Heavy metal element extraction method and device based on deep eutectic solvent

Abstract

The invention relates to the technical field of environmental protection, in particular to a heavy metal element extraction method and device based on a deep-eutectic solvent, and the method comprises the following steps: S1, preparing the deep-eutectic solvent; s2, performing characterization detection on the deep eutectic solvent: performing characterization detection on a hydrogen bond donor and a hydrogen bond receptor in the deep eutectic solvent by using a Fourier transform infrared spectrometer; s3, extraction of heavy metal elements: preparing a to-be-extracted product containing the heavy metal elements, adding the eutectic solvent into the to-be-extracted product according to the weight ratio of 1: (10-15), and stirring the eutectic solvent for 45-50 minutes by using a magnetic stirrer at the environment temperature of 70-72 DEG C; adding 5-8mL of ultrapure water into the deep-eutectic solvent after stirring is finished, carrying out preliminary filtration to obtain filtrate, transferring the obtained filtrate into a 50-100mL volumetric flask, carrying out constant volume and uniform shaking by using the ultrapure water, and carrying out secondary filtration to obtain a to-be-detected solution; s4, heavy metal element detection.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental protection, and particularly relates to a method and device for extracting heavy metal elements based on a deep eutectic solvent. Background Art

[0002] With the rapid development of human industrialization, metal products are widely used in various fields of life, bringing great convenience to human life while also bringing great crises. The environmental damage caused by heavy metal pollution has become an environmental problem that cannot be ignored.

[0003] In the prior art, many sample treatment methods have been developed to solve the problems of enrichment and separation of various analytes in different matrices. Different treatment methods are adopted for different forms of samples. For solid samples, dry ashing, wet digestion, microwave digestion and other methods are mainly used to convert the samples into a form soluble in water. Liquid samples are enriched or separated by liquid-liquid extraction. However, the sample treatment methods in the prior art are often complex in operation, consume a large amount of reagents, and cause relatively large environmental pollution and pose a serious threat to the health of experimental personnel.

[0004] In summary, how to solve the problems of complex operation, large reagent consumption, relatively large environmental pollution and serious threat to the health of experimental personnel in the sample treatment methods of the prior art has become a difficult problem that needs to be solved urgently in this field. Therefore, it is necessary to propose a safe method and device for extracting heavy metal elements based on a deep eutectic solvent. Summary of the Invention

[0005] To solve the above problems, the present invention provides a method and device for extracting heavy metal elements based on a deep eutectic solvent. By using an efficient and simple preparation method to prepare a deep eutectic solvent, using a characterization and detection device to characterize and detect the prepared deep eutectic solvent to determine its effectiveness, and using an improved extraction method to extract heavy metal elements, safe and efficient treatment of heavy metal elements is realized.

[0006] To achieve the above object, the technical solution of the present invention is as follows: A method for extracting heavy metal elements based on a deep eutectic solvent, comprising the following steps: S1, Preparation of deep eutectic solvent: Mix a hydrogen bond donor and a hydrogen bond acceptor in a proportion to obtain a mixed solution; use one of the methods of grinding method, heating and stirring method, vacuum evaporation method, freeze-drying method, twin-screw extrusion method or microwave irradiation method to prepare a deep eutectic solvent for the mixed solution; the deep eutectic solvent includes a hydrophilic deep eutectic solvent and a hydrophobic deep eutectic solvent.

[0007] S2, Characterization and Detection of Deep Eutectic Solvents: Use a Fourier transform infrared spectrometer to characterize and detect hydrogen bond donors and hydrogen bond acceptors in the deep eutectic solvent to obtain an infrared spectrum. Observe the blue shift of the O-H bond in the deep eutectic solvent through the infrared spectrum to analyze whether new hydrogen bonds are formed; if the O-H bond shows a blue shift in the deep eutectic solvent, it indicates the formation of hydrogen bonds. S3, Heavy Metal Element Extraction: Prepare the extractant containing heavy metal elements. Add the deep eutectic solvent to the extractant at a weight ratio of 1:10 - 15. At an environmental temperature of 70 - 72 °C, use a magnetic stirrer to stir the deep eutectic solvent with a magnetic force of 600 rpm for 45 - 50 min; after stirring, add 5 - 8 mL of ultrapure water to the deep eutectic solvent, and perform preliminary filtration through a 0.45 - 0.5 μm filter membrane to obtain a filtrate. Transfer the obtained filtrate to a 50 - 100 mL volumetric flask, dilute it to volume with ultrapure water and shake well, and then filter it again through a 0.45 - 0.5 μm filter membrane to obtain the test solution.

[0008] S4, Heavy Metal Element Detection: Use an inductively coupled plasma optical emission spectrometer to detect the test solution to obtain a test report, and analyze the recovery rate of heavy metal elements through the test report.

[0009] Furthermore, in S1, the grinding method steps are as follows: Mix the hydrogen bond donor and the hydrogen bond acceptor at a weight ratio of 1:1, and then grind them in a mortar with a pestle at an environmental temperature of 22 - 26 °C for 45 - 60 min to obtain the deep eutectic solvent.

[0010] Furthermore, in S1, the heating and stirring method steps are as follows: Mix the hydrogen bond donor and the hydrogen bond acceptor at a weight ratio of 1:1 to obtain a mixed solution. Heat the mixed solution to 80 - 85 °C and stir the mixed solution for 50 - 60 min to obtain the deep eutectic solvent.

[0011] Furthermore, in S1, the vacuum evaporation method steps are as follows: Mix the hydrogen bond donor and the hydrogen bond acceptor at a weight ratio of 1:1 to obtain a mixed solution. Evaporate the mixed solution with a rotary evaporator at a heating temperature of 50 - 52 °C to obtain the evaporated solution; put the evaporated solution into a desiccator containing silica gel and dry it to a constant weight to obtain the deep eutectic solvent.

[0012] Furthermore, in S1, the freeze-drying method steps are as follows: Mix the hydrogen bond donor and the hydrogen bond acceptor at a weight ratio of 1:1 to obtain a mixed solution. Centrifuge the mixed solution for 20 - 35 min, then cool it at -80 °C, and finally perform freeze-drying with a freeze dryer to obtain the deep eutectic solvent.

[0013] Further, in S1, the steps of the twin-screw extrusion method are as follows: Mix a hydrogen bond donor and a hydrogen bond acceptor in a weight ratio of 1:1 to obtain a mixed solution. Add the obtained mixed solution to a preheated twin-screw extruder and extrude for 45 - 60 minutes to obtain a deep eutectic solvent.

[0014] Further, in S1, the steps of the microwave irradiation method are as follows: Mix a hydrogen bond donor and a hydrogen bond acceptor in a weight ratio of 1:1 to obtain a mixed solution. Irradiate the mixed solution with microwave for 20 - 25 s to obtain a deep eutectic solvent.

[0015] Further, in S2, the methods for characterizing and detecting the deep eutectic solvent also include nuclear magnetic resonance hydrogen spectroscopy and ultraviolet-visible-near-infrared absorption photometry.

[0016] Further, in S4, after obtaining the test report, use the IBM SPSS software to perform a t-test on the test report and analyze the statistical significance of the test report.

[0017] The above scheme has the following beneficial effects: 1. The sample treatment method in the prior art is complex in operation. The method of the present invention only requires the operator to prepare the deep eutectic solvent in advance and store it. In the target to be purified, add the deep eutectic solvent in proportion, then adjust the environmental temperature, and stir the mixed solution to extract heavy metal elements, so as to achieve environmental purification. Compared with the prior art, its operation steps are simple and efficient, and can improve the extraction efficiency of heavy metal elements.

[0018] 2. The present invention provides a variety of different preparation methods for preparing deep eutectic solvents. The deep eutectic solvents prepared by different preparation methods can be used in different scenarios, thereby effectively increasing the scope of application of the deep eutectic solvent. And different preparation methods have different advantages. Among them, the deep eutectic solvent prepared by the grinding method is mainly used for pharmaceuticals. The heating and stirring method is simple in operation and has low equipment requirements. Compared with the heating method, the vacuum evaporation method uses a lower temperature and is more suitable for components with higher melting points. The microwave irradiation method requires a short time and has high preparation efficiency. These preparation methods are all simple in operation, practical and efficient, which makes it more feasible to extract heavy metal elements using deep eutectic solvents and provides a good basis for the subsequent extraction of heavy metal elements.

[0019] 3. The sample treatment methods in the prior art require the use of a large amount of chemical additives to extract various heavy metal elements. While reducing heavy metal pollution, it may also bring new chemical pollution and may pose hazards to personnel in the environment. In contrast to the prior art, the deep eutectic solvent prepared by the present invention has advantages such as good thermal stability, low vapor pressure, being green and non-toxic, and also has certain biocompatibility. Thus, while reducing heavy metal pollution, it does not cause new pollution to the environment and avoids harming personnel in the environment.

[0020] 4. The sample treatment methods in the prior art require a large amount of adsorbents and purifying agents. The raw material components of these adsorbents and purifying agents are diverse and expensive. At the same time, when preparing these adsorbents and purifying agents, some expensive instruments are often required for preparation, which greatly increases the cost of environmental governance. The deep eutectic solvent prepared by the present invention can be made only using a hydrogen bond donor and a hydrogen bond acceptor as raw materials. The raw materials are simply obtained and have extremely low raw material costs. Moreover, its preparation method is also diverse, with simple operation and low equipment requirements, resulting in a low preparation cost. Therefore, using the deep eutectic solvent prepared by the present invention to extract heavy metal elements can greatly reduce the cost of environmental governance.

[0021] Furthermore, a heavy metal element extraction device based on a deep eutectic solvent operates according to the heavy metal element extraction method based on a deep eutectic solvent, and includes a base and a controller. A spherical stirring tank is fixedly connected to the top of the base. The side wall of the stirring tank is symmetrically rotatably connected with central rods. One end of each central rod penetrates through the side wall of the stirring tank and extends into the stirring tank to be fixedly connected with an arc-shaped plate. A first stirring rod is arranged between adjacent arc-shaped plates. Both ends of the first stirring rod are respectively hinged to the arc-shaped plates adjacent to it. A second stirring rod is fixedly connected to the middle of the first stirring rod. The first stirring rod and the second stirring rod are perpendicular to each other. A number of stirring rings of different sizes are fixedly connected to both the first stirring rod and the second stirring rod. Sliders are hinged to both ends of the second stirring rod. Sliding grooves for the sliders to slide are symmetrically opened on the upper and lower sides of the stirring tank. Liquid inlets and liquid outlets are respectively opened at the top and bottom of the stirring tank. Control valves are communicated at the liquid inlets and liquid outlets. The controller is used to control the opening and closing of the control valves, thereby controlling the liquid inlet and liquid outlet of the stirring tank. A driving member is fixedly connected to the outer side wall of the stirring tank. The output shaft of the driving member is coaxially fixedly connected to the adjacent central rod. The controller is used to control the operation of the driving member, thereby driving the central rod to rotate.

[0022] Beneficial effects: By controlling the driving member to start through the controller, the central rod is driven to rotate. The rotation of the central rod will drive the arc-shaped plate to rotate, thereby driving the first stirring rod and the second stirring rod to rotate, and then driving a number of stirring rings of different sizes to rotate, so as to uniformly mix the deep eutectic solvent and the target substance, and achieve the extraction of heavy metal elements.

[0023] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the method for extracting heavy metal elements based on deep eutectic solvents of the present invention.

[0025] Figure 2 It is a front view of the device for extracting heavy metal elements based on deep eutectic solvents of the present invention.

[0026] Figure 3 It is a front sectional view of the device for extracting heavy metal elements based on deep eutectic solvents of the present invention.

[0027] Figure 4 It is an axonometric sectional view of the device for extracting heavy metal elements based on deep eutectic solvents of the present invention.

[0028] Figure 5 It is an infrared spectrum diagram of the deep eutectic solvent in the method for extracting heavy metal elements based on deep eutectic solvents of the present invention.

[0029] Figure 6 It is a 1H NMR spectrum diagram of the deep eutectic solvent in the method for extracting heavy metal elements based on deep eutectic solvents of the present invention.

[0030] Figure 7 It is an experimental flow chart of Experiment 1 in the method for extracting heavy metal elements based on deep eutectic solvents of the present invention.

[0031] Figure 8 It is a bar chart of the influence of hydrogen bond donor type on extraction efficiency in the method for extracting heavy metal elements based on deep eutectic solvents of the present invention.

[0032] Figure 9 It is a bar chart of the influence of the molar ratio of deep eutectic solvents on the extraction efficiency of cadmium, copper, iron, and zinc in the method for extracting heavy metal elements based on deep eutectic solvents of the present invention.

[0033] The reference numerals in the accompanying drawings of the specification include: 1, base; 2, stirring tank; 3, central rod; 4, arc plate; 5, first stirring rod; 6, slider; 7, second stirring rod; 8, stirring ring; 9, liquid inlet. DETAILED DESCRIPTION OF THE INVENTION

[0034] The following is a further detailed description through specific embodiments: Example 1: As Figure 1 , Figure 5 , Figure 6 , Figure 7 , Figure 8 and Figure 9As shown, a method for extracting heavy metal elements based on deep eutectic solvents includes the following steps: S1. Preparation of deep eutectic solvents: Mix a hydrogen bond donor and a hydrogen bond acceptor in a certain proportion to obtain a mixed solution; use one of the methods of grinding method, heating and stirring method, vacuum evaporation method, freeze-drying method, twin-screw extrusion method or microwave irradiation method to prepare deep eutectic solvents for the mixed solution. Among them, deep eutectic solvents include hydrophilic deep eutectic solvents and hydrophobic deep eutectic solvents.

[0035] The steps of the grinding method are as follows: Mix the hydrogen bond donor and the hydrogen bond acceptor in a weight ratio of 1:1, and then grind them in a mortar with a pestle at an ambient temperature of 22°C for 45 minutes to obtain deep eutectic solvents.

[0036] The steps of the heating and stirring method are as follows: Mix the hydrogen bond donor and the hydrogen bond acceptor in a weight ratio of 1:1 to obtain a mixed solution, heat the mixed solution to 80°C, and stir the mixed solution for 50 minutes to obtain deep eutectic solvents.

[0037] The steps of the vacuum evaporation method are as follows: Mix the hydrogen bond donor and the hydrogen bond acceptor in a weight ratio of 1:1 to obtain a mixed solution, evaporate the mixed solution with a rotary evaporator at a heating temperature of 50°C to obtain an evaporated solution; put the evaporated solution into a desiccator containing silica gel and dry it to a constant weight to obtain deep eutectic solvents.

[0038] The steps of the freeze-drying method are as follows: Mix the hydrogen bond donor and the hydrogen bond acceptor in a weight ratio of 1:1 to obtain a mixed solution, centrifuge the mixed solution for 20 minutes, then cool it at -80°C, and finally perform freeze-drying through a freeze-dryer to obtain deep eutectic solvents.

[0039] The steps of the twin-screw extrusion method are as follows: Mix the hydrogen bond donor and the hydrogen bond acceptor in a weight ratio of 1:1 to obtain a mixed solution, add the obtained mixed solution to a preheated twin-screw extruder and extrude it for 45 minutes to obtain deep eutectic solvents.

[0040] The steps of the microwave irradiation method are as follows: Mix the hydrogen bond donor and the hydrogen bond acceptor in a weight ratio of 1:1 to obtain a mixed solution, and irradiate the mixed solution with microwave for 20 s to obtain deep eutectic solvents.

[0041] In this embodiment, the heating and stirring method is used to prepare deep eutectic solvents. In this embodiment, when preparing hydrophilic deep eutectic solvents, mix glycerol, ethylene glycol, formic acid, acetic acid, malic acid, lactic acid, malonic acid, maleic acid and choline chloride in an equimolar ratio to obtain a mixed solution. In a magnetic stirrer, heat the mixed solution to 90°C and stir to obtain a heated and stirred mixed solution. Transfer the heated and stirred mixed solution to a vacuum drying oven and vacuum dry it in an 80°C environment for 4 h to obtain hydrophilic deep eutectic solvents.

[0042] When preparing a hydrophobic deep eutectic solvent, menthol and methyltrioctylammonium chloride are mixed in a molar ratio of 3:7. The mixture is placed on a rotary heater rotating at 600 rpm and mixed in an environment at 60 °C until a yellow transparent liquid is formed, obtaining the hydrophobic deep eutectic solvent.

[0043] S2. Characterization and detection of the deep eutectic solvent: Use a Fourier transform infrared spectrometer to characterize and detect the hydrogen bond donors and hydrogen bond acceptors in the deep eutectic solvent to obtain an infrared spectrum. Observe the blue shift of the O-H bond in the deep eutectic solvent through the infrared spectrum and analyze whether new hydrogen bonds are formed.

[0044] The characterization and detection methods of the deep eutectic solvent also include nuclear magnetic resonance hydrogen spectroscopy and ultraviolet-visible-near-infrared absorption photometry.

[0045] In this experiment, the potassium bromide tablet pressing method is used. Use a Fourier transform infrared spectrometer to characterize and detect the hydrogen bond donors and hydrogen bond acceptors in the deep eutectic solvent. First, weigh 0.60 g of potassium bromide, put it in an oven to dry, grind it in a mortar for 5 min, add the prepared deep eutectic solvent, put it into a tablet press to form a tablet, and then put it into the infrared spectrometer. Set the scanning band to 600 - 4000 cm -1 and the number of scans to 30 times, with a resolution of 4 cm -1 to obtain an infrared spectrum. Observe the blue shift of the O-H bond in the deep eutectic solvent through the infrared spectrum and analyze whether new hydrogen bonds are formed; if the O-H bond shows a blue shift in the deep eutectic solvent, it indicates the formation of hydrogen bonds and the successful preparation of the deep eutectic solvent.

[0046] S3. Heavy metal element extraction: Prepare the extract to be tested containing heavy metal elements. Add the deep eutectic solvent to the substance to be extracted at a weight ratio of 1:10 - 15. At an environmental temperature of 70 °C, use a magnetic stirrer to stir the deep eutectic solvent with a magnetic force of 600 rpm for 45 min; after stirring, add 5 mL of ultrapure water to the deep eutectic solvent, and perform preliminary filtration through a 0.5 μm filter membrane to obtain a filtrate. Transfer the obtained filtrate to a 50 - 100 mL volumetric flask, dilute it to volume with ultrapure water and shake well, and then filter it again through a 0.45 μm filter membrane to obtain the test solution.

[0047] S4. Heavy metal element detection: Use an inductively coupled plasma emission spectrometer to detect the test solution to obtain a test report, and analyze the recovery rate of heavy metal elements through the test report. After obtaining the test report, use the IBM SPSS software to perform a t-test on the test report to analyze the statistical significance of the test report.

[0048] The specific experimental process is as follows: Experiment 1: Study on the pretreatment of litter by deep eutectic solvents for metal elements I. Preparation of litter samples Collect the bamboo leaf litter in the bamboo forest of Qingshan Town, Hangzhou as samples. All the collected samples are stored in plastic bags and dried in an oven at 80 °C before use. After the samples are crushed by a pulverizer, they are sieved through a 120-mesh sieve and stored in a pre-washed and dried polyethylene container at room temperature. The preparation method of the spiked sample is as follows: Mix 50 mL of the working analytical solution with 5 g of the sample and shake well in a shaker for 3 hours. Filter the suspension, and the spiked sample is dried and placed at 100 °C.

[0049] II. Optical Characterization of Deep Eutectic Solvents Different types of deep eutectic solvents were synthesized using choline chloride as a hydrogen bond acceptor, and taking maleic acid as an example, the effect of hydrogen bonds on the eutectic system was studied by FTIR spectroscopy.

[0050] As Figure 5 shown, it was found that compared with maleic acid, the -OH characteristic peak in the deep eutectic solvent shifted from 3440 cm -1 to 2881 cm -1 , which can be attributed to the formation of hydrogen bonds between choline chloride and maleic acid. In addition, characteristic peaks at 1708 cm -1 and 1630 cm -1 were observed in the deep eutectic solvent, indicating that maleic acid and choline chloride were successfully synthesized to form a deep eutectic solvent.

[0051] After the preparation of maleic acid-based deep eutectic solvent, the purity and structural precision of the deep eutectic solvent were analyzed by HNMR to verify the composition of the constituent compounds. The positions of the peaks observed in the spectrum are affected by factors such as the choice of locking solvent, temperature, concentration, and other relevant parameters. These nuclear magnetic resonance examinations are crucial for confirming the integrity and purity of the deep eutectic solvents, verifying their suitability for further analysis and applications.

[0052] The HNMR spectrum is as Figure 6 shown, choline chloride is (a), maleic acid is (b), and CHCl-Ma is (c). Several different peaks can be observed, and each peak corresponds to a specific hydrogen environment within the maleic acid-choline chloride deep eutectic solvent. As Figure 6As shown, the peak of maleic acid at 6.28 ppm can be attributed to the alkyl chain of the methyl group (R-CH3). In the spectrum of choline chloride, the peak appearing in the range of 3.45 ppm represents the methylene group (R-CH2-R), while the observed peak value is approximately 3.98 ppm, corresponding to the methyl group (R3C-H). In the 1H NMR spectrum of the formed deep eutectic solvent, the methyl peak of maleic acid at 6.28 ppm and the methylene peak of choline chloride at 3.45 ppm can be clearly observed. However, the methyl peak of choline chloride originally at 3.98 ppm shows a chemical shift at 3.81 ppm, and at the same time, a small peak appears at 6.66 ppm. This is caused by the hydrogen bond formed between maleic acid and choline chloride. The 1H NMR spectrum helps to comprehensively understand its composition and molecular interactions.

[0053] III. Selection of Hydrogen Bond Donors in Deep Eutectic Solvent Systems In this experiment, choline chloride was used as the hydrogen bond acceptor, and alcohols and carboxylic acids were used as the hydrogen bond donors. Choline chloride was mixed with alcohols and carboxylic acids in a ratio of 1:1 and reacted under heating at 90 °C until a homogeneous solvent was formed. Eight deep eutectic solvent systems were prepared respectively: choline chloride - glycerol, choline chloride - ethylene glycol, choline chloride - formic acid, choline chloride - acetic acid, choline chloride - lactic acid, choline chloride - malic acid, choline chloride - malonic acid, choline chloride - maleic acid.

[0054] As Figure 7 shown, accurately weigh 0.1 g of litter powder, add it to 1.5 g of the deep eutectic solvent system, and react at 70 °C under magnetic stirring at 600 rpm for 45 min. After the reaction, add 5 mL of ultrapure water to fully dissolve the deep eutectic solvent, and filter to obtain the filtrate. Transfer the obtained solution to a 50 mL volumetric flask, dilute it to the mark with deionized water, shake well, filter through a 0.45 μm filter membrane, and perform elemental quantitative analysis by ICP-OES.

[0055] The extraction performance of deep eutectic solvents depends on the properties of the hydrogen bond acceptor and the hydrogen bond donor. In this study, choline chloride was used as the hydrogen bond acceptor, and the effect of the hydrogen bond acceptor on the extraction of metal cations from bamboo leaf litter was further studied. For deep eutectic solvents with glycerol and ethylene glycol as the hydrogen bond donors, their extraction efficiencies for Cd were 98% and 96% respectively. However, the extraction efficiencies for iron were only 6% and 7%. This can be attributed to the poor proton activity and complexation ability of alcohol-based deep eutectic solvents. The formed complexes are based on chloride ions and are similar to metal in the oxidized state.

[0056] As Figure 8As shown, the results indicate that in the deep eutectic solvent system, the carboxylic acid-based hydrogen bond donor has a better extraction effect on heavy metal cations in bamboo leaf litter than the alcohol-based one. Among them, maleic acid has the best extraction effect on heavy metal cations in bamboo leaf litter. The recovery rates of Cd, Cu, Fe, and Zn by the deep eutectic solvent based on maleic acid and choline chloride are 98%, 89%, 86%, and 90% respectively. Therefore, the deep eutectic solvent system based on maleic acid was selected for further research.

[0057] IV. Selection of the molar ratio of the deep eutectic solvent system composition After screening the hydrogen bond donors of the deep eutectic solvent system, the maleic acid-based deep eutectic solvent was selected as the extraction medium. The dissolution of heavy metal cations by the deep eutectic solvent depends on the proton activity and complexation ability of the deep eutectic solvent. The synthesis ratio of the hydrogen bond donor and the hydrogen bond acceptor has a great influence on the extraction performance of the deep eutectic solvent system. The molar ratios of the hydrogen bond acceptor to the hydrogen bond donor were changed, and deep eutectic solvents with molar ratios of 2:1, 1:1, 1:1.5, and 1:2 were prepared respectively. Taking the extraction efficiencies of Cu, Cd, Fe, and Zn as the investigation indexes, the molar ratio with the best extraction efficiency was determined. Weigh 0.1 g of litter powder and add it to 1.5 g of the deep eutectic solvent system. React at 70 °C under magnetic stirring at 600 rpm for 45 min. After extraction, add 5 mL of ultrapure water to fully dissolve the deep eutectic solvent, and filter to obtain the supernatant. Transfer the obtained solution to a 50 mL volumetric flask, dilute it to volume with ultrapure water, shake well, and perform elemental quantitative analysis by ICP-OES.

[0058] As Figure 9 shown, with the decrease of choline chloride in the synthesis process, the recovery rates of the four heavy metal cations of Cu, Cd, Fe, and Zn first increase and then decrease. Obviously, the extraction effect of synthesizing choline and maleic acid with a molar ratio of 1:1 is the best. The recovery rates of Cd and Zn can reach 100% and 95% respectively. As mentioned above, the proton of the carboxylic acid, as a good oxygen acceptor of metal complexes, leads to the formation of chlorides with metals. When the relative composition of maleic acid increases to 1:2 (ChCl:Ma), this property remains basically unchanged. In addition, with the increase of the molar ratio of maleic acid, the solid components of the ChCl-Ma solvent form a liquid eutectic at a higher temperature, resulting in the inability of the deep eutectic solvent to form a stable homogeneous liquid at 80 °C. Therefore, the molar ratio of 1:1 (ChCl:Ma) was selected as the optimal ratio for the deep eutectic solvent to extract metals from plant litter.

[0059] Experiment 2: Accuracy analysis of the method for extracting metal elements from litter by deep eutectic solvent I. Determination of accuracy The accuracy of the extraction method was verified using the GBW10022 reference material as a sample. 0.1 g of the GBW10022 reference material was weighed and added to 1.5 g of the malic acid-choline chloride DES system. The reaction was carried out at 70 °C under a magnetic force of 600 rpm for 45 min. After extraction, 5 mL of ultrapure water was added to fully dissolve the DES, and the filtrate was obtained by filtration. The obtained solution was transferred to a 50 mL volumetric flask and made up to the mark with ultrapure water and shaken well. After filtration through a 0.45 μm filter membrane, elemental quantitative analysis was performed using ICP-OES. As shown in Table 1, the recoveries of these heavy metal elements were all above 95%, indicating that the obtained results were in agreement with the certified values.

[0060] Table 1 Determination of copper, iron, zinc and cadmium in GBW10022 by the extraction method II. Method detection limit and quantification limit Three times the signal-to-noise ratio (S / N) was used as the detection limit (MDLs) of this method, and ten times the signal-to-noise ratio was the quantification limit (LOQ) of this method. A malic acid-based deep eutectic solvent (1:1) was prepared. 0.5 g was taken and dissolved in 5 mL of deionized water, diluted 20 times, and the contents of cadmium, copper, iron and zinc in the blank solution were measured, repeating ten times. The standard deviation (SD) of each element was calculated separately. The MDLs of Cd, Cu, Fe and Zn were 0.04, 0.18, 0.70 and 0.59 mg / kg respectively, which were lower than those of the traditional wet digestion method. The quantification limit calculated by ten times the standard deviation was 0.13, 0.60, 2.30, 1.96 mg / kg.

[0061] III. Repeatability The repeatability of the method was established by measuring the elemental contents of 10 spiked samples. The RSD values of these samples were all below 3.40. In addition, the reproducibility of this method was evaluated by analyzing the spiked samples using different instruments and at different time intervals. The RSD values of all elements under all conditions were below 6.44.

[0062] The collected litter samples were subjected to acid digestion and deep eutectic solvent extraction respectively.

[0063] Among them, the acid digestion method was as follows. 0.10 g of the litter sample, 5.0 mL of concentrated H2SO4 and 2.0 mL of H2O2 were added to a 50 mL digestion tube. The graphite digestion cell was preheated to 200 °C first, the digestion tube was placed in the graphite digestion cell, and the reaction was carried out for 1 hour until the sample was dissolved. Then it was cooled to room temperature and diluted to 50 mL with ultrapure water. The elements contained in it were measured using ICP-OES, and all samples were measured in parallel three times.

[0064] ​In the obtained results, the extraction efficiency of each element reached over 90%. Meanwhile, the sample concentration measured by the deep eutectic solvent extraction method was consistent with the results measured by the wet digestion method. Moreover, in most cases, the reproducibility of the results obtained by the CHCl-Ma extraction method was better than that of the wet digestion method. In addition, the accuracy of this method was further verified by comparison with the wet digestion method. The test showed that there was no significant difference between the results obtained by the developed method and the wet method at the 95% confidence level. According to the power calculation, the energy consumption of the developed method was only one-fifth of the energy required for wet digestion.

[0065] The sample treatment method in the prior art is complex in operation. This method only requires the operator to prepare the deep eutectic solvent in advance and store it. For the target to be purified, add the deep eutectic solvent in proportion, then adjust the ambient temperature, and stir the mixed solution to extract heavy metal elements, thus realizing the purification of the environment; compared with the prior art, its operation steps are simple and efficient, and can improve the extraction efficiency of heavy metal elements.

[0066] The sample treatment method in the prior art requires the use of a large amount of chemical additives to achieve the extraction of various heavy metal elements. While reducing heavy metal pollution, it may also bring new chemical pollution and may pose a hazard to the personnel in the environment; compared with the prior art, the deep eutectic solvent prepared by this method has the advantages of good thermal stability, low vapor pressure, green and non-toxic, etc., and also has a certain biocompatibility, thus achieving the reduction of heavy metal pollution without causing new pollution to the environment and avoiding harm to the personnel in the environment.

[0067] The deep eutectic solvent prepared by this method can be made only by using a hydrogen bond donor and a hydrogen bond acceptor as raw materials. The raw materials for its production are easily obtained and the raw material cost is extremely low; and its preparation method is also diverse, with simple operation and low equipment requirements, making its preparation cost relatively low; thus, using the deep eutectic solvent prepared by the present invention to extract heavy metal elements can greatly reduce the cost of environmental governance.

[0068] Example 2: As Figure 2 、 Figure 3 and Figure 4As shown in the figure, the difference from the above embodiment is that a heavy metal element extraction device based on a deep eutectic solvent includes a base 1 and a controller. A spherical stirring tank 2 is bolted to the top of the base 1. Central rods 3 are symmetrically and rotatably connected to the side walls of the stirring tank 2. One end of each central rod 3 penetrates through the side wall of the stirring tank 2 and extends into the stirring tank 2, where an arc-shaped plate 4 is bolted. A first stirring rod 5 is arranged between adjacent arc-shaped plates 4. Both ends of the first stirring rod 5 are respectively hinged to the adjacent arc-shaped plates 4. A second stirring rod 7 is integrally formed in the middle of the first stirring rod 5. The first stirring rod 5 and the second stirring rod 7 are perpendicular to each other. A number of stirring rings 8 of different sizes are integrally formed on both the first stirring rod 5 and the second stirring rod 7. Sliders 6 are hinged to both ends of the second stirring rod 7. Chutes for the sliders 6 to slide are symmetrically opened on the upper and lower sides of the stirring tank 2. An inlet 9 and a drain outlet are respectively opened at the top and bottom of the stirring tank 2. Control valves are connected to both the inlet 9 and the drain outlet. The controller is used to control the opening and closing of the control valves, thereby controlling the liquid inlet and outlet of the stirring tank 2. A driving member is bolted to the outer side wall of the stirring tank 2. The output shaft of the driving member is coaxially bolted to the adjacent central rod 3. The controller is used to control the operation of the driving member, thereby driving the central rod 3 to rotate.

[0069] In this embodiment, the driving member is a servo motor.

[0070] The specific implementation process is as follows: In this embodiment, the output shaft of the servo motor is coaxially bolted to the left central rod 3.

[0071] The operator controls the servo motor to start through the controller. The output shaft of the servo motor drives the central rod 3 to rotate. Since the central rod 3 is hinged to the arc-shaped plate 4, the rotation of the central rod 3 will drive the left arc-shaped plate 4 to rotate, and then drive the first stirring rod 5 and the second stirring rod 7 to rotate. At the same time, the rotation of the first stirring rod 5 and the second stirring rod 7 will also drive a number of stirring rings 8 of different sizes to rotate, thereby uniformly mixing the deep eutectic solvent and the sample and realizing the extraction of heavy metal elements.

[0072] During this process, the first stirring rod 5 will also drive the right arc-shaped plate 4 and the central rod 3 to rotate, thus realizing its own stable rotation. Since the two arc-shaped plates 4 are arc-shaped and the first stirring rod 5 is hinged to the arc-shaped plate 4, the two ends of the first stirring rod 5 will generate eccentric rotation along with the arc-shaped plate 4, so that the whole first stirring rod 5 generates a three-dimensional rotation and drives the stirring rings 8 on the first stirring rod 5 to move. Compared with the stirring rod that only rotates on its own in place in the prior art, the stirring range of the first stirring rod 5 is larger, so that a better stirring effect can be produced.

[0073] Meanwhile, since both the upper and lower ends of the second stirring rod 7 are hinged to the slider 6, and the slider 6 is in sliding fit with the chute, the second stirring rod 7 will drive the slider 6 to slide along the chute when rotating, making the second stirring rod 7 rotate more stably. Compared with the prior art where only one-way stirring is performed, the design in which the first stirring rod 5 and the second stirring rod 7 are perpendicular to each other can further expand the stirring range, improve the uniformity of stirring, and thus improve the stirring efficiency, enabling the deep eutectic solvent to better extract heavy metal elements from the sample.

[0074] A sealing film is fixedly bonded to the outside of the chute at the top, and the chute at the bottom is sealed with the base 1; during the stirring process, the control valves at the liquid inlet 9 and the liquid outlet are closed through the controller, thereby effectively avoiding material leakage during the stirring process.

[0075] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for extracting heavy metal elements based on deep eutectic solvents, characterized in that, It includes the following steps: S1, Preparation of deep eutectic solvent: Mix a hydrogen bond donor and a hydrogen bond acceptor in a certain proportion to obtain a mixed solution; use one of the methods of grinding method, heating and stirring method, vacuum evaporation method, freeze-drying method, twin-screw extrusion method or microwave irradiation method to prepare the deep eutectic solvent for the mixed solution; Among them, the deep eutectic solvent includes hydrophilic deep eutectic solvent and hydrophobic deep eutectic solvent; S2, Characterization and detection of deep eutectic solvent: Use a Fourier transform infrared spectrometer to characterize and detect the hydrogen bond donor and hydrogen bond acceptor in the deep eutectic solvent; Observe the situation of O-H bonds in the deep eutectic solvent through infrared spectroscopy and analyze whether new hydrogen bonds are formed; If the O-H bond shows a blue shift in the deep eutectic solvent, it indicates the formation of hydrogen bonds; S3, Heavy metal element extraction: Prepare an extract to be extracted containing heavy metal elements, and add the deep eutectic solvent to the extract to be extracted at a weight ratio of 1:10 - 15; At an ambient temperature of 70 - 72 °C, use a magnetic stirrer to stir the deep eutectic solvent with a magnetic force of 600 rpm for 45 - 50 min; After stirring, add 5 - 8 mL of ultrapure water to the deep eutectic solvent, and perform preliminary filtration through a 0.45 - 0.5 μm filter membrane to obtain a filtrate. Transfer the obtained filtrate to a 50 - 100 mL volumetric flask, make up the volume with ultrapure water and shake well, and then filter again through a 0.45 - 0.5 μm filter membrane to obtain a test solution; S4, Heavy metal element detection: Use an inductively coupled plasma emission spectrometer to detect the test solution to obtain a test report, and analyze the recovery rate of heavy metal elements through the test report.

2. The heavy metal element extraction method based on the deep eutectic solvent according to claim 1, wherein In S1, the steps of the grinding method are as follows: Mix the hydrogen bond donor and the hydrogen bond acceptor in a weight ratio of 1:1, and then grind them in a mortar with a pestle at an ambient temperature of 22 - 26 °C for 45 - 60 min to obtain the deep eutectic solvent.

3. The heavy metal element extraction method based on deep eutectic solvents according to claim 2, wherein In S1, the steps of the heating and stirring method are as follows: Mix the hydrogen bond donor and the hydrogen bond acceptor in a weight ratio of 1:1 to obtain a mixed solution, heat the mixed solution to 80 - 85 °C, and stir the mixed solution for 50 - 60 min to obtain the deep eutectic solvent.

4. The method for extracting heavy metal elements based on deep eutectic solvents according to claim 3, wherein In S1, the steps of the vacuum evaporation method are as follows: Mix the hydrogen bond donor and the hydrogen bond acceptor in a weight ratio of 1:1 to obtain a mixed solution, evaporate the mixed solution with a rotary evaporator at a heating temperature of 50 - 52 °C to obtain an evaporated solution; Put the evaporated solution into a desiccator containing silica gel and dry it to a constant weight to obtain the deep eutectic solvent.

5. The method for extracting heavy metal elements based on deep eutectic solvents according to claim 4, wherein In S1, the steps of the freeze-drying method are as follows: Mix the hydrogen bond donor and the hydrogen bond acceptor in a weight ratio of 1:1 to obtain a mixed solution, centrifuge the mixed solution for 20 - 35 min, then cool it at -80 °C, and finally perform freeze-drying through a freeze-dryer to obtain the deep eutectic solvent.

6. The method for extracting heavy metal elements based on deep eutectic solvents according to claim 5, wherein In S1, the steps of the twin-screw extrusion method are as follows: Mix the hydrogen bond donor and the hydrogen bond acceptor in a weight ratio of 1:1 to obtain a mixed solution, add the obtained mixed solution to a preheated twin-screw extruder and extrude for 45 - 60 min to obtain the deep eutectic solvent.

7. The method for extracting heavy metal elements based on deep eutectic solvents according to claim 6, wherein In S1, the steps of the microwave irradiation method are as follows: Mix the hydrogen bond donor and the hydrogen bond acceptor in a weight ratio of 1:1 to obtain a mixed solution, and irradiate the mixed solution with microwave for 20 - 25 s to obtain a deep eutectic solvent.

8. The method for extracting heavy metal elements based on deep eutectic solvents according to claim 7, characterized in that, In S2, the methods for characterizing and detecting the deep eutectic solvent also include nuclear magnetic resonance hydrogen spectrum detection method and ultraviolet-visible-near-infrared absorption photometry method.

9. The method for extracting heavy metal elements based on deep eutectic solvents according to claim 8, wherein, In S4, after obtaining the test report, use the IBMSPSS software to perform a t-test on the test report to analyze the statistical significance of the test report.

10. A heavy metal element extraction device based on a deep eutectic solvent operates based on the heavy metal element extraction method based on a deep eutectic solvent according to any one of the above claims 1-9, characterized in that, It includes a base (1) and a controller; A spherical stirring tank (2) is fixedly connected to the top of the base (1). The side wall of the stirring tank (2) is symmetrically rotatably connected with a central rod (3). One end of each central rod (3) penetrates through the side wall of the stirring tank (2) and extends into the stirring tank (2) to be fixedly connected with an arc-shaped plate (4). A first stirring rod (5) is arranged between adjacent arc-shaped plates (4). Both ends of the first stirring rod (5) are respectively hinged to the adjacent arc-shaped plates (4); A second stirring rod (7) is fixedly connected to the middle of the first stirring rod (5). The first stirring rod (5) and the second stirring rod (7) are perpendicular to each other. A number of stirring rings (8) of different sizes are fixedly connected to both the first stirring rod (5) and the second stirring rod (7); Sliders (6) are hinged to both ends of the second stirring rod (7); Sliding grooves for the sliders (6) to slide are symmetrically opened on the upper and lower sides of the stirring tank (2); Liquid inlets (9) and liquid outlets are respectively opened at the top and bottom of the stirring tank (2); Control valves are connected to both the liquid inlet (9) and the liquid outlet; The controller is used to control the opening and closing of the control valve, and thus control the liquid inlet and outlet of the stirring tank (2); A driving member is fixedly connected to the outer side wall of the stirring tank (2). The output shaft of the driving member is coaxially fixedly connected to the adjacent central rod (3). The controller is used to control the operation of the driving member, and thus drive the central rod (3) to rotate.

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