A red mud co-thermal desorption material and its preparation method and application

Abstract

The present invention discloses a red mud co-thermal desorption material and its preparation method and application. PANI / MCM-41 is first prepared using MCM-41, aniline, and ammonium persulfate in an ice bath. The PANI / MCM-41 is then mixed with red mud and heated to react to form the red mud co-thermal desorption material PANI / MCM-41 / RM (PMRM). The present invention adopts a simple co-thermal desorption method. The prepared red mud co-thermal desorption material can not only be used to treat chromium pollution in water, but can also be used as a PRB material and enhance the EKR-PRB technology to remediate chromium-contaminated soil, thereby achieving the purpose of waste recycling and waste treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste recycling and environmental protection, and specifically relates to a red mud co-thermal desorption material and a preparation method and application thereof. Background Art

[0002] Heavy metals have a significant impact on the ecological environment, and heavy metal pollution is a major environmental issue. Chromium is one of the most difficult heavy metal contaminants to remove from the soil. Red mud (RM) is the polluted waste residue discharged after the extraction of alumina from bauxite. It appears red due to the large amount of Fe2O3 it contains. EKR-PRB technology is a combined electrokinetic and permeable reaction wall remediation technology. It can leverage the technical advantages of electrokinetic remediation and permeable reaction walls, and through electromigration, electroosmosis, and electrophoresis, pollutants in the soil are migrated to the established permeable reaction wall, thereby remediating soil pollution. Among them, the choice of permeable reaction wall filler directly affects the specific effect of the remediation.

[0003] Chinese patent CN201611162010.0 discloses a method for preparing a lanthanum-modified red mud chromium removal adsorbent. This adsorbent can adsorb 17.3465 mg / g of hexavalent chromium in water. Chinese patent CN201210399838.3 discloses a method for preparing a highly efficient composite chromium removal adsorbent. Two grams of this adsorbent, placed in 100 ml of a 10 mg / L chromium solution, can remove 75% of the chromium after 72 hours. However, these materials remove chromium more slowly and adsorb relatively low amounts. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a highly efficient red mud co-thermal desorption material, and applies it to the remediation of chromium-contaminated water and soil, thereby achieving the purpose of waste recycling and waste treatment.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] A method for preparing a red mud co-thermal desorption material comprises the following steps:

[0007] (1) Preparation of PANI / MCM-41:

[0008] MCM-41 is added to an acid solution and stirred evenly, and then an aniline solution is added and stirred continuously to form an aniline / MCM-41 mixture; ammonium persulfate is added to the same acid solution and stirred to form an ammonium persulfate solution; the ammonium persulfate solution is then quickly added to the aniline / MCM-41 mixture, stirred evenly, then stopped stirring, and the reaction is continued; the resulting product is filtered, washed, dried, and ground to prepare PANI / MCM-41;

[0009] (2) Preparation of red mud co-thermal desorption material:

[0010] PANI / MCM-41 or PANI / MCM-41 after multiple adsorption-desorption cycles was mixed with red mud and placed in a tube furnace. Nitrogen was connected at a rate of 1 L / min, and the temperature was raised to the platform temperature at a rate of 5°C / min and kept warm for 2 h. After cooling, the mixture was taken out, washed to neutrality, dried, and ground to obtain the red mud co-thermal desorption material.

[0011] Preferably, in step (1), the acid solution is selected from any one of HCl, CA, and H2SO4; the type of acid will directly affect the shape of the polyaniline. For example, the polyaniline prepared by hydrochloric acid and sulfuric acid has a nanofiber or nanorod structure. The nanofibers generated by hydrochloric acid are shorter, and the nanofibers generated by sulfuric acid are denser. The polyaniline prepared by CA is mainly a network of stacked nanorods, and is relatively dense.

[0012] Preferably, in step (1), the concentration of the acid solution is 0.5 to 1.5 M.

[0013] Preferably, in step (1), the molar ratio of MCM-41 to aniline is 1:(5-15); a higher amount of aniline will directly affect the adsorption performance and the morphology of the composite material. For example, the higher the aniline content, the easier it is for polyaniline to agglomerate, but the active sites of the material will also increase accordingly;

[0014] Preferably, in step (1), the molar ratio of aniline to ammonium persulfate is 1:1.

[0015] Preferably, in step (1), the reaction condition is ice bath reaction for 12 hours.

[0016] Preferably, in step (1), the stirring is carried out in an ice bath; the ice bath reaction will affect the morphology and specific surface area of ​​polyaniline, thereby affecting the adsorption performance of PANI / MCM-41. For example, the ice bath can slow down the polymerization rate of polyaniline, making the morphology more dispersed and the specific surface area larger;

[0017] Preferably, in step (1), the drying temperature is 60° C. and the drying time is 12 h.

[0018] Preferably, in step (2), the mass ratio of PANI / MCM-41 to red mud is 1:(0.5-2);

[0019] Preferably, in step (2), the red mud is selected from any one of Bayer process red mud, hybrid process red mud and sintering process red mud.

[0020] Preferably, in step (2), the platform temperature is 500-700°C;

[0021] Preferably, in step (2), the drying temperature is 60°C.

[0022] Preferably, in step (2), the PANI / MCM-41 after multiple adsorption-desorption cycles is specifically:

[0023] ① Adsorption:

[0024] 1.1 Place potassium dichromate in an oven and dry at 120°C for 24 hours. Accurately weigh 2.829 g of the dried potassium dichromate, dissolve it in a small amount of water, and transfer it to a 1 L volumetric flask. Bring the volume to the mark and shake well to prepare a 1000 mg / L Cr(VI) stock solution.

[0025] 1.2 Prepare 50 ml of a 400 mg / L chromium solution using the Cr(VI) stock solution and adjust the pH to 2 with 0.1 M HCl and NaOH. Weigh 75 mg of PANI / MCM-41 and add it to the beaker containing the solution.

[0026] 1.3 Place the beaker on a water bath constant temperature oscillator, adjust the speed to 180 r / min and the temperature to 25°C;

[0027] 1.4 Take samples after shaking for 10, 20, 30 minutes and 1, 2, 3, 4, 5, and 6 hours. Take 1 mL of the solution and filter it through a 0.45 μm syringe filter into a 15 mL centrifuge tube.

[0028] 1.5 Dilute the solution 10 times and measure the concentration of the solution using a flame atomic absorption spectrophotometer (AAS).

[0029] ②Desorption:

[0030] 2.1 Filter the adsorbed PANI / MCM-41 using a 0.45 μm filter membrane.

[0031] 2.2 The adsorbed PANI / MCM-41 was placed in 10% ammonia water and stirred at room temperature for 1 h. After completion, the mixture was filtered through a 0.45 μm filter membrane and washed with deionized water until the material was neutral.

[0032] 2.3 Place the material in 1 M HCl and stir at room temperature for 2 h, then filter, rinse repeatedly with deionized water and dry.

[0033] The present invention also provides a red mud co-thermal desorption material prepared by the above preparation method.

[0034] The present invention also provides the use of the red mud co-thermal desorption material prepared by the above preparation method in treating chromium pollution in water bodies.

[0035] Preferably, the specific application method of red mud co-thermal desorption material in treating chromium pollution in water is:

[0036] 3.1 Place potassium dichromate in an oven and dry at 120°C for 24 h. Accurately weigh 2.829 g of the dried potassium dichromate, dissolve it in a small amount of water, and transfer it to a 1 L volumetric flask. Bring the volume to the mark and shake well to prepare a 1000 mg / L Cr(VI) stock solution.

[0037] 3.2 Prepare 50 ml of a 50 mg / L chromium solution using the Cr(VI) stock solution and adjust the pH to 2 with 0.1 M HCl and NaOH. Weigh 75 mg of PMRM and add it to the beaker containing the solution.

[0038] 3.3 Place the beaker on a water bath constant temperature oscillator, adjust the speed to 180 r / min and the temperature to 25°C;

[0039] 3.4 Take samples after shaking for 10, 20, 30 minutes and 1, 2, 3, 4, 5, and 6 hours. Take 1 mL of the solution and filter it through a 0.45 μm syringe filter into a 15 mL centrifuge tube.

[0040] 3.5 Dilute the solution 10 times and measure the concentration of the solution using a flame atomic absorption spectrophotometer (AAS).

[0041] The present invention also provides the use of the red mud co-thermal desorption material prepared by the above preparation method as a PRB material to enhance EKR-PRB to repair chromium-contaminated soil.

[0042] Preferably, the specific application method of the red mud co-thermal desorption material as a PRB material and enhanced EKR-PRB to repair chromium-contaminated soil is:

[0043] 4.1 Sun-dry the soil, remove impurities, and then crush and sieve (100 mesh). Accurately weigh 13.62g of potassium dichromate and thoroughly dissolve it in 18L of deionized water. Evenly mix 3L of the prepared solution per kilogram of soil at a water-to-soil ratio of 3:1. Place the resulting mud-water mixture in a well-ventilated area and age it for 3 months, stirring the soil thoroughly every 3 days to ensure uniform soil dyeing. The measured soil Cr(VI) concentration was 598.56mg / kg, and the total chromium concentration was 792.81mg / kg.

[0044] 4.2 Place the contaminated soil in the remediation device and the PMRM in the material room. Adjust the electric remediation voltage to 2 V / cm, use distilled water as the anolyte, and 0.1 M citric acid as the catholyte, and remediate for 120 hours.

[0045] 4.3 Use microwave digestion instrument to treat soil samples. The specific steps are as follows: weigh 0.4g of soil sample and transfer it to a digestion tank. Add 6ml HNO3, 3ml HCl and 2ml HF in sequence and place it in an acid removal instrument. Remove the acid at 120℃ for 30min. After cooling to room temperature, remove the digestion tube and add 2ml HNO3 and 1ml HF. Place it in a microwave digestion instrument and digest it according to the program of digestion at 150℃ for 10min, 170℃ for 5min and 190℃ for 45min. After the digestion instrument cools to room temperature, remove the digestion tank, add 2ml HClO4 and place it in the acid removal instrument again. Remove the acid at 180℃ until the solution becomes viscous. Use 1% HNO3 to make up to 100ml.

[0046] 4.4 Measure hexavalent chromium in soil according to HJ 1082-2019: Accurately weigh 5.0 g of soil and place it in a beaker. Add 50.0 ml of sodium carbonate / sodium hydroxide extraction solution, followed by 400 mg of magnesium chloride and 0.5 ml of dipotassium hydrogen phosphate-potassium dihydrogen phosphate buffer solution. Seal the beaker and stir at room temperature for 5 minutes. Then, heat and stir to 90°C–95°C for 60 minutes. After cooling, filter the beaker, adjust the pH of the filtrate to 7.5 ± 0.5 with nitric acid, and dilute to 100 ml.

[0047] 4.5 Pass the fixed volume liquid through a 0.45 μm filter membrane to dilute the solution to the appropriate concentration, and measure the solution concentration using a graphite furnace atomic absorption spectrometer;

[0048] Preferably, the repair device is composed of organic glass. The entire device is a cylinder with a diameter of 33cm and a height of 12cm. From the outside to the inside, it is divided into four parts: cathode chamber, soil chamber, material chamber, and anode chamber. The cathode chamber is six cylinders with a diameter of 3cm, which have a gap in the direction of the anode chamber. The material chamber is a hollow cylinder with an outer diameter of 6cm and an inner diameter of 3cm. The inner hollow part is the anode chamber, and uniform small holes are opened on the walls of the anode chamber and the material chamber. Filter paper is used to separate the cathode chamber, soil chamber, material chamber, and anode chamber. A stainless steel electrode rod is placed in the anode chamber as an anode, and a graphite electrode rod is placed in the cathode chamber as a cathode.

[0049] Beneficial effects of the present invention:

[0050] The present invention adopts a simple co-pyrolysis method to prepare a red mud-based adsorption material. The material is easy to prepare and combines PANI / MCM-41 that has been recycled and is ready for disposal with waste - red mud. The material can not only be used as an adsorption material for treating chromium-contaminated water sources, but can also be used as a PRB material and enhance the EKR-PRB combined remediation of chromium-contaminated soil, thereby achieving the purpose of waste recycling and waste treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present invention and, together with the description, serve to explain the principles of the invention, in which:

[0052] Figure 1 FT-IR images of the materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention are shown;

[0053] Figure 2 1 are SEM images of Example 1, Comparative Example 1, Comparative Example 2, and red mud of the present invention, wherein (a) and (b) are SEM images of red mud, (c) and (d) are SEM images of 700RM of Comparative Example 1, (e) is a SEM image of 700PM of Comparative Example 2, and (f) is a SEM image of PMRM1 of Example 1;

[0054] Figure 3 is a top view of the repair device in Application Example 3 and Comparative Application Example 3 of the present invention;

[0055] Figure 4 is a physical picture of the repair device in Application Example 3 and Comparative Application Example 3 of the present invention;

[0056] Figure 5 1 is a curve showing the change in adsorption amount over time of Application Example 1, Application Example 2, Comparative Application Example 1, and Comparative Application Example 2 of the present invention;

[0057] Figure 6 1 is the XPS spectrum of the material before and after adsorption of Application Example 1 of the present invention, wherein (a) is the total spectrum before and after the reaction, (b) is the Fe peak fitting before the reaction, (c) is the Cr peak fitting, and (d) is the Fe peak fitting after the reaction;

[0058] Figure 7 It is the hexavalent chromium removal rate of each sampling point of Application Example 3 of the present invention and Comparative Application Example 3.

[0059] Figure 8 is the ratio of the total chromium after reaction to the total chromium before reaction at each sampling point in Application Example 3 of the present invention and Comparative Application Example 3;

[0060] Figure 9 The SEM images of PANI / MCM-41 in Example 3 and Example 4 of the present invention are shown, wherein (a) and (b) are comparisons of the SEM images of PANI / MCM-41 in Example 3 before and after 5 cycles, and (c) and (d) are SEM images of PMRM4 in Example 4;

[0061] Figure 10 is the removal rate of hexavalent chromium in the five adsorption-desorption cycles of PANI / MCM-41 in Example 3;

[0062] Figure 11The graphs show the adsorption amount of Application Example 1, Application Example 4, and Application Example 5 changing with time.

[0063] Reference numerals: Figure 3 1-1. Cathode chamber, 1-2. Soil chamber, 1-3. Material chamber, 1-4. Anode chamber, 1-5. Stainless steel electrode rod, 1-6. Graphite electrode rod. DETAILED DESCRIPTION

[0064] The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. To simplify the disclosure of the present invention, the components and configurations of specific examples are described below. Of course, these are merely examples and are not intended to limit the present invention. In addition, the present invention may repeat reference numbers and / or reference letters in different examples. Such repetition is for the purpose of simplicity and clarity and does not in itself indicate the relationship between the various embodiments and / or configurations discussed.

[0065] Example 1

[0066] (1) Preparation of PANI / MCM-41:

[0067] Add 0.18g of MCM-41 to a 1M hydrochloric acid solution and stir for 2 hours. Then, add 0.93ml of aniline solution and continue stirring on ice for 2 hours. Add ammonium persulfate at a 1:1 molar ratio of ammonium persulfate to aniline to the same acid solution as the aniline / MCM-41 mixture and stir on ice for 2 hours. Quickly add the ammonium persulfate solution to the aniline / MCM-41 mixture, stir for 5 minutes, then stop stirring and allow to react on ice for 12 hours. The resulting product is filtered through a 0.45μm polytetrafluoroethylene filter, washed three times with deionized water and anhydrous ethanol, dried in a forced air drying oven at 60°C for 12 hours, and finally ground thoroughly.

[0068] (2) Preparation of red mud co-thermal desorption material PMRM1:

[0069] PANI / MCM-41 and Bayer red mud were fully mixed in a ratio of 1:1, placed in a tube furnace, and nitrogen was connected at a rate of 1 L / min. The material was heated to 700°C at a rate of 5°C / min and kept warm for 2 hours. After cooling to room temperature in the instrument, it was taken out and washed with deionized water until neutral. It was dried in an oven at 60°C and the sample was named PMRM1.

[0070] Example 2

[0071] (1) Preparation of PANI / MCM-41: Same as Example 1.

[0072] (2) Preparation of red mud co-thermal desorption material PMRM2:

[0073] PANI / MCM-41 and Bayer red mud were fully mixed in a ratio of 2:1, placed in a tube furnace, and nitrogen was connected at a rate of 1 L / min. The material was heated to 700°C at a rate of 5°C / min and kept warm for 2 hours. After cooling to room temperature in the instrument, it was taken out and washed with deionized water until neutral. It was dried in an oven at 60°C and named PMRM2.

[0074] Example 3

[0075] (1) Preparation of PANI / MCM-41: Same as Example 1.

[0076] (2) PANI / MCM-41 was subjected to five adsorption-desorption cycle experiments:

[0077] ① Adsorption:

[0078] 1. Place potassium dichromate in an oven and dry at 120°C for 24 hours. Accurately weigh 2.829 g of the dried potassium dichromate, dissolve it in a small amount of water, and transfer it to a 1 L volumetric flask. Bring the volume to the mark and shake well to prepare a 1000 mg / L Cr(VI) stock solution.

[0079] 2. Prepare 50 ml of 400 mg / L chromium solution using Cr(VI) stock solution and adjust to pH 2 with 0.1 M HCl and NaOH. Weigh 75 mg of PANI / MCM-41 and add it to the beaker containing the solution.

[0080] 3. Place the beaker on a water bath constant temperature oscillator, adjust the speed to 180r / min and the temperature to 25℃;

[0081] 4. Take samples after shaking for 10, 20, 30 minutes and 1, 2, 3, 4, 5, and 6 hours. Take 1 mL of the solution and filter it through a 0.45 μm syringe filter into a 15 mL centrifuge tube.

[0082] 5. Dilute the solution 10 times and measure the concentration of the solution using a flame atomic absorption spectrophotometer (AAS).

[0083] ②Desorption:

[0084] 1. Filter the adsorbed PANI / MCM-41 with a 0.45 μm filter membrane;

[0085] 2. Place the adsorbed PANI / MCM-41 in 10% ammonia water and stir at room temperature for 1 hour. After completion, filter with a 0.45 μm filter membrane and wash the material with deionized water until neutral;

[0086] 3. Place the material in 1M HCl and stir at room temperature for 2 hours, then filter, rinse repeatedly with deionized water and dry;

[0087] Then five adsorption–desorption cycle experiments were carried out under the same conditions.

[0088] (3) Preparation of red mud co-thermal desorption material PMRM3:

[0089] PANI / MCM-41 and Bayer red mud were fully mixed in a ratio of 1:1, placed in a tube furnace, and nitrogen was connected at a rate of 1 L / min. The material was heated to 700°C at a rate of 5°C / min and kept warm for 2 hours. After cooling to room temperature in the instrument, it was taken out and washed with deionized water until neutral. It was dried in an oven at 60°C and named PMRM3.

[0090] from Figure 9 (a) and (b) SEM images of PANI / MCM-41 before and after 5 cycles in Example 3. It can be seen that after 5 adsorption-desorption cycles, the PANI / MCM-41 structure becomes broken; Figure 2 The removal rate of hexavalent chromium in the five adsorption-desorption cycle experiments of PANI / MCM-41 in Example 3 can be seen. As the number of adsorption-desorption cycle experiments increases, although the hexavalent chromium removal rate gradually decreases, the PANI / MCM-41 combined with red mud after multiple cycles still has a high hexavalent chromium adsorption capacity, and the purpose of treating waste with waste can still be achieved.

[0091] Example 4

[0092] (1) Preparation of PANI / MCM-41:

[0093] Add 0.18g of MCM-41 to a 1M CA solution and stir for 2 hours. Then, add 0.93ml of aniline solution and continue stirring on ice for 2 hours. Add ammonium persulfate at a 1:1 molar ratio of ammonium persulfate to aniline to the same acid solution as the aniline / MCM-41 mixture and stir on ice for 2 hours. Rapidly add the ammonium persulfate solution to the aniline / MCM-41 mixture, stir for 5 minutes, then stop stirring and allow to react on ice for 12 hours. The resulting product is filtered through a 0.45μm polytetrafluoroethylene filter, washed three times with deionized water and anhydrous ethanol, dried in a forced air oven at 60°C for 12 hours, and finally ground thoroughly.

[0094] (2) Preparation of red mud co-thermal desorption material PMRM4:

[0095] PANI / MCM-41 and Bayer red mud were fully mixed in a ratio of 1:1, placed in a tube furnace, and nitrogen was connected at a rate of 1 L / min. The material was heated to 700°C at a rate of 5°C / min and kept warm for 2 hours. After cooling to room temperature in the instrument, it was taken out and washed with deionized water until neutral. It was dried in an oven at 60°C and named PMRM4.

[0096] Comparative Example 1

[0097] The Bayer red mud was placed in a tube furnace, nitrogen was connected at a rate of 1 L / min, and the material was heated to 700°C at a heating rate of 5°C / min and kept warm for 2 hours. After cooling to room temperature in the instrument, it was taken out and washed with deionized water until it was neutral. It was dried in an oven at 60°C and the sample was named 700RM.

[0098] Comparative Example 2

[0099] (1) Preparation of PANI / MCM-41:

[0100] Add 0.18g of MCM-41 to a 1M hydrochloric acid solution and stir for 2 hours. Then add 0.93ml of aniline solution and continue stirring on ice for 2 hours. Add ammonium persulfate at a 1:1 molar ratio of ammonium persulfate to aniline to the same acid solution as the aniline / MCM-41 mixture and stir on ice for 2 hours. Quickly add the ammonium persulfate solution to the aniline / MCM-41 mixture, stir for 5 minutes, then stop stirring and allow to react on ice for 12 hours. The resulting product is filtered through a 0.45μm polytetrafluoroethylene filter, washed three times with deionized water and anhydrous ethanol, dried in a forced air drying oven at 60°C for 12 hours, and finally thoroughly ground.

[0101] (2) Preparation of 700 PM of material of Comparative Example 2:

[0102] PANI / MCM-41 was placed in a tube furnace, nitrogen was introduced at a rate of 1 L / min, and the material was heated to 700°C at a heating rate of 5°C / min and kept warm for 2 h. After cooling to room temperature in the instrument, it was taken out and washed with deionized water until neutral. It was then dried in an oven at 60°C and named 700PM.

[0103] FT-IR images of 700PM, 700RM, and PMRM1 are as follows: Figure 1 As shown in the figure, 2923cm -1 The characteristic peak at 1630cm is due to the stretching vibration of the C-H bond. -1 The stretching vibration of -COOH is caused by the -COOH at 1577cm -1 The characteristic peak at 1408 cm corresponds to the stretching vibration of C=C bond, C=N bond or C=O bond. -1The stretching and deformation vibrations of OH are at 1118 cm -1 The characteristic peak of CN bond is at 1000cm -1 The stretching vibration of Si-O bond is at 618 cm -1 The bending vibration of CH is at 461 cm -1 The peaks at the positions correspond to the asymmetric stretching vibrations of the Fe-O bonds of Fe2O3 and Fe3O4. Compared with 700PM and 700RM, the Fe-O peak of PMRM1 is smaller. This is because the iron phase changes with increasing temperature.

[0104] SEM images of red mud, 700PM, 700RM, and PMRM1 are shown in Figure 2. Figure 2 As shown, Figure 2 (a) and (b) are SEM images of red mud. It can be seen that the unmodified red mud is more agglomerated and has a sharper surface. Figure 2 (c) and (d) are SEM images of 700RM. It can be seen from the figures that the 700RM particles are obviously dispersed and the surface becomes smoother. Figure 2 (e) is the SEM image of 700PM. The polyaniline originally filled between the MCM-41 collapsed and gradually became spherical around the MCM-41. Figure 2 (f) is the SEM image of RMPM1. It is not difficult to see from the figure that red mud and polyaniline / MCM-41 are successfully composited together.

[0105] Application Example 1

[0106] Step 1: Dry potassium dichromate in an oven at 120°C for 24 hours. Accurately weigh 2.829 g of the dried potassium dichromate, dissolve it in a small amount of water, and transfer it to a 1 L volumetric flask. Bring the volume to the mark and shake well to prepare a 1000 mg / L Cr(VI) stock solution.

[0107] Step 2: Prepare 50 ml of a 50 mg / L chromium solution using the Cr(VI) stock solution and adjust the pH to 2 with 0.1 M HCl and NaOH. Weigh 75 mg of the PMRM1 prepared in Example 1 and add it to the beaker containing the solution.

[0108] Step 3: Place the beaker on a water bath constant temperature oscillator, adjust the speed to 180 r / min and the temperature to 25°C;

[0109] Step 4: Take samples after shaking for 10, 20, 30 minutes and 1, 2, 3, 4, 5, and 6 hours. Take 1 mL of the solution and filter it through a 0.45 μm syringe filter into a 15 mL centrifuge tube.

[0110] Step 5: Dilute the solution 10 times and measure the concentration of the solution using a flame atomic absorption spectrophotometer (AAS).

[0111] Application Example 2

[0112] Step 2: Prepare 50 ml of a 50 mg / L chromium solution using the Cr(VI) stock solution and adjust the pH to 2 using 0.1 M HCl and NaOH. Weigh 75 mg of the PMRM2 prepared in Example 2 and add it to the beaker containing the solution.

[0113] The other steps are the same as those in Application Example 1.

[0114] Application Example 3

[0115] Step 1: Dry the soil, remove impurities, and then crush and sieve (100 mesh). Accurately weigh 13.62g of potassium dichromate and fully dissolve it in 18L of deionized water. Mix each kilogram of soil with 3 liters of the prepared solution according to a water-to-soil ratio of 3:1. Place the resulting mud-water mixture in a ventilated place and age it for 3 months. During this period, stir the soil thoroughly every 3 days to ensure uniform soil dyeing. The measured Cr(VI) concentration of the soil was 598.56mg / kg, and the total chromium concentration was 792.81mg / kg.

[0116] Step 2: Place the contaminated soil in the remediation device and PMRM1 in the material chamber. Adjust the electric remediation voltage to 2 V / cm, use distilled water as the anolyte, and 0.1 M citric acid as the catholyte, and remediate for 120 hours.

[0117] Step 3: Use a microwave digester to treat the soil sample. The specific steps are as follows: weigh 0.4g of the soil sample and transfer it to a digestion tank. Add 6ml HNO3, 3ml HCl and 2ml HF in sequence and put it into an acid-driving instrument. First, drive the acid at 120℃ for 30min. After cooling to room temperature, take out the digestion tube and add 2ml HNO3 and 1ml HF. Put it into a microwave digester and digest it according to the program of digestion at 150℃ for 10min, digestion at 170℃ for 5 minutes and digestion at 190℃ for 45min. After the digestion instrument cools to room temperature, take out the digestion tank, add 2ml HClO4 and put it into the acid-driving instrument again. Drive the acid at 180℃ until the solution becomes viscous, and use 1% HNO3 to make the volume to 100ml;

[0118] Step 4: Measure hexavalent chromium in the soil according to HJ 1082-2019; Accurately weigh 5.0g of soil and place it in a beaker. Add 50.0ml of sodium carbonate / sodium hydroxide extraction solution, then add 400mg of magnesium chloride and 0.5ml of dipotassium hydrogen phosphate-potassium dihydrogen phosphate buffer solution. After sealing, stir at room temperature for 5 minutes, then heat and stir to 90℃~95℃ and maintain for 60 minutes. After cooling, filter, adjust the pH of the filtrate to 7.5±0.5 with nitric acid, and dilute to 100ml.

[0119] Step 5: Pass the fixed volume liquid through a 0.45 μm filter membrane to dilute the solution to an appropriate concentration, and measure the solution concentration using a graphite furnace atomic absorption spectrometer.

[0120] Among them, the repair device in step 2 is made of plexiglass. The whole device is a cylinder with a diameter of 33 cm and a height of 12 cm. From the outside to the inside, it consists of four parts: cathode chamber 1-1, soil chamber 1-2, material chamber 1-3, and anode chamber 1-4; cathode chamber 1-1 is six cylinders with a diameter of 3 cm, which have a gap facing the direction of anode chamber 1-4. Material chamber 1-3 is a hollow cylinder with an outer diameter of 6 cm and an inner diameter of 3 cm. The inner hollow part is the anode chamber 1-4, and uniform small holes are opened on the walls of anode chamber 1-4 and material chamber 1-3. Filter paper is used to separate the cathode chamber 1-1, soil chamber 1-2, material chamber 1-3 and anode chamber 1-4. A stainless steel electrode rod 1-5 is placed as an anode in the anode chamber 1-4, and a graphite electrode rod 1-6 is placed as a cathode in the cathode chamber 1-1. Soil samples are taken at different distances from the anode for analysis, and they are numbered as sampling points S1, S2, S3, S4, and S5. The top view of the specific device is as follows. Figure 3 As shown, the actual device is as follows Figure 4 shown.

[0121] Application Example 4

[0122] Step 2: Prepare 50 ml of a 50 mg / L chromium solution using the Cr(VI) stock solution and adjust the pH to 2 using 0.1 M HCl and NaOH. Weigh 75 mg of PMRM3 prepared in Example 3 and add it to the beaker containing the solution.

[0123] The other steps are the same as those in Application Example 1.

[0124] Application Example 5

[0125] Step 2: Prepare 50 ml of a 50 mg / L chromium solution using the Cr(VI) stock solution and adjust the pH to 2 using 0.1 M HCl and NaOH. Weigh 75 mg of the PMRM4 prepared in Example 4 and add it to the beaker containing the solution.

[0126] The other steps are the same as those in Application Example 1.

[0127] Comparative Application Example 1

[0128] Step 2: Prepare 50 ml of a 50 mg / L chromium solution using the Cr(VI) stock solution and adjust the pH to 2 with 0.1 M HCl and NaOH. Weigh 75 mg of the 700RM prepared in Comparative Example 1 and add it to the beaker containing the solution.

[0129] The other steps are the same as those in Application Example 1.

[0130] Comparative Application Example 2

[0131] Step 2: Prepare 50 ml of a 50 mg / L chromium solution using the Cr(VI) stock solution and adjust the pH to 2 with 0.1 M HCl and NaOH. Weigh 75 mg of the 700 PM prepared in Comparative Example 2 and add it to the beaker containing the solution.

[0132] The other steps are the same as those in Application Example 1.

[0133] The curve of the adsorption capacity of the material changing with time is as follows Figure 5 As shown in the figure, it is not difficult to see that the materials quickly adsorbed hexavalent chromium ions in the solution in the first 30 minutes, and all reached adsorption equilibrium within about 6 hours. The adsorption amounts of PMRM1 and PMRM2 (more than 40 mg / g) were higher than those of 700PM and 700RM. The adsorption amount of PMRM1, PMRM3 and PMRM4 materials changed with time as shown in the figure. Figure 11 As shown in the figure, it is not difficult to see that the adsorption trend of PMRM3 and PMRM4 is the same as that of PMRM1. Although the adsorption amount of PMRM3 and PMRM4 is lower than that of PMRM1, the adsorption still exceeds 40 mg / g.

[0134] XPS spectra before and after PMRM1 adsorption Figure 6 As shown, Figure 6 (a) is the overall XPS spectrum of the material before and after adsorption. It can be seen from the figure that a Cr peak appears in the overall spectrum after adsorption, indicating that Cr is successfully adsorbed by the material. Figure 6 (b) and (d) are the peak fitting of Fe before and after adsorption. Figure 6 The two peaks at 709.08 and 722.28 in (b) correspond to Fe(Ⅱ) ions, the two peaks at 711.18 and 724.48 correspond to Fe(Ⅲ) ions, the two peaks at 715.18 and 727.98 are satellite peaks of Fe(Ⅱ) ions, and the two peaks at 718.68 and 732.28 are satellite peaks of Fe(Ⅲ) ions. Figure 6 In (d), the two peaks at 709.58 and 722.78 correspond to Fe(II) ions, the two peaks at 711.38 and 724.88 correspond to Fe(III) ions, the two peaks at 715.28 and 727.68 are satellite peaks of Fe(II) ions, and the two peaks at 719.38 and 732.18 are satellite peaks of Fe(III) ions. Comparing the two figures, we can see that the proportion of Fe(II) decreases, indicating that Fe(II) ions react with Fe(III) ions during the adsorption process. Figure 6(c) is the peak fitting of Cr after adsorption. The two peaks at 576.28 and 585.98 correspond to Cr(Ⅲ) ions, and the two peaks at 578.58 and 587.68 correspond to Cr(Ⅵ) ions, indicating that Cr(Ⅵ) is reduced to Cr(Ⅲ) ions when being adsorbed by the material, which corresponds to the change of Fe ions.

[0135] Comparative Application Example 3

[0136] Step 2: Place the contaminated soil in the remediation device, adjust the electric remediation voltage to 2V / cm, use distilled water as the anolyte and 0.1M citric acid as the catholyte, and remediate for 120 hours;

[0137] The other steps are the same as those in Application Example 3.

[0138] The hexavalent chromium removal rate at each sampling point is as follows: Figure 7 As shown in the figure, it can be seen that the hexavalent chromium removal rates of S1 to S5 after adding PMRM1 in Application Example 3 were 68.551%, 90.44%, 96.872%, 96.9% and 97.088%, respectively. Overall, they were higher than the 36.601%, 81.171%, 92.611%, 93.793% and 96.188% without adding PMRM1.

[0139] The change of total chromium ratio after reaction is as follows Figure 8 As shown, it can be seen that after the repair is completed, the total chromium ratio in the comparative application example 3 is higher than that in the application example 3, especially at S1. This is because the presence of PRB enables more Cr(VI) to migrate to the anode chamber and be fixed on PMRM1.

[0140] Other embodiments of the present invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention herein. The present invention is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the invention and include common knowledge or customary techniques in the art. The description and examples are to be considered as exemplary only, with the true scope and spirit of the invention being indicated by the claims.

[0141] It should be understood that the present invention is not limited to the exact construction described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for preparing a red mud co-thermal desorption material, characterized in that: The following steps are involved: (1) Preparation of PANI / MCM-41: Add MCM-41 to the acid solution and stir evenly, then add aniline solution and continue stirring to form an aniline / MCM-41 mixed solution; add ammonium persulfate to the same acid solution and stir to form an ammonium persulfate solution; Subsequently, the ammonium persulfate solution is quickly added to the aniline / MCM-41 mixture, and the stirring is stopped after uniformity, and the reaction is continued; the resulting product is filtered, washed, dried, and ground to prepare PANI / MCM-41; (2) Preparation of red mud co-thermal desorption material: The PANI / MCM-41 or the PANI / MCM-41 after multiple adsorption-desorption cycles is mixed with red mud and placed in a tube furnace, nitrogen is connected at a rate of 1 L / min, the temperature is raised to the platform temperature at a heating rate of 5°C / min, and then kept warm for 2 hours. After cooling, it is taken out, washed to neutrality, dried, and ground to obtain the red mud co-thermal desorption material.

2. The preparation method according to claim 1, characterized in that In step (1), the acid solution is selected from any one of HCl, CA, and H2SO4; and the concentration of the acid solution is 0.5 to 1.5M.

3. The preparation method according to claim 1, characterized in that In step (1), the molar ratio of the MCM-41 to the aniline is 1:(5-15); the molar ratio of the aniline to the ammonium persulfate is 1:

1.

4. The preparation method according to claim 1, characterized in that In step (1), the reaction conditions are ice bath reaction for 12 hours.

5. The preparation method according to claim 1, characterized in that In step (1), the stirring is carried out in an ice bath; the drying temperature is 60° C., and the drying time is 12 h.

6. The preparation method according to claim 1, characterized in that In step (2), the mass ratio of the PANI / MCM-41 to the red mud is 1:(0.5-2); the red mud is selected from any one of Bayer process red mud, hybrid process red mud, and sintering process red mud.

7. The preparation method according to claim 1, characterized in that In step (2), the platform temperature is 500-700°C; and the drying temperature is 60°C.

8. The red mud co-thermal desorption material prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the red mud co-thermal desorption material prepared by the preparation method according to any one of claims 1 to 7 in treating chromium pollution in water bodies.

10. Use of the red mud co-thermal desorption material prepared by the preparation method according to any one of claims 1 to 7 as a PRB material to enhance EKR-PRB remediation of chromium-contaminated soil.

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