Chong Tian

Efficient removal of elemental mercury (Hg0) by SBA-15-Ag adsorbents

A novel adsorbent based on Ag-loaded SBA-15 was prepared by a facile wet chemical method for the removal of elemental mercury (Hg0, the most challenging form) for the first time. The adsorbent shows excellent Hg0 removal capacity (>60 μg g−1 at 150 °C) in real flue gas and cyclic performance.

Nanocomposites of graphene oxide, Ag nanoparticles, and magnetic ferrite nanoparticles for elemental mercury (Hg0) removal

Mercury emission from combustion flue gas causes considerable environmental challenges and serious adverse health threats, and elemental mercury (Hg0) is the most challenging chemical form for removal. In this work, four types of graphene oxide (GO) based composite adsorbents were successfully synthesized by depositing Ag nanoparticles (NPs) and/or magnetic ferrite NPs on GO sheets (denoted as GO, GO–Ag, MGO and MGO–Ag), characterized and applied for the removal of Hg0 for the first time. The presence of Ag NPs on GO greatly enhances the Hg0 removal capability of GO–Ag and MGO–Ag as compared to that of pure GO, which is mainly attributed to the amalgamation of Hg0 on Ag NPs. MGO–Ag shows the best Hg0 removal performance and thermal tolerance among the four types of adsorbents developed, which can effectively capture Hg0 up to 150–200 °C in a simulated flue gas environment and can be also effectively recycled and reused. Our results indicate that the graphene oxide based composites (i.e. MGO–Ag) have significant potential applications for mercury emission control in coal-fired power plants.

Influence of carbonation under oxy-fuel combustion flue gas on the leachability of heavy metals in MSWI fly ash

Due to the high cost of pure CO2, carbonation of MSWI fly ash has not been fully developed. It is essential to select a kind of reaction gas with rich CO2 instead of pure CO2. The CO2 uptake and leaching toxicity of heavy metals in three typical types of municipal solid waste incinerator (MSWI) fly ash were investigated with simulated oxy-fuel combustion flue gas under different reaction temperatures, which was compared with both pure CO2 and simulated air combustion flue gas. The CO2 uptake under simulated oxy-fuel combustion flue gas were similar to that of pure CO2. The leaching concentration of heavy metals in all MSWI fly ash samples, especially in ash from Changzhou, China (CZ), decreased after carbonation. Specifically, the leached Pb concentration of the CZ MSWI fly ash decreased 92% under oxy-fuel combustion flue gas, 95% under pure CO2 atmosphere and 84% under the air combustion flue gas. After carbonation, the leaching concentration of Pb was below the Chinese legal limit. The leaching concentration of Zn from CZ sample decreased 69% under oxy-fuel combustion flue gas, which of Cu, As, Cr and Hg decreased 25%, 33%, 11% and 21%, respectively. In the other two samples of Xuzhou, China (XZ) and Wuhan, China (WH), the leaching characteristics of heavy metals were similar to the CZ sample. The speciation of heavy metals was largely changed from the exchangeable to carbonated fraction because of the carbonation reaction under simulated oxy-fuel combustion flue gas. After carbonation reaction, most of heavy metals bound in carbonates became more stable and leached less. Therefore, oxy-fuel combustion flue gas could be a low-cost source for carbonation of MSWI fly ash.

Arsenic Emissions and Speciations in High-temperature Treatment of a Typical High Arsenic Coal

A series of experiments on release behaviors of arsenic in thermal treatment, e.g., pyrolysis, combustion, and gasification, of a typical high arsenic coal were conducted in a laboratory-scale drop tube furnace. Mineralogy of the coal and ashes was characterized by X-ray diffraction and field emission scanning electron microscope with energy dispersive X-ray spectrometer. Distributions and speciations of arsenic in the coal and ashes were determined by using the inductively coupled plasma mass spectrometry and time-of-flight secondary ion mass spectrometry. The results indicated that quartz and pyrite in coal would transformed into mullite and hematite. The decompositions of pyrite are followed by the unreacted coal modal and controlled by the surface sulfur vapor pressure, and pyrite would be transformed to Fe or Fe2O3 finally. Bleeding ration of arsenic in air combustion, CO2 gasification, and N2 pyrolysis is 85, 65, and 45 %, respectively, at 1300 °C. Arsenic is obviously enriched in the fine particles of size around 0.1–0.2 μm both in coal combustion and gasification. The arsenic species of arsenic in fine particles generated from coal gasification is As2O5, As, AsO, Ca3(AsO4)2.

Photocatalytic Reduction of CO2 Over Sol-Gel Derived Copper-Doped Titania Catalysts

Different doping concentration of copper-doped titania was synthesized by sol-gel method, and the samples were characterized by X-ray diffraction (XRD); Field emission scanning electron microscope (FSEM-EDX); Specific surface area and Pore size analyzer (BET); Thermo gravimetric-differential thermal analyzer (TG-DTA) respectively. The photocatalytic reduction of CO2 experiments was carried out in a photocatalytic reactor. CO2 was discharged into a quartz reactor with catalyst suspended in NaHCO3 solution, and illuminated under UV irradiation at the wavelength of 253.7 nm for 10 h continuously. The results confirmed that in the copper modified TiO2 samples, the crystalline form of TiO2 exists as anatase; only on the high CuO loading sample (>10%), the CuO peaks appears obviously; the grain size of all the sol-gel derived CuO-TiO2 samples were nearly 30 nm, and the copper particles were consistent and dispersed on the surface of TiO2. CO2 can be reduced into methanol in the presence of NaHCO3 solution over CuO-TiO2 catalyst. The doping concentration of 5% CuO-TiO2 performed best catalytic effect, with the methanol yield of 27 mg (g-cata)−1 in 10 h. With increasing reaction time, yield of methanol was promoted.