Valorization of Spent Bleaching Clay via Silica Modification for High‐Performance Rhodamine B Adsorption: Optimization, Isotherm, and Kinetic Analysis

ABSTRACT This study investigated the valorization of spent bleaching clay (SBC) to produce high‐surface‐area adsorbents for dye removal. Unlike conventional regeneration routes that involve high‐temperature treatment and result in surface deterioration, the organic matter on SBC was replaced with cetyltrimethylammonium bromide, followed by silica modification of the interlayer structure. The obtained materials were compared with raw bleaching clay (RBC) and pyrolyzed bleaching clay (PBC). The surface areas of PBC and silica‐modified bleaching clay (Si‐BC) were 49.92 and 96.77 m 2 /g, respectively. A 3‐factor, 3‐level design was used to evaluate Rhodamine B (Rh‐B) removal performance. For all samples, removal efficiency decreased with increasing pH. Among the tested isotherms, the Khan model provided the best fit. Langmuir monolayer capacities were 230.8, 69.9, and 131.8 mg/g for RBC, PBC, and Si‐BC, respectively. Kinetic results indicated pseudo‐second‐order behavior for RBC, Elovich kinetics for PBC, and pseudo‐first‐order behavior for Si‐BC. Thermodynamic analysis showed that Rh‐B adsorption onto RBC and PBC was exothermic and spontaneous, whereas adsorption onto Si‐BC was endothermic but still spontaneous. Overall, silica modification significantly enhanced the structural properties and adsorption performance of SBC‐derived materials.