Percent Base Saturation

A soil parameter of historical importance is the percent base saturation, defined as 

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Soil CEC is composed of two types of constituents (1) weak Lewis acid metals, commonly referred to as bases (e.g., Ca2+, Mg2+, K+, and Na+) and (2) relatively strong Lewis acid metals, H+, and heavy metals, depending on the nature of the sample, for example, geologic waste or natural soil (Al3+, H+, Fe2+, Fe3+, and Mn2+). The term percent base saturation is commonly used to describe the percent of the sum of exchangeable bases relative to the CEC near pH 7 or at pH 7 (CEC ). The equation for percent base saturation is given as... 

Figure 3.43. The relationship between soil suspension pH and percent base saturation (from Magdoff and Bartlett, 1985, with permission).

An empirical relationship between pH and percent base saturation is shown in Figure 3.43. This relationship appears to be linear, but this does not imply any mechanistic molecular meaning, because soils or clay minerals contain many different functional sites. The general behavior of these data, however, is of practical value. For example, a sample with base saturation of approximately 20% will exhibit a pH of approximately 5, while a pH of approximately 7 suggests a percent base saturation of 100%. 

Based on your calculations in problems 17 and 18, estimate the percent base saturation of the sample and discuss its practical significance. 

Soil pH buffering appears to play a major controlling role in NH3 volatilization. The potential of soil to buffer pH depends on mineralogical composition, percent base saturation, type of exchangeable cations, and CEC. An empirical formula for soil pH buffering, noted as B, is given by (Avnimelech and Laher, 1977)... 

Here, percent base saturation is simply the percentage of total cation exchange capacity (CEC) that is balanced by the base cations, and j x) symbolizes an unspecified function of some variable x. It is this equation that is in part the basis for the importance given historically to percent base saturation in soil. In actual fact, the relationship between pH and percent base saturation in soils, while statistically significant, is weak. As a result, percent base saturation and pH are unreliable predictors of one another, although there is clearly a tendency for soils with low pH to have low percent base saturation. 

The reason for the poor correlation between percent base saturation and pH is apparent in the assumptions needed to obtain equation 5.11 that is, the H -Ca exchange model oversimplifies the buffering response of soil solids to acid inputs. Specifically, the complicating involvement of in soil acidity must be considered. Reaction 5.9 cannot proceed very far before adsorbed H" begins to attack and dissolve the mineral on which it is adsorbed. This serves to consume H+, releasing structural A1 into soluble form ... 

The lime requirement of soils was at one time defined as the amount of CaCOs (or its equivalent in any other alkaline material) needed to neutralize all exchangeable acidity and bring the soil to 100 percent base saturation. This would raise the soil pH to 7 or higher, and is generally neither economical nor agronomically advisable. Lime requirement is now more rationally based on the quantity of lime required to reduce exchangeable and soluble Al to a nontoxic level for the particular crop to be grown. 

In Ihe early literature dealing with soil acidity, soils were characterized by their percent base saturation at specified pH levels. Soils with low percent base saturation values were considered to be dominated by kaolinite and hydrous oxide minerals, but soils of high percent base saturation were considered to be dominated by 2 1-type minerals, such as montmorillonite, vermiculite, chlorite, and the micas. Base saturation is a criterion of soil taxonomy in the U.S. soil classification scheme. Fifty percent base saturation (based on soil CEC at pH 7) is one criterion for distinguishing between mollic epipedons (dark, high organic horizons) and their umbric (low organic) counterparts. 

Figure 3.10. Time series of predictions with the acidification model PnET-BGC of changes in stream chemistry at Hubbard Brook to changes in past and potential future emissions of sulfur dioxide and nitrogen oxides, including the 1990 Amendments of the Clean Air Act and moderate and aggressive emission control scenarios. Shown are model-predicted stream concentrations of sulfate, nitrate, acid neutralizing capacity, pH and dissolved inorganic aluminum, and soil percent base saturation. Measured values are indicated for comparison...

Table 12. CEC and Percent Base Saturation Value for Tirau Ash Subsoil by Various Methods (from Birrell [1961b])...

Percent Calculation of Base Percent Base Saturation Saturation as... 

Thus, in spite of the high estimations of the reserves of bitumen, the two conditions of vital concern for the economic development of tar-sand deposits are the concentration of the resource, or the percent bitumen saturation, and its accessibility, usually measured by the overburden thickness. Recovery methods are based either on mining combined with some further processing or operation... 

Soils in southeastern Lee County are classified as Ultisols. They are moist soils that have argillic horizons and base saturations of less than 35 percent. Ultisols develop in areas that have long frost-free seasons, abundant rainfall, and adequate ground-water supplies. 

Forest Soil base saturation of 20% or higher (i.e., the percent of available cations in the soil that are bases) Calcium to aluminum molar ratio in the soil solution of 1.0 or greater... 

The core is removed between floods and weighed in order to determine fluid saturations. The saturation is checked against that obtained from the volume of the produced fluids in most cases, the volume determination and the mass determination of saturation differed by only 2 to 3 percent in saturation. The volume-determined saturations were used in the reported results. The emulsion characteristics and recovery efficiencies of alkaline floods discussed are listed in Table 1. The end-point saturations, permeabilities and wettabilities (as inferred from contact angle measurement) are listed in Table 2. The dimensions and properties of the unconsolidated Ottawa sandpacks used in these alkaline floods are listed in Table 3. Neutral pH floods are also listed. The neutral pH floods offer a base line for the recovery efficiencies of the alkaline floods. 

Isomerization is promoted by either acids or bases. Higher alkylbenzenes are isomerized in the presence of AlCb/HCl or BF3/HF olefins with most mineral acids, acid salts and silica-alumina saturated hydrocarbons with AlCb or AlBr,3 promoted by 0.1 percent of olefins. 

Relative Humidity ratio of the vapor pressure of water in air compared to the saturated vapor pressure of pure water at the same temperature, measure of the amount of water vapor in an air mass expressed as percent of how much water vapor that air mass can hold Relative Mass mass measured with respect to a standard, atomic masses based on C-12 standard... 

Samples were eluted in the reverse direction by using the Milton-Roy pump with the pulse dampener removed. The eluant flow (50-75 mL/min at 200-300 lb/in.2) was monitored at 254 nm by using an Altex 153 detector with a biochemical flow cell. Elution with each solvent was continued until the detector response returned to base line. All columns were eluted with acetonitrile this solvent was preceded by 4.5 M NaCl/0.04 M HC1 and 0.04 M HC1 elutions on the MP-1 column and by 4.5 M NaCl and distilled water elutions on the MP-50 column. The aqueous column effluents were adjusted to pH 2 (MP-1) or pH 11 (MP-50) and then extracted three times with dichloromethane. The acetonitrile column effluents were saturated with NaCl to separate the water, which was extracted twice more with acetonitrile. Fifty percent aliquots of the processed organic solvents from each respective column were concentrated in Kudema-Danish evaporators to a final volume of about 10 mL (any remaining water was removed as the low-boiling azeotrope in the process) to give 25,000 1... 

Figure 11.4 depicts a cross-section of a membrane with a layer of calcium carbonate scale on the surface. The concentration of calcium at the membrane surface, Z, is higher than that in the bulk feed, X, since the concentration at the surface has reached saturation. The membrane passes salts based on what concentration is actually next to the membrane. In this case, the membrane is exposed to a saturated concentration, not the lower bulk solution concentration. Even though the percent passage of calcium through the membranes stays constant, the scaled membrane will yield higher permeate concentration of calcium. This is because the concentration of calcium that the membrane is exposed to at the membrane surface is higher than the bulk solution concentration of calcium, [Z],[X]. 

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