741 research outputs found
Characterisation of Mo and V interactions with ferrihydrite as an analogue for deep-sea hydrothermal plumes processes (abstract of paper presented at: 17th Annual V. M. Goldschmidt Conference Cologne, Germany August 2007)
No full textAdsorption studies of Mo and V onto ferrihydrite
No full textIn this paper, the kinetics of Mo and V (100 ?M) uptake on ferrihydrite (FHY) were evaluated in batch, mono-sorbate systems at pH between 4 and 9, and in bi-sorbate systems in the presence of P (100 ?M) at pH 7. In the Mo and V single-sorbate experiments, 100% adsorption was observed at pH values below 6 and 8, respectively. Above the point of zero charge (PZC = 7.97) of FHY, the adsorption efficiency for Mo dropped dramatically (20% at pH 8) while V showed high uptake efficiencies even at pH 9 (60% efficiency). The results from the bi-sorbate experiments (Mo-P and V-P) showed that at pH 7, P out-competed (97%) Mo for binding sites on FHY, while in the V-P binary system only ?44% of the binding sites are occupied by P with the remaining sites being occupied by V. <br/
The metagenomics of biosilicification: causes and effects
No full textIn order to determine the links between geochemical parameters controlling the formation of silica sinter in hot springs and their associated microbial diversity, a detailed characterisation of the waters and of in situ-grown silica sinters was combined with molecular phylogenetic analyses of the bacterial communities in Icelandic geothermal environments. At all but one site, the microorganisms clearly affected, and in part controlled, the formation of the macroscopic textures and structures of silica sinter edifices. In addition, the class and genera level phylogenetic diversity and distribution appeared to be closely linked to variations in temperature, salinity and pH regimes
The size and polydispersity of silica nanoparticles under simulated hot spring conditions
No full textThe nucleation and growth of silica nanoparticles in supersaturated geothermal waters was simulated using a flow-through geothermal simulator system. The effect of silica concentration ([SiO2]), ionic strength (IS), temperature (T) and organic additives on the size and polydispersity of the forming silica nanoparticles was quantified. A decrease in temperature (58 to 33°C) and the addition of glucose restricted particle growth to sizes <20 nm, while varying [SiO2] or ISdid not affect the size (30-35 nm) and polydispersity (±9 nm) observed at 58°C. Conversely, the addition of xanthan gum induced the development of thin films that enhanced silica aggregation
Particle motion in Stokes flow near a plane fluid-fluid interface. Part 1. Slender body in a quiescent fluid.
No full textConsiders translation and rotation, each in three mutually orthogonal directions, thus determining the components of the hydrodynamic resistance tensors which relate the total hydrodynamic force and torque on the particle to its translational and angular velocities for a completely arbitrary translational and angular motion. Calculates trajectories for a freely rotating particle under the action of an applied force either normal or parallel to a flat interface.-from Author
Particle motion in Stokes flow near a plane fluid-fluid interface. Part 2. Linear shear and axisymmetric straining flows.
No full textConsiders the motion of a sphere or a slender body in the presence of a plane fluid-fluid interface with an arbitrary viscosity ratio, when the fluids undergo a linear undisturbed flow. Determines the motion of a neutrally buoyant particle freely suspended in the flow. The theory yields general trajectory equations for an arbitrary viscosity ratio. Among the most interesting results for motion of slender bodies is the generalization of the Jeffrey orbit equations for linear simple shear flow. -from Author
Nucleation pathways in electrolyte solutions
No full textThe nucleation of a solid crystalline phase from an electrolyte solution is a long-standing subject of scientific investigations; however, neither pathways nor rates can be confidently predicted from classical nucleation theory (CNT). Moreover, results from recent experimental and theoretical studies call into question underlying assumptions of that theory, such as the nature of the species that form a stable nucleus and whether that process occurs directly from solution or following a liquid–liquid separation process. Here we provide a framework for how to interpret current investigations of solid formation from electrolyte solutions by reviewing the findings of some recent investigations. These experimental and computational studies probe nucleation pathways and rates in both homogeneous and heterogeneous environments and the processes of liquid–liquid phase separation and cluster aggregation
Impact of atmospheric deposition on N and P geochemistry in the southeastern Levantine basin
No full textAeolian dust was collected from 2001 to 2003, as part of a longer-term study, to estimate the nutrient input to the Levantine basin from atmospheric deposition. Adsorption experiments, using dust samples from six individual dust storms, showed insignificant adsorption of phosphate onto dry deposited Saharan dust. Thus adsorption onto dust can be discounted as a reason for the high nitrogen:phosphorus (N:P) ratio in the deep water of the eastern basin. A single dust storm sample from the Western Mediterranean was able to adsorb some phosphate from seawater, and it is speculated that this may be linked to the action of acid aerosols on the dust during cloud formation, or to the varying chemical composition in different sources of dust.
Dry atmospheric deposition is an important net supplier of both N and P to the eastern basin. Leachable inorganic nitrogen concentrations and fluxes are higher in background (non-storm) samples than in storm samples, probably due to the smaller grain size and aerosol source. Total P is supplied naturally with the dust, as shown by the close correlation between total P and Al (r2=0.95). However, there is a poor correlation between leachable inorganic P (LIP) and Al (r2=0.20), which may be related to grain-size effects and/or recycling processes in the atmosphere. Even so, the supply of LIP to surface waters is greatest during dust storms due to comparatively high deposition of aerosol material. While atmospheric input of P during dust storms does not produce significant in situ increases in chlorophyll, probably due to rapid microbial grazing, it does represent an important proportion of the long-term nutrient input to the basin. This may be increasing as the frequency of dust storms increases
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Nucleation, growth, and aggregation of mineral phases: Mechanisms and kinetic controls
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