CN113750962A

CN113750962A - Method for preparing modified biochar by co-pyrolyzing red mud and pennisetum hydridum straws and application of modified biochar

Info

Publication number: CN113750962A
Application number: CN202111068379.6A
Authority: CN
Inventors: 秦俊豪; 王希; 李媛文; 邓暮娟; 黎华寿
Original assignee: South China Agricultural University
Current assignee: South China Agricultural University
Priority date: 2021-09-13
Filing date: 2021-09-13
Publication date: 2021-12-07

Abstract

The invention discloses a method for preparing modified biochar by co-pyrolyzing red mud and pennisetum hydridum straws, which comprises the following steps: s1, drying the red mud, crushing, grinding and sieving the dried red mud to obtain red mud powder; s2, drying the harvested pennisetum hydridum straws, crushing into sections, grinding, crushing and sieving to obtain pennisetum hydridum straw powder; s3, weighing red mud powder and pennisetum hydridum straw powder according to the mass ratio of 1:3, and uniformly mixing in a container to obtain a mixture; and S4, carrying out high-temperature pyrolysis on the mixture, and cooling to obtain the modified biochar. The red mud modified biochar prepared by the invention can reduce the cost, realize resource utilization of industrial waste red mud and improve the capability of passivating heavy metals.

Description

Method for preparing modified biochar by co-pyrolyzing red mud and pennisetum hydridum straws and application of modified biochar

Technical Field

The invention relates to the technical field of biomass carbonization, in particular to a method for preparing modified biochar by co-pyrolyzing red mud and pennisetum hydridum straws and application thereof.

Background

The red mud is a high-alkalinity industrial solid waste generated in the alumina industry, has the characteristics of good particle dispersibility, large specific surface area and other porous materials, and mainly comprises iron oxide, alumina, silicon dioxide, calcium oxide and the like, according to data, most alumina production plants can produce 1-2 t of red mud every time 1t of alumina is produced, and by 2015, the alumina production capacity of China reaches nearly seven million tons, which accounts for about one half of the total production capacity of the whole world, and the red mud stockpile is huge. At present, the main disposal mode of the red mud still depends on deep pit landfill, open-air accumulation, red mud dam building and the like, not only occupies a large amount of land resources, but also seriously pollutes the surrounding environment, particularly easily causes dam break under the condition of severe climate, and seriously threatens the production and life safety of the surrounding environment and residents.

With the increasing prominence of the soil pollution problem, the heavy metal pollution of the soil becomes a hot problem of social attention at present. The long-term stacking of mine waste rocks and tailings generated by mineral product collection, processing and other activities easily enables heavy metals contained in the mine waste rocks and tailings to continuously diffuse and migrate in soil bodies under the natural effects of surface runoff, rainwater leaching, wind and the like, and meanwhile, Pb, Zn, As and associated elements Cd, Cr and Cu in the tailings generated by mining the mineral deposits enter the soil through surface water scouring and rainwater leaching and are accumulated, so that the pollution of surrounding soil and water environment is caused. The main sources of heavy metals in the soil around the mine are acid mine wastewater, dust and tailings. The soil is used as a medium for crops to live, the content or residual quantity of various pollutants in the soil and the pollution degree directly influence the quality and edible safety of the crops, and the accumulation of heavy metals in the soil can be absorbed by the negative electrode of the crops, so that potential risks are generated to the health of people through the indirect connection of a food chain. Taking a big Baoshan mining area in North Guangdong province of Guangdong province As an example, the average concentration of heavy metals As and Cd in the surrounding soil respectively reaches 218.07 and 2.453mg/kg, which are far beyond the second-level standard value of the soil environment, the content of Cd and As in farmland in the big Baoshan sewage irrigation area seriously exceeds the agricultural land soil pollution risk control standard (GB15618-2018), and the overproof percentage respectively reaches 89.5% and 69.2%; and the Cd and As contents of the overground parts of the vegetables also exceed the standards in the vegetable sanitary standard (GB 13106-1994) and the food pollutant limit (GB 2762-2017)

In recent years, due to rapid development of electronic industry, the updating speed of electronic and electric products is rapidly increased, and electronic wastes are increased day by day. Most of the past electronic garbage dismantling factories are dismantled and recycled in a production mode of a household workshop. The simple original disassembly mode and random open-air stacking and burning enable a large amount of acid liquor and residues to be directly discharged and permeate into local water and soil environments, and the local environments are seriously polluted. Taking the Qingyuan of Guangdong province As an example, the contents of a plurality of heavy metal elements in the surface soil of farmlands near the electronic waste dismantling plants of the stone corner town and the Longtang town show different degrees of enrichment, one or more heavy metals in a surface soil sample of 72.7 percent exceed the environmental quality evaluation standard of the producing area of the edible agricultural products, and the pollution is mainly Cu, Cd, Pb and Zn, wherein the pollution proportion of Cd is the highest, the average value of the potential ecological hazard indexes of As is in a very slight hazard state, Cd is in a very strong hazard state, and the potential ecological hazard indexes of 60 percent are distributed in a range of more than medium hazard.

At present, the domestic and foreign methods for treating the heavy metal pollution of soil mainly comprise three methods: physical repair, chemical repair, and biological repair; the passivation repair is an important method in chemical repair, and has the advantages of economy, quickness, high efficiency and the like. The principle of passivation restoration is that heavy metals in soil are adsorbed, precipitated, complexed, oxidized and reduced by applying a passivating agent, so that the biological effectiveness and the mobility of the heavy metals are reduced, and the restoration purpose is achieved. The biochar is a high-carbon-content and highly aromatic solid substance generated by high-temperature pyrolysis of biomass under the condition of limited oxygen or oxygen deficiency, has physicochemical properties of large specific surface area, rich functional groups, high pH value and the like, and is a passivation material with low preparation cost, strong effect stability, wide raw material source and obvious repair effect. Although the existing biochar has achieved certain effect in the aspect of environmental remediation, the biochar still has some defects that the adsorption capacity is small. Therefore, physicochemical properties of the biochar are improved by methods such as physical chemistry and the like at present, the modification can increase the pore volume of the biochar and the types and the number of surface functional groups, and the modified biochar has stronger environmental benefits in the aspects of heavy metal pollution in-situ remediation and the like.

However, in the current research reports, the modified biochar is usually modified by adding a pure reagent, so that the cost is high; the characteristic of the red mud is directly utilized as an adsorbent, and the risk of secondary pollution exists.

Disclosure of Invention

The invention aims to provide a method for preparing modified biochar by co-pyrolyzing red mud and pennisetum hydridum straws, so as to solve the problems that the existing modified biochar is high in production cost and the red mud of industrial waste is recycled.

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

a method for preparing modified biochar by co-pyrolysis of red mud and pennisetum hydridum straws comprises the following steps:

s1, drying the red mud, crushing, grinding and sieving the dried red mud to obtain red mud powder;

s2, drying the harvested pennisetum hydridum straws, crushing into sections, grinding, crushing and sieving to obtain pennisetum hydridum straw powder;

s3, weighing red mud powder and pennisetum hydridum straw powder according to the mass ratio of 1:3, and uniformly mixing in a container to obtain a mixture;

and S4, carrying out high-temperature pyrolysis on the mixture, and cooling to obtain the modified biochar.

Further, the sieving in the step S1 is a 0.075mm sieve.

Further, the sieving in the step S2 is a 0.25mm sieve.

Further, the container is a pyrolysis box, the pyrolysis box is placed in a muffle furnace, nitrogen is introduced for protection, the temperature is raised to 700 ℃ for pyrolysis for 2 hours, and the modified biochar is prepared after cooling.

The invention also aims to provide application of the modified biochar prepared by the method in remediation of heavy metal contaminated soil.

The invention further aims to provide application of the modified biochar prepared by the method in crop planting.

Preferably, the crop planting comprises water spinach.

Compared with the prior art, the invention has the following effects:

according to the invention, the novel passivation material, namely the red mud modified biochar, is prepared by comprehensively utilizing the pennisetum hydridum straw and red mud mixing and co-pyrolysis manner, so that the cost can be reduced, the problem of resource utilization of industrial waste red mud is solved, the capacity of passivating heavy metals is improved, especially the pH value of rhizosphere soil can be obviously improved, the effective state content of heavy metals As and Cd in the rhizosphere soil is reduced, the content of heavy metals As and Cd on the upper part of a water spinach ground is obviously reduced, and the resource utilization rate is high.

Drawings

FIG. 1 is a flow chart of a method for preparing modified charcoal by co-pyrolyzing red mud and pennisetum hydridum straws provided by the invention;

FIG. 2 is a schematic representation of the dry weight of the above-ground parts and the underground parts of water spinach under different treatments according to an embodiment of the present invention;

fig. 3 is an XRD schematic diagram of pennisetum hydridum biochar and two red mud modified biochar provided by the embodiment of the present invention;

in the above figures, CK represents a blank group, BIOC represents a carbonized biochar control group containing 2.5% pennisetum hydridum in soil, BIOA represents modified biochar containing 2.5% of iron-rich red mud 1, and BIOS represents modified biochar containing 2.5% of calcium-rich red mud 2.

Detailed Description

The invention is described in further detail below with reference to the following figures and embodiments:

as shown in fig. 1, a method for preparing modified biochar by co-pyrolyzing red mud and pennisetum hydridum straws comprises the following steps:

Example one

(I) test materials

The soil to be tested 1 is taken from farmland plough layer soil polluted by the mine of Dabaoshan county, Wengyuan, Shaoguan city, Guangdong province and is marked as mine polluted soil; the soil to be tested 2 is collected from electronic garbage dismantling of Longtang town in Qingyuan city, Guangdong province, and the farmland plough layer soil with peripheral pollution is taken out and recorded as electronic dismantling soil. Removing large impurities on the surface of the soil, then air-drying, mashing and mixing uniformly for later use. A part of soil is respectively sieved by a 2mm sieve, the pH, total nitrogen, total phosphorus, available phosphorus, alkaline hydrolysis nitrogen and organic matters of the two types of soil to be tested are analyzed by adopting a soil agro-chemical conventional analysis method, and specific results are shown in Table 1. Then, part of the soil was sieved through a 0.15mm sieve, and the background values of the total As and Cd contents in the soil were determined, and the specific results are shown in Table 2. The test soil remaining for the potting experiment was screened 5mm for future use.

TABLE 1 physicochemical Properties of the soil tested

TABLE 2 heavy Metal content (mg/kg) of the soil tested

The red mud to be tested selects two red mud types generated by different production modes in the alumina industry, and is the main two red mud types generated in the alumina industry. The red mud 1 to be tested is red mud generated by producing alumina by a Bayer process by using Australian ore as a main raw material, and the iron content of the red mud is extremely high; the red mud 2 to be tested is the red mud generated by producing alumina by a sintering method, and the red mud has higher calcium content. Drying the red mud, grinding into powder, and sieving with a 0.075mm sieve for later use.

Pennisetum hydridum for preparing biochar and modified biochar materials is collected from agricultural practice base of southern China agricultural university in Guangdong province, harvested pennisetum hydridum straws are dried in the sun and smashed into sections, then ground and smashed by a machine, and sieved by a 0.25mm sieve for later use.

(II) Experimental method

Weighing 150g of crushed and sieved pennisetum hydridum stalks in a pyrolysis box, respectively adding 50g of prepared red mud 1 and red mud 2 to be tested, fully and uniformly mixing, meanwhile, weighing 200g of pennisetum hydridum stalk powder in the pyrolysis box, putting the mixture in a muffle furnace, and introducing high-purity N₂The control time is 30min (the temperature program of the muffle furnace is 10 ℃/min); setting the temperature in the muffle furnace to 700 ℃, controlling the time to be 2 hours at 700 ℃, and cooling to obtain the biochar sample. Recording biochar prepared by taking pennisetum hydridum as a raw material as BIOC; the modified charcoal prepared by using the red mud 1 and the pennisetum hydridum as raw materials is marked as BIOA, and the modified charcoal prepared by using the red mud 2 and the pennisetum hydridum as raw materials is marked as BIOS.

The experimental design treatment is as follows: a blank group (CK), a control group (2.5% biochar BIOC) and an experimental group (2.5% modified carbon BIOA and BIOS) are set by taking the test soil 1 (mine contaminated soil) as background soil. Wherein no reagent is added to the soil in blank group (CK); the soil in the control group (2.5% biochar-BIOC) contains 2.5% biochar; the experimental groups (2.5% modified carbon) were divided into two groups, one containing 2.5% BIOA in soil and the other containing 2.5% BIOS in soil, each of which was set up in triplicate. Referring to the above method, a blank group (CK), a control group (2.5% biochar-BIOC), and an experimental group (2.5% modified carbon-BIOA, BIOS) were set with the test soil 2 (electronic disassembled soil) as background soil. 1.5kg of prepared soil of each group is respectively put into plastic flowerpots (with the length of 20cm and the width of 13.5cm and the height of 5cm), and then water spinach with uniform growth vigor is cut, and 2 plants are cut in each flowerpot. The experimental time is from 18 days 11 and 2021 and 8 days 1, 2020, tap water is used for ensuring sufficient water supply during the experimental period, and 2.5g of compound fertilizer is applied after one month of permanent planting.

After harvesting the water spinach, separating the overground part and the underground part, washing the water spinach with tap water, washing the water spinach twice with deionized water, drying the water spinach by using absorbent paper, putting a fresh plant sample into an envelope, marking the envelope, putting the envelope into an oven at 105 ℃ for deactivation of enzymes for 30min, setting the oven at 45 ℃, drying the sample to constant weight, and recording the dry weight of the sample. The plant samples were then ground in a mortar and filled into sealed bags for use.

And (3) measuring the pH value of rhizosphere soil:

placing rhizosphere soil in a small beaker at the initial stage of swamp cabbage permanent planting, adding deionized water (soil: water: 1: 5), stirring uniformly, standing until water and soil are layered obviously, placing an SX-620 pen type pH meter into supernatant liquor to measure pH, recording data, and pouring the water and soil back into the flowerpot after measuring. The rhizosphere soil pH was again measured immediately before the water spinach harvest, as described above (soil: water: 1: 5).

Measuring the total amount of As and Cd on the middle and upper parts and the underground parts of the water spinach:

accurately weighing about 0.20-0.25g of dry samples of aerial parts and underground parts of water spinach, placing into a polytetrafluoroethylene digestion tube, simultaneously setting reagent air and national rice standard substance GBW (E)100349 for quality control, and adding 10mL of high-grade pure HNO₃After the pre-digestion is finished, closing the cover, placing the cover in a microwave digestion instrument for digestion, taking out the microwave digestion instrument after the digestion is finished, opening the cover in a fume hood, removing the acid until the height of the liquid level is about 1-2cm, taking out the microwave digestion instrument, and cooling to room temperature. Pouring the cooled digestion solution into a marked 25mL volumetric flask, then using ultrapure water to perform constant volume treatment to 25mL, and filtering the solution to a marked small white bottle to be detected. Measuring the concentrations of As and Cd in the diluent by ICP-MS, and calculating the content (mg. kg) of As and Cd in each part of the water spinach^-1)。

Determination of effective states of As and Cd in rhizosphere soil:

weighing 5.0g of naturally air-dried rhizosphere soil into a 50mL centrifuge tube with a cover, adding 25mL of 0.1mol/L calcium chloride solution, covering, shaking uniformly, placing in a shaking table, shaking at 250rpm for one hour, and thenFiltering with qualitative filter paper to obtain a white bottle, and filtering with 0.22 μm microporous membrane. Measuring the concentration of As and Cd in the diluent by ICP-MS, and calculating the effective state content (mg. kg) of rhizosphere soil^-1)。

The data obtained from the above tests were collated with Excel 2016, subjected to one-way anova by SPSS22.0, and plotted with Excel 2016.

(III) analysis of results

1. Rhizosphere soil pH analysis under different treatments

As can be seen from Table 3, the pH difference of the rhizosphere soil in different treatment groups is significant (p is less than 0.05) no matter the soil is polluted mine soil or electronic disassembled soil, and the soil pH of the control group and the experimental group is significantly higher than that of the blank group. Wherein the pH of the BIOS rhizosphere soil is highest, and the pH of the CK rhizosphere soil is lowest. Therefore, the pH value of the soil can be obviously improved by adding the biochar and the red mud modified biochar, and the pH value of the soil is obviously improved by the red mud modified biochar.

TABLE 3 analysis of test soil pH under different treatments

2 analysis of the dry weight of the overground part and the underground part of the water spinach under different treatments

As can be seen from FIG. 2, the difference between the dry weights of the underground part and the underground part of the swamp cabbage in the experimental group of BIOS and BIOA treatment and the control group of BIOC and the blank group of CK is not significant (p is greater than 0.05). However, analysis shows that the water spinach dry weight of the control group and the experimental group is obviously higher than that of the blank group, and the dry weight of the experimental group is slightly higher than that of the control group.

3. Analysis of As and Cd content in the upper part and the lower part of the water spinach under different treatments

As content analysis of the water spinach overground part and the underground part is shown in Table 4, the As content of the water spinach overground part in the experimental group in the mine polluted soil is remarkably lower than that of the blank group and the control group (p is less than 0.05), but the difference between the control group and the blank group is not remarkable (p is more than 0.05). Further analysis shows that the content of As in the underground parts of the swamp cabbage in the control group and the swamp cabbage in the experimental group is obviously lower than that in the blank group (p <0.05), and the content of As in the BIOS treatment in the experimental group is the lowest. In the electronic dismantling soil, the content of As at the upper part of the swamp cabbage of the experimental group is obviously lower than that of the control group and the blank group (p is less than 0.05), but the difference between the treatment of the BIOA and the treatment of the BIOS of the experimental group is not obvious (p is more than 0.05). The content of As in the lower part of the water spinach shows a trend that: BIOS < BIOA < BIOC < CK, and the difference is significant (p < 0.05).

Cd content analysis of the swamp cabbage overground part and the underground part is shown in Table 4, and the Cd content of the swamp cabbage overground part in the experimental group in the mine polluted soil is remarkably lower than that of the blank group (p is less than 0.05), but the Cd content is not remarkably different from that of the control group (p is more than 0.05). The content of Cd in the lower part of the cabbage processed by the BIOS in the experimental group is the lowest and is obviously lower than that of the processing such as BIOA, BIOC, CK and the like (p is less than 0.05). In the electronic dismantling soil, the Cd contents of the overground part and the underground part of the cabbage processed by the experimental group BIOS and BIOA are both obviously lower than those of the control group and the blank group (p is less than 0.05).

In conclusion, the two types of red mud modified biochar BIOS and BIOA can obviously reduce the As and Cd contents of the overground part and the underground part of the Chinese cabbage in the mine polluted soil and the electronic disassembled soil.

TABLE 4 analysis of As and Cd content in the above and under parts of water spinach treated differently

4. Analysis of content of As and Cd in effective state of rhizosphere soil under different treatments

As shown in Table 5, the content of As and Cd in the effective state of the rhizosphere soil is reduced by 57.3%, 80.0% and 81.3% on average and the content of Cd in the effective state is reduced by 24.3%, 56.8% and 94.6% on average in the mine polluted soil under the treatment of BIOC, BIOA and BIOS. The content of the available As and the content of the available Cd in the experimental group and the control group are both obviously lower than that of the blank group CK (p is less than 0.05). In the electronic disassembled soil, the content of effective As of rhizosphere soil is reduced by 54.2%, 87.5% and 65.6% on average under the treatment of BIOC, BIOA and BIOS, and the content of effective Cd is reduced by 29.5%, 88.5% and 38.5% on average. The presenting trends are as follows: BIOS < BIOA < BIOC < CK, and the difference is significant (p < 0.05).

TABLE 5 analysis of As and Cd contents in soil in effective states under different treatments

5. XRD pattern analysis of pennisetum hydridum biochar and two red mud modified biochar

As can be seen from XRD (X-ray diffraction) patterns of the pennisetum hydridum biochar and the two red mud modified biochar, compared with the pennisetum hydridum biochar, the two red mud modified biochar both show richer material compositions, wherein BIOA is rich in iron, and BIOS is rich in calcium.

From the above, it can be seen that:

(1) the red mud modified biochar can obviously reduce the contents of heavy metals As and Cd in the water spinach in the soil for disassembling mine pollution and electronic garbage, and can not obviously influence the growth of the water spinach.

(2) The application of the red mud modified charcoal can obviously improve the pH value of rhizosphere soil, and the improvement effect of the red mud modified charcoal BIOS with higher calcium content is most obvious; the same red mud modified biochar has similar pH improvement effects on different soils.

(3) The red mud modified biochar can obviously reduce the effective state contents of heavy metals As and Cd in rhizosphere soil in mine pollution and electronic waste dismantling pollution. In the mine polluted soil, the content of the effective As of the rhizosphere soil is reduced by 57.3%, 80.0% and 81.3% on average under the treatment of BIOC, BIOA and BIOS, and the content of the effective Cd is reduced by 24.3%, 56.8% and 94.6% on average. In the electronic disassembled soil, the content of effective As of rhizosphere soil is reduced by 54.2%, 87.5% and 65.6% on average under the treatment of BIOC, BIOA and BIOS, and the content of effective Cd is reduced by 29.5%, 88.5% and 38.5% on average.

(4) Compared with the content of effective As and Cd in rhizosphere soil in mine polluted soil and electronic disassembled soil, the red mud modified biochar has better effect of reducing the effective As and Cd in the rhizosphere soil in the mine polluted soil, wherein the effect of BIOS is better than that of BIOA. In the electronic disassembled soil, compared with BIOS treatment, BIOA has better effect of reducing the effective As and Cd in the rhizosphere soil.

The foregoing is merely an example of the present invention and common general knowledge in the art of designing and/or characterizing particular aspects and/or features is not described in any greater detail herein. It should be noted that, for those skilled in the art, without departing from the technical solution of the present invention, several variations and modifications can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicability of the patent. The scope of the claims of the present application shall be determined by the contents of the claims, and the description of the embodiments and the like in the specification shall be used to explain the contents of the claims.

Claims

1. a method for preparing modified biochar by co-pyrolysis of red mud and bamboo straw straw, is characterized in that, comprises:

S1, drying the red mud, the dried red mud is crushed, ground and sieved to obtain red mud powder;

S2, drying the harvested bamboo grass straws in the sun, smashing them into knots, then grinding, crushing, and sieving to obtain the royal bamboo grass straw powder;

S3, take by weighing the red mud powder and the royal bamboo grass straw powder in a ratio of 1:3 by mass ratio, and mix them evenly in the container to obtain a mixture;

S4, the mixture is pyrolyzed at high temperature, and the modified biochar is obtained after cooling.

2 . The method for preparing modified biochar by co-pyrolysis of red mud and bamboo straw according to claim 1 , wherein the sieving in the step S1 is to pass a 0.075mm sieve. 3 .

3. The method for preparing modified biochar by co-pyrolysis of red mud and bamboo straw straw according to claim 1, wherein the sieving in the step S2 is to pass a 0.25mm sieve.

4. the method for preparing modified biochar by co-pyrolysis of a kind of red mud and bamboo straw straw according to claim 1, is characterized in that: described container is a pyrolysis box, and the pyrolysis box is put into a muffle furnace and Introduce nitrogen protection, then heat up to 700 °C for pyrolysis for 2 h, and cool to obtain modified biochar.

5. Application of the modified biochar obtained by the method according to any one of claims 1-4 in the remediation of heavy metal contaminated soil.

6. Application of the modified biochar obtained by the method according to any one of claims 1-4 in crop planting.

7. The application according to claim 6, wherein the crop planting comprises water spinach.