A method for preparing cobalt sulfide electron probe standard by nanomilling and high-pressure synthesis technology

Abstract

The application provides a method for preparing a cobalt sulfide electron probe standard sample by nanogrinding and high-pressure synthesis technology, which takes arsenopyrite monomineral powder as a matrix, adds metal cobalt powder into the matrix, ensures that the cobalt content in an initial sample composed of the arsenopyrite monomineral powder and the metal cobalt powder is greater than or equal to 0.2 wt%, selects an ethanol dispersant, obtains sample powder with nanoscale size by mechanical ball milling with the size of grinding balls changed, applies axial load to the sample powder, cold-presses the sample powder into a consolidated sample, and obtains a cobalt-containing arsenopyrite electron probe standard sample after polishing. The application solves the problem of low or uneven cobalt content in natural cobalt-containing sulfides, and successfully prepares a cobalt-containing arsenopyrite electron probe standard sample meeting the uniformity requirement under submicron spatial resolution by using nanogrinding technology and high-pressure synthesis sample preparation method.

Description

Technical Field

[0001] This application relates to the field of mineral detection technology, and in particular to a method for preparing cobalt-containing sulfide electron probe standards by nano-grinding and high-pressure synthesis technology. Background Technology

[0002] Cobalt is an important raw material for manufacturing high-temperature alloys, hard alloys, magnetic alloys, and cobalt-containing compounds, and is widely used in high-tech fields such as national defense, aerospace, and electronics. Cobalt is located in Group VIII of the fourth period of the periodic table and possesses both chalcophile and siderophile properties. Cobalt-containing minerals have complex and varied compositions, mainly existing in two forms: high-cobalt-free minerals and low-cobalt-containing isomorphous cobalt minerals. High-cobalt-free minerals are mainly composed of cobaltite, cobalt-cobaltite, copper-cobaltite, and cobalt-arsenite, while isomorphous cobalt minerals are mainly composed of nickel pyrite, pyrite, pyrrhotite, and arsenopyrite. Furthermore, cobalt-containing minerals are characterized by fine particle size, low cobalt content, and association with elements such as copper and nickel. Currently, in-situ analytical techniques for observing the occurrence state of cobalt and determining the content of major and trace elements mainly include scanning electron microscopy, electron probe microanalysis, and laser ablation inductively coupled plasma mass spectrometry. Electron probe microanalysis combines high spatial resolution (~1μm), real-time electron image observation, and quantitative analysis of major and trace elements, making it a key technology for investigating scientific issues such as the occurrence state, distribution patterns, and enrichment processes of cobalt.

[0003] Electron probe microanalysis (EPMA) is an interdisciplinary product of electron optics and X-ray spectroscopy. Its basic principle is to use a focused high-energy electron beam to excite X-rays of the elements contained in a sample. By measuring the intensity of characteristic X-rays at specific wavelengths and comparing them with standard materials (standards), the content of constituent elements in the sample can be obtained through calibration calculations. Therefore, high-quality EPA standards are crucial for elemental quantitative analysis, instrument calibration, and quality control at the sub-micron scale. Currently, EPA standards for cobalt sulfides are mainly high-cobalt-content calibration standards such as elemental Co, oxides (CoO), and ductile (Co content 15.45 wt%), which cannot meet the quality control requirements for low-cobalt-content sulfides. Furthermore, EPA standards are mostly internal laboratory standards, limited in quantity, and poorly distributed, making them difficult to obtain commercially.

[0004] Because the trace element composition in natural sulfides (such as pyrite, arsenopyrite, and arsenic pyrite) is difficult to homogenize, in-situ sulfide standards are currently mainly prepared through artificial synthesis. However, standards prepared using existing artificial synthesis methods, such as sintering, high-temperature melting, and hydrothermal synthesis, are only suitable for large-spot component detection and not for electron probe microanalysis due to their high porosity, poor elemental homogeneity, and stringent synthesis conditions that hinder mass production. Currently, artificial synthesis methods cannot mass-produce cobalt-containing sulfide electron probe standards with uniform trace element composition within the micrometer range. Therefore, there is an urgent need to develop a new cobalt-containing sulfide electron probe standard with trace element quality monitoring capabilities. Summary of the Invention

[0005] Therefore, this application aims to propose a method for preparing cobalt-containing sulfide electron probe standards using nano-grinding and high-pressure synthesis techniques, thereby overcoming the technical deficiencies and standard gaps in existing artificially synthesized cobalt-containing sulfide electron probe standards. This application addresses the problem of low cobalt content in cobalt-containing sulfide raw materials by supplementing them with metallic cobalt. Through the innovative combination of nano-grinding technology and high-pressure synthesis, cobalt-containing sulfide electron probe standards meeting the requirements for trace cobalt element analysis in cobalt-containing sulfides are successfully prepared. This achieves the requirement of component uniformity at sub-micron spatial resolution, overcoming the problem of poor spatial resolution in existing artificially synthesized standards. The cobalt-containing sulfide electron probe standards prepared using this method can be widely applied in fields such as mineral resources and planetary science.

[0006] To achieve the aforementioned objectives, the technical solution of this application is implemented as follows: This application provides a method for preparing cobalt sulfide electron probe standards using nano-grinding and high-pressure synthesis techniques, comprising the following steps: S1. Raw Material Preparation Using arsenopyrite single mineral powder as the matrix, the cobalt content in the matrix was determined; If the cobalt content in the matrix is ​​<0.2wt%, then add metallic cobalt powder to the matrix and mix thoroughly. The initial sample composed of arsenopyrite single mineral powder and metallic cobalt powder will then have a cobalt content ≥0.2wt%. S2. Nano-grinding The initial sample was added to an ethanol dispersant to prepare an initial sample dispersion; the initial sample dispersion was mechanically ball-milled to obtain sample powder with a particle size of submicron. S3. Cold pressing The sample powder is loaded into a mold, and an axial load is applied to the sample powder through a pressure head to cold press the sample powder into a solidified sample. After the solidified sample is demolded and polished, a cobalt-arsenic pyrite electron probe standard is obtained.

[0007] Furthermore, arsenopyrite monominerals were separated from natural copper-nickel sulfide ores, ground, and passed through a 200-mesh sieve to obtain arsenopyrite monomineral powder as the matrix.

[0008] Furthermore, the cobalt powder used is cobalt powder that has passed through a 200-mesh sieve.

[0009] Furthermore, in step S1, if the cobalt content in the matrix is ​​≥0.2wt%, then arsenopyrite single mineral powder is used as the initial sample.

[0010] Furthermore, the mechanical ball milling process includes first using grinding balls with a diameter of 1 mm for 60-90 minutes; then using grinding balls with a diameter of 0.5 mm for more than 30 minutes.

[0011] Furthermore, when using grinding balls with a diameter of 1 mm for ball milling, the ball-to-material ratio is 40~60:1, and when using grinding balls with a diameter of 0.5 mm for ball milling, the ball-to-material ratio is 80~120:1.

[0012] Furthermore, after nano-grinding, the particle size of the sample powder is ≤500nm.

[0013] Furthermore, the cold pressing process includes gradually increasing the load from atmospheric pressure to 2 GPa within 80-120 minutes, holding the pressure for 100-140 minutes, and then gradually reducing the load to atmospheric pressure.

[0014] Furthermore, the polishing process includes immersing the solidified sample in epoxy resin, and after the epoxy resin has cured, removing the epoxy resin from the top of the solidified sample to expose the surface of the solidified sample, and then polishing it to obtain a cobalt-arsenic pyrite electron probe standard.

[0015] Furthermore, the surface roughness of the cobalt-arsenic pyrite electron probe standard is in the submicron range.

[0016] Compared with existing technologies, this application proposes a method for preparing cobalt sulfide electron probe standards using nano-grinding and high-pressure synthesis techniques. This application has at least the following beneficial effects: (1) Due to the non-uniform composition of natural sulfide samples such as natural arsenopyrite, the major and trace element compositions of natural sulfide samples vary greatly at the micron-submicron scale, making them unsuitable for direct use as electron probe standards. To address this, this application creatively proposes an artificial synthesis process that combines nano-grinding technology with high-pressure synthesis. By grinding natural samples into ultrafine powder with a particle size of nanometers, and then using cold pressing technology to press the ultrafine powder under high pressure to synthesize a dense, solidified sample with high strength, high density, low cracks, and uniform major and trace element compositions at the micron-submicron scale, a cobalt-containing arsenopyrite standard sample without obvious mineral inclusions, with uniform and accurate major and trace element compositions, is suitable for in-situ analysis of major and trace elements in arsenopyrite.

[0017] (2) The beam spot size of an electron probe is usually about 1 micrometer. Conventional grinding techniques can only produce micrometer-sized particles from natural mineral samples. For the size dimension of the electron probe beam spot, the composition of a sample synthesized from conventional micrometer-sized powder particles will be considered extremely non-uniform, and therefore cannot be used as an electron probe standard. In order to grind natural samples to the submicrometer level, or even to the nanometer level, this application pioneered the use of nano-grinding technology in the field of geology. After summarizing a large amount of experimental experience, ethanol was used as a dispersant. Through the optimized design of the grinding ball size and ball milling time, natural mineral samples were ground into nano-sized powders with a scale significantly smaller than the beam spot, thereby ensuring that the standard composition distribution within the electron probe beam spot coverage area is uniform, thus meeting the in-situ standard requirements of micrometer-level spatial resolution.

[0018] (3) Electron probe standards must have a flat, dense, and robust surface. However, samples prepared by existing sintering or high-temperature melting methods are prone to uneven crystallization and lack a dense and robust structure. During polishing, the sample surface is easily crushed and slag is lost, making it difficult to achieve a dense and flat surface. Therefore, this application innovatively uses a cold-pressing process to obtain a solidified sample under high pressure. The sample is not only dense and robust, but also, because it is pressed at room temperature, the sulfur in the cobalt sulfide will not volatilize due to high temperature, thus avoiding changes in the matrix composition. As a result, this application has successfully prepared a dense, robust, uniformly composed, and low-cobalt-content sulfide-based electron probe standard.

[0019] (4) The preparation method of this application has simple procedures and high process maturity. Unlike hydrothermal synthesis, it does not require strict process parameter control. The preparation method of this application is easier to implement and has a high yield. It has good prospects for commercial mass production of cobalt sulfide electron probe standard samples with uniform distribution of trace elements in the micrometer range, and provides basic technical support for my country to carry out mineral exploration and extraterrestrial mineral resource scientific research. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a powder particle size distribution diagram of the initial sample after ball milling in Example 1, as determined using a laser particle size analyzer. Figure 2 Metallographic structures of the arsenopyrite electron probe standard samples prepared in Example 1 and Comparative Example 1, characterized using a microscope; Figure 3 BSE images of the arsenopyrite electron probe standards prepared in Example 1 and Comparative Example 1, characterized using scanning electron microscopy; Figure 4 SEI images of the arsenopyrite electron probe standards prepared in Example 1 and Comparative Example 1, characterized using scanning electron microscopy; Figure 5 for Figure 3 The image shown is a magnified view of the BSE image of the region below the electron probe standard in Example 1. Figure 6 for Figure 3 The red box in the upper region of the electron probe standard in Comparative Example 1 represents the S element distribution map obtained by WDS elemental surface scanning analysis. Figure 7 for Figure 3 The image shows the S element distribution map obtained by WDS elemental surface scanning analysis of the region below the electron probe standard in Example 1. Figure 8 for Figure 3 The image shows the Fe element distribution map obtained by WDS elemental surface scanning analysis of the region below the electron probe standard in Example 1. Figure 9 for Figure 3 The image shows the Co element distribution map obtained by WDS elemental surface scanning analysis in the area below the electron probe standard in Example 1. Figure 10 This is a comparison chart showing the Co content obtained from the electron probe standard of Example 1 by analysis using EPMA, LA-ICP-MS, and solution-based ICP-MS. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be noted that the described embodiments are only some embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0023] Unless otherwise stated, all temperatures described herein are in degrees Celsius (°C), all component contents are expressed as weight percentages (wt%), and all tissue contents are expressed as volume percentages (vol%). When numerical ranges are mentioned in the specification and claims, the upper and lower limits of the range are included by default. Preferred technical solutions can be freely combined as needed, unless specifically specified. Those skilled in the art should understand that the specific data and parameters described in the embodiments are illustrative and do not constitute a limitation of this application. In the following embodiments and comparative examples, all components used are monomers or compounds known in the art, and all equipment involved is standardized equipment known in the art, all of which can be obtained commercially or prepared using conventional techniques.

[0024] This application provides a method for preparing cobalt sulfide electron probe standards using nano-grinding and high-pressure synthesis techniques, comprising the following steps: S1. Raw Material Preparation Using arsenopyrite single mineral powder as the matrix, the cobalt content in the matrix was determined; If the cobalt content in the matrix is ​​≥0.2wt%, then arsenopyrite single mineral powder is used as the initial sample; If the cobalt content in the matrix is ​​<0.2wt%, then metallic cobalt powder is added to the matrix and mixed thoroughly. The cobalt content in the initial sample composed of arsenopyrite single mineral powder and metallic cobalt powder is ≥0.2wt%. The metallic cobalt powder used in this application is metallic cobalt powder that has passed through a 200-mesh sieve.

[0025] The arsenopyrite monomineral used in this application can be obtained by sorting from natural copper-nickel sulfide ores, grinding them, and passing them through a 200-mesh sieve to obtain arsenopyrite monomineral powder as the matrix. As an optional embodiment, the arsenopyrite monomineral powder can be ultrasonically cleaned in an alcohol medium to remove excess impurities. As an optional embodiment, the ultrasonically cleaned arsenopyrite monomineral powder can be placed in a drying cabinet and dried at 80°C for more than 20 hours to achieve complete drying.

[0026] As an optional implementation, this application uses XRF and ICP-MS methods to determine the major and trace element composition of arsenopyrite single mineral powder, thereby determining the cobalt content in the matrix.

[0027] This application requires that the cobalt content in the initial sample be ≥0.2wt% to ensure that the cobalt content in the initial sample meets the elemental detection limit of the electron probe under conventional analytical conditions. Electron probes are typically used to test major elements with a content >1.0wt%, which are commonly referred to in the art as elemental calibration standards; that is, as long as the content of the element to be detected is high enough, it is sufficient. For example, pure cobalt metal or CoO can be used as a calibration standard for detecting cobalt. However, with the development of analytical methods, electron probes are now also commonly used to test trace elements with contents of 100~10000ppm (content <1wt%). Existing calibration standards are difficult to effectively monitor extremely low contents of trace elements, making it impossible to determine analytical errors. As an important metallic element, the detection and mining of even low-content cobalt in sulfides is receiving increasing attention. However, due to the scarcity of cobalt trace element standards, it is currently difficult to conduct large-scale research on the detection of low-cobalt-content sulfides. Based on this, this application proposes the development of an electron probe microanalysis (EPMA) standard sample for monitoring and analyzing extremely low levels of cobalt in cobalt-containing sulfides. This standard sample allows for the monitoring of the accuracy and quality of the EMA instrument. However, to achieve the detection limit of the EMA, the cobalt content in the initial sample must be ≥0.2 wt%. To meet this requirement, when the cobalt content in the arsenopyrite monomineral powder matrix is ​​less than 0.2 wt%, this application creatively proposes adding metallic cobalt powder to the matrix to ensure that the cobalt content in the initial sample composed of arsenopyrite monomineral powder and metallic cobalt powder is ≥0.2 wt%. To meet the accuracy requirements for adding metallic cobalt powder, it can be added by weighing using an electronic balance.

[0028] S2. Nano-grinding The initial sample is added to an ethanol dispersant to prepare an initial sample dispersion; the initial sample dispersion is then mechanically ball-milled to obtain sample powder with a submicron particle size. Preferably, after nano-milling, the sample powder particle size is ≤500nm.

[0029] Electron probe microanalysis (EPMA) is an in-situ analytical technique. Its greatest advantage lies in its high spatial resolution, enabling the analysis of particles as small as a few micrometers. Therefore, EMA standards, whether for calibration or monitoring, require a dense solid sample with uniform major and trace element composition at the micrometer to submicrometer scale. Since the composition of natural sulfide samples varies considerably, this application proposes a method for preparing cobalt-containing sulfide standards through artificial synthesis. Specifically, the natural sample is first ground into a very fine powder, and then synthesized into a cobalt-containing sulfide solid standard through high-pressure pressing.

[0030] Conventional grinding processes typically yield particles with a size of 38–75 micrometers, and existing ultrafine grinding techniques only produce particles with a size of 5–10 micrometers. Since the elemental composition of natural samples remains inhomogeneous at these particle sizes, and the electron probe beam is typically only about 1 micrometer, using natural particle powder obtained through conventional grinding processes for sample synthesis will result in a sample with an inhomogeneous composition, unsuitable for use as a standard. However, if natural samples are ground into nanoscale (<500 nm) powder, this particle size is significantly smaller than the electron probe beam diameter. As long as the nanoparticles are thoroughly and uniformly mixed, the composition within the electron probe beam coverage area will be uniform, meeting the requirements for compositional uniformity in standard samples. Therefore, this application creatively proposes the use of mechanical ball milling technology in the geological field. Through the selection of dispersants and the optimized design of grinding ball size and ball-to-particle ratio, the initial sample is ground into sample powder with a particle size reaching the submicron level, and more preferably, the initial sample powder is ground to a particle size ≤500 nm.

[0031] Based on extensive experimental research, this application found that using ethanol as a dispersant can achieve ball milling of the initial sample powder to a particle size of less than 500 nm. However, when using distilled water as a dispersant, the particle size of the initial sample powder decreases with increasing ball milling time when the ball milling time is less than 60 min. But when the ball milling time exceeds 60 min, as the particle size of the initial sample powder continues to decrease, fine particles will severely adhere to the surface of larger particles, and severe agglomeration will also occur between the fine particles. In this case, the particle size of the initial sample powder will actually increase with increasing ball milling time. To solve the problem of adhesion and agglomeration of the initial sample powder during long-term ball milling, the inventors attempted to use grinding balls with smaller diameters for ball milling. Since the space between the small-sized grinding balls is small, it is not possible to efficiently ball mill larger initial powder particles. Therefore, this application proposes to first use larger-sized grinding balls with a diameter of 1 mm for 60-90 min in the first stage, and then use smaller-sized grinding balls with a diameter of 0.5 mm for 30 min in the second stage. Experiments have shown that the ball milling process described above failed to improve the problems of powder adhesion and agglomeration. In the second stage, after using smaller grinding balls with a diameter of 0.5 mm for ball milling, the particle size of the initial sample powder will further increase with the increase of ball milling time.

[0032] Considering the limited dispersing effect of distilled water on the initial sample powder, ethanol was selected as the dispersant. The initial sample powder was added to the ethanol dispersant to prepare a dispersion, which was then subjected to ball milling experiments. The experiments showed that, using ethanol as the dispersant and 1mm diameter grinding balls, even with a milling time exceeding 60 minutes, the particle size of the initial sample powder continued to decrease with increasing milling time. However, when the milling time exceeded 90 minutes, the particle size of the initial sample powder no longer showed significant change, indicating that after 90 minutes of milling, the 1mm diameter grinding balls were no longer sufficient to meet the current particle size requirements. To further reduce the particle size after ball milling, after milling with 1mm grinding balls for 90 minutes, smaller diameter grinding balls (0.5mm) were used for another 30 minutes of milling. The initial sample powder particle size was finally reduced to below 500nm, which met the requirements for in-situ standards with micron-level spatial resolution.

[0033] Therefore, the ball milling process of this application was formulated: using ethanol as a dispersant, ball milling with 1 mm diameter grinding balls for 60-90 min; then using 0.5 mm diameter grinding balls for at least 30 min, thereby obtaining sample powder with a particle size of less than 500 nm. As an optional implementation, the ball-to-particle ratio when using 1 mm diameter grinding balls can be set to 40-60:1, and the ball-to-particle ratio when using 0.5 mm diameter grinding balls can be set to 80-120:1. This application concludes that, compared with distilled water, ethanol dispersant can effectively solve the problem of adhesion and agglomeration of fine powders during ball milling. At the same time, after ball milling with 1 mm grinding balls for 90 min, the powder particle size has almost reached its limit. Continuing to increase the ball milling time will not significantly change the particle size of the initial sample powder. At this point, switching to 0.5 mm grinding balls and continuing ball milling will significantly reduce the powder particle size again, indicating that the grinding ball size and ball milling time have a significant impact on the grinding efficiency of powder samples with different particle sizes.

[0034] This application does not impose any particular limitations on the preparation method of the initial sample dispersion or the amount of ethanol used, as long as an appropriate amount of ethanol dispersant is used and stirred to fully disperse the initial sample powder in the ethanol dispersant. As an optional embodiment, the mass ratio of the initial sample to the ethanol dispersant can be 5:65 to 145.

[0035] As an optional implementation, the initial sample is ultrasonically cleaned for 10-20 minutes before nano-grinding begins, and this ultrasonic cleaning can be repeated 1-5 times. After ultrasonic cleaning, the initial sample is dried by placing it in a drying cabinet at 80°C for at least 20 hours to achieve complete drying.

[0036] S3. Cold pressing The sample powder is loaded into a mold, and an axial load is applied to the sample powder through a pressure head to cold press the sample powder into a solidified sample. After the solidified sample is demolded and polished, a cobalt-arsenic pyrite electron probe standard is obtained.

[0037] Electron probe standard samples should be solid samples with a smooth and robust surface. The nanopowder obtained in step S2 cannot be directly applied to the electron probe instrument and requires sample preparation to obtain a solid sample. Conventional sample preparation methods include sintering and remelting, hot molding, and cold isostatic pressing. While sintering and remelting the powder can yield a solid sample, the sintering process is prone to uneven crystallization, leading to further uneven distribution of the solid sample's composition. If hot molding is used to heat and press the powder, since the sample is a sulfide, excessively high temperatures may cause sulfur to volatilize, thus altering the matrix composition of the solid sample. Solid samples obtained through conventional cold isostatic pressing still have relatively loose powder particles, resulting in high porosity. This makes the sample prone to breakage and chipping during subsequent polishing, making it difficult to achieve a dense and smooth surface. Therefore, in order to meet the requirements of electron probe standard for solid sample density and surface smoothness, this application uses cold pressing technology to obtain a dense and robust solid sample under high pressure, thereby obtaining a low-cobalt-content sulfide electron probe standard with a smooth surface and uniform composition. Based on extensive experimental experience, this application designs the cold pressing process as follows: the load is gradually increased from atmospheric pressure to 2 GPa within 80–120 min, and after holding the pressure for 100–140 min, the load is gradually reduced to atmospheric pressure, thereby preparing a solidified sample with high strength, high density, and low cracking properties.

[0038] As an optional implementation, before the cold pressing process begins, the initial sample powder is dried by placing it in a drying cabinet and drying it at 80°C for more than 20 hours to achieve a completely dry state.

[0039] This application does not specifically limit the polishing process. Polishing the surface roughness of the solidified sample to the submicron level is sufficient to meet the requirements for cobalt-arsenic pyrite electron probe standard. As an optional implementation, the polishing process of this application includes immersing the solidified sample in epoxy resin, waiting for the resin to cure, using coarse sandpaper to grind off the top epoxy resin of the solidified sample to expose the surface of the solidified sample, and then using a fully automatic polishing machine to polish the surface of the solidified sample. After coarse polishing, fine polishing and high polishing are performed sequentially, a cobalt-arsenic pyrite electron probe standard is obtained. The process involves three stages: Coarse polishing: The sample is polished sequentially using P400 (~38μm) and P1000 (~13μm) sandpaper, with water added as a polishing solution. This process takes approximately 15 minutes. Fine polishing: The sample is polished sequentially at 6μm, 3μm, and 1μm, with polishing solution of the corresponding size added. This process takes approximately 30 minutes. Ultimately, a fine polishing process is performed using 0.5μm polishing powder (zircon powder) to achieve a submicron-level smooth surface roughness in the consolidated sample. This process takes approximately 1 hour. This process yields a dense and smooth cobalt-arsenic pyrite electron probe standard.

[0040] The present application will now be described in more detail with reference to exemplary embodiments. The following embodiments or experimental data are intended to illustrate the present application by way of example, and it should be clear to those skilled in the art that the present application is not limited to these embodiments or experimental data.

[0041] The cold pressing process in all embodiments and comparative examples of this application uses a piston-cylinder press. This press can automatically control the applied pressure through a preset program. The pressure control gauge is precisely regulated by a DC motor, gradually increasing the hydraulic pressure to drive the 36cm diameter hydraulic cylinder at the bottom of the press upwards. This applies an axial load to the sample powder through the carbide indenter, creating a pseudo-triaxial static rock pressure environment within the press's vacuum chamber. In this application, the carbide indenter is a cylinder with a diameter of Φ12.7mm, and the mold is a hollow carbide cylinder with an inner diameter of Φ12.7mm. After the powder sample is loaded into the mold, it is slowly compacted and spread. The powder sample is compacted into a solidified sample under the interaction of the indenter and the mold. Before cold pressing, the indenter and mold are cleaned with alcohol.

[0042] Example 1 The preparation of cobalt sulfide-containing electron probe standard includes the following steps: S1. Raw Material Preparation Arsine pyrite (CoSul) monominerals were separated from natural copper-nickel sulfide ores, ground, and passed through a 200-mesh sieve to obtain arsine pyrite monomineral powder as the matrix. The matrix powder was ultrasonically cleaned in alcohol for 15 minutes, and then placed in a drying cabinet and dried at 80°C for 20 hours. 20g of matrix powder was weighed using an electronic balance, and the major and trace elements in the matrix powder were determined by XRF and ICP-MS methods, respectively. The cobalt content in the arsenopyrite monomineral powder was 0.21wt%, and thus arsenopyrite monomineral powder was used as the initial sample. S2. Nano-grinding Weigh a certain amount of initial sample, perform ultrasonic cleaning twice, each time for 15 minutes, and then place it in a drying cabinet at 80°C for 20 hours. Add 5g of initial sample to 95g of ethanol dispersant to prepare 100g of initial sample dispersion. Then, mechanically ball-mill the initial sample dispersion according to the following process: First, use 1mm diameter grinding balls and grind for 75 minutes at a ball-to-material ratio of 50:1; then use 0.5mm grinding balls and grind for 30 minutes at a ball-to-material ratio of 100:1. The particle size of the powder in the initial ball-milled sample was determined using a laser particle size analyzer, and the results are as follows: Figure 1 As shown, D(50) < 0.28 μm and D(90) < 0.44 μm, indicating that 50% of the powder particles in the sample have a particle size < 0.28 μm and 90% have a particle size < 0.44 μm, which means that the particle size of the sample powder has reached the submicron level after ball milling. S3. Cold pressing The sample powder was placed in a drying cabinet and dried at 80°C for 20 hours. The sample powder is loaded into the mold and slowly compacted to fill the mold. The mold is then placed in the vacuum chamber of the press, and the hydraulic cylinder at the bottom of the press is driven to move upward so that the press head contacts the sample powder in the mold. According to the preset program, the load on the sample powder is linearly increased from atmospheric pressure to 2 GPa within 100 minutes. After holding the pressure for 120 minutes, the load is gradually reduced to atmospheric pressure, and the sample powder is cold-pressed into a solidified sample. After standing for 1 hour, the mold is removed, and the solidified sample is demolded and removed. The solidified sample was immersed in epoxy resin. After the resin cured, the top epoxy resin of the solidified sample was removed using coarse sandpaper to expose the surface of the solidified sample. The surface of the solidified sample was then polished using a fully automatic polishing machine. The specific process is as follows: Coarse polishing: The surface of the solidified sample was polished sequentially using P400 and P1000 sandpaper for a total of 15 minutes, with water added as polishing fluid during the process; Fine polishing: The surface of the solidified sample was polished sequentially with 6μm, 3μm and 1μm polishing for a total of 30 minutes, with polishing fluid of the corresponding size added during the process; Fine polishing: The surface of the solidified sample was polished with 0.5μm zircon powder for 1 hour to achieve a submicron level of surface roughness and smoothness. This process yielded a cobalt-arsenic pyrite electron probe standard.

[0043] Example 2 The preparation of cobalt sulfide-containing electron probe standard includes the following steps: S1. Raw Material Preparation Arsine pyrite monominerals were separated from natural copper-nickel sulfide ores, ground, and passed through a 200-mesh sieve to obtain arsine pyrite monomineral powder as the matrix. The matrix powder was ultrasonically cleaned in alcohol for 15 minutes, and then placed in a drying cabinet and dried at 70°C for 22 hours. 20g of matrix powder was weighed using an electronic balance, and the major and trace element compositions in the matrix powder were determined using XRF and ICP-MS methods, respectively. The cobalt content in the arsenopyrite monomineral powder was 0.18wt%. An appropriate amount of metallic cobalt powder that had passed through a 200-mesh sieve was weighed using an electronic balance and added to the matrix. After thorough mixing, an initial sample composed of arsenopyrite monomineral powder and metallic cobalt powder was obtained, with a cobalt content of 0.22wt%. S2. Nano-grinding Weigh a certain amount of initial sample, perform ultrasonic cleaning twice, each time for 15 minutes, and then place it in a drying cabinet at 70°C for 22 hours. Add 5g of initial sample to 65g of ethanol dispersant to prepare 70g of initial sample dispersion. Then, mechanically ball mill the initial sample according to the following process: First, use 1mm diameter grinding balls and grind for 60 minutes at a ball-to-material ratio of 60:1; then use 0.5mm grinding balls and grind for 30 minutes at a ball-to-material ratio of 120:1. The particle size of the initial sample after ball milling was determined by a laser particle size analyzer. The test results showed that D(50) < 0.27 μm and D(90) < 0.43 μm, indicating that the particle size of the sample powder after ball milling has reached the submicron level. S3. Cold pressing The sample powder was placed in a drying cabinet and dried at 70°C for 22 hours. The sample powder is loaded into the mold and slowly compacted to fill the mold. The mold is then placed in the vacuum chamber of the press, and the hydraulic cylinder at the bottom of the press is driven to move upward so that the press head contacts the sample powder in the mold. According to the preset program, the load on the sample powder is linearly increased from atmospheric pressure to 2 GPa within 80 minutes. After holding the pressure for 100 minutes, the load is gradually reduced to atmospheric pressure, and the sample powder is cold-pressed into a solidified sample. After standing for 1 hour, the mold is removed, and the solidified sample is demolded and removed. The subsequent polishing process was the same as in Example 1. After polishing, the surface roughness of the solidified sample reached the submicron level and became smooth, thus preparing a cobalt-arsenic pyrite electron probe standard.

[0044] Example 3 The preparation of cobalt sulfide-containing electron probe standard includes the following steps: S1. Raw Material Preparation Arsine pyrite monominerals were separated from natural copper-nickel sulfide ores, ground, and passed through a 200-mesh sieve to obtain arsine pyrite monomineral powder as the matrix. The matrix powder was ultrasonically cleaned in alcohol for 15 minutes, and then placed in a drying cabinet and dried at 60°C for 24 hours. 20g of matrix powder was weighed using an electronic balance, and the major and trace element compositions in the matrix powder were determined using XRF and ICP-MS methods, respectively. The cobalt content in the arsenopyrite monomineral powder was 0.16wt%. An appropriate amount of metallic cobalt powder that had passed through a 200-mesh sieve was weighed using an electronic balance and added to the matrix. After thorough mixing, an initial sample composed of arsenopyrite monomineral powder and metallic cobalt powder was obtained, with a cobalt content of 0.20wt%. S2. Nano-grinding Weigh a certain amount of initial sample, perform ultrasonic cleaning twice, each time for 15 minutes, and then place it in a drying cabinet at 60°C for 24 hours. Add 5g of initial sample to 125g of ethanol dispersant to prepare 130g of initial sample dispersion. Then, mechanically ball mill the initial sample according to the following process: First, use 1mm diameter grinding balls and grind for 90 minutes at a ball-to-material ratio of 40:1; then use 0.5mm grinding balls and grind for 30 minutes at a ball-to-material ratio of 80:1. The particle size of the initial sample after ball milling was determined by a laser particle size analyzer. The test results showed that D(50) < 0.29 μm and D(90) < 0.45 μm, indicating that the particle size of the sample powder after ball milling has reached the submicron level. S3. Cold pressing The sample powder was placed in a drying cabinet and dried at 60°C for 24 hours. The sample powder is loaded into the mold and slowly compacted to fill the mold. The mold is then placed in the vacuum chamber of the press, and the hydraulic cylinder at the bottom of the press is driven to move upward so that the press head contacts the sample powder in the mold. According to the preset program, the load on the sample powder is linearly increased from atmospheric pressure to 2 GPa within 120 minutes. After holding the pressure for 140 minutes, the load is gradually reduced to atmospheric pressure, and the sample powder is cold-pressed into a solidified sample. After standing for 1 hour, the mold is removed, and the solidified sample is demolded and taken out. The subsequent polishing process was the same as in Example 1. After polishing, the surface roughness of the solidified sample reached the submicron level and became smooth, thus preparing a cobalt-arsenic pyrite electron probe standard.

[0045] Comparative Example 1 The preparation of cobalt sulfide electron probe standards using conventional grinding processes includes the following steps: S1. Raw Material Preparation The initial sample was prepared using the same raw materials and preparation process as in Example 1, namely, arsenopyrite monomineral powder that had been ground and passed through a 200-mesh sieve was used as the initial sample, and the cobalt content in the arsenopyrite monomineral powder was 0.21 wt%. S2. Conventional grinding Similar to Example 1, a certain amount of initial sample was weighed and subjected to two ultrasonic cleanings, each lasting 15 minutes. The sample was then placed in a drying cabinet and dried at 80°C for 20 hours. Weigh 5g of initial sample and manually grind the initial sample using a mortar and pestle. After grinding for 180 minutes, pass the sample through a 400-mesh sieve. Select the powder that does not pass through the sieve as the sample powder, i.e., the powder with a particle size of 200~400 mesh sieve. The particle size of the sample powder is 38~75μm. S3. Cold pressing The sample powder was cold-pressed using the same cold-pressing process as in Example 1 to prepare a solidified sample; the solidified sample was polished using the same polishing process as in Example 1 to prepare a cobalt-arsenic pyrite electron probe standard.

[0046] Component homogeneity verification of electron probe standard The arsenopyrite electron probe standards prepared in Example 1 and Comparative Example 1 were observed under a microscope. Figure 2 The metallographic structures of the electron probe standards of Example 1 and Comparative Example 1 are shown. Figure 2 The left side is the standard sample of Example 1. Figure 2 The right side shows the standard sample of Comparative Example 1. As can be seen, within the 200 μm scale range, the particle structure of the electron probe standard sample of Example 1 is almost invisible, while the particle structure of the electron probe standard sample of Comparative Example 1 is clearly visible.

[0047] Carbon films were deposited on the surfaces of the arsenopyrite electron probe standards prepared in Example 1 and Comparative Example 1 to form conductors for scanning electron microscopy testing.

[0048] Figure 3 The images shown are BSE images of the electron probe standards of Example 1 and Comparative Example 1 characterized using scanning electron microscopy. Figure 3 The upper area is the standard sample of Comparative Example 1. Figure 3 The area below is the standard sample of Example 1; Figure 4 The images shown are SEI images of the electron probe standards of Example 1 and Comparative Example 1 characterized using scanning electron microscopy. Figure 4 The upper area is the standard sample of Comparative Example 1. Figure 4 The area below is the standard sample from Example 1. Figure 3 and 4As can be seen, the particle size, compositional uniformity, and flatness of the standard sample obtained by nano-grinding in Example 1 are significantly better than those of the standard sample prepared by conventional grinding in Comparative Example 1.

[0049] Figure 5 As shown Figure 3 The image shows a magnified view of the BSE image of the electron probe standard sample of Example 1 in the lower middle region. The BSE image of the standard sample obtained by nano-grinding in Example 1 was observed. The results show that the composition of the arsenopyrite sample in Example 1 is uniform, and there are no obvious component rings or inclusions.

[0050] right Figure 3 The representative performed WDS elemental surface scan analysis on the area within the red box above the electron probe standard in Example 1. The results are as follows: Figure 6 As shown, the standard sample prepared by conventional grinding has large particles, resulting in an extremely uneven distribution of sulfur. Figure 6 The red area represents the region where sulfur content is concentrated.

[0051] right Figure 3 The region below the electron probe standard in Example 1 was subjected to WDS elemental surface scan analysis, wherein the S elemental composition distribution is as follows: Figure 7 As shown, the Fe elemental composition distribution is as follows: Figure 8 As shown, the distribution of Co elemental composition is as follows: Figure 9 As shown. By Figures 7-9 It is evident that the distribution of the three elements S, Fe, and Co is extremely uniform.

[0052] To further verify the uniformity of major and trace element composition in the arsenopyrite electron probe standard prepared in Example 1, in-situ major element determination was performed using electron probe microanalysis (EMPA). Twenty points were randomly selected on a cross-section of the EMPA standard from Example 1 for testing and analysis. The test results are shown in Table 1. As shown in Table 1, the relative standard deviations (RSDs) of the major elements As, Fe, and S contents in the arsenopyrite EMPA standard were only 0.81%, 1.34%, and 1.93%, respectively, while the RSDs of the trace elements Co and Ni contents were 6.69% and 7.20%, respectively, all meeting the requirements for uniform distribution of major and trace elements in the EMPA standard. The average Co content in the standard was 0.20%, consistent with the Co content in the initial sample.

[0053] Table 1. Electron probe microanalysis results of the arsenopyrite standard sample in this application.

[0054] The major and trace elements of the arsenopyrite electron probe standard prepared in Example 1 were determined using LA-ICP-MS analysis. Ten points were randomly selected on a cross-section of the electron probe standard in Example 1 for testing and analysis. The results showed that the major and trace element composition of the CoSul arsenopyrite electron probe standard in Example 1 was uniformly distributed. The relative standard deviations (RSDs) of major elements such as As, Fe, and S were all less than 2%, and the relative standard deviations (RSDs) of trace elements such as Co, Ni, Cu, Pb, Zn, Te, Se, Bi, As, and Mn were all less than 10%, making it suitable as a monitoring standard for in-situ analysis of major and trace elements. In addition, three samples were randomly selected from the nano-ground sample powder in Example 1, and the nano-ground sample powder in Example 1 was tested using solution-based ICP-MS analysis to determine the trace element values ​​of the arsenopyrite electron probe standard prepared in Example 1. The test results also showed that the major and trace element composition of the CoSul arsenopyrite electron probe standard in Example 1 was uniformly distributed, making it suitable as a monitoring standard for in-situ analysis of major and trace elements. The Co element content and its relative standard deviation obtained by LA-ICP-MS analysis and solution-based ICP-MS analysis are shown in Table 2.

[0055] Table 2. LA-ICP-MS and ICP-MS analysis results of Co element in the electron probe microanalysis standard of arsenopyrite in this application.

[0056] A comparison was made between the Co content data obtained from in-situ analysis (EPMA and LA-ICP-MS) and whole-rock analysis (ICP-MS), such as... Figure 10 As shown, the Co content obtained from the three analyses is consistent within the error range, indicating that the CoSul arsenopyrite electron probe standard prepared in Example 1 of this application has no obvious mineral inclusions, and the major and trace element components are uniform and accurately determined. It is suitable for electron probe standards for in-situ major and trace analysis of the same matrix.

[0057] Research on ball milling process using ethanol and distilled water as dispersants Step 1. Prepare sample powder Arsenopyrite (CoSul) single mineral separated from natural copper-nickel sulfide ore was selected, ground, and passed through a 200-mesh sieve to obtain primary arsenopyrite single mineral powder with a particle size ≤75μm. The primary arsenopyrite single mineral powder was then conventionally ground using a ball mill to obtain sample powder with a particle size of 5~10μm. Three groups of sample powders were selected, and the particle size of the sample powders was determined using a laser particle size analyzer. The test results are shown in Table 3. Among them, the particle size of the sample powder in the first group was D(50)<2.83μm and D(90)<8.35μm, the particle size of the sample powder in the second group was D(50)<2.79μm and D(90)<8.26μm, and the particle size of the sample powder in the third group was D(50)<2.76μm and D(90)<8.16μm.

[0058] Step 2. Nano-grinding Two 5g portions were selected from the first group of sample powders and labeled as group 1-1 and group 1-2; two 5g portions were selected from the second group of sample powders and labeled as group 2-1 and group 2-2; two 5g portions were selected from the third group of sample powders and labeled as group 3-1 and group 3-2. Groups 1-1, 2-1, and 3-1 used distilled water as the dispersant, while groups 1-2, 2-2, and 3-2 used ethanol as the dispersant. All samples were subjected to mechanical ball milling, as follows: 5g of sample powder was added to 145g of dispersant to prepare a 150g sample powder dispersion. The dispersion was ball-milled for 120 minutes using 1mm diameter grinding balls at a ball-to-powder ratio of 60:1. Then, 0.5mm grinding balls were used to ball-mill the dispersion for 30 minutes at a ball-to-powder ratio of 120:1. During mechanical ball milling, the process was stopped every 30 minutes, and the particle size of the sample powder was measured using a laser particle size analyzer. Then, the next 30-minute stage of ball milling was performed until the entire ball milling process was completed. The laser particle size analyzer results for each group of sample powders are shown in Table 3.

[0059] As shown in Table 3, distilled water was used as the dispersant for the sample powders in groups 1-1, 2-1, and 3-1. When the ball milling time was less than 60 min, the particle size D(90) of the sample powder decreased with the increase of the ball milling time. However, when the ball milling time exceeded 60 min, as the particle size of the sample powder continued to decrease, the fine particles would adhere severely to the surface of the larger particles, and severe agglomeration would also occur between the fine particles. The particle size D(90) of the sample powder would instead increase with the increase of the ball milling time. To address the adsorption and agglomeration issues of sample powders during prolonged ball milling, parallel control groups (groups 1-2, 2-2, and 3-2) corresponding to groups 1-1, 2-1, and 3-1 were subjected to parallel ball milling experiments using ethanol as a dispersant. Table 3 shows that when the ball milling time was less than 90 min, the particle sizes D(50) and D(90) of each group of sample powders decreased significantly with increasing milling time. When the milling time exceeded 90 min, the powder particle size almost reached the milling limit, and the sample powder no longer decreased significantly. No adsorption or agglomeration of fine powder particles was observed throughout the entire ball milling process. This demonstrates that, compared to distilled water, ethanol dispersant can effectively solve the problem of adhesion and agglomeration of tiny powders during ball milling. Therefore, ethanol was selected as the dispersant in this application.

[0060] Table 3. Effects of dispersant, milling time, and grinding ball diameter on milling efficiency (μm)

[0061] Table 3 also shows that after ball milling with larger grinding balls, switching to smaller grinding balls for further ball milling can further reduce the particle size of the powder after ball milling. It is understandable that this conclusion only applies to ethanol dispersants. For distilled water dispersants, as shown in the experimental results of groups 1-1, 2-1, and 3-1, after ball milling with 0.5mm grinding balls for 30 minutes, the particle size will continue to increase due to the adhesion and agglomeration of fine powder particles. Therefore, when using distilled water dispersants, the particle size of the sample powder after mechanical ball milling can only be reduced to D(90) of 4.07~4.18μm, which cannot achieve nano-grinding. However, for the parallel control groups (groups 1-2, 2-2, and 3-2) using ethanol as the dispersant, after ball milling with 0.5mm grinding balls for 30 minutes, the particle size of the sample powder decreased significantly again, ultimately yielding sample powder with a particle size D(90) ≤ 0.42μm. The particle size of all three groups of sample powders was reduced to below 500nm, which meets the requirements for in-situ standards with micron-level spatial resolution. Therefore, this application establishes the following mechanical ball milling process: using ethanol as the dispersant, using 1mm diameter grinding balls, and ball milling for 60-90 minutes at a ball-to-material ratio of 40-60:1; then using 0.5mm diameter grinding balls, and ball milling for at least 30 minutes at a ball-to-material ratio of 80-120:1, to obtain sample powder with a submicron particle size.

[0062] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, and process improvements that fall within the spirit and principles of this application shall be included within the scope of protection of the claims of this application.

Claims

1. A method for preparing cobalt sulfide electron probe standards using nano-grinding and high-pressure synthesis techniques, characterized in that, Includes the following steps: S1. Raw Material Preparation Using arsenopyrite single mineral powder as the matrix, the cobalt content in the matrix was determined; If the cobalt content in the matrix is ​​<0.2wt%, then add metallic cobalt powder to the matrix and mix thoroughly. The initial sample composed of arsenopyrite single mineral powder and metallic cobalt powder will then have a cobalt content ≥0.2wt%. S2. Nano-grinding The initial sample was added to an ethanol dispersant to prepare an initial sample dispersion; the initial sample dispersion was mechanically ball-milled to obtain sample powder with a particle size of submicron. S3. Cold pressing The sample powder is loaded into a mold, and an axial load is applied to the sample powder through a pressure head to cold press the sample powder into a solidified sample. After the solidified sample is demolded and polished, a cobalt-arsenic pyrite electron probe standard is obtained.

2. The method for preparing cobalt-containing sulfide electron probe standard samples by nano-grinding and high-pressure synthesis technology according to claim 1, characterized in that, Arsine pyrite monominerals were separated from natural copper-nickel sulfide ores, ground, and passed through a 200-mesh sieve to obtain arsine pyrite monomineral powder as the matrix.

3. The method for preparing cobalt-containing sulfide electron probe standard samples by nano-grinding and high-pressure synthesis technology according to claim 1, characterized in that, The cobalt powder used is cobalt powder that has passed through a 200-mesh sieve.

4. The method for preparing cobalt-containing sulfide electron probe standards by nano-grinding and high-pressure synthesis technology according to claim 1, characterized in that, In step S1, if the cobalt content in the matrix is ​​≥0.2wt%, then arsenopyrite single mineral powder is used as the initial sample.

5. The method for preparing cobalt-containing sulfide electron probe standard samples by nano-grinding and high-pressure synthesis technology according to claim 1, characterized in that, The mechanical ball milling process includes first using grinding balls with a diameter of 1 mm for 60-90 minutes; then using grinding balls with a diameter of 0.5 mm for more than 30 minutes.

6. The method for preparing cobalt-containing sulfide electron probe standard samples by nano-grinding and high-pressure synthesis technology according to claim 5, characterized in that, When using grinding balls with a diameter of 1 mm for ball milling, the ball-to-material ratio is 40~60:1, and when using grinding balls with a diameter of 0.5 mm for ball milling, the ball-to-material ratio is 80~120:

1.

7. The method for preparing cobalt-containing sulfide electron probe standard samples by nano-grinding and high-pressure synthesis technology according to claim 1, characterized in that, After nano-grinding, the particle size of the sample powder is ≤500nm.

8. The method for preparing cobalt-containing sulfide electron probe standard samples by nano-grinding and high-pressure synthesis technology according to claim 1, characterized in that, The cold pressing process includes gradually increasing the load from atmospheric pressure to 2 GPa within 80-120 minutes, holding the pressure for 100-140 minutes, and then gradually reducing the load to atmospheric pressure.

9. The method for preparing cobalt-containing sulfide electron probe standard samples by nano-grinding and high-pressure synthesis technology according to claim 1, characterized in that, The polishing process includes immersing the solidified sample in epoxy resin, and after the epoxy resin has cured, removing the epoxy resin from the top of the solidified sample to expose the surface of the solidified sample. After polishing, a cobalt-arsenic pyrite electron probe standard is obtained.

10. The method for preparing cobalt-containing sulfide electron probe standard samples by nano-grinding and high-pressure synthesis technology according to claim 1, characterized in that, The surface roughness of the cobalt-arsenic pyrite electron probe standard is in the submicron range.

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