Dissolution capacity

The protocol involving NaOAc-HOAc at pH 5 was first proposed and used by Jackson (1958) to remove carbonates from calcareous soils to analyze soil cation exchange characteristics (Grossman and Millet, 1961). Other researchers used HOAc for the extraction of metals from sediments and soils (Nissenbaum, 1972 Mclaren and Crawford, 1973). Tessier et al. (1979) first used the NaOAc-HOAc solution at pH 5 to dissolve the carbonate fraction from sediments. Since then, the NaOAc-HOAc buffer has been widely used as a specific extractant for the carbonate phase in various media (Tessier et al., 1979 Hickey and Kittrick, 1984 Rapin et al., 1986 Mahan et al., 1987 Han et al., 1992 Clevenger, 1990 Banin et al., 1990). Despite its widespread use, this step is not free from difficulties, and further optimization is required in its application. Questions arise with regard to this step in the elemental extraction from noncalcareous soils, the dissolution capacity and dissolution rates imposed by the buffer at various pHs, and the possibility that different carbonate minerals may require different extraction protocols (Grossman and Millet, 1961 Tessier et al., 1979). 

Dissolution Capacity of NaOAc-HOAc Solutions at Various pHs... 

The effective dissolution capacity of the NaOAc-HOAc buffer solutions at various pHs in the CARB step of the current SSD protocol is estimated from the maximum quantity of Ca released (Fig. 4.2). When the buffer solution is at pH 5.0, almost all CaC03 can be dissolved from calcareous soils with about 45-50% CaC03 at this step. For soils with higher carbonate contents, a second dose of the buffer solution must be added to complete the dissolution step. 

Water has a high helium dissolution capacity, and groundwaters in nature contain helium in a concentration range spanning over five orders of magnitude, as seen in Table 14.1. In all these cases the partial helium pressure in the aquifers was orders of magnitude below the hydrostatic pressure, not to mention the lithostatic pressure, ensuring no gas losses took place. 

These processes occur by precipitation through evaporative concentration of a solute in the aqueous medium until its dissolution capacity is exceeded. Then, a solid is formed and deposited either as a sediment or on a nearby surface. These products are called evaporites. A typical example is the deposition and formation of calcium carbonate stalactites and stalagmites. Evaporation is a major process in arid areas and it influences the chemistry of surface waters. That is why in saline lakes, inland seas, or even in estuaries, evaporites of NaCl or NaCl/KCl and deposits of CaS04 and CaC03 are formed. Here, CaS04 generally precipitates first, and then NaCl. 

Fig. 12.tl The ratio between the detrital and the opal content of sediments may be the major controlling factor for the dissolution capacity of opal and therefore for the asymptotic increase of silicic acid pore water concentrations with sediment depth and the release of silicic acid to the bottom water, a) benthic silicic acid flux as a function of the detrital to opal mass ratio in surface sediments b) model-predicted fluxes for two hypothetical sets of sediment. The TOC is assumed constant with 3 wt%. The data originate from different sources (modified after Dixit and Van Cappellen 2003). 

The tensile strength increases with duration and especially with diamine amount, correlated with the continuously decreasing in the dissolution capacity of the resulting products (for 5% p-PhDA in the initial mixture the polymer becomes practically insoluble) requires to take a crosslinking reaction into account which proceeds by hydrogen chloride elimination between the diamine and the chlorine in PVC. 

When Co(OAc)2 or Mn(OAc)2 were used alone as catalysts and less oxygen was applied (instead of pure oxygen, air was appUed and a solvent with a lower oxygen dissolution capacity was used) the reaction stopped at pinane-2-hydroperoxide. The authors used enriched cis-pinane (>96%) and reported 37% as the highest yield to pinane-2-hydroperoxide. 

Liposomes made of cholesterol and egg lecithin (molar ratio 0.3) are solubilized by BS at different speeds and in the order TDOTCDO TC>TUCD[11]. At equilibrium the dissolution capacity of the different BS is about the same[11]. 

Detailed dissolution study of magnetite powder was carried out using these formulations. Typical results showing the dissolution capacity of the above formulations is presented in Table I. It is evident that the EDTA based formulations (1) and (3) are kinetically superior to the formulation containing picolinic acid. The kinetic studies indicated at the dissolution follows the cubic rate law. It was also observed that the conditions for dissolution of magnetite by these dilute chemical formulations are also favourable to the dissolution of nickel ferrite. 

Organic acid blends and mixtures of HCl and organic acids are useful in higher-temperature applications (>300°F). Also, such mixtures can extend live acid reaction—by combining the full dissolution capacity of a certain strength of HCl (e.g., 15%) and further dissolution capacity from an additional organic acid (e.g., 10% acetic or formic acid). 

Evaporation induced phase separation (EIPS) - where the homogeneous polymer solution contains two or more solvents of different dissolution capacities, the more volatile solvent can be evaporated. 

The bubble size in these cells tends to be the smallest (10 to 50 Im) as compared to the dissolved-air and dispersed-air flotation systems. Also, very httle turbulence is created by the bubble formation. Accordingly, this method is attractive for the separation of small particles and fragile floes. To date, electroflotation has been applied to effluent treatment and sludge thickening. However, because of their bubble generation capacity, these units are found to be economically attractive for small installations in the flow-rate range of 10 to 20 mVh. Electroflotation is not expected to be suitable for potable water treatment because of the possible heavy metal contamination that can arise due to the dissolution of the electrodes. 

The anode capacity is the total coulombic charge (current x time) produced by unit mass of an anode as a result of electrochemical dissolution. It is normally expressed in ampere hours per kilogram (Ah/kg) although the inverse of anode capacity, i.e. the consumption rate (kg/Ay) is sometimes used. 

Lanthanum oxide is valence invariant, and does not exhibit any oxygen storage capacity, but it effectively stabilizes 5/-AI2O3. It spreads over the alumina surface and provides a barrier against dissolution of rhodium in the support. 

During the lifetime of a root, considerable depletion of the available mineral nutrients (MN) in the rhizosphere is to be expected. This, in turn, will affect the equilibrium between available and unavailable forms of MN. For example, dissolution of insoluble calcium or iron phosphates may occur, clay-fixed ammonium or potassium may be released, and nonlabile forms of P associated with clay and sesquioxide surfaces may enter soil solution (10). Any or all of these conversions to available forms will act to buffer the soil solution concentrations and reduce the intensity of the depletion curves around the root. However, because they occur relatively slowly (e.g., over hours, days, or weeks), they cannot be accounted for in the buffer capacity term and have to be included as separate source (dCldl) terms in Eq. (8). Such source terms are likely to be highly soil specific and difficult to measure (11). Many rhizosphere modelers have chosen to ignore them altogether, either by dealing with soils in which they are of limited importance or by growing plants for relatively short periods of time, where their contribution is small. Where such terms have been included, it is common to find first-order kinetic equations being used to describe the rate of interconversion (12). 

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