Equilibrium, kinetic and thermodynamic studies of Cr(VI) adsorption from aqueous solution onto manganese oxide coated sand grain (MOCSG)

Hexavalent chromium, Cr(VI), is a highly toxic metal ion endowed with mutagenic and carcinogenic properties. In the present work, manganese oxide coated sand grain (MOCSG) was prepared, characterized and used for the removal of Cr(VI) from aqueous solution. The functional groups present on the prepared material were confirmed through Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction spectroscopy (XRD), Scanning electron microscopy (SEM), and Energy dispersive X-ray spectroscopy (EDX). Optimum parameters for batch adsorption experiments were: 500 μg/L Cr(VI) concentration, 8.0 g/L MOCSG dosage, solution pH 6.0, and 60 minute contact time. Langmuir maximum adsorption capacity at 25 °C was 227.27 μg/g. The adsorption data better fitted to Freundlich isotherm model, and Dubinin-Radushkevich isotherm energy values indicated physical adsorption. The adsorption was spontaneous, and endothermic process, which followed pseudo-second order kinetics. The high Cr(VI) removal, rapid adsorption kinetics, and stability of adsorbent, indicate that MOCSG is an efficient adsorbent for the removal of Cr(VI).