Isotherm modeling, kinetic study and optimization of batch parameters for effective removal of Acid Blue 45 using tannery waste

Abstract

The present study describes the potential of Chrome Shavings (CS), a tannery waste, for the removal of AB 45 dye. A Central Composite Design was employed for framing the experimental design matrix. To facilitate the optimization of various batch parameters (pH, adsorbent dosage and initial dye concentration), Response Surface Methodology (RSM) was applied. The numerical optimization was performed in two different ways by setting the lower and upper limits within the range of −α and +α. From an industrial perspective the second numerical optimization was considered to be best, which predicted 92.93% as highest removal efficiency when adsorbent dosage, pH and initial dye concentration were found to be 2.64g/L, 0.98 and 234.09mg/L respectively. This result was validated by performing a confirmatory test which showed a 1% deviation from the predicted model. The constants of different isotherms, kinetics and thermodynamics were studied. The maximum adsorption capacity of CS obtained from Langmuir isotherm was found to be 83.33 (303K), 90.90 (313K) and 100mg/g (323K). The activation energy was calculated as 845.15 (303K), 912.87 (313K) and 1118.034kJ/mol (323K) using D–R isotherm. The kinetics of adsorption followed pseudo-second-order reaction and the values of rate constant were calculated as 0.0013(303K), 0.0016(313K) and 0.0021mg/g/min (323K). The result of Weber–Morris model revealed that this adsorption process involved complex rate controlling steps. From the Boyd's model, the major rate controlling step was observed to be film diffusion. The thermodynamics study revealed that the adsorption process was spontaneous and endothermic in nature. The thermodynamics parameters such as Gibb's free energy (ΔG°), change in enthalpy (ΔH°) and change in entropy (ΔS°) at normal temperature were found to be −6.31kJ/mol, 11.98kJ/mol and 0.06kJ/mol/K respectively. The basic surface structural changes before and after adsorption were studied using SEM and FT-IR analysis. Infrared studies indicated the influence of amino, hydroxyl and carboxyl groups in the adsorption of AB 45 dye. This study depicted that CS can be used as an effective and economically viable adsorbent for the removal of AB 45 dye.