Utilization of wastes from bioethanol production for the fabrication of new adsorbents for the removal of toxic dye in water

Cationic dyes, even at low concentrations, pose serious risks to aquatic ecosystems and contribute to environmental pollution. Effective removal of these dyes is therefore essential for protecting water resources and marine life. This study investigates lignosulfonate-based adsorbents (L, LS, and LSR-F) for the removal of crystal violet (CV) dye from wastewater. Structural and physicochemical characterization using FTIR, Raman spectroscopy, SEM, TGA, and CHNS analysis confirmed the successful synthesis and functionalization of the adsorbents. Under optimal conditions (pH 8, 150 mg/L CV, 0.1 g adsorbent dose, room temperature), LSR-F achieved 98% removal efficiency within 15 min. Kinetic modeling with five approaches (pseudo-first-order, pseudo-second-order, intraparticle diffusion, Boyd, and Elovich) revealed that adsorption followed the pseudo-second-order model, suggesting chemisorption as the dominant mechanism. Isotherm studies indicated that the Langmuir model best described the adsorption process, with LSR-F exhibiting a maximum adsorption capacity of 73.53 mg/g. Thermodynamic analysis further showed that the process was spontaneous and endothermic. Overall, LSR-F demonstrates excellent potential as a cost-effective, sustainable adsorbent for removing toxic cationic dyes from wastewater. By utilizing bio-industrial residues, this approach supports multiple Sustainable Development Goals (SDGs), particularly SDG 6 (Clean Water and Sanitation), SDG 12 (Responsible Consumption and Production), SDG 13 (Climate Action), and SDG 14 (Life Below Water).