| Solidago canadensis (SC) is an invasive plant which reproduces prolifically and spreads rapidly,it comes to be a serious threat to agricultural production, afforestation and ecological environment of our country, especially in the Yangtze River Delta region. The major components of SC are cellulose and lignin, which are a good potential precursor for activated carbon (AC). This will not only provide a cheap raw material for preparation of AC, but also help to deal with the solid waste challenge in China. Considering the electric heating slowly at activation period, in this paper, the ACs made from SC utilizing microwave activation method and electric heating method, respectively, and KOH as activating agent. And then the differences of adsorption properties between the two ACs were investigated. The environmental impacts of energy consumption and carbon emissions for both activation methods were evaluated by life cycle assessment.In the process of preparation of activated carbons, the carbonization temperature of the raw material was determined for 400℃through thermogravimetric analysis, and carbonization time was selected 90 min. In the activate stage, microwave heating and electrical heating were applied, and the optimum conditions of the two kinds heating mode were determined, respectively. Microwave heating results indicated that the optimum conditions were the ratio of KOH/C 2 g/g, microwave radiation time 6 min and microwave power 700 W. The adsorption amount of methylene blue and iodine, the activation yield and the surface area of AC prepared from optimum conditions by microwave heating method were 302.4 mg/g,1470.3 mg/g,53.8% and 1888 m2/g, respectively. Electrical heating results indicated that the optimum conditions were the ratio of KOH/C 3 g/g, activation time 90 min and activation temperature 800℃. The adsorption amount of methylene blue and iodine, the activation yield and the surface area of AC prepared from optimum conditions by electrical heating method were 436.5 mg/g,2153.6 mg/g,46.9% and 2215 m2/g, respectively.The ACs have been characterized by means of low temperature N2 adsorption-desorption, specific surface area, pore volume and pore size distribution were calculated through BET method, micropore distribution and full-bore distribution were analysed by HK method and DFT method, respectively. The surface physical and chemical properties of the ACs have been characterized by means of SEM, XRD, and FTIR spectra.Activated carbon MWAC which was prepared by microwave method and GYAC, a commercially available AC, were used as raw material to adsorb cadmium ion in aqueous solution. The effects of AC dosing quantity, solution initial concentration, solution initial pH and adsorption time on the carbon adsorption quantity were studied. The experimental data were analyzed with Langmuir and Freundlich adsorption isothermal equations, which showed that Langmuir isotherm can better describe adsorption equilibrium of cadmium ion on AC. The experimental data were also analyzed by pseudo-first order and pseudo-second order dynamic adsorption model, which indicated that pseudo-second order dynamic model can better fit adsorption curve.The AC regeneration with microwave regeneration method was studied. The result showed that microwave power, microwave irradiation time and acidity had large affection on AC regeneration. The optimum process condition is microwave power is 700W, microwave irradiation time 5min and acidity pH 2, the adsorption amount of regenerated AC relatively to initial activated carbon was about 97%. The life cycle assessment results of the process of two activation methods show that the microwave method is superior to the electric heating in environmental impacts, the reason is that the electric heating method consumed more power and needed more active agent in the activation phase.In summary, this paper proposed a new way of using Solidago canadensis. Compared to electrical heating method, microwave method can increase efficiency, save energy and reduce environmental pollution. The activated carbons have many millipores, with larger adsorption capacity. Using the ACs to treat heavy metal wastewater can recycle precious metals and reduce the harm of heavy metals in the environment and the human body.
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