Method for realizing low-temperature detoxification of dioxin in fly ash by adding trace alpha-MnO2

Abstract

The invention relates to the technical field of solid waste treatment and environmental protection, in particular to a method for realizing low-temperature degradation of dioxin in fly ash by adding trace alpha-MnO2. According to the method, a trace amount of manganese-based catalyst and the waste incineration fly ash are fully and uniformly mixed, the mixture is put into a heat treatment furnace in an oxygen-deficient atmosphere, and the problem that solid-phase reaction contact is difficult is effectively solved under the condition that a large amount of catalyst does not need to be added through the high dispersity and the synergistic effect of the trace amount of catalyst in a solid-phase matrix; according to the method, the treatment energy consumption and the material cost are remarkably reduced, the operation is simple and convenient, deep degradation and thorough detoxification of dioxin in the fly ash are realized, the purposes of reducing pollution and carbon are achieved, meanwhile, secondary pollution is avoided, and a solid environmental safety guarantee is provided for subsequent resource utilization of the fly ash.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment and environmental protection technology, and in particular to a method for low-temperature detoxification of dioxins in fly ash by adding trace amounts of α-MnO2. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Dioxins are colorless, odorless, and highly toxic fat-soluble substances. They are a large class of substances that can bind to aromatic hydrocarbon acceptors, leading to various biochemical changes. Dioxin compounds are among the most toxic compounds known, possessing teratogenic, carcinogenic, and mutagenic properties, and the ability to damage the human reproductive and immune systems. Fly ash, as a key solid carrier for dioxin accumulation, generally has high dioxin toxicity equivalents (300–1000 ng I-TEQ / kg), making it a significant environmental risk source. Therefore, fly ash is the main carrier of dioxin emissions during waste incineration and must be removed.

[0004] Currently, dioxin treatment methods mainly include flue gas purification devices, activated carbon adsorption, catalytic decomposition, chemical treatment, flue gas quenching, and electron beam irradiation. Flue gas purification devices primarily utilize water in wet scrubbers to remove tiny fly ash particles in the flue gas that have adsorbed dioxins. Activated carbon adsorption utilizes its large specific surface area to adsorb dioxins. Catalytic decomposition methods mainly use catalysts such as iron-manganese and vanadium-titanium catalysts to degrade dioxin pollutants in industrial flue gas into non-toxic small molecules for emission. Chemical treatment involves injecting ammonia into the flue gas to control the generation of precursors or injecting calcium oxide to absorb HCl. Flue gas quenching technology rapidly cools the tail-end industrial flue gas to 200-300℃, avoiding the temperature range where dioxins are generated, thereby reducing dioxin production. Electron beam irradiation uses an electron beam to decompose reactive substances such as reactive oxygen species in the flue gas, thereby destroying the chemical structure of dioxins.

[0005] Among existing treatment methods, catalytic decomposition has attracted much attention. However, traditional catalytic decomposition methods are usually carried out at high temperatures, resulting in huge energy consumption, severe equipment corrosion, and high operating costs, making it difficult to meet the current strategic needs of "pollution reduction and carbon reduction." In contrast, catalytic decomposition at low temperatures of 300-400 °C has significant advantages in reducing energy consumption and costs, and has good prospects for industrialization. However, how to achieve efficient degradation and detoxification of dioxins under such mild low-temperature conditions has always been a technical challenge that urgently needs to be overcome in this field.

[0006] Current research on low-temperature catalytic degradation mainly focuses on dioxin treatment in the gas phase, with insufficient attention paid to solid fly ash matrices containing complex compositions (heavy metals, chlorides, unburned carbon, etc.). In solid-phase systems, pollutants adhere to the surface of fly ash particles, raising the question of ensuring effective physical contact and chemical reaction between the added catalyst and the solid pollutants. In the field of solid-phase catalytic treatment, to overcome the difficulties in contact between solid particles and low mass transfer efficiency, it is generally considered necessary to maintain a certain catalyst dosage (e.g., above 1 wt%) to ensure sufficient distribution density and contact probability of the catalyst in the large solid matrix. However, systematic research is currently lacking on the dispersion behavior of catalysts in complex fly ash matrices and their specific impact on dioxin degradation at trace amounts (e.g., at the 0.1 wt%). Existing technologies have not yet revealed a special relationship between catalyst dosage and degradation efficiency in specific low-temperature solid-phase reaction systems, where trace amounts of catalyst, due to higher dispersion and stronger synergistic effect with the matrix, may actually have a better catalytic effect than higher dosages (e.g., above 1 wt%). Therefore, there is an urgent need in this field for a new technology that is low in cost, highly resistant to poisoning, can overcome the problem of solid-phase contact, and can achieve low-temperature and efficient detoxification with trace amounts of additives. Summary of the Invention

[0007] In view of this, the present invention provides a method for low-temperature detoxification of dioxins in fly ash by adding trace amounts of α-MnO2. This method involves thoroughly mixing trace amounts of manganese-based catalyst with waste incineration fly ash and then introducing it into a heat treatment furnace under an oxygen-deficient atmosphere. Utilizing the high dispersibility and synergistic effect of the trace catalyst in the solid matrix, the method effectively overcomes the problem of difficult solid-phase reaction contact without the need for large-scale catalyst addition. This significantly reduces energy consumption and material costs, is simple to operate, and achieves deep degradation and complete detoxification of dioxins in fly ash, thus achieving the goal of "pollution reduction and carbon reduction." Simultaneously, it avoids secondary pollution and provides a solid environmental safety guarantee for the subsequent resource utilization of fly ash.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution: This invention provides a method for low-temperature detoxification of dioxins in fly ash by adding trace amounts of α-MnO2, comprising the following steps: The α-MnO2 catalyst was incorporated into the fly ash to be treated, and after thorough mixing, it was subjected to heat treatment.

[0009] Furthermore, the amount of α-MnO2 catalyst added is 0.1 wt% to 1.0 wt% of the fly ash mass; preferably 0.1 to 0.5 wt%. This invention has found that in this specific solid-phase reaction system, the relationship between catalyst dosage and degradation efficiency is not a simple linear one, but rather exhibits a non-linear relationship where trace amounts yield the best results. Specifically, the degradation and detoxification effects with a trace addition of 0.1 wt% are not only significantly better than the blank group without catalyst, but also better than the experimental group with higher addition amounts (e.g., 5 wt%). This indicates that the catalyst has optimal dispersion and activity within the trace amount range, while excessive addition can lead to catalyst agglomeration and active site shielding, resulting in an inhibitory effect. This discovery allows this invention to achieve optimal treatment results while reducing treatment costs.

[0010] Furthermore, the α-MnO2 catalyst is a nano-α-MnO2 catalyst; furthermore, the morphology of the α-MnO2 catalyst is nanorod-like, nanowire-like, nanotube-like, or nanofiber-like, etc. The nanostructured α-MnO2 catalyst has a large specific surface area and abundant surface active sites, improving the contact efficiency with fly ash particles.

[0011] Furthermore, the mixing method is stirring. Thorough mixing can break up catalyst agglomeration, allowing nano-sized catalyst particles to be uniformly distributed in the gaps between fly ash particles, forming an effective synergistic reaction interface between α-MnO2 and fly ash matrix.

[0012] Furthermore, the heat treatment temperature is 300~400 ℃, preferably 400 ℃; the heat treatment time is 30~120 min, preferably 90 min.

[0013] Furthermore, the heat treatment is carried out under an inert atmosphere, such as nitrogen, argon, or helium. The process is conducted in a heat treatment furnace under an inert atmosphere, such as nitrogen, to prevent the de novo synthesis of dioxins.

[0014] Furthermore, the total degradation rate of dioxins is above 99.0%, preferably 99.49%; the total detoxification rate of dioxins is above 99.0%, preferably 99.64%; and the residual dioxin toxicity equivalent after treatment can be reduced to 1.35 ng I-TEQ / kg, which is close to the level of harmlessness.

[0015] The concentration of dioxins in the gaseous emissions during the heat treatment process was extremely low, with a maximum value of only about 0.08 pg. This indicates that dioxins are mainly degraded and destroyed in situ in the solid phase, rather than being desorbed and transferred to the gas phase by heat, thus effectively avoiding secondary pollution in the gas phase.

[0016] The main chemical component of waste incineration fly ash is CaO. By utilizing the CaO component of the fly ash itself and the added trace amount of α-MnO2 to form a synergistic catalytic system, the energy barrier of dioxin molecule degradation reaction is effectively reduced, promoting the breaking of C-Cl bonds and the opening of CO bonds in dioxin molecules.

[0017] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) This invention breaks through the traditional understanding that solid-phase catalysis usually relies on high loading. By introducing a small amount of α-MnO2 catalyst, the excellent dispersibility of nanoparticles in fly ash matrix is ​​fully utilized, and the catalytic degradation and detoxification effect is better than that of conventional loading at extremely low material cost, which significantly improves the economic benefits of the treatment process.

[0018] (2) This invention achieves efficient detoxification of dioxins in fly ash under low-temperature heat treatment conditions of 300~400 ℃, with a detoxification rate of up to 99.64%. Compared with the traditional high-temperature melting process, this method operates in a mild temperature range, which is conducive to reducing energy consumption and equipment operating costs, and is in line with the national "dual carbon" target.

[0019] (3) This invention solves the problems of difficult solid-phase reaction contact and secondary pollution. Through thorough physical mixing and in-situ solid-phase catalytic degradation, it ensures that dioxins are completely decomposed on the surface of fly ash particles, avoiding the transfer of pollutants to the gas phase. The process is green and environmentally friendly, providing a safety guarantee for subsequent resource utilization. Detailed Implementation

[0020] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0021] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0022] Example 1: The selected fly ash was produced by a grate incinerator, containing 28.64% CaO, 16.25% Cl, 7.85% potassium salt, 3.85% sodium salt, and 6.98% SO3.

[0023] The selected fly ash is thoroughly mixed without adding any catalyst, and then preheated by introducing nitrogen gas into the heat treatment furnace.

[0024] The temperature of the heat treatment furnace was set to 400 ℃, the residence time was 90 min, and the resulting product was rapidly cooled using an indirect water-cooled heat exchanger.

[0025] The treated fly ash showed a dioxin degradation rate of 98.91%, a detoxification rate of 95.84%, and a dioxin residue of 15.47 ng-TEQ / kg.

[0026] The treated flue gas undergoes deep purification via activated carbon adsorption unit as a safeguard to further capture potential trace pollutants, followed by wet scrubbing. Dioxins in both the solid and gas phases meet the requirements of the "Technical Specification for Pollution Control of Fly Ash from Municipal Solid Waste Incineration" (HJ 1134-2020).

[0027] Example 2: The selected fly ash was produced by a grate incinerator. Its main chemical components included 32.96% CaO, 16.83% Cl, 4.04% K2O, 6.99% Na2O, and 9.97% SO3.

[0028] The selected fly ash was thoroughly mixed with 0.1 wt% of α-MnO2 nanorod catalyst, and then preheated by passing nitrogen gas through a heat treatment furnace.

[0029] The temperature of the heat treatment furnace was set to 400 ℃, the residence time was 90 min, and the resulting product was rapidly cooled using an indirect water-cooled heat exchanger.

[0030] The treated fly ash showed a dioxin degradation rate of 99.49%, a detoxification rate of 99.64%, and a dioxin residual toxicity equivalent of 1.35 ng I-TEQ / kg.

[0031] The treated flue gas undergoes deep purification via activated carbon adsorption unit as a safeguard to further capture potential trace pollutants, followed by wet scrubbing. Dioxins in both the solid and gas phases meet the requirements of the "Technical Specification for Pollution Control of Fly Ash from Municipal Solid Waste Incineration" (HJ 1134-2020).

[0032] Example 3: The selected fly ash is fly ash produced by grate furnace incinerator. Its main chemical components include CaO content of 33.50%, Cl content of 16.50%, K2O content of 4.10%, Na2O content of 6.80%, and SO3 content of 9.85%.

[0033] The selected fly ash was thoroughly mixed with 0.1 wt% of α-MnO2 nanorod catalyst, and then preheated by passing nitrogen gas through a heat treatment furnace.

[0034] The temperature of the heat treatment furnace was set to 400 ℃, the residence time was 90 min, and the resulting product was rapidly cooled using an indirect water-cooled heat exchanger.

[0035] The treated fly ash showed a dioxin degradation rate of 99.45%, a detoxification rate of 99.62%, and a dioxin residual toxicity equivalent of 1.42 ng I-TEQ / kg.

[0036] The treated flue gas undergoes deep purification via activated carbon adsorption unit as a safeguard to further capture potential trace pollutants, followed by wet scrubbing. Dioxins in both the solid and gas phases meet the requirements of the "Technical Specification for Pollution Control of Fly Ash from Municipal Solid Waste Incineration" (HJ 1134-2020).

[0037] Example 4: The selected fly ash was produced by a grate incinerator. Its main chemical components included 32.10% CaO, 17.10% Cl, 3.95% K2O, 7.10% Na2O, and 10.15% SO3.

[0038] The selected fly ash was thoroughly mixed with 1.0 wt% of α-MnO2 nanorod catalyst, and then preheated by passing nitrogen gas through a heat treatment furnace.

[0039] The temperature of the heat treatment furnace was set to 400 ℃, the residence time was 90 min, and the resulting product was rapidly cooled using an indirect water-cooled heat exchanger.

[0040] The treated fly ash showed a dioxin degradation rate of 99.30%, a detoxification rate of 99.42%, and a dioxin residual toxicity equivalent of 2.15 ng I-TEQ / kg.

[0041] The treated flue gas undergoes deep purification via activated carbon adsorption unit as a safeguard to further capture potential trace pollutants, followed by wet scrubbing. Dioxins in both the solid and gas phases meet the requirements of the "Technical Specification for Pollution Control of Fly Ash from Municipal Solid Waste Incineration" (HJ 1134-2020).

[0042] Example 5: The selected fly ash is fly ash produced by grate furnace incinerator. Its main chemical components include CaO content of 33.10%, Cl content of 16.90%, K2O content of 4.05%, Na2O content of 7.05%, and SO3 content of 9.90%.

[0043] The selected fly ash was thoroughly mixed with 5.0 wt% of α-MnO2 nanorod catalyst, and then preheated by passing nitrogen gas through a heat treatment furnace.

[0044] The temperature of the heat treatment furnace was set to 400 ℃, the residence time was 90 min, and the resulting product was rapidly cooled using an indirect water-cooled heat exchanger.

[0045] The treated fly ash showed a dioxin degradation rate of 98.00%, a detoxification rate of 97.10%, and a dioxin residual toxicity equivalent of approximately 10.80 ng I-TEQ / kg.

[0046] The treated flue gas undergoes deep purification via activated carbon adsorption unit as a safeguard to further capture potential trace pollutants, followed by wet scrubbing. Dioxins in the gas phase all meet the requirements of the "Technical Specification for Pollution Control of Fly Ash from Municipal Solid Waste Incineration" (HJ 1134-2020).

[0047] From Examples 1-5, the following conclusions can be drawn: Example 1, without the addition of a catalyst, serves as a control. Although this example enables the degradation of dioxins in fly ash to meet standard requirements, it is difficult to achieve a higher level of deep detoxification, and the degradation efficiency may fluctuate. Example 2, with only 0.1 wt% of a trace amount of catalyst, achieves a degradation rate as high as 99.49% and a detoxification rate of 99.64%. This confirms that within the trace amount range, catalyst particles have the best dispersion and contact probability with pollutants in the fly ash matrix, achieving optimal treatment results at the lowest cost. In Example 3, the fly ash composition changed, but with the optimal catalyst dosage of 0.1 wt%, extremely high degradation and detoxification efficiencies (>99%) were still maintained, demonstrating the process's good adaptability to fluctuations in raw material composition. In Example 4, the catalyst dosage was increased to 1.0 wt%. Although the degradation rate reached 99.30%, it did not improve compared to Example 1, but rather slightly decreased; in other words, increasing the catalyst dosage tenfold did not bring better detoxification results, but instead increased treatment costs. In Example 5, when the catalyst was added in excess to 5.0 wt%, the detoxification effect decreased instead. This indicates that in the solid-phase reaction system, the excess catalyst may cause agglomeration, trigger mass transfer limitation, or hinder the effective formation of the synergistic catalytic interface between α-MnO2 and fly ash components due to excessive coverage of the matrix surface, thereby inhibiting the degradation reaction of dioxins.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for low-temperature detoxification of dioxins in fly ash by adding trace amounts of α-MnO2, characterized in that, Includes the following steps: The α-MnO2 catalyst was incorporated into the fly ash to be treated, and after thorough mixing, it was subjected to heat treatment. The amount of α-MnO2 catalyst added is 0.1~1.0 wt% of the fly ash mass.

2. The method as described in claim 1, characterized in that, The amount of α-MnO2 catalyst added is 0.1~0.5 wt% of the fly ash mass.

3. The method as described in claim 1, characterized in that, The α-MnO2 catalyst is a nano-α-MnO2 catalyst.

4. The method as described in claim 1, characterized in that, The morphology of α-MnO2 catalysts is nanorod-like, nanowire-like, nanotube-like, or nanofiber-like.

5. The method as described in claim 4, characterized in that, The morphology of the α-MnO2 catalyst is nanorod-like.

6. The method as described in claim 1, characterized in that, The mixing method is stirring.

7. The method as described in claim 1, characterized in that, The heat treatment temperature is 300~400 ℃; the heat treatment time is 30~120 min.

8. The method as described in claim 6, characterized in that, The heat treatment temperature is 400 ℃; the heat treatment time is 90 min.

9. The method as described in claim 1, characterized in that, The heat treatment is carried out in an inert atmosphere, which is nitrogen, argon or helium.

10. The method as described in claim 1, characterized in that, The total degradation rate of dioxins is over 99.0%; the total detoxification rate of dioxins is over 99.0%.