Calcium alginate-regenerated spent bleaching earth composite beads for efficient removal of methylene blue

This study aims to find an alternative method to the landfill of spent bleaching earth (SBE), which is a solid waste generated by the refining of edible oil that causes enormous ecological and environmental problems. This solid waste is clay loaded with impurities, colourants, and a large amount of oil entrained during the various stages of refining. In this study, the SBE was initially regenerated (RSBE) by thermal processing in a muffle furnace (temperature: 400 degrees C, time: 1 h) followed by washing with an HCl solution. Then, the regenerated materials were encapsulated with calcium alginate (Alg) to form adsorbent composite beads (Alg-RSBE). Different Alg/RSBE ratios were applied during materials elaboration, yielding beads denoted Alg-RSBE 1/1 (1/1, w/w), Alg-RSBE 1/2 (1/2, w/w), and Alg-RSBE 1/3 (1/3, w/w), respectively. The Alg-RSBE composite beads were characterized by several methods (FTIR, SEM, EDX, TGA, pH(PZC)) and used as adsorbents of methylene blue (MB) in a fixed-bed adsorption system. The adsorption of MB was studied at different experimental conditions such as contact time and initial MB concentration. The results showed that the kinetics of MB adsorption fitted to pseudo-second-order kinetics and the adsorption isotherm fitted to Langmuir isotherm. Among the three types of Alg-RSBE composite beads, Alg-RSBE 1/1 presents the highest MB adsorption capacity at 833.33 mg/g. Intraparticle and film diffusion equations were used to evaluate the kinetic data. Finally, the regeneration study showed that MB dye was successfully desorbed from Alg-RSBE 1/1 with removal percentages from 93.32% to 88.15% after six cycles.