Removal of basic dyes in binary system by adsorption using rarasaponin–bentonite: Revisited of extended Langmuir model

The preparation of organo-bentonite via microwave radiation using natural surfactant (i.e. rarasaponin) from the tropical soapfruit pericarps of Sapindus rarak was conducted in this work. The adsorption performance of bentonite and its modified form was studied for the removal of two dyes (i.e. methylene blue and malachite green) in single and binary systems. Langmuir and Freundlich models were applied to evaluate adsorption equilibrium data in single systems. From physical meaning interpretation of the model parameters, it was found that Langmuir model gave the best representation. A new approach in representing binary experimental isotherms with extended Langmuir model incorporating fractional surface coverage in 3D mesh plot was also verified. The results show that recently proposed modification of extended Langmuir model could be used to evaluate binary adsorption data well with reasonable fitted parameter value.

► Binary adsorption of malachite green and methylene blue using clay-based adsorbent. ► Revisited of extended Langmuir model with inclusion of fractional surface coverage. ► Representation of binary experimental isotherm and the model fit in 3D mesh plot.