A core crystal granulation process for calcium chloride recycling and enhanced fluorine resource recovery

Abstract

The present disclosure relates to the field of wastewater treatment technology, and in particular to a nucleation granulation process for calcium chloride recycling and enhanced fluorine resource recovery. This process uses calcium hydroxide and a small amount of calcium chloride as a crystallization inducer. Fluoride ions consume calcium ions in the calcium chloride during the process, leaving residual chloride ions in the treated wastewater. The treated wastewater is then circulated back to the wastewater. When calcium hydroxide is added again, the residual chloride ions combine with the calcium ions in the calcium hydroxide to form calcium chloride, which then reacts with fluoride ions to form calcium fluoride. This achieves the goal of calcium chloride regeneration, enhanced fluorine resource recovery, and reduced treatment costs.

Description

Technical Field

[0001] The present disclosure relates to the technical field of wastewater treatment, and in particular to a core crystal granulation process for recycling calcium chloride and enhancing fluorine resource recovery. Background Art

[0002] The amount of industrial wastewater discharged is increasing, and the amount of various pollutants discharged is also increasing. Among them, hydrofluoric acid wastewater contains a large amount of fluoride ions and acidic and alkaline organic matter, which is very harmful to the environment and human body. It needs to be pre-purified before being discharged into the pipeline network or the environment at the factory.

[0003] Existing technology typically uses chemical precipitation to treat fluorine chemical wastewater. This primarily involves physical and chemical treatment, where chemicals and fluoride ions are added to form a precipitate, which then forms a sludge. This sludge is removed in a sedimentation tank. The defluorinated supernatant enters a discharge tank, and the sludge enters a dehydration system for dehydration and drying before being outsourced. Existing purification processes are unable to completely remove fluoride ions, and a large amount of suspended solids remain in the supernatant, affecting the purified water quality. Further improvement is needed.

[0004] In recent years, research on the application of nuclear crystallization granulation technology to fluoride-containing wastewater has been increasing, with some success. This technology effectively reduces chemical dosage and avoids the production of high-water-content sludge, while also enabling efficient recovery of fluoride ions from wastewater, creating additional economic benefits for businesses. Calcium chloride and calcium hydroxide are commonly used chemicals for fluoride removal, but the high cost of calcium chloride leads to high water treatment costs and poor economic returns.

[0005] Therefore, it is of great significance to reduce the cost of adding chemical agents in treating fluoride-containing wastewater using nuclear crystal granulation technology. Summary of the Invention

[0006] In order to solve the above technical problems, the present disclosure provides a core crystal granulation process for recycling calcium chloride and enhancing fluorine resource recovery. The core crystal granulation process reduces water treatment costs by reducing the amount of calcium chloride used while ensuring the treatment effect, and has good application prospects.

[0007] The present disclosure provides a core crystal granulation process for calcium chloride recycling and enhanced fluorine resource recovery, the core crystal granulation process comprising the following steps:

[0008] Under initial working conditions:

[0009] Acidic fluorine-containing wastewater, calcium chloride, calcium hydroxide and seed crystals are mixed, and the seed crystals are placed in a fluidized state by controlling the hydraulic parameters of the water body; the seed crystals induce fluoride ions in the acidic fluorine-containing wastewater to react with calcium ions and nucleate and grow on the surface of the seed crystals in the form of calcium fluoride to form granules;

[0010] The remaining chloride ions after the reaction react with the remaining hydrogen ions in the water to form hydrochloric acid which is stored in the treated water. Part of the treated water is discharged and part is stored for subsequent reflux.

[0011] Wherein, the added molar amount of calcium chloride is 1 / 10 to 1 / 6 of the molar amount of fluoride ions in the reaction system;

[0012] The added molar amount of calcium hydroxide is 1 / 5 to 1 / 4 of the molar amount of fluoride ions in the reaction system;

[0013] When the amount of treated water to be stored reaches the set value:

[0014] The reflux ratio of the treated water is determined according to the fluoride ion concentration in the acidic fluoride-containing wastewater, and then the amount of the acidic fluoride-containing wastewater and the discharge amount of the treated water are adjusted to ensure that the calcium chloride addition ratio remains unchanged, the calcium hydroxide addition ratio is increased, and the stored treated water is controlled to flow back into the reaction system according to the determined reflux ratio; at this time, the hydrochloric acid in the reflux water reacts with the calcium hydroxide to generate calcium chloride, and the calcium ions in the obtained calcium chloride continue to react with the fluoride ions and nucleate and grow on the surface of the seed crystal in the form of calcium fluoride, thereby realizing the cyclic regeneration of calcium chloride and enhancing the recovery of fluorine resources.

[0015] This disclosure addresses the high cost of crystallization agents used in existing crystallization granulation processes for treating fluorine-containing wastewater. A crystallization granulation process that utilizes calcium chloride recycling to enhance fluorine resource recovery is designed, aiming to reduce water treatment costs by reducing the amount of calcium chloride used. This process uses a combination of calcium hydroxide and a small amount of calcium chloride as crystallization agents. Since the fluoride ions consume the calcium ions in the calcium chloride during the process, residual chloride ions remain in the treated wastewater. The treated wastewater is then circulated back to the surface. When calcium hydroxide is added again, the residual chloride ions combine with the calcium ions in the calcium hydroxide to form calcium chloride, which then reacts with the fluoride ions to form calcium fluoride. This achieves the goal of regenerating calcium chloride to enhance fluorine resource recovery and reduce treatment costs.

[0016] The specific cycle equation is as follows:

[0017] Ca(OH)2+2HF→CaF2+2H2O

[0018] Ca(Cl)2+2HF→CaF2+2HCl

[0019] 2HCl+Ca(OH)2→CaCl2+2H2O

[0020] In the present disclosure, hydraulic parameters such as flow rate can be adjusted by those skilled in the art according to relevant parameters such as seed crystal dosage and wastewater quality.

[0021] The set value of the stored treated water volume is adjusted according to the return ratio of the treated water.

[0022] The following are preferred technical solutions of the present disclosure, but are not intended to limit 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.

[0023] As a preferred technical solution of the present disclosure, before the mixing, the pH of the acidic fluorine-containing wastewater is adjusted to 4 to 5, for example, 4, 4.2, 4.4, 4.6, 4.8 or 5, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0024] Generally speaking, due to the strong initial acidity of acidic fluorine-containing wastewater, alkaline substances such as sodium hydroxide are usually used to pre-adjust its pH to avoid interaction with seed crystals, thereby causing seed crystal loss and a decrease in fluorine resource recovery efficiency.

[0025] As a preferred technical solution of the present disclosure, the seed crystals include one or more of quartz sand, dolomite, brucite, ZSM-5 zeolite or marble powder.

[0026] As a preferred technical solution of the present disclosure, when the fluoride ion concentration in the acidic fluoride-containing wastewater does not exceed 1000 mg / L, the reflux rate of treated water is 1 to 1.2 times the amount of acidic fluoride-containing wastewater, for example, 1 time, 1.05, 1.1 times or 1.2 times, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0027] In the present disclosure, when the reflux rate of the treated water is 1 times the amount of the acidic fluorine-containing wastewater, it means that all the treated water obtained is refluxed.

[0028] As a preferred technical solution of the present disclosure, when the fluoride ion concentration in the acidic fluoride-containing wastewater is greater than 1000 mg / L and less than 5000 mg / L, the reflux rate of treated water is 3 to 3.2 times the amount of acidic fluoride-containing wastewater, for example, 3 times, 3.1 times or 3.2 times, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0029] As a preferred technical solution of the present disclosure, when the fluoride ion concentration in the acidic fluoride-containing wastewater is not less than 5000 mg / L, the reflux rate of treated water is 5 to 5.2 times the amount of acidic fluoride-containing wastewater, for example, 5 times, 5.1 times or 5.2 times, etc., but is not limited to the listed values, and other values ​​not listed within this range are also applicable.

[0030] The present disclosure designs different reflux ratios based on the specific fluoride ion concentration of the acidic fluoride-containing wastewater. On the one hand, this can fully utilize the residual chloride ions in the effluent; on the other hand, it can adjust the supersaturation of calcium fluoride in the system and enhance the heterogeneous nucleation efficiency of calcium fluoride on the surface of the seed crystal. If the reflux ratio is too small, the supersaturation of the system will increase sharply, the self-nucleation effect will be enhanced, and a large amount of high-water content sludge will be generated, resulting in a decrease in the fluoride ion recovery efficiency.

[0031] As a preferred technical solution of the present disclosure, when the concentration of fluoride ions in the treated water is lower than 10 mg / L, the reflux is stopped and all the treated water is discharged.

[0032] As a preferred technical solution of the present disclosure, the core crystal granulation process is carried out using a core crystal granulation device, and the core crystal granulation device includes a core crystal granulation reactor and a storage tank;

[0033] The lower end of the side wall of the nuclear crystal granulation reactor is respectively provided with a wastewater inlet for introducing acidic fluorine-containing wastewater; two crystal inducer addition ports, one for introducing calcium chloride solution and the other for introducing calcium hydroxide solution; and a reflux port for achieving reflux of treated water;

[0034] A water outlet is provided at the top or upper end of the side wall of the nuclear crystal granulation reactor for discharging the treated water in the nuclear crystal granulation reactor;

[0035] The bottom end of the nuclear crystal granulation reactor is provided with a granulation discharge port for discharging the granulation;

[0036] The storage tanks are respectively provided with a water storage inlet for receiving part of the treated water from the water outlet of the core crystal granulation reactor; and a water storage outlet for discharging the treated water in the storage tank to the reflux port of the core crystal granulation reactor.

[0037] Preferably, the wastewater inlet, the crystal inducer addition port and the reflux port are located at the same height.

[0038] As a preferred technical solution of the present disclosure, the core crystal granulation process includes:

[0039] Under initial working conditions:

[0040] filling seed crystals into the nuclear crystal granulation reactor;

[0041] Adjust the pH of acidic fluoride-containing wastewater to 4-5;

[0042] The adjusted acidic fluorine-containing wastewater, calcium chloride solution and calcium hydroxide solution are respectively introduced into the seed crystal granulation reactor to make the seed crystals in a fluidized state; the seed crystals induce the fluoride ions and calcium ions in the water to react and form nuclei and growth on the surface of the seed crystals in the form of calcium fluoride to form granules;

[0043] The chloride ions remaining after the reaction react with the hydrogen ions remaining in the water to form hydrochloric acid which is stored in the treated water. Part of the treated water is discharged and part is stored for subsequent reflux.

[0044] The added molar amount of calcium chloride is 1 / 10 to 1 / 6 of the molar amount of fluoride ions in the reaction system;

[0045] The added molar amount of calcium hydroxide is 1 / 5 to 1 / 4 of the molar amount of fluoride ions in the reaction system;

[0046] After the water volume in the storage tank reaches the set value:

[0047] The reflux ratio of the treated water is determined according to the fluoride ion concentration in the acidic fluoride-containing wastewater, and then the water inlet volume and the treated water discharge volume of the acidic fluoride-containing wastewater are adjusted to ensure that the addition ratio of calcium chloride remains unchanged, the addition ratio of calcium hydroxide is increased, and the treated water in the storage tank is controlled to reflux to the nucleus crystal granulation reactor according to the determined reflux ratio; at this time, the hydrochloric acid in the reflux water reacts with the calcium hydroxide to generate calcium chloride, and the calcium ions in the obtained calcium chloride continue to react with the fluoride ions and nucleate and grow on the surface of the seed crystal in the form of calcium fluoride, thereby realizing the cyclic regeneration of calcium chloride and enhancing the recovery of fluorine resources.

[0048] As a preferred technical solution of the present disclosure, the filling height of the seed crystal is 20 to 40% of the effective height of the nuclear crystal granulation reactor, for example, 20%, 25%, 30%, 35% or 40%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0049] Preferably, the hydraulic retention time of the acidic fluorine-containing wastewater in the core crystallization granulation reactor is not less than 5 minutes, for example, 5 minutes, 6 minutes, 8 minutes, 10 minutes, 11 minutes, 12 minutes or 15 minutes, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0050] The technical solution provided by the embodiments of the present disclosure has the following advantages over the prior art:

[0051] (1) The present invention addresses the problem of high cost of crystallization agents used in existing crystallization granulation processes for treating acidic fluorine-containing wastewater, and designs a crystallization granulation process that recycles calcium chloride to enhance fluorine resource recovery. This process uses a combination of calcium hydroxide and a small amount of calcium chloride as crystallization agents. Since the fluoride ions consume the calcium ions in the calcium chloride during the process, the residual chloride ions are present in the treated wastewater. The treated wastewater is circulated and refluxed. When calcium hydroxide is added again, the residual chloride ions combine with the calcium ions in the calcium hydroxide to form calcium chloride, which continues to react with the fluoride ions to form calcium fluoride. This achieves the purpose of regenerating calcium chloride to enhance fluorine resource recovery and reduce treatment costs.

[0052] (2) The disclosed nuclear crystal granulation process requires a small amount of reagents to be added, does not generate sludge, has a short treatment process, and recovers high-quality calcium fluoride. It simultaneously achieves water purification and resource recovery and utilization of fluoride, which is beneficial to production and application. DETAILED DESCRIPTION

[0053] 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 therein can be combined with each other in the absence of conflict.

[0054] 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.

[0055] The present disclosure provides a nucleus crystal granulation device, comprising a nucleus crystal granulation reactor and a storage tank;

[0056] The lower end of the side wall of the nuclear crystal granulation reactor is respectively provided with a wastewater inlet for introducing acidic fluorine-containing wastewater; two crystal inducer addition ports, one for introducing calcium chloride solution and the other for introducing calcium hydroxide solution; and a reflux port for achieving reflux of treated water;

[0057] Furthermore, the wastewater inlet, the crystal inducer addition port and the reflux port are located at the same height;

[0058] A water outlet is provided at the top or upper end of the side wall of the nuclear crystal granulation reactor for discharging the treated water in the nuclear crystal granulation reactor;

[0059] The bottom end of the nuclear crystal granulation reactor is provided with a granulation discharge port for discharging the granulation;

[0060] The storage tanks are respectively provided with a water storage inlet for receiving part of the treated water from the water outlet of the core crystal granulation reactor; and a water storage outlet for discharging the treated water in the storage tank to the reflux port of the core crystal granulation reactor.

[0061] The following core crystal granulation processes are all carried out using the core crystal granulation device.

[0062] Example 1

[0063] This embodiment provides a core crystal granulation process for calcium chloride recycling and enhanced fluorine resource recovery, comprising:

[0064] Under initial working conditions:

[0065] Filling dolomite into the core crystal granulation reactor to a filling height of 20% of the effective height of the core crystal granulation reactor;

[0066] The pH of the acidic fluoride-containing wastewater with a fluoride ion concentration of 1000 mg / L was adjusted to 4 using sodium hydroxide;

[0067] The regulated acidic fluoride wastewater was washed with 30m 3 / h flow rate into the nuclear crystal granulation reactor, and at the same time, the calcium chloride solution is fed at a rate of 0.3m 3 / h flow rate, calcium hydroxide solution at 0.3m 3 / h is passed into the nuclear crystal granulation reactor to make the dolomite in a fluidized state; the dolomite induces the fluoride ions and calcium ions in the water to react and nucleate and grow on the surface of the dolomite in the form of calcium fluoride to form granules;

[0068] The remaining chloride ions after the reaction react with the remaining hydrogen ions in the water to form hydrochloric acid which is stored in the treated water. Part of the treated water is discharged and the other part is stored for subsequent reflux.

[0069] The added molar amount of calcium chloride is 1 / 10 of the molar amount of fluoride ions in the reaction system;

[0070] The added molar amount of calcium hydroxide is 1 / 5 of the molar amount of fluoride ions in the reaction system;

[0071] When the water volume in the storage tank reaches 15m 3 back:

[0072] According to the fluoride ion concentration in the acidic fluoride-containing wastewater, the reflux ratio of the treated water is determined to be 100%, and then the inflow of the acidic fluoride-containing wastewater is adjusted to 15m 3 / h, the treated water discharge is 15m 3 / h, at the same time, ensure that the addition ratio of calcium chloride remains unchanged, the addition ratio of calcium hydroxide is adjusted to 2 / 5, and the treated water in the storage tank is controlled at 15m 3 / h is refluxed into the seed crystal granulation reactor; at this time, the hydrochloric acid in the reflux water reacts with the calcium hydroxide to generate calcium chloride, and the calcium ions in the obtained calcium chloride continue to react with the fluoride ions and nucleate and grow on the surface of the seed crystal in the form of calcium fluoride, thereby realizing the cyclic regeneration of calcium chloride and enhancing the recovery of fluorine resources.

[0073] When the concentration of fluoride ions in the treated water is lower than 10 mg / L, the reflux is stopped and all the treated water is discharged.

[0074] Example 2

[0075] This embodiment provides a core crystal granulation process for calcium chloride recycling and enhanced fluorine resource recovery, comprising:

[0076] Under initial working conditions:

[0077] Filling dolomite into the core crystal granulation reactor to a filling height of 30% of the effective height of the core crystal granulation reactor;

[0078] The pH of the acidic fluoride-containing wastewater with a fluoride ion concentration of 4900 mg / L was adjusted to 4 using sodium hydroxide;

[0079] The regulated acidic fluoride wastewater was heated to 40m 3 / h flow rate into the nuclear crystal granulation reactor, and at the same time, the calcium chloride solution is fed at a rate of 0.4m 3 / h flow rate, calcium hydroxide solution at 0.4m 3 / h is passed into the nuclear crystal granulation reactor to make the dolomite in a fluidized state; the dolomite induces the fluoride ions and calcium ions in the water to react and nucleate and grow on the surface of the dolomite in the form of calcium fluoride to form granules;

[0080] The remaining chloride ions after the reaction react with the remaining hydrogen ions in the water to form hydrochloric acid which is stored in the treated water. Part of the treated water is discharged and the other part is stored for subsequent reflux.

[0081] The added molar amount of calcium chloride is 1 / 8 of the molar amount of fluoride ions in the reaction system;

[0082] The added molar amount of calcium hydroxide is 1 / 4 of the molar amount of fluoride ions in the reaction system;

[0083] When the water volume in the storage tank reaches 30m 3 back:

[0084] According to the fluoride ion concentration in the acidic fluoride-containing wastewater, the reflux ratio of the treated water is determined to be 300%, and then the inflow of the acidic fluoride-containing wastewater is adjusted to 10m 3 / h, the treated water discharge is 10m 3 / h, at the same time, ensure that the addition ratio of calcium chloride remains unchanged, the addition ratio of calcium hydroxide is adjusted to 1 / 3, and the treated water in the storage tank is controlled at 30m 3 / h is refluxed into the seed crystal granulation reactor; at this time, the hydrochloric acid in the reflux water reacts with the calcium hydroxide to generate calcium chloride, and the calcium ions in the obtained calcium chloride continue to react with the fluoride ions and nucleate and grow on the surface of the seed crystal in the form of calcium fluoride, thereby realizing the cyclic regeneration of calcium chloride and enhancing the recovery of fluorine resources.

[0085] When the concentration of fluoride ions in the treated water is lower than 10 mg / L, the reflux is stopped and all the treated water is discharged.

[0086] Example 3

[0087] This embodiment provides a core crystal granulation process for calcium chloride recycling and enhanced fluorine resource recovery, comprising:

[0088] Under initial working conditions:

[0089] Filling dolomite into the core crystal granulation reactor to a filling height of 30% of the effective height of the core crystal granulation reactor;

[0090] The pH of the acidic fluoride-containing wastewater with a fluoride ion concentration of 10,000 mg / L was adjusted to 4 using sodium hydroxide;

[0091] The regulated acidic fluoride wastewater was 3 / h flow rate into the nuclear crystal granulation reactor, and at the same time, the calcium chloride solution is fed at a rate of 0.6m 3 / h flow rate, calcium hydroxide solution at 0.6m 3 / h is passed into the nuclear crystal granulation reactor to make the dolomite in a fluidized state; the dolomite induces the fluoride ions and calcium ions in the water to react and nucleate and grow on the surface of the dolomite in the form of calcium fluoride to form granules;

[0092] The remaining chloride ions after the reaction react with the remaining hydrogen ions in the water to form hydrochloric acid which is stored in the treated water. Part of the treated water is discharged and the other part is stored for subsequent reflux.

[0093] The added molar amount of calcium chloride is 1 / 9 of the molar amount of fluoride ions in the reaction system;

[0094] The added molar amount of calcium hydroxide is 9 / 40 of the molar amount of fluoride ions in the reaction system;

[0095] When the water volume in the storage tank reaches 25m 3 back:

[0096] According to the fluoride ion concentration in the acidic fluoride-containing wastewater, the reflux ratio of the treated water is determined to be 500%, and then the inflow of the acidic fluoride-containing wastewater is adjusted to 5m 3 / h, the treated water discharge is 5m 3 / h, at the same time, ensure that the addition ratio of calcium chloride remains unchanged, the addition ratio of calcium hydroxide is adjusted to 2 / 5, and the treated water in the storage tank is controlled at 25m 3 / h is refluxed into the seed crystal granulation reactor; at this time, the hydrochloric acid in the reflux water reacts with the calcium hydroxide to generate calcium chloride, and the calcium ions in the obtained calcium chloride continue to react with the fluoride ions and nucleate and grow on the surface of the seed crystal in the form of calcium fluoride, thereby realizing the cyclic regeneration of calcium chloride and enhancing the recovery of fluorine resources.

[0097] When the concentration of fluoride ions in the treated water is lower than 10 mg / L, the reflux is stopped and all the treated water is discharged.

[0098] The core crystal granulation process for enhancing fluorine resource recovery by adopting the calcium chloride recycling regeneration disclosed in the present invention can save more than 30% of the amount of calcium chloride crystal inducer and reduce the processing cost by more than 38%.

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

[0100] The foregoing description is intended only to provide specific embodiments of the present disclosure, intended to enable those skilled in the art to understand and implement the present disclosure. Various modifications to these embodiments will be readily 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 is not intended to be limited to the embodiments described herein, but rather to be construed in the broadest manner consistent with the principles and novel features disclosed herein.

Claims

1. A calcium chloride recycling and regeneration process for enhanced fluorine resource recovery, characterized in that: The core crystal granulation process comprises the following steps: Under initial working conditions: Acidic fluoride-containing wastewater, calcium chloride, calcium hydroxide and seed crystals are mixed, and the seed crystals are placed in a fluidized state by controlling the hydraulic parameters of the water body; the seed crystals induce fluoride ions and calcium ions in the water body to react and nucleate and grow on the surface of the seed crystals in the form of calcium fluoride to form granules; The remaining chloride ions after the reaction react with the remaining hydrogen ions in the water to form hydrochloric acid which is stored in the treated water. Part of the treated water is discharged and part is stored for subsequent reflux. Wherein, the added molar amount of calcium chloride is 1 / 10 to 1 / 6 of the molar amount of fluoride ions in the reaction system; The added molar amount of calcium hydroxide is 1 / 5 to 1 / 4 of the molar amount of fluoride ions in the reaction system; When the amount of treated water to be stored reaches the set value: The reflux ratio of the treated water is determined according to the fluoride ion concentration in the acidic fluoride-containing wastewater, and then the amount of the acidic fluoride-containing wastewater and the discharge amount of the treated water are adjusted to ensure that the addition ratio of calcium chloride remains unchanged, the addition ratio of calcium hydroxide is increased, and the stored treated water is controlled to flow back to the reaction system according to the determined reflux ratio; at this time, the hydrochloric acid in the reflux water reacts with the calcium hydroxide to generate calcium chloride, and the calcium ions in the obtained calcium chloride continue to react with the fluoride ions and nucleate and grow on the surface of the seed crystal in the form of calcium fluoride, thereby realizing the cyclic regeneration of calcium chloride and enhancing the recovery of fluorine resources.

2. The core crystal granulation process according to claim 1, wherein Before the mixing, the pH of the acidic fluorine-containing wastewater is adjusted to 4-5.

3. The core crystal granulation process according to claim 1, characterized in that: The seed crystals include one or more of quartz sand, dolomite, brucite, ZSM-5 zeolite or marble powder.

4. The nuclear crystal granulation process according to claim 1 or 2, wherein: When the fluoride ion concentration in the acidic fluoride-containing wastewater does not exceed 1000 mg / L, the reflux rate of the treated water is 1 to 1.2 times the amount of the acidic fluoride-containing wastewater.

5. The nuclear crystal granulation process according to claim 1 or 2, characterized in that: When the fluoride ion concentration in the acidic fluoride-containing wastewater is greater than 1000 mg / L and less than 5000 mg / L, the reflux rate of the treated water is 3 to 3.2 times the amount of the acidic fluoride-containing wastewater.

6. The nuclear crystal granulation process according to claim 1 or 2, characterized in that: When the fluoride ion concentration in the acidic fluoride-containing wastewater is not less than 5000 mg / L, the reflux rate of the treated water is 5 to 5.2 times the amount of the acidic fluoride-containing wastewater.

7. The nuclear crystal granulation process according to any one of claims 1 to 6, characterized in that: When the concentration of fluoride ions in the treated water is lower than 10 mg / L, the reflux is stopped and all the treated water is discharged.

8. The nuclear crystal granulation process according to any one of claims 1 to 7, characterized in that: The nucleus crystal granulation process is carried out using a nucleus crystal granulation device, which includes a nucleus crystal granulation reactor and a storage tank; The lower ends of the side walls of the nuclear crystal granulation reactor are respectively provided with wastewater inlets for introducing acidic fluorine-containing wastewater; Two crystal-inducing agent injection ports, one for introducing calcium chloride solution and the other for introducing calcium hydroxide solution; and a reflux port for achieving reflux of treated water; A water outlet is provided at the top or upper end of the side wall of the nuclear crystal granulation reactor for discharging the treated water in the nuclear crystal granulation reactor; The bottom end of the nuclear crystal granulation reactor is provided with a granulation discharge port for discharging the granulation; The storage tanks are respectively provided with water storage inlets for receiving part of the treated water from the water outlet of the core crystal granulation reactor; and, a water storage outlet for discharging the treated water in the storage tank to a reflux port of the nucleus crystallization granulation reactor; Preferably, the wastewater inlet, the crystal inducer addition port and the reflux port are located at the same height.

9. The core crystal granulation process according to claim 8, characterized in that: The nucleation granulation process comprises: Under initial working conditions: filling seed crystals into the nuclear crystal granulation reactor; Adjust the pH of acidic fluoride-containing wastewater to 4-5; The adjusted acidic fluorine-containing wastewater, calcium chloride solution and calcium hydroxide solution are respectively introduced into the seed crystal granulation reactor to make the seed crystals in a fluidized state; the seed crystals induce the fluoride ions in the acidic fluorine-containing wastewater to react with the calcium ions and nucleate and grow on the surface of the seed crystals in the form of calcium fluoride to form granules; The remaining chloride ions after the reaction react with the remaining hydrogen ions in the water to form hydrochloric acid which is stored in the treated water. Part of the treated water is discharged and part is stored for subsequent reflux. The added molar amount of calcium chloride is 1 / 10 to 1 / 6 of the molar amount of fluoride ions in the reaction system; The added molar amount of calcium hydroxide is 1 / 5 to 1 / 4 of the molar amount of fluoride ions in the reaction system; After the water volume in the storage tank reaches the set value: The reflux ratio of the treated water is determined according to the fluoride ion concentration in the acidic fluoride-containing wastewater, and then the water inlet volume and the treated water discharge volume of the acidic fluoride-containing wastewater are adjusted to ensure that the addition ratio of calcium chloride remains unchanged, the addition ratio of calcium hydroxide is increased, and the treated water in the storage tank is controlled to reflux to the nucleus crystal granulation reactor according to the determined reflux ratio; at this time, the hydrochloric acid in the reflux water reacts with the calcium hydroxide to generate calcium chloride, and the calcium ions in the obtained calcium chloride continue to react with the fluoride ions and nucleate and grow on the surface of the seed crystal in the form of calcium fluoride, thereby realizing the cyclic regeneration of calcium chloride and enhancing the recovery of fluorine resources.

10. The core crystal granulation process according to claim 9, characterized in that: The filling height of the seed crystals is 20 to 40% of the effective height of the nuclear crystal granulation reactor; Preferably, the hydraulic retention time of the acidic fluorine-containing wastewater in the core crystallization granulation reactor is not less than 5 minutes.