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

Abstract

The invention discloses a method for analyzing an existence form of an As element in pyrite based on multi-method combination. The method comprises the following steps: S1, selecting pyrite particles containing multi-stage annular bands as a to-be-detected object; s2, carrying out electron probe analysis, and delineating a further analysis area; s3, the substitution property of As to Fe or S is judged, and the existence form of the As element is preliminarily judged; s4, performing focused ion beam processing and spherical aberration transmission electron microscope analysis, and shooting HAADF and ABF images; and S5, analyzing the spherical aberration transmission electron microscope image by using DigilMicrograph data processing software, and analyzing the intensity difference of Z-contrast microscopic images of different atomic sites and the atomic space occupation abnormal conditions of heavy elements and light elements in the ABF image. Based on the combination of the electron probe and the spherical aberration transmission electron microscope, the existence form of the As element in the pyrite is finely analyzed from the micron scale to the nanometer scale, the credibility is high, and the substantive evidence is sufficient.

Description

Technical Field

[0001] The invention belongs to the technical field of mineral micro-area analysis, and specifically is a method for analyzing the existence form of As element in pyrite based on multi-method combination. Background Art

[0002] Pyrite (FeS 2 ) is the most widely distributed sulfide mineral in the earth's crust, usually containing trace elements in the form of isomorphism, especially As, Co and Ni. Arsenopyrite is defined as pyrite with arsenic content ranging from a few parts per million to 19wt%, which is usually closely related to the enrichment of economically important metals such as Au, Ag, U, and Cu. The study of the existence form of As in pyrite can provide a lot of information on the genesis and evolution mechanism of pyrite and the genesis of ore deposits, so the study of the existence form of As in pyrite has very important practical application value.

[0003] The analysis of the existence form of As in pyrite is currently mainly based on electron probe or XPS analysis, but the electron probe can only infer the existence form of As based on the linear trend of the data in the Fe-S-As (at%) ternary diagram, lacking substantial evidence; XPS has high requirements for sample preparation and preservation, and the test results are easily affected by air oxidation, resulting in low credibility. Therefore, a new technical method is needed to analyze the existence form of As in pyrite in a more intuitive and reliable way. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for analyzing the As element in pyrite based on an electron probe and a spherical aberration transmission electron microscope, which is based on the combination of an electron probe and a spherical aberration transmission electron microscope and has high credibility and sufficient substantial evidence.

[0005] The object of the present invention is achieved through the following technical scheme: a method for analyzing the existence form of As element in pyrite based on multi-method combination, comprising the following steps:

[0006] S1. Process the rock sample for optical thin section making, and select the pyrite particles containing multi-period ring zones as the test object through optical observation;

[0007] S2. Polish the selected pyrite particles to remove the surface oxide layer; then perform electron probe analysis to obtain the As content of pyrite in different ring zones, and dot the ring zones of As-rich pyrite from the core to the edge with a spacing of 1 micron, and circle the area with As content higher than a preset threshold as a further transmission electron microscope analysis area;

[0008] 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;

[0009] 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;

[0010] S5. Use DigitalMicrograph data processing software to analyze the spherical aberration transmission electron microscope image taken in step S4, analyze the intensity difference of the Z contrast microscopic image of different atomic sites and the abnormal space occupancy of heavy and light element atoms in the ABF image, and obtain the mineralogical evidence of the existence form of As atoms in the pyrite lattice.

[0011] When performing electron probe analysis in step S2, the pyrite is first sprayed with a carbon conductive film, and then the pyrite sprayed with the carbon conductive film is subjected to electron probe point test analysis 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; and the analysis results are calibrated using the national standard GB / T15617-2002.

[0012] In step S4, 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 + The target area circled in step S2 was FIB-sliced ​​using a focused ion beam scanning electron microscope (FIB-SEM) for ion beam damage 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, and the TEM foil was finally FIB-thinned and cleaned to a thickness of less than 100 nm.

[0013] In step S4, the specific method of spherical aberration transmission electron microscopy analysis is: the TEM foil after FIB thinning and cleaning is welded on the copper mesh and taken out, and then the copper mesh with arsenopyrite TEM foil is placed in a JEM-ARM300F2 cold field emission aberration-corrected transmission electron microscope, and the FIB thinned sample is subjected to STEM analysis to take HAADF and ABF images of the As-rich area of ​​pyrite.

[0014] The beneficial effects of the present invention are as follows: the present invention is based on the combination of an electron probe and a spherical aberration transmission electron microscope, and conducts a detailed analysis of the existence form of the As element in pyrite from micrometer to nanometer scales. It has high credibility and sufficient substantive evidence, avoids invalid, inefficient, and destructive analysis work, broadens the mineralogical research method system, and meets the needs of industry insiders for quickly and accurately analyzing the existence form of trace elements in natural mineral rocks. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flow chart of the method for analyzing the existence form of As element in pyrite based on multi-method combination in the embodiment;

[0016] Figure 2 Schematic diagram of the variation trend of As element in each ring zone of multi-stage pyrite in the embodiment;

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

[0018] Figure 4 Schematic diagram of the FIB processing position of arsenopyrite and the preparation, removal, transfer and thinning of TEM foil in the embodiment;

[0019] Figure 5 Schematic diagram of determining the location of As atoms based on HAADF and ABF images of arsenopyrite under a spherical aberration transmission electron microscope in the embodiment. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0021] like Figure 1 As shown, a method for analyzing the existence form of As element in pyrite based on multiple methods combined with the present invention comprises the following steps:

[0022] S1. Prepare thin sections of rock samples, and select pyrite particles containing multi-period rings as the test object through optical observation. First, the conventional rock thin section sample preparation method in the industry is used to obtain ordinary optical observation thin sections of the original rock sample, so as to meet the size requirements of the subsequent experimental instruments for the sample to be tested. Then, by observing the characteristics of pyrite in the thin section, select multi-period coexisting pyrite as the test object. The pyrite sample to be tested must not show any phase change process and oxidation in petrographic and optical observation.

[0023] In step S1, the sample surface morphology is analyzed 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. Optical observation equipment based on optical microscope, scanning electron microscope and electron probe can be magnified at a greater multiple, and the morphological observation of the pyrite to be tested can be clearer and more specific, and can complement and verify each other with the optical microscope in morphological observation, but scanning electron microscope and electron probe experiments require a certain economic cost, so mineralogy research is generally based on optical microscope observation in the early stage, and scanning electron microscope and electron probe observation can be carried out after further selecting the object to be tested to obtain higher quality pyrite morphological characteristics, so in the actual operation process, the appropriate instrument can be selected as needed.

[0024] In this embodiment, the ORTHPUAN-POL polarizing microscope produced by Leica and the NANOSEM450 scanning electron microscope produced by FEI were used to observe and photograph the morphology of pyrite in the rock thin section. The pyrite in the entire thin section was first observed by the ORTHPUAN-POL polarizing microscope, and the observed multi-phase coexisting pyrite was photographed and the area was circled. Then the optical thin section was gold-plated, and the gold-plated thin section was scanned and analyzed using the NANO SEM450 scanning electron microscope under the conditions of 30kV and 70μA. The instrument was equipped with an APPOLO ray energy dispersive spectrometer (EDS) produced by EDAX, and the multi-phase coexisting pyrite circled under the optical microscope was photographed with high-precision images and elemental composition was analyzed by scanning electron microscope. The optical microscope obtains the optical characteristics of 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 method magnification can reach 10,000 times. The observations of optical microscope and scanning electron microscope are closely integrated and interconnected for the research of the entire method. Based on a large number of optical microscope observations and photos, the position and morphological characteristics of the object to be measured are captured, and then the appropriate points are selected for scanning electron microscope observations to capture detailed morphological information at a scale that cannot be achieved by optical microscopes, and verify each other.

[0025] 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 pyrite in different ring zones, and the ring zones of As-rich pyrite are dotted from the core to the edge with a spacing of 1 micron, and the area with As content higher than the preset threshold is circled as the area for further transmission electron microscopy analysis.

[0026] In this step, the carbon conductive film is first sprayed on the pyrite, and then the JEOLJXA-8230 electron probe analyzer produced by Japan Electronics Corporation is used to perform electron probe point test analysis on the pyrite sprayed with the carbon conductive film; the acceleration voltage is 20kV, the current is 20nA, the beam spot diameter is 1μm and the counting time is 10s; the national standard GB / T15617-2002 is used to calibrate the analysis results. The main test element types are 16 elements such as Fe, S, As, Co, and Ni. Since the theoretical sum of the percentage content of the left and right elements of each mineral should be 100%, but because the element types are very complex, 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 the total amount of electronic probe analysis above 99.5% is the best, and the data is credible. Measuring other elements in pyrite has two main functions. First, if only Fe, S, and As are tested, the total amount of electron probe testing is insufficient and the data as a whole is unreliable. Second, it is necessary to exclude the abnormality of other elements and determine whether only the As content is abnormal, so that the analysis of transmission electron microscopy is more convincing. Therefore, it is necessary to test 16 elements such as Fe, S, As, Co, and Ni. After obtaining the content of each element, points are made from the core to the edge with a spacing of 1 micron to conduct a more detailed study of the ring zone of As-rich pyrite.

[0027] The As content analyzed by the present invention means that there must be and only one As content as the main trace element in the pyrite sample to be tested, and other elements such as Co, Ni or Cu should have a lower content or no content. If a sample with a higher content of other elements appears, the sample is reselected. In the case of natural samples, it is difficult to screen the elements when making the sample. Therefore, it can only be confirmed in this step based on the electron probe analysis that only the As content in the pyrite is high. If the sample does not meet the requirements, it can only be reselected. And based on the research on trace elements in pyrite in recent decades, it is shown that there is basically only one or no abnormal content of elements in pyrite except Fe and S. It is a common phenomenon to find an abnormality of one trace element through electron probe analysis.

[0028] 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 (at%) 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;

[0029] In this step, the variation trend of As content (wt%) at each point from the core to the edge of a single arsenopyrite particle is first analyzed by graphing. Figure 2As shown; then the wt% value of the electron probe data of the elements measured at each point of arsenopyrite (39 points in total) is converted into at% value, and the at% values ​​of the three elements Fe, S, and As at all points are projected into the Fe-S-As (at%) ternary diagram, and the substitution properties of As for Fe or S are judged according to the overall linear trend of the data point arrangement. If the data trend is parallel to the As-Fe direction, it means that As replaces Fe, if it is parallel to the As-S direction, it means that As replaces S, and if it is perpendicular to the Fe-S direction, it means that As replaces both S and Fe. In this embodiment, the projected results show the data composition trend of arsenopyrite perpendicular to the connection direction of Fe-S, indicating the simultaneous presence of As 1- For S 1- Substitution and As 3+ Fe 2+ Replacement, such as Figure 3 shown.

[0030] 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 (HAADF) and annular bright field (ABF) images of the As-rich area of ​​nanoscale pyrite;

[0031] 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 damage focused ion beam scanning electron microscopy FIB-SEM, such as Figure 4 (a); the target area circled in step S2 is sliced ​​by FIB, as shown in Figure 4 As shown in (b), a TEM foil with a length and width of 6 μm was made, and the TEM foil was taken out and transferred using an Omniprobe AutoProbe 200 micromanipulator at 30 kV and 1 pA current, as shown in Figure 4 (c) The TEM foil is then subjected to final FIB thinning and cleaning, as shown in Figure 4 (d) to make the thickness less than 100nm, and 60nm is used in this embodiment, and then the TEM foil thinned and cleaned by FIB is welded to the copper mesh and taken out. Then the copper mesh with arsenopyrite TEM foil is put into a spherical aberration transmission electron microscope for analysis, focusing on taking HAADF and ABF images of the As-rich area of ​​pyrite at the nanoscale, as shown in FIG. Figure 5 shown.

[0032] The specific method of spherical aberration transmission electron microscopy analysis is: the JEM-ARM300F2 cold field emission aberration-corrected transmission electron microscope produced by JEOL of Japan is used to perform STEM analysis on the sample after FIB thinning, and to take HAADF and ABF images of the As-rich area of ​​pyrite. The microscope is equipped with a cold field emission electron gun (X-CFEG) with high brightness, high coherence and low energy broadening; a condenser spherical aberration corrector (COSMO); a BF / ABF / HAADF detector; and a dual-detector super spectrometer (EDS). The acceleration voltage used in this embodiment is 300 kV and the magnification is 40 Mx.

[0033] S5. Analyze the spherical aberration transmission electron microscope images taken in step S4 using DigitalMicrograph data processing software, analyze the intensity differences of the Z contrast microscopic images of different atomic sites and the abnormalities of the spatial occupancy of heavy and light element atoms in the ABF image, and obtain the mineralogical evidence of the existence of As atoms in the pyrite lattice. Use DigitalMicrograph data processing software to perform drift correction and filtering on all atomic-scale STEM images and then process and analyze the raw data.

[0034] The present invention can conduct reliable analysis of the existence form of As element in pyrite based on geochemical and mineralogy research by combining an electron probe and a spherical aberration transmission electron microscope. Based on the above steps, it is shown that the method of the present invention for analyzing the existence form of As element in pyrite based on the combination of multiple methods is effective and reliable. The method can identify the existence form of trace elements in pyrite from micrometer to 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 intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. A method for analyzing the existence form of As in pyrite based on multi-method combination, characterized in that: The following steps are involved: S1. Process the rock sample for optical thin section making, and select the pyrite particles containing multi-period ring zones as the test object through optical observation; S2. Polish the selected pyrite particles to remove the surface oxide layer; then perform electron probe analysis to obtain the As content of pyrite in different ring zones, and dot the ring zones of As-rich pyrite from the core to the edge with a spacing of 1 micron, and circle the area with As content higher than a preset threshold as a further transmission electron microscope analysis area; 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; S5. Use DigitalMicrograph data processing software to analyze the spherical aberration transmission electron microscope image taken in step S4, analyze the intensity difference of the Z contrast microscopic image of different atomic sites and the abnormal space occupancy of heavy and light element atoms in the ABF image, and obtain the mineralogical evidence of the existence form 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 is characterized in that: When performing electron probe analysis in step S2, the pyrite is first sprayed with a carbon conductive film, and then the pyrite sprayed with the carbon conductive film is subjected to electron probe point test analysis 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; and the analysis results are calibrated using the national standard GB / T15617-2002.

3. The method for analyzing the existence form of As element in pyrite based on multiple methods according to claim 1 is characterized in that: In step S4, 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 + The target area circled in step S2 was FIB-sliced ​​using a focused ion beam scanning electron microscope (FIB-SEM) for ion beam damage 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, and the TEM foil was finally FIB-thinned and cleaned to a thickness of less than 100 nm.

4. The method for analyzing the existence form of As element in pyrite based on multiple methods according to claim 3 is characterized in that: In step S4, the specific method of spherical aberration transmission electron microscopy analysis is: the TEM foil after FIB thinning and cleaning is welded on the copper mesh and taken out, and then the copper mesh with arsenopyrite TEM foil is placed in a JEM-ARM300F2 cold field emission aberration-corrected transmission electron microscope, and the FIB thinned sample is subjected to STEM analysis to take HAADF and ABF images of the As-rich area of ​​pyrite.

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