Modified coconut shell biochar as well as preparation method and application thereof

Abstract

The invention relates to the technical field of biochar, in particular to modified coconut shell biochar as well as a preparation method and application thereof. The invention provides a preparation method of modified coconut shell biochar, which comprises the following steps: activating coconut shell biochar in an acidic solution, soaking in a mixed aqueous solution of ferric chloride and ferrous chloride, and reacting under an alkaline condition to obtain magnetic coconut shell biochar; and adding the obtained magnetic coconut shell biochar and kaolin powder into a sodium alginate solution, reacting under an alkaline condition, and carbonizing to obtain the modified coconut shell biochar. The modified coconut shell biochar provided by the invention has good heavy metal adsorption capacity and more stable ferromagnetism, and can be separated from a matrix more easily, so that secondary pollution to the matrix is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of biochar, and in particular to a modified coconut shell biochar and a preparation method and application thereof. Background Art

[0002] Biochar is a carbon material produced by the pyrolysis of biomass. Its raw materials come from a wide range of sources, including common agricultural and forestry wastes such as crop straw, bamboo and peanut shells. The structural characteristics and physical and chemical properties of biochar itself give it a high adsorption capacity, and it can be used to adsorb organic pollutants and heavy metals in water, soil and sludge. However, the biochar products that are currently widely used are mostly in powder form. After being used to adsorb heavy metals in sewage, soil or sludge, the powdered biochar is often mixed with the matrix, resulting in heavy metals or organic matter being adsorbed by biochar, but still difficult to separate from the water body or solid matrix, thus failing to completely solve the problem of heavy metal pollution.

[0003] At present, in order to make biochar adsorbed with heavy metals easier to separate from sewage, soil or sludge, there is an existing technology that modifies biochar to make it ferromagnetic to achieve easier separation from the matrix (such as patents with application numbers 201611024652.4, 201910226818.8 and 202010846744.0). However, this method is only effective when used to remove biochar from water bodies. In the process of interacting with solid matrices such as soil or sludge, the ferromagnetism of biochar is easily damaged, resulting in a separation effect that is not obvious. Summary of the invention

[0004] In view of this, the present invention provides a modified coconut shell biochar and a preparation method and application thereof. The modified coconut shell biochar has good heavy metal adsorption capacity and more stable ferromagnetism, can be more easily separated from the matrix, and avoids secondary pollution.

[0005] In order to solve the above technical problems, the present invention provides a method for preparing modified coconut shell biochar, comprising the following steps:

[0006] S1. After the coconut shell biochar is activated in an acidic solution, it is immersed in a mixed aqueous solution of ferric chloride and ferrous chloride, the pH of the solution is adjusted to 10-11, and the solution is stirred at 60-70° C. for 2-4 hours under an inert atmosphere, filtered, washed, and dried to obtain magnetic coconut shell biochar;

[0007] S2. Add the magnetic coconut shell biochar and kaolin powder into the sodium alginate solution, adjust the solution pH to 9-10, stir and react at 90-110° C. for 1-3 hours, filter, wash and dry after the reaction, and carbonize at 300-400° C. in an inert atmosphere to obtain modified coconut shell biochar.

[0008] The present invention activates coconut shell biochar in an acidic solution and then puts it into an iron-containing solution, so that the iron hydroxide generated by iron ions under alkaline conditions is adsorbed on the inner pore surface of the activated coconut shell biochar, giving the coconut shell biochar ferromagnetism, which is convenient for subsequent separation from matrices such as soil, sludge or water. The magnetic coconut shell biochar and kaolin powder are added to the sodium alginate solution together, and the cations such as silicon and aluminum on the surface of the kaolin interact with the hydroxyl and carboxyl groups in the sodium alginate molecules to generate a gel with a mesh structure and adhere to the surface of the magnetic coconut shell biochar, thereby increasing the heavy metal adsorption amount and protecting the iron hydroxide in the internal pores of the biochar to be more stably adsorbed in the pores of the magnetic coconut shell biochar without being affected by the matrix, thereby reducing the loss of ferromagnetism during the interaction between the magnetic coconut shell biochar and the solid matrix. Finally, after the high-temperature carbonization step, the specific surface area of ​​the modified coconut shell biochar is further increased, and the heavy metal adsorption capacity is improved.

[0009] In combination with the first aspect, the carbonization time is 4 to 6 hours.

[0010] In combination with the first aspect, the activation of the coconut shell biochar in an acidic solution specifically comprises: placing the coconut shell biochar in an acidic solution for activation reaction for 1 to 3 hours, filtering, washing, and drying.

[0011] In combination with the first aspect, the acidic solution is an aqueous solution of phosphoric acid or hydrochloric acid with a concentration of 2 to 4 mol / L. The coconut shell biochar is acidified to have a larger specific surface area and higher reaction activity.

[0012] In combination with the first aspect, in the mixed aqueous solution of ferric chloride and ferrous chloride, the concentration of iron ions is 2 to 8 mol / L, preferably 5 mol / L.

[0013] In combination with the first aspect, the molar ratio of ferric chloride to ferrous chloride is 3:1.

[0014] In combination with the first aspect, the concentration of the coconut shell biochar in the mixed aqueous solution of ferric chloride and ferrous chloride is 40-60 g / L, preferably 50 g / L.

[0015] In combination with the first aspect, the particle size of the kaolin powder is 10 to 50 μm. The kaolin powder within this particle size range helps to increase the specific surface area of ​​kaolin and promotes the interaction between the cations on its surface and the sodium alginate.

[0016] Preferably, the particle size of the kaolin powder is 20 to 30 μm.

[0017] In combination with the first aspect, the mass ratio of the magnetic coconut shell biochar to kaolin powder is 3-5:1, and the concentration of the sodium alginate solution is 2-5 mol / L.

[0018] Preferably, the concentration of the mixture of magnetic coconut shell biochar and kaolin powder in the sodium alginate solution is 35-60 g / L.

[0019] The second aspect of the present invention provides a modified coconut shell biochar, which is prepared according to the above-mentioned preparation method of modified coconut shell biochar.

[0020] A third aspect of the present invention provides an application of modified coconut shell biochar in soil, sludge or sewage treatment.

[0021] When the modified coconut shell biochar is used in soil or sludge composting, the addition amount is 10wt% to 20wt%, and the modified coconut shell biochar is mixed into the soil or sludge sample and mixed evenly for heavy metal adsorption. After the composting is completed, the compost product is mixed with water to form a suspension, and the modified coconut shell biochar adsorbed with heavy metals is separated from the compost product by an external magnetic field. When the modified coconut shell biochar is used to remove heavy metals from sewage, the addition amount is 5wt% to 10wt%, and after the heavy metal removal is completed, the biochar is separated from the water body by an external magnetic field.

[0022] The beneficial effects obtained by the present invention are as follows: the modified coconut shell biochar provided by the present invention has excellent heavy metal adsorption capacity, and the removal efficiency of heavy metals in simulated polluted water and soil is above 95%; and the modified coconut shell biochar has a cross-linked network structure, which can ensure that the iron hydroxide in the internal pores of the biochar is more stably adsorbed in the pores of the magnetic coconut shell biochar, thereby reducing the loss of ferromagnetism during the reaction between the biochar and the solid matrix, providing a guarantee for separating the biochar from the solid matrix as much as possible, and the recovery rate after adsorbing the heavy metals in the simulated polluted water is above 98%, and the recovery rate after adsorbing the heavy metals in the simulated soil can also be maintained at above 95%, thereby solving the problem that the existing powdered biochar is difficult to separate from the matrix and causes secondary pollution. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] In view of the fact that the current magnetic biochar easily loses its magnetism and is prone to incomplete separation when treating solid matrices such as soil or sludge, the present invention provides a modified coconut shell biochar, which not only has excellent ability to adsorb heavy metals, but also has a cross-linked network structure that makes the ferromagnetism of the biochar more stable, thereby ensuring the separation of the biochar from the solid matrix.

[0025] The technical solution of the present invention is described in more detail below through specific examples. In the following examples and comparative examples, the ferric chloride used is ferric chloride hexahydrate, and the ferrous chloride is ferrous chloride tetrahydrate.

[0026] Example 1

[0027] This embodiment provides a method for preparing modified coconut shell biochar, comprising the following steps:

[0028] S1. Activate 200g of coconut shell biochar in 3mol / L phosphoric acid aqueous solution for 2h, filter and wash with water, dry and grind, and then immerse in 4L of a mixed aqueous solution of ferric chloride and ferrous chloride with an iron ion concentration of 5mol / L (the molar ratio of ferric chloride to ferrous chloride is 3:1), adjust the solution pH to 10-11 with alkali solution, stir and react at 65°C in an inert atmosphere for 3h, filter, wash and dry to obtain magnetic coconut shell biochar.

[0029] S2. Add 100 g of the magnetic coconut shell biochar prepared in step S1 and 25 g of kaolin powder (particle size 30 μm) into 2.5 L of 4 mol / L sodium alginate solution, adjust the solution pH to 9-10 with alkali solution, stir and react at 100° C. for 2.5 h, filter, wash and dry after the reaction, carbonize at 350° C. in an inert atmosphere for 5 h, and cool to obtain modified coconut shell biochar.

[0030] Example 2

[0031] This embodiment provides a method for preparing modified coconut shell biochar, comprising the following steps:

[0032] S1. Activate 200g of coconut shell biochar in 4mol / L hydrochloric acid aqueous solution for 1h, filter and wash with water, dry and grind, and then immerse in 5L of a mixed aqueous solution of ferric chloride and ferrous chloride with an iron ion concentration of 2mol / L (the molar ratio of ferric chloride to ferrous chloride is 3:1), adjust the solution pH to 10-11 with alkali solution, stir and react at 60°C in an inert atmosphere for 4h, filter, wash and dry to obtain magnetic coconut shell biochar.

[0033] S2. Add 100 g of the magnetic coconut shell biochar prepared in step S1 and 20 g of kaolin powder (particle size 10 μm) into 2 L of 2 mol / L sodium alginate solution, adjust the solution pH to 9-10 with alkali solution, stir and react at 90° C. for 3 h, filter, wash and dry after the reaction, carbonize at 400° C. in an inert atmosphere for 4 h, and cool to obtain modified coconut shell biochar.

[0034] Example 3

[0035] This embodiment provides a method for preparing modified coconut shell biochar, comprising the following steps:

[0036] S1. Activate 180g of coconut shell biochar in a 2mol / L hydrochloric acid aqueous solution for 3h, filter and wash with water, dry and grind, and then immerse in 3L of a mixed aqueous solution of ferric chloride and ferrous chloride with an iron ion concentration of 8mol / L (the molar ratio of ferric chloride to ferrous chloride is 3:1), adjust the solution pH to 10-11 with alkali solution, stir and react at 70°C in an inert atmosphere for 2h, filter, wash and dry to obtain magnetic coconut shell biochar.

[0037] S2. Add 105 g of the magnetic coconut shell biochar prepared in step S1 and 35 g of kaolin powder (particle size 10 μm) into 4 L of 5 mol / L sodium alginate solution, adjust the solution pH to 9-10 with alkali solution, stir and react at 110°C for 2 h, filter, wash and dry after the reaction, carbonize at 300°C in an inert atmosphere for 6 h, and cool to obtain modified coconut shell biochar.

[0038] Comparative Example 1

[0039] This comparative example provides a method for preparing modified coconut shell biochar, and the preparation steps include:

[0040] S1. Same as step S1 in embodiment 1.

[0041] S2. Add 125 g of the magnetic coconut shell biochar prepared in step S1 to 2.5 L of 4 mol / L sodium alginate solution, adjust the pH of the solution to 9-10 with alkali solution, stir and react at 100°C for 2.5 h, filter, wash and dry after the reaction, carbonize at 350°C in an inert atmosphere for 5 h, and cool to obtain modified coconut shell biochar.

[0042] Comparative Example 2

[0043] This comparative example provides a method for preparing modified coconut shell biochar, and its preparation steps are similar to those of Example 1, except that the kaolin powder in step S2 is replaced with diatomaceous earth of the same mass and the same particle size, and the remaining steps are the same as those of Example 1.

[0044] Comparative Example 3

[0045] This comparative example provides a method for preparing modified coconut shell biochar, and its preparation steps are similar to those of Example 1, except that the carbonization step is not performed in step S2, and the remaining steps are the same as those of Example 1.

[0046] Comparative Example 4

[0047] This comparative example provides a method for preparing modified coconut shell biochar, and the preparation steps include:

[0048] S1. Activate 200 g of coconut shell biochar in 3 mol / L phosphoric acid aqueous solution for 2 h, filter and wash with water, dry and crush, carbonize at 350 ° C in an inert atmosphere for 5 h, cool, and immerse in 4 L of a mixed aqueous solution of ferric chloride and ferrous chloride with an iron ion concentration of 5 mol / L (the molar ratio of ferric chloride to ferrous chloride is 3:1), adjust the pH of the solution to 10-11 with alkali solution, stir and react at 65 ° C in an inert atmosphere for 3 h, filter, wash and dry to obtain magnetic coconut shell biochar.

[0049] S2. Add 100 g of the magnetic coconut shell biochar prepared in step S1 and 25 g of kaolin powder (particle size 30 μm) into 2.5 L of 4 mol / L sodium alginate solution, adjust the pH of the solution to 9-10 with alkali solution, stir and react at 100° C. for 2.5 h, and after the reaction is completed, filter, wash and dry to obtain modified coconut shell biochar.

[0050] Test Example 1

[0051] The sewage contaminated by heavy metals was simulated by using the homemade sewage in the laboratory (i.e., adding a certain amount of heavy metals to distilled water), and the modified coconut shell biochar provided by the present invention was used to adsorb the heavy metals in the sewage. Specifically, 100 g (denoted as X) of the modified coconut shell biochar obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were added to 1 L (denoted as V1) of sewage, and stirred continuously at room temperature for 1 to 2 hours. After that, the modified coconut shell biochar was separated from the water body under the condition of a magnetic field, and the concentration of heavy metal ions in the water body before and after the adsorption by the biochar was detected. The removal efficiency of each heavy metal ion was calculated according to the concentration, and the separated biochar was dried and weighed (denoted as Y), the volume of the water body after separation (denoted as V2) was measured, and the recovery rate of the biochar was calculated. The results are shown in Table 1.

[0052] The removal efficiency is calculated according to the following formula:

[0053] Removal efficiency (%) = (concentration of the heavy metal ion in the water before adsorption * V1 - concentration of the heavy metal ion in the water after adsorption * V2) / (concentration of the heavy metal ion in the water before adsorption * V1) * 100%.

[0054] The recovery rate of biochar was calculated according to the following formula:

[0055] Recovery rate (%) = (Y-the sum of the mass loss of each element before and after adsorption) / X*100%,

[0056] The sum of the mass losses of the elements before and after adsorption = (the sum of the concentrations of the elements before adsorption * V1 - the sum of the concentrations of the elements after adsorption * V2), and the concentrations of the elements before and after adsorption are expressed in mg / L.

[0057] Table 1

[0058]

[0059] Test Example 2

[0060] The contaminated soil prepared in the laboratory (i.e., a certain amount of heavy metals was added to the clean dry soil) was used to simulate the soil contaminated by heavy metals, and the modified coconut shell biochar provided by the present invention was used to adsorb the heavy metals in the soil. Specifically, 100 g (denoted as X) of the modified coconut shell biochar obtained in Examples 1 to 3 and Comparative Examples 1 to 4 was added to 500 g (denoted as Y1) of soil, and stirred continuously for 1 to 2 hours at room temperature. Then, 2 L of water was added, and the modified coconut shell biochar was separated from the soil suspension under magnetic field conditions. The concentrations of heavy metal ions in the soil before and after biochar adsorption were detected, and the removal efficiency was calculated according to the concentration difference. The separated biochar and soil were dried and weighed (denoted as M and Y2, respectively), and the recovery rate of biochar was calculated. The results are shown in Table 2.

[0061] The removal efficiency is calculated according to the following formula:

[0062] Removal efficiency (%) = (concentration of the heavy metal ion in the soil before adsorption * Y1 - concentration of the heavy metal ion in the soil after adsorption * Y2) / (concentration of the heavy metal ion in the soil before adsorption * Y1) * 100%.

[0063] The recovery rate of biochar was calculated according to the following formula:

[0064] Recovery rate (%) = (M-the sum of the mass loss of each element before and after adsorption) / X*100%,

[0065] The sum of the mass losses of the elements before and after adsorption = (the sum of the concentrations of the elements before adsorption * Y1 - the sum of the concentrations of the elements after adsorption * Y2), and the concentrations of the elements before and after adsorption are expressed in mg / g.

[0066] Table 2

[0067]

[0068] What is described above is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing modified coconut shell biochar, characterized in that: The following steps are involved: S1. After the coconut shell biochar is activated in an acidic solution, it is immersed in a mixed aqueous solution of ferric chloride and ferrous chloride, the pH of the solution is adjusted to 10-11, and the solution is stirred at 60-70° C. for 2-4 hours under an inert atmosphere, filtered, washed, and dried to obtain magnetic coconut shell biochar; S2. Add the magnetic coconut shell biochar and kaolin powder into the sodium alginate solution, adjust the solution pH to 9-10, stir and react at 90-110° C. for 1-3 hours, filter and dry after the reaction, and carbonize at 300-400° C. in an inert atmosphere to obtain modified coconut shell biochar.

2. The method for preparing modified coconut shell biochar according to claim 1, characterized in that: The activation of the coconut shell biochar in an acidic solution specifically comprises: placing the coconut shell biochar in an acidic solution for activation reaction for 1 to 3 hours, filtering, washing, and drying.

3. The method for preparing modified coconut shell biochar according to claim 1 or 2, characterized in that: The acidic solution is an aqueous solution of phosphoric acid or hydrochloric acid with a concentration of 2-4 mol / L.

4. The method for preparing modified coconut shell biochar according to claim 1, characterized in that: In the mixed aqueous solution of ferric chloride and ferrous chloride, the concentration of the iron ions is 2-8 mol / L.

5. The method for preparing modified coconut shell biochar according to claim 4, characterized in that: The molar ratio of the ferric chloride to ferrous chloride is 3:

1.

6. The method for preparing modified coconut shell biochar according to claim 1, characterized in that: The concentration of the coconut shell biochar in the mixed aqueous solution of ferric chloride and ferrous chloride is 40-60 g / L.

7. The method for preparing modified coconut shell biochar according to claim 1, characterized in that: The particle size of the kaolin powder is 10 to 50 μm.

8. The method for preparing modified coconut shell biochar according to claim 1, characterized in that: The mass ratio of the magnetic coconut shell biochar to the kaolin powder is 3-5:1, and the concentration of the sodium alginate solution is 2-5 mol / L.

9. A modified coconut shell biochar, characterized in that: The modified coconut shell biochar is prepared according to the method for preparing the modified coconut shell biochar according to any one of claims 1 to 8.

10. Use of the modified coconut shell biochar according to claim 9 in soil, sludge or sewage treatment.

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