A modified montmorillonite for synergistically repairing heavy metals and organic pollutants in soil, and a preparation method and application thereof

Abstract

The application belongs to the technical field of contaminated soil remediation, and particularly relates to modified montmorillonite for synergistically remediating heavy metals and organic pollutants in soil as well as a preparation method and application thereof. Hexadecyl trimethyl ammonium bromide (CTAB) and dodecyl trimethyl ammonium bromide (DTAB) are used as modifiers to prepare organic modified montmorillonite, and mercury ions (Hg 2+ ) and acetochlor (ACR) are used as representative substances of heavy metals and organic pollutants to study the effects of the two kinds of organic modified montmorillonite on remediation of Hg 2+ and ACR compound contaminated soil. The results show that the two kinds of organic modified montmorillonite have good removal effects on Hg 2+ and ACR in real soil samples, and can simultaneously remove Hg 2+ and ACR in soil. The removal rates of CTAB modified montmorillonite and DTAB modified montmorillonite can both reach more than 90%. The organic modified montmorillonite prepared by using CTAB and DTAB as modifiers can simultaneously remove Hg 2+ and ACR in soil, and can synergistically remediate Hg 2+ and ACR compound contaminated soil.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of contaminated soil remediation, and particularly relates to an organic modified montmorillonite for synergistically remediating heavy metals and organic pollutants in soil as well as a preparation method and application thereof. BACKGROUND

[0002] In recent years, due to the rapid development of global industry, the production and consumption of mercury has increased greatly, resulting in a large amount of mercury being discharged into the natural environment. Therefore, mercury pollution has become a global environmental problem, and soil and water bodies are being subjected to more and more serious mercury pollution, which further endangers human health through the food chain. At present, the problem of mercury pollution has attracted widespread attention worldwide.

[0003] Acetochlor (ACR) is a non-selective herbicide, which has high herbicidal activity, especially for annual grass weeds, and has been widely used in global agricultural production, saving a large amount of manpower and material resources for agricultural production. However, the degradation products of ACR remaining in the soil can endanger human health through the food chain.

[0004] With the large-scale production of mercury and the large-scale use of ACR in agricultural production, mercury and ACR enter the soil at the same time or successively, forming a combined pollution of the soil. Therefore, it is of great significance to develop a remediation agent that can simultaneously remove mercury and ACR from the soil for soil pollution control and remediation and agricultural product safety.

[0005] Montmorillonite, also known as microcrystalline kaolinite or gel kaolinite, is a hydrous layered silicate mineral with a monoclinic crystal structure. Its main component is octahedral montmorillonite particles, which are composed of aluminum oxide octahedra in the middle and silicon oxide tetrahedra on the top and bottom, forming a three-layer sheet structure clay mineral. It contains water and some exchangeable cations between the crystal structure layers, has a high ion exchange capacity, and has a high water absorption and swelling capacity. The interlayer cations are exchangeable and can exchange with heavy metal ions, so montmorillonite has good adsorption of heavy metal ions. In addition, after proper modification of montmorillonite with inorganic or organic substances, a large interlayer space can be obtained, which can reduce the hydrophilicity of the interlayer microenvironment and significantly improve its adsorption capacity for hydrophobic organic compounds. Therefore, modified montmorillonite is expected to adsorb both heavy metal ions and hydrophobic organic compounds.

[0006] For a long time, domestic and foreign researchers have conducted a lot of research on modified montmorillonite, but these studies are more focused on the preparation of modified montmorillonite and the adsorption performance of modified montmorillonite for a single heavy metal ion or organic pollutant. There is little research on the combined pollution of heavy metals and organic pesticides, and there is no report on the simultaneous remediation of soil heavy metals and organic pollutants using modified montmorillonite. SUMMARY

[0007] In view of the above problems in the prior art, the present application selects cetyltrimethylammonium bromide (CTAB) and dodecyltrimethylammonium bromide (DTAB) as modifiers to prepare two kinds of modified montmorillonite capable of synergistically repairing mercury and ACR composite pollution, and the effects of the two kinds of modified montmorillonite on synergistically repairing mercury and ACR composite pollution are studied, which provides a new direction for synergistically repairing heavy metals and organic pollutants in agricultural production.

[0008] The present application achieves the above-mentioned purposes by adopting the following technical solutions:

[0009] A modified montmorillonite for synergistically repairing heavy metals and organic pollutants in soil, wherein the modified montmorillonite is obtained by modifying montmorillonite with a modifier, and the modifier is cetyltrimethylammonium bromide (CTAB) and / or dodecyltrimethylammonium bromide (DTAB).

[0010] The present application also provides a preparation method of the above-mentioned organically modified montmorillonite, and the steps of the preparation method are as follows:

[0011] (1) detecting the cation exchange capacity (CEC) of the montmorillonite;

[0012] (2) preparing the modified montmorillonite

[0013] A certain amount of water (preferably 50 mL of water for 1 g of montmorillonite) is added to the montmorillonite, and the mixture is stirred and dispersed uniformly, then a modifier solution is added, and then the pH of the solution is adjusted to 6-11; then the solution is oscillated at 40-80℃ for 4-8 h, after the reaction is completed, the solution is left to stand, centrifuged (preferably at 3000 r / min for 10 min), and the solid after centrifugation is fully dried (preferably at 60℃ for 30 h) to obtain the organically modified montmorillonite, which is stored in the dark.

[0014] Preferably, the modifier solution in step (2) is a CTAB solution or a DTAB solution.

[0015] Preferably, in step (2), when the modifier solution is a CTAB solution, the pH of the solution is adjusted to 6, the oscillation reaction temperature is 70℃, and the reaction time is 6 h.

[0016] Preferably, in step (2), when the modifier solution is a DTAB solution, the pH of the solution is adjusted to 8, the oscillation reaction temperature is 50℃, and the reaction time is 6 h.

[0017] Preferably, in the step (2), the adding ratio of the modifier is X1, wherein the X1 = the amount of substance of the modifier in the modifier solution / (the CEC of the montmorillonite x the mass of the montmorillonite) = 0.5-2.5; more preferably, when the CTAB solution is added, the X1 = 0.5, and when the DTAB solution is added, the X1 = 1.

[0018] Preferably, the CTAB solution is a 10wt% CTAB ethanol solution, and the DTAB solution is a 10wt% DTAB water solution.

[0019] The application also provides the use of the modified montmorillonite as described above in the remediation of soil contaminated by heavy metals and organic pollutants.

[0020] Preferably, the heavy metal is mercury, and the organic pollutant is acetochlor.

[0021] Preferably, the specific steps of the use are as follows: the modified montmorillonite is used in the soil contaminated by mercury ions and acetochlor for adsorption reaction, the adsorption temperature is 20-25°C, the adsorption time is 15-20 days, the pH of the soil during the adsorption is 7, and the water content of the soil is 70% of the saturated water holding capacity of the soil.

[0022] Preferably, the mass concentration of the modified montmorillonite added to the soil is 1g / kg.

[0023] More preferably, the concentration of the mercury ions in the soil is ≦0.4mg / kg, and the concentration of the acetochlor is ≦15mg / kg.

[0024] Compared with the prior art, the technical scheme of the application has the following advantages and beneficial effects:

[0025] The organic modified montmorillonite prepared by the application has a quite remarkable effect in simultaneously adsorbing heavy metal ions and organic pollutants, and can be directly applied in the remediation of soil contaminated by heavy metal ions and organic pollutants. The existing researches on the modified montmorillonite are mainly about the adsorption of the modified montmorillonite on a single heavy metal ion or organic pollutant, and the research on the heavy metal and organic pesticide composite pollution has not been reported. The montmorillonite is a layered silicate clay mineral with montmorillonite as the main component and containing water, and the interlayer cations thereof are exchangeable and can be exchanged with heavy metal ions, so the montmorillonite has good adsorption on heavy metal ions. After the montmorillonite is modified by organic matter, a huge interlayer space can be obtained, the hydrophilicity of the interlayer microenvironment can be reduced, and the adsorption capacity of the montmorillonite on hydrophobic organic compounds can be significantly improved. In the application, the conditions for simultaneously adsorbing heavy metal ions and organic pollutants by the organic modified montmorillonite are optimized, the organic modified montmorillonite is applied in the remediation of soil contaminated by Hg 2+ and ACR under the optimized conditions, and quite remarkable effects are achieved. When the concentration of Hg 2+The removal rates of CTAB modified montmorillonite and DTAB modified montmorillonite for them can reach more than 90% when the concentration is less than 0.2 mg / kg and the ACR concentration is less than 10 mg / kg, and they also have good adsorption effect on Pb 2+ and Cd 2+ in the soil. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 XRD diffraction pattern of the modified montmorillonite with different amounts of CTAB in Example 1;

[0027] Figure 2 XRD diffraction pattern of the modified montmorillonite with different amounts of DTAB in Example 1;

[0028] Figure 3 XRD diffraction pattern of the modified montmorillonite with different amounts of Saponin in Example 1;

[0029] Figure 4 XRD pattern of the modified montmorillonite with different amounts of TX-7 in Example 1;

[0030] Figure 5 Infrared spectrum of CTAB, CTAB-MMT and MMT in Example 1;

[0031] Figure 6 Infrared spectrum of DTAB, DTAB-MMT and MMT in Example 1.

[0032] Figure 7 XRD pattern of CTAB-MMT prepared at different temperatures in Example 2;

[0033] Figure 8 XRD pattern of DTAB-MMT prepared at different temperatures in Example 2.

[0034] Figure 9 XRD pattern of CTAB-MMT prepared at different pH values in Example 3;

[0035] Figure 10 XRD pattern of DTAB-MMT prepared at different pH values in Example 3;

[0036] Figure 11 Adsorption capacity of MMT, CTAB-MMT and DTAB-MMT for Hg 2+ and ACR in Example 4;

[0037] Figure 12 Effect of adsorption time on the adsorption of Hg 2+ by CTAB-MMT and DTAB-MMT in Example 4;

[0038] Figure 13 Effect of different time on adsorption of ACR by CTAB-MMT and DTAB-MMT in Example 4;

[0039] Figure 14 Effect of pH on adsorption of Hg 2+ by modified montmorillonite in Example 4;

[0040] Figure 15 Effect of pH on adsorption of ACR by modified montmorillonite in Example 4;

[0041] Figures 16-17 Effect of adsorption temperature on adsorption of Hg 2+ and ACR by modified montmorillonite in Example 4, respectively;

[0042] Figure 18 and Figure 19 Effect of concentration of Hg 2+ and ACR on adsorption capacity of modified montmorillonite, respectively. DETAILED DESCRIPTION

[0043] The technical solutions of the present application will be described in detail below in combination with specific embodiments.

[0044] Some of the equipment used in the following examples are as follows: XRD-7000 X-ray powder diffractometer (Japan Shimadzu), Fourier infrared spectrometer (USA Nicolet), Hydra II C full-automatic mercury meter (USA Leman), high-performance liquid chromatograph (China Dalian Yilite Instrument EClassical 3200).

[0045] The main chemical reagents used in the following examples are as follows: cetyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium bromide (DTAB), tea saponin (Saponin), alkylphenol polyoxyethylene (7) ether (TX-7) and mercury standard solution (1000 μg / ml), all of which are analytical pure and purchased from China National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0046] The CTAB solution used in the examples is a 10wt% CTAB ethanol solution, and the DTAB solution is a 10wt% DTAB aqueous solution.

[0047] The montmorillonite (MMT) used in the following examples is montmorillonite KSF purchased from Aldrin, with the item number M109699.

[0048] In the following examples, unless otherwise specified, the solution used for adjusting pH is 0.1 mol / L hydrochloric acid and / or 0.1 mol / L sodium hydroxide solution.

[0049] Example 1 An organic modified montmorillonite for synergistically remediating soil contaminated by mercury ions and acetochlor is prepared by the following method:

[0050] (1) Determination of Cation Exchange Capacity (CEC) of Montmorillonite

[0051] The cation exchange capacity (CEC) of montmorillonite is determined by barium chloride-sulfuric acid exchange method. 0.5 g of montmorillonite is accurately weighed into a centrifuge tube, and the weight of the centrifuge tube after adding the montmorillonite is recorded. Then 20 mL of 0.5 mol / L BaCl2 solution is added, and stirred with a glass rod for 4 min. The supernatant is discarded after centrifugation at 3000 r / min for 5 min. The above-mentioned operations of adding BaCl2 solution, stirring and centrifugation are repeated twice. 20 mL of distilled water is added to the montmorillonite after the last centrifugation, stirred with a glass rod for 1 min, and then centrifuged at 3000 r / min for 5 min. The supernatant is discarded, and the weight of the centrifuge tube together with the montmorillonite is weighed again. 25 mL of 0.1 mol / L sulfuric acid solution is added to the centrifuge tube, stirred thoroughly, and centrifuged after 20 min. 10 mL of the supernatant is taken into a conical flask, and titrated with 0.1 mol / L standard sodium hydroxide solution. At the same time, 10 mL of 0.1 mol / L sulfuric acid solution is taken into another conical flask, and titrated with the standard sodium hydroxide solution. The difference between the two titration results is used to calculate the cation exchange capacity of the montmorillonite. According to this method, the cation exchange capacity of the montmorillonite used in this experiment is 75 cmol / kg.

[0052] (2) Preparation of CTAB and DTAB Organic Montmorillonite

[0053] Accurately weigh 5 g of dry montmorillonite, add 250 mL of distilled water to it, and stir until uniform. Add CTAB or DTAB solution equivalent to 0.5-2.5 times the CEC of the montmorillonite (in the present application, the multiple of the CEC of the montmorillonite = the amount of substance (mol) of CTAB or DTAB in the CTAB or DTAB solution / (the CEC of the montmorillonite x the mass of the montmorillonite) (mol)), adjust to the desired pH (pH 6 for CTAB-modified organic montmorillonite, and pH 8 for DTAB-modified organic montmorillonite), place the beaker in a water bath shaker, and shake at a certain temperature (70°C for CTAB-modified organic montmorillonite, and 50°C for DTAB-modified organic montmorillonite) for 6 h. Take it out and let it stand for 30 min, centrifuge at 3000 r / min for 10 min, dry the solid after centrifugation in a 60°C drying oven for 30 h, grind the dried solid and pass it through a 200-mesh sieve to obtain organic-modified montmorillonite, which is placed in a brown jar for later use. The montmorillonite modified by CTAB and DTAB is denoted as CTAB-MMT and DTAB-MMT, respectively, and different organic-modified montmorillonites are denoted as C x -MMT, D x -MMT, x = the amount of substance (mol) of CTAB or DTAB in the CTAB or DTAB solution / (the CEC of the montmorillonite x the mass of the montmorillonite) (mol).

[0054] (3) Preparation of Saponin and TX-7 organic montmorillonite

[0055] Accurately weigh 5 g of dry montmorillonite, add 250 mL of the prepared Saponin or TX-7 aqueous solution with a mass percentage concentration of 0.2%-0.7%, and adjust the pH to 7. Then, place the beaker in a water bath shaker, shake at 25°C for 6 h, take it out and let it stand for 30 min, centrifuge at 3000 r / min for 10 min, and then dry in a 60°C drying oven for 30 h. Grind and pass through a 200-mesh sieve to obtain organic-modified montmorillonite, which is placed in a brown jar for later use. The obtained organic-modified montmorillonite is denoted as S x -MMT and TX x -MMT, x is the mass percentage concentration of the modifier Saponin or TX-7 aqueous solution.

[0056] (4) Structure and characterization of organic-modified montmorillonite

[0057] The X-ray diffraction (XRD) patterns of the montmorillonite and the organic modified montmorillonite samples obtained in steps (2) and (3) were characterized and analyzed by using an X-ray powder diffractometer. The Cu Kα ray (λ = 0.1542 nm) was used in the measurement, the scanning speed was 8.0° / min, the scanning step was 0.02°, and the scanning range was 2°-80°.

[0058] The infrared spectra of the montmorillonite and the organic modified montmorillonite samples obtained in steps (2) and (3) were characterized by using a Fourier infrared spectrometer. The montmorillonite or the organic modified montmorillonite sample was mixed with KBr in a mass ratio of 1:100 in a corundum mortar, and was ground and pressed into a sheet. The obtained sample sheet was placed in the instrument for analysis, and the scanning range was 500-4000 cm -1 .

[0059] In this example, two cationic surfactants (CTAB and DTAB) and two nonionic surfactants (Saponin and TX-7) were selected as the organic modifiers of the montmorillonite, and the effects of different modifiers on the modification of the montmorillonite were investigated. The XRD results are shown in Figures 1-4 , wherein Figure 1 is the XRD diffraction pattern of the modified montmorillonite with different amounts of CTAB; Figure 2 is the XRD diffraction pattern of the modified montmorillonite with different amounts of DTAB; Figure 3 is the XRD diffraction pattern of the modified montmorillonite with different amounts of Saponin; Figure 4 is the XRD pattern of the modified montmorillonite with different amounts of TX-7, and "0" in the figure represents the XRD of the purified montmorillonite.

[0060] In the XRD patterns of the montmorillonite and the organic modified montmorillonite, the first peak represents the size of the interlayer distance of the montmorillonite and the organic modified montmorillonite. As can be seen from Figure 1 and Figure 2 , the peak values of the first peaks of the C x -MMT and D x -MMT are obviously different from those of the MMT, which indicates that the two modifiers CTAB and DTAB have a great influence on the interlayer distance of the MMT, and the interlayer distance of the montmorillonite modified by CTAB and DTAB changes obviously. In addition, the amounts of the two modifiers CTAB and DTAB also have a great influence on the interlayer distance of the montmorillonite. When the amount of CTAB is 0.5 times the CEC of the montmorillonite, the peak value of the first peak is the largest, and when the amount of DTAB is 1 times the CEC of the montmorillonite, the peak value of the first peak is the largest. When the amounts of the two modifiers are further increased, the interlayer distance of the modified montmorillonite shows a downward trend, which may be due to the fact that the excess modifier adheres to the surface of the montmorillonite and blocks the interlayer channel, thereby reducing the interlayer distance. As can be seen from Figure 1 and Figure 2It can also be seen that C x -MMT and D x In the XRD pattern of MMT, except the first peak, other peak values have no obvious change, indicating that CTAB and DTAB inserted into the MMT interlayer did not destroy the original structure of the montmorillonite.

[0061] From Figure 3 and Figure 4 It can be seen that S x -MMT and TX x In the XRD pattern of MMT, the first peak position did not change, but the peak value decreased with the increase of the concentration of Saponin and TX-7, which indicated that the addition of Saponin and TX-7 reduced the interlayer spacing of the montmorillonite. It can be seen that the modification of the montmorillonite by the two nonionic surfactants cannot increase the interlayer spacing of the montmorillonite, and has the phenomenon of blocking the interlayer spacing, which will reduce the original adsorption effect of the montmorillonite. The modification effect of different modifiers on the montmorillonite has obvious influence. The interlayer spacing of the modified montmorillonite increases, which can increase the adsorption effect of the montmorillonite, and the interlayer spacing of the modified montmorillonite decreases, which will reduce the adsorption effect of the montmorillonite. According to the above experimental results, CTAB and DTAB are selected as the modifier of the montmorillonite.

[0062] In order to further investigate whether CTAB and DTAB are inserted into the interlayer of MMT, the CTAB and DTAB modified MMT obtained in step (2) was respectively subjected to infrared scanning (in which the amount of CTAB is 0.5 times of the CEC of the montmorillonite, and the amount of DTAB is 1 times of the CEC of the montmorillonite), and the results are shown in Figure 5 and Figure 6 It can be seen from Figure 5 that in the infrared spectrum of the CTAB modified montmorillonite (CTAB-MMT), in addition to the characteristic absorption peak of MMT itself, the characteristic absorption peak of CTAB also appears, that is, the absorption peak of methylene (-CH2) appears at wave number of 2848cm -1 and 2917cm -1 , which indicates that CTAB is indeed inserted into the interlayer of MMT. It can be seen from Figure 6 that in the infrared spectrum of the DTAB modified montmorillonite (DTAB-MMT), in addition to the characteristic absorption peak of MMT itself, the characteristic absorption peak of DTAB also appears, that is, the absorption peak of -CH2 appears at wave number of 2854cm -1 and 2915cm -1 , which indicates that DTAB is also inserted into the interlayer of MMT. The above experimental results show that the CTAB and DTAB modified montmorillonite is successfully prepared.

[0063] Example 2

[0064] In order to investigate the influence of temperature on the layer spacing of modified montmorillonite, the CTAB-MMT and DTAB-MMT were prepared in the same way as in Example 1, except that the temperature of the oscillation reaction in step (2) of Example 1 was changed to 40, 50, 60, 70 and 80°C, respectively, the amount of CTAB was 0.5 times the CEC of the montmorillonite, and the amount of DTAB was 1 times the CEC of the montmorillonite. The XRD patterns of the modified montmorillonite obtained at different temperatures are shown in Figure 7 and Figure 8 Figure 7 is the XRD pattern of CTAB-MMT prepared at different temperatures; Figure 8 is the XRD pattern of DTAB-MMT prepared at different temperatures). Figure 7 It can be seen from the above that the temperature has a greater influence on the layer spacing of CTAB-MMT. Within the temperature range of 40-70°C, the layer spacing of CTAB-MMT increases with increasing temperature. When the temperature exceeds 70°C, the layer spacing of CTAB-MMT gradually decreases. Therefore, in the following experiments, the oscillation reaction temperature is set to 70°C when using CTAB as the modifier to prepare modified montmorillonite. Figure 8 It can be seen from the above that the temperature has a smaller influence on the layer spacing of DTAB-MMT. When the temperature is 50°C, the layer spacing of DTAB-MMT is slightly larger. In the following experiments, the oscillation reaction temperature is set to 50°C when using DTAB as the modifier to prepare modified montmorillonite.

[0065] Example 3

[0066] In order to investigate the influence of pH on the layer spacing of modified montmorillonite, the CTAB-MMT was prepared at 70°C and the DTAB-MMT was prepared at 50°C in the same way as in Example 2, except that the pH in step (2) was changed to 6, 7, 8, 9, 10 and 11, respectively. The XRD patterns of the modified montmorillonite obtained at different pH values are shown in Figure 9 and Figure 10 Figure 9 is the XRD pattern of CTAB-MMT prepared at different pH values; Figure 10 is the XRD pattern of DTAB-MMT prepared at different pH values). Figure 9 and Figure 10 It can be seen from the above that the pH has little influence on the layer spacing of CTAB-MMT and DTAB-MMT. The layer spacing of CTAB-MMT is slightly larger when the pH is equal to 6, and the layer spacing of DTAB-MMT is slightly larger when the pH is equal to 8. Therefore, in the following experiments, the pH is set to 6 and 8, respectively, when preparing CTAB-MMT and DTAB-MMT.

[0067] Example 4 Adsorption test of organic montmorillonite ​​

[0068] (1) Take 0.2g modified organic montmorillonite into a 100mL beaker, add 25mL Hg 2+ solution with concentration of 5mg / L and 25mL ACR solution with concentration of 160mg / L respectively, adjust pH to 7, then put the beaker into a water bath oscillator, oscillate and adsorb at normal temperature (20-25℃) for 120min, then centrifugalize, take supernatant, respectively measure the content of Hg 2+ and ACR in the supernatant, calculate the adsorption capacity of sample to Hg 2+ and ACR by difference method with the following formula (Hg) .

[0069] Q (Hg) =(m 总 -m 液 ) / m 土 , Q (ACR) =(m 总 -m 液 ) / m 土 , wherein Q (Hg) and Q (ACR) are the adsorption capacity of Hg 2+ and ACR respectively, m 总 is the total mass of Hg 2+ or ACR added, m 液 is the mass of Hg 2+ or ACR in supernatant after centrifugalization, and m 土 is the mass of modified organic montmorillonite added.

[0070] In the above adsorption test, the content of Hg 2+ is determined by HydraⅡC automatic mercury analyzer. The content of ACR is determined by high performance liquid chromatography, wherein C18 column is used, the mobile phase is mixed solvent of anhydrous methanol and water (volume ratio is 85:15), and the absorption wavelength of ultraviolet detector is set to 225nm.

[0071] In the present application, CTAB modified montmorillonite prepared at pH=6, DTAB modified montmorillonite prepared at pH=8 and montmorillonite are used for corresponding adsorption test.

[0072] The results are shown in Table 1. Figure 11 The adsorption capacity of montmorillonite modified by CTAB to mercury is 0.4mg / g, and the adsorption capacity to ACR is 15.07mg / g; the adsorption capacity of montmorillonite modified by DTAB to mercury is 0.52mg / g, and the adsorption capacity to ACR is 17.44mg / g. Figure 11 It is shown that, compared with MMT, CTAB-MMT and DTAB-MMT have higher adsorption capacity to Hg 2+The adsorption capacities of Hg were increased by 53.85% and 100.00%, respectively, and the adsorption capacities of ACR were increased by 242.50% and 296.36%, respectively. This indicates that the montmorillonite modified with CTAB and DTAB has a better adsorption capacity for Hg. 2+ Both the adsorption capacity of ACR and Hg were significantly increased. 2+ The adsorption capacity of montmorillonite and its ACR is also significantly improved. This is mainly because after montmorillonite is modified with CTAB and DTAB, organic ammonium ions replace some of the exchangeable cations in montmorillonite, reducing water film resistance, increasing the CEC of montmorillonite, expanding the distance between crystal layers, increasing carbon content, and improving hydrophobicity, resulting in improved Hg adsorption capacity of the modified montmorillonite. 2+ Both the adsorption capacity of ACR and the adsorption capacity of ACR increased significantly.

[0073] (2) Modified montmorillonite on Hg 2+ The adsorption of ACR requires a certain amount of time to reach the dynamic equilibrium of adsorption-desorption. Therefore, after changing the shaking adsorption time in step (1), the corresponding adsorption amount was measured to examine the effect of time on the adsorption of Hg by modified montmorillonite. 2+ And the effect of ACR, the results are as follows Figure 12 and Figure 13 As shown ( Figure 12 The adsorption time for Hg adsorption by CTAB-MMT and DTAB-MMT 2+ The impact; Figure 13 (Effect of different time points on the adsorption of ACR by CTAB-MMT and DTAB-MMT). Figure 12 This indicates that CTAB-MMT and DTAB-MMT have an effect on Hg 2+ The adsorption capacity of both types of modified montmorillonite increases rapidly in the initial stage, then the rate of increase slows down, eventually reaching a dynamic equilibrium. 2+ The adsorption capacity of all molecules reached 50% within 10 minutes and reached equilibrium around 120 minutes, indicating that they are effective against Hg. 2+ The adsorption is a fast reaction. This is mainly because Hg is present in the early stage of the adsorption reaction. 2+ The concentration is relatively high, Hg 2+ There is also a high chance of contact with modified montmorillonite. In addition, there are many vacant adsorption sites on the surface of modified montmorillonite in the initial stage of adsorption, which is conducive to Hg. 2+ The adsorption effect is also relatively strong. With prolonged adsorption time, the adsorption sites gradually reach saturation, eventually reaching a dynamic equilibrium. The adsorption of ACR by CTAB-MMT and DTAB-MMT is similar to their adsorption of Hg. 2+ The adsorption of [the substance] exhibits the same trend: the adsorption rate is very fast in the initial stage and then slows down, eventually reaching a dynamic equilibrium, which takes about 120 minutes.

[0074] (3) Hg when the solution pH is different 2+ Furthermore, the different forms of ACR in solution affect the effect of modified montmorillonite on Hg. 2+ To investigate the adsorption effect of ACR, this experiment examined the influence of different pH solutions on the adsorption performance of modified montmorillonite. The pH value in step (1) was adjusted, and the corresponding adsorption amount was measured to investigate the effect of pH on the adsorption of Hg by modified montmorillonite. 2+ And the effect of ACR, the results are as follows Figure 14 and Figure 15 As shown ( Figure 14 pH effect on the adsorption of Hg by modified montmorillonite 2+ The impact; Figure 15 (Effect of pH on the adsorption of ACR by modified montmorillonite). Figure 14 This indicates that the pH of the solution affects the adsorption of Hg by modified montmorillonite. 2+ The effect is significantly affected; as the pH of the solution increases, the two modified montmorillonite materials have a greater impact on Hg. 2+ The adsorption capacity of both increased significantly. This is mainly because, at higher pH levels, modified montmorillonite can effectively adsorb Hg. 2+ Exchange adsorption occurs, while Hg 2+ It can also react with OH - The combination produces Hg(OH)2 precipitate (its solubility product constant is very small, K... sp =3.0×10 -26 Montmorillonite can also act as a seed crystal during the precipitation of Hg(OH)2, resulting in co-precipitation. This is beneficial for modifying montmorillonite to react with Hg. 2+ Adsorption. Figure 15 The results indicate that the pH of the solution has a relatively small effect on the adsorption capacity of modified montmorillonite for ACR. As the pH of the solution increases, the adsorption capacity of both modified montmorillonite for ACR decreases slowly. This is mainly because ACR is a weakly basic substance; at lower pH levels, the tertiary nitrogen atoms in ACR can react with H+. + The combination to form positive ions facilitates the exchange of cations between ACR and modified montmorillonite. Therefore, modified montmorillonite has a better adsorption effect on ACR at a lower pH. However, since ACR is a weak base, the pH of the solution has little effect on the adsorption effect of modified montmorillonite on ACR.

[0075] (4) Modified montmorillonite on Hg 2+ The adsorption of ACR is closely related to temperature, therefore this experiment investigated the effect of different temperatures on the adsorption performance of modified montmorillonite. The adsorption amount was measured after changing the temperature during the shaking adsorption in step (1), and the results were as follows ( Figure 16 and Figure 17 The effects of adsorption temperature on the adsorption of Hg by modified montmorillonite are as follows: 2+ (and the effect of adsorption ACR) indicates that temperature affects the adsorption of Hg by modified montmorillonite. 2+Both modified montmorillonite and ACR have a significant impact on the effect of temperature. As the temperature increases, the effect of the two modified montmorillonite on Hg... 2+ Both the adsorption capacity of modified montmorillonite and ACR decreased significantly. This is mainly because the modified montmorillonite has a significantly reduced adsorption capacity for Hg. 2+ Both the adsorption process of ACR and the adsorption process of ACR are exothermic, and increasing the temperature is not conducive to the adsorption process.

[0076] (5) Change the Hg in step (1) 2+ After determining the concentration of ACR, the corresponding adsorption amount was measured. Figure 18 and Figure 19 Hg 2+ The effect of ACR concentration on the adsorption capacity of modified montmorillonite. Figure 18 It can be known that Hg 2+ At lower concentrations, the concentration of Hg has a greater impact on the adsorption capacity of modified montmorillonite. 2+ At higher concentrations, the effect of concentration on the adsorption capacity of modified montmorillonite is relatively small. This is because in Hg... 2+ At lower concentrations, the adsorption capacity of modified montmorillonite does not reach saturation; at this point, the adsorption capacity of modified montmorillonite increases with Hg. 2+ The concentration increases with increasing Hg; 2+ When the concentration increases to a certain level, the adsorption capacity of modified montmorillonite reaches saturation. At this point, further addition of Hg... 2+ Concentration, effect of modified montmorillonite on Hg 2+ The adsorption capacity hardly changes anymore. Figure 19 This indicates that the concentration of ACR has an effect on the adsorption capacity of modified montmorillonite related to Hg. 2+ Similarly, at low concentrations, the adsorption capacity of modified montmorillonite for ACR increases with increasing concentration. Once the saturation adsorption capacity of modified montmorillonite for ACR is reached, further increases in the ACR concentration result in minimal change in the adsorption capacity of modified montmorillonite for ACR.

[0077] Example 5: Modified montmorillonite and its effect on Hg in actual samples 2+ and the adsorption effect of ACR

[0078] To investigate the effect of modified montmorillonite on Hg levels in actual soil samples (yellow-brown soil (topsoil, 0–20 cm), collected from Mufu Village, Mufu Subdistrict, Enshi City, Hubei Province; soil samples were air-dried, ground, sieved, and stored for later use after removing stones and plant roots), 2+ To investigate the adsorption effect of ACR, a certain amount of Hg was added to the soil in this experiment. 2+ After adding ACR, CTAB-modified montmorillonite prepared at pH=6, DTAB-modified montmorillonite prepared at pH=8, and montmorillonite were added respectively. A control experiment was conducted to assess the effect of modified montmorillonite on Hg levels in actual soil samples. 2+The adsorption effects of the modified montmorillonite on Hg

[0079] In 1 kg of soil sample (the physicochemical indexes are shown in Table 1), different amounts of 5 mg / L Hg (NO3) 2 solution and 160 mg / L ACR solution were added, and then 1 g of modified montmorillonite (CTAB-MMT or DTAB-MMT) was added. After mixing, water was added to 70% of the saturated water holding capacity of the soil, and water was added to 70% of the saturated water holding capacity of the soil every day. After 15 days, the Hg 2+ and ACR removal rates were calculated by the TCLP (toxicity characteristic leaching procedure) test. The experiment was carried out at room temperature (20-25 ℃). The results (Table 2) show that when the concentrations of Hg 2+ and ACR in the soil sample are low, the CTAB-MMT and DTAB-MMT have good removal effects on them, and the removal rates can reach more than 90%. With the increasing concentrations of Hg 2+ and ACR in the soil, the removal rates of the CTAB-MMT and DTAB-MMT on them gradually decrease, but the removal effect of the DTAB-MMT on Hg 2+ and ACR is better than that of the CTAB-MMT. The above results show that the CTAB-MMT and DTAB-MMT have good removal effects on Hg 2+ and ACR in real soil samples, and can simultaneously remove Hg 2+ and ACR in the soil.

[0080] Table 1 Physicochemical properties of the soil samples to be treated (n=3)

[0081]

[0082] Table 2 Adsorption effects of the modified montmorillonite on Hg 2+ and ACR in the soil samples (n=3)

[0083]

[0084] The present application uses two cationic surfactants, CTAB and DTAB, as organic modifiers to prepare two kinds of organic modified montmorillonite. The two kinds of modified montmorillonite have good adsorption effects on Hg 2+ and ACR, and have good adsorption effects on Hg 2 + and ACR in real soil samples. Compared with the reported modified montmorillonite for adsorbing single inorganic ions or organic molecules, the organic modified montmorillonite prepared by using CTAB and DTAB as modifiers can simultaneously remove Hg 2+ and ACR in the soil, and can synergistically repair the soil contaminated by Hg 2+ and ACR.

Claims

1. Application of modified montmorillonite in the synergistic remediation of mercury and acetochlor contaminated soil, wherein the modified montmorillonite is obtained by modifying montmorillonite with hexadecyltrimethylammonium bromide (CTAB) or dodecyltrimethylammonium bromide (DTAB); the mass concentration of modified montmorillonite added to the mercury and acetochlor contaminated soil is 1 g / kg, wherein, The mercury ion concentration is ≤0.4 mg / kg, and the acetochlor concentration is ≤15 mg / kg. The specific application steps are as follows: the modified montmorillonite is used in soil contaminated with both mercury ions and acetochlor for adsorption. The adsorption temperature is 20-25℃, the adsorption time is 15-20 days, the soil pH is 7 during adsorption, and the soil water content is maintained at 70% of the soil's saturated water holding capacity during the adsorption process. The modified montmorillonite is characterized by the following steps in its preparation: (1) Detection of cation exchange capacity (CEC) of montmorillonite; (2) Preparation of modified montmorillonite Montmorillonite was mixed with water and stirred to disperse it evenly. A modifier solution was then added, and the pH of the solution was adjusted to 6 or 8. The reaction was then carried out at 50 or 70°C with shaking for 6 hours. After the reaction was completed, the mixture was allowed to stand, centrifuged, and the solid was thoroughly dried to obtain organically modified montmorillonite. The modified agent was stored in the dark. The proportion of the modifier added was X1, where X1 = the amount of modifier in the modifier solution / (CEC of montmorillonite × mass of montmorillonite) = 0.5-2.

5. The modifier solution was either a CTAB solution or a DTAB solution, where the CTAB solution was a 10 wt% CTAB ethanol solution and the DTAB solution was a 10 wt% DTAB aqueous solution. When the modifier solution is CTAB solution, adjust the pH of the solution to 6, shake the reaction at 70℃, and react for 6 hours. X1 = 0.

5. When the modifier solution is DTAB solution, adjust the solution pH to 8, shake the reaction temperature to 50℃, and react for 6 hours. X1 = 1.

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