CN107350283B - Method for repairing heavy metal soil by using magnesium silicate-hydrothermal carbon composite material - Google Patents
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- B—PERFORMING OPERATIONS; TRANSPORTING
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Abstract
The invention discloses a method for repairing heavy metal soil by using a magnesium silicate-hydrothermal carbon composite material, which comprises the following steps: fully mixing the magnesium silicate-hydrothermal carbon composite material with the heavy metal contaminated soil, and reacting the magnesium silicate-hydrothermal carbon composite material with the heavy metal in the soil to form a stable chemical form of the heavy metal, thereby completing the restoration of the heavy metal soil; the magnesium silicate-hydrothermal carbon composite material comprises massive porous magnesium silicate and spherical porous hydrothermal carbon, and the hydrothermal carbon is loaded on the surface and in pores of the magnesium silicate. The method has the advantages of low cost, simplicity, high efficiency, environmental friendliness and the like, and has good repairing effect on the soil polluted by single cadmium and the soil polluted by composite heavy metal.
Description
Technical Field
The invention belongs to the technical field of heavy metal soil remediation, and particularly relates to a method for remediating heavy metal soil by using a magnesium silicate-hydrothermal carbon composite material.
Background
The heavy metal pollution of soil is one of the most extensive and most harmful environmental problems in the current environmental pollution. Heavy metals in soil are of great concern because of their poor mobility, long persistence, and the inability to be easily degraded. According to the national soil pollution state survey bulletin published by the ministry of environmental protection and the ministry of national soil resources 2014: the soil environment conditions of the whole country are not optimistic, the soil pollution of partial regions is serious, the quality of the cultivated land soil environment is great, and the soil environment problem of industrial and mining abandoned lands is prominent. The artificial activities of the industrial and mining industry, the agriculture and the like and the high background value of the soil environment are main causes of soil pollution or exceeding standards. The total overproof rate of the national soil is 16.1 percent, wherein the proportion of slightly, moderately and severely polluted points is 11.2 percent, 2.3 percent, 1.5 percent and 1.1 percent respectively.
The repair technology of heavy metal contaminated soil is mainly divided into in-situ repair and ex-situ repair. The in-situ repair mode mainly comprises a physical technology, a chemical technology and a biological repair technology. The physical technology comprises a soil dressing and soil turning method, heat treatment separation, electrokinetic repair, isolation embedding and the like. Chemical techniques include chemical fixation, chemical leaching, chemical redox, and the like. Bioremediation techniques include phytoremediation, microbial remediation, animal remediation, and the like. The bioremediation method generally has the problems of low remediation efficiency, high treatment cost and the like. The traditional physical repair methods such as landfill, physical leaching, soil turning repair and the like have large engineering quantity and high cost, and often cause the damage of the soil structure and the loss of certain nutrient elements. The chemical fixation method is emphasized due to the characteristics of simple operation, low investment and the like, and the conventional soil remediation agents such as lime and biochar compost have certain problems, such as large dosage, certain influence such as agglomeration and the like on the physical properties of soil caused by long-term use of lime, reduction of the overall fertility level, easy decomposition of compost in the soil and weak remediation effect on heavy metals. Therefore, the key for improving the method lies in developing a more efficient, environment-friendly and low-cost soil chemical fixation repairing agent.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a method for repairing heavy metal soil by using a magnesium silicate-hydrothermal carbon composite material, which is low in cost, simple, efficient and environment-friendly.
In order to solve the technical problems, the invention adopts the following technical scheme:
a method for repairing heavy metal soil by using a magnesium silicate-hydrothermal carbon composite material comprises the following steps:
fully mixing the magnesium silicate-hydrothermal carbon composite material with the heavy metal contaminated soil, and reacting the magnesium silicate-hydrothermal carbon composite material with the heavy metal in the soil to form a stable chemical form of the heavy metal, thereby completing the restoration of the heavy metal soil; the magnesium silicate-hydrothermal carbon composite material comprises massive porous magnesium silicate and spherical porous hydrothermal carbon, and the hydrothermal carbon is loaded on the surface and in pores of the magnesium silicate.
Preferably, the average particle size of the hydrothermal carbon is 500 nm-1000 nm, and the hydrothermal carbon loading is 20% -80% of the mass of the magnesium silicate-hydrothermal carbon composite material.
In the method for repairing heavy metal soil by using the magnesium silicate-hydrothermal carbon composite material, preferably, the addition amount of the magnesium silicate-hydrothermal carbon composite material relative to the heavy metal contaminated soil is 1 wt% -10 wt%; the repair time is 7-90 days.
In the method for repairing heavy metal soil by using the magnesium silicate-hydrothermal carbon composite material, the water content of the soil is preferably maintained at 50-80% of the maximum water holding capacity during the repairing period.
In the method for repairing heavy metal soil by using the magnesium silicate-hydrothermal carbon composite material, preferably, the heavy metal comprises cadmium, zinc, copper and/or lead.
In the method for repairing heavy metal soil by using the magnesium silicate-hydrothermal carbon composite material, preferably, the magnesium silicate-hydrothermal carbon composite material is prepared by the following steps:
(1) ultrasonically dispersing magnesium silicate into water to obtain a magnesium silicate dispersion liquid;
(2) adding a carbon source and an organic acid into the magnesium silicate dispersion liquid obtained in the step (1), carrying out hydrothermal reaction, and filtering after the reaction is finished to obtain a precipitate product;
(3) and (3) adding the precipitation product obtained in the step (2) into alkali liquor to get through the pore channel blocked by the hydrothermal carbon, and filtering to obtain the magnesium silicate-hydrothermal carbon composite material.
In the method for remediating heavy metal soil by using a magnesium silicate-hydrothermal carbon composite material, in the step (2), the organic acid preferably includes acrylic acid or vinyl imidazole. The carbon source comprises glucose, cellulose, starch, sucrose, cyclodextrin, fructose or maltose.
Preferably, in the step (2), when the carbon source is glucose and the organic acid is acrylic acid, the mass ratio of the magnesium silicate to the glucose to the acrylic acid is 1: 2-4: 0.2-0.4.
Preferably, the temperature of the hydrothermal reaction is 160-220 ℃ and the time is 16-24 hours.
In the method for repairing heavy metal soil by using magnesium silicate-hydrothermal carbon composite material, preferably, in the step (3), the concentration of OH-in the alkali liquor is 0.5-1M.
In the method for repairing heavy metal soil by using the magnesium silicate-hydrothermal carbon composite material, preferably, in the step (1), the magnesium silicate is prepared by the following method: dropwise adding a magnesium sulfate solution into a sodium silicate solution, and magnetically stirring for 0.5-4 hours to obtain a mixed solution, wherein the mass ratio of magnesium silicate to sodium sulfate is 4.5: 5-1: 1; and transferring the obtained mixed solution into a hydrothermal reaction kettle for hydrothermal synthesis reaction at the hydrothermal temperature of 110-220 ℃ for 12-24 h, and filtering after the reaction is finished to obtain the magnesium silicate.
Compared with the prior art, the invention has the advantages that:
1. the invention utilizes the magnesium silicate-hydrothermal carbon composite material to repair heavy metal soil, the microstructure of the magnesium silicate-hydrothermal carbon composite material is that spherical porous hydrothermal carbon is loaded on the surface and in pores of blocky porous magnesium silicate, particles of the magnesium silicate are irregular blocky under larger magnification, the magnesium silicate is dispersed uniformly, fluffy and porous, and the gaps among particles are larger, thus being beneficial to adsorption. In addition, the surface of the silicon-magnesium adhesive has two groups of silicon hydroxyl (Si-OH) and magnesium oxyl (Mg-O), the adsorption capacity is far greater than that of natural minerals, and functional groups (such as hydroxyl, carboxyl and the like) on the surface of hydrothermal carbon are beneficial to carrying out chelation reaction with the silicon hydroxyl and the magnesium oxyl, so that the loading capacity (the loading calculated value is more than 80%) of the hydrothermal carbon on the surface of the magnesium silicate is improved, the hydrothermal carbon and the magnesium silicate are firmly combined, and the stability of the magnesium silicate-hydrothermal carbon composite material is improved. The hydrothermal carbon microstructure is spherical and porous, has few closed pores caused by the blockage of amorphous carbon, has rich pore structure and high specific surface area, and thus has excellent adsorption performance. In conclusion, the magnesium silicate-hydrothermal carbon composite material has strong adsorption capacity on heavy metals. In addition, the magnesium silicate-hydrothermal carbon composite material has negative charges on the surface, and can fix the heavy metal with positive charges on the surface of the material through electrostatic attraction. The hydroxyl functional group and magnesium ion on the surface of the material can also react with heavy metals such as cadmium, zinc, copper, lead and the like in soil through ion exchange, so that the heavy metals form stable chemical forms and are fixed on the surface of the material. Prevent the environmental migration and diffusion of the heavy metal and reduce the toxic degree of the heavy metal in the environment. Therefore, the magnesium silicate-hydrothermal carbon composite material can effectively adsorb and fix the ionic heavy metal in the soil and reduce the toxic action of the ionic heavy metal.
2. Besides strong heavy metal adsorption regulation capacity, the magnesium silicate-hydrothermal carbon composite material can also play a role in improving the physicochemical properties of soil after being applied to the soil, such as increasing the pH value of the soil, increasing the water-soluble carbon content of the soil and the like. This is because: the magnesium silicate-hydrothermal carbon composite material is alkaline, so that the acid value of part of soil can be neutralized after the magnesium silicate-hydrothermal carbon composite material enters the soil, meanwhile, Na, Mg and other ions in the composite material can be dissolved out to improve the salt base saturation of the soil, and the levels of exchangeable hydrogen ions and exchangeable aluminum ions of the soil are reduced through the absorption effect. To raise the soil pH. The material contains partial water-soluble carbon, and the partial water-soluble carbon is dissolved out after the material is applied into soil, so that the content of the water-soluble carbon is increased. Meanwhile, hydrothermal carbon on the surface of the material is likely to be slowly decomposed by microorganisms, and the content of water-soluble carbon in soil is increased.
3. The magnesium silicate-hydrothermal carbon composite material mainly comprises magnesium silicate and hydrothermal carbon, which are nontoxic, green, low-cost and environment-friendly materials, and can not bring toxic action to the soil environment after being applied to soil. And the repair cost is low.
4. According to the invention, the magnesium silicate-hydrothermal carbon composite material is prepared by adopting a hydrothermal synthesis method, and the addition of acrylic acid can generate cycloaddition with the hydrothermal carbon composite material in the hydrothermal carbon forming process to form more conjugation, so that more adsorption effective sites are increased. Subsequently, alkali is added for activation, so that hydroxide ions react with carbon atoms in the hydrothermal carbon, closed pores caused by blockage of the hydrothermal carbon during hydrothermal carbonization can be opened, original pores are enlarged, the specific surface area is increased, and a rich pore structure is formed.
5. The control of the mass ratio of silicon to magnesium and the hydrothermal temperature have a great influence on the morphological characteristics of magnesium silicate. The invention preferably prepares the magnesium silicate by a hydrothermal synthesis method, the hydrothermal temperature is controlled at 160-220 ℃ and the time is controlled at 16-24 h under the condition that the silicon-magnesium ratio is 4.5: 5-1: 1, so that the fluffy and porous irregular blocky magnesium silicate is synthesized, and the specific surface is up to 417.26m2The adsorption capacity of the magnesium silicate is far better than that of other clay minerals or magnesium silicates in other shapes.
Drawings
FIG. 1 is a transmission electron micrograph of magnesium silicate prepared in step (a).
FIG. 2 is a scanning electron microscope image of a magnesium silicate-hydrothermal carbon composite material used in an embodiment of the present invention.
FIG. 3 is a transmission electron micrograph of a magnesium silicate-hydrothermal carbon composite used in an example of the present invention.
FIG. 4 is a Fourier infrared spectrum of a magnesium silicate-hydrothermal carbon composite used in an embodiment of the present invention.
FIG. 5 is a comparison graph of the content of cadmium in soil in an extracted state after the cadmium-contaminated soil is repaired by magnesium silicate-hydrothermal carbon composite materials with different addition amounts.
FIG. 6 is a comparison graph of the content of heavy metals in the soil in an extracted state after the magnesium silicate-hydrothermal carbon composite materials with different addition amounts are used for repairing the soil polluted by the composite heavy metals.
FIG. 7 is a graph showing the comparison of the pH value of soil after cadmium-contaminated soil is repaired by magnesium silicate-hydrothermal carbon composite materials with different addition amounts.
FIG. 8 is a comparison graph of pH changes of soil after composite heavy metal contaminated soil is repaired by magnesium silicate-hydrothermal carbon composite materials with different addition amounts.
Detailed Description
The invention is further described below with reference to the drawings and specific preferred embodiments of the description, without thereby limiting the scope of protection of the invention.
The magnesium silicate-hydrothermal carbon composite material used in the following examples was prepared by the following method:
(a) 4.5g of sodium silicate is dissolved in 20ml of water to obtain a sodium silicate solution; dissolving 5g of magnesium sulfate in 15ml of water to obtain a sodium silicate solution, slowly dropwise adding the obtained magnesium sulfate solution into the sodium silicate solution, and magnetically stirring the solution for lh after the dropwise adding is finished to obtain a mixed solution. And transferring the obtained mixed solution into a hydrothermal reaction kettle for hydrothermal synthesis reaction at the hydrothermal temperature of 180 ℃ for 24 hours, filtering after the reaction is finished, washing for three times with water, centrifuging, and drying at the temperature of 60 ℃ for 12 hours to obtain the magnesium silicate. Weighing 1000mg of magnesium silicate, and ultrasonically dispersing the magnesium silicate into 35ml of deionized water to obtain a magnesium silicate dispersion liquid;
FIG. 1 is a TEM image of the magnesium silicate obtained in step (a), from which it can be seen that the microstructure of magnesium silicate is a fluffy and porous block.
(b) Adding 4000mg of glucose and 400mg of acrylic acid into the magnesium silicate dispersion liquid obtained in the step (a), uniformly mixing, carrying out ultrasonic reaction at 25-45 ℃ for 0.5h to dissolve the glucose, fully and uniformly mixing the acrylic acid, the glucose and the magnesium silicate, transferring into a hydrothermal synthesis kettle, carrying out hydrothermal reaction at 180 ℃ for 24h, filtering after the reaction is finished, washing and drying to obtain a precipitate product;
(c) adding the precipitation product obtained in the step (b) into 0.1M sodium hydroxide solution, and stirring for 1h to open the pore channel blocked by the hydrothermal carbon and increase the specific surface area of the hydrothermal carbon. Filtering after the completion, washing with water and absolute ethyl alcohol in sequence, centrifuging, and finally drying at 60 ℃ for 12h to obtain the magnesium silicate-hydrothermal carbon composite material.
Fig. 2 is an SEM image of the obtained magnesium silicate-hydrothermal carbon composite material, and fig. 3 is a TEM image of the obtained magnesium silicate-hydrothermal carbon composite material, from which it can be seen that the overall microstructure of the magnesium silicate-hydrothermal carbon composite material is a black-gray fluffy porous block, and the spherical hydrothermal carbon is successfully supported on the surface and in the pores of the block porous magnesium silicate and is chemically bonded with the magnesium silicate. Wherein the particle size of the hydrothermal carbon is 500-1000 nm.
FIG. 4 is a Fourier infrared spectrum of the obtained magnesium silicate-hydrothermal carbon composite material, and it can be seen that the composite material has a larger number of oxygen-containing functional groups, such as hydroxyl and carboxyl, compared with magnesium silicate monomers.
The thermogravimetric analysis of the magnesium silicate-hydrothermal carbon composite is shown in fig. 5. The loading of the hydrothermal carbon was calculated as follows: the weight loss of magnesium silicate-hydrothermal carbon is about 45% at 200-800 deg.C, including the weight loss of magnesium silicate in this temperature range, such as volatilization of water of hydration (about 8%), and the weight loss due to hydrothermal carbon oxidation. Therefore, the carbon-loading amount of the material is the weight loss of magnesium silicate-hydrothermal carbon, and the load calculation result is 37%.
Example 1:
the invention relates to a method for repairing cadmium contaminated soil by using a magnesium silicate-hydrothermal carbon composite material, which comprises the following steps:
(1) preparing cadmium-polluted soil: the test soil is collected from the Yuenu mountain of the lake south, cadmium-contaminated soil is prepared by a method of artificially adding a cadmium solution, and the cadmium-contaminated soil is cultured at a constant temperature of 25 ℃ for two months, so that the cadmium form tends to be stable. The total cadmium content in the soil is measured to be 8.4mg/kg by a graphite furnace digestion method. Soil remediation experiments were subsequently performed.
(2) Repairing cadmium-polluted soil: preparing four groups of cadmium-polluted soil with the same weight after being stabilized in the step (1), wherein magnesium silicate-hydrothermal carbon composite materials accounting for 1% of the weight of the cadmium-polluted soil are added into the first group and are uniformly mixed; adding magnesium silicate-hydrothermal carbon composite material accounting for 3 percent of the weight of the cadmium-polluted soil into the second group, and uniformly mixing; adding magnesium silicate-hydrothermal carbon composite material accounting for 5wt% of cadmium-polluted soil into the third group, and uniformly mixing; the fourth group did not add any repairing agent and served as a blank control group. And (3) respectively supplementing water to the four groups of cadmium-polluted soil by using deionized water, so that the water content of the cadmium-polluted soil is kept to be about 60% of the maximum field water capacity. After 7 days of stabilization, 0.01M calcium chloride is used as an extractant to respectively extract heavy metals, CaCl and the like in four groups of cadmium-polluted soil2The leaching method can better reflect the bioavailability of the heavy metal Cd in the soil. And measuring the cadmium content by an inductively coupled plasma emission spectrometer (ICP-OES). The results are shown in fig. 5, and the soil remediation effect is shown by the fixation rate of cadmium. Immobilization rate as treatment group heavy metalsContent/blank heavy metal content, results are shown in table 1.
TABLE 1 comparison table of the fixation effect of magnesium silicate-hydrothermal carbon composite material with different addition amounts on cadmium in soil after restoration
| |
1 |
3 |
5% addition ratio |
| Fixation ratio (%) of cadmium | 15.80 | 61.70 | 86.74 |
As can be seen from FIG. 5, CaCl in the soil added with the repairing agent2The cadmium in the extracted state is obviously reduced, the cadmium content in the extracted state is reduced along with the increase of the addition amount of the composite material, and the optimal dosage is 5 percent, which shows that the magnesium silicate-hydrothermal carbon composite material can effectively reduce the bioavailability of the cadmium in the soil, reduce the toxic action of the cadmium on animals and plants, and improve the soil quality. As shown in Table 1, the repairing effect reached 86% or more when the material addition amount was 5% after 7 days of repair. The repairing agent can achieve good repairing effect in a short time. Therefore, the composite material can be applied to the remediation and treatment of the cadmium-polluted soil.
Example 2:
the invention relates to a method for repairing composite heavy metal contaminated soil by using a magnesium silicate-hydrothermal carbon composite material, which comprises the following steps:
(1) collecting the composite heavy metal contaminated soil: the composite heavy metal contaminated soil is collected from a lead-zinc mine contaminated area in Chenzhou, Hunan, and the lead content is determined to reach 155 mg/kg; the zinc content reaches 531.5 mg/kg; the copper content was 113 mg/kg. The content of lead, zinc and copper in the soil surface layer of the area is about two times of the soil environment quality standard of China.
(2) Repairing the composite heavy metal contaminated soil: preparing four groups of composite heavy metal contaminated soil in the step (1) with the same weight, wherein a magnesium silicate-hydrothermal carbon composite material accounting for 1% of the weight of the composite heavy metal contaminated soil is added into the first group, and the materials are uniformly mixed; adding magnesium silicate-hydrothermal carbon composite material accounting for 3% of the weight of the composite heavy metal contaminated soil into the second group, and uniformly mixing; adding magnesium silicate-hydrothermal carbon composite material accounting for 5wt% of the composite heavy metal contaminated soil into the third group, and uniformly mixing; the fourth group did not add any repairing agent and served as a blank control group. And (3) respectively supplementing water to the four groups of compound heavy metal contaminated soil by using deionized water, so that the water content of the compound heavy metal contaminated soil is kept at about 60% of the maximum field water capacity. After 60 days of stabilization, the content of heavy metals in an acid-soluble state in the soil polluted by the compound heavy metals is measured by a TCLP method. And detected by inductively coupled plasma emission spectroscopy (ICP-OES). The results are shown in FIG. 6. The immobilization rate of each heavy metal is shown in table 2.
TABLE 2 comparison table of the fixation effect of magnesium silicate-hydrothermal carbon composite material with different addition amounts on each heavy metal in soil after restoration
| |
1 |
3 |
5% addition ratio |
| Fixation ratio (%) of copper | 22.32 | 55.35 | 73.21 |
| Fixation ratio of lead (%) | 3.62 | 29.30 | 53.32 |
| Fixation ratio (%) of Zinc | 10.75 | 20.28 | 32.97 |
As can be seen from FIG. 6, the contents of copper, lead and zinc, which are heavy metals in an acid extraction state, in the repaired soil are all reduced with the increase of the addition amount of the magnesium silicate-hydrothermal carbon composite material, and the optimal dosage is 5%, which shows that the magnesium silicate-hydrothermal carbon composite material can effectively and simultaneously fix a plurality of heavy metals, reduce the bioavailability, reduce the toxicity to animals and plants and improve the soil quality. As can be seen from Table 2, the magnesium silicate-hydrothermal carbon composite material has a copper repairing effect of more than 73% and a lead repairing effect of more than 53%. Meanwhile, the zinc-zinc alloy has a repairing effect of more than 32%. The material can be applied to the remediation of the soil polluted by the composite heavy metal, in particular to the soil polluted by the copper and lead composite.
Example 3: research of magnesium silicate-hydrothermal carbon composite material on soil restoration physicochemical property
Preparing three groups of cadmium-polluted soil stabilized in the step (1) of the example 1 with the same weight, wherein magnesium silicate-hydrothermal carbon composite materials accounting for 1 percent of the weight of the cadmium-polluted soil are added into the first group, and the materials are uniformly mixed; adding magnesium silicate-hydrothermal carbon composite material accounting for 3 percent of the weight of the cadmium-polluted soil into the second group, and uniformly mixing; and adding a magnesium silicate-hydrothermal carbon composite material accounting for 5 percent of the weight of the cadmium-polluted soil into the third group, and uniformly mixing. And (3) respectively supplementing water to the three groups of cadmium-polluted soil by using deionized water, so that the water content of the cadmium-polluted soil is kept to be about 60% of the maximum field water capacity. After 30 days of stabilization, the water-soluble organic carbon content was extracted with water as a solvent and measured with a TOC instrument, and the results are shown in Table 3. The pH of the soil was measured by a pH meter, and the results are shown in fig. 7.
Preparing three groups of composite heavy metal contaminated soil of the step (1) in the embodiment 2 with the same weight, wherein magnesium silicate-hydrothermal carbon composite material accounting for 1 percent of the weight of the composite heavy metal contaminated soil is added into the first group, and the materials are uniformly mixed; adding magnesium silicate-hydrothermal carbon composite material accounting for 3% of the weight of the composite heavy metal contaminated soil into the second group, and uniformly mixing; and adding a magnesium silicate-hydrothermal carbon composite material accounting for 5 percent of the weight of the composite heavy metal contaminated soil into the third group, and uniformly mixing. And (3) respectively supplementing water to the three groups of compound heavy metal contaminated soil by using deionized water, so that the water content of the compound heavy metal contaminated soil is kept to be about 60% of the maximum field water capacity. After 30 days of stabilization, the water-soluble organic carbon content was extracted with water as a solvent and measured with a TOC instrument, and the results are shown in Table 3. The pH of the soil was measured by a pH meter, and the results are shown in fig. 8.
TABLE 3 Water-soluble carbon content in soil contaminated by single cadmium and composite heavy metals after magnesium silicate-hydrothermal carbon composite addition
As can be seen from fig. 7 and 8, the pH of the soil changed after the magnesium silicate-hydrothermal carbon composite material was added, and the pH of both acidic soils increased with the addition of the material. The material can improve the pH value of the soil, the increase of the pH value of the soil is beneficial to the fixation of heavy metal in the soil, and the content of part of exchangeable heavy metal ions can be reduced. As can be seen from Table 3, the addition of the material not only increases the pH value of the soil, but also increases the content of water-soluble carbon in the soil, which indicates that the addition of the magnesium silicate-hydrothermal carbon composite material also has certain influence on the physicochemical properties of the soil, and can improve the soil quality.
The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-described embodiments. All technical schemes belonging to the idea of the invention belong to the protection scope of the invention. It should be noted that modifications and embellishments within the scope of the invention may be made by those skilled in the art without departing from the principle of the invention, and such modifications and embellishments should also be considered as within the scope of the invention.
Claims (6)
1. A method for repairing heavy metal soil by using a magnesium silicate-hydrothermal carbon composite material comprises the following steps:
fully mixing the magnesium silicate-hydrothermal carbon composite material with the heavy metal contaminated soil, and reacting the magnesium silicate-hydrothermal carbon composite material with the heavy metal in the soil to form a stable chemical form of the heavy metal, thereby completing the restoration of the heavy metal soil; the magnesium silicate-hydrothermal carbon composite material comprises blocky porous magnesium silicate and spherical porous hydrothermal carbon, wherein the hydrothermal carbon is loaded on the surface and in pores of the magnesium silicate, the average particle size of the hydrothermal carbon is 500-1000 nm, and the hydrothermal carbon loading is 20-80% of the mass of the magnesium silicate-hydrothermal carbon composite material; the addition amount of the magnesium silicate-hydrothermal carbon composite material relative to the heavy metal contaminated soil is 5-10 wt%;
the magnesium silicate-hydrothermal carbon composite material is prepared by the following method:
(1) ultrasonically dispersing magnesium silicate into water to obtain a magnesium silicate dispersion liquid; the magnesium silicate is prepared by the following method: dropwise adding a magnesium sulfate solution into a sodium silicate solution, and magnetically stirring for 0.5-4 hours to obtain a mixed solution, wherein the mass ratio of sodium silicate to magnesium sulfate is 4.5: 5-1: 1; transferring the obtained mixed solution into a hydrothermal reaction kettle for hydrothermal synthesis reaction at 180 ℃ for 24 hours, and filtering after the reaction is finished to obtain magnesium silicate;
(2) adding a carbon source and an organic acid into the magnesium silicate dispersion liquid obtained in the step (1), carrying out hydrothermal reaction, and filtering after the reaction is finished to obtain a precipitate product; the organic acid is acrylic acid; the carbon source is glucose; the mass ratio of the magnesium silicate to the glucose to the acrylic acid is 1: 2-4: 0.2-0.4;
(3) and (3) adding the precipitation product obtained in the step (2) into alkali liquor to get through the pore channel blocked by the hydrothermal carbon, and filtering to obtain the magnesium silicate-hydrothermal carbon composite material.
2. The method for repairing heavy metal soil by using the magnesium silicate-hydrothermal carbon composite material as claimed in claim 1, wherein the repairing time is 7-90 days.
3. The method for remediating heavy metal soil using a magnesium silicate-hydrothermal carbon composite as claimed in claim 1, wherein the water content of the soil is maintained at 50% to 80% of the maximum water holding capacity during remediation.
4. The method for remediating heavy metal soil using a magnesium silicate-hydrothermal carbon composite as claimed in claim 1, wherein the heavy metal comprises cadmium, zinc, copper and/or lead.
5. The method for remediating heavy metal soil by using the magnesium silicate-hydrothermal carbon composite material as claimed in claim 1, wherein in the step (2), the temperature of the hydrothermal reaction is 160-220 ℃ and the time is 16-24 h.
6. The method for remediating heavy metal soil using magnesium silicate-hydrothermal carbon composite as claimed in claim 1, wherein in the step (3), OH in the lye-The concentration of (B) is 0.5M to 1M.
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