Composite fillers, methods of making the same, permeable reactive walls, and applications thereof

Abstract

The present application provides a kind of composite filler, its preparation method, permeable reaction wall and its application.The composite filler includes first component and second component, the first component includes first powder and second powder mixed together, the second component includes peroxymonosulfate PMS as oxidant and third powder and fourth powder mixed together, wherein third powder includes biochar and adsorbed type layered double hydroxide LDH1 loaded on the surface of the biochar, and fourth powder includes the biochar and catalytic type layered double hydroxide LDH2 loaded on the surface of the biochar.The composite filler of the present application can treat the composite pollution of groundwater under the influence of groundwater level fluctuation of unsaturated aquifer.

Description

Technical Field

[0001] This invention relates to the field of groundwater environmental engineering, and more particularly to composite fillers for treating multiple types of pollution in groundwater, their preparation methods, permeable reactive walls (PRBs) using the composite fillers, and methods for treating complex groundwater pollution using PRBs under the influence of groundwater level fluctuations in unsaturated aquifers. The fields covered by this invention include first-level disciplines such as geological resources and geological engineering, environmental science and engineering, and materials science and engineering. Background Technology

[0002] Current PRB (Plasma Reinforced Bioreactor) systems are predominantly large-scale reactors, primarily based on a circulating water multi-layer infiltration ex-situ treatment mechanism. In-situ PRB walls are typically constructed through extensive excavation and filling, or utilize large-scale shallow groundwater treatment systems. When addressing pollutant remediation, existing PRB packing materials are often designed for single pollutant types. During the maintenance phase of remediation, re-excavation is usually employed to replace the packing material and maintain performance. Furthermore, the packing materials are mostly adsorption-type, with reactive packing materials targeting relatively singular pollutants. Existing products offer relatively simple packing material fabrication methods and mature processes. The manufacturing and construction process for PRB structures is straightforward, generally involving material preparation, on-site excavation, material filling, and subsequent excavation, maintenance, and filling.

[0003] Large-scale reaction facilities often involve extraction-type off-site treatment, such as wastewater treatment plants. Due to the large surface space occupied by these facilities, their high construction costs, and the difficulty in site selection, most treatment plants treat groundwater and surface water pollution through off-site extraction and re-release, which is extremely costly among water pollution treatment methods.

[0004] There are also large-scale deep reaction devices, distinct from fixed treatment sites. While these offer some flexibility, the high proportion of ineffective volume in these large-scale devices results in high construction costs for practical applications. The preparation of adsorbent materials or fillers in the products mostly employs common methods for preparing mesoporous materials, generally involving raw material pretreatment followed by calcination. The preparation methods for reactive fillers are more diverse, but the types are fewer. The existing PRB unit structure layout is mostly carried out through excavation followed by backfilling. It is difficult to construct interconnected, wall-like structures underground without excavation.

[0005] The main reason for the technical problems and defects in current PRB products is the high cost of applying and testing new materials or new fillers, which makes it difficult to conduct PRB application research and development. This limits the scope of contact and research methods for technical and testing personnel with new materials or new fillers. Reducing the production and application costs of materials is the main problem faced by PRB in field and indoor testing applications.

[0006] In particular, the existing PRB filler has at least one of the following disadvantages and problems:

[0007] 1. For the existing PRB filler structure, the adsorption material pollution treatment efficiency is low, the reaction material pollution degradation persistence is poor, and the pollution in the unsaturated zone changes with the migration and transformation process of the groundwater level all the year round, which leads to the fact that the existing filler structure cannot maintain high degradation efficiency of the pollutants under the periodic operation of the stratum fixed position.

[0008] 2. When facing the pollutants in the groundwater, the existing reaction-type PRB filler structure has poor structural stability when facing different pollutants, has high solubility, and is easy to become a direct source of secondary pollution in the groundwater. In addition, the reaction-type material also has incomplete reaction, which can be solved by increasing the filler, improving the filler composition, optimizing the wall parameters and reaction form, etc. However, it is still difficult to achieve risk-free degradation for pollutants such as low / high valence compounds or ions, low halogenated compounds and other intermediate products. The existing adsorption-type PRB filler structure has desorption characteristics when the material reaches the adsorption saturation state, which is the main reason for the secondary pollution of this type of material.

[0009] 3. Since the cost of PRB is relatively high, for most of the existing fillers, environmental regeneration is an important means of cost saving. Non-renewable fillers still need to be excavated again and filled with new materials after a period of time, which increases the application cost of PRB. The number of times of regeneration of renewable fillers also shows a lower trend due to the properties of the fillers and the movement of groundwater. The implementation of the regeneration means for renewable fillers is also located in the ex-situ operation (excavation or extraction) and then the corresponding regeneration operation, which is also a major item of expenditure.

[0010] Therefore, there is still a need for a new PRB filler and its preparation process which at least improves any of the above aspects. SUMMARY

[0011] In view of the above deficiencies of the prior art, the purpose of the application is to provide a new composite filler for treating multiple pollution types in groundwater, a preparation method thereof, a permeable reaction wall (PRB) using the new composite filler, and a method for treating composite pollution in groundwater under the influence of groundwater level fluctuation in unsaturated aquifer using the permeable reaction wall.

[0012] In particular, the novel filler of the present application is a novel filler structure using at least two LDHs (layered double hydroxides) and BC (biochar) as base materials, in combination with nZVI (nano zero-valent iron) as a strong reducing agent and PMS (persulfate) as a strong oxidizing agent, adopting a layout corresponding to the characteristics of the material treatment, to achieve the treatment (degradation, adsorption and removal) of multiple pollution types in groundwater. The composite filler of the present application can be used in the unsaturated aquifer of the shallow (1-50m) soil containing less rock stratum, and is a corresponding treatment measure specified for the special case of the change of pollution migration path caused by the fluctuation of groundwater level in the unsaturated zone. Based on the PRB unit, a large reaction wall is constructed underground to achieve the continuous treatment, degradation and adsorption of multiple pollution types (most organic pollution types, most inorganic salt ion pollution types and / or most heavy metal pollution types) in groundwater.

[0013] Specifically, the present application provides:

[0014] The first aspect relates to a composite filler for treating multiple pollution types in groundwater, comprising a first component and a second component, the first component and the second component, the first component comprising a first powder and a second powder mixed together, and the second component comprising persulfate PMS, a third powder and a fourth powder.

[0015] The first powder comprises biochar, adsorbed type layered double hydroxide LDH1 loaded on the surface of the biochar, and nano zero-valent iron nZVI loaded on the LDH1,

[0016] The second powder comprises the biochar, catalytic type layered double hydroxide LDH2 loaded on the surface of the biochar, and the nano zero-valent iron nZVI loaded on the LDH2,

[0017] The third powder comprises biochar and the adsorbed type layered double hydroxide LDH1 loaded on the surface of the biochar,

[0018] The fourth powder comprises biochar and the catalytic type layered double hydroxide LDH2 loaded on the surface of the biochar.

[0019] The LDH1 and the LDH2 are represented by the following formula:

[0020] ([M 1-x 2+ M x 3+ (OH)2] x+ [A n- ]·zH2O)

[0021] wherein for the LDH1, M 2+ is Mg 2+ , M3+ Al 3+ , for LDH2, M 2+ Ni 2+ , M 3+ Fe 3+ ,

[0022] X is the molar ratio M 3+ / (M 2+ + M 3+ ), A n- is an interlayer anion comprising CI - and CO3 2- , n is the number of negative charges, and z is the number of interlayer structural water, wherein the first component and the second component are kept and used separately from each other.

[0023] The second aspect relates to a method for preparing a composite filler for treating multiple pollution types in groundwater, comprising the following steps: S1 - providing a first component, the first component comprising a first powder and a second powder; S2 - providing a second component, the second component comprising a third powder, a fourth powder, and a persulfate salt PMS as an oxidizing agent; S3 - separately sealing and packaging the first component and the second component independently to obtain the composite filler, wherein step S1 comprises the following steps: S11 - providing the first powder, wherein the step S11 comprises: S111 - providing a mixed solution E comprising magnesium chloride hydrate and aluminum chloride hydrate; S112 - providing a mixed solution F comprising NaOH and Na2CO3; S113 - placing a solution C comprising formamide into a first reaction vessel, then adding the solution E and the solution F, adjusting the pH value to 8-10, stirring the reaction under inert atmosphere at a temperature of 80-100°C for 50-70 minutes, then transferring to a second reaction vessel, and continuing to stir the reaction under inert atmosphere at a temperature of 120-130°C for 8-9 hours, and cooling after the reaction to obtain a reaction mixture I; S114 - adding the reaction mixture I to a solution IV comprising NN-dimethylformamide and ethanol, ultrasonic aging for 8-14 hours, washing the obtained reaction gel, and grinding in a grinder to obtain a slurry of adsorbed layered double hydroxide LDH1; S115 - loading nano zero-valent metal nZVI onto the adsorbed layered double hydroxide LDH1 to obtain an LDH1-nZVI material structure; S116 - mixing the LDH1-nZVI material structure with a dispersion liquid comprising biochar, and reacting in a reaction vessel under inert gas protection at a temperature of 110-120°C for 6-8 hours to obtain a first reaction product, S117 - drying and grinding the first reaction product to obtain the first powder; S12 - providing the second powder, wherein the step S12 comprises: S121 - providing a mixed solution A comprising nickel chloride hydrate and iron chloride hydrate; S122 - providing a mixed solution B comprising NaOH and Na2CO3; S123 - placing a solution C comprising formamide into a third reaction vessel, then adding the solution A and the solution B, adjusting the pH value to 8-10, stirring the reaction under inert atmosphere at a temperature of 60-100°C for 30-60 minutes, then transferring to a fourth reaction vessel, and continuing to stir the reaction under inert atmosphere at a temperature of 110-130°C for 5-9 hours, and cooling after the reaction to obtain a reaction mixture II; S124 - adding the reaction mixture to a solution III comprising NN-dimethylformamide and ethanol, ultrasonic aging for 8-14 hours, washing the obtained reaction gel, and grinding in a grinder to obtain a slurry of catalytic layered double hydroxide LDH2; S125 - loading nano zero-valent metal nZVI onto the catalytic layered double hydroxide LDH2 to obtain an LDH2-nZVI material structure;S126 - mixing the LDH2-nZVI material structure with a dispersion liquid containing biochar, and reacting in a reaction vessel under inert gas protection at a temperature of 100-120℃ for 6-8 hours to obtain a second reaction product, S127 - drying and grinding the second reaction product to obtain a second powder; S13 - blending the first powder and the second powder together to obtain the first component, wherein the step S2 comprises the following steps: S21 - providing a third powder, wherein the step S21 comprises: S211 - mixing the slurry of adsorbed layered double hydroxide LDH1 obtained in step S114 with a dispersion liquid containing biochar, and reacting in a reaction vessel under inert gas protection at a temperature of 110-120℃ for 6-8 hours to obtain a third reaction product; S212 - drying and grinding the first reaction product to obtain a third powder; S22 - providing a fourth powder, wherein the step S12 comprises: S221 - mixing the slurry of catalytic layered double hydroxide LDH2 obtained in S124 with a dispersion liquid containing biochar, and reacting in a reaction vessel under inert gas protection at a temperature of 110-120℃ for 6-8 hours to obtain a fourth reaction product; S222 - drying and grinding the fourth reaction product to obtain a fourth powder; S23 - blending the third powder and the fourth powder together to obtain the powder filler part of the second component; S24 - mixing the powder filler part of the second component with PMS to obtain the second component.

[0024] The third aspect relates to a permeable reactive wall, characterized by comprising a first tubular structure unit and a second tubular structure unit, wherein the first tubular structure unit contains a first component, and the second tubular structure unit contains a second component.

[0025] The fourth aspect relates to a method for treating complex pollution of groundwater under the influence of fluctuation of non-saturated aquifer groundwater level using a permeable reactive wall, comprising connecting a plurality of first tubular structure units and a plurality of second tubular structure units according to the depth of pollutant migration, span, speed and type of pollution source in the actual site to construct the permeable reactive wall.

[0026] The beneficial effects of the present application are as follows:

[0027] 1) The application of the new PRB filler structure in the invention meets the application properties of high efficiency, durability, environmental protection, economy, convenience and pollution applicability, which is an environmentally friendly green technology. The high efficiency and durability of the PRB filler in the invention are reflected in the improvement of pollution interception performance and degradation coupling ability, and the service life of the single filler is greatly prolonged. The environmental protection is mainly reflected in the fact that the materials used in the filler structure have little impact on the ecological environment in terms of raw materials, preparation process, application and maintenance. Except for the filler and maintenance materials, the device itself and the materials used for assembly are environmentally friendly. The economy is mainly reflected in the significant reduction of material production cost, and the maintenance cost is reduced due to the antibacterial characteristics of the filler structure in the invention and the more convenient filler maintenance form. At the same time, the convenient material acquisition form and mature material production process make the multi-type composite filler structure have good environmental applicability. The pollution applicability is reflected in the fact that the filler structure in the invention can degrade common types of pollutants in groundwater (including most inorganic salt type, heavy metal type and organic pollution type). In addition to the improvement of basic adsorption capacity, it can degrade various types of pollutants and convert them into environmentally friendly substances. Compared with traditional fillers, this greatly expands the applicability of fillers to groundwater pollution.

[0028] 2) The PRB using the composite filler of the invention includes a plurality of tubular PRB unit structures. The tubular PRB unit structure device of the invention has low preparation cost and simple equipment preparation process. It is reasonable to customize and prefabricate the device according to the actual site use conditions, determine the types and proportions of the internal filler structure, determine the structure proportion of the PRB unit equipment and scale wall, select the materials of each related part in the pipe arrangement PRB structure, customize and pre-assemble the structure unit in the factory, and arrange and construct in the site. The factory pre-assembly reduces the construction difficulty, shortens the construction period, and has low requirements for the proportion, number and comprehensive quality of construction personnel. The unit type PRB in the invention solves the problem of difficult site selection and arrangement of large PRB devices in the past by using small grid structure units. At the same time, the flexibility of the unit type wall is different due to different arrangement methods and forms.

[0029] 3) Unit configuration PRB maintenance, due to the filler in the LDHs with memory reconstruction features, its adsorption, slow release, antibacterial, catalytic properties can be reconstructed with LDHs, this kind of reconstruction can be divided into pollution-free inorganic salt intercalation update and in-situ generation of LDHs (intercalation update type remodeling by injecting Na2SO4, Na2CO3 and / or NaCl, in-situ reconstruction by injecting Na2CO3, NaOH, stabilizer), which can make LDHs have characteristics again and make maintenance more convenient. The PMS in the filler structure is a consumable substance. In order to maintain the high efficiency and durability of the single PRB unit in the unsaturated aquifer pollution plume, it needs to be supplemented and injected regularly according to the actual treatment effect. The oxidizing agent and reducing agent in the filler structure are common environmentally friendly substances. This periodical injection type of supplementing avoids the excavation work during the maintenance of the material performance of the PRB project, and saves a lot of maintenance cost. If longitudinal single pipe connection arrangement is adopted, the materials in the unit pipe can be directly taken out and replaced without excavation.

[0030] 4) By in-situ growth of xanthic acid modified nano zero-valent iron on LDH, the catalytic degradation effect of the composite filler is further improved, and the agglomeration of nano zero-valent iron is prevented; BRIEF DESCRIPTION OF DRAWINGS

[0031] The accompanying drawings are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the principles of the application.

[0032] Figure 1 For the tubular PRB structure unit (first or second tubular unit) according to the embodiment of the application, wherein A is a plan view, B is a cross-sectional view, and C is a side view;

[0033] Figure 2 An embodiment of a permeable reactive wall PRB assembled by tubular PRB structure units (pipe-pipe rigid connection mode) is shown, the upper drawing is a side view, and the lower drawing is a plan view.

[0034] Figure 3 Another embodiment of a permeable reactive wall PRB assembled by tubular PRB structure units (pipe-plate-pipe rigid connection mode) is shown, the upper drawing is a side view, and the lower drawing is a plan view.

[0035] Figure 4 Other connection embodiments of the tubular PRB structure unit are shown, including pipe-plate-pipe (plate type splicing) type (A), pipe-pipe cross application type (B), and pipe-plate-pipe cross application type (C).

[0036] Figure 5 The cross-sectional view (upper drawing) and plan view (lower drawing) of the pipe-pipe cross application type of the tubular PRB structure unit under excavation conditions are shown.

[0037] Figure 6 Cross-sectional view (top) and plan view (bottom) of a flexible connection type of a pipe PRB structure unit under excavation conditions.

[0038] Figure 7 Schematic diagram of a site arrangement of a vertical pipe structure unit arranged longitudinally, wherein the top view is a cross-sectional view and the bottom view is a plan view.

[0039] Figure 8 Schematic diagram of a site arrangement of a horizontal pipe structure unit arranged longitudinally, wherein the top view is a cross-sectional view and the bottom view is a plan view.

[0040] Figure 9 Schematic diagram of a site arrangement of a PRB structure unit of a horizontal pipe arranged horizontally, wherein the left view is a horizontal arrangement of connection material and the right view is a horizontal arrangement of pipe pair pull connection.

[0041] Figure 10 Schematic diagram of a site arrangement of a PRB structure unit for a pollution form of a point source or similar point source, wherein the left view is a circular arrangement and the right view is a square arrangement.

[0042] Figure 11 SEM photos of the third powder (A) and the fourth powder (B) obtained in Preparation Example 2 are shown.

[0043] Figure 12 SEM photos of the first powder (A) and the second powder (B) obtained in Preparation Example 1 are shown. DETAILED DESCRIPTION

[0044] In order for those skilled in the art to better understand the technical solutions in the embodiments of the present application, the technical solutions of the present application will be described clearly and completely below with reference to the drawings.

[0045] In view of the above-mentioned problems of the existing PRB technology, the research and development cost of the material or filler itself needs to be considered. The application cost can also be reduced by starting from the structure and arrangement form of the PRB device through comprehensive measurement. Other problems such as the maintenance cost of the PRB, the secondary pollution problem, the environmental protection cycle problem, the construction applicability problem, the pollution applicability range, etc. are all considered after the application cost of the new material or new filler is reduced.

[0046] In view of the above, aspects of the present invention provide a composite filler for treating multiple pollution types in groundwater, comprising a first component and a second component, the first powder comprising biochar, an adsorptive layered double hydroxide LDH1 supported on a pore surface of the biochar, and nano zero-valent iron nZVI supported on the LDH1, and the second powder comprising the biochar, a catalytic layered double hydroxide LDH2 supported on a pore surface of the biochar, and the nano zero-valent iron nZVI supported on the LDH2, wherein LDH1 and LDH2 are represented by the following formulae:

[0047] ([M 1-x 2+ M x 3+ (OH)2] x+ [A n- ]·zH2O)

[0048] wherein for LDH1, M 2+ is Mg 2+ , M 3+ is Al 3+ , for LDH2, M 2+ is Ni 2+ , M 3+ is Fe 3+ , X is a molar ratio of M 3+ / (M 2+ + M 3+ ) (0.2 to 0.4), A n- is an interlayer anion comprising Cl - and CO3 2- , n is a number of negative charges (2-4), and z is a number of interlayer structure crystallization water (2-5 crystallization waters).

[0049] Preferably, the nano zero-valent iron nZVI is a fulvic acid-modified nano zero-valent iron nZVI grown in situ on the adsorptive layered double hydroxide LDH1 and the catalytic layered double hydroxide LDH2 in the presence of a fulvic acid of mineral origin.

[0050] The biochar (BC) can be prepared from at least one selected from reed, acorus, shrub, tree leaf, seaweed, phytoplankton, seed husk, fruit peel, corn straw by acid washing, alkali washing, drying, and thermal grinding. The biochar has a specific surface area of 600-1100 m 2 / g, a porosity of 30-70%, a particle size of 50-200 mesh, and an average diameter of pores of 10-50 nm.

[0051] In particular, the filler structure used in the present invention is a composite filler of three types of materials or a combination of two types of composite fillers with an oxidizing agent, respectively MgAl-Cl -&CO3 2— LDH, NiFe-Cl - &CO3 2- LDHs with zero-valent iron and biochar or LDHs with biochar and PMS (the particle size of biochar should be selected according to the actual site porous medium conditions, because the modified composite material based on BC has no obvious change in the permeability coefficient K of the medium, so the filler structure should be set to 2-10 times the permeability coefficient of the actual site porous medium), when treating the corresponding pollution, BC and LDHs can be captured without distinction, LDHs exchange interlayer ions and achieve temporary storage while adsorbing, compared with the adsorption and desorption process of biochar, it has a clear mitigation trend, the modified composite filler has a slow-release type, which makes the contact between the reaction degrading oxidant PMS and reducing agent nZVI and pollutants more sufficient in unit time, improves the reaction efficiency, avoids secondary pollution caused by insufficient reaction, at the same time, the expanded specific surface area and refined pore structure make the material adsorption capacity further improved. Consumables can be transported through the infusion pipeline in the linked reaction unit to achieve the replenishment effect and prolong the service life of the single filler structure. At the same time, due to the occurrence of reduction and oxidation reaction, the consumed nZVI exists in the form of Fe 2+ , Fe 3+ in the filler structure, which promotes the catalytic reaction again, forms a new single-element LDHs structure with the injected alkaline NaOH and Na2CO3, and can perform this process when the degradation efficiency decreases to close to the simple adsorption effect, or inject Na2SO4, Na2CO3, NaCl solution to complete the intercalation reconstruction of the material and realize updating, but this process must be carried out when nZVI and PMS still have oxidation and reduction properties. For the supplement of oxidant (PMS), its supplement also realizes the updating of LDHs intercalation structure. In general, supplementing PMS can realize the supplement of oxidant and the updating of LDHs intercalation at the same time, but when supplementing reducing agent nZVI, the updating of LDHs structure is in the form of new single-element LDHs structure formed by the reaction of divalent and trivalent iron ions and newly injected alkali in situ. This updating form provides a reasonable way for the recycling and utilization of materials in treating pollution.

[0052] The mesoporous adsorption type material can adsorb and degrade various pollutants in the water body, but the pollution capture mechanism of the process is temporary. The reduced filler structure in the application uses nZVI loaded LDHs to complex and refine the pores of the biochar, and the oxidized filler structure uses LDHs to complex and refine the pores of the biochar and uses PMS to achieve the purpose of oxidizing and degrading groundwater pollution, and the form of the composite material can enhance the pollution adsorption capacity. When the composite filler is used for reaction and degradation, the LDHs can be used as a fixed and slow-release type material for various pollution forms. ① In the treatment of metal ions, the surface functional group complex bond, interlayer anion coprecipitation, crystal surface electrostatic attraction, surface coprecipitation and the like can be realized. ② In the treatment of pollution type inorganic anions, interlayer anion intercalation adsorption exchange, electrostatic force adsorption, ligand exchange and the like can be realized. ③ In the treatment of organic pollution, the oxidation reaction process can be realized on the surface by using the electron transition energy to realize the degradation of low valence state organic pollutants. nZVI and PMS can be used as oxidants and reductants respectively to further stimulate the redox reaction. In the absence of light in the groundwater, LDHs lack the way of electron transition caused by light, and it is difficult to exert its own catalytic properties, but in the participation of nZVI and PMS, the electron change in the redox reaction makes up for the light excitation electron transition form required in the original LDHs, and the corresponding catalytic sites in the LDHs are activated, so that the corresponding redox reaction is strengthened under the synergistic catalysis of the heterogeneous material. After the adsorption type material is captured and released, the catalytic type LDHs are involved, the reaction and degradation efficiency of each pollution per unit time is improved, and due to the slow-release performance, the reaction time of the same amount of pollutants flowing through the filler structure is increased, so that the reaction is ensured to be thorough and the secondary pollution is reduced. This combined mechanism can oxidize and reduce most of the organic pollutants, inorganic anion pollution and part of the heavy metal pollution which needs to adjust the valence to reduce the pollution. At the same time, nZVI and PMS are used as complementary materials to maintain the catalytic properties of each PRB unit. The iron ions generated after the reaction of nZVI can catalyze the degradation reaction again, the single-element LDHs are regenerated by injecting alkaline substances to continue catalyzing the reaction, and the blockage caused by the precipitation of metal materials is reduced. After the injection of PMS completes the oxidation reaction, the interlayer of the original composite LDHs can be updated with anions to restore the adsorption and slow-release capacity of the LDHs. Therefore, the composite filler structure system of the application can realize long-term and efficient degradation of various pollutants in the complex unsaturated aquifer groundwater.

[0053] In the filler structure of the application, the main filling means is material compounding and adding, and the composite material is obtained in the corresponding preparation place. The types, specifications and models of the required materials are determined before construction, and are transported to the construction site after preparation, and the PRB unit filler is filled in advance, and is mixed and stirred during the adding, and is discharged and packed into the fixed filter bag of the PRB unit.

[0054] In summary, the application of the PRB composite filler structure in the present application meets the application properties of high efficiency, durability, environmental protection, economy, convenience and wide applicability to pollution, which is an environmentally friendly green technology. The high efficiency and durability of the PRB filler are reflected in the improvement of the pollution interception performance and the degradation coupling ability, and the single filler use cycle is greatly prolonged. The environmental protection mainly reflects that the materials used in the filler structure have little impact on the ecological environment in terms of raw materials, preparation process, application and maintenance. Except for the filler and maintenance materials, the device itself and the materials used for assembly are environmentally friendly. The economy mainly reflects the significant reduction in material production cost, and the antibacterial characteristics of the filler structure in the application and the more convenient filler maintenance form reduce the maintenance cost. At the same time, the convenient material acquisition form and the mature flow material production process make the filler structure of the composite combination of multiple types have good environmental applicability. The wide applicability to pollution is reflected in that the filler structure used in the application can degrade common multiple types of pollutants in groundwater (including most inorganic salt type, heavy metal type and organic pollution type). In addition to the improvement of the basic adsorption capacity, it can achieve degradation of multiple types of pollutants, which is converted into environmentally friendly substances. Compared with traditional fillers, this greatly widens the application range of fillers to groundwater pollution.

[0055] The second aspect of the present application provides a method for preparing a composite filler, comprising the following steps: S1-providing a first component, the first component comprising a first powder and a second powder; S2-providing a filler part of a second component, comprising a third powder and a fourth powder; S3-separately and independently sealing the first component and the second component to obtain the composite filler, wherein step S1 comprises the following steps: S11-providing a first powder, wherein the step S11 comprises: S111-providing a mixed solution E comprising magnesium chloride hydrate and aluminum chloride hydrate; S112-providing a mixed solution F comprising NaOH and Na2CO3; S113-placing a solution C comprising formamide into a first reaction container, then adding the solution E and the solution F, adjusting the pH value to 8-10, stirring the reaction under inert atmosphere at a temperature of 80-100°C for 50-70 minutes, then transferring to a second reaction container, and continuing to stir the reaction under inert atmosphere at a temperature of 120-130°C for 8-9 hours, after the reaction is completed, cooling to obtain a reaction mixture I; S114-adding the reaction mixture I into a solution IV comprising NN-dimethylformamide and ethanol, ultrasonic aging for 8-14 hours, washing the obtained reaction gelatin and grinding in a grinder to obtain a slurry of adsorbed layered double hydroxide LDH1; S115-loading nanometer zero-valent metal nZVI on the adsorbed layered double hydroxide LDH1 to obtain an LDH1-nZVI material structure; S116-mixing the LDH1-nZVI material structure with a dispersion liquid comprising biochar, and reacting in a reaction container under inert gas protection at a temperature of 110-120°C for 6-8 hours to obtain a first reaction product, S117-drying and grinding the first reaction product to obtain the first powder; S12-providing a second powder, wherein the step S12 comprises: S121-providing a mixed solution A comprising nickel chloride hydrate and iron chloride hydrate; S122-providing a mixed solution B comprising NaOH and Na2CO3; S123-placing a solution C comprising formamide into a third reaction container, then adding the solution A and the solution B, adjusting the pH value to 8-10, stirring the reaction under inert atmosphere at a temperature of 60-100°C for 30-60 minutes, then transferring to a fourth reaction container, continuing to stir the reaction under inert atmosphere at a temperature of 110-130°C for 5-9 hours, after the reaction is completed, cooling to obtain a reaction mixture II; S124-adding the reaction mixture into a solution III comprising NN-dimethylformamide and ethanol, ultrasonic aging for 8-14 hours, washing the obtained reaction gelatin and grinding in a grinder to obtain a slurry of catalytic layered double hydroxide LDH2; S125-loading nanometer zero-valent metal nZVI on the catalytic layered double hydroxide LDH2 to obtain an LDH2-nZVI material structure;S126 - mixing the LDH2-nZVI material structure with a dispersion liquid containing biochar, and reacting in a reaction vessel under inert gas protection at a temperature of 100-120℃ for 6-8 hours to obtain a second reaction product; S127 - grinding the second reaction product after drying to obtain a second powder; S13 - blending the first powder and the second powder together to obtain the first component.

[0056] The step S2 comprises the following steps: S21 - providing a third powder, wherein the step S21 comprises: S211 - mixing the slurry of the adsorption type layered double hydroxide LDH1 obtained in step S114 with a dispersion liquid containing biochar, and reacting in a reaction vessel under inert gas protection at a temperature of 110-120℃ for 6-8 hours to obtain a third reaction product; S212 - grinding the third reaction product after drying to obtain a third powder; S22 - providing a fourth powder, wherein the step S12 comprises: S221 - mixing the slurry of the catalytic type layered double hydroxide LDH2 obtained in S124 with a dispersion liquid containing biochar, and reacting in a reaction vessel under inert gas protection at a temperature of 110-120℃ for 6-8 hours to obtain a fourth reaction product; S222 - grinding the fourth reaction product after drying to obtain a fourth powder; S23 - blending the third powder and the fourth powder together to obtain the powder filler part of the second component; S24 - mixing the powder filler part of the second component with PMS to obtain the second component.

[0057] Preferably, the step 115 comprises: dissolving the mine fulvic acid in water under a protective gas atmosphere, then adding an aqueous solution containing ferric chloride and ethanol, stirring, then adding the slurry of the adsorption type layered double hydroxide LDH1, ultrasonic oscillation to uniformly disperse, then adding sodium borohydride solution drop by drop, continuing to react for 50-70 min, then filtering, washing, and drying to obtain the LDH1-nZVI material structure; and the step 125 comprises: dissolving the mine fulvic acid in water under a protective gas atmosphere, then adding ferric chloride and ethanol, stirring, then adding the slurry of the catalytic type layered double hydroxide LDH2, ultrasonic oscillation to uniformly disperse, then adding sodium borohydride solution drop by drop, continuing to react for 40-60 min, then filtering, washing, and drying to obtain the LDH2-nZVI material structure.

[0058] Preferably, the concentrations of the aluminum chloride hydrate solution and the magnesium chloride hydrate solution are 0.010 mol / L to 0.03 mol / L and 0.030 to 0.090 mol / L, respectively, and the concentrations of the nickel chloride hydrate and the ferric chloride hydrate solution are 0.0500 mol / L to 0.1000 mol / L and 0.0200 mol / L to 0.0500 mol / L, respectively.

[0059] Preferably, the step S123 comprises pre-stirring for 5-10 minutes by using a heating mill stirrer after adding the formamide-containing solution C into the first reaction container, then adding solution E and F into the first reaction container by using infusion tubes respectively, then heating and stirring the reaction at a temperature of 60-100°C for 45-50 minutes under nitrogen protection, wherein the capacity of the second reaction container is greater than that of the first reaction container, and the dropping speed of solution E and F is 3-5 ml / min. The step 223 comprises: pre-stirring for 8-12 minutes by using a heating mill stirrer after adding the formamide-containing solution C into the third reaction container, then adding solution A and B into the third reaction container by using infusion tubes respectively, then heating and stirring the reaction at a temperature of 80-100°C for 50-70 minutes under nitrogen protection, wherein the capacity of the fourth reaction container is greater than that of the third reaction container, and the dropping speed of solution A and B is 6-8 ml / min. The needle diameter of the infusion tube can be 0.30 to 0.60 μm.

[0060] In the composite filler structure of the present application, the biochar in the synthetic composite material is widely sourced and can be flexibly selected from various bio-waste (fruit shells, plant straws, etc.), is low in price, simple in preparation process, and the raw material for preparing LDHs can be metal ion-containing industrial wastewater (the present application can use Ni 2+ , Fe 3+ , Mg 2+ , Al 3+The industrial wastewater) or low price metal salt and strong alkali are added dropwise and reacted at a temperature of 60-150 DEG C. The process flow is simple and mature, the material cost is low, and the interlayer growth inhibitor used can be reused after material filtration. For the commonly used oxidant PMS and reducing agent nZVI, batch products can be made by reusing industrial solid waste, and the two substances can be purchased in large quantities in the corresponding industrial manufacturers and normal e-commerce channels. When the equipment conditions are met, self-preparation can be carried out, and the preparation method is simple, and the direct cost of the daily PRB maintenance consumables is low. nZVI can also be prepared in situ to further improve the catalytic degradation effect. During PRB maintenance, LDHs can be used to increase the number of material recycling times due to its excellent updating and reconstruction characteristics. At the same time, due to the further refinement of the pore structure of BC after being compounded as a carrier, the adsorption performance of the unit volume material is enhanced, and the permeability of the raw material is hardly affected. During the maintenance process, the iron ion circulation and iron compound precipitation problems caused by the application of nZVI can be solved by reconstructing LDHs with iron ions. In addition, the alkali solution and non-polluting metal salts added during the anion intercalation updating and structure reconstruction of LDHs have a certain inhibitory effect on the proliferation of microorganisms. At the same time, due to the antibacterial property of LDHs material itself, the easy growth of microorganisms in the pore is well improved after being compounded with biochar, ensuring the self-cleaning property of the material system and prolonging the single use cycle of the filler structure. The use of the filler structure in the application can avoid the high PRB material maintenance cost caused by multiple excavation and replacement of fillers. The filler structure and maintenance materials used in the application are environmentally friendly substances and will not cause secondary pollution to the environment before and after the pollution removal reaction. At the same time, the use of maintenance materials has a one-time multiple effect, which ensures the efficient and thorough degradation of the reaction filler to pollution, updates the performance of the catalytic, slow-release and adsorption materials, and improves the material recycling times with a lower maintenance cost. The composite filler structure of the application not only efficiently and durably degrades pollutants, but also prolongs the application cycle of the first round of materials. In addition, during the preparation process, in addition to the necessary power consumption, the reagents used can be recycled and have less environmental impact.

[0061] The third aspect of the application provides a permeable reactive wall PRB, comprising a first tubular structure unit and a second tubular structure unit, wherein the first tubular structure unit contains a first component, and the second tubular structure unit contains a second component.

[0062] The material of the PRB tubular structure unit is selected from stainless steel, PVC, PMMA and other common application pipeline materials with high strength and low price according to the actual site conditions. The material selection needs to consider the application durability and the deflection deformation caused by the complex physical and chemical fields in the underground space, so as to ensure that the PRB structure unit does not slip and overturn to reduce the effective contact area between the water surface of the PRB structure unit and the underground water flow line within the design period, so as to weaken the reaction and removal effect of the PRB on the underground water pollutants. Under the condition that the material selection can ensure long-term application, the corresponding maintenance cost is reduced and the service life is prolonged. The PRB tubular structure is bonded, flow-guided and anti-seepage arranged at the unit linking contact position under the condition of excavating the soil layer by using epoxy resin and other impermeable adhesive materials, so as to prevent the pollutants at the weak connection of each pipe unit from seepage, so that the PRB presents partial failure around the connection line. The flexible impermeable connection form is used to improve the flexibility, reduce the preparation and use of the filler and device structure, and reduce the application cost of the PRB. Under the condition of not excavating, the pipe unit is pressed into a single pipe, an outer permeable sleeve is formed, pipe-pipe connection and pipe-plate-pipe connection are formed, the use effect of the flexible material is the same, the preparation and use of the filler and device structure are reduced, and the excavation cost is avoided, so that the application cost of the PRB is greatly reduced.

[0063] The PRB structure adopts a small pipe unit device to form a regular or irregular PRB pipe wall, and the design concept of the ring layer pipe structure of the unit pipe and the filler saves the use of materials, reduces the material filling cost, improves the space utilization rate of the materials, and improves the applicability and flexibility of the PRB reaction device in dealing with complex aquifer compared with the large PRB reaction device. The connection mode under the condition of excavation adopts the environmental protection anti-seepage connection glue assisted limiting screw tension connection, the corresponding hole form is designed according to the unit structure, the epoxy resin and other anti-seepage glue materials are applied at the connection boundary between the water surface and the backwater surface of the pipe unit connection, so as to achieve the effects of anti-seepage, flow guidance and adhesion, ensure the good sealing property of the PRB structure, make the underground water in the unsaturated zone flow uniformly and reasonably to the filler structure, improve the PRB arrangement flexibility by using the flexible impermeable connection form, reduce the preparation and use of the filler and device structure, improve the pollutant capture capacity of the PRB in the face of underground water level fluctuation aquifer, and avoid partial failure of the pipe PRB structure around the connection boundary. Under the condition of not excavating, the pipe unit is pressed into a rigid single pipe, a slide rail is formed on the outer side of the single pipe, pipe-pipe connection and pipe-plate-pipe connection are formed, the use effect of the flexible material is the same, the preparation and use of the filler and device structure are reduced, the overall property of the PRB structure is improved, and the PRB structure is more suitable for wide arrangement under good soil layer conditions.

[0064] The first and second tubular structure units are also linked with a delivery pipe for supplementing consumed nZVI and PMS, or delivering alkaline NaOH and Na2CO3 to form new single-element LDH structures in the composite filler, or delivering a solution containing Na2SO4, Na2CO3 and / or NaCl to perform intercalation reconstruction of LDH1 and LDH2, provided that nZVI and PMS still have redox properties. The delivery pipe is of great significance, and is the key to ensuring that the filler structure maintains high and persistent pollution degradation efficiency. The material selection needs to consider chemical and mechanical properties such as alkaline resistance, durability, strength, and temperature stress. The presence of the delivery pipe provides a basis for the in-situ continuous updating of the filler structure and the efficient maintenance of pollution degradation, greatly reducing the maintenance cost of the PRB.

[0065] The fourth aspect of the present application provides a method for treating composite pollution of groundwater by the PRB under the influence of fluctuation of groundwater level in the unsaturated aquifer, comprising connecting a plurality of first tubular structure units and a plurality of second tubular structure units according to the migration depth, span, speed and type of the pollution source in the actual site, to construct the permeable reactive wall.

[0066] Using groundwater pollution migration simulation software, a gridded model for simulating site groundwater pollution can be constructed, and the migration path of inert and non-inert solutes in the unsaturated aquifer of groundwater can be predicted, especially in combination with the simulation prediction under the condition of fluctuation of actual site groundwater level, to show the influence of groundwater level on the change of pollution migration and transformation path. The existing geomagnetic method technology can be used to evaluate the feasibility and adjust the scheme implementation, and then the corresponding pollution site PRB arrangement form is used to arrange the seriously polluted underground area or the pollution concentrated area. When the pollution source is known, it can be set at the corresponding high-concentration pollution stratum depth to prevent further diffusion after entering the soil. When there is existing pollution, the pollution migration path based on the groundwater flow line is predicted by software, and the PRB form in the application is arranged at the intersection of the migration path and the PRB structure unit wall (the contact surface effect of the best pollution collection is 90° intersection). According to the existing pollution source form and pollution migration characteristics, the arrangement mode is reasonably selected to reduce the high application cost caused by blindness and randomness of site area arrangement.

[0067] The PRB and site arrangement mode thereof adopt the pipe type PRB structure, in particular, the grid type pipe type PRB structure. The grid type pipe type PRB device refines the treatment site unsaturated aquifer, and is more suitable for the regional micro treatment of large scale pollution sites. The pipe type PRB structure unit selects common application type pipe materials with high strength and low price such as stainless steel, PVC and PMMA, the water side and the backwater side of the connection of the pipes under the excavation condition are arranged by using epoxy resin and other impermeable adhesive materials for flow guiding and impermeable and bonding, so that the PRB structure can more flexibly cope with the complex stress conditions of underground space and save the manufacturing cost of the bearing wall, and the filling form of the sheet layer filler saves the material usage and better copes with the pollution capture problem in the pollution migration path change process caused by the underground water level fluctuation. The flexible impermeable cloth connection form is used to improve the flexibility of the device, reduce the preparation and use of a large amount of fillers and device structures, and be more suitable for the use of complex unsaturated aquifer. Under the condition of no excavation, the pipe unit is pressed into the pipe, the rigid single pipe outer permeable sleeve form is used, the pipe-pipe connection and pipe-plate-pipe connection form are used, the use effect of the flexible material is consistent, the preparation and use of the fillers and device structures are reduced, the integrity of the PRB structure is increased, and the PRB structure is more suitable for the wide arrangement under the good soil layer condition.

[0068] The pipe PRB structure needs to face complex soil layer conditions (such as the non-homogeneity of porous medium, the different scale rock mass existing in the soil layer and the like) and active underground hydraulic activities in the actual application arrangement of the unsaturated aquifer. According to the gradation of the actually measured regional soil, the previous pollution area geomagnetic survey and the actual site underground water variation amplitude and flow velocity determination test, the vertical pipe type, the horizontal pipe type and the pipe cloth connection type can be selected. When the underground water flow velocity is fast, the variation amplitude is large and the soil condition is good, the vertical pipe type is preferentially selected. When a large amount of sandstone exists, the vertical pipe type or the horizontal pipe type can be selected. When the underground water flow velocity is slow, the variation amplitude is small and the soil condition is good, the pipe cloth connection type can be selected. In the case that the known pollution source exists, the PRB can be arranged at the corresponding unsaturated zone high concentration pollution stratum depth to prevent the further diffusion after the pollution enters the deep soil. In the case that the existing pollution exists, the PRB can be arranged at the intersection of the migration path and the PRB structure unit wall (the contact surface effect of the optimal pollution collection is 90° intersection). According to the existing pollution source form and the pollution migration characteristics, the arrangement mode is reasonably selected. For example, when the unsaturated zone serious surface source infiltration type pollution (the range type pollution of the dry season broken river bed and small farmland or the surface pollution in the soil close to the pollution source) exists, the horizontal pipe parallel horizontal arrangement form can be selected to prevent the surface source infiltration. The arrangement of the filler layer is more recommended for the large area scale surface source pollution form. When the existing or newly migrated pollution far away from the pollution source is treated, according to the pollution migration characteristics and the spatial position of the arranged PRB in the pollution migration path, the vertical column form of the vertical pipe or the horizontal pipe is selected to better adapt to the complex unsaturated aquifer. In addition, when the similar point source pollution form exists in the relatively shallow unsaturated aquifer, the arc cylinder or square cylinder arrangement form can be selected to adopt the range surrounding and treatment mode for the treatment. In the application, the arrangement form of the PRB in the site better increases the applicability of the pipe structure unit PRB in the treatment of various pollutants in the complex underground aquifer.

[0069] The material used in the pipe PRB structure unit and the related pipe wall in the application is basically the non-reactive inert material, so that the secondary reaction to generate other pollution forms is avoided when facing various pollutions in the underground water, and the treatment difficulty is increased. The flexible non-permeable connection form is used to collect the various pollutions in the underground water in sections and concentrate the treatment in the pipe unit. Under the condition that the excavation is not carried out, the rigid single pipe outer layer permeable sleeve form is used to carry out the pipe-pipe connection and the pipe-plate-pipe connection form, and the use effect of the flexible material is consistent. The preparation and use of the filler and the device structure are reduced, the PRB structure integrity is increased, and the PRB structure is more suitable for the wide arrangement under the good soil layer condition.

[0070] The various site arrangements of the PRB of the present application rely on the reasonable prediction of the migration path of each pollutant under the condition of groundwater level fluctuation of the unsaturated aquifer by simulation software, wherein the path prediction of inert pollutants is more in line with the groundwater flow line, but the migration of non-inert pollutants such as nitrogen and some heavy metal ions needs to be based on the premise of clear possible transformation path, and a model is constructed which is more in line with the actual pollutant migration and transformation, and the type, composition ratio and maintenance means of the corresponding filler are designed according to the transformation form.

[0071] The tubular PRB structural unit or even the pipe arrangement PRB structure can be prepared and assembled in the factory, transported to the actual site, and then the material is filled when the PRB is buried in the PRB buried pollution control area of the unsaturated aquifer designed in advance. The PRB unit is pre-assembled and unit material is filled when the wall is set, and the assembled PRB wall is placed in batches at the designed elevation. When the wall is not set up but reaches a certain height, the wall can be filled in advance, and the stability of the wall is ensured by arranging and burying at the same time. In the construction of several pipe structures in the invention, only the vertical pipe structure can be used for pressure-in type wall forming method. The pipe arrangement can be pre-assembled on the ground to form a wall, and then connected to the underground wall by pressure-in or single pipe pressure-in. This greatly improves the construction efficiency of PRB. Except for the vertical pipe structure, the remaining horizontal pipe structure and pipe arrangement connection type are constructed by setting the wall after excavation and filling. According to the actual engineering situation, the method of setting and filling at the same time can be adopted.

[0072] The site arrangement of PRB should be considered comprehensively according to the target pollutant, pollution source type, simulation migration and transformation path, and actual site unsaturated aquifer. Overall, the site arrangement of the pipe arrangement PRB structure has low requirements for the professional comprehensive quality of construction personnel, and the assembly type construction form makes the overall construction difficulty smaller. The overall process of PRB construction is clear and the construction process can be flexibly controlled.

[0073] The unit type PRB solves the problem that the previous PRB large device is difficult to arrange in the actual site, and the flexibility of the unit type wall body is different due to different arrangement methods and forms. When the unit type PRB is maintained, the LDHs in the filler have the memory reconstruction feature, the adsorption, the slow release, the bacteriostasis and the catalysis can be re-acquired with the reconstruction of the LDHs, and the reconstruction form can be divided into the intercalation update of the non-pollution type inorganic salt and the in-situ generation of the LDHs (the intercalation update type remodeling is carried out by injecting Na2SO4, Na2CO3 and NaCl, the in-situ reconstruction is carried out by injecting Na2CO3, NaOH and a stabilizer), and the LDHs can be re-acquired with the characteristics, and the maintenance is more convenient. The nZVI and the PMS in the composite filler structure are consumable substances, in order to keep the single PRB unit in the unsaturated aquifer pollution plume to treat the pollution efficiently and durably, the injection needs to be supplemented regularly in combination with the actual treatment effect, the two kinds of oxidants and the reducing agent are common environment-friendly substances, the periodical injection type supplement form avoids the excavation work in the performance of the PRB engineering maintenance material, and a large amount of maintenance cost is saved, when the longitudinal single pipe connection arrangement is adopted, the material in the unit pipe can be directly taken out and replaced, and the excavation is not needed again.

[0074] Figure 1 For the first or second tubular PRB structure unit according to the embodiment of the application, wherein A is a top view, B is a cross-sectional view, and C is a side view. The tubular PRB structure unit can include ① a single pipe top cover (to prevent falling objects, to replace fillers, to monitor underground water level, and to monitor treatment and sampling), ② a tension limiter, ③ an outer layer bearing permeable pipe (with multiple pores in the side wall), ④ a two-way permeable nylon filter screen, ⑤ a supporting steady flow head, ⑥ an external screw, ⑦ an internal screw, ⑧ a maintenance material conveying connecting pipe (conveying pipe), ⑨ composite filler LDHs-nZVI@BC or LDHs@BC, and ⑩ a rigid cone head. Permeable holes.

[0075] Figure 2 An embodiment of a permeable reactive barrier PRB assembled by the tubular PRB structure unit (pipe-pipe rigid connection mode) is shown, the upper drawing is a side view, and the lower drawing is a top view. Figure 3 Another embodiment of a permeable reactive barrier PRB assembled by the tubular PRB structure unit (pipe-plate-pipe rigid connection mode) is shown, the upper drawing is a side view, and the lower drawing is a top view. In addition to the plurality of tubular PRB structure units, the permeable reactive barrier PRB also includes A U-shaped prefabricated track connecting fastener, and A plate type permeable wall unit.

[0076] Figure 4Other connection examples of tubular PRB structure unit are shown, including tube-plate-tube (plate splicing) type (A); tube-tube cross application type (B); tube-plate-tube cross application type (C). The above connection modes are all pressed-in rigid connection forms. Figure 5 The side view (top) and top view (bottom) of the PRB structure unit under the condition of excavation are shown. Figure 6 The side view (top) and top view (bottom) of the PRB structure unit under the condition of excavation are shown. The flexible connection type PRB also includes For soft materials such as epoxy resin, etc. (to prevent seepage, guide flow and limit position), For flexible impermeable materials and For ring-type rolling belt.

[0077] Figure 7 The schematic diagram of the site arrangement of the vertical pipe structure unit arranged longitudinally is shown, wherein the top view is a sectional view and the bottom view is a top view. Figure 8 The schematic diagram of the site arrangement of the horizontal pipe structure unit arranged longitudinally is shown, wherein the top view is a sectional view and the bottom view is a top view. The longitudinal arrangement is for pollution treatment in the migration process away from the pollution source. Figure 9 The schematic diagram of the site arrangement of the PRB structure unit with horizontal pipe arrangement is shown, wherein the left view is a connection material horizontal arrangement and the right view is a pipe pull connection horizontal arrangement. The horizontal arrangement is for small-range area source pollution. Figure 10 The schematic diagram of the site arrangement of the PRB structure unit for point source or similar point source pollution is shown, wherein the left view is a circular arrangement and the right view is a square arrangement.

[0078] Examples

[0079] NiCl2·6H2O, FeCl3·6H2O, ferric chloride hexahydrate, magnesium chloride hexahydrate, NaOH and Na2CO3 were purchased from Shanghai Macklin; formamide and peroxymonosulfate PMS were purchased from Shanghai Aldrin; DMF (N-N dimethylformamide) was purchased from Shanghai Aldrin; ethanol was anhydrous ethanol; water for testing was pure water (TDS < 5 ppm); BC was straw biochar (about 100 mesh); nZVI was spherical zero-valent iron with a diameter of about 500 nm.

[0080] Preparation Example 1

[0081] Step 1 - Preparation of the first powder

[0082] The 0.08 mol magnesium chloride hexahydrate and 0.04 mol aluminum chloride hexahydrate were dissolved in 100 ml of water, stirred for 30 min, and prepared into a mixed solution system E with a total metal ion concentration of 1 mol / L. A 100 ml mixed solution system F was prepared, which contained a 2 mol / L NaOH solution and a 0.2 mol / L Na2CO3 solution, and was dissolved and stirred for 30 min. A volume percentage of 33.3% formamide solution was prepared, stirred for 30 min, and the formamide solution was poured into the reaction container (heated grinding stirrer) and pre-stirred for 6 min. The solution systems E and F were added into the reaction container at the same time using infusion tubes (the dropwise addition speed was about 3.75 ml / min, and the needle diameter was 0.45 mm), and heated to 100°C under N2 protection, ground, and stirred for 45 min, and the PH was maintained at about 10. Then the reaction solution was transferred to a large flask and heated to 130°C under N2 protection, sealed and stirred for 9 h. After the reaction was cooled, solution system D (a mixed solution of DMF: ethanol in a volume ratio of 1:1) was added and ultrasonically treated for 3 h, and then aged for 14 h. The reaction gel was obtained by alternating centrifugal washing with ethanol and water, poured into a high-speed grinder, and a uniform LDH1 thin layer slurry was obtained. The nZVI was mixed with water according to a stacking volume ratio (nZVI: LDH1) of 13:1 (i.e., a mass ratio of 35:1), ultrasonically treated for 12 min, transferred to a heated high-speed grinding stirrer, and reacted for 50 min. Then it was transferred to a large flask, sealed and heated and stirred for 10 h under N2 protection, naturally cooled, filtered, vacuum dried for 14 h, and then ground, thereby obtaining the LDH1-nZVI material structure.

[0083] The biochar BC was dried and crushed after acid washing and alkali washing, and then mixed with water and ultrasonically treated for 1 h. The mixture was stirred for 40 min according to a stacking volume ratio (BC-LDH1: nZVI) of 70:1 (i.e., a mass ratio of 25:1), poured into a heated grinding stirrer, and reacted for 50 min under N2 protection. Then it was transferred to a large flask and heated to 130°C for 8 h to obtain the product. The product was filtered, dried at 60°C, and then ground for 20 min to obtain the LDH1-nZVI@BC first powder. The SEM photo of the first powder is shown in FIG. A. Figure 12 A.

[0084] Step 2 - Preparation of the second powder

[0085] A mixed solution system A was prepared by dissolving 0.0667 mol of NiCl2·6H2O and 0.0333 mol of FeCl3·6H2O in 100 ml of water, stirring for 30 min, and preparing a mixed solution system with a total metal ion concentration of 1 mol / L. A 100 ml mixed solution system B was prepared, which contained a 2 mol / L NaOH solution and a 0.2 mol / L Na2CO3 solution, was dissolved and stirred for 30 min. A volume percentage = 33% formamide solution was prepared, stirred for 30 min, and the formamide solution was poured into a reaction container (a heated grinding stirrer) and pre-stirred for 5 min. Solution systems A and B were added to the reaction container at the same time using infusion tubes (the dropwise addition speed was about 3.75 ml / min, and the needle diameter was 0.45 mm), and heating, grinding, and stirring were performed under N2 protection at 100°C for 45 min, while maintaining a pH of about 10. The reaction solution was then transferred to a large flask and heated at 120°C under N2 protection for 8 h while being sealed and stirred. After the reaction was cooled, solution system D (a mixed solution of DMF:ethanol in a volume ratio of 1:1) was added and ultrasonically treated for 2 h, and then aged for 12 h. The reaction gel was washed by alternating ethanol and water through centrifugation, poured into a high-speed grinder, and a uniform LDH2 thin layer slurry was obtained.

[0086] The nZVI was mixed with water at a stacking volume ratio (nZVI:LDHs) of 13:1 (i.e., a mass ratio of 32:1) and ultrasonically treated for 10 min, transferred to a heated high-speed grinding stirrer, and reacted for 60 min. The reaction product was then transferred to a large flask, heated and stirred under N2 protection for 12 h, naturally cooled, suction filtered, vacuum dried for 10 h, and then ground to obtain an LDH2-nZVI material structure.

[0087] The biochar BC was dried and crushed, mixed with water and ultrasonically treated for 1 h, and then mixed and stirred at a stacking volume ratio (BC:LDH2-nZVI) of 70:1 (i.e., a mass ratio of 20:1) for 45 min. The mixture was poured into a heated grinding stirrer and reacted under N2 protection for 50 min. The reaction product was then transferred to a large flask and heated at 120°C for 8 h to obtain a product. The product was suction filtered, dried at 60°C, and then ground for 20 min to obtain an LDH2-nZVI@BC second powder. The SEM image of the second powder is shown in FIG. B. Figure 12 B as shown

[0088] Step 3 - The first powder and the second powder were mixed to obtain a first component.

[0089] Preparation Example 2

[0090] The uniform LDH1 thin layer slurry obtained from Step 1 of Preparation Example 1 was mixed with biochar BC in a ratio of 70:1 (i.e. 25:1 by mass) by volume of the stack after being ultrasonically agitated for 1 h with water, stirred for 40 min, poured into a heated grinding blender, reacted for 50 min under N2protection, then transferred to a large flask and heated at 130 °C for 8 h. The resulting product was filtered, dried at 60 °C, and ground for 20 min to obtain a third powder of LDH1@BC. The SEM photo of the third powder is shown in FIG. 2B. Figure 11 A.

[0091] The uniform LDH2 thin layer slurry obtained from Step 2 of Preparation Example 1 was mixed with biochar BC in a ratio of 70:1 (i.e. 20:1 by mass) by volume of the stack after being ultrasonically agitated for 1 h with water, stirred for 45 min, poured into a heated grinding blender, reacted for 50 min under N2protection, then transferred to a large flask and heated at 120 °C for 8 h. The resulting product was filtered, dried at 60 °C, and ground for 20 min to obtain a fourth powder of LDH2@BC. The SEM photo of the fourth powder is shown in FIG. 2B. Figure 11 B.

[0092] The third powder and the fourth powder were mixed to obtain the filler portion of the second component.

[0093] Preparation Example 3

[0094] The first powder and the second powder were prepared according to the method of Example 1, except that in the step of preparing the first powder, an aqueous solution of mine fulvic acid (6% by weight) was prepared, then an aqueous solution containing ferric chloride (5.83 g) and ethanol (200 ml) was added, after stirring, the LDH1 thin layer slurry was added, ultrasonic oscillation was performed for 30 min to uniformly disperse it, then 80 ml of a sodium borohydride solution with a concentration of 1.2 mol / L was added dropwise, the reaction was continued for 30 min, then the product was filtered, washed, and dried to obtain the LDH1-nZVI material structure; in the step of preparing the second powder, an aqueous solution of mine fulvic acid (8% by weight) was prepared, then an aqueous solution containing ferric chloride (5.83 g) and ethanol (180 ml) was added, after stirring, the LDH2 thin layer slurry was added, ultrasonic oscillation was performed for 40 min to uniformly disperse it, then 80 ml of a sodium borohydride solution with a concentration of 1.2 mol / L was added dropwise, the reaction was continued for 80 min, then the product was filtered, washed, and dried to obtain the LDH2-nZVI material structure.

[0095] Test Example

[0096] The composite filler was placed in a two-way permeable nylon filter screen, and then the filter screen was placed in the first PRB unit pipe or the second PRB unit pipe. Then the first or second PRB unit pipe filled with the filler was respectively placed in the first PRB unit or the second PRB unit according to the following steps. Figure 2The connection modes shown are assembled into a PRB oxidation wall or a PRB reduction wall.

[0097] The preliminary geological exploration revealed that the soil in the design pollution control area of the industrial park is mainly silt, which belongs to a low-permeability medium layer, has good particle size gradation, less developed karst, and less rock and gravel. Therefore, the pipes are pressed in, and biochar with a corresponding mesh number whose permeability coefficient is 3 times that of the original soil layer is selected as the load carrier. The pipes are connected by the outside slide rail on one side and pressed in. A thin layer of epoxy resin is applied to the slide rail connection before pressing. The PRB unit pipe is made of stainless steel, and the side wall is uniformly distributed with multiple permeable pores with an average diameter of 5 mm. The terrain of the contaminated site is surveyed by physical survey based on electromagnetic technology, and the area through which the pollution migrates is reasonably predicted after being input into the simulation software. The underground water in the contaminated site is sampled and detected, and the underground water pollution data of the site is collected, while the model accuracy is continuously calibrated. The assembled PRB wall is transported to the design layout site near the industrial park and loaded into the corresponding designed contaminated stratum according to the corresponding pollution treatment principle. The groundwater in the industrial park site commonly contains the following main components: heavy metal lead, antibiotic carbamazepine, phosphate, nitrogen, etc. After three days of assembling the PRB wall, the groundwater is sampled and detected at the outlet area of the wall. The Pb concentration, TP concentration, CBZ concentration, and TN concentration in the groundwater permeated in the corresponding pollution control area are detected. Then, the sampling and testing are performed again after continuous operation for three months. Then, the solution of Na2CO3 and NaOH (the concentrations are NaOH solution 1 mol / L and Na2CO3 solution 0.2 mol / L, and the injection flow rate of a single wall unit is 500 ml / d) is injected through the delivery pipe. After a single injection of 500 ml, the heavy metal lead content, phosphate content, CBZ content, and TN content in the groundwater at the original sampling site are tested again after continuous operation for one week. The input flow rate of the PMS solution used for the oxidation wall unit (the input flow rate is 80 ml / d, and the input concentration is 1 mmol / l), the test filler is taken out and soaked in a high-concentration NaCl solution for 8 h, the filler is washed and dried, and then the filler is loaded into the device again and detected after one week of application of each cycle of soaking and drying. The values of each pollutant in the groundwater sample after one week of application of each cycle of soaking and drying are detected. Table 1 below shows the composition of the examples and the comparative examples.

[0098] Table 1

[0099]

[0100] Before the PRB was arranged, the groundwater at the site was sampled three times in three consecutive days. The results showed that: 1. The average concentration of heavy metal lead was 0.147 mg / L; 2. The average concentration of total phosphorus was 14.73 mg / L; 3. The average concentration of CBZ was 0.170 mg / L; 4. The average concentration of total nitrogen was 47.25 mg / L. After the PRB was arranged, the groundwater at the permeable end was sampled continuously. The results are shown in Table 2.

[0101] Table 2

[0102]

[0103]

[0104] The test method for the content of heavy metal lead, phosphate and N in groundwater is as follows:

[0105] At the groundwater monitoring hole, the groundwater sampling device was used for sampling. If the sample was not located at the monitoring hole and the groundwater was shallow, the soil drill was used for on-site drilling and sampling.

[0106] If transfer was required, the sample was stored in a low-temperature sealed container in the dark. After pretreatment, the sample was detected on site using a UV spectrophotometer to determine the concentration.

[0107] UV spectrophotometer method (product model: Hashi DR1900, wavelength range: 340-800 nm, automatically identifies the corresponding sample measurement wavelength according to the measurement mode or reagent type and range, reflects the parameters: concentration mg / l).

[0108] The test method for the concentration of CBZ carbamazepine in groundwater is as follows: At the groundwater monitoring hole, the groundwater sampling device was used for sampling. If the sample was not located at the monitoring hole and the groundwater was shallow, the soil drill was used for on-site drilling and sampling. If transfer was required, the sample was stored in a low-temperature sealed container in the dark. The sample was sent to the testing agency for determination of the concentration using a liquid chromatograph.

[0109] It can be seen that compared with Comparative Examples 1-3, the composite filler of Example 1-2 can better degrade and treat various coexisting pollutants in groundwater, such as heavy metals, organic pollutants, phosphate and nitrogen pollutants, etc., especially for organic pollution and nitrogen pollution, a sustained and efficient removal effect can be maintained, and the use of PMS and nZVI in the PRB has a synergistic effect while maintaining the sustained and efficient oxidation and reduction reaction. This treatment effect is still sustained after 3 months, although it has decreased. By supplementing Na2CO3 and NaOH solution, the intercalation of inorganic salts in the interlayer structure of LDHs and the in-situ generation of LDHs can be promoted. Although the composite filler is difficult to restore to the treatment efficiency of the first 3 days, it still has high efficient degradation and treatment capacity. After that, by soaking in high concentration NaCL solution to increase the number of recycling, it also prolongs the service life of the filler, ensuring the sustained and efficient degradation of pollution. Example 2 achieves the optimal synergistic degradation and catalytic effect.

[0110] Although the present application has been described in detail with reference to the foregoing embodiments, it should be understood that those skilled in the art can make modifications to the technical solutions described in the foregoing embodiments, or make equivalent replacements to some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application. Any changes or replacements that can be easily thought of by those skilled in the art within the scope of the disclosed technology should be covered within the protection scope of the present application.

Claims

1. A composite filler for treating multiple types of pollution in groundwater, characterized in that... It includes a first component and a second component, the first component comprising a first powder and a second powder mixed together, the second component comprising a third powder and a fourth powder as filler portions, and additionally added peroxymonosulfate PMS. The first powder comprises biochar, an adsorbed layered double hydroxide LDH1 supported on the surface of the biochar, and nano-zero valent iron nZVI supported on the LDH1. The second powder comprises the biochar, a catalytic layered double hydroxide LDH2 supported on the surface of the biochar, and nano-zero-valent iron nZVI supported on the LDH2. The third powder contains biochar and the adsorbed layered double hydroxide LDH1 supported on the surface of the biochar. The fourth powder comprises biochar and the catalytic layered double hydroxide LDH2 supported on the surface of the biochar. LDH1 and LDH2 are represented by the following formula: [M 1-x 2+ M x 3+ (OH)2] x+ [A n- ]·zH2O For LDH1, M 2+ Mg 2+ M 3+ For Al 3+ For LDH2, M 2+ For Ni 2+ M 3+ For Fe 3+ , X represents the molar ratio M. 3+ / ( M 2+ + M 3+ A n- For containing Cl - and CO3 2- The interlayer anions, where n is the number of negative charges and z is the number of water molecules in the interlayer structure, wherein the first component and the second component are mutually isolated for maintenance and use, wherein the nano-zero-valent iron nZVI is nano-zero-valent iron nZVI modified by mineral fulvic acid grown in situ on the adsorption-type layered double hydroxide LDH1 and the catalytic-type layered double hydroxide LDH2 in the presence of mineral fulvic acid, and wherein the biochar is obtained by acid washing, alkali washing, drying and hot grinding of at least one of reeds, calamus, shrubs, leaves, seaweed, phytoplankton, seed shells, fruit peels and corn stalks, wherein the specific surface area of ​​the biochar is 600-1100 m². 2 / g, with a porosity of 30-70%, a particle size of 50-200 mesh, and an average pore diameter of 10-50nm.

2. The method for preparing the composite filler for treating multiple types of pollution in groundwater according to claim 1, characterized in that... Includes the following steps: S1 - Provides a first component, the first component comprising a first powder and a second powder; S2 provides a second component, which includes a third powder, a fourth powder, and persulfate PMS as an oxidant; S3 - Seal and package the first component and the second component separately to obtain the composite filler, wherein step S1 includes the following steps: S11 - Providing a first powder, wherein step S11 includes: S111 - Provides a mixed solution E containing magnesium chloride hydrate and aluminum chloride hydrate; S112 - Provides a mixed solution F containing NaOH and Na2CO3; S113 - Place solution C containing formamide into the first reaction vessel, then add solution E and solution F, adjust the pH to 8-10, stir the reaction at 80-100℃ under an inert atmosphere for 50-70 minutes, then transfer to the second reaction vessel, and continue stirring the reaction at 120-130℃ under an inert atmosphere for 8-9 hours. After the reaction is completed, cool to obtain reaction mixture I. S114 - Add reaction mixture I to solution IV containing N-dimethylformamide and ethanol, sonicate for 8-14 hours, wash the resulting reaction gel, and grind it in a grinder to obtain a slurry of adsorbed layered double hydroxide LDH1; S115 - Nano-zero-valent iron nZVI is loaded onto the adsorbed layered double hydroxide LDH1 to obtain the LDH1-nZVI material structure; S116 - The LDH1-nZVI material structure is mixed with a dispersion containing biochar, and reacted in a reaction vessel at 110-120°C for 6-8 hours under inert gas protection to obtain the first reaction product. S117 - The first reaction product is dried and then ground to obtain the first powder; S12 - Providing a second powder, wherein step S12 includes: S121 - Provides a mixed solution A containing nickel chloride hydrate and ferric chloride hydrate; S122 - Provides a mixed solution B containing NaOH and Na2CO3; S123 - Place solution C containing formamide into the third reaction vessel, then add solution A and solution B, adjust the pH to 8-10, stir the reaction at 60-100℃ under an inert atmosphere for 30-60 minutes, then transfer to the fourth reaction vessel, continue stirring the reaction at 110-130℃ under an inert atmosphere for 5-9 hours, and cool after the reaction to obtain reaction mixture II; S124 - The reaction mixture is added to solution III containing N-dimethylformamide and ethanol, ultrasonically aged for 8-14 hours, the resulting reaction gel is washed and ground in a grinder to obtain a slurry of catalytic layered double hydroxide LDH2; S125 - Nano-zero-valent iron nZVI is loaded onto the catalytic layered double hydroxide LDH2 to obtain the LDH2-nZVI material structure; S126 - The LDH2-nZVI material structure is mixed with a dispersion containing biochar, and reacted in a reaction vessel at 100-120°C for 6-8 hours under inert gas protection to obtain a second reaction product. S127 - The second reaction product is dried and then ground to obtain a second powder; S13 - The first powder and the second powder are mixed together to obtain the first component. The step S2 mentioned above includes the following steps: S21 - Providing a third powder, wherein step S21 includes: S211 - The slurry of adsorbed layered double hydroxide LDH1 obtained in step S114 is mixed with a dispersion containing biochar and reacted in a reaction vessel at a temperature of 110-120°C for 6-8 hours under inert gas protection to obtain the third reaction product. S212 - The third reaction product is dried and then ground to obtain a third powder; S22 - Provide a fourth powder, wherein step S12 includes: S221 - The slurry of the catalytic layered double hydroxide LDH2 obtained in S124 is mixed with a dispersion containing biochar and reacted in a reaction vessel at a temperature of 110-120°C for 6-8 hours under inert gas protection to obtain the fourth reaction product. S222 The fourth reaction product is dried and then ground to obtain the fourth powder; S23 - The third powder and the fourth powder are mixed together to obtain the powder filler portion of the second component; S24 - The powder filler portion of the second component is mixed with PMS to obtain the second component.

3. The preparation method according to claim 2, characterized in that, Step 115 includes: dissolving mineral-derived fulvic acid in water under a protective gas atmosphere, then adding an aqueous solution containing ferric chloride and ethanol, stirring, adding a slurry of adsorbed layered double hydroxide LDH1, ultrasonically vibrating to ensure uniform dispersion, then adding sodium borohydride solution dropwise, continuing the reaction for 50-70 minutes, filtering, washing, and drying to obtain the LDH1-nZVI material structure; and Step 125 includes: under a protective gas atmosphere, dissolving mineral-derived fulvic acid in water, then adding ferric chloride and ethanol, stirring, adding a slurry of catalytic layered double hydroxide LDH2, ultrasonically oscillating it to make it uniformly dispersed, then adding sodium borohydride solution dropwise, continuing the reaction for 40-60 minutes, filtering, washing, and drying to obtain the LDH2-nZVI material structure.

4. The preparation method according to claim 2, characterized in that, The concentrations of the aluminum chloride hydrate solution and the magnesium chloride hydrate solution are 0.010 mol / L to 0.03 mol / L and 0.030 to 0.090 mol / L, respectively, and the concentrations of the nickel chloride hydrate solution and the ferric chloride hydrate solution are 0.0500 mol / L to 0.1000 mol / L and 0.0200 mol / L to 0.0500 mol / L, respectively.

5. The preparation method according to claim 2, characterized in that... Step S113 includes adding the formamide-containing solution C to the first reaction vessel, pre-stirring it for 5-10 minutes using a heated grinding and stirring machine, then simultaneously adding solutions E and F to the first reaction vessel using infusion tubes, and then heating and stirring the reaction at a temperature of 60-100°C for 45-50 minutes under nitrogen protection, wherein the capacity of the second reaction vessel is greater than that of the first reaction vessel, and the dripping rate of solutions E and F is 3-5 ml / min; Step S123 includes: after adding the formamide-containing solution C to the third reaction vessel, pre-stirring with a heated grinding and stirring machine for 8-12 minutes; then simultaneously adding solutions A and B dropwise into the third reaction vessel using infusion tubes; and then heating and stirring the reaction at 80-100°C for 50-70 minutes under nitrogen protection, wherein the capacity of the fourth reaction vessel is greater than that of the third reaction vessel, and the dropping rate of solutions A and B is 6-8 ml / min; and The diameter of the needle in the infusion tubing is 0.30 to 0.60 μm.

6. A permeable reactive wall, characterized in that... It includes a first tubular structural unit and a second tubular structural unit, wherein the first tubular structural unit contains the first component as described in any one of claims 1 to 2, and the second tubular structural unit contains the second component as described in any one of claims 1 to 2.

7. A method for treating complex pollution of groundwater using the permeable reactive wall of claim 6 under the influence of groundwater level fluctuations in an unsaturated aquifer, characterized in that... Multiple first tubular structural units and multiple second tubular structural units are connected according to the actual site's pollutant migration depth, span, speed, and pollutant source type to construct the permeable reactive wall.

8. The method according to claim 7, characterized in that, The first and second tubular structural units are also connected to delivery pipes to replenish the consumed PMS, or to deliver alkaline NaOH and Na2CO3 to form new single-element LDH structures in the composite filler, or to deliver solutions containing Na2SO4, Na2CO3 and / or NaCl for intercalation reconstruction of LDH1 and LDH2, provided that nZVI and PMS still have redox properties.

Images