A method for preparing a passivating agent using attapulgite and the passivating agent and its application

Abstract

The present invention provides a method for preparing a passivator using attapulgite, a passivator and its application, and belongs to the technical field of passivator preparation. In the present invention, the functional groups in the modifier react with the active sites on the surface of the attapulgite (such as silanol groups and aluminum alcohol groups), and are bound to the surface of the attapulgite by chemical bonding or physical adsorption, thereby changing its surface properties and charge distribution, and enhancing the adsorption selectivity and affinity for heavy metal ions. Modified attapulgite, nano zero-valent iron and potassium dihydrogen phosphate are compounded to give play to their respective advantages and act synergistically. The modified attapulgite provides adsorption sites and complexing ability, the nano zero-valent iron reduces heavy metals, and the potassium dihydrogen phosphate precipitates heavy metals, thereby jointly improving the passivation effect on a variety of heavy metals.

Description

Technical Field

[0001] The present invention relates to the technical field of passivator preparation, and in particular to a method for preparing a passivator by using attapulgite, the passivator and its application. Background Art

[0002] Background of the invention With the acceleration of global industrialization and urbanization, the problem of heavy metal pollution in soil has become increasingly serious and has become a major hidden danger threatening the ecological environment and human health.

[0003] Heavy metal pollutants such as cadmium (Cd), lead (Pb), mercury (Hg), chromium (Cr), and the metalloid arsenic (As) are persistent, bioaccumulative, and toxic. Once in the soil, they are difficult to degrade or eliminate through natural processes. These heavy metals accumulate in the soil, altering its physical, chemical, and biological properties, leading to a decrease in soil fertility and changes in the structure of microbial communities. This, in turn, affects the growth and development of crops, reducing the yield and quality of agricultural products. Furthermore, heavy metals can enter the human body through bioaccumulation in the food chain, causing various diseases. For example, cadmium can cause itai-itai disease, and lead can affect the development of the nervous system, posing a potential threat to human health.

[0004] Currently, numerous remediation technologies are available for heavy metal contaminated soil, including physical, chemical, and biological remediation. While physical remediation techniques, such as soil removal and electroremediation, can reduce heavy metal content in soil to a certain extent, they suffer from high costs, extensive engineering efforts, and potential damage to soil structure. While bioremediation techniques, such as phytoremediation and microbial remediation, are environmentally friendly, they have long remediation cycles and are limited by factors such as the species of organisms and environmental conditions, making them difficult to meet the demand for rapid remediation.

[0005] Chemical passivation remediation technology has become a research hotspot due to its ease of operation, relatively low cost, and ability to rapidly reduce the bioavailability of heavy metals in soil. This technology primarily involves adding a passivating agent to the soil and utilizing chemical reactions between the passivating agent and the heavy metals, such as adsorption, precipitation, and complexation, to reduce the mobility and bioavailability of heavy metals in the soil.

[0006] As a natural clay mineral, attapulgite has a unique crystal structure, a large specific surface area and good adsorption properties, and has attracted widespread attention in the field of soil passivation agent preparation. However, the existing methods for preparing passivation agents using attapulgite as raw material have many shortcomings. On the one hand, most conventional treatment methods have limited activation of attapulgite, failing to fully utilize its potential adsorption and ion exchange capacity, resulting in poor fixation of heavy metals by the passivation agent; on the other hand, the passivation agents prepared by traditional modification methods are not stable enough in complex soil environments and are easily affected by factors such as soil pH and redox potential, making it difficult for the passivation effect to last. In addition, existing attapulgite-based passivation agents often have a good passivation effect on a single heavy metal, but when faced with soil contaminated by multiple heavy metals, their synergistic passivation ability is weak and cannot meet the actual needs of remediation of contaminated soil.

[0007] In summary, the development of a method for preparing an efficient, stable attapulgite-based passivating agent that can synergistically passivate multiple heavy metals has important practical significance, which is also the key problem that the present invention is committed to solving. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for preparing a passivator using attapulgite, the passivator and its application, and to provide a better material for the existing technology.

[0009] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0010] The present invention provides a method for preparing a passivating agent, comprising the following steps:

[0011] The attapulgite is subjected to acidification treatment and drying treatment in sequence to obtain pretreated attapulgite;

[0012] Mixing attapulgite with a modifier and washing to obtain modified attapulgite;

[0013] The modified attapulgite nano-zero-valent iron and potassium dihydrogen phosphate are mixed and ball-milled to obtain a passivating agent.

[0014] Preferably, the acid used in the acidification treatment is a hydrochloric acid solution with a mass fraction of 6 to 7%;

[0015] The liquid-to-solid ratio of the acidification treatment is 7 to 9:1 mL / g;

[0016] The reaction temperature of the acidification treatment is 60-70°C;

[0017] The reaction time of the acidification treatment is 3 to 4 hours.

[0018] Preferably, the drying temperature is 100-120°C;

[0019] The grinding mesh number of the drying process is 300 to 400 meshes.

[0020] Preferably, the modifier is composed of citric acid and urea in a molar ratio of 1:2 to 1:3;

[0021] The total concentration of the modifier is 0.5 to 0.8 mol / L;

[0022] The preparation reaction temperature of the modifier is 80-90°C;

[0023] The preparation reaction time of the modifier is 2 to 3 hours.

[0024] Preferably, the solid-liquid ratio of the attapulgite and the modifier is 1:5 to 1:8 (g / mL);

[0025] The reaction temperature of the attapulgite and the modifier is 50-60°C;

[0026] The reaction time of mixing the attapulgite and the modifier is 4 to 6 hours.

[0027] Preferably, the attapulgite and the modifier are washed 1 to 3 times after mixing;

[0028] The drying temperature after the attapulgite and the modifier are mixed is 60-70°C.

[0029] Preferably, the mixing mass ratio of the modified attapulgite, nano zero-valent iron and potassium dihydrogen phosphate is 4:2:1 to 6:2:1.

[0030] Preferably, the rotation speed of the ball mill is 300-400 r / min;

[0031] The ball milling time is 2 to 3 hours.

[0032] The present invention also provides a passivating agent prepared by the above preparation method.

[0033] The present invention also provides the use of the above passivating agent in reducing heavy metal pollution in soil;

[0034] The application amount of the passivating agent is 1500-2000 kg / hm 2 ;

[0035] The passivating agent is applied by mixing it with water to form a slurry, spraying it and then plowing the land;

[0036] The tillage depth is 20 to 30 cm.

[0037] Technical effects and advantages of the present invention:

[0038] The present invention prepares a passivator based on attapulgite, which has many significant technical effects and advantages. By acidifying and modifying the attapulgite, and compounding it with nano-zero-valent iron and potassium dihydrogen phosphate, the passivator significantly enhances the adsorption, fixation and chemical conversion capabilities of various heavy metals (such as cadmium, lead, zinc, etc.) in the soil, effectively reducing the bioavailability of heavy metals, reducing their migration in the soil-plant system, and thus reducing the risk of food chain pollution. The present invention forms a relatively stable structure in the modification process of attapulgite, making it difficult for the passivator to decompose or lose in the complex soil environment, and can continue to play a passivating role on heavy metals for a long time, ensuring the durability of the repair effect.

[0039] Because attapulgite is a natural clay mineral with abundant reserves and low cost, using it as the main raw material to prepare a passivation agent is cost-effective in large-scale soil remediation applications, which helps reduce remediation costs, improve the economy and feasibility of remediation technology, and provide an economical and affordable material option for the widespread treatment of heavy metal pollution in soil. The entire preparation process does not use any environmentally harmful chemicals, and the passivation agent can exist stably and function in the soil without causing secondary pollution to the soil ecosystem. It conforms to the concept of green and environmentally friendly remediation and helps protect the health and sustainability of the soil ecological environment. It is not only suitable for soils with varying degrees of heavy metal contamination, but can also cope with complex situations of multiple heavy metal combined pollution. It provides an effective solution for the remediation of various types of heavy metal contaminated soils and is of great significance for ensuring the safe use of soil resources and maintaining ecological balance. DETAILED DESCRIPTION

[0040] The present invention provides a method for preparing a passivating agent, comprising the following steps:

[0041] The attapulgite is subjected to acidification treatment and drying treatment in sequence to obtain pretreated attapulgite;

[0042] Mixing attapulgite with a modifier and washing to obtain modified attapulgite;

[0043] The modified attapulgite nano-zero-valent iron and potassium dihydrogen phosphate are mixed and ball-milled to obtain a passivating agent.

[0044] In the present invention, the functional groups in the modifier react with the active sites on the surface of the attapulgite (such as silanol groups and aluminum alcohol groups), and are bound to the surface of the attapulgite through chemical bonding or physical adsorption, thereby changing its surface properties and charge distribution and enhancing the adsorption selectivity and affinity for heavy metal ions.

[0045] In the present invention, nano zero-valent iron has strong reducing properties, and some heavy metals (such as cadmium and lead) in the soil exist in a high valent state, with strong toxicity and mobility. Nano zero-valent iron can reduce it to a low valent state, such as reducing hexavalent chromium to trivalent chromium. Trivalent chromium is more likely to form insoluble compounds, reducing the mobility and biological effectiveness of heavy metals. Potassium dihydrogen phosphate provides phosphate ions, which form insoluble phosphate precipitates with heavy metal ions (such as lead and cadmium), such as lead phosphate, cadmium phosphate, etc., to reduce the concentration of heavy metal ions in the soil solution and achieve passivation. Modified attapulgite, nano zero-valent iron and potassium dihydrogen phosphate are compounded in a mass ratio of 5:2:1 to give play to their respective advantages and work synergistically. Modified attapulgite provides adsorption sites and complexing ability, nano zero-valent iron reduces heavy metals, and potassium dihydrogen phosphate precipitates heavy metals, jointly improving the passivation effect on multiple heavy metals.

[0046] In the present invention, preferably, the acid for the acidification treatment is a hydrochloric acid solution with a mass fraction of 6 to 7%; the liquid-to-solid ratio of the acidification treatment is 7 to 9:1 mL / g; the reaction temperature for the acidification treatment is 60 to 70° C.; and the reaction time for the acidification treatment is 3 to 4 hours.

[0047] In the present invention, preferably, the drying temperature is 100-120°C; the grinding mesh size is 300-400 mesh. Preferably, the modifier comprises citric acid and urea in a molar ratio of 1:2-1:3; the total concentration of the modifier is 0.5-0.8 mol / L; the reaction temperature for preparing the modifier is 80-90°C; and the reaction time for preparing the modifier is 2-3 hours. Preferably, the solid-to-liquid ratio of the attapulgite and modifier is 1:5-1:8 (g / mL); the reaction temperature for the attapulgite and modifier is 50-60°C; and the reaction time for the attapulgite and modifier is 4-6 hours. Preferably, the attapulgite and modifier are washed 1-3 times after mixing; and the drying temperature after mixing the attapulgite and modifier is 60-70°C. Preferably, the mass ratio of the modified attapulgite, nano zero-valent iron and potassium dihydrogen phosphate is 4:2:1 to 6:2:1. Preferably, the rotation speed of the ball mill is 300 to 400 r / min and the ball milling time is 2 to 3 hours.

[0048] The present invention also provides a passivating agent prepared by the above preparation method.

[0049] The present invention also provides the use of the above passivating agent in reducing soil heavy metal pollution; the application amount of the passivating agent is 1500-2000 kg / hm 2 The passivating agent is applied by mixing it with water to form a slurry, spraying it and then plowing the land; the plowing depth is 20 to 30 cm.

[0050] In the present invention, the application method can also be: the passivator is mixed with an appropriate amount of fine sand or organic fertilizer in a certain proportion, evenly spread on the soil surface using a spreading device, and then deep plowing is carried out using a deep plow, with the deep plowing depth controlled at 20-30 cm to fully mix the passivator with the soil. This method uses fine sand to improve the air permeability and water permeability of the soil, which helps to better contact the passivator with soil particles. The organic fertilizer not only provides nutrients to the soil, but also helps to improve soil structure and enhance the soil's adsorption capacity for heavy metals, further enhancing the passivation effect.

[0051] For smaller areas with relatively concentrated pollution, a hole-dose method can be used. This involves digging holes at regular intervals in the contaminated soil, applying the passivation agent directly into the holes, then covering them with soil and watering them appropriately to allow the passivation agent to take effect locally. This method allows for more precise remediation of severely contaminated sites, reduces the amount of passivation agent used, and improves remediation efficiency.

[0052] For some sloping land or areas prone to soil erosion, it is possible to consider mixing the passivator with a water-retaining agent, soil improver, etc., and then applying it in strips. Ditches are dug along the contour lines, and the mixed material is applied into the ditch and then covered with soil. This can not only effectively prevent the loss of passivator caused by soil erosion, but also improve the water and fertilizer retention capacity of the sloping soil to a certain extent, promote the interaction between the passivator and the soil, and enhance the passivation effect on heavy metals.

[0053] In some soil remediation scenarios in facility agriculture, it can be applied in conjunction with an irrigation system. The passivator is dissolved or suspended in the irrigation water and evenly transported to the soil around the crop roots through drip irrigation, micro-sprinkler irrigation, and other methods. This application method not only improves the uniformity of passivator application, but also reduces manual operation costs and allows the application amount of the passivator to be flexibly adjusted according to the crop growth stage and soil pollution status. Since irrigation water can carry the passivator deep into the soil, it helps it to fully contact and react with soil particles. It is especially suitable for facility cultivation environments that require high soil permeability.

[0054] For heavy clay soils, shallow soil loosening can be performed first, such as using a disc harrow or rotary tiller to create a loose surface layer. The passivator should then be evenly applied to the loosened soil surface, followed by a second tillage operation at a depth of 20-30 cm. This approach facilitates faster penetration and diffusion of the passivator, increasing its contact area with heavy metals in the soil and improving passivation efficiency. Furthermore, this loosening-first, passivator-applying, and then tillage approach can improve the aeration and water permeability of heavy clay soils, creating a more favorable soil environment for crop growth. For highly acidic, heavy metal-contaminated soils, an appropriate amount of alkaline amendment, such as lime, can be applied before applying the passivator to adjust the soil pH to near neutral. Once the soil pH stabilizes, the passivator can be applied according to the aforementioned method. This is because the active ingredients in the passivator react more efficiently with heavy metals under suitable pH conditions, significantly enhancing the passivation effect. At the same time, regulating the soil pH value can also help reduce the solubility and mobility of heavy metals in acidic environments, and synergize with the effect of passivators to more effectively reduce soil heavy metal pollution.

[0055] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0056] Example 1

[0057] 1. Attapulgite pretreatment

[0058] The collected attapulgite ore was crushed to 250 mesh.

[0059] The crushed attapulgite was placed in a 6.5% by mass hydrochloric acid solution with a liquid-solid ratio of 8:1 (mL / g), and stirred at 65° C. for 3.5 hours.

[0060] After the reaction is completed, the attapulgite is separated from the hydrochloric acid solution by vacuum filtration, and then repeatedly rinsed with deionized water until the pH value of the filtrate reaches 6.5.

[0061] The washed attapulgite was dried in an oven at 108°C to a constant weight, and then ground into 350 mesh powder for later use.

[0062] 2. Modifier Preparation

[0063] Citric acid and urea were weighed and mixed in deionized water at a molar ratio of 1:2.5 to prepare a mixed solution with a total concentration of 0.65 mol / L.

[0064] The mixed solution was transferred to a three-necked flask equipped with a condenser reflux device and stirred at 85°C for 2.5 hours.

[0065] 3. Modification of attapulgite

[0066] The pretreated attapulgite powder was added to the prepared modifier solution at a solid-liquid ratio of 1:6.5 (g / mL), and the mixture was stirred at 55°C for 5 hours.

[0067] After the reaction was completed, the product was separated by centrifugation and washed twice with anhydrous ethanol.

[0068] The washed product was placed in a vacuum drying oven at 65° C. and dried to a constant weight to obtain modified attapulgite.

[0069] 4. Preparation of passivating agent

[0070] Modified attapulgite, nano zero-valent iron and potassium dihydrogen phosphate were weighed and mixed in a mass ratio of 5:2:1.

[0071] The mixture was added into a planetary ball mill and ball-milled at a rotation speed of 350 r / min for 2.5 hours to obtain a passivating agent.

[0072] 5. Application of passivating agent

[0073] The prepared passivation agent was applied to heavy metal contaminated soil at an application rate of 1750 kg / hm2. 2 .

[0074] Before application, mix the passivator with an appropriate amount of water to make a slurry, then evenly spread it on the soil surface by spraying, and then plow the soil to a depth of 25 cm to allow the passivator to be fully mixed with the soil.

[0075] Example 2

[0076] 1. Attapulgite pretreatment

[0077] The collected attapulgite ore was crushed to 200 mesh.

[0078] The crushed attapulgite was placed in a 5% by mass hydrochloric acid solution with a liquid-to-solid ratio of 10:1 (mL / g), and stirred at 60° C. for 3 hours.

[0079] After the reaction is completed, the attapulgite is separated from the hydrochloric acid solution by vacuum filtration, and then repeatedly rinsed with deionized water until the pH value of the filtrate reaches 6.

[0080] The washed attapulgite was dried in an oven at 105°C to a constant weight, and then ground into 300 mesh powder for later use.

[0081] 2. Modifier Preparation

[0082] Citric acid and urea were weighed and mixed in deionized water at a molar ratio of 1:2 to prepare a mixed solution with a total concentration of 0.5 mol / L.

[0083] The mixed solution was transferred to a three-necked flask equipped with a condenser reflux device and stirred at 80°C for 2 hours.

[0084] 3. Modification of attapulgite

[0085] The pretreated attapulgite powder was added to the prepared modifier solution at a solid-liquid ratio of 1:5 (g / mL), and the mixture was stirred at 50°C for 4 hours.

[0086] After the reaction was completed, the product was separated by centrifugation and washed with anhydrous ethanol three times.

[0087] The washed product was placed in a vacuum drying oven at 60° C. and dried to a constant weight to obtain modified attapulgite.

[0088] 4. Preparation of passivating agent

[0089] Modified attapulgite, nano zero-valent iron and potassium dihydrogen phosphate were weighed and mixed in a mass ratio of 4:2:1.

[0090] The mixture was added into a planetary ball mill and ball-milled at a rotation speed of 300 r / min for 2 hours to obtain a passivating agent.

[0091] 5. Application of passivating agent

[0092] The prepared passivation agent was applied to heavy metal contaminated soil at a rate of 1500 kg / hm2. 2 .

[0093] Before application, mix the passivator with an appropriate amount of water to make a slurry, then evenly spread it on the soil surface by spraying, and then plow the soil to a depth of 20 cm to allow the passivator to be fully mixed with the soil.

[0094] Example 3

[0095] 1. Attapulgite pretreatment

[0096] The collected attapulgite ore was crushed to 300 mesh.

[0097] The crushed attapulgite was placed in a hydrochloric acid solution with a mass fraction of 8%, with a liquid-solid ratio of 6:1 (mL / g), and stirred at 70°C for 4 hours.

[0098] After the reaction is completed, the attapulgite is separated from the hydrochloric acid solution by vacuum filtration, and then repeatedly rinsed with deionized water until the pH value of the filtrate reaches 7.

[0099] The washed attapulgite was dried in an oven at 110°C to a constant weight, and then ground into 400 mesh powder for later use.

[0100] 2. Modifier Preparation

[0101] Citric acid and urea were weighed and mixed in deionized water at a molar ratio of 1:3 to prepare a mixed solution with a total concentration of 0.8 mol / L.

[0102] The mixed solution was transferred to a three-necked flask equipped with a condenser reflux device and stirred at 90° C. for 3 hours.

[0103] 3. Modification of attapulgite

[0104] The pretreated attapulgite powder was added to the prepared modifier solution at a solid-liquid ratio of 1:8 (g / mL), and the mixture was stirred at 60°C for 6 hours.

[0105] After the reaction was completed, the product was separated by centrifugation and washed once with anhydrous ethanol.

[0106] The washed product was placed in a vacuum drying oven at 70° C. and dried to a constant weight to obtain modified attapulgite.

[0107] 4. Preparation of passivating agent

[0108] Modified attapulgite and nano zero-valent iron were weighed and mixed in a mass ratio of 3:1.

[0109] The mixture was added into a planetary ball mill and ball-milled at a rotation speed of 400 r / min for 3 hours to obtain a passivating agent.

[0110] 5. Application of passivating agent

[0111] The prepared passivation agent was applied to heavy metal contaminated soil at a rate of 2000 kg / hm2. 2 .

[0112] Before application, mix the passivator with an appropriate amount of water to make a slurry, then evenly spread it on the soil surface by spraying, and then plow the soil to a depth of 30cm to allow the passivator to be fully mixed with the soil.

[0113] Comparative Example 1

[0114] 1. Attapulgite pretreatment

[0115] The collected attapulgite ore was crushed to 250 mesh.

[0116] The crushed attapulgite was placed in a 6.5% by mass hydrochloric acid solution with a liquid-solid ratio of 8:1 (mL / g), and stirred at 65° C. for 3.5 hours.

[0117] After the reaction is completed, the attapulgite is separated from the hydrochloric acid solution by vacuum filtration, and then repeatedly rinsed with deionized water until the pH value of the filtrate reaches 6.5.

[0118] The washed attapulgite was dried in an oven at 108°C to a constant weight, and then ground into 350 mesh powder for later use.

[0119] 2. Modifier Preparation

[0120] Citric acid and urea were weighed and mixed in deionized water at a molar ratio of 1:2.5 to prepare a mixed solution with a total concentration of 0.65 mol / L.

[0121] The mixed solution was transferred to a three-necked flask equipped with a condenser reflux device and stirred at 85°C for 2.5 hours.

[0122] 3. Modification of attapulgite

[0123] The pretreated attapulgite powder was added to the prepared modifier solution at a solid-liquid ratio of 1:6.5 (g / mL), and the mixture was stirred at 55°C for 5 hours.

[0124] After the reaction was completed, the product was separated by centrifugation and washed twice with anhydrous ethanol.

[0125] The washed product was placed in a vacuum drying oven at 65° C. and dried to a constant weight to obtain modified attapulgite.

[0126] 4. Preparation of passivating agent

[0127] Modified attapulgite, nano zero-valent iron and potassium dihydrogen phosphate were weighed and mixed in a mass ratio of 5:2:1.

[0128] The mixture was added into a planetary ball mill and ball-milled at a rotation speed of 350 r / min for 2.5 hours to obtain a passivating agent.

[0129] 5. Application of passivating agent

[0130] The prepared passivation agent was applied to heavy metal contaminated soil at an application rate of 1750 kg / hm2. 2 .

[0131] Before application, mix the passivator with an appropriate amount of water to make a slurry, then evenly spread it on the soil surface by spraying, and then plow the soil to a depth of 25 cm to allow the passivator to be fully mixed with the soil.

[0132] Experimental example

[0133] Experimental Materials

[0134] 1. Soil: Select a heavy metal contaminated farmland soil, whose main heavy metal pollutants are cadmium (Cd), lead (Pb), and zinc (Zn).

[0135] 2. Passivator: the passivator prepared in Example 1;

[0136] The passivator prepared in Comparative Example 1 (referred to as the control group passivator)

[0137] 3. Experimental instruments: atomic absorption spectrometer, electronic balance, soil sieve, constant temperature incubator, stirrer, centrifuge, pH meter, etc.

[0138] Experimental methods:

[0139] 1. Soil pretreatment

[0140] After the collected contaminated soil is naturally air-dried, a soil sample <2 mm is sieved using a soil sieve for later use.

[0141] The initial contents of heavy metals cadmium, lead and zinc in the soil after pretreatment were determined. The soil samples were digested with aqua regia-hydrofluoric acid, and the heavy metal contents in the digestate were determined using an atomic absorption spectrometer.

[0142] 2. Application of passivating agent

[0143] Experimental group: Weigh a certain amount of passivating agent prepared in Example 1 and 2 The passivator dosage corresponding to the mass of soil used in the experiment was calculated based on the ratio of % to % of the total weight of the soil. The passivator was mixed with an appropriate amount of water to form a uniform slurry. The slurry was evenly applied on the surface of 1 kg of soil by spraying. The slurry was then thoroughly stirred with a blender to simulate field plowing to a depth of 25 cm to ensure that the passivator and soil were fully mixed.

[0144] Control group: Weigh the same mass of the control group passivator and mix it with 1 kg of soil in the same way according to the recommended dosage of the product.

[0145] 3. Cultivation Experiment

[0146] The two treated soils were placed in plastic pots, maintained at 60% of their field capacity, and incubated at 25°C for 60 days. The soils were weighed regularly during the incubation period, and water was added to maintain a constant soil moisture.

[0147] 4. Sample Analysis

[0148] After the incubation period, two groups of soil samples were collected. Three replicates were set for each treatment to improve the accuracy of the experiment.

[0149] Available heavy metals were extracted from the soil using a DTPA extractant (0.005 mol / L DTPA-0.01 mol / L CaCl2-0.1 mol / L triethanolamine, pH 7.3). A 5.00 g air-dried soil sample was placed in a 50 mL centrifuge tube. 20.00 mL of DTPA extractant was added and the tube was shaken at 200 rpm for 2 h at 25°C. The tube was then centrifuged at 4000 rpm for 15 min. The supernatant was collected and the available cadmium, lead, and zinc contents were determined using atomic absorption spectrometry.

[0150] The pH values ​​of the two groups of soil were measured at the same time. The glass electrode method was used. 10.00 g of air-dried soil sample was weighed into a 50 mL beaker, 25.00 mL of deionized water was added, and the mixture was stirred evenly. After standing for 30 min, the pH value was measured using a pH meter.

[0151] The experimental results are shown in Table 1 below:

[0152] Table 1 Passivation agent test results

[0153]

[0154] Result Analysis

[0155] Available heavy metal content: The data show that after applying the passivator prepared in Example 1, the available cadmium, lead, and zinc contents in the soil were significantly lower than those in the control group. The available cadmium content decreased by approximately 38.82%, the available lead content decreased by approximately 34.34%, and the available zinc content decreased by approximately 26.94%, indicating that the passivator in Example 1 has a better passivation effect on heavy metals and can more effectively reduce the bioavailability of heavy metals.

[0156] Soil pH: The pH of the soil in the experimental group was 7.25, while that in the control group was 6.80. The passivation agent in Example 1 increased the soil pH, which may have helped promote the precipitation and adsorption of heavy metals, further enhancing the passivation effect. The passivation agent in the control group had a relatively modest effect.

[0157] In summary, the passivator prepared in Example 1 performed better than the passivator in the comparative example in reducing the effective content of heavy metals in soil, and had a better soil heavy metal passivation effect.

[0158] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a passivating agent, characterized in that: The following steps are involved: The attapulgite is subjected to acidification treatment and drying treatment in sequence to obtain pretreated attapulgite; Mixing attapulgite with a modifier and washing to obtain modified attapulgite; The modified attapulgite, nano zero-valent iron and potassium dihydrogen phosphate are mixed and ball-milled to obtain a passivating agent; The solid-liquid ratio of the attapulgite and the modifier is 1:5 to 1:8 (g / mL); The reaction temperature of the attapulgite and the modifier is 50-60°C; The reaction time of mixing the attapulgite and the modifier is 4 to 6 hours; The mixed mass ratio of the modified attapulgite, nano zero-valent iron and potassium dihydrogen phosphate is 4:2:1 to 6:2:1; The ball mill has a rotation speed of 300-400 r / min; The ball milling time is 2 to 3 hours; The acid for the acidification treatment is a hydrochloric acid solution with a mass fraction of 6 to 7%; The liquid-to-solid ratio of the acidification treatment is 7 to 9:1 mL / g; The reaction temperature of the acidification treatment is 60-70°C; The reaction time of the acidification treatment is 3 to 4 hours; The modifier is composed of citric acid and urea in a molar ratio of 1:2 to 1:3 mixed in deionized water to prepare a mixed solution with a total concentration of 0.5 to 0.8 mol / L; The preparation reaction temperature of the modifier is 80-90°C; The preparation reaction time of the modifier is 2 to 3 hours.

2. The preparation method according to claim 1, characterized in that The drying temperature is 100-120°C; The grinding mesh number of the drying process is 300 to 400 meshes.

3. The preparation method according to claim 1, characterized in that The attapulgite and the modifier are washed 1 to 3 times after being mixed; The drying temperature after the attapulgite and the modifier are mixed is 60-70°C.

4. A passivating agent obtained by the preparation method according to any one of claims 1 to 3.

5. Use of the passivating agent according to claim 4 in alleviating heavy metal pollution in soil; The application amount of the passivating agent is 1500-2000 kg / hm 2 ; The passivating agent is applied by mixing it with water to form a slurry, spraying it and then plowing the land; The tillage depth is 20 to 30 cm.

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