Rapid detection method for residual sodium persulfate in soil

Abstract

The invention relates to the technical field of soil detection, and particularly discloses a rapid detection method for residual sodium persulfate in soil, which comprises the following steps: S1, measuring the moisture content of soil; s2, calculating the mass of a soil dry basis according to the water content, adding deionized water into the soil to be detected, uniformly stirring, adding a flocculating agent, and filtering to obtain a soil leachate; s3, taking the soil leachate in the S2, and adding dilute sulfuric acid; s4, adding potassium iodide into the solution in S3, uniformly stirring, and carrying out dark treatment; s5, titrating the solution in S4 with a sodium thiosulfate standard solution, adding a starch indicator when the solution becomes light yellow, ending titration when the solution becomes colorless, and measuring the volume of the consumed sodium thiosulfate standard solution; and S6, calculating the content of sodium persulfate in the to-be-detected soil dry basis. The rapid detection method for residual sodium persulfate in soil provided by the invention can effectively remove humus colloid in the soil leachate, and improves the accuracy and reliability of the detection result.

Description

Technical Field

[0001] The invention relates to the technical field of soil detection, and in particular to a rapid detection method for residual sodium persulfate in soil. Background Art

[0002] In the process of soil remediation, oxidants are usually needed to degrade pollutants such as petroleum hydrocarbons and non-water-soluble chlorinated solvents in the soil into low-toxic and low-harm or even non-toxic substances. Among them, sodium persulfate is an efficient and stable oxidant with low by-product hazards, but because of its dangerous properties such as irritation and combustion-supporting, it is still unfriendly to the soil environment. Often after the oxidation process, excessive use of reagents often leads to sodium persulfate residues in the soil. Measuring the concentration of sodium persulfate in the soil requires the use of iodine titration or other methods, which requires sampling and processing of the soil, and a series of operating procedures to obtain its concentration.

[0003] In the existing detection method, potassium iodide standard solution is mixed with sodium persulfate, placed in a dark place, and then titrated with sodium thiosulfate standard solution with starch as an indicator until it is colorless. However, since the soil may contain humus colloids, the prepared soil extract will become turbid and colored under the interference of humus colloids, which will hinder the color development of the indicator during detection, and the color change of the extract cannot be clearly observed, thereby affecting the accuracy of the test results. Summary of the invention

[0004] In order to effectively remove humus colloids in soil leachate and improve the accuracy and reliability of detection results, the present application provides a rapid detection method for residual sodium persulfate in soil.

[0005] The present application provides a rapid detection method for residual sodium persulfate in soil, which adopts the following technical scheme: A rapid detection method for residual sodium persulfate in soil comprises the following steps: S1: Measure the moisture content of the soil to be tested; S2: Calculate the mass of the dry basis of the soil to be tested based on the moisture content in S1 as m 1 , add deionized water to the soil to be tested, stir evenly, and add a mass of (10%-20%) m 1 After filtration, the volume of flocculant is V 1 of soil leachate; S3: Take the soil leachate in S2 with a volume V, add dilute sulfuric acid to adjust the pH of the solution, and obtain solution A; S4: Add (10%-15%) m 1 of potassium iodide, stir evenly, and place in a dark place for a while to obtain solution B; S5: Titrate solution B with a sodium thiosulfate standard solution of concentration c. When the solution turns light yellow, add 2-4 drops of starch indicator. When the solution turns from blue to colorless, the titration endpoint is reached. The volume of sodium thiosulfate standard solution consumed is V. 2 ; S6: Calculate the content of sodium persulfate in the dry basis of the soil to be tested:

[0006] By adopting the above technical scheme, the present application can realize the rapid detection of residual sodium persulfate in the soil through the above steps, shorten the detection time and improve the detection efficiency. Among them, by measuring the moisture content of the soil and calculating the dry basis mass, the actual content of sodium persulfate in the soil can be more accurately reflected, reducing the impact of moisture content changes on the test results. Adding a flocculant to remove the colloidal particles contained in the soil ensures the clarity of the soil leachate, avoids the turbid and colored test liquid from hindering the color development reaction, and can more clearly observe the color change of the liquid during the detection process, thereby improving the accuracy and reliability of the test results. In addition, by adding a starch indicator, the titration end point can be observed more intuitively, ensuring the accurate judgment of the titration end point, and further improving the accuracy of the test results.

[0007] Preferably, the flocculant is modified polyaluminium chloride, and the preparation method of the modified polyaluminium chloride is as follows: first, zeolite is added to a 1 mol / L NaCl solution at a solid-liquid ratio of 1:10, stirred and shaken for 4-6 hours, the supernatant is discarded, and the mixture is washed with deionized water for multiple times, dried, and ground to 200-250 meshes; then, calcined at 280-300°C for 2-3 hours, and cooled to obtain a pretreated zeolite; the pretreated zeolite and polyaluminium chloride are uniformly mixed at a mass ratio of 5:3, and 3% NaHCO3 is added to the zeolite and polyaluminium chloride at a solid-liquid ratio of 1:(1.2-1.5). 3 solution; then, adding a 10% PVA solution according to a solid-liquid ratio of 1: (0.7-0.9), stirring to form a mass, making particles with a particle size of 3-5 mm, and drying; finally, calcining at 280-300°C for 1-2h, and cooling to obtain modified polyaluminium chloride.

[0008] By adopting the above technical solution, zeolite-modified polyaluminium chloride has a higher floc growth rate and sedimentation rate, removes colloids and other turbid substances in the soil leachate, reduces the turbidity of the soil leachate, improves the clarity of the soil leachate, and makes the color change of the solution easy to observe, so as to improve the accuracy of the test results. 3The solution can improve the pore structure of polyaluminium chloride, which is beneficial to increase the adsorption of colloids. Modified polyaluminium chloride has electrical neutralization and coagulation effects in water, neutralizes the surface charge of colloid particles in water, eliminates the electrostatic repulsion between particles, makes them lose stability, and thus induces coagulation and sedimentation between particles.

[0009] Preferably, the soil moisture content in S1 is measured by a drying method.

[0010] Preferably, the soil to be tested in S2 is an original soil sample.

[0011] By adopting the above technical solution, the soil to be tested is dried to remove free water and hygroscopic water in the soil, which can improve the accuracy of the measurement result.

[0012] Preferably, the mass fraction of the soil leachate in S2 is 7%-8%.

[0013] By adopting the above technical solution, a soil extract with a mass fraction of 7%-9% is obtained after adding a flocculant and filtering, and the change in the color of the solution in the subsequent titration process can be observed more clearly, thereby improving the accuracy and reliability of the detection results.

[0014] Preferably, the mass fraction of the dilute sulfuric acid added in S3 is 15%-25%.

[0015] By adopting the above technical solution and adding an appropriate amount of dilute sulfuric acid, the reaction is carried out in a weakly acidic environment.

[0016] Preferably, the dark treatment time in S4 is 1-2 h.

[0017] By adopting the above technical solution, since iodine molecules are easily volatilized and oxidized under light conditions, potassium iodide is added to S4 and placed in a dark place for 1-2 hours to ensure that the generated iodine molecules react completely, reduce iodine loss, and ensure the accuracy of titration.

[0018] Preferably, multiple groups of parallel experiments are set for the soil samples to be tested, and the content of sodium persulfate in the soil is taken as the average value of the multiple groups of parallel experiments.

[0019] By adopting the above technical solution and setting up multiple groups of parallel experiments, the accidental errors that may occur in a single experiment can be reduced, thereby improving the accuracy of measuring the sodium persulfate content in the soil, thereby better reflecting the actual content of sodium persulfate in the soil.

[0020] This application has the following beneficial effects: 1. In the present application, the present application can realize the rapid detection of residual sodium persulfate in the soil through the above steps, shorten the detection time and improve the detection efficiency. Among them, by measuring the moisture content of the soil and calculating the dry basis mass, the actual content of sodium persulfate in the soil can be more accurately reflected, and the influence of moisture content change on the test results can be reduced. Adding a flocculant to remove the colloidal particles contained in the soil ensures the clarity of the soil leachate, avoids the turbid and colored test liquid from hindering the color development reaction, and can more clearly observe the color change of the liquid during the detection process, thereby improving the accuracy and reliability of the test results. In addition, by adding a starch indicator, the titration end point can be observed more intuitively, ensuring the accurate judgment of the titration end point, and further improving the accuracy of the test results.

[0021] 2. In this application, zeolite-modified polyaluminium chloride is used, which has a high floc growth rate and sedimentation rate, removes colloids and other turbid substances in the soil leachate, reduces the turbidity of the soil leachate, improves the clarity of the soil leachate, and makes the color change of the solution easy to observe, so as to improve the accuracy of the test results. 3 The solution can improve the pore structure of polyaluminium chloride, which is beneficial to increase the adsorption of colloids. Modified polyaluminium chloride has electrical neutralization and coagulation effects in water, neutralizes the surface charge of colloid particles in water, eliminates the electrostatic repulsion between particles, makes them lose stability, and thus induces coagulation and sedimentation between particles. DETAILED DESCRIPTION

[0022] Preparation Example Preparation Example 1 Preparation of modified polyaluminium chloride: First, 50 g of zeolite was added to 500 ml of 1 mol / L NaCl solution, stirred and shaken for 4 h, the supernatant was discarded, the mixture was washed with deionized water for several times, dried, and ground to 200 mesh; then, the mixture was calcined at 300 ° C for 2 h, and the pretreated zeolite was obtained after cooling; the pretreated zeolite was evenly mixed with 30 g of polyaluminium chloride, and 96 ml of 3% NaHCO was added. 3 solution; then, add 56 ml of 10% PVA solution, stir to form a mass, make particles with a particle size of 3 mm, and dry; finally, calcine at 280°C for 2h, and obtain modified polyaluminium chloride after cooling.

[0023] Preparation Example 2 Preparation of modified polyaluminium chloride: First, 50 g of zeolite was added to 500 ml of 1 mol / L NaCl solution, stirred and shaken for 6 h, the supernatant was discarded, and the mixture was washed with deionized water for several times, dried, and ground to 250 mesh; then, the mixture was calcined at 300 ° C for 3 h, and the pretreated zeolite was obtained after cooling; the pretreated zeolite was evenly mixed with 30 g of polyaluminium chloride, and 120 ml of 3% NaHCO was added. 3 solution; then, add 72 ml of 10% PVA solution, stir to form a mass, make particles with a particle size of 5 mm, and dry; finally, calcine at 300°C for 1 hour, and obtain modified polyaluminium chloride after cooling. Example

[0024] Example 1 A rapid detection method for residual sodium persulfate in soil comprises the following steps: S1: Use the drying method to measure the moisture content of the soil to be tested ω; where, The soil samples in this step are not used in subsequent steps.

[0025] S2: Calculate the mass of the dry basis of the soil to be tested as m according to the moisture content ω in S1 1 , add deionized water to the soil to be tested, stir evenly, add (10%-20%) m 1 Modified polyaluminium chloride (prepared in Preparation Example 1) was filtered to obtain a volume of V 1 of soil leachate; where m 1 =m / (1+ω), m is the mass of the soil to be tested, and the soil to be tested in this step is the original soil sample without any treatment; the mass fraction of the soil leachate is 7%-8%.

[0026] S3: Take the soil leachate in S2 with a volume V, add 15%-25% by mass of dilute sulfuric acid to adjust the pH of the solution to 5.0-6.0, and obtain solution A.

[0027] S4: Add (10%-15%) m 1 Potassium iodide, stir evenly, and place in a dark place to react for 1-2 hours to obtain solution B. The reaction principle of this step is: 2I - +S 2 O 8 2- →I 2 +2SO 4 2- .

[0028] S5: Titrate solution B with a sodium thiosulfate standard solution of concentration c. When the solution turns light yellow, add 2-4 drops of starch indicator. When the solution turns from blue to colorless, the titration endpoint is reached. The volume of sodium thiosulfate standard solution consumed is V. 2 ; In this step, the sodium thiosulfate standard solution is titrated in an acidic environment to determine the amount of sodium persulfate and potassium iodide reacting in S4. The reaction principle of this step is: I 2 +2S 2 O 3 2- →2I - +S 4 O 6 2- .

[0029] S6: Calculate the content of sodium persulfate in the dry basis of the soil to be tested according to the above reagent dosage and the corresponding proportional relationship in the reaction principle: Where, c is the concentration of sodium thiosulfate solution, mol / L; V 2 is the volume of sodium thiosulfate standard solution consumed, L; m 1 is the mass of the dry basis of the soil to be tested, g; V 1 is the total volume of the soil leachate to be tested, ml; V is the volume of the soil leachate used in the experiment, ml.

[0030] Example 2 A rapid detection method for residual sodium persulfate in soil comprises the following steps: S1: Take some soil samples and measure the moisture content of the soil to be tested by drying method, which is 25%.

[0031] S2: Take another m = 10g of original soil, add 6ml of deionized water, stir evenly, add 0.8g of modified polyaluminium chloride (prepared in Preparation Example 1), and filter to obtain a volume of V 1 = 16 ml of soil leachate; where m 1 =8g, the mass fraction of soil leachate is 7%.

[0032] S3: Set up 4 parallel experiments. V = 4 ml of soil leaching solution was taken from S2 in each parallel experiment, and 20% by mass of dilute sulfuric acid was added to each parallel experiment to adjust the pH to 6.0.

[0033] S4: Add 0.8 g potassium iodide to each parallel experiment, stir evenly, and place in the dark for 2 h; S5: Use sodium thiosulfate standard solution with concentration of c=0.1mol / L to titrate the mixed solution in 4 sets of parallel experiments. When the solution turns light yellow, add 3 drops of starch indicator. When the solution turns from blue to colorless, it is the titration end point. The volumes of sodium thiosulfate standard solution consumed are 2ml, 3ml, 3ml, and 4ml respectively. The average titration amount of the four sets of parallel experiments is 3ml.

[0034] S6: Calculate the content of sodium persulfate in the dry basis of the soil to be tested according to the above reagent dosage and the corresponding proportional relationship in the reaction principle:

[0035] Example 3 A rapid detection method for residual sodium persulfate in soil comprises the following steps: S1: Take some soil samples and measure the moisture content of the soil to be tested by drying method, which is 25%.

[0036] S2: Take another m = 10g of original soil, add 6ml of deionized water, stir evenly, add 1.6g of modified polyaluminium chloride (prepared in Preparation Example 2), and filter to obtain a volume of V 1 = 16 ml of soil leachate; where m 1 =8g, the mass fraction of soil leachate is 8%.

[0037] S3: Set up 4 parallel experiments. V = 4 ml of soil leaching solution was taken from S2 in each parallel experiment, and 20% by mass of dilute sulfuric acid was added to each parallel experiment to adjust the pH to 6.0.

[0038] S4: Add 1.2 g potassium iodide to each parallel experiment, stir evenly, and place in the dark for 2 h; S5: Use sodium thiosulfate standard solution with concentration of c=0.1mol / L to titrate the mixed solution in 4 sets of parallel experiments. When the solution turns light yellow, add 3 drops of starch indicator. When the solution turns from blue to colorless, it is the titration end point. The volumes of sodium thiosulfate standard solution consumed are 3ml, 4ml, 3ml, and 4ml respectively. The average titration amount of the four sets of parallel experiments is 3.5ml.

[0039] S6: Calculate the content of sodium persulfate in the dry basis of the soil to be tested according to the above reagent dosage and the corresponding proportional relationship in the reaction principle:

[0040] Comparative Example Comparative Example 1 A rapid detection method for residual sodium persulfate in soil, which differs from Example 2 in that unmodified polyaluminium chloride is used to replace the modified polyaluminium chloride in S2, comprising the following steps: (1) Take some soil samples and measure the moisture content of the soil to be tested by the drying method, which is 25%.

[0041] (2) Take m = 10 g of the original soil, add 6 ml of deionized water, stir evenly, add 0.8 g of polyaluminium chloride, and filter to obtain a volume of V 1 = 16 ml of soil leachate; where m 1 =8g, the mass fraction of soil leachate is 55%.

[0042] (3) Four parallel experiments were set up. V = 4 ml of soil extract was taken from S2 in each parallel experiment, and 20% by mass of dilute sulfuric acid was added to each parallel experiment to adjust the pH to 6.0.

[0043] (4) Add 0.8 g of potassium iodide to each parallel experiment, stir evenly, and place in a dark place for 2 h.

[0044] (5) The mixed solutions in the four parallel experiments were titrated with a sodium thiosulfate standard solution with a concentration of c = 0.1 mol / L. When the solution turned light yellow, 3 drops of starch indicator were added. The titration endpoint was when the solution turned from blue to colorless. The volumes of sodium thiosulfate standard solution consumed were 7 ml, 8 ml, 9 ml, and 8 ml, respectively. The average titration amount of the four parallel experiments was 8 ml.

[0045] (6) According to the above reagent dosage and the corresponding proportional relationship in the reaction principle, calculate the content of sodium persulfate in the dry basis of the soil to be tested:

[0046] Comparative Example 2 A rapid detection method for residual sodium persulfate in soil, which differs from Example 2 in that modified polyaluminium chloride is not added to S2, comprises the following steps: (1) Take some soil samples and measure the moisture content of the soil to be tested by the drying method, which is 25%.

[0047] (2) Take m = 10 g of the original soil, add 6 ml of deionized water, stir evenly, and obtain a volume of V 1 = 16 ml of soil leachate; where m 1 =8g, the mass fraction of soil leachate is 65%.

[0048] (3) Four parallel experiments were set up. V = 4 ml of soil extract was taken from S2 in each parallel experiment, and 20% by mass of dilute sulfuric acid was added to each parallel experiment to adjust the pH to 6.0.

[0049] (4) Add 0.8 g of potassium iodide to each parallel experiment, stir evenly, and place in the dark for 2 h; (5) The mixed solutions in the four parallel experiments were titrated with a sodium thiosulfate standard solution with a concentration of c = 0.1 mol / L. When the solution turned light yellow, 3 drops of starch indicator were added. The titration endpoint was when the solution turned from blue to colorless. The volumes of sodium thiosulfate standard solution consumed were 11 ml, 10 ml, 9 ml, and 10 ml, respectively. The average titration amount of the four parallel experiments was 10 ml.

[0050] (6) According to the above reagent dosage and the corresponding proportional relationship in the reaction principle, calculate the content of sodium persulfate in the dry basis of the soil to be tested:

[0051] According to the comparison data of Example 2 and Comparative Example 1, it can be seen that in Comparative Example 1, since the polyaluminium chloride added in step (2) has not been modified, the adsorption and sedimentation effect on the colloidal particles in the soil leachate is not obvious, resulting in the solution still being turbid and colored during titration in step (5), thereby affecting the judgment of the titration end point. In Example 1, zeolite is used to modify polyaluminium chloride, and it is added to the soil leachate to adsorb and sediment turbid substances such as colloids in the soil leachate. Among them, the modified polyaluminium chloride has electrical neutralization and coagulation effects in the water body, neutralizes the surface charge of the colloidal particles in the water, eliminates the electrostatic repulsion between the particles, thereby inducing coagulation and sedimentation between the particles, and has a higher floc growth rate and sedimentation rate, which can significantly reduce the turbidity of the soil leachate, making the color change of the solution during titration easy to observe, and making the judgment of the titration end point more sensitive, thereby improving the accuracy of the test results.

[0052] According to the comparison data between Example 2 and Comparative Example 2, in Comparative Example 2, since the soil leachate prepared in step (2) does not remove the colloidal particles in the solution, the clarity of the solution is affected, resulting in unclear color display in the titration of step (5), affecting the determination of the titration endpoint, thereby consuming more sodium thiosulfate titration solution, further affecting the accuracy of the test result, and causing the test result to be high. On the contrary, in Example 1, the colloidal particles in the soil leachate are removed by modified polyaluminium chloride, so that the soil leachate maintains a high clarity, and the change in the solution color can be clearly observed in the titration link. In the four parallel tests, the amount of sodium thiosulfate titration solution consumed in each experiment is within a reasonable range, thereby ensuring the accuracy and reliability of the test results, and better reflecting the actual content of sodium persulfate in the soil.

[0053] The above examples are merely illustrative of the present invention and do not constitute a limitation on the protection scope of the present invention. After reading this specification, those skilled in the art may make modifications to the specific implementation mode without creative contribution as needed, but as long as they are within the scope of the claims of this application, they are protected by the patent law.

Claims

1. A rapid detection method for residual sodium persulfate in soil, characterized in that: The following steps are involved: S1: Measure the moisture content of the soil to be tested; S2: Calculate the mass of the dry basis of the soil to be tested as m1 according to the moisture content in S1, add deionized water to the soil to be tested, stir evenly, add a flocculant with a mass of (10%-20%) m1, and filter to obtain a soil leachate with a volume of V1; S3: Take the soil leachate in S2 with a volume V, add dilute sulfuric acid to adjust the pH of the solution to 5.0-6.0, and obtain solution A; S4: Add (10%-15%) ml of potassium iodide to solution A in S3, stir evenly, and place in a dark place for a period of time to obtain solution B; S5: Titrate solution B with a sodium thiosulfate standard solution of concentration c. When the solution turns light yellow, add 2-4 drops of starch indicator. When the solution turns from blue to colorless, the titration endpoint is reached. The volume of sodium thiosulfate standard solution consumed is V2. S6: Calculate the content of sodium persulfate in the dry basis of the soil to be tested:

2. The rapid detection method for residual sodium persulfate in soil according to claim 1, characterized in that: The flocculant is modified polyaluminium chloride, and the preparation method of the modified polyaluminium chloride is as follows: First, zeolite is added to a 1 mol / L NaCl solution at a solid-liquid ratio of 1:10, stirred and shaken for 4-6 hours, the supernatant is discarded, and the mixture is washed with deionized water for multiple times, dried, and ground to 200-250 meshes; then, the mixture is calcined at 280-300°C for 2-3 hours, and the pretreated zeolite is obtained after cooling; the pretreated zeolite and polyaluminium chloride are mixed uniformly at a mass ratio of 5:3, and a 3% NaHCO3 solution is added to the zeolite and polyaluminium chloride at a solid-liquid ratio of 1:(1.2-1.5); then, a 10% PVA solution is added at a solid-liquid ratio of 1:(0.7-0.9), stirred into agglomerates, and particles with a particle size of 3-5 mm are prepared, and dried; finally, the mixture is calcined at 280-300°C for 1-2 hours, and the modified polyaluminium chloride is obtained after cooling.

3. The rapid detection method for residual sodium persulfate in soil according to claim 1, characterized in that: The soil moisture content in S1 is measured by a drying method.

4. The rapid detection method for residual sodium persulfate in soil according to claim 1, characterized in that: The soil to be tested in S2 is an original soil sample.

5. The rapid detection method for residual sodium persulfate in soil according to claim 1, characterized in that: The mass fraction of the soil leachate in S2 is 7%-8%.

6. The rapid detection method for residual sodium persulfate in soil according to claim 1, characterized in that: The mass fraction of the dilute sulfuric acid added to S3 is 15%-25%.

7. The rapid detection method for residual sodium persulfate in soil according to claim 1, characterized in that: The dark treatment time in S4 is 1-2 hours.

8. The rapid detection method for residual sodium persulfate in soil according to claim 1, characterized in that: The soil samples to be tested are set up with multiple groups of parallel experiments, and the content of sodium persulfate in the soil is taken as the average value of the multiple groups of parallel experiments.

Images