| Water as an essential part in peoples’ daily life, plays an important role in the development of economy and social production. In recent years, with the development of economy, large amounts of copper smelting acidic wastewater is discharged, which not only makes the body of water heavy metals pollution more and more serious, but also cause a serious waste of heavy metals resources. Therefore, it’s important to take measures to properly handle this kind of wastewater. Currently, methods that are being used to remove heavy metal ions from copper smelting acidic wastewater include chemical precipitation, ion exchange, membrane filtration, electrochemical treatment technologies, etc. However biosorption is now recognized as an effective and economic method for heavy metal wastewater treatment because of the advantages of wide raw material sources, low cost, its high effectiveness in reducing the heavy metal ions and no secondary pollution, etc. in addition, biosorption treatment is particularly suitable to treat dilute heavy metal wastewater.Water hyacinth, which was obtained through chemical modification, was selected as a bio-adsorbent in the treatment of the aqueous solution containing Cu2+, Zn2+, Pb2+ in this paper. The effect of solution pH, amount of adsorbent, initial concentration, agitating time, and temperature on the sorption process was investigated; water hyacinth desorption property was also studied; the adsorption kinetics, thermodynamics and sorption isotherm were analyzed, and the adsorption mechanism for removal of Cu2+, Zn2+, Pb2+ with water hyacinth was discussed. The experimental results showed that the optimal pH value for adsorption of Cu2+, Zn2+, Pb2+ with water hyacinth was 4.5,5.0 and 5.0 and the optimal dosage of adsorbent was 4.5 g/L,5 g/L, and 3.5 g/L respectively, the sorption processes were quick, which can achieve adsorption equilibrium in 80min, and fit well with pseudo-second-order kinetic models, the equilibrium adsorption capacity of biomass were 15.62,9.036 and 28.64 mg/g. the influence of temperature on removal of Cu2+, Zn2+, Pb2+ by water hyacinth was not obvious. The Gibbs free energy changes for all kinds of heavy metal ions were negative, which illustrated that adsorption process could undergo spontaneously. The enthalpy changes for Cu2+ and Pb2+ were negative, which indicated that water hyacinth for Cu2+ and Pb2+ adsorption were exothermic process. But for Zn+ ion was endothermic process because the enthalpy change was more than zero. Langmuir isotherm equation could well describe the adsorption behavior of Cu2+, Zn2+, Pb2+ions on water hyacinth, and the maximal volume of the biomass to Cu2+, Zn2+, Pb2+ions, calculated from Langmuir isotherm equation, were 22.51, 14.3 and 81mg/g respectively. The average adsorption free energy was calculated to be less than 8 kJ/mol for Cu2+, Zn2+, Pb2+ ions by D-R isotherm equation, which was comparable to physical adsorption. Fourier transform infrared spectrum of carboxyl and amino groups of water hyacinth with and without metal uptake had shown a difference, which indicated that chemical adsorption also played an important role in adsorption of Cu2+, Zn2+, Pb2+ions using water hyacinth, water hyacinth possessed a stable adsorption capacity,although the adsorption rate of Cu2+, Zn2+ and Pb2+ decreased after repeated use for three times. So it was helpful to reduce the cost of adsorption, by recycling biosorbent of water hyacinth. |
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