Iau-Ren Ie

Enhancing the adsorption of vapor-phase mercury chloride with an innovative composite sulfur-impregnated activated carbon

Mercury chloride (HgCl(2)) is the major mercury derivate emitted from municipal solid waste incinerators, which has high risk to the environment and human health. This study investigated the adsorption of vapor-phase HgCl(2) with an innovative composite sulfurized activated carbon (AC), which was derived from the pyrolysis, activation, and sulfurization of waste tires. The composite sulfur-impregnation process impregnated activated carbon with aqueous-phase sodium sulfide (Na(2)S) and followed with vapor-phase elemental sulfur (S(0)). Thermogravimetric analysis (TGA) was applied to investigate the adsorptive capacity of vapor-phase HgCl(2) using the composite sulfurized AC. The operating parameters included the types of composite sulfurized AC, the adsorption temperature, and the influent HgCl(2) concentration. Experimental results indicated that the sulfur-impregnation process could increase the sulfur content of the sulfurized AC, but decreased its specific surface area. This study further revealed that the composite sulfurized AC impregnated with aqueous-phase Na(2)S and followed with vapor-phase S(0) (Na(2)S+S(0) AC) had much higher saturated adsorptive capacity of HgCl(2) than AC impregnated in the reverse sequence (S(0)+Na(2)S AC). A maximum saturated adsorptive capacity of HgCl(2) up to 5236 μg-HgCl(2)/g-C was observed for the composite Na(2)S+S(0) AC, which was approximately 2.00 and 3.17 times higher than those for the single Na(2)S and S(0) ACs, respectively.

Enhanced photocatalytic oxidation of gaseous elemental mercury by TiO2 in a high temperature environment

The photo-oxidation of Hg(0) in a lab-scale reactor by titanium dioxide (TiO2) coated on the surface of glass beads was investigated at high temperatures. TiO2 was calcinated at four different temperatures of 300 °C, 400 °C, 500 °C and 600 °C (noted as Ti300, Ti400, Ti500 and Ti600) and characterized for its physicochemical properties. The calcinated TiO2 coating on the glass beads was then tested to compare the photo-oxidation efficiencies of Hg(0) with an incident light of 365 nm. The results showed that the oxidation efficiencies of Hg(0) for Ti400 and Ti500 were higher than those of Ti300 and Ti600. To enhance the photo-oxidation efficiency of Hg(0), Ti400 was selected to examine the wave lengths (λ) of 254 nm, 365 nm and visible light with various influent Hg(0) concentrations. The effects of irradiation strength and the presence of oxygen on the photo-oxidation efficiency of Hg(0) were further investigated, respectively. This study revealed that the wave length (λ) of 254 nm could promote the photo-oxidation efficiency of Hg(0) at 140 and 160 °C, while increasing the influent Hg(0) concentration and could enhance the photo-oxidation rate of Hg(0). However, the influence of 5% O2 present in the flue gas for the enhancement of Hg(0) oxidation was limited. Moreover, the intensity of the incident wave length of 365 nm and visible light were demonstrated to boost the photo-oxidation efficiency of Hg(0) effectively.

Partition and Tempospatial Variation of Gaseous and Particulate Mercury at a Unique Mercury-Contaminated Remediation Site

ABSTRACT This study investigated the seasonal variation and spatial distribution of gaseous and particulate mercury at a unique mercury-contaminated remediation site located at the near-coastal region of Tainan City, Taiwan. Gaseous elemental mercury (GEM), particulate mercury (PTM), and dustfall mercury (DFM) were measured at six nearby sites from November 2009 to September 2010. A newly issued Method for Sampling and Analyzing Mercury in Air (National Institute of Environmental Analysis [NIEA] Method A304.10C) translated from U.S. Environmental Protection Agency (EPA) Method IO-5, was applied for the measurement of atmospheric mercury in this particular study. One-year field measurements showed that the seasonal averaged concentrations of GEM and PTM were in the range of 5.56–12.60 and 0.06–0.22 ng/m3, respectively, whereas the seasonal averaged deposition fluxes of DFM were in the range of 27.0–56.8 g/km2-month. The maximum concentrations of GEM and PTM were 38.95 and 0.58 ng/m3, respectively. The atmospheric mercury apportioned as 97.42–99.87% GEM and 0.13–2.58% PTM. As a whole, the concentrations of mercury species were higher in the springtime and summertime than those in the wintertime and fall. The southern winds generally brought higher mercury concentrations, whereas the northern winds brought relatively lower mercury concentrations, to the nearby fishing villages. This study revealed that the mercury-contaminated remediation site, an abandoned chlor-alkali manufacturing plant, was the major mercury emission source that caused severe atmospheric mercury contamination over the investigation region. The hot spot of mercury emissions was allocated at the southern tip of the abandoned chlor-alkali manufacturing plant. On-site continuous monitoring of GEM at the mercury-contaminated remediation site observed that GEM concentrations during the open excavation period were 2–3 times higher than those during the nonexcavation period. IMPLICATIONS A manual and an auto-monitoring technique were successfully applied to sample gaseous and particulate mercury at a unique mercury-contaminated remediation site and further measured with a cold-vapor atomic fluorescence spectrometry (CVAFS). The mercury-contaminated remediation site was announced as a supersite of mercury contamination by the Environmental Protection Bureau (EPB) of Tainan City in 2003, causing significant contamination of atmospheric mercury over the investigation region. Both ambient temperature and prevailing wind direction played critical roles on the tempospatial variation and partition of gaseous and particulate mercury in the ambient atmosphere.

Enhanced mercuric chloride adsorption onto sulfur-modified activated carbons derived from waste tires

A number of activated carbons derived from waste tires were further impregnated by gaseous elemental sulfur at temperatures of 400 and 650 °C, with a carbon and sulfur mass ratio of 1:3. The capabilities of sulfur diffusing into the micropores of the activated carbons were significantly different between 400 and 650 °C, resulting in obvious dissimilarities in the sulfur content of the activated carbons. The sulfur-impregnated activated carbons were examined for the adsorptive capacity of gas-phase mercuric chloride (HgCl2) by thermogravimetric analysis (TGA). The analytical precision of TGA was up to 10−6 g at the inlet HgCl2 concentrations of 100, 300, and 500 μg/m3, for an adsorption time of 3 hr and an adsorption temperature of 150 °C, simulating the flue gas emitted from municipal solid waste (MSW) incinerators. Experimental results showed that sulfur modification can slightly reduce the specific surface area of activated carbons. High-surface-area activated carbons after sulfur modification had abundant mesopores and micropores, whereas low-surface-area activated carbons had abundant macropores and mesopores. Sulfur molecules were evenly distributed on the surface of the inner pores after sulfur modification, and the sulfur content of the activated carbons increased from 2–2.5% to 5–11%. After sulfur modification, the adsorptive capacity of HgCl2 for high-surface-area sulfurized activated carbons reached 1.557 mg/g (22 times higher than the virgin activated carbons). The injection of activated carbons was followed by fabric filtration, which is commonly used to remove HgCl2 from MSW incinerators. The residence time of activated carbons collected in the fabric filter is commonly about 1 hr, but the time required to achieve equilibrium is less than 10 min. Consequently, it is worthwhile to compare the adsorption rates of HgCl2 in the time intervals of <10 and 10–60 min. Implications: Waste tires constitute potential carbonaceous materials for the production of activated carbons, which is a typical control technology for removing HgCl2 from municipal solid waste (MSW) incinerators. The adsorption of HgCl2 with sulfur-impregnated activated carbons has seldom been investigated in regard to the variation in HgCl2 adsorption with a specific surface area and pore size distribution of the activated carbons during the HgCl2 adsorption process. In this work, sulfur-impregnated activated carbons were produced from waste tires and then examined for their adsorptive capacities of HgCl2 using thermogravimetric analysis (TGA).

Source Allocation of Long-Range Asian Dusts Transportation across the Taiwan Strait by Innovative Chemical-Assisted Identification Methods

This study used the backward trajectory calculation to obtain the transportation routes of Asian dusts and further combined the chemical composition with the enrichment factor (EF) and the grey relational analysis (GR) to identify the potential sources of eighteen Asian dust storm (ADS) events. The results showed that the chemical compositions of atmospheric particles sampled at the Pescadores Islands were very similar to source soils fugitively emitted from Inner Mongolia, which could assist in identifying the source regions of Asian dusts. This study further compared the source allocation of Asian dusts obtained from EF, GR, and backward trajectory, which showed that the source regions of Asian dusts obtained from these three methods were quite similar. The similarity of backward trajectory and GR reached as high as 83.3%. Moreover, the similarity of backward trajectory calculation and EF or GR was up to 77.8% while that of the GR and EF was up to 83.3%. Overall, these three methods can successfully allocate the source regions of Asian dusts by 66.7%. Moreover, these innovative chemical-assisted methods can be successfully applied to identify the source regions of Asian dusts for 18 ADS events.