CN110487758B - Method for measuring arsenic, selenium and lead in coal-fired power plant coal and combustion byproducts thereof - Google Patents
Method for measuring arsenic, selenium and lead in coal-fired power plant coal and combustion byproducts thereof Download PDFInfo
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Abstract
The invention discloses a method for measuring arsenic, selenium and lead in coal-fired power plant coal and combustion byproducts thereof, which comprises the steps of firstly weighing a sample in a digestion tank, sequentially adding a proper amount of nitric acid, hydrochloric acid and hydrofluoric acid, and carrying out microwave digestion after sealing; after digestion, acid removing treatment is carried out; then preparing liquid to be detected; preparing corresponding current-carrying, reducing agent and standard series solution; and (4) making a standard series curve, and obtaining the content of arsenic, selenium and lead in the sample by corresponding the data of the test sample with the standard curve. The method overcomes the defects of the traditional arsenic, selenium and lead content determination method by effectively pretreating coal of a coal-fired power plant and combustion byproducts thereof, reasonably proportioning reagents and setting instrument parameters, can stably digest and fully extract arsenic, selenium and lead in a sample, solves the problems of complex coal quality and interference of residual acid on a measurement result, and can accurately measure the content of arsenic, selenium and lead in the coal-fired power plant coal and combustion products thereof.
Description
Technical Field
The invention relates to a method for measuring arsenic, selenium and lead in coal of a coal-fired power plant and combustion byproducts thereof, belonging to the technical field of detection.
Background
Arsenic, selenium and lead are common toxic trace elements in coal, enter human bodies through modes of breathing, skin adsorption or food intake and the like, cause damage to central nerves and various organs of the human bodies, are accumulative elements, and can cause cancer after long-term chronic poisoning. According to statistics and estimation, the percentage of heavy metals discharged by various pollution sources in the whole world is calculated, wherein 2-6% of arsenic, 6-13% of selenium and 0.2-1.2% of lead come from coal-fired power plants.
Arsenic, selenium and lead in coal as fired for coal fired power plants are generally directed along the entire process, in three directions: the fly ash exists in the fly ash which is captured by a dust remover from bottom slag and flue gas after coal combustion; secondly, the flue gas exists in the desulfurized gypsum after passing through the desulfurizing tower; and thirdly, the residual smoke is discharged into the atmosphere. Research shows that most of trace elements in coal are enriched in fly ash and desulfurized gypsum. The desulfurized gypsum and the fly ash are the most main solid wastes of coal-fired power plants and are one of the main sources of the solid wastes in China. The method has the advantages of large occupied area and high labor cost, and has great harm to the environment due to the potential of secondary release of trace elements. Therefore, the method can accurately master and measure the arsenic, selenium and lead contents in the coal of the coal-fired power plant and the combustion byproducts thereof, and can provide guidance for the pretreatment of coal utilization, the control of the trace element emission pollution of the coal-fired power plant, the reutilization of coal-fired solid wastes and the like.
In recent years, some analysis and detection instruments are used for detecting arsenic, selenium and lead, for example, an X-ray absorption fine structure spectrum and an X-ray absorption near-edge structure can generate corresponding spectral characteristics for heavy metal elements, but the two technologies have higher detection limit for samples and are only suitable for analyzing samples with high element content, but are not suitable for trace elements of arsenic, selenium and lead in coal and combustion products thereof. Graphite furnace atomic absorption spectrometry and inductively coupled plasma-atomic emission spectrometry can simultaneously measure a plurality of heavy metal elements, but complex pretreatment steps are required, the detection sensitivity is relatively low, and the detection limit is high. The hydride generation-atomic fluorescence spectrometry has the advantages of high sensitivity, low detection limit and the like, and is suitable for detecting arsenic, selenium and lead with lower concentration in coal and combustion byproducts thereof.
In the sample pretreatment aspect, some researchers mix the sample with the aldka reagent for the burn and the arsenic molybdenum blue spectrophotometry, which both take longer, the aldka reagent burns for at least five hours, and the subsequent treatment is added, so that the whole experiment period is at least two days. The pressurized microwave digestion method becomes a wider sample pretreatment method due to the advantages of tightness, high efficiency, stability, small introduced pollution and the like, and various research institutions set different digestion programs and digestion reagents for different sample types. However, the components of coal are complex, the component proportion difference of different coal rank coals is large, and the existing digestion method can not completely digest all coal types. The process of removing acid after microwave digestion is also particularly critical, if the acid removal is not thorough, the residual strong oxidizing acid such as nitric acid can oxidize the element to be measured to a higher valence state, liquid phase interference is generated, and certain heavy metals exist in the acid, so that certain errors can be caused to the measurement result.
Therefore, the method for stably digesting, extracting and accurately measuring the arsenic, selenium and lead in the coal-fired power plant coal and the combustion byproducts thereof has very important practical significance for migration transformation and distribution characteristics of the arsenic, selenium and lead in the coal-fired power plant coal and the solid wastes after combustion thereof and secondary release problems caused by the migration transformation and distribution characteristics.
Disclosure of Invention
In order to solve the problems in the prior art, the invention aims to provide a method for measuring arsenic, selenium and lead in coal of a coal-fired power plant and combustion byproducts thereof.
In order to achieve the purpose, the technical scheme of the invention is as follows: a method for measuring arsenic, selenium and lead in coal of coal-fired power plant and combustion by-products thereof. The method comprises the following steps:
(1) microwave digestion: weighing 0.1-1g of coal, bottom slag, fly ash or gypsum, placing the coal, bottom slag, fly ash or gypsum in a Teflon digestion tank, adding mixed acid, sealing the digestion tank, heating to 220 ℃ from room temperature, performing gradient heating and pressurizing digestion at different gears at regular time, wherein the temperature range of the heating and pressurizing digestion is 120-220 ℃, the pressure range is 5-3MPa, the time is 3-20min, cooling to below 80 ℃ after digestion, taking out the digestion tank from a microwave digestion instrument, and placing the digestion tank in a fume hood;
(2) acid dispelling for the digestion solution: washing and transferring the liquid in the digestion tank to a polytetrafluoroethylene beaker by using deionized water, placing the polytetrafluoroethylene beaker on an electric heating plate for heating and acid dispelling, wherein the set temperature of the electric heating plate is 110-; adding a proper amount of deionized water when the liquid in the polytetrafluoroethylene beaker is nearly dry, performing secondary acid removal, and stopping acid removal when the liquid in the polytetrafluoroethylene beaker is nearly dry for the second time;
(3) preparing a solution to be detected: transferring the liquid in the polytetrafluoroethylene beaker in the step 2 into a 100ml volumetric flask, washing with deionized water for three times, transferring the washing liquid into the volumetric flask together, and adding hydrochloric acid to fix the volume;
(4) preparation of reagents for atomic fluorescence: the current carrying used for measuring the elements is hydrochloric acid solution with a fixed volume ratio, and then a reducing agent is added;
(5) drawing a standard curve: accurately preparing 10ml of standard use liquid with the concentration of 50ppb, wherein a standard curve is prepared by respectively using hydrochloric acid solutions with the volume ratios of 3%, 10% and 1% by adopting an atomic fluorescence-automatic dilution method to obtain a standard curve consisting of standard series of 10ppb, 20ppb, 30ppb, 40ppb and 50ppb, and the correlation degree R2 of each standard curve is required to be more than 0.9997;
(6) and (3) measuring the prepared solution to be measured: measuring the solution to be measured prepared in the step 3 by using an atomic fluorescence spectrometer and a hollow cathode lamp to obtain the fluorescence intensity, and comparing the fluorescence intensity with the standard curve obtained in the step 5 to obtain the corresponding element concentration;
(7) determination of blank: additionally arranging a blank group, not reinforcing a solid sample, simultaneously operating with the sample to be detected according to the steps (1) to (6), and taking the measured value as the content of the corresponding element of the blank;
preferably, when the element to be measured is arsenic, 3ml of hydrochloric acid and 3-5g of thiourea are added into the volumetric flask in the step 3, the volumetric flask is fixed to the constant volume and shaken up, heated in a constant-temperature water bath at 50 ℃ for 30min and then cooled and stood to be used as a solution to be measured of the arsenic element; in the step 4, the determination element is arsenic element, the current carrying is hydrochloric acid solution with the volume ratio of 3%, and the reducing agent is mixed solution of 0.5% of potassium hydroxide and 1% of potassium borohydride; in the step 5, the standard use solution is arsenic, and 0.3-0.5g of thiourea is added into the standard use solution; step 6, the hollow cathode lamp is an arsenic hollow cathode lamp, and the corresponding arsenic concentration is obtained; and 7, blank corresponding elements in the step 7 are arsenic elements.
Preferably, when the element to be measured is selenium, adding 10ml of hydrochloric acid into the volumetric flask in the step 3, and then, fixing the volume, shaking up and standing to obtain a solution to be measured of the selenium element; step 4, determining that the element is selenium element, wherein the current carrying used for determining the selenium element is a hydrochloric acid solution with the volume ratio of 10%, and the reducing agent is a mixed solution of 0.2% of potassium hydroxide and 1% of potassium borohydride; step 5, the standard use solution is selenium; step 6, the hollow cathode lamp is a selenium hollow cathode lamp, and the corresponding selenium concentration is obtained; and 7, the corresponding blank element is selenium element.
Preferably, when the element to be measured is lead, adding 1ml of hydrochloric acid into the volumetric flask in the step 3, and then, shaking up and standing to a constant volume to obtain a solution to be measured of the lead element; step 4, determining that the element is lead element, wherein the current carrying used for determining the lead element is hydrochloric acid solution with the volume ratio of 1%, and the reducing agent is mixed solution of 1% of potassium hydroxide, 1% of potassium borohydride and 1% of potassium ferricyanide; the standard use solution in the step 5 is lead; step 6, the hollow cathode lamp is a lead hollow cathode lamp, and the corresponding lead concentration is obtained; and step 7, the corresponding blank element is lead element.
Preferably, the composition of the mixed acid solution in the step 1 is 6ml of HNO3, 2ml of HCl and 2ml of HF.
Preferably, in the step 1, the step of gradient temperature rise and pressurization of the microwave digestion instrument from the first gear to the sixth gear comprises: 120 ℃, 5MPa, 3 min; at 150 ℃, 10MPa for 3 min; 170 ℃ and 15MPa for 3 min; 190 ℃, 20MPa, 3 min; at 210 ℃, 25MPa, 20 min; 220 ℃, 30MPa and 20 min.
Preferably, the reducing agent is prepared by adding potassium hydroxide to completely dissolve the potassium hydroxide and then adding potassium borohydride.
Preferably, the reducing agent for the lead element is added with potassium hydroxide for complete dissolution, then potassium borohydride is added, and finally potassium ferricyanide is added.
Preferably, in step 5 and step 6, the atomic fluorescence spectrometer uses high-purity argon as a carrier gas, and the working conditions are set as follows: the lamp current is 55-70mA, the negative high pressure is 250-270V, the height of the atomizer is 7.5-8.0mm, the flow rate of the carrier gas is 380-420ml/min, the delay time is 0.5-1.0s, and the reading time is 7-10 s.
Compared with the prior art, the invention has the beneficial effects that: 1. the method overcomes the defects of the traditional arsenic, selenium and lead content determination method by effectively pretreating coal of a coal-fired power plant and combustion byproducts thereof, reasonably proportioning reagents and setting instrument parameters, can stably digest and fully extract arsenic, selenium and lead in a sample, solves the problems of complex coal quality and interference of residual acid on a measurement result, and can accurately measure the content of arsenic, selenium and lead in the coal-fired power plant coal and combustion products thereof. 2. The microwave digestion scheme can stably digest and fully extract arsenic, selenium and lead in the coal and combustion byproducts thereof, the acid removing process can fully eliminate the influence of residual acid in the digestion solution, and the atomic fluorescence spectrometry can accurately measure the concentrations of the arsenic, the selenium and the lead in the digestion solution obtained after pretreatment.
Drawings
FIG. 1 is a diagram: as measured in examples 1-3 and comparative example.
FIG. 2 is a diagram of: se measured in examples 1-3 and comparative example.
FIG. 3 is a diagram of: measurement of Pb in examples 1 to 3 and comparative example.
Detailed Description
The invention is further illustrated by the following examples: in the embodiment, in addition to the digestion mixed acid scheme, another two mixed acid schemes are selected for comparison with the traditional wet digestion method, and the specific operations are as follows:
example 1:
weighing three parts of 0.1g of solid sample (coal, bottom slag, fly ash or gypsum), respectively placing the three parts in three Teflon digestion tanks, sequentially adding 6ml of HNO3, 2ml of HCl and 2ml of HF, then sealing the digestion tanks, carrying out digestion in a microwave digestion instrument, heating from room temperature to 220 ℃, heating from one grade to six grades (120 ℃, 5MPa, 3 min; 150 ℃, 10MPa, 3 min; 170 ℃, 15MPa, 3 min; 190 ℃, 20MPa, 3 min; 210 ℃, 25MPa, 20 min; 220 ℃, 30MPa, 20min) at regular time and gradient temperature rise and pressurization digestion, cooling to below 80 ℃ after digestion, taking out the tanks from the microwave digestion instrument and placing the tanks in a ventilation digestion cabinet.
And respectively flushing and transferring the liquid in the three digestion tanks to three polytetrafluoroethylene beakers by using deionized water, placing the polytetrafluoroethylene beakers on an electric heating plate for heating and acid dispelling, setting the temperature of the electric heating plate to be 130 ℃, adding a proper amount of deionized water when the liquid in the polytetrafluoroethylene beakers is nearly dry, carrying out secondary acid dispelling, and stopping acid dispelling when the liquid in the polytetrafluoroethylene beakers is nearly dry.
Respectively transferring the liquid in three polytetrafluoroethylene beakers into three 100ml volumetric flasks, washing with deionized water for three times, transferring the washing liquid into the volumetric flasks together, numbering a, b and c, adding 3ml hydrochloric acid and 5g thiourea into the volumetric flask a, then uniformly shaking to a constant volume, heating in a 50 ℃ constant temperature water bath for 30min, cooling and standing to obtain a solution to be measured as arsenic element, adding 10ml hydrochloric acid into the volumetric flask b, uniformly shaking to a constant volume, standing to obtain a solution to be measured as selenium element, adding 1ml hydrochloric acid into the volumetric flask a, uniformly shaking to a constant volume, and standing to obtain a solution to be measured as lead element.
Preparing a reagent for atomic fluorescence, wherein a current carrying used for measuring arsenic is a hydrochloric acid solution with the volume ratio of 3%, and a reducing agent is a mixed solution of 0.5% potassium hydroxide and 1% potassium borohydride after the potassium hydroxide is completely dissolved; the current carrying used for measuring the selenium element is a hydrochloric acid solution with the volume ratio of 10%, and the reducing agent is a mixed solution of 0.2% potassium hydroxide and 1% potassium borohydride after being completely dissolved; the current carrying used for measuring the lead element is a hydrochloric acid solution with the volume ratio of 1%, the reducing agent is 1% potassium hydroxide which is completely dissolved, then, the% potassium borohydride is added, and finally, the 1% potassium ferricyanide mixed solution is added.
10ml of standard use solution of arsenic, selenium and lead with the concentration of 50ppb is accurately prepared, wherein 0.5g of thiourea is added into the standard use solution of arsenic, the standard curve is prepared by adopting an atomic fluorescence-automatic dilution method by using hydrochloric acid solutions with the volume ratios of 3%, 10% and 1%, so as to obtain standard curves consisting of standard series of 10ppb, 20ppb, 30ppb, 40ppb and 50ppb, and the correlation degree R2 of each standard curve is required to be more than 0.9997.
Setting parameters of an atomic fluorescence spectrometer, using high-purity argon as carrier gas, and setting working conditions as follows: the lamp current is 55-70mA, the negative high pressure is 250-270V, the height of the atomizer is 7.5-8.0mm, the flow rate of the carrier gas is 380-420ml/min, the delay time is 0.5-1.0s, and the reading time is 7-10 s. And measuring the prepared solution to be detected to obtain the fluorescence intensity, and comparing the fluorescence intensity with a standard curve to obtain the corresponding concentrations of arsenic, selenium and lead.
And (3) additionally arranging a blank group, not reinforcing a solid sample, simultaneously operating with the sample to be detected according to the steps (1) to (6), and taking the measured value as the contents of white arsenic, selenium and lead.
Table 1 shows the results of the detection of arsenic, selenium and lead for the samples:
according to the results, the microwave digestion method can fully extract the coals of different coal grades and the arsenic, selenium and lead in the combustion by-products of the coals, such as bottom slag, fly ash and desulfurized gypsum, the RSD of the measurement result of the hydride generation-atomic fluorescence spectrometry is within 10%, and the standard recovery rate is between 80 and 120%, so that the measurement result of the method is accurate and reliable.
Example 2.3
The other steps are the same as example 1, but the mixed acid scheme is different, wherein, the mixed acid schemes of examples 1-3 are respectively shown in Table 1:
TABLE 1 Mixed acid System
| Mixed acid system | Species of | Dosage (ml) |
| Example 1 | HNO3-HCl-HF | 6-2-2 |
| Example 2 | HNO3-HCl-H2O2 | 6-2-2 |
| Example 3 | HNO3-HCl-H2SO4 | 6-2-2 |
Comparative example 1: wet digestion method
Weigh 0.1g of sample into a Teflon beaker and add 6ml of HNO32ml HCl and 2ml HF, covered with a watch glass and then placed in an air hood overnight.
The next day the beaker was placed on an electric heating plate for digestion, the temperature of which was set at 180 ℃. When a large amount of white dense smoke is emitted from the beaker, observing the color of the solution in the beaker and the color of the residual sample, if the solution is nearly transparent and the residual sample is grey white, determining that the sample is completely digested, taking down and cooling, and then carrying out the next step; if the solution is turbid or the residual sample is dark brown, cooling, adding a proper amount of mixed acid solution, and placing on an electric heating plate for continuous digestion.
The cooled solution in the beaker was transferred to a 1000ml volumetric flask and the work of the work-up was the same as in the microwave digestion process described above.
Digestion and measurement of results
The results of microwave digestion and wet digestion using three different mixed acid systems are shown in table 3, and the measurement results are shown in table 4:
TABLE 3 digestion results
TABLE 4 measurement results (wherein the mixed acids one, two and three correspond to examples 1 to 3, respectively)
As shown in FIGS. 1 to 3, it can be seen from the digestion results and the measurement results that HNO was present3-HCl-HF mixed acid system and HNO3-HCl-H2SO4The mixed acid system has better digestion effect on the sample, can completely digest the sample, and has HNO3-HCl-H2O2The mixed acid system is mainly used for digesting samples such as food, medicines and the like, wherein H2O2Can only destroy organic tissues in samples, and the content of silicate in coal-fired power plant coal, fly ash and bottom slag is higher, so H2O2The digestion effect on the coal-fired power plant sample is poor, and HF has a good decomposition effect on silicon dioxide and silicate.
Albeit HNO3-HCl-H2SO4The mixed acid system can digest the sample well, but the measured value is still low because the boiling point of the sulfuric acid is high, the sulfuric acid cannot be driven in by the general acid-driving process, the acidity requirement of the measurement process of the atomic fluorescence photometer is strict, and the existence of the sulfuric acid has a great influence on the measurement result. Further, as a result of observing the measurement of Pb, it was found that the measurement of Pb in the digestion system III was extremely low because sulfuric acid reacted with Pb in the sample to produce PbSO4Precipitate and cannot be detected later by the instrument.
Measurement result of wet digestion and HNO3The results of the measurement of the-HCl-HF mixed acid system are relatively close, mainly because the tightness is poor during the digestion process, so that the loss of arsenic and selenium is relatively high, and the lead element is not volatile, so that the measurement result is relatively good. However, the wet digestion has the disadvantages of long operation period and open to mixed acid solutionThe liquid heating risk is high. In summary, four sample digestion methods, HNO3The microwave digestion of the-HCl-HF mixed acid system has the advantages of complete digestion, short operation period and less loss of elements to be detected.
The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that are not thought of through the inventive work should be included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope defined by the claims.
Claims (4)
1. A method for measuring arsenic, selenium and lead in coal of a coal-fired power plant and combustion byproducts thereof is characterized by comprising the following steps: the method comprises the following steps:
step 1, microwave digestion: weighing 0.1-1g of coal, bottom slag, fly ash or gypsum, placing the coal, bottom slag, fly ash or gypsum in a Teflon digestion tank, adding mixed acid, sealing the digestion tank, heating to 220 ℃ from room temperature, performing gradient heating and pressurizing digestion at different gears at regular time, wherein the temperature range of the heating and pressurizing digestion is 120-220 ℃, the pressure range is 5-3MPa, the time is 3-20min, cooling to below 80 ℃ after digestion, taking out the digestion tank from a microwave digestion instrument, and placing the digestion tank in a fume hood;
step 2, acid dispelling of the digestion solution: washing and transferring the liquid in the digestion tank to a polytetrafluoroethylene beaker by using deionized water, placing the polytetrafluoroethylene beaker on an electric heating plate for heating and acid removal, setting the temperature of the electric heating plate to be 110-;
step 3, preparing a solution to be detected: transferring the liquid in the polytetrafluoroethylene beaker in the step 2 into a 100ml volumetric flask, washing with deionized water for three times, transferring the washing liquid into the volumetric flask together, and adding hydrochloric acid to fix the volume;
step 4, preparing a reagent for atomic fluorescence: the current carrying used for measuring the elements is hydrochloric acid solution with a fixed volume ratio, and then a reducing agent is added;
step 5, drawing a standard curve: accurately preparing 10ml with a concentration of 50ppb standard use solutions of arsenic, selenium and lead, wherein the standard use solutions respectively use hydrochloric acid solutions with volume ratios of 3%, 10% and 1% to configure standard curves by adopting an atomic fluorescence-automatic dilution method to obtain standard curves consisting of standard series of 10ppb, 20ppb, 30ppb, 40ppb and 50ppb, and correlation degree R of each standard curve is required2＞0.9997；
Step 6, measuring the prepared solution to be measured: measuring the solution to be measured prepared in the step 3 by using an atomic fluorescence spectrometer and a hollow cathode lamp to obtain the fluorescence intensity, and comparing the fluorescence intensity with the standard curve obtained in the step 5 to obtain the corresponding element concentration;
step 7 determination of blank: additionally arranging a blank group, not reinforcing a solid sample, simultaneously operating with the sample to be detected according to the steps 1-6, and taking the measured value as the content of the corresponding element of the blank;
when the element to be measured is arsenic, adding 3ml of hydrochloric acid into the volumetric flask in the step 3, adding 3-5g of thiourea, fixing the volume, shaking up, heating in a constant-temperature water bath at 50 ℃ for 30min, cooling and standing to serve as a solution to be measured of the arsenic element; in the step 4, the determination element is arsenic element, the current carrying is hydrochloric acid solution with the volume ratio of 3%, and the reducing agent is mixed solution of 0.5% of potassium hydroxide and 1% of potassium borohydride; the standard use solution in the step 5 is arsenic standard use solution, and 0.3-0.5g of thiourea is added into the standard use solution; step 6, the hollow cathode lamp is an arsenic hollow cathode lamp, and the corresponding arsenic concentration is obtained; step 7, the blank corresponding element is arsenic element;
when the element to be measured is selenium, adding 10ml of hydrochloric acid into the volumetric flask in the step 3, and then fixing the volume, shaking up and standing to obtain a solution to be measured of the selenium element; step 4, determining that the element is selenium element, wherein the current carrying used for determining the selenium element is a hydrochloric acid solution with the volume ratio of 10%, and the reducing agent is a mixed solution of 0.2% of potassium hydroxide and 1% of potassium borohydride; step 5, the standard use solution is selenium standard use solution; step 6, the hollow cathode lamp is a selenium hollow cathode lamp, and the corresponding selenium concentration is obtained; step 7, corresponding blank elements are selenium elements;
when the determination element is lead, adding 1ml of hydrochloric acid into the volumetric flask in the step 3, and then carrying out constant volume shaking and standing to obtain a solution to be determined of the lead element; step 4, determining that the element is lead element, wherein the current carrying used for determining the lead element is hydrochloric acid solution with the volume ratio of 1%, and the reducing agent is mixed solution of 1% of potassium hydroxide, 1% of potassium borohydride and 1% of potassium ferricyanide; the standard use solution in the step 5 is lead standard use solution; step 6, the hollow cathode lamp is a lead hollow cathode lamp, and the corresponding lead concentration is obtained; step 7, corresponding blank elements are lead elements;
the composition of the mixed acid solution in the step 1 is 6ml of HNO3, 2ml of HCl and 2ml of HF;
in the step 1, the step of gradient temperature rise and pressurization of the microwave digestion instrument from the first gear to the sixth gear comprises the following steps: 120 ℃, 5MPa, 3 min; at 150 ℃, 10MPa for 3 min; 170 ℃ and 15MPa for 3 min; 190 ℃, 20MPa, 3 min; at 210 ℃, 25MPa, 20 min; 220 ℃, 30MPa and 20 min.
2. The method of claim 1, wherein the reducing agent is potassium hydroxide and potassium borohydride are added after potassium hydroxide is completely dissolved.
3. The method of claim 1, wherein the reducing agent for lead is added with potassium hydroxide to dissolve completely, then added with potassium borohydride, and finally added with potassium ferricyanide.
4. The method for measuring As, Se and Pb in coal-fired power plant coal and its combustion byproducts as claimed in claim 1, wherein in step 5 and step 6, the atomic fluorescence spectrometer uses high purity argon as carrier gas, and the operating conditions are set as follows: the lamp current is 55-70mA, the negative high pressure is 250-270V, the height of the atomizer is 7.5-8.0mm, the flow rate of the carrier gas is 380-420ml/min, the delay time is 0.5-1.0s, and the reading time is 7-10 s.
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