Removal of Cr(VI) from synthetic solutions using water caltrop shell as a low-cost biosorbent

Water caltrop (WC) shell was investigated as a potential biosorbent for the removal of Cr(VI) ions from aqueous solutions. FT-IR spectrum of WC exhibited different functional groups such as carboxyl-group, amino-group, and hydroxyl-groups. Biosorption capacity obtained is 98.04 mg/g at pH 2.0, initial Cr(VI) concentration 100 mg/L, 1?g/L biosorbent-dose, 100 rpm rotational speed, and 60?min equilibration time. The biosorption process follows Langmuir adsorption isotherm (R-2?=?0.989) and pseudo-second-order kinetic model (R-2?=?0.998) with separation factor found between 0.11 and 0.37. Thermodynamics parameters reveal that biosorption process is endothermic, spontaneous, and entropy-driven at lower concentrations.