Whole-Process Pollution Control for Cost-Effective and Cleaner Chemical Production A Case Study of the Tungsten Industry in China

In this research,a methodology named whole-process pollution control(WPPC)is demonstrated that improves the effectiveness of process optimization.This methodology considers waste/emission treatment as a step of the whole production process with respect to the minimization of cost and environmental impact for the whole process.The following procedures are introduced in a WPPC process optimization:①a material and energy flow investigation and optimization based on a systematic understanding of the distribution and physiochemical properties of potential pollutants;②a process optimization to increase the utilization efficiency of different elements and minimize pollutant emissions;and③an evaluation to reveal the effectiveness of the optimization strategies.The production of ammonium paratungstate was chosen for the case study.Two factors of the different optimization schemes-namely the cost-effectiveness factor and the environmental impact indicator-were evaluated and compared.This research demonstrates that by considering the nature of potential pollutants,technological innovations,economic viability,environmental impacts,and regulation requirements,WPPC can efficiently optimize a metal production process.

Continuous generation of lattice oxygen via redox engineering for boosting toluene degradation performances

Excellent performances promoted by lattice oxygen have attracted wide attention for catalytic degradation of volatile organic compounds(VOCs).However,how to control the continuous regeneration of lattice oxygen from the support is seldom reported.In this study,we selected sepiolite supported manganese-cobalt oxides(Co_(x)Mn_(100-x)O_(y))as model catalysts by tuning Co/(Co+Mn)mass ratio(x=3%,10%,15%,and 20%)to enhance toluene degradation efficiency,owing to lattice oxygen regeneration by redox cycle existing at the interface and Mn species with high valence state,initiated by cobalt catalytic performance under the role of crystal field stability phase.The results of activity test show that the sepiolite-Co_(15)Mn_(85)O_(y)catalyst exhibit outperformances at 193℃with 10,000 h^(-1)GHSV.In addition,the catalyst existed at the bottom of the"volcano"curve correlated T_(50)or T_(90)with Co/(Co+Mn)weight ratio is sepiolite-Co_(15)Mn_(85)O_(y),conforming its outperformance.Further characterized by investigating active sites structural and electronic properties,the essential of superior catalytic activity is attributed to the grands of lattice oxygen continuous formation resulted from redox engineering based on the high atomic ratio of surface lattice oxygen with continuous refilled from the support and that of Mn^(4+)/Mn^(3+)cycle initiated by cobalt catalytic behaviors.All in all,redox engineering,not only promotes grands of active species reversible regeneration,but supplies an alternative catalyst design strategy towards the terrific efficiency-to-cost ratio performance.

Distinct synergetic effects in the ozone enhanced photocatalytic degradation of phenol and oxalic acid with Fe^(3+)/TiO_2 catalyst

In this work, phenol and oxalic acid(OA) degradation in an ozone and photocatalysis integrated process was intensively conducted with Fe^(3+)/TiO_2 catalyst. The ferrioxalate complex formed between Fe^(3+) and oxalate accelerated the removal of OA in the ozonation, photolysis and photocatalytic ozonation process, for its high reactivity with ozone and UV. Phenol was degraded in ozonation and photolysis with limited TOC removal rates, but much higher TOC removal was achieved in photocatalytic ozonation due to the generation of ·OH. The sequence of UV light and ozone in the sequential process also influences the TOC removal, and ozone is very powerful to oxidize intermediates catechol and hydroquinone to maleic acid. Fenton or photo-Fenton reactions only played a small part in Fe^(3+)/TiO_2catalyzed processes, because Fe^(3+) was greatly reduced but not regenerated in many cases.The synergetic effect was found to be highly related with the property of the target pollutants. Fe^(3+)/TiO_2 catalyzed system showed the highest ability to destroy organics, but the TiO_2 catalyzed system showed little higher synergy.

Laccase immobilized on magnetic nanoparticles by dopamine polymerization for 4-chlorophenol removal

In this work, a new immobilization method based on dopamine(DA) self-polymerization was developed for laccase immobilization on magnetic nanoparticles(Fe_3O_4 NPs). To optimize the immobilization condition including reaction pH, DA concentration and enzyme concentration, a central composite response surface method was applied. The optimal condition was determined as p H value of 5.92, laccase concentration of 0.25 mg mL^(-1) and DA concentration of 12.74 mg mL^(-1), under which a high enzyme activity recovery of 88.17% was obtained.By comparing with free laccase, the stabilities of immobilized laccase towards p H, thermostability, storage were enhanced significantly.Approximately 60% of relative activity for immobilized laccase was remained after being incubated for 6 h at 50℃, but the free laccase only remained 25%. After 40 days of storage at 4℃, the laccase immobilized by DA kept about 89% of its original activity, but the free laccase only retained 48%. After recycled 10 times, the relative activity of immobilized laccase still retained 70%. The immobilized laccase was then applied to catalyze the degradation of 4-chlorophenol(4-CP), 86% percentage of 4-CP was removed within 2 h. After degraded 10 times, the relative activity of immobilized laccase still remained 64% of its initial activity, which exhibits an excellent reusability and operational stability.

Evaluation of sulfur trioxide detection with online isopropanol absorption method

Measurement of the SO3 concentration in flue gas is important to estimate the acid dew point and to control corrosion of downstream equipment. SO3 measurement is a difficult question since SO3 is a highly reactive gas, and its concentration is generally two orders of magnitude lower than the SO2 concentration. The SO3 concentration can be measured online by the isopropanol absorption method; however, the reliability of the test results is relatively low. This work aims to find the error sources and to evaluate the extent of influence of each factor on the measurement results. The test results from a SO3 analyzer showed that the measuring errors are mainly caused by the gas–liquid flow ratio, SO2 oxidation, and the side reactions of SO3. The error in the gas sampling rate is generally less than 13%. The isopropanol solution flow rate decreases 3% to 30% due to the volatilization of isopropanol, and accordingly, this will increase the apparent SO3 concentration. The amount of SO2 oxidation is linearly related to the SO2 concentration. The side reactions of SO3 reduce the selectivity of SO42- to nearly 73%. As sampling temperature increases from180 to 300°C, the selectivity of SO42- decreases from 73% to 50%. The presence of H2 O in the sample gas helps to reduce the measurement error by inhibiting the volatilization of the isopropanol and weakening side reactions. A formula was established to modify the displayed value, and the measurement error was reduced from 25%–54% to less than 15%.

Coupling mechanism of activated carbon mixed with dust for flue gas desulfurization and denitrification

To clarify the effect of coking dust, sintering dust and fly ash on the activity of activated carbon for various industrial flue gas desulfurization and denitrification, the coupling mechanism of the mixed activated carbon and dust was investigated to provide theoretical reference for the stable operation. The results show that coking dust had 34% desulfurization efficiency and 10% denitrification efficiency;correspondingly, sintering dust and fly ash had no obvious desulfurization and denitrification activities. For the mixture of activated carbon and dust, the coking dust reduced the desulfurization and denitrification efficiencies by blocking the pores of activated carbon, and its inhibiting effect on activated carbon was larger than its own desulfurization and denitrification activity. The sintering dust also reduced the desulfurization efficiency on the activated carbon while enhancing the denitrification efficiency. Fly ash blocked the pores of activated carbon and reduced its reaction activity. The reaction activity of coking dust mainly came from the surface functional groups, similar to that of activated carbon. The reaction activity of sintering dust mainly came from the oxidative property of Fe_2O _3, which oxidized NO to NO_2 and promoted the fast selectively catalytic reduction(SCR) of NO to form N_2. Sintering dust was activated by the joint action of activated carbon, and both had a coupling function. Sintering dust enhanced the adsorption and oxidation of NO, and activated carbon further promoted the reduction of NO_x by NH_3;thus, the denitrification efficiency increased by 5%-7% on the activated carbon.

Adsorption and desorption of SO_2, NO and chlorobenzene on activated carbon

Activated carbon（AC） is very effective for multi-pollutant removal; however, the complicated components in flue gas can influence each other＇s adsorption. A series of adsorption experiments for multicomponents, including SO_2, NO, chlorobenzene and H2 O,on AC were performed in a fixed-bed reactor. For single-component adsorption, the adsorption amount for chlorobenzene was larger than for SO_2 and NO on the AC. In the multi-component atmosphere, the adsorption amount decreased by 27.6% for chlorobenzene and decreased by 95.6% for NO, whereas it increased by a factor of two for SO_2,demonstrating that a complex atmosphere is unfavorable for chlorobenzene adsorption and inhibits NO adsorption. In contrast, it is very beneficial for SO_2 adsorption. The temperature-programmed desorption（TPD） results indicated that the binding strength between the gas adsorbates and the AC follows the order of SO_2〉 chlorobenzene 〉 NO. The adsorption amount is independent of the binding strength. The presence of H2 O enhanced the component effects, while it weakened the binding force between the gas adsorbates and the AC. AC oxygen functional groups were analyzed using TPD and X-ray photoelectron spectroscopy（XPS） measurements. The results reveal the reason why the chlorobenzene adsorption is less affected by the presence of other components. Lactone groups partly transform into carbonyl and quinone groups after chlorobenzene desorption. The chlorobenzene adsorption increases the number of C = O groups, which explains the positive effect of chlorobenzene on SO_2 adsorption and the strong NO adsorption.

Activated carbon enhanced ozonation of oxalate attributed to HO·oxidation in bulk solution and surface oxidation: Effect of activated carbon dosage and pH

Ozonation of oxalate in aqueous phase was performed with a commercial activated carbon（AC）in this work. The effect of AC dosage and solution pH on the contribution of hydroxyl radicals（HOU） in bulk solution and oxidation on the AC surface to the removal of oxalate was studied. We found that the removal of oxalate was reduced by tert-butyl alcohol（tBA） with low dosages of AC,while it was hardly affected by tBA when the AC dosage was greater than 0.3 g/L. tBA also inhibited ozone decomposition when the AC dosage was no more than 0.05 g/L, but it did not work when the AC dosage was no less than 0.1 g/L. These observations indicate that HOUin bulk solution and oxidation on the AC surface both contribute to the removal of oxalate. HOU oxidation in bulk solution is significant when the dosage of AC is low, whereas surface oxidation is dominant when the dosage of AC is high. The oxalate removal decreased with increasing pH of the solution with an AC dosage of 0.5 g/L. The degradation of oxalate occurs mainly through surface oxidation in acid and neutral solution, but through HOUoxidation in basic bulk solution. A mechanism involving both HOUoxidation in bulk solution and surface oxidation was proposed for AC enhanced ozonation of oxalate.

Enhanced formation of trihalomethane disinfection byproducts from halobenzoquinones under combined UV/chlorine conditions

Halobenzoquinones(HBQs)are highly toxic disinfection byproducts(DBPs)and are also precursors of other DBPs such as trihalomethanes(THMs).The formation of THMs from HBQs during chlorine-only and UV/chlorine processes with or without bromide was investigated experimentally.Density functional theory(DFT)reactivity descriptors were also applied to predict the nucleophilic/electrophilic reactive sites on HBQs and intermediates.The results were combined to explain the different behaviors of 2,6-dichloro-1,4-benzoquinone(2,6-DCBQ)and tetrachloro-1,4-benzoquinone(TCBQ)and to propose mechanism for the promoting roles of UV and hydroxylation of HBQs in THMs formation.Under UV/chlorine,UV significantly enhanced THMs formation from 2,6-DCBQ compared to chlorine-only,mainly due to the production of OH-DCBQ^(*).Excited 2,6-DCBQ^(*)by UV benefited nucleophilic hydrolysis to produce OH-DCBQ^(*),which favored electrophilic attack by chlorine,thereby inducing more THMs formation.UV/chlorine modestly promoted THMs formation from TCBQ compared to chlorine-only.Hydroxylation of TCBQ and UV irradiation were both important in promoting THMs formation due to the high electrophilic property of OH-TCBQ and TCBQ^(*).Meanwhile,hydroxylation of HBQs and CHCl3 formation were enhanced at higher pH.This work suggested that enhanced formation of THMs from HBQs should be considered in the application of combined UV and chlorine processes.

Enhanced nitrogen removal upon the addition of volatile fatty acids from activated sludge by combining calcium peroxide and low-thermal pretreatments

This study investigated a combined low-thermal and CaO_(2)pretreatment to enhance the volatile fatty acid(VFA)production from waste activated sludge(WAS).The fermentative product was added to a sequencing batch reactor(SBR)as an external carbon source to enhance nitrogen removal.The results showed that the combined pretreatment improved WAS solubilization,releasing more biodegradable substrates,such as proteins and polysaccharides,from TB-EPS to LB-EPS and S-EPS.The maximum VFA production of 3529±188 mg COD/L was obtained in the combined pretreatment(0.2 g CaO_(2)/g VS+70℃for 60 min),which was 2.1 and 1.4-fold of that obtained from the sole low-thermal pretreatment and the control test,respectively.Consequently,when the fermentative liquid was added as an external denitrification carbon source,the effluent total nitrogen decreased to Class A of the discharge standard for pollutants in rural wastewater treatment plants in most areas of China.

Recovery and reuse of floc sludge for high-performance capacitors

In this paper,floc sludge was transformed into porous carbon matrix composites by acidification and KOH activation at high temperature and used as an electrode material for application in capacitors.The effects of different treatment processes on the electrochemical properties of sludge materials were compared.The results of electrochemical tests showed that the sludge electrode exhibited excellent energy storage performance after HNO3 acidification and KOH activation with a mass ratio of 3:1(KOH/C).The specific capacitance of the sludge electrode reached 287 F/g at a current density of 1 A/g.In addition,the sludge electrode material showed excellent cycle stability(specific capacity retained at 93.4%after 5000 cycles at 5 A/g).Based on XRD,FTIR,SEM,TEM,and BET surface analysis,the morphology of sludge electrode materials can be effectively regulated by chemical pretreatment.The best-performing material showed a 3D porous morphology with a large specific surface area(2588 m^(2)/g)and optimal pore size distribution,improving ion channels and charge conductivity.According to the life cycle assessment of floc sludge utilization,it reduced the resource consumption and toxicity risk by more than 90%compared with ordinary sludge disposal processes.This work provided a cost-effective and eco-friendly sludge reuse method and demonstrated the application potential of sludge-based materials in high-performance supercapacitors.

Investigation of solution chemistry to enable efficient lithium recovery from low-concentration lithium-containing wastewater

In the production of lithium-ion batteries(LIBs)and recycling of spent LIBs,a large amount of low-concentration lithium-containing wastewater(LCW)is generated.The recovery of Li from this medium has attracted significant global attention from both the environmental and economic perspectives.To achieve effective Li recycling,the features of impurity removal and the interactions among different ions must be understood.However,it is generally dificult to ensure highly efficient removal of impurity ions while retaining Li in the solution for further recovery.In this study,the removal of typical impurity ions from LCW and the interactions between these species were systematically investigated from the thermodynamic and kinetics aspects.It was found that the main impurities(e.g.,Fe^+,AIP^+,Ca^2+,and Mg^2+)could be efficiently removed with high Li recovery by control-ling the ionic strength of the solution.The mechanisms of Fe^3+,Al^+,Ca^2+,and Mg^2+removal were investigated to identify the controlling steps and reaction kinetics.It was found that the precipitates are formed by a zero-order reaction,and the activation energies tend to be low with a sequence of fast chemical reactions that reach equilibrium very quickly.Moreover,this study focused on Li loss during removal of the impurities,and the corresponding removal rates of Fe^+,Al^+,Ca^2+,and Mg^2+were found to be 99.8%,99.5%,99%,and 99.7%,respectively.Conse-quently,high-purity LisPO4 was obtained via one-step precipitation.Thus,this research demonstrates a potential route for the effective recovery of Li from low-concentra-tion LCW and for the appropriate treatment of acidic LCW.

In-situ synthesis of N, S co-doped hollow carbon microspheres for efficient catalytic oxidation of organic contaminants

Metal-free heteroatom doped nanocarbons are promising alternatives to the metal-based materials in catalytic ozonation for destruction of aqueous organic contaminants. In this study, N, S co-doped hollow carbon microspheres (NSCs) were synthesized from the polymerization products during persulfate wet air oxidation of benzothiazole. The contents of doped N and S as well as the structural stability were maneuvered by adjusting the subsequent N_(2)-annealing temperature. Compared with the prevailing single-walled carbon nanotubes, the N_(2)-annealed NSCs demonstrated a higher catalytic ozonation activity for benzimidazole degradation. According to the quantitative structure-activity relationship (QSAR) analysis, the synergistic effect between the graphitic N and the thiophene-S which redistributed the charge distribution of the carbon basal plane contributed to the activity enhancement of the N_(2)-annealed NSCs. Additionally, the hollow structure within the microspheres served as the microreactor to boost the mass transfer and reaction kinetics via the nanoconfinement effects. Quenching and electron paramagnetic resonance (EPR) tests revealed that benzimidazole degradation was dominated by the produced singlet oxygen (^(1)O_(2)) species, while hydroxyl radicals (^(·)OH) were also generated and participated. This study puts forward a novel strategy for synthesis of heteroatom-doped nanocarbons and sheds a light on the relationship between the active sites on the doped nanocarbons and the catalytic performance.

Characterization strategy of polymeric transition metal species transformation for high-purity metal recovery

The aqueous metal species with similar chemical properties are usually extracted together,limiting deep separation for high-purity metal.However,rare attention has been paid to metal speciation characterization and transformation during separation.Herein,the hydrolysis evolution of polymeric metal species was investigated systematically by electrospray ionization time-of-flight mass spectrometry(ESI-TOF-MS).The transformation evolutions were visualized with respect to characteristic vanadium species(V_(1),V_(2),V_(3),V_(4) and V_(10)),chromium species(Cr_(1) and Cr_(2)),tungsten(W_(1),W_(2),W_(4),W_(6) and W_(10))and molybdenum(Mo_(1),Mo_(2) and Mo_(4))species.The key characteristics(such as specfic pHs and concentrations)for speciation variation were revealed.The polymerization behavior of several transition metals can be semiquantitative characterized by this strategy.The sufficient speciation transformation provides a solid base for metal speciation chemistry,and guides further development of high-purity metal recovery.

Dendritic BiVO4 decorated with MnOx co-catalyst as an efficient hierarchical catalyst for photocatalytic ozonation

An appropriate co-catalyst can significantly promote the photocatalytic efficacy, but this has been seldom studied in the visible-light photocatalysis combined with ozone, namely photocatalytic ozonation. In this work, a dendritic bismuth vanadium tetraoxide (BiVO4) material composited with highly dispersed MnOv nanoparticles was synthesized, and its catalytic activity is 86.6% higher than bare BiVO4 in a visible light and ozone combined process. Catalytic ozonation experiments, ultraviolet- visible (UV-Vis) diffuse reflectance spectra and photoluminescence spectra jointly indicate that MnOA plays a triple role in this process. MnOv strengthens the light adsorption and promotes the charge separation on the composite material, and it also shows good activity in catalytic ozonation. The key reactive species in this process is OH, and various pathways for its generation in this process is proposed. This work provides a new direction of catalyst preparation and pushes forward the application of photocatalytic ozonation in water treatment.

Hg^0 removal from flue gas over different zeolites modified by Fe Cl_3

The elemental mercury removal abilities of three different zeolites（Na A, Na X, HZSM-5）impregnated with iron（Ⅲ） chloride were studied on a lab-scale fixed-bed reactor. X-ray diffraction, nitrogen adsorption porosimetry, Fourier transform infrared spectroscopy,X-ray photoelectron spectroscopy, and temperature programmed desorption（TPD） analyses were used to investigate the physicochemical properties. Results indicated that the pore structure and active chloride species on the surface of the samples are the key factors for physisorption and oxidation of Hg0, respectively. Relatively high surface area and micropore volume are beneficial to efficient mercury adsorption. The active Cl species generated on the surface of the samples were effective oxidants able to convert elemental mercury（Hg0）into oxidized mercury（Hg2＋）. The crystallization of Na Cl due to the ion exchange effect during the impregnation of Na A and Na X reduced the number of active Cl species on the surface, and restricted the physisorption of Hg0. Therefore, the Hg0 removal efficiencies of the samples were inhibited. The TPD analysis revealed that the species of mercury on the surface of Fe Cl3–HZSM-5 was mainly in the form of mercuric chloride（Hg Cl2）, while on Fe Cl3–Na X and Fe Cl3–Na A it was mainly mercuric oxide（HgO）.

Gas-phase and particle-phase PCDD/F congener distributions in the flue gas from an iron ore sintering plant

The activated carbon injection-circulating fluidized bed（ACI-CFB）-bag filter coupling technique was studied in an iron ore sintering plant. For comparison, the removal efficiencies under the conditions without or with ACI technology were both evaluated. It was found that the polychlorinated dibenzo-p-dioxins and dibenzofuran（PCDD/F） removal efficiency for total international toxic equivalence quantity（I-TEQ） concentration was improved from 91.61% to 97.36% when ACI was employed, revealing that ACI was very conducive to further controlling the PCDD/F emissions. Detailed congener distributions of PCDD/Fs in the gas-phase and particle-phase of the Inlet and Outlet samples were determined. Additionally, the PCDD/F distribution for the Fly ash-with ACI sample of was also studied.