铝基介孔吸附材料的合成与As（Ⅴ）吸附性能研究

【作者】 韩彩芸；

【导师】 罗永明；

【作者基本信息】 昆明理工大学 ， 环境工程， 2013， 博士

【摘要】 吸附法具有操作简单、去除效率高、不产生或很少产生二次污染且吸附剂可循环使用等优点,因而受到人们关注。氧化铝被联合国环境规划署(UNEPA)认定为高效去除砷污染的吸附剂之一。但传统氧化铝对砷的吸附存在容小、吸附速率慢且pH范围窄等不足。本论文系统研究了介孔氧化铝、稀土和过渡金属改性的介孔氧化铝对As(Ⅴ)的吸附行为、特征和机理。本研究所取得的结论(成果)归纳如下：1.用非离子表面活性剂为模板在室温下合成了介孔氧化铝。与传统方法相比较,该合成方法具有如下特点：①非离子表面活性剂成本低、毒性小且易生物降解；②以水为合成介质,避免了传统方法中有机溶剂的大量使用；③室温合成,避免了高温晶化(≥100℃),有利于降低能耗；④以异丙醇铝替代传统方法中的仲丁醇铝,大大降低了合成成本。2.研究了制备条件(铝源和焙烧温度)对介孔氧化铝吸附As(Ⅴ)性能的影响,得出最佳的铝源为异丙醇铝,最佳焙烧温度是400℃；最优吸附剂MA-R-400吸附As(V)的最优pH范围(3.0-6.5)大于商业氧化铝(5.5-6.0),其在近中性(pH=6.6±0.1)条件下,饱和吸附容量为36.6mg/g(大于已有报道的传统氧化铝—15.5mg/g)；3.利用响应曲面优化法对影响介孔氧化铝MA-R-400吸附As(V)性能的因素进行优化研究,得出溶液pH和初始浓度是影响吸附性能的关键因素,吸附温度和时间对其吸附性能的影响较小,该吸附剂吸附As(V)的最优吸附条件为吸附时间720min,温度60℃,pH3.90,初始As(V)浓度130mg/L,此时吸附容量是39.06mg/g。此外,对不同pH条件下的吸附机理进行详细的研究,得出pH=2.0(酸性)时,介孔纯氧化铝通过氢键和静电作用两种方式分别吸附溶液中的H3As04和H2AsO4-; pH=6.6(近中性)时H2As04和HAsO42可与纯氧化铝的质子化羟基官能团通过静电作用而吸附；pH=10.0(碱性)时,H2As04和HAsO42与吸附在纯氧化铝酸性位点上的OH-通过离子交换反应来进行吸附。4.首次系统地研究了稀土金属(Ce、Y、Eu、Pr和Sm)改性介孔氧化铝对As(V)吸附性能的影响,得出稀土金属Y、Sm、Eu和Pr改性的介孔氧化铝对As(V)的吸附容量显著增加,分别为改性前的1.70倍、1.48倍、1.44倍和1.37倍,但Ce改性的介孔氧化铝对As(Ⅴ)的吸附容量略有下降(0.85倍)；Y的最佳负载量为10wt.%;吸附剂10%Y-MA吸附As(Ⅴ)的最优pH范围(2.5-7.5)大于介孔氧化铝(3.0-6.5)。此外,对不同pH条件下的吸附机理进行详细的研究,得出pH=2.0(酸性)时,H2AsO4-借助溶液中大量的抗衡离子H+吸附在10%Y-MA的碱性中心；pH=6.6(近中性)时,H2AsO4-和HAsO42-通过静电作用吸附在含有抗衡离子H+的10%Y-MA碱性中心和载体氧化铝的酸性中心；pH=9.0(碱性)时,H2AsO4-和HAsO42--在10%Y-MA上的吸附主要是通过(a)与吸附在载体一氧化铝酸性中心的OH-进行离子交换反应来吸附,(b)与氧化钇碱性中心通过抗衡离子H+来吸附。5.首次系统地研究了过渡金属(Fe、Cu、Co、Zn和Ni)改性的介孔氧化铝对As(Ⅴ)吸附性能的影响,得出改性后介孔氧化铝对As(Ⅴ)的吸附性能显著增加,过渡金属Fe、Cu、Co、Zn和Ni改性介孔氧化铝对As(Ⅴ)的吸附容量是改性前的2.63倍、2.04倍、1.77倍、1.58倍和1.30倍；硫酸铁改性介孔氧化铝吸附As(Ⅴ)的性能明显优于氯化铁和硝酸铁改性的；Fe的最佳负载量为10wt.%;10%FeS-MA吸附去除As(Ⅴ)的pH范围(2-11)明显大于介孔氧化铝和稀土改性介孔氧化铝。此外,对不同pH条件下的吸附机理进行详细的研究,得出pH=2.0(酸性)时,H2As04-通过静电作用吸附在10%FeS-MA上；pH=6.6(近中性)和pH=9.0(碱性)时,带正电荷的10%FeS-MA通过静电作用吸附溶液中的H2AsO4-和HAsO42-。6.介孔纯氧化铝、10%Y-MA和10%FeS-MA对As(Ⅴ)的吸附都属于吸热反应,升高温度有利于吸附反应的发生；它们对As(Ⅴ)的吸附动力学都符合准二级动力学方程,即“表面反应”是其吸附速率的控制步骤；共存阴离子NO3-和对SO42-它们的吸附性能几乎没有影响,但PO43-和F-的存在会使它们对As(Ⅴ)的吸附性能急剧下降。7.介孔铝基材料中吸附剂比表面积不是影响它们吸附As(Ⅴ)性能的主要因素,但介孔氧化铝的吸附性能受材料介孔数量和羟基数量的影响,改性材料吸附性能受负载活性成分的种类和量的影响。更多还原

【Abstract】 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-和HAsO42-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.更多还原