A soil passivator based on hydrotalcite and its preparation method and application

Abstract

The application discloses a soil passivator based on hydrotalcite and a preparation method and application thereof, and the preparation method comprises the following steps: uniformly and simultaneously dropping a mixed salt solution A containing calcium ions, magnesium ions and iron ions and a NaOH solution into a three-necked flask, keeping stirring, obtaining a dark yellow slurry after fully mixing, and then performing aging treatment, and then sequentially performing centrifugation, washing until the filtrate is neutral, and drying to obtain a ternary calcium-magnesium-iron precursor; mixing a mixed salt solution B containing silicate and dihydrogen phosphate with the ternary calcium-magnesium-iron precursor, performing reaction, performing centrifugation, and drying the precipitate to obtain the soil passivator based on hydrotalcite. The soil passivator can provide multiple reaction sites in the interlayer and the surface, and can react with heavy metal ions to form complex and precipitate, so that the toxicity of heavy metals in the soil is effectively reduced, and the soil fertility is significantly improved, and the soil passivator has a comprehensive environmental remediation and improvement effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste resource utilization and soil heavy metal pollution control, in particular to a soil passivator based on hydrotalcite and a preparation method and application thereof, and more particularly to a soil passivator of iron-magnesium-calcium ternary layered double hydroxide intercalated with silicate and dihydrogen phosphate and a preparation method and application thereof. BACKGROUND

[0002] With the acceleration of global industrialization and urbanization, heavy metal pollution, especially toxic heavy metals such as arsenic (As), cadmium (Cd) and lead (Pb), has become a serious environmental problem. Due to the high toxicity, persistence and accumulation of these heavy metals, they pose a great threat to the ecological environment and human health. Therefore, how to efficiently and durably control soil heavy metal pollution is imminent.

[0003] At present, the remediation methods for soil heavy metal pollution mainly include physical, chemical and biological remediation, among which chemical remediation is widely used due to its high efficiency, economy and less environmental impact. Common chemical passivators, such as lime compounds, phosphates and biochar, can reduce the bioavailability of heavy metals and reduce their accumulation in plants and food chains. However, these materials have weak adsorption capacity and are prone to desorption, resulting in non-durable remediation effect, and require a large amount of repeated use, increasing the remediation cost.

[0004] Layered double hydroxides (LDHs), as an emerging passivation material, exhibit unique advantages in heavy metal pollution control. The abundant hydroxyl groups on the surface of LDHs can passivate heavy metal cations through chemical precipitation or surface complexation mechanism; while heavy metal anions can be captured into the interlayer structure of LDHs through anion exchange. In addition, the intercalation property of LDHs enables the synthesis of various functionalized LDHs by intercalating different anions, which can effectively immobilize heavy metal ions by forming anion-metal complexes. However, the immobilization effect of traditional LDHs may not be stable enough, and is prone to desorption or dissolution, leading to the re-release of heavy metals. In addition, their long-term stability under complex environmental conditions is poor, and the immobilization efficiency may be affected by factors such as pH value, temperature and heavy metal concentration. Finally, traditional LDHs lack sufficient functional modification, making it difficult to optimize for different heavy metals. SUMMARY

[0005] In view of the above deficiencies existing at present, the application provides a layered silicate and dihydrogen phosphate intercalated iron-magnesium-calcium ternary layered double hydroxide soil passivator and a preparation method and application thereof. The layered silicate and dihydrogen phosphate intercalated iron-magnesium-calcium ternary layered double hydroxide soil passivator can provide multiple reaction sites in the interlayer and on the surface, and can react with heavy metal ions to effectively reduce the toxicity of heavy metals in the soil and significantly improve the soil fertility.

[0006] In order to achieve the above-mentioned purpose, the application provides a preparation method of a soil passivator based on hydrotalcite, comprising the following steps:

[0007] S1, dissolving a calcium source, a magnesium source and an iron source in water and fully dissolving to obtain a mixed salt solution A containing calcium ions, magnesium ions and iron ions; uniformly and simultaneously dropping the mixed salt solution A and a NaOH solution into a three-necked flask, keeping stirring, and fully mixing to obtain a dark yellow slurry;

[0008] S2, after the dark yellow slurry is subjected to aging treatment, sequentially performing centrifugation, washing until the filtrate is neutral, and drying to obtain a ternary calcium-magnesium-iron precursor;

[0009] S3, dissolving a salt containing silicate and a salt containing dihydrogen phosphate in water and fully dissolving to obtain a mixed salt solution B containing silicate and dihydrogen phosphate; fully mixing the mixed salt solution B with the ternary calcium-magnesium-iron precursor and performing reaction, and then performing centrifugation and drying the precipitate to obtain the soil passivator based on hydrotalcite.

[0010] According to an aspect of the application, in step S1, the calcium source includes at least one of calcium chloride, calcium nitrate and calcium sulfate; the magnesium source includes at least one of magnesium chloride hexahydrate, magnesium nitrate and magnesium sulfate; and the iron source includes at least one of ferric chloride hexahydrate, ferric nitrate and ferric sulfate.

[0011] According to an aspect of the application, in step S1, the ratio of the total molar amount of calcium ions and magnesium ions to the molar amount of iron ions is 2-3:1.

[0012] According to an aspect of the application, in step S1, the molar ratio of calcium ions, magnesium ions and iron ions is 2:1:1.

[0013] According to an aspect of the application, in step S1, the dropping rate is 1.5-10 ml / min; and the stirring rate is 480-800 r / min.

[0014] According to an aspect of the application, in step S2, the aging treatment temperature is 20-60℃, the aging treatment time is 8-24 h; and the drying temperature is 60-100℃.

[0015] According to one aspect of the present application, in step S3, the molar ratio of the silicate to the dihydrogen phosphate is 1:1.

[0016] According to one aspect of the present application, in step S3, the cations in the mixed salt solution A are calcium ions, magnesium ions and iron ions, and the anions in the mixed salt solution B are silicate and dihydrogen phosphate; the components of the soil passivator are composed of the above-mentioned cations and anions.

[0017] Based on the same inventive concept, the present application also provides a hydrotalcite-based soil passivator prepared by the above-mentioned preparation method.

[0018] Based on the same inventive concept, the present application also provides the application of the above-mentioned hydrotalcite-based soil passivator in reducing the activity of As, Pb and Cd in soil and providing soil fertility.

[0019] The present application has the following beneficial effects:

[0020] (1) The present application uses calcium salt, magnesium salt and iron salt as raw materials, and prepares a ternary calcium-magnesium-iron layered double hydroxide soil passivator with intercalated silicate and dihydrogen phosphate by a simple co-precipitation synthesis process, which has the advantages of high efficiency, low cost and long-term stability.

[0021] (2) The ternary calcium-magnesium-iron layered double hydroxide soil passivator with intercalated silicate and dihydrogen phosphate of the present application can significantly improve the fertility of soil.

[0022] (3) The soil passivator of the present application contains a large amount of hydroxyl groups, which can interact with As, Pb and Cd in soil to form coordination bonds, providing corresponding reaction sites for heavy metal fixation, so as to achieve the purpose of stabilizing heavy metals in soil. In addition, the unique layered structure of the present application enables heavy metal ions to undergo ion exchange with metal cations in LDHs to form stable mineral phases, thereby reducing the solubility of heavy metals and preventing their re-release and migration.

[0023] (4) The soil passivator of the present application has good passivation effect on As, Pb and Cd in soil, and significantly reduces the migration ability of each heavy metal in soil after the addition of the passivator, thereby reducing the toxicity of heavy metals in soil. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The XRD comparison chart of the products prepared in Example 1 and Comparative Example 1 of the present application;

[0025] Figure 2 The FTIR comparison chart of the products prepared in Example 1 and Comparative Example 1 of the present application;

[0026] Figure 3This is a comparison chart showing the adsorption of arsenic, cadmium, and lead in solution by the products prepared in Examples 1-5 of this invention.

[0027] Figure 4 A comparison of the adsorption of arsenic, cadmium, and lead in solution at different aging temperatures;

[0028] Figure 5 A comparative graph showing the adsorption of arsenic, cadmium, and lead in solution at different aging times. Detailed Implementation

[0029] To make the present invention easier to understand, specific embodiments are described below to further illustrate the invention. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical terms used below have the same meaning as understood by those skilled in the art; unless otherwise specified, the raw materials and reagents involved herein can be purchased commercially or obtained by known methods.

[0030] Example 1

[0031] A method for preparing a layered iron-magnesium-calcium ternary layered double hydroxide soil passivating agent containing intercalated silicate and dihydrogen phosphate groups includes the following steps:

[0032] (1) Accurately weigh 8.8784g CaCl2, 8.132g MgCl2·6H2O and 10.812g FeCl3·6H2O using an analytical balance; disperse them in 100mL deionized water, stir, and then place them in an ultrasonic machine for 5min to sonicate them evenly, so as to obtain metal salt solution A.

[0033] (2) Prepare a 4 mol / L NaOH solution: Accurately weigh NaOH solid, dissolve it in distilled water, transfer the solution to a volumetric flask, make up to the required volume, and mix thoroughly to obtain a 4 mol / L NaOH solution.

[0034] (3) Then, metal salt solution A and 4 mol / L NaOH solution were simultaneously added dropwise to the flask while stirring. The titration rate was controlled at 5 ml / min and the stirring rate was controlled at 600 r / min. After stirring, the resulting dark yellow slurry was aged at 30°C for 16 h. The aged slurry was then centrifuged, washed until neutral, and then dried in an 80°C drying oven. After drying, it was ground into a fine powder using a mortar and pestle. The precipitate obtained was the CaMgFe-LDH precursor.

[0035] (4) Weigh 21.97 g of Na2SiO3 and 28.08 g of NaH2PO4·2H2O (in a proportion of 1:1 of molar concentration of silicate to dihydrogen phosphate) into water, ultrasonic for 5 min until completely dissolved, and mix the CaMgFe-LDH precursor with the dissolved solution. After the reaction is completed, centrifuge it, and dry the obtained precipitate in an oven at 80°C. The final product is a ternary calcium-magnesium-iron layered double hydroxide soil passivator with intercalated silicate and dihydrogen phosphate.

[0036] Example 2

[0037] A method for preparing a ternary calcium-magnesium-iron layered double hydroxide soil passivator with intercalated silicate and dihydrogen phosphate, comprising the following steps:

[0038] (1) Accurately weigh 4.437 g of CaCl2, 16.264 g of MgCl2·6H2O and 10.812 g of FeCl3·6H2O with an analytical balance, and disperse them in 100 mL of deionized water. After stirring, ultrasonic for 7 min in an ultrasonic machine to obtain a metal salt solution A.

[0039] (2) Prepare a 4 mol / L NaOH solution: accurately weigh NaOH solid, dissolve it in distilled water, and transfer the solution to a volumetric flask. After diluting to the required volume, mix well to obtain a 4 mol / L NaOH solution.

[0040] (3) Then, simultaneously drop the metal salt solution A and the 4 mol / L NaOH solution into the flask, stirring while dropping, and control the titration rate at 3 ml / min. The stirring rate is controlled at 480 r / min. After stirring, the obtained dark yellow slurry is placed in a 40°C environment for aging for 18 h. Then, the aged slurry is centrifuged and washed to neutral. After centrifugation, it is placed in a 80°C drying oven for drying. After drying, grind the obtained precipitate into fine powder with a mortar. The obtained precipitate is a CaMgFe-LDH precursor.

[0041] (4) Weigh 21.97 g of Na2SiO3 and 28.08 g of NaH2PO4·2H2O (in a proportion of 1:1 of molar concentration of silicate to dihydrogen phosphate) into water, ultrasonic for 5 min until completely dissolved, and mix the CaMgFe-LDH precursor with the dissolved solution. After the reaction is completed, centrifuge it, and dry the obtained precipitate in an oven at 80°C. The final product is a ternary calcium-magnesium-iron layered double hydroxide soil passivator with intercalated silicate and dihydrogen phosphate.

[0042] Example 3

[0043] A preparation method of a soil passivator of a ternary layered double hydroxide of Ca-Mg-Fe with intercalated silicate and dihydrogen phosphate, comprising the following steps:

[0044] (1) accurately weigh 4.437g of CaCl2, 8.132g of MgCl2·6H2O and 10.812g of FeCl3·6H2O with an analytical balance; disperse them in 100mL of deionized water, and after stirring, respectively place them in an ultrasonic machine for ultrasonic treatment for 3min to make them uniformly dispersed, to obtain a metal salt solution A.

[0045] (2) prepare a 3mol / L NaOH solution: accurately weigh NaOH solid, dissolve it in distilled water, and transfer the solution to a volumetric flask, make up to the required volume after mixing thoroughly, to obtain a 3mol / L NaOH solution.

[0046] (3) then simultaneously drop the metal salt solution A and the 3mol / L NaOH solution into the flask, stirring while dropping, and control the dropping rate at 1.5mL / min; control the stirring rate at 500r / min, after stirring, place the obtained dark yellow slurry in a 20℃ environment for aging for 8h, then centrifuge the aged slurry, wash until neutral, and after centrifugation, place it in a 80℃ drying oven for drying, after drying, grind it into fine powder with a mortar, and the obtained precipitate is the CaMgFe-LDH precursor.

[0047] (4) weigh 17.088g of Na2SiO3 and 21.841g of NaH2PO4·2H2O (according to the molar concentration ratio of silicate to dihydrogen phosphate of 1:1), dissolve them in water, and ultrasonic treat for 3min until they are completely dissolved, and mix the CaMgFe-LDH precursor with the dissolved solution, centrifuge after the reaction is completed, and dry the obtained precipitate in an 80℃ oven, and finally the obtained product is the ternary Ca-Mg-Fe layered double hydroxide soil passivator with intercalated silicate and dihydrogen phosphate.

[0048] Example 4

[0049] A preparation method of a soil passivator of a ternary layered double hydroxide of Ca-Mg-Fe with intercalated silicate and dihydrogen phosphate, comprising the following steps:

[0050] (1) accurately weigh 4.437g of CaCl2, 8.132g of MgCl2·6H2O and 10.812g of FeCl3·6H2O with an analytical balance; disperse them in 100mL of deionized water, and after stirring, respectively place them in an ultrasonic machine for ultrasonic treatment for 3min to make them uniformly dispersed, to obtain a metal salt solution A.

[0051] (2) Preparation of 2.4 mol / L NaOH solution: accurately weigh NaOH solid, dissolve in distilled water, and transfer the solution to a volumetric flask, make up to the required volume after mixing thoroughly, to obtain a 2.4 mol / L NaOH solution.

[0052] (3) Then metal salt solution A and 4 mol / L NaOH solution are simultaneously dropped into the flask, stirring while dropping, the titration rate is controlled at 7 mL / min; the stirring rate is controlled at 700 r / min, after stirring, the obtained dark yellow slurry is aged at 50°C for 12 h, then the aged slurry is centrifuged, washed to neutral, and dried in a 80°C drying oven after centrifugation, and ground into fine powder with a mortar after drying, the obtained precipitate is the CaMgFe-LDH precursor.

[0053] (4) 14.647 g of Na2SiO3 and 18.721 g of NaH2PO4·2H2O (in a molar ratio of 1:1 of silicate to dihydrogen phosphate) are weighed and dissolved in water, and ultrasonic is applied for 9 min until they are completely dissolved, and the CaMgFe-LDH precursor is mixed with the dissolved solution, and after the reaction is completed, it is centrifuged, and the obtained precipitate is dried in an 80°C oven, and finally the obtained product is the ternary calcium-magnesium-iron layered double hydroxide soil passivator with intercalated silicate and dihydrogen phosphate.

[0054] Example 5

[0055] A preparation method of a ternary iron-magnesium-calcium layered double hydroxide soil passivator with intercalated silicate and dihydrogen phosphate, comprising the following steps:

[0056] (1) 2.218 g of CaCl2, 8.132 g of MgCl2·6H2O and 10.812 g of FeCl3·6H2O are accurately weighed with an analytical balance; dispersed in 100 mL of deionized water, and after stirring, ultrasonic is applied for 10 min in an ultrasonic machine to make them uniformly dispersed, to obtain metal salt solution A.

[0057] (2) Preparation of 2.4 mol / L NaOH solution: accurately weigh NaOH solid, dissolve in distilled water, and transfer the solution to a volumetric flask, make up to the required volume after mixing thoroughly, to obtain a 2.4 mol / L NaOH solution.

[0058] (3) Then the metal salt solution A, 4 mol / L NaOH solution is dropped into the flask at the same time, stirring while dropping, the titration rate is controlled at 10 mL / min; the stirring rate is controlled at 800 r / min, after the stirring is completed, the obtained dark yellow slurry is placed in the condition of 60℃ for aging for 24h, then the aged slurry is centrifuged, washed to neutral, placed in the drying oven at 80℃ after centrifugation, dried, and ground into fine powder with a mortar after drying, the obtained precipitate is the CaMgFe-LDH precursor.

[0059] (4) 14.647g of Na2SiO3 and 18.721g of NaH2PO42H2O (according to the molar concentration ratio of silicate to dihydrogen phosphate of 1:1) are weighed and dissolved in water, ultrasonic for 10 min until completely dissolved, and the CaMgFe-LDH precursor is fully mixed with the dissolved solution, after the reaction is completed, it is centrifuged, the obtained precipitate is dried in an oven at 80℃, and finally the obtained product is the ternary calcium magnesium iron layered double hydroxide soil passivator with intercalated silicate and dihydrogen phosphate.

[0060] Comparative Example 1

[0061] The difference between this comparative example and Example 1 is that step (4) of intercalation is not performed, specifically: the precipitate obtained in step (3) is dried in an oven at 80℃, and finally the obtained product is the ternary calcium magnesium iron layered double hydroxide soil passivator.

[0062] Comparative Example 2

[0063] The difference between this comparative example and Example 1 is that step (4) of dihydrogen phosphate intercalation is not performed, specifically: 21.97g of Na2SiO3 is weighed and dissolved in water, ultrasonic for 5 min until completely dissolved, and the CaMgFe-LDH precursor is fully mixed with the dissolved solution, after the reaction is completed, it is centrifuged, the obtained precipitate is dried in an oven at 80℃, and finally the obtained product is the ternary calcium magnesium iron layered double hydroxide soil passivator with intercalated silicate.

[0064] Comparative Example 3

[0065] The difference between this comparative example and Example 1 is that step (4) of silicate intercalation is not performed, specifically: 28.08g of NaH2PO42H2O is weighed and dissolved in water, ultrasonic for 5 min until completely dissolved, and the CaMgFe-LDH precursor is fully mixed with the dissolved solution, after the reaction is completed, it is centrifuged, the obtained precipitate is dried in an oven at 80℃, and finally the obtained product is the ternary calcium magnesium iron layered double hydroxide soil passivator with intercalated silicate.

[0066] Performance detection and result analysis:

[0067] The products prepared in Example 1 and Comparative Example 1 (Comparative Example 1 was a ternary calcium-magnesium-iron layered double hydroxide precursor; Example 1 was a ternary calcium-magnesium-iron layered double hydroxide soil passivating agent with intercalated silicate and dihydrogen phosphate) were subjected to X-ray diffraction (XRD) tests, and the results are as follows: Figure 1 As shown. By Figure 1 It can be seen that the CaMgFe-LDH precursor of Comparative Example 1 exhibits characteristic diffraction peaks of 003, 006, 113, and 115 at 11.408°, 24.164°, 33.981°, and 62.726°, indicating that the hydrotalcite has a layered structure and an ordered crystal arrangement. After anion intercalation in Example 1 of this application, the original 003 and 006 peaks disappeared, and new 002 and 004 peaks appeared at 11.103° and 22.312°, respectively. According to the Bragg equation, the interlayer spacing of the original and modified layers is respectively... and and The changes were minor, but the interlayer structure maintained an integer multiple relationship, proving that the intercalation did not destroy the layered characteristics of the hydrotalcite, but only made an orderly adjustment.

[0068] The products prepared in Example 1 and Comparative Example 1 (Comparative Example 1 was a ternary calcium-magnesium-iron layered double hydroxide precursor; Example 1 was a ternary calcium-magnesium-iron layered double hydroxide soil passivating agent with intercalated silicate and dihydrogen phosphate) were subjected to Fourier transform infrared (FTIR) testing, and the results are as follows: Figure 2 As shown. By Figure 2 It can be seen that, for the ternary calcium-magnesium-iron layered double hydroxide precursor of Comparative Example 1, the infrared spectrum at 3445.4 cm⁻¹... -1 and 1620.88cm -1 The vibrations are OH stretching vibration and HOH bending vibration, respectively, indicating the presence of water molecules in the interlayer; 1470.6 cm -1 and 1416.3cm -1 The characteristic peak of carbonate ions is likely related to the reaction with CO2 in the air. In Example 1 of this application, after intercalation of anions, the characteristic peaks of OH and HOH showed slight shifts, reflecting changes in the interlayer environment; the most significant shift was at 1030.57 cm⁻¹. -1 The new characteristic peak, attributed to the Si-O vibration of silicate, indicates successful intercalation; 603.03 cm⁻¹ -1 and 562.8cm -1 The peak of the ion is consistent with the characteristic vibration of the hydrogen phosphate ion, proving that it also successfully intercalated; although silicate and hydrogen phosphate ions successfully intercalated, the characteristic peak of carbonate ion (1470.7 cm⁻¹) was not observed. -1 and 1415.4cm -1 The presence of these ions indicates that some carbonate ions were not completely replaced, which may be related to the role of CO2 in the reaction process.

[0069] The influence of the layered double hydroxide soil passivator prepared by different magnesium sources, calcium sources, and iron sources in Example 1-5 on the adsorption of arsenic, cadmium, and lead in the solution was explored, and the results are shown in Table 1-3. Figure 3 Figure 3 It can be seen that when the metal molar ratio of (calcium + magnesium) to iron is 3:1 and the molar ratio of iron to magnesium to calcium is 1:1:2, the adsorption capacity of the material for arsenic, cadmium, and lead is the largest, and the removal efficiency is the highest. The molar ratio of iron to magnesium to calcium is selected as the best molar ratio, and the influence of the aging temperature on the adsorption of arsenic, cadmium, and lead in the solution was explored, and the results are shown in Table 1-3. Figure 4 Figure 4 It can be seen that an aging temperature of 30°C can obtain a higher removal efficiency. Under this temperature range, the crystal structure of hydrotalcite can maintain good stability and efficiently adsorb heavy metal ions. When the temperature exceeds 30°C, the adsorption capacity of the material for arsenic, cadmium, and lead slowly decreases. The molar ratio of iron to magnesium to calcium is selected as the best molar ratio, and the aging temperature is selected as 30°C, and the influence of different aging times on the adsorption of arsenic, cadmium, and lead in the solution was explored, and the results are shown in Table 1-3. Figure 5 Figure 5 It can be seen that an aging time of 16h can obtain a higher removal efficiency for arsenic, cadmium, and lead. When the aging time exceeds 16h, the adsorption capacity of the material for cadmium and lead shows a downward trend, so 16h is selected as the best aging time in the subsequent experiment.

[0070] The soil passivator described in Example 1 was tested, and the specific scheme was as follows:

[0071] 100g of heavy metal contaminated soil samples were placed in plastic bottles, and the soil passivators of Example 1, Comparative Examples 1-3 were added according to the soil mass fraction: 0%, 0.5%, 1%, 3%, 5%, 7%, 9%, and 11%. Water was added according to the soil moisture content of about 60%, and then stirred evenly and sealed with plastic wrap for static culture for one month, with the temperature set to 25°C. After the culture was completed, the soil was taken out, and the effective state content of arsenic, cadmium, and lead in the passivated and remediated soil was extracted by DTPA extractant, and the results are shown in Tables 1-3.

[0072] Table 1 Effective state content of heavy metal (Cd) after soil passivation

[0073]

[0074] Table 2 Effective state content of heavy metal (Pb) after soil passivation

[0075]

[0076] ​​​

[0077] Table 3 Available heavy metal (As) content in soil after soil passivation

[0078]

[0079] As can be seen from Tables 1-3, the ternary calcium-magnesium-iron layered double hydroxide soil passivation agent with intercalated silicate and dihydrogen phosphate can significantly reduce the available content of Cd, Pb and As in soil, and has a certain passivation effect on Cd, Pb and As in contaminated soil. The available content of Cd, Pb and As in soil without adding passivation agent is 3.02 mg / kg, 153.7 mg / kg and 3.135 mg / kg, respectively. After adding the four soil passivation agents, the available content of Cd, Pb and As in soil will decrease (the available content of Cd, Pb and As in soil after adding the ternary iron-magnesium-calcium layered double hydroxide soil passivation agent with intercalated silicate and dihydrogen phosphate, the ternary iron-magnesium-calcium layered double hydroxide soil passivation agent, the ternary iron-magnesium-calcium layered double hydroxide soil passivation agent with only intercalated silicate, and the ternary iron-magnesium-calcium layered double hydroxide soil passivation agent with only intercalated dihydrogen phosphate, respectively, is reduced by 24.1%, 8.7%, 9.65% and 10.2% for the available content of Cd, by 50.4%, 25.4%, 35.1% and 39.6% for the available content of Pb, and by 28.5%, 12.1%, 13.6% and 15.5% for the available content of As, respectively, at the maximum). It is obvious that the available content of Cd, Pb and As in soil decreases most obviously after adding the ternary calcium-magnesium-iron layered double hydroxide soil passivation agent with intercalated silicate and dihydrogen phosphate, and when the content of the passivation agent increases from 0% to 3%, the available content of Cd, Pb and As decreases by 24.1%, 25.7% and 28.5%, respectively. However, for Cd and As, when the amount of the passivation agent exceeds 3%, the available content of Cd and As increases slowly, so 3% is selected as the best amount of the passivation agent in the subsequent experiment.

[0080] The soil passivation agents of Example 1 and Comparative Examples 1-3 were added to soil at an amount of 3% of the mass of soil, water was added to the soil at a water content of about 60%, and the mixture was stirred uniformly and then covered with plastic wrap for static culture for one month at a temperature of 25°C. After the culture was completed, the available silicon and available phosphorus in the soil were measured. The results are shown in Tables 4-5.

[0081] Table 4 Available silicon content in soil after treatment with the ternary iron-magnesium-calcium layered double hydroxide soil passivation agent with intercalated silicate and dihydrogen phosphate

[0082]

[0083] Table 5 Available phosphorus content in soil after treatment with the ternary iron-magnesium-calcium layered double hydroxide soil passivation agent with intercalated silicate and dihydrogen phosphate

[0084]

[0085] As can be seen from Tables 4-5, the effective silicon and phosphorus contents in the soil treated by the comparative example 1 ternary calcium magnesium iron layered double hydroxide soil passivator almost did not change; compared with the ternary iron magnesium calcium layered double hydroxide soil passivator layer-inserted with only silicate and the ternary iron magnesium calcium layered double hydroxide soil passivator layer-inserted with only dihydrogen phosphate, the effective silicon and phosphorus contents in the soil treated by the example 1 ternary calcium magnesium iron layered double hydroxide soil passivator layer-inserted with silicate and dihydrogen phosphate increased significantly (after the ternary calcium magnesium iron layered double hydroxide soil passivator layer-inserted with silicate and dihydrogen phosphate was added into the soil, the maximum increase of the effective silicon content in the soil was 51.8%; after the ternary iron magnesium calcium layered double hydroxide soil passivator layer-inserted with only silicate was added into the soil, the maximum increase of the effective silicon content in the soil was 25.4%; after the ternary iron magnesium calcium layered double hydroxide soil passivator layer-inserted with only dihydrogen phosphate was added into the soil, the effective silicon content in the soil changed little. After the ternary calcium magnesium iron layered double hydroxide soil passivator layer-inserted with silicate and dihydrogen phosphate was added into the soil, the effective phosphorus content in the soil increased by 3.27 times; after the ternary iron magnesium calcium layered double hydroxide soil passivator layer-inserted with only silicate was added into the soil, the effective phosphorus content in the soil changed little; after the ternary iron magnesium calcium layered double hydroxide soil passivator layer-inserted with only dihydrogen phosphate was added into the soil, the effective phosphorus content in the soil increased by 1.21 times.). Specifically, after the ternary calcium magnesium iron layered double hydroxide (LDH) layer-inserted with silicate and dihydrogen phosphate was used as a soil passivator to treat the soil, the effective silicon and phosphorus contents in the soil experienced different changes. In the early stage (1-5 days), silicate and dihydrogen phosphate were rapidly released from the LDH, resulting in a rapid increase of the effective silicon and phosphorus contents (37.1% and 1.89 times, respectively); then, after 7 days, the concentrations of the effective silicon and phosphorus began to decrease due to a decrease in the release amount of silicon and phosphorus from the LDH or due to the reaction or adsorption of silicon and phosphorus with minerals in the soil; from 9 days to 30 days, the release of silicon and phosphorus entered a slow stage, and with the passage of time, the release rate slowed down, and the effective silicon and phosphorus in the soil gradually recovered and remained stable, and the release of silicon and phosphorus gradually increased, possibly due to the slow-release effect and the help of microorganisms.

[0086] The above merely provides a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which shall be covered by the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A method for preparing a soil passivant based on hydrotalcite, characterized in that, The method comprises the following steps: S1, dissolving a calcium source, a magnesium source and an iron source in water and fully dissolving to obtain a mixed salt solution A containing calcium ions, magnesium ions and iron ions; uniformly and simultaneously dropping the mixed salt solution A and a NaOH solution into a three-necked flask while keeping stirring, and after fully mixing, obtaining a dark yellow slurry; S2, after aging treatment of the dark yellow slurry, sequentially performing centrifugation, washing until the filtrate is neutral, and drying to obtain a ternary calcium-magnesium-iron precursor; S3, dissolving a salt containing silicate and a salt containing dihydrogen phosphate in water and fully dissolving to obtain a mixed salt solution B containing silicate and dihydrogen phosphate; after fully mixing and reacting the mixed salt solution B with the ternary calcium-magnesium-iron precursor, performing centrifugation and drying the precipitate to obtain a soil passivator based on hydrotalcite.

2. The method for preparing a hydrotalcite-based soil deactivator according to claim 1, characterized by, In step S1, the calcium source includes at least one of calcium chloride, calcium nitrate and calcium sulfate; the magnesium source includes at least one of magnesium chloride hexahydrate, magnesium nitrate and magnesium sulfate; and the iron source includes at least one of iron chloride hexahydrate, iron nitrate and iron sulfate.

3. The method for preparing a hydrotalcite-based soil deactivator according to claim 1, characterized by, In step S1, the ratio of the total molar amount of calcium ions and magnesium ions to the molar amount of iron ions is 2-3:

1.

4. The method for preparing a hydrotalcite-based soil deactivator according to claim 1, characterized by, In step S1, the molar ratio of calcium ions, magnesium ions and iron ions is 2:1:

1.

5. The method of preparing a hydrotalcite-based soil deactivator according to claim 1, characterized by, In step S1, the dropping rate is 1.5-10 ml / min; and the stirring rate is 480-800 r / min.

6. The method of preparing a hydrotalcite-based soil deactivator according to claim 1, characterized by, In step S2, the aging treatment temperature is 20-60℃, the aging treatment time is 8-24 h; and the drying temperature is 60-100℃.

7. The method of preparing a hydrotalcite-based soil deactivator according to claim 1, characterized by, In step S3, the molar ratio of silicate to dihydrogen phosphate is 1:

1.

8. The method of preparing a hydrotalcite-based soil deactivator according to claim 1, characterized by, The cations in the mixed salt solution A are calcium ions, magnesium ions and iron ions, the anions in the mixed salt solution B are silicate and dihydrogen phosphate, and the components of the soil passivator are composed of the above cations and anions.

9. A soil passivant based on hydrotalcite, characterized in that, The soil passivator is prepared by the method of any one of claims 1-8.

10. Application of the soil passivator based on hydrotalcite in claim 9 in reducing the activity of As, Pb and Cd in soil and improving soil fertility.

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