A composite structure adsorbent for solidifying heavy metals in solid waste thermal treatment and its preparation method

Abstract

This invention relates to the field of adsorbent technology, and in particular to a composite structure adsorbent for solidifying heavy metals in solid waste thermal treatment and its preparation method. The composite structure adsorbent of this invention uses spherical ultrafine fly ash as the core and zeolite as the outer shell; the zeolite is obtained by hydrothermal reaction of broken-shell ultrafine fly ash after alkali melting. This invention combines the high-temperature resistance of fly ash, the physical adsorption of the outer shell zeolite material, and the chemical solidification effect of the core high-volcanic ash material to successfully prepare a composite structure adsorbent material that can efficiently solidify heavy metals under high-temperature conditions. This improves the solidification rate of heavy metals under solid waste thermal treatment conditions such as cement kiln co-processing and incinerators, ensuring the environmental safety of solid waste thermal treatment processes.

Description

Technical Field

[0001] This invention relates to the field of adsorbent technology, and in particular to a composite structure adsorbent for solidifying heavy metals in the thermal treatment of solid waste and its preparation method. Background Technology

[0002] Combustible solid wastes such as municipal solid waste, oil sludge, industrial solid waste, agricultural solid waste, sewage sludge, and medical waste can be thermally treated using specialized incinerators and cement kiln co-processing technologies to achieve waste reduction, harmlessness, and resource recovery. However, most wastes contain certain amounts of heavy metals such as lead (Pb), cadmium (Cd), zinc (Zn), arsenic (As), barium (Ba), and copper (Cu). If these heavy metals are not effectively solidified in ash, they will migrate into the atmosphere and soil, causing direct pollution and harming the ecological environment and human health. In particular, semi-volatile heavy metals (Pb, Cd, Zn) will partially volatilize into the gaseous phase under the high-temperature environment of thermal treatment. When the flue gas temperature decreases, these heavy metal vapors will condense into fine particles through homogeneous or heterogeneous nucleation, suspended in the flue gas, with a very low proportion solidified inside the ash.

[0003] In-situ capture of heavy metals using adsorbents and subsequent chemical solidification of these metals using activated silica-alumina-calcium phases is a promising technology for controlling heavy metal emissions. However, currently used mineral adsorbents, geopolymer adsorbents, and oxide adsorbents undergo phase transformation and structural collapse at temperatures above 1100℃, significantly reducing their adsorption and solidification rates for heavy metals at high temperatures. Kaolinite-based mineral adsorbents may even completely lose their adsorption capacity. Therefore, developing adsorbents that can efficiently adsorb and solidify heavy metals at high temperatures is crucial for improving the environmental safety of waste treatment processes. Summary of the Invention

[0004] Based on the above, this invention provides a composite structure adsorbent (hereinafter referred to as: composite structure adsorbent) for solidifying heavy metals in the heat treatment of solid waste and its preparation method.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] One of the technical solutions of this invention is a composite structure adsorbent for solidifying heavy metals in the heat treatment of solid waste, with spherical ultrafine fly ash as the core and zeolite as the outer shell.

[0007] The zeolite is obtained by hydrothermal reaction of crushed ultrafine fly ash after alkali melting.

[0008] Furthermore, the specific surface area of ​​the composite adsorbent for solidifying heavy metals in the solid waste heat treatment is not less than 700 m². 2 / kg.

[0009] Furthermore, the spherical ultrafine fly ash is obtained by sorting fly ash with a median particle size of less than 5 μm and a specific surface area of ​​not less than 800 m². 2 / kg of fly ash.

[0010] Furthermore, the pulverized ultrafine fly ash is obtained by grinding fly ash to obtain a median particle size of less than 5 μm and a specific surface area of ​​not less than 900 m². 2 / kg of fly ash.

[0011] The second technical solution of the present invention is a method for preparing a composite structure adsorbent for solidifying heavy metals in the above-mentioned solid waste heat treatment, comprising the following steps:

[0012] Step 1: The shell-breaking ultrafine fly ash and sodium hydroxide are subjected to alkaline melting treatment, and then water is added for hydrothermal reaction to obtain a zeolite phase suspension.

[0013] Step 2: Add spherical ultrafine fly ash to the zeolite phase suspension, stir, centrifuge to dry the resulting solid, grind it to obtain the composite structure adsorbent for solidifying heavy metals in the heat treatment of solid waste.

[0014] Furthermore, in step 1, the alkali melting treatment specifically involves holding the solution at 500-600℃ for 2 hours.

[0015] Temperatures below the aforementioned range for alkali melting treatment are detrimental to the complete polymerization reaction, while temperatures above the aforementioned range will cause decomposition of the reaction products. Therefore, the present invention preferably limits the alkali melting treatment temperature to 500-600°C.

[0016] Further, in step 1, the hydrothermal reaction specifically involves stirring and heating at 80-100℃ and 600-1000r / min for 1-2 hours.

[0017] When the temperature and time of the hydrothermal reaction exceed the above settings, the reaction will be incomplete, and some products will exist in the form of NASH gel instead of zeolite.

[0018] Furthermore, in step 2, the stirring time is not less than 10 minutes.

[0019] The purpose of stirring is to ensure that the spherical ultrafine fly ash particles are evenly dispersed in the suspension, and to ensure that the zeolite phase completely coats the spherical ultrafine fly ash. This can be achieved by appropriately extending the stirring time.

[0020] Furthermore, in step 2, the drying process specifically involves drying at 105±5℃ for 8 hours.

[0021] Furthermore, in step 2, the powder is ground to a specific surface area of ​​not less than 700 m². 2 / kg. Grinding processes can employ equipment such as ball mills, Raymond mills, roller mills, disc mills, and air jet mills.

[0022] Grind to a specific surface area of ​​not less than 700 m² 2 / kg falls into the category of ultrafine powder; if the specific surface area is less than 700m² 2 A decrease of / kg will reduce the adsorption efficiency of the adsorbent.

[0023] Furthermore, the mass ratio of the broken-shell ultrafine fly ash to the sodium hydroxide, spherical ultrafine fly ash and water is 20-40:5-8:50-80:80.

[0024] Within the above-mentioned range, the ratio of sodium hydroxide to the broken-shell ultrafine fly ash facilitates the rapid polymerization reaction of active silica-alumina in the fly ash, thereby generating zeolite. Within the above-mentioned range, the ratio of sodium hydroxide to spherical ultrafine fly ash and water also facilitates the smooth progress of step 2 (the coating step); otherwise, it may result in incomplete or uneven zeolite coating on the surface of the spherical ultrafine fly ash.

[0025] This invention uses fly ash as the main raw material to prepare a composite structure adsorbent, and addresses different functional requirements by varying the particle morphology of the fly ash. Specifically, highly active, high-specific-surface-area broken-shell ultrafine fly ash is used as the main raw material for zeolite production, thereby accelerating the formation of the zeolite phase and improving its purity; highly spherical ultrafine fly ash is used as the core material to improve the dispersibility of the adsorbent; thus, a composite structure adsorbent with spherical ultrafine fly ash as the core and zeolite phase as the outer shell is prepared. This combines the strong adsorption of heavy metals by the porous zeolite phase in the outer shell with the high pozzolanic activity of the ultrafine fly ash in the core for chemical solidification of heavy metals, achieving highly efficient solidification of heavy metals under high-temperature conditions.

[0026] The present invention discloses the following technical effects:

[0027] The composite adsorbent of this invention preferably uses fly ash, which has excellent high-temperature stability, as raw material. A zeolite shell with strong adsorption capacity is constructed on the outside of the highly active fly ash. The zeolite contains numerous framework-like cavities and surface unsaturated charges, resulting in highly efficient physical adsorption of heavy metals. The core of the composite adsorbent is highly spherical ultrafine fly ash, which, on the one hand, provides support and improves the dispersibility of the adsorbent powder; on the other hand, its high specific surface area and high pozzolanic activity facilitate the chemical bonding of the silica-alumina phase with heavy metals. This gives the composite adsorbent a coupled effect of physical adsorption and chemical solidification. Furthermore, both the core and shell materials of the composite adsorbent exhibit excellent high-temperature stability, eliminating adsorption deactivation caused by structural collapse and crystal transformation under high-temperature environments. Therefore, the composite adsorbent of this invention can efficiently solidify heavy metals discharged during solid waste heat treatment.

[0028] This invention combines the high-temperature resistance of fly ash, the physical adsorption of the outer shell zeolite material, and the chemical solidification of the core high-volcanic ash material to successfully prepare a composite structure adsorbent material that can efficiently solidify heavy metals under high-temperature conditions. This material can improve the solidification rate of heavy metals under solid waste thermal treatment conditions such as cement kiln co-processing and incinerators, and ensure the environmental safety of solid waste thermal treatment processes. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the preparation process of the composite structure adsorbent of the present invention.

[0031] Figure 2 The images shown are SEM images of the broken-shell ultrafine fly ash and spherical ultrafine fly ash used in the embodiments and comparative examples of this invention; the left image is of broken-shell ultrafine fly ash, and the right image is of spherical ultrafine fly ash.

[0032] Figure 3 The particle size distribution of the broken-shell ultrafine fly ash and spherical ultrafine fly ash used in the embodiments and comparative examples of this invention.

[0033] Figure 4 This is the calcination experimental apparatus of the present invention; in the figure, 1-gas cylinder; 2-float flowmeter; 3-thermocouple; 4-tube furnace; 5-corundum crucible; 6-tail gas treatment device.

[0034] Figure 5 This is a SEM image of the zeolite structure prepared in step 1 of Examples 1-4 of the present invention.

[0035] Figure 6 This is a SEM image of the composite structure adsorbent prepared in Example 4 of the present invention. Detailed Implementation

[0036] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0037] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0038] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0039] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0040] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0041] Unless otherwise specified, all raw materials used in the embodiments and comparative examples of this invention can be obtained from commercially available sources.

[0042] The raw materials and properties used in the embodiments and comparative examples of this invention are as follows:

[0043] Crushed ultrafine fly ash: a byproduct of coal-fired power plants, obtained by ultrafine grinding of Grade I fly ash, with a median particle size (d). 50 The particle size is 2–3 μm, and its chemical composition, microstructure, and particle size distribution are shown in Table 1. Figure 2 Middle left image and Figure 3 As shown, the specific surface area is 1042 m². 2 / kg.

[0044] Spherical ultrafine fly ash: median particle size (d 50 The particle size is 1.5–2.5 μm, obtained from the separation of Class I fly ash; its chemical composition, microstructure, and particle size distribution are shown in Table 1. Figure 2 The middle right picture and Figure 3 As shown, the specific surface area is 768 m². 2 / kg.

[0045] Table 1 Chemical composition of ultrafine fly ash, wt%

[0046]

[0047] Sodium hydroxide: Commercially available industrial caustic soda flakes with a solid mass fraction greater than 96 wt.%.

[0048] Water: tap water.

[0049] A schematic diagram of the preparation process of the composite structure adsorbent of this invention is shown below. Figure 1 As shown.

[0050] SEM images of the shattered ultrafine fly ash and spherical ultrafine fly ash used in the embodiments and comparative examples of this invention are shown below. Figure 2 As shown; the left image is of broken-shell ultrafine fly ash, and the right image is of spherical ultrafine fly ash.

[0051] The particle size distribution of the broken-shell ultrafine fly ash and spherical ultrafine fly ash used in the embodiments and comparative examples of this invention is as follows: Figure 3 As shown.

[0052] The calcination experimental apparatus of this invention is as follows: Figure 4 As shown in the figure; 1-gas cylinder; 2-float flow meter; 3-thermocouple; 4-tube furnace; 5-corundum crucible; 6-tail gas treatment device.

[0053] Examples 1-4

[0054] In Examples 1-4, the raw material composition of the composite structure adsorbent, by mass parts, consists of 20-40 parts of broken-shell ultrafine fly ash, 5-8 parts of sodium hydroxide, 50-80 parts of spherical ultrafine fly ash, and 80 parts of water (see Table 2 for specific raw material composition).

[0055] The preparation method of the composite structure adsorbent for solidifying heavy metals in the above-mentioned solid waste heat treatment specifically includes the following steps:

[0056] Step 1, Preparation of zeolite phase suspension: Sodium hydroxide and crushed ultrafine fly ash raw materials are mixed and alkali-melted at 500℃ for 2 hours. After cooling, water is added and the mixture is dissolved and heated for 2 hours at 90℃ and 800 r / min using a magnetic stirrer to obtain the zeolite phase suspension (Zeolite structure SEM image as shown). Figure 5 As shown), the specific process is as follows: Figure 1 As shown.

[0057] Step 2, Preparation of composite structure adsorbent: Add spherical ultrafine fly ash to the zeolite phase suspension and stir for 10 minutes to ensure that the spherical ultrafine fly ash particles are uniformly dispersed in the suspension, ensuring that the zeolite phase completely coats the spherical ultrafine fly ash. Centrifuge and dry at 105±5℃ for 8 hours, then grind to a specific surface area of ​​not less than 700 m². 2 / kg, the resulting powdered product is the composite structure adsorbent.

[0058] Table 2. Proportions of Composite Adsorbents (by mass)

[0059]

[0060] The curing rate of heavy metals by the composite structure adsorbents prepared in Examples 1-4 above was tested using the following methods:

[0061] use Figure 4 The calcination experimental setup shown was configured with a heating program of 800℃-1200℃-1450℃ at a heating rate of 20℃ / min. A corundum crucible containing adsorbent and 0.5% (by mass of adsorbent) heavy metals (PbO, CdO, and ZnO were tested for their solidification rates) was slowly pushed into the tubular furnace tube from one end for calcination. The furnace door was sealed while the gas cylinder valve was opened to allow airflow within the furnace tube, with the flow rate controlled at 1 L / min using a float flowmeter. Three tail gas absorption bottles were connected to the end of the furnace tube via high-temperature resistant silicone tubing. Two of the bottles contained 250 mL of a mixed absorbent solution of 5% HNO3 and 20% H2O2, while the other contained silica gel desiccant for absorbing heavy metals from the tail gas. After the calcination experiment, the crucible containing the sample was removed and rapidly cooled to room temperature using a fan. The calcined material was digested using the HNO3-HCl-HF-H2O2 method, and the heavy metal content was determined by ICP-MS. The results are shown in Table 3.

[0062] The formula for calculating the solidification rate of heavy metals by composite structure adsorbents is as follows:

[0063]

[0064] In the formula: R: the solidification rate of heavy metals in the adsorbent (100%);

[0065] K: The content of heavy metals in the sample after calcination (mg / kg);

[0066] S: The content of heavy metals in the sample before calcination (mg / kg);

[0067] LOI: Loss on ignition (%) of the sample.

[0068] Table 3. Solidification rate (%) of heavy metals by composite structure adsorbents

[0069] project PbO CdO ZnO Example 1 86 92 95 Example 2 90 93 92 Example 3 85 90 89 Example 4 92 94 96

[0070] The results showed that the composite structure adsorbents prepared in Examples 1-4 of the present invention can efficiently solidify heavy metals emitted in the solid waste heat treatment process; taking the co-processing of solid waste in a cement kiln as an example, without the use of adsorbents, the solidification rates of PbO, CdO and ZnO by cement clinker were 15%, 17% and 21%, respectively.

[0071] SEM image of the composite structure adsorbent prepared in Example 4 is shown below. Figure 6 As shown in the diagram, the spherical shapes are fly ash particles, and the outer layer is a zeolite layer. Figure 6 It can be seen that the composite adsorbent prepared in Example 4 has a core-shell structure.

[0072] Comparative Example 1

[0073] The only difference from Example 4 is that the preparation process of the zeolite phase suspension is omitted, and only spherical ultrafine fly ash is used as the adsorbent. The specific preparation steps are as follows:

[0074] Spherical ultrafine fly ash was dried at 105±5℃ for 8 hours, and then ground to a specific surface area of ​​not less than 700 m². 2 / kg, the resulting powdered product is the adsorbent.

[0075] The adsorbent prepared in this comparative example was subjected to the same heavy metal solidification rate test as in Example 4. The results showed that the solidification rate of the adsorbent prepared in this comparative example was 23% for PbO, 30% for CdO, and 32% for ZnO.

[0076] Comparative Example 2

[0077] The only difference from Example 4 is that in step 1, the broken-shell ultrafine fly ash is replaced with a specific surface area of ​​420 m². 2 / kg of Grade I fly ash (chemical composition is the same as that of broken-shell ultrafine fly ash).

[0078] The adsorbent prepared in this comparative example was subjected to the same heavy metal solidification rate test as in Example 4. The results showed that the solidification rate of the adsorbent prepared in this comparative example was 38% for PbO, 43% for CdO, and 49% for ZnO.

[0079] Comparative Example 3

[0080] The only difference from Example 4 is that in step 1, the broken-shell ultrafine fly ash is replaced with spherical ultrafine fly ash.

[0081] The adsorbent prepared in this comparative example was subjected to the same heavy metal solidification rate test as in Example 4. The results showed that the solidification rate of the adsorbent prepared in this comparative example was 41% for PbO, 47% for CdO, and 51% for ZnO.

[0082] Comparative Example 4

[0083] The only difference from Example 4 is that, in step 2, the spherical ultrafine fly ash is replaced with a specific surface area of ​​420 m². 2 / kg of Grade I fly ash (chemical composition is the same as spherical ultrafine fly ash).

[0084] The adsorbent prepared in this comparative example was subjected to the same heavy metal solidification rate test as in Example 4. The results showed that the solidification rate of the adsorbent prepared in this comparative example was 40% for PbO, 46% for CdO, and 50% for ZnO.

[0085] Comparative Example 5

[0086] The only difference from Example 4 is that in step 2, the spherical ultrafine fly ash is replaced with broken-shell ultrafine fly ash.

[0087] The adsorbent prepared in this comparative example was subjected to the same heavy metal solidification rate test as in Example 4. The results showed that the solidification rate of the adsorbent prepared in this comparative example was 43% for PbO, 49% for CdO, and 52% for ZnO.

[0088] This invention proposes a (fly ash-based) composite structure adsorbent for solidifying heavy metals in solid waste heat treatment and its preparation method. By combining shell physical adsorption and core chemical solidification, heavy metals emitted in solid waste heat treatment processes can be efficiently solidified.

[0089] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A composite structure adsorbent for solidifying heavy metals in the thermal treatment of solid waste, characterized in that, It uses spherical ultrafine fly ash as the core and zeolite as the outer shell; The zeolite is obtained by hydrothermal reaction of shell-crushed ultrafine fly ash after alkali melting. The spherical ultrafine fly ash is obtained by sorting fly ash, with a median particle size of less than 5 μm and a specific surface area of ​​not less than 800 m². 2 / kg fly ash; The pulverized ultrafine fly ash is obtained by grinding fly ash, with a median particle size of less than 5 μm and a specific surface area of ​​not less than 900 m². 2 / kg fly ash; The preparation steps of the composite structure adsorbent for solidifying heavy metals in the solid waste heat treatment include: Step 1: The shell-breaking ultrafine fly ash and sodium hydroxide are subjected to alkaline melting treatment, and then water is added for hydrothermal reaction to obtain a zeolite phase suspension. Step 2: Add spherical ultrafine fly ash to the zeolite phase suspension, stir, centrifuge to dry the resulting solid, grind it to obtain the composite structure adsorbent for solidifying heavy metals in the heat treatment of solid waste; The hydrothermal reaction specifically involves stirring and heating at 80-100℃ and 600-1000r / min for 1-2 hours. The mass ratio of the broken-shell ultrafine fly ash to the sodium hydroxide, spherical ultrafine fly ash and water is 20-40:5-8:50-80:

80.

2. The composite structure adsorbent for solidifying heavy metals in solid waste heat treatment according to claim 1, characterized in that, The specific surface area of ​​the composite adsorbent for solidifying heavy metals in the solid waste heat treatment is not less than 700 m². 2 / kg.

3. The composite structure adsorbent for solidifying heavy metals in solid waste heat treatment according to claim 1, characterized in that, In step 1, the alkali melting treatment specifically involves holding the solution at 500-600℃ for 2 hours.

4. The composite structure adsorbent for solidifying heavy metals in solid waste heat treatment according to claim 1, characterized in that, In step 2, the drying process specifically involves drying at 105±5℃ for 8 hours.

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