Optimization study of adsorption parameters for removal of Cr(VI) using Magnolia leaf biomass by response surface methodology

The removal of chromium (Cr) using waste biomass is one of the most important issues throughout the world. In the present study, Magnolia leaf, a forest waste, is employed as novel and available adsorbent to abate Cr(VI) from simulated solution through batch study. The effects of operating variables on biosorption were analyzed using a multi-step response surface methodology (RSM). The optimum biosorption conditions were determined at the initial Cr(VI) concentration of 40.0 mg L⁻¹, pH of 2.0, contact time 45.0 min and dose of 0.5 g. At optimum conditions, the biosorption capacity of Magnolia leaf for Cr(VI) was found to be 3.96 mg g⁻¹ that reflects the removal of 98.8%. The obtained data matched with the pseudo-second-order rate (R² = 0.987) expression and fitted the Langmuir isotherm (R² = 0.999) very well. The thermodynamic parameters such as ΔH°, ΔS° and ΔG° for the Cr(VI) biosorption were calculated at six different temperatures. The surface characteristics and the existence of chromium of the biomass, before and after biosorption, were studied through scanning electron micrographs–energy-dispersive X-ray spectroscopy (SEM–EDX) and Fourier transform infrared (FTIR) analysis. The present results indicate that Magnolia leaf is a suitable low-cost bio-material to remove Cr(VI) from aqueous solutions.