Jianrong Qiu

Catalytic oxidation of gas-phase elemental mercury by nano-Fe2O3

Heterogeneous oxidation of gas-phase Hg0 by nano-Fe2O3 was investigated on a fixed bed reactor, and the effects of oxygen concentration, bed temperature, water vapour concentration and particle size have been discussed. The results showed that Hg0 could be oxidized by active oxygen atom on the surface of nano-Fe2O3 as well as lattice oxygen in nano-Fe2O3. Among the factors that affect Hg0 oxidation by nano-Fe2O3, bed temperature plays an important role. More than 40% of total mercury was oxidized at 300 degrees C, however, the test temperature at 400 degrees C could cause sintering of nano-catalyst, which led to a lower efficiency of Hg0 oxidation. The increase of oxygen concentration could promote mercury oxidation and led to higher Hg0 oxidation efficiency. No obvious mercury oxidation was detected in the pure N2 atmosphere, which indicates that oxygen is required in the gas stream for mercury oxidation. The presence of water vapour showed different effects on mercury oxidation depending on its concentration. The lower content of water vapour could promote mercury oxidation, while the higher content of water vapour inhibits mercury oxidation.

Vaporization of heavy metals during thermal treatment of model solid waste in a fluidized bed incinerator

This paper investigated the volatilization behavior of heavy metals during thermal treatment of model solid waste in a fluidized bed reactor. Four metal chlorides (Cd, Pb, Cu and Zn) were chosen as metal sources. The influence of redox conditions, water and mineral matrice on heavy metal volatilization was investigated. In general, Cd shows significant vaporization especially when HCl was injected, while Cu and Pb vaporize moderately and Zn vaporization is negligible. Increasing oxygen concentration can lower heavy metal vaporization. Heavy metal interactions with the mineral matter can result in the formation of stable metallic species thus playing a negative effect on their behavior. However, HCl can promote the heavy metal release by preventing the formation of stable metallic species. The chemical sorption (either physical or chemical) inside the pores, coupled with the internal diffusion of gaseous metal species, may also control the vaporization process. With SO(2) injected, Cd and Pb show a higher volatility as a result of SO(2) reducing characteristics. From the analysis, the subsequent order of heavy metal volatility can be found: Cd>Cu≥Pb≫Zn.

Physical and chemical characterization of ashes from a municipal solid waste incinerator in China.

In this study we analyzed the characteristics of bottom and fly ashes from a municipal solid waste incinerator in China. The physical properties of particle size distribution and morphology were evaluated. At the chemical level, the chemical composition, heavy metal leaching behavior and BCR sequential extraction procedure (the Community Bureau of Reference, now the European Union ‘Measurement and Testing Programme’) were determined. The main mineralogical crystalline phases in raw and leached bottom and fly ashes were also identified. For the bottom ashes, the concentration of heavy metals showed a slight decrease with an increase in particle size, and most of the heavy metal concentrations in fly ashes were higher than those in bottom ashes. The results of the toxicity characteristic leaching procedure indicated that, among the metals, the concentrations of lead (Pb) and copper (Cu) in fly ash leachate exceeded thresholds, while the concentrations of studied heavy metals in bottom ash leachate were all below the regulatory limit. The BCR results indicated that more easily mobilized forms (acid exchangeable) were predominant for cadmium and zinc; in contrast, the largest amount of Pb, Cu and manganese were associated with iron/manganese oxide, organic matter/sulfide fractions, or were residual.

Effects of SO2 and NO on removal of VOCs from simulated flue gas by using activated carbon fibers at low temperatures

Abstract Volatile organic compounds (VOCs) have serious detrimental effects on the environment and the health of human beings. The removal of pollutants from coal-fired power plants by activated carbon fiber (ACF) adsorption is a promising method. In this study, hydrogen peroxide (H 2 O 2 ) was used to modify ACF samples and the methods of N 2 adsorption isotherm and XPS (X-ray photoelectron spectroscopy) were utilized to characterize the ACF samples. The adsorption tests of VOC (toluene as a typical representative) based on ACF were conducted and the effects of SO 2 and NO on the adsorption of toluene were investigated. It was found that H 2 O 2 modification had no impact on the BET surface and pore volume of the ACF sample, although it increased the oxygen groups on the ACF surface. The results also indicated that SO 2 or NO inhibited the adsorption of VOC on ACF, and this inhibition strengthened with an increase in the concentration of SO 2 or NO. It is also found that the coexistence of SO 2 and NO deteriorates the adsorption of VOCs on ACF more seriously than the single existence of SO 2 or NO.

Kinetic model for calcium sulfate decomposition at high temperature

Abstract A modified shrinking unreacted-core model, based on thermogravimetric analysis, was developed to investigate CaSO4 decomposition in oxy-fuel combustion, especially under isothermal condition which is difficult to achieve in actual experiments due to high-temperature corrosion. A method was proposed to calculate the reaction rate constant for CaSO4 decomposition. Meanwhile, the diffusion of SO2 and O2, and the sintering of CaO were fully considered during the development of model. The results indicate that the model can precisely predict the decomposition of CaSO4 under high SO2 concentration (>1100×10−6). Concentrations of SO2 and O2 on the unreacted-core surface were found to increase first and then decrease with increasing temperature, and the average specific surface area and porosity of each CaO sintering layer decreased with increasing time. The increase of SO2 and/or O2 concentration inhibited CaSO4 decomposition. Moreover, the kinetics of CaSO4 decomposition had obvious dependence on temperature and the decomposition rate can be dramatically accelerated with increasing temperature.

Effect of surface oxygen/nitrogen groups on hydrogen chloride removal using modified viscose-based activated carbon fibers

Activated carbon fibers (ACFs) can effectively remove pollutants including nitrogen oxides, sulfur oxides and trace metals due to their rich micropores and large specific surface area. This work aims to investigate the roles of surface carbon–oxygen and nitrogen–oxygen species on the removal of hydrogen chloride (HCl) using viscose-based ACFs. To evaluate the effect of surface carbon–oxygen and nitrogen–oxygen groups, commercial viscose-based ACFs were treated by thermal treatment (900 °C) and chemical impregnation using H2O2, HNO3 and Cu(NO3)2. Pore volumes, average pore sizes and specific surface areas were separately characterized by t-plot method, density functional theory and Brunauer–Emmett–Teller theory. The surface morphology of the ACFs was observed by a scanning electron microscope. An X-ray photoelectron spectroscopy (XPS) technique was applied to determine the specific ratios of surface oxygen and nitrogen groups. Temperature programmed desorption was performed to investigate HCl adsorption behaviors over the ACFs. As experimental results, the thermal process decreased the carbon–oxygen groups while H2O2 impregnation increased the carbon–oxygen groups (especially carbonyl and carboxyl). Nitroso and nitro groups were introduced onto the carbon surface after HNO3 and Cu(NO3)2 treatments. The removal efficiency of HCl was improved slightly by H2O2 modification due to the increase of carbon–oxygen groups, and significantly by HNO3 and Cu(NO3)2 treatments because of newly formed nitrogen–oxygen groups. Nitroso and nitro groups show significant promotion of HCl retention ability over the ACFs surface. Moreover, HCl removal efficiency was much more influenced by nitroso than nitro groups.

Adsorptive Removal of SO2 from Coal Burning by Bamboo Charcoal

Bamboo charcoal (BC) is an environmentally friendly, low-cost and renewable bioresource with porous structure. The adsorption property of bamboo charcoal for sulfur dioxide was investigated through a parametric study conducted with a bench-scale bed and mechanism study by BET, XPS, and temperature pro-grammed desorption (TPD). The varying parameters investigated include particle size of BC, moisture, oxygen, nitric oxide. The experimental data suggest that BC has a good adsorption potential for SO2, which removal efficiency is greatly dependent upon the operation conditions. This study provides a good reference for BC to be used for SO2 removal in the actual flue gas over a wide range of conditions and further provided the preliminary experimental studies and theoretical discussion for bamboo charcoal to be used in multiple pollutants removing.

Effect of CO2 on the removal of NO over viscose-based activated carbon fibers

Adsorption experiments under varied conditions were carried out in a laboratory-scale fixed bed reactor to investigate the effect of CO2 on the removal of NO over the viscose-based activated carbon fibers (ACFs). Pore volumes, average pore size, and specific surface area were separately determined by t-plot method, density functional theory, and Brunauer–Emmett–Teller theory. Surface functional groups were examined by X-ray photoelectron spectroscopy. Moreover, temperature programmed desorption was applied to investigate the NO adsorption behavior over the carbon surface. Based on the extensive information obtained, effect of CO2 on the removal of NO over the ACF surface was fully discussed. The results indicated that CO2 inhibited the adsorption and oxidation of NO over the ACF surface mainly because (1) CO2 and NO molecules compete for the limited active sites over the ACF surface; (2) CO2 could restrain the formation of oxygen groups derived of adsorbed O2 over the ACF surface; and (3) CO2 hinders direct reactions between NO and O2 molecules.