Reclamation of malachite green-bearing wastewater using desert date seed shell: adsorption isotherms, desorption and reusability studies

Abstract

A low-cost activated carbon adsorbent was prepared from desert date seed shell (DDSS) and utilized for the removal of hazardous malachite green (MG) from aqueous solution using batch mode technique. Different isotherm models were applied to acquire the theoretical data of MG adsorption onto the adsobent at variable initial concentration of 100-1000 mg dm^-3. Based on the coefficient of determination (R²), isotherm models exhibit the following sequence: Freundlich > Langmuir > Redlich-Peterson > Temkin > Jovanovic > Harkin- Jura > Elovich > Dubinin-Radushkevic. The maximum monolayer capacity of the adsorbent was found to be 312.5 mg g^-1 at 303 K. The mean free energy value (0.91 kJ mol^-1) obtained from D-R isotherm suggests that the adsorption process follows physisorption mechanism. Desorption studies for reusability revealed that acetic acid offered the best recovery (52.09%) and the process follow pseudo-second-order kinetics. The conducted reusability test revealed the decline of the adsorbent performance from 96.5% MG removal down to 70.5% MG removal after 5 successive adsorption/desorption cycles.

Keywords: Activated Carbon, Desorption, Isotherms, Malachite Green, Reusability