Method for extracting and separating different forms of selenium in soil and application

Abstract

The present disclosure provides a method for extracting and separating different forms of selenium in soil and application, wherein the method for extracting and separating different forms of selenium in soil comprises: placing soil raw materials in a mixed solution of sodium pyrophosphate and potassium dihydrogen phosphate to react, obtaining precipitate and extraction liquid; filtering the extraction liquid by using a filter membrane to obtain filtrate, and quantitatively analyzing the first form of selenium in the filtrate and the zero-valent nanometer selenium on the filter membrane after filtration; according to the total amount of selenium, the content of the first form of selenium and the content of the zero-valent nanometer selenium in the soil raw materials, the content of the second form of selenium remaining in the precipitate is determined by using the difference method for quantitative analysis.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of environmental analytical chemistry, and particularly relates to a method for extracting and separating different forms of selenium in soil and application. BACKGROUND

[0002] Selenium is one of the essential trace elements for human and animal growth, and the intake of selenium-rich agricultural products is a safe and effective way to supplement selenium. Due to the uneven distribution of selenium in the environment, applying selenium fertilizer to crops can effectively increase the selenium content in crops. Among them, nano selenium (SeNPs) fertilizer is expected to become a new type of fertilizer to replace traditional selenite and selenite selenium fertilizer due to its low toxicity and high utilization rate. However, the use of nano selenium fertilizer leads to the entry of nano selenium into the environment, forming a new type of pollutant. As the direct contact matrix of nano selenium fertilizer, zero-valent nano selenium in soil will undergo a series of morphological transformations, which may cause harm to the environment and organisms. The forms of selenium in soil include metallic selenium compounds, organic selenium compounds (selenocystine SeCys2, selenomethionine SeMet, etc.), +4 valence selenite, +6 valence selenate, and zero-valent nano selenium. Among them, zero-valent nano selenium has high biocompatibility and low toxicity, and selenium compounds have strong toxicity to the human body, which is related to the valence. The toxicity of four-valent selenium is the largest, followed by six-valent selenium.

[0003] At present, the extraction of selenium in soil mainly adopts sequential extraction method, which is complicated and inefficient. With the increase of extraction steps, morphological transformation of elements may occur during the extraction process, affecting the test results. Moreover, the extraction process of related methods often focuses on the combined form of selenium in soil rather than the chemical form, and there is no report on the separation and determination of different chemical forms of selenium in soil. Therefore, it is urgent to develop a new method for extracting and separating zero-valent nano selenium and other forms of selenium in soil. Valence and content analysis of selenium in soil is of great significance for further evaluation of its environmental impact and health risk. SUMMARY

[0004] In view of the above technical problems, the present disclosure provides a method for extracting and separating different forms of selenium in soil and application, in order to at least partially solve the above-mentioned technical problems.

[0005] In order to solve the above technical problems, the technical scheme provided by the present disclosure is as follows:

[0006] As one aspect of the present disclosure, a method for extracting and separating different forms of selenium in soil is provided, comprising:

[0007] After the soil raw material is placed in a mixed solution of sodium pyrophosphate and potassium dihydrogen phosphate and reacted, a precipitate and an extraction solution are obtained;

[0008] The extraction solution is filtered by a filter membrane to obtain a filtrate, and the first form selenium in the filtrate and the zero-valent nanometer selenium on the filter membrane after filtration are quantitatively analyzed.

[0009] According to the total selenium content, the first form selenium content and the zero-valent nanometer selenium content in the soil raw material, the second form selenium content remaining in the precipitate is determined by using the difference method quantitative analysis.

[0010] In one of the embodiments, the concentration of sodium pyrophosphate in the mixed solution is 4-6 mM.

[0011] The molar concentration ratio of sodium pyrophosphate to potassium dihydrogen phosphate in the mixed solution is 10000-15000:2-4.

[0012] In one of the embodiments, the addition ratio of the soil raw material to the mixed solution is 1:180-1:220 g / mL.

[0013] In one of the embodiments, the first form selenium includes at least one of tetravalent selenium, hexavalent selenium and organic selenium, wherein the organic selenium includes at least one of selenomethionine and selenocysteine.

[0014] The second form selenium is a negative divalent metal selenide.

[0015] In one of the embodiments, the filter membrane is a microporous membrane with adsorption effect, including at least one of nylon microporous membrane and polyvinylidene fluoride microporous membrane.

[0016] The pore size of the microporous membrane is 0.22-0.8 μm.

[0017] In one of the embodiments, after the filter membrane after filtration is digested by nitric acid, a digestion solution is obtained, and the content of the zero-valent nanometer selenium is obtained by inductively coupled plasma mass spectrometry quantitative analysis.

[0018] The filtrate is separated and quantitatively analyzed by high performance liquid chromatography tandem inductively coupled plasma mass spectrometry to obtain the content of the first form selenium.

[0019] In one of the embodiments, the method for measuring the total selenium content in the soil raw material includes:

[0020] After the soil raw material is pre-digested and microwave-digested by nitric acid, hydrofluoric acid and hydrogen peroxide, the acid is removed and the volume is fixed, and the total selenium content in the soil raw material is obtained by inductively coupled plasma mass spectrometry quantitative analysis.

[0021] In one of the embodiments, the temperature of the water bath digestion treatment includes 70-75℃, and the time includes 6-8h.

[0022] In one embodiment, the volume ratio of nitric acid, hydrofluoric acid, and hydrogen peroxide is 4:1:1; the pre-digestion treatment time is 6 to 8 hours; the microwave digestion treatment is a programmed temperature rise, with a temperature of 100 to 180°C and a time of 60 to 120 minutes.

[0023] As another aspect of this disclosure, a method for extracting and separating different forms of selenium from soil is provided for application in environmental health risk assessment.

[0024] Based on the above technical solution, the method and application for extracting and separating different forms of selenium from soil provided in this disclosure uses a mixed solution of sodium pyrophosphate and potassium dihydrogen phosphate to treat the soil. Sodium pyrophosphate can effectively disperse / dissolve soil organic matter, releasing zero-valent selenium nanoparticles that are tightly bound to the soil, and extracting nano-selenium and other extractable selenium forms (tetravalent selenium, hexavalent selenium, and organic selenium) from the soil. Then, the zero-valent nano-selenium and other different forms of extractable selenium are separated and extracted from the soil by membrane filtration. Zero-valent nano-selenium is adsorbed onto the membrane, while other forms of extractable selenium remain in the filtrate. Metal selenides (divalent selenium), which are tightly bound to the soil, are not easily soluble in water and cannot be extracted by the mixed solution, thus remaining in the soil. Quantification is performed using the difference method. The technical solution provided in this disclosure, based on membrane filtration to separate nano-selenium, extracts different forms of selenium from soil in one step using a sodium pyrophosphate mixed solution. The operation is relatively simple, with high sensitivity, achieving convenient separation and accurate quantitative analysis of zero-valent selenium and other forms of selenium in soil. It has low operating costs, effectively improves detection efficiency, and has large-scale application prospects. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the technical route for extracting and separating different forms of selenium from soil in the embodiments of this disclosure;

[0026] Figure 2 This is a comparison diagram of the adsorption of different forms of selenium by nylon microporous membranes in the embodiments of this disclosure;

[0027] Figure 3 The recovery rates of different forms of selenium extracted from soil in the embodiments of this disclosure;

[0028] Figure 4 The recovery rates of zero-valent nano-selenium extracted from different types of solutions in Example 2 of this disclosure;

[0029] Figure 5 The recovery rate of zero-valent nano-selenium extracted from sodium pyrophosphate solutions of different concentrations in Example 3 of this disclosure;

[0030] Figure 6 The recovery rate of zero-valent nano-selenium extracted from soil and mixed solution at different ratios in Example 4 of this disclosure;

[0031] Figure 7 The recovery rates of zero-valent nano-selenium extracted after treatment with different homogenization methods in Example 5 of this disclosure;

[0032] Figure 8 The recovery rate of zero-valent nano-selenium extracted after treatment by different phase separation methods in Example 6 of this disclosure;

[0033] Figure 9 The recovery rate of tetravalent selenium extracted by adding different phosphates and sulfates in Example 7 of this disclosure;

[0034] Figure 10 The recovery rate of tetravalent selenium extracted with different amounts of potassium dihydrogen phosphate in Example 8 of this disclosure is given. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0036] Currently, the main method for extracting selenium from soil is sequential extraction. However, with the increase in extraction steps, non-specific extraction and speciation can occur, affecting the extraction test results. Furthermore, these extraction methods often focus on the bound state of selenium rather than its chemical form, and methods for separating zero-valent selenium nanoparticles (SeNPs) and other selenium forms in soil are lacking. Therefore, there is a need to develop a simple and accurate method for the extraction and separation of chemically derived selenium. In the process of realizing this disclosure, it was discovered that sodium pyrophosphate solution can disperse and dissolve soil organic matter, which is beneficial for the release of zero-valent selenium nanoparticles (SeNPs). This allows for one-step extraction of SeNPs and other extractable selenium forms from soil. Selective adsorption based on membranes can effectively separate SeNPs and other extractable selenium forms. High-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) is then used to separate and quantify other extractable selenium forms.

[0037] In view of the technical problems existing in the related technologies, this disclosure provides a method and application for extracting and separating different forms of selenium in soil. Based on membrane filtration and chromatography technology, the method uses sodium pyrophosphate for extraction and separation, accurately determines the content of SeNPs and other forms of selenium in soil, has low operating costs, and has high application development prospects.

[0038] Specifically, as one aspect of this disclosure, this disclosure provides a method for extracting and separating different forms of selenium from soil, comprising:

[0039] Soil raw materials were reacted in a mixed solution of sodium pyrophosphate and potassium dihydrogen phosphate to obtain precipitate and extract.

[0040] The extract was filtered through a filter membrane to obtain a filtrate. The first form of selenium in the filtrate and the zero-valent selenium nanoparticles on the filter membrane after filtration were quantitatively analyzed.

[0041] Based on the total selenium content, the content of first-form selenium, and the content of zero-valent nano-selenium in the soil raw materials, the content of second-form selenium remaining in the precipitate was determined by quantitative analysis using the difference method.

[0042] According to embodiments of this disclosure, sodium pyrophosphate (TSPP) solution can disperse and dissolve soil organic matter, which is beneficial for the release of SeNPs. Potassium dihydrogen phosphate can promote the extraction of tetravalent selenium. The mixed solution can extract SeNPs and other extractable selenium from the soil in one step. The mixed solution of sodium pyrophosphate and potassium dihydrogen phosphate has good extraction efficiency for different forms of selenium. The extracted selenium is in its chemical form, and selective adsorption based on a membrane can effectively separate SeNPs and other extractable selenium, thereby achieving the separation and quantification of other extractable selenium forms.

[0043] According to embodiments of this disclosure, a certain amount of soil raw material is placed in a centrifuge tube, and a mixed solution of sodium pyrophosphate and potassium dihydrogen phosphate is added. After shaking at room temperature for at least 1 hour, the mixture is sonicated for at least 30 minutes to react. The sample suspension is then placed in the dark at room temperature for at least 6 hours to precipitate large soil particles, resulting in soil precipitate and extract. 3-5 mL of the extract is taken from 1-2 cm below the liquid surface for subsequent quantitative analysis. The extract contains dissolved zero-valent nano-selenium and first-form selenium, including at least one of tetravalent selenium, hexavalent selenium, and organic selenium, wherein organic selenium includes at least one of selenomethionine and selenocysteine. The obtained precipitate is soil precipitate containing unextracted second-form selenium, which is a negative divalent metal selenium oxide tightly bound to the soil. Metal selenides are not easily soluble in water and are retained in the soil precipitate. The content of metal selenium oxide is calculated and analyzed based on the total selenium content of the soil raw material using the difference method.

[0044] According to embodiments of this disclosure, the concentration of sodium pyrophosphate in the mixed solution is 4–6 mM, for example, 4 mM, 5 mM, 5.5 mM, 6 mM, etc.; the molar ratio of sodium pyrophosphate to potassium dihydrogen phosphate in the mixed solution is 10000–15000:2–4, for example, 10000:4, 12000:4, 13000:3, 14000:2, 15000:2, etc. If the sodium pyrophosphate concentration is too low, zero-valent nano-selenium in the soil cannot be fully released from the soil into the mixed solution of sodium pyrophosphate and potassium dihydrogen phosphate, thus affecting the test results.

[0045] According to the embodiments of this disclosure, the addition ratio of soil raw material to mixed solution is 1:180 to 1:220 g / mL, for example, it can be 1:180, 1:190, 1:200, 1:210, 1:220, etc. When the ratio of soil raw material to mixed solution is less than 1:180, the extractable selenium (zero-valent nano-selenium) in the soil raw material cannot be completely extracted by the mixed solution, and some of it remains in the soil, affecting the test results.

[0046] According to embodiments of this disclosure, the filter membrane is a microporous membrane with adsorption function, including at least one of nylon microporous membrane and polyvinylidene fluoride microporous membrane, used to adsorb zero-valent selenium nanoparticles from the extract onto the filter membrane and separate zero-valent selenium nanoparticles from selenium in its first form; the pore size of the microporous membrane is 0.22 to 0.8 μm, for example, it can be 0.22 μm, 0.45 μm, 0.8 μm, etc., or a microporous membrane with a larger or smaller pore size that can separate zero-valent selenium nanoparticles and selenium in its first form can be selected according to the actual situation.

[0047] According to embodiments of this disclosure, the filter membrane can selectively adsorb nanoparticles without adsorbing their ionic state through adsorption. After filtering the extract using the filter membrane, zero-valent selenium nanoparticles in the extract are adsorbed onto the filter membrane, while other forms of selenium remain in the filtrate. The filtrate is collected for subsequent quantitative analysis. The filtered membrane is transferred to a centrifuge tube, and 2-3 mL of nitric acid and 2-3 mL of pure water are added. The zero-valent selenium nanoparticles on the filtered membrane are digested in a water bath using nitric acid. The digestion temperature includes 70-75°C, for example, 70°C, 72°C, 73°C, 75°C, etc., and the digestion time includes 6-8 hours, for example, 6 hours, 6.5 hours, 7 hours, 8 hours, etc., to completely digest the zero-valent selenium nanoparticles. The digested solution is then obtained. After dilution, the digested solution is analyzed and quantified using inductively coupled plasma mass spectrometry (ICP-MS) to obtain the content of zero-valent selenium nanoparticles. During the ICP-MS determination, an oxygen reaction / collision cell is used, and the monitored isotopes are selectively... 78 Se or 80 To reduce background interference, select SE. 78 Se is more effective when used as the monitored isotope.

[0048] According to embodiments of this disclosure, high-performance liquid chromatography-tandem inductively coupled plasma mass spectrometry (HPLC-ICP-MS / MS) is used to separate and quantify filtrate, which can separate different forms of selenium and obtain the content of the first form of selenium. Specifically, the filtrate is introduced into the HPLC-ICP-MS / MS system, and a Hamilton PRP-X100 anion exchange column is selected. The outlet of the HPLC column is connected to the nebulizer of the ICP-MS / MS system through a PEEK capillary tube. The injection volume of the filtrate is 45-50 μL, the mobile phase is 85-95 mM ammonium acetate solution, the flow rate is set to 0.9-1.0 mL / min, and the retention time is 30-35 min to completely elute the target analytes, thereby completing the separation and quantification of tetravalent selenium, hexavalent selenium, selenomethionine, and selenocysteine.

[0049] According to embodiments of this disclosure, the total selenium content in soil is determined by digesting soil raw materials. The content of metal selenides is quantified using a difference method. The content of metal selenides is obtained by subtracting the content of zero-valent nano-selenium and the content of first-form selenium from the total selenium content. The method for determining the total selenium content in soil raw materials includes:

[0050] Pre-digestion of soil samples using nitric acid, hydrofluoric acid, and hydrogen peroxide is employed to remove any potentially generated gases, thereby reducing pressure and ensuring safety during subsequent microwave digestion. The volume ratio of nitric acid, hydrofluoric acid, and hydrogen peroxide is 4:1:1. A certain amount of soil sample is added to a digestion tube, followed by the sequential addition of 4 mL of nitric acid, 1 mL of hydrofluoric acid, and 1 mL of hydrogen peroxide. Pre-digestion is carried out at room temperature for 6–8 hours, e.g., 6 hours, 6.5 hours, 7 hours, or 8 hours. Following microwave digestion, the acid is removed and the volume is adjusted. The microwave digestion temperature ranges from 100–180℃, e.g., 100℃, 110℃, 120℃, 150℃, or 180℃. Temperatures that are too low will result in incomplete digestion, while temperatures that are too high cannot guarantee safe reaction. Therefore, microwave digestion of soil within this temperature range ensures complete digestion of the soil sample while guaranteeing reaction safety. Microwave digestion times range from 60 to 120 minutes, for example, 60, 70, 80, 100, or 120 minutes. Depending on the specific program, the microwave temperature can fluctuate by around 10°C, and the processing time can vary within a 5-minute range. A possible microwave digestion program is: heating to 100-110°C at a rate of 10°C / min and holding for 5-10 minutes; then heating to 150-160°C within 10 minutes and holding for 5-10 minutes; finally heating to 180-190°C within 10 minutes and holding for 30-35 minutes. This program can be adjusted according to actual conditions. Inductively coupled plasma mass spectrometry (ICP-MS) is then used for quantification to determine the total selenium content in the soil sample.

[0051] As another aspect of this disclosure, a method for extracting and separating different forms of selenium from soil is provided for application in environmental health risk assessment.

[0052] To make the objectives, technical solutions, and advantages of this disclosure clearer, the technical solutions and principles of this disclosure are further illustrated below with reference to specific embodiments and accompanying drawings. It should be noted that the specific embodiments described below are merely illustrative examples, and the scope of protection of this disclosure is not limited thereto.

[0053] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available. Unless otherwise specified, specific techniques or conditions in the examples are conventional methods and can be performed according to the techniques or conditions described in the literature or the product instructions.

[0054] Figure 1 This is a schematic diagram of the technical route for extracting and separating different forms of selenium from soil in the embodiments of this disclosure. Figure 1 The method provided in this disclosure can be demonstrated in that, specifically, a certain amount of soil sample is placed in a centrifuge tube, and a mixed solution of sodium pyrophosphate and potassium dihydrogen phosphate is added to the centrifuge tube to disperse the soil organic matter, forming a suspension; nano-selenium and other extractable selenium (tetravalent selenium, hexavalent selenium, and organic selenium) in the soil are extracted in one step. After the extraction and sedimentation reaction is complete, the upper extract and soil precipitate are obtained in the centrifuge tube. The precipitate contains metal selenides that are not easily soluble in water, and the upper extract contains zero-valent nano-selenium, organic selenium, and tetravalent selenium. Zero-valent selenium and hexavalent selenium were extracted and then separated by membrane filtration. During the filtration process, nano-selenium was adsorbed onto the filter membrane, while organic selenium, tetravalent selenium, and hexavalent selenium were not adsorbed by the filter membrane and remained in the filtrate. The content of zero-valent nano-selenium was determined by inductively coupled plasma mass spectrometry (ICP-MS). Organic selenium (selenomethionine, selenocysteine), tetravalent selenium, and hexavalent selenium in the filtrate were separated by high-performance liquid chromatography-tandem ICP-MS, and their contents were obtained separately. The content of metal selenides in the precipitate was then obtained by subtraction based on the total selenium content in the soil.

[0055] Example 1

[0056] A method for extracting and separating different forms of selenium from soil, by Figure 1 This illustration schematically demonstrates the technical route for extracting and separating different forms of selenium from soil in embodiments of this disclosure.

[0057] After preparing a mixed solution of 5 mM sodium pyrophosphate and 1.2 μM potassium dihydrogen phosphate, 0.2 g of soil raw material was placed in a 50 mL centrifuge tube, and 40 mL of the mixed solution of sodium pyrophosphate and potassium dihydrogen phosphate was added. The mixture was shaken on a shaker at 200 rpm for 1 h and then sonicated for 30 min to form a suspension. The sample suspension was placed in a dark environment at room temperature for 6 h to precipitate large soil particles, forming a precipitate and extract.

[0058] 3 mL of the extract was taken 1 cm below the liquid surface and filtered through a nylon microporous membrane with a pore size of 0.45 μm. The filtrate and the filtered membrane were obtained. The filtered membrane was transferred to a 10 mL centrifuge tube, and 2 mL of concentrated nitric acid and 2 mL of ultrapure water were added. The mixture was then incubated in a water bath at 70 °C for 6 h to digest the zero-valent selenium nanoparticles, allowing them to dissolve in the digestion solution. After diluting the digested solution, the content of zero-valent selenium nanoparticles was determined using inductively coupled plasma mass spectrometry. The detection limit for zero-valent selenium nanoparticles in the soil was found to be 0.02 μg / g. Figure 2 This is a comparison diagram of the adsorption of different forms of selenium by nylon microporous membranes in the embodiments of this disclosure. Figure 2 It can be seen that the nylon microporous membrane has an adsorption rate of 83% for SeNPs, while the adsorption rate for other forms of selenium is less than 10%.

[0059] The collected filtrate was introduced into high performance liquid chromatography-inductively coupled plasma mass spectrometry. The mobile phase was 90 mM ammonium acetate solution, and the flow rate was 1 mL / min for 30 min to separate different forms of selenium and obtain the contents of tetravalent selenium, hexavalent selenium, and organic selenium (selenomethionine and selenocysteine).

[0060] The total selenium content in soil samples was determined by digestion. 0.05 g of soil sample was placed in a digestion tube, and 4 mL of nitric acid, 1 mL of hydrofluoric acid, and 1 mL of hydrogen peroxide were added sequentially for pre-digestion for 6 hours. Subsequently, microwave digestion was performed, followed by acid removal and volume adjustment. The microwave digestion program was set as follows: 10 min to 100℃, hold for 5 min; 10 min to 150℃, hold for 5 min; and finally 10 min to 180℃, hold for 30 min. The total selenium content in the soil was then determined by inductively coupled plasma mass spectrometry (ICP-MS), and the content of metal selenides in the soil was calculated using the difference method based on the content of zero-valent nano-selenium, tetravalent selenium, hexavalent selenium, and organic selenium.

[0061] Figure 3 To illustrate the recovery rates of different forms of selenium extracted from soil in this embodiment of the present disclosure, such as... Figure 3 As shown, the method provided in this disclosure can effectively separate and extract different forms of selenium in soil. In addition to metal selenides in soil, the mixed solution of sodium pyrophosphate and potassium dihydrogen phosphate has good extraction efficiency for different forms of selenium.

[0062] Example 2

[0063] The same extraction and separation method as in Example 1 was used in the soil, except that the mixed solution of sodium pyrophosphate and potassium dihydrogen phosphate was replaced with ultrapure water (UP), sodium pyrophosphate solution, methyl ammonium hydroxide (TMAH), potassium nitrate (KNO3), and sodium nitrate (NaNO3), respectively.

[0064] Figure 4 The recovery rate of zero-valent nano-selenium extracted from different types of solutions in Example 2 of this disclosure is determined by... Figure 4 It can be seen that the recovery rate of sodium pyrophosphate solution is the highest, reaching 83%.

[0065] Example 3

[0066] The same extraction and separation method as in Example 1 was used in the soil, except that the mixed solution of sodium pyrophosphate and potassium dihydrogen phosphate was replaced with a sodium pyrophosphate solution of different concentrations. Figure 5 The recovery rate of zero-valent nano-selenium extracted from sodium pyrophosphate solutions of different concentrations in Example 3 of this disclosure is determined by... Figure 5 It can be seen that the recovery rate of sodium pyrophosphate for the extraction of zero-valent nano-selenium is in the range of 70% to 85% at different concentrations. Among them, the recovery rate is the highest when the concentration of sodium pyrophosphate solution is 5mM, showing a better recovery level.

[0067] Example 4

[0068] The same extraction and separation method as in Example 1 was used, except that the amount of soil raw material added was changed and the ratio of soil to mixed solution was adjusted.

[0069] Figure 6 The recovery rate of zero-valent selenium nanoparticles extracted from soil and mixed solution at different ratios in Example 4 of this disclosure is determined by... Figure 6 It can be seen that the recovery rate of zero-valent nano-selenium is highest when the ratio of soil to mixed solution is 1:200.

[0070] Example 5

[0071] The same extraction and separation method as in Example 1 was used, the only difference being the homogenization method after the soil and the mixed solution were mixed, which was changed to ultrasonic method, cell disruption method and oscillation method respectively.

[0072] Figure 7 The recovery rate of zero-valent selenium nanoparticles after treatment with different homogenization methods in Example 5 of this disclosure is given by... Figure 7 It can be seen that the recovery rate of zero-valent nano-selenium extracted after ultrasonic treatment and oscillation method is relatively high.

[0073] Example 6

[0074] The same extraction and separation method as in Example 1 was used in the soil, except that the phase separation method after the soil reacted with the mixed solution was changed. The phase separation methods were centrifugation (6000g, 3000g, 1000g), 0.45μm nylon microporous membrane separation, and sedimentation (SED) separation. Figure 8 The recovery rate of zero-valent selenium nanoparticles after treatment by different phase separation methods in Example 6 of this disclosure is determined by... Figure 8 It can be seen that the recovery rate of zero-valent nano-selenium after separating soil sediment and extract by sedimentation is much higher than that of centrifugation and membrane separation methods.

[0075] Analysis of Examples 2-6 shows that, based on the effects of different extractable selenium form solution types, solution concentrations, soil-to-solution ratios, homogenization methods, and phase separation methods on the extraction efficiency of zero-valent nano-selenium, the optimal treatment conditions for extracting zero-valent nano-selenium from soil can be determined as follows: extraction using 5 mM sodium pyrophosphate solution, a soil-to-solution ratio of 1:200, ultrasonic treatment for 30 min, sedimentation for 6 h, and then taking the upper extract for analysis.

[0076] Example 7

[0077] The same extraction and separation method as in Example 1 was used for soil extraction, except that the potassium dihydrogen phosphate in the mixed solution of sodium pyrophosphate and potassium dihydrogen phosphate was replaced with no potassium dihydrogen phosphate, sodium sulfate, sodium phosphate, and sodium hydrogen phosphate, respectively, to investigate the effect of the addition of phosphate and sulfate on the extraction of tetravalent selenium. Figure 9 To improve the recovery rate of tetravalent selenium extraction by adding different phosphates and sulfates in Example 7 of this disclosure, the following parameters were used: Figure 9 It can be seen that adding potassium dihydrogen phosphate has a positive impact on the recovery of tetravalent selenium.

[0078] Example 8

[0079] The same extraction and separation method as in Example 1 was used in the soil, the only difference being the change in the amount of potassium dihydrogen phosphate added to the mixed solution of sodium pyrophosphate and potassium dihydrogen phosphate. Figure 10 The recovery rate of tetravalent selenium extracted with different amounts of potassium dihydrogen phosphate in Example 8 of this disclosure is determined by... Figure 10 It can be seen that adding 1.2 μM potassium dihydrogen phosphate can promote the extraction of tetravalent selenium, and the molar ratio of sodium pyrophosphate to potassium dihydrogen phosphate is 12500:3.

[0080] Example 9

[0081] The same extraction and separation method as in Example 1 was used in the soil, the only difference being that the soil samples tested were replaced. As shown in Table 1, metal selenides were detected in all 6 soil samples, selenomethionine (SeMet) was detected in 5 soil samples, and zero-valent selenium nanoparticles were detected in 1 sample.

[0082] Table 1. Detection results of different forms of selenium in six soil samples.

[0083]

[0084] Six soil samples were spiked with different forms of selenium: 1.14 μg / g of zero-valent nano-selenium, 1 μg / g of tetravalent selenium, 1 μg / g of hexavalent selenium, 1 μg / g of selenomethionine, 1 μg / g of selenocystine, and 1 μg / g of metal selenide.

[0085] As shown in Table 2, at a spiked concentration of 1 μg / g, the recoveries of SeNPs in soil samples were 79.9%–149%, Se(IV) were 62.3%–110%, Se(VI) were 108%–115%, SeMet was 75.4%–92.4%, and SeCys2 was 52.5%–94.2%, indicating that the method proposed in this disclosure can effectively extract and separate SeNPs and other different forms of selenium from environmental soil samples.

[0086] Table 2. Detection results and recovery rates of different selenium forms in six soil samples after calibration.

[0087]

[0088]

[0089] The method and its application for extracting and separating different forms of selenium from soil disclosed herein utilizes a mixed solution of sodium pyrophosphate and potassium dihydrogen phosphate to extract nano-selenium and other extractable selenium from soil. The method employs membrane filtration and high-performance liquid chromatography-tandem inductively coupled plasma mass spectrometry (HPLC-ICP-MS) to achieve the separation and accurate quantitative analysis of SeNPs and other extractable selenium in environmental soil. The method has a detection limit of 0.02 μg / g, high sensitivity for content detection, and is simple to operate with low operating costs, making it suitable for large-scale industrial applications.

[0090] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A method for extracting and separating different forms of selenium from soil, comprising: After reacting the soil raw material in a mixed solution of sodium pyrophosphate and potassium dihydrogen phosphate, different forms of selenium in the soil are extracted in one step to obtain precipitate and extract. The concentration of sodium pyrophosphate in the mixed solution is 4-6 mM. The extract includes zero-valent nano-selenium and first form of selenium. The first form of selenium includes tetravalent selenium, hexavalent selenium, and organic selenium. The organic selenium includes at least one of selenomethionine and selenocysteine. The extract was filtered using a filter membrane to obtain a filtrate. The first form of selenium in the filtrate and the zero-valent selenium nanoparticles on the filter membrane after filtration were quantitatively analyzed. The filter membrane was a microporous membrane with adsorption properties. Based on the total selenium content in the soil raw material, the content of the first form of selenium, and the content of the zero-valent nano-selenium, the content of the second form of selenium remaining in the precipitate is determined by quantitative analysis using the difference method. The second form of selenium is a divalent metal selenide.

2. The method according to claim 1, wherein, The molar ratio of sodium pyrophosphate to potassium dihydrogen phosphate in the mixed solution is 10000-15000:2-4.

3. The method according to claim 1, wherein, The ratio of the soil raw material to the mixed solution is 1:180~1:220 g / mL.

4. The method according to claim 1, wherein, The microporous membrane includes at least one of nylon microporous membrane and polyvinylidene fluoride microporous membrane; The pore size of the microporous membrane is 0.22~0.8μm.

5. The method according to claim 1, wherein, The filtered membrane was digested in a water bath with nitric acid to obtain a digestion solution, which was then analyzed quantitatively by inductively coupled plasma mass spectrometry to determine the content of the zero-valent selenium nanoparticles. The filtrate was separated and quantified using high performance liquid chromatography-tandem inductively coupled plasma mass spectrometry to obtain the content of the first form of selenium.

6. The method according to claim 1, wherein, The method for determining the total selenium content in the soil raw material includes: The soil raw material was pre-digested and microwave-digested using nitric acid, hydrofluoric acid, and hydrogen peroxide. After acid removal and volume adjustment, the total selenium content in the soil raw material was obtained by inductively coupled plasma mass spectrometry analysis.

7. The method according to claim 5, wherein, The water bath digestion process is carried out at a temperature of 70-75°C for 6-8 hours.

8. The method according to claim 6, wherein, The volume ratio of nitric acid, hydrofluoric acid, and hydrogen peroxide is 4:1:1; The placement time for the pre-digestion treatment includes 6-8 hours; The microwave digestion process involves programmed temperature increases, with temperatures ranging from 100 to 180°C and time ranging from 60 to 120 minutes.

9. An application of the method as described in any one of claims 1 to 8 in environmental health risk assessment.

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