The Equilibrium and Thermodynamics of Methylene Blue Uptake onto Ekowe Clay; Influence of Acid Activation and Calcination

Daniel C. Emeniru, Okechukwu D. Onukwuli, Pere-ere DouyeWodu, Bernard I. Okoro

The equilibrium isotherm study verified that the linear Freundlich model best explained the adsorption data and mechanism. The maximum adsorption capacities, 9.709, 13.889, and 18.868g/g for RS, RCS and ACS respective obtained from the Langmuir isotherm model at 25^oC. Verifiable with increased filtration rates, acid activation and calcination improved the clay porosity and the total surface area; RS-22.04, RCS-30.36 m²g^-1 and ACS-40.92m²g^-1. Sample PZCs were less than solution pH indicating cation affinity and enhanced dye adsorption. Dye uptake varied with temperature and adsorption equilibrates around 80min. Langmuir model (ΔG˚<-5KJ/mol) and thermodynamics (ΔG˚>-18kJ/mol and ΔH) revealed a spontaneous and exothermic physisorption of MB dye onto the raw and modified samples. ΔS^* suggested an associative adsorption mechanism and ΔS^o proposed an induced randomness and changes at the solute/solvent interface.