Equilibrium, Thermodynamic and Kinetic Studies on Adsorption of a Basic Dye by Citrullus Lanatus Rind

Abstract

An effective biosorbent was developed from Citrullus Lanatus Rind and its various biosorption characteristics were studied for removing a basic dye (Crystal Violet) from its aqueous solution. A series of experiments were conducted in a batch system to assess the effects of the system variables such as contact time, biosorbent dosage, pH, initial dye concentration, temperature, particle size and agitation speed. The biosorbent studied exhibits high efficiency for crystal violet adsorption and the equilibrium states could be achieved in 180 min for the different initial concentrations. The equilibrium adsorption data were analyzed by the Langmuir, Freundlich, Tempkin and Harkins-Jura isotherm models. The equilibrium data indicates the following order to fit the isotherms: Freundlich > Tempkin > Harkins-Jura isotherm > Langmuir. The maximum dye adsorption capacity was found to be 11.99 mg/g at 50°C. The biosorption kinetics was found to follow pseudo-second-order rate kinetic model, with good correlation (R = 0.99) and the intra particle diffusion as one 2 of the rate determining steps. Different thermodynamic parameters, like Gibb's free energy (Δ G), enthalpy (Δ H) and entropy (Δ S) of the adsorption process have also been evaluated. The thermodynamic parameters of crystal violet biosorption indicated, the process was spontaneous and endothermic. The results indicated that the biosorbent studied was found to be a promising alternative for the adsorption of crystal violet from aqueous solution.