Abstract
The aim of this study is to evaluate adsorption kinetics, isotherms and thermodynamic parameters of anionic textile dye (Acid
Red 88) onto montmorillonitic clay from aqueous solutions. The parameters of pH, initial dye concentrations, temperature, and
the adsorbent dosage were investigated experimentally. Four kinetic models including pseudo-second order, pseudo-nth order,
Bangham’s equation and double exponential equation (DEE) were selected to follow the adsorption process. The dynamic data
were fitted the DEE well and also followed the pseudo-nth order model. The adsorption data obtained were well described by the
Langmuir isotherm model. The maximum adsorption capacity was found to be 588 mg/g at 20 oC. Thermodynamic parameters
such as activation energy (Ea), Gibbs free energy (ΔG0), enthalpy (ΔH0) and entropy (ΔS0) were also evaluated. The negative
value of change in Gibbs free energy indicates that adsorption of AR88 on montmorillonitic clay is spontaneous. The anionic dye
molecules can be adsorbed on montmorillonitic clay particles, even when their surface charge (or zeta potential) is negative.
Interactions leading to adsorption of anionic dyes (AR88) onto the clay may cause from the following mechanisms: hydrogen
bonding, electrostatic interaction, hydrophobic interaction, anion exchange and dye-dye interactions. The results show that
montmorillonitic clay could be employed as low-cost material for the removal of acid dyes from textile effluents.