Assessment of raw, acid-modified and chelated biomass for sequestration of hexavalent chromium from aqueous solution using Sterculia villosa Roxb. shells

This study reveals the efficient bio-sorption of Cr(VI) species from simulated wastewater using raw (RSV), acid-activated (PSV) and chelated-activated (PSV-C) Sterculia villosa Roxb. shells. Batch optimization experiments were carried out for determining the optimal pH, dosage of bio-sorbent, initial Cr(VI) concentration and incubation temperature. Physico-chemical alterations in the bio-sorbents prior and following bio-sorption of Cr(VI) species were characterized. Equilibrated experimental data at different temperatures was evaluated as a function of time for understanding the isotherm, kinetics and thermodynamics of the bio-sorption process. Sorption rates for all the bio-sorbents (RSV, PSV and PSV-C) alternately fitted to the Langmuir isotherm model and Langmuir maximum adsorption capacity for RSV, PSV and PSV-C were found to be 57.78, 163.51 and 188.68 mg/g, respectively. Cr(VI) sorption by these bio-sorbents followed pseudo-second–order kinetics. Thermodynamic studies suggest endothermic interaction and increased degree of randomness between the bio-sorbents and Cr(VI) species. Regeneration of the bio-sorbents following sorption–desorption revealed that it can be reused and recycled for several times for Cr(VI) removal from wastewater.