Method for preparing fly ash heavy metal stabilizing agent from waste SCR denitration catalyst, fly ash heavy metal stabilizing agent and application thereof

Abstract

The present application belongs to the field of hazardous solid waste resource utilization and heavy metal pollution control technology, and discloses a method for preparing fly ash heavy metal stabilization agent from waste SCR denitration catalyst. After the waste SCR denitration catalyst is cleaned and crushed, calcium oxide is added for mechanical ball milling activation to obtain pretreated powder; a mixed solution of gluconic acid and citric acid is used as a leaching agent to leach the pretreated powder to obtain leaching liquid and leaching residue; ferrous sulfate and magnesium oxide are added to the leaching liquid to adjust the pH value to greater than 7, then the leaching residue is added, stirred, and subjected to controlled oxidation treatment to obtain colloidal material; the colloidal material is dried and crushed to obtain the fly ash heavy metal stabilization agent. Organic acid leaching and leaching residue back-doping are adopted to avoid deep separation of strong acid and strong base and high-temperature melting route, and to reduce secondary waste liquid and residue; the fly ash heavy metal stabilization agent fixes heavy metals through multiple mechanisms such as surface complexation, precipitation, ion exchange, alkaline buffer and physical wrapping.

Description

Technical Field

[0001] This invention belongs to the field of hazardous solid waste resource utilization and heavy metal pollution control technology, specifically involving a method for preparing fly ash heavy metal stabilizing agents using waste SCR denitrification catalysts. Background Technology

[0002] SCR (Selective Catalytic Reduction) denitrification technology is widely used in industries such as coal-fired power plants, steel mills, and waste incineration. Vanadium-tungsten-titanium SCR denitrification catalysts typically use anatase TiO2 as a support, V2O5 as the active component, and WO3 or MoO3 as an additive. After long-term service, the catalyst will become unusable due to clogging, poisoning, wear, sintering, or a decrease in mechanical strength. Waste SCR denitrification catalysts contain a high proportion of TiO2 and certain amounts of valuable elements such as V and W. Direct disposal not only wastes resources but also creates pressure for hazardous waste management.

[0003] Existing resource utilization routes for spent SCR denitrification catalysts mostly focus on hydrometallurgical recovery of vanadium, tungsten, and titanium products, or the use of spent catalyst powder as adsorbents, building material admixtures, or melt-solidification raw materials. Hydrometallurgy typically requires strong acids, strong alkalis, high-temperature roasting, or multi-stage extraction and separation, resulting in a long process and high pressure for waste liquid treatment; simply preparing adsorbents or building material admixtures makes it difficult to fully utilize the synergistic stabilizing effects of vanadium, tungsten, and titanium components.

[0004] Waste incineration fly ash and some coal-fired fly ash often contain heavy metals such as Pb, Cd, Cr, Hg, and As. Existing fly ash stabilizing agents mainly include cement, lime, phosphates, sulfides, and organic chelating agents. Among them, organic chelating agents have lower dosage but higher cost, and limited adaptability to different heavy metal forms; inorganic agents have lower cost but require larger dosage and have significant compressive strength, but some systems lack long-term stability for elements such as Cd, Hg, and As.

[0005] Current research includes the co-melting treatment of spent SCR denitrification catalysts and fly ash, the preparation of heavy metal catalysts from spent SCR denitrification catalysts, and the separation and recovery of vanadium, tungsten, and titanium from spent SCR denitrification catalysts. However, no research has been reported on the preparation of fly ash heavy metal stabilizing agents using spent SCR denitrification catalysts. Summary of the Invention

[0006] The first objective of this invention is to provide a method for preparing fly ash heavy metal stabilizing agents from waste SCR denitrification catalysts.

[0007] The second objective of this invention is to provide a fly ash heavy metal stabilizing agent.

[0008] A third objective of this invention is to provide the application of fly ash heavy metal stabilizing agents.

[0009] To achieve the above objectives, the present invention provides the following specific technical solutions.

[0010] First, this invention provides a method for preparing fly ash heavy metal stabilizing agents from spent SCR denitrification catalysts, comprising: After cleaning and crushing the waste SCR denitrification catalyst, calcium oxide was added for mechanical ball milling activation to obtain pretreated powder. A mixed solution of gluconic acid and citric acid was used as the leaching agent to leach the pretreated powder, resulting in a leachate and a leaching residue. Ferrous sulfate was first added to the leachate, then magnesium oxide was added to adjust the pH value to be greater than 7, then the leachate residue was added, stirred, and controlled oxidation was carried out to obtain colloidal material. The colloidal material was dried and pulverized to obtain a fly ash heavy metal stabilizing agent.

[0011] Secondly, this invention provides a fly ash heavy metal stabilizing agent, which, on a dry basis, contains: Based on Fe2O3, the active iron content is 8%~22%; Based on CaO+MgO, the active calcium and magnesium content is 8%~25%. Based on V2O5, the active vanadium content is 0.5%~3.0%; Based on WO3, the active tungsten content is 1.0% to 6.0%. Based on TiO2, the active titanium content is 35%~65%; The balance consists of SiO2, Al2O3, sulfate, organic ligands, water of crystallization, and unavoidable impurities.

[0012] The above-mentioned fly ash heavy metal stabilizing agent is obtained by treating waste SCR denitrification catalyst.

[0013] Finally, this invention provides the application of the above-mentioned fly ash heavy metal stabilizing agent.

[0014] Compared with the prior art, one or more technical solutions of the present invention can achieve at least one of the following beneficial effects: Organic acid leaching and leaching residue re-mixing are adopted to avoid deep separation of strong acids and strong bases and high-temperature melting routes, thereby reducing secondary waste liquid and residue; Heavy metal stabilizing agents in fly ash can fix heavy metals through multiple mechanisms such as surface complexation, precipitation, ion exchange, alkaline buffering, and physical encapsulation.

[0015] It is suitable for integration with existing solid waste pretreatment and fly ash stabilization chemical sections in power plants or waste incineration plants. Detailed Implementation

[0016] In a first aspect, some embodiments of the present invention provide a method for preparing a fly ash heavy metal stabilizing agent from waste SCR denitrification catalyst, comprising: After cleaning and crushing the waste SCR denitrification catalyst, calcium oxide was added for mechanical ball milling activation to obtain pretreated powder. A mixed solution of gluconic acid and citric acid was used as the leaching agent to leach the pretreated powder, resulting in a leachate and a leaching residue. Ferrous sulfate was first added to the leachate, then magnesium oxide was added to adjust the pH value to be greater than 7, then the leachate residue was added, stirred, and controlled oxidation was carried out to obtain colloidal material. The colloidal material was dried and pulverized to obtain a fly ash heavy metal stabilizing agent.

[0017] (1) Adding calcium oxide to the waste SCR denitrification catalyst can improve the efficiency of dry ball milling on the one hand, and provide a mild pre-alkalization environment on the other hand, which is conducive to the coordination and migration of vanadium and tungsten components in the organic acid system.

[0018] Furthermore, in some preferred embodiments, the amount of calcium oxide added is 0.5% to 2.0% of the mass of the waste SCR denitrification catalyst.

[0019] Furthermore, in some preferred embodiments, the ball milling speed for mechanical ball milling activation is 200~500 r / min, and the ball milling time is 1~3 h.

[0020] Furthermore, in some preferred embodiments, the particle size D50 of the pretreated powder is ≤10μm.

[0021] (2) A mixed solution of gluconic acid and citric acid is used as the leaching agent. Glucosic acid and citric acid have hydroxyl and carboxyl groups, which can form a coordination migration system with vanadium and tungsten oxide anions, while the main carrier components such as TiO2, SiO2, and Al2O3 are mainly retained in the solid phase.

[0022] Furthermore, in some preferred embodiments, the total organic acid concentration in the mixed solution is 0.5~1.5 mol / L.

[0023] Furthermore, in some preferred embodiments, the molar ratio of gluconic acid to citric acid in the mixed solution is (1~3):1.

[0024] Furthermore, in some preferred embodiments, the leaching temperature is 40~60°C; the leaching time is 2~4 hours.

[0025] Furthermore, in some preferred embodiments, the initial liquid-to-solid ratio is 5-10 mL / g when leaching the pretreated powder.

[0026] Furthermore, in some preferred embodiments, when leaching the pretreated powder, leaching is terminated when the pH value of the leaching system is 2.0 to 4.5.

[0027] (3) Add ferrous sulfate and magnesium oxide to the leachate. Magnesium oxide provides Mg. 2+ And buffering alkalinity, ferrous sulfate provides Fe 2+ Under controlled oxidation conditions, the two can form Fe / Mg layered bimetallic hydroxides and hydrated iron oxides. The leaching residue from the re-admixture provides TiO2, surface hydroxyl groups, a silica-alumina framework, and a microporous structure.

[0028] Furthermore, in some preferred embodiments, the ferrous sulfate is ferrous sulfate heptahydrate.

[0029] Furthermore, in some preferred embodiments, the amount of ferrous sulfate heptahydrate added is 8% to 18% of the mass of the leachate.

[0030] Furthermore, in some preferred embodiments, magnesium oxide is added until the pH of the system reaches 7.8 to 8.8.

[0031] Furthermore, in some preferred embodiments, the leaching residue is fully recycled in either wet or dry form.

[0032] Furthermore, in some preferred embodiments, the specific process of the controlled oxidation treatment is as follows: bubbling oxidation in an oxygen-containing atmosphere, and controlling the oxidation-reduction potential to be 100~350mV.

[0033] Furthermore, in some preferred embodiments, the controlled oxidation treatment temperature is 20~60°C.

[0034] Furthermore, in some preferred embodiments, the bubbling oxidation time is 0.5 to 3 hours.

[0035] Furthermore, in some preferred embodiments, after the controlled oxidation treatment, Fe in the system 2+ The retention rate is 10% to 60%.

[0036] By limiting complete oxidation, some Fe can be... 2+ It participates in the formation of layered structures and generates active sites for hydrated iron oxides, thus facilitating the fixation of both anionic and cationic heavy metals.

[0037] Secondly, some embodiments of the present invention provide a fly ash heavy metal stabilizing agent, which, on a dry basis, contains: Based on Fe2O3, the active iron content is 8%~22%; Based on CaO+MgO, the active calcium and magnesium content is 8%~25%. Based on V2O5, the active vanadium content is 0.5%~3.0%; Based on WO3, the active tungsten content is 1.0% to 6.0%. Based on TiO2, the active titanium content is 35%~65%; The balance consists of SiO2, Al2O3, sulfate, organic ligands, water of crystallization, and unavoidable impurities.

[0038] Furthermore, the aforementioned fly ash heavy metal stabilizing agent is obtained through the method described in the first aspect.

[0039] Thirdly, some embodiments of the present invention provide specific applications of the aforementioned fly ash heavy metal stabilizing agent, wherein the fly ash heavy metal stabilizing agent is mixed and stirred evenly with fly ash and water, and then cured.

[0040] Furthermore, in some preferred embodiments, the heavy metals that need to be stabilized in the fly ash include at least one of Pb, Cd, Cr, Hg, and As.

[0041] Furthermore, in some preferred embodiments, the amount of the fly ash heavy metal stabilizing agent is 3% to 7% of the dry weight of the fly ash, the amount of water is 15% to 35% of the dry weight of the fly ash, and the curing time is 12 to 72 hours.

[0042] To further clarify, during the curing process, keep the mixture moist and avoid significant water loss, dust, or rain.

[0043] Furthermore, in some preferred embodiments, the curing temperature is 5~40℃ and the relative humidity is not less than 50%.

[0044] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0045] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0046] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0047] The spent SCR denitrification catalysts described in the following examples and comparative examples are decommissioned honeycomb vanadium-tungsten-titanium catalysts from coal-fired power plants; the fly ash is municipal solid waste incineration fly ash. Leaching toxicity testing was performed using the acetic acid buffer solution method specified in HJ / T 300, and the test results were compared with the relevant control limits for municipal solid waste incineration fly ash entering the site in Table 1 of GB16889-2024. Unless otherwise stated, all percentages are by mass.

[0048] Example 1 (1) Take 80.0 kg of waste honeycomb SCR denitrification catalyst from a coal-fired power plant. Its main components (mass content) are: TiO2 78.5%, WO3 4.2%, V2O5 1.8%, SiO2 6.1%, Al2O3 3.5%, CaO 2.1%, As2O3 0.12%, with the remainder being other unavoidable impurities. After cleaning with compressed air, crush it to a particle size D50≤5mm using a jaw crusher. Add 0.8 kg of calcium oxide and put it into a ball mill for dry ball milling at 300 r / min for 2 h to obtain 80.8 kg of pretreated powder with a D50 of 6.4 μm.

[0049] (2) 80.8 kg of pretreated powder was added to a 500 L enamel-lined reactor, and 400 L of a mixed solution of gluconic acid and citric acid was added, wherein the concentration of gluconic acid was 0.6 mol / L, the concentration of citric acid was 0.3 mol / L, and the total organic acid concentration was 0.9 mol / L. The mixture was stirred and leached at 50℃ and 150 r / min for 3 h. After leaching (the pH value at the leaching endpoint was 3.3), the mixture was filtered to obtain 372 L of vanadium-tungsten leaching solution with a mass of approximately 409 kg; and 116 kg of titanium-containing leaching residue with a water content of approximately 34.0%, corresponding to a dry basis mass of approximately 76.6 kg. The vanadium leaching rate was found to be 86.8%, and the tungsten leaching rate was 72.5%.

[0050] (3) The vanadium-tungsten leaching solution was transferred to a reactor, and 48 kg of ferrous sulfate heptahydrate, accounting for 11.7% of the leaching solution mass, was added under stirring. After it dissolved, 14 kg of lightly calcined magnesium oxide was added, and the pH was adjusted to 8.4. Then, all 116 kg of titanium-containing leaching residue was added, and the reaction was stirred for 1 h. After that, compressed air was bubbled through for oxidation for 1.5 h, and the redox potential was controlled at about 220 mV. The ferrous ion retention rate in the system was measured to be about 34%, forming a gray-brown composite colloidal slurry.

[0051] (4) The reaction slurry was dried at 105°C to a moisture content of approximately 3.6%, and then mechanically pulverized to a D50 of 13 μm to obtain approximately 117 kg of fly ash heavy metal stabilizing agent. Upon testing, the agent, on a dry basis, contained: Based on Fe2O3, it contains 11.9% active iron; Based on CaO+MgO, the active calcium and magnesium content is 14.2%. Based on V2O5, 1.2% of vanadium is active; Based on WO3, it contains 2.9% active tungsten; Based on TiO2, the active titanium content is 53.1%. The remainder consists of SiO2, Al2O3, sulfate, organic ligands, water of crystallization, and unavoidable impurities.

[0052] Comparative Example 1 This comparative example is basically the same as Example 1, except that in step (2), only a 0.9 mol / L gluconic acid solution is used as the leaching agent, and citric acid is not added. The vanadium leaching rate was found to be 62.4%, and the tungsten leaching rate was 42.0%.

[0053] Comparative Example 2 This comparative example is basically the same as Example 1, except that in step (2), only a 0.9 mol / L citric acid solution is used as the leaching agent, and no gluconic acid solution is added. The vanadium leaching rate was found to be 70.6%, and the tungsten leaching rate was 55.3%.

[0054] Comparative Example 3 This comparative example is basically the same as Example 1, except that in step (2), the leaching agent is replaced with a 0.9 mol / L sulfuric acid solution, and the mixed solution of gluconic acid and citric acid is not used. The vanadium leaching rate was found to be 78.1%, and the tungsten leaching rate was 66.0%.

[0055] Example 2 This embodiment is basically the same as Embodiment 1, except that in step (2), the molar ratio of gluconic acid to citric acid is adjusted to 3:1, the total organic acid concentration is 0.9 mol / L, the leaching temperature is 50℃, and the leaching time is 3 h. The vanadium leaching rate was found to be 90.5%, and the tungsten leaching rate was 75.8%. The dry weight of the titanium-containing leaching residue was approximately 75.9 kg, and it was all recycled. The final dry weight of the reagent contained: Based on Fe2O3, it contains 11.7% active iron; Based on CaO+MgO, the active calcium and magnesium content is 14.1%. Based on V2O5, the active vanadium content is 1.3%. Based on WO3, it contains 3.1% active tungsten; Based on TiO2, the active titanium content is 52.6%. The remainder consists of SiO2, Al2O3, sulfate, organic ligand residues, water of crystallization, and unavoidable impurities.

[0056] Example 3 This embodiment is basically the same as Example 1, except that in step (3), the amount of ferrous sulfate heptahydrate added is 35 kg, accounting for about 8.6% of the mass of the leachate; the amount of lightly calcined magnesium oxide added is 12 kg, and the pH is adjusted to 8.1; the bubbling oxidation time is 1 h, the redox potential is controlled at about 160 mV, and the ferrous ion retention rate is about 48%. The final reagent dry basis contains: Based on Fe2O3, it contains 9.2% active iron; Based on CaO+MgO, the active calcium and magnesium content is 12.8%. Based on V2O5, the active vanadium content is 1.3%. Based on WO3, it contains 3.0% active tungsten; Based on TiO2, the active titanium content is 56.0%. The remainder consists of SiO2, Al2O3, sulfate, organic ligand residues, water of crystallization, and unavoidable impurities.

[0057] Example 4 (1) Take 80.0 kg of waste honeycomb SCR denitrification catalyst from a coal-fired power plant. Its main components (mass content) are: TiO2 78.5%, WO3 4.2%, V2O5 1.8%, SiO2 6.1%, Al2O3 3.5%, CaO 2.1%, As2O3 0.12%, with the remainder being other unavoidable impurities. After cleaning with compressed air, crush it to a particle size D50≤5mm using a jaw crusher. Add 0.4 kg of calcium oxide and put it into a ball mill for dry ball milling at 200 r / min for 3h to obtain 80.4 kg of pretreated powder with a D50 of 8.6μm.

[0058] (2) 80.4 kg of pretreated powder was added to a 1000 L enamel-lined reactor, and 520 L of a mixed solution of gluconic acid and citric acid was added, wherein the concentration of gluconic acid was 0.25 mol / L, the concentration of citric acid was 0.25 mol / L, and the concentration of total organic acids was 0.5 mol / L. The mixture was stirred and leached at 40℃ and 150 r / min for 4 h. After leaching, the mixture was filtered to obtain 492 L of vanadium-tungsten leaching solution with a mass of approximately 525 kg; and 119 kg of titanium-containing leaching residue with a water content of approximately 35%, corresponding to a dry basis mass of approximately 77.4 kg. The vanadium leaching rate was found to be 74.0%, and the tungsten leaching rate was 58.0%.

[0059] (3) The vanadium-tungsten leaching solution was transferred to a reactor, and 42 kg of ferrous sulfate heptahydrate (8% of the leaching solution mass) was added under stirring. After it dissolved, 12 kg of lightly calcined magnesium oxide was added, and the pH was adjusted to 7.8. Then, all 119 kg of titanium-containing leaching residue was added, and the reaction was stirred for 1 h. After that, compressed air was introduced at 40°C for bubbling oxidation for 0.5 h, and the redox potential was controlled at about 100 mV. The ferrous ion retention rate in the system was measured to be about 60%, forming a gray-brown composite colloidal slurry.

[0060] (4) The reaction slurry was dried at 105°C to a moisture content of approximately 3.6%, and then mechanically pulverized to a D50 of 13 μm to obtain approximately 114 kg of fly ash heavy metal stabilizing agent. Upon testing, the agent, on a dry basis, contained: Based on Fe2O3, it contains 10.8% active iron; Based on CaO+MgO, the active calcium and magnesium content is 12.7%. Based on V2O5, it contains 1.1% active vanadium; Based on WO3, it contains 2.4% active tungsten; Based on TiO2, the active titanium content is 55.8%. The remainder consists of SiO2, Al2O3, sulfate, organic ligand residues, water of crystallization, and unavoidable impurities.

[0061] Example 5 (1) Take 80.0 kg of waste honeycomb SCR denitrification catalyst from a coal-fired power plant. Its main components (mass content) are: TiO2 78.5%, WO3 4.2%, V2O5 1.8%, SiO2 6.1%, Al2O3 3.5%, CaO 2.1%, As2O3 0.12%, with the remainder being other unavoidable impurities. After cleaning with compressed air, crush it to a particle size D50≤5mm using a jaw crusher. Add 1.6 kg of calcium oxide and put it into a ball mill for dry ball milling at 500 r / min for 1 h to obtain 81.6 kg of pretreated powder with a D50 of 5.1 μm.

[0062] (2) 81.6 kg of pretreated powder was added to a 1000 L enamel-lined reactor, along with 800 L of a mixed solution of gluconic acid and citric acid, wherein the concentration of gluconic acid was 1.0 mol / L, the concentration of citric acid was 0.5 mol / L, and the total organic acid concentration was 1.5 mol / L. The mixture was stirred and leached at 60℃ and 150 r / min for 2 h. After leaching (the final pH value was 2.4), the mixture was filtered to obtain 720 L of vanadium-tungsten leaching solution, with a mass of approximately 800 kg; and 112 kg of titanium-containing leaching residue, with a water content of approximately 33.0%, corresponding to a dry weight of approximately 5.0 kg. The vanadium leaching rate was found to be 92.6%, and the tungsten leaching rate was 79.0%.

[0063] (3) The vanadium-tungsten leaching solution was transferred to a reactor, and 96 kg of ferrous sulfate heptahydrate, accounting for 12% of the leaching solution mass, was added under stirring. After it dissolved, 22 kg of lightly calcined magnesium oxide was added, and the pH was adjusted to 8.8. Then, all 112 kg of titanium-containing leaching residue was added, and the reaction was stirred for 1 h. After that, compressed air was introduced at 60°C for 3 h of bubbling oxidation, and the redox potential was controlled at about 350 mV. The ferrous ion retention rate in the system was measured to be about 10%, forming a gray-brown composite colloidal slurry.

[0064] (4) The reaction slurry was dried at 105°C to a moisture content of approximately 3.6%, and then mechanically pulverized to a D50 of 13 μm to obtain approximately 166 kg of fly ash heavy metal stabilizing agent. Upon testing, the agent, on a dry basis, contained: Based on Fe2O3, it contains 17.3% active iron; Based on CaO+MgO, the active calcium and magnesium content is 15.8%. Based on V2O5, it contains 0.9% active vanadium; Based on WO3, it contains 2.1% active tungsten; Based on TiO2, the active titanium content is 39.3%; The remainder consists of SiO2, Al2O3, sulfate, organic ligand residues, water of crystallization, and unavoidable impurities.

[0065] Application Example 1 Fly ash from a waste incineration plant was taken, and the reagent obtained in Example 1 was added to the fly ash at 0%, 3%, 5%, and 7% of the dry weight of the fly ash, respectively. The amount of water added was 25% of the dry weight of the fly ash. After stirring for 10 minutes, the mixture was cured for 24 hours and then subjected to leaching toxicity testing. The results are shown in Table 1.

[0066] Table 1 The limits set by GB16889-2024 are: Pb 0.25 mg / L, Cd 0.15 mg / L, Cr 6+ 1.5mg / L, Hg 0.05mg / L, As0.3mg / L.

[0067] As shown in Table 1, when the dosage of the reagent obtained in Example 1 is 5%, the leaching concentrations of Pb, Cd, Cr(VI), Hg and As in fly ash are all lower than the limits specified in GB 16889-2024.

[0068] Application Comparative Example 1 The difference from Application Example 1 is that the reagent obtained from Comparative Example 1 is added to the fly ash at 5% of the dry weight of the fly ash.

[0069] The toxicity test results were as follows: Pb 0.36 mg / L, Cd 0.20 mg / L, Cr(VI) 0.54 mg / L, Hg 0.009 mg / L, and As 0.14 mg / L. The leaching concentrations of Pb and Cd exceeded the limits specified in GB 16889-2024.

[0070] Comparative Example 1 and Application Comparative Example 1 show that the single gluconic acid system has insufficient synergistic migration ability for vanadium and tungsten, resulting in insufficient vanadium and tungsten active components participating in precipitation and complexation fixation in the final reagent, and a decrease in stabilization effect.

[0071] Application Comparative Example 2 The difference from Application Example 1 is that the reagent obtained from Comparative Example 2 is added to the fly ash at 5% of the dry weight of the fly ash.

[0072] The toxicity test results were as follows: Pb 0.28 mg / L, Cd 0.18 mg / L, Cr(VI) 0.48 mg / L, Hg 0.008 mg / L, and As 0.13 mg / L. The leaching concentrations of Pb and Cd were still higher than the limits specified in GB 16889-2024, indicating that although the single citric acid system was an improvement over the single gluconic acid system, its stabilization effect was still insufficient.

[0073] Application Comparative Example 3 The difference from Application Example 1 is that the reagent obtained from Comparative Example 3 is added to the fly ash at 5% of the dry weight of the fly ash.

[0074] The toxicity test results were as follows: Pb 0.30 mg / L, Cd 0.19 mg / L, Cr(VI) 0.52 mg / L, Hg 0.009 mg / L, and As 0.14 mg / L.

[0075] Comparative Example 3 and Application Example 3 show that although the sulfuric acid system can leach some vanadium-tungsten components, it cannot provide bridging and sustained-release coordination of residual gluconic acid / citric acid ligands in subsequent reactions. Furthermore, the strong acid system increases the neutralization load and salt accumulation, which is detrimental to the formation of a uniform and stable Fe / Mg layered bimetallic hydroxide-hydrated iron oxide composite colloidal system. Therefore, the Pb and Cd leaching concentrations in Application Example 3 are still higher than the limits, and the overall stabilization effect is lower than that in Application Example 1.

[0076] Application Example 2 The difference from Application Example 1 is that the agent obtained in Example 2 is added to the fly ash at 4% of the dry weight of the fly ash.

[0077] The toxicity test results were as follows: Pb 0.13 mg / L, Cd 0.07 mg / L, Cr(VI) 0.31 mg / L, Hg 0.005 mg / L, and As 0.08 mg / L.

[0078] Example 2 and Application Example 2 demonstrate that when the molar ratio of gluconic acid to citric acid is adjusted to 3:1, the leaching rates of vanadium and tungsten increase, and the vanadium and tungsten active components in the resulting reagent are slightly higher. Under the low doping condition of 4%, the leaching concentrations of Pb, Cd, Cr(VI), Hg, and As are all below the limit values ​​and are significantly better than the treatment results of Application Example 1 at the 3% doping level, indicating that the stabilization effect of low doping is improved.

[0079] Application Example 3 The difference from Application Example 1 is that the agent obtained in Example 3 is added to the fly ash at 5% of the dry weight of the fly ash.

[0080] The toxicity test results were as follows: Pb 0.19 mg / L, Cd 0.12 mg / L, Cr(VI) 0.40 mg / L, Hg 0.007 mg / L, and As 0.11 mg / L.

[0081] Example 3 and Application Example 3 illustrate that, under conditions of reduced dosage of ferrous sulfate heptahydrate and magnesium oxide, and reduced oxidation intensity, the number of active sites for iron and magnesium in the reagent decreases, and the fixation effect of cationic heavy metals such as Pb and Cd is reduced compared to Application Example 1; however, the full re-adsorption of titanium-containing leaching residue still provides adsorption carrier, surface hydroxyl sites, and physical encapsulation effect, so that the leaching concentration of each heavy metal still meets the relevant limits.

[0082] Application Example 4 The difference from Application Example 1 is that the agent obtained in Example 4 is added to the fly ash at 5% of the dry weight of the fly ash.

[0083] The toxicity test results were as follows: Pb 0.22 mg / L, Cd 0.14 mg / L, Cr(VI) 0.46 mg / L, Hg 0.008 mg / L, and As 0.13 mg / L.

[0084] Example 4 and Application Example 4 illustrate that when the total organic acid concentration, calcium oxide addition, iron and magnesium dosage, and oxidation intensity are all at low boundary conditions, the iron and magnesium active sites and vanadium-tungsten active components in the reagent are all lower than in Example 1, the stabilization effect is relatively weak, and the Pb and Cd leaching concentrations are close but still lower than the limit values, demonstrating the feasibility of the lower limit of the process parameters.

[0085] Application Example 5 The difference from Application Example 1 is that the agent obtained in Example 5 is added to the fly ash at 5% of the dry weight of the fly ash.

[0086] The toxicity test results were as follows: Pb 0.09 mg / L, Cd 0.05 mg / L, Cr(VI) 0.23 mg / L, Hg 0.003 mg / L, and As 0.06 mg / L.

[0087] Example 5 and Application Example 5 illustrate that, under conditions of high total organic acid concentration, high dosage of ferrous sulfate and magnesium oxide, and high redox potential, although the mass percentage of vanadium, tungsten, and titanium in the reagent is diluted due to the increase in the iron-magnesium colloidal component, the active sites of the iron-magnesium layered bimetallic hydroxide and hydrated iron oxide increase, thus resulting in a better overall stabilization effect on Pb, Cd, Cr(VI), Hg, and As than in Example 1.

[0088] Table 2 Comparison of heavy metal stabilization effects of different agents at representative dosages in fly ash As can be seen from the examples and comparative examples, the present invention can convert vanadium, tungsten, titanium and carrier components in waste SCR denitrification catalyst into fly ash heavy metal stabilizing agent under mild conditions by mechanical activation with calcium oxide, selective coordination leaching with gluconic acid / citric acid, in-situ construction of iron-magnesium composite colloid with ferrous sulfate and magnesium oxide, and full re-incorporation of titanium-containing leaching residue.

[0089] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a fly ash heavy metal stabilizing agent from spent SCR denitrification catalyst, characterized in that, include: After cleaning and crushing the waste SCR denitrification catalyst, calcium oxide was added for mechanical ball milling activation to obtain pretreated powder. A mixed solution of gluconic acid and citric acid was used as the leaching agent to leach the pretreated powder, resulting in a leachate and a leaching residue. Ferrous sulfate was first added to the leachate, then magnesium oxide was added to adjust the pH value to be greater than 7, then the leachate residue was added, stirred, and controlled oxidation was carried out to obtain colloidal material. The colloidal material was dried and pulverized to obtain a fly ash heavy metal stabilizing agent.

2. The method according to claim 1, characterized in that, Includes at least one of the following features (a) to (d): (a) The amount of calcium oxide added is 0.5% to 2.0% of the mass of the waste SCR denitrification catalyst; (b) The ball milling speed for mechanical ball milling activation is 200~500 r / min; (c) The ball milling time is 1~3 hours; (d) The particle size D50 of the pretreated powder is ≤10μm.

3. The method according to claim 1, characterized in that, Includes at least one of the following features (e) to (i): (e) The total concentration of organic acids in the mixed solution is 0.5~1.5 mol / L; (f) The molar ratio of gluconic acid to citric acid in the mixed solution is (1~3):1; (g) The leaching temperature is 40~60℃; the leaching time is 2~4h; (h) When leaching pretreated powder, the initial liquid-to-solid ratio is 5~10mL / g; (i) When leaching the pretreated powder, the leaching is stopped when the pH of the leaching system is 2.0 to 4.

5.

4. The method according to claim 1, characterized in that, The ferrous sulfate is ferrous sulfate heptahydrate; the amount of ferrous sulfate heptahydrate added is 8% to 18% of the mass of the leachate.

5. The method according to claim 1, characterized in that, Add magnesium oxide until the pH of the system reaches 7.8-8.

8.

6. The method according to claim 1, characterized in that, The specific process of the controlled oxidation treatment is as follows: bubbling oxidation in an oxygen-containing atmosphere, and controlling the oxidation-reduction potential to be 100~350mV.

7. The method according to claim 6, characterized in that, Includes at least one of the following features (j) to (l): (j) The controlled oxidation treatment temperature is 20~60℃; (k) The bubbling oxidation time is 0.5~3h; (l) After the controlled oxidation treatment, Fe in the system 2+ The retention rate is 10% to 60%.

8. A fly ash heavy metal stabilizing agent, characterized in that, On a dry basis, it contains: Based on Fe2O3, the active iron content is 8%~22%; Based on CaO+MgO, the active calcium and magnesium content is 8%~25%. Based on V2O5, the active vanadium content is 0.5%~3.0%; Based on WO3, the active tungsten content is 1.0% to 6.0%. Based on TiO2, the active titanium content is 35%~65%; The balance consists of SiO2, Al2O3, sulfate, organic ligands, water of crystallization, and unavoidable impurities.

9. The fly ash heavy metal stabilizing agent according to claim 8, characterized in that, It is prepared by the preparation method according to any one of claims 1-7.

10. The specific application of the fly ash heavy metal stabilizing agent according to claim 8 or 9, characterized in that, The fly ash heavy metal stabilizing agent is mixed with fly ash and water until homogeneous, and then cured.

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