This study involves the kinetics and thermodynamics of adsorption for the remediation of Fast Green (FG) from aqueous solution by used black tea leaves (UBTL) as a low cost adsorbent. The effects of initial dye concentration, contact time, solution pH and processing temperature on the adsorption kinetics were investigated in batch process. Kinetic parameters and related correlation coefficients for pseudo-first order, pseudo-second order kinetic and Elovich models were calculated and discussed. The results revealed that the adsorption kinetics is in good agreement with the pseudo- second order equation. The equilibrium amount adsorbed obtained at 30oC is 114.4 mg/g which was found to increase with the increase of adsorption temperature, suggested endothermic nature of the adsorption. Thermodynamic parameters such as enthalpy change (ΔHº), free energy change (ΔGº) and entropy change (ΔSº) were calculated from the equilibrium adsorption constant, and the adsorption of FG on UBTL at pH 6.0 was found to be spontaneous, endothermic and physisorption in nature. Again, the equilibrium amount adsorbed calculated from pseudo-second order kinetic plots for different initial pH of solution and was found to decrease with decrease of solution pH from 6.0 to 2.0 indicating the electrostatic repulsion between cationic FG+ with protonated UBTL surface at low pH and a probable mechanism was proposed.
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