| Water is one of the most important and basic natural resources. It is not only a fundament of human survival, but also is a key of social and economic sustainable development. China is not only facing the problem of water shortage, water pollution, and more and more cause for concern and attention. Chromium is an important industrial raw material in the production; there is no alternative in many areas of the material. Chromium emissions from extensive use and unreasonable emissions, resulting in surface water and groundwater pollution.Usually chromium-containing wastewater treatment methods are chemical precipitation, electrochemical method, ion exchange, membrane separation, biological and adsorption; various methods have advantages and disadvantages. Adsorption is widely used in the treatment of industrial wastewater emissions. Adsorption process is simple, repeated use of renewable sorbent. Finding cheap, good adsorption capacity of adsorbent for wastewater treatment has become a hot research at home and abroad. Lignite reserves is very rich in Yunnan Province, and sulphonated coal have been used as ion exchanger for softening hard water long time ago, here sulfonation lignite derived from Yunnan Xianfeng lignite was prepared and investigated. Eupatorium is a kind of weed where it grows no other plant can grow. It spreads fastly and difficulty to control in China. Activated carbon derived from Eupatorium was prepared in this research. With good thermal stability, chemical stability and electrochemical reversibility, polyaniline show good microwave absorption properties of the electromagnetic potential solution and melt processing performance, easy to obtain and simple synthesis method etc. Due to the unique phenomenon of polyaniline doping characteristics, it is now the hottest conductive polymer material. Polyaniline at home and abroad for heavy metal removal from wastewater treatment was less reported, here the sulfuric acid doped polyaniline was prepared by rapid mixing method.In this research, hexavalent chromium ion in wastewater was selected as the research object, sulfonated lignite, polyaniline doped with sulfuric acid and activated carbon derived from Eupatorium were used as the sorbent to remove hexavalent chromium ions in water and its adsorption mechanism were studied. The surface area and surface morphology of sulfuric acid doped polyaniline fibers and activated carbon derived from Eupatorium adsorbent were measured and analyzed. The results show that the surface area of activated carbon derived from Eupatorium is1184.19m2·g-1and the preparation method is feasible. Polyaniline doped with sulfuric acid has a large surface area (203.7m2·g-1), good mechanical properties and high thermal stability.The properties of sulfuric acid doped polyaniline fibers and activated carbon derived from Eupatorium in removal of hexavalent chromium ion from wastewater were studied in batch studies, including the adsorption isotherms, adsorbent dosage, pH, adsorption time and temperature. The mechanism, thermodynamics and dynamics of the hexavalent chromium ion adsorption were also studied, the results showed that:The adsorption behavavior of Cr (VI) onto the sulfonated lignite show that the time reached adsorption equilibrium is1hour. When the pH is around2, the highest removal efficiency was obtained, maybe involving the reduction of hexavalent chromium in the low pH. Thermodynamic parameters for the adsorption system were determinated, ΔG=-4.43kJ·mol-1to-5.71kJ·mol-1,ΔH=14.16kJ·mol-1, ΔS=63.42J·K-1·mol-1. The positive values of both AH and AS suggest the adsorption process is an endothermic reaction with increasing in randomness at the solid-liquid interface. AG values obtained were negative, indicated that the adsorption of Cr (VI) ion on the sulphonated lignite was a spontaneous adsorption process. The kinetics process can be described by Elovich equation. The adsorption equilibrium data are consistent with Langmuir equation. Adsorption process can be promoted at higher temperature.The adsorption behavavior of Cr (VI) onto the polyaniline fibers doped with sulfuric acid show that adsorption time is1.5hours to reach the equilibrium. In less than3in the pH, the highest removal efficiency was obtained.4g·L-1of adsorbent is enough for the quantitative removal of Cr (VI) ions for the given experimental conditions. Thermodynamic parameters for the adsorption system is AG=-10.76kJ·mol-1to-13.13kJ·mol-1, ΔH=23.87kJ·mol-1, AS=118.20J·K-1mol-1, which shows the adsorption of Cr (VI) ion on the sulfuric acid doped polyaniline is a spontaneous, endothermic, entropy process. Pseudo second equation can describe the adsorption of Cr (VI) in sulfuric acid doped polyaniline fibers, the adsorption equilibrium data are consistent with Langmuir equation, and adsorption process can be promoted at higher temperature. The results of using intraparticle diffusion equation show that the rate of diffusion is not only the control process; there may be other types of spontaneous dynamic control process.The Cr (Ⅵ) maximum adsorption capacity of eupatorium activated carbon is36.22mg·g-1Adsorption time is40minutes to reach that equilibrium. When the pH is around2, the highest removal efficiency was obtained. Thermodynamics parameters for the adsorption system is ΔG=-0.76kJ·mol-1to-2.91kJ·mol-1, AH=15.02kJ·mol-1, ΔS=53.85J·K-1·mol-1, which shows the adsorption of the Cr (Ⅵ) ion on Eupatorium activated carbon is spontaneous, endothermic Pseudo second equation can describe the Cr (Ⅵ) adsorption on the eupatorium activated carbon in dynamic behavior. The adsorption equilibrium data are consistent with Langmuir equation. Adsorption process can be promoted at higher temperature. The results of using intraparticle diffusion equation show that the adsorption of the Cr (Ⅵ) ion on Eupatorium activated carbon is controled by diffusion of particles in the early, and late is controled by diffusion of particles and film diffusion. |
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