【作者】 张华；

【导师】 张学洪；

【作者基本信息】 广西大学 ， 制糖工程， 2013， 博士

【摘要】 活性炭一般具有孔隙发达、比表面积大、表面官能团丰富和活性高等特点,是水处理中应用非常广泛的吸附剂。国内外开展了大量有关活性炭制备及其用于含重金属废水、印染废水等处理的研究。然而,采用煤炭和其他不可再生资源制备活性炭成本很高。为了寻找制备活性炭原料的新来源,不少学者把目光投向来源广泛、再生性强以及无二次污染的农业废弃物。柚子是我国主要水果之一,在南方许多地区大量种植。通常柚皮未被利用就直接丢弃。目前有关以柚皮为原料采用氯化锌活化法制备活性炭,并进行污水处理的研究尚未见报道。本文以柚皮为原料,采用氯化锌活化法制备柚皮基活性炭,并针对不同典型污染物进行了吸附处理研究。通过红外光谱、X射线衍射、扫描电子显微镜等分析方法和吸附动力学、热力学等理论,系统研究了柚皮基活性炭物理化学性质,以及吸附废水中氨氮、磷、碱性染料亚甲蓝、酸性染料刚果红和六价铬的机理,并讨论了pH、温度和吸附时间等因素对吸附容量的影响。主要研究结论：(1)利用农业废弃物柚子皮为活性炭原料,采用ZnCl2活化法制备柚皮基活性炭,设计正交试验确定最佳制备工艺条件：ZnCl2溶液质量分数20%,液料质量比为3.0：1,活化温度和时间分别为500℃、80min。所得柚皮基活性炭得率为35.36%,碘吸附值为851mg/g。其BET比表面积为1045m2/g,孔容积为7.471cm3/g,孔平均直径为1.430nm。红外光谱分析结果说明,柚皮基活性炭表面主要存在羟基、羧基、胺基和吡喃酮等官能团。样品的零电点为5.67。(2)利用柚皮基活性炭处理含Cr(Ⅵ)废水。研究结果表明,吸附时间12h达到吸附平衡,在pH等于1.0时,吸附效果最好。Temkin和Langmuir模型可以很好地描述Cr(vi)吸附过程；Langmuir单分子层饱和吸附量达到145.47mg/g。根据Dubinin-Radushkevich模型计算的吸附自由能为9.93、17.72和20.82kJ/mol, Cr (Ⅵ)吸附以化学吸附为主。准二级动力学模型能很好地拟合柚皮基活性炭吸附Cr(Ⅵ)的动力学实验数据。颗粒内扩散模型和Boyd模型研究表明,膜扩散系数和孔扩散系数均值分别为3.72×10-13cm2/s和5.99×10-12cm2/s,吸附过程由膜扩散和颗粒内扩散共同控制,膜扩散为主控步骤。柚皮基活性炭吸附Cr(Ⅵ)的⊿G在-0.32kJ/mol和-20.06kJ/mol之间,⊿H在39.85kJ/mol和342.93kJ/mol之间,⊿S在134.91kJ/(mol·K)和829.51kJ/(mol·K)之间,说明吸附是一个自发吸热熵增过程。吸附机理主要涉及几方面作用：活性炭表面带电基团(羟基、羧基和胺基)通过静电引力吸附Cr(Ⅵ)离子；吸附的Cr(Ⅵ)离子在强酸条件下还原为三价铬,一部分进入溶液系统,一部分与炭基质发生反应形成螯合物。(3)利用柚皮基活性炭处理含碱性染料亚甲蓝(MB)废水。吸附初期吸附速率很快,2h后吸附基本平衡。pH2.0～10.0范围吸附量无明显变化。Temkin和Langmuir模型可以很好地描述MB吸附过程,Langmuir单分子层最大饱和吸附量达到234.26mg/g。根据Dubinin-Radushkevich模型计算吸附自由能均值为18.53kJ/mol, MB吸附以化学吸附为主。准二级动力学模型能够很好地描述柚皮基活性炭吸附MB的动力学实验数据。颗粒内扩散模型和Boyd模型分析表明,膜扩散系数和孔扩散系数均值分别为2.85×10-12cm2/s和2.30×10-10cm2/s,吸附过程受膜扩散和颗粒内扩散影响,其中膜扩散为主控步骤。柚皮基活性炭吸附MB的⊿G在-19.44kJ/mol和-24.77kJ/mol之间,⊿H在64.63kJ/mol和67.50kJ/mol之间,⊿S在276.65kJ/(mol·K)和277.98kJ/(mol·K)之间,吸附是一个自发吸热过程。吸附机理包括静电相互作用、氢键作用和电子供体受体作用。(4)利用柚皮基活性炭处理含酸性染料刚果红(CR)废水。吸附2h后反应基本平衡,pH3.0～10.0范围吸附量无明显变化。Freundlich模型可以很好地描述CR吸附过程；利用Dubinin-Radushkevich模型计算吸附自由能的平均值为12.73kJ/mol,反应过程以化学离子交换吸附为主。准二级动力学和Elovich模型能够很好地用于描述柚皮基活性炭吸附CR过程。颗粒内扩散模型分析表明：膜扩散系数和孔扩散系数均值分别为3.72×10-13cm2/s和5.99×10-12cm2/s,吸附过程由膜扩散和颗粒内扩散联合控制,其中膜扩散为主控步骤。实验条件下,柚皮基活性炭吸附CR的⊿G在-3.72kJ/mol和-15.17kJ/mol之间,⊿H在45.35kJ/mol和49.54kJ/mol之间,⊿S在154.00kJ/(mol·K)和166.05kJ/(mol·K)之间,反应属于自发吸热过程。柚皮基活性炭吸附CR时,静电引力和氢键作用为吸附过程主要作用力。(5)利用柚皮基活性炭处理含氨氮废水。吸附5h后反应基本平衡。Freundlich和Temkin模型可以很好地描述氨氮吸附过程；准二级动力学和Elovich模型描述柚皮基活性炭吸附氨氮的动力学实验数据达到显著相关。利用Dubinin-Radushkevich模型计算吸附自由能的平均值为9.19kJ/mol,吸附过程以化学离子交换吸附为主。颗粒内扩散模型和Boyd模型分析表明：柚皮基活性炭吸附氨氮的膜扩散系数和孔扩散系数均值分别为6.65×10-13和1.15×10-11cm2/s,吸附过程由膜扩散和颗粒内扩散联合控制,其中膜扩散为限速步骤。实验条件下,柚皮基活性炭吸附氨氮的⊿G在-4.26kJ/mol和-4.73kJ/mol之间,⊿H在1.48kJ/mol和2.58kJ/mol之间，⊿s在19.74kJ/(mol·K)和23.29kJ/(mol·K)之间,吸附为自发吸热过程。柚皮基活性炭吸附氨氮时,静电引力和范德华力作用为吸附过程主要作用力。(6)利用柚皮基活性炭处理含磷废水。吸附3h后反应基本平衡。Freundlich和Dubinin-Radushkevich模型都可以反映柚皮基活性炭吸附磷特征,磷吸附属于多分子层吸附。准二级动力学和Elovich模型能很好地描述柚皮基活性炭对磷的吸附动力学过程。吸附自由能的平均值为8.43kJ/mol,吸附过程以化学离子交换吸附为主。颗粒内扩散模型和Boyd模型分析表明,膜扩散系数和孔扩散系数的平均值分别为5.16×10-13cm2/s和5.03×10-12cm2/s，吸附过程主要受膜扩散控制。实验条件下,柚皮基活性炭吸附磷的⊿G在-2.29kJ/mol和-4.03kJ/mol之间,⊿H在2.68kJ/mol和23.15kJ/mol之间,⊿S在18.38kJ/(mol·K)和86.48kJ/(mol·K)之间,吸附为自发吸热过程。柚皮基活性炭吸附磷时,静电引力和范德华力为吸附过程主要作用力。更多还原

【Abstract】 Activated carbons, known as very effective adsorbents, are used widely due to their highly developed porosity, large surface area, variable characteristics of surface chemistry, and high degree of surface reactivity. There are many studies on the development of preparation of activated carbon and application for the removal of specific pollutants from aqueous phase, mainly heavy metals, dyes and etc, at home and abroad. However, the costs of activated carbon preparation from coal and other non-renewable sources are too expensive. In search of new and alternative source as a precursor for the preparation of activated carbon, many agricultural wastes have been studied. The raw materials obtained from agricultural wastes have attracted people’s attention because of their wide resources, renewability and no second pollution. Grapefruit is one of the principal fruits in the south of China with high production. After processing, grapefruit peels are generally discarded as a waste in large scale. Till now, nothing on the preparation of activated carbon from grapefruit peel waste by zinc chloride and treatment of the wastewater has been reported. This dissertation is concerned with the synthesis of activated carbons derived from grapefruit peel by chemical activation with zinc chloride and the removal of different pollution from aqueous solution. Samples were characterized by using FTIR, SEM and XRD techniques, etc. The principles of kinetics, isotherms and thermodynamics about the sorption of ammonia nitrogen, phosphate, Methylene Blue (MB), Congo Red (CR) and hexavalent chromium on the prepared samples were studied. The influence of several operating parameters, such as pH, contact time and initial concentrations of adsorbate on the adsorption capacity, were also investigated. The main conclusions of this study are as follows:(1) The low-cost activated carbon was prepared from grapefruit peel, an agricultural waste material, by chemical activation with zinc chloride. The optimal conditions for the production of activated carbon by orthogonal test were:20%zinc chloride solution concentration,3.0:1mass ratio of liquid to solid,500℃activation temperature and80min. activation time, resulting in35.36%of carbon yield and851mg/g of iodine adsorption value. At this optimal condition, the BET surface area of GAC was found as1045m2/g. The pore volume of GAC is estimated to be7.471cm3/g. The mean pore size of GAC is estimated to be1.430nm. The FT-IR spectroscopy result indicates that the carbons produced are rich in surface functional groups, such as hydroxy, amide, carboxyl and pyrone groups. The pHpzc value of GAS was5.67.(2) Adsorption of Cr(VI) onto GAC was investigated in a batch system. The results show that it takes12hours to reach the equilibrium. Cr(VI) removal is pH dependent and found to be maximum at pH1.0. Temkin and Langmuir isotherm model fitted the data well. The maximum monolayer adsorption capacity of Cr(VI) onto GAC was calculated as145.47mg/g. The mean free sorption energy was calculated as9.93,17.72and20.82kJ/mol respectively. It is very likely that Cr(VI) adsorption onto GAC is chemical in nature. The adsorption kinetic was well fitted to the pseudo-second-order model. Intraparticle diffusion model and Boyd model suggested that average values of the film diffusion coefficient (D1) and the pore diffusion coefficient (D2) were3.72×10-13and5.99×10-12cm2/s. Adsorption was both by film diffusion and intraparticle diffusion and the external mass transfer was the rate-determining. Thermodynamic parameters for the adsorption system were determinated,△G=-0.32kJ/mol～-20.06kJ/mol,△H=39.85kJ/mol～342.93kJ/mol,△S=134.91kJ/(mol·K)-829.51kJ/(mol·K). The negative value of△G showed spontaneous nature of adsorption. The positive values of both△H and△S suggest the adsorption process is an endothermic reaction increasing in randomness at the solid-liquid interface. Possible adsorption mechanism involved three processes:(Ⅰ) adsorption of Cr(VI) ions onto charged groups such as hydroxy, carboxyl and amines groups;(Ⅱ) reduction of Cr(Ⅵ) to Cr(Ⅲ) in the acidic medium;(Ⅲ) reduction releasing Cr(Ⅲ) to the aqueous phase or complexation.(3) Adsorption of MB onto GAC was investigated in a batch system. The results show that it takes2hours to reach the equilibrium. The MB removal was not affected over pH range of2.0～10.0. Temkin and Langmuir isotherm model fitted the data well. The maximum monolayer adsorption capacity of MB onto GAC was calculated as234.26mg/g. The adsorption kinetic was well fitted to the pseudo-second-order model. The mean free sorption energy was calculated as18.53kJ/mol. The adsorption of MB onto GAC was mainly attributed to the chemical adsorption. Intraparticle diffusion model and Boyd model suggested that average values of the film diffusion coefficient (D1) and the pore diffusion coefficient (D2) were2.85×10-12and2.30×10-10cm2/s. Adsorption process was affected by both film diffusion and intraparticle diffusion and film-diffusion dominate the adsorption rate. Thermodynamic parameters for the adsorption system were determinated,△G=-19.44 kJ/mol～-24.77kJ/mol,△H=64.63kJ/mol～67.50kJ/mol,△S=276.65kJ/(mol·K)-277.98kJ/(mol·K). The adsorption process of MB was endothermic and spontaneous. Possible adsorption mechanism was proposed as follows:electrostatic interactions, hydrogen bonding formation and electron donor-acceptor interactions.(4) Adsorption of CR onto GAC was investigated in a batch system. The results show that it takes2hours to reach the equilibrium. The CR removal was not affected over pH range of3.0-10.0. Freundlich model fitted the data well. The mean free sorption energy was calculated as12.73kJ/mol. The adsorption of CR onto GAC was mainly attributed to the chemical ion exchange adsorption. The adsorption kinetic was well fitted to the pseudo-second-order model and Elovich model. Intraparticle diffusion model and Boyd model suggested that average values of the film diffusion coefficient (D1) and the pore diffusion coefficient (D2) were3.72×10-13and5.99×10-12cm2/s. Adsorption process was both handled by film diffusion and intraparticle diffusion and film-diffusion dominate the adsorption rate. Thermodynamic parameters for the adsorption system were determinated,△G=-3.72kJ/mol～-15.17kJ/mol,△H=45.35kJ/mol～49.54kJ/mol,△S=154.00kJ/(mol·K)～166.05kJ/(mol·K). The adsorption process of CR was endothermic and spontaneous. Possible adsorption mechanism was proposed as follows:electrostatic interactions, hydrogen bonding formation.(5) Adsorption of ammonia nitrogen onto GAC was investigated in a batch system. The results show that it takes5hours to reach the equilibrium. Temkin and Freundlich model fitted the data well. The adsorption kinetic was well fitted to the pseudo-second-order model and Elovich model. The mean free sorption energy was calculated as9.19kJ/mol. The adsorption of ammonia nitrogen onto GAC was mainly attributed to the Chemical ion-exchange adsorption. Intraparticle diffusion model and Boyd model suggested that average values of the film diffusion coefficient (D1) and the pore diffusion coefficient (D2) were6.65×10-13and1.15×10-11cm2/s. Adsorption process was both handled by film diffusion and intraparticle diffusion and film-diffusion was the rate-limiting step. Thermodynamic parameters for the adsorption system were determinated,△G=-4.26kJ/mol～-4.73kJ/mol,△H=1.48kJ/mol～2.58kJ/mol,△S=19.74kJ/(mol-K)-23.29kJ/(mol·K). The adsorption process of ammonia nitrogen was endothermic and spontaneous. Possible adsorption mechanism was proposed as follows:electrostatic interactions and Van der Wals forces.(6) Adsorption of phosphate onto GAC was investigated in a batch system. The results show that it takes3hours to reach the equilibrium. Freundlich and Dubinin-Radushkevich model fitted the data well. The adsorption kinetic was well fitted to the pseudo-second-order model and Elovich model. The mean free sorption energy was calculated as8.43kJ/mol. The adsorption of phosphate onto GAC was mainly attributed to the Chemical ion-exchange adsorption. Intraparticle diffusion model and Boyd model suggested that average values of the film diffusion coefficient (D1) and the pore diffusion coefficient (D2) were5.16×10-13and5.03×10-12cm2/s. Adsorption process was dominated by film diffusion. Thermodynamic parameters for the adsorption system were determinated,△G=-2.29kJ/mol～-4.03kJ/mol,△H=2.68kJ/mol～23.15kJ/mol,△S=18.38kJ/(mol·K)～86.48kJ/kJ/(mol—K). The adsorption process of phosphate was endothermic and spontaneous. Possible adsorption mechanism was proposed as follows:electrostatic interactions and Van der Wals forces.更多还原