Hydrotalcite-based soil passivator as well as preparation method and application thereof

Abstract

The invention discloses a hydrotalcite-based soil passivator and a preparation method and application thereof.The preparation method comprises the following steps that a mixed salt solution A containing calcium ions, magnesium ions and iron ions and a NaOH solution are dropwise added into a three-necked flask at the same time at the constant speed, stirring is kept, sufficient mixing is conducted, dark yellow slurry is obtained, aging treatment is conducted, and the hydrotalcite-based soil passivator is obtained; sequentially centrifuging and washing until filtrate is neutral, and drying to obtain a ternary calcium-magnesium-iron precursor; mixing a mixed salt solution B containing silicate radicals and dihydrogen phosphate radicals; and fully mixing with a ternary calcium-magnesium-iron precursor, reacting, centrifuging, and drying the precipitate to obtain the hydrotalcite-based soil passivator. According to the soil passivator, multiple reaction sites are provided between layers and on the surface, the soil passivator and heavy metal ions are subjected to complexation, precipitation and other reactions, the toxicity of heavy metal in soil is effectively reduced, meanwhile, the soil fertility is remarkably improved, and the comprehensive environment repairing and improving effect is achieved.

Description

Technical Field

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

[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 huge threat to the ecological environment and human health. Therefore, how to efficiently and permanently treat 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 because of its high efficiency, economy and low impact on the environment. 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 easy to desorb, resulting in a short-lasting remediation effect and the need for large-scale repeated use, which increases the cost of remediation.

[0004] Layered double hydroxides (LDHs), as an emerging passivation material, show their unique advantages in the treatment of heavy metal pollution. The abundant hydroxyl groups on the surface of LDHs can passivate heavy metal cations through chemical precipitation or surface complexation mechanisms; while heavy metal anions can be captured in the interlayer structure of LDHs through anion exchange. In addition, the intercalation properties of LDHs enable the synthesis of a variety of functionalized LDHs by inserting different anions, and these functionalized LDHs can effectively fix heavy metal ions by forming anionic metal complexes. However, the fixation effect of traditional LDHs may not be stable enough, and they are prone to desorption or dissolution, resulting in the re-release of heavy metals. In addition, their long-term stability under complex environmental conditions is poor, and the fixation efficiency may be affected by factors such as pH, temperature and heavy metal concentration. Finally, traditional LDHs lack sufficient functional modification and are difficult to optimize for different heavy metals. Summary of the invention

[0005] In view of the above-mentioned shortcomings that currently exist, the present invention provides a soil passivator of an iron-magnesium-calcium ternary layered double hydroxide intercalated with silicate and dihydrogen phosphate, and a preparation method and application thereof. The soil passivator of an iron-magnesium-calcium ternary layered double hydroxide intercalated with silicate and dihydrogen phosphate of the present invention can provide multiple reaction sites between layers and on the surface to react with heavy metal ions such as complexation and precipitation, thereby effectively reducing the toxicity of heavy metals in the soil and significantly improving soil fertility.

[0006] In order to achieve the above object, the present invention provides a method for preparing a soil passivator based on hydrotalcite, comprising the following steps:

[0007] S1. Dissolve a calcium source, a magnesium source, and an iron source in water and fully dissolve them to obtain a mixed salt solution A containing calcium ions, magnesium ions, and iron ions; drip the mixed salt solution A and the NaOH solution into a three-necked flask at a uniform speed and simultaneously, keep stirring, and after fully mixing, obtain a dark yellow slurry;

[0008] S2, subjecting the dark yellow slurry to aging treatment, centrifuging, washing until the filtrate is neutral, and drying to obtain a ternary calcium magnesium iron precursor;

[0009] S3, dissolving the salt containing silicate and the salt containing dihydrogen phosphate in water and fully dissolving them 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 reacting them, centrifuging and drying the precipitate to obtain a soil passivator based on hydrotalcite.

[0010] According to one aspect of the present invention, 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 one aspect of the present invention, 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 one aspect of the present invention, in step S1, the molar ratio of calcium ions, magnesium ions and iron ions is 2:1:1.

[0013] According to one aspect of the present invention, in step S1, the dripping rate is 1.5-10 ml / min; the stirring rate is 480-800 r / min.

[0014] According to one aspect of the present invention, in step S2, the temperature of the aging treatment is 20-60°C, the time of the aging treatment is 8-24h; and the temperature of the drying is 60-100°C.

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

[0016] According to one aspect of the present invention, 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 salts 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 invention also provides a soil passivator based on hydrotalcite, which is prepared by the above-mentioned preparation method.

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

[0019] Beneficial effects of the present invention:

[0020] (1) The present invention uses calcium salt, magnesium salt and iron salt as raw materials to prepare a ternary calcium magnesium iron layered double hydroxide soil passivator with intercalated silicate and dihydrogen phosphate through 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 of the present invention, which is intercalated with silicate and dihydrogen phosphate, can significantly improve the fertility of the soil.

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

[0023] (4) The soil passivator of the present invention can have a good passivation effect on As, Pb and Cd in the soil. After the passivator is added, the migration capacity of each heavy metal in the soil is significantly reduced, thereby reducing the toxicity of heavy metals in the soil. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0026] Figure 3This is a comparison chart of the adsorption of arsenic, cadmium and lead in the solution by the products prepared in Examples 1 to 5 of the present invention;

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

[0028] Figure 5 This is a comparison chart of the adsorption of arsenic, cadmium and lead in the solution at different aging times. DETAILED DESCRIPTION

[0029] To make the present invention easier to understand, the present invention is further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. Unless otherwise defined, the professional terms used below are consistent with the meanings understood by professional and technical personnel in the field; unless otherwise specified, the raw materials and reagents involved in this article can be purchased from the market or prepared by known methods.

[0030] Example 1

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

[0032] (1) Accurately weigh 8.8784 g of CaCl using an analytical balance. 2 、8.132g MgCl 2 6H 2 O and 10.812 g FeCl 3 6H 2 O; dispersed in 100 mL of deionized water, stirred and placed in an ultrasonic machine for 5 min to make it evenly dispersed to obtain a metal salt solution A.

[0033] (2) Preparation of 4 mol / L NaOH solution: Accurately weigh solid NaOH, dissolve it in distilled water, transfer the solution to a volumetric flask, dilute 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 dripped into the flask simultaneously, stirring while dripping, and the titration rate was controlled at 5 ml / min; the stirring rate was controlled at 600 r / min. After the stirring was completed, the dark yellow slurry was aged at 30°C for 16 h, and then the aged slurry was centrifuged and washed to neutrality. After centrifugation, it was dried in a drying oven at 80°C, and then ground into fine powder with a mortar. The obtained precipitate was the CaMgFe-LDH precursor.

[0035] (4) Weigh 21.97 g Na 2 SiO 3 , 28.08 g NaH 2 PO 4 ·2H 2 O (according to the molar concentration ratio of silicate: dihydrogen phosphate of 1:1) was dissolved in water, ultrasonicated for 5 minutes until it was completely dissolved, and the CaMgFe-LDH precursor was fully mixed with the dissolved solution. After the reaction was completed, it was centrifuged, and the obtained precipitate was placed in an oven at 80°C to dry. The final product was a ternary calcium magnesium iron layered double hydroxide soil passivator intercalated with silicate and dihydrogen phosphate.

[0036] Example 2

[0037] A method for preparing a soil passivating agent of iron-magnesium-calcium ternary layered double hydroxide intercalated with silicate and dihydrogen phosphate comprises the following steps:

[0038] (1) Accurately weigh 4.437 g of CaCl using an analytical balance. 2 、16.264g MgCl 2 6H 2 O and 10.812 g FeCl 3 6H 2 O; dispersed in 100 mL of deionized water, stirred and placed in an ultrasonic machine for 7 min to make it evenly dispersed to obtain a metal salt solution A.

[0039] (2) Preparation of 4 mol / L NaOH solution: Accurately weigh solid NaOH, dissolve it in distilled water, transfer the solution to a volumetric flask, dilute to the required volume, and mix thoroughly to obtain a 4 mol / L NaOH solution.

[0040] (3) Then, the metal salt solution A and 4 mol / L NaOH solution were dripped into the flask simultaneously, and the titration rate was controlled at 3 ml / min. The stirring rate was controlled at 480 r / min. After the stirring was completed, the dark yellow slurry was aged at 40 ° C for 18 h. The aged slurry was then centrifuged and washed to neutrality. After centrifugation, it was dried in a drying oven at 80 ° C. After drying, it was ground into fine powder with a mortar. The obtained precipitate was the CaMgFe-LDH precursor.

[0041] (4) Weigh 21.97 g Na 2 SiO 3 , 28.08 g NaH 2 PO 4 ·2H 2 O (according to the molar concentration ratio of silicate: dihydrogen phosphate being 1:1) was dissolved in water, ultrasonicated for 7 minutes until it was completely dissolved, and the CaMgFe-LDH precursor was fully mixed with the dissolved solution. After the reaction was completed, it was centrifuged, and the obtained precipitate was placed in an oven at 80°C to dry. The final product was a ternary calcium magnesium iron layered double hydroxide soil passivator intercalated with silicate and dihydrogen phosphate.

[0042] Example 3

[0043] A method for preparing a soil passivating agent of iron-magnesium-calcium ternary layered double hydroxide intercalated with silicate and dihydrogen phosphate comprises the following steps:

[0044] (1) Accurately weigh 4.437 g of CaCl using an analytical balance. 2 、8.132g MgCl 2 6H 2 O and 10.812 g FeCl 3 6H 2 O; dispersed in 100 mL of deionized water, stirred and placed in an ultrasonic machine for 3 min to make it evenly dispersed to obtain a metal salt solution A.

[0045] (2) Preparation of 3 mol / L NaOH solution: Accurately weigh solid NaOH, dissolve it in distilled water, transfer the solution to a volumetric flask, dilute to the required volume, and mix thoroughly to obtain a 3 mol / L NaOH solution.

[0046] (3) Then, metal salt solution A and 3 mol / L NaOH solution were dripped into the flask simultaneously, stirring while dripping, and the titration rate was controlled at 1.5 mL / min; the stirring rate was controlled at 500 r / min. After the stirring was completed, the dark yellow slurry was aged at 20°C for 8 h, and then the aged slurry was centrifuged and washed to neutrality. After centrifugation, it was dried in a drying oven at 80°C, and then ground into fine powder with a mortar. The obtained precipitate was the CaMgFe-LDH precursor.

[0047] (4) Weigh 17.088 g Na 2 SiO 3 , 21.841 g NaH 2 PO 4 ·2H 2 O (according to the molar concentration ratio of silicate: dihydrogen phosphate of 1:1) was dissolved in water, ultrasonicated for 3 minutes until it was completely dissolved, and the CaMgFe-LDH precursor was fully mixed with the dissolved solution. After the reaction was completed, it was centrifuged, and the obtained precipitate was placed in an oven at 80°C to dry. The final product was a ternary calcium magnesium iron layered double hydroxide soil passivator intercalated with silicate and dihydrogen phosphate.

[0048] Example 4

[0049] A method for preparing a soil passivating agent of iron-magnesium-calcium ternary layered double hydroxide intercalated with silicate and dihydrogen phosphate comprises the following steps:

[0050] (1) Accurately weigh 4.437 g of CaCl using an analytical balance. 2 、4.066g MgCl 2 6H 2 O and 10.812 g FeCl 3 6H 2 O; dispersed in 100 mL of deionized water, stirred and placed in an ultrasonic machine for 9 min to make it evenly dispersed, to obtain a metal salt solution A.

[0051] (2) Preparation of 2.4 mol / L NaOH solution: Accurately weigh solid NaOH, dissolve it in distilled water, transfer the solution to a volumetric flask, dilute to the required volume, and mix thoroughly to obtain a 2.4 mol / L NaOH solution.

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

[0053] (4) Weigh 14.647 g Na 2 SiO 3 , 18.721 g NaH 2 PO 4 ·2H 2 O (according to the molar concentration ratio of silicate: dihydrogen phosphate of 1:1) was dissolved in water, ultrasonicated for 9 minutes until it was completely dissolved, and the CaMgFe-LDH precursor was fully mixed with the dissolved solution. After the reaction was completed, it was centrifuged, and the obtained precipitate was placed in an oven at 80°C to dry. The final product was a ternary calcium magnesium iron layered double hydroxide soil passivator intercalated with silicate and dihydrogen phosphate.

[0054] Example 5

[0055] A method for preparing a soil passivating agent of iron-magnesium-calcium ternary layered double hydroxide intercalated with silicate and dihydrogen phosphate comprises the following steps:

[0056] (1) Accurately weigh 2.218 g of CaCl using an analytical balance. 2 、8.132g MgCl 2 6H 2 O and 10.812 g FeCl 3 6H 2 O; dispersed in 100 mL of deionized water, stirred and placed in an ultrasonic machine for 10 min to make it evenly dispersed, to obtain a metal salt solution A.

[0057] (2) Preparation of 2.4 mol / L NaOH solution: Accurately weigh solid NaOH, dissolve it in distilled water, transfer the solution to a volumetric flask, dilute to the required volume, and mix thoroughly to obtain a 2.4 mol / L NaOH solution.

[0058] (3) Then, the metal salt solution A and 4 mol / L NaOH solution were dripped into the flask simultaneously, and the titration rate was controlled at 10 mL / min; the stirring rate was controlled at 800 r / min. After the stirring was completed, the dark yellow slurry was aged at 60°C for 24 h, and then the aged slurry was centrifuged, washed to neutrality, and dried in an 80°C drying oven after centrifugation. After drying, it was ground into fine powder with a mortar. The obtained precipitate was the CaMgFe-LDH precursor.

[0059] (4) Weigh 14.647 g Na 2 SiO 3 , 18.721 g NaH 2 PO 4 2H 2 O (according to the molar concentration ratio of silicate: dihydrogen phosphate of 1:1) was dissolved in water, ultrasonicated for 10 minutes until it was completely dissolved, and the CaMgFe-LDH precursor was fully mixed with the dissolved solution. After the reaction was completed, it was centrifuged and the obtained precipitate was placed in an oven at 80°C to dry. The final product was a ternary calcium magnesium iron layered double hydroxide soil passivator intercalated with silicate and dihydrogen phosphate.

[0060] Comparative Example 1

[0061] The difference between this comparative example and Example 1 is that the intercalation in step (4) is not performed. Specifically, the precipitate obtained in step (3) is placed in an oven at 80° C. and dried, and the final product obtained is a 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 the dihydrogen phosphate intercalation in step (4) is not performed. Specifically, 21.97 g Na 2 SiO 3 Dissolve it in water, ultrasonicate for 5 minutes until it is completely dissolved, and fully 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 the intercalated silicate ternary calcium magnesium iron layered double hydroxide soil passivator.

[0064] Comparative Example 3

[0065] The difference between this comparative example and Example 1 is that the silicate intercalation in step (4) is not performed. Specifically, 28.08 g NaH 2 PO 4 2H 2O is dissolved in water and ultrasonicated for 5 minutes until it is completely dissolved, and the CaMgFe-LDH precursor is fully mixed with the dissolved solution. After the reaction is completed, it is centrifuged and the obtained precipitate is placed in an oven at 80°C to dry. The final product is the intercalated silicate ternary calcium magnesium iron layered double hydroxide soil passivator.

[0066] Performance testing and result analysis:

[0067] The products prepared in Example 1 and Comparative Example 1 (Comparative Example 1 is a ternary calcium magnesium iron layered double hydroxide precursor; Example 1 is a ternary calcium magnesium iron layered double hydroxide soil passivator intercalated with silicate and dihydrogen phosphate) were subjected to X-ray diffraction (XRD) test, and the results are as follows: Figure 1 As shown. Figure 1 It can be seen that the CaMgFe-LDH precursor of Comparative Example 1 observed characteristic diffraction peaks such as 003, 006, 113, and 115 at 11.408°, 24.164°, 33.981°, and 62.726°, indicating that hydrotalcite has a layered structure and an orderly crystal arrangement. After the anion intercalation of Example 1 of the present 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 original and modified interlayer spacings are and and The change is small, but the interlayer structure maintains an integer multiple relationship, which proves that the intercalation does not destroy the layered characteristics of hydrotalcite, but only makes orderly adjustments.

[0068] The products prepared in Example 1 and Comparative Example 1 (Comparative Example 1 is a ternary calcium magnesium iron layered double hydroxide precursor; Example 1 is a ternary calcium magnesium iron layered double hydroxide soil passivator intercalated with silicate and dihydrogen phosphate) were subjected to infrared (FTIR) testing, and the results are as follows: Figure 2 As shown. 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 and 1620.88cm -1 OH stretching vibration and HOH bending vibration, respectively, indicating the presence of water molecules between the layers; 1470.6cm -1 and 1416.3cm -1 It is the characteristic peak of carbonate, which may be related to CO in the air. 2 After the anion was intercalated in Example 1 of the present application, the characteristic peaks of OH and HOH shifted slightly, reflecting the change of the interlayer environment; the most significant one was 1030.57 cm -1 The new characteristic peak is attributed to the Si-O vibration of silicate, indicating its successful intercalation; 603.03cm-1 and 562.8cm -1 The peak of carbonate (1470.7 cm) is consistent with the characteristic vibration of hydrogen phosphate, proving that it is also successfully intercalated. Although silicate and hydrogen phosphate are successfully intercalated, the characteristic peak of carbonate (1470.7 cm -1 and 1415.4cm -1 ) still exists, indicating that part of the carbonate ions have not been completely replaced, which may be related to the CO 2 is related to the role of.

[0069] The effects of the ternary calcium magnesium iron layered double hydroxide soil passivator prepared by different molar ratios of magnesium source, calcium source and iron source in Examples 1 to 5 on the adsorption of arsenic, cadmium and lead in the material solution were investigated. The results are as follows: Figure 3 As shown. Figure 3 It can be seen that when the metal molar ratio of (calcium + magnesium) / iron is 3:1, and the molar ratio of iron:magnesium:calcium is 1:1:2, the material has the largest adsorption capacity for arsenic, cadmium and lead, and the removal efficiency is the highest. The molar ratio of iron:magnesium:calcium is 1:1:2 as the optimal molar ratio, and the effect of aging temperature as a single factor variable on the material's adsorption of arsenic, cadmium and lead in the solution is explored. The results are as follows Figure 4 As shown. Figure 4 It can be seen that an aging temperature of 30°C can achieve a higher removal efficiency. In 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 material's adsorption capacity for arsenic, cadmium and lead slowly decreases. The molar ratio of iron: magnesium: calcium was selected as 1:1:2 as the optimal molar ratio, and the aging temperature was selected as 30°C. The effect of different aging times as single factor variables on the material's adsorption of arsenic, cadmium and lead in the solution was explored. The results are as follows: Figure 5 As shown. Figure 5 It can be seen that an aging time of 16 hours can achieve a higher removal efficiency for arsenic, cadmium and lead; when the aging time exceeds 16 hours, the adsorption capacity of the material for cadmium and lead shows a downward trend, so 16 hours is selected as the optimal aging time in subsequent experiments.

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

[0071] Weigh 100g of heavy metal contaminated soil sample and place it in a plastic bottle. Add the soil passivators of Example 1 and Comparative Examples 1 to 3 of the present application according to the soil passivator mass fraction: 0%, 0.5%, 1%, 3%, 5%, 7%, 9% and 11% respectively. Add water according to the soil moisture content of about 60%, stir evenly, seal with plastic wrap and culture statically for one month, and set the temperature to 25°C. After the culture is completed, take out the soil, and use DTPA leaching agent to extract the effective content of arsenic, cadmium and lead in the passivated and repaired soil. The results are shown in Table 1-3.

[0072] Table 1 Available content of heavy metals (Cd) in soil after passivation

[0073]

[0074] Table 2 Available content of heavy metals (Pb) after soil passivation

[0075]

[0076]

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

[0078]

[0079] As shown in Tables 1 to 3, the ternary calcium magnesium iron layered double hydroxide soil passivator with intercalated silicate and dihydrogen phosphate can significantly reduce the effective content of Cd, Pb and As in the soil, and has a certain passivation effect on Cd, Pb and As in the contaminated soil. The effective contents of Cd, Pb and As in the soil without the addition of passivator are 3.02 mg / kg, 153.7 mg / kg and 3.135 mg / kg respectively. After adding four soil passivators, the effective contents of Cd, Pb and As in the soil will all decrease (after adding the ternary iron magnesium calcium layered double hydroxide soil passivator with intercalated silicate and dihydrogen phosphate, the ternary iron magnesium calcium layered double hydroxide soil passivator, the ternary iron magnesium calcium layered double hydroxide soil passivator with only intercalated silicate, and the ternary iron magnesium calcium layered double hydroxide soil passivator with only intercalated dihydrogen phosphate to the soil, the effective Cd content decreased by 24.1%, 8.7%, 9.65% and 10.2% respectively, the effective Pb content decreased by 50.4%, 25.4%, 35.1% and 39.6% respectively, and the effective As content decreased by 28.5%, 12.1%, 13.6% and 15.5% respectively). Obviously, the effective content of Cd, Pb and As in the soil decreased most significantly after adding intercalated silicate and dihydrogen phosphate ternary calcium magnesium iron layered double hydroxide soil passivator. Among them, when the dosage increased from 0% to 3%, the effective content of Cd, Pb and As decreased by 24.1%, 25.7% and 28.5% respectively. However, for Cd and As, when the addition amount of passivator exceeded 3%, their effective content slowly increased, so 3% was selected as the optimal addition amount of passivator in subsequent experiments.

[0080] The soil passivators of Example 1 and Comparative Examples 1 to 3 were added to the soil at an amount of 3% of the soil mass, and water was added according to the soil moisture content of about 60%. After uniform stirring, the soil was sealed with a plastic wrap and statically cultured for one month, and the temperature was set to 25°C. After the culture was completed, the effective silicon and effective phosphorus fertility index in the soil were measured. The results are shown in Tables 4-5.

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

[0082]

[0083] Table 5 Intercalated silicate, dihydrogen phosphate ternary iron magnesium calcium layered double hydroxide soil passivator soil available phosphorus content

[0084]

[0085] As can be seen from Tables 4 to 5, the effective silicon and effective phosphorus contents of the soil after treatment with the ternary calcium magnesium iron layered double hydroxide soil passivator of Comparative Example 1 are almost unchanged; compared with the ternary iron magnesium calcium layered double hydroxide soil passivator with only intercalated silicate and the ternary iron magnesium calcium layered double hydroxide soil passivator with only intercalated dihydrogen phosphate, the effective silicon and effective phosphorus contents of the soil after treatment with the ternary calcium magnesium iron layered double hydroxide soil passivator with intercalated silicate and dihydrogen phosphate of Example 1 of the present application are significantly increased (the effective silicon content of the soil after the ternary calcium magnesium iron layered double hydroxide soil passivator with intercalated silicate and dihydrogen phosphate is added to the soil is increased by 51.8% at most; the ternary calcium magnesium iron layered double hydroxide soil passivator with only intercalated silicate is significantly increased after treatment with ... After the iron-magnesium-calcium layered double hydroxide soil passivator was added to the soil, the soil's available silicon content increased by 25.4% at most; after the ternary iron-magnesium-calcium layered double hydroxide soil passivator with only dihydrogen phosphate was added to the soil, the soil's available silicon content did not change much. After the ternary calcium-magnesium-iron layered double hydroxide soil passivator with silicate and dihydrogen phosphate was added to the soil, the soil's available phosphorus content increased by 3.27 times; after the ternary iron-magnesium-calcium layered double hydroxide soil passivator with only silicate was added to the soil, the soil's available phosphorus content did not change much; after the ternary iron-magnesium-calcium layered double hydroxide soil passivator with only dihydrogen phosphate was added to the soil, the soil's available phosphorus content increased by 1.21 times. ). Specifically, after the ternary calcium-magnesium-iron layered double hydroxide (LDH) with silicate and dihydrogen phosphate was used as a soil passivator to treat the soil, the contents of available silicon and available phosphorus in the soil experienced different changes. In the early stage of treatment (1-5 days), silicate and dihydrogen phosphate were rapidly released from LDH, resulting in a rapid increase in the contents of available silicon and available phosphorus (increased by 37.1% and 1.89 times, respectively); then, after the 7th day, due to the decrease in the release of silicon and phosphorus in LDH, or due to the reaction or adsorption of silicon and phosphorus with minerals in the soil, the concentrations of available silicon and available phosphorus began to decrease; from the 9th to the 30th day, the release of silicon and phosphorus entered a slow stage, and as time went on, the release rate slowed down, and the available silicon and available phosphorus in the soil gradually recovered and remained stable, which may be due to the slow release effect and the help of microorganisms, and the release of silicon and phosphorus gradually increased.

[0086] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the art within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for preparing a soil passivator based on hydrotalcite, characterized in that: The following steps are involved: S1. Dissolve a calcium source, a magnesium source, and an iron source in water and fully dissolve them to obtain a mixed salt solution A containing calcium ions, magnesium ions, and iron ions; drip the mixed salt solution A and the NaOH solution into a three-necked flask at a uniform speed and simultaneously, keep stirring, and after fully mixing, obtain a dark yellow slurry; S2, subjecting the dark yellow slurry to aging treatment, centrifuging, washing until the filtrate is neutral, and drying to obtain a ternary calcium magnesium iron precursor; S3, dissolving the salt containing silicate and the salt containing dihydrogen phosphate in water and fully dissolving them 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 reacting them, centrifuging and drying the precipitate to obtain a soil passivator based on hydrotalcite.

2. The method for preparing a soil passivator based on hydrotalcite according to claim 1, characterized in that: 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.

3. The method for preparing a soil passivator based on hydrotalcite according to claim 1, characterized in that: 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 soil passivator based on hydrotalcite according to claim 1, characterized in that: In step S1, the molar ratio of calcium ions, magnesium ions and iron ions is 2:1:

1.

5. The method for preparing a hydrotalcite-based soil passivator according to claim 1, characterized in that: In step S1, the dripping rate is 1.5-10 ml / min; the stirring rate is 480-800 r / min.

6. The method for preparing a hydrotalcite-based soil passivator according to claim 1, characterized in that: In step S2, the temperature of the aging treatment is 20-60°C, the time of the aging treatment is 8-24h; the temperature of the drying is 60-100°C.

7. The method for preparing a soil passivator based on hydrotalcite according to claim 1, characterized in that: In step S3, the molar ratio of the silicate to the dihydrogen phosphate is 1:

1.

8. The method for preparing a hydrotalcite-based soil passivator according to claim 1, characterized in that: 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 salts and dihydrogen phosphate; the components of the soil passivator are composed of the above cations and anions.

9. A soil passivator based on hydrotalcite, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the hydrotalcite-based soil passivator according to claim 9 in reducing the activity of As, Pb, and Cd in soil and improving soil fertility.

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