CN112619600A

CN112619600A - Method for preparing modified biochar by utilizing plant wastes and application

Info

Publication number: CN112619600A
Application number: CN202011210668.0A
Authority: CN
Inventors: 何超; 张悦康; 黄伟明; 仇荣亮; 汤叶涛
Original assignee: Sun Yat Sen University
Current assignee: Sun Yat Sen University
Priority date: 2020-11-03
Filing date: 2020-11-03
Publication date: 2021-04-09

Abstract

The invention discloses a method for preparing modified biochar by utilizing plant wastes and application thereof. Compared with other carbon-based adsorbents of the same type, the modified charcoal prepared by the invention has good adsorption performance on phosphate; the technology has the characteristics of low energy consumption, simple operation and short treatment period in the treatment and resource utilization of the plant wastes, and can fully realize the aims of reduction, harmlessness and resource utilization of the biomass solid wastes.

Description

Method for preparing modified biochar by utilizing plant wastes and application

Technical Field

The invention relates to the technical field of phosphate adsorption by using biochar, and particularly relates to a method for preparing modified biochar by using plant wastes and application of the modified biochar.

Background

With the increase of the production activities of human industry and agriculture, a large amount of nutrient elements in closed or semi-closed water bodies such as lakes, reservoirs, gulfs and the like are enriched, autotrophic organisms are promoted to grow vigorously, algae such as blue algae, red algae and the like can be rapidly propagated, the growth period is shortened, and therefore water eutrophication is another outstanding problem in China at present. Algae and other plankton are decomposed by aerobic microorganisms after death, and dissolved oxygen in water is continuously consumed, or the algae and other plankton are decomposed by anaerobic microorganisms, and gases such as hydrogen sulfide are continuously generated, so that the water quality is deteriorated from two aspects, and a large amount of fishes and other aquatic organisms are killed. During the decay process of algae and other plankton residues, a large amount of nutrients such as nitrogen, phosphorus and the like are released into human water for the utilization of new-generation organisms such as algae and the like. Therefore, the eutrophic water body is difficult to self-purify and recover to a normal state even if the source of external nutrient substances is cut off.

Since phosphorus is an essential element for all organisms as an important cellular component and is difficult to replace by other elements, phosphate rock is a non-renewable resource as the most important source of phosphorus. The annual production of phosphate rock worldwide increases, and it is predicted that the peak of production of phosphorus resources will occur in 2035 years, after which the phosphorus resources will be in a state of shortage. On one hand, the shortage of phosphorus resources, non-regeneration and difficult replacement are realized, and on the other hand, the continuous consumption of phosphorus, serious phosphorus resource loss and water pollution are realized, which contradict that the phosphorus resources in natural water and wastewater are required to be effectively recycled. Commonly used phosphate removal methods include biological, chemical, and adsorption methods. The removal efficiency of the biological method is low, the mechanism is complex, and the process is not easy to control; although the chemical method has high removal rate, chemical reagents need to be added, so that the treatment cost is increased, and secondary pollution is possibly caused; the adsorption method for removing phosphorus has high selectivity and cyclicity, can make up for the defects of the traditional physical, chemical and biological methods to a certain extent, and is proved to be an efficient and feasible agricultural non-point source pollution control technology. The biochar is used as a main product of pyrolysis, has a structure with high surface porosity, a large specific surface area, a large number of oxygen-containing functional groups, graphite and the like, can obtain a large additional value by further processing, and is widely used for adsorbing various pollutants to treat polluted wastewater and repair polluted soil at present.

CN110756166A discloses a corncob-loaded magnesium-modified adsorbing material and a preparation method and application thereof, but the adsorbing effect on P is low.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a method for preparing modified biochar by utilizing plant wastes and application thereof.

The first purpose of the invention is to provide a method for preparing modified biochar by utilizing plant wastes.

The second purpose of the invention is to provide the modified biochar prepared by any one of the methods.

The third purpose of the invention is to provide the application of the modified biochar in adsorbing phosphate.

According to the research, the residue ramie leaves of the soil heavy metal polluted phytoremediation harvest are used as a raw material, the ramie leaves are modified by divalent magnesium ions and subjected to Mg loading treatment to prepare a high-performance phosphate adsorbent, the law that modified carbon adsorbs phosphate in an aqueous solution is explored, and the modified biochar is further used for efficiently recovering nitrogen and phosphorus in sludge hydrothermal solution, so that a high-quality organic fertilizer product is prepared. Compared with other carbon-based adsorbents of the same type, the modified biochar prepared by the invention has great advantages in adsorbing phosphate, and because the sludge contains a large amount of phosphorus, nitrogen and phosphorus need to be separated from a solid phase in the process of upgrading the sludge as a solid fuel; the waste hydrothermal solution is rich in nitrogen and phosphorus, and the screened modified biochar is used for recycling nitrogen and phosphorus to prepare a high-quality organic fertilizer product, so that high-value utilization of agricultural wastes and sludge is realized.

In order to achieve the purpose, the invention is realized by the following technical scheme:

the invention claims a method for preparing modified biochar by utilizing plant wastes, which comprises the steps of fully mixing and infiltrating plant dry powder, magnesium salt and water, drying at low temperature, fully grinding, and then carrying out pyrolysis reaction in a nitrogen atmosphere to obtain the modified biochar.

Preferably, the plant dry powder is prepared by cleaning, drying, crushing, sieving and drying the plant to constant weight.

More preferably, the mesh number of the sieve is 50-100 meshes; the drying temperature is 60-105 ℃.

Further preferably, the mesh number of the sieve is 80 meshes; the temperature for drying was 65 ℃.

Preferably, the plant is ramie leaves.

Preferably, the mass ratio of the magnesium element in the magnesium salt to the plant powder is 0.12-0.96: 1.

more preferably, the mass ratio of the magnesium element in the magnesium salt to the plant powder is 0.48: 1.

preferably, the thorough mixing is: continuously oscillating for 12-24 h at the temperature of 25 ℃ and the rpm of 160; then stirring at 100-120 rpm and 60-80 ℃.

More preferably, the thorough mixing is: continuously oscillating for 24 hours at the temperature of 25 ℃ and the rpm of 160; then, the mixture was stirred at 120rpm and 80 ℃.

Preferably, the mixture is dried and then crushed by a sieve of 0.2-0.5 mm.

More preferably, after air drying, it is crushed through a 0.5mm sieve.

Preferably, the pyrolysis reaction conditions are that the reaction temperature is 300-600 ℃, the reaction time is 0.5-4 h, and drying is carried out at 60-80 ℃.

More preferably, the pyrolysis reaction is carried out at a reaction temperature of 500 ℃ for 2h and at a temperature of 65 ℃.

The modified biochar prepared by any one of the methods also belongs to the protection scope of the invention.

The invention further claims the application of the modified biochar in adsorbing phosphate.

Preferably, the modified biochar is fully mixed with a sample to be adsorbed in an aqueous solution.

More preferably, the modified biochar is fully mixed with a sample to be adsorbed in an aqueous solution, and Cl is reduced as much as possible^-、NO^3-、SO₄ ^2-The concentration of (c).

Preferably, the modified biochar and a sample to be adsorbed are fully mixed in an aqueous solution, and the initial pH is adjusted to be 4.5 respectively.

Preferably, the modified biochar and a sample to be adsorbed are fully mixed in an aqueous solution, and the full mixing is performed by continuously oscillating at 120-160 rpm for 12-24 h at 25 ℃.

More preferably, the modified biochar and the sample to be adsorbed are fully mixed in the water solution, and the full mixing is continuously shaking at 160rpm for 24h at 25 ℃.

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

the invention finds that the modified carbon synthesized by a biomass impregnation-pyrolysis method has a great potential for adsorbing phosphate in a solution. Mg (magnesium)²⁺The introduction of the method greatly improves the adsorption capacity of the biochar, and the adsorption capacity is not Mg²⁺182.5 times of the modified biochar; with modification of Mg in the carbon²⁺The content is increased, the carbonization degree is increased, and the hydrophilicity and the polarity are continuously enhanced; supported Mg²⁺Mainly in the form of MgO crystals and a small amount of Mg (OH)₂In the form of and in the amount of Mg²⁺The content is in direct proportion; mg (magnesium)²⁺The introduction of the method improves the surface pore structure of the biochar, and the pore diameter and the pore volume are increased. Meanwhile, the method can also utilize pH and coexisting anions to correspondingly adjust, is suitable for the resource treatment of the ramie leaves, has the characteristics of low energy consumption, simple operation and short treatment period in the treatment and resource utilization of plant wastes, and can fully realize the aims of reduction, harmlessness and resource utilization of solid wastes.

Drawings

FIG. 1 is a graph showing the effect of solution pH on P adsorption in an example of the present invention.

FIG. 2 is a graph showing the effect of the coexistence of anions on P adsorption of modified carbon in comparative examples of the present invention.

Detailed Description

The invention is described in further detail below with reference to the drawings and specific examples, which are provided for illustration only and are not intended to limit the scope of the invention. The test methods used in the following examples are all conventional methods unless otherwise specified; the materials, reagents and the like used are, unless otherwise specified, commercially available reagents and materials.

Example 1 modified biochar with phosphate adsorbent prepared from Ramie leaves, residue of agricultural waste

Washing, drying and crushing the collected residue ramie leaves, sieving the powder by a 80-mesh sieve, and drying the powder to constant weight at 65 ℃ to obtain powder, wherein a magnesium chloride solution and the ramie leaf powder are mixed, and the mass ratio of magnesium ions to the ramie leaf powder is 0.12: placing the mixed solution in a gas bath constant-temperature oscillation box, continuously oscillating at 160rpm for 24h at 25 ℃, then steaming the solution to be nearly sticky under the conditions of 120rpm of a magnetic stirrer and 80 ℃, transferring the solution to a blast drying box, drying overnight at 105 ℃, taking out, crushing the solution by a high-speed multifunctional crusher for 2min, sieving the crushed solution by a 0.5mm sieve, finally placing the crushed solution in an electric heating tube furnace for pyrolysis, and carrying out pyrolysis reaction under the nitrogen environment, wherein the pyrolysis reaction conditions are that the reaction temperature is 500 ℃, the reaction time is 2h, and drying is carried out at 65 ℃ to obtain the modified biochar.

Example 2 modified biochar with phosphate adsorbent prepared from Ramie leaves, residue of agricultural waste

Washing, drying and crushing the collected residue ramie leaves, sieving the powder by a 80-mesh sieve, and drying the powder to constant weight at 65 ℃ to obtain powder, wherein a magnesium chloride solution and the ramie leaf powder are mixed, and the mass ratio of magnesium ions to the ramie leaf powder is 0.24: placing the mixed solution in a gas bath constant-temperature oscillation box, continuously oscillating at 160rpm for 24h at 25 ℃, then steaming the solution to be nearly sticky under the conditions of 120rpm of a magnetic stirrer and 80 ℃, transferring the solution to a blast drying box, drying overnight at 105 ℃, taking out, crushing the solution by a high-speed multifunctional crusher for 2min, sieving the crushed solution by a 0.5mm sieve, finally placing the crushed solution in an electric heating tube furnace for pyrolysis, and carrying out pyrolysis reaction under the nitrogen environment, wherein the pyrolysis reaction conditions are that the reaction temperature is 500 ℃, the reaction time is 2h, and drying is carried out at 65 ℃ to obtain the modified biochar.

Example 3 modified biochar with phosphate adsorbent prepared from Ramie leaves, residue of agricultural waste

Washing, drying and crushing the collected residue ramie leaves, sieving the powder by a 80-mesh sieve, and drying the powder to constant weight at 65 ℃ to obtain powder, wherein a magnesium chloride solution and the ramie leaf powder are mixed, and the mass ratio of magnesium ions to the ramie leaf powder is 0.48: placing the mixed solution in a gas bath constant-temperature oscillation box, continuously oscillating at 160rpm for 24h at 25 ℃, then steaming the solution to be nearly sticky under the conditions of 120rpm of a magnetic stirrer and 80 ℃, transferring the solution to a blast drying box, drying overnight at 105 ℃, taking out, crushing the solution by a high-speed multifunctional crusher for 2min, sieving the crushed solution by a 0.5mm sieve, finally placing the crushed solution in an electric heating tube furnace for pyrolysis, and carrying out pyrolysis reaction under the nitrogen environment, wherein the pyrolysis reaction conditions are that the reaction temperature is 500 ℃, the reaction time is 2h, and drying is carried out at 65 ℃ to obtain the modified biochar.

Example 4 modified biochar with phosphate adsorbent prepared from Ramie leaves, residue of agricultural waste

Washing, drying and crushing the collected residue ramie leaves, sieving the powder by a 80-mesh sieve, and drying the powder to constant weight at 65 ℃ to obtain powder, wherein a magnesium chloride solution and the ramie leaf powder are mixed, and the mass ratio of magnesium ions to the ramie leaf powder is 0.72: placing the mixed solution in a gas bath constant-temperature oscillation box, continuously oscillating at 160rpm for 24h at 25 ℃, then steaming the solution to be nearly sticky under the conditions of 120rpm of a magnetic stirrer and 80 ℃, transferring the solution to a blast drying box, drying overnight at 105 ℃, taking out, crushing the solution by a high-speed multifunctional crusher for 2min, sieving the crushed solution by a 0.5mm sieve, finally placing the crushed solution in an electric heating tube furnace for pyrolysis, and carrying out pyrolysis reaction under the nitrogen environment, wherein the pyrolysis reaction conditions are that the reaction temperature is 500 ℃, the reaction time is 2h, and drying is carried out at 65 ℃ to obtain the modified biochar.

Example 5 modified biochar with phosphate adsorbent prepared from Ramie leaves, residue of agricultural waste

Washing, drying and crushing the collected residue ramie leaves, sieving the powder by a 80-mesh sieve, and drying the powder to constant weight at 65 ℃ to obtain powder, wherein a magnesium chloride solution and the ramie leaf powder are mixed, and the mass ratio of magnesium ions to the ramie leaf powder is 0.96: placing the mixed solution in a gas bath constant-temperature oscillation box, continuously oscillating at 160rpm for 24h at 25 ℃, then steaming the solution to be nearly sticky under the conditions of 120rpm of a magnetic stirrer and 80 ℃, transferring the solution to a blast drying box, drying overnight at 105 ℃, taking out, crushing the solution by a high-speed multifunctional crusher for 2min, sieving the crushed solution by a 0.5mm sieve, finally placing the crushed solution in an electric heating tube furnace for pyrolysis, and carrying out pyrolysis reaction under the nitrogen environment, wherein the pyrolysis reaction conditions are that the reaction temperature is 500 ℃, the reaction time is 2h, and drying is carried out at 65 ℃ to obtain the modified biochar.

Comparative example 1

Cleaning, drying and crushing the collected residue ramie leaves, sieving the residue ramie leaves with a 80-mesh sieve, drying the residue ramie leaves at 65 ℃ to constant weight to prepare powder, mixing deionized water with the ramie leaf powder, placing the mixed solution in a gas bath constant-temperature oscillation box, continuously oscillating the mixed solution at the temperature of 25 ℃ for 24 hours at 160rpm, then steaming the solution to be nearly sticky under the conditions of a magnetic stirrer at the temperature of 120rpm and 80 ℃, transferring the solution to a blast drying box, drying the dried solution overnight at 105 ℃, taking the dried solution out, crushing the crushed solution for 2min by a high-speed multifunctional crusher, sieving the crushed solution by a 0.5mm sieve, finally placing the crushed solution in an electric heating tubular furnace for pyrolysis, and carrying out pyrolysis reaction under the nitrogen environment, wherein the conditions of the pyrolysis reaction are that the reaction temperature is 500 ℃, the reaction time is 2 hours, and drying the crushed solution.

Example 6 adsorption of phosphate by modified biochar

First, experiment method

30mL of 100mg of PL were measured out^-1Phosphoric acid salt (KH)₂PO₄) The solution was put in 150mL Erlenmeyer flasks, 1M HCl, 3M HCl, 1M NaOH, 3M NaOH were used as pH adjusting agents to adjust the initial pH to 4.5, 0.03g of the modified carbons prepared in examples 1 to 5 and comparative example 1 was added to each Erlenmeyer flask, the mixture was placed in a gas bath constant temperature shaking box, continuously shaken at 160rpm for 24 hours at 25 ℃ and vacuum filtered through a 0.45 μ M filter membrane to determine the residual phosphate concentration in the liquid.

Second, experimental results

The results are shown in table 1, and the adsorption amount of phosphate to the modified biochar is increased with the increase of the mass ratio of magnesium to biomass, and when the mass ratio of magnesium ions to biomass reaches 0.48: 1, the adsorption capacity reaches the maximum value, and the adsorption capacity of the modified biochar to phosphate is 63.88mg of Pg^-1The adsorption amount is not Mg²⁺182.5 times (63.88 ÷ 0.35 ═ 182.5) times as much biochar as modified; as the magnesium to biomass mass ratio continues to increase, the amount of adsorption also decreases because the Mg loading is saturated. Therefore, the optimal ratio of magnesium to biomass mass of the modified biochar under biomass impregnation-pyrolysis treatment is 0.48: 1.

table 1:

	mass of magnesium ion and powder of ramie leaf	Adsorption amount of phosphate (mg P g)^-1)
			Comparative example 1	0：1	0.35
Example 1	0.12：1	35.52
			Example 2	0.24：1	41.08
Example 3	0.48：1	63.88
			Example 4	0.72：1	60.76
Example 5	0.96：1	60.43

Example 7 adsorption of phosphate by modified biochar

30mL of 100mg of PL were measured out^-1Phosphoric acid salt (KH)₂PO₄) The solution is put into a 150mL conical flask, 1M HCl, 3M HCl, 1M NaOH and 3M NaOH are used as pH regulators, the initial pH is respectively regulated to 2.5, 4.5, 6.5, 8.5 and 10.5, 0.03g of the modified carbon prepared in the example 2 is continuously added into each conical flask, the mixed solution is placed in a gas bath constant-temperature oscillation box, the mixed solution is continuously oscillated at 160rpm for 24 hours at 25 ℃, vacuum filtration is carried out through a 0.45-micron filter membrane, and the concentration of the residual phosphate in the liquid is measured.

As a result, as shown in FIG. 1, the phosphorus adsorption amount was calculated to be 67.32mg of Pg^-1、78.34mg P g^-1、62.15mg P g^-1、48.38mg P g^-1And 31.17mg of P g^-1(FIG. 1), the modified carbon has the highest phosphate adsorption capacity at pH 4.5, and the adsorption amount decreases as the pH increases.

Example 8

100mg/L phosphate (KH) at an initial concentration of 30mL₂PO₄) Dissolving KCl and KNO in certain amount in the solution respectively₃，K₂SO₄In which Cl is present^-、NO₃ ^-、SO₄ ^2-The concentrations are 0.1M and 0.01M respectively; adjusting the pH of the solution to 4.5 in each cone0.03g of the modified carbon prepared in example 1 was added continuously to the flask, the mixture was continuously shaken at 160rpm for 24 hours at 25 ℃ and filtered through a 0.45 μm filter membrane for vacuum filtration, and the concentration of the residual phosphate in the liquid was measured

The results are shown in FIG. 2, Cl^-、NO^3-、SO₄ ^2-At concentrations of 0.1M, the amounts of adsorbed substances were calculated to be 74, 73, 71mg of Pg^-1；Cl^-、NO₃ ^-、SO₄ ^2-At concentrations of 0.01M, the amounts of adsorption were calculated to be 76, 76.5, 74mg of Pg^-1(ii) a Example 5 describes that KCl and KNO were not added₃,K₂SO₄In the case of (2), the adsorbed amount of phosphorus was found to be 78mg of Pg^-1Therefore, when the adsorption of phosphate is carried out, Cl in the system should be minimized^-、NO₃ ^-、SO₄ ^2-The concentration of (c).

Example 9

First, experiment method

The surface morphology and the element characteristics of the modified biochar prepared in example 3 can be characterized by scanning electron microscopy-energy spectroscopy (SEM-EDS).

Second, experimental results

The results show that the difference of the surface morphology of BC (biochar prepared in comparative example 1) and MgBC (modified biochar prepared in example 3) is obvious as seen from the low magnification of a scanning electron microscope, the surface of BC is relatively flat, the number of pores is small, the surface of MgBC is rough, the structure is loose, and the pore structure is increased due to the irregular distribution of carbon particles; according to a high magnification power diagram (multiplied by 15,000), a plurality of spherical and convex white particles are distributed on the surface of the MgBC, and the energy spectrum of the MgBC also shows that a new peak appears at the Mg position after modification, the peak height at the O position is increased, so that the surface appearance and the element characteristics of the modified biochar in which the white particles increased on the surface of the biochar are magnesium oxide or hydroxide biochar can be characterized by a scanning electron microscope-energy spectrum (SEM-EDS). According to the low magnification of a scanning electron microscope, the difference of the surface forms of BC and MgBC is obvious, the surface of BC is relatively flat, the number of pores is small, the surface of MgBC is rough and loose, and the pore channel structure is increased due to the irregular distribution of carbon particles; from a high magnification plot (x 15,000), it can be observed that the MgBC surface is distributed with many spherical, convex white particles.

Application example adsorption application of phosphorus in sludge hydrothermal solution

Taking 80g of dewatered sludge (the water content is about 80%) to a quartz lining of a 250mL hydrothermal reaction kettle, adding 15mL of 2M hydrochloric acid, placing the lining into the reaction kettle, sealing a flange, opening an air inlet and outlet valve to introduce nitrogen into the reaction kettle, closing the valve after 15min, setting the reaction condition to be reaction at 220 ℃ for 30min, starting magnetic stirring after the temperature reaches 220 ℃, and setting the stirring speed to be 300 rpm. After the reaction is finished, the solid phase and the liquid phase are separated by vacuum filtration, and the liquid phase is collected.

Measuring 30mL of sludge hydrothermal solution into a 50mL centrifuge tube, continuously adding 0.03g of modified carbon prepared in example 1 into the centrifuge tube, placing the mixed solution into a gas bath constant-temperature oscillation box, carrying out oscillation treatment at the temperature of 25 ℃ and the rpm of 160, taking liquid phase samples by a needle tube at proper time intervals, measuring the concentration of the samples, and calculating that the adsorption amount of phosphorus is 207.58mg of Pg^-1。

Claims

1. A method for preparing modified biochar by utilizing plant wastes is characterized in that plant dry powder, magnesium salt and water are fully mixed, soaked, dried and then fully ground, and then pyrolysis reaction is carried out under the nitrogen atmosphere to obtain the modified biochar.

2. The method according to claim 1, wherein the plant dry powder is prepared by washing, drying, pulverizing, sieving and drying the plant to constant weight.

3. The method according to claim 2, wherein the mesh number of the screen is 50-100 meshes; the drying temperature is 60-105 ℃.

4. The method according to claim 1, wherein the mass ratio of the magnesium element in the magnesium salt to the plant powder is 0.12-0.96: 1.

5. the method of claim 1, wherein the sufficient mixing is: continuously oscillating for 12-24 h at the temperature of 25 ℃ and the rpm of 160; then stirring at 100-120 rpm and 60-80 ℃.

6. The method according to claim 1, wherein the pyrolysis reaction is carried out at a reaction temperature of 300 to 600 ℃ for 0.5 to 4 hours and at a temperature of 60 to 80 ℃ for drying.

7. A modified biochar produced by the method of any one of claims 1 to 6.

8. Use of the modified biochar of claim 7 for adsorbing phosphate.

9. Use according to claim 8, characterized in that the modified biochar according to claim 7 is mixed well with the sample to be adsorbed in an aqueous solution.

10. Use according to claim 9, characterized in that the modified charcoal according to claim 7 is mixed with the sample to be adsorbed in an aqueous solution sufficiently to minimize Cl^-、NO^3-、SO₄ ^2-The concentration of (c).