Method for analyzing the form of existence of as element in pyrite based on multi-method combination

Abstract

The application discloses a method for analyzing the existence form of As elements in pyrite based on a combination of multiple methods, which comprises the following steps: S1, selecting pyrite particles containing multiple ring zones as the object to be detected; S2, performing electron probe analysis to circumscribe the further analysis area; S3, judging the substitution property of As to Fe or S to preliminarily determine the existence form of As elements; S4, performing focused ion beam processing and spherical aberration transmission electron microscope analysis to shoot HAADF and ABF images; and S5, analyzing the spherical aberration transmission electron microscope images by using DigitalMicrograph data processing software to analyze the intensity difference of Z contrast microscopic images of different atomic sites and the abnormal atomic space occupation of heavy elements and light elements in the ABF images. The application is based on the combination of electron probe and spherical aberration transmission electron microscope, can finely analyze the existence form of As elements in pyrite from the micron to nanometer scale, and has high reliability and sufficient substantial evidence.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of mineral micro-area analysis, and particularly relates to a method for analyzing the existence form of As elements in pyrite based on a combination of multiple methods. BACKGROUND

[0002] Pyrite (FeS2) is the most widely distributed sulfide mineral in the crust, and usually contains trace elements in the form of isomorphism, especially As, Co and Ni. Arsenic pyrite is defined as pyrite with arsenic content ranging from several parts per million to 19wt%, and this isomorphism is usually closely related to the enrichment of economically important metals such as Au, Ag, U and Cu. The study on the existence form of As in pyrite can provide a large amount of information on the genetic evolution mechanism of pyrite and the genesis of the deposit, so the study on the existence form of As in pyrite has very important practical application value.

[0003] At present, the analysis of the existence form of As in pyrite is mainly based on electron probe or XPS analysis, but the electron probe can only speculate the existence form of As according to the linear trend of the data in the Fe-S-As (at%) ternary diagram, and lacks substantial evidence; the sample preparation and preservation requirements of XPS are relatively high, and the test results are easily affected by air oxidation, so the results are not high in reliability. Therefore, a new type of technology for analyzing the existence form of As in pyrite is needed, which can be more intuitive and the results are more reliable. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a method for analyzing the existence form of As elements in pyrite based on electron probe and spherical aberration transmission electron microscopy, which can finely analyze the existence form of As elements in pyrite from micron to nanometer scale, and has high reliability and sufficient substantial evidence.

[0005] The purpose of the present application is achieved by the following technical scheme: a method for analyzing the existence form of As elements in pyrite based on a combination of multiple methods, comprising the following steps:

[0006] S1, performing optical thin section preparation treatment on the rock sample, and selecting pyrite particles containing multiple ring zones as the measured object through optical observation;

[0007] S2, polishing the selected pyrite particles to remove the surface oxidation layer, and then performing electron probe analysis to obtain the As element content of different ring zones of pyrite, and sequentially marking the As-rich pyrite ring zones at an interval of 1 micron from the core to the edge, and circumscribing the region with As element content higher than a preset threshold value as a further transmission electron microscopy analysis region;

[0008] S3, analyze the obtained pyrite As element content, analyze the change of As element content from the core to the edge of pyrite, draw the Fe-S-As ternary diagram, judge the linear trend of the data, judge the substitution property of As to Fe or S, and preliminarily determine the existence form of As element;

[0009] S4, the target area circled in step S2 is processed by focused ion beam, and then ball difference transmission electron microscope analysis is carried out, and high angle annular dark field and annular bright field images of nanoscale pyrite As-rich area are taken;

[0010] S5, the ball difference transmission electron microscope images taken in step S4 are analyzed by using DigitalMicrograph data processing software, the intensity difference of Z contrast micrograph images of different atomic sites and the abnormal situation of heavy element and light element atomic space occupation in ABF image are analyzed, and the mineralogical evidence of the existence form of As atom in pyrite crystal lattice is obtained.

[0011] When the electron probe analysis in step S2 is carried out, the pyrite is first sprayed with a carbon conductive film, and then the pyrite with sprayed carbon conductive film is tested and analyzed by point position of JEOL JXA-8230 electron probe analyzer; the acceleration voltage is 20kV, the current is 20nA, the beam spot diameter is 1μm and the counting time is 10s; the analysis results are corrected by using national standard GB / T15617-2002.

[0012] In step S4, the specific method of focused ion beam processing is: using a focused ion beam scanning electron microscope FIB-SEM equipped with Ga + ion source and capable of depositing Pt to protect the TEM foil from damage by Ga + ion beam, FIB slicing is carried out on the target area circled in step S2, a TEM foil with a length of 6 microns is made, the TEM foil is taken out and transferred using Omniprobe AutoProbe 200 micro-manipulator at 30kV and 1pA current, and finally FIB thinning and cleaning are carried out on the TEM foil to make its thickness less than 100nm.

[0013] In step S4, the specific method of ball difference transmission electron microscope analysis is: the FIB thinned and cleaned TEM foil is welded on the copper mesh and taken out, then the copper mesh with arsenic pyrite TEM foil is put into JEM-ARM300F2 cold field emission aberration corrected transmission electron microscope, the FIB thinned sample is analyzed by STEM, and the HAADF and ABF images of pyrite As-rich area are taken.

[0014] The method for analyzing the existence form of As elements in pyrite based on multi-method combination has the advantages that the existence form of As elements in pyrite is finely analyzed from the micron to nanometer scale based on the electron probe and spherical aberration transmission electron microscope, the reliability is high, the substantial evidence is sufficient, the invalid, inefficient and damaging analysis work is avoided, the mineralogy research method system is widened, and the demand of people in the industry for quickly and accurately analyzing the existence form of trace elements in natural minerals and rocks is met. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 A flowchart of the method for analyzing the existence form of As elements in pyrite based on multi-method combination in the embodiment;

[0016] Figure 2 A schematic diagram of the change trend of As elements in each ring of multi-stage pyrite in the embodiment;

[0017] Figure 3 A ternary diagram of Fe-S-As (at%) of arsenic pyrite in the embodiment;

[0018] Figure 4 A schematic diagram of FIB processing position and TEM foil preparation, taking out, transferring and thinning of arsenic pyrite in the embodiment;

[0019] Figure 5 A schematic diagram of judging the existence position of As atoms according to the HAADF and ABF images of arsenic pyrite under spherical aberration transmission electron microscope in the embodiment. DETAILED DESCRIPTION

[0020] The technical scheme of the present application will be further described below with reference to the drawings.

[0021] As Figure 1 shown, the method for analyzing the existence form of As elements in pyrite based on multi-method combination comprises the following steps:

[0022] S1, the rock sample is subjected to optical thin section processing, and the pyrite particles containing multi-stage rings are selected as the measured object through optical observation. First, the conventional rock thin section sample preparation method in the industry is adopted to obtain the ordinary optical observation thin optical section of the original rock sample, so that the size requirement of the measured sample for subsequent experimental instruments is met, and then the characteristics of the pyrite in the optical thin section are observed, and the multi-stage coexisting pyrite is selected as the measured object, and the measured pyrite sample does not appear any phase change process and oxidation in petrography and optical observation.

[0023] In step S1, the sample surface morphology analysis is performed by optical observation, and the equipment used for optical observation includes but is not limited to the following microscopic equipment: optical microscope, scanning electron microscope, electron probe. The optical microscope is a basic optical observation equipment, and the scanning electron microscope and the electron probe can be magnified at a larger magnification, and the morphology observation of the pyrite to be measured can be clearer and more specific. The morphology observation can be complementary to the optical microscope, but the scanning electron microscope and the electron probe experiment need certain economic cost, and therefore, in mineralogical research, the observation based on the optical microscope is generally performed in the early stage, and after the object to be measured is selected, the observation of the scanning electron microscope and the electron probe can be performed to obtain higher quality pyrite morphology characteristics. Therefore, in the actual operation process, appropriate instruments can be selected according to the needs.

[0024] In this embodiment, the ORTHPUAN-POL polarizing microscope produced by Leica Company and the NANOSEM450 scanning electron microscope produced by FEI Company are used to observe and photograph the pyrite in the rock thin section. First, the ORTHPUAN-POL polarizing microscope is used to observe the pyrite in the whole thin section, and the multi-stage coexisting pyrite observed is photographed and the area is circled. Then, the thin section is gold plated, and under the condition of 30 kV and 70 μA, the gold plated thin section is scanned and analyzed by using the NANO SEM450 scanning electron microscope. The instrument is equipped with the APPOLO ray energy dispersive spectrometer (EDS) produced by EDAX Company. The multi-stage coexisting pyrite circled under the optical microscope is photographed and analyzed in terms of element composition by using the scanning electron microscope. The optical microscope obtains the optical characteristics of the pyrite, and the magnification is generally within 200 times. The scanning electron microscope can obtain higher magnification and higher definition photos based on electronic imaging, and the magnification can reach 10,000 times. The observation of the optical microscope and the scanning electron microscope is closely combined and interlocked for the whole method. Based on a large amount of observation and photography of the optical microscope, the position and morphological characteristics of the object to be measured are captured, and then the scanning electron microscope is used to observe the appropriate point to capture detailed morphological information that cannot be obtained by the optical microscope, and the observation of the optical microscope and the scanning electron microscope is mutually verified.

[0025] In step S2, the selected pyrite particles are polished to remove the surface oxidation layer, and then electron probe analysis is performed to obtain the As element content of different zoned pyrites. The zoned pyrite rich in As is dotted at an interval of 1 micron from the core to the edge, and the area with As element content higher than the preset threshold value is circled as the further transmission electron microscope analysis area.

[0026] In this step, first spray carbon conductive film on pyrite, and then use JEOL JXA-8230 electron probe analyzer produced by Japanese electronic company to test and analyze the pyrite with sprayed carbon conductive film; the acceleration voltage is 20 kV, the current is 20 nA, the beam spot diameter is 1 μm and the counting time is 10 s; the analysis results are corrected by using national standard GB / T15617-2002. The main test element types are 16 elements such as Fe, S, As, Co, Ni, etc. Since the percentage content of each kind of mineral theoretically adds up to 100% on the left and right, but due to the complexity of element types, the electron probe analysis can only analyze the content of all major elements in the mineral as much as possible. For pyrite, the data of total amount above 99.5% by electron probe analysis is the best, and the data is reliable. Measuring other elements in pyrite has two main effects, one is that if only Fe, S and As are tested, the total amount of electron probe test is not enough, and the overall data is not reliable; the second is to exclude whether other elements contain abnormal conditions, determine whether there is only an abnormality of As element content, so that the transmission electron microscope analysis is more convincing, therefore, 16 elements such as Fe, S, As, Co, Ni need to be tested. After obtaining the content of each element, the annulus of As-rich pyrite is studied more finely by marking points at intervals of 1 micrometer from the core to the edge.

[0027] The As content analyzed in the present application refers to that in the pyrite sample to be measured, and only one kind of As content is the main trace element, and other elements such as Co, Ni or Cu should have a low content or no content. If the sample has a high content of other elements, the sample needs to be selected again. In the case of natural samples, it is difficult to screen elements when preparing samples, so it can only be verified that the pyrite indeed has a high content of As element after electron probe analysis. If the sample does not meet the requirements, it can only be selected again. Based on the research on trace elements in pyrite in recent decades, it is shown that the content of elements other than Fe and S in pyrite will basically have only one kind of abnormality or no abnormality. Through electron probe analysis, it is found that one kind of trace element has an abnormality, which is a common phenomenon.

[0028] S3, analyze the obtained As content of pyrite, analyze the change of As content from the core to the edge of pyrite, and draw a Fe-S-As (at%) ternary diagram to judge the linear trend of data, judge the substitution property of As to Fe or S, and preliminarily determine the existence form of As element;

[0029] In this step, first analyze the change trend of As element content (wt%) from the core to the edge of arsenopyrite single particle, as shown in Figure 2The wt% values of the electron probe data of each point of arsenopyrite (a total of 39 points) were converted into at% values, and the at% values of Fe, S, and As of all points were plotted into the Fe-S-As (at%) ternary diagram. According to the overall linear trend of the data points, the substitution properties of As for Fe or S were determined. If the data trend is parallel to the As-Fe direction, it means that As substitutes Fe; if the data trend is parallel to the As-S direction, it means that As substitutes S; and if the data trend is perpendicular to the Fe-S direction, it means that As substitutes both S and Fe. In this embodiment, the point plotting result shows that the data composition trend of arsenopyrite is perpendicular to the connecting direction of Fe-S, indicating that there is both substitution of As 1- for S 1- and substitution of As 3+ for Fe 2+ , as shown in Figure 3 .

[0030] S4, performing focused ion beam processing on the target region circled in step S2, and then performing spherical aberration transmission electron microscopy analysis to take high-angle annular dark-field (HAADF) and annular bright-field (ABF) images of the nanoscale arsenopyrite As-rich region;

[0031] The specific method of focused ion beam processing is as follows: a focused ion beam scanning electron microscope (FIB-SEM) equipped with a Ga + ion source and capable of depositing Pt to protect the TEM foil from damage by the Ga + ion beam is used, as shown in Figure 4 (a); the target region circled in step S2 is FIB-sliced, as shown in Figure 4 (b), to make a TEM foil with a length of 6 microns and a width of 6 microns, and the TEM foil is taken out and transferred using an Omniprobe AutoProbe 200 micro-manipulator at 30 kV and a current of 1 pA, as shown in Figure 4 (c). The TEM foil is then finally FIB-thinned and cleaned, as shown in Figure 4 (d), to a thickness of less than 100 nm, and in this embodiment, the thickness is 60 nm, and then the FIB-thinned and cleaned TEM foil is welded on a copper mesh for taking out. After that, the copper mesh with the arsenopyrite TEM foil is placed in a spherical aberration transmission electron microscope for analysis, and the HAADF and ABF images of the nanoscale arsenopyrite As-rich region are taken, as shown in Figure 5 .

[0032] The specific method of the spherical aberration transmission electron microscope analysis is as follows: the FIB thinned sample is subjected to STEM analysis by using a JEM-ARM300F2 cold field emission aberration correction transmission electron microscope produced by Japan JEOL Company, and HAADF and ABF images of the As-rich pyrite region are shot. The microscope is provided with a cold field emission electron gun (X-CFEG) with high brightness, high coherence and low energy spread; a condenser spherical aberration corrector (COSMO); a BF / ABF / HAADF detector; a double-detector super energy spectrometer (EDS), and the acceleration voltage used in the embodiment is 300kv, and the magnification is 40Mx.

[0033] S5, the spherical aberration transmission electron microscope images shot in step S4 are analyzed by using DigitalMicrograph data processing software, the intensity difference of the Z contrast micrographs of different atomic sites is analyzed, and the abnormal situation of heavy element and light element atomic space occupation in the ABF image is analyzed, so that the mineralogical evidence of the existence form of As atoms in the pyrite crystal lattice is obtained. After drift correction and filtering of all atomic scale STEM images, the original data are processed and analyzed by using DigitalMicrograph data processing software.

[0034] The present application can analyze the existence form of As elements in pyrite by the combination of electron probe and spherical aberration transmission electron microscope, based on the research of geochemistry and mineralogy. Based on the above steps, it is shown that the method for analyzing the existence form of As elements in pyrite based on the combination of multiple methods of the present application is effective and reliable, the method can identify the existence form of trace elements in pyrite from the micron to the atomic scale, and can provide a reliable identification method for the existence form of other key metal elements.

[0035] Those skilled in the art will appreciate that the embodiments described herein are presented for the purpose of helping the reader to understand the principles of the present application, and should be understood as not limiting the protection scope of the present application to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations according to the technical inspiration disclosed in the present application without departing from the essence of the present application, and these modifications and combinations still fall within the protection scope of the present application.

Claims

1. A method for analyzing the existence form of As in pyrite based on a combination of multiple methods, characterized in that: The following steps are involved: S1. Prepare optical thin sections of rock samples and select pyrite particles containing multiple zonations as test objects through optical observation. S2. The selected pyrite particles are polished to remove the surface oxide layer; then, electron probe analysis is performed to obtain the As content of the pyrite in different ring zones. The ring zones of the As-rich pyrite are marked sequentially with a spacing of 1 micron from the core to the edge, and the areas with As content above a preset threshold are identified as areas for further transmission electron microscopy analysis; S3. Analyze the As content of the obtained pyrite, analyze the change of As content from the core to the edge of the pyrite, and draw a Fe-S-As ternary diagram to determine the linear trend of the data, determine the substitution properties of As for Fe or S, and make a preliminary determination of the existence form of the As element; S4, performing focused ion beam processing on the target area circled in step S2, and then performing spherical aberration transmission electron microscopy analysis to capture high-angle annular dark field and annular bright field images of the nanoscale pyrite As-rich area; The specific method of focused ion beam processing is: using a Ga + Ion source and capable of depositing Pt to protect TEM foil from Ga + Ion beam damaged focused ion beam scanning electron microscopy (FIB-SEM) was used to perform FIB sectioning of the target area circled in step S2 to produce a TEM foil with a length and width of 6 μm. The TEM foil was removed and transferred using an Omniprobe AutoProbe 200 micromanipulator at 30 kV and 1 pA. The TEM foil was then finally FIB thinned and cleaned to a thickness of less than 100 nm. The specific method for spherical aberration transmission electron microscopy analysis is as follows: the TEM foil after FIB thinning and cleaning is welded to a copper grid and then removed. The copper grid with the arsenopyrite TEM foil is then placed in a JEM-ARM300F2 cold field emission aberration-corrected transmission electron microscope. The FIB-thinned sample is subjected to STEM analysis, and HAADF and ABF images of the As-rich region of the pyrite are captured. S5. Use DigitalMicrograph data processing software to analyze the spherical aberration transmission electron microscope image taken in step S4, analyze the intensity differences of the Z-contrast microscopic images of different atomic sites and the abnormalities in the spatial occupancy of heavy and light element atoms in the ABF image, and obtain mineralogical evidence for the existence of As atoms in the pyrite lattice.

2. The method for analyzing the existence form of As element in pyrite based on multiple methods according to claim 1, characterized in that: When performing electron probe analysis in step S2, a carbon conductive film is first sprayed on the pyrite, and then an electron probe point test analysis is performed on the pyrite sprayed with the carbon conductive film using a JEOL JXA-8230 electron probe analyzer; the acceleration voltage is 20 kV, the current is 20 nA, the beam spot diameter is 1 μm, and the counting time is 10 s; the analysis results are calibrated using the national standard GB / T15617-2002.

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