WO2023197712A1

WO2023197712A1 - Method for determining mercury and arsenic in briquettes based on atomic fluorescence spectrometry and digestion of briquettes using hydrothermal synthesis reactor

Info

Publication number: WO2023197712A1
Application number: PCT/CN2023/071498
Authority: WO
Inventors: 陈娟; 武建军; 刘喆; 闫龙; 闫涛; 张一昕; 郭振坤; 郭旸; 李健; 王玉飞
Original assignee: 中国矿业大学; 榆林学院; 国家煤及盐化工产品质量监督检验中心(榆林)(榆林市产品质量监督检验所)
Priority date: 2022-04-14
Filing date: 2023-01-10
Publication date: 2023-10-19
Also published as: CN114720445A

Abstract

A method for determining mercury and arsenic in briquettes based on atomic fluorescence spectrometry and digestion of briquettes using a hydrothermal synthesis reactor, comprising: adding a certain amount of briquettes and a proper amount of mixed acid into a polytetrafluoroethylene sealed tank, which has been subjected to soaking, cleaning and preheating, for pre-digestion until a gas is released, after the reaction eases, capping, placing the polytetrafluoroethylene sealed tank into a stainless steel sleeve for sealing, placing the stainless steel sleeve into an electrothermal blast drying oven for closed heating digestion, and then performing acid removal and volume fixing operations to obtain a digestion solution to be tested; and preparing a standard series of solutions of mercury and arsenic elements, drawing a standard curve, then using an atomic fluorescence spectrometer to test the obtained digestion solution to be tested to obtain a fluorescence intensity, and performing conversion by means of the standard curve to obtain the content of corresponding elements in the briquettes.

Description

A method for the determination of mercury and arsenic in coal briquettes based on hydrothermal synthesis reactor digestion of coal briquettes and atomic fluorescence spectrometry

This application is required to be submitted to the China Patent Office on April 14, 2022. The application number is 202210389850. The priority of the Chinese patent application "Method", the entire content of which is incorporated into this application by reference.

Technical field

The invention relates to the field of liquid phase chemistry, and specifically relates to a method for determining mercury and arsenic in coal briquettes based on hydrothermal synthesis reaction kettle digestion of coal briquettes and atomic fluorescence spectrometry.

Background technique

Coal is a complex geological product composed of a variety of organic matter and inorganic minerals. Briquettes are made of coal as the base material, and are compounded by adding a variety of different types of binders (such as coal pitch, coal tar, starch, humic acid, biomass, etc.). The chemical composition is more complex than that of raw coal itself, among which endowments There are dozens of harmful or potentially harmful trace elements, such as Cr, Cl, Pb, Hg, Se, As, etc. Compared with the normal harmful elements, the content of trace elements is extremely low, the forms of occurrence are complex and diverse, and the toxicity is high. , will be gradually released and enriched during thermal processing and utilization processes such as pyrolysis and combustion, causing pollution to the ecological environment including the atmosphere, water, and soil, and further endangering human health. Under the requirements of the "double carbon" goal, it is particularly important to accurately measure trace harmful elements in briquettes and study release and control technologies for their clean utilization and waste disposal and other environmental issues.

At present, there is a lack of research on trace harmful elements in briquettes. Previous research mainly focused on raw coal, that is, raw coal is first pretreated in the laboratory, specifically digesting the sample into a solution or transferring the elements to be measured into the solution. It can be measured by inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma optical emission spectrometry (ICP-AES), atomic absorption spectrometry (AAS) and atomic fluorescence spectrometry. It can be seen that sample pretreatment-digestion is a key step in instrument analysis, which determines the accuracy and precision of the test results. There is currently no unified method and standard for reference on the pretreatment and digestion of briquettes, and there are no reports in the literature.

Compared with raw coal, briquettes have a certain degree of particularity and complexity, mainly reflected in their complex chemical composition, which contains a large number of organic macromolecules, inorganic minerals and carbonaceous particles that are not easily digested; their volatile content is high, and a large amount of gases produced by digestion are easily Leading to an excessive increase in pressure; the bonding interaction between the various binders added to the coal and the coal particles will weaken the interaction with the acid. Therefore, based on the analysis and reference to the raw coal digestion pretreatment and trace element content determination methods It is extremely necessary to combine the characteristics of coal briquettes to explore a set of pretreatment methods suitable for briquettes to maximize the transfer of elements to be measured into the solution without pollution or loss.

At present, the pretreatment and digestion methods for raw coal include electric heating plate atmospheric pressure exposure digestion method, microwave digestion method, ashing-digestion method, etc. Among them, the electric hot plate atmospheric pressure open digestion method directly digests the coal sample with mixed acid in an open container. This method uses an electric hot plate to heat the sample, and the sample is heated unevenly. In the process, a large amount of acid is used to form acid mist, which affects the environment and can easily cause Cross-infection. If used for digestion of briquette samples, due to the complexity and particularity of the briquette composition, the compatibility between the briquettes and the mixed acid is not good, and when the temperature and pressure do not reach the ideal state, it is difficult for the sample to be completely dissolved, causing measurement problems. The results were seriously distorted, the method detection limit was high, and the acid dosage was large. Microwave digestion method is advanced and reliable, but the equipment cost is high and it is difficult to popularize it. If it is used for digestion of coal samples, the interaction between the binder and coal particles in the coal weakens the interaction with the acid. To achieve the clear and transparent digestion effect, a large amount of acid will be used, and the acidification time will be long in the later stage, which cannot ensure that the volatile elements are not released. Escape and acid decomposition can easily produce a large amount of nitrogen gas, causing deformation of the digestion tank. Secondly, the addition of organic binders in the coal briquettes results in a higher volatile content. During digestion, the volume of the fluid in the closed digestion tank expands and the pressure increases sharply. , there is a potential risk of causing the reaction to go out of control and causing the digestion tank to burst. In the ashing-digestion method, the test is ashed and then digested with mixed acid. The ashing step is cumbersome. However, most of the organic binders (starch, biomass, coal tar) in the briquettes have low decomposition temperatures and are prone to volatile traces during the ashing process. Large amounts of elements (such as Hg, As) escape with organic volatiles, resulting in low measurement results.

Contents of the invention

In order to solve the above problems, the present invention provides a method for determining mercury and arsenic in coal briquettes based on hydrothermal synthesis reactor digestion briquette-atomic fluorescence spectrometry, which adopts a sealed, efficient, simple and safe hydrothermal synthesis reactor The digestion pretreatment of coal briquettes was realized, and the content of trace elements represented by Hg and As in the briquettes was accurately measured using atomic fluorescence spectrometry. The invention can eliminate difficulties in digestion caused by the complex composition of the coal briquettes, excessive pressure caused by the digestion and release of high volatile organic binders in the coal briquettes, and loss of easily volatile trace elements due to heating volatilization under the conditions of low acid content and short time consumption. problem, ensuring the thoroughness and safety of digestion of briquette samples, and enabling accurate detection of trace element content.

In order to achieve the above objects, the technical solutions adopted by the present invention are:

A method for determining mercury and arsenic in coal briquettes based on digestion of coal briquettes in a hydrothermal synthesis reactor and atomic fluorescence spectrometry, including the following steps:

S1. Preprocessing:

Rinse the polytetrafluoroethylene sealed tank and the containers of the hydrothermal synthesis reactor repeatedly with tap water and deionized water, gently scrub the inner wall with a soft brush until it is clean, and soak it in a nitric acid solution with a mass concentration of 10% overnight. , take it out, wash it three times with ultrapure water, and after washing away the surface nitric acid, place the sealed jar in a blast drying oven at 80°C, dry and preheat for 30 minutes, and set aside;

S2. Coal pretreatment:

Weigh an appropriate amount of briquettes, dry them at 105°C to constant weight, and grind them through a 200-mesh sieve;

S3. Predigestion: Weigh 50mg of pretreated coal briquettes (accurate to 0.0002g) and place it at the bottom of a preheated PTFE sealed tank. Add mixed acid and let it stand for 30 minutes. Use the PTFE sealed tank that comes with it. Heat is pre-digested, and when the gas is released completely and the reaction tends to ease, the PTFE sealed jar is capped;

S4. Sealed digestion: Put the capped PTFE sealed jar into a stainless steel sleeve, press and seal the PTFE sealed jar with the lid of the stainless steel sleeve, and put the entire reaction kettle into electric blast drying Heating in the box at 180°C for 4 hours, keeping the kettle upright and stable;

S5. Acid drive: Take out the hydrothermal synthesis reaction kettle and cool it to room temperature, open the stainless steel sleeve lid and the lid of the sealed tank one by one, pour the digested coal into the PTFE crucible, rinse the sealed tank and lid with 5% hydrochloric acid, Pour the rinsing liquid into the polytetrafluoroethylene crucible and place it on an electric hot plate for acid treatment. The acid treatment temperature is 140°C. Stop acid treatment when the solution becomes colloid;

S6. Stabilize the volume: Rinse the polytetrafluoroethylene crucible at least 3 times with 5% hydrochloric acid (in the present invention, unless otherwise specified, the 5% hydrochloric acid or 5% hydrochloric acid solution used refers to hydrochloric acid with a mass concentration of 5%) , move the flushing solution into a 50ml volumetric flask, and adjust the volume to the mark with 5% hydrochloric acid, leave it for 10 minutes, and transfer it to an HDPE plastic vial as the digestion solution to be tested for later use;

S7. Preparation of standard stock solution: Accurately measure 0.10ml of the national standard solution of mercury and the national standard solution of arsenic in a 100ml volumetric flask, dilute to the mark with 5% hydrochloric acid solution, shake well, and leave it for 10 minutes to obtain a concentration of 1.0μg/ml mercury. Primary standard stock solution and arsenic primary standard stock solution with a concentration of 1.0 μg/ml, for later use;

Accurately measure a certain volume of mercury primary standard stock solution and arsenic primary standard stock solution and place them in 100ml volumetric flasks respectively, and dilute to volume with 5% hydrochloric acid solution to prepare a secondary standard stock solution;

S8. Preparation of standard solution: Take a certain amount of secondary standard stock solution, adjust the volume to a certain scale with standard medium, obtain a series of concentration standard solutions, and use an atomic fluorescence spectrometer to test and draw a standard curve;

S9. Determination of the element content of the digestion solution to be tested: Use an atomic fluorescence spectrometer to test the digestion solution to be tested obtained in step S6. Repeat the measurement three times to obtain the fluorescence intensity. The corresponding elements in the briquettes can be obtained by converting the standard curve in step S8. content;

S10. Blank value measurement: Set up a special blank group, that is, no digested sample is added, and the sample to be tested is digested at the same time according to the above steps. The obtained blank sample to be tested is measured repeatedly 6 times, the standard deviation of the test results is calculated, and the average value of the 6 measurements is used as the test sample. The blank value content of the corresponding element in the test sample.

Further, in step S2, the briquette is prepared by the following method:

Measure 100 ml of NaOH solution with a mass concentration of 2.0% and place it in a beaker. Add 5% (adding 5% biomass powder means that the volume ratio of the mass of biomass powder to NaOH solution is 5g:100ml). The biomass powder that has been crushed in the third stage to ≤0.2mm is stirred and heated at 80°C for 2 hours, and then cooled to obtain modified biomass; the modified biomass, asphalt, and tar residue are mixed in a mass ratio of 1:6:3 Compound in proportions and mix evenly to obtain a composite binder;

The pulverized coal and the composite binder are mixed in a ratio of 7:3 and placed in a molding machine for cold pressing to obtain a cylindrical briquette with a size of Φ30mm×30mm.

Further, in step S3, 4 ml of HNO ₃ , 2 ml of HF, 1 ml of HClO ₄ , and 1 ml of H ₂ O ₂ were added in sequence.

Further, in step S7, the secondary standard stock solution is prepared by the following method: accurately measure 5.00 ml of the mercury primary standard stock solution and place it in a 100 ml volumetric flask, and adjust the volume to the mark with 5% hydrochloric acid solution to obtain a concentration of 50 ng. /ml mercury secondary standard stock solution; accurately measure 10.00ml arsenic primary standard stock solution and place it in a 100ml volumetric flask, and dilute to the mark with 5% hydrochloric acid solution to obtain an arsenic secondary standard stock solution with a concentration of 100ng/ml. .

Further, in step S8, the preparation of the series of concentration standard solutions is: accurately measure 0, 1.00, 2.00, 4.00, 8.00, 10.00ml mercury secondary standard stock solution into six 100ml volumetric flasks, and use 5% hydrochloric acid to determine the concentration. Volume up to the mark to obtain a series of mercury standard series solutions with concentrations of 0, 0.50, 1.00, 2.00, 4.00, and 5.00ng/ml;

Accurately measure 0, 1.00, 2.00, 4.00, 8.00, 10.00ml arsenic secondary standard stock solution into six 100ml volumetric flasks, and use arsenic standard medium to adjust the volume to the mark to obtain concentrations of 0, 1.00, 2.00, 4.00, 8.00, 10.00ng/ml arsenic standard series solution.

Further, the arsenic standard medium is a mixed solution of 5% hydrochloric acid + 1% thiourea + 1% ascorbic acid (specific steps for preparing arsenic standard medium: 5g concentrated hydrochloric acid + 1g thiourea + 1g ascorbic acid, dissolved in 100 ml of water).

Further, in step S8, the carrier current tested by the atomic fluorescence spectrometer is 5% hydrochloric acid solution, the carrier gas is high-purity argon, the pressure is 0.25MPa, the flow rate of the carrier gas is 400ml/min; the lamp current is 60~30mA. , the negative high voltage is 240V, the atomizer height is 10mm, the shield flow rate is 1000ml/min, the reading time is 15s, and the delay time is 1.0s.

Further, in step S8, the mercury standard curve drawn by testing with an atomic fluorescence spectrometer is IF=2499.409c+48.011 Formula 1. In Formula 1, IF represents the fluorescence intensity of mercury, and c represents the concentration of mercury in the solution; the arsenic standard curve is IF=122.398c+7.946 Formula 2. In Formula 2, IF represents the fluorescence intensity of arsenic, and c represents the concentration of arsenic in the solution.

Further, in step S9, when measuring the mercury element content with an atomic fluorescence spectrometer, the reducing agent is a mixed solution of 1% potassium borohydride + 0.2% sodium hydroxide (referring to 1g potassium borohydride + 0.2g sodium hydroxide, dissolved into 100 ml of water, the same below); when measuring arsenic content with an atomic fluorescence spectrometer, the reducing agent is a mixed solution of 2% potassium borohydride + 0.5% sodium hydroxide.

The invention has the following beneficial effects:

1) The hydrothermal synthesis reactor is used to digest coal briquettes, which has the characteristics of a high-pressure sealed environment. From a thermodynamic perspective, the digestion liquid steam circulates throughout the sealed tank at a certain pressure, and the pressurized steam quickly introduces heat into the coal briquette sample with extremely strong penetrating power. , forming a mode that enhances heat transfer and promotes digestion, effectively avoiding the problem of traditional open electric hot plate digestion that causes sample surface digestion due to temperature gradients and makes internal digestion difficult. From a kinetic perspective, during the heating process, the mixed acid solution can generate thermal energy several orders of magnitude higher than that of the solid sample. The strong vibration of the chemical bonds of polar molecules in the liquid phase intensifies the friction and collision with adjacent molecules, especially the molecules of the solid sample. It accelerates the mass transfer and digestion reaction rate of molecules, weakens the interaction force between coal particles and binder, and basically eliminates the influence of the complex composition of coal briquettes. On the other hand, the mixed acid solution with higher thermal energy forms convection and creates disturbance, which can eliminate the dissolved inactive surface layer on the surface of the solid material, thereby exposing the new solid interface and allowing better contact with the acid. Reasonable mixed acid preparation The digestion solution fully reacts with the coal sample, ensuring complete digestion of the coal, greatly reducing the amount of acid used, shortening the digestion time, and dissolving some insoluble substances.

2) In line with the principles of using the least amount of acid, simple digestion procedures, and optimal digestion results, it is key to explore the mixed acid system and its reasonable ratio. The organic matter content in briquettes is relatively high, and a considerable amount of inorganic acid must be used to ensure complete digestion. Only conventional concentrated nitric acid (currently recognized as the best pretreatment reagent) and hydrofluoric acid (the only acid that can decompose silica and silicates, must be used) were used for the test. It was found that the digestion was incomplete and there was precipitation at the bottom of the sample solution. Therefore, it is necessary to strengthen the destruction of organic tissues and add perchloric acid to promote the digestion of organic matter. The strong oxidizing property of hydrogen peroxide oxidizes and decomposes the organic matter side chains and functional groups of the coal briquettes, thereby completely decomposing the organically bound mercury and oxidizing it at the same time. Some metals greatly improve the digestion effect. The mixed acid system of the present invention does not contain hydrochloric acid, which is used by most scholars. Chlorine can form polyatomic ions, which is the main interference with the available isotopes of 75As, and also has certain interference with Se, Cr, Ge, etc. The present invention avoids the use of sulfuric acid, because sulfuric acid has a high boiling point and cannot be purified by the general acid-catching process. The atomic fluorescence spectrometry measurement process has strict acidity requirements, and the residual sulfuric acid has a greater impact on the measurement results. In this regard, through comparative experiments with different mixed acid ratios, digestion times and digestion temperatures, it was concluded that the total mixed acid consumption per digested 50mg of coal briquettes was 8ml (less than 10ml), and the mixed acid ratio was HNO ₃ : HF: HClO ₄ : H ₂ O ₂ = 4 :2:1:1, the digestion tank is heated at 180°C for 4 hours, and there is no need to use programmed temperature and pressure mode to obtain a transparent and clear digestion solution.

3) Use the energy of preheating the PTFE sealed tank to strengthen the oxidation effect of the mixed acid on the volatile organic binder in the coal briquettes and release a large amount of gas, which is equivalent to a certain degree of pressure relief in the early stage to eliminate the sudden increase in pressure caused by the closed digestion. The potential safety hazard of the kettle body exploding. In addition, the PTFE sealed jar is hydrophobic, which greatly reduces contamination during the sample dissolution process.

4) In a closed environment, the loss of mixed acid and volatile elements is small, and the digestion is complete. The Hg and As content is tested using atomic fluorescence spectrometry, and the detection limit is low, which effectively guarantees the accuracy of the measurement results. In addition, this method has the advantages of simple operation, mild and controllable conditions, low pollution, low blank value, short time consumption, and cheap instruments. It is an ideal solution for coal digestion pretreatment.

Instructions with pictures

Figure 1 is a schematic flow chart of the method for determining mercury and arsenic in coal briquettes based on hydrothermal synthesis reactor digestion of coal briquettes and atomic fluorescence spectrometry according to the present invention;

Figure 2 is a mercury standard curve obtained in the embodiment of the present invention; IF=2499.409c+48.011, R ² =0.9999;

Figure 3 is a standard curve diagram of arsenic obtained in the embodiment of the present invention; IF=122.398c+7.946, R ² =0.9997;

Figure 4 is a comparison diagram before and after digestion of the hydrothermal synthesis reactor of coal A in Example 1 of the present invention;

Figure 5 is a comparison view before and after the open electric heating plate digestion of coal type A in Comparative Example 1 of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the embodiments and drawings.

Example 1

As shown in Figure 1, a method for determining mercury and arsenic in coal briquettes based on hydrothermal synthesis reactor digestion of coal briquettes and atomic fluorescence spectrometry includes the following steps:

(1) Pretreatment: Rinse the polytetrafluoroethylene sealed tank and the containers of the hydrothermal synthesis reactor repeatedly with tap water and deionized water, gently scrub the inner wall with a soft brush until it is clean, and place it at a mass concentration of 10% Soak in nitric acid solution overnight, take it out, wash it three times with ultrapure water, wash away the surface nitric acid, place the sealed jar in a blast drying oven at 80°C, dry and preheat for 30 minutes, and set aside;

(2) Coal pretreatment:

(3) Predigestion: Weigh 50mg of pretreated coal briquettes (accurate to 0.0002g) and place it at the bottom of a preheated polytetrafluoroethylene sealed tank, add mixed acid, let stand for 30 minutes, and use the polytetrafluoroethylene sealed tank to automatically Pre-digest with heat. When the gas is released completely and the reaction tends to ease, the PTFE sealed jar is capped;

(4) Sealed digestion: Put the capped PTFE sealed jar into a stainless steel sleeve, press and seal the PTFE sealed jar with the lid of the stainless steel sleeve, and put the entire reaction kettle into an electric blast Heating at 180°C for 4 hours in a drying oven, keeping the kettle upright and stable;

(5) Acid drive: Take out the hydrothermal synthesis reaction kettle and cool it to room temperature, open the stainless steel sleeve lid and the lid of the sealed tank one by one, pour the digested coal into the PTFE crucible, and rinse the sealed tank and lid with 5% hydrochloric acid , pour the rinsing liquid into the crucible together, and place it on an electric hot plate for acidification treatment. The acidification temperature is 140°C. Stop acidification when the solution becomes colloid;

(6) Adjust the volume: Rinse the polytetrafluoroethylene crucible with 5% hydrochloric acid at least 3 times, transfer the rinse liquid into a 50ml volumetric flask, and adjust the volume to the mark with 5% hydrochloric acid, leave it for 10 minutes, and transfer it to an HDPE plastic vial as the digestion solution to be tested. spare;

(7) Preparation of standard stock solution: Accurately measure 0.10ml of mercury national standard solution and arsenic national standard solution in a 100ml volumetric flask, dilute to volume with 5% hydrochloric acid solution, shake well, and leave for 10 minutes to obtain a concentration of 1.0μg/ml Mercury primary standard stock solution and arsenic primary standard stock solution with a concentration of 1.0 μg/ml, for later use;

(8) Standard solution preparation: Take a certain amount of secondary standard stock solution, adjust the volume to a certain scale with standard medium, obtain a series of concentration standard solutions, and use an atomic fluorescence spectrometer to test and draw a standard curve;

(9) Determination of the element content of the digestion solution to be tested: Use an atomic fluorescence spectrometer to test the digestion solution to be tested obtained in step S6. Repeat the measurement three times to obtain the fluorescence intensity. The corresponding value in the briquette is obtained by converting the standard curve in step S8. content of elements;

(10) Blank value measurement: Set up a special blank group, that is, no digested sample is added, and it is digested at the same time as the sample to be tested according to the above steps. The obtained blank sample to be tested is measured repeatedly 6 times. The standard deviation of the test results is calculated, and the average value of the 6 measurements is taken as Blank value content of the corresponding element in the sample to be tested.

In this embodiment, in step (2), the briquettes are prepared by the following method: collecting sunflower seed skins, drying them naturally and crushing them in three stages to less than or equal to 0.2mm, and then preparing a NaOH solution with a mass concentration of 2.0%. Measure 100 ml of 2.0% NaOH solution into a clean beaker, add 5% sunflower seed hull powder, stir and heat at 80°C for 2 hours, then cool to prepare a modified sunflower seed hull binder. Asphalt, tar residue and modified sunflower seed peel are mixed in a ratio of 6:3:1 to prepare composite binder A. Pulverized coal and composite binder A are mixed in a ratio of 7:3 and placed in a molding machine for cold pressing. That is, Φ30mm×30mm cylindrical coal briquette A is obtained.

For example, in some embodiments, the mass concentration of the NaOH solution can be 1.5% or 2.5%. The ratio of asphalt, tar residue and modified sunflower seed peel in composite binder A can be 4:2:4, 4:3:3, 4:4:2, 5:3:2, 5:2:3, 5:4:1, 6:2:2, 6:1:3. The ratio of pulverized coal to composite binder A can be 8:2 or 9:1.

In this embodiment, step (3) is specifically: add 4 ml of concentrated HNO ₃ , 2 ml of HF, 1 ml of HClO ₄ , and 1 ml of H ₂ O ₂ in sequence, and the total reagent amount does not exceed 10 ml.

For example, in some embodiments, the volume ratio of HNO ₃ : HF: HClO ₄ : H ₂ O ₂ in the mixed acid can be 5:2:0.5:0.5, 3:3:1:1, 3.5:2.5: 1:1.

In this example, in step (7), 5.00 ml of the mercury primary standard stock solution is accurately measured and placed in a 100 ml volumetric flask, and the volume is adjusted to the mark with 5% hydrochloric acid solution. The concentration of the obtained mercury secondary standard stock solution is 50 ng/ml. . Accurately measure 10.00ml of the arsenic primary standard stock solution and place it in a 100ml volumetric flask, and dilute to the mark with 5% hydrochloric acid solution. The concentration of the obtained arsenic secondary standard stock solution is 100ng/ml.

In this example, in step (8), accurately measure 0, 1.00, 2.00, 4.00, 8.00, and 10.00ml of mercury secondary standard stock solutions into six 100ml volumetric flasks, and dilute to the mark with 5% hydrochloric acid to obtain the concentration. It is 0, 0.50, 1.00, 2.00, 4.00, 5.00ng/ml mercury standard series solutions.

Accurately measure 0, 1.00, 2.00, 4.00, 8.00, 10.00ml arsenic secondary standard reserve into six 100ml volumetric flasks, and use arsenic standard medium to adjust the volume to the mark to obtain concentrations of 0, 1.00, 2.00, 4.00, 8.00, 10.00 ng/ml arsenic standard series solution, in which the arsenic standard medium is a mixed solution of 5% hydrochloric acid + 1% thiourea + 1% ascorbic acid.

In this embodiment, in step (8), the carrier current of the atomic fluorescence spectrometer used is a hydrochloric acid solution with a mass concentration of 5%, the carrier gas is high-purity argon, the pressure is 0.25MPa, and the flow rate is 400ml/min. In addition, the lamp current is 60~30mA, the negative high voltage is 240V, the atomizer height is 10mm, the shield flow rate is 1000ml/min, the reading time is 15s, and the delay time is 1.0s.

In this embodiment, in step (8), an atomic fluorescence spectrometer is used to test and draw a mercury standard curve as IF=2499.409c+48.011 Formula 1, correlation coefficient: R ² =0.9999, and the linear relationship is good (as shown in Figure 2). In Formula 1, IF represents the fluorescence intensity of mercury, and c represents the concentration of mercury in the solution. The arsenic standard curve is IF=122.398c+7.946 Equation 2, correlation coefficient: R ² =0.9997, and the linear relationship is good (as shown in Figure 3). In Formula 2, IF represents the fluorescence intensity of arsenic, and c represents the concentration of arsenic in the solution.

In this embodiment, when measuring the mercury element content with an atomic fluorescence spectrometer in step (9), the reducing agent is a 1% potassium borohydride + 0.2% sodium hydroxide mixed solution. When measuring arsenic content with an atomic fluorescence spectrometer, the reducing agent is a mixed solution of 2% potassium borohydride + 0.5% sodium hydroxide.

Example 2

Others are the same as in Example 1, except that the biomass in the composite binder is different. In this embodiment, the biomass is corn straw, and the obtained composite binder B is formed with pulverized coal to prepare briquette B as a digestion sample.

Comparative example 1

Use an open electric heating plate to digest coal A.

Comparative example 2

Use an open electric heating plate to digest coal B.

The specific steps of Comparative Example 1 and Comparative Example 2 are as follows:

Weigh 50 mg of coal A and B into two clean polytetrafluoroethylene crucibles, add HNO ₃ 5ml, HF2ml, HClO ₄ 1ml, H ₂ O ₂ 1ml respectively, cover them and place them on an electric hot plate for heating and digestion. , the temperature of the electric hot plate is maintained at 180°C.

Observe the color of the digestion liquid and the color of the remaining solid in the crucible. When the color of the liquid is almost clear and transparent, and the solid is off-white, the sample digestion is considered complete. If the solution is turbid and deep in color and the solid sample is dark brown, you need to add mixed acid and place it on an electric hot plate to continue digestion. In this comparative example 1 and 2, when complete digestion, for every 50 mg of briquettes, add the mixed acid amount HNO ₃ 5ml, HF2ml, HClO ₄ 1ml, H ₂ O ₂ 1ml for the first time, and add the mixed acid amount for the second time. Half of the times is HNO ₃ 2.5ml, HF 1ml, HClO ₄ 0.5ml, H ₂ O ₂ 0.5ml. The final total mixed acid consumption is 22.5ml, that is, 12.5ml HNO ₃ +5ml HF+2.5ml HClO ₄ +2.5mlH ₂ O ₂ , digestion time 10h.

The digestion solution in the above-mentioned crucible is heated with an electric hot plate at 140°C to drive away the acid. When the solution becomes colloid, stop driving away the acid. Rinse the polytetrafluoroethylene crucible at least 3 times with 5% hydrochloric acid. Move the rinse liquid together into a 50ml volumetric flask and adjust it to the volume. to the mark, leave it for 10 minutes, and transfer it to an HDPE plastic vial for testing. The post-processing work is the same as the above-mentioned hydrothermal synthesis reactor digestion treatment method.

Comparison of digestion results is shown in Figures 4 and 5. Figure 4 is a comparison chart before and after digestion of the hydrothermal synthesis reactor of Coal A in Example 1 of the present invention; Figure 5 is an open electric heating of Coal A in Comparative Example 1 of the present invention. Comparison of plates before and after digestion. The specific digestion results are shown in Table 1, and the measurement results are shown in Tables 2 and 3.

Table 1 Comparison of digestion results

Table 2 Sample blank test results

It can be seen from Table 2 that the average values of the six Hg and As content tests in the blank solution were 0.0009 μg/L and 0.6471 μg/L respectively, which were used as the blank values for the Hg and As content detection in the samples to be tested. The standard deviation SD of repeated detection values was 0.0082 μg/L and 0.0108 μg/L respectively.

Table 3 Examples and Comparative Examples Test Results

It can be seen from Table 3 that the detection values of Hg and As in Example 1 and Example 2 are higher than those in Comparative Examples 1 and 2. It can be seen that the hydrothermal synthesis reactor has better digestion effect and less element loss than the open electric heating plate. The standard deviation of repeated measurements is small and the uncertainty is less than 1. The measurement results of this method are accurate and reliable, and the testing efficiency is high.

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above. Those skilled in the art can make various variations or modifications within the scope of the claims, which does not affect the essence of the present invention.

Claims

A method for digesting coal briquettes based on hydrothermal synthesis reactor, which is characterized by including the following steps:

S1. Preprocessing:

Rinse the polytetrafluoroethylene sealed tank and the containers of the hydrothermal synthesis reactor repeatedly with tap water and deionized water, scrub the inner wall until clean, soak it in a nitric acid solution with a mass concentration of 10% overnight, take it out, and rinse it with ultrapure water. Wash with water three times. After washing away the surface nitric acid, place the sealed jar in a blast drying oven at 80°C, dry and preheat for 30 minutes, and set aside;

S2. Coal pretreatment:

Weigh an appropriate amount of briquettes, dry them at 105°C to constant weight, and grind them through a 200-mesh sieve;

S3. Predigestion: Weigh 50 mg of pretreated coal briquettes and place them at the bottom of a preheated PTFE sealed tank. Add mixed acid and let stand for 30 minutes. Use the heat generated by the PTFE sealed tank to predigest. Wait until the gas When the release is complete and the reaction tends to ease, the polytetrafluoroethylene sealed jar is capped; the volume ratio of HNO 3 : HF: HClO 4 : H 2 O 2 in the mixed acid is 4:2:1:1, 5:2 :0.5:0.5, 3:3:1:1 or 3.5:2.5:1:1;

S4. Sealed digestion: Put the capped PTFE sealed jar into a stainless steel sleeve, press and seal the PTFE sealed jar with the lid of the stainless steel sleeve, and put the entire reaction kettle into electric blast drying Heat in the box at 180°C for 4 hours, keeping the kettle upright and stable.
The method according to claim 1, characterized in that: in step S3, the mixed acid is HNO 3 4ml, HF 2ml, HClO 4 1ml and H 2 O 2 1ml.
A method for determining mercury and arsenic in coal briquettes based on hydrothermal synthesis reactor digestion of coal briquettes and atomic fluorescence spectrometry, which is characterized by including the following steps:

S1 to S4, digest the briquettes according to the method described in claim 1 or 2;

S5. Acid drive: Take out the hydrothermal synthesis reaction kettle and cool it to room temperature, open the stainless steel sleeve lid and the lid of the sealed tank one by one, pour the digested coal into the PTFE crucible, rinse the sealed tank and lid with 5% hydrochloric acid, Pour the rinsing liquid into the polytetrafluoroethylene crucible and place it on an electric hot plate for acid treatment. The acid treatment temperature is 140°C. Stop acid treatment when the solution becomes colloid;

S6. Distill the volume: Rinse the polytetrafluoroethylene crucible with 5% hydrochloric acid at least 3 times, transfer the rinse liquid into a 50ml volumetric flask, and dilute the volume to the mark with 5% hydrochloric acid, leave it for 10 minutes, and transfer it to an HDPE plastic vial as the digestion solution to be tested for later use. ;

S7. Preparation of standard stock solution: Accurately measure 0.10ml of the national standard solution of mercury and the national standard solution of arsenic in a 100ml volumetric flask, dilute to the mark with 5% hydrochloric acid solution, shake well, and leave it for 10 minutes to obtain a concentration of 1.0μg/ml mercury. Primary standard stock solution and arsenic primary standard stock solution with a concentration of 1.0 μg/ml, for later use;

Accurately measure a certain volume of mercury primary standard stock solution and arsenic primary standard stock solution and place them in 100ml volumetric flasks respectively, and dilute to volume with 5% hydrochloric acid solution to prepare a secondary standard stock solution;

S8. Preparation of standard solution: Take a certain amount of secondary standard stock solution, adjust the volume to a certain scale with standard medium, obtain a series of concentration standard solutions, and use an atomic fluorescence spectrometer to test and draw a standard curve;

S9. Determination of the element content of the digestion solution to be tested: Use an atomic fluorescence spectrometer to test the digestion solution to be tested obtained in step S6. Repeat the measurement three times to obtain the fluorescence intensity. The corresponding elements in the briquettes can be obtained by converting the standard curve in step S8. content.
The method according to claim 3, characterized in that: it also includes S10, blank value measurement: a blank group is specially set up, that is, no digestion sample is added, and the sample to be tested is digested simultaneously with the sample to be tested according to the above steps, and the blank sample to be tested is repeatedly measured for 6 times, calculate the standard deviation of the test results, and the average of the 6 measurements is used as the blank value content of the corresponding element in the sample to be tested.
The method according to claim 1 or 2 or 3 or 4, characterized in that: in step S2, the briquette is prepared by the following method:

Measure 100 ml of NaOH solution with a mass concentration of 2.0% and place it in a beaker. Add 5% biomass powder that is naturally dried and crushed to ≤0.2mm in three stages. Stir and heat at 80°C for 2 hours, then cool to obtain the modified biomass powder. Substance; compound the modified biomass with asphalt and tar residue in a ratio of 1:6:3, and after mixing, a composite binder is obtained;

The pulverized coal and the composite binder are mixed in a mass ratio of 7:3 and placed in a molding machine for cold pressing to obtain a cylindrical coal briquette with a size of Φ30mm×30mm.
The method according to claim 3 or 4, characterized in that: in step S7, the secondary standard stock solution is prepared by the following method: accurately measure 5.00 ml of the mercury primary standard stock solution and place it in a 100 ml volumetric flask, and use 5 Dilute the % hydrochloric acid solution to the mark to obtain a mercury secondary standard stock solution with a concentration of 50ng/ml; accurately measure 10.00ml of the arsenic primary standard stock solution and place it in a 100ml volumetric flask, and dilute to the mark with 5% hydrochloric acid solution to obtain Arsenic secondary standard stock solution with a concentration of 100ng/ml.
The method according to claim 3 or 4, characterized in that: the preparation of a series of concentration standard solutions in step S8 is:

Accurately measure 0, 1.00, 2.00, 4.00, 8.00, 10.00ml of mercury secondary standard stock solution into six 100ml volumetric flasks, and dilute to the mark with 5% hydrochloric acid to obtain concentrations of 0, 0.50, 1.00, 2.00, 4.00, 5.00ng/ml mercury standard series solution;

Accurately measure 0, 1.00, 2.00, 4.00, 8.00, 10.00ml arsenic secondary standard stock solution into six 100ml volumetric flasks, and use arsenic standard medium to adjust the volume to the mark to obtain concentrations of 0, 1.00, 2.00, 4.00, 8.00, 10.00ng/ml arsenic standard series solution.
The method according to claim 7, characterized in that the arsenic standard medium is a mixed solution of 5% hydrochloric acid + 1% thiourea + 1% ascorbic acid.
The method according to claim 3 or 4, characterized in that: in step S8, the carrier current tested by the atomic fluorescence spectrometer is 5% hydrochloric acid solution, the carrier gas is high-purity argon, the pressure is 0.25MPa, and the flow rate is 400ml /min; the lamp current is 60~30mA, the negative high voltage is 240V, the atomizer height is 10mm, the shield flow rate is 1000ml/min, the reading time is 15s, and the delay time is 1.0s.
The method according to claim 3 or 4, characterized in that: in step S8, the mercury standard curve drawn by testing with an atomic fluorescence spectrometer is IF=2499.409c+48.011 Formula 1, where IF represents the fluorescence intensity of mercury, c represents the concentration of mercury in the solution;

The arsenic standard curve is IF=122.398c+7.946 Formula 2. In Formula 2, IF represents the fluorescence intensity of arsenic, and c represents the concentration of arsenic in the solution.
The method according to claim 3 or 4, characterized in that: in step S9, when the mercury element content is measured with an atomic fluorescence spectrometer, the reducing agent is a 1% potassium borohydride + 0.2% sodium hydroxide mixed solution; the atomic fluorescence spectrometer is used to measure When the arsenic element content is high, the reducing agent is a mixed solution of 2% potassium borohydride + 0.5% sodium hydroxide.
The method according to claim 5, characterized in that in step S2, the biomass is sunflower seed hulls or corn straw.
The method according to claim 5, characterized in that: in step S2, the mass concentration of the NaOH solution is 1.5% or 2.5%.
The method according to claim 5, characterized in that in step S2, the ratio of pulverized coal to the composite binder is 8:2 or 9:1.