Contact interactions sedimentation

We observed from the column data that uranium in solution is not very mobile when the solution contacts the sediments used in the experiment. We expected that the oxidized uranium [U(VI)] in the pregnant lixiviant would be reduced and immobilized by solu-tion/sediment interactions, and this is what happened in the experiments after two to three pore volumes were eluted. The actual removal of uranium from solution may occur by adsorption onto mineral surfaces, which produces localized high concentra-... 

The methods and quantitative characteristics used in the analysis of the contact interactions between the particles can be applied to the processes involving the formation of sediments. This can be verified experimentally in sedimentation experiments with hydrophobic spherical particles (e.g., methylated glass or fluoropolymers) in a medium of a different polarity. The sedimentation of hydrophobic particles in low-polarity media, such as propanol or butanol, is of lyophilic type. The sedimentation of such particles in polar media, such as water or ethylene glycol, follows the lyophobic scheme. Similar to the case of experimental contact interaction studies, one can also observe a gradual transition from one type of sedimentation to the other. One particnlar example is the sedimentation of hydrophobic particles in aqueous solutions of alcohols. As the system becomes more lyophilic with the shift to alcohols with lower polarity or with an increase in the alcohol concentration, a transition from lyophobic sedimentation to lyophilic sedimentation takes place. A gradual decrease in the volume of the sediment is observed. Small additives of surfactants that make the surface of the particles hydrophilic have a similar effect. The concentration of an alcohol... 

This brief description of the processes of the formation of particle sediments is important in numerous applications. Many of these abundant processes are governed by contact interactions and their critical role in controlling the properties of the dense or porous structure that is being formed. 

James et al. (2003) inferred, on the basis of comparison between experimental results and natural data, that upwelling rate is another parameter that is critical to interpretation of Li isotope signatures of pore fluids. At low temperatures (<100°C), Li may be lost to fluids by sediments (Chan et al. 1994a). However, enrichment in Li of pore fluids to concentrations greater than that of seawater near basement contacts may more prevalently reflect slow rate of upwelling, as fluid-sediment interaction is thereby favored. This interpretation is consistent with data from a variety of samples from ridge flanks (e.g., Elderfield et al. 1999 Wheat and Mottl 2000). 

The strong correlation between sediment load in a stream and corresponding radioaerosol discharge emphasizes the importance of interactions between soils and radioaerosols in contact. The results to date... 

For a detailed discussion of the various pathways and stoichiometries, see reference 14. However, the question remains open as to which redox process provides the electrons for reaction 6. When buried in sediments, ferric iron may be used by microorganisms as an electron acceptor (15-17). On the other hand, it also comes into contact with reductants like H2S (18, 19). Although microbial reduction of ferric oxides using sulfide as the reductant has not yet been documented (17), various studies support a purely chemical interaction between these two compounds (20-22). 

Sorption coefficients quantitatively describe the extent to which an organic chemical is distributed at equilibrium between an environmental solid (i.e., soil, sediment, suspended sediment, wastewater solids) and the aqueous phase it is in contact with. Sorption coefficients depend on (1) the variety of interactions occurring between the solute and the solid and aqueous phases and (2) the effects of environmental and/or experimental variables such as organic matter quantity and type, clay mineral content and type, clay to organic matter ratio, particle size distribution and surface area of the sorbent, pH, ionic strength, suspended particulates or colloidal material, temperature, dissolved organic matter (DOM) concentration, solute and solid concentrations, and phase separation technique. 

Particle interaction. Scattering theory does not take account of physical interactions between particles. In concentrated systems such as pastes or sediments, the particles are in contact with each other and different theories have to be used to describe their ultrasonic behaviour [64,65]. The ultrasonic properties can be affected, even in dilute systems, if flocculation occurs. The dependence of the ultrasonic properties of a material on the degree of particle interaction allows ultrasonics to be used to investigate this phenomenon. 

Particles will still collide, but the frequency or the impact of the collisions can be minimised. What happens when the particles do come into close contact The encounters may lead to permanent contact of solid particles or to coalescence of liquid droplets. If they are allowed to continue unchecked, the colloidal system destroys itself through growth of the disperse phase and excessive creaming or sedimentation of the large particles. Whether these collisions result in permanent contact or whether the particles rebound and remain free depends on the forces of interaction, both attractive and repulsive, between the particles, and on the nature of the surface of the particles. 

The interaction between the carbonate cycle and the organic carbon cycle takes place under a variety of circumstances. At one end of the spectrum, carbonate chemistry may be under direct enzymic control (see Chapter 2.2). It may take place within cells, within organisms, or within micro-environments in close contact with living tissues (e.g., molluscan mantle). At the other extreme, where products of metabolic activities modify the overall chemistry of the environment, carbonate dissolution or precipitation may be influenced indirectly. The closer the contact between the organism and the substrate, the more specific are the biogenic dissolution and crystallization patterns that remain as traces of biological activity in sediments. 

In the curvilinear case where all hydrodynamic interactions between the two particles are considered, only those small particles in the shaded area denoted as Ac can come into contact with the larger particle. The area Ac can be determined numerically. The result is that the actual collision rate is less than the rectilinear rate, and the actual mass-transport coefficient is equal to t(Ac/Ar)PDS(ij)]. Han and Lawler (24) calculated reductions in the rectilinear transport rate by differential sedimentation ranging from about 0.3 to 0.001, so the effects of hydrodynamic interactions on this transport process can be substantial in many cases. 

A simplified version of the carbon cycle is given in Fig. 7.9. By far the largest reservoir is in marine sediments and sedimentary materials on land (20000000 GtC), mainly in the form of CaC03. However, most of this material is not in contact with the atmosphere and cycles through the solid Earth on geological timescales (see Section 4.1). It therefore plays only a minor role in the short-term cycle of carbon considered here. The next largest reservoir is seawater (about 39 000 GtC), where the carbon is mainly in the dissolved form as HC03 and C03 . However, the deeper parts of the oceans, which contain most of the carbon (38 100 GtC), do not interact with the atmosphere at all rapidly, as discussed in... 

Sedimentation is the process by which oil is deposited on the bottom of the sea or other water body. While the process itself is not well understood, certain facts about it are. Most sedimentation noted in the past has occurred when oil droplets reached a higher density than water after interacting with mineral matter in the water column. This interaction sometimes occurs on the shoreline or very close to the shore. Once oil is on the bottom, it is usually covered by other sediment and degrades very slowly. In a few well-studied spills, a significant amount (about 10%) of the oil was sedimented on the sea floor. Such amounts can be very harmful to biota that inevitably come in contact with the oil on the sea bottom. Because of the difficulty of studying this, data are limited. 

The interaction in a two-body collision in a dilute suspension has been expanded to provide a useful and quantitative understanding of the aggregation and sedimentation of particulate matter in a lake. In this view, Brownian diffusion, fluid shear, and differential sedimentation provide contact opportunities that can change sedimentation processes in a lake, particularly when solution conditions are such that the particles attach readily as they do in Lake Zurich [high cc(i,j)exp]. Coagulation provides a conceptual framework that connects model predictions with field observations of particle concentrations and size distributions in lake waters and sediment traps, laboratory determinations of attachment probabilities, and measurements of the composition and fluxes of sedimenting materials (Weilenmann et al., 1989). 

The oceans play a major role in the global cycles of most elements. There are several reasons for this. As is evident in images from space, most of the Earth s surface is ocean. When viewed from space, we see mostly water because oceans cover 71% of the Earth s surface. The oceans are in interactive contact with the lithosphere, atmosphere, and biosphere, and virtually all elements pass through the ocean at some point in their cycles. Given sufficient time, the water and sediments of the ocean are the receptacle of most natural and anthropogenic elements and compounds. 

The soil solution is the interface between soil and the other three active environmental compartments—atmosphere, biosphere, and hydrosphere (Fig. 1.1). The boundaries are dashed lines to indicate that matter and energy move actively from one compartment to another the environmental compartments are closely interactive rather than isolated. The interface between marine sediments and seawater, and between groundwater and subsoils, is chemically much the same as the interface between surface soils and the soil solution. Sediments remove and release ions from the bodies of water they contact by the same processes as the interface between the soil and the soil solution. 

Interactions of Proteins at Solid-Liquid Interfaces Contact Angle, Adsorption, and Sedimentation Volume Measurements... 

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