A method for extracting perfluorophosphoric acid from soil by coupling acid-base extractants

Abstract

The present invention provides a method for extracting perfluorophosphoric acid from soil by coupling an acid-base extractant, and relates to the technical field of soil pollutant extraction. The present invention uses alkaline methanol to perform alkaline extraction on the soil, and then uses acidic methanol to perform acidic extraction. Perfluorophosphoric acid in the soil tends to be strongly bound to soil organic matter. The present invention uses alkaline methanol and acidic methanol to perform acid-base extractant coupling extraction, which can make the perfluorophosphoric acid bound to organic matter be more fully released, and the extraction rate of perfluorophosphoric acid is high. The recovery rate of each perfluorophosphoric acid is greater than 60%, and the average recovery rate is 75.7%. Compared with the use of alkaline methanol, acidic methanol and pure methanol as extractants, the acid-base extractant coupling method provided by the present invention has significantly improved the comprehensive extraction effect of perfluorophosphoric acid in soil, providing a strong guarantee for the screening and control of perfluorophosphoric acid in soil.

Description

Technical Field

[0001] The present invention relates to the technical field of soil pollutant extraction, and in particular to a method for extracting perfluorophosphoric acid in soil by coupling an acid-base extractant. Background Art

[0002] Per- and polyfluoroalkyl substances (PFAS) are a new class of pollutants that have attracted significant attention in recent years due to their persistence, bioaccumulation, and toxicity. PFAS are released into the soil through point sources such as fluorination plants, metal plating plants, and wastewater treatment plants, or diffuse sources such as atmospheric deposition and runoff, potentially impacting human health directly or indirectly. Some new PFAS not only exhibit greater environmental persistence and long-range transport than traditional PFAS, but also exhibit similar or even greater bioaccumulation and toxicological effects. Therefore, it is necessary to monitor and investigate the concentrations of various PFAS in the environment, particularly novel PFAS alternatives such as perfluorophosphoric acids (PFPAs).

[0003] In recent years, mainstream academic literature has begun reporting the use of ultrasonic extraction methods for soil PFAS extraction, primarily using methanol or alkaline methanol. For example, the US Environmental Protection Agency (EPA) Method 1633 uses 0.3% v / v ammonia-methanol extraction for soil PFAS extraction, though PFPAs are excluded. However, ultrasound attenuates as it passes through the container walls and may not be sufficient to completely extract PFAS adsorbed in soil. Accelerated solvent extraction (ASE) is considered a superior method for extracting organic matter from soil. Standards such as "HJ783-2016 Extraction of Organic Matter from Soil and Sediment Using Pressurized Fluid Extraction" recommend ASE for organic matter extraction. Its advantages lie in its ability to significantly reduce organic solvent usage, accelerate extraction speed, and improve extraction efficiency and sample recovery by increasing temperature and pressure. Furthermore, it operates within a closed system to minimize environmental contamination.

[0004] Currently, few studies have reported on the concentrations of emerging PFASs in soil. ASE extraction of PFAS from solids has primarily focused on traditional long-chain PFASs (such as perfluorocarboxylic acids and perfluorosulfonic acids). Mainstream studies use pure methanol or ammonia-methanol extraction to extract per- and polyfluoroalkyl compounds (PFASs) from soil. However, when applied to target PFPAs, matrix spike recoveries of these PFASs are low. Therefore, an effective extraction method for PFPAs in soil is urgently needed. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide a method for extracting perfluorophosphoric acid from soil by coupling an acid-base extractant. The acid-base extractant coupling extraction method provided by the present invention has a high extraction rate for perfluorophosphoric acid in soil.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for extracting perfluorophosphoric acid in soil by coupling an acid-base extractant, comprising the following steps:

[0008] The soil and alkaline methanol are first mixed and subjected to alkaline extraction to obtain an alkaline extract and a residue;

[0009] The residue is mixed with acidic methanol for a second time, and subjected to acid extraction to obtain an acidic extract;

[0010] The alkaline extract and the acidic extract are combined and concentrated to obtain perfluorophosphoric acid.

[0011] Preferably, the alkaline methanol comprises ammonia water and methanol; the volume fraction of ammonia in the alkaline methanol is 0.1-0.5%;

[0012] The ratio of the mass of the soil to the volume of alkaline methanol is 1 g:7.5-20 mL.

[0013] Preferably, the acidic methanol comprises carboxylic acid and methanol, and the volume fraction of the carboxylic acid in the acidic methanol is 2-6%; the carboxylic acid comprises formic acid and / or acetic acid;

[0014] The ratio of the mass of the soil to the volume of the acidic methanol is 1 g:7.5-20 mL.

[0015] Preferably, the first mixed raw material further includes quartz sand.

[0016] Preferably, the mass ratio of the soil to the quartz sand is 1:0.5-2.

[0017] Preferably, the alkaline extraction and the acidic extraction independently comprise pressurized fluid extraction, shaking extraction or ultrasonic extraction.

[0018] Preferably, the conditions for the pressurized fluid extraction include: an extraction temperature of 100-120° C., and the extraction times of the alkaline pressurized fluid extraction and the acidic pressurized fluid extraction are independently 20-30 minutes.

[0019] Preferably, the conditions for the oscillation extraction include: an extraction temperature of 55-65° C., the number of alkaline oscillation extraction and acidic oscillation extraction is independently 2-3 times, and the time of a single oscillation extraction is 20-30 minutes.

[0020] Preferably, the conditions of the ultrasonic extraction include: extraction temperature of 55-65° C., ultrasonic power of 400-1000 W, the number of alkaline ultrasonic extraction and acidic ultrasonic extraction is independently 2-3 times, and the time of a single ultrasonic extraction is 15-30 min.

[0021] Preferably, the perfluorophosphonic acid includes one or more of perfluorohexylphosphonic acid (PFHxPA), perfluorooctylphosphonic acid (PFOPA), perfluorodecylphosphonic acid (PFDPA), chloroperfluorohexylphosphonic acid (Cl-PFHxPA) and chloroperfluorooctylphosphonic acid (Cl-PFOPA).

[0022] Perfluorophosphoric acid in soil tends to strongly bind to soil organic matter. The present invention uses alkaline methanol and acidic methanol for acid-base extraction coupling, which can more fully release perfluorophosphoric acid bound to organic matter, resulting in a high extraction rate for perfluorophosphoric acid. The recovery rate of each perfluorophosphoric acid is greater than 60%, with an average recovery rate of 75.7%. Compared with using alkaline methanol, acidic methanol, and pure methanol as extraction agents, the acid-base extraction coupling method provided by the present invention significantly improves the comprehensive extraction efficiency of PFHxPA, PFOPA, PFDPA, Cl-PFHxPA, and Cl-PFOPA in soil, providing a strong guarantee for the screening and control of perfluorophosphoric acid in soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is the standard curve of PFHxPA in Example 2;

[0024] Figure 2 is the standard curve of PFOPA in Example 2;

[0025] Figure 3 is the standard curve of PFDPA in Example 2;

[0026] Figure 4 is the standard curve of Cl-PFHxPA in Example 2;

[0027] Figure 5 This is the standard curve of Cl-PFOPA in Example 2. DETAILED DESCRIPTION

[0028] The present invention provides a method for extracting perfluorophosphoric acid in soil by coupling an acid-base extractant, comprising the following steps:

[0029] The soil and alkaline methanol are first mixed and subjected to alkaline extraction to obtain an alkaline extract and a residue;

[0030] The residue is mixed with acidic methanol for a second time, and subjected to acid extraction to obtain an acidic extract;

[0031] The alkaline extract and the acidic extract are combined and concentrated to obtain perfluorophosphoric acid.

[0032] Unless otherwise specified, the materials and equipment used in the present invention are all commercially available products in the art.

[0033] The invention first mixes soil and alkaline methanol, performs alkaline extraction, and obtains alkaline extract and residue.

[0034] In the present invention, the alkaline methanol preferably comprises aqueous ammonia and methanol; the volume fraction of ammonia in the alkaline methanol is preferably 0.1-0.5%, and in specific embodiments, it can be 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%. In the present invention, the mass fraction of the aqueous ammonia is preferably 25-28%, and in specific embodiments, it can be 25%, 26%, 27%, or 28%.

[0035] In the present invention, the soil is preferably freeze-dried, ground and sieved before use; the sieve size is preferably 60 mesh, and the undersize is used.

[0036] In the present invention, the ratio of the mass of the soil to the volume of alkaline methanol is preferably 1 g:7.5-20 mL. In specific embodiments, it can be 1 g:7.5 mL, 1 g:8 mL, 1 g:9 mL, 1 g:10 mL, 1 g:11 mL, 1 g:12 mL, 1 g:13 mL, 1 g:14 mL, 1 g:15 mL, 1 g:16 mL, 1 g:17 mL, 1 g:18 mL, 1 g:19 mL or 1 g:20 mL.

[0037] In the present invention, the raw materials of the first mixture preferably also include quartz sand, and the first mixing preferably includes: mixing soil and quartz sand to obtain a soil-quartz mixture, and mixing the soil-quartz mixture with alkaline methanol; mixing the soil-quartz mixture with alkaline methanol preferably comprises adding alkaline methanol to the soil-quartz mixture.

[0038] In the present invention, the mass ratio of the soil to the quartz sand is preferably 1:0.5 to 2, and in specific embodiments, can be 1:0.5, 1:1, 1:1.5, or 1:2. The present invention increases the dispersibility of perfluorophosphoric acid in the soil by adding quartz sand, which is beneficial for improving the extraction rate of perfluorophosphoric acid.

[0039] In the present invention, the alkaline extraction preferably includes pressurized fluid extraction, oscillation extraction or ultrasonic extraction.

[0040] In the present invention, the conditions for pressurized fluid extraction preferably include: an extraction temperature of 100-120°C, which can be 100°C, 105°C, 110°C, 115°C or 120°C in specific embodiments; and an alkaline pressurized fluid extraction time of 20-30 min, which can be 20 min, 22 min, 25 min, 28 min or 30 min in specific embodiments.

[0041] In the present invention, the pressurized fluid extraction preferably includes accelerated solvent extraction, and the accelerated solvent extraction is preferably performed on an accelerated solvent extraction evaporator Extreva ASE. Specifically, an extraction cell filter membrane is added to the bottom of the filter, the soil sample is added, and a portion of alkaline methanol is filled. Then, the remaining alkaline methanol is continuously introduced to perform alkaline extraction. After that, nitrogen is purged to expel the residual extractant, which is then combined with the extract obtained by the alkaline extraction to obtain an alkaline extract. In the present invention, the soil sample preferably includes soil and quartz sand. In the present invention, the ratio of the mass of the soil in the soil sample to the volume of the extraction cell is preferably 0.1-0.4 g:1 mL. In specific embodiments, it can be 0.1 g:1 mL, 0.15 g:1 mL, 0.2 g:1 mL, 0.25 g:1 mL, 0.3 g:1 mL, 0.35 g:1 mL, or 0.4 g:1 mL. In the present invention, the volume of the extraction cell is preferably 5-10 mL, and in specific embodiments, it can be 5 mL, 6 mL, 7 mL, 8 mL, 9 mL, or 10 mL. The mass of the soil in the soil sample is preferably 1-2 g, and in specific embodiments, it can be 1 g, 1.2 g, 1.5 g, 1.8 g, or 2 g. In the present invention, the nitrogen purge time is preferably 45-60 s, and in specific embodiments, it can be 45 s, 50 s, 55 s, or 60 s. In the present invention, the volume of the partial alkaline methanol preferably accounts for 40-50% of the volume of the extraction cell, and in specific embodiments, it can be 40%, 42%, 45%, 48%, or 50%. In the present invention, the flow rate of the remaining alkaline methanol is 0.2-0.4 mL / min, and in specific embodiments, it can be 0.2 mL / min, 0.25 mL / min, 0.3 mL / min, 0.35 mL / min, or 0.4 mL / min.

[0042] In the present invention, the conditions of the oscillation extraction preferably include: an extraction temperature of 55-65°C, which can be 55°C, 58°C, 60°C, 62°C or 65°C in specific embodiments; the number of alkaline oscillation extractions is 2-3 times, and the time of a single oscillation extraction is 20-30 minutes, which can be 20 minutes, 22 minutes, 25 minutes, 28 minutes or 30 minutes in specific embodiments.

[0043] In the present invention, the conditions of the ultrasonic extraction preferably include: an extraction temperature of 55-65°C, which may be 55°C, 58°C, 60°C, 62°C or 65°C in specific embodiments; an ultrasonic power of 400-1000W, which may be 400W, 500W, 600W, 700W, 800W, 900W or 1000W in specific embodiments; the number of alkaline ultrasonic extractions is 2-3 times, and the time for a single ultrasonic extraction is 20-30 min, which may be 20 min, 22 min, 25 min, 28 min or 30 min in specific embodiments.

[0044] After obtaining the residue, the present invention secondly mixes the residue with acidic methanol and performs acid extraction to obtain an acidic extract.

[0045] In the present invention, the acidic methanol preferably includes carboxylic acid and methanol; the carboxylic acid preferably includes formic acid and / or acetic acid; the volume fraction of carboxylic acid in the acidic methanol is preferably 2-6%, and in specific embodiments it can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5% or 6%.

[0046] In the present invention, the ratio of the mass of the soil to the volume of the acidic methanol is preferably 1 g:7.5-20 mL. In specific embodiments, it can be 1 g:7.5 mL, 1 g:8 mL, 1 g:9 mL, 1 g:10 mL, 1 g:11 mL, 1 g:12 mL, 1 g:13 mL, 1 g:14 mL, 1 g:15 mL, 1 g:16 mL, 1 g:17 mL, 1 g:18 mL, 1 g:19 mL or 1 g:20 mL.

[0047] In the present invention, the acidic extraction preferably includes pressurized fluid extraction, oscillation extraction or ultrasonic extraction.

[0048] In the present invention, the conditions for pressurized fluid extraction preferably include: an extraction temperature of 100-120°C, which may be 100°C, 105°C, 110°C, 115°C or 120°C in specific embodiments; an acidic pressurized fluid extraction time of 20-30 min, which may be 20 min, 22 min, 25 min, 28 min or 30 min in specific embodiments; and a flow rate of acidic methanol of 0.2-0.4 mL / min, which may be 0.2 mL / min, 0.25 mL / min, 0.3 mL / min, 0.35 mL / min or 0.4 mL / min in specific embodiments.

[0049] In the present invention, the conditions for the oscillation extraction preferably include: an extraction temperature of 55-65°C, and in specific embodiments, it can be 55°C, 58°C, 60°C, 62°C, or 65°C; the number of acidic oscillation extractions is 2-3 times, and the time for a single oscillation extraction is 20-30 minutes, and in specific embodiments, it can be 20 minutes, 22 minutes, 25 minutes, 28 minutes, or 30 minutes. In the present invention, the oscillation extraction can be performed by first performing alkaline extraction 2-3 times and then performing acidic extraction 2-3 times; the oscillation extraction can also be performed by alternating alkaline extraction and acidic extraction; during the alternating process, alkaline extraction is performed first.

[0050] In the present invention, the conditions for the ultrasonic extraction preferably include: an extraction temperature of 55-65°C, which may be 55°C, 58°C, 60°C, 62°C, or 65°C in specific embodiments; an ultrasonic power of 400-1000W, which may be 400W, 500W, 600W, 700W, 800W, 900W, or 1000W in specific embodiments; 2-3 acidic ultrasonic extractions, and a single ultrasonic extraction time of 20-30 minutes, which may be 20 minutes, 22 minutes, 25 minutes, 28 minutes, or 30 minutes in specific embodiments. In the present invention, the ultrasonic extraction may be performed by first performing alkaline extraction 2-3 times and then performing acidic extraction 2-3 times; the ultrasonic extraction may also be performed by alternating alkaline and acidic extractions; and alkaline extraction is performed first during the alternating process.

[0051] After obtaining the alkaline extract and the acidic extract, the present invention combines the alkaline extract and the acidic extract and concentrates them to obtain perfluorophosphoric acid. The present invention has no special limitation on the concentration, and a concentration method familiar to those skilled in the art can be used, such as vacuum evaporation; the temperature of the vacuum evaporation is preferably 40-55°C, and in specific embodiments, it can be 40°C, 45°C, 50°C or 55°C; the vacuum degree of the vacuum evaporation is preferably 3-5psi, and in specific embodiments, it can be 3psi, 3.5psi, 4psi, 4.5psi or 5psi; the vacuum evaporation is preferably carried out under a nitrogen flow, and the flow rate of the nitrogen flow is preferably 200-800mL / min, and in specific embodiments, it can be 200mL / min, 300mL / min, 400mL / min, 500mL / min, 600mL / min, 700mL / min or 800mL / min.

[0052] In the present invention, the perfluorophosphoric acid preferably includes one or more of perfluorohexyl phosphoric acid, perfluorooctyl phosphoric acid, perfluorodecyl phosphoric acid, chloro-perfluorohexyl phosphoric acid and chloro-perfluorooctyl phosphoric acid.

[0053] To further illustrate the present invention, the method for extracting perfluorophosphoric acid from soil by coupling an acid-base extractant provided by the present invention is described in detail below with reference to the following examples, but these examples should not be construed as limiting the scope of protection of the present invention.

[0054] In the following examples and comparative examples:

[0055] Quartz sand: analytical grade.

[0056] Ammonia water: concentration is 25wt%, analytical grade.

[0057] Isotopic internal standards: 13 C4-8:2 polyfluorophosphate diester ( 13 C4-8:2 diPAP, Wellington, Canada).

[0058] Basic methanol: Add 12 mL of 25 wt% aqueous ammonia to 988 mL of methanol to obtain basic methanol.

[0059] Acidic methanol: Add 40 mL of glacial acetic acid (AR, 99.5% purity) to 960 mL of methanol and shake to obtain acidic methanol.

[0060] Mobile phase A (15 mM ammonium acetate-0.3% ammonia in water): Mix 1.156 g of ammonium acetate, 30 mL of 25 wt% ammonia water (analytical grade), and 970 mL of water and sonicate for 3 min to obtain mobile phase A.

[0061] Accelerated solvent extraction evaporator Extreva ASE (Thermo Fisher Scientific, USA) was used.

[0062] LC-MS instrument: ultra-high performance liquid chromatography-triple quadrupole tandem mass spectrometry UHPLC-MS / MS (1290-6475, Agilent, USA).

[0063] Example 1

[0064] After removing foreign matter, the soil samples were freeze-dried to remove water, ground, and passed through a 60-mesh sieve, and the sieve portion was used as the matrix.

[0065] The Extreva ASE accelerated solvent extraction evaporator was used to extract perfluorophosphoric acid from soil using an acid-base coupled extraction agent. The specific steps were as follows: A filter membrane was placed at the bottom of the filter. 1g of matrix was loaded into a 5mL extraction cell. 50μL of a 1mg / L isotope internal standard solution was added. The solution was allowed to stand for 8 hours under ventilation to simulate the actual behavior of the target PFPAs in soil. After the solvent dried, quartz sand was added to a depth of 3-5mm from the top of the extraction cell. The cell cap was then replaced and shaken to mix thoroughly. Be careful not to contaminate the cell body or cap threads with solid particles such as sample or quartz sand. Wipe them clean before tightening.

[0066] Add 50% of the extraction cell volume of alkaline methanol, then pass alkaline methanol at a flow rate of 0.25mL / min for 20min, then add 50% of the extraction cell volume of acidic methanol, then pass acidic methanol at a flow rate of 0.25mL / min for 20min, nitrogen purge for 60s, vacuum evaporate at a temperature of 40℃, a total nitrogen flow rate of 200mL / min, and a vacuum degree of 3psi to obtain 1mL of the sample solution to be tested. Among them, the extraction temperature is 100℃,

[0067] The sample solution to be tested is subjected to LC-MS detection to obtain the detection result of perfluorophosphoric acid. The LC-MS detection conditions are as follows:

[0068] Liquid chromatography conditions: The chromatographic column was an ACQUITY BEH C18 (1.7 μm, 2.1 × 100 mm, Waters), the column temperature was 40°C; the mobile phase A was 15 mM ammonium acetate-0.3% ammonia-water, and the mobile phase B was methanol; the mobile phase flow rate was 0.3 mL / min; the injection volume was 5 μL; the elution program was a gradient elution (see Table 1), with a stop time of 10 min and a delay time of 3 min.

[0069] Table 1 Gradient elution program

[0070]

[0071] Mass spectrometry conditions: ESI negative mode and multiple reaction monitoring (MRM) mode were used, with ESI temperature of 350°C, carrier gas flow rate of 11 L / min, sheath gas temperature of 400°C, sheath gas flow rate of 13 L / min, nozzle voltage of 500 V, nebulizer voltage of 30 psi, and capillary voltage of 4000 V.

[0072] The matrix spike recoveries of each PFPAs were calculated after deducting the matrix background value, as shown in Table 2.

[0073] Table 2 PFPAs matrix spike recovery

[0074]

[0075] As shown in Table 2, the acid-base extraction reagent provided by the present invention is used to extract PFPAs from soil, and the matrix spiked recovery rate of PFPAs is 63.6% to 81.6%.

[0076] It was shown that the method provided by the present invention is suitable for the effective extraction of five PFPAs in soil.

[0077] Comparative Example 1

[0078] The only difference from Example 1 is that the extraction solvent is alkaline methanol.

[0079] Comparative Example 2

[0080] The only difference from Example 1 is that the extraction solvent is acidic methanol.

[0081] Comparative Example 3

[0082] The only difference from Example 1 is that the extraction solvent is pure methanol.

[0083] The recoveries of PFPAs in comparative examples 1 to 3 are shown in Table 3.

[0084] Table 3 Comparison of PFPAs matrix spike recovery rates of other extractants in Example 1 and Comparative Examples 1-3

[0085]

[0086] As shown in Table 3, compared with the use of alkaline methanol and pure methanol as extractants, the acid-base extractant coupling method provided by the present invention significantly improves the comprehensive extraction effect of PFHxPA, PFOPA, PFDPA, Cl-PFHxPA, and Cl-PFOPA in soil, providing a strong guarantee for the screening and control of PFPAs pollutants in soil.

[0087] Example 2

[0088] (1) Linear relationship of standard curve.

[0089] Standards: PFHxPA, PFOPA, PFDPA, Cl-PFHxPA, and Cl-PFOPA standard solutions (50 ppm) were purchased from Wellington. The purity of PFHxPA was >98%.

[0090] Preparation of standard solutions: Accurately measure 20 μL of each of the five standard solutions (50 ppm) and dilute to 1 ppm with methanol to obtain a mixed standard stock solution (each standard has the same concentration). Accurately measure 20 μL of the internal standard solution (50 ppm) and dilute to 1 ppm with methanol to obtain an internal standard stock solution. Add 50 μL of the internal standard stock solution and dilute the mixed standard stock solution in a stepwise manner with methanol. Mix thoroughly to obtain a series of standard solutions. The concentrations of the individual standards in the series of standard solutions are 0.5 ng / mL, 1 ng / mL, 2 ng / mL, 5 ng / mL, 10 ng / mL, 20 ng / mL, and 50 ng / mL, respectively. The concentration of the isotopic internal standard in each standard solution is 50 ng / mL.

[0091] Each standard solution was subjected to LC-MS detection according to the conditions of Example 1, and a standard curve was drawn with the concentration of the standard solution as the horizontal axis and the corresponding peak area as the vertical axis. Figures 1 to 5 , and obtain the linear equation, see Table 4.

[0092] Table 4 PFPAs standard curve

[0093]

[0094] As shown in Table 4, the linear range of PFPAs was wide and the linear relationship was good when the acid-base extractant coupled extraction method provided by the present invention was used for extraction and LC-MS detection.

[0095] (2) Detection limit and quantification limit.

[0096] The limit of quantification (LOQ) was determined based on the concentration at which the ratio of the signal (S) of the measured component to the baseline noise (N) was 10 (S / N=10), and the limit of detection (LOD) was determined based on the concentration at which S / N=3. The results are shown in Table 5.

[0097] Table 5 Detection limits and quantification limits of PFPAs

[0098]

[0099] As shown in Table 5, the acid-base extraction coupled extraction method provided by the present invention resulted in low detection limits and quantification limits for PFPAs detected by LC-MS, indicating that the acid-base extraction coupled extraction method provided by the present invention has a high extraction rate for the five PFPAs in soil.

[0100] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for extracting perfluorophosphoric acid from soil using an acid-base extraction agent coupling method, comprising the following steps: The soil and alkaline methanol are first mixed and subjected to alkaline extraction to obtain an alkaline extract and a residue; the alkaline methanol is ammonia water and methanol; The volume fraction of ammonia in the alkaline methanol is 0.1-0.5%; The residue is mixed with acidic methanol for a second time, and acid extraction is performed to obtain an acidic extract; the acidic methanol is carboxylic acid and methanol, and the volume fraction of the carboxylic acid in the acidic methanol is 2-6%; The alkaline extract and the acidic extract are combined and concentrated to obtain perfluorophosphoric acid; The perfluorophosphoric acid includes one or more of perfluorohexyl phosphoric acid, perfluorooctyl phosphoric acid, perfluorodecyl phosphoric acid, chloro-perfluorohexyl phosphoric acid and chloro-perfluorooctyl phosphoric acid.

2. The method according to claim 1, characterized in that The ratio of the mass of the soil to the volume of alkaline methanol is 1 g:7.5-20 mL.

3. The method according to claim 1, characterized in that The carboxylic acid comprises formic acid and / or acetic acid; The ratio of the mass of the soil to the volume of the acidic methanol is 1 g:7.5-20 mL.

4. The method according to claim 1, wherein The first mixed raw materials also include quartz sand.

5. The method according to claim 1 or 4, characterized in that The mass ratio of the soil to the quartz sand is 1:0.5-2.

6. The method according to any one of claims 1 to 4, characterized in that The alkaline extraction and the acidic extraction independently include pressurized fluid extraction, shaking extraction or ultrasonic extraction.

7. The method according to claim 6, characterized in that The conditions for the pressurized fluid extraction include: an extraction temperature of 100-120° C., and the extraction times of the alkaline pressurized fluid extraction and the acidic pressurized fluid extraction are independently 15-30 minutes.

8. The method according to claim 6, characterized in that The conditions for the oscillation extraction include: an extraction temperature of 55-65° C., the number of alkaline oscillation extraction and the number of acidic oscillation extraction are independently 2-3 times, and the time of a single oscillation extraction is 20-30 minutes.

9. The method according to claim 6, characterized in that The ultrasonic extraction conditions include: extraction temperature of 55-65° C., ultrasonic power of 400-1000 W, the number of alkaline ultrasonic extraction and acidic ultrasonic extraction is independently 2-3 times, and the time of a single ultrasonic extraction is 20-30 minutes.

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