A method for preparing biochar modified with ferric chloride and calcium chloride and a method for enhancing phosphate adsorption.

Abstract

This invention discloses a method for modifying biochar using ferric chloride and calcium chloride, and a method for enhancing phosphate adsorption. The preparation method includes the following steps: (1) mixing and impregnating the original biochar with a solution of ferric chloride and calcium chloride, and shaking the mixture thoroughly; (2) filtering the mixture to remove the supernatant, and drying the remaining solid material to obtain the modified biochar material; (3) placing the modified biochar material into a tube furnace, continuously introducing nitrogen gas into the tube furnace, and carbonizing at a high temperature of 600±5℃ for 2±0.1h. After the tube furnace cools to room temperature, the material is removed, cleaned, and dried to obtain biochar modified using ferric chloride and calcium chloride. The modification with ferric chloride and calcium chloride increases the adsorption active sites of the biochar, increases its specific surface area, makes its structure more porous, and enhances the adsorption effect.

Description

Technical Field

[0001] This invention relates to a method for adsorbing phosphate using modified biochar, specifically to a method for preparing modified biochar using a combination of ferric chloride and calcium chloride, and a method for enhancing phosphate adsorption. Background Technology

[0002] Even after treatment in septic tanks, the phosphorus content in the excrement and urine of scattered farming households remains high. The discharge of large amounts of sewage into rivers, reservoirs, and lakes leads to increased phosphorus levels in these water bodies, which in turn easily causes eutrophication and threatens human health and environmental safety through the food chain.

[0003] Currently, the main methods for phosphorus removal include chemical precipitation, advanced oxidation, electrochemical methods, and adsorption. Among these, adsorption is considered a more economical, efficient, and easy-to-operate method due to its simplicity, environmental friendliness, and reusability.

[0004] Biochar is a novel porous carbon-based material produced through the anaerobic pyrolysis of biomass. It is commonly used for water purification, resource recovery, and soil fertilization. The raw materials for biochar are abundant, primarily including carbon-rich substances such as agricultural and forestry waste, animal manure, and urban sludge. Biomass-derived adsorbents are characterized by sustainability, low cost and high efficiency, biodegradability, and environmental friendliness. Biochar adsorbents, in particular, possess chemical stability, are non-toxic, low-cost, have a large specific surface area, a porous structure, and are rich in functional groups, making them valuable for large-scale applications.

[0005] Biochar's porosity and abundant functional groups provide numerous adsorption sites for phosphate. Studies have shown that the presence of metal ions during biochar pyrolysis alters the functional groups, ion exchange capacity, and electronegativity on the biochar surface, thereby enhancing its phosphate adsorption capacity. However, the adsorption capacity of raw biochar for phosphate is typically limited. Therefore, research into modifying raw biochar to improve its phosphate adsorption efficiency is crucial for the treatment of eutrophication in water bodies.

[0006] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing biochar modified with ferric chloride and calcium chloride and a method for enhancing phosphate adsorption. This method solves the problem of limited adsorption capacity of the original biochar. The modified biochar has improved adsorption performance for phosphate and is stable in nature, with less influence from the pH of the phosphate solution.

[0008] To achieve the above objectives, the present invention provides a method for preparing biochar modified using a combination of ferric chloride and calcium chloride, the method comprising the following steps:

[0009] (1) The raw biochar is mixed with ferric chloride and calcium chloride solution and impregnated, and the mixture is shaken thoroughly; wherein, the mass-volume ratio of the raw biochar to the ferric chloride and calcium chloride solution is 1g:10-15mL, and the volume ratio of ferric chloride solution to calcium chloride solution in the ferric chloride and calcium chloride solution is (1-4):(4-1), and the concentrations of the ferric chloride solution and the calcium chloride solution are the same;

[0010] (2) The mixture was filtered to remove the supernatant, and the remaining solid material was dried to obtain the modified biochar material.

[0011] (3) The modified biochar material was placed in a tube furnace and nitrogen gas was continuously introduced into the tube furnace for high-temperature carbonization at 600±5℃ for 2±0.1h. After the tube furnace cooled down to room temperature, it was taken out, cleaned and dried to obtain biochar modified by ferric chloride and calcium chloride.

[0012] Preferably, in step (1), the mass-to-volume ratio of the original biochar to the ferric chloride and calcium chloride solution is 1 g: 10 mL.

[0013] Preferably, in step (1), the concentrations of the ferric chloride solution and the calcium chloride solution are 1 mol / L.

[0014] Preferably, in step (1), the mixing and impregnation time is 2 to 12 hours.

[0015] Preferably, in step (1), the oscillation is carried out in a horizontal shaking table with a rotation speed of 150±5 rpm / min and a temperature of 30±1℃.

[0016] Preferably, in steps (2) and (3), the drying temperature is 100℃±0.5℃.

[0017] Preferably, in step (3), the modified biochar material is placed in a quartz crucible, and after the crucible is placed in a tube furnace, nitrogen gas is continuously introduced for 30 minutes to keep the air in the tube furnace in an oxygen-deficient state. Nitrogen gas is continued to be introduced to raise the temperature to 600±5℃ for pyrolysis and carbonization for 2±0.1h. After the temperature drops to below 40℃, the nitrogen gas is turned off and the crucible is removed. The pyrolyzed biochar is then cleaned and dried.

[0018] Another object of the present invention is to provide a method for enhancing phosphate adsorption using biochar modified with ferric chloride and calcium chloride, the method comprising: treating a phosphate-containing solution with biochar modified with ferric chloride and calcium chloride obtained by the preparation method described above for 50 min at a pH of 2.5–11 and a temperature of 30 ± 0.5 °C, and removing CO3 from the phosphate-containing solution before phosphorus removal. 2- .

[0019] Preferably, HCO3 in the phosphate-containing solution also needs to be removed before phosphorus removal. - .

[0020] Preferably, SO4 in the phosphate-containing solution also needs to be removed before phosphorus removal. 2- .

[0021] Preferably, NO3 in the phosphate-containing solution also needs to be removed before phosphorus removal. - .

[0022] Preferably, Cl in the phosphate-containing solution also needs to be removed before phosphorus removal. - .

[0023] The present invention provides a method for preparing biochar modified with a combination of ferric chloride and calcium chloride, and a method for enhancing phosphate adsorption. This method solves the problem of limited adsorption capacity of original biochar and has the following advantages:

[0024] (1) In this invention, ferric chloride and calcium chloride are added by impregnation before pyrolysis. The adsorption results of phosphate show that the modified biochar has a higher adsorption capacity for PO4. 3- The adsorption capacity increased significantly;

[0025] (2) The biochar modified by the combination of ferric chloride and calcium chloride is stable and less affected by the pH of phosphate solution. Its adsorption efficiency can reach more than 80% at room temperature. It is simple, convenient and efficient to use, and the biochar material prepared is inexpensive and readily available.

[0026] (3) The adsorption effect of biochar on phosphate can be enhanced after the combined modification of ferric chloride and calcium chloride. The adsorption of phosphate by biochar in this invention is significantly enhanced, and the removal efficiency of phosphate in water reaches more than 96%.

[0027] (4) The present invention utilizes biochar modified with ferric chloride and calcium chloride to improve the adsorption performance of phosphate, which is beneficial for application in environmental fields such as eutrophication remediation of water bodies. Attached Figure Description

[0028] Figure 1 This is a SEM image of biochar modified with ferric chloride and calcium chloride in Example 1 of the present invention.

[0029] Figure 2This is a SEM image of the original biochar from Comparative Example 1 of this invention.

[0030] Figure 3 Experimental Example 1 of this invention illustrates the adsorption of PO4 by different biochar materials. 3- Adsorption effect.

[0031] Figure 4 Example 1 of this invention illustrates the adsorption of PO4 by biochar at different time points. 3- Adsorption effect.

[0032] Figure 5 Example 1 of this invention illustrates the adsorption of PO4 by biochar at different pH levels. 3- Adsorption effect.

[0033] Figure 6 This invention provides experimental example 1 of biochar adsorption of PO4 at different dosages. 3- Adsorption effect.

[0034] Figure 7 Example 1 of this invention describes the adsorption of PO4 by biochar in the presence of coexisting ions. 3- Adsorption effect.

[0035] Figure 8 This is the isothermal adsorption curve of biochar A2 at a temperature of 303K in Experimental Example 1 of the present invention. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] It should be noted that: for conditions not specifically specified in the examples, standard conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0038] In this invention, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are used for simplicity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible secondary ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0039] The features mentioned in this invention can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification, provided that there is no contradiction in the combination of these features. Each feature disclosed in the specification can be replaced by any alternative feature that provides the same, equivalent, or similar purpose. Therefore, unless otherwise specified, the disclosed features are merely general examples of equivalent or similar features.

[0040] This invention provides a method for preparing biochar modified with a combination of ferric chloride and calcium chloride, and a method for enhancing phosphate adsorption. The addition of ferric chloride and calcium chloride increases the amount of metal ions in the biochar. During pyrolysis, the presence of ferric and calcium ions promotes the formation of oxygen-containing functional groups (carbonyl, hydroxyl, and carboxyl groups) on the surface of the biochar, thereby enhancing the ion exchange and complexation capacity of the biochar with phosphate, and thus improving the biochar's ability to adsorb PO4. 3- Its adsorption capacity. In addition, biochar has good adsorption capacity for PO4. 3- During the adsorption process, surface precipitation and π-actions of biochar may occur. Because biochar carries a positive charge after being loaded with iron and calcium ions, biochar reacts with PO4. 3- There may also be electrostatic attraction between them. Therefore, this invention significantly improves the adsorption of phosphates by using ferric chloride and calcium chloride in combination with modified biochar.

[0041] The following examples, comparative examples, and experimental cases provide a detailed description of the preparation method of biochar modified with ferric chloride and calcium chloride and the method for enhancing phosphate adsorption provided by the present invention.

[0042] Example 1

[0043] A biochar modified by a combination of ferric chloride and calcium chloride is prepared by the following method:

[0044] (1) The original biochar (purchased from Sinopharm Reagent Group, granular activated carbon) was impregnated with ferric chloride and calcium chloride solution. The mass-to-volume ratio of biochar to metal salt solution was 10 g:100 mL, and the volume ratio of ferric chloride to calcium chloride solution was 3:2, both with a concentration of 1 mol / L. The mixture was placed in a constant temperature shaker at 30±0.5℃ and shaken thoroughly at 150 rpm / min for 2 h. The mixture was filtered, the supernatant was removed, and the remaining solid material was dried in an oven at 100℃ to obtain the modified biochar.

[0045] (2) Place the biochar obtained in step (1) into a quartz crucible and place it in a tube furnace to prepare a biochar sample using the oxygen-limited heating method. The specific method of oxygen-limited heating is as follows: After placing the crucible into the tube furnace, continuously purge with nitrogen for 30 minutes to keep the air in the tube furnace in an oxygen-deficient state. Continue to purge with nitrogen to raise the temperature to 600℃ for pyrolysis and carbonization for 2 hours. After cooling to below 40℃, turn off the nitrogen and remove the crucible. Wash the pyrolyzed biochar with deionized water and dry it at 100℃. After drying, remove and store it for later use, and designate it as biochar A2. Figure 1 The image shown is a SEM image of biochar modified using a combination of ferric chloride and calcium chloride.

[0046] Comparative Example 1

[0047] The same raw biochar as in Example 1 was washed, dried, and set aside as biochar A1. Figure 2 The image shown is a SEM image of the original biochar.

[0048] Comparative Example 2

[0049] A ferric chloride-modified biochar, the specific preparation method of which is as follows:

[0050] (1) The original biochar, identical to that in Example 1, was impregnated with ferric chloride solution. The mass-to-volume ratio of biochar to metal salt solution was 10 g: 100 mL. The mixture was placed in a constant temperature shaker at 30 ± 0.5 °C and shaken thoroughly at 150 rpm / min for 2 h. The mixture was then filtered to remove the supernatant. The remaining solid material was dried in an oven at 100 °C to obtain the modified biochar.

[0051] (2) Place the biochar obtained in step (1) into a quartz crucible and place it in a tube furnace to prepare a biochar sample using the oxygen-limited heating method. The specific method of oxygen-limited heating is as follows: after placing the crucible into the tube furnace, continuously introduce nitrogen gas for 30 minutes to keep the air in the tube furnace in an oxygen-deficient state. Continue to introduce nitrogen gas to heat up to 600℃ for pyrolysis and carbonization for 2 hours. After cooling down to below 40℃, turn off the nitrogen gas and remove the crucible. Wash the pyrolyzed biochar with deionized water and dry it at 100℃. After drying, take it out and store it for later use, and record it as biochar A3.

[0052] Comparative Example 3

[0053] A calcium chloride-modified biochar, the specific preparation method of which is as follows:

[0054] (1) The original biochar, identical to that in Example 1, was impregnated with calcium chloride solution. The mass-to-volume ratio of biochar to metal salt solution was 10 g: 100 mL. The mixture was placed in a constant temperature shaker at 30 ± 0.5 °C and shaken thoroughly at 150 rpm / min for 2 h. The mixture was then filtered to remove the supernatant. The remaining solid material was dried in an oven at 100 °C to obtain the modified biochar.

[0055] (2) Place the biochar obtained in step (1) into a quartz crucible and place it in a tube furnace to prepare a biochar sample using the oxygen-limited heating method. The specific method of oxygen-limited heating is as follows: after placing the crucible into the tube furnace, continuously introduce nitrogen gas for 30 minutes to keep the air in the tube furnace in an oxygen-deficient state. Continue to introduce nitrogen gas to heat up to 600℃ for pyrolysis and carbonization for 2 hours. After cooling down to below 40℃, turn off the nitrogen gas and remove the crucible. Wash the pyrolyzed biochar with deionized water and dry it at 100℃. After drying, take it out and store it for later use, and record it as biochar A4.

[0056] Experimental Example 1: Removal of PO4 from Wastewater 3- Adsorption test

[0057] 1. Adsorption effects of different materials

[0058] 0.5 g of the biochar prepared above, A1 (Comparative Example 1), A2 (Example 1), A3 (Comparative Example 2), and A4 (Comparative Example 3), were added to 150 mL of PO4 solution, respectively. 3- In a 15 mg / L solution, the initial pH was maintained at 7 ± 0.1. The mixture was placed in a constant-temperature shaker at 30 ± 0.5 °C and shaken at 150 rpm / min for 2 h. The sample was then filtered through a 0.45 μm microporous membrane, and the PO4 content in the solution was determined using the ammonium molybdate spectrophotometric method. 3- The concentration.

[0059] Four types of biochar, A1, A2, A3, and A4, against PO4 3- The adsorption efficiency is shown in Figure 3 The adsorption capacities of biochar A1, A2, A3, and A4 for phosphate were 1.32, 4.16, 3.25, and 1.48 mg / g, respectively, with removal efficiencies of 56.79%, 90.62%, 70.37%, and 32.03%. The adsorption capacity of biochar A2 modified with ferric chloride and calcium chloride was significantly higher than that of biochar A1, being 3.16 times that of the original biochar, indicating that the modified biochar A2 can improve the adsorption capacity for PO4. 3- Adsorption capacity.

[0060] 2. Adsorption effect of biochar A2 at different times

[0061] Add 0.5 g of the biochar A2 prepared in Example 1 to 150 mL of PO43- In a 50 mg / L solution, the initial pH was maintained at 7 ± 0.1. The mixture was placed in a constant-temperature shaker at 30 ± 0.5℃ and shaken at 150 rpm / min for 0–8 h. The sample was then filtered through a 0.45 μm microporous membrane, and the PO4 content in the solution was determined using the ammonium molybdate spectrophotometric method. 3- The concentration.

[0062] Biochar A2's effect on PO4 at different times 3- Adsorption capacity see Figure 4 Early biochar's effect on PO4 3- The adsorption is relatively rapid, which may be related to the presence of a large number of available active sites and high-affinity groups on the material surface. The adsorption capacity increases slowly over time, reaching a maximum around 420 min, possibly due to the reduction in active sites and pores, causing the biochar to reach saturation.

[0063] 3. Adsorption effect of biochar A2 at different pH levels

[0064] Add 0.5 g of the biochar A2 prepared in Example 1 to 150 mL of PO4 3- In a 20 mg / L solution, the initial pH was controlled at 2.5, 3, 5, 7, 9, 10, and 11. The mixture was placed in a constant-temperature shaker at 30 ± 0.5 °C and shaken at 150 rpm / min for 2 h. The sample was then filtered through a 0.45 μm microporous membrane, and the PO4 content in the solution was determined using the ammonium molybdate spectrophotometric method. 3- The concentration.

[0065] Biochar A2 at different pH values ​​affects PO4 3- The adsorption capacity and removal efficiency are shown in Figure 5 Biochar exhibits good PO4 concentration in the pH range of 2.5–11. 3- The removal efficiency was all above 80%, indicating that the biochar modified by the combined modification of ferric chloride and calcium chloride is stable and less affected by the pH of the phosphate solution, which is conducive to large-scale application.

[0066] 4. Adsorption effect of A2 at different dosages

[0067] 0.1 g, 0.3 g, 0.5 g, 0.7 g, and 1 g of biochar A2 prepared in Example 1 were added to 150 mL of PO4 solution, respectively. 3- In a 20 mg / L solution, with the initial pH controlled at 7, the mixture was placed in a constant-temperature shaker at 30 ± 0.5 °C and shaken at 150 rpm / min for 2 h. The sample was then filtered through a 0.45 μm microporous membrane, and the PO4 content in the solution was determined using the ammonium molybdate spectrophotometric method. 3- The concentration.

[0068] Biochar A2 on PO4 at different dosages 3- The adsorption capacity and removal efficiency are shown in Figure 6 When the amount of biochar is greater than 0.5g, it affects PO4. 3- The removal efficiency was all above 90%, indicating that the biochar modified with ferric chloride and calcium chloride has a good removal effect on phosphate solution, which is conducive to large-scale application.

[0069] 5. Adsorption effect of A2 in the presence of coexisting ions

[0070] 0.5 g of the biochar A2 prepared in Example 1 was added to 150 mL of PO4. 3- In a solution with a concentration of 20 mg / L, the solution contains 0.01 M Cl. - NO3 - CO3 2- HCO3 - and SO4 2- The mixture was placed in a constant-temperature shaker at 30±0.5℃ and shaken at 150 rpm / min for 2 hours. The sample was then filtered through a 0.45 μm microporous membrane, and the PO4 content in the solution was determined using the ammonium molybdate spectrophotometric method. 3- The concentration.

[0071] Biochar A2 in the presence of coexisting ions for PO4 3- The adsorption capacity and removal efficiency are shown in Figure 7 The order of influence of anions on phosphate adsorption is: Cl - <NO3 - <SO4 2- <HCO3 - <CO3 2- CO3 2- The existence of PO4 3- Adsorption had the greatest impact, with a removal rate of only 7.5%.

[0072] 6. Drawing the isothermal adsorption curve of biochar A2

[0073] Add 0.5 g of the biochar A2 prepared in Example 1 to 150 mL of PO4 3- Solutions with concentrations of 5, 10, 20, 50, 100, and 200 mg / L were prepared, with the initial pH maintained at 7 ± 0.1. The mixtures were then placed in a constant-temperature shaker at 30 ± 0.5℃ and shaken at 150 rpm / min for 2 hours. The samples were then filtered through a 0.45 μm microporous membrane, and the PO4 content in the solutions was determined using ammonium molybdate spectrophotometry. 3- The concentration.

[0074] See the diagram for adsorption isotherms. Figure 6This indicates that at a temperature of 303 K, the experimental data of biochar A2 modified with ferric chloride and calcium chloride are more consistent with the Freundlich isotherm, suggesting that biochar A2 has a better effect on PO42. 3- The adsorption type belongs to multilayer adsorption.

[0075] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for enhancing phosphate adsorption using a combination of ferric chloride and calcium chloride with modified biochar, characterized in that, The method includes: The aforementioned method utilizes ferric chloride and calcium chloride combined modified biochar to treat phosphate-containing solutions for 50 minutes at a pH of 2.5–11 and a temperature of 30 ± 0.5°C. Prior to phosphorus removal, CO32- in the phosphate-containing solution needs to be removed. 2- ; The method for preparing biochar using ferric chloride and calcium chloride combined modification includes the following steps: (1) The raw biochar is mixed with ferric chloride and calcium chloride solution and impregnated, and the mixture is shaken thoroughly; wherein, the mass-volume ratio of the raw biochar to the ferric chloride and calcium chloride solution is 1g: 10~15mL, and the volume ratio of ferric chloride solution to calcium chloride solution in the ferric chloride and calcium chloride solution is 3: 2, the concentrations of the ferric chloride solution and the calcium chloride solution are the same, and the concentrations of the ferric chloride solution and the calcium chloride solution are 1 mol / L; (2) The mixture was filtered to remove the supernatant, and the remaining solid material was dried to obtain the modified biochar material; (3) The modified biochar material was placed in a tube furnace and nitrogen gas was continuously introduced into the tube furnace for high-temperature carbonization at 600±5℃ for 2±0.1 h. After the tube furnace cooled down to room temperature, it was taken out, cleaned and dried to obtain biochar modified by ferric chloride and calcium chloride.

2. The method according to claim 1, characterized in that, In step (1), the mixing and impregnation time is 2 to 12 hours.

3. The method according to claim 1, characterized in that, In step (1), the oscillation is carried out in a horizontal shaking table with a rotation speed of 150±5 rpm / min and a temperature of 30±1℃.

4. The method according to claim 1, characterized in that, In steps (2) and (3), the drying temperature is 100℃±0.5℃.

5. The method according to claim 1, characterized in that, In step (3), the modified biochar material is placed in a quartz crucible. After the crucible is placed in a tube furnace, nitrogen gas is continuously introduced for 30 min to keep the air in the tube furnace in an oxygen-deficient state. Nitrogen gas is continued to be introduced to raise the temperature to 600±5℃ for pyrolysis and carbonization for 2±0.1 h. After the temperature drops to below 40℃, the nitrogen gas is turned off and the crucible is removed. The pyrolyzed biochar is then cleaned and dried.

6. The method according to claim 1, characterized in that, Before phosphorus removal, it is also necessary to remove HCO3 from the phosphate-containing solution. - .

7. The method according to claim 1, characterized in that, Before phosphorus removal, SO4 in the phosphate-containing solution also needs to be removed. 2- .

8. The method according to claim 1, characterized in that, Before phosphorus removal, NO3 in the phosphate-containing solution also needs to be removed. - .

9. The method according to claim 1, characterized in that, Before phosphorus removal, it is also necessary to remove Cl from the phosphate-containing solution. - .

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