CN111821946A - Preparation method of modified remediation plant biochar for cadmium-contaminated soil remediation - Google Patents

Abstract

The invention discloses a preparation method of modified restoration plant biochar for restoring cadmium contaminated soil, which comprises the following steps: (1) harvesting the restoration plants containing heavy metals with certain concentration, washing, drying, crushing and sieving to obtain a biomass raw material; (2) placing the biomass in a tubular furnace under nitrogen atmosphere for high-temperature carbonization, keeping the pyrolysis temperature at 400-700 ℃, keeping the residence time for 1-2h, cooling to room temperature, and grinding to obtain the repair plant biochar with different pyrolysis temperatures; (3) spreading a certain mass of the repair plant biochar in a glass ware with the thickness of about 2mm, and placing the glass ware under an ultraviolet lamp of 250W for irradiating for 8-24 h; (4) and (4) taking out the culture dish after the irradiation is finished, and obtaining the modified restoration plant biochar. The phytobiocarbon repairing material prepared by the method is low in toxic leaching amount, environmentally acceptable and simple in preparation method, and the modified biochar effectively inhibits the effectiveness and the mobility of heavy metals in soil, so that the double values of safe disposal and resource recycling of hazardous wastes are realized.

Description

Preparation method of modified remediation plant biochar for cadmium-contaminated soil remediation

technical field

The present invention relates to the technical field of environmental protection, in particular to a treatment for plants containing heavy metal cadmium after remediation of cadmium-contaminated soil, which is prepared into remediation plant biochar and the above-mentioned biochar is modified for reuse.

Background technique

Heavy metal pollution in soil has become an environmental problem that needs to be solved urgently. Large amounts of heavy metals accumulated in soil are mainly caused by human activities, such as mining, wastewater and pesticides. As one of the major heavy metal pollutants, cadmium poses a serious threat to the safety of the entire agricultural production due to its extremely high toxicity and non-biodegradability. Multiple studies have shown that the presence of excess cadmium in soil can negatively affect plant growth, including brown spotting, curling and even leaf drop. In addition, cadmium accumulated in foods such as wheat and rice can also have a major impact on human health, leading to various diseases such as pneumonia, hypertension and osteoporosis. Therefore, it is urgent to find an effective method to treat cadmium-contaminated soil.

Phytoremediation is a technology that uses plants to absorb, degrade, transform and fix heavy metals in soil to achieve the purpose of remediating contaminated soil. Due to its strong adsorption capacity for heavy metals, high economy and easy operation, it has been widely used in heavy metal soil remediation. However, remediation plants often contain high content of heavy metals and have the risk of secondary pollution. Therefore, the safe disposal of remediation plant residues is an urgent problem to be solved. Common treatment methods for plant restoration include direct landfill, incineration, composting, pyrolysis, etc. Among them, pyrolysis technology refers to the method of heating and disposing of biomass under anaerobic conditions. After pyrolysis, the remediation plants can be decomposed into combustible fuels such as gas, liquid, and solid, which can be used separately, and the solid is biochar. Pyrolysis technology can not only achieve a volume reduction efficiency of more than 90%, but also has a low heat treatment temperature, and the closed furnace is not conducive to the volatilization and migration of heavy metals. Reuse of energy.

Generally, biochar has a rich void structure and a large specific surface area. Biochar is a kind of insoluble, stable, highly aromatic, carbon-rich solid substance with developed pore structure, many negative charges, strong ion exchange capacity, and excellent adsorption performance, showing strong resistance to heavy metal cations. Adsorption capacity. Biochar not only improves soil fertility and plant growth, but also reduces the levels of heavy metals in plants by fixing its bioavailability in the soil. The preparation of biochar comes from a wide range of sources, including agricultural waste, livestock manure, sludge, etc. Therefore, it is feasible to obtain biochar by pyrolysis of remediation plants and use it for the treatment of soil heavy metal pollution.

However, unmodified biochars often have limited effects on heavy metals in soil, and modification treatments are needed to improve their performance. The modification of biochar can usually be divided into chemical, physical modification, impregnation modification, etc. But these methods are accompanied by many problems, such as high economic cost and poor effect. At the same time, such modification methods may increase the risk of leaching of heavy metals contained in the remediation of plant biochar. Ultraviolet radiation can not only increase the specific surface area of biomass, but also introduce oxygen-containing functional groups on its surface, and it is not easy to cause secondary pollution. Therefore, it is of great significance to combine the remediation plant biochar with ultraviolet radiation to prepare an ultraviolet modified remediation plant biochar material and enhance its ability to inhibit the effectiveness of the heavy metal cadmium in the soil.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for preparing plant biochar that has environmental acceptability and can effectively reduce the effectiveness and mobility of heavy metal cadmium in soil, so as to realize the dual value of safe disposal of hazardous waste and recycling of resources .

The present invention solves the above-mentioned technical problems with the following technical solutions:

(1) Harvesting restoration plants containing a certain concentration of heavy metals, and obtaining biomass raw materials after washing, drying, grinding and sieving;

(2) The biomass raw materials are placed in a tube furnace under nitrogen atmosphere for high temperature carbonization, the pyrolysis temperature is kept at 400-700°C, the residence time is 1-2h, cooled to room temperature, and ground to obtain different pyrolysis temperatures. Restoration of plant biochar;

(3) Take a certain quality of restoration plant biochar and spread it on a glass vessel of about 2mm, and place it under a 250W UV lamp for 8-24h;

(4) After the irradiation, take out the petri dish and cool it to room temperature to obtain the modified and repaired plant biochar.

Further, the heavy metal remediation plant in the step (1) is a cadmium pollution remediation plant, and the biomass raw material passes through a 50-mesh standard sieve after being ground.

Further, the biomass raw material is rape or ryegrass.

Further, in the step (2), the heating rate is 20°C·min- ¹ , the nitrogen flow rate is 0.5L·min- ¹ , and the biochar is ground and passed through a 100-mesh sieve.

Further, the petri dish in the step (3) is placed on an electric hot plate to keep the temperature of the biochar at 80°C.

Further, in the step (3), the radiation distance between the culture dish and the ultraviolet lamp is kept at 40 cm.

The present invention provides the modified remediation plant biochar prepared according to the method of the present invention.

In addition, the present invention also provides that the modified remediation plant biochar is applied to the treatment of heavy metal polluted soil, which comprises the following steps:

(1) Add modified remediation plant biochar to heavy metal-contaminated soil according to 0.2%-0.6% of the soil mass, and the biochar is fully mixed with the soil surface;

(2) Water the soil regularly to keep the soil moisture at 60% of the maximum water holding capacity in the field.

Further, the heavy metal polluted soil is cadmium polluted soil.

Compared with the prior art, the beneficial effects of the present invention are:

(1) the biochar toxicity leaching amount prepared by the present invention is low, according to the leaching experiment with reference to the method of "solid waste leaching toxicity leaching method horizontal oscillation method (HJ557-2010)" method, the modified remediation plant biochar obtained is put into distilled water respectively , nitric acid/sulfuric acid mixed solution, glacial acetic acid, the concentration of cadmium in the leaching solution is far lower than the standard identification value of leaching toxicity (GB5085.3-2007), it can be seen that this method is environmentally acceptable, the preparation method is simple, easy to industrialized production, and No additional environmental hazard is caused, and the problem of safe disposal of hazardous waste is achieved (refer to Example 6).

(2) The present invention uses ultraviolet radiation to modify the repaired plant biochar, and the scanning electron microscope results show that compared with the unmodified biochar, there are more irregular corrosion pores on the surface of the modified biochar; at the same time, the pore structure It is more uniform and the impurities in the channel are unclogged, which is beneficial to increase its surface area. The results of infrared spectroscopy showed that the content of carboxyl functional groups on the surface of the modified biochar was significantly increased, indicating that its complexation with heavy metals was enhanced. The introduction of ultraviolet radiation is not only simple to operate, but also free of secondary pollution (refer to Example 5).

(3) The modified and repaired plant biochar provided by the present invention can effectively reduce the available state content of heavy metals in the soil and the heavy metal content of each organ in the plant, and the treatment period is short, the passivation efficiency is high, and the resource utilization is achieved. Purpose (refer to Examples 7 and 8).

Description of drawings

Fig. 1 is the SEM image of repairing plant biochar and modified repairing plant biochar in Example 5;

FIG. 2 is the FTIR image of the remediation plant biochar and the modified remediation plant biochar in Example 5. FIG.

Detailed ways

The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Example 1:

The present embodiment provides a method for preparing a modified and repaired plant biochar for remediation of cadmium-contaminated soil. The specific process is as follows:

(1) get rapeseed with a cadmium content of 0.14 mg kg ^-1 , wash it with deionized water, dry it in an oven to a constant weight, grind the rapeseed and pass through a 50-mesh sieve to obtain biomass raw materials, wait for use;

(2) The rapeseed was placed in a tube furnace, nitrogen was continuously introduced at a rate of 0.5L·min ^-1 , heated to 600°C, and the residence time was 1h. After the temperature in the furnace was naturally cooled to room temperature, it was taken out and ground. After 100-mesh sieve, rape biochar is obtained, which is ready for use;

(3) Take 10 g of rape biochar and spread it on a glass vessel of about 2 mm, and place the petri dish on an electric hot plate to keep the temperature of the biochar at 80°C. Then it was placed under a 250W UV lamp for 16h, and the distance between the culture dish and the UV lamp was kept at 40cm;

(4) After the irradiation, the petri dish was taken out, cooled to room temperature, and the modified rape biochar was obtained, which was set aside.

Example 2:

The present embodiment provides a method for preparing a modified and repaired plant biochar for remediation of cadmium-contaminated soil. The specific process is as follows:

(1) get rapeseed with a cadmium content of 0.14 mg kg ^-1 , wash it with deionized water, dry it in an oven to a constant weight, grind the rapeseed and pass through a 50-mesh sieve to obtain biomass raw materials, wait for use;

(2) The rapeseed was placed in a tube furnace, nitrogen was continuously introduced at a rate of 0.5L·min ^-1 , heated to 400°C, and the residence time was 2h. After the temperature in the furnace was naturally cooled to room temperature, it was taken out and ground. After 100-mesh sieve, rape biochar is obtained, which is ready for use;

(3) Take 10 g of rape biochar and spread it on a glass vessel of about 2 mm, and place the petri dish on an electric hot plate to keep the temperature of the biochar at 80°C. Then it was placed under a 250W UV lamp for 16h, and the distance between the culture dish and the UV lamp was kept at 40cm;

(4) After the irradiation, the petri dish was taken out, cooled to room temperature, and the modified rape biochar was obtained, which was set aside.

Example 3:

The present embodiment provides a method for preparing a modified and repaired plant biochar for remediation of cadmium-contaminated soil. The specific process is as follows:

(1) get the ryegrass that the cadmium content is 3.86mg kg ^-1 , after washing with deionized water, place after drying in an oven to constant weight, grind the ryegrass and pass a 50-mesh sieve to obtain biomass raw materials ,stand-by;

(2) Place the ryegrass in a tube furnace, continuously feed nitrogen at a rate of 0.5L·min ^-1 , heat up to 600°C, and the residence time is 1h. After the temperature in the furnace is naturally cooled to room temperature, it is taken out and ground. After passing through a 100-mesh sieve, ryegrass biochar is obtained, which is ready for use;

(3) Take 10 g of ryegrass biochar and spread it on a glass vessel of about 2 mm, and place the petri dish on an electric hot plate to keep the temperature of the biochar at 80°C. Then it was placed under a 250W UV lamp for 16h, and the distance between the culture dish and the UV lamp was kept at 40cm;

(4) After irradiation, take out the petri dish, cool to room temperature, and obtain modified ryegrass biochar, which is ready for use.

Example 4:

The present embodiment provides a method for preparing a modified and repaired plant biochar for remediation of cadmium-contaminated soil. The specific process is as follows:

(1) get the ryegrass that the cadmium content is 3.86mg kg ^-1 , after washing with deionized water, place after drying in an oven to constant weight, grind the ryegrass and pass a 50-mesh sieve to obtain biomass raw materials ,stand-by;

(2) Place the ryegrass in a tube furnace, continuously feed nitrogen at a rate of 0.5L·min ^-1 , heat up to 500°C, and the residence time is 1h. After the temperature in the furnace is naturally cooled to room temperature, it is taken out and ground. After passing through a 100-mesh sieve, ryegrass biochar was obtained;

(3) Take 10 g of ryegrass biochar and spread it on a glass vessel of about 2 mm, and place the petri dish on an electric hot plate to keep the temperature of the biochar at 80°C. Then it was placed under a 250W UV lamp for 8h, and the distance between the Petri dish and the UV lamp was kept at 40cm;

(4) After irradiation, take out the petri dish, cool to room temperature, and obtain modified ryegrass biochar, which is ready for use.

Example 5:

In this example, scanning electron microscope (SEM) analysis was carried out on the rape biochar and ryegrass biochar A, B, and the modified rape biochar and modified ryegrass biochar C, D prepared in the above-mentioned Example 1 and Example 3. and infrared spectroscopy (FTIR) analysis.

The scanning electron microscope results showed that there were more irregular corrosion pores on the surface of the modified biochar than that of the unmodified biochar. At the same time, the pore structure is more uniform and the impurities in the channel are unclogged, which is beneficial to increase its surface area. The results of infrared spectroscopy showed that the content of carboxyl functional groups on the surface of the modified biochar was significantly increased, indicating that its complexation with heavy metals was enhanced.

Example 6:

In this example, a toxicity leaching experiment was carried out on the modified remediation plant biochar prepared in the above examples 1-4. The leaching experiment refers to the method of "Solid Waste Leaching Toxicity Leaching Method Horizontal Oscillation Method (HJ557-2010)", using water leaching, nitric acid/sulfuric acid mixed solution (60:40, w/w; pH: 4.20±0.05) and glacial acetic acid (pH : 2.88 ± 0.05) To carry out the toxicity leaching test: take 20 mL of deionized water, add 1 g of UV-modified and repaired plant biochar, shake for 8h, 18h and 18h in a constant temperature water bath shaking box at room temperature, centrifugal filter, measure the supernatant Cadmium content in the liquid. At the same time, a blank test (without biochar) was performed to eliminate experimental errors.

Table 1 Concentration of heavy metal cadmium (mg·L ^-1 ) in the leaching solution of different modified plant biochars

The identification value of heavy metals in the standard identification value of leaching toxicity (GB5085.3-2007) is based on the total amount. "ND" means not detected.

It can be seen from Table 1 that the concentration of cadmium in the leaching solution of the modified remediation plant biochar containing heavy metals is far lower than the standard identification value of leaching toxicity (GB5085.3-2007) under the three conditions, indicating that it is environmentally acceptable. It can be safely used in the treatment of heavy metal contaminated soil.

Example 7:

In this example, the rape biochar and the modified rape biochar prepared in Example 1 were used to treat the heavy metal cadmium-contaminated soil respectively. The basic physical and chemical properties of the tested soil were: pH 8.03, organic matter ^20.6g ·kg The cation exchange capacity is 10.36cmol·kg ^-1 , the total amount of cadmium is 1.97mg·kg ^-1 , and the cadmium content is higher than the risk screening value of "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard (Trial)" (GB15618-2018). The remediation process was as follows: the above two types of biochar were added to the soil according to 0.4% of the soil mass, and the control group was the soil without biochar addition, and three replicates were set for each treatment. After mixing the soil, put it into a culture pot, add coriander seeds after aging at a constant temperature for a week, and use deionized water to replenish the soil to keep the soil water content at about 60% of the field capacity. Soil and plant samples from each treatment group were collected and analyzed after 30 days of crop growth.

Effect detection: Determination of soil available cadmium, soil pH value, and cadmium content in the aboveground and underground parts of coriander. The results are shown in Table 2.

Table 2 Effects of different treatments on soil and plants

It can be seen from Table 2 that after rape or modified rape biochar was applied to cadmium-contaminated soil, compared with the control, the pH value of the soil increased to a certain extent, and the available cadmium in the soil decreased by 22.8% and 35.9%, respectively. The cadmium content in the aerial part of coriander decreased by 72.4% and 77.8%, and the cadmium content in the underground part of coriander decreased by 32.0% and 40.8%, respectively. Therefore, after the remediation plant biochar obtained by the present invention, especially the modified remediation plant biochar is applied to the soil, the content of available cadmium in the soil can be effectively reduced, and the cadmium in different tissues of the planted coriander can be greatly reduced content.

Example 8:

The present embodiment adopts the ryegrass biochar obtained in Example 3 and the modified ryegrass biochar to treat the heavy metal cadmium-contaminated soil respectively, and the basic physical and chemical properties of the tested soil are: pH8.03, organic matter ^20.6g kg- ^1. The cation exchange capacity is 10.36cmol·kg ^-1 , the total amount of cadmium is 1.97mg·kg ^-1 , and the cadmium content is higher than the risk screening value of "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard (Trial)" (GB15618-2018). The remediation process was as follows: the above two biochars were added to the soil according to 0.6% of the soil mass, and the control group was the soil without biochar addition, and three replicates were set for each treatment. After mixing the soil, put it into a culture pot, add coriander seeds after aging at a constant temperature for a week, and use deionized water to replenish the soil to keep the soil water content at about 60% of the field capacity. Soil and plant samples from each treatment group were collected and analyzed after 30 days of crop growth.

Effect detection: Measure soil available cadmium, soil pH value, and cadmium content in the aboveground and underground parts of coriander. The results are shown in Table 3.

Table 3 Effects of different treatments on soil and plants

The results in Table 3 show that ryegrass or modified ryegrass biochar can also significantly reduce the available cadmium content in soil, reaching 38.5% and 51.4%, respectively. At the same time, the cadmium content in different parts of coriander is also significantly reduced, indicating that the biochar prepared by the invention can effectively inhibit the availability and migration of cadmium in soil.

The above detailed description is a specific description of one of the feasible embodiments of the present invention, which is not intended to limit the scope of the present invention. Any equivalent implementation or modification that does not depart from the present invention shall be included in the present invention. within the scope of the technical solution.

Claims (9)

1. a preparation method for the modified repairing plant biochar for cadmium-contaminated soil remediation, is characterized in that: comprise the steps: (1) Harvesting restoration plants containing a certain concentration of heavy metals, and obtaining biomass raw materials after washing, drying, grinding and sieving; (2) The biomass raw material is placed in a tube furnace under nitrogen atmosphere for high temperature carbonization, the pyrolysis temperature is kept at 400-700°C, the residence time is 1-2h, cooled to room temperature, and ground to obtain the restoration of plant biochar; (3) Take a certain quality of restoration plant biochar and spread it in a glass vessel, and place it under an ultraviolet lamp for 8-24 hours; (4) After the irradiation, take out the petri dish and cool it to room temperature to obtain the modified and repaired plant biochar. 2. the preparation method of the modified remediation plant biochar for cadmium-contaminated soil remediation according to claim 1, is characterized in that: the plant containing certain concentration heavy metal in described step (1) is cadmium-contaminated remediation plant, and The biomass raw materials were ground and passed through a 50-mesh standard sieve. 3. The preparation method of the modified remediation plant biochar for remediation of cadmium-contaminated soil according to claim 1 or 2, wherein the raw material of the cadmium-contaminated soil remediation biomass is rape or ryegrass. 4. The preparation method of modified and repaired plant biochar for remediation of cadmium-contaminated soil according to claim 3, wherein the heating rate in the step (2) is 20°C·min ⁻¹ , and the nitrogen flow rate is was 0.5L·min ^-1 , and the biochar was ground and passed through a 100-mesh sieve. 5. the preparation method of the modified remediation plant biochar for cadmium-contaminated soil remediation according to claim 3, is characterized in that: the remediation plant biochar of certain quality in described step (3) is flat by the thickness of 2mm Spread in a petri dish and place the petri dish on a hot plate to keep the temperature of the biochar at 80°C. 6 . The method for preparing modified and remediated plant biochar for cadmium-contaminated soil remediation according to claim 3 , wherein the radiation distance between the petri dish and the ultraviolet lamp in the step (3) is maintained at 40 cm. 7 . 7. A modified remediation plant biochar for remediation of cadmium-contaminated soil, characterized in that the modified remediation plant biochar is prepared by the method of any one of the above claims 1-6. 8. using the modified remediation plant biochar of claim 7 to be applied to the treatment of heavy metal polluted soil, it comprises the steps: (1) Add modified remediation plant biochar to heavy metal-contaminated soil according to 0.2%-0.6% of the soil mass, and the biochar is fully mixed with the soil surface; (2) Water the soil regularly to keep the soil moisture at 60% of the maximum water holding capacity in the field. 9. The modified remediation plant biochar according to claim 8 is applied to the treatment of heavy metal polluted soil, wherein the heavy metal polluted soil is cadmium polluted soil.

Images