Stirring and heating device and method for measuring hexavalent chromium in soil and sediment

Abstract

The invention discloses a stirring and heating device and method for measuring hexavalent chromium in soil and sediment, the stirring and heating device comprises a stirring and heating cabin and a power cabin, a stirring and heating cabin cover is arranged above the stirring and heating cabin, a magnetic stirring device and a driving motor are arranged in the power cabin, and a beaker bracket and a heating pipe are arranged in the stirring and heating cabin; the heating pipe is located on the inner bottom face of the stirring and heating cabin, the beaker bracket is located above the heating pipe, stirring and heating cabin cover open holes and a stirring and heating cabin cover handle are arranged above the stirring and heating cabin cover, and the number and the position of the stirring and heating cabin cover open holes correspond to those of the beaker bracket. The lower end of the central rotating shaft is connected with an output shaft of the driving motor, the upper end of the central rotating shaft penetrates through the central position of the stirring and heating cabin cover, and an infrared temperature measuring device is arranged at the upper end of the central rotating shaft. The method can effectively improve the detection efficiency and precision of hexavalent chromium in soil and sediments.

Description

Technical Field

[0001] The present invention relates to the technical field of hexavalent chromium detection, and particularly to a stirring and heating device and method for determining hexavalent chromium in soil and sediment. Background Art

[0002] Hexavalent chromium is a common pollutant in soil and sediment, with high toxicity and carcinogenicity. Exceeding the standard of hexavalent chromium will affect the growth and development of plants, damage the soil ecosystem, and affect soil fertility and productivity. It can be absorbed by plant roots through the soil, thereby affecting the overall growth of plants, reducing the yield and quality of plants. Hexavalent chromium is not easily adsorbed by soil particles, is easy to migrate and cause groundwater pollution. Hexavalent chromium can invade the human body through digestion, respiratory tract, skin and mucous membranes, and there is a carcinogenic risk for long-term contact or ingestion. According to the national environmental protection standard "Soil Environmental Quality Standard" (GB 15618-2018), the content of hexavalent chromium in soil should not exceed 0.1 mg / kg. Accurately detecting the content of hexavalent chromium in soil can timely discover the pollution situation, provide a basis for taking appropriate environmental protection and treatment measures, and thus ensure human health and ecological environment safety.

[0003] The regulations on the stirring and heating device used in the experiment in the national standard HJ1082-2019 "Determination of Hexavalent Chromium in Soil and Sediment - Alkaline Solution Extraction - Flame Atomic Absorption Spectrophotometry" are relatively general, lacking detailed operation instructions and performance requirements. The traditional stirring and heating device has problems with insufficient accuracy in temperature control. It can only sense the water temperature outside the beaker, unable to measure the temperature inside the solution, resulting in a temperature difference between the inside and outside of the beaker, and the uniformity of the water temperature is also poor. This deficiency in temperature difference and uniformity is particularly obvious when processing multiple samples. The degree of stirring and heating of each sample is different, and the stirring rate is not specified, so it is impossible to ensure sufficient stirring. The cover of the stirring and heating device is a separate plastic cover with poor heat preservation effect, and it is impossible to always pay attention to whether the state of the solution in the beaker of the heating device has splashed, thus affecting the extraction rate and efficiency. The national standard uses membrane filtration by suction for the suspension after leaching. The soil and sediment precipitate easily clog the filter membrane, and it is basically filtered drop by drop, with extremely low suction filtration efficiency. Due to the pressure difference inside and outside the suction filtration device, the precipitate gels, and it is impossible to thoroughly wash the leaching solution wrapped in the precipitate, ultimately resulting in deviation of the experimental results. In terms of sample testing, the national standard uses atomic absorption for determination. On the one hand, an air compressor and acetylene are required during the determination process, which poses a great safety hazard. On the other hand, the detection limit is high and cannot meet the testing requirements. Summary of the Invention

[0004] The object of the present invention is to solve the problems raised in the above-mentioned background technology, and then a stirring and heating device and method for determining hexavalent chromium in soil and sediment are proposed. The disclosed device of the present invention can monitor the temperature of the solution in the beaker in real time by setting an infrared temperature measuring device, ensure the temperature uniformity of the solution in the beaker and control the temperature fluctuation of the solution within the range of ±1°C, thereby improving the detection accuracy; the disclosed method of the present invention detects hexavalent chromium by an inductively coupled plasma emission spectrometer, improves safety, and solves the problem of calculating over-limit results by establishing a working curve and a calculation formula.

[0005] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0006] A stirring and heating device for determining hexavalent chromium in soil and sediment, including a stirring and heating chamber, and a power chamber installed below. A stirring and heating chamber cover is arranged above the stirring and heating chamber. A magnetic stirring device and a driving motor are arranged in the power chamber. A beaker bracket and a heating pipe are arranged in the stirring and heating chamber. The heating pipe is located at the inner bottom surface of the stirring and heating chamber, and the beaker bracket is located above the heating pipe. A stirring and heating chamber cover opening and a stirring and heating chamber cover handle are arranged above the stirring and heating chamber cover. The number and position of the stirring and heating chamber cover openings correspond to those of the beaker bracket. A central rotating shaft is further arranged in the stirring and heating chamber. The lower end of the central rotating shaft is connected to the output shaft of the driving motor, and the upper end of the central rotating shaft passes through the central position of the stirring and heating chamber cover, and an infrared temperature measuring device is arranged at the upper end of the central rotating shaft.

[0007] Preferably, a device controller is arranged on the side surface of the stirring and heating chamber, and the device controller is electrically connected to the infrared temperature measuring device, the magnetic stirring device and the driving motor.

[0008] Preferably, a drain pipe is arranged below the stirring and heating chamber.

[0009] Preferably, the stirring and heating chamber cover is made of transparent glass material.

[0010] A method for determining hexavalent chromium in soil and sediment includes the following steps:

[0011] S1. Crush and grind the air-dried sample, pass it through a nylon sieve with a pore size of 0.15 mm (100 mesh), and then place it in a dryer for testing.

[0012] S2. Weigh 5.0 g of the sample processed in step 1 and place it in a 250 mL beaker, add 50.0 mL of alkaline extraction solution, then add 400 mg of magnesium chloride and 0.5 mL of potassium hydrogen phosphate-potassium dihydrogen phosphate buffer solution, and perform extraction solution leaching.

[0013] S3. Place the beaker on the beaker bracket, add a magnetic stir bar, cover it with a watch glass, add laboratory secondary water parallel to the liquid level of the beaker solution into the stirring and heating chamber, cover the stirring and heating chamber lid, turn on the device controller, set the rotation speed to 500 r / min, the stirring time to 5 min, stir at room temperature for 5 min, then adjust the device controller, set the temperature to 98 °C, the time to 2 h, and the rotation speed to 500 r / min. After stirring is completed, open the drain pipe to drain the wastewater.

[0014] S4. After taking out the beaker and cooling it, transfer it to a 100 mL centrifuge tube, centrifuge at 5000 r / min for 10 min, pour the supernatant into the original 250 mL beaker, then rinse the centrifuge tube with a small amount of water, disperse the soil at the bottom by shaking or ultrasonication, centrifuge for another 10 min, take the supernatant, and combine it with the supernatant from the first centrifugation.

[0015] S5. Adjust the pH of the test solution to 7.5 ± 0.5 with nitric acid, then transfer the solution with adjusted pH to a 200 mL volumetric flask, make up the volume to the mark and shake well. If a precipitate appears after adjusting the pH, filter it with filter paper before determination. If the determination cannot be carried out immediately after adjusting the pH, store the sample sealed at 0 - 4 °C, and it can be stored for 30 d.

[0016] S6. Repeat the above S2 - S5 without adding samples to set up a blank control experimental group.

[0017] S7. Pipette 0.00 mL, 0.10 mL, 0.20 mL, 0.50 mL, 1.00 mL, 2.00 mL of hexavalent chromium standard stock solution (100 mg / L) into a 250 ml beaker respectively, prepare working curve solutions according to the steps of sample preparation, and use an inductively coupled plasma optical emission spectrometer to detect the hexavalent chromium concentration in the solution. The reference concentrations are: 0.00 mg / L, 0.10 mg / L, 0.20 mg / L, 0.50 mg / L, 1.00 mg / L, 2.00 mg / L. Measure in ascending order of concentration. Take the hexavalent chromium concentration as the abscissa and the intensity as the ordinate to establish a working curve.

[0018] S8. Carry out the determination of the sample under the same analytical conditions as those for the establishment of the working curve, and carry out the determination of the blank sample under the same analytical conditions as those for the sample determination.

[0019] S9. Calculate the content of hexavalent chromium in the soil or sediment using the following formula:

[0020]

[0021] where: w is the content of hexavalent chromium in the soil sample, mg / kg;

[0022] ρ is the concentration of hexavalent chromium in the sample, mg / L;

[0023] V Fixed volume of the sample, mL;

[0024] D Dilution factor of the sample;

[0025] m Weight of the soil sample taken, g;

[0026] W dm Dry matter content of the soil sample, %.

[0027] Preferably, the alkaline extraction solution is prepared by dissolving 30 g of sodium carbonate and 20 g of sodium hydroxide in water, diluting and fixing the volume to 1 L, storing it in a sealed polyethylene bottle, and ensuring that its pH value is greater than 11.5 before use.

[0028] Preferably, the potassium hydrogen phosphate - potassium dihydrogen phosphate buffer solution is prepared by dissolving 87.1 g of potassium hydrogen phosphate and 68.0 g of potassium dihydrogen phosphate in water, diluting and fixing the volume to 1 L.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] 1. The disclosed device of the present invention can monitor the temperature of the solution in the beaker in real time by setting an infrared temperature measurement device, ensuring the temperature uniformity of the solution in the beaker and controlling the temperature fluctuation of the solution within the range of ±1°C, thereby improving the detection accuracy; the disclosed method of the present invention detects hexavalent chromium by an inductively coupled plasma emission spectrometer, improving safety, and solves the problem of calculating over - limit results by establishing a working curve and a calculation formula.

[0031] 2. The stirring and heating chamber cover of the disclosed device of the present invention is made of transparent glass material, which has a better heat preservation effect and can observe the state of the sample in the beaker at any time.

[0032] 3. Multiple beakers can be placed on the beaker bracket of the disclosed device of the present invention, and the samples in multiple beakers can be stirred and heated, shortening the experimental time and improving the pre - treatment efficiency.

[0033] 4. The disclosed method of the present invention increases the temperature of the leaching solution and prolongs the leaching time to ensure the extraction rate of hexavalent chromium.

[0034] 5. The disclosed method of the present invention centrifuges the suspension multiple times with a centrifuge to ensure the centrifugation rate of the sample. The sample for on - machine determination is clear and free of impurities, preventing impurities from clogging the nebulizer and greatly improving the filtration efficiency at the same time.

[0035] 6. The disclosed method of the present invention uses an inductively coupled plasma emission spectrometer, and changes the working gas to argon, reducing the safety risk, lowering the detection limit of determination, ensuring that the result of hexavalent chromium is more stable and accurate, and improving the reliability of the experimental results. Description of the Drawings

[0036] Figure 1 Isometric structure schematic diagram of the disclosed device of the present invention;

[0037] Figure 2 Front elevation sectional view of the disclosed device of the present invention;

[0038] Figure 3 Top plan sectional view of the disclosed device of the present invention.

[0039] Wherein: 1, infrared temperature measuring device; 2, handle of stirring and heating chamber cover; 3, stirring and heating chamber cover; 4, device controller; 5, stirring and heating chamber; 6, central rotating shaft; 7, opening on stirring and heating chamber cover; 8, magnetic stirring device; 9, beaker bracket; 10, heating tube; 11, drain pipe; 12, drive motor; 13, power chamber. Specific embodiments

[0040] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0041] As Figures 1 - 3 shown, a stirring and heating device for measuring hexavalent chromium in soil and sediment includes a stirring and heating chamber 5 and a power chamber 13 installed below. A stirring and heating chamber cover 3 is provided above the stirring and heating chamber 5. A magnetic stirring device 8 and a drive motor 12 are provided in the power chamber 13. A beaker bracket 9 and a heating tube 10 are provided in the stirring and heating chamber 5. The heating tube 10 can heat the solution in the stirring and heating chamber 5 and control the solution temperature through the infrared temperature measuring device 1 to achieve constant temperature or variable temperature control. Multiple beakers can be placed above the beaker bracket 9 to conduct multiple groups of experiments simultaneously, improving the detection efficiency and reducing errors at the same time. A rotor is placed in the beaker, and the magnetic stirring device 8 controls the rotation of the rotor to stir the solution in the beaker. The heating tube 10 is located at the inner bottom surface of the stirring and heating chamber 5, and the beaker bracket 9 is located above the heating tube 10. An opening 7 and a handle 2 of the stirring and heating chamber cover are provided above the stirring and heating chamber cover 3. The number and position of the openings 7 on the stirring and heating chamber cover correspond to those of the beaker bracket 9. A central rotating shaft 6 is also provided in the stirring and heating chamber 5. The lower end of the central rotating shaft 6 is connected to the output shaft of the drive motor 12. The upper end of the central rotating shaft 6 passes through the center position of the stirring and heating chamber cover 3, and an infrared temperature measuring device 1 is provided at the upper end of the central rotating shaft 6. The infrared temperature measuring device 1 detects the temperature of the solution in the beaker through the opening 7 on the stirring and heating chamber cover.

[0042] As Figure 1 and Figure 2As shown, a device controller 4 is provided on the side of the stirring and heating chamber 5. The device controller 4 is electrically connected to the infrared temperature measuring device 1, the magnetic stirring device 8, and the drive motor 12, and the intelligent control of the stirring environment temperature, stirring speed, and stirring time is realized through the device controller 4.

[0043] As Figures 1 - 3 As shown, a drain pipe 11 is provided below the stirring and heating chamber 5. After the experiment is completed, the medium solution in the stirring and heating chamber 5 is discharged through the drain pipe 11; the stirring and heating chamber cover (3) is made of transparent glass material, and the medium solution in the stirring and heating chamber 5 and the sample in the beaker can be observed in real time.

[0044] A method for determining hexavalent chromium in soil and sediment includes the following steps:

[0045] S1. Crush and grind the air-dried sample, pass it through a nylon sieve with a pore size of 0.15 mm (100 mesh), and place it in a dryer for future measurement to complete the preliminary preparation of the sample.

[0046] S2. Weigh 5.0 g of the sample treated in step 1 and place it in a 250 mL beaker, add 50.0 mL of alkaline extraction solution, then add 400 mg of magnesium chloride and 0.5 mL of potassium hydrogen phosphate-potassium dihydrogen phosphate buffer solution for extraction solution leaching.

[0047] S3. Place the beaker on the beaker bracket 9, add a magnetic stir bar, cover it with a watch glass, add laboratory secondary water parallel to the liquid level of the beaker solution in the stirring and heating chamber 5, cover the stirring and heating chamber cover 3, turn on the device controller 4, set the rotation speed to 500 r / min, the stirring time to 5 min, stir at room temperature for 5 min, then adjust the device controller 4, set the temperature to 98 °C, the time to 2 h, and the rotation speed to 500 r / min. After stirring is completed, open the drain pipe 11 to drain the waste water.

[0048] S4. After taking out the beaker and cooling it, transfer it to a 100 mL centrifuge tube, centrifuge at 5000 r / min for 10 min, pour the supernatant into the original 250 mL beaker, then rinse the centrifuge tube with a small amount of water, disperse the soil at the bottom by shaking or ultrasonication, then centrifuge for 10 min, take the supernatant, and combine it with the supernatant from the first centrifugation to ensure complete leaching.

[0049] S5. Adjust the pH of the test solution to 7.5 ± 0.5 with nitric acid, then transfer the solution with adjusted pH to a 200 mL volumetric flask, make up the volume and shake well. If a precipitate appears after adjusting the pH, filter it with filter paper before measurement. If the measurement cannot be carried out immediately after adjusting the pH, store the sample sealed at 0 - 4 °C for up to 30 days.

[0050] S6. Repeat the above S2 - S5 without adding the sample to set up a blank control experimental group.

[0051] S7. Respectively pipette 0.00 mL, 0.10 mL, 0.20 mL, 0.50 mL, 1.00 mL, 2.00 mL of the hexavalent chromium standard stock solution (100 mg / L) into a 250 ml beaker. According to the steps of sample preparation, prepare the working curve solutions. Use an inductively coupled plasma optical emission spectrometer to detect the concentration of hexavalent chromium in the solutions. The reference concentrations are: 0.00 mg / L, 0.10 mg / L, 0.20 mg / L, 0.50 mg / L, 1.00 mg / L, 2.00 mg / L. Measure in ascending order of concentration. Take the hexavalent chromium concentration as the abscissa and the intensity as the ordinate to establish the working curve;

[0052] S8. Perform the determination of the sample under the same analytical conditions as those for the establishment of the working curve, and perform the determination of the blank sample under the same analytical conditions as those for the sample determination;

[0053] S9. Calculate the content of hexavalent chromium in the soil or sediment using the following formula,

[0054]

[0055] where: w is the content of hexavalent chromium in the soil sample, mg / kg;

[0056] ρ is the concentration of hexavalent chromium in the sample, mg / L;

[0057] V is the fixed volume of the sample, mL;

[0058] D is the dilution factor of the sample;

[0059] m is the weight of the soil sample taken, g;

[0060] W dm The dry matter content of the soil sample, %.

[0061] The alkaline extraction solution is prepared by dissolving 30 g of sodium carbonate and 20 g of sodium hydroxide in water, diluting and fixing the volume to 1 L, and storing it in a sealed polyethylene bottle. It is necessary to ensure that its pH value is greater than 11.5 before use.

[0062] The potassium hydrogen phosphate - potassium dihydrogen phosphate buffer solution is prepared by dissolving 87.1 g of potassium hydrogen phosphate and 68.0 g of potassium dihydrogen phosphate in water, diluting and fixing the volume to 1 L.

[0063] In the description of the present invention, the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "vertical", "horizontal", etc. is based on the orientation or positional relationship shown in the drawings, and is only for describing the present invention rather than requiring the present invention to be constructed or operated in a specific orientation. Therefore, it should not be construed as a limitation on the present invention. The terms "connected" and "coupled" in the present invention should be understood in a broad sense. For example, it can be a connection or a detachable connection; it can be a direct connection or an indirect connection through an intermediate component. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0064] The above is the preferred operation mode of the present invention. The description of the specific operation mode is only for better understanding the idea of the present invention. For those of ordinary skill in the art, several improvements or equivalent replacements can be made according to the principle of the present invention, and these improvements or equivalent replacements are also considered to fall within the protection scope of the present invention.

Claims

1. A stirring and heating device for determining hexavalent chromium in soil and sediment, comprising a stirring and heating chamber (5) and a power chamber (13) installed below, a stirring and heating chamber cover (3) being arranged above the stirring and heating chamber (5), characterized in that: A magnetic stirring device (8) and a driving motor (12) are arranged in the power compartment (13); a beaker bracket (9) and a heating tube (10) are arranged in the stirring and heating compartment (5); the heating tube (10) is located on the inner bottom surface of the stirring and heating compartment (5); the beaker bracket (9) is located above the heating tube (10); a stirring and heating compartment cover opening (7) and a stirring and heating compartment cover handle (2) are arranged above the stirring and heating compartment cover (3); the number and position of the stirring and heating compartment cover opening (7) correspond to those of the beaker bracket (9); a central rotating shaft (6) is also arranged in the stirring and heating compartment (5); the lower end of the central rotating shaft (6) is connected to the output shaft of the driving motor (12); the upper end of the central rotating shaft (6) passes through the center position of the stirring and heating compartment cover (3); and an infrared temperature measuring device (1) is arranged at the upper end of the central rotating shaft (6).

2. A stirring and heating device for determining hexavalent chromium in soil and sediment according to claim 1, characterized in that: A device controller (4) is arranged on the side of the stirring and heating chamber (5), and the device controller (4) is electrically connected to the infrared temperature measuring device (1), the magnetic stirring device (8) and the driving motor (12).

3. A stirring and heating device for determining hexavalent chromium in soil and sediment according to claim 1, characterized in that: A drainage pipe (11) is arranged below the stirring and heating chamber (5).

4. A stirring and heating device for determining hexavalent chromium in soil and sediment according to claim 1, characterized in that: The stirring and heating chamber cover (3) is made of transparent glass.

5. A method for determining hexavalent chromium in soil and sediment, characterized in that A stirring and heating device for determining hexavalent chromium in soil and sediment according to any one of claims 1 to 4 comprises the following steps: S1. The air-dried sample was crushed and ground, passed through a nylon sieve with a pore size of 0.15 mm (100 mesh), and then placed in a dryer for testing; S2, weigh 5.0g of the sample treated in step 1 and place it in a 250mL beaker, add 50.0mL of alkaline extract, then add 400mg of magnesium chloride and 0.5mL of dipotassium hydrogen phosphate-potassium dihydrogen phosphate buffer solution, and leaching the extract; S3. Place the beaker on the beaker holder (9), add a magnet, cover with a watch glass, add laboratory secondary water parallel to the liquid level of the beaker solution into the stirring and heating chamber (5), cover with the stirring and heating chamber cover (3), turn on the device controller (4), set the speed to 500 r / min, the stirring time to 5 min, stir at room temperature for 5 min, then adjust the device controller (4), set the temperature to 98°C, the time to 2 h, the speed to 500 r / min, and after stirring is completed, open the drain pipe (11) to discharge the waste water. S4. After cooling down the beaker, transfer it to a 100mL centrifuge tube and centrifuge at 5000r / min for 10min. Pour the supernatant into the original 250mL beaker and rinse the centrifuge tube with a small amount of water. Shake or ultrasonically break up the soil at the bottom and centrifuge for another 10min. Take the supernatant and combine it with the supernatant from the first centrifugation. S5. Use nitric acid to adjust the pH of the solution to be tested to 7.5±0.5, then transfer the solution with adjusted pH to a 200mL volumetric flask, make up to volume and shake well. If precipitation occurs after pH adjustment, filter it with filter paper and then measure it. If the pH cannot be measured immediately after adjustment, seal the sample and store it at 0-4 degrees Celsius for 30 days. S6. Repeat the above steps S2-S5 without adding any sample, and set up a blank control experimental group; S7, respectively take 0.00mL, 0.10mL, 0.20mL, 0.50mL, 1.00mL, 2.00mL hexavalent chromium standard solution (100mg / L) and place it in a 250ml beaker, prepare a working curve solution according to the sample preparation steps, and use an inductively coupled plasma emission spectrometer to detect the hexavalent chromium concentration in the solution. The reference concentrations are: 0.00mg / L, 0.10mg / L, 0.20mg / L, 0.50mg / L, 1.00mg / L, 2.00mg / L, and the concentrations are measured in order from low to high, with the hexavalent chromium concentration as the horizontal coordinate and the intensity as the vertical coordinate to establish a working curve; S8. Performing measurement of the sample under the same analytical conditions as those for establishing the working curve, and performing measurement of the blank sample under the same analytical conditions as those for measuring the sample; S9. Calculate the hexavalent chromium content in soil or sediment using the following formula: Where: w is the content of hexavalent chromium in the soil sample, mg / kg; ρ is the concentration of hexavalent chromium in the sample, mg / L; V Sample volume, mL D. Dilution multiple of the sample; m is the weight of the soil sample, g; W dm Dry matter content of soil samples, %.

6. A method for determining hexavalent chromium in soil and sediment according to claim 5, characterized in that: The alkaline extract is prepared by dissolving 30 g of sodium carbonate and 20 g of sodium hydroxide in water, diluting the solution to 1 L, and storing the solution in a sealed polyethylene bottle. The pH value must be greater than 11.5 before use.

7. A method for determining hexavalent chromium in soil and sediment according to claim 5, characterized in that: The dipotassium hydrogen phosphate-potassium dihydrogen phosphate buffer solution is prepared by dissolving 87.1 g of dipotassium hydrogen phosphate and 68.0 g of potassium dihydrogen phosphate in water and diluting the solution to a constant volume of 1 L.

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