【作者】 李颖；

【导师】 岳钦艳；

【作者基本信息】 山东大学 ， 环境工程， 2010， 博士

【摘要】 天然水中存在着大量的重金属元素、天然有机质和粘土颗粒物,其中,重金属污染物不仅污染性强、生物可降解性差,而且各组分之间的相互作用引发的复合污染尤为严重,受到人们的高度重视。吸附是水环境中固液界面普遍存在的作用方式,在很大程度上决定着重金属污染物的形态转化和迁移,因而,对水中污染物之间吸附特性的系统研究,在预测和防治天然水污染工作中具有重要的理论意义和实际意义。本论文在综合国内外大量相关文献的基础上,选取重金属Cr、Cu、Zn及腐殖酸、高岭土为研究对象,通过研究金属离子与腐殖酸的吸附行为、络合常数和作用机制,明确了重金属元素在不同形态间的转化过程；探讨了腐殖酸在水中的两种存在形式与高岭土相结合的差异性,确定了基本反应单元；深入研究了溶解态腐殖酸对高岭土吸附重金属的影响作用,并对作用机理进行了分析。主要研究内容及结果如下：1.采用静态吸附法研究了腐殖酸对水中Cr2O72-、Cu2+、Zn2+的吸附和脱附性能,分析了不同反应条件下的吸附机理。结果表明,腐殖酸对Cr2O72-的还原作用是控制整个反应体系的重要步骤,还原成的Cr3+通过离子交换被吸附到腐殖酸上；而Cu2+和Zn2+在腐殖酸上的吸附机理与pH有关,酸性条件下吸附力以离子交换为主,中性条件下以配位络合为主。用不同的动力学模型验证了吸附行为,结果表明,拟二级动力学方程最适合描述各个浓度和温度下三种金属离子在腐殖酸上的吸附过程。在20℃、2 mg/L溶液中,腐殖酸对Cr2O72-、Cu2+、Zn2+的平衡吸附量分别为0.77 mg/g,8.59 mg/g和1.52 mg/g。当初始浓度增加时,平衡吸附量随之增加,吸附速率反而减小,表明高浓度下达到特定的吸附率需要更长的时间；随着温度的升高,平衡吸附量和吸附速率常数增大,说明化学反应是控制吸附速率的主要步骤,升温有利于反应的进行。2.结合不同实验条件对腐殖酸的两种基本结构类型——水杨酸型和邻苯二甲酸型与高岭土的作用机制进行研究,考察了pH、盐浓度、硬度对吸附效果的影响。结果表明,不同pH下腐殖酸与高岭土的结合形式有所不同。在pH 4-7时,吸附主要依靠高岭土的端面带电基团与腐殖酸中羧基的表面配位作用进行,腐殖酸主要以邻苯二甲酸的形式与高岭土结合；当pH>7时,强大的静电斥力阻碍了反应的发生,羧基的配位能力逐渐被羟基取代,此时,腐殖酸与高岭土的作用单元以水杨酸形式为主。整个吸附过程可用Fruendlich吸附模型进行模拟,ΔH值约等于配位交换能量值(≈40 KJ/mol),证实吸附的主要作用力是表面配位。水中的盐离子Na+和硬度金属离子Ca2+、Mg2+对腐殖酸的去除率也有一定影响,主要是通过压缩双电层、絮凝和架桥作用来实现的。3.通过研究溶解态腐殖酸对高岭土吸附Cr2O72-的促进作用,并结合不同实验条件对吸附效果的影响,推断反应机理。研究结果表明,高岭土、腐殖酸和Cr2O72-的三重物质体系的吸附过程实际上包括Cr2O72-直接与高岭土端面基团SOH2+形成SOH2+／Cr2O72-表面络合物,以及Cr2O72-被腐殖酸还原成Cr3+后,通过静电作用而实现在粘土表面吸附的过程。平衡实验数据可由Langmuir方程描述,升温有利于反应的进行,吸附质与吸附剂之间存在的范德华力、氢键力、疏水键力等,以及溶液中未被吸附的吸附质分子的熵增,都是促使吸附进行的驱动力,吸附过程为物理吸附。水中的盐离子Na+和硬度离子Ca2+、Mg2+对三元体系中Cr(VI)的去除率有抑制作用,原因是外加离子改变了高岭土的表面电荷,并且使腐殖酸絮凝,从而减弱了腐殖酸对Cr(VI)的还原性,降低了吸附率。三种离子对混合体系cr(VI)吸附率的影响顺序为Mg2+>Ca2+>Na+。这一结果证实了吸附体系属于非专性吸附,表面静电吸引是主要的吸附力。4.采用离子交换平衡法研究了腐殖酸铜和腐殖酸锌的络合稳定常数与络合—沉淀机制,考察了pH、高岭土含量、盐浓度及腐殖酸添加量对高岭土吸附Cu2+、Zn2+的影响,进而揭示反应机理。结果表明,溶液中腐殖酸含量的增加使Cu2+、Zn2+的吸附率明显下降,原因是大量的腐殖酸分子通过络合作用结合金属离子,形成腐殖酸—金属络合物留存在溶液中,从而减少了其在粘土上的吸附量。pH=4时,腐殖酸铜和腐殖酸锌的络合稳定常数分别为2.54和1.85。通过腐殖酸与Cu2+、Zn2+络合稳定性的进一步研究证实：腐殖酸与Cu2+、Zn2+的络合—沉淀机制和腐殖酸对金属离子的容纳能力有关,二者通过离子交换、配位络合和共沉淀等多种机制发生作用,在低浓度下,生成的可溶性络合物是导致cu2+、Zn2+吸附率降低的主要原因。动力学研究表明,高岭土／金属二元体系与高岭土／腐殖酸／金属三元体系的吸附过程均符合拟二级动力学方程,说明腐殖酸的存在并没有改变金属离子在粘土上的吸附机理。更多还原

【Abstract】 There are a lot of heavy metals, natural organic matters and clay particles in natural water. It has been paid more attention to the contaminants for their polluting hazard and poor biodegrability, especially, combined pollution caused by the interactions between pollutants. Adsorption is a common action on the solid liquid interface, which is important to form transformation and migration of heavy metals in water. Therefore, it is essentially to study on the adsorption properties and relationships between aqueous pollutants in theory and actual in practice.Synthetizing references, relationships of humic acid (HA), kaolin particles and heavy metals including Cr, Cu and Zn were studied. The adsorption properties and complexing constants of metal ions and HA were investigated to define the species transformation of metal elements. And the difference of two forms of HA combined with kaolin was discussed. Furthermore, the influence of dissolved HA on the metal adsorption onto kaolin was explained mainly.The main contents and results are following:1. Adsorption/desorption properties of particulate HA for Cr2O72-, Cu2+ and Zn2+ were studied by static adsorption method and mechanism under different conditions was analyzed. The results showed that the reducibility of HA in process of Cr2O72-adsorption was the control step, while the mechanism of Cu2+/Zn2+ adsorption onto granular HA was related to pH. The adsorption force was ion exchange in acidic solution and complexation in neutral condition. Three kinetic models were used to fit the experimental data, and it was found that the pseudo-second-order equation was most appropriate to describe the adsorption kinetics with different initial concentrations and s. The saturated adsorption uptake of Cr(VI), Cu2+ and Zn2+ were 0.77 mg/g,8.59 mg/g and 1.52 mg/g, respectively. With increasing concentration, the saturated amount adsorbed increased but the adsorption rate declined, which meant that it needed more time to reach the same percentage in high concentration. In addition, the equilibrium adsorption amount and rate constant increased with increasing temperature, which indicated the adsorption mechanism. Increasing temprature favored for the adsorption proceeding.2. Combined with the influence of different experimental condition on the adsorption of kaolin and the two basic forms of dissolved HA, the reaction mechanism was studied. The results showed that the adsorption took place mainly by the complexation between the charged groups on kaolin surface and carboxyls of HA in pH range 4-7. Above pH 7, the complexing ability of carboxyl was weaker than that of hydroxy because of electrostatic repulsion, so the form of salicylic acid (SA) became dominant rather than the form of phthalic acid (PA). The results of adsorption thermodynamics indicated that the adsorption could be described well by Freundlich model and the adsorption process was favourable. The positive AH indicated the endothermic process and its value was about 40 kJ/mol accounted for the surface complexation. Additional salt ions, e.g. Na+, Ca2+ and Mg2+ were also influential to HA removal, which accured by compression of double charged, flocculation and bridging effect.3. The adsorption mechanism was concluded based on the study of effect of HA on Cr(VI) adsorption onto kaolin. The results showed that in the kaolin/Cr2O72-/HA ternary system, the adsorption mechanism of kaolin for Cr(VI) actually included complexation between Cr2O72- and SOH2+, as well as reduction reaction, by which Cr2O72- was reduced to Cr3+ by HA molecule. The whole adsorption process could be simulated by the Langmuir adorption model. Both the Van der Waals force, hydrogen bond force and hydrophobic bond force and the increase of entropy of unadsorbed Cr in solution were the driving force for the adsorption process. The inhibited effect of ionic strength on adsorption was remarkable because HA molecules could be flocculated and thereby reducibility was weakened. So the Cr removal decreased. The order of salt ions affected the adsorption percentage of Cr(VI) was Mg2+>Ca2+>Na+ which fact confirmed the non-specific adsorption system and the main adsorption force was surface electrostatic attraction.4. Based on the static adsorption method, the complexing stable constants of Cu-HA and Zn-HA were determined and the precipitation interaction was investigated. By studying the influence factors on the adsorption, the mechanism of HA affecting the Cu2+/Zn2+ adsorption on kaolin was revealed. The results showed that the increasing amount of HA in solution declined the metal cations adsorption obviously due to the formation of dissolved complex. On the same condition, the complexing stable constants of Cu-HA and Zn-HA were 2.54 and 1.85, respectively. Through the study of precipitation interaction between HA and metals, the precipitation mechanism was concluded. It is found that the stability of HA-metal complex was related to the holding capacity of HA for metals. The precipitation mechanism was comprehensive, including ion exchange, complexing reaction and coprecipitation, etc. In low concentration, dissolved HA-metal complex was the primary reason to decrease metal adsorption. The pseudo-second-order model best described the adsorption behavior of Cu2+/Zn2+ onto kaolin particle in planar and ternary system. It is indicated that the existing of HA in solution didn’t change the adsorption mechanism.更多还原