Bioremediation of Zn(II) by biosorption across aqueous phase on to surface of eucalyptus leaf powder has been investigated in present research work. The adsorptive potential of eucalyptus leaf powder was evaluated as function of pH, temperature, contact time, agitation rate and particle size. Maximum metal ion uptake and percentage removal capacity of eucalyptus leaf powder were 23.5 mg g À1 and 94%, respectively, at optimized pH 5, 20 AE 18C, contact time 6 h, particle size 0.5 mm and agitation rate 200 rpm. The biomass surface analysis revealed the fact that the biomass surface was heterogeneous and porous in nature. The functional groups like amine, amide, carboxyl, hydroxyl, and methyl groups, significantly important for metal ion binding were present on biomass surface in tremendous amount. Additionally, the Fourier transformation IR spectrum analysis of acid and base activated eucalyptus leaf biomass ruled out all the possibilities of the presence of surface functional groups mentioned above. The reaction rate was studied by applying two rate limiting models pseudo first and pseudo second order. Pseudo second order model was found to be more suitable (R 2 ¼ 0.998) in comparison to pseudo first order (R 2 ¼ 0.724). Adsorption equilibrium of batch stirred reaction data fitting shows the dominance of Langmuir isotherm (R 2 ¼ 0.99) against Freundlich isotherm (R 2 ¼ 0.887) model with equipartitional involvement of both film and intra particle diffusion as rate limiting steps at differential status of contact time.Keywords: Bioremediation; Intra particle diffusion; Langmuir isotherm; Pseudo second order reaction; Zn(II) ion
IntroductionThe rapid and tremendous industrial development during last decade has increased the heavy metal pollution in environment [1,2]. Heavy metals are non-biodegradable and have tendency to get accumulated inside the human body via incorporation through food chain [3][4][5][6][7]. Major industrial operations unit like metallurgy, steel production, paint and pigment industry, copper smelting unit, acid mine drainage, electroplating, and metal finishing significantly contribute to heavy metal pollution in natural water streams [8][9][10][11][12]. Various remedial technologies/unit operations viz. osmosis, electro coagulation and flocculation, reverse osmosis, solvent extraction, hydroxide precipitation, and membrane separation have been adopted to remove heavy metals across liquid phase [13,14]. In general, all these above mentioned technologies are expensive, lead to generation of secondary chemical sludge containing heavy metals, making the disposal of sludge questionable, and ineffective in removing heavy metals including Zn(II), Cd(II), Pb(II), Cu(II), and Cr(III) at low concentration levels ranging between 1 and 100 mg L À1 [10,[15][16][17][18][19]. Zinc is one of the elements of heavy metal series. Though zinc is an essential element of life but its exposure beyond permissible limit, defined by United States Environmental Protection Agency, World Health Organization, Canadian Wate...