A method for dolomite cluster isotope purification treatment

Abstract

The application discloses a dolomite cluster isotope purification treatment method, comprising: acetic acid neutralization liquid leaching treatment, obtaining powder samples AW0, AW1 and AW2, then respectively performing X diffraction mineral content test (XRD) and cluster isotope test on the AW0, AW1 and AW2, performing linear regression analysis on dolomite content and cluster isotope data of the tested AW0, AW1 and AW2 samples, and using a linear regression formula obtained by the test results of the AW0, AW1 and AW2 to calculate cluster isotope values of dolomite components and calcite components of the sample. The application adopts an offline acetic acid neutralization liquid leaching method, performs step-by-step leaching on minerals mixed with dolomite and calcite, and then performs mineral content and cluster isotope test, so that cluster isotope compositions of dolomite and calcite components in the whole rock sample can be accurately obtained through material balance calculation of two end members.

Description

Technical Field

[0001] This invention relates to the field of isotope geochemistry, and in particular to a method for purifying isotopes of dolomite clusters. Background Technology

[0002] Cluster isotope studies of carbonate rocks are at the forefront of geochemistry, particularly in the field of stable isotope research. This index has wide applications in paleoclimate, paleotectonic, diagenetic evolution, and thermal history reconstruction. Compared to traditional carbon and oxygen isotopes, cluster isotope testing requires higher purity and precision of the gas sample, and the testing and purification methods are also more complex.

[0003] For carbonate rock samples in nature, the cluster isotopic compositions recorded by different carbonate minerals (such as dolomite and calcite) vary considerably after exposure to high temperatures or deep burial. In cluster isotope testing of carbonate rock samples, because most whole-rock samples contain both dolomite and calcite, the results cannot accurately reflect the cluster isotopic compositions of pure dolomite and pure calcite minerals, thus affecting subsequent research results.

[0004] Current methods for separating stable isotopes in carbonate minerals are mainly based on the difference in thermodynamic stability between calcite and dolomite. Specifically, the reaction rates of calcite and dolomite with phosphoric acid differ. By controlling the reaction time and helium purging rate, the carbon dioxide gas produced by the reactions of dolomite and calcite is collected separately, as illustrated in application CN201410835794.3, "Online Method for Determining Carbon and Oxygen Isotopes of Calcite and Dolomite in Mixed Samples." While this method is relatively effective for separating carbon and oxygen isotopes in dolomite and calcite, it still exhibits significant errors in determining cluster isotopes. The main reasons are: (1) The online separation process requires a long reaction time (up to 80 hours), which leads to a large amount of oxygen isotope exchange between the carbon dioxide digested by phosphoric acid and the water vapor in the reaction tank, resulting in a large error; (2) During the reaction process, in addition to the differences in the thermodynamic stability of the minerals themselves, the reaction rate also includes factors such as powder fineness, specific surface area, phosphoric acid concentration and the size of the device reaction tank, which will lead to a decrease in the purity of the acid-digested carbon dioxide, and cannot accurately reflect the cluster isotope composition of dolomite and calcite minerals; (3) The cluster isotope testing time is long, with a single sample testing time of 3 to 5 hours, which is much longer than the traditional carbon and oxygen isotope testing time (30 minutes). This means that the online separation method cannot effectively control the time, thus directly affecting the cluster isotope testing results.

[0005] Furthermore, due to the stability of acetic acid itself, it is often used in isotope geochemical analysis and testing. However, most acetic acid leaching methods are used to filter out non-carbonate minerals in the sample, such as the application CN202110624757.8 entitled "A Method for Neodymium Isotope Extraction and Analysis of Carbonate Rocks Based on Chemical Leaching of Standard Materials". However, they rarely consider the influence of different minerals (dolomite and calcite) in carbonate rocks on isotope testing, which leads to the neglect of geochemical information of different carbonate rock minerals in testing and subsequent applications.

[0006] Therefore, it is necessary to propose a method for purifying dolomite cluster isotopes to solve the above problems. Summary of the Invention

[0007] The technical problem to be solved by this invention is to improve the accuracy of isotope testing of different carbonate mineral clusters and obtain high-quality cluster isotope data results, and proposes a method for purifying dolomite cluster isotopes.

[0008] This method for purifying dolomite cluster isotopes uses an offline approach to separate and purify whole-rock powder samples, avoiding the contamination and impact on cluster isotope results caused by traditional online methods that control reaction time and temperature.

[0009] The processing method specifically includes the following steps:

[0010] Step 1: Acetic acid neutralization filtration treatment: The ground whole rock powder sample is labeled AW0; AW0 is leached with acetic acid neutralization solution; after treatment, ultrapure water is added, and the mixture is stirred thoroughly. A portion of the solution is removed using a burette and labeled AW1; the remaining solution is then added to ultrapure water and centrifuged to remove the supernatant; the residue remaining after centrifugation is dissolved in acetic acid neutralization solution for a period of time, and then ultrapure water is added and stirred. A portion of the solution is removed using a burette and labeled AW2; ultrapure water is added to AW1 and AW2 respectively, and the mixture is allowed to stand for a period of time. The supernatant is removed from each sample, and then the samples are dried to obtain powder samples AW1 and AW2 respectively.

[0011] Step 2: Take 10-50 mg each of the dried powder samples AW1 and AW2 and the original sample AW0, place them on a glass slide, mix the ultrapure water with the powder samples evenly, put them in an oven to dry, and perform XRD tests on the dried samples.

[0012] Step 3: Take 10-20 mg of AW0, AW1 and AW2 samples respectively for cluster isotope testing. After the three samples are rapidly digested with phosphoric acid at 90℃ for 20-30 minutes, the gas is purified.

[0013] Step 4: The three purified carbon dioxide gases were transferred to a MAT 253 isotope ratio mass spectrometer for cluster isotope analysis.

[0014] Step 5: Perform linear regression analysis on the dolomite content and cluster isotope data of the tested AW0, AW1 and AW2 samples;

[0015] Step 6: The linear regression formula obtained from the test results of AW0, AW1, and AW2 is used to calculate the cluster isotope values ​​of the dolomite and calcite components of the sample.

[0016] Further, the specific method for leaching with acetic acid neutralization solution in step one is as follows: Select 50-200 mg of milled whole-rock powder sample, labeled AW0; leach with 5-15 ml of acetic acid neutralization solution for approximately 5-15 minutes; add ultrapure water to 200 ml of the filtered sample, stir thoroughly, and transfer 50-100 ml of solution using a burette, labeled AW1; add ultrapure water to the remaining solution to 200 ml, centrifuge for 10 minutes, and remove the supernatant; [The remaining...] The remaining residue was dissolved in acetic acid neutralization solution for 24 hours. After filtration, ultrapure water was added to the filter residue to 200 ml, and the mixture was stirred thoroughly. 50-100 ml of the uniformly stirred solution was transferred out with a burette and labeled as AW2. Samples AW1 and AW2 were added to 500-1000 ml of ultrapure water respectively, and allowed to stand for 24 hours to remove the supernatant. The above water addition and standing steps were repeated 2-3 times. The samples were then placed in an oven for 24-48 hours to dry, thus obtaining powdered samples AW1 and AW2 respectively.

[0017] The acetic acid neutralization solution is prepared by first diluting glacial acetic acid with an original concentration of 95% to a concentration of 10% with ultrapure water, then adding sodium bicarbonate to neutralize the acetic acid solution to a pH of 7-7.5. The final product is the acetic acid neutralization solution.

[0018] The phosphoric acid used was a 105% superconcentration phosphoric acid, and the dosage was 3.5 cm. 3 .

[0019] Furthermore, in step five, the correlation coefficient R in the linear regression... 2 A value greater than 0.9, within the 95% confidence interval, is considered an acceptable result.

[0020] Implementing the embodiments of the present invention has the following beneficial effects:

[0021] This invention discloses a method for purifying dolomite cluster isotopes. It employs an offline acetic acid neutralization leaching method to perform stepwise leaching of minerals simultaneously containing dolomite and calcite, followed by mineral content and cluster isotope testing. Through end-component mixture mass balance calculations, the cluster isotope composition of dolomite and calcite components in whole-rock samples is accurately obtained. Compared to traditional acid hydrolysis methods, this invention offers high operability, eliminating the need for a closed-loop system and lowering the phosphoric acid hydrolysis temperature for stepwise reactions. It achieves higher purity, reducing the risk of incomplete or uneven sample reactions leading to the contamination of carbon dioxide from different mineral hydrolysis processes, which could lower the accuracy of cluster isotope testing. Furthermore, it eliminates the need for long reaction times and low reaction temperatures, avoiding the exchange of oxygen isotopes with phosphoric acid during testing, thus significantly improving accuracy. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the process for purifying isotopes of dolomite clusters.

[0024] Figure 2 X-ray diffraction data of a standard sample containing a mixture of carbon, oxygen, and cluster isotopes are shown in the figure.

[0025] Figure 3 The image shows the X-ray diffraction data of carbon, oxygen, and cluster isotopes in a modern carbonate rock sample.

[0026] Figure 4 The image shows the X-ray diffraction data of carbon, oxygen, and cluster isotopes in ancient carbonate rock samples. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Please see Figure 1 , Figure 1 This is a schematic flowchart of the dolomite cluster isotope purification method. The dolomite cluster isotope purification method includes:

[0029] Acetic acid neutralization solution filtration treatment:

[0030] Select 50-200 mg whole-rock powder samples after grinding and label them as AW0;

[0031] 5-15 ml of acetic acid neutralization solution (made by first diluting 95% glacial acetic acid with ultrapure water to a concentration of 10%, then adding sodium bicarbonate to neutralize the acetic acid solution to a pH of 7-7.5, resulting in the final acetic acid neutralization solution) was used to leach AW0 for approximately 5-15 minutes. This short reaction time effectively avoids oxygen isotope exchange caused by excessively long acid hydrolysis reaction time, and also prevents incomplete reaction of easily soluble carbonate rock components. The cluster isotope test results of AW1 can serve as an effective constraint for subsequent calculations, avoiding large calculation errors caused by the dolomite content of AW1 and AW2 being too close.

[0032] After leaching, add ultrapure water to 200 ml of the sample and stir thoroughly. Use a burette to transfer 50 to 100 ml of the uniformly stirred solution and label it AW1.

[0033] Add ultrapure water to the remaining solution until it reaches 200 ml, then centrifuge for 10 minutes and remove the supernatant.

[0034] The remaining residue was dissolved in acetic acid neutralization solution for 24 hours. After filtration, ultrapure water was added to the filter residue to 200 ml, and the mixture was stirred thoroughly. 50-100 ml of the solution was transferred out using a burette and labeled as AW2. The longer reaction time in this step ensures that most of the easily soluble carbonate rock minerals dissolve. The measured cluster isotope results are close to the theoretical cluster isotope values ​​of pure dolomite components, thus effectively reducing the deviation of the cluster isotopes of pure dolomite components obtained in subsequent calculations.

[0035] Add 500 to 1000 ml of ultrapure water to samples AW1 and AW2 respectively, let stand for 24 hours to remove the supernatant, repeat the above water addition and standing steps 2 to 3 times, and then place the samples in an oven for 24 to 48 hours to dry, thus obtaining powder samples AW1 and AW2 respectively.

[0036] Take 10-50 mg each of dried powder samples AW1 and AW2 and the original sample AW0, place them on a glass slide, mix ultrapure water with the powder samples evenly, put them in an oven to dry, and perform XRD tests on the dried samples.

[0037] Cluster isotope analysis was performed on 10–20 mg samples of AW0, AW1, and AW2, respectively. The three samples were reacted with 105% ultraconcentrated phosphoric acid (using 3.5 cm³ of solution) at 90°C. 3After rapid digestion for 20-30 minutes, the gas is purified. This shorter reaction time overcomes the problem of oxygen isotope exchange with phosphate caused by excessively long reaction times and low reaction temperatures in existing methods, greatly improving the accuracy of cluster isotope testing.

[0038] The three purified carbon dioxide gases were transferred to a MAT 253 isotope ratio mass spectrometer for cluster isotope analysis.

[0039] Linear regression analysis was performed on the dolomite content and cluster isotope data of the tested AW0, AW1, and AW2 samples, and the correlation coefficient R0 was calculated. 2 A value greater than 0.9, within the 95% confidence interval, is considered an acceptable result.

[0040] The linear regression formula obtained from the test results of AW0, AW1, and AW2 was used to calculate the cluster isotope values ​​of the dolomite and calcite components of the sample.

[0041] The above-mentioned method for isotope purification of dolomite clusters can also be used to calculate the carbon and oxygen isotope composition of dolomite and calcite components.

[0042] Reliability verification of this method:

[0043] The feasibility and accuracy of the method of the present invention were verified by using three types of typical carbonate rock samples: standard sample mixture (Example 1), modern carbonate rock (Example 2), and ancient carbonate rock (Example 3).

[0044] Example 1

[0045] (1) First, Carrara calcite standard and NIST-88b dolomite standard were selected as the standard samples for this experiment. 10 grams of Carrara calcite standard powder and 10 grams of NIST-88b dolomite standard powder were mixed in equal mass and labeled as DCMIX-0.

[0046] (2) The mixed sample was treated four times according to the aforementioned phosphoric acid leaching method, with a 5-minute interval between each leaching, to obtain four treated samples: DCMIX-1, -2, -6 and -00.

[0047] (3) All samples were subjected to XRD and carbon, oxygen, and cluster isotope analysis. The results were subjected to linear regression, as shown in Table 1. As can be seen from Table 1, the correlation was good (R0). 2 >0.9), using conventional linear regression methods, the isotopic results of pure dolomite and calcite components were calculated. The error between these results and the actual standard sample test results is within the 95% confidence interval. Please refer to [link / reference]. Figure 2 , Figure 2The X-ray diffraction data of the mixed carbon, oxygen, and cluster isotopes of the standard sample are shown in the following diagrams: (A) Cross plot of carbon isotopes and dolomite content; (B) Cross plot of oxygen isotopes and dolomite content; (C) Cross plot of cluster isotopes and dolomite content. Furthermore, the theoretically calculated values ​​obtained by mixing with the standard sample are within the 95% confidence interval, and the standard error is less than 0.03‰ (internationally recognized as reliable data with a standard error less than 0.03‰), indicating that the method has good effectiveness and accuracy.

[0048] Table 1. Results of cluster isotope and X-ray diffraction tests using the standard sample mixing method.

[0049]

[0050] Example 2

[0051] (1) Select dolomite from Bahamian carbonate boreholes for leaching treatment, and perform cluster isotope and XRD tests on the samples after treatment according to the above steps.

[0052] (2) Use the test data for two-terminal calculations, please refer to Figure 3 And Table 2, Figure 3 The images show the X-ray diffraction data of carbon, oxygen, and cluster isotopes in modern carbonate rock samples: (A) Cross-plot of cluster isotopes and dolomite content in sample 1; (B) Cross-plot of cluster isotopes and dolomite content in sample 2; (C) Cross-plot of cluster isotopes and dolomite content in sample 3. Calculations indicate that the temperature of the dolomite cluster isotopes is higher than that of the coexisting calcite cluster isotopes, which is consistent with actual geological processes. The test results are within the 95% confidence interval, and the standard error is less than 0.03‰, indicating that the data are accurate and reliable.

[0053] Table 2. Results of cluster isotope and X-ray diffraction tests on purified modern carbonate rock samples.

[0054]

[0055] Example 3

[0056] Core samples from two wells in the central Sichuan Basin, China, were selected for verification. Eight core samples were collected, including pure carbonate rock samples and mixed carbonate rock samples. Each sample group underwent two acetic acid leaching processes. After processing, the samples were subjected to X-ray diffraction and cluster isotope analysis (see Table 3). Table 3 shows that the correlation of each sample group was good, with R... 2 >0.9, please see Figure 4 , Figure 4The following are X-ray diffraction (XRD) results of carbon, oxygen, and cluster isotopes in ancient carbonate rock samples: (A) Cross-plot of cluster isotopes and dolomite content in sample LBC-45; (B) Cross-plot of cluster isotopes and dolomite content in sample LBC-46; (C) Cross-plot of cluster isotopes and dolomite content in sample GDM-36; (D) Cross-plot of cluster isotopes and dolomite content in sample GDM-37; (E) Cross-plot of cluster isotopes and dolomite content in sample GDM-39; (F) Cross-plot of cluster isotopes and dolomite content in sample GDM-33; (G) Cross-plot of cluster isotopes and dolomite content in samples YNSP-22 & 17; (H) Cross-plot of cluster isotopes and dolomite content in sample YNSP-23. The test results were within the 95% confidence interval and the standard error was less than 0.03‰. The results showed that the isotopic temperatures of pure dolomite clusters were all lower than those of calcite clusters, which is consistent with geological understanding.

[0057] Table 3. Results of cluster isotope and X-ray diffraction tests on purified modern carbonate rock samples.

[0058] sample Dolomite content <![CDATA[Δ 47 (‰)]]> sample Dolomite content <![CDATA[Δ 47 (‰)]]> LBC-45-AW0 0.7 0.532776 GDM-39-AW0 0.9 0.499485 LBC-45-AW1 0.9 0.560987 GDM-39-AW1 0.1 0.426488 LBC-45-AW2 0.55 0.526511 GDM-39-AW2 0.55 0.481666 LBC-46-AW0 0.15 0.467677 GDM-33-AW0 0.95 0.493973 LBC-46-AW1 0.9 0.538844 GDM-33-AW1 0.5 0.482479 LBC-46-AW2 0.75 0.534577 GDM-33-AW2 0.15 0.459033 GDM-36-AW0 0.9 0.516578 YNSP-22&17-AW0 0.99 0.467718 GDM-36-AW1 0.2 0.453893 YNSP-22&17-AW1 0.55 0.435043 GDM-36-AW2 0.05 0.435567 YNSP-22&17-AW2 0.05 0.415142 GDM-37-AW0 0.95 0.509583 YNSP-23-AW0 0.98 0.467718 GDM-37-AW1 0.3 0.463547 YNSP-23-AW1 0.79 0.467029 GDM-37-AW2 0.05 0.409196 YNSP-23-AW2 0.03 0.417304

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for purifying isotopes of dolomite clusters, characterized in that, Includes the following steps: Step 1: Acetic acid neutralization solution filtration treatment: The whole rock powder sample after grinding is labeled as AW0; AW0 is leached with acetic acid neutralization solution; after treatment, ultrapure water is added, and the mixture is stirred thoroughly. A portion of the solution is removed using a burette and labeled as AW1; the remaining solution is then added to ultrapure water and centrifuged to remove the supernatant. After centrifugation, the remaining residue was dissolved in acetic acid neutralization solution for a period of time, then ultrapure water was added and stirred. A portion of the solution was removed using a burette and labeled as AW2. Ultrapure water was added to AW1 and AW2 respectively, and the supernatant was removed. The supernatant was then removed and dried to obtain powder samples AW1 and AW2 respectively. Step 2: Take 10-50 mg each of the dried powder samples AW1 and AW2 and the original sample AW0, place them on a glass slide, mix the ultrapure water with the powder samples evenly, put them in an oven to dry, and perform XRD tests on the dried samples. Step 3: Take 10-20 mg of AW0, AW1 and AW2 samples respectively for cluster isotope testing. After the three samples are rapidly digested with phosphoric acid at 90℃ for 20-30 minutes, the gas is purified. Step 4: The three purified carbon dioxide gases were transferred to a MAT 253 isotope ratio mass spectrometer for cluster isotope analysis. Step 5: Perform linear regression analysis on the dolomite content and cluster isotope data of the tested AW0, AW1 and AW2 samples; Step 6: The linear regression formula obtained from the test results of AW0, AW1, and AW2 is used to calculate the cluster isotope values ​​of the dolomite and calcite components of the sample.

2. The method for purifying dolomite cluster isotopes according to claim 1, characterized in that, The specific method for acetic acid neutralization leaching in step one is as follows: Select 50-200 mg of milled whole-rock powder sample, labeled AW0; leach with 5-15 ml of acetic acid neutralization solution for approximately 5-15 minutes; add ultrapure water to 200 ml of the filtered sample and stir thoroughly; transfer 50-100 ml of the uniformly stirred solution using a burette, labeled AW1; add ultrapure water to the remaining solution to 200 ml, centrifuge for 10 minutes, and transfer the supernatant. The remaining residue was dissolved in acetic acid neutralization solution for 24 hours. After filtration, ultrapure water was added to 200 ml of the residue and stirred thoroughly. 50-100 ml of the solution was transferred out with a burette and labeled as AW2. Samples AW1 and AW2 were added to 500-1000 ml of ultrapure water respectively and allowed to stand for 24 hours to remove the supernatant. The above water addition and standing steps were repeated 2-3 times. The samples were then placed in an oven for 24-48 hours to dry, thus obtaining powdered samples AW1 and AW2 respectively.

3. The method for purifying dolomite cluster isotopes according to claim 2, characterized in that, The acetic acid neutralization solution is prepared by first diluting glacial acetic acid with an original concentration of 95% to a concentration of 10% with ultrapure water, then adding sodium bicarbonate to neutralize the acetic acid solution to a pH of 7-7.

5. The final product is the acetic acid neutralization solution.

4. The method for purifying dolomite cluster isotopes according to claim 1, characterized in that, In step three, the phosphoric acid used is a 105% super-concentration phosphoric acid, and the dosage is 3.5 cm³. 3 .

5. The method for purifying dolomite cluster isotopes according to claim 1, characterized in that, In step five, the correlation coefficient R in linear regression 2 A value greater than 0.9, within the 95% confidence interval, is considered an acceptable result.

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