Freundlich parameters

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 1.25, the Freundlich parameters are presented for benzene adsorption on several ... 

Xia and Ball (1999) measured sorption isotherms for a series of chlorinated benzenes and PAHs for an aquitard material (foc = 0.015 kg oc kg-1 solid) from a formation believed to date to the middle to late Miocene. Hence, compared to soils or recent sediment POM, the organic matter present in this aquitard material can be assumed to be fairly mature and/or contain char particles from prehistoric fires. A nonlinear isotherm was found for TeCB (fitting Eq. 9-2) and the following Freundlich parameters were reported XreCBF = 128(mg g 1)(mg mL 1) "T CBand "TeCB = 0.80. For partitioning of TeCB to this material (linear part of the isotherm at higher concentrations), the authors found a Kioc value of 4.2 x 104 L kg oc. 

The compound-soil interaction is reflected in the following parameters kd = 1.0 cm3/g (distribution coefficient) NEQ = 1.1 (Freundlich parameter) kt = 0.01 h (forward kinetic reaction rate) k2 = 0.02 h (backward kinetic reaction rate) U = 1.2 (nonlinear kinetic parameter) k3 = 0.01 hr1 (forward kinetic reaction rate) k4 = 0.02 Ir1 (backward kinetic reaction rate) W = 1.3 (non-linear kinetic parameter) k5 = 0.01 h (forward kinetic reaction rate) k6 = 0.02 Ir1 (backward kinetic reaction rate), ks = 0.005 (irreversible reaction rate). 

The values of kinetic and Freundlich parameters (k, Kp, and Ng), obtained from runs carried out with different amounts of catalyst, are reported in Figure 12 vs. the absorbed photon flow per unit mass of catalyst. These values show the same feature of Langmuir parameters obtained for benzyl alcohol oxidation, that is, they decrease by decreasing the photon flow absorbed by the unit mass of catalyst. As in the case of benzyl alcohol, the consideration that the photon flow absorbed by the unit mass of catalyst is the parameter mainly affecting the photoadsorption phenomenon is strengthened by the results reported in Figure 12. 

Published values of Freundlich parameters Kf and l/n) are relatively sparse, but are currently available for at least 60 pesticide compounds (Barbash, unpublished compilation). 

TABLE 9 Summary of Freundlich Parameters for Cd Adsorption on a Commercial Activated Carbon as a Function of pH and EDTA Chelation... 

In an ambitious study, Shirgaonkar et al. [422] analyzed the uptake of 24 phenols by a commercial activated carbon and attempted to correlate the experimental data (Freundlich parameters primarily) with molecular parameters, with a view to understanding the process of adsorption. However, they concluded rather vaguely that [t]o understand the phenomena of adsorption, an insight into the interaction of adsorbate with adsorbent and adsorbate with solvent are [sic] necessary. They did note that the nature of substituents also affects the adsorption, but their results did not reveal the nature of this dependence. 

TABLE 28 Freundlich Parameters for Phenol Uptakes by Commercial and Chemically Modified Activated Carbons... 

Table 2 Freundlich parameters for the adsorption of MTBE on different activated carbons... 

Carbon Tempera- Concentration Matrix Freundlich parameters Refs. 

Carbon Temperature [°C] Concentration MTBE Matrix Freundlich parameters K n [(mg/g)(L/mg)> ] Refs. 

TABLE 4. Freundlich parameters for the systems heavy metals-adsorbents at 25°C. 

Langmuir-Freundlich parameters Langmuir-Freundlich parameters ... 

Tlie values in Table 1.24 should be seen only as a first guide or rough approximation since the parameters could be widely different with different carbons. For instance, in Table 1.25, the Freundlich parameters aie presented for benzene adsoiption on several types of activated carbons. 

Adsorption isotherms at 37°C on all surfaces fit the Freundlich equation. The Freundlich parameters varied uniformly with copolymer composition. 

K and n are the Freundlich parameters derived in batch experiments. k is the respective rate constant. 

The first two-box model includes a reversible Freundlich reaction followed by an irreversible first order process. There are four independent parameters the Freundlich parameters, K and n, a reversible rate constant, r, and an irreversible rate constant, k. Initial estimates for the Freundlich parameters were obtained from independent isotherm fits of the data after approximately 2 weeks of adsorption. Fitting the kinetic data by eye provided the initial estimates for r and k. 

Table I gives Freundlich parameters for selected additional systems where the isotherm was established with many data taken over a wide concentration range. Most of these isotherms are nonlinear. Inspection of Figure 2a and Table I reveal the following. /) Nonlinearity applies to both polar and apolar compounds, ii) Nonlinearity applies to soils both high and low in NOM. Hi) Nonlinearity is a characteristic of sorption to humic materials because it occurs even in soils with very little mineral content. Many of our studies have been carried out on Pahokee peat soil, a high-organic ( -7% ash), well-humified reference material. This material consists of jagged amber-like translucent particles containing opaque inclusions, and is absent of undecomposed plant fibers. Furthermore, nonlinearity persists in cases where the mineral component of the peat has been stripped by HF/HCl treatment (cf., entry 1 vs entry 15, Table I), iv) Nonlinearity is not an artifact of insufficient equilibration time, since isotherms typically become increasingly nonlinear with time.

TABLE 7. Langmuir-Freundlich Parameters for N2, CH4 and CO2 sorbed in silicalite-1 at 25 C... 

For an arbitrary value of the Freundlich parameter, numerical calculation is involved. Kawai and Suzuki (1984) presented similar diagrams of concentration decrease for this case. Typical calculation results are given... 

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