PRB filling material for groundwater pollution remediation and preparation method thereof

Abstract

The invention relates to a PRB filling material for groundwater pollution remediation and a preparation method thereof.According to the PRB filling material for groundwater pollution remediation, a deposition-precipitation method is adopted, an LDHs material is evenly loaded on biochar, meanwhile, chelating agent anions are inserted into an interlayer structure of the LDHs material through the technical means of roasting, dipping and drying, and finally the PRB filling material is prepared. The method is used for heavy metal pollution remediation of underground water. The preparation process is simple, the preparation cost is low, the performance of adsorbing and stabilizing heavy metals in underground water is excellent, and the problem of secondary pollution is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of groundwater remediation, and in particular to a PRB filling material for groundwater pollution remediation and a preparation method thereof. Background Art

[0002] With the rapid advancement of modernization and industrialization, groundwater pollution is becoming increasingly serious. Heavy metals (Cd, Pb, As, etc.) are a typical groundwater pollutant that is persistent and difficult to degrade or destroy. In addition, heavy metals in groundwater can also accumulate through the food chain, endangering human health. Therefore, it is of great significance to develop effective groundwater heavy metal pollution remediation technology.

[0003] Permeable reaction 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 in the process of flowing through the reaction wall. Active materials are the core of PRB technology, and common ones include zeolite, activated carbon, limestone, etc. 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 CN110872138A discloses a method for treating farmland drainage using engineering waste as PRB filler. The engineering waste used in this method is iron ore slag, magnesite slag, calcined magnesite slag and other materials. Chinese invention patent CN106409371A discloses a hydroxyapatite-coated PRB filling material, a preparation method thereof, and an application method for removing uranium from groundwater. The method uses a hydroxyapatite-coated PRB filling material prepared by using silicon- and / or calcium-containing inert natural materials as the main body and H3PO4 solution as a synthetic material. However, in existing reports, the interception performance, stability, and environmental protection of PRB filling materials for heavy metals need to be further improved. Summary of the invention

[0004] In order to solve the above problems, the present invention designs a PRB filling material for groundwater pollution remediation and a preparation method thereof. The preparation method adopts a sedimentation precipitation method to uniformly load the LDHs material on the biochar, and utilizes the large specific surface area of ​​the biochar to limit the agglomeration of the LDHs material to the greatest extent. The prepared PRB filling material can utilize the rich hydroxyl, carbonyl and other functional groups contained on the surface of the biochar to strongly adsorb heavy metals in groundwater, thereby enhancing the capture effect of the LDHs material on heavy metals.

[0005] In order to solve the above technical problems, the present invention provides a method for preparing a PRB filling material for groundwater pollution remediation, which is characterized by comprising the following steps:

[0006] S1: Add biochar and deionized water into the reactor, heat the mixture to 60-90°C, start stirring, continuously inject the salt solution and precipitant solution into the reactor through a pump, control the feed flow of the salt solution and the precipitant solution, and control the pH value of the mixed solution in the reactor at 9-12. After the feeding is completed, continue stirring and allow the mixed solution in the reactor to age at 60-90°C for 2-12 hours;

[0007] S2: filtering, washing and drying the mixed solution in step S1, and then placing the dried powder in a tube furnace and calcining at 300-500° C. for 2-5 hours under an inert atmosphere;

[0008] S3: placing the powder obtained in step S2 in a chelating agent solution, stirring in a water bath at 60-80° C. for 2-4 hours, and then drying to obtain a PRB filling material.

[0009] Further: the salt solution in the above step S1 is one of a mixed solution of magnesium nitrate and aluminum nitrate, a mixed solution of iron nitrate and aluminum nitrate, and a mixed solution of calcium nitrate and aluminum nitrate, and the precipitant in the above step S1 is one of sodium carbonate and potassium carbonate.

[0010] Furthermore: in the above step S1, a mixed solution collecting trolley is arranged directly below the bottom discharge port of the reactor, a supporting part connected thereto is arranged on the outer side wall of the reactor, the reactor is connected to the support plate through the suspended support of the supporting part, a plurality of supporting columns are arranged at the bottom of the support plate, auxiliary side panels connected thereto are arranged on the left and right outer walls of the mixed solution collecting trolley, the bottom of the auxiliary side panels is connected to the track running wheels through support rods, the mixed solution collecting trolley is connected to the track through the track running wheels, a filter screen filtering assembly is arranged in the lower end of the mixed solution collecting trolley, the outer walls of the filter screen filtering assembly are in contact with the inner wall of the mixed solution collecting trolley, the filter screen filtering assembly is also detachably connected to the vibrating electric cylinder installed at the bottom of the mixed solution collecting trolley, and a valve assembly connected to the liquid outlet is also arranged at the bottom of the mixed solution collection trolley.

[0011] Furthermore: the track passes through the filter cleaning chamber and extends into the drying chamber. The filter cleaning chamber is divided into a filter chamber on the left and a cleaning chamber on the right. A valve connecting pipe assembly is provided at the bottom of each of the filter chamber and the cleaning chamber. The valve connecting pipe assembly is composed of a connecting end head, a telescopic pipe part and a telescopic electric cylinder. The connecting end head is connected to the telescopic pipe part and is lifted and lowered by the drive of the telescopic electric cylinder. The telescopic pipe part in the filter chamber is connected to the mixed solution collection pipe, and the telescopic pipe part in the cleaning chamber is connected to the flushing water collection pipe. A first mounting plate is horizontally fixed in the upper end of the cleaning chamber, and the bottom of the first mounting plate is fixed to the bottom of the cleaning chamber. A plurality of flushing pipes are fixed from left to right, and a plurality of rinse nozzles are installed at the bottom of the flushing pipes from front to back. The plurality of flushing pipes are connected with a first conveying pipe arranged on the top of the first mounting plate, and the first conveying pipe is connected with the water tank through a hose. A first lifting electric cylinder is installed on the top of the cleaning chamber, and the output shaft end of the first lifting electric cylinder is connected to the transmission plate. A first transmission guide rod is connected to the bottom of the left and right ends of the transmission plate respectively, and a first guide through hole is opened on the top of the cleaning chamber relative to the position of the first transmission guide rod. The first transmission guide rod extends into the cleaning chamber along the first guide through hole and is connected to the first mounting plate.

[0012] Furthermore: the valve assembly includes an outer valve body, an inner valve body, a valve core and a spring, the upper end of the outer valve body is fixed to the bottom of the mixed solution collection cart, the top of the outer valve body is provided with a liquid inlet connected to the liquid outlet, the lower end of the outer valve body is open, the inner valve body is arranged in the outer valve body and its upper end is fixedly connected to the outer valve body, the upper end of the inner valve body is connected to the liquid inlet, and the lower end of the inner valve body is sealed, the valve core is piston-type and slides up and down between the inner valve body and the outer valve body, the valve core is connected to the inner wall of the upper end of the outer valve body through a spring, a liquid outlet hole is provided on the side wall of the inner valve body, the liquid outlet hole is sealed by the valve core, and the connecting end head is extended into the outer valve body under the action of the telescopic electric cylinder to squeeze the valve core to open the liquid outlet hole, the inner diameter of the connecting end head is larger than the outer diameter of the inner valve body, and the outer diameter of the connecting end head is smaller than the inner diameter of the outer valve body.

[0013] Furthermore: a guide frame for guiding the chamber door is provided on the left side wall of the drying chamber, and the chamber door is driven by the box door switch electric cylinder installed on the top of the drying chamber to slide up and down along the guide frame, and a notch is provided at the lower end of the chamber door relative to the position of the track, and a plurality of electric heating tubes are installed on the inner wall of the drying chamber, and a second mounting plate is horizontally fixed in the upper end of the drying chamber, and a plurality of heating gas injection pipes are fixed from left to right at the bottom of the second mounting plate, and a plurality of nozzles are installed at the bottom of the heating gas injection pipe from front to back, and the plurality of heating gas injection pipes are connected to the second conveying pipe arranged on the top of the second mounting plate, and the second conveying pipe is connected to the heating gas conveying pipe through a telescopic pipe, and a second lifting electric cylinder is installed on the top of the drying chamber, and the output shaft end of the second lifting electric cylinder is connected to the second transmission plate, and a second transmission guide rod is connected to the bottom of the left and right ends of the second transmission plate, and a second guide through hole is provided at the top of the drying chamber relative to the position of the second transmission guide rod, and the second transmission guide rod extends into the drying chamber along the second guide through hole and is connected to the second mounting plate.

[0014] Furthermore: the chelating agent in the above step S3 is one of citric acid, oxalic acid and malic acid.

[0015] Further: A PRB filling material for groundwater pollution remediation prepared by the above preparation method is composed of biochar and a layered double hydroxide loaded on the biochar, the mass ratio of the layered double hydroxide to the biochar is 1:1-1:5, wherein the layered double hydroxide is formed by loading a salt solution and a precipitant solution on the biochar by a sedimentation precipitation method, the molar ratio of magnesium to aluminum, iron to aluminum, and calcium to aluminum in the salt solution is 3:1-8:1, and a chelating agent anion is inserted into the interlayer structure of the layered double hydroxide, and the molar ratio of the chelating agent to the layered double hydroxide is 1:5-1:20.

[0016] Further: The effect of the PRB filling material for groundwater pollution remediation is verified by a PRB column experiment, which specifically includes the following steps:

[0017] A1: PRB filling material is filled in the reaction column, and quartz sand is filled above and below the reaction column as a permeable layer;

[0018] 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;

[0019] A3: After 24 hours, sample and analyze the solution at the upper outlet of the reaction column to detect the concentration of heavy metal ions.

[0020] Further: the amount of the PRB filling material in the above step A1 is 50-100 g, and the heavy metal ion in the heavy metal ion aqueous solution in the above step A2 is Pb 2+ 、Cd2+ 、Ni 2+ , Cu 2+ One or more of the above, the concentration of metal ions is 1-20 mg / L, and the solution flow rate is 1-20 mL / min.

[0021] After adopting the above structure, the beneficial effects of the present invention are as follows:

[0022] 1. The present invention uses a sedimentation precipitation method to uniformly load the LDHs material on biochar, and utilizes the large specific surface area of ​​biochar to limit the agglomeration of the LDHs material to the greatest extent. The prepared PRB filling material can utilize the rich hydroxyl, carbonyl and other functional groups contained on the surface of biochar to strongly adsorb heavy metals in groundwater, thereby enhancing the capture effect of the LDHs material on heavy metals;

[0023] 2. The present invention utilizes the unique "memory effect" of LDHs materials, and inserts chelating agent anions into the LDHs interlayer structure by means of inert atmosphere calcination and solution impregnation. The chelating agent anions will form stable chelates with the heavy metal ions adsorbed by the composite material, further consolidating the passivation effect of heavy metals;

[0024] 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.

[0025] 4. The present invention adopts a mixed solution collection cart to sequentially send the collected mixed solution into the filtering and cleaning chamber and the drying chamber for filtering, washing and drying, which greatly improves the production efficiency of PRB filling materials and plays a role in increasing practical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0027] Figure 1 This is a diagram of the usage status of the mixed solution collection cart.

[0028] Figure 2 Diagram of the internal structure of the mixed solution collection cart.

[0029] Figure 3 The figure is a structural diagram of the valve assembly.

[0030] Figure 4 This is the internal structure diagram of the filter cleaning chamber.

[0031] Figure 5 This is a diagram of the internal structure of the drying chamber. DETAILED DESCRIPTION

[0032] The present invention provides a method for preparing a PRB filling material for groundwater pollution remediation, which specifically comprises the following steps:

[0033] S1: Add biochar and deionized water into the reactor, heat the mixture to 60-90°C, start stirring, continuously inject the salt solution and precipitant solution into the reactor through a pump, control the feed flow of the salt solution and the precipitant solution, and control the pH value of the mixed solution in the reactor at 9-12. After the feeding is completed, continue stirring and allow the mixed solution in the reactor to age at 60-90°C for 2-12 hours;

[0034] S2: filtering, washing and drying the mixed solution in step S1, and then placing the dried powder in a tube furnace and calcining at 300-500° C. for 2-5 hours under an inert atmosphere;

[0035] S3: placing the powder obtained in step S2 in a chelating agent solution, stirring in a water bath at 60-80° C. for 2-4 hours, and then drying to obtain a PRB filling material.

[0036] The present invention uses a sedimentation precipitation method to uniformly load the LDHs material on biochar, utilizes the large specific surface area of ​​biochar, and limits the aggregation of LDHs material to the greatest extent. The prepared PRB filling material can utilize the strong adsorption of heavy metals in groundwater by the abundant functional groups such as hydroxyl and carbonyl contained on the surface of biochar, and strengthen the capture effect of LDHs material on heavy metals. In addition, the present invention has a simple preparation process, a low preparation cost, uses environmentally friendly materials, and has no secondary pollution problem.

[0037] The salt solution in the above step S1 is one of a mixed solution of magnesium nitrate and aluminum nitrate, a mixed solution of iron nitrate and aluminum nitrate, and a mixed solution of calcium nitrate and aluminum nitrate. The precipitant in the above step S1 is one of sodium carbonate and potassium carbonate.

[0038] like Figure 1 and Figure 2 In the step S1 shown, a mixed solution collecting trolley 4 is arranged directly below the bottom discharge port of the reactor 1, a support portion 2 connected thereto is arranged on the outer side wall of the reactor, the reactor is connected to the support plate 3 through the suspended support of the support portion, a plurality of support columns 6 are arranged at the bottom of the support plate, auxiliary side panels 13 connected thereto are arranged on the left and right outer walls of the mixed solution collecting trolley, the bottom of the auxiliary side panels is connected to the track running wheels 15 through support rods 14, the mixed solution collecting trolley is connected to the track 5 through the track running wheels, a filter screen filtering assembly 12 is arranged in the lower end of the mixed solution collecting trolley, the outer walls of the filter screen filtering assembly are in contact with the inner wall of the mixed solution collecting trolley, the filter screen filtering assembly is also detachably connected to the vibrating electric cylinder installed at the bottom of the mixed solution collecting trolley, and a valve assembly 17 connected to the liquid outlet is also arranged at the bottom of the mixed solution collection trolley.

[0039] like Figure 1and Figure 4 The track shown passes through the filter cleaning chamber 7 and extends into the drying chamber 10. The filter cleaning chamber is divided into a filter chamber on the left and a cleaning chamber on the right. A valve connecting pipe assembly 8 is provided at the bottom of each of the filter chamber and the cleaning chamber. The valve connecting pipe assembly is composed of a connecting end head, a telescopic pipe part and a telescopic electric cylinder. The connecting end head is connected to the telescopic pipe part and is lifted and lowered by the drive of the telescopic electric cylinder. The telescopic pipe part in the filter chamber is connected to the mixed solution collection pipe, and the telescopic pipe part in the cleaning chamber is connected to the flushing water collection pipe. A first mounting plate 18 is horizontally fixed in the upper end of the cleaning chamber, and the bottom of the first mounting plate is fixed from left to right. There are several flushing pipes 19, and several rinse nozzles are installed at the bottom of the flushing pipes from front to back. The several flushing pipes are connected to the first delivery pipe 20 arranged on the top of the first mounting plate, and the first delivery pipe is connected to the water tank through a hose 24. A first lifting electric cylinder 21 is installed on the top of the cleaning chamber, and the output shaft end of the first lifting electric cylinder is connected to the transmission plate 22. A first transmission guide rod 23 is connected to the bottom of the left and right ends of the transmission plate respectively. A first guide through hole is opened on the top of the cleaning chamber relative to the position of the first transmission guide rod. The first transmission guide rod extends into the cleaning chamber along the first guide through hole and is connected to the first mounting plate.

[0040] like Figure 3 The valve assembly shown includes an outer valve body 17-1, an inner valve body 17-2, a valve core 17-3 and a spring 17-4. The upper end of the outer valve body is fixed at the bottom of the mixed solution collecting trolley. The top of the outer valve body is provided with a liquid inlet 17-5 connected with the liquid outlet. The lower end of the outer valve body is open. The inner valve body is arranged in the outer valve body and its upper end is fixedly connected with the outer valve body. The upper end of the inner valve body is connected with the liquid inlet, and the lower end of the inner valve body is sealed. The valve core is piston-type and slides up and down between the inner valve body and the outer valve body. The valve core is connected to the inner wall of the upper end of the outer valve body through a spring. A liquid outlet 17-6 is provided on the side wall of the inner valve body. The liquid outlet is sealed by the valve core. The connecting end head is extended into the outer valve body under the action of the telescopic electric cylinder to squeeze the valve core to open the liquid outlet. The inner diameter of the connecting end head is larger than the outer diameter of the inner valve body, and the outer diameter of the connecting end head is smaller than the inner diameter of the outer valve body.

[0041] like Figure 5A guide frame 32 for guiding a chamber door 31 is provided on the left side wall of the drying chamber shown in the figure. The chamber door is driven by a door switch electric cylinder installed on the top of the drying chamber to slide up and down along the guide frame. A notch is provided at the lower end of the chamber door relative to the position of the track. A plurality of electric heating tubes 29 are installed on the inner wall of the drying chamber. A second mounting plate 25 is horizontally fixed in the upper end of the drying chamber. A plurality of heating gas injection pipes 26 are fixed from left to right at the bottom of the second mounting plate. A plurality of nozzles are installed at the bottom of the heating gas injection pipe from front to back. The plurality of heating gas injection pipes are connected to a second conveying pipe 27 arranged on the top of the second mounting plate. The second conveying pipe is connected to the heating gas conveying pipe 11 through a telescopic pipe 30. A second lifting electric cylinder 28 is installed on the top of the drying chamber. The shaft end of the second lifting electric cylinder is connected to a second transmission plate. A second transmission guide rod is connected to the bottom of the left and right ends of the second transmission plate. A second guide through hole is provided at the top of the drying chamber relative to the position of the second transmission guide rod. The second transmission guide rod extends into the drying chamber along the second guide through hole and is connected to the second mounting plate.

[0042] The present invention adopts a mixed solution collecting trolley to sequentially send the collected mixed solution into a filtering and cleaning chamber and a drying chamber for filtering, washing and drying, thereby greatly improving the production efficiency of the PRB filling material and playing a role in increasing practical performance.

[0043] The chelating agent in the above step S3 is one of citric acid, oxalic acid and malic acid.

[0044] A PRB filling material for groundwater pollution remediation prepared by the above preparation method is composed of biochar and layered double hydroxide loaded on biochar, the mass ratio of layered double hydroxide to biochar is 1:1-1:5, wherein the layered double hydroxide is formed by loading a salt solution and a precipitant solution on biochar by a deposition precipitation method, the molar ratio of magnesium to aluminum, iron to aluminum, and calcium to aluminum in the salt solution is 3:1-8:1, and a chelating agent anion is inserted into the interlayer structure of the layered double hydroxide, and the molar ratio of the chelating agent to the layered double hydroxide is 1:5-1:20. The present invention utilizes the unique "memory effect" of LDHs materials, and inserts the chelating agent anion into the LDHs interlayer structure by means of inert atmosphere calcination and solution impregnation, and the chelating agent anion will form a stable chelate with the heavy metal ions adsorbed by the composite material, further consolidating the passivation effect of heavy metals.

[0045] The effect of the above-mentioned PRB filling material for groundwater pollution remediation is verified by a PRB column experiment, which specifically includes the following steps:

[0046] A1: PRB filling material is filled in the reaction column, and quartz sand is filled above and below the reaction column as a permeable layer;

[0047] 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;

[0048] A3: After 24 hours, sample and analyze the solution at the upper outlet of the reaction column to detect the concentration of heavy metal ions.

[0049] The amount of the PRB filling material in step A1 is 50-100 g. In the heavy metal ion aqueous solution in step A2, the heavy metal ion is Pb 2+ 、Cd 2+ 、Ni 2+ , Cu 2+ One or more of the above, the concentration of metal ions is 1-20 mg / L, and the solution flow rate is 1-20 mL / min.

[0050] Example 1

[0051] Add biochar and deionized water into the reactor, heat the mixture to 60°C, start stirring, and continuously inject the mixed solution of magnesium nitrate and aluminum nitrate and sodium carbonate solution into the reactor through a pump. Among them, the molar ratio of magnesium to aluminum is 3:1. Control the solution feed flow rate, control the pH value of the mixed solution in the reactor at 9, continue stirring after the feeding is completed, and let the mixed solution in the reactor age for 12 hours at 60°C. Filter, wash and dry the mixed solution, and then place the dried powder in a tube furnace and roast it at 300°C for 5 hours under an inert atmosphere. Place the powder in a citric acid solution, stir in a 60°C water bath for 4 hours, and then dry to obtain a PRB filling material. In the material, the mass ratio of layered double hydroxide to biochar is 1:1. The molar ratio of chelating agent to layered double hydroxide is 1:5.

[0052] Example 2

[0053] Add biochar and deionized water into the reactor, heat the mixture to 90°C, start stirring, and continuously inject the mixed solution of ferric nitrate and aluminum nitrate and sodium carbonate solution into the reactor through a pump. Among them, the molar ratio of iron to aluminum is 8:1. Control the solution feed flow rate, control the pH value of the mixed solution in the reactor at 12, continue stirring after the feeding is completed, and let the mixed solution in the reactor age for 2 hours at 90°C. Filter, wash and dry the mixed solution, and then place the dried powder in a tube furnace and roast it at 500°C for 2 hours under an inert atmosphere. Place the powder in oxalic acid solution, stir in a water bath at 80°C for 2 hours, and then dry to obtain PRB filling material. In the material, the mass ratio of layered double hydroxide to biochar is 1:5. The molar ratio of chelating agent to layered double hydroxide is 1:20.

[0054] Example 3

[0055] Add biochar and deionized water into the reactor, heat the mixture to 80°C, start stirring, and continuously inject the mixed solution of calcium nitrate and aluminum nitrate and potassium carbonate solution into the reactor through a pump. Among them, the molar ratio of calcium to aluminum is 5:1. Control the solution feed flow rate, control the pH value of the mixed solution in the reactor at 10, continue stirring after the feeding is completed, and let the mixed solution in the reactor age at 80°C for 10h. Filter, wash and dry the mixed solution, and then place the dried powder in a tube furnace and roast it at 400°C for 3h under an inert atmosphere. Place the powder in a malic acid solution, stir in a 70°C water bath for 3h, and then dry to obtain a PRB filling material. In the material, the mass ratio of layered double hydroxide to biochar is 1:2. The molar ratio of chelating agent to layered double hydroxide is 1:10.

[0056] Example 4

[0057] Add biochar and deionized water to the reactor, heat the mixture to 70°C, start stirring, and continuously inject the mixed solution of magnesium nitrate and aluminum nitrate and potassium carbonate solution into the reactor through a pump. Among them, the molar ratio of magnesium to aluminum is 6:1. Control the solution feed flow rate, control the pH value of the mixed solution in the reactor at 11, continue stirring after the feeding is completed, and let the mixed solution in the reactor age at 70°C for 8h. Filter, wash and dry the mixed solution, and then place the dried powder in a tube furnace and roast it at 350°C for 5h under an inert atmosphere. Place the powder in a citric acid solution, stir in a water bath at 80°C for 4h, and then dry to obtain a PRB filling material. In the material, the mass ratio of layered double hydroxide to biochar is 1:4. The molar ratio of chelating agent to layered double hydroxide is 1:8.

[0058] Example 5

[0059] Add biochar and deionized water to the reactor, heat the mixture to 60°C, start stirring, and continuously inject the mixed solution of ferric nitrate and aluminum nitrate and potassium carbonate solution into the reactor through a pump. Among them, the molar ratio of iron to aluminum is 7:1. Control the solution feed flow rate, control the pH value of the mixed solution in the reactor at 10, continue stirring after the feeding is completed, and let the mixed solution in the reactor age for 5 hours at 60°C. Filter, wash and dry the mixed solution, and then place the dried powder in a tube furnace and roast it at 400°C for 4 hours under an inert atmosphere. Place the powder in oxalic acid solution, stir in a water bath at 65°C for 3 hours, and then dry to obtain PRB filling material. In the material, the mass ratio of layered double hydroxide to biochar is 1:5. The molar ratio of chelating agent to layered double hydroxide is 1:15.

[0060] Comparative Example 1

[0061] Add deionized water to the reactor, heat the mixture to 60°C, start stirring, and continuously inject the mixed solution of magnesium nitrate and aluminum nitrate and sodium carbonate solution into the reactor through a pump. The molar ratio of magnesium to aluminum is 3:1. Control the solution feed flow rate and control the pH value of the mixed solution in the reactor to 9. After the feeding is completed, continue stirring and age the mixed solution in the reactor at 60°C for 12 hours. Filter, wash and dry the mixed solution.

[0062] Comparative Example 2

[0063] Add biochar and deionized water into the reactor, heat the mixture to 90°C, start stirring, and continuously inject the mixed solution of ferric nitrate and aluminum nitrate and sodium carbonate solution into the reactor through a pump. Among them, the molar ratio of iron to aluminum is 8:1. Control the solution feed flow rate and control the pH value of the mixed solution in the reactor at 12. After the feeding is completed, continue stirring and let the mixed solution in the reactor age at 90°C for 2h. Filter, wash and dry the mixed solution, and then place the dried powder in a tubular furnace and roast it at 450°C for 2h under an inert atmosphere. The mass ratio of layered double hydroxide to biochar is 1:5.

[0064] Test Example 1

[0065] 50g 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 20 mg / L, was injected from the bottom of the reaction column using a peristaltic pump at a flow rate of 10 mL / min. After 24 hours, the solution at the outlet of the upper part of the reaction column was sampled and analyzed to detect the concentration of heavy metal ions and calculate the removal rate of Cd. As shown in the following table:

[0066] <![CDATA[Cd 2+ Removal rate (%)]]> Example 1 98.2 Example 2 97.6 Example 3 98.1 Example 4 99.2 Example 5 99.0 Comparative Example 1 85.5 Comparative Example 2 91.7

[0067] Table 1 shows the Cd content in the solution. 2+ Removal rate

[0068] 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 PRB filling material for groundwater pollution remediation, characterized in that: The specific steps include: S1: Add biochar and deionized water into the reactor, heat the mixture to 60-90°C, start stirring, continuously inject the salt solution and precipitant solution into the reactor through a pump, control the feed flow of the salt solution and the precipitant solution, and control the pH value of the mixed solution in the reactor at 9-12. After the feeding is completed, continue stirring and allow the mixed solution in the reactor to age at 60-90°C for 2-12 hours; S2: filtering, washing and drying the mixed solution in step S1, and then placing the dried powder in a tube furnace and calcining at 300-500° C. for 2-5 hours under an inert atmosphere; S3: placing the powder obtained in step S2 in a chelating agent solution, stirring in a water bath at 60-80° C. for 2-4 hours, and then drying to obtain a PRB filling material.

2. The method for preparing a PRB filling material for groundwater pollution remediation according to claim 1, characterized in that: The salt solution in the above step S1 is one of a mixed solution of magnesium nitrate and aluminum nitrate, a mixed solution of iron nitrate and aluminum nitrate, and a mixed solution of calcium nitrate and aluminum nitrate. The precipitant in the above step S1 is one of sodium carbonate and potassium carbonate.

3. The method for preparing a PRB filling material for groundwater pollution remediation according to claim 1, characterized in that: In the above step S1, a mixed solution collecting trolley (4) is arranged directly below the bottom discharge port of the reactor (1), a supporting part (2) connected to the reactor is arranged on the outer wall of the reactor, and the reactor is connected to the supporting plate (3) by the supporting part in a suspended manner, and a plurality of supporting columns 6 are arranged at the bottom of the supporting plate), auxiliary side panels (13) connected to the reactor are arranged on the left and right outer walls of the mixed solution collecting trolley, and the bottom of the auxiliary side panels is connected to the track running wheel (15) through a supporting rod (14), and the mixed solution collecting trolley is connected to the track (5) through the track running wheel, and a filter screen filtering assembly (12) is arranged in the lower end of the mixed solution collecting trolley, and the outer walls of the filter screen filtering assembly are in contact with the inner wall of the mixed solution collecting trolley, and the filter screen filtering assembly is also detachably connected to the vibrating electric cylinder installed at the bottom of the mixed solution collecting trolley, and the bottom of the mixed solution collecting trolley is also provided with a valve assembly (17) connected to the liquid outlet.

4. The method for preparing a PRB filling material for groundwater pollution remediation according to claim 3, characterized in that: The track passes through the filter cleaning chamber (7) and extends into the drying chamber (10). The filter cleaning chamber is further divided into a filter chamber on the left and a cleaning chamber on the right. A valve connecting pipe assembly (8) is provided at the bottom of each of the filter chamber and the cleaning chamber. The valve connecting pipe assembly is composed of a connecting end head, a telescopic pipe part and a telescopic electric cylinder. The connecting end head is connected to the telescopic pipe part and is lifted and lowered by the drive of the telescopic electric cylinder. The telescopic pipe part in the filter chamber is connected to the mixed solution collection pipe, and the telescopic pipe part in the cleaning chamber is connected to the flushing water collection pipe. A first mounting plate (18) is horizontally fixed in the upper end of the cleaning chamber, and a A plurality of flushing pipes (19) are provided at the bottom of the flushing pipes from front to back. The plurality of flushing pipes are connected to a first delivery pipe (20) arranged at the top of a first mounting plate. The first delivery pipe is connected to a water storage tank via a hose (24). A first lifting electric cylinder (21) is provided at the top of the cleaning chamber. The shaft end of the first lifting electric cylinder is connected to a transmission plate (22). The bottoms of the left and right ends of the transmission plate are respectively connected to a first transmission guide rod (23). A first guide through hole is provided at the top of the cleaning chamber at a position relative to the first transmission guide rod. The first transmission guide rod extends into the cleaning chamber along the first guide through hole and is connected to the first mounting plate.

5. The method for preparing a PRB filling material for groundwater pollution remediation according to claim 4, characterized in that: The valve assembly comprises an outer valve body (17-1), an inner valve body (17-2), a valve core (17-3) and a spring (17-4). The upper end of the outer valve body is fixed to the bottom of the mixed solution collecting trolley. The top of the outer valve body is provided with a liquid inlet (17-5) connected to the liquid outlet. The lower end of the outer valve body is open. The inner valve body is arranged in the outer valve body and its upper end is fixedly connected to the outer valve body. The upper end of the inner valve body is connected to the liquid inlet. The lower end of the inner valve body is sealed. The valve core is piston-type and slides up and down between the inner valve body and the outer valve body. The valve core is connected to the inner wall of the upper end of the outer valve body through a spring. A liquid outlet hole (17-6) is provided on the side wall of the inner valve body. The liquid outlet hole is sealed by the valve core. The connecting end head extends into the outer valve body under the action of the telescopic electric cylinder to squeeze the valve core to open the liquid outlet. The inner diameter of the connecting end head is larger than the outer diameter of the inner valve body, and the outer diameter of the connecting end head is smaller than the inner diameter of the outer valve body.

6. The method for preparing a PRB filling material for groundwater pollution remediation according to claim 4, characterized in that: A guide frame (32) for guiding a chamber door (31) is arranged on the left side wall of the drying chamber. The chamber door is driven by a door switch electric cylinder installed on the top of the drying chamber to slide up and down along the guide frame. A notch is provided at the lower end of the chamber door relative to the position of the track. A plurality of electric heating pipes (29) are installed on the inner wall of the drying chamber. A second mounting plate (25) is horizontally fixed in the upper end of the drying chamber. A plurality of heating gas injection pipes (26) are fixed from left to right at the bottom of the second mounting plate. A plurality of nozzles are installed at the bottom of the heating gas injection pipe from front to back. The body injection pipeline is connected to the second delivery pipeline (27) arranged on the top of the second mounting plate, and the second delivery pipeline is connected to the heating gas delivery pipeline (11) through the telescopic pipeline (30). A second lifting electric cylinder (28) is installed on the top of the drying chamber, and the output shaft end of the second lifting electric cylinder is connected to the second transmission plate. The bottom of the left and right ends of the second transmission plate are respectively connected to a second transmission guide rod. A second guide through hole is opened on the top of the drying chamber relative to the position of the second transmission guide rod. The second transmission guide rod extends into the drying chamber along the second guide through hole and is connected to the second mounting plate.

7. The method for preparing a PRB filling material for groundwater pollution remediation according to claim 1, characterized in that: The chelating agent in the above step S3 is one of citric acid, oxalic acid and malic acid.

8. A method for preparing a PRB filling material for groundwater pollution remediation according to any one of claims 1 to 7, characterized in that: A PRB filling material for groundwater pollution remediation prepared by the above preparation method is composed of biochar and layered double hydroxide loaded on the biochar, the mass ratio of the layered double hydroxide to the biochar is 1:1-1:5, the layered double hydroxide is formed by loading a salt solution and a precipitant solution on the biochar by a sedimentation precipitation method, the molar ratio of magnesium to aluminum, iron to aluminum, and calcium to aluminum in the salt solution is 3:1-8:1, and a chelating agent anion is inserted into the interlayer structure of the layered double hydroxide, and the molar ratio of the chelating agent to the layered double hydroxide is 1:5-1:

20.

9. The method for preparing a PRB filling material for groundwater pollution remediation according to claim 8, characterized in that: The effect of the PRB filling material for groundwater pollution remediation is verified by a PRB column experiment, which specifically comprises the following steps: A1: PRB filling material is filled in the reaction column, and quartz sand is filled 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 24 hours, sample and analyze the solution at the upper outlet of the reaction column to detect the concentration of heavy metal ions.

10. The method for preparing a PRB filling material for groundwater pollution remediation according to claim 9, characterized in that: The amount of the PRB filling material in step A1 is 50-100 g. In the heavy metal ion aqueous solution in step A2, the heavy metal ion is Pb 2+ 、Cd 2+ 、Ni 2+ , Cu 2+ One or more of the above, the concentration of metal ions is 1-20 mg / L, and the solution flow rate is 1-20 mL / min.

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