Method for preparing FeS / FeSn carbon aerogel and repairing hexavalent chromium contaminated soil

Abstract

The invention discloses a method for preparing FeS / FeSn carbon aerogel and repairing hexavalent chromium contaminated soil, which comprises the following steps: preparing SA-Fe < 3 + > by using sodium alginate (SA) as biomass, adding SA-Fe < 3 + > gel into a Na2S solution, stirring, dissolving, standing, transferring the mixed solution into a culture dish, freezing in a refrigerator, transferring into a freeze dryer, and drying to obtain the FeS / FeSn carbon aerogel. And drying, grinding into powder by using a planetary ball mill, putting into a quartz boat, and carrying out constant-temperature pyrolysis in a tubular furnace to prepare the FeS / FeSn carbon aerogel. And uniformly mixing the FeS / FeSn carbon aerogel with the to-be-repaired chromium-polluted soil, adding water to maintain the water content of the soil to be 60-80 wt%, and repairing for 1-4 weeks at normal temperature. The FeS / FeSn carbon aerogel prepared by the method disclosed by the invention has a relatively good removal effect on Cr (VI) under acidic, neutral and alkaline conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation and discloses a FeS / FeS n Preparation of carbon aerogel and method for remediation of hexavalent chromium contaminated soil. Background Art

[0002] China is the world's largest producer of chromium chemicals. Cr(VI) is highly mobile in the environment and is 100 times more toxic than Cr(III). It is carcinogenic, teratogenic, and mutagenic. The remediation of Cr(VI)-contaminated soil is a technical challenge that urgently needs to be addressed.

[0003] FeS nanoparticles have a large specific surface area and reaction activity, and can remove Cr(VI) through adsorption and reduction, which has unique advantages in the remediation of Cr(VI) pollution. Using porous carbon materials to load and modify FeS nanoparticles can effectively prevent the agglomeration and oxidation of nanoparticles. 2+ As the iron source, S 2- As a sulfur source, the most commonly used preparation method is to load the formed FeS onto the surface of carbon materials under aqueous conditions, but Fe 2+ Ions are easily oxidized in air, requiring nitrogen protection during the preparation process. Furthermore, the carbon material must be prepared before FeS loading, increasing material preparation costs. Furthermore, FeS loading is uneven across the biochar surface. In particular, FeS-carbon-loaded materials, while highly effective at removing Cr(VI) under acidic conditions, are less effective under neutral and alkaline conditions.

[0004] Sodium alginate (SA) is a product extracted from brown algae or sargassum. It is a random linear block copolymer composed of α-L-guluronic acid (G segment) and β-D-mannuronic acid (M segment) bonded by 1,4 glycosidic bonds. SA reacts with polyvalent metal ions (such as Ca 2+ 、Fe 3+ After mixing, the metal ions chelate with multiple oxygen-containing functional groups of the GG block to form a three-dimensional network structure gel, so that the metal ions are evenly dispersed in the alginate gel.

[0005] In view of the shortcomings of conventional FeS carbon modified materials, this patent uses sodium alginate as biomass and 3+ Cross-linking to form a three-dimensional network structure gel alginate-Fe 3+ , gel cross-linked Fe 3+ Slowly released in alkaline sulfiding agent solution 2- Forming alginic acid-FeS / S (SA-FeS / S), alginic acid-Fe 3+ Medium Fe 3+The distribution is uniform, and a mixed sol with uniform distribution of FeS / S is formed during the slow release process. The sol material is freeze-dried and ground with a planetary ball mill and then placed in a quartz boat. It is pyrolyzed at a constant temperature in a tube furnace under high temperature and oxygen deficiency conditions, and part of the FeS and S form FeS n , and finally formed BC@FeS / FeS n -T (T represents the pyrolysis temperature). The main reaction formula is as follows:

[0006] 2Fe 3+ +S 2- →2Fe 2+ +S(1)

[0007] Fe 2+ +S 2- →FeS(2)

[0008] Fe 3+ +3OH - →Fe(OH)3(3)

[0009] 2Fe(OH)3+3S 2- →2FeS+6OH - +S(4)

[0010]

[0011] FeS / FeS n The carbon aerogel is mixed evenly with the chromium-contaminated soil to be repaired, water is added to maintain the soil moisture content at 60-80 wt% and the repair is carried out at room temperature. n Carbon aerogel has a good removal effect on Cr(VI) in aqueous solution under pH conditions of 2, 4, 7, and 9. Summary of the Invention

[0012] Based on the above analysis, the present invention discloses a new material FeS / FeS n Preparation method of carbon aerogel and FeS / FeS n Carbon aerogel reduction of Cr(VI) in soil, adding 1% FeS / FeS n The removal efficiency of Cr(VI) in 100 mg / kg Cr(VI) contaminated soil after 28 days of carbon aerogel remediation reached more than 96%.

[0013] The present invention is achieved through the following technical means:

[0014] The present invention first discloses a FeS / FeS n A method for preparing a carbon aerogel, comprising:

[0015] (1) Dissolve 30 g of sodium alginate in 1 L of deionized water and stir thoroughly with an electric stirrer to obtain a sodium alginate solution;

[0016] (2) Prepare 3 L of 0.3 mol / L FeCl3 solution with deionized water. The FeCl3 concentration in the solution is 0.3 mol / L.

[0017] (3) Sodium alginate solution was dropped into FeCl3 solution, and after standing for 24 hours, it was washed with deionized water to prepare sodium alginate-Fe 3+ gel;

[0018] (4) preparing a Na2S solution with a concentration of 0.3 mol / L and adjusting the pH of the solution to 9-12;

[0019] (5) The washed sodium alginate-Fe 3+ The gel was placed in Na2S solution and stirred for 30 min, and then allowed to react for 24 h;

[0020] (6) After standing, the mixed solution was transferred to a Petri dish, placed in a refrigerator for 24 h, and then transferred to a freeze dryer for 48 h. After drying, it was ground using a planetary ball mill for 30 min.

[0021] (7) The gel after ball milling was placed in a tubular furnace, vacuumed, and introduced with nitrogen at a nitrogen flow rate of 100 mL / min. The temperature was raised to 200°C at a heating rate of 5°C / min, and then raised to 600-700°C at a heating rate of 10°C / min. After pyrolysis at a constant temperature for 3 h, the gel was cooled at a cooling rate of 10°C / min. When the temperature in the tube dropped to room temperature, the material was taken out to obtain FeS / FeS. n Carbon aerogel.

[0022] Furthermore, in step (4), the pH of the solution is regulated to be 12.

[0023] Furthermore, the heating rate in step (7) is increased to 700°C.

[0024] The present invention discloses a FeS / FeS prepared by any of the above preparation methods. n Carbon aerogel.

[0025] The present invention also discloses a method for applying the above FeS / FeS n The remediation method of carbon aerogel in hexavalent chromium contaminated soil includes:

[0026] FeS / FeS n The carbon aerogel is mixed evenly with the hexavalent chromium contaminated soil to be repaired, and water is added to maintain the soil moisture content at 60-80wt%, and the process is carried out at room temperature.

[0027] Furthermore, the FeS / FeS n The dosage of carbon aerogel is 1-3% of the mass of contaminated soil;

[0028] The concentration of hexavalent chromium in the soil to be remediated is 50 to 100 mg / kg;

[0029] The pH value of the hexavalent chromium contaminated soil to be repaired is 4.5-5.5, and the particle size is 75-200 μm.

[0030] Furthermore, the FeS / FeS n The addition amount of carbon aerogel was 1% of the mass of the contaminated soil, the concentration of hexavalent chromium in the soil to be repaired was 100 mg / kg, and after 28 days of continuous repair, the Cr(VI) content in the soil decreased by 96.8%.

[0031] The present invention also discloses a method for applying the above FeS / FeS n The method for adsorbing hexavalent chromium solution by carbon aerogel comprises:

[0032] Under the conditions of pH 2, 4, 7, and 9, the concentrations of Cr(VI) solutions were 50, 100, 200, 300, 400, 500, and 1000 mg·L -1 , the adsorption temperature is 25-35℃, and the adsorption time is 30min.

[0033] The beneficial effects of the present invention are:

[0034] 1. FeS / FeS prepared by the present invention n Carbon aerogel has a high removal capacity for Cr(VI) solution under acidic, neutral and alkaline conditions. Under pH 2, 4, 7 and 9, the concentration of Cr(VI) solution is 50, 100, 200, 300, 400, 500 and 1000 mg·L -1 , BC@FeS / FeS n The thermodynamic data of Cr(VI) adsorption on -700 conform to the Langmuir model, and the fitted maximum adsorption capacities are 767.8, 694.8, 656.3, and 599.7 mg·g, respectively. -1 .

[0035] 2. The present invention provides a method for using FeS / FeS n Method for reducing Cr(VI) in soil by carbon aerogel. This method adds 1% FeS / FeS n The removal efficiency of carbon aerogel for Cr(VI) in 100 mg / kg Cr(VI) contaminated soil reached over 96%. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 BC@FeS / FeSn -XRD pattern of T;

[0037] Figure 2 BC@FeS / FeS n -T comparison of adsorption capacity of Cr(VI) in solution;

[0038] Figure 3 This is the fitting diagram of the thermodynamic data of Cr(VI) adsorption under pH 2, 4, 7, and 9 conditions. DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of the present invention.

[0040] Example 1

[0041] Take 30g of sodium alginate (SA) and dissolve it in 1L of deionized water. Stir it thoroughly with an electric stirrer to obtain a sodium alginate solution.

[0042] Prepare 3 L of 0.3 mol / L FeCl3 solution with deionized water;

[0043] Sodium alginate solution was dropped into FeCl3 solution, and after standing for 24 hours, it was washed with deionized water to prepare alginate-Fe 3+ gel;

[0044] Prepare 0.3 mol / L Na2S solution and adjust the pH of the solution to 12;

[0045] The washed alginate-Fe 3+ The gel was placed in Na2S solution and stirred for 30 min, and then allowed to react for 24 h;

[0046] After standing, the mixed solution was transferred to a Petri dish, placed in a refrigerator for 24 hours, and then transferred to a freeze dryer for 48 hours. After drying, it was ground in a planetary ball mill for 30 minutes.

[0047] The gel after ball milling was placed in a tube furnace, vacuumed, and introduced with nitrogen at a nitrogen flow rate of 100 mL / min. The temperature was raised to 200°C at a heating rate of 5°C / min, and then raised to 700°C at a heating rate of 10°C / min. After constant temperature pyrolysis at 700°C for 3 h, it was cooled at a cooling rate of 10°C / min. When the temperature in the tube dropped to room temperature, the material was taken out to obtain FeS / FeS. n Carbon aerogel (denoted as BC@FeS / FeS n-700).

[0048] Comparative Example 1

[0049] Compared with Example 1, the preparation method of this part is different only in that:

[0050] The crushed gel was pyrolyzed in a tubular furnace at different temperatures, including 500°C, 600°C, and 800°C, respectively, and denoted as BC@FeS / FeS n -500, BC@FeS / FeS n -600, BC@FeS / FeS n -800.

[0051] Test Example 1

[0052] Comparative Example 1 prepared BC@FeS / FeS n -700, BC@FeS / FeS prepared in Comparative Example 1 n -500, BC@FeS / FeS n -600, BC@FeS / FeS n -800 XRD pattern, the specific results are as follows Figure 1 Shown: BC@FeS / FeS n -500, BC@FeS / FeS n -600, BC@FeS / FeS n The absorption peak of -700 shows three strong diffraction peaks at 2θ=31.81°, 45.84° and 56.71°. Compared with the FeS standard card (PDF#49-1632), the diffraction peaks at 31.81° and 56.71° correspond to the (100) and (110) crystal planes respectively. n The diffraction peak of FeS at -800° is significantly weakened, with only a weak diffraction peak at 2θ=31.81°. n -500, BC@FeS / FeS n -600 and BC@FeS / FeS n -700 has a diffraction peak at 2θ=32.99°, which corresponds to the (020) crystal plane of FeS2 compared with the standard card of FeS2 (PDF#65-2567); there are two diffraction peaks at 2θ=30.16° and 35.02°, which corresponds to the (020) crystal plane of FeS2 compared with the standard card of FeS2 (PDF#65-2567). 11 Standard card (PDF#10-0437), with Fe9S 11 The (012) and (107) crystal planes of BC@FeS / FeS n -600 and BC@FeS / FeS n-700 has a diffraction peak at 2θ=19.1°, compared with Fe9S 10 Standard card (PDF#34-1470), with Fe9S 10 The (104) crystal plane of BC@FeS / FeS n -700 has two diffraction peaks at 2θ=29.49° and 75.24°, which correspond to the (121) and (062) crystal planes of Fe3S when compared with the standard card of Fe3S (PDF#52-0973).

[0053] Comparative Example 2

[0054] Compared with Example 1, the preparation method of this part is different only in that:

[0055] The pH of sodium sulfide solution is different. Prepare 0.3mol / L Na2S solution and adjust the pH of Na2S solution to 5, 9, and 11 respectively. Under the condition of pH 5, alginate-Fe 3+ The gel formed FeS precipitate with Na2S, but the alginate gel did not dissolve and no alginate-FeS / S sol was formed. The composite materials prepared under pH 9 and 11 were labeled as BC@FeS / FeS n -700-9, BC@FeS / FeS n -700-11, its adsorption performance for Cr(VI) is lower than that of BC@FeS / FeS n -700 and pH 9 under the conditions of alginate-Fe 3+ The gel dissolves slowly.

[0056] Test Example 2

[0057] Comparison of material removal performance of Cr(VI)

[0058] Weigh 0.015g BC@FeS / FeS n -500, BC@FeS / FeS n -600, BC@FeS / FeS n -700, BC@FeS / FeS n Add 100 mL of Cr(VI)-800 to a pH 2, 100 mL of Cr(VI)-800, and 50 mg / L of Cr(VI) solution, respectively. Place the conical flask in a shaker for 24 hours, remove it, and dilute the supernatant solution to measure the Cr(VI) concentration using a UV-visible spectrophotometer. Perform three parallel experiments for each series.

[0059] BC@FeS / FeS n -500, BC@FeS / FeS n -600, BC@FeS / FeS n -700 (i.e., FeS / FeS prepared in Example 1n Carbon aerogel), BC@FeS / FeS n -800 has the adsorption capacity of Cr(VI) in solution. Figure 2 As shown, it can be observed that BC@FeS / FeS n -700 has the largest adsorption capacity of Cr(VI) of 365.9 mg / g, and BC@FeS / FeS n -800 has the lowest adsorption capacity of Cr(VI) of 95.3 mg / g, and BC@FeS / FeS n -500, BC@FeS / FeS n -600 for Cr(VI) adsorption capacity were 215.7 mg / g and 321.9 mg / g respectively.

[0060] Test Example 3

[0061] BC@FeS / FeS n -700 (i.e., FeS / FeS prepared in Example 1 n Isothermal adsorption experiment of Cr(VI) on carbon aerogel. 100 mL of pH=2 and concentrations of 50, 100, 200, 300, 400, 500, and 1000 mg·L were added to a ground-mouth conical flask. -1 Cr(VI) reaction solution, 12.0 mg FeS / FeS n Carbon aerogel, place the conical flask in a constant temperature shaker at 25℃ and 120r·min -1 The adsorption was carried out under the same conditions for 30 minutes. After the adsorption was completed, 1 mL of the solution was taken to test the concentration of Cr(VI). The FeS / FeS n Thermodynamic experiments on the adsorption of Cr(VI) on carbon aerogel. FeS / FeS n The data of Cr(VI) adsorption on carbon aerogels have better fitting effect in Langmuir adsorption model (R 2 =0.9553, 0.9733, 0.9789, 0.9828), and the maximum adsorption capacities of Langmuir model fitting were 767.8, 694.8, 656.3, 599.7 mg·g -1 . Data such as Figure 3 .

[0062] Test Example 4

[0063] Experiment on removing Cr(VI) from soil

[0064] 20.00 g of Cr(VI) contaminated soil (100 mg / kg) was accurately weighed and added to a beaker. 0.2 g, 0.4 g, and 0.6 g (1%, 2%, and 3%) of the FeS / FeS prepared in Example 1 were added to the beaker.n The carbon aerogel was added to a beaker and mixed evenly. 15 g of deionized water was added (maintaining the soil moisture content at 75%). The reaction system was weighed and recorded, covered with polyethylene film, and stored in a cool place. The system was weighed and watered daily to maintain a constant weight. After 28 days, the soil in the beaker was transferred to a Petri dish. After the soil was dried in a freeze dryer, the Cr(VI) content in the soil was tested using alkaline solution extraction-flame atomic absorption spectrophotometry. n The Cr(VI) content in soil with carbon aerogel addition of 1%, 2%, and 3% was reduced by 96.8%, 97.5%, and 98.3%, respectively.

[0065] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. FeS / FeS n A method for preparing a carbon aerogel, comprising: (1) Sodium alginate solution was dropped into ferric chloride solution, allowed to stand for 24 hours and then washed with deionized water to obtain sodium alginate-Fe 3+ Set aside the gel; (2) Sodium alginate-Fe 3+ The gel was placed in 1 L of Na2S solution, stirred, and allowed to stand for reaction to obtain a first mixed solution; (3) The first mixed solution was transferred to a culture dish, placed in a refrigerator for freezing, and then transferred to a freeze dryer for drying. After drying, the mixture was ground using a planetary ball mill. (4) The ground material is placed in a tube furnace, vacuumed, and heated under nitrogen protection for constant temperature pyrolysis. After completion, the temperature is cooled to room temperature to obtain FeS / FeS n Carbon aerogel.

2. The preparation method according to claim 1, wherein: The sodium alginate solution in step (1) is prepared by the following method: Dissolve 30g of sodium alginate in 1L of deionized water and fully dissolve to obtain a sodium alginate solution; The ferric chloride solution is prepared by the following method: Prepare 3 L of FeCl3 solution with deionized water, where the FeCl3 concentration is 0.3 mol / L.

3. The preparation method according to claim 1, wherein: Step (2) The concentration of the Na2S solution is 0.3 mol / L and the pH value is 9-12; The stirring time is 30 minutes, and the reaction is allowed to stand for 24 hours.

4. The preparation method according to claim 1, wherein: The freezing time in the refrigerator in step (3) is 24 hours, the drying time in the freeze dryer is 48 hours, and the grinding time is 30 minutes.

5. The preparation method according to claim 1, wherein: In step (4), the nitrogen flow rate is 100 mL / min, the temperature is raised to 200°C at a heating rate of 5°C / min, then raised to 600-700°C at a heating rate of 10°C / min, and then cooled at a cooling rate of 10°C / min.

6. FeS / FeS prepared according to any one of the preparation methods of claims 1 to 5 n Carbon aerogel.

7. An application of the FeS / FeS according to claim 6 n The remediation method of carbon aerogel in hexavalent chromium contaminated soil includes: 1-3% of the soil mass of FeS / FeS n The carbon aerogel is evenly mixed with the hexavalent chromium contaminated soil to be repaired. The concentration of hexavalent chromium in the soil to be repaired is 50-100 mg / kg, the pH value of the hexavalent chromium contaminated soil is 4.5-5.5, the particle size is 75-200 μm, water is added to maintain the soil moisture content at 60-80 wt%, and the repair is carried out at 25-35°C for 1-4 weeks.

8. The repair method according to claim 7, wherein: 1% FeS / FeS of soil mass n The carbon aerogel was evenly mixed with the hexavalent chromium-contaminated soil to be repaired. The concentration of hexavalent chromium in the soil to be repaired was 100 mg / kg, the pH value of the hexavalent chromium-contaminated soil was 4.5-5.5, the particle size was 75-200 μm, and water was added to maintain the soil moisture content at 60-80 wt%. After repair at 25-35°C for 4 weeks, the Cr(VI) content in the soil was reduced by 96.8%.

9. An application of the FeS / FeS according to claim 6 n The method for adsorbing hexavalent chromium solution by carbon aerogel comprises: Under the conditions of pH 2, 4, 7, and 9, the concentrations of Cr(VI) solutions were 50, 100, 200, 300, 400, 500, and 1000 mg·L -1 , the adsorption temperature is 25-35℃, and the adsorption time is 30min.

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