Dual application of natural clay material for decolorization and adsorption of methylene blue dye

Abstract In this study, a clay sample recovered from an archaeological excavation from the Krobo Mountains in Ghana was examined for its potential to decolorize and adsorb cationic methylene blue. The raw and calcined clay samples were characterized with XRD, SEM, FTIR and EDX. The supernatant obtained by washing the raw clay with 70% ethanol solution decolorized methylene blue. The decolorization of methylene blue was independent of calcination temperature up to 300°C. The clay material subjected to calcination temperature at 600°C showed strong adsorption towards cationic methylene blue. The equilibrium adsorption data fitted well with the Freundlich isotherm indicating adsorption unto heterogeneous surface with the interaction between the adsorbed molecules which is not restricted to the formation of a monolayer. The data also fitted well with the Weber and Morris model which described the rate-controlling steps. The intra-particle diffusion was controlled by pore and surface diffusion. In addition, the adsorption data followed a pseudo-second-order kinetic model, indicating a chemisorption process. The results highlight a unique property of the clay material as an effective decolorizing and adsorption agent for the removal of water-soluble dyes from contaminated water bodies.