The kinetics and thermodynamics of the removal of methyl orange from water, by using kaolinite clay from Lobatse, was investigated spectrophotometrically using the batch technique. The adsorption rate and the capacity increased with increasing initial MO concentration, with decreasing solution pH and with decreasing temperature indicating a physisorption process. The adsorption kinetics data fitted the pseudo second order model best. However, the possibility of a three body collision mechanism at the rate determining step was discounted on grounds of very low probability. Instead two simultaneous two body collisions mechanism at the rate determining step was preferred as it has a higher probability. The two simultaneous body collisions were identified as the adsorption of the dye on the external, and on the internal surfaces of Lobatse clay. The external surface is thought to be the virgin unhidden surface while the internal surface is either in pores or in the narrow gaps between adsorbed molecules on the pre-adsorbed surface. Results from the thermodynamic study fitted the Freundlich model best indicating heterogeneity of the surface of the clay sample.

Keywords: Adsorption, Methyl orange, Lobatse clay, Kinetics, Thermodynamics

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