【作者】 孙慧敏；

【导师】 王益权；

【作者基本信息】 西北农林科技大学 ， 农业环境保护与食品安全， 2011， 博士

【摘要】 针对灌溉水体和土壤污染愈加严重的客观现实,以及为了进一步揭示重金属污染物在具有不同类型胶体体系土壤中的迁移及环境行为,深入研究无机胶体和胶体携带污染物在多孔介质中传输机理与相关理论,将极大的促进对于地下水污染的认识和对废水处理的研究与应用。尽管前人对土壤介质中污染物的迁移研究已取得了丰硕成果,但是,仍然有许多工作亟待研究和进一步完善。以往研究文献中,只是对在土壤介质中单一重金属离子污染物的迁移研究工作很多,而对重金属与无机胶体的复合物、且与传输介质均能够发生反应的复合污染物的迁移规律研究尚显不足。基于国内外学科发展动态与客观实际的迫切需要,本论文选取了土壤体系中常见的两种不同结构类型的粘土矿物胶体高岭石和蒙脱石作为主要实验材料,通过室内模拟实验和数学模型分析的手段,在分别研究两种无机胶体和重金属铅在多孔介质中迁移规律、无机胶体与重金属铅的相互作用规律基础上,重点研究了无机矿物胶体与土壤重金属铅的复合体在多孔介质中迁移时的分异特征与迁移规律,同时,探求了重金属污染物的修复原理与技术,取得了以下主要结论：(1)粘土矿物胶体在饱和多孔介质中的运移会受到介质性质、胶体类型及孔隙水流速等物理化学条件的影响。石英砂介质的表面特性(水洗处理和烘烤处理)差异,导致粘土矿物胶体在该介质中运移过程时受到的吸附力不同,是影响胶体运移的外因；而粘土矿物胶体结构类型不同、粒径差异显著,决定着粘土矿物胶体在运移过程中的吸附和沉积反应,是影响胶体运移的内因；平均孔隙水流速变化(胶体运移速度)所产生的剪切力不同,影响着胶体移动性；溶液的pH值和离子强度会强烈地影响粘土矿物胶体的表面电荷和ξ电位,随胶体类型的不同,其影响程度差异显著,均是影响胶体运移的环境条件。(2)不同类型的粘土矿物胶体对Pb2+均具有一定的吸附性,但吸附机制与特点有明显不同。高岭石对Pb2+的吸附主要是离子交换作用机制的饱和性吸附,而蒙脱石则是离子交换机制的非饱和性吸附,Pb的饱和度直接影响着不同类型胶体对其吸附与解吸过程。pH是重金属离子在胶体溶液中的吸附和解吸行为的重要影响因素,不同类型的粘土矿物胶体对溶液pH的反应有所不同,溶液pH对以可变电荷为主的高岭石吸附Pb2+影响较大,而对于以永久负电荷为主的蒙脱石影响相对较小。离子强度也是影响胶体和重金属吸附和解吸行为的重要因素,在不同离子强度下,不同类型粘土矿物胶体表面吸附Pb2+的解吸过程均随着时间的变化呈阶段性分布,即初始的快速解吸反应之后伴随着一个缓慢的解吸过程,高岭石随着离子强度的增加,吸附Pb2+的解吸量逐渐增大,蒙脱石胶体则当离子强度达到一定程度后会抑制其解吸,并且在同一离子强度下解吸量远小于高岭石胶体Pb2+的解吸量,进一步证明两种不同类型粘土矿物胶体对重金属的吸附机制有所不同。由粘土矿物胶体对铅的吸附-解吸特性可以推断,当外界环境中低浓度的Pb2+进入土壤,将立即被吸附固定,使Pb2+有效性降低。但是,当外来高浓度的Pb2+进入土壤环境,土壤的吸附作用导致Pb2+在土壤中不断累积,最终达到在总量上饱和。受外界环境变化的影响,如降雨、灌溉和施肥等,就会导致吸附在土壤胶体上的Pb2+的解吸释放而产生更大的生态风险。因此,研究铅在土壤中的迁移规律,才能更好地治理土壤铅的污染。(3)与单纯的胶体运移相比,铅在饱和多孔介质中的运移更复杂,涉及静态和动态反应,导致运移过程中有大量的铅残留在多孔介质中。铅的这种很强的与其他材料结合的趋势,及其在多孔介质中具有低流动性,是造成土壤铅污染的主要原因。粘土矿物胶体在多孔介质中的移动能够加速铅的移动,导致其提前出流。证明了天然胶体可以作为“运输者”以促进重金属的运移；虽然以胶体吸附态铅形式作为输入物质,但在多孔介质中的运移过程,粘土矿物胶体和铅的迁移并不是完全同步,说明粘土矿物胶体和铅作为双反应性复合体进行迁移,在迁移过程中时刻存在着铅在无机胶体与介质相之间的再分配问题。因此,在描述胶体与重金属污染物复合体在多孔介质中迁移特征时,需要以物质检出时间为指标的“迁移速率”和以检出量为指标的“迁移能力”两个指标,才能够完整地表征在有运输载体情况下重金属离子的迁移规律,因为在多孔介质中污染物“迁移峰面”移动快的,未必迁移出的量就一定大。(4)同样是胶体和铅的协同运输,粘土矿物胶体在铅污染的多孔介质中的运移,胶体和铅的相关性高于胶体与铅的吸附体在多孔介质中的运移情况。主要原因是两种不同状况下,铅与胶体之间的吸附或解吸过程与方向不同,对铅的携带与移动能力不同。在多孔介质中,胶体与铅的协同运输中存在着“吸附携带”和“解吸滞留”两种现象。“吸附携带”是给被Pb污染的介质中仅加入无机胶体,胶体对Pb的吸附携带,具有清除Pb污染物的过程；而“解吸滞留”是指胶体与Pb污染物的复合体一同进入到未被污染的多孔介质中,污染物Pb从胶体上解吸下来,而滞留在多孔介质中,对介质却发生了污染过程。对于以上两种情况可以将其称之为“胶体对污染物的解吸和吸附过程效应”。(5)沉积在多孔介质中的胶体可以通过增加孔隙水流速、降低溶液离子浓度和用稀碱溶液淋洗等方法进行释放与修复。当土壤环境由于污水灌溉等原因而具有了较高的离子强度,之后在不断的降低离子强度的过程中,土壤中的胶体物质便会产生增量释放,使吸附在土壤胶体上的污染物质的迁移加剧,由此便可能对深层土壤环境和地下水环境产生威胁。那么,此时可以通过人为调节离子强度的变化,例如灌水等方式来进行人为管理,降低对环境的危害。(6)利用Langmuir模型和HYDRUS-1D软件处理粘土矿物胶体对铅的吸附解吸实验以及粘土矿物胶体和铅在多孔介质中的穿透实验的数据,相关性可达到显著水平。更多还原

【Abstract】 Irrigation water and soil contamination is getting worse, in order to reveal the migration machanism and environmental behavior of of heavy metal pollutants in soil with different colloidal systems, we investigated the mechanism and related theory of inorganic colloids and colloids bounded contaminants transport in porous media, which will benefit the understanding of groundwater pollution and improve the research and application on wastewater treatment. Most scitensists have achieved a lot of successfull results on the research of contaminants migration in soil media, but much work need to be studied and further improved. Based on the past literature, most work focused on the trasnport of contaminant with a single heavy metal ion in the soil media, while the research of the transport mechanism of complexes consisted of heavy metals and inorganic colloids, and the complex contaminants which have reactive characters with the migration media is inadequate. Based on the develement of discipline at home and abroad and the crtitical need for objective reality, this study selected kaolinite and montmorillonite as the main experimental material, which are two different structure colloidal clay minerals in common types soil. Using laboratory experiments and mathematical model simulation, based on the study of transport mechanism of the two inorganic colloids and Pb in porous media, and the interaction of inorganic colloid and Pb, this study focused on the differentiation and migration mechanism of complexs transport in porous media, which consisted of inorganic mineral colloid and Pb, and explored the remediation principle and technology for heavy metal pollutants. This thesis achieved the following major conclusions:(1) The characters of media, colloid type and pore water physical and chemical conditions will impact the transport of clay mineral colloids in saturated porous media. The difference surface characteristics of quartz sand (washed sand and baked sand) results the different absorption force to colloidal clay mineral in the transport process, which is the external factors affecting colloid transport. The difference of clay minaral colloidal structure and significant difference of particle size determines the reaction of adsorption and deposition during the colloidal clay mineral migration, which is the internal factor affecting colloid transport. The change of shear stress generated from the varity of pore water velocity (colloid transport velocity) will affect the colloidal mobility, also pH and ionic strength (IS) of solution will strongly affect the surface charge andξpotential of colloidal clay minerals, which is the environmental conditions impacting the colloid transport, and the effect was significantlly difference,(2) All the different types of clay mineral colloids have some adsorption on Pb2+, but the adsorption mechanism and characteristics are significantly different, the adsorption of Pb2+ on kaolinite is mainly saturation adsorption of exchange mechanism, though the montmorillonite is unsaturated adsorption of ion exchange mechanism. pH is an important factor to impact heavy metal ions adsorption and desorption in colloidal suspension, different clay mineral colloids have different reaction with solution pH. The solution pH has greater impact to the adsorption of Pb2+ on kaolinite which mainly has pH variable charge, but which has relatively small impact to the adsorption of Pb2+ on montmorillonite which mainly has permanent negative charge. Ionic strength also is an important affect factor to the adsorption and desorption of colloid and heavy metals, in different ionic strength, the desorption process of adsorbed Pb2+ in different types clay mineral colloids surface was distributed to different stage over time, the first stage is initial fast desorption, followed with a slow desorption process, and as the increasing of ionic strength, the desorption quantity of adsorbed Pb2+on kaolinite gradually increasing. But montmorillonite colloid will inhibit the desorption of adsorbed Pb2+ when the ionic strength reach a certain concentration, and at the same ionic strength concentration, the desorption quantity of Pb2+ is far less than kaolinite, which further show the adsorption mechanism of two different types colloidal clay minerals have different mechanism to adsorpt heavy metals. The characteristics of Pb adsorption-desorption on the clay mineral colloids further showed, when the low concentration of Pb2+ got into the soil, the Pb2+ would immediately be attracted and stabliablized, and the Pb2+ activity decreased. However, when high concentration Pb2+ got into soil, because of soil adsorption, the Pb2+ accumulated in the soil and saturated eventually. The changing of external environment, such as rainfall, irrigation and fertilization, will lead to soil colloids adsorbed Pb2+ desorption, which release a greater ecological risk. Therefore, only the understanding of mechanism of lead migration in soil was improve, that the soil lead pollution could be controlled.(3) Compared with the pure colloid transport, the Pb transport in saturated porous media was more complicated, including static and dynamic reaction, resulting abundant Pb stored in the porous media in the migration process. Such a strong trend of Pb combining with other materials and low movability in porous media is the main reason of Pb contamination in soil.Clay mineral colloids can accelerate the migration of Pb in porous media, resulting the Pb leach out ahead of schedule. Which proved that natural colloid can be a "carrier" to accelerate the migration of heavy metals. Although the input material was colloid adsorbed Pb, but the transport of colloidal clay minerals and lead in porous media was not synchronized absolutely, which showed that colloidal clay minerals and Pb migrated as a two-reaction complex, furthermore Pb would always redistribute between inorganic colloids and the media in the migration process. Thus, when describing the migration characteristics of complex of colloids and heavy metal pollutants in porous media, the two indicators, "migration rate" whose indicator was material detection time, and "migration ability" whose indicator was detection quantity, were indispensable to characterize the migration of heavy metal ions in the case of a transport carrier.(4) As colloid and lead facilitated transport, when clay mineral colloids transported in Pb contaminated porous media, the correlation of colloid and Pb is much higher than the correlation of colloid and complex. The main reason is that in the two different situations, the peocess and direction of adsorption and desorption between Pb and colloid are different, and the ability of Pb carrying and migration is different, thus there are "adsorption carrying" and "desorption retardation" phenomenas. "Adsorption carrying" is the process that the colloid is added to the contaminated media, which erased the pollutants via adsorption carrying. "Desorption retardation" is the process that when the complex of colloid and pollutants was added into the porous media, contaminants desorbed from colloids, which was retarded in porous media, so the porous media was cotaminatinated. Fot the two cases mentioned above, they can be named as "adsorption and desorption process effect of colloids on pollutants".(5) Colloids deposited in porous media can be release and remediation via increasing the pore water velocity, reducing the ionic concentration, leaching with diluted alkali solution and other methods. When the soil has a high ionic strength, no matter it was irrigated with sewage or other reasons, then in the ionic strength decreasing process, the colloidal substances in soil will release produce incremental release, which will inhance the migration of contaminants adsorbed on soil colloids, which may threaten deep soil and groundwater. The harm to the environment can be reduced via artificially adjusting the ionic strength, such as artificial irrigation and other management method.(6) When dealing with the data of Pb adsorption and desorption on colloidal clay mineral experiments and transport of clay minerals and colloids in porous media experiments, the data resulting from Langmuir model and the HYDRUS-1D software has significant correlation.更多还原