Fractal kinetics for sorption of Methylene blue dye at the interface of Alginate Fullers earth composite beads

The present work highlights the kinetics of sorption of Methylene blue dye (MB) through Alginate-Fuller's earth (ALFE) composite bead interface using the fractal approach. The ALFE beads were characterized using FESEM, FTIR, and BET surface analysis studies. The specific surface area and pore volume of the ALFE beads as obtained by BET analysis are 11.6412 m(2)/g, and 3.2953 cm(3)/g respectively indicating mesoporosity. Montmorillonite was found to be the major component of Fullers earth from XRD analysis. The bead's adsorption efficiency was optimized for different experimental conditions like pH, adsorbent dosage, MB concentration, and contact time. The adsorption data was found to fit well using the Freundlich and modified Langmuir-Freundlich adsorption isotherm model, thereby reflecting the adsorbent's energetically heterogeneous surface. The heterogeneity exponent 'h' was more than zero, thereby proving the fractal approach to be more appropriate for explaining sorption's kinetics. The time-dependant pseudo first order instantaneous rate coefficient k(inst, 1) when plotted against the contact time showed a gradual decrease, thereby bringing out the presence of three different stages in the sorption process differing in their sites of sorption and also in the amount of MB sorbed. The ALFE beads were reusable, and the simulated kinetic data using the fractal approach could be instrumental in designing a continuous flow reactor in an MB dye treatment plant. (C) 2021 Elsevier B.V. All rights reserved.