of the present disclosure, the pH of the fluorine-containing wastewater in step (2) is adjusted by a pH regulator before it is introduced into the nucleus crystal granulation reactor.

[0033] As a preferred technical solution of the present disclosure, the pH adjuster includes sodium hydroxide solution and / or hydrochloric acid.

[0034] Preferably, the pH of the fluorine-containing wastewater is adjusted to 6-8, such as 6, 6.5, 7 or 8, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0035] Preferably, the hourly flow rate of the wastewater to be treated is 10-20 times the volume of the nuclear crystal granulation reactor, for example 10 times, 12 times, 14 times, 16 times, 18 times or 20 times, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0036] Preferably, the crystal inducing agent comprises a calcium chloride solution.

[0037] Preferably, the concentration of the calcium chloride solution is 3000-10000 mg / L, for example 3000 mg / L, 4000 mg / L, 5000 mg / L, 6000 mg / L, 7000 mg / L, 8000 mg / L, 9000 mg / L or 10000 mg / L, but is not limited to the listed values, and other unlisted values ​​within the range are equally applicable.

[0038] Preferably, the flow rate of the inducing agent is 10-20% of the flow rate of the wastewater to be treated, such as 10%, 22%, 14%, 16%, 18% or 20%, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0039] Preferably, the particle size of the granules is 2-3 mm, for example, 2 mm, 2.2 mm, 2.4 mm, 2.6 mm, 2.8 mm or 3 mm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0040] In the present disclosure, the granules generated by the seed crystals in the actual application process have low water content, so that the solid-liquid separation efficiency is high. At the same time, the obtained granules have high purity, no pollution to recycled water, and have certain economic value.

[0041] Compared with the prior art, the technical solution provided by the embodiments of the present disclosure has the following advantages:

[0042] (1) The preparation method of the seed crystal for recovering fluoride ions in fluoride-containing wastewater provided in the present disclosure is simple, convenient, low-cost, uses pure raw materials, and does not contain other pollutants, which is conducive to industrial production.

[0043] (2) The crystal seeds prepared in the present invention can enhance the recovery of fluoride ions in practical applications, so that the fluoride ions in the water body selectively adhere to the crystal seeds and grow into large-size grains, greatly improving the utilization rate of the crystal seeds; at the same time, the water content of the generated granules is reduced, the solid-liquid separation efficiency is improved, and the obtained granules have a high purity, do not pollute the recycled water, and have certain economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0046] Figure 1 This is a Raman spectrum of the seed crystals used to recover fluoride ions from fluoride-containing wastewater as described in Example 1 of the present disclosure;

[0047] Figure 2 This is an XRD diagram of the seed crystal for recovering fluoride ions from fluoride-containing wastewater as described in Example 1 of the present disclosure;

[0048] Figure 3 This is a Raman spectrum of the seed crystals used to recover fluoride ions from fluoride-containing wastewater as described in Example 3 of the present disclosure;

[0049] Figure 4 This is the XRD diagram of the seed crystals used to recover fluoride ions from fluoride-containing wastewater as described in Example 3 of the present disclosure. DETAILED DESCRIPTION

[0050] In order to more clearly understand the above-mentioned objectives, features and advantages of the present disclosure, the scheme of the present disclosure will be further described below. It should be noted that the embodiments of the present disclosure and the features in the embodiments can be combined with each other without conflict.

[0051] In the following description, many specific details are set forth to facilitate a full understanding of the present disclosure, but the present disclosure may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present disclosure, rather than all of the embodiments.

[0052] Example 1

[0053] This embodiment provides a method for preparing seed crystals and a core crystal granulation process for recovering fluoride ions in fluoride-containing wastewater. The preparation method comprises:

[0054] (1) Add 100 mL of deionized water to a four-necked flask, weigh calcium oxide, add it to the four-necked flask, control the mass ratio of calcium oxide to water to be 30:1, stir for 15 minutes, and obtain a calcium hydroxide solution;

[0055] (2) adding a 30 wt % phosphoric acid solution to the calcium hydroxide solution obtained in step (1) at a rate of 3 seconds per drop, stirring while dropping, and controlling the pH value of the reaction system to be 6, the reaction temperature to be 45° C., and the reaction time to be 120 min; then performing solid-liquid separation, and obtaining a molar ratio of Ca to P in the solid to be 1:1; then washing with deionized water, drying the washed solid at 105° C., and then crushing it into particles with an average particle size of 0.36 mm to obtain seed crystals for recovering fluoride ions in fluoride-containing wastewater.

[0056] The seed crystal obtained in this embodiment is characterized, and its Raman spectrum is as follows: Figure 1 Its XRD pattern is shown in Figure 2 As shown. Figure 1 It can be seen that at about 963cm -1 (Stretching vibration peak of PO bond), 585cm -1 (stretching vibration peak of OPO bond) and 434cm -1 There is a peak at (stretching vibration peak of OPO bond); at the same time, the peaks at 34.7°, 46.7°, 49.3° and 59.9° in the XRD graph mean that the seed crystal is successfully synthesized.

[0057] The seed crystals prepared in this embodiment are used to carry out a nucleation granulation process, including:

[0058] (1) filling the seed crystals for recovering fluoride ions from fluoride-containing wastewater into a 2 m high and 10 L volume nuclear crystal granulation reactor, the filling height being 25% of the height of the nuclear crystal granulation reactor;

[0059] (2) Fluoride-containing wastewater with a fluoride ion concentration of 800 mg / L and a pH of 7.2 is introduced from the lower part of the nuclear crystal granulation reactor at a flow rate of 100 L / h. At the same time, a calcium chloride solution with a concentration of 3000 mg / L is introduced from the lower part of the nuclear crystal granulation reactor at a flow rate of 10 L / h, so that the seed crystals are fluidized and react. The regenerated water obtained after the reaction flows out from the upper part of the nuclear crystal granulation reactor; the granulated body obtained after the reaction is discharged from the bottom of the nuclear crystal granulation reactor.

[0060] Example 2

[0061] This embodiment provides a method for preparing seed crystals and a core crystal granulation process for recovering fluoride ions in fluoride-containing wastewater. The preparation method comprises:

[0062] (3) Add 100 mL of deionized water to a four-necked flask, weigh calcium oxide, add it to the four-necked flask, control the mass ratio of calcium oxide to water to be 50:1, stir for 15 minutes, and obtain a calcium hydroxide solution;

[0063] (4) adding a 50 wt % phosphoric acid solution to the calcium hydroxide solution obtained in step (1) at a rate of 5 s / drop, stirring while dropping, and controlling the pH value of the reaction system to 8, the reaction temperature to 55° C., and the reaction time to 150 min; then performing solid-liquid separation, and obtaining a molar ratio of Ca to P in the solid to be 3:1; then washing with deionized water, drying the washed solid at 105° C., and then crushing it into particles with an average particle size of 0.25 mm to obtain seed crystals for recovering fluoride ions from fluoride-containing wastewater.

[0064] The seed crystals prepared in this embodiment are used to carry out a nucleation granulation process, including:

[0065] (1) filling the seed crystals for recovering fluoride ions from fluoride-containing wastewater into a 2 m high and 20 L volume nuclear crystal granulation reactor, the filling height being 115% of the height of the nuclear crystal granulation reactor;

[0066] (2) Fluoride-containing wastewater with a fluoride ion concentration of 2000 mg / L and a pH of 7.2 is introduced from the lower part of the nuclear crystal granulation reactor at a flow rate of 300 L / h. At the same time, a calcium chloride solution with a concentration of 7000 mg / L is introduced from the lower part of the nuclear crystal granulation reactor at a flow rate of 60 L / h, so that the seed crystals are fluidized and react. The regenerated water obtained after the reaction flows out from the upper part of the nuclear crystal granulation reactor; the granulated body obtained after the reaction is discharged from the bottom of the nuclear crystal granulation reactor.

[0067] Example 3

[0068] This embodiment provides a method for preparing seed crystals and a core crystal granulation process for recovering fluoride ions in fluoride-containing wastewater. The preparation method comprises:

[0069] (5) Add 100 mL of deionized water to a four-necked flask, weigh calcium oxide, add it to the four-necked flask, control the mass ratio of calcium oxide to water to be 60:1, stir for 15 minutes, and obtain a calcium hydroxide solution;

[0070] (6) adding a 60 wt % phosphoric acid solution to the calcium hydroxide solution obtained in step (1) at a rate of 3 seconds per drop while stirring, and controlling the pH value of the reaction system to be 10, the reaction temperature to be 60° C., and the reaction time to be 250 min; then performing solid-liquid separation, and obtaining a molar ratio of Ca to P in the solid to be 5:1; then washing with deionized water, drying the washed solid at 105° C., and then crushing it into particles with an average particle size of 0.28 mm to obtain seed crystals for recovering fluoride ions from fluoride-containing wastewater.

[0071] The seed crystal obtained in this embodiment is characterized, and its Raman spectrum is as follows: Figure 3 Its XRD pattern is shown in Figure 4 As shown. Figure 3 It can be seen that at about 963cm -1 (Stretching vibration peak of PO bond), 585cm -1 (stretching vibration peak of OPO bond) and 434cm -1 There is a peak at (stretching vibration peak of OPO bond); at the same time, the peaks at 34.7°, 46.7°, 49.3° and 59.9° in the XRD graph mean that the seed crystal is successfully synthesized.

[0072] The seed crystals prepared in this embodiment are used to carry out a nucleation granulation process, including:

[0073] (1) filling the seed crystals for recovering fluoride ions from fluoride-containing wastewater into a 2 m high and 30 L volume nuclear crystal granulation reactor, the filling height being 25% of the height of the nuclear crystal granulation reactor;

[0074] (2) Fluoride-containing wastewater with a fluoride ion concentration of 3000 mg / L and a pH of 7.2 is introduced from the lower part of the nuclear crystal granulation reactor at a flow rate of 600 L / h. At the same time, a calcium chloride solution with a concentration of 10000 mg / L is introduced from the lower part of the nuclear crystal granulation reactor at a flow rate of 90 L / h, so that the seed crystals are fluidized and react. The regenerated water obtained after the reaction flows out from the upper part of the nuclear crystal granulation reactor; the granulated body obtained after the reaction is discharged from the bottom of the nuclear crystal granulation reactor.

[0075] Example 4

[0076] This embodiment provides a method for preparing seed crystals and a core crystal granulation process for recovering fluoride ions in fluoride-containing wastewater. The preparation method refers to the preparation method in Example 1, with the only difference being that in step (2), after solid-liquid separation, the molar ratio of Ca to P in the obtained solid is 0.2:1.

[0077] Example 5

[0078] This embodiment provides a method for preparing seed crystals and a core crystal granulation process for recovering fluoride ions in fluoride-containing wastewater. The preparation method refers to the preparation method in Example 3, with the only difference being that in step (2), after solid-liquid separation, the molar ratio of Ca to P in the obtained solid is 7:1.

[0079] Comparative Example 1

[0080] This embodiment provides a seed crystal and core crystal granulation process for recovering fluoride ions in fluoride-containing wastewater. The seed crystals are quartz sand and dolomite, respectively, and the particle size is the same as that of the seed crystals described in Example 5.

[0081] The two kinds of seed crystals of this comparative example were used to replace the seed crystals described in Example 1 to carry out the nuclear crystal granulation process, and the other conditions remained unchanged.

[0082] Comparative Example 2

[0083] This embodiment provides a seed crystal and core crystal granulation process for recovering fluoride ions in fluoride-containing wastewater. The seed crystals are quartz sand and dolomite, respectively, and the particle size is the same as that of the seed crystals described in Example 5.

[0084] The two kinds of seed crystals of this comparative example were used to replace the seed crystals described in Example 2 to carry out the nuclear crystal granulation process, and the other conditions remained unchanged.

[0085] Comparative Example 3

[0086] This embodiment provides a seed crystal and core crystal granulation process for recovering fluoride ions in fluoride-containing wastewater. The seed crystals are quartz sand and dolomite, respectively, and the particle size is the same as that of the seed crystals described in Example 5.

[0087] The two types of crystal seeds of this comparative example were used to replace the crystal seeds described in Example 3 to carry out the nuclear crystal granulation process, and the other conditions remained unchanged.

[0088] Comparative Example 4

[0089] This embodiment provides a seed crystal and core crystal granulation process for recovering fluoride ions in fluoride-containing wastewater. The seed crystals are quartz sand and dolomite, respectively, and the particle size is the same as that of the seed crystals described in Example 5.

[0090] The two crystal seeds of this comparative example were used to replace the crystal seeds described in Example 4 to carry out the nuclear crystal granulation process, and the other conditions remained unchanged.

[0091] Comparative Example 5

[0092] This embodiment provides a seed crystal and core crystal granulation process for recovering fluoride ions in fluoride-containing wastewater. The seed crystals are quartz sand and dolomite, respectively, and the particle size is the same as that of the seed crystals described in Example 5.

[0093] The two crystal seeds of this comparative example were used to replace the crystal seeds described in Example 5 to carry out the nuclear crystal granulation process, and the other conditions remained unchanged.

[0094] The quartz sand and dolomite used in the above comparative examples were purchased from Green Building New Materials Technology (Wuhan) Co., Ltd.

[0095] After the core crystal granulation process was performed in the above Examples 1-5 and Comparative Examples 1-5, the removal rate of fluoride ions in the fluoride-containing wastewater, the purity, moisture content and particle size of the granules were measured. The results are shown in Table 1.

[0096] Table 1

[0097]

[0098] Compared with existing commercial seed crystals, the seed crystals prepared by the preparation method disclosed in the present invention have a fluoride ion removal rate of more than 93.4%, a granulation purity of more than 85.3%, and a granulation moisture content of less than 6.2% in actual applications; and by further controlling the preparation condition parameters, the fluoride ion removal rate is made to be more than 99.2%, the granulation purity is more than 94.7%, the granulation moisture content is less than 2.2%, and the granulation particle size is more than 2.0 mm, which effectively improves the fluoride ion recovery rate and achieves the purpose of reducing costs and increasing efficiency in the fluoride-containing wastewater treatment process.

[0099] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0100] The above description is only a specific embodiment of the present disclosure, so that those skilled in the art can understand or implement the present disclosure. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure will not be limited to the embodiments described herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing seed crystals for recovering fluoride ions from fluoride-containing wastewater, characterized in that: The preparation method comprises the following steps: The phosphoric acid solution is added to the calcium hydroxide solution for reaction. During the reaction, stirring is continued and the pH value is controlled. After the reaction, solid-liquid separation and drying are performed in sequence to obtain seed crystals for recovering fluoride ions in fluoride-containing wastewater.

2. The preparation method according to claim 1, characterized in that: The concentration of the phosphoric acid solution is 30-60 wt %.

3. The preparation method according to claim 1 or 2, characterized in that: The calcium hydroxide solution is obtained by reacting calcium oxide with water; The mass ratio of calcium oxide to water is (30-60):

1.

4. The preparation method according to any one of claims 1 to 3, characterized in that The phosphoric acid solution is added dropwise to the calcium hydroxide solution at a speed of 3-5 seconds / drop.

5. The preparation method according to any one of claims 1 to 4, characterized in that: During the reaction, the pH is controlled at 6-10.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The reaction temperature is 45-60°C; Preferably, the reaction time is 150-250 min.

7. The preparation method according to any one of claims 1 to 6, characterized in that: After the solid-liquid separation, the molar ratio of Ca to P in the obtained solid is (1-5):1; Preferably, the drying temperature is 100-110°C; Preferably, the drying is followed by crushing; Preferably, after the crushing, the average particle size of the seed crystals used to recover fluoride ions in fluoride-containing wastewater is 0.25-0.36 mm.

8. A seed crystal for recovering fluoride ions from fluoride-containing wastewater prepared by the preparation method according to any one of claims 1 to 7.

9. A nuclear crystal granulation process, characterized in that: The nuclear crystal granulation process is carried out by using the seed crystals for recovering fluoride ions from fluoride-containing wastewater prepared by the preparation method according to any one of claims 1 to 7 or by using the seed crystals for recovering fluoride ions from fluoride-containing wastewater according to claim 8; The core crystal granulation process comprises: (1) filling the seed crystals for recovering fluoride ions from fluoride-containing wastewater into a nuclear crystal granulation reactor; (2) Fluorine-containing wastewater and a crystal-inducing agent are introduced from the lower part of the nuclear crystal granulation reactor to make the seed crystals fluidized and react, and the regenerated water obtained after the reaction flows out from the upper part of the nuclear crystal granulation reactor; the granulated body obtained after the reaction is discharged from the bottom of the nuclear crystal granulation reactor.

10. The core crystal granulation process according to claim 9, characterized in that: The filling height of the seed crystals for recovering fluoride ions from fluoride-containing wastewater in step (1) is 15-25% of the height of the nuclear crystal granulation reactor; Preferably, the concentration of fluoride ions in the fluoride-containing wastewater in step (2) does not exceed 4000 mg / L; Preferably, the pH of the fluorine-containing wastewater in step (2) is adjusted by a pH regulator before it is introduced into the nucleus crystal granulation reactor; Preferably, the pH adjuster comprises sodium hydroxide solution and / or hydrochloric acid; Preferably, the pH of the fluorine-containing wastewater is adjusted to 6-8; Preferably, the hourly flow rate of the wastewater to be treated is 10-20 times the volume of the nuclear crystal granulation reactor; Preferably, the crystal inducing agent comprises a calcium chloride solution; Preferably, the concentration of the calcium chloride solution is 3000-10000 mg / L; Preferably, the flow rate of the crystal inducing agent is 10-20% of the flow rate of the wastewater to be treated; Preferably, the particle size of the granules is 2-3 mm.

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