Method for determining trace elements in cassiterite

Abstract

The embodiment of the invention provides a cassiterite microelement determination method. The cassiterite microelement determination method comprises the following steps: selecting a cassiterite sample and weighing; adding the weighed cassiterite sample into a preset Carius tube, slowly adding high-purity HBr subjected to secondary distillation into the tube, sealing and heating the preset Carius tube, and dissolving the sample; diluting the dissolved sample solution to a constant volume; carrying out ICPMS (Inductively Coupled Plasma Mass Spectrometry) measurement on the diluted and constant-volume sample solution, and processing measured data. According to the method, the usage amount of the sample is reduced, complete dissolution of cassiterite and complete decomposition of most elements are achieved, the loss of the sample and part of volatile elements in the sealed digestion process is small, and the method is particularly important for precious or rare samples. A very clean cassiterite digestion environment is provided, and interference of background signals is reduced. The operability is high, the application range is wide, the efficiency is greatly improved, and large-scale popularization and application conditions are achieved. The ICPMS technology is high in sensitivity, and high-precision determination of the cassiterite trace elements is realized.

Description

Technical Field

[0001] The embodiments of the present disclosure belong to the technical field of the study of tin deposit metallogenesis, and particularly relate to a method for determining trace elements in cassiterite. Background Art

[0002] Cassiterite, with a chemical composition of SnO2, is a tetragonal oxide mineral with a rutile-type structure. Its common form is a double-cone short columnar body and it is the main occurring mineral of tin. Various trace elements can be accommodated in the cassiterite lattice in the form of solid solutions, including W, Fe, Hf, Zr, Ti, Mn, Al, Nb, Ta, U, REE, Be, In, etc. These elements may enter the cassiterite lattice by substituting Sn 4+ or may exist in the form of exsolved mineral inclusions. Cassiterite of different genetic origins has different chemical compositions, and the composition of cassiterite will also change in different metallogenic stages of the same deposit. The formation temperature and pressure of cassiterite are relatively wide, and its physical and chemical properties are stable, making it an ideal carrier for tracing the metallogenic processes of magmatic-hydrothermal deposits.

[0003] Currently, the main instruments used for determining trace elements in cassiterite include laser ablation inductively coupled plasma mass spectrometer (LA-ICPMS), inductively coupled plasma mass spectrometer (ICPMS), inductively coupled plasma atomic emission spectroscopy (ICPAES), electron probe microanalyzer (EPMA), etc. Among them, ICPMS has the advantages of low detection limit, high sensitivity,

[0004] simple spectral lines, wide dynamic range, and simultaneous measurement of multiple elements. It has been applied early,

[0005] with a wide range and mature technology. Cassiterite is a refractory mineral and insoluble in traditional acids. When using ICPMS to test trace elements in cassiterite, complete digestion of the sample is the key.

[0006] Currently, the main methods for dissolving cassiterite samples are acid dissolution method, alkali dissolution method, and special reagent reduction method.

[0007] Among them, the method of using mixed acid digestion for ICPMS to determine trace elements in cassiterite is as follows: multiple acids such as HF, HCl, HNO3, H2SO4, HClO4, etc. are used in combination, and cassiterite is subjected to high-temperature and high-pressure acid dissolution in an open or PTFE high-pressure digestion tank. However, the acid dissolution method requires a large amount of sample, requires a low sample mesh size, cannot completely digest cassiterite, and requires repeated digestion multiple times after residues appear, which takes a long time and has a low recovery rate; on the other hand, neither the open nor the PTFE high-pressure digestion tank achieves complete sealing, and acid spillage may occur at high temperatures, resulting in direct loss of elements and affecting the accuracy of trace element testing.

[0008] The alkali dissolution method mainly uses sodium peroxide to digest cassiterite. The alkali dissolution method can decompose the sample more completely, and the sample solution can remain clear for a long time. However, the alkali fusion method is prone to introducing a large amount of alkali metal ions, resulting in too high salt content in the solution. The acidified extraction solution cannot be directly measured on the machine. High-fold dilution is adopted, which affects the accuracy of analysis. In addition, the nebulizer and sampling cone are easily blocked during the measurement process. On the other hand, this method uses more reagents, which is not conducive to environmental protection. The operation is cumbersome, time-consuming and laborious, and requires the analyst to have rich operation experience.

[0009] Based on the many problems existing in the acid dissolution method, alkali dissolution method, etc., special reagents such as CO-KCN were developed to reduce and decompose cassiterite. However, KCN is highly toxic and not suitable for large-scale popularization and use. The experimental conditions are harsh. In addition, the applicable range is limited and it is only suitable for measuring tin and copper in geological samples.

[0010] In summary, none of the existing methods can achieve high-recovery digestion of cassiterite and high-precision measurement of trace elements in cassiterite under the premise of simple operation, environmental friendliness and strong controllability.

[0011] In view of the above problems, it is necessary to propose a method for measuring trace elements in cassiterite that is reasonably designed and effectively solves the above problems. Summary of the Invention

[0012] An embodiment of the present disclosure aims to at least solve one of the technical problems existing in the prior art, and provides a method for measuring trace elements in cassiterite.

[0013] An embodiment of the present disclosure provides a method for measuring trace elements in cassiterite, the method comprising:

[0014] Step 1: Select a cassiterite sample and weigh it;

[0015] Step 2: Add the weighed cassiterite sample into a preset Carius tube, and slowly add highly pure HBr of secondary distillation into the preset Carius tube. After sealing and heating the preset Carius tube, complete sample dissolution;

[0016] Step 3: Dilute and make the volume constant for the dissolved sample solution;

[0017] Step 4: Perform ICPMS measurement on the diluted and volume-constant sample solution, and process the measured data to obtain the trace elements of the cassiterite sample.

[0018] Optionally, the slowly adding highly pure HBr of secondary distillation into the preset Carius tube in Step 2 includes:

[0019] Slowly add 2 mL to 8 mL of highly pure HBr of secondary distillation into the preset Carius tube.

[0020] Optionally, the complete sample dissolution after sealing and heating the preset Carius tube in step two includes:

[0021] After adding the high-purity HBr, rapidly cool the solution with liquid nitrogen to solidify it;

[0022] Melt and seal the top of the preset Carius tube with an oxygen-acetylene flame, and transfer it to a metal steel sleeve;

[0023] Place the preset Carius tube in an oven and heat it at 230°C to 240°C for 72 h to 75 h for sample dissolution.

[0024] Optionally, the dilution and volume determination of the dissolved sample solution in step three includes:

[0025] After the preset Carius tube cools, open the preset Carius tube and take out the dissolved sample;

[0026] Dilute the dissolved sample to a volume of 20 mL, take 0.1 mL of the solution, and then dilute it to 10 mL.

[0027] Optionally, the selection and weighing of the cassiterite sample in step one includes:

[0028] Select a cassiterite sample and grind the selected cassiterite sample to 200 mesh;

[0029] Weigh 0.5 mg to 5 mg of the ground cassiterite sample.

[0030] Optionally, the ICP-MS determination of the diluted and volume-determined sample solution in step four includes:

[0031] Use rhodium and rhenium as internal standards to perform ICP-MS determination on the diluted and volume-determined sample solution.

[0032] Optionally, the preset Carius tube includes a main body part and a thin neck connected to the main body part. Among them, the end of the thin neck has a sample inlet; the internal volume range of the preset sample dissolution tube is 8 mL to 10 mL.

[0033] Optionally, the length range of the main body part is 5 cm to 6 cm, the outer diameter range of the main body part is 19 mm to 20 mm, and the wall thickness range of the main body part is 3 mm to 4 mm;

[0034] The length range of the thin neck is 5 mm to 6 mm, the outer diameter range of the thin neck is 10 mm to 11 mm, and the wall thickness range of the thin neck is 1.5 mm to 2.0 mm.

[0035] The method for determining trace elements in cassiterite according to the embodiments of the present disclosure uses a high-purity HBr solution to achieve complete digestion of cassiterite under the conditions of high-temperature and high-pressure sealing in a preset Carius tube, and then realizes high-precision testing of trace elements in cassiterite. This method for determining trace elements in cassiterite not only reduces the sample usage, achieves complete dissolution of cassiterite and complete decomposition of most elements, but also reduces the loss of samples and some volatile elements during the sealed digestion process, which is particularly important for precious or rare samples. Since the acid does not volatilize during the sample dissolution process and repeatedly refluxes in the system, only a small amount of purified HBr is required to complete the digestion of cassiterite, reducing the possibility of environmental pollution. It provides a very clean environment for cassiterite digestion, reducing the interference of background signals. It has strong operability and a wide application range, greatly improving the efficiency and having the conditions for large-scale popularization and use. The ICPMS technology has high sensitivity and can have a low blank value while ensuring high-precision testing of as many trace elements as possible. Description of the Drawings

[0036] Figure 1 FIG. is a schematic flowchart of a method for determining trace elements in cassiterite according to an embodiment of the present disclosure. Detailed Embodiments

[0037] To enable those skilled in the art to better understand the technical solutions of the embodiments of the present disclosure, the following further describes the embodiments of the present disclosure in detail with reference to the drawings and specific embodiments.

[0038] As Figure 1 shown, the embodiments of the present disclosure provide a method for determining trace elements in cassiterite, and the method for determining trace elements in cassiterite specifically includes:

[0039] Step 1: Select a cassiterite sample and weigh it.

[0040] Specifically, select a cassiterite sample, grind the selected cassiterite sample to 200 meshes, and weigh 0.5 mg to 5 mg of the ground cassiterite sample. Preferably, in this embodiment, 5 mg of the cassiterite sample is weighed after grinding.

[0041] Step 2: Add the weighed cassiterite sample to a preset Carius tube, slowly add high-purity HBr distilled twice to the preset Carius tube, seal and heat the preset Carius tube, and then perform complete sample dissolution.

[0042] The main body of the Carius tube commonly used in traditional laboratories is 20 cm long and the internal volume is about 32 mL. If a conventional Carius tube is used, most of the space will be left unused, resulting in waste of resources and being unfavorable for forming a high-pressure condition to promote the digestion of cassiterite. In this embodiment, in order to achieve complete dissolution of the cassiterite sample, a corresponding preset sample dissolution tube is provided. In this embodiment, the preset sample dissolution tube is a preset Carius tube.

[0043] The preset Carius tube includes a main body portion and a thin neck portion connected to the main body portion. Among them, the end of the thin neck portion has a sample inlet; the internal volume range of the preset sample dissolution tube is 8 mL to 10 mL. Preferably, the internal volume of the preset Carius tube is 8 mL.

[0044] The length range of the main body portion is 5 cm to 6 cm, the outer diameter range of the main body portion is 19 mm to 20 mm, and the wall thickness range of the main body portion is 3 mm to 4 mm. Preferably, the length of the main body portion is 5 cm, the outer diameter of the main body portion is 19 mm, and the wall thickness range of the main body portion is 3 mm.

[0045] The length range of the thin neck portion is 5 mm to 6 mm, the outer diameter range of the thin neck portion is 10 mm to 11 mm, and the wall thickness range of the thin neck portion is 1.5 mm to 2.0 mm. Preferably, the length of the thin neck portion is 6 mm, the outer diameter of the thin neck portion is 10 mm, and the wall thickness of the thin neck portion is 1.5 mm.

[0046] The preset Carius tube provided by the embodiments of the present disclosure reduces the usage amount of cassiterite samples and improves the utilization rate of the instrument space. At the same time, it can provide sufficient temperature and pressure to ensure that the cassiterite samples are completely digested. In addition, the preset Carius tube can adapt to various sample types and digestion conditions. In addition to cassiterite, it can be extended to the digestion of other trace samples, including solid, liquid, and semi-solid samples.

[0047] Step two can specifically include: adding the weighed cassiterite sample to the preset Carius tube, and slowly adding 2 mL to 8 mL of secondary distilled high-purity HBr into the preset Carius tube. Preferably, in this embodiment, 8 mL of secondary distilled high-purity HBr is slowly added into the preset Carius tube.

[0048] After adding the high-purity HBr, use liquid nitrogen to rapidly cool down to solidify the solution. Melt and seal the top of the preset Carius tube with an oxygen-acetylene flame, and move it into a metal steel sleeve.

[0049] Place the preset Carius tube in an oven and heat it at 230 °C to 240 °C, and keep it warm for 72 h to 75 h for sample dissolution. Preferably, in this embodiment, place the preset Carius tube in an oven and heat it at 230 °C and keep it warm for 72 h for complete sample dissolution.

[0050] During the dissolution process of cassiterite, the strong acidity of hydrobromic acid (HBr) can provide the necessary acidic environment for the dissolution of cassiterite. Through secondary distillation, the concentration of hydrobromic acid is further increased. Combining with the high-temperature and high-pressure sealed environment formed by the metal steel sleeve and the preset Carius tube, the purified acid can efficiently promote the complete dissolution of cassiterite. In addition, since hydrobromic acid does not volatilize during the dissolution process and repeatedly refluxes within the system, only a small amount of high-purity hydrobromic acid is required to complete the digestion of cassiterite.

[0051] In this embodiment, only high-purity HBr solution is used, and under the conditions of high-temperature and high-pressure sealing of the preset Carius tube, the complete digestion of cassiterite can be achieved. There is no need to use multiple acids for digestion, and a large amount of alkali metal ions will not be introduced during the digestion process. On the premise of resource conservation and environmental friendliness, a cassiterite digestion method with simple operation, strong applicability, and wide application range has been developed.

[0052] Step 3: Dilute and make the volume constant for the dissolved sample solution.

[0053] Specifically, first, after the preset Carius tube cools down, open the preset Carius tube and take out the dissolved sample.

[0054] Secondly, dilute the sample solution with Q water to a suitable concentration. Specifically, make the volume of the dissolved sample constant to 20 mL, take 0.1 mL of the solution, and then make the volume constant to 10 mL.

[0055] Step 4: Perform ICP-MS determination on the diluted and volume-constant sample solution, and process the measured data to obtain the various trace elements of the cassiterite sample.

[0056] Specifically, use rhodium and rhenium as internal standards to perform ICP-MS determination on the diluted and volume-constant sample solution. After exporting the measured data, perform offline calibration processing to obtain the various trace elements of the cassiterite sample.

[0057] The method for determining trace elements in cassiterite according to the embodiments of the present disclosure uses a high-purity HBr solution to achieve complete digestion of cassiterite under the conditions of high-temperature and high-pressure sealing in a preset Carius tube, and then realizes high-precision testing of trace elements in cassiterite. This method for determining trace elements in cassiterite not only reduces the sample usage amount, achieves complete dissolution of cassiterite and complete decomposition of most elements, but also has less loss of samples and some volatile elements during the sealed digestion process, which is particularly important for precious or rare samples. Since HBr does not volatilize during the sample dissolution process and repeatedly refluxes in the system, only a small amount of purified HBr is required to complete the digestion of cassiterite. This process not only reduces the acid usage amount, but also reduces the environmental pollution caused by acid mist volatilization, and at the same time provides a very clean digestion environment, effectively reducing the interference of background signals. The experimental process has strong operability and a wide application range, greatly improving the efficiency and having the conditions for large-scale popularization and use. The ICPMS technology has high sensitivity and can have a low blank value while ensuring high-precision testing of as many trace elements as possible.

[0058] The following will specifically describe the method for determining trace elements in cassiterite according to the embodiments of the present disclosure in conjunction with the embodiments.

[0059] In this embodiment, three 5-mg ground cassiterite samples and one 0.5-mg ground cassiterite sample are respectively weighed and denoted as sample SN1, sample SN2, sample SN3, and sample SN4. The samples SN1, SN2, SN3, and SN4 are respectively added to a preset Carius tube. 4 mL of doubly distilled high-purity HBr is slowly added to the preset Carius tube containing sample SN1, 6 mL of doubly distilled high-purity HBr is slowly added to the preset Carius tube containing sample SN2, 8 mL of doubly distilled high-purity HBr is slowly added to the preset Carius tube containing sample SN3, and 2 mL of doubly distilled high-purity HBr is slowly added to the preset Carius tube containing sample SN4. After adding high-purity HBr to each preset Carius tube, the solution is rapidly cooled with liquid nitrogen to solidify, the top of the preset Carius tube is melted and sealed with an oxygen-acetylene flame, and then it is moved into a metal steel sleeve. The preset Carius tube is placed in an oven and heated at 230 °C for 72 h for sample dissolution.

[0060] After each preset Carius tube cools down, the preset Carius tube is opened, and the dissolved sample is taken out. The dissolved sample is made up to 20 mL, 0.1 mL of the solution is taken, and then it is made up to 10 mL. Rhodium and rhenium are used as internal standards, and ICPMS determination is performed on each diluted and made-up sample solution. After the measured data is exported, off-line correction processing is performed to obtain the content of some trace elements in the cassiterite sample as shown in Table 1.

[0061] The trace elements of cassiterite in sample SN1, sample SN2, sample SN3, and sample SN4 measured by the cassiterite trace element determination method of this embodiment were compared with the trace elements of cassiterite measured by in-situ LA-ICP-MS. As can be seen from Table 1, taking the in-situ measurement sample results as the reference standard, cassiterite was treated by the preset solution method. As the volume of the secondary purified HBr solution increased, the recovery rate of cassiterite increased significantly. When 8 mL of secondary purified HBr was used, the dissolution recovery rate of cassiterite could stably reach over 90%. In addition, for samples with a smaller mass (0.5 mg), by optimizing the solution dosage in the embodiments of the present disclosure, even with a lower volume of solution, a recovery rate of over 80% could still be achieved, thus significantly improving the flexibility and adaptability of the treatment process while ensuring the recovery efficiency.

[0062] Table 1 Partial element contents of cassiterite measured by in-situ LA-ICP-MS and cassiterite measured by the preset Carius tube ICP-MS solution method

[0063]

[0064] It can be understood that the above embodiments are merely exemplary embodiments adopted to illustrate the principles of the embodiments of the present disclosure. However, the embodiments of the present disclosure are not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the embodiments of the present disclosure, and these modifications and improvements are also regarded as the protection scope of the embodiments of the present disclosure.

Claims

1. A method for determining trace elements in cassiterite, characterized in that, The method includes: Step 1: Select a cassiterite sample and weigh it. Step 2: Add the weighed cassiterite sample into a preset Carius tube, slowly add highly pure HBr distilled twice into the preset Carius tube, seal and heat the preset Carius tube, and perform complete sample dissolution. Step 3: Dilute and make the volume constant for the dissolved sample solution. Step 4: Perform ICPMS determination on the diluted and volume-constant sample solution, process the measured data, and obtain the various trace elements of the cassiterite sample.

2. The method according to claim 1, characterized in that, In Step 2, the slow addition of highly pure HBr distilled twice into the preset Carius tube includes: Slowly add 2 mL to 8 mL of highly pure HBr distilled twice into the preset Carius tube.

3. The method according to claim 1, wherein In Step 2, the complete sample dissolution after sealing and heating the preset Carius tube includes: After adding the highly pure HBr, rapidly cool the solution to solidify it using liquid nitrogen. Melt and seal the top end of the preset Carius tube with an oxygen-acetylene flame, and transfer it to a metal steel sleeve. Place the preset Carius tube in an oven and heat it at 230°C to 240°C and keep it warm for 72 h to 75 h for complete sample dissolution.

4. The method according to claim 1, characterized in that In Step 3, the dilution and volume constant setting for the dissolved sample solution includes: After the preset Carius tube cools down, open the preset Carius tube and take out the dissolved sample. Make the volume of the dissolved sample constant to 20 mL, take 0.1 mL of the solution, and then make the volume constant to 10 mL.

5. The method according to claim 1, wherein In Step 1, the selection of the cassiterite sample and weighing it includes: Select a cassiterite sample and grind the selected cassiterite sample to 200 mesh. Weigh 0.5 mg to 5 mg of the ground cassiterite sample.

6. The method according to claim 1, wherein In Step 4, the ICPMS determination on the diluted and volume-constant sample solution includes: Use rhodium and rhenium as internal standards to perform ICPMS determination on the diluted and volume-constant sample solution.

7. The method according to claim 1, characterized in that, The preset Carius tube includes a main body part and a thin neck part connected to the main body part. Among them, the end of the thin neck part has a sample inlet; the internal volume range of the preset sample dissolution tube is 8 mL to 10 mL.

8. The method according to claim 7, wherein The length range of the main body part is 5 cm to 6 cm, the outer diameter range of the main body part is 19 mm to 20 mm, and the wall thickness range of the main body part is 3 mm to 4 mm. The length range of the thin neck part is 5 mm to 6 mm, the outer diameter range of the thin neck part is 10 mm to 11 mm, and the wall thickness range of the thin neck part is 1.5 mm to 2.0 mm.

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