Determination of adsorptive properties of expanded vermiculite for the removal of C. I. Basic Red 9 from aqueous solution: Kinetic, isotherm and thermodynamic studies

• Adsorption efficiency of expanded vermiculite for BR9 was examined in detail.
• A short contact time is sufficient to reach the adsorption equilibrium.
• BR9 adsorption changed the sign of clay surface charge from negative to positive.
• Ethyl alcohol solution improved the dye desorption from spent vermiculite.
• Expanded vermiculite as an alternative adsorbent may be used in wastewater treatment.

The adsorption characteristics of toxic Basic Red 9 (BR9) onto expanded vermiculite were determined. The effect of contact time, initial dye concentration, pH and temperature on the adsorption process was investigated. The adsorption amount of BR9 onto expanded vermiculite increased with increasing initial dye concentration and pH, but it displayed a decrease with increasing temperature. The adsorption kinetics of BR9 followed the pseudo second-order model. Freundlich model provided the best fitting with the experimental adsorption isotherm data obtained at 25, 35 and 45 °C. Thermodynamic parameters indicated that the adsorption process was exothermic, occurred spontaneously and led to an increase in the randomness at the solid/solution interface. The desorption of dye from spent adsorbent was investigated in water, ethyl alcohol and benzyl alcohol. The sign of the zeta potential value of clay changed from negative to positive due to the adsorption of BR9 onto expanded vermiculite. The adsorption of BR9 led to some changes in the FTIR spectrum of adsorbent material. The maximum adsorption capacity of expanded vermiculite for BR9 adsorption is comparable with other adsorbents reported in the literature. Therefore, expanded vermiculite as an efficient and economical adsorbent may be used for the removal of dyes from wastewaters.

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