| The pollution of toxic and hazardous compounds in water is the focus and difficult point in treatment all over the world. Based on the comprehesive summary of the national and international researching results in related fields, this paper made a thorough study about the way of strengthening the removal of typical toxic pollutants in water such as phenol,aniline and hexavalent chromium,and regenerating or modifying activated carbon by the process of microwave irradiation combined with activated carbon.The paper also made a deep discussion about the influencing factors and the functional mechanism of the above ways.Single factor and orthogonal tests showed that the process of microwave irradiation directly combined with activated carbon can significantly improve the phenol removal efficiency in a very short period of time。The phenol removal efficiency raised with the increasing in microwave irradiation time, microwave power and the amount of activated carbon, and it turned to its best when the PH in the solution isn’t greater than8.2. Compared with the traditional adsorption of activated carbon at the same action time, the phenol removal efficiency improved by16.6%～29.5%when5～10g of activated carbon was added into100ml water sample with the concentration of1000mg phenol/L at300W～700W microwave irradiation for5min～30min.It had been studied about the quantitative relations between the concentration of phenol and CODcr,and the qualitative analysis of phenol wastewater samples irradiated by microwave or not using full scan of ultraviolet spectrootometer and chromatogray-mass spectrometer. The results showed that the main functional mechanism of strengthening removal of enol in the process of activated carbon-microwave irradiation is accelerating adsorption because of the heating caused by microwave,and that there is not any catalytic oxidation and mineralization for phenol in this treatment. The scanning electron microscope(SEM) and the BET surface area for activated carbon had been analyzed; and the results showed that microwave irradiation let the surface of activated carbon rough and formed a clear crack, the average pore size decreased, the surface area and total pore volume increased, which was another reason of improving removal efficiency of phenol.Single factor and orthogonal tests under N2atmosere or not had been investigated.The results showed that the main factors affecting the regenerate effect of activated carbon irradiated by microwave were first the time of microwave regeneration,then microwave power,and last the amount of activated carbon.The flow of nitrogen and the moisture rate of activated carbon had little impact on the regenerate effect. Compared the effect of microwave regeneration of saturated wet activated carbon directly with that of wet activated carbon being dried by the conventional heatibg before microwave regeneration,the former is much better,and it is the recommended method for regeneration of activated carbon in this paper.It had been done that comparing the correlativity among the microwave energy consumption rate,the removal rate of phenol,the regeneration rate of activated carbon and the value of the microwave efficiency indicator Ez in the processes of microwave irradiation combined with activated carbon or two microwave regeneration activated carbon methods. The results showed that the higher the microwave energy consumption rate,the higher the removal rate of phenol or the regeneration rate of activated carbon,but the value of Ez decreasing gredually.However, at the same microwave energy consumption rate,the higher the microwave power,the higher the removal rate of phenol,the regeneration rate of activated carbon and the value of the microwave efficiency indicator Ez.So it could be determined that, the better conditions of microwave regeneration of activated carbon under nitrogen atmosere were that:10g activated carbon was irradiated by microwave at700W with the nitrogen flow of251/h for15min, and its regeneration rate would reach102.8%, the value of Ez,0.24mg/(g.kJ), and the regeneration energy consumption,45kJ/gGAC.The better conditions of microwave regeneration of activated carbon without any gas was that:10g activated carbon was irradiated by microwave at700W for5min, and the regeneration rate would reach73.9%, the value of Ez,0.31mg/(g.kJ), and the regeneration energy consumption,21kJ/gGAC. However, the regeneration rate of activated carbon and the value of microwave efficiency indicator of the former were both higher than the latter under the same condition,so the former is the better method for regeneration of activated carbon. On the other hand,the value of microwave efficiency indicator in the process of microwave regeneration activated carbon is higher than that of microwave irradiation combined with activated carbon on the whole,so it was proved that the former process was a more economical and effective way than the latter.The study also showed that a good regeneration effect could still be gotten after the activated carbon was regenerated repeatly for multiple times.Under the nitrogen flow of1001/h,the regeneration rate could stay stable at above90%when lOg activated carbon were irradiated by microwave at700W for30min after7times of repeated regenerations, and without any gas,the regeneration rate could also stay stable at70%or so when lOg activated carbon were irradiated by microwave at500W for35min after5times repeated regenerations.Conditions for the preparation of nitric acid-microwave modified activated carbon GACH-M are:5g of original carbon,0.78mol/1of nitric acid concentration,600W of microwave power, microwave irradiation for5min, and501/h of nitrogen flow. The removal efficiency of aniline for GACH-M adsorption was about90%under the condition of appropriate PH of5-12, which was14.1%higher than that of original carbon; and the Cr (VI) removal efficiency could reach to94.3%, which was44%higher than that of original carbon.Conditions for the preparation of microwave modified activated carbon under nitrogen atmosere or no carrier gas are:9g of original carbon,600W of microwave power, microwave irradiation for7min, and501/h of nitrogen flow if nitrogen gas is needed.The removal effects of organisms such as aniline for the above two kinds of microwave modified activated carbon were both increased by about20%compared with original carbon, but the removal rate of Cr (VI) was not high.The mechanism of microwave regeneration activated carbon loaded by phenol is that:first,phenol was warmed up to be desorbed or distilled from the activated carbon with the increasing temperature of the reaction system, then,it would start complex pyrolysis and condensation reactions under the conditions of high temperature in the microwave oven.A large part of phenol was decomposed to low boiling point substances such as C,CO, H2,etc., and a small part of it was split into other organisms. The higher the microwave regenerative power,the more thoroughly the high-temperatured pyrolysis reaction for organic adsorbate,and the fewer kinds of the organic matter in eshausted gas. When irradiated by low microwave power, there were various of pyrolysis products in the eshausted gas.But under nitrogen atmosere,the temperature of reaction system would reduce,and phenol was not completely decomposed, so there were a variety of organic compounds in the eshausted gas.Heated by microwave or passing through by reducing nitrogen,the acidity oxygen-containing groups on the surface of activated carbon decreased because of decomposition, the basic groups,zero charge,non-polarity and hydroilicity increased, which is a good way of modifying activated carbon to strengthen the removal of weak polar and hydroobic organisms.However, it doesn’t benefit for the modified activated carbon to adsorb polar metal ions. The basic groups and acidic groups on the surface of nitric acid-microwave modified activated carbon were both lower than that of original carbon,and the zero charge increased.The surface chemical properties of modified activated carbon is advantageous to the removal of both hydroobic substances and polar cations,which is the better method for activated carbon to be modified. |
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