Valorization of food wastes (orange seeds) as adsorbent for dye retention from aqueous medium

In order to understand the adsorption process mechanism and to evaluate the adsorptive properties of the citrus powder, the equilibrium, thermodynamic, and kinetic of the adsorption of the anionic reactive dye Orange 16 on the powder of orange seeds were studied using different theoretical models. The equilibrium adsorption data analyzed by Freundlich, Langmuir, and Dubinin–Radushkevich isotherm models revealed that Langmuir model best describes the dye sorption processes. The monolayer adsorption capacity of 1,111.11 mg/g reached at 25°C and the values of the mean free energy (E) obtained from the Dubinin–Radushkevich model (5.45–6.48 kJ/mol) indicated a porous structure of the adsorbents and suggest that the physical adsorption is the main adsorption type involved in this studied processes. The values of the thermodynamic parameters (ΔG, ΔH, and ΔS) showed that the adsorption of tested dyes was feasible, spontaneous, and endothermic under examined conditions. The FTIR spectroscopy was used to characterize the adsorbent before and after loading the dyes in order to obtain additional information about possible ways to bind the dyes by the adsorbent. The obtained results showed that orange seeds, a waste material from food industry could be considered an efficient adsorbent for the removal of some textile dyes (especially with relatively low molecular weight) from aqueous media.