Congo red dye adsorption on dry green pea husk: Effects of process parameters and modeling approaches

Background: Congo red (CR), a harmful dye present in water, requires effective removal methods. This study investigated the utilization of dry green pea husk (DGPH) and its charcoal (CGPH) as economical and eco-friendly adsorbents. Methods: Various factors, including contact time, pH, adsorbent dosage, initial concentration, and temperature, were investigated to assess their impact on the adsorption process. Also, different models (isotherms, kinetics, and thermodynamics) were compared to describe the adsorption phenomenon. Results: Equilibrium adsorption was achieved within 30 minutes for both adsorbents. The optimum pH for CR removal was determined to be 2. The adsorption capacity decreased by increasing the adsorbent dosage, whereas it increased by increasing the initial dye concentration. The Langmuir isotherm model demonstrated the best fit for DGPH, while the Freundlich model exhibited the best fit for CGPH. The pseudo-second-order model displayed a superior fit for both adsorbents. To assess the spontaneity and feasibility of the adsorption process, thermodynamic parameters including enthalpy, entropy, and Gibbs free energy were computed. The results indicated that the adsorption of CR on DGPH was endothermic and favorable at lower temperatures, whereas the adsorption on CGPH was exothermic and favorable at higher temperatures. The negative values of Gibbs free energy for the CGPH adsorbent confirmed the spontaneous nature of the adsorption process. Conclusion: The study establishes that green pea husk and its charcoal are effective and environmentally friendly alternatives for the removal of CR from water.