Bio-Sorption Potential of V. zizanioides Grass and Roots for the Removal of Cr (VI)

Abstract

This research aims to investigate the bio-sorption potential of V. zizanioides as a bio-adsorbent for removal of Cr (VI) from aqueous solution. Batch experiments were carried out with grass and roots of V. zizanioides in order to analyze biosorptive potential. The performance parameters of the biosorbents covered contact time, adsorbent dosage, initial concentration, temperature and pH of the aqueous solution. It was observed that the solution pH significantly affects the Cr (VI) removal efficiency using raw (grass and roots of V. zizanioides ). Therefore, the grass and roots were treated by acid and base solution to get higher sorption behavior. The higher removal efficiency (98% and 92%) has been achieved using acid treated grass and roots at 1 (mg/L) of Cr (VI) concentration respectively. Biosorbent and chromium interaction was investigated by Langmuir and Freundlich isotherms for the proposed bio-adsorption process. The maximum adsorption capacity was observed (0.42 mg/g and 0.199 mg/g) using grass and roots respectively. The data best fitted the Langmuir model indicating monolayer adsorption. Kinetic aspects were examined to achieve thermodynamic equilibrium and found that the rate of adsorption has good correlation with pseudo-second-order kinetics. In addition, diffusion models demonstrate that intraparticle diffusion is the sole rate-limiting step in this particular bio-sorption. An evaluation of thermodynamic parameters, namely ΔH°, ΔS° and ΔG°, indicate that the adsorption was feasible, spontaneous and endothermic in nature. The low values of ΔH° and ΔG° correspond to physical adsorption. The results reveal that V. zizanioides can be successfully used to remove Cr (VI) from aqueous solution.