Biosorption potential of Gliricidia sepium leaf powder to sequester hexavalent chromium from synthetic aqueous solution

Abstract

Biosorption potential of Gliricidia sepium leaf powder (GSL) was investigated for elimination of hexavalent chromium (Cr(VI)) from synthetic waste-water. Behavioral effects on sorption of Cr(VI) over the biosorbent surface due to variation in pH, biosorbent-sorbate contact time, biosorbent dosage, initial chromium concentration, batch incubation temperature and agitation speed were analyzed using batch experiments. Characterization of the biosorbent includes point of zero charge evaluation, C-H-N-S analysis, Mercury intrusion porosimetry study, Scanning Electron Microscopy (SEM), Energy-dispersive X-ray (EDX) elemental analysis and Fourier Transform Infrared (FT-IR) analysis. The optimum parameters for maximal elimination (99.90%) of Cr(VI) with residual concentration of 0.48 mg/L were found at pH 2.0, contact time of 120 min, 0.3 g of biosorbent dosage, agitation speed of 100 rpm and 50 mg/L of Cr(VI) as the initial concentration. Freundlich isotherm model gave the best fit with the equilibrium data with adsorption capacity of 35.71 mg/g at pH 2 and 50 mg/L of Cr(VI)initial concentration. Pseudo-second order model best described the adsorption kinetics. Thermodynamic parameters validated the biosorption process as feasible, exothermic and stable. Desorption-regeneration experiments were performed with 0.5 N NaOH showed reasonable performances at equilibrium time. The data depicted the reusability of GSL as a promising, eco-friendly and economic biosorbent for Cr(VI) sequestration.