Method for synchronously analyzing occurrence forms of sulfur and mercury in coal containing fine-grained pyrite

Abstract

The invention belongs to the technical field of detection of morphological sulfur and morphological mercury in coal, and provides a method for synchronously analyzing occurrence forms of sulfur and mercury in coal containing fine-grained pyrite. The method comprises the following steps: sequentially adding a magnesium chloride solution, a hydrogen chloride solution and a hydrogen fluoride solution into a coal sample S0, stirring, carrying out suction filtration, drying to respectively obtain residues S1, S2 and S3, carrying out plasma low-temperature ashing on the residue S3 to obtain low-temperature ash SP, respectively determining the contents of sulfur and mercury in the coal sample, the residues and the low-temperature ash, and determining the content of mercury in the coal sample, the residues and the low-temperature ash. The sulfur content and the mercury content in different occurrence forms in the coal are obtained through step-by-step subtraction. According to the method, plasma low-temperature ashing is carried out on the residue S3 only containing organic matter and sulfide minerals, and fine-grained pyrite and organic matter in coal are effectively separated; the sulfur content and the mercury content in different occurrence forms in the coal are synchronously analyzed by adopting a step-by-step chemical extraction and plasma low-temperature ashing combined technology, and errors caused by different sulfur and mercury analysis methods are effectively reduced.

Description

Technical Field

[0001] The invention relates to the technical field of detection of sulfur and mercury forms in coal, and in particular to a method for synchronously analyzing the occurrence forms of sulfur and mercury in coal containing fine-grained pyrite. Background Art

[0002] The sulfur compounds released during the thermal conversion of coal can corrode equipment, poison catalysts, pollute the environment, and harm human health. Mercury, as a global pollutant, has attracted widespread attention from countries around the world due to its high toxicity, long migration distance, strong persistence, and bioaccumulation in the environment.

[0003] The occurrence forms of sulfur and mercury in coal determine their possible transformation and migration behaviors during thermal conversion, and are the basis for evaluating the environmental impact of sulfur and mercury in coal. Sulfur in coal mainly exists in two forms: inorganic sulfur and organic sulfur. Inorganic sulfur is mainly sulfide sulfur, sulfate sulfur and a small amount of elemental sulfur. In addition to pyritic sulfur, there are other low-content non-pyritic sulfides in coal, such as marcasite, sphalerite, etc. Sulfate sulfur can be divided into exchangeable sulfates and acid-soluble sulfates, which are usually present in coal at low levels. Although the sulfate content in oxidized coal may increase locally, there is very little elemental sulfur in coal. Organic sulfur mainly includes thiols, sulfides and sulfur heterocycles (thiophenes, thioketones, sulfoxides, sulfones). In many coals, especially high-sulfur coal (S t >3%), sulfide sulfur is the main form of occurrence. In other coals, especially low sulfur coal (S t <1%), organic sulfur is dominant. Mercury in coal mainly exists in pyrite, marcasite, organic matter, or in the form of a single substance. Some scholars believe that mercury and pyrite coexist in the coal matrix in the form of a solid solution, and pyrite is the main carrier of elemental mercury. Others believe that the presence of organic matter in coal is closely related to mercury, and mercury may be related to finely dispersed pyrite under the protection of the coal matrix. Mercury in high-sulfur coal is mainly related to pyrite, and the concentration of mercury in coal depends on the sulfide content. There are many combinations of mercury in low-sulfur coal, the most common of which are organically bound mercury and sulfide-bound mercury. Pyrite in coal can be divided into coarse-grained pyrite (>60μm) and fine-grained pyrite (<60μm) according to the size of the particle size. Coarse-grained pyrite is easily removed by washing, while fine-grained pyrite is embedded in the organic components of coal through chemical bonds. Very small fine-grained pyrite can be combined with inorganic sulfur, thiophene and heterocyclic compounds through -S- bonds, and can also be combined with organic compounds through Fe-S bonds of other molecules except pyrite. The smaller the pyrite particles, the closer the interaction with organic matter, and the more difficult it is to effectively separate fine-grained pyrite and organic matter.

[0004] At present, the form of sulfur in coal is mainly analyzed and determined according to the national standard method (GB / T 215-2003 Determination of various forms of sulfur in coal). The national standard method divides sulfur in coal into three categories: sulfate sulfur, pyrite sulfur and organic sulfur. The coal sample is boiled with dilute hydrochloric acid to extract the sulfate in the coal and generate barium sulfate precipitation. The sulfate sulfur content in the coal is calculated based on the mass of barium sulfate. The iron in the non-sulfide iron in the coal is extracted with hydrochloric acid, and the coal sample after extraction is leached with dilute nitric acid. The iron (Fe 2+ ), and then calculate the content of iron sulfide sulfur in the coal by the mass of iron. Or use atomic absorption spectrophotometry to determine the iron in the nitric acid leaching solution, and then calculate the content of iron sulfide sulfur in the coal by the mass of iron. o,ad =S t,ad -(S s,ad +S p,ad ) is subtracted to obtain the organic sulfur content. This method does not subdivide sulfate sulfur; only pyrite sulfur is analyzed, and iron-free sulfide sulfur is not analyzed; for coal containing fine-grained pyrite, nitric acid cannot be completely leached, which will make the pyrite sulfur content low and the organic sulfur content high. The analysis method of the occurrence form of mercury in coal, the prior art discloses a step-by-step chemical extraction method, and the Chinese patent application with publication number CN 108982575A discloses a detection method and device for the occurrence form of mercury in the solid phase, which uses a step-by-step chemical extraction method to extract the sample to obtain a solid residue; the mercury content in the original solid sample and the obtained solid residue is determined to obtain the distribution results of different forms of mercury in the original solid sample. This method can divide the mercury in coal into five different occurrence forms: mercury bound in the form of ion exchange, mercury bound in carbonate / sulfate / oxide / phosphate, mercury bound in silicate / aluminosilicate, mercury bound in sulfide, and organically bound mercury. During the step-by-step chemical extraction process, the mixture is stirred and shaken at room temperature and dried at room temperature, which results in incomplete extraction and long drying time. The last step of nitric acid extraction in this method also results in incomplete extraction of fine-grained pyrite. The use of different analytical techniques and incomplete classification of sulfur and mercury forms may lead to errors in the correlation analysis between sulfur and mercury. In addition, the fine-grained pyrite in coal is bound to the organic matter in the coal through covalent bonds. During the nitric acid digestion process for the determination of sulfide sulfur and sulfide-bound mercury in the coal, the fine-grained pyrite will be blocked by the organic matter in the coal and escape dissolution, resulting in low levels of sulfide sulfur and sulfide-bound mercury and high levels of organic sulfur and organic-bound mercury.

[0005] Therefore, it has become an urgent problem to be solved by technical personnel in this field to propose an analysis method that can effectively avoid the influence of fine-grained pyrite in coal and realize the synchronous analysis of sulfur and mercury in different occurrence forms in coal. Summary of the invention

[0006] The purpose of the present invention is to provide a method for simultaneously analyzing the occurrence forms of sulfur and mercury in coal containing fine-grained pyrite in order to overcome the shortcomings of the prior art. Its purpose is to solve the technical problems that the existing methods for analyzing the occurrence forms of sulfur and mercury in coal are different and the measured results are inaccurate due to the influence of fine-grained pyrite in the coal.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for synchronously analyzing the occurrence forms of sulfur and mercury in coal containing fine-grained pyrite, comprising the following steps:

[0009] 1) adding the coal sample S0 into the magnesium chloride solution, stirring, filtering and drying in sequence to obtain the residue S1;

[0010] 2) adding the residue S1 into a hydrogen chloride solution, stirring, filtering and drying in sequence to obtain a residue S2;

[0011] 3) adding the residue S2 into a hydrogen fluoride solution, stirring, filtering, and drying in sequence to obtain a residue S3;

[0012] 4) Plasma low-temperature ashing is performed on the residue S3 until the residue S3 reaches a constant weight, thereby obtaining low-temperature ash SP;

[0013] 5) The contents of sulfur and mercury in coal sample S0, residue S1, residue S2, residue S3 and low-temperature ash SP were determined respectively, and the sulfur content and mercury content in five different occurrence forms in coal were obtained by step-by-step subtraction.

[0014] Preferably, the coal sample S0 is raw coal containing fine-grained pyrite or clean coal containing fine-grained pyrite, and the particle size of the coal sample S0 is 0.1-1 mm.

[0015] Preferably, the molar concentration of the magnesium chloride solution in step 1) is 0.8-1.2 mol / L, and the mass volume ratio of the coal sample S0 to the magnesium chloride solution is 1 g:4-6 mL.

[0016] Preferably, the mass concentration of the hydrogen chloride solution in step 2) is 17-20%, and the mass volume ratio of the residue S1 to the hydrogen chloride solution is 1 g:5-7 mL.

[0017] Preferably, the mass concentration of the hydrogen fluoride solution in step 3) is 38-42%, and the mass volume ratio of the residue S2 to the hydrogen fluoride solution is 1 g: 6.5-8.5 mL.

[0018] Preferably, when the coal sample S0 is added in step 1), the temperature of the magnesium chloride solution is 45-55° C. and the rotation speed is 470-530 r / min;

[0019] Step 2) When adding the residue S1, the temperature of the hydrogen chloride solution is 45-55°C and the rotation speed is 470-530 r / min;

[0020] Step 3) When adding the residue S2, the temperature of the hydrogen fluoride solution is 45-55°C and the rotation speed is 470-530 r / min.

[0021] Preferably, the stirring speed in steps 1) to 3) is independently 470 to 530 r / min, the stirring temperature is independently 45 to 55° C., and the stirring time is independently 10 to 14 h.

[0022] Preferably, in step 1) to step 3), the filtrate is filtered until the pH value of the filtrate reaches 7; the drying temperature is independently 55 to 65° C., and the drying time is independently 18 to 48 hours.

[0023] Preferably, the power of the plasma low-temperature ashing in step 4) is 100-300 W, and the plasma low-temperature ashing to constant weight is performed once every 2 hours until the change between two weighings is ≤1%.

[0024] The beneficial effects of the present invention include the following:

[0025] 1) Fine-grained pyrite is embedded in the organic components of coal through chemical bonds. It is difficult to effectively separate the two with existing technologies, which brings difficulties to the detection of sulfur and mercury in sulfide minerals and sulfur and mercury in organic matter. The present invention uses the combined technology of step-by-step chemical leaching and plasma low-temperature ashing to not only effectively solve the problem of difficulty in separating fine-grained pyrite from organic matter, but also achieves the purpose of synchronously and accurately detecting sulfur and mercury in different occurrence forms in coal containing fine-grained pyrite, avoiding the errors caused by different sulfur and mercury analysis methods in the analysis of sulfur and mercury occurrence forms.

[0026] 2) The present invention provides a method for synchronously analyzing the occurrence forms of sulfur and mercury in coal containing fine-grained pyrite. The raw coal is leached by a step-by-step chemical leaching method to obtain a solid residue S3 containing organic matter and sulfide minerals; the solid residue is subjected to plasma low-temperature ashing to completely oxidize the organic matter in the coal while ensuring that the inorganic minerals do not decompose or transform into each other, thereby obtaining low-temperature ash containing only sulfide minerals, effectively separating the fine-grained pyrite and organic matter in the coal, and more accurately analyzing the sulfur content and mercury content in the organic matter, and the sulfur content and mercury content in the sulfide minerals; the sulfur content and mercury content in the raw coal, the residues of each step of the step-by-step chemical leaching, and the low-temperature ash are determined, and the content is multiplied by the extraction yield and the ash residue to standardize the sulfur and mercury content, and the sulfur content and mercury content in different occurrence forms in the coal are obtained by step-by-step subtraction.

[0027] 3) The present invention subdivides the sulfur in different occurrence forms in coal, and subdivides the three categories of sulfate sulfur, pyrite sulfur and organic sulfur in the national standard method into five categories: exchangeable sulfur (mainly exchangeable sulfate sulfur), HCl-soluble sulfur (mainly acid-soluble sulfate sulfur), HF-soluble sulfur, organic sulfur and sulfide sulfur. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The photos of pyrite morphology of MDCD raw coal, HDG clean coal and MHJ raw coal under an optical microscope of the present invention;

[0029] Figure 2 The content ratio of sulfur and mercury in different occurrence forms in MDCD coal is analyzed for Example 1;

[0030] Figure 3 XRD spectra of low temperature ash under different ashing power conditions of Example 1 and Comparative Example 1;

[0031] Figure 4 The content ratio of sulfur and mercury in different occurrence forms in HDG coal is analyzed for Example 2;

[0032] Figure 5 XRD spectra of HDGS3 obtained at different leaching temperatures of HF solution in Example 2 and Comparative Example 2, as well as raw coal and HDGS2, wherein the heated HDGS3 is Example 2, and the unheated HDGS3 is Comparative Example 2;

[0033] Figure 6 The content ratio of sulfur and mercury in different occurrence forms in MHJ coal is analyzed for Example 3;

[0034] Figure 7 The content ratio of sulfur and mercury in different occurrence forms in MDCD coal, HDG coal and MHJ coal in Examples 1 to 3 is shown;

[0035] Figure 8 The content ratio of sulfur and mercury in different occurrence forms in MHJ coal is analyzed for comparative example 3;

[0036] Fig. 9 This is the pyrite morphology of the MDCD raw coal in Comparative Example 4 under an optical microscope;

[0037] Fig.10 The morphology of pyrite of MDCDS4 of Comparative Example 5 under an optical microscope;

[0038] Fig.11 The content ratio of sulfur and mercury in different occurrence forms in MDCD coal is analyzed for comparative example 5;

[0039] Fig.12 This is a morphological picture of pyrite of HDGS4 of Comparative Example 6 under an optical microscope;

[0040] Fig.13 The content ratio of sulfur and mercury in different occurrence forms in HDG coal is analyzed for comparative example 6;

[0041] Fig.14 The morphology of pyrite of MHJS4 of Comparative Example 7 under an optical microscope;

[0042] Fig.15 The content ratio of sulfur and mercury in different occurrence forms in MHJ coal is analyzed for comparative example 7;

[0043] Fig.16 The content percentage of sulfur forms in MDCD, HDG and MHJ coals is analyzed for Comparative Example 8. DETAILED DESCRIPTION

[0044] The present invention provides a method for synchronously analyzing the occurrence forms of sulfur and mercury in coal containing fine-grained pyrite, comprising the following steps:

[0045] 1) adding the coal sample S0 into the magnesium chloride solution, stirring, filtering and drying in sequence to obtain the residue S1;

[0046] 2) adding the residue S1 into a hydrogen chloride solution, stirring, filtering and drying in sequence to obtain a residue S2;

[0047] 3) adding the residue S2 into a hydrogen fluoride solution, stirring, filtering, and drying in sequence to obtain a residue S3;

[0048] 4) Plasma low-temperature ashing is performed on the residue S3 until the residue S3 reaches a constant weight, thereby obtaining low-temperature ash SP;

[0049] 5) The contents of sulfur and mercury in coal sample S0, residue S1, residue S2, residue S3 and low-temperature ash SP were determined respectively, and the sulfur content and mercury content in five different occurrence forms in coal were obtained by step-by-step subtraction.

[0050] In the present invention, the coal sample S0 is preferably raw coal containing fine-grained pyrite or clean coal containing fine-grained pyrite, and the particle size of the coal sample S0 is preferably 0.1 to 1 mm.

[0051] In the present invention, the molar concentration of the magnesium chloride solution in step 1) is preferably 0.8-1.2 mol / L, more preferably 0.9-1.1 mol / L, and more preferably 1 mol / L. The mass volume ratio of the coal sample S0 and the magnesium chloride solution is preferably 1 g: 4-6 mL, more preferably 1 g: 4.5-5.5 mL, and more preferably 1 g: 5 mL.

[0052] In the present invention, the mass concentration of the hydrogen chloride solution in step 2) is preferably 17-20%, more preferably 18-19%, and the mass volume ratio of the residue S1 to the hydrogen chloride solution is preferably 1 g: 5-7 mL, more preferably 1 g: 5.5-6.5 mL, and more preferably 1 g: 6 mL.

[0053] In the present invention, the mass concentration of the hydrogen fluoride solution in step 3) is preferably 38-42%, more preferably 39-41%, and more preferably 40%. The mass volume ratio of the residue S2 and the hydrogen fluoride solution is preferably 1 g: 6.5-8.5 mL, more preferably 1 g: 7-8 mL, and more preferably 1 g: 7.5 mL.

[0054] In the present invention, the magnesium chloride (MgCl2) solution and the hydrogen chloride (HCl) solution are preferably placed in a glass conical bottle; the hydrogen fluoride (HF) solution is preferably placed in a polytetrafluoroethylene beaker with a cover.

[0055] In the present invention, when the coal sample S0 is added in step 1), the temperature of the magnesium chloride solution is preferably 45-55°C, more preferably 48-52°C, more preferably 50°C, and the rotation speed is preferably 470-530r / min, more preferably 500r / min;

[0056] Step 2) When adding the residue S1, the temperature of the hydrogen chloride solution is preferably 45-55°C, more preferably 48-52°C, more preferably 50°C, and the rotation speed is preferably 470-530 r / min, more preferably 500 r / min;

[0057] In step 3), when the residue S2 is added, the temperature of the hydrogen fluoride solution is preferably 45-55° C., more preferably 48-52° C., more preferably 50° C., and the rotation speed is preferably 470-530 r / min, more preferably 500 r / min.

[0058] In the present invention, the stirring speed in step 1) to step 3) is independently preferably 470-530 r / min, and more preferably 500 r / min; the stirring temperature is independently preferably 45-55°C, more preferably 48-52°C, and more preferably 50°C; the stirring time is independently preferably 10-14h, more preferably 11-13h, and more preferably 12h.

[0059] In steps 1) to 3) of the present invention, it is preferred that the filtrate is filtered until the pH value of the filtrate is 7; the drying temperature is independently preferably 55 to 65°C, more preferably 58 to 62°C, more preferably 60°C, and the drying time is independently preferably 18 to 48h, more preferably 24 to 36h, more preferably 24h.

[0060] In the present invention, the power of the plasma low-temperature ashing in step 4) is preferably 100-300 W, more preferably 150-250 W, and more preferably 200 W. The plasma low-temperature ashing to constant weight is preferably weighed once every 2 hours until the change between two weighings is ≤1%.

[0061] In the present invention, step 5) determines the contents of sulfur and mercury in the raw coal S0, residue S1, residue S2, residue S3 and low-temperature ash SP, and multiplies the measured sulfur content and mercury content in the five substances by the leaching yield and the ash residue standardized sulfur content and mercury content, and obtains the sulfur content and mercury content in five different occurrence forms in the coal by stepwise difference subtraction.

[0062] In the present invention, the five different occurrence forms of sulfur and mercury in coal are exchangeable sulfur and mercury, HCl-soluble sulfur and mercury, HF-soluble sulfur and mercury, organic sulfur and organically bound mercury, sulfide sulfur and sulfide-bound mercury.

[0063] In the present invention, the measured sulfur content and mercury content in the five substances are multiplied by the leaching yield and the ash residue standardized sulfur content and mercury content, and the specific calculation method for obtaining the sulfur content and mercury content in five different occurrence forms in coal by step-by-step difference subtraction is as follows: 1) Calculation of standardized mercury content: standardized mercury content in MDCDS1=mercury content in MDCDS1×leaching yield of MDCDS1, standardized mercury content in MDCDS2=mercury content in MDCDS2×leaching yield of MDCDS1×leaching yield of MDCDS2, standardized mercury content in MDCDS3=mercury content in MDCDS3×leaching yield of MDCDS1×leaching yield of MDCDS2×leaching yield of MDCDS3; standardized mercury content in MDCDSP=mercury content in MDCDSP×leaching yield of MDCDS1×leaching yield of MDCDS2×leaching yield of MDCDS3×ash residue of MDCDSP;

[0064] 2) The mercury content in different occurrence forms is obtained by subtracting the standardized mercury content: exchangeable mercury content = mercury content in MDCD - standardized mercury content in MDCDS1, HCl soluble mercury content = standardized mercury content in MDCDS1 - standardized mercury content in MDCDS2, HF soluble mercury content = standardized mercury content in MDCDS2 - standardized mercury content in MDCDS3, organically bound mercury content = standardized mercury content in MDCDS3 - standardized mercury content in MDCDSP, sulfide bound mercury content = standardized mercury content in MDCDSP.

[0065] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0066] In the embodiment, magnesium chloride (MgCl2) solution and hydrogen chloride (HCl) solution are placed in a glass conical bottle; hydrogen fluoride (HF) solution is placed in a polytetrafluoroethylene beaker with a lid; a glass suction filtration bottle and a ceramic Büchner funnel are used for suction filtration after leaching the magnesium chloride solution and the hydrogen chloride solution, and a polytetrafluoroethylene suction filtration bottle and a Büchner funnel are used for suction filtration after leaching the hydrogen fluoride solution;

[0067] In the embodiment, MDCD raw coal, HDG clean coal and MHJ raw coal are respectively from Hujierte Mining Area Coal Mine in Ordos, Inner Mongolia, Heidaigou Coal Mine in Ordos, Inner Mongolia and Meihuajing Coal Mine in Yinchuan, Ningxia; the coal samples are air-dried, ground, sieved to 0.1-1 mm, and stored in a dryer for later use.

[0068] Figure 1 The pyrite morphology of MDCD raw coal, HDG clean coal and MHJ raw coal under an optical microscope is shown in FIG. Figure 1 It can be seen that MDCD coal mainly contains coarse-grained pyrite with a particle size greater than 60μm, HDG coal mainly contains fine-grained pyrite with a particle size less than 60μm after washing, and MHJ coal contains both coarse-grained pyrite and fine-grained pyrite.

[0069] Example 1

[0070] This example analyzes the contents of sulfur and mercury in different occurrence forms in MDCD raw coal.

[0071] Add 25mL of 1mol / L MgCl2 solution to a 50mL conical flask, add 5g of MDCD raw coal to the conical flask while stirring at 500r / min at 50℃, mix evenly, and continue stirring at 50℃ for 12h for leaching. After leaching, filter and wash until the pH value of the filtrate is 7, and place the filter cake in a forced air drying oven at 60℃ for 24h. The dried sample is named MDCDS1 and sealed for storage.

[0072] Add 24 mL of 18-19% HCl solution to a 50 mL conical flask, add 4 g of MDCDS1 to the conical flask while stirring at 500 r / min at 50°C, mix well, and continue stirring at 50°C for 12 hours for leaching. After leaching, filter and wash until the pH value of the filtrate is 7, and dry the filter cake in a forced air drying oven at 60°C for 24 hours. The dried sample is named MDCDS2 and sealed for later use.

[0073] Add 22.5 mL of 40% HF solution to a 50 mL polytetrafluoroethylene beaker, add 3 g of MDCDS2 to a conical flask while stirring at 500 r / min at 50 ° C, mix well, and continue stirring at 50 ° C for 12 hours for leaching. After leaching, filter and wash until the pH value of the filtrate is 7, and place the filter cake in a forced air drying oven at 60 ° C for 24 hours. The dried sample is named MDCDS3 and sealed for storage.

[0074] Place 1 g of MDCDS3 in a plasma low-temperature ashing instrument and ash to constant weight at a power of 200 W (weigh once every 2 hours, and the change between two consecutive weighings is ≤1%) to obtain low-temperature ash MDCDSP and seal it for future use.

[0075] The sulfur and mercury contents in MDCD, MDCDS1, MDCDS2, MDCDS3 and MDCDSP were determined using a high-frequency carbon-sulfur analyzer (HCS-140) and a Lumex RA-915 mercury analyzer solid accessory (Pyro915+), respectively. The determined sulfur and mercury contents were multiplied by the leaching yield and the ash residue-normalized sulfur and mercury contents, and the sulfur and mercury contents in different occurrence forms in MDCD coal were obtained by stepwise subtraction.

[0076] Figure 2 The content ratio of sulfur and mercury in different occurrence forms in MDCD coal is analyzed for Example 1. Figure 2 It can be seen that the main occurrence forms of sulfur in MDCD coal are sulfide sulfur (41.6%), HCl-soluble sulfur (32.8%) and organic sulfur (15.1%); the main occurrence forms of mercury in MDCD coal are sulfide-bound mercury (50.2%), HCl-soluble mercury (30.8%) and organic-bound mercury (15.3%); the exchangeable sulfur and mercury, HF-soluble sulfur and mercury in coal account for a small proportion.

[0077] Comparative Example 1

[0078] The power of plasma low-temperature ashing of MDCDS3 in Example 1 was changed from 200 W to 150 W and 250 W respectively, and the other conditions were the same as in Example 1.

[0079] The ashing times for ashing powers of 150 W, 200 W and 250 W are 120 h, 72 h and 48 h respectively. With the increase of ashing power, the ashing time decreases gradually. Figure 3 The XRD spectra of low temperature ash under different ashing power conditions of Example 1 and Comparative Example 1 are shown in FIG. Figure 3It can be seen that the bulge peak attributed to carbon in the 150W low-power ash has not completely disappeared, proving that the ashing is incomplete at this power; the bulge peak attributed to carbon in the 200W low-power ash has completely disappeared, leaving only the diffraction peak of pyrite, and the intensity of the diffraction peak of pyrite has increased; when the ashing power is 250W, the intensity of the diffraction peak of pyrite begins to weaken, and at this power the mineral crystal structure has changed, the symmetry and integrity of the mineral peak have deteriorated, and destructive interference occurs between the distances between the reflection surfaces, resulting in a significant decrease in the intensity of the diffraction peak. The best ashing power is 200W between ashing efficiency and avoiding high-temperature mineral evolution.

[0080] Example 2

[0081] This example analyzes the contents of sulfur and mercury in different occurrence forms in HDG clean coal.

[0082] Add 25mL of 1mol / L MgCl2 solution to a 50mL conical flask, add 5g HDG clean coal to the conical flask while stirring at 500r / min at 50℃, mix evenly, and continue stirring at 50℃ for 12h for leaching. After leaching, filter and wash until the pH value of the filtrate is 7, and place the filter cake in a forced air drying oven at 60℃ for 24h. The dried sample is named HDGS1 and sealed for storage.

[0083] Add 24 mL of 18-19% HCl solution to a 50 mL conical flask, add 4 g of HDGS1 to the conical flask while stirring at 500 r / min at 50°C, mix well, and continue stirring at 50°C for 12 hours for leaching. After leaching, filter and wash until the pH value of the filtrate is 7, and place the filter cake in a forced air drying oven at 60°C for 24 hours. The dried sample is named HDGS2 and sealed for storage.

[0084] Add 22.5 mL of 40% HF solution to a 50 mL polytetrafluoroethylene beaker, add 3 g of HDGS2 to a conical flask while stirring at 500 r / min at 50°C, mix well, and continue stirring at 50°C for 12 h for leaching. After leaching, filter and wash until the pH value of the filtrate is 7, and place the filter cake in a forced air drying oven at 60°C for 24 h. The dried sample is named HDGS3 and sealed for storage.

[0085] Place 1 g of HDGS3 in a plasma low-temperature ashing instrument and ash to constant weight at a power of 200 W (weigh once every 2 hours, and the change between two consecutive weighings is ≤1%) to obtain low-temperature ash HDGSP and seal it for future use.

[0086] The sulfur and mercury contents in HDG, HDGS1, HDGS2, HDGS3 and HDGSP were determined using a high-frequency carbon-sulfur analyzer (HCS-140) and a Lumex RA-915 mercury analyzer solid accessory (Pyro915+), respectively. The determined sulfur and mercury contents were multiplied by the leaching yield and the ash residue-normalized sulfur and mercury contents, and the sulfur and mercury contents in different occurrence forms in HDG coal were obtained by stepwise subtraction.

[0087] Figure 4 The content ratio of sulfur and mercury in different occurrence forms in HDG coal is analyzed for Example 2. Figure 4 It can be obtained that the main occurrence forms of sulfur in HDG coal are organic sulfur (66.8%) and sulfide sulfur (18.8%); the main occurrence forms of mercury in HDG coal are organically bound mercury (74.4%) and sulfide bound mercury (16.5%); the exchangeable sulfur and mercury, HCl-soluble sulfur and mercury, and HF-soluble sulfur and mercury in coal account for a small proportion.

[0088] Comparative Example 2

[0089] The temperature at which the HF solution was used to extract HDGS2 in Example 2 was changed from 50°C to 25°C, and the other conditions were the same as in Example 2.

[0090] Figure 5 The XRD spectra of HDGS3 obtained at different HF leaching temperatures in Example 2 and Comparative Example 2, as well as the raw coal and HDGS2, are shown in FIG. Figure 5 It can be seen that the boehmite in HDGS2 cannot be completely leached using HF solution at room temperature (25°C), but the boehmite in HDGS2 can be completely leached using HF solution at 50°C.

[0091] Example 3

[0092] This example analyzes the contents of sulfur and mercury in different occurrence forms in MHJ raw coal.

[0093] Add 25 mL of 1 mol / L MgCl2 solution to a 50 mL conical flask, add 5 g of MHJ raw coal to the conical flask while stirring at 500 r / min at 50 ° C, mix evenly, and continue stirring at 50 ° C for 12 hours for leaching. After leaching, filter and wash until the pH value of the filtrate is 7, and place the filter cake in a forced air drying oven at 60 ° C for 24 hours. The dried sample is named MHJS1 and sealed for storage.

[0094] Add 24 mL of 18-19% HCl solution to a 50 mL conical flask, add 4 g of MHJS1 to the conical flask while stirring at 500 r / min at 50°C, mix well, and continue stirring at 50°C for 12 h for leaching. After leaching, filter and wash until the pH value of the filtrate is 7, and dry the filter cake in a forced air drying oven at 60°C for 24 h. The dried sample is named MHJS2 and sealed for later use.

[0095] Add 22.5 mL of 40% HF solution to a 50 mL polytetrafluoroethylene beaker, add 3 g of MHJS2 to a conical flask while stirring at 500 r / min at 50 ° C, mix well, and continue stirring at 50 ° C for 12 hours for leaching. After leaching, filter and wash until the pH value of the filtrate is 7, and place the filter cake in a forced air drying oven at 60 ° C for 24 hours. The dried sample is named MHJS3 and sealed for storage.

[0096] Place 1 g of MHJS3 in a plasma low-temperature ashing instrument and ash to constant weight at a power of 200 W (weigh once every 2 hours, and the change between two consecutive weighings is ≤1%) to obtain low-temperature ash MHJSP and seal it for future use.

[0097] The sulfur and mercury contents in MHJ, MHJS1, MHJS2, MHJS3 and MHJSP were determined using a high-frequency carbon-sulfur analyzer (HCS-140) and a Lumex RA-915 mercury analyzer solid accessory (Pyro915+), respectively. The determined sulfur and mercury contents were multiplied by the leaching yield and the ash residue-normalized sulfur and mercury contents, and the sulfur and mercury contents in different occurrence forms in MHJ coal were obtained by stepwise subtraction.

[0098] Figure 6 The content ratio of sulfur and mercury in different occurrence forms in MHJ coal is analyzed for Example 3. Figure 6 It can be seen that the main occurrence forms of sulfur in MHJ coal are sulfide sulfur (48.4%) and organic sulfur (26.8%); the main occurrence forms of mercury in MHJ coal are sulfide-bound mercury (60.8%) and organic-bound mercury (29.5%); the exchangeable sulfur and mercury, HCl-soluble sulfur and mercury, and HF-soluble sulfur and mercury in coal account for a small proportion.

[0099] Comparative Example 3

[0100] The difference between this comparative example and Example 3 is that plasma low-temperature ashing is placed before step-by-step chemical leaching, and the specific steps are as follows:

[0101] 1 g of MHJ raw coal was placed in a plasma low-temperature ashing instrument and ashed to constant weight at a power of 200 W. After 13 times of ashing, low-temperature ash MHJSP was obtained and sealed and stored for later use.

[0102] Add 15 mL of 1 mol / L MgCl2 solution to a 50 mL conical flask, add 3 g of MHJSP to the conical flask while stirring at 500 r / min at 50 ° C, mix well, and continue stirring at 50 ° C for 12 h for leaching. After leaching, filter and wash until the pH value of the filtrate is 7, and place the filter cake in a forced air drying oven at 60 ° C for 24 h. The dried sample is named MHJS1 and sealed for storage.

[0103] Add 12mL of 18-19% HCl solution to a 50mL conical flask, add 2g of MHJS1 to the conical flask while stirring at 500r / min at 50°C, mix well, and continue stirring at 50°C for 12h for leaching. After leaching, filter and wash until the pH value of the filtrate is 7, and dry the filter cake in a forced air drying oven at 60°C for 24h. The dried sample is named MHJS2 and sealed for later use.

[0104] Add 7.5 mL of 40% HF solution to a 50 mL polytetrafluoroethylene beaker, add 1 g of MHJS2 to a conical flask while stirring at 500 r / min at 50°C, mix well, and continue stirring at 50°C for 12 h for leaching. After leaching, filter and wash until the pH value of the filtrate is 7, and dry the filter cake in a forced air drying oven at 60°C for 24 h. The dried sample is named MHJS3 and sealed for later use.

[0105] The sulfur and mercury contents in MHJ, MHJSP, MHJS1, MHJS2 and MHJS3 were determined by high-frequency carbon-sulfur analyzer (HCS-140) and Lumex RA-915 mercury analyzer solid accessories (Pyro915+), respectively. The determined sulfur and mercury contents were multiplied by the leaching yield and the ash residue-normalized sulfur and mercury contents, and the sulfur and mercury contents in different occurrence forms in MHJ coal were obtained by step-by-step subtraction.

[0106] Figure 8 For comparative example 3, the content ratio of sulfur and mercury in different occurrence forms in MHJ coal is analyzed. Figure 6 Comparative analysis shows that the contents of exchangeable sulfur and mercury are reduced, while the contents of organic sulfur and organically bound mercury are increased. The reason is that under the condition of 200W, the exchangeable sulfur and mercury with low thermal stability are decomposed and released. In addition, the amount of coal ashed by plasma low-temperature ashing is at most 1g, and the obtained low-temperature ash needs to be chemically leached step by step, which requires multiple low-temperature ashings and takes a long time. Therefore, the present invention places plasma low-temperature ashing after step-by-step chemical leaching for better effect.

[0107] Comparative Example 4

[0108] In this comparative example, MDCD raw coal with a particle size less than 200 μm was selected to observe the morphology of pyrite under an optical microscope, and other conditions were the same as those in Example 1.

[0109] The pyrite morphology of the MDCD raw coal in Comparative Example 4 under an optical microscope is as follows: Fig. 9 As shown, through Figure 1 Comparative analysis shows that the pyrite in MDCD coal with a particle size less than 200 μm is severely broken and cannot objectively reflect the occurrence form of pyrite in coal.

[0110] Comparative Example 5

[0111] This comparative example is the same as Example 1, except that the plasma low-temperature ashing is replaced by HNO3 solution leaching, and the different occurrence forms of sulfur and mercury in the MDCD raw coal are analyzed.

[0112] The difference from Example 1 is that 35 mL of HNO3 solution with a mass concentration of 9.3-9.7% is added to a 50 mL conical flask, 1 g of MDCDS3 is added to the conical flask while stirring at a speed of 500 r / min at 50°C, and after mixing evenly, stirring is continued at 50°C for 12 hours for leaching. After the leaching is completed, the filtrate is filtered and washed until the pH value of the filtrate is 7, and the filter cake is placed in a blast drying oven at 60°C and dried for 24 hours. The dried sample is named MDCDS4 and sealed and stored for later use.

[0113] Fig.10 The morphology of pyrite of MDCDS4 of Comparative Example 5 under an optical microscope is shown in FIG. Fig.10 It can be seen that MDCDS4 does not contain pyrite after nitric acid extraction, which proves that nitric acid can effectively extract coarse-grained pyrite in coal.

[0114] Fig.11 For comparative example 5, the content ratio of sulfur and mercury in different occurrence forms in MDCD raw coal is analyzed. Fig.11 It can be obtained that the main occurrence forms of sulfur in MDCD coal are sulfide sulfur (41.5%), HCl-soluble sulfur (32.8%) and organic sulfur (15.2%); the main occurrence forms of mercury in MDCD coal are sulfide-bound mercury (50.0%), HCl-soluble mercury (30.8%) and organic-bound mercury (15.5%); the exchangeable sulfur and mercury, HF-soluble sulfur and mercury in coal account for a small proportion.

[0115] By comparing the differences between organic sulfur and sulfide sulfur, organic bound mercury and sulfide bound mercury in the MDCD coal obtained in Example 1 and Comparative Example 5, it is found that the sulfide sulfur in the comparative example is 0.1% lower than that in the example, that is, the proportion of fine pyrite in the MDCD coal is 0.1%. The sulfide bound mercury in the comparative example is 0.2% lower than that in the example, indicating that for coal containing only coarse pyrite, the method of the present invention has no obvious advantages over the prior art.

[0116] Comparative Example 6

[0117] This comparative example is the same as Example 2, except that the plasma low-temperature ashing is replaced by HNO3 solution leaching, and the different occurrence forms of sulfur and mercury in the HDG clean coal are analyzed.

[0118] The difference from Example 2 is that 35 mL of HNO3 solution with a mass concentration of 9.3-9.7% is added to a 50 mL conical flask, 1 g of HDGS3 is added to the conical flask while stirring at 500 r / min at 50°C, and after mixing evenly, stirring is continued at 50°C for 12 hours for leaching. After the leaching is completed, the filtrate is filtered and washed until the pH value of the filtrate is 7, and the filter cake is placed in a blast drying oven at 60°C for 24 hours. The dried sample is named HDGS4 and sealed for storage.

[0119] Fig.12 The morphology of pyrite of HDGS4 of Comparative Example 6 under an optical microscope is shown in FIG. Fig.12 It can be seen that HDGS4 contains fine-grained pyrite after nitric acid leaching, which proves that nitric acid cannot completely leach the fine-grained pyrite in coal.

[0120] Fig.13 For comparative example 6, the content ratio of sulfur and mercury in different occurrence forms in HDG coal is analyzed. Fig.13 It can be seen that the main occurrence form of sulfur in HDG coal is organic sulfur (78.4%); the main occurrence form of mercury in HDG coal is organically bound mercury (79.3%); exchangeable sulfur and mercury, HCl-soluble sulfur and mercury, HF-soluble sulfur and mercury, sulfide sulfur and sulfide-bound mercury in coal account for a small proportion.

[0121] By comparing the differences between organic sulfur and sulfide sulfur, organic bound mercury and sulfide bound mercury in HDG coal obtained in Example 2 and Comparative Example 6, it is found that the sulfide sulfur in the comparative example is 11.6% lower than that in the example, that is, the proportion of fine pyrite in HDG coal is 11.6%. The sulfide bound mercury in the comparative example is 4.9% lower than that in the example, indicating that for clean coal mainly containing fine pyrite, the method of the present invention is more advantageous than the prior art in analyzing the occurrence forms of sulfur and mercury in coal.

[0122] Comparative Example 7

[0123] This comparative example is the same as Example 3, except that the plasma low-temperature ashing is replaced by HNO3 solution leaching, and the different occurrence forms of sulfur and mercury in the MHJ raw coal are analyzed.

[0124] The difference from Example 3 is that 35 mL of HNO3 solution with a mass concentration of 9.3-9.7% is added to a 50 mL conical flask, 1 g of MHJS3 is added to the conical flask while stirring at a speed of 500 r / min at 50°C, and after mixing evenly, stirring is continued at 50°C for 12 hours for leaching. After the leaching is completed, the filtrate is filtered and washed until the pH value of the filtrate is 7, and the filter cake is placed in a blast drying oven at 60°C and dried for 24 hours. The dried sample is named MHJS4 and sealed for storage.

[0125] Fig.14 The morphology of pyrite of MHJS4 of Comparative Example 7 under an optical microscope is shown in FIG. Fig.14 It can be seen that MHJS4 contains fine-grained pyrite after nitric acid leaching, which proves that nitric acid cannot completely leach the fine-grained pyrite in coal.

[0126] Fig.15 For comparative example 7, the content ratio of sulfur and mercury in different occurrence forms in MHJ coal is analyzed. Fig.15 It can be seen that the main occurrence forms of sulfur in MHJ coal are sulfide sulfur (39.4%) and organic sulfur (35.8%); the main occurrence forms of mercury in MHJ coal are sulfide-bound mercury (54.6%) and organic-bound mercury (35.7%); the exchangeable sulfur and mercury, HCl-soluble sulfur and mercury, and HF-soluble sulfur and mercury in coal account for a small proportion.

[0127] By comparing the differences between organic sulfur and sulfide sulfur, organic bound mercury and sulfide bound mercury in the MHJ coal obtained in Example 3 and Comparative Example 7, it is found that the sulfide sulfur in the comparative example is 9.0% lower than that in the example, that is, the proportion of fine-grained pyrite in the MHJ coal is 9.0%. The sulfide bound mercury in the comparative example is 6.2% lower than that in the example, indicating that for coal containing both coarse-grained pyrite and fine-grained pyrite, the method of the present invention is more advantageous than the prior art in analyzing the occurrence forms of sulfur and mercury in coal.

[0128] Comparative Example 8

[0129] This comparative example adopts the national standard method to analyze the form of sulfur in MDCD, HDG and MHJ coals.

[0130] Fig.16For the analysis of the proportion of sulfur in the morphology of MDCD, HDG and MHJ coals in Comparative Example 8, the results of sulfate sulfur, pyrite sulfur and organic sulfur in the three types of coals obtained by the analysis of Comparative Example 8 were compared with the results of HCl-soluble sulfur, sulfide sulfur and organic sulfur in the three types of coals in Examples 1 to 3. It can be found that the sulfate sulfur in the three types of coals is 1.3%, 2.2% and 1.0% larger than the HCl-soluble sulfur, respectively. The reason is that the sulfate in the national standard method includes exchangeable sulfate and acid-soluble Sulfate; pyrite sulfur is 1.8%, 8.1%, and 5.9% smaller than sulfide sulfur, respectively, and organic sulfur is 0.5%, 6.1%, and 4.9% larger, respectively. The reason is that sulfide sulfur includes not only iron-containing sulfides but also non-iron-containing sulfides, and the national standard method only measures iron-containing sulfides. In addition, HDG and MHJ coals both contain fine-grained pyrite, which cannot be completely leached by nitric acid, resulting in a smaller content of sulfide sulfur and sulfide-bound mercury, and a larger content of organic sulfur and organic-bound mercury. This shows that for coal containing fine-grained pyrite, the method of the present invention is more accurate than the prior art in analyzing the form of sulfur in coal.

[0131] Through the analysis and comparison of the embodiments and comparative examples, it can be seen that the present invention can not only subdivide sulfur and mercury in different occurrence forms in coal, but also effectively separate organic matter and fine-grained pyrite in coal through the combined technology of step-by-step chemical leaching and plasma low-temperature ashing, so that the content analysis of sulfur and mercury in different occurrence forms in coal is more accurate, and the purpose of synchronously obtaining the content of sulfur and mercury in different occurrence forms in coal can be achieved, thereby reducing the errors caused by analyzing the forms of sulfur and mercury in coal by different analysis methods.

[0132] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for simultaneously analyzing the occurrence forms of sulfur and mercury in coal containing fine-grained pyrite, characterized in that: The following steps are included: 1) adding the coal sample S0 into the magnesium chloride solution, stirring, filtering and drying in sequence to obtain the residue S1; 2) adding the residue S1 into a hydrogen chloride solution, stirring, filtering and drying in sequence to obtain a residue S2; 3) adding the residue S2 into a hydrogen fluoride solution, stirring, filtering, and drying in sequence to obtain a residue S3; 4) Plasma low-temperature ashing is performed on the residue S3 until the residue S3 reaches a constant weight, thereby obtaining low-temperature ash SP; 5) The contents of sulfur and mercury in coal sample S0, residue S1, residue S2, residue S3 and low-temperature ash SP were determined respectively, and the sulfur content and mercury content in five different occurrence forms in coal were obtained by step-by-step subtraction.

2. The method according to claim 1, characterized in that The coal sample S0 is raw coal containing fine-grained pyrite or clean coal containing fine-grained pyrite, and the particle size of the coal sample S0 is 0.1-1 mm.

3. The method according to claim 1 or 2, characterized in that: Step 1) The molar concentration of the magnesium chloride solution is 0.8-1.2 mol / L, and the mass volume ratio of the coal sample S0 to the magnesium chloride solution is 1 g: 4-6 mL.

4. The method according to claim 3, characterized in that Step 2) The mass concentration of the hydrogen chloride solution is 17-20%, and the mass volume ratio of the residue S1 to the hydrogen chloride solution is 1 g: 5-7 mL.

5. The method according to claim 3, characterized in that: Step 3) The mass concentration of the hydrogen fluoride solution is 38-42%, and the mass volume ratio of the residue S2 to the hydrogen fluoride solution is 1 g: 6.5-8.5 mL.

6. The method according to claim 4 or 5, characterized in that: Step 1) When adding the coal sample S0, the temperature of the magnesium chloride solution is 45-55°C and the rotation speed is 470-530r / min; Step 2) When adding the residue S1, the temperature of the hydrogen chloride solution is 45-55°C and the rotation speed is 470-530 r / min; Step 3) When adding the residue S2, the temperature of the hydrogen fluoride solution is 45-55°C and the rotation speed is 470-530 r / min.

7. The method according to claim 6, characterized in that The stirring speed of steps 1) to 3) is independently 470 to 530 r / min, the stirring temperature is independently 45 to 55° C., and the stirring time is independently 10 to 14 h.

8. The method according to claim 6, characterized in that In step 1) to step 3), the filtrate is filtered until the pH value of the filtrate is 7; the drying temperature is independently 55 to 65° C., and the drying time is independently 18 to 48 hours.

9. The method according to claim 1 or 8, characterized in that: Step 4) The power of the plasma low-temperature ashing is 100-300W, and the plasma low-temperature ashing is performed until constant weight is obtained by weighing once every 2 hours until the change between two weighings is ≤1%.

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