Developing Biosorbents from Agricultural Waste: Fava Bean Shells for Efficient Dye Removal

In this study, two biosorbents were developed from fava bean shells (FBS) dried fava bean shells (DFBS) and fava bean shell charcoal (FBSC) and their adsorption performance for congo red (CR) dye was compared. Adsorption was evaluated under varying conditions of temperature, initial dye concentration (C۰), adsorbent dose, contact time, and pH. At pH < ۴, FBSC exhibited superior adsorption capacity (Qe) and removal efficiency (۹۹%) compared to DFBS (۹۰%), highlighting the enhancement achieved through carbonization. Adsorption data were fitted to seven isotherm models; although the Langmuir model (Qm), showed high correlation, the calculated monolayer capacities differed from experimental maxima due to heterogeneous surface properties and broad concentration ranges, while Freundlich and Halsey models provided a physically meaningful description (R² > ۰.۹). Kinetic studies indicated that the pseudo-second-order model best described the adsorption process (R² = ۰.۹۹۲۸ for DFBS, ۰.۹۹۹۸ for FBSC), suggesting that chemisorption is dominant, with reasonable fits also obtained using the Elovich and intra-particle diffusion models (R² > ۰.۹). Thermodynamic analysis, based on dimensionless equilibrium constants, revealed that adsorption onto FBSC is spontaneous and endothermic with increased randomness at the adsorbent–adsorbate interface, whereas adsorption onto DFBS is spontaneous but slightly exothermic, reflecting moderate interactions. These findings indicate that FBSC is an efficient, economical, and environmentally friendly biosorbent for dye removal from aqueous solutions.

کلیدواژه ها:

Congo red ، Biosorbents ، Wastewater Treatment ، Isotherm models ، Thermodynamic analysis