A stepwise chemical extraction method based on the study of the occurrence state of rare earth elements in thermally transformed coal

Abstract

The present invention discloses a stepwise chemical extraction method based on the study of the occurrence state of rare earth elements in thermally transformed coal. The specific steps are as follows: using a variety of reagents (H2O-CH3COONH4-HCl-HNO3-H2O2-HF) and indirectly quantifying the occurrence state of rare earth elements in coal through a six-step stepwise chemical extraction system, namely water-soluble state, ion-exchange state, carbonate-bound state, sulfide-bound state, organic-bound state, and aluminosilicate-bound state. The research of the present invention on the indirect method - stepwise chemical extraction experiment for the study of the occurrence state of rare earth elements in thermally transformed coal not only helps to deeply understand the geochemical behavior of rare earth elements in thermally transformed coal, but also provides a reference for the research method of the occurrence state of rare earth elements in coal, and can also provide a scientific basis for the recovery and utilization of rare earth elements, having important environmental and economic significance.

Description

Technical Field

[0001] The present invention relates to the technical field of element extraction and state research, and more specifically, to a step-by-step chemical extraction method for studying the occurrence state of rare earth elements in thermally transformed coal. Background Art

[0002] Rare earth elements (REY) are widely used as geochemical indicators for studying the sedimentary environment and later changes of ore deposits due to their consistency and predictability in geochemical processes. In addition, the excellent magnetic, optical, and electrical properties of rare earth elements play a key role in traditional industries such as military, petrochemical, and metallurgy, as well as emerging fields such as permanent magnets, photovoltaic thin films, and catalysts. Therefore, REY has become an important strategic resource for promoting the upgrading of traditional industries, the development of high-tech industries, and the progress of national defense technology, and its value is irreplaceable.

[0003] The study of the occurrence state of REY in coal is very important. It not only provides us with valuable information on peat deposition, coal diagenesis, the formation of coal-bearing basins, and the evolution of regional geological backgrounds, but also has an important impact on aspects such as coal mining, coal preparation, combustion, and comprehensive utilization in practical applications. In particular, the occurrence patterns of REY in coal and coal ash are crucial for developing methods and technologies for extracting REY from coal or coal ash.

[0004] There are various methods for studying the occurrence state of elements in coal. The specific analysis methods are mainly divided into two categories: indirect methods and direct methods. Among them, indirect methods include statistical analysis (mainly including correlation analysis, cluster analysis, and principal component analysis), float-sink method (or density separation), and step-by-step chemical extraction method; direct methods include optical microscopy, proton-induced X-ray emission (PIXE), high-sensitivity high-resolution ion probe (SHRIMP), transmission electron microscopy (TEM), scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDS), electron probe analysis (EMPA), X-ray photoelectron spectroscopy (XPS), laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), and time-of-flight secondary ion mass spectrometry (TOF-SIMS).

[0005] Researchers' understanding of the occurrence state of REY in coal largely depends on indirect methods such as multivariate statistical analysis and sequential chemical extraction experiments. Based on these analysis methods, elements that are weakly or not correlated with the ash yield, remain in the residual organic matter during sequential chemical extraction, and are enriched in the light components during density separation are generally considered to have organic affinity. However, these methods also have some drawbacks. For example, the correlation analysis method in multivariate statistics may sometimes lead to incorrect understandings and judgments. In some cases, an element with a good correlation with the ash yield may not necessarily indicate that it occurs in minerals. In addition, during sequential chemical extraction and density separation experiments, some elements occur in tiny mineral particles. Because they are wrapped by organic matter and enriched in the organic light components or because they cannot be leached out by acid during sequential chemical extraction, they may be misidentified as occurring in organic matter.

[0006] Researchers' understanding of the occurrence state of rare earth elements in thermally altered coal is still not clear enough. The research methods are not systematic and comprehensive enough, and there are significant differences in viewpoints. Especially for the indirect method of sequential chemical extraction experiments, the extraction methods vary, and the total extraction rates of some elements in various forms do not reach between 80% and 120%. The reliability of the experimental data needs to be considered. Therefore, how to improve sequential extraction to ensure the extraction rate and provide a reliable basis for scientific research is an urgent problem for those skilled in the art. Summary of the Invention

[0007] In view of this, the present invention improves the indirect method - sequential chemical extraction for the study of the occurrence state of REY in thermally altered coal, effectively ensuring the total extraction rate of various forms and improving the reliability of the data.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] A sequential chemical extraction method for studying the occurrence state of rare earth elements in thermally altered coal, comprising the following steps:

[0010] Step 1: Extraction of water-soluble state

[0011] Weigh the coal sample that has been air-dried, decontaminated, ground, and sieved, disperse it in deionized water, seal it, and place it on a shaker for shaking treatment. After the treatment is completed, cool it to room temperature, then filter it by suction to separate. Add deionized water to the filtrate to make up the volume for ICP-MS measurement;

[0012] Step 2: Extraction of ion-exchange state

[0013] Take the solid residue from Step 1, dry it, cool it to room temperature, and disperse it in CH3COONH4 solution. Seal it and place it on a shaker for shaking treatment. After the treatment is completed, cool it to room temperature, then filter it by suction to separate. Add deionized water to the filtrate to make up the volume for ICP-MS measurement;

[0014] Step 3: Extraction of carbonate-bound state

[0015] Dry the solid residue obtained in Step 2, disperse it in dilute HCl after cooling to room temperature, seal it, and place it on a shaker for shaking treatment. After the treatment is completed, cool it to room temperature, then perform suction filtration to separate. Add deionized water to the filtrate to make up the volume for ICP-MS measurement;

[0016] Step 4: Extraction of sulfide-bound state

[0017] Dry the solid residue obtained in Step 3, disperse it in dilute HNO3 after cooling to room temperature, seal it, and heat it for digestion on a hot plate. After the digestion is completed, let it cool naturally to room temperature, then perform suction filtration to separate. Add deionized water to the filtrate to make up the volume for ICP-MS measurement;

[0018] Step 5: Extraction of organic-bound state

[0019] Dry the solid residue obtained in Step 4, disperse it in dilute HNO3 after cooling to room temperature, seal it, and place it on a shaker for shaking treatment. After the treatment is completed, cool it to room temperature, add H2O2, then seal it and set air holes on the seal, and then perform water bath heating for extraction. After the extraction is completed, cool it to room temperature, add CH3COONH4 solution, continue water bath extraction. After the extraction is completed, let it cool naturally to room temperature, then perform suction filtration to separate. Add deionized water to the filtrate to make up the volume for ICP-MS measurement;

[0020] Step 6: Extraction of aluminosilicate-bound state

[0021] Dry and weigh the solid residue obtained in Step 5, then add dilute HNO3 and HF, perform super microwave digestion. After the digestion is completed, transfer the digestion solution to a PFA sample dissolution cup, place it on a hot plate to drive off the acid at 180 °C until it is the size of a soybean, then add 5 mL of HNO3 diluted by 1 time, cover it and extract for 4 h. After cooling, make up the volume with deionized water for ICP-MS testing.

[0022] Preferably, the sieving in Step 1 is through a 200-mesh sieve.

[0023] Preferably, the mass-volume ratio of the coal sample to deionized water in Step 1 is 1 g:30 mL; the shaker treatment parameters in Steps 1 - 3 and 5 are: 18 - 22 °C, 200 r / min, and treat for 12 h.

[0024] Preferably, the drying temperature in Steps 2 - 5 is 50 °C and the time is 6 h.

[0025] Preferably, the concentration of the CH3COONH4 solution in Step 2 is 1 mol / L, and the volume ratio of the CH3COONH4 solution to the deionized water in Step 1 is 1:1.

[0026] Preferably, the concentration of dilute HCl in step 3 is 3%, and the volume ratio of dilute HCl to deionized water in step 1 is 1:1.

[0027] Preferably, the concentration of dilute HNO3 in step 4 is 5%, and the volume ratio of dilute HNO3 to deionized water in step 1 is 1:1; the heating temperature of the hot plate is 180 °C, and the heating digestion time is 30 min.

[0028] Preferably, the concentration of dilute HNO3 in step 5 is 20%, and the volume ratio of dilute HNO3 to deionized water in step 1 is 1:6; the volume ratio of H2O2 to HNO3 is 3:1. After adding H2O2, the water bath temperature is 85 °C, and the extraction time is 5 h; the concentration of CH3COONH4 is 1 mol / L, and the volume ratio of CH3COONH4 to HNO3 is 1:1. After adding CH3COONH4, the water bath temperature is 85 °C, and the extraction time is 5 h.

[0029] Preferably, in step 6, based on the weight of the solid residue, the volume ratio of HNO3 added during the digestion and extraction processes to the sample mass is 100 mL:1 g, the volume ratio of HNO3:HF = 5:2, and HNO3:H2O = 1:1;

[0030] The super microwave digestion procedure is as follows:

[0031] The basic load of the digestion vessel consists of 330 mL of deionized water, 30 mL of 30% H2O2, and 2 mL of 98% H2SO4. The initial nitrogen gas pressure is 50 bar, and the maximum temperature is 240 °C. The microwave digestion procedure is as follows:

[0032]

[0033]

[0034] Preferably, during the suction filtration process in steps 1 - 5, deionized water is used to wash the container, and the washing liquid is filtered together.

[0035] From the above technical solutions, it can be seen that compared with the prior art, the present invention discloses a step-by-step chemical extraction method for studying the occurrence state of rare earth elements in thermally metamorphosed coal, having the following beneficial effects:

[0036] The research of the present invention focuses on the indirect method - step-by-step chemical extraction experiment for studying the occurrence state of rare earth elements in thermally metamorphosed coal. It not only helps to deeply understand the geochemical behavior of rare earth elements in thermally metamorphosed coal, but also provides a reference for the research method of the occurrence state of rare earth elements in coal, and can also provide a scientific basis for the recovery and utilization of rare earth elements, having important environmental and economic significance. Brief Description of the Drawings

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the attached drawings required for the description of the embodiments or the prior art. Obviously, the attached drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other attached drawings can also be obtained according to the provided attached drawings.

[0038] Figure 1 It is the flow chart of the step-by-step chemical extraction experiment of the present invention;

[0039] Figure 2 It is the extraction rate of rare earth elements in the coal sample by the method of Example 1;

[0040] Figure 3 It is the proportion diagram of the step-by-step chemical extraction form of rare earth elements in the coal sample by the method of Example 1;

[0041] Figure 4 It is the extraction rate of rare earth elements in the coal sample of Comparative Example 1;

[0042] Figure 5 It is the diagram of the organic matter situation of the flotation coal sample in Comparative Example 2. Specific embodiments

[0043] The following will clearly and completely describe the technical solutions of the present invention in combination with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0044] Example 1

[0045] Instruments and drugs required for the experiment:

[0046] Balance: accurate to 1.0000 g;

[0047] Polytetrafluoroethylene (PFA) sample dissolution cup;

[0048] 150 mL conical flask; suction filtration device;

[0049] 40% HF (GR), 65% HNO3 (GR), 36% HCl (GR), 98% H2SO4 (GR) purified by sub-boiling distillation through an acid purification system; 30% H2O2 (GR); CH3COONH4 (MOS); deionized water;

[0050] Nylon filter membrane with a diameter of 50 mm and a pore size of 0.45 μm;

[0051] Sample pretreatment: The coal samples collected are first air-dried naturally, and then calcite and other impurity veins are removed with a cutting machine. After crushing, the coal samples are ground into fine particles with an agate mortar and passed through a 200-mesh sieve.

[0052] Specific steps:

[0053] The first step (water-soluble state): Weigh 1 g ± 0.0005 g of coal sample into a 150 mL conical flask (number the conical flask before weighing and record its weight for subsequent calculation of the sample mass involved in each form extraction). Add 30 mL of deionized water, seal it with a sealing film, place it in a shaker, and shake it at 20 ± 2 °C and 200 r / min for 12 h. Then take out the sample, cool it to room temperature, and filter it by suction for separation (number the suction filtration device before suction filtration and record the weight of the bottom conical flask for finally reading the constant volume weight after suction filtration is completed). Wash the conical flask three times with 5 mL of deionized water, filter the three washing solutions together into the extraction solution, and squeeze out a small amount of deionized water with a wash bottle to rinse the liquid splashed on the inner wall of the device during suction filtration, ensuring that all the extracted elements are transferred to the suction filtration liquid as much as possible. Add deionized water to the clear liquid filtered by suction to make the volume up to 50 mL for ICP-MS testing.

[0054] Note: One blank sample and one parallel sample are made simultaneously in the experiment.

[0055] The second step (ion-exchange state): The solid residue in the first step is placed in an oven at 50 °C for about 6 h to ensure complete drying. After cooling to room temperature, scrape all the samples into the corresponding conical flask with a weighing spoon, weigh and record. Add 30 mL of 1 mol / L CH3COONH4, and the oscillation, suction filtration, and volume fixing steps are the same as those in the first step.

[0056] The third step (carbonate-bound state): The solid residue in the second step is placed in an oven at 50 °C for about 6 h to ensure complete drying. After cooling to room temperature, scrape all the samples into the corresponding conical flask with a weighing spoon, weigh and record. Add 30 mL of dilute HCl (3%), and the oscillation, suction filtration, and volume fixing steps are the same as those in the first step.

[0057] The fourth step (sulfide-bound state): The solid residue in the third step is placed in an oven at 50 °C for about 6 h to ensure complete drying. After cooling to room temperature, scrape all the samples into the corresponding conical flask with a weighing spoon, weigh and record. Add 30 mL of dilute HNO3 (5%), seal it with a sealing film, and then place it on a hot plate at 180 °C for digestion for 30 min (after digestion is completed, turn off the hot plate, and wait until it cools to room temperature before taking the conical flask away from the hot plate to prevent the sealing film from being sucked and broken or the conical flask from cracking due to sudden temperature drop). The suction filtration and volume fixing steps are the same as those in the first step.

[0058] Step 5 (Organically bound state): The solid residue in Step 4 is placed in an oven at 50 °C for about 6 h to ensure complete drying. After cooling to room temperature, use a weighing spoon to scrape all the sample into the corresponding conical flask, weigh and record; add 5 mL of dilute HNO3 (20%), seal with a sealing film, place it in a shaker, shake at 20 ± 2 °C and 200 r / min for 12 h; then take out the sample, after cooling to room temperature, add 15 mL, seal with a sealing film and puncture some holes with a syringe, extract at 85 °C in a water bath for 5 h; after cooling to room temperature, add 5 mL of 1 mol / L CH3COONH4, extract at 85 °C in a water bath for 5 h; after cooling to room temperature, the procedures of suction filtration and volume fixation are the same as in Step 1;

[0059] Step 6 (Silicate-aluminate bound state): The solid residue in Step 5 is dried at 50 °C for about 6 h to ensure complete drying. Weigh 0.05 g ± 0.0005 g of the sample into a TFM digestion tube, add 5 mL of HNO3 and 2 mL of HF to the coal sample, and use the UltraClave microwave digester of Milestone Company to carry out digestion according to the set program. Then transfer the digestion solution completely to a 15 mL polytetrafluoroethylene (PFA) sample dissolution cup, evaporate the acid on a hot plate at 180 °C until the size of a soybean, then add 5 mL of HNO3 diluted by 1 time, cover and extract for 4 h, cool, and dilute to 50 mL with deionized water for ICP-MS testing.

[0060] Super microwave digestion program settings:

[0061] The basic load of the digestion tank consists of 330 mL of deionized water, 30 mL of H2O2 and 2 mL of H2SO4. The initial nitrogen pressure is set at 50 bar and the maximum temperature is set at 240 °C. The microwave digestion program is shown in the following table.

[0062] Step Time / h:min:s Temperature / °C Pressure / bar Power / W 1 00：12：00 60 100 1000 2 00：20：00 125 100 1000 3 00：08：00 160 130 1000 4 00：15：00 240 160 1200 5 00：60：00 240 160 1000 Cooling time 00：60：00

[0063] The coal quality data and vitrinite random reflectance (R o,ran ) used in Experiment 1 are shown in Table 1. According to the GB / T15224.1-2018 standard, the ash content (A d ) of the coal samples in the study area varies widely, ranging from extra-low ash coal to extra-high ash coal. The average ash content of the raw coal (LD7-7, LD7-8) not affected by magma is 14.01%, classified as low ash coal. The A d value of the thermally metamorphosed coal (LD7-1 to L7-6) affected by magma fluctuates greatly, ranging from 9.07% to 46.79%, with an average of 21.20%. The average moisture content (M ad ) of the raw coal is 1.92%, while the M ad of the thermally metamorphosed coal ranges from 0.71% to 2.08%, with an average of 1.28%. The volatile matter (V daf) The average value is 34.51%, while the V of the thermally transformed coal daf ranges from 7.69% to 20.03%, with an average value of 13.95%.

[0064] According to the international coal classification standard ISO 11760, the R of the raw coal (LD7-7, LD7-8) samples o,ran has an average value of 0.86% and is classified as medium-rank bituminous coal; the R of the thermally transformed coal (LD7-1 to LD7-6) samples o,ran ranges from 1.39% to 3.83%, with an average value of 2.47%, and its coal rank transitions from medium-rank bituminous coal to high-rank anthracite.

[0065] According to the GB / T 15224.2-2021 standard, the total sulfur content (S t,d ) of the raw coal samples used in the experiment has an average value of 0.2% and is classified as extra-low sulfur coal. In contrast, the total sulfur content (S t,d ) of the thermally transformed coal samples ranges from 0.35% to 3.57%, with an average value of 1.14%.

[0066] Table 1 Proximate analysis and ultimate analysis of coal samples

[0067] Sample number <![CDATA[M ad / %]]> <![CDATA[A d / %]]> <![CDATA[V daf / %]]> <![CDATA[R o,ran / %]]> Coal rank <![CDATA[S t,d / %]]> LD7-1 2.08 46.79 10.77 3.83 High-rank anthracite 3.57 LD7-2 1.86 31.33 7.69 2.64 High-rank anthracite 1.15 LD7-3 0.79 9.07 15.29 2.30 High-rank anthracite 0.66 LD7-4 0.71 16.63 20.03 1.98 Medium-rank bituminous coal 0.35 LD7-5 1.45 11.66 9.98 2.70 High-rank anthracite 0.58 LD7-6 0.77 11.71 19.95 1.39 Medium-rank bituminous coal 0.52 LD7-7 2.05 14.00 34.92 0.85 Medium-rank bituminous coal 0.25 LD7-8 1.78 14.01 34.11 0.87 Medium-rank bituminous coal 0.15

[0068] After adjusting the types and concentrations of the extractants by the method of Example 1, as Figure 2 、 3 shown, the extraction rates of the six-step extraction forms of 15 rare earth elements in the experimental coal samples are basically between 80% - 120%. And through the analysis of the proportion of coal quality and organic-bound state, the present invention not only ensures the normal extraction rate, but also greatly increases the discrimination degree between the organic-bound state and the silicate-aluminate-bound state, and more accurately extracts the rare earth elements associated with the organic components in coal. The proportion of the organic-bound state of rare earth elements in two raw coal samples not affected by magma is higher than that in the thermally transformed coal, and the middle-heavy rare earth elements show stronger organic affinity than the light rare earth elements.

[0069] Comparative Example 1

[0070] The difference from Example 1 is that 5% dilute HNO3 is used as the extractant when extracting the organic-bound rare earth elements in the coal sample in the fifth step.

[0071] The results are as Figure 4 shown. This method seems unable to extract the organic-bound rare earth elements as completely as possible. And this method has certain limitations and cannot ensure that the total extraction rate of rare earth elements in all samples is within the ideal range of 80% - 120%. In addition, there is also uncertainty in distinguishing the organic-bound state and the silicate-aluminate-bound state of rare earth elements by this method, which will affect the accurate assessment of the occurrence state of rare earth elements in coal.

[0072] Comparative Example 2

[0073] Density separation method, using trichloromethane (CHCl3) specific gravity liquid (1.47 g / cm 3 ) to float out the organic matter. The upper and lower layers of the flotation liquid are extracted to obtain organically bound and carbonate-bound states.

[0074] The density of clay minerals is generally 2.4 - 2.6 g / cm 3 , and the density of pyrite is 4.9 - 5.2 g / cm 3 . Therefore, tribromomethane (2.89 g / cm 3 ) is used to separate the clay minerals and pyrite to obtain aluminosilicate-bound and carbonate-bound states.

[0075] However, separation based on density cannot guarantee complete flotation of specific components, and errors are inevitable. Moreover, through experiments, it is found that density separation is not applicable to all coal samples, especially thermally transformed coal samples. Due to the complexity of their coal components, stratification may not occur, or due to the loss of organic matter caused by coal metamorphism, it may even lead to the inability to float out the organic matter from the upper layer of CHCl3, as shown Figure 5 below.

[0076] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other. The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A step-by-step chemical extraction method based on the study of the occurrence state of rare earth elements in coal, characterized in that: The following steps are involved: Step 1: Water-soluble extraction Weigh the coal sample after air-drying, impurity removal, grinding and sieving, disperse it in deionized water, seal it and place it on a shaker for shaking. After the treatment is completed, cool it to room temperature, filter it and separate it. Add deionized water to the filtrate to make up the volume for ICP-MS measurement; Step 2: Ion exchange extraction The solid residue from step 1 is dried, cooled to room temperature, dispersed in an ammonium acetate solution, sealed, and placed on a shaker for shaking. After the treatment, it is cooled to room temperature, then filtered and separated, and the filtrate is fixed to volume with deionized water for ICP-MS measurement; Step 3: Carbonate-bound extraction The solid residue in step 2 is dried, cooled to room temperature, dispersed in dilute hydrochloric acid, sealed, and placed on a shaker for shaking. After the treatment is completed, it is cooled to room temperature, then filtered and separated, and the filtrate is added with deionized water to make up to volume for ICP-MS measurement; Step 4: Sulfide-bound extraction The solid residue in step 3 is dried, cooled to room temperature and then dispersed in dilute nitric acid. After sealing, it is heated on a hot plate for digestion. After digestion, it is naturally cooled to room temperature, then filtered and separated. Deionized water is added to the filtrate to make up the volume for ICP-MS measurement. Step 5: Organically bound state extraction The solid residue in step 4 is dried, cooled to room temperature and then dispersed in dilute nitric acid, sealed and placed on a shaker for shaking, cooled to room temperature after treatment, sealed after adding H2O2 and provided with pores on the seal, then extracted by heating in a water bath, cooled to room temperature after extraction, and then added with ammonium acetate solution, and continued to extract in a water bath, cooled naturally to room temperature after extraction, then filtered and separated, and the filtrate was fixed to volume with deionized water for ICP-MS measurement; Step 6: Aluminosilicate Bound State Extraction Take the solid residue in step 5, dry it and weigh it, then add 65% HNO3 and 40% HF for super microwave digestion. After the digestion is completed, transfer the digestion solution to the PFA sample cup and place it on a hot plate at 180°C to drive the acid until it is almost dry and appears as a white or light yellow-green semi-solid viscous state with a sample droplet diameter of 0.5 cm. Then add 5mL of purified 65% HNO3 and H2O, cover and extract for 4h, cool and make up to volume with deionized water for ICP-MS testing; The amount of HNO3 added during digestion and extraction was 0.1 mL / mg, based on the weight of the solid residue, with a volume ratio of HNO3:HF = 5:2, HNO3:H2O = 1:1; The super microwave digestion program is: The basic load of the digestion tank consisted of 330 ml ultrapure water, 30 ml 30% H2O2 and 2 ml 98% H2SO4, the initial nitrogen pressure was 50 bar, the maximum temperature was 240 °C, and the microwave digestion program was as follows: 。 2. A step-by-step chemical extraction method based on the study of the occurrence state of rare earth elements in coal according to claim 1, characterized in that: The sieving in step 1 is through a 200 mesh sieve.

3. The step-by-step chemical extraction method based on the study of the occurrence state of rare earth elements in coal according to claim 1 is characterized in that: The mass volume ratio of the coal sample to deionized water in step 1 is 1 g / 30 mL; the shaking table treatment parameters in steps 1 to 3 and 5 are: 18-22° C., 200 r / min, and treatment for 12 hours.

4. The step-by-step chemical extraction method based on the study of the occurrence state of rare earth elements in coal according to claim 1 is characterized in that: The drying temperature in step 2 to step 5 is 50° C. and the time is 6 hours.

5. The step-by-step chemical extraction method based on the study of the occurrence state of rare earth elements in coal according to claim 1 is characterized in that: The concentration of the ammonium acetate solution in step 2 is 1 mol / L, and the volume ratio of the ammonium acetate solution to the deionized water in step 1 is 1:

1.

6. The step-by-step chemical extraction method based on the study of the occurrence state of rare earth elements in coal according to claim 1 is characterized in that: The concentration of the dilute hydrochloric acid in step three is 3%, and the volume ratio of the dilute hydrochloric acid to the deionized water in step one is 1:

1.

7. The step-by-step chemical extraction method based on the study of the occurrence state of rare earth elements in coal according to claim 1 is characterized in that: The concentration of the dilute nitric acid in step 4 is 5%, and the volume ratio of the dilute nitric acid to the deionized water in step 1 is 1:1; the heating temperature of the hot plate is 180° C., and the heating digestion time is 30 min.

8. The step-by-step chemical extraction method based on the study of the occurrence state of rare earth elements in coal according to claim 1 is characterized in that: The concentration of dilute nitric acid in step 5 is 20%, the volume ratio of dilute nitric acid to deionized water in step 1 is 1:6; the volume ratio of H2O2 to dilute nitric acid is 3:1, and H2O2 is added. The water bath temperature was 85°C and the extraction time was 5h. The ammonium acetate concentration was 1 mol / L, the volume ratio of ammonium acetate to dilute nitric acid was 1:1, and the water bath temperature was 85°C after adding ammonium acetate, and the extraction time was 5h.

9. The step-by-step chemical extraction method based on the study of the occurrence state of rare earth elements in coal according to claim 1, characterized in that: In the filtration process from step 1 to step 5, the container is washed with deionized water and the washing liquid is filtered together.

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