Nano zeolite / kaolin composite adsorbent as well as preparation method and application thereof

Abstract

The invention discloses a nano zeolite / kaolin composite adsorbent as well as a preparation method and application thereof. The preparation method comprises the following steps: preparing a modified ZSM-5 molecular sieve from nano zeolite; carrying out peptizing treatment on kaolin to obtain peptized kaolin; and carrying out composite granulation on the modified ZSM-5 molecular sieve and peptized kaolin, and carrying out grinding and graded screening to prepare the nano zeolite / kaolin composite adsorbent. The mineralization characteristic of kaolin and the ion screening function of the modified ZSM-5 molecular sieve are organically combined, a synergistic effect system of the nano zeolite / kaolin composite adsorbent is developed, lasting curing of heavy metal is achieved through structural reconstruction of a molecular level, the problems that the heavy metal concentration is increased and the leaching toxicity is high after the Xinjiang coal is subjected to blending combustion are solved, and the application prospect is wide. And the leaching toxicity reaches the standard requirement through lattice stabilization.

Description

Technical Field

[0001] The invention belongs to the field of nanocomposites, and relates to a nanozeolite / kaolin composite adsorbent, a preparation method thereof and an application thereof. Background Art

[0002] In recent years, with the continuous increase in the blending ratio of Xinjiang coal in power plants in the northwest region, due to the unique geological origin of Xinjiang coalfields (such as volcanic activities, continental sedimentation and deep fluid actions), the content of heavy metal elements (such as Cd, Pb, etc.) in its coal is generally higher than that in coalfields in North China and Northeast China. Among them, the cadmium (Cd) content in the Zhundong coalfield can reach 0.5 - 2.5 mg / kg, and the lead (Pb) content in the Yili coalfield is as high as 25 - 50 mg / kg, significantly exceeding the average value of commercial coal (Cd: 0.1 - 1.0 mg / kg, Pb: 10 - 30 mg / kg). During the combustion process, these heavy metals are easily transported with the flue gas, causing the risk of secondary pollution. In particular, Cd, due to its high volatility (>85% enters the gas phase) and strong toxicity, has been included in the key control list of the "Emission Standards for Air Pollutants from Thermal Power Plants".

[0003] However, with the accumulation of practical experience and the continuous improvement of environmental protection standards, the blending and disposal of coal in coal-fired power plants face severe challenges in popularization and application. Test data shows that the blending of Xinjiang coal will cause a sharp increase of 200% - 300% in the content of volatile heavy metals such as cadmium and lead in the flue gas. These heavy metal elements not only pose a serious threat to human health, but also have long-term adverse effects on the atmospheric environment. To address this problem, some conventional treatment technologies are mainly adopted in the industry at present, mainly by installing a wet flue gas desulfurization device at the tail or injecting an activated carbon adsorbent. However, these methods face many problems in practical applications. On the one hand, the operating costs of these methods are high, with an annual additional cost of about 1.8 - 3 million yuan per thousand tons of treatment volume, which is undoubtedly a heavy economic burden for coal-fired power plants. On the other hand, the adsorption efficiency of these methods is unstable, and the adsorption efficiency fluctuates between 40% - 60% under actual working conditions, making it difficult to achieve an ideal treatment effect. More seriously, these methods are also prone to problems such as secondary solid waste pollution during use.

[0004] Therefore, it is urgent to solve the problem of the sharp increase in heavy metal content during the blending of Xinjiang coal in existing coal-fired power plants. Summary of the Invention

[0005] The purpose of the invention is to provide a nanozeolite / kaolin composite adsorbent, a preparation method thereof and an application thereof, so as to solve the problems in the prior art that the adsorption efficiency of heavy metals in the blended flue gas is unstable and prone to secondary solid waste pollution.

[0006] To achieve the above purpose, the invention adopts the following technical solutions: A preparation method of a nanozeolite / kaolin composite adsorbent, comprising: Preparing a modified ZSM-5 molecular sieve using nanozeolite; Performing peptization treatment on kaolin to obtain peptized kaolin; Compounding and granulating the modified ZSM-5 molecular sieve and the peptized kaolin, and preparing the nanozeolite / kaolin composite adsorbent through grinding and classification screening.

[0007] Furthermore, the preparation process of preparing the modified ZSM-5 molecular sieve using the nanozeolite is as follows: Calcining the nanozeolite at 550 - 600 °C for 4 h to activate the nanozeolite; Preparing a solution according to a molar ratio of SiO2:Al2O2:TPAOH:H2O = 1:0.02:0.2:30, dispersing the activated nanozeolite in the prepared solution, performing ultrasonic treatment for 30 min, adding NaOH to adjust the pH to 10 - 11, and performing dynamic crystallization at 170 - 180 °C for 48 - 72 h; After filtering and washing the crystallized nanozeolite by suction, calcining it at 550 °C for 6 h to remove the TPAOH template and obtain the ZSM-5 molecular sieve; Exchanging the ZSM-5 molecular sieve with a 0.5 - 0.6 M NH4NO3 solution at a liquid-solid ratio of 8 - 10:1 at 80 °C for 3 times, 2 h each time, converting it into an H-type ZSM-5 molecular sieve, and calcining it at 500 °C for 3 h to prepare the modified ZSM-5 molecular sieve.

[0008] Furthermore, the peptization treatment process of the kaolin is as follows: Mixing kaolin with 3 M hydrochloric acid at a solid-liquid ratio of 1:5, refluxing and stirring at 90 °C for 4 h to perform acid washing on the kaolin; Mixing the acid-washed kaolin with a 0.5 M NaOH solution at a solid-liquid ratio of 1:3, performing ultrasonic treatment at 60 °C for 1 h, centrifuging and separating until the pH is neutral, drying at 105 °C until the moisture content < 2%, and crushing and sieving through a 200-mesh sieve to obtain the peptized kaolin.

[0009] Furthermore, the molar ratio of the modified ZSM-5 molecular sieve to the peptized kaolin is 1:3 - 5.

[0010] Furthermore, the pore diameter of the modified ZSM-5 molecular sieve is 2 - 5 nm.

[0011] Furthermore, the compounding granulation process is as follows: Mixing the modified ZSM-5 molecular sieve and the peptized kaolin, and adding 5 wt% silica sol and 2 wt% carboxymethyl cellulose; Extrusion granulation is carried out using a twin-screw extruder, with an extrusion pressure of 15 - 20 MPa, a forming humidity of 25 - 30%, and the resulting particle diameter is 2 - 3 mm; The obtained particles are kept at 600 °C for 2 h to form a stable Si-O-Al network structure, ground and sieved through a 200-mesh sieve to obtain the nanozeolite / kaolin composite adsorbent.

[0012] A nanozeolite / kaolin composite adsorbent prepared by the described preparation method, with the particle size of the nanozeolite / kaolin composite adsorbent ≤ 200 mesh.

[0013] Application of the described nanozeolite / kaolin composite adsorbent in the directional solidification of heavy metals exuded from the blended combustion of Xinjiang coal in coal-fired power plants. In the pre-treatment stage of blended combustion, the nanozeolite / kaolin composite adsorbent is uniformly mixed into the blended coal pulverized coal. After entering the incineration stage, the active silicon-aluminum components in the nanozeolite / kaolin composite adsorbent react with the free heavy metals in the incineration fly ash through melting-recrystallization reaction to realize the transformation of the heavy metal form from the exchangeable state to the residual state.

[0014] Furthermore, the mass of the nanozeolite / kaolin composite adsorbent is 1% - 6% of the mass of the blended coal.

[0015] Furthermore, the temperature in the incineration stage is 850 - 1050 °C.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a preparation method of a nanozeolite / kaolin composite adsorbent. Nanozeolite with a high specific surface area and strong adsorption activity and kaolin rich in silicon and aluminum are selected. By preparing the nanozeolite into a modified ZSM-5 molecular sieve with a size of 2 - 5 nm and compounding and granulating it with peptized kaolin, through precise proportion mixing, mechanical grinding and classification screening processes, a nanozeolite / kaolin composite adsorbent with a hierarchical pore structure is prepared. The present invention organically combines the mineralization characteristics of kaolin and the ion sieving function of the modified ZSM-5 molecular sieve, develops a synergistic action system of the nanozeolite / kaolin composite adsorbent, and fully exerts the synergistic adsorption characteristics of the two, which can greatly improve the heavy metal solidification efficiency.

[0017] The present invention also provides an application of a nano-zeolite / kaolin composite adsorbent in the directional solidification of heavy metals leached from Xinjiang coal blending in coal-fired power plants. In the combustion pretreatment stage, the nano-zeolite / kaolin composite adsorbent is evenly mixed into the coal powder. After entering the incineration link, under high temperature conditions, the active silicon-aluminum components in the nano-zeolite / kaolin composite adsorbent and the free Cd, Pb and other heavy metals in the incineration fly ash undergo a melting-recrystallization reaction, and are directional converted into a silicate aluminate mineral phase with a tetrahedral structure, forming a thermodynamically stable mullite-type lattice encapsulation structure, and realizing the transformation of the heavy metal form from an exchangeable state to a residual state. The present invention achieves the irreversible morphological transformation of heavy metals from an exchangeable state to a residual state by precisely controlling the adsorbent ratio and the incineration conditions, and utilizing the mullite lattice formed by high-temperature reconstruction of silicon-aluminum-based materials, significantly reducing the risk of environmental migration. The durable solidification of heavy metals is achieved through structural reconstruction at the molecular level, with the advantages of simple process flow, controllable operating costs and low risk of secondary pollution. The high-temperature in-situ solidification process of the present invention locks heavy metals in the mineral phase at the molecular level, combining the properties of deep solidification of heavy metals and resource utilization of fly ash, while meeting the environmental protection standards for hazardous waste landfills, and providing a new economical and efficient path for the safe utilization of solid waste.

[0018] The present invention verifies the toxicity leaching experiment of the fly ash generated by the final combustion, and the heavy metal leaching concentration reaches the limit value requirements of the "Hazardous Waste Landfill Pollution Control Standard" (GB 18598-2019), and has both process simplicity (adsorbent blending ratio <5%), stability and long-term effectiveness, and controllable treatment costs. It can be directly disposed of by anti-seepage safe landfill, or after activation treatment, it can be used as a roadbed material, ceramsite raw material, etc. to achieve resource utilization, and can replace the dependence on the exhaust gas purification system required by traditional technology. The equipment transformation cost is reduced by more than 50%, breaking through the limitation that traditional adsorption technology can only reduce the total concentration, and solving the problem of high leaching toxicity of heavy metals (such as Cd, Pb) in the fly ash after Xinjiang coal blending. Through lattice stabilization, the leaching toxicity reaches the GB5085.3-2007 standard requirements, which has significant engineering application value and provides an innovative solution for coal-fired power plants to achieve environmental protection standards for the coordinated disposal of fly ash. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 The present invention is a schematic diagram of the preparation method and application process of the nano-zeolite / kaolin composite adsorbent.

[0021] Figure 2 SEM-EDS diagram of heavy metals in fly ash particles after treatment by the present invention. Detailed implementation manners

[0022] To enable those skilled in the art to understand the features and effects of the present invention, the following will generally explain and define the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meanings understood by those skilled in the art for the present invention. In case of conflict, the definitions in this specification shall prevail.

[0023] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0024] In this article, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of a numerical range or percentage range should be considered to have covered and specifically disclosed all possible sub-ranges and individual values within the range (including integers and fractions).

[0025] In this article, unless otherwise specified, terms such as "comprising", "including", "containing", "having", or similar terms cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A only comprises a".

[0026] In this article, for the sake of brevity of description, all possible combinations of all technical features in each embodiment or example are not described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered to be within the scope described in this specification.

[0027] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0028] Conventional instruments and equipment in the art are used in the following examples. For the experimental methods without specific conditions noted in the following examples, they are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following examples. Unless otherwise stated, commercially available products are used, and their specifications are the conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0029] The present invention will be further described in detail below with reference to the accompanying drawings: The present invention provides a method for preparing a nanozeolite / kaolin composite adsorbent, which specifically includes the following steps: Step 1: Prepare a modified ZSM-5 molecular sieve using nanozeolite with a high specific surface area and strong adsorption activity. The pore diameter of the prepared modified ZSM-5 molecular sieve is 2-5 nm.

[0030] Among them, the preparation process of the modified ZSM-5 molecular sieve includes: 1. Activation of nanozeolite: Calcinate the nanozeolite at 550-600 °C for 4 h to remove surface organic impurities and expose active silicon-aluminum sites; 2. Hydrothermal synthesis: Prepare a solution according to the molar ratio of SiO2:Al2O2:TPAOH (tetrapropylammonium hydroxide):H2O = 1:0.02:0.2:30. Disperse the activated nanozeolite in the prepared solution, perform ultrasonic treatment for 30 min with a power of 300 W, add NaOH to adjust the pH to 10-11, and perform dynamic crystallization at 170-180 °C for 48-72 h with a stirring rate of 200 rpm; 3. Calcination: After filtering and washing the crystallized nanozeolite, calcine it at 550 °C for 6 h with a heating rate of 2 °C / min to remove the TPAOH template and form a stable microporous structure to obtain the ZSM-5 molecular sieve; 4. Modification: Exchange the ZSM-5 molecular sieve with a 0.5-0.6 M NH4NO3 solution at a liquid-solid ratio of 8-10:1 at 80 °C for 3 times, 2 h each time, to convert it into an H-type ZSM-5 molecular sieve; 5. Secondary calcination: Calcinate the H-type ZSM-5 molecular sieve at 500 °C for 3 h to prepare the modified ZSM-5 molecular sieve.

[0031] Step 2: Perform peptization treatment on silicon-rich and aluminum-rich kaolin to obtain peptized kaolin.

[0032] The peptization treatment process of kaolin is as follows: 1. Acid activation: Mix kaolin with 3 M hydrochloric acid at a solid-liquid ratio of 1:5, reflux and stir at 90 °C for 4 h to remove impurities such as Fe2O3; 2. Alkali digestion of kaolin: After pickling, the kaolin is ultrasonically treated with 0.5M NaOH solution at a solid-liquid ratio of 1:3 at 60 °C for 1 h, with a treatment frequency of 40 kHz, and centrifuged until the pH is neutral. 3. Drying: The treated kaolin is dried at 105 °C until the moisture content is <2%, crushed and sieved through a 200-mesh sieve to obtain de-gummed kaolin.

[0033] Step 3: The modified ZSM-5 molecular sieve and de-gummed kaolin are compounded and granulated at a molar ratio of 1:3 - 5. Through mechanical grinding and classification screening processes, the particle size is controlled to be ≤200 mesh to prepare a nano-zeolite / kaolin composite adsorbent.

[0034] The compound granulation process is as follows: 1. Compound ratio: The modified ZSM-5 and de-gummed kaolin are mixed, and 5 wt% silica sol is added as a binder and 2 wt% carboxymethyl cellulose is added as a pore-forming agent. 2. Extrusion: A twin-screw extruder is used for extrusion granulation. The extrusion pressure is 15 - 20 MPa, the forming humidity is 25 - 30%, and the obtained particle diameter is 2 - 3 mm. 3. Calcination: Heat up to 600 °C at a heating rate of 5 °C / min, and keep the obtained particles at 600 °C for 2 h to form a stable Si-O-Al network structure. 4. Screening: Grind and sieve through a 200-mesh sieve to obtain a nano-zeolite / kaolin composite adsorbent.

[0035] The nano-zeolite / kaolin composite adsorbent prepared by the present invention exhibits a unique "adsorption-bonding-lattice substitution" triple action mechanism in a laboratory-simulated combustion environment (850 - 1050 °C, oxidative atmosphere): Kaolin melts at high temperature to form a silicate-aluminate grid, providing a framework structure for heavy metal solidification; the modified ZSM-5 molecular sieve prepared from nano-zeolite selectively captures Cd 2+ (hydrated ionic radius 0.25 nm) and Pb 2+ (0.40 nm) through its regular pores of 2 - 5 nm, and anchors the heavy metals at the lattice sites through ion exchange. Particularly importantly, during the rapid cooling stage of combustion flue gas (50 - 80 °C per minute), the heavy metal ions will be locked in the non-equilibrium aluminosilicate glass phase to form a stable tetrahedral structure of [SiO4]-[AlO4]-[MO x .

[0036] The present invention also provides an application of the nano-zeolite / kaolin composite adsorbent in the directional solidification of heavy metals exuded from the co-combustion of Xinjiang coal in coal-fired power plants, specifically including: In the co-firing pretreatment stage, the nano-zeolite / kaolin composite adsorbent is uniformly mixed into the blended coal according to the ratio of 1% - 6% of the mass of the pulverized coal. Physical blending and mechanical stirring are used to ensure uniform solid-solid contact, creating a material basis for subsequent high-temperature reactions. After entering the incineration process, it is incinerated under high-temperature conditions of 850 - 1050 °C. The active silicon-aluminum components in the nano-zeolite / kaolin composite adsorbent react with free heavy metals such as Cd and Pb in the incineration fly ash through melting-recrystallization reactions, and are directionally transformed into silicate mineral phases with a tetrahedral structure, forming a thermodynamically stable mullite-type lattice wrapping structure, realizing the transformation of the heavy metal form from the exchangeable state to the residual state.

[0037] The following further describes the present invention in detail through specific examples: Example 1: 50 g of nano-Beta zeolite (SiO2 / Al2O3 = 25:1) with a high specific surface area and strong adsorption activity was pre-calcined at 600 °C for 4 h to activate the nano-zeolite. 500 mL of deionized water was added to 120 mL of TPAOH solution to prepare a solution. The activated nano-Beta zeolite was dispersed in the prepared solution, ultrasonicated for 30 min, 4.8 g of NaOH was added to adjust the pH to 10.5, and dynamically crystallized at 175 °C for 60 h with a stirring rate of 200 rpm. After the crystallized nano-Beta zeolite was filtered and washed, it was calcined at 550 °C for 6 h with a heating rate of 2 °C / min to remove the TPAOH template, obtaining ZSM-5 molecular sieve. The ZSM-5 molecular sieve and 0.6 M NH4NO3 solution were exchanged 3 times at a liquid-solid ratio of 8:1 at 80 °C for 2 h each time to be transformed into H-type ZSM-5 molecular sieve, and calcined at 500 °C for 3 h to prepare a modified ZSM-5 molecular sieve. The silicon-aluminum-rich kaolin was mixed with 3 M hydrochloric acid at a solid-liquid ratio of 1:5 and refluxed and stirred at 90 °C for 4 h for acid washing of the kaolin. The acid-washed kaolin and 0.5 M NaOH solution were ultrasonically treated at a solid-liquid ratio of 1:3 at 60 °C for 1 h, centrifuged until the pH was neutral, dried at 105 °C until the moisture content < 2%, and crushed through a 200-mesh sieve to obtain peptized kaolin. The modified ZSM-5 molecular sieve and peptized kaolin were mixed at a molar ratio of 1:3, and 5 wt% silica sol and 2 wt% carboxymethyl cellulose were added. Extrusion granulation was carried out using a twin-screw extruder with an extrusion pressure of 15 MPa and a forming humidity of 30%, and the obtained particles had a diameter of 3 mm. The obtained particles were kept at 600 °C for 2 h to form a stable Si-O-Al network structure, and through mechanical grinding and classification screening processes, the particle size was controlled to be ≤ 200 mesh to prepare the nano-zeolite / kaolin composite adsorbent.

[0038] In this example, the weight ratio of Xinjiang coal in the blended coal is 70%, and among them, Cd2+ The content of Pb is 50 mg / kg 2+ The content of [Cd] is 200 mg / kg. In the co - firing pretreatment stage, the nano - zeolite / kaolin composite adsorbent is uniformly mixed into the blended coal at a ratio of 3% of the mass of the pulverized coal. Through physical blending and mechanical stirring, solid - solid uniform contact is ensured to create a material basis for subsequent high - temperature reactions. After entering the incineration stage, it is incinerated at 850 °C for 2 h. After co - firing, the leaching concentration of Cd in the fly ash is reduced from 5 mg / L to 2 mg / L, and the leaching concentration of Pb is reduced from 10 mg / L to 4 mg / L. The leaching toxicity is reduced by more than 50%, achieving double control of the total heavy metal content and leaching toxicity. Through SEM - EDS analysis, it is found that the heavy metals in the treated fly ash particles show a uniform microcrystalline encapsulation morphology, as Figure 2 shown. The obvious characteristic peak of melilite (Ca2MgSi2O7) is detected by XRD, proving the formation of a thermodynamically stable mineral phase.

[0039] Example 2: The difference from Example 1 is that the modified ZSM - 5 molecular sieve and peptized kaolin are compounded and granulated at a molar ratio of 1:5. Through mechanical grinding and classification screening processes, the particle size is controlled to be ≤200 mesh, and the nano - zeolite / kaolin composite adsorbent is prepared.

[0040] In this example, the weight ratio of Xinjiang coal in the blended coal is 90%, where the content of Cd 2+ is 80 mg / kg, and the content of Pb 2+ is 300 mg / kg. In the co - firing pretreatment stage, the nano - zeolite / kaolin composite adsorbent is uniformly mixed into the blended coal at a ratio of 5% of the mass of the pulverized coal. Through physical blending and mechanical stirring, solid - solid uniform contact is ensured to create a material basis for subsequent high - temperature reactions. After entering the incineration stage, it is incinerated at 900 °C for 1.5 h. After co - firing, the leaching concentration of Cd in the fly ash is reduced from 8 mg / L to 3 mg / L, and the leaching concentration of Pb is reduced from 15 mg / L to 6 mg / L, and the leaching toxicity is reduced by more than 60%.

[0041] Example 3: The difference from Example 1 is that in the co - firing pretreatment stage, the nano - zeolite / kaolin composite adsorbent is uniformly mixed into the blended coal at a ratio of 6% of the mass of the pulverized coal. The specific surface area of the adsorbent detected by BET is 420 m 2 / g. At pH = 5 and 25 °C, the heavy metal adsorption capacity: Pb 2+ is 135 mg / g, and Cd 2+ is 98 mg / g.

[0042] Example 4: The difference from Example 1 is that the weight ratio of Xinjiang coal in the blended coal is 50%, and the Cd 2+ content is 60 mg / kg, and the Pb 2+ content is 250 mg / kg. The incineration process is carried out at 950 °C (oxidizing atmosphere, O2>6%) for 1.5 h, and then cooled by a water spray quenching system, and the cooling rate is 70 °C / min. After co-incineration, XRD shows that mullite (3Al2O3·2SiO2) and Cd / Pb-substituted aluminosilicate crystal phases are formed in the fly ash ([AlO4]-[CdO4] peak position shifts by 0.15°). For the TCLP leaching of fly ash: Cd 2+ 1.8 mg / L, a decrease of 70%, and Pb 2 + 3.2 mg / L, a decrease of 68%.

[0043] Example 5: The difference from Example 1 is that 5% of CeO2 is introduced to modify the ZSM-5 molecular sieve to enhance the Lewis acid sites, and then granulated after being compounded with kaolin, and the particle size is ≤150 mesh. The blended coal sample is pulverized coal with high Cl⁻ (1.2 wt%) (Cd 2+ content is 80 mg / kg, and Pb 2+ content is 300 mg / kg). The nano-zeolite / kaolin composite adsorbent is uniformly mixed into the blended coal according to the ratio of 4% of the pulverized coal mass, and incinerated at 900 °C for 1.5 h under high temperature conditions. After co-incineration, the leaching toxicity of Cd / Pb in the fly ash is reduced to 0.9 mg / L and 2.1 mg / L respectively.

[0044] Example 6: The difference from Example 1 is that the weight ratio of Xinjiang coal in the blended coal is 30% (Cd 2+ content is 40 mg / kg, and Pb 2+ content is 180 mg / kg). In the co-incineration pretreatment stage, the nano-zeolite / kaolin composite adsorbent is uniformly mixed into the blended coal according to the ratio of 1.5% of the pulverized coal mass, and the specific surface area of the adsorbent is 420 m 2 / g. The incineration process is carried out at 850 °C for 1.5 h; then cooled by a nitrogen curtain slow cooling, and the cooling rate is 50 °C / min. After co-incineration, the heavy metal fixation rate of the fly ash is Cd 2+ 91.2%, and Pb 2+ 94.5%, and the treatment capacity per unit adsorbent is increased by 3 times.

[0045] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a nano zeolite / kaolin composite adsorbent, characterized in that: include: Preparation of modified ZSM-5 molecular sieve using nano zeolite; Performing degumming treatment on kaolin to obtain degummed kaolin; The modified ZSM-5 molecular sieve and the degelled kaolin are composited into granules, and the nano-zeolite / kaolin composite adsorbent is prepared by grinding and grading.

2. The method for preparing a nano zeolite / kaolin composite adsorbent according to claim 1, characterized in that: The preparation process of the nano zeolite to prepare the modified ZSM-5 molecular sieve is: The nano-zeolite was activated by calcining the nano-zeolite at 550-600°C for 4 hours; Prepare a solution with a molar ratio of SiO2:Al2O2:TPAOH:H2O=1:0.02:0.2:30, disperse the activated nano zeolite in the prepared solution, treat with ultrasound for 30 min, add NaOH to adjust the pH to 10-11, and dynamically crystallize at 170-180°C for 48-72 h; The crystallized nano-zeolite was filtered and washed, and then calcined at 550°C for 6 h to remove the TPAOH template and obtain the ZSM-5 molecular sieve. The ZSM-5 molecular sieve was exchanged with 0.5~0.6M NH4NO3 solution at a liquid-to-solid ratio of 8~10:1 at 80°C for 3 times, each time for 2 hours, converted into H-type ZSM-5 molecular sieve, and calcined at 500°C for 3 hours to prepare a modified ZSM-5 molecular sieve.

3. The method for preparing a nano zeolite / kaolin composite adsorbent according to claim 1, characterized in that: The degumming process of the kaolin is as follows: Kaolin was mixed with 3M hydrochloric acid at a solid-liquid ratio of 1:5, and refluxed and stirred at 90°C for 4 h to acid-wash the kaolin; The acid-washed kaolin and 0.5M NaOH solution were ultrasonically treated at 60°C for 1 h at a solid-liquid ratio of 1:3, centrifuged until the pH was neutral, dried at 105°C to a moisture content of <2%, and crushed through a 200-mesh sieve to obtain degelled kaolin.

4. The method for preparing a nano zeolite / kaolin composite adsorbent according to claim 1, characterized in that: The molar ratio of the modified ZSM-5 molecular sieve to the degelled kaolin is 1:3-5.

5. The method for preparing the nano zeolite / kaolin composite adsorbent according to claim 1, characterized in that: The pore size of the modified ZSM-5 molecular sieve is 2-5 nm.

6. The method for preparing a nano zeolite / kaolin composite adsorbent according to claim 1, characterized in that: The composite granulation process is: The modified ZSM-5 molecular sieve was mixed with degelled kaolin, and 5wt% silica sol and 2wt% carboxymethyl cellulose were added; A twin-screw extruder is used for extrusion granulation, the extrusion pressure is 15-20 MPa, the molding humidity is 25-30%, and the obtained particle diameter is 2-3 mm; The obtained particles were kept at 600°C for 2 hours to form a stable Si-O-Al network structure, and then ground and passed through a 200-mesh sieve to obtain a nano-zeolite / kaolin composite adsorbent.

7. A nano zeolite / kaolin composite adsorbent prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The particle size of the nano zeolite / kaolin composite adsorbent is ≤200 meshes.

8. The use of the nano-zeolite / kaolin composite adsorbent according to claim 7 in the directional solidification of heavy metals leached from Xinjiang coal in coal-fired power plants, characterized in that: In the pretreatment stage of incineration, the nano zeolite / kaolin composite adsorbent is evenly mixed into the mixed coal. After entering the incineration stage, the active silicon-aluminum components in the nano zeolite / kaolin composite adsorbent undergo a melting-recrystallization reaction with the free heavy metals, realizing the transformation of the heavy metal form from the exchangeable state to the residual state.

9. The use of the nano-zeolite / kaolin composite adsorbent according to claim 8 in the directional solidification of heavy metals leached from Xinjiang coal in coal-fired power plants, characterized in that: The mass of the nano-zeolite / kaolin composite adsorbent is 1% to 6% of the mass of the mixed coal.

10. The use of the nano-zeolite / kaolin composite adsorbent according to claim 8 in the directional solidification of heavy metals leached from Xinjiang coal blending in coal-fired power plants, characterized in that: The temperature of the incineration stage is 850~1050℃.

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