Determination of equilibrium, kinetic and thermodynamic parameters for the adsorption of Brilliant Green dye from aqueous solutions onto eggshell powder

The removal of the Brilliant Green (BG) dye using hen eggshell powder (abundantly available and a total waste material) has been explored. Adsorption studies for the dye removal by eggshell powder has been carried out under varying experimental conditions of adsorbent dose, temperature, contact time, initial dye concentration and pH. The equilibrium data has been studied using the Langmuir isotherm equation. Mono layer adsorption capacity of hen eggshell powder for BG dye is found to be 44.7 mg/g, 34.23 mg/g and 30.23 mg/g at temperatures 303, 313 and 323 K respectively. The kinetic study on BG suggests that the adsorption follows the pseudo-second order kinetics. Adsorption follows both surface adsorption and intra-particle diffusion mechanisms. The Arrhenius energy of activation observed from the experimental data is found to be -15.88 kJ/mol which suggests that the energy barriers are absent in the adsorption process and the reaction is exothermic. The thermodynamic study on BG reveals that the reaction is spontaneous, exothermic and proceeds with decreased randomness at the solid-solution interface as the entropy change (-19.08 J/mol/K) is negative.