阅读说明：本技术 一种蒙脱石复合材料及其吸附重金属的应用 (Montmorillonite composite material and application thereof in heavy metal adsorption ) 是由 卜红玲 刘承帅 陈曼佳 徐文坡 胡淑捷 雷琴凯 于 2021-09-13 设计创作，主要内容包括：本发明公开了一种蒙脱石复合材料及其吸附重金属的应用。这种蒙脱石复合材料包括蒙脱石和水铁矿；水铁矿分散于蒙脱石的外表面。本发明的蒙脱石复合材料具有较大的BET比表面积,以及多级孔隙结构特征,既保留了蒙脱石的孔结构特点,又具有水铁矿的孔结构特征；带正电荷的水铁矿颗粒与层面带负电荷的蒙脱石颗粒牢固结合,形成稳定的蒙脱石复合材料；该复合材料具有典型的层状结构硅酸盐矿物和水铁矿的结构特征,水铁矿纳米颗粒呈现球形颗粒结构,被蒙脱石片层所包裹。将本发明的蒙脱石复合材料应用到多种重金属的水体或场地土壤环境中,能够有效对环境中的重金属进行有效去除。(The invention discloses a montmorillonite composite material and application thereof in heavy metal adsorption. The montmorillonite composite material comprises montmorillonite and ferrihydrite; the ferrihydrite is dispersed on the outer surface of the montmorillonite. The montmorillonite composite material has larger BET specific surface area and multilevel pore structure characteristics, not only retains the pore structure characteristics of montmorillonite, but also has the pore structure characteristics of ferrihydrite; the ferrihydrite particles with positive charges are firmly combined with the montmorillonite particles with negative charges on the layer surface to form a stable montmorillonite composite material; the composite material has the structural characteristics of typical layered structure silicate minerals and ferrihydrite, and ferrihydrite nanoparticles are in a spherical particle structure and are wrapped by montmorillonite sheets. The montmorillonite composite material is applied to water bodies of various heavy metals or field soil environments, and can effectively remove the heavy metals in the environments.)

1. A montmorillonite composite material, characterized in that the montmorillonite composite material comprises montmorillonite and ferrihydrite; the ferrihydrite is dispersed on the outer surface of the montmorillonite.

2. The montmorillonite composite material as claimed in claim 1, wherein the specific surface area of the montmorillonite composite material is not less than 146.6m²/g。

3. The montmorillonite composite material according to claim 1, wherein the total pore volume of the montmorillonite composite material is not less than 0.156cm³/g。

4. The montmorillonite composite material according to claim 1, wherein the cation exchange capacity of montmorillonite is not less than 90 mmoL/g.

5. The method for producing a montmorillonite composite material as claimed in any one of claims 1 to 4, characterized by comprising the steps of:

1) mixing the iron source solution and the montmorillonite solution to obtain a mixed solution;

2) adding a strong base solution into the mixed solution obtained in the step 1) to obtain a suspension;

3) aging the suspension obtained in the step 2), and coagulating and separating the suspension to obtain the montmorillonite composite material.

6. The method for producing a montmorillonite composite material according to claim 5, wherein the iron source in step 1) is at least one of ferric chloride or ferric nitrate.

7. The method for producing a montmorillonite composite material according to claim 5, wherein the mass ratio of Fe to montmorillonite in the iron source solution in step 1) is (0.5-3): 1.

8. the method for producing a montmorillonite composite material according to claim 5, characterized in that the pH value at which the suspension is obtained in step 2) is 6.5 to 7.5.

9. The method for producing a montmorillonite composite according to claim 5, characterized in that the aging time in step 3) is 3-7 h.

10. Use of the montmorillonite composite of any one of claims 1-4 in adsorbing heavy metals.

Technical Field

The invention relates to the field of mineral materials, in particular to a montmorillonite composite material and application thereof in heavy metal adsorption.

Background

The clay minerals such as montmorillonite and the like have abundant reserves, are cheap and easily available, are environment-friendly and are the predominant non-metallic minerals in China. Montmorillonite materials have special structures and properties such as abundant micropores, higher specific surface area and larger pore volume, and are applied to adsorption and control of toxic substances such as heavy metals and organic pollutants in recent years. Montmorillonite is structurally characterized by two layers of silicon-oxygen tetrahedrons sandwiching a layer of aluminum oxy octahedron. Due to isomorphous substitution (e.g. Al between octahedral layers)³⁺Is coated with Mg²⁺Or Fe²⁺By substitution of Si between tetrahedral layers⁴⁺Is covered with Al³⁺Substitution, etc.) between layers, there is an excess negative charge that attracts Na between montmorillonite layers by electrostatic action⁺And Ca²⁺And electrostatic equilibrium is achieved. Because the active sites of the natural montmorillonite are occupied, the binding force of cations and montmorillonite sheets is weak, and the cations can be exchanged by other cations (including inorganic cations and organic cations), so that the adsorption efficiency is low; and the surface of the montmorillonite is usually electronegative, which makes the montmorillonite have poor adsorption effect on anionic heavy metals.

The modified montmorillonite is a commonly used means at present, and the pore structure, the hydrophilicity and the hydrophobicity and the charge property of the montmorillonite can be changed by modifying the montmorillonite, so that the adsorption and removal effects of the montmorillonite on heavy metals and organic pollutants are obviously influenced. In recent years, modification of montmorillonite mainly includes organic modification and inorganic modification. However, most organic reagents are used in the organic modification process, for example, CN112237901A discloses a preparation method of novel composite modified montmorillonite for treating chromium-containing wastewater, the invented material has higher hexavalent chromium adsorption performance, but the preparation process of the material needs to use toxic and harmful substances such as cetylpyridinium chloride and the like, and secondary pollution is caused to the environment. The inorganic modification method is mainly characterized in that the space between montmorillonite layers is increased through pillaring, the specific surface area is increased, for example, CN111718719A discloses a vulcanized nano zero-valent iron-acid activated montmorillonite composite material, and a preparation method and application thereof. Therefore, a composite material which is simple in preparation process, green, pollution-free and low in price and can realize high-efficiency adsorption of heavy metal ions is needed to be found.

Disclosure of Invention

In order to solve the problems of potential environmental pollution caused by modified montmorillonite and low adsorption efficiency of montmorillonite on heavy metals in the prior art, the invention aims to provide a montmorillonite composite material; the second purpose of the invention is to provide a preparation method of the montmorillonite composite material; the invention also aims to provide the application of the montmorillonite composite material in heavy metal adsorption.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a montmorillonite composite material comprises montmorillonite and ferrihydrite; the ferrihydrite is dispersed on the outer surface of the montmorillonite.

Preferably, the specific surface area of the montmorillonite composite material is more than or equal to 146.6m²(ii)/g; further preferably, the specific surface area of the montmorillonite composite material is 146.6 to 250m²(ii)/g; still further preferably, a montmorillonite composite materialHas a specific surface area of 146.6-230.6m²(ii)/g; the specific surface area is measured by a BET method.

Preferably, the total pore volume of the montmorillonite composite material is more than or equal to 0.156cm³(ii)/g; further preferably, the total pore volume of the montmorillonite composite is 0.156 to 0.210cm³(ii)/g; still further preferably, the total pore volume of the montmorillonite composite is 0.156 to 0.198cm³(ii)/g; the total pore volume is measured using the BET method.

Preferably, the cation exchange capacity of the montmorillonite is more than or equal to 90 mmoL/g; further preferably, the cation exchange capacity of montmorillonite is not less than 110 mmoL/g.

The second aspect of the present invention provides a method for producing the above-mentioned montmorillonite composite material.

A preparation method of the montmorillonite composite material comprises the following steps:

1) mixing the iron source solution and the montmorillonite solution to obtain a mixed solution;

2) adding a strong base solution into the mixed solution obtained in the step 1) to obtain a suspension;

3) aging the suspension obtained in the step 2), coagulating and separating the suspension to obtain the montmorillonite composite material.

Preferably, in the preparation method of the montmorillonite composite material, the montmorillonite in the step 1) is calcium-based montmorillonite; further preferably, the purity of the montmorillonite is more than or equal to 70 percent; still more preferably, the purity of montmorillonite is not less than 85%.

In some preferred embodiments of the present invention, the montmorillonite in step 1) of the method for producing the montmorillonite composite material is selected from the group consisting of calcium montmorillonite.

Preferably, in the preparation method of the montmorillonite composite material, in the step 1), the iron source is at least one of ferric chloride or ferric nitrate; further preferably, the iron source in step 1) is ferric chloride.

Preferably, in the preparation method of the montmorillonite composite material, the mass ratio of Fe in the iron source solution in the step 1) to montmorillonite is (0.5-3): 1; further preferably, the mass ratio of Fe to montmorillonite in the iron source solution in the step 1) is 2: 1.

preferably, in the preparation method of the montmorillonite composite material, the pH value of the suspension obtained in the step 2) is 6.5-7.5; it is further preferred that the suspension obtained in step 2) has a pH of 7.0.

Preferably, in the preparation method of the montmorillonite composite material, the strong alkali solution in the step 2) is at least one of a sodium hydroxide solution, a potassium hydroxide solution and a calcium hydroxide solution; further preferably, the strong alkali solution in the step 2) is at least one of sodium hydroxide solution and potassium hydroxide solution; still more preferably, the strong alkali solution in the step 2) is a sodium hydroxide solution.

Preferably, in the preparation method of the montmorillonite composite material, when the strong alkali solution in the step 2) is a sodium hydroxide solution, the concentration of the sodium hydroxide solution is 0.5-2 mol/L; further preferably, the concentration of the sodium hydroxide solution is 0.8-1.5 mol/L; still more preferably, the concentration of the sodium hydroxide solution is 1 mol/L.

Preferably, in the preparation method of the montmorillonite composite material, when the strong alkali solution in the step 2) is a sodium hydroxide solution, the dropping speed of the sodium hydroxide solution added into the mixed solution obtained in the step 1) is 0.1-12 mL/min; further preferably, the dropping speed of the sodium hydroxide solution added into the mixed solution obtained in the step 1) in the step 2) is 0.1-10 mL/min; when the sodium hydroxide solution is added into the mixed solution obtained in the step 1), the dropping speed is 0.1-0.5mL/min when the pH is close to neutral, and when the pH is close to neutral, the dropping speed of the sodium hydroxide solution is too fast, so that the pH is suddenly increased, and precipitates are generated.

Preferably, in the preparation method of the montmorillonite composite material, the aging time in the step 3) is 3-7 h; further preferably, the aging time in the step 3) is 4-6 h; aging is carried out at room temperature.

Preferably, in the preparation method of the montmorillonite composite material, a sodium hydroxide solution is required to be added dropwise in the aging process of the suspension in the step 3); further preferably, the concentration of the sodium hydroxide solution is 0.5-2 mol/L; further preferably, the concentration of the sodium hydroxide solution is 1 mol/L.

Preferably, in the preparation method of the montmorillonite composite material, the pH value of the suspension is 6.5-7.5 when the suspension is coagulated in the step 3); it is further preferred that the pH of the suspension in step 3) is 7.0 when the suspension coagulates.

Preferably, the preparation method of the montmorillonite composite material, step 3), further comprises the steps of freeze drying and grinding the montmorillonite composite material.

The invention also provides application of the montmorillonite composite material in heavy metal adsorption.

Preferably, the montmorillonite composite material is applied to adsorbing at least one of heavy metals of chromium, cadmium, arsenic, lead, copper, zinc, nickel and mercury; further preferably, the montmorillonite composite material is applied to adsorbing at least one of heavy metals of chromium, cadmium, arsenic and lead; still further preferably, the montmorillonite composite material is applied to adsorbing heavy metals of chromium and cadmium.

The invention also provides a method for adsorbing heavy metal by adopting the montmorillonite composite material, which comprises the following steps:

1) mixing the montmorillonite composite material with heavy metal wastewater, and reacting to obtain a mixed solution;

2) separating the mixed liquor in the step 1) to remove solids, thereby realizing the removal of heavy metals in the wastewater.

Preferably, in the method for adsorbing heavy metals by using the montmorillonite composite material, in the step 1), the heavy metal is at least one of chromium, cadmium, arsenic, lead, copper, zinc, nickel and mercury; further preferably, the heavy metal in the step 1) is at least one of chromium, cadmium, arsenic and lead; still further preferably, the heavy metals in step 1) are chromium and cadmium.

Preferably, in the method for adsorbing heavy metal by using the montmorillonite composite material, the mass ratio of the montmorillonite composite material to the heavy metal in the step 1) is 1: (0.01-0.05); further preferably, the mass ratio of the montmorillonite composite material to the heavy metal in the step 1) is 1: (0.02-0.03); still further preferably, the mass ratio of the montmorillonite composite material to the heavy metal in the step 1) is 1: 0.02.

preferably, in the method for adsorbing heavy metal by using the montmorillonite composite material, the concentration of the heavy metal in the heavy metal wastewater in the step 1) is 10-260 mg/L; further preferably, the concentration of the heavy metal in the heavy metal wastewater in the step 1) is 30-80 mg/L; still more preferably, the heavy metal concentration of the heavy metal in step 1) is 50 mg/L.

Preferably, the method for adsorbing heavy metal by the montmorillonite composite material has the advantages that the reaction time in the step 1) is 5-1440 min; further preferably, the reaction time in step 1) is 10 to 1440 min.

Preferably, the method for adsorbing heavy metal by the montmorillonite composite material is that the reaction in the step 1) is carried out under the condition of oscillation or stirring; further preferably, the reaction in step 1) is carried out under shaking conditions.

Preferably, the method for adsorbing heavy metal by the montmorillonite composite material has the advantages that the pH value of the reaction in the step 1) is 3-6; further preferably, the pH of the reaction in step 1) is 4 to 5.

Preferably, in the method for adsorbing heavy metals by the montmorillonite composite material, the separation mode in the step 2) is one of centrifugation and sedimentation; further preferably, the separation in step 2) is performed by centrifugation.

The invention has the beneficial effects that:

(1) the montmorillonite composite material has larger BET specific surface area and multilevel pore structure characteristics, not only retains the pore structure characteristics of montmorillonite, but also has the pore structure characteristics of ferrihydrite; the ferrihydrite particles with positive charges are firmly combined with the montmorillonite particles with negative charges on the layer surface to form a stable montmorillonite composite material; the composite material has the structural characteristics of typical layered structure silicate minerals and ferrihydrite, and ferrihydrite nanoparticles are in a spherical particle structure and are wrapped by montmorillonite sheets.

(2) The montmorillonite composite material prepared by the invention has higher specific surface area and larger pore volume, and the specific surface area can reach 230.6m²The pore volume can reach 0.198cm³The material has higher adsorption capacity to heavy metals, particularly chromium and cadmium, the pore structure distribution of the obtained material is more orderly, and the development of the microporous structure is favorable for the adsorption of the heavy metals.

(3) According to the invention, by adopting a method for synthesizing ferrihydrite, montmorillonite particles are loaded in the ferrihydrite synthesis process, so that the ferrihydrite-loaded montmorillonite composite material is obtained. The material has the advantages that the structure characteristics of montmorillonite are kept, the structure characteristics of the ferrihydrite are also realized, the modification of the pore structure is realized, and a certain effect is realized on the stability of the ferrihydrite. Due to the change of the charge property and the increase of surface groups of the montmorillonite composite material, the montmorillonite composite material has better adsorption effect on anionic heavy metals (such as Cr (VI)) and cationic heavy metals (such as Cd (II)).

(4) The whole synthesis process flow of the montmorillonite composite material is carried out at normal temperature and normal pressure, the energy consumption is low, the adopted process flow and equipment are simple, the operation is convenient, the preparation period is short, the production process cost is low, and the large-scale production is easy; the montmorillonite is a common non-metal mineral resource, is rich in reserves, cheap and easy to obtain, environment-friendly, and free of byproducts such as waste water, waste gas and waste residue which are difficult to control in the implementation process; the montmorillonite composite material is powdery, can be stored in a sealed manner under a dry condition, does not cause any secondary pollution in the preparation process of the composite material, can avoid secondary pollution to the environment while improving the heavy metal adsorption effect, and can be used for solving the problem of heavy metal pollution of water or soil in China.

(5) The montmorillonite composite material has the advantages of high efficiency, low cost, simple and convenient operation and the like, and can be widely used for treating wastewater and soil in a plurality of fields such as tanning, electroplating, metallurgy, pharmacy, ferrochrome smelting, pigment, chromate chemical industry and the like.

Drawings

FIG. 1 is an XRD pattern of a montmorillonite raw material, ferrihydrite and the montmorillonite composite material prepared in example 3;

FIG. 2 is a scanning electron microscope photograph of the montmorillonite composite material prepared in example 3;

FIG. 3 is an infrared spectrum of a montmorillonite raw material, ferrihydrite and the montmorillonite composite material prepared in example 3;

FIG. 4 is a nitrogen isothermal adsorption-desorption graph of the montmorillonite composite prepared in example 3;

FIG. 5 is a Zeta potential diagram of a montmorillonite raw material and a montmorillonite composite material prepared in example 3;

FIG. 6 is a graph showing the adsorption removal of Cr (VI) by the montmorillonite composites prepared in examples 1-3;

FIG. 7 is a graph showing the adsorption removal of Cd (II) by the montmorillonite composite material prepared in example 3-5;

FIG. 8 is a bar graph of the montmorillonite composite material prepared in example 1 used for adsorbing and removing Cr (VI) in contaminated soil.

Detailed Description

The present invention will be described in further detail with reference to specific examples. The starting materials, reagents or equipment used in the examples are, unless otherwise specified, either conventionally commercially available or may be obtained by methods known in the art. Unless otherwise indicated, the testing or testing methods are conventional in the art.

Example 1

The method for preparing the montmorillonite composite material comprises the following steps:

(1) 1.40g of montmorillonite was added to 250mL of FeCl with a concentration of 0.2mol/L₃And (3) fully stirring the solution, wherein the initial Fe/montmorillonite mass ratio of the obtained mixed solution is 1: 0.5;

(2) dropwise adding 300mL of NaOH solution with the concentration of 1mol/L into the mixed solution obtained in the step (1) at the speed of 0.5mL/min, and continuously stirring until the pH value is 7.0 to obtain precursor suspension of the composite material;

(3) aging the precursor suspension obtained in the step (2) at room temperature for 4h, and adjusting the pH value to 7.0 by using the NaOH solution obtained in the step (2);

(4) and (4) centrifuging the suspension obtained in the step (3) to obtain a reaction product, namely the montmorillonite composite material, and freeze-drying and storing the montmorillonite composite material.

The specific surface area of the montmorillonite composite material prepared in this example was 230.6m measured by the Brunauer-Emmett-Teller (BET) method²(iv)/g, total pore volume 0.183cm³(iii) the specific surface area of micropores of the montmorillonite composite material was 105.7m²Per g, micropore volume of 0.067cm³/g。

Using potassium dichromate (K)₂Cr₂O₇) As a Cr (VI) source, the Cr (VI) concentrations are respectively 10mg/L, 20mg/L, 30mg/L, 40mg/L, 50mg/L, 100mg/L, 140mg/L, 180mg/L, 220mg/L and 260 mg/L. The montmorillonite composite material is tested for Cr (VI) adsorption capacity by an adsorption experiment under the following experimental conditions: the adsorbent content was 2.5g/L, room temperature, pH 4.5. As a result, the saturated adsorption amount of Cr (VI) by the montmorillonite composite material of the present example was 22.6mg/g at room temperature.

Example 2

The method for preparing the montmorillonite composite material comprises the following steps:

(1) 1.87g of montmorillonite was added to 250mL of FeCl with a concentration of 0.2mol/L₃And (3) fully stirring the solution, wherein the initial Fe/montmorillonite mass ratio of the obtained mixed solution is 1.5: 1;

(2) dropwise adding 300mL of NaOH solution with the concentration of 1mol/L into the mixed solution obtained in the step (1) at the speed of 0.5mL/min, and continuously stirring until the pH value is 7.0 to obtain precursor suspension of the composite material;

(3) aging the precursor suspension obtained in the step (2) at room temperature for 4h, and adjusting the pH value to 7.0 by using the NaOH solution obtained in the step (2);

(4) and (4) centrifuging the suspension obtained in the step (3) to obtain a reaction product, namely the montmorillonite composite material, and freeze-drying and storing the montmorillonite composite material.

The specific surface area of the montmorillonite composite prepared in this example was 165.9m measured by the BET method²(ii)/g, total pore volume 0.191cm³/g。

Using potassium dichromate (K)₂Cr₂O₇) As a Cr (VI) source, the Cr (VI) concentrations are respectively 10mg/L, 20mg/L, 30mg/L, 40mg/L, 50mg/L, 100mg/L, 140mg/L, 180mg/L, 220mg/L and 260 mg/L. The montmorillonite composite material is tested for Cr (VI) adsorption capacity by an adsorption experiment under the following experimental conditions: the adsorbent content was 2.5g/L, room temperature, pH 4.5. As a result, the saturated adsorption amount of Cr (VI) by the montmorillonite composite material of the present example was 20.8mg/g at room temperature.

Example 3

The method for preparing the montmorillonite composite material comprises the following steps:

(1) 2.8g of montmorillonite was added to 250mL of FeCl at a concentration of 0.2mol/L₃And (3) fully stirring the solution, wherein the initial Fe/montmorillonite mass ratio of the obtained mixed solution is 1: 1;

(2) dropwise adding 300mL of NaOH solution with the concentration of 1mol/L into the mixed solution obtained in the step (1) at the speed of 0.5mL/min, and continuously stirring until the pH value is 7.0 to obtain precursor suspension of the composite material;

(3) aging the precursor suspension obtained in the step (2) at room temperature for 4h, and adjusting the pH value to 7.0 by using the NaOH solution obtained in the step (2);

(4) and (4) centrifuging the suspension obtained in the step (3) to obtain a reaction product, namely the montmorillonite composite material, and freeze-drying and storing the montmorillonite composite material.

The specific surface area of the montmorillonite composite material prepared in this example was 146.6m measured by the BET method²In terms of/g, total pore volume of 0.156cm³/g。

Using potassium dichromate (K)₂Cr₂O₇) As a Cr (VI) source, the Cr (VI) concentrations are respectively 10mg/L, 20mg/L, 30mg/L, 40mg/L, 50mg/L, 100mg/L, 140mg/L, 180mg/L, 220mg/L and 260 mg/L. The montmorillonite composite material is tested for Cr (VI) adsorption capacity by an adsorption experiment under the following experimental conditions: the adsorbent content was 2.5g/L, room temperature, pH 4.5. As a result, the saturated adsorption amount of Cr (VI) to the montmorillonite composite material of the present example was 17.8mg/g at room temperature.

The XRD pattern of the montmorillonite composite material prepared in this example is shown in figure 1, and the d of montmorillonite in the montmorillonite composite material₀₀₁The value is about 1.29nm, and the pure montmorillonite composite material d₀₀₁The value is about 1.53nm, and the prior art shows that the montmorillonite loads hydroxyl iron ions d₀₀₁The value was 1.50. + -. 0.02nm, indicating that the montmorillonite composite prepared in this example had mainly ferric ions and no hydroxyl iron ions in the interlayer region, and had the structural characteristics of typical layered structure silicate minerals and ferrihydrite.

This exampleThe scanning electron microscope image of the prepared montmorillonite composite material is shown in figure 2, and the ferrihydrite nano-particles are in a spherical particle structure and are wrapped by the montmorillonite in a sheet layer. The infrared spectrogram of the montmorillonite composite material prepared in this example is shown in figure 3, the montmorillonite composite material is a mixed phase of ferrihydrite particles wrapping montmorillonite, and the montmorillonite characteristic group Si-O-Si stretching vibration peak (1033 cm) in the mixed phase^-1) Si-O-Al stretching vibration peak (519 cm)^-1) And Si-O-Si deformation vibration peak (466 cm)^-1) Equal cm^-1And a hydroxyl group of ferrihydrite structure (3395 cm)^-1) Adsorbed water (1618 cm)^-1) And (4) waiting for characteristic peaks. Compared with a pure ferrihydrite material, the montmorillonite composite material has the advantages that the characteristic peak of absorbed water is reduced; compared with a pure montmorillonite material, the montmorillonite composite material has the characteristics of the characteristic peaks of ferrihydrite and montmorillonite, and the vibration peak of the structural hydroxyl group is gradually shifted to a low wave number. This is due to the loading of the weakly crystalline ferrihydrite on the surface, which indicates a tight bond between the two phases.

The nitrogen isothermal adsorption-desorption curve of the montmorillonite composite material prepared in the embodiment is shown in the attached figure 4, and it can be seen that the montmorillonite composite material has an obvious H3 type hysteresis loop, and belongs to an IV (a) type isothermal adsorption curve, which shows that the composite material has obvious mesoporous and microporous characteristics, the pore structure distribution of the obtained montmorillonite composite material is more ordered, and the development of the microporous structure is favorable for heavy metal adsorption. FIG. 5 is a Zeta potential diagram of the montmorillonite composite material and the montmorillonite raw material prepared in example 3, and it can be seen from FIG. 5 that pH is in the range of 2-12, the Zeta potential of the montmorillonite raw material is negative, and therefore, the montmorillonite raw material has a strong electrostatic adsorption effect on cationic heavy metals such as Cd, while for the montmorillonite composite material, the Zeta potential is between ferrihydrite and the montmorillonite raw material and gradually approaches a positive value, indicating that the montmorillonite composite material can adsorb anionic heavy metals.

Example 4

The method for preparing the montmorillonite composite material comprises the following steps:

(1) 4.2g of montmorillonite was added to 250mL of FeCl at a concentration of 0.2mol/L₃Stirring thoroughly in the solution to obtain the initial Fe/montmorillonite mixed solutionThe mass ratio is 1: 1.5;

(2) dropwise adding 300mL of NaOH solution with the concentration of 1mol/L into the mixed solution obtained in the step (1) at the speed of 0.5mL/min, and continuously stirring until the pH value is 7.0 to obtain precursor suspension of the composite material;

(3) aging the precursor suspension obtained in the step (2) at room temperature for 4h, and adjusting the pH value to 7.0 by using the NaOH solution obtained in the step (2);

(4) and (4) centrifuging the suspension obtained in the step (3) to obtain a reaction product, namely the montmorillonite composite material, and freeze-drying and storing the montmorillonite composite material.

The specific surface area of the montmorillonite composite material prepared in this example was 194.3m measured by the BET method²(iv)/g, total pore volume 0.198cm³/g。

Example 5

The method for preparing the montmorillonite composite material comprises the following steps:

(1) 5.6g of montmorillonite was added to 250mL of FeCl at a concentration of 0.2mol/L₃Fully stirring the solution, wherein the initial Fe/montmorillonite mass ratio of the obtained mixed solution is 0.5: 1;

(2) dropwise adding 300mL of NaOH solution with the concentration of 1mol/L into the mixed solution obtained in the step (1) at the speed of 0.5mL/min, and continuously stirring until the pH value is 7.0 to obtain precursor suspension of the composite material;

(3) aging the precursor suspension obtained in the step (2) at room temperature for 4h, and adjusting the pH value to 7.0 by using the NaOH solution obtained in the step (2);

(4) and (4) centrifuging the suspension obtained in the step (3) to obtain a reaction product, namely the montmorillonite composite material, and freeze-drying and storing the montmorillonite composite material.

The specific surface area of the montmorillonite composite prepared in this example was 173.8m measured by the BET method²(ii)/g, total pore volume 0.164cm³/g。

Example 6

The montmorillonite composites prepared in examples 1-3 were subjected to Cr (VI) adsorption experiments.

The specific steps of adsorbing and removing Cr (VI) by the montmorillonite composite material are as follows:

(1) with potassium dichromate (K)₂Cr₂O₇) 300mL of simulated wastewater with a Cr (VI) concentration of 50mg/L and a pH of 4.5 is prepared as a Cr (VI) source.

(2) Weighing 0.10g of the montmorillonite composite material obtained in the examples 1-3, adding the montmorillonite composite material into a 50mL centrifuge tube, adding 40mL of Cr (VI) solution with the initial concentration of 50mg/L, and determining the number of reaction centrifuge tubes to be arranged according to the number of samples and repeated samples;

(3) placing the mixed reaction solution on a horizontal oscillator for oscillation at room temperature;

(4) taking out reaction samples for centrifugation after the reactions are carried out for 5, 10, 60, 180, 360, 720 and 1440min respectively; after the supernatant is diluted by a proper amount, the concentration of heavy metal Cr (VI) ions in the solution is measured by adopting inductively coupled plasma emission spectrometry (ICP-OES), and the removal rate of Cr (VI) in different time is calculated according to the concentration of Cr (VI) ions in the solution before and after adsorption.

FIG. 6 is a graph of the change in Cr (VI) removal rate at different time points. As can be seen from FIG. 6, all three montmorillonite composites can adsorb and remove Cr (VI) in a short time. The Cr (VI) removal rate of Fhy-Mnt-1:0.5 (the mass ratio of Fe/montmorillonite is 1: 0.5) samples in the solution is the highest; at 1440min, the removal rate of Cr (VI) of the montmorillonite composite material prepared by the method 1 reaches 86.3%, the removal rate of Cr (VI) of the montmorillonite composite material prepared by the method 2(Fhy-Mnt-1.5:1) reaches 76.2%, and the removal rate of Cr (VI) of the montmorillonite composite material prepared by the method 3(Fhy-Mnt-1:1) reaches 60.1%.

Example 7

The montmorillonite composites prepared in examples 3-5 were subjected to Cd (II) adsorption experiments.

The method comprises the following steps of (II) adsorbing and removing Cd by the montmorillonite composite material:

(1) cadmium nitrate (Cd (NO)₃)₂) 300mL of simulated wastewater with a Cd (II) concentration of 50mg/L and a pH of about 4.5 was prepared as a source of Cd (II).

(2) Weighing 0.10g of montmorillonite composite material, adding the montmorillonite composite material into a 50mL centrifuge tube, adding 40mL of Cd (II) solution with the initial concentration of 50mg/L, and determining the number of reaction centrifuge tubes to be arranged according to the number of samples and repeated samples;

(3) placing the mixed reaction solution on a horizontal oscillator for oscillation at room temperature;

(4) after the reaction is carried out for 10 min, 30 min, 60 min, 180 min, 360 min, 960 min and 1440min, three reaction samples are respectively taken out and centrifuged; and (3) after the supernatant is diluted by a proper multiple, determining the concentration of Cd (II) ions in the solution by adopting ICP-OES, and calculating the removal rate of Cd (II) in different time according to the concentration of Cd (II) in the solution before and after adsorption.

FIG. 7 is a graph of the removal rate of Cd (II) at different time points. As can be seen from FIG. 7, all three montmorillonite composites can adsorb and remove Cd (II) in a short time. The removal rate of Cd (II) of Fhy-Mnt-1:1.5 (the mass ratio of Fe to montmorillonite is 1: 1.5) samples in the solution is the highest; at 1440min, the removal rate of Cd (II) of the montmorillonite composite material reaches 68.5%, Fhy-Mnt-0.5:1 (the mass ratio of Fe to montmorillonite is 0.5:1) the removal rate of Cd (II) of the montmorillonite composite material reaches 60.7%, and the removal rate of Cd (II) of the Fhy-Mnt-1:1 (the mass ratio of Fe to montmorillonite is 1:1) of the montmorillonite composite material reaches 55.1%.

Example 8

The montmorillonite composite material prepared in example 1 was used for adsorbing and removing Cr (VI) in contaminated soil, and experimental soil used in this example was soil from Taishan city and county of Taishan city of Guangdong province.

(1) Preparing soil suspension according to the water-soil mass ratio of 10:1, wherein the content of Cr (VI) in the obtained soil suspension is 50 mg/L;

(2) adding the montmorillonite composite material prepared in the example 1 into the soil suspension obtained in the step (1), adding the montmorillonite composite material according to the mass ratio of the montmorillonite composite material to the soil of 1:40, and setting contrast treatment without the montmorillonite composite material;

(3) the mixed reaction system is placed on a horizontal oscillator for 24 hours under the condition of room temperature. After the reaction, the supernatant was diluted by an appropriate factor, and the concentration of Cr (VI) ions in the solution was measured by inductively coupled plasma emission spectrometry (ICP-OES).

FIG. 8 is a graph showing the removal rate of Cr (VI) adsorbed on the soil from the montmorillonite composite, and it can be seen from the content of Cr (VI) in the soil before and after the treatment with the montmorillonite composite that the removal rate of Cr (VI) in the soil after the treatment with the montmorillonite composite is 30.5% higher than that of the control without the montmorillonite composite. From the above results, it is understood that the montmorillonite composite material of the present invention can effectively reduce the content of cr (vi) in soil.

The foregoing is merely a preferred embodiment of the present invention, and it should be noted that the above-described preferred embodiment should not be construed as limiting the present invention. It will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the spirit and scope of the invention, and these modifications and adaptations should be considered within the scope of the invention.