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This paper studies the synergism between transition metals (TMs) and activated carbon (AC) as a catalyst support used in the catalytic decomposition of PCBs. A series of AC-supported TM catalysts was prepared according to two distinct methods: impregnation and ion exchange which were defined as LaTM-C and IRTM-C, respectively. The catalytic reactions between 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB-153) and AC-supported Fe, Ni, Cu and Zn catalysts were conducted under N 2 atmosphere. Changes in the nature of the catalysts as well as the decomposition mechanism of PCB-153 are discussed. Important findings include: (i) a higher metal concentration and a better metal distribution on AC is realized using ion-exchange, despite a lower AC specific surface area, (ii) IRTM-C had better effects on the decomposition of PCB-153 than LaTM-C, (iii) the role of Ni, Cu, and Fe as electron donors in PCB dechlorination was evaluated vs. the stability of Zn, and (iv) both temperature and chemical composition of TM catalysts influenced the decomposition efficiency of PCBs. [ABSTRACT FROM AUTHOR]

In this study, the synergism between activated carbon (AC) as a catalyst support and transition metals (TMs) is used to destroy low concentrations of PCBs. AC-supported TM catalysts were prepared according to two different methods: impregnation and ion exchange. Thermal reactions between 2,2′,4,4′,5,5’-hexachlorobiphenyl (PCB-153) and catalysts generated using AC-supported Ni or Cu ion exchange were conducted under a N 2 atmosphere and resulted in a decomposition efficiency > 99.0%. Decomposition efficiency of PCB-153, the residual PCB-153 distribution, and the fingerprint characteristics of the decomposition products are investigated. Important findings include: (i) establishing a ranking of TM reactivities with respect to PCB decomposition of: Ni > Cu > Zn > Fe, (ii) PCB degradation reactions proceed via adsorption, reaction, and desorption, (iii) for ion-exchange-type catalysts, the activation energy order was IRNi-C < IRCu-C < IRZn-C < IRFe-C, which matches the order of the catalytic effects of the catalyst. [ABSTRACT FROM AUTHOR]

The decomposition efficiency of polychlorinated biphenyls (PCBs) was determined using elemental iron (Fe) and three iron (hydr)oxides, i.e., α-Fe 2 O 3 , Fe 3 O 4 , and α-FeOOH, as catalysts. The experiments were performed using four distinct PCB congeners (PCB-209, PCB-153, and the coplanar PCB-167 and PCB-77) at temperatures ranging from 180 °C to 380 °C and under an inert, oxidizing or reducing atmosphere composed of N 2 , N 2 + O 2 , or N 2 + H 2 . From these three options N 2 showed to provide the best reaction atmosphere. Among the iron compounds tested, Fe 3 O 4 showed the highest activity for decomposing PCBs. The decomposition efficiencies of PCB-209, PCB-167, PCB-153, and PCB-77 by Fe 3 O 4 in an N 2 atmosphere at 230 °C were 88.5%, 82.5%, 69.9%, and 66.4%, respectively. Other inorganic chlorine (Cl) products which were measured by the amount of inorganic Cl ions represented 82.5% and 76.1% of the reaction products, showing that ring cleavage of PCBs was the main elimination process. Moreover, the dechlorination did not require a particular hydrogen donor. We used X-ray photoelectron spectroscopy to analyze the elemental distribution at the catalyst’s surface. The O/Fe ratio influenced upon the decomposition efficiency of PCBs: the lower this ratio, the higher the decomposition efficiency. X-ray absorption near edge structure spectra showed that α-Fe 2 O 3 effectively worked as a catalyst, while Fe 3 O 4 and α-FeOOH were consumed as reactants, as their final state is different from their initial state. Finally, a decomposition pathway was postulated in which the Cl atoms in ortho -positions were more difficult to eliminate than those in the para - or meta -positions. [ABSTRACT FROM AUTHOR]

Abstract: An activated carbon (AC) containing a high concentration (374mgg−1) of Fe was prepared by carbonization of an ion-exchange resin. To examine its chemical reactivity as a catalyst to decompose 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB-153), the decomposition parameters of temperature and time were varied under air or N2. Decomposition at 350°C was achieved within 15min under air and 30min under N2, and the efficiency of PCB-153 decomposition was 99.7% and 98.0%, respectively. An analysis of inorganic chloride ions revealed that PCB-153 was mineralized effectively during the decomposition. The Brunauer–Emmett–Teller (BET) surface area and pore volume of the AC were measured to assess the adsorption capacity before and after the decomposition. The differences between decomposition under air and N2 reflected the differences in the BET surface and pore volume measurements. A decomposition pathway was postulated, and the reactive characteristics of chlorine atoms loaded on the benzene rings followed the order of para > meta > ortho, which agrees with the calculated results from a density functional theory study. [Copyright &y& Elsevier]

Abstract: A link tooth wheel-cylinder non-thermal plasma reactor was set up to investigate the degradation of phenol in the mists. In addition, the decomposition efficiency of phenol, TOC removal, and byproduct formation were investigated. The stable discharge was achieved in both air and the mist condition. The decomposition efficiency and TOC removal increased with increasing the input power. For the input power of 3.6W, the phenol decomposition and TOC removal reached 90% and 47%, respectively. Phenol degradation byproducts were identified as small molecular organic acids, including formic acid, acetic acid, and oxalic acid. Their masses in the trapped solutions first increased and then decreased slightly with increasing the input power. Therefore, the biodegradation capacity of the phenol degradation byproducts can be improved. [Copyright &y& Elsevier]

Abstract: Polysulfide was produced and tested for use as an inexpensive chemical agent for the solidification/stabilization of lead in fly ash, generating little hydrogen sulfide gas. According to the equations and , this agent was expected to achieve long-term stability of disposed Pb. The leachate concentration of Pb in fly ash after sulfide treatment showed a decrease–increase–decrease trend. We also compared Pb leaching behavior from an aging/weathering experiment to thermodynamic modeling using the database from the Geochemist’s Workbench software. Thermodynamic modeling indicated the tendency that when the precipitate was formed in the order of PbO, PbCO3·PbO, and PbCO3, the total concentration of soluble Pb will be lowered. The leaching curve of Pb in fly ash without a lime slurry injection system was close to PbO, whose activity was initially near 1, but when leaching time increased, it shifted to that of PbCO3·PbO, before finally ending at that of PbCO3. However, Ca(OH)2 sprayed on fly ash interfered with the carbonation process of Pb. [Copyright &y& Elsevier]

Abstract: The process of destroying polychlorinated biphenyls (PCBs) generates exhaust gases that contain low quantities of PCBs, which cannot be disposed of easily. Activated carbon (AC) can be used to adsorb residual PCBs after disposal of high-level PCBs. We examined the chemical reactivity of AC-supported iron as a catalyst to decompose PCB-153, and varied three decomposition parameters (temperature, time and iron concentration) under an atmosphere of either air or N2. We measured the Brunauer–Emmett–Teller (BET) surface area and pore volume of AC to assess the adsorption capacity of AC before and after decomposition. At low temperatures the adsorption process was more important than the decomposition process. The decomposition process was completed within 30 and 60min under air and N2, respectively. The efficiency of PCB-153 decomposition at 350°C for 120min was ∼100.0% and 97.1% under air and N2, respectively. Analysis of inorganic chloride ions revealed that PCB-153 was effectively destroyed during decomposition. The differences between decomposition under air and N2 reflected differences in BET surface and pore volume. [Copyright &y& Elsevier]

The effects of gas compositions on NOx reduction and NH3 slip by selective non-catalytic reduction (SNCR) with NH3 were investigated in a simulated cement precalciner atmosphere. The results show that the presence of H2O improves NOx reduction and widens the reduction temperature window significantly. O2 is indispensable for reducing NOx. The optimum reduction temperature decreases and the temperature window widens to a lower temperature with the increase of O2 content. In addition, the increase of O2 content also results in a decrease of the maximum NOx reduction efficiency. The effect of SO2 on NOx reduction is negligible in the simulated precalciner atmosphere. To increase CO concentration makes NO reduction take place at relatively low temperatures. However, NH3 will tend to be oxidized into NO instead of reducing NO after entering the stream containing O2 at high temperatures if it is initially blended with a high concentration of CO in an oxygen-free environment. The increase of H2O, O2, SO2 or CO concentration is helpful to reduce NH3 slip in the temperature region below 900°C. These effects are resulted from the fact that the generation and consumption of O and OH radicals which are crucial to NO reduction and formation can be influenced by the four gas compositions. In industrial operation of SNCR for cement precalciner, these effects should be taken into account to increase NOx reduction efficiency and avoid NH3 slip. [ABSTRACT FROM AUTHOR]

Highlights: [•] The thermal degradation of HCB is observed in the presence of CaO. [•] Efficient dechlorination and polymerization of HCB is achieved at 380–400°C. [•] The mass unbalance in thermal degradation is explained by polymerization. [•] Amorphous carbon is identified as the outcome of polymerization. [•] A method for qualify the carbon as a reaction product is provided. [ABSTRACT FROM AUTHOR]

In this study a NZVI was prepared by the liquid phase reduction method. The modified NZVI obtained was characterized by BET, TEM and XRD. The results showed that the iron in the PEG-4000 modified material is mainly zero-valent iron with a stable crystal structure. It has a uniform particle size, ranging from 20 to 80 nm, and a larger specific surface area than CTAB modified NZVI, SDS modified NZVI and commercial zero-valent iron. The two surfactants CTAB and SDS are also selected as solubilizers, the results showed that the two selected surfactants obviously solubilize trichloroethylene in soil. Compared with commercial zero-valent iron, PEG-4000 modified NZVI is better removed trichloroethylene from soil; Also, the optimal operational parameters were obtained. When the experimental conditions were: PEG-4000 modified NZVI dosage 1.0 g/L, CTAB/SDS concentration equal to the CMC, SDS concentration was 2.0 × CMC, CTAB was concentration 1.0 × CMC and the vibration speed 150 r/min, the removal efficiency of trichloroethylene in a soil-water system reached 100% after 4 h. Both NZVI combined with CTAB and NZVI combined with SDS followed fitted first order reaction kinetics during the removal of trichloroethylene and their reaction rate constant k was 0.6869 mg/(L·h) and 0.5659 mg/(L·h), respectively. According to the chloride ion detection test, the trichloroethylene degradation is mainly due to reductive dechlorination. [ABSTRACT FROM AUTHOR]

Dioxins generated by iron and steel industry account for the majority of industrial dioxins emissions. This study compares the performance of different additives (including calcium sulphate dehydrate CaSO 4 ·2H 2 O; calcium polysulphide CaS x ; ammonium sulphate (NH 4 ) 2 SO 4 ; 4-methylthiosemicarbazide H 3 C-SC(NH) 2 NH 2 and thiourea H 2 NCSNH 2 ) as suppressant of chlorinated aromatics in iron ore sintering. The formation of chlorobenzenes (CBz) and polychlorinated biphenyls (PCBs), used as surrogates for dioxins, was suppressed significantly in the present of various inhibitors (1 wt%) except for CaSO 4 ·2H 2 O. Moreover, a larger molar ratio of (S + N)/Cl leads to a higher suppression efficiency, so that the inhibition capacity of (NH 4 ) 2 SO 4 on both CBz and PCBs was weaker than H 2 NCSNH 2 . The generation of dioxin-like PCBs (Co- or dl-PCB) was also analysed. [ABSTRACT FROM AUTHOR]

Abstract: In this study, solubilization of PAHs from a manufactured gas plant (MGP) soil and two artificially spiked soils using fatty acid methyl esters (FAME) was investigated. PAH removals from both the MGP and the spiked soils by FAME, methanol, soybean oil, hydroxypropyl-β-cyclodextrin, Triton X-100, and Tween 80 were compared. The effect of FAME:MGP soil ratios on PAH removals was also investigated. Results showed that the FAME mixture synthesized by our lab was more efficient than the cyclodextrin and the two surfactants used for PAH removal from the spiked soils with individual PAH concentrations of 200 and 400mgkg−1. However, the difference among three PAH removals by the FAME, soybean oil and methanol was not quite pronounced. The FAME synthesized and market biodiesel exhibited better performance for PAH removals (46% and 35% of total PAH) from the weathered contaminated MGP soil when compared with the other agents (0–31%). Individual PAH removals from the weathered MGP soil were much lower than those from the spiked soils. The percentages of total PAH removals from the MGP soil were 59%, 46%, and 51% for the FAME:MGP soil ratios of 1:2, 1:1, and 2:1, respectively. These results showed that the FAME could be a more attractive alternative to conventional surfactants in ex situ washing of PAH-contaminated soils. [Copyright &y& Elsevier]

In this research, a novel iron based bimetallic nanoparticles (Fe–Ni) supported on activated carbon (AC) were synthesized and employed as an activator of persulfate in polycyclic aromatic hydrocarbons (PAHs) polluted sites remediation. AC-supported Fe–Ni activator was prepared according to two-step reduction method: the liquid phase reduction and H 2 - reduction under high temperature (600 °C), which was defined as Fe–Ni/AC. Characterizations using micropore physisorption analyzer, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HR-TEM) showed that the synthetic material had large specific surface area, nano-size and carbon-encapsulated metal particles, moreover, the lattice fringes of metals were clearly defined. The PAH compound types and their concentrations were determined by gas chromatography mass spectrometry (GC-MS) with SIM mode, the method detection limit (MDL) was estimated to about 0.21 μg/kg for PAHs, and the average recovery of PAHs was 96.3%. Mechanisms of PAH oxidation degradation with the reaction system of Fe–Ni/AC activated persulfate were discussed, the results showed that short-life free radicals, such as SO 4 −·, OH·, and OOH· were generated simultaneously, which acted as strong oxidizing radicals, resulting in the oxidation and almost complete opening of the PAH rings. Image 1 • A novel bimetallic iron-based/AC was synthesized by two-step reduction method. • The prepared Fe–Ni/AC belongs to carbon-encapsulated metal nanoscale particles. • Quantification and quality control for 19 types of PAHs in soils was determined. • OH·, OOH·, SO 4 −· short-lived free radicals are responsible for PAHs degradation. • Both heating and metals improved the generation of SO 4 −· from persulfate. [ABSTRACT FROM AUTHOR]