Two series of ZSM-5 and beta zeolites were pretreated in 1.0 mol/L HNO3 solution at room temper-ature for various time periods. The catalytic performances of their Fe-exchanged products in N2O decomposition were evalu...Two series of ZSM-5 and beta zeolites were pretreated in 1.0 mol/L HNO3 solution at room temper-ature for various time periods. The catalytic performances of their Fe-exchanged products in N2O decomposition were evaluated. The Fe-zeolite catalysts were characterized using N2 adsorp-tion-desorption, inductively coupled plasma optical emission spectroscopy, X-ray diffraction, ultra-violet-visible spectroscopy, temperature-programmed desorption of NH3, and scanning and trans-mission electron microscopies. For the ZSM-5 zeolite, acid leaching primarily takes place on the crystal surface and the particle size is reduced, therefore the pore channels are shortened. However, because of the good stability of MFI zeolites, the acid does not greatly penetrate the pore channels and new mesopores are not created. For the beta zeolite, because the amorphous material is in-clined to dissolve（deagglomerate）, some of the micropores are slightly dilated. The improved cata-lytic activities can be explained by the increased active Fe loading as a result of structural changes.展开更多
In this study,spent WO_(3)/V_(2)O_(5)-TiO_(2) catalysts used for selective catalytic reduction were treated by a hydrometallurgical process to comprehensively recover valuable metallic elements,such as W,V,and Ti.Al a...In this study,spent WO_(3)/V_(2)O_(5)-TiO_(2) catalysts used for selective catalytic reduction were treated by a hydrometallurgical process to comprehensively recover valuable metallic elements,such as W,V,and Ti.Al and Si impurities were preferentially removed by selective micro wave-assisted alkali leaching.W and V were leached by enhanced high-pressure leaching with efficiencies estimated at 95% and 81%.The leaching of W and V followed the nuclear shrinkage model controlled by the combination of product layer diffusion and interfacial chemical reaction.A synergistic extraction was applied to separate W and V using an extractant mixture of di-(2-ethylhexyl)phosphoric acid P204 and the primary amine N1923.The extraction efficiencies of V and W reached 86.5% and 6.3%,respectively,with a separation coefficient(V/W) of 95.30.The product was precipitated after extraction to yield ammonium paratung state(APT) and NH_(4)VO_(3).The TiO_(2)catalyst carrier residue meets commercial specifications for reuse.This comprehensive recovery process with the characteristics of high-pressure leaching and synergistic extraction realizes the resourceful utilization of the spent catalysts.展开更多
Wastewater treatment is essential to guarantee human health and ecological security.Catalytic ozonation with nanocatalysts is a widely studied and efficient treatment technology.However,this method has always been lim...Wastewater treatment is essential to guarantee human health and ecological security.Catalytic ozonation with nanocatalysts is a widely studied and efficient treatment technology.However,this method has always been limited by nanocatalysts disadvantages such as easily loss,difficult to separate and reuse,and catalytic ability decay caused by aggregation,which could cause severe resources waste and potential risk to human health and ecosystem.To remedy these challenges,a magnetic-void-porous MnFe_(2)O_(4)/carbon microsphere shell nanocatalyst(CMS-MnFe_(2)O_(4))was successfully synthesized using renewable natural microalgae.The separation test showed CMS-MnFe_(2)O_(4) was rapidly separated within 2 min under an external magnetic field.In catalytic ozonation of oxalic acid(OA),CMS-MnFe_(2)O_(4) showed efficient and stable catalytic efficiency,reaching a maximum total organic carbon removal efficiency of 96.59% and maintained a 93.88% efficiency after 4 cycles.The stable catalytic efficiency was due to the supporting effects of the carbon microsphere shell,which significantly enhanced CMS-MnFe_(2)O_(4) chemical stability and reduced the metal ions leaching to 10-20% of MnFe_(2)O_(4) through electron transfer.To explore the catalytic mechanism,radical experiments were conducted and a new degradation pathway of OA involving superoxide anions rather than hydroxyl radicals was proposed.Consequently,this study suggests that an efficient,recyclable,stable,and durable catalyst for catalytic ozonation could be prepared.展开更多
An intensified oxidative acid leaching of copper–cadmium-bearing slag featuring using high-efficient oxygen carrier, such as activated carbon, was investigated to achieve high leaching rate of valuable metals. The ef...An intensified oxidative acid leaching of copper–cadmium-bearing slag featuring using high-efficient oxygen carrier, such as activated carbon, was investigated to achieve high leaching rate of valuable metals. The effects of leaching variables, including agitation rate, sulfuric acid concentration, temperature, slag particle size, activated carbon and cupric ion concentration, were examined. It is found that leaching rates of cadmium and zinc both exceed 99 % in a very short time, but for copper, leaching rate of 99 % is achieved under the optimized leaching parameters, which are agitation rate of 100 r·min^(-1), sulfuric acid concentration of 15 wt%, leaching temperature of 80 ℃, slag particle size of 48–75 lm, activated carbon concentration of 3 g·L^(-1),liquid-to-solid ratio of 4:1, oxygen flow rate of 0.16 L·min^(-1),and leaching time of 60 min. The macro-leaching kinetics of copper metal was analyzed, and it is concluded that the inner diffusion is the controlling step, with apparent activation energy of 18.6 kJ·mol^(-1). The leaching solution with pH value of 2–4 can be designed to selectively extract valuable metals without neutralization, and the leaching residue can be treated by prevailing Pb smelting process.展开更多
Selective catalytic reduction(SCR) catalyst waste is a hazardous solid waste that seriously threatens the environment and public health.In this study,a thermal melting technology is proposed for the treatment of waste...Selective catalytic reduction(SCR) catalyst waste is a hazardous solid waste that seriously threatens the environment and public health.In this study,a thermal melting technology is proposed for the treatment of waste SCR catalysts.The melting characteristics and mineral phase transformation of waste SCR catalysts blended with three different groups of additives were explored by heating stage microscopy,thermogravimetric analysis/differential scanning calorimetry(TG/DSC) analysis,thermodynamic simulation,and X-ray diffraction(XRD) analysis;heavy metal leaching toxicity was tested by inductively coupled plasma-atomic emission spectrometry(I CP-AES) analysis.The results indicated that the melting point of waste SCR catalysts can be effectively reduced with proper additives.The additive formula of 39.00% Fe2 O3(in weight),6.50% CaO,3.30% SiO2,and 1.20% Al2 O3 achieves the optimal fluxing behavior,significantly decreasing the initial melting temperature from 1223℃ to1169℃.Furthermore,the whole heating process of waste SCR catalysts can be divided into three stages:the solid reaction stage,the sintering stage,and the primary melting stage.The leaching concentrations of V,As,Pb,and Se are significantly reduced,from 10.64,1.054,0.195,and 0.347 mg/L to 0.178,0.025,0.048,and 0.003 mg/L,respectively,much lower than the standard limits after melting treatment,showing the strong immobilization capacity of optimal additives for heavy metals in waste SCR catalysts.The results demonstrate the feasibility of harmless melting treatments for waste SCR catalysts with relatively low energy consumption,providing theoretical support for a novel method of disposing of hazardous waste SCR catalysts.展开更多
基金supported by the National Natural Science Foundation of China (21307144,21307007)Science of Technology Development Plan of Jilin Province of China (20140520150JH)~~
文摘Two series of ZSM-5 and beta zeolites were pretreated in 1.0 mol/L HNO3 solution at room temper-ature for various time periods. The catalytic performances of their Fe-exchanged products in N2O decomposition were evaluated. The Fe-zeolite catalysts were characterized using N2 adsorp-tion-desorption, inductively coupled plasma optical emission spectroscopy, X-ray diffraction, ultra-violet-visible spectroscopy, temperature-programmed desorption of NH3, and scanning and trans-mission electron microscopies. For the ZSM-5 zeolite, acid leaching primarily takes place on the crystal surface and the particle size is reduced, therefore the pore channels are shortened. However, because of the good stability of MFI zeolites, the acid does not greatly penetrate the pore channels and new mesopores are not created. For the beta zeolite, because the amorphous material is in-clined to dissolve（deagglomerate）, some of the micropores are slightly dilated. The improved cata-lytic activities can be explained by the increased active Fe loading as a result of structural changes.
基金financially supported by Beijing Natural Science Foundation (No. 2222049)the National Natural Science Foundation of China (Nos. 52025042 and 51621003)National Key R&D Program of China (No. 2018YFC1901700)。
文摘In this study,spent WO_(3)/V_(2)O_(5)-TiO_(2) catalysts used for selective catalytic reduction were treated by a hydrometallurgical process to comprehensively recover valuable metallic elements,such as W,V,and Ti.Al and Si impurities were preferentially removed by selective micro wave-assisted alkali leaching.W and V were leached by enhanced high-pressure leaching with efficiencies estimated at 95% and 81%.The leaching of W and V followed the nuclear shrinkage model controlled by the combination of product layer diffusion and interfacial chemical reaction.A synergistic extraction was applied to separate W and V using an extractant mixture of di-(2-ethylhexyl)phosphoric acid P204 and the primary amine N1923.The extraction efficiencies of V and W reached 86.5% and 6.3%,respectively,with a separation coefficient(V/W) of 95.30.The product was precipitated after extraction to yield ammonium paratung state(APT) and NH_(4)VO_(3).The TiO_(2)catalyst carrier residue meets commercial specifications for reuse.This comprehensive recovery process with the characteristics of high-pressure leaching and synergistic extraction realizes the resourceful utilization of the spent catalysts.
基金financially supported by the China special S&T project on treatment and control of water pollution(2017ZX07402002).
文摘Wastewater treatment is essential to guarantee human health and ecological security.Catalytic ozonation with nanocatalysts is a widely studied and efficient treatment technology.However,this method has always been limited by nanocatalysts disadvantages such as easily loss,difficult to separate and reuse,and catalytic ability decay caused by aggregation,which could cause severe resources waste and potential risk to human health and ecosystem.To remedy these challenges,a magnetic-void-porous MnFe_(2)O_(4)/carbon microsphere shell nanocatalyst(CMS-MnFe_(2)O_(4))was successfully synthesized using renewable natural microalgae.The separation test showed CMS-MnFe_(2)O_(4) was rapidly separated within 2 min under an external magnetic field.In catalytic ozonation of oxalic acid(OA),CMS-MnFe_(2)O_(4) showed efficient and stable catalytic efficiency,reaching a maximum total organic carbon removal efficiency of 96.59% and maintained a 93.88% efficiency after 4 cycles.The stable catalytic efficiency was due to the supporting effects of the carbon microsphere shell,which significantly enhanced CMS-MnFe_(2)O_(4) chemical stability and reduced the metal ions leaching to 10-20% of MnFe_(2)O_(4) through electron transfer.To explore the catalytic mechanism,radical experiments were conducted and a new degradation pathway of OA involving superoxide anions rather than hydroxyl radicals was proposed.Consequently,this study suggests that an efficient,recyclable,stable,and durable catalyst for catalytic ozonation could be prepared.
基金financially supported by the National Science&Technology Pillar Program during the Twelfth Five-Year Plan Period of China(No.2012BAC12B01)the Major Scientific and Technological Special Project of Hunan Province,China(No.2012FJ1010)。
文摘An intensified oxidative acid leaching of copper–cadmium-bearing slag featuring using high-efficient oxygen carrier, such as activated carbon, was investigated to achieve high leaching rate of valuable metals. The effects of leaching variables, including agitation rate, sulfuric acid concentration, temperature, slag particle size, activated carbon and cupric ion concentration, were examined. It is found that leaching rates of cadmium and zinc both exceed 99 % in a very short time, but for copper, leaching rate of 99 % is achieved under the optimized leaching parameters, which are agitation rate of 100 r·min^(-1), sulfuric acid concentration of 15 wt%, leaching temperature of 80 ℃, slag particle size of 48–75 lm, activated carbon concentration of 3 g·L^(-1),liquid-to-solid ratio of 4:1, oxygen flow rate of 0.16 L·min^(-1),and leaching time of 60 min. The macro-leaching kinetics of copper metal was analyzed, and it is concluded that the inner diffusion is the controlling step, with apparent activation energy of 18.6 kJ·mol^(-1). The leaching solution with pH value of 2–4 can be designed to selectively extract valuable metals without neutralization, and the leaching residue can be treated by prevailing Pb smelting process.
基金Project supported by the National Key Research and Development Program of China (No. 2018YFB0604104)。
文摘Selective catalytic reduction(SCR) catalyst waste is a hazardous solid waste that seriously threatens the environment and public health.In this study,a thermal melting technology is proposed for the treatment of waste SCR catalysts.The melting characteristics and mineral phase transformation of waste SCR catalysts blended with three different groups of additives were explored by heating stage microscopy,thermogravimetric analysis/differential scanning calorimetry(TG/DSC) analysis,thermodynamic simulation,and X-ray diffraction(XRD) analysis;heavy metal leaching toxicity was tested by inductively coupled plasma-atomic emission spectrometry(I CP-AES) analysis.The results indicated that the melting point of waste SCR catalysts can be effectively reduced with proper additives.The additive formula of 39.00% Fe2 O3(in weight),6.50% CaO,3.30% SiO2,and 1.20% Al2 O3 achieves the optimal fluxing behavior,significantly decreasing the initial melting temperature from 1223℃ to1169℃.Furthermore,the whole heating process of waste SCR catalysts can be divided into three stages:the solid reaction stage,the sintering stage,and the primary melting stage.The leaching concentrations of V,As,Pb,and Se are significantly reduced,from 10.64,1.054,0.195,and 0.347 mg/L to 0.178,0.025,0.048,and 0.003 mg/L,respectively,much lower than the standard limits after melting treatment,showing the strong immobilization capacity of optimal additives for heavy metals in waste SCR catalysts.The results demonstrate the feasibility of harmless melting treatments for waste SCR catalysts with relatively low energy consumption,providing theoretical support for a novel method of disposing of hazardous waste SCR catalysts.
