Abstract
Water lettuce (WL), a common aquatic plant, was studied as a potential adsorbent for the removal of toxic malachite green (MG) in a batch adsorption system. The batch adsorption studies included the effects of pH, ionic strength, dye concentration, thermodynamics and kinetics studies, estimation of activation energy, and regeneration experiments. Elemental analysis of the adsorbent was determined by X-ray fluorescence, while the functional groups were characterised by Fourier transform infrared spectrophotometer. Experiments involving the effects of pH and ionic strength indicated that hydrophobic-hydrophobic interactions might be the dominant force of attraction for the MG-WL adsorption system. The Freundlich isotherm model best represented the adsorption systems, while the Langmuir model predicted maximum adsorption capacity (qm) of 99.0 mg g-1 at 25°C. Weber-Morris model suggested intraparticle diffusion was not rate-limiting, while the Boyd model suggested film diffusion may be the rate-limiting step. Thermodynamics studies indicated spontaneity and endothermic reaction, while the Arrhenius studies indicated a physical adsorption dominant process with the activation energy estimated to be at 12.6 kJ mol-1. Spent adsorbent was regenerated with 0.1 mol L-1 NaOH and it was effective even after five cycles.
