【作者】 赵崇；

【导师】 吴晓芙； 胡曰利；

【作者基本信息】 中南林业科技大学 ， 环境科学与工程， 2008， 硕士

【摘要】 人工湿地以其低能耗、低运行成本等优点,近年来得到了广泛应用。利用人工湿地处理含重金属离子废水是一种新兴的工艺。但是人工湿地也有一些缺点制约了它的推广,如占地面积大,处理能力及效率较低,抗有机及重金属离子水力负荷能力有限,受季节气候影响等。在人工湿地中加入一个吸附单元,利用填料对污染物的强大吸附性能,可以有效解决上述问题。但是至今为止,人工湿地尚未有统一的规范指南,吸附单元的设计及运行的一些基本参数更是没有确定。吸附单元的设计与填料的选择需要知道污水处理量、起始污染物浓度与填料吸附能力及用量的基本关系,其涉及液/固体系吸附机理问题。前人在利用经典吸附理论描述在液/固体系中发生的吸附行为时,经常会出现参数不稳定的现象。在许多情况下,吸附剂浓度效应(经典等温曲线随吸附剂浓度增大而降低的现象)是导致经典方程参数不稳定的主要原因。且经典方程受基本函数关系的限制,不能在已知起始离子浓度C0和吸附剂浓度W0的条件下计算吸附量。因此,改进和完善液/固体系吸附理论、建立更为科学实用的吸附定量模型,不仅能为人工湿地的工程设计提供基础数据与参数,同时在环境界面化学研究中也具有一定理论意义。利用人造沸石(化学纯,粒径0.45～0.90mm)作为吸附剂,水为溶剂,在起始浓度为0.25" 3mmol/L,吸附剂浓度为0.5～2.5g/L的浓度范围内,设计了一系列实验,来研究Zn2+、Cd2+和K+单一及混合离子体系中的吸附特性与吸附机制。主要目的是获得基础数据,检测混合离子体系中的吸附效果,分析吸附体系组成分,然后建立可以用来预测混合离子吸附体系的平衡吸附量预测模型。本研究得出的主要结论概括如下：1)人造沸石表现出很强的阳离子吸附性能,其阳离子饱和吸附量约为7.8mmol/g。利用人造沸石来去除废水中的混合金属离子可取得良好的处理效果。2)实验证明交换与竞争性吸附是人造沸石吸附Zn2+、Cd2+、和K+主要途径,温度对离子吸附量的影响不显著；：3)经典等温吸附线存在明显的吸附剂浓度效应,不同W0水平上的离子吸附等温线之间存在显著差异,基本趋势是吸附等温线随吸附剂浓度W0增大而下降,用经典等温曲线描述人造沸石对混合金属离子的吸附过程时,经典方程参数呈现显著差异。用经典方程计算吸附量时,模拟值与实测值相差很大。说明Langmuir与Freundlich方程均不能用来描述综合样本试验数据。4)平衡离子吸附密度qe为C0/W0(起始点液相离子浓度C0与吸附剂浓度W0的比值)与Ce/W0(平衡液相离子浓度Ce与W0的比值)两者之差。重复测试证实qe、Ce/W0与C0/W0三者具有一一对应的关系。观察到的现象表明液/固相离子吸附体系中的强度因子不是Ce而是固相的qe与液相的Ce/W0。5)混合离子体系中离子的吸附竞争能力基本遵循等当量浓度定律,若A离子的初始浓度为C0A,混和离子体系总当量浓度为C0T,则平衡时A离子的吸附当量qeA=qeTC0A/C0T。6)基于单一离子系统的四组分模型,进一步提出适用于混合离子体系的平衡吸附模型：qeT={c0T+qmT-[(c0T+qmT)2-4c0TqmT(1-k)]1/2}/[2(1-k)]分析表明,新的混合离子平衡吸附方程适用于人造沸石对Zn2+、Cd2+、K+混合离子的吸附行为的描述。四组分模型从理论上合理地解释了经典等温吸附曲线存在吸附剂浓度效应与参数不稳定的原因。新方程的参数稳定、物理意义明确,在检测的离子浓度与吸附剂浓度变化范围内模拟值的精确度高。更多还原

【Abstract】 Accounted for by its characters of low energy consumption and low operation and maintenance cost, constructed wetlands (CW) has been widly used in different countries as treatment systems for municipal sewage and stormwater As a new trend the CW technology has been adopted in recent years in treatment of wastewaters containing heavy metal pollutants. The application of CW techniques, however, has been limited to certain areas mainly due to their relatively low treatment efficiency, large land use area, low capacity to resist hydraulic, organic and heavy metal pollutant loads and particularly instability to seasonal changes. As an effective solution to above mentioned problems, introduction of an adsorption buffer unit into a CW and using materials with high adsorption capacity can improve its treatment efficiency as well as enhance its sustainability. There have been very few studis focusing on processes design and parameter estimation for establishing adsorption buffer units in CW systems. Therefore there have been so far no standardized guidelines and handbooks that can be used for design and costruction of CW systems for treatment of different types of wastewaters. For selection of proper adsorbents and design of buffer units for removal of metal ions it needs to know the quantitative relationship between the amount of wastewater to be treated, the metal ion concentration in the wastewater, the adsorption capacity of the adsorbent and the adsorbent quantity to be used for reducing the metal ion concentration to a stipulated discharge standard. This involves mechanisms of ion adsorption in liquid/solid systems.The parameter inconstancy problem has been frequently recognized by many researchers when describing adsorption kinetics in liquid/solid systems. In many situations, the adsorbent concentration effect (a phenomenon of decline of traditionally defined adsorption isotherms with increasing adsorbent concentration) has been considered to be the main reason for the parameter inconstancy problem. As limited by their defined functions, classical models cannot count ion adsorption for a given adsorption system with known initial ion concentration Co and adsorbent concentration Wo. Improvement of existing liquid/solid adsorption theories and establishment of quantitative adsorption relationships are of both theoretical and practical significances not only for scientific research in the field of environmental interface chemistry but also for use of CW technology in wastewater treatment engineering practices. Using synthetic zeolite (chemically pure, diameter 0.45-0.90mm) as the adsorbent and distilled water as the solvent, designed experiments were carried out to investigate the adsorption characteristic and mechanisms of Zn2+,Cd2+ and K+ in mono- and multiple ionic species systems in the range of initial ion concentration 0.25- 3.0 mmol/L and adsorbent concentration 0.5" 2.5 g/L. The main objective was to obtain basic data, test the adsorbent effect in multiple ionic species system, analyze the adsorption system component factors, and establish proper prediction models which can be used to describe ion adsorption in multiple ionic species system.The main results obtained from this study are summarized as follows:(1)Synthetic Zeolite has a very high cationic adsorption capacity and its maximum cation adsorption capacity is approximately 7.8 mmol/L. It is thus that this type of synthetic minerals can be well used as fine wetland fillers for removal of cationic pollutants from wastewaters.(2) Ion exchange and adsorption competition were found to be the main mechanisms for ion adsorption in the tested mixed ionic species system. Temperature was not shown to have significant effects on ion adsorption within the tested range between 15 and 45℃.(3) There were obviously effects of adsorbent concentration (W0) on the traditional adsorption isotherms (i.e., qe-Ce curves); The difference between ion adsorption isotherm curves obtained at different W0 levels was remarkable. The basic trend was that the qe-Ce curves declined apparently with increasing Wo.(4) The equilibrium adsorption density qe is the difference between C0/W0 (the ratio of initial ion concentration C0 to adsorbent concentration Wo) and Ce/W0 (the ratio of equilibrium ion concentration in liquid phase to adsorbent concentration). Repeated tests indicate that these three ion/adsorbent ratios are closely related with unique values in the tested range. The argument to support this intensity factor concept is that it is the relative level of ion quantity to adsorbent quantity that determines the direction and the rate of ion adsorption reactions. The observed phenomenon indicates that the intensity factor in liquid/solid ion adsorption systems is not Ce but Ce/W0 in the liquid phase and Qe/W0 in the solid phase.(5) Ion adsorption in mixed ionic species systems follows baxically the mass law in chemical equivalent, i.e., if use C0A to denote the equivalent concentration of ion A, C0T to stand for the total system equivalent ion concentration (sum of the concentration for all ionic species present in the mixed system) and qeA to represent the adsorption mole density, we have:qeA=qeTC0A/C0T.(6) Based on the four adsorption components model established for single ionic species systems, an extended model for mixed ionic species systems has been further developed by applying the mass law in chemical equivalent:qeT={c0T+qmT-[(c0T+qmT)2-4c0TqmT(1-k)]1/2}[2(1-k)]Analytical results confirm that the extended model can be well used to describe ion adsorption phenomena for Zn2+、Cd2+ and K+ adsorptions in syntheric zeolite-aqueous solutions.The developed model gives reasonabl explanations to observed adsorbent concentration effect and parameter inconstancy problems associated with classical adsorption models. The new medol, with stable and meaningful parameters fit well the experimental data obtained from the examined samples and its prediction accuracy is satisfactory.更多还原