【作者】 熊佰炼；

【导师】 张进忠；

【作者基本信息】 西南大学 ， 环境科学， 2009， 硕士

【摘要】 重金属是对生态环境危害极大的一类污染物,废水中的可溶性重金属离子经过水生食物链的富集,最终由水产品进入人体,会给人类带来严重的毒害影响。目前,去除水中重金属离子的方法主要有化学沉淀法、氧化还原法、离子交换法、电解法和膜过滤法。但是,这些方法存在运行成本高、操作繁琐、易造成二次污染等缺点;另一方面,它们主要适用于处理金属离子浓度较高的废水。当重金属离子浓度低时,处理效率较低。近年来,生物吸附法以其高效、环境友好的特点引起了广大研究者的高度关注。本文利用甘蔗原渣（原渣）和微波作用下尿素改性甘蔗渣（改性渣）为吸附剂,采用静态摇瓶实验,吸附去除废水中低浓度的Cd²⁺和Cr³⁺。本研究对吸附条件进行了优化,探讨了NaCl、CaCl₂、KCl、MgCl₂四种无机盐对吸附的影响;获得了甘蔗渣吸附Cd²⁺。和Cr³⁺的动力学和热力学特征、两种重金属离子的竞争吸附特征;采用HNO₃、HCl为解吸剂,探讨了洗脱剂浓度对解吸能力的影响;并采用红外光谱分析法,对改性前后和吸附重金属离子前后的甘蔗渣进行了表征。获得了如下的研究成果:1.原渣和改性渣吸附Cd²⁺的最佳pH为6,吸附Cr³⁺的最佳pH为4。温度对吸附的影响不显著。两种吸附剂对重金属离子的吸附速率都较高,前5 min的吸附率已超过60%,原渣和改性渣吸附Cd²⁺的平衡时间为2 h,吸附Cr³⁺的平衡时间为12 h左右。Cd²⁺浓度较低时,原渣对Cd²⁺的吸附量随初始浓度的增加而较快增加;Cd²⁺浓度为83 mg/L时,吸附量为4.79 mg·g^-1。在实验的浓度范围内,改性渣吸附Cd²⁺、原渣和改性渣吸附Cr³⁺的量均随初始浓度的增加而持续增大,吸附没有达到饱和。2.吸附热力学参数显示,两种吸附剂吸附Cd²⁺的过程均为放热的物理过程;原渣吸附Cr³⁺的过程为吸热的物理过程,改性渣吸附Cr³⁺的过程为吸热过程,兼有物理吸附和化学吸附。本研究中的所有吸附过程均为自发过程。两种吸附剂吸附Cd²⁺和Cr³⁺的动力学过程均可用二级动力学模型描述,决定系数在0.99以上。两种吸附剂吸附Cd²⁺和Cr³⁺的等温吸附行为均可用Langmuir模型来描述,决定系数在0.99左右。原渣对Cd²⁺、Cr³⁺的最大吸附量分别为4.88 mg/g和6.33 mg/g:改性渣对Cd²⁺、Cr³⁺的最大吸附量分别为12.38 mg/g和23.92 mg/g。通过改性反应,甘蔗渣对这两种离子的吸附能力有了明显的提高。3.废水中Na⁺、Ca²⁺、K⁺、Mg²⁺的不同浓度组合对Cd²⁺的吸附都有一定的促进作用。废水中Ca²⁺的存在对Cr³⁺的吸附有较大的抑制作用。废水中Cr³⁺、Cd²⁺共存时,原渣和改性渣都优先吸附Cr³⁺,对Cd²⁺的吸附量明显降低;Cd²⁺的存在对Cr³⁺的吸附没有明显的影响。4.HCl、HNO₃都能较好地洗脱吸附在原渣上的Cd²⁺,洗脱率在98%以上;但对改性渣上的Cd²⁺洗脱效果不好。HCl、HNO₃对两种吸附剂上的Cr³⁺洗脱效果不好,洗脱率均在15%以下。5.通过对甘蔗渣改性前后、吸附重金属离子前后的红外光谱分析,推断出两种吸附剂吸附金属离子的机理不同:原渣吸附Cd²⁺和Cr³⁺起重要作用的基团是-OH,而改性渣为N-H、C-N和C=O等含氮、氧的官能团。更多还原

【Abstract】 Heavy metal is a kind pollutant with high toxicity in ecological environment. Some dissolved heavy metal ions can be enriched in aquatic food chains, enter into human bodies through aquatic products, and thus brings about serious poisoning to human beings. Up to now, some methods including chemical precipitation, oxidation-reduction, ion exchange, electrolysis and membrane diltration, are used to remove heavy metal ions in water. However, these methods have some disadvantages, such as high running cost, cumbersome operation, and easy to cause secondary pollution. On ther other hand, they are mainly used to remove heavy metal ions with high concentration in waste water. The treatment efficiency is very low when these methos are used to remove heavy metal ions with low concentration in waste water. Recently, the biological adsorption method attracts many scientists’ concern owing to its high efficiency and environmental-friendly.In this thesis, the bagasse and modified bagasse which was modified with urea under the microwave irradiation were used to adsorbents to adsorb Cd²⁺ and Cr³⁺ with low concentration in wate water by using static shaking experiment. The adsorption conditions were optimized, and the effects of four inorganic salts including NaCl,CaCl₂,KC1 and MgCl₂ on adsorption were also examined. Adsorption thermodynamics and kinetics characteristics of bagasses to Cd²⁺ and Cr³⁺ and competitive adsorption initial pH, initial metal ion concentration, the adsorbing time, solid/liquid ratio and desorption characteristic were obtained. Effect of the concentration of eluants （HNO₃ and HC1） on desorption capability. The bagasses before and after modification and before and after adsorption were characterised by using infrared spectrophotometnc analysis. The achievements were obtained as follows.1.The optimal pH was 6 when the original bagasse and the modified bagasse were used to adsorb Cd²⁺,and the optimal pH was 4 when they were used to adsorb Cr³⁺.Effect of temperatire on adsorption was not prominent. The adsorption rates were both high when the two adsorbents were used to adsorb the two heavy metal ions. The adsorption ratio exceeded 60% at 5 min, the adsorption equilibrium time of the two adsorbents to Cd²⁺ was 2 h, while ca. 12 h to Cr³⁺.When the concentration of Cd²⁺ was low, the adsorption amount of the original bagasse to Cd²⁺ increased with the initial concentration. When the concentration of Cd²⁺ was 83 mg/L, the adsorption amount was 4.79 mg·g^-1.In the range of the original concentration of the two heavy metal ions, the adsorption amounts of the modified bagasse to Cd²⁺ and the original and modified bagasse to Cr³⁺ both increased with increasing the original concentration of the two heavy metal ions, the adsorptions didn’t reach saturation.2.Thermodynamic parameters showed that the adsorption processes of the two adsorbents to Cd²⁺ were both exothermic physical adsorption processes. The adsorption process of the original bagasse to Cr³⁺ was an endothermic physical adsorption process; the adsorption process of the modified bagasse to Cr³⁺ was an endothermic adsorption process with the physical and chemical adsorption simultaneously. All of the adsorption processes were spontaneous processes in this study. Both of the adsorption processes of the two adsorbents to Cd²⁺ and Cr³⁺ can be described by the second kinetic equation, and the coefficient of determination were over 0.99. The isothermal adsorption behaviors of these processes can be described by Langmuir model, and the coefficient of determination were about 0.99. The maximum adsorption amounts of Cd²⁺ and Cr³⁺ by the original bagasse were 4.88 mg·g^-1 and 6.33 mg·g^-1,while 12.38 mg·g^-1 and 23.92 mg·g^-1 by the modified bagasse, respectively. It can be seen that the adsorption capacity of the modified bagasse to the two heavy metal ions can be improved significantly.3.The combination of Na⁺,Ca²⁺,K⁺ and Mg²⁺ in waste water can improve the adsorption of Cd²⁺. Calcium ion in waste water can inhibit the adsorption of Cr³⁺.When Cd²⁺ and Cr³⁺ coexist in waste water, both of the tow adsorbents adsorb Cr³⁺ first, and the adsorption amount of Cd²⁺ decreases significantly. No obvious influence on the adsorption amount of Cd²⁺ can be found in the presence of Cr³⁺.4.Both of HC1 and HNO₃ can well elute the adorbed Cd²⁺ on the original bagasse, and the desorption ratio was more than 98%. However, the elution ratio was very low for the adsorbed Cd²⁺ on the modified bagasse, and the desorption ratio was less than 15%.5.It can be concluded that the adsorption mechanisms of the two adsobents to the two metal ions are quite different by analyzing the IR spetra of the bagasses before and after modification and before and after adsorption. Hydroxy group plays an important role in the adsorption of the original bagasse to Cd²⁺ and Cr³⁺,while N-H, C-N,C=O for the modified bagasse.更多还原