A cadmium-contaminated soil remediation agent and a cadmium-contaminated soil remediation method

Abstract

The present invention belongs to the technical field of heavy metal pollution control, and is specifically a cadmium-contaminated soil remediation agent and a method for remediating cadmium-contaminated soil. The cadmium-contaminated soil remediation agent of the present invention is composed of 29.4 to 32.5 parts by mass of catalytic weathered siderite powder and 67.5 to 70.6 parts by mass of limestone powder; the catalytic weathered siderite powder is prepared by a method comprising the following steps: granulating a mixture composed of ferrous chloride, siderite powder and water to obtain a granular material, sealing the granular material and standing it for 6 to 24 hours to obtain a catalytic weathered siderite powder; the mass ratio of ferrous chloride to siderite powder is (7.04 to 7.89): (2.11 to 2.96), and the mass of water is 5 to 10% of the total mass of ferrous chloride and siderite powder. The cadmium-contaminated soil remediation agent of the present invention has a good and long-lasting remediation effect on cadmium-contaminated soil.

Description

Technical Field

[0001] The invention belongs to the technical field of heavy metal pollution control, and specifically relates to a cadmium-contaminated soil repair agent and a cadmium-contaminated soil repair method. Background Art

[0002] At present, soil remediation agents are mainly used to control the cadmium content of rice planted in cadmium-contaminated soil. There are four main types of soil remediation agents for cadmium-contaminated soil: ① Chemical remediation agents. Many chemical remediation agents can reduce the biological activity of cadmium in soil in research and application. Such as sulfur compounds, phosphorus and calcium plasma, reducing agents, etc. However, the long-term use of chemical remediation agents will have a certain impact on the growth of microorganisms and plants in the soil, and some formulations still have problems such as toxicity and residuality. ② Natural precipitants. Natural precipitants refer to adding other substances to the soil so that cadmium ions react with additives to form relatively stable precipitation products. For example, calcium hydroxide precipitation, phosphate precipitation, etc. Natural precipitants can achieve the purpose of repairing the soil on the basis of protecting the original organisms. ③ Biological remediation agents. Biological remediation agents are a type of high-performance special soil conditioner, mainly composed of some special strains, bacterial communities and plant extracts. Under the action of microbial and plant growth, as well as absorption, enrichment and stabilization of cadmium ions, the harmful effects of cadmium ions in the soil can be removed, prevented and mitigated. This type of repair agent can be used in various forms and is widely used in agricultural production and ecological protection. It has good development prospects, but the repair time is too long, the selection of microbial populations is difficult, and there is a possibility of endangering biodiversity. ④ Plasma repair agent. Plasma repair agent extracts metal ions from the soil through plasma technology, and the extracted ions are removed from cadmium through a low-aging system. This technology uses the strong electron impact ability of plasma technology to remove metal ions, and treats cadmium ions through activation energy in an oxygen atmosphere. This method is more suitable for the remediation of soils with high concentrations and large contaminated areas, and has limitations for the remediation of large areas of low-concentration cadmium-contaminated farmland soil. Summary of the invention

[0003] In view of the above problems, the present invention provides a cadmium-contaminated soil remediation agent and a cadmium-contaminated soil remediation method, which are used to solve the problems of poor remediation effect, poor stability and safety, high remediation cost, great operating difficulty and environmental risk, and poor sustainability of current cadmium-contaminated soil remediation agents.

[0004] To achieve the above object, the technical solution adopted by the present invention is:

[0005] A cadmium-contaminated soil remediation agent is composed of 29.4-32.5 parts by mass of catalytically weathered siderite powder and 67.5-70.6 parts by mass of limestone powder; the catalytically weathered siderite powder is prepared by a method comprising the following steps: spraying water on a mixture consisting of ferrous chloride and siderite powder under stirring to obtain a mixture, granulating the mixture to obtain a granular material, and then sealing and standing the granular material for 6-24 hours to obtain the catalytically weathered siderite powder; the mass ratio of ferrous chloride to siderite powder in the mixture is (7.04-7.89):(2.11-2.96), and the mass of water is 5-10% of the total mass of ferrous chloride and siderite powder.

[0006] Preferably, the particle size of the siderite powder is not less than 100 mesh.

[0007] Preferably, the particle size of the limestone powder is not less than 10 mesh.

[0008] Preferably, the mass fraction of ferrous carbonate in the siderite powder is not less than 80%.

[0009] Preferably, the mass fraction of calcium carbonate in the limestone powder is not less than 90%.

[0010] Preferably, the average particle size of the granular material is 1-2 mm.

[0011] The technical solution of the method for repairing cadmium-contaminated soil of the present invention is:

[0012] A method for repairing cadmium-contaminated soil comprises the following steps: applying the cadmium-contaminated soil repair agent as described above to the soil to be repaired for repair.

[0013] Preferably, the application amount of the cadmium-contaminated soil remediation agent is 520~547kg / mu.

[0014] When the cadmium-contaminated soil repair method of the present invention is implemented, the cadmium-contaminated soil repair agent can be evenly spread into the field, and then the land is cultivated to fully mix the cadmium-contaminated soil repair agent with the cultivated layer soil, and finally the farmland is irrigated to ensure that the farmland soil is in a moist state. During irrigation, a pump can be used, and the water surface is based on not covering the soil layer, and supplementary irrigation is often performed to keep the field with sufficient water without overflowing the soil layer, so as to avoid the loss of the cadmium-contaminated soil repair agent.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) It has the characteristics of high stability, green environmental protection and low environmental risk. The lattice energy and energy coefficient of siderite and calcium carbonate are similar, the weathering rate under natural conditions is similar, and it has high stability. The raw materials used in the present invention mainly come from natural minerals, and the elements contained therein are also common elements in rocks and soils, mainly iron, calcium, carbon, oxygen and other elements. After being applied to the soil, the change in the corresponding elements in the soil is very small, ranging from 0.046 to 0.092%, and the overall impact on the soil composition is small. In addition, the elements in the repair agent provided by the present invention are essential nutritional elements for plants, which can enhance the activity of the soil and are beneficial to the growth of plants.

[0017] (2) It has the characteristics of low difficulty in operation and low cost of restoration. The preparation and use of the cadmium-contaminated soil restoration agent of the present invention only include conventional operations such as crushing, fine grinding, stirring, spraying, granulation, broadcasting, and rotary tillage. The operation difficulty is low and it is easy to master and promote. After nearly three years of experiments, small tests, pilot tests and promotion tests by the inventors, the comprehensive cost of repairing cadmium-contaminated soil using the restoration agent of the present invention is ≤1,500 yuan / mu, which is much lower than the current restoration cost of 20,000 yuan / mu on the market.

[0018] (3) It has the characteristics of ecological sustainability. The raw materials used in the cadmium-contaminated soil remediation agent of the present invention are mostly natural mineral materials, among which ferrous chloride is a catalyst with a relatively small dosage. In the process of premixing and storage, ferrous chloride and siderite begin to react, reducing the amount of decomposition in the field. When added to paddy field soil, the changes that occur are similar to the natural weathering process of these minerals, maintaining a harmonious and unified relationship with the environment, and having almost no effect on the overall function of the paddy field ecosystem. When the cadmium-contaminated soil remediation agent of the present invention is used, it can be selected during the winter fallow period, which will not interrupt the production of the farmland ecosystem and meet the time sustainability of the ecological environment system. When the cadmium-contaminated soil remediation agent of the present invention is used, in-situ remediation is adopted, and the spatial position of the farmland soil is not changed, which meets the spatial sustainability of the ecological environment system. When the cadmium-contaminated soil remediation agent of the present invention is used, there is no need to change the current utilization status of paddy fields, there is no need to change the planting habits of farmers, and there is no need to make special requirements for agricultural production. It can ensure that the cadmium content of rice does not exceed the standard, improve the economic and ecological benefits of cadmium-contaminated paddy field soil, and meet the sustainability of the ecological environment system in resource optimization. DETAILED DESCRIPTION

[0019] The working principle of the cadmium contaminated soil repair agent of the present invention is as follows:

[0020] In the present invention, siderite powder and ferrous chloride are mixed and then sprayed with water. The ferrous chloride with strong hygroscopicity absorbs water. While stirring and spraying water, the siderite powder wraps the ferrous chloride crystals to form agglomerated particles, thereby ensuring full contact between the siderite and the ferrous chloride. This creates favorable conditions for the subsequent addition of the mixture to the farmland soil for continued hydrolysis reaction, decomposition reaction and oxidation reaction, thereby maintaining the repair effect.

[0021] When limestone powder is mixed with the mixture of ferrous chloride and siderite again, the H provided by the hydrolysis of ferrous chloride ＋ ions, which promote the weathering and decomposition of limestone, increase the carbonic acid content in the soil, and promote the formation of carbonates; the limestone is in full contact with siderite and ferrous chloride to prevent the loss of nutrients caused by acidification during the hydrolysis of ferrous chloride.

[0022] When the cadmium-contaminated soil remediation agent of the present invention is applied to the soil, the concentration of ferrous ions and carbonate ions can be increased, and then a series of chemical reactions are performed to play a remediation role. The specific reactions that occur are as follows:

[0023] ① Mineral decomposition reaction. Ferrous chloride hydrolyzes to produce a large amount of H ＋ ions and ferrous hydroxide; H ＋ Ions act on siderite and limestone, accelerating their decomposition to form free ferrous ions and bicarbonate. The chemical reactions that occur in this process are as follows:

[0024]

[0025] ② Iron oxide formation reaction. First, siderite and ferrous chloride are directly oxidized to form iron oxides; second, the ferrous hydroxide and free ferrous ions produced by the decomposition of siderite and the hydrolysis of ferrous chloride are unstable and quickly decompose, oxidize or hydrate to form stable iron oxides; the iron oxides formed mainly include: lepidocrocite (γ-FeOOH), goethite (α-FeOOH), hematite (α-Fe2O3), jasonite (Fe2O3·xH2O), ferrihydrite (Fe2O3·H2O), hematite (γ-Fe2O3), etc. The chemical reactions that occur in this process are as follows:

[0026]

[0027] ③ Carbonate mineral conversion reaction. With the participation of limestone, on the one hand, the limestone undergoes slow weathering and decomposition, maintaining a stable balance of calcium carbonate, bicarbonate and calcium ions in the soil system. Calcium carbonate is always in a repeated exchange process of dissolution and precipitation; on the other hand, excess limestone can eliminate the remaining H ＋ ions. The chemical reactions that occur in this process are as follows:

[0028]

[0029] When the cadmium-contaminated soil remediation agent of the present invention is applied to the soil, the various iron oxides generated can undergo continuous transformation with each other, as shown below:

[0030] ① Iron oxides fix heavy metals such as cadmium. The various iron oxides generated are mostly in the form of tiny crystals with a very high specific surface area (generally greater than 100m 2 / g). This property makes iron oxides widely used as adsorbents, capable of absorbing dissolved ions, molecules and gases. The iron element in most iron oxides is in a trivalent state. Trivalent iron oxides have high stability and low solubility, and iron elements are easily replaced by other cations.

[0031] The transformation of iron oxides can be divided into local structural changes and crystal structure reconstruction. Local structural changes occur in the solid phase, specifically manifested as the rearrangement of internal atoms in the form of a single crystal, or the connection of the initial iron oxide with the transformed iron oxide through the crystal axis. Crystal structure reconstruction includes two processes: the dissolution of iron oxides and complete separation, and the reprecipitation of dissolved ions to form a new form. Crystal structure reconstruction is more likely to occur.

[0032] The surface functional groups of iron oxides have a strong adsorption effect on heavy metals, which is specifically manifested in the interaction between the hydroxyl functional groups on the surface of iron oxides and heavy metal cations or heavy metal oxygen-containing acid radicals. 2+ , Pb 2+ ,Cr 3+ , As 5+ etc.) interact with the deprotonated surface hydroxyl functional groups to form mononuclear or binuclear complexes. 3- , CrO2 4- ) are adsorbed by iron oxides due to electrostatic effects, because they have one or more atoms with a pair of lone electrons, which can act as donors in the coordination bond and form complexes with the oxygen atoms in the OH functional groups on the surface of iron oxides.

[0033] ② Carbonates assist in fixing heavy metals such as cadmium. On the one hand, in the “carbon dioxide + carbonate + bicarbonate + H + In the "ion" equilibrium system, free Cd 2+ The ions will combine with carbonate to form stable cadmium carbonate, which may also co-precipitate with calcium carbonate, or Cd 2+ Ions replace Ca 2+ The ions enter the calcium carbonate lattice and cadmium is fixed in a carbonate-bound state. On the other hand, the addition of CaCO3 will cause changes in the equilibrium constant and binding energy of the adsorption reaction of the soil system. At the same time, the addition of CaCO3 will reduce the degree of desorption of cadmium in the soil and improve the ability to solidify cadmium.

[0034] ③Balancing effect. Siderite and coarse limestone particles are added to the soil. On the one hand, they ensure that the divalent iron Fe formed by iron oxides in the soil 2+ The source of "Fe 2+ In the "ion + dissolved oxygen + iron oxide" equilibrium system, high concentration of Fe is maintained for a long time. 2+ ions, which is conducive to the equilibrium reaction to form iron oxides, thereby achieving the effect of long-term fixation of heavy metals such as cadmium by iron oxides; on the other hand, calcium carbonate slowly decomposes, "carbon dioxide + carbonate + bicarbonate + H + The system maintains a dynamic balance in the long term, promotes the formation of carbonates of heavy metals such as cadmium, and inhibits the dissolution of carbonates of heavy metals such as cadmium, thereby achieving the effect of long-term fixation of heavy metals such as cadmium by carbonates.

[0035] In addition, according to the Felsman energy formula, the lattice energy U of siderite, calcite, and hematite can be calculated to be 724.69, 647.93, and 3828.70 kcal / gram molecule, respectively; according to the concept of energy coefficient (q=U / μ), the energy coefficient q of siderite, calcite, and hematite can be calculated to be 6.4, 6.47, and 23.98 kcal / gram, respectively. The energy coefficient represents the energy required to generate or destroy each gram of mineral or rock, that is, in the same surface environment, the smaller the value of the energy coefficient, the easier it is to destroy the lattice and chemical weathering. Therefore, in the "siderite, limestone, iron oxide" system of paddy soil, the order of easy oxidation and decomposition is siderite>limestone>>hematite (iron oxide), siderite has the smallest energy coefficient and is most susceptible to oxidation and decomposition; while iron oxides such as hematite are the most difficult to undergo chemical weathering and are the most stable minerals.

[0036] In order to enable those skilled in the art to better understand the technical solution, the present invention is described in detail below in conjunction with embodiments. The description in this section is only exemplary and explanatory and should not have any limiting effect on the scope of protection of the present invention.

[0037] 1. The specific embodiments of the cadmium contaminated soil remediation agent of the present invention are as follows:

[0038] Example 1

[0039] The cadmium contaminated soil remediation agent of the present embodiment is prepared by a method comprising the following steps:

[0040] (1) The natural siderite ore is coarsely crushed, finely crushed, finely ground, passed through a 100-mesh sieve, and the sieve residue is collected to obtain siderite ore powder.

[0041] (2) Ferrous chloride and siderite powder in a mass ratio of 7.89:2.11 were stirred in a dry environment for 40 minutes to be fully mixed to obtain a mixture; under stirring conditions, water in an amount of 5% of the mass of the mixture was sprayed into the mixture, and the spraying was completed after 20 minutes to obtain a mixture; the mixture was extruded and granulated by a double-roll granulator to obtain granules with an average particle size of 1 mm, and the granules were placed in an iron barrel and sealed for 6 hours to obtain catalytic weathered siderite powder.

[0042] (3) The natural limestone is coarsely crushed, finely crushed, and finely ground, and passed through a 10-mesh sieve. The sieved material is collected to obtain limestone powder.

[0043] (4) 32.5 parts by mass of catalytic weathered siderite powder and 67.5 parts by mass of limestone powder were mixed uniformly to obtain a soil remediation agent.

[0044] Example 2

[0045] The cadmium contaminated soil remediation agent of the present embodiment is prepared by a method comprising the following steps:

[0046] (1) The natural siderite ore is coarsely crushed, finely crushed, finely ground, passed through a 100-mesh sieve, and the sieve residue is collected to obtain siderite ore powder.

[0047] (2) Ferrous chloride and siderite powder in a mass ratio of 7.04:2.96 were stirred in a dry environment for 40 minutes to be fully mixed to obtain a mixture; under stirring conditions, water in a mass of 10% of the mass of the mixture was sprayed into the mixture, and the spraying was completed after 20 minutes to obtain a mixture; the mixture was extruded and granulated by a double-roll granulator to obtain granules with an average particle size of 1.5 mm, and the granules were placed in an iron barrel and sealed for 24 hours to obtain catalytic weathering siderite powder.

[0048] (3) The natural limestone is coarsely crushed, finely crushed, and finely ground, and passed through a 10-mesh sieve. The sieved material is collected to obtain limestone powder.

[0049] (4) 29.4 parts by mass of catalytic weathered siderite powder and 70.6 parts by mass of limestone powder were mixed uniformly to obtain a soil remediation agent.

[0050] Example 3

[0051] The cadmium contaminated soil remediation agent of the present embodiment is prepared by a method comprising the following steps:

[0052] (1) The natural siderite ore is coarsely crushed, finely crushed, finely ground, passed through a 100-mesh sieve, and the sieve residue is collected to obtain siderite ore powder.

[0053] (2) Ferrous chloride and siderite powder in a mass ratio of 7.47:2.53 were stirred in a dry environment for 40 minutes to be fully mixed to obtain a mixture; under stirring conditions, water in an amount of 7% of the mass of the mixture was sprayed into the mixture, and the spraying was completed after 20 minutes to obtain a mixture; the mixture was extruded and granulated by a double-roll granulator to obtain granules with an average particle size of 2 mm, and the granules were placed in an iron barrel and sealed for 12 hours to obtain catalytic weathered siderite powder.

[0054] (3) The natural limestone is coarsely crushed, finely crushed, and finely ground, and passed through a 10-mesh sieve. The sieved material is collected to obtain limestone powder.

[0055] (4) 31 parts by mass of catalytic weathered siderite powder and 69 parts by mass of limestone powder were mixed uniformly to obtain a soil remediation agent.

[0056] Comparative Example 1

[0057] The cadmium-contaminated soil remediation agent of this comparative example is prepared by a method comprising the following steps:

[0058] (1) The natural siderite ore is coarsely crushed, finely crushed, finely ground, passed through a 100-mesh sieve, and the sieve residue is collected to obtain siderite ore powder.

[0059] (2) The natural limestone is coarsely crushed, finely crushed, and finely ground, and passed through a 10-mesh sieve. The sieved material is collected to obtain limestone powder.

[0060] (3) 32.5 parts by mass of siderite powder and 67.5 parts by mass of limestone powder were mixed uniformly to obtain a soil remediation agent.

[0061] Comparative Example 2

[0062] The cadmium-contaminated soil remediation agent of this comparative example is the catalytic weathering siderite powder in Example 1.

[0063] Comparative Example 3

[0064] The cadmium-contaminated soil remediation agent of this comparative example is the limestone powder in Example 1.

[0065] Comparative Example 4

[0066] The cadmium-contaminated soil remediation agent of this comparative example is prepared by a method comprising the following steps:

[0067] (1) The natural goethite is coarsely crushed, finely crushed, finely ground, and passed through a 100-mesh sieve. The sieved material is collected to obtain goethite powder.

[0068] (2) The ferrous chloride and goethite powders in a mass ratio of 7.89:2.11 were stirred for 40 minutes in a dry environment to be fully mixed to obtain a mixture; under stirring conditions, water in an amount of 5% of the mass of the mixture was sprayed into the mixture, and the spraying was completed after 20 minutes to obtain a mixture; the mixture was extruded and granulated by a double-roll granulator to obtain granules with an average particle size of 1 mm, and the granules were placed in an iron barrel and sealed for 6 hours to obtain catalytic weathering powder.

[0069] (3) The natural limestone is coarsely crushed, finely crushed, and finely ground, and passed through a 10-mesh sieve. The sieved material is collected to obtain limestone powder.

[0070] (4) 32.5 parts by mass of catalytic weathering powder and 67.5 parts by mass of limestone powder were mixed uniformly to obtain a soil remediation agent.

[0071] Comparative Example 5

[0072] The cadmium-contaminated soil remediation agent of this comparative example is prepared by a method comprising the following steps:

[0073] (1) The natural hematite is coarsely crushed, finely crushed, and finely ground, and passed through a 100-mesh sieve. The sieved material is collected to obtain hematite powder.

[0074] (2) The ferrous chloride and hematite powders in a mass ratio of 7.89:2.11 were stirred in a dry environment for 40 minutes to be fully mixed to obtain a mixture; under stirring conditions, 5% of the mass of the mixture was sprayed into the mixture, and the spraying was completed after 20 minutes to obtain a mixture; the mixture was extruded and granulated by a double-roll granulator to obtain granules with an average particle size of 1 mm, and the granules were placed in an iron barrel and sealed for 6 hours to obtain catalytic weathering powder.

[0075] (3) The natural limestone is coarsely crushed, finely crushed, and finely ground, and passed through a 10-mesh sieve. The sieved material is collected to obtain limestone powder.

[0076] (4) 32.5 parts by mass of catalytic weathering powder and 67.5 parts by mass of limestone powder were mixed evenly to obtain a soil remediation agent.

[0077] Comparative Example 6

[0078] The cadmium-contaminated soil remediation agent of this comparative example is prepared by a method comprising the following steps:

[0079] (1) The natural siderite ore is coarsely crushed, finely crushed, finely ground, passed through a 100-mesh sieve, and the sieve residue is collected to obtain siderite ore powder.

[0080] (2) Ferrous sulfate and siderite powder in a mass ratio of 7.89:2.11 were stirred in a dry environment for 40 minutes to be fully mixed to obtain a mixture; under stirring conditions, water in an amount of 5% of the mass of the mixture was sprayed into the mixture, and the spraying was completed after 20 minutes to obtain a mixture; the mixture was extruded and granulated by a double-roll granulator to obtain granules with an average particle size of 1 mm, and the granules were placed in an iron barrel and sealed for 6 hours to obtain catalytic weathering siderite powder.

[0081] (3) The natural limestone is coarsely crushed, finely crushed, and finely ground, and passed through a 10-mesh sieve. The sieved material is collected to obtain limestone powder.

[0082] (4) 32.5 parts by mass of catalytic weathered siderite powder and 67.5 parts by mass of limestone powder were mixed uniformly to obtain a soil remediation agent.

[0083] Comparative Example 7

[0084] The cadmium-contaminated soil remediation agent of this comparative example is prepared by a method comprising the following steps:

[0085] (1) The natural siderite ore is coarsely crushed, finely crushed, finely ground, passed through a 100-mesh sieve, and the sieve residue is collected to obtain siderite ore powder.

[0086] (2) The ferric chloride and siderite powder in a mass ratio of 7.89:2.11 were stirred for 40 minutes in a dry environment to be fully mixed to obtain a mixture; under stirring conditions, 5% of the mass of the mixture was sprayed into the mixture, and the spraying was completed after 20 minutes to obtain a mixture; the mixture was extruded and granulated by a double-roll granulator to obtain granules with an average particle size of 1 mm, and the granules were placed in an iron barrel and sealed for 6 hours to obtain catalytic weathering siderite powder.

[0087] (3) The natural limestone is coarsely crushed, finely crushed, and finely ground, and passed through a 10-mesh sieve. The sieved material is collected to obtain limestone powder.

[0088] (4) 32.5 parts by mass of catalytic weathered siderite powder and 67.5 parts by mass of limestone powder were mixed uniformly to obtain a soil remediation agent.

[0089] Comparative Example 8

[0090] The cadmium-contaminated soil remediation agent of this comparative example is prepared by a method comprising the following steps:

[0091] (1) The natural siderite ore is coarsely crushed, finely crushed, finely ground, passed through a 100-mesh sieve, and the sieve residue is collected to obtain siderite ore powder.

[0092] (2) Ferrous chloride and siderite powder in a mass ratio of 7.89:2.11 were stirred in a dry environment for 40 minutes to be fully mixed to obtain a mixture.

[0093] (3) The natural limestone is coarsely crushed, finely crushed, and finely ground, and passed through a 10-mesh sieve. The sieved material is collected to obtain limestone powder.

[0094] (4) 32.5 parts by mass of the mixed material and 67.5 parts by mass of limestone powder were uniformly mixed to obtain a soil remediation agent.

[0095] Comparative Example 9

[0096] The cadmium-contaminated soil remediation agent of this comparative example is prepared by a method comprising the following steps:

[0097] (1) The natural siderite ore is coarsely crushed, finely crushed, finely ground, passed through a 100-mesh sieve, and the sieve residue is collected to obtain siderite ore powder.

[0098] (2) Stirring ferrous chloride and water to obtain a mixture; then stirring the mixture and siderite powder to obtain a mixture, extruding and granulating the mixture with a double-roll granulator to obtain a granular material with an average particle size of 1 mm, and sealing the granular material in an iron barrel for 6 hours to obtain catalytic weathering siderite powder. The mass ratio of ferrous chloride to siderite powder is 7.89:2.11, and the mass of water is 5% of the total mass of ferrous chloride and siderite powder.

[0099] (3) The natural limestone is coarsely crushed, finely crushed, and finely ground, and passed through a 10-mesh sieve. The sieved material is collected to obtain limestone powder.

[0100] (4) 32.5 parts by mass of catalytic weathered siderite powder and 67.5 parts by mass of limestone powder were mixed uniformly to obtain a soil remediation agent.

[0101] 2. The specific embodiments of the method for repairing cadmium-contaminated soil of the present invention are as follows:

[0102] The method for repairing cadmium-contaminated soil of this embodiment comprises the following steps: applying any cadmium-contaminated soil repair agent in Examples 1-3 to a paddy field, then cultivating the land, so that the cadmium-contaminated soil repair agent is fully mixed with the cultivated layer soil, and finally irrigating the farmland. Specifically, a pump can be used to fully irrigate the farmland, and the water surface should not exceed the soil layer, and supplementary irrigation should be performed frequently to keep the field both fully hydrated and not full of the unearthed layer. Among them, the application amount of the cadmium-contaminated soil repair agent is 520~547kg / mu, and the specific amount can be determined according to the degree of cadmium contamination in the soil to be repaired and the repair effect to be achieved. In general, the larger the application amount of the cadmium-contaminated soil repair agent within the range of 520~547kg / mu, the better the repair effect and the faster the repair speed.

[0103] Test Case

[0104] In order to evaluate the repair effect of the cadmium-contaminated soil remediation agent of each embodiment and comparative example, the cadmium-contaminated soil remediation agent of each embodiment and comparative example was evenly spread into the same rice field (547 kg of cadmium-contaminated soil remediation agent was applied per mu of rice field), and then the land was cultivated to fully mix the cadmium-contaminated soil remediation agent with the plough layer soil, and finally the farmland was irrigated to ensure that the farmland soil was in a moist state, and the cadmium activity of the farmland soil was gradually reduced after balancing for 30 days, and then rice was planted. The rice varieties include early rice and late rice. After the experiment, the cadmium concentration C and the exchangeable cadmium concentration C0 in the rice field without the application of the cadmium-contaminated soil remediation agent, the exchangeable cadmium concentration C1 in the rice field with the application of the cadmium-contaminated soil remediation agent, the cadmium concentration C2 of the early rice planted in the rice field without the application of the cadmium-contaminated soil remediation agent and the cadmium concentration C3 of the late rice, the cadmium concentration C4 of the early rice planted in the rice field with the application of the cadmium-contaminated soil remediation agent and the cadmium concentration C5 of the late rice, and the experimental results are shown in Table 1. Among them, exchangeable cadmium refers to the sum of water-soluble cadmium and ion-exchangeable cadmium in the soil.

[0105] Table 1 The remediation effects of cadmium-contaminated soil remediation agents of various examples and comparative examples

[0106] Restorative Agent C (μg / kg) C0(μg / kg) C1(μg / kg) C2 (μg / kg) C3 (μg / kg) C4 (μg / kg) C5 (μg / kg) Example 1 1.5034 0.5427 0.1653 2.7703 2.0210 0.1412 0.1310 Example 2 1.5034 0.5427 0.1954 2.7703 2.0210 0.1601 0.1405 Example 3 1.5034 0.5427 0.1804 2.7703 2.0210 0.1506 0.1413 Comparative Example 1 1.5034 0.5427 0.5028 2.7703 2.0210 2.1213 1.9308 Comparative Example 2 1.5034 0.5427 0.5106 2.7703 2.0210 1.2171 2.4012 Comparative Example 3 1.5034 0.5427 0.4889 2.7703 2.0210 1.9108 0.9801 Comparative Example 4 1.5034 0.5427 0.4175 2.7703 2.0210 1.7204 1.8659 Comparative Example 5 1.5034 0.5427 0.5068 2.7703 2.0210 1.8192 1.7358 Comparative Example 6 1.5034 0.5427 0.3752 2.7703 2.0210 0.8532 0.7958 Comparative Example 7 1.5034 0.5427 0.4718 2.7703 2.0210 0.9216 0.8106 Comparative Example 8 1.5034 0.5427 0.4175 2.7703 2.0210 1.6752 1.8365 Comparative Example 9 1.5034 0.5427 0.3765 2.7703 2.0210 0.7562 0.8317

[0107] It can be seen from Table 1 that, compared with the cadmium-contaminated soil remediation agent of the comparative example, the cadmium-contaminated soil remediation agent of the present invention can effectively reduce the exchangeable cadmium concentration in the paddy field, the cadmium concentration of early rice and the cadmium concentration of late rice, and improve the economic and ecological benefits of cadmium-contaminated paddy field soil. It can be seen from Example 1, Comparative Example 4 and Comparative Example 5 that after the siderite powder is replaced with goethite powder or hematite powder, the remediation effect of the soil remediation agent becomes worse, indicating that the compound use of ferrous chloride and siderite powder has the best remediation effect; it can be seen from Example 1, Comparative Example 6 and Comparative Example 7 that after the ferrous chloride is replaced with ferric chloride or ferrous sulfate, the remediation effect of the soil remediation agent becomes worse, which may be due to the poor reducibility of ferric chloride, which cannot form a wide variety of iron oxides, but can only form iron hydroxide, resulting in the ability of a single type of iron oxide to fix cadmium. The force is poor; and ferrous sulfate contains sulfate ions, which react with calcium ions to form precipitation, resulting in an imbalance between calcium carbonate, bicarbonate and calcium ions in the soil system, causing the repair effect to deteriorate; as shown in Example 1 and Comparative Example 8, after ferrous chloride and siderite powder are mixed in a dry environment, since ferrous chloride and siderite powder do not react, and siderite powder does not wrap ferrous chloride crystals, ferrous chloride and siderite powder are not in close contact, and during subsequent use, siderite powder cannot play a role through reaction, causing a repair effect deviation. As shown in Example 1 and Comparative Example 9, ferrous chloride is first mixed with water, and then mixed with siderite powder, and the siderite powder cannot be wrapped with ferrous chloride. It is also impossible to achieve the wrapping of ferrous chloride by siderite powder, and ferrous chloride can only be infiltrated into the gap of siderite powder in the form of solution, and ferrous ions in ferrous chloride solution are easily oxidized, resulting in a large amount of ferrous chloride converted into ferric chloride.

[0108] In addition, after applying the cadmium-contaminated soil remediation agent, continuous observation and monitoring for 3 years showed that the exchangeable cadmium concentration of the paddy field applied with the cadmium-contaminated soil remediation agent of Examples 1-3 was less than 20% of the exchangeable cadmium concentration C0 in the third year, and the cadmium content of the rice was stable below 0.20 μg / kg; while the exchangeable cadmium concentration of the paddy field applied with the cadmium-contaminated soil remediation agent of Comparative Examples 1-9 was greater than 40% of the exchangeable cadmium concentration C0 in the third year, and the cadmium content of the rice was greater than 0.20 μg / kg. Therefore, the cadmium-contaminated soil remediation agent of the present invention has a long-term remediation effect.

[0109] It should be noted that, in this article, the terms: include, contain and any other variants are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. Specific examples are used in this article to illustrate the principle and implementation of the technical solution of the present invention. The above examples are only used to help understand the method of the present invention and its core idea. The above is only a preferred implementation of the present invention. It should be pointed out that due to the limitations of textual expression and the objective existence of infinite specific structures, for ordinary technicians in this technical field, without departing from the principle of the present invention, several improvements, modifications or changes can be made, and the above technical features can also be combined in an appropriate manner; these improvements, modifications, changes or combinations, or the direct application of the concept and technical solution of the present invention to other occasions without improvement, should be regarded as the protection scope of the present invention.

Claims

1. A cadmium-contaminated soil remediation agent, characterized in that: The invention is composed of 29.4-32.5 parts by mass of catalytically weathered siderite powder and 67.5-70.6 parts by mass of limestone powder; the catalytically weathered siderite powder is prepared by a method comprising the following steps: spraying water on a mixture consisting of ferrous chloride and siderite powder under stirring to obtain a mixture, granulating the mixture to obtain a granular material, and then sealing and standing the granular material for 6-24 hours to obtain the catalytically weathered siderite powder; the mass ratio of ferrous chloride to siderite powder in the mixture is 7.04-7.89:2.11-2.96, the mass of water is 5-10% of the total mass of ferrous chloride and siderite powder; the particle size of the siderite powder is not less than 100 mesh, the particle size of the limestone powder is not less than 10 mesh, and the average particle size of the granular material is 1-2 mm.

2. The cadmium-contaminated soil remediation agent according to claim 1, characterized in that: The mass fraction of ferrous carbonate in the siderite powder is not less than 80%.

3. The cadmium-contaminated soil remediation agent according to claim 1, characterized in that: The mass fraction of calcium carbonate in the limestone powder is not less than 90%.

4. A method for remediating cadmium-contaminated soil, characterized in that: The following steps are involved: The cadmium-contaminated soil remediation agent according to any one of claims 1 to 3 is applied to the soil to be remediated for remediation.

5. The method for remediating cadmium-contaminated soil according to claim 4, characterized in that: The application amount of the cadmium-contaminated soil remediation agent is 520-547 kg / mu.

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