Method for solidifying metal in soil around tailing area

Abstract

The invention belongs to the technical field of prevention and treatment of farmland soil around a tailing area, and particularly relates to a method for solidifying metal in soil around the tailing area. According to the method, biochar and nano zero-valent iron are added into soil around a tailing area, and soybeans are planted. According to the method, the biochar and the nanoscale zero-valent iron are added into the soil polluted by the various metals around the tailing area, the various metals are solidified through the biochar and the nanoscale zero-valent iron, nutrient substances are provided for crops, migration of the metals to the crops is remarkably reduced, and the yield of the crops is increased. Therefore, the purposes of reducing the enrichment of various metals in crops, promoting the growth and development of the crops and guaranteeing the quality of agricultural products are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of farmland soil prevention and control around tailing areas, and particularly relates to a method for solidifying metals in the soil around tailing areas. Background Art

[0002] Processes such as the mining and beneficiation of metal mineral resources will generate a large amount of tailings. A large amount of various metal elements often remain in the tailings and migrate to the underground and surrounding soil through abiotic and biotic actions, causing pollution of the surrounding water bodies and farmland soil. As a result, a certain amount of metals are absorbed and accumulated by the surrounding crops, affecting the yield and quality of agricultural products, and ultimately endangering human health.

[0003] Currently, the main method for the ecological restoration of tailing areas is physical remediation, which mainly includes soil replacement, soil exchange, deep plowing and turning of the soil, etc. Although it is easy to operate, quick to take effect, and has a wide range of applications, the remediation cost is relatively high, and there is a risk of damaging the soil structure. Therefore, it is only suitable for the remediation of small areas of polluted soil and not suitable for the remediation of large areas of metal-polluted soil such as farmland. Therefore, for the multi-metal polluted soil around tailing areas, it is necessary to seek a method with a short repair cycle, low input cost, which can improve the soil characteristics around tailing areas, is beneficial to the growth and development of crops, and will not cause secondary pollution. Summary of the Invention

[0004] To solve the above problems, the present invention provides a method for solidifying metals in the soil around tailing areas. The steps include adding biochar and nano-zero valent iron to the soil around tailing areas and planting soybeans.

[0005] Further, it includes a pretreatment step of air-drying and sieving the soil around tailing areas.

[0006] Further, the biochar is corn straw biochar.

[0007] Further, the particle diameter of the nano-zero valent iron is < 100 nm.

[0008] Further, the addition amount of biochar is 3% of the mass of the soil around tailing areas, and the addition amount of nano-zero valent iron is 0.5% of the mass of the soil around tailing areas.

[0009] The present invention has the following beneficial effects:

[0010] (1) The method of the present invention for solidifying various metals in the soil around tailing areas based on biochar and nano-zero valent iron can realize the safe utilization of the soil around tailing areas on the premise of reducing metal migration.

[0011] (2) The addition of biochar and nano-zero valent iron in the method of the present invention can improve the soil nutrient level, especially increase the content of soil organic matter, total carbon, total organic carbon, total nitrogen and total phosphorus.

[0012] (3) The method of the present invention for immobilizing multiple metals in the soil around the tailings area based on biochar and nano zero-valent iron adds biochar and nano zero-valent iron to immobilize multiple metals and reduce the mobility of soil metals.

[0013] (4) The method of the present invention for immobilizing multiple metals in the soil around the tailings area based on biochar and nano zero-valent iron can increase the water-holding and fertilizer-holding capacities of the soil and promote the growth and development of crops.

[0014] (5) The method of the present invention for immobilizing multiple metals in the soil around the tailings area based on biochar and nano zero-valent iron significantly reduces the absorption and accumulation of multiple metals by crops in the soil improved by biochar and nano zero-valent iron. Description of the Drawings

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0016] Figure 1 For the proportion of the contents of exchangeable state, carbonate-bound state, iron and manganese oxide-bound state, organic matter-bound state and residual state of As in the rhizosphere soil measured by the Tessier sequential extraction method at 45 days and 100 days;

[0017] Figure 2 For the proportion of the contents of exchangeable state, carbonate-bound state, iron and manganese oxide-bound state, organic matter-bound state and residual state of Cd in the rhizosphere soil measured by the Tessier sequential extraction method at 45 days and 100 days;

[0018] Figure 3 For the proportion of the contents of exchangeable state, carbonate-bound state, iron and manganese oxide-bound state, organic matter-bound state and residual state of Cr in the rhizosphere soil measured by the Tessier sequential extraction method at 45 days and 100 days;

[0019] Figure 4 For the proportion of the contents of exchangeable state, carbonate-bound state, iron and manganese oxide-bound state, organic matter-bound state and residual state of Cu in the rhizosphere soil measured by the Tessier sequential extraction method at 45 days and 100 days;

[0020] Figure 5 For the proportion of the contents of exchangeable state, carbonate-bound state, iron and manganese oxide-bound state, organic matter-bound state and residual state of Pb in the rhizosphere soil measured by the Tessier sequential extraction method at 45 days and 100 days;

[0021] Figure 6 is the As content in each part of the soybean plant;

[0022] Figure 7 is the Cd content in each part of the soybean plant;

[0023] Figure 8 is the Cr content in each part of the soybean plant;

[0024] Figure 9 is the Cu content in each part of the soybean plant;

[0025] Figure 10 is the Pb content in each part of the soybean plant;

[0026] Figure 11 are the dry weights of each part and the total biomass of the soybean plants at 45 days;

[0027] Figure 12 are the dry weights of each part and the total biomass of the soybean plants at 100 days;

[0028] Figure 13 is the protein content in the soybean grains. Detailed implementation modes

[0029] Now, various exemplary implementation modes of the present invention will be described in detail. In the examples, unless otherwise specified, the methods are all conventional methods, and the reagents, unless otherwise specified, are all conventional commercially available reagents or reagents prepared by conventional methods. This detailed description should not be construed as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and implementation modes of the present invention.

[0030] It should be understood that the terms described in the present invention are only for describing specific implementation modes and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0031] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0032] Without departing from the scope or spirit of the present invention, various modifications and variations can be made to the specific embodiments of the specification of the present invention, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are merely exemplary.

[0033] Regarding the use of "comprising", "including", "having", "containing", etc. in this article, they are all open-ended terms, meaning including but not limited to.

[0034] The room temperature in the present invention refers to 25 ± 3 °C.

[0035] The embodiments of the present invention provide a method for immobilizing multiple metals in the soil around the tailings area with biochar and nano-zero-valent iron. Biochar and nano-zero-valent iron are added to the soil around the tailings area, and soybeans are planted.

[0036] Biochar and nano-zero-valent iron can not only achieve the safe utilization of the soil around the tailings area on the premise of reducing metal migration, but also improve the soil nutrient level, especially increase the contents of soil organic matter, total carbon, total organic carbon, total nitrogen and total phosphorus, reduce the mobility of soil metals, and at the same time increase the water-holding and fertilizer-holding capacities of the soil, promote the growth and development of crops, and significantly reduce the absorption and accumulation of multiple metals by crops.

[0037] In the embodiments of the present invention, taking soybeans as an example, the influence on soybean plants after improvement is tested. The specific method is as follows:

[0038] Step 1: Air-dry the soil collected from around the tailings area and pass it through a 40-mesh nylon sieve.

[0039] Step 2: Add biochar and nano-zero-valent iron to the soil in Step 1 in sequence and mix evenly.

[0040] Step 3: Add water to the soil treated in Step 2, stir evenly, and keep it in stable culture at room temperature for 7 days. During this period, spray an appropriate amount of water every day to keep the soil moisture content at 25% - 30%.

[0041] Step 4: Select intact and uniformly sized soybean seeds, soak the soybean seeds in a 10% (volume fraction) H2O2 solution for 15 minutes, wash the soaked seeds three times with pure water, place them on a moist gauze cloth, and place them in a constant temperature incubator at 25 °C for germination.

[0042] Step 5: Select the germinated soybean seeds in Step 4 and plant them in the soil treated in Step 3. During the growth of soybeans, keep the soil moisture content at 25% - 30%, the photoperiod at 12 hours of light and 12 hours of darkness, and the cultivation temperature at 25 ± 3 °C.

[0043] Step 6: After the soybean plants are cultured for a certain period of time respectively, collect the rhizosphere soil of the soybean plants and analyze its characteristics;

[0044] Step 7: Clean the harvested soybean plants in Step 6, separate the roots, root nodules, stems, leaves and grains, and calculate the dry weight of each part, the total biomass, the metal content and the protein content in the grains.

[0045] In the embodiments of the present invention, before the biochar and nano zero-valent iron are added to the soil around the tailings area, it also includes a pretreatment step of air-drying and sieving the soil around the tailings area.

[0046] In the embodiments of the present invention, the soil around the tailings area is collected from the area around the iron tailings reservoir in Huairou District, Beijing.

[0047] In the embodiments of the present invention, the biochar is corn straw biochar (prepared under anoxic conditions at 550 °C in a muffle furnace, with a specific surface area of 59.59 m 2 / g and an average pore diameter of 5.10 nm), which has a good pore structure and a large specific surface area, can change the bioavailability and occurrence form of metals in the soil, and convert the form with greater toxicity to crops and microorganisms (exchangeable state) into forms with less toxicity (iron and manganese oxide-bound state, organic matter-bound state) and non-toxic forms (residual state).

[0048] In the embodiments of the present invention, the diameter of the nano zero-valent iron particles is < 100 nm.

[0049] In the embodiments of the present invention, the biochar addition amount is 0% - 3%, and the nano-hydroxy zero-valent iron addition amount is 0% - 0.5%, and neither is 0.

[0050] In the embodiments of the present invention, the soybean variety is Zhonghuang 37, 10 seeds are sown in each pot, and when the soybeans grow to the seedling stage, thinning is carried out, and 6 plants are left in each pot.

[0051] In the embodiments of the present invention, when the soybeans grow for 45 days and 100 days respectively, they are harvested.

[0052] In the embodiments of the present invention, collect the soil in the soybean rhizosphere, dry it for 24 hours with a vacuum freeze dryer and pass through a 60-mesh nylon sieve, and analyze the rhizosphere soil characteristics, including the contents of organic matter, total carbon, total organic carbon, total nitrogen and total phosphorus. Use the Tessier sequential extraction method to analyze the 5 occurrence forms of metals in the soil (exchangeable state, carbonate-bound state, iron and manganese oxide-bound state, organic matter-bound state and residual state).

[0053] In the embodiments of the present invention, clean the harvested soybean plants, divide them into roots, root nodules, stems, leaves and grains, and after drying for 48 hours in a vacuum freeze dryer to remove moisture, calculate the dry weight of each part and the total biomass.

[0054] In an embodiment of the present invention, after the roots, root nodules, stems, leaves and grains of soybean plants are microwave digested, the metal contents of each part are detected by ICP-OES. The specific detection method is a conventional operation means in the art.

[0055] In an embodiment of the present invention, the Kjeldahl method is used to determine the total nitrogen content in soybean grains and calculate its protein content.

[0056] In an embodiment of the present invention, the metals include As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn.

[0057] The present invention is further described below through indoor pot experiments. The above are only preferred embodiments of the present invention and do not limit the protection scope of the present invention. Example 1

[0058] Air-dry the soil around the tailings area and pass it through a 40-mesh nylon sieve; add 0.25 g of nano zero-valent iron to 500 g of the soil around the tailings area and stir well with water. Incubate stably at room temperature for 7 days. During this period, spray an appropriate amount of water every day to keep the soil moisture content at 25% - 30%; select intact and uniform-sized soybean seeds, soak them in a 10% (volume fraction) H2O2 solution for 15 minutes first, then wash them three times with pure water, place them on a moist gauze cloth, and put them in a constant temperature incubator at 25 °C for germination. Sow the germinated soybeans in the soil around the tailings area after 7 days of stable cultivation. Sow 10 seeds in each pot. Thin out the seedlings when the soybeans grow to the seedling stage, leaving 6 plants in each pot. During the growth of soybeans, keep the soil moisture content at 25% - 30% and maintain the growth environment temperature at 25 ± 3 °C; after the soybeans grow for 45 days and 100 days respectively, harvest the soybean plants, collect the rhizosphere soil of the soybean plants, and analyze its characteristics; wash the harvested soybean plants clean, separate the roots, root nodules, stems, leaves and grains, calculate the dry weight of each part and the total biomass, and further analyze the contents of As, Cd, Cr, Cu and Pb in different parts and the protein content in the grains. Example 2

[0059] Set up the same pot experiment as in Example 1, except that: add 2.5 g of nano zero-valent iron (particle diameter < 100 nm) to the soil around the tailings area. Example 3

[0060] Set up the same pot experiment as in Example 1, except that: add 15 g of biochar to the soil around the tailings area. Example 4

[0061] Set up the same pot experiment as in Example 1, except that: add 15 g of biochar and 2.5 g of nano zero-valent iron (particle diameter < 100 nm) to the soil around the tailings area.

[0062] The rhizosphere soil collected after soybean harvest was vacuum freeze-dried and passed through a 60-mesh nylon sieve, and the contents of organic matter, total carbon, total organic carbon, total nitrogen and total phosphorus in the rhizosphere soil were measured. The data are shown in Table 1.

[0063] Table 1 Characteristics of soybean rhizosphere soil

[0064]

[0065] Note: CK indicates no addition of biochar and nano-zero valent iron, that is, the control group.

[0066] Analysis of Table 1 shows that compared with the control group (CK), the addition of biochar and nano-zero valent iron increased the contents of organic matter, total carbon, total organic carbon, total nitrogen and total phosphorus in the soybean rhizosphere soil, and improved the soil nutrient level. In particular, in Example 3 and Example 4 with biochar addition, the contents of organic matter, total carbon, total organic carbon, total nitrogen and total phosphorus in the rhizosphere soil at 45 days were 6.12 - 6.59 times, 2.38 - 2.42 times, 6.12 - 6.59 times, 2.50 - 2.61 times and 1.15 - 1.16 times that of CK, respectively. The addition of biochar had the largest increase in soil organic matter. Organic matter plays an important role in both metal complexation and adsorption reactions, and can affect the bioavailability of metal elements, thereby affecting the absorption and enrichment of metals by crops. While significantly increasing the soil carbon content, biochar also significantly increased the contents of nitrogen and phosphorus in the soil. Therefore, the application of biochar can directly improve the soil nutrient level and provide additional carbon, nitrogen and phosphorus sources for crops and soil microorganisms. In addition, biochar can adsorb nutrients through its abundant pores and large specific surface area, and slowly release nutrients, and can serve as a "nutrient package" for crops and microorganisms in the soil for a long time.

[0067] The five occurrence forms of metals in the rhizosphere soil at 45 days and 100 days were measured by the Tessier sequential extraction method: exchangeable state, carbonate-bound state, iron and manganese oxide-bound state, organic matter-bound state and residual state, and the content ratios of each metal form were as Figures 1-5 shown.

[0068] From Figures 1-5It can be seen that the metals in the rhizosphere soil at 45 days and 100 days are mainly in the residual state, which cannot be absorbed by crops and pose a relatively low risk to the surrounding ecological environment. The exchangeable state and carbonate-bound state of metals are also known as the available state of metals. Both can be absorbed and utilized by crops and microorganisms, and metals in these two forms are prone to migrate among soil-crops-microorganisms. The single application or combined application of biochar and nano-zero valent iron significantly reduced the content and proportion of the exchangeable state and carbonate-bound state of various metals in the soil, promoted the transformation of mobile metals into potentially mobile and stable forms, and the ability of biochar to passivate metals was stronger than that of nano-zero valent iron. As the growth time of soybeans extended, the available state content of metals in the rhizosphere soil of different treatments showed a downward trend, which may be attributed to the positive effects of the two materials and the absorption of crop roots. In addition, the effect of the combined application of the two materials was better than that of the single material, and the changes in the content of various metal forms were related to the application rates of the two materials.

[0069] Referring to the "Microwave Digestion Method for Heavy Metals in Soils (HJ832-2017)", 0.20 g samples of soybean roots, nodules, stems, leaves, and seeds obtained in Examples 1, 2, 3, and 4 were weighed into digestion vessels respectively, and 6 mL of concentrated nitric acid and 2 mL of concentrated hydrochloric acid were added for digestion. After digestion was completed, the digestion solution was transferred to a 25 mL volumetric flask and made up to the mark, shaken well, and the concentrations of As, Cd, Cr, Cu, and Pb were detected by ICP-OES, and the metal contents in each part of the soybean plant were calculated. The results are as Figures 6-10 shown.

[0070] It can be Figures 6-10 seen that compared with CK, the reduction effect of the As content in each organ of the soybean plants in Examples 2, 3, and 4 was better, and biochar and nano-zero valent iron showed a synergistic effect. The addition of both materials reduced the Cd concentrations in soybean roots, leaves, and seeds. The treatment in Example 4 had the best effect on reducing Cd in seeds, which was 34.38% lower than the CK treatment. In addition, compared with CK, the application of biochar and nano-zero valent iron both reduced the contents of Cr, Cu, and Pb in soybean plants, and the combined application of the two materials showed a certain synergistic effect. This is mainly due to the fact that biochar and nano-zero valent iron reduced the mobility and bioavailability of various metals in the soil, thereby reducing the bioaccumulation of soybeans.

[0071] The soybean plants at 45 days and 100 days were divided into roots, stems, leaves, and seeds, and the dry weights of each part and the total biomass were calculated, as Figures 11-12As shown. The application of biochar and nano-zero valent iron can both promote the growth of soybean plants. Compared with CK, the total biomass of Examples 1, 2, 3 and 4 increased by 7.75%, 4.13%, 12.92% and 5.17% respectively at 45 days. More importantly, biochar and nano-zero valent iron increased the yield of soybean grains. Compared with the dry weight of CK grains, the soybean grain yields of Examples 1, 2, 3 and 4 increased by 7.21% - 17.12%, and Example 4 was more conducive to the increase of soybean grain yield.

[0072] The content of protein in soybean grains was determined and calculated by the Kjeldahl method, as Figure 13 shown. Compared with the control group, both nano-zero valent iron and biochar treatments increased the protein content in soybean grains. The protein contents in grains of Examples 1, 2, 3 and 4 increased by 10.49%, 6.19%, 2.59% and 6.58% respectively compared with CK, and the promoting effect of nano-zero valent iron was more significant than that of biochar. It shows that the application of nano-zero valent iron and biochar has an obvious promoting effect on the protein accumulation in soybean grains and can improve the quality of soybeans.

[0073] The above-described embodiments are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for solidifying metals in the soil around the solidified tailings area, characterized in that, The steps include adding biochar and nano zero-valent iron to the soil around the tailings area and planting soybeans.

2. The method according to claim 1, characterized in that It includes a pretreatment step of air-drying and sieving the soil around the tailings area.

3. The method according to claim 1, characterized in that The biochar is corn straw biochar.

4. The method according to claim 1, characterized in that The particle diameter of the nano zero-valent iron is <100 nm.

5. The method according to claim 1, wherein The addition amount of the biochar is 3% of the mass of the soil around the tailings area, and the addition amount of the nano zero-valent iron is 0.5% of the mass of the soil around the tailings area.

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