Method for deep removal and recovery of calcium poisoning of waste scr catalyst for denitration of cement kiln flue gas

Abstract

The application provides a cement kiln flue gas denitration waste SCR catalyst calcium poisoning deep removal and recovery method, and belongs to the technical field of hazardous waste resource recovery, which can at least partially solve the problem that the existing method cannot meet the deep removal of calcium in the waste SCR catalyst of the cement kiln and the efficient recovery of valuable metals. The application first carries out a blowing, crushing and ball milling pretreatment process on the waste SCR catalyst to obtain waste SCR powder, then calcines the waste SCR powder in a reducing atmosphere to convert the insoluble calcium-containing phase into an acid-soluble calcium-containing phase, and adopts an acid leaching solution to realize the removal of calcium impurities, and obtains decalcification residue and titanium-rich residue through solid-liquid separation, and the vanadium, tungsten and titanium in the decalcification residue are recovered through processes such as alkali leaching or acidolysis, solvent extraction and the like. The application can realize the deep removal of calcium in the waste SCR catalyst, effectively eliminate the adverse effects of calcium impurities on the subsequent vanadium, tungsten and titanium recovery process, and effectively improve the recovery efficiency and product purity of vanadium, tungsten and titanium.

Description

Technical Field

[0001] This invention belongs to the field of hazardous waste resource recovery technology, specifically relating to a method for deep removal and recovery of calcium poisoning from spent SCR catalysts in cement kiln flue gas denitrification. Background Technology

[0002] With increasingly stringent environmental emission standards, selective catalytic reduction (SCR) denitrification technology is being rapidly adopted in the cement industry. Cement kiln flue gas is characterized by high temperature (300℃~400℃), high dust concentration (up to 80g / Nm³~120g / Nm³), and high CaO content (accounting for 40%~60% of the dust). During SCR denitrification operation, a large amount of CaO dust in the flue gas will deposit and penetrate into the catalyst pores, reacting chemically with the active components and support in the catalyst to form a series of insoluble calcium-containing phases such as CaSO4, CaV2O6, CaTiO3, and CaWO4, leading to severe "calcium poisoning" and deactivation of the catalyst.

[0003] The mass fraction of CaO in waste SCR catalyst from cement kilns can typically reach 10%–25%, far exceeding that of waste catalysts from coal-fired power plants (typically CaO <2%). These calcium species not only exist in the form of physical deposition, but more importantly, they react with TiO2 supports to form perovskite-type CaTiO3 solid solutions, and react with V2O5 to form complex oxides such as CaV2O6, making the occurrence of calcium extremely complex and its chemical properties stable.

[0004] Currently, the recycling technology for spent SCR catalysts is mainly developed for catalysts from coal-fired power plants, with typical processes being alkaline leaching or acid leaching. Alkaline leaching uses NaOH solution to leach V and W under high temperature or pressure, while calcium remains as insoluble Ca(OH)₂ or CaTiO₃, co-existing with the titanium slag. For spent catalysts from cement kilns with extremely high calcium content, the CaO content in the alkaline leaching residue can still be over 15%, resulting in severely substandard purity of subsequent titanium dioxide products (CaO is a critical impurity in titanium dioxide, requiring <0.01%), making it unusable as a raw material for titanium dioxide recycling. Acid leaching uses concentrated sulfuric acid to dissolve Ti, V, W, and Ca together at high temperature. Although titanium can be extracted, the large amount of calcium entering the titanium solution easily forms calcium sulfate and metatitanic acid co-precipitates during the hydrolysis to prepare titanium dioxide, which are extremely difficult to separate, severely affecting the whiteness and dispersibility of the titanium dioxide. Furthermore, the acid leaching process generates a large amount of calcium-containing waste acid, resulting in high treatment costs.

[0005] In existing technologies, some CaO can be removed by washing or flotation before acid leaching, but physical removal is basically ineffective against calcium that has already reacted with TiO2 to form CaTiO3. Some have also attempted to decalcify the spent catalyst by acid leaching with NH4Cl solution or dilute hydrochloric acid, but this results in a significant loss of TiO2 (the acid solubility of titanium can reach 15%–30%), making it counterproductive. Therefore, the deep removal of calcium and efficient recovery of valuable metals from spent SCR catalysts in cement kilns have always been major technical challenges in this sub-field, and to date, there is a lack of economically feasible dedicated treatment methods.

[0006] Therefore, a method for deep removal and recovery of calcium poisoning from spent SCR catalysts in cement kiln flue gas denitrification is proposed. Summary of the Invention

[0007] The present invention aims to solve at least one of the technical problems existing in the prior art, and provides a method for deep removal and recovery of calcium poisoning in waste SCR catalysts from cement kiln flue gas denitrification.

[0008] This invention provides a method for deep removal and recovery of calcium poisoning from spent SCR catalyst in cement kiln flue gas denitrification, comprising the following steps: S1. Pre-treat the waste SCR catalyst to obtain waste SCR powder; S2. The waste SCR powder is calcined in a reducing atmosphere to convert at least part of the insoluble calcium-containing phase into a calcium-containing phase that can be dissolved under preset acid leaching conditions, and at least part of the titanium-containing phase into low-valence titanium oxide that is insoluble under preset acid leaching conditions, to obtain the calcined product. S3. The roasted product is leached with an acid leaching solution under the preset acid leaching conditions to obtain a leaching slurry. The leaching slurry is then separated into solid and liquid components to obtain a calcium-containing leachate and a decalcified residue. S4. The decalcified slag is treated by selecting either an alkaline leaching recovery route or a direct acidolysis recovery route. When the alkaline leaching recovery route is selected, vanadium and tungsten are introduced into the alkaline leaching solution to obtain titanium-rich slag. When the direct acidolysis recovery route is selected, acidolysis material is formed. The acidolysis material is subjected to water leaching and solid-liquid separation to obtain titanium-containing acid leaching solution. The titanium-containing acid leaching solution is hydrolyzed to separate metatitanic acid and vanadium and tungsten-containing hydrolysis mother liquor. The metatitanic acid is then calcined to obtain titanium dioxide product.

[0009] Furthermore, the particle size of the waste SCR powder is no greater than 75 μm.

[0010] Specifically, the sparingly soluble calcium-containing phases in the spent SCR catalyst include one or more of calcium sulfate, calcium titanate, calcium metavanadate, and calcium tungstate; the total calcium content of the spent SCR catalyst, calculated as CaO, is 10wt% to 30wt%.

[0011] Specifically, in step S2, the reduction calcination temperature is 550℃~900℃; the reduction calcination time is 0.5h~5h.

[0012] Specifically, in step S2, the reducing atmosphere is a mixture of a reducing gas and nitrogen or argon; the volume fraction of the reducing gas is 5% to 50%; the reducing gas includes at least one of hydrogen, carbon monoxide and methane.

[0013] Specifically, in step S3, the acid leaching solution is any one of hydrochloric acid solution, acetic acid solution, and formic acid solution.

[0014] Further, the preset acid leaching conditions are as follows: the solid-liquid ratio of the roasted product to the acid leaching solution is 1g:3mL to 1g:10mL; the concentration of the acid leaching solution is 0.5mol / L to 3mol / L; the leaching time of the acid leaching solution is 0.5h to 4h; and the leaching temperature of the acid leaching solution is 25℃ to 50℃.

[0015] Furthermore, step S3 also includes the following step: evaporating and crystallizing the calcium-containing leachate to obtain calcium acetate, calcium chloride, or calcium formate.

[0016] Furthermore, in step S4, the alkaline leaching recovery process includes the following steps: leaching the decalcified slag with sodium hydroxide solution at 80°C to 120°C, and separating the solid and liquid to obtain an alkaline leaching solution containing vanadium and tungsten and titanium-rich slag; precipitating the alkaline leaching solution stepwise to recover vanadium and tungsten in sequence; or extracting the alkaline leaching solution to recover tungsten and vanadium in sequence; and washing and drying the titanium-rich slag in sequence.

[0017] Specifically, in step S4, the decalcified slag is acidified with concentrated sulfuric acid at a concentration of 75wt%–90wt% and an acid-to-material mass ratio of 1.5–1.8:1 at 150°C–200°C to obtain acidified material; the acidified material is subjected to water leaching and solid-liquid separation to obtain titanium-containing acid leaching solution; the titanium-containing acid leaching solution is hydrolyzed, and solid-liquid separation is performed to obtain metatitanic acid and hydrolysis mother liquor containing vanadium and tungsten; the metatitanic acid is calcined; vanadium is separated and recovered from the hydrolysis mother liquor, and tungsten is recovered from the mother liquor after vanadium separation.

[0018] The beneficial effects of this invention are as follows: 1. This invention changes the occurrence forms of calcium and titanium in waste SCR powder by reducing and roasting it, reducing and decomposing the insoluble calcium-containing phase into acid-soluble calcium oxide, reducing titanium into low-valence titanium oxide, and selectively decalcifying it under acid leaching solution conditions, thereby effectively improving the calcium removal rate and reducing the titanium loss rate. 2. In the decalcification process of this invention, one or more of dilute hydrochloric acid, dilute acetic acid, and dilute formic acid are used to avoid the corrosion of equipment by strong acids. Moreover, the calcium-containing leachate can produce calcium acetate or calcium chloride as byproducts, with no waste acid discharge, making it green and environmentally friendly. 3. The calcium content of the material after decalcification is effectively reduced by the present invention, which makes the subsequent alkaline leaching recovery of vanadium and tungsten and titanium slag preparation of titanium dioxide highly compatible with the waste catalyst recovery process of coal-fired power plants. It can be directly connected to existing production lines, and the industrialization threshold is low. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the steps of a method for deep removal and recovery of calcium poisoning from waste SCR catalyst in cement kiln flue gas denitrification according to a specific embodiment of the present invention. Figure 2 A simplified flowchart illustrating the steps of a method for deep removal and recovery of calcium poisoning from waste SCR catalyst in cement kiln flue gas denitrification, which is another specific embodiment of the present invention. Figure 3 This is a schematic diagram showing the changes in the content of the main components before and after reduction roasting and decalcification in acid leaching solution in Example 1 of the present invention; Figure 4 This is a schematic diagram illustrating the effect of calcination temperature on calcium leaching rate and titanium loss rate in this invention. Detailed Implementation

[0020] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] like Figure 1 As shown in the specific embodiment of the present invention, the method for deep removal and recovery of calcium poisoning from waste SCR catalyst in cement kiln flue gas denitrification includes the following steps: S1, pretreating the waste SCR catalyst to obtain waste SCR powder; S2, calcining the waste SCR powder under a reducing atmosphere, so that at least part of the insoluble calcium-containing phase is converted into a calcium-containing phase that can be dissolved under preset acid leaching conditions, and at least part of the titanium-containing phase is converted into low-valent titanium oxides that are insoluble under preset acid leaching conditions, to obtain the calcined product; S3, using an acid leaching solution under the preset acid leaching conditions... The roasted product is leached to obtain a leaching slurry. The leaching slurry is then subjected to solid-liquid separation to obtain a calcium-containing leaching solution and decalcified slag. S4: The decalcified slag is treated by selecting either an alkaline leaching recovery route or a direct acidolysis recovery route. When the alkaline leaching recovery route is selected, vanadium and tungsten are introduced into the alkaline leaching solution to obtain titanium-rich slag. When the direct acidolysis recovery route is selected, an acidolysis material is formed. The acidolysis material is subjected to water leaching and solid-liquid separation to obtain a titanium-containing acid leaching solution. The titanium-containing acid leaching solution is then hydrolyzed to separate metatitanic acid and vanadium- and tungsten-containing hydrolysis mother liquor. The metatitanic acid is then calcined to obtain titanium dioxide products.

[0022] In one specific implementation, the waste SCR powder is reconstructed through reduction calcination and selective leaching with dilute acid. This process breaks down the stable lattice structure of the insoluble calcium-containing phase in the waste SCR powder, transforming it into a soluble state. At the same time, the titanium-containing phase is transformed into a low-valence oxide that is thermodynamically stable under acidic conditions. This achieves deep removal of calcium and solid-phase retention of titanium under mild conditions, laying the foundation for the high-purity recovery of valuable metals in the future.

[0023] Furthermore, the particle size of the waste SCR powder is no greater than 75 μm.

[0024] In the above embodiments, by controlling the particle size of the waste SCR powder, the specific surface area of ​​the material is increased, which is conducive to the full progress of the gas-solid reaction in the subsequent reduction roasting process, thereby effectively improving the uniformity of phase transformation and the reaction rate.

[0025] Furthermore, the sparingly soluble calcium-containing phases in the spent SCR catalyst include one or more of calcium sulfate, calcium titanate, calcium metavanadate, and calcium tungstate; the total calcium content of the spent SCR catalyst, calculated as CaO, is 10wt% to 30wt%.

[0026] Furthermore, in step S2, the reduction calcination temperature is 550℃~900℃; the reduction calcination time is 0.5h~5h.

[0027] Further, in step S2, the reducing atmosphere is a mixture of a reducing gas and nitrogen or argon; the volume fraction of the reducing gas is 5% to 50%; the reducing gas includes at least one of hydrogen, carbon monoxide and methane.

[0028] Based on the above basic implementation method, the waste SCR powder obtained in step S1 is placed in an atmosphere furnace and calcined at 550℃~900℃ for 0.5h~5h under a reducing atmosphere to allow the insoluble calcium-containing phase in the catalyst to undergo a reduction decomposition reaction. The calcium-containing phase includes one or more of calcium titanate (CaTiO3), calcium metavanadate (CaV2O6), calcium tungstate (CaWO4), and calcium sulfate (CaSO4). Among them, CaTiO3 can be reduced and decomposed into calcium oxide (CaO) and low-valent titanium oxide, CaV2O6 is reduced into CaO and low-valent vanadium oxide, CaWO4 is reduced into CaO and tungsten dioxide (WO2) or tungsten (W), and CaSO4 is reduced into CaO or calcium sulfide (CaS) to obtain the calcined product.

[0029] Furthermore, in step S3, the acid leaching solution is any one of hydrochloric acid solution, acetic acid solution, and formic acid solution.

[0030] Further, the preset acid leaching conditions are as follows: the solid-liquid ratio of the roasted product to the acid leaching solution is 1g:3mL to 1g:10mL; the concentration of the acid leaching solution is 0.5mol / L to 3mol / L; the leaching time of the acid leaching solution is 0.5h to 4h; and the leaching temperature of the acid leaching solution is 25℃ to 50℃.

[0031] Furthermore, step S3 also includes the following step: evaporating and crystallizing the calcium-containing leachate to obtain calcium acetate, calcium chloride, or calcium formate.

[0032] In the above embodiments, the calcium in the calcination product exists in the form of free CaO, which is highly soluble in acid leaching solutions; while titanium exists in the form of low-valence oxides, which have a very low dissolution rate in acid leaching solutions (especially weak acids such as acetic acid), and is almost insoluble; under room temperature or slightly heated conditions, calcium is efficiently and selectively dissolved in a mild acid leaching solution such as dilute acetic acid to obtain a calcium-containing leachate, controlling the titanium loss rate to within 5%, and reducing the calcium content of the material after solid-liquid separation to below 0.5%, effectively reducing the impact on the quality of subsequent titanium products.

[0033] Further, in step S4, the alkaline leaching recovery process includes the following steps: leaching the decalcified slag with sodium hydroxide solution at 80℃~120℃, and separating the solid and liquid to obtain an alkaline leaching solution containing vanadium and tungsten and titanium-rich slag; precipitating the alkaline leaching solution stepwise to recover vanadium and tungsten in sequence; or extracting the alkaline leaching solution to recover tungsten and vanadium in sequence; and washing and drying the titanium-rich slag in sequence.

[0034] In the above embodiments, when using the alkaline leaching recovery route, the alkaline leaching solution is precipitated in steps. The stepwise precipitation process is as follows: Dilute sulfuric acid is added dropwise to the alkaline leaching solution at room temperature to adjust the pH to 8.0–9.0. Ammonium chloride solid is added and stirred for 2 hours. Vanadium selectively forms ammonium metavanadate precipitate, which is separated by filtration to obtain solid ammonium metavanadate, while the tungsten-containing component remains in the filtrate. Dilute sulfuric acid is added dropwise to the vanadium-removed tungsten filtrate to adjust the pH to 1–2, and stirred for 1.5 hours to precipitate tungstic acid, which is then filtered to obtain tungstic acid. Ammonium metavanadate and tungstic acid are calcined separately to recover the precipitate. Ammonium metavanadate and tungstic acid, after calcination, yield vanadium pentoxide (V₂O₅) and tungsten trioxide (WO₃), respectively. Alternatively, the alkaline leaching solution can be extracted, with the following extraction process: First, selective tungsten extraction is performed: maintaining a strongly alkaline environment (pH > 12) in the leaching solution, a quaternary ammonium salt extractant is prepared with an organic solvent to form an organic phase, and the clear alkaline solution is subjected to multi-stage countercurrent extraction. Under the strongly alkaline system, tungstate ions preferentially combine with the extractant and enter the organic phase, while most vanadate ions remain in the aqueous raffinate, achieving selective and preferential separation of tungsten. The organic phase containing tungsten is then back-extracted using an ammonium salt solution to obtain a high-purity ammonium tungstate enriched solution. The pH of the ammonium tungstate enriched solution is adjusted to strongly acidic, and tungstate ions hydrolyze to precipitate yellow tungstic acid. After washing and drying, a high-purity tungstic acid precursor is obtained, which can then be calcined to obtain the WO₃ product. Vanadium extraction from the raffinate was then performed: the vanadium-containing aqueous raffinate after tungsten separation was collected, and the pH of the system was adjusted to a weakly alkaline range of 9.5–11.5, converting the vanadium components in the system into easily extractable polyvanadate. The pH-adjusted solution was then subjected to multi-stage extraction using a suitable extractant, selectively loading vanadate onto the organic phase to achieve vanadium enrichment and separation. The vanadium-loaded organic phase was back-extracted using an ammonium salt system to obtain a vanadium-rich solution. Ammonium chloride was added to the vanadium-rich solution, and the specific binding effect of vanadate and ammonium ions under weakly alkaline conditions precipitated white ammonium metavanadate crystals. After solid-liquid separation, washing, and drying, a high-purity ammonium metavanadate precursor was obtained, which, after calcination, yielded V2O5. The titanium-rich slag was washed and dried, and titanium dioxide was prepared by sulfuric acid acid hydrolysis.

[0035] Further, in step S4, the direct acidolysis recovery route includes the following steps: acidolysis of the decalcified slag with concentrated sulfuric acid at a concentration of 75wt% to 90wt% and an acid-to-material mass ratio of 1.5 to 1.8:1 at 150°C to 200°C to obtain acidolysis material; water leaching and solid-liquid separation of the acidolysis material to obtain titanium-containing acid leaching solution; hydrolysis of the titanium-containing acid leaching solution, followed by solid-liquid separation to obtain metatitanic acid and a hydrolysis mother liquor containing vanadium and tungsten; calcination of the metatitanic acid; separation and recovery of vanadium from the hydrolysis mother liquor, and recovery of tungsten from the mother liquor after vanadium separation.

[0036] In the above embodiments, when using the direct acidolysis recovery route, after concentrated sulfuric acid acidolysis, process water is added to the system for dilution and leaching. The system is kept warm and stirred to dissolve soluble sulfates of titanium, vanadium, and tungsten, while calcium impurities precipitate as solid calcium sulfate. Solid-liquid separation is achieved by hot pressure filtration. The solid phase is calcium sulfate residue, and the liquid phase is an acidic leachate containing titanium oxysulfate, vanadium, and tungsten. Iron or aluminum powder is added to the acidic leachate for reduction, reducing high-valent titanium to easily hydrolyzable trivalent titanium, while simultaneously reducing high-valent vanadium and tungsten. After reduction, the solution is allowed to settle to remove suspended fine solid impurities, yielding a clear and refined titanium solution. The refined titanium solution is heated to boiling for hot water hydrolysis, where titanium oxysulfate hydrolyzes to generate a white precipitate of metatitanic acid. The hydrolysis mother liquor and metatitanic acid filter cake are separated by pressure filtration. The hydrolysis mother liquor is collected for later use, and the metatitanic acid filter cake is washed multiple times to remove free sulfuric acid, vanadium, and tungsten impurities. The washed metatitanic acid... The titanium dioxide product is obtained after high-temperature calcination in a rotary kiln, crystal transformation, dehydration, and desulfurization. V and W in the hydrolysis mother liquor are recovered using ion exchange resin. The specific steps are as follows: S1, Mother liquor pretreatment adsorption: The hydrolysis mother liquor is cooled to room temperature, and the pH of the solution is adjusted to 2.0–3.0 with a small amount of dilute sulfuric acid. Suspended fine solid impurities are removed by filtration to obtain a clear pre-exchange liquor. The pre-exchange liquor is passed uniformly from top to bottom through an ion exchange column packed with D201 type strong basic anion exchange resin. Dynamic adsorption occurs at room temperature and pressure. Vanadium and tungsten are adsorbed by the resin in the form of vanadium oxide anions and polytungstate anions. The liquid is continuously passed through until the resin is saturated. The tail liquid, free of vanadium and tungsten, is collected and returned to the acid hydrolysis process for recycling. S2, Water washing and impurity removal: After adsorption saturation, the resin column is flushed forward with deionized water to remove residual sulfuric acid and soluble impurities from the resin pores until the pH of the effluent is reduced. Nearly neutral; S3, Stepwise desorption: 2 mol / L dilute hydrochloric acid is introduced into the resin column as a elution agent, and dynamic elution is performed at room temperature. Vanadium anions loaded on the resin are selectively desorbed, and the vanadium elution solution is collected. The overall vanadium recovery rate is 89%. After vanadium elution, the resin column is washed again with water to remove residual hydrochloric acid. Then, 3 mol / L sodium hydroxide solution is introduced into the resin column as a tungsten elution agent, and tungstate is completely desorbed to obtain a tungsten-enriched solution. The overall tungsten recovery rate is 92%. S4, Resin regeneration and recycling: After desorption, the resin is rinsed sequentially with dilute hydrochloric acid and sodium chloride conversion solution to restore the resin to the chloride form, which can be reused for the adsorption of the next batch of mother liquor. The vanadium elution solution and tungsten-enriched solution are neutralized, precipitated, and calcined respectively to obtain V2O5 and WO3 products.

[0037] To help better understand the present invention, the following embodiments of this application disclose some specific implementation processes and comparative processes of the method for deep removal and recovery of calcium poisoning from waste SCR catalyst in cement kiln flue gas denitrification. The specific implementation processes and comparative processes include the exemplary embodiments 1 to 3 and comparative examples 1 and 2. The waste SCR catalyst used in the embodiments and comparative examples of the present invention is a honeycomb vanadium pentoxide-tungsten trioxide supported titanium dioxide (V2O5-WO3 / TiO2) catalyst taken from the SCR denitrification unit of a 5000t / d cement clinker production line and operated for about 32000h. After normalization, the chemical composition of the spent SCR catalyst was analyzed by XRF. By mass fraction, it included: 63.6% titanium dioxide (TiO2), 4.1% tungsten trioxide (WO3), 0.73% vanadium pentoxide (V2O5), 18.1% calcium oxide (CaO), 5.6% silicon dioxide (SiO2), 2.4% aluminum oxide (Al2O3), 3.1% sulfur trioxide (SO3), 0.6% alkali metal oxides (K2O+Na2O), 1.7% iron oxide (Fe2O3), and 0.07% other substances. During the XRF test, CaTiO3, CaV2O6, CaWO4, and CaSO4 were all classified as CaO.

[0038] Example 1 provides a method for deep removal and recovery of calcium poisoning from spent SCR catalyst in cement kiln flue gas denitrification, comprising the following steps: S1. The honeycomb V2O5-WO3 / TiO2 catalyst is successively subjected to blowing, crushing and ball milling until the proportion of 200 mesh powder reaches 95%, and honeycomb V2O5-WO3 / TiO2 catalyst powder is obtained. The catalyst powder is dried at 110℃ for 4 hours for later use. S2. Take 300g of the catalyst powder prepared in step S1, spread it evenly in the corundum boat, and place the corundum boat in a tube furnace. Introduce a mixed gas of hydrogen (H2) and nitrogen (N2) with a flow rate of 0.6L / min, wherein the volume fraction of H2 is 20%. Raise the temperature in the tube furnace to 750℃ at a heating rate of 8℃ / min, hold for 2h, and then cool the catalyst powder to room temperature with the furnace under N2 protection to obtain 285g of calcined product. S3. Add 285g of the calcined product prepared in step S2 to 1500ml of acetic acid solution with a concentration of 1.5mol / L and a solid-liquid ratio of 1:5.3. Immerse the product in a water bath at 45℃ with stirring at 400r / min for 1.5h. After filtration, wash the filter cake with 200ml of deionized water to obtain a decalcified filter cake with a dry weight of 229g. Combine the filtrate and washings, concentrate by evaporation, and cool to crystallize, obtaining 208g of calcium acetate tetrahydrate crystals with a purity of 98.5%, achieving a calcium crystal recovery rate of 95%. S4. The decalcified filter cake prepared in step S3 is added to a NaOH solution containing 20wt% sodium hydroxide (NaOH) at a solid-liquid ratio of 1:4. The mixture is stirred and leached at 110℃ for 3 hours. After solid-liquid separation, an alkaline leaching solution containing V and W and titanium-rich slag are obtained. The leaching rate of V in the alkaline leaching solution is 94.1%, and the leaching rate of W is 95.5%. The alkaline leaching solution is then precipitated stepwise with ammonium chloride (NH4Cl). The specific precipitation process is as follows: at room temperature, dilute sulfuric acid is added dropwise to the alkaline leaching solution to adjust the pH to 8.0–9.0. Solid ammonium chloride (the amount of ammonium chloride is 2.5 times the amount of vanadium in the system) is added, and the mixture is stirred for 2 hours. Vanadium selectivity… Ammonium metavanadate precipitate was generated, and the solid ammonium metavanadate was obtained by filtration. The tungsten-containing component remained in the filtrate. Dilute sulfuric acid was added dropwise to the tungsten filtrate after vanadium removal to adjust the pH to 1-2. The mixture was stirred for 1.5 h to precipitate tungstic acid, which was then filtered to obtain tungstic acid. The ammonium metavanadate and tungstic acid were calcined separately to recover the ammonium metavanadate and tungstic acid. After calcination, 2.1 g of V2O5 product with a purity of 98.3% and 11.9 g of WO3 product with a purity of 98.8% were obtained. After washing and drying the titanium-rich slag, the internal TiO2 content was 91.6 wt% and the CaO content was 0.12 wt%. Titanium dioxide was prepared by acid hydrolysis of the titanium-rich slag with sulfuric acid.

[0039] In step S2 of this embodiment, XRD analysis of the calcined product showed that the diffraction peaks of CaTiO3 and CaSO4 in the calcined product completely disappeared, and obvious CaO diffraction peaks appeared; the diffraction peaks of TiO2 weakened, and broadened characteristic peaks of low-valent titanium oxide (TiO) appeared; in step S3, ICP-OES analysis of the combined filtrate and washing liquid and the decalcified filter cake showed that the calcium leaching rate was 96.8%, the titanium loss rate was 2.1%, and the content of CaO in the decalcified filter cake was 0.76 wt%, the content of TiO2 was 81.60 wt%, the content of WO3 was 5.30 wt%, and the content of V2O5 was 0.94 wt%. Example 2 differs from Example 1 in that, in step S2, the reducing atmosphere is adjusted to a CO / N2 mixture, with a CO volume fraction of 30%, the calcination temperature is adjusted to 800℃, and the holding time is adjusted to 1.5 h; in step S3, the acetic acid solution is adjusted to 1 mol / L dilute hydrochloric acid, the water bath temperature is adjusted to 25℃, and the leaching time is adjusted to 2 h. All other steps and parameters are consistent with Example 1. Testing showed that the calcium leaching rate in the leachate was 95.2%, and the titanium dissolution rate was 3.8%. After alkaline leaching of the decalcified residue, the V and W leaching rates were 93.5% and 94.8%, respectively.

[0040] Example 3 differs from Example 1 in that, in step S2, the reducing atmosphere is adjusted to a CH4 / N2 mixture, with a CH4 volume fraction of 10%; the calcination temperature is adjusted to 850℃; and the holding time is adjusted to 1 hour. In step S3, the 1.5 mol / L DE1 acetic acid solution is adjusted to a 2 mol / L acetic acid solution; the water bath temperature is adjusted to 50℃; and the leaching time is adjusted to 1 hour. All other steps and parameters are the same as in Example 1. Testing showed that the calcium leaching rate in the leachate was 97.1%, and the titanium dissolution rate was 1.9%. The purity of the obtained calcium acetate was 98.1%.

[0041] Example 4 differs from Example 1 in that, in step S4, 200g of the decalcified filter cake obtained in step S3 is taken and acidified with 80wt% concentrated sulfuric acid at 180℃ for 2 hours, wherein the acid-to-material ratio of concentrated sulfuric acid to decalcified filter cake is 1.6:1. After acidification, process water is added to the system for dilution and leaching, and the system is kept warm and stirred to dissolve soluble sulfates of titanium, vanadium, and tungsten, while calcium impurities precipitate as solid calcium sulfate. Solid-liquid separation is achieved by hot pressure filtration, with the solid phase being calcium sulfate slag and the liquid phase being titanium oxide containing sulfate. Acidic leaching solutions of vanadium and tungsten; iron or aluminum powder is added to the acidic leaching solution for reduction, reducing high-valent titanium to easily hydrolyzable trivalent titanium, while simultaneously reducing high-valent vanadium and tungsten; after reduction, the solution is allowed to settle to remove suspended fine solid impurities, yielding a clear and refined titanium solution; the refined titanium solution is heated to boiling for hot hydrolysis, where titanium sulfate oxyhydrate hydrolyzes to produce a white precipitate of metatitanic acid; the mother liquor and metatitanic acid filter cake are separated by pressure filtration, the mother liquor is collected for later use, and the metatitanic acid filter cake is washed repeatedly with water to remove free sulfuric acid, vanadium, and tungsten impurities; the washed metatitanic acid filter cake... Titanic acid is fed into a rotary kiln for high-temperature calcination. After crystal transformation, dehydration, and desulfurization, titanium dioxide is obtained. This titanium dioxide product has a TiO2 content of 97.8%, a whiteness of 96.3%, and a CaO content of 0.008%, meeting the standards for superior-grade titanium dioxide. V and W in the hydrolysis mother liquor are recovered using ion exchange resin. The specific steps are as follows: S1, Mother Liquor Pretreatment Adsorption: The hydrolysis mother liquor is cooled to room temperature, and the pH of the solution is adjusted to 2.0–3.0 with a small amount of dilute sulfuric acid. Suspended fine solid impurities are removed by filtration. The clarified pre-exchange solution is obtained. This pre-exchange solution is then uniformly passed from top to bottom into an ion exchange column packed with D201 type strong basic anion exchange resin. Dynamic adsorption occurs at room temperature and pressure. Vanadium and tungsten are adsorbed by the resin as vanadium oxide anions and polytungstate anions, respectively. The solution is continuously passed through until the resin is saturated. The tail liquid, free of vanadium and tungsten, is collected and recycled back to the acidolysis process. S2, Water washing to remove impurities: After adsorption saturation, the resin column is flushed forward with deionized water to remove residual sulfuric acid and soluble impurities from the resin pores until the pH of the effluent is reached. The solution is near neutral. S3, Stepwise Desorption: A 2 mol / L dilute hydrochloric acid solution is introduced into the resin column for dynamic elution at room temperature. Vanadium anions loaded on the resin are selectively desorbed, and the vanadium elution solution is collected, with a vanadium recovery rate of 89%. After vanadium elution, the resin column is washed again with water to remove residual hydrochloric acid. Then, a 3 mol / L sodium hydroxide solution is introduced into the resin column as a tungsten elution agent, resulting in complete desorption of tungstate ions to obtain a tungsten-enriched solution with a tungsten recovery rate of 92%. S4, Resin Regeneration and Recycling: After desorption, the resin is rinsed sequentially with dilute hydrochloric acid and sodium chloride conversion solution to restore it to its chloride form, allowing it to be reused for the next batch of mother liquor adsorption. The vanadium elution solution and tungsten-enriched solution are neutralized, precipitated, and calcined to obtain V2O5 and WO3 products. The remaining steps and parameters are consistent with Example 1.

[0042] Comparative Example 1: 300g of the same honeycomb V2O5-WO3 / TiO2 catalyst powder as in Example 1 was taken and leached directly with 1.5mol / L acetic acid at 45℃ for 1.5h without reduction calcination. All other steps and parameters were the same as in Example 1. After solid-liquid separation, analysis showed that the calcium leaching rate was 21.3% due to the insolubility of most CaTiO3, and the titanium leaching rate reached 11.5% due to the partial dissolution of TiO2 under acidic conditions. The CaO content of the titanium-rich slag after alkaline leaching of the decalcified slag was 14.6%.

[0043] Comparative Example 2: 300g of the same honeycomb V2O5-WO3 / TiO2 catalyst powder as in Example 1 was taken and directly leached at 110℃ for 3 hours in a 20wt% NaOH solution without any decalcification treatment. All other steps and parameters were the same as in Example 1. After solid-liquid separation, the CaO content in the titanium-rich slag was found to be 19.3%, while the TiO2 content was only 62.8%. The titanium dioxide obtained from this titanium-rich slag via sulfuric acid acid hydrolysis had a CaO content as high as 0.15% and a whiteness of only 90.1%.

[0044] Combination Figure 4 As shown, the calcium leaching rate increases rapidly with the calcination temperature from 500℃ to 650℃; the calcium leaching rate remains at a high level in the range of 650℃ to 800℃; at 750℃, the calcium leaching rate is 96.8% and the titanium loss rate is 2.1%, indicating superior overall performance; when the temperature is further increased, the calcium leaching rate does not continue to increase, while the titanium loss rate shows an upward trend. Therefore, the preferred calcination temperature is 650℃ to 800℃, and more preferably 750℃.

[0045] Combination Figure 3As shown, compared with the untreated honeycomb V2O5-WO3 / TiO2 catalyst, the decalcified slag obtained in Example 1 had a CaO content of 0.76 wt%, which was effectively reduced compared to the 18.1 wt% in the honeycomb V2O5-WO3 / TiO2 catalyst, thus effectively improving the decalcification effect. The TiO2, WO3, and V2O5 contents in the decalcified slag were 81.6 wt%, 5.3 wt%, and 0.94 wt%, respectively, which were effectively increased compared to the 63.6 wt%, 4.1 wt%, and 0.73 wt% in the honeycomb V2O5-WO3 / TiO2 catalyst, fully meeting the process requirements for subsequent vanadium-tungsten recovery and titanium dioxide preparation. The experimental results of Comparative Example 1 also show that omitting the reduction roasting step and directly acid leaching not only resulted in a calcium leaching rate of less than 25%, but also increased titanium dissolution loss. The experimental results of Comparative Examples 2 and 4 show that directly recovering valuable components without decalcification treatment resulted in titanium dioxide products with excessive calcium content and substandard whiteness, failing to meet the quality requirements for qualified products. Therefore, the treatment method provided by this invention has high decalcification efficiency, low titanium loss rate, green and environmentally friendly process with no waste acid emission, and can also produce high-purity calcium salt as a by-product. At the same time, it can be directly industrialized by relying on the existing waste SCR catalyst recycling production line of coal-fired power plants. It can efficiently and cleanly recover various valuable components in waste SCR catalysts from cement kiln flue gas denitrification, solve the industry pain point of high calcium poisoning waste catalysts being difficult to recycle and utilize, and has good prospects for industrial application and economic and environmental benefits.

[0046] In summary, the embodiments disclosed herein have at least the following technical effects: 1. This invention changes the occurrence form of calcium and titanium in waste SCR powder by reducing and roasting it, reducing and decomposing the insoluble calcium-containing phase into acid-soluble calcium oxide, reducing titanium into low-valence titanium oxide, and highly selectively decalcifying it under acid leaching solution conditions, thereby effectively improving the calcium removal rate and reducing the titanium loss rate. 2. In the decalcification process of this invention, one or more of dilute hydrochloric acid, dilute acetic acid, and dilute formic acid are used to avoid the corrosion of equipment by strong acids. Moreover, the calcium-containing leachate can produce calcium acetate or calcium chloride as byproducts, with no waste acid discharge, making it green and environmentally friendly. 3. The calcium content of the material after decalcification is effectively reduced by the present invention, which makes the subsequent alkaline leaching recovery of vanadium and tungsten and titanium slag preparation of titanium dioxide highly compatible with the waste catalyst recovery process of coal-fired power plants. It can be directly connected to existing production lines, and the industrialization threshold is low.

[0047] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for deep removal and recovery of calcium poisoning from spent SCR catalyst in cement kiln flue gas denitrification, characterized in that, Includes the following steps: S1. Pre-treat the waste SCR catalyst to obtain waste SCR powder; S2. The waste SCR powder is calcined in a reducing atmosphere to convert at least part of the insoluble calcium-containing phase into a calcium-containing phase that can be dissolved under preset acid leaching conditions, and at least part of the titanium-containing phase into low-valence titanium oxide that is insoluble under preset acid leaching conditions, to obtain the calcined product. S3. The roasted product is leached with an acid leaching solution under the preset acid leaching conditions to obtain a leaching slurry. The leaching slurry is then separated into solid and liquid components to obtain a calcium-containing leaching solution and a decalcified residue. S4. The decalcified slag is treated by selecting either an alkaline leaching recovery route or a direct acidolysis recovery route. When the alkaline leaching recovery route is selected, vanadium and tungsten are introduced into the alkaline leaching solution to obtain titanium-rich slag. When the direct acidolysis recovery route is selected, acidolysis material is formed. The acidolysis material is subjected to water leaching and solid-liquid separation to obtain titanium-containing acid leaching solution. The titanium-containing acid leaching solution is hydrolyzed to separate metatitanic acid and vanadium and tungsten-containing hydrolysis mother liquor. The metatitanic acid is then calcined to obtain titanium dioxide product.

2. The method for deep removal and recovery of calcium poisoning from spent SCR catalyst in cement kiln flue gas denitrification according to claim 1, characterized in that, The particle size of the waste SCR powder is no greater than 75 μm.

3. The method for deep removal and recovery of calcium poisoning from spent SCR catalyst in cement kiln flue gas denitrification according to claim 1, characterized in that, The sparingly soluble calcium-containing phases in the spent SCR catalyst include one or more of calcium sulfate, calcium titanate, calcium metavanadate, and calcium tungstate; the total calcium content of the spent SCR catalyst, calculated as CaO, is 10wt% to 30wt%.

4. The method for deep removal and recovery of calcium poisoning from spent SCR catalyst in cement kiln flue gas denitrification according to claim 1, characterized in that, In step S2, the reduction calcination temperature is 550℃~900℃; the reduction calcination time is 0.5h~5h.

5. The method for deep removal and recovery of calcium poisoning from spent SCR catalyst in cement kiln flue gas denitrification according to claim 4, characterized in that, In step S2, the reducing atmosphere is a mixture of a reducing gas and nitrogen or argon; the volume fraction of the reducing gas is 5% to 50%; the reducing gas includes at least one of hydrogen, carbon monoxide and methane.

6. The method for deep removal and recovery of calcium poisoning from spent SCR catalyst in cement kiln flue gas denitrification according to claim 1, characterized in that, In step S3, the acid leaching solution is any one of hydrochloric acid solution, acetic acid solution, and formic acid solution.

7. The method for deep removal and recovery of calcium poisoning from spent SCR catalyst in cement kiln flue gas denitrification according to claim 6, characterized in that, The preset acid leaching conditions are as follows: the solid-liquid ratio of the roasted product to the acid leaching solution is 1g:3mL to 1g:10mL; the concentration of the acid leaching solution is 0.5mol / L to 3mol / L; the leaching time of the acid leaching solution is 0.5h to 4h; and the leaching temperature of the acid leaching solution is 25℃ to 50℃.

8. The method for deep removal and recovery of calcium poisoning from spent SCR catalyst in cement kiln flue gas denitrification according to claim 1, characterized in that, Step S3 also includes the following steps: The calcium-containing leachate is evaporated and crystallized to obtain calcium acetate, calcium chloride, or calcium formate.

9. The method for deep removal and recovery of calcium poisoning from spent SCR catalyst in cement kiln flue gas denitrification according to any one of claims 1 to 8, characterized in that, In step S4, the alkaline leaching recovery route treatment includes the following steps: The decalcified slag is leached with sodium hydroxide solution at 80℃~120℃, and solid-liquid separation is performed to obtain an alkaline leaching solution containing vanadium and tungsten and titanium-rich slag; the alkaline leaching solution is precipitated stepwise to recover vanadium and tungsten in sequence; or the alkaline leaching solution is extracted to recover tungsten and vanadium in sequence; the titanium-rich slag is washed and dried in sequence.

10. The method for deep removal and recovery of calcium poisoning from spent SCR catalyst in cement kiln flue gas denitrification according to any one of claims 1 to 8, characterized in that, In step S4, the direct acid hydrolysis recovery route includes the following steps: The decalcified slag is acidified with concentrated sulfuric acid at a concentration of 75wt%–90wt% and an acid-to-material mass ratio of 1.5–1.8:1 at 150℃–200℃ to obtain acidified material. The acidified material is then subjected to water leaching and solid-liquid separation to obtain a titanium-containing acid leaching solution. The titanium-containing acid leaching solution is then hydrolyzed, and solid-liquid separation is performed to obtain metatitanic acid and a hydrolysis mother liquor containing vanadium and tungsten. The metatitanic acid is then calcined. Vanadium is separated and recovered from the hydrolysis mother liquor, and tungsten is recovered from the mother liquor after vanadium separation.

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