A FeS / FeS n Preparation of carbon aerogels and methods for remediation of hexavalent chromium contaminated soil

Abstract

The application discloses a kind of FeS / FeS n Preparation of carbon aerogel and method for repairing hexavalent chromium contaminated soil, comprising: with sodium alginate (SA) as biomass, SA-Fe 3+ , is prepared 3+ Gel is added to Na2S solution, stirring, dissolving, standing, the mixed solution is transferred to a petri dish, put into refrigerator and freeze-dried in a freeze dryer, after drying, the powder is ground into powder by a planetary ball mill and put into a quartz boat, and FeS / FeS n Carbon aerogel is prepared by pyrolysis in a tube furnace at constant temperature. n The FeS / FeS n Carbon aerogel prepared by the application has good removal effect on Cr (Ⅵ) under acidic, neutral and alkaline conditions.

Description

Technical Field

[0001] This invention relates to the field of soil remediation technology and discloses a FeS / FeS n Preparation of carbon aerogel and methods for remediation of hexavalent chromium contaminated soil. Background Technology

[0002] China is the world's largest producer of chromium chemicals. Cr(VI) is highly mobile in the environment and its toxicity is 100 times that of Cr(III). It has carcinogenic, teratogenic and mutagenic effects. Soil remediation contaminated with Cr(VI) is a technical problem that urgently needs to be solved.

[0003] FeS nanoparticles, due to their large specific surface area and high reactivity, can remove Cr(VI) through adsorption and reduction, exhibiting unique advantages in the remediation of Cr(VI) pollution. Loading and modifying FeS nanoparticles with porous carbon materials can effectively prevent nanoparticle aggregation and oxidation. Using Fe... 2+ For iron source, S 2- Using sulfur as a source, loading the formed FeS onto the surface of carbon materials under aqueous conditions is the most common preparation method. However, Fe... 2+ FeS ions are easily oxidized in air, requiring nitrogen protection during the preparation process. Furthermore, preparing the carbon material before loading FeS increases the material preparation cost. Moreover, the FeS loading onto the biochar surface is uneven; in particular, while FeS-loaded materials exhibit strong Cr(VI) removal efficiency under acidic conditions, their Cr(VI) removal efficiency is poor under neutral and alkaline conditions.

[0004] Sodium alginate (SA) is a product extracted from brown algae or Sargassum fusiforme. It is a random linear block copolymer composed of α-L-guluronic acid (G segment) and β-D-mannuronic acid (M segment) linked by 1,4-glycosidic bonds. SA can react 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, which makes the metal ions uniformly dispersed in the alginate gel.

[0005] Given the shortcomings of conventional FeS carbon-modified materials, this patent uses sodium alginate as biomass, combined with Fe... 3+ Cross-linking forms a three-dimensional network structure gel of alginate-Fe 3+ gel crosslinked Fe 3+ It is slowly released in alkaline sulfurizing agent solution and reacts with S 2- Formation of alginate-FeS / S (SA-FeS / S), alginate-Fe 3+ Fe 3+The FeS / S mixed sol is uniformly distributed and formed during the slow-release process. After freeze-drying, the sol material is ground in a planetary ball mill and placed in a quartz boat. It is then pyrolyzed in a tube furnace under high-temperature and oxygen-deficient conditions, where some of the FeS and S form FeS2. n Ultimately, BC@FeS / FeS is formed. n -T (T represents the pyrolysis temperature). The main reaction formulas are 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 was mixed evenly with the chromium-contaminated soil to be remediated, water was added to maintain the soil moisture content at 60-80 wt%, and remediation was carried out at room temperature. The FeS / FeS aerogel prepared in this invention... n Carbon aerogels showed good removal effects on Cr(VI) in aqueous solutions under pH conditions of 2, 4, 7, and 9. Summary of the Invention

[0012] Based on the above analysis, this invention discloses a novel material FeS / FeS n Preparation method of carbon aerogel, and the use of FeS / FeS n A method for reducing Cr(VI) in soil using carbon aerogel, by adding 1% FeS / FeS n Carbon aerogel remediation achieved a Cr(VI) removal efficiency of over 96% in Cr(VI) contaminated soil with a concentration of 100 mg / kg after 28 days.

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

[0014] This invention first discloses a FeS / FeS n Methods for preparing carbon aerogels include:

[0015] (1) Take 30g of sodium alginate material and add it to 1L of deionized water to dissolve it. Stir it thoroughly with an electric stirrer to obtain sodium alginate solution.

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

[0017] (3) Add sodium alginate solution dropwise to FeCl3 solution, let stand for 24 hours, and then wash with deionized water to prepare sodium alginate-FeCl3 solution. 3+ gel;

[0018] (4) Prepare a Na2S solution with a concentration of 0.3 mol / L and adjust the pH of the solution to 9-12.

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

[0020] (6) After standing, transfer the mixed solution to a petri dish, freeze it in a refrigerator for 24 hours, then transfer it to a freeze dryer to dry for 48 hours. After drying, grind it with a planetary ball mill for 30 minutes.

[0021] (7) The gel pulverized by ball milling was placed in a tube furnace, vacuumed, and purged with nitrogen at a flow rate of 100 mL / min. The temperature was increased to 200°C at a heating rate of 5°C / min, then increased to 600–700°C at a heating rate of 10°C / min. After pyrolysis at a constant temperature for 3 hours, the temperature was cooled at a cooling rate of 10°C / min. The material was removed after the temperature inside the tube dropped to room temperature, yielding FeS / FeS. n Carbon aerogel.

[0022] Further, the pH of the solution is adjusted to 12 in step (4).

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

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

[0025] The present invention also discloses a method using the above-mentioned FeS / FeS n Remediation methods for carbon aerogels in hexavalent chromium-contaminated soil include:

[0026] FeS / FeS n The carbon aerogel was mixed evenly with the hexavalent chromium contaminated soil to be remediated, and water was added to maintain the soil moisture content at 60-80 wt%, and the process was 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 50–100 mg / kg;

[0029] The hexavalent chromium contaminated soil to be remediated has a pH value of 4.5–5.5 and a particle size of 75–200 μm.

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

[0031] The present invention also discloses a method using the above-mentioned FeS / FeS n Methods for adsorbing hexavalent chromium solutions using carbon aerogel include:

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

[0033] The beneficial effects of this invention are as follows:

[0034] 1. The FeS / FeS prepared by this invention n Carbon aerogels exhibit high removal rates of Cr(VI) solutions under acidic, neutral, and alkaline conditions. Cr(VI) solution concentrations of 50, 100, 200, 300, 400, 500, and 1000 mg·L⁻¹ were measured at pH 2, 4, 7, and 9. -1 BC@FeS / FeS n The thermodynamic data for Cr(VI) adsorption at -700°C conform to the Langmuir model, with the maximum fitted adsorption capacities being 767.8, 694.8, 656.3, and 599.7 mg·g⁻¹, respectively. -1 .

[0035] 2. This invention provides a method using FeS / FeS n A method for reducing Cr(VI) in soil using carbon aerogel, this method involves adding 1% FeS / FeS n The removal efficiency of carbon aerogel for Cr(VI) in soil contaminated with 100 mg / kg Cr(VI) reached over 96%. Attached Figure Description

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

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

[0038] Figure 3 The figure shows the fitting of thermodynamic data for Cr(VI) adsorption under pH conditions of 2, 4, 7, and 9. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the described embodiments of this invention are within the scope of protection of this invention.

[0040] Example 1

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

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

[0043] Sodium alginate solution was added dropwise to FeCl3 solution, allowed to stand for 24 hours, and then washed with deionized water to prepare alginate-FeCl3 solution. 3+ gel;

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

[0045] After cleaning, alginic acid-Fe 3+ The gel was placed in Na2S solution and stirred for 30 min, then allowed to stand for 24 h to react.

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

[0047] The gel, pulverized by a ball mill, was placed in a tube furnace, evacuated, and purged with nitrogen at a flow rate of 100 mL / min. The temperature was increased to 200°C at a rate of 5°C / min, then increased to 700°C at a rate of 10°C / min. After pyrolysis at 700°C for 3 hours, the temperature was cooled at a rate of 10°C / min until the temperature inside the tube reached room temperature. The resulting material was then removed, yielding FeS / FeS₂. n Carbon aerogel (denoted as BC@FeS / FeS) n-700).

[0048] Comparative Example 1

[0049] Compared to Example 1, the only difference in the preparation method of this part is:

[0050] The pulverized gel underwent high-temperature pyrolysis in a tubular furnace at different temperatures, including 500℃, 600℃, and 800℃, denoted as BC@FeS / FeS respectively. n -500, BC@FeS / FeS n -600, BC@FeS / FeS n -800.

[0051] Experimental Example 1

[0052] Comparative Example 1: BC@FeS / FeS n -700, BC@FeS / FeS prepared in Comparative Example 1 n -500, BC@FeS / FeS n -600, BC@FeS / FeS n The XRD pattern at -800° is shown in the figure. Figure 1 As shown: BC@FeS / FeS n -500, BC@FeS / FeS n -600, BC@FeS / FeS n The absorption peak at -700°C shows three relatively strong diffraction peaks at 2θ = 31.81°, 45.84°, and 56.71°. Comparing this to 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. The difference lies in BC@FeS / FeS... n The FeS diffraction peak at -800° is significantly weakened, with only a weak diffraction peak at 2θ = 31.81°. BC@FeS / FeS n -500, BC@FeS / FeS n -600 and BC@FeS / FeS n -700 shows one diffraction peak at 2θ = 32.99°, corresponding to the (020) crystal plane of FeS2 according to the standard card (PDF#65-2567); there are two diffraction peaks at 2θ = 30.16° and 35.02°, corresponding to the (020) crystal plane of FeS2 according to the standard card (PDF#65-2567); 11 The standard card (PDF#10-0437), with Fe9S 11 The (012) and (107) crystal planes correspond. BC@FeS / FeS n -600 and BC@FeS / FeS n-700 shows one diffraction peak at 2θ = 19.1°, compared to Fe9S 10 The standard card (PDF#34-1470), with Fe9S 10 The (104) crystal plane corresponds to 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 to Example 1, the only difference in the preparation method of this part is:

[0055] The pH of sodium sulfide solutions varies. Prepare 0.3 mol / L Na₂S solutions and adjust the pH to 5, 9, and 11 respectively. Under pH 5 conditions, alginate-Fe 3+ The gel reacted with Na₂S to form FeS precipitate, but the alginate gel did not dissolve, and no alginate-FeS / S sol was formed. The composite material prepared under pH conditions 9 and 11 was labeled 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 conditions, alginate-Fe 3+ The gel dissolves slowly.

[0056] Experimental Example 2

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

[0058] Weigh 0.015g BC@FeS / FeS n -500, BC@FeS / FeS n -600, BC@FeS / FeS n -700, BC@FeS / FeS n -800 mg / L Cr(VI) solutions at pH 2, 100 mL, and 50 mg / L were added respectively. The conical flasks were placed in a shaker and shaken for 24 hours. The supernatant solution was then taken, diluted, and the Cr(VI) concentration was measured using a UV-Vis spectrophotometer. Three parallel experiments were performed for each series.

[0059] BC@FeS / FeS n -500, BC@FeS / FeS n -600, BC@FeS / FeS n -700 (i.e., the FeS / FeS obtained in Example 1)n Carbon aerogel), BC@FeS / FeS n -800 adsorption capacity of Cr(VI) in solution is as follows Figure 2 As shown, BC@FeS / FeS can be observed. n The maximum adsorption capacity of Cr(VI) at -700 is 365.9 mg / g, BC@FeS / FeS n The lowest adsorption capacity for Cr(VI) at -800 was 95.3 mg / g, BC@FeS / FeS n -500, BC@FeS / FeS n The adsorption capacities of -600 for Cr(VI) were 215.7 mg / g and 321.9 mg / g, respectively.

[0060] Experimental Example 3

[0061] BC@FeS / FeS n -700 (i.e., the FeS / FeS obtained in Example 1) n Isothermal adsorption experiment of Cr(VI) by carbon aerogel. 100 mL of carbon aerogel with pH = 2 and mass concentrations of 50, 100, 200, 300, 400, 500, and 1000 mg·L⁻¹ were added to ground glass conical flasks. -1 12.0 mg FeS / FeS were added to each of the Cr(VI) reaction solutions. n Carbon aerogel was produced by placing an Erlenmeyer flask on a constant-temperature shaker at 25°C and 120 rpm. -1 Under the same conditions, the adsorption was performed by shaking for 30 min. After shaking, 1 mL of the solution was taken to test the Cr(VI) concentration. FeS / FeS were then tested under the same conditions at pH 4, 7, and 9. n Thermodynamic experiments on the adsorption of Cr(VI) by carbon aerogel. FeS / FeS n The data on Cr(VI) adsorption by carbon aerogel showed better fit in the Langmuir adsorption model (R0). 2 =0.9553, 0.9733, 0.9789, 0.9828), and the maximum adsorption capacities fitted by the Langmuir model were 767.8, 694.8, 656.3, and 599.7 mg·g⁻¹, respectively. -1 Data such as Figure 3 .

[0062] Test Example 4

[0063] Experiment on Removal of Cr(VI) from Soil

[0064] Accurately weigh 20.00 g of Cr(VI) contaminated soil (100 mg / kg) and add it to a beaker. Then, add 0.2 g, 0.4 g, and 0.6 g (1%, 2%, and 3%) of the FeS / FeS mixture prepared in Example 1.n Carbon aerogel was added to a beaker and mixed thoroughly. 15g of deionized water was added (to maintain soil moisture content at 75%). The reaction system was weighed and recorded. The mixture was covered with polyethylene film and stored in a cool place. Water was added and weighed daily to maintain a constant weight. After 28 days, the soil in the beaker was transferred to a petri dish. After drying the soil in a freeze dryer, the Cr(VI) content in the soil was determined using alkaline extraction-flame atomic absorption spectrophotometry. (FeS / FeS) n The Cr(VI) content in soils with carbon aerogel additions of 1%, 2%, and 3% decreased by 96.8%, 97.5%, and 98.3%, respectively.

[0065] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A FeS / FeS n Method of preparing a carbon aerogel, comprising: (1) Sodium alginate solution was dropped into ferric chloride solution, and after standing for 24 h, it was washed with deionized water to prepare sodium alginate-Fe 3+ gel ready for use; (2) Sodium alginate-Fe 3+ The gel was placed in 1 L of 0.3 mol / L Na2S solution and stirred for 30 min, adjusting the pH of the solution to 9-12; the reaction was allowed to stand for 24 h to obtain the first mixed solution. (3) The first mixed solution was transferred to a petri dish, frozen in a refrigerator for 24 h, then transferred to a freeze dryer and dried for 48 h. After drying, it was ground in a planetary ball mill for 30 min. (4) The ground material was placed in a tube furnace, and under vacuum and nitrogen protection, it was heated to a constant temperature for pyrolysis. The nitrogen flow rate was 100 mL / min, and the temperature was increased to 200 ℃ at a heating rate of 5 ℃ / min. Then, the temperature was increased to 600~700 ℃ at a heating rate of 10 ℃ / min, and then cooled at a cooling rate of 10 ℃ / min 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 30 g of sodium alginate in 1 L of deionized water until fully dissolved to obtain a sodium alginate solution. The ferric chloride solution is prepared by the following method: Prepare 3L of FeCl3 solution with deionized water. The concentration of FeCl3 in the solution is 0.3 mol / L.

3. A FeS / FeS prepared by the method according to claim 1 or 2 n Carbon aerogel.

4. An application of the FeS / FeS according to claim 3 n Remediation methods for carbon aerogels in hexavalent chromium-contaminated soil include: Add 1-3% FeS / FeS by weight of soil n The carbon aerogel was mixed evenly with the hexavalent chromium contaminated soil to be remediated. The concentration of hexavalent chromium in the soil to be remediated was 50-100 mg / kg, the pH value of the hexavalent chromium contaminated soil was 4.5-5.5, and the particle size was 75-200 μm. Water was added to maintain the soil moisture content at 60-80 wt%, and the remediation was carried out at 25-35 ℃ for 1-4 weeks.

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

6. An application of the FeS / FeS according to claim 5 n Methods for adsorbing hexavalent chromium solutions using carbon aerogel include: Under pH conditions of 2, 4, 7, and 9, the concentrations of Cr(VI) solutions were 50, 100, 200, 300, 400, 500, and 1000 mg·L⁻¹. -1 The adsorption temperature was 25~35 ℃ and the adsorption time was 30 min.

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