CN112191229A

CN112191229A - Preparation method and application of Mg/Ca-loaded modified tobacco stalk biochar

Info

Publication number: CN112191229A
Application number: CN202011127798.8A
Authority: CN
Inventors: 王风; 何秋平; 罗元; 张克强
Original assignee: Agro Environmental Protection Institute Ministry of Agriculture
Current assignee: Agro Environmental Protection Institute Ministry of Agriculture; Agro Environmental Protection Institute Ministry of Agriculture and Rural Affairs
Priority date: 2020-10-19
Filing date: 2020-10-19
Publication date: 2021-01-08
Anticipated expiration: 2040-10-19
Also published as: CN112191229B

Abstract

The invention relates to a preparation method of Mg/Ca loaded modified tobacco stalk biochar, which is characterized in that tobacco stalk powder is added into MgCl₂And adding eggshell powder into the solution, stirring, drying for the first time, pyrolyzing, cleaning, drying for the second time, grinding and sieving to obtain the Mg/Ca-loaded modified tobacco stalk biochar. The invention is through MgCl₂The pretreatment and the egg shell doping are carried out to prepare the Mg/Ca-loaded tobacco stalk metal biochar composite material, and the Mg/Ca biochar composite material is used for HPO under the condition of high pH₄ ^2‑The method has the advantages of representing higher adsorption capacity, successfully solving the problem of the reduction of the adsorption capacity of the single metal Mg loaded biochar under the condition of high pH, and improving the pH adaptability of the single metal Mg loaded biochar. The test result can provide reference for the preparation of the low-cost metal biochar composite material and provide a technique for removing phosphorus from the alkaline water bodyThe method can provide a new idea for the treatment of the waste with high Ca content and the mixed treatment of the waste.

Description

Preparation method and application of Mg/Ca-loaded modified tobacco stalk biochar

Technical Field

The invention belongs to the field of adsorption materials, and relates to a biochar material, in particular to a method for Mg/Ca-loaded modified tobacco stalk biochar and application thereof.

Background

Phosphorus is an essential element for growth of animals and plants, but excessive phosphorus discharged into a water body causes eutrophication and serious damage to a water ecosystem. How to scientifically and reasonably recover the phosphate in the wastewater is of great significance. The biochar is a residue of biomass thermochemical conversion under the condition of no oxygen or limited oxygen, has the characteristics of high porosity, specific surface area, certain surface functional groups and the like, and is a recognized multifunctional environmental material capable of being applied to soil fertilization, pollutant adsorption and the like. Generally, the biochar carbon layer prepared by pyrolysis at the high temperature (600-700 ℃) has good tissue, high aromaticity, lower polarity and better adsorption performance. However, the adsorption capacity of pure biochar materials to phosphate is limited, and a method for loading Mg on biochar is proposed for improving the adsorption capacity of the biochar materials. The method comprises the steps of directly soaking biomass in Mg solution with certain concentration, and then pyrolyzing at the temperature of 400-900 ℃, thereby preparing the magnesium-loaded biochar.

However, the adsorption capacity of pure magnesium-loaded biochar is limited by the environmental pH, and is stronger at low pH and weaker at high pH, because phosphorus is HPO at high pH₄ ^2-Present, but HPO₄ ^2-Are not easily removed by adsorption, so the invention is directed to HPO under high pH conditions₄ ^2-The designed adsorbing material solves the problem of influence of phosphorus existing form on the adsorbing effect of the material, thereby improving the pH adaptability of the material.

Disclosure of Invention

The invention aims to adsorb HPO under high pH condition₄ ^2-Therefore, the ability of the magnesium-loaded charcoal to adapt to pH is improved, a preparation method of the Mg/Ca-loaded modified tobacco stalk charcoal is provided, the Mg/Ca charcoal composite material also shows higher adsorption capacity to phosphorus under the condition of high pH, and the problem of the reduction of the adsorption capacity of the single metal Mg-loaded charcoal under the condition of high pH is solved.

Another object of the invention is to achieve metal loading of biochar by mixed pyrolysis of different wastes.

The technical scheme adopted by the invention for solving the technical problem is as follows:

a preparation method of Mg/Ca loaded modified tobacco stalk biochar,

adding tobacco stem powder into MgCl according to the mass ratio of Mg to tobacco stem of 0.12:1-0.48:1₂Adding egg shell powder into the solution, wherein the mass ratio of the egg shells to the tobacco stalks is 0.25:1-1:1, stirring for 1h at room temperature, drying for 8 h in a drying oven at 105 ℃, transferring the mixture into a porcelain crucible, heating to 700 ℃ at 5 ℃/min in a muffle furnace for pyrolysis for 2h, taking out after the temperature in the furnace is cooled to room temperature, cleaning for three times by deionized water, carrying out vacuum filtration, drying for 6 h at 105 ℃, grinding and sieving by a 60-mesh sieve to obtain the Mg/Ca-loaded modified tobacco stalk biochar.

The eggshell powder is prepared by washing eggshells with deionized water, drying, grinding and sieving with a 100-mesh sieve.

Moreover, the composition comprises the following components in percentage by weight: the content of C was 32.35%, the content of H was 1.61%, the content of O was 13.08%, the content of Ca was 11.89%, the content of Mg was 30.85%, and the content of N was 0.65%.

Moreover, the Langmuir fitting maximum adsorption capacity of the composite material is 210.66mg/g, and the adsorption capacity is more than 270mg/g in the pH range of 3-12; MgO and CaCO with Mg and Ca as active components in sheet and fungus shape₃Is loaded on the surface of the biological carbon and extends to the space at the edge.

An application of Mg/Ca loaded modified tobacco stalk biochar in adsorbing phosphorus.

Adsorption of Mg/Ca-loaded modified tobacco stalk biochar on HPO₄ ^2-The application of (1).

The invention has the advantages and positive effects that:

the invention is through MgCl₂The Mg/Ca-loaded tobacco stalk metal biochar composite material is prepared by pretreatment and eggshell doping, the problem that the adsorption capacity of single metal Mg-loaded biochar is reduced under the high pH condition is successfully solved, the Mg/Ca biochar composite material has higher adsorption capacity on phosphorus under the high pH condition, and HPO is realized₄ ^2-Is effectively removed. The test result can provide reference for the preparation of the low-cost metal biochar composite material, and meanwhile, the test result can provide reference for the preparation of the low-cost metal biochar composite materialAlso provides a new idea for the disposal and treatment of waste with high Ca content.

Drawings

FIG. 1 is a quasi-first order, quasi-second order fit curve (where a is BC, M-C1, M-C2, M-C3, and b is EM-C24);

FIG. 2 is a W-M internal diffusion model fitting curve (where a is BC, M-C1, M-C2, M-C3, and b is EM-C24);

FIG. 3 is the adsorption isotherm for phosphate (where a is BC, M-C1, M-C2, M-C3, and b is EM-C24);

FIG. 4 is a graph of the adsorption effect of pH on M-C2;

FIG. 5 is a graph of the pH effect on EM-C adsorption.

FIG. 6 is an SEM photograph of BC, M-C2, EM-C24 (where a is BC, b is M-C2, and C is EM-C24);

FIG. 7 is a Fourier transform infrared spectrum of BC, M-C2, EM-C24;

FIG. 8 is an XRD pattern of BC, M-C2, EM-C24.

Detailed Description

The present invention is further illustrated by the following specific examples, which are intended to be illustrative, not limiting and are not intended to limit the scope of the invention. The adsorption capacity of the material is expressed in the examples in terms of adsorption capacity (mg/g), and a larger value indicates a stronger adsorption capacity.

Example 1

A preparation method of Mg/Ca loaded modified tobacco stalk biochar comprises the steps of adding 20g of tobacco stalk powder into 180mLMgCl according to the mass ratio of Mg to tobacco stalks of 0.3:1₂And adding 20g of egg shell powder into the solution, stirring the mixture at room temperature for 1h, drying the mixture in an oven at 105 ℃ for 8 h, transferring the mixture into a porcelain crucible, heating the mixture to 700 ℃ at a speed of 5 ℃/min in a muffle furnace for pyrolysis for 2h, taking the mixture out after the temperature in the furnace is cooled to room temperature, washing the mixture with deionized water for three times, carrying out vacuum filtration, drying the mixture at 105 ℃ for 6 h, and grinding the dried mixture through a 60-mesh sieve to obtain the Mg/Ca-loaded modified tobacco stalk biochar. The biochar was named EM-C24.

Kinetics of phosphate adsorption and isotherm study

Preparing MgCl with different mass concentrations₂Solution ofThe mass ratio of Mg to tobacco stalk is 0:1, 0.12:1, 0.3:1 and 0.48:1 respectively, 20g of tobacco stalk powder is added into 180mL of MgCl with different mass concentrations₂Stirring the solution for 1 hour at the room temperature of 800rpm by using a constant-temperature magnetic stirrer (IT-09A-5 type), drying the solution for 8 hours in a 105 ℃ oven, transferring the mixture into a ceramic crucible, heating the mixture to 700 ℃ at the speed of 5 ℃/min in a muffle furnace (SX2F-2.5-10 type), pyrolyzing the mixture for 2 hours, cooling the temperature in the furnace to the room temperature, taking the cooled mixture out, cleaning the cooled mixture with deionized water for three times, carrying out vacuum filtration, drying the mixture for 6 hours at the temperature of 105 ℃, slightly crushing the dried mixture for 60 meshes to obtain Mg-loaded tobacco stalk biochar, and respectively naming the biochar as BC, M-C1, M-C2 and M-C3 according to the Mg adding amount.

0.05g of biochar was added to a 100mL Erlenmeyer flask containing 30mL of a phosphorus solution, followed by shaking at 180rpm in a constant temperature shaking incubator at 25 ℃ for a certain period of time. The suspension was then filtered through a 0.45 μm filter head, the phosphorus concentration was measured at a wavelength of 700nm using a molybdenum-antimony anti-chromogenic, two-beam ultraviolet-visible spectrophotometer (TU-1901), and the adsorption performance was evaluated by varying the initial phosphorus concentration and adsorption time, the experimental results being listed in Table 1.

TABLE 1 kinetics and isotherm adsorption test results (data units in mg/g)

Setting the mass ratio of Mg to tobacco stalk as 0.3:1, adding 20g of tobacco stalk powder into 180mLMgCl₂Adding 5g, 10g, 15g and 20g of eggshell powder into the mixed system respectively, stirring for 1h at room temperature, drying for 8 h in a 105 ℃ oven, transferring the mixture into a porcelain crucible, heating to 700 ℃ at a speed of 5 ℃/min in a muffle furnace for pyrolysis for 2h, taking out after the temperature in the furnace is cooled to room temperature, washing with deionized water for three times, carrying out vacuum filtration, drying for 6 h at 105 ℃, grinding and sieving with a 60-mesh sieve to obtain the Mg/Ca-loaded modified tobacco stalk biochar. According to the quality of the doped egg shells, the biochar is divided intoAre respectively named as EM-C21, EM-C22, EM-C23 and EM-C24.

Kinetic equations using quasi-first, quasi-second, and W-M internal diffusion models (equation ln (q)_e-q_t)＝lnq_e-k₁t、

q_t＝k_ipt^1/2+ C) the adsorption results of M-C1, M-C2, M-C3 and EMC-24 were subjected to data fitting, the adsorption mechanism of phosphate was investigated, and the adsorption effect was evaluated. The quasi-first-order and quasi-second-order fitting results are shown in fig. 1 and table 2, and the fitting results of the W-M internal diffusion model are shown in fig. 2 and table 3.

The results in figure 1 show that the phosphate adsorption rate of the 4 biochar types is high in the first 4 hours, the adsorption rate gradually becomes low in the time period of 4-12 hours, and the adsorption balance is achieved in about 12 hours. The virgin carbon (BC) showed phosphorus release over the indicated time. The results of the fit in table 2 show that the goodness of fit of the quasi-second order kinetic model is significantly higher than that of the quasi-first order, indicating that the adsorption rate of magnesium loaded biochar and EM-C24 to phosphate is controlled by the chemisorption mechanism involving electron sharing or electron transfer between carbon and phosphate and the formation of new compounds.

As can be seen from FIG. 2, M-C1, M-C2, M-C3 and EM-C24 are q within the first 4h_tThe rate of increase is faster, q after 4h_tThe rate of increase becomes slow and the fit is not a straight line through the origin, indicating that intraparticle diffusion is not the controlling step of the adsorption process and that the adsorption behavior of intraparticle diffusion gradually decreases as adsorption proceeds. Meanwhile, the fitting results in Table 3 show that the internal diffusion rate K is increased with the increase of the magnesium loading and the addition of the eggshell_ipAn increasing trend is exhibited because the addition of Mg to the egg shell leads to an increase in the active metal content of the material and intra-particle diffusion adsorption occurs more easily.

Table 2 fitting parameter results

TABLE 3 results of piecewise fitting parameters for the internal diffusion model

Researches the adsorption thermodynamics of M-C1, M-C2, M-C3 and EM-C24 on phosphate by using the thermodynamic equation (equation) of Langmuir and Freundlich models

Q_e＝K_FC_e ^1/n) And fitting data of experimental results, discussing the adsorption mechanism of magnesium-loaded biochar for adsorbing phosphate, and evaluating the adsorption effect of the biochar. The results are shown in FIG. 3 and Table 4.

The results in FIG. 3 show that the equilibrium concentrations and the adsorption amounts of M-C1, M-C2, M-C3 and EM-C24 under the condition of initial low phosphorus concentration are not different greatly, the equilibrium concentration is gradually reduced along with the increase of the initial phosphorus concentration, the adsorption amounts are obviously increased and tend to be balanced, and the 4 adsorption materials are more suitable for the adsorption of phosphate with medium and high concentration under the same adsorption condition, and are particularly suitable for the adsorption of which the initial phosphate concentration is changed to the range of 200-300 mgP/L.

The results in table 4 show that the goodness of fit of the Langmuir model is significantly higher than that of the Freundlich model, which indicates that the carbon material has uniform surface and no interaction between phosphates, and the phosphate adsorption process is monomolecular layer chemical adsorption occurring on the surface of the adsorbent, indirectly indicates that the material can be better suitable for medium and high concentrations. From the results of the Freundlich model fitting, it can be seen that although the goodness of fit is not high, the addition amount of the metal is also shown to be in direct proportion to the unit concentration adsorption amount of the material, and phosphate is easily adsorbed after the charcoal is loaded with the metal.

TABLE 4 isotherm fitting parameters

Magnesium-loaded tobacco stalk charcoal (M-C2) adsorbs phosphate under different pH conditions

100mL of 500mgP/L was taken, pH was adjusted to 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 with 0.2MHCl and 0.6MNaOH, 30mL of the above solution and 0.05g of M-C2 biochar were added to a 100mL Erlenmeyer flask, shaken at 180rpm for 24h at 25 ℃, filtered through a 0.45 μm filter head and the phosphorus concentration was determined, and run 3 was repeated for each run. The results are shown in FIG. 4, Table 5.

FIG. 4 shows the phosphate adsorption capacity of M-C2 at different initial pH conditions, illustrating that adsorption of phosphate by the magnesium loaded tobacco stalk carbon has a limitation on environmental pH. The results show that M-C2 has better adsorption capacity to phosphate under acidic conditions, the adsorption capacity is in the range of 235.8-237.8mgP/g within the range of 3-5, and the adsorption capacity is slowly reduced to 229.8 and 205mgP/g with the increase of pH value to 6 and 7. However, the adsorption capacity of M-C2 for phosphate sharply decreases after the solution is changed from acidic to alkaline conditions, and when the pH value is increased to 8, the adsorption capacity is reduced to 162.45mgP/g, and when the pH value is continuously increased to 12, the adsorption capacity is reduced to 135.2 mgP/g. The adsorption capacity of the pure Mg-loaded tobacco stalk charcoal is sharply reduced along with the increase of the pH value of the solution mainly due to three reasons, namely H₃PO₄，H₂PO₄ ^-And HPO₄ ^2-The dissociation constants of (a) were 2.12,7.21 and 12.31, respectively. Therefore, at a solution pH value of 2.12-7.21, the phosphate ions are mainly in the form of H₂PO₄ ^-When the pH is between 7.21 and 12.31, the phosphate ions are mainly in the form of HPO₄ ^2-. As the pH of the solution increases, H₂PO₄ ^-Will gradually change into HPO₄ ^2-The former has low adsorption energy and is easier to be adsorbed, so that the pH value is increased, the adsorption capacity is reduced, the increase of the pH value of the solution can cause the protonation and deprotonation degree of the material to change, thereby influencing the electrostatic adsorption effect, and the-OH in the solution can compete with phosphate ions for active adsorption sites under the condition of high pH.

Mg/Ca loaded modified tobacco stalk biochar (EM-C2) adsorbs phosphate under different pH conditions

100mL of 500mgP/L was taken, pH was adjusted to 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 with 0.2MHCl and 0.6MNaOH, 30mL of the above solution and 0.05gEM-C2 biochar were added to a 100mL Erlenmeyer flask, shaken at 180rpm for 24h at 25 ℃, filtered through a 0.45 μm filter head and the phosphorus concentration was determined, and run 3 was repeated for each run. The results are shown in fig. 5, table 5. As can be seen from fig. 5 and table 5, the adsorption capacity of biochar under alkaline conditions was significantly improved after the addition of the eggshell. Under alkaline conditions, the adsorption capacity of EM-C is improved by more than 80% compared with that of M-C2, wherein EM-C24 shows excellent adsorption performance in the pH range of 3-12, and the adsorption capacity is more than 270 mg/g. This is because the Ca-based adsorbing material has applicability under high pH conditions, CaCO₃、Ca₃(PO₄)₂KSP of 2.9X 10-9, KSP of 2.0X 10-29 and KSP of 26.8X 10-39 respectively, and CaCO introduced by adding egg shell₃CaCO due to Ksp gap after phosphate encounter₃Will be towards Ca₃(PO₄)₂And calcium hydroxy phosphate to fix phosphorus

TABLE 5pH influence experiment results (data units in mg/g)

Analysis of physical and chemical properties of materials

The invention adopts a mixed pyrolysis method to prepare a plurality of biochar, selects materials with high performance and quality, and utilizes a plasma spectrometer (ICP-OES) and an Element Analyzer (EA) to measure the contents of Ca, Mg and C, H, O, N, S of the tobacco stalks and the biochar, and the result is shown in Table 6.

TABLE 6 chemical element composition of main materials

As can be seen from Table 6, the C content of the tobacco stalks before pyrolysis was 38.57%, while the oxygen content was as high as 42.65%. After pyrolysis to char, the oxygen content of the biomass drops sharply, while the C content rises. The main reason is due to the pyrolysis volatilization of moisture, cellulose, lignin and hemicellulose. After Mg is loaded, the total mass is increased, the mass of the biomass is relatively reduced, so that the content of Ca in the magnesium-loaded biochar is reduced, and the content of C is sharply reduced. When the eggshell is doped, the content of C in the biochar is slightly reduced, and the content of O and Ca is increased, mainly because the main component of the eggshell is CaCO₃The addition of egg shells introduces C, Ca and O elements.

The morphologies of BC, M-C2, EM-C24 at different magnifications were analyzed using a FEIInspectF50(FSEM) instrument, as shown in FIG. 6. The BC surface is smooth, and the local surface has wrinkles which are mainly caused by the appearance of the biomass, but after Mg is loaded, the M-C2 surface is obviously rough, the granular feeling is enhanced, the pore structure is obviously increased, and objects such as granules, sheets and the like appear, which shows that the active Mg component is successfully loaded on the surface of the biochar; after magnesium and egg shells are added simultaneously, the surface roughness of EM-C24 is further increased, the granular feel is further enhanced, and flaky and fungiform substances are obviously seen. The chemical agent can be added by analyzing the weight percentage of Ca and Mg on the surface through energy spectrum analysis, the metal Mg can realize the rapid and large-amount loading of the metal Mg, and the Ca loading on the biochar can also be realized by mixing and pyrolyzing the metal Mg in the manner of eggshells. The loading capacity is consistent with the analysis result of ICP-OES, which shows that the metal is finally loaded on the surface of the biochar to play a role.

In order to investigate the influence of the loaded metal on the material groups, Fourier transform infrared spectroscopy analysis was performed on BC, M-C2 and EM-C24 respectively, as shown in FIG. 7, in BC, the absorption peak was few, 1440cm^-1The absorption peak of (A) is mainly derived from C-H stretching vibration in aliphatic series. After Mg loading, at wave number 1583cm^-1A broad absorption peak appears, which may result from a bending vibration of-OH, at 459cm^-1The sharp absorption peak appears mainly from the stretching vibration of Mg — O. When the egg shells are doped, the wave number is 3700cm^-1An absorption peak derived from-OH stretching vibration and 878cm were observed^-1Derived from CO₃ ^2-The absorption peak of (1).

Utilizing an X-ray diffraction analyzer to perform wide-angle diffraction of 5-85 degrees on BC, M-C2 and EM-C24, analyzing the phase composition of the biochar, as shown in figure 8, the wider diffraction peak of the biochar at about 22 degrees is mainly caused by graphitization and aromatization of organic matters in the biomass at high temperature, and the diffraction peak at about 29.5 degrees is mainly CaCO₃(PDF #72-1214) caused by diffraction of the (104) crystal plane in the physical phase. In M-C2, the diffraction peak is mainly from MgO (PDF #75-0447), and it is shown that MgO is highly crystalline on the surface of charcoal, since Mg (OH) Cl is decomposed and converted into MgO in the range of 450-650 ℃. Whereas in EM-C24, the phase is mainly with MgO and CaCO₃This is likely due to the loading of Mg and CaCO, respectively₃Resulting from incomplete decomposition at 700 ℃.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various changes and modifications can be made without departing from the inventive concept, and these changes and modifications are all within the scope of the present invention.

Claims

1. A preparation method of Mg/Ca loaded modified tobacco stalk biochar is characterized by comprising the following steps:

2. The method of claim 1, wherein: the eggshell powder is obtained by washing eggshells with deionized water, drying, grinding and sieving with a 100-mesh sieve.

3. The Mg/Ca-loaded modified tobacco stalk biochar prepared by the method of claim 1 is characterized in that: comprises the following components in percentage by weight: the content of C was 32.35%, the content of H was 1.61%, the content of O was 13.08%, the content of Ca was 11.89%, the content of Mg was 30.85%, and the content of N was 0.65%.

4. The Mg/Ca-loaded modified tobacco stalk biochar prepared by the method of claim 1 is characterized in that: the maximum adsorption capacity of the composite material Langmuir is 210.66mg/g, and the adsorption capacity is more than 270mg/g in the pH range of 3-12; MgO and CaCO with Mg and Ca as active components in sheet and fungus shape₃Is loaded on the surface of the biological carbon and extends to the space at the edge.

5. The application of the Mg/Ca-loaded modified tobacco stalk biochar prepared by the method of claim 1 in phosphorus adsorption.

6. The Mg/Ca-loaded modified tobacco stalk biochar prepared by the method of claim 1 for adsorbing HPO₄ ^2-The application of (1).