CN113980695A

CN113980695A - Treatment method of plant biomass for enriching heavy metals

Info

Publication number: CN113980695A
Application number: CN202111354218.3A
Authority: CN
Inventors: 覃建军; 彭佩钦; 龙坚; 侯红波; 李民峰
Original assignee: Central South University of Forestry and Technology
Current assignee: Central South University of Forestry and Technology
Priority date: 2021-11-12
Filing date: 2021-11-12
Publication date: 2022-01-28

Abstract

The invention belongs to the technical field of resource environment, and particularly relates to a treatment method of heavy metal enriched plant biomass. According to the invention, plants growing in heavy metal contaminated soil are pyrolyzed, and biomass is pyrolyzed into biochar at 400-800 ℃, so that air pollution is avoided, and the environmental risk is low; the method has the advantages that the nitric acid solution with the pH value of 1-3 is used for leaching the biochar, the specific surface area of the biochar can be increased, the P-O functional groups on the surface of the biochar are increased, the adsorption capacity of the biochar is enhanced, a large amount of residual heavy metals in the biochar are precipitated through separation treatment, and the recycling rate is improved.

Description

Treatment method of plant biomass for enriching heavy metals

Technical Field

The invention belongs to the technical field of resource environment, and particularly relates to a treatment method of heavy metal enriched plant biomass.

Background

The heavy metal pollution of soil restricts the agricultural economy and poses a great threat to human health. Plant extraction is the most promising technology for remedying the heavy metal pollution of the soil at present, uses solar energy as power, transfers the heavy metal in the soil to the overground part which is relatively easy to treat by utilizing plants, and has the advantages of low cost and large-scale application. However, after the plant extraction is completed, a large amount of harmful biomass is produced, and for example, when the heavy metal contaminated soil is remediated by using Indian mustard (Brassica juncea), 6 tons of biomass containing heavy metals can be produced. If the treatment is improper, heavy metals can enter the environment again to cause secondary pollution, various resources can be wasted, and the development of plant extraction technology is limited.

At present, the treatment method of enriching the heavy metal plant biomass mainly comprises incineration and composting, wherein the incineration is to put the biomass into an incinerator, carry out combustion reaction through excessive air, and simultaneously realize reduction and resource utilization, but the treatment method has the defects of easy air pollution and high operation cost; the composting is a technology for degrading organic matters in solid wastes by using microorganisms, and can produce fertilizers, but the treatment period is long (2-3 months), the large-scale treatment cost is high, and leachate in the composting process needs to be strictly controlled. How to safely and efficiently treat enriched heavy metal biomass and realize the recycling of heavy metals and nutrient elements is a problem to be solved urgently.

Disclosure of Invention

The invention aims to provide a method for enriching heavy metal plant biomass, which realizes the recycling of heavy metals and nutrient elements in the heavy metal plant biomass, and has the advantages of low environmental risk and high resource utilization rate.

In order to achieve the above purpose, the invention provides the following technical scheme:

the invention provides a treatment method of plant biomass for enriching heavy metals, which comprises the following steps:

pyrolyzing plants growing in the heavy metal contaminated soil to obtain biochar; leaching and separating the biochar to obtain leaching liquor and modified biochar;

the pyrolysis temperature is 400-800 ℃, and the time is 1.5-2.5 h;

the reagent for leaching treatment comprises a nitric acid solution with pH of 1-3.

Preferably, the pyrolysis temperature is increased at the rate of 5-10 ℃/min during pyrolysis.

Preferably, nitrogen is introduced during pyrolysis; the flow rate of the nitrogen is 150-250 mL/min.

Preferably, the heavy metal comprises one or more of Cd and Zn.

Preferably, the plant comprises a heavy metal-enriched plant.

Preferably, the heavy metal-enriched plant comprises a hyperaccumulator plant or elephant grass.

Preferably, after the leaching liquor is obtained, the pH value of the leaching liquor is adjusted to 9-12, and then the leaching liquor is separated to obtain the alkali precipitation leaching liquor.

The invention also provides application of the modified biochar obtained by the treatment method in adsorbing water pollutants.

Preferably, the water body contaminant comprises a dye.

The invention also provides application of the alkali precipitation leaching liquor obtained by the treatment method in preparation of liquid fertilizer.

The invention provides a treatment method of plant biomass for enriching heavy metals, which comprises the following steps: pyrolyzing plants growing in the heavy metal contaminated soil to obtain biochar; leaching and separating the biochar to obtain leaching liquor and modified biochar; the pyrolysis temperature is 400-800 ℃, and the pyrolysis time is 1.5-2.5 h; the leaching treatment comprises leaching the biochar by using a nitric acid solution with the pH value of 1-3. According to the invention, the biomass is pyrolyzed into the biochar at 400-800 ℃, so that the air is not polluted, and the environmental risk is low; the method has the advantages that the nitric acid solution with the pH value of 1-3 is used for leaching the biochar, so that the specific surface area of the biochar can be increased, the P-O functional groups on the surface of the biochar are increased, and the adsorption capacity of the biochar is enhanced. The separation treatment is to precipitate a large amount of heavy metals remained in the biochar, so that the recovery rate is improved.

The invention takes potassium hydroxide as a reagent for separation treatment, and can also supplement K element for the leaching liquor while precipitating heavy metal, so that the K element with higher concentration than other nutrient elements in the leaching liquor is further improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments will be briefly described below.

FIG. 1 is a flow chart of the process for treating grassiness biomass growing in heavy metal-enriched contaminated soil according to the present invention;

FIG. 2 is HNO₃An infrared spectrogram of the modified biochar;

FIG. 3 is HNO₃Electron microscope Scan (SEM) of modified biochar;

FIG. 4 is the morphological distribution of Cd and Zn in biochar formed at 500 ℃;

FIG. 5 shows the results of adsorption kinetics test of the biochar on MB and KNR;

fig. 6 shows the results of isothermal adsorption tests of biochar on MB and KNR.

Detailed Description

The invention provides a treatment method for enriching heavy metal biomass, which comprises the following steps:

the pyrolysis temperature is 400-800 ℃, and the pyrolysis time is 1.5-2.5 h;

the leaching treatment comprises leaching the biochar by using a nitric acid solution with the pH value of 1-3.

The invention carries out pyrolysis on plants growing in the heavy metal contaminated soil to obtain the biochar. When the pyrolysis is carried out, the pyrolysis temperature is preferably gradually increased at a rate of 5-10 ℃/min, and more preferably 5 ℃/min. The invention calculates the pyrolysis time from the time of heating up to the pyrolysis temperature. The pyrolysis temperature is preferably 400-800 ℃, more preferably 400-500 ℃ or 500-800 ℃, more preferably 450 ℃ or 550-750 ℃, and most preferably 450 ℃ or 600-700 ℃; the pyrolysis time is preferably 1.5-2.5 h, and more preferably 2 h. In the present invention, the pyrolysis is preferably carried out while introducing nitrogen gas. The flow rate of the nitrogen is preferably 150-250 mL/min, and more preferably 200 mL/min. The pyrolysis according to the invention is preferably carried out in a pyrolysis furnace. According to the invention, nitrogen is introduced, an anaerobic environment can be created, plants growing in heavy metal contaminated soil are pyrolyzed in a high-temperature environment, and plant biomass growing in heavy metal contaminated soil is pyrolyzed into biochar by limiting the temperature, time, heating speed and nitrogen flow rate of the pyrolysis process, so that combustion treatment is not required, air pollution is avoided, and environmental risk is low. The biochar prepared by pyrolysis at 500 ℃ has the advantages of low energy consumption, high nutrient content and low heavy metal content, and has a good resource utilization prospect.

In the present invention, the plant growing in the heavy metal contaminated soil is preferably a heavy metal-enriched plant, and more preferably a hyperaccumulator plant or elephant grass.

Before the plant is pyrolyzed, the plant is washed, dried, crushed and sieved in sequence to obtain plant powder. In the present invention, the plants growing in the heavy metal contaminated soil are preferably super accumulating plants, and more preferably elephant grass. The elephant grass is preferably elephant grass stem. The particle size of the plant powder particles is preferably 50-100 meshes, and more preferably 60 meshes. According to the invention, the plants planted in the heavy metal contaminated soil for 150-200 days are preferably pyrolyzed, and more preferably for 180 days. The heavy metal of the present invention preferably comprises one or more of Cd and Zn, and more preferably a mixture of Cd and Zn. The method can especially realize the enrichment of 180d elephant grass planted in Cd and Zn composite polluted soil; the biomass of the grassiness plants adsorbed with a large amount of heavy metals is effectively recycled, and the follow-up utilization of the plants is guaranteed.

After the biochar is obtained, the invention carries out extraction treatment and separation treatment on the biochar to obtain leach liquor and modified biochar. The reagent for leaching treatment comprises a nitric acid solution with the pH value of 1-3. The pH of the nitric acid solution is preferably 1-3, more preferably 1.5-2.5, and even more preferably 2. The preparation method of the nitric acid solution with the pH value of 1-3 preferably comprises the step of mixing the nitric acid solution with the mass concentration of 10% -20% with water, and more preferably, the nitric acid solution with the mass concentration of 15% with water. The nitric acid solution with the pH value of 1-3 has an extraction effect, can extract heavy metal elements in the biochar, increases the pore diameter and functional groups such as carboxyl and hydroxyl on the surface of the biochar, enhances the adsorption capacity of the biochar, and realizes modification of the biochar, so that the modified biochar has a good adsorption effect on water pollutants.

The invention separates the leaching liquor and the modified biochar obtained by leaching treatment to respectively obtain the leaching liquor and the modified biochar. The mode of separation according to the invention preferably comprises shaking and filtration. The oscillation time is preferably 2.5-3.5 h, and is further preferably 3 h; the temperature during the oscillation is preferably 20 to 30 ℃, and more preferably 25 ℃. The filtration treatment of the present invention preferably uses a filter membrane having a pore size of 0.22 to 0.45. mu.m, and more preferably a filter membrane having a pore size of 0.45. mu.m.

After obtaining the leaching liquor, the pH value of the leaching liquor is preferably adjusted by the invention, and then the leaching liquor is separated (preferably filtered) to obtain the alkali precipitation leaching liquor. When the pH value of the leaching liquor is adjusted, the pH value of the leaching liquor is preferably adjusted to 9-12, more preferably 9.5-11.5, and even more preferably 10-11. In the present invention, potassium hydroxide or sodium hydroxide is preferably used to adjust the pH of the leach liquor, and potassium hydroxide is more preferably used. The mass concentration of the potassium hydroxide according to the present invention is preferably 35% to 45%, and more preferably 40%. The invention has no special requirements on the filtering mode, and the well-known filtering mode is adopted. According to the invention, the leaching liquor is subjected to pH regulation by using the pH regulator, an alkaline environment is provided, a large amount of heavy metals in the leaching liquor can be precipitated, then the leaching liquor after alkaline precipitation is obtained by removing the precipitate, and the leaching liquor can be used as a liquid fertilizer, so that the recovery rate of heavy metal-enriched plants is improved. The potassium hydroxide contains a large amount of K elements, and the potassium hydroxide used as a pH regulator can also supplement the K elements in the leaching liquor while precipitating heavy metals, so that the K elements with higher concentration than other nutrient elements in the original leaching separation liquid are further improved, and the potassium hydroxide can be used as a liquid K fertilizer.

The invention also provides application of the modified biochar obtained by the method in adsorbing water body pollutants. The water body pollutant of the invention preferably comprises dye, and further preferably cationic dye Methylene Blue (MB) and/or anionic dye reactive brilliant blue (KNR). The dye in the water pollution is from the industries of textile, cosmetic manufacturing or printing and the like, and can cause symptoms of vomiting, headache, dyspnea and the like. The modified biochar obtained by the method enlarges the specific surface area, increases the P-O functional groups on the surface of the biochar, and has strong adsorption capacity on water pollutants.

The invention also provides application of the alkali precipitation leaching liquor obtained by the method in preparation of liquid fertilizer. The invention utilizes potassium hydroxide to carry out alkali precipitation separation treatment on the leaching liquor, and can supplement K element in the leaching liquor while precipitating heavy metal, so that the K element with higher concentration than other nutrient elements in the leaching liquor is further improved.

In order to further illustrate the present invention, the following detailed description of the treatment method of the plant biomass rich in heavy metal provided by the present invention is made with reference to the accompanying drawings and examples, but they should not be construed as limiting the scope of the present invention.

Example 1

The elephant grass is planted in the Cd and Zn combined pollution farmland for 180 days, the average concentration of Cd and Zn in elephant grass stems is 4.08mg/kg and 155.74mg/kg respectively, and the average concentration of Cd and Zn in elephant grass leaves is 0.37mg/kg and 24.56mg/kg respectively. The concentration of Cd in the elephant grass leaves does not exceed the Chinese feed sanitation standard (1mg/kg), and the concentration of Zn is lower, and the elephant grass stems are used as raw materials to prepare the biochar.

Cleaning elephant grass stems, drying, crushing, sieving with a 60-mesh sieve, placing in a quartz boat, putting in a tube furnace, and pyrolyzing at 400 ℃ for 2h to prepare biochar. In the pyrolysis process, the nitrogen flow rate is 200mL/min, and the heating rate is 5 ℃/min, so as to obtain the biochar.

Example 2

The difference from example 1 is that the pyrolysis temperature is 500 ℃.

Example 3

The difference from example 1 is that the pyrolysis temperature is 600 ℃.

Example 4

The difference from example 1 is that the pyrolysis temperature is 700 ℃.

Example 5

The difference from example 1 is that the pyrolysis temperature is 800 ℃.

Test example 1

The yields of biochar obtained in examples 1 to 5 were measured, and the biochar obtained in examples 1 to 5 was measured using ICP-MS for a mixed acid (HNO)₃/HClO₄V/v 85: 15%) and the results are shown in table 1.

TABLE 1 yield and content of each element of biochar at different treatment temperatures

Temperature (. degree.C.)	Example 1	Example 2	Example 3	Example 4	Example 5
						Yield of	29.32％a	27.55％a	24.62％b	22.17％c	17.92％d
Cd(mg/kg)	0.64±0.01a	0.21±0.01b	0.22±0.02b	0.15±0.02c	0.14±0.01c
						Zn(mg/kg)	242.89±5.16b	247.67±4.79b	270.50±4.32a	155.25±3.15c	64.73±2.42c
K(g/kg)	28.13±1.03b	35.81±1.66a	27.84±1.19b	33.78±1.59a	29.30±0.61b
						Ca(g/kg)	2.23±0.42c	3.29±0.57ab	2.62±0.23bc	2.90±0.21bc	3.94±0.47a
Mg(g/kg)	3.18±0.22c	4.03±0.15b	3.38±0.24c	4.20±0.20b	5.00±0.12a
						Fe(g/kg)	0.07±0.00d	0.20±0.01a	0.11±0.00c	0.12±0.01c	0.16±0.01b
P(g/kg)	0.20±0.02b	0.15±0.01b	0.10±0.01c	0.16±0.02b	0.92±0.05a

Note: the yield is the quality of biochar produced after pyrolysis/the quality of grass-like stems.

As can be seen from Table 1, the biomass of the elephant grass, which grows in the heavy metal contaminated soil at 400 ℃, 500 ℃, 600 ℃, 700 ℃ and 800 ℃, can be enriched by pyrolyzing the elephant grass stem and can be converted into biochar. The pyrolysis at 400 ℃ and 500 ℃ of the invention is obviously higher than the biochar yield at other temperatures, and is respectively 29.32 percent and 27.55 percent. However, the Cd content of the biochar prepared at 400 ℃ is obviously higher than that of other biochar, and the Cd content of the biochar prepared at 500 ℃ and 600 ℃ is not obviously different but is obviously higher than that of the biochar prepared at 700 ℃ and 800 ℃. The biological carbon prepared at 600 ℃ has the highest Zn content, which is obviously higher than other biological carbon. The Zn content difference of the biochar prepared at 400 ℃ and 500 ℃ is not obvious, but is obviously higher than that of the biochar prepared at 700 ℃ and 800 ℃. The biochar prepared at 500 ℃ has the highest K and Fe contents of 35.81g/kg and 0.20g/kg respectively, and the contents of Ca, Mg and P are relatively high. The charcoal prepared at 500 ℃ has the best effect and has the advantages of low energy consumption, low heavy metal and high nutrient.

Example 6

1g of the biochar prepared in example 2 was placed in a 100mL Erlenmeyer flask, soaked with 60mL deionized water, and soaked with 15% HNO₃The pH value was adjusted to 1, shaking was carried out at 25% for 3h, and then filtration was carried out through a microporous membrane having a pore size of 0.45 μm to obtain 60mL of a leaching solution and 1g of modified biochar.

Example 7

The same as example 6, except that 15% HNO was used₃The pH value is adjusted to 2, and 60mL of leaching liquor and 1g of modified biochar are obtained.

Example 8

The same as example 6, except that 15% HNO was used₃The pH value is adjusted to 3, and 60mL of leaching liquor and 1g of modified biochar are obtained.

Comparative example 1

The same as example 6, except that pH adjustment was not used, 60mL of the leachate and 1g of modified biochar were obtained.

Test example 2

ICP-MS is utilized to measure the concentration of each element in the leaching liquor obtained in the embodiments 6-8, the extraction efficiency of different elements is calculated, and the detection results are shown in Table 2.

TABLE 2 concentration of elements and extraction efficiency of leach liquors obtained by different treatment modes

Note: the extraction yield is the concentration of the element (μ g/mL) x volume of the leach solution (mL) ÷ mass of biochar (g), and the concentration of the other elements is mg/L except that the unit of the concentration of Cd is ug/L.

As can be seen from Table 2, the heavy metal elements in the biochar can be leached by using a nitric acid solution with pH of 1-3. The extraction rate of nutrient elements is the best under the condition of pH value of 1, and the extraction rates of K, Ca, Mg, Fe and P are respectively 88.30%, 78.06%, 64.14%, 53.15% and 75.78%. The biochar is obtained by leaching treatment with a nitric acid solution with pH of 1, the content of heavy metal is lowest, the pollution risk is low, the K concentration reaches 527.00mg/L, and the nutrition is rich.

Test example 3

Fourier infrared spectroscopy is used for researching the surface functional groups of the modified biochar obtained in the examples 6-8 and the non-leached biochar, and the result is shown in figure 2. In FIG. 2, BC500-Ut, BC500-1, BC500-2 and BC500-3 represent unmodified biochar, and modified biochar prepared in example 6, example 7 and example 8, respectively.

As can be seen from FIG. 2, the HNO passed through at pH 1₃The modified biochar obtained by leaching treatment and separation treatment has richer surface functional patterns, particularly P-O, and the P-O can improve the specific capacity of the solution, so that the adsorption capacity of pollutants is increased.

Test example 4

The shapes of the modified biochar obtained in examples 6-8 and the non-leached biochar are observed by scanning an electron microscope, and the result is shown in fig. 3. BC500-Ut, BC500-1, BC500-2 and BC500-3 in FIG. 3 respectively compare with modified biochar prepared in example 1, example 6, example 7 and example 8; the meanings of BC500-Ut, BC500-1, BC500-2 and BC500-3 are the same as those below, and will not be described further.

As can be seen from FIG. 3, the unmodified biochar had a rough surface and was attached with irregular substances, which had been subjected to HNO of pH 3₃The modified biochar obtained by leaching and separation treatment has smooth surface and is subjected to HNO with pH of 2₃The modified biochar obtained by leaching and separation treatment has micropores and is subjected to HNO with pH of 1₃The modified biochar obtained by leaching and separation even has a larger mesoporous structure.

Test example 5

(1) Measuring the specific surface areas of the modified biochar obtained in examples 6-8 and comparative example 1 respectively by using a specific surface area analyzer;

(2) measuring the pH values of the leaching solutions obtained in examples 6-8 and comparative example 1 respectively by using a pH meter;

(3) using mixed acids (HNO)₃/HClO₄V/v is 85:15) digesting and detecting the total concentration of heavy metals in the modified biochar obtained in the embodiments 6-8 and the comparative example 1;

(4) and evaluating the potential environmental risks of the heavy metals in the modified biochar obtained in the embodiment 6-8 and the non-leached biochar by using a risk evaluation index (RAC).

(5) The content of heavy metals in different forms in the modified biochar obtained in examples 6-8 and comparative example 1 was detected by a BCR continuous extraction method.

(1) The results of the measurements (1) to (4) are shown in Table 3 below. (5) The results are shown in FIG. 4, where F1 is in the acid extractable state, F2 is in the reducible state, F3 is in the oxidizable state, and F4 is in the residue state of the corresponding heavy metal.

TABLE 3 HNO₃Comparison of general Properties of modified biochar

Note: BC500-Ut, BC500-1, BC500-2 and BC500-3 represent modified biochar prepared in comparative example 1, example 6, example 7 and example 8, respectively; RAC-Cd represents acid extractable state-Cd (i.e. F1 state); RAC-Zn represents acid extractable state-Zn (i.e., F1 state).

From Table 3, HNO can be seen₃The pH value of the modified biochar is reduced and is in direct proportion to the pH value of the extracting solution. Adjusting the pH value to 1, wherein the pH value of the modified charcoal is 7.12; the specific surface area of the modified biochar is adjusted to 1 and is 38.50 times that of the unmodified biochar to 66.99m²/g；HNO₃The heavy metal environmental risk of the modified grassiness biochar is reduced, Cd and Zn respectively represent Low Risk (LR) and Medium Risk (MR) in the unmodified biochar, Cd can be reduced to No Risk (NR) by adjusting the pH value to be 1 and 2, Zn can be reduced to low risk, and the risk level of the biochar can not be changed by adjusting the pH value to be 3.

FIG. 4 shows biochar by HNO₃The proportion of Cd and Zn in acid extractable state is reduced, the proportion of Cd and Zn in residue state is increased, and the lower the pH of the extracting solution is, the lower the proportion of acid extractable state isThe residue state changes inversely with pH. From BC500-Ut to BC500-1, the proportion of the Cd acid in an extractable state is changed from 9.52% to 0.86%, and the proportion of the Zn acid in an extractable state is changed from 18.11% to 2.78%; the proportion of Cd residue is changed from 22.54% to 53.35%, and the proportion of Zn residue is changed from 17.98% to 53.18%;

from BC500-Ut to BC500-2, the proportion of the Cd acid in an extractable state is changed from 9.52% to 0.93%, and the proportion of the Zn acid in an extractable state is changed from 18.11% to 8.65%; the proportion of Cd residue is changed from 22.54% to 50.36%, and the proportion of Zn residue is changed from 17.98% to 43.02%;

from BC500-Ut to BC500-3, the proportion of the Cd acid in an extractable state is changed from 9.52% to 1.35%, and the proportion of the Zn acid in an extractable state is changed from 18.11% to 13.72%; the content of Cd in the residue was changed from 22.54% to 39.84%, and the content of Zn in the residue was changed from 17.98% to 32.30%. Indicating the HNO prepared by the invention₃The environmental risk of heavy metals in the modified biochar is reduced.

Application example 1

1. Adsorption kinetics experiment: unmodified prepared in example 2 and HNO prepared in example 6, 7 and 8₃The modified biochar was used for adsorption kinetics tests of the cationic dye Methylene Blue (MB) and the anionic dye reactive brilliant blue (KNR).

The adsorption mode is as follows: mixing 50mg of biochar and 25mL of MB (700mg/L) in a centrifuge tube, and respectively oscillating for 1, 2, 8, 16, 24, 48, 72 and 96 hours at the oscillation rate of 120 r/min;

mixing 50mg of biochar and 25mLKNR (60mg/L) in a centrifuge tube, and oscillating for 1, 2, 8, 16, 24, 48, 72 and 96 hours respectively after mixing; the oscillation rate was 120 r/min.

After the shaking is finished, the supernatant is immediately filtered through a 0.45-micron membrane, the adsorption quantity of the four biochar to MB and KNR is measured by an ultraviolet spectrophotometer, and the test results are shown in figure 5 and tables 4-5.

TABLE 4 adsorption of MB at different oscillation times

TABLE 5 adsorption of MB at different oscillation times

As can be seen from tables 4-5 and FIG. 5, the adsorption amounts of the four biochar to MB and KNR show a sharp rising trend within 48h of mixed adsorption, and tend to be balanced after 48h, and the modified biochar obtained in example 6 by adjusting the pH value to 1 has better adsorption capacities to MB and KNR.

2. Adsorption isotherm experiments: unmodified prepared in example 2 and HNO prepared in example 6, 7 and 8₃The modified biochar was used for adsorption isotherm tests of the cationic dye Methylene Blue (MB) and the anionic dye reactive brilliant blue (KNR).

The adsorption mode is as follows: weighing 6 parts of 50mg of biochar, and mixing the biochar with 25mL of MB with the concentration of 100mg/L, 400mg/L, 700mg/L, 1000mg/L, 1300mg/L and 1600mg/L in a centrifuge tube in sequence for 48 h;

6 parts of 50mg biochar is weighed and mixed with 25mL of KNR with the concentration of 20mg/L, 80mg/L, 140mg/L, 200mg/L, 260mg/L and 320mg/L in a centrifuge tube for 48 hours by oscillation.

After the oscillating adsorption is completed, the supernatant is immediately filtered through a 0.45-micron membrane, the concentrations of the two dyes are measured by an ultraviolet spectrophotometer, the adsorbed dye amount is obtained according to the following formula, and the results of the adsorption isothermal test are shown in tables 6-7 and fig. 6.

Adsorbed dye amount (initial dye concentration-dye concentration at adsorption equilibrium) x solution volume

TABLE 6 MB adsorption isotherm experimental results

TABLE 7 KNR adsorption isothermal experiment results

As can be seen from tables 6-7 and FIG. 6, the adsorption amounts of the four biochar to MB and KNR show a sharp rising trend within 48h of mixed adsorption, the adsorption amounts tend to be balanced after 48h, the maximum adsorption amount of MB obtained by fitting an adsorption isothermal model is 101.13mg/g, the equation model coefficient is 100.9, and the maximum adsorption amount of MB obtained by adjusting the pH value to 1 in example 6 is 100.9 mg/g; the maximum KNR adsorption amount obtained by the fitting of the adsorption isothermal model is 13.23mg/g, the coefficient of the equation model is 12.9, and the maximum KNR adsorption amount of the modified biochar obtained by adjusting the pH value to 1 in example 6 is 12.9 mg/g.

3. Adsorption-desorption experiments

According to the results of adsorption kinetics and adsorption isotherm experiments, the modified biochar prepared in example 6 was selected and recorded as BC500-1, and adsorption-desorption repeated experiments were performed with an initial MB concentration of 800mg/L and a KNR concentration of 80mg/L, and the adsorption procedure was the same as in the adsorption experiments above. After each adsorption, desorption was carried out, and the process was repeated 5 times.

The analysis steps are as follows: the washing with deionized water and filtration were repeated to remove residual dye on the charcoal, and then 25mL KCl (0.5mol/L) was added and shaken at 120r/min for 2h at room temperature. After centrifugation, the supernatant was removed and dried and the adsorption was repeated.

The results of the repeated adsorption-desorption tests are shown in table 8, the MB adsorption amount of the biochar modified by adjusting the pH to 1 for 2-5 times can reach 87.57% -90.83% for the first time, the biochar can be recycled through adsorption-desorption, and the KNR adsorption amount is only 42.44% -51.62% for the first time.

TABLE 8 adsorption amounts upon reuse of BC500-1

As can be seen from the data in table 8, the modified charcoal obtained by adjusting the pH of example 6 to 1 has better adsorption performance on MB.

Example 9

30mL of the filtrate obtained in example 6, which had pH of 1, was placed in a 50mL centrifuge tube, the pH of the filtrate was adjusted to 9, 10, 11, and 12 with 40% KOH, and the filtrate was shaken at 25 ℃ for 3 hours and then filtered to obtain a heavy metal precipitate and a nutrient solution, and the concentrations of the elements and the residual ratios in the leaching solutions after the precipitation separation were as shown in Table 9.

TABLE 9 concentration of elements and residual ratio in leach liquor after precipitation separation step

As can be seen from the data in Table 9, when the pH value of the filtrate is adjusted to 9, the filtrate can have a low heavy metal residue rate, when the pH value is adjusted to 10, no heavy metal residue exists in the filtrate, and nutrient elements in the filtrate are high, so that the filtrate can be used as a production condition for producing high-nutrient liquid fertilizer.

The embodiments show that the method provided by the invention does not pollute the air, has low environmental risk, pyrolyzes the plant biomass growing in the heavy metal polluted soil into the biochar, can increase the pore diameter of the biochar, increases the P-O functional groups on the surface of the biochar, enhances the adsorption capacity of the biochar, precipitates a large amount of heavy metals remaining in the activated carbon in separation treatment, and improves the recycling rate.

Although the above embodiments have been described in detail, they are only a part of the embodiments of the present invention, not all of the embodiments, and other embodiments can be obtained without inventive step according to the embodiments, and all of the embodiments belong to the protection scope of the present invention.

Claims

1. A treatment method for enriching heavy metal plant biomass comprises the following steps:

the pyrolysis temperature is 400-800 ℃, and the time is 1.5-2.5 h;

2. The process according to claim 1, wherein the pyrolysis temperature is increased at a rate of 5 to 10 ℃/min.

3. The process according to claim 2, characterized in that nitrogen is introduced during the pyrolysis; the flow rate of the nitrogen is 150-250 mL/min.

4. The treatment method of claim 1, wherein the heavy metal comprises one or more of Cd and Zn.

5. The treatment method of claim 1, wherein the plant comprises a heavy metal-enriched plant.

6. The treatment method according to claim 5, wherein the heavy metal-enriched plant comprises a hyperaccumulator plant or elephant grass.

7. The treatment process according to any one of claims 1 to 6, wherein after obtaining the leach liquor, further comprising adjusting the pH of the leach liquor to 9 to 12 and separating to obtain the alkaline leach liquor.

8. The modified biochar obtained by the treatment method of any one of claims 1-7 is applied to adsorbing water body pollutants.

9. The use of claim 8, wherein the water body contaminant comprises a dye.

10. Use of the alkaline leach liquor from the treatment process of claim 7 in the preparation of liquid fertilizer.