Study on the removal of hexavalent chromium using a new biosorbent

Peppermint leaves (PML) have been explored as an effective and cheap adsorbent for removal of toxic Cr(VI) ions from aqueous solutions using batch system. Adsorption of Cr(VI) ions onto PML was found to be pH dependent and maximum removal of Cr(VI) ions was obtained at pH 2. It was also found that after 180 min of PML contact with chromium solution at the concentration of 0.3846 mmol/L, more than 95% of Cr(VI) ions can be removed. The equilibrium data were fitted with the Langmuir and Freundlich models. The adsorption kinetic data were best fitted with the pseudo-second-order. The activation energy Ea of the adsorption process was determined as 23 kJ mol−1, which may indicate a physisorption process. The Gibbs free energy, enthalpy, and entropy of the process were also determined, and their values revealed that the process is spontaneous and endothermic accompanied with randomness at the solid/solution interface.