Sunflower stem: a novel and economical scavenger for Hg(II) ions from aqueous solutions and its kinetic and thermodynamic investigation

Abstract

Summary The sorption of > 93% of Hg(II) ions is achieved onto sunflower stem (50 mg/4.5 cm3) from deionized water (D.W.) in 10 minutes equilibration time between two phases. The kinetics of sorption follows Reichenberg, Lagergren and Morris-Weber equations. The first order rate constant of sorption computed from Lagergren equation is 0.28 ± 0.01 min-1. The sorption data obey Dubinin–Radushkevich (D–R) and Freundlich isotherms. The Freundlich sorption capacity K F = 13 ± 6 mmol g-1, 1/n = 0.68 ± 0.03 and D–R saturation capacity C m = (2.9 ± 0.4)×102 μmol g-1, β = -0.0047 ± 0.0002 mol2 kJ-2 and mean free energy = 10.3 ± 0.2 kJ mol-1. The variation of sorption with temperature (293–318 K) gives ΔH = - 32 ± 2 kJ mol-1, ΔS = 123 ± 6 J mol-1 K-1, ΔG 298K = - 4.30 ± 0.05 kJ mol-1. Ascorbate, Sr(II) and Y(III) enhance the sorption whereas disufite, iodide, Cd(II), bisulfite and thiocyanate suppress the sorption. Selectivity studies indicate that Hg(II) ions can be separated from I(I) and Cs(I) using sunflower stem column. The sorbent may be used as a scavenger for the preconcentration of Hg(II) ions from its very dilute solutions or treatment of industrial and municipal effluents containing Hg(II) ions. A possible mechanism of biosorption of Hg(II) ions onto the sunflower stem is suggested.