A device and method for separating microplastics in soil

Abstract

The application discloses a soil micro-plastic separation device and method. The device comprises a sample suspension conveying pipe, a first hopper is arranged at the lower end of the sample suspension conveying pipe, a fan is communicated with the first hopper and the side of the sample suspension conveying pipe, a sample inlet is arranged on the upper side of the sample suspension conveying pipe, at least one cyclone separation device is communicated with the upper side of the sample suspension conveying pipe, a collection bin is communicated with the top outlet of the cyclone separation device, and a second hopper is communicated with the bottom outlet of the cyclone separation device. The method utilizes different gravity principles to pre-separate lighter micro-plastics and heavier soil particles, and the subsequent flotation treatment sample amount is greatly reduced, the flotation solution amount is reduced, the generated contaminated soil is reduced, the extraction time is shortened, manpower and material resources are saved, and the rapid separation of a large amount of samples can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of soil detection, in particular to a soil microplastic separation device and method. BACKGROUND

[0002] Plastics are widely used as indispensable products in modern society. Plastics gradually form solid particles or fragments with a particle size of less than 5 mm after long-term physical and chemical and biological effects such as light, pyrolysis, collision and wear, and oxidation. These small plastic particles are called microplastics. Plastic film mulching is widely used in farmland in China. The residual plastic film in the soil is gradually decomposed into microplastic particles every year, which continuously enriches in sediments, soil and other media, and then affects soil properties, soil functions and biodiversity, and interacts with soil minerals, humic acid, residual pesticides, fertilizers and other organic pollutants in the soil, which has a potential pollution to crops growing in the soil, thereby having a more profound impact on the ecological environment. The separation of microplastics in sediments is obviously different from that of microplastics in water samples. Due to the presence of solid media such as sediments, the separation procedure and steps are more complex.

[0003] For the separation of microplastics in soil, the commonly used method is floatation, which has a recovery rate of more than 90% for various microplastics, such as saturated sodium chloride solution, sodium polytungstate solution, calcium chloride solution, sodium iodide solution, zinc chloride solution, etc. for separating microplastics in sediments.

[0004] Since the traditional soaking and floatation separation method according to the density principle is complicated, troublesome to operate, time-consuming and labor-intensive, and has low efficiency, the high-efficiency floatation agents such as sodium iodide solution and zinc chloride are relatively expensive, increasing the separation cost. And due to the low content of microplastics, in order to obtain enough detection samples, a large amount of soil needs to be floated, and a large amount of floatation solution is used, which causes secondary pollution to the soil and brings trouble to the subsequent treatment. SUMMARY

[0005] In view of the above problems, the present application discloses a soil microplastic separation device and method, which utilizes different principles of gravity to pre-separate lighter microplastics and heavier soil particles, significantly reduces the amount of samples for subsequent floatation treatment, reduces the amount of floatation solution, reduces the pollution of soil, shortens the extraction time, saves manpower and material resources, and can realize rapid separation of a large amount of samples.

[0006] In order to achieve the above technical purpose, the present application adopts the following technical solutions:

[0007] The application discloses a device for separating microplastics in soil, which comprises a sample suspension conveying pipe, a first hopper arranged at the lower end of the sample suspension conveying pipe, a fan communicated with the side of the sample suspension conveying pipe above the first hopper, a sample inlet arranged at the upper side of the sample suspension conveying pipe, at least one cyclone separation device communicated with the upper side of the sample suspension conveying pipe, a collection bin communicated with the top outlet of the cyclone separation device, and a second hopper communicated with the bottom outlet of the cyclone separation device.

[0008] Preferably, a plurality of pairs of baffle groups are arranged in the sample suspension conveying pipe, and two adjacent pairs of baffle groups are staggered.

[0009] Preferably, each pair of baffle groups is symmetrically arranged on the side wall of the sample suspension conveying pipe.

[0010] Preferably, the baffle groups are arranged to be inclined upward from the side wall of the sample suspension conveying pipe to the center of the sample suspension conveying pipe.

[0011] Preferably, the baffle groups comprise a main plate, one end of the main plate is connected with the side wall of the sample suspension conveying pipe, and a plurality of parallel branch plates are arranged on the two sides of the main plate along the axis of the main plate.

[0012] Preferably, a vibration feeder is arranged at the sample inlet.

[0013] Preferably, the upper end of the sample suspension conveying pipe is communicated with the cyclone separation device through an elbow pipe, and the inner diameter of the elbow pipe is gradually reduced from the sample suspension conveying pipe to the cyclone separation device.

[0014] Preferably, a glass fiber filter membrane is arranged on the side of the second collection bin.

[0015] The application further discloses a method for separating microplastics by using the above device, and the specific steps are as follows.

[0016] Step 1, the fan is turned on to form an air flow upward from the bottom of the sample suspension conveying pipe;

[0017] Step 2, dry and ground soil is put into the sample suspension conveying pipe through the vibration feeder;

[0018] Step 3, under the resistance of the baffle groups, a disturbed turbulent air flow is formed in the sample suspension conveying pipe, the microplastic particles and soil particles with light quality are brought into the cyclone separation device, and the soil particles with heavy quality fall into the first hopper at the lower end of the pipe;

[0019] Step 4, most of the soil particles contact the wall of the cyclone separation device and then enter the second hopper below due to the different centrifugal forces caused by the density difference between the microplastic particles and the soil particles, and a small amount of dust with light quality enters the collection bin together with the microplastic particles.

[0020] Advantages of the present application

[0021] The present application separates the lighter plastics and heavier soil particles by using the cyclone device, the subsequent flotation treatment sample amount is greatly reduced, the flotation solution consumption is reduced, and the soil is not polluted; the extraction time is shortened, and manpower and material resources are saved. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description only constitute some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0023] Figure 1 It is a schematic diagram of the overall structure of the present application;

[0024] Figure 2 It is a schematic diagram of the baffle group structure;

[0025] In the figure: 1, fan, 2, sample suspension conveying pipe, 3, baffle group, 3-1, main plate, 3-2, branch plate, 5, vibration feeder, 7, variable diameter conveying pipe, 8, cyclone separation device, 9, first hopper, 10, second hopper, 11, collection bin. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments only constitute some embodiments of the present application, not all embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0027] In the description of the present application, it should be understood that the terms "inner", "outer", "left", "right" indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore it cannot be understood as a limitation of the present application.

[0028] Embodiment one

[0029] Please refer to Figure 1The application provides a micro-plastic separation device in soil, which comprises a sample suspension conveying pipe 2, a vibration feeder 5, a sealable feeding port and a cyclone separation device 8; the vibration feeder 5 is installed on the upper side of the sample suspension conveying pipe 5, the bottom of the sample suspension conveying pipe 2 is connected to a first hopper 9, a fan 1 is connected to the side of the sample suspension conveying pipe 2 above the first hopper 9, a variable-diameter conveying pipe 7 is installed on the upper end of the sample suspension conveying pipe 2, the other end of the variable-diameter conveying pipe is connected to the feeding port of the cyclone separation device 8, the upper end outlet of the cyclone separation device 8 is connected to a collection bin 11, and the lower end outlet of the cyclone separation device 8 is connected to a second hopper 10.

[0030] The material of the sample suspension conveying pipe 2 is stainless steel, the inner diameter of the suspension pipe is 10 cm, the height is 1 m, and a plurality of staggered baffle groups 3 are arranged in the pipe. Figure 2 As shown in the drawings, the baffle group comprises a main stem plate 3-1 with a length of 5 cm and a width of 0.5 cm and a branch plate 3-2 with a length of 3 cm and a width of 0.5 cm, and a plurality of branch plates are symmetrically arranged on both sides of the main stem plate in the length direction of the main stem plate in a tooth shape. The surface of the branch plate 3-2 is designed to be rough and concave-convex, the tooth width is 0.5 cm, and the tooth pitch is 0.5 cm. The main stem plate 3-1 is installed at an upward angle of 30 degrees with the inner wall of the sample suspension conveying pipe 2. The baffle groups 3 are arranged in five layers in the sample suspension conveying pipe 2 at intervals of 15 cm, and the baffle groups in each layer are arranged in opposite directions. Adjacent two layers are staggered, that is, the two baffle groups 3 in the first layer are arranged in the 12 o'clock and 6 o'clock directions, the two baffle groups 3 in the second layer are arranged in the 3 o'clock and 9 o'clock directions, and the two baffle groups 3 in the third layer are arranged in the 12 o'clock and 6 o'clock directions.

[0031] A feeding port is arranged on the upper side of the sample suspension conveying pipe 2, a vibration feeder 5 is used to control the feeding speed of 50-200 g / min, the feeding port is inserted into the middle position of the suspension pipe, and the feeding port is sealable and closable with a cover plate and a lock.

[0032] The bottom of the sample suspension conveying pipe 2 is provided with a conical first hopper 9, which is also made of stainless steel and has a height of 20 cm. The bottom of the hopper can be opened for cleaning, and a stainless steel sheet with a downward angle is arranged in the hopper, which has a length of 5 cm to 1 cm and is uniformly distributed. The stainless steel sheet plays a role in preventing dust from being suspended again.

[0033] The upper end of the sample suspension conveying pipe 2 is connected to the feeding port of the cyclone separation device 8 through a variable-diameter conveying pipe 7. The variable-diameter conveying pipe 7 is connected to the feeding port of the cyclone device through variable-diameter connection. The inner diameter of the end connected to the sample suspension conveying pipe 2 is 10 cm, the inner diameter of the end connected to the cyclone separation device 8 is changed to 5 cm, and the length of the variable-diameter section is 20 cm.

[0034] The cyclone separation device 8 is a cyclone separator in the prior art, which can separate microplastics from soil according to different densities of soil and microplastics. A second dust hopper 10 with a rectangular upper part and a conical lower part is installed below the cyclone separation device. The second dust hopper is also made of stainless steel and has a height of 30 cm. The bottom of the dust hopper can be opened for cleaning.

[0035] To improve the separation effect, multiple cyclone dust removal devices can be connected in series to form a multi-stage separation combination device.

[0036] The top discharge port of the cyclone separation device 8 is connected to a collection bin 11 through a section of inverted L-shaped pipe and a section of S-shaped pipe. The pipe diameters of the L-shaped pipe and the S-shaped pipe are both 5 cm.

[0037] The collection bin is a rectangular cuboid with a length of 20 cm, a width of 10 cm, and a height of 10 cm. One side is installed with a 0.45-micron glass fiber filter membrane.

[0038] Example Two

[0039] The process of separating microplastic particles and soil particles using the device is as follows:

[0040] The dried and ground soil is uniformly dropped from the upper part of the pipe at a speed of 50-100 grams per minute through a vibrating feeder 5. There is an upward airflow in the pipe, and the pipe is equipped with a staggered distribution of comb-shaped baffle groups 3 at a certain angle. The baffle groups 3 disturb the airflow to form a complete turbulent airflow in the pipe, improving the carrying capacity of the gas on the material. The lighter microplastic particles and soil particles are carried into the cyclone separation device 8, and the heavier soil particles fall into the first dust hopper 9 at the lower end of the pipe. The lighter microplastic particles and soil particles enter the cyclone device 8, and due to the difference in centrifugal force between the microplastic particles and the soil particles , the soil particles have a density that is less than the density of the microplastic particles. Most of the soil particles contact the wall of the cyclone separation device 8 and enter the second dust hopper 10 below. A small amount of dust and microplastic particles are discharged through the exhaust pipe, enter the collection bin 11 through a section of conveying pipe, and are filtered by the 0.45-micron filter membrane installed at the outlet of the collection bin. The outlet area is five to ten times larger than the cross-sectional area of the front pipe to reduce the resistance caused by the filter membrane.

[0041] The principle of the cyclone separation device is that the cyclone separation device has a structure of a cylindrical upper part connected to a conical lower part. By adjusting the appropriate air flow speed and the size of the cyclone device, the soil gas containing microplastics enters from the feed inlet in a tangential direction of the cylinder at a high speed. The air flow changes from linear motion to circular motion and flows upward and downward. The upward air flow is blocked by the top cover and returns. The downward air flow makes spiral motion from top to bottom in the cylindrical part and the conical part (referred to as outer spiral flow). The soil gas containing microplastics generates centrifugal acceleration during rotation. Because the centrifugal force generated by the soil particles is much larger than the air viscosity resistance, the soil particles generate radial motion away from the rotation center. Therefore, the soil particles are thrown to the inner wall of the cylinder, and the soil particles are separated from the microplastic particles as soon as they come into contact with the wall and are discharged into the second hopper along the wall of the conical part. The microplastics, due to their small density, move along the conical part with the downward rotating outer spiral flow and move towards the center of the dust collector when the conical part is contracted. When the air flow reaches a certain position at the lower end of the conical part, a spiral motion air flow (referred to as inner spiral flow) is formed in the middle of the dust collector in the same rotating direction from bottom to top, and is discharged outward through the upper discharge port. Subsequently, the air flow enters the collection bin through the curved pipeline. The side wall of the collection bin is provided with a 0.45-micron glass fiber filter membrane, which can filter and capture microplastic particles.

[0042] The total height of the cylinder body of the cyclone separator is generally appropriate to be 4 times the diameter of the cylinder body. Therefore, under the condition that the total height of the cylinder body is constant, appropriately increasing the height of the conical cylinder part is beneficial to improve the dust removal efficiency. Generally, the height of the cylindrical part is 1.5 times the diameter of the cylinder, and the height of the conical cylinder is 2.5 times the diameter of the cylinder, which can obtain a relatively ideal dust removal efficiency.

[0043] It is generally considered that the diameter of the exhaust pipe is appropriate to be 0.5-0.6 times the diameter of the cylinder. If the exhaust pipe is inserted too shallow, the dust-containing air flow at the inlet is directly introduced into the exhaust pipe, which affects the dust removal efficiency. If the exhaust pipe is inserted too deep, the friction surface between the air flow and the pipe wall increases, which increases the resistance loss. At the same time, the distance between the exhaust pipe and the bottom of the conical cylinder is shortened, which increases the opportunity of secondary mixing and discharge of dust. Generally, the insertion depth of the exhaust pipe is appropriate to be slightly lower than the position of the bottom of the inlet.

[0044] The air flow speed of the inlet is controlled between 12-20 m / s, and the maximum is not more than 25 m / s. Generally, 14 m / s is appropriate.

[0045] The foregoing description of the disclosed embodiments enables a person skilled in the art to make or use the application. Modifications of these embodiments will occur to persons of skill in the art, and that the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Therefore, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A device for separating microplastics in soil, characterized in that, The device comprises a sample suspension conveying pipe (2), a first hopper (9) arranged at the lower end of the sample suspension conveying pipe (2), a fan (1) communicated above the first hopper (9) and at the side of the sample suspension conveying pipe (2), a sample inlet arranged at the upper side of the sample suspension conveying pipe (2), at least one cyclone separation device (8) communicated above the sample suspension conveying pipe (2), a top discharge port of the cyclone separation device (8) connected to an S-shaped pipe through a section of inverted L-shaped pipe, and a collection bin (11) communicated with the S-shaped pipe; and a second hopper (10) communicated with the bottom outlet of the cyclone separation device (8). A plurality of pairs of baffle groups (3) are arranged in the sample suspension conveying pipe (2), and two pairs of adjacent baffle groups are arranged alternately; that is, two baffle groups (3) of the first layer are arranged in the 12 o'clock and 6 o'clock directions, two baffle groups (3) of the second layer are arranged in the 3 o'clock and 9 o'clock directions, and two baffle groups (3) of the third layer are arranged in the 12 o'clock and 6 o'clock directions. The baffle group (3) comprises a main plate (3-1), one end of the main plate (3-1) is connected to the side wall of the sample suspension conveying pipe (2), and a plurality of parallel branch plates (3-2) are arranged on both sides of the main plate (3-1) along the axis of the main plate (3-1), and the surface of the branch plate (3-2) is designed as a rough concave-convex surface.

2. The device for separating microplastics in soil according to claim 1, wherein, Each pair of baffle groups (3) is symmetrically arranged on the side wall of the sample suspension conveying pipe (2) about the axis of the sample suspension conveying pipe (2).

3. The device for separating microplastics in soil according to claim 1, wherein, The baffle group (3) is arranged obliquely upward from the side wall of the sample suspension conveying pipe (2) to the center of the sample suspension conveying pipe (2).

4. The device for separating microplastics in soil according to claim 1, wherein, A vibration feeder (5) is arranged at the sample inlet.

5. The device for separating microplastics in soil according to claim 1, wherein, The upper end of the sample suspension conveying pipe (2) is communicated with the cyclone separation device (8) through an elbow pipe, and the inner diameter of the elbow pipe is gradually reduced from the sample suspension conveying pipe to the cyclone separation device.

6. The device for separating microplastics in soil according to claim 1, wherein, A glass fiber filter membrane is arranged on the side of the collection bin (11).

7. A method for separating microplastics by using the separation device of claim 1, and the specific steps are as follows: Step 1: Turn on the fan to form an air flow upward at the bottom of the sample suspension conveying pipe (2); Step 2: Put dry and ground soil into the sample suspension conveying pipe (2) through the vibration feeder (5); Step 3: Under the resistance of the baffle group (3), a turbulent air flow is formed in the sample suspension conveying pipe (2), the microplastic particles and soil particles with lighter quality are brought into the cyclone separation device (8), and the soil particles with heavier quality fall into the first hopper (9) at the lower end of the pipe; Step 4: By using the different centrifugal forces caused by the density difference between the microplastic particles and the soil particles, most of the soil particles contact the wall of the cyclone separation device and then enter the second hopper (10) below, and a small amount of dust with lighter quality enters the collection bin (11) together with the microplastics.

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