A method for extracting and detecting carbonate-bound fluorescent dissolved organic matter

Abstract

The present invention relates to the technical field of chemical analysis of carbonate geological samples, and proposes a method for extracting and detecting carbonate-bound fluorescent dissolved organic matter. The method comprises ashing the sample, washing with deionized water, washing with a sodium hydroxide solution, acidolysis with an acetic acid solution, three-dimensional fluorescence spectrum testing, and parallel factor analysis, thereby obtaining carbonate-bound fluorescent dissolved organic matter indices C1 / (Ca+Mg), C2 / (Ca+Mg), and C3 / (Ca+Mg). The method 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.

Description

Technical Field

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

[0002] Carbonate minerals have a broad adsorption effect on dissolved organic matter in the surrounding water during their crystallization. This allows some of the dissolved organic matter to be stored stably for a long time by entering the interior of the carbonate mineral crystals. This can also be used to recover the dissolved organic matter information of the surrounding 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 the dissolved organic matter inside the carbonate mineral crystals is extracted by acid hydrolysis, these components often release interfering organic matter or adsorb target components, resulting in insufficient accuracy of traditional extraction methods.

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

[0004] This technology has the following disadvantages: it directly acid-hydrolyzes the sample and collects the acid solution for testing, without removing the fluorescent dissolved organic matter adsorbed on the calcite surface. This part of the fluorescent dissolved organic matter is in direct contact with the external environment and is easily adsorbed or desorbed with changes in environmental conditions. Therefore, it cannot be used to effectively reflect the fluorescent dissolved organic matter information of the environmental water body when calcite crystallizes; the acid hydrolysis reagent used in this technology is dilute hydrochloric acid, which is a strong acid and can cause large fluctuations in the pH values of the acid solution of different samples, while 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 tested; this technology 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, Ingalls et al. (2003) conducted an extraction and detection scheme for carbonate-bound fluorescent dissolved organic matter analysis of biological bones as follows: grind the biological bone sample into a 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. The NaClO solution in the glass bottle needs to be replaced on the 3rd and 6th days to achieve the most complete oxidation and removal of dissolved organic matter adsorbed on the outside of the carbonate minerals; after 8 days, remove the NaClO solution from 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 that has been burned, 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 the 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 shortcomings: 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 and removal. Therefore, adsorbed dissolved organic matter may still exist on the outer surface of carbonate minerals. This dissolved organic matter will be released into the acid hydrolysis solution during the acid hydrolysis of carbonate minerals, resulting in an inflated concentration of carbonate-bound dissolved organic matter. This technology requires the detection of dissolved organic carbon concentration, and the filtered acid hydrolysis solution is a high-salt solution with a potentially low dissolved organic carbon concentration. Therefore, the detection error is large and the damage to the instrument is significant. This technology can only obtain the organic carbon content of carbonate-bound dissolved organic matter and cannot obtain information on the properties 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, and is therefore 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 purpose 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] In order to solve the above technical problems, the technical solutions adopted in this application are:

[0010] The embodiment of the present application provides a method for extracting and detecting carbonate-bound fluorescent dissolved organic matter, comprising the following steps: S1. weighing a carbonate rock sample and ashing it in a muffle furnace to obtain an ashed sample; S2. adding deionized water to the ashed sample, mixing it, shaking it, centrifuging it, removing the supernatant, and repeating this step once to obtain a cleaned sample A; S3. adding sodium hydroxide solution to the cleaned sample A, mixing it, shaking it, centrifuging it, removing the supernatant, and repeating this step three times to obtain a cleaned sample B; S4. adding acetic acid solution to the cleaned sample B, mixing it, shaking it, centrifuging it, collecting the supernatant, and filtering it with a polyethersulfone filter head to obtain an acid hydrolyzate; and S5. The acid hydrolysis solution was subjected to a three-dimensional fluorescence test to obtain three-dimensional fluorescence spectral data. S6. The three-dimensional fluorescence spectral data were subjected to parallel factor analysis to obtain the fluorescence intensities of the three fluorescent components C1, C2 and C3, with the unit being mRSU / L. S7. The acid hydrolysis solution was diluted with dilute nitric acid, and the Ca-Mg ion concentration was measured by inductively coupled plasma emission spectrometry, with the unit being mmol / L. S8. By combining the fluorescence intensity and the Ca-Mg ion concentration, three groups of carbonate-bound fluorescent dissolved organic matter indices C1 / (Ca+Mg), C2 / (Ca+Mg) and C3 / (Ca+Mg) were obtained, with the unit being RSU / mol, which respectively represent the contents of the C1, C2 and C3 components in the carbonate mineral per unit amount of substance.

[0011] Furthermore, in step S1, the mass fraction of the 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.

[0012] Furthermore, in 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.

[0013] Furthermore, in step S2, the amount of the sample after ashing is weighed to be 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.

[0014] 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 centrifugation time is 10 min.

[0015] 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 centrifugation speed is 4000 rpm, and the centrifugation time is 10 min; the pore size of the polyethersulfone filter head is 0.45 μm.

[0016] 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.

[0017] 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 the blank value to be deducted in subsequent sample tests.

[0018] Furthermore, in step S6, the parallel factor analysis is specifically as follows: taking the three-dimensional fluorescence spectrum data within the excitation wavelength range of 280-450 nm and the emission wavelength range of 380-550 nm, and 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.

[0019] Furthermore, in step S7, the mass fraction of the dilute nitric acid is 2%, and the dilution ratio is 10 times.

[0020] The principle of the present invention is that dissolved organic matter can exist in carbonate minerals in three main forms: adsorption on crystal boundaries, existence in fluid inclusions, and embedding in the crystal structure. Dissolved organic matter existing in different forms is not only difficult to effectively identify on a macroscopic scale, but also cannot be effectively separated in a targeted manner. At the same time, dissolved organic matter existing in various 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 operational nature of carbonate-bound fluorescent dissolved organic matter as "fluorescent dissolved organic matter that can be proven to be ultimately retained due to the protective effect of carbonate minerals after a series of pretreatment processes to fully eliminate the interference of dissolved organic matter existing in non-carbonate phase components in the sample."

[0021] Ashing: Ashing at 530°C for 2 hours removes as much organic matter as possible from the exterior of carbonate minerals while ensuring that the carbonate minerals do not undergo significant decomposition, thereby preserving as much organic matter as possible within them. Furthermore, the high-temperature treatment destroys the crystal structure of non-carbonate mineral components (primarily clay) in the sample, significantly reducing their ability to adsorb fluorescent dissolved organic matter released by acid decomposition.

[0022] Deionized water washing: The ashing sample is washed twice to remove some of the suspended or soluble substances in the sample. These substances may release or adsorb fluorescent dissolved organic matter during the acid hydrolysis process, interfering with the effective extraction of carbonate-bound fluorescent dissolved organic matter.

[0023] Sodium hydroxide solution cleaning: Through four cleanings, the fluorescent dissolved organic matter present in the non-carbonate mineral components of the sample that can be extracted by sodium hydroxide solution is removed as much as possible to prevent it from being released during the subsequent acid hydrolysis process and interfering with the effective extraction of carbonate-bound fluorescent dissolved organic matter.

[0024] C1, C2, and C3 represent three potential fluorescence phenomena that were decomposed from the complex three-dimensional fluorescence spectral signal obtained through parallel factor analysis. Each fluorescence phenomenon has specific excitation and emission wavelengths, and can represent a class of fluorescent dissolved organic matter components with similar chemical properties. On this basis, the parallel factor analysis step can further provide the signal intensity of the three components in each sample, thereby realizing the qualitative and quantitative identification of fluorescent dissolved organic matter.

[0025] 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 unit amount of carbonate minerals in the carbonate rock sample.

[0026] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects:

[0027] 1. The chemical reagents used in this application are less toxic, require less sample volume, and have a simple pretreatment process. The test of carbonate-bound fluorescent dissolved organic matter is convenient, the analysis cost is very low, and rapid analysis and testing of large quantities of samples can be achieved.

[0028] 2. The excitation wavelength and emission wavelength ranges selected in the parallel factor analysis phase of this application can effectively remove the signal region of the three-dimensional fluorescence spectrum that is significantly affected by experimental contamination, while stabilizing the optimal number of components of the model to 3 components, which is conducive to the comparison of analysis results between different batches.

[0029] 3. This 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.

[0030] 4. This application can perform high-precision qualitative and quantitative characterization of extracted carbonate-bound fluorescent dissolved organic matter, and has good geological application prospects.

[0031] 5. This application has a high extraction rate for carbonate-bound fluorescent dissolved organic matter, and the experimental results are stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 This is a schematic flow chart of a method for extracting and detecting carbonate-bound fluorescent dissolved organic matter provided by the present invention. DETAILED DESCRIPTION

[0034] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0035] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to specific embodiments.

[0036] like Figure 1 As shown, based on the basic theoretical concept of the present invention, a method for extracting and detecting carbonate-bound fluorescent dissolved organic matter is proposed, comprising the following steps:

[0037] S1. The collected carbonate rock samples were coarsely crushed into small pieces with a particle size of approximately 1 cm, and then ground to 200 mesh using a sample crusher. The mass fraction of carbonate minerals in the carbonate rock samples should be greater than 50%.

[0038] S2. Weigh 0.25 ± 0.05 g of the ground carbonate rock sample and place it in a 20 mL ceramic crucible. Ash the sample in a muffle furnace at 530°C for 2 h to obtain an ashed sample.

[0039] S3. Weigh 0.025 ± 0.002 g of the ashed sample and place it in a 15 mL centrifuge tube. Add 10 mL of deionized water and mix thoroughly. Oscillate the tube at 70 rpm for 12 h on a rocking oscillator. Centrifuge the tube at 4000 rpm for 10 min. Remove as much supernatant as possible. Repeat this step once to obtain cleaned sample A.

[0040] S4. Add 10 mL of 0.1 M sodium hydroxide solution to cleaned sample A. Mix thoroughly and shake on a rocker at 70 rpm for 12 h. Centrifuge at 4000 rpm for 10 min. Remove as much supernatant as possible. Repeat this step three times to obtain cleaned sample B.

[0041] S5. Add 10 mL of 0.5 M acetic acid (fluorescent grade) to the cleaned sample B. Mix thoroughly and shake on a tumbling shaker at 70 rpm for 12 h. Centrifuge at 4000 rpm for 10 min. Collect the supernatant and filter through a 0.45 μm polyethersulfone filter to obtain the acid hydrolyzate.

[0042] S6. Perform three-dimensional fluorescence analysis on the filtered acid solution using a Horiba Jobin Yvon Aqualog fluorescence analyzer. The excitation wavelength range was set to 280–450 nm, and the emission wavelength range was the instrument default. Before the acid solution analysis, a three-dimensional fluorescence analysis was performed on deionized water with a resistivity greater than 18 MΩ·cm. This 3D fluorescence spectrum served as the blank value to be deducted from the subsequent acid solution analysis to obtain the 3D fluorescence spectral data.

[0043] S7. Compile all three-dimensional fluorescence spectral data tested and perform parallel factor analysis on the three-dimensional fluorescence spectra within the excitation wavelength range of 280-450 nm and the emission wavelength range of 380-550 nm. Normalize the sample fluorescence signal using the Raman scattering signal intensity (measured in "Raman scattering units" (RSUs), where 1 RSU = 1000 mRSUs) of deionized water at an excitation wavelength of 350 nm and an emission wavelength of 397 nm as the standard. This results in the fluorescence intensities of the three fluorescent components C1, C2, and C3 in each test sample expressed in mRSU / L.

[0044] S8. Dilute the acid solution 10-fold with 2% (mass fraction) dilute nitric acid and measure the Ca-Mg ion concentration (in mmol / L) using inductively coupled plasma optical emission spectrometry.

[0045] S9. The three groups of carbonate-bound fluorescent dissolved organic matter indices obtained by combining fluorescence intensity and Ca-Mg ion concentration include three sets of data, namely C1 / (Ca+Mg), C2 / (Ca+Mg) and C3 / (Ca+Mg), all in units of RSU / mol, which respectively represent the contents of C1, C2 and C3 components in carbonate minerals per unit amount of substance.

[0046] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0047] Example

[0048] In order to evaluate the effectiveness of the above-mentioned technical route for the extraction of carbonate-bound fluorescent dissolved organic matter in carbonate rocks, this example uses a laboratory synthetic calcite sample and a geological sample without carbonate mineral components as the carbonate mineral component end members and non-carbonate mineral component end members in the simulated carbonate rock sample, respectively, and prepares simulated carbonate rocks with carbonate mineral mass fractions of 75% and 50% according to a mass ratio of 3:1 and 1:1, respectively.

[0049] Among them, the laboratory-synthesized calcite samples include Cal-0, Cal-1 and Cal-2. All three use fulvic acid as simulated dissolved organic matter and are synthesized under three conditions: no fulvic acid, relatively low fulvic acid concentration and relatively high fulvic acid concentration.

[0050] Geological samples without carbonate mineral components include pure shale and pure siliceous rock, which can comprehensively represent the non-carbonate mineral end members found in common carbonate rock samples. The pure shale sample has a total organic carbon content of 4.7%, a silicon content of 29.2%, an aluminum content of 7.6%, and a potassium content of 6.7%, indicating that it is primarily composed of clay minerals. The pure siliceous rock sample has a total organic carbon content of 2.7%, a silicon content of 44.1%, an aluminum content of 0.4%, and a potassium content of 0.3%, indicating that it is primarily composed of silica.

[0051] In this example, Cal-0 was used as a blank sample. Fourteen replicates of these blank samples were used to extract and analyze carbonate-bound fluorescent dissolved organic matter. The established method detection limits for C1, C2, and C3 components in the acid hydrolyzate were 94.7 mRSU / L, 26.0 mRSU / L, and 51.3 mRSU / L, respectively. Based on these limits, this example evaluated the technical effectiveness from the following three perspectives.

[0052] Test 1

[0053] Based on the examples, this test 1 was used to evaluate the effect of non-carbonate mineral components in carbonate rock samples on the extraction of carbonate-bound fluorescent dissolved organic matter.

[0054] This test 1 conducted this evaluation by testing the acid solution extracted from the simulated carbonate rock sample prepared with Cal-0. The results are shown in Table 1:

[0055] Table 1 Test results of simulated carbonate rock sample acid solution prepared with Cal-0

[0056]

[0057] The test results show that, except for the C1 and C2 components of the sample prepared with a mass ratio of Cal-0 and pure siliceous rock of 1:1, whose test results were higher than the detection limits of the corresponding fluorescent components (9.4% and 33.8% higher, respectively), the test values of other fluorescent components were all lower than the detection limits of the corresponding fluorescent components. This indicates that in conventional carbonate rock samples, except for the siliceous component, which may make a certain contribution to the extraction of C1 and C2 components in the acid hydrolysis solution when the content is high, the effect of non-carbonate mineral components on the extraction of various fluorescent components in carbonate-bound fluorescent dissolved organic matter is generally negligible.

[0058] Test 2

[0059] Based on the examples, this test 2 was used to evaluate the stability of the carbonate-bound fluorescent dissolved organic matter extraction.

[0060] In this test 2, three independent analyses of carbonate-bound fluorescent dissolved organic matter indicators were conducted on simulated carbonate rock samples prepared with Cal-1 and Cal-2. The average concentrations of the fluorescent components in the acid hydrolyzed solutions obtained from the three tests and the relative standard deviations (RSDs) of the contents of each fluorescent component in the samples are shown in Table 2. Table 2 shows the test results of the acid hydrolyzed solutions 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 from the three independent analyses (the test values of the C1 component in the acid hydrolyzed solutions of the samples prepared with Cal-1 were all below or only slightly above the detection limit, so the corresponding RSD value of C1 / (Mg+Ca) was not calculated).

[0061] Table 2 Test results of acid hydrolysis solution and relative standard deviation of the test results of each fluorescent component of carbonate-bound fluorescent dissolved organic matter

[0062]

[0063] The results show that, except for the samples prepared with Cal-1, whose C1 component test values in the acid hydrolyzate were all below or only slightly above the detection limit, and the slightly higher RSD value of the C3 component content (10.7%) in the sample prepared with Cal-0 and pure siliceous rock in a 1:1 mass ratio, all other RSD values were less than 6.9%. This indicates that in conventional carbonate rock samples, except for the siliceous component that may affect the stability of the C3 component extraction when its content is high, the effect of non-carbonate mineral components on the extraction stability of various fluorescent components in carbonate-bound fluorescent dissolved organic matter is generally negligible.

[0064] Test 3

[0065] Based on Example 1 and Test 2, this Test 3 is used to evaluate the extraction rate of carbonate-bound fluorescent dissolved organic matter.

[0066] Based on the data tested in the stability assessment phase, this test 3 further calculated the extraction rate of each fluorescent component of carbonate-bound fluorescent dissolved organic matter in the simulated carbonate rock sample relative to the corresponding fluorescent component in the pure carbonate mineral. The average extraction rate obtained from three independent analyses is shown in Table 3. Table 3 shows the test results of the acid hydrolysis solutions of the simulated carbonate rock samples prepared with Cal-1 and Cal-2 and the average extraction rate of each fluorescent component of carbonate-bound fluorescent dissolved organic matter (the test values of the C1 component in the acid hydrolysis solution of the sample prepared with Cal-1 were all below or only slightly above the detection limit, so the average extraction rate of this fluorescent component was not calculated).

[0067] Table 3 Test results of acid hydrolysis solution and average extraction rate of each fluorescent component of carbonate-bound fluorescent dissolved organic matter

[0068]

[0069] 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 sample to the content of the corresponding pure carbonate mineral tested in the sample, which is used to evaluate the influence of non-carbonate minerals on the extraction of carbonate-bound fluorescent dissolved organic matter in the actual carbonate rock sample. The data in the table show that, except for the samples prepared with Cal-1 because the test values of the C1 component in the acid solution were all below or only slightly above the detection limit, the average extraction rate of the C3 component of the samples prepared with Cal-1 and pure siliceous rock at a mass ratio of 3:1 and 1:1 were both greater than 110% (110.7% and 122.3% respectively). The average extraction rate of the C1 component of the sample prepared with Cal-2 and pure shale at a mass ratio of 1:1 was lower (68.3%). The average extraction rates of all other calculated samples were between 80% and 10%. 5%, and the average extraction rates of each component of the simulated carbonate rock samples with the same non-carbonate mineral composition and a carbonate mineral content of 75% were better than those of the simulated carbonate rock samples with a carbonate mineral content of 50% (i.e., closer to 100%). This shows that in conventional carbonate rock samples, except for the clay component having a high influence on the extraction rate of the C1 component and the siliceous component having a high influence on the extraction rate of the C3 component, the non-carbonate mineral component has a relatively small effect on the extraction rate of each fluorescent component in the carbonate-bound fluorescent dissolved organic matter.

[0070] 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 invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also 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 ash it in a muffle furnace to obtain an ashed sample; S2. Deionized water was added to the ashing sample, mixed, shaken, centrifuged, and the supernatant was removed. This step was repeated once to obtain a cleaned sample A; S3. After washing, sodium hydroxide solution was added to the sample A, mixed and shaken, centrifuged, and the supernatant was removed. This step was repeated three times to obtain a washed 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. The acid solution was subjected to a three-dimensional fluorescence test by a fluorescence analyzer to obtain three-dimensional fluorescence spectrum data; S6. performing parallel factor analysis on the three-dimensional fluorescence spectral data, wherein the parallel factor analysis specifically comprises: taking the three-dimensional fluorescence spectral data within the excitation wavelength range of 280-450 nm and the emission wavelength range of 380-550 nm, and normalizing the fluorescence signal of the acid hydrolyzate 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, in units of RSU, to obtain the fluorescence intensities of the three fluorescent components C1, C2, and C3, in units of mRSU / L; S7. The acid solution was diluted with dilute nitric acid and the Ca-Mg ion concentration was measured 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 indices 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 step S1, the mass fraction of the 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 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, wherein In step S2, the amount of the sample after ashing is 0.025±0.002 parts by mass, the shaking speed is 70 rpm, the shaking time is 12 h, and the centrifugal speed is 4000 rpm, and the centrifugal time is 10 min.

5. The method according to claim 1, wherein 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 centrifugation 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, and the shaking 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.

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 in subsequent sample tests.

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

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