Separation of nano-colloids in soils

The study of the physicochemical behaviour of colloids and particles in nature has emerged as a scientific problem of critical importance because of the widespread acknowledgement of their significance in controlling the speciation and fate of essential nutrients and contaminants in the aquatic and soil environments （Ledin et al., 1995; Lead et al., 1999, Doucet et al., 200 l; McCarthy et al., 1989; Koterba et al., 1993; Kretzschmar et al., 1999）. Se＇quaris and Lewandowski （2003） developed a method based on sedimentation and centrifugation steps to fractionate agricultural top soils after suspension in water. However, progress in the field has been limited by the lack of appropriate techniques for the isolation and characterization of colloids and particles in their native form （Lead et al., 1997）. The primary difficulties in separation and analysis are colloidal instability and their small size and low concentration. As a result, reliable, unbiased and minimally perturbing methods for sampling and fractionation are primary requirements for the study of colloids and particles if valuable information is to be obtained. In recent years, cross-flow ultra-filtration （CFUF） has become one of the most commonly used techniques for collecting and separating freshwater and marine colloids and particles （Petrus evski et al., 1995; Gustafsson et al., 1999; Benoit et al., 1999; Sigg et al., 2000; Gue＇guen et al., 2002; Benedetti et al., 2003）. CFUF has hitherto been used for studies of the biogeochemical cycling of a variety of elements, such as carbon （Benner et al., 1992; Santschi et al., 1998）, radionuclides （Moran et al., 1992）, trace metals （Reitmeyer et al., 1996） and nutrients （Bauer et al., 1996）. The purpose of this study was to develop a protocol to fractionate particles in soil, to measure particle size distributions and to quantify chemical characteristics within different particle size fractions.     

Metal ions bound to colloids from database to field systems

Nowadays, environmental problems related to soil pollution with heavy metals are numerous, therefore, it is important to understand metal behavior in aquatic sediments and soils and to appreciate their transfer. The fate of the metals in the environment is closely related to their interactions with the major reactive compartments （organic matter, iron and manganese oxides, clays）. The objective of this work is to develop an approach based on the combination of several models to study metal ion speciation in different environmental systems. Models used to describe the interactions of metals with the main reactive phases in the soil are CD-MUSIC （amorphous and crystallized iron oxides）, NICA-Donnan （organic matter and manganese oxides）, and cationic ion exchange model （clays）. Firstly, this work implies the definition of generic parameters to describe the interactions of the studied metals with iron and manganese oxides, a part of this information is missing in the literature. Then, after the validation of the approach by comparison with analytical results, this multi-surface model is applied to test sites corresponding to a soil and to two riverine environments. These new models give good predictions of the behavior of major and trace metal ions even in heterogeneous system characteristics of the natural environment. The measured free metal concentrations in the solution are in agreement with those obtained from model calculations.     

地下咸水与水库水体交换过程中沉积物胶体释放规律

以天津滨海地区北大港水库为研究对象,采用室内柱试验,研究地下咸水与水库水体交换过程中不同位置沉积物胶体释放以及盐分释放/截留的动态特征,同时对沉积物胶体释放、盐分释放/截留机理进行了探讨。研究结果表明:水库不同位置地下咸水与水库水体交换过程中,盐分的归宿不同:接近水库入口处的沉积物能将盐分截留下来,而出水口沉积物却将盐分释放转移到水体。随孔隙体积数的增加,沉积物胶体累计释放量逐渐增加,入库口、库中心、出库口最大累计释放量分别为3.275 mg/g、0.386 mg/g和1.382 mg/g;胶体累计释放量随孔隙体积数的变化曲线符合直线型,胶体释放速率变化很小。盐分的释放或截留是沉积物颗粒的粒径、胶体含量、含盐量等多种因素作用的结果,水库水体与沉积物中的盐分处于动态平衡状态,当沉积物中含盐量高于平衡浓度时,其盐分会向水体中释放,同时吸附在胶体上的盐分也会随着胶体的释放而释放;反之,水体中的盐分会向沉积物中迁移被截留下来,沉积物粒径越小,越易吸附水中的盐分。胶体的释放规律可以用双电层理论得到很好的解释。     

饱和多孔介质中胶体沉淀释放过程的数值模拟

地下环境中可移动的胶体能够促进强烈吸附的污染物质的运移,而胶体自身在运移过程中也会伴随发生沉淀、释放。根据高岭石胶体的土柱出流实验,对不同离子强度条件下胶体在饱和多孔介质中的沉淀和释放行为进行分析,并采用不同模型对其过程进行数值模拟。结果表明,离子强度是影响胶体沉淀和释放过程的重要因素,随着离子强度的增加,胶体的出流峰值逐渐降低,即胶体在多孔介质中的沉淀量逐渐增大,且沉淀速率系数K d 与离子强度成正相关;模型拟合的释放系数与NaCl 浓度显著相关,Grolimund 模型可以很好地模拟胶体的沉淀过程（R 2 >0.95）,但不能准确地模拟释放过程;而胶体运移方程耦合溶质运移方程能够模拟不同离子强度影响下胶体的释放过程（R 2 >0.9）     

胶体颗粒在潜流带中沉积过程及机制

潜流带是河流地表水和地下水交混区域,是河流中重要的物质能量交换和水生生物栖息的场所,而胶体颗粒在潜流带中沉积,会改变潜流带中的水动力结构和生态环境。本文利用室内循环水槽实验和多物理场耦合的数值模拟方法,旨在研究胶体颗粒在河流上覆水与潜流带中的迁移过程和胶体颗粒在潜流带中沉积分布特征及其对不同因素的响应规律。结果表明:河流上覆水中胶体会逐渐被河床截留且截留胶体集中于河床浅层;沙波水平方向截留量呈现出迎水面较高、背水面较低的趋势;胶体在潜流带沉积的主要机制是潜流交换、颗粒沉降与河床截留作用。本文能为胶体颗粒在潜流带中的生态环境作用研究提供科学依据,并为河流生态环境修复、河流健康管理提供理论支持。     

北印度洋—南海表层水体中浮游动物胶体虫(放射虫)的物种多样性、生物地理及其季节变化

具有共生体的浮游动物胶体虫在寡营养海域的有机碳循环和硅循环过程中发挥着重要的作用,但对于胶体虫的研究较为薄弱。文章利用走航式采样和虎红染色方法,首次揭示了北印度洋—马六甲海峡—南海跨多个海域表层水中胶体虫的物种多样性、生物地理及其季节变化。研究海区胶体虫的物种数非常丰富,春季17种、冬季高达27种;北印度洋—马六甲海峡的多样性在春季普遍低于南海、但在冬季则高于南海,表明北印度洋—南海生物多样性的区域地理分布受东亚季风影响显著。胶体虫群落结构的变化也存在生物地理上的差异、且受东亚季风影响显著,如胶球虫科(Collosphaeridae)在春冬季均具绝对优势、球虫科(Sphaerozoidae)只在冬季显著增加;春季和冬季的优势种组成也有不同,表明表层水体中胶体虫的群落组成受季节变化影响显著,东亚季风影响下表层水混合增强,导致属种组成发生显著变化,进而表现出季节变化是控制研究海区胶体虫群落结构的主因。胶体虫的丰度则与区域环境密切相关,如马六甲海峡至巽他陆架春、冬季均较低,南海次之,北印度洋春、冬季都相对较高,反映出其对特定海洋环境的适应性,推测大尺度下区域的影响要高于季风变化的控制。可见,...