Heavy metal contaminated soil remediation method based on foliar barrier agent assisted soil passivation

Abstract

The present invention discloses a method for remediating heavy metal-contaminated soil based on foliar barrier agent-assisted soil passivation, comprising the following steps: S1, humic acid separation and purification: S1-1, primary separation and purification; S1-2, secondary separation and purification; S2, soil passivator preparation: S2-1, iron talc modification; S2-2, raw material mixing; S3, foliar barrier agent preparation; S4, contaminated soil remediation: S4-1, contaminated soil remediation; S4-2, crop maintenance-assisted soil passivation. The present invention extracts humic acid to obtain humic acid suitable for subsequent preparation of soil passivator and fulvic acid suitable for subsequent preparation of foliar barrier agent, which can improve the synergistic effect between soil passivation and foliar barrier control, is easy to prepare and has low cost, and can further improve the passivation effect of heavy metals in soil by cooperating with modified iron talc, especially has a good effect on the barrier control of heavy metals in double-season rice planting.

Description

Technical Field

[0001] The invention relates to the technical field of soil regeneration, and in particular to a method for repairing heavy metal-contaminated soil based on foliar barrier agent-assisted soil passivation. Background Art

[0002] Heavy metals accumulate in the roots of crops, enter the leaves, and then enter the fruits. They enter the human body through the food chain, causing damage to human bones, kidneys, liver and other organs, thus causing a series of diseases. Therefore, it is crucial to strengthen the management of heavy metals in the soil.

[0003] In-situ passivation remediation technology is a common soil Cd pollution remediation technology. Its advantages are simple operation, short cycle, low cost, and obvious effect. By applying soil passivators, the form of heavy metals in the soil is changed, reducing their mobility and achieving a barrier effect.

[0004] Foliar barrier agents can effectively reduce the heavy metal content of crops. After years of field trials, the application of foliar barrier agents in lightly and heavily polluted farmland can reduce the absorption of heavy metal cadmium by rice by an average of 30-40%. Foliar barrier agents can adjust the balanced absorption of nitrogen, phosphorus and potassium in crops, improve the utilization rate of fertilizers, and more effectively use nutrients to increase crop yields.

[0005] However, at present, there are many types of soil pollution, and the use of a single technology often does not achieve a good treatment effect. At present, few people have conducted in-depth research on the combination of soil passivation and foliar barrier control technology. Although many scholars have combined the two in their research, if they are simply superimposed, the effect of 1+1 greater than 2 often does not appear. On the contrary, due to the increase in costs, it may even lead to an effect of 1+1 less than 2. Or it may be affected by the soil environment and the types of heavy metal pollution, making it difficult to achieve universal promotion and application. Therefore, in-depth research and exploration is still needed in this direction. Summary of the invention

[0006] In view of the above-mentioned problems, the present invention provides a method for remediating heavy metal contaminated soil based on foliar barrier agent-assisted soil passivation.

[0007] The technical solution of the present invention is:

[0008] The heavy metal contaminated soil remediation method based on foliar barrier agent assisted soil passivation includes the following steps:

[0009] S1. Separation and purification of humic acid:

[0010] S1-1, primary separation and purification: taking humic acid and adding NaOH solution, the weight ratio of the humic acid to the NaOH solution is 1:3-7, the mass concentration of the NaOH solution is 40-60%, stirring and centrifuging, removing the precipitate to obtain a primary supernatant, adding dilute acid to the primary supernatant to a pH value of 2±0.2 to obtain a primary mixed solution, stirring and centrifuging to obtain a humic acid precipitate, and removing the humic acid precipitate to obtain a secondary supernatant as a crude fulvic acid extract;

[0011] S1-2, secondary separation and purification: evaporating, crystallizing and concentrating the crude fulvic acid extract prepared in S1-1 to obtain a fulvic acid concentrate;

[0012] S2. Preparation of soil passivator:

[0013] S2-1, talc modification: natural talc is crushed and sieved to obtain talc powder, the talc powder is calcined to obtain primary modified talc powder, the primary modified talc powder is completely immersed in a CaCl2 solution with a molar concentration of 2-4 mol / L for 6-12 h to obtain secondary modified talc powder;

[0014] S2-2, raw material mixing: the humic acid precipitate prepared in S1-1, the secondary modified talc powder prepared in S2-1 and hydroxyapatite are mixed in a mass ratio of 1:2:6-10 to obtain a first soil passivator, and the humic acid precipitate prepared in S1-1, the secondary modified talc powder prepared in S2-1 and attapulgite are mixed in a mass ratio of 1:2:6-10 to obtain a second soil passivator;

[0015] S3, preparation of foliar control agent: the fulvic acid concentrate prepared in S1-2 is mixed with ZnCl2 solution to obtain a first foliar control agent containing 5-8 mg / L of ZnCl2, and the fulvic acid crude extract prepared in S1-1 is mixed with ZnCl2 solution to obtain a second foliar control agent containing 10-12 mg / L of ZnCl2;

[0016] S4. Remediation of contaminated soil:

[0017] S4-1, contaminated soil remediation: the first soil passivator or the second soil passivator prepared in S2-2 is evenly applied to the heavy metal contaminated soil to be treated to remediate the heavy metal contaminated soil, and the application amount is 120-150 kg / mu;

[0018] S4-2. Crop maintenance and soil passivation: dilute the first foliar barrier agent or the second foliar barrier agent prepared in S3 by 300-500 times with water, and spray it on the leaves of crops to maintain the crops and assist in passivation of heavy metals in the soil. The application amount is 100-150 ml / mu / time.

[0019] Furthermore, the dilute acid in S1 is a hydrochloric acid solution with a mass concentration of 20-30%.

[0020] Furthermore, in S2-1, the natural talc is crushed through a 80-100 mesh sieve, the calcination temperature is 600-650° C., and the calcination time is 5-10 min.

[0021] Description: By selecting natural talc as one of the main raw materials of soil passivator, talc is rich in symbiosis with quartz (flint), siderite, magnetite, black hard chlorite and iron serpentine, etc. It belongs to the monoclinic system mineral with a unique high iron content of up to 33.60%, and the cleavage surface is complete. After modification, it is 2+ The combination effect is good.

[0022] Furthermore, the weight ratio of the primary modified talc powder to the CaCl2 solution in S2-1 is 1:3~7.

[0023] Note: Reasonably adjust the ratio so that the primary modified talc powder is completely immersed in the CaCl2 solution.

[0024] Furthermore, the mass concentration of the ZnCl2 solution in S3 is 30-40%.

[0025] Furthermore, in S4-1, the application amount of the first soil passivator is 130-150 kg / mu, and the application amount of the second soil passivator is 120-140 kg / mu.

[0026] Note: Reasonably control the application amount of soil passivators, appropriately increase the application amount of the first soil passivator during the first application, and appropriately reduce the application amount of the second soil passivator during the second application to avoid excessive accumulation of other heavy metals in the soil and avoid reducing soil fertility.

[0027] Furthermore, in S4-1, the dilution multiple of the first foliar barrier agent is 300-400 times, and the dilution multiple of the second foliar barrier agent is 400-500 times.

[0028] Note: By reasonably controlling the dilution multiple of the foliar control agent and thus indirectly controlling the application amount, it is possible to avoid excessive soil acidification while ensuring the foliar control effect.

[0029] Furthermore, the heavy metal contaminated soil is double-season rice planting soil,

[0030] The double-season rice is divided into early rice and late rice. The early rice is sown in mid-to-late March and transplanted in mid-to-late April. One to two weeks before planting the early rice, the first soil passivator is applied to the soil according to the application amount in S4-1. During the tillering period after transplanting, the first foliar barrier control agent is diluted according to the dilution multiple in S4-2 and sprayed on the rice leaves. The spraying is performed once every 5 to 7 days, for a total of 2 times.

[0031] The late rice is sown in mid-to-late June and transplanted in mid-to-late July. One to two weeks before planting the late rice, the second soil passivator is applied to the soil according to the application amount in S4-1. During the tillering period after transplanting, the second foliar barrier control agent is diluted according to the dilution multiple in S4-2 and sprayed on the rice leaves. The spraying is performed once every 5 to 7 days, for a total of 2 times.

[0032] The beneficial effects of the present invention are:

[0033] (1) The heavy metal contaminated soil remediation method based on foliar barrier agent assisted soil passivation of the present invention extracts humic acid to obtain humic acid suitable for the subsequent preparation of soil passivator and fulvic acid suitable for the subsequent preparation of foliar barrier agent, which can improve the synergistic effect between soil passivation and foliar barrier, is easy to prepare and has low cost. At the same time, the modified talc can further improve the passivation effect of heavy metals in the soil, especially for the barrier control of heavy metals in double-season rice planting soil.

[0034] (2) The heavy metal contaminated soil remediation method based on foliar barrier agent assisted soil passivation of the present invention optimizes the preparation process of the soil passivator, wherein the humic acid precipitate and the heavy metals in the soil undergo electrostatic attraction and complexation to adsorb the heavy metals; talc is introduced and modified to change its specific surface area and pore structure; 2+ After treatment, it is easier to exchange ions with heavy metals in the soil. At the same time, the high Fe content (33.6%) in talc allows Fe and Ca to exchange and adsorb heavy metal ions, inhibiting the upward transport of heavy metal ions from the roots of crops. Finally, hydroxyapatite and attapulgite can improve the pH value of the soil to make the soil weakly alkaline, which is more conducive to the precipitation of heavy metals and the formation of complexes. Among them, hydroxyapatite is used for one application mainly for Pb and Cd in the soil, and attapulgite with high calcium content is used for secondary application to increase the proportion of residual heavy metals.

[0035] (3) The heavy metal contaminated soil remediation method based on foliar barrier agent assisted soil passivation of the present invention optimizes the preparation process of foliar barrier agent, wherein fulvic acid enters the plant body to form a complex with heavy metals, thereby reducing the migration capacity of heavy metals; Zn 2+It makes up for the lack of this element in soil passivators, and uses it to act on the leaves to meet the nutritional needs of the leaves and reduce the absorption of heavy metal elements from the roots. The concentration of fulvic acid applied once is higher, while the concentration of fulvic acid applied twice is lower, which can ensure the leaf barrier effect while avoiding soil acidification.

[0036] (4) The heavy metal contaminated soil remediation method based on foliar barrier agent assisted soil passivation of the present invention reasonably adjusts the amount of humic acid precipitate in the soil passivator and the amount of fulvic acid crude extract and fulvic acid concentrate in the foliar barrier agent, so as to fully utilize and balance the humic acid raw materials as much as possible, achieve the purpose of continuous production, reduce costs and increase efficiency, realize industrial production, and generate good economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a flow chart of the heavy metal contaminated soil remediation method based on foliar barrier agent assisted soil passivation of the present invention;

[0038] Figure 2 is the Cd content in the early rice and late rice grains after restoration in each case of Experimental Example 1 of the present invention;

[0039] Figure 3 It is the Cd content in the roots of early rice and late rice after restoration in each case in Experimental Example 1 of the present invention. DETAILED DESCRIPTION

[0040] Example 1: A method for remediating heavy metal-contaminated soil based on foliar barrier agent-assisted soil passivation, such as Figure 1 As shown, the following steps are included:

[0041] S1. Separation and purification of humic acid:

[0042] S1-1, primary separation and purification: take humic acid and add NaOH solution, stir and centrifuge, the weight ratio of humic acid to NaOH solution is 1:4, the mass concentration of NaOH solution is 50%, remove the precipitate to obtain a primary supernatant, add 23% mass concentration of hydrochloric acid solution to the primary supernatant to obtain a primary mixed solution, continue to add dilute acid to the primary mixed solution to adjust the pH of the primary mixed solution to 2, stir and centrifuge to obtain humic acid precipitate, remove the humic acid precipitate to obtain a secondary supernatant as a crude fulvic acid extract;

[0043] S1-2, secondary separation and purification: evaporating, crystallizing and concentrating the crude fulvic acid extract prepared in S1-1 to obtain a fulvic acid concentrate;

[0044] S2. Preparation of soil passivator:

[0045] S2-1, talc modification: natural talc was crushed through a 90-mesh sieve to obtain talc powder, the talc powder was calcined to obtain primary modified talc powder, the calcination temperature was 620°C, the calcination time was 7 min, the primary modified talc powder was completely immersed in a CaCl2 solution with a molar concentration of 3 mol / L for 8 h, the weight ratio of the primary modified talc powder to the CaCl2 solution was 1:4, and secondary modified talc powder was obtained;

[0046] S2-2, raw material mixing: the humic acid precipitate prepared in S1-1, the secondary modified talc powder prepared in S2-1 and hydroxyapatite are mixed in a mass ratio of 1:2:8 to obtain a first soil passivator, and the humic acid precipitate prepared in S1-1, the secondary modified talc powder prepared in S2-1 and attapulgite are mixed in a mass ratio of 1:2:8 to obtain a second soil passivator;

[0047] S3. Preparation of foliar control agent: Mix the fulvic acid concentrate prepared in S1-2 with a ZnCl2 solution to obtain a first foliar control agent containing 6 mg / L of ZnCl2; mix the fulvic acid crude extract prepared in S1-1 with a ZnCl2 solution having a mass concentration of 35% to obtain a second foliar control agent containing 11 mg / L of ZnCl2;

[0048] S4. Remediation of contaminated soil:

[0049] S4-1, contaminated soil remediation: the first soil passivator or the second soil passivator prepared in S2-2 is evenly applied to the heavy metal contaminated soil to be treated to remediate the heavy metal contaminated soil, the application amount of the first soil passivator is 140 kg / mu, and the application amount of the second soil passivator is 130 kg / mu;

[0050] S4-2. Crop maintenance and soil passivation: dilute the first foliar barrier agent or the second foliar barrier agent prepared in S3 with water, and spray it on the leaves of crops to maintain the crops and assist in passivating heavy metals in the soil. The dilution multiple of the first foliar barrier agent is 350 times, and the dilution multiple of the second foliar barrier agent is 450 times. The application amount is 120 ml / mu / time.

[0051] Embodiment 2: This embodiment differs from Embodiment 1 in that:

[0052] S1-1. Primary separation and purification: add humic acid to NaOH solution, stir and centrifuge, the weight ratio of humic acid to NaOH solution is 1:3, the mass concentration of NaOH solution is 40%, remove the precipitate to obtain a primary supernatant, add 20% mass concentration hydrochloric acid solution to the primary supernatant to obtain a primary mixed solution, continue to add dilute acid to the primary mixed solution to adjust the pH of the primary mixed solution to 1.8, stir and centrifuge to obtain humic acid precipitate, and remove the humic acid precipitate to obtain a secondary supernatant as a crude fulvic acid extract.

[0053] Embodiment 3: This embodiment differs from Embodiment 1 in that:

[0054] S1-1. Primary separation and purification: add humic acid to NaOH solution, stir and centrifuge, the weight ratio of humic acid to NaOH solution is 1:7, the mass concentration of NaOH solution is 60%, remove the precipitate to obtain a primary supernatant, add 30% mass concentration hydrochloric acid solution to the primary supernatant to obtain a primary mixed solution, continue to add dilute acid to the primary mixed solution to adjust the pH of the primary mixed solution to 2.2, stir and centrifuge to obtain humic acid precipitate, and remove the humic acid precipitate to obtain a secondary supernatant as a crude fulvic acid extract.

[0055] Note: In Examples 2 and 3, the specific parameters for the primary separation and purification of humic acid were adjusted. The adjustments made were routine adjustments within a reasonable range. Similar effects can be obtained by selecting any set of data in Example 1 or Examples 2 and 3 as needed.

[0056] Embodiment 4: This embodiment differs from Embodiment 1 in that:

[0057] S2-1, talc modification: natural talc was crushed through a 100-mesh sieve to obtain talc powder, the talc powder was calcined to obtain primary modified talc powder, the calcination temperature was 600°C, the calcination time was 5 min, the primary modified talc powder was completely immersed in a CaCl2 solution with a molar concentration of 2 mol / L for 6 h, the weight ratio of the primary modified talc powder to the CaCl2 solution was 1:3, and secondary modified talc powder was obtained;

[0058] S2-2, raw material mixing: the humic acid precipitate prepared in S1-1, the secondary modified talc powder prepared in S2-1 and hydroxyapatite are mixed in a mass ratio of 1:2:6 to obtain a first soil passivator; the humic acid precipitate prepared in S1-1, the secondary modified talc powder prepared in S2-1 and attapulgite are mixed in a mass ratio of 1:2:6 to obtain a second soil passivator.

[0059] Embodiment 5: This embodiment differs from Embodiment 1 in that:

[0060] S2-1, talc modification: natural talc was crushed through an 80-mesh sieve to obtain talc powder, the talc powder was calcined to obtain primary modified talc powder, the calcination temperature was 650°C, the calcination time was 10 min, the primary modified talc powder was completely immersed in a CaCl2 solution with a molar concentration of 4 mol / L for 12 h, the weight ratio of the primary modified talc powder to the CaCl2 solution was 1:7, and secondary modified talc powder was obtained;

[0061] S2-2, raw material mixing: the humic acid precipitate prepared in S1-1, the secondary modified talc powder prepared in S2-1 and hydroxyapatite are mixed in a mass ratio of 1:2:10 to obtain a first soil passivator; the humic acid precipitate prepared in S1-1, the secondary modified talc powder prepared in S2-1 and attapulgite are mixed in a mass ratio of 1:2:10 to obtain a second soil passivator.

[0062] Note: The specific parameters for the preparation of the soil passivator were adjusted in Examples 4 and 5, wherein the finer the natural talc, the lower the calcination temperature, the shorter the time, and the reduced amount of subsequent raw materials. On the contrary, the coarser the natural talc, the higher the calcination temperature, the longer the time, and the increased amount of subsequent raw materials. The preparation parameters in Examples 1 and 4 and 5 can all achieve similar effects.

[0063] Embodiment 6: This embodiment differs from Embodiment 1 in that:

[0064] S3. Preparation of foliar control agent: Mix the fulvic acid concentrate prepared in S1-2 with ZnCl2 solution to obtain a first foliar control agent containing 5 mg / L of ZnCl2; mix the fulvic acid crude extract prepared in S1-1 with ZnCl2 solution having a mass concentration of 30% to obtain a second foliar control agent containing 10 mg / L of ZnCl2.

[0065] Embodiment 7: This embodiment differs from Embodiment 1 in that:

[0066] S3. Preparation of foliar control agent: Mix the fulvic acid concentrate prepared in S1-2 with ZnCl2 solution to obtain a first foliar control agent containing 8 mg / L of ZnCl2; mix the fulvic acid crude extract prepared in S1-1 with ZnCl2 solution having a mass concentration of 40% to obtain a second foliar control agent containing 12 mg / L of ZnCl2.

[0067] Note: In Examples 6 and 7, the specific parameters for preparing the leaf barrier agent were adjusted. The adjustments made were routine adjustments within a reasonable range. Similar effects can be obtained by selecting any set of data in Example 1 or Examples 6 and 7 as needed.

[0068] Embodiment 8: This embodiment differs from Embodiment 1 in that:

[0069] S4-1, contaminated soil remediation: the first soil passivator or the second soil passivator prepared in S2-2 is evenly applied to the heavy metal contaminated soil to be treated to remediate the heavy metal contaminated soil, the application amount of the first soil passivator is 130 kg / mu, and the application amount of the second soil passivator is 120 kg / mu;

[0070] S4-2. Crop maintenance and soil passivation: dilute the first foliar barrier agent or the second foliar barrier agent prepared in S3 with water, and spray it on the leaves of crops to maintain the crops and assist in passivating heavy metals in the soil. The dilution multiple of the first foliar barrier agent is 300 times, and the dilution multiple of the second foliar barrier agent is 400 times. The application amount is 100 ml / mu / time.

[0071] Embodiment 9: This embodiment differs from Embodiment 1 in that:

[0072] S4-1, contaminated soil remediation: the first soil passivator or the second soil passivator prepared in S2-2 is evenly applied to the heavy metal contaminated soil to be treated to remediate the heavy metal contaminated soil, the application amount of the first soil passivator is 150 kg / mu, and the application amount of the second soil passivator is 140 kg / mu;

[0073] S4-2. Crop maintenance and soil passivation: dilute the first foliar barrier agent or the second foliar barrier agent prepared in S3 with water, and spray it on the leaves of crops to maintain the crops and assist in passivating heavy metals in the soil. The dilution multiple of the first foliar barrier agent is 400 times, and the dilution multiple of the second foliar barrier agent is 500 times. The application amount is 150 ml / mu / time.

[0074] Note: The specific contaminated soil remediation method was adjusted in Examples 8 and 9, wherein the greater the dilution factor of the foliar barrier agent, the smaller the application amount, and conversely, the smaller the dilution factor of the foliar barrier agent, the larger the application amount, and the preparation parameters in Examples 1 and 8 and 9 can all achieve similar effects.

[0075] Example 10: This example is an application of a heavy metal contaminated soil remediation method based on foliar barrier agent assisted soil passivation. The heavy metal contaminated soil remediation method based on foliar barrier agent assisted soil passivation of Example 1 is applied to double-season rice planting.

[0076] Double-season rice is divided into early rice and late rice. Early rice is sown in mid-to-late March and transplanted in mid-to-late April. Ten days before planting early rice, the first soil passivator is applied to the soil according to the application amount in S4-1. During the tillering period after transplanting, the first foliar control agent is diluted according to the dilution multiple in S4-2 and sprayed on the rice leaves. Spray once every 6 days, for a total of 2 times.

[0077] Late rice is sown in mid-to-late June and transplanted in mid-to-late July. Ten days before planting late rice, the second soil passivator is applied to the soil according to the application amount in S4-1. During the tillering period after transplanting, the second foliar barrier is diluted according to the dilution multiple in S4-2 and sprayed on the rice leaves. Spray once every 6 days, for a total of 2 times.

[0078] Embodiment 11: This embodiment differs from Embodiment 10 in that:

[0079] Double-season rice is divided into early rice and late rice. Early rice is sown in mid-to-late March and transplanted in mid-to-late April. One week before planting early rice, the first soil passivator is applied to the soil according to the application amount in S4-1. During the tillering period after transplanting, the first foliar barrier control agent is diluted according to the dilution multiple in S4-2 and sprayed on the rice leaves. Spray once every 5 days, for a total of 2 times;

[0080] Late rice is sown in mid-to-late June and transplanted in mid-to-late July. One week before planting late rice, the second soil passivator is applied to the soil according to the application amount in S4-1. During the tillering period after transplanting, the second foliar barrier is diluted according to the dilution multiple in S4-2 and sprayed on the rice leaves. Spray once every 5 days, for a total of 2 times.

[0081] Embodiment 12: This embodiment differs from Embodiment 10 in that:

[0082] Double-season rice is divided into early rice and late rice. Early rice is sown in mid-to-late March and transplanted in mid-to-late April. Two weeks before planting early rice, the first soil passivator is applied to the soil according to the application amount in S4-1. During the tillering period after transplanting, the first foliar control agent is diluted according to the dilution multiple in S4-2 and sprayed on the rice leaves. Spray once every 7 days, for a total of 2 times;

[0083] Late rice is sown in mid-to-late June and transplanted in mid-to-late July. Two weeks before planting late rice, the second soil passivator is applied to the soil according to the application amount in S4-1. During the tillering period after transplanting, the second foliar barrier is diluted according to the dilution multiple in S4-2 and sprayed on the rice leaves. Spray once every 7 days for a total of 2 times.

[0084] Experimental Example 1: In order to verify the feasibility of the present invention, we conducted a field test according to the application method in Example 10 and compared it with several groups of comparative examples. In the comparative examples, except for the selected soil passivator and foliar barrier agent, the other parameters were the same as those in Example 10:

[0085] Comparative Example 1: The soil passivator is quicklime, and the foliar control agent is the most commonly used monosilicic acid foliar control agent on the market;

[0086] Comparative Example 2: The soil passivator is a mixture of hydroxyapatite and humic acid in a weight ratio of 1:1, and the foliar control agent is the most commonly used monosilicic acid foliar control agent on the market;

[0087] Comparative Example 3: The soil passivator is a mixture of attapulgite and humic acid in a weight ratio of 1:1, and the foliar control agent is the most commonly used monosilicic acid foliar control agent on the market;

[0088] Comparative Example 4: The soil passivator is a mixture of hydroxyapatite, attapulgite and humic acid in a weight ratio of 1:1:1, and the foliar control agent is a mixture of the most commonly used monosilicic acid foliar control agent on the market and humic acid in a weight ratio of 1:1;

[0089] The field test method is: soil remediation will be carried out in farmland in heavy metal-contaminated areas starting in 2023. The block size of each case is 6m×6m=36m 2 The field management methods were the same. After the two rice harvests matured, the rice grains and roots were collected and washed with water before testing. The results were as follows: Figure 2~3 shown.

[0090] first, Figure 2 We determined the Cd content in the grains. The content of heavy metals in the grains can most directly reflect the comprehensive control effect of heavy metals in the soil. In the case of no treatment agent, both the early rice and the late rice in the blank control group contained high Cd, far exceeding the national regulation of 0.2 mg / kg. After applying various treatment agents, the situation improved. Specifically, the soil passivator quicklime in Comparative Example 1, as the most widely used treatment agent, can improve the pH of the soil and promote the precipitation of heavy metals. It can play a certain control effect in combination with the monosilicic acid foliar barrier agent, but the effect is limited.

[0091] In Comparative Examples 2 and 3, the soil passivation agent using hydroxyapatite or attapulgite + humic acid significantly improved the blocking and passivation effect of Cd, which is also foreseeable based on the prior art. Clay minerals contain a large number of hydroxyl groups and exchangeable cations, which can effectively adsorb and fix Cd in the soil; at the same time, humus carries a negative charge under the action of deprotonation, and the adsorption capacity of Cd is enhanced through electrostatic attraction or complexation with Cd;

[0092] In Comparative Example 4, the use of monosilicic acid foliar control agent + humic acid can further improve the control effect. This is because when humic acid is used in the foliar control agent, the humic acid can react with Cd after entering the plant body, reducing the mobile Cd in the plant cells and reducing the migration ability of Cd, thereby causing a portion of Cd to be retained in the stems and leaves, further reducing the Cd content in the grains.

[0093] The Cd content in Example 10 is the lowest, reaching the national standard of 0.2 mg / kg, which also confirms what we mentioned in the beneficial effects: the humic acid precipitate and the heavy metals in the soil undergo electrostatic attraction and complexation to adsorb the heavy metals; the talc is introduced and modified to change its specific surface area and pore structure; 2+ After treatment, it is easier to exchange ions with heavy metals in the soil. At the same time, the high Fe content (33.6%) in talc allows Fe and Ca to exchange and adsorb heavy metal ions, inhibiting the upward transport of heavy metal ions from crop roots. Finally, hydroxyapatite and attapulgite can improve the pH value of the soil to make the soil weakly alkaline, which is more conducive to the precipitation of heavy metals and the formation of complexes. Among them, hydroxyapatite is used for one application mainly for Pb and Cd in the soil, and attapulgite with high calcium content is used for secondary application to increase the proportion of residual heavy metals. At the same time, fulvic acid enters the plant body to complex with heavy metals, reducing the migration capacity of heavy metals. Zn 2+ It makes up for the lack of this element in soil passivators, and uses it to act on the leaves to meet the nutritional needs of the leaves and reduce the absorption of heavy metal elements from the roots. The concentration of fulvic acid applied once is higher, while the concentration of fulvic acid applied twice is lower, which can ensure the leaf barrier effect while avoiding soil acidification.

[0094] The same trend was also shown in the comparison of yield increase: the dry weight of rice grains in Example 10 increased by 19% and 21% for early rice and late rice, respectively, compared with the blank control group, which was better than the other four control groups.

[0095] We then compared the Cd content in the roots of the crops, e.g. Figure 3 As shown, the trend shown is similar to that in the seeds, but Example 10 is closer to Comparative Example 4, indicating that the foliar barrier agent in Example 10 can play an important barrier effect.

[0096] Without adding any treatment agent, both the early rice and late rice in the blank control group contained high Cd, far exceeding the national regulation of 0.2 mg / kg. After applying various treatment agents, the situation improved. Specifically, the soil passivator quicklime in Comparative Example 1, as the most widely used treatment agent, can improve the pH of the soil and promote the precipitation of heavy metals. It can play a certain control effect in combination with the monosilicic acid foliar barrier agent, but the effect is limited.

[0097] Experimental Example 2: In order to verify the universal applicability of the method of the present invention, we conducted a potted experiment according to the method in Example 1. The specific method is: 10 kg of As and Hg contaminated paddy soil was taken, placed in a plant climate incubator, base fertilizer was added, and soil passivator was added according to the method in step S4-1. The rice seeds were soaked in hydrogen peroxide for 20 minutes, washed with water, and cultured at a constant temperature in a plant climate incubator until germination. Then, when the seeds were cultured to the tillering stage, foliar barrier agents were applied according to the method in S4-2. The soil and seeds were taken for testing, and the results are shown in Table 1.

[0098] Table 1 Heavy metal contents in soil and seeds

[0099]

[0100] It can be seen that the method in Example 1 of the present invention can also achieve a good control effect on heavy metal elements other than Cd, with the effective As in the soil reduced by 52%, the effective Hg in the soil reduced by 60%, the As in the grains reduced by 42%, and the Hg in the grains reduced by 48%, indicating that the method of the present invention has a certain general applicability.

Claims

1. A method for remediating heavy metal-contaminated soil based on foliar barrier agent-assisted soil passivation, characterized in that: The following steps are involved: S1. Separation and purification of humic acid: S1-1, primary separation and purification: adding humic acid to a NaOH solution, wherein the weight ratio of the humic acid to the NaOH solution is 1:3-7, and the mass concentration of the NaOH solution is 40-60%, stirring and centrifuging, removing the precipitate to obtain a first supernatant, adding dilute acid to the first supernatant to obtain a pH value of 2±0.2 to obtain a mixed solution, stirring and centrifuging to obtain a humic acid precipitate, and removing the humic acid precipitate to obtain a second supernatant as a crude fulvic acid extract; S1-2, secondary separation and purification: evaporating, crystallizing and concentrating the crude fulvic acid extract prepared in S1-1 to obtain a fulvic acid concentrate; S2. Preparation of soil passivator: S2-1, talc modification: natural talc is crushed and sieved to obtain talc powder, the talc powder is calcined to obtain a first modified talc powder, the first modified talc powder is completely immersed in a CaCl2 solution with a molar concentration of 2 to 4 mol / L for 6 to 12 hours to obtain a second modified talc powder; S2-2, raw material mixing: the humic acid precipitate prepared in S1-1, the second modified iron talc powder prepared in S2-1 and hydroxyapatite are mixed in a mass ratio of 1:2:6-10 to obtain a first soil passivator, and the humic acid precipitate prepared in S1-1, the second modified iron talc powder prepared in S2-1 and attapulgite are mixed in a mass ratio of 1:2:6-10 to obtain a second soil passivator; S3, preparation of foliar control agent: the fulvic acid concentrate prepared in S1-2 is mixed with ZnCl2 solution to obtain a first foliar control agent containing 5-8 mg / L of ZnCl2, and the fulvic acid crude extract prepared in S1-1 is mixed with ZnCl2 solution to obtain a second foliar control agent containing 10-12 mg / L of ZnCl2; S4. Remediation of contaminated soil: S4-1, contaminated soil remediation: the first soil passivator or the second soil passivator prepared in S2-2 is evenly applied to the heavy metal contaminated soil to be treated to remediate the heavy metal contaminated soil, and the application amount is 120-150 kg / mu; S4-2, crop maintenance and soil passivation: dilute the first foliar barrier agent or the second foliar barrier agent prepared in S3 by 300 to 500 times with water, and spray it on the leaves of crops to maintain the crops and assist in passivation of heavy metals in the soil. The application amount is 100 to 150 ml / mu / time; The heavy metal contaminated soil is double-season rice planting soil, The double-season rice is divided into early rice and late rice. The early rice is sown in mid-to-late March and transplanted in mid-to-late April. One to two weeks before planting the early rice, the first soil passivator is applied to the soil according to the application amount in S4-1. During the tillering period after transplanting, the first foliar barrier control agent is diluted according to the dilution multiple in S4-2 and sprayed on the rice leaves. The spraying is performed once every 5 to 7 days, for a total of 2 times. The late rice is sown in mid-to-late June and transplanted in mid-to-late July. One to two weeks before planting the late rice, the second soil passivator is applied to the soil according to the application amount in S4-1. During the tillering period after transplanting, the second foliar barrier control agent is diluted according to the dilution multiple in S4-2 and sprayed on the rice leaves. The spraying is performed once every 5 to 7 days, for a total of 2 times.

2. The method for remediating heavy metal contaminated soil based on foliar barrier agent-assisted soil passivation according to claim 1, characterized in that: The dilute acid in S1 is a hydrochloric acid solution with a mass concentration of 20-30%.

3. The method for remediating heavy metal contaminated soil based on foliar barrier agent-assisted soil passivation according to claim 1, characterized in that: In the S2-1, the natural talc is crushed through a 80-100 mesh sieve, the calcination temperature is 600-650° C., and the calcination time is 5-10 min.

4. The method for remediating heavy metal contaminated soil based on foliar barrier agent-assisted soil passivation according to claim 1, characterized in that: The weight ratio of the first modified iron talc powder to the CaCl2 solution in S2-1 is 1:3-7.

5. The method for remediating heavy metal contaminated soil based on foliar barrier agent-assisted soil passivation according to claim 1, characterized in that: The mass concentration of the ZnCl2 solution in the S3 is 30-40%.

6. The method for remediating heavy metal contaminated soil based on foliar barrier agent-assisted soil passivation according to claim 1, characterized in that: In the S4-1, the application amount of the first soil passivator is 130-150 kg / mu, and the application amount of the second soil passivator is 120-140 kg / mu.

7. The method for remediating heavy metal contaminated soil based on foliar barrier agent-assisted soil passivation according to claim 1, characterized in that: In the S4-1, the dilution multiple of the first foliar barrier agent is 300 to 400 times, and the dilution multiple of the second foliar barrier agent is 400 to 500 times.

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