Tracking of arsenics during the thermal stabilization of an AsH3 scrubber sludge.

Toxic arsenics in an AsH(3) scrubber sludge were thermally stabilized in the temperature range of 973-1,373 K. To better understand how the high-temperature treatments can stabilize arsenics in the sludge, their synchrotron X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra of arsenics were determined. It is found that the reduced arsenic leachability may be associated with the formation of As(2)O(5) (51-59%) and embedded As(V) within the Ca(3)(PO(4))(2) matrix (41-49%) in the stabilized sludge. In addition, the As-O bond distances in the stabilized As(2)O(5) are much less than that of normal As(2)O(5) by 0.05-0.07 Å. The shorter As-O bond distances accompanied with the higher bonding energy also have a contribution to the thermal stabilization of arsenics.

Microwave-induced nanoscale zero-valent iron degradation of perchloroethylene and pentachlorophenol.

UNLABELLED: Microwave (MW) is applied to enhance perchloroethylene (PCE) or pentachlorophenol (PCP) removal using zero-valent iron (ZVI; Fe(0)) as the dielectric medium. ZVI has a much higher dielectric loss factor (39.5) than other media; it is capable of absorbing MW radiation rapidly to speed up the release of electrons, leading to rises of the ZVI particle surface temperature. If the MW power is continued, excessive electricity will accumulated inside ZVI particles, resulting in sparks. The results show that during the initial 5 sec (700 W), the linear aliphatic PCE has a faster decomposing rate than the ringed PCP (82.0% vs. 4.8%) because less energy is required for decomposing the linear-chlorine bond (90 kcal mol(-1)) than ring-chlorine bonds (95 kcal mol(-1)). Later the removal rate for either PCE or PCP remains the same when the exposure time is between 5 and 60 sec. Without MW irradiation, linear PCE molecules have larger surface area to contact ZVI, and hence they have better removal efficiencies than PCP molecules. Using Fe(0) as a microwave dielectric medium to treat PCE or PCP is a new and worthwhile treatment technology; it is environmentally friendly, and its use will eliminate the secondary pollution. IMPLICATIONS: Nanoscale iron particles are characterized by high surface-area-to-volume ratios, high specific surface area, and high surface reactivity. With a much higher dielectric loss factor, it is capable of absorbing MW radiation rapidly to speed up the release of electrons, leading to rise in temperature. The time needed to achieve a satisfactory treatment is also reduced, leading to significant saving of energy consumption to make this method cost-effective and also environmentally friendly for the industry to pursuit sustainable development.

Enhanced degradation of chlorobenzene in aqueous solution using microwave-induced zero-valent iron and copper particles.

Microwaves were applied to reduce the activation energy of chlorobenzene in aqueous solution and enhance its removal using nanoscale zero-valent iron (Fe0) or zero-valent copper (Cu0) particles as dielectric media. When Fe0 and Cu0 particles absorb microwave energy, the electrical potential difference causes the metal electrons to rotate faster, thus producing more heat. The microwave-irradiated metal particles reduced the chlorobenzene activation energy by 6.1 kJ/mol (13.3 kJ/mol versus 19.4 kJ/mol) for Fe0 and 5.4 kJ/mol (15.8 kJ/mol versus 21.4 kJ/mol) for Cu0 and enhanced the chlorobenzene removal 4.1 times (82.8% versus 20.4%) for Fe0 and 3.7 times (72.1% versus 19.5%) for Cu0. The Fe0 has a higher standard reduction potential than Cu0; it is capable of removing more chlorobenzene than Cu0 (82.8% versus 72.1%). Using the microwave-induced nano-scale iron or copper particle is effective in treating toxic organic substances, as demonstrated in this study.

Visible-light-sensitized dechlorination of perchloroethylene.

An aqueous reaction mixture containing perchloroethylene (PCE), a photosensitizer, and an electron donor was irradiated by visible lamps to facilitate a sunlight-sensitized dechlorination reaction. Various types of lamps, electron donors, and photosensitizers were examined, to compare the rates of dechlorination. Of the six photosensitizers evaluated, methylene blue was the most effective. Electron donors varied in effectiveness, as follows: trimethylamine > triethylamine > tributylamine. The intermediates and reaction products were identified by a purge-and-trap gas chromatography mass spectrometer system. The photosensitized dechlorination method degraded PCE via an electron-transfer-relay mechanism. Degradation products identified were trichloroethylene, dichloroethylenes, and chloroethylene. It seems a sequential dechlorination pathway was followed. The PCE dechlorination in a natural sunlight irradiation test was shown to be more effective than any of the simulated visible light sources. The result supports the feasibility of future development of solar-powered dechlorination remediation systems with the use of sunlight, nontoxic dyes, and electron donors.

Pyrolysis of spill oils adsorbed on zeolites with product oils recycling.

Experimentally, a feasibility study for adsorption and catalytic pyrolysis of spill oils on Cu/ZSM-5 for recycling of light oils has been conducted in the present work. The adsorption and pyrolysis of model compounds such as heptane, toluene, and diesel (to stimulate the spill oils) on Cu/ZSM-5 have been investigated on a continuous fixed-bed reactor. By component fitted X-ray absorption near edge structural (XANES) spectroscopy, catalytic active species such as metallic copper (Cu) (77-84%) and Cu(2)O (6-7%) are found in the channels of ZSM-5 during pyrolysis of heptane or toluene. Pyrolysis of diesel effected by Cu/ZSM-5 yields gas (C(1)-C(5)) (32%) and light oil (68%) that can be used as auxiliary fuels.

Reducing nitric oxide into nitrogen via a radio-frequency discharge.

NO/N(2)/O(2)/H(2)O mixtures are usually converted into HNO(3) and/or NO(2) using different discharge approaches. In this study, a radio-frequency discharge was successfully used to reduce NO mainly into N(2) at a low pressure (4kPa). The influences of experimental parameters, including carrier gas, inlet concentration of NO, O(2), steam, and applied power, are discussed. At least 95.7% of the total N atoms converted from NO into N(2). Other traces of byproducts were N(2)O and HNO(2), but neither HNO(3) nor NO(2) were detected. In addition, conversion of NO apparently increased with elevated applied power or decreased inlet concentration of O(2), reaching 92.8% and 74.2% for the NO/N(2)/O(2) (2%) and NO/N(2)/O(2) (6%)/H(2)O (10%) mixtures, respectively, at 120W. In addition, from the optical emission spectra, a large amount of N(2) (first positive band and second positive band) and NO (gamma system) were observed, and the important reactions for NO removal and N(2) formation are proposed.

An efficient technology to treat heavy metal--lead--contaminated soil by microwave radiation.

Microwave (MW) technology can be used to vitrify contaminated soil wastes and immobilize heavy metal ions in soils. More than 93% of the Pb(II)-contaminated soil was vitrified to a glass/ceramic formation after 30 min of MW radiation. In a 6-year study, the Pb(II) concentration of the vitrified soil in the leaching test was less than 1.0 mg/l, which is substantially below the USEPA regulatory limit of 5.0 mg/l.