A biomass modified carbon heavy metal adsorbent and a preparation method and application thereof

Abstract

The application discloses a biomass modified carbon heavy metal adsorbent and a preparation method and application thereof. The biomass modified carbon heavy metal adsorbent is prepared from agricultural and forestry biomass wastes as raw materials and a composite active system composed of metal salts, phosphorus and sulfur ions as a modified component. The biomass modified carbon heavy metal adsorbent has developed pores, rich metal, phosphorus and sulfur active functional groups and aromatic and conjugated unsaturated structures, and is used for deep purification treatment of wastewater or waste gas containing heavy metals such as mercury, thallium and chromium.

Description

Technical Field

[0001] This invention belongs to the field of environmental pollution prevention and purification and biomass waste resource utilization technology, specifically relating to a biomass modified carbon heavy metal adsorbent, its preparation method and application. Background Technology

[0002] With the development of industries such as non-ferrous smelting, mining, electroplating, leather making, chemicals, and waste incineration, the problem of wastewater and exhaust gas emissions containing heavy metal pollutants such as mercury, thallium, chromium, and cadmium has become increasingly prominent. Heavy metal pollutants are characterized by high toxicity, high mobility, difficulty in degradation, easy accumulation, and significant biomagnification effects. Once they enter water bodies, the atmosphere, soil, and the food chain, they will cause serious harm to ecological environment safety and human health.

[0003] Currently, heavy metal treatment technologies mainly include chemical precipitation, oxidation-reduction, membrane separation, ion exchange, electrochemical methods, biological methods, and adsorption. Chemical precipitation is simple to operate, but consumes a large amount of reagents and easily generates large amounts of heavy metal-containing sludge. Membrane separation has good treatment effects, but membrane fouling is difficult to solve and operating costs are high. Ion exchange has strong selectivity, but resin costs are high and regeneration is complex. Electrochemical methods have high treatment efficiency, but energy consumption and equipment maintenance costs are high. Biological methods are environmentally friendly, but the overall treatment cycle is long and has strict requirements on treatment conditions. In contrast, adsorption has advantages such as simple process, high removal efficiency, low operating costs, wide applicability, and ease of engineering integration, making it an important technical route for the deep purification of heavy metal wastewater and exhaust gas.

[0004] The core of adsorption methods lies in developing efficient, stable, and low-cost adsorption materials. Among these, carbon-based adsorbents have attracted widespread attention in the purification of water and gaseous pollutants due to their large specific surface area, well-developed pore structure, and good chemical stability. Activated carbon is currently a relatively mature carbon-based adsorbent, capable of removing some heavy metal pollutants through pore filling, physical adsorption, and surface functional group interactions. However, traditional activated carbon is mostly derived from coal, which relies on non-renewable fossil resources. The extraction and preparation of raw materials present problems such as high energy consumption, large carbon emissions, ecological disturbance, and difficulty in impurity control. Compared to coal-based carbon, biomass-based carbon uses agricultural and forestry waste and food processing byproducts as its main raw materials, offering advantages such as renewability, wide availability, low cost, and environmental friendliness. The development and utilization of biomass-based carbon can not only reduce dependence on coal resources but also achieve high-value utilization of biomass waste, reducing the environmental pressure caused by open burning, stockpiling and decay, and waste disposal.

[0005] However, biochar prepared using conventional carbonization methods often suffers from underdeveloped pore structures, limited specific surface area, and insufficient number of surface-active functional groups. Its adsorption capacity, selectivity, and long-term stable fixation ability for heavy metal pollutants are insufficient to meet the requirements of deep wastewater and waste gas treatment. To improve the adsorption performance of biochar for heavy metal pollutants, functional modification is usually necessary. Existing biochar modification methods mostly employ a post-impregnation process, where finished biochar is prepared first, and then liquid-phase impregnation modification is performed using the finished biochar as a carrier. While this method is relatively simple to operate, the modifier is difficult to fully and uniformly penetrate the internal pores of the carbon material, easily leading to the active components being mainly distributed on the outer surface of the material, resulting in uneven loading, low utilization of active sites, and easy loss during use. Simultaneously, some modification methods require the use of high-concentration strong acids and bases, resulting in high raw material costs and environmental risks; the loading process reaction system is complex, easily causing active component aggregation, pore blockage, or structural damage; some processes require multiple impregnation and washing steps, resulting in long process flows, high energy consumption, and large amounts of waste liquid generated.

[0006] Therefore, developing a biomass-modified carbon heavy metal adsorbent that can be easily synthesized in situ, has a wide range of raw material sources, a well-developed pore structure, a uniform distribution of active components, and also has multiple synergistic active sites is of great practical significance and application value for improving the adsorption, complexation, and stable fixation capacity of heavy metal pollutants, and achieving low-cost, high-efficiency, and engineered deep purification of wastewater and exhaust gas containing heavy metals. Summary of the Invention

[0007] To overcome the problems of low adsorption capacity, slow adsorption rate, and insufficient surface active sites in the adsorption of heavy metal pollutants by existing ordinary biochar, and to solve the shortcomings of existing modification methods such as complex process flow, cumbersome operation steps, uneven distribution of active components after modification, insufficient stability, and poor industrial adaptability, the present invention aims to provide a biomass-modified carbon heavy metal adsorbent, its preparation method, and its application. Using agricultural and forestry biomass waste as a carbon source, a porous biomass carbon matrix is ​​constructed through high-temperature molten salt carbonization, achieving metal site loading. Then, phosphorus and sulfur-containing active components are uniformly dispersed and loaded onto the pores and surface of the carbon material through in-situ phosphorus and sulfur grinding modification. Subsequently, a medium-temperature secondary ripening and activation promotes the reaction between the metal, phosphorus, and sulfur components and the carbon matrix. Finally, a biomass-modified carbon heavy metal adsorbent with a well-developed pore structure, rich metal, phosphorus, and sulfur functional groups, an aromatic carbon skeleton, and a conjugated C=C structure is obtained, exhibiting a strong affinity for heavy metals. This adsorbent is used for the deep purification treatment of wastewater or waste gas containing heavy metals.

[0008] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution: A method for preparing a biomass-modified carbon heavy metal adsorbent includes the following steps: (1) After acid leaching, the bulk biomass is air-dried, crushed and screened to obtain pretreated biomass raw materials; (2) The pretreated biomass raw materials and the combined molten salt activator are mixed evenly and carbonized at high temperature under a protective atmosphere to obtain a porous biochar intermediate; the combined molten salt activator includes zinc salt, copper salt, ferrous salt and potassium salt. (3) The porous biochar intermediate is mixed with phosphorus- and sulfur-containing modifiers and modified by mechanical force to obtain the modified porous biochar intermediate; (4) The modified porous biochar intermediate is subjected to medium-temperature secondary ripening and activation to obtain biochar modified heavy metal adsorbent.

[0009] Preferably, in step (1), the biomass bulk material is straw, sawdust, bamboo shavings, bagasse, coffee grounds, or rice husks, etc.

[0010] Preferably, in step (1), the acid leaching is performed by soaking in dilute hydrochloric acid with a mass concentration of 0.5-3% for 1-12 hours to remove some ash, impurities and soluble inorganic matter, so that the surface is moderately loose; the air drying temperature is 50-80℃, and the moisture content after air drying is less than 15%; crushing and sieving make the particle size less than 4 mm, preferably less than 2 mm.

[0011] Preferably, in step (2), the zinc salt, copper salt, ferrous salt and potassium salt in the combined molten salt activator are their respective chlorides, the mass ratio of pretreated biomass raw material to combined molten salt activator is 1:0.03 to 1:0.18, and the mass ratio of zinc salt, copper salt, ferrous salt and potassium salt in the combined molten salt activator is 0.5 to 2:0.5 to 2:3 to 8:1 to 4, preferably 1:1:6:2.

[0012] Preferably, in step (2), the protective atmosphere is nitrogen, argon or a mixture thereof, the high-temperature carbonization temperature is 500-900℃, and the carbonization time is 1-6h, so that the biomass undergoes dehydration, pyrolysis, aromatization and carbonization reactions, and at the same time, under the template, etching and catalytic effects of the molten salt activator, a multi-level porous structure is formed, and the metal sites are supported.

[0013] Preferably, in step (3), the phosphorus-containing modifier is selected from one or more of the following industrial by-products: phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, potassium dihydrogen phosphate, and dipotassium hydrogen phosphate; the sulfur-containing modifier is selected from one or more of elemental sulfur, thiourea, sodium sulfide, ammonium sulfide, and sodium thiosulfate; the mass ratio of phosphorus in the porous biochar intermediate and the phosphorus in the phosphorus-containing modifier to sulfur in the sulfur-containing modifier is 1:0.03-0.1:0.01-0.2.

[0014] Preferably, in step (3), the mechanical force is applied by grinding in a mortar and pestle, planetary ball milling, vibratory ball milling, or stirring ball milling, with a temperature ranging from room temperature to 80°C and a time of 5–240 min. Under mechanical force, the phosphorus- and sulfur-containing modifiers are refined, dispersed, and enter the pore structure of the porous biochar intermediate. Simultaneously, they interact with functional groups such as hydroxyl, carboxyl, and carbonyl groups on the surface of the biochar material, resulting in the uniform dispersion and loading of phosphorus and sulfur active components onto the surface and within the pores of the biochar.

[0015] Preferably, in step (4), the temperature of the medium-temperature secondary ripening and activation is 250-450℃ and the time is 0.5-6 h, so that the metal, phosphorus and sulfur components and the porous biomass carbon matrix undergo further dehydration condensation, bonding and surface reconstruction reactions, promote the formation of aromatic carbon skeleton and conjugated C=C structure, and form stable active sites such as PO, P=O, P-OH, CS, SH, SS, Me-S.

[0016] The present invention also provides a biomass-modified carbon heavy metal adsorbent prepared by the above preparation method.

[0017] The present invention also provides the application of the above-mentioned biomass modified carbon heavy metal adsorbent, which is used for the deep purification treatment of wastewater or waste gas containing heavy metals; the heavy metals include one or more of mercury, thallium, chromium and cadmium.

[0018] Preferably, the heavy metal-containing wastewater includes smelting wastewater, mining wastewater, electroplating wastewater, leather tanning wastewater, chemical wastewater, and combinations thereof; when the biomass-modified carbon heavy metal adsorbent is used to treat the heavy metal-containing wastewater, the initial concentration of heavy metals in the wastewater is 0.01–800 mg / L, the pH value of the wastewater is 1–8, and the adsorption temperature is 5–60℃.

[0019] Preferably, the biomass-modified carbon heavy metal adsorbent can be used by powder addition, fixed bed filling, adsorption column filling, filter element loading, particle molding, or membrane carrier loading; when used to treat waste gas containing heavy metals, the adsorbent can be sprayed into the flue, filled into the flue gas purification device, or molded and loaded onto other carriers for use.

[0020] High-temperature carbonization and pore-forming with combined molten salt activators creates a well-developed porous structure in biomass char, providing abundant diffusion channels and adsorption space, which facilitates the entry and enrichment of heavy metal pollutants into the adsorbent. Under high-temperature conditions, the combined molten salt activator forms a molten or semi-molten salt phase, promoting biomass carbonization and pore formation through salt templates, catalytic cracking, and pore etching, thereby increasing the specific surface area and pore structure development of the adsorbent. Components such as copper, iron, and zinc in the molten salt can participate in the formation of metal active sites during carbonization and aging, which can complex, redox, or catalytically transform heavy metal pollutants. Phosphorus and sulfur-containing modifiers introduce functional sites such as PO, P=O, P-OH, CS, SH, SS, or Me-S during mechanical modification and medium-temperature aging activation, which can complex and exchange ions with heavy metals. The aromatic carbon skeleton and conjugated C=C structure formed during biomass carbonization have a certain electron transport capacity, which can participate in the reduction and transformation of heavy metals, and can also enhance the adsorption and enrichment capacity of heavy metals through π-electron interactions.

[0021] Furthermore, the functional groups on the adsorbent surface can undergo protonation or deprotonation, thereby electrostatically adsorbing positively or negatively charged heavy metal ions and oxygen-containing anions. The aromatic carbon structure, yoke C=C structure, phosphorus-containing and sulfur-containing groups, and metal components on the adsorbent surface work synergistically to promote electron transfer and reduce the migration of heavy metals through sulfidation, complexation, precipitation, and pore fixation.

[0022] This invention constructs a biomass-modified carbon heavy metal adsorbent with a combination of well-developed pore structure, active metal components, phosphorus and sulfur functional groups, aromatic carbon skeleton, and conjugated C=C structure through a technical route of "centralized biomass pretreatment - combined molten salt high-temperature carbonization for pore formation - in-situ mechanical modification of phosphorus and sulfur - medium-temperature secondary curing and activation". This adsorbent can be used for the deep purification of wastewater and exhaust gas containing heavy metals such as mercury, thallium, chromium, and cadmium.

[0023] The biomass-modified carbon heavy metal adsorbent described in this invention can be applied in different ways depending on the wastewater or waste gas treatment scenario. When used for the deep treatment of wastewater containing heavy metals, the adsorbent can be directly added to the reaction tank in powder form, and after stirring and reaction, solid-liquid separation can be achieved through sedimentation, filtration, or pressure filtration; alternatively, the adsorbent can be prepared as granular or columnar materials and filled into fixed beds, adsorption columns, or filter cartridges to achieve continuous treatment; or the adsorbent can be loaded onto membrane materials, non-woven fabrics, ceramic carriers, or other porous carriers for use in combined water treatment devices. When used for the purification of waste gas containing heavy metals, the adsorbent can be directly sprayed into the flue to fully contact mercury and other heavy metal pollutants in the flue gas; it can also be filled into a flue gas purification device to form a fixed bed adsorption unit; or it can be molded, bonded, or coated and then loaded onto filter bags, filter cartridges, honeycomb ceramics, activated carbon fibers, or other carriers for use. This invention does not limit the specific form of use of the adsorbent. As long as the biomass modified carbon heavy metal adsorbent prepared by the method described in this invention is used for the deep purification treatment of wastewater or waste gas containing heavy metals, it should fall within the protection scope of this invention.

[0024] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention uses biomass waste as raw material to realize the resource utilization of waste biomass. The raw material sources are wide and the price is low.

[0025] (2) The high-temperature molten salt carbonization pore-forming process can simultaneously realize the pore structure construction during the biomass carbonization process, forming a multi-level channel with micropores, mesopores and macropores coexisting, and simultaneously realize the loading of metal sites.

[0026] (3) The phosphorus and sulfur in-situ grinding modification process is adopted. The active components of phosphorus and sulfur are uniformly dispersed and enter the pores through mechanical force, avoiding the problems of uneven distribution of active components, low loading efficiency and large amount of waste liquid generated in traditional impregnation modification.

[0027] (4) Multiple active sites work together to achieve efficient and stable fixation of highly toxic heavy metals, which can be used for the treatment of single heavy metal wastewater and multi-metal composite pollution wastewater.

[0028] (5) The process of this invention is simple and the equipment requirements are low. It can be completed using conventional carbonization furnaces, ball mills, drying ovens and other equipment, and has good feasibility for scale-up preparation and engineering application. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0030] Example 1

[0031] A certain amount of coffee grounds was soaked in 1% dilute hydrochloric acid for 8 hours, rinsed briefly with water, and air-dried at 60℃ until the moisture content was less than 10%. The air-dried coffee grounds were then crushed and sieved. 100 g of pretreated coffee grounds were weighed and 10 g of a combined molten salt activator was added, wherein the mass ratio of zinc chloride, copper chloride, ferrous chloride, and potassium chloride was 1:1:6:2. The pretreated coffee grounds and the combined molten salt activator were thoroughly mixed and placed in a tube furnace. The temperature was increased to 750℃ at 15℃ / min under a nitrogen atmosphere and held for 2 hours. After carbonization, the mixture was cooled to room temperature to obtain a porous biochar intermediate. 10 g of the porous biochar intermediate was taken and phosphoric acid and sodium sulfide were added as phosphorus and sulfur modifiers. The mass ratio of biochar intermediate, phosphorus, and sulfur was 1:0.05:0.10. The mixture was placed in a ball mill and mechanically ground at room temperature for 60 minutes. The ground and modified material was placed in a heating furnace and matured and activated at 350℃ for 2 hours. After curing for h, the mixture was naturally cooled to room temperature and then sieved to obtain biomass-modified char heavy metal adsorbent with a specific surface area of ​​763 m². 2 / g.

[0032] Simulated heavy metal-containing wastewater with pH=3 was prepared, with mercury concentrations of 2 ppm, thallium concentrations of 2 ppm, chromium concentrations of 10 ppm, and cadmium concentrations of 2 ppm. Biomass-modified charcoal heavy metal adsorbent was added to the simulated wastewater, and the mixture was stirred and reacted at room temperature for 10 min. The solution was then filtered, and the concentrations of each heavy metal in the filtrate were measured. After treatment, the mercury concentration decreased to 0 ppm, the thallium concentration decreased to 0.002 ppm, the chromium concentration decreased to 0.08 ppm, and the cadmium concentration decreased to 0.007 ppm. The removal efficiencies for mercury, thallium, chromium, and cadmium were 100%, 99.90%, 99.20%, and 99.65%, respectively. The total heavy metal concentration decreased from 16 ppm to 0.089 ppm, with an overall removal efficiency of approximately 99.44%. The results indicate that the biomass-modified charcoal heavy metal adsorbent has a rapid and efficient simultaneous removal capacity for multiple heavy metal pollutants, including mercury, thallium, chromium, and cadmium, under acidic conditions.

[0033] Example 2

[0034] A certain amount of sawdust was soaked in 1% dilute hydrochloric acid for 1 hour, rinsed briefly with water, and then air-dried at 60℃ until the moisture content was below 8%. The air-dried sawdust was then crushed and sieved. 100 g of pretreated sawdust was weighed and 8 g of a combined molten salt activator was added, wherein the mass ratio of zinc chloride, copper chloride, ferrous chloride, and potassium chloride was 2:2:4:2. The pretreated sawdust and the combined molten salt activator were thoroughly mixed and placed in a tube furnace. The furnace was heated to 700℃ at 10℃ / min under an argon atmosphere and held for 3 hours. After carbonization, the mixture was cooled to room temperature to obtain a porous biochar intermediate. 10 g of the porous biochar intermediate was taken and ammonium dihydrogen phosphate and elemental sulfur were added as phosphorus and sulfur modifiers, so that the mass ratio of biochar intermediate, phosphorus, and sulfur was 1:0.06:0.2. The mixture was placed in a ball mill and mechanically ground at room temperature for 90 minutes. min; then the ground and modified material was placed in a heating furnace and matured at 320℃ for 3 h. After maturity, it was naturally cooled to room temperature and sieved to obtain biomass modified carbon heavy metal adsorbent with a specific surface area of ​​931 m². 2 / g.

[0035] Simulated heavy metal-contaminated wastewater with pH=5 was prepared, containing 100 ppm mercury and 10 ppm thallium. Biomass-modified charcoal heavy metal adsorbent was added to the simulated wastewater, and the mixture was stirred at room temperature for 60 min. The solution was then filtered, and the concentrations of each heavy metal in the filtrate were measured. After treatment, the mercury concentration decreased to 0.003 ppm, and the thallium concentration decreased to 0.002 ppm. The removal efficiencies for mercury and thallium were 99.997% and 99.98%, respectively. The results demonstrate that the biomass-modified charcoal heavy metal adsorbent exhibits excellent deep purification capabilities for water bodies contaminated with high concentrations of both mercury and thallium.

[0036] Example 3

[0037] A certain amount of bamboo shavings was soaked in 2% dilute hydrochloric acid for 3 hours, rinsed briefly with water, and air-dried at 70℃ until the moisture content was below 10%. The air-dried bamboo shavings were then crushed and sieved. 100 g of pretreated bamboo shavings were weighed and 12 g of a combined molten salt activator was added, wherein the mass ratio of zinc chloride, copper chloride, ferrous chloride, and potassium chloride was 2:2:5:1. The pretreated bagasse and the combined molten salt activator were thoroughly mixed and placed in a tube furnace. The furnace was heated to 850℃ at 15℃ / min under a nitrogen atmosphere and held for 1 hour. After carbonization, the mixture was cooled to room temperature to obtain a porous biochar intermediate. 10 g of the porous biochar intermediate was taken and phosphoric acid and ammonium sulfide were added as phosphorus and sulfur modifiers. The mass ratio of biochar intermediate, phosphorus, and sulfur was 1:0.06:0.01. The mixture was placed in a ball mill and mechanically ground at 60℃ for 120 minutes. The ground and modified material was placed in a heating furnace and matured at 250℃ for 4 hours. After maturation, it was naturally cooled to room temperature and sieved to obtain biomass-modified char heavy metal adsorbent with a specific surface area of ​​632 m². 2 / g.

[0038] Waste acid from a lead-zinc smelter was collected, containing mercury at 32.23 ppm, thallium at 24.53 ppm, chromium at 2.88 ppm, and cadmium at 12.12 ppm. Biomass-modified carbon heavy metal adsorbent was added to the waste acid containing heavy metals, and the mixture was stirred at 45°C for 30 min. The solution was then filtered, and the concentrations of each heavy metal in the filtrate were measured. The results showed that after treatment, the mercury concentration decreased to 0.002 ppm, the thallium concentration to 0.001 ppm, the chromium concentration to 0.01 ppm, and the cadmium concentration to 0.009 ppm. The removal efficiencies for mercury, thallium, chromium, and cadmium were 99.994%, 99.996%, 99.65%, and 99.93%, respectively; the total heavy metal concentration decreased from 71.76 ppm to 0.022 ppm, with an overall removal efficiency of approximately 99.97%. The results showed that the biomass-modified carbon heavy metal adsorbent has a rapid and efficient simultaneous removal capacity for a variety of heavy metal pollutants under actual wastewater conditions.

[0039] Example 4

[0040] The biomass-modified carbon heavy metal adsorbent obtained in Example 1 was loaded into a fixed-bed flue gas purification device, and mercury-containing simulated flue gas was introduced, with the flue gas temperature controlled at 80°C. The mercury-containing simulated flue gas produced elemental mercury through a mercury permeation tube, and the mercury concentration was measured in real time using an RA915 mercury analyzer. A mass flow meter was used to precisely control the flow rates of each component gas to simulate the composition of the flue gas; the total gas flow rate was 1 L / min, and the initial Hg was... 0 Concentration 200±2μg / m 3 Under a pure N2 atmosphere, the Hg level within 1 hour... 0The removal rate was 99.4%; under an atmosphere of N2 + 8% H2O + 50ppm HCl + 200 ppm SO2, Hg was reduced within 1 hour. 0 The removal rate was 99.2%.

[0041] The results show that the adsorbent has a good capture capacity for gaseous mercury and can maintain a high mercury removal efficiency even in the presence of typical flue gas components, exhibiting good resistance to moisture and acid gas interference. This embodiment demonstrates that the adsorbent of the present invention is suitable not only for the treatment of wastewater containing heavy metals but also for the deep purification treatment of waste gas containing heavy metals.

[0042] Example 5

[0043] The biomass-modified char heavy metal adsorbent obtained in Example 2 was sprayed into a volume of 1 m³. 3 In the pilot-scale injection tower, elemental mercury was generated by a mercury generator. The mercury concentration was measured in real time using an RA915 mercury analyzer. The gas flow rate was controlled by a flue gas flow valve. (Hg) 0 The initial concentration was 80±1 μg / m 3 The flue gas flow rate is 1m³. 3 Hg / min, temperature 100℃, under pure N2 atmosphere, within 1 hour 0 The removal rate was 98.6%.

[0044] Example 6

[0045] The biomass-modified carbon heavy metal adsorbent prepared in Example 1 was further granulated to obtain granular adsorbent, which was then packed into an adsorption column to form a fixed-bed adsorption unit. Simulated composite wastewater containing mercury, thallium, chromium, and cadmium, with each heavy metal concentration of 2 ppm, was prepared and continuously passed through the adsorption column. The influent pH was 4, and the adsorption temperature was room temperature. The concentrations of mercury, thallium, chromium, and cadmium in the effluent from the adsorption column were significantly reduced, and the removal efficiency of each heavy metal exceeded 99%. The results indicate that the biomass-modified carbon heavy metal adsorbent still possesses good heavy metal capture capacity and operational stability under continuous flow conditions.

[0046] This embodiment illustrates that the adsorbent of the present invention can be used not only by powder addition, but also by granulation, fixed bed filling, adsorption column packing, filter cartridge loading or membrane carrier loading, etc., and is suitable for continuous deep purification treatment of wastewater containing heavy metals.

[0047] Comparative Example 1

[0048] A certain amount of coffee grounds was soaked in 1% dilute hydrochloric acid for 8 hours, rinsed briefly with water, and air-dried at 60℃ until the moisture content was below 10%. The air-dried coffee grounds were then crushed and sieved. 100 g of the pretreated coffee grounds were weighed and placed in a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 750℃ at 15℃ / min and held for 2 hours. After carbonization, the mixture was cooled to room temperature to obtain a porous biochar intermediate. 10 g of the porous biochar intermediate was placed in a ball mill and mechanically ground at room temperature for 60 minutes. The ground and modified material was placed in a heating furnace and matured at 350℃ for 2 hours. After maturation, the mixture was naturally cooled to room temperature and sieved to obtain a comparative biochar modified heavy metal adsorbent with a specific surface area of ​​497 m². 2 / g.

[0049] Simulated heavy metal-containing wastewater with pH=3 was prepared, with mercury concentration of 2 ppm, thallium concentration of 2 ppm, chromium concentration of 10 ppm, and cadmium concentration of 2 ppm. A comparative biomass-modified charcoal heavy metal adsorbent was added to the simulated wastewater, and the mixture was stirred at room temperature for 10 min. The solution was then filtered, and the concentrations of each heavy metal in the filtrate were measured. After treatment, the mercury concentration decreased to 0.93 ppm, the thallium concentration decreased to 0.81 ppm, the chromium concentration decreased to 6.80 ppm, and the cadmium concentration decreased to 1.21 ppm. The calculated removal efficiencies for mercury, thallium, chromium, and cadmium were 53.50%, 59.50%, 32.00%, and 39.50%, respectively; the initial concentration of total heavy metals in the water decreased from 16 ppm to 9.75 ppm, and the overall heavy metal removal efficiency was approximately 39.06%. The results indicate that the comparative biomass charcoal has a certain removal capacity for the above-mentioned heavy metals, but its removal efficiency is significantly lower than that of the adsorbent obtained in Example 1.

[0050] This comparative example illustrates that ordinary biochar that has not undergone combined molten salt carbonization for pore formation and in-situ grinding modification with phosphorus and sulfur has insufficient pore structure and surface active sites, making it difficult to achieve efficient and simultaneous removal of multiple heavy metals.

[0051] Comparative Example 2

[0052] A certain amount of coffee grounds was soaked in 1% dilute hydrochloric acid for 8 hours, rinsed briefly with water, and air-dried at 60℃ until the moisture content was less than 10%. The air-dried coffee grounds were then crushed and sieved. 100 g of the pretreated coffee grounds were weighed and placed in a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 750℃ at 15℃ / min and held for 2 hours. After carbonization, the mixture was cooled to room temperature to obtain a porous biochar intermediate. 10 g of the porous biochar intermediate was taken and phosphoric acid and sodium sulfide were added as phosphorus and sulfur modifiers. The mass ratio of biochar intermediate, phosphorus, and sulfur was 1:0.05:0.10. The mixture was placed in a ball mill and mechanically ground at room temperature for 60 minutes. The ground and modified material was placed in a heating furnace and matured at 350℃ for 2 hours. After maturation, the mixture was naturally cooled to room temperature and sieved to obtain a comparative biochar heavy metal adsorbent with a specific surface area of ​​478 m². 2 / g.

[0053] Simulated heavy metal-containing wastewater with pH=3 was prepared, with mercury concentrations of 2 ppm, thallium concentrations of 2 ppm, chromium concentrations of 10 ppm, and cadmium concentrations of 2 ppm. Biomass-modified charcoal heavy metal adsorbent was added to the simulated wastewater, and the mixture was stirred and reacted at room temperature for 10 min. The solution was then filtered, and the concentrations of each heavy metal in the filtrate were measured. After treatment, the mercury concentration decreased to 0.77 ppm, the thallium concentration decreased to 0.64 ppm, the chromium concentration decreased to 6.08 ppm, and the cadmium concentration decreased to 0.57 ppm. Calculations showed that the removal efficiencies for mercury, thallium, chromium, and cadmium were 61.50%, 68.00%, 39.20%, and 71.50%, respectively; the total heavy metal concentration in the water decreased from 16 ppm to 8.06 ppm, with an overall heavy metal removal efficiency of approximately 49.63%. The results indicate that the biochar exhibits some removal capacity for the aforementioned heavy metals, but its removal efficiency is significantly lower than that of the adsorbent obtained in Example 1.

[0054] This comparative example illustrates that ordinary biochar without combined molten salt carbonization for pore formation has insufficient pore structure, making it difficult to achieve efficient and simultaneous removal of multiple heavy metals.

[0055] Comparative Example 3

[0056] A certain amount of coffee grounds was soaked in 1% dilute hydrochloric acid for 8 hours, rinsed briefly with water, and air-dried at 60℃ until the moisture content was less than 10%. The air-dried coffee grounds were then crushed and sieved. 100 g of pretreated coffee grounds were weighed and 10 g of a combined molten salt activator was added, wherein the mass ratio of zinc chloride, copper chloride, ferrous chloride, and potassium chloride was 1:1:6:2. The pretreated coffee grounds and the combined molten salt activator were thoroughly mixed and placed in a tube furnace. The temperature was increased to 750℃ at 15℃ / min under a nitrogen atmosphere and held for 2 hours. After carbonization, the mixture was cooled to room temperature to obtain a porous biochar intermediate. 10 g of the porous biochar intermediate was placed in a ball mill and mechanically ground at room temperature for 60 minutes. The ground and modified material was placed in a heating furnace and matured at 350℃ for 2 hours. After maturation, the mixture was naturally cooled to room temperature and sieved to obtain a comparative biomass modified carbon heavy metal adsorbent with a specific surface area of ​​823 m². 2 / g.

[0057] Simulated heavy metal-containing wastewater with pH=3 was prepared, with mercury concentration of 2 ppm, thallium concentration of 2 ppm, chromium concentration of 10 ppm, and cadmium concentration of 2 ppm. Biomass-modified charcoal heavy metal adsorbent was added to the simulated wastewater, and the mixture was stirred and reacted at room temperature for 10 min. The solution was then filtered, and the concentrations of each heavy metal in the filtrate were measured. After treatment, the mercury concentration decreased to 0.85 ppm, the thallium concentration decreased to 0.67 ppm, the chromium concentration decreased to 6.11 ppm, and the cadmium concentration decreased to 0.63 ppm. The calculated removal efficiencies for mercury, thallium, chromium, and cadmium were 57.50%, 66.50%, 38.90%, and 68.50%, respectively; the total heavy metal concentration in the water decreased from 16 ppm to 8.26 ppm, with an overall heavy metal removal efficiency of approximately 48.38%. The results indicate that the biomass charcoal has a certain removal capacity for the above-mentioned heavy metals, but its removal efficiency is significantly lower than that of the adsorbent obtained in Example 1.

[0058] This comparative example illustrates that ordinary biochar that has not undergone in-situ grinding and modification with phosphorus and sulfur has insufficient surface active sites, making it difficult to achieve efficient and simultaneous removal of multiple heavy metals.

[0059] Comparative Example 4

[0060] A certain amount of coffee grounds was soaked in 1% dilute hydrochloric acid for 8 hours, rinsed briefly with water, and air-dried at 60℃ until the moisture content was less than 10%. The air-dried coffee grounds were then crushed and sieved. 100 g of pretreated coffee grounds were weighed and 10 g of molten potassium chloride activator was added. The pretreated coffee grounds and molten potassium chloride activator were thoroughly mixed and placed in a tube furnace. The temperature was increased to 750℃ at 15℃ / min under a nitrogen atmosphere and held for 2 hours. After carbonization, the mixture was cooled to room temperature to obtain a porous biochar intermediate. 10 g of the porous biochar intermediate was taken and phosphoric acid and sodium sulfide were added as phosphorus and sulfur modifiers. The mass ratio of biochar intermediate, phosphorus, and sulfur was 1:0.05:0.10. The mixture was placed in a ball mill and mechanically ground at room temperature for 60 minutes. The ground and modified material was placed in a heating furnace and matured and activated at 350℃ for 2 hours. After curing for h, the mixture was naturally cooled to room temperature and then sieved to obtain the comparative biomass modified carbon heavy metal adsorbent, which had a specific surface area of ​​703 m². 2 / g.

[0061] Simulated heavy metal-containing wastewater with pH=3 was prepared, with mercury concentrations of 2 ppm, thallium concentrations of 2 ppm, chromium concentrations of 10 ppm, and cadmium concentrations of 2 ppm. Biomass-modified charcoal heavy metal adsorbent was added to the simulated wastewater, and the mixture was stirred and reacted at room temperature for 10 min. The solution was then filtered, and the concentrations of each heavy metal in the filtrate were measured. After treatment, the mercury concentration decreased to 1.08 ppm, the thallium concentration decreased to 1.34 ppm, the chromium concentration decreased to 4.32 ppm, and the cadmium concentration decreased to 0.57 ppm. Calculations showed that the removal efficiencies for mercury, thallium, chromium, and cadmium were 57.50%, 66.50%, 38.90%, and 68.50%, respectively; the total heavy metal concentration in the water decreased from 16 ppm to 8.26 ppm, with an overall heavy metal removal efficiency of approximately 48.38%. The results indicate that the biomass charcoal has a certain removal capacity for the above-mentioned heavy metals, but its removal efficiency is significantly lower than that of the adsorbent obtained in Example 1.

[0062] This comparative example demonstrates that combined molten salt carbonization can improve the pore structure of materials. In contrast, materials prepared using a single molten salt carbonization method have limited pore development and insufficient number of active sites.

[0063] Comparative Example 5

[0064] A certain amount of coffee grounds was soaked in 1% dilute hydrochloric acid for 8 hours, rinsed briefly with water, and air-dried at 60℃ until the moisture content was below 10%. The air-dried coffee grounds were then crushed and sieved. 100 g of the pretreated coffee grounds were weighed and 10 g of a combined molten salt activator was added, wherein the mass ratio of zinc chloride, copper chloride, ferrous chloride, and potassium chloride was 1:1:6:2. The pretreated bagasse and the combined molten salt activator were thoroughly mixed and placed in a tube furnace. The furnace was heated to 750℃ at a rate of 15℃ / min under a nitrogen atmosphere and held at that temperature for 2 hours. After carbonization, the mixture was cooled to room temperature to obtain a porous biochar intermediate. 10g of the porous biochar intermediate was taken and impregnated with phosphoric acid and sodium sulfide as phosphorus-sulfur modifiers at a mass ratio of 1:0.05:0.10 for 6 hours. After impregnation, the mixture was dried at 80℃ and allowed to cool naturally to room temperature. The resulting biochar modified heavy metal adsorbent had a specific surface area of ​​678 m². 2 / g.

[0065] Simulated heavy metal-containing wastewater with pH=3 was prepared, containing 2 ppm mercury, 2 ppm thallium, 10 ppm chromium, and 2 ppm cadmium. Comparative porous biochar material prepared by the post-impregnation method was added to the simulated wastewater and stirred at room temperature for 10 min. The mixture was then filtered, and the concentrations of each heavy metal in the filtrate were measured. After treatment, the mercury concentration decreased to 0.73 ppm, the thallium concentration to 0.62 ppm, the chromium concentration to 5.80 ppm, and the cadmium concentration to 0.47 ppm. The removal efficiencies for mercury, thallium, chromium, and cadmium were 63.50%, 69.00%, 42.00%, and 76.50%, respectively; the initial concentration of total heavy metals in the water decreased from 16 ppm to 7.62 ppm, with an overall heavy metal removal efficiency of approximately 52.38%. The results indicate that the comparative porous biochar material obtained by the post-impregnation method has a certain adsorption capacity for heavy metal pollutants, but the overall removal efficiency is lower than that of the adsorbent obtained in Example 1.

[0066] This comparative example illustrates that the combined molten salt carbonization pore-forming method can improve the pore structure of the material. However, when phosphorus and sulfur active components are introduced by post-impregnation, the modifier is difficult to fully and uniformly enter the internal pores of the carbon material. This easily leads to the active components being mainly distributed on the outer surface of the material, resulting in problems such as uneven loading, low utilization of active sites, and easy loss during use. Consequently, there are insufficient effective heavy metal chemical adsorption sites on the material surface, making it difficult to achieve efficient complexation and stable fixation of heavy metal pollutants.

[0067] Comparative Example 6

[0068] Coffee grounds were pretreated, combined with molten salt high-temperature carbonization for pore formation, and modified by in-situ mechanical grinding with phosphorus and sulfur according to the method in Example 1. However, after grinding, no secondary ripening and activation at medium temperature was performed. The adsorbent was directly obtained by sieving, with a specific surface area of ​​618 m². 2 / g.

[0069] The adsorbent was used to treat simulated heavy metal-containing wastewater at pH 3, with simulated concentrations of mercury (2 ppm), thallium (2 ppm), chromium (10 ppm), and cadmium (2 ppm). After stirring for 10 min at room temperature, the solution was filtered, and the concentrations of each heavy metal in the filtrate were measured. After treatment, the mercury concentration decreased to 0.57 ppm, the thallium concentration decreased to 0.52 ppm, the chromium concentration decreased to 2.08 ppm, and the cadmium concentration decreased to 0.27 ppm. The calculated removal efficiencies for mercury, thallium, chromium, and cadmium were 71.50%, 74.00%, 79.20%, and 86.50%, respectively; the total heavy metal concentration decreased from 16 ppm to 3.44 ppm, with an overall removal efficiency of approximately 78.50%. The results indicate that the adsorbent has a certain removal capacity for heavy metals, but its adsorption stability and overall removal efficiency are lower than those of the adsorbent obtained in Example 1.

[0070] This comparative example illustrates that medium-temperature secondary ripening and activation helps to promote further dehydration condensation, chemical bonding, solid-phase diffusion, and surface reconstruction reactions between metal, phosphorus, and sulfur components and the porous biomass carbon matrix, thereby forming more stable heavy metal adsorption active sites.

Claims

1. A method for preparing a biomass-modified carbon heavy metal adsorbent, characterized in that, Includes the following steps: (1) After acid leaching, the bulk biomass is air-dried, crushed and screened to obtain pretreated biomass raw materials; (2) The pretreated biomass raw materials and the combined molten salt activator are mixed evenly and carbonized at high temperature under a protective atmosphere to obtain a porous biochar intermediate; the combined molten salt activator includes zinc salt, copper salt, ferrous salt and potassium salt. (3) The porous biochar intermediate is mixed with phosphorus- and sulfur-containing modifiers and modified by mechanical force to obtain the modified porous biochar intermediate; (4) The modified porous biochar intermediate is subjected to medium-temperature secondary ripening and activation to obtain biochar modified heavy metal adsorbent.

2. The preparation method according to claim 1, characterized in that, In step (1), the biomass bulk material is one or more of the following: straw, sawdust, bamboo shavings, bagasse, coffee grounds, and rice husks.

3. The preparation method according to claim 1, characterized in that, In step (1), the acid leaching is performed by soaking in dilute hydrochloric acid with a mass concentration of 0.5-3% for 1-12 hours; the air drying temperature is 50-80℃, and the moisture content after air drying is less than 15%; crushing and sieving are performed to make the particle size less than 4 mm.

4. The preparation method according to claim 1, characterized in that, In step (2), the zinc salt, copper salt, ferrous salt and potassium salt in the combined molten salt activator are their respective chlorides. The mass ratio of the pretreated biomass raw material to the combined molten salt activator is 1:0.03 to 1:0.18, and the mass ratio of the zinc salt, copper salt, ferrous salt and potassium salt in the combined molten salt activator is 0.5 to 2:0.5 to 2:3 to 8:1 to 4.

5. The preparation method according to claim 1, characterized in that, In step (2), the protective atmosphere is nitrogen, argon or a mixture thereof, the high-temperature carbonization temperature is 500-900℃, and the carbonization time is 1-6h.

6. The preparation method according to claim 1, characterized in that, In step (3), the phosphorus-containing modifier is selected from one or more of the following industrial by-products: phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, potassium dihydrogen phosphate, and dipotassium hydrogen phosphate; the sulfur-containing modifier is selected from one or more of elemental sulfur, thiourea, sodium sulfide, ammonium sulfide, and sodium thiosulfate; the mass ratio of phosphorus in the porous biochar intermediate and the phosphorus-containing modifier to sulfur in the sulfur-containing modifier is 1:0.03-0.1:0.01-0.

2.

7. The preparation method according to claim 1, characterized in that, In step (3), the mechanical force method is mortar grinding, planetary ball milling, vibratory ball milling or stirring ball milling, the temperature is room temperature to 80℃, and the time is 5 to 240 min.

8. The preparation method according to claim 1, characterized in that, In step (4), the temperature for the medium-temperature secondary ripening and activation is 250–450℃, and the time is 0.5–6 h.

9. The biomass-modified carbon heavy metal adsorbent prepared by the preparation method according to any one of claims 1-8.

10. The application of the biomass-modified carbon heavy metal adsorbent according to claim 9, characterized in that, It is used for the deep purification treatment of wastewater or waste gas containing heavy metals; the heavy metals include one or more of mercury, thallium, chromium, and cadmium.