Preparation method and application of biochar / magnetic iron gel particle adsorbent

Abstract

The present application relates to a kind of preparation methods of biochar / magnetic iron gel particle adsorbent, which uses residual sludge of sewage treatment plant as raw material, is activated by zinc salt, and is prepared into sludge-based biochar by carbonization;Biochar is mixed with chitosan solution, ammonium sulfate ferric salt and ammonium ferrous sulfate salt are added and injected into lye to form gel pellet, crosslinking solidification is carried out by crosslinking agent, and freeze-drying is carried out, to obtain biochar / magnetic iron gel particle adsorbent.The adsorbent has good anti-interference ability to anion in natural water body, and can still efficiently remove phosphorus in municipal sewage and river water;Adsorption capacity can still maintain a high level after desorption and regeneration cycle by acid and alkali solution, and can also be applied to fixed bed column adsorption process.

Description

Technical Field

[0001] This invention relates to the field of adsorbent technology, and in particular to a method for preparing a biochar / magnetic iron gel particle adsorbent. Background Technology

[0002] Phosphorus is an essential nutrient element in aquatic ecosystems, but excessively high phosphorus concentrations in natural water bodies can lead to eutrophication, causing algal blooms, decreased dissolved oxygen, and the death of aquatic organisms, severely disrupting the ecological balance of the water body. Currently, biochar adsorption of phosphorus from water bodies has become a research hotspot due to its simplicity and low cost. As a carbonization product of organic solid waste, biochar achieves preliminary resource recovery from solid waste. However, unmodified biochar has limited adsorption sites and poor phosphorus adsorption capacity; for example, biochar prepared from nut shells has a specific surface area of ​​328.96 m². 2 The saturated adsorption capacity for phosphorus is only 7.567 mg / g, which is insufficient to meet the actual phosphorus removal requirements of water bodies.

[0003] To improve the phosphorus adsorption performance of biochar, existing technologies mostly employ metal modification or organic modification: modifying the surface of biochar with metals such as Fe, Mg, and Ca allows for efficient phosphorus adsorption through the formation of precipitates between the metal and phosphates, while simultaneously altering the surface chemical properties of the biochar to enhance electrostatic attraction; modifying with organic materials such as chitosan can enhance adsorption efficiency through the affinity of its amino groups for phosphorus, and the solidification effect of chitosan can prevent adsorbent loss in water bodies. However, existing modified biochar still has many problems: some modified adsorbents only show good phosphorus removal effects in deionized water systems, and their adsorption performance drops significantly in natural water bodies and municipal wastewater containing various interfering ions; research on the practical application processes of adsorbents is insufficient, lacking pilot-scale application data such as column adsorption, making it difficult to achieve large-scale promotion; at the same time, research on the mechanism of phosphorus adsorption by biochar is mostly focused on microscopic physicochemical reactions, with a lack of analysis from a macroscopic energy perspective, failing to provide comprehensive theoretical support for the design of highly efficient adsorbents.

[0004] Therefore, developing a modified biochar phosphorus removal adsorbent that combines high adsorption capacity, strong anti-interference ability, recyclability, and applicability to actual water bodies, while clarifying its adsorption mechanism, has become an urgent technical problem to be solved in the field of phosphorus pollution control in water bodies. Summary of the Invention

[0005] This invention addresses the problems of low adsorption capacity, poor anti-interference ability, and insufficient practical application of existing biochar phosphorus removal adsorbents by providing a method for preparing a biochar / magnetic iron gel particle adsorbent. This method uses sewage sludge from wastewater treatment plants as raw material to prepare biochar, realizing the high-value resource utilization of solid waste. Through Fe3O4 magnetic modification and chitosan solidification, highly efficient phosphorus removal gel particles are prepared. At the same time, the phosphorus adsorption mechanism and practical application conditions of this adsorbent are clarified, providing theoretical and technical support for its large-scale application.

[0006] Therefore, it is necessary to provide a method for preparing biochar / magnetic iron gel particle adsorbent, including the following steps: S1. The sludge is pretreated, mixed with zinc salt solution, and carbonized to obtain sludge-based biochar; S2. Mix chitosan with sludge-based biochar to obtain a biochar / chitosan mixture; S3. Ferrous ammonium sulfate and ferrous ammonium sulfate are mixed with biochar / chitosan mixture, then alkali solution is added, and after aging, a crosslinking agent is added to carry out a crosslinking reaction to obtain the biochar / magnetic iron gel particle adsorbent. Wherein, the ferric ammonium sulfate is NH4Fe(SO4)2·12H2O; The ferrous ammonium sulfate is (NH4)2Fe(SO4)2·6H2O.

[0007] Furthermore, in step S1, the carbonization temperature is 450-550℃.

[0008] Furthermore, in step S1, the concentration of the zinc salt solution is 1-2 mol / L.

[0009] Further, in step S1, the pretreatment of the sludge includes the following steps: exposing the sludge to the sun, drying it at 100-105℃, and then grinding it to a particle size of 0.10-0.15mm.

[0010] Specifically, this invention uses wastewater treatment plant sludge as raw material to prepare biochar, realizing high-value recycling of solid waste, significantly reducing the raw material cost of adsorbents, and solving the environmental problems of sludge disposal, thus achieving both environmental and economic benefits.

[0011] Furthermore, the sludge has a moisture content of 70-80%.

[0012] Further, in step S2, the mass ratio of chitosan to sludge-based biochar is 1-2:1-3.

[0013] Furthermore, in step S3, the aging temperature is 55-65°C.

[0014] Furthermore, in step S3, the alkaline solution is ammonia.

[0015] Furthermore, in step S3, the crosslinking agent is glutaraldehyde.

[0016] This invention also provides an application of the product prepared by the above method in phosphorus adsorption in water, comprising the following steps: The adsorbent is added to the phosphorus-containing water body, and the pH of the water body is controlled at 2-5 to adsorb the phosphorus.

[0017] Furthermore, after adsorption is complete, the adsorbent is desorbed and regenerated using 0.1 mol / L HCl, H2SO4, NaOH, or KOH solution, and can be recycled. This adsorbent can also be applied to fixed-bed column adsorption processes to achieve continuous phosphorus removal treatment of phosphorus-containing water bodies.

[0018] Specifically, this adsorbent can be applied to fixed-bed column adsorption processes, and its adsorption performance and diffusion mechanism at different flow rates have been clarified. This provides specific process parameters for its large-scale and continuous treatment of phosphorus-containing water bodies, and it has good prospects for practical application.

[0019] The present invention has the following beneficial effects: This invention utilizes sludge from wastewater treatment plants to prepare biochar, achieving high-value resource utilization of solid waste. Highly efficient phosphorus removal gel particles are prepared through Fe3O4 magnetic modification and chitosan solidification. This invention clarifies the phosphorus adsorption mechanism of the adsorbent from both microscopic and macroscopic perspectives. Microscopically, the main mechanism is the chemical precipitation of phosphorus by Fe, supplemented by pore filling, hydrogen bonding, and electrostatic attraction. Macroscopically, through approximate site energy distribution (ASED) analysis, it is confirmed that the homogeneous and concentrated high-energy adsorption site distribution on the adsorbent surface, as well as the high affinity for phosphorus, are key to its efficient phosphorus removal, providing comprehensive theoretical guidance for the design of highly efficient phosphorus removal adsorbents. This adsorbent effectively removes Cl from natural water bodies. - SO4 2- NO3 - Common anions have good anti-interference ability, only high concentrations of CO32- 2- Slight competitive inhibition exists; however, it maintains high phosphorus adsorption performance in municipal sewage and natural river water, with an adsorption capacity of up to 37.94 mg / g in municipal sewage, overcoming the limitation of existing adsorbents that are only suitable for deionized water systems. The adsorbent after phosphorus adsorption can be regenerated by desorption with acid and alkali solutions. After multiple cycles, the phosphorus adsorption capacity can still maintain a high level, significantly reducing the operating cost in practical applications and possessing the potential for large-scale promotion. Attached Figure Description

[0020] Figure 1 The image is a scanning electron microscope (SEM) image of the biochar / magnetic iron gel particles (MB-Fe) of Example 1 of the present invention. Figure 2 The N2 adsorption / desorption isotherms and pore size distribution before and after phosphorus adsorption by MB-Fe in Example 1 are shown. Figure 3 The VSM spectrum of MB-Fe in Example 1; Figure 4 The effect of solution pH on phosphorus adsorption by MB-Fe in Example 1; in: Figure 4 (a) Phosphorus adsorption amount in Example 1 at different pH values; Figure 4 (b) is the surface pH of Example 1. pzc The determination.

[0021] Figure 5 The kinetic fitting curve for phosphorus adsorption by MB-Fe in Example 1; Figure 6 The isotherm and thermodynamic fitting curve of MB-Fe adsorption of phosphorus in Example 1; Figure 7 This is a performance test of MB-Fe in practical applications for Example 1; in: Figure 7 (a) Test for external ion interference; Figure 7 (b) refers to recyclability; Figure 7 (c) is the column adsorption breakthrough curve. Detailed Implementation

[0022] To more clearly illustrate the technical solution of the present invention, the following embodiments are provided. Unless otherwise stated, the raw materials, reactions, and post-processing methods appearing in the embodiments are all commercially available raw materials and technical methods well known to those skilled in the art.

[0023] The terms "preferred," "more preferably," and "more suitable" used in this invention refer to embodiments of the invention that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this invention.

[0024] It should be understood that, except in any operational instance or otherwise indicated, all figures representing the amounts of ingredients used, for example, in the specification and claims, should be understood to be modified in all cases by the term "about". Therefore, unless otherwise stated, the numerical parameters set forth in the following specification and appended claims are approximations varying with the desired performance to be obtained according to the invention.

[0025] Chitosan: 95% deacetylation.

[0026] Example 1 A method for preparing a biochar / magnetic iron gel particle adsorbent includes the following steps: S1. The residual sludge with a moisture content of 75% was exposed to the sun and then dried in an oven at 105℃ for 2 hours. It was then ground into a powder of 0.15 mm using a grinder, soaked in a 2 mol / L ZnCl2 solution, removed and dried in an oven at 105℃. Subsequently, it was placed in a carbonization furnace and carbonized at 500℃ for 2 hours. The carbonization product was repeatedly washed with deionized water until the pH of the supernatant stabilized at 7, thus obtaining sludge-based biochar. S2. Dissolve 1g of chitosan in 50mL of acetic acid solution, stir magnetically for 30min until the chitosan is completely dissolved, add 1g of sludge-based biochar, and continue stirring magnetically for 1h to obtain a biochar / chitosan mixture. S3. Dissolve 0.9 g of NH4Fe(SO4)2·12H2O and 0.39 g of (NH4)2Fe(SO4)2·6H2O in 100 mL of deionized water and stir magnetically for 10 min until completely dissolved. Then slowly add the above biochar / chitosan mixture and continue stirring magnetically for 2 h to ensure uniform mixing. Inject the mixture into a 0.1 mol / L ammonia solution using a peristaltic pump at a rate of 5 mL / min to form gel microspheres. Place the gel microspheres and ammonia solution together in a 60 °C water bath for 24 h to age. Then inject 10 mL of 50 wt% glutaraldehyde solution and continue stirring for 2 h to allow the microspheres to crosslink and solidify. Remove the solidified gel microspheres, wash them three times with deionized water, and dry them in a -60 °C freeze dryer for 24 h to obtain the biochar / magnetic iron gel particle adsorbent (MB-Fe). The scanning electron microscope image of the biochar / magnetic ferrogel particle adsorbent (MB-Fe) is shown below. Figure 1 As shown, from Figure 1 It can be seen that both contain a large number of mesopores. After phosphorus adsorption, the specific surface area and pore volume decrease slightly, proving that pore filling is one of the adsorption mechanisms. The VSM spectrum of the biochar / magnetic iron gel particle adsorbent (MB-Fe) is as follows: Figure 3 As shown, MB-Fe possesses excellent magnetic properties.

[0027] Test Example 1 Phosphorus adsorption performance test of biochar / magnetic iron gel particle adsorbent in Example 1; Static batch adsorption experiment: Take 0.1g of MB-Fe adsorbent prepared in Example 1, add it to a 250mL beaker, inject 100mL of 100mg / L KH2PO4 solution, place it in a 293K constant temperature water bath shaker, and shake at 150r / min for 24h; after shaking, take the supernatant, and determine the remaining phosphorus concentration by spectrophotometry at 700nm, and calculate the adsorption amount.

[0028] The results showed that the saturated adsorption capacity of the adsorbent for phosphorus at 293 K reached 87.79 mg / g; Effect of pH on adsorption performance: Prepare 100 mg / L KH2PO4 solutions and adjust the pH of the solutions to 2, 3, 4, 5, 6, 8, 10, and 12 with 0.1 mol / L HCl and NaOH. Test the pH according to the static batch adsorption experimental method described above.

[0029] The results showed that within the pH range of 2-5, the adsorption capacity of the adsorbent for phosphorus increased with increasing pH, reaching its maximum at pH=5. However, above pH 5, the adsorption capacity decreased significantly with further increases in pH. This is because at pH > 5, the adsorbent surface is negatively charged, leading to electrostatic repulsion with the negatively charged phosphate. Figure 4 As can be seen from (a)-(b), the optimal adsorption pH for MB-Fe is 2~5.

[0030] Effect of temperature on adsorption performance: The phosphorus adsorption capacity of the adsorbent on 100 mg / L KH2PO4 solution was tested under constant temperature conditions of 20℃, 30℃ and 40℃ according to the above static batch adsorption experimental method.

[0031] The results showed that the adsorption capacity increased significantly with increasing temperature, with a saturated adsorption capacity of 91.90 mg / g at 30℃ and 102.61 mg / g at 40℃, proving that the adsorption process is endothermic.

[0032] Test results are as follows Figure 2 , Figure 4 (a)-(b) Figure 5 , Figure 6 As shown; where: Figure 4 (a) The phosphorus adsorption amount in Example 1 at different pH values, indicating that the optimal adsorption pH for MB-Fe is 2-5; Figure 4 (b) is the surface pH of Example 1. pzc The determination. Figure 5 The kinetic fitting curves for phosphorus adsorption by MB-Fe in Example 1 are shown; they include pseudo-first-order kinetics and pseudo-second-order kinetics, indicating that pseudo-second-order kinetics better matches the adsorption process, and that chemisorption is dominant. Figure 6 The isotherms and thermodynamic fitting curves for phosphorus adsorption by MB-Fe in Example 1 are shown, including the Langmuir and Freundlich models.

[0033] Test Example 2 Anti-interference ability test of biochar / magnetic iron gel particle adsorbent in Example 1; Prepare a 100 mg / L KH2PO4 solution, and add NaCl, Na2SO4, NaNO3 and Na2CO3 to the solution to make the concentrations of each anion reach 0.001 mol / L, 0.005 mol / L and 0.01 mol / L, respectively. Under the conditions of 20℃ and pH=5, test the adsorption capacity according to the static batch adsorption experiment method of Test Example 1.

[0034] Figure 7 The results in (a) show that Cl - SO4 2- NO3 - Within the concentration range of 0.001~0.01 mol / L, there is almost no effect on the phosphorus adsorption capacity of the adsorbent; CO3 2- At a concentration of 0.001 mol / L, there was no significant inhibition on the adsorption capacity. At concentrations of 0.005 mol / L and 0.01 mol / L, the adsorption capacity decreased slightly, but still remained above 70 mg / g, demonstrating that the adsorbent has good anti-interference ability.

[0035] Test Example 3 Application test of biochar / magnetic iron gel particle adsorbent in actual water bodies in Example 1; Water bodies with a phosphorus concentration of 10 mg / L were prepared using deionized water, municipal sewage, and Beisha River water as water sources. The water quality indicators of municipal sewage and river water are shown in Table 1. The phosphorus adsorption capacity of the adsorbent was tested under the conditions of 293 K and pH=5 according to the static batch adsorption experiment method of Test Example 1.

[0036] Table 1. Partial water quality indicators of municipal sewage and river water using the biochar / magnetic iron gel particle adsorbent of Example 1 It can be seen that the adsorption capacity of the adsorbent in deionized water is 82.35 mg / g, and the adsorption capacity in river water is 80.12 mg / g, with almost no decrease; the adsorption capacity in municipal sewage is 37.94 mg / g, which, although decreased, still remains at a high level, proving that the adsorbent is suitable for the treatment of phosphorus pollution in natural water bodies and municipal sewage.

[0037] Test Example 4 Regeneration and recycling performance test of biochar / magnetic iron gel particle adsorbent in Example 1; After adsorbing phosphorus, the MB-Fe adsorbent was used as a desorption solution with 0.1 mol / L HCl, H2SO4, NaOH, and KOH solutions, respectively. The solid-liquid ratio of MB-Fe adsorbent to desorption solution was 1:100. After shaking for 2 hours, the adsorbent was magnetically separated and recovered. It was washed with deionized water until neutral, freeze-dried, and then used for the next adsorption experiment. The cycle was repeated 5 times, and the amount of phosphorus adsorbed in each cycle was tested.

[0038] like Figure 7 (b) shows that the adsorption capacity decreased slightly after the first and second cycles, and the decrease became gradual from the third cycle onwards. After 5 cycles, the adsorption capacity of the adsorbents desorbed from HCl, H2SO4, NaOH and KOH for phosphorus was 37.12 mg / g, 35.26 mg / g, 28.95 mg / g and 27.81 mg / g, respectively, which proves that the adsorbent has good cyclic regeneration performance.

[0039] Test Example 5 Column adsorption performance test of biochar / magnetic iron gel particle adsorbent in Example 1; A hollow glass column with an inner diameter of 1.5 cm and a length of 10 cm was used as the adsorption column. 4.47 g of MB-Fe adsorbent prepared in Example 1 was filled with the column, and a 10 mg / L KH2PO4 solution was prepared. The solution was passed through the adsorption column at flow rates of 1 mL / min and 5 mL / min, respectively. Water samples were taken at regular intervals to determine the phosphorus concentration, and breakthrough curves were plotted to calculate the total adsorption.

[0040] Figure 7 (c) The results show that at a low flow rate of 1 mL / min, the breakthrough time of the adsorption column is longer, and the total phosphorus adsorption reaches 41.06 mg / g; at a flow rate of 5 mL / min, the breakthrough time is shortened, and the total adsorption is 37.71 mg / g; the breakthrough curves were fitted using the Adams-Bohart model and the Thomas model, and R... 2 The values ​​are all greater than 0.95, indicating that the diffusion of phosphorus on the adsorbent is determined by both external and internal diffusion.

[0041] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0042] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a biochar / magnetic iron gel particle adsorbent, characterized in that, Includes the following steps: S1. The sludge is pretreated, mixed with zinc salt solution, and carbonized to obtain sludge-based biochar; S2. Mix chitosan with sludge-based biochar to obtain a biochar / chitosan mixture; S3. Ferrous ammonium sulfate and ferrous ammonium sulfate are mixed with biochar / chitosan mixture, then alkali solution is added, and after aging, a crosslinking agent is added to carry out a crosslinking reaction to obtain the biochar / magnetic iron gel particle adsorbent. Wherein, the ferric ammonium sulfate is NH4Fe(SO4)2·12H2O; The ferrous ammonium sulfate is (NH4)2Fe(SO4)2·6H2O.

2. The method for preparing the biochar / magnetic iron gel particle adsorbent according to claim 1, characterized in that, In step S1, the carbonization temperature is 450-550℃.

3. The method for preparing the biochar / magnetic iron gel particle adsorbent according to claim 1, characterized in that, In step S1, the concentration of the zinc salt solution is 1-2 mol / L.

4. The method for preparing the biochar / magnetic iron gel particle adsorbent according to claim 1, characterized in that, In step S1, the pretreatment of the sludge includes the following steps: exposing the sludge to the sun, drying it at 100-105℃, and then grinding it to a particle size of 0.10-0.15mm.

5. The method for preparing the biochar / magnetic iron gel particle adsorbent according to claim 1, characterized in that, The sludge has a moisture content of 70-80%.

6. The method for preparing the biochar / magnetic iron gel particle adsorbent according to claim 1, characterized in that, In step S2, the mass ratio of chitosan to sludge-based biochar is 1-2:1-3.

7. The method for preparing the biochar / magnetic iron gel particle adsorbent according to claim 1, characterized in that, In step S3, the aging temperature is 55-65℃.

8. The method for preparing the biochar / magnetic iron gel particle adsorbent according to claim 1, characterized in that, In step S3, the alkaline solution is ammonia.

9. The method for preparing the biochar / magnetic iron gel particle adsorbent according to claim 1, characterized in that, In step S3, the crosslinking agent is glutaraldehyde.

10. The application of a product prepared by any one of claims 1-9 in the adsorption of phosphorus in water, characterized in that, Includes the following steps: The adsorbent is added to the phosphorus-containing water body, and the pH of the water body is controlled at 2-5 to adsorb the phosphorus.

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