Method for enhancing phytoremediation of cadmium-containing soils

Abstract

The application belongs to the field of soil heavy metal remediation, and specifically discloses a method for enhancing plant remediation of cadmium-containing soil, which comprises mixing cadmium-containing soil and a reinforcing material, and then performing plant remediation; the reinforcing material comprises montmorillonite, phosphate rock and steel slag. In the application, the reinforcing material and plant remediation are combined to achieve synergy and enhance the plant remediation effect.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of phytoremediation of heavy metal contaminated soil, and particularly relates to a method for remediation of cadmium-containing soil. BACKGROUND

[0002] In the past two decades, China's economic construction has achieved rapid and efficient development, but the environmental problems caused by it have become increasingly prominent. According to the report of the Ministry of Natural Resources, soil heavy metal pollution has become the most prominent environmental problem.

[0003] Cadmium (Cd) is a highly hazardous carcinogenic heavy metal, which can cause bone metabolic disorders, ostealgia, kidney damage and other diseases. Cd is active and easy to diffuse and flow in soil. In China, rice is the staple food in the areas south of the Yangtze River, and rice is a crop that is easy to accumulate Cd. For a long time, Cd has formed a heavy metal pollution cycle of mining enterprises-soil pollution-rice-bio-Cd chronic poisoning, which is continuously accumulated through the food chain. Therefore, it is urgent to control and remediate Cd pollution in soil, which is of great significance to China's sustainable development, food safety and national health.

[0004] Phytoremediation is a technology that plants are planted in situ in heavy metal contaminated soil, and the growth of plants is used to extract, transfer and transform heavy metal pollutants. Phytoremediation has low cost, and after vegetation is formed, it also has the effect of protecting topsoil, reducing erosion and improving water and soil loss, and has been widely used in mine reclamation, control and landscape remediation in heavy metal pollution affected areas. At present, the difficulty that restricts the development of phytoremediation technology is that the secretion released by the root system of the plant changes the rhizosphere soil environment, which increases the solubility, transfer ability and bioavailability of heavy metals in the soil, causing the activity, toxicity and transfer ability of heavy metals to increase during the phytoremediation process, which increases the safety risk of the phytoremediation project. In view of this problem, it is urgent to combine the remediation material solidification and stabilization method with the phytoremediation method to develop a combined remediation method for remediation material-plant to control Cd pollution in soil. The solidification ability of the material is used to solidify Cd in the soil, and then the slow release of Cd is promoted through the physiological activity of the plant, and the extraction and absorption of Cd are promoted, so as to realize the safe remediation and control of Cd pollution in a low toxicity state. SUMMARY

[0005] In view of the problem that the extraction rate of phytoremediation of cadmium-containing soil is not ideal, the first object of the present application is to provide a method for strengthening phytoremediation of cadmium-containing soil, which aims to improve the extraction effect of cadmium.

[0006] A method for strengthening phytoremediation of cadmium-containing soil, which mixes cadmium-containing soil and a strengthening material, and then performs phytoremediation.

[0007] The strengthening material comprises montmorillonite, phosphate rock and steel slag.

[0008] The application researches and finds that the innovative use of the reinforcing material containing montmorillonite, phosphate rock and steel slag components in combination and the plant remediation process can realize the synergy, can improve the enrichment in the cadmium-containing soil, and improve the extraction effect of the plant, and further improve the remediation effect of the cadmium-containing soil.

[0009] In the application, the combination of the components of the reinforcing material is the key to improve the plant remediation effect. The synergistic reinforcing material can adjust the soil permeability, structure, soil pH, provide primary nutrients for plant remediation, improve soil fertility, promote the activity of soil microorganisms, help the recovery and stability of the soil ecosystem, and help to improve the enrichment and extraction effect of cadmium in the soil.

[0010] Preferably, the montmorillonite is starch-modified montmorillonite. The application researches and finds that the use of starch-modified montmorillonite helps to further combine with other components, further improves the synergistic effect of the combination of the reinforcing material and the plant remediation, and further improves the remediation effect of the cadmium-containing soil.

[0011] Preferably, the starch-modified montmorillonite is obtained by liquid-solid separation and drying after liquid-phase compounding of montmorillonite and starch.

[0012] Preferably, the starch is cassava starch.

[0013] Preferably, the weight ratio of starch and montmorillonite is 2-4:5.

[0014] In the application, the particle size of the montmorillonite is not particularly limited, and can be-200 mesh to +400 mesh.

[0015] In the application, the phosphate rock can be fluorapatite. The particle size thereof can be, for example, -40 mesh to +100 mesh.

[0016] In the application, the particle size of the steel slag can be-100 mesh to +200 mesh.

[0017] The application researches further show that, on the basis of the combination of the components of the reinforcing material, further controlling the proportion of the components can further improve the synergistic effect, further combine with the plant remediation method, and further improve the remediation effect of the cadmium-containing soil.

[0018] Preferably, in the reinforcing material, the weight ratio of montmorillonite, phosphate rock and steel slag is 1-8:1-5:1-5; preferably 4-5:1-3:1-2 (2-5:0.5-3:1); and further preferably 2.5-5:1-3:1. Research shows that the preferred proportion can obtain a better synergistic modification effect.

[0019] The amount of the reinforcing material can be adjusted according to the content of cadmium in the cadmium-containing soil, and preferably is 200-4000 g / m 2 ; preferably is 400-1200 g / m 2 ; that is, the reinforcing material is 0.5-10 wt% of the soil, further preferably is 1-3 wt%, further preferably is 1.5-3.5 wt%, and most preferably is 2-2.5 wt%. It is found that the preferred proportion can obtain a better reinforcing synergistic effect.

[0020] In the present application, the reinforcing material is helpful for synergistically improving the effect of phytoremediation. It is also found that further synergistically controlling the phytoremediation plant is helpful for further improving the combined synergistic effect of the reinforcing material and phytoremediation, and is helpful for further improving the remediation effect of the cadmium-containing soil. Preferably, the phytoremediation plant is one of Solanum nigrum, Cynodon dactylon, Ramie, Paraheterotheca, and Small Comfrey; and further preferably is Solanum nigrum.

[0021] In the present application, the cadmium-containing soil and the reinforcing material are mixed, and then the plant seeds are sown, and the plant is cultivated for phytoremediation. The sowing amount of the plant seeds is 50-250 g / m 2 , which can be 0.001-0.5 wt% of the soil, and further can be 0.05-0.2 wt%.

[0022] In the present application, the period of phytoremediation can be adjusted according to the remediation situation. Considering the synergistic process of the present application, it has an excellent synergistic remediation effect, which can significantly shorten the remediation period. Considering the remediation efficiency, the period of phytoremediation in the present application can be 45-75 days.

[0023] In the present application, the plant remediation stage also allows the addition of fertilizers as needed; the fertilizer can be a conventional component in the industry that can help plant growth, and the amount thereof can be adjusted as needed. For example, considering the treatment efficiency, the application amount of the fertilizer can be 10-300 g / m 2 ; (for example, it can be 0.02-0.75 wt% of the soil) and further can be 180-300 g / m 2 .

[0024] In the present application, the remediation time can be selectively extended or the remediation cycle can be recycled according to the soil condition, Cd content, and the like.

[0025] Advantages

[0026] The present application researches and finds that the innovative use of the reinforcing material containing montmorillonite, phosphate rock and steel slag components in cooperation and the plant remediation process can realize cooperation, can improve the enrichment in the cadmium-containing soil, and improve the extraction effect of plants, and further improve the remediation effect of the cadmium-containing soil. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The repair effect comparison chart of adding materials and not adding materials in Comparative Example 1 (the added material group is Example 3A);

[0028] Figure 2 The repair effect comparison chart of having plants and not having plants in Comparative Example 2 (the plant group is Example 3A);

[0029] Figure 3 The repair effect chart after lacking one or two materials in Comparative Example 3 (the experimental column group is Example 3A).

[0030] DETAILED DESCRIPTION

[0031] Preparation of soil:

[0032] 30 kg of clean soil (referring to the soil not containing Cd) is placed in an oven and dried for 24 h, and after drying, it is ground to be fine without obvious coarse particles.

[0033] The experimental soil can be the clean soil described above, and cadmium-containing reagents are added to artificially and accurately control the cadmium content of the experimental soil.

[0034] Modified montmorillonite material

[0035] The modified montmorillonite material is starch-modified montmorillonite, and in the following cases, unless otherwise stated, it is prepared by the following typical modification method:

[0036] 3 g of cassava starch and 50 mL of deionized water are shaken in a 50℃ shaker for 24 h; 5 g of montmorillonite and 250 mL of deionized water are shaken in a room temperature shaker for 24 h; the starch and montmorillonite solution are mixed, stirred with a magnetic stirrer at room temperature for 2 h, centrifuged in a 9000 rpm centrifuge, washed with deionized water for 3 times, and dried at 45℃, and finally the material is ground to below 200 mesh and stored in a desiccator for standby.

[0037] The phosphate rock is purchased from Shandong Anhe Chemical Co., Ltd., and the main component is fluorapatite (chemical formula, Ca 10 (PO4)6F2), containing total phosphorus (P2O5) 10-35%.

[0038] The steel slag is purchased from Hebei Fangji New Material Technology Co., Ltd., and the specification is 20-40 mm.

[0039] Phosphorite, steel slag, the phosphorite is broken to-40~+100 mesh by using a jaw crusher for standby, and then the steel slag is broken to-10 mesh by using a jaw crusher, and then is ground to-100 mesh by using a ceramic ball mill for standby.

[0040] The reinforcing material comprises modified montmorillonite material, phosphorite and steel slag.

[0041] Preparation of the reinforcing material: the modified montmorillonite, the phosphorite and the steel slag are mixed according to the required weight parts, and then the mixture is obtained.

[0042] The phytoremediation is carried out by using a potting method, the soil to be treated and the reinforcing material are added in a flowerpot with a size of 10 cm*10 cm, and then plants are planted, the plants are placed in a greenhouse, and water is poured regularly, and the plants are photographed, and the remediation period is 2 months.

[0043] During the phytoremediation stage, the fertilizer can be selectively supplemented, and the fertilizer can be regularly adjusted according to the needs of the plants, and in the following cases, the bio-fermented chicken manure of Jiangxi Fengji Agricultural Development Co., Ltd. is used unless otherwise stated, and the nitrogen, phosphorus and potassium contents are ≧5%, and the organic matter content is >45%.

[0044] The fertilizer can be directly sown, or can be mixed and added together during the mixing process of the reinforcing material.

[0045] The amount of the fertilizer is not particularly required, for example, can be 180-300 g / m 2 , that is, 0.45-0.75% of the weight of the soil.

[0046] Plant adsorption amount determination:

[0047] Five plants are taken out from the pots, the soil and microorganisms on the surface of the vegetation are cleaned using tap water, a yardstick is used to measure the plant height (above ground, underground and whole plant), a balance is used to measure the wet weight of the plant (whole plant), three kinds of plant vegetation are placed in a 50°C oven for 7h, after drying, the vegetation is divided into above-ground and underground parts using scissors, and is crushed using a marvelet mortar and scissors. After crushing, the samples are digested in aqua regia, the whole digestion process is carried out in a Gena NA DS-360L graphite digester (China Guangzhou Analysis and Test Center), and the samples after digestion are measured by ICP-MS to determine the heavy metal concentration.

[0048] Soil property analysis:

[0049] About 15g of soil in each pot is taken according to the five-point sampling method, the soil is naturally air-dried, and after air-drying, the soil is crushed using a marvelet mortar. The pH (acidity and alkalinity), Eh (oxidation-reduction potential) and Ec (conductivity) of the soil are measured. The test principle and process are as follows:

[0050] Step a: Measurement of soil pH, 10 g of air-dried soil sample was weighed into a 50 mL beaker, 25 mL of deionized water was added, and the container was sealed with plastic wrap and stirred with a magnetic stirrer for 2 min, then left to stand for 30 min, and then the measurement was completed within 1 h using a pH meter.

[0051] Step b: Measurement of soil Eh, 50 g of moist soil sample was weighed into a 50 mL beaker, and then the measurement was completed within 1 h using an Eh meter.

[0052] Step c: Measurement of soil Ec, 20 g of air-dried soil sample was weighed into a 250 mL conical flask, 100 mL of deionized water at 20°C ± 1°C was added, and the container was sealed with plastic wrap and placed in a reciprocating horizontal constant temperature shaker and shaken for 30 min. After the shaking was completed, the conical flask was removed and transferred to a centrifuge tube and treated by centrifugation at 3000 r / min, and then tested in an Ec tester.

[0053] Example 1

[0054] In this example, the initial concentration of heavy metal Cd element in the soil was 7.5 mg / kg, and the plant seeds were respectively nightshade, Bermudagrass, ramie, false stinkgrass, small veronica, and the sowing density was 70 g / m 2 , the greenhouse temperature was 35°C, the humidity was above 85%, the illumination time was > 12 h, and it was suitable for seed germination.

[0055] The specific steps are as follows:

[0056] 10 kg of clean soil was placed in an oven and dried for 24 h, and after drying, it was ground to a fine powder without obvious coarse particles. Each time, 400 g of soil was taken, and the reinforcing material (which contained 8 parts by weight of modified montmorillonite, 4 parts by weight of phosphorite, and 3 parts by weight of steel slag) was mixed with the soil (the reinforcing material was 2% of the weight of the soil), in addition, fertilizer (0.45% of the weight of the soil) was also added, and 300 mg / L of Cd 2+Heavy metal ion solution 10 mL and mixed with soil evenly, soil surface treatment flat, for planting plants, evenly sowing 0.7 g of nightshade seeds in the flowerpot, planting centipedegrass, ramie, false odor grass, small cornflower seeds (0.7 g of each plant) in the other 4 pots respectively, setting two groups of parallel controls for each plant, the amount of seeds sown is the same, covering soil 2 mm on the surface, gently and evenly spraying water (cannot destroy the surface soil), placing in the greenhouse. Regular watering. After 60 days of plant cultivation, measuring plant height, dry weight, fresh weight; collecting plant aboveground / underground parts (plant rhizosphere soil) and soil samples to determine heavy metal content. As shown in Tables 1, 2 (basic properties of soil after remediation): the adsorption amount of Cd by nightshade is obviously higher than that of other plants, and nightshade can reduce soil pH, increase oxidation-reduction potential and conductivity, which is helpful for plant absorption of heavy metals and promotes the enrichment of heavy metals in plants.

[0057] Table 1 heavy metal content table of digested plants

[0058]

[0059] Note: a: the aboveground part refers to the heavy metal content in plant stems and leaves;

[0060] b: the underground part refers to the heavy metal content in plant roots;

[0061] c: (soil Cd content before remediation-soil Cd content after remediation) / soil Cd content before remediation x 100%.

[0062] Table 2 basic properties of soil before and after treatment

[0063]

[0064] Example 2

[0065] Compared with Example 1, the only difference is that for the nightshade group, only the amount of reinforcing material added is changed, so that the content of reinforcing material in soil is 0.5%, 1%, 2%, 3%, 5% and 10% respectively, and other operations and parameters are the same as those of the nightshade group in Example 1:

[0066] For example, the steps are:

[0067] The initial concentration of heavy metal Cd element in soil is 7.5 mg / kg, and the amount of remediation material is 200 g / m 2 (equivalent to 0.5% of soil weight), 400 g / m 2 (equivalent to 1% of soil weight), 800 g / m 2 (equivalent to 2% of soil weight), 1200 g / m 2 (equivalent to 3% of soil weight), 2000 g / m 2(5% of the weight of the soil), 4000 g / m 2 (10% of the weight of the soil), the plant seeds are nightshade, the greenhouse temperature is above 35℃, the humidity is 85%, and the light time > 12h is suitable for seed germination.

[0068] Table 3: Plant heavy metal content table

[0069]

[0070] Example 3

[0071] Compared with the experimental group of the reinforcing material added amount of 2% of the weight of the soil in Example 2, the difference is only that the proportion of modified montmorillonite, phosphate rock and steel slag in the reinforcing material is changed. That is, the weight ratio of modified montmorillonite, phosphate rock and steel slag in the reinforcing material is 5:3:1 (group A), 5:1:3 (group B), 1:3:5 (group C), 1:5:3 (group D), 3:1:5 (group E), 3:5:1 (group F), and other operations and parameters are the same as those of the group with the added amount of 2% in Example 2; the results of each group are shown in Table 4:

[0072] Table 4: Plant heavy metal content table

[0073]

[0074] As shown in Table 4: the addition of modified montmorillonite material, phosphate rock and steel slag according to 5:3:1 is more helpful for the adsorption of Cd 2+ by nightshade.

[0075] Example 4

[0076] Compared with group A of Example 3, the difference is only that the Cd 2+ content in the soil before treatment is 3.0 mg / kg, and other operations and parameters are the same as those of Example 3A, and the results of each group are shown in Table 5:

[0077] Table 5: Plant heavy metal content table

[0078]

[0079] Comparative Example 1

[0080] Compared with group A of Example 3, the difference is only that the Cd Figure 1 content in the soil before treatment is 3.0 mg / kg, and other operations and parameters are the same as those of Example 3A, and the results of each group are shown in Table 5:

[0081] Comparative Example 2

[0082] Compared with Group A of Example 3, the only difference is that Solanum nigrum is not planted, and other operations and parameters are the same as those of Example 3A. The effect is far from that of phytoremediation, such as Figure 2

[0083] Comparative Example 3

[0084] Compared with Group A of Example 3, the only difference is that the total amount of the reinforcing material is unchanged, and the types and proportions of the components are changed, and the experimental groups are as follows:

[0085] Group A: The reinforcing material is 100% modified montmorillonite;

[0086] Group B: The reinforcing material is 100% phosphate rock.

[0087] Group C: The reinforcing material is 100% steel slag.

[0088] Group D: In the reinforcing material, montmorillonite is missing, and the proportions of other components are the same

[0089] Group E: In the reinforcing material, phosphate rock is missing, and the proportions of other components are the same

[0090] Group F: In the reinforcing material, steel slag is missing, and the proportions of other components are the same

[0091] The experimental results are shown in Figure 3 Without any component, the heavy metal adsorption capacity decreases under the condition that the total amount of the reinforcing material is unchanged.

[0092] From the above examples and comparative examples, it can be seen that the present application provides a soil remediation method for comprehensive utilization of starch modified montmorillonite, phosphate rock and steel slag. By reasonable proportioning and processing technology, the content of heavy metals in soil is successfully reduced, the soil structure and fertility are improved, and the growth and root development of plants are promoted, and the remediation efficiency of Solanum nigrum is improved. The technology shows excellent effect in remediation of heavy metal contaminated soil, and can be widely applied in industrial areas, farmland and ecological environment remediation fields.

[0093] The above examples are only part of the embodiments of the present application. In actual application, according to different characteristics of contaminated soil and the degree of heavy metal pollution, the amount of soil remediation material can be flexibly adjusted. When the concentration of heavy metals in contaminated soil is high, the use amount of remediation material is appropriately increased, which is helpful to improve the remediation effect. For the skilled person, the above description is only one specific embodiment of the present application, and should not be regarded as a limitation on the scope of the application. Any modification, equivalent replacement and deformation under the technical spirit and principle of the present application should be included in the protection scope of the present application.​

Claims

1. A method for enhancing phytoremediation of cadmium-containing soil, characterized in that, The cadmium-containing soil was mixed with reinforcement materials, and then plant seeds were sown to cultivate plants for phytoremediation. The reinforcing material includes montmorillonite, phosphate rock, and steel slag; In the aforementioned reinforcing material, the montmorillonite is starch-modified montmorillonite; The phosphate rock mentioned is fluorapatite; In the aforementioned reinforcing material, the weight ratio of montmorillonite, phosphate rock, and steel slag is 4~5:1~3:1~2; The plant species used for phytoremediation is black nightshade; The reinforcing material accounts for 1.5 to 3.5 wt% of the soil weight; The sowing rate of the plant seeds is 50~250g / m². 2 .

2. The method for enhancing phytoremediation of cadmium-containing soil as described in claim 1, characterized in that, The starch-modified montmorillonite is obtained by solid-liquid separation and drying after liquid-phase compounding of montmorillonite and starch.

3. The method for enhancing phytoremediation of cadmium-containing soil as described in claim 2, characterized in that, The starch mentioned is tapioca starch.

4. The method for enhancing phytoremediation of cadmium-containing soil as described in claim 2, characterized in that, The weight ratio of starch to montmorillonite is 2 to 4:

5.

5. The method for enhancing phytoremediation of cadmium-containing soil as described in any one of claims 1 to 4, characterized in that, In the aforementioned reinforcing material, the weight ratio of montmorillonite, phosphate rock, and steel slag is 5:3:

1.

6. The method for enhancing phytoremediation of cadmium-containing soil as described in claim 1, characterized in that, The amount of the reinforcing material used is 200~4000 g / m². 2 .

7. The method for enhancing phytoremediation of cadmium-containing soil as described in claim 1, characterized in that, The cycle for phytoremediation is 45 to 75 days.

8. The method for enhancing phytoremediation of cadmium-containing soil as described in claim 1, characterized in that, Fertilizer is also added during the phytoremediation phase.

9. The method for enhancing phytoremediation of cadmium-containing soil as described in claim 8, characterized in that... The application rate of the fertilizer is 180~300g / m³. 2 .

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