Preparation method and application of multi-element doped zero-valent iron

Abstract

The invention discloses a preparation method of a multi-element doped zero-valent iron material and application of the multi-element doped zero-valent iron material in saline-alkali soil, nitrogen-doped biochar is prepared through dipping-pyrolysis, 200g of agate ball-milling beads and nitrogen-modified biochar are loaded into an agate ball-milling tank, the mass ratio of elemental sulfur powder to micron-sized iron powder is 2: 1: 7 (all the operations are performed in an anaerobic operation box), and the nitrogen-modified biochar is loaded into the agate ball-milling tank. Uniformly mixing and then putting the mixture into a ball mill to start ball milling, wherein nitrogen is used as protective gas in the ball milling process; the ball milling speed is 300 r / min, the ball milling time is 4 h, and after ball milling is finished, the nitrogen-carbon-sulfur ternary doped zero-valent iron material is obtained through separation and storage in the nitrogen atmosphere. The nitrogen-carbon-sulfur ternary doped zero-valent iron material has a good effect on improvement of saline-alkali soil.

Description

Technical Field

[0001] The present invention relates to the field of functional composite materials, and in particular to a preparation method and application of nitrogen-carbon-sulfur ternary doped zero-valent iron. Background Art

[0002] Zero-valent iron is a chemically active metal with strong reducing ability, good electrochemical properties, coordination chemical properties, and environmental friendliness. It can directly reduce or indirectly catalyze oxidation and degrade pollutants, thereby reducing their toxicity. It exhibits the characteristics of environmental friendliness, low price, strong catalytic effect and wide range of applications. It has been used in industrial water treatment or groundwater remediation.

[0003] In recent years, zero-valent iron (ZVI) has been widely used in various fields of soil or water pollution ecological restoration due to its huge specific surface area and high reactivity, and has good performance against various pollutants. ZVI has a core-shell structure with Fe 0 As the core, with iron oxide as the shell. The metal core provides electrons, while the oxide shell adsorbs pollutants through electrostatic interactions or van der Waals forces. When it reacts with metal ions, an adsorption mechanism may occur according to the electrode potential of the metal ions. However, it is easy to agglomerate and passivate in the soil, resulting in a reduction in adsorption sites, so it is considered to be modified for use. According to the characteristics of Tianjin Binhai saline-alkali soil, the selection of sulfide and nitride doping can improve the electronic selectivity of ZVI and accelerate the release of iron ions; carbonization can enhance the hydrophobicity of ZVI, and can also improve the ball milling efficiency and dispersibility of the material, increase the contact area of ​​ZVI, and break through the passivation problem of ZVI in alkaline soil. For example, Dong et al. found that due to the presence of the FeS layer, the passivation of the ZVI surface can be reduced, the service life of ZVI can be increased, and S-nZVI still maintains high activity after aging for 30 days, and continuously releases ferrous ions; therefore, ternary doping such as carbon, sulfur, and nitrogen can combine the advantages of the three, improve ball milling efficiency, further improve the persistence of ZVI activity, and more efficiently regulate the release of ferrous ions. At present, there is a lack of research on the effect of nitrogen, carbon and sulfur doped zero-valent iron (NCS-ZVI) on improving saline-alkali land, which deserves further study. Summary of the invention

[0004] The present invention aims to provide a method for preparing NCS-ZVI by mechanical ball milling, and to explore its improvement effect on saline-alkali soil and its influence on corn growth through pot experiments and salt washing experiments. The leaching effect of the material on the total salt ions in the soil and its migration and transformation characteristics are analyzed through soil column leaching experiments, and an attempt is made to construct a series of repair and improvement technologies that are compatible with the NCS-ZVI modifier.

[0005] In order to solve the above technical problems, the technical solution of the present invention is: A method for preparing multinary doped zero-valent iron comprises the following steps: 200 g of agate ball milling beads and nitrogen-modified biochar, elemental sulfur powder and micron-sized iron powder were placed in an agate ball milling jar in a mass ratio of 2:1:7 (all the above operations were carried out in an anaerobic operation box), mixed evenly and placed in a ball mill for ball milling. Nitrogen was used as a protective gas during the ball milling process. The ball milling speed was 300 r / min and the ball milling time was 4 h. After the ball milling, the obtained NCS-ZVI material was separated and stored in a nitrogen atmosphere. In order to compare the performance differences between doped and undoped zero-valent iron, the undoped original micron-sized iron powder and the single sulfided iron powder were ball milled under the same conditions to obtain ball-milled micron-sized zero-valent iron (M-ZVI) and sulfided zero-valent iron (S-ZVI).

[0006] Another object of the present invention is to provide a multinary doped zero-valent iron prepared by the preparation method of the above-mentioned nitrogen-carbon-sulfur ternary doped zero-valent iron.

[0007] Another object of the present invention is to provide a method for screening the application scheme of nitrogen-carbon-sulfur ternary doped zero-valent iron, comprising the following steps: Soil + water + nitrogen-carbon-sulfur ternary doped zero-valent iron was placed in a PP tube to prepare a soil colloidal solution, which was placed in a shaking incubator and reacted for 0, 1-30 days.

[0008] Preferably, as a preferred embodiment, the shaking table speed in the application is 180 rpm.

[0009] Compared with the prior art, the present invention has the following beneficial effects: (1) The surface of the nitrogen-carbon-sulfur ternary doped material NCS-ZVI of the present invention can form adsorption sites of iron hydroxide, sulfide, and nitrogen doping, which can adsorb and fix salt ions such as soil sodium, and continuously release Fe into the soil. 2+ On the one hand, it can form new minerals to fix salts, and on the other hand, it can replace sodium ions from soil colloids.

[0010] (2) The sulfide released by NCS-ZVI can reduce the pH of saline-alkali soil after a series of chemical reactions. In addition, the released iron and ferrous ions can significantly increase the content of soluble salt in the soil through replacement reactions with soil colloids, thereby promoting the formation of large aggregates.

[0011] (3) NCS-ZVI can significantly increase the Na + , K + , Ca 2+ Mg 2+ and SO4 2-The soluble salt ion content of the soil increased. The leaching experiment showed that compared with the S-ZVI, M-ZVI and ferrous sulfate (FS) treatment groups, the leaching efficiency of NCS-ZVI for the main salt ions was significantly increased. It is worth noting that with the increase in the amount of NCS-ZVI added, the remaining Na + , K + , Ca 2+ Mg 2+ and SO4 2- Both gradually decrease, but K + , Ca 2+ and Mg 2+ The residual amount is relatively higher, indicating that NCS-ZVI can selectively retain a part of K while promoting salt ion elution. + , Ca 2+ and Mg 2+ Plasma to maintain soil fertility. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Shown is a schematic diagram of the salt washing experiment operation; Figure 2 The effect of zero-valent iron sulfide on the soluble salt ion Na before and after soil salt washing is shown. + (a), K + (b) Ca 2+ (c) Mg 2+ (d) Cl - (e) SO4 2- (f) and HCO3 - (g) the impact; Figure 3 The effect of zero-valent iron sulfide on soil Fe 2+ (a) and the effect of free total iron (b); Figure 4 The soluble salt ions Na in the soil column eluate are shown + (a), K + (b) Ca 2+ (c) Mg 2+ (d) Cl - (e) SO4 2- (f) and HCO3 - (g) Changes with PV. DETAILED DESCRIPTION

[0013] The content of the present invention can be more easily understood by selecting the following detailed description of the preferred implementation method of the present invention and the embodiments included. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those of ordinary skill in the art to which the present invention belongs. When there is a contradiction, the definition in this specification shall prevail. As used herein, the term "prepared by..." is synonymous with "comprising". The terms "comprising", "including", "having", "containing" or any other variation thereof used herein are intended to cover non-exclusive inclusions. For example, the composition, step, method, product or device comprising the listed elements need not be limited to those elements, but may include other elements that are not clearly listed or elements inherent to such composition, step, method, product or device.

[0014] In addition, the indefinite articles "a" and "an" before the elements or components of the present invention have no restrictions on the quantity requirements (i.e. the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the elements or components in the singular form also include the plural form, unless the number is obviously intended to be in the singular form.

[0015] 1. Embodiment 1 A method for preparing a nitrogen-carbon-sulfur ternary doped zero-valent iron material comprises the following steps: 200 g of agate ball milling beads and nitrogen-modified biochar, elemental sulfur powder and micron-sized iron powder were placed in an agate ball milling jar in a mass ratio of 2:1:7 (all the above operations were carried out in an anaerobic operation box), mixed evenly and placed in a ball mill for ball milling. Nitrogen was used as a protective gas during the ball milling process. The ball milling speed was 300 r / min and the ball milling time was 4 h. After the ball milling, the obtained NCS-ZVI material was separated and stored in a nitrogen atmosphere. In order to compare the performance differences between doped and undoped zero-valent iron, the undoped original micron-sized iron powder and the single sulfided iron powder were ball milled under the same conditions to obtain ball-milled micron-sized zero-valent iron (M-ZVI) and sulfided zero-valent iron (S-ZVI).

[0016] 2. Colloid Experiment Preparation of colloid: Select the surface soil of Tianjin Binhai saline-alkali land, air-dry and grind it, then pass it through a 60-mesh soil nylon sieve. Add 50g soil and 1L water to a beaker, ultrasonically disperse for 25 minutes, and let it stand overnight. After passing the suspension through a 300-mesh sieve, place it in a 3L beaker, add water to 3L and let it stand for 1.5 hours, remove the 0-5cm liquid on the surface (particle size less than 2μm), and repeat several times until the supernatant is clear. The taken suspension is evaporated to 1 / 5 of the water in an 80℃ water bath, and then placed in a 60℃ oven for drying.

[0017] Reaction process: 2g soil colloid + 30ml water + 0.02g amendment (ferrous sulfate, desulfurized gypsum, nitrogen-carbon-sulfur ternary doped zero-valent iron) were placed in a 50ml PP tube and placed in a shaker at 180rpm for 0, 1, 3, 5, 10, 20, and 30 days. At the same time, a PP tube without amendment was used as a blank control, and each treatment was repeated 3 times. After the corresponding number of days, centrifuge at 4000 rpm for 10 min, and the supernatant was taken to determine K + 、Na + , Ca 2+ Mg 2+ concentration.

[0018] 3. Salt washing experiment The salt washing experiment was set up to simulate field irrigation measures. 150 ml of distilled water was taken to leach the potted plants from top to bottom, and a plastic jar (9 cm high, 10 cm in diameter) was placed outside the pot to receive the water. The potted plants were taken out after 5 hours. The relevant indicators were then set. The operation diagram is shown in the figure below. Figure 1 shown.

[0019] Soil Fe 2+ Aluminum sulfate leaching solution is used for extraction, and free iron oxide is extracted by DCB (sodium dithionite-sodium citrate-sodium bicarbonate) method. After the above leaching solution is colored by dropping o-phenanthroline solution, colorimetry is performed at a wavelength of 510nm using an ultraviolet spectrophotometer.

[0020] 4. Soil column experiment The experimental treatment is as follows: (1) 150 g saline-alkali soil (CK) (2) 150 g saline-alkali soil + ferrous sulfate FS (3) 150 g saline-alkali soil + desulfurized gypsum SG (4) 150 g saline-alkali soil + ball-milled zero-valent iron M-ZVI (6) 150 g saline-alkali soil + sulfide zero-valent iron S-ZVI (7) 150 g saline-alkali soil + nitrogen, carbon and sulfur ternary doped zero-valent iron NCS-ZVI Before the experiment, the mixed dry and wet aged soil was air-dried and passed through a 2 mm sieve before filling the soil column. The soil column was filled with 2-3 cm of quartz sand and glass fiber. The experiment could be started after the soil column was filled. After the experiment started, distilled water was passed into the soil column using a medium-pressure constant flow pump to saturate it. During the experiment, water was collected at the outlet at regular intervals to measure relevant indicators. Each soil column was passed through 27 pore volumes (PV). Inductively coupled plasma spectrometer (ICP-OES) was used to determine the Ca in the leaching solution. 2+ and Mg 2+ , Na + and K+ Determined by flame photometry. Determined by ion chromatograph (ICS-600) 2- , Cl - and HCO3 - concentration.

[0021] Determination of pore volume (PV): Weigh the air-dried soil and the soil column filled with water after the experiment, and the difference between the two divided by the density of water is PV.

[0022] The effects of different materials on soil pH are shown in Table 1. Compared with the CK, M-ZVI and S-ZVI control groups, the same amount of NCS-ZVI can significantly reduce the soil pH (p<0.05), indicating that the addition of NCS-ZVI (L1 and L2 high and low doses) can effectively reduce the pH of saline-alkali land. The soil pH after L1 and L2 treatments was 0.41% and 0.47% lower than that of the CK treatment group, respectively. At the same time, the table shows that ball-milled zero-valent iron (M-ZVI) can significantly increase soil pH, which may be because ball-milled zero-valent iron is oxidized to Fe in the soil. 2+ and Fe 3+ OH is released in the process - Since most of the surface of NCS-ZVI is FeS, S2 2- and S n 2- , where S2 2- and S n 2- It can continuously release hydrogen ions into the soil. FeS is converted into iron oxides and hydroxides through hydrolysis and oxidation, and H + , resulting in a decrease in soil pH. Therefore, the soil pH in the NCS-ZVI treatment group was significantly lower than that in the CK, M-ZVI and S-ZVI treatment groups.

[0023] Table 1 Soil pH and EC values ​​after adding different materials Table 2 Changes in total soluble salts before and after soil desalination with different materials Table 1, Table 2, Figure 2 Shows the effects of different amendments on soil salinity, including EC, Na + , Ca 2+ Mg 2+ , K + 、SO4 2- , Cl - 、HCO3 - and CO3 2-Etc. EC is an important indicator reflecting the total amount of soluble salt ions in the soil. Both the control and target amendments significantly increased soil EC, and the two doses (L1 and L2) of the target amendment NCS-ZVI increased EC more significantly. On the one hand, it is related to the soluble ions dissolved by the amendments in the soil, such as FS and SG, which are very easily soluble in water; on the other hand, the release of cations by the amendments in the soil will also replace the sodium ions in the soil colloids, resulting in an increase in soil EC.

[0024] The effects of the amendments on the total soluble salt content of the soil before and after salt washing are shown in Table 2. 2+ Mg 2+ Cation-rich amendments such as + The replacement increases the soil salt content. It can be seen from the table that the order of the degree of soil salinity increased by the modifiers is SG>FS>S-ZVI>L2>L1>CK>M-ZVI. With the increase in the amount of NCS-ZVI added, the total soil salt content increased significantly. Compared with before salt washing, the soil salinity of the CK, FS, SG, M-ZVI, S-ZVI, L1, and L2 treatment groups decreased by 53.3%, 55.4%, 56.2%, 43.8%, 51.8%, 57.6%, and 63.4%, respectively, after salt washing. It can be seen that NCS-ZVI can significantly improve the leaching efficiency of soil salt. This should be because NCS-ZVI promotes the formation of large soil aggregates, thereby improving the soil structure.

[0025] Depend on Figure 2 It can be seen that Na + It is the main soluble cation in soil, followed by Ca 2+ The anion is mainly SO4 2- and Cl - In the form of HCO3 - The content is low and basically does not contain CO3 2- The results show that the main compounds of salinization in the area are NaCl and Na2SO4. The figure also shows the effect of the amendments on the characteristics of water-soluble salt ions in the soil before and after salt washing. The addition of FS, SG, M-ZVI, S-ZVI, L1 and L2 before salt washing has a significant effect on the characteristics of water-soluble salt ions in the soil. + The content of Na in soil increased significantly compared with CK, increasing by 9%, 25%, 3%, 29%, 48% and 76.2% respectively. + The content of the improver showed an increasing trend. 2+ Mg 2+ , K + The influence of Na + The soil Na in the treatment of NCS-ZVI after salt washing was similar.+ The content was significantly reduced compared with the control treatment. + The content showed a trend of gradual decrease, among which the content of the treatment group with the largest addition amount L2 was the lowest, decreasing by 33.3%. It can be seen that with the increase of the amount of amendment added, the Na content in the soil before and after salt washing + This may be because NCS-ZVI improves the soil structure of saline-alkali land, making the soil Na + Different from before salt washing, the improver treatment group after salt washing had no significant effect on the other three cations Ca 2+ Mg 2+ , K + The influence of Na + With the increase of NCS-ZVI addition, the Ca 2+ Mg 2+ , K + The content of NCS-ZVI was reduced to a relatively low degree and was partially retained in the soil. This shows that the addition of NCS-ZVI can not only effectively increase the Na + The leaching effect can also retain some mineral ions that are beneficial to soil crops (such as Ca 2+ Mg 2+ , K + ), to reduce soil fertility loss.

[0026] For soil SO4 2- For example, the sulfate formed on the surface of the material leads to an increase in the sulfate in the soil, resulting in a higher content after salt washing than in CK. In addition, it can be seen from the figure that before and after salt washing, the soil SO4 2- The contents of SO4 in the soil were significantly higher than those in CK, which indicated that both treatments would increase the soil burden. 2- There is a risk of toxicity to crops. Soil HCO3 - Very low content, CO3 2- The content is 0. This is because the content of these two ions is greatly affected by the soil pH. + It can combine with the two to become CO2 and H2O and reduce the content of the two in the soil, so its content is positively correlated with the soil pH value.

[0027] In summary, soil improved by nitrogen-carbon-sulfur ternary doped zero-valent iron is more suitable for leaching, which can reduce the free activity of soil colloidal sodium and alleviate the risk of secondary salinization of the soil.

[0028] Depend on Figure 3 a It can be seen that NCS-ZVI can significantly increase the Fe content in the improved soil 2+This phenomenon may be due to the FeS formed on the surface of the material, which improves the electronic conductivity of the material surface, thereby continuously releasing iron ions into the soil. Figure 3 b It can be seen that the average free iron content of the soil after adding materials is in the order of L2>L1>S-ZVI>M-ZVI>FS>SG>CK. The free iron content of the soil after L2 improvement is 8 mg / g, which is almost doubled compared with CK. This may be because the Fe released by zero-valent iron sulfide 2+ After oxidation and crystallization, it is transformed into iron (hydroxide) such as goethite or hematite, forming free iron oxide (Fe d ). Therefore, the content of free iron in the soil can be significantly increased after the zero-valent iron sulfide material improves the soil. Some studies have pointed out that the content of free iron oxide in the soil is negatively correlated with pH, ​​which may be the reason why the zero-valent iron sulfide material can significantly reduce the pH of the soil. The changes in the content of free iron in the soil and aggregates are also closely related, because Fe d It can act as a bridge in soil particles and form a complex of iron and soil microparticles through electrostatic attraction and adsorption.

[0029] The change of the salinity of the eluent flowing out of the soil column with the pore volume in the soil column experiment is as follows: Figure 3 As shown, from Figure 4 It can be seen that the soil column of the treatment group with zero-valent iron sulfide (NCS-ZVI) has a Na + The content has reached the lowest point, while the ball-milled zero-valent iron and FS treatment groups can only be eluted to the lowest point at about 13PV. At the same time, the Na content of the eluent of the NCS-ZVI treatment group at 1PV + The content was significantly higher than that of other treatment groups, nearly 5 times higher than that of CK, indicating that NCS-ZVI can not only efficiently replace Na + , and can also promote leaching. This may be because NCS-ZVI can improve soil structure, increase the proportion of soil macroaggregates, and improve soil leaching efficiency. Figure 4 Compared with the SG and FS control groups, the Ca content in the eluent of the NCS-ZVI group was 2+ Mg 2+ , K + The content of ions of nutrients is relatively low and reaches the lowest content at a smaller PV. This result is similar to the results of the salt washing experiment, confirming that NCS-ZVI can preserve more Ca 2+ Mg 2+ , K + , while leaching out more Na + , while improving saline-alkali soil, it is more conducive to the retention of soil nutrients.

[0030] Depend on Figure 4It can be seen that NCS-ZVI bm SO4 2- The elution of SG and FS treatment groups reached the lowest point at about 6 PV, while the FS treatment group reached the lowest point at about 12 PV. 2 The content was significantly higher than that of other groups, proving that these two control treatments can increase the soil salt burden and are not conducive to leaching. - Very low content, CO3 2- The content is 0 and is greatly affected by soil pH.

[0031] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A method for preparing a multinary doped zero-valent iron material, characterized in that: The following steps are involved: Nitrogen-doped biochar was prepared by impregnation-pyrolysis. 200 g of agate ball milling beads and nitrogen-modified biochar, elemental sulfur powder and micron-sized iron powder were placed in an agate ball mill in a mass ratio of 2:1:

7. The above operations were all carried out in an anaerobic operation box. After mixing evenly, the mixture was placed in a ball mill for ball milling. Nitrogen was used as a protective gas during the ball milling process. After the ball milling was completed, the obtained NCS-ZVI material was separated and stored in a nitrogen atmosphere.

2. The method for preparing a multinary doped zero-valent iron material according to claim 1, characterized in that: The preparation method of the nitrogen-modified biochar is: The Enteromorpha was dried and ground into powder, and then placed in a pyrolysis furnace. Under a nitrogen atmosphere, the temperature was increased at a rate of 1-10°C, and the pyrolysis was performed at a constant temperature for 0.5-5h. After natural cooling, the black solid was taken out to obtain nitrogen-doped biochar.

3. The method for preparing a multinary doped zero-valent iron material according to claim 1, characterized in that: The ball milling speed is 300 r / min, and the ball milling time is 4 h.

4. The nitrogen-carbon-sulfur multinary doped zero-valent iron material prepared by the preparation method of the multinary doped zero-valent iron material according to claim 1 or 2.

5. The multinary doped zero-valent iron material according to claim 4 can promote the leaching of soluble salts in saline-alkali soil and the reduction of soil alkalinity.

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