Efficient synergistic soil heavy metal solidifying agent and application thereof in soil remediation

Abstract

The application discloses a kind of high-efficiency synergic soil heavy metal solidifying agent and its application in heavy metal contaminated soil remediation, it includes polymer solidifying agent, humic acid and hydroxyapatite, wherein, polymer solidifying agent is ABA type three-block copolymer with acrylic acid and acrylamide as monomer, A section is acrylic acid, B section is acrylamide.ABA three-block copolymer segmented function design realizes the synchronous efficient combination of cadmium and other cation heavy metals and arsenic and other anion heavy metals;Synergic system has remarkable synergistic effect, and the adsorption effect is excellent, formula optimization is reasonable and environment-friendly, humic acid is natural organic carbon source, can improve soil fertility, hydroxyapatite has good environmental compatibility, realizes the adsorption effect of soil heavy metal reinforcement.

Description

Technical Field

[0001] This invention relates to the field of environmental protection and soil remediation technology, specifically to a highly efficient synergistic soil heavy metal solidification agent and its application in the remediation of heavy metal contaminated soil. Background Technology

[0002] With the acceleration of industrialization, the development of mineral resources, and the unreasonable use of pesticides and fertilizers in agricultural production, soil heavy metal pollution has become increasingly serious, and has become one of the key environmental problems that restrict the safe use of land resources and threaten the ecological environment and human health.

[0003] Among numerous soil heavy metal remediation technologies, solidification technology has become one of the most widely used core technologies due to its advantages such as short remediation cycle, simple operation, and relatively low cost. It is especially suitable for the rapid remediation of moderately to heavily contaminated soils. Currently, existing soil heavy metal solidification agents are mainly divided into inorganic and organic types. Inorganic solidification agents (such as ordinary silicate cement, lime, phosphate, etc.) are widely used because of their readily available raw materials and high solidification strength. For example, patent number CN121571454A provides a phosphate remediation agent that greatly improves the remediation efficiency of contaminated soil, enhances remediation stability, and inhibits secondary leaching of phosphorus during the remediation process. Organic solidification agents (such as biochar, organic polymers, etc.) are environmentally friendly and cause minimal soil disturbance. For example, patent number CN121755544A discloses a method for in-situ passivation of available cadmium in soil using fulvic acid, realizing the resource utilization of highly lead-contaminated soil. Patent CN114958382A discloses a method for improving the remediation effect of heavy metals in soil using pumpkin seed shells, corn stalks, peanut shells, and phosphoric acid. However, current solidifying agents all suffer from low efficiency in the simultaneous solidification of complex heavy metals (especially cadmium and arsenic coexisting systems), leading to secondary problems such as soil compaction and decreased fertility.

[0004] Therefore, developing a novel soil heavy metal solidification agent that can simultaneously and efficiently solidify multiple heavy metal pollutants, has no risk of secondary pollution, and is also soil-friendly has important research significance and application value. Summary of the Invention

[0005] To address the problems existing in soil stabilization technology, the present invention adopts the following technical solution: This invention provides a highly efficient synergistic soil heavy metal solidification agent, which comprises a polymeric solidification agent, humic acid and hydroxyapatite. The polymeric solidification agent is an ABA-type triblock copolymer with acrylic acid and acrylamide as monomers, wherein segment A is acrylic acid and segment B is acrylamide.

[0006] By employing a block structure design, the polymer curing agent is endowed with the ability to target and bind to different types of heavy metals. This study found that using an ABA triblock copolymer design, the carboxyl groups (-COOH) of the A-segment polyacrylic acid can bind to Pb. 2+ Cd 2+ When heavy metals form stable chelates, the amide groups (-CONH2) of polyacrylamide in segment B can adsorb AsO4 via hydrogen bonding. 3- AsO3 3- The heavy metal oxides solve the problem of insufficient ability of traditional single polymers to simultaneously cure composite heavy metals, and the block structure improves the stability and weather resistance of the polymer, ensuring long-term curing effect.

[0007] The synergistic effect between different components in this invention is key to the simultaneous and efficient solidification of heavy metal pollutants. Through a three-tiered synergistic effect—chelation by ABA triblock copolymer, complexation and aggregation by humic acid, and precipitation and adsorption by hydroxyapatite—efficient solidification of composite heavy metals is achieved. This invention demonstrates that controlling the proportions of different components can further improve the synergistic solidification effect.

[0008] Preferably, the mass ratio of ABA-type triblock copolymer polymer curing agent, humic acid and hydroxyapatite is 30~60:10~30:5~20.

[0009] Preferably, the mass ratio of ABA-type triblock copolymer polymer curing agent, humic acid and hydroxyapatite is 35~50:15~20:5~10.

[0010] Preferably, the ABA-type triblock copolymer polymer curing agent, humic acid and hydroxyapatite need to be pretreated: after vacuum drying at 60~65℃ to constant weight, they are ground using a steel ball mill and passed through a 200-mesh standard sieve to ensure that the particle size is ≤75μm, so as to avoid agglomeration and affect the function.

[0011] Preferably, the grinding speed is 300 r / min and the grinding time is 30 min.

[0012] Any of the above-mentioned high-efficiency synergistic soil heavy metal solidification agents is suitable for in-situ or ex-situ remediation of soils contaminated with single or combined Cd and As, such as farmland, industrial sites, and mining areas. Specific applications include the following steps: Remove construction waste, weeds, and tree roots from the contaminated area, and deeply till the soil to a depth of 30-40cm to ensure that the deep contaminated soil is exposed. Adjust the soil moisture content to 35%~45%; The highly efficient synergistic soil heavy metal solidification agent is spread and mixed evenly with the contaminated soil. The mixing ratio of the solidification agent to the contaminated soil is between 1% and 5% based on the dry weight of the soil. Contaminated soil is maintained using in-situ or ex-situ remediation methods, with pH values ​​monitored every 2-3 days to ensure stability at 6.0-7.5.

[0013] Preferably, the moisture content is increased by spraying deionized water, and decreased by sun drying or mechanical ventilation.

[0014] Preferably, the in-situ repair and natural maintenance should be carried out for 10-14 days, with regular spraying to keep the moisture content at 30%-50%.

[0015] Preferably, the ectopic repair is covered with a moisturizing film for 7-10 days of sealed maintenance.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. The segmented functional design of ABA triblock copolymers enables the simultaneous and efficient binding of cationic heavy metals such as cadmium (Cd) and anionic heavy metals such as arsenic (As); 2. The synergistic system significantly enhances the adsorption effect, the formula is optimized and reasonable and environmentally friendly. Humic acid is a natural organic carbon source that can improve soil fertility, and hydroxyapatite has good environmental compatibility, thus achieving enhanced adsorption of heavy metals in the soil. Attached Figure Description

[0017] Figure 1 The results of gel permeation chromatography (GPC) analysis of the triblock copolymer polymer curing agent synthesized in Example 1 are shown. Figure 2 Infrared spectral data of the triblock copolymer polymer curing agent synthesized in Example 1; Figure 3 This is a scanning electron microscope (SEM) image of the triblock copolymer polymer curing agent synthesized in Example 1. Detailed Implementation

[0018] The total amount of heavy metals in the soil used in this invention was tested according to the "Soil Environmental Quality Standard for Construction Land Soil Pollution Risk Control" (GB36600-2018). The metal concentration was measured by inductively coupled plasma optical emission spectrometry (ICP-OES). The total amount of As heavy metal was 86.32 mg / kg, and the available content was 2.64 mg / kg, which is considered moderate pollution. The total amount of Cd heavy metal was 2.36 mg / kg, and the available content was 0.57 mg / kg, which is considered severe pollution. The soil pH was 6.46, which is considered weakly acidic soil.

[0019] Soil pH was determined using the potentiometric method, in accordance with the HJ962-2018 standard. 10.0 g of soil sample (passed through a 2 mm sieve) was weighed into a beaker, 50 mL of water was added, the beaker was sealed, and the mixture was stirred with a magnetic stirrer for 5 minutes. After standing for 30 minutes, the pH was measured using a pH meter.

[0020] The following examples and comparative examples all use in-situ restoration methods.

[0021] Example 1 (1) The preparation of ABA-type triblock copolymer polymer curing agent is carried out by the following steps: 1. Preparation of A-block polymer by RAFT polymerization: Deionized water was used as solvent, acrylic acid (AA) as monomer, 3-((((1-carboxyethyl)thio)carbonthio)thio)propionic acid (CETCTP) as RAFT chain transfer agent, and ammonium persulfate (APS)-sodium sulfinate (SFS) as redox initiation system; under argon protection, the reaction was stirred at 20°C for 24 h, the reaction solution was dialyzed through a dialysis bag with MWCO=3500Da for 48 h, and freeze-dried to obtain powdered A-block polymer.

[0022] 2. Preparation of AB block copolymer by RAFT chain extension: Using the above-mentioned A block as a macromolecular RAFT chain transfer agent and acrylamide (AM) as the second monomer, the APS-SFS initiation system was used; the reaction was carried out at 20℃ with stirring for 24h, purified by dialysis and then freeze-dried to obtain powdered AB block polymer (GPC confirmed that the molecular weight reached the target value).

[0023] 3. Preparation of ABA triblock copolymer by ammonolysis and thiol oxidative coupling: The AB block copolymer was dissolved in deionized water, and an oxidative environment was established by purging with oxygen for 30 min; n-butylamine was added at 278 times the molar number of the thiocarbonyl groups at the end of the AB block chain, and the reaction was stirred at 50℃ for 24 h to achieve desulfurization to generate thiol groups (-SH) and thiol oxidative coupling to form disulfide bonds (-SS-); the molecular weight increase was monitored in real time by SEC during the reaction process, and the product was purified by dialyzing through a 3500 Da dialysis bag for 48 h, and freeze-dried to obtain a light yellow or white powdery ABA triblock copolymer.

[0024] (2) Synthesize ABA triblock copolymer according to step 1. Mix ABA triblock copolymer polymer curing agent, humic acid and hydroxyapatite in a weight ratio of 40:18:8, ball mill and sieve to obtain composite curing agent.

[0025] (3) Mix the composite solidifying agent with the heavy metal contaminated soil evenly. The mixing ratio of the solidifying agent to the contaminated soil is 3%. Sprinkle water regularly to maintain the soil moisture content at about 40%. After standing for 10 days, take a sample to test the heavy metal content in the soil. The results are shown in Table 1.

[0026] The FTIR spectrum of the synthesized triblock copolymer polymer curing agent is shown in Figure 2, at 3366.5 cm⁻¹. -1 With 3190.5 cm -1A broad and strong characteristic absorption peak appears at 2932.1 cm⁻¹, corresponding to the stretching vibrations of associated hydroxyl (-OH) and amino (-NH) groups in the molecule, indicating that the curing agent contains a large number of polar hydrophilic groups; -1 The sharp absorption peak at 1671.1 cm⁻¹ is due to the stretching vibration of saturated CH bonds, proving that the curing agent has an aliphatic carbon chain skeleton; -1 With 1606.4 cm -1 The strong double peaks at 1452.1 cm⁻¹ correspond to the amide I band (C=O stretching vibration) and the amide II band (NH bending vibration + CN stretching vibration), respectively, indicating the presence of amide functional groups in the molecule; -1 The characteristic peak at 1190.7 cm⁻¹ is attributed to the CH deformation vibration and the asymmetric stretching vibration of the carboxylate group. -1 With 1123.9 cm -1 The broad absorption peak at that point corresponds to the stretching vibration of the CO bond.

[0027] In summary, this curing agent is rich in polar functional groups such as hydroxyl, amino, amide, and carboxyl groups, and also has a long polymer chain structure. It can achieve the agglomeration and solidification of soil particles and the stabilization of pollutants through multiple functions such as hydrogen bonding, ion exchange, chelation reaction, and particle bridging and cementation, and has excellent potential for soil remediation applications.

[0028] Figure 3 shows a scanning electron microscope (SEM) image of the synthesized triblock copolymer polymer curing agent. As can be seen from the image, the curing agent exhibits a typical self-assembled microstructure of a triblock copolymer: the main body is a continuous long-chain polymer backbone with multiple enlarged spherical branch nodes distributed on the main chain, forming a dendritic network precursor with a multi-branched structure, proving that the target triblock copolymer was successfully synthesized and that the molecular chain structure is complete. A large number of uniformly sized and well-dispersed spherical micelle particles, ranging in size from tens to hundreds of nanometers, are distributed in the background, with no obvious aggregation, indicating that the curing agent has excellent amphiphilicity and dispersion stability.

[0029] Comparative Example 1 Compared with Example 1, the only difference is that the polymer curing agent was prepared using a conventional free radical polymerization method to prepare the acrylic acid-acrylamide random copolymer, and the specific steps are as follows: 1. Monomer mixing: Acrylic acid (AA) and acrylamide (AM) (in the same proportion as the monomers in this invention) are added to deionized water to prepare a monomer mixture with a mass concentration of 20%~30%. After stirring evenly, the pH value of the system is adjusted to 4.5~5.5. 2. Initiation of polymerization: Add potassium persulfate (1.0%~2.0% of the total mass of AA and AM, consistent with the amount of initiator in this invention) to the monomer mixture, purge with nitrogen for 30 min to remove oxygen, heat to 70~80℃, and stir at a constant temperature for 4~6 h to obtain the crude product of acrylic acid-acrylamide random copolymer; 3. Post-purification treatment: Cool the crude product to room temperature, precipitate it 2-3 times with a 30% ethanol solution, filter to remove unreacted monomers and small molecule impurities; place the precipitate in a vacuum drying oven at 60-65℃ and dry it to constant weight, then pulverize it through a 100-mesh sieve to obtain the comparative random copolymer curing agent.

[0030] Example 2 Compared with Example 1, the only difference is that the weight ratio of ABA-type triblock copolymer polymer curing agent, humic acid and hydroxyapatite is 30:10:5.

[0031] Example 3 Compared with Example 1, the only difference is that the weight ratio of ABA-type triblock copolymer polymer curing agent, humic acid and hydroxyapatite is 60:30:10.

[0032] Example 4 Compared to Example 1, the only difference is that the mixing ratio of the solidifying agent to the contaminated soil is 1%.

[0033] Example 5 The only difference from Example 1 is that the mixing ratio of the solidifying agent to the contaminated soil is 5%.

[0034] Example 6 Compared with Example 1, the only difference is that watering is done regularly to maintain the soil moisture content at around 30%.

[0035] Example 7 Compared with Example 1, the only difference is that watering is done regularly to maintain the soil moisture content at around 50%.

[0036] Comparative Example 2 The only difference from Example 1 is that the polymer curing agent used is polyacrylic acid.

[0037] Comparative Example 3 The only difference from Example 1 is that the polymer curing agent used is polyacrylamide.

[0038] Comparative Example 4 The only difference from Example 1 is that only a single ABA-type triblock copolymer polymer curing agent is used.

[0039] Comparative Example 5 Compared to Example 1, the only difference is that only humic acid is used as the curing agent.

[0040] Comparative Example 6 The only difference from Example 1 is that only hydroxyapatite is used as the curing agent.

[0041] Comparative Example 7 Compared with Example 1, the only difference is that the weight ratio of ABA-type triblock copolymer polymer curing agent, humic acid and hydroxyapatite is 10:40:40.

[0042] Comparative Example 8 The only difference from Example 1 is that the mixing ratio of the solidifying agent to the contaminated soil is 8%.

[0043] Comparative Example 9 Compared with Example 1, the only difference is that watering is done regularly to maintain the soil moisture content at around 10%.

[0044] Comparative Example 10 Compared with Example 1, the only difference is that watering is done regularly to maintain the soil moisture content at around 80%.

[0045] Table 1. Heavy metal content in soils of examples / comparative examples The comparison between Example 1 and Comparative Example 1 shows that the targeting function of the triblock copolymer is the key to achieving simultaneous and efficient solidification of Cd and As composite heavy metal pollution, and the random copolymer cannot achieve the same effect.

[0046] The comparison of Examples 1, 2, and 3 with Comparative Example 7 shows that the ratio of ABA triblock copolymer: humic acid: hydroxyapatite = 30~60: 10~30: 5~20 can maximize the synergistic effect. Deviating from this range will significantly reduce the curing effect, and 40:18:8 is the optimal ratio.

[0047] The comparison between Example 1 and Comparative Examples 4, 5, and 6 shows that the synergistic effect of ABA triblock copolymer, humic acid, and hydroxyapatite is the guarantee for achieving deep curing, while the curing effect of a single component is poor.

[0048] The comparison between Examples 1, 4, and 5 and Comparative Example 8 shows that the optimal dosage of the curing agent is 3% of the dry weight of the soil. Insufficient dosage will result in incomplete curing, while excessive dosage will lead to increased costs and reduced curing effect.

[0049] The comparison of Examples 1, 6, and 7 with Comparative Examples 9 and 10 shows that the solidification effect is best when the soil moisture content is controlled at 30%~50% (optimal 40%); both too low and too high moisture content will reduce the reaction efficiency of the solidifying agent and heavy metals.

Claims

1. A highly efficient synergistic soil heavy metal solidification agent, characterized in that, It contains a polymer curing agent, humic acid and hydroxyapatite. The polymer curing agent is an ABA-type triblock copolymer with acrylic acid and acrylamide as monomers, where segment A is acrylic acid and segment B is acrylamide.

2. The highly efficient synergistic soil heavy metal solidification agent as described in claim 1, characterized in that, The mass ratio of ABA-type triblock copolymer polymer curing agent, humic acid and hydroxyapatite is 30~60:10~30:5~20.

3. The highly efficient synergistic soil heavy metal solidification agent as described in claim 2, characterized in that, The mass ratio of ABA-type triblock copolymer polymer curing agent, humic acid and hydroxyapatite is 35~50:15~20:5~10.

4. The highly efficient synergistic soil heavy metal solidification agent as described in claim 1, characterized in that, The ABA-type triblock copolymer polymer curing agent, humic acid and hydroxyapatite need to be pretreated: after vacuum drying at 60~65℃ to constant weight, they are ground using a steel ball mill and passed through a 200-mesh standard sieve to ensure that the particle size is ≤75μm.

5. The highly efficient synergistic soil heavy metal solidification agent as described in claim 4, characterized in that, The grinding speed was 300 r / min, and the grinding time was 30 min.

6. The application of a highly efficient synergistic soil heavy metal solidification agent as described in any one of claims 1-5 in the remediation of heavy metal contaminated soil, characterized in that, Includes the following steps: Remove construction waste, weeds, and tree roots from the contaminated area, and deeply till the soil to a depth of 30-40cm to ensure that the deep contaminated soil is exposed. Adjust the soil moisture content to 35%~45%; The highly efficient synergistic soil heavy metal solidification agent is spread and mixed evenly with the contaminated soil. The mixing ratio of the solidification agent to the contaminated soil is between 1% and 5% based on the dry weight of the soil. Contaminated soil is maintained using in-situ or ex-situ remediation methods, with pH values ​​monitored every 2-3 days to ensure stability at 6.0-7.

5.

7. The application as described in claim 6, characterized in that, Increase the moisture content by spraying deionized water, and decrease the moisture content by air drying or mechanical ventilation.

8. The application as described in claim 6, characterized in that, In-situ repair and natural maintenance for 10-14 days, with regular misting to maintain moisture content at 30%-50%.

9. The application as described in claim 6, characterized in that, For ectopic repair, cover with a moisturizing film for 7-10 days of occlusive care.

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