Separation method and device for soil granular organic matters and mineral binding organic matters

Abstract

The invention provides a method for separating granular organic matters and mineral binding organic matters in soil, which comprises particle size separation and density separation, and the separation of the granular organic matters and the mineral binding organic matters in the soil is realized by combining the particle size separation and the density separation. The invention discloses a separation device for soil granular organic matters and mineral binding organic matters. The separation device structurally comprises a soil-water mixing module, a screen, a wet screen monitoring module, a fine aggregate collecting box and a density grading pretreatment module, the soil-water mixing module is located above the screen and the wet screening monitoring module, and the screen is arranged between the soil-water mixing module and the wet screening monitoring module to achieve particle size grading of soil particles. The fine aggregate collecting box is located below the wet screening monitoring module, and the fine aggregate collecting box is mounted at the top of the density grading pretreatment module; according to the method, experimental errors caused by only adopting a single particle size grading method or a single density grading method are effectively avoided.

Description

Technical Field

[0001] The invention discloses a method and a device for separating soil granular organic matter and mineral-bound organic matter, belonging to the technical field of soil analysis and detection. Background Art

[0002] In recent years, in order to gain a deeper understanding of the composition and circulation mechanism of soil organic carbon, a large amount of research work has focused on subdividing soil organic matter into components with specific significance. Among them, dividing soil organic matter into particulate organic matter (POM) and mineral-associated organic matter (MAOM) based on morphological and functional differences is considered to be one of the best ways to understand and predict the dynamics of soil organic carbon. Therefore, efficient and accurate division of soil POM and MAOM is a prerequisite and necessary condition for conducting research on soil organic matter and soil carbon cycle.

[0003] In routine experimental operations, soil POM and MAOM are usually separated by particle size classification and density classification. Particle size classification uses a simple wet sieving method to collect the soil particles larger than 53 μm as POM, and those smaller than 53 μm as MAOM. Density classification uses centrifugation to separate the soil particles with a density less than 1.65 g / cm 3 The part collected is POM, greater than 1.65g / cm 3 pointed out that relying on a single physical classification method would lead to certain deviations in the experimental results. For example, MAOM separated by particle size classification contains some fine particulate organic matter (Fine Particulate Organic Matter, FPOM); similarly, MAOM separated by density classification would contain some heavy particulate organic matter (Heavy Particulate Organic Matter, HPOM); therefore, the comprehensive use of particle size classification and density classification methods, and the exploration of the best combination to separate soil POM and MAOM, is of great significance for ensuring the accurate separation of soil components and reducing test errors.

[0004] When conducting experiments to separate POM and MAOM in soil, researchers can use a combination of particle size classification and density classification methods; specifically, two different operating procedures can be used in the experiment: density classification first and then particle size classification, and particle size classification first and then density classification; although there is no significant difference in the efficiency of achieving separation of POM and MAOM between these two operating procedures, different operating sequences will have different effects on the arrangement of experimental steps and the feasibility of equipment integration; among them, the invention patent application with patent publication number CN116060432A discloses a method for physically separating different organic matter components in soil. The experimental sequence adopted in the invention patent application is density classification first and then particle size classification. The advantage of the invention is that light organic carbon is distinguished by density separation before particle size screening of POM and MAOM, with high accuracy. Nevertheless, this method has some limitations in the separation of POM and MAOM in soil by first performing density classification and then performing particle size classification: (1) It involves multiple steps of filtration, rinsing, and drying. When multiple soil samples need to be processed, this method is cumbersome and time-consuming. (2) The process of first performing density classification and then performing particle size classification requires the centrifugation step to be placed before the wet screening operation, which makes it difficult to integrate the workflow on a single device. In addition, given the current lack of experimental devices specifically designed for separating soil POM and MAOM, a variety of conventional equipment such as standard experimental sieves, oscillating shakers, and conical flasks are generally used for manual operations. There is an urgent need to develop a special experimental device based on first performing particle size classification and then density classification to separate POM and MAOM.

[0005] However, in actual soil, POM and MAOM are usually aggregated together. If particle size classification is performed first and then density classification is performed, if POM and MAOM are not well dispersed during the particle size classification process, some MAOM will be aggregated into large particles and screened into POM, resulting in inaccurate final classification results. Therefore, it is usually necessary to first disperse the soil with a dispersant when performing particle size classification. However, the dispersants commonly used in the prior art are soil dispersants, which often produce toxic sites during the process of dispersing the soil, which is not conducive to subsequent research and analysis of the separated soil. For example, the traditional soil dispersant sodium hexametaphosphate ((NaPO3)6) is easy to form complexes with metal ions in the soil, resulting in biological toxicity, which is not conducive to subsequent experiments such as microbial community determination. Summary of the invention

[0006] The present invention proposes a method and device for separating soil particulate organic matter and mineral-bound organic matter, the purpose of which is to combine particle size classification with density classification, so as to overcome the problem that the prior art cannot combine particle size classification with density classification to separate soil particulate organic matter (POM) and mineral-bound organic matter (MAOM).

[0007] The technical solution of the present invention is a method for separating particulate organic matter and mineral-bound organic matter in soil, which includes particle size separation and density separation. The separation of particulate organic matter and mineral-bound organic matter in soil is achieved by combining particle size separation and density separation.

[0008] Furthermore, the separation of particulate organic matter and mineral-bound organic matter in the soil by combining particle size separation and density separation specifically includes: Step 1), the soil to be separated and the chitosan-BCN nanoparticle aqueous solution are stirred and mixed to form a soil slurry to be separated; Step 2), separating the coarse soil aggregates from the soil slurry to be separated by a sieve; Step 3) separating fine soil aggregates from the soil slurry remaining after separating the coarse soil aggregates in step 2) by density separation.

[0009] Furthermore, before the density separation in step 3), a sodium polytungstate solution is added to the soil slurry remaining after the coarse soil aggregates are separated.

[0010] Furthermore, the preparation method of the chitosan-BCN nanoparticles comprises: Step (1) preparing BCN nanoparticles; Step (2) preparing chitosan-BCN nanoparticle dispersant.

[0011] Furthermore, the step (1) of preparing BCN nanoparticles specifically comprises: Step (1-1) dissolving boron trioxide and melamine in distilled water and placing the mixture in a constant temperature water bath with magnetic stirring to form a first mixture; Step (1-2) The first mixture is transferred to a forced air drying oven for drying, the obtained powder is placed in a crucible with a cover, and the mixture is placed in a muffle furnace for calcination to obtain BCN nanoparticles.

[0012] Furthermore, the step (2) of preparing the chitosan-BCN nanoparticle dispersant specifically comprises: Step (2-1) adding chitosan into an aqueous acetic acid solution and stirring to form a chitosan solution; Step (2-2) dispersing the BCN nanoparticles prepared in step (1) in distilled water and ultrasonically forming a BCN solution; Step (2-3) adds the BCN solution dropwise into the chitosan solution and stirs, and adjusts the pH with sodium hydroxide to form a precipitate, washes the precipitate and freeze-dries it to obtain a chitosan-BCN nanoparticle dispersant.

[0013] Furthermore, in the step (1-1), the mass concentrations of boron trioxide and melamine dissolved in distilled water are 60 g / L to 70 g / L and 70 g / L to 80 g / L, respectively; the temperature of the constant temperature water bath in the step (1-1) is 60°C to 80°C; the magnetic stirring time in the step (1-1) is preferably 8h to 24h; when the first mixture is transferred to a forced air drying oven for drying in the step (1-2), the drying temperature is 60°C to 80°C and the drying time is 12h to 24h; when the first mixture is placed in a muffle furnace for calcination in the step (1-2), the calcination temperature is 1000°C to 1200°C and the calcination time is 3h to 5h.

[0014] Furthermore, in the step (2-1), the mass concentration of chitosan in the chitosan solution is 2.5 g / L to 3 g / L; the volume ratio of acetic acid to water in the acetic acid aqueous solution in the step (2-1) is 1:60 to 1:40; the mass concentration of BCN in the BCN solution in the step (2-2) is 7 g / L to 9 g / L; the volume ratio of the BCN solution to the chitosan solution in the step (2-3) is 1:1 to 3:2; the pH range for adjusting the pH with sodium hydroxide in the step (2-3) is 8 to 10; when the chitosan-BCN nanoparticle dispersant is prepared by freeze-drying after washing in the step (2-3), the freeze-drying temperature is -50°C to -20°C and the drying time is 16h to 24h.

[0015] A device for separating soil particulate organic matter and mineral-bound organic matter, the structure of which includes a soil-water mixing module 1, a screen 2, a wet screening monitoring module 3, a fine aggregate collection box 4, and a density grading pretreatment module 5; the soil-water mixing module 1 is located above the screen 2 and the wet screening monitoring module 3, and the screen 2 is arranged between the soil-water mixing module 1 and the wet screening monitoring module 3 to achieve particle size classification of soil particles; the fine aggregate collection box 4 is located below the wet screening monitoring module 3, and the fine aggregate collection box 4 is installed on the top of the density grading pretreatment module 5.

[0016] Furthermore, the soil-water mixing module 1 includes a switch slide bar 11, a paddle stirrer 12, a straight-moving control valve 13, and a water delivery hose 14; the switch slide bar 11 is used to open the soil-water mixing module 1 when adding soil samples and related solutions, and to close the soil-water mixing module 1 when the soil-water mixing work is in progress; the soil-water mixing module 1 completes the mixing and mixing of the soil to be separated and the chitosan-BCN nanoparticles by the paddle stirrer 12, and the mass ratio of the soil to be separated to the chitosan-BCN nanoparticles is 100: (0.5-2); at the same time, the paddle stirrer 12 is provided with a water spray hole, and a water spray hole is provided. It is connected to an external water source through a water hose 14; the screen 2 is a 53μm particle size screen; the wet screening monitoring module 3 is connected to the screen 2 through a telescopic support rod 31; a magnetic node end 32 is arranged on the inner wall of the wet screening monitoring module 3, and the magnetic node end 32 is used to automatically adsorb the turbidity sensor 33, the liquid level sensor 34 and the flow rate sensor 35; the density grading pretreatment module 5 is equipped with an oscillating platform 51, and the oscillating platform 51 is used to place the fine aggregate collection box 4; two linear conveyor belts 52 are also arranged on the oscillating platform 51; the density grading pretreatment module 5 is also equipped with a control panel 54 and a 220V power interface 53.

[0017] Beneficial effects of the present invention: 1) The separation technology of soil POM and MAOM involved in the present invention uses a combination of particle size classification and density classification methods, effectively avoiding the experimental error caused by using only a single particle size classification method or a single density classification method; 2) In the soil-water mixing process, the method of the present invention prepares chitosan-BCN nanoparticles (Chitosan / Nano-BCN) to replace the traditional soil dispersant sodium hexametaphosphate ((NaPO3)6), which effectively avoids the biological toxicity caused by the formation of complexes between sodium hexametaphosphate ((NaPO3)6) and metal ions in the soil; in addition, the use of Chitosan / Nano-BCN does not lead to a significant increase in the mortality rate of soil microbial cells, and is therefore conducive to the subsequent microbial community determination and other experiments; 3) The present invention further designs a separation device for soil particulate organic matter and mineral-bound organic matter. The separation device adopts a telescopic support rod, a magnetic node end, and a linear conveyor belt, etc., to achieve flexible assembly and disassembly between the 53μm particle size screen and the wet screening monitoring module, the sensor and the wet screening monitoring module, and the fine aggregate collection box and the density classification module; these designs are not only convenient for replacing or equipping module components of different specifications according to different experimental requirements, but also convenient for easily collecting different types of soil organic matter components after the separation work is completed; 4) The separation device of the present invention is provided with a wet screening monitoring module, which can accurately control the end of the wet screening operation; in indoor experiments, the clarification of the screened water is usually used as the standard for judging the completion of the wet screening work. The application of the turbidity sensor avoids the large error that may be caused by relying on human eye judgment, thereby improving the accuracy of particle size classification; 5) The method of the present invention uses a "particle size-density" combined method to separate POM and MAOM in soil. The experimental sequence of first performing particle size classification and then density classification effectively solves the problem that it is difficult to integrate density classification and then particle size classification on a single device. Theoretically, after particle size classification, the part of the soil sample with a particle size greater than 53 μm can be directly classified as POM; for fine aggregates with a particle size less than 53 μm, density classification is used to further separate the particles with a density less than 1.65 g / cm 3 The present invention realizes the purpose of separating soil particulate organic matter (POM) and mineral-bound organic matter (MAOM) by combining particle size classification with density classification. 6) The separation device of the present invention realizes the automated processing of soil POM and MAOM separation experiments, including key steps such as soil-water mixing, wet screening operations, and density grading pretreatment, which significantly reduces the manpower requirements during the experiment. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Attached Figure 1 It is a schematic structural diagram of the separation device of the present invention.

[0019] Attached Figure 2 It is a schematic diagram of the structure of the soil-water mixing module in the separation device of the present invention.

[0020] Attached Figure 3 It is a structural schematic diagram of the wet screening monitoring module in the separation device of the present invention.

[0021] Attached Figure 4 It is a structural schematic diagram of a density classification pretreatment module in the separation device of the present invention.

[0022] Attached Figure 5 It is a front view schematic diagram of the working stage in the separation device of the present invention.

[0023] Attached Figure 6 It is a scanning electron microscope (SEM) image of the chitosan-BCN nanoparticles (Chitosan / Nano-BCN) prepared by the present invention.

[0024] Attached Figure 7 This is the XRD pattern of chitosan-BCN nanoparticles (Chitosan / Nano-BCN).

[0025] Attached Figure 8FT-IR graph of chitosan-BCN nanoparticles (Chitosan / Nano-BCN).

[0026] Attached Fig. 9 This is a comparison chart of the effects of different soil dispersants on soil-water mixing.

[0027] Attached Fig.10 This is a comparison chart of the effects of different soil dispersants on the physiological state of soil microbial cells.

[0028] In the attached drawing, 1 is a soil-water mixing module, 2 is a screen, 3 is a wet screening monitoring module, 4 is a fine aggregate collection box, 5 is a density grading pretreatment module, 11 is a switch slide bar, 12 is a paddle agitator, 13 is a straight-moving control valve, 14 is a water supply hose, 31 is a telescopic support rod, 32 is a magnetic node end, 33 is a turbidity sensor, 34 is a liquid level sensor, 35 is a flow rate sensor, 36 is a display panel, 51 is an oscillation platform, 52 is a linear conveyor belt, 53 is a 220V power interface, and 54 is a control panel. DETAILED DESCRIPTION

[0029] A method for separating soil particulate organic matter and mineral-bound organic matter, the method comprising particle size separation and density separation, and separation of particulate organic matter (POM) and mineral-bound organic matter (MAOM) in soil is achieved by combining particle size separation and density separation.

[0030] The separation of particulate organic matter (POM) and mineral-bound organic matter (MAOM) in soil by combining particle size separation and density separation specifically includes the following steps: Step 1), the soil to be separated and the chitosan-BCN nanoparticle aqueous solution are stirred and mixed to form a soil slurry to be separated; Step 2), separating the coarse soil aggregates from the soil slurry to be separated by a sieve; this step is a wet screening process, and the coarse soil aggregates refer to the coarse soil aggregates with a particle size greater than 53 μm, and the coarse soil aggregates are soil particulate organic matter (POM); Step 3) separating fine soil aggregates from the soil slurry remaining after separating the coarse soil aggregates in step 2) by density separation; the fine soil aggregates refer to soil aggregates with a particle size of less than 53 μm, and the fine soil aggregates are mineral-bound organic matter (MAOM).

[0031] In the present invention, the dispersion of soil coarse aggregates and soil fine aggregates is promoted through the interaction between chitosan-BCN nanoparticles (Chitosan / Nano-BCN) in the chitosan-BCN nanoparticle aqueous solution and soil particles.

[0032] In the present invention, chitosan-BCN nanoparticles (Chitosan / Nano-BCN) are used as soil dispersants. Chitosan (Chitosan) has excellent biocompatibility and biodegradability, and can promote the dispersion of aggregates by interacting with the negative charges on the surface of soil particles. Chitosan can also enhance the dispersion effect by adsorption and regulating flocculation. BCN nanoparticles have low biological toxicity to soil microorganisms, and Nano-BCN can also provide strong dispersing ability. Chitosan-BCN nanoparticles replace the traditional soil dispersant sodium hexametaphosphate ((NaPO3)6), effectively avoiding the damage to soil microorganisms caused by the formation of complexes between sodium hexametaphosphate ((NaPO3)6) and metal ions in the soil.

[0033] In the step 3), before density separation, a sodium polytungstate solution is preferably added to the soil slurry remaining after the coarse soil aggregates are separated, so as to perform density classification on the fine aggregate soil slurry.

[0034] The preparation method of chitosan-BCN nanoparticles (Chitosan / Nano-BCN) comprises: Step (1) preparing BCN nanoparticles; Step (2) preparing chitosan-BCN nanoparticle (Chitosan / Nano-BCN) dispersant.

[0035] The step (1) of preparing BCN nanoparticles specifically comprises: Step (1-1) dissolving boron trioxide and melamine in distilled water and placing the mixture in a constant temperature water bath with magnetic stirring to form a first mixture; Step (1-2) The first mixture is transferred to a forced air drying oven for drying, the obtained powder is placed in a crucible with a cover, and the mixture is placed in a muffle furnace for calcination to obtain BCN nanoparticles.

[0036] The step (2) of preparing a chitosan-BCN nanoparticle (Chitosan / Nano-BCN) dispersant specifically comprises: Step (2-1) adding chitosan into an aqueous acetic acid solution and stirring to form a chitosan solution; Step (2-2) dispersing the BCN nanoparticles prepared in step 1) in distilled water and ultrasonicating to form a BCN solution; Step (2-3) adds the BCN solution dropwise into the chitosan solution and stirs, and adjusts the pH with sodium hydroxide to form a precipitate, washes the precipitate and freeze-dries it to prepare a chitosan-BCN nanoparticle (Chitosan / Nano-BCN) dispersant.

[0037] In the step (1-1), the mass concentrations of boron trioxide and melamine dissolved in distilled water are preferably 60 g / L to 70 g / L and 70 g / L to 80 g / L, respectively (the mass concentration of boron trioxide in distilled water is 60 g / L to 70 g / L, and the mass concentration of melamine dissolved in distilled water is 70 g / L to 80 g / L).

[0038] The temperature of the constant temperature water bath in step (1-1) is preferably 60° C. to 80° C.; the magnetic stirring time in step 1-1) is preferably 8 h to 24 h.

[0039] When the first mixture is transferred to a forced air drying oven for drying in step (1-2), the drying temperature is preferably 60°C to 80°C, and the drying time is preferably 12h to 24h. When the first mixture is placed in a muffle furnace for calcination in step (1-2), the calcination temperature is preferably 1000°C to 1200°C, and the calcination time is preferably 3h to 5h.

[0040] The mass concentration of chitosan in the chitosan solution in step (2-1) is preferably 2.5 g / L to 3 g / L; the volume ratio of acetic acid to water in the acetic acid aqueous solution in step (2-1) is 1:60 to 1:40.

[0041] The mass concentration of BCN in the BCN solution in the step (2-2) is preferably 7 g / L to 9 g / L.

[0042] In the step (2-3), the volume ratio of the BCN solution to the chitosan solution is 1:1 to 3:2; the pH range of the pH adjusted by sodium hydroxide in the step (2-3) is preferably 8 to 10; when the chitosan-BCN nanoparticle (Chitosan / Nano-BCN) dispersant is prepared by freeze-drying after washing in the step (2-3), the freeze-drying temperature is preferably -50°C to -20°C, and the drying time is preferably 16h to 24h.

[0043] A device for separating soil particulate organic matter and mineral-bound organic matter, the structure of which includes a soil-water mixing module 1, a screen 2, a wet screening monitoring module 3, a fine aggregate collection box 4, and a density grading pretreatment module 5; the soil-water mixing module 1 is located above the screen 2 and the wet screening monitoring module 3, and the screen 2 is arranged between the soil-water mixing module 1 and the wet screening monitoring module 3 to achieve particle size grading of soil particles; the fine aggregate collection box 4 is located below the wet screening monitoring module 3, and the fine aggregate collection box 4 is installed on the top of the density grading pretreatment module 5; the fine aggregate collection box 4 is used to collect soil fine aggregate mixed liquid after particle size grading, and the fine aggregate collection box 4 is installed on the top of the density grading pretreatment module 5, and can be freely combined with the density grading pretreatment module 5 to complete the density grading pretreatment work.

[0044] The soil-water mixing module 1 comprises a switch slide bar 11, a paddle stirrer 12, a straight-moving control valve 13, and a water delivery hose 14; the switch slide bar 11 is used to open the soil-water mixing module 1 when adding soil samples and related solutions, and to close the soil-water mixing module 1 when the soil-water mixing work is in progress; the soil-water mixing module 1 completes the mixing and mixing of the soil to be separated and the chitosan-BCN nanoparticles (Chitosan / Nano-BCN) through the paddle stirrer 12, the mass ratio of the soil to be separated and the chitosan-BCN nanoparticles is preferably 100: (0.5-2), and the mass ratio of the soil to be separated and the chitosan-BCN nanoparticles is further preferably 100: 1, wherein the prepared chitosan-BCN nanoparticles (Chitosan / Nano-BCN) are used as soil dispersants, Nan o-BCN provides strong dispersing ability, while Chitosan enhances the dispersing effect by adsorption and regulating flocculation; Chitosan / Nano-BCN replaces the traditional soil dispersant sodium hexametaphosphate ((NaPO3)6), effectively avoiding the damage to soil microorganisms caused by the formation of complexes between sodium hexametaphosphate ((NaPO3)6) and metal ions in the soil; in order to adapt to soils with different characteristics, the speed of the paddle agitator 12 can be adjusted between 90 and 150 rpm, and the working time is set to 1 to 3 hours; at the same time, the paddle agitator 12 is provided with a water spray hole and is connected to an external water source through a water hose 14; after completing the soil-water mixing work, the water spray hole can be used for water replenishment to complete the flushing and subsequent wet screening work in the soil-water mixing module 1; the mixed soil slurry is discharged to the screen 2 through the straight-line control valve 13 for further wet screening.

[0045] The sieve 2 is preferably a 53 μm particle size sieve with a mesh size of 270. Given that 53 to 60 μm is considered to be effective in distinguishing soil POM and MAOM, the sieve can be replaced with different mesh sizes according to different experimental requirements to achieve flexible experimental configuration.

[0046] The wet screening monitoring module 3 is connected to the screen 2 through a telescopic support rod 31; after the wet screening operation is completed, the telescopic support rod 31 can lift one side of the screen 2 to tilt it so as to collect coarse soil aggregates; a magnetic node end 32 is configured on the inner wall of the wet screening monitoring module 3, and the magnetic node end 32 is used to automatically adsorb the turbidity sensor 33, the liquid level sensor 34 and the flow rate sensor 35, so as to monitor the status of the wet screening operation in real time; specifically, the turbidity sensor 33 is used to determine the termination time of the wet screening operation. When the turbidity measurement value is close to 0NTU, it can be considered that the particle size separation work is completed and the wet screening operation can be terminated. During the wet screening process, the liquid level sensor 34 and the flow rate sensor 35 are used to monitor the soil slurry state. Once the soil slurry overflows or the flow rate is too fast, the system will automatically suspend the operation; the outer wall of the wet screening monitoring module 3 is equipped with a display panel 36, and the display panel 36 is connected to the turbidity sensor 33, the liquid level sensor 34, and the flow rate sensor 35 through an RS-232 serial interface, and is used to display various data during the wet screening operation in real time.

[0047] The fine aggregate collection box 4 is used to collect soil aggregates with a particle size less than 53 μm after wet screening and perform subsequent density classification pretreatment. Its design can be flexibly assembled with the device body.

[0048] The density grading pretreatment module 5 is equipped with an oscillating platform 51, which is used to place the fine aggregate collection box 4; in addition, two linear conveyor belts 52 are arranged on the oscillating platform 51, which are used to take out the fine aggregate collection box 4 filled with soil slurry after the density grading pretreatment is completed; the density grading pretreatment module 5 is also equipped with a control panel 54, which is used to set and adjust the operating parameters of the oscillating platform 51, including the oscillation frequency and oscillation time; the density grading pretreatment module 5 is also provided with a 220V power supply interface 53 to ensure the stable operation of the device.

[0049] The device for separating soil particulate organic matter and mineral-bound organic matter proposed in the present invention realizes the separation of soil particulate organic matter and mineral-bound organic matter based on the "particle size-density" combination method; the separation device greatly reduces the manual operation during the working process, making the operator's operation of separating POM and MAOM in the soil more efficient and simple. Example 1

[0050] The technical solution for implementing the present invention will be further described below in conjunction with the accompanying drawings in the present invention.

[0051] like Figure 1 and Figure 5As shown, a device for separating soil particulate organic matter and mineral-bound organic matter comprises a soil-water mixing module 1, a 53 μm particle size screen 2, a wet screening monitoring module 3, a fine aggregate collection box 4 and a density grading pretreatment module 5 arranged in sequence from top to bottom; in the working stage, the 53 μm particle size screen 2 is placed between the soil-water mixing module 1 and the wet screening monitoring module 3 to complete the wet screening operation; in addition, the screens 2 of different mesh sizes can be freely replaced according to different experimental requirements or designs; the fine aggregate collection box 4 is used to collect fine aggregate soil slurry after wet screening, and is placed on the density grading pretreatment module 5 for subsequent density grading pretreatment work.

[0052] like Figure 2 As shown, the soil-water mixing module 1 is equipped with a switch slide bar 11 for controlling the opening and closing of the soil-water mixing module 1; the soil-water mixing module 1 includes a paddle stirrer 12 for mixing the soil sample to be separated with the prepared soil dispersant chitosan-BCN nanoparticles (Chitosan / Nano-BCN) before the wet screening operation to form a homogeneous soil slurry; specifically, the rotation speed of the paddle stirrer 122 is set at 90 to 150 rpm, which can mix the soil sample evenly, and the mixing time lasts for 2 hours; at the same time, the paddle stirrer 12 is provided with a water spray hole, and is connected to an external water source through a water supply hose 14 to meet the flushing in the module and the water replenishment requirements in the subsequent wet screening work; a straight-line control valve 13 is provided at the bottom of the soil-water mixing module 1; during the operation of the paddle stirrer 12, the straight-line control valve 13 will be in a closed state; after the mixing work is completed, the straight-line control valve 13 remains open to discharge the soil slurry and perform subsequent soil slurry wet screening.

[0053] The preparation process of soil dispersant chitosan-BCN nanoparticles (Chitosan / Nano-BCN) used in the soil-water mixing process is as follows: dissolve boron trioxide and melamine in distilled water and place them in a 70°C constant temperature water bath for magnetic stirring for 12 hours to form a first mixture; wherein the mass concentrations of boron trioxide and melamine dissolved in distilled water are 66.962 g / L and 75.672 g / L, respectively; transfer the first mixture to a 70°C forced air drying oven for drying for 18 hours, place the obtained powder in a covered crucible, and place it in a 1100°C muffle furnace for calcination for 4 hours to obtain BCN nanoparticles; add chitosan to an acetic acid aqueous solution and stir to form a chitosan solution; wherein the mass concentration of chitosan in the chitosan solution is preferably 2.87 g / L; the volume ratio of acetic acid to water in the acetic acid aqueous solution is 1:50; disperse the prepared BCN nanoparticles in distilled water and ultrasonically form a BCN solution; wherein the mass concentration of BCN in the BCN solution is preferably 8.33 g / L; the BCN solution was added dropwise into the chitosan solution with stirring, wherein the volume ratio of the BCN solution to the chitosan solution was 1:1; and the pH was adjusted to 9 with sodium hydroxide, and after washing, the chitosan-BCN nanoparticles (Chitosan / Nano-BCN) were freeze-dried at -40°C for 18h to obtain a dispersant.

[0054] like Figure 3 As shown, a telescopic support rod 31 is provided at the top of the wet screening monitoring module 3 for connecting the 53 μm particle size screen 2; after the wet screening work is completed, the telescopic support rod 31 can lift one side of the 53 μm particle size screen 2 to tilt it so as to collect coarse soil aggregates; the inner wall of the wet screening monitoring module 3 is equipped with a magnetic node end 32, and the turbidity sensor 33, the liquid level sensor 34 and the flow rate sensor 35 can be automatically adsorbed on the magnetic node end 32 to realize automatic monitoring of the wet screening process; the turbidity sensor 33 is used to determine the end time of the wet screening operation. When the turbidity measurement value is close to 0 NTU, the device will indicate that the particle size separation work has been completed; the liquid level sensor 34 and the flow rate sensor 35 are responsible for monitoring the water level and flow rate; during the wet screening operation, if the water level exceeds the position of the liquid level sensor or the flow rate is too fast, the system will automatically suspend the operation to prevent the soil slurry from overflowing; a display panel 36 is installed on the outside of the turbidity recognition module 3, which is connected to each sensor through an RS-232 serial interface and can display various data in the wet screening operation in real time.

[0055] like Figure 3As shown, the fine aggregate collection box 4 is used to collect soil aggregates with a particle size less than 53 μm after wet screening, and can be placed on the density grading pretreatment module 5; the density grading pretreatment module 5 is equipped with an oscillation platform 51, on which a linear conveyor belt 52 is installed, which is specifically used to take out the fine aggregate collection box 4 after the density pretreatment operation is completed; in addition, the density grading pretreatment module 5 is equipped with a control panel 54, which allows experimenters to set and adjust the operating parameters of the oscillation platform 51, including the oscillation frequency and oscillation time; the density grading pretreatment module is also provided with a 220V power supply interface 53 to ensure stable power supply and operation of the equipment.

[0056] The present invention adopts a "particle size-density" combination method and is equipped with a wet screening monitoring module to improve the accuracy of wet screening, which helps to assist operators to obtain more accurate separation results; in addition, the device is based on the experimental process of first particle size classification and then density classification, which not only realizes the integration and automation of soil particulate organic matter and mineral-bound organic matter separation, but also simplifies the operating steps and greatly improves work efficiency. Example 2

[0057] Experiment on separation of particulate organic matter and mineral-bound organic matter in riverbank soil: Soil-water mixing to prepare homogenous soil slurry; Taking riverbank soil with a moisture content of 20% as an example, the experimenters prepared 50g of soil sample (passed through a 2mm sieve) and added it to the soil-water mixing module 1, and at the same time supplemented 500mg of chitosan-BCN nanoparticles (Chitosan / Nano-BCN) as a soil dispersant; then, the soil-water mixing module 1 was kept in a closed state by operating the switch slide bar 11, and the paddle agitator 12 was set to 90 revolutions per minute and continued to run for 1 hour; during this process, the straight-line control valve 13 remained closed until the paddle agitator 12 stopped working to ensure the formation of a uniform soil slurry; after the mixing was completed, the straight-line control valve 13 was opened to discharge the soil slurry; after the soil slurry was discharged, the paddle agitator 12 was connected to an external water source through a water hose 14, and continued to spray water and continue to run to clean the residual soil slurry in the module and perform subsequent wet screening; Wet screening separation; After the soil-water mixing process is completed, the straight-line control valve 13 opens and discharges the soil slurry, and the soil slurry continues to pass through the 53μm particle size screen 2 for particle size classification; during this process, water is continuously added to the soil-water mixing module 1 to ensure that the wet screening process can be carried out continuously; during the wet screening process, the operator needs to pay attention to the display panel 36 in the wet screening monitoring module 3; when the turbidity sensor 33 senses that the turbidity of the filtered water is close to 0NTU, the display panel 36 will prompt that the wet screening operation is completed; when the liquid level sensor 34 detects that the water level is too high or the flow rate sensor 35 senses that the soil slurry flow rate is too fast, the display panel 34 will prompt to suspend water addition; after the wet screening operation is completed, the telescopic support rod 31 is controlled to lift one side of the 53μm particle size screen 2 to collect the coarse aggregates (i.e. POM) on the screen after wet screening.

[0058] Density classification pretreatment; After the wet screening separation is completed, the soil slurry with a particle size less than 53 μm is collected in the fine aggregate collection box 4; in order to extract the particles with a density less than 1.65 g / cm 3 In order to remove the light particulate organic matter, the experimenter added 200 ml of sodium polytungstate (SPT) solution to the fine aggregate collection box 4 for density grading of the fine aggregate slurry; at the same time, the fine aggregate collection box 4 was installed on the oscillation platform 51 of the density grading pretreatment module 5, and by setting an amplitude of 20 mm on the control panel 54, the density grading pretreatment module 5 worked continuously for 6 hours to ensure that the fine aggregate slurry was fully dispersed; after the density grading pretreatment work was completed, the linear conveyor belt 52 took out the fine aggregate collection box 4; in order to further remove the fine aggregate slurry dispersed in the fine aggregate collection box 4, it was necessary to centrifuge for 30 minutes at 24°C and a speed of 10000 rpm to extract the light particulate organic matter.

[0059] In the separation process of POM and MAOM, sodium hexametaphosphate ((NaPO3)6) is often used as a dispersant, but its biological toxicity may interfere with subsequent experimental measurements (such as microbial community analysis); in contrast, chitosan has excellent biocompatibility and biodegradability, and can promote the dispersion of aggregates by interacting with the negative charges on the surface of soil particles; at the same time, BCN nanoparticles have low biological toxicity to soil microorganisms; in summary, in order to maintain a good dispersion effect while reducing the destructiveness to soil microorganisms, the present invention prepares chitosan-BCN nanoparticles (Chitosan / Nano-BCN), which is not only non-biotoxic, but also has excellent biocompatibility and biodegradability, and can promote the dispersion of aggregates by interacting with the negative charges on the surface of soil particles, and enhance the dispersion effect by adsorption and regulation of flocculation; at the same time, BCN nanoparticles have low biological toxicity to soil microorganisms, and Nano-BCN can also provide strong dispersion ability; attached Figure 6 is a scanning electron microscope (SEM) image of chitosan-BCN nanoparticles (Chitosan / Nano-BCN) prepared in Example 1 of the present invention; Figure 6 The SEM images in the figure show that the surface of chitosan-BCN nanoparticles (Chitosan / Nano-BCN) is rough, and there are a large number of pores on the surface and between the particles, which can significantly improve the dispersion performance of soil aggregates and meet the dual requirements of the experiment for dispersants.

[0060] Attached Figure 7 The XRD pattern of chitosan / Nano-BCN prepared in Example 1 is shown in the attached figure. Figure 7 It can be seen that chitosan-BCN nanoparticles (Chitosan / Nano-BCN) present most of the typical peaks of boron nitride (JCPDS 34-0421), for example, typical characteristic diffraction peaks are shown at 26.76° and 41.60°, corresponding to (002) and (100) of boron nitride, and the broad peak shown at 18.30° corresponds to the characteristic peak of chitosan, indicating that chitosan-BCN nanoparticles have been effectively synthesized.

[0061] Attached Figure 8 The FT-IR image of chitosan / Nano-BCN prepared in Example 1 is shown in the accompanying Figure 8 It can be seen that chitosan-BCN nanoparticles (Chitosan / Nano-BCN), 807 cm -1 The special peak at 1393 cm corresponds to the BNB bending vibration, while the -1 The peak at 1123 cm corresponds to the stretching vibration of BN. The typical peaks of BNB bending vibration and BN stretching vibration of boron nitride and chitosan at 1123 cm -1 The CO stretching vibration at 3400 cm-1 was confirmed, confirming the successful synthesis of chitosan and BCN nanoparticles. In addition, a strong OH stretching vibration peak (3400 cm-1) was found in chitosan / Nano-BCN nanoparticles. -1 ), indicating that there are OH groups on the surface of chitosan-BCN; therefore, the interaction between the OH groups of chitosan-BCN and OH groups, NH2 groups, etc. helps chitosan-BCN to improve the dispersion performance of soil aggregates.

[0062] Attached Fig. 9Figure 3 Effects of different soil dispersants on soil-water mixing: (a) Laser confocal scanning images of soil-water mixtures without addition, with addition of sodium hexametaphosphate ((NaPO3)6) and with addition of chitosan-BCN nanoparticles (Chitosan / Nano-BCN); (b) Final MAOM determination results after no addition, with addition of sodium hexametaphosphate ((NaPO3)6) and with addition of chitosan-BCN nanoparticles (Chitosan / Nano-BCN); Fig. 9 It can be seen that compared with no addition and addition ((NaPO3)6), the addition of Chitosan / Nano-BCN not only effectively reduced the formation of soil macroaggregates and complexes with larger particle sizes, but also improved the final MAOM measurement results, indicating that the addition of Chitosan / Nano-BCN is more effective in promoting soil dispersion.

[0063] Attached Fig.10 Effects of different soil dispersants on the physiological state of soil microbial cells: (a) Laser confocal fluorescence images of cell death in soil samples without additives, chitosan-BCN nanoparticles (Chitosan / Nano-BCN) and sodium hexametaphosphate ((NaPO3)6); (b) Evaluation of the number of dead cells in different soil samples based on laser confocal scanning images; Fig.10 It can be seen that compared with the soil background value without adding chemical reagents, the addition of chitosan-BCN nanoparticles (Chitosan / Nano-BCN) did not cause significant death of soil microbial cells, while the addition of sodium hexametaphosphate ((NaPO3)6) significantly led to an increase in the number of dead soil microbial cells; therefore, in the present invention, chitosan-BCN nanoparticles (Chitosan / Nano-BCN) replace traditional sodium hexametaphosphate ((NaPO3)6) to reduce interference with in situ soil microorganisms, which is helpful for the development of subsequent related experiments (such as microbial community determination, etc.).

[0064] Although the present invention has been described above, the present invention is not limited to the above-mentioned specific implementation modes. The above-mentioned embodiments are merely examples of the separation of POM and MAOM in riverbank soil, and are not restrictive. Under the guidance of the present invention, ordinary technicians in this field can make many adjustments to the details of the invention (such as changes to different aperture screens in the particle size screening module and different types of oscillation platform configurations, etc.) without departing from the purpose of the present invention. These are all within the scope of protection of the present invention.

Claims

1. A method for separating soil particulate organic matter and mineral-bound organic matter, characterized in that It includes particle size separation and density separation, and the separation of particulate organic matter and mineral-bound organic matter in the soil is achieved by combining particle size separation and density separation.

2. The method for separating soil particulate organic matter and mineral-bound organic matter according to claim 1, characterized in that The separation of particulate organic matter and mineral-bound organic matter in soil by combining particle size separation and density separation specifically includes: Step 1), the soil to be separated and the chitosan-BCN nanoparticle aqueous solution are stirred and mixed to form a soil slurry to be separated; Step 2), separating the coarse soil aggregates from the soil slurry to be separated by a sieve; Step 3) separating fine soil aggregates from the soil slurry remaining after separating the coarse soil aggregates in step 2) by density separation.

3. The method for separating soil particulate organic matter and mineral-bound organic matter according to claim 2, characterized in that In step 3), before the density separation, a sodium polytungstate solution is added to the soil slurry remaining after the coarse soil aggregates are separated.

4. The method for separating soil particulate organic matter and mineral-bound organic matter according to claim 2, characterized in that The preparation method of the chitosan-BCN nanoparticles comprises: Step (1) preparing BCN nanoparticles; Step (2) preparing chitosan-BCN nanoparticle dispersant.

5. The method for separating soil particulate organic matter and mineral-bound organic matter according to claim 4, characterized in that The step (1) of preparing BCN nanoparticles specifically comprises: Step (1-1) dissolving boron trioxide and melamine in distilled water and placing the mixture in a constant temperature water bath with magnetic stirring to form a first mixture; Step (1-2) The first mixture is transferred to a forced air drying oven for drying, the obtained powder is placed in a crucible with a cover, and the mixture is placed in a muffle furnace for calcination to obtain BCN nanoparticles.

6. The method for separating soil particulate organic matter and mineral-bound organic matter according to claim 4, characterized in that The step (2) of preparing the chitosan-BCN nanoparticle dispersant specifically comprises: Step (2-1) adding chitosan into an aqueous acetic acid solution and stirring to form a chitosan solution; Step (2-2) dispersing the BCN nanoparticles prepared in step (1) in distilled water and ultrasonically forming a BCN solution; Step (2-3) adds the BCN solution dropwise into the chitosan solution and stirs, and adjusts the pH with sodium hydroxide to form a precipitate, washes the precipitate and freeze-dries it to obtain a chitosan-BCN nanoparticle dispersant.

7. The method for separating soil particulate organic matter and mineral-bound organic matter according to claim 5, characterized in that In the step (1-1), the mass concentrations of boron trioxide and melamine dissolved in distilled water are 60 g / L to 70 g / L and 70 g / L to 80 g / L, respectively; the temperature of the constant temperature water bath in the step (1-1) is 60° C. to 80° C.; the magnetic stirring time in the step (1-1) is preferably 8 h to 24 h; when the first mixture is transferred to a forced air drying oven for drying in the step (1-2), the drying temperature is 60° C. to 80° C. and the drying time is 12 h to 24 h; when the first mixture is placed in a muffle furnace for calcination in the step (1-2), the calcination temperature is 1000° C. to 1200° C. and the calcination time is 3 h to 5 h.

8. The method for separating soil particulate organic matter and mineral-bound organic matter according to claim 6, characterized in that The mass concentration of chitosan in the chitosan solution in the step (2-1) is 2.5 g / L to 3 g / L; the volume ratio of acetic acid to water in the acetic acid aqueous solution in the step (2-1) is 1:60 to 1:40; the mass concentration of BCN in the BCN solution in the step (2-2) is 7 g / L to 9 g / L; the volume ratio of the BCN solution to the chitosan solution in the step (2-3) is 1:1 to 3:2; the pH range for adjusting the pH with sodium hydroxide in the step (2-3) is 8 to 10; when freeze-drying after washing to obtain the chitosan-BCN nanoparticle dispersant in the step (2-3), the freeze-drying temperature is -50°C to -20°C and the drying time is 16h to 24h.

9. A device for separating soil granular organic matter and mineral-bound organic matter, characterized in that Including soil -water mixing module (1), screen (2), wet screening monitoring module (3), fine aggregate collection box (4), density grading pretreatment module (5); the soil-water mixing module (1) is located above the screen (2) and the wet screening monitoring module (3), the screen (2) is arranged between the soil-water mixing module (1) and the wet screening monitoring module (3) to achieve particle size classification of soil particles; the fine aggregate collection box (4) is located below the wet screening monitoring module (3), and the fine aggregate collection box (4) is installed on the top of the density grading pretreatment module (5).

10. The device for separating soil particulate organic matter and mineral-bound organic matter according to claim 9, characterized in that The soil-water mixing module (1) comprises a switch slide bar (11), a paddle stirrer (12), a straight-moving control valve (13), and a water delivery hose (14); the switch slide bar (11) is used to open the soil-water mixing module (1) when adding soil samples and related solutions, and to close the soil-water mixing module (1) when the soil-water mixing work is in progress; the soil-water mixing module (1) completes the mixing and mixing of the soil to be separated and the chitosan-BCN nanoparticles by the paddle stirrer (12), and the mass ratio of the soil to be separated to the chitosan-BCN nanoparticles is 100:(0.5-2); at the same time, the paddle stirrer (12) is provided with a water spray hole, and is connected to an external The wet screening monitoring module (3) is connected to a water source; the screen (2) is a 53 μm particle size screen; the wet screening monitoring module (3) is connected to the screen (2) via a telescopic support rod (31); a magnetic node end (32) is arranged on the inner wall of the wet screening monitoring module (3), and the magnetic node end (32) is used to automatically adsorb a turbidity sensor (33), a liquid level sensor (34) and a flow rate sensor (35); the density grading pretreatment module (5) is equipped with an oscillating platform (51), and the oscillating platform (51) is used to place a fine aggregate collection box (4); two linear conveyor belts (52) are also arranged on the oscillating platform (51); the density grading pretreatment module (5) is also equipped with a control panel (54) and a 220V power supply interface (53).

Images