【作者】 周海兰；

【导师】 吴晓芙；

【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】 随着工业化进程的加快,大量的重金属废水被直接排入到江河湖泊造成水体重金属含量急剧升高,导致我国各大水系受到了不同程度的重金属污染,水体重金属污染不仅加剧了可用水资源的短缺,而且也直接影响到饮水安全、粮食生产和农作物安全,最终危害人类健康。采用人工湿地处理含重金属离子废水是一种新兴工艺,其低能耗、低运行成本的优点吸引着众多研究者的关注。然而,与传统处理方法相比,人工湿地的缺点是处理能力及效率较低、占地面积较大、抗有机、重金属污染负荷与水力负荷能力有限并受季节气候的影响。在人工湿地中引入一个吸附单元添加具有高效吸附性能的填料是解决上述问题的有效方法之一。经典吸附方程都将等温条件下平衡吸附密度qe表达为平衡液相离子浓度e的一元函数,大量的实验结果证明经典等温曲线存在明显的吸附剂浓度效应(随着吸附剂浓度增大,传统意义上的吸附等温线下降的现象),前人认为吸附剂浓度效应是溶液离子强度和pH值引起的,为了消除吸附剂对离子吸附的影响,往往采取引入缓冲溶液来控制系统的pH值和离子强度的办法；而后人则认为离子吸附反应的方向与速率取决于系统中离子量与吸附剂量的相对水平,产生吸附剂浓度效应的根本原因是由于液/固相离子吸附体系中的强度因子不是qe和Ce而是固相qe和液相的Ce/W0,因此,在做qe-Ce曲线图中必然存在吸附剂浓度效应。依据吸附系统中四个必要吸附组成成分(液相离子Ce、固相离子Qe、未被占据的吸附点wc、被离子占据的吸附点wc)提出了一个新的平衡离子吸附密度预测方程,但此方程基于单一离子吸附系统提出,其是否可用于混合离子体系有待于进一步的研究。因此,研究吸附剂浓度效应产生的真正原因、验证新的吸附定量模型在混合离子体系中的应用对于改进和完善液/固吸附理论具有重要意义。针对上述问题,本研究选用蒸馏水反复洗涤后烘干的蛭石作为吸附剂和蒸馏水作为溶剂,在起始浓度0.2mmol/L-2.0mmol/L和吸附剂浓度50-150g/L范围内,布置了一系列蛭石——水溶液混合离子体系和蛭石——缓冲溶液体系中对锌、镉、氨等的吸附试验以研究其吸附特征和吸附机理。主要研究结果如下：(1)天然蛭石具有储量丰富、价格低廉、吸附容量大、对环境无毒无害且容易再生等优点,能迅速、有效地去除水溶液中的Zn2_、Cd2+、NH4+,适合作为人工湿地的填料；蛭石——水溶液体系中离子吸附的主要机制为交换性吸附；由于存在吸附点竞争效应,共存阳离子能抑制Zn2+、Cd2+的吸附。(2)缓冲实验结果表明：离子强度和pH值不是产生Wo应的根本原因,缓冲溶液的引入不仅没有消除吸附剂浓度,还增大了实验误差；缓冲系统存在着强烈的离子吸附竞争,大量其它阳离子的存在极大地抑制了Zn2+、Cd2+的吸附,致使缓冲系统的吸附量远远低于非缓冲系统。(3)在混合离子体系中,重复测试证实平衡离子吸附密度qe与C0/W0(起始点液相离子浓度C0与吸附剂浓度Wo的比值)与Ce/W0(平衡液相离子浓度Ce与Wo的比值)三者之间仍具有一一对应关系,观察到的现象再次表明液/固相混合离子吸附体系中的强度因子也不是qe和Ce而是固相的qe和液相Ce/W0。(4)在单一离子吸附系统中基于四组分模型推导出的平衡吸附预测模型：qe={co+qm-[(co+qm)2-4coqm(1-k)]1/2}/[2(1-k] co=C0/W0可进一步用来预测液/固混合离子体系的平衡吸附密度qe,qe-Co方程对混合离子体系的平衡吸附密度qe的预测证明：在混合离子系统中所有离子的吸附竞争能力遵循等当量浓度定律,即系统吸附的总当量为系统被吸附离子种类的当量和：qeT=∑qei,而离子A的吸附当量qeA为系统离子吸附总当量qeT与系统A离子浓度当量CoA与系统总离子浓度当量的比值的乘积,即qeA=(A离子的当量/总离子的当量)*qeT。(5)新模型对混合离子吸附系统中吸附密度qe的预测实验结果表明在较大检测范围内与实测数据拟合较好；新模型也可用来预测缓冲体系的平衡液相离子浓度Ce,但其预测的精确度比非缓冲系统差。更多还原

【Abstract】 Along with the accelerated industrialization course, a mass of heavy metal containing waste waters was discharged into rivers and lakes, resulting in sever pollutions of heavy metals. Not only was the shortage of useable water resource directly affected by heavy metal pollution, but also the security of drinking water, food and crop production, and the health of human being were endangered. As a new technology developed in recent years with characters of low energy consumption and operation and maintenance cost, constructed wetlands (CW) used for treatment of wastewaters containing heavy metal pollutants have received great attention in fields of environmental science and ecology. Compared with that of conventional treatment processes, however, the application of CW techniques 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 using materials with high adsorption capacity into a CW system can improve its treatment efficiency as well as enhance its sustainability.All traditional adsorption isotherms, when being applied to describe the ion adsorption in liquid/soild systems, define the equilibrium ion adsorption density qe as a single function of the ion concentration in bulk solution Ce.Results from a large number of studies,however, show that there were obviously effects of adsorbent concentration on the traditional adsorption isotherms(i.e.,a phenomenon of decline of the traditionally defined adsorption isotherms with increasing adsorbent concentration).Many scholars think that changes in system ionic strength and pH value are the main factors responsible for the adsorbent effect and thus in order to eliminate this impact they usually adopt a buffer system for control of solution pH value and ionic strength when conducting their adsorption tests. Later studies, however, have demonstrated that the direction and the rate of ion adsorption reactions is dependent on the relative level of ion quantity to adsorbent quantity, which suggests that the intensity factor in liquid/solid ion adsorption systems is not Ce but Ce/Wo in liquid phase and Qe/W0 in the solid phase, and therefore there will be an adsorbent effect when qe is plottedto against Ce.Based on presence of four essential adsorption components(ion in liquid phase Ce,ion on solid surface Qe,covered adsorption site wc and uncovered adsorption site wu) in the adsorption system, a qe-Ce/W0 adsorption isotherm model has been established. The new model, however,has been tested so far only for single ionic species systems and whether or not it can be used for mixed ion system needs further investigations.Therefore, it is of great significance to test the basic relationship among ion adsorption components in mixed ionic species systems so as to improve the liquid/soild ion adsorption theory.Using vermiculite(0.2-0.4mm, dried after rinsed with distrilled water) as the adsorbent and distrilled water as the solvent, designed experiments were carried out to investigate the adsorption characteristic and mechanisms of Zn2+、Cd2+ and NH4+ in both buffer solutions and mixed ion species systems in the range of initial ion concentration 0.2-2.0 mmol/L and adsorbent concentration 50～150 g/L.The results obtained from the tests are summarized as follows:(1) Accounted for by its nontoxic nature, low cost renewable and high cation adsorption capacity, the natural vermiculite was proved to be a fine wetland filler wetland for removal of Zn2+、Cd2+ and NH4+ from wastewaters. Ion exchange was found to be the main mechanism for Zn2+ and Cd2+ adsorption in the tested system.Because of adsorption competition, coexisting cation can inhibit the adsorption of Zn2+ and Cd2+.(2) Results from buffer experiments show that ionic strength and pH are not the fundamental cause of W0 effect; introduction of buffer solution has not eliminated the adsorbent effect, but instead, increased the experimental error. Strong adsorption competition exists in buffer system and the existence of large number of other cationic spcies has greatly inhibited adsorption of Zn2+ and Cd2+.Due to adsorption of other types of ions,the potential adsorption capacity available for Zn2+ and Cd2+ in buffer system is below that in the non-buffer system.(3) In the mixed system, repeated tests indicated that the three ion/adsorbent ratios (the adsorption density qe, the ratio of initial ion concentration to adsorbent concentrationC0/W0 and the ratio of equilibrium ion concentration in liquid phase to adsorbent concentration Ce/Wo)are closely related with unique values in the tested ranges. The observed phenomenon indicates that the proposed intensity factor theory holds basically in mixed ionic species adsorption systems.(4) Based on the four adsorption components model proposed for single ionic species adsorption systems, qe={co+qm-[(co+qm) 2-4coqm (1-k)]1/2}/[2(1-k)]co=C0/W0a new model extend for mix ionic species systems has been developed by assuming that in the mixed system adsorption competence of all ions abide by the rule of equivalent concentration,i.e.,the total equivalent adsorption of the system equals to the sum of equivalent amount of different ionic species adsorbed by the system:qeT=∑qei, and thus the equivalent adsorption density of ion A(qeA) equals to the sumof equivalent adsorption density of all ions presence in the system(qeT) multiplying the ratio initial equivalent concentration of ion A(CoA) to the sum of initial equivalent concentration of ionic species present in the system (C0T), i.e.,qeA=(C0A/C0A)*qeT.(5) The model extended for mixed ionic spscies systems fit well the experimental data obtained from the examined sample in the tested rangle with satisfactory prediction accurary.The model can also be used to predict equilibrium liquid ion concentration Ce in buffer systems though its accurary level is lower than that in non-buffer systems.更多还原