Preparation method of modified biochar material and application of modified biochar material in cadmium-containing wastewater treatment

Abstract

The invention provides a preparation method of a modified biochar material and application of the modified biochar material in cadmium-containing wastewater treatment, and relates to the technical field of biochar adsorbent preparation. The method comprises the following steps: pretreating biomass, loading Fe2O3 nanoparticles on the surface of the biomass, mixing the product with potassium carbonate, pre-carbonizing, modifying by using sodium sulfide, and finally calcining to obtain the modified biochar material. According to the technical scheme, the sulfur-containing functional groups and the Fe2O3 nanoparticles are modified on the biochar at the same time, a large number of active sites can be provided for the biochar, meanwhile, the passivation effect on cadmium is synergistically improved, efficient adsorption of cadmium is achieved, pre-carbonization can enter the biochar by means of CO2 generated in the thermal decomposition process of potassium carbonate to generate pore channels, and the adsorption efficiency of cadmium is improved. The material is endowed with more pore structures, and the specific surface area and adsorption capacity of the modified material are improved. By adopting the preparation method provided by the invention, the modified biochar material with excellent cadmium adsorption performance can be prepared.

Description

Technical Field

[0001] This invention relates to the field of biochar adsorbent preparation technology, and in particular to a method for preparing modified biochar material and its application in the treatment of cadmium-containing wastewater. Background Technology

[0002] With the rapid development of industry and agriculture, heavy metals enter water bodies through mining, metallurgy, machinery manufacturing, electroplating, and chemical processes. They then migrate and transform within the water through various pathways, posing a significant potential threat to the natural environment and organisms. Among these, cadmium (Cd) is one of the most common and serious heavy metal pollutants, possessing high toxicity and carcinogenicity, and has become a major factor endangering water quality and safety. Therefore, there is an urgent need to develop an efficient, green, and sustainable remediation strategy for treating cadmium-polluted water bodies.

[0003] Biochar is a porous carbon-based material produced by the anaerobic pyrolysis of biomass. It is commonly used for water purification, resource recovery, and soil fertilization. Biomass-derived adsorbents are characterized by sustainability, low cost and high efficiency, biodegradability, and environmental friendliness. Biochar adsorbents, in particular, possess chemical stability, non-toxicity, low cost, large specific surface area, porous structure, and abundant functional groups, making them valuable for large-scale applications. Studies have shown that biochar adsorbents are effective against Cd. 2+ It exhibits adsorption properties, but its affinity for Cd is limited. 2+ Biochar has limited adsorption capacity. Therefore, modification of biochar is necessary to improve its adsorption capacity for Cd. 2+ The adsorption efficiency is of great significance for wastewater treatment.

[0004] In view of this, it is necessary to design a method for preparing modified biochar materials and their application in the treatment of cadmium-containing wastewater in order to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing modified biochar materials and their application in the treatment of cadmium-containing wastewater.

[0006] To achieve the above-mentioned objectives, in a first aspect, the present invention provides a method for preparing modified biochar material, comprising the following steps:

[0007] S1. Pretreatment of biomass:

[0008] S2. Load Fe2O3 nanoparticles onto the pretreated biomass, mix the Fe2O3 nanoparticle-loaded biomass with potassium carbonate, pre-carbonize it, modify the pre-carbonized product with sodium sulfide solution, and then calcine it to obtain modified biochar material.

[0009] Preferably, in step S2, the mass ratio of the biomass loaded with Fe2O3 nanoparticles to the potassium carbonate is (1:1)-(1:2).

[0010] Preferably, in step S2, the method for loading Fe2O3 nanoparticles onto the pretreated biomass is as follows: the pretreated biomass is added to a ferric chloride solution and stirred for 4-8 hours.

[0011] Preferably, the concentration of the ferric chloride solution is 0.5-1.0 mol / L; the solid-liquid ratio of the biomass to the ferric chloride solution is 1:10.

[0012] Preferably, in step S2, the pre-carbonization temperature is 300°C and the time is 0.8-1.2 h.

[0013] Preferably, in step S2, the concentration of the sodium sulfide solution is 0.5-1.0 mol / L, the solid-liquid ratio of the pre-carbonized product to the sodium sulfate solution is 1:10, and the calcination temperature is 650℃ for 2-3 hours.

[0014] Preferably, in step S1, the pretreatment of biomass includes the following steps: acid leaching of biomass with phosphoric acid solution and nitric acid solution in sequence, and washing with anhydrous ethanol and water; wherein the concentration of phosphoric acid solution is 0.15-0.25 mol / L, and the concentration of nitric acid solution is 0.4-0.6 mol / L.

[0015] Preferably, the solid-liquid ratio of the biomass to the phosphoric acid solution is 1:10, and the contact time between the two is 9-13 hours.

[0016] Secondly, the present invention provides a modified biochar material, wherein the modified biochar material has a specific surface area of ​​900-1100 m². 2 / g, with a porosity of 75-80%.

[0017] Thirdly, this invention provides an application of modified biochar material in the treatment of cadmium-containing wastewater.

[0018] The beneficial effects of this invention are:

[0019] 1. The method for preparing modified biochar material provided by this invention involves loading Fe2O3 nanoparticles onto the surface of biomass, mixing the product with potassium carbonate, pre-carbonizing it, modifying it with sodium sulfide, and finally calcining it to obtain the modified biochar material. In the above technical solution, by simultaneously modifying the biochar with sulfur-containing functional groups and Fe2O3 nanoparticles, a large number of active sites can be provided for the biochar, while synergistically improving the passivation effect on cadmium, achieving efficient cadmium adsorption. Pre-carbonization not only promotes the formation of biomass carbonization but also allows CO2 generated during the thermal decomposition of potassium carbonate to enter the biochar, creating pores and giving the material a more porous structure, thus increasing the specific surface area and adsorption capacity of the modified material. Using the preparation method provided by this invention, modified biochar material with excellent cadmium adsorption can be obtained.

[0020] 2. The preparation method provided by this invention, which first acid-leaches biomass with phosphoric acid and nitric acid, and then modifies it, can enhance Cd2+. 2+ The conversion from the soluble state to a more stable form effectively immobilized Cd in the biochar during adsorption. 2+ To improve the Cd content of biomass modified materials 2+ Adsorption capacity; secondly, it effectively removes organic / inorganic impurities from biomass, significantly improves product purity, retains more cellulose skeleton, increases the types and number of functional groups on the surface of biochar, and increases the specific surface area of ​​modified materials.

[0021] 3. The preparation method provided by the present invention can adjust the adsorption performance of the modified material by controlling the concentration of ferric chloride solution, the concentration of modified sodium sulfide solution, and the mass of potassium carbonate added during the loading process of Fe2O3 nanoparticles, thereby endowing the modified material with excellent cadmium adsorption performance. Attached Figure Description

[0022] Figure 1 This is a SEM image of the original biochar used in Example 1 of the present invention;

[0023] Figure 2 This is a SEM image of the modified biochar material prepared in Example 1 of the present invention;

[0024] Figure 3 The modified biochar material prepared in Example 1 of this invention adsorbs Cd. 2+ The subsequent SEM image;

[0025] Figure 4 EDS image of the original biochar used in Example 1 of this invention;

[0026] Figure 5 This is an EDS image of the modified biochar material prepared in Example 1 of the present invention;

[0027] Figure 6The modified biochar material prepared in Example 1 of this invention adsorbs Cd. 2+ The EDS diagram afterward. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0030] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0031] This invention provides a method for preparing modified biochar material, comprising the following steps:

[0032] S1. Pretreatment of biomass:

[0033] S2. Fe2O3 nanoparticles are loaded onto pretreated biomass. The resulting biomass is mixed with potassium carbonate and pre-carbonized. The pre-carbonized product is then modified using sodium sulfide solution and calcined to obtain modified biochar material with a specific surface area of ​​900-1100 m². 2 / g, with a porosity of 75-80%.

[0034] The above technical solution, by pretreating biomass, can increase the types and number of functional groups on the biomass surface, and simultaneously increase its specific surface area, which is beneficial for subsequently loading Fe2O3 nanoparticles onto it. Furthermore, the active functional groups (such as -OH, -COOH, etc.) introduced during the modification process can enhance the performance of Cd-containing biomass in subsequent applications. 2+ Fixation, thereby increasing the Cd content of the modified material. 2+ Adsorption capacity; By loading Fe2O3 nanoparticles onto biomass, the composite material can be endowed with magnetism, which is beneficial for recycling; by pre-carbonizing the biomass loaded with Fe2O3 nanoparticles together with potassium carbonate, the biomass can be carbonized to form biochar, and the CO2 generated during the thermal decomposition of potassium carbonate can enter the biochar to create pores, giving the material more porous structure, increasing the specific surface area of ​​the modified material and thus improving its adsorption capacity; by modifying with sodium sulfide, sulfur-containing functional groups can be loaded onto the biochar, resulting in Cd. 2+Adsorption provides complexation and ion exchange sites, increasing the Cd content of the modified material. 2+ In addition to the adsorption effect, the sulfur-containing functional groups can also synergistically enhance the modified material's adsorption capacity for Cd with Fe2O3 nanoparticles. 2+ This enhances the passivation ability of the modified material, thereby improving its resistance to Cd. 2+ Adsorption effect.

[0035] In some embodiments, in step S1, the pretreatment of biomass is carried out according to the following steps: the biomass is washed, dried, crushed, and sieved to obtain biomass powder; the biomass powder is then subjected to acid leaching treatment with phosphoric acid solution and nitric acid solution in sequence, followed by washing with anhydrous ethanol and water multiple times until the supernatant is neutral, and then dried to obtain pretreated biomass. The source of the biomass is agricultural waste, preferably peanut shells.

[0036] Specifically, the concentration of the phosphoric acid solution is 0.15-0.25 mol / L, and the concentration of the nitric acid solution is 0.4-0.6 mol / L. The solid-liquid ratio of biomass powder to both the phosphoric acid and nitric acid solutions is 1:10 (g:mL). The contact time between the biomass powder and both the phosphoric acid and nitric acid solutions is 9-13 hours, and the washing is performed 3-5 times. A 60-90 mesh sieve is used for sieving. The drying temperature and time can be adjusted as needed; no further restrictions are imposed here.

[0037] In the above technical solution, by simultaneously treating biomass with phosphoric acid and nitric acid, phosphoric acid can selectively dissolve hemicellulose and some amorphous cellulose, thereby disrupting the dense structure of the biomass. Secondly, after phosphoric acid treatment, Cd2+ can be enhanced in subsequent applications. 2+ The conversion from the soluble state to a more stable form effectively immobilized Cd in the biochar during adsorption. 2 + To improve the Cd content of biomass modified materials 2+ Adsorption capacity. Furthermore, by utilizing the oxidizing properties of nitric acid to oxidize the surface functional groups of biomass (e.g., generating -COOH, -OH), nitric acid can activate the surface functional groups of biochar, thereby improving the material's adsorption capacity for Cd. 2+ The adsorption effect is good, and the combination of the two acids can more thoroughly remove organic / inorganic impurities from biomass, significantly improve product purity, retain more cellulose skeleton, increase the types and number of functional groups on the surface of biochar, and increase specific surface area.

[0038] In some embodiments, in step S2, the loading of Fe2O3 nanoparticles onto the pretreated biomass is carried out as follows: the pretreated biomass is added to a ferric chloride solution, stirred for 4-8 hours, subjected to solid-liquid separation, washed 3-5 times, and dried to obtain the biomass loaded with Fe2O3 nanoparticles. Specifically, the concentration of the ferric chloride solution in the above process is 0.5-1.0 mol / L, and the solid-liquid ratio of biomass to ferric chloride solution is 1:10.

[0039] In some embodiments, in step S2, the mass ratio of biomass loaded with Fe2O3 nanoparticles to potassium carbonate is (1:1)-(1:2). By controlling the ratio within this range, not only can the biomass be fully carbonized, but a uniform and stable pore structure can also be formed inside. If the ratio is too high or the potassium carbonate is too low, the pre-carbonization will be incomplete or uneven, and the pore structure formed in the biochar will be limited, affecting the overall effect of the modified material. If the ratio is too low or the potassium carbonate is too high, too many pore structures will be formed in the biochar, affecting the structural stability of the material. The pre-carbonization temperature is 300℃, the time is 0.8-1.2h, the temperature rise rate from 20-25℃ to 300℃ is 10℃ / min, and the thermal decomposition temperature of potassium carbonate is 270℃. Under the above conditions, not only can potassium carbonate be thermally decomposed, but the pre-carbonization of biomass can also be completed.

[0040] In some embodiments, in step S2, the concentration of the sodium sulfide solution is 0.5-1.0 mol / L, and the solid-liquid ratio of the pre-carbonized product to the sodium sulfide solution is 1:10 (in g:mL). This allows the biochar material to be successfully loaded with sulfur-containing functional groups. If the ratio is too high or the sodium sulfide is too low, the surface and pores of the biochar will not be able to load enough sulfur-containing functional groups, affecting the overall effect of the modified material. If the ratio is too low or the sodium sulfide is too high, the excess sodium sulfide or the precipitates generated by the reaction may block the original pores of the biochar or cover its surface active sites, thereby affecting the adsorption effect of the modified material.

[0041] In some embodiments, in step S2, the calcination temperature is 650°C, the time is 2-3 hours, the calcination process is carried out in an inert atmosphere, such as argon or nitrogen, and the heating rate from 20-25°C to 650°C is 5°C / min.

[0042] In the above technical solution, biochar is prepared by using a two-step pyrolysis method (pre-carbonization and carbonization), which can gradually form a uniform pore structure in the biochar, improve the stability and adsorption of the biochar, and effectively avoid the collapse of the biochar pore structure during the calcination process, which would affect the adsorption performance of the modified material.

[0043] The preparation method of the modified biochar material provided by the present invention and its application in the treatment of cadmium-containing wastewater will be further explained below with reference to specific embodiments:

[0044] Example 1

[0045] This embodiment prepares a modified biochar material, and the preparation method includes the following steps:

[0046] 10g of peanut shell powder that has passed through an 80-mesh sieve was soaked in 100mL of 0.2mol / L phosphoric acid and 100mL of 0.5mol / L nitric acid for 12h, then washed several times with anhydrous ethanol and distilled water until the supernatant was neutral, and dried to complete the pretreatment of peanut shell powder.

[0047] The pretreated peanut shell powder was added to 100 mL of a 0.5 mol / L ferric chloride solution and stirred for 6 hours. Solid-liquid separation was performed, and the filter cake was washed multiple times. Next, the resulting product was mixed evenly with 15 g of potassium carbonate and calcined in a muffle furnace at a heating rate of 10 °C / min to 300 °C for 1 hour. After calcination, the product was added to 100 mL of a 0.5 mol / L sodium sulfide solution and stirred for 6 hours. Solid-liquid separation was performed, and the filter cake was washed multiple times, dried, and then placed in a tube furnace. Under an argon atmosphere, the temperature was increased to 650 °C at a heating rate of 5 °C / min and heated for 2.5 hours. After natural cooling to 25 °C, the product was removed, washed with water, and dried to obtain the modified biochar material. It should be noted that, unless otherwise specified, the reagents and raw materials used in the embodiments of this invention can be obtained commercially.

[0048] SEM image of pretreated peanut shell powder as shown below Figure 1 As shown, the SEM image of the modified biochar material is as follows. Figure 2 As shown in the figure, comparing the two figures, it can be seen that the porosity of the modified material obtained after modification is significantly improved compared with peanut shell powder, and the material surface is rough with a large number of honeycomb pores and Fe2O3 particles attached to the surface (white particles shown in red circles in the figure).

[0049] Example 2

[0050] This embodiment prepares a modified biochar material, and the preparation method includes the following steps:

[0051] 10g of peanut shell powder that has passed through an 80-mesh sieve was soaked in 100mL of 0.2mol / L phosphoric acid and 100mL of 0.5mol / L nitric acid for 12h, then washed several times with anhydrous ethanol and distilled water until the supernatant was neutral, and dried to complete the pretreatment of peanut shell powder.

[0052] The pretreated peanut shell powder was added to 100 mL of 0.5 mol / L ferric chloride solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. Then, the obtained product was mixed evenly with 15 g of potassium carbonate and calcined in a muffle furnace at a heating rate of 10 °C / min to 300 °C for 1 h. After calcination, the product was added to 100 mL of 0.7 mol / L sodium sulfide solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. After drying, the product was placed in a tube furnace and heated to 650 °C at a heating rate of 5 °C / min in an argon atmosphere for 2.5 h. After natural cooling to 25 °C, the product was removed, washed with water, and dried to obtain the modified biochar material.

[0053] Example 3

[0054] This embodiment prepares a modified biochar material, and the preparation method includes the following steps:

[0055] 10g of peanut shell powder that has passed through an 80-mesh sieve was soaked in 100mL of 0.2mol / L phosphoric acid and 100mL of 0.5mol / L nitric acid for 12h, then washed several times with anhydrous ethanol and distilled water until the supernatant was neutral, and dried to complete the pretreatment of peanut shell powder.

[0056] The pretreated peanut shell powder was added to 100 mL of 0.5 mol / L ferric chloride solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. Then, the obtained product was mixed evenly with 15 g of potassium carbonate and calcined in a muffle furnace at a heating rate of 10 °C / min to 300 °C for 1 h. After calcination, the product was added to 100 mL of 0.8 mol / L sodium sulfide solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. After drying, the product was placed in a tube furnace and heated to 650 °C at a heating rate of 5 °C / min in an argon atmosphere for 2.5 h. After natural cooling to 25 °C, the product was removed, washed with water, and dried to obtain the modified biochar material.

[0057] Example 4

[0058] This embodiment prepares a modified biochar material, and the preparation method includes the following steps:

[0059] 10g of peanut shell powder that has passed through an 80-mesh sieve was soaked in 100mL of 0.2mol / L phosphoric acid and 100mL of 0.5mol / L nitric acid for 12h, then washed several times with anhydrous ethanol and distilled water until the supernatant was neutral, and dried to complete the pretreatment of peanut shell powder.

[0060] The pretreated peanut shell powder was added to 100 mL of 0.5 mol / L ferric chloride solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. Then, the obtained product was mixed evenly with 15 g of potassium carbonate and calcined in a muffle furnace at a heating rate of 10 °C / min to 300 °C for 1 h. After calcination, the product was added to 100 mL of 1.0 mol / L sodium sulfide solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. After drying, the product was placed in a tube furnace and heated to 650 °C at a heating rate of 5 °C / min in an argon atmosphere for 2.5 h. After natural cooling to 25 °C, the product was removed, washed with water, and dried to obtain the modified biochar material.

[0061] Example 5

[0062] This embodiment prepares a modified biochar material, and the preparation method includes the following steps:

[0063] 10g of peanut shell powder that has passed through an 80-mesh sieve was soaked in 100mL of 0.2mol / L phosphoric acid and 100mL of 0.5mol / L nitric acid for 12h, then washed several times with anhydrous ethanol and distilled water until the supernatant was neutral, and dried to complete the pretreatment of peanut shell powder.

[0064] The pretreated peanut shell powder was added to 100 mL of 0.75 mol / L ferric chloride solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. Then, the obtained product was mixed evenly with 15 g of potassium carbonate and calcined in a muffle furnace at a heating rate of 10 °C / min to 300 °C for 1 h. After calcination, the product was added to 100 mL of 0.7 mol / L sodium sulfide solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. After drying, the product was placed in a tube furnace and heated to 650 °C at a heating rate of 5 °C / min in an argon atmosphere for 2.5 h. After natural cooling to 25 °C, the product was removed, washed with water, and dried to obtain the modified biochar material.

[0065] Example 6

[0066] This embodiment prepares a modified biochar material, and the preparation method includes the following steps:

[0067] 10g of peanut shell powder that has passed through an 80-mesh sieve was soaked in 100mL of 0.2mol / L phosphoric acid and 100mL of 0.5mol / L nitric acid for 12h, then washed several times with anhydrous ethanol and distilled water until the supernatant was neutral, and dried to complete the pretreatment of peanut shell powder.

[0068] The pretreated peanut shell powder was added to 100 mL of 0.85 mol / L ferric chloride solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. Then, the obtained product was mixed evenly with 15 g of potassium carbonate and calcined in a muffle furnace at a heating rate of 10 °C / min to 300 °C for 1 h. After calcination, the product was added to 100 mL of 0.7 mol / L sodium sulfide solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. After drying, the product was placed in a tube furnace and heated to 650 °C at a heating rate of 5 °C / min in an argon atmosphere for 2.5 h. After natural cooling to 25 °C, the product was removed, washed with water, and dried to obtain the modified biochar material.

[0069] Example 7

[0070] This embodiment prepares a modified biochar material, and the preparation method includes the following steps:

[0071] 10g of peanut shell powder that has passed through an 80-mesh sieve was soaked in 100mL of 0.2mol / L phosphoric acid and 100mL of 0.5mol / L nitric acid for 12h, then washed several times with anhydrous ethanol and distilled water until the supernatant was neutral, and dried to complete the pretreatment of peanut shell powder.

[0072] The pretreated peanut shell powder was added to 100 mL of a 1.0 mol / L ferric chloride solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. Then, the obtained product was mixed evenly with 15 g of potassium carbonate and calcined in a muffle furnace at a heating rate of 10 °C / min to 300 °C for 1 h. After calcination, the product was added to 100 mL of a 0.7 mol / L sodium sulfide solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. After drying, the product was placed in a tube furnace and heated to 650 °C at a heating rate of 5 °C / min in an argon atmosphere for 2.5 h. After natural cooling to 25 °C, the product was removed, washed with water, and dried to obtain the modified biochar material.

[0073] Example 8

[0074] This embodiment prepares a modified biochar material, and the preparation method includes the following steps:

[0075] 10g of peanut shell powder that has passed through an 80-mesh sieve was soaked in 100mL of 0.2mol / L phosphoric acid and 100mL of 0.5mol / L nitric acid for 12h, then washed several times with anhydrous ethanol and distilled water until the supernatant was neutral, and dried to complete the pretreatment of peanut shell powder.

[0076] The pretreated peanut shell powder was added to 100 mL of 0.75 mol / L ferric chloride solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. Then, the obtained product was mixed evenly with 12 g of potassium carbonate and calcined in a muffle furnace at a heating rate of 10 °C / min to 300 °C for 1 h. After calcination, the product was added to a 0.7 mol / L sodium sulfide solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. After drying, the product was placed in a tube furnace and heated to 650 °C at a heating rate of 5 °C / min in an argon atmosphere for 2.5 h. After natural cooling to 25 °C, the product was removed, washed with water, and dried to obtain the modified biochar material.

[0077] Example 9

[0078] This embodiment prepares a modified biochar material, and the preparation method includes the following steps:

[0079] 10g of peanut shell powder that has passed through an 80-mesh sieve was soaked in 100mL of 0.2mol / L phosphoric acid and 100mL of 0.5mol / L nitric acid for 12h, then washed several times with anhydrous ethanol and distilled water until the supernatant was neutral, and dried to complete the pretreatment of peanut shell powder.

[0080] The pretreated peanut shell powder was added to 100 mL of 0.75 mol / L ferric chloride solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. Then, the obtained product was mixed evenly with 20 g of potassium carbonate and calcined in a muffle furnace at a heating rate of 10 °C / min to 300 °C for 1 h. After calcination, the product was added to 100 mL of 0.7 mol / L sodium sulfide solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. After drying, the product was placed in a tube furnace and heated to 650 °C at a heating rate of 5 °C / min in an argon atmosphere for 2.5 h. After natural cooling to 25 °C, the product was removed, washed with water, and dried to obtain the modified biochar material.

[0081] Furthermore, this invention also tested the application performance of the modified biochar materials prepared in Examples 1 to 9 in adsorbing cadmium from cadmium-containing wastewater. The specific test method is as follows: 0.1 g of modified biochar material was added to 50 mL of a cadmium-containing solution with a concentration of 50 mg / L, and adsorption was carried out for 12 h at pH = 6 and a temperature of 25°C. Based on the concentration of the cadmium-containing solution before and after adsorption, the adsorption efficiency of the modified biochar material for cadmium in water was calculated, as shown in Table 1. Comparing the adsorption efficiencies of Examples 1 to 4 and Comparative Example 1, it can be seen that sodium sulfide modification can improve the adsorption effect of biochar to a certain extent, and with the increase of sodium sulfide concentration, the adsorption efficiency of the modified biochar material for Cd... 2+The adsorption capacity is significantly improved because as the sodium sulfide concentration increases, more sulfur-containing functional groups such as S=O, S—O, C—S, and C=S are introduced. This also facilitates the formation of a porous structure in the biochar, thereby increasing the adsorption capacity of the modified material. Secondly, since Example 4 only shows a small improvement in adsorption efficiency compared to Example 3, and considering economic factors, the optimal sodium sulfide concentration is chosen to be 0.7 mol / L. Comparing the adsorption efficiencies of Example 2 and Comparative Example 2 shows that ferric chloride modification can improve the adsorption capacity of biochar for Cd. 2+ The improved adsorption effect is due to the simultaneous modification of the biochar with iron-containing particles and sulfur-containing functional groups, which enhances the adsorption capacity of the modified biochar material for Cd. 2+ The passivation effect of the modified material on Cd is observed by comparing the adsorption efficiencies of Examples 5 to 7. 2+ The adsorption efficiency showed a trend of first increasing and then decreasing. Considering economic factors, the optimal concentration of the ferric chloride solution was chosen to be 0.75 mol / L. The SEM image of the modified biochar material prepared in Example 1 after adsorbing cadmium is shown below. Figure 3 As shown, compare it with Figure 2 Comparative analysis reveals a significant reduction in porosity, with the biochar surface exhibiting sheet-like or granular aggregates. This is due to the precipitation of CdCO3 or Cd(OH)2 on the biochar surface. The EDS image of the pretreated peanut shell powder in Example 1 is shown below. Figure 4 As shown, the EDS diagram of the modified biochar material is as follows: Figure 5 As shown, the EDS diagram of the modified biochar material after adsorbing cadmium is as follows. Figure 6 As shown, comparison Figure 5 and Figure 4 It can be seen that the modified biochar material has an increased Fe content compared to the pretreated peanut shell powder, indicating that Fe2O3 nanoparticles were successfully loaded in the modified material. Simultaneously, the increased S content indicates that S-containing functional groups were successfully loaded in the modified material. (Comparison) Figure 6 and Figure 5 It can be seen that a Cd peak exists in the modified biochar material after cadmium adsorption. This result further verifies the adsorption performance of the modified biochar material for cadmium in water.

[0082] Table 1 shows the adsorption efficiency of modified biochar materials prepared in Examples 1 to 9 for cadmium in water.

[0083] project Adsorption efficiency (%) Example 1 94.64 Example 2 97.74 Example 3 98.02 Example 4 98.48 Example 5 99.17 Example 6 99.44 Example 7 99.02 Example 8 98.29 Example 9 99.25

[0084] Comparative Example 1

[0085] The only difference between this comparative example and Example 1 is that the step of modifying the peanut shell powder with sodium sulfide is omitted. The preparation method includes the following steps:

[0086] 10g of peanut shell powder that has passed through an 80-mesh sieve was soaked in 100mL of 0.2mol / L phosphoric acid and 100mL of 0.5mol / L nitric acid for 12h, then washed several times with anhydrous ethanol and distilled water until the supernatant was neutral, and dried to complete the pretreatment of peanut shell powder.

[0087] The pretreated peanut shell powder was added to 100 mL of 0.5 mol / L ferric chloride solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. Then, the obtained product was mixed evenly with 15 g of potassium carbonate and calcined in a muffle furnace at a heating rate of 10 °C / min to 300 °C for 1 h. After calcination, the product was placed in a tube furnace and heated to 650 °C at a heating rate of 5 °C / min in an argon atmosphere for 2.5 h. After natural cooling to 25 °C, the product was removed, washed with water, and dried to obtain the modified biochar material.

[0088] Comparative Example 2

[0089] The only difference between this comparative example and Example 2 is that the step of modifying the peanut shell powder with ferric chloride is omitted. The preparation method includes the following steps:

[0090] 10g of peanut shell powder that has passed through an 80-mesh sieve was soaked in 100mL of 0.2mol / L phosphoric acid and 100mL of 0.5mol / L nitric acid for 12h, then washed several times with anhydrous ethanol and distilled water until the supernatant was neutral, and dried to complete the pretreatment of peanut shell powder.

[0091] The pretreated peanut shell powder was mixed with 15g of potassium carbonate and calcined in a muffle furnace at a heating rate of 10℃ / min to 300℃ for 1h. After calcination, the product was added to 100mL of 0.7mol / L sodium sulfide solution and stirred for 6h. Solid-liquid separation was performed, and the filter cake was washed and dried several times. It was then placed in a tube furnace and heated to 650℃ at a heating rate of 5℃ / min in an argon atmosphere for 2.5h. After natural cooling to 25℃, it was removed, washed with water, and dried to obtain the modified biochar material.

[0092] Comparative Example 3

[0093] The only difference between this comparative example and Example 5 is that the pretreatment of peanut shell powder is different from that in Example 5. The pretreatment is carried out as follows: 10g of peanut shell powder that has passed through an 80-mesh sieve is soaked in 100mL of 0.5mol / L nitric acid for 12h, and then washed multiple times with anhydrous ethanol and distilled water until the supernatant is neutral. After drying, the pretreatment of peanut shell powder is completed.

[0094] The pretreated peanut shell powder was added to 100 mL of 0.75 mol / L ferric chloride solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. Then, the obtained product was mixed evenly with 15 g of potassium carbonate and calcined in a muffle furnace at a heating rate of 10 °C / min to 300 °C for 1 h. After calcination, the product was added to 100 mL of 0.7 mol / L sodium sulfide solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. After drying, the product was placed in a tube furnace and heated to 650 °C at a heating rate of 5 °C / min in an argon atmosphere for 2.5 h. After natural cooling to 25 °C, the product was removed, washed with water, and dried to obtain the modified biochar material.

[0095] Comparative Example 4

[0096] The only difference between this comparative example and Example 5 is that the pretreatment of the peanut shell powder is only performed with phosphoric acid, and the specific preparation method includes the following steps:

[0097] 10g of peanut shell powder that has passed through an 80-mesh sieve was soaked in 100mL of 0.2mol / L phosphoric acid for 12h, then washed several times with anhydrous ethanol and distilled water until the supernatant was neutral, and dried to complete the pretreatment of peanut shell powder.

[0098] The pretreated peanut shell powder was added to 100 mL of 0.75 mol / L ferric chloride solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. Then, the obtained product was mixed evenly with 15 g of potassium carbonate and calcined in a muffle furnace at a heating rate of 10 °C / min to 300 °C for 1 h. After calcination, the product was added to 100 mL of 0.7 mol / L sodium sulfide solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. After drying, the product was placed in a tube furnace and heated to 650 °C at a heating rate of 5 °C / min in an argon atmosphere for 2.5 h. After natural cooling to 25 °C, the product was removed, washed with water, and dried to obtain the modified biochar material.

[0099] Comparative Example 5

[0100] The only difference between this comparative example and Example 5 is that the peanut shell powder is not pretreated with anhydrous ethanol for washing. The specific preparation method includes the following steps:

[0101] 10g of peanut shell powder that has passed through an 80-mesh sieve was soaked in 100mL of 0.2mol / L phosphoric acid and 100mL of 0.5mol / L nitric acid for 12h, respectively, and washed several times with distilled water until the supernatant was neutral. The powder was then dried to complete the pretreatment of the peanut shell powder.

[0102] The pretreated peanut shell powder was added to 100 mL of 0.75 mol / L ferric chloride solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. Then, the obtained product was mixed evenly with 15 g of potassium carbonate and calcined in a muffle furnace at a heating rate of 10 °C / min to 300 °C for 1 h. After calcination, the product was added to 100 mL of 0.7 mol / L sodium sulfide solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. After drying, the product was placed in a tube furnace and heated to 650 °C at a heating rate of 5 °C / min in an argon atmosphere for 2.5 h. After natural cooling to 25 °C, the product was removed, washed with water, and dried to obtain the modified biochar material.

[0103] Comparative Example 6

[0104] The only difference between this comparative example and Example 5 is that the pre-carbonization temperature is different from that in Example 5, and the specific preparation method includes the following steps:

[0105] 10g of peanut shell powder that has passed through an 80-mesh sieve was soaked in 100mL of 0.2mol / L phosphoric acid and 100mL of 0.5mol / L nitric acid for 12h, then washed several times with anhydrous ethanol and distilled water until the supernatant was neutral, and dried to complete the pretreatment of peanut shell powder.

[0106] The pretreated peanut shell powder was added to 100 mL of 0.75 mol / L ferric chloride solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. Then, the obtained product was mixed evenly with 15 g of potassium carbonate and calcined in a muffle furnace at a heating rate of 10 °C / min to 200 °C for 1 h. After calcination, the product was added to 100 mL of 0.7 mol / L sodium sulfide solution and stirred for 6 h. Solid-liquid separation was performed, and the filter cake was washed multiple times. After drying, the product was placed in a tube furnace and heated to 650 °C at a heating rate of 5 °C / min in an argon atmosphere for 2.5 h. After natural cooling to 25 °C, the product was removed, washed with water, and dried to obtain the modified biochar material.

[0107] Under the aforementioned test conditions, the performance of the modified biochar materials prepared in Comparative Examples 1 to 6 in adsorbing cadmium from cadmium-containing wastewater was tested. The results are shown in Table 2. Comparing the adsorption efficiency of Example 5 with Comparative Examples 3 and 4, Example 5 showed a higher adsorption efficiency. This is because the simultaneous pretreatment of biomass with phosphoric acid and nitric acid avoids the collapse of the biochar surface, which would damage the biochar framework structure and ensure that the pore structure of the biochar is more interconnected. Specifically, during the pretreatment process, phosphoric acid can promote the formation of -OH and C=O, strengthen the complexation between the modified material and heavy metal ions, and enhance the adsorption of cadmium (Cd). 2+ The transformation from the soluble state to a more stable form makes Cd 2+Nitric acid, with its strong oxidizing properties, not only modifies the biochar but also activates surface functional groups, increases porosity and specific surface area, thereby enhancing the passivation performance of biochar for heavy metals. Furthermore, oxidized biochar exhibits several times higher adsorption capacity for cadmium ions compared to untreated biochar. Therefore, nitric acid leaching of biochar significantly improves its ability to adsorb Cd ions. 2+ The adsorption capacity was compared with that of Example 5 and Comparative Example 5. The results showed that washing biochar with anhydrous ethanol during the pretreatment process could effectively remove fat-soluble substances and cellulose from the surface of peanut shells, thereby improving the pore structure and surface chemical properties of biochar, increasing the yield of biochar during pyrolysis, increasing the proportion of oxygen-containing functional groups in biochar, and enhancing the adsorption capacity of biochar.

[0108] Table 2 shows the adsorption efficiency of modified biochar materials prepared in Example 1 and Comparative Examples 1 to 6 for cadmium in water.

[0109] project Adsorption efficiency (%) Example 1 94.64 Comparative Example 1 87.29 Comparative Example 2 88.92 Comparative Example 3 91.57 Comparative Example 4 92.69 Comparative Example 5 93.06 Comparative Example 6 89.31

[0110] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a modified biochar material, characterized in that, Includes the following steps: S1. Pretreatment of biomass: S2. Load Fe2O3 nanoparticles onto the pretreated biomass, mix the Fe2O3 nanoparticle-loaded biomass with potassium carbonate, pre-carbonize it, modify the pre-carbonized product with sodium sulfide solution, and then calcine it to obtain modified biochar material.

2. The preparation method according to claim 1, characterized in that, In step S2, the mass ratio of the biomass loaded with Fe2O3 nanoparticles to the potassium carbonate is (1:1)-(1:2).

3. The preparation method according to claim 1, characterized in that, In step S2, the method for loading Fe2O3 nanoparticles onto the pretreated biomass is as follows: the pretreated biomass is added to a ferric chloride solution and stirred for 4-8 hours.

4. The preparation method according to claim 3, characterized in that, The concentration of the ferric chloride solution is 0.5-1.0 mol / L; the solid-liquid ratio of the biomass to the ferric chloride solution is 1:

10.

5. The preparation method according to claim 1, characterized in that, In step S2, the pre-carbonization temperature is 300°C and the time is 0.8-1.2 h.

6. The preparation method according to claim 1, characterized in that, In step S2, the concentration of the sodium sulfide solution is 0.5-1.0 mol / L, the solid-liquid ratio of the pre-carbonized product to the sodium sulfide solution is 1:10, and the calcination temperature is 650℃ for 2-3 hours.

7. The preparation method according to claim 1, characterized in that, In step S1, the pretreatment of biomass includes the following steps: acid leaching of biomass with phosphoric acid solution and nitric acid solution in sequence, followed by washing with anhydrous ethanol and water; the concentration of the phosphoric acid solution is 0.15-0.25 mol / L, and the concentration of the nitric acid solution is 0.4-0.6 mol / L.

8. The preparation method according to claim 1, characterized in that, The solid-liquid ratio of biomass to the phosphoric acid solution is 1:10, and the contact time between the two is 9-13 hours.

9. A modified biochar material prepared by the preparation method according to any one of claims 1-8, characterized in that, The modified biochar material has a specific surface area of ​​900-1100 m². 2 / g, with a porosity of 75-80%.

10. The application of a modified biochar material prepared by the preparation method according to any one of claims 1-8 or the modified biochar material according to claim 9 in the treatment of cadmium-containing wastewater.

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