A method for preparing a modified adsorbent using peanut shells and smelting blast furnace slag and application thereof

Abstract

This invention discloses a method and application for preparing modified adsorbents using peanut shells and blast furnace slag, belonging to the field of environmental functional material preparation technology. This invention mixes agricultural waste peanut shells and industrial blast furnace slag in a specific ratio, and obtains crude biochar through gradient low-temperature co-pyrolysis. Then, a dual modification process of urea-ferric chloride composite doping and microwave-assisted phosphoric acid activation is used to prepare the modified adsorbent. This invention overcomes the limitations of single raw materials and single modification through the synergistic combination and dual modification of peanut shells and blast furnace slag, realizing the synergistic resource utilization of agricultural waste and metallurgical solid waste. Its core lies in constructing a synergistic closed loop of "adsorption-oxidation-complexation-fixation": co-pyrolysis forms a multi-level porous structure to achieve rapid physical adsorption; multi-metal oxides in blast furnace slag form multi-element stable complexes with arsenic; Fe-N co-doping introduces active sites, and As... 3+ Efficient oxidation to As 5+ The carrier properties of blast furnace slag can disperse Fe-N sites, preventing agglomeration and deactivation, and then form insoluble phosphate precipitates via phosphate groups. The oxidized As... 5+ Irreversible fixation is achieved by forming insoluble phosphate precipitates using phosphate groups. This invention has advantages such as high arsenic removal capacity, strong anti-interference ability, low process energy consumption, and good industrial feasibility, while also offering both environmental and economic benefits.

Description

Technical Field

[0001] This invention relates to the field of environmental functional materials preparation technology, specifically a method and application for preparing modified adsorbents using peanut shells and blast furnace slag. Background Technology

[0002] Blast furnace slag is one of the main solid wastes generated by the metallurgical industry. my country's annual blast furnace slag emissions exceed 200 million tons. Currently, its main disposal methods are landfilling or road construction. Landfilling consumes a large amount of land resources, and the heavy metal ions and harmful substances contained in blast furnace slag can easily seep into the soil and groundwater, causing secondary pollution. Blast furnace slag is a multi-component composite inorganic solid waste, mainly composed of SiO2, Al2O3, and FeO, and also contains active metal oxides such as CaO, MgO, and MnO. Existing technologies have included some studies combining biomass with metallurgical solid waste for wastewater treatment, but these have several shortcomings: some studies only use blast furnace slag for heavy metal passivation in soil, not for arsenic removal from smelting wastewater; other studies use high-temperature pyrolysis processes (temperatures exceeding 600℃), which are energy-intensive, costly, and prone to causing the loss of active components in the blast furnace slag, hindering large-scale industrial production.

[0003] Peanut shells are a huge waste product in agricultural production, with my country producing over 10 million tons annually. Currently, their disposal mainly involves incineration, landfill, or indiscriminate dumping, causing serious resource waste and contributing to environmental problems such as air and soil pollution. Peanut shells possess unique composition and structural characteristics, with a moderate ratio of cellulose, lignin, and pectin, and their surface is rich in oxygen-containing active groups such as hydroxyl, carboxyl, and phenolic hydroxyl groups. After pyrolysis, they can form a flexible porous structure with hierarchical channels. Simultaneously, the biochar formed from peanut shell pyrolysis has good formability, solving the problem of easy loss of active components. Combining biochar with peanut shells can achieve complementary advantages and improve the arsenic removal performance of adsorbents.

[0004] However, existing modification processes are mostly single-modification processes, which cannot simultaneously solve the problems of low adsorption capacity, weak anti-interference ability, and poor resistance to As. 3+ Problems such as poor oxidation effect make it unsuitable for the complex system of smelting wastewater; some existing technologies only achieve As oxidation through simple Fe-N co-doping. 3+ To As 5+ The oxidation process involves no subsequent specific fixation steps, resulting in oxidized As... 5+ It is prone to re-dissolving and does not combine with the multi-component synergistic complexation effect of metallurgical solid waste, thus limiting the stability and efficiency of arsenic removal.

[0005] Therefore, developing a method for preparing a modified adsorbent that enables the synergistic resource utilization of agricultural waste and metallurgical solid waste, with low energy consumption, high adsorption capacity, strong selectivity for arsenic, and high stability has become a pressing technical problem to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of existing adsorbents, such as low arsenic removal capacity, weak anti-interference ability, and poor adaptability, the failure of peanut shells and blast furnace slag to achieve synergistic arsenic removal, high energy consumption and insufficient industrial feasibility of modification processes, and the inability of single modification to meet multiple arsenic removal needs, this invention provides a method and application for preparing modified adsorbents using peanut shells and blast furnace slag. This invention constructs a synergistic closed loop of "adsorption-oxidation-complexation-immobilization" through the synergistic combination and dual modification of peanut shells and blast furnace slag: co-pyrolysis forms a hierarchical porous structure to achieve rapid physical adsorption; multi-metal oxides in blast furnace slag form multi-element stable complexes with arsenic; Fe-N co-doping introduces active sites, thereby removing As... 3+ Efficient oxidation to As 5+ The carrier properties of blast furnace slag can disperse Fe-N sites, preventing agglomeration and deactivation, and then form insoluble phosphate precipitates via phosphate groups. The oxidized As... 5+ Irreversible fixation is achieved by forming insoluble phosphate precipitates using phosphate groups. The modified adsorbent prepared by this method has advantages such as high arsenic removal capacity, strong anti-interference ability, low process energy consumption, and good industrial feasibility, combining environmental protection and economic benefits.

[0007] The method for preparing modified adsorbents using peanut shells and blast furnace slag as described in this invention specifically includes the following steps: (1) Wash the peanut shells, crush them and sieve them to obtain peanut shell powder; crush the blast furnace slag, ball mill it and sieve it to obtain blast furnace slag powder. Put the peanut shell powder and blast furnace slag powder into a high-speed mixer at a certain mass ratio and mix for 15~20 minutes to obtain mixed raw materials.

[0008] (2) The mixed raw materials are placed in an atmosphere tube furnace and subjected to low-temperature co-pyrolysis under nitrogen atmosphere protection. After the pyrolysis is completed, the mixture is cooled to room temperature, the product is taken out, and then crushed in a pulverizer and passed through a 100-110 mesh sieve to obtain crude biochar.

[0009] (3) Mix urea and ferric chloride in a certain mass ratio, add deionized water to dissolve, stir for 15-20 min, and after complete dissolution, prepare a composite dopant; place the composite dopant and crude biochar in a water bath in a certain mass ratio and stir, control the water bath temperature to 60-70℃, then keep the temperature constant for 2-3 h and place it in a vacuum drying oven, set the drying temperature to 80-90℃, and dry for 12-14 h to obtain modified biochar.

[0010] (4) Measure analytical grade phosphoric acid, dilute it with deionized water, stir evenly, and prepare phosphoric acid activator. Add modified biochar to phosphoric acid activator, stir evenly, and soak for 30-35 min. Then put it into a microwave reactor for activation, stirring once every 30-35 s to ensure uniform activation. After activation, filter by vacuum filtration at a pressure of 0.04-0.06 MPa for 10-15 min. After separating the filter residue, wash the filter residue with deionized water until the pH of the washing liquid is 6.5-7.5 (neutral). Put the washed filter residue into a vacuum drying oven, set the drying temperature to 80-90℃, and dry for 12-14 h. Put the dried product into a pulverizer for pulverization and pass it through a 100-mesh sieve to obtain modified adsorbent.

[0011] Preferably, the raw material pretreatment method in step (1) of the present invention is as follows: peanut shells are washed and dried at 80~85℃ for 4~6 hours, crushed for 5~10 minutes and passed through an 80~100 mesh sieve to obtain peanut shell powder; blast furnace slag is crushed to a particle size ≤5mm, ball-milled at a ball-to-material ratio of (5~8):(1~1.5) for 20~30 minutes and passed through a 100~120 mesh sieve to obtain blast furnace slag powder.

[0012] Preferably, the mass ratio of peanut shell powder to blast furnace slag powder in the mixed raw materials of the present invention is (5~7):1.

[0013] Preferably, the low-temperature co-pyrolysis method of the present invention is a gradient heating low-temperature co-pyrolysis, specifically: the tubular furnace is heated to 200-220°C at a heating rate of 5-10°C / min and held for 0.5-1h; then heated to 400-450°C at a heating rate of 3-5°C / min and held for 1.5-2h; finally, heated to 550-600°C at a heating rate of 2-3°C / min and held for 0.5-1h.

[0014] Preferably, the mass ratio of urea to ferric chloride in the urea-ferric chloride composite dopant of the present invention is (3~5):1, and the concentration is 0.5~1.0 mol / L.

[0015] Preferably, the mass ratio of the urea-ferric chloride composite dopant to crude biochar in this invention is 1:(8~10).

[0016] Preferably, the concentration of the phosphoric acid activator of the present invention is 0.8~1.2 mol / L.

[0017] Preferably, the liquid-to-solid ratio of the phosphoric acid activator to the modified biochar in this invention is (8~12) mL:1g.

[0018] Preferably, the conditions for microwave-assisted activation according to the present invention are: microwave power of 300~400W and microwave activation time of 1~2min.

[0019] The peanut shell-blast furnace slag co-pyrolysis composite modified adsorbent prepared by the method of the present invention can be used to remove arsenic from wastewater.

[0020] Compared with the prior art, the present invention provides a method and application for preparing modified adsorbents using peanut shells and blast furnace slag, which has the following beneficial effects: (1) This invention achieves complementary advantages of raw materials by synergistically combining peanut shells and blast furnace slag, and designs a dual modification process of "urea-ferric chloride composite doping + microwave-assisted phosphoric acid activation", which achieves the beneficial effect of improving the adsorption performance of the adsorbent.

[0021] The multi-component structure of blast furnace slag can form a multi-dimensional synergistic arsenic removal system: the complex active components in blast furnace slag can form stable Fe-As complexes with arsenic, achieving chemical fixation of arsenic and enhancing the chemical complexation effect; adjusting the surface charge of the adsorbent to positive charge significantly improves the electrostatic adsorption capacity for negatively charged arsenate and arsenite ions; simultaneously, these complex active components can synergistically remove As with Fe-N active sites. 3+ Oxidized to As 5+ This enhances oxidation efficiency. Furthermore, the complex active components provide skeletal support, forming a rigid porous structure. This not only significantly improves the mechanical strength and stability of the adsorbent, preventing breakage and loss during use, but also effectively disperses active components such as FeO and CaO, as well as Fe-N active sites, preventing their aggregation and deactivation. At the same time, it increases the specific surface area of ​​the adsorbent, providing more adsorption sites. The various components of blast furnace slag work together synergistically to form a comprehensive system of "complexation-oxidation-charge regulation-skeletal support," which is far superior to the arsenic removal effect of pure FeO alone.

[0022] Meanwhile, the unique composition and structural characteristics of peanut shells are key to achieving synergistic compatibility with blast furnace slag. The flexible porous structure and abundant oxygen-containing groups formed after pyrolysis of peanut shells create a unique synergistic effect with the rigid framework and polymetallic oxides of blast furnace slag. This synergistic effect cannot be achieved by using other biomass. Specifically, the hierarchical porous structure formed after peanut shell pyrolysis uniformly carries complex active components such as FeO, CaO, MgO, MnO, SiO2, and Al2O3 in blast furnace slag, preventing the aggregation and deactivation of various active components. Simultaneously, the hydroxyl and carboxyl groups on the surface of peanut shells form a multi-element synergistic effect with the polymetallic oxides such as FeO, CaO, and MgO in blast furnace slag. This solves the problems of low adsorption capacity and weak anti-interference ability of peanut shells alone, as well as the problems of difficulty in forming and limited adsorption performance of blast furnace slag alone. Furthermore, it overcomes the shortcomings of single pure metal oxides (such as pure FeO) which lack framework support, have few active sites, and have poor arsenic removal stability. The synergistic compatibility of these two components achieves uniform dispersion and stable loading of active components.

[0023] Furthermore, the Fe-N active site of the present invention does not solely achieve As 3+ Instead of oxidation, it involves complexation with multiple components of blast furnace slag and fixation of phosphate groups to form a closed-loop "oxidation-complexation-fixation" arsenic removal system. This is fundamentally different from the existing simple Fe-N co-doping arsenic removal mechanism: existing technologies rely solely on the oxidation properties of Fe-N sites to remove As... 3+ Convert to As 5+ Subsequently, As was achieved solely through simple physical adsorption. 5+ Removal, lack of specific fixation, and prone to arsenic desorption; in this invention, the Fe-N active sites complete the As removal process. 3 + To As 5+ After oxidation, polymetallic oxides in blast furnace slag form stable complexes with arsenic. Microwave-assisted phosphoric acid activation can rapidly activate the pore structure of the adsorbent, increase the specific surface area, and simultaneously introduce phosphate groups, which react with As... 5+ The formation of insoluble phosphate precipitates enables the removal of arsenic, and the porous carrier characteristics of blast furnace slag can effectively disperse Fe-N active sites, preventing their agglomeration and deactivation, and further improving oxidation efficiency.

[0024] (2) This invention achieves a triple benefit of "waste treatment + resource recycling + wastewater treatment" by precisely co-pyrolyzing peanut shells and blast furnace slag to form an adsorbent and applying it to remove arsenic from wastewater. On the one hand, agricultural waste peanut shells (annual emissions of over 10 million tons) and industrial blast furnace slag (annual emissions of over 200 million tons) are transformed into highly efficient arsenic removal adsorbents, replacing traditional incineration and landfill disposal methods, reducing the pollution of the atmosphere, soil and groundwater caused by solid waste dumping, and realizing the resource utilization of solid waste. On the other hand, it efficiently removes arsenic from smelting wastewater, reducing the harm of arsenic pollution to the ecological environment and human health. The treated wastewater can be directly discharged or recycled, further reducing water pollution and promoting the green and low-carbon development of the smelting industry, with outstanding environmental value.

[0025] (3) The present invention also has significant economic benefits and industrial feasibility. The raw materials of the present invention are all industrial waste and agricultural waste, which are widely available and inexpensive. Compared with traditional inorganic adsorbents, the raw material cost is reduced by more than 40%. The preparation process adopts gradient low-temperature co-pyrolysis and microwave-assisted activation, which reduces energy consumption by more than 30% compared with traditional high-temperature modification. Moreover, the process is precise and controllable, the steps are simple, and no complex equipment is required. It can be directly produced on a large scale using the existing production equipment of smelting enterprises, which greatly reduces the preparation and industrial application costs. Detailed Implementation

[0026] The blast furnace slag used in the embodiments of the present invention belongs to the solid waste of the iron and steel smelting industry. It is the final slag discharged during the blast furnace ironmaking process. Its main components are SiO2 (35~40wt%), Al2O3 (6~16wt%), FeO (1~2wt%), CaO (35~40wt%), MgO (4~12wt%), and MnO (0.2~1wt%).

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1 A method for preparing a modified adsorbent using peanut shells and blast furnace slag, comprising the following steps: (1) Take 120g of agricultural waste peanut shells, remove surface impurities, rinse with deionized water 3 times, and dry in an 80℃ forced-air drying oven for 5h; after drying, put them into a pulverizer, pulverize for 8min, pass through a 90-mesh standard sieve, collect the sieve material as peanut shell powder, and seal for later use; take 20g of blast furnace slag, put it into a crusher to crush to a particle size ≤5mm, then put it into a ball mill, ball mill at a ball-to-material ratio of 7:1 for 20min, pass through a 110-mesh sieve, collect the sieve material as blast furnace slag powder, and seal for later use.

[0029] (2) 120g of peanut shell powder and 20g of blast furnace slag powder (mass ratio 6:1) were mixed in a high-speed mixer for 18min. After the mixture was evenly mixed, it was placed in a tube furnace and nitrogen gas was introduced. The temperature was raised from room temperature to 200℃ (heating rate 5℃ / min) and held for 0.8h; the temperature was raised from 200℃ to 420℃ (heating rate 4℃ / min) and held for 1.8h; the temperature was raised from 420℃ to 580℃ (heating rate 2.5℃ / min) and held for 0.5h. After co-pyrolysis, nitrogen gas was introduced and the mixture was naturally cooled to room temperature. After crushing, it was passed through a 100-mesh sieve to obtain crude biochar.

[0030] (3) Weigh 18g of urea and 4.5g of ferric chloride, add deionized water to dissolve, stir for 18min to prepare a 0.8mol / L composite dopant solution; take 128g of crude biochar, add it to the composite dopant solution (composite dopant to crude biochar mass ratio 1:9), put it in a 65℃ constant temperature water bath, and soak at a constant temperature for 2.5h; after soaking, put it in an 85℃ vacuum drying oven to dry for 13h to obtain doped modified biochar.

[0031] (4) Measure analytical grade phosphoric acid, dilute it with deionized water, and prepare a 1 mol / L phosphoric acid activator; take 100 g of doped modified biochar, add it to 1000 mL of phosphoric acid activator (liquid-solid ratio 10:1), stir evenly and soak for 30 min; put it in a microwave reactor and activate it with microwave power of 350 W for 1.5 min, stirring once every 30 s during the process; after activation, vacuum filter it with pressure of 0.04 MPa for 12 min, wash the filter residue with deionized water until pH=7.0; put it in a vacuum drying oven at 85℃ and dry it for 13 h; after pulverizing, pass it through a 100 mesh sieve to obtain the target adsorbent.

[0032] Example 2 A method for preparing a modified adsorbent using peanut shells and blast furnace slag, comprising the following steps: (1) Take 100g of agricultural waste peanut shells, remove surface impurities, rinse with deionized water 3 times, and dry in an 80℃ forced-air drying oven for 4 hours; after drying, put them into a pulverizer, pulverize for 10 minutes, pass through an 80-mesh standard sieve, collect the sieve material as peanut shell powder, and seal for later use; take 20g of blast furnace slag, put it into a crusher to crush to a particle size ≤5mm, then put it into a ball mill, ball mill at a ball-to-material ratio of 5:1 for 30 minutes, pass through a 100-mesh sieve, collect the sieve material as blast furnace slag powder, and seal for later use.

[0033] (2) 100g of peanut shell powder and 20g of blast furnace slag powder (mass ratio 5:1) were mixed in a high-speed mixer for 20min. After the mixture was evenly mixed, it was placed in a tube furnace and nitrogen gas was introduced. The temperature was raised from room temperature to 200℃ (heating rate 5℃ / min) and held for 0.5h; the temperature was raised from 200℃ to 400℃ (heating rate 3℃ / min) and held for 2h; the temperature was raised from 400℃ to 550℃ (heating rate 2℃ / min) and held for 0.5h. After co-pyrolysis, nitrogen gas was introduced and the mixture was naturally cooled to room temperature. After crushing, it was passed through a 100-mesh sieve to obtain crude biochar.

[0034] (3) Weigh 12g of urea and 4g of ferric chloride, add deionized water to dissolve, stir for 20min to prepare a 0.5mol / L composite dopant solution; take 128g of crude biochar, add it to the composite dopant solution (composite dopant to crude biochar mass ratio 1:8), put it in a 60℃ constant temperature water bath, and soak it at a constant temperature for 3h; after soaking, put it in an 80℃ vacuum drying oven to dry for 14h to obtain doped modified biochar.

[0035] (4) Measure analytical grade phosphoric acid, dilute it with deionized water, and prepare 0.8 mol / L phosphoric acid activator; take 100 g of doped modified biochar, add it to 800 mL of phosphoric acid activator (liquid-solid ratio 8:1), stir evenly and soak for 30 min; put it in a microwave reactor and activate it with microwave power of 300 W for 2 min, stirring once every 30 s during the process; after activation, vacuum filter it with pressure of 0.04 MPa for 15 min, wash the filter residue with deionized water until pH=6.5; put it in a vacuum drying oven at 80℃ and dry for 14 h; after pulverizing, pass it through a 100 mesh sieve to obtain the target adsorbent.

[0036] Example 3 A method for preparing a modified adsorbent using peanut shells and blast furnace slag, comprising the following steps: (1) Take 140g of agricultural waste peanut shells, remove surface impurities, rinse with deionized water 3 times, and dry in an 85℃ forced-air drying oven for 6 hours; after drying, put them into a pulverizer, pulverize for 5 minutes, pass through a 100-mesh standard sieve, collect the sieve material as peanut shell powder, and seal for later use; take 20g of blast furnace slag, put it into a crusher to crush to a particle size ≤5mm, then put it into a ball mill, ball mill at a ball-to-material ratio of 8:1.5 for 30 minutes, pass through a 120-mesh sieve, collect the sieve material as blast furnace slag powder, and seal for later use.

[0037] (2) 140g of peanut shell powder and 20g of blast furnace slag powder (mass ratio 7:1) were mixed in a high-speed mixer for 15min. After the mixture was evenly mixed, it was placed in a tube furnace and nitrogen gas was introduced. The temperature was raised from room temperature to 220℃ (heating rate 10℃ / min) and held for 1h; the temperature was raised from 220℃ to 450℃ (heating rate 5℃ / min) and held for 1.5h; the temperature was raised from 450℃ to 600℃ (heating rate 3℃ / min) and held for 1h. After co-pyrolysis, nitrogen gas was introduced and the mixture was naturally cooled to room temperature. After crushing, it was passed through a 110-mesh sieve to obtain crude biochar.

[0038] (3) Weigh 15g of urea and 3g of ferric chloride, add deionized water to dissolve, stir for 15min to prepare a 1mol / L composite dopant solution; take 180g of crude biochar, add it to the composite dopant solution (composite dopant to crude biochar mass ratio 1:10), put it in a 70℃ constant temperature water bath, and soak it at a constant temperature for 2h; after soaking, put it in a 90℃ vacuum drying oven to dry for 12h to obtain doped modified biochar.

[0039] (4) Measure analytical grade phosphoric acid, dilute it with deionized water, and prepare a 1.2 mol / L phosphoric acid activator; take 100 g of doped modified biochar, add it to 1200 mL of phosphoric acid activator (liquid-solid ratio 12:1), stir evenly and soak for 35 min; put it in a microwave reactor and activate it with microwave power of 400 W for 1 min, stirring once every 35 s during the process; after activation, vacuum filter it with pressure of 0.06 MPa for 10 min, wash the filter residue with deionized water until pH=7.5; put it in a vacuum drying oven at 90℃ and dry it for 12 h; after pulverizing, pass it through a 100 mesh sieve to obtain the target adsorbent.

[0040] Comparative Example 1 The difference between this comparative example and Example 1 is that pure FeO powder is used instead of blast furnace slag powder. The remaining steps and process parameters are exactly the same, as follows: (1) Take 120g of agricultural waste peanut shells, remove surface impurities, rinse with deionized water 3 times, and dry in an 80℃ forced-air drying oven for 5h; after drying, put them into a pulverizer, pulverize for 8min, pass through a 90-mesh standard sieve, collect the sieve material as peanut shell powder, and seal for later use; take 20g of analytical grade FeO powder, seal for later use.

[0041] (2) 120g of peanut shell powder and 20g of FeO powder (mass ratio 6:1) were mixed in a high-speed mixer for 18min. After the mixture was evenly mixed, it was placed in a tube furnace and nitrogen gas was introduced. The temperature was raised from room temperature to 200℃ (heating rate 5℃ / min) and held for 0.8h; the temperature was raised from 200℃ to 420℃ (heating rate 4℃ / min) and held for 1.8h; the temperature was raised from 420℃ to 580℃ (heating rate 2.5℃ / min) and held for 0.5h. After co-pyrolysis, nitrogen gas was introduced and the mixture was naturally cooled to room temperature. After pulverization, it was passed through a 100-mesh sieve to obtain crude biochar.

[0042] (3) Weigh 18g of urea and 4.5g of ferric chloride, add deionized water to dissolve, stir for 18min to prepare a 0.8mol / L composite dopant solution; take 128g of crude biochar, add it to the composite dopant solution (composite dopant to crude biochar mass ratio 1:9), put it in a 65℃ constant temperature water bath, and soak at a constant temperature for 2.5h; after soaking, put it in an 85℃ vacuum drying oven to dry for 13h to obtain doped modified biochar.

[0043] (4) Measure analytical grade phosphoric acid, dilute it with deionized water, and prepare a 1 mol / L phosphoric acid activator; take 100 g of doped modified biochar, add it to 1000 mL of phosphoric acid activator (liquid-solid ratio 10:1), stir evenly and soak for 30 min; put it in a microwave reactor and activate it with microwave power of 350 W for 1.5 min, stirring once every 30 s during the process; after activation, vacuum filter it with pressure of 0.04 MPa for 12 min, wash the filter residue with deionized water until pH=7.0; put it in a vacuum drying oven at 85℃ and dry it for 13 h; after pulverizing, pass it through a 100 mesh sieve to obtain the comparative adsorbent.

[0044] Comparative Example 2 The difference between this comparative example and Example 1 is that corn stalks are used instead of peanut shells; the remaining steps and process parameters are exactly the same, as follows: (1) Take 120g of agricultural waste corn stalks, remove surface impurities, rinse with deionized water 3 times, and dry in an 80℃ forced-air drying oven for 5h; after drying, put them into a pulverizer, pulverize for 8min, pass through a 90-mesh standard sieve, collect the sieve material as peanut shell powder, and seal for later use; take 20g of blast furnace slag, put it into a crusher to crush to a particle size ≤5mm, then put it into a ball mill, ball mill at a ball-to-material ratio of 7:1 for 20min, pass through a 110-mesh sieve, collect the sieve material as blast furnace slag powder, and seal for later use.

[0045] (2) 120g of peanut shell powder and 20g of blast furnace slag powder (mass ratio 6:1) were mixed in a high-speed mixer for 18min. After the mixture was evenly mixed, it was placed in a tube furnace and nitrogen gas was introduced. The temperature was raised from room temperature to 200℃ (heating rate 5℃ / min) and held for 0.8h; the temperature was raised from 200℃ to 420℃ (heating rate 4℃ / min) and held for 1.8h; the temperature was raised from 420℃ to 580℃ (heating rate 2.5℃ / min) and held for 0.5h. After co-pyrolysis, nitrogen gas was introduced and the mixture was naturally cooled to room temperature. After crushing, it was passed through a 100-mesh sieve to obtain crude biochar.

[0046] (3) Weigh 18g of urea and 4.5g of ferric chloride, add deionized water to dissolve, stir for 18min to prepare a 0.8mol / L composite dopant solution; take 128g of crude biochar, add it to the composite dopant solution (composite dopant to crude biochar mass ratio 1:9), put it in a 65℃ constant temperature water bath, and soak at a constant temperature for 2.5h; after soaking, put it in an 85℃ vacuum drying oven to dry for 13h to obtain doped modified biochar.

[0047] (4) Measure analytical grade phosphoric acid, dilute it with deionized water, and prepare a 1 mol / L phosphoric acid activator; take 100 g of doped modified biochar, add it to 1000 mL of phosphoric acid activator (liquid-solid ratio 10:1), stir evenly and soak for 30 min; put it in a microwave reactor and activate it with microwave power of 350 W for 1.5 min, stirring once every 30 s during the process; after activation, vacuum filter it with pressure of 0.04 MPa for 12 min, wash the filter residue with deionized water until pH=7.0; put it in a vacuum drying oven at 85℃ and dry it for 13 h; after pulverizing, pass it through a 100 mesh sieve to obtain the comparative adsorbent.

[0048] Comparative Example 3 The difference between this comparative example and Example 1 is that a single urea is used instead of a composite dopant; the remaining steps and process parameters are exactly the same, as follows: (1) Take 120g of agricultural waste peanut shells, remove surface impurities, rinse with deionized water 3 times, and dry in an 80℃ forced-air drying oven for 5h; after drying, put them into a pulverizer, pulverize for 8min, pass through a 90-mesh standard sieve, collect the sieve material as peanut shell powder, and seal for later use; take 20g of blast furnace slag, put it into a crusher to crush to a particle size ≤5mm, then put it into a ball mill, ball mill at a ball-to-material ratio of 7:1 for 20min, pass through a 110-mesh sieve, collect the sieve material as blast furnace slag powder, and seal for later use.

[0049] (2) 120g of peanut shell powder and 20g of blast furnace slag powder (mass ratio 6:1) were mixed in a high-speed mixer for 18min. After the mixture was evenly mixed, it was placed in a tube furnace and nitrogen gas was introduced. The temperature was raised from room temperature to 200℃ (heating rate 5℃ / min) and held for 0.8h; the temperature was raised from 200℃ to 420℃ (heating rate 4℃ / min) and held for 1.8h; the temperature was raised from 420℃ to 580℃ (heating rate 2.5℃ / min) and held for 0.5h. After co-pyrolysis, nitrogen gas was introduced and the mixture was naturally cooled to room temperature. After crushing, it was passed through a 100-mesh sieve to obtain crude biochar.

[0050] (3) Weigh 18g of urea, add deionized water to dissolve it, stir and make a dopant solution; take 162g of crude biochar, add it to the dopant solution (mass ratio of dopant to crude biochar 1:9), put it in a 65℃ constant temperature water bath, and soak it at a constant temperature for 2.5h; after soaking, put it in an 85℃ vacuum drying oven to dry for 13h to obtain doped modified biochar.

[0051] (4) Measure analytical grade phosphoric acid, dilute it with deionized water, and prepare a 1 mol / L phosphoric acid activator; take 100 g of doped modified biochar, add it to 1000 mL of phosphoric acid activator (liquid-solid ratio 10:1), stir evenly and soak for 30 min; put it in a microwave reactor and activate it with microwave power of 350 W for 1.5 min, stirring once every 30 s during the process; after activation, vacuum filter it with pressure of 0.04 MPa for 12 min, wash the filter residue with deionized water until pH=7.0; put it in a vacuum drying oven at 85℃ and dry it for 13 h; after pulverizing, pass it through a 100 mesh sieve to obtain the comparative adsorbent.

[0052] Comparative Example 4 The difference between this comparative example and Example 1 is that a single ferric chloride is used instead of the composite dopant; the remaining steps and process parameters are exactly the same, as follows: (1) Take 120g of agricultural waste peanut shells, remove surface impurities, rinse with deionized water 3 times, and dry in an 80℃ forced-air drying oven for 5h; after drying, put them into a pulverizer, pulverize for 8min, pass through a 90-mesh standard sieve, collect the sieve material as peanut shell powder, and seal for later use; take 20g of blast furnace slag, put it into a crusher to crush to a particle size ≤5mm, then put it into a ball mill, ball mill at a ball-to-material ratio of 7:1 for 20min, pass through a 110-mesh sieve, collect the sieve material as blast furnace slag powder, and seal for later use.

[0053] (2) 120g of peanut shell powder and 20g of blast furnace slag powder (mass ratio 6:1) were mixed in a high-speed mixer for 18min. After the mixture was evenly mixed, it was placed in a tube furnace and nitrogen gas was introduced. The temperature was raised from room temperature to 200℃ (heating rate 5℃ / min) and held for 0.8h; the temperature was raised from 200℃ to 420℃ (heating rate 4℃ / min) and held for 1.8h; the temperature was raised from 420℃ to 580℃ (heating rate 2.5℃ / min) and held for 0.5h. After co-pyrolysis, nitrogen gas was introduced and the mixture was naturally cooled to room temperature. After crushing, it was passed through a 100-mesh sieve to obtain crude biochar.

[0054] (3) Weigh 4.5g of ferric chloride, add it to deionized water to dissolve it, and stir to make a dopant solution; take 40.5g of crude biochar, add it to the dopant solution (mass ratio of dopant to crude biochar 1:9), put it in a 65℃ constant temperature water bath, and soak it at a constant temperature for 2.5h; after soaking, put it in an 85℃ vacuum drying oven to dry for 13h to obtain doped modified biochar.

[0055] (4) Measure analytical grade phosphoric acid, dilute it with deionized water, and prepare a 1 mol / L phosphoric acid activator; take 100 g of doped modified biochar, add it to 1000 mL of phosphoric acid activator (liquid-solid ratio 10:1), stir evenly and soak for 30 min; put it in a microwave reactor and activate it with microwave power of 350 W for 1.5 min, stirring once every 30 s during the process; after activation, vacuum filter it with pressure of 0.04 MPa for 12 min, wash the filter residue with deionized water until pH=7.0; put it in a vacuum drying oven at 85℃ and dry it for 13 h; after pulverizing, pass it through a 100 mesh sieve to obtain the comparative adsorbent.

[0056] Comparative Example 5 The difference between this comparative example and Example 1 is that the traditional low-temperature co-pyrolysis process is used instead of the gradient temperature rise low-temperature co-pyrolysis process. The remaining steps and process parameters are exactly the same, as follows: (1) Take 120g of agricultural waste peanut shells, remove surface impurities, rinse with deionized water 3 times, and dry in an 80℃ forced-air drying oven for 5h; after drying, put them into a pulverizer, pulverize for 8min, pass through a 90-mesh standard sieve, collect the sieve material as peanut shell powder, and seal for later use; take 20g of blast furnace slag, put it into a crusher to crush to a particle size ≤5mm, then put it into a ball mill, ball mill at a ball-to-material ratio of 7:1 for 20min, pass through a 110-mesh sieve, collect the sieve material as blast furnace slag powder, and seal for later use.

[0057] (2) 120g of peanut shell powder and 20g of blast furnace slag powder (mass ratio 6:1) were mixed in a high-speed mixer for 18min. After the mixture was evenly mixed, it was placed in a tube furnace and nitrogen gas was introduced. The room temperature was raised to 580℃ (heating rate 2.5℃ / min) and kept at that temperature for 3.1h. After co-pyrolysis, nitrogen gas was introduced and the mixture was naturally cooled to room temperature. After crushing, it was passed through a 100-mesh sieve to obtain crude biochar.

[0058] (3) Weigh 18g of urea and 4.5g of ferric chloride, add deionized water to dissolve, stir for 18min to prepare a 0.8mol / L composite dopant solution; take 128g of crude biochar, add it to the composite dopant solution (composite dopant to crude biochar mass ratio 1:9), put it in a 65℃ constant temperature water bath, and soak at a constant temperature for 2.5h; after soaking, put it in an 85℃ vacuum drying oven to dry for 13h to obtain doped modified biochar.

[0059] (4) Measure analytical grade phosphoric acid, dilute it with deionized water, and prepare a 1 mol / L phosphoric acid activator; take 100 g of doped modified biochar, add it to 1000 mL of phosphoric acid activator (liquid-solid ratio 10:1), stir evenly and soak for 30 min; put it in a microwave reactor and activate it with microwave power of 350 W for 1.5 min, stirring once every 30 s during the process; after activation, vacuum filter it with pressure of 0.04 MPa for 12 min, wash the filter residue with deionized water until pH=7.0; put it in a vacuum drying oven at 85℃ and dry it for 13 h; after pulverizing, pass it through a 100 mesh sieve to obtain the comparative adsorbent.

[0060] The peanut shell-blast furnace slag co-pyrolysis composite modified adsorbent prepared in Example 1 and the comparative adsorbents prepared in each comparative example were applied to remove arsenic from arsenic-containing wastewater. The arsenic-containing wastewater came from the sulfuric acid workshop of a zinc smelter in Southwest China, which produced a large amount of arsenic and other impurities after washing smelting flue gas. Ultrapure water was used to adjust the arsenic concentration to 50 mg / L. The specific application steps were as follows: the pH of the 50 mg / L arsenic-containing wastewater was adjusted to 4 ± 0.5; 1 g / L of adsorbent was added to 50 mL of arsenic-containing wastewater, and the mixture was stirred at 350 rpm for 24 h at room temperature and pressure. The concentration of metal ions in the filtrate after the reaction was completed was determined by ICP method.

[0061] The main components of arsenic-containing wastewater are shown in Table 1.

[0062] Table 1 The concentration of metal ions in the filtrate after arsenic removal was determined by ICP method, as shown in Table 2.

[0063] Table 2 The peanut shell-blast furnace slag co-pyrolysis composite modified adsorbent prepared in Example 1 can reduce the arsenic concentration in arsenic-containing wastewater with an initial concentration of 50 mg / L and a pH of 4 to 0.29 mg / L, achieving an arsenic removal rate of 99.42%. The adsorbent prepared in Comparative Example 1 can reduce the arsenic concentration in arsenic-containing wastewater with an initial concentration of 50 mg / L and a pH of 4 to 12.05 mg / L, achieving an arsenic removal rate of 75.90%. The adsorbent prepared in Comparative Example 2 can reduce the arsenic concentration in arsenic-containing wastewater with an initial concentration of 50 mg / L and a pH of 4 to 9.92 mg / L, achieving an arsenic removal rate of... The arsenic removal rate was 80.16%; the adsorbent prepared in Comparative Example 3 reduced the arsenic concentration in arsenic-containing wastewater with an initial concentration of 50 mg / L and a pH of 4 to 15.78 mg / L, with an arsenic removal rate of 68.44%; the adsorbent prepared in Comparative Example 4 reduced the arsenic concentration in arsenic-containing wastewater with an initial concentration of 50 mg / L and a pH of 4 to 13.31 mg / L, with an arsenic removal rate of 73.38%; the adsorbent prepared in Comparative Example 5 reduced the arsenic concentration in arsenic-containing wastewater with an initial concentration of 50 mg / L and a pH of 4 to 10.99 mg / L, with an arsenic removal rate of 78.02%. The comparison showed that the modified adsorbent prepared in Example 1 could remove arsenic more selectively.

[0064] In Comparative Example 1, the arsenic removal rate decreased significantly after replacing blast furnace slag with pure FeO. This is because pure FeO lacks a framework support, easily agglomerates leading to a reduction in active sites, and lacks charge regulation, auxiliary complexation, and synergistic oxidation effects. It can only achieve single-component complexation and Fe-N oxidation, failing to form a multi-component synergistic arsenic removal system. Furthermore, the adsorbent's insufficient mechanical strength makes it prone to breakage and loss, further reducing the arsenic removal effect. This demonstrates that the synergistic effect of all components of blast furnace slag is key to the efficient and stable arsenic removal of the adsorbent in this invention, far superior to the effect of pure FeO alone.

[0065] In Comparative Example 2, the arsenic removal rate also decreased after replacing peanut shells with corn stalks. The reasons are: ① Corn stalks have a high cellulose content, resulting in a fine and easily collapsing pore structure after pyrolysis, making it unable to form a stable hierarchical porous structure and weakening its ability to carry the active components of blast furnace slag; ② The porous structures formed after pyrolysis of corn stalks are all rigid, lacking a "flexible-rigid composite" effect with the rigid framework of blast furnace slag, resulting in a simple overall pore structure and few adsorption sites for the adsorbent. These results demonstrate that peanut shells are irreplaceable. Their unique composition and structural characteristics are key to achieving precise synergy with multiple components of blast furnace slag, efficiently loading active components, and improving arsenic removal efficiency. Other biomass cannot achieve this exclusive synergistic effect.

[0066] In Comparative Example 3, the arsenic removal rate also decreased after replacing the composite dopant with a single urea. This is because a single urea can only introduce nitrogen (N) to the adsorbent, but cannot provide active sites for Fe-N co-doping, thus lacking the ability to remove As. 3+ Oxidized to As 5+The core oxidation sites can only be removed by physical adsorption and simple complexation with blast furnace slag. This is insufficient for removing the more toxic and difficult-to-remove As. 3+ Without oxidation effect, and with nitrogen doping alone unable to form a synergistic oxidative complexation effect with blast furnace slag, the adsorbent's removal of arsenic is limited to physical adsorption, making it prone to arsenic desorption and significantly reducing arsenic removal efficiency and stability.

[0067] In Comparative Example 4, the arsenic removal rate also decreased after replacing the composite dopant with a single ferric chloride. This is because ferric chloride alone can only introduce Fe; without the synergistic doping of N, efficient Fe-N active sites cannot be formed. Fe tends to aggregate on the adsorbent surface, resulting in poor dispersion of oxidation active sites and low oxidation efficiency, thus hindering the removal of As. 3+ The oxidation effect is greatly weakened; at the same time, the lack of N element to combine with oxygen-containing groups on the surface of the adsorbent makes it impossible to improve the charge characteristics and complexation ability of the adsorbent surface, making it difficult to form a synergistic arsenic removal system with the polymetallic oxides of blast furnace slag. It can only rely on the simple complexation effect of Fe element to remove a small amount of arsenic, and the arsenic removal capacity and efficiency are significantly reduced.

[0068] In Comparative Example 5, the arsenic removal rate decreased after replacing the gradient heating low-temperature co-pyrolysis process with the traditional low-temperature co-pyrolysis process. This is because the traditional one-step heating pyrolysis process cannot achieve stepwise pyrolysis activation of peanut shells and blast furnace slag. During the low-temperature stage, the volatiles in the peanut shells are released rapidly and violently, easily causing pore collapse and preventing the formation of a uniform hierarchical porous structure, thus significantly reducing adsorption sites. Simultaneously, the active metal oxides in the blast furnace slag are prone to agglomeration and sintering during rapid heating, losing their complexing and oxidizing activity and failing to form a stable composite structure with the peanut shells. This results in a double decrease in the physical adsorption and chemical complexing / oxidation capabilities of the adsorbent. Furthermore, rapid heating also leads to weak interfacial bonding between the peanut shells and blast furnace slag, making component separation more likely during subsequent modification and use, further reducing the arsenic removal effect. In contrast, the gradient heating process enables slow pyrolysis and pore formation of the peanut shells and gradual activation and dispersion of the blast furnace slag, ensuring the formation of a structurally stable, pore-rich, and uniformly active composite crude biochar, laying a good foundation for subsequent modification.

[0069] This invention constructs a triple synergistic arsenic removal mechanism through the synergistic formulation of composite raw materials, gradient low-temperature co-pyrolysis, and dual modification process optimization. It not only solves the technical pain points of traditional adsorbents such as low adsorption capacity, weak anti-interference ability, and poor regeneration performance, but also realizes the organic combination of solid waste resource utilization and wastewater treatment. It has significant technical advantages, environmental benefits, economic benefits, and industrial application prospects. Compared with traditional adsorbents, it is more suitable for large-scale application in arsenic removal scenarios in smelting wastewater.

[0070] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a modified adsorbent using peanut shells and blast furnace slag, characterized in that: Peanut shells and blast furnace slag are used as raw materials. After pretreatment, the raw materials are mixed evenly in a certain mass ratio to obtain mixed raw materials. The mixed raw materials are subjected to low-temperature co-pyrolysis to obtain crude biochar. The crude biochar is modified with urea-ferric chloride composite dopant to obtain modified biochar. Subsequently, it is activated with phosphoric acid activator using microwave assistance to obtain modified adsorbent.

2. The method for preparing a modified adsorbent using peanut shells and blast furnace slag according to claim 1, characterized in that: The raw material pretreatment method is as follows: peanut shells are washed and dried at 80~85℃ for 4~6 hours, crushed for 5~10 minutes and passed through an 80~100 mesh sieve to obtain peanut shell powder; blast furnace slag is crushed to a particle size ≤5mm, ball-milled at a ball-to-material ratio of (5~8):(1~1.5) for 20~30 minutes and passed through a 100~120 mesh sieve to obtain blast furnace slag powder.

3. The method for preparing a modified adsorbent using peanut shells and blast furnace slag according to claim 1, characterized in that: The mass ratio of peanut shell powder to blast furnace slag powder in the mixed raw materials is (5~7):

1.

4. The method for preparing a modified adsorbent using peanut shells and blast furnace slag according to claim 1, characterized in that: The low-temperature co-pyrolysis method is a gradient heating low-temperature co-pyrolysis, specifically: the tubular furnace is heated to 200-220℃ at a heating rate of 5-10℃ / min and held for 0.5-1h; then heated to 400-450℃ at a heating rate of 3-5℃ / min and held for 1.5-2h; finally heated to 550-600℃ at a heating rate of 2-3℃ / min and held for 0.5-1h.

5. The method for preparing a modified adsorbent using peanut shells and blast furnace slag according to claim 1, characterized in that: The mass ratio of urea to ferric chloride in the urea-ferric chloride composite dopant is (3~5):1, and the concentration is 0.5~1.0 mol / L.

6. The method for preparing a modified adsorbent using peanut shells and blast furnace slag according to claim 1, characterized in that: The mass ratio of the urea-ferric chloride composite dopant to the crude biochar is 1:(8~10).

7. The method for preparing a modified adsorbent using peanut shells and blast furnace slag according to claim 1, characterized in that: The concentration of the phosphoric acid activator is 0.8~1.2 mol / L.

8. The method for preparing a modified adsorbent using peanut shells and blast furnace slag according to claim 1, characterized in that: The liquid-to-solid ratio of the phosphoric acid activator to the modified biochar is (8~12) mL:1g.

9. The method for preparing a modified adsorbent using peanut shells and blast furnace slag according to claim 1, characterized in that: The conditions for microwave-assisted activation are: microwave power of 300~400W and microwave activation time of 1~2min.

10. The application of the modified adsorbent prepared by the method according to any one of claims 1 to 9 in the removal of arsenic from wastewater.

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