| Activated carbon is considered as “an all-round adsorbent” because of its large specificsurface area and abundant pores. There are adequate raw materials for production of activatedcarbon. And it is widely used in almost all fields of national economics such as food, catalysis,medicine, energy storage and separation because of the characteristics of acid-proof alkali,insoluble in water and organic solvents, easy regeneration and no pollution. With the rapiddevelopment of economy and the resulting environmental problems have become a hot topic,activated carbon has played an increasingly important role in the control of wastewatercontaining toxic heavy metal. As a kind of typical heavy metal pollutants with high toxicity,mercury has attracted much attention."Twelfth Five-Year" environmental protection plan isfocused on the control of heavy metal mercury in waste water. Nowadays our country is in thestage of rapid development of industrialization and urbanization. Wastewater containingmercury discharged by chlor-alkali, plastics, smelting and battery industries caused not onlydrinking-water contamination. Moreover, mercury in wastewater could transfer to air and soilcausing pollution of air and agricultural products by evaporation, sedimentation and other ways.It could further move to human and animal bodies by food chain. To control the emission ofmercury in waste water effectively is a current urgent task. The main research contents andstructure of this paper are concluded as follows:1.Influence of pore structure in bamboo activated carbon to aqueous Hg2+adsorptionperformanceBamboo activated carbon, bought from FuXing carbon technology company (Jianou cityof Fujian Province), was used as raw material. The influence of pore structure in bambooactivated carbon to its Hg2+adsorption performance was investigated. The results showed that:The pore structure of activated carbon was an important factor that affected the adsorptionbehavior of aqueous Hg2+. Meanwhile, it was found that aqueous Hg2+adsorption properties ofactivated carbon had a positive correlation to its specific surface area and micropore volume. The aqueous Hg2+adsorption properties of activated carbon were enhanced with the increase ofits specific surface area and micropore volume. Additionally, the adsorption behavior wasaffected by the pore size distribution as well. Micropores and little mesopores in activatedcarbon were the main adsorption sites for Hg2+. The removal efficiency of activated carbonwith an average pore diameter of2nm could reach above78%.2.Single-factor test and adsorption kinetics of aqueous Hg2+with bamboo activated carbonActivated carbon adsorption method was used to remove the aqueous Hg2+. The influenceof pH value of solution, initial concentration of Hg2+, dosage of activated carbon andadsorption temperature on adsorption properties of bamboo activated carbon were studied.Theresults showed that:(1) The adsorption process of aqueous Hg2+using bamboo activatedcarbon was a coexisting physical process of adsorption and desorption. It was an exothermicreaction, and low temperature was more favorable to adsorption. Comparing with that of80℃,the removal efficiency of Hg2+under20℃was32%higher, and adsorption capacity wasimproved by50%.(2) pH value of solution is an important index that affected removalefficiency of aqueous Hg2+. The acidic environment significantly improved the removalefficiency of Hg2+, and bamboo activated carbon displayed the best adsorption properties whenpH=4.(3) Hg2+adsorption kinetics of bamboo activated carbon indicated that Lagergrenpseudo-second-order kinetics equation was entirely fitting for the adsorption process. Thewhole process consisted of two parts: First, Hg2+in solution diffused to the activated surfaceand was adsorbed on the active sites of activated carbon surface. This process completed invery short time. Second, Hg2+entered the mesopores and micropores of activated carbonthrough macropores, and then reacted with the internal adsorption active sites. The secondprocess was carried out very slow.3.Removal of aqueous Hg2+with modified bamboo activated carbonKBr, KI and S were used for the modification of bamboo activated carbon to improve itsadsorption properties. Inductively coupling plasma emission spectrograph was used todetermine the concentration of Hg2+in the filtrate. Adsorption properties of activated carbonwere characterized by removal efficiency and adsorption capacity of Hg2+. The adsorption mechanism was also investigated. The results showed that: the specific surface area of themodified activated carbon decreased, while the removal efficiency and adsorption capacity ofHg2+increased. It could be inferred that chemical adsorption played a major role in theadsorption process. Compared with the unmodified bamboo activated carbon, the removalefficiency and adsorption capacity of activated carbon modified with KBr, KI and S increasedin different degrees. And S-KBr-AC performed the best, whose removal efficiency was as highas96.6%, the adsorption capacity was2.898mg/g, about1.31times as high as the unmodifiedactivated carbon. Bamboo activated carbon materials with high adsorption properties ofaqueous Hg2+were obtained through the modification. The combination of physical andchemical adsorption of Hg2+was enhanced after modification. The research also had importantreference value for the removal of wastewater containing Cr, Cd, Pb, As and other heavy metalions. |
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