Preparation method for jointly modifying biochar by utilizing ferric chloride and calcium chloride and method for enhancing phosphate adsorption

Abstract

The invention discloses ferric chloride and calcium chloride combined modified biochar, a preparation method thereof and a method for enhancing phosphate adsorption, and the preparation method comprises the following steps: (1) mixing and dipping original biochar with a ferric chloride and calcium chloride solution, and fully shaking and shaking up the mixed solution; (2) carrying out suction filtration on the mixed solution to remove supernate, and drying residual solid substances to obtain a modified biochar material; and (3) putting the modified biochar material into a tubular furnace, continuously introducing nitrogen into the tubular furnace, carrying out high-temperature carbonization at 600 + / -5 DEG C for 2 + / -0.1 h, cooling the tubular furnace to room temperature, taking out, cleaning, and drying to obtain the biochar jointly modified by ferric chloride and calcium chloride. Adsorption active sites of the biochar can be increased after joint modification of ferric chloride and calcium chloride, the specific surface area of the biochar is increased, the structure of the biochar is looser, and the adsorption effect is enhanced.

Description

Technical Field

[0001] The invention relates to a method for adsorbing phosphate by using modified biochar, and in particular to a method for preparing biochar by using ferric chloride and calcium chloride to jointly modify the biochar and a method for enhancing the adsorption of phosphate. Background Art

[0002] The phosphorus content of feces and urine of scattered farmers is still high after being treated in septic tanks. A large amount of fecal wastewater is discharged into rivers, reservoirs, lakes and other water bodies, resulting in an increase in phosphorus content in the water bodies, which in turn easily causes eutrophication of water bodies and threatens human health and environmental safety through the food chain.

[0003] At present, the main methods for removing phosphorus include chemical precipitation, advanced oxidation, electrochemical, adsorption, etc. Among them, the adsorption method is considered to be a more economical, efficient and easy-to-operate method because of its simplicity, environmental friendliness and reusability.

[0004] Biochar is an emerging porous carbon-based material that is produced by pyrolysis of biomass under anaerobic conditions and is commonly used for water purification, resource recovery and soil fertilization. The raw materials of biochar are abundant, mainly including agricultural and forestry wastes, animal manure, urban sludge and other carbon-rich substances. Adsorbents derived from biomass are sustainable, low-cost and high-efficiency, biodegradable and environmentally friendly. The biochar adsorbents made from them are chemically stable, non-toxic and low-cost, large specific surface area, porous structure and rich in functional groups, which are very valuable for large-scale applications.

[0005] The porosity and rich functional groups of biochar provide many adsorption sites for the adsorption of phosphate. Studies have shown that the presence of metal ions during the pyrolysis of biochar will change the functional groups, ion exchange capacity and electronegativity on the surface of biochar, thereby improving the adsorption capacity of biochar for phosphate. However, the adsorption capacity of raw biochar for phosphate is usually limited, so it is necessary to study the modification of raw biochar to improve its adsorption efficiency for phosphate, which is of great significance for the treatment of eutrophication of water bodies.

[0006] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0007] The purpose of the present invention is to provide a method for preparing biochar modified by ferric chloride and calcium chloride and a method for enhancing the adsorption of phosphate, which solves the problem of limited adsorption capacity of original biochar. The modified biochar has improved adsorption performance for phosphate, and has stable properties and is less affected by the pH value of phosphate solution.

[0008] In order to achieve the above object, the present invention provides a method for preparing biochar by using ferric chloride and calcium chloride to jointly modify the biochar, and the preparation method comprises the following steps:

[0009] (1) Mixing and impregnating the original biochar with ferric chloride and calcium chloride solutions, and shaking the mixture thoroughly; wherein the mass volume ratio of the original biochar to the ferric chloride and calcium chloride solutions is 1 g:10-15 mL, and in the ferric chloride and calcium chloride solutions, the volume ratio of the ferric chloride solution to the 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) filtering the mixed solution to remove the supernatant, and drying the remaining solid matter to obtain a modified biochar material;

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

[0012] Preferably, in step (1), the mass 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 concentration of the ferric chloride solution and the calcium chloride solution is 1 mol / L.

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

[0015] Preferably, in step (1), the shaking is carried out in a horizontal shaking incubator at a rotation speed of 150±5 rpm / min and a temperature of 30±1°C.

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

[0017] Preferably, in step (3), the modified biochar material is placed in a quartz crucible, and after the crucible is placed in a tubular furnace, nitrogen is continuously introduced for 30 minutes to keep the air in the tubular furnace excluded and in an oxygen-deficient state, and nitrogen is continued to be introduced to raise the temperature to 600±5°C and pyrolyze and carbonize for 2±0.1 hours. When the temperature drops to below 40°C, the nitrogen is turned off and the crucible is taken out, and the pyrolyzed biochar is cleaned and dried.

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

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

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

[0021] Preferably, before phosphorus removal, it is also necessary to remove NO3 from the phosphate solution. - .

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

[0023] The method for preparing biochar by using ferric chloride and calcium chloride to jointly modify the biochar and the method for enhancing the adsorption of phosphate of the present invention solves the problem of limited adsorption capacity of the original biochar and has the following advantages:

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

[0025] (2) The biochar modified by the combination of ferric chloride and calcium chloride in the present invention has stable properties, is less affected by the pH of the phosphate solution, has an adsorption efficiency of more than 80% at room temperature, is simple, convenient and efficient to use, and the prepared biochar material is cheap and readily available;

[0026] (3) The present invention can enhance the adsorption effect of biochar on phosphate after being modified by ferric chloride and calcium chloride. The adsorption of phosphate by biochar in the present invention is significantly enhanced, and the removal efficiency of phosphate in water is as high as more than 96%;

[0027] (4) The present invention utilizes biochar modified by ferric chloride and calcium chloride to improve the adsorption performance of phosphate, which is beneficial for application in environmental fields such as water eutrophication remediation. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0030] Figure 3 This is the experimental example 1 of the present invention, which shows that different biochar materials adsorb PO4 3- adsorption effect.

[0031] Figure 4 The adsorption of PO4 by biochar at different times in Experimental Example 1 of the present invention 3- adsorption effect.

[0032] Figure 5 This is the adsorption of PO4 by biochar at different pH values ​​in Experimental Example 1 of the present invention. 3- adsorption effect.

[0033] Figure 6 The adsorption of PO4 by biochar at different doses in Experimental Example 1 of the present invention 3- adsorption effect.

[0034] Figure 7 This is the adsorption of PO4 by biochar in the presence of coexisting ions in Experimental Example 1 of the present invention 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 DESCRIPTION

[0036] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] It should be noted that if the specific conditions are not specified in the examples, the experiments were carried out according to conventional conditions or the conditions recommended by the manufacturer. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased from the market.

[0038] In the present invention, all features defined in the form of numerical ranges or percentage ranges, such as values, quantities, contents and concentrations, are only for brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

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

[0040] The present invention provides a method for preparing biochar by using ferric chloride and calcium chloride to jointly modify the biochar and a method for enhancing the adsorption of phosphate. The addition of ferric chloride and calcium chloride leads to an increase in metal ions in the biochar. The presence of iron and calcium ions during pyrolysis promotes the formation of oxygen-containing functional groups (carbonyl, hydroxyl, carboxyl) on the surface of the biochar, thereby enhancing the ion exchange capacity and complexing capacity of the biochar with phosphate, thereby improving the biochar's phosphate absorption. 3- In addition, biochar has a strong adsorption capacity for PO4 3- The adsorption process of biochar may involve surface precipitation and π action. Since biochar carries positive charge on its surface after loading iron and calcium ions, the biochar and PO4 3- There may also be electrostatic attraction between them. Therefore, the present invention significantly improves the adsorption of phosphate by using ferric chloride and calcium chloride combined with modified biochar.

[0041] The following is a detailed description of a method for preparing biochar using ferric chloride and calcium chloride to modify the biochar and a method for enhancing the adsorption of phosphate provided by the present invention through embodiments, comparative examples and test examples.

[0042] Example 1

[0043] A biochar modified by ferric chloride and calcium chloride, the preparation method of which is as follows:

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

[0045] (2) The biochar obtained in step (1) is placed in a quartz crucible, placed in a tubular furnace, and a biochar sample is prepared by an oxygen-limited heating method. The specific method of oxygen-limited heating is as follows: after the crucible is placed in the tubular furnace, nitrogen is continuously introduced for 30 minutes to keep the air in the tubular furnace in an oxygen-deficient state, and nitrogen is continued to be introduced to raise the temperature to 600°C for pyrolysis and carbonization for 2 hours. When the temperature drops to below 40°C, the nitrogen is turned off and the crucible is taken out. The pyrolyzed biochar is washed with deionized water and dried at 100°C. After drying, it is taken out and stored for later use, and is recorded as biochar A2. Figure 1 Shown is the SEM image of biochar modified by combined use 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 for later use, and recorded as biochar A1. Figure 2 Shown is the SEM image of the original biochar.

[0048] Comparative Example 2

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

[0050] (1) The original biochar same as that in Example 1 was impregnated with ferric chloride solution, the mass volume ratio of biochar to metal salt solution was 10 g:100 mL, and the mixed solution was placed in a constant temperature shaker at 30±0.5°C and fully shaken at 150 rpm / min for 2 h. The mixed solution was filtered, the supernatant was removed, and the remaining solid matter was placed in a 100°C oven for drying to obtain the modified biochar;

[0051] (2) The biochar obtained in step (1) is placed in a quartz crucible, placed in a tubular furnace, and a biochar sample is prepared by an oxygen-limited heating method. The specific method of oxygen-limited heating is as follows: after the crucible is placed in the tubular furnace, nitrogen is continuously introduced for 30 minutes to keep the air in the tubular furnace in an oxygen-deficient state, and nitrogen is continued to be introduced to raise the temperature to 600°C for pyrolysis and carbonization for 2 hours. When the temperature drops to below 40°C, the nitrogen is turned off and the crucible is taken out. The pyrolyzed biochar is washed with deionized water and dried at 100°C. After drying, it is taken out and stored for later use, and recorded as biochar A3.

[0052] Comparative Example 3

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

[0054] (1) The original biochar same as that in Example 1 was impregnated with a calcium chloride solution, the mass volume ratio of biochar to metal salt solution was 10 g:100 mL, and the mixed solution was placed in a constant temperature shaker at 30±0.5°C and fully shaken at 150 rpm / min for 2 h. The mixed solution was filtered, the supernatant was removed, and the remaining solid matter was placed in a 100°C oven for drying to obtain the modified biochar;

[0055] (2) The biochar obtained in step (1) is placed in a quartz crucible, placed in a tubular furnace, and a biochar sample is prepared by an oxygen-limited heating method. The specific method of oxygen-limited heating is as follows: after the crucible is placed in the tubular furnace, nitrogen is continuously introduced for 30 minutes to keep the air in the tubular furnace in an oxygen-deficient state, and nitrogen is continued to be introduced to raise the temperature to 600°C for pyrolysis and carbonization for 2 hours. When the temperature drops to below 40°C, the nitrogen is turned off and the crucible is taken out. The pyrolyzed biochar is washed with deionized water and dried at 100°C. After drying, it is taken out and stored for later use, and is recorded as biochar A4.

[0056] Test Example 1 Removal of PO4 from wastewater 3- Adsorption test

[0057] 1. Adsorption effect of different materials

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

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

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

[0061] 0.5 g of biochar A2 prepared in Example 1 was added to 150 mL of PO43- In a solution with a concentration of 50 mg / L, the initial solution pH was controlled to be maintained at 7±0.1, and the mixed solution was placed in a constant temperature shaker at 30±0.5°C and shaken at 150 rpm / min for 0 to 8 hours. The sample was filtered through a 0.45 μm microporous membrane and the PO4 content in the solution was determined by ammonium molybdate spectrophotometry. 3- concentration.

[0062] Effect of biochar A2 on PO4 at different times 3- Adsorption capacity Figure 4 , the effect of biochar on PO4 3- The adsorption of biochar was faster, which may be related to the presence of a large number of available active sites and high affinity groups on the surface of the material. As time increased, the adsorption capacity increased slowly and reached a maximum value at around 420 min, which may be due to the reduction of active sites and pores, and the biochar reached a saturated state.

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

[0064] 0.5 g of 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 initial solution pH was controlled at 2.5, 3, 5, 7, 9, 10 and 11, and 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 filtered through a 0.45μm microporous membrane and the PO4 content in the solution was determined by ammonium molybdate spectrophotometry. 3- concentration.

[0065] Effect of biochar A2 on PO4 at different pH 3- The adsorption capacity and removal efficiency are shown in Figure 5 , biochar has a great influence on PO4 in the pH range of 2.5 to 11 3- The removal efficiencies were all above 80%, indicating that the biochar modified by ferric chloride and calcium chloride was stable in nature and less affected by the pH of phosphate solution, which was 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 the biochar A2 prepared in Example 1 were added to 150 mL of PO4 3- The initial solution pH was controlled at 7 in a solution with a concentration of 20 mg / L. The mixed solution was placed in a constant temperature shaker at 30 ± 0.5 °C and shaken at 150 rpm / min for 2 h. The sample was filtered through a 0.45 μm microporous membrane and the PO4 content in the solution was determined by ammonium molybdate spectrophotometry. 3- concentration.

[0068] Effect of 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, the effect on PO4 3- The removal efficiencies were all above 90, indicating that the biochar modified by ferric chloride and calcium chloride had a good removal effect on phosphate solution and was conducive to large-scale application.

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

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

[0071] Effect of biochar A2 on PO4 in the presence of coexisting ions 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 presence of PO4 3- Adsorption had the greatest impact, with a removal rate of only 7.5%.

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

[0073] 0.5 g of biochar A2 prepared in Example 1 was added to 150 mL of PO4 3- The concentrations of 5, 10, 20, 50, 100, and 200 mg / L were controlled to maintain the initial solution pH at 7 ± 0.1, and the mixed solution was placed in a constant temperature shaker at 30 ± 0.5 ° C and shaken at 150 rpm / min for 2 hours. The sample was filtered through a 0.45 μm microporous membrane and the PO4 content in the solution was determined by ammonium molybdate spectrophotometry. 3- concentration.

[0074] Draw the adsorption isotherm Figure 6, indicating that at a temperature of 303 K, the experimental data of biochar A2 modified by ferric chloride and calcium chloride are more consistent with the Freundlich isotherm curve, indicating that biochar A2 has a better effect on PO4 3- The adsorption type belongs to multilayer adsorption.

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

Claims

1. A method for preparing biochar by using ferric chloride and calcium chloride to modify the biochar, characterized in that: The preparation method comprises the following steps: (1) Mixing and impregnating the original biochar with ferric chloride and calcium chloride solutions, and shaking the mixture thoroughly; wherein the mass volume ratio of the original biochar to the ferric chloride and calcium chloride solutions is 1 g:10-15 mL, and in the ferric chloride and calcium chloride solutions, the volume ratio of the ferric chloride solution to the calcium chloride solution is (1-4):(4-1), and the concentrations of the ferric chloride solution and the calcium chloride solution are the same; (2) filtering the mixed solution to remove the supernatant, and drying the remaining solid matter to obtain a modified biochar material; (3) The modified biochar material is placed in a tubular furnace, and nitrogen is continuously introduced into the tubular furnace to perform high-temperature carbonization at 600±5°C for 2±0.1h. After the tubular furnace is cooled to room temperature, the material is taken out, cleaned, and dried to obtain biochar modified by ferric chloride and calcium chloride.

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

3. The preparation method according to claim 1, characterized in that: In step (1), the shaking is carried out in a horizontal shaking incubator at a rotation speed of 150±5 rpm / min and a temperature of 30±1°C.

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

5. The preparation method according to claim 1, characterized in that: In step (3), the modified biochar material is placed in a quartz crucible, and after the crucible is placed in a tubular furnace, nitrogen is continuously introduced for 30 minutes to keep the air in the tubular furnace excluded and in an oxygen-deficient state, and nitrogen is continued to be introduced to raise the temperature to 600±5°C and pyrolyze and carbonize for 2±0.1 hours. When the temperature drops to below 40°C, the nitrogen is turned off and the crucible is taken out, and the pyrolyzed biochar is cleaned and dried.

6. A method for enhancing phosphate adsorption by using ferric chloride and calcium chloride in combination with modified biochar, characterized in that: The method includes: The biochar obtained by the preparation method according to any one of claims 1 to 5 and modified by ferric chloride and calcium chloride is treated with a phosphate solution at a pH of 2.5 to 11 and 30 ± 0.5 ° C for 50 minutes, and CO3 in the phosphate solution needs to be removed before phosphorus removal. 2- .

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

8. The method according to claim 6, characterized in that Before removing phosphorus, it is also necessary to remove SO4 from the phosphate solution. 2- .

9. The method according to claim 6, characterized in that Before removing phosphorus, it is also necessary to remove NO3 from the phosphate solution. - .

10. The method according to claim 6, characterized in that Before removing phosphorus, it is also necessary to remove Cl in the phosphate solution. - .

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