Soil heavy metal determination method based on pXRF

Abstract

The invention discloses a pXRF-based soil heavy metal determination method, and belongs to the technical field of soil heavy metal detection. The determination method comprises a soil sample pretreatment step and a step of carrying out detection by using a portable X-ray fluorescence spectrum analyzer, and the soil sample pretreatment step comprises the following steps: taking soil, adding water, stirring, adding a polar organic solvent which has a boiling point of less than 100 DEG C and is mutually soluble with water, stirring, centrifuging, and drying to obtain the pretreated soil sample. When the organic solvent is used for treatment, the drying rate of the soil sample can be increased, the soil sample cannot be gathered again in the drying process, the dried soil sample has good dispersity, the treatment links of grinding and sieving can even be omitted before a portable X-ray fluorescence spectrum analyzer is used for detection, the detection time is shortened, and the detection efficiency is improved. And rapid determination of soil heavy metals is realized.

Description

Technical Field

[0001] This application belongs to the technical field of soil heavy metal detection, and specifically relates to a method for determining soil heavy metals based on pXRF. Background Technique

[0002] Soil is a natural resource on which human beings depend for survival. However, with the acceleration of the urbanization and industrialization processes, the soil environment is facing unprecedented threats, and the pollution situation is becoming increasingly serious. The problem of soil heavy metal pollution caused by heavy metal pollutants is particularly serious. Heavy metals are relatively difficult to migrate in the soil, can only move within a small range, and cannot be decomposed by microorganisms. They will only gradually extend in the food chain and ultimately enter the human body, affecting physical health.

[0003] Rapid and accurate determination of soil heavy metals plays a crucial role in the investigation, assessment, and remediation of soil heavy metal pollution. Traditional laboratory methods for determining soil heavy metals, such as spectrophotometry, atomic fluorescence spectroscopy (AFS), atomic absorption spectroscopy (AAS), inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma optical emission spectroscopy (ICP-OES), etc. These analytical instruments are expensive, the detection cost is high, and the sample pretreatment is cumbersome and time-consuming. The treatment process may also cause secondary pollution. X-ray fluorescence spectroscopy (XRF) has been widely used in many fields due to its advantages of simultaneous determination of multiple elements, rapidity, non-destructive detection, and low detection cost. The X-ray fluorescence spectroscopy using a portable X-ray fluorescence spectrometer is called portable X-ray fluorescence spectroscopy (pXRF), which is a new type of detection technology. Its pretreatment process is simple, for example, it does not require digestion and can be directly detected by pressing tablets; the analysis period is short; it can accurately and rapidly measure the heavy metal content in the soil. Moreover, in-situ determination can be carried out on-site through a portable X-ray fluorescence spectrometer, which can avoid blind large-scale sampling and greatly save the experimental cost.

[0004] In the actual application process, the physical and chemical properties of soil have a certain impact on the soil heavy metal determination method based on pXRF. As recorded in "Review on the Application of Portable XRF in Soil Heavy Metal Monitoring" (DOI: 10.19694 / j.cnki.issn2095 - 2457.2019.22.037), soil particle size and moisture content (soil water) are the key factors affecting the measurement accuracy. The main reason is that soil particle size affects the penetration efficiency of characteristic radiation. For large - particle - size samples, the penetration depth of characteristic radiation decreases, resulting in inaccurate detection results; soil moisture, as a primary X - ray barrier and a scatterer of secondary X - rays, affects the absorption of characteristic X - rays. For example, when the soil moisture content is large, characteristic X - rays are prone to scattering, resulting in a low detection result.

[0005] Pretreatment of soil by drying, grinding, and sieving can reduce soil moisture, decrease soil particle size, and improve the detection accuracy of the soil heavy metal determination method based on pXRF. However, these pretreatment steps still require a large amount of time, increasing the work intensity and unable to achieve rapid determination of heavy metals. In the existing technology, drying usually adopts the method of heating and drying. Although heating and drying can shorten the drying time by removing water in the soil, the soil after heating and drying is extremely hard, which will undoubtedly increase the grinding difficulty, and metal grinders generally also bring pollution. Summary of the Invention

[0006] 1. Problems to be Solved

[0007] In view of the technical problem that the drying efficiency and grinding difficulty cannot be balanced in the pretreatment process of the above - mentioned soil heavy metal determination method based on pXRF, this application provides a new soil sample pretreatment method. This pretreatment method includes first pretreating the soil with a polar organic solvent whose boiling point is less than 100 °C and is miscible with water, and then drying (naturally air - drying or heating and drying). The pretreated soil sample has a significantly improved drying efficiency, and the dried soil has good dispersibility, reducing the difficulty of subsequent grinding and sieving. Even the grinding and sieving treatment links can be omitted, and it can be directly tested on the machine (portable X - ray fluorescence spectrometer) to achieve rapid determination of soil heavy metals.

[0008] 2. Technical Solutions

[0009] To solve the above problems, the technical solutions adopted in this application are as follows:

[0010] This application provides a soil heavy metal determination method based on pXRF. This determination method includes a soil sample pretreatment step and a detection step using a portable X - ray fluorescence spectrometer. Among them, the soil sample pretreatment step includes:

[0011] Take soil, add water and stir, then add a polar organic solvent with a boiling point less than 100 °C and miscible with water, stir, centrifuge and dry to obtain a pretreated soil sample; The inventor found through research that using the above organic solvent treatment can improve the drying rate of the soil sample, and the soil sample will not re-aggregate during the drying process. The dried soil sample has good dispersibility and can even omit the grinding and sieving treatment steps before detection using a portable X-ray fluorescence spectrometer, reducing the determination time and achieving rapid determination of soil heavy metals.

[0012] Further, in the above pretreatment step, weigh 3 - 5 g of soil. When using a portable X-ray fluorescence spectrometer for detection, only about 1 g of the sample needs to be taken. Therefore, only an appropriate weight of soil sample needs to be taken during the pretreatment process, and 3 - 5 g basically meets the requirements. However, if a large number of parallel detections of the sample or other purposes are required, it can also be weighed according to the experimental needs.

[0013] Further, in the above pretreatment step, the water is deionized water, which can avoid the influence of ions in the water on the heavy metal ions in the soil.

[0014] Further, in the above pretreatment step, relative to 3 - 5 g of soil sample, 1 - 2 ml of deionized water is added to the weighed soil.

[0015] Further, in the above pretreatment step, the addition of water and stirring includes stirring methods such as vortexing.

[0016] Further, in the above pretreatment step, the time for adding water and stirring is 20 - 60 s. The purpose is to make the water and soil fully mixed to form a slurry. The purpose of forming a slurry is to quickly disperse the soil and ensure that the soil has good dispersibility and uniformity.

[0017] Further, in the above pretreatment step, the time for adding water and stirring is 30 s.

[0018] Further, in the above pretreatment step, the polar organic solvent with a boiling point less than 100 °C and miscible with water includes alcohol organic solvents and / or ketone organic solvents.

[0019] Further, the above alcohol organic solvents include: methanol and / or ethanol. Further still, the above alcohol organic solvent is ethanol.

[0020] Further, the above ketone organic solvents include: acetone and / or butanone. Further still, the above ketone organic solvent is acetone.

[0021] Further, the usage amount of the above organic solvent is 1 - 4 times the volume of the added water.

[0022] Further, in the above pretreatment step, the stirring after adding the organic solvent includes stirring methods such as vortexing.

[0023] Further, in the above pretreatment step, the stirring time after adding the organic solvent is 20 - 60 s, and the purpose is to promote the full mutual solubility of the organic solvent and the water in the soil sample.

[0024] Further, in the above pretreatment step, the stirring time after adding the organic solvent is 30 s.

[0025] Further, in the above pretreatment step, centrifugation includes centrifuging at 4000 - 6000 r / min for 3 - 5 min, and the purpose is to promote the separation of the soil and the solution (organic solvent and water).

[0026] Further, in the above pretreatment step, drying includes natural air drying or heating and drying.

[0027] Further, in the above pretreatment step, heating and drying includes heating at 150 - 160 °C for 3 - 5 min, and heating and drying can further improve the drying efficiency.

[0028] Further, for the soil sample after the above pretreatment, its water content is less than 1% (by mass).

[0029] Further, for the soil sample after the above pretreatment, the proportion of soil with a particle size less than 0.2 mm is greater than 50% (by mass).

[0030] Further, for the soil sample after the above pretreatment, the proportion of soil with a particle size less than 0.2 mm is greater than 60% (by mass).

[0031] Further, for the soil sample after the above pretreatment, the proportion of soil with a particle size less than 0.2 mm is greater than 70% (by mass).

[0032] Further, for the soil sample after the above pretreatment, the proportion of soil with a particle size less than 0.2 mm is greater than 80% (by mass).

[0033] Further, for the soil sample after the above pretreatment, the proportion of soil with a particle size less than 0.2 mm is greater than 90% (by mass).

[0034] Further, for the soil sample after the above pretreatment, its hardness is less than 20 kgf.

[0035] Further, for the soil sample after the above pretreatment, its hardness is less than 15 kgf.

[0036] Further, the above detection step using a portable X-ray fluorescence spectrometer includes:

[0037] Seal the bottom of the pXRF sample cup completely with a special polypropylene film for X-ray, and fix it with a collar. Take about 1 g of the pre-treated soil sample, put it into the sample cup and compact it to ensure that the test surface of the sample is flat. After completion, place it in the pXRF sample chamber for measurement.

[0038] Further, in the above method for determining heavy metals in soil based on pXRF, the heavy metals in the soil include any one or more of Pb, Cu, Ni, Zn, and Cd.

[0039] Further, in the above method for determining heavy metals in soil based on pXRF, the soil includes any one or more of blue soil, yellow soil, red soil, black soil, and white soil.

[0040] This application also provides the application of the above method for determining heavy metals in soil based on pXRF in detecting heavy metals in soil.

[0041] Further, in the above application, the soil includes any one or more of blue soil, yellow soil, red soil, black soil, and white soil.

[0042] Further, in the above application, the heavy metals in the soil include any one or more of Pb, Cu, Ni, Zn, and Cd.

[0043] 3. Beneficial effects

[0044] Compared with the prior art, the beneficial effects of this application are as follows:

[0045] (1) The method for determining heavy metals in soil based on pXRF provided by this application includes a soil pre-treatment step and a detection step using a portable X-ray fluorescence spectrometer. Among them: the soil pre-treatment is to first mix a polar organic solvent with a boiling point less than 100 °C and miscible with water with the soil sample, and then dry it. This pre-treatment method can improve the drying efficiency of the soil sample and achieve rapid drying of the soil.

[0046] (2) For the method for determining heavy metals in soil based on pXRF provided by this application, the dried soil sample has good dispersibility and can be directly used for pXRF detection by crushing with fingers or without grinding and sieving, realizing rapid determination by pXRF.

[0047] (3) For the method for determining heavy metals in soil based on pXRF provided by this application, the pre-treated soil sample has low water content and small particle size, effectively avoiding the influence of soil moisture and particle size on the detection accuracy, thereby realizing accurate determination by pXRF.

[0048] (4) The soil heavy metal determination method provided by this application verifies its applicability to the detection of common heavy metals Pb, Cu, Ni, Zn, and Cd in soil, and provides an efficient sample pretreatment method for the rapid and accurate determination of soil heavy metals. Description of the Drawings

[0049] Figure 1 It shows the changes in soil quality under natural air-drying conditions for the ethanol treatment group and the control group.

[0050] Figure 2 It shows the changes in soil quality under natural air-drying conditions for the acetone treatment group and the control group.

[0051] Figure 3 It shows the pictures of the soil after drying for the ethanol treatment group and the control group (the left side is the control group, and the right side is the treatment group). From top to bottom, they are blue soil, yellow soil, red soil, black soil, and white soil.

[0052] Figure 4 It shows the pictures of the soil after drying for the acetone treatment group and the control group (the left side is the control group, and the right side is the treatment group). From top to bottom, they are blue soil, yellow soil, red soil, black soil, and white soil.

[0053] Figure 5 It shows the soil sieving rate (10 mesh, 2 mm) for the ethanol treatment group and the control group.

[0054] Figure 6 It shows the soil sieving rate (10 mesh, 2 mm) for the acetone treatment group and the control group.

[0055] Figure 7 It shows the soil hardness for the ethanol treatment group and the control group.

[0056] Figure 8 It shows the soil hardness for the acetone treatment group and the control group.

[0057] Figure 9 It shows the soil SEM images for the treatment group and the control group (the left side is the control group, and the right side is the treatment group). From top to bottom, they are blue soil, yellow soil, red soil, black soil, and white soil.

[0058] Figures 10-14 It shows the regression analysis of the soil heavy metal pXRF detection results for the ethanol treatment group and the control group. Figures 10-14 In sequence, they are Pb, Cu, Ni, Zn, and Cd.

[0059] Figures 15-19 It shows the heavy metal concentrations in the supernatant after centrifugation of the five types of soil. Figures 15-19 In sequence, they are blue soil, yellow soil, red soil, black soil, and white soil. Detailed Embodiments

[0060] The following further describes this application in combination with specific embodiments.

[0061] It should be noted that terms such as "upper", "lower", "left", "right", "middle", etc. cited in this specification are only for the sake of clarity in narration and are not used to limit the scope of implementation. The change or adjustment of their relative relationship, without substantial change in the technical content, should also be regarded as the scope within which this application can be implemented.

[0062] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0063] For those not specified in the examples, they are carried out under conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0064] As used herein, the term "about" is used to provide flexibility and imprecision associated with a given term, measurement, or value. Those skilled in the art can easily determine the degree of flexibility of a specific variable.

[0065] As used herein, the term "at least one of..." is intended to be synonymous with "one or more of...". For example, "at least one of A, B, and C" clearly includes only A, only B, only C, and their respective combinations.

[0066] Concentrations, amounts, and other numerical data may be presented herein in a range format. It should be understood that such range formats are used only for convenience and brevity and should be interpreted flexibly as including not only the values explicitly recited as the limits of the range but also all individual values or sub-ranges subsumed within the stated range as if each value and sub-range were explicitly recited. For example, the numerical range of about 1 to about 4.5 should be interpreted as including not only the explicitly recited limit values of 1 to about 4.5 but also the individual numbers (such as 2, 3, 4) and sub-ranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that recite only one numerical value, such as "less than about 4.5", which should be interpreted as including all of the above values and ranges. In addition, this interpretation should apply regardless of the breadth of the range or feature described.

[0067] As used in this application, "polarity" refers to the non-uniformity of charge distribution in a covalent bond or molecule, and "polar organic solvent" refers to an organic solvent whose molecules have polarity.

[0068] In this application, the portable X-ray fluorescence spectrometer is the E-max100 sold by Suzhou Jiapu Co., Ltd. This application does not limit the specific portable X-ray fluorescence spectrometer, as long as it can detect the pretreated samples. The specific operation steps of the portable X-ray fluorescence spectrometer can be carried out with reference to the conventional conditions or the conditions recommended by the manufacturer.

[0069] In this application, the high-speed refrigerated centrifuge is the Sigma 3K15 sold by Xima Centrifuge (Yangzhou) Co., Ltd.

[0070] In this application, the atomic absorption spectrometer is the AAS vario 6 sold by Analytik Jena AG.

[0071] In this application, the vortex mixer is the SN-Vortex-1 sold by Shanghai Shangpu Instrument Equipment Co., Ltd.

[0072] In this application, the soil hardness tester is the FM-204TR sold by Guangzhou Lantai Instruments Co., Ltd.

[0073] In this application, unless otherwise specified, the anhydrous ethanol used is of analytical grade and is purchased from Nanjing Chemical Reagent Co., Ltd.

[0074] In this application, the experimental soils used are soils with different properties selected from different regions of our country, including five kinds of soils such as green soil from Taizhou, Zhejiang, yellow soil from Xiangtan, Hunan, red soil from Yingtan, Jiangxi, black soil from Harbin, Heilongjiang, and white soil from Baicheng, Jilin.

[0075] Example 1

[0076] This example provides the influence of organic solvent pretreatment on the soil drying efficiency (rate) under natural air-drying conditions.

[0077] In this example, the organic solvent is a polar organic solvent with a boiling point less than 100 °C and miscible with water. Specifically, in this example, the organic solvents are ethanol and acetone.

[0078] In this example, in order to visually reflect the drying efficiency through the change in soil quality, according to the volume ratio of soil, water, and organic solvent in the technical solution, the experimental design of the influence of organic solvent pretreatment on soil drying efficiency is as follows:

[0079] Take 12 g of air-dried soil sample (stored in the laboratory, taken from Guilin, Guangxi) in a 50 ml centrifuge tube, add 8 ml of deionized water, and vortex for 60 s using a vortex mixer to fully mix the soil and water evenly to form a slurry. It should be noted that when a polar organic solvent with a boiling point less than 100 °C and miscible with water is directly added to the soil sample, the soil dispersion rate is slow and the dispersion is not uniform. However, adding water to form a slurry helps to shorten the soil dispersion time and ensure good dispersion and uniformity of the soil;

[0080] Add 0 ml (control group), 8 ml, 16 ml, and 32 ml of ethanol or acetone solution to four groups respectively, with three parallels in each group;

[0081] Vortex for 30 s, centrifuge at 5000 r / min for 3 min, and pour out the supernatant;

[0082] Conduct a 7-day soil natural air-drying kinetics experiment. During this period, the samples are stored in a fume hood and ensure they are in the same environment. Weigh the centrifuge tube (containing soil) using a weighing balance, and then weigh it every 24 h and record the weight.

[0083] Result analysis:

[0084] Under the four treatment conditions, the soil mass change is as Figure 1 and Figure 2 shown, where Figure 1 is the ethanol treatment group and the control group, Figure 2 is the acetone treatment group and the control group. The drying rate is expressed by the reduction in soil mass. The results show that after treatment with ethanol and acetone, the natural air-drying rate of the soil is accelerated. Compared with the natural air-drying without pretreatment with organic solvents, when treated under the condition of ethanol or acetone:water = 4:1 (volume ratio), the air-drying rate is increased by about 2 times.

[0085] Example 2

[0086] This example provides the effect of organic solvent pretreatment on soil dispersibility.

[0087] During the research process of Example 1, the inventor found that the soil presented a loose state after pretreatment with ethanol and acetone and natural air-drying. Therefore, further research was carried out on its dispersibility.

[0088] In this example, five soils from different regions of China with different properties are selected as experimental soils. The five soils are blue soil taken from Taizhou, Zhejiang, yellow soil taken from Xiangtan, Hunan, red soil taken from Yingtan, Jiangxi, black soil taken from Harbin, Heilongjiang, and white soil taken from Baicheng, Jilin. The normal moisture content of the five soils is between 20% and 40%.

[0089] Referring to Example 1, the experiment on the effect of organic solvent pretreatment on soil dispersibility specifically includes:

[0090] Take about 12 g of five kinds of soil in a 50-ml centrifuge tube, add about 8 ml of deionized water, vortex until it becomes slurry, add about 32 ml of ethanol or acetone solution, vortex for 30 s, centrifuge at 5000 r / min for 3 min, and then pour out the supernatant as the treatment group. Heat it on a hot plate at 150 °C for about 30 min. The control group is the soil without the addition of ethanol or acetone treatment.

[0091] Result analysis:

[0092] (1) Appearance of soil samples

[0093] After the five kinds of soil are pretreated with organic solvents, heated and dried, gently tap the centrifuge tube 3 - 5 times, and then pour out the soil sample. The results are as Figure 3 and Figure 4 shown. Among them, Figure 3 is for the ethanol treatment and the control group, Figure 4 is the appearance picture of the acetone treatment group and the control group. On the left side of each picture is the control group, and on the right side is the treatment group. From top to bottom are blue soil, yellow soil, red soil, black soil and white soil. The results show that the soil samples in the control group show obvious hardening and caking phenomena, while the soil samples treated with ethanol and acetone show good dispersibility.

[0094] (2) Sieve passing rate and hardness of soil samples

[0095] Sieve the soil of the treatment group and the control group through a sample sieve. The results are as Figure 5 and Figure 6 shown. Among them, Figure 5 is for the ethanol treatment group and the control group, Figure 6 is the sieve passing rate of the acetone treatment group and the control group. The results show that the highest sieve passing rate (10 mesh, 2 mm) of the soil treated with ethanol is 98.67%, and the sieve passing rates of the five kinds of soil are all above 90%. The highest sieve passing rate (10 mesh, 2 mm) of the dried soil without ethanol treatment is 7.88%. There is a large difference between the two. The highest sieve passing rate (10 mesh, 2 mm) of the soil treated with acetone is 77%. The highest sieve passing rate (10 mesh, 2 mm) of the dried soil without acetone treatment is 4.98%.

[0096] Further, by gently rubbing with fingers, the soil in the treatment group can reach a sieve passing rate close to 100% (100 mesh, 0.15 mm). However, due to the large hardness of the soil in the control group, it cannot be dispersed only by gently rubbing with fingers and must be ground in a mortar. The soil hardness well explains this behavior. The soil hardness of the ethanol, acetone treatment groups and the control group is as Figure 7 and Figure 8As shown, the hardness values of the ethanol-treated soils are relatively small. The hardness values of the five soils are 8.40, 3.54, 2.01, 4.09, and 4.49 respectively. The hardness values of the five soils after drying without ethanol treatment are 40.00, 31.13, 37.01, 34.19, and 35.84 respectively, with the unit of kgf.

[0097] It can be seen from this that the soil samples treated with ethanol or acetone have good dispersibility.

[0098] (3) Microstructure of soil samples

[0099] Further characterize the surface morphologies of the ethanol-treated group and the control group of soil samples from a microscopic perspective. The results are as Figure 9 shown. It can be seen from the figure that the arrangement of soil particles in the control group is regular, the contact is closer, the pores between particles shrink, resulting in a decrease in volume after drying and the phenomenon of hardening and caking; for the treatment group, it can be clearly observed that there are micro-aggregates smaller than 50μm formed in the soil, there are larger pores between particles (compared with the control group), and there are no aggregated or bonded particles. The larger pore space promotes the dispersion of the soil.

[0100] Example 3

[0101] This example provides a method for determining heavy metals in soil based on pXRF, including the soil sample pretreatment step and the detection step using a portable X-ray fluorescence spectrometer.

[0102] In this example, the heavy metal elements to be determined include five common ones: Pb, Cu, Ni, Zn, and Cd.

[0103] In this example, the soils include blue soil, yellow soil, red soil, black soil, and white soil.

[0104] The method for determining heavy metals in soil based on pXRF specifically includes:

[0105] Weigh 3g of each of the five soils, add about 1ml of deionized water, vortex for 30s until it becomes slurry, add 4ml of ethanol or acetone solution, vortex for 30s, centrifuge at 5000r / min for 3min, then pour out the supernatant, and place the remaining soil sample on a hot plate to heat and dry (180°C, 5min);

[0106] Seal the bottom of the pXRF sample cup completely with a special polypropylene film for X-rays and fix it with a neck ring. Directly take about 1g of the soil sample pretreated with ethanol or acetone, put it into the sample cup and compact it to ensure that the test surface of the sample is flat. After the sample preparation is completed, place it in the pXRF sample chamber for determination.

[0107] In this example, the control group is ground through a 100-mesh sieve and about 1g is weighed for pXRF determination.

[0108] Result analysis:

[0109] The test results are shown in Table 1. The p value of the paired-sample t-test is > 0.05, indicating that there is no significant difference between the treatment group and the control group. Further, the pXRF test results of soil heavy metals in the control group and the ethanol treatment group were compared through regression analysis. The results are as Figures 10-14 shown. The R 2 of the five heavy metals is > 0.96. The results of the paired-sample t-test and regression analysis show that the method for determining soil heavy metals based on pXRF provided by this application can be used for the accurate determination of soil heavy metals, although the treatment steps of grinding and sieving are omitted.

[0110] Table 1 pXRF test data of the control group and the treatment group (mg / kg)

[0111]

[0112]

[0113] Example 4

[0114] This example provides a study on whether heavy metal loss is caused in the method for determining soil heavy metals based on pXRF provided by this application.

[0115] In the pre-treatment steps of the method for determining soil heavy metals based on pXRF provided by this application, there are steps such as vortex and centrifugation, which may cause heavy metal loss.

[0116] To further verify the reliability of this method, an atomic absorption spectrometer (AAS) was used to measure the concentrations of five heavy metals, namely Pb, Cu, Ni, Zn, and Cd, in the supernatant according to the national standard (GB / T 15337-2008). The results are as Figures 15-19 shown. Among them, CK is the control group, that is, the supernatant centrifuged and poured without ethanol treatment, and CL is the treatment group, that is, the supernatant centrifuged and poured after ethanol treatment.

[0117] In the five soils treated with ethanol, the concentrations of the five heavy metals in the supernatant are all lower than 0.2 ppm. The pXRF test data of the five heavy metals in the five soils and the heavy metal test data in the supernatant are shown in Table 2. The results show that except for the Cd errors of yellow soil and blue soil being 3.33% and 1.22%, the other errors are all lower than 1%.

[0118] Table 2 pXRF and AAS test data of soil heavy metals (mg / kg) and errors

[0119]

[0120] In summary, a method for determining heavy metals in soil based on pXRF proposed in this application can achieve rapid drying and uniform dispersion of soil samples, and at the same time will not cause loss of heavy metals. When using a portable X-ray fluorescence spectrometer for detection, there is no need for grinding and sieving again, and rapid and accurate determination of heavy metals in soil based on pXRF can be achieved.

Claims

1. A method for determining heavy metals in soil based on pXRF, characterized in that, The determination method includes a soil sample pretreatment step and a detection step using a portable X-ray fluorescence spectrometer. Among them, the soil sample pretreatment step includes: taking soil, adding water and stirring, then adding a polar organic solvent with a boiling point less than 100 °C and miscible with water, stirring, centrifuging and drying to obtain a pretreated soil sample.

2. The method for determining heavy metals in soil based on pXRF according to claim 1, wherein For the pretreated soil sample, its water content is less than 1%; and / or the proportion of soil with a particle size less than 0.2 mm is greater than 50%; and / or the hardness is less than 20 kgf.

3. A method for determining heavy metals in soil based on pXRF according to claim 1 or 2, characterized in that, The organic solvent includes an alcohol organic solvent and / or a ketone organic solvent.

4. The method for determining heavy metals in soil based on pXRF according to claim 3, wherein The alcohol organic solvent includes: methanol and / or ethanol; the ketone organic solvent includes: acetone and / or butanone.

5. A method for determining heavy metals in soil based on pXRF according to claim 4, characterized in that, The alcohol organic solvent is ethanol; the ketone organic solvent is acetone.

6. A method for determining heavy metals in soil based on pXRF according to claim 4 or 5, characterized in that 3 - 5 g of the soil is taken; the usage amount of water is 1 - 2 ml; the usage amount of the organic solvent is 1 - 4 times the volume of the added water.

7. The method for determining heavy metals in soil based on pXRF according to claim 6, wherein The adding water and stirring includes vortex stirring, and the stirring time is 20 - 60 s; the stirring after adding the organic solvent includes vortex stirring, and the stirring time is 20 - 60 s.

8. A method for determining heavy metals in soil based on pXRF according to claim 7, characterized in that, The drying includes natural air drying or heating drying, and the heating drying includes heating at 150 - 160 °C for 3 - 5 min.

9. A method for determining heavy metals in soil based on pXRF according to any one of claims 1-8, characterized in that, The detection step using the portable X-ray fluorescence spectrometer includes: Seal the bottom of the pXRF sample cup completely with a special X-ray polypropylene film and fix it with a neck ring. Take about 1 g of the pretreated soil sample, put it into the sample cup and compact it to ensure that the sample test surface is flat, and then place it in the pXRF sample chamber for determination after completion.

10. A method for determining heavy metals in soil based on pXRF according to claim 9, characterized in that, The heavy metals in the soil include any one or more of Pb, Cu, Ni, Zn, and Cd.

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