Integrated flue gas multi-pollutant adsorbent based on alkaline sludge as well as preparation method and application of integrated flue gas multi-pollutant adsorbent

Abstract

The invention discloses a flue gas multi-pollutant integrated adsorbent based on alkaline sludge as well as a preparation method and application of the flue gas multi-pollutant integrated adsorbent based on alkaline sludge, low-value treated sludge is converted into a functional environment-friendly material with a high additional value, and closed-loop circulation and resource upgrading of waste in a power plant are realized; the raw materials are almost zero-cost wastes, and the main processing cost is low-medium-temperature hydrothermal and calcining processes and is far lower than that of purchasing commercial activated carbon or a special mercury removal catalyst; meanwhile, the two environmental protection problems of water treatment sludge treatment and flue gas deep purification are solved, and the requirements of circular economy and clean production are met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial solid waste resource utilization and air pollution control, and particularly relates to a flue gas multi-pollutant integrated adsorbent based on alkaline sludge and a preparation method and application thereof. BACKGROUND

[0002] A large amount of alkaline sludge mainly composed of calcium carbonate (CaCO3), magnesium hydroxide (Mg(OH)2) and a small amount of silicates and aluminates is generated in the double-alkali softening process of circulating water in a thermal power plant. The current mainstream disposal method is landfill after dewatering, which not only occupies land and consumes disposal costs, but also fails to realize effective utilization of the rich calcium and magnesium resources. At the same time, the flue gas treatment is facing the pressure of simultaneous control of multiple pollutants, and in particular, the deep removal of SO3 acid mist (leading to the "blue smoke" phenomenon and equipment corrosion) and heavy metal mercury is still a technical difficulty.

[0003] In the prior art, there are studies on the preparation of flue gas desulfurization agents using natural limestone, slaked lime or industrial by-products. However, the effect of directly using untreated alkaline sludge is very poor due to its small specific surface area, undeveloped pores and low reactivity. There are also studies on the preparation of calcium-based materials by high-temperature calcination of sludge, but the energy consumption is high, and the low-temperature desulfurization active component of Mg(OH)2 is destroyed. At present, there is a lack of a technology that can convert double-alkali sludge into a special adsorbent suitable for the integrated removal of multiple pollutants in flue gas at low cost and high efficiency.

[0004] Therefore, it is of great significance to develop a process for converting alkaline sludge into high-value flue gas purification materials by directional activation and modification, so as to realize waste treatment with waste in thermal power plants and reduce the comprehensive cost of environmental protection. SUMMARY

[0005] The present application aims to at least partially solve one of the technical problems in the related art.

[0006] To this end, an embodiment of the present application proposes a flue gas multi-pollutant integrated adsorbent based on alkaline sludge and a preparation method and application thereof.

[0007] In a first aspect, the present application proposes a preparation method of a flue gas multi-pollutant integrated adsorbent based on alkaline sludge, comprising the following steps: (1) drying, dewatering, crushing and grinding the double-alkali alkaline sludge, and then analyzing the CaO and MgO contents thereof, and adjusting the contents according to the required molar ratio of calcium to magnesium to obtain an adjusted powder; (2) mixing the adjusted powder, a pore former and water to prepare a slurry, and placing the slurry in a high-pressure reaction kettle for hydrothermal reaction, and then washing and filtering the slurry to obtain a filter cake; (3) dispersing the filter cake in a solution containing a precursor of an active component, impregnating or co-precipitating in equal volume, and drying to obtain a modified powder; (4) mixing the modified powder with a binder to form a granule, and calcining under inert gas to obtain an adsorbent.

[0008] Further, in step (1), the double-alkali method basic sludge is dried, water is removed, crushed, and ground to 150 mesh or more.

[0009] Further, in step (1), the temperature for drying and removing water is 105-120°C, and the time is 4-10h.

[0010] Further, in step (1), the calcium-magnesium molar ratio is adjusted by adding quicklime (CaO) or light-burned magnesium oxide (MgO), and the calcium-magnesium molar ratio is 1:1-4:1.

[0011] Further, in step (2), the temperature for hydrothermal reaction is 120-200°C, and the time is 2-8h.

[0012] Further, the pore-forming agent is a thermally decomposable organic matter or an inorganic salt, the thermally decomposable organic matter includes at least one of urea, sodium carboxymethyl cellulose, and the inorganic salt includes at least one of sodium chloride and ammonium bicarbonate.

[0013] Further, the addition amount of the pore-forming agent is 5%-20% of the mass of the adjusted powder.

[0014] Further, the solution containing a precursor of an active component includes 0.5-5wt% of a halide and 2-8wt% of a transition metal oxide precursor, wherein the halide includes at least one of NaCl and KI, and the transition metal oxide precursor includes at least one of Fe(NO3)3 and Cu(NO3)2.

[0015] Further, the solution containing a precursor of an active component further includes 1-5wt% of an alkaline strengthening component, and the alkaline strengthening component includes at least one of Na2CO3 and KOH.

[0016] Further, in step (3), the temperature for drying is 80-120°C, and the time is 4-12h.

[0017] Further, the addition amount of the binder is 3%-10% of the mass of the modified powder.

[0018] Further, the particle size of the granule is 1-5mm.

[0019] Further, in step (4), the calcination temperature is 300-500°C, and the time is 0.5-2h.

[0020] Further, the inert gas is one of nitrogen and argon.

[0021] In a second aspect, the present application provides a flue gas multi-pollutant integrated adsorbent prepared by the method of the first aspect, wherein the specific surface area of the adsorbent is 50-150 m 2 / g.

[0022] In a third aspect, the present application provides an application of the flue gas multi-pollutant integrated adsorbent prepared by the method of the first aspect or the flue gas multi-pollutant integrated adsorbent of the second aspect in simultaneous removal of sulfur dioxide, sulfur trioxide acid mist and heavy metal mercury in coal-fired flue gas.

[0023] Compared with the prior art, the present application has the following beneficial effects: The present application converts low-value disposal sludge into high-value functional environmental protection materials, realizes closed-loop circulation and resource upgrading of internal waste of power plants, and solves the problems of water treatment sludge disposal and flue gas deep purification.

[0024] The adsorbent of the present application has the functions of chemical adsorption (Ca / Mg component removes SO2 / SO3), physical adsorption (porous structure) and catalytic oxidation (transition metal / halogen removes mercury), and shows integrated and cooperative removal capacity. 0 In a suitable temperature range, the SO2 removal rate is >90%, the SO3 removal rate is >95%, and the gaseous mercury removal rate is >75%. BRIEF DESCRIPTION OF DRAWINGS

[0025] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description, taken in conjunction with the accompanying drawings, in which: Figure 1 The present application provides a preparation method of a flue gas multi-pollutant integrated adsorbent based on alkaline sludge. DETAILED DESCRIPTION

[0026] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, in which the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present application, and cannot be understood as limiting the present application.

[0027] The present application provides a flue gas multi-pollutant integrated adsorbent based on alkaline sludge, a preparation method thereof and an application thereof.

[0028] As Figure 1 shown, the preparation method of the flue gas multi-pollutant integrated adsorbent based on alkaline sludge of the application comprises the following steps: (1) After drying, removing water, crushing and grinding the double-alkali method alkaline sludge, analyze the CaO and MgO content, and according to the required calcium-magnesium molar ratio of the adsorbent, the adjusted powder is obtained; (2) The adjusted powder, pore-forming agent and water are mixed to form a slurry, which is placed in a high-pressure reaction kettle for hydrothermal reaction. After the reaction is completed, the filter cake is obtained by washing and filtering; (3) The filter cake is dispersed in a solution containing an active component precursor, and after equal volume impregnation or co-precipitation, the modified powder is obtained by drying; (4) The modified powder is mixed with a binder to form a particle, which is calcined under inert gas to obtain the adsorbent.

[0029] Among them, step (1) is the raw material pretreatment and adjustment process. The raw material pretreatment process is to dry, remove water, crush and grind the double-alkali method alkaline sludge to more than 150 mesh to obtain a powder. The drying temperature is 105-120℃, and the time is 4-10h.

[0030] The adjustment process is to analyze the CaO and MgO content in the powder, and to adjust the powder according to the required calcium-magnesium molar ratio of the adsorbent to obtain the adjusted powder. The calcium-magnesium molar ratio is adjusted by adding low-cost quicklime (CaO) or light-burned magnesium oxide (MgO), and the calcium-magnesium molar ratio is 1:1-4:1.

[0031] It should be noted here that in the field of materials science and inorganic chemical industry, when the composition of substances containing calcium and magnesium is quantitatively analyzed (such as X-ray fluorescence spectroscopy XRF and chemical titration method), regardless of their original form of carbonate, hydroxide or silicate, the final result is usually converted and reported as the mass percentage of CaO and MgO. This is an internationally accepted standard reporting format, which facilitates comparison and calculation of data from different sources. The calcium and magnesium in the raw sludge are not 100% in the form of pure CaCO3 and Mg(OH)2, and a part of them may exist in other forms (such as calcium silicate and calcium sulfate), and the report of CaO and MgO is a form-independent total amount expression, which is more accurate and stable.

[0032] Step (2) is the hydrothermal activation and pore expansion process. The adjusted powder, pore-forming agent and water are mixed to form a slurry, which is placed in a high-pressure reaction kettle for hydrothermal reaction. After the reaction is completed, the filter cake is obtained by washing and filtering.

[0033] The slurry has a solid content of 10%~30%. It is placed in a high-pressure reactor and subjected to hydrothermal reaction at 120-200℃ and autogenous pressure for 2-8 hours. CaCO3 and Mg(OH)2 react with impurities such as silicates, transforming amorphous CaCO3 and Mg(OH)2 into highly active nanosheet or needle-like hydrated calcium silicate (CSH) gels and hydrotalcite (LDH) precursors, significantly increasing specific surface area and active sites.

[0034] The main reaction process is as follows: (1) Formation of hydrated calcium silicate (CSH) gel, the main reaction is: xCa 2+ + 2xOH - + ySiO3 2- + mH2O →(CaO)x·(SiO2)y·(H2O)m (CSH gel). Ca 2+ With SiO3 2- Ions combine in solution to form short-chain calcium silicate hydrate cores. These cores grow in an amorphous or very low-crystallinity manner, connecting to form nanoscale sheet-like, fibrous, or network structures. The Ca / Si ratio (x / y) is modulated by the ion concentration ratio and pH value in the solution. CSH gels are amorphous or semi-crystalline, possessing a large internal surface area and abundant silanol (-Si-OH) and calcium hydroxyl (Ca-OH) active sites.

[0035] (2) Formation of hydrotalcite-like (LDHs) structures, the main reaction being: 6Mg 2+ + 2AlO2 - + 16OH - + CO3 2- + 4H₂O → [Mg₆Al₂(OH)₂] 16 CO3·4H2O(s). Mg 2+ and AlO2 - In an alkaline environment, it reacts with interlayer anions (CO3). 2- (From air or dissolved carbonates) Mg is assembled together. 2+ And Al 3+ (from AlO2) - Hydrolysis produces) and OH - Forming positively charged [M] 1-x M' x (OH)2] x + Layered plates (M=Mg, M'=Al), with CO3 passing between the layers. 2- By balancing the charges, water molecules fill the gaps, eventually crystallizing and growing into a regular nanolayered structure. LDHs are highly crystalline nanosheets with adjustable layers (e.g., Mg / Al ratio) and exchangeable anions between layers.

[0036] During growth, CSH nanofibers / sheets and LDH nanosheets interweave, support, and encapsulate each other, forming a "reinforced concrete"-like composite that endows the material with excellent mechanical strength. The disordered stacking of these nanoparticles naturally generates abundant mesopores (2-50 nm). Simultaneously, the previously added pore-forming agents decompose or dissolve at this stage, synergistically creating a hierarchical pore structure. The surface of the final product is covered with Si-OH / Ca-OH from CSH, Mg-OH / Al-OH from LDHs, and exchangeable anions between layers, constituting a multifunctional adsorption and catalytic active surface.

[0037] If CaO or MgO was used in the preparation process in step (1), CaO or MgO can provide highly active reaction precursors during the hydrothermal reaction, driving the hydrothermal reaction: the original sludge CaCO3 and Mg(OH)2 have relatively low reactivity and slow dissolution under low-temperature hydrothermal conditions. The supplemented CaO and MgO react rapidly and violently upon contact with water, providing a high concentration of Ca. 2+ Mg 2+ and OH - The addition of ions greatly accelerates the kinetics of subsequent reactions. On one hand, it creates a strongly alkaline environment, promoting the dissolution and reaction of silicon and aluminum impurities: the hydration of the supplemented oxides (especially CaO) significantly increases the pH of the hydrothermal system (up to >12). In this strongly alkaline, high-temperature, and high-pressure environment, the originally inert amorphous SiO2, silicates, and aluminates in the sludge become soluble, with silicate ions (SiO3) forming the soluble form. 2- ), aluminate (AlO2) - The silicon and aluminum sources are introduced into the liquid phase in the form of calcium silicate hydrate (CSH) gel and magnesium aluminum layered double hydroxides (LDHs), providing essential silicon and aluminum sources for the subsequent generation of high-value-added hydrated calcium silicate (CSH) gel and magnesium aluminum layered double hydroxides (LDHs). On the other hand, the pore structure can be refined and stabilized through a dissolution-precipitation process. The dissolution-reprecipitation process of highly active Ca(OH)2 and Mg(OH)2 under hydrothermal conditions is itself a delicate "pore-forming" and "structural reorganization" process. The newly formed CSH and LDH nanocrystals overlap each other during growth, naturally forming abundant mesopores (2-50 nm) and some macropores. The addition of oxides ensures that this process is fully and uniformly carried out, thereby stabilizing and optimizing the pore structure generated by the previous physical pore-forming agent (such as urea).

[0038] The pore-forming agent is a thermally decomposable organic compound or inorganic salt. The thermally decomposable organic compound includes at least one of urea and sodium carboxymethyl cellulose, and the inorganic salt includes at least one of sodium chloride and ammonium bicarbonate. The amount of pore-forming agent added is 5% to 20% of the mass of the prepared powder.

[0039] Step (3) is the process of surface modification and loading of active components. The filter cake is dispersed in a solution containing the precursor of active components. The active components are loaded onto the surface and pores of the material by equal volume impregnation or co-precipitation. Then, the modified powder is obtained by drying.

[0040] In some embodiments, the active component precursor includes a halide and a transition metal oxide precursor, wherein the halide is used to provide halide ions to promote Hg 0 Oxidation and fixation: Transition metal oxide precursors are used to provide redox active sites for the catalytic oxidation of SO2 and Hg. 0 .

[0041] The halide includes at least one of NaCl and KI, and the transition metal oxide precursor includes at least one of Fe(NO3)3 and Cu(NO3)2.

[0042] The mass fraction of halides in the solution containing the active component precursor is 0.5% to 5%, and the mass fraction of transition metal oxide precursor is 2% to 8%.

[0043] In some embodiments, the active component precursor further includes an alkaline enhancement component to further enhance the chemisorption capacity for acidic gases. The alkaline enhancement component includes at least one of Na₂CO₃ and KOH, and the mass fraction of the alkaline enhancement component in the solution containing the active component precursor is 1% to 5%.

[0044] Understandably, alkaline enhancement components are not necessary. If the raw sludge itself has extremely high calcium and magnesium content (for example, sludge from high-hardness water), and the calcium-magnesium substrate formed after hydrothermal activation is already sufficiently alkaline, then no additional alkaline enhancer needs to be added. Otherwise, it is necessary to add one.

[0045] In some embodiments, the drying temperature in step (3) is 80~120℃ and the time is 4~12h.

[0046] Step (4) is the molding and activation process. The modified powder is mixed with the binder and then formed into particles with a particle size of 1~5mm by extrusion or rolling granulation. The adsorbent is obtained by calcination under an inert gas.

[0047] The binder includes at least one of bentonite and silica sol, and the amount of the binder added is 3% to 10% of the mass of the modified powder.

[0048] The calcination temperature is 300~500℃, the time is 0.5~2h, and the inert gas is either nitrogen or argon. The calcination process removes residual organic matter, stabilizes the pore structure, and avoids excessive decomposition of Mg(OH)2, forming a porous composite calcium-magnesium-based flue gas purification adsorbent as the final product.

[0049] The adsorbent of this invention is prepared by the method of this invention. The adsorbent is a porous particle with a specific surface area of ​​50-150 m². 2 / g, with well-developed pores and a surface rich in basic sites, halogen sites, and active centers of transition metal oxides.

[0050] The adsorbent of this invention is used for the simultaneous removal of sulfur dioxide, sulfuric acid trioxide mist, and heavy metal mercury from coal-fired flue gas. The application method involves loading the adsorbent prepared according to this invention into a fixed-bed adsorption tower or moving-bed system, placing it in a suitable location in the flue gas duct after the flue gas dust collector and before the flue gas heat exchanger (flue gas temperature window 150-250℃). After adsorption saturation, the adsorbent can be used as a supplementary calcium source for desulfurization gypsum production or safely landfilled (because the mercury has been stably fixed, the leaching risk is low).

[0051] The present invention will be described below with reference to specific embodiments. Example 1 Take 1 kg of dry sludge powder from a power plant's dual-alkali process (CaO content 40%, MgO content 25%), add lightly calcined MgO powder to adjust the Ca:Mg molar ratio to 2:1. Mix with deionized water to form a 20% slurry, add 5 wt% urea as a pore-forming agent, and react in a high-pressure reactor at 180℃ for 4 hours.

[0052] After the reaction, the mixture was filtered, and the filter cake was immersed in a solution containing 5% Fe(NO3)3 and 3% KI for 2 hours before filtration.

[0053] The obtained material was mixed with 5% bentonite and granulated to a particle diameter of Φ3mm. The granules were then calcined at 400℃ under a N2 atmosphere for 1 hour to obtain the finished adsorbent.

[0054] In simulated flue gas (containing SO2 2000ppm, SO3 50ppm, Hg) 0 20 μg / m 3 In a balanced atmosphere of 5% O2 and 3% N2, the gas was tested at 180°C with a space velocity of 3000 h⁻¹. -1 Its breakthrough time (based on an outlet SO2 concentration > 200 ppm) exceeds 24 hours, SO2 removal rate > 90%, SO3 removal rate > 95%, and simultaneous mercury removal efficiency is stable at over 85%.

[0055] Example 2 Take 1 kg of dry sludge powder from a power plant's dual-alkali process (CaO content 40%, MgO content 25%), add lightly calcined MgO powder to adjust the Ca:Mg molar ratio to 2:1. Mix with deionized water to form a 20% slurry, add 5 wt% ammonium bicarbonate as a pore-forming agent, and react in a high-pressure reactor at 180℃ for 4 hours.

[0056] After the reaction, the mixture was filtered, and the filter cake was immersed in a solution containing 5% Fe(NO3)3 and 3% KI for 2 hours before filtration.

[0057] The obtained material was mixed with 5% bentonite and granulated to a particle diameter of Φ3mm. The granules were then calcined at 400℃ under a N2 atmosphere for 1 hour to obtain the finished adsorbent.

[0058] In simulated flue gas (containing SO2 2000ppm, SO3 50ppm, Hg) 0 20 μg / m 3 In a balanced atmosphere of 5% O2 and 3% N2, the gas was tested at 180°C with a space velocity of 3000 h⁻¹. -1 SO2 removal rate >90%, SO3 removal rate >95%, and simultaneous mercury removal efficiency is consistently above 75%.

[0059] Example 3 Take 1 kg of dry sludge powder from a power plant's dual-alkali process (CaO content 40%, MgO content 25%), add lightly calcined MgO powder to adjust the Ca:Mg molar ratio to 2:1. Mix with deionized water to form a 20% slurry, add 5 wt% urea as a pore-forming agent, and react in a high-pressure reactor at 180℃ for 4 hours.

[0060] After the reaction, the mixture was filtered, and the filter cake was immersed in a solution containing 5% Cu(NO3)2 and 3% KI for 2 hours before filtration.

[0061] The obtained material was mixed with 5% bentonite and granulated to a particle diameter of Φ3mm. The granules were then calcined at 400℃ under a N2 atmosphere for 1 hour to obtain the finished adsorbent.

[0062] In simulated flue gas (containing SO2 2000ppm, SO3 50ppm, Hg) 0 20 μg / m 3 In a balanced atmosphere of 5% O2 and 3% N2, the gas was tested at 180°C with a space velocity of 3000 h⁻¹. -1 SO2 removal rate >80%, SO3 removal rate >95%, and simultaneous mercury removal efficiency is consistently above 85%.

[0063] Comparative Example 1 Take 1 kg of dry sludge powder from a power plant's dual-alkali process (CaO content 40%, MgO content 25%), add lightly calcined MgO powder to adjust the Ca:Mg molar ratio to 2:1. Mix with deionized water to form a 20% slurry, add 5 wt% urea as a pore-forming agent, and react in a high-pressure reactor at 180℃ for 4 hours.

[0064] After the reaction, the mixture was filtered, and the filter cake was immersed in a 3% KI solution for 2 hours before filtration.

[0065] The obtained material was mixed with 5% bentonite and granulated to a particle diameter of Φ3mm. The granules were then calcined at 400℃ under a N2 atmosphere for 1 hour to obtain the finished adsorbent.

[0066] In simulated flue gas (containing SO2 2000ppm, SO3 50ppm, Hg) 0 20 μg / m 3 In a balanced atmosphere of 5% O2 and 3% N2, the gas was tested at 180°C with a space velocity of 3000 h⁻¹. -1 SO2 removal rate >90%, SO3 removal rate >95%, and simultaneous mercury removal efficiency between 40% and 60%.

[0067] Comparative Example 2 Take 1 kg of dry sludge powder from a power plant's dual-alkali process (CaO content 40%, MgO content 25%), add lightly calcined MgO powder to adjust the Ca:Mg molar ratio to 2:1. Mix with deionized water to form a 20% slurry, add 5 wt% urea as a pore-forming agent, and react in a high-pressure reactor at 180℃ for 4 hours.

[0068] After the reaction, the filter cake was filtered and then immersed in a solution containing 5% Fe(NO3)3 for 2 hours before filtration.

[0069] The obtained material was mixed with 5% bentonite and granulated to a particle diameter of Φ3mm. The granules were then calcined at 400℃ under a N2 atmosphere for 1 hour to obtain the finished adsorbent.

[0070] In simulated flue gas (containing SO2 2000ppm, SO3 50ppm, Hg) 0 20 μg / m 3 In a balanced atmosphere of 5% O2 and 3% N2, the gas was tested at 180°C with a space velocity of 3000 h⁻¹. -1 SO2 removal rate >85%, SO3 removal rate >95%, and simultaneous mercury removal efficiency between 40% and 60%.

[0071] As can be seen from Examples 1-3 and Comparative Examples 1 and 2, when only halides or only transition metal oxide precursors are used to modify the powder, it is not conducive to the long-term stable removal of mercury. It is necessary to use both in combination to achieve the optimal synergistic removal efficiency of SO2, SO3 and Hg.

[0072] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms may refer to different embodiments or examples. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0073] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0074] Although embodiments of the invention have been shown and described, those skilled in the art will understand 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 claims and their equivalents.

Claims

1. A method for preparing an integrated multi-pollutant adsorbent for flue gas based on alkaline sludge, characterized in that, Includes the following steps: (1) After drying, dewatering, crushing and grinding the alkaline sludge of the double alkali method, analyze its CaO and MgO content, and adjust the powder according to the required calcium-magnesium molar ratio of the adsorbent. (2) The prepared powder, pore-forming agent and water are mixed to form a slurry, which is placed in a high-pressure reactor for hydrothermal reaction. After the reaction is completed, the filter cake is obtained by washing and filtering. (3) The filter cake is dispersed in a solution containing the active component precursor, impregnated or co-precipitated in equal volume, and then dried to obtain the modified powder; (4) The modified powder is mixed with the binder to form particles, which are then calcined under an inert gas to obtain the adsorbent.

2. The method as described in claim 1, characterized in that, In step (1), the alkaline sludge produced by the double alkali method is dried, dehydrated, crushed, and ground to a mesh size of 150 or higher. And / or, the drying temperature in step (1) is 105~120℃ and the time is 4~10h; And / or, in step (1), the calcium-magnesium molar ratio is adjusted by adding quicklime (CaO) or lightly calcined magnesium oxide (MgO), and the calcium-magnesium molar ratio is 1:1 to 4:

1.

3. The method as described in claim 1, characterized in that, The hydrothermal reaction in step (2) is carried out at a temperature of 120~200℃ for 2~8 hours. And / or, the pore-forming agent is a thermally decomposable organic compound or an inorganic salt, wherein the thermally decomposable organic compound includes at least one of urea and sodium carboxymethyl cellulose, and the inorganic salt includes at least one of sodium chloride and ammonium bicarbonate; And / or, the amount of the pore-forming agent added is 5% to 20% of the mass of the prepared powder.

4. The method as described in claim 1, characterized in that, The solution containing the active component precursor includes 0.5-5 wt% of a halide and 2-8 wt% of a transition metal oxide precursor, wherein the halide includes at least one of NaCl and KI, and the transition metal oxide precursor includes at least one of Fe(NO3)3 and Cu(NO3)2.

5. The method as described in claim 4, characterized in that, The solution containing the active component precursor also includes 1-5 wt% of an alkaline strengthening component, wherein the alkaline strengthening component includes at least one of Na2CO3 and KOH.

6. The method as described in claim 1, characterized in that, The drying temperature in step (3) is 80~120℃ and the time is 4~12h.

7. The method as described in claim 1, characterized in that, The amount of binder added is 3% to 10% of the mass of the modified powder; And / or, the particle size is 1~5mm.

8. The method as described in claim 1, characterized in that, In step (4), the calcination temperature is 300~500℃ and the time is 0.5~2h; And / or, the inert gas is one of nitrogen or argon.

9. A multi-pollutant integrated adsorbent for flue gas based on alkaline sludge, characterized in that, The adsorbent is prepared by the method according to any one of claims 1 to 8, wherein the specific surface area of ​​the adsorbent is 50 to 150 m². 2 / g.

10. The application of the adsorbent prepared by the method according to any one of claims 1 to 8 or the adsorbent according to claim 9 in the simultaneous removal of sulfur dioxide, sulfuric acid trioxide mist and heavy metal mercury in coal-fired flue gas.

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