Carbonized spent bleaching earth as a low-cost adsorbent: A facile revalorization strategy via response surface methodology

As a statistical/mathematical and optimization tool, Response-Surface-Methodology (RSM) was applied for implementing a systematic route for one-step-controlled carbonization of Spent-Bleaching-Earth (SBE). The main annealing factors, viz. time and temperature, based on methylene blue (MB) adsorption efficiency as a response, were analyzed/optimized through RSM along with a Face-Centered-Composite-Design. Regenerated samples at three levels of time (30-120 min) and temperature (400-600 degrees C) were utilized in the same-condition adsorption process. The maximum removal efficiency was predicted 31.07 % at the estimated optimal condition (540.76 degrees C, 119.45 min), which was in agreement with the experimental results (28.15 %) achieved at the optimum condition by carbonized SBE (CSBE). Characterization analyses (FTIR, SEM, EDS, XRD, BET, and TGA) were carried out to compare the characteristics of samples. Furthermore, the diminution of MB by CSBE was studied at diverse solution pHs, adsorption times, adsorbent dosages, initial MB concentrations, and adsorption temperatures. The adsorption mechanism was best expressed by pseudo-second-order kinetics and Langmuir isotherm models with maximum adsorption capacity of 53.91 mg g(-1). The thermodynamics and reusability studies confirm the spontaneity and endothermic nature of the adsorption process, and adsorbent reusability, respectively. The proposed methodology offered a simple practical fabrication pathway to improve the efforts in SBE thermally regeneration process.