Adsorption Characteristics of Organic Dyes on Alumina Powder from Aqueous Solutions

Adsorption of industrially important dyes (Acid Red 88, Acid Orange 8 and Bismark Brown R) on alumina from aqueous media has been investigated as a function of shaking time, amount of adsorbent, concentration of adsorbate and temperature. It is noted that the adsorption of Acid Red 88, Acid Orange 8 and Bismark Brown R on alumina decreases with an increase in temperature. The results obtained show that the adsorption isotherms at different temperatures are S-type and obey the Freundlich type of adsorption equation. Isosteric heats of adsorption (qst) have also been calculated at different coverages from the adsorption isosters and have been interpreted. The qst values for all the adsorption systems decrease with increasing surface coverage indicating that the alumina used possessed a heterogeneous surface with sites of different activities. The results also indicate that initial adsorption, whether by chemical or physical means, occurs first on the most active sites and then, as the concentration of adsorbate is increased, on sites of lesser activity.

Application of zeolite prepared from Egyptian kaolin for the removal of heavy metals: II. Isotherm models

In this study, the adsorption behavior of zeolites A and X, which are prepared from very cheap local Egyptian clay (kaolin), with respect to Cu(2+), Cd(+2), Cr(+2), Ni(+2) and Zn(2+) has been studied. The batch method has been employed, using metal solutions ranging from 100 to 400 mg/L. The distribution coefficients (K(d)) and adsorption percent were determined for the adsorption system as a function of sorbate concentration. In the uptake evaluation part of the study, adsorption ratios of metal cations on zeolites A and X match to Langmuir, Freundlich, and Dubinin-Kaganer-Radushkevich (DKR) adsorption isotherm data. Also, every cation exchange capacity for metals has been calculated. According to the equilibrium studies, the selectivity sequence can be given as Pb(2+)>Cd(2+)>Cu(2+)>Zn(2+)>Ni(2+). It was found that the uptake depend on hydrated ion diameter. This study may attract more interest due to the presence of large reservoirs of very cheap kaolin in Egypt from which both zeolite types were prepared.

Adsorption of dyes from aqueous solutions on activated charcoal

Adsorption of industrially important dyes namely bromophenol blue, alizarine red-S, methyl blue, methylene blue, eriochrome black-T, malachite green, phenol red and methyl violet from aqueous media on activated charcoal has been investigated. The effect of shaking time, pH and temperature on the adsorption behaviour of these dyes has been studied. It was noted that adsorption of all the dyes on activated charcoal decreases with an increase in the pH and the temperature. The adsorption isotherms at different temperatures were found to be of L-type. Adsorption data was fitted to Freundlich, BET and Langmuir isotherms and various adsorption parameters have been calculated. The thermodynamic parameters such as DeltaG, DeltaH and DeltaS were calculated from the slopes and intercepts of the linear variation of lnK against 1/T, where K is the adsorption coefficient obtained from Langmuir equation, was used. The calculated values for the heat of adsorption and the free energy indicate that adsorption of dyes is favored at low temperatures and the dyes are chemisorbed on activated charcoal.

On the Applicability of the Langmuir Equation to Estimation of Adsorption Equilibrium Constants on a Powdered Solid from Aqueous Solution

The Langmuir adsorption equation has become popular for summarizing solution-solid adsorption data and estimating adsorption equilibrium constants. The applicability of the Langmuir equation to estimation of adsorption equilibrium constants at solid-aqueous solution interfaces was theoretically examined in terms of (1) comparisons of solid-solution adsorption with solid-gas adsorption, (2) deductions of the Langmuir mathematical expression for the nonelectrolyte/solvent exchange, the phase exchange, the ion exchange, and the simple association reactions, and (3) the fitting procedure. The restrictive assumptions underlying the Langmuir equation for solid-gas adsorption may not be valid for adsorption of solute of small molecules or ions by a powdered solid surface from the aqueous solution phase. The fit of adsorption data to the Langmuir mathematical expression cannot be ascertained solely by the linearity of the commonly used equilibrium concentration/amount adsorbed versus the equilibrium concentration plot and does not provide the actual mechanism of the loss of small molecules or ions from aqueous solution. Therefore, the parameters of fitting to the Langmuir mathematical expression may not provide an unambiguous chemical meaning. In addition, we attempt to bring attention to the importance of the standard states of surface phase and solution phase. Copyright 2000 Academic Press.