Biosorption of malachite green by eggshells: Mechanism identification and process optimization

• Removal of malachite green by eggshells via biosorption was investigated.
• Response Surface Methodology was employed to model and optimize the process.
• The investigation was focused on proposing and describing the removal mechanism of the dye.
• Eggshells appeared to be promising biosorbent for dyes-containing wastewater treatment.

In the present work, eggshells were used to remove a dye (malachite green) from wastewater. The study was focused on identification and describing the binding mechanism of the dye by eggshells in a biosorption process optimized by Response Surface Methodology based on the Box–Behnken Design. The mechanism of biosorption was determined by characterization of the biosorbent before and after biosorption using scanning electron microscopy, X-ray diffraction analysis, the Brunauer–Emmett–Teller isotherm method, Fourier transform infrared spectroscopy. The second-order polynomial equation and 3D response surface plots were used to quantitatively determine the relationships between dependent and independent variables. The obtained results suggested the mechanism of wastewater treatment that included physical adsorption, alkaline fading phenomenon and microprecipitation. The results of the present study showed that waste eggshells have the potential to be used as an inexpensive but effective biosorbent useful in wastewater treatment.