| Adsorption has attracted considerable attention due to the following advantages such as easy operation, high removal efficiency, not produing harmful byproducts and recycling use. According to the classification made by United Nations Environmental Program agency (UNEPA), activated alumina is one of the most available adsorbents for removing arsenic from contaminated water. Nevertheless, traditional commercial activated alumina (TCAA) generally suffers from the drawbacks of low adsorption capacity, slow adsorption rate and narrow working pH region. So, it is necessary to further study alumina for arsenic(V) removal.In this dissertation, the behaviors, characteristics together with adsorption mechanism of mesoporous alumina (MA), rare-earth and transition metal modified MA for removing arsenic(V) were investigated in detail, and the corresponding results are summarized and listed as follows:1. Mesoporous alumina (MA) has been synthesized by using nonionic triblock copolymer EO20PO70EO20(Pluronic P123) under room temperature (RT). Compared with conventional method, the advantages of our synthesis route are listed as follows:(i) nonionic surfactants with respect to cation and anion templates have attracted much attention owing to low-cost, nontoxic as well as biodegradable,(ii) MA was synthesized within water media, which avoid the extensive use of organic solvents of the conventional synthesis methods,(iii) mesostructures of MA were formed under AT, which will be favor of energy-saving due to the avoiding high-temperature crystallization (≥100℃),(iv) the cost of MA synthesis was significantly reduced by replacing the expensive aluminum sec-butoxide with aluminum tri-isopropoxide.2. The effects of synthesis conditions including aluminium source and calcinated temperature on the performances of mesoporous alumina for As(V) removal were measured. It was found that MA-R-400synthesized by aluminium isopropoxide and calcinated at400℃exhibits the best behaviors for As(V) adsorption, and the correspondingly worked pH region for MA-R-400(3.0-6.5) was wider than commercial active alumina (5.5-6.0). It was also noted that the saturated adsorption capacity at pH=6.6±0.1was36.6mg/g, which was far higher than that of traditional commercial activated alumina.3. Response surface methodology was employed to optimize important adsorption parameters and to investigate the interactive effects of these variables on arsenic adsorption capacity of MA-R-400. It was noticeable that pH and initial concentration play a key role in determining the adsorption capacity of MA-R-400while the influence of adsorption time and temperature could be ignored. The optimal parameters of adsorption process was listed as below:time720min, adsorption temperature60℃, initial pH3.90, initial As(V) concentration130mg/L, and the maximum adsorption capacity was about39.06mg/g. In addition, the As(V) adsorption mechanisms over MA-R-400under various pH were investigated in detail, which could be proposed as follows:1) at pH=2.0, H3ASO4and H2ASO4-were adsorbed via hydrogen bond and electrostatic interaction, respectively;2) at pH=6.6, arsenic species (H2ASO4-and HASO42-) were removed via electrostatic interaction together with ion exchange;3) at pH=10.0, HASO42-was adsorbed by MA via ion exchange together with adsorption.4. The As(V) adsorption performance of alumina modified with rare earth metals were investigated. It was found that the As(V) adsorption capacity of alumina modified with Y, Eu, Pr and Sm were improved significantly, the corresponding value was1.70times,1.44times,1.37times and1.48times to pure alumina, respectively. However, the adsorption capacity of alumina modify with Ce was reduced to0.85times. The optimum loading of Y was10wt.%, and then10%Y-MA was the optimum adsorbent. The worked pH region for10%Y-MA was2.5-7.5, which was higher than mesoporous alumina. Besides, As(V) adsorption mechanisms over10%Y-MA under various pH were investigated in detail, which could be proposed as follows:1) at pH=2.0, H2ASO4-was adsorbed on alkaline center of adsorbent by electrostatic interaction between counter ion H+,2) at pH=6.6, H2ASO4-and HASO42-were adsorbed to alkaline center by counter ion H+,3) at pH=9.0, H2ASO4-and HASO42-were adsorbed on weakly acidic centers and alkaline center of adsorbent by electrostatic interaction.5. The As(V) adsorption performance of alumina modified with transition metals were investigated. It was shown that the adsorption capacity of alumina modified with Fe, Cu, Co, Zn and Ni were improved significantly, the corresponding value was2.63times,2.04times,1.77times,1.58times and1.30times to pure alumina, respectively. The adsorption performance of alumina modified with ferric sulfate was higher than alumina modify with ferric chloride and ferric nitrate, and the optimum loading of Fe was10wt.%. The As(V) removal by10%FeS-MA was higher than mesoporous alumina and modified with rare earth metals when the pH in the region of2-11. Additionally, As(V) adsorption mechanisms over10%FeS-MA under various pH were investigated in detail, which could be proposed as follows:1) at pH=2.0, H2AsO4-was adsorbed on10%FeS-MA by electrostatic interaction,2) at pH=6.6and9.0, H2AsO4-å'ŒHAsO42-were adsorbed on positively charged of10%FeS-MA by electrostatic interaction.6. Some common features of As(V) adsorption on pure mesoporous alumina, alumina modified with rare earth and conventional transition metals were obtained, just as follows:1) the thermodynamic parameters illustrated that As(V) adsorption was a spontaneous and endothermic process,2) the kinetics data were well fitted to pseudo-second-order, which implies that "surface reaction" might be the rate limiting step,3) the influence of coexisting anions on As(V) removal demonstrated that the removal was slightly affected by the presence of NO3-and SO42-, while the presence of PO43-and F-caused a sharp fall in removal effectiveness.7. Specific surface area of mesoporous aluminum base materials dose not greatly influence the As(V) adsorption capacity. However, the amount of mesoporous and hydroxyl groups play an important role in As(V) adsorption capacity of mesoporous pure alumina, and the type and amount of active ingredient play a key role in As(V) adsorption capacity of composite material. |
PDF Full Text Request