Preparation method of soil heavy metal chelating agent

Abstract

The invention discloses a soil heavy metal chelating agent, the chelating agent comprises a chelating agent I and a chelating agent II, the chelating agent I is composed of fly ash and domestic sludge, and the chelating agent II is a modified sodium alginate compound; the mass ratio of the chelating agent I to the chelating agent II is (15-20): (3-5). According to the invention, the chelating agent I is composed of the fly ash and the domestic sludge, the modified sodium alginate compound is used as the chelating agent II, and the two chelating agents are cooperatively used in the soil reclamation of the strip mine dump, so that a series of environmental problems caused by mining activities can be effectively improved, and the reasonable utilization of land resources is promoted.

Description

Technical Field

[0001] The invention belongs to the technical field of soil remediation, and in particular, relates to a method for preparing a soil heavy metal chelating agent. Background Art

[0002] In recent years, the proportion of open-pit mines in my country's coal mines has continued to increase and has achieved considerable development. As one of the important forms of coal production, open-pit mining has the advantages of low production cost, high safety performance, and high resource utilization, providing a large amount of basic materials for the rapid development of the economy and society. The Zhundong open-pit coal mine is located in an ecologically fragile area with severe soil erosion and land desertification. The large-scale and high-intensity development of coal resources has damaged the regional ecological environment and land resources.

[0003] The open-pit mining of coal resources has gradually increased the number of spoil dumps and occupied a large amount of land resources. The main problem faced in the reclamation of spoil dumps is the shortage of surface soil resources or the barrenness of the covering soil. In the process of regional ecological restoration, foreign soil is generally selected to solve such problems; on the other hand, coal resources will produce solid wastes such as fly ash and coal chemical waste slag during the mining, processing and combustion process. The amount of solid waste generated by open-pit mining is high and the production rate is fast. The stockpile is often greater than the consumption, and the dumping occupies land and pollutes the environment. The current stockpile of bulk solid waste in the country is about 60 billion tons, and the stockpile increases by about 3 billion tons each year. In order to consolidate the concept of green development, prevent and control environmental pollution caused by solid waste, and promote fundamental improvement of the ecological environment, it is necessary to reasonably utilize solid waste resources in the process of soil reclamation and ecological reconstruction of open-pit mine spoil dumps. On the one hand, it can effectively reduce the land area occupied by solid waste resources in landfill and stockpiling, and on the other hand, it can also reduce the economic cost of soil and ecological restoration in coal mining areas.

[0004] As for coal-based solid waste, due to its large stock and high heavy metal content, direct use in regional soil ecological restoration is likely to increase the risk of heavy metal migration, and the lack of organic matter will easily lead to poor soil fertility in the dumping ground, which is not suitable for plant growth; therefore, it is of no help in improving soil nutrient status, water regulation performance and basic physical and chemical properties of soil. Summary of the invention

[0005] The primary purpose of the present invention is to provide a soil heavy metal chelating agent and a preparation method thereof, so as to achieve the purpose of solidifying soil heavy metals, improving soil structure and increasing soil fertility.

[0006] To this end, the present invention provides the following technical solutions.

[0007] One aspect of the present invention provides a soil heavy metal chelator, which includes a chelator I and a chelator II, wherein the chelator I is composed of fly ash and domestic sludge, and the chelator II is a modified sodium alginate complex; the mass ratio of the chelator I to the chelator II is (15-20): (3-5).

[0008] As a preferred embodiment of the present invention, the mass ratio of fly ash to domestic sewage sludge is (2-10):(1-3).

[0009] As a preferred embodiment of the present invention, the fly ash and domestic sewage sludge are mixed evenly.

[0010] As a preferred embodiment of the present invention, the domestic sewage sludge is air-dried, crushed, and non-powdery materials are removed; further preferably, it is air-dried, crushed, and sieved, and the sieve hole is preferably 2-5 mm, more preferably 2 mm.

[0011] As a preferred embodiment of the present invention, the modified sodium alginate complex is formed by compounding modified sodium alginate and cyclodextrin in an alkaline environment.

[0012] As a preferred embodiment of the present invention, the modified sodium alginate is obtained by modifying sodium alginate with a modifier.

[0013] As a preferred embodiment of the present invention, the modifier is selected from one or a mixture of two or more of aniline, diphenylamine, o-phenylenediamine, p-diphenylamine and m-diphenylamine.

[0014] As a preferred embodiment of the present invention, the amount of the modifier added is 1-3% of the mass of the sodium alginate.

[0015] As a preferred embodiment of the present invention, the preparation method of the modified sodium alginate is: dissolving sodium alginate in water to obtain a sodium alginate solution with a mass concentration of 1 to 5%, then heating the solution to 40 to 50°C and adding a modifier to the solution and stirring the solution for 2 to 6 hours, cooling the solution to room temperature after the reaction is completed, and freeze-drying the obtained product to obtain modified sodium alginate.

[0016] As a preferred embodiment of the present invention, the preparation method of the modified sodium alginate composite is:

[0017] Sodium alginate is dissolved in water to obtain a sodium alginate solution with a mass concentration of 1 to 5%, and then the solution is heated to 40 to 50° C., a modifier is added to the solution, and the solution is stirred for reaction for 2 to 6 hours. After the reaction is completed, the solution is cooled to room temperature, and the obtained product is freeze-dried to obtain modified sodium alginate;

[0018] Cyclodextrin and functional monomer are dissolved in an organic alcohol / ammonium bicarbonate solution in a mass ratio of 1:1-3 to obtain a cyclodextrin / functional monomer mixed solution with a total mass fraction of 1-5%, and then modified sodium alginate and an initiator are added to react. After the reaction is completed, a cross-linking agent is added and stirred for 2-4 hours. After the stirring is completed, the mixture is allowed to stand for 20-40 minutes, and finally filtered, washed, and dried to obtain a modified sodium alginate complex in the form of microspheres.

[0019] As a preferred embodiment of the present invention, the functional monomer is selected from one or a mixture of two or more of monomethyl itaconate, dimethyl itaconate, acrylate, methacrylate, 2-sulfoethyl acrylate, monomethyl maleate, and dimethyl maleate.

[0020] As a preferred embodiment of the present invention, the organic alcohol / ammonium bicarbonate solution is prepared by mixing organic alcohol, ammonium bicarbonate and water in a volume mass ratio of 10-20 mL: 1-5 g: 100 mL.

[0021] As a preferred embodiment of the present invention, the organic alcohol is selected from any one of methanol, ethanol, 1-propanol and 1-butanol.

[0022] As a preferred embodiment of the present invention, the initiator is selected from any one of sodium persulfate, potassium persulfate and ammonium persulfate.

[0023] As a preferred embodiment of the present invention, the added amount of the initiator is 0.3-0.5% of the mass of the functional monomer.

[0024] As a preferred embodiment of the present invention, the modified sodium alginate is added in an amount with a mass ratio of 1 to 5:1 to the functional monomer.

[0025] As a preferred embodiment of the present invention, the cross-linking agent is selected from any one of catechol, hydroquinone, resorcinol, glutaraldehyde and urotropine.

[0026] As a preferred embodiment of the present invention, the added amount of the cross-linking agent is 0.1-0.2% of the mass of the modified sodium alginate.

[0027] As a preferred embodiment of the present invention, the modified sodium alginate complex in the form of microspheres is further processed:

[0028] The obtained microsphere-shaped modified sodium alginate complex is placed in a 1-5% hydrofluoric acid solution and stirred at 200-400 rpm for 4-6 minutes to obtain a modified sodium alginate complex porous microsphere; the modified sodium alginate complex porous microsphere is placed in a 0.05-0.1% silane coupling agent, and then an inorganic chelating agent is added and stirred at room temperature for 10-20 minutes, and finally taken out and dried. After the above further treatment, it can be used as chelating agent II.

[0029] As a preferred embodiment of the present invention, the silane coupling agent is selected from any one of vinyl triethoxy silane, vinyl trimethoxy silane and vinyl tri (β-methoxyethoxy) silane.

[0030] As a preferred embodiment of the present invention, the inorganic chelating agent is sodium dihydrogen phosphate and / or sodium sulfide.

[0031] As a preferred embodiment of the present invention, the added amount of the inorganic chelating agent is 0.5 to 1 times the mass of the modified sodium alginate composite porous microspheres.

[0032] By means of the above technical solution, the present invention has at least the following advantages:

[0033] The present invention uses fly ash and domestic sludge to form a chelating agent I, and a modified sodium alginate complex as a chelating agent II. The two chelating agents are used in combination in soil reclamation of open-pit mine dumps, which can effectively improve a series of environmental problems caused by mining activities, thereby promoting the rational use of land resources.

[0034] Fly ash (FA) is an industrial waste residue discharged from the flue, which is formed by coal powder passing through a furnace at 1300-1500℃ under suspended combustion conditions and then cooling the hot surface. Because fly ash has a wide range of application prospects, its application research in soil improvement is increasing. Studies have found that fly ash has a beneficial effect on regulating soil pH and can solidify heavy metals in the soil. Fly ash has air permeability, adsorption, coagulation, coagulation and precipitation effects, which can reduce the bulk density of wet soil, improve soil air permeability and water permeability, increase the number of soil aggregates, trace elements, fertility, promote the activity of soil microorganisms and enzymes, and improve soil structure.

[0035] Sewage sludge (SS) is the sediment formed in the wastewater treatment process of domestic sewage treatment plants. It is a semi-solid waste between inorganic and organic. At present, the main methods of treating and disposing of domestic sludge are landfill, reclamation, incineration and agricultural composting. Studies have shown that land use of treated sewage sludge can contribute to sustainable environmental management by returning organic matter and nutrients to the soil, and can be used as a soil improvement material; in terms of improving saline-alkali land, the application of sludge can effectively improve the nutrient status of the soil, reduce the risk of heavy metal migration, reduce the acidity and alkalinity of the soil, and improve the soil nutrient status, water regulation performance and basic physical and chemical properties of the soil; in terms of improving plant growth, sludge can significantly increase the height, diameter at breast height, leaf area and survival rate of crop seedlings after soil improvement.

[0036] Sodium alginate is an anionic high molecular weight polysaccharide polymer, mainly derived from the cell wall and intercellular matrix of brown algae. Its molecular formula is (C6H7O6Na)n, and it is composed of two stereoisomeric units, α-L-guluronic acid (G unit) and β-D-mannuronic acid (M unit), connected by β-1,4-glycosidic bonds. The composition and structural differences of the two isomeric units G and M will significantly change the characteristics of the gel. Multiple negatively charged G units can form a cavity structure around metal ions, and a large number of cavity structures are stacked to form a three-dimensional network structure, commonly known as the "egg lattice" structure, which is then cross-linked with metal ions to form a composite material with an excellent three-dimensional interconnected structure. The carboxyl group and pyranose oxygen atom of sodium alginate can form a stable five-membered chelate with metal ions, providing binding sites for the adsorption process. The presence of hydroxyl and carboxyl groups in sodium alginate is conducive to modification, so that the modified product has a larger specific surface area and more active sites, thereby improving the adsorption performance. Therefore, the present invention can further improve the solidification effect on metal ions by modifying sodium alginate and introducing a variety of negatively charged active groups.

[0037] On the one hand, the present invention uses sodium alginate as a matrix, and introduces amino groups into sodium alginate through the modification of a modifier, which can not only introduce anionic groups, but also increase the steric hindrance when a subsequent cross-linking agent acts, thereby forming larger holes and improving the flexibility of the polymer grid interpenetrating structure. On the other hand, the present invention uses modified sodium alginate as a polymer carrier, and introduces a monomer combination of cyclodextrin and functional monomers into the modified sodium alginate under the action of an initiator, thereby initiating polymerization to form a polymer, and finally forming a bridge bond between polymer molecular chains under the cross-linking action of a cross-linking agent, and becoming a high polymer with a three-dimensional structure, so that the modified sodium alginate complex finally obtained not only has multiple hydrophilic groups but also has a large amount of negative charges, and also has a variety of pore structures of a three-dimensional network. Thereby, it has a strong adsorption and covalent binding effect on soil heavy metals, and also has good water retention and fertilizer retention performance.

[0038] Therefore, the present invention uses the above three substances as soil heavy metal chelating agents, and through reasonable compatibility, it can play a synergistic role, thereby reducing the risk of heavy metal migration when coal-based solid waste is used for regional soil ecological restoration, and improving the soil fertility of the spoil dump and promoting plant growth.

[0039] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail as follows. DETAILED DESCRIPTION

[0040] In order to make the technical means, creative features, objectives and effects of the present invention easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] Unless otherwise specified, the percentage contents involved in the present invention refer to mass percentage for solid-liquid mixture and solid phase □ solid phase mixture, and refer to volume percentage for liquid phase □ liquid phase mixture.

[0042] Unless otherwise specified, the percentage concentrations referred to in the present invention all refer to final concentrations, which refer to the percentage of the added component in the system after the addition of the component.

[0043] The temperature parameters in the present invention, if not specifically limited, allow for both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows the temperature to fluctuate within the precision range controlled by the instrument.

[0044] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.

[0045] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0046] 1. Soil sample collection

[0047] Soil samples were collected in May 2024. Soil was collected from the mine dump and the reclaimed plantation in accordance with the Soil Agrochemical Analysis. Sampling was carried out along the "S"-shaped route, and the surface soil at 0 to 20 cm was taken with a soil drill (because the distribution and changes of nutrients in the surface 0 to 20 cm soil are the most obvious and representative), placed in a plastic bag, labeled, and the soil samples were brought back to the laboratory and placed in a ventilated and cool place for air drying. After air drying, large clods of soil were broken up, and plant roots, dead branches and leaves, animal and plant residues, and stones mixed in the soil were picked out. After passing through a 2 mm sieve, they were sealed and stored in a plastic bag.

[0048] 2. Source of raw materials

[0049] The fly ash is taken from Huaxin Power Plant. It is powdery, grayish white, and fine particles. It is low-calcium fly ash. The fly ash itself is grayish white powder, so it does not need to be sieved and can be used directly.

[0050] Domestic sludge was obtained from the sewage treatment plant of the Zhundong Hongshaquan open-pit coal mine, which produces about 33.1t / a of sludge, with organic matter as the main component. To facilitate the use of sludge, it was spread on the ground for natural air drying. When it reached a semi-dry state, large pieces of sludge were crushed in time to avoid forming hard lumps that were difficult to crush. After the sludge was air-dried, it was crushed with a mortar. During the crushing process, impurities and plant roots were removed. The sludge sample was passed through a 2mm sieve, and the part that could not pass through was re-rolled and sieved until all the samples passed through the sieve. The sieved samples were stored in plastic bags, marked and sealed for subsequent experiments.

[0051] Embodiment 1:

[0052] Preparation of chelating agent I: Mix fly ash and domestic sewage sludge in a mass ratio of 6:2.

[0053] Preparation of chelating agent II: Sodium alginate was dissolved in water to obtain a sodium alginate solution with a mass concentration of 3%, and then the solution was heated to 45°C and diphenylamine (the amount added was 2% of the mass of sodium alginate) was added to the solution and stirred for 4 hours. After the reaction was completed, it was cooled to room temperature and the obtained product was freeze-dried to obtain modified sodium alginate. Cyclodextrin and methacrylate were dissolved in an ethanol / ammonium bicarbonate solution (mixed with ethanol, ammonium bicarbonate and water in a volume mass ratio of 15 mL: 3 g: 100 mL) in a mass ratio of 1:2 to obtain a cyclodextrin / methacrylate mixed solution with a mass fraction of 3%, and then modified sodium alginate (added in a mass ratio of 3:1 to methacrylate) and ammonium persulfate (added in an amount of 0.4% of the mass of methacrylate) were added to react for 2 hours. After the reaction, catechol (added in an amount of 0.15% of the mass of modified sodium alginate) was added and stirred for 3 hours. After stirring, the mixture was allowed to stand for 30 minutes, and finally filtered, washed and dried to obtain chelating agent II.

[0054] In this embodiment, the chelating agent is a chelating agent I and a chelating agent II in a mass ratio of 20:5.

[0055] Embodiment 2:

[0056] Preparation of chelating agent I: Mix fly ash and domestic sewage sludge in a mass ratio of 2:3.

[0057] Preparation of chelating agent II: Sodium alginate was dissolved in water to obtain a sodium alginate solution with a mass concentration of 5%, and then the solution was heated to 40°C and o-phenylenediamine (the amount added was 1% of the mass of sodium alginate) was added to the solution and stirred for 6 hours. After the reaction was completed, it was cooled to room temperature and the obtained product was freeze-dried to obtain modified sodium alginate. Cyclodextrin and dimethyl maleate were dissolved in an ethanol / ammonium bicarbonate solution (mixed with ethanol, ammonium bicarbonate and water in a volume mass ratio of 10 mL: 1 g: 100 mL) in a mass ratio of 1:1 to obtain a cyclodextrin / dimethyl maleate mixed solution with a mass fraction of 5%, and then modified sodium alginate (added in a mass ratio of 1:1 to dimethyl maleate) and ammonium persulfate (added in an amount of 0.3% of the mass of dimethyl maleate) were added to react. After the reaction, resorcinol (added in an amount of 0.1% of the mass of modified sodium alginate) was added and stirred for 2 hours. After the stirring was completed, the mixture was allowed to stand for 40 minutes, and finally filtered, washed and dried to obtain chelating agent II.

[0058] In this embodiment, the chelating agent is a chelating agent I and a chelating agent II in a mass ratio of 18:4.

[0059] Embodiment 3:

[0060] Preparation of chelating agent I: Mix fly ash and domestic sewage sludge in a mass ratio of 10:1.

[0061] Preparation of chelating agent II: Sodium alginate was dissolved in water to obtain a sodium alginate solution with a mass concentration of 1%, and then the solution was heated to 50°C and p-diphenylamine (the amount added was 3% of the mass of sodium alginate) was added to the solution and stirred for 2 hours. After the reaction was completed, it was cooled to room temperature and the obtained product was freeze-dried to obtain modified sodium alginate. Cyclodextrin and dimethyl itaconate were dissolved in an ethanol / ammonium bicarbonate solution (mixed with ethanol, ammonium bicarbonate and water in a volume mass ratio of 20 mL:5 g:100 mL) in a mass ratio of 1:3 to obtain a cyclodextrin / dimethyl itaconate mixed solution with a mass fraction of 1%, and then modified sodium alginate (added in a mass ratio of 5:1 to dimethyl itaconate) and ammonium persulfate (added in an amount of 0.5% of the mass of dimethyl itaconate) were added to react. After the reaction, hydroquinone (added in an amount of 0.2% of the mass of modified sodium alginate) was added and stirred for 4 hours. After the stirring was completed, the mixture was allowed to stand for 20 minutes, and finally filtered, washed and dried to obtain chelating agent II.

[0062] In this embodiment, the chelating agent is a chelating agent I and a chelating agent II in a mass ratio of 15:3.

[0063] Embodiment 4:

[0064] Preparation of chelating agent I: Mix fly ash and domestic sewage sludge in a mass ratio of 6:2.

[0065] Preparation of chelating agent II: Sodium alginate was dissolved in water to obtain a sodium alginate solution with a mass concentration of 3%, and then the solution was heated to 45°C and diphenylamine (the amount added was 2% of the mass of sodium alginate) was added to the solution and stirred for 4 hours. After the reaction was completed, it was cooled to room temperature and the obtained product was freeze-dried to obtain modified sodium alginate. Cyclodextrin and methacrylate were dissolved in an ethanol / ammonium bicarbonate solution (mixed by ethanol, ammonium bicarbonate and water in a volume mass ratio of 15 mL: 3 g: 100 mL) in a mass ratio of 1:2 to obtain a cyclodextrin / methacrylate mixed solution with a mass fraction of 3%, and then modified sodium alginate (added in a mass ratio of 3:1 to methacrylate) and ammonium persulfate (added in an amount of 0.4% of the mass of methacrylate) were added to react. After the reaction, catechol (added in an amount of 0.15% of the mass of modified sodium alginate) was added and stirred for 3 hours. After the stirring was completed, it was allowed to stand for 30 minutes, and finally filtered, washed and dried to obtain modified sodium alginate composite microspheres. The obtained modified sodium alginate composite microspheres were placed in a 3% hydrofluoric acid solution and stirred at 300 rpm for 5 minutes to obtain modified sodium alginate composite porous microspheres. The modified sodium alginate composite porous microspheres were placed in 0.075% vinyltriethoxysilane, and then sodium dihydrogen phosphate was added (the amount added was 0.75 times the mass of the modified sodium alginate composite porous microspheres), stirred at room temperature for 15 minutes, and finally taken out and dried to obtain chelating agent II.

[0066] In this embodiment, the chelating agent is a chelating agent I and a chelating agent II in a mass ratio of 20:5.

[0067] Comparative Example 1:

[0068] Preparation of chelating agent I: Mix fly ash and domestic sewage sludge in a mass ratio of 6:2.

[0069] Preparation of chelating agent II: cyclodextrin and methacrylate were dissolved in an ethanol / ammonium bicarbonate solution (composed of ethanol, ammonium bicarbonate and water mixed in a volume mass ratio of 15 mL: 3 g: 100 mL) in a mass ratio of 1:2 to obtain a cyclodextrin / methacrylate mixed solution with a mass fraction of 3%, and then sodium alginate (added in a mass ratio of 3:1 to methacrylate) and ammonium persulfate (added in an amount of 0.4% of the mass of methacrylate) were added to react for 2 hours. After the reaction was completed, catechol (added in an amount of 0.15% of the mass of sodium alginate) was added and stirred for 3 hours. After the stirring was completed, the mixture was allowed to stand for 30 minutes, and finally filtered, washed, and dried to obtain chelating agent II.

[0070] In this comparative example, the chelating agent is a chelating agent I and a chelating agent II in a mass ratio of 20:5.

[0071] That is, in this comparative example, relative to Example 1, the sodium alginate is not modified.

[0072] Comparative Example 2:

[0073] Preparation of chelating agent I: Mix fly ash and domestic sewage sludge in a mass ratio of 6:2.

[0074] Preparation of chelating agent II: Sodium alginate was dissolved in water to obtain a sodium alginate solution with a mass concentration of 3%, and then the solution was heated to 45°C and diphenylamine (the amount added was 2% of the mass of sodium alginate) was added to the solution and stirred for reaction for 4 hours. After the reaction was completed, it was cooled to room temperature and the obtained product was freeze-dried to obtain modified sodium alginate, which was directly used as chelating agent II.

[0075] In this comparative example, the chelating agent is a chelating agent I and a chelating agent II in a mass ratio of 20:5.

[0076] That is, in this comparative example, relative to Example 1, the modified sodium alginate does not form a modified sodium alginate composite.

[0077] Comparative Example 3:

[0078] Preparation of chelating agent II: Sodium alginate was dissolved in water to obtain a sodium alginate solution with a mass concentration of 3%, and then the solution was heated to 45°C and diphenylamine (the amount added was 2% of the mass of sodium alginate) was added to the solution and stirred for 4 hours. After the reaction was completed, it was cooled to room temperature and the obtained product was freeze-dried to obtain modified sodium alginate. Cyclodextrin and methacrylate were dissolved in an ethanol / ammonium bicarbonate solution (mixed with ethanol, ammonium bicarbonate and water in a volume mass ratio of 15 mL: 3 g: 100 mL) in a mass ratio of 1:2 to obtain a cyclodextrin / methacrylate mixed solution with a mass fraction of 3%, and then modified sodium alginate (added in a mass ratio of 3:1 to methacrylate) and ammonium persulfate (added in an amount of 0.4% of the mass of methacrylate) were added to react for 2 hours. After the reaction, catechol (added in an amount of 0.15% of the mass of modified sodium alginate) was added and stirred for 3 hours. After stirring, the mixture was allowed to stand for 30 minutes, and finally filtered, washed and dried to obtain chelating agent II.

[0079] That is, in this comparative example, compared with Example 1, only the chelating agent II component is used.

[0080] Comparative Example 4:

[0081] Preparation of chelating agent I: Mix fly ash and domestic sewage sludge in a mass ratio of 6:2.

[0082] That is, in this comparative example, compared with Example 1, only the chelating agent I component is used.

[0083] Experiment 1: Detection of the effect of different chelating agents on soil heavy metal fixation

[0084] 1. Preparation of bionic soil simulating heavy metal pollution:

[0085] First, exogenous soluble heavy metal salts were dissolved in deionized water to prepare a simulated exogenous heavy metal solution containing 70 mg / kg zinc ions, 10 mg / kg lead ions, 10 mg / kg cadmium ions, 3.5 mg / kg arsenic ions and 20 mg / kg copper ions.

[0086] Then, the chelating agent (Examples 1-4 and Comparative Examples 1-4) and the soil sample were mixed evenly in a mass ratio of 25:250, and then mixed evenly with a simulated exogenous heavy metal solution in a solid-liquid ratio of 1:0.5 (ie, 1 g:0.5 ml) to obtain a soil mixture.

[0087] Finally, the obtained soil mixture was transferred to a circular mold (Φ50mm×H100mm), and an oscillator was used to remove bubbles and the surface was flattened to complete the preparation. After curing for 24h under natural conditions, the mixture was demoulded and sealed in a polyethylene bag, and then transferred to a standard curing box (temperature 20±2℃, relative humidity 95%) for 28 days to obtain bionic soil, and the soil heavy metal leaching test was carried out.

[0088] 2. Soil heavy metal leaching was completed according to the method required by China HJ / T 557-2010. The concentrations of zinc ions, lead ions, cadmium ions, arsenic ions and copper ions in the soil leaching solution were determined by inductively coupled plasma mass spectrometry (ICP-MS, PerkinElmer Nexlon 300X). The specific operations were as follows:

[0089] Using a mixed nitric acid / sulfuric acid solution with a pH of 2 as the leaching solution, soak the bionic soil in a bucket containing 1L of leaching solution at a fixed solid-liquid ratio of 1:10 (i.e. 1g:10ml), and seal the bucket mouth. The sampling time is set to 1d, 28d, and 112d, respectively. Each time, about 5mL of the leaching solution is taken with a syringe, and filtered into a 10mL centrifuge tube using a 0.45μm filter membrane to obtain the leaching solution to be tested. During the test, the same variable part was tested 3 times to calibrate the experimental error. After sampling, the immersion solution was filled to a constant volume of 1L. The results are shown in Table 1-5.

[0090] Table 1 Curing effect on zinc ions

[0091]

[0092] Note: The blank group is the soil without adding chelating agent.

[0093] Table 2 Curing effect on lead ions

[0094]

[0095] Note: The blank group is the soil without adding chelating agent.

[0096] Table 3 Curing effect on cadmium ions

[0097]

[0098] Note: The blank group is the soil without adding chelating agent.

[0099] Table 4 Curing effect on arsenic ions

[0100]

[0101] Note: The blank group is the soil without adding chelating agent.

[0102] Table 5 Curing effect on copper ions

[0103]

[0104] Note: The blank group is the soil without adding chelating agent.

[0105] From the results of Tables 1-5, it can be seen that, compared with the blank group, the release of each metal ion can be effectively reduced by adding a chelating agent. Compared with the addition of the chelating agent in Comparative Examples 1-4, the concentration of each metal ion in the leachate can be further reduced by adding the chelating agent in Examples 1-4. It can be seen that the chelating agent of the present invention has excellent heavy metal chelating ability and can be used in soil reclamation to reduce the migration of heavy metals in the soil.

[0106] Test Example 2: Testing of water and fertilizer retention performance of different improved soils

[0107] By using the intermittent soil column leaching method to conduct infiltration tests on different treatments of improved soil, the water and fertilizer retention mechanisms of different improved soils were studied, and a comprehensive comparative analysis was conducted on the water and fertilizer retention capacity of the soil after adding chelating agents and pure soil. The results are shown in Table 6.

[0108] Table 6 Effect test of water and fertilizer retention capacity of different bionic soils

[0109]

[0110]

[0111] It can be seen from the results in Table 6 that, compared with the bionic soil of comparative examples 1 to 4, the bionic soil obtained by the chelating agent of examples 1 and 4 of the present invention can keep soil moisture from being lost, and can effectively improve soil water holding capacity, nutrient fertility and other properties.

[0112] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes by using the methods and technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A soil heavy metal chelating agent, characterized in that: The chelating agent comprises a chelating agent I and a chelating agent II, wherein the chelating agent I is composed of fly ash and domestic sludge, and the chelating agent II is a modified sodium alginate complex; the mass ratio of the chelating agent I to the chelating agent II is (15-20): (3-5).

2. The soil heavy metal chelating agent according to claim 1, characterized in that: The mass ratio of the fly ash to the domestic sewage sludge is (2-10):(1-3).

3. The soil heavy metal chelating agent according to claim 1 or 2, characterized in that: The modified sodium alginate complex is formed by compounding modified sodium alginate and cyclodextrin in an alkaline environment.

4. The soil heavy metal chelating agent according to claim 3, characterized in that: The preparation method of the modified sodium alginate composite is as follows: Sodium alginate is dissolved in water to obtain a sodium alginate solution with a mass concentration of 1 to 5%, and then the solution is heated to 40 to 50° C., a modifier is added to the solution, and the solution is stirred for reaction for 2 to 6 hours. After the reaction is completed, the solution is cooled to room temperature, and the obtained product is freeze-dried to obtain modified sodium alginate; Cyclodextrin and functional monomer are dissolved in an organic alcohol / ammonium bicarbonate solution in a mass ratio of 1:1-3 to obtain a cyclodextrin / functional monomer mixed solution with a mass fraction of 1-5%, and then modified sodium alginate and an initiator are added to react. After the reaction is completed, a cross-linking agent is added and stirred for 2-4 hours. After the stirring is completed, the mixture is allowed to stand for 20-40 minutes, and finally filtered, washed, and dried to obtain a modified sodium alginate complex in the form of microspheres.

5. The soil heavy metal chelating agent according to claim 4, characterized in that: The modifier is selected from one or a mixture of two or more of aniline, diphenylamine, o-phenylenediamine, p-diphenylamine, and m-diphenylamine; The amount of the modifier added is 1-3% of the mass of the sodium alginate.

6. The soil heavy metal chelating agent according to claim 4, characterized in that: The functional monomer is selected from the group consisting of monomethyl itaconate, dimethyl itaconate, acrylate, methacrylate, 2-sulfoethyl acrylate, monomethyl maleate, dimethyl maleate, or a mixture of two or more thereof.

7. The soil heavy metal chelating agent according to claim 4, characterized in that: The organic alcohol / ammonium bicarbonate solution is prepared by mixing organic alcohol, ammonium bicarbonate and water in a volume mass ratio of 10-20 mL: 1-5 g: 100 mL; The organic alcohol is selected from any one of methanol, ethanol, 1-propanol and 1-butanol.

8. The soil heavy metal chelating agent according to claim 4, characterized in that: The initiator is selected from any one of sodium persulfate, potassium persulfate and ammonium persulfate; the added amount of the initiator is 0.3-0.5% of the mass of the functional monomer.

9. The soil heavy metal chelating agent according to claim 4, characterized in that: The modified sodium alginate is added in an amount with a mass ratio of 1 to 5:1 to the functional monomer.

10. The soil heavy metal chelating agent according to claim 4, characterized in that: The cross-linking agent is selected from any one of catechol, hydroquinone, resorcinol, glutaraldehyde and hexamethylenetetramine; the added amount of the cross-linking agent is 0.1-0.2% of the mass of the modified sodium alginate.

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