A regeneration method for hollow microspheres capable of absorbing heavy metals

Abstract

The invention provides a regeneration method for hollow microspheres capable of adsorbing heavy metals, and belongs to the technical field of heavy metal contaminated soil remediation. The invention utilizes calcium disodium ethylenediaminetetraacetate in a backwashing solution to complex with cadmium in used hollow heavy metal adsorption microspheres, so that cadmium is leached from the microspheres. Meanwhile, Ca and Na in calcium disodium ethylenediaminetetraacetate are ion-exchanged with cadmium to reduce the cadmium content in the microspheres. Ca in calcium disodium ethylenediaminetetraacetate is ion-exchanged with other cations in the microsphere material to perform re-crosslinking to maintain the mechanical strength of the material. Calcium laurate in the backwashing solution complexes metal cations and is adsorbed on the surface of the microsphere material to reduce surface tension and weaken adhesion between cadmium ions and the microsphere material. Cadmium is backwashed from the microsphere material to obtain pretreated microspheres. The mechanical strength is improved through crosslinking to obtain regenerated hollow heavy metal adsorption microspheres.

Description

Technical Field

[0001] The invention relates to the technical field of heavy metal contaminated soil remediation, and in particular to a method for regenerating hollow microspheres capable of absorbing heavy metals. Background Art

[0002] Heavy metal pollution mainly comes from industrial pollution, such as electroplating, mining, steel and non-ferrous metal smelting, etc., and industrial pollution is mostly discharged into the environment through waste residue, wastewater and waste gas. Heavy metals cannot be biodegraded into harmless substances and can be enriched in plants, animals and humans, thus causing great harm to the environment and human health.

[0003] At present, the main ways to remediate soil cadmium pollution include physical remediation, chemical remediation and biological remediation. Physical remediation includes guest soil method, electrochemical method and thermal treatment method. Guest soil method is to clear the contaminated soil and then backfill it with uncontaminated soil; electrochemical method is to add chemical agents to the contaminated soil to increase the conductivity and acidity of the soil, so that cadmium ions are dissolved and extracted; thermal treatment method is to volatilize cadmium in the soil by high temperature. Chemical remediation mainly uses stabilizers and modifiers to reduce the biological effectiveness of cadmium by changing the physical and chemical properties of the soil. For example, lime, calcium sulfate and other substances are used to increase the pH value of the soil, so that cadmium ions form insoluble hydroxides or carbonates in the soil. Biological remediation is to use the absorption and transformation ability of certain microorganisms or plants to reduce the cadmium content in the soil. For example, some microorganisms can produce organic acids to dissolve cadmium in the soil; and some plants such as rice have strong tolerance and absorption to cadmium, which can reduce the cadmium content in the soil to a certain extent. However, the above methods have limited effects on improving soil environmental quality, and have shortcomings such as long cycle, damage to soil structure, and difficulty in material recovery.

[0004] With the development of science and technology, new soil cadmium reduction materials and application technologies have emerged in the prior art. These materials have the advantages of high removal efficiency, short repair cycle, no impact on agricultural activities and production seasons, etc. For example, the Chinese invention patent with authorization announcement number CN117244535B discloses a preparation of floating hollow microspheres and their application in soil cadmium reduction. The heavy metal adsorption is achieved by applying the heavy metal adsorption functional microspheres into moist soil. After adsorption, water is poured into the field to make it float and recover it, so as to achieve the goal of rapid and efficient reduction of soil cadmium. However, if the heavy metal adsorption functional microsphere material is not regenerated after large-scale application and recovery in the field, it will not only cause a waste of resources, but also form solid waste that is easy to cause secondary pollution. In order to improve the recycling rate of resources, it is a technical problem that the prior art urgently needs to solve to provide a regeneration method for heavy metal adsorption functional microspheres. Summary of the invention

[0005] The object of the present invention is to provide a method for regenerating hollow microspheres that can adsorb heavy metals. The method provided by the present invention meets the demand for recycling and cyclic utilization of hollow heavy metal adsorption microspheres after application, and the regenerated hollow heavy metal adsorption microspheres have stable mechanical properties and excellent cadmium removal effect.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for regenerating hollow microspheres capable of adsorbing heavy metals, comprising the following steps:

[0008] The used hollow heavy metal adsorption microspheres in the soil are collected, washed and filtered in sequence, and then backwashed with a backwashing solution to obtain pre-treated microspheres;

[0009] After mixing the pretreated microspheres and the crosslinking agent, crosslinking and drying are performed in sequence to obtain regenerated hollow heavy metal adsorption microspheres;

[0010] The backwash solution is an aqueous solution containing calcium disodium ethylenediaminetetraacetate and calcium laurate;

[0011] The cross-linking agent is an aqueous solution containing borax, calcium chloride and acetic acid.

[0012] Preferably, the concentration of calcium disodium EDTA in the backwash solution is 0.001-1 mol / L.

[0013] Preferably, the concentration of calcium laurate in the backwash solution is 0.00004-0.04 mol / L.

[0014] Preferably, the mass ratio of the filtered hollow heavy metal adsorption microspheres to the backwash solution is 1:(2-60).

[0015] Preferably, the number of backwashing is 1 to 5 times, and the time of each backwashing is 0.2 to 6 hours;

[0016] Preferably, the backwashing comprises: mixing the filtered hollow heavy metal adsorption microspheres and the backwashing solution and then shaking to obtain pretreated microspheres;

[0017] The mass ratio of the filtered hollow heavy metal adsorption microspheres to the backwash solution is 1:(3-50); the oscillation rate is 50-250r / min.

[0018] Preferably, the concentration of calcium chloride in the cross-linking agent is 1-20 g / L.

[0019] Preferably, the mass ratio of the pretreated microspheres to the crosslinking agent is 1:(3-15).

[0020] Preferably, the cross-linking is carried out under stirring conditions, and the cross-linking time is 0.5 to 4 hours.

[0021] Preferably, the drying temperature is 40-60° C., and the drying time is 4-12 min.

[0022] The invention provides a regeneration method for hollow microspheres capable of absorbing heavy metals. The collected used hollow heavy metal adsorbing microspheres are sequentially cleaned and filtered to remove the mud and sand on the surface of the microsphere material and filter out the water. Then, the microspheres are backwashed with a backwashing solution to obtain pretreated microspheres. Calcium disodium ethylenediaminetetraacetate (abbreviated as EDTA-CaNa2) in the backwashing solution can be complexed with cadmium in the used hollow microspheres to leach the cadmium from the microspheres and generate a stable complex. Meanwhile, Ca and Na in EDTA-CaNa2 can further reduce the cadmium content in the material by exchanging with cadmium ions. Moreover, Ca in EDTA-CaNa2 can also exchange ions with other cations on the main chain fragments in the microsphere material during the backwashing process to make the microsphere material Re-crosslinking can still be performed during the backwashing process to maintain the mechanical strength of the material; calcium laurate in the backwashing solution is an anionic surfactant with good heavy metal dissolution ability, and the micelle surface is negatively charged, and metal cations can be complexed by ionic bonds, and calcium laurate can be adsorbed on the surface of the microsphere material, and the adhesion of cadmium ions to the microsphere material is weakened by reducing the surface tension. During the backwashing process, when the bond energy between the cadmium ions and the microsphere material is reduced to less than the bond energy between the cadmium ions and the cations in the backwashing solution, the cadmium can be backwashed from the microsphere material. At the same time, the calcium in calcium laurate can protect the mechanical strength of the material and reduce the damage of the microspheres during the backwashing process; the pretreated microspheres and the crosslinking agent are mixed and crosslinked to further improve the mechanical strength to obtain regenerated hollow heavy metal adsorption microspheres. The method provided by the present invention is simple to operate, the regenerated hollow heavy metal adsorption microspheres have stable mechanical properties, have excellent cadmium removal effects, and meet the needs of recycling and recycling hollow heavy metal adsorption microspheres after application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 These are actual pictures of the hollow heavy metal adsorption microspheres before and after regeneration after use in Example 1 of the present invention, wherein the left picture is before regeneration and the right picture is after regeneration.

[0024] Figure 2 These are actual pictures of the hollow heavy metal adsorption microspheres before and after regeneration after use in Comparative Example 5 of the present invention, wherein the left picture is before regeneration and the right picture is after regeneration. DETAILED DESCRIPTION

[0025] The present invention provides a method for regenerating hollow microspheres capable of adsorbing heavy metals, comprising the following steps:

[0026] The used hollow heavy metal adsorption microspheres in the soil are collected, washed and filtered in sequence, and then backwashed with a backwashing solution to obtain pre-treated microspheres;

[0027] After mixing the pretreated microspheres and the crosslinking agent, crosslinking and drying are performed in sequence to obtain regenerated hollow heavy metal adsorption microspheres;

[0028] The backwash solution is an aqueous solution containing calcium disodium ethylenediaminetetraacetate and calcium laurate;

[0029] The cross-linking agent is an aqueous solution containing borax, calcium chloride and acetic acid.

[0030] In the present invention, unless otherwise specified, the raw materials used are conventional commercial products in the art.

[0031] The present invention has no special restrictions on the cleaning and filtering methods, and the sand on the surface of the microsphere material can be removed by using water, and the water can be filtered out.

[0032] In the present invention, the concentration of calcium disodium ethylenediaminetetraacetate in the backwash solution is preferably 0.001-1 mol / L; the concentration of calcium laurate in the backwash solution is preferably 0.00004-0.04 mol / L. In the present invention, the concentration ratio of calcium disodium ethylenediaminetetraacetate to calcium laurate in the backwash solution is preferably 25:1.

[0033] In the present invention, the mass ratio of the filtered hollow heavy metal adsorption microspheres to the backwash solution is preferably 1: (2-60), more preferably 1: (3-50). The present invention controls the mass ratio of the filtered hollow heavy metal adsorption microspheres to the backwash solution within the above range to give full play to the effect of the backwash solution and remove cadmium from the filtered hollow heavy metal adsorption microspheres.

[0034] In the present invention, the number of backwashing is preferably 1 to 5 times, and the time of each backwashing is preferably 0.2 to 6 hours, and more preferably 0.5 to 4 hours. In the present invention, the backwashing includes: mixing the filtered hollow heavy metal adsorption microspheres and the backwashing solution and then shaking to obtain pretreated microspheres; the mass ratio of the filtered hollow heavy metal adsorption microspheres to the backwashing solution is 1: (3 to 50), and more preferably 1: (10 to 20); the shaking rate during the backwashing process is preferably 50 to 250 r / min, and more preferably 100 to 200 r / min. The present invention controls the number of backwashing, time, mass ratio of the filtered hollow heavy metal adsorption microsphere material and the backwashing solution, and shaking rate within the above range to provide a backwashing effect, cooperate with the backwashing solution to backwash cadmium from the microsphere material, reduce the cadmium content in the regenerated hollow heavy metal adsorption microspheres, restore its adsorption capacity for heavy metals in the soil, and improve the regeneration effect.

[0035] In the present invention, the concentration of calcium chloride in the cross-linking agent is preferably 1-20 g / L, more preferably 2-10 g / L; the concentration of borax in the cross-linking agent is preferably 5-30 g / L, more preferably 10-20 g / L. In the present invention, the preparation of the cross-linking agent preferably includes: dispersing calcium chloride and borax in water, and then adjusting the pH to neutral with acetic acid.

[0036] In the present invention, the mass ratio of the pretreated microspheres to the crosslinking agent is preferably 1:(3-15), more preferably 1:(5-10). The present invention controls the mass ratio of the pretreated microspheres to the crosslinking agent within the above range to promote the molecular chains in the pretreated microspheres to fully crosslink, improve the mechanical strength of the microspheres, reduce the damage to the microspheres during the backwashing process, and avoid the prepared regenerated hollow heavy metal adsorption microspheres from being damaged during the use again.

[0037] In the present invention, the cross-linking is preferably carried out under stirring conditions, the stirring speed is preferably 30 to 300 r / min, more preferably 50 to 250 r / min; the cross-linking temperature is preferably room temperature; the cross-linking time is preferably 0.5 to 4 hours. The present invention controls the cross-linking conditions, temperature and time within the above ranges to promote the smooth progress of the cross-linking reaction and improve the mechanical properties of the prepared regenerated hollow heavy metal adsorption microspheres.

[0038] In the present invention, the drying temperature is preferably 40-60° C., and the drying time is preferably 4-12 hours. The present invention removes the residual solvent by drying, which is beneficial to the stable storage of the prepared regenerated hollow heavy metal adsorption microspheres.

[0039] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] The initial microspheres in the present invention are prepared according to the prior art Chinese patent CN 117244535A to obtain hollow heavy metal adsorption microspheres. The average cadmium content in the hollow heavy metal adsorption microspheres after use in the soil collected in the embodiments and comparative examples of the present invention is 14 mg / kg, and the cadmium content in the microspheres is determined by inductively coupled plasma mass spectrometry (ICP-MS).

[0041] Example 1

[0042] A method for regenerating hollow heavy metal adsorption microspheres, comprising the following steps:

[0043] Collect 5 g of the used hollow heavy metal adsorption microspheres in the soil, add them into clean water to rinse once until there is no sediment, filter to remove the water, and then backwash them with a backwash solution to obtain pretreated microspheres;

[0044] The concentration of calcium disodium ethylenediaminetetraacetate in the backwash solution is 0.001 mol / L, and the concentration of calcium laurate in the backwash solution is 0.00004 mol / L;

[0045] The mass ratio of the filtered hollow heavy metal adsorption microspheres to the backwash solution is 1:10;

[0046] The number of backwashing is 1, and the time of each backwashing is 2 hours; the oscillation rate during the backwashing process is 200r / min;

[0047] After mixing the pretreated microspheres and the crosslinking agent, crosslinking is performed at room temperature and a rotation speed of 200 r / min for 0.5 h, and then filtering and standing for 8 h in sequence, and then drying at 50° C. for 8 h to obtain regenerated hollow heavy metal adsorption microspheres;

[0048] The concentration of calcium chloride in the cross-linking agent is 5 g / L; the concentration of borax in the cross-linking agent is 18 g / L; the preparation of the cross-linking agent includes: dispersing calcium chloride and borax in water, and then adjusting the pH to neutral with acetic acid; the mass ratio of the pretreated microspheres to the cross-linking agent is 1:10.

[0049] Comparative Example 1

[0050] The used hollow heavy metal adsorption microspheres were regenerated according to the method of Example 1, except that the backwash solution was an aqueous solution of HCl with a concentration of 0.01 mol / L.

[0051] Comparative Example 2

[0052] The used hollow heavy metal adsorption microspheres were regenerated according to the method of Example 1, except that the backwash solution was a HNO3 aqueous solution with a concentration of 0.01 mol / L.

[0053] Comparative Example 3

[0054] The used hollow heavy metal adsorption microspheres were regenerated according to the method of Example 1, except that the backwash solution was an acetic acid aqueous solution with a concentration of 0.01 mol / L.

[0055] Comparative Example 4

[0056] The used hollow heavy metal adsorption microspheres were regenerated according to the method of Example 1, except that the backwash solution was an EDTA aqueous solution with a concentration of 0.001 mol / L.

[0057] Comparative Example 5

[0058] The used hollow heavy metal adsorption microspheres were regenerated according to the method of Example 1, except that the backwash solution was an EDTA-2Na aqueous solution with a concentration of 0.001 mol / L.

[0059] Comparative Example 6

[0060] The used hollow heavy metal adsorption microspheres were regenerated according to the method of Example 1, except that the backwash solution was an EDTA-CaNa2 aqueous solution with a concentration of 0.001 mol / L.

[0061] Study on the effect of different backwash solutions on cadmium elution

[0062] The cadmium content of the pretreated microspheres obtained after backwashing in Example 1 and Comparative Examples 1 to 6 was determined by inductively coupled plasma mass spectrometry (ICP-MS), and the regeneration was repeated 3 times in parallel. The average cadmium content in the hollow heavy metal adsorption microspheres after use was 14 mg / kg. According to the following formula, the cadmium elution rates of different backwashing solutions in Example 1 and Comparative Examples 1 to 6 were calculated, and the results are shown in Table 1.

[0063] Cadmium removal rate = (14 mg / kg - cadmium content of pre-treated microspheres) ÷ 14 mg / kg × 100%;

[0064] Table 1 Cadmium elution rate of different backwash solutions in Example 1 and Comparative Examples 1 to 6

[0065]

[0066] As can be seen from Table 1, compared with the backwash solutions in the comparative examples, the backwash solution used in Example 1, i.e., the EDTA-CaNa2+calcium laurate composite backwash solution, has the best elution effect on cadmium in the microspheres, and the cadmium elution rates are 1.24 times and 4.71 times of EDTA-2Na and HNO3, respectively. Compared with EDTA-CaNa2, the EDTA-CaNa2+calcium laurate composite backwash solution increases the cadmium elution rate of cadmium in the microspheres by 14.4%.

[0067] In addition, except for EDTA-CaNa2 and EDTA-CaNa2 + calcium laurate composite backwashing solution, all other backwashing solutions are acidic, and have a certain corrosive and dissolving effect on the microsphere material. The solutions after backwashing treatment are all turbid. At the same time, after cross-linking, the surface of the regenerated microsphere material has different degrees of damage. The backwashing solution EDTA-CaNa2 + calcium laurate composite backwashing solution used in Example 1 is clear after backwashing treatment, and the actual pictures of the hollow heavy metal adsorption microspheres before and after regeneration after use in Example 1 of the present invention are as follows: Figure 1 As shown, the left picture is before regeneration, and the right picture is after regeneration; the actual pictures of the hollow heavy metal adsorption microspheres before and after regeneration in Comparative Example 5 are as follows Figure 2 As shown, the left picture is before regeneration, and the right picture is after regeneration. Figure 1 It can be seen that the regenerated hollow heavy metal adsorption microspheres obtained after cross-linking in Example 1 are of uniform size, smooth surface and substantially undamaged; Figure 1 and Figure 2 By comparison, it can be seen that compared with the hollow heavy metal adsorption microspheres regenerated in Example 1, the regenerated hollow heavy metal adsorption microspheres obtained in Comparative Example 5 are significantly smaller, and the surface is dull, rough and damaged.

[0068] Study on the effect of different backwashing time on cadmium elution effect

[0069] In order to explore the effect of different backwashing times on the cadmium elution effect, according to the same method as Example 1, Examples 2 to 4 were set to regenerate the used hollow heavy metal adsorption microspheres, and the regeneration was repeated 3 times in parallel. The difference from Example 1 is that the backwashing times of Examples 2 to 4 are 0.5h, 1h and 4h, respectively. The cadmium elution rates of the pretreated microspheres obtained at different backwashing times in Examples 2 to 4 were calculated according to the above method, and the results are shown in Table 2.

[0070] Table 2 Effect of different backwashing time on elution of cadmium from pretreated microspheres in Examples 1 to 4

[0071]

[0072] It can be seen from Table 2 that the EDTA-CaNa2 + calcium laurate composite backwash solution prepared in Examples 1 to 4 of the present invention has an elution rate of cadmium in the microspheres of 15.31% to 19.67% when the backwash time is 0.5 to 4 hours. As the backwash time increases, the cadmium elution rate gradually increases. During backwashing, 1 to 4 hours can be selected as the backwash time to ensure the backwash effect.

[0073] To investigate the effect of the mass ratio of the hollow heavy metal adsorption microspheres and the backwash solution after three different filtrations (referred to as the backwash solid-liquid ratio) on the elution effect of cadmium in the microspheres.

[0074] In order to explore the effect of different backwash solid-liquid ratios on the cadmium elution effect, according to the same method as Example 1, Examples 5 to 7 were set to regenerate the used hollow heavy metal adsorption microspheres, and the regeneration was repeated 3 times in parallel. The difference from Example 1 is that the backwash solid-liquid ratios of Examples 5 to 7 are 1:5, 1:8 and 1:20, respectively. The cadmium elution rate of the pretreated microspheres in Examples 5 to 7 was calculated according to the above method, and the results are shown in Table 3.

[0075] Table 3 Effect of different backwash solid-liquid ratios on cadmium elution effect in microspheres

[0076]

[0077] It can be seen from Table 3 that the EDTA-CaNa2 + calcium laurate composite backwash solution prepared in Examples 1, 5 to 7 of the present invention has a cadmium elution rate of 9.31% to 40.49% in the microspheres when the backwash solid-liquid ratio is 1 / 5 to 1 / 20. As the solid-liquid ratio increases, the cadmium elution rate gradually increases. When the backwash solid-liquid ratio is increased to 1 / 20, the cadmium elution rate in the microspheres is 4.35 times that when the solid-liquid ratio is 1 / 5. The solid-liquid ratio can be appropriately increased during backwashing to ensure the backwashing effect of the microspheres.

[0078] Investigate the effect of four different backwash solution concentrations on the elution of cadmium from microspheres

[0079] In order to explore the effect of the concentration of the backwash solution in different backwash solutions (i.e., the sum of the concentration of calcium disodium ethylenediaminetetraacetate and the concentration of calcium laurate) on the cadmium elution effect, according to the same method as Example 1, Examples 8 to 11 were set to regenerate the used hollow heavy metal adsorption microspheres, and the regeneration was repeated 3 times in parallel. The difference from Example 1 is that the concentrations of calcium disodium ethylenediaminetetraacetate in the backwash solutions of Examples 8 to 10 are 0.002, 0.003, 0.005, and 0.01 mol / L, respectively, and the concentrations of calcium laurate are 0.00008, 0.00012, 0.0002, and 0.0004 mol / L, respectively. The cadmium elution rate of the pretreated microspheres in Examples 8 to 10 was calculated according to the above method, and the results are shown in Table 4.

[0080] Table 4 Effect of different backwash concentrations on cadmium elution effect

[0081]

[0082]

[0083] As shown in Table 4, when the concentration of the EDTA-CaNa2+calcium laurate composite backwash solution in Examples 1, 8 to 10 of the present invention is 0.001 to 0.01 mol / L, the elution rate of cadmium in the microspheres is 18.67% to 60.22%. As the concentration of EDTA-CaNa2+calcium laurate in the backwash solution increases, the elution rate also gradually increases. When the concentration in the backwash solution is 0.01 mol / L, the EDTA-CaNa2+calcium laurate composite backwash solution can wash out most of the cadmium adsorbed in the microspheres at one time.

[0084] Investigate the effect of five different backwash times on the elution of cadmium from microspheres

[0085] In order to explore the effect of different backwashing times on the cadmium elution effect, according to the same method as Example 1, Examples 15 to 18 were set to regenerate the used hollow heavy metal adsorption microspheres, and the regeneration was repeated 3 times in parallel. The difference from Example 1 is that the backwashing times of Examples 15 to 18 are 1, 2, 3 and 4, respectively. The cadmium elution rate of the pretreated microspheres in Examples 15 to 18 was calculated according to the following formula, and the results are shown in Table 5.

[0086] Table 5 Effect of different backwash times on elution of cadmium from microspheres

[0087]

[0088]

[0089] It can be seen from Table 5 that when the number of backwashing times increases, the amount of cadmium eluted in a single time gradually decreases. After four consecutive backwashing times, the elution rate of cadmium in the microspheres reaches 93.13%.

[0090] Performance Testing

[0091] Dynamic thermal mechanical analysis (DMA) was used to measure the compressive strength of the hollow heavy metal adsorption microspheres before and after regeneration in Example 15. The results are shown in Table 6.

[0092] Table 6 Compressive strength of hollow heavy metal adsorption microspheres before and after regeneration

[0093] sample Initial microspheres Regenerated hollow heavy metal adsorption microspheres Mechanical strength (MPa) 1.46 1.43

[0094] It can be seen from Table 6 that the mechanical strength of the initial microspheres is 1.46 MPa, and the mechanical strength of the hollow heavy metal adsorption microspheres regenerated in Example 15 is 1.43 MPa, indicating that the regeneration method provided by the present invention has no significant effect on the mechanical strength of the microspheres.

[0095] In order to study the cadmium removal effect of the regenerated hollow heavy metal adsorption microspheres prepared by the method provided by the present invention, the following experiment was conducted:

[0096] The total cadmium content of cadmium-contaminated soil was 2.77 mg / kg, and the cadmium content extracted by 0.01 M calcium chloride was 0.392 mg / kg;

[0097] Weigh 100 g of the above-mentioned cadmium-contaminated dry soil, add 50 mL of deionized water and stir evenly, add 0.63 g of microspheres, stir thoroughly and let stand for 24 hours until the material adsorbs heavy metals, then add 45 mL of deionized water and stir, and then recover through a filter screen. The initial microspheres, the regenerated hollow heavy metal adsorption microspheres prepared in Example 15, and the hollow heavy metal adsorption microspheres after use in the collected soil are set up in three parallel groups, and the 0.01 M calcium chloride extractable cadmium content in the soil after application is determined, the soil calcium chloride extractable cadmium removal rate is calculated, and the calcium chloride extractable cadmium content in the soil extract is determined by ICP-MS.

[0098] Table 7 Removal effect of different microspheres on cadmium extracted from soil by calcium chloride

[0099]

[0100]

[0101] It can be seen from Table 7 that the removal rate of cadmium in the form of calcium chloride extractable by the regenerated hollow heavy metal adsorption microspheres prepared in Example 15 in cadmium-contaminated soil is comparable to that of the initial microspheres, while the cadmium removal effect of the used hollow heavy metal adsorption microspheres is poor. Therefore, the regeneration method provided by the present invention regenerates the used hollow heavy metal adsorption microspheres, which can significantly improve the removal effect of cadmium in soil, and the removal effect is comparable to that of the initial microspheres.

[0102] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for regenerating hollow microspheres for adsorbing heavy metals, characterized in that: The following steps are involved: The used hollow microspheres for adsorbing heavy metals in the soil are collected, washed and filtered in sequence, and then backwashed with a backwashing solution to obtain pre-treated microspheres; After mixing the pretreated microspheres and the crosslinking agent, crosslinking and drying are performed in sequence to obtain regenerated hollow microspheres for adsorbing heavy metals; The backwash solution is an aqueous solution containing calcium disodium ethylenediaminetetraacetate and calcium laurate; The cross-linking agent is an aqueous solution containing borax, calcium chloride and acetic acid; The concentration of calcium disodium EDTA in the backwash solution is 0.001-1 mol / L; The concentration of calcium laurate in the backwash solution is 0.00004-0.04 mol / L.

2. The regeneration method according to claim 1, characterized in that: The mass ratio of the filtered heavy metal adsorbed hollow microspheres to the backwash solution is 1:(2~60).

3. The regeneration method according to claim 1, characterized in that: The number of backwashing is 1 to 5 times, and the time of each backwashing is 0.2 to 6 hours.

4. The regeneration method according to claim 1 or 3, characterized in that: The backwashing comprises: mixing the filtered heavy metal adsorbed hollow microspheres with the backwashing solution and shaking them to obtain pre-treated microspheres; The mass ratio of the filtered heavy metal adsorbing hollow microspheres to the backwashing solution is 1: (3-50); the oscillation rate is 50-250 r / min.

5. The regeneration method according to claim 1, characterized in that: The concentration of calcium chloride in the cross-linking agent is 1-20 g / L.

6. The regeneration method according to claim 1, characterized in that: The mass ratio of the pretreated microspheres to the crosslinking agent is 1:(3-15).

7. The regeneration method according to claim 1, characterized in that: The cross-linking is carried out under stirring conditions, and the cross-linking time is 0.5 to 4 hours.

8. The regeneration method according to claim 1, characterized in that: The drying temperature is 40-60° C., and the drying time is 4-12 hours.

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