Freundlich-adsorption coefficients

K = Freundlich adsorption coefficient from TABLE IV. ds = bulk density of soil from TABLE I. 

Transport of the herbicides by vapor diffusion on moist soil was shown to be directly related to vapor pressure and inversely related to water solubility. Transport of the herbicides by leaching was shown to be inversely related to the Freundlich adsorption coefficient which in turn was directly related to the octanol/water partition coefficient and inversely related to water solubility (16). 

Freundlich adsorption coefficients (K) and distribution coefficients (Kd), which are indexes of the adsorption capacity of the various HAs for the pesticides, are reported in Tables 4.6 and 4.7. Regardless of the nature of the HA, rimsulfuron is adsorbed in amounts about 10 times higher than those of imazethapyr, which in turn is adsorbed in amounts about two times higher than those of alachlor (Table 4.6). Trans- and dx-chlordane are absorbed in amounts more than one order of magnitude than those of triallate (Table 4.7). Furthermore, trans-chlordane appears to be more adsorbed than dx-chlordane by any HA examined. 

TABLE 4 Physicochemical Properties of Substituted Nitrobenzenes, the Freundlich Adsorption Coefficients (Kf), and the Hammett Constants of Substituents (cr)... 

FIGURE 14 Freundlich adsorption coefficients K of substituted nitrobenzenes plotted as their logarithm versus the Hammett constants of substituents. (From Ref. 9.)... 

The adsorption coefficients (K) were determined using the equation for the Freundlich adsorption isotherm ... 

Freundlich Soil Adsorption Coefficients. Control experiments indicated that all of the compounds were stable in the stock solutions, in the adsorption solutions, and in the soil during these studies. A preliminary adsorption run conducted to determine the time required for equilibration of the herbicides between water and soil indicated that ca. 3 hours shaking was adequate. 

TABLE IV. Adsorption Coefficients for Butylate, Alachlor, and Metolachlor in Keeton Soil at Various Temperatures Obtained Using the Freundlich Equation. ... 

Monkiedje et al. [10] investigated the fate of niclosamide in aquatic system both under laboratory and field conditions. The octanol/watcr partition coefficient (Kaw) of niclosamide was 5.880 x 10 4. Adsorption isotherm studies indicated that the Freundlich parameters (K, n) for niclosamide were 0.02 and 4.93, respectively, for powder activated carbon (PAC), and 9.85 x 10 5 and 2.81, respectively, for silt loam soil. The adsorption coefficient (Aoc) for the drug was 0.02 for PAC, and 4.34 x 10-3 for the same soil. Hydrolysis of niclosamide occurred in distilled water buffer at pH above 7. No photolysis of the drug was observed in water after exposure to long-wave UV light for 4 h. Similarly, neither chemically volatilized from water following 5 h of sample aeration. Under field conditions, niclosamide persisted in ponds for over 14 days. The half-life of niclosamide was 3.40 days. 

Table 15. Freundlich and Soil Adsorption Coefficients of Organic Chemicals and Metals... 

The value of the partition coefficient, Kip, is given by the product, focKioc, where/ic and Kjoc apply only to the natural organic matter into which the sorbate can penetrate. The value of Kif is less well understood, but recent observations suggest it should be related to the quantity of adsorbent present (e.g., the fraction of black carbon in a solid matrix, /bc) and the particular compound s black-carbon-normalized adsorption coefficient (e.g., Klhc). Typical values of the Freundlich exponent are near 0.7. Hence, in a first approximation the data should fit ... 

Thus, the passage from an adsorption isotherm of a pure substance to the corresponding adsorption isotherm of a mixture is very easy, supposing that the model of a nonuniform surface is applicable and adsorption coefficients are proportional. If, for instance, adsorption of pure gas A is described by the Freundlich isotherm (135), then for adsorption of A from mixture... 

TABLE 4.6. Freundlich Adsorption Constants (1In and K) and Distribution Coefficients (Kd) for Adsorption of Alachlor (Generally Linear Isotherms), Imazethapyr (Nonlinear Freundlich Isotherms), and Rimsulfuron (Langmuir Isotherms) on Humic Acids (HAs) Isolated from Two Sewage Sludges (SSI and SS2), a Soil Amended with 10tha 1yr 1 of SSI for 2 Years (SOI + SSI), and a Soil Amended with 40(ha 1yr 1 of SS2 for 2 Years (S02 + SS2), with the Corresponding Unamended Soils (SOI and S02, Respectively) (from Senesi et al., 2001)... 

The kinetic orders in eqn. (62) are also unusual, being entirely predictable from the stoichiometric coefficients of the reaction. The resulting orders are mostly fractional. One could easily misunderstand this outcome as indicating Freundlich adsorption of the reactants, a warning against too facile an... 

Due to the effects of molecular size and shape and pore structure on the kinetics, the model cannot be used for general predictive purposes. In practice, in order to predict PAC adsorption, a series of experiments must first be carried out using the compound of interest, the activated carbon to be applied, and the water in which it is to be used. Equilibrium parameters, determined from the Freundlich adsorption isotherm equation, are used as input into a computer-based HSDM, which uses the method of least squares to minimize the difference between the experimental kinetic data points and the HSDM fit of the data [10]. When the best fit is achieved, the resultant kinetic parameters (liquid film mass transfer coefficient, k(, and the surface diffusion coefficient, DJ can then be used for the prediction of adsorption behavior under different conditions. 

Adsorption. The solution used to evaluate the pesticide transport equation, Equation 4a, assumes a linear adsorption isotherm that is constant with depth. However, linearity may not be the case for some pesticides and the adsorption coefficient will almost never be constant with depth. The rationale for using a linear model is initially based on the Freundlich isotherm... 

A smaller value of 1/n indicates a stronger bond between dispersant and particle surface. To identify the adsorption behavior of dispersant, data are fitted with Langmuir and Freundlich adsorption models, and the adsorption model with a higher correlation coefficient values is chosen. 

Both Langmuir and Freundlich adsorption equihbrium isotherm models were used to determine the adsorption equilibrium of the samples treated using different types of plasma [56-57]. The correlation coefficient, R -value was determined from the model curve and the results are shown in Table 12.5. 

DDF against time for different adsorption coefficients and a Freundlich type adsorption isotherm. 

The distribution coefficient assumes that adsorption is linear (i.e., the amount of adsorption is directly proportional to the concentration of the compound in solution) and is actually a special case of the Langmuir and Freundlich isotherms, which are nonlinear.31 32... 

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