EDXRF accurate detection method for heavy metal content in wet soil

Abstract

The invention discloses an EDXRF accurate detection method for the content of heavy metals in wet soil, and belongs to the technical field of soil heavy metal detection. According to the method, the change characteristic that the background spectrum intensity of a high-energy part in a soil EDXRF spectrum is gradually increased along with the increase of the soil moisture content is utilized; the net integral intensity value of the target heavy metal characteristic spectrum peak in the corresponding dry soil under the non-moisture influence is inversed by the net integral intensity of the target heavy metal characteristic spectrum peak in the wet soil EDXRF spectrum and the integral intensity of the high-energy part background spectrum, and then the value is used as an input; the target heavy metal content EDXRF quantitative analysis model established based on the dry soil is utilized for inversion, accurate detection of the target heavy metal content in the wet soil is achieved, and the problem that accurate measurement of the heavy metal content in the wet soil is difficult to achieve through the current EDXRF spectrum technology is solved. The method is suitable for EDXRF direct analysis and detection of the heavy metal content in field wet soil pollution condition investigation.

Description

Technical Field

[0001] This invention belongs to the field of soil testing technology, and specifically relates to an accurate EDXRF detection method for heavy metal content in moist soil. Background Technology

[0002] Due to rapid socio-economic and industrial development, heavy metal pollutants (such as cadmium (Cd), nickel (Ni), lead (Pb), mercury (Hg), copper (Cu), chromium (Cr), and zinc (Zn)) generated by industrial emissions, agricultural activities (such as fertilizer and pesticide application), mining, and urban expansion have accumulated in soil, leading to a severe global problem of heavy metal soil pollution. For example, 34.9% of industrial waste sites and 33.4% of mining areas in my country have some degree of heavy metal soil pollution (Journal of Environmental Management, 2019, 251: 1009512; Science of the Total Environment, 2021, 780: 146557), and in some areas, the heavy metal content in the soil far exceeds the safety threshold. Heavy metals, due to their recalcitrant nature, bioaccumulation, and biotoxicity, accumulate in soil, altering the soil's ecological environment, poisoning soil flora, fauna, and microorganisms, disrupting soil ecological functions and system balance, and reducing crop quality and yield. Furthermore, they can pose health risks to humans through the food chain. Therefore, achieving rapid on-site detection of heavy metals in soil is of paramount importance for preventing and controlling heavy metal pollution in soil, protecting ecosystem security, promoting agricultural development, and safeguarding human health.

[0003] Currently, in the detection of heavy metals in soil, although traditional laboratory testing methods such as graphite furnace atomic absorption spectrometry (AAS), inductively coupled plasma mass spectrometry (ICP-MS), and atomic fluorescence spectrometry (AFS) have advantages such as high sensitivity and good accuracy, and have always dominated the accurate detection of heavy metal content, these methods all require on-site sampling and offline laboratory analysis. This has disadvantages such as complex sample pretreatment, slow detection speed, long analysis time, and poor timeliness. In addition, the heavy metal detection process relies on large-scale instruments and equipment and professional personnel, which is costly and makes it difficult to meet the needs of rapid detection and screening of heavy metal pollution in large-scale, multi-site soil.

[0004] In comparison, energy-dispersive X-ray fluorescence (EDXRF) spectroscopy has become an important technology for rapid on-site detection of heavy metals due to its numerous advantages, including non-destructive nature, no need for complex sample pretreatment, simple instrumentation, convenient operation, fast analysis speed, and simultaneous detection of multiple elements. With the continuous development of mobile and portable EDXRF heavy metal detection equipment, EDXRF spectroscopy has been widely applied in geological exploration, industrial manufacturing, resource surveys, and environmental monitoring. In the environmental field, it has become a crucial technique for rapid on-site investigation and analysis of heavy metals in soil, showing broad application prospects in soil heavy metal pollution surveys, remediation detection, and emergency response.

[0005] However, when EDXRF spectroscopy is used for on-site detection of heavy metals in soil, the differences in soil physicochemical properties have a significant impact on the accuracy of quantitative detection of heavy metals. Related studies have shown that soil moisture changes the properties of the soil matrix and produces absorption and scattering effects on X-rays. Therefore, soil moisture (i.e., soil water content) is a key factor affecting the accurate detection of heavy metals by EDXRF (Metallurgical Analysis, 2018, 38(7):20-26; China Environmental Monitoring, 2019, 35(6):129-137). However, during field investigations of heavy metal pollution in soil, the soil is often not completely dry due to weather conditions such as rain, snow, frost, and dew, as well as the depth of the soil. Instead, it has a certain degree of moisture, and the soil moisture content varies at different points in the horizontal direction and at different depths in the vertical direction. This makes it difficult for EDXRF spectroscopy to accurately measure the content of heavy metals in soil. On-site drying of the soil reduces the efficiency of heavy metal detection and increases the cost of sample processing. Therefore, how to achieve direct and accurate measurement of heavy metal content in moist soil remains a pain point and difficulty in the current field application of EDXRF spectroscopy.

[0006] To address the aforementioned issues, an accurate EDXRF detection method for heavy metal content in moist soil was established to obtain accurate information on heavy metal content in moist soil at different moisture contents. This method plays a vital role and is of great significance for accurately assessing the heavy metal pollution status and remediation effectiveness of soil, and for precisely determining soil environmental risks. Summary of the Invention

[0007] To address the challenge of accurately measuring heavy metal content in moist soil using existing EDXRF spectroscopy techniques due to moisture content limitations, this invention aims to overcome these shortcomings by providing an accurate EDXRF detection method for heavy metals in moist soil. This method improves the accuracy of EDXRF spectroscopy in on-site heavy metal detection in soil. Based on the characteristic that the high-energy background spectrum in soil EDXRF spectra exhibits a regular variation with soil moisture content, this method first establishes a quantitative relationship between the ratio of the net integrated intensity of the target heavy metal characteristic peak in the EDXRF spectra of moist soil and its corresponding dry soil at different moisture contents, and the integrated intensity of the high-energy background spectrum in the moist soil EDXRF spectra. This establishes a calculation model for the net integrated intensity of the target heavy metal characteristic peak in dry soil, using both the net integrated intensity of the target heavy metal characteristic peak in the moist soil EDXRF spectra and the integrated intensity of the high-energy background spectrum as variables. Furthermore, by utilizing this quantitative relationship model between the net integrated intensity of the target heavy metal characteristic peak in the dry soil EDXRF spectra and the standard content of that heavy metal, the accurate inversion of the target heavy metal content in the soil is achieved, thus realizing the accurate detection of heavy metal content in moist soil.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] An accurate EDXRF method for detecting heavy metal content in moist soil includes the following steps:

[0010] Step 1: Prepare a series of dry soil samples with different contents of the target heavy metal.

[0011] Different amounts of the target heavy metal pollutants were added to the soil, and after being thoroughly mixed, the soil was dried in an oven. After the dried soil was thoroughly ground, a fixed amount of soil with a mass of m was weighed and spread evenly in a sample cup. A Mylar membrane was then placed on the surface of the sample cup without wrinkles and fixed with a neck ring to prepare a series of dried soil samples with different contents of the target heavy metals.

[0012] Step 2: Measure the EDXRF spectra of a series of dry soil samples with different target heavy metal contents.

[0013] Under the same measurement conditions, a series of dry soil samples with different target heavy metal contents obtained in step 1 were subjected to EDXRF spectral measurements to obtain the corresponding EDXRF spectra of different dry soil samples.

[0014] Step 3: Obtain the standard content values ​​of the target heavy metals and their net integral intensity values ​​of EDXRF characteristic peaks in a series of dry soil samples.

[0015] The content of the target heavy metal in the dried soil sample prepared in step 1 was measured by the heavy metal content standard detection method, and a series of standard content values ​​C of the target heavy metal in the dried soil sample were obtained.

[0016] The EDXRF spectra of the dry soil samples measured in step 2 were denoised using the wavelet default threshold method combined with the Savitzky-Golay smoothing filter. Then, the peak and valley of the denoised EDXRF spectra were identified using the extreme value method. The identified series of peaks and valleys were then fitted with a cubic smoothing spline with a penalty term correction to obtain the background spectrum of the EDXRF spectra. For each dry soil sample, the EDXRF spectrum obtained after denoising using the wavelet default threshold method combined with the Savitzky-Golay method was subtracted from the fitted background spectrum to obtain the net EDXRF spectrum of each dry soil sample. Based on the theoretical energy value of the target heavy metal characteristic spectral peak, the characteristic spectral peak of the target heavy metal in the net EDXRF spectrum of each dry soil sample was identified. The net integral intensity F of the entire spectral peak between the left starting point and the right ending point of the target heavy metal characteristic spectral peak was calculated according to the following formula (1).

[0017] F = (1)

[0018] In the formula, l and r represent the energy values ​​of the left-hand start and right-hand end points of the characteristic spectral peak of the target heavy metal, respectively, and F i This represents the net intensity of the spectral peak corresponding to the energy value i between l and r.

[0019] Step 4: Establish an EDXRF quantitative analysis model for the target heavy metal content based on dry soil samples.

[0020] Based on the standard content values ​​C of the target heavy metals and the net integral intensity values ​​F of the EDXRF characteristic peaks of heavy metals in a series of dry soil samples obtained in step 3, C is used as the dependent variable and F is used as the independent variable to perform linear fitting on the two, thereby establishing a quantitative analysis model of the target heavy metal content EDXRF based on dry soil samples, as shown in formula (2).

[0021] (2)

[0022] Step 5: Prepare a series of moist soil samples containing the target heavy metal with different moisture contents.

[0023] Different amounts of the target heavy metal pollutants were added to the soil according to step 1. After thorough mixing, the soil was dried and ground thoroughly. Multiple soil samples with a mass of m1 were weighed into petri dishes, and a certain amount of deionized water was added to each. After thorough mixing, the samples were placed in an oven and heated at low temperature. The soil samples were taken out at different heating times. When the temperature dropped to room temperature, the mass of the soil was weighed and recorded as m2. The water content w of the soil sample was calculated according to the following formula (3). By controlling the heating time, a series of moist soil samples containing the target heavy metals and with different water contents were obtained.

[0024] w = (3)

[0025] Step 6: Measure the EDXRF spectra of a series of moist soil samples.

[0026] Weigh a certain mass of each moist soil sample prepared in step 5 (if there are clumps, they need to be crushed) and spread it evenly in a sample cup. Cover the surface of the sample cup with a Mylar membrane without wrinkles and fix it with a neck ring. Perform EDXRF spectral measurement under the same measurement conditions as in step 2 to obtain the EDXRF spectra of a series of moist soil samples prepared in step 5 that contain the target heavy metal and have different moisture contents.

[0027] Step 7: Calculate the integrated intensity of the high-energy background spectrum and the net integrated intensity of the target heavy metal characteristic peaks in the EDXRF spectra of moist soil at different moisture contents.

[0028] The wavelet default threshold method combined with Savitzky-Golay smoothing filtering was used to denoise the EDXRF spectra of the moist soil samples measured in step 6. Then, the extreme value method was used to identify the peaks and valleys of the denoised EDXRF spectra. The identified peaks and valleys were then fitted with a cubic smoothing spline with a penalty term correction to obtain the background spectrum of the EDXRF spectrum of each moist soil sample. The background spectrum of the high-energy part from 7.5 keV to 27 keV was extracted. The integral intensity F of the background spectrum of the high-energy part from 7.5 keV to 27 keV in the EDXRF spectrum of each moist soil sample was calculated according to the following formula (4). BI '.

[0029] F BI ' = (4)

[0030] In the formula, i refers to the energy value of the horizontal axis in the EDXRF spectrum, and F BI'i' represents the background spectral intensity corresponding to energy value i in the EDXRF spectrum of the moist soil sample. a is the energy value of the left starting point of the selected high-energy background spectrum, which is 7.5 keV; b is the energy value of the right ending point of the selected high-energy background spectrum, which is 27 keV.

[0031] The net EDXRF spectra of moist soil samples at different moisture contents were obtained by subtracting the fitted background spectrum from the denoised EDXRF spectrum of the moist soil sample after the wavelet default threshold method combined with Savitzky-Golay smoothing filtering method. Based on the theoretical energy values ​​of the target heavy metal characteristic peaks, the characteristic peaks of the target heavy metal in the net EDXRF spectra of each moist soil sample were identified. The net integral intensity F' of the entire peak between the left start point and the right end point of the target heavy metal characteristic peak was calculated according to the following formula (5).

[0032] F'= (5)

[0033] In the formula, l and r represent the energy values ​​of the left-hand start and right-hand end points of the characteristic spectral peak of the target heavy metal, respectively, and F i ' represents the net intensity of the spectral peak corresponding to the energy value i between l and r.

[0034] Step 8: Obtain the net integral intensity value of the characteristic peaks of the target heavy metal in the moist soil in the corresponding dry soil EDXRF spectrum.

[0035] The series of moist soil samples containing the target heavy metal and with different moisture contents prepared in step 5 were dried to obtain the corresponding dry soil sample. After each dry soil sample was thoroughly ground, a fixed amount of soil with a mass of m was weighed and spread in a sample cup as in step 1. A Mylar membrane was covered on the surface of the sample cup without wrinkles and fixed with a neck ring. EDXRF spectral measurement was performed on each dry soil sample under the same measurement conditions as in step 2. The net integral intensity F of the entire peak between the left start point and the right end point of the characteristic peak of the target heavy metal in the EDXRF spectrum of the dry soil sample corresponding to each moist soil sample was obtained according to the method in step 3.

[0036] Step 9: Establish a quantitative relationship model between the ratio of the net integral intensity of the characteristic peaks of the target heavy metal in the EDXRF spectra of dry soil and wet soil and the integral intensity of the background spectrum in the high-energy part of the EDXRF spectrum of wet soil.

[0037] For each moist soil sample obtained in step 5, the ratio k of the net integrated intensity F of the target heavy metal characteristic peak in the corresponding dry soil EDXRF spectrum obtained in step 8 to the net integrated intensity F' of the target heavy metal characteristic peak in the moist soil EDXRF spectrum obtained in step 7 is calculated according to the following formula (6). k is used as the dependent variable, and the integrated intensity F' of the high-energy background spectrum (7.5 keV to 27 keV) in the moist soil EDXRF spectrum obtained in step 7 is used as the independent variable. BI Using ' as the independent variable, establish the ratio of the net integrated intensity k of the characteristic peaks in the EDXRF spectra of the target heavy metal in dry soil and wet soil, and the integral intensity F of the high-energy background spectrum in the EDXRF spectrum of wet soil. BI The quantitative relationship model between them is shown in formula (7).

[0038] k = (6)

[0039] k = f(F BI ') (7)

[0040] Step 10: Establish an inversion model for the net integral intensity of the target heavy metal characteristic spectral peaks in the EDXRF spectrum of dry soil, with the net integral intensity of the target heavy metal characteristic spectral peaks in the EDXRF spectrum of moist soil and the integral intensity of the high-energy background spectrum as variables.

[0041] Based on the ratio k of the net integral intensity of the characteristic peaks of the target heavy metal in the EDXRF spectra of dry and moist soil established in step 9, and the integral intensity F of the high-energy background spectrum in the EDXRF spectrum of moist soil... BI A quantitative relationship model between them (specifically, formula (7)) is further established, based on the net integral intensity F' of the characteristic peak of the target heavy metal in the EDXRF spectrum of moist soil and the integral intensity F' of the high-energy background spectrum. BI The inversion model for the net integral intensity F of the target heavy metal characteristic peak in the EDXRF spectrum of dry soil with ' as variable is shown in Equation (8).

[0042] F = f(F BI ')×F' (8)

[0043] Step 11: Accurate inversion of the target heavy metal content in the moist soil to be tested.

[0044] For the moist soil sample to be tested, perform EDXRF spectral measurements as described in step 6, and obtain the integrated intensity F of the high-energy background spectrum (7.5 keV to 27 keV) in the moist soil EDXRF spectrum using the same method as in step 7. BI ', and the net integral intensity F' of the characteristic spectral peaks of the target heavy metal, and then using F BI' and F' are independent variables. The net integral intensity value F of the target heavy metal characteristic peak in the EDXRF spectrum of the dry soil corresponding to the wet soil sample is calculated according to formula (8) in step 10. Substituting the F value into the EDXRF quantitative analysis model of the target heavy metal content based on the dry soil sample established in step 4 (specifically formula (2)) can realize the accurate EDXRF detection of the target heavy metal content in the wet soil.

[0045] In the above technical solution, the standard detection methods for heavy metal content in step 3 include flame atomic absorption spectrophotometry, inductively coupled plasma mass spectrometry, graphite furnace atomic absorption spectrophotometry, atomic fluorescence spectrometry, etc. The corresponding standard detection method should be adopted according to the target heavy metal.

[0046] In the above technical solution, when obtaining the net integral intensity of the target heavy metal characteristic peak in the EDXRF spectrum of a series of prepared dry soil samples in step 3, obtaining the net integral intensity of the target heavy metal characteristic peak in the EDXRF spectrum of a series of prepared moist soil samples in step 7, obtaining the net integral intensity of the target heavy metal characteristic peak in the EDXRF spectrum of dry soil samples corresponding to each moist soil sample in step 8, and obtaining the net integral intensity of the target heavy metal characteristic peak in the EDXRF spectrum of the moist soil sample to be tested in step 11, the left starting energy value and the right ending energy value used to calculate the net integral intensity of the same target heavy metal characteristic peak in different soil samples are the same in the four steps.

[0047] In the above technical solution, the original soil used in step 1 to prepare a series of dry soil samples with different target heavy metal contents, the original soil used in step 5 to prepare a series of moist soil samples containing target heavy metals with different moisture contents, and the soil to be tested in step 11 should all belong to the same soil type.

[0048] Based on the above method, the present invention further provides a soil heavy metal detection system, which includes: an EDXRF spectrometer containing an Ag target X-ray tube and a silicon drift detector; a data processing unit storing the quantitative analysis model and the inversion model; and a background spectral analysis module for calculating the background spectral integral intensity of 7.5 keV to 27 keV.

[0049] Beneficial effects:

[0050] This invention addresses the challenge of accurately measuring heavy metal content in moist soil using EDXRF spectroscopy. It leverages the characteristic that the high-energy background spectral intensity in soil EDXRF spectra varies systematically with soil moisture content. By combining the net integral intensity of the target heavy metal characteristic peak in the moist soil EDXRF spectrum with the integrated intensity of the high-energy background spectrum, the net integral intensity value of the target heavy metal characteristic peak in the dry soil EDXRF spectrum (without moisture influence) is retrieved. Then, a quantitative analysis model for heavy metal content based on the net integral intensity of elemental characteristic peaks in the dry soil EDXRF spectrum is used for inversion, achieving accurate detection of target heavy metal content in moist soil. This solves the problem of large errors in measuring heavy metal content in moist soil using EDXRF spectroscopy due to moisture influence, and avoids the energy-intensive and time-consuming process of on-site drying of moist soil for EDXRF heavy metal detection. This provides a rapid, efficient, and low-cost analytical method for accurate investigation and assessment of heavy metal pollution in field soils. Attached Figure Description

[0051] Figure 1 : Schematic diagram of an accurate EDXRF detection method for heavy metal content in moist soil.

[0052] Figure 2 Net EDXRF characteristic peaks of Ni element in dry soil samples with different Ni contents.

[0053] Figure 3 Linear fitting diagram between the standard content of Ni element in dry soil and the net integral intensity of its Kα characteristic spectral peak.

[0054] Figure 4 Background spectra of soil EDXRF spectra at different moisture contents.

[0055] Figure 5 Background spectra of soil EDXRF spectra in the energy range of 7.4 keV to 27 keV at different moisture contents.

[0056] Figure 6 Background spectral integral intensity of soil EDXRF spectra in the energy range of 7.4 keV to 27 keV under different moisture contents.

[0057] Figure 7 :k and F BI A quantitative relationship model between them. Detailed Implementation

[0058] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the scope of protection of the present invention should include all the contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement all the contents of the claims of the present invention.

[0059] Example:

[0060] This embodiment uses nickel (Ni), a typical heavy metal pollutant in the environment, as the research object, and uses the method of the present invention to carry out an EDXRF accurate detection study of the content of heavy metal Ni in moist soil.

[0061] The whole process is as follows Figure 1 As shown, an accurate EDXRF detection method for heavy metal content in moist soil includes the following steps:

[0062] Step 1: Prepare a series of dry soil samples with different contents of the target heavy metal.

[0063] Different amounts of the target heavy metal pollutants were added to the soil, and after being thoroughly mixed, the soil was dried in an oven. After the dried soil was thoroughly ground, a fixed amount of soil with a mass of m was weighed and spread evenly in a sample cup. A Mylar membrane was then placed on the surface of the sample cup without wrinkles and fixed with a neck ring to prepare a series of dried soil samples with different contents of the target heavy metals.

[0064] In this embodiment, a series of dried soil samples with different contents of the target heavy metal Ni were prepared from uncontaminated farmland soil. The original soil type used was brown soil. Different volumes of Ni were added to the soil samples. 2+ A standard solution of nickel nitrate (Ni(NO3)2) with a mass concentration of 100 mg / L was thoroughly stirred and then dried in an oven at 60℃. After the sample was completely dried and cooled to room temperature, the soil was thoroughly ground using a ceramic mortar. Then, 5 g of a fixed mass of soil was weighed and spread evenly in a circular sample cup made of polytetrafluoroethylene with an inner diameter of 31 mm. A Mylar membrane was then placed on the surface of the sample cup without wrinkles and fixed with a neck ring to prepare a series of dried soil samples with different contents of the target heavy metal Ni.

[0065] Step 2: Measure the EDXRF spectra of a series of dry soil samples with different target heavy metal contents.

[0066] Under the same measurement conditions, a series of dry soil samples with different target heavy metal contents obtained in step 1 were subjected to EDXRF spectral measurements to obtain the corresponding EDXRF spectra of different dry soil samples.

[0067] In this embodiment, under the same measurement conditions, EDXRF spectral measurements were performed on a series of dried soil samples with different Ni content obtained in step 1 to obtain the corresponding EDXRF spectra of different dried soil samples. The same measurement conditions were used for the EDXRF spectral measurements of different samples: the instrument used was an EDXRF spectrometer from AMPTEK, the excitation source was a Min-X-ray tube, the target material was an Ag target, two 10 mils Al primary filters were installed in front of the tube, and the EDXRF detection device was an SDD-123 silicon drift detector; before the EDXRF spectral measurement, the X-ray tube operating voltage was set to 40 kV, the operating current to 20 μA, the pulse shaping time to 6.4 μs, and the gain to 47.47; the soil sample was placed flat, and the EDXRF spectral measurement of the soil sample was performed at a position 1.6 cm away from the instrument detection window, and the cumulative time of the spectral signal for a single measurement was 120 s.

[0068] To ensure that the measured EDXRF spectrum of each soil sample accurately represents the characteristics of that soil sample and to avoid random errors, this step of EDXRF spectrum measurement requires that, for each dry soil sample, EDXRF spectrum measurements be performed at different points on the sample measurement surface under the same measurement conditions. Finally, the average value of the EDXRF spectra at different points on the same sample measurement surface is used to represent the EDXRF spectrum of that soil sample.

[0069] Step 3: Obtain the standard content values ​​of the target heavy metals and their net integral intensity values ​​of EDXRF characteristic peaks in a series of dry soil samples.

[0070] The content of the target heavy metal in the dried soil sample prepared in step 1 was measured by the heavy metal content standard detection method, and a series of standard content values ​​C of the target heavy metal in the dried soil sample were obtained.

[0071] The EDXRF spectra of the dry soil samples measured in step 2 were denoised using the wavelet default threshold method combined with the Savitzky-Golay smoothing filter. Then, the peak and valley of the denoised EDXRF spectra were identified using the extreme value method. The identified series of peaks and valleys were then fitted with a cubic smoothing spline with a penalty term correction to obtain the background spectrum of the EDXRF spectra. For each dry soil sample, the EDXRF spectrum obtained after denoising using the wavelet default threshold method combined with the Savitzky-Golay method was subtracted from the fitted background spectrum to obtain the net EDXRF spectrum of each dry soil sample. Based on the theoretical energy value of the target heavy metal characteristic spectral peak, the characteristic spectral peak of the target heavy metal in the net EDXRF spectrum of each dry soil sample was identified. The net integral intensity F of the entire spectral peak between the left starting point and the right ending point of the target heavy metal characteristic spectral peak was calculated according to the following formula (1).

[0072] F = (1)

[0073] In the formula, l and r represent the energy values ​​of the left-hand start and right-hand end points of the characteristic spectral peak of the target heavy metal, respectively, and F i This represents the net intensity of the spectral peak corresponding to the energy value i between l and r.

[0074] In this embodiment, inductively coupled plasma mass spectrometry (ICP-MS) is used as a standard detection method for heavy metal content to measure the content of the target heavy metal Ni in each dry soil sample prepared in step 1, and a series of standard content values ​​C of the target heavy metal Ni in the dry soil samples are obtained. The specific standard content values ​​C of Ni in different dry soil samples are shown in Table 1.

[0075] Table 1. Standard content values ​​of the target heavy metal Ni in a series of dried soil samples.

[0076] The EDXRF spectra of each dry soil sample measured in step 2 were denoised using a wavelet default thresholding method combined with Savitzky-Golay smoothing filtering. Then, the extreme value method was used to identify peaks and valleys in the denoised EDXRF spectra. The identified peaks and valleys were then fitted using a cubic smoothing spline with a penalty term correction to obtain the background spectrum of the EDXRF spectrum. For each dry soil sample, the EDXRF spectrum obtained after denoising using the wavelet default thresholding method combined with Savitzky-Golay was subtracted from the fitted background spectrum to obtain the net EDXRF spectrum of each dry soil sample. Based on the theoretical energy value of 7.47 keV of the characteristic peak of the target heavy metal Ni Kα, the characteristic peak of the target heavy metal Ni in the net EDXRF spectrum of each dry soil sample was identified. Therefore, the characteristic peak of Ni Kα in the net EDXRF spectra of a series of dry soil samples with different Ni contents is as follows: Figure 2 As shown in the figure. The net integral intensity F of the entire spectrum peak between the left starting point (energy of 7.308 keV) and the right ending point (energy of 7.700 keV) of the characteristic spectrum peak of the target heavy metal Ni Kα is calculated according to the above formula (1). Then, the net integral intensity F of the characteristic spectrum peak of Ni Kα in the net EDXRF spectrum of dry soil samples with different Ni contents in Table 1 is shown in Table 2.

[0077] Table 2. Net integrated intensity of Ni Kα characteristic spectral peaks in a series of dried soil samples with different Ni contents.

[0078] Step 4: Establish an EDXRF quantitative analysis model for the target heavy metal content based on dry soil samples.

[0079] Based on the standard content values ​​C of the target heavy metals and the net integral intensity values ​​F of the EDXRF characteristic peaks of heavy metals in a series of dry soil samples obtained in step 3, C is used as the dependent variable and F is used as the independent variable to perform linear fitting on the two, thereby establishing a quantitative analysis model of the target heavy metal content EDXRF based on dry soil samples, as shown in formula (2).

[0080] (2)

[0081] In this embodiment, based on the standard content values ​​C of the target heavy metal Ni in a series of dry soil samples obtained in step 3 (as shown in Table 1) and the net integral intensity values ​​F of the Ni Kα characteristic spectral peak (as shown in Table 2), a linear fit was performed on C as the dependent variable and F as the independent variable. The results are as follows: Figure 3 As shown, an EDXRF quantitative analysis model for the target heavy metal Ni content based on dry soil samples was established, as shown in formula (3).

[0082] C = 0.1112×F-196.9003 (3)

[0083] In the formula: C is the standard content value of heavy metal Ni in the dry soil sample, and F is the net integral intensity value of the Ni Kα characteristic peak in the EDXRF spectrum of the dry soil sample.

[0084] Step 5: Prepare a series of moist soil samples containing the target heavy metal with different moisture contents.

[0085] Following step 1, different amounts of the target heavy metal pollutants were added to the soil, thoroughly mixed, dried, and ground. Multiple soil samples with a mass of m1 were then weighed into petri dishes, and a certain amount of deionized water was added to each. After thorough mixing, the samples were placed in an oven and heated at a low temperature. The soil samples were removed at different heating times, and when the temperature dropped to room temperature, the mass of the soil was weighed and recorded as m2. The water content w of the soil sample was calculated according to the following formula (4). By controlling the heating time, a series of moist soil samples containing the target heavy metals and with different water contents were obtained.

[0086] w = (4)

[0087] In this embodiment, the original soil used to prepare a series of moist soil samples containing the target heavy metal Ni with different moisture contents in this step is the same as the original soil used to prepare a series of dry soil samples with different Ni contents in step 1. All samples were taken from uncontaminated agricultural land, and the soil type was brown soil. A certain volume of Ni was added to the soil according to the method in step 1.2+ A standard solution of nickel nitrate (Ni(NO3)2) with a mass concentration of 100 mg / L was thoroughly stirred, dried, and ground. Multiple soil samples, each weighing 20g (denoted as m1), were placed in petri dishes, and a certain amount of deionized water was added to each. After thorough stirring, the samples were placed in an oven and heated at 40℃. Soil samples were removed at different heating times, and their mass was measured and recorded as m2 after the temperature dropped to room temperature. The water content w of the soil sample was calculated according to the above formula (4). By controlling the heating time, a series of moist soil samples containing the target heavy metal Ni with different water contents were obtained. In this embodiment, five series (five batches) of moist soil samples containing the target heavy metal Ni with different water contents were prepared according to the above method. The water content range of each series (batch) of soil samples was 0–50%.

[0088] Step 6: Measure the EDXRF spectra of a series of moist soil samples.

[0089] Weigh a certain mass of each moist soil sample prepared in step 5 (if there are clumps, they need to be crushed) and spread it evenly in a sample cup. Cover the surface of the sample cup with a Mylar membrane without wrinkles and fix it with a neck ring. Perform EDXRF spectral measurement under the same measurement conditions as in step 2 to obtain the EDXRF spectra of a series of moist soil samples prepared in step 5 that contain the target heavy metal and have different moisture contents.

[0090] In this embodiment, a certain mass of each moist soil sample obtained in step 5 (if there are clumps, they need to be crushed) is weighed and spread evenly in a circular sample cup made of polytetrafluoroethylene with an inner diameter of 31 mm. A Mylar membrane is covered on the surface of the sample cup without wrinkles and fixed with a neck ring. EDXRF spectroscopy is performed under the same measurement conditions as in step 2 to obtain the EDXRF spectra of a series of moist soil samples containing the target heavy metal Ni and with different moisture contents obtained in step 5. The same measurement conditions were used for each moist soil sample to perform EDXRF spectral measurements: the instrument used was an EDXRF spectrometer from AMPTEK, the excitation source was a Min-X-ray tube, the target material was an Ag target, two 10 mils Al primary filters were installed in front of the tube, and the EDXRF detection device was an SDD-123 silicon drift detector; before the EDXRF spectral measurement, the X-ray tube operating voltage was set to 40 kV, the operating current to 20 μA, the pulse shaping time to 6.4 μs, and the gain to 47.47; the soil sample was placed flat, and the EDXRF spectral measurement of the soil sample was performed at a distance of 1.6 cm from the instrument detection window, with a single measurement spectral signal accumulation time of 120 s.

[0091] To ensure that the measured EDXRF spectrum of each moist soil sample accurately represents the characteristics of the moist soil sample and to avoid random errors, this step requires EDXRF spectral measurements to be performed at different points on the sample measurement surface under the same measurement conditions. Finally, the average value of the EDXRF spectra at different points on the same sample measurement surface is used to represent the EDXRF spectrum of the moist soil sample.

[0092] Step 7: Calculate the integrated intensity of the high-energy background spectrum and the net integrated intensity of the target heavy metal characteristic peaks in the EDXRF spectra of moist soil at different moisture contents.

[0093] The EDXRF spectra of the moist soil samples measured in step 6 were denoised using the wavelet default threshold method combined with the Savitzky-Golay smoothing filter. Then, the peak and valley of the denoised EDXRF spectra were identified using the extreme value method. The identified series of peak and valley points were curve-fitted using a cubic smoothing spline with a penalty term correction to obtain the background spectrum of the EDXRF spectrum of each moist soil sample. The background spectrum of the high-energy part from 7.5 keV to 27 keV was extracted. The integral intensity F of the background spectrum of the high-energy part from 7.5 keV to 27 keV in the EDXRF spectrum of each moist soil sample was calculated according to the following formula (5). BI '.

[0094] F BI ' = (5)

[0095] In the formula, i refers to the energy value of the horizontal axis in the EDXRF spectrum, and F BI 'i' represents the background spectral intensity corresponding to energy value i in the EDXRF spectrum of the moist soil sample. a is the energy value of the left starting point of the selected high-energy background spectrum, which is 7.5 keV; b is the energy value of the right ending point of the selected high-energy background spectrum, which is 27 keV.

[0096] The net EDXRF spectra of moist soil samples with different moisture contents are obtained by subtracting the fitted background spectrum from the denoised EDXRF spectrum of moist soil samples after the wavelet default threshold method combined with Savitzky-Golay smoothing filtering method. Based on the theoretical energy values ​​of the target heavy metal characteristic peaks, the characteristic peaks of the target heavy metals in the net EDXRF spectra of each moist soil sample are identified. The net integral intensity F' of the entire peak between the left start point and the right end point of the target heavy metal characteristic peak is calculated according to the following formula (6).

[0097] F'= (6)

[0098] In the formula, l and r represent the energy values ​​of the left-hand start and right-hand end points of the characteristic spectral peak of the target heavy metal, respectively, and F i ' represents the net intensity of the spectral peak corresponding to the energy value i between l and r.

[0099] This embodiment uses a wavelet default thresholding method combined with Savitzky-Golay smoothing filtering to denoise the EDXRF spectra of the moist soil samples measured in step 6. Then, an extremum method is used to identify peaks and valleys in the denoised EDXRF spectra. The identified peaks and valleys are then curve-fitted using a penalized cubic smoothing spline to obtain the background spectrum of each moist soil EDXRF spectrum. Specifically, as follows... Figure 4 As shown, the background spectrum in the high-energy range of 7.5 keV to 27 keV was extracted, specifically as follows: Figure 5 As shown, the integrated intensity F of the high-energy background spectrum between 7.5 keV and 27 keV is calculated according to the above formula (5). BI Then, the integrated intensity value F of the high-energy background spectrum between 7.5 keV and 27 keV in the EDXRF spectrum of each moist soil sample with different moisture contents is... BI 'Specifically as Figure 6 As shown.

[0100] In this embodiment, the EDXRF spectrum of the moist soil after denoising by wavelet default thresholding combined with Savitzky-Golay smoothing filtering is subtracted from the fitted background spectrum to obtain the net EDXRF spectrum of each moist soil sample with different moisture contents. Based on the theoretical energy value of 7.47 keV of the characteristic peak of the target heavy metal Ni, the Kα characteristic peak of the target heavy metal Ni in the net EDXRF spectrum of each moist soil sample is identified. The energy value of the valley point on the left side of the Ni Kα characteristic peak is 7.308 keV, and the energy value of the valley point on the right side is 7.700 keV. According to the above formula (6), the net integral intensity F' of the entire peak between the starting point on the left side (energy of 7.308 keV) and the ending point on the right side (energy of 7.700 keV) of the target heavy metal Ni Kα characteristic peak is calculated. The net integral intensity F' of the Ni Kα characteristic peak in a series of moist soil samples containing the target heavy metal Ni with different moisture contents obtained in step 5 is shown in Table 3.

[0101] Table 3. Net integrated intensity F' of the characteristic spectral peak of the target heavy metal Ni Kα in different moist soils

[0102] Step 8: Obtain the net integral intensity value of the characteristic peaks of the target heavy metal in the moist soil in the corresponding dry soil EDXRF spectrum.

[0103] The series of moist soil samples containing the target heavy metal and with different moisture contents prepared in step 5 were dried to obtain the corresponding dry soil sample. After each dry soil sample was thoroughly ground, a fixed amount of soil with a mass of m was weighed and spread in a sample cup as in step 1. A Mylar membrane was covered on the surface of the sample cup without wrinkles and fixed with a neck ring. EDXRF spectral measurement was performed on each dry soil sample under the same measurement conditions as in step 2. The net integral intensity F of the entire peak between the left start point and the right end point of the characteristic peak of the target heavy metal in the EDXRF spectrum of the dry soil sample corresponding to each moist soil sample was obtained according to the method in step 3.

[0104] In this embodiment, a series of moist soil samples containing the target heavy metal Ni and with different moisture contents, prepared in step 5, were placed in a 60℃ oven for drying to obtain a corresponding dry soil sample. After the samples were completely dried and cooled to room temperature, each dry soil sample was thoroughly ground and mixed evenly using a ceramic mortar. Following the method in step 1, 5 g of a fixed mass of dry soil was weighed and spread evenly in a sample cup. A Mylar membrane was then placed wrinkle-free over the sample cup surface and secured with a neck ring. EDXRF spectral measurements were performed on each dry soil sample under the same conditions as in step 2. Specifically, the instrument used was an EDXRF spectrometer from AMPTEK, the excitation source was a Min-X-ray tube, the target material was an Ag target, two 10 mils Al primary filters were installed in front of the tube, and the EDXRF detection device was an SDD-123 silicon drift detector. Before the EDXRF spectral measurement, the X-ray tube operating voltage was set to 40 kV, the operating current to 20 μA, and the pulse shaping time to 6.4 seconds. The gain was 47.47 μs. The soil sample was placed flat, and EDXRF spectral measurements were performed at a distance of 1.6 cm from the instrument's detection window. The cumulative time for a single measurement was 120 s. To avoid random errors, for each dry soil sample, EDXRF spectral measurements were performed at different points on the sample's measurement surface under the same conditions. The average value of the EDXRF spectra at different points on the same sample's measurement surface was then used to represent the EDXRF spectrum of that soil sample.

[0105] For each moist soil sample and its corresponding dry soil sample, the net integral intensity F of the entire peak between the left starting point (energy 7.308 keV) and the right ending point (energy 7.700 keV) of the characteristic Ni Kα peak in the EDXRF spectrum was obtained according to the method in step 3. The net integral intensity of the Ni Kα characteristic peak in the dry soil sample corresponding to each moist soil sample is shown in Table 4.

[0106] Table 4. Net integrated intensity F of the Ni Kα characteristic spectral peak in the dry soil corresponding to each moist soil.

[0107] Step 9: Establish a quantitative relationship model between the ratio of the net integral intensity of the characteristic peaks of the target heavy metal in the EDXRF spectra of dry soil and wet soil and the integral intensity of the background spectrum in the high-energy part of the EDXRF spectrum of wet soil.

[0108] For each moist soil sample obtained in step 5, the ratio k of the net integrated intensity F of the target heavy metal characteristic peak in the corresponding dry soil EDXRF spectrum obtained in step 8 to the net integrated intensity F' of the target heavy metal characteristic peak in the moist soil EDXRF spectrum obtained in step 7 is calculated according to the following formula (7). k is used as the dependent variable, and the integrated intensity F' of the high-energy background spectrum (7.5 keV to 27 keV) in the moist soil EDXRF spectrum obtained in step 7 is used as the independent variable. BI Using ' as the independent variable, establish the ratio of the net integrated intensity k of the characteristic peaks in the EDXRF spectra of the target heavy metal in dry soil and wet soil, and the integral intensity F of the high-energy background spectrum in the EDXRF spectrum of wet soil. BI The quantitative relationship model between them is shown in formula (8).

[0109] k = (7)

[0110] k = f(F BI ') (8)

[0111] In this embodiment, for each moist soil sample obtained in step 5, the ratio k of the net integral intensity F of the target heavy metal Ni Kα characteristic peak in the EDXRF spectrum of the corresponding dry soil obtained in step 8 to the net integral intensity F' of the target heavy metal Ni Kα characteristic peak in the EDXRF spectrum of the moist soil obtained in step 7 is calculated according to the above formula (7). The specific ratio k of the net integral intensity k of the Ni Kα characteristic peak in the EDXRF spectrum of the corresponding dry soil and the moist soil for each moist soil sample obtained in step 5 is shown in Table 5.

[0112] Table 5. Ratio of net integral intensity of Kα characteristic peak in EDXRF spectra of Ni in dry and moist soils.

[0113] Using the average k value of five batches of soil samples at the same moisture content in Table 5 as the dependent variable, and the values ​​obtained in step 7... Figure 6 The integrated intensity F of the high-energy background spectrum (7.5 keV–27 keV) in the EDXRF spectrum of moderately moist soil. BIUsing ' as the independent variable, the ratio of the net integrated intensity k of the Kα characteristic peak in the EDXRF spectra of the target heavy metal Ni in dry and moist soils was established, along with the integrated intensity F of the high-energy background spectrum in the EDXRF spectra of moist soil. BI The quantitative relationship model between ' is shown in formula (9), where k and F BI The quantitative relationship between them is as follows: Figure 7 As shown.

[0114] k = 0.35013 + (9)

[0115] Step 10: Establish an inversion model for the net integral intensity of the target heavy metal characteristic spectral peaks in the EDXRF spectrum of dry soil, with the net integral intensity of the target heavy metal characteristic spectral peaks in the EDXRF spectrum of moist soil and the integral intensity of the high-energy background spectrum as variables.

[0116] Based on the ratio k of the net integral intensity of the characteristic peaks of the target heavy metal in the EDXRF spectra of dry and moist soil established in step 9, and the integral intensity F of the high-energy background spectrum in the EDXRF spectrum of moist soil... BI A quantitative relationship model between them (specifically, formula (8)) is further established, based on the net integral intensity F' of the characteristic peak of the target heavy metal in the EDXRF spectrum of moist soil and the integral intensity F' of the high-energy background spectrum. BI The inversion model for the net integral intensity F of the target heavy metal characteristic peak in the EDXRF spectrum of dry soil with ' as variable is shown in Equation (10).

[0117] F = f(F BI ')×F' (10)

[0118] In this embodiment, the ratio of the net integrated intensity k of the Kα characteristic peak in the EXRF spectra of the target heavy metal Ni in dry and moist soil, established in step 9, and the integrated intensity F of the high-energy background spectrum in the 7.5 keV to 27 keV range in the EXRF spectra of moist soil are used as the basis for this embodiment. BI A quantitative relationship model between them (see formula (9) above) is further established, based on the net integral intensity F' of the characteristic spectral peak of the target heavy metal Ni Kα in the EDXRF spectrum of moist soil and the high-energy background spectral integral intensity F' between 7.5 keV and 27 keV. BI The inversion model for the net integral intensity F of the characteristic peak of the target heavy metal Ni Kα in the EDXRF spectrum of dry soil with ' as variable is shown in Equation (11).

[0119] F = (11)

[0120] Step 11: Accurate inversion of the target heavy metal content in the moist soil to be tested.

[0121] For the moist soil sample to be tested, perform EDXRF spectral measurements as described in step 6, and obtain the integrated intensity F of the high-energy background spectrum (7.5 keV to 27 keV) in the moist soil EDXRF spectrum using the same method as in step 7. BI ', and the net integral intensity F' of the characteristic spectral peaks of the target heavy metal, and then using F BI ' and F' are independent variables. The net integral intensity value F of the target heavy metal characteristic peak in the EDXRF spectrum of the dry soil corresponding to the wet soil sample is calculated according to formula (10) in step 10. Substituting the F value into the EDXRF quantitative analysis model of the target heavy metal content based on the dry soil sample established in step 4 (specifically formula (2)) can realize the accurate EDXRF detection of the target heavy metal content in the wet soil.

[0122] In this embodiment, for a batch of moist soil samples containing the heavy metal Ni (the soil type of the moist soil to be tested is the same as the original soil used in steps 1 and 5, which is brown soil), EDXRF spectral measurements were performed on them in the manner of step 6. To avoid random errors, the average value of the EDXRF spectra at different points on the same measurement surface of the sample was used to represent the EDXRF spectrum of the moist soil sample in the same way as in step 6. The integrated intensity F of the high-energy background spectrum between 7.5 keV and 27 keV in the EDXRF spectrum of each moist soil was obtained using the same method as in step 7. BI ', and the net integrated intensity F' of the characteristic spectral peak of the target heavy metal Ni Kα, and then using F BI ' and F' are independent variables. The net integral intensity value F of the characteristic peak of the target heavy metal Ni Kα in the EDXRF spectrum of the dry soil corresponding to the wet soil sample is calculated according to formula (11) in step 10. The F value is substituted into the EDXRF quantitative analysis model of the target heavy metal Ni content based on the dry soil sample established in step 4 (specifically formula (3)). Through calculation, the accurate EDXRF detection of the heavy metal Ni content in wet soil based on the method of this invention can be achieved.

[0123] To verify the accuracy of the method proposed in this invention, the net integral intensity F' of the Ni Kα characteristic peak in the EDXRF spectrum of a batch of wet soil containing heavy metal Ni was directly substituted into the EDXRF quantitative analysis model of heavy metal Ni content based on dry soil samples established in step 4 to invert the content value of heavy metal Ni in wet soil. Then, after drying the series of wet soil samples, the actual content of heavy metal Ni was measured by the ICP-MS heavy metal standard detection method. The Ni content value measured by ICP-MS was then used as the true value. The relative error of the heavy metal Ni content value inverted by the method of this invention and the relative error of the heavy metal Ni content value inverted directly by the net integral intensity of the Ni Kα characteristic peak in wet soil were calculated according to the following formula (12). The relative errors obtained by the two methods were compared to verify the accuracy of the method proposed in this invention. The specific results are shown in Table 6. It can be seen that the relative error of the method proposed in this invention in retrieving the content of heavy metal Ni is between 5.86% and 16.44%, which is significantly lower than the relative error of 10.86% to 34.63% of the direct inversion of Ni content using the net integral intensity of the Ni Kα characteristic peak in the EDXRF spectrum of moist soil. This result shows that the method proposed in this invention can be used for accurate EDXRF detection of the content of heavy metal Ni in moist soil.

[0124] ER = (12)

[0125] In the formula, C' is the inversion value of the heavy metal Ni content, C is the true value of the heavy metal Ni content measured by ICP-MS, and ER is the relative error of the heavy metal content.

[0126] Table 6. Accuracy verification results of the method proposed in this invention

[0127] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. An accurate EDXRF method for detecting heavy metal content in moist soil, characterized in that... Includes the following steps: Step 1: Establish an EDXRF quantitative analysis model for the target heavy metals in dry soil: Where C is the standard content of the target heavy metal, and F is the net integral intensity of the characteristic peak of the target heavy metal in the EDXRF spectrum of dry soil; Step 2: Establish the ratio of the net integrated intensity k of the characteristic peaks of the target heavy metal in the EDXRF spectra of dry and moist soil to the integrated intensity F of the high-energy background spectrum in the EDXRF spectra of moist soil. BI The quantitative relationship model is: k = f(F) BI '), where k = F / F', F' is the net integral intensity of the characteristic peak of the target heavy metal in the EDXRF spectrum of moist soil, F BI The integrated intensity of the background spectrum is in the energy range of 7.5 keV to 27 keV. Step 3: Based on Step 2, construct an inversion model for the net integral intensity of the target heavy metal characteristic peaks in the EDXRF spectrum of the corresponding dry soil from moist soil: F = f(F BI ')×F'; Step 4: Perform EDXRF spectral measurements on the moist soil to be tested to obtain F' and F'. BI '; Step 5: Place F' and F BI Substitute the values ​​into the inversion model of step three to calculate the net integral intensity F of the target heavy metal characteristic spectral peak in the dry soil corresponding to the moist soil. Step 6: Substitute F into the quantitative analysis model of Step 1 to obtain the target heavy metal content in the wet soil to be tested.

2. The method according to claim 1, characterized in that: The establishment of the quantitative analysis model in step one includes: Prepare dried soil samples with different target heavy metal contents; Measure its EDXRF spectrum and calculate the net integrated intensity F of the characteristic peaks of the target heavy metal; The heavy metal content C was determined using a standard detection method. Fit a linear relationship between C and F.

3. The method according to claim 1, characterized in that: The establishment of the quantitative relationship model in step two includes: Prepare moist soil samples containing the target heavy metal with a moisture content of 0-50%; Measure its EDXRF spectrum and calculate F' and F BI '; After drying the moist soil, the corresponding EDXRF spectrum of the dried soil was measured and the F value was calculated. Calculate the value of k and fit k to F BI The functional relationship between them.

4. The method according to claim 1, characterized in that: In step four, F' and F BI The method to obtain ' is as follows: Denoising was achieved by combining wavelet default thresholding with Savitzky-Golay smoothing filtering on the EDXRF spectrum of moist soil. The peaks and valleys of the denoised EDXRF spectrum were identified using the extreme value method, and then the background spectrum was fitted using a cubic smoothing spline with a penalty term correction. F was calculated by extracting the background spectrum from 7.5 keV to 27 keV. BI '; The net integral intensity F' of the target heavy metal characteristic spectral peaks is calculated after subtracting the background spectrum.

5. The method according to claim 1, characterized in that: The high-energy background spectral integral intensity F in the EDXRF spectrum of the moist soil BI The formula for calculating ' is: F BI ' = ； Where a = 7.5 keV, b = 27 keV, F bi ' represents the background spectral intensity corresponding to an energy value of i.

6. The method according to claim 1, characterized in that: The formula for calculating the net integral intensity F' of the target heavy metal characteristic peak in the EDXRF spectrum of the moist soil is as follows: F '= ； In the formula, l and r represent the energy values ​​of the left-hand start and right-hand end points of the characteristic spectral peak of the target heavy metal, respectively, and F i ' represents the net intensity of the spectral peak corresponding to the energy value i between l and r.

7. The method according to claim 1, characterized in that: The target heavy metal includes at least one of Cd, Ni, Pb, Hg, Cu, Cr, and Zn.

8. The method according to claim 1, characterized in that: The dry soil samples, moist soil samples, and soil samples used to build the model were all of the same soil type.

9. The method according to claim 1, characterized in that: The EDXRF measurement conditions in step four are as follows: Excitation source: Ag target X-ray tube, voltage 40 kV, current 20 μA; Detector: Silicon drift detector; Cumulative time ≥ 120 s.

10. A soil heavy metal detection system, characterized in that... Configured to perform the method of any one of claims 1-9, comprising: EDXRF spectrometer, including Ag target X-ray tube and silicon drift detector; The data processing unit stores the quantitative analysis model and the inversion model; The background spectral analysis module is used to calculate the integrated intensity of the background spectrum from 7.5 keV to 27 keV.

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