CN116200199A - Modified montmorillonite for synergistic remediation of heavy metals and organic pollutants in soil, and preparation method and application thereof - Google Patents

Abstract

The invention belongs to the technical field of polluted soil remediation, and in particular relates to modified montmorillonite for carrying out synergistic remediation on heavy metals and organic pollutants in soil, a preparation method and application thereof, wherein Cetyl Trimethyl Ammonium Bromide (CTAB) and Dodecyl Trimethyl Ammonium Bromide (DTAB) are used as modifiers to prepare organic modified montmorillonite, and mercury ions (Hg) are used as the modifier ²⁺ ) And Acetochlor (ACR) as representative substances of heavy metals and organic pollutants, to repair Hg for two organically modified montmorillonite ²⁺ And the effect of ACR composite polluted soil are researched. The results show that the two organically modified montmorillonite can be used for treating Hg in a real soil sample ²⁺ The ACR has good removal effect, and can simultaneously remove Hg in soil ²⁺ ACR. The removal rate of CTAB modified montmorillonite and DTAB modified montmorillonite can reach more than 90%. The organic modified montmorillonite prepared by using CTAB and DTAB as the modifier can simultaneously remove Hg in soil ²⁺ And ACR, can be against Hg ²⁺ And the soil subjected to the combined pollution of ACR is subjected to synergistic restoration.

Description

A modified montmorillonite for synergistic remediation of heavy metals and organic pollutants in soil Soil and its preparation method and application

technical field

The invention belongs to the technical field of contaminated soil remediation, and in particular relates to an organically modified montmorillonite for synergistic remediation of heavy metals and organic pollutants in soil, a preparation method and application thereof.

Background technique

In recent years, due to the rapid development of global industry, the production and consumption of mercury have increased on a large scale, resulting in a large amount of mercury being released into the natural environment. Therefore, mercury pollution has become a global environmental problem, and soil and water bodies are suffering from more and more serious mercury pollution, which in turn endangers human health through the food chain. At present, the problem of mercury pollution has aroused widespread concern from people all over the world.

Acetochlor (ACR) is a herbicide with high herbicidal activity, especially for annual gramineous weeds, and has been widely used in agricultural production around the world. Agricultural production saves a lot of manpower and material resources. However, the degradation products of ACR remaining in the soil can endanger human health through the food chain.

With the mass production of mercury and the extensive use of ACR in agricultural production, mercury and ACR enter the soil simultaneously or successively, forming compound pollution to the soil. Therefore, it is of great significance to develop a remediation agent that can simultaneously remove mercury and ACR in soil for soil pollution control and remediation and agricultural product safety.

Montmorillonite (montmorillonite) is also known as microcrystalline kaolinite or jiaolingite. Montmorillonite crystals are monoclinic hydrous layered silicate minerals. Its main components are octahedral montmorillonite particles, and the middle is Alumina-oxygen octahedron is a clay mineral with a three-layer sheet structure composed of silicon-oxygen tetrahedrons on the upper and lower sides. It contains water and some exchanged cations between the crystal structure layers. It has a high ion exchange capacity and a high water absorption and expansion capacity. The interlayer cations are exchangeable and can be exchanged with heavy metal ions, so montmorillonite has good adsorption capacity for heavy metal ions. In addition, after appropriate inorganic or organic modification, montmorillonite can obtain a huge interlayer domain space, which can reduce the hydrophilicity of the interlayer microenvironment and significantly improve its adsorption capacity for hydrophobic organic compounds. Therefore, the modified montmorillonite is expected to adsorb both heavy metal ions and hydrophobic organic compounds.

For a long time, researchers at home and abroad have done more research on modified montmorillonite, but these studies focus more on the preparation of modified montmorillonite, the effect of modified montmorillonite on a single heavy metal ion or organic There are few studies on the adsorption performance of pollutants, and there are few studies on the combined pollution of heavy metals and organic pesticides, and the use of modified montmorillonite to achieve synergistic remediation of soil heavy metals and organic pollutants has not been reported.

Contents of the invention

In view of the above-mentioned problems in the prior art, the present invention selects cetyltrimethylammonium bromide (CTAB), two kinds of cationic surfactants of dodecyltrimethylammonium bromide (DTAB) as modifying agent, Two kinds of modified montmorillonites that can synergistically remediate mercury and ACR composite pollution were prepared, and the effects of these two modified montmorillonites on synergistic remediation of mercury and ACR composite pollution were studied. The results showed that synergistic remediation of heavy metals in agricultural production and organic pollutants provide a new direction.

The present invention realizes above-mentioned purpose, and the technical scheme that takes is:

A modified montmorillonite for synergistic restoration of heavy metals and organic pollutants in soil, the modified montmorillonite is obtained by modifying the montmorillonite with a modifier, and the modifier is hexadecyl Trimethylammonium bromide (CTAB) and/or dodecyltrimethylammonium bromide (DTAB).

The present invention also provides a preparation method of the above-mentioned organically modified montmorillonite, the steps of the preparation method are as follows:

(1) Detect the cation exchange capacity (CEC) of montmorillonite;

(2) Preparation of modified montmorillonite

Add a certain amount of water to the montmorillonite (preferably add 50mL of water to 1g of montmorillonite), stir and disperse evenly, add the modifier solution to it, and then adjust the pH of the solution to 6-11; then at 40-80°C Shake the reaction for 4-8h, let stand after the reaction, centrifuge (preferably centrifuge at 3000r/min for 10min), and dry the solid after centrifugation (preferably at 60°C for 30h) to obtain organically modified montmorillonite, keep away from light save.

Preferably, the modifying agent solution in the step (2) is a CTAB solution or a DTAB solution.

Preferably, in the step (2), when the modifying agent solution is a CTAB solution, the pH of the solution is adjusted to 6, the oscillation reaction temperature is 70° C., and the reaction time is 6 hours.

Preferably, in the step (2), when the modifying agent solution is a DTAB solution, the pH of the solution is adjusted to 8, the oscillation reaction temperature is 50° C., and the reaction time is 6 hours.

Preferably, in the step (2), the addition ratio of the modifier is X ₁ , and the X ₁ = amount of the modifier in the modifier solution/(montmorillonite CEC×montmorillonite mass)=0.5-2.5; more preferably, when adding CTAB solution, said X ₁ =0.5, and when adding DTAB solution, said X ₁ =1.

Preferably, the CTAB solution is a 10wt% CTAB ethanol solution, and the DTAB solution is a 10wt% DTAB aqueous solution.

The present invention also provides the application of the above-mentioned modified montmorillonite in synergistic restoration of heavy metal and organic pollutant composite polluted soil.

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

Preferably, the specific steps of the application are: use it in mercury ion and acetochlor composite polluted soil for adsorption reaction, the adsorption temperature is 20-25°C, the adsorption time is 15-20 days, and the soil pH=7, soil water content is 70% of soil saturated water holding capacity.

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

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

Compared with the prior art, the technical solution of the present invention has the following advantages and beneficial effects:

The organically modified montmorillonite prepared by the invention has a remarkable effect of simultaneously adsorbing heavy metal ions and organic pollutants, and can be directly applied to remediation of compound polluted soil by heavy metal ions and organic pollutants. The existing research on modified montmorillonite is mainly the adsorption of a single heavy metal ion or organic pollutant by modified montmorillonite, and the research on the combined pollution of heavy metals and organic pesticides has not been reported yet. Montmorillonite is a layered silicate clay mineral with montmorillonite as the main component and containing water. Its interlayer cations are exchangeable and can be exchanged with heavy metal ions. Therefore, montmorillonite has great Good adsorption. After montmorillonite is modified by organic matter, it can obtain huge interlayer domain space, reduce the hydrophilicity of the interlayer microenvironment, and significantly improve its adsorption capacity for hydrophobic organic compounds. The present invention optimizes the conditions for organically modified montmorillonite to simultaneously adsorb heavy metal ions and organic pollutants, and applies it to the remediation of Hg ²⁺ and ACR composite polluted soil under optimized conditions, and has achieved very significant results Effect. When the Hg2 ⁺ concentration in the soil sample is less than 0.2mg/kg, and the ACR concentration is less than 10mg/kg, the removal rates of CTAB modified montmorillonite and DTAB modified montmorillonite can reach more than 90%. It also has a good adsorption effect on Pb ²⁺ and Cd ²⁺ in soil.

Description of drawings

Fig. 1 is the XRD diffraction pattern of the modified montmorillonite of different consumption CTAB among the embodiment 1;

Fig. 2 is the XRD diffraction pattern of the modified montmorillonite of different consumption DTAB in embodiment 1;

Fig. 3 is the XRD diffraction pattern of the modified montmorillonite of different consumption Saponin in embodiment 1;

Fig. 4 is the XRD spectrum of the modified montmorillonite of the TX-7 of different consumption in embodiment 1;

Fig. 5 is the infrared spectrogram of CTAB, CTAB-MMT and MMT among the embodiment 1;

Fig. 6 is the infrared spectrogram of DTAB, DTAB-MMT and MMT in embodiment 1.

Fig. 7 is the XRD pattern of the CTAB-MMT prepared under different temperatures in embodiment 2;

Figure 8 is the XRD patterns of DTAB-MMT prepared at different temperatures in Example 2.

Fig. 9 is the XRD pattern of CTAB-MMT prepared under different pHs in embodiment 3;

Fig. 10 is the XRD pattern of the DTAB-MMT prepared under different pHs in embodiment 3;

Fig. 11 is the adsorption capacity figure of MMT, CTAB-MMT and DTAB-MMT to Hg ²⁺ and ACR in embodiment 4;

Fig. 12 is the influence of adsorption time on CTAB-MMT and DTAB-MMT adsorption ^Hg in embodiment 4;

Fig. 13 is the influence of different time on CTAB-MMT and DTAB-MMT adsorption ACR in embodiment 4;

Fig. 14 is the influence of pH on the adsorption of ^Hg of modified montmorillonite in embodiment 4;

Fig. 15 is the influence of pH on the adsorption ACR of modified montmorillonite in embodiment 4;

Fig. 16-Fig. 17 are respectively the influence of adsorption temperature on the adsorption of Hg ²⁺ and adsorption ACR of modified montmorillonite in embodiment 4;

Figure 18 and Figure 19 respectively show the influence of the concentration of Hg ²⁺ and ACR on the adsorption capacity of modified montmorillonite.

Detailed ways

The technical solutions of the present invention will be described in detail below in conjunction with specific embodiments.

Part of the equipment used in the following examples is as follows: XRD-7000 type X-ray powder diffractometer (Shimadzu, Japan), Fourier transform infrared spectrometer (Nicolet, U.S.), HydraⅡC automatic mercury measuring instrument (Leaman, U.S.), high performance liquid phase Chromatography (EClassical 3200, Dalian, China).

Main chemical reagent cetyltriethylammonium bromide CTAB, dodecyltrimethylammonium bromide DTAB, tea saponin (Saponin), alkylphenol polyoxyethylene (7) ether ( TX-7) and mercury standard solution (1000 μg/ml) were of analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd., China.

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

The montmorillonite (MMT) used in the following examples is montmorillonite KSF purchased from Aladdin, product number M109699.

Unless otherwise specified in the following examples, the solution used to adjust the pH is 0.1 mol/L hydrochloric acid and/or 0.1 mol/L sodium hydroxide solution.

Embodiment 1 A kind of organically modified montmorillonite that carries out synergistic restoration of mercury ion and acetochlor compound polluted soil is prepared by the following method:

(1) Determination of the cation exchange capacity of montmorillonite

The cation exchange capacity (CEC) of montmorillonite was determined by barium chloride-sulfuric acid exchange method. Accurately weigh 0.5g of montmorillonite and put it into a centrifuge tube, and record the weight of the centrifuge tube after adding montmorillonite, then add 20mL of BaCl _solution with a concentration of 0.5mol/L to it, stir with a glass rod for 4min, and then add Centrifuge at a speed of 3000r/min for 5min, discard the supernatant, and repeat the above-mentioned addition of BaCl ₂ solution, stirring and centrifugation twice. Add 20mL of distilled water to the montmorillonite after the last centrifugation, stir with a glass rod for 1min, then centrifuge at a speed of 3000r/min for 5min, discard the supernatant, and weigh the weight of the centrifuge tube and montmorillonite again . Add 25 mL of sulfuric acid solution with a concentration of 0.1 mol/L to the centrifuge tube, stir well, let stand for 20 minutes and then centrifuge, take 10 mL of the supernatant in a conical flask, and titrate with 0.1 mol/L standard sodium hydroxide solution. At the same time, pipette 10 mL of 0.1 mol/L sulfuric acid solution into another Erlenmeyer flask, and also titrate with standard sodium hydroxide solution, and use the difference between the two titration results to calculate the cation exchange capacity of montmorillonite. According to this method, the cation exchange capacity of the montmorillonite used in this experiment was 75 cmol/kg.

(2) Preparation of CTAB and DTAB organomontmorillonite

Accurately weigh 5 g of dry montmorillonite, add 250 mL of distilled water to it, and stir evenly. Add the CTAB or DTAB solution that is equivalent to montmorillonite CEC 0.5-2.5 times respectively (corresponding to the amount (mol)/(montmorillonite CEC multiple=CTAB or DTAB material amount (mol)/(montmorillonite CEC in CTAB or DTAB solution) of montmorillonite CEC CEC × montmorillonite mass) (mol), adjusted to the required pH (the pH of CTAB modified organomontmorillonite is 6, the pH of DTAB modified organomontmorillonite is 8), put the beaker into In a water bath shaker, shake and react for 6 hours at a certain temperature (the temperature for CTAB modified organomontmorillonite is 70°C, and the temperature for DTAB modified organomontmorillonite is 50°C), take it down and let it stand for 30min, and then Centrifuge at 3000r/min for 10min, dry the centrifuged solid in a drying oven at 60°C for 30h, grind the dried solid and pass through a 200-mesh sieve to obtain organically modified montmorillonite, which is put in a brown jar for later use. By CTAB The montmorillonite modified with DTAB is recorded as CTAB-MMT and DTAB-MMT respectively, and different organically modified montmorillonites are respectively recorded as C _x -MMT and D _x -MMT according to the amount of CTAB or DTAB, and x=CTAB Or the amount of substance of CTAB or DTAB in the DTAB solution (mol)/(CEC of montmorillonite×mass of montmorillonite) (mol).

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

Accurately weigh 5g of dried montmorillonite, add 250mL of prepared Saponin or TX-7 aqueous solution with a mass percentage concentration of 0.2%-0.7%, adjust the pH to 7, put the beaker into a water bath shaker, and Shake and react at 25°C for 6h, remove and let stand for 30min, centrifuge at 3000r/min for 10min, then dry in a drying oven at 60°C for 30h, grind and pass through a 200-mesh sieve to obtain organically modified montmorillonite, which is placed in a brown wide-mouth Reserve in bottle. The obtained organically modified montmorillonite is recorded as S _x -MMT and TX _x -MMT according to the mass percentage concentration of Saponin or TX-7 aqueous solution, and x is the mass percentage concentration of modifier Saponin or TX-7 aqueous solution .

(4) Structure and characterization of organically modified montmorillonite

The X-ray diffraction (XRD) collection of illustrative plates of the organically modified montmorillonite sample that montmorillonite and steps (2) and (3) obtain adopt X-ray powder diffractometer to carry out characterization and analysis, adopt the Kα ray (λ of Cu during measurement) =0.1542nm), the scanning speed is 8.0°/min, the scanning step is 0.02°, and the scanning range is 2°-80°.

The infrared spectra of the montmorillonite and the organically modified montmorillonite samples obtained in steps (2) and (3) were characterized by a Fourier transform infrared spectrometer. The montmorillonite or organically modified montmorillonite sample and KBr were mixed in an agate mortar with a mass ratio of 1:100, fully ground and pressed into tablets, and the obtained sample slices were put into the instrument for analysis, scanned The range is 500-4000cm ^-1 .

Selected two kinds of cationic surfactants (CTAB and DTAB) and two kinds of nonionic surfactants (Saponin and TX-7) in the present embodiment as the organic modifier of montmorillonite, investigated different modifiers to The influence of the modification effect of montmorillonite, its XRD result is shown in Figure 1-4, wherein Fig. 1 is the XRD diffraction pattern of the modified montmorillonite of different dosage CTAB; Fig. 2 is the modified montmorillonite of different dosage DTAB The XRD diffraction pattern of soil; Fig. 3 is the XRD diffraction pattern of the modified montmorillonite of different dosages of Saponin; Fig. 4 is the XRD pattern of the modified montmorillonite of different dosages of TX-7, "0" in the figure represents purified XRD of Montmorillonite.

In the XRD pattern of montmorillonite and organically modified montmorillonite, the first peak represents the size of the layer spacing of montmorillonite and organically modified montmorillonite. It can be seen from Figure 1 and Figure 2 that the peaks of the first peaks of C _x -MMT and D _x -MMT are significantly different from those of MMT, which shows that the two modifiers of CTAB and DTAB have a great influence on the interlayer spacing of MMT , the interlayer spacing of montmorillonite changed significantly after CTAB and DTAB modification. In addition, the amount of CTAB and DTAB two modifiers also has a great influence on the interlayer spacing of montmorillonite. The peak of the first peak is the largest when the amount of CTAB is equivalent to 0.5 times the CEC of montmorillonite, and the amount of DTAB is equivalent to When the CEC of montmorillonite is 1 times, the peak of the first peak is the largest. When the amount of these two modifiers is further increased, the interlayer spacing of the modified montmorillonite shows a downward trend, which may be due to the excessive modifier attached to the surface of the montmorillonite to block the interlayer channels, thus making the interlayer spacing decrease. It can also be seen from Figure 1 and Figure 2 that in the XRD patterns of C _x -MMT and D _x -MMT, except for the first peak, other peaks have no obvious changes, indicating that CTAB and DTAB are inserted into the MMT layer. The original structure of montmorillonite was not destroyed.

It can be seen from Figure 3 and Figure 4 that in the XRD patterns of _Sx -MMT and _TXx -MMT, the position of the first peak does not change, but the peak decreases with the increase of the concentration of Saponin and TX-7, which shows that Saponin and TX-7 The addition of TX-7 reduces the layer spacing of montmorillonite. It can be seen that these two non-ionic surfactants modified montmorillonite can not increase the layer spacing of montmorillonite, and there is a phenomenon of blocking the layer spacing, which will reduce the original adsorption effect of montmorillonite. Different modifiers have obvious effects on the modification effect of montmorillonite. The increased interlayer spacing of modified montmorillonite can increase the adsorption effect of montmorillonite, and the interlayer spacing of modified montmorillonite can be reduced. If it is small, the adsorption effect of montmorillonite will be reduced. According to the above experimental results, CTAB and DTAB were selected as modifiers of montmorillonite.

In order to further investigate whether CTAB and DTAB are inserted between the sheets of MMT, the CTAB obtained in step (2) and the MMT modified by DTAB were scanned by infrared (wherein the amount of CTAB is equivalent to 0.5% of the CEC of montmorillonite). times, the amount of DTAB is equivalent to 1 times the CEC of montmorillonite), the results are shown in Figure 5 and Figure 6. It can be seen from Figure 5 that in the infrared spectrum of CTAB-modified montmorillonite (CTAB-MMT), in addition to the characteristic absorption peaks of MMT itself, there are also characteristic absorption peaks of CTAB, that is, at wavenumbers of 2848cm ^-1 and 2917cm ^-1 The absorption peak of methylene (-CH ₂ ) appeared at , which indicated that CTAB was indeed inserted into the interlamellar of MMT. It can be seen from Figure 6 that in addition to the characteristic absorption peaks of MMT itself in the infrared spectrum of DTAB-modified montmorillonite (DTAB-MMT), there are also characteristic absorption peaks of DTAB, that is, at wavenumbers of 2854cm ^-1 and 2915cm ^- 1 The absorption peak of -CH ₂ appeared at ¹ , which indicated that DTAB was also inserted into the interlamellar of MMT. The above experimental results show that CTAB and DTAB modified montmorillonite was successfully prepared.

Example 2

In order to investigate the influence of temperature on the interlayer spacing of modified montmorillonite, on the basis of the experimental steps of CTAB-MMT and DTAB-MMT prepared in Example 1, the temperature of the oscillation reaction in step (2) of Example 1 was changed to 40, 50, 60, 70, 80 ℃, the amount of CTAB is 0.5 times the CEC of montmorillonite, the amount of DTAB is 1 times the CEC of montmorillonite, the XRD of the modified montmorillonite obtained at different temperatures The spectra are shown in Figure 7 and Figure 8 (Figure 7 is the XRD spectrum of CTAB-MMT prepared at different temperatures; Figure 8 is the XRD spectrum of DTAB-MMT prepared at different temperatures). It can be seen from Figure 7 that the temperature has a great influence on the interlayer spacing of CTAB-MMT. In the temperature range of 40-70 °C, the interlayer spacing of CTAB-MMT increases with the increase of temperature. When the temperature exceeds 70 °C, CTAB-MMT The layer spacing of MMT gradually decreases again. Therefore, in the following experiments, when using CTAB as a modifier to prepare modified montmorillonite, the shaking reaction temperature was set to 70°C. It can be seen from Figure 8 that the temperature has little effect on the interlayer spacing of DTAB-MMT. When the temperature is 50°C, the interlayer spacing of DTAB-MMT is slightly larger. In the following experiments, when using DTAB as a modifier to prepare modified montmorillonite , and the shaking reaction temperature was set to 50°C.

Example 3

In order to investigate the effect of pH on the interlayer spacing of modified montmorillonite, in this example, on the basis of preparing CTAB-MMT at a shaking reaction temperature of 70°C and preparing DTAB-MMT at 50°C in Example 2, step (2) was changed respectively. Adjust the pH to be 6, 7, 8, 9, 10, 11, the XRD patterns of the modified montmorillonite obtained under different pHs are shown in Figure 9 and Figure 10 (Figure 9 is the XRD of CTAB-MMT prepared under different pH Spectrum; Fig. 10 is the XRD pattern of DTAB-MMT prepared under different pH). It can be seen from Figure 9 and Figure 10 that the pH has little effect on the interlayer spacing of CTAB-MMT and DTAB-MMT, the interlayer spacing of CTAB-MMT is slightly larger when the pH is equal to 6, and the interlayer spacing of DTAB-MMT is slightly larger when the pH is equal to 8. Therefore, in the following experiments, when preparing CTAB-MMT and DTAB-MMT two modified montmorillonites, the pH was set to 6 and 8, respectively.

Embodiment 4 organic montmorillonite adsorption test

(1) Take 0.2g of modified organic montmorillonite and place it in a 100mL beaker, add 25mL of Hg ²⁺ mercury nitrate solution with a concentration of 5mg/L and 25mL of ACR solution with a concentration of 160mg/L, and adjust the pH to 7 , put the beaker into a water bath shaker, shake and adsorb at room temperature (20-25°C) for 120min, then centrifuge, take the supernatant, and measure the Hg ²⁺ and ACR contents in the supernatant, respectively, by Using the difference method, use the following formula to calculate the adsorption amount Q _(Hg) of the sample for Hg ²⁺ and ACR.

Q _(Hg) = (m _total -m _liquid )/m _soil , Q _(ACR) = (m _total -m _liquid )/m _soil , where Q _(Hg) and Q _(ACR) are Hg ²⁺ and ACR respectively m is the _total mass of Hg ²⁺ or ACR added, m _solution is the mass of Hg ²⁺ or ACR in the supernatant after centrifugation, and m _soil is the mass of added modified organic montmorillonite.

In the above adsorption test, the content of Hg ²⁺ was measured by HydraⅡC automatic mercury analyzer. ACR content adopts high-performance liquid chromatography to measure, adopts C18 column during determination, mobile phase is the mixed solvent of anhydrous methanol and water (volume ratio is 85:15), and the absorption wavelength of ultraviolet detector is set to 225nm.

In the present invention, the CTAB modified montmorillonite prepared when the pH=6, the DTAB modified montmorillonite and the montmorillonite prepared when the pH=8 in Example 3 were used for corresponding adsorption tests.

The results are shown in Figure 11. The adsorption capacity of montmorillonite modified by CTAB to mercury is 0.4 mg/g, and the adsorption capacity to ACR is 15.07 mg/g; the adsorption capacity of montmorillonite modified by DTAB to mercury It is 0.52mg/g, and the adsorption capacity for ACR is 17.44mg/g. Figure 11 shows that compared with MMT, the adsorption capacity of CTAB-MMT and DTAB-MMT for Hg ²⁺ increased by 53.85% and 100.00%, respectively, and the adsorption capacity for ACR increased by 242.50% and 296.36%, respectively. This shows that the adsorption capacity of montmorillonite modified by CTAB and DTAB to Hg ²⁺ and ACR is significantly increased, and their adsorption capacity to Hg ²⁺ and ACR is also significantly improved. This is mainly because after the montmorillonite is modified by CTAB and DTAB, the organic ammonium ions replace part of the exchangeable cations in the montmorillonite, which reduces the water film resistance, increases the CEC of the montmorillonite, and expands the crystal layer The distance between them increased the carbon content and improved the hydrophobicity, resulting in a significant increase in the adsorption capacity of the modified montmorillonite for Hg ²⁺ and ACR.

(2) The adsorption of Hg ²⁺ and ACR on modified montmorillonite requires a certain amount of time to reach the dynamic equilibrium of adsorption-desorption. Therefore, after changing the time of shock adsorption in step (1), the corresponding adsorption amount is detected to investigate the effect of time on The effect of modified montmorillonite on the adsorption of Hg ²⁺ and ACR, the results are shown in Figure 12 and Figure 13 (Figure 12 is the effect of adsorption time on CTAB-MMT and DTAB-MMT adsorption of Hg ²⁺ ; Figure 13 is the effect of different time on the adsorption of Hg 2+ Effect of CTAB-MMT and DTAB-MMT on adsorption of ACR). Figure 12 shows that the adsorption capacity of CTAB-MMT and DTAB-MMT to Hg ²⁺ increases rapidly in a short period of time at the initial stage, then increases slowly, and finally reaches a dynamic equilibrium. The adsorption capacity of these two modified montmorillonites to Hg ²⁺ reached 50% within 10 minutes, and reached equilibrium in about 120 minutes, which indicated that their adsorption to Hg ²⁺ was a fast reaction. This is mainly because the concentration of Hg ²⁺ in the early stage of the adsorption reaction is relatively large, and the chance of contact between Hg ²⁺ and the modified montmorillonite is also great. In addition, there are many vacant adsorption sites on the surface of the modified montmorillonite at the initial stage of adsorption, which is harmful to Hg ²⁺ . ⁺ Adsorption is also relatively strong. With the prolongation of the adsorption time, the adsorption sites gradually reached saturation, and finally reached a dynamic equilibrium. The adsorption of CTAB-MMT and DTAB-MMT to ACR has the same trend as the adsorption of Hg ²⁺ , and the adsorption speed is very fast in the first stage, and then the adsorption speed slows down, and finally gradually reaches the dynamic equilibrium. The time is also around 120min.

(3) When the pH of the solution is different, the existence forms of Hg ²⁺ and ACR in the solution are also different, which in turn affects the adsorption effect of modified montmorillonite on Hg ²⁺ and ACR. Therefore, this experiment investigated the effect of different pH solutions on the modification The influence of montmorillonite adsorption performance, after changing the pH adjustment value in step (1), detect the corresponding adsorption amount to investigate the effect of pH on the adsorption of Hg ²⁺ and ACR of modified montmorillonite, the results are shown in Figure 14 and Figure 15 (Figure 14 is the effect of pH on the adsorption of Hg ²⁺ by modified montmorillonite; Figure 15 is the effect of pH on the adsorption of ACR by modified montmorillonite). Figure 14 shows that the pH of the solution has a great influence on the adsorption of Hg ²⁺ by the modified montmorillonite. As the pH of the solution increases, the adsorption capacity of the two modified montmorillonites for Hg ²⁺ increases significantly. This is mainly because at a higher pH, the modified montmorillonite can not only exchange and adsorb Hg ²⁺ , but also combine with OH ^- to ^produce Hg(OH) ₂ precipitation (its solubility product constant is very small , K _sp =3.0×10 ^-26 ), and the montmorillonite can be used as a seed crystal during the precipitation of Hg(OH) ₂ to produce co-precipitation, which is beneficial to the adsorption of Hg ²⁺ by the modified montmorillonite. Figure 15 shows that the pH of the solution has little effect on the adsorption of ACR by the modified montmorillonite, and as the pH of the solution increases, the adsorption capacity of the two modified montmorillonites for ACR decreases slowly. This is mainly because ACR is a weakly alkaline substance. When the pH is low, the tertiary nitrogen atoms in ACR can combine with H ⁺ to form positive ions, which is beneficial to the exchange of cations between ACR and modified montmorillonite, so the pH is relatively low. The modified montmorillonite has a better adsorption effect on ACR, but since ACR is a weak base, the pH of the solution has little effect on the adsorption of ACR by the modified montmorillonite.

(4) The adsorption of modified montmorillonite to Hg ²⁺ and ACR is closely related to temperature, so this experiment investigated the effect of different temperatures on the adsorption properties of modified montmorillonite. After changing the temperature during the oscillating adsorption in step (1), the corresponding adsorption amount was detected. The results (Figure 16 and Figure 17 are the effects of adsorption temperature on the adsorption of Hg ²⁺ and adsorption ACR of the modified montmorillonite respectively) show that the temperature has a great influence on the modified montmorillonite. The adsorption capacity of modified montmorillonite for Hg ²⁺ and ACR has a great influence. With the increase of temperature, the adsorption capacity of two kinds of modified montmorillonite for Hg ²⁺ and ACR decreased obviously. This is mainly because the adsorption process of modified montmorillonite to Hg ²⁺ and ACR is exothermic, and increasing the temperature is not conducive to the generation of adsorption.

(5) After changing the concentration of Hg ²⁺ and ACR in step (1), the corresponding adsorption capacity was detected. Figure 18 and Figure 19 respectively show the influence of the concentration of Hg ²⁺ and ACR on the adsorption capacity of modified montmorillonite. It can be seen from Figure 18 that when the concentration of Hg ²⁺ is small, its concentration has a greater influence on the adsorption capacity of the modified montmorillonite, and when the concentration of Hg ²⁺ is high, the concentration has little effect on the adsorption capacity of the modified montmorillonite . This is because when the Hg ²⁺ concentration is small, the adsorption capacity of the modified montmorillonite does not reach saturation, and the adsorption capacity of the modified montmorillonite increases with the increase of the Hg ²⁺ concentration; when the Hg ²⁺ concentration increases to To a certain extent, the adsorption capacity of modified montmorillonite reaches saturation, and at this time, increasing the concentration of Hg ²⁺ , the adsorption capacity of modified montmorillonite for Hg ²⁺ hardly changes. Figure 19 shows that the effect of the concentration of ACR on the adsorption capacity of modified montmorillonite is similar to that of Hg ²⁺ . Also at low concentrations, the adsorption capacity of modified montmorillonite to ACR increases with the increase of its concentration. When it reaches After the saturated adsorption capacity of modified montmorillonite to ACR, and then increase the concentration of ACR, the adsorption capacity of modified montmorillonite to ACR changes little.

The adsorption effect of modified montmorillonite to ^Hg and ACR in the actual sample in embodiment 5

In order to investigate the modified montmorillonite on the actual soil samples (soil samples are yellow brown soil (surface soil, 0 ~ 20cm), taken from Mufu Village, Mufu Office, Enshi City, Hubei Province, the collected soil samples were removed from stones and plants After the rhizome, it is air-dried, ground, sieved, and stored for future use) for the adsorption effect of Hg ²⁺ and ACR in the experiment. After adding a certain amount of Hg ²⁺ and ACR in the soil, add the pH value in Example 3 respectively. =6 when the prepared CTAB modified montmorillonite, DTAB modified montmorillonite and montmorillonite prepared when the pH=8, through the control test, the modified montmorillonite to the Hg ²⁺ and montmorillonite in the actual soil sample The adsorption effect of ACR was evaluated.

Add different amounts of 5mg/L of mercury nitrate solution and 160mg/L of ACR solution in 1kg of soil samples to be treated (see Table 1 for physical and chemical indicators), and then add 1g of modified montmorillonite (CTAB-MMT or DTAB- MMT), after mixing evenly, add water to 70% of the saturated water holding capacity of the soil, replenish water regularly to 70% of the saturated water holding capacity of the soil every day, and calculate the removal rate of ^Hg and ACR by the toxicity leaching test (TCLP) of the soil after 15 days, The experiments were all carried out at room temperature (20-25°C). The results (table 2) show that when the concentrations of Hg ²⁺ and ACR in the soil sample are low, CTAB-MMT and DTAB-MMT all have good removal effects on them, and the removal rate can reach more than 90%. The removal rate of CTAB-MMT and DTAB-MMT decreased gradually when the concentration of ²⁺ and ACR in the soil increased gradually, but the removal effect of DTAB-MMT on Hg ²⁺ and ACR was better than that of CTAB-MMT. The above results show that CTAB-MMT and DTAB-MMT have good removal effects on Hg ²⁺ and ACR in real soil samples, and can remove Hg ²⁺ and ACR in soil at the same time.

Table 1 Physicochemical properties of soil samples to be treated (n=3)

Table 2 Adsorption effect of modified montmorillonite on Hg ²⁺ and ACR in soil samples (n=3)

The present invention utilizes two cationic surfactants, CTAB and DTAB, as organic modifiers to prepare two organically modified montmorillonites. These two modified montmorillonites have good adsorption effects on Hg ²⁺ and ACR. It has good adsorption effect on Hg ^{2 +} and ACR in real soil samples. Compared with the reported adsorption of modified montmorillonite on a single inorganic ion or organic molecule, the organically modified montmorillonite prepared by using CTAB and DTAB as modifiers can remove Hg ²⁺ and ACR in the soil at the same time. Synergistic remediation of Hg ²⁺ and ACR compound polluted soil.

Claims (9)

1. A modified montmorillonite that carries out synergistic restoration of heavy metals and organic pollutants in soil, said modified montmorillonite is made of montmorillonite through cetyltrimethylammonium bromide CTAB and/or dodecyl trimethylammonium bromide Alkyltrimethylammonium bromide DTAB modification obtained. 2. a preparation method of modified montmorillonite described in claim 1, is characterized in that, the step of described preparation method is as follows: (1) Detect the cation exchange capacity CEC of montmorillonite; (2) Preparation of modified montmorillonite Add water and stir the montmorillonite to disperse evenly, add modifier solution to it, and then adjust the pH of the solution to 6-11; then shake and react at 40-80°C for 4-8 h, after the reaction is completed, let it stand still, and centrifuge , the centrifuged solid is fully dried to obtain an organically modified montmorillonite, which is stored away from light; the addition ratio of the modifier is X ₁ , and the X ₁ = the amount of the modifier in the modifier solution/ (CEC of montmorillonite×mass of montmorillonite)=0.5-2.5; the modifier solution is CTAB solution or DTAB solution. 3. The preparation method according to claim 2, characterized in that, in the 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°C, and the reaction time is 6 h, X ₁ =0.5. 4. The preparation method according to claim 2, characterized in that, in the 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°C, and the reaction time is 6 h, X ₁ =1. 5. preparation method according to claim 2, is characterized in that, described CTAB solution is the CTAB ethanol solution of 10wt%, and DTAB solution is the DTAB aqueous solution of 10wt%. 6. an application of the modified montmorillonite claimed in claim 1 in synergistic restoration of heavy metal and organic pollutant compound polluted soil. 7. The application of the modified montmorillonite obtained by any one of the preparation methods of claims 2-5 in synergistic restoration of heavy metal and organic pollutant compound polluted soil. 8. The application according to claim 7 or 6, wherein the heavy metal is mercury, and the organic pollutant is acetochlor. 9. according to the described application of claim 8, it is characterized in that, the concrete steps of described application are: use described modified montmorillonite in mercury ion and acetochlor composite polluted soil to carry out adsorption reaction, described adsorption The temperature is 20-25 ℃, the adsorption time is 15-20 days, the pH of the soil is 7 during the adsorption, and the water content of the soil is kept at 70% of the saturated water holding capacity of the soil during the adsorption process.

Images