Method for separating, quantitatively characterizing and recycling soil rare earth nano colloid

Abstract

The invention provides a method for separating, quantitatively characterizing and recycling soil rare earth nano colloid. The method comprises the following steps: weighing a soil sample, settling the soil sample, and collecting particles with the particle size of less than 1000nm in a soil colloid solution. The soil nano-colloid is separated and characterized by combining an asymmetric flow field flow instrument, a multi-angle laser light scattering instrument and an inductively coupled plasma mass spectrometry, and a characterization result is obtained. According to the method, various instruments are combined, so that the rare earth nano colloids with different particle sizes are accurately and effectively separated and represented. And setting a plurality of recovery time periods according to the characterization result, and recovering the rare earth nano colloids with different particle sizes in different recovery time periods. And according to a quantitative characterization result, the rare earth nano colloid with the target particle size is precisely recycled in a targeted manner by utilizing an asymmetric flow field flow instrument. According to the method, not only can the nanoscale rare earth colloid of 5-70 nm be efficiently recycled, but also the submicron rare earth colloid of 300-350 nm can be effectively recycled, and the recycling efficiency is high.

Description

Technical Field

[0001] The present invention relates to the technical field of soil chemistry, and in particular to a method for separating, quantitatively characterizing and recovering soil rare earth nano-colloids. Background Art

[0002] Rare earth elements (REEs) are a collective term for 17 elements in Group IIIB of the periodic table, including scandium, yttrium, and lanthanides. Due to their unique electronic structure and physicochemical properties, REEs are widely used in industries such as electronics, petrochemicals, metallurgy, machinery, and high-tech. In the soil environment, the distribution of REEs is remarkably heterogeneous. The vast majority of REEs are not present in free form in soil solutions. Instead, they are tightly bound to other soil components through a complex series of chemical reactions, including hydrolysis, precipitation, complexation, adsorption, and redox reactions. These REEs are adsorbed on the surfaces of soil particles or form new colloids, resulting in a stable solid phase in the soil. REEs in the environment are highly bioavailable. Rare earth nanocolloids are released and transported through mechanisms such as ion exchange and soil colloid co-migration. They can be absorbed by terrestrial plants and taken up by microorganisms and higher organisms from sediments. REEs enter the human body through the food chain, and excessive or long-term exposure to them can cause irreversible harm to human health. Therefore, it is necessary to use effective separation and characterization technology to clarify the concentration of rare earth nanocolloids in the environment. At the same time, efficient recovery technology can be used to recover rare earth nanocolloids from the soil. This can not only reduce the release of rare earth nanocolloids in the environment and reduce the pollution of rare earth nanocolloids to the soil, but also help to recycle and utilize resources.

[0003] Currently, the more common methods for separating nanocolloids include ultracentrifugation, membrane separation, chromatography, magnetic separation, and field flow separation. Different centrifugation methods are selected based on the size of the target nanocolloids. Ultracentrifugation is primarily used to separate nanocolloids with varying sedimentation velocities. Membrane separation offers fast separation speeds and a wide range of applicability, but is less effective for separating low-concentration rare earth nanocolloids. Chromatography allows for simultaneous quantitative analysis of samples, but its ability to handle high-concentration rare earth nanocolloids is limited. Magnetic separation offers high separation efficiency and specificity, but its applicability is limited. The natural abundance of rare earth elements in the Earth's crust ranges from 63 mg / kg for Ce to 0.30 mg / kg for Tm. Their formation is influenced by geochemical characteristics, geological structure, mineralogical properties, plate tectonics, and biological processes, resulting in a wide range of rare earth element concentrations and size distributions in soil. Given that field-flow fractionation exhibits high resolution and detection capabilities for nanocolloids with a wide size range when dealing with complex matrices, field-flow fractionation is suitable for the separation of soil rare earth nanocolloids.

[0004] Inductively coupled plasma mass spectrometry has become a key tool for the quantitative characterization of soil rare earth nanocolloids due to its advantages such as high sensitivity, low detection limit, simultaneous analysis of multiple elements, high resolution, high precision and strong resistance to matrix interference, providing strong support for related research.

[0005] In the field of rare earth recovery, chemical precipitation is a common method that has attracted attention due to its simple operation and low cost, but the subsequent treatment of the precipitate is relatively complicated and costly. Although the ion exchange method has high selectivity and efficiency, it is costly and easily interfered with by other ions in the solution. The extraction method has high separation efficiency, but the operation is complicated, the regeneration process is time-consuming, and the organic reagents may cause harm to the environment. The adsorption method is simple to operate, has a large adsorption capacity, is environmentally friendly, but has limited regeneration capacity. These technologies are mainly suitable for the recovery of high-concentration rare earths, and have regeneration limitations and potential harm to the environment. However, the above methods have low recovery efficiency for low-concentration rare earth nanocolloids. At present, research on the recovery of soil rare earth nanocolloids, especially methods that integrate separation, quantitative characterization and recovery, is still in its infancy, and there are few related technologies. Summary of the Invention

[0006] To overcome the problems existing in the related art, the purpose of the present invention is to provide a method for separating, quantitatively characterizing and recovering soil rare earth nanocolloids. This method is applicable to rare earth nanocolloids with a wide size range and can also accurately recover low-concentration rare earth nanocolloids of various particle sizes.

[0007] A method for separating, quantitatively characterizing and recovering soil rare earth nanocolloids, comprising:

[0008] S1: Weighing a soil sample, settling the soil sample, and collecting a soil colloidal solution;

[0009] S2: Separation and characterization of soil nanocolloids using asymmetric flow field flow instrumentation, multi-angle laser light scattering instrumentation, and inductively coupled plasma mass spectrometry to obtain characterization results;

[0010] S3: setting a plurality of recovery time periods according to the characterization results, and recovering rare earth nano-colloids of different particle sizes in different recovery time periods.

[0011] In a preferred technical solution of the present invention, in step S3, a first recovery time period, a second recovery time period and a third recovery time period are set, the start time of the first recovery time period is 5 minutes, and the end time of the first recovery time period is 10 minutes; the start time of the second recovery time period is 10 minutes, and the end time of the second recovery time period is 20 minutes; the start time of the third recovery time period is 40 minutes, and the end time of the third recovery time period is 50 minutes.

[0012] In a preferred technical solution of the present invention, in the first recovery time period, rare earth nano-colloids with a particle size range of 5nm-26nm are recovered; in the second recovery time period, rare earth nano-colloids with a particle size range of 26nm-70nm are recovered; in the third recovery time period, rare earth nano-colloids with a particle size range of 300nm-350nm are recovered.

[0013] In a preferred technical solution of the present invention, before step S2, the method further includes taking 1.5 ml of the soil colloid solution and transferring it into a matching injection bottle, and placing the injection bottle on a sample rack of the field flow instrument.

[0014] In a preferred technical solution of the present invention, in step S2, the sample outflow tube of the multi-angle laser light scattering instrument coupled with the asymmetric flow field flow instrument is connected to the sample inlet tube of the inductively coupled plasma mass spectrometer to separate and quantitatively characterize the rare earth nanocolloids in the soil colloidal solution.

[0015] In a preferred technical solution of the present invention, in step S1, 12.5 g of air-dried and sieved soil sample is weighed and placed in a 150 mL headspace bottle; 25 mL of ultrapure water is added to the headspace bottle, and the headspace bottle is vortex-oscillated at 150 rpm at 25° C. for 6 hours; after the shaking is completed, ultrapure water is added to the headspace bottle, and after shaking, the sedimentation time is determined according to the sedimentation height. After the sedimentation is completed, the supernatant is collected to obtain a soil colloidal solution.

[0016] In a preferred technical solution of the present invention, the amount of ultrapure water is 75 ml, the sedimentation time is 12 h 3 min, and the particle size of the soil colloid solution is less than 1000 nm.

[0017] In a preferred technical solution of the present invention, the flow rate of the injection stage of the asymmetric flow field flow instrument is 0.3 mL / min, and the injection time is 10 min; the flow rate of the cross flow of the asymmetric flow field flow instrument decreases from 2.5 mL / min to 1.5 mL / min, and then from 1.5 mL / min to 0 mL / min.

[0018] In a preferred technical solution of the present invention, the channel membrane of the asymmetric flow field flow instrument is a polyethersulfone membrane with a pore size of 1 kDa.

[0019] In a preferred technical solution of the present invention, the scattered light angle detected by the multi-angle laser light scattering instrument is 90°.

[0020] The beneficial effects of the present invention are:

[0021] The present invention provides a method for separating, quantitatively characterizing and recovering soil rare earth nano-colloids, comprising weighing a soil sample, settling the soil sample, and collecting a soil colloid solution, wherein the particle size of the particles in the soil colloid solution is less than 1000 nm. In combination with an asymmetric flow field flow meter, a multi-angle laser light scattering instrument and an inductively coupled plasma mass spectrometer, the soil nano-colloids are separated and characterized to obtain characterization results. The present invention combines multiple instruments to accurately separate and characterize rare earth nano-colloids of different particle sizes. Multiple recovery time periods are set according to the characterization results, and rare earth nano-colloids of different particle sizes are recovered within different recovery time periods. Based on the results of the quantitative characterization, the asymmetric flow field flow meter is used to precisely recover rare earth nano-colloids of the target particle size. Based on the relationship between the peak time and the separation particle size, the specific time period for collecting the target particle size is delineated. The present invention enables precise recovery of low-concentration rare earth nanocolloids of specific particle sizes. It not only efficiently recovers nanoscale rare earth colloids of 5-70 nm, but also effectively recovers submicron-scale rare earth colloids of 300-350 nm, achieving high recovery efficiency. Furthermore, the present invention can simultaneously recover rare earth colloids of multiple particle sizes. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a flow chart of the method for separating, quantitatively characterizing and recovering soil rare earth nanocolloids of the present invention;

[0023] Figure 2 This is a peak diagram of the soil colloid component of the present invention in a multi-angle laser light scattering instrument;

[0024] Figure 31 is a distribution diagram of rare earth elements in the soil colloid component of the present invention. DETAILED DESCRIPTION

[0025] The preferred embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although preferred embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to make the present invention more thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0026] Example 1

[0027] like Figure 1 As shown, this embodiment provides a method for separating, quantitatively characterizing and recovering soil rare earth nanocolloids, comprising:

[0028] S1: Weighing a soil sample, settling the soil sample, and collecting a soil colloid solution.

[0029] S2: Soil nanocolloids were separated and characterized by combining asymmetric flow field flow instrumentation, multi-angle laser light scattering instrumentation and inductively coupled plasma mass spectrometry to obtain characterization results.

[0030] S3: setting a plurality of recovery time periods according to the characterization results, and recovering rare earth nano-colloids of different particle sizes in different recovery time periods.

[0031] Before step S2, the method further includes taking 1.5 ml of the soil colloid solution and transferring it into a matching injection bottle, and placing the injection bottle on a sample rack of the field flow instrument.

[0032] Soil colloids are tiny particles in the soil with a diameter of less than 1000 nm. These particles are so small that they generally fall within the colloid category. For example, clay minerals are a major component of soil colloids. Clay mineral particles like montmorillonite and illite typically range in size from a few nanometers to several hundred nanometers. They possess a large specific surface area, which refers to the surface area per unit mass of a substance. The specific surface area of soil colloids can reach several square meters or even tens of square meters per gram, enabling them to adsorb large amounts of substances.

[0033] Rare earth elements refer to scandium (Sc), yttrium (Y) and lanthanide elements in Group IIIB of the periodic table. Rare earth elements have a unique electronic structure, which gives them special magnetic, optical and electrical properties.

[0034] Light rare earth elements include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), and europium (Eu). They are primarily used in industry to manufacture magnetic materials, optical glass, and catalysts. For example, neodymium iron boron (NdFeB) permanent magnets are currently the highest-performing permanent magnets and are widely used in electronic devices and electric vehicles.

[0035] Heavy rare earth elements (HREs) include gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and yttrium (Y). They play an irreplaceable role in high-tech and defense fields, such as in the manufacture of laser materials, nuclear reactor control materials, and high-precision electronic devices. For example, dysprosium and terbium are key elements in the manufacture of high-performance permanent magnets used in high-end fields such as aerospace and military equipment.

[0036] ICP-MS was used to measure rare earth standard samples at concentrations of 0.5, 1, 5, 10, 20, 50, 100, and 200 ppb, and a calibration curve for rare earth elements was obtained by fitting. A 1.5 ml aliquot of a soil colloidal suspension with particles less than 1000 nm was transferred to a matching injection vial and placed in the sample holder of the field flow instrument. The sample outlet of the MALS (Multi-Angle Laser Light Scattering) instrument, coupled to the asymmetric flow field flow instrument, was connected to the injection tube of the ICP-MS (Inductively Coupled Plasma Mass Spectrometry) to separate and quantitatively characterize the soil rare earth nanocolloids in the soil colloidal solution.

[0037] The soil colloid solution contains rare earth elements such as La, Pr, Eu, Dy, Tm, Gd, Sm, Tb, Ho and Lu. The particle size and peak time of different rare earth nanocolloids are different.

[0038] In step S3, the first recovery time period, the second recovery time period and the third recovery time period are set. The start time of the first recovery time period is 5 minutes, and the end time of the first recovery time period is 10 minutes; the start time of the second recovery time period is 10 minutes, and the end time of the second recovery time period is 20 minutes; the start time of the third recovery time period is 40 minutes, and the end time of the third recovery time period is 50 minutes.

[0039] In the first recovery time period, rare earth nano-colloids with a particle size range of 5nm-26nm are recovered; in the second recovery time period, rare earth nano-colloids with a particle size range of 26nm-70nm are recovered; in the third recovery time period, rare earth nano-colloids with a particle size range of 300nm-350nm are recovered.

[0040] Based on the quantitative characterization results, an asymmetric flow field flow instrument was used to precisely recover rare earth nanocolloids of the target particle size. The specific steps were as follows: 1.5 mL of soil colloid solution was placed in an injection vial and recovery mode was activated on the field flow instrument interface. The peak elution time during the separation and quantitative characterization experiment was calculated. Due to the positive correlation between peak elution time and particle size, smaller particles were eluted earlier, indicating that smaller particles had an earlier peak elution time.

[0041] Define a specific time period for collecting the target particle size. Determine the volume of the recovered rare earth nanocolloids of the target particle size based on the product of the designated continuous collection time and the detector effluent flow rate, and place a recovery bottle of the corresponding volume. Set the detector effluent flow rate to 0.5mL / min. If collecting rare earth nanocolloids in the particle size range of 5-70nm, set the corresponding collection time to 5-20min, and the volume of the recovered rare earth nanocolloid suspension is 7.5mL. When the separation program runs to the set time period, the fraction collector will automatically start, and the probe will inject the effluent into a clean recovery bottle to achieve the recovery of different rare earth nanocolloids.

[0042] Based on the data characterized by combining multiple instruments, rare earth nano-colloids of target particle size are precisely recovered in a targeted manner. If rare earth nano-colloids with a particle size range of 5nm-26nm are recovered from soil solution, the field flow recovery interface is set to start recovery from the 5th minute and end at the 10th minute. If rare earth nano-colloids with a particle size range of 26nm-70nm are recovered from soil solution, the field flow recovery interface is set to start recovery from the 10th minute and end at the 20th minute. If rare earth nano-colloids with a particle size range of 300nm-350nm are recovered from soil solution, the field flow recovery interface is set to start recovery from the 40th minute and end at the 50th minute.

[0043] The present embodiment provides a method for separating, quantitatively characterizing and recovering soil rare earth nano-colloids, comprising weighing a soil sample, settling the soil sample, and collecting a soil colloid solution, wherein the particle size of the particles in the soil colloid solution is less than 1000 nm. In combination with an asymmetric flow field flow meter, a multi-angle laser light scattering instrument and an inductively coupled plasma mass spectrometer, the soil nano-colloids are separated and characterized to obtain characterization results. The present invention combines multiple instruments to accurately separate and characterize rare earth nano-colloids of different particle sizes. Multiple recovery time periods are set according to the characterization results, and rare earth nano-colloids of different particle sizes are recovered within different recovery time periods. Based on the results of the quantitative characterization, the asymmetric flow field flow meter is used to precisely recover the rare earth nano-colloids of the target particle size. According to the relationship between the peak time and the separation particle size, the specific time period for collecting the target particle size is delineated. The present invention enables precise recovery of low-concentration rare earth nanocolloids of specific particle sizes. It not only efficiently recovers nanoscale rare earth colloids of 5-70 nm, but also effectively recovers submicron-scale rare earth colloids of 300-350 nm, achieving high recovery efficiency. Furthermore, the present invention can simultaneously recover rare earth colloids of multiple particle sizes.

[0044] Example 2

[0045] This embodiment provides a method for separating, quantitatively characterizing, and recovering soil rare earth nanocolloids. This embodiment is based on Example 1 and describes the differences from Example 1. The method includes:

[0046] S1: Weighing a soil sample, settling the soil sample, and collecting a soil colloid solution.

[0047] S2: Soil nanocolloids were separated and characterized by combining asymmetric flow field flow instrumentation, multi-angle laser light scattering instrumentation and inductively coupled plasma mass spectrometry to obtain characterization results.

[0048] S3: setting a plurality of recovery time periods according to the characterization results, and recovering rare earth nano-colloids of different particle sizes in different recovery time periods.

[0049] In step S1, 12.5 g of an air-dried and sieved soil sample is weighed and placed in a 150 mL headspace bottle; 25 mL of ultrapure water is added to the headspace bottle, and the headspace bottle is vortex-oscillated at 150 rpm at 25° C. for 6 hours; after the shaking is completed, ultrapure water is added to the headspace bottle, shaken well, and the sedimentation time is determined according to the sedimentation height. After the sedimentation is completed, the supernatant is collected to obtain a soil colloidal solution, and the particle size of the colloidal particles in the soil colloidal solution is less than 1000 nm.

[0050] The amount of the ultrapure water is 75 ml, the sedimentation time is 12 hours and 3 minutes, and the particle size of the soil colloid solution is less than 1000 nm.

[0051] The settling time is calculated using Stokes' formula:

[0052]

[0053] Where t is the settling time in seconds, L is the settling depth of the soil particles in cm, and η is the viscosity of water in g / (cm·s). At 20°C, η = 1.002×10 -3 g / (cm·s); at 25℃, η=0.890×10 - 3 g / (cm·s). d is the diameter of the soil particle, in mm. ρ s is the soil particle density, which is 2.65g / cm 3 ,ρ f is the density of water, and g is the acceleration due to gravity.

[0054] The flow rate of the injection phase of the asymmetric flow field flow instrument is 0.3 mL / min, and the injection is continued for 10 minutes to ensure that the sample fully enters the system. The initial flow rate of the cross flow of the asymmetric flow field flow instrument is set to 2.5 mL / min to promote uniform distribution of the sample during the injection process. During the elution process, the cross flow decreases from 2.5 mL / min to 1.5 mL / min and then from 1.5 mL / min to 0 mL / min in the form of a power function. The entire stage lasts for 1 hour. The duration of the flushing phase is set to 0.5 minutes to remove residual substances in the system. The flow rate of the effluent is always kept at 0.5 mL / min throughout the process.

[0055] During the experiment, the scattered light angle for MALS detection was set to 90° to reduce interference from reflections from the sample cell walls and multiple scattering, thereby improving measurement accuracy. A polyethersulfone (PES) membrane with a pore size of 1 kDa was selected as the channel membrane for the asymmetric flow field flow instrument. This PES membrane only allows dissolved substances to pass through. While removing dissolved rare earth elements, the PES membrane's material properties, chemical stability, and low adsorption also ensure separation efficiency.

[0056] A sodium chloride solution with a concentration of 25 μM was used as the mobile phase in the flushing process to create a low-salt environment close to soil pore water, maintaining the natural morphology of soil nanocolloids without significantly affecting subsequent characterization.

[0057] The flow rate of the asymmetric flow field flow instrument in this embodiment during the injection phase is 0.3 mL / min, and the injection time is 10 min. The cross-flow flow rate of the asymmetric flow field flow instrument decreases from 2.5 mL / min to 1.5 mL / min, and then from 1.5 mL / min to 0 mL / min. The channel membrane of the asymmetric flow field flow instrument is a polyethersulfone membrane with a pore size of 1 kDa. This PES membrane only allows dissolved substances to pass through. While removing dissolved rare earth elements, the material property adaptability, chemical stability, and low adsorption of the PES membrane can also ensure separation efficiency.

[0058] Example 3

[0059] This embodiment provides a method for separating, quantitatively characterizing, and recovering soil rare earth nanocolloids. This embodiment is based on Example 1 and describes the differences from Example 1. The method includes:

[0060] S1: Weighing a soil sample, settling the soil sample, and collecting a soil colloid solution.

[0061] S2: Soil nanocolloids were separated and characterized by combining asymmetric flow field flow instrumentation, multi-angle laser light scattering instrumentation and inductively coupled plasma mass spectrometry to obtain characterization results.

[0062] S3: setting a plurality of recovery time periods according to the characterization results, and recovering rare earth nano-colloids of different particle sizes in different recovery time periods.

[0063] Figure 2 The peak diagram of the soil colloid component in the multi-angle laser light scattering instrument of the present invention is shown in FIG. Figure 2 It can be seen that there are three main peaks of rare earth elements in soil colloids. The first main peak appears between 5min-10min, corresponding to rare earth nanocolloids with a particle size range of 5nm-26nm; the second main peak appears around 15min, corresponding to rare earth nanocolloids with a particle size range of 26nm-70nm; the third main peak appears between 40min-45min, corresponding to rare earth nanocolloids with a particle size range of 300nm-350nm.

[0064] Figure 3 is a distribution diagram of rare earth elements in the soil colloid component of the present invention, and Table 1 is a table of rare earth element concentrations of different particle sizes.

[0065] Table 1

[0066]

[0067] Depend on Figure 3It can be seen that the distribution concentration of rare earth elements in soil colloids is uneven. The concentration of the first group of elements, such as La, Gd, Pr, Sm, and Eu, accounts for more than 50% in the 300nm-350nm range, more than 20% in the 5nm-26nm range, and less than 15% in the 26nm-70nm range. The concentration of the second group of elements, such as Tb, Dy, Ho, Tm, and Lu, in the 300nm-350nm range is greater than that in the 5nm-70nm range, and the concentration of the second group of elements is lower than that of the first group in the 5nm-26nm, 26nm-70nm, and 300nm-350nm ranges.

[0068] This embodiment provides a method for separating, quantitatively characterizing, and recovering rare earth nanocolloids in soil, which can reflect the natural concentration of rare earth nanocolloids in the soil. Different time periods are set to separately recover rare earth nanocolloids with particle sizes in the ranges of 5nm-26nm, 26nm-70nm, and 300nm-350nm, thereby specifically recovering rare earth nanocolloids of different particle sizes.

[0069] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, apparatus, article, or method comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, apparatus, article, or method. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, apparatus, article, or method comprising the element.

[0070] The above description is only a preferred embodiment of the present application and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for separating, quantitatively characterizing and recovering soil rare earth nanocolloids, characterized in that: include: S1: Weighing a soil sample, settling the soil sample, and collecting a soil colloidal solution; S2: Separation and characterization of soil nanocolloids using asymmetric flow field flow instrumentation, multi-angle laser light scattering instrumentation, and inductively coupled plasma mass spectrometry to obtain characterization results; S3: setting a plurality of recovery time periods according to the characterization results, and recovering rare earth nano-colloids of different particle sizes in different recovery time periods.

2. The method for separating, quantitatively characterizing and recovering soil rare earth nanocolloids according to claim 1, characterized in that: In step S3, the first recovery time period, the second recovery time period and the third recovery time period are set. The start time of the first recovery time period is 5 minutes, and the end time of the first recovery time period is 10 minutes; the start time of the second recovery time period is 10 minutes, and the end time of the second recovery time period is 20 minutes; the start time of the third recovery time period is 40 minutes, and the end time of the third recovery time period is 50 minutes.

3. The method for separating, quantitatively characterizing and recovering soil rare earth nanocolloids according to claim 2, characterized in that: In the first recovery time period, rare earth nano-colloids with a particle size range of 5nm-26nm are recovered; in the second recovery time period, rare earth nano-colloids with a particle size range of 26nm-70nm are recovered; in the third recovery time period, rare earth nano-colloids with a particle size range of 300nm-350nm are recovered.

4. The method for separating, quantitatively characterizing and recovering soil rare earth nanocolloids according to claim 1, characterized in that: Before step S2, the method further includes taking 1.5 ml of the soil colloid solution and transferring it into a matching injection bottle, and placing the injection bottle on a sample rack of the field flow instrument.

5. The method for separation, quantitative characterization and recovery of soil rare earth nanocolloids according to claim 1, characterized in that: In step S2, the sample outflow tube of the multi-angle laser light scattering instrument coupled with the asymmetric flow field instrument is connected to the sample inlet tube of the inductively coupled plasma mass spectrometer to separate and quantitatively characterize the rare earth nano-colloids in the soil colloidal solution.

6. The method for separation, quantitative characterization and recovery of soil rare earth nanocolloids according to claim 1, characterized in that: In step S1, 12.5 g of air-dried and sieved soil sample was weighed and placed in a 150 mL headspace bottle; 25 mL of ultrapure water was added to the headspace bottle, and the headspace bottle was vortex-oscillated at 150 rpm at 25° C. for 6 h; after the shaking was completed, ultrapure water was added to the headspace bottle, and the sedimentation time was determined according to the sedimentation height after shaking. After the sedimentation was completed, the supernatant was collected to obtain a soil colloidal solution.

7. The method for separating, quantitatively characterizing and recovering soil rare earth nanocolloids according to claim 6, characterized in that: The amount of the ultrapure water is 75 ml, the sedimentation time is 12 hours and 3 minutes, and the particle size of the soil colloid solution is less than 1000 nm.

8. The method for separation, quantitative characterization and recovery of soil rare earth nanocolloids according to claim 1, characterized in that: The flow rate of the injection stage of the asymmetric flow field flow instrument is 0.3 mL / min, and the injection time is 10 min; the flow rate of the cross flow of the asymmetric flow field flow instrument decreases from 2.5 mL / min to 1.5 mL / min, and then from 1.5 mL / min to 0 mL / min.

9. The method for separating, quantitatively characterizing and recovering soil rare earth nanocolloids according to claim 1, characterized in that: The channel membrane of the asymmetric flow field flow instrument is a polyethersulfone membrane with a pore size of 1 kDa.

10. The method for separation, quantitative characterization and recovery of soil rare earth nanocolloids according to claim 5, characterized in that: The scattered light angle detected by the multi-angle laser light scattering instrument is 90°.

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