CN109163960B - Method for sequentially extracting arsenic and selenium in different forms from fly ash under assistance of microwaves - Google Patents
Method for sequentially extracting arsenic and selenium in different forms from fly ash under assistance of microwaves Download PDFInfo
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Abstract
A microwave-assisted method for sequentially extracting arsenic and selenium in different forms from fly ash, which adopts a microwave digestion instrument, adds different extracting agents and extracts arsenic and selenium in different adsorption states under different microwave conditions, comprises the following steps: performing early-stage treatment on a fly ash sample; extracting arsenic and selenium in a non-specific adsorption state (form 1); extracting arsenic and selenium in a specific adsorption state (form 2); amorphous and weak crystalline iron-aluminum hydrated oxide combined state (form 3) arsenic-selenium extraction, wherein different forms of arsenic-selenium require different microwave extraction powers, temperatures and times. Compared with the traditional oscillation extraction scheme, the method greatly shortens the extraction time, has stable result and presents high repeatability and reproducibility.
Description
Technical Field
The invention relates to a method for sequentially extracting arsenic and selenium in different forms from fly ash under the assistance of microwaves, belonging to the technical field of analytical chemistry.
Background
In global coal consumption, nearly 50% of coal consumption is used in the power industry, and burning of large amounts of coal causes extremely serious problems with emission of Trace Elements (TEs). The present research proves that the fly ash has obvious enrichment effect on arsenic and selenium. The environmental effect of the fly ash is not accurately evaluated by the concentration of arsenic and selenium element in the fly ash singly, and the arsenic and selenium in different occurrence states have close relation with bioavailability, toxicity, mobility and the like. At present, most morphological analysis research is established on a Tessier method, a BCR method of European Union certification is developed subsequently, but the extraction efficiency of arsenic and selenium is not satisfactory. The Wenzel method is used for extracting and optimizing the form of arsenic and selenium elements in environmental media, and is widely applied to analysis of arsenic and selenium in various environmental media. However, the extraction method of the traditional Wenzel method is oscillation extraction, and the period is long, so a method for rapidly and stably extracting arsenic and selenium form in fly ash is urgently needed to be found, and the method is still a hot spot and a leading-edge subject of research in the field of analytical chemistry.
Disclosure of Invention
The invention provides a method for sequentially extracting arsenic and selenium in different forms from fly ash by microwave assistance, aiming at the problems in the prior art, the method utilizes the heating effect of a microwave energy source and combines with the traditional method to extract solution, and respectively carries out microwave-assisted sequential extraction on a specific adsorption state, a non-specific adsorption state and an amorphous and weak crystalline iron-aluminum hydrated oxide binding state under different microwave conditions.
The technical problem of the invention is solved by the following technical scheme:
a microwave-assisted method for sequentially extracting arsenic and selenium in different forms from fly ash is characterized in that a microwave digestion instrument is adopted, different extracting agents are added, and arsenic and selenium in different adsorption states are extracted under different microwave conditions, and the method comprises the following steps:
a. pretreatment of a fly ash sample: grinding a fly ash sample, freeze-drying for 24 hours, sieving with a 200-mesh sieve, storing the sieved sample in a dryer with the temperature of 22 +/-1 ℃ and the relative humidity of 40 +/-5%, and balancing for later use;
b. extraction of arsenic and selenium in non-specific adsorption state (form 1): form 1 extraction of arsenic: weighing 0.5g of the fly ash sample treated in the step a into a microwave digestion tank, adding 12.5mL of 0.05M ammonium sulfate solution, performing microwave extraction at 3000W and 130 ℃ for 460 and 500s, placing the extracted suspension into a centrifugal tube for centrifugation, taking the supernatant, filtering for hydride-atomic fluorescence spectrum analysis, and leaving residue B1 for use; form 1 extraction of selenium: weighing 0.5g of the fly ash sample treated in the step a into a microwave digestion tank, adding 12.5mL of 0.05M ammonium sulfate solution, performing microwave extraction at 3000W and 60 ℃ for 460 and 500s, placing the extracted suspension into a centrifugal tube for centrifugation, taking the supernatant, filtering for hydride-atomic fluorescence spectrum analysis, and leaving residue B2 for use;
c. extraction of arsenic and selenium in specific adsorption state (form 2): form 2 arsenic extraction: adding 12.5mL of 0.05M ammonium dihydrogen phosphate into the residue B1 after the non-specific adsorption arsenic is extracted in the step B for three times, transferring the residue B1 into a digestion tank, performing microwave extraction at 3000W and 50 ℃ for 220-260s, placing the extraction suspension in a centrifugal tube for centrifugation, taking the supernatant for filtration and performing hydride-atomic fluorescence spectroscopy analysis, and reserving the residue C1; form 2 extraction of selenium: adding 12.5mL of 0.05M ammonium dihydrogen phosphate into the residue B2 after the non-specific adsorption selenium is extracted in the step B for three times, transferring the residue B2 into a digestion tank, performing microwave extraction at 3000W and 60 ℃ for 220-260s, placing the extraction suspension in a centrifugal tube for centrifugation, taking the supernatant for filtration and performing hydride-atomic fluorescence spectroscopy analysis, and reserving the residue C2;
d. extraction of arsenic selenium in amorphous and weakly crystalline iron-aluminium hydrated oxide bound state (form 3): form 3 arsenic extraction: adding 0.2M ammonium oxalate buffer solution into the residue C1 for three times to total 12.5mL, transferring to a digestion tank, performing microwave extraction at 3000W and 50 ℃ for 110-130s, placing the extraction suspension in a centrifugal tube for centrifugation, taking the supernatant, filtering for hydride-atomic fluorescence spectrum analysis, and reserving the residue D1; form 3 extraction of selenium: adding 0.2M ammonium oxalate buffer solution into the residue C2 for three times to total 12.5mL, transferring to a digestion tank, performing microwave extraction at 50 ℃ for 110-130s at 2000W, placing the extraction suspension in a centrifugal tube for centrifugation, taking the supernatant, filtering for hydride-atomic fluorescence spectrum analysis, and reserving the residue D2;
e. extraction of arsenic and selenium in a fully crystalline iron-aluminum oxide binding state (form 4): form 4 arsenic extraction: adding 25mL of a mixed solution of 0.2M ammonium oxalate buffer solution and 0.1M ascorbic acid into residue D1, heating in a visible light water bath at 90 ℃ for 30min, centrifuging, taking supernatant, continuously adding 12.5mL of ammonium oxalate buffer solution with the value of 0.2M, pH being 3.25 into the residual residue, shaking for 10 min in a dark place, centrifuging under the same condition, uniformly mixing and filtering 37.5 mL of the two supernatants together for hydride-atomic fluorescence spectrometry, and keeping residue E1 for later use; form 4 extraction of selenium: adding 25mL of a mixed solution of 0.2M ammonium oxalate buffer solution and 0.1M ascorbic acid into the residue D2, heating in a visible light water bath at 90 ℃ for 30min, centrifuging, and taking a supernatant; adding 12.5ml of ammonium oxalate buffer solution with the value of 0.2M, pH being 3.25 into the residual residue, shaking for 10 min in dark, centrifuging under the same condition, mixing 37.5 ml of the two supernatants uniformly, filtering, and performing hydride-atomic fluorescence spectrometry to obtain residue E2 for later use;
f. extraction of arsenic and selenium in residue state (form 5): form 5 arsenic extraction: adding 4mL of nitric acid, 1mL of hydrofluoric acid and 1mL of hydrogen peroxide into the residue E1 for microwave digestion, cooling, centrifuging, taking supernatant, filtering and carrying out hydride-atomic fluorescence spectrometry; form 5 extraction of selenium: adding 4mL of nitric acid, 1mL of hydrofluoric acid and 1mL of hydrogen peroxide into the residue E2 for microwave digestion, cooling, centrifuging, taking supernatant, filtering and carrying out hydride-atomic fluorescence spectrometry.
In the step b, the heating extraction is performed in stages in the extraction process of the arsenic in the form 1, and the method comprises the following steps:
in the first stage, the pressure of a microwave digestion instrument is set to be 1.0MPa, the power is set to be 3000W, the temperature is increased from normal temperature to 80 ℃, the temperature rising time is 30s, and the constant temperature time is 30 s;
in the second stage, the pressure of the microwave digestion instrument is adjusted to be 1.5MPa, the power is 3000W, the temperature is increased from 80 ℃ to 110 ℃, the temperature rising time is 30s, and the constant temperature time is 30 s;
and in the third stage, the pressure of the microwave digestion instrument is adjusted to be 2.0MPa, the power is 3000W, the temperature is increased from 110 ℃ to 130 ℃, the temperature rise time is 60s, and the constant temperature time is 480 s.
In the step b, in the extraction process of the selenium in the form 1, the extraction conditions are as follows: setting the pressure of the microwave digestion instrument to be 1.0MPa, the power to be 3000W, the temperature to be raised from room temperature to 60 ℃, the temperature rise time to be 30s and the constant temperature time to be 480 s.
In the microwave-assisted method for sequentially extracting arsenic and selenium in different forms from the fly ash, in the step c, in the extraction of arsenic in the form 2, the extraction conditions are as follows: setting the pressure of the microwave digestion instrument to be 1.0MPa, the power to be 3000W, the temperature to be raised from room temperature to 50 ℃, the temperature raising time to be 60s and the constant temperature time to be 240 s.
In the microwave-assisted method for sequentially extracting arsenic and selenium in different forms from the fly ash, in the step c, in the extraction of selenium in the form 2, the extraction conditions are as follows: setting the pressure of the microwave digestion instrument to be 1.0MPa, the power to be 2000W, the temperature to be raised from room temperature to 60 ℃, the temperature raising time to be 60s and the constant temperature time to be 240 s.
In the microwave-assisted method for sequentially extracting arsenic and selenium in different forms from the fly ash, in the step d, in the extraction of arsenic in the form 3, the extraction conditions are as follows: setting the pressure of the microwave digestion instrument to be 1.0MPa, the power to be 3000W, the temperature to be raised from room temperature to 50 ℃, the temperature raising time to be 60s and the constant temperature time to be 120 s.
In the microwave-assisted method for sequentially extracting arsenic and selenium in different forms from the fly ash, in the step d, in the extraction of the selenium in the form 3, the extraction conditions are as follows: the pressure of the microwave digestion instrument is set to be 1.0MPa, the power is set to be 2000W, the temperature is increased from room temperature to 50 ℃, the temperature rising time is 60s, and the constant temperature time is 120 s.
In the microwave-assisted method for sequentially extracting arsenic and selenium in different forms from fly ash, ammonium sulfate, ammonium dihydrogen phosphate and ammonium oxalate in the steps b-d are superior pure reagents, and the pH value of the ammonium oxalate buffer solution adopted in the step d is 3.25.
In the method for sequentially extracting arsenic and selenium in different forms from fly ash under the assistance of microwave, the working parameters of analysis by using a hydride-atomic fluorescence spectrometer in the steps b-d are as follows: the negative high voltage is 270V, the lamp current is 60mA, the atomizer height is 8mm, the atomizer temperature is 200 ℃, the carrier gas flow is 400mL/min, the shield gas flow is 800 mL/min, the reading time is 7.0s, and the delay time is 1.3 s.
In the microwave-assisted method for sequentially extracting arsenic and selenium in different forms from the fly ash, in the step f, the form 5 arsenic and selenium is digested and extracted in stages under the following extraction conditions:
in the first stage, the pressure of a microwave digestion instrument is set to be 1.0MPa, the power is set to be 3000W, the temperature is increased from room temperature to 100 ℃, the temperature rising time is 500s, and the constant temperature time is 60 s;
in the second stage, the pressure of the microwave digestion instrument is set to be 1.5MPa, the power is set to be 3000W, the temperature is increased from 100 ℃ to 130 ℃, the temperature rising time is set to be 200s, and the constant temperature time is set to be 60 s;
in the third stage, the pressure of the microwave digestion instrument is set to be 2.0MPa, the power is set to be 3000W, the temperature is increased from 130 ℃ to 160 ℃, the temperature-rising time is set to be 200s, and the constant-temperature time is set to be 60 s;
and in the fourth stage, setting the pressure of the microwave digestion instrument to be 1.0MPa, the power to be 3000W, the temperature to be increased from 160 ℃ to 180 ℃, the temperature-increasing time to be 500s and the constant temperature time to be 1200 s.
The principle of freeze drying: the method comprises the steps of freezing a wet raw material in a sample below a freezing point to convert moisture in the sample into solid ice, directly converting the ice into steam in a vacuum environment to remove the solid ice, and condensing the steam by using a steam condenser in a vacuum system to dry the sample. The freeze drying can lead the water in the sample to be directly sublimated into water vapor without passing through a liquid phase, and when ice is sublimated, gaps are left in the dried residual substances, so that the biological and chemical structural integrity of the sample is reserved, and the subsequent chemical analysis is convenient to carry out.
Principle of microwave energy source extraction: under the radiation of microwave energy, the polar molecules change their orientation rapidly with the change of microwave frequency, and the molecules rub against each other, absorbing microwave energy results in the temperature rise of the extracting solution. Microwave heating is a direct heating mode, and not only the heating is rapid, and the heating is also more even, and is efficient compared with the traditional heating mode. The change of the microwave frequency can cause the rapid transformation of the orientation of the electromagnetic field, the polar molecules of the reagent and the sample can transform the orientation along with the rapid change of the electromagnetic field, the mutual friction among the molecules is increased, which is equivalent to that the surfaces of the reagent and the sample are constantly updated, and the surface of the sample is constantly contacted with new reagent, so that the chemical reaction of the reagent and the sample is accelerated, and the efficient and stable extraction effect is achieved.
According to the method, the microwave energy source is used for replacing the traditional mechanical oscillation energy source to extract arsenic and selenium in different forms from the fly ash, so that the extraction time is greatly shortened, the extraction time of the traditional Wenzel method (oscillation extraction method) exceeds 24.5h, the extraction time of the method is controlled within 1h, the extraction efficiency is improved, and the extraction has good repeatability and reproducibility; the average recovery rates of the nonspecific adsorption-state arsenic and selenium extracted by microwave are respectively 96.2% and 114.8% of the average recovery rate of the mechanical oscillation of the traditional Wenzel method; the average recovery rate of arsenic and selenium in specific adsorption states is 104.5 percent and 105.4 percent of that of the traditional Wenzel method respectively; the average recovery rates of amorphous and weak crystalline iron-aluminum hydrated oxide combined arsenic and selenium are respectively 103.9% and 122.7% of the traditional Wenzel method, the extraction recovery rate is high, the time is short, and the extraction efficiency is greatly improved.
Drawings
FIG. 1 is a process flow diagram of the extraction method of the present invention.
Detailed Description
The invention utilizes the characteristics of arsenic and selenium with different forms in the fly ash to carry out rapid extraction. Arsenic and selenium in the fly ash are roughly divided into three forms: three forms of adsorption state, combination state and residue state. Sequential extraction is an important means of simulating the flowability characteristics of heavy metals under specific environmental conditions. The adsorption state refers to the form of the elements adsorbed on clay, humus and other components. Specifically, the method can be divided into a non-specific adsorption state and a specific adsorption state, and the two states are mainly distinguished whether the element has specific affinity action on a specific group or not. The stability of the adsorbed elements is poor, the influence of environmental factors is great, and the environmental threat is maximum; the binding state refers to the existence form of elements combined with the iron-aluminum-water and the oxide, namely, the combination generated after the reaction with the iron-aluminum-water oxide or part of elements coated on the surface of the sediment particles. The method can be divided into an amorphous and weak crystalline iron-aluminum hydrated oxide combined state and a fully crystalline iron-aluminum hydrated oxide combined state, the heavy metal in the form has poor stability under the reducing condition, and when the oxidation-reduction potential (Eh) of the environment is changed, the heavy metal can be released, so that the method has potential hazard; the residue state is the existing form of elements in primary and secondary mineral lattices, can exist stably in nature for a long time and is not easy to be absorbed by organisms, and the environmental toxicity is low.
The present invention is further illustrated by the following examples.
The microwave extraction experiment is correspondingly carried out with blank experiments, and the blank experiments comprise instrument blanks and reagent extraction blanks. Instrument blank experiment: after the atomic fluorescence instrument is started to operate, instrument blank inspection is carried out, the inspection method comprises the steps of walking 5% hydrochloric acid and mixed reducing liquid (1% potassium borohydride and 0.5% potassium hydroxide) for 5 times to obtain a basic blank value, and the instrument automatically calibrates test data by utilizing a self-contained workstation. Sample blank experiment: and (3) synchronously carrying out a blank extracting solution experiment in the sample experiment process, only adding an extracting solution and not adding a fly ash sample, and carrying out measurement and analysis in the same procedure as the sample test. The microwave extraction method is used for respectively carrying out microwave digestion-assisted sequential extraction on arsenic and selenium in different forms for different time lengths and different powers.
Example 1
Collecting a fly ash sample of a power plant in Hebei, grinding the fly ash sample, freeze-drying the ground fly ash sample at a low temperature for 24 hours, sieving the ground fly ash sample by using an automatic horizontal reciprocating vibration sieving machine to sieve the fly ash sample with a 200-mesh sieve, balancing the obtained sample under the condition specified by GB/T32722, and calibrating the pressure and the temperature of a microwave digestion instrument before an experiment.
Extraction of non-specific adsorption state arsenic: weighing 0.5g of fly ash sample subjected to balance treatment in a microwave digestion tank, adding 12.5mL of ammonium sulfate solution and 0.05M of ammonium sulfate solution, oscillating to fully mix the fly ash sample with an extracting solution, screwing the inner tank of the digestion tank, screwing an outer tank of the digestion tank by 45 degrees under an initial resistance state, setting the program of the microwave digestion instrument in three steps, carrying out microwave digestion for 8min when the power of the microwave digestion instrument is 3000W and the temperature is 130 ℃, cooling an extraction suspension to room temperature after the microwave is finished, transferring the extraction suspension into a 50mL centrifugal tube, centrifuging the extraction suspension for 15min at the rotating speed of 3000r/min, taking supernatant, filtering the supernatant through a 0.45-micrometer microporous water system filter membrane, placing 1mL of filtered arsenic extracting solution into 3mL of mixed solution of 5% dilute hydrochloric acid and 1mL of 5% thiourea-ascorbic acid, fully mixing and standing the mixed solution for 30min, and carrying out hydride-atomic fluorescence spectrum analysis; the extraction of non-specific adsorption selenium is the same as the extraction of arsenic, the program of a microwave digestion instrument is further set to microwave digestion conditions, microwave digestion is carried out for 8min at 3000W and 60 ℃, the centrifugation of the extracted suspension is the same as the operation step of arsenic, after the centrifugation and filtration, 1mL of filtered selenium extract is put into 4mL of 5% dilute hydrochloric acid, and after the selenium extract and the arsenic are fully mixed and kept stand for 1h, hydride-atomic fluorescence spectrometry is carried out; after the atomic fluorescence instrument is started to operate, performing instrument blank inspection by walking 5% hydrochloric acid and mixed reducing solution (1% potassium borohydride and 0.5% potassium hydroxide) for 5 times to obtain a basic blank value, and automatically calibrating test data by using a self-contained workstation; extraction experiments of arsenic and selenium with different forms are carried out in 5 groups of parallel experiments, and simultaneously, extraction solution blank experiments are carried out: the detection analysis of the same procedure as the sample test is carried out by adding only the extraction solution and not adding the fly ash sample, and after the blank of the extraction solution is deducted in the detection analysis, the average concentration of the non-specific adsorption state (form 1) arsenic and selenium is respectively 2.28 +/-0.56 mg/kg and 1.98 +/-0.34 mg/kg. The average concentration of nonspecific arsenic selenium extracted by oscillation by the traditional Wenzel method is 2.68 plus or minus 0.62 mg/kg and 1.87 plus or minus 0.42 mg/kg respectively. The average recovery rates of the microwave-assisted extraction of the nonspecific adsorption state arsenic and selenium by the method are 85.1 percent and 105.9 percent of that of the traditional oscillation extraction respectively.
Extracting specific adsorption state arsenic: and adding 12.5mL of 0.05M ammonium dihydrogen phosphate into the residues B1 and B2 after the non-specific adsorption state arsenic and selenium are extracted for three times, washing the residues in the centrifugal tube, transferring the residues back to a digestion tank, uniformly mixing, extracting the arsenic and selenium under the conditions of 3000W and 50 ℃, extracting for 4min, 2000W and 60 ℃, and extracting for 4min, wherein the treatment method and the detection method of the extracted sample are the same as those of the non-specific adsorption state arsenic and selenium. Finally, the average concentrations of the arsenic and selenium in the specific adsorption state (form 2) are respectively 6.88 +/-1.14 mg/kg and 1.17 +/-0.19 mg/kg, and the average concentrations measured by shaking the form 2 by the traditional Wenzel method are respectively 8.56 +/-1.21 mg/kg and 1.11 +/-0.22 mg/kg. The average recovery rate of arsenic and selenium in the microwave-assisted extraction form 2 is 80.4 percent and 105.4 percent of that of the traditional extraction method.
Extraction of amorphous and weakly crystalline iron-aluminium hydrated oxide bound state (form 3) arsenic: adding 12.5mL of ammonium oxalate buffer solution with the value of 0.2M, pH being 3.25 into residues C1 and C2 for extracting the specific adsorption state arsenic and selenium respectively for three times, washing the residues in the centrifugal tube, transferring the residues back to a digestion tank, mixing uniformly, extracting the arsenic and the selenium under the extraction conditions of 3000W and 50 ℃, 2min, 2000W and 50 ℃, 2min, wherein the treatment method and the detection method of the extracted sample are the same as the method of the non-specific adsorption state arsenic and selenium. Finally, the average concentrations of arsenic and selenium in specific adsorption states (form 2) are 23.82 +/-3.15 mg/kg and 2.22 +/-0.20 mg/kg respectively, and the average concentrations measured by shaking the form 2 arsenic and selenium by the traditional Wenzel method are 22.93 +/-5.58 mg/kg and 1.81 +/-0.67 mg/kg respectively. The average recovery rate of arsenic and selenium in the microwave-assisted extraction form 2 is 103.9 percent and 122.7 percent of that of the traditional extraction method.
Extraction of arsenic in the bound state (form 4) of fully crystalline iron-aluminium oxide: to the residue D1 after extraction of amorphous and weakly crystalline iron-aluminum hydrated oxide bound arsenic, 25mL of a mixed solution of 0.2M ammonium oxalate and 0.1M ascorbic acid was added at a pH of 3.25, and the mixture was mixed well and subjected to a visible light water bath at 90 ℃ for 30 min. Centrifuging at the rotating speed of 3000r/min for 15min, and transferring the supernatant to a centrifuge tube; 12.5ml of 0.2M, pH-value 3.25 ammonium oxalate buffer solution is added into the residual residue, the mixture is shaken for 10 min in the dark, centrifuged under the same conditions, and a total of 37.5 ml of the two supernatants are mixed uniformly. The selenium extraction procedure is the same as for arsenic. The treatment and detection analysis methods of form 4 arsenic selenium before detection and analysis are the same as those of form 1, and the average concentrations of arsenic selenium in the fully crystalline iron-aluminum oxide binding state (form 4) are 0.83-0.92mg/kg and 0.14-0.17mg/kg respectively.
Extraction of arsenic in the residue (form 5): adding a mixed solution of 4mL of nitric acid, 1mL of hydrofluoric acid and 1mL of hydrogen peroxide into the residue E1 for extracting the fully-crystalline iron-aluminum oxide combined arsenic, digesting in a microwave digestion instrument, heating to drive acid to about 1mL after digestion, and fixing the volume of deionized water to 50mL, wherein the selenium extraction step is the same as the arsenic extraction step. The treatment and detection analysis methods of form 4 arsenic selenium before detection and analysis are the same as those of form 1, and the average concentrations of arsenic selenium in the residue state (form 5) are respectively 3.42-3.86mg/kg and 1.79-1.86 mg/kg.
The reproducibility test is carried out on the extraction method, and the relative standard deviation of the result is between 2.3% and 7.7% when 7 parallel tests are carried out on the sample, which shows that the microwave extraction method has good reproducibility.
Example 2
A fly ash sample from a power plant in Shanxi was collected and processed as in example 1.
And (3) extraction of nonspecific adsorption arsenic and selenium: the extraction method and the process are the same as the example 1, the average concentration of the nonspecific adsorption state arsenic selenium obtained by detection and analysis (form 1) is 3.76 +/-0.43 mg/kg and 2.57 +/-0.33 mg/kg respectively, and the average concentration of the nonspecific adsorption state arsenic selenium extracted by oscillation by the traditional Wenzel method is 3.91 +/-0.62 mg/kg and 2.86 +/-0.42 mg/kg respectively. The average recovery rates of the microwave-assisted extraction of the nonspecific adsorption state arsenic and selenium by the method are respectively 96.2 percent and 89.9 percent of that of the traditional oscillation extraction.
Extracting specific adsorption state arsenic and selenium: the extraction method and the process are the same as the example 1, the average concentration of the arsenic selenium in the specific adsorption state (form 2) obtained by detection and analysis is 5.86 +/-0.72 mg/kg and 3.14 +/-0.28 mg/kg respectively, and the average concentration of the arsenic selenium in the form 2 measured by shaking by the traditional Wenzel method is 5.61 +/-0.82 mg/kg and 3.69 +/-0.55 mg/kg respectively. The average recovery rate of arsenic and selenium in the microwave-assisted extraction form 2 is 104.5 percent and 85.1 percent of that of the traditional extraction method.
Extraction of arsenic selenium in amorphous and weakly crystalline iron-aluminium hydrated oxide bound state (form 3): the extraction method and the process are the same as the example 1, the average concentrations of the amorphous and weak crystalline iron-aluminum hydrated oxide combined state (form 3) arsenic and selenium obtained by detection and analysis are respectively 9.16 +/-0.98 mg/kg and 3.14 +/-0.47 mg/kg, and the average concentrations of the form 3 arsenic and selenium obtained by the traditional Wenzel method are respectively 10.39 +/-1.84 mg/kg and 2.67 +/-0.41 mg/kg. The average recovery rate of the arsenic and selenium extracted by the microwave-assisted extraction method of the form 3 is 88.2 percent and 117.6 percent of that of the traditional method.
The extraction method and process are the same as example 1, and the average concentrations of arsenic and selenium in the binding state of the fully crystalline iron-aluminum oxide (form 4) obtained by detection and analysis are 1.27-1.39 mg/kg and 0.64-0.77 mg/kg respectively.
The extraction method and process are the same as example 1, and the average concentration of arsenic and selenium in residue state (form 5) obtained by detection and analysis is 5.47-5.91 mg/kg and 2.05-2.54 mg/kg respectively.
The reproducibility test is carried out on the extraction method, and the relative standard deviation of the result is between 3.1% and 8.2% after 7 parallel tests are carried out on the sample, which shows that the microwave extraction method has good reproducibility.
Example 3
The national standard substance GBW08401 was collected as a fly ash sample, and the sample treatment was the same as in example 1.
And (3) extraction of nonspecific adsorption arsenic and selenium: the extraction method and the process are the same as the example 1, the average concentration of the nonspecific adsorption state arsenic selenium obtained by detection and analysis (form 1) is respectively 4.04 +/-0.64 mg/kg and 0.31 +/-0.06 mg/kg, and the average concentration of the nonspecific adsorption state arsenic selenium extracted by oscillation by the traditional Wenzel method is respectively 4.55 +/-0.52 mg/kg and 0.27 +/-0.04 mg/kg. The average recovery rates of the microwave-assisted extraction of the nonspecific adsorption state arsenic and selenium by the method are respectively 88.8 percent and 114.8 percent of that of the traditional oscillation extraction.
Extracting specific adsorption state arsenic and selenium: the extraction method and the process are the same as the example 1, the average concentration of the arsenic and selenium in the specific adsorption state (form 2) obtained by detection and analysis is 3.56 +/-0.51 mg/kg and 0.04 +/-0.02 mg/kg respectively, and the average concentration of the arsenic and selenium in the form 2 measured by shaking by the traditional Wenzel method is 4.41 +/-0.65 mg/kg and 0.05 +/-0.02 mg/kg respectively. The average recovery rate of arsenic and selenium in the microwave-assisted extraction form 2 is 80.7 percent and 80.0 percent of that of the traditional extraction method.
Extraction of arsenic selenium in amorphous and weakly crystalline iron-aluminium hydrated oxide bound state (form 3): the extraction method and the process are the same as the example 1, the average concentrations of the amorphous and weak crystalline iron-aluminum hydrated oxide combined state (form 3) arsenic and selenium obtained by detection and analysis are respectively 3.56 +/-0.24 mg/kg and 0.09 +/-0.03 mg/kg, and the average concentrations of the form 3 arsenic and selenium obtained by the traditional Wenzel method are respectively 3.43 +/-0.17 mg/kg and 0.11 +/-0.02 mg/kg. The average recovery rate of the arsenic and selenium extracted by the microwave-assisted extraction method is 103.8 percent and 81.8 percent of that of the traditional method.
The extraction method and the process are the same as the example 1, and the average concentration of arsenic and selenium in the binding state (form 4) of the fully-crystalline iron-aluminum oxide obtained by detection and analysis is lower than the detection limit of an instrument.
The extraction method and process are the same as example 1, and the average concentration of arsenic and selenium in residue state (form 5) obtained by detection and analysis is 3.66-3.8 mg/kg and 0.59-0.64 mg/kg respectively.
The reproducibility test is carried out on the extraction method, and the relative standard deviation of the result is between 2.7% and 9.4% when 7 parallel tests are carried out on the sample, which shows that the microwave extraction method has good reproducibility.
Claims (3)
1. A method for sequentially extracting arsenic and selenium with different forms from fly ash under the assistance of microwave is characterized in that: adopting a microwave digestion instrument, adding different extracting agents, and extracting arsenic and selenium in different adsorption states under different microwave conditions, wherein the method comprises the following steps:
a. pretreatment of a fly ash sample: grinding a fly ash sample, freeze-drying for 24 hours, sieving with a 200-mesh sieve, storing the sieved sample in a dryer with the temperature of 22 +/-1 ℃ and the relative humidity of 40 +/-5%, and balancing for later use;
b. form 1 extraction of non-specific adsorption state arsenic selenium: form 1 extraction of arsenic: weighing 0.5g of the fly ash sample treated in the step a into a microwave digestion tank, adding 12.5mL of 0.05M ammonium sulfate solution, performing microwave extraction at 3000W and 130 ℃ for 460 and 500s, placing the extracted suspension into a centrifugal tube for centrifugation, taking the supernatant, filtering for hydride-atomic fluorescence spectrum analysis, and leaving residue B1 for use; form 1 extraction of selenium: weighing 0.5g of the fly ash sample treated in the step a into a microwave digestion tank, adding 12.5mL of 0.05M ammonium sulfate solution, performing microwave extraction at 3000W and 60 ℃ for 460 and 500s, placing the extracted suspension into a centrifugal tube for centrifugation, taking the supernatant, filtering for hydride-atomic fluorescence spectrum analysis, and leaving residue B2 for use;
c. extraction of form 2 specific adsorption arsenic selenium: form 2 arsenic extraction: adding 12.5mL of 0.05M ammonium dihydrogen phosphate into the residue B1 after the non-specific adsorption arsenic is extracted in the step B for three times, transferring the residue B1 into a digestion tank, performing microwave extraction at 3000W and 50 ℃ for 220-260s, placing the extraction suspension in a centrifugal tube for centrifugation, taking the supernatant for filtration and performing hydride-atomic fluorescence spectroscopy analysis, and reserving the residue C1; form 2 extraction of selenium: adding 12.5mL of 0.05M ammonium dihydrogen phosphate into the residue B2 after the non-specific adsorption selenium is extracted in the step B for three times, transferring the residue B2 into a digestion tank, performing microwave extraction at 2000W and 60 ℃ for 220-260s, placing the extraction suspension in a centrifugal tube for centrifugation, taking the supernatant for filtration and performing hydride-atomic fluorescence spectrum analysis, and reserving the residue C2;
d. form 3 extraction of amorphous and weakly crystalline iron-aluminium hydrated oxide bound arsenic selenium: form 3 arsenic extraction: adding 0.2M ammonium oxalate buffer solution into the residue C1 for three times to total 12.5mL, transferring to a digestion tank, performing microwave extraction at 3000W and 50 ℃ for 110-130s, placing the extraction suspension in a centrifugal tube for centrifugation, taking the supernatant, filtering for hydride-atomic fluorescence spectrum analysis, and reserving the residue D1; form 3 extraction of selenium: adding 0.2M ammonium oxalate buffer solution into the residue C2 for three times to total 12.5mL, transferring to a digestion tank, performing microwave extraction at 50 ℃ for 110-130s at 2000W, placing the extraction suspension in a centrifugal tube for centrifugation, taking the supernatant, filtering for hydride-atomic fluorescence spectrum analysis, and reserving the residue D2;
e. form 4 extraction of fully crystalline iron-aluminum oxide combined arsenic-selenium: form 4 arsenic extraction: adding 25mL of a mixed solution of 0.2M ammonium oxalate buffer solution and 0.1M ascorbic acid into residue D1, heating in a visible light water bath at 90 ℃ for 30min, centrifuging, taking supernatant, continuously adding 12.5mL of ammonium oxalate buffer solution with the value of 0.2M, pH being 3.25 into the residual residue, shaking for 10 min in a dark place, centrifuging under the same condition, uniformly mixing and filtering 37.5 mL of the two supernatants together for hydride-atomic fluorescence spectrometry, and keeping residue E1 for later use; form 4 extraction of selenium: adding 25mL of a mixed solution of 0.2M ammonium oxalate buffer solution and 0.1M ascorbic acid into the residue D2, heating in a visible light water bath at 90 ℃ for 30min, centrifuging, and taking a supernatant; adding 12.5ml of ammonium oxalate buffer solution with the value of 0.2M, pH being 3.25 into the residual residue, shaking for 10 min in dark, centrifuging under the same condition, mixing 37.5 ml of the two supernatants uniformly, filtering, and performing hydride-atomic fluorescence spectrometry to obtain residue E2 for later use;
f. form 5 extraction of residual arsenic and selenium: form 5 arsenic extraction: adding 4mL of nitric acid, 1mL of hydrofluoric acid and 1mL of hydrogen peroxide into the residue E1 for microwave digestion, cooling, centrifuging, taking supernatant, filtering and carrying out hydride-atomic fluorescence spectrometry; form 5 extraction of selenium: adding 4mL of nitric acid, 1mL of hydrofluoric acid and 1mL of hydrogen peroxide into the residue E2 for microwave digestion, cooling, centrifuging, taking supernatant, filtering and carrying out hydride-atomic fluorescence spectrometry;
in the step b, in the extraction process of the form 1 arsenic, the temperature rise extraction is carried out in stages, and the method comprises the following steps:
in the first stage, the pressure of a microwave digestion instrument is set to be 1.0MPa, the power is set to be 3000W, the temperature is increased from normal temperature to 80 ℃, the temperature rising time is 30s, and the constant temperature time is 30 s;
in the second stage, the pressure of the microwave digestion instrument is adjusted to be 1.5MPa, the power is 3000W, the temperature is increased from 80 ℃ to 110 ℃, the temperature rising time is 30s, and the constant temperature time is 30 s;
in the third stage, the pressure of the microwave digestion instrument is adjusted to be 2.0MPa, the power is 3000W, the temperature is increased from 110 ℃ to 130 ℃, the temperature rise time is 60s, and the constant temperature time is 480 s;
in the step b, in the extraction process of the form 1 selenium, the extraction conditions are as follows: setting the pressure of a microwave digestion instrument to be 1.0MPa, the power to be 3000W, the temperature to be raised from room temperature to 60 ℃, the temperature raising time to be 30s and the constant temperature time to be 480 s;
in the step c, in the extraction of the form 2 arsenic, the extraction conditions are as follows: setting the pressure of a microwave digestion instrument to be 1.0MPa, the power to be 3000W, the temperature to be increased from room temperature to 50 ℃, the temperature-increasing time to be 60s and the constant temperature time to be 240 s;
in the step c, in the extraction of the form 2 selenium, the extraction conditions are as follows: setting the pressure of a microwave digestion instrument to be 1.0MPa, the power to be 2000W, heating the temperature from room temperature to 60 ℃, the heating time to be 60s, and the constant temperature time to be 240 s;
in the step d, in the extraction of the form 3 arsenic, the extraction conditions are as follows: setting the pressure of a microwave digestion instrument to be 1.0MPa, the power to be 3000W, the temperature to be increased from room temperature to 50 ℃, the temperature-increasing time to be 60s and the constant temperature time to be 120 s;
in the step d, in the extraction of the form 3 selenium, the extraction conditions are as follows: setting the pressure of a microwave digestion instrument to be 1.0MPa, the power to be 2000W, the temperature to be 50 ℃ from room temperature, the temperature rise time to be 60s and the constant temperature time to be 120 s;
in the step f, the form 5 arsenic selenium is digested and extracted by stages under the following extraction conditions:
in the first stage, the pressure of a microwave digestion instrument is set to be 1.0MPa, the power is set to be 3000W, the temperature is increased from room temperature to 100 ℃, the temperature rising time is 500s, and the constant temperature time is 60 s;
in the second stage, the pressure of the microwave digestion instrument is set to be 1.5MPa, the power is set to be 3000W, the temperature is increased from 100 ℃ to 130 ℃, the temperature rising time is set to be 200s, and the constant temperature time is set to be 60 s;
in the third stage, the pressure of the microwave digestion instrument is set to be 2.0MPa, the power is set to be 3000W, the temperature is increased from 130 ℃ to 160 ℃, the temperature-rising time is set to be 200s, and the constant-temperature time is set to be 60 s;
and in the fourth stage, setting the pressure of the microwave digestion instrument to be 1.0MPa, the power to be 3000W, the temperature to be increased from 160 ℃ to 180 ℃, the temperature-increasing time to be 500s and the constant temperature time to be 1200 s.
2. The microwave-assisted method for sequentially extracting arsenic and selenium in different forms from fly ash according to claim 1, which is characterized in that: in the steps b to d, the ammonium sulfate, the ammonium dihydrogen phosphate and the ammonium oxalate are all superior pure reagents, and the pH value of the ammonium oxalate buffer solution adopted in the step d is 3.25.
3. The microwave-assisted method for sequentially extracting arsenic and selenium in different forms from fly ash according to claim 2, wherein the method comprises the following steps: in the steps b-d, the hydride-atomic fluorescence spectrometer is adopted to analyze the working parameters as follows: the negative high voltage is 270V, the lamp current is 60mA, the atomizer height is 8mm, the atomizer temperature is 200 ℃, the carrier gas flow is 400mL/min, the shield gas flow is 800 mL/min, the reading time is 7.0s, and the delay time is 1.3 s.
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| CN112557243B (en) * | 2020-11-13 | 2021-11-19 | 瀚蓝绿电固废处理(佛山)有限公司 | Method for analyzing selenium form in fly ash |
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