A method for preparing a modified adsorbent using corn stalks and smelting solid waste and application thereof

Abstract

This invention discloses a method and application for preparing modified adsorbents using corn stalks and metallurgical solid waste, belonging to the field of environmental functional material preparation technology. Addressing the problems of high energy consumption, low adsorption capacity, and poor selectivity in existing biochar preparation methods, this invention employs low-temperature co-pyrolysis of corn stalks coupled with desulfurization ash from metallurgical processes, and innovatively introduces a combined process of zinc chloride-phosphate composite modification and microwave-assisted activation. The CaO, Fe2O3, and Al2O3 components in the desulfurization ash synergistically catalyze the pyrolysis of corn stalks to form a well-developed porous structure, achieving solid waste resource utilization. Microwave assistance promotes the penetration of the modifier into the pores of the biochar, zinc chloride etching increases the specific surface area and pore volume, and phosphate groups enhance the specific adsorption of arsenic ions through complexation. All three synergistically improve adsorption performance. This invention overcomes the technical bottlenecks of high energy consumption in existing high-temperature pyrolysis, the defects in the adsorption performance of single modifiers, and low solid waste utilization rates. It achieves the synergistic resource utilization of agricultural waste and industrial solid waste, with a simple process, low cost, environmental friendliness, and the ability to be mass-produced. It can be widely applied in the treatment of arsenic pollution in water and soil.

Description

Technical Field

[0001] This invention relates to the field of environmental functional material preparation technology, specifically a method and application for preparing modified adsorbents using corn stalks and metallurgical solid waste. Background Technology

[0002] Desulfurization ash from smelting is one of the largest solid waste emissions from the smelting industry, with an annual output exceeding ten million tons. The main components of desulfurization ash include CaO, SiO2, Al2O3, and Fe2O3, making it complex and difficult to treat. Direct dumping not only occupies land resources but also causes secondary pollution. Currently, the mainstream treatment method for desulfurization ash is landfill, which not only occupies a large amount of land resources but also easily leads to leaching of soluble salts and metal oxides into soil and water bodies by rainwater, causing secondary pollution. Limited attempts at resource utilization, such as manufacturing building materials and roadbed fillers, only achieve low-value-added utilization and are affected by compositional fluctuations, resulting in unstable product performance and hindering large-scale promotion. Due to the complexity and non-uniformity of its composition, high-value-added resource utilization technologies remain difficult to develop, becoming an industry-wide challenge for solid waste treatment in the smelting industry.

[0003] Corn stalks are mainly composed of cellulose, hemicellulose, and lignin, with high carbon content and abundant porous precursors. Pyrolysis of corn stalks to produce biochar with basic adsorption properties can not only realize the resource utilization of agricultural waste but also reduce air pollution caused by straw burning. However, the pore structure of raw corn stalks is prone to collapse after pyrolysis, resulting in few surface-active functional groups, low adsorption capacity for arsenic, and poor selectivity, making it difficult to meet the needs of practical pollution control. Furthermore, the pyrolysis temperature of corn stalks alone is typically between 500-700℃, leading to high energy consumption and high production costs, which is not conducive to large-scale production and also fails to meet the needs of practical pollution control.

[0004] While existing technologies have attempted to co-pyrolyze biomass and metallurgical solid waste, these methods primarily employ high-temperature pyrolysis (above 500℃) and lack integration with composite modification processes. This fails to simultaneously address the multiple demands of energy reduction, solid waste resource utilization, and improved adsorption performance. Co-pyrolyzing metallurgical desulfurization ash and corn stalks to prepare modified biochar holds promise for overcoming the technical bottleneck of high-value-added resource utilization of desulfurization ash, improving the performance of corn stalk-based biochar, and simultaneously achieving the synergistic disposal of agricultural and industrial solid waste. Therefore, developing a method for preparing modified biochar that enables the synergistic resource utilization of agricultural waste and metallurgical solid waste, with low energy consumption, high adsorption capacity, and strong arsenic selectivity, has become a pressing technical challenge in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, such as high energy consumption in biochar preparation, low arsenic adsorption capacity, poor selectivity, and low resource utilization rate of corn stalks and metallurgical solid waste, this invention provides a method and application for preparing modified adsorbents using corn stalks and metallurgical solid waste. This method involves low-temperature co-pyrolysis of corn stalks and metallurgical solid waste (desulfurization ash), reducing energy consumption while achieving resource utilization of solid waste. Furthermore, a zinc chloride-phosphate composite modifier combined with microwave-assisted rapid activation overcomes the limitations of single modifiers. The modified adsorbent prepared by this method significantly improves arsenic adsorption capacity and selectivity, and the process is simple, low-cost, and scalable, offering significant economic and environmental benefits.

[0006] The method for preparing modified adsorbents using corn stalks and metallurgical solid waste as described in this invention specifically includes the following steps: (1) Corn stalks are crushed, sieved, and dried to obtain corn stalk powder; desulfurization ash from smelting solid waste is crushed, ground, sieved, and dried to obtain desulfurization ash powder.

[0007] (2) Mix corn stalk powder with desulfurization ash powder, and stir the mixed powder at a speed of 300~500r / min for 15~20min to form a mixed raw material.

[0008] (3) The mixed raw materials are placed in a tube furnace for low-temperature co-pyrolysis. After the pyrolysis is completed, the resulting product is washed with deionized water 3 to 5 times and dried in a drying oven at 105 to 110°C for 12 to 16 hours to obtain preliminary biochar.

[0009] (4) Prepare zinc chloride-phosphoric acid composite modifier.

[0010] (5) Mix the preliminary biochar prepared in step (3) with the zinc chloride-phosphoric acid composite modifier prepared in step (4), and put it into a microwave reactor for activation. After the reaction is completed, take out the reaction product, wash it with deionized water until the pH of the washing solution is 6.5~7.5, and then dry it in a drying oven at 105~110℃ for 12~16h. After passing through a 100~120 mesh sieve, the modified adsorbent is obtained.

[0011] Preferably, the corn stalks of the present invention are crushed, passed through an 80-120 mesh sieve, and dried at 105-110℃ for 20-24 hours to obtain corn stalk powder; the desulfurization ash is crushed, passed through a 100-200 mesh sieve, and dried at 100-105℃ for 8-12 hours to obtain desulfurization ash powder.

[0012] Preferably, the mixed powder of the present invention includes corn stalk powder and desulfurization ash powder, and the mass ratio of corn stalk powder to desulfurization ash powder is 7~9:1~3.

[0013] Preferably, the conditions for low-temperature co-pyrolysis according to the present invention are: heating the tubular furnace to 300-400°C at a heating rate of 5-10°C / min, and the pyrolysis time is 60-90min.

[0014] As a preferred embodiment, the preparation method of the zinc chloride-phosphoric acid composite modifier of the present invention is as follows: first, measure a certain volume of deionized water, slowly add zinc chloride powder, stir until completely dissolved, then slowly add phosphoric acid, and continue stirring for 10-15 minutes to obtain a uniform composite modifier.

[0015] Preferably, the zinc chloride-phosphoric acid composite modifier of the present invention comprises, by mass percentage, 5%~15% zinc chloride, 3%~8% phosphoric acid, and the remainder being deionized water.

[0016] Preferably, the solid-liquid ratio of the mixed powder after low-temperature co-pyrolysis treatment to the zinc chloride-phosphoric acid composite modifier is (1~1.5) g: (10~20) mL.

[0017] Preferably, the microwave-assisted activation conditions of the present invention are: power of 300~500W and activation time of 2~3min.

[0018] This invention also provides an application of a modified adsorbent prepared from corn stalks and smelting solid waste for the removal of arsenic from wastewater.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) Low-temperature co-pyrolysis of corn stalks and desulfurization ash is adopted. The carbonaceous precursor characteristics of corn stalks and the catalytic characteristics of desulfurization ash form a structure-component synergy, achieving the triple effect of "low-temperature pyrolysis - pore construction - solid waste utilization". The desulfurization ash adheres to the surface of corn stalk fibers and can catalyze the pyrolysis of cellulose and hemicellulose of the stalks at low temperature, avoiding the energy consumption problem and pore collapse problem of high-temperature pyrolysis of corn stalks alone; at the same time, corn stalks provide a dispersion carrier for the catalytic components of desulfurization ash, avoiding the reduction in catalytic efficiency caused by the agglomeration of desulfurization ash itself. By selectively using agricultural waste (corn stalks) and industrial solid waste (desulfurization ash) which are widely available and inexpensive, as co-pyrolysis raw materials, the problems of pollution from corn stalk burning and desulfurization ash stockpiling are solved. At the same time, the performance is complementary and synergistic, producing high-performance adsorbent materials, turning waste into treasure, and has significant economic and environmental benefits.

[0020] (2) By utilizing the synergistic catalytic properties of components such as CaO, Al2O3, and Fe2O3 in the desulfurization ash, the beneficial effects of achieving efficient pyrolysis and significantly reducing production energy consumption under low-temperature conditions (300-400℃) are achieved. The strongly alkaline oxide CaO in the desulfurization ash undergoes a neutralization reaction with the organic acids produced by the pyrolysis of corn stalks, breaking the hydrogen bonds and glycosidic bonds of cellulose and hemicellulose in corn stalks, and reducing the activation energy of corn stalk pyrolysis. The amphoteric oxides Al2O3 and Fe2O3 in the desulfurization ash act as porous catalytic carriers, adsorbing the pyrolysis intermediates of corn stalks and promoting their further pyrolysis into small molecule gases. At the same time, they form pore templates at the pyrolysis sites, guiding the pyrolysis of corn stalks to form a well-developed microporous + mesoporous multi-level pore structure. Meanwhile, the fibrous structure of corn stalks provides an attachment carrier for the catalytic components of the smelting desulfurization ash, allowing the catalytic reaction to occur precisely at the pyrolysis sites of the stalks, thereby improving the pyrolysis efficiency.

[0021] (3) The synergistic modification using a zinc chloride + phosphoric acid composite modifier, combined with microwave-assisted rapid activation, achieved the beneficial effect of improving the adsorption capacity and specific adsorption ability of the adsorbent. Specifically, after the zinc chloride-phosphoric acid composite modifier penetrates into the crude biochar under microwave assistance, the etching effect of zinc chloride provides more surface sites for the loading of phosphate groups. Meanwhile, the phosphate metal salt formed by phosphoric acid and metal oxides in the desulfurization ash can act as a "buffer site" for zinc chloride etching, preventing excessive etching of the biochar pores from collapsing. The two mutually restrict and promote each other, ultimately forming a modified biochar adsorbent with well-developed pores and abundant surface adsorption sites. Simultaneously, the adsorbent surface contains abundant phosphate groups. The introduction of phosphate groups enhances the specific adsorption of arsenic, improves anti-interference ability, and maintains good adsorption performance even in complex aquatic environments.

[0022] (5) The green preparation process, combining low-temperature co-pyrolysis and microwave-assisted activation, achieves the beneficial effects of simple process, controllable operation, environmental friendliness, and low cost, which is in line with the concept of green and sustainable development. The entire preparation process requires no complex equipment, is easy to operate, has controllable parameters, and generates no toxic or harmful gases or waste liquids, making the preparation process green and environmentally friendly. This adsorbent can be used for the adsorption and treatment of arsenic in water and soil. After adsorption, it can be reused through desorption and regeneration, further reducing the cost of use. The entire preparation process generates no toxic or harmful gases, and the adsorbent can be reused through desorption and regeneration after adsorption saturation. Detailed Implementation

[0023] The smelting desulfurization ash used in this invention is a byproduct of dry / semi-dry desulfurization processes in the non-ferrous / iron smelting industry. Its main source is the desulfurization systems for zinc, lead, and iron smelting flue gas, making it one of the largest solid wastes emitted by the smelting industry, with an annual production exceeding ten million tons. The main chemical components of this smelting desulfurization ash are CaO (30-50 wt%), Al2O3 (8-20 wt%), Fe2O3 (5-15 wt%), and SiO2 (8-20 wt%), and it also contains small amounts of MgO, CaSO3, and CaSO4.

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1 A method for preparing a modified adsorbent using corn stalks and desulfurization ash from metallurgical solid waste, comprising the following specific steps: (1) Remove impurities such as stones and weeds from dry, mold-free corn stalks, crush them with a pulverizer, and pass them through an 80-mesh sieve to obtain corn stalk powder; place the corn stalk powder in an oven at 105℃ for 24 hours, take it out and place it in a desiccator to cool to room temperature for later use; select desulfurization ash produced in the smelting industry, remove large impurities, crush it with a pulverizer, and pass it through a 100-mesh sieve to obtain desulfurization ash powder; place the desulfurization ash powder in an oven at 100℃ for 12 hours, take it out and place it in a desiccator to cool to room temperature for later use.

[0026] (2) Mix the corn stalk powder and desulfurized ash powder after pretreatment in step (1) at a mass ratio of 7:3, put them into a high-speed mixer, adjust the mixing speed to 300 r / min, mix for 20 min, and obtain a uniform mixed raw material.

[0027] (3) Place the mixed raw material obtained in step (2) into a tube furnace and first introduce nitrogen into the tube furnace; then, raise the temperature of the tube furnace to 300°C at a heating rate of 5°C / min and maintain this temperature for low-temperature co-pyrolysis for 90 min; after the pyrolysis is completed, stop heating and continue to introduce nitrogen until the temperature of the tube furnace cools to room temperature, take out the product, wash it three times with deionized water to remove the soluble impurities remaining on the surface, and then dry it in an oven at 105°C for 16 h to obtain preliminary biochar.

[0028] (4) Take 1000 mL of deionized water and place it in a beaker. While stirring, slowly add 50 g of zinc chloride powder and stir until completely dissolved. Then slowly add 35 mL of analytical grade phosphoric acid with a concentration of 85% (corresponding to a phosphoric acid mass concentration of 3%) and continue stirring for 15 min to obtain a uniform composite modifier (zinc chloride mass concentration of 5% and phosphoric acid mass concentration of 3%).

[0029] (5) Weigh 10g of the biochar obtained in step (3) and mix it with 100mL of the composite modifier prepared in step (4) (solid-liquid ratio 1g:10ml). Place it in a microwave reactor, adjust the microwave power to 300W, and the microwave-assisted activation time to 2min. After the microwave activation is completed, take out the reaction product, wash it with deionized water until the pH of the washing solution is 6.5 to remove the residual modifier on the surface, and then dry it in an oven at 105℃ for 16h. After drying, pulverize it with a pulverizer and pass it through a 100-mesh sieve to obtain the modified adsorbent.

[0030] Example 2 A method for preparing a modified adsorbent using corn stalks and desulfurization ash from metallurgical solid waste, comprising the following specific steps: (1) Remove impurities such as stones and weeds from dry, mold-free corn stalks, crush them with a pulverizer, and pass them through a 100-mesh sieve to obtain corn stalk powder; place the corn stalk powder in an oven at 108℃ for 20 hours, take it out and place it in a desiccator to cool to room temperature for later use; select desulfurization ash produced in the smelting industry, remove large impurities, crush it with a pulverizer, and pass it through a 150-mesh sieve to obtain desulfurization ash powder; place the desulfurization ash powder in an oven at 105℃ for 10 hours, take it out and place it in a desiccator to cool to room temperature for later use.

[0031] (2) Mix the corn stalk powder and desulfurized ash powder after pretreatment in step (1) at a mass ratio of 8:2, put them into a high-speed mixer, adjust the mixing speed to 400 r / min, mix for 18 min, and obtain a uniform mixed raw material.

[0032] (3) Place the mixed raw material obtained in step (2) into a tube furnace and first introduce nitrogen into the tube furnace; then, raise the temperature inside the tube furnace to 350°C at a heating rate of 8°C / min and maintain this temperature for low-temperature co-pyrolysis for 75 min; after the pyrolysis is completed, stop heating and continue to introduce nitrogen until the temperature inside the tube furnace cools to room temperature, take out the product, wash it 5 times with deionized water to remove the soluble impurities remaining on the surface, and then dry it in an oven at 108°C for 14 h to obtain preliminary biochar.

[0033] (4) Take 1000 mL of deionized water and place it in a beaker. While stirring, slowly add 100 g of zinc chloride powder and stir until completely dissolved. Then slowly add 59 mL of analytical grade phosphoric acid with a concentration of 85% (corresponding to a phosphoric acid mass concentration of 5%) and continue stirring for 12 min to obtain a uniform composite modifier (zinc chloride mass concentration of 10% and phosphoric acid mass concentration of 5%).

[0034] (5) Weigh 10g of the biochar obtained in step (3) and mix it with 150mL of the composite modifier prepared in step (4) (solid-liquid ratio 1g:15ml). Place it in a microwave reactor, adjust the microwave power to 400W, and the microwave-assisted activation time to 2.5min. After the microwave activation is completed, take out the reaction product, wash it with deionized water until the pH of the washing solution is 7.0 to remove the residual modifier on the surface, and then dry it in an oven at 108℃ for 14h. After drying, pulverize it with a pulverizer and pass it through a 100-mesh sieve to obtain the modified adsorbent.

[0035] Example 3 A method for preparing a modified adsorbent using corn stalks and desulfurization ash from metallurgical solid waste, comprising the following specific steps: (1) Remove impurities such as stones and weeds from dry, mold-free corn stalks, crush them with a pulverizer, and pass them through a 120-mesh sieve to obtain corn stalk powder; place the corn stalk powder in an oven at 110℃ for 20 hours, take it out and place it in a desiccator to cool to room temperature for later use; select desulfurization ash produced in the smelting industry, remove large impurities, crush it with a pulverizer, and pass it through a 200-mesh sieve to obtain desulfurization ash powder; place the desulfurization ash powder in an oven at 105℃ for 8 hours, take it out and place it in a desiccator to cool to room temperature for later use.

[0036] (2) Mix the corn stalk powder and desulfurized ash powder after pretreatment in step (1) at a mass ratio of 9:1, put them into a high-speed mixer, adjust the mixing speed to 500 r / min, mix for 15 min, and obtain a uniform mixed raw material.

[0037] (3) Place the mixed raw material obtained in step (2) into a tube furnace and first introduce nitrogen into the tube furnace; then, raise the temperature of the tube furnace to 400°C at a heating rate of 10°C / min and maintain this temperature for low-temperature co-pyrolysis for 60 min; after the pyrolysis is completed, stop heating and continue to introduce nitrogen until the temperature of the tube furnace cools to room temperature, take out the product, wash it 4 times with deionized water to remove the soluble impurities remaining on the surface, and then dry it in an oven at 110°C for 12 h to obtain preliminary biochar.

[0038] (4) Take 1000 mL of deionized water and place it in a beaker. While stirring, slowly add 150 g of zinc chloride powder and stir until completely dissolved. Then slowly add 94 mL of analytical grade phosphoric acid with a concentration of 85% (corresponding to a phosphoric acid mass concentration of 8%) and continue stirring for 10 min to obtain a uniform composite modifier (zinc chloride mass concentration of 15% and phosphoric acid mass concentration of 8%).

[0039] (5) Weigh 15g of biochar obtained in step (3) and mix it with 200mL of composite modifier prepared in step (4) (solid-liquid ratio 1.5g:20ml). Place it in a microwave reactor, adjust the microwave power to 500W, and the microwave-assisted activation time to 3min. After microwave activation, take out the reaction product, wash it with deionized water until the pH of the washing solution is 7.5 to remove the residual modifier on the surface, and then dry it in an oven at 110℃ for 12h. After drying, pulverize it with a pulverizer and pass it through a 120-mesh sieve to obtain the modified adsorbent.

[0040] Comparative Example 1 The difference between this comparative example and Example 1 is that it uses single corn stalks without desulfurization ash as raw material; the other steps are the same, as follows: (1) Remove stones, weeds and other impurities from the dry, mold-free corn stalks, crush them with a pulverizer, and pass them through an 80-mesh sieve to obtain corn stalk powder; place the corn stalk powder in an oven at 105℃ for 24 hours, take it out and place it in a desiccator to cool to room temperature for later use.

[0041] (2) Place the corn stalk powder obtained in step (1) into a tube furnace and first introduce nitrogen into the tube furnace; then, raise the temperature inside the tube furnace to 300°C at a heating rate of 5°C / min and maintain this temperature for low-temperature co-pyrolysis for 90 min; after the pyrolysis is completed, stop heating and continue to introduce nitrogen until the temperature inside the tube furnace cools to room temperature, take out the product, wash it three times with deionized water to remove the soluble impurities remaining on the surface, and then dry it in an oven at 105°C for 16 h to obtain preliminary biochar.

[0042] (3) Take 1000mL of deionized water and place it in a beaker. While stirring, slowly add 50g of zinc chloride powder and stir until completely dissolved. Then slowly add 35mL of analytical grade phosphoric acid with a concentration of 85% (corresponding to a phosphoric acid mass concentration of 3%) and continue stirring for 15min to obtain a uniform composite modifier (zinc chloride mass concentration of 5% and phosphoric acid mass concentration of 3%).

[0043] (4) Weigh 10g of the biochar obtained in step (3) and mix it with 100mL of the composite modifier prepared in step (3) (solid-liquid ratio 1g:10ml). Place it in a microwave reactor, adjust the microwave power to 300W, and the microwave-assisted activation time to 2min. After the microwave activation is completed, take out the reaction product, wash it with deionized water until the pH of the washing solution is 6.5 to remove the residual modifier on the surface, and then dry it in an oven at 105℃ for 16h. After drying, pulverize it with a pulverizer and pass it through a 100-mesh sieve to obtain the modified adsorbent.

[0044] Comparative Example 2 The difference between this comparative example and Example 1 is that zinc chloride is used as the modifier; the other steps are the same, as follows: (1) Remove impurities such as stones and weeds from dry, mold-free corn stalks, crush them with a pulverizer, and pass them through an 80-mesh sieve to obtain corn stalk powder; place the corn stalk powder in an oven at 105℃ for 24 hours, take it out and place it in a desiccator to cool to room temperature for later use; select desulfurization ash produced in the smelting industry, remove large impurities, crush it with a pulverizer, and pass it through a 100-mesh sieve to obtain desulfurization ash powder; place the desulfurization ash powder in an oven at 100℃ for 12 hours, take it out and place it in a desiccator to cool to room temperature for later use.

[0045] (2) Mix the corn stalk powder and desulfurized ash powder after pretreatment in step (1) at a mass ratio of 7:3, put them into a high-speed mixer, adjust the mixing speed to 300 r / min, mix for 20 min, and obtain a uniform mixed raw material.

[0046] (3) Place the mixed raw material obtained in step (2) into a tube furnace and first introduce nitrogen into the tube furnace; then, raise the temperature of the tube furnace to 300°C at a heating rate of 5°C / min and maintain this temperature for low-temperature co-pyrolysis for 90 min; after the pyrolysis is completed, stop heating and continue to introduce nitrogen until the temperature of the tube furnace cools to room temperature, take out the product, wash it three times with deionized water to remove the soluble impurities remaining on the surface, and then dry it in an oven at 105°C for 16 h to obtain preliminary biochar.

[0047] (4) Take 1000mL of deionized water and place it in a beaker. While stirring, slowly add 50g of zinc chloride powder and stir until completely dissolved to obtain a uniform modifier.

[0048] (5) Weigh 10g of the biochar obtained in step (3) and mix it with 100mL of the modifier prepared in step (4) (solid-liquid ratio 1g:10ml). Place it in a microwave reactor, adjust the microwave power to 300W, and the microwave-assisted activation time to 2min. After the microwave activation is completed, take out the reaction product, wash it with deionized water until the pH of the washing solution is 6.5 to remove the residual modifier on the surface, and then dry it in an oven at 105℃ for 16h. After drying, pulverize it with a pulverizer and pass it through a 100-mesh sieve to obtain the modified adsorbent.

[0049] Comparative Example 3 The difference between this comparative example and Example 1 is that blast furnace slag (another typical solid waste from the smelting industry, with a composition significantly different from desulfurization ash, mainly composed of CaSiO3, Al2O3, and MgO, without a clear CaO and Fe2O3 synergistic catalytic system) was used as a substitute for smelting solid waste. The adsorbent was prepared using the same process as corn stalks, with the remaining steps being identical, as detailed below: (1) Remove impurities such as stones and weeds from dry, mold-free corn stalks, crush them with a pulverizer, and pass them through an 80-mesh sieve to obtain corn stalk powder; place the corn stalk powder in an oven at 105℃ for 24 hours, take it out and place it in a desiccator to cool to room temperature for later use; select blast furnace slag produced in the smelting industry, remove large impurities, crush it with a pulverizer, and pass it through a 100-mesh sieve to obtain slag powder; place the slag powder in an oven at 100℃ for 12 hours, take it out and place it in a desiccator to cool to room temperature for later use.

[0050] (2) Mix the corn stalk powder and slag powder after pretreatment in step (1) at a mass ratio of 7:3, put them into a high-speed mixer, adjust the mixing speed to 300 r / min, mix for 20 min, and obtain a uniform mixed raw material.

[0051] (3) Place the mixed raw material obtained in step (2) into a tube furnace and first introduce nitrogen into the tube furnace; then, raise the temperature of the tube furnace to 300°C at a heating rate of 5°C / min and maintain this temperature for low-temperature co-pyrolysis for 90 min; after the pyrolysis is completed, stop heating and continue to introduce nitrogen until the temperature of the tube furnace cools to room temperature, take out the product, wash it three times with deionized water to remove the soluble impurities remaining on the surface, and then dry it in an oven at 105°C for 16 h to obtain preliminary biochar.

[0052] (4) Take 1000 mL of deionized water and place it in a beaker. While stirring, slowly add 50 g of zinc chloride powder and stir until completely dissolved. Then slowly add 35 mL of analytical grade phosphoric acid with a concentration of 85% (corresponding to a phosphoric acid mass concentration of 3%) and continue stirring for 15 min to obtain a uniform composite modifier (zinc chloride mass concentration of 5% and phosphoric acid mass concentration of 3%).

[0053] (5) Weigh 10g of the biochar obtained in step (3) and mix it with 100mL of the composite modifier prepared in step (4) (solid-liquid ratio 1g:10ml). Place it in a microwave reactor, adjust the microwave power to 300W, and the microwave-assisted activation time to 2min. After the microwave activation is completed, take out the reaction product, wash it with deionized water until the pH of the washing solution is 6.5 to remove the residual modifier on the surface, and then dry it in an oven at 105℃ for 16h. After drying, pulverize it with a pulverizer and pass it through a 100-mesh sieve to obtain the modified adsorbent.

[0054] The modified adsorbent prepared in Example 1 and the adsorbents prepared in Comparative Examples 1, 2, and 3 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 7 ± 0.5; 2 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.

[0055] The main components of arsenic-containing wastewater are shown in Table 1.

[0056] Table 1 The concentration of metal ions in the filtrate after arsenic removal was determined by ICP method, as shown in Table 2.

[0057] Table 2 The corn stalk and metallurgical solid waste co-pyrolysis-microwave-assisted 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 7 to 0.35 mg / L, with an arsenic removal rate of 99.30%. 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 7 to 9.34 mg / L, with an arsenic removal rate of 81.32%. 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 7 to 11.24 mg / L, with an arsenic removal rate of 77.52%. The adsorbent prepared in Comparative Example 3 can reduce the arsenic concentration in arsenic-containing wastewater with an initial concentration of 50 mg / L and a pH of 7 to 10.09 mg / L, with an arsenic removal rate of 79.82%. Through comparison, it was found that the composite modified adsorbent prepared in Example 1 can better selectively remove arsenic. Compared to Comparative Example 1, the addition of desulfurization ash in this example has a significant catalytic effect on the low-temperature pyrolysis of corn stalks, which can greatly increase the specific surface area and pore volume of biochar. Furthermore, the components of the desulfurization ash itself can participate in the adsorption reaction of arsenic, making it one of the core raw materials for achieving high arsenic removal rates. Without desulfurization ash, even after composite modification, the adsorption performance of the product from the low-temperature pyrolysis of corn stalks alone still decreases significantly, proving that the synergistic effect of the two is irreplaceable. In Comparative Example 2, although single zinc chloride modification can increase the specific surface area, it lacks specific adsorption sites, has poor anti-interference ability, and low adsorption capacity. The combination of the two can achieve synergistic effects of pore etching and specific site construction, and reacts in situ with the alkaline metal oxides of crude biochar, greatly improving adsorption performance. This proves that the selection of the composite modifier is based on targeted design according to the characteristics of the raw materials, rather than a conventional combination. In Comparative Example 3, blast furnace slag was used as a substitute for desulfurization ash. Although both are smelting solid wastes, blast furnace slag lacks the unique CaO, Fe2O3, and Al2O3 synergistic catalytic system found in desulfurization ash. This prevents the catalytic cracking and pore construction of corn stalks during low-temperature pyrolysis, and also prevents in-situ reaction with the zinc chloride-phosphoric acid composite modifier to form specific arsenic removal sites. Consequently, the arsenic removal rate is significantly lower than in Example 1. This result demonstrates that not all smelting solid wastes can synergistically achieve high arsenic removal performance with corn stalks. The synergistic catalytic and adsorption effects of the oxides in the complex composition of the blast furnace slag selected in this invention are the core of the technical effect. This invention demonstrates a clear focus and innovation in the selection of smelting solid wastes, rather than simply a combination of solid wastes.

[0058] This invention employs a core process of "synergistic low-temperature co-pyrolysis of dual solid wastes," achieving breakthroughs in both energy consumption and solid waste utilization. It constructs a highly efficient activation system combining "composite modification + microwave assistance," overcoming the performance limitations of single modification methods. This invention not only significantly improves the arsenic removal performance of biochar adsorbents but also establishes a new paradigm for the synergistic resource utilization of agricultural and industrial solid wastes, possessing significant environmental and economic benefits and broad industrial application prospects.

[0059] 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 corn stalks and metallurgical solid waste, characterized in that: Using corn stalks and desulfurization ash from metallurgical solid waste as raw materials, the raw materials are crushed, sieved, and dried to obtain a mixed powder. The mixed powder is then subjected to low-temperature co-pyrolysis treatment, followed by activation treatment with a zinc chloride-phosphoric acid composite modifier to obtain a modified adsorbent.

2. The method for preparing modified adsorbents using corn stalks and metallurgical solid waste according to claim 1, characterized in that: The corn stalks are crushed, passed through an 80-120 mesh sieve, and dried at 105-110℃ for 20-24 hours to obtain corn stalk powder; the desulfurization ash is crushed, passed through a 100-200 mesh sieve, and dried at 100-105℃ for 8-12 hours to obtain desulfurization ash powder.

3. The method for preparing modified adsorbents using corn stalks and metallurgical solid waste according to claim 1, characterized in that: The mixed powder includes corn stalk powder and desulfurization ash powder, with a mass ratio of corn stalk powder to desulfurization ash powder of 7~9:1~3.

4. The method for preparing modified adsorbents using corn stalks and metallurgical solid waste according to claim 1, characterized in that, The conditions for the low-temperature co-pyrolysis are as follows: the tubular furnace is heated to 300-400℃ at a heating rate of 5-10℃ / min, and the pyrolysis time is 60-90min.

5. The method for preparing a modified adsorbent using corn stalks and metallurgical solid waste according to claim 1, characterized in that, The preparation method of the zinc chloride-phosphoric acid composite modifier is as follows: first, measure a certain volume of deionized water, slowly add zinc chloride powder, stir until completely dissolved, then slowly add phosphoric acid, and continue stirring for 10-15 minutes to obtain a uniform composite modifier.

6. The method for preparing a modified adsorbent using corn stalks and metallurgical solid waste according to claim 1, characterized in that, The zinc chloride-phosphoric acid composite modifier comprises, by mass percentage, 5%~15% zinc chloride, 3%~8% phosphoric acid, and the remainder is deionized water.

7. The method for preparing a modified adsorbent using corn stalks and metallurgical solid waste according to claim 1, characterized in that, The solid-liquid ratio of the mixed powder after low-temperature co-pyrolysis treatment to the zinc chloride-phosphoric acid composite modifier is (1~1.5) g: (10~20) mL.

8. The method for preparing a modified adsorbent using corn stalks and metallurgical solid waste according to claim 1, characterized in that, The conditions for microwave-assisted activation are: power of 300~500W and activation time of 2~3min.

9. The application of the modified adsorbent prepared by the method according to any one of claims 1 to 8 in the removal of arsenic from wastewater.

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