Remediation agent for lead-cadmium combined pollutants and preparation and application thereof

Abstract

The application provides a lead-cadmium composite pollutant remediation agent and preparation and application thereof. The lead-cadmium composite pollutant remediation agent is in a microspheric core-shell structure, the core-shell structure comprises an inner core and an outer shell, the inner core is an amorphous iron-manganese oxide, and the outer shell is a sodium alginate-chitosan composite slow-release material. Compared with the prior art, the lead-cadmium composite pollutant remediation agent has good slow-release performance and stable slow-release performance. The amorphous iron-manganese oxide can be slowly released into contaminated soil and contaminated water, so that the lead and cadmium in the contaminated soil and contaminated water can be simultaneously removed. The removal rate of lead can reach more than 99%, and the removal rate of cadmium can reach more than 70%.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of heavy metal pollution remediation, in particular to a lead and cadmium composite pollutant remediation agent and its preparation and application. BACKGROUND

[0002] The heavy metal pollutant remediation agent materials developed at the present stage are mostly short-range governance for single property heavy metal pollution, and less attention is paid to long-term remediation of composite heavy metals Pb and Cd pollution.

[0003] At present, the commonly used soil lead, cadmium and arsenic heavy metal pollution stable remediation technology can be divided into physical remediation technology, biological remediation technology and chemical solidification / stabilization remediation technology. Among them, the physical remediation technology is not suitable for soil with large pollution area, the biological remediation technology has high environmental requirements, and the chemical solidification / stabilization remediation technology has relatively good comprehensive treatment effect, and is the mainstream technology for remediation of contaminated soil at home and abroad. At present, various traditional stabilizing materials used in chemical remediation technology, such as clay minerals, biological organic matter and metal oxides, are mostly limited to single heavy metal pollution, and mainly for short-range single remediation, which cannot solve the problem of slow migration of composite heavy metals in soil and long-term pollution.

[0004] In the existing research, the heavy metal soil remediation agent mainly repairs single heavy metal, and cannot repair heavy metal composite pollution at the same time. Or when repairing heavy metal composite pollution soil, the slow-release effect is poor, and the repair timeliness is short.

[0005] Therefore, it is necessary to provide a lead and cadmium composite pollutant remediation agent to solve the problems of the existing remediation agent that cannot repair lead and cadmium composite pollution at the same time, poor slow-release effect and the like, and provide a new idea and material basis for heavy metal lead and cadmium pollution treatment in soil. SUMMARY

[0006] The main purpose of the present application is to provide a lead and cadmium composite pollutant remediation agent and its preparation and application, which aims to solve the problems of the existing remediation agent that cannot repair lead and cadmium composite pollution at the same time, poor slow-release effect and the like.

[0007] To achieve the above purpose, the present application provides a lead and cadmium composite pollutant remediation agent, which is a core-shell structure in the form of microspheres, the core-shell structure comprises a core and a shell, the core is amorphous iron-manganese oxide, and the shell is sodium alginate-chitosan composite slow-release material.

[0008] The present application also provides a preparation method of a lead and cadmium composite pollutant remediation agent, comprising the following steps:

[0009] S1, providing amorphous iron-manganese oxide particles.

[0010] S2, mixing the amorphous iron-manganese oxide particles with a sodium alginate solution and adding an anionic surfactant, ultrasonic dispersion to obtain a dispersion liquid.

[0011] S3, providing a chitosan solution, mixing the chitosan solution with the dispersion liquid to obtain a mixed liquid.

[0012] S4, mixing the mixed liquid and an emulsified solution to obtain a suspension emulsion; cross-linking the suspension emulsion with calcium chloride to obtain the lead-cadmium compound pollutant remediation agent; wherein the mass fraction of chitosan in the suspension emulsion is 10-30%, and the diameter of the microspheres of the lead-cadmium compound pollutant remediation agent is less than 1 mm.

[0013] Further, in step S1, the preparation method of the amorphous iron-manganese oxide particles comprises mixing potassium permanganate and ferrous sulfate, and performing microwave hydrothermal reaction to obtain the amorphous iron-manganese oxide particles; wherein the mass-volume ratio of the potassium permanganate, the ferrous sulfate and water is 0.2-0.6 g: 0.1-0.3 g: 20-40 mL; the microwave hydrothermal reaction is performed under the condition of pH=2-4, and the reaction time is 24-72 min.

[0014] Further, in step S2, the mass-volume ratio of the amorphous iron-manganese oxide particles, sodium alginate and water is 0.1-0.3 g: 0.1-0.5 g: 40-60 mL.

[0015] Further, in step S2, the anionic surfactant comprises sodium dodecyl sulfonate, primary alkyl sulfonate, alpha-sulfo fatty acid methyl ester or sodium cocoyl oxyethyl sulfonate; and the ultrasonic dispersion time is 10-20 min.

[0016] Further, in step S3, the preparation method of the chitosan solution is specifically dissolving chitosan in acetic acid solution; wherein the mass-volume ratio of the chitosan, the acetic acid and water is 2-4 g: 2-4 g: 80-120 mL.

[0017] Further, in step S4, the emulsified solution comprises liquid paraffin, Span and water mixed according to the volume ratio of 1-5: 0.5-1.5: 4-8; and the mixed volume ratio of the chitosan solution and the dispersion liquid is 7: 3-9: 1.

[0018] Further, in step S4, the cross-linking reaction specifically comprises injecting and titrating the suspension emulsion into a calcium chloride solution to obtain the lead-cadmium compound pollutant remediation agent; wherein the injection and titration height is 0.5-2 cm; and the injection and titration flow rate is 0.25-4 mL / min.

[0019] Further, the cross-linking reaction step is followed by solid-liquid separation, washing and drying in step S4; the solid-liquid separation process comprises separation by filtration; the washing process comprises using petroleum ether as a washing agent; and the drying process comprises freeze drying at a temperature of -50 to -40 DEG C for 12 to 24 hours.

[0020] The application also provides a use of the lead-cadmium compound pollutant remediation agent, and the lead-cadmium compound pollutant remediation agent is used to remediate contaminated soil and water bodies; the initial lead concentration in the lead-cadmium compound pollutant is greater than or equal to 50 mg / L, and the initial cadmium concentration is greater than or equal to 50 mg / L; and the dosage concentration of the lead-cadmium compound pollutant remediation agent is less than or equal to 2 g / L.

[0021] The application achieves the following beneficial effects:

[0022] The lead-cadmium compound pollutant remediation agent provided by the application has a core-shell structure in the form of microspheres. The core-shell structure comprises an inner core and an outer shell. The inner core is an amorphous iron-manganese oxide, and the outer shell is a sodium alginate-chitosan composite slow-release material. The core-shell structure has good slow-release performance and stable slow-release performance. The amorphous iron-manganese oxide can be slowly released into contaminated soil and water bodies, thereby achieving the synchronous removal of lead and cadmium in the contaminated soil and water bodies. The removal rate of lead can be greater than 99%, and the removal rate of cadmium can be greater than 70%.

[0023] The preparation method of the lead-cadmium compound pollutant remediation agent provided by the application comprises the following steps: preparing amorphous iron-manganese oxide particles as the inner core material of the lead-cadmium compound pollutant remediation agent by microwave hydrothermal synthesis, and preparing a self-assembled outer shell of the lead-cadmium compound pollutant remediation agent by emulsion cross-linking to encapsulate the iron-manganese oxide particles in the outer shell. The obtained lead-cadmium compound pollutant remediation agent has stable slow-release performance during the entire lead and cadmium removal period. The preparation method is simple and convenient to operate. All the preparation reagents used are non-toxic and harmless. No waste liquid is discharged during the entire material synthesis and slow-release heavy metal removal process, and no environmental pollution is caused. The method is green and environmentally friendly. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained according to the structures shown in the drawings without any creative effort.

[0025] Figure 1 The figure is a schematic diagram of the preparation process of the lead-cadmium compound pollutant remediation agent of the application.

[0026] Figure 2The external and sectioned morphology characterization diagram of the lead-cadmium composite pollutant repair agent obtained in Example 1 is shown in Figure 1, wherein a is the external morphology diagram of the lead-cadmium composite pollutant repair agent, b is the sectioned diagram of the lead-cadmium composite pollutant repair agent, c is the external morphology diagram of the lead-cadmium composite pollutant repair agent after dehydration and drying, and d is the sectioned diagram of the lead-cadmium composite pollutant repair agent after dehydration and drying.

[0027] Figure 3 The X-ray diffraction diagram of the amorphous iron-manganese oxide particles obtained in step 1 of Example 1 is shown in Figure 2.

[0028] Figure 4 The lead release performance diagram of the lead-cadmium composite pollutant repair agent obtained in Examples 1-3 is shown in Figure 3.

[0029] Figure 5 The cadmium release performance diagram of the lead-cadmium composite pollutant repair agent obtained in Examples 1-3 is shown in Figure 4.

[0030] Figure 6 The swelling performance diagram of the lead-cadmium composite pollutant repair agent obtained in Examples 1-3 is shown in Figure 5.

[0031] Figure 7 The drug loading and encapsulation efficiency diagram of the lead-cadmium composite pollutant repair agent obtained in Examples 1-3 is shown in Figure 6.

[0032] Figure 8 The comparison diagram of the release performance of different materials on lead and cadmium in Comparative Example 1 is shown in Figure 7, wherein a is the comparison diagram of the release performance on lead, and b is the comparison diagram of the release performance on cadmium.

[0033] The implementation, functional features and advantages of the present application will be further described with reference to the accompanying drawings. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0035] It should be noted that the following examples and features in the examples can be combined with each other without conflict. It should also be understood that the terms used in the embodiments of the present application are for describing specific specific embodiments, and are not intended to limit the protection scope of the present application.

[0036] Unless otherwise defined, all technical and scientific terms used in the present disclosure have the same meanings as those commonly understood by one of ordinary skill in the art in the field of the technology to which this application pertains and as described in the present disclosure, and any method and material similar or equivalent in function to those described herein can be used to implement the present application. It should be understood that, as a kind of description to the present application, without affecting the actual understanding of the technical scheme of the present application, "2Theta (degree)" can be represented as 2 times the diffraction angle, "Intensity (a.u.)" can be represented as intensity or saturation, "Time (h)" can be represented as the slow-release duration, "Removal efficiency (%)" can be represented as removal efficiency (i.e. slow-release performance), "Swelling ratio (%)" can be represented as swelling ratio, "Drug loading efficiency (%)" can be represented as drug loading, and "Entrapment efficiency (%)" can be represented as entrapment efficiency.

[0037] When the embodiments give numerical ranges, it should be understood that, unless otherwise stated by the present application, each numerical range of two endpoints and any one numerical value between the two endpoints can be selected. The test method in the following examples, which is not specified in the specific conditions, is generally carried out according to the conventional conditions, or according to the conditions recommended by the manufacturer. The materials or reagents required in the following examples, unless otherwise specified, are commercially available.

[0038] In order to efficiently and synchronously repair the lead-cadmium combined pollutants, and to have good slow-release performance in the lead-cadmium combined pollutants, the present application provides a lead-cadmium combined pollutant repair agent, which is a microspherical core-shell structure, the core-shell structure comprises a core and a shell, the core is an amorphous iron-manganese oxide, and the shell is a sodium alginate-chitosan composite slow-release material.

[0039] The core-shell structure has good slow-release performance; the slow-release performance is stable. The amorphous iron-manganese oxide can be slowly released into the contaminated soil and water body, so as to realize the synchronous removal of lead and cadmium in the contaminated soil and water body. The removal rate of lead can reach more than 99%, and the removal rate of cadmium can reach more than 70%.

[0040] The present application also provides a preparation method of the lead-cadmium combined pollutant repair agent, comprising the following steps:

[0041] S1, providing amorphous iron-manganese oxide particles. It should be noted that the amorphous iron-manganese oxide particles are a kind of weakly crystalline particle material, which has a large specific surface area and a large number of active hydroxyl groups on the surface, and can synchronously remove lead and cadmium in the contaminated environment.

[0042] S2, mixing the amorphous iron-manganese oxide particles with a sodium alginate solution and adding an anionic surfactant, ultrasonic dispersion, to obtain a dispersion. It should be noted that sodium alginate is a high molecular polymer linked by β-D-mannuronic acid and α-L-guluronic acid, and its large number of carboxyl groups can exhibit polyanion behavior in aqueous solution and have certain adhesion.

[0043] The chemical structure of sodium alginate is as follows:

[0044] S3, providing a chitosan solution, mixing the dispersion to obtain a mixed solution.

[0045] S4, mixing the mixed solution and the emulsion solution to obtain a suspension emulsion; cross-linking the suspension emulsion with calcium chloride to obtain a lead-cadmium compound pollutant repair agent; wherein the mass fraction of chitosan in the suspension emulsion is 10-30%, and the diameter of the microspheres of the lead-cadmium compound pollutant repair agent is <1mm.

[0046] Specifically, the preparation process of the lead-cadmium compound pollutant repair agent can be as shown in the following schematic diagram: Figure 1 Wherein, "CS" can represent chitosan, "SA+AIMOP" can represent the mixture of sodium alginate solution and amorphous iron-manganese oxide particles, "LP+Span-80" can represent the mixture of liquid paraffin and Span-80, "Water phase" can represent the aqueous phase, "Oil" can represent the organic phase, and "Slow release" can represent slow release.

[0047] The above method is to prepare the core material of the lead-cadmium compound pollutant repair agent by microwave hydrothermal method, and to prepare the self-assembled shell of the lead-cadmium compound pollutant repair agent by emulsion cross-linking to encapsulate the iron-manganese oxide particles therein, so that the obtained lead-cadmium compound pollutant repair agent has stable slow release performance during the entire lead and cadmium removal period. The preparation method is simple and convenient to operate; all the preparation reagents used are non-toxic and harmless, and there is no waste liquid discharge during the entire material synthesis and heavy metal slow release removal process, which will not pollute the environment and is green and environmentally friendly.

[0048] Further, in step S1, the preparation method of the amorphous iron-manganese oxide particles includes mixing potassium permanganate and ferrous sulfate and performing microwave hydrothermal reaction to obtain amorphous iron-manganese oxide particles; wherein the mass-volume ratio of potassium permanganate, ferrous sulfate and water is 0.2-0.6g: 0.1-0.3g: 20-40mL; the microwave hydrothermal reaction is performed under the condition of pH=2-4, and the reaction time is 24-72min.

[0049] Specifically, in the aqueous solution of potassium permanganate and ferrous sulfate, ammonia water or sulfuric acid is added to adjust the pH, and then the ultrasonic dispersion operation, mechanical stirring operation are sequentially performed, and then the microwave hydrothermal reaction is performed until the reaction is completed, and the separation operation is performed to obtain the amorphous iron manganese oxide particles which are washed and dried for standby. The separation operation here can be to separate the liquid after the microwave hydrothermal reaction by using a suction filtration device; the washing operation can be to repeatedly wash the amorphous iron manganese oxide particles obtained after separation until the filtrate becomes clear.

[0050] Among them, potassium permanganate and ferrous sulfate can generate amorphous iron manganese oxide particles under microwave conditions, and the reaction principle is mainly as follows:

[0051]

[0052] Further, in step S2, the mass-volume ratio of amorphous iron manganese oxide particles, sodium alginate and water is 0.1-0.3 g:0.1-0.5 g:40-60 mL.

[0053] Further, in step S2, the anionic surfactant includes sodium dodecyl sulfonate, primary alkyl sulfonate, alpha-sulfo fatty acid methyl ester or sodium cocoyl oxyethyl sulfonate; the ultrasonic dispersion time is 10-20 min.

[0054] Further, in step S3, the preparation method of the chitosan dissolving solution is specifically to dissolve chitosan in acetic acid solution; wherein the mass-volume ratio of chitosan, acetic acid and water is 2-4 g:2-4 g:80-120 mL.

[0055] Further, in step S4, the emulsion solution includes liquid paraffin, span and water mixed according to the volume ratio of 1-5:0.5-1.5:4-8; the mixed volume ratio of chitosan dissolving solution and dispersion solution is 7:3-9:1.

[0056] Specifically, liquid paraffin, span and water can be mixed in the order of 1-5 mL:0.5-1.5 mL:4-8 mL by ultrasonic dispersion and then mechanical stirring to obtain an emulsion solution.

[0057] Further, in step S4, the cross-linking reaction specifically includes injecting and titrating the suspension emulsion into the calcium chloride solution to obtain a lead-cadmium combined pollutant repair agent; wherein the injection titration height is 0.5-2 cm; the injection titration flow rate is 0.25-4 mL / min. Under the titration height and flow rate conditions, the prepared lead-cadmium combined pollutant repair agent has uniform particle size, regular morphology and no obvious tailing phenomenon.

[0058] Further, the cross-linking reaction step in step S4 further comprises solid-liquid separation, washing and drying; the solid-liquid separation process comprises separation by filtration; the washing process comprises using petroleum ether as a washing agent; and the drying process comprises freeze drying at -50 to -40℃ for 12 to 24 hours, so as to sufficiently remove water molecules in surface bonding state and adsorption state of the repairing agent without affecting the overall structure of the repairing agent. Specifically, the solid-liquid separation can be performed by using a Buchner funnel.

[0059] The application further provides a use of the lead-cadmium compound pollutant repairing agent. The lead-cadmium compound pollutant repairing agent is used to repair contaminated soil and water, wherein the initial lead concentration of the lead-cadmium compound pollutant is greater than or equal to 50 mg / L, the initial cadmium concentration is greater than or equal to 50 mg / L, and the dosage concentration of the lead-cadmium compound pollutant repairing agent is less than or equal to 2 g / L.

[0060] In order to further understand the application, examples are provided as follows:

[0061] Example 1

[0062] 1. Preparation of amorphous iron-manganese oxide particles

[0063] 0.2 g of potassium permanganate, 0.1 g of ferrous sulfate and 20 mL of water are mixed, and ammonia water and / or sulfuric acid are added to adjust the pH to 2; ultrasonic dispersion is performed for 5 min, mechanical stirring is performed for 10 min, and microwave hydrothermal reaction is performed for 24 min until the reaction is completed, to obtain amorphous iron-manganese oxide particles; the particles are washed and dried for standby use.

[0064] 2. Preparation of a dispersion

[0065] 0.1 g of the dried amorphous iron-manganese oxide particles obtained in step 1 and 0.1 g of sodium alginate are uniformly stirred, 20 mg of an anionic surfactant sodium dodecyl sulfonate is added, and 40 mL of water is added, and ultrasonic dispersion is performed for 10 min until the dispersion is uniform, to obtain a dispersion for standby use.

[0066] 3. Preparation of a mixed solution

[0067] 3% chitosan is dissolved in a 3% dilute acetic acid solution to obtain a chitosan solution.

[0068] 7 mL of the above chitosan solution and 3 mL of the dispersion obtained in step 2 are mixed to obtain a mixed solution.

[0069] 4. Preparation of a suspension solution

[0070] 2.5 mL of liquid paraffin, 1.5 mL of Span-80 and 4 mL of water are mixed to obtain an emulsified solution.

[0071] The obtained emulsified solution was mixed with the mixed solution obtained in step 3, stirred for 10 min, and ultrasonically treated for 5 min to mix uniformly, to obtain a suspension emulsion.

[0072] 5. Preparation of a lead-cadmium combined pollutant remediation agent

[0073] The suspension emulsion obtained in step 4 was crosslinked by injection titration using calcium chloride, and was filtered, washed with petroleum ether, and freeze-dried at -45℃ for 16 h to obtain a lead-cadmium combined pollutant remediation agent. The titration height was 0.5 cm, and the titration flow rate was 0.25 mL / min.

[0074] Example 2

[0075] 1. Preparation of amorphous iron-manganese oxide particles

[0076] 0.3 g of potassium permanganate, 0.2 g of ferrous sulfate, and 30 mL of water were mixed, and ammonia water and / or sulfuric acid were added to adjust the pH to 3; ultrasonic dispersion was performed for 5 min, mechanical stirring was performed for 10 min, and microwave hydrothermal reaction was performed for 36 min until the reaction was completed, to obtain amorphous iron-manganese oxide particles; the particles were washed and dried for standby use.

[0077] 2. Preparation of a dispersion

[0078] 0.2 g of the dried amorphous iron-manganese oxide particles obtained in step 1 and 0.3 g of sodium alginate were uniformly stirred, 20 mg of an anionic surfactant alkyl sulfonate was added, and 50 mL of water was added, and ultrasonic dispersion was performed for 15 min until the dispersion was uniform, to obtain a dispersion for standby use.

[0079] 3. Preparation of a mixed solution

[0080] 3% chitosan was dissolved in a 3% dilute acetic acid solution to obtain a chitosan solution.

[0081] 8 mL of the above chitosan solution and 2 mL of the dispersion obtained in step 2 were mixed to obtain a mixed solution.

[0082] 4. Preparation of a suspension solution

[0083] 3 mL of liquid paraffin, 2 mL of Span-80, and 6 mL of water were mixed to obtain an emulsified solution.

[0084] The obtained emulsified solution was mixed with the mixed solution obtained in step 3, stirred for 10 min, and ultrasonically treated for 5 min to mix uniformly, to obtain a suspension emulsion.

[0085] 5. Preparation of a lead-cadmium combined pollutant remediation agent

[0086] The cross-linking reaction of the suspension emulsion obtained in step 4 is carried out by injection titration using calcium chloride, and the product is separated by filtration, washed with petroleum ether, and freeze-dried at -50°C for 12h to obtain the lead-cadmium compound remediation agent. The titration height is 1cm and the titration flow rate is 2mL / min.

[0087] Example 3

[0088] 1. Preparation of amorphous iron-manganese oxide particles

[0089] 0.4g of potassium permanganate, 0.1g of ferrous sulfate, and 30mL of water are mixed, and ammonia water and / or sulfuric acid are added to adjust the pH to 4; ultrasonic dispersion is performed for 5min, mechanical stirring is performed for 10min, and microwave hydrothermal reaction is performed for 72min until the reaction is completed to obtain amorphous iron-manganese oxide particles; the product is washed and dried for standby use.

[0090] 2. Preparation of dispersion liquid

[0091] 0.3g of the dried amorphous iron-manganese oxide particles obtained in step 1 and 0.5g of sodium alginate are uniformly stirred, 20mg of anionic surfactant α-sulfo fatty acid methyl ester or sodium cocoyl oxyethyl sulfonate is added, and 60mL of water is added, and ultrasonic dispersion is performed for 20min until the dispersion is uniform to obtain a dispersion liquid for standby use.

[0092] 3. Preparation of mixed solution

[0093] 3% chitosan is dissolved in 3% dilute acetic acid solution to obtain a chitosan dissolution solution.

[0094] 9mL of the above chitosan dissolution solution and 1mL of the dispersion liquid obtained in step 2 are mixed to obtain a mixed solution.

[0095] 4. Preparation of suspension solution

[0096] 5mL of liquid paraffin, 1.5mL of span-80, and 8mL of water are mixed to obtain an emulsified solution.

[0097] The obtained emulsified solution is mixed with the mixed solution obtained in step 3, stirred for 10min, and ultrasonically dispersed for 5min to obtain a suspension emulsion.

[0098] 5. Preparation of lead-cadmium compound remediation agent

[0099] The cross-linking reaction of the suspension emulsion obtained in step 4 is carried out by injection titration using calcium chloride, and the product is separated by filtration, washed with petroleum ether, and freeze-dried at -40°C for 24h to obtain the lead-cadmium compound remediation agent. The titration height is 2cm and the titration flow rate is 4mL / min.

[0100] Analysis Example 1

[0101] Morphological and structural characterization of the lead-cadmium composite pollutant remediation agent obtained in Example 1

[0102] 1. Comparison of external and slice morphology characterization of lead-cadmium composite pollutant remediation agents

[0103] The morphology and size of the lead-cadmium composite pollutant remediation agent were observed using a Tecnai F2 G20 high-resolution field emission transmission electron microscope (FEI, USA). Figure 2 As shown. From Figure 2 As can be seen from parts a and b, the original lead-cadmium composite pollutant remediation agent, namely the slow-release microsphere particles, exhibits an average diameter of about 900 μm, presenting a relatively uniform coarse spherical shape; the overall sample is relatively uniformly dispersed, but after a period of stillness, some samples show some agglomeration.

[0104] Compared to the external morphology of lead-cadmium composite pollutant remediation agents, the sliced ​​lead-cadmium composite pollutant remediation agents also exhibit a uniform, coarse spherical shape overall, such as... Figure 2 As shown in sections c and d, the interior of the slice has a porous and loose morphology, which is typical of calcium alginate microspheres.

[0105] 2. Characterization of the crystal structure of the amorphous iron-manganese oxide particles obtained in step 1 of Example 1

[0106] X-ray diffraction energy dispersive spectroscopy was used to characterize the crystal structure of amorphous iron-manganese oxide particles. For example... Figure 3 As shown, the XRD pattern shows weak diffraction peaks, with weak characteristic peaks at 30°-40° and 45°-55°, indicating poor crystal structure and no obvious characteristic diffraction peaks. This suggests that the iron-manganese oxide particles exist in an amorphous structure. Amorphous iron-manganese oxide particles may have a higher specific surface area, which is beneficial for the fixation of heavy metals such as lead and cadmium.

[0107] Example 4

[0108] Performance Study of Lead-Cadmium Composite Pollutant Remediation Agents Prepared in Examples 1-3 on Lead and Cadmium

[0109] Under optimized experimental conditions, lead and cadmium ion solutions with a concentration of 1000 mg / L were prepared and serially diluted to concentrations of 0.5–100 mg / L. The pH was adjusted to the desired values ​​(4–7) using HNO3 and NaOH solutions. A pH meter (pHS-3G, Shanghai Leici) was used for pH testing. The concentrations of lead and cadmium ions were analyzed using an ICP-OES analyzer, and values ​​from three different adsorption bands were taken. The minimum RSD was selected as the data reference.

[0110] 400 mg of lead-cadmium composite pollutant remediation agent was mixed with 200 mL of lead and cadmium ion-containing solution, the fixed removal temperature was 30°C, and the oscillation box was oscillated at 150 r / min for 30 d. The slow-release performance and adsorption of the lead-cadmium composite pollutant remediation agent were explored, as follows.

[0111] 1. Slow-release performance of lead-cadmium composite pollutant remediation agent for lead

[0112] The initial lead concentration was fixed at 50 mg / L, and the initial pH was 7. The slow-release performance of lead is shown in Figure 4 , wherein Figure 4 The slow-release performance of the lead-cadmium composite pollutant remediation agent prepared in Examples 1-3 for lead in the middle part of 0-50 h can be seen to have a significant improvement in the fixation efficiency of lead, from 13.4% to 97.7%. By comparison, it can be found that the slow-release microspheres with 30% chitosan content have the best effect. As shown in Figure 4 The slow-release performance of lead can be seen to have a faster fixation rate. All slow-release fixatives reach a fixation efficiency close to 100% on the fourth day, and the lead in the fixative remains stable without dissolution and release in the subsequent 30 d experiment.

[0113] 2. Slow-release performance of lead-cadmium composite pollutant remediation agent for cadmium

[0114] The initial cadmium concentration was fixed at 50 mg / L, and the initial pH was 7. As shown in Figure 5 The slow-release performance of cadmium can be seen to be good. In the initial fourteen days, the fixation efficiency of cadmium has a certain improvement, and different chitosan ratios of slow-release fixatives all have a certain burst release phenomenon.

[0115] Among them, the lead-cadmium composite pollutant remediation agent prepared in Example 1 (chitosan content 10%) had a burst release phenomenon around the 6th day, and basically reached a fixed balance around the 9th day, with a balance fixation rate of 84.5%;

[0116] The lead-cadmium composite pollutant remediation agent prepared in Example 2 (chitosan content 20%) had a burst release phenomenon around the 11th day, and basically reached a fixed balance around the 18th day, with a balance fixation rate of 75.4%;

[0117] The lead-cadmium composite pollutant remediation agent prepared in Example 3 (chitosan content 30%) had a burst release phenomenon around the 14th day, and basically reached a fixed balance around the 21st day, with a balance fixation rate of 72.1%. By comparison, it can be found that the slow-release effect of the lead-cadmium composite pollutant remediation agent prepared in Example 3 is the best, but the fixation efficiency of the lead-cadmium composite pollutant remediation agent prepared in Example 1 is the highest.

[0118] 3. Swelling efficiency of lead-cadmium composite pollutant remediation agent

[0119] To explore the hydrophilic effect of the lead-cadmium combined pollutant remediator, the swelling efficiency of the lead-cadmium combined pollutant remediator was explored, as shown in Figure 6

[0120] It can be found that the swelling degree of the lead-cadmium combined pollutant remediator is related to the porosity of the polymer network and the interaction between the polymer and the solvent. As a component of the lead-cadmium combined pollutant remediator, the lead-cadmium combined pollutant remediator prepared in Example 1 exhibits the best hydrophilicity. With the increase of the proportion of the chitosan component, the hydrophilicity of the lead-cadmium combined pollutant remediator gradually decreases. Under neutral conditions, the order of the water absorption of the lead-cadmium combined pollutant remediator is the lead-cadmium combined pollutant remediator prepared in Example 1 (chitosan content 10%) > the lead-cadmium combined pollutant remediator (chitosan content 20%) > the lead-cadmium combined pollutant remediator prepared in Example 3 (chitosan content 30%).

[0121] 4. Swelling drug loading and encapsulation efficiency of the lead-cadmium combined pollutant remediator

[0122] The drug loading and encapsulation efficiency of the slow-release microspheres were explored, as shown in Figure 7 It can be found that the drug loading and encapsulation efficiency of the slow-release microspheres decrease with the increase of the proportion of the chitosan component in the lead-cadmium combined pollutant remediator. Under neutral conditions, the order of the drug loading and encapsulation efficiency of the lead-cadmium combined pollutant remediator is the lead-cadmium combined pollutant remediator prepared in Example 1 (chitosan content 10%) > the lead-cadmium combined pollutant remediator (chitosan content 20%) > the lead-cadmium combined pollutant remediator prepared in Example 3 (chitosan content 30%). Among them, the highest drug loading and encapsulation efficiency of the lead-cadmium combined pollutant remediator prepared in Example 1 (chitosan content 10%) reaches 5.14% and 42.13%, respectively.

[0123] Comparative Example 1

[0124] Comparison of the lead and cadmium slow-release fixation performance of the lead-cadmium combined pollutant remediator prepared in Example 3 (chitosan content 30%) and the traditional stabilizing materials (ferroferric oxide particles, cellulose and montmorillonite) used in the current chemical remediation technology

[0125] Under the optimized experimental conditions, the lead and cadmium ion solution with a concentration of 1000 mg / L was prepared and gradiently diluted to a concentration of (0.5-100 mg / L). The pH value was adjusted to the required value (4-7) by using HNO3 and NaOH solutions. The pH testing instrument was a pH meter (pHS-3G, Shanghai Ray Meter); the lead and cadmium ion concentration was analyzed and determined by an ICP-OES measuring instrument, and the minimum RSDs value was selected as the data reference.

[0126] ​400mg of various repair agents were mixed with 200ml of lead and cadmium ion-containing solution, the removal temperature was fixed at 30°C, the oscillation box was oscillated at 150r / min for 30d, and the slow-release performance and adsorption of the lead and cadmium composite pollutant repair agent were explored.

[0127] The initial lead and cadmium concentration was fixed at 50mg / L, and the initial pH was 7. Figure 8 The slow-release performance of the lead and cadmium composite pollutant repair agent (30% chitosan content) prepared in Example 3 can be compared with that of the same condition parameters, ferroferric oxide particles, cellulose, montmorillonite and the slow-release performance of the lead and cadmium composite pollutant repair agent (30% chitosan content) prepared in Example 3.

[0128] From Figure 8 As can be seen from a, the lead and cadmium composite pollutant repair agent (30% chitosan content) prepared in Example 3 is better than the other three materials in terms of lead removal rate and slow-release performance. Among them, the removal of lead by montmorillonite and ferroferric oxide particles basically reached equilibrium in 1h, with an equilibrium removal rate of about 52.6% and 29.6%, and the removal of lead by cellulose basically reached equilibrium in 4h, with an equilibrium removal rate of about 42.4%. It is obvious that the removal rate and slow-release performance of the above three materials are weaker than that of the lead and cadmium composite pollutant repair agent (30% chitosan content) prepared in Example 3 (4d, 100%).

[0129] From Figure 8 As can be seen from b, for cadmium, montmorillonite and ferroferric oxide particles basically reached equilibrium in 2-4h, with an equilibrium removal rate of about 23.9% and 16.4%, and cellulose basically reached equilibrium in 4-8h, with an equilibrium removal rate of about 34.0%. The removal rate and slow-release performance of the above three materials are weaker than that of the slow-release type fixing agent (21d, 72.1%) described in the patent. According to the above results, it is speculated that montmorillonite and ferroferric oxide particles are mainly physical adsorption, and the removal of lead and cadmium by cellulose includes physical adsorption and chemical adsorption, so the limited specific surface area, fewer active sites and the original structure not designed limit the effect of traditional materials in slow-release removal of heavy metals.

[0130] The lead and cadmium composite pollutant repair agent (30% chitosan content) prepared in Example 3 has a large specific surface area of amorphous iron and manganese oxide particles in the core material, a large number of active sites, and a specific core-shell structure design, which can exhibit good slow-release performance in solution medium.

[0131] To sum up, in the above technical scheme of the present application, the above is only a preferred embodiment of the present application, and does not limit the patent scope of the present application, and any equivalent structural transformation made under the technical concept of the present application, using the content of the present application specification and drawings, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A lead-cadmium complex contaminant remediation agent, characterized by, The lead-cadmium compound pollutant remediation agent is in the form of microspheres with a core-shell structure, the core-shell structure comprises a core and a shell, the core is an amorphous iron-manganese oxide, and the shell is a sodium alginate-chitosan composite slow-release material; the diameter of the microspheres of the lead-cadmium compound pollutant remediation agent is less than 1 mm. ​ 2. A method for preparing a lead-cadmium complex contaminant remediation agent, characterized by, The method comprises the steps of: S1, providing amorphous iron-manganese oxide particles; S2, mixing the amorphous iron-manganese oxide particles with a sodium alginate solution and adding an anionic surfactant, and ultrasonic dispersion to obtain a dispersion liquid; the mass-volume ratio of the amorphous iron-manganese oxide particles, sodium alginate and water is 0.1-0.3 g: 0.1-0.5 g: 40-60 mL; S3, providing a chitosan dissolved solution, and mixing the chitosan dissolved solution with the dispersion liquid to obtain a mixed liquid; S4, mixing the mixed liquid with an emulsifying solution to obtain a suspension emulsion, and performing cross-linking reaction on the suspension emulsion and calcium chloride to obtain the lead-cadmium compound pollutant remediation agent; wherein the mass fraction of chitosan in the suspension emulsion is 10-30%; the lead-cadmium compound pollutant remediation agent is in the form of microspheres with a core-shell structure, the core-shell structure comprises a core and a shell, the core is an amorphous iron-manganese oxide, and the shell is a sodium alginate-chitosan composite slow-release material; the diameter of the microspheres of the lead-cadmium compound pollutant remediation agent is less than 1 mm; and the emulsifying solution comprises liquid paraffin, span and water mixed in a volume ratio of 1-5: 0.5-1.5: 4-8.

3. The method of claim 2, wherein the lead-cadmium complex contaminant remediation agent is prepared by the steps of: (a) mixing a lead compound and a cadmium compound in a solvent; (b) adding a reducing agent to the mixture; and (c) adding a chelating agent to the mixture. In step S1, the preparation method of the amorphous iron-manganese oxide particles comprises mixing potassium permanganate and ferrous sulfate, and performing microwave hydrothermal reaction to obtain the amorphous iron-manganese oxide particles; wherein the mass-volume ratio of the potassium permanganate, the ferrous sulfate and water is 0.2-0.6 g: 0.1-0.3 g: 20-40 mL; The microwave hydrothermal reaction is performed under the condition of pH=2-4, and the reaction time is 24-72 min.

4. The method of claim 2, wherein the lead-cadmium complex contaminant remediation agent is prepared by the steps of: (a) mixing a lead compound and a cadmium compound in a solvent; (b) adding a reducing agent to the mixture; and (c) adding a chelating agent to the mixture. In step S2, the anionic surfactant comprises sodium dodecyl sulfonate, primary alkyl sulfonate, alpha-sulfo fatty acid methyl ester or sodium cocoyl oxyethyl sulfonate; The ultrasonic dispersion lasts for 10-20 min.

5. The method of claim 2, wherein the lead-cadmium complex contaminant remediation agent is prepared by the steps of: (a) mixing a lead compound and a cadmium compound in a solvent; (b) adding a reducing agent to the mixture; and (c) adding a chelating agent to the mixture. In step S3, the preparation method of the chitosan dissolved solution is specifically dissolving chitosan in an acetic acid solution; wherein the mass-volume ratio of the chitosan, the acetic acid and water is 2-4 g: 2-4 g: 80-120 mL.

6. The method of claim 2, wherein the lead-cadmium complex contaminant remediation agent is prepared by the steps of: (a) mixing a lead compound and a cadmium compound in a solvent; (b) adding a reducing agent to the mixture; and (c) adding a chelating agent to the mixture. In step S4, the mixing volume ratio of the chitosan dissolved solution and the dispersion liquid is 7: 3-9:

1.

7. The method of claim 2, wherein the lead-cadmium complex contaminant remediation agent is prepared by the steps of: (a) mixing a lead compound and a cadmium compound in a solvent; (b) adding a reducing agent to the mixture; and (c) adding a chelating agent to the mixture. In step S4, the cross-linking reaction specifically comprises injecting and titrating the suspension emulsion into a calcium chloride solution to obtain the lead-cadmium compound pollutant remediation agent; wherein the height of the injection and titration is 0.5-2 cm; and the flow rate of the injection and titration is 0.25-4 mL / min.

8. The method of claim 2, wherein the lead-cadmium complex contaminant remediation agent is prepared by the steps of: (a) mixing a lead compound and a cadmium compound in a solvent; (b) adding a reducing agent to the mixture; and (c) adding a chelating agent to the mixture. In step S4, the cross-linking reaction step is followed by solid-liquid separation, washing and drying; The solid-liquid separation process comprises filtration separation; The washing process comprises using petroleum ether as a washing agent; The drying process comprises freeze-drying at a set temperature of-50--40℃ for 12-24 h.

9. Use of a lead-cadmium complex contaminant remediation agent, characterized in that, The lead-cadmium compound pollutant remediation agent as claimed in claim 1 or prepared by the method as claimed in any one of claims 2-8 is used to remediate contaminated soil and water body. The initial lead concentration in the lead-cadmium compound pollutant is ≥50 mg / L, and the initial cadmium concentration is ≥50 mg / L. The dosage concentration of the lead-cadmium compound pollutant remediation agent is ≤2 g / L.

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