Hydrous ferric oxide (HFO) colloids formed, in strictly anoxic conditions upon oxidation of Fe2+ ions adsorbed on mineral surface, were investigated under in situ conditions by contact mode atomic force microscopy (AFM). Freshly cleaved and acid-etched large single crystals of near endmember phlogopite were pre-equilibrated with dissolved Fe(II) and then reacted with Hg(II), As(V) and trichlorethene (TCE)-bearing solutions at 25 °C and 1 atm. HFO structures are found to be of nanometer scale. The As(V)–Fe(II) and Hg(II)–Fe(II) reaction products are round (25 nm) microcrystallites located predominantly on the layer edges and are indicative of an accelerated Fe(II) oxidation rate upon formation of Fe(II) inner sphere surface complexes with the phyllosilicate edge surface sites. On the other hand, TCE–Fe(II)–phlogopite reaction products are needle-shaped (45 nm long) particles located on the basal plane along the Periodic Bond Chains (PCBs) directions. Experiments with additions of sodium chloride confirm the importance of the Fe(II) adsorption step in the control of the overall heterogeneous Fe(II)–TCE electron transfer reaction.
Kinetic measurements at the nanomolar level of Hg° formed upon reduction of Hg(II) by Fe(II) in presence of phlogopite particles provide further convincing evidence for reduction of Hg(II)aq coupled to the oxidation of Fe(II) adsorbed at the phlogopite–fluid interface, and indicate that sorption of Fe(II) to mineral surfaces enhances the reduction rate of Hg(II) species. The Hg(II) reduction reaction follows a first-order kinetic law. Under our experimental conditions, which were representative of many natural systems, 80% of the mercury is transferred to the atmosphere as Hg° in less than 2 h.
The reduction of a heavy metal (Hg), a toxic oxyanion (arsenate ion) and a chlorinated solvent (TCE) thus appear to be driven by the high reactivity of adsorbed Fe(II). This is of environmental relevance since these three priority pollutants are that way reductively transformed to a volatile, an immobilizable and a biodegradable species, respectively. Such kinetic data and reaction pathways are important in the evaluation of natural evaluation scenarios, in the optimization of Fe(II)/mineral mixtures as reductants in technical systems, and in general, in predicting the fate and transport of pollutants in natural systems. 相似文献
Concentrations of 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were determined in 14 sediment samples collected from four sites in the Mai Po Marshes Nature Reserve (within a RAMSAR Site) and from another six sites in Victoria Harbour and along the Hong Kong coastline. Elevated levels of PCDDs, and particularly OCDD, were detectable in all samples collected from the Mai Po Marshes and five of the six sites. In contrast to PCDDs, PCDFs were mainly found in sediment samples collected from industrial areas (Kwun Tong and To Kwa Wan) in Victoria Harbour. PCDD/F levels and congener profiles in the samples from the Mai Po Marshes Nature Reserve in particular show strong similarities to those reported in studies which have attributed similar elevated PCDD concentrations to nonanthropogenic PCDD sources. 相似文献
In order to study the damage patterns of natural gas and water pipelines in the Ji-Ji earthquake, a GIS database and analysis procedures were established. Repair statistics was obtained from major natural gas companies and the Taiwan Water Supply Corporation (TWSC), and entered into the system. Then, repair rates (RR) were calculated. Previously, damage was analyzed without considering the corresponding pipeline material and diameters. In this study, new attempts were made to collect more data including those related to the composition of pipelines to provide a more detailed analysis of the relationship between earthquake forces and the resulting damage. Statistical analysis was also conducted to understand the correlation between RR and seismic parameters such as the peak ground acceleration, peak ground velocity, and spectrum intensity. 相似文献
This paper presents a framework for assessing the economic impact of disruption in transportation that can relate the physical
damage to transportation networks to economic losses. A spatial computable general equilibrium (SCGE) model is formulated
and then integrated with a transportation model that can estimate the traffic volumes of freight and passengers. Economic
equilibrium under a disruption in the transportation network is computed subject to the condition that the adjustment of labor
and capital inputs is restricted; the model reflects slow adjustment of these linked to the state of recovery. As a case study,
the model reviews the large Niigata-Chuetsu earthquake of 2004. Considering the damage to the transportation infrastructure,
the model indicates the extent of the economic losses arising from the earthquake distributed over regions as a consequence
of the intra- and interregional trade in a regional economy. The results show that 20% of the indirect losses occur in the
Niigata region directly affected by the earthquake, whereas 40% of the total losses are experienced in the Kanto region and
non-negligible losses reach rather remote zones of the country such as Okinawa. 相似文献
Italian sinkholes, which are mainly related to karst phenomena (i.e., solution sinkholes, collapse sinkholes, etc.), are widespread
along the Apennine ridge and in pedemontane areas where there are carbonatic bedrock outcrops. However, other collapses, which
seem unrelated to karst dissolution, have been identified in plain areas with a thick sedimentary cover over buried bedrock.
The main goal of this work is to study the geological, geomorphological, and structural setting of these areas to identify
the possible mechanism of the generation and evolution of these collapses. About 750 cases were identified by research based
on historical archives, specific geological literature, and information from local administrations. Geological, geomorphological,
and hydro-geochemical surveys were conducted in 300 cases, supported by literature, borehole, and seismic data. A few examples
were discarded because they could be ascribed to karst dissolution, volcanic origin (i.e., maar), or anthropogenic causes.
Field studies regarding the other 450 cases are in progress. These cases occur along the Tyrrhenian margin (Latium, Abruzzo,
Campania, Tuscany) in tectonic, coastal, and alluvial plains close to carbonate ridges. These plains are characterized by
the presence of pressurized aquifers in the buried bedrock, overlaid by unconsolidated sediments (i.e., clay, sands, pyroclastic
deposits, etc.). The majority of these collapses are aligned along regional master and seismogenetic faults. About 50% of
the studied cases host small lakes or ponds, often characterized by highly mineralized springs enriched with CO2 and H2S. The Periadriatic margin does not seem to be affected by these phenomena, and only a few cases have been found in Sicily,
Sardinia, and Liguria. The obtained scenarios suggests that this type of collapse could be related to upward erosion through
vertical conduits (i.e., deep faults) caused by deep piping processes whose erosive strength is increased by the presence
of acidic fluids. In order to distinguish these collapses from typical karst dissolution phenomena, they are defined as deep
piping sinkholes (DPS). 相似文献