Showing papers on "Freundlich equation published in 1992"

A distributed reactivity model for sorption by soils and sediments. 1. Conceptual basis and equilibrium assessments

Abstract: Contaminant sorption by soils and sediments is characterized as a multiple reaction phenomenon. The approach is predicated on the observation that most natural soils and sediments are intrinsically heterogeneous even at the microscopic scale; that is, variable in composition and structure at both interparticle and intraparticle scales. Heterogeneity is demonstrated for a number of soils which, on the basis of conventional macroscopic properties, would be considered homogeneous. That such heterogeneities are reflected in sorption reactions which differ between soils and between different fractions of soil is also demonstrated. A composite model, the distributed reactivity model (DRM), is introduced to characterize intrinsic heterogeneities in the properties and behaviors of soils and sediments and to capture the resulting nonlinearities of sorption isotherms. Finally, the significance of particle-scale heterogeneity and distributed reactivity is illustrated by using measured parameters and DRM calculations to characterize differences in the relative sorption behavior of soils comprising different mass fractions of differently reactive components. 31 refs., 9 figs., 2 tabs.

The biosorpnon of copperod by C. vulgaris and Z. ramigera

Abstract: The adsorption of copper(II) ions to dead cells of Chlorella vulgaris and Zoogloea ramigera was investigated. Optimum initial pH of the adsorption medium was found to be 4.0–4.5 for both microorganisms. In general, higher adsorptive uptake was observed at 25°C. The initial adsorption rate of metal ion increased by increasing metal ion concentration for C. vulgaris and Z. ramigera up to 150–200 mg l‐1 and 100–125 mg l‐1, respectively. Freundlich constants were determined from the Freundlich adsorption isotherms of two microorganisms.

Sorption of heavy metals by the soil fungi Aspergillus niger and Mucor rouxii

Abstract: Sorption of the nitrate salts of cadmium(II), copper(II), lanthanum(III) and silver(I) by two fungi, Aspergillus niger and Mucor rouxii, was evaluated using Freundlich adsorption isotherms and energy dispersive X-ray electron microscopy. The linearized Freundlich isotherm described the metal sorption data well for metal concentrations of 5 μm-1 Mm metal. Differences in metal binding were observed among metals, as well as between fungal species. Calculated Freundlich K values indicated that metal binding decreased in the order La3+ ⩾ Ag+ > Cu2+ > Cd2+. However, sorption of Ag+ was greater than that of La3+ from solutions of 0.1 and 1 mM metal and likely due to precipitation at the cell wall surface. At the 1 mM initial concentration, there were no significant differences between the two fungi in metal sorption, except for Ag+ binding. At the 5 μM concentration, there was no difference between the fungi in their sorption capacities for the four metals. Electron microscopy-energy dispersive X-ray analysis indicated that silver precipitated onto cells as colloidal silver. The results indicate that Freundlich isotherms may be useful for describing short-term metal sorption by fungal biomass and for comparison with other soil constituents in standardized systems.

Uptake of cadmium from water by beech leaves

Abstract: Uptake of cadmium from aqueous solutions by beech leaves has been studied. The effect of several factors on both rate and amount of this uptake has been studied. These factors include concentration of leaves, concentration of cadmium, pH, competing ions and drying leaves. The pattern of the curves showing the loss of cadmium from solution has been explained. Applicability of the Freundlich adsorption isotherm on the present results has been examined and the parameters of this isotherm have been calculated. The order of reaction between cadmium ions and beech leaves has been determined and a mechanism for this reaction has been suggested.

Influence of organic matter and its clay complexes on metolachlor adsorption on soil

Abstract: The absorption of metolachlor, 2-chloro-6′-ethyl-N-(2-methoxy-1-methylethyl)acet-o-toluidide was studied on three soils of various physical and chemical properties. Adsorption isotherms conformed to the Freundlich equation. The kf values increased with increasing organic carbon content of the soils. However, variations in koc values by a factor of four were observed within three natural soils. For a given soil, the koc values remained essentially unchanged after lowering the carbon content by hydrogen peroxide oxidation. These results suggest that the contribution of organic matter to total metolachlor adsorption process is influenced by association mechanisms between organic and inorganic soil constituents. Studies with mixtures of clay and organic matter indicate that the interaction between the two soil components reduces the surfaces available for metolachlor adsorption.

Adsorption/Desorption characteristics of lead on various types of soil

Abstract: Laboratory studies were conducted to address the phenomena of adsorption/desorption of lead onto various types of soils, both in the absence and presence of the chelating agent, ethylenediaminetetracetic acid (EDTA). The linear and Freundlich isotherm models provided adequate description of the adsorption/desorption behavior. Over the range of EDTA concentrations employed in the study (0.1 to 0.10M), no significant difference in the isotherm parameters was observed as a result of the applied EDTA concentration. The presence of EDTA significantly altered the adsorption/desorption behavior of lead on the soil, resulting in less of the metal being adsorbed. The soil with the higher silt/clay content had a greater amount of lead adsorbed onto it (as compared with the sandy soil). 17 refs., 8 figs., 11 tabs.

A model for the impact of soil solution Ca: Al ratio, soil moisture and temperature on tree base cation uptake

Abstract: A model for tree base cation uptake has been developed, dependent on the soil solution concentration of Al3+, divalent base cations such as Ca2+, Mg2+ and H+ ions, modelled with a Mikaelis-Menten type of expression based on the molar BC∶Al ratio, where BC is the sum of the divalent non-toxic base cations Ca2+ and Mg2+. The expression has the form of counteracting adsorption isoterms for BC and Al to the tree root. The effect of toxic levels of Hg and Pb is incorporated into the model, using root adsorption as the mechanism, and parameterization against experimental data. The expression is modified with an expression accounting for the effect of heavy metal toxicity and soil water content. The dependence of the uptake rate on soil moisture content can be shown to have the form of a Freundlich adsorption isotherm for water. The available data indicate an activation energy of 47 kJ−1 mol for base cation uptake to trees. Data from the literature was used to estimate the rate coefficients and ion selectivity coefficients for typical coniferous and decideous trees in Sweden and Germany. The model indicates that Ca2+ and Mg2+ is effective in mitigating Al3+ toxicity to tree roots, and that increasing the Ca2++Mg2+ soil solution concentration has a promotive effect on base cation uptake. Above a certain limit base cation uptake becomes independent of the solution base cation concentration. This is consistent with field observations, and may be developed to become a tool for assessing the impact of soil chemistry changes on forest growth rate and health status. Field data from the Swedish Forest Survey indicate that uptake depend on the square root of the soil solution base cation availability originating from weathering and deposition input, which is consistent with the BC∶Al expression of the model.

Adsorption, activity and kinetic properties of urease on montmorillonite, aluminium hydroxide and AL(OH)x-montmorillonite complexes

Abstract: The adsorption of urease on a montmorillonite (M), a non-crystalline aluminium hydroxide (AL) and an Al(OH) x -montmorillonite complex (AM) as well as the activity, the kinetics and the stability of the enzyme-clay mineral complexes were studied. The equilibrium adsorption isotherms of urease on clay minerals fitted both the Langmuir or the Freundlich equations. The Langmuir adsorption isotherm of the enzyme on M was of H type (“high affinity”) whereas the isotherms on AL and AM were of L type (“Langmuir”). On adding up to 21.2mg of enzyme g −1 clay, the amount of urease held on the clay minerals followed the order M > AM > AL throughout the pH range explored (4.0–9.0). The adsorption of urease on M, AM and AL was differently affected by pH. The specific activity of enzyme immobilized on M and AM was relatively high (71 and 64% respectively) as compared to that of the free enzyme; in contrast the specific activity of urease adsorbed on AL was considerably reduced (15%). The free and immobilized urease showed similar pH- and temperature-activity profiles and both states obeyed Michaelis-Menten kinetics. The V max and K m parameters, as well as the thermal stability of adsorbed urease were always lower than those of the free urease, whereas the proteolytic stability of urease held on AL was higher than that of the enzyme free or adsorbed on M and AM. Finally, it was ascertained that the covering of the surfaces of montmorillonite with different amounts of OH-A1 species reduced the quantity as well as the activity of adsorbed enzyme.

Sorption of Low Molecular Weight Organic Contaminants by Fly Ash: Considerations for the Enhancement of Cutoff Barrier Performance

Abstract: Experimental measurements indicate that class F fly ashes have significant capacity for sorption of low molecular weight organic contaminants from aqueous solution, the capacity being related to the carbon content and to other properties specific to the fly ashes tested. Correlations of Freundlich sorption capacity parameters with the respective octanol-water partition coefficients and the aqueous solubilities of the organic contaminants were highly significant.

Removal of Rhodamine-B by biogas waste slurry from aqueous solution

Abstract: The ability of biogas waste slurry to adsorb a basic dye (Rhodamine-B) has been investigated. The parameters include agitation time, initial dye concentration, pH and adsorbent dosage. The rate controlling step is mainly intraparticle diffusion. The adsorption rate constant was found to be 2.9 × 10−2 min−1 at 20 mg L−1 initial dye concentration. The adsorption conforms with Freundlich isotherm. Removal of the dye was at least 90% in the entire pH range from 2.3 to 11.2. Desorption of the dye in 50% (v/v) acetic acid to the extent of 69.7% indicates that most of the dye is held by the adsorbent by chemisorption.

Removal of copper(II) using vermiculite

Abstract: Copper(II) removal efficiency by vermiculite has been investigated through laboratory experiments. The removal phenomenon appears to be consistent with an ion-exchange (exchange adsorption) process. The batch sorption equilibria follows Freundlich adsorption isotherm. The uptake of copper(II) is a function of the pH of the solution and increases with increasing pH. Increasing ionic strength and the presence of soluble complexing agents such as ethylene diamine tetraacetic acid (EDTA) decrease the sorption of copper(II). The presence of other divalent cations like calcium impede dhte uptake of copper(II)

Adsorption of Mercury from Wastewater by Fly Ash

Abstract: The effectiveness of fly ash in adsorbing mercury from wastewater has been studied. Batch kinetic and isotherm studies have been carried out to determine the effect of contact time, pH and temperature on the adsorption. It has been found that a contact time of 2 h is necessary for the adsorption to reach equilibrium. The optimum pH was found to be between 5.0 and 5.5. The adsorption isotherm data were described adequately by both the Langmuir and the Freundlich models. The adsorption process was found to be endothermic.

Ion exchangers in radioactive waste management

Abstract: Adsorption of strontium ions from aqueous solution of Sr(NO3)2 on synthetic sodium titanate [(NaO)x(TiO)y(OH)z] powder has beet investigated as a function of contact time, Sr(II) concentration and temperature. X-ray diffraction studies indicated poor crystallinity of the synthetic sodium titanate, which became more crystalline after annealing at ca. 1173 K for 6 h in air. The adsorption of strontium ions on sodium titanate was favored at higher concentrations of the adsorbate and at lower temperatures. The kinetics of the process follows a first-order rate law with respect to adsorptive concentration and obeys the Freundlich isotherm in the entire range of adsorptive concentration. The process of adsorption in the present system has been found to be of the ion-exchange type.

Adsorption-desorption of trichloroethylene in granular media

Abstract: Sorption studies were conducted to determine the adsorption and desorption characteristics of a common synthetic chemical, trichloroethylene (TCE) in four granular media; sandy loam soil, organic top soil, peat moss and granular activated carbon (GAC). The results showed that the Freundlich Isotherm satisfactorily represents adsorption and desorption of dissolved TCE in these media and that the organic carbon content is an important factor in both processes. The soil-water partition coefficient (K oc) for TCE suggests that it will migrate quickly through soil.

Adsorption equilibrium data for substituted phenols on activated carbon

Abstract: Adsorption equillibria for 24 phenols were studied on Filtrasorb-400 activated carbon at 30±2 o C. The Freundlich constants k and n were determined. A new model was developed using a thermodynamic approach, and an equation was obtained which is similar to the Freundlich model with constants J and m. The constant J was correlated against the number of carbon atoms in the adsorbate and its measured solubility in water

Modeling Boron Adsorption on Kaolinite

Abstract: Boron adsorption at constant ionic strength (0.09 _+ 0.01 moles/liter of KC10, or Ca(C104)2) on 0.2-2 #m clay fraction of pretreated kaolinite was modeled using both phenomenological equations and surface complexation reactions. Phenomenological equations were expressed as linear relationships between the distribution coefficient and adsorption density or equilibrium concentration. The normalized form of the isotherms allowed the distribution coefficient to be predicted over a wide range of adsorption densities or equilibrium concentrations and pH. The Langmuir isotherm revealed a weak two-part linear trend supported by a similar behavior of the van Bemmelen-Freundlich isotherm. Potential adsorption mechanisms were assessed from these isotherms. The bases for the inner-sphere (surface coordination) and outer-sphere (ion-pair) surface reactions were postulated, and equations were developed and incor- porated into the generalized triple-layer surface-complexation model (TL(g)-SCM). Boron adsorption was best modeled using the inner-sphere complexes. The results confirm that the generalized triple-layer surface-complexation model can provide information regarding plausible reactions at the substrate/aque- ous interface. Intrinsic constants for postulated surface reactions were derived as fitting parameters over a range of pH and initial boron concentrations. Equilibrium adsorption studies conducted in labo- ratory model systems have provided the basis for the understanding of the surface chemistry of minerals. The bulk of the thermodynamic data extracted from these equilibrium adsorption studies has been based on experimental observations of metal-ion adsorption onto well-characterized substrates, consisting predom- inantly of metal-oxides. Models using highly detailed laboratory information have been widely applied for the oxide-solution interfacial reactions. Extensive studies of boron adsorption and fixation on clay min- erals have stemmed from boron's importance as an essential micronutrient, paleosalinity indicator, and trace component of fossil fuel wastes. There is, how- ever, limited evidence of the application of these mod- els to boron adsorption on kaolinite. This paper will attempt to address the application of these detailed modeling techniques to boron adsorption on kaolinite using the published experimental data of Mattigod et al. (1985). The application of the concepts and mathematical formalism of coordination chemistry to ion-particle interaction forms the basis of the surface-coordination or site-binding models. These models incorporate ex- plicit solution speciation and reaction stoichiometry, and are therefore useful devices for understanding the physico-chemical nature of the surface-complexation reactions. The constant capacitance surface complex- ation model (CC-SCM) has been used by Goldberg and Glaubig (1985, 1986) to predict boron adsorption be- havior on oxides and clay minerals including kaolinite.

Adsorption of organic matter from a wet phosphoric acid using activated carbon: equilibrium study

Abstract: Organic matter removal from dark green industrial phosphoric acid is essential to avoid foaming and emulsions that strongly obstruct the recovery of uranium in liquid-liquid extraction. The purpose of this paper is to report the equilibrium adsorption isotherms of organic matter contained in industrial phosphoric acid adsorbed onto activated carbon and the Langmuir, Freundlich and Redlich-Peterson constants obtained.

Adsorption isotherms of pigments from alkali-refined vegetable oils with clay minerals

Abstract: Adsorption isotherms of pigments from alkali-refined oils (rapeseed, soybean, wheatgerm, safflower, corn, cottonseed and sunflower) were measured to investigate the applicability of the Langmuir and Freundlich equations and to elucidate the adsorption characteristics of pigments on sepiolites and standard activated clay. The Freundlich equation was more applicable to the experimental adsorption isotherms. The equilibrium amount adsorbed, acidity, pore size distribution and inflection of the Freundlich isotherms could be explained by assuming that pigments were adsorbed on the stronger acid sites in smaller pores at low concentration, and then in the larger ones when the concentration increased. The amount adsorbed increased with a rise in adsorption temperatures from 70 to 110°C, and the heat of adsorption was below 10 kcal/mol. The results indicate that pigments were physically adsorbed on the acid sites activated at higher adsorption temperatures.