Preparation method and application of iron / calcium-rich magnetic sludge biochar

Abstract

The application discloses a preparation method and application of iron / calcium-rich magnetic sludge biochar, fully utilizes solid wastes such as sewage sludge, household garbage and oyster shells, takes iron-rich sludge and household garbage as main raw materials, obtains a magnetic biochar precursor through pyrolysis and carbonization, then prepares a calcium ion solution by using oyster shells and dilute hydrochloric acid, and finally loads the calcium ions into the magnetic biochar precursor through a water bath heating mode to obtain the iron / calcium-rich magnetic sludge biochar. The high content of organic matters and iron elements in the iron-rich sludge and the rich calcium elements in the oyster shells are utilized to provide high magnetism and a large number of active sites for the biochar, and the adsorption performance and recovery capacity of the magnetic biochar used as a water treatment adsorbent are improved. The iron and calcium elements in the solid wastes are jointly fixed into the biochar body, the application capacity of the biochar as an adsorbent is improved, the preparation cost is reduced, and the economic benefit is high and the application is environment-friendly.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization and harmless utilization, and relates to a method for preparing iron / calcium-rich magnetic sludge biochar and its application. Background Technology

[0002] With the continuous growth of the global population and rapid economic development, the disposal of solid waste and the pollution of water resources have become global challenges. Iron-rich sludge has a complex composition, containing high levels of toxic substances and heavy metals; the most widespread methods of disposing of municipal solid waste are incineration and landfill, leading to potential bacterial and viral pollution of the soil and atmosphere; and the large accumulations of discarded oyster shells, with their easily decomposing meat residue, not only occupy land resources but also pose potential hazards to air and water sources. If these solid wastes are not properly treated, they pose significant threats to the environment and human health. Given the characteristics of iron-rich sludge, municipal solid waste, and oyster shells, the search for an environmentally friendly resource utilization method is increasingly urgent.

[0003] Pyrolysis is a treatment method that involves heating materials under anaerobic conditions. It can effectively fix heavy metals and reduce the land area occupied by solid waste. As a relatively environmentally friendly treatment method, pyrolysis has the potential to become an advantageous resource utilization pathway for the aforementioned solid wastes. Biochar, a solid product obtained from pyrolysis, has shown great application potential in water pollution control and soil remediation due to its large specific surface area, high porosity, and abundant functional groups.

[0004] Numerous reports indicate that biochar has been widely used in the adsorption of acetaminophen in water. China is now the world's largest producer and exporter of acetaminophen, and its discharge into water bodies has adverse effects on human, animal, and plant health. Therefore, treating acetaminophen pollution in wastewater is crucial. Previously, activated carbon used for purifying acetaminophen-containing wastewater was mostly derived from resources such as wood or coal, resulting in relatively high production costs and low practical value. Biochar, prepared from solid waste, precisely overcomes these shortcomings.

[0005] Metal ion-modified biochar has received widespread attention in the field of wastewater remediation due to its low cost, simple preparation, and high safety.

[0006] Iron ion modification not only improves adsorption performance but also gives biochar a magnetic advantage that facilitates recovery. CN116272995A discloses a high-efficiency magnetic sludge-based biochar material, its preparation method, and its application. This material uses only iron-rich sludge as raw material and is calcined under a reducing atmosphere to obtain magnetic biochar, which is then used for photoactivated degradation of organic pollutants in water. However, when applied to wastewater pollutant removal, the magnetic biochar particles attract each other and aggregate at the bottom of the wastewater, potentially leading to uneven pollutant removal at certain oscillation rates, thus limiting its practical application.

[0007] Calcium ions are widely used in biochar modification due to their safety and stability. CN113842881A discloses a method for preparing and applying oyster shell powder-enhanced hydrothermal biochar, which is used for the removal of microplastics and heavy metals in aquaculture. It is obtained by directly ball-milling calcined oyster shell powder with specially treated biomass materials. However, the calcined oyster shell powder itself has poor adsorption performance. Directly mixing oyster shell powder into biochar will block the pores of the biochar, hindering the application of biochar with pore action as the dominant adsorption mechanism.

[0008] A comprehensive analysis of domestic and international research reveals no reports on the preparation of magnetic biochar materials that utilize iron-rich sludge as an iron source and oyster shells as a calcium source to promote the mutual adsorption of iron and calcium ions. Therefore, the challenge of this application is to develop a low-cost biochar material with good adsorption performance that is easily magnetically separated and recovered. Summary of the Invention

[0009] To address the aforementioned deficiencies or improvement needs of existing technologies, the present invention aims to provide a method for preparing and applying iron-rich / calcium-rich magnetic sludge biochar. This method directly uses iron-rich sludge as the iron source and oyster shells as the calcium source, while simultaneously coupling it with municipal solid waste to prepare iron-rich / calcium-rich magnetic sludge biochar. This solves the resource utilization problem of iron-rich sludge, municipal solid waste, and oyster shells, achieving the goal of turning waste into waste. The preparation method uses iron-rich sludge and municipal solid waste as the main raw materials. A magnetic biochar precursor is prepared through raw material pretreatment and pyrolysis. Then, a calcium ion solution prepared by reacting dilute hydrochloric acid with oyster shell powder is mixed with the magnetic biochar precursor in water. After water bath heating, the final iron-rich / calcium-rich magnetic sludge biochar is obtained, resulting in excellent application effects in wastewater removal.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A method for preparing iron-rich / calcium-rich magnetic sludge biochar, the method comprising the following steps:

[0012] S1. Dry and crush the iron-rich sludge and the collected domestic waste separately, and mix them evenly according to the mass ratio of iron-rich sludge: domestic waste = 3-5:1 to obtain a mixture of iron-rich sludge and domestic waste.

[0013] S2. The mixture of iron-rich sludge and domestic waste is placed in a tube furnace and pyrolyzed under an inert protective atmosphere. After cooling, it is ground to below 200 mesh to obtain magnetic biochar precursor.

[0014] S3. While stirring continuously, slowly add oyster shell powder to dilute hydrochloric acid until no further reaction occurs. Filter the solution through qualitative filter paper to remove insoluble matter and obtain a calcium ion solution. On average, 0.05–0.06 g of oyster shell powder is consumed per mL of dilute hydrochloric acid.

[0015] S4. Mix the magnetic biochar precursor with a calcium ion solution, add deionized water to achieve a solid-liquid ratio of 1:15-30, heat in a water bath at a temperature of 60-100℃ for 1-3 hours, cool, wash with deionized water, filter, dry to constant weight, and grind to below 200 mesh to obtain iron-rich / calcium magnetic sludge biochar; the amount of calcium ion solution added is 5-20 mL / 1g magnetic biochar precursor.

[0016] Preferably, the total organic matter content of the iron-rich sludge is 54 wt%, the moisture content is 83 wt%, and the moisture content after drying is controlled to be below 3 wt%. The main components are: TFe2O3 45.60 wt%, SiO2 19.00 wt%, Al2O3 12.60 wt%, CaO 4.13 wt%, and other substances 18.67 wt%. The moisture content of the domestic waste is 58 wt%, and the moisture content after drying is controlled to be below 3 wt%. The physical composition is: kitchen waste 56 wt%, plastics 21 wt%, paper 13 wt%, wood and bamboo 5 wt%, textiles 4 wt%, and rubber 1 wt%.

[0017] The drying process described in step S1 is as follows: drying at 105±5℃ for 24 hours.

[0018] Preferably, the pyrolysis process in step S2 is as follows: under the condition of introducing nitrogen gas at a rate of 80-100 mL / min, heating to 700-1000℃ for 2 hours at a heating rate of 8-12℃ / min. More preferably, the pyrolysis process is as follows: under the condition of introducing nitrogen gas at a rate of 100 mL / min, heating to 800℃ for 2 hours at a heating rate of 10℃ / min.

[0019] Preferably, the particle size range of the iron-rich sludge and municipal solid waste after crushing is controlled as follows: fabrics, wood, and paper materials <2mm, and other powdery materials <60 mesh.

[0020] In some embodiments of the present invention, preferably, the particle size range after crushing in step S1 is controlled as follows: fabrics, wood, and paper-like materials <2mm, and other powdery materials <60 mesh.

[0021] Preferably, the concentration of the dilute hydrochloric acid in step S3 is 1 to 1.5 mol / L, and the particle size of the oyster shell powder in step S3 is <100 mesh.

[0022] Preferably, in step S4, the amount of magnetic biochar precursor added is 1g, the amount of calcium ion solution added is 10-20mL, the solid-liquid ratio is 1:15-20, the water bath heating temperature is 80±5℃, and the water bath heating time is 1.5-2h; the drying process in step S4 is carried out at 80±5℃ for 24 hours. Too high a water bath heating temperature or too long a time is detrimental to the adsorption effect in wastewater. In some embodiments of the present invention, preferably, the water bath heating conditions are 80℃ and the heating time is 2h.

[0023] Secondly, the present invention provides an iron-rich / calcium-rich magnetic sludge biochar, which is obtained by the above-mentioned preparation method. The iron-rich / calcium-rich magnetic sludge biochar has a flower-like morphology on its surface, with iron elements distributed in flakes on the flower-like surface and calcium ions also dispersed on the flower-like surface.

[0024] Thirdly, this invention provides an application of the aforementioned iron-rich / calcium-rich magnetic sludge biochar for the adsorption of wastewater or sewage, especially for the treatment of acetaminophen-containing wastewater. The specific process is as follows: at 25°C, 2-3 g / L of iron-rich / calcium-rich magnetic sludge biochar is added to acetaminophen-containing wastewater with a concentration of 5-100 mg / L, and the reaction is carried out at a speed of 100-200 rpm in the dark until the adsorption equilibrium is reached, thereby achieving pore adsorption of acetaminophen.

[0025] The removal rate of acetaminophen is not less than 60%, and the equilibrium adsorption capacity is not less than 30 mg / g.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] The main raw materials used in this invention are iron-rich sludge, domestic waste, and oyster shells from solid waste. Oyster shells are rich in calcium carbonate (over 95%), which reacts with hydrochloric acid to generate free calcium ions. Then, the three react synergistically in a water bath, loading the calcium ions onto biochar. The biochar, after water bath heating, exhibits a flower-like morphology, with iron elements distributed in flakes on the flower-like surface. Calcium ions are also dispersed on the flower-like surface, reducing agglomeration during the magnetic biochar adsorption process. Simultaneously, the active sites are exposed, further improving adsorption performance and ensuring efficient removal of organic matter from wastewater. This invention overcomes the shortcomings of existing technologies, such as reduced adsorption efficiency due to the incorporation of small-surface-area particles during direct room-temperature impregnation or direct pyrolysis mixing, as well as higher energy consumption and pore blockage.

[0028] The raw materials used in this invention are inexpensive, readily available, and produced in large quantities, effectively solving the problems of environmental damage and land resource occupation caused by solid waste in current disposal methods. Compared with ordinary sludge biochar, the preparation process is simpler, significantly reducing production costs and energy consumption, which is conducive to large-scale industrial production and enhances market competitiveness.

[0029] Iron-rich sludge has a high iron content, allowing for the production of easily recyclable magnetic biochar without the need for an external iron source. Adding approximately 20% municipal solid waste by mass to the iron-rich sludge increases the overall calorific value and carbon content of the raw materials, improves pyrolysis efficiency, and dilutes the heavy metal content in the iron-rich sludge. Furthermore, the high carbon, hydrogen, and volatile matter content in municipal solid waste promotes the formation of internal pores in the biochar during co-pyrolysis, thereby increasing the biochar's specific surface area, adsorption capacity, and practical value.

[0030] This application utilizes the high-value-added resources of iron-rich sludge and municipal solid waste. Under the action of water bath heating, oyster shell powder is introduced for modification to prepare an iron-rich / calcium-rich magnetic sludge biochar. This biochar has a good adsorption effect on acetaminophen pharmaceutical wastewater. Compared with sludge biochar without added iron and calcium, the iron-rich / calcium-rich magnetic sludge biochar of this application has a 17.98% higher removal rate when adsorbing acetaminophen at a concentration of 100 mg / L, demonstrating a significant removal effect. Attached Figure Description

[0031] Figure 1 The image shows the SEM image of the iron / calcium-rich magnetic sludge biochar obtained in Example 3 and the corresponding iron / calcium element distribution map.

[0032] Figure 2 The image shows a comparison of the magnetization curves of the materials obtained in Examples 1, 3, and 5.

[0033] Figure 3 The images show a comparison of the XRD patterns of the materials obtained in Examples 1 and 3. Detailed Implementation

[0034] To better understand the present invention, the following embodiments are provided for further explanation, but the present invention is not limited to the examples below.

[0035] The sludge raw materials used in the following examples were municipal sludge produced by a wastewater treatment plant in Tianjin. Sludge produced by adding iron salts during the wastewater treatment stage is called iron-rich sludge, while sludge produced without adding iron salts during the wastewater treatment stage is called non-iron-rich sludge. As a comparative example, the main components of both are shown in Table 1. In addition, through a survey of the sorted household waste materials in a residential area of ​​Tianjin, the main physical composition of the household waste was obtained, as shown in Table 2.

[0036] Table 1 shows the main chemical components of the municipal sludge used in the following examples.

[0037] Element <![CDATA[TFe2O3]]> <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[P2O5]]> <![CDATA[SO3]]> CaO other Iron-rich sludge (wt%) 45.60 19.00 12.60 7.09 4.83 4.13 6.75 Non-iron-rich sludge (wt%) 11.90 34.00 24.30 8.65 5.39 6.98 8.78

[0038] Table 2 shows the physical composition of the household waste used in the following examples.

[0039] category kitchen waste Plastics Paper Wood and bamboo fabrics rubber Percentage (wt%) 56.00 21.00 13.00 5.00 4.00 1.00

[0040] In all the following embodiments, the pyrolysis step is as follows: The dried and pulverized raw materials are mixed evenly at a mass ratio of municipal sludge to domestic waste of 4:1. The mixture is placed in a tube furnace and heated to 800°C for 2 hours under nitrogen gas flow at a rate of 10°C / min. After cooling to room temperature, the mixture is removed, ground, and passed through a 200-mesh sieve to obtain the biochar precursor. The product obtained from the pyrolysis of iron-rich sludge is a magnetic biochar precursor, while the product obtained from the pyrolysis of non-iron-rich sludge is a non-magnetic biochar precursor.

[0041] In all the following examples, a calcium ion solution was prepared in advance. Oyster shell powder was slowly added to 1 mol / L dilute hydrochloric acid under continuous stirring until no further reaction occurred. The insoluble matter was then filtered off using qualitative filter paper to obtain the calcium ion solution. On average, 0.05–0.06 g of oyster shell powder was consumed per mL of dilute hydrochloric acid.

[0042] Example 1

[0043] The magnetic biochar precursor was washed with deionized water, filtered, dried to constant weight, and ground to below 200 mesh without water bath heating.

[0044] Example 2

[0045] Mix 1g of the magnetic biochar precursor with 20mL of deionized water, heat in a water bath at 80℃ for 2h, cool, wash with deionized water, filter, dry to constant weight, and grind to below 200 mesh to obtain iron-rich magnetic biochar.

[0046] Example 3

[0047] Mix 1g of the magnetic biochar precursor with 10mL of the calcium ion solution, add 10mL of deionized water, heat in a water bath at 80℃ for 2h, cool, wash with deionized water, filter, dry to constant weight, and grind to below 200 mesh to obtain iron-rich / calcium magnetic biochar.

[0048] Figure 2 The magnetization curve shows that the magnetization intensity reaches 18.20 emu / g, which is sufficient for magnetic separation under a magnetic field. This indicates that the present application can still maintain good magnetic recovery performance after introducing calcium, and can be recycled.

[0049] Example 4

[0050] Mix 1g of the magnetic biochar precursor with 20mL of the calcium ion solution, and add deionized water to ensure a solid-liquid ratio of 1:20. Heat in an 80℃ water bath for 2 hours. After cooling, wash with deionized water, filter, and dry to constant weight. Grind to below 200 mesh to obtain iron-rich / calcium magnetic biochar.

[0051] Example 5

[0052] The non-magnetic biochar precursor was washed with deionized water, filtered, dried to constant weight, and ground to below 200 mesh without water bath heating.

[0053] Example 6

[0054] Mix 1g of the non-magnetic biochar precursor with 10mL of the calcium ion solution, add 10mL of deionized water, heat in an 80℃ water bath for 2h, cool, wash with deionized water, filter, dry to constant weight, and grind to below 200 mesh to obtain non-magnetic biochar.

[0055] The biochar obtained in all examples was added to acetaminophen wastewater with a concentration of 100 mg / L at a dosage of 2 g / L at 25°C, and the reaction was carried out by shaking at 150 rpm in the dark until adsorption equilibrium was reached after 48 h.

[0056] The solution at adsorption equilibrium was passed through a 0.45 μm filter membrane, and its absorbance was measured at an absorption wavelength of 244 nm using a UV spectrophotometer. The equilibrium concentration Ce was calculated based on the standard curve of acetaminophen, and the corresponding equilibrium adsorption capacity q was calculated using the following formula:

[0057]

[0058] The formula for calculating the removal rate is:

[0059]

[0060] In the formula, C0 and Ce , respectively, are the initial and equilibrium concentrations (mg / L) of the acetaminophen filtrate, V is the volume of the acetaminophen solution (L), and m is the mass (g) of the adsorbent used.

[0061] The equilibrium adsorption capacity and removal rate of acetaminophen in Examples 1-6 are shown in Table 3.

[0062] Table 3 shows the equilibrium adsorption capacity and removal rate of biochar adsorbed on acetaminophen wastewater obtained in Examples 1-6.

[0063]

[0064] Compared to Example 5, the magnetic biochar prepared using iron-rich sludge in Example 1 showed a 2.93% increase in removal rate, verifying the promoting effect of iron on adsorption. However, compared to Examples 1 and 5, the removal rates in Examples 3 and 6, with the addition of calcium ion solution, increased by 10.96% and decreased by 4.09%, respectively. This phenomenon indicates that the increased adsorption capacity only occurs when calcium and iron are present together. (See surface morphology...) Figure 1 The results showed that iron elements were distributed in a plate-like pattern on the flower cluster surface, and calcium ions were also dispersed on the flower cluster surface, reducing the aggregation phenomenon during the magnetic biochar adsorption process. At the same time, the active sites were exposed, further improving the adsorption performance. However, in biochar with low iron content, loading calcium ions may clog the pores, leading to a decrease in adsorption capacity. Example 2 further confirmed that the adsorption capacity increased when water bath heating was performed without the addition of calcium ion solution compared to the method without water bath heating. This is because pore collapse occurs only in the presence of iron-rich sludge and does not lead to a significant increase in adsorption capacity. In addition, Examples 3 and 4 show that 10 mL of calcium ion solution is the most suitable addition amount. If too much calcium ion is added, it may also clog the pores and lead to a decrease in adsorption capacity.

[0065] In Examples 3 and 4 of this invention, the removal rate is not less than 60% under the condition that the equilibrium adsorption capacity is above 30 mg / g. The acetaminophen wastewater has excellent removal performance and superior economic benefits and performance.

[0066] As can be seen from the above adsorption application examples, this invention, based on the composition and structural characteristics of iron-rich sludge and oyster shell powder, can produce iron / calcium-rich magnetic biochar materials that are simple to process, inexpensive, environmentally friendly, and easy to separate through reasonable control. These materials have good development prospects in the field of wastewater removal.

[0067] Matters not covered in this invention are common knowledge.

Claims

1. Use of iron / calcium-rich magnetic sludge biochar, characterized by: For the treatment of acetaminophen wastewater, the specific process is as follows: at 25℃, 2-3 g / L of iron-rich / calcium-rich magnetic sludge biochar is added to acetaminophen wastewater with a concentration of 5-100 mg / L, and the reaction is carried out by shaking at 100-200 rpm in the dark until the adsorption equilibrium is reached. The removal rate of acetaminophen is not less than 60%, and the equilibrium adsorption capacity is not less than 30 mg / g; The preparation method of iron-rich / calcium magnetic sludge biochar includes the following steps: S1. Dry and crush the iron-rich sludge and the collected domestic waste separately, and mix them evenly according to the mass ratio of iron-rich sludge: domestic waste = 3-5: 1 to obtain a mixture of iron-rich sludge and domestic waste. S2. The mixture of iron-rich sludge and domestic waste is placed in a tube furnace and pyrolyzed under an inert protective atmosphere. After cooling, it is ground to below 200 mesh to obtain magnetic biochar precursor. S3. While stirring continuously, slowly add oyster shell powder to dilute hydrochloric acid until no further reaction occurs. Filter the solution through qualitative filter paper to remove insoluble matter and obtain a calcium ion solution. On average, 0.05~0.06 g of oyster shell powder is consumed per mL of dilute hydrochloric acid. S4. Mix the magnetic biochar precursor with a calcium ion solution, add deionized water to achieve a solid-liquid ratio of 1:15-30, heat in a water bath at a temperature of 60-100℃ for 1-3 hours, cool, wash with deionized water, filter, dry to constant weight, and grind to below 200 mesh to obtain iron-rich / calcium magnetic sludge biochar; the amount of calcium ion solution added is 5-20 mL / 1g magnetic biochar precursor.

2. Use according to claim 1, characterized in that: The total organic matter content of the iron-rich sludge in step S1 is 40-70 wt%, and the moisture content after drying is controlled at 0-5 wt%, with the main component TFe2O3 content at 30-60 wt%. The moisture content of the dried municipal solid waste is controlled at 0-5 wt%, and its physical composition is as follows: kitchen waste 46-66 wt%, plastics 16-27 wt%, paper 10-16 wt%, wood and bamboo 3-7 wt%, textiles 3-5 wt%, and rubber 0.5-1.5 wt%. The drying process described in step S1 is as follows: drying at 105±5℃ for 24 hours.

3. Use according to claim 1, characterized in that: The pyrolysis process described in step S2 is as follows: under the condition of passing nitrogen gas at a rate of 80-100 mL / min, the temperature is increased to 700-1000℃ for 2 hours at a heating rate of 8-12℃ / min.

4. Use according to claim 1, characterized in that: In step S1, the particle size range after crushing is controlled as follows: fabrics, wood, and paper materials < 2 mm, and other powdery materials < 60 mesh.

5. The use according to claim 1, characterized in that: The concentration of the dilute hydrochloric acid in step S3 is 1~1.5 mol / L, and the particle size of the oyster shell powder in step S3 is <100 mesh.

6. Use according to claim 1, characterized in that: In step S4, the amount of magnetic biochar precursor added is 1 g, the amount of calcium ion solution added is 10-20 mL, the solid-liquid ratio is 1:15-20, the water bath heating temperature is 80±5℃, and the water bath heating time is 1.5-2 h; the drying process in step S4 is: 80±5℃ for 24 h.

7. The application according to claim 1, characterized in that: The surface morphology of the iron-rich / calcium-rich magnetic sludge biochar is flower-like, with iron elements distributed in flakes on the flower-like surface and calcium ions also dispersed on the flower-like surface.

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