A method for determining heavy metals in soil aggregates based on dry fraction-wet screening method

Abstract

The application discloses a method for determining heavy metals in soil aggregates based on dry-sieving-wet-sieving method, mainly comprising the following steps: S1, natural air-drying undisturbed soil at room temperature to mature the soil sample; S2, dispersing the matured soil along the natural cracks of the soil sample, and performing initial sieving on the sample through a 10mm sieve, and placing the sample on the top layer of a dry-sieving set to perform dry sieving, and weighing each layer of soil sample; S3, taking another soil sample sieved initially, and collecting each layer of soil sample after dry sieving; S4, setting a wet-sieving set, and placing the layered soil sample in the dry-sieving set into the corresponding wet-sieving set to perform wet sieving; and S5, mixing the samples after wet sieving according to rules to obtain wet-sieved soil aggregate samples of different particle sizes. The application can further determine the source of heavy metals in different particle size aggregates, reduces the loss of soil heavy metals caused by the loss of low particle size aggregates in the sieving process, and the result is closer to the true value.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of soil detection, and particularly relates to a method for determining heavy metals in soil aggregates based on a dry-sieving-wet-sieving method. BACKGROUND

[0002] With the rapid development of industry and agriculture, illegal discharge of industrial wastewater, unreasonable use of pesticides and fertilizers and other phenomena have increased great pressure on farmland ecosystems. The United Nations Environment Programme (UNEP) established a special resolution on Cd and Pb pollution at the Board to promote global action to reduce the harmful effects of Cd and Pb and to repair heavy metals in soil. Excessive accumulation of Cd and Pb in farmland soil reduces yield by being absorbed into crops through crop roots, and enters human life through the food chain, posing a threat to human health. Therefore, it is urgent to carry out research on the degradation of heavy metals (PTE) in the soil-crop system. In the soil-crop system, soil structure is an important property of soil, and changes in the structure affect the cycling and release processes of different elements in the soil, especially the adsorption and desorption processes of PTE such as Cd and Pb in the soil, which directly affect the availability of PTE in the soil. Therefore, accurate determination of the content of heavy metals in aggregates is an important basis for related research.

[0003] The types and amounts of heavy metals in soil aggregates are different because aggregates of different sizes can have different textures and porosities. Soil aggregates can be divided into macroaggregates (> 250 μm) and microaggregates (< 250 μm) according to their particle size, and each aggregate can be further divided into coarse macroaggregates (> 2000 μm), fine macroaggregates (2000-250 μm), microaggregates (250-53 μm) and powder-clay aggregates (< 53 μm); it can also be divided into stable aggregates and non-stable aggregates according to its resistance to external force. The separation of aggregate particles is the first step to explore the structure of the aggregate. Dry screening method and wet screening method have been widely used in the separation of soil aggregates. The dry screening method is to weigh the air-dried soil sample, place it on the top of the nested screen, shake it and collect the residual soil sample in each screen, which is the sample of different aggregate size. The wet screening method invented by Elliott et al. measures the water-stable aggregates of soil: first, the undisturbed soil sample is air-dried in a greenhouse, and then the dried soil sample is gently passed through a 10 mm soil screen. Then the soil sample is placed on a 2, 0.25, 0.053 mm nested screen for screening, and the weight of the remaining aggregates on the screen is recorded and the percentage in the loose soil sample is calculated. According to the above percentage, the soil sample is prepared and placed on the nested screen for wet screening. Before starting the wet screening, the soil sample is moistened, then the screen is shaken up and down, and the aggregates on each screen are collected and washed into an aluminum box, which is dried at 60℃ and weighed. In turn, the contents of macroaggregates, microaggregates, microaggregates and powder clay are obtained (%).

[0004] The dry screening method measures the mechanical stability of the original soil aggregates, which can reflect the distribution characteristics of the soil aggregates in the natural state because it causes less damage to the transient and temporary organic cementing materials in the soil. However, the dry screening method mainly obtains macroaggregates because the decomposition of multi-level aggregates is not complete, resulting in the adhesion of multi-level aggregates. The wet screening method measures the water-stable aggregates of soil, which can reflect the potential water erosion resistance of soil. Although the wet screening method can maximize the dispersion of multi-level aggregates, it destroys the non-water-stable aggregates in the soil, causing them to disintegrate into smaller aggregates. For the soil aggregates divided by the two methods, there is a large error in directly collecting and measuring the content of heavy metals in each level of aggregates, and the loss of heavy metals in each level of aggregates is too large. Moreover, the heavy metals remaining in the water and the device cannot be clearly determined from which level of aggregates. SUMMARY

[0005] The purpose of the present invention is to fill the gap in the prior art, and to provide a method for determining heavy metals in soil aggregates based on dry-wet screening. The technical scheme of the present invention is as follows:

[0006] S1: air-drying the undisturbed soil at room temperature to allow the soil sample to mature;

[0007] S2: The matured soil is dispersed along the natural cracks of the soil sample, the sample is primary screened through a 10mm sieve, and the sample is placed on the top layer of a dry screening set for dry screening, and the soil samples of each layer are collected and weighed;

[0008] S3: Another 50g of the soil sample screened through a 10mm sieve is taken, and after dry screening, the soil samples of each layer are collected and recorded as soil layered samples a, b, c, d, and e from top to bottom;

[0009] S4: A wet screening set is set up, the soil layered sample X of the ith layer in the dry screening set is placed in the corresponding ith layer of the wet screening set, the wet screening set is placed in ultrapure water for 5 minutes and shaken for 2 minutes, after the suspended particles in the water are settled, different particle size water stable soil aggregate samples are obtained, the soil aggregate sample in the ith layer of the wet screening set is recorded as Xi, the supernatant sample with uniformly mixed solutes is recorded as X5, and the soil aggregate sample precipitated at the bottom of the barrel is recorded as X6, each layer of aggregate sample and the supernatant sample with uniformly mixed solutes are collected;

[0010] S5: The samples after wet screening are mixed according to the following rules to obtain different particle size wet screened soil aggregate total samples:

[0011] 1st grade aggregate total sample: T1=a1;

[0012] 2nd grade aggregate total sample: T2=a2+b2;

[0013] 3rd grade aggregate total sample: T3=a3+b3+c3;

[0014] 4th grade aggregate total sample: T4=a4+b4+c4+d4;

[0015] Aggregate clay total sample: Tclay=a6+b6+c6+d6;

[0016] S6: The heavy metal content of the soil layered sample e, each particle size wet screened soil aggregate total sample, and multiple supernatant samples is determined, and the heavy metal content is recorded as M Y , wherein Y is the soil layered sample e, the different particle size wet screened soil aggregate total sample, or the supernatant sample X5, and the heavy metal content of the different particle size wet screened soil aggregate is obtained as follows:

[0017] 1st grade aggregate heavy metal content: M1=M T1 +M a5 ;

[0018] 2nd grade aggregate heavy metal content: M2=M T2 +M b5 ;

[0019] 3rd grade aggregate heavy metal content: M3=MT3 +M c5 ;

[0020] 4th level aggregate heavy metal content is M4=M T4 +M d5 ;

[0021] aggregate clay heavy metal content is M 粘 =M T粘 +M e .

[0022] Preferably, in S1, the standard for maturation of the soil sample is that the water content of the soil sample measured continuously for 3 days does not change, which means maturation is complete.

[0023] Preferably, in S2, the dry screening set is stacked from top to bottom with 2, 0.5, 0.25, and 0.106 mm sieves; when dry screening, the dry screening frequency is 200 times / min, and the oscillation is 2 min.

[0024] Preferably, in S4, the wet screening set is stacked from top to bottom with 2, 0.5, 0.25, and 0.106 mm sieves; the oscillation amplitude is 3 cm, and the frequency is 30 times / min.

[0025] Preferably, in S4, i is a positive integer from 1 to 4, and X is a, b, c, or d.

[0026] The present application provides a method for standardizing the determination of heavy metals in water-stable aggregates, which can further clarify the source of heavy metals in different particle size aggregates during the process of refining aggregate grouping. The present application can effectively collect different particle size water-stable aggregates, and reduce the loss of soil heavy metals caused by the loss of low particle size aggregates during the screening process. Compared with the traditional method, the present application has a wider range and the measured total content of heavy metals is closer to the true value. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a schematic diagram of a method for determining heavy metals in soil aggregates based on dry screening-wet screening method;

[0028] Figure 2 is a schematic diagram of a method for determining heavy metals in soil aggregates based on dry screening-wet screening method. DETAILED DESCRIPTION

[0029] The embodiments of the present application will be described in detail below with reference to the accompanying drawings. A method for determining heavy metals in soil aggregates based on dry screening-wet screening method, characterized in that:

[0030] S1: The undisturbed soil is naturally air-dried at room temperature to allow the soil sample to mature; the standard for the maturation of the soil sample is that the water content of the soil sample remains unchanged for 3 consecutive days.

[0031] S2: The matured soil is dispersed along the natural cracks of the soil sample, the sample is initially screened through a 10mm sieve, and the sample is placed on the top layer of a dry screening set for dry screening, and the soil samples of each layer are collected and weighed; the dry screening set has 2, 0.5, 0.25, and 0.106mm sieves stacked from top to bottom; during dry screening, the dry screening frequency is 200 times / min, and the oscillation time is 2min.

[0032] S3: Another 50g of the soil sample screened through a 10mm sieve is collected, and after dry screening, the soil samples of each layer are collected and recorded as soil layer samples a, b, c, d, and e from top to bottom;

[0033] S4: A wet screening set is set up, which has 2, 0.5, 0.25, and 0.106mm sieves stacked from top to bottom; the soil layer sample X of the i-th layer in the dry screening set is placed in the corresponding i-th layer of the wet screening set, and after standing in ultrapure water for 5min, the wet screening set is oscillated for 2min, with an oscillation amplitude of 3cm and a frequency of 30 times / min. After the suspended particles in the water are settled, different particle size water-stable soil aggregate samples are obtained, which are recorded as Xi in the i-th layer of the wet screening set, X5 as the supernatant sample with uniformly mixed solutes, and X6 as the soil aggregate sample settled at the bottom of the barrel. Collect each layer of aggregate sample and the supernatant sample with uniformly mixed solutes; i is a positive integer from 1 to 4, and X is a, b, c, and d.

[0034] S5: The samples after wet screening are mixed according to the following rules to obtain different particle size wet screening soil aggregate total samples:

[0035] 1st aggregate total sample: T1=a1;

[0036] 2nd aggregate total sample: T2=a2+b2;

[0037] 3rd aggregate total sample: T3=a3+b3+c3;

[0038] 4th aggregate total sample: T4=a4+b4+c4+d4;

[0039] Aggregate clay total sample: Tclay=a6+b6+c6+d6;

[0040] S6: The heavy metal content of the soil layer sample e, each particle size wet screening soil aggregate total sample, and multiple supernatant samples is determined, and the heavy metal content is recorded as M Y, wherein Y is the soil layering sample e, the total sample of different particle size wet-sieved soil aggregates or the supernatant sample X5, the heavy metal content of different particle size wet-sieved soil aggregates can be obtained as follows:

[0041] The heavy metal content of 1st grade aggregates is M1=M T1 +M a5 ;

[0042] The heavy metal content of 2nd grade aggregates is M2=M T2 +M b5 ;

[0043] The heavy metal content of 3rd grade aggregates is M3=M T3 +M c5 ;

[0044] The heavy metal content of 4th grade aggregates is M4=M T4 +M d5 ;

[0045] The heavy metal content of aggregate clay is M 粘 =M T粘 +M e .

Claims

1. A method for determining heavy metals in soil aggregates based on dry-wet sieving, characterized in that: S1: Allow the undisturbed soil to air dry naturally at room temperature to allow the soil sample to mature. S2: Disperse the matured soil along the natural cracks in the soil sample, pass the sample through a 10mm sieve for initial screening, place the sample on the top layer of the dry sieve set for dry screening, collect soil samples from each layer and weigh them. S3: Take another 50g of soil sample that has passed through a 10mm sieve. After dry sieving, collect soil samples from each layer separately and record them as soil layer samples a, b, c, d, and e from top to bottom. S4: Set up a wet sieve set. Place the soil layer sample X from the i-th layer of the dry sieve set into the corresponding i-th layer of the wet sieve set. Let the wet sieve set stand in ultrapure water for 5 minutes and then shake for 2 minutes. After the suspended particles in the water settle, water-stable soil aggregate samples of different particle sizes are obtained. Let the soil aggregate sample in the i-th layer of the wet sieve set be Xi, let the supernatant sample with uniform solute mixing be X5, and let the soil aggregate sample settled at the bottom of the bucket be X6. Collect the aggregate sample and the supernatant sample with uniform solute mixing from each layer. i is a positive integer from 1 to 4, and X is a, b, c, d. S5: Mix the wet-sieved samples according to the following rules to obtain total samples of wet-sieved soil aggregates of different particle sizes: Total sample size of Grade 1 aggregates: T1 = a1; Total sample size of grade 2 aggregates: T2 = a2 + b2; Total sample size of grade 3 aggregates: T3 = a3 + b3 + c3; Total sample size of grade 4 aggregates: T4 = a4 + b4 + c4 + d4; Total sample size of aggregated clay particles: T_clay = a6 + b6 + c6 + d6; Wherein, a1-a4 represent soil aggregate samples of sample a after dry sieving and wet sieving that fall into layers 1-4 respectively; b2-b4 represent soil aggregate samples of sample b after dry sieving and wet sieving that fall into layers 2-4 respectively; c3-c4 represent soil aggregate samples of sample c after dry sieving and wet sieving that fall into layers 3-4 respectively; d4 represents soil aggregate samples of sample d after dry sieving and wet sieving that fall into layer 4; a6, b6, c6, and d6 are soil aggregate samples of samples a, b, c, and d after dry sieving and wet sieving that settle at the bottom of the bucket respectively. S6: The heavy metal content of soil stratified sample e, the total sample of wet-sieved soil aggregates of each particle size, and multiple sets of supernatant samples were determined respectively. The heavy metal contents of different particle size wet-sieved soil aggregates can be obtained as follows: The heavy metal content of grade 1 aggregates is M1 = M T1 +M a5 ; The heavy metal content of grade 2 aggregates is M2 = M T2 +M b5 ; The heavy metal content of grade 3 aggregates is M3 = M T3 +M c5 ; The heavy metal content of grade 4 aggregates is M4 = M T4 +M d5 ; The heavy metal content of the agglomerate clay particles is M 粘 =M T粘 +M e . Among them, M T1 -M T4 These represent the heavy metal content of the total sample of aggregates from grades 1 to 4; M a5 M b5 M c5 M d5 These represent the heavy metal content of the supernatant samples after wet sieving of samples a, b, c, and d (after dry sieving); M T粘 M represents the heavy metal content of the total sample of aggregated clay particles; e This represents the heavy metal content of sample e after dry sieving.

2. The method for determining heavy metals in soil aggregates based on dry-wet sieving according to claim 1, characterized in that: In S1, the standard for soil sample maturation is that the moisture content of the soil sample remains unchanged for three consecutive days, which indicates that maturation is complete.

3. The method for determining heavy metals in soil aggregates based on dry-wet sieving according to claim 1, characterized in that: In S2, the dry sieving kit has sieves of 2, 0.5, 0.25, and 0.106 mm stacked from top to bottom; during dry sieving, the dry sieving frequency is 200 times / min, and the vibration lasts for 2 minutes.

4. The method for determining heavy metals in soil aggregates based on dry-wet sieving according to claim 1, characterized in that: In S4, the wet sieve set has sieves of 2, 0.5, 0.25, and 0.106 mm stacked from top to bottom; the vibration amplitude is 3 cm and the frequency is 30 times / min.

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