Adsorptive Removal of Vat Yellow 4 on Activated Mucuna pruriens (Velvet Bean) Seed Shells Carbon

Abstract

Aim: To study the removal of vat yellow 4 from wastewater on activated carbon produced from Mucuna pruriens seed shells (MPS). Methodology: The seed sample was activated using two methods and carbonized at 500°C for 2 hours to produce two different adsorbents. The physicochemical properties of the adsorbents were determined. Their structural elucidation were established using Fourier transform infrared (FTIR), X-ray Fluorescence (XRF), X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) spectral techniques. The effect of process variables such as particle size, adsorbent dose, pH, dye concentration and solution temperature on the process of adsorption were studied using batch operation. Three isotherm and four kinetic models were used to study the adsorption process. The linear regression method of analysis was used to model the experimental data. The adequacy of the models was tested using the correlation coefficient (R2). The thermodynamic parameters, changes in standard free energy (∆G0), entropy (∆S0) and enthalpy (∆H0) were also evaluated. Results: The results showed that adsorption is influenced by particle size, adsorbent dose, contact time, initial pH of solution, solution temperature and dye concentration. Maximum adsorption capacity for vat yellow 4 on the adsorbents was observed at pH of 2. The equilibrium data fitted well to the Langmiur, Freundlich and Temkin models. The Langmuir isotherm was found to have the best fit to the experimental data suggesting monolayer adsorption on a homogeneous surface. The pseudo second-order kinetic model was found to best describe the experimental data and the adsorption process was controlled by film diffusion. The adsorption process has been found to be feasible, spontaneous and endothermic in nature. The spontaneity of the process increased with increase in the solution temperature. Conclusion: This study has shown that Mucuna pruriens seed shells, an agro waste, can be used for the removal of vat yellow 4 from wastewater. The phosphoric acid treated adsorbent performed better than the sodium chloride treated adsorbent.