Aqueous phase from dissolution experiments

Micelles forming above the c.m.c. incorporate hydrophobic molecules in addition to those dissolved in the aqueous phase, which results in apparently increased aqueous concentrations. It has to be noted, however, that a micelle-solubilised chemical is not truly water-dissolved, and, as a consequence, is differently bioavailable than a water-dissolved chemical. The bioavailability of hydrophobic organic compounds was, for instance, reduced by the addition of surfactant micelles when no excess separate phase compound was present and water-dissolved molecules became solubilised by the micelles [69], In these experiments, bacterial uptake rates were a function of the truly water-dissolved substrate concentration. It seems therefore that micellar solubilisation increases bioavailability only when it transfers additional separate phase substrate into the aqueous phase, e.g. by increasing the rates of desorption or dissolution, and when micelle-solubilised substrate is efficiently transferred to the microorganisms. Theoretically, this transfer can occur exclusively via the water phase, involving release of substrate molecules from micelles, molecular diffusion through the aqueous phase and microbial uptake of water-dissolved molecules. This was obviously the case, when bacterial uptake rates of naphthalene and phenanthrene responded directly to micelle-mediated lowered truly water-dissolved concentrations of these chemicals [69]. These authors concluded from their experiments that micellar naphthalene and phenanthrene had to leave the micellar phase and diffuse through the water phase to become... 

Final composition of the aqueous phase. The final compositions of the waters resulting from the three dissolution experiments have been summarized and listed together with compositions of waters from natural systems (Table VI). The experimental and natural basalt waters have very similar compositions. However, the experimental quartz monzonite water has a higher than natural K content while the shale water has higher than natural K and Na contents. The HCO3 content of each of the experimental waters is higher than the content of its natural counterpart while the oposite is true for 04. 

Carbon dioxide pressures from 1 to 75 atmospheres and temperatures from 0° to 80°C were assessed. Since the liquid phase is in contact with the coal and is responsible for mineral matter dissolution, its composition would be expected to have a bearing on ash reduction in the coal. The solubility of CO2 in the liquid phase increases as the CO2 pressure increases and may be related to swelling of coal structure (although not linearly). Table I summarizes a set of experiments directed toward determining the effect of aqueous phase concentration of CO2 on the treated product ash content for Pittsburgh Seam coal. At low CO2 concentrations,... 

Solubilization as a bulk reaction Molecular dissolution and diffusion of oil into the aqueous phase takes place, with a subsequent uptake of oil molecules by surfactant micelles [156-161]. This mechanism is operative for oils (like benzene, hexane, etc.), which exhibit a sufficiently high solubility in pure water. Theoretical models have been developed and verified against the experiment [157,159-161]. The bulk solubilization includes the following processes. First, oil molecules are dissolved from the surface of an oil drop into water. Kinetically, this process can be characterized by a mass transfer coefficient. Next, by molecnlar diffnsion, the oil molecules penetrate in the water phase, where they react with the micelles. Thus, the concentration of free oil molecules dimmishes with the distance from the oil-water interface. In other words, solubilization takes place in a certain zone around the droplet [159,160]. 

Release of trace elements such as strontium from feldspar is also observed to be nonstoichio-metric (Brantley et al, 1998). At pH 3, bytownite, microcline, and albite aU release strontium at an initially fast rate that slows to near stoichiometric values at steady state. In addition, aqueous strontium is enriched in Sr compared to the bulk mineral early in dissolution. All feldspars smdied evenmally released strontium in isotopic abundance roughly equal to that of the bulk mineral. Nonstoichiometric release of strontium was explained by the presence of defects or accessory phases in the minerals. Taylor et al. (2000) also reported that the initial dissolution of labradorite was nonstoichiometric during dissolution in column reactors with inlet solution pH 3, but that the mineral dissolved and released strontium stoichiometrically at steady state. In contrast to the earlier work, however, Sr/ Sr in solution did not differ from that of the bulk labradorite during dissolution in the column experiments. 

The highest residual traces of Cr(VI) occur in the anodic sections of the experimental cells. Cr(VI) removal from aqueous solutions is enhanced by the presence of ferric iron oxyhydroxide phases, as Cr(VI) adsorbs onto FeOOH (e.g. Aoki and Munemori, 1982 Mesuere and Fish, 1992a,b Mukhopadhyay, Sundquist, and Schmitz, 2007). The amount of released by anodic electrode dissolution primarily depends on the applied current and the duration of the passage of the current through the electrodes (e.g. Mukhopadhyay, Sundquist, and Schmitz, 2007). Differences in the lateral extent of iron mineralization in the three experiments illustrate that the buffering capacity of the soils influenced the spatial extents of the zone of Cr(VI) reduction and complementary alkaline zone. The Warwick soil (experiment A) operated at half the applied voltage to experiments B and C, experienced the furthest advance of iron mineralization from the anode array, quickly developed a sharp pH jump, and attained the most acidic conditions. Collectively, these attributes indicate that the Warwick soil had a comparatively low buffering capacity relative to the other two soils examined. 

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