PRB active material with core-shell structure and preparation method thereof

Abstract

The invention relates to a PRB active material with a core-shell structure and a preparation method thereof.According to the method, an inert material is adopted as a carrier, a layer of active material is loaded on the surface and in pore channels of the carrier, the active material is composed of nanoscale zero-valent iron, a natural mineral material and a porous material, and the inert carrier provides high mechanical strength for the active material; and the nano zero-valent iron, the natural mineral material and the porous material exist on the carrier in a coating state, so that the contact area is large, and the permeability is good. The PRB active material with the core-shell structure prepared by the invention is simple in preparation process and relatively low in cost, and has a relatively good industrial application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of groundwater pollution remediation, and in particular to a PRB active material with a core-shell structure and a preparation method thereof. Background Art

[0002] Heavy metal pollution (Cr, Pb, As, etc.) is the main problem of groundwater pollution. Compared with other pollution factors, heavy metals are persistent and difficult to degrade or destroy. In addition, heavy metals in groundwater will also be enriched through the food chain, endangering human health. Therefore, it is of great significance to develop effective groundwater heavy metal pollution remediation technology.

[0003] Permeable reactive wall (PRB) technology is an economical, simple and efficient in-situ remediation technology for groundwater pollution. This technology is to implant a wall between the soil and groundwater and fill the wall with active materials. Through natural or artificial hydraulic gradients, pollutants in the groundwater are converted into low-toxic or non-toxic components when flowing through the reactive wall. Active materials are the core of PRB technology, and their performance directly determines the stability and practicality of PRB technology.

[0004] In recent years, in order to further improve the remediation effect of PRB technology on groundwater, researchers have tried to prepare new active materials. Chinese invention patent CN105502671B discloses PRB fillers for repairing Pb / Cd pollution, and their preparation methods and effect verification methods. The PRB active materials in the invention are composed of 10% quartz sand, 20% dry straw or composite straw, 20% fly ash-based zeolite, 20% iron-manganese nodules, 20% fly ash and 10% quartz sand. Chinese invention patent CN104803486B discloses a permeable reaction wall material and preparation method for repairing chromium pollution in groundwater. The active material of PRB in this method is composed of a mixture of reaction medium, quartz sand and soil. The reaction medium is a granular material, including reducing media sodium bisulfite, sodium thiosulfate, sodium dithionite, and citric acid, the adsorption medium is activated carbon, apatite, peat, diatomaceous earth, and the biological medium is humic acid, straw, sawdust, straw, and cement. However, in existing reports, most PRB active materials are in powder or granular form. After long-term use, the powder is prone to compaction and the granules are prone to breakage, which affects the overall repair effect of PRB. Summary of the invention

[0005] In order to solve the above problems, the present invention designs a core-shell structured PRB active material and a preparation method thereof, wherein the core-shell structured PRB active material uses cordierite or alumina as a carrier, loads nano zero-valent iron, natural mineral materials and porous materials, effectively solves the problem of insufficient mechanical strength of traditional PRB filling materials, and has strong stability.

[0006] In order to solve the above technical problems, the present invention provides a method for preparing a core-shell structured PRB active material, which is characterized by comprising the following steps:

[0007] S1: weigh natural mineral materials and porous materials in a mass ratio of 1:1-1:4, add them into deionized water, solid-liquid ratio of 1:5-1:10, adjust the pH value to 1-5, add inorganic binder, and ball mill for 4-8h;

[0008] S2: Prepare an organic binder solution with a mass fraction of 3-6%, add it to the mixed solution after ball milling in step S1, and the volume ratio of the two is 2:1-10:1. After stirring and mixing evenly, immerse the carrier in the mixed solution, take it out after 5-30 minutes, remove the residual mixed solution on the surface and pores of the carrier with compressed air, dry it, and then calcine it at 400-600℃ for 4-8h in an inert atmosphere;

[0009] S3: placing the support material obtained by calcining in step S2 in a ferric chloride solution, soaking it at room temperature for 1-4 hours, and then drying it. Then, placing the support material loaded with Fe ions in a NaBH4 or KBH4 aqueous solution, soaking it at room temperature for 2-6 hours under an inert atmosphere, taking it out, washing it with water, and drying it to obtain a core-shell structured PRB active material.

[0010] Further: the natural mineral material in the above step S1 is one of sepiolite, attapulgite, kaolin, and montmorillonite, the porous material in the above step S1 is one of biochar and graphene oxide, and the inorganic binder in the above step S1 is one of aluminum sol and silica sol.

[0011] Furthermore: the organic binder solution prepared in the above step S2 is mixed with the mixed liquid after ball milling in step S1 in a stirring tank, and the stirring tank is composed of a support plate, a material storage tank, a material guide cover, an upper tank body and a lower tank body, and the support plate is suspended by a plurality of columns arranged at the bottom, and the upper end of the upper tank body is open and fixed to the bottom of the support plate, and a feed port is provided on the support plate above the upper tank body, and the upper end of the lower tank body extends into the lower end of the upper tank body through a lifting mechanism, and the outer wall size of the lower tank body matches the inner wall size of the upper tank body, and a liquid outlet is provided at the bottom of the lower tank body, and two material storage tanks are provided, and the two material storage tanks and a material guide cover are arranged on a slide plate from left to right in sequence, and a placement cylinder for placing the material storage tank is provided on the slide plate, and the upper The two lower ends are open, the material storage tank is placed into the placing cylinder from the upper end and is supported and connected to the support seat on the inner wall of the placing cylinder through a support rod, a guide groove is provided on the top of the support seat, the lower end of the support rod extends into the guide groove and is connected to the weighing sensor, two material storage tanks and a slide plate just below a material guide cover are provided with discharge ports matching the feed ports, the three discharge ports on the slide plate pass through the feed port in sequence through a double electric cylinder translation mechanism, two stirring motors are respectively installed on the support plates on the front and rear sides of the double electric cylinder translation mechanism, the output shaft of the stirring motor extends into the upper tank body and is connected to the stirring mechanism, a filter assembly is horizontally arranged in the lower end of the lower tank body, the outer walls of the filter assembly are in contact with the inner wall of the lower tank body, a vibrating electric cylinder is also installed at the bottom of the lower tank body, the vibrating electric cylinder extends into the lower tank body and is connected to the filter assembly.

[0012] Furthermore: the dual electric cylinder translation mechanism includes a slide rail, a first translation drive electric cylinder and a second translation drive electric cylinder. The slide rail is arranged on the top of the support plate and placed left and right. The slide plate is connected to the slide rail through a slide groove opened at the bottom. The first translation drive electric cylinder is installed on the top of the right end of the slide plate. The second translation drive electric cylinder is installed on the top of the right end of the support plate. The extension directions of the output shaft ends of the first translation drive electric cylinder and the second translation drive electric cylinder are parallel to the slide rail. The output shaft end of the first translation drive electric cylinder is connected to the output shaft end of the second translation drive electric cylinder through a coupling.

[0013] Furthermore: the lifting mechanism includes a lifting electric cylinder and an L-shaped slide, an L-shaped slide is arranged on each of the left and right sides of the lower tank body, a guide through hole matching the column is opened on the L-shaped slide, the L-shaped slide is connected to the column through the guide through hole, a lifting electric cylinder is arranged on the bottom of the support plate directly above the two L-shaped slides, the output shaft ends of the two lifting electric cylinders are respectively connected to an L-shaped slide, the L-shaped slide is driven by the lifting electric cylinder to slide up and down and is connected to the column, wherein a servo motor is installed on the L-shaped slide on the left side, the output shaft of the servo motor is connected to the left outer wall of the lower tank body, and the right outer wall of the lower tank body is connected to the L-shaped slide on the right side through a rotating shaft.

[0014] Furthermore: the organic binder in the above step S2 is one of hydroxypropyl cellulose, hydroxymethylpropyl cellulose, and carboxyethyl cellulose; the carrier in the above step S2 is made of cordierite or alumina, and has a shape of honeycomb, spherical, strip, or ring.

[0015] Furthermore: the soaking-drying step described in the above step S2 can be repeated multiple times until the mass fraction of the natural mineral material and porous material loaded on the carrier reaches 3-5%.

[0016] Furthermore: A core-shell structured PRB active material prepared by the above preparation method is composed of a carrier and a shell material loaded on the carrier, and the shell material is specifically composed of the following components in terms of mass fraction: the mass fraction of natural mineral materials and porous materials is 80-90%, the mass fraction of Al2O3 or SiO2 is 5-15%, and the mass fraction of Fe is 5-10%.

[0017] Further: the effect of the core-shell structured PRB active material is verified by a PRB column experiment, which specifically includes the following steps:

[0018] A1: PRB filling materials with core-shell structure are loaded into the reaction column, and quartz sand is loaded above and below the reaction column as a permeable layer;

[0019] A2: Prepare an aqueous solution containing heavy metal ions and use a peristaltic pump to inject the solution from the bottom of the reaction column;

[0020] A3: After a certain period of time, sample and analyze the solution at the outlet of the upper part of the reaction column to detect the concentration of heavy metal ions.

[0021] Furthermore: the filling amount of the core-shell structure PRB filling material is 50-100g, and the heavy metal ion is Cr2O7 2- , Pb 2+ 、Cd 2+ 、Ni 2+ , Cu 2+ One or more of the above, the concentration of heavy metal ions is 1-20 mg / L, and the solution flow rate is 1-20 mL / min.

[0022] After adopting the above structure, the beneficial effects of the present invention are as follows:

[0023] 1. The core-shell structured PRB filling material prepared by the present invention uses cordierite or alumina as a carrier to load nano zero-valent iron, natural mineral materials and porous materials, effectively solving the problem of insufficient mechanical strength of traditional PRB filling materials and having strong stability;

[0024] 2. The core-shell structured PRB filling material prepared by the present invention has the characteristics of a core-shell structure. The carrier is inert cordierite or alumina, and the active material is loaded nano zero-valent iron, natural mineral materials and porous materials. The active material is attached to the surface or pores of the carrier in a relatively thin coating state, which increases the contact area, reduces the penetration depth, enhances the effective contact between the active material and the pollutant, and improves the removal effect of the material on the pollutant.

[0025] 3. The preparation process of the present invention is simple, the preparation cost is low, environmentally friendly materials are used, and there is no secondary pollution problem.

[0026] 4. The stirring tank used in the present invention can automatically add corresponding amounts of organic binder solution and carrier according to the amount of the ball-milled mixed solution added, without manual addition. It has the advantages of easy use, accurate addition of dosage, and practicality and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0028] Figure 1 Schematic diagram of the structure of the mixing tank.

[0029] Figure 2 This is a structural diagram of the connection between the storage tank and the placement cylinder.

[0030] In the figure: 1 is a support plate, 2 is an upper tank body, 3 is a lower tank body, 4 is a material storage tank, 5 is a material guide cover, 6 is a slide plate, 7 is a slide rail, 8 is a first translation drive electric cylinder, 9 is a second translation drive electric cylinder, 10 is a lifting electric cylinder, 11 is a column, 12 is an L-shaped slide seat, 13 is a servo motor, 14 is a rotating shaft, 15 is a filter assembly, 16 is a vibration electric cylinder, 17 is a support rod, 18 is a weighing sensor, 19 is a placement cylinder, and 20 is a support seat. DETAILED DESCRIPTION

[0031] The present invention provides a method for preparing a core-shell structured PRB active material, which specifically comprises the following steps:

[0032] S1: weigh natural mineral materials and porous materials in a mass ratio of 1:1-1:4, add them into deionized water, solid-liquid ratio of 1:5-1:10, adjust the pH value to 1-5, add inorganic binder, and ball mill for 4-8h;

[0033] S2: Prepare an organic binder solution with a mass fraction of 3-6%, add it to the mixed solution after ball milling in step S1, and the volume ratio of the two is 2:1-10:1. After stirring and mixing evenly, immerse the carrier in the mixed solution, take it out after 5-30 minutes, remove the residual mixed solution on the surface and pores of the carrier with compressed air, dry it, and then calcine it at 400-600℃ for 4-8h in an inert atmosphere;

[0034] S3: placing the support material obtained by calcining in step S2 in a ferric chloride solution, soaking it at room temperature for 1-4 hours, and then drying it. Then, placing the support material loaded with Fe ions in a NaBH4 or KBH4 aqueous solution, soaking it at room temperature for 2-6 hours under an inert atmosphere, taking it out, washing it with water, and drying it to obtain a core-shell structured PRB active material.

[0035] The natural mineral material in the above step S1 is one of sepiolite, attapulgite, kaolin, and montmorillonite, the porous material in the above step S1 is one of biochar and graphene oxide, and the inorganic binder in the above step S1 is one of aluminum sol and silica sol.

[0036] The organic binder solution prepared in step S2 and the mixed solution after ball milling in step S1 are mixed in a stirring tank. Figure 1 and Figure 2The mixing tank shown is composed of a support plate 1, a material storage tank 4, a material guide cover 5, an upper tank body 2 and a lower tank body 3. The support plate is suspended by a plurality of columns 11 arranged at the bottom. The upper end of the upper tank body is open and fixed to the bottom of the support plate. A feed port is provided on the support plate above the upper tank body. The upper end of the lower tank body extends into the lower end of the upper tank body through a lifting mechanism. The outer wall size of the lower tank body matches the inner wall size of the upper tank body. A liquid outlet is provided at the bottom of the lower tank body. Two material storage tanks are provided. Two material storage tanks and a material guide cover are arranged on a slide plate 6 from left to right in sequence. A placement cylinder 19 for placing the material storage tank is provided on the slide plate. The upper and lower ends of the placement cylinder are open, and the material storage tank is placed into the placement cylinder from the upper end. It is supported and connected to a support seat 20 on the inner wall of the placement cylinder through a support rod 17, a guide groove is provided on the top of the support seat, the lower end of the support rod extends into the guide groove and is connected to a weighing sensor 18, two material storage tanks and a slide plate just below a material guide cover are provided with discharge ports matching the feed port, the three discharge ports on the slide plate pass through the feed port in sequence through a double electric cylinder translation mechanism, two stirring motors are respectively installed on the support plates on the front and rear sides of the double electric cylinder translation mechanism, the output shaft of the stirring motor extends into the upper tank body and is connected to the stirring mechanism, a filter assembly 15 is horizontally arranged in the lower end of the lower tank body, the outer walls of the filter assembly are in contact with the inner wall of the lower tank body, a vibrating electric cylinder 16 is also installed at the bottom of the lower tank body, the vibrating electric cylinder extends into the lower tank body and is connected to the filter assembly. One of the two storage tanks on the support plate is used to store 3-6% organic binder solution, and the other is used to store the carrier; during operation, a certain amount of ball-milled mixed liquid is poured into the lower tank body through the material guide cover, and then the organic binder solution is added in proportion to mix, and after stirring and mixing evenly, the carrier is immersed in the mixed solution and soaked for 5-30 minutes, and then the liquid outlet at the bottom is opened to discharge and collect the mixed liquid, and then the lower tank body is lowered to separate it from the upper tank body, and then the lower tank body is turned over to pour out the soaked carrier. The stirring tank used in the present invention can automatically add the corresponding amount of organic binder solution and carrier according to the amount of ball-milled mixed liquid added, without manual addition, and has the advantages of easy use, accurate dosage, and practicality and efficiency. And through the design of the vibrating electric cylinder, all the carriers remaining on the filter assembly can be dumped out.

[0037] like Figure 1The double electric cylinder translation mechanism shown includes a slide rail 7, a first translation drive electric cylinder 8 and a second translation drive electric cylinder 9. The slide rail is arranged on the top of the support plate and placed left and right. The slide plate is connected to the slide rail through a slide groove provided at the bottom. The first translation drive electric cylinder is installed on the top of the right end of the slide plate, and the second translation drive electric cylinder is installed on the top of the right end of the support plate. The extension direction of the output shaft ends of the first translation drive electric cylinder and the second translation drive electric cylinder are parallel to the slide rail. The output shaft end of the first translation drive electric cylinder is connected to the output shaft end of the second translation drive electric cylinder through a coupling. When the first translation drive electric cylinder and the second translation drive electric cylinder are not started, the material guide cover faces the feed port. When the second translation drive electric cylinder is started, the material storage tank containing the organic binder solution faces the feed port. After the first translation drive electric cylinder and the second translation drive electric cylinder are started, the material storage tank containing the carrier faces the feed port.

[0038] like Figure 1 The lifting mechanism shown includes a lifting electric cylinder 10 and an L-shaped slide 12. An L-shaped slide is respectively arranged on the left and right sides of the lower tank body. The L-shaped slide is provided with a guide through hole matching the column. The L-shaped slide is connected to the column through the guide through hole. A lifting electric cylinder is respectively arranged at the bottom of the support plate directly above the two L-shaped slides. The output shaft ends of the two lifting electric cylinders are respectively connected to an L-shaped slide. The L-shaped slide is driven by the lifting electric cylinder to slide up and down and is connected to the column. A servo motor 13 is installed on the L-shaped slide on the left side. The output shaft of the servo motor is connected to the left outer wall of the lower tank body. The right outer wall of the lower tank body is connected to the L-shaped slide on the right side through a rotating shaft 14.

[0039] The organic binder in the above step S2 is one of hydroxypropyl cellulose, hydroxymethyl propyl cellulose, and carboxyethyl cellulose; the carrier in the above step S2 is made of cordierite or alumina, and has a shape of honeycomb, spherical, strip, or ring.

[0040] The soaking-drying step described in the above step S2 can be repeated multiple times until the mass fraction of the natural mineral material and porous material loaded on the carrier reaches 3-5%.

[0041] A core-shell structured PRB active material prepared by the above preparation method is composed of a carrier and a shell material loaded on the carrier, wherein the shell material is specifically composed of the following components in terms of mass fraction: a natural mineral material and a porous material with a mass fraction of 80-90%, an Al2O3 or SiO2 mass fraction of 5-15%, and a Fe mass fraction of 5-10%.

[0042] The effect of the above-mentioned core-shell structured PRB active material is verified by a PRB column experiment, which specifically includes the following steps:

[0043] A1: PRB filling materials with core-shell structure are loaded into the reaction column, and quartz sand is loaded above and below the reaction column as a permeable layer;

[0044] A2: Prepare an aqueous solution containing heavy metal ions and use a peristaltic pump to inject the solution from the bottom of the reaction column;

[0045] A3: After a certain period of time, sample and analyze the solution at the outlet of the upper part of the reaction column to detect the concentration of heavy metal ions.

[0046] The filling amount of the PRB filling material of the core-shell structure is 50-100g, and the heavy metal ion is Cr2O7 2- , Pb 2+ 、Cd 2+ 、Ni 2+ , Cu 2+ One or more of the above, the concentration of heavy metal ions is 1-20 mg / L, and the solution flow rate is 1-20 mL / min.

[0047] Example 1

[0048] According to the mass ratio of 1:1, attapulgite and biochar were weighed separately, added to deionized water, solid-liquid ratio of 1:5, pH value was adjusted to 1, silica sol was added, and ball milling was carried out for 4 hours. A 3% mass fraction of hydroxymethyl propyl cellulose solution was prepared and added to the mixed solution after ball milling, the volume ratio of the two was 2:1, and after stirring and mixing evenly, the cordierite honeycomb was immersed in the mixed solution, taken out after 5 minutes, and the residual mixed solution on the surface and / or pores of the carrier was removed by compressed air, dried, and then calcined at 600℃ for 4 hours under an inert atmosphere. Among them, the mass fraction of attapulgite and biochar loaded on the carrier is 4%.

[0049] The calcined cordierite honeycomb was placed in a ferric chloride solution, soaked at room temperature for 1 hour, and dried. The carrier material loaded with Fe ions was then placed in a NaBH4 aqueous solution, soaked at room temperature for 3 hours under an inert atmosphere, taken out, washed with water, and dried to obtain a core-shell structured PRB active material.

[0050] The composition of the shell material loaded on the carrier is: the mass fraction of attapulgite and biochar is 80%, the mass fraction of SiO2 is 15%, and the mass fraction of Fe is 5%.

[0051] Example 2

[0052] According to the mass ratio of 1:4, kaolin and graphene oxide were weighed separately, added to deionized water, solid-liquid ratio of 1:10, pH value was adjusted to 5, aluminum sol was added, and ball milling was performed for 8 hours. A 6% hydroxypropyl cellulose solution was prepared and added to the mixed solution after ball milling, the volume ratio of the two was 10:1, and after stirring and mixing evenly, the cordierite ring was immersed in the mixed solution, taken out after 30 minutes, and the mixed solution remaining on the surface and / or pores of the carrier was removed by compressed air, dried, and then calcined at 500°C for 5 hours under an inert atmosphere. Among them, the mass fraction of kaolin and graphene oxide loaded on the carrier is 3%.

[0053] The calcined support material was placed in a ferric chloride solution, soaked at room temperature for 4 hours, and dried. The support material loaded with Fe ions was then placed in a KBH4 aqueous solution, soaked at room temperature for 2 hours under an inert atmosphere, taken out, washed with water, and dried to obtain a core-shell structured PRB active material.

[0054] The composition of the shell material loaded on the carrier is: the mass fraction of kaolin and graphene oxide is 90%, the mass fraction of Al2O3 is 5%, and the mass fraction of Fe is 5%.

[0055] Example 3

[0056] Weigh sepiolite and biochar in a mass ratio of 1:2, add them to deionized water, solid-liquid ratio of 1:8, adjust the pH value to 2, add silica sol, and ball mill for 4 hours. Prepare a 3% mass fraction carboxyethyl cellulose solution and add it to the mixed solution after ball milling. The volume ratio of the two is 5:1. After stirring and mixing evenly, immerse the alumina ball in the mixed solution, take it out after 10 minutes, use compressed air to remove the residual mixed solution on the surface and / or pores of the carrier, dry it, and repeat the immersion-drying steps 3 times. Then calcine at 400℃ for 8 hours in an inert atmosphere. Among them, the mass fraction of sepiolite and biochar loaded on the carrier is 5%.

[0057] The calcined support material was placed in a ferric chloride solution, soaked at room temperature for 2 hours, and dried. The support material loaded with Fe ions was then placed in a NaBH4 aqueous solution, soaked at room temperature for 6 hours under an inert atmosphere, taken out, washed with water, and dried to obtain a core-shell structured PRB active material.

[0058] The composition of the shell material loaded on the carrier is: the mass fraction of sepiolite and biochar is 85%, the mass fraction of SiO2 is 10%, and the mass fraction of Fe is 5%.

[0059] Example 4

[0060] According to the mass ratio of 1:3, kaolin and graphene oxide were weighed separately, added to deionized water, the solid-liquid ratio was 1:6, the pH value was adjusted to 3, aluminum sol was added, and ball milling was carried out for 6 hours. A 4% mass fraction of hydroxymethyl propyl cellulose solution was prepared and added to the mixed solution after ball milling. The volume ratio of the two was 4:1. After stirring and mixing evenly, the alumina strip was immersed in the mixed solution. After 20 minutes, it was taken out and the residual mixed solution on the surface and / or pores of the carrier was removed with compressed air, and dried. The immersion-drying steps were repeated 3 times. Then calcined at 500℃ for 4 hours in an inert atmosphere. Among them, the mass fraction of kaolin and graphene oxide loaded on the carrier is 4.5%.

[0061] The calcined support material was placed in a ferric chloride solution, soaked at room temperature for 2 hours, and dried. The support material loaded with Fe ions was then placed in a KBH4 aqueous solution, soaked at room temperature for 2 hours under an inert atmosphere, taken out, washed with water, and dried to obtain a core-shell structured PRB active material.

[0062] The composition of the shell material loaded on the carrier is as follows: the mass fraction of kaolin and graphene oxide is 80%, the mass fraction of Al2O3 is 10%, and the mass fraction of Fe is 10%.

[0063] Example 5

[0064] Weigh sepiolite and biochar in a mass ratio of 1:2, add them to deionized water, solid-liquid ratio of 1:8, adjust pH value to 4, add silica sol, and ball mill for 5h. Prepare 5% hydroxypropyl cellulose solution by mass fraction, add it to the mixed solution after ball milling, the volume ratio of the two is 8:1, stir and mix evenly, immerse cordierite honeycomb in the mixed solution, take it out after 15 minutes, remove the residual mixed solution on the surface and / or pores of the carrier with compressed air, dry it, and then calcine it at 550℃ for 6h in an inert atmosphere. Among them, the mass fraction of sepiolite and biochar loaded on the carrier is 3.5%.

[0065] The calcined support material was placed in a ferric chloride solution, soaked at room temperature for 1 hour, and dried. The support material loaded with Fe ions was then placed in a NaBH4 aqueous solution, soaked at room temperature for 4 hours under an inert atmosphere, taken out, washed with water, and dried to obtain a core-shell structured PRB active material.

[0066] The composition of the shell material loaded on the carrier is as follows: the mass fraction of sepiolite and biochar is 90%, the mass fraction of SiO2 is 5%, and the mass fraction of Fe is 5%.

[0067] Comparative Example 1

[0068] According to the mass ratio of 1:1, attapulgite and biochar were weighed separately, added to deionized water, solid-liquid ratio of 1:5, pH value was adjusted to 1, silica sol was added, and ball milling was carried out for 4 hours. A 3% mass fraction of hydroxymethyl propyl cellulose solution was prepared and added to the mixed solution after ball milling, the volume ratio of the two was 2:1, and after stirring and mixing evenly, the cordierite honeycomb was immersed in the mixed solution, taken out after 5 minutes, and the residual mixed solution on the surface and / or pores of the carrier was removed by compressed air, dried, and then calcined at 600℃ for 4 hours under an inert atmosphere. Among them, the mass fraction of attapulgite and biochar loaded on the carrier is 4%.

[0069] The composition of the shell material loaded on the carrier is: the mass fraction of attapulgite and biochar is 84%, and the mass fraction of SiO2 is 16%.

[0070] Test Example 1

[0071] 40g of PRB filling material was filled in the reaction column, and quartz sand was filled above and below the reaction column as a permeable layer. 2- The aqueous solution of ions, with a concentration of 5 mg / L, was injected from the bottom of the reaction column using a peristaltic pump at a flow rate of 2 mL / min. The solution at the outlet of the upper part of the reaction column was sampled and analyzed regularly to detect Cr2O7 2- The concentration of Cr2O7 2- As shown in the following table:

[0072]

[0073] Table 1 shows the Cr2O7 in solution 2- Removal rate

[0074] Test Example 2

[0075] 40g of PRB filling material was filled in the reaction column, and quartz sand was filled above and below the reaction column as a permeable layer. 2+ The aqueous solution of ions, with a concentration of 10 mg / L, was injected from the bottom of the reaction column using a peristaltic pump at a flow rate of 2 mL / min. The solution at the outlet of the upper part of the reaction column was sampled and analyzed regularly to detect Pb 2+ The concentration of Pb 2+ As shown in the following table:

[0076]

[0077] Table 2 shows the Pb content in the solution 2+ Removal rate

[0078] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a core-shell structured PRB active material, characterized in that: The specific steps include: S1: weigh natural mineral materials and porous materials in a mass ratio of 1:1-1:4, add them into deionized water, solid-liquid ratio of 1:5-1:10, adjust the pH value to 1-5, add inorganic binder, and ball mill for 4-8h; S2: Prepare an organic binder solution with a mass fraction of 3-6%, add it to the mixed solution after ball milling in step S1, and the volume ratio of the two is 2:1-10:

1. After stirring and mixing evenly, immerse the carrier in the mixed solution, take it out after 5-30 minutes, remove the residual mixed solution on the surface and pores of the carrier with compressed air, dry it, and then calcine it at 400-600℃ for 4-8h in an inert atmosphere; S3: placing the support material obtained by calcining in step S2 in a ferric chloride solution, soaking it at room temperature for 1-4 hours, and then drying it. Then, placing the support material loaded with Fe ions in a NaBH4 or KBH4 aqueous solution, soaking it at room temperature for 2-6 hours under an inert atmosphere, taking it out, washing it with water, and drying it to obtain a core-shell structured PRB active material.

2. The method for preparing a core-shell PRB active material according to claim 1, characterized in that: The natural mineral material in the above step S1 is one of sepiolite, attapulgite, kaolin, and montmorillonite, the porous material in the above step S1 is one of biochar and graphene oxide, and the inorganic binder in the above step S1 is one of aluminum sol and silica sol.

3. The method for preparing a core-shell PRB active material according to claim 1, characterized in that: The organic binder solution prepared in the above step S2 is mixed with the mixed solution after ball milling in step S1 in a stirring tank. The stirring tank is composed of a support plate (1), a material storage tank (4), a material guide cover (5), an upper tank body (2) and a lower tank body (3). The support plate is suspended by a plurality of columns (11) arranged at the bottom. The upper end of the upper tank body is open and fixed to the bottom of the support plate. A feed inlet is provided on the support plate above the upper tank body. The upper end of the lower tank body extends into the lower end of the upper tank body through a lifting mechanism. The outer wall size of the lower tank body matches the inner wall size of the upper tank body. The bottom of the lower tank body is provided with a liquid outlet. Two material storage tanks are provided. The two material storage tanks and a material guide cover are arranged on a slide plate (6) from left to right in sequence. The slide plate is provided with a placement tube (19) for placing the material storage tank. The upper Both ends of the lower part are open. The material storage tank is placed into the placement tube from the upper end thereof and supported and connected to a support seat (20) on the inner wall of the placement tube through a support rod (17). A guide groove is provided on the top of the support seat. The lower end of the support rod extends into the guide groove and is connected to a weighing sensor (18). Discharge ports matching the feed port are provided on the two material storage tanks and a slide plate directly below a material guide cover. The three discharge ports on the slide plate pass through the feed port in sequence through a double electric cylinder translation mechanism. Two stirring motors are respectively installed on the support plates on the front and rear sides of the double electric cylinder translation mechanism. The output shaft of the stirring motor extends into the upper tank body and is connected to the stirring mechanism. A filter assembly (15) is horizontally arranged in the lower end of the lower tank body. The outer walls of the filter assembly are in contact with the inner wall of the lower tank body. A vibrating electric cylinder (16) is also installed at the bottom of the lower tank body. The vibrating electric cylinder extends into the lower tank body and is connected to the filter assembly.

4. The method for preparing a core-shell PRB active material according to claim 3, characterized in that: The dual electric cylinder translation mechanism comprises a slide rail (7), a first translation drive electric cylinder (8) and a second translation drive electric cylinder (9), wherein the slide rail is arranged on the top of the support plate and is placed left and right, the slide plate is connected to the slide rail via a slide groove provided at the bottom, the first translation drive electric cylinder is installed on the top of the right end of the slide plate, and the second translation drive electric cylinder is installed on the top of the right end of the support plate, the extension directions of the output shaft ends of the first translation drive electric cylinder and the second translation drive electric cylinder are parallel to the slide rail, and the output shaft end of the first translation drive electric cylinder is connected to the output shaft end of the second translation drive electric cylinder via a coupling.

5. The method for preparing a core-shell PRB active material according to claim 3, characterized in that: The lifting mechanism comprises a lifting electric cylinder (10) and an L-shaped slide (12), wherein an L-shaped slide is arranged on each of the left and right sides of the lower tank body, and a guide through hole matching the column is opened on the L-shaped slide, and the L-shaped slide is connected to the column through the guide through hole, and a lifting electric cylinder is arranged at the bottom of each of the support plates directly above the two L-shaped slides, and the output shaft ends of the two lifting electric cylinders are respectively connected to an L-shaped slide, and the L-shaped slide is connected to the column by being driven by the lifting electric cylinder to slide up and down, wherein a servo motor (13) is installed on the L-shaped slide located on the left side, and the output shaft of the servo motor is connected to the left outer wall of the lower tank body, and the right outer wall of the lower tank body is connected to the L-shaped slide located on the right side through a rotating shaft (14).

6. The method for preparing a core-shell PRB active material according to claim 1, characterized in that: The organic binder in the above step S2 is one of hydroxypropyl cellulose, hydroxymethyl propyl cellulose, and carboxyethyl cellulose; the carrier in the above step S2 is made of cordierite or alumina, and has a shape of honeycomb, spherical, strip, or ring.

7. The method for preparing a core-shell PRB active material according to claim 1, characterized in that: The soaking-drying step described in the above step S2 can be repeated multiple times until the mass fraction of the natural mineral material and porous material loaded on the carrier reaches 3-5%.

8. A method for preparing a core-shell PRB active material according to any one of claims 1 to 7, characterized in that: A core-shell structured PRB active material prepared by the above preparation method is composed of a carrier and a shell material loaded on the carrier, wherein the shell material is specifically composed of the following components in terms of mass fraction: a natural mineral material and a porous material with a mass fraction of 80-90%, an Al2O3 or SiO2 mass fraction of 5-15%, and a Fe mass fraction of 5-10%.

9. The method for preparing a core-shell PRB active material according to claim 8, characterized in that: The effect of the core-shell structured PRB active material is verified by a PRB column experiment, which specifically includes the following steps: A1: PRB filling materials with core-shell structure are loaded into the reaction column, and quartz sand is loaded above and below the reaction column as a permeable layer; A2: Prepare an aqueous solution containing heavy metal ions and use a peristaltic pump to inject the solution from the bottom of the reaction column; A3: After a certain period of time, sample and analyze the solution at the outlet of the upper part of the reaction column to detect the concentration of heavy metal ions.

10. The method for preparing a core-shell PRB active material according to claim 9, characterized in that: The core-shell structure PRB filling material filling amount is 50-100g, and the heavy metal ion is Cr2O7 2- , Pb 2+ 、Cd 2+ 、Ni 2+ , Cu 2+ One or more of the above, the concentration of heavy metal ions is 1-20 mg / L, and the solution flow rate is 1-20 mL / min.

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