Preparation method and application of magnetic charcoal-chitosan composite material

Abstract

The invention belongs to the technical field of biochar materials, and particularly relates to a modified biochar material, a preparation method of the modified biochar material and application of the modified biochar material to removal of heavy metal in wastewater. And combining with a chitosan solution to prepare the final magnetic charcoal-chitosan composite material through a hydrothermal method. The material is simple and convenient in preparation process, relatively low in production cost and relatively short in production period, and the obtained magnetic charcoal-chitosan composite material has a unique effect of removing lead (Pb (II)) and chromium (Cr (VI)) in wastewater. And the heavy metal content of the treated wastewater containing the heavy metals can effectively reach the primary standard of Integrated Wastewater Discharge Standard GB 9897-1996. The method can remove the heavy metals in the wastewater within 20 hours, and is efficient, simple and high in practicability. In the treatment process, only stirring and precipitating equipment is used, so that the investment is less.

Description

Technical Field

[0001] This invention belongs to the field of water pollution treatment technology. After identifying a derivative carbon material based on magnetic biochar and modified with chitosan, the original biomass material is modified by imparting magnetism to the biochar and introducing chitosan into the biochar with a large specific surface area. The study explores the influence of various factors on the removal of Pb(II) and Cr(VI) from water using the magnetic biochar-chitosan composite material, providing a scientific basis for the construction of effective magnetic biochar-chitosan composite materials and the removal of heavy metals from water. Background Art

[0002] In recent years, the technology of converting biomass waste into biochar, bio-oil and biogas through pyrolysis carbonization has received widespread attention. Biochar has been found to have multiple environmental benefits such as carbon sequestration and emission reduction, promoting plant growth, maintaining soil fertility, and adsorbing heavy metals. Among them, due to the high harm of heavy metals to the human body and their destructiveness to environmental quality, the use of biochar to purify heavy metals in wastewater has attracted widespread attention from scholars. Biochar is a carbon-rich product formed by thermochemical reactions of biomass residues in an oxygen-deficient environment. In recent years, it has received widespread attention due to its potential carbon sequestration capacity, soil improvement function, and pollutant remediation function. Biochar is usually prepared by pyrolysis at a temperature of 350-750 °C, and has the following physical and chemical characteristics: a specific surface area of about 10-600 m 2 / g, mostly mesoporous structures with rough and disordered pores; negatively charged functional groups such as carboxyl groups and phenolic / hydroquinone compounds are formed on the surface; and the biomass is rich in minerals such as K, Ca, Mg, Fe, and P. During the conversion of biomass to biochar, the pore structure, surface functional groups, and mineral composition formed significantly influence the biochar's ability to fix different heavy metals in wastewater.

[0003] Biochar is widely used in environmental and agricultural applications. However, due to its simple preparation process, diverse raw material sources, and limited surface group types, chemical methods are needed to modify certain biochar properties to improve their performance. Currently, there are two main methods for biochar modification. One involves treating the biochar with chemical reagents (acidic or alkaline solutions) after preparation. Oxidation activators are a common treatment method. Biochar is immersed in an oxidizing agent, oxidizing the surface and increasing the number of oxygen-containing functional groups on the treated biochar surface, which enhances its adsorption capacity for target pollutants. Another method involves mixing the biochar with a solid modifying material during preparation. This modified biochar acquires new surface structures and properties, exhibiting enhanced adsorption properties for organic matter and heavy metals in water. A common modification material is impregnation with metal ions, resulting in the formation of metal oxides on the surface. The modified biochar then reacts with adsorbed substances through electrostatic attraction and ion exchange.

[0004] The modified biochar shows good adsorption effect and has great application prospects. It has a huge improvement effect on water bodies contaminated by heavy metal ions. It can reuse the contaminated water bodies and greatly reduce the harm of polluted water bodies to soil, plants and human bodies. It has high environmental and social benefits.

[0005] Patents in the Chinese patent database involving biochar-based chitosan composite carbon materials for heavy metal removal from water include CN105236507A, "Method for Removing Hexavalent Chromium from Wastewater Using a Composite Adsorbent of β-cyclodextrin Chitosan and Walnut Shell Biochar," which requires pre-treatment of chitosan to obtain β-cyclodextrin chitosan and ultrasonic dispersion of the carbon material, resulting in cumbersome preparation steps. CN108311117B, "A Magnetic Biochar Material for Heavy Metal Wastewater Treatment and Its Preparation Method," and CN110142032B, "Chitosan Biochar Composite Material and Its Preparation Method and Application," require gelation followed by calcination, requiring high pretreatment requirements. CN116889862A, "A Chitosan-Stabilized Magnetic Luffa Biochar Composite Adsorbent and Its Preparation Method and Application," utilizes a single material. These materials can only remove hexavalent chromium from water, with a narrow removal range and limited universal applicability. CN110801814A "A preparation method for a new magnetic amino walnut shell biochar adsorbent" and CN111570494B "A method for remediating heavy metal contaminated soil" are only used to remove divalent cadmium from water, and the effect is only good when the pH is 6; CN117732448A "A water purifier for sewage treatment and its preparation method" only mentions the removal of divalent copper ions; CN109277083A "A ferromagnetic biochar ball for purifying water and its preparation method and application" only removes divalent copper ions from wastewater. Hexavalent chromium and the dye methylene blue, and the removal rate is only about 50%, which is relatively low in efficiency. Regarding CN115337912A "A magnetic cross-linked chitosan-polyethyleneimine / biochar composite gel particle and preparation method", although it has an adsorption effect on three heavy metal ions of lead, copper, and chromium, the material production cost is high, the time is long, the carbonization temperature is as high as 1200°C, and small amounts of multiple feedings are required during gelation, the effective product yield is low, and the efficiency is high only when the heavy metal ion concentration is low. It is far less low-cost and versatile than the present invention. CN117225368A "A magnetic biochar based on Chuanxiong medicinal residue and its preparation method and application" can also simultaneously adsorb chromium, arsenic and lead ions, but the materials used are single and only specific Chuanxiong medicinal residue can be used. At the same time, it has a high heavy metal adsorption rate only at a pH of 4, and does not have the wide material selection range and application range of the present invention; CN112755962A "An adsorption material for removing lead, copper and cadmium in groundwater and its preparation method and application" is suitable for removing lead, copper and cadmium metal ions in water bodies, but the removal rate of chromium ions is less than 60%, and the applicable pH range is not mentioned; CN110368907A "A remover for deep removal of arsenic and cadmium ions in wastewater and its preparation method" requires the introduction of protein to improve the binding effect on heavy metal ions during the preparation process, and the protein extraction process is relatively complicated. The treatment only mentions the removal of cadmium ions and arsenic ions in water bodies, and does not mention the effect of removing lead ions.Based on this, the invention developed a chitosan-doped magnetic biochar composite material as a material for removing heavy metals such as lead (Pb(Ⅱ)) and chromium (Cr(VI)) from water. The material selection is diverse, the production cost is low, the reaction process is simple and fast, and the invention has good universality and stability, and is also recyclable. Summary of the Invention

[0006] The purpose of the present invention is to provide a chitosan biochar composite material and its preparation method and application, which has low cost, simple process, simple separation and recovery of adsorbent and wastewater, and solves the problem of heavy metal pollution in water bodies.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present invention is as follows: the crushed biochar material is mixed with the iron ion solution, carbonized to obtain magnetic biochar, chitosan solution is added, mixed evenly, and then added with alkaline solution for reaction, washed with water and dried to obtain a magnetic biochar-chitosan composite material.

[0008] Preparation of magnetic biochar-chitosan composite material, the specific steps are as follows: (1) The dried biomass is crushed, carbonized at high temperature in the absence of oxygen, and then ground and sieved after cooling to obtain raw biochar; (2) The original biochar is mixed with the iron ion solution, and after ultrasonic stirring for a period of time, the solid and liquid are separated. The resulting yellow sample is dried to obtain the iron-doped biochar; (3) Carbonizing the iron-doped biochar at high temperature in the absence of oxygen, grinding and sieving the resulting magnetic biochar after cooling; (4) The magnetic biochar and chitosan solution are mixed, heated and stirred for a period of time, filtered, rinsed, and dried to obtain a magnetic biochar-chitosan composite adsorption material.

[0009] In the step (1), the heating rate of the tubular furnace is 3-10°C / min, and the temperature is kept for 2-5 hours.

[0010] In the step (2), ultrasonic instrument is used for ultrasonication for 5-8 hours and stirring is performed for 5-8 hours.

[0011] The oven temperature in step (2) is 50-80°C, and the drying time is 24-28 hours.

[0012] In step (3), the temperature of the tubular furnace is 500-800°C, and the heating rate is 5-8°C / min.

[0013] In step (4), 2-8 mol / L acetic acid solution and 0.5-2 mol / L glutaraldehyde solution are added to the chitosan solution, and the solution is heated in a water bath at 60-80°C for 20-40 minutes. The pH is adjusted to 10 and the heating is continued for 2-3 hours.

[0014] In step (4), the oven temperature is 50-70°C and the drying time is 24-28 hours.

[0015] The present invention has the following characteristics:

[0016] 1. A magnetic biochar-chitosan composite material has been developed to solve the problem of heavy metal pollutants in urban domestic water and industrial water. It has a good adsorption and removal effect on Pb(Ⅱ) and Cr(VI), and has good economic benefits and important environmental significance.

[0017] 2. The magnetic biochar-chitosan composite material has good universality when used for adsorption, and has good stability and excellent desorption and regeneration effects.

[0018] 3. When magnetic biochar is loaded with chitosan, a certain concentration of glutaraldehyde is added to the solution. The amino groups in the chitosan molecules undergo a cross-linking reaction with the aldehyde groups in glutaraldehyde to form imine bonds. This structure is stable and can form gelation at the molecular level, making the material more stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 are the SEM images of biochar, magnetic biochar, and chitosan magnetic biochar samples;

[0020] Figure 2 This is the DES spectrum analysis diagram of biochar, magnetic biochar, and chitosan magnetic biochar;

[0021] Figure 3 This is the XRD characterization diagram of chitosan magnetic biochar;

[0022] Figure 4 It is the FTIR graph of biochar, magnetic biochar, chitosan, and chitosan magnetic biochar;

[0023] Figure 5 is the hysteresis loop diagram of chitosan magnetic biochar;

[0024] Figure 6 It is a pseudo-second-order kinetic equation model for the adsorption of Pb (II) and Cr (VI) by chitosan magnetic biochar;

[0025] Figure 7 It is the Freundlich equation model for the adsorption of Pb(Ⅱ) and Cr(Ⅵ) by chitosan magnetic biochar;

[0026] Figure 8 It is a process flow chart. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the examples. It is understood that the following examples should not be construed as limiting the present invention.

[0028] Table 1 Comparison of results of the examples Example Glutaraldehyde (1%) added amount (mL) Mass loss of synthetic materials after washing and drying (%) Adsorption capacity for Pb(Ⅱ) (mg / g) Adsorption capacity for Cr(VI) (mg / g) Adsorption capacity of Pb(Ⅱ) after five cycles (mg / g) Adsorption capacity of Cr(VI) after five cycles (mg / g) 1 0 61.0 11.88 8.91 5.56 3.85 2 0 60.8 8.55 8.78 4.23 3.91 3 0 58.5 3.95 10.14 2.88 5.22 4 0 62.2 8.36 7.96 4.15 4.05 5 0 57.8 10.25 9.86 5.67 5.13 6 0 58.8 10.22 5.86 5.82 4.98 7 10 37.2 14.51 10.23 11.82 8.99 8 15 36.5 14.92 10.42 12.30 9.02 9 20 36.8 14.88 15.45 12.15 12.76 Example

[0029] A preparation method and application of a magnetic biochar-chitosan composite material include the following steps: weighing 1.2 g of magnetic biochar and 0.8 g of chitosan (biochar to chitosan mass ratio of 3:2).

[0030] (1) Pomelo peel biomass after crushing through 120 mesh was placed in a beaker, and 100 mL of FeCl3 (concentration 0.75 mol / L) solution was added. The biomass was ultrasonicated in an ultrasonic instrument at room temperature for 2 h. After ultrasonication, it was stirred with a magnetic stirrer for 6 h. After separation by suction, a yellow sample was obtained. The yellow sample was placed in an oven at 55 °C and dried for 24 h. The dried sample was then placed in a tube furnace and heated at 5 °C·min under argon atmosphere. -1 The temperature was raised to 600 °C, followed by carbonization at 600 °C for 2.5 h, cooling down to room temperature, and then taken out and ground to obtain a magnetic biochar sample; (2) Weigh 1.2 g of the magnetic biochar sample obtained in step (1) and add it to a 65 °C water bath. Then add 0.8 g of chitosan completely dissolved in 100 mL of 2% acetic acid solution. After heating in a water bath for 30 min, add 1 mol / L NaOH dropwise to the mixed solution until the pH is equal to 10. Heat in a water bath for 2 h. (3) The insoluble matter in the solution prepared in step (2) was filtered and repeatedly rinsed with deionized water and ethanol to clean the residual NaOH and other substances, and then placed in an oven at 55 ° C for 24 h and dried for use to obtain a magnetic biochar-chitosan composite material; (4) When used, the initial concentrations of Pb (II) and Cr (VI) solutions were 0.6 mg / L and 5.5 mg / L, respectively, with a volume of 50 mL. 80 g of magnetic biochar-chitosan composite material and heavy metal solution were added to a 150 mL conical flask, the pH was controlled at 5.0, and the reaction was shaken for 10 h on a constant temperature shaker at 180 rpm, maintaining the water temperature at 50 °C. The residual Pb (II) and Cr (VI) concentrations in the solution were measured, and the adsorption capacity of the material for Pb (II) was calculated to be 11.88 mg / g, and the adsorption capacity for Cr (VI) was calculated to be 8.91 mg / g.

[0031] Comparative Example 2: A preparation method and application of a magnetic biochar-chitosan composite material, comprising the following steps: weighing 1.0 g of magnetic biochar and 1.0 g of chitosan (biochar to chitosan mass ratio of 1:1).

[0032] (1) Pomelo peel biomass after crushing through 120 mesh was placed in a beaker, and 100 mL of FeCl3 (concentration 0.75 mol / L) solution was added. The biomass was ultrasonicated in an ultrasonic instrument at room temperature for 2 h. After ultrasonication, it was stirred with a magnetic stirrer for 6 h. After separation by suction, a yellow sample was obtained. The yellow sample was placed in an oven at 55 °C and dried for 24 h. The dried sample was then placed in a tube furnace and heated at 5 °C·min under argon atmosphere. -1 The temperature was raised to 600 °C, followed by carbonization at 600 °C for 2.5 h, cooling down to room temperature, and then taken out and ground to obtain a magnetic biochar sample; (2) Weigh 1.0 g of the magnetic biochar sample obtained in step (1) and add it to a 65 °C water bath. Then add 1.0 g of chitosan completely dissolved in 100 mL of 2% acetic acid solution. After heating in a water bath for 30 min, add 1 mol / L NaOH dropwise to the mixed solution until the pH is equal to 10. Heat in a water bath for 2 h. (3) The insoluble matter in the solution prepared in step (2) was filtered and repeatedly rinsed with deionized water and ethanol to clean the residual NaOH and other substances, and then placed in an oven at 55 ° C for 24 h and dried for use to obtain a magnetic biochar-chitosan composite material; (4) When used, the initial concentrations of Pb (II) and Cr (VI) solutions were 0.6 mg / L and 5.5 mg / L, respectively, with a volume of 50 mL. 80 g of magnetic biochar-chitosan composite material and heavy metal solution were added to a 150 mL conical flask, the pH was controlled at 5.0, and the reaction was shaken for 10 h on a constant temperature shaker at 180 rpm, maintaining the water temperature at 50 °C. The residual Pb (II) and Cr (VI) concentrations in the solution were measured, and the adsorption capacity of the material for Pb (II) was calculated to be 8.55 mg / g, and the adsorption capacity for Cr (VI) was calculated to be 8.78 mg / g.

[0033] Comparative Example 3: A preparation method and application of a magnetic biochar-chitosan composite material include the following steps: weighing 1.2 g of magnetic biochar and 0.8 g of chitosan (biochar to chitosan mass ratio of 3:2).

[0034] (1) Pomelo peel biomass after crushing through 120 mesh was placed in a beaker, and 100 mL of FeCl3 (concentration 0.75 mol / L) solution was added. The biomass was ultrasonicated in an ultrasonic instrument at room temperature for 2 h. After ultrasonication, it was stirred with a magnetic stirrer for 6 h. After separation by suction, a yellow sample was obtained. The yellow sample was placed in an oven at 55 °C and dried for 24 h. The dried sample was then placed in a tube furnace and heated at 5 °C·min under argon atmosphere.-1 The temperature was raised to 600 °C, followed by carbonization at 600 °C for 2.5 h, cooling down to room temperature, and then taken out and ground to obtain a magnetic biochar sample; (2) Weigh 1.2 g of the magnetic biochar sample obtained in step (1) and add it to a 65°C water bath. Then add 0.8 g of chitosan completely dissolved in 100 mL of 2% acetic acid solution. After heating in a water bath for 30 min, add 1 mol / L NaOH dropwise to the mixed solution until the pH reaches 10. Heat in a water bath for 2 h. (3) The insoluble matter in the solution prepared in step (2) was filtered and repeatedly rinsed with deionized water and ethanol to clean the residual NaOH and other substances, and then placed in an oven at 55 ° C for 24 h and dried for use to obtain a magnetic biochar-chitosan composite material; (4) When used, the initial concentrations of Pb (II) and Cr (VI) solutions were 0.6 mg / L and 5.5 mg / L, respectively, with a volume of 50 mL. 80 g of magnetic biochar-chitosan composite material and heavy metal solution were added to a 150 mL conical flask, the pH was controlled at 2.0, and the reaction was shaken for 10 h on a constant temperature shaker at 180 rpm, maintaining the water temperature at 50 °C. The residual Pb (II) and Cr (VI) concentrations in the solution were measured, and the adsorption capacity of the material for Pb (II) was calculated to be 3.95 mg / g, and the adsorption capacity for Cr (VI) was calculated to be 10.14 mg / g.

[0035] Comparative Example 4: A preparation method and application of a magnetic biochar-chitosan composite material include the following steps: weighing 1.2 g of magnetic biochar and 0.8 g of chitosan (biochar to chitosan mass ratio of 3:2).

[0036] (1) Pomelo peel biomass after crushing through 120 mesh was placed in a beaker, and 100 mL of FeCl3 (concentration 0.75 mol / L) solution was added. The biomass was ultrasonicated in an ultrasonic instrument at room temperature for 2 h. After ultrasonication, it was stirred with a magnetic stirrer for 6 h. After separation by suction, a yellow sample was obtained. The yellow sample was placed in an oven at 55 °C and dried for 24 h. The dried sample was then placed in a tube furnace and heated at 5 °C·min under argon atmosphere. -1 The temperature was raised to 600 °C, followed by carbonization at 600 °C for 2.5 h, cooling down to room temperature, and then taken out and ground to obtain a magnetic biochar sample; (2) Weigh 1.2 g of the magnetic biochar sample obtained in step (1) and add it to a 65 °C water bath. Then add 0.8 g of chitosan completely dissolved in 100 mL of 2% acetic acid solution. After heating in a water bath for 30 min, add 1 mol / L NaOH dropwise to the mixed solution until the pH is equal to 10. Heat in a water bath for 2 h. (3) The insoluble matter in the solution prepared in step (2) was filtered and repeatedly rinsed with deionized water and ethanol to clean the residual NaOH and other substances, and then placed in an oven at 55 ° C for 24 h and dried for use to obtain a magnetic biochar-chitosan composite material; (4) When used, the initial concentrations of Pb (II) and Cr (VI) solutions were 0.6 mg / L and 5.5 mg / L, respectively, with a volume of 50 mL. 80 g of the magnetic biochar-chitosan composite and the heavy metal solution were added to a 150 mL conical flask, the pH was controlled at 5.0, and the reaction was shaken for 10 h on a constant temperature shaker at 180 rpm, maintaining the water temperature at 20 °C. The residual Pb (II) and Cr (VI) concentrations in the solution were measured, and the adsorption capacity of the material for Pb (II) was calculated to be 8.36 mg / g, and the adsorption capacity for Cr (VI) was calculated to be 7.96 mg / g.

[0037] Comparative Example 5: A preparation method and application of a magnetic biochar-chitosan composite material include the following steps: weighing 1.2 g of magnetic biochar and 0.8 g of chitosan (biochar to chitosan mass ratio of 3:2).

[0038] (1) Pomelo peel biomass after crushing through 120 mesh was placed in a beaker, and 100 mL of FeCl3 (concentration 0.75 mol / L) solution was added. The biomass was ultrasonicated in an ultrasonic instrument at room temperature for 2 h. After ultrasonication, it was stirred with a magnetic stirrer for 6 h. After separation by suction, a yellow sample was obtained. The yellow sample was placed in an oven at 55 °C and dried for 24 h. The dried sample was then placed in a tube furnace and heated at 5 °C·min under argon atmosphere. -1 The temperature was raised to 600 °C, followed by carbonization at 600 °C for 2.5 h, cooling down to room temperature, and then taken out and ground to obtain a magnetic biochar sample; (2) Weigh 1.2 g of the magnetic biochar sample obtained in step (1) and add it to a 65 °C water bath. Then add 0.8 g of chitosan completely dissolved in 100 mL of 2% acetic acid solution. After heating in a water bath for 30 min, add 1 mol / L NaOH dropwise to the mixed solution until the pH is equal to 10. Heat in a water bath for 2 h. (3) The insoluble matter in the solution prepared in step (2) was filtered and repeatedly rinsed with deionized water and ethanol to clean the residual NaOH and other substances, and then placed in an oven at 55 ° C for 24 h and dried for use to obtain a magnetic biochar-chitosan composite material; (4) When used, the initial concentrations of Pb (II) and Cr (VI) solutions were 0.6 mg / L and 5.5 mg / L, respectively, with a volume of 50 mL. 80 g of magnetic biochar-chitosan composite material and heavy metal solution were added to a 150 mL conical flask, the pH was controlled at 5.0, and the reaction was shaken for 5 h on a constant temperature shaker at 180 rpm, maintaining the water temperature at 50 °C. The residual Pb (II) and Cr (VI) concentrations in the solution were measured, and the adsorption capacity of the material for Pb (II) was calculated to be 10.25 mg / g, and the adsorption capacity for Cr (VI) was calculated to be 9.86 mg / g.

[0039] Comparative Example 6: A preparation method and application of a magnetic biochar-chitosan composite material include the following steps: weighing 1.2 g of magnetic biochar and 0.8 g of chitosan (biochar to chitosan mass ratio of 3:2).

[0040] (1) Pomelo peel biomass after crushing through 120 mesh was placed in a beaker, and 100 mL of FeCl3 (concentration 0.75 mol / L) solution was added. The biomass was ultrasonicated in an ultrasonic instrument at room temperature for 2 h. After ultrasonication, it was stirred with a magnetic stirrer for 6 h. After separation by suction, a yellow sample was obtained. The yellow sample was placed in an oven at 55 °C and dried for 24 h. The dried sample was then placed in a tube furnace and heated at 5 °C·min under argon atmosphere. -1 The temperature was raised to 600 °C, followed by carbonization at 600 °C for 2.5 h, cooling down to room temperature, and then taken out and ground to obtain a magnetic biochar sample; (2) Weigh 1.2 g of the magnetic biochar sample obtained in step (1) and add it to a 65 °C water bath. Then add 0.8 g of chitosan completely dissolved in 100 mL of 2% acetic acid solution. After heating in a water bath for 30 min, add 1 mol / L NaOH dropwise to the mixed solution until the pH is equal to 10. Heat in a water bath for 2 h. (3) The insoluble matter in the solution prepared in step (2) was filtered and repeatedly rinsed with deionized water and ethanol to clean the residual NaOH and other substances, and then placed in an oven at 55 ° C for 24 h and dried for use to obtain a magnetic biochar-chitosan composite material; (4) When used, the initial concentrations of Pb (II) and Cr (VI) solutions were 0.6 mg / L and 5.5 mg / L, respectively, with a volume of 50 mL. Potassium dihydrogen phosphate was added to make the initial total phosphorus concentrations 100 and 600 mg / L. 80 g of magnetic biochar-chitosan composite material and heavy metal solution were added to a 150 mL conical flask, and the pH was controlled at 5.0. The reaction was shaken for 10 h on a constant temperature shaker at a speed of 180 rpm, maintaining the water temperature at 50 °C. The residual Pb (II) and Cr (VI) concentrations in the solution were measured. It was calculated that when the total phosphorus concentration was 100 mg / L, the material had an adsorption capacity of 11.21 mg / g for Pb (II) and 9.18 mg / g for Cr (VI). When the total phosphorus concentration was 600 mg / L, the material had an adsorption capacity of 6.89 mg / g for Pb (II) and 8.98 mg / g for Cr (VI). mg / g.

[0041] (5) When used, the initial concentrations of Pb (II) and Cr (VI) solutions were 0.6 mg / L and 5.5 mg / L, respectively, with a volume of 50 mL. Sodium fluoride was added to make the initial fluoride concentrations 50 and 300 mg / L, respectively. 80 g of magnetic biochar-chitosan composite material and heavy metal solution were added to a 150 mL conical flask, and the pH was controlled to 5.0. The reaction was shaken for 10 h on a constant temperature shaker at a speed of 180 rpm, maintaining the water temperature at 50 °C. The residual Pb (II) and Cr (VI) concentrations in the solution were measured. It was calculated that when the total fluorine concentration was 50 mg / L, the material had an adsorption capacity of 11.09 mg / g for Pb (II) and 8.91 mg / g for Cr (VI). When the total fluorine concentration was 300 mg / L, the material had an adsorption capacity of 10.22 mg / g for Pb (II) and 5.86 mg / g for Cr (VI). mg / g.

[0042] Comparative Example 7: A preparation method and application of a magnetic biochar-chitosan composite material include the following steps: weighing 1.2 g of magnetic biochar and 0.8 g of chitosan (biochar to chitosan mass ratio of 3:2).

[0043] (1) Pomelo peel biomass after crushing through 120 mesh was placed in a beaker, and 100 mL of FeCl3 (concentration 0.75 mol / L) solution was added. The biomass was ultrasonicated in an ultrasonic instrument at room temperature for 2 h. After ultrasonication, it was stirred with a magnetic stirrer for 6 h. After separation by suction, a yellow sample was obtained. The yellow sample was placed in an oven at 55 °C and dried for 24 h. The dried sample was then placed in a tube furnace and heated at 5 °C·min under argon atmosphere. -1 The temperature was raised to 600 °C, followed by carbonization at 600 °C for 2.5 h, cooling down to room temperature, and then taken out and ground to obtain a magnetic biochar sample; (2) Weigh 1.2 g of the magnetic biochar sample obtained in step (1) and add it to a 65 °C water bath. Then add 0.8 g of chitosan completely dissolved in 100 mL of 2% acetic acid solution. After heating in a water bath for 30 min, add 1 mol / L NaOH dropwise to the mixed solution until the pH is equal to 10. Immediately add 10 mL of 1% glutaraldehyde solution and react in a 65 °C water bath for 2 h under continuous stirring. (3) The insoluble matter in the solution prepared in step (2) was filtered and repeatedly rinsed with deionized water and ethanol to clean the residual NaOH and other substances, and then placed in an oven at 55 ° C for 24 h and dried for use to obtain a magnetic biochar-chitosan composite material; (4) When used, the initial concentrations of Pb (II) and Cr (VI) solutions were 0.6 mg / L and 5.5 mg / L, respectively, with a volume of 50 mL. 80 g of magnetic biochar-chitosan composite material and heavy metal solution were added to a 150 mL conical flask, the pH was controlled at 5.0, and the reaction was shaken for 10 h on a constant temperature shaker at 180 rpm, maintaining the water temperature at 50 °C. The residual Pb (II) and Cr (VI) concentrations in the solution were measured, and the adsorption capacity of the material for Pb (II) was calculated to be 14.51 mg / g, and the adsorption capacity for Cr (VI) was calculated to be 10.23 mg / g.

[0044] Comparative Example 8: A preparation method and application of a magnetic biochar-chitosan composite material include the following steps: weighing 1.2 g of magnetic biochar and 0.8 g of chitosan (biochar to chitosan mass ratio of 3:2).

[0045] (1) Pomelo peel biomass after crushing through 120 mesh was placed in a beaker, and 100 mL of FeCl3 (concentration 0.75 mol / L) solution was added. The biomass was ultrasonicated in an ultrasonic instrument at room temperature for 2 h. After ultrasonication, it was stirred with a magnetic stirrer for 6 h. After separation by suction, a yellow sample was obtained. The yellow sample was placed in an oven at 55 °C and dried for 24 h. The dried sample was then placed in a tube furnace and heated at 5 °C·min under argon atmosphere. -1 The temperature was raised to 600 °C, followed by carbonization at 600 °C for 2.5 h, cooling down to room temperature, and then taken out and ground to obtain a magnetic biochar sample; (2) Weigh 1.2 g of the magnetic biochar sample obtained in step (1) and add it to a 65 °C water bath. Then add 0.8 g of chitosan completely dissolved in 100 mL of 2% acetic acid solution. After heating in a water bath for 30 min, add 1 mol / L NaOH dropwise to the mixed solution until the pH is equal to 10. Immediately add 15 mL of 1% glutaraldehyde solution and react in a 65 °C water bath for 2 h under continuous stirring. (3) The insoluble matter in the solution prepared in step (2) was filtered and repeatedly rinsed with deionized water and ethanol to clean the residual NaOH and other substances, and then placed in an oven at 55 ° C for 24 h and dried for use to obtain a magnetic biochar-chitosan composite material; (4) When used, the initial concentrations of Pb (II) and Cr (VI) solutions were 0.6 mg / L and 5.5 mg / L, respectively, with a volume of 50 mL. 80 g of magnetic biochar-chitosan composite material and heavy metal solution were added to a 150 mL conical flask, the pH was controlled at 5.0, and the reaction was shaken for 10 h on a constant temperature shaker at 180 rpm, maintaining the water temperature at 50 °C. The residual Pb (II) and Cr (VI) concentrations in the solution were measured, and the adsorption capacity of the material for Pb (II) was calculated to be 14.92 mg / g, and the adsorption capacity for Cr (VI) was calculated to be 10.42 mg / g.

[0046] Comparative Example 9: A preparation method and application of a magnetic biochar-chitosan composite material include the following steps: weighing 1.2 g of magnetic biochar and 0.8 g of chitosan (biochar to chitosan mass ratio of 3:2).

[0047] (1) Pomelo peel biomass after crushing through 120 mesh was placed in a beaker, and 100 mL of FeCl3 (concentration 0.75 mol / L) solution was added. The biomass was ultrasonicated in an ultrasonic instrument at room temperature for 2 h. After ultrasonication, it was stirred with a magnetic stirrer for 6 h. After separation by suction, a yellow sample was obtained. The yellow sample was placed in an oven at 55 °C and dried for 24 h. The dried sample was then placed in a tube furnace and heated at 5 °C·min under argon atmosphere. -1 The temperature was raised to 600 °C, followed by carbonization at 600 °C for 2.5 h, cooling down to room temperature, and then taken out and ground to obtain a magnetic biochar sample; (2) Weigh 1.2 g of the magnetic biochar sample obtained in step (1) and add it to a 65 °C water bath. Then add 0.8 g of chitosan completely dissolved in 100 mL of 2% acetic acid solution. After heating in a water bath for 30 min, add 1 mol / L NaOH dropwise to the mixed solution until the pH is equal to 10. Immediately add 20 mL of 1% glutaraldehyde solution and react in a 65 °C water bath for 2 h under continuous stirring. (3) The insoluble matter in the solution prepared in step (2) was filtered and repeatedly rinsed with deionized water and ethanol to clean the residual NaOH and other substances, and then placed in an oven at 55 ° C for 24 h and dried for use to obtain a magnetic biochar-chitosan composite material; (4) When used, the initial concentrations of Pb (II) and Cr (VI) solutions were 0.6 mg / L and 5.5 mg / L, respectively, with a volume of 50 mL. 80 g of magnetic biochar-chitosan composite material and heavy metal solution were added to a 150 mL conical flask, the pH was controlled at 5.0, and the reaction was shaken for 10 h on a constant temperature shaker at 180 rpm, maintaining the water temperature at 50 °C. The residual Pb (II) and Cr (VI) concentrations in the solution were measured, and the adsorption capacity of the material for Pb (II) was calculated to be 14.88 mg / g, and the adsorption capacity for Cr (VI) was calculated to be 10.45 mg / g.

[0048] Comparison summary: Comparison between Example 1 and Comparative Example 2 shows that the adsorption effect of the biochar-chitosan composite material prepared by controlling the mass ratio of biochar to chitosan to 3:2 is better than that of the biochar to chitosan composite material prepared by controlling the mass ratio of biochar to chitosan to 1:1.

[0049] Comparison between Example 1 and Comparative Example 3 shows that, when used, the material has better adsorption efficiency for Pb(II) when the pH value is controlled at 5, and the higher the pH value of the solution, the stronger the electrostatic attraction of the material to Pb(II). The material has better adsorption efficiency for Cr(VI) when the pH value is controlled at 2, and the lower the pH value of the solution, the stronger the electrostatic attraction of the material to Cr(VI).

[0050] A comparison between Example 1 and Comparative Example 4 shows that controlling the reaction temperature at 50°C is better than 20°C in practice. This is likely because increasing the temperature accelerates the migration of heavy metals, thereby increasing the internal and external diffusion rates. Furthermore, increasing the temperature decreases the viscosity of the solution, facilitating the precipitation of Pb(II) and Cr(VI).

[0051] Comparison between Example 1 and Comparative Example 5 shows that the adsorption capacity increases with the increase of reaction time.

[0052] Comparison between Example 1 and Comparative Example 6 shows that the total phosphorus concentration has an influence on the Pb content of the mixed solution of Pb (II) and Cr (VI).2+ The adsorption efficiency of Cr 6+ The total fluorine concentration has little effect on the Pb(Ⅱ) and Cr(VI) mixed solution. 2 + The adsorption of Cr 6+ The adsorption efficiency is affected.

[0053] Comparison between Example 1 and Comparative Examples 7, 8 and 9 shows that the adsorption capacity of Pb(II) and Cr(VI) by the material after adding glutaraldehyde is significantly improved.

[0054] Main performance indicators and test methods of the present invention Measurement of heavy metal ion concentration: All heavy metal ion concentration data were obtained using inductively coupled plasma optical emission spectrometry (ICP-OES). Before sample testing, a calibration curve was generated by measuring a series of standard samples containing all the tested heavy metal ions at varying concentrations. The elemental spectra of the two heavy metal ions used in this experiment were (Cr 267.716 r and Pb 220.353 r). Diluting the sample solution with 5% nitric acid solution maintained the stability of the heavy metal ions, thereby ensuring the accuracy of the experimental data.

[0055] Result analysis: Result calculation: Adsorption amount q e It is used to evaluate the adsorption capacity of biochar for heavy metal ions, and its mathematical expression is:

[0056] Here C0 and C e represents the concentration of heavy metal ions in the initial state and equilibrium state (mg / L), respectively; v and M are the volume of the solution system (L) and the mass of biochar (g), respectively.

[0057] In addition, removal rate (R%) is also used to express the adsorption effect of biochar on pollutants, that is, The expression is as follows:

[0058] Where C0 and C t Represent the concentration of heavy metal ions (mg / L) in the initial system and after time t (min), respectively.

[0059] 1. When preparing magnetic biochar-chitosan composite materials, the material prepared when the mass ratio of biochar to chitosan is controlled to be 3:2 has the best adsorption effect.

[0060] 2. The factors that affect the application of magnetic biochar-chitosan composite materials include: pH, temperature, reaction time, and total phosphorus and fluoride ions in the solution.

[0061] 3. The removal of heavy metals from water by chitosan magnetic biochar is mainly achieved through chemical adsorption mechanism, among which the removal of Pb(II) is more inclined to surface coordination exchange, while the removal of Cr(VI) involves more physical adsorption.

Claims

1. A preparation method and application of a magnetic biochar-chitosan composite material, comprising the following steps: (1) The dried biomass is crushed, carbonized at high temperature in the absence of oxygen, and then ground and sieved after cooling to obtain raw biochar; (2) The original biochar is mixed with the iron ion solution, and after ultrasonic stirring for a period of time, the solid and liquid are separated. The resulting yellow sample is dried to obtain the iron-doped biochar; (3) Carbonizing the iron-doped biochar at high temperature in the absence of oxygen, grinding and sieving the resulting magnetic biochar after cooling; (4) mixing the magnetic biochar and chitosan solution, heating and stirring for a period of time, filtering, rinsing, and drying to obtain a magnetic biochar-chitosan composite adsorption material; (5) A certain amount of magnetic biochar-chitosan composite adsorption material is mixed with wastewater, stirred for a period of time, and then the solid and liquid are separated. The filtrate is the treated heavy metal wastewater.

2. The preparation method and application of a magnetic biochar-chitosan composite material according to claim 1, characterized in that: In step (1), the biomass is Rutaceae peel or fruit leaf, the protective gas in the carbonization process is argon or nitrogen, the heating rate is 3-10 ° C / min, the holding temperature is 500-700 ° C, the holding time is 2-5 h, and the cooling rate is 10-20 ° C / min.

3. The preparation method and application of a magnetic biochar-chitosan composite material according to claim 1, characterized in that: In the step (2), the ultrasonic time in the ultrasonic instrument is 5-8 h, and the stirring time is 5-8 h.

4. The preparation method and application of a magnetic biochar-chitosan composite material 8 according to claim 1, characterized in that: In step (2), the drying temperature is 50-80°C and the drying time is 24-28 hours.

5. The preparation method and application of a magnetic biochar-chitosan composite material according to claim 1, characterized in that: In the step (3), the protective gas for the carbonization process is argon or nitrogen, the heating rate is 5-8 °C / min, the holding temperature is 600-800 °C, the holding time is 2-3 h, and the cooling rate is 10-20 °C / min.

6. The preparation method and application of a magnetic biochar-chitosan composite material according to claim 1, characterized in that: In step (4), 2-8 mol / L acetic acid solution and 0.5-2 mol / L glutaraldehyde solution are added to the chitosan solution at 60-80°C for 20-40 min.

7. The preparation method and application of a magnetic biochar-chitosan composite material according to claim 1, characterized in that: In step (4), alkaline solution is used to adjust the pH to 9-11, the temperature to 60-80°C, and heating is performed for 2-3 hours.

8. The preparation method and application of a magnetic biochar-chitosan composite material according to claim 1, characterized in that: In step (4), the filtration is performed using a suction filter, the rinsing is performed using deionized water and ethanol, and the drying is performed using an oven at a temperature of 50-70° C. for 24-28 h.

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