Undersaturation

Surface water Is usually undersaturated in calcium ions (Ca ). Where (even saturated) surface water mixes with sea water, mixing zone corrosion will dissolve calcium carbonate. Evidence of this occurring may be seen on islands. 

Open chain hydrocarbons which are undersaturated, i.e. having at least one carbon-carbon double bond are part of the olefin series, and have the ending -ene . Those with one carbon-carbon double bond are called mono-olefins or alkenes, for example ethylene CH2 = CH2. 

When the pressure of a volatile oil or black oil reservoir is above the bubble point, we refer to the oil as undersaturated. When the pressure is at the bubble point we refer to it as saturated oil, since if any more gas were added to the system it could not be dissolved in the oil. The bubble point is therefore the saturation pressure for the reservoir fluid. 

Assuming an initial reservoir pressure above the bubble point (undersaturated reservoir oil), only one phase exists in the reservoir. The volume of oil (rm or rb) at reservoir conditions of temperature and pressure is calculated from the mapping techniques discussed in Section 5.4. 

Solution gas drive (or depletion drive) Gas cap drive Water drive with a large underlying aquifer Undersaturated oil (no gas cap) Saturated oil with a gas cap Saturated or undersaturated oil... 

In some undersaturated reservoirs with non commercial quantities of gas but too much to flare, gas has be used to fuel gas turbines and generate electricity for local use. 

Seed crystals added to undersaturated system no initial breeding... 

For undersaturated cake with S < 1, saturation can be inferred from the weight fraction of sohds and the porosity of the cake, together with the sohd and liquid densities ... 

Undersaturated The same quantities of solute and solvent are mixed, as for the above ease, but the system is then heated for about 20 min above the required temperature (if solubility inereases with temperature) so that most, but not all, of the solid is dissolved. The solution is then eooled and agitated at a given temperature for a long period, to allow the exeess solid to deposit and an apparent equilibrium to be reaehed. 

The solubility of calcite and aragonite increases with increasing pressure and decreasing temperature in such a way that deep waters are undersaturated with respect to calcium carbonate, while surface waters are supersaturated. The level at which the effects of dissolution are first seen on carbonate shells in the sediments is termed the lysocline and coincides fairly well with the depth of the carbonate saturation horizon. The lysocline commonly lies between 3 and 4 km depth in today s oceans. Below the lysocline is the level where no carbonate remains in the sediment this level is termed the carbonate compensation depth. 

Evaporite deposition is a much more episodic process and thus difficult to quantify. Because seawater is significantly undersaturated with respect to common evaporitic minerals, like gypsum and halite, evaporites are only formed when restricted circulation develops in an ocean basin in which evaporation exceeds precipitation. A geologically recent example is the Mediterranean Sea of 5-6 Myr ago. At this time excess evaporation exceeded the supply of ocean water through shallow inlet(s) from the Atlantic Ocean. As salinity increased, first CaS04, then NaCl precipitated. Over time, salt deposits 2-3 km thick formed. This thickness represents about 40 desiccations of the entire... 

To increase the permeability of a certain region of the reservoir, the liquid-absorbed water is evaporated by heating the portion to a temperature above the boiling point of water, taking into account the ambient pressure [897,1487]. The liquid water is evaporated by injecting a water-undersaturated gas, such as heated nitrogen, into the reservoir. 

Leaching of nuclides implanted into adjacent minerals has been suggested for the supply of Rn into the vadose zone. Where there are intermittent undersaturated conditions, i.e., in soils or rocks where the water table lowers seasonally, the low stopping power of air allows atoms ejected from minerals to be implanted across pore spaces. These atoms will then be available for leaching... 

The unusual occurrence of ( " U/ U) ratios less than one were observed in waters from the weathered zone around the Koongarra ore deposit (Yanase et al. 1995). While this could be due to prior leaching and depletion of from the U that is now released by weathering, it was suggested that this reflects implantation of recoil into phases more resistant to weathering during undersaturated conditions in this zone. 

When the steric size of the substituents increases, no adducts with bulky (Et3N) or less basic (EtzO) donors are formed with (Me3C)2Si= NSi(CMe3)3.14 The structure of the benzophenone adduct is quite remarkable.16 Instead of the expected cycloaddition product, the carbonyl oxygen atom is coordinated to the undersaturated silicon atom. 

Most primary and secondary minerals found in soil systems are barely soluble in the soil solution. The amount of mass from the bulk phase to hydrated ions in soil solution is negligible compared to the total mass of the solid phase. In arid and semi-arid soils, concentrations of most trace metals in soil solution may be controlled by their carbonates and to some extent by their hydroxides. Other than carbonates, trace elements in arid and semi-arid soils may also occur as sulfate, phosphate or siliceous compounds, or as a minor component adsorbed on the surface of various solid phase components. The solubility of carbonates, sulfates and other common minerals of trace elements in arid and semi-arid soils will be discussed in Chapter 5. Badawy et al. (2002) reported that in near neutral and alkaline soils representative of alluvial, desertic and calcareous soils of Egypt, the measured Pb2+ activities were undersaturated with regard to the solubility of... 

Dang et al. (1994) observed that the experimentally determined solubility lines for Zn2+ in 14 soil solutions from southern Queensland with soil pH from 7.45-8.98 and 0.08-2.07% CaC03 were not undersaturated with respect to the solubility of any known mineral form of Zn. Therefore, they suggested that Zn2+ activity was mainly controlled by adsorption-desorption reactions in these soils. Similar observation on solubility of Cr(VI) in arid soils was reported by Rai et al. (1989). In the absence of a solubility controlling solid phase, Cr(VI) aqueous concentrations under slightly alkaline conditions may be primarily controlled by adsorption/desorption reactions (Rai et al., 1989). Chromuim(VI) is adsorbed by iron and aluminum oxides, and kaolinite and its adsorption decreases with increasing pH. 

In Fig. 24 points A and A represent the equal solubilities at the temperature T0 of the pure enantiomers, while E represents the solubility of the eutectic mixture. AEA is the solubility-composition curve, above which undersaturated solutions exist and below which a saturated solution is in equilibrium with the two solid phases, D and L. Figure 21 shows that, with an increase in temperature, A and A move toward the pure enantiomers D and L, while E moves toward the pure eutectic. All of these trends indicate an increase in solubility upon increasing the temperature. 

Figure 8-2 shows the depth profiles of the saturation index omegadel), the solution rate, and the respiration rate. At the shallowest depths, the saturation index changes rapidly from its supersaturated value at the sediment-water interface, corresponding to seawater values of total dissolved carbon and alkalinity, to undersaturation in the top layer of sediment. Corresponding to this change in the saturation index is a rapid and unresolved variation in the dissolution rate. Calcium carbonate is precipitating... 

Under ideal circumstances, certain chemical processes which are relatively sluggish may possibly be used for water dating. Near-surface water which is low in dissolved silica, for example, might be undersaturated with respect to silica which in turn would suggest that the water is less than 10 years old and probably less than a few months old. Unfortunately, the large number of variables which control dissolution or precipitation of minerals in natural systems probably can never be defined with sufficient precision to enable more than the most general, qualitative dati ng. 

Mass transfer can be described in more sophisticated ways. By taking in the previous example to represent time, the rate at which feldspar dissolves and product minerals precipitate can be set using kinetic rate laws, as discussed in Chapter 16. The model calculates the actual rates of mass transfer at each step of the reaction progress from the rate constants, as measured in laboratory experiments, and the fluid s degree of undersaturation or supersaturation. 

The simplest open-system model involves a reactant which, if it is a mineral, is undersaturated in an initial fluid. The reactant is gradually added into the equilibrium system over the course of the reaction path (Fig. 2.3). The reactant dissolves irreversibly. The process may cause minerals to become saturated and precipitate or... 

In kinetic reaction paths (discussed in Chapter 16), the rates at which minerals dissolve into or precipitate from the equilibrium system are set by kinetic rate laws. In this class of models, reaction progress is measured in time instead of by the nondimensional variable . According to the rate law, as would be expected, a mineral dissolves into fluids in which it is undersaturated and precipitates when supersaturated. The rate of dissolution or precipitation in the calculation depends on the variables in the rate law the reaction s rate constant, the mineraTs surface area, the degree to which the mineral is undersaturated or supersaturated in the fluid, and the activities of any catalyzing and inhibiting species. 

Once we have calculated the distribution of species in the fluid, we can determine the degree to which it is undersaturated or supersaturated with respect to the many minerals in the thermodynamic database. Only a few of the minerals can exist in equilibrium with the fluid, which is therefore undersaturated or supersaturated with respect to each of the rest. For any mineral A , we can write a reaction,... 

The fluid is undersaturated if Qi is less than A). This condition indicates that Reaction 3.34 has not proceeded to the right far enough to reach the saturation point, either because the water has not been in contact with sufficient amounts of the mineral or has not reacted with the mineral long enough. Values of Qi greater than A), on the other hand, indicate that the reaction needs to proceed to the left to reach equilibrium. In this case, the fluid is supersaturated with respect to the mineral. 

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