Method for preparing fluorapatite based on PFAS

Abstract

The invention belongs to the technical field of environmental protection and resource recovery, and relates to a method for preparing fluorapatite based on PFAS. The preparation method comprises the following steps: mixing pretreated calcium oxide, phosphorus-containing calcium salt and PFAS, grinding and calcining to obtain the fluorapatite. According to the method, the low-cost calcium-containing oxide is used as a reactant, directional conversion and stabilization treatment of the pollutant PFAS are achieved, the reaction product is recyclable phosphate ore, and a new reference thought is provided for degradation of the PFAS in the environment.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental protection and resource recovery, and in particular to a method for preparing fluoroapatite based on PFAS. Background Art

[0002] Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals that are widely used in modern life and production due to their excellent hydrophobicity, oleophobicity, antifouling and chemical stability. However, this type of chemical also has ecological accumulation toxicity and persistence, is difficult to degrade, and has toxic effects on the human immune and endocrine systems, posing a great potential risk. PFOS and PFOA are key new pollutants to be controlled. In addition, requirements for perfluorinated compounds in drinking water are also put forward, namely perfluorooctanoic acid (limit 8×10 -5 mg / L) and perfluorooctane sulfonic acid (limit 4×10 -5 Currently, a large amount of PFAS has flowed into the environment and has been widely detected in soil, surface water, groundwater, sewage sludge and landfill leachate.

[0003] Representative compounds of PFAS mainly include perfluoroalkyl carboxylic acid compounds and perfluoroalkyl sulfonic acid compounds, and their main constituent elements include carbon and fluorine. Fluorine is the most electronegative element in the periodic table, making the bond energy of CF as high as 460kJ·mol -1 , the corresponding bond energy of CC is also increased. This feature makes PFAS have excellent properties such as high stability and durability and is used in chemical, clothing and furniture, food packaging, ammunition and military industries. At the same time, it is precisely because CF is difficult to break and has reaction inertness that PFAS can persist in the environment and can migrate long distances through a variety of environmental media. At present, the disposal methods of PFAS include: adsorption, chemical oxidation, chemical reduction and biodegradation, but they all have the disadvantages of high disposal cost, unsatisfactory removal effect and the generation of short-chain fluorides.

[0004] Adsorption technology is mostly used to remove PFAS in solutions, mainly by using the attraction of adsorbents to adsorbates. The working principle includes one or more of ion exchange, electrostatic effect, bridging effect, hydrogen bonding, van der Waals force, etc. The biggest disadvantage of adsorption technology is that it only transfers PFAS from one medium to another, and does not actually degrade it to achieve the purpose of harmlessness.

[0005] Chemical oxidation technology mainly uses active oxides with strong oxidizing properties to degrade PFAS. The degradation systems currently included mainly include Fenton and Fenton-like reaction systems, sulfate radical degradation systems, electrochemical degradation systems, and ultrasonic chemical degradation systems. The main working principle is decarboxylation-hydroxylation-elimination-hydrolysis. Chemical oxidation technology has the risk that PFAS may be transformed into more difficult to degrade pollutants and generate short-chain fluorides.

[0006] Chemical reduction techniques include aq - reduction technology and ZVI degradation technology, but due to poor environmental adaptability and complicated reaction conditions, they are still some distance away from practical application.

[0007] Biodegradation technology mainly utilizes microbial metabolism to convert organic matter into carbon dioxide and water. However, the biodegradation efficiency is low, and it is easy to convert into short-chain fluorides, causing secondary pollution, and it is possible to convert into more toxic long-chain fluorides.

[0008] Based on the shortcomings of the above removal methods, how to obtain a new conversion method that not only has high conversion efficiency and completely degrades PFAS, but also can recycle the fluorine element and has low raw material costs, and can also convert PFAS present in solids, and is no longer limited to aqueous solutions, has become a difficult problem that technicians in this field urgently need to overcome. Summary of the invention

[0009] The purpose of the present invention is to provide a method for preparing fluoroapatite based on PFAS, by combining cheap and readily available calcium-containing compounds with PFAS, modifying it and generating reusable phosphate rock, thereby achieving the harmless transformation of PFAS and providing a new reference idea for the degradation of PFAS in the environment.

[0010] To achieve the above object, the present invention provides the following solutions:

[0011] One of the technical solutions of the present invention is to provide a method for preparing fluoroapatite based on PFAS, comprising the following steps:

[0012] The pretreated calcium oxide, phosphorus calcium salt and PFAS are mixed, ground and calcined to obtain the fluorapatite.

[0013] Furthermore, the pretreated calcium-containing oxide is prepared by heating calcium oxide (CaO) to 900° C. at a heating rate of 15° C. / min and then calcining for 60 to 120 minutes.

[0014] Calcining CaO in a muffle furnace can, on the one hand, remove the moisture contained in CaO, and on the other hand, activate the lattice structure of CaO, which is more conducive to the subsequent reaction.

[0015] Furthermore, the molar ratio of the Ca element, the P element and the F element in the system after the calcium oxide, the phosphorus calcium salt and the PFAS are mixed is 5:3:1.

[0016] Furthermore, the phosphorus-containing calcium salt includes at least one of calcium hydrogen phosphate dihydrate, calcium pyrophosphate and calcium phosphate.

[0017] Furthermore, the PFAS includes perfluorooctanoic acid (PFOA) and / or perfluorododecanoic acid (PFDoA).

[0018] Furthermore, the grinding is hand grinding or ball grinding.

[0019] Preferably, the hand grinding time is 10 minutes.

[0020] Preferably, the ball milling speed is 1600-1800 rpm and the time is 30 min.

[0021] During the ball milling process, the mill is operated for 60 seconds and then rested for 30 seconds to reduce the side reactions caused by frictional heat. The milling jar is made of corundum (Al2O3) and the grinding balls are made of zirconium oxide (ZrO2). This device can ensure that the mixture is not worn and does not participate in chemical reactions.

[0022] Furthermore, the calcination temperature is 900° C., the heating rate is 15° C. / min, and the calcination time is 120 min.

[0023] The formation of fluorapatite is closely related to calcium and phosphorus. In nature, most fluorapatite is formed by the crystallization of calcium and phosphorus from rocks and melts. Calcium phosphate, calcium pyrophosphate and calcium hydrogen phosphate dihydrate are not only rich in calcium and phosphorus but also cheap and easy to obtain. They are the best choices for gathering fluorine to form fluorapatite.

[0024] The second technical solution of the present invention is to provide a method for harmless treatment of PFAS pollutants, comprising the following steps:

[0025] Calcium oxide, phosphorus-containing calcium salt and PFAS pollutants are used as reactants, which are mixed, ground and calcined to complete the harmless treatment of PFAS pollutants and obtain fluoroapatite.

[0026] Furthermore, the calcium oxide is obtained by heating the calcium-containing oxide to 900° C. at a heating rate of 15° C. / min and then calcining for 60 to 120 minutes.

[0027] Furthermore, the molar ratio of the Ca element, the P element and the F element in the system after the calcium oxide, the phosphorus-containing calcium salt and the PFAS pollutant are mixed is 5:3:1.

[0028] Furthermore, the phosphorus-containing calcium salt includes at least one of calcium hydrogen phosphate dihydrate (CaHPO4·2H2O), calcium pyrophosphate (Ca2P2O7) and calcium phosphate (Ca3(PO4)2).

[0029] Furthermore, the PFAS includes perfluorooctanoic acid (PFOA, C8HF 15 O2) and / or perfluorododecanoic acid (PFDoA, C 12 HF 23 O2).

[0030] Furthermore, the grinding is hand grinding or ball grinding.

[0031] Preferably, the hand grinding time is 10 minutes.

[0032] Preferably, the ball milling speed is 1600-1800 rpm and the time is 30 min.

[0033] Furthermore, the calcination temperature is 900° C., the heating rate is 15° C. / min, and the calcination time is 120 min.

[0034] The third technical solution of the present invention is to provide a method for resource treatment of PFAS pollutants, the steps comprising:

[0035] Calcium oxide, phosphorus-containing calcium salts and PFAS pollutants are used as reactants, which are mixed, ground and calcined to complete the resource processing of PFAS pollutants and obtain fluoroapatite.

[0036] The present invention discloses the following technical effects:

[0037] The present invention uses cheap calcium oxide as a reactant to achieve directional conversion and stabilization treatment of the pollutant PFAS, and the reaction product is recyclable phosphate rock, thereby achieving the recycling of F back into the fluorophosphate rock.

[0038] The present invention uses calcium oxide and phosphorus-containing calcium salt as calcination additives, which are low-priced and easily available, have a simple reaction process, are easy to operate, and can be promoted and applied on a large scale.

[0039] The method of the present invention provides a reference idea for solving PFAS pollution at the current stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] 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 will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0041] Figure 1 For hand grinder-C8HF 15 O2+Ca3(PO4)2, ball milling-C8HF 15 O2+Ca3(PO4)2, calcined-C8HF 15 O2+Ca3(PO4)2, hand grinding-C 12 HF 23 O2+Ca3(PO4)2, ball milling-C 12 HF 23 O2+Ca3(PO4)2, calcined-C 12 HF 23 Crystal comparison diagram of O2+Ca3(PO4)2;

[0042] Figure 2 The microscopic morphology of the fluoroapatite products prepared in Example 9 and Example 12, wherein a is Example 9, b is a partial enlarged view of a, c is Example 12, and d is a partial enlarged view of c;

[0043] Figure 3 This is the energy spectrum element analysis diagram of the fluoroapatite product prepared in Example 9;

[0044] Figure 4 This is the energy spectrum elemental analysis diagram of the fluoroapatite product prepared in Example 12. DETAILED DESCRIPTION

[0045] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0046] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0047] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0048] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0049] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0050] In a specific embodiment of the present invention, the ball milling jar used for ball milling is made of corundum (Al2O3), and the grinding balls are made of zirconium oxide (ZrO2).

[0051] Example 1

[0052] Raw material hand grinding process steps:

[0053] S1. Pretreatment of calcium oxide: CaO is placed in a muffle furnace and heated to 900°C at a heating rate of 15°C / min and maintained for 120 minutes. After the calcination is completed, the calcium oxide is cooled to room temperature and taken out and placed in a drying dish for storage;

[0054] S2. Treatment of phosphorus-containing calcium salt: drying the dihydrated calcium hydrogen phosphate in an oven at 60° C. for 12 hours, and placing it in a drying dish for later use;

[0055] S3. Mix 0.3980 g of calcium oxide, 1.8136 g of calcium hydrogen phosphate dihydrate and 0.1 g of perfluorooctanoic acid, put them in a mortar, and mix and grind them manually (10 min). Collect the thoroughly ground mixture for later use.

[0056] Example 2

[0057] Raw material ball milling process steps:

[0058] S1. Pretreatment of calcium oxide: CaO is placed in a muffle furnace and heated to 900°C at a heating rate of 15°C / min and maintained for 120 minutes. After the calcination is completed, the calcium oxide is cooled to room temperature and taken out and placed in a drying dish for storage;

[0059] S2. Treatment of phosphorus-containing calcium salt: drying the dihydrated calcium hydrogen phosphate in an oven at 60° C. for 12 hours, and placing it in a drying dish for later use;

[0060] S3. 0.3980 g of calcium oxide, 1.8136 g of calcium hydrogen phosphate dihydrate and 0.1 g of perfluorooctanoic acid were mixed, and the mixture was placed in a planetary ball mill for thorough mixing and grinding (1600 rpm, 30 min). The thoroughly ground mixture was collected for later use.

[0061] Example 3

[0062] The steps for preparing PFAS-based fluoroapatite are:

[0063] Raw material ball milling process steps:

[0064] S1. Pretreatment of calcium oxide: CaO is placed in a muffle furnace and heated to 900°C at a heating rate of 15°C / min and maintained for 120 minutes. After the calcination is completed, the calcium oxide is cooled to room temperature and taken out and placed in a drying dish for storage;

[0065] S2. Treatment of phosphorus-containing calcium salt: drying the dihydrated calcium hydrogen phosphate in an oven at 60° C. for 12 hours, and placing it in a drying dish for later use;

[0066] S3, after mixing 0.3980 g of calcium oxide, 1.8136 g of calcium hydrogen phosphate dihydrate and 0.1 g of perfluorooctanoic acid, placing the mixture in a planetary ball mill for thorough mixing and grinding (1600 rpm, 30 min), collecting the thoroughly ground mixture for later use, and obtaining a mixed material;

[0067] S4. The mixed material is placed in a muffle furnace and heated to 900° C. at a heating rate of 15° C. / min and maintained for 120 min. After the reaction is completed, the mixed material is cooled to room temperature and the reaction product is taken out to obtain fluoroapatite.

[0068] Example 4

[0069] Raw material hand grinding process steps:

[0070] S1. Pretreatment of calcium oxide: CaO is placed in a muffle furnace and heated to 900°C at a heating rate of 15°C / min and maintained for 120 minutes. After the calcination is completed, the calcium oxide is cooled to room temperature and taken out and placed in a drying dish for storage;

[0071] S2. Treatment of phosphorus-containing calcium salt: drying the calcium pyrophosphate in an oven at 60° C. for 12 hours, and placing it in a drying dish for later use;

[0072] S3. Mix 0.3980 g of calcium oxide, 1.3808 g of calcium pyrophosphate and 0.1 g of perfluorooctanoic acid, put them in a mortar, and mix and grind them manually (10 min). Collect the thoroughly ground mixture for later use.

[0073] Example 5

[0074] Raw material ball milling process steps:

[0075] S1. Pretreatment of calcium oxide: CaO is placed in a muffle furnace and heated to 900°C at a heating rate of 15°C / min and maintained for 120 minutes. After the calcination is completed, the calcium oxide is cooled to room temperature and taken out and placed in a drying dish for storage;

[0076] S2. Treatment of phosphorus-containing calcium salt: drying the calcium pyrophosphate in an oven at 60° C. for 12 hours, and placing it in a drying dish for later use;

[0077] S3. Mix 0.3980 g of calcium oxide, 1.3808 g of calcium pyrophosphate and 0.1 g of perfluorooctanoic acid, place in a planetary ball mill for thorough mixing and grinding (1600 rpm, 30 min), and collect the thoroughly ground mixture for later use.

[0078] Example 6

[0079] The steps for preparing PFAS-based fluoroapatite are:

[0080] Raw material ball milling process steps:

[0081] S1. Pretreatment of calcium oxide: CaO is placed in a muffle furnace and heated to 900°C at a heating rate of 15°C / min and maintained for 120 minutes. After the calcination is completed, the calcium oxide is cooled to room temperature and taken out and placed in a drying dish for storage;

[0082] S2. Treatment of phosphorus-containing calcium salt: drying the calcium pyrophosphate in an oven at 60° C. for 12 hours, and placing it in a drying dish for later use;

[0083] S3, after mixing 0.3980 g of calcium oxide, 1.3808 g of calcium pyrophosphate and 0.1 g of perfluorooctanoic acid, placing the mixture in a planetary ball mill for thorough mixing and grinding (1600 rpm, 30 min), collecting the thoroughly ground mixture for later use, and obtaining a mixed material;

[0084] S4. The mixed material is placed in a muffle furnace and heated to 900° C. at a heating rate of 15° C. / min and maintained for 120 min. After the reaction is completed, the mixed material is cooled to room temperature and the reaction product is taken out to obtain fluoroapatite.

[0085] Example 7

[0086] Raw material hand grinding process steps:

[0087] S1. Pretreatment of calcium oxide: CaO is placed in a muffle furnace and heated to 900°C at a heating rate of 15°C / min and maintained for 120 minutes. After the calcination is completed, the calcium oxide is cooled to room temperature and taken out and placed in a drying dish for storage;

[0088] S2. Treatment of phosphorus-containing calcium salts: drying the calcium phosphate in an oven at 60° C. for 12 hours, and placing it in a drying dish for later use;

[0089] S3. 0.0995 g of calcium oxide, 1.6344 g of calcium phosphate and 0.1 g of perfluorooctanoic acid were mixed, placed in a mortar, and fully mixed and ground manually (10 min). The fully ground mixture was collected for later use to obtain a mixed material, which was recorded as hand-ground-C8HF 15 O2+Ca3(PO4)2.

[0090] Example 8

[0091] Raw material ball milling process steps:

[0092] S1. Pretreatment of calcium oxide: CaO is placed in a muffle furnace and heated to 900°C at a heating rate of 15°C / min and maintained for 120 minutes. After the calcination is completed, the calcium oxide is cooled to room temperature and taken out and placed in a drying dish for storage;

[0093] S2. Treatment of phosphorus-containing calcium salts: drying the calcium phosphate in an oven at 60° C. for 12 hours, and placing it in a drying dish for later use;

[0094] S3. 0.0995 g of calcium oxide, 1.6344 g of calcium phosphate and 0.1 g of perfluorooctanoic acid were mixed and placed in a planetary ball mill for thorough mixing and grinding (1600 rpm, 30 min). The thoroughly ground mixture was collected for later use to obtain a mixed material, which was recorded as ball-milled-C8HF 15 O2+Ca3(PO4)2.

[0095] Example 9

[0096] The steps for preparing PFAS-based fluoroapatite are:

[0097] Raw material ball milling process steps:

[0098] S1. Pretreatment of calcium oxide: CaO is placed in a muffle furnace and heated to 900°C at a heating rate of 15°C / min and maintained for 120 minutes. After the calcination is completed, the calcium oxide is cooled to room temperature and taken out and placed in a drying dish for storage;

[0099] S2. Treatment of phosphorus-containing calcium salts: drying the calcium phosphate in an oven at 60° C. for 12 hours, and placing it in a drying dish for later use;

[0100] S3, after mixing 0.0995 g of calcium oxide, 1.6344 g of calcium phosphate and 0.1 g of perfluorooctanoic acid, placing the mixture in a planetary ball mill for thorough mixing and grinding (1600 rpm, 30 min), collecting the thoroughly ground mixture for later use, and obtaining a mixed material;

[0101] S4. The mixed material is placed in a muffle furnace and heated to 900°C at a heating rate of 15°C / min and maintained for 120 minutes. After the reaction is completed, the mixture is cooled to room temperature and the reaction product is taken out to obtain fluoroapatite, which is recorded as calcined-C8HF 15 O2+Ca3(PO4)2.

[0102] Example 10

[0103] The steps for preparing PFAS-based fluoroapatite are:

[0104] S1. Pretreatment of calcium oxide: CaO is placed in a muffle furnace and heated to 900°C at a heating rate of 15°C / min and maintained for 120 minutes. After the calcination is completed, the calcium oxide is cooled to room temperature and taken out and placed in a drying dish for storage;

[0105] S2. Treatment of phosphorus-containing calcium salt: drying the dihydrated calcium hydrogen phosphate in an oven at 60° C. for 12 hours, and placing it in a drying dish for later use;

[0106] S3, after mixing 0.3944 g of calcium oxide, 1.7969 g of calcium hydrogen phosphate dihydrate and 0.1 g of perfluorododecanoic acid, put them in a mortar, mix and grind them manually (10 min), and collect the fully ground mixture for later use;

[0107] S4. The mixed material is placed in a muffle furnace and heated to 900° C. at a heating rate of 15° C. / min and maintained for 120 min. After the reaction is completed, the mixed material is cooled to room temperature and the reaction product is taken out to obtain fluoroapatite.

[0108] Embodiment 11

[0109] The steps for preparing PFAS-based fluoroapatite are:

[0110] S1. Pretreatment of calcium oxide: CaO is placed in a muffle furnace and heated to 900°C at a heating rate of 15°C / min and maintained for 120 minutes. After the calcination is completed, the calcium oxide is cooled to room temperature and taken out and placed in a drying dish for storage;

[0111] S2. Treatment of phosphorus-containing calcium salt: drying the calcium pyrophosphate in an oven at 60° C. for 12 hours, and placing it in a drying dish for later use;

[0112] S3, after mixing 0.3944 g of calcium oxide, 1.3681 g of calcium pyrophosphate and 0.1 g of perfluorododecanoic acid, place the mixture in a planetary ball mill for thorough mixing and grinding (1600 rpm, 30 min), and collect the thoroughly ground mixture for later use;

[0113] S4. The mixed material is placed in a muffle furnace and heated to 900° C. at a heating rate of 15° C. / min and maintained for 120 min. After the reaction is completed, the mixed material is cooled to room temperature and the reaction product is taken out to obtain fluoroapatite.

[0114] Example 12

[0115] The steps for preparing PFAS-based fluoroapatite are:

[0116] Raw material ball milling process steps:

[0117] S1. Pretreatment of calcium oxide: CaO is placed in a muffle furnace and heated to 900°C at a heating rate of 15°C / min and maintained for 120 minutes. After the calcination is completed, the calcium oxide is cooled to room temperature and taken out and placed in a drying dish for storage;

[0118] S2. Treatment of phosphorus-containing calcium salts: drying the calcium phosphate in an oven at 60° C. for 12 hours, and placing it in a drying dish for later use;

[0119] S3, after mixing 0.0986 g of calcium oxide, 1.6194 g of calcium phosphate and 0.1 g of perfluorododecanoic acid, placing the mixture in a planetary ball mill for thorough mixing and grinding (1600 rpm, 30 min), collecting the thoroughly ground mixture for later use, and obtaining a mixed material;

[0120] S4. The mixed material is placed in a muffle furnace and heated to 900°C at a heating rate of 15°C / min and maintained for 120 min. After the reaction is completed, the mixture is cooled to room temperature and the reaction product is taken out to obtain fluoroapatite, which is recorded as calcined-C. 12 HF 23 O2+Ca3(PO4)2.

[0121] Embodiment 13

[0122] Raw material hand grinding process steps:

[0123] S1. Pretreatment of calcium oxide: CaO is placed in a muffle furnace and heated to 900°C at a heating rate of 15°C / min and maintained for 120 minutes. After the calcination is completed, the calcium oxide is cooled to room temperature and taken out and placed in a drying dish for storage;

[0124] S2. Treatment of phosphorus-containing calcium salts: drying the calcium phosphate in an oven at 60° C. for 12 hours, and placing it in a drying dish for later use;

[0125] S3. 0.0986 g of calcium oxide, 1.6194 g of calcium phosphate and 0.1 g of perfluorododecanoic acid were mixed, placed in a mortar, and fully mixed and ground manually (10 min). The fully ground mixture was collected for later use to obtain a mixed material, which was recorded as hand-grinded-C. 12 HF23 O2+Ca3(PO4)2.

[0126] Embodiment 14

[0127] Raw material ball milling process steps:

[0128] S1. Pretreatment of calcium oxide: CaO is placed in a muffle furnace and heated to 900°C at a heating rate of 15°C / min and maintained for 120 minutes. After the calcination is completed, the calcium oxide is cooled to room temperature and taken out and placed in a drying dish for storage;

[0129] S2. Treatment of phosphorus-containing calcium salts: drying the calcium phosphate in an oven at 60° C. for 12 hours, and placing it in a drying dish for later use;

[0130] S3. 0.0986 g of calcium oxide, 1.6194 g of calcium phosphate and 0.1 g of perfluorododecanoic acid were mixed and placed in a planetary ball mill for thorough mixing and grinding (1600 rpm, 30 min). The thoroughly ground mixture was collected for later use to obtain a mixed material, which was recorded as ball mill-C. 12 HF 23 O2+Ca3(PO4)2.

[0131] Test example

[0132] Figure 1 For hand grinder-C8HF 15 O2+Ca3(PO4)2, ball milling-C8HF 15 O2+Ca3(PO4)2, calcined-C8HF 15 O2+Ca3(PO4)2, hand grinding-C 12 HF 23 O2+Ca3(PO4)2, ball milling-C 12 HF 23 O2+Ca3(PO4)2, calcined-C 12 HF 23 Crystal comparison diagram of O2+Ca3(PO4)2. Figure 1The conversion products of PFOA and PFDoA under three different conditions are shown. PFOA and PFDoA are converted under the conditions of three embodiments (Examples 7 to 9 and Examples 12 to 14), among which a large amount of conversion occurs under calcination conditions. It is worth noting that, as can be seen in the figure, when the compounds are mixed by hand grinding or ball milling, some reactions have already occurred at this time. At the same time, compared with the mixed products under calcination, hydroxyapatite is produced, and according to the characteristics of the fluorine element, these hydroxyapatites will continue to be converted into fluoroapatite. The formation of hydroxyapatite is at room temperature, due to the high humidity of the air, the hygroscopic properties of CaO and the water produced by the reaction, all of which provide -OH for the production of hydroxyapatite. In addition, CaCO3 is produced under the experimental conditions of hand grinding or ball milling, while only CaO is produced by calcination. The reason is that local high temperature will appear during hand grinding or ball milling, and CaO will contact and combine with CO2 in the air to form CaCO3. High temperature calcination not only blocks the CO2 atmosphere from contacting CaO, but also decomposes the CaCO3 generated during the heating process into CaO.

[0133] Figure 2 The microscopic morphology pictures of the fluoroapatite products prepared in Examples 9 and 12, wherein a is Example 9, b is a partial enlarged picture of a, c is Example 12, and d is a partial enlarged picture of c. Figure 2 It can be seen that the microscopic morphology of the products obtained under the reaction conditions of Ca3(PO4)2 and the two PFAS is not much different. The reaction products are mostly short rods with round ends and a cylindrical middle, and their sizes are in the micrometer level.

[0134] Figure 3 This is the energy spectrum element analysis diagram of the fluoroapatite product prepared in Example 9; Figure 4 This is the energy spectrum element analysis diagram of the fluoroapatite product prepared in Example 12. Figures 3-4 The element distribution also shows that the calcined products mainly include Ca, O, P, and F. Figure 1 The XRD data in can confirm that the reaction product is fluorapatite.

[0135] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing fluoroapatite based on PFAS, characterized in that the steps include: The pretreated calcium oxide, phosphorus calcium salt and PFAS are mixed, ground and calcined to obtain the fluorapatite.

2. The method according to claim 1, characterized in that The pretreated calcium-containing oxide is prepared by heating calcium oxide to 900° C. at a heating rate of 15° C. / min and then calcining for 60 to 120 minutes.

3. The method according to claim 1, characterized in that The molar ratio of the Ca element, the P element and the F element in the system after the calcium oxide, the phosphorus calcium salt and the PFAS are mixed is 5:3:

1.

4. The method according to claim 1, characterized in that: The phosphorus-containing calcium salt includes at least one of calcium hydrogen phosphate dihydrate, calcium pyrophosphate and calcium phosphate.

5. The method according to claim 1, characterized in that The PFAS includes PFOA and / or PFDoA.

6. The method according to claim 1, characterized in that The grinding is hand grinding or ball grinding.

7. The method according to claim 6, characterized in that The hand milling time is 10 minutes; the ball milling speed is 1600-1800 rpm, and the time is 30 minutes.

8. The method according to claim 1, characterized in that: The calcination temperature is 900° C., the heating rate is 15° C. / min, and the calcination time is 120 min.

9. A method for harmless treatment of PFAS pollutants, characterized in that the steps include: Calcium oxide, phosphorus-containing calcium salt and PFAS pollutants are used as reactants, which are mixed, ground and calcined to complete the harmless treatment of PFAS pollutants and obtain fluoroapatite.

10. A method for recycling PFAS pollutants, characterized in that the steps include: Calcium oxide, phosphorus-containing calcium salts and PFAS pollutants are used as reactants, which are mixed, ground and calcined to complete the resource processing of PFAS pollutants and obtain fluoroapatite.

Images