Method for extracting and detecting boron and molybdenum trace elements in coal gangue

Abstract

This invention relates to the field of coal-based solid waste resource utilization technology, and discloses a method for extracting and detecting trace elements boron and molybdenum in coal gangue, comprising two parallel methods: alkali fusion and acid dissolution. In the alkali fusion method, coal gangue is mixed with anhydrous sodium carbonate at a ratio of 1:8, and the mixture is heated stepwise to 900-920℃ for 30 minutes. The melt is then dissolved in hot water and hydrochloric acid to obtain the test solution. In the acid dissolution method, coal gangue is pretreated by calcination at 550℃, digested with a mixed acid (hydrochloric acid, nitric acid, hydrofluoric acid, and perchloric acid in a volume ratio of 3:1:3:1) at 200℃, and the acid is removed before dissolving in hydrochloric acid to obtain the test solution. The boron and molybdenum contents in both test solutions are determined spectrophotometrically. Boron is determined using the methylimine colorimetric method at a wavelength of 420 nm, and molybdenum is determined using the ammonium thiocyanate extraction method at a wavelength of 470 nm. This invention provides two methods suitable for the extraction and detection of trace elements boron and molybdenum in coal gangue, with advantages of thorough decomposition, good repeatability, and high accuracy.

Description

Technical Field

[0001] This invention relates to the field of coal-based solid waste resource utilization technology, and more specifically, to a method for extracting and detecting trace elements boron and molybdenum in coal gangue. Background Technology

[0002] Coal gangue is a solid waste generated during coal mining and washing, and it is one of the largest industrial solid wastes emitted in my country. Statistics show that the cumulative stockpile of coal gangue in my country has exceeded 5 billion tons, and it continues to increase by hundreds of millions of tons annually. The large-scale stockpiling of coal gangue not only occupies significant land resources but also poses a serious pollution risk to the surrounding environment. In recent years, with the deepening development of the circular economy and green mining concepts, the resource utilization of coal gangue has become a research hotspot.

[0003] Coal gangue contains a variety of trace elements, among which boron (B), molybdenum (Mo), and selenium (Se) have significant resource value. Boron is an essential trace element for plant growth and has wide applications in agricultural production; molybdenum is an important strategic metal widely used in steel, chemical, and electronics industries. Extracting these trace elements from coal gangue can not only realize the resource utilization of solid waste but also alleviate the supply and demand imbalance of related resources.

[0004] However, the extraction and detection of trace elements in coal gangue faces numerous technical challenges. First, the coal gangue matrix is ​​complex, mainly composed of aluminosilicate minerals, and trace elements are often contained within stable mineral lattices, making effective extraction difficult. Second, elements such as boron and molybdenum are easily lost through volatilization or adsorption during sample pretreatment, affecting the accuracy of detection.

[0005] Currently, alkali fusion and acid dissolution are the two main methods for decomposing silicate samples. Alkali fusion (such as sodium carbonate fusion) involves the reaction of sodium carbonate with silicate at high temperatures to produce soluble sodium silicate and sodium aluminate, thereby releasing trace elements from the sample. However, it suffers from problems such as unclear melting conditions and incomplete separation of interfering ions. Acid dissolution (such as tetraacid digestion) uses hydrofluoric acid to disrupt the silicate lattice, releasing trace elements into the solution. However, the digestion conditions significantly affect the repeatability and accuracy of the results, especially the significant differences in digestion effects at different ignition temperatures.

[0006] Therefore, establishing a simple, thorough, and reproducible method for the extraction and detection of trace elements boron and molybdenum in coal gangue is of great significance for the resource utilization of coal gangue. Summary of the Invention

[0007] In view of this, the present invention proposes a method for the extraction and detection of trace elements boron and molybdenum in coal gangue, aiming to solve the problems of incomplete extraction and poor repeatability of trace elements in coal gangue in the current technology.

[0008] To achieve the above objectives, the present invention adopts the following technical solution. This invention proposes a method for extracting and detecting trace elements boron and molybdenum in coal gangue, the method comprising alkali fusion and acid dissolution methods: (1) The alkaline fusion method includes the following steps: The coal gangue sample was mixed with anhydrous sodium carbonate at a mass ratio of 1:8 to obtain a mixed sample. The mixed sample was first heated at 500~600℃ for 10 min, and then heated to 900~920℃ to melt for 30 min to completely decompose the sample and obtain the decomposed sample. Remove the decomposed sample, rotate it while it is still hot to solidify the melt, and transfer the molten material into a beaker; Add hot water and hydrochloric acid to a beaker to completely dissolve the molten metal and obtain the test solution; (2) The acid dissolution method includes the following steps: Coal gangue samples were pretreated by calcination at 550℃ to obtain ashed samples; The ashed sample was placed in a digestion container and a mixed acid of hydrochloric acid, nitric acid, hydrofluoric acid and perchloric acid was added for digestion. The volume ratio of hydrochloric acid, nitric acid, hydrofluoric acid and perchloric acid was 3:1:3:1. The digestion container was heated at 200°C until the sample was completely dissolved. Heat to remove acid until nearly dry, add 6 mol / L hydrochloric acid to dissolve the residue, filter and make up to volume to obtain the test solution; The contents of boron and molybdenum in the test solution are determined by spectrophotometry using either the alkali fusion method or the acid dissolution method.

[0009] Furthermore, in the alkali fusion method, the specific steps for mixing the coal gangue sample with anhydrous sodium carbonate are as follows: place the coal gangue sample in a crucible covered with finely ground anhydrous sodium carbonate, add 7 / 8 of the total amount of anhydrous sodium carbonate to the crucible in several portions, and stir with a glass rod after each addition to ensure uniform mixing. Spread the remaining 1 / 8 of the anhydrous sodium carbonate evenly on the surface of the mixture.

[0010] Furthermore, in the alkali fusion method, the ratio of hydrochloric acid to anhydrous sodium carbonate is 5:1, that is, 20mL of 1:1 hydrochloric acid is added for every 4g of anhydrous sodium carbonate used.

[0011] Furthermore, in the acid dissolution method, the conditions for the calcination pretreatment are as follows: the coal gangue sample is heated to 550°C at a heating rate of 5°C / min to 10°C / min and held for 2h to 4h; the mass-volume ratio of the ashed sample to the mixed acid is 0.1g:10mL to 15mL.

[0012] Furthermore, in the acid dissolution method, the heating digestion time is 6h~8h. If the sample is not completely dissolved during this period, a mixed acid of nitric acid, hydrofluoric acid and perchloric acid is added to continue digestion. The volume ratio of nitric acid, hydrofluoric acid and perchloric acid in the added mixed acid is 1:3:1.

[0013] Furthermore, the determination of boron content in the test solution employs the methylimine colorimetric method, with the specific steps as follows: Add the test solution to saturated BaCO3 solution until a brownish-red precipitate is formed, heat to a gentle boil, filter, and take the filtrate into a volumetric flask; Add ammonium acetate buffer and methylimine colorimetric solution, shake well, dilute with water to the mark, and store at 23°C in the dark for 2 hours. The boron content was determined by colorimetric analysis at a wavelength of 420 nm using a spectrophotometer, and calculated based on the boron standard curve.

[0014] Furthermore, the ammonium acetate buffer solution is prepared by dissolving 150g of ammonium acetate in 240mL of deionized water and slowly adding 75mL of glacial acetic acid and mixing thoroughly; the methylimine colorimetric solution is prepared by dissolving 0.9g of methylimine and 2g of ascorbic acid in 60mL of deionized water, heating to dissolve, and then diluting to 100mL.

[0015] Furthermore, the determination of molybdenum content in the test solution employs the ammonium thiocyanate extraction method, with the specific steps as follows: Take the test solution and place it in a separatory funnel. Add ferric chloride solution, sodium nitrate solution, ammonium thiocyanate solution and stannous chloride solution in sequence, and shake well after each addition. Add purified isopropyl ether, shake for 2-3 minutes, let stand to separate the layers and remove the aqueous phase, transfer the organic phase to a centrifuge tube and centrifuge for 5 minutes to remove trace amounts of water. The molybdenum content was calculated by colorimetric determination at a wavelength of 470 nm using a spectrophotometer, based on the molybdenum standard curve.

[0016] Furthermore, the purification method of the isopropyl ether is as follows: place the isopropyl ether in a separatory funnel, wash it with a mixture of stannous chloride, ammonium thiocyanate and water in a volume ratio of 1:1:1, the volume of the washing solution being 1 / 10 of the volume of the isopropyl ether, shake and let stand to separate the layers, discard the aqueous phase, and then wash with 2 mol / L hydrochloric acid, repeating 4 to 5 times.

[0017] Furthermore, the method also includes the extraction and detection of selenium, with selenium being determined using hydride generation-atomic fluorescence spectrometry or inductively coupled plasma mass spectrometry.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention provides two parallel methods for the extraction and detection of trace elements boron and molybdenum in coal gangue, which can be flexibly selected according to laboratory conditions and sample characteristics, and have strong applicability.

[0019] 2. In this invention, the alkali fusion method optimizes the melting conditions and adopts stepwise heating melting, which effectively avoids sample splashing, ensures that the melting reaction is fully carried out, decomposition is thorough, and the element recovery rate is high.

[0020] 3. In this invention, the acid dissolution method was first discovered to have the best repeatability for the extraction of boron and molybdenum under the four-acid digestion method under the 550℃ ignition condition, which is significantly better than the 830℃ ignition condition. This provides a key basis for the selection of pretreatment conditions for the accurate detection of trace elements in coal gangue.

[0021] 4. Both the alkali fusion method and the acid dissolution method described in this invention combine mature spectrophotometric detection technology, are easy to operate, low in cost, and suitable for the analysis and testing of batch samples. Attached Figure Description

[0022] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a comparison chart of the melting results of different alkali fluxes in the alkali fusion method of this invention.

[0023] Figure 2 This is a comparison chart showing the results of extracting boron using the tetraacid digestion method under calcination conditions of 550℃ and 830℃ in the acid dissolution method of this invention.

[0024] Figure 3 This is a comparison chart showing the results of extracting molybdenum using the tetraacid digestion method under calcination conditions of 550℃ and 830℃ in the acid dissolution method of this invention. Detailed Implementation

[0025] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0026] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included within this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0027] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0028] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0029] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0030] This invention proposes a method for extracting and detecting trace elements boron and molybdenum in coal gangue, the method comprising alkali fusion and acid dissolution methods: (1) The alkaline fusion method includes the following steps: The coal gangue sample was mixed with anhydrous sodium carbonate at a mass ratio of 1:8 to obtain a mixed sample. The mixed sample was first heated at 500~600℃ for 10 min, and then heated to 900~920℃ to melt for 30 min to completely decompose the sample and obtain the decomposed sample. Remove the decomposed sample, rotate it while it is still hot to solidify the melt, and transfer the molten material into a beaker; Add hot water and hydrochloric acid to a beaker to completely dissolve the molten metal and obtain the test solution; (2) The acid dissolution method includes the following steps: Coal gangue samples were pretreated by calcination at 550℃ to obtain ashed samples; The ashed sample was placed in a digestion container and a mixed acid of hydrochloric acid, nitric acid, hydrofluoric acid and perchloric acid was added for digestion. The volume ratio of hydrochloric acid, nitric acid, hydrofluoric acid and perchloric acid was 3:1:3:1. The digestion container was heated at 200°C until the sample was completely dissolved. Heat to remove acid until nearly dry, add 6 mol / L hydrochloric acid to dissolve the residue, filter and make up to volume to obtain the test solution; The contents of boron and molybdenum in the test solution are determined by spectrophotometry using either the alkali fusion method or the acid dissolution method.

[0031] In this invention, the specific steps for mixing the coal gangue sample with anhydrous sodium carbonate in the alkali fusion method are as follows: the coal gangue sample is placed in a crucible covered with finely ground anhydrous sodium carbonate, and 7 / 8 of the total amount of anhydrous sodium carbonate is added to the crucible in several portions. After each addition, the mixture is stirred with a glass rod to ensure uniform mixing. The remaining 1 / 8 of the anhydrous sodium carbonate is spread evenly on the surface of the mixture.

[0032] In this invention, the ratio of hydrochloric acid to anhydrous sodium carbonate in the alkali fusion method is 5:1, that is, 20mL of 1:1 hydrochloric acid is added for every 4g of anhydrous sodium carbonate used.

[0033] This invention incorporates anhydrous sodium carbonate in the alkaline fusion method. The anhydrous sodium carbonate completely releases boron and molybdenum from the aluminosilicate lattice of coal gangue. At high temperatures (900-920°C), it reacts with the aluminosilicate matrix of coal gangue to generate soluble sodium silicate and sodium aluminate, completely disintegrating the stable mineral structure and releasing the boron and molybdenum trace elements trapped within the lattice. It forms a eutectic system with the coal gangue, lowering the sample melting temperature and ensuring complete melting and decomposition, thus avoiding incomplete decomposition leading to low element extraction rates. The anhydrous sodium carbonate also maintains the alkalinity of the molten system, converting boron and molybdenum into soluble salts, reducing element volatilization and loss, and improving the detection recovery rate. Furthermore, layered spreading and staged mixing increase the contact area with the sample, preventing uneven local reactions and ensuring complete melting and stable results.

[0034] In this invention, the conditions for the calcination pretreatment in the acid dissolution method are as follows: the coal gangue sample is heated to 550°C at a heating rate of 5°C / min to 10°C / min and kept at that temperature for 2h to 4h; the mass-volume ratio of the ashing sample to the mixed acid is 0.1g:10mL to 15mL.

[0035] In this invention, the acid dissolution method involves heating and digestion for 6 to 8 hours. If the sample is not completely dissolved during this period, a mixture of nitric acid, hydrofluoric acid, and perchloric acid is added to continue the digestion. The volume ratio of nitric acid, hydrofluoric acid, and perchloric acid in the added mixture is 1:3:1.

[0036] In this invention, the order of adding the mixed acids is as follows: hydrochloric acid is added, followed by nitric acid, then hydrofluoric acid, and finally perchloric acid.

[0037] This invention incorporates a mixed acid in the acid dissolution method, comprising hydrochloric acid, nitric acid, hydrofluoric acid, and perchloric acid. Hydrofluoric acid strongly disrupts the aluminosilicate mineral lattice of coal gangue, breaking down the silicon-oxygen tetrahedral structure and completely releasing the boron and molybdenum encased in the lattice. Nitric acid strongly oxidizes and decomposes reducing components such as organic matter and sulfides in coal gangue, preventing element adsorption or reduction loss. Hydrochloric acid provides a strongly acidic medium, dissolving metal oxides and salts, converting boron and molybdenum into soluble ionic states, and stabilizing the analyte. Perchloric acid deeply oxidizes residual impurities at high temperatures, while simultaneously helping to eliminate hydrofluoric acid, removing matrix interference, and ensuring accurate subsequent spectrophotometric detection.

[0038] In this invention, the endpoint of heating to remove acid to near dryness is: the digestion solution evaporates until there is no free acid liquid, and a yellow wet salt-like solid residue remains, with no obvious liquid flow, and does not evaporate to completely dry and crack, so as to avoid the loss of boron and molybdenum elements due to complete evaporation.

[0039] In this invention, the test solution is filtered through a 0.45μm filter membrane and then diluted to a 25mL volumetric flask.

[0040] In this invention, the determination of boron content in the test solution employs the methylimine colorimetric method, and the specific steps are as follows: Add the test solution to saturated BaCO3 solution until a brownish-red precipitate is formed, heat to a gentle boil, filter, and take the filtrate into a volumetric flask; Add ammonium acetate buffer and methylimine colorimetric solution, shake well, dilute with water to the mark, and store at 23°C in the dark for 2 hours. The boron content was determined by colorimetric analysis at a wavelength of 420 nm using a spectrophotometer, and calculated based on the boron standard curve.

[0041] In this invention, the ammonium acetate buffer solution is prepared by dissolving 150g of ammonium acetate in 240mL of deionized water and slowly adding 75mL of glacial acetic acid and mixing thoroughly; the methylimine colorimetric solution is prepared by dissolving 0.9g of methylimine and 2g of ascorbic acid in 60mL of deionized water, heating to dissolve and then diluting to 100mL.

[0042] In this invention, the determination of molybdenum content in the test solution is performed using the ammonium thiocyanate extraction method, and the specific steps are as follows: Take the test solution and place it in a separatory funnel. Add ferric chloride solution, sodium nitrate solution, ammonium thiocyanate solution and stannous chloride solution in sequence, and shake well after each addition. Add purified isopropyl ether, shake for 2-3 minutes, let stand to separate the layers and remove the aqueous phase, transfer the organic phase to a centrifuge tube and centrifuge for 5 minutes to remove trace amounts of water. The molybdenum content was calculated by colorimetric determination at a wavelength of 470 nm using a spectrophotometer, based on the molybdenum standard curve.

[0043] In this invention, the purification method of the isopropyl ether is as follows: the isopropyl ether is placed in a separatory funnel and washed with a mixture of stannous chloride, ammonium thiocyanate and water in a volume ratio of 1:1:1, the volume of the washing solution being 1 / 10 of the volume of the isopropyl ether. After shaking and allowing the layers to separate, the aqueous phase is discarded, and then washed with 2 mol / L hydrochloric acid. This process is repeated 4 to 5 times.

[0044] The alkaline fusion method provided by this invention optimizes the fusion conditions and employs a stepwise heating and melting method. First, the sample is preheated at 500-600℃ to allow for a preliminary reaction with sodium carbonate, then the temperature is increased to 900-920℃ for complete melting. This effectively avoids sample splashing at high temperatures and ensures a thorough melting reaction. After the melt solidifies while hot, it is dissolved in hot water and hydrochloric acid. The reaction of sodium carbonate with hydrochloric acid generates a large amount of CO2 gas, which helps to disperse and dissolve the molten material. This method effectively destroys the aluminosilicate structure of coal gangue, achieving complete extraction of boron and molybdenum, and has the advantages of thorough decomposition and high element recovery rate.

[0045] The acid dissolution method provided by this invention systematically studies the effect of different ignition temperatures on the digestion effect of coal gangue samples. It verifies that high-temperature ignition (830℃) destroys the stability of the extraction process, while ignition at 550℃ can effectively balance the relationship between organic matter removal and element retention, which not only fully destroys the organic matter structure of coal gangue, but also avoids the volatilization loss of target elements.

[0046] The test solutions obtained by the two methods described in this invention are all measured for boron and molybdenum content using the same spectrophotometric method, ensuring the comparability of the test results.

[0047] In this invention, the method further includes the extraction and detection of selenium, which is determined by hydride generation-atomic fluorescence spectrometry or inductively coupled plasma mass spectrometry.

[0048] In this invention, unless otherwise specified, all raw materials required for preparation are commercially available products well known to those skilled in the art.

[0049] The following is in conjunction with the appendix Figure 1-3 The embodiments and examples provide a detailed description of the technical solutions provided by the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0050] Example 1: Extraction of boron and molybdenum by alkaline fusion Take 0.2 g of coal gangue sample (accurate to 0.0001 g) and place it in a platinum crucible lined with finely ground anhydrous sodium carbonate. Separately weigh 1.6 g of anhydrous sodium carbonate, adding 1.4 g in several portions to the crucible, stirring with a glass rod after each addition to ensure thorough mixing. Spread the remaining 0.2 g of anhydrous sodium carbonate evenly on the surface of the mixture. Place the crucible in a muffle furnace and heat at 550 °C for 10 min, then increase the temperature to 920 °C for 30 min to melt. Remove the crucible and observe while hot. A concave shape, uniform surface, and absence of air bubbles and insoluble matter indicate complete melting. Rotate the crucible while hot to solidify the melt on the crucible wall, then transfer the molten material to a 25 mL beaker. Clean the crucible with a small amount of hot water and a 1:1 hydrochloric acid solution, scrub the crucible wall with a glass rod with a rubber tip, and cover with a watch glass to completely dissolve the molten material. This solution is the test solution.

[0051] Example 2: Extraction of boron and molybdenum by acid dissolution Take a coal gangue sample, crush and grind it, then pass it through a 100-mesh sieve and mix it thoroughly. Spread the pretreated coal gangue sample evenly in a ceramic boat, place it in a muffle furnace, and heat it to 550℃ at a heating rate of 8℃ / min, holding it at that temperature for 3 hours. After cooling, obtain an ashed sample. Weigh 0.1g of the ashed sample (accurate to 0.0001g) and place it in a polytetrafluoroethylene beaker. Add hydrochloric acid, nitric acid, hydrofluoric acid, and perchloric acid in sequence, with a volume ratio of 3:1:3:1, for a total mixed acid volume of approximately 12mL. Cover the beaker and shake it until the powder at the bottom is fully dispersed. Place the beaker on a 200℃ hot plate for digestion. After heating for 2.5 hours, open the lid and observe the sample dissolution. If the sample is not completely dissolved, add nitric acid, hydrofluoric acid, and perchloric acid (volume ratio 1:3:1) and continue heating for digestion. After heating and digestion for approximately 6 hours, if any black solid remains undissolved, open the lid and continue heating to remove the acid. After evaporation to dryness, a yellow solid will appear. Turn off the heating plate and add 10 mL of 6 mol / L hydrochloric acid to the beaker to dissolve the residue. If there are insoluble substances such as black precipitate in the sample, filter through a 0.45 μm filter membrane to obtain a clear solution, and dilute to a 25 mL volumetric flask to obtain the test solution.

[0052] Example 3: Determination of boron content (methyleneimine colorimetric method) 1. Reagent preparation: Anhydrous sodium carbonate (analytical grade): Dry and grind before use.

[0053] Saturated BaCO3 solution.

[0054] 1:1 HCl (analytical grade).

[0055] Methylimine colorimetric solution: Dissolve 0.9g of methylimine and 2g of ascorbic acid in 60mL of deionized water, heat to completely dissolve, and dilute to 100mL.

[0056] Ammonium acetate buffer: Dissolve 150g of ammonium acetate (analytical grade) in 240mL of deionized water, slowly add 75mL of glacial acetic acid (analytical grade) and mix well. Store in a plastic bottle.

[0057] Boron standard solution (0.1 g / L): Weigh 0.0572 g of dry boric acid and dilute to 100 mL. This is a 100 μg / mL boron standard solution. Store in a dry plastic bottle. When using, dilute 20 times to make a 5 μg / mL boron standard solution.

[0058] 2. Colorimetric Development and Measurement: Add the test solution to saturated BaCO3 solution until a brownish-red precipitate forms. Heat to a gentle boil, filter, and dilute to volume. Transfer the filtrate to a 25 mL volumetric flask, add 10 mL of ammonium acetate buffer, shake well, add 5 mL of methylimine colorimetric solution, shake well, dilute to the mark with water, and shake well. Store at 23°C in the dark for 2 hours, then perform colorimetric determination at a wavelength of 420 nm using a spectrophotometer.

[0059] 3. Standard curve creation: Pipette 0, 0.25, 0.50, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, and 5.0 mL of 5 μg / mL boron standard solution into ten 25 mL volumetric flasks. Add 10 mL of ammonium acetate buffer, shake well, add 5.0 mL of methylimine colorimetric solution, mix well, add water to the mark, shake well, and store at 23°C in the dark for 2 hours. Measure the colorimetrically at a wavelength of 420 nm using a spectrophotometer.

[0060] Example 4: Determination of molybdenum content (ammonium thiocyanate extraction method) 1. Reagent preparation: Hydrochloric acid (analytical grade), nitric acid, hydrofluoric acid, and perchloric acid.

[0061] 100g / L SnCl2 solution: Dissolve 10g of stannous chloride (SnCl2, analytical grade) in 10mL of concentrated hydrochloric acid, heating if necessary. After dissolution, dilute with deionized water to 100mL. Prepare fresh.

[0062] 49 g / L FeCl3 solution: Dissolve 8.1669 g of ferric chloride (FeCl3·6H2O) in deionized water and dilute to 100 mL.

[0063] 425 g / L NaNO3 solution: Dissolve 42.5 g of sodium nitrate (NaNO3, analytical grade) in deionized water and dilute to 100 mL.

[0064] 100g / L NH4SCN solution: Dissolve 50g of ammonium thiocyanate (NH4SCN, analytical grade) in deionized water and dilute to 500mL.

[0065] Isopropyl ether: Purify according to the method described in this invention before use.

[0066] Standard molybdenum solution.

[0067] 2. Colorimetric Development and Measurement: Transfer the test solution to a 60 mL separatory funnel, and add 1 mL of 49 g / L FeCl3 solution, 1 mL of 425 g / L NaNO3 solution, 5 mL of 100 g / L NH4SCN solution, and 5 mL of 100 g / L SnCl2 solution sequentially. Shake thoroughly after each addition. Finally, accurately add 10 mL of purified isopropyl ether, shake for 2–3 min, allow to stand for layering, separate the aqueous phase, transfer the organic phase to a centrifuge tube, centrifuge for 5 min to remove trace amounts of water. Measure the centrifuged solution colorimetrically at 470 nm.

[0068] 3. Standard curve creation: Measure 0, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, and 8.0 mL of 1 μg / mL Mo standard solution into a separatory funnel, add 9 mL of 6 mol / L HCl to each, and add water to a total volume of about 40 mL. The color development steps are the same as above.

[0069] Example 5: Repeatability verification of acid dissolution method Using the acid dissolution method of Example 2, three parallel determinations were performed on the same coal gangue sample. Under ignition conditions at 550℃, the boron concentrations were 541.061 ppm, 672.143 ppm, and 569.543 ppm, with a mean of 594.25 ppm and an RSD of 11.60%. The molybdenum concentrations were 15.794 ppm, 14.652 ppm, and 17.060 ppm, with a mean of 15.84 ppm and an RSD of 7.58%. Under ignition conditions at 830℃, the boron concentrations were 543.481 ppm, 435.408 ppm, and 139.462 ppm, with a mean of 372.78 ppm and an RSD of 56.11%. The molybdenum concentrations were 13.173 ppm, 34.695 ppm, and 68.329 ppm, with a mean of 38.73 ppm and an RSD of 71.78%.

[0070] Experimental results show that high-temperature calcination (830℃) disrupts the stability of the extraction process, while calcination at 550℃ can effectively balance the relationship between organic matter removal and element retention. It fully destroys the organic matter structure of coal gangue and avoids the volatilization loss of target elements. Furthermore, the tetraacid digestion method under 550℃ calcination conditions has the best repeatability for the extraction of boron and molybdenum.

[0071] Example 6: Results of Alkali Fusion Method Using the alkaline fusion method described in Example 1, the same coal gangue sample was analyzed. The boron concentrations were 1133.3 ppm and 2099.95 ppm (different samples), and the molybdenum concentrations were 125.36 ppm and 34.22 ppm. This result indicates that the alkaline fusion method is effective for extracting high-content samples.

[0072] In summary, the extraction and detection method for boron and molybdenum trace elements in coal gangue described in this invention provides two schemes: alkali fusion and acid dissolution. These can be selected according to laboratory conditions and sample characteristics, meeting the needs of batch sample testing. Under 550℃ ignition conditions, the mean value of the three parallel samples for boron was 594.25 ppm, with a relative standard deviation (RSD) of 11.60%; the mean value of the three parallel samples for molybdenum was 15.84 ppm, with an RSD of 7.58%. However, under 830℃ ignition conditions, the RSD for boron reached as high as 56.11%, and the RSD for molybdenum reached as high as 71.78%, indicating significantly poor repeatability. Furthermore, the acid dissolution method exhibits excellent repeatability under 550℃ ignition, while the alkali fusion method provides thorough decomposition, solving the industry pain points of difficult matrix digestion and easy element loss in coal gangue, and possessing industrial value for the resource utilization of coal gangue.

[0073] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. The scope of protection of the present invention is determined by the appended claims.

[0074] It should be noted that when numerical ranges are involved in this invention, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. To avoid redundancy, this invention describes preferred embodiments.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for extracting and detecting trace elements boron and molybdenum in coal gangue, characterized in that, The method includes either alkali fusion or acid dissolution: (1) The alkaline fusion method includes the following steps: The coal gangue sample was mixed with anhydrous sodium carbonate at a mass ratio of 1:8 to obtain a mixed sample. The mixed sample was first heated at 500~600℃ for 10 min, and then heated to 900~920℃ to melt for 30 min to completely decompose the sample and obtain the decomposed sample. Remove the decomposed sample, rotate it while it is still hot to solidify the melt, and transfer the molten material into a beaker; Add hot water and hydrochloric acid to a beaker to completely dissolve the molten metal and obtain the test solution; (2) The acid dissolution method includes the following steps: Coal gangue samples were pretreated by calcination at 550℃ to obtain ashed samples; The ashed sample was placed in a digestion container and a mixed acid of hydrochloric acid, nitric acid, hydrofluoric acid and perchloric acid was added for digestion. The volume ratio of hydrochloric acid, nitric acid, hydrofluoric acid and perchloric acid was 3:1:3:

1. The digestion container was heated at 200°C until the sample was completely dissolved. Heat to remove acid until nearly dry, add 6 mol / L hydrochloric acid to dissolve the residue, filter and make up to volume to obtain the test solution; The contents of boron and molybdenum in the test solution are determined by spectrophotometry using either the alkali fusion method or the acid dissolution method.

2. The method according to claim 1, characterized in that, In the alkaline fusion method, the specific steps for mixing the coal gangue sample with anhydrous sodium carbonate are as follows: place the coal gangue sample in a crucible covered with finely ground anhydrous sodium carbonate, add 7 / 8 of the total amount of anhydrous sodium carbonate to the crucible in several portions, and stir with a glass rod after each addition to ensure uniform mixing. Spread the remaining 1 / 8 of the anhydrous sodium carbonate evenly on the surface of the mixture.

3. The method according to claim 1, characterized in that, In the alkaline fusion method, the ratio of hydrochloric acid to anhydrous sodium carbonate is 5:

1.

4. The method according to claim 1, characterized in that, In the acid dissolution method, the conditions for calcination pretreatment are as follows: the coal gangue sample is heated to 550°C at a heating rate of 5°C / min to 10°C / min and held for 2h to 4h; the mass-volume ratio of the ashed sample to the mixed acid is 0.1g:10mL to 15mL.

5. The method according to claim 1, characterized in that, In the acid dissolution method, the heating digestion time is 6h~8h. If the sample is not completely dissolved during this period, a mixed acid of nitric acid, hydrofluoric acid and perchloric acid is added to continue digestion. The volume ratio of nitric acid, hydrofluoric acid and perchloric acid in the added mixed acid is 1:3:

1.

6. The method according to claim 1, characterized in that, The determination of boron content in the test solution uses the methylimine colorimetric method, and the specific steps are as follows: Add the test solution to saturated BaCO3 solution until a brownish-red precipitate is formed, heat to a gentle boil, filter, and take the filtrate into a volumetric flask; Add ammonium acetate buffer and methylimine colorimetric solution, shake well, dilute with water to the mark, and store at 23°C in the dark for 2 hours. The boron content was determined by colorimetric analysis at a wavelength of 420 nm using a spectrophotometer, and calculated based on the boron standard curve.

7. The method according to claim 6, characterized in that, The ammonium acetate buffer solution was prepared by dissolving 150g of ammonium acetate in 240mL of deionized water and slowly adding 75mL of glacial acetic acid and mixing thoroughly; the methylimine colorimetric solution was prepared by dissolving 0.9g of methylimine and 2g of ascorbic acid in 60mL of deionized water, heating to dissolve and then diluting to 100mL.

8. The method according to claim 1, characterized in that, The determination of molybdenum content in the test solution was performed using the ammonium thiocyanate extraction method, and the specific steps are as follows: Take the test solution and place it in a separatory funnel. Add ferric chloride solution, sodium nitrate solution, ammonium thiocyanate solution and stannous chloride solution in sequence, and shake well after each addition. Add purified isopropyl ether, shake for 2-3 minutes, let stand to separate the layers and remove the aqueous phase, transfer the organic phase to a centrifuge tube and centrifuge for 5 minutes to remove trace amounts of water. The molybdenum content was calculated by colorimetric determination at a wavelength of 470 nm using a spectrophotometer, based on the molybdenum standard curve.

9. The method according to claim 8, characterized in that, The purification method of the isopropyl ether is as follows: place the isopropyl ether in a separatory funnel, wash it with a mixture of stannous chloride, ammonium thiocyanate and water in a volume ratio of 1:1:1, the volume of the washing solution is 1 / 10 of the volume of the isopropyl ether, shake and let stand to separate the layers, discard the aqueous phase, and then wash with 2 mol / L hydrochloric acid, repeating 4 to 5 times.

10. The method according to claim 1, characterized in that, The method also includes the extraction and detection of selenium, which is determined by hydride generation-atomic fluorescence spectrometry or inductively coupled plasma mass spectrometry.

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