Use Of Eucalyptus Urophylla Waste As Sorbents To Remove Lead, Nickel And Chromium Ions From Aqueous Solution

Heavy metal contamination has been attracting more and more attention of many people recently in China. Eucalyptus urophylla have been widely planted in Guangxi, China and there are massive forestal wastes which can be hardly made the best use of. Theoretically, these materials contain active groups and can be utilized to reduce heavy metals through chelation and complexation. The aim of the present research was to evaluate the adsorption capacity of modified eucalyptus urophylla bark (MEUB) and leaf (MEUL) made from Guangxi’s eucalyptus waste, for lead (Pb(Ⅱ)), nickel (Ni(Ⅱ)) and hexavalent chromium (Cr(Ⅵ)) removal to develop abundant, inexpensive and effective sorbents. Effects of operating conditions, adsorption equilibrium and kinetic experimental data of these heavy metals adsorption onto MEUB and MEUL were studied. Modern instrumental analysis was applied to seek the removal mechanism of these heavy metals. And potential of the sorbents applied for electroplating wastewater treatment was preliminarily explore. The conclusions can be drawn as follows:(1) Initial solution pH, biosorbent dosage, initial solution concentration, temperature, contact time and ionic strength were significant factors for removal of these three heavy metals from aqueous solutions. The maximum adsorption capacities for Pb(Ⅱ), Ni(Ⅱ) and Cr(Ⅵ) appear at pH5.0,4.0and2.0, respectively. The Cr(Ⅵ) adsorption capacity increased with an increase in temperature. There is a high competition in the Cu(Ⅱ)-Ni(Ⅱ) binary system. Furthermore, Cu(Ⅱ) has the ascendant position. The presence of Cu(Ⅱ) and Ni(Ⅱ) enhances the removal effciency of Cr(Ⅵ).(2) The adsorption equilibrium data of Pb(Ⅱ) and Ni(Ⅱ) on MEUB and MEUL with a low concentration were well interpreted by the Freundlich and Langmuir isotherm separately. Freundlich, Langmuir and Dubinin-Radushkevich isotherm models had a poor fitting for equilibrium data of Cr(Ⅵ). All of three heavy metals adsorption processes obeyed the pseudo-second-order kinetics. Thermodynamic parameters suggest a spontaneous, endothermic reaction and increase in randomness at the solid-liquid interface during the Cr(Ⅵ) adsorption.(3) The isoelectric point of metal-loaded sorbents increased. Fourier transform infrared (FTIR) spectra illustrate that the MEUB and MEUL contain complex functional groups. C-OH of phenol group and C=O group may be involve in Pb(Ⅱ) removal as well. Cr(Ⅵ) may react with mang groups including-OH, C=C, C-O and C=O on the surface of sorbents during adsorption and desorption.(4) The desorption effenciency of Pb(Ⅱ) using acid desorbents from MEUB and MEUL was close to100%. On the contrary, alkali desorbents were the best of all desorbents for Cr(Ⅵ)-loaded sorbents.(5) The applicability of the sorbents has been demonstrated by removing Cr(Ⅵ) and TCr from Cr-containing electroplating wastewater. Meanwhile, parts of coexist ions has been reduced.(6) Pb(Ⅱ) and Ni(Ⅱ) adsorption onto the MEUB and MEUL is physisorption process, while Cr(Ⅵ) adsorption is chemisorption process.In summary, the results confirm that the materials from eucalyptus urophylla waste are the abundant, locally available, low-cost, technically feasible and highly efficient sorbents for heavy metal-contained wastewater treatment.