A soil amendment of modified sepiolite, its preparation method and use

Abstract

The application belongs to the technical field of inorganic material preparation, and provides a preparation method of modified sepiolite, which comprises the following steps: dispersing Zn(NO3)2.6H2O and AgNO3 in water to obtain an Ag-ZnO suspension; dispersing sepiolite (SEP), FeNO3.9H2O and FeSO4.7H2O in water, uniformly adjusting pH, and obtaining Fe3O4-SEP; mixing the Ag-ZnO suspension, a hexamethylenetetramine solution and the Fe3O4-SEP suspension to perform hydrothermal reaction, and obtaining a precursor; and obtaining the modified sepiolite Ag-Zn-Fe / SEP after calcination. The pore diameter of the nano material prepared by the application is reduced, the BET specific surface area is increased, and a path is opened for realizing efficient repair of heavy metal pollution.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of inorganic material preparation, and relates to a preparation of a modified sepiolite material. BACKGROUND

[0002] With the development of industry and agriculture, soil heavy metal pollution is increasing. Cadmium (Cd) is one of the most harmful metal pollutants in soil, which poses a potential threat to humans through the food chain due to its high water solubility, relative mobility, bioaccumulation and non-degradability. Therefore, the remediation of cadmium-contaminated soil becomes extremely important. Compared with organic pollution, the core problem of heavy metal pollution is its non-degradation. Effective remediation techniques include immobilizing the pollutants (such as chemical stabilization), separating (such as washing and flotation) or extracting (such as phytoremediation). Soil washing and flotation methods are usually associated with high cost and soil structure degradation, while off-site remediation limits its widespread use on contaminated soil. Phytoremediation technology is limited by its high time-consuming process, slow growth rate and biomass production. As an alternative technology, in-situ remediation by adsorbing or precipitating heavy metals in soil to reduce the migration of heavy metals to water, plants and other environmental media, and inhibit the migration of heavy metals in situ, has become a development trend. This process is efficient, cost-effective, easy to operate and less destructive.

[0003] The total content of heavy metals in soil is not the key factor of its mobility and ecological toxicity, which largely depends on the binding state or specific form of heavy metals. Studies have found that the metal concentration in plants is closely related to the metal concentration of the exchangeable component. Therefore, the key to remediate heavy metal contaminated soil is to reduce the mobility and bioavailability of metals. Common amendments include biochar, alkaline compounds, phosphorus-containing materials, clay minerals and organic matter, etc. However, in some cases, the above amendments may have adverse effects on the immobilization of heavy metals. For example, some organic amendments have been found to increase the solubility of heavy metals in soil, providing soluble organic compounds. With the decomposition of organic matter, the remediation capacity may decrease over time. In addition, due to the high pH value of soil, the further use of high alkalinity amendments such as lime, fly ash, clay minerals, etc. is limited. In summary, an ideal amendment should be safe to use and easy to produce, compatible with plants and non-toxic, easy to handle and apply, and reduce the bioavailability of metals.

[0004] Sepiolite (SEP) is a fibrous, hydrated magnesium-aluminum silicate clay mineral with an ideal chemical formula of Si 12 O 30Mg8(OH)4(OH2)4·nH2O, wherein n is usually 8, which decreases with different drying temperature and vacuum. It extends along the fiber direction, and its structure is formed by channels and blocks. At the edge of the structure, the channels are filled with water coordinated with Mg. These blocks are composed of a central octahedral sheet containing magnesium and two tetrahedral silicon sheets. The modification degree of sepiolite acid modification is affected by the concentration of acid, modification time, etc. The degree of modification can be represented by the demetallization rate of sepiolite. The higher the concentration of acid, the stronger the demetallization ability of sepiolite, but the demetallization rate gradually decreases with the increase of acid concentration. With the increase of modification time, the demetallization rate increases. When the modification treatment is carried out for a certain time, the demetallization rate no longer increases obviously. It is possible that H + diffuses gradually to the deep of the channel, and H + The concentration gradually decreases, and the magnesium content of sepiolite gradually decreases. Therefore, the optimal acid concentration and modification time are determined by experiments. The ion exchange modification of sepiolite is to replace the iron ions in the sepiolite framework with metal ions, so that the sepiolite produces moderate strength acid or alkali, and does not change its structure. The structures of sepiolite mines in different regions are similar, but their compositions are different. The content of aluminum in sepiolite will greatly affect its ion exchange performance. At present, more researches are carried out on the pre-activation treatment of sepiolite, and the adsorption performance and catalytic performance are investigated. The activation treatment is to remove the water molecules in the channels by heating or acid treatment within a certain temperature range, so as to form a large number of cavities with large internal surface area, which can adsorb and store macromolecules, and at the same time, the cross section of the internal channel of the crystal is increased, so that the adsorbed molecules are more easily entered, and the adsorption and ion exchange capacity is improved. In addition, magnetization of magnetite is also a common modification technology for clay minerals, which can improve the immobilization capacity. SUMMARY

[0005] In view of the problems existing in the current soil modifier, the application provides a preparation method of modified sepiolite, the specific surface area of which can be adjusted, and the obtained material has high porosity and large specific surface area.

[0006] Another object of the application is to provide an application of the above-mentioned modified sepiolite in adsorbing heavy metals in soil.

[0007] To achieve the above object, the application adopts the following technical scheme.

[0008] A preparation method of modified sepiolite, comprising the following steps:

[0009] (1) dispersing Zn(NO3)2·6H2O and AgNO3 in water to obtain an Ag-ZnO suspension;

[0010] (2) dispersing sepiolite (SEP), FeNO3·9H2O and FeSO4·7H2O uniformly in water, adjusting the pH to obtain a composite solution, and washing and drying to obtain Fe3O4-SEP;

[0011] (3) mixing the Ag-ZnO suspension and the hexamethylenetetramine (HMTA) solution, and then adding the Fe3O4-SEP suspension to carry out the hydrothermal reaction, and obtaining the precursor after washing and drying the product;

[0012] (4) calcining the precursor to obtain the modified sepiolite Ag-Zn-Fe / SEP.

[0013] The sepiolite has not been pickled, and impurities exist in the sepiolite, so that the nanomaterial adsorption sites for adsorbing heavy metal ions are occupied, and the adsorption capacity of the sepiolite is reduced. Therefore, the sepiolite is the sepiolite that has been pickled and heated at 100-300 DEG C. The impurities in the natural sepiolite can be removed by pickling, and the pore diameter is correspondingly reduced due to the expansion of the internal pores of the heated sepiolite, so that the specific surface area is increased, and the adsorption capacity is enhanced. The sepiolite heated at 100-300 DEG C can gradually remove the zeolite water and increase the adsorption capacity without damaging the internal crystal framework.

[0014] In the above method, the mass ratio of deionized water to Ag-ZnO in the Ag-ZnO suspension is preferably 150:1-300:1, and more preferably 200:1.

[0015] In the above method, the mass ratio of Ag-ZnO to Fe3O4 in the Fe3O4-SEP is (0-0.03):1, and the more preferred ratio is 0.01:1, and the mass of Ag-ZnO in the above ratio is not 0.

[0016] In the above method, the Ag-ZnO suspension can be added to the Fe3O4-SEP composite solution, or the Fe3O4-SEP solution can be added to the Ag-ZnO suspension, and the Ag-ZnO suspension is preferably added to the Fe3O4-SEP composite solution.

[0017] The shear force can be provided by any stirring and shearing equipment, and the ultrasonic crushing oscillation is provided by an ultrasonic crusher. The preferred shearing stirring speed is controlled at 2000-10000 revolutions / min, and the stirring time is 15-60 minutes.

[0018] In the above method, the hydrothermal reaction temperature is 90 DEG C, and the reaction time is 30-45 minutes. The calcination temperature is 100-300 DEG C, and the calcination time is 3 hours.

[0019] A modified sepiolite obtained by the above preparation method.

[0020] The application of the above modified sepiolite in adsorbing heavy metal pollutants.

[0021] The application has the following advantages:

[0022] The application combines Ag-ZnO, Fe3O4 and sepiolite together by solution co-precipitation method and hydrothermal synthesis method, and obtains a nano adsorption material with adjustable specific surface area, high porosity and large specific surface area by controlling the amount of Ag-ZnO added. In the presence of Ag-ZnO particles, the pore size of the blended nanoparticles is reduced, and the BET specific surface area is increased, so that the heavy metal adsorption performance of the Ag-Zn-Fe / SEP nano adsorption material is higher than that of the Fe3O4-SEP nanoparticle. The Ag-Zn-Fe / SEP nano adsorption material of the application is an ideal choice for adsorbing heavy metals, and can be used for efficient repair of heavy metal contaminated environment. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a scanning electron microscope image of Fe3O4-SEP composite material (left) and Ag-Zn-Fe / SEP nano adsorption material (right);

[0024] Figure 2 is the adsorption performance parameters of Fe3O4-SEP composite material and Ag-Zn-Fe / SEP nano adsorption material on heavy metal cadmium (Cd) in different adsorption time periods;

[0025] Figure 3 is the equilibrium adsorption capacity q of Fe3O4-SEP composite material and Ag-Zn-Fe / SEP nano adsorption material on heavy metal cadmium (Cd) e ;

[0026] Figure 4 is the adsorption rate R (%) of Fe3O4-SEP composite material and Ag-Zn-Fe / SEP nano adsorption material on heavy metal cadmium (Cd) adsorption. DETAILED DESCRIPTION

[0027] The application will be further described below in combination with examples and drawings, but the application is not limited by the following examples.

[0028] Example 1 Preparation of Ag-Zn-Fe / SEP nano material

[0029] (1) Wash the natural sepiolite with ultrapure water and immerse it in an acid solution (pH 2.0) to remove impurities; then heat at 300℃ for 3 hours, and gradually cool to room temperature;

[0030] (2) Weigh 1 part by weight of sepiolite and immerse it in 100 mL of ultrapure water, and ultrasonically disperse for 10 minutes;

[0031] Then add 0.8 parts by weight of FeNO3·9H2O and 0.28 parts by weight of FeSO4·7H2O, and stir the solution under the condition of 60℃ water bath heating for 15 minutes;

[0032] Then 1M NaOH was added dropwise until the solution pH reached 9, and heating and stirring was continued for 30 minutes;

[0033] After cooling to room temperature, the product was centrifuged and repeatedly washed with ultrapure water until the filtrate was neutral, and dried at 80°C overnight to obtain the Fe3O4-SEP composite material;

[0034] 0.1 parts by weight of the Fe3O4-SEP composite material was weighed and dispersed in 10 parts of water to obtain a Fe3O4-SEP suspension by stirring;

[0035] (3) 0.835 parts by weight of Zn(NO3)2·6H2O was dispersed in 40 parts by weight of water to dissolve;

[0036] Then, 10 parts by weight of a 1% hexamethylene tetramine (HMTA) solution and 0.8 parts by weight of silver nitrate were added and stirred for 1 hour;

[0037] Then the Fe3O4-SEP suspension in step (2) was added, and stirring was continued until a uniform solution was obtained;

[0038] The resulting mixture was transferred to an autoclave and heated at 90°C for 5 hours;

[0039] The product was washed with water and ethanol 3 times and dried at 60°C overnight to obtain the precursor;

[0040] (4) The precursor was calcined at 300°C for 3h to obtain the Ag-Zn-Fe / SEP composite nanomaterial Ag-Zn-Fe / SEP 1% containing 1wt% Ag-Zn-Fe.

[0041] The network structure inside the sepiolite did not change before and after modification, but the surface of the internal fibers was smooth and filamentous before modification, but after modification Ag-ZnO adhered to the surface of the internal fibers, making the surface of the internal fibers rough.

[0042] Example 2 Preparation of Ag-Zn-Fe / SEP nanomaterial

[0043] (1) The natural sepiolite was washed with ultrapure water and immersed in an acid solution (pH 2.0) to remove impurities; then heated at 300°C for 3 hours and gradually cooled to room temperature;

[0044] (2) 1 parts by weight of sepiolite was immersed in 100 mL of ultrapure water and ultrasonically dispersed for 10 minutes;

[0045] Then 0.8 parts by weight of FeNO3·9H2O and 0.28 parts by weight of FeSO4·7H2O were added, and the solution was stirred for 15 minutes under the condition of a 60°C water bath;

[0046] Then 1 M NaOH was added dropwise until the solution pH reached 9, and heating and stirring was continued for 30 minutes;

[0047] After cooling to room temperature, the product was centrifuged and repeatedly washed with ultrapure water until the filtrate was neutral, and dried at 80°C overnight to obtain the Fe3O4-SEP composite material;

[0048] 0.1 parts by weight of the Fe3O4-SEP composite material was weighed and dispersed in 10 parts of water to obtain a Fe3O4-SEP suspension;

[0049] (3) 1.67 parts by weight of Zn(NO3)2·6H2O was dispersed in 40 parts by weight of water to dissolve;

[0050] Then, 10 parts by weight of a 1% hexamethylene tetramine (HMTA) solution and 1.6 parts by weight of silver nitrate were added and stirred for 1 hour;

[0051] Then the Fe3O4-SEP suspension in step (2) was added, and stirring was continued until a uniform solution was obtained;

[0052] The resulting mixture was transferred to an autoclave and heated at 90°C for 5 hours;

[0053] The product was washed with water and ethanol 3 times and dried at 60°C overnight to obtain the precursor;

[0054] (4) The precursor was calcined at 300°C for 3h to obtain the Ag-Zn-Fe / SEP composite nanomaterial Ag-Zn-Fe / SEP 2% containing 2wt% Ag-Zn-Fe.

[0055] Example 3 Preparation of Ag-Zn-Fe / SEP nanomaterial

[0056] (1) The natural sepiolite was washed with ultrapure water and immersed in an acid solution (pH 2.0) to remove impurities; then heated at 300°C for 3 hours and gradually cooled to room temperature;

[0057] (2) 1 part by weight of sepiolite was immersed in 100 mL of ultrapure water and ultrasonically dispersed for 10 minutes;

[0058] Then 0.8 parts by weight of FeNO3·9H2O and 0.28 parts by weight of FeSO4·7H2O were added, and the solution was stirred at 60°C water bath heating condition for 15 minutes;

[0059] Then 1 M NaOH was added dropwise until the solution pH reached 9, and heating and stirring was continued for 30 minutes;

[0060] After cooling to room temperature, the product was centrifuged and repeatedly washed with ultrapure water until the filtrate was neutral, and dried at 80°C overnight to obtain the Fe3O4-SEP composite material;

[0061] Weigh 0.1 parts by weight of Fe3O4-SEP composite material into 10 parts of water and stir to disperse to obtain a Fe3O4-SEP suspension;

[0062] (3) Dissolve 3.37 parts by weight of Zn(NO3)2·6H2O in 40 parts by weight of water;

[0063] Then, add 10 parts by weight of 1% hexamethylene tetramine (HMTA) solution and 3.37 parts by weight of silver nitrate and stir for 1 hour;

[0064] Then add the Fe3O4-SEP suspension in step (2) and continue stirring until a uniform solution is obtained;

[0065] Transfer the resulting mixture to an autoclave and heat at 90°C for 5 hours;

[0066] Wash the product with water and ethanol 3 times and dry at 60°C overnight to obtain the precursor;

[0067] (4) Calcine the precursor at 300°C for 3h to obtain Ag-Zn-Fe / SEP composite nanomaterial Ag-Zn-Fe / SEP 3% containing 3wt% Ag-Zn-Fe.

[0068] Preparation of Fe3O4-SEP nanomaterial

[0069] (1) Wash the natural sepiolite with ultrapure water and immerse it in an acid solution (pH 2.0) to remove impurities; then heat at 300°C for 3 hours and gradually cool to room temperature;

[0070] (2) Weigh 1 part by weight of sepiolite into 100 mL of ultrapure water and ultrasonically disperse for 10 minutes;

[0071] Then add 0.8 parts by weight of FeNO3·9H2O and 0.28 parts by weight of FeSO4·7H2O and stir the solution under the condition of a 60°C water bath for 15 minutes;

[0072] Then add 1M NaOH dropwise until the solution pH reaches 9 and continue heating and stirring for 30 minutes;

[0073] After cooling to room temperature, centrifuge the product and rinse repeatedly with ultrapure water until the filtrate is neutral and dry at 80°C overnight to obtain the Fe3O4-SEP composite material.

[0074] Application Example 1 Adsorption of nanomaterials on heavy metal cadmium (Cd)

[0075] Materials prepared in Examples 1-3 and Fe3O4-SEP prepared in the comparative example were subjected to heavy metal adsorption tests:

[0076] Weigh 20 mg of nano-adsorbent material into 5 mL of deionized water, and ultrasonic until uniform suspension.

[0077] About 500 g of soil was obtained from certified organic farms, washed repeatedly with 10 times the volume of deionized water, and then dried in an oven. A cadmium ion solution was prepared with cadmium nitrate; it was added to the soil until the specified concentration (300 mg / L) was reached, homogenized and air dried.

[0078] 20 g of the above soil was added to each nano-adsorbent material solution, then placed in a shaker at 20°C for 120 min; after centrifugation at 3000 rpm, the supernatant was aspirated, and the metal concentration was tested using an atomic absorption spectrometer.

[0079] Equilibrium adsorption capacity q of nano-adsorbent material for heavy metal cadmium e And (R%) adsorption rate (R) can be calculated by equations (1) and (2):

[0080]

[0081] Where C0and C e (mg / L) represent the initial and final concentrations of cadmium ions, respectively; in this study, M is the mass of nano-adsorbent material, M = 20 mg; V is the volume of supernatant solution after centrifugation of the diluted soil during the experiment, V = 20 mL.

[0082] Adsorption kinetics analysis of nano-materials as Figure 2 shown: the adsorption rate of Fe3O4-SEP composite material and Ag-Zn-Fe / SEP nano-adsorbent material for heavy metal cadmium (Cd) rapidly increased between 10-60 min, then gradually slowed down from 60-80 min, and finally reached equilibrium after 80 min. The change in adsorption rate is mainly due to the presence of abundant adsorption sites on Fe3O4-SEP composite material and Ag-Zn-Fe / SEP nano-adsorbent material in the early stage, and the high concentration of adsorbed ions in the solution. As the adsorption process proceeds, the adsorption sites decrease, the ion concentration decreases, and the adsorption rate slows down until equilibrium is reached.

[0083] The maximum adsorption capacity of Ag-Zn-Fe / SEP nano-adsorbent material for heavy metal ion cadmium (Cd) is shown in Figure 3 249.89 mg / L.

[0084] As Figure 4As shown, the adsorption efficiency of Fe3O4-SEP composite and Ag-Zn-Fe / SEP nanoadsorbent as adsorbents for heavy metal ions cadmium (Cd) reached more than 70%, among which Ag-Zn-Fe / SEP1% showed higher adsorption performance than other materials, and the adsorption efficiency reached more than 85%.

Claims

1. An application of modified sepiolite in the adsorption of heavy metal cadmium in soil, characterized in that, The preparation method of modified sepiolite includes the following steps: (1) Disperse Zn(NO3)2·6H2O and AgNO3 in water to obtain a mixed solution; (2) After dispersing sepiolite, FeNO3·9H2O and FeSO4·7H2O evenly in water, the pH was adjusted to obtain a composite solution. After washing and drying, Fe3O4-SEP was obtained. (3) Mix the mixture in step (1) with the hexamethylenetetramine solution, then add Fe3O4-SEP suspension for hydrothermal reaction, and wash and dry the product to obtain the precursor. (4) Modified sepiolite Ag-Zn-Fe / SEP was obtained by calcining the precursor; The sepiolite is sepiolite that has been acid-washed and heated to 100℃-300℃; The hydrothermal reaction temperature is 90℃, and the reaction time is 30-45 minutes; the calcination temperature is 100-300℃, and the calcination time is 3 hours. The content of Ag-Zn-Fe in modified sepiolite is 1wt%, 2wt%, or 3wt%.

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