Adsorption of Cr (III) and Cr (VI) ions on muscovite mica: Experimental and molecular modeling studies

• Adsorption studies of Cr (III) and Cr (VI) on muscovite mica. • DFT simulation of pH-specific species of Cr (III) and Cr (VI) • Adsorption efficiency of Cr (III) better than Cr (VI) • Adsorption mechanism governed by Cr O and H-bond configurations. The article explores the possibility of adsorption of Cr (III) and Cr (VI) ions on muscovite mica for the first time. The adsorption behaviors of both the ions on the mineral have been compared vide experimental and molecular modeling studies. Experiments have been carried out to find out the effects of different operating parameters on the adsorption of the metal ions, while Density Functional Theory (DFT) based simulations have been conducted to understand the adsorption mechanisms of various Cr (III) and Cr (VI) species, occurring at different pH, on muscovite (0 0 1) surface. The maximum metal removal efficiencies obtained for Cr (III) and Cr (VI) are about 15.6 mg/g and 1.74 mg/g, respectively. The trend of adsorption energies calculated using DFT supports this finding. The simulation studies depict the nature of bonding of various possible Cr ions, at different pH levels, on the muscovite surface and reveal that the patterns Cr-O bonds and hydrogen bonds define the adsorption mechanism. The Partial Density of States (PDOS) calculations provide a further understanding of the involvement of different orbitals of Cr, O, H of the Cr ion and O atom of muscovite surface in the metal-mineral interaction.