Method for repairing heavy metal contaminated soil by using plants and recycling heavy metal contaminated soil

Abstract

The invention discloses a method for repairing heavy metal contaminated soil through plants and recycling the heavy metal contaminated soil. According to the method, a proper amount of iron-containing fertilizer is applied while phytoremediation is conducted, iron nutrients are provided for plants, and heavy metal contaminated soil is remedied in cooperation with the plants. Restoration plants are rich in biomass after being harvested, biological source potassium humate can be prepared, reduction, harmlessness and recycling are achieved, iron in the plants plays a catalytic role in the process, and the yield of the potassium humate can be increased. As an efficient organic potash fertilizer, potassium humate can improve soil quality, promote plant growth and improve crop stress resistance, potassium humate prepared from remediation plants is recycled to polluted soil, soil remediation is promoted, virtuous cycle of soil and plants is achieved, the rest of potassium humate can be sold, and economic benefits are obtained.

Description

Technical Field

[0001] The present invention relates to the field of environmental governance, and particularly relates to a method for phytoremediating heavy metal contaminated soil and resource recycling. Background Art

[0002] Soil is an important part of the terrestrial ecosystem on Earth and an important natural resource. Soil quality affects many aspects such as crop cultivation, plant growth, environmental quality, and human health, and is of great significance for maintaining the ecosystem. However, with the development of industry, mining, and agriculture, the problem of soil pollution has become increasingly serious, especially the problem of heavy metal pollution. Currently, the main pollutants affecting the soil environmental quality of agricultural land are heavy metals. Some studies have shown that most soil pollutions present as combined pollutions, and soil pollution phenomena such as Cd, Pb, As, Cu, Cr, Zn, Hg, etc. have occurred in many places. Among them, the heavy metals cadmium, lead, zinc, and copper seriously exceed the standards, and in some areas, they even exceed the standard value by 3 to 4 times.

[0003] Soil heavy metal pollution will cause problems such as a decline in soil quality and a reduction in crop yields. At the same time, it will also harm the water and atmospheric environments, threaten human health, exacerbate global climate change, and affect the sustainable development of society. Therefore, the problem of soil heavy metal pollution has attracted people's attention. Currently, heavy metal contaminated soil remediation technologies mainly include physical technologies, chemical technologies, biological technologies, and combined remediation technologies. Among them, phytoremediation refers to using the absorption, volatilization, rhizofiltration, degradation, stabilization, etc. of plants to purify pollutants in the soil to purify polluted sites. Compared with physical and chemical remediation technologies, phytoremediation technology has the least interference to the soil system, does not damage the soil structure, is environmentally friendly, and has a wide range of applications, so it has received more and more attention. However, with the application of phytoremediation technology, a large number of remediation plants rich in heavy metals have also emerged, and how to correctly and reasonably dispose of the remediation plants has become another problem. Currently, the commonly used methods for disposing of remediation plants include composting, landfilling, incineration, liquid phase extraction, pyrolysis, etc. The composting method has simple technology and low cost, but it requires a large amount of land and a long cycle; the landfilling method has simple technology, low cost, and high efficiency, but it is easy to cause secondary pollution and occupies a large amount of land resources; the incineration method has a good volume reduction effect and can recycle energy, but it is easy to produce secondary pollution and has high energy consumption; the liquid phase extraction method is still mainly studied in the laboratory, with less industrial application, and is affected by the extractant, often only able to extract a single substance, and is not suitable for disposing of plants that have remediated composite polluted sites; the pyrolysis technology decomposes plants under anaerobic conditions to produce three components: solid, liquid, and gas, enriches heavy metals in the solid product, and the pyrolysis gas and bio-oil can be recycled. Summary of the Invention

[0004] The object of the present invention is to overcome the drawbacks and deficiencies of the prior art, and to provide a method for phytoremediation of heavy metal contaminated soil and resource recycling.

[0005] The object of the present invention is achieved by the following technical solutions:

[0006] A method for phytoremediation of heavy metal contaminated soil and resource recycling, comprising the following steps:

[0007] (1) Plant Pennisetum giganteum seedlings in the contaminated land, perform normal field management and fertilization, apply iron fertilizer during this period, and harvest the Pennisetum giganteum after the plants mature;

[0008] (2) Dry, crush and sieve the harvested Pennisetum giganteum to obtain Pennisetum giganteum powder, take samples to measure the organic matter content, mix it with hydrochloric acid solution, and pyrolyze it under an inert atmosphere to obtain a weathered coal precursor;

[0009] (3) Mix the weathered coal precursor with potassium hydroxide solution, calcine it, take out the product after the calcination is completed, add water to mix and filter, and dry the filtrate to obtain potassium humate;

[0010] (4) Repeat steps (1) to (3), and apply the potassium humate prepared in step (3) during the planting process in step (1) to achieve the remediation of heavy metal contaminated soil.

[0011] The iron fertilizer described in step (1) is ferrous sulfate; preferably a 5 g / L ferrous sulfate solution, and the application amount is 200 mL / plant.

[0012] The application time of the iron fertilizer described in step (1) is 3 to 5 months after planting the seedlings.

[0013] The harvesting time described in step (1) is 6 to 8 months after planting the seedlings.

[0014] The sieving described in step (2) is through a 100-mesh sieve.

[0015] The concentration of the hydrochloric acid solution described in step (2) is 1 to 2 mol / L.

[0016] The pyrolysis conditions described in step (2) are pyrolysis at 200 to 300 °C for 1 to 3 h; preferably pyrolysis at 250 °C for 2 h.

[0017] The concentration of the potassium hydroxide solution described in step (3) is 20 to 40 wt%.

[0018] The mass ratio of potassium hydroxide to organic matter in the Pennisetum giganteum in the potassium hydroxide solution described in step (3) is 1 to 2:5.

[0019] The calcination conditions in step (3) are calcination at 200 - 400°C for 1 - 3 h; preferably, calcination is carried out at 300°C for 2 h.

[0020] The repetition in step (4) is repeated 1 - 3 times.

[0021] The heavy metals mentioned are metal elements with a specific gravity greater than 5; preferably cadmium or copper.

[0022] The heavy metal - contaminated soil is soil with a cadmium content of 1 - 2 mg / kg or soil with a copper content of 500 - 700 mg / kg.

[0023] The application of the method for phytoremediation of heavy metal - contaminated soil and resource recycling in the preparation of potassium humate.

[0024] The application of the method for phytoremediation of heavy metal - contaminated soil and resource recycling in the treatment of heavy metal - contaminated soil.

[0025] The present invention has the following advantages and effects compared with the prior art:

[0026] Plants such as Pennisetum giganteum, Solanum nigrum, Sedum plumbizincicola, etc. have a strong absorption capacity for heavy metals in the soil, and have a certain tolerance to heavy metals. They can grow in heavy metal - contaminated soil, enrich heavy metals in the soil, and these plants often have developed roots and a large biomass. Utilizing these characteristics, using such plants as remediation plants to remediate heavy metal - contaminated soil can achieve good results. During phytoremediation, an appropriate amount of iron - containing fertilizer is applied to provide iron nutrients for the plants and synergistically remediate heavy metal - contaminated soil with the plants. After the remediation plants are harvested, they are rich in a large amount of biomass and can be used to produce biogenic potassium humate, realizing reduction, harmlessness, and resource utilization. During this process, the iron in the plants plays a catalytic role and can improve the yield of potassium humate. Potassium humate, as an efficient organic potassium fertilizer, can improve soil quality, promote plant growth, and enhance the stress resistance of crops. Recycling the potassium humate produced from the remediation plants to the contaminated soil can promote soil remediation and achieve a virtuous cycle between the soil and plants. The remaining potassium humate can be sold externally to obtain economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is the technical roadmap of the present invention.

[0028] Figure 2 It is the comparison chart of the yield of potassium humate prepared by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] The present invention will be further described in detail below in conjunction with the embodiments and the drawings, but the embodiments of the present invention are not limited thereto.

[0030] In the following implementation examples, if the specific test conditions are not specified, they are generally in accordance with the conventional test conditions or the test conditions recommended by the reagent company. The materials, reagents, etc. used, unless otherwise specified, are all reagents and materials obtained through commercial channels.

[0031] Example 1

[0032] (1) The experimental site is in Yili Kazakh Autonomous Prefecture, Xinjiang Uygur Autonomous Region. Cadmium-polluted soil with a total cadmium content of 1.12 mg / kg is selected. The soil is plowed, leveled, ditched, and ridged. 50 kg of compound fertilizer is applied per mu as the base fertilizer. Giant king grass seedlings are transplanted, with a plant spacing of 30 - 40 cm and a row spacing of 100 - 150 cm. When the plant height reaches 20 - 30 cm, 10 - 15 kg of nitrogen fertilizer is top-dressed per mu to promote its growth and tillering. After 4 months of planting, 200 mL of 5 g / L FeSO4 iron fertilizer is sprayed on each plant. When planting for 7 months, the giant king grass is harvested.

[0033] (2) The harvested giant king grass is washed and blanched in an oven at 105°C for 30 min, then the oven temperature is adjusted to 70°C and dried to a constant weight. After drying, it is pulverized with a plant pulverizer and sieved through a 100-mesh sieve. 5 g of giant king grass is weighed and placed in a crucible, and the organic matter content in the giant king grass powder is determined by the loss-on-ignition method. The pre-treated giant king grass powder is weighed into a porcelain boat, 5 mL of 1 mol / L hydrochloric acid solution and 15 mL of deionized water are added, mixed evenly, and then dried in an oven at 70°C. The porcelain boat is placed in a tubular furnace, nitrogen is passed through to expel air, and catalytic pyrolysis is carried out in the tubular furnace at a pyrolysis temperature of 250°C for 2 h with a heating rate of 5°C / min to obtain a weathered coal precursor. The weathered coal precursor is mixed evenly with a 30% KOH solution (the mass ratio of KOH to the organic matter of giant king grass is 0.3:1), placed in an oven at 300°C and calcined for 2 h (heating rate 5°C / min). After the calcination is completed, it is immediately taken out and poured into 100 mL of deionized water for water quenching. The solid-liquid mixture is filtered, and the filtrate is dried to obtain potassium humate, denoted as HA-K-1.

[0034] (3) In the soil where giant king grass was planted in step (1), giant king grass is continued to be planted with the same planting method. A certain area is selected to apply the potassium humate obtained in step (2), which is applied simultaneously with the base fertilizer, 5 - 6 kg of potassium humate is applied per mu, and the rest is not applied with potassium humate for the second repair.

[0035] Example 2

[0036] (1) In this embodiment, the main heavy metal pollutant in the contaminated soil is Cu, with a content of 612.74 mg / kg. The soil is plowed, leveled, ditched, and ridged. 50 kg of compound fertilizer is applied per mu as the base fertilizer, and Pennisetum giganteum seedlings are transplanted, maintaining a plant spacing of 30 - 40 cm and a row spacing of 100 - 150 cm. When the plants reach a height of 20 - 30 cm, 10 - 15 kg of nitrogen fertilizer is top-dressed per mu to promote their growth and tillering. After 4 months of planting, 200 mL of 5 g / L FeSO4 iron fertilizer is sprayed on each plant. When the plants are planted for 7 months, the Pennisetum giganteum is harvested.

[0037] (2) The harvested Pennisetum giganteum is washed and blanched in an oven at 105°C for 30 min, and then the oven temperature is adjusted to 70°C and dried to a constant weight. After drying, it is pulverized with a plant pulverizer and sieved through a 100-mesh sieve. 5 g of Pennisetum giganteum is weighed and placed in a crucible, and the organic matter content in the Pennisetum giganteum powder is determined by the loss-on-ignition method. The pretreated Pennisetum giganteum powder is weighed into a porcelain boat, and 1 mol / L hydrochloric acid solution and deionized water are added and mixed evenly. The porcelain boat is placed in a tubular furnace, nitrogen is passed through to expel air, and catalytic pyrolysis is carried out in the tubular furnace at a pyrolysis temperature of 250°C for 2 h to obtain a precursor of weathered coal-like substance. The precursor of weathered coal-like substance is mixed evenly with 30% KOH solution (the mass ratio of KOH to the organic matter of Pennisetum giganteum is 0.3), placed in an oven at 300°C and calcined for 2 h. After the calcination is completed, it is immediately taken out and poured into deionized water for water quenching. The solid-liquid mixture is filtered, and the filtrate is dried to obtain potassium humate, denoted as HA-K-2.

[0038] (3) Pennisetum giganteum is continuously planted in the soil where Pennisetum giganteum was planted in step (1) using the same planting method. Potassium humate obtained in step (2) is applied to some areas, and the rest are not applied. The second repair is carried out in the same way as above.

[0039] Comparative Example 1

[0040] Referring to the method of Example 1, Pennisetum giganteum is planted in different areas of cadmium-contaminated land, except that FeSO4 iron fertilizer is not applied in step (1), and the rest of the methods are the same.

[0041] Comparative Example 2

[0042] Referring to the method of Example 2, Pennisetum giganteum is planted in different areas of copper-contaminated land, except that FeSO4 iron fertilizer is not applied in step (1), and the rest of the methods are the same.

[0043] Example 3

[0044] After the second repair in Example 1 and Example 2, soil samples are taken from the areas where potassium humate is applied and not applied respectively, and the content of available heavy metals in the soil is determined by ICP-MS method. The results are shown in Table 1.

[0045] Table 1 Content of available heavy metals in soil

[0046]

[0047] As can be seen from Table 1, Pennisetum giganteum has good removal effects on cadmium and copper in soil. In addition, by comparing different areas with and without potassium humate application, it can be found that the application of potassium humate can promote phytoremediation of heavy metal-contaminated soil with cadmium, reduce the content of available heavy metals in the soil, and improve the removal rate of soil heavy metals.

[0048] Example 4

[0049] After harvesting the Pennisetum giganteum in the first remediation of Example 1, Example 2, Comparative Example 1, and Comparative Example 2, it was dried, crushed, and sieved according to the method of Example 1. The Pennisetum giganteum powder was taken to determine the heavy metal content in the biomass of each group (the cadmium content in Example 1 and Comparative Example 1, and the copper content in Example 2 and Comparative Example 2).

[0050] Table 2 Heavy metal content in Pennisetum giganteum powder

[0051]

[0052]

[0053] Example 5

[0054] Referring to the method in step (2) of Example 1, the Pennisetum giganteum obtained from the second harvest in Example 1, 2, Comparative Example 1, and 2 was used as the raw material to prepare potassium humate.

[0055] Comparative Example 3

[0056] The Pennisetum giganteum harvested for the first time in Comparative Example 2 was dried, crushed, and sieved according to the method of Example 1. The Pennisetum giganteum powder was taken, and 5 g of the treated Pennisetum giganteum powder was placed in a tube furnace. 1 mol / L hydrochloric acid solution, 1% FeCl3 (1% of the organic matter mass of the Pennisetum giganteum powder), and deionized water were added and mixed evenly. The porcelain boat was placed in the tube furnace, nitrogen was passed through to discharge the air, and catalytic pyrolysis was carried out in the tube furnace at a pyrolysis temperature of 250 °C for 2 h to obtain a weathered coal precursor. The weathered coal precursor was mixed evenly with 30% KOH solution (the mass ratio of KOH to the organic matter of Pennisetum giganteum was 0.3), placed in an oven at 300 °C for roasting for 2 h. After the roasting was completed, it was immediately taken out and poured into deionized water for water quenching. The solid-liquid mixture was filtered, and the filtrate was dried to obtain potassium humate, and the yield was calculated.

[0057] Example 6

[0058] The potassium humate yields in each example and comparative example were calculated according to the following formula, and the results are as Figure 2 shown.

[0059] Yield of potassium humate = mass of potassium humate / (mass of Pennisetum giganteum powder + mass of KOH)

[0060] The experimental results show that in Example 1, the yield of potassium humate is 83%, in Example 2 the yield of potassium humate is 80%, in Comparative Example 1 the yield of potassium humate is 54%, and in Comparative Example 2 the yield of potassium humate is 49%. In Comparative Example 3, the yield of potassium humate is 80%, indicating that applying iron fertilizer during the cultivation of Pennisetum giganteum can increase the yield of humic acid, achieving a better effect than adding only an iron catalyst.

[0061] Example 7

[0062] The potassium humate and residues prepared in each example and comparative example were subjected to microwave digestion respectively, and the cadmium content in the potassium humate and residues in Example 1 and Comparative Example 1, and the copper content in the potassium humate and residues in Example 2 and Comparative Example 2 were determined by ICP-MS method, as shown in Table 3.

[0063] Table 3 Heavy metal content in potassium humate and residues

[0064]

[0065]

[0066] The experimental results show that the heavy metal content in the potassium humate prepared by this method is relatively low, meeting the requirements for heavy metal content in GB / T33804-2017 "Potassium Humate for Agricultural Use", and the copper content meets the requirements for trace elements in NY 1428-2010. Most of the heavy metals absorbed by plants remain in the residues. After treatment, this part of the residues can be landfilled, or the heavy metals in them can be extracted for recycling.

[0067] The above examples are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above examples. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for phytoremediation of heavy metal contaminated soil and resource recycling, characterized in that It includes the following steps: (1) Plant Pennisetum giganteum seedlings in the contaminated soil, conduct normal field management and fertilization, apply iron fertilizer during this period, and harvest the Pennisetum giganteum after the plants mature; (2) Dry, crush and sieve the harvested Pennisetum giganteum to obtain Pennisetum giganteum powder, take samples to measure the organic matter content, mix it with hydrochloric acid solution, and pyrolyze it under an inert atmosphere to obtain a precursor of weathered coal-like substance; (3) Mix the precursor of weathered coal-like substance with potassium hydroxide solution, roast it, take out the product after roasting, add water to mix and filter, and dry the filtrate to obtain potassium humate; (4) Repeat steps (1) to (3), and apply the potassium humate prepared in step (3) during the planting process in step (1) to achieve the remediation of heavy metal contaminated soil.

2. The method according to claim 1, wherein: The iron fertilizer in step (1) is ferrous sulfate.

3. The method according to claim 1, wherein: The application time of the iron fertilizer in step (1) is 3 to 5 months after planting the seedlings; The harvesting time in step (1) is 6 to 8 months after planting the seedlings.

4. The method according to claim 1, wherein: The sieving in step (2) is through a 100-mesh sieve; The concentration of the hydrochloric acid solution in step (2) is 1 to 2 mol / L.

5. The method according to claim 1, wherein: The pyrolysis conditions in step (2) are pyrolysis at 200 to 300 °C for 1 to 3 h.

6. The method according to claim 1, wherein: The concentration of the potassium hydroxide solution in step (3) is 20 to 40 wt%; The mass ratio of potassium hydroxide to organic matter in the Pennisetum giganteum in the potassium hydroxide solution in step (3) is 1 to 2:

5.

7. The method according to claim 1, wherein: The roasting conditions in step (3) are roasting at 200 to 400 °C for 1 to 3 h.

8. The method according to claim 1, wherein: The repetition in step (4) is repeated 1 to 3 times; The heavy metal is a metal element with a specific gravity greater than 5; The heavy metal contaminated soil is soil with a cadmium content of 1 to 2 mg / kg or soil with a copper content of 500 to 700 mg / kg.

9. Application of the method for phytoremediation of heavy metal contaminated soil and resource recycling as described in any one of claims 1 to 8 in the preparation of potassium humate.

10. Application of the method for phytoremediation of heavy metal contaminated soil and resource recycling as described in any one of claims 1 to 8 in the treatment of heavy metal contaminated soil.

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