Preparation method and application of modified Fe3S4 for removing Cr (VI)

Abstract

The invention discloses a preparation method and application of modified Fe3S4 for removing Cr (VI). The preparation method comprises the following steps: firstly, preparing nano ferroferric sulfide, then adding ferroferric sulfide nanoparticles, sodium citrate, deionized water and absolute ethyl alcohol into a three-necked flask according to a certain proportion, heating to 20-60 DEG C in a water bath in a nitrogen atmosphere, and stirring for a certain period of time; after the reaction, a product is immediately collected through magnetic separation and is washed with ethyl alcohol, vacuum freeze drying is conducted, the sodium citrate modified ferroferric sulfide nano-particles are obtained, and the reducing performance of the ferroferric sulfide nano-particles can be remarkably improved through surface modification of sodium citrate. According to the method, the sodium citrate modified ferriferrous sulfide nano-particles are added into the Cr (VI) polluted soil and are uniformly stirred, so that the Cr (VI) is removed, and the method is simple to operate and easy to popularize.

Description

Technical Field

[0001] The invention belongs to the technical field of heavy metal contaminated soil remediation, and specifically relates to a preparation method and application of sodium citrate modified ferroferric tetrasulfide for efficient remediation of heavily hexavalent chromium contaminated soil. Background Art

[0002] Chromium (Cr) is an important raw material widely used in modern industries such as metallurgy, chemical industry, leather tanning, and refractory materials. The generation of a large amount of chromium-containing waste brings tremendous pressure and challenges to the environment. These human activities will produce a large amount of wastewater and soil contaminated by chromium, leading to serious environmental and public health problems. Hexavalent chromium (Cr(VI)) and trivalent chromium (Cr(III)) are the two most stable valence states in the environment. The toxicity of Cr(VI) is 300 times that of Cr(III). Long-term exposure to Cr(VI) can induce liver failure, reproductive failure, chronic headaches, respiratory diseases, nosebleeds and many other diseases. Therefore, removing Cr(VI) pollutants from soil is of great significance.

[0003] Given the high toxicity and mobility of hexavalent chromium (Cr(VI)), while trivalent chromium (Cr(III)) exhibits lower toxicity and better stability, the development of reducing materials that can reduce Cr(VI) to Cr(III) is a key strategy for treating chromium pollution. In recent years, nanoscale iron-based materials (such as zero-valent iron, iron oxides, and iron sulfides) have attracted extensive attention in the treatment of Cr pollution due to their high reactivity and environmental friendliness. Nanoscale iron trisulfide (Fe3S4) has a cubic spinel structure, and the Fe(II) and S(II) contained on its surface both exhibit good reduction activity and frequent electronic transitions, making it an excellent Cr(VI) reducing agent. However, in practical applications, this material is prone to agglomeration due to its small particle size, and a passivation layer is easily formed on the surface, which limits its reactivity. When treating heavily hexavalent chromium-contaminated soil, it often requires a higher dosage and a longer remediation cycle. Therefore, it is necessary to modify the nanoscale Fe3S4 material to solve the problems of agglomeration and passivation.

[0004] A large number of studies have shown that the addition of organic acid salts with high affinity for metals can effectively inhibit the formation of passivation film and significantly improve the reaction efficiency of reduction reactions. In addition, the addition of organic acid salts can also make the particle surface negatively charged, thereby preventing particle aggregation. Sodium citrate (SC), as a typical small molecule organic acid salt, has a good interaction with Fe(II)-OH on the surface of Fe3S4, and can introduce carboxyl groups into the material surface through complexation reaction. Existing studies have shown that it has achieved positive effects in enhancing the dispersibility and reaction efficiency of iron-based materials. Therefore, sodium citrate is used to modify the surface of nano-Fe3S4 in order to improve its ability to reduce Cr(VI) in soil, thereby overcoming the problem of easy aggregation and passivation of nano-iron-based materials and achieving the goal of "low addition, high efficiency" to treat heavily Cr(VI)-contaminated soil. Summary of the invention

[0005] In order to overcome the shortcomings of existing nano iron-based materials, the present invention provides a preparation method and application of sodium citrate modified ferroferric tetrasulfide for efficiently repairing severely hexavalent chromium contaminated soil.

[0006] The first aspect of the present application provides a method for preparing sodium citrate-modified iron tetrasulfide, specifically: S1. Preparation of nano-iron tetrasulfide (Fe3S4): Dissolve ferric chloride hexahydrate and thiourea in ethylene glycol and stir at room temperature to completely dissolve them to form a carmine solution; The above solution was transferred into a stainless steel autoclave, sealed, placed in a blast dryer, and the reaction temperature and reaction time were set; After the reactor is cooled to room temperature, the black product in the inner tank is collected, washed with deionized water and anhydrous ethanol for several times, and then vacuum-frozen and dried to obtain iron tetrasulfide nanoparticles; S2, sodium citrate (SC) modification: A certain proportion of iron tetrasulfide nanoparticles, sodium citrate, deionized water, and anhydrous ethanol were added to a three-necked flask, heated to 20°C-60°C in a water bath under a nitrogen atmosphere, and stirred for a certain period of time; The product was collected by magnetic separation immediately after the reaction, washed with ethanol, and freeze-dried in vacuum to obtain sodium citrate-modified iron tetrasulfide nanoparticles.

[0007] The second aspect of the present application provides a sodium citrate-modified iron tetrasulfide, which is prepared by the above method.

[0008] The third aspect of the present application provides an application of sodium citrate-modified ferroferric sulfide in the repair of severely hexavalent chromium-contaminated soil. Specifically: The sodium citrate-modified FeS4 nanoparticles and the hexavalent chromium-contaminated soil were fully mixed, and then deionized water was added to maintain a certain moisture content in the system.

[0009] Preferably, the amount of material added is 0.4% (4 g of material per 1 kg of contaminated soil); Preferably, the moisture content is 40%-60%.

[0010] Compared with the prior art, the present invention has the following advantages and effects: (1) The present invention adds sodium citrate to the contaminated soil to modify FeS4 nanoparticles, and stirs the mixture evenly to degrade pollutants. The operation is simple and easy to promote.

[0011] (2) The material prepared by the present invention will not cause secondary pollution, and can react at room temperature, normal pressure, and in an aerobic environment, without the need for additional sound, light, electricity, and other energy, thus saving energy.

[0012] (3) The material prepared by the present invention has a good remediation effect on severely hexavalent chromium contaminated soil with an initial Cr(VI) content of 664.98±19.09 mg / kg. The addition of 0.4% can reduce the hexavalent chromium concentration in the soil to 11.59 mg / kg within 1 day and to 5.51 mg / kg within 7 days, which is lower than the screening value for soil pollution risk of Class II construction land in China (5.7 mg / kg, see the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard GB36600-2018" of the Ministry of Ecology and Environment). The dosage is low and the remediation efficiency is high.

[0013] (4) The present invention has good long-term stability, and the soil chromium form is transformed from the more mobile exchangeable state (F1) to the iron-manganese oxide-bound state (F3) and the residual state (F5). The hexavalent chromium content in the soil continued to decrease within 30 days, and then only increased slightly from 2.76 mg / kg to 5.56 mg / kg, which is still lower than the soil pollution risk screening value of Class II construction land in China. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The X-ray powder diffraction patterns of iron tetrasulfide (Fe3S4) and sodium citrate-modified iron tetrasulfide (Fe3S4-SC) prepared in Example 1 of the present invention; Figure 2 This is a Fourier infrared spectrum of sodium citrate modified iron tetrasulfide prepared in Example 1 of the present invention; Figure 3 The hexavalent chromium content in soil measured in Example 2 and Comparative Example 1, and different letters indicate significant differences between different treatment groups (P<0.05); Figure 4 is the distribution ratio of soil chromium binding forms measured in Example 2 and Comparative Example 1;

[0015] Figure 5 The 7-day soil hexavalent chromium removal rates measured in Example 2, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 are shown in Table 1. Different letters indicate significant differences among different treatment groups (P<0.05). DETAILED DESCRIPTION

[0016] The present invention will be further described and illustrated below in conjunction with the embodiments and the accompanying drawings.

[0017] Example 1

[0018] A sodium citrate-modified ferroferric sulfide is prepared by the following method: (1) Dissolve 0.59 g of ferric chloride hexahydrate and 0.46 g of thiourea in 60 mL of ethylene glycol and stir at room temperature for 20 min to completely dissolve them to form a carmine solution; (2) The above solution was transferred to a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, sealed, and placed in a blast dryer. The reaction temperature was set to 180°C and the reaction time was set to 12 h. (3) After the reactor is cooled to room temperature, the black product in the inner tank is collected by an external magnetic field separation method, washed with deionized water and anhydrous ethanol three times respectively, and then vacuum freeze-dried to obtain iron tetrasulfide nanoparticles; (4) Add iron tetrasulfide nanoparticles, sodium citrate, deionized water, and anhydrous ethanol in a ratio of 1 mol:0.6 mol:60 L:10 L into a three-necked flask, heat to 40 °C in a water bath under a nitrogen atmosphere, and stir at 300 r / min for 1 h; (5) After the reaction, the product was immediately collected by magnetic separation, washed with ethanol three times, and vacuum freeze-dried to obtain sodium citrate-modified iron tetrasulfide nanoparticles (Fe3S4-SC), which were finally stored in a -80°C refrigerator; The obtained iron tetrasulfide and the iron tetrasulfide modified by sodium citrate were placed under X-ray powder diffractometer for scanning, and the results are as follows: Figure 1 As shown, it can be seen that iron tetrasulfide was successfully synthesized and has a good structure. The crystal structure of the particles is almost unaffected after being modified by sodium citrate.

[0019] The obtained iron tetrasulfide and the iron tetrasulfide modified by sodium citrate were scanned under a Fourier transform infrared spectrometer, and the results were as follows: Figure 2 As shown, 1566, 1345cm -1 Two typical carboxylate absorption peaks can be seen at - ) and symmetric stretching vibration peaks vs (COO - ), indicating that sodium citrate modification was successful.

[0020] Example 2

[0021] This embodiment provides a method for remediating severely hexavalent chromium contaminated soil using ferrous sulfide modified by sodium citrate (referred to as Fe3S4-SC group), as follows: (1) The original hexavalent chromium contaminated soil (with an initial hexavalent chromium content of 664.98 mg / kg) was collected, air-dried, and ground through a 2.0 mm sieve to obtain the hexavalent chromium contaminated soil to be treated.

[0022] (2) Weigh 10 g of the above-mentioned hexavalent chromium-contaminated soil to be treated into a 50 mL centrifuge tube, add 0.04 g of sodium citrate-modified iron tetrasulfide nanoparticles and mix well, add 4 mL of deionized water to make the water content of the system 40%, stir evenly, and repair for 60 days.

[0023] (3) Multiple parallel experiments were conducted, with destructive sampling performed at 1, 7, 15, 30, and 60 days. The samples were freeze-dried immediately after sampling and the hexavalent chromium content in the soil was determined according to the USEPA Method 3060A alkaline digestion method and the USEPA Method 7196A colorimetric method. The chromium speciation of the soil sample taken at 15 days was determined according to the Tessier five-step extraction method.

[0024] Comparative Example 1 This comparative example provides a method for repairing severely hexavalent chromium contaminated soil using ferroferric sulfide (referred to as Fe3S4 group), as follows:

[0025] (1) The original hexavalent chromium contaminated soil (with an initial hexavalent chromium content of 664.98 mg / kg) was collected, air-dried, and ground through a 2.0 mm sieve to obtain the hexavalent chromium contaminated soil to be treated.

[0026] (2) Weigh 10 g of the above-mentioned hexavalent chromium-contaminated soil to be treated into a 50 mL centrifuge tube, add 0.04 g of iron tetrasulfide nanoparticles and mix well, add 4 mL of deionized water to make the water content of the system 40%, stir evenly, and repair for 60 days.

[0027] (3) Multiple parallel experiments were conducted, with destructive sampling performed at 1, 7, 15, 30, and 60 days. The samples were freeze-dried immediately after sampling and the hexavalent chromium content in the soil was determined according to the USEPA Method 3060A alkaline digestion method and the USEPA Method 7196A colorimetric method. The chromium speciation of the soil sample taken at 15 days was determined according to the Tessier five-step extraction method.

[0028] Comparative Example 2 This comparative example provides a method for repairing severely hexavalent chromium contaminated soil using ferroferric oxide (referred to as Fe3O4 group), as follows: (1) The original hexavalent chromium contaminated soil (with an initial hexavalent chromium content of 664.98 mg / kg) was collected, air-dried, and ground through a 2.0 mm sieve to obtain the hexavalent chromium contaminated soil to be treated.

[0029] (2) Weigh 10 g of the hexavalent chromium contaminated soil to be treated in a 50 mL centrifuge tube, add 0.04 g of commercial ferrosoferric oxide nanoparticles and mix well, add 4 mL of deionized water to make the water content of the system 40%, stir evenly, and repair for 7 days.

[0030] (3) Multiple parallel experiments were conducted, destructive sampling was performed on the 7th day, and the samples were freeze-dried immediately after sampling. The hexavalent chromium content in the soil was determined according to the USEPA Method 3060A alkaline digestion method and the USEPA Method 7196A colorimetric method.

[0031] Comparative Example 3 This comparative example provides a method for repairing severely hexavalent chromium contaminated soil using ferrous sulfide (referred to as FeS group), as follows: (1) The original hexavalent chromium contaminated soil (with an initial hexavalent chromium content of 664.98 mg / kg) was collected, air-dried, and ground through a 2.0 mm sieve to obtain the hexavalent chromium contaminated soil to be treated.

[0032] (2) Weigh 10 g of the hexavalent chromium contaminated soil to be treated in a 50 mL centrifuge tube, add 0.04 g of commercial ferrous sulfide particles and mix well, add 4 mL of deionized water to make the water content of the system 40%, stir evenly, and repair for 7 days.

[0033] (3) Multiple parallel experiments were conducted, destructive sampling was performed on the 7th day, and the samples were freeze-dried immediately after sampling. The hexavalent chromium content in the soil was determined according to the USEPA Method 3060A alkaline digestion method and the USEPA Method 7196A colorimetric method.

[0034] Comparative Example 4 This comparative example provides a method for remediating soil contaminated with severe hexavalent chromium using nano-zero-valent iron (referred to as nZVI group) relative to Example 2, as follows: (1) The original hexavalent chromium contaminated soil (with an initial hexavalent chromium content of 664.98 mg / kg) was collected, air-dried, and ground through a 2.0 mm sieve to obtain the hexavalent chromium contaminated soil to be treated.

[0035] (2) Weigh 10 g of the hexavalent chromium contaminated soil to be treated in a 50 mL centrifuge tube, add 0.04 g of commercial nano zero-valent iron particles and mix well, add 4 mL of deionized water to make the water content of the system 40%, stir evenly, and repair for 7 days.

[0036] (3) Multiple parallel experiments were conducted, destructive sampling was performed on the 7th day, and the samples were freeze-dried immediately after sampling. The hexavalent chromium content in the soil was determined according to the USEPA Method 3060A alkaline digestion method and the USEPA Method 7196A colorimetric method.

[0037] like Figure 3 As shown, after 7 days of restoration by sodium citrate-modified iron tetrasulfide (Fe3S4-SC) in Example 2, the Cr(VI) content in the soil was 5.52 mg / kg, which was lower than the risk screening value of soil pollution for Class II construction land in China (5.7 mg / kg, see the Ministry of Ecology and Environment's "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard GB36600-2018"), while the Cr(VI) content in the control group in Comparative Example 1 to which iron tetrasulfide (Fe3S4) was added was 45.24 mg / kg, which was significantly higher than the Fe3S4-SC group (p<0.05). After 60 days of restoration by sodium citrate-modified iron tetrasulfide (Fe3S4-SC) in Example 2, the Cr(VI) content in the soil only increased from 2.76 mg / kg to 5.56 mg / kg, which was still lower than the risk screening value of soil pollution for Class II construction land in China, while the Cr(VI) content in the soil in Comparative Example 1 was as high as 16.77 mg / kg. It can be seen that sodium citrate-modified ferroferric sulfide can effectively repair soil severely contaminated by hexavalent chromium, and has good long-term stability.

[0038] like Figure 4 As shown, after 15 days of restoration by sodium citrate-modified ferrous tetrasulfide (Fe3S4-SC) in Example 2, the exchangeable state (F1) of soil Cr significantly decreased to below the detection limit, the proportion of iron-manganese oxide-bound state (F3) significantly increased to 53.12%, and the residual state (F5) significantly increased to 22.93%. In the control group of comparative example 1, in which ferrous tetrasulfide (Fe3S4) was added, the exchangeable state (F1) of soil Cr significantly decreased to below the detection limit, the proportion of iron-manganese oxide-bound state (F3) significantly increased to 54.20%, and the residual state (F5) significantly increased to 21.22%. It can be seen that the sodium citrate-modified ferrous tetrasulfide material provided by the present invention can convert soil Cr from the less stable exchangeable state (F1) to the more stable iron-manganese oxide-bound state (F3) and residual state (F5), which is beneficial to the reduction and stabilization of hexavalent chromium and has broad application prospects.

[0039] like Figure 5As shown, after 7 days of repair, the Cr removal rates of Fe3S4-SC, Fe3S4, nZVI, FeS, and Fe3O4 groups reached 99.17%, 93.13%, 45.08%, 17.22%, and 16.87%, respectively, and the Fe3S4-SC group was significantly (p>0.05) higher than the other treatment groups. It can be seen that the sodium citrate-modified ferroferric sulfide material provided by the present invention has significant advantages over traditional iron-based materials in terms of repair efficiency, and can achieve the goal of "low dosage, high efficiency" treatment of severely Cr (VI) contaminated soil.

[0040] The above embodiment is only a preferred implementation of the present invention and is not intended to limit the scope of the present invention. A person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, equivalent transformations and simple replacements based on the present invention fall within the scope of protection of the present invention.

Claims

1. A method for preparing sodium citrate-modified ferroferric sulfide, characterized in that The method comprises the following steps: S1. Preparation of nano-iron tetrasulfide: Dissolve ferric chloride hexahydrate and thiourea in ethylene glycol and stir at room temperature to completely dissolve them to form a carmine solution; The above solution was transferred into a stainless steel autoclave, sealed, placed in a blast dryer, and the reaction temperature and reaction time were set; After the reactor is cooled to room temperature, the black product in the inner tank is collected, washed with deionized water and anhydrous ethanol for several times, and then vacuum-frozen and dried to obtain iron tetrasulfide nanoparticles; S2, sodium citrate modification: A certain proportion of iron tetrasulfide nanoparticles, sodium citrate, deionized water, and anhydrous ethanol were added to a three-necked flask, heated to 20°C-60°C in a water bath under a nitrogen atmosphere, and stirred for a certain period of time; The product was collected by magnetic separation immediately after the reaction, washed with ethanol, and freeze-dried in vacuum to obtain sodium citrate-modified iron tetrasulfide nanoparticles.

2. The method for preparing sodium citrate-modified ferroferric sulfide according to claim 1, characterized in that: The stainless steel autoclave is lined with polytetrafluoroethylene.

3. The method for preparing sodium citrate-modified ferroferric sulfide according to claim 2, characterized in that: The reaction temperature in the stainless steel autoclave was 180°C and the reaction time was 12 h.

4. The method for preparing sodium citrate-modified ferroferric sulfide according to claim 1, characterized in that: The black product in the inner container is collected by an external magnetic field separation method.

5. The method for preparing sodium citrate-modified ferroferric sulfide according to claim 1, characterized in that: The mixture was stirred at 300 r / min in a water bath for 1 h.

6. The method for preparing sodium citrate-modified ferroferric sulfide according to claim 1, characterized in that: The ratio of the iron tetrasulfide nanoparticles, sodium citrate, deionized water and anhydrous ethanol is 1 mol:0.6 mol:60 L:10 L.

7. The method for preparing sodium citrate-modified ferroferric sulfide according to claim 1, characterized in that: The water bath heating temperature is 40°C.

8. A sodium citrate-modified ferroferric sulfide prepared by the method according to any one of claims 1 to 7.

9. Use of the sodium citrate-modified ferroferric sulfide according to claim 8 in repairing soil heavily contaminated by hexavalent chromium.

10. The use according to claim 9, characterized in that: The sodium citrate-modified iron tetrasulfide nanoparticles and the hexavalent chromium-contaminated soil are fully mixed, and then deionized water is added to maintain a certain moisture content in the sodium citrate-modified iron tetrasulfide nanoparticles and hexavalent chromium-contaminated soil system.

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