Low-cost rock sample cadmium isotope purification method and application

Abstract

The invention provides a low-cost rock sample cadmium isotope purification method and application, and relates to the technical field of isotope analysis. Comprising the following steps: firstly adding hydrofluoric acid-perchloric acid-nitric acid mixed acid and Cd double diluents, heating and dissolving a sample, and then adding hydrochloric acid to remove silicon; then purifying cadmium through a two-step method: step 1, removing matrix elements, Pd, In and most of Sn by using AG1 resin, and recovering a Cd component; 2, TBP resin is used for adsorbing Sn under the condition of 3-6 M hydrochloric acid, Sn interference is eliminated by means of the characteristic that the TBP resin strongly retains Sn and does not adsorb Cd, and separation of Cd and Sn is completed. According to the step, Sn can be eliminated, In, Zr and Mo can be removed at the same time, and interference of compound ion peaks of the elements on testing can be eliminated. And finally, adding perchloric acid and nitric acid to nitrate trace organic matters in sample components, and evaporating the sample to dryness. The method has the advantages of low cost, low background, high preparation efficiency, less waste liquid and the like, and has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of isotope analysis technology, specifically relating to a low-cost method for purifying cadmium isotopes in rock samples, and particularly to a separation technique using AG1 anion exchange resin and TBP resin in combination, applied to the separation of cadmium isotopes in rock samples. Background Technology

[0002] Cadmium (Cd) is a typical rare element, exhibiting chalcophilicity, lithophilicity, and volatility under different geological conditions. Biologically, it is both a nutrient element (closely related to the metabolism of phosphorus (P) and zinc (Zn)) and a highly toxic element. Both its geochemical and biochemical properties make Cd an important research subject for scientists.

[0003] Over the past 20 years, Cd isotopes have demonstrated promising applications in cosmochemistry, paleoenvironmental evolution, mineral deposit genesis, ecology, and environmental science, yielding a wealth of high-quality research results. The Cd isotope ratios in different geological reservoirs generally exhibit relatively small variations; therefore, the prerequisite for effective tracing of Cd isotopes in these fields is obtaining high-precision ratio data, typically with a δ¹⁸O value of [missing information]. 114 Cd (relative to NIST 3108 standard) 114 Cd / 110 The accuracy of the Cd ratio must be at least better than 0.15‰. Current analytical methods primarily rely on two instruments: thermal ionization mass spectrometry (TIMS) and multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). However, before using these mass spectrometers, specialized chemical separation techniques must be employed to purify high-purity cadmium components from geological samples.

[0004] Rock samples have complex and variable matrix element compositions, and these matrix elements can significantly affect the sensitivity of mass spectrometry tests, necessitating their complete removal. Furthermore, Pd, In, and Sn are the main isotopes causing interference in mass spectrometry tests. Pd and In are extremely rare in natural samples, with crustal abundances of 1.74 ppb and 50 ppb, respectively, while Cd has a crustal abundance of 75 ppb. The Pd / Cd ratio and In / Cd ratio in crustal samples are 0.023 and 0.670, respectively. Sn, on the other hand, has a crustal abundance of 1500 ppb, with a Sn / Cd ratio reaching 20. In some Sn-rich minerals or contaminated mine soils, the Sn / Cd ratio can even exceed 500. Therefore, Sn is the most significant interfering element for Cd testing in natural rock samples.

[0005] To improve the separation efficiency of cadmium components, existing technologies propose using a two-step ion exchange resin separation method to separate the components in rock samples. The first step typically aims to remove some matrix elements (K, Na, Ca, Mg, Al, Fe, Ti) and interference from Pd and In, as well as most Sn interference. The second step aims to further remove the remaining Sn interference. There are five main methods:

[0006] (1) Anion exchange two-step separation technology: for example, the first step uses Bio-Rad AG1 or Bio-Rad AGMP-1 anion exchange resin column; the second step still uses AG1 resin column.

[0007] (2) Two-step separation technology of anion-binding TRU special resin: For example, the first step uses Bio-Rad AG1 or Bio-Rad AGMP-1 anion resin column; the second step uses TRU special resin column, and concentrated hydrochloric acid is used to load the column. Sn is strongly adsorbed on the TRU column, while Cd is not adsorbed, thereby achieving the purpose of further removing Sn.

[0008] (3) Two-step separation technology using anion-bonded U-TEVA special resin: For example, the first step uses Bio-Rad AG1 or Bio-Rad AGMP-1 anion resin column; the second step uses U-TEVA special resin column.

[0009] (4) Two-step separation technology using anion exchange and BPHA special resin: For example, the first step uses Bio-Rad AG1 or Bio-Rad AGMP-1 anion exchange resin column; the second step uses BPHA special resin column.

[0010] (5) Two-step separation technology using anion-bonded TOPO special resin: For example, the first step uses Bio-Rad AG1 or Bio-Rad AGMP-1 anion resin column; the second step uses TOPO special resin column.

[0011] The five cadmium isotope separation techniques mentioned above are all applicable to the preparation of Cd in rock samples. However, the first method requires two anion exchange column preparations, resulting in a large sample elution volume, high reagent consumption, and significant waste liquid generation. The final evaporation and concentration of the Cd solution is also time-consuming. The other four methods use different special resins as materials for the second step of Sn removal, achieving better Sn removal effects, lower reagent consumption, faster sample elution, and higher preparation efficiency. However, the first two special resins (TRU and U-TEVA) are expensive, and the latter two special resins (BPHA and TOPO) are currently in the stage of laboratory research and development, and cannot be commercially purchased or widely used. Therefore, it is urgent to explore a commercially viable and low-cost special resin for Cd separation and to develop a low-cost method for cadmium isotope purification in rock samples. Summary of the Invention

[0012] The technical problem to be solved by the present invention is to provide a low-cost method for purifying cadmium isotopes in rock samples. This method can achieve low-cost separation and purification of cadmium isotope components in rock samples, is simple to operate, has high preparation efficiency, and produces little waste liquid. It is especially suitable for the separation of geological samples with high Sn / Cd ratios.

[0013] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0014] In a first aspect, the present invention provides a low-cost method for purifying cadmium isotopes from rock samples, comprising the following steps:

[0015] (1) Weigh the rock sample, add mixed acid and cadmium double diluent at 3.5 times the cadmium dose of the sample, keep it at 160~190℃ for 3~5 days in a sealed container to ensure that the sample is fully dissolved, then cool to room temperature and evaporate the sample solution to dryness, then add hydrochloric acid with a molar concentration of 3M~6M, and heat to 100~150℃ to remove silicon; the mixed acid is a mixture of hydrofluoric acid, perchloric acid and nitric acid;

[0016] (2) Two-step purification of cadmium:

[0017] Step 1: After complete silicon removal, the sample was dissolved in hydrochloric acid with a molar concentration of 3M~6M and passed through an AG1 anion exchange column to remove matrix elements and most of the interfering isotopes. The matrix elements included K, Ca, Na, Mg, Al, Fe, and Ti; the interfering isotopes included Pd, In, and most of Sn. The Cd fraction was recovered, and the recovered Cd fraction contained (2.4±0.24)% Sn.

[0018] Step 2: The Cd fraction is evaporated to dryness, dissolved in hydrochloric acid with a molar concentration of 3M~6M, and then passed through a TBP resin exchange column to remove residual Sn, while eliminating potential interference caused by In, Zr and Mo elements, to obtain a high-purity Cd component.

[0019] (3) After the high-purity Cd component is evaporated to dryness, perchloric acid and nitric acid are added, and the mixture is sealed and heated at 160~180℃ for 1~2 hours to nitrate the trace organic matter in the sample component; then the sample is evaporated to dryness, and 1 ml of hydrochloric acid is added, and the mixture is sealed and heated at 160~180℃ for 1~2 hours. Finally, the sample is evaporated to dryness to obtain the final product.

[0020] Furthermore, the cadmium double diluent in step (1) is 108 Cd- 116 Cd dual diluent. Theoretically, 106 Cd- 108 Cd, 108 Cd- 116 Cd,106 Cd- 111 Cd, 111 Cd- 113 Cd double diluent can also be replaced 108 Cd- 116 Cd dual diluent and achieve comparable technical effects.

[0021] Furthermore, in step (1), the sample is physically pulverized to 200 mesh to obtain sample powder.

[0022] Furthermore, the rock weight in step (1) is 10~40mg; correspondingly, the concentration and volume of each acid in the mixed acid added in step (1) are as follows: the concentration of hydrofluoric acid is 29±2.9M and the volume is 1.5~2.5ml; the concentration of perchloric acid is 11.8±1M and the volume is 0.5~0.6ml; the concentration of nitric acid is 15±1M and the volume is 0.1~0.3ml; the volume of perchloric acid added in step (3) is 0.1~0.2ml and the volume of nitric acid is 0.5~0.6ml.

[0023] Furthermore, in step (2), the amount of AG1 resin packed in the AG1 anion exchange column is 0.9~1.1 ml.

[0024] Furthermore, in step (2), the TBP resin filling amount of the TBP resin exchange column is 0.13~0.15ml.

[0025] Furthermore, the specific elution and separation process of the AG1 anion exchange column in step (2) is as follows:

[0026] .

[0027] Furthermore, the specific elution and separation process of the TBP resin exchange column in step (3) is as follows:

[0028] .

[0029] Furthermore, the rock samples include, but are not limited to, GSD-11, GSS-1a, NOD-P1, and NOD-A1.

[0030] Secondly, the present invention provides an application of the above-mentioned low-cost method for cadmium isotope purification of rock samples in cadmium isotope analysis and testing of rock samples.

[0031] The principle of this invention is as follows:

[0032] Achieving high-precision cadmium (Cd) isotope ratio testing requires high-quality Cd purification technology, particularly eliminating Sn's isotopic interference with Cd. The purification method proposed in this invention first involves adding a mixed acid (hydrofluoric acid-perchloric acid-nitric acid) and an appropriate amount of Cd dual diluent, followed by heating to dissolve the sample. Then, hydrochloric acid with a molar concentration of 3M~6M is added, and the sample is heated to remove silica. Next, a two-step method is used to remove matrix elements and isotopic interference from the sample, mainly including: First, AG1 resin is used to remove the rock matrix, Pd, In, and most of Sn (approximately 97.6%), while simultaneously recovering the Cd component. Second, utilizing the characteristic of TBP resin under 3M~6M hydrochloric acid conditions, especially 6M hydrochloric acid conditions, which exhibits extremely strong Sn retention (>99%) while retaining no Cd, approximately 2.4% of the Sn remaining in the Cd component is further removed, completing the separation of Cd and Sn. This also eliminates potential interference from In, Zr, and Mo elements, yielding a high-purity Cd component. Both resin separation steps used hydrochloric acid with a molar concentration of 3M to 6M as the eluent, which achieved excellent separation results. Finally, perchloric acid and nitric acid were added to nitrate trace amounts of organic matter in the sample components, and the sample was evaporated to dryness to obtain the final product.

[0033] The present invention has the following beneficial effects:

[0034] (1) The method for purifying cadmium isotopes in rock samples proposed in this invention employs a two-step separation technique using AG1 resin and TBP resin, which can separate high-purity cadmium components from complex rock matrices. Compared with traditional two-step separation techniques, although high-purity cadmium can be separated from rocks, the preparation cost of existing techniques is high. This invention uses TBP resin instead of TRU and U-TEVA as the extraction resin. The price of commercially available domestic TBP resin is only 5% of that of French TRU resin and U-TEVA resin, which can significantly reduce the preparation cost; the AG1 resin used in the first step is a gel-type resin, which has strong selectivity and low cost.

[0035] (2) For rock sample analysis, the background level of the process directly affects the accuracy of the test results. This invention can reduce the background level by half, resulting in a low process blank, and can significantly improve the success rate of high-precision analysis of cadmium isotopes in trace rock samples.

[0036] (3) The TBP resin in this invention can not only effectively remove Sn, but also efficiently remove Zr, In and Mo. When Cd is tested using a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS), the composite ion peaks of these elements often interfere with the Cd isotope test. Therefore, this advantage is unmatched by other resins. It is particularly important for some special rocks and minerals and has broad application potential. Common rocks and minerals with high Zr content mainly include nepheline syenite, alkaline granite, and kaolinite. The Zr content in the weathering crust of some alkaline rocks is as high as 1%, and its Zr / Cd ratio can even reach 100,000. Rocks and minerals with high Mo content include molybdenite and deep-sea iron-manganese nodules, and their Mo / Cd ratio is often greater than 50. Rocks and minerals with high In content mainly include limonite in the sulfide oxidation zone, polymetallic deposits rich in cassiterite, and lead antimony, and their In / Cd ratio is often greater than 50. TBP resin has the advantage of simultaneously removing Sn-Zr-In-Mo, which is very helpful in solving the sample purification problem faced by geological samples with high Sn, high In, high Zr and high Mo contents.

[0037] (4) The sample elution volume of the method of the present invention is small, the amount of reagent consumed is small, and the amount of waste liquid generated is small.

[0038] In summary, this method offers advantages such as low cost, low background, high preparation efficiency, and minimal waste liquid, representing a significant innovation in Cd isotope separation technology and possessing strong application prospects. It is particularly suitable for geological samples with high Sn / Cd ratios, high Zr / Cd ratios, high Mo / Cd ratios, and high In / Cd ratios. Detailed Implementation

[0039] To better understand the above-described objects, features, and advantages of the present invention, the present invention will be further described in detail below with reference to specific embodiments. Many specific details are set forth in the following description to provide a thorough understanding of the present invention; however, the present invention may also be implemented in other ways different from those described herein, and therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0040] In the following embodiments, the raw materials used are sourced from:

[0041] TBP resin (particle size 80~120 mesh, Beijing Ruilekang Separation Technology Co., Ltd.)

[0042] MOS pure hydrochloric acid (purified once by sub-boiling distillation, Sinopharm Chemical Reagent Co., Ltd.)

[0043] MOS pure nitric acid (purified once by sub-boiling distillation, Sinopharm Chemical Reagent Co., Ltd.)

[0044] MOS pure hydrofluoric acid (purified once by sub-boiling distillation, Sinopharm Chemical Reagent Co., Ltd.)

[0045] Superior grade perchloric acid (purified once by sub-boiling distillation, Merck Chemicals GmbH, Germany).

[0046] High-purity hydrogen peroxide (purity: 99.99%, Sinopharm Chemical Reagent Co., Ltd.).

[0047] High purity 108 Cd diluent (purity: >70.4%, Isoflex, USA).

[0048] High purity 116 Cd diluent (purity: >98.7%, Oak Ridge National Laboratory, USA).

[0049] High purity 108 Cd- 116 Cd diluent: The above-mentioned diluent was purchased from Isoflex Inc. and Oak Ridge National Laboratory. 108 Cd and 116 After dissolving the Cd diluent in nitric acid, a solution of 1.56 ppm was prepared at a 1:1 weight ratio. 108 Cd- 116 Cd double diluent solution.

[0050] NIST 3108 cadmium isotope standard solution (99.999%, U.S. National Institute of Standards and Technology).

[0051] Ultrapure water (Millipore Simplicity ultrapure water system, Millipore Corporation, USA, with an output conductivity of 18.2 MΩ / cm).

[0052] AG1-X8 resin (200~400 mesh, Bio-Rad, USA).

[0053] This invention provides a method for purifying cadmium isotopes in rock samples, primarily employing a two-step separation technique using AG1 resin and TBP resin. This method can separate high-purity cadmium components from complex rock matrices. Specifically, it includes the following steps:

[0054] (1) Weigh a trace amount (10~40mg) of rock sample and pre-crush the sample to 200 mesh to obtain sample powder. Add mixed acid and cadmium double diluent 3.5 times the cadmium dose of the sample, place on a hot plate at 160~190℃ and keep warm for 3~5 days in a sealed container to ensure complete dissolution of the sample. Use a dissolution container with a polytetrafluoroethylene liner for dissolution. After cooling to room temperature, evaporate the sample solution to dryness, then add hydrochloric acid with a molar concentration of 3M~6M, and heat to 100~150℃ to remove silicon. As a preferred embodiment, the cadmium double diluent is preferably made of... 108Cd- 116 Cd double diluent.

[0055] The mixed acid in this invention is a mixture of hydrofluoric acid, perchloric acid, and nitric acid. The concentration of hydrofluoric acid is 29M, the concentration of perchloric acid is 11.8M, and the concentration of nitric acid is 15M. For 10-40 mg of rock samples, the mixture is prepared by mixing 1.5-2.5 ml of hydrofluoric acid, 0.5-0.6 ml of perchloric acid, and 0.1-0.3 ml of nitric acid. In the mixed acid, hydrofluoric acid is the core reagent for dissolving the rock, and the aforementioned acid concentrations and mixing ratios ensure good dissolution.

[0056] (2) Two-step purification of cadmium:

[0057] Step 1: After complete silicon removal, the sample is dissolved again with hydrochloric acid at a molar concentration of 3M~6M. The sample is then passed through an AG1 anion exchange column to remove matrix elements and most of the interfering isotopes. Matrix elements include K, Ca, Na, Mg, Al, Fe, and Ti; interfering isotopes include Pd, In, and most of Sn (approximately 97.6%). The Cd fraction is recovered. Approximately 2.4% Sn remains in the recovered Cd fraction. Sn will interfere with the test, so further Sn removal is required.

[0058] The AG1 resin packing volume for the AG1 anion exchange column is 0.9~1.1 ml. Within this packing volume range, the preparation process will not be altered, ensuring separation efficiency while avoiding excessive resin waste.

[0059] Step 2: The Cd fraction is evaporated to dryness, dissolved in hydrochloric acid with a molar concentration of 3M~6M, and then passed through a tributyl phosphate (TBP) resin exchange column to remove residual Sn. At the same time, In, Zr and Mo elements are eliminated in this process, which can effectively eliminate the interference of the composite ion peaks of the above elements on the test, and obtain high-purity Cd component.

[0060] The TBP resin packing volume for a tributyl phosphate (TBP) resin exchange column is 0.13~0.15 ml. Within this packing volume range, the separation effect is ensured without excessive resin waste.

[0061] (3) After the high-purity Cd component is evaporated to dryness on a hot plate, 11.8~12M perchloric acid and 14~15M nitric acid are added, and the mixture is sealed and heated at 160~180℃ for 1~2 hours to nitrate the trace organic matter in the sample component. The volume of perchloric acid and nitric acid added should not be excessive. Excessive reagents will cause the sample to evaporate slowly, especially since perchloric acid has a high boiling point and is not easy to evaporate. Therefore, the volume of perchloric acid should be controlled to be 0.1~0.2ml and the volume of nitric acid to be 0.5~0.6ml. Then the sample is evaporated to dryness, sealed and heated on a hot plate at 160~180℃ for 1~2 hours, and finally the sample is evaporated to dryness to obtain the final product.

[0062] The method of this invention first involves heating the sample thoroughly after adding a mixed acid (hydrofluoric acid-perchloric acid-nitric acid) and an appropriate amount of Cd dual diluent, followed by adding hydrochloric acid with a molar concentration of 3M~6M and heating to remove silicon. Then, a two-step method is used to remove matrix elements and isotope interference from the sample, mainly including: First, using AG1 resin to remove the rock matrix, Pd, In, and most of Sn, while simultaneously recovering the Cd component; Second, utilizing the characteristic of TBP resin under 6M hydrochloric acid conditions that it has extremely strong Sn retention (>99%) while not retaining Cd, the remaining approximately 2.4% Sn in the Cd component is further removed, completing the separation of Cd and Sn, while simultaneously eliminating interference from In, Zr, and Mo elements, resulting in a high-purity Cd component. Finally, perchloric acid and nitric acid are added to nitrate trace organic matter in the sample component, and the sample is evaporated to dryness to obtain the final product.

[0063] The two-step process for removing matrix elements and isotopic interference from samples is shown in Table 1 below:

[0064]

[0065] The following examples illustrate this in detail.

[0066] First, to achieve the best purification effect while ensuring the highest possible recovery rate, an artificially mixed standard solution was used to study the optimal adsorption conditions. This mixed standard solution consisted of 5 μg Cd and various elements that could cause interference in the test (5 μg Sn, 5 μg In, 5 μg Zr, and 5 μg Mo). Three portions of the above artificially mixed standard solution were evaporated to dryness, and the samples were dissolved in 0.3 ml of 1M hydrochloric acid, 0.3 ml of 3M hydrochloric acid, and 0.3 ml of 6M hydrochloric acid, respectively. The solutions were then passed through TBP resin microcolumns (filled with 0.13 ml TBP resin) pre-washed with 1M, 3M, and 6M hydrochloric acid, respectively. The eluents were collected stepwise according to the methods in Tables 2, 3, and 4 (eluents numbered F1 to F9 sequentially), and the recovery rates of various elements in the nine eluents were tested using ICP-MS mass spectrometry.

[0067]

[0068]

[0069]

[0070] The test results (Tables 2, 3, and 4) show that Sn exhibits excellent adsorption efficiency (>99%) in both 3M and 6M hydrochloric acid media. In the main Cd-enriched fractions (F5, F6, F8, and F9), each fraction contains less than 0.32% Sn. Particularly in the 6M hydrochloric acid medium, it demonstrates even better removal efficiency for Mo, Zr, and In. As shown in Table 4, receiving and combining the eluents from F8 and F9 yields 99.8% Cd, with the combined solution containing only 0.53% Sn, 0.07% Mo, and 2.3% Zr. Using the preparation process described in Table 4, 99.7% of Sn can be removed in a single step, while 99.8% of Cd can be recovered. Combined with the separation method using AG1 resin in the previous step, the final two-step column chromatography scheme recovers 99.4% of Cd, with only 0.03% Sn remaining.

[0071] The following examples demonstrate the use of 6M hydrochloric acid as the eluent for the separation of Cd, and provide examples of purification and separation of different rock samples. The examples below illustrate the use of an exchange column packed with 1 mL of AG1 anion exchange resin (specifically, an AG1-X8 resin exchange column) and an exchange column packed with 0.13 mL of TBP resin.

[0072] Example 1

[0073] (1) Weigh 40 mg of GSD-11 sediment sample, add 2 ml of 29 M hydrofluoric acid, 0.2 ml of 14 M nitric acid, 0.5 ml of 11.8 M perchloric acid, and an appropriate amount of 108 Cd- 116 Cd double diluent, place all three in a sealed melting vessel and keep it at 160℃ on a hot plate for 4 days.

[0074] After the sample dissolving apparatus has cooled to room temperature, evaporate the sample solution in the dissolving apparatus to dryness, then add 2 ml of 6M hydrochloric acid and heat to remove silicon.

[0075] (2) Two-step purification of cadmium:

[0076] Step 1: After complete silicon removal, dissolve the sample in 1 ml of 6M hydrochloric acid. Then, separate the sample according to the procedure in Step 1 of Table 1. Pre-wash with high-purity water and 6M hydrochloric acid sequentially, then sequentially wash the exchange column packed with 1 ml of AG1 anion exchange resin with 3 ml of 6M hydrochloric acid, 12 ml of 0.4M hydrochloric acid, and 12 ml of a mixed acid (0.1M hydrobromic acid + 0.5M nitric acid). This washing removes the matrix elements (K, Ca, Na, Mg, Al, Fe, Ti), In, Pd, Zn, Mo, and most (approximately 97%) of Sn. Finally, elute and recover Cd from the AG1 resin with 8 ml of 2M nitric acid. Approximately 2.4% Sn remains in the recovered Cd fraction, which will interfere with the test; therefore, further Sn removal is required.

[0077] Step 2: Collect the Cd-rich (>99.7%) sample solution that has been removed from the matrix, Pd, In and most of Sn in Step 1, evaporate it to dryness, and pre-wash it with high-purity water and 6M hydrochloric acid in sequence according to the procedure in Step 2 of Table 1. Then, dissolve the sample with 0.3 ml of 6.0 M hydrochloric acid. After the sample solution is cooled to room temperature, pass it through an exchange column filled with 0.13 ml of TBP resin to remove residual Sn and eliminate potential interference caused by In, Zr and Mo elements, and separate the high-purity Cd fraction.

[0078] (3) Evaporate the separated high-purity Cd fraction to dryness on a hot plate at 160℃. Add 0.1 ml of 12M perchloric acid and 0.5 ml of 15M nitric acid. Seal the sample dissolving apparatus and heat it on a hot plate at 160℃ for 2 hours to nitrate the trace organic matter in the sample components. Then evaporate the sample to dryness. Add 1 ml of 6M hydrochloric acid. Seal the sample dissolving apparatus and heat it on a hot plate at 160℃ for 1 hour. Finally, open the sample dissolving apparatus and evaporate the sample to dryness on a hot plate at 180℃ to obtain the final product.

[0079] Example 2

[0080] The difference between this embodiment and Embodiment 1 is that this embodiment uses 10mg soil standard sample GSS-1a.

[0081] Example 3

[0082] The difference between this embodiment and Embodiment 1 is that this embodiment uses 10mg of manganese crust standard sample NOD-P1.

[0083] Example 4

[0084] The difference between this embodiment and Embodiment 1 is that this embodiment uses 10mg of manganese crust standard sample NOD-A1.

[0085] The cadmium samples prepared in each embodiment were subjected to Cd isotope analysis using thermal ionization mass spectrometry. All results were expressed in internationally accepted delta-index (δ¹²) values. 114Cd representation (δ) 114 Cd = ([( 114 Cd / 110 Cd) sample / ( 114 Cd / 110 Cd) NIST 3108 The result of the multiplication table is shown in Table 5-8.

[0086]

[0087]

[0088]

[0089]

[0090] Tables 5-8 list the results of multiple analyses of four different rock standard samples using the purification method proposed in this invention. The test results show that the δ0.05 of all rock standard samples... 114 The internal precision of the Cd ratio is less than ±0.09‰, with most internal precisions exceeding ±0.05‰, consistent with the reference values ​​within the analytical error range. Specifically, the external precision of multiple analyses of the sample GSD-11 (J. Anal. Atomic Spectrom. 2020, 35, 713–727), which has an extremely high Sn / Cd (500) ratio, is better than ±0.04‰, indicating the method's stability and reliability. These data demonstrate that the present invention has excellent preparation effects on rock samples, suggesting that the combined separation technology based on AG1 resin and TBP resin has promising application prospects for Cd isotope preparation in rock samples.

[0091] In addition, to verify the actual effect of using AG1 resin column and TBP resin column in combination for Cd isotope testing, two mixed standard solutions with high Sn / Cd ratios, NIST 3108-M and AAS-M, were prepared. The Sn / Cd ratio of these two solutions was 200, which is much higher than the Sn / Cd ratio of natural samples (5~20). The composition of the mixed standard is shown in Table 9, and eight portions of each mixed standard were prepared.

[0092]

[0093] The proposed two-step preparation method was used to prepare NIST 3108-M and AAS-M mixed standards, and the results were verified by dual-dilution thermal ionization mass spectrometry (DS-TIMS). The results are shown in Tables 10 and 11.

[0094]

[0095]

[0096] As shown in Tables 10 and 11, the mixed standard solutions NIST3108 and AAS exhibit good internal precision (<0.035‰) for single-analysis and external precision (<0.050‰) for multiple analyses, consistent with the reference values ​​within the error range. No Sn interference signal was observed during TIMS testing. These test results demonstrate that the proposed method not only performs well with Sn but also achieves high-quality Cd separation, even for rock samples with extremely high Sn / Cd ratios.

[0097] In summary, the cadmium isotope purification method for rock samples proposed in this invention employs a two-step separation technique using AG1 resin and TBP resin, which can separate high-purity cadmium components from complex rock matrices. The second step uses TBP resin instead of TRU and U-TEVA as the extraction resin, significantly reducing preparation costs. The AG1 resin used in the first step is a gel-type resin, offering high selectivity and low cost. The sample elution volume is small, reagent consumption is low, and waste liquid is minimal. Furthermore, TBP resin not only efficiently removes Sn but also strongly eliminates Zr, In, and Mo simultaneously. When using multiple receiver inductively coupled plasma mass spectrometry (MC-ICP-MS), the molecular ion peaks formed by these elements binding with argon and oxygen cause strong interference. Therefore, the advantage of TBP resin in simultaneously removing Sn-In-Zr-Mo is unmatched by other resins. It is particularly valuable for applications involving geological samples with high Zr, In, and Mo contents, such as nepheline syenite, alkaline granite, and kaolinite, where Zr content can reach as high as 1% in the weathering crust of some alkaline rocks, with Zr / Cd ratios even reaching 100,000. It is also suitable for high-Mo molybdenite, deep-sea iron-manganese nodules, and polymetallic nodules. Furthermore, it is applicable to high-In sulfide oxidation zones containing limonite, cassiterite-rich polymetallic deposits, and lead antimony deposits. It is especially suitable for geological samples with high Sn / Cd ratios, as well as high Zr / Cd, Mo / Cd, and In / Cd ratios.

[0098] This invention can also reduce the process background by half, with a process blank (tested by isotope dilution method) of only 20-30 pg, which is significantly lower than the 40-200 pg of traditional technical solutions, and can significantly improve the success rate of high-precision analysis of cadmium isotopes in trace rock samples.

[0099] It should be noted that those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of this invention without departing from the spirit and scope of this invention should be covered within the scope of the claims of this invention.

Claims

1. A low-cost method for purifying cadmium isotopes from rock samples, characterized in that, Includes the following steps: (1) Weigh the rock sample, add mixed acid and cadmium double diluent at 3.5 times the cadmium dose of the sample, keep it at 160~190℃ for 3~5 days in a sealed container to dissolve the sample, then cool it to room temperature and evaporate the sample solution to dryness, then add hydrochloric acid with a molar concentration of 3M~6M, and heat to 100~150℃ to remove silicon; the mixed acid is a mixture of hydrofluoric acid, perchloric acid and nitric acid; (2) Two-step purification of cadmium: Step 1: After complete silicon removal, the sample was dissolved in hydrochloric acid with a molar concentration of 3M~6M and passed through an AG1 anion exchange column to remove matrix elements and most of the interfering isotopes. The matrix elements included K, Ca, Na, Mg, Al, Fe, and Ti; the interfering isotopes included Pd, In, and most of Sn. The Cd fraction was recovered, and the recovered Cd fraction contained (2.4±0.24)% Sn. Step 2: The Cd fraction is evaporated to dryness, dissolved in hydrochloric acid with a molar concentration of 3M~6M, and then passed through a TBP resin exchange column to remove residual Sn, while eliminating interference caused by In, Zr and Mo elements, to obtain a high-purity Cd component. (3) After the high-purity Cd component is evaporated to dryness, perchloric acid and nitric acid are added, and the mixture is sealed and heated at 160~180℃ for 1~2 hours to nitrate the trace organic matter in the sample component; then the sample is evaporated to dryness, and 1 ml of hydrochloric acid is added, and the mixture is sealed and heated at 160~180℃ for 1~2 hours. Finally, the sample is evaporated to dryness to obtain the final product.

2. The low-cost method for purifying cadmium isotopes from rock samples according to claim 1, characterized in that, The cadmium double diluent in step (1) is 108 Cd- 116 Cd double diluent.

3. The low-cost method for purifying cadmium isotopes from rock samples according to claim 1, characterized in that, In step (1), the sample is physically crushed to 200 mesh to obtain sample powder.

4. The low-cost method for purifying cadmium isotopes from rock samples as described in claim 1, characterized in that, In step (1), the weight of the rock is 10~40mg; correspondingly, the concentration and volume of each acid in the mixed acid added in step (1) are as follows: the concentration of hydrofluoric acid is 29±2.9 M and the volume is 1.5~2.5ml; the concentration of perchloric acid is 11.8±1M and the volume is 0.5~0.6ml; the concentration of nitric acid is 15±1 M and the volume is 0.1~0.3ml; the volume of perchloric acid added in step (3) is 0.1~0.2ml and the volume of nitric acid is 0.5~0.6ml.

5. The low-cost method for purifying cadmium isotopes from rock samples according to any one of claims 1 to 4, characterized in that, In step (2), the amount of AG1 resin packed in the AG1 anion exchange column is 0.9~1.1 ml.

6. The low-cost method for purifying cadmium isotopes from rock samples as described in any one of claims 1 to 4, characterized in that, In step (2), the TBP resin filling volume of the TBP resin exchange column is 0.13~0.15 ml.

7. The low-cost method for purifying cadmium isotopes from rock samples as described in claim 5, characterized in that, The specific elution and separation process of the AG1 anion exchange column in step (2) is as follows: 。 8. The low-cost method for purifying cadmium isotopes from rock samples as described in claim 5, characterized in that, The specific elution and separation process of the TBP resin exchange column in step (2) is as follows: 。 9. The low-cost method for purifying cadmium isotopes from rock samples as described in any one of claims 1 to 4, characterized in that, Rock samples include, but are not limited to, GSD-11, GSS-1a, NOD-P1, and NOD-A1.

10. The application of the low-cost method for cadmium isotope purification of rock samples according to any one of claims 1 to 9 in the analysis and testing of cadmium isotopes in rock samples.

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