Equilibrium, kinetic and diffusion mechanism of Cr(VI) adsorption onto activated carbon derived from wood apple shell

Abstract

In the present investigation, adsorbent activated charcoal was prepared from wood apple shell by chemical activation and used for Cr(VI) removal from aqueous solutions. Powdered wood apple shell was activated by acid H₂SO₄ and heat treatment in muffle furnace at 600 °C for 2 h. The specific surface area of prepared activated carbon was found to be 1898 m² g⁻¹. Batch adsorption studies reveal that the prepared activated charcoal has a significant capacity for adsorption of Cr(VI) from aqueous solutions. The equilibrium adsorption isotherms investigated in this study include Langmuir and Freundlich at 300 K. The Cr(VI) adsorption was found to be maximum (>95.0%) at pH 1.8. Very small amount of adsorbent activated carbon (1.25 g L⁻¹) could remove >95.0% Cr(VI) from aqueous solution of initial concentration 75 mg L⁻¹. The Langmuir monolayer adsorption capacity of Cr(VI) adsorption on activated carbon was found to be 151.51 mg g⁻¹. The dimensionless separation factor (R_L) signifies a favorable adsorption of Cr(VI) on activated charcoal. Adsorption kinetic studies reveal that the adsorption of Cr(VI) onto activated carbon was pseudo-second order chemisorptions and follows film-diffusion as well as intra-particle pore-diffusion mechanism.