A comparative study of the removal of Cr(VI) from synthetic solution using natural biosorbents

Biosorbents prepared from the waste of Arachis hypogea (peanut) shells, Ziziphus mauritiana (Indian jujube/Ber) sawdust and Cassia fistula (amaltas) leaves were used for the removal of Cr(VI) from aqueous media. The prepared biosorbents were characterized by FT-IR, SEM, surface area and pore size analysis. The effects of various parameters like pH, temperature, contact time, adsorbent dose and concentration of Cr(VI) on the sorption of Cr(VI) were investigated. Kinetic studies were carried out and it was observed that equilibrium was established at 360 minutes for each biosorbent system. The applicability of Freundlich and Langmuir adsorption isotherms was investigated. The maximum adsorption capacity of each of the biosorbents in terms of monolayer coverage (qmax) was determined. The qmax for the peanut shell (P. Shell), sawdust (S. Dust) and Cassia fistula leaves (C. F. Leaves) biosorbents was 4.32, 3.66 and 4.48 mg g(-1), respectively. The adsorption kinetics data was explained by applying the two kinetic equations i.e. the Lagergren pseudo-first order equation and the pseudo-second order equation. It was found that each system followed the pseudo-second order equation, which confirmed the chemical nature of the biosorption process. Thermodynamics parameters such as Delta G, Delta H and Delta S were calculated for each biosorbent system.