Extraction and detection method of carbonate bound state fluorescence dissolved organic matter

Abstract

The invention relates to the technical field of chemical analysis of carbonate geological samples, and provides an extraction and detection method of carbonate bound-state fluorescence dissolved organic matters, which comprises the following steps: ashing a sample, cleaning with deionized water, cleaning with a sodium hydroxide solution, acidolysis with an acetic acid solution, three-dimensional fluorescence spectrum testing and parallel factor analysis. According to the method, carbonate bound state fluorescence dissolved organic matter indexes C1 / (Ca + Mg), C2 / (Ca + Mg) and C3 / (Ca + Mg) are obtained, the influence of non-carbonate mineral components in an actual carbonate rock sample on extraction of the carbonate bound state fluorescence dissolved organic matter can be reduced to a negligible level, and qualitative and quantitative characterization is carried out on the extracted carbonate bound state fluorescence dissolved organic matter.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical analysis of carbonate geological samples, and more specifically, to a method for extracting and detecting carbonate-bound fluorescent dissolved organic matter. Background Art

[0002] Carbonate minerals have a wide range of adsorption effects on the dissolved organic matter in the environmental water during their crystallization. This enables some dissolved organic matter to be stably preserved in the form of entering the interior of carbonate mineral crystals for a long time and can be used to restore the information of the dissolved organic matter in the environmental water during the crystallization of carbonate minerals. This part of the dissolved organic matter can be called carbonate-bound dissolved organic matter, and the dissolved organic matter with fluorescent properties can be further called carbonate-bound fluorescent dissolved organic matter. In geological research, due to the complex composition of actual carbonate rock samples, which often contain non-carbonate mineral components such as clay and silica, when extracting the dissolved organic matter inside carbonate mineral crystals by acidolysis, these components often release interfering organic matter or adsorb the target components, resulting in insufficient accuracy of traditional extraction methods.

[0003] In the prior art, the method proposed by Pearson et al. (2020) for the extraction and detection of carbonate-bound fluorescent dissolved organic matter analysis of laboratory-synthesized calcite is as follows: Weigh calcite and place it in a centrifuge tube, add dilute hydrochloric acid to the centrifuge tube, and after all the calcite is dissolved, collect the acidolysis solution; perform three-dimensional fluorescence detection on the collected acidolysis solution using a Horiba Jobin Yvon Aqualog fluorescence analyzer, and perform parallel factor analysis on all the three-dimensional fluorescence spectral data obtained from the detection using MATLAB.

[0004] This technique has the following drawbacks: This technique directly acidolyzes the sample and collects the acidolysis solution for detection without removing the fluorescent dissolved organic matter adsorbed on the surface of calcite. This part of the fluorescent dissolved organic matter is in direct contact with the external environment and is prone to adsorption or desorption behavior with changes in environmental conditions, so it cannot be used to effectively reflect the information of the fluorescent dissolved organic matter in the environmental water during the crystallization of calcite; the acidolysis reagent used in this technique is dilute hydrochloric acid, which is a strong acid and can cause significant fluctuations in the pH values of the acidolysis solutions of different samples, and the fluorescence intensity and fluorescence peak position of the detected three-dimensional fluorescence spectrum are closely related to the pH value of the sample to be measured; this technique does not consider the influence of non-carbonate mineral components in actual carbonate rock samples on the extraction of carbonate-bound fluorescent dissolved organic matter, so it is not suitable for extracting carbonate-bound fluorescent dissolved organic matter in actual carbonate rock samples.

[0005] In the prior art, the extraction and detection scheme of carbonate-bound fluorescent dissolved organic matter analysis for biological bones by Ingalls et al. (2003) is as follows: grind the biological bone sample into powder; place the sample in a glass bottle after high temperature treatment; add NaClO solution, seal the glass bottle and continuously shake it at room temperature for 8 days, and replace the NaClO solution in the glass bottle on the 3rd and 6th days to achieve the oxidation and removal of dissolved organic matter adsorbed on the outside of carbonate minerals as fully as possible; after 8 days, remove the NaClO solution in the glass bottle, add hydrochloric acid to it, and collect the acid solution; filter the acid solution using a 0.7 μm Whatman glass filter membrane after calcination, and collect the filtered acid solution; detect the dissolved organic carbon concentration in the filtered acid solution using a Shimadzu dissolved organic carbon analyzer, and calculate the carbon content in carbonate-bound dissolved organic matter based on the results.

[0006] Although this technical solution takes into account the removal of dissolved organic matter adsorbed on the outside of carbonate minerals, it still has the following disadvantages: this technology only determines that the dissolved organic matter adsorbed on the outside of carbonate minerals can be oxidized and removed to the greatest extent after 8 days of NaClO solution oxidation treatment, but it does not represent complete oxidation removal. Therefore, there may still be adsorbed dissolved organic matter on the outer surface of carbonate minerals. This part of dissolved organic matter will be released into the acid hydrolysis solution during the acid hydrolysis of carbonate minerals, thereby making the detected carbonate-bound dissolved organic matter concentration too high; this technology requires the detection of dissolved organic carbon concentration, and the filtered acid hydrolysis solution is a high-salt solution, and the dissolved organic carbon concentration may be low, so the detection error is large and the damage to the instrument is large; this technology can only obtain the organic carbon content of carbonate-bound dissolved organic matter, and cannot obtain the property information of carbonate-bound dissolved organic matter; this technology does not consider the influence of non-carbonate mineral components in actual carbonate rock samples on the extraction of carbonate-bound dissolved organic matter, so it is not suitable for extracting carbonate-bound dissolved organic matter in actual carbonate rock samples.

[0007] Therefore, in view of the defects of the existing technology, it is necessary to design a qualitative and quantitative method that can effectively eliminate the influence of non-carbonate mineral components in carbonate rocks on the extraction of carbonate-bound dissolved organic matter, and can directly extract and accurately detect carbonate-bound dissolved organic matter, so as to solve the problem of insufficient accuracy of existing extraction and detection technologies for carbonate-bound dissolved organic matter in carbonate rocks. Summary of the invention

[0008] The object of the present invention is to provide a method for extracting and detecting carbonate-bound fluorescent dissolved organic matter, which can reduce the influence of non-carbonate mineral components in actual carbonate rock samples on the extraction of carbonate-bound fluorescent dissolved organic matter to a negligible level, and qualitatively and quantitatively characterize the extracted carbonate-bound fluorescent dissolved organic matter.

[0009] To solve the above technical problems, the technical solution adopted in this application is as follows: The embodiment of this application provides a method for extracting and detecting carbonate-bound fluorescent dissolved organic matter, including the following steps: S1. Weigh a carbonate rock sample and perform ashing treatment in a muffle furnace to obtain an ashed sample. S2. Add deionized water to the ashed sample, mix well, then shake and centrifuge, and remove the supernatant. Repeat this step once to obtain a washed sample A. S3. Add a sodium hydroxide solution to the washed sample A, mix well, then shake and centrifuge, and remove the supernatant. Repeat this step three times to obtain a washed sample B. S4. Add an acetic acid solution to the washed sample B, mix well, then shake and centrifuge, collect the supernatant, and filter it with a polyethersulfone filter head to obtain an acidolysis solution. S5. Perform three-dimensional fluorescence testing on the acidolysis solution with a fluorescence analyzer to obtain three-dimensional fluorescence spectral data. S6. Perform parallel factor analysis on the three-dimensional fluorescence spectral data to obtain the fluorescence intensities of three fluorescence components C1, C2, and C3, with the unit of mRSU / L. S7. Dilute the acidolysis solution with dilute nitric acid and test the Ca-Mg ion concentration with an inductively coupled plasma emission spectrometer, with the unit of mmol / L. S8. Obtain three groups of carbonate-bound fluorescent dissolved organic matter indexes C1 / (Ca+Mg), C2 / (Ca+Mg), and C3 / (Ca+Mg), with the unit of RSU / mol, by combining the fluorescence intensity and the Ca-Mg ion concentration, which respectively represent the contents of components C1, C2, and C3 in carbonate minerals per unit amount of substance.

[0010] Further, in step S1, the mass fraction of carbonate minerals in the carbonate rock sample is greater than 50%, and the particle size of the carbonate rock sample powder is 200 mesh.

[0011] Further, in step S1, the weighed amount of the carbonate rock sample is 0.25±0.05 parts by mass, the temperature during the ashing treatment is 530°C, and the ashing treatment time is 2 h.

[0012] Further, in step S2, the weighed amount of the ashed sample is 0.025±0.002 parts by mass, the shaking speed is 70 rpm, and the shaking time is 12 h; the centrifugation speed is 4000 rpm, and the centrifugation time is 10 min.

[0013] Furthermore, in step S3, the amount of sodium hydroxide solution added is 10 parts by volume of 0.1 M sodium hydroxide solution, the shaking speed is 70 rpm, the shaking time is 12 h; the centrifugal speed is 4000 rpm, and the centrifugal time is 10 min.

[0014] Furthermore, in step S4, the amount of acetic acid solution added is 10 parts by volume of 0.5 M acetic acid (fluorescent pure) solution, the oscillation speed is 70 rpm, the oscillation time is 12 h; the centrifugal speed is 4000 rpm, and the centrifugation time is 10 min; the pore size of the polyethersulfone filter head is 0.45 μm.

[0015] Furthermore, in step S5, the excitation wavelength range set by the fluorescence analyzer during the test is 280-450 nm, and the emission wavelength range is the default value of the fluorescence analyzer.

[0016] Furthermore, in step S5, before the acid solution test, a three-dimensional fluorescence test is performed on deionized water with a resistivity greater than 18 MΩ·cm, and its three-dimensional fluorescence spectrum is used as a blank value to be deducted for subsequent sample testing.

[0017] Further, in step S6, the parallel factor analysis is specifically as follows: taking the three-dimensional fluorescence spectrum data within the range of 280-450 nm excitation wavelength and 380-550 nm emission wavelength, using the Raman scattering signal intensity of deionized water at an excitation wavelength of 350 nm and an emission wavelength of 397 nm as the standard for normalizing the fluorescence signal of the acid hydrolyzate, the unit is RSU, thereby obtaining the fluorescence intensity of the three fluorescent components C1, C2 and C3, the unit is mRSU / L.

[0018] Furthermore, in step S7, the mass fraction of the dilute nitric acid is 2%, and the dilution factor is 10 times.

[0019] The principle of the present invention is that dissolved organic matter can exist in carbonate minerals in three main forms: adsorbed on crystal boundaries, present in fluid inclusions, and embedded in crystal structures. Dissolved organic matter existing in different forms is not only difficult to be effectively identified on a macroscopic level, but also cannot be effectively separated in a targeted manner. At the same time, dissolved organic matter existing in other forms (such as dissolved organic matter associated with clay / metal oxide adsorption, biological residues, kerogen, etc.) is also inevitably present in actual geological samples. Therefore, the present invention defines the operationality of carbonate-bound fluorescent dissolved organic matter as "fluorescent dissolved organic matter that can be proved to be ultimately retained due to the protective effect of carbonate minerals after a series of pre-treatment processes are used to fully eliminate the interference of dissolved organic matter existing in non-carbonate phase components in the sample."

[0020] Ashing treatment: By subjecting the sample to ashing treatment at 530 °C for 2 hours, the organic matter outside the carbonate minerals can be removed as fully as possible, while ensuring that the carbonate minerals do not decompose significantly, so that the organic matter inside them is retained as fully as possible. In addition, the crystal structures of the non-carbonate mineral components (mainly clay components) in the sample will be damaged during the high-temperature treatment, resulting in a significant reduction in their adsorption capacity for the fluorescent dissolved organic matter released during the acid digestion of the sample.

[0021] Deionized water washing: The ashed sample is washed twice to remove some of the suspended or soluble substances in the sample, which may release or adsorb fluorescent dissolved organic matter during acid digestion and interfere with the effective extraction of carbonate-bound fluorescent dissolved organic matter.

[0022] Sodium hydroxide solution washing: Through 4 washes, the fluorescent dissolved organic matter associated with the non-carbonate mineral components that can be extracted by the sodium hydroxide solution in the sample is removed as much as possible, avoiding its release during subsequent acid digestion and interfering with the effective extraction of carbonate-bound fluorescent dissolved organic matter.

[0023] C1, C2, and C3 represent three potential fluorescence phenomena separated from the complex three-dimensional fluorescence spectral signals obtained by test through parallel factor analysis. Each fluorescence phenomenon has a specific excitation wavelength and emission wavelength, and can represent a class of fluorescent dissolved organic matter components with similar chemical properties. The parallel factor analysis step can further give the signal intensities of the three components in each sample on this basis, thus realizing the qualitative and quantitative identification of fluorescent dissolved organic matter.

[0024] C1 / (Ca + Mg), C2 / (Ca + Mg), and C3 / (Ca + Mg) respectively represent the contents of C1, C2, and C3 components in the bound fluorescent dissolved organic matter contained in the carbonate minerals per unit amount of substance in the carbonate rock sample.

[0025] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects: 1. The chemical reagents used in this application have low toxicity, small sample consumption, simple pretreatment process, convenient testing of carbonate-bound fluorescent dissolved organic matter, very low analysis cost, and can realize rapid analysis and testing of a large number of samples.

[0026] 2. The selected excitation wavelength and emission wavelength ranges in the parallel factor analysis step of this application can effectively cut off the signal regions in the three-dimensional fluorescence spectrum that are significantly affected by experimental contamination, and at the same time stabilize the optimal number of components of the model to 3 components, which is conducive to the comparison of analysis results between different batches.

[0027] 3. The present application can reduce the influence of non-carbonate mineral components in actual carbonate rock samples on the extraction of carbonate-bound fluorescent dissolved organic matter to a negligible level.

[0028] 4. The present application can perform high-precision qualitative and quantitative characterization on the extracted carbonate-bound fluorescent dissolved organic matter, and has good geological application prospects.

[0029] 5. The present application has a high extraction rate for carbonate-bound fluorescent dissolved organic matter, and the stability of the experimental results is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0031] Figure 1 It is a schematic flowchart of a method for extracting and detecting carbonate-bound fluorescent dissolved organic matter provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those not specified in the embodiments, they are carried out according to 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.

[0033] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to specific embodiments.

[0034] As Figure 1 shown, based on the basic theoretical route concept of the present invention, a method for extracting and detecting carbonate-bound fluorescent dissolved organic matter is proposed, including the following steps: S1. Coarsely crush the collected carbonate rock samples into small pieces with a particle size of about 1 cm, and then grind them to 200 meshes through a crusher. The mass fraction of carbonate minerals in the carbonate rock samples is greater than 50%; S2. Weigh 0.25 ± 0.05 g of the ground carbonate rock samples and place them in a 20 mL ceramic crucible, and perform ashing treatment in a muffle furnace at 530 °C for 2 h to obtain the ashed samples; S3. Weigh 0.025 ± 0.002 g of the ashed sample, place it in a 15 mL centrifuge tube, add 10 mL of deionized water, mix well, shake it with a rotary shaker at a speed of 70 rpm for 12 h, then centrifuge it at a speed of 4000 rpm for 10 min, remove the supernatant as much as possible, and repeat this step once to obtain the washed sample A; S4. Add 10 mL of 0.1 M sodium hydroxide solution to the washed sample A, mix well, shake it with a rotary shaker at a speed of 70 rpm for 12 h, then centrifuge it at a speed of 4000 rpm for 10 min, remove the supernatant as much as possible, and repeat this step three times to obtain the washed sample B; S5. Add 10 mL of 0.5 M acetic acid (fluorescent grade) solution to the washed sample B, mix well, shake it with a rotary shaker at a speed of 70 rpm for 12 h, then centrifuge it at a speed of 4000 rpm for 10 min, collect the supernatant, and filter it with a 0.45 μm polyethersulfone filter head to obtain the acidolysis solution; S6. Perform three-dimensional fluorescence testing on the filtered acidolysis solution using a Horiba Jobin Yvon Aqualog fluorescence analyzer. Set the excitation wavelength range to 280 - 450 nm, and the emission wavelength range to the default value of the instrument. Before testing the acidolysis solution, first perform three-dimensional fluorescence testing on deionized water with a resistivity greater than 18 MΩ·cm, and use its three-dimensional fluorescence spectrum as the blank value to be deducted for subsequent acidolysis solution testing to obtain three-dimensional fluorescence spectrum data; S7. Compile all the tested three-dimensional fluorescence spectrum data, perform parallel factor analysis on the three-dimensional fluorescence spectrum within the excitation wavelength range of 280 - 450 nm and the emission wavelength range of 380 - 550 nm. Use the Raman scattering signal intensity (in "Raman scattering units", i.e., RSU, 1 RSU = 1000 mRSU) at the excitation wavelength of 350 nm and the emission wavelength of 397 nm of deionized water as the standard for normalizing the fluorescence signal of the sample, so as to obtain the fluorescence intensities of the three fluorescence components C1, C2, and C3 in each tested sample, with the unit of mRSU / L; S8. Dilute the acidolysis solution 10 times with 2% dilute nitric acid, and test the Ca-Mg ion concentration using an inductively coupled plasma emission spectrometer, with the unit of mmol / L; S9. The three sets of carbonate-bound fluorescent dissolved organic matter indicators obtained by combining the fluorescence intensity and the Ca-Mg ion concentration include three sets of data, namely C1 / (Ca + Mg), C2 / (Ca + Mg), and C3 / (Ca + Mg), with the unit of RSU / mol, respectively representing the contents of the C1, C2, and C3 components in carbonate minerals per unit amount of substance.

[0035] The features and performance of the present invention will be further described in detail below in conjunction with embodiments.

[0036] Embodiment To evaluate the effect of the above technical route on the extraction of carbonate-bound fluorescent dissolved organic matter in carbonate rocks, in this embodiment, laboratory-synthesized calcite samples and geological samples without carbonate mineral components are used as the end members of carbonate minerals and non-carbonate minerals in the simulated carbonate rock samples, respectively. Simulated carbonate rocks with carbonate mineral mass fractions of 75% and 50% are prepared according to mass ratios of 3:1 and 1:1, respectively.

[0037] Among them, the laboratory-synthesized calcite samples include three samples, Cal-0, Cal-1, and Cal-2. All three are synthesized with fulvic acid as the simulated dissolved organic matter under three conditions: without fulvic acid, relatively low fulvic acid concentration, and relatively high fulvic acid concentration.

[0038] The geological samples without carbonate mineral components include two samples, pure shale and pure siliceous rock, which can comprehensively represent the end members of non-carbonate minerals in common carbonate rock samples. Among them, the total organic carbon content of the pure shale sample is 4.7%, the silicon content is 29.2%, the aluminum content is 7.6%, and the potassium content is 6.7%, indicating that its composition is mainly clay minerals; the total organic carbon content of the pure siliceous rock sample is 2.7%, the silicon content is 44.1%, the aluminum content is 0.4%, and the potassium content is 0.3%, indicating that its composition is basically silicon dioxide.

[0039] In this embodiment, Cal-0 is used as a blank sample. By extracting and testing carbonate-bound fluorescent dissolved organic matter from 14 blank replicate samples, the method detection limits of components C1, C2, and C3 in the acid digestion solution are established as 94.7 mRSU / L, 26.0 mRSU / L, and 51.3 mRSU / L, respectively. On this basis, the technical effect evaluation is carried out from the following three aspects.

[0040] Test 1 Based on the embodiment, this Test 1 is used to evaluate the influence of non-carbonate mineral components in carbonate rock samples on the extraction of carbonate-bound fluorescent dissolved organic matter.

[0041] This Test 1 conducts this evaluation by testing the acid digestion solution extracted from the simulated carbonate rock samples prepared with Cal-0. The results are shown in Table 1: Table 1 Test situation of the acid digestion solution of the simulated carbonate rock samples prepared with Cal-0

[0042] According to the test results, except that the test results of the C1 component and the C2 component of the sample prepared by mixing Cal-0 and pure siliceous rock at a mass ratio of 1:1 are higher than the detection limits of the corresponding fluorescent components (9.4% and 33.8% higher respectively), the measured values of other fluorescent components are lower than the detection limits of the corresponding fluorescent components. This indicates that in conventional carbonate rock samples, except that when the siliceous component is present in relatively high content, it may contribute to the C1 component and the C2 component in the extracted acidolysis solution to a certain extent, the influence of non-carbonate mineral components on the extraction of each fluorescent component in carbonate-bound fluorescent dissolved organic matter can be generally ignored.

[0043] Test 2 Based on the examples, this Test 2 is used to evaluate the stability of the extraction of carbonate-bound fluorescent dissolved organic matter.

[0044] This Test 2 independently analyzes the indicators of carbonate-bound fluorescent dissolved organic matter in the simulated carbonate rock samples prepared with Cal-1 and Cal-2 three times. The average values of the concentrations of each fluorescent component in the acidolysis solution obtained from the three tests and the relative standard deviation values (RSD values) of the contents of each fluorescent component in the samples are shown in Table 2. Table 2 shows the test conditions of the acidolysis solution for the three independent analyses of the simulated carbonate rock samples prepared with Cal-1 and Cal-2 and the relative standard deviations of the test results of the contents of each fluorescent component in carbonate-bound fluorescent dissolved organic matter (since the measured values of the C1 component in the acidolysis solution of the samples prepared with Cal-1 are all lower than or only slightly higher than the detection limit, the RSD value of the corresponding C1 / (Mg+Ca) is not calculated).

[0045] Table 2 Test conditions of the acidolysis solution and relative standard deviations of the test results of the contents of each fluorescent component in carbonate-bound fluorescent dissolved organic matter

[0046] It can be seen from the results that except that the RSD value of the content of the samples prepared with Cal-1 is not calculated because the measured values of the C1 component in the acidolysis solution are all lower than or only slightly higher than the detection limit, and the RSD value of the C3 component content of the sample prepared by mixing Cal-0 and pure siliceous rock at a mass ratio of 1:1 (which is 10.7%) is slightly higher, all other RSD values are less than 6.9%. This indicates that in conventional carbonate rock samples, except that when the siliceous component is present in relatively high content, it may affect the stability of the extraction of the C3 component, the influence of non-carbonate mineral components on the extraction stability of each fluorescent component in carbonate-bound fluorescent dissolved organic matter can be generally ignored.

[0047] Test 3 Based on the examples and Test 2, this Test 3 is used to evaluate the extraction rate of carbonate-bound fluorescent dissolved organic matter.

[0048] This test 3 is based on the data tested in the stability evaluation session, and further calculates the extraction rates of the fluorescent components of carbonate-bound fluorescent dissolved organic matter in the simulated carbonate rock samples relative to the corresponding fluorescent components in the pure carbonate minerals. The average extraction rates obtained from 3 independent analyses are shown in Table 3. Table 3 presents the test results of the acid digestion solutions and the average extraction rates of the fluorescent components of carbonate-bound fluorescent dissolved organic matter for the simulated carbonate rock samples prepared with Cal-1 and Cal-2 in 3 independent analyses (the test values of the C1 component in the acid digestion solutions of the samples prepared with Cal-1 are all lower than or only slightly higher than the detection limit, so the average extraction rate of this fluorescent component is not calculated).

[0049] Table 3 Test Results of Acid Digestion Solutions and Average Extraction Rates of Fluorescent Components of Carbonate-Bound Fluorescent Dissolved Organic Matter

[0050] In Table 3, the extraction rate is the ratio of the content of each fluorescent component of carbonate-bound fluorescent dissolved organic matter tested in the simulated carbonate rock samples to the content tested in the corresponding pure carbonate minerals of the samples, and is used to evaluate the influence of non-carbonate minerals on the extraction of carbonate-bound fluorescent dissolved organic matter in actual carbonate rock samples. From the data in the table, it can be seen that except for the samples prepared with Cal-1, for which the average extraction rate of the C1 component in the acid digestion solution is not calculated because the test values are all lower than or only slightly higher than the detection limit, the average extraction rates of the C3 component in the samples prepared with Cal-1 and pure siliceous rock at mass ratios of 3:1 and 1:1 are both greater than 110% (110.7% and 122.3% respectively), the average extraction rate of the C1 component in the sample prepared with Cal-2 and pure shale at a mass ratio of 1:1 is relatively low (68.3%), and all other calculated average extraction rates are between 80% and 105%. Also, the average extraction rates of each component in the simulated carbonate rock samples with the same non-carbonate mineral composition and a carbonate mineral content of 75% are better than those of the corresponding components in the simulated carbonate rock samples with a carbonate mineral content of 50% (i.e., closer to 100%), indicating that in conventional carbonate rock samples, except for the relatively high influence of clay components on the extraction rate of the C1 component and siliceous components on the extraction rate of the C3 component, the influence of non-carbonate mineral components on the extraction rates of the fluorescent components in carbonate-bound fluorescent dissolved organic matter is generally small.

[0051] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

Claims

1. A method for extracting and detecting carbonate-bound fluorescent dissolved organic matter, characterized in that: The following steps are involved: S1. Weigh a carbonate rock sample and perform a ash treatment in a muffle furnace to obtain an ashed sample; S2. Add deionized water to the ashing sample, mix well, shake, centrifuge, remove the supernatant, and repeat this step once to obtain a cleaned sample A; S3. Add sodium hydroxide solution to the cleaned sample A, mix well, shake, centrifuge, remove the supernatant, and repeat this step 3 times to obtain a cleaned sample B; S4. Add acetic acid solution to the cleaned sample B, mix well, shake, centrifuge, collect the supernatant, and filter with a polyethersulfone filter to obtain an acid solution; S5. Performing a three-dimensional fluorescence test on the acid solution by a fluorescence analyzer to obtain three-dimensional fluorescence spectrum data; S6. Performing parallel factor analysis on the three-dimensional fluorescence spectrum data to obtain the fluorescence intensities of the three fluorescent components C1, C2 and C3 in units of mRSU / L; S7. dilute the acid solution with dilute nitric acid and test the Ca-Mg ion concentration by inductively coupled plasma emission spectrometry in mmol / L; S8. By combining the fluorescence intensity and the Ca-Mg ion concentration, three groups of carbonate-bound fluorescent dissolved organic matter indicators C1 / (Ca+Mg), C2 / (Ca+Mg) and C3 / (Ca+Mg) are obtained, and the unit is RSU / mol.

2. The method according to claim 1, characterized in that In the step S1, the mass fraction of carbonate mineral content in the carbonate rock sample is greater than 50%, and the particle size of the carbonate rock sample powder is 200 mesh.

3. The method according to claim 1, characterized in that In the step S1, the carbonate rock sample is weighed in an amount of 0.25±0.05 parts by mass, the temperature during the ashing treatment is 530° C., and the ashing treatment time is 2 h.

4. The method according to claim 1, characterized in that: In the step S2, the sample weight after ashing is 0.025±0.002 parts by mass, the shaking speed is 70 rpm, the shaking time is 12 h; the centrifugal speed is 4000 rpm, and the centrifugal time is 10 min.

5. The method according to claim 1, characterized in that: In step S3, the amount of sodium hydroxide solution added is 10 parts by volume of 0.1 M sodium hydroxide solution, the shaking speed is 70 rpm, the shaking time is 12 h; the centrifugal speed is 4000 rpm, and the centrifugal time is 10 min.

6. The method according to claim 1, characterized in that In step S4, the amount of acetic acid solution added is 10 parts by volume of 0.5 M acetic acid solution, the shaking speed is 70 rpm, the shaking time is 12 h; the centrifugal speed is 4000 rpm, and the centrifugal time is 10 min; the pore size of the polyethersulfone filter head is 0.45 μm.

7. The method according to claim 1, characterized in that In step S5, the excitation wavelength range set by the fluorescence analyzer during the test is 280-450 nm, and the emission wavelength range is the default value of the fluorescence analyzer.

8. The method according to claim 1, characterized in that In step S5, before the acid solution test, a three-dimensional fluorescence test is performed on deionized water with a resistivity greater than 18 MΩ·cm, and its three-dimensional fluorescence spectrum is used as a blank value to be deducted for subsequent sample testing.

9. The method according to claim 8, characterized in that In step S6, the parallel factor analysis is specifically as follows: taking the three-dimensional fluorescence spectrum data within the range of 280-450 nm excitation wavelength and 380-550 nm emission wavelength, using the Raman scattering signal intensity of deionized water at an excitation wavelength of 350 nm and an emission wavelength of 397 nm as the standard for normalizing the fluorescence signal of the acid hydrolyzate, the unit is RSU, thereby obtaining the fluorescence intensity of the three fluorescent components C1, C2 and C3, the unit is mRSU / L.

10. The method according to claim 1, characterized in that In step S7, the mass fraction of dilute nitric acid is 2%, and the dilution factor is 10 times.

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