| Heavy metal wastewater is one kind of the industrial wastewater which is the most serious pollution to environment and hazard to human health. So far, active carbon adsorption method is often adopted in a variety of heavy metal wastewater treatment. In this study, the modified granular activated carbon(GAC) was prepared by iron chloride using immersion-heating technique and then applied to increase the adsorption capacity of heavy metal such as Cr(â…¥) and Pb(â…¡).The characterization methods of physicochemical properties on activated carbon(GAC) and iron chloride modified activated carbon(Fe-GAC) such as BET(specific surface area test), SEM(scanning electron microscope), XRD(X-ray diffraction), FT-IR(Fourier transform infrared spectroscope analysis), Bohem functional group titration etc. The result reveals that the specific surface area and total volume of Fe-GAC were decreased slightly while the average pore size increased. The oxygen acidic functional groups increased by 15.1%, thus enhanced the surface polarity and help to improve the heavy metal adsorption capacity,and a small amount of ferric oxide were observed attached on the hole wall of GAC. Generally, the adsorption performance were determined by the surface physicochemical properties. In this study, we consider the change of chemical properties was the major factor for the improvement of adsorption capacity.After inspecting the influences adsorption factors such as dosage of adsorbents, adsorption time, p H value, initial concentration and temperature respectively, we found that when the initial concentration of Cr(â…¥) was 10mg/L and the optimal adsorbent dosage of Fe-GAC was 4g/L, the removal rate reached to 98.23% and the equilibrium time was 300 min, with comparison to 78.32% removed by GAC. Similarly, with the optimal dosage of Fe-GAC was 2g/L, the removal rate of Pb(â…¡) reached to 82.89% compared to 69.45% removed by GAC, and the equilibrium time was 60 min compared to 180 min of GAC.As concerned with the p H value, range from 4 to 10, an elevation would be beneficial to adsorb Pb(â…¡) while not conducive to adsorb Cr(â…¥). With the dosage of adsorbent were fixed, the removal rate of Cr(â…¥) an Pb(â…¡) decreased with the increase of initial metal concentration. With the temperature increase, the removal rate of Cr(â…¥) an Pb(â…¡) increased slightly, which indicated that the absorption reactions were endothermic reactions.In addition, Fe-GAC was also used for real electroplating wastewater treatment under the optimal operation conditions. The water quality can reach the Cr(â…¥) emission requirement(0.2mg/L) in the table two of electroplating industry pollutant discharge standard(GB21900-2008).According to the adsorption results of Cr(â…¥) an Pb(â…¡), the mechanism and laws were studied from two aspects of thermodynamics and kinetics. Both two adsorbents(GAC and Fe-GAC) are conformed to Langmuir adsorption isotherm equation, and the correlation coefficients R2 were above 0.99. Both the adsorption data are well conformed to the Lagergren second-level rate equation with the correlation coefficients R2 more than 0.99. |
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