Synergistic action of adsorption and reductive properties of ash derived from distilled Mentha piperita plant waste in removal of Cr(VI) from aqueous solution.

Adsorption behavior of Mentha Plant Ash (MPA) in removal of Cr(VI) from aqueous solution was analyzed as a function of different pH (3.0-8.0), different concentration of Cr(VI) (10-50 mg L-1), contact time (0-90 min) and doses of adsorbent (0.1-0.5 g/100 mL). Adsorption of Cr(VI) onto MPA was found to be dependent on pH condition of the solution and showed maximum removal of Cr(VI) at pH 3.0. The study of adsorption kinetics on Cr(VI) removal by MPA showed that pseudo-second order kinetic model was more suitable to describe the Cr(VI) removal by adsorption onto MPA. Results on Cyclic Voltammetry study of MPA treated with Cr(VI) solution revealed the reduction of Cr(VI) to Cr(III) and Cr(II) by MPA particles through multi-step electron transfer reactions. A combined effect of adsorption and reduction properties of MPA was particularly responsible for removal and transformation of Cr(VI). These attributes of MPA were contributed by many active Cr(VI) binding and electron donating ligands present on the MPA surface as evident from FTIR and XPS analysis of MPA.