Effects of two chelating agents (EDTA and DTPA) on the autochthonous vegetation of a soil polluted with Cu, Zn and Cd

Chelating agents are thought to be useful for the remediation of metal-polluted soils with adequate organic matter, but the effects of these substances on the plants or seed bank of plant communities that occur in the soils are relatively unknown. In this work, the effects of two chelating substances (EDTA and DTPA) on a wet grassland plant community affected by the presence of the abandoned copper mine "Fernandito" (Garganta de los Montes, Madrid) were compared. A microcosm bioassay (6 months) was designed using the soil's top layer containing the grassland's seed bank. This soil showed a high Cu pollution level, significant contents of Zn and Cd (1120, 190, and 15 ppm, respectively), a pH of 5 and an OM content of 6.2%. The soil was subjected to three different treatments: a) untreated soil (control), b) the addition of 1 g/kg EDTA, or of c) 1 g/kg DTPA. The results presented here are those related to the plant cover, species richness, aboveground and subterranean biomass and chemical composition of the most abundant plants. Neither EDTA nor DTPA caused intense negative effects on the plants rather they significantly increased the amount of copper accumulated in aboveground parts and roots. In particular, Agrostis castellana and Corrigiola telephiifolia extracted high amounts of copper when grown in the soil with added EDTA, although they showed some nutritional imbalances (lower P contents). In contrast, lower metal concentrations were detected in plants grown in the DTPA amended soil.     

Continuous and cyclic oxidation of T91 ferritic steel under steam

The oxidation behaviour of T91 ferritic steel in steam has been studied under isothermal and non-isothermal conditions within a temperature range between 575 and 700 °C. Isothermal treatments resulted in parabolic oxidation kinetics. Three clearly defined oxide layers constituted the oxide scales. The innermost layer was a (Fe,Cr)₃O₄. The intermediate layer was porous magnetite (Fe₃O₄) followed by a compact thinner layer of hematite (Fe₂O₃). Under non-isothermal conditions the oxide scales were irregular and evidently cracked. An increase of the oxidation temperature produces an acceleration of the oxidation process, causing an increase of the oxide scale thickness that depends on the temperature increase and the exposure time.     

Relation Between the Arc-Root Fluctuations, the Cold Boundary Layer Thickness and the Particle Thermal Treatment

In plasma spraying, the arc-root fluctuations, modifying the length and characteristics of the plasma jet, have an important influence on particle thermal treatment. These voltage fluctuations are strongly linked to the thickness of the cold boundary layer (CBL), surrounding the arc column. This thickness depends on the plasma spray parameters (composition and plasma forming gas mass flow rate, arc current, etc.) and the plasma torch design (anode-nozzle internal diameter and shape, etc.). In order to determine the influence of these different spray parameters on the CBL properties and voltage fluctuations, experiments were performed with two different plasma torches from Sulzer Metco. The first one is a PTF4 torch with a cylindrical anode-nozzle, working with Ar-H₂ plasma gas mixtures and the second one is a 3MB torch with either a conical or a cylindrical anode-nozzle, working with N₂-H₂ plasma gas mixtures. Moreover, arc voltage fluctuations influence on particle thermal treatment was studied through the measurements of transient temperature and velocity of particles, issued from an yttria partially stabilized zirconia powder with a size distribution between 5 and 25 μm. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Characterization of synthetic hydrocalumite-type [Ca2Al(OH)6]NO3·mH2O: Effect of the calcination temperature

A lamellar hydrocalumite-type [Ca₂Al(OH)₆]NO₃·mH₂O, (HC), was synthesized and characterized by X-ray diffraction analysis (XRD), surface area, pore size measurements, CO₂-Thermal Programmed Desorption, and later tested as catalysts in the double bond isomerization of 1-butene. The layered structure of HC collapses above 523 K yielding an amorphous material at 573 K which upon calcination at 873–973 K transforms into a mixture of CaO and mayenite Ca₁₂Al₁₄O₃₃. The calcination temperature has a marked effect in the formation of basic sites. Thus for example, HC calcined at 1073 K shows 90% of strong basic sites (CO₂ desorption at 1023 K) while they are absent in HC calcined at 573–673 K. HC calcined at 973 K shows high catalytic activity (74% conversion) in the isomerization of 1-butene without any appreciable deactivation after 4 h on stream.     

Effect of elemental sulfur in the crosslinking reaction of poly(vinyl chloride) with tetramethyl thiuram disulfide

The effect of elemental sulfur (S₈) and tetramethyl thiuram disulfide (TMTD) on the chemical crosslinking of PVC is studied. The tensile strength, elongation at break, and gel content of crosslinked and uncrosslinked PVC molded samples, cured at different times in hot air, are evaluated. It was found that crosslinking PVC with TMTD improves its mechanical properties, and adding S₈ produces a slight improvement. Also, the S₈ presence accelerated the PVC/TMTD crosslinking reaction when the crosslinking reaction was carried out under shear forces, but not when the curing was done in hot air, where the S₈ retards the process.     

Effect of Tempering on the Oxidation Behaviour of a Roll-Grade High-Speed Steel During Thermal Cycling

Oxidation of Metals - The oxidation characteristics of a roll-grade high-speed steel with different tempering heat treatments were studied under thermal cycling conditions at 650 °C...     

Photometer measurement of polydisperse aerosols

The photometer measurement of respirable aerosol mass concentration is widely employed in air pollution monitoring. Using the Mie theory of light scattering and the built-in optical parameters of some photometers, the output signal was theoretically calculated and related to the real aerosol mass concentration.. The definition of the mass sensitivity in combination with the device calibration constants enables the photometer response bias calculation as a function of the main aerosol parameters (index of refraction, particle density, particle size distribution). The respirable fraction (Soderholm (1989) Ann. occup. Hyg. 33, 301–320; Comité Européen de Normalisation (1993) EN 481; International Standards Organisation (1993) DIS 7708; American Conference of Governmental Industrial Hygienists (1994) Cincinnati, OH, pp. 42–45) of the ambient aerosol was used as a reference concentration for the calculation of the bias. The photometer response bias maps were built for four mineral dusts and a wide range of their aerosol distributions. The method makes possible an estimation of the photometer response bias in measuring various aerosols when the instrument is calibrated against any other aerosol.     

A combined analysis of backward trajectories and aerosol chemistry to characterise long-range transport episodes of particulate matter: the Madrid air basin, a case study

This study has investigated the influence of synoptic weather patterns and long-range transport episodes on the concentration levels of airborne particulate matter (TSP, PM10 and PM2.5) and some major ions (SO(4)(2-), NO(3)(-) and NH(4)(+)) at a background rural station in central Spain. Air mass back-trajectories arriving at the site in 1999-2005 have been analysed by statistical methods. First, cluster analysis was used to group trajectories into 8 clusters depending on their direction and speed. Meteorological scenarios associated to each cluster have been obtained and interpreted. Then, the incidence of different air mass transport patterns on particle concentrations and composition recorded at this station was evaluated. This evaluation included PM10 and PM2.5 concentrations and chemical composition data, obtained at three representative sites of the Madrid air basin during sampling campaigns carried out in the course of the 1999-2005 period. Finally, a residence time analysis of trajectories was also performed to detect remote sources and transport pathways. Significantly elevated concentrations of TSP and PM10 were observed for Northern African flows as a consequence of the transport of mineral dust. Significant inter-cluster differences were also observed for PM2.5 and secondary inorganic compounds, with the highest concentrations associated with low baric gradient situations and Southern European flows. The residence time analysis confirmed that current TSP and PM10 concentrations in central Spain are likely to be influenced significantly by long-range transport of desert dust from different desert regions in North Africa. Furthermore, emissions from continental Europe with a high time of residence in the western and central areas of the Mediterranean basin, seem to significantly influence PM2.5 and secondary inorganic aerosol concentrations in this region.     

Atmospheric mercury depletion event study in Ny-Alesund (Svalbard) in spring 2005. Deposition and transformation of Hg in surface snow during springtime

A field campaign was conducted in Ny-Alesund (78 degrees 54'N, 11 degrees 53'E), Svalbard (Norway) during April and May 2005. An Atmospheric Mercury (Hg) Depletion Event (AMDE) was observed from the morning of April 24 until the evening of April 27. Transport of already Hg and ozone (O3) depleted air masses could explain this observed depletion. Due to a snowfall event during the AMDE, surface snow Hg concentrations increased two fold. Hg deposition took place over a short period of time corresponding to 3-4 days. More than 80% of the deposited Hg was estimated to be reemitted back to the atmosphere in the days following the event. During the campaign, we observed night and day variations in surface snow Hg concentrations, which may be the result of gaseous elemental mercury (GEM) oxidation to divalent Hg at the snow/air interface by daylight surface snow chemistry. Finally, a decrease in the reactive Hg (HgR) fraction of total Hg (HgT) in the surface snow was observed during spring. We postulate that the transformation of HgR to a more stable form may occur in Arctic snow during spring.