Cadmium and arsenic combined polluted soil conditioner and application thereof

Abstract

The invention belongs to the technical field of soil remediation, and particularly relates to a cadmium and arsenic combined contaminated soil conditioner and application thereof. The conditioner is compounded by an oxidizing agent and iron modified humic acid according to the mass ratio of 2: (3-10), and the iron modified humic acid is prepared according to the following method: dissolving ferrous sulfate in water, then adding humic acid to obtain a suspension, fully stirring the suspension, then filtering, and sequentially drying and grinding filter residues to obtain the iron modified humic acid. The conditioner provided by the invention can respectively generate adsorption, precipitation and coprecipitation effects with cadmium and arsenic in soil without generating antagonism, can simultaneously reduce leaching activity and bioavailability of cadmium and arsenic in soil, and ensures safe production of agricultural products.

Description

Technical Field

[0001] The invention belongs to the technical field of soil remediation, and in particular relates to a soil conditioner for soil contaminated with cadmium and arsenic and its application. Background Art

[0002] Since the beginning of the 21st century, soil pollution has become one of the global environmental problems. According to the properties of pollutants, soil pollution can be divided into inorganic pollution, organic pollution and biological pollution. The accumulation of cadmium and arsenic in the soil not only harms the soil ecosystem and plant ecosystem, but also enters the human body through the food chain and polluted groundwater, posing risks to human health. Therefore, the remediation of cadmium and arsenic contaminated soil is an important part of soil pollution control and risk prevention and control.

[0003] In the soil environment, cadmium and arsenic have different chemical properties. Cadmium often exists in the form of cations and has a tendency to lose electrons, while arsenic mainly exists in the form of arsenic oxide anions (HAsO 4 2- , H 2 AsO 4- , H 2 AsO 3- , HAsO 3 2- ) and has a tendency to gain electrons. Due to the difference in properties, there are great differences in the treatment of cadmium and arsenic contaminated farmland. For cadmium and arsenic compound contaminated farmland, since there is often an antagonistic effect between the agents during the treatment process, it is currently a research problem to find a conditioner that can efficiently and simultaneously treat cadmium and arsenic compound contaminated farmland.

[0004] In 2017, the China Environmental Restoration Network published a practical list of 11 soil and groundwater investigation and restoration technologies and restoration agents from eight units, nine of which involved restoration agents for heavy metal-contaminated soils, such as the JSGY series of agents developed by Jiangsu Gaia Environmental Technology Co., Ltd., the Series of agents, CCT series of agents developed by Nanjing Qingke Zhongsheng Environmental Technology Co., Ltd., etc. The main components of the composite heavy metal contaminated soil passivation agents on the market include clay minerals, reducing agents, chelating agents, gelling materials, etc., which mainly achieve the stabilization of heavy metals in contaminated soil through adsorption, reduction, chelation, solidification and other mechanisms. However, there are the following problems: (1) The combination of agents is unreasonable. For example, the JSGY-1 agent combines the reducing agent with nanomaterials, inorganic nutrients and other agents for application. On the one hand, the reducing agent reduces Fe and Mn in the soil to release arsenic, increasing the migration activity of arsenic. On the other hand, the reducing agent reduces As(V) to As(III), increasing the toxicity of arsenic. (2) Improper selection of agents, such as Clay minerals are used in JSGY-3 and ion mineralization stabilizers. Clay minerals usually have a negative charge on their surface and have good adsorption properties for cadmium. However, since clay minerals and arsenic oxygen anions have the same electrical properties and repel each other, their adsorption of arsenic is poor. (3) The action mechanism of the agent is single, and it is difficult to produce a good passivation effect on different forms of heavy metals in the soil. (4) These agents all have problems such as poor targeting, large agent addition ratio, high disposal cost, and difficulty in large-scale application. Summary of the invention

[0005] The purpose of the present invention is to provide a soil conditioner for cadmium and arsenic composite contamination in view of the above shortcomings, which solves the problems of high cost, poor passivation effect, poor adaptability to changes in soil properties, and inability to effectively treat cadmium and arsenic composite contaminated cultivated land in existing heavy metal contaminated soil passivation agents.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] A soil conditioner for cadmium and arsenic composite pollution is prepared by compounding an oxidant and iron-modified humic acid in a mass ratio of 2:3-10.

[0008] In some preferred embodiments, the oxidizing agent comprises potassium permanganate or sodium persulfate.

[0009] The present invention also provides a method for preparing the iron-modified humic acid, comprising dissolving ferrous sulfate in water and then adding humic acid to obtain a suspension, fully stirring the suspension and then filtering it, and sequentially drying and grinding the filter residue to obtain the product.

[0010] In some preferred embodiments, the mass ratio of ferrous sulfate, water and humic acid is 1:50-100:5-10.

[0011] In some preferred embodiments, the suspension is stirred for 15-30 min.

[0012] In some preferred embodiments, the particle size of the iron-modified humic acid is less than 100 mesh.

[0013] The present invention also provides the iron-modified humic acid obtained by the above-mentioned preparation method.

[0014] The present invention also provides the use of the iron-modified humic acid in the treatment of soil contaminated by cadmium and arsenic.

[0015] The present invention also provides application of the above-mentioned conditioner in the treatment of soil contaminated by cadmium and arsenic.

[0016] In some preferred embodiments, the contaminated soil is mixed with 1-4‰ of the conditioning agent by weight and cured under natural conditions for no less than 7 days.

[0017] It should be noted that iron-modified humic acid is the main component of the composite conditioner of the present invention. Humic acid is a complex natural macromolecular organic matter with a complex chemical structure, containing a variety of active functional groups such as carboxyl, alcoholic hydroxyl, phenolic hydroxyl, quinone carbonyl and keto carbonyl, which can adsorb and complex with a variety of heavy metal ions in the soil, reducing the migration activity of heavy metals in the soil. Humic acid is iron-modified by a special process, and iron ion active sites are loaded in humic acid, and the iron ion active sites are precipitated and coprecipitated with arsenic and cadmium respectively, which can simultaneously enhance the passivation of humic acid to two different heavy metals of arsenic and cadmium in the soil, effectively reduce the migration activity of cadmium and arsenic, and achieve the purpose of repairing cadmium and arsenic composite contaminated soil at the same time. At the same time, iron-modified humic acid can regulate the soil nutrition structure, reduce the absorption of heavy metals by crops, and further reduce the content of heavy metals in crops, while achieving the dual benefits of repair and yield increase.

[0018] The oxidant in the compound agent can oxidize arsenite in the soil into arsenate, which is less toxic and easier to be adsorbed by the soil, thereby enhancing the soil's ability to adsorb arsenic. It can also prevent Fe(III) from being reduced to Fe(II) to release the adsorbed arsenic. The oxidant can promote the formation of ferrite crystals on the surface and pores of iron-modified humic acid, thereby enhancing the passivation of cadmium.

[0019] The beneficial effects of the present invention are:

[0020] 1. The conditioner of the present invention can produce adsorption, precipitation and co-precipitation effects with cadmium and arsenic in the soil respectively without producing antagonistic effects, and can simultaneously reduce the leaching activity and biological effectiveness of cadmium and arsenic in the soil, thereby ensuring the safe production of agricultural products.

[0021] 2. The present invention utilizes iron salt to appropriately modify humic acid, and utilizes the iron salt to adsorb and co-precipitate with cadmium and arsenic in a humid environment, thereby ingeniously enhancing the passivation effect of humic acid on cadmium and arsenic, two heavy metals with greatly different properties in the soil;

[0022] 3. The preparation process of the conditioning agent of the present invention is simple, the cost of the agent used is low, the agent is highly targeted, and the agent addition ratio is low, which solves the problem of high cost of repairing existing passivation agents. At the same time, the experiment proves that the composite conditioning agent has a certain degree of yield-increasing effect on agricultural products, and the farmers have a high degree of acceptance, which is convenient for large-scale promotion and application;

[0023] 4. The composite agent of the present invention is stable, reliable, green and environmentally friendly, and the dosage of a single agent is low, which solves the secondary pollution and "seedling burning" problems caused by the remediation of heavy metal-contaminated soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a layout diagram of the dryland experiment points of the present invention;

[0025] Figure 2 The distribution of cadmium in the dry land of the present invention before adding pesticides;

[0026] Figure 3 This is the distribution of arsenic in the dry land of the present invention before adding the drug;

[0027] Figure 4 The distribution of effective cadmium at the harvest time after the dry land in the experiment of the present invention was treated with pesticides;

[0028] Figure 5 The figure shows the distribution of effective arsenic at the harvest time after adding pesticides to the dry land in the experiment of the present invention. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following.

[0030] Example 1

[0031] Preparation of iron-modified humic acid:

[0032] By weight, 1 part of ferrous sulfate was dissolved in 50 parts of water, and then 10 parts of humic acid (source: Chongqing City) were added to obtain a suspension. The suspension was stirred for 0.5 hours and then filtered. The filter residue was dried, ground, and sieved through a 100-mesh sieve to obtain the product.

[0033] Example 2

[0034] A soil conditioner for cadmium and arsenic composite pollution (CMEE-Soil Guard Cd&As) is prepared by compounding sodium persulfate and the iron-modified humic acid prepared in Example 1 in a mass ratio of 2:3.

[0035] Comparative Example 1

[0036] Unmodified humic acid.

[0037] Comparative Example 2

[0038] A soil conditioner is prepared by compounding ferrous sulfate and humic acid in a mass ratio of 1:10.

[0039] Comparative Example 3

[0040] A soil conditioner is prepared by compounding sodium persulfate and the conditioner in comparative example 2 in a mass ratio of 2:3.

[0041] 1. Soil culture experiment:

[0042] The test soil was contaminated soil from a certain place, and its physical and chemical properties are shown in Table 1 below.

[0043] Table 1

[0044]

[0045] The contaminated soil for testing was naturally dried, ground, and passed through a 5 mm sieve for later use. Accurately weigh a certain amount of the agents of Example 1, Example 2, and Comparative Examples 1-3 above and add them to 200.0 g of the test soil, stir evenly, add 120 mL of water, stir evenly again, move the sample into a polypropylene box for curing for 7 days, dry the sample in a 50 ° C oven, grind it through an 80 mesh sieve for testing. Under the same conditions, a blank group was set up without adding the composite agent, and 2 parallel groups were set up for each.

[0046] The available cadmium content and available arsenic content in the soil were measured respectively, and the reduction rate was calculated. Among them, the available cadmium content in the soil was measured according to "Determination of Available Elements in Soil 8 - Diethyltriaminepentaacetic Acid Extraction-Inductively Coupled Plasma Emission Spectrometry" (HJ 804-2016). The available arsenic content in the soil was determined according to the sodium bicarbonate method, the method is: accurately weigh 10.00g of the sample to be tested and add it to a 50mL centrifuge tube, add 20.0mL of 0.5mol·L -1 NaHCO 3 The solution was shaken at room temperature for 120 min (speed 180 r / min -1 ), centrifuge, filter, and detect the arsenic concentration in the filtrate to be C1μg / L, then the effective arsenic concentration in the soil is 2C1μg / Kg.

[0047] The experimental results are shown in Table 2 below.

[0048] Table 2

[0049] Experimental Group Chemical dosage ratio (‰) Dosage of drug (g) Reduction rate of available arsenic (%) Reduction rate of effective cadmium (%) Example 1 3 0.6 24.18 18.62 Example 2 3 0.6 29.4 26.3 Comparative Example 1 3 0.6 18.2 14.9 Comparative Example 2 3 0.6 22.2 16.3 Comparative Example 3 3 0.6 24.2 19.5

[0050] According to Table 2, unmodified humic acid also has a certain passivation effect on cadmium and arsenic in the soil. After the humic acid is iron-based, the passivation effect of humic acid on cadmium in the soil can be effectively enhanced. Compared with directly mixing humic acid with iron salt, the modified method of the present invention has a more obvious enhancement on the passivation effect of humic acid.

[0051] Although iron-modified humic acid has a good conditioning effect, the use of modified agents alone will bring the following problems:

[0052] (1) The cost of farmland management is high. Modified agents have a certain preparation cost to a certain extent. The large-scale application of modified agents will increase the cost of farmland management.

[0053] (2) It brings the risk of "seedling burn". Large-scale application of a single agent may cause the concentration of the soil solution to be greater than the concentration of the root hair cell sap. As a result, the water in the root hair cell sap will penetrate into the soil solution. In this way, the root hair cells will not only fail to absorb water, but will also lose water, causing the plant to wilt and lead to "seedling burn".

[0054] (3) There is a risk of secondary pollution. Large-scale application of a single agent may cause soil nutrient imbalance, which is not conducive to the normal growth of crops.

[0055] Based on this, the present invention adopts a compound agent of oxidant and iron-modified humic acid to form a good synergistic treatment mechanism and complementary enhancement effect between the agents, which can further improve the treatment effect of the agents while avoiding the above-mentioned problems.

[0056] 2. Potted Plant Experiment:

[0057] The main steps are as follows:

[0058] S1. The contaminated soil at a certain location for testing is naturally dried and fully mixed before the first sampling and monitoring.

[0059] S2. Weigh 5.0 kg of the test soil and add it to the flowerpot, then add 0.25 kg of organic fertilizer, a certain amount of the composite conditioner prepared in Example 2 (FT1 group, FT2 group, FT3 group) and 750 mL of water, stir evenly, maintain for 7 days, and conduct the second sampling monitoring.

[0060] S3. After planting cabbage, care for it for 6 to 7 weeks and conduct the third sampling monitoring.

[0061] Under the same conditions, no compound drug was added, a blank group (CK) was set up, and commercially available Series of drugs and JSGY series of drugs were used as control groups.

[0062] The treatment group, blank group and control group were set up in triplicate. The content of available heavy metals in soil and heavy metals in cabbage were monitored.

[0063] The experimental results are shown in Table 3 below.

[0064] Table 3

[0065]

[0066] According to Table 3, the following conclusions can be drawn:

[0067] (1) The second monitoring was conducted 7 days after the addition of the compound conditioner. It can be seen that the content of available arsenic and available cadmium in the soil of the control group (FCK) remained basically unchanged. The content of available arsenic and available cadmium in the soil of the treatment groups (FT1, FT2 and FT3) decreased with the increase of the dosage of the compound conditioner, and the rate of decrease slowed down. When the dosage ratio of the compound conditioner was 4‰, the content of available arsenic and available cadmium in the soil decreased by 21.8% and 33.3%, respectively.

[0068] (2) The third monitoring was conducted 3 months after the cabbage was planted. It can be seen that the content of available arsenic and available cadmium in the soil of the control group (FCK) was lower than that of the previous two monitorings. This is mainly because the growth of cabbage absorbed some arsenic and cadmium in the soil. The content of available arsenic and available cadmium in the soil of the treatment groups (FT1, FT2 and FT3) was further reduced compared with the previous two monitorings, but the reduction was smaller. The content of arsenic and cadmium in the cabbage of the treatment groups (FT1, FT2 and FT3) was significantly lower than that of the control group (FCK), and the treatment effect was significant.

[0069] (3) During the experiment, the growth of cabbage in the treatment group and the control group was similar, indicating that the conditioner would not affect the normal growth of crops when the application amount was less than 4‰.

[0070] It can be seen that the application of the composite agent provided by the present invention can effectively reduce the content of available arsenic and available cadmium in the soil, reduce the absorption of arsenic and cadmium in the soil by cabbage, and achieve the purpose of safe utilization of soil contaminated by cadmium and arsenic.

[0071] (4) The cadmium content in the cabbage was lower than that in the control group (FCK) under the same dosage of the agent (the addition ratio was 3%). The passivation effect on cadmium was: FT2>JSGY> Judging from the changes in the available arsenic content in the soil and the arsenic content in cabbage, And JSGY agents have no significant passivation effect on arsenic in the soil.

[0072] 3. Field Experiment

[0073] The field experiment was carried out from March to September 2020, and the main steps were as follows:

[0074] S1. The experimental site was selected in March, and finally a dry land with cadmium and arsenic co-contaminated was selected in Shuijiang Town, Nanchuan District, Chongqing City to carry out field experiments on compound conditioning agents.

[0075] S2. In early April, the leased dry land was demarcated for experimental plots with a size of 5m×5m. After the plots were demarcated, the first sampling and monitoring was carried out.

[0076] S3. At the end of April, add the agent in Example 2 as planned, till and mix well, and maintain under natural conditions for two weeks. After the maintenance, conduct a second sampling and monitoring.

[0077] S4. Planting of dryland corn in early May, with the same number of crops planted in each plot.

[0078] S5. Corn was harvested in mid-August and the third sample was collected.

[0079] S6. Complete sample testing and data analysis and generate a report in September.

[0080] The amount of conditioning agent is calculated according to the following formula:

[0081] m=S×Apl×Pb×v×1000

[0082] m—drug dosage, kg;

[0083] S—regional area, m2;

[0084] Apl—the thickness of the soil tillage layer, generally 15 to 20 cm, and 0.2 m is taken for calculation;

[0085] Pb—soil bulk density, generally 1.4 to 1.7, take 1.5 for calculation;

[0086] ν—Agent dosage ratio, that is, the ratio of agent mass to soil mass.

[0087] The experimental field is a typical farmland with combined pollution of cadmium and arsenic, with a total area of ​​0.5 mu. Figure 1 As shown in the figure, a total of 3 treatments and 1 blank control (SCK) were set up, with 3 parallels for each treatment. The experimental field was divided into 21 plots, and the experimental parameters are shown in Table 4. The spacing between each plot was 0.5m, and single row and single irrigation were implemented. All plots were separated by shallow trenches to prevent fertilizer and water from flowing between plots. Corn was planted in each treatment with a planting density of 17cm×23cm, and 4 to 5 basic seedlings per hole.

[0088] Table 4

[0089]

[0090] Experimental results:

[0091] (1) First monitoring (before dosing)

[0092] The distribution of cadmium, available cadmium, arsenic and available arsenic in the experimental dry land before the application of pesticides is shown in Table 5 and Appendix Figure 2 and attached Figure 3 As shown in Figure 2, it can be seen that the distribution of cadmium and arsenic in the experimental dry land is generally uniform.

[0093] Table 5

[0094]

[0095] (2) Second monitoring (two weeks after dosing)

[0096] Two weeks after the addition of the drug, the available cadmium and available arsenic in the experimental dryland soil were sampled and monitored. The results are shown in Table 6.

[0097] Table 6

[0098]

[0099]

[0100] According to Table 6, we can see that:

[0101] ① In the second monitoring, the contents of available cadmium and available arsenic in the blank control soil increased.

[0102] ②In the second monitoring, the contents of available arsenic and available cadmium in the soil of the treatment group were reduced, and the higher the amount of agent added, the lower the contents of available arsenic and available cadmium in the soil. This shows that the application of the conditioner can significantly reduce the contents of available arsenic and available cadmium in the soil at the same time.

[0103] (3) The third monitoring (corn harvest period)

[0104] Sampling and monitoring were carried out during the corn harvest period. The results are shown in Table 7 and Appendix Figure 4 and attached Figure 5 shown.

[0105] Table 7

[0106]

[0107] According to Table 7, Figure 4 and attached Figure 5 It can be seen that:

[0108] ① In the third monitoring of the dryland experiment, the contents of available arsenic and available cadmium in the soil of the treatment group were reduced, and the higher the amount of agent added, the lower the contents of available arsenic and available cadmium in the soil.

[0109] ②The average cadmium and arsenic contents in corn in the blank control group were 0.283 mg / kg and 0.290 mg / kg, respectively, which exceeded the limit standards of "National Food Safety Standard Limit of Contaminants in Food" (GB2672-2017). The cadmium and arsenic contents in corn in the treatment group were significantly lower than those in the blank control.

[0110] ③The corn yield in the treatment group was higher than that in the blank control group, and the conditioner had a certain effect on increasing corn yield.

[0111] The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art do not deviate from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

Claims

1. A method for preparing iron-modified humic acid, characterized in that: The method comprises dissolving ferrous sulfate in water and then adding humic acid to obtain a suspension, fully stirring the suspension and then filtering the suspension, and sequentially performing drying and grinding steps on the filter residue to obtain the product.

2. The method for preparing iron-modified humic acid according to claim 1, characterized in that: The mass ratio of ferrous sulfate, water and humic acid is 1:50-100:5-10.

3. The method for preparing iron-modified humic acid according to claim 1, characterized in that: The suspension is stirred for 15-30 min.

4. The method for preparing iron-modified humic acid according to claim 1, characterized in that: The particle size of the iron-modified humic acid is less than 100 meshes.

5. The iron-modified humic acid obtained according to the preparation method according to any one of claims 1 to 4.

6. Use of the iron-modified humic acid according to claim 5 in the treatment of soil contaminated by cadmium and arsenic.

7. A soil conditioner for cadmium and arsenic composite pollution, characterized in that: The oxidant and the iron-modified humic acid according to claim 5 are compounded in a mass ratio of 2:3-10.

8. The soil conditioner for cadmium and arsenic composite contamination according to claim 7, characterized in that: The oxidizing agent includes potassium permanganate or sodium persulfate.

9. Use of the conditioner according to claim 7 or 8 in the treatment of soil contaminated by cadmium and arsenic.

10. The use according to claim 9, characterized in that: The contaminated soil is mixed with the conditioning agent at 1-4‰ of its mass, and cured under natural conditions for no less than 7 days.

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