Phenol Freundlich isotherm

FIGURE 20.9 Freundlich isotherm for phenol adsorbed on Frio Core. (From U.S. EPA, Assessing the Geochemical Fate of Deep-Well-Injected Hazardous Waste A Reference Guide, EPA/625/6-89/025a, U.S. EPA, Cincinnati, OH, June 1990.)... 

The secondary effluent from a biological treatment plant is treated with the activated carbon adsorption process and allowed to arrive at eqnilibrinm. The equilibrium data in terms of phenol are given below. Determine the constants for the Langmuir and Freundlich isotherms. 

Activated granular carbon is used to treat water contaminated with phenol. The granular carbon is mixed with the water at 25°C and stirred thoroughly until equilibrium is reached. The equilibrium at 25°C can be represented by the Freundlich isotherm,... 

Kitagara ° nsed two commercial granular activated carbons for the adsorption of phenol, p.nitrophenol, and 2,4 dichlorophenol from aqueous solutions, and found that the adsorption data could be explained by the Freundlich isotherm equation. The adsorption at a given concentration decreased with increase in the temperature of adsorption, although the rate of adsorption increased with increase in the adsorption temperature. Scharifov derived a mathematical model for the adsorption of phenols by activated carbons from aqueous solutions and obtained an equation for the static adsorption isotherm, which could help in the calculation of adsorption of phenol at any concentration. Chakravorti and Weber used batch and fixed-bed systems for the removal of phenol from aqueous solutions by activated carbons. The pore-diffusion model and a homogenous solid model were used to explain the results. 

For (3-CD polymers crosslinked with EP the sorption order of investigated phenols was p-cresol > ffl-cresol > o-cresol = phenol [63]. The Freundlich isotherms were used to describe the equilibrium adsorption data. It is worthnoting that the CD polymer crosslinked by EP can be efficiently regenerated using methanol. Due to the high cost of these polymers, they would not be convenient for bulk separation, but they may be used for potable water purification or for the recovery of valuable solutes in pharmaceutical plants. 

We wUl now touch upon some of these factors. First, let s look at what we mean by system isotherm. Freundlich liquid phase isotherm studies can be used to establish the adsorptive capacity of activated carbon over a range of different concentrations. Under standard conditions, the adsorptive capacity of activated carbon increases as the concentration increases, until we reach a point of maximum saturation capacity. An example of an isotherm for phenol is shown in Figure 8. 

The Freundlich liquid phase isotherm can be used to determine the effect of solubility on the adsorptive capacity of activated carbon over a range of different concentrations. Phenol is highly soluble due to its polar nature whilst, in comparison, tetrachloroethylene (PCE) has a low solubility due to being non-polar. In the isotherms illustrated, the concentration of phenol is low relative to its solubility limit and consequently, the adsorptive capacity peaks at 18% maximum (see Figure 9). In comparison the concentration of tetrachloroethylene is relatively close to its solubility limit and, accordingly, the adsorptive capacity is exceptionally good. 

Two researches studied the adsorptive properties of montmorillonite clay modified by tetra-butyl ammonium (Akgay, 2004, 2005). The adsorption of p-chlorophenol in this clay was done in batch with 20 mL of pollutant solution to 0.1 g of clay, at 25°C for 16 h. The adsorption isotherms were adjusted according to the models of Freundlich and Dubinin-Radushkevich. The kinetic and thermodynamic parameters pointed to the application of organoclay as adsorbent effective of phenolic compounds in contaminated effluents. 

The adsorption of binary organic mixtures by a porous carbon was studied by Takeuchi and Furaya, the components being chosen such that some were accepted by and some excluded from 0.5 nm micropores. The experimental results could be represented by a combination of Freundlich adsorption isotherms, the parameters of which could be related to the physical properties of the adsorptives, and it was found possible to predict satisfactorily the adsorption isotherms of new systems. The adsorption by and desorption from active carbon has been reported by Andreikova, Kondratov, and Kogan, who found that adsorption from (unspecified) organic solvents decreased in the series phenol > quinoline > phenanthrene > acenaphthene > naphthalene. In desorption, acidic compounds are best desorbed with a mixture of methanol and dichloroethane but for basic compounds benzene is most effective. 

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