Preparation method of heavy metal polluted soil stabilizing agent, heavy metal polluted soil stabilizing agent and application of heavy metal polluted soil stabilizing agent

Abstract

The invention discloses a preparation method of a heavy metal contaminated soil stabilizing agent, the heavy metal contaminated soil stabilizing agent and application of the heavy metal contaminated soil stabilizing agent, and relates to the technical field of solid waste treatment.The preparation method of the heavy metal contaminated soil stabilizing agent comprises the following steps that cereal straw is subjected to alkaline modification, and modified cereal straw is obtained; mixing the modified cereal straw with ardealite, and performing heat treatment to obtain a first mixture; the first mixture and blast furnace slag powder are mixed and smashed, and a second mixture is obtained; and mixing the second mixture with industrial alkaline residues to obtain the heavy metal polluted soil stabilizing agent. The raw materials used in the invention are all solid waste materials and are green and environment-friendly, and the prepared heavy metal polluted soil stabilizing agent can adsorb and complex heavy metals in the heavy metal polluted soil through hydration products formed by hydration of the agent, so that the heavy metals are fixed, and the migration of pollutants is effectively inhibited.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste treatment, and in particular to a preparation method of a heavy metal contaminated soil stabilization agent, a heavy metal contaminated soil stabilization agent and applications thereof. Background Art

[0002] Heavy metals in soil come from a variety of sources, including natural processes and human activities, such as mining, industrial emissions, and pesticide use. When the concentration of certain heavy metal elements in the soil exceeds the normal background value or the prescribed safety standard, it is called heavy metal contaminated soil. Because it cannot be stabilized or degraded by itself, it will cause the accumulation and sedimentation of heavy metals in the soil, causing the concentration of heavy metals in the soil to far exceed the background. Long-term accumulation will not only change the structure and function of the soil, but also enter the bodies of animals and humans through the food chain, thus threatening human health. Summary of the invention

[0003] The main purpose of the present invention is to provide a preparation method of a heavy metal contaminated soil stabilization agent, a heavy metal contaminated soil stabilization agent and its application, aiming to solve the problem of high heavy metal concentration in soil in the prior art.

[0004] To achieve the above object, the present invention provides a method for preparing a heavy metal contaminated soil stabilization agent, comprising the following steps:

[0005] S10, performing alkaline modification on the cereal straw to obtain modified cereal straw;

[0006] S20, mixing the modified cereal straw and phosphogypsum, and performing heat treatment to obtain a first mixture;

[0007] S30, mixing the first mixture and blast furnace slag powder, and crushing them to obtain a second mixture;

[0008] S40, mixing the second mixture with industrial alkali slag to obtain the heavy metal contaminated soil stabilization agent.

[0009] In one embodiment, the mass of the heavy metal contaminated soil stabilization agent raw material is W, the mass of the blast furnace slag powder is W1, the mass of the phosphogypsum is W2, the mass of the cereal straw is W3, and the mass of the industrial alkali slag is W4, wherein:

[0010] W1:W=(50~70):100, W2:W=(30~50):100;

[0011] W3: (W1+W2)=(10~20):100, W4: (W1+W2)=(10~20):100.

[0012] In one embodiment, step S10 comprises: soaking the cereal straw with an alkaline solution to obtain modified cereal straw;

[0013] Wherein, the cereal straw includes at least one of corn straw, wheat straw and rice straw; and / or,

[0014] The soaking time is 20 to 26 hours; and / or,

[0015] The alkaline solution comprises a sodium hydroxide solution or a calcium hydroxide solution; and / or,

[0016] The mass concentration of alkali in the alkaline solution is 1.3-1.7%; and / or,

[0017] The mass ratio of the alkaline solution to the cereal straw is (8-12):1.

[0018] In one embodiment, in step S20, the temperature of the heat treatment is 600-800° C.; and / or,

[0019] In step S20, the heat treatment time is 1.5 to 2.5 hours; and / or,

[0020] In step S30, the pulverizing method includes ball milling, the rotation speed of the ball mill is 300 to 500 r / min, and the time of the ball milling is 15 to 25 min.

[0021] In one embodiment, in step S40:

[0022] The mixing speed is 100-150 r / min; and / or,

[0023] The mixing time is 3 to 5 minutes.

[0024] The present invention also provides a heavy metal contaminated soil stabilization agent, which is prepared by the aforementioned preparation method of the heavy metal contaminated soil stabilization agent.

[0025] The present invention also provides an application of the aforementioned heavy metal contaminated soil stabilization agent in solidifying heavy metals in heavy metal contaminated soil.

[0026] In one embodiment, the aforementioned application comprises the following steps:

[0027] S10, mixing the heavy metal contaminated soil stabilization agent and the heavy metal contaminated soil to obtain a dry basis mixture;

[0028] S20, mixing the dry base mixture with water to obtain a wet base mixture;

[0029] S30, pressing the wet-base mixture into a shape, and allowing it to stand for curing to allow it to undergo a hydration reaction, thereby obtaining treated heavy metal contaminated soil.

[0030] In one embodiment, in step S10, the heavy metal in the heavy metal contaminated soil includes at least one of copper, cadmium, hexavalent chromium and lead, and the mass concentration of the heavy metal in the heavy metal contaminated soil is 40 to 18000 mg / kg; and / or,

[0031] In step S10, the mass ratio of the heavy metal contaminated soil stabilization agent to the heavy metal contaminated soil is (10-30): (70-90); and / or,

[0032] In step S20, the mass percentage of water in the wet-base mixture is 15-20%; and / or,

[0033] In step S30, the pressing pressure is 50-58 kN, and the pressing rate is 5-7 kN / min; and / or,

[0034] In step S30, the curing temperature is 18-22°C, the curing humidity is 94-96%, and the curing time is 7-28 days.

[0035] In one embodiment, step S20 includes: sequentially mixing the dry base mixture and water for a first time and a second time;

[0036] Wherein, the rotation speed of the first mixing is 100-150 r / min; and / or,

[0037] The first mixing time is 3 to 5 minutes; and / or,

[0038] The second mixing speed is 250-300 r / min; and / or,

[0039] The second mixing time is 2 to 3 minutes.

[0040] The present invention provides a preparation method of a heavy metal contaminated soil stabilization agent, a heavy metal contaminated soil stabilization agent and an application thereof, wherein cereal straw is subjected to alkaline modification to destroy cellulose structures such as cellulose and lignin in the cereal straw, increase and enlarge the pores on the fiber wall of the cereal straw, increase the channels entering the interior of the fiber wall from the outside, and also expand the specific surface area of ​​the channels; at the same time, the hydrogen bonds between the hydroxyl groups in the crystalline region of the wood fiber in the cereal straw are weakened, the orientation of the fiber molecules is improved, and the hydroxyl groups on the cellulose and hemicellulose molecules are exposed. After the modified grain straw is mixed with phosphogypsum, the phosphogypsum adheres to the surface of the grain straw to form a covering layer. During the heat treatment process: on the one hand, the internal pores of the modified grain straw are further enlarged during the heat treatment process, and a carbon skeleton is gradually formed. Due to the influence of the modification treatment, the pores on the surface of the obtained carbon skeleton are more and larger, and the specific surface area is larger, providing more accommodation space for heavy metal ions. At the same time, the ash residue after carbonization of the modified grain straw is alkaline, which can provide an alkaline environment for the subsequent hydration reaction and promote the hydration process; on the other hand, during the heat treatment process, the alkaline substances in the modified grain straw and the exposed hydroxyl groups on its surface alkalize the phosphogypsum, removing impurities such as phosphoric acid, chloride and sulfide in the phosphogypsum, so that the main component of the phosphogypsum is converted from CaSO4·2H2O to CaSO4, providing sulfate ions for the subsequent hydration reaction and promoting the full hydration reaction. The addition of blast furnace slag powder and industrial alkali slag provides the main reaction components and alkaline environment for the subsequent hydration reaction, respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0042] Figure 1 The X-ray diffraction pattern of the phosphogypsum raw material in Example 1 provided by the present invention;

[0043] Figure 2 This is the X-ray diffraction pattern of the stabilizing agent in Example 1 provided by the present invention after hydration for 28 days;

[0044] Figure 3 The microscopic morphology of the stabilizing agent in Example 1 provided by the present invention after hydration for 28 days;

[0045] Figure 4The microscopic morphology of the composite heavy metal contaminated soil having the contents of Cu, Cd, Cr(VI) and Pb of 6000 mg / kg, 40 mg / kg, 1000 mg / kg and 10,000 mg / kg respectively in Example 7 provided by the present invention after being solidified by the stabilizing agent by the method of Example 1 for 28 days;

[0046] Figure 5 The X-ray diffraction spectrum of the composite heavy metal contaminated soil in Example 7 provided by the present invention, wherein the contents of Cu, Cd, Cr(VI) and Pb are 6000 mg / kg, 40 mg / kg, 1000 mg / kg and 10,000 mg / kg respectively;

[0047] Figure 6 The X-ray diffraction spectrum of the composite heavy metal contaminated soil in Example 7 provided by the present invention, in which the contents of Cu, Cd, Cr(VI) and Pb are 6000 mg / kg, 40 mg / kg, 1000 mg / kg and 10,000 mg / kg respectively, after being solidified with a stabilizing agent for 28 days using the method of Example 1.

[0048] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0049] To make the purpose, technical scheme and advantages of the embodiment of the present invention clearer, the technical scheme in the embodiment of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiment, it is carried out according to the normal conditions or the conditions recommended by the manufacturer. If the reagents or instruments used do not specify the manufacturer, they are all conventional products that can be purchased commercially. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes, taking "A and / or B" as an example, including scheme A, or scheme B, or schemes that A and B meet at the same time. In addition, the technical schemes between the various embodiments can be combined with each other, but must be based on the ability of ordinary technicians in the field to achieve. When the combination of technical solutions is contradictory or cannot be achieved, it should be considered that the combination of such technical solutions does not exist, and is not within the scope of protection required by the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present invention.

[0050] Heavy metals in soil come from a variety of sources, including natural processes and human activities, such as mining, industrial emissions, and pesticide use. When the concentration of certain heavy metal elements in the soil exceeds the normal background value or the prescribed safety standard, it is called heavy metal contaminated soil. Because it cannot be stabilized or degraded by itself, it will cause the accumulation and sedimentation of heavy metals in the soil, causing the concentration of heavy metals in the soil to far exceed the background. Long-term accumulation will not only change the structure and function of the soil, but also enter the bodies of animals and humans through the food chain, thus threatening human health.

[0051] In view of this, the present invention provides a method for preparing a heavy metal contaminated soil stabilization agent, comprising the following steps:

[0052] S10, performing alkaline modification on the cereal straw to obtain modified cereal straw;

[0053] S20, mixing the modified cereal straw and phosphogypsum, and performing heat treatment to obtain a first mixture;

[0054] S30, mixing the first mixture and blast furnace slag powder, and crushing them to obtain a second mixture;

[0055] S40, mixing the second mixture with industrial alkali slag to obtain the heavy metal contaminated soil stabilization agent.

[0056] In the technical scheme of the present invention, the cereal straw is alkaline-modified, which destroys the cellulose structures such as cellulose and lignin in the cereal straw, increases and enlarges the pores on the fiber wall of the cereal straw, increases the channels from the outside to the inside of the fiber wall, and also expands the specific surface area of ​​the channels; at the same time, the hydrogen bonds between the hydroxyl groups in the crystalline region of the wood fiber in the cereal straw are weakened, the orientation of the fiber molecules is improved, and the hydroxyl groups on the cellulose and hemicellulose molecules are exposed. After the modified grain straw is mixed with phosphogypsum, the phosphogypsum adheres to the surface of the grain straw to form a covering layer. During the heat treatment process: on the one hand, the internal pores of the modified grain straw are further enlarged during the heat treatment process, and a carbon skeleton is gradually formed. Due to the influence of the modification treatment, the pores on the surface of the obtained carbon skeleton are more and larger, and the specific surface area is larger, providing more accommodation space for heavy metal ions. At the same time, the ash residue after carbonization of the modified grain straw is alkaline, which can provide an alkaline environment for the subsequent hydration reaction and promote the hydration process; on the other hand, during the heat treatment process, the alkaline substances in the modified grain straw and the exposed hydroxyl groups on its surface alkalize the phosphogypsum, removing impurities such as phosphoric acid, chloride and sulfide in the phosphogypsum, so that the main component of the phosphogypsum is converted from CaSO4·2H2O to CaSO4, providing sulfate ions for the subsequent hydration reaction and promoting the full hydration reaction. The addition of blast furnace slag powder and industrial alkali slag provides the main reaction components and alkaline environment for the subsequent hydration reaction, respectively.

[0057] It should be noted that during the heat treatment process, the alkalinity of the modified grain straw and the exposed hydroxyl groups on the surface of the modified grain straw on the phosphogypsum refers to the reaction of the alkaline substances in the modified grain straw with the acidic substances in the phosphogypsum (in the form of H3PO4, H2PO4 - 、HPO4 2- PO4 3- In the presence of soluble phosphorus (P2O5) and fluoride (F - )reaction.

[0058] The blast furnace slag, phosphogypsum and industrial alkali slag in the raw materials are dry, that is, they are dried in advance at 100-110° C. to constant weight and then sieved to have a particle size of 80-120 meshes.

[0059] Blast furnace slag is a solid waste produced by industrial blast furnace ironmaking, and its surface structure is loose and porous.

[0060] In some embodiments of the present invention, the mass of the heavy metal contaminated soil stabilization agent raw material is W, the mass of the blast furnace slag powder is W1, the mass of the phosphogypsum is W2, the mass of the cereal straw is W3, and the mass of the industrial alkali slag is W4, wherein:

[0061] W1:W=(50~70):100, W2:W=(30~50):100;

[0062] W3: (W1+W2)=(10~20):100, W4: (W1+W2)=(10~20):100.

[0063] In the technical solution of the present invention, W1:W can be 50:100, 60:100 or 70:100, W2:W can be 30:100, 40:100 or 50:100, W3:(W1+W2) can be 10:100, 15:100 or 20:100, W4:(W1+W2) can be 10:100, 15:100 or 20:100. The quality of the raw materials within the above range can ensure that the heavy metal contaminated soil stabilization agent has a good solidification effect on the heavy metals in the heavy metal contaminated soil.

[0064] In some embodiments of the present invention, step S10 includes: soaking the cereal straw with an alkaline solution to obtain modified cereal straw;

[0065] Wherein, the cereal straw includes at least one of corn straw, wheat straw and rice straw; and / or,

[0066] The soaking time is 20 to 26 hours; and / or,

[0067] The alkaline solution comprises a sodium hydroxide solution or a calcium hydroxide solution; and / or,

[0068] The mass concentration of alkali in the alkaline solution is 1.3-1.7%; and / or,

[0069] The mass ratio of the alkaline solution to the cereal straw is (8-12):1.

[0070] In the technical solution of the present invention, the cereal straw is alkaline-modified by the above method, and the alkali metal content in the modified cereal straw is high, and the pores on the fiber wall of the cereal straw are more and larger, and there are more exposed hydroxyl groups on the cellulose and hemicellulose molecules.

[0071] In some embodiments of the present invention, in step S20, the temperature of the heat treatment is 600-800°C; and / or, in step S20, the time of the heat treatment is 1.5-2.5h; and / or, in step S30, the crushing method includes ball milling, the rotation speed of the ball mill is 300-500r / min, and the time of the ball mill is 15-25min.

[0072] In the technical solution of the present invention, in step S20, the temperature of the heat treatment can be 600°C, 700°C or 800°C, and the time of the heat treatment can be 1.5h, 2h or 2.5h. The heat treatment temperature and time within the above range can ensure that: (1) the alkalization reaction between the modified cereal straw and the phosphogypsum is more complete, (2) the phosphate impurities in the phosphogypsum are removed and its main component is converted into CaSO4, and (3) the modified cereal straw is fully carbonized to form a carbon skeleton.

[0073] In step S30, the rotation speed of the ball mill can be 300r / min, 400r / min or 500r / min, and the ball milling time can be 15min, 20min or 25min. The particle size of the phosphogypsum after ball milling becomes smaller, which increases the surface area of ​​the phosphogypsum in contact with water during the hydration process; and during the ball milling process, the heat generated by the collision and friction between the particles can melt the surface of the particles to form a new active surface, which is beneficial to the hydration reaction; the stress and energy generated during the ball milling process can also promote the transformation of the crystal structure of the phosphogypsum, making it easier to participate in the hydration reaction, and promoting the transformation of the mineral crystal and lattice structure during hydration.

[0074] In some embodiments of the present invention, in step S40: the mixing speed is 100-150 r / min; and / or the mixing time is 3-5 min.

[0075] In the technical solution of the present invention, in step S40: the mixing speed is 100r / min, 120r / min or 150r / min, and the mixing time is 3min, 4min or 5min. The mixing speed and time within the above range can ensure that the raw materials of the heavy metal contaminated soil stabilization agent are mixed more evenly, the contact area between the four raw materials is large, and the subsequent hydration reaction is easier to carry out.

[0076] The present invention also provides a heavy metal contaminated soil stabilization agent, which is prepared by the above-mentioned preparation method of the heavy metal contaminated soil stabilization agent. Therefore, it has all the beneficial effects of the heavy metal contaminated soil stabilization agent, which will not be described one by one here. The raw materials of the stabilization agent of the present invention are all solid waste materials, which are green and environmentally friendly.

[0077] The present invention also provides an application of the aforementioned heavy metal contaminated soil stabilization agent in solidifying heavy metals in heavy metal contaminated soil. Therefore, it has all the beneficial effects of the heavy metal contaminated soil stabilization agent, which will not be repeated here. The heavy metal contaminated soil stabilization agent of the present invention can replace cement-based materials, avoid the large amount of carbon dioxide, sulfur dioxide, carbon monoxide, solid waste and a large amount of industrial wastewater generated in the cement production process, and reduce environmental pollution.

[0078] In some embodiments of the present invention, the aforementioned application comprises the following steps:

[0079] S10, mixing the heavy metal contaminated soil stabilization agent and the heavy metal contaminated soil to obtain a dry basis mixture;

[0080] S20, mixing the dry base mixture with water to obtain a wet base mixture;

[0081] S30, pressing the wet-base mixture into a shape, and allowing it to stand for curing to allow it to undergo a hydration reaction, thereby obtaining treated heavy metal contaminated soil.

[0082] In the technical solution of the present invention, the dry-base mixture is mixed with water to form a wet-base mixture. The addition of water helps to start and promote the chemical reaction between the stabilizing agent and the heavy metal, and helps the subsequent molding process.

[0083] The main substrates of the hydration reaction during the static curing process are the active substances CaO, Al2O3 and SiO2 in blast furnace slag powder and the main component CaSO4 after mixed burning of phosphogypsum.

[0084] The principle of its hydration reaction is as follows: first, after the stabilizing agent is mixed with water, the industrial alkali slag is first dissolved in the water, providing an alkaline environment for the system and promoting the process of the hydration reaction. Secondly, the phosphogypsum after mixed burning hydrates quickly, and its main component CaSO4 reacts quickly with water in an alkaline environment to crystallize into CaSO4·2(H2O), and they are interlaced and superimposed to form a supporting skeleton, so that the overall structure can have good mechanical properties in the early stage. However, due to the irregular shape of the crystals and their loose distribution, the overall structure is not tight and has many pores. After that, as the hydration reaction proceeds further, crystals continue to form, and at the same time, the aluminum oxygen bonds and silicon oxygen bonds in the system break, and react with calcium sulfate to form a part of calcium sulfonate (AFt), which fills the internal structure pores together with CaSO4·2(H2O) crystals, reducing the porosity of the overall structure. Thirdly, the hydration of blast furnace slag is relatively slow, but the high content of CaO, SiO2 and Al2O3 in it undergoes a volcanic ash reaction in an alkaline environment. As the curing time increases, the surface structure of each mineral component is gradually corroded by water molecules and alkaline components, causing it to 4+ 、Al 3+ ) is dissolved in the system, and a large amount of AFt is generated under the stimulation of the sulfate component in the system, which fills the overall structure in the form of long needles or short columns. In addition, the dispersed mineral ions are recombined to generate a large amount of hydrated calcium silicate (CSH) and hydrated calcium aluminosilicate (CASH) gels to wrap the various crystal components in the system in a network structure. At the same time, the generated Aft, CSH gel and CASH gel are combined with the heavy metal ions in the contaminated soil to generate a stable compound structure, so that the stabilization agent can play a role in solidifying the heavy metals in the contaminated soil. The specific reaction formula is as follows:

[0085] CaSO4+2H2O→CaSO4·2H2O;

[0086] Al2O3+2OH - →2AlO2 - +H2O;

[0087] SiO2+2OH - →SiO3 2- +H2O;

[0088] 6Ca 2+ +2AlO2 - +3(SO4) 2- +28H2O→Ca6[Al(OH)6]2·(SO4)3·26H2O;

[0089]

[0090] Through the above application steps, the heavy metal contaminated soil stabilization agent can adsorb and complex the heavy metals in the heavy metal contaminated soil through the hydration products formed by its hydration action, so that the heavy metals are more fully fixed, thereby effectively inhibiting the migration of pollutants.

[0091] In some embodiments of the present invention, in step S10, the heavy metal in the heavy metal contaminated soil includes at least one of copper, cadmium, hexavalent chromium and lead, and the mass concentration of the heavy metal in the heavy metal contaminated soil is 40 to 18000 mg / kg. That is, the heavy metal in the heavy metal contaminated soil can be any one of copper, cadmium, hexavalent chromium and lead, or two or more of copper, cadmium, hexavalent chromium and lead, all within the protection scope of the present invention. The mass concentration of the heavy metal in the heavy metal soil can be 40 mg / kg, 400 mg / kg, 4000 mg / kg, 4000 mg / kg or 18000 mg / kg, and its mass concentration within this range can ensure a good curing effect.

[0092] In some embodiments of the present invention, in step S10, the mass ratio of the heavy metal contaminated soil stabilization agent to the heavy metal contaminated soil is (10-30): (70-90). The mass ratio of the heavy metal contaminated soil stabilization agent to the heavy metal contaminated soil can be 10:90, 20:80 or 30:70, and the mass ratio within the above range can ensure that the heavy metal contaminated soil is fully hydrated.

[0093] In some embodiments of the present invention, in step S20, the mass percentage of water in the wet-based mixture is 15-20%. The mass percentage of water in the wet-based mixture can be 15%, 18% or 20%, and the mass percentage within the above range can ensure sufficient hydration.

[0094] In some embodiments of the present invention, in step S30, the pressing pressure is 50 to 58 kN, and the pressing rate is 5 to 7 kN / min; and / or, in step S30, the curing temperature is 18 to 22°C, the curing humidity is 94 to 96%, and the curing time is 7 to 28 days. The pressing pressure can be 50kN, 55kN or 58kN, the pressing rate can be 5kN / min, 6kN / min or 7kN / min, the curing temperature can be 18°C, 20°C or 22°C, the curing humidity can be 94%, 95% or 96%, and the curing time can be 7 days, 14 days or 28 days. The pressing conditions and curing conditions within the above range can ensure that the hydration of the heavy metal contaminated soil stabilization agent in the wet-based mixture is more sufficient, and more hydration products Aft, CSH gel and CASH gel are generated. These hydration products can be more fully combined with the heavy metals in the heavy metal contaminated soil to form a stable compound structure, thereby better solidifying the heavy metals in the contaminated soil.

[0095] In some embodiments of the present invention, step S20 includes: mixing the dry base mixture and water for a first time and a second time in sequence; wherein the rotation speed of the first mixing is 100 to 150 r / min; and / or the time of the first mixing is 3 to 5 min; and / or the rotation speed of the second mixing is 250 to 300 r / min; and / or the time of the second mixing is 2 to 3 min.

[0096] In the technical solution of the present invention, the purpose of the first mixing is pre-wetting, and the purpose of the second mixing is to allow the reagent components to fully contact with the heavy metals in the heavy metal contaminated soil.

[0097] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present invention, and are not used to limit the present invention.

[0098] Example 1

[0099] A heavy metal contaminated soil stabilization agent, the raw materials of which include blast furnace slag powder, phosphogypsum, grain straw and industrial alkali slag; wherein:

[0100] The mass percentage of blast furnace slag powder in the heavy metal contaminated soil stabilization agent is 50%;

[0101] The mass percentage of phosphogypsum in the heavy metal contaminated soil stabilization agent is 50%;

[0102] Cereal straw accounts for 10% of the total mass of blast furnace slag powder and phosphogypsum;

[0103] Industrial alkali slag accounts for 10% of the total mass of blast furnace slag powder and phosphogypsum;

[0104] The heavy metal contaminated soil stabilization agent is prepared by the following method:

[0105] Step (1), placing blast furnace slag powder, phosphogypsum and industrial alkali slag in a constant temperature drying oven, setting the temperature to 105° C., drying to constant weight, taking them out and sieving them, so that the particle size of blast furnace slag powder and phosphogypsum is 80 to 200 mesh;

[0106] Step (2), soaking the cereal straw in a 1.5% mass concentration NaOH solution for 24 hours for alkaline modification treatment, then rinsing with water and adjusting the pH to neutral;

[0107] Step (3), placing the phosphogypsum and the modified cereal straw in a muffle furnace and burning them at 600° C. for 2 hours to obtain a first mixture;

[0108] Step (4), placing the first mixture and blast furnace slag powder in a planetary vertical ball mill at a speed of 400 r / min for 20 min for mechanical activation to obtain a second mixture;

[0109] Step (5), mixing the second mixture and industrial alkali slag in a cement mortar mixer to obtain a heavy metal stabilization agent, and sealing and storing the agent.

[0110] Example 2

[0111] A heavy metal contaminated soil stabilization agent, the raw materials of which include blast furnace slag powder, phosphogypsum, grain straw and industrial alkali slag; wherein:

[0112] The mass percentage of blast furnace slag powder in the heavy metal contaminated soil stabilization agent is 60%;

[0113] The mass percentage of phosphogypsum in the heavy metal contaminated soil stabilization agent is 40%;

[0114] Cereal straw accounts for 15% of the total mass of blast furnace slag powder and phosphogypsum;

[0115] Industrial alkali slag accounts for 15% of the total mass of blast furnace slag powder and phosphogypsum.

[0116] The preparation method of the heavy metal contaminated soil stabilization agent is the same as that in Example 1.

[0117] Example 3

[0118] A heavy metal contaminated soil stabilization agent, the raw materials of which include blast furnace slag powder, phosphogypsum, grain straw and industrial alkali slag; wherein:

[0119] The mass percentage of blast furnace slag powder in the heavy metal contaminated soil stabilization agent is 70%;

[0120] The mass percentage of phosphogypsum in the heavy metal contaminated soil stabilization agent is 30%;

[0121] Cereal straw accounts for 20% of the total mass of blast furnace slag powder and phosphogypsum;

[0122] Industrial alkali slag accounts for 20% of the total mass of blast furnace slag powder and phosphogypsum.

[0123] The preparation method of the heavy metal contaminated soil stabilization agent is the same as that in Example 1.

[0124] Example 4

[0125] A heavy metal contaminated soil stabilization agent, the raw materials of which include blast furnace slag powder, phosphogypsum, grain straw and industrial alkali slag; wherein:

[0126] The mass percentage of blast furnace slag powder in the heavy metal contaminated soil stabilization agent is 50%;

[0127] The mass percentage of phosphogypsum in the heavy metal contaminated soil stabilization agent is 50%;

[0128] Cereal straw accounts for 15% of the total mass of blast furnace slag powder and phosphogypsum;

[0129] Industrial alkali slag accounts for 20% of the total mass of blast furnace slag powder and phosphogypsum.

[0130] The preparation method of the heavy metal contaminated soil stabilization agent is the same as that in Example 1.

[0131] Example 5

[0132] A heavy metal contaminated soil stabilization agent, the raw materials of which include blast furnace slag powder, phosphogypsum, grain straw and industrial alkali slag; wherein:

[0133] The mass percentage of blast furnace slag powder in the heavy metal contaminated soil stabilization agent is 60%;

[0134] The mass percentage of phosphogypsum in the heavy metal contaminated soil stabilization agent is 40%;

[0135] Cereal straw accounts for 20% of the total mass of blast furnace slag powder and phosphogypsum;

[0136] Industrial alkali slag accounts for 15% of the total mass of blast furnace slag powder and phosphogypsum.

[0137] The preparation method of the heavy metal contaminated soil stabilization agent is the same as that in Example 1.

[0138] Example 6

[0139] A heavy metal contaminated soil stabilization agent, the raw materials of which include blast furnace slag powder, phosphogypsum, grain straw and industrial alkali slag; wherein:

[0140] The mass percentage of blast furnace slag powder in the heavy metal contaminated soil stabilization agent is 70%;

[0141] The mass percentage of phosphogypsum in the heavy metal contaminated soil stabilization agent is 30%;

[0142] Cereal straw accounts for 10% of the total mass of blast furnace slag powder and phosphogypsum;

[0143] Industrial alkali slag accounts for 20% of the total mass of blast furnace slag powder and phosphogypsum.

[0144] The preparation method of the heavy metal contaminated soil stabilization agent is the same as that in Example 1.

[0145] Example 7

[0146] The invention discloses an application of a heavy metal contaminated soil stabilization agent in solidifying heavy metals in the heavy metal contaminated soil, comprising the following steps:

[0147] (1) A heavy metal contaminated soil stabilization agent and a composite heavy metal contaminated soil are uniformly mixed at 25° C. to obtain a dry basis mixture; wherein the mass ratio of the composite heavy metal contaminated soil stabilization agent to the heavy metal contaminated soil is 30:70; the heavy metals in the composite heavy metal contaminated soil are copper (Cu), cadmium (Cd), hexavalent chromium [Cr(VI)] and lead (Pb), and the contents of Cu, Cd, Cr(VI) and Pb are 6000 mg / kg, 40 mg / kg, 1000 mg / kg and 10,000 mg / kg, respectively.

[0148] The preparation method of the above-mentioned composite heavy metal contaminated soil is as follows: the soil is taken from the clay near Changqing Garden in Wuhan City (natural moisture content w: 17.2%; natural density ρ: 1.96g / cm 3 , plastic limit w p : 17.9%, liquid limit w L: 38.5%, cohesion c: 62kPa), collected at a depth of 30 to 50 cm below the surface, and after the soil is naturally air-dried, plant roots, gravel and other foreign matter are removed, and then weighed after sieving through a 2mm aperture. Referring to the soil quality standard (GB15618-2018), after preparing the heavy metal solution using copper nitrate, cadmium nitrate, potassium dichromate and lead nitrate analytical pure reagents and deionized water, the set concentrations of Cu(NO3)2, Cd(NO3)2, K2Cr2O7 and Pb(NO3)2 solutions are evenly sprayed into the soil to make the soil sample reach the set concentration. After adding deionized water, stir, seal and cure for 30 days under standard curing conditions until the heavy metal ions are fully mixed with the soil to make heavy metal contaminated soil. The contaminated soil is crushed and sieved through a 2mm aperture to obtain contaminated soil with a particle size of less than 2mm for use.

[0149] (2) mixing the dry base mixture and water in a cement mortar mixer at a low speed of 150 r / min for 5 minutes, and then adjusting the cement mortar mixer to rotate at a high speed of 250 r / min for 3 minutes to mix the materials evenly, thereby obtaining a wet base mixture; the mass percentage of water in the wet base mixture is 20%;

[0150] (3) Weigh the wet base mixture and place it in The compacted solid body was placed in a standard curing box and cured for 7 days under standard curing conditions (temperature 20°C, humidity 95%).

[0151] Example 8

[0152] The invention discloses an application of a heavy metal contaminated soil stabilization agent in solidifying heavy metals in the heavy metal contaminated soil, comprising the following steps:

[0153] (1) mixing a heavy metal contaminated soil stabilization agent and a composite heavy metal contaminated soil at 25° C. to obtain a dry basis mixture; wherein the mass ratio of the composite heavy metal contaminated soil stabilization agent to the heavy metal contaminated soil is 20:80; the heavy metals in the composite heavy metal contaminated soil are copper (Cu), cadmium (Cd), hexavalent chromium [Cr(VI)] and lead (Pb), and the contents of Cu, Cd, Cr(VI) and Pb are 6000 mg / kg, 40 mg / kg, 1000 mg / kg and 10,000 mg / kg, respectively;

[0154] (2) mixing the dry base mixture and water in a cement mortar mixer at a low speed of 150 r / min for 5 minutes, and then adjusting the cement mortar mixer to rotate at a high speed of 250 r / min for 3 minutes to mix the materials evenly, thereby obtaining a wet base mixture; the mass percentage of water in the wet base mixture is 20%;

[0155] (3) Weigh the wet base mixture and place it in The compacted solid body was placed in a standard curing box and cured for 7 days under standard curing conditions (temperature 20°C, humidity 95%).

[0156] Example 9

[0157] The invention discloses an application of a heavy metal contaminated soil stabilization agent in solidifying heavy metals in the heavy metal contaminated soil, comprising the following steps:

[0158] (1) mixing a heavy metal contaminated soil stabilization agent and a composite heavy metal contaminated soil at 25° C. to obtain a dry basis mixture; wherein the mass ratio of the composite heavy metal contaminated soil stabilization agent to the heavy metal contaminated soil is 10:90; the heavy metals in the composite heavy metal contaminated soil are copper (Cu), cadmium (Cd), hexavalent chromium [Cr(VI)] and lead (Pb), and the contents of Cu, Cd, Cr(VI) and Pb are 6000 mg / kg, 40 mg / kg, 1000 mg / kg and 10,000 mg / kg, respectively;

[0159] (2) mixing the dry base mixture and water in a cement mortar mixer at a low speed of 150 r / min for 5 minutes, and then adjusting the cement mortar mixer to rotate at a high speed of 250 r / min for 3 minutes to mix the materials evenly, thereby obtaining a wet base mixture; the mass percentage of water in the wet base mixture is 20%;

[0160] (3) Weigh the wet base mixture and place it in The compacted solid body was placed in a cylindrical stainless steel mold and high-pressure formed using an electro-hydraulic servo press at a molding pressure of 55 kN and a pressing rate of 5 kN / min, and then left to stand for 1 min to prevent the solid body from rebounding. The compacted solid body was placed in a standard curing box and cured for 7 days under standard curing conditions (temperature 20°C, humidity 95%).

[0161] Comparative Example 1

[0162] Compared with Example 1, Comparative Example 1 is different in that:

[0163] There is no grain straw in the raw materials of the heavy metal stabilization agent, and no grain straw is added during the preparation process.

[0164] Comparative Example 2

[0165] Compared with Example 1, Comparative Example 2 is different in that:

[0166] During the preparation of the heavy metal stabilization agent, step (2) is not performed.

[0167] Comparative Example 3

[0168] Compared with Example 1, Comparative Example 3 is different in that:

[0169] In the preparation process of the heavy metal stabilization agent, modified grain straw, phosphogypsum, blast furnace slag powder and industrial alkali slag are directly mixed.

[0170] Performance Testing

[0171] The phosphogypsum in Example 1 was subjected to X-ray diffraction, and the results were as follows: Figure 1 shown.

[0172] Depend on Figure 1 It can be seen that the main components of phosphogypsum raw materials are dihydrate gypsum (CaSO4·2H2O), pentahydrate magnesia [Al2Mg4(OH) 12 (CO3)(H2O)3], calcium phosphate [CaHPO4(H2O)2], etc.

[0173] X-ray diffraction analysis was performed on the stabilized agent in Example 1 after hydration for 28 days. The results are as follows: Figure 2 As shown, the mass ratio of water to stabilizing agent is 2:5, the hydration time is 28 days, and the hydration temperature is 25°C.

[0174] Depend on Figure 2 It can be seen that the stabilizer formed by the synergistic combination of various components generates the main hydration products of dihydrate gypsum, calcite, quartz, calcium sulfonate and calcite after hydration. Among them, the production of calcite is related to the carbonation of hydration products during the curing process, and the carbonate ions in the raw materials mainly come from the modified grain straw. In addition, the high diffraction peaks of dihydrate gypsum, quartz and calcite in the mineral crystal phase indicate that the various components in the system have a good synergistic effect, which promotes the hydration reaction. On the other hand, the generated hydration products fill the internal pores of the material, improve the density of the overall structure, and thus enhance the strength performance.

[0175] The microscopic morphology of the stabilized agent in Example 1 was observed after hydration for 28 days. Figure 3 As shown, the mass ratio of water to stabilizing agent is 2:5, the hydration time is 28 days, and the hydration temperature is 25°C.

[0176] Depend on Figure 3Scanning electron microscopy (SEM) observations show that the hydration products generated under alkaline conditions are evenly and densely distributed, among which needle-shaped or short-columnar calcium aluminate fills the pores, and a large amount of amorphous C-(A)-SH gel generated by hydration wraps various mineral crystals inside the structure.

[0177] The microscopic morphology of the composite heavy metal contaminated soil in Example 7 with the contents of Cu, Cd, Cr(VI) and Pb being 6000 mg / kg, 40 mg / kg, 1000 mg / kg and 10,000 mg / kg respectively after being solidified by the stabilizing agent by the method of Example 1 for 28 days was observed. The results are as follows: Figure 4 shown.

[0178] like Figure 4 As shown, the hydration products (CSH gel and Aft) generated by the hydration of the stabilizing agent change their structures after reacting with the heavy metal ions in the contaminated soil, thereby generating a stable compound structure.

[0179] X-ray diffraction analysis was performed on the composite heavy metal contaminated soil in Example 7, wherein the contents of Cu, Cd, Cr(VI) and Pb were 6000 mg / kg, 40 mg / kg, 1000 mg / kg and 10,000 mg / kg, respectively. The results are as follows: Figure 5 shown.

[0180] like Figure 5 As shown, the mineral components containing heavy metals in the original heavy metal contaminated soil are Pb5O8, Pb(NO3)OH, CuO, CdO2, Cd(OH)2, Cd(NO3)2, Na2CrO4, Cr2O6, etc.

[0181] The composite heavy metal contaminated soil in Example 7 with Cu, Cd, Cr(VI) and Pb contents of 6000 mg / kg, 40 mg / kg, 1000 mg / kg and 10,000 mg / kg respectively was solidified with a stabilizing agent by the method of Example 1 for 28 days and then subjected to X-ray diffraction analysis.

[0182] Depend on Figure 6 It is known that after being solidified by stabilizing agents, mineral phases such as calcium silicate hydrate (CSH) and ettringite (AFt) in the hydration products can encapsulate heavy metal ions. Some of them will undergo ion exchange or addition, so that heavy metals are combined with calcium and silicon ions to form a stable structure, thereby stabilizing lead, cadmium, copper and hexavalent chromium ions in contaminated soil.

[0183] The heavy metal contaminated soil stabilization reagents of Examples 1 to 6 were used to fix the heavy metals in the composite heavy metal contaminated soil by the methods of Examples 7, 8 and 9, respectively, and the heavy metal contaminated soil stabilization reagents of Comparative Examples 1 to 3 were used to fix the heavy metals in the composite heavy metal contaminated soil by the method of Example 7. The toxicity results of the leachate in the contaminated soil before solidification and the contaminated soil after solidification were tested according to the national standard "Hazardous Waste Identification Standard-Leaching Toxicity Identification" (GB5085.3-2007), and the leaching test was carried out according to the Chinese Environmental Protection Standard "Solid Waste Toxicity Leaching Method Sulfuric Acid and Nitric Acid Method" (HJ / T300-2007). The test results are shown in Table 1.

[0184] Table 1 Concentrations of four heavy metals in the leachate of heavy metal contaminated soil

[0185]

[0186] As shown in Table 1, the heavy metal stabilization agents of the present embodiment can significantly reduce the heavy metal leaching amount, and the leaching amount meets the requirements of the national standard "Hazardous Waste Identification Standard-Leaching Toxicity Identification" (GB5085.3-2007), the leaching concentration limit of copper is 100 mg / L, the leaching concentration limit of cadmium is 1 mg / L, the leaching concentration limit of hexavalent chromium is 5 mg / L, and the leaching concentration limit of lead is 5 mg / L. The leaching concentration in the embodiment is much lower than the standard value.

[0187] The mechanical properties of the consolidated bodies after hydration of the heavy metal contaminated soil stabilization reagents of Examples 1 to 6 and Comparative Examples 1 to 3 were tested. The specific method of hydrating the consolidated body is as follows: water and stabilizing agent are placed in a cement slurry mixer at a mass ratio of 2:5 and stirred at a low speed of 150r / min for 90s and at a high speed of 250r / min for 120s to obtain a slurry. The slurry is injected into a mold with a size of 40mm×40mm×160mm, vibrated and compacted, and sealed with plastic wrap and placed in a standard curing box (20±2℃, humidity ≥95%) for 28 days to obtain a consolidated body. According to the Chinese standard GB / T17671-2021, a fully automatic microcomputer-controlled electro-hydraulic servo pressure testing machine (DYE-300S, YiCe Instrument Equipment (Hebei) Co., Ltd., China) is used to test the compressive and flexural strength of the consolidated body, and the results are shown in Table 2.

[0188] Table 2 Mechanical properties of hydrated solid bodies of Examples 1 to 6 and Comparative Examples 1 to 3

[0189] Stabilizing Agents Compressive strength(MPa) Flexural strength(MPa) Example 1 34.25 4.76 Example 2 40.1 6.51 Example 3 36.84 5.17 Example 4 37.61 5.01 Example 5 39.01 7.27 Example 6 33.68 5.33 Comparative Example 1 26.33 3.99 Comparative Example 2 25.41 3.84 Comparative Example 3 20.61 3.35

[0190] As can be seen from Table 2, the lack of a large amount of calcium and silicon ions in the system of Comparative Example 1 reduces the hydration products. The unmodified straw in Comparative Example 2 causes some impurities to remain in the calcined phosphogypsum, resulting in insufficient hydration reaction. The mechanical properties of Comparative Example 3 are the worst, because the CaSO4 content in the system is insufficient, resulting in relatively few hydration products. The mechanical properties of the hydrated solid body mainly come from its hydration products. Among them, the main component CaSO4 in the system quickly reacts with water in an alkaline environment to crystallize to form CaSO4·2(H2O), and they are staggered and superimposed to form a supporting skeleton, so that the overall structure can have good mechanical properties in the early stage. However, due to the irregular shape of the crystals and the loose distribution, the overall structure is not tight and has more pores. After that, as the hydration reaction proceeds further, crystals continue to form, and at the same time, the aluminum oxygen bonds and silicon oxygen bonds in the system break, and a part of AFt is generated during the hydration reaction, which fills the internal structure pores together with the crystals, reducing the porosity of the overall structure, thereby improving the overall strength. The hydration of slag is relatively slow, but the high content of CaO, SiO2 and Al2O3 in it can produce pozzolanic reaction in an alkaline environment. As the curing time increases, the surface structure of each mineral component is gradually corroded by water molecules and alkaline components, causing it to be in ionic form (Si 4+ 、Al 3+ ) is dissolved in the system, and a large amount of AFt is generated under the stimulation of the sulfate component in the system in the form of long needles or short columns to fill the overall structure. In addition, the dispersed mineral ions are recombined to generate a large amount of C-(A)-SH gel to wrap the various crystal components in the system in a network structure, thereby significantly improving the macroscopic mechanical properties of the consolidated body in the later stage of hydration.

[0191] The above are only preferred embodiments of the present invention, and do not limit the patent scope of the present invention. For those skilled in the art, the present invention may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the patent protection scope of the present invention.

Claims

1. A method for preparing a heavy metal contaminated soil stabilization agent, characterized in that: The following steps are involved: S10, performing alkaline modification on the cereal straw to obtain modified cereal straw; S20, mixing the modified cereal straw and phosphogypsum, and performing heat treatment to obtain a first mixture; S30, mixing the first mixture and blast furnace slag powder, and crushing them to obtain a second mixture; S40, mixing the second mixture with industrial alkali slag to obtain the heavy metal contaminated soil stabilization agent.

2. The method for preparing the heavy metal contaminated soil stabilization agent according to claim 1, characterized in that: The mass of the heavy metal contaminated soil stabilization agent raw material is W, the mass of the blast furnace slag powder is W1, the mass of the phosphogypsum is W2, the mass of the grain straw is W3, and the mass of the industrial alkali slag is W4, wherein: W1:W=(50~70):100, W2:W=(30~50):100; W3: (W1+W2)=(10~20):100, W4: (W1+W2)=(10~20):

100.

3. The method for preparing the heavy metal contaminated soil stabilization agent according to claim 1, characterized in that: Step S10 comprises: soaking the cereal straw with an alkaline solution to obtain modified cereal straw; Wherein, the cereal straw includes at least one of corn straw, wheat straw and rice straw; and / or, The soaking time is 20 to 26 hours; and / or, The alkaline solution comprises a sodium hydroxide solution or a calcium hydroxide solution; and / or, The mass concentration of alkali in the alkaline solution is 1.3-1.7%; and / or, The mass ratio of the alkaline solution to the cereal straw is (8-12):

1.

4. The method for preparing the heavy metal contaminated soil stabilization agent according to claim 1, characterized in that: In step S20, the heat treatment temperature is 600-800° C.; and / or, In step S20, the heat treatment time is 1.5 to 2.5 hours; and / or, In step S30, the pulverizing method includes ball milling, the rotation speed of the ball mill is 300 to 500 r / min, and the time of the ball milling is 15 to 25 min.

5. The method for preparing the heavy metal contaminated soil stabilization agent according to claim 1, characterized in that: In step S40: The mixing speed is 100-150 r / min; and / or, The mixing time is 3 to 5 minutes.

6. A heavy metal contaminated soil stabilization agent, characterized in that: The heavy metal contaminated soil stabilization agent is prepared by the preparation method of the heavy metal contaminated soil stabilization agent as described in any one of claims 1 to 5.

7. Use of the heavy metal contaminated soil stabilization agent as claimed in claim 6 in solidifying heavy metals in heavy metal contaminated soil.

8. The use according to claim 7, characterized in that The following steps are involved: S10, mixing the heavy metal contaminated soil stabilization agent and the heavy metal contaminated soil to obtain a dry basis mixture; S20, mixing the dry base mixture with water to obtain a wet base mixture; S30, pressing the wet-base mixture into a shape, and allowing it to stand for curing to allow it to undergo a hydration reaction, thereby obtaining treated heavy metal contaminated soil.

9. The use according to claim 8, characterized in that In step S10, the heavy metal in the heavy metal contaminated soil includes at least one of copper, cadmium, hexavalent chromium and lead, and the mass concentration of the heavy metal in the heavy metal contaminated soil is 40 to 18000 mg / kg; and / or, In step S10, the mass ratio of the heavy metal contaminated soil stabilization agent to the heavy metal contaminated soil is (10-30): (70-90); and / or, In step S20, the mass percentage of water in the wet-base mixture is 15-20%; and / or, In step S30, the pressing pressure is 50-58 kN, and the pressing rate is 5-7 kN / min; and / or, In step S30, the curing temperature is 18-22°C, the curing humidity is 94-96%, and the curing time is 7-28 days.

10. The use according to claim 8, characterized in that Step S20 includes: sequentially mixing the dry base mixture and water for a first time and a second time; Wherein, the rotation speed of the first mixing is 100-150 r / min; and / or, The first mixing time is 3 to 5 minutes; and / or, The second mixing speed is 250-300 r / min; and / or, The second mixing time is 2 to 3 minutes.

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