胶体在地下水中的环境行为特征及其研究方法探讨

在收集查阅国内外已有研究资料的基础上,对地下水中胶体稳定性、迁移机制以及模拟预测方法进行了详细归纳和总结。研究表明,胶体稳定性主要受自身理化性质和水文地球化学条件的影响,其受控于胶体粒径、形态、电势电位以及地下水的pH、离子强度等条件。胶体在多孔介质中的迁移机制主要表现为胶体沉积和形变阻塞,其中针对胶体稳定性的差异性,胶体沉积过程分别表现为表面封阻和过滤熟化。目前有关胶体在地下水中迁移的模拟技术已发展得日益成熟,但结合多孔介质非均质性和胶体化学性质非均质性的数学模型还需进一步探讨。     

石油沥青质的吸附、沉淀机理及其影响因素

对于原油中石油沥青质的存在状态尚无统一认识,存在多种石油胶体体系理论模型。沥青质有两种方式从石油中分离出来,即吸附和沉淀,它们具有完全不同的机理。吸附的沥青质不能被溶解,要通过解吸才能消除,且解吸过程相对溶解而言很慢。沉淀是由于石油胶体体系的变化引起的,而吸附则是由石油胶体体系以及体系外的水介质环境和周围岩石矿物特征等所控制的。影响吸附的主要因素有:矿物本身的化学性质和结构特征、矿物质表面水层的性质、原油组成。影响沉淀的因素主要有:原油的组成、温度和压力、石油所处的状态、孔隙特征。低渗储层比高渗储层更容易导致沥青质的沉淀。     

Monodisperse and polydisperse colloid transport in water-saturated fractures with various orientations: Gravity effects

Numerical experiments are conducted to examine the effects of gravity on monodisperse and polydisperse colloid transport in water-saturated fractures with uniform aperture. Dense colloids travel in water-saturated fractures by advection and diffusion while subject to the influence of gravity. Colloids are assumed to neither attach onto the fracture walls nor penetrate the rock matrix based on the assumptions that they are inert and their size is larger than the pore size of the surrounding solid matrix. Both the size distribution of a colloid plume and colloid density are shown to be significant factors impacting their transport when gravitational forces are important. A constant-spatial-step particle-tracking code simulates colloid plumes with increasing densities transporting in water-saturated fractures while accounting for three forces acting on each particle: a deterministic advective force due to the Poiseuille flow field within the fracture, a random force caused by Brownian diffusion, and the gravitational force. Integer angles of fracture orientation with respect to the horizontal ranging from ±90° are considered: three lognormally distributed colloid plumes with mean particle size of 1 μm (averaged on a volumetric basis) and standard deviation of 0.6, 1.2 and 1.8 μm are examined. Colloid plumes are assigned densities of 1.25, 1.5, 1.75 and 2.0 g/cm³. The first four spatial moments and the first two temporal moments are estimated as functions of fracture orientation angle and colloid density. Several snapshots of colloid plumes in fractures of different orientations are presented. In all cases, larger particles tend to spread over wider sections of the fracture in the flow direction, but smaller particles can travel faster or slower than larger particles depending on fracture orientation angle.     

影响粘土胶体稳定性的因素研究

本文研究了我国六种蒙脱石及高岭石和伊利石胶体的粘度和稳定性、探讨了胶体浓度、pH值和ESP的影响及其机理。     

巢湖的稀土元素地球化学特征

采用液-液萃取法和ICP-MS测试技术对巢湖的溶解态稀土元素进行了分析。结果表明,巢湖的溶解态稀土的含量与世界淡水相当,丰水期的样品含量高于其他季节。pH值和悬浮物、胶体是控制巢湖水体中溶解态稀土含量的主要因素。巢湖的溶解态稀土的分布模式以平坦型为主,少数呈现重稀土富集。丰水期和枯水期的溶解态稀土的(La/Yb)N值从西半湖区到东半湖区呈现有规律性的逐渐增大,并且丰水期的(La/Yb)N值低于枯水期。在富营养化湖泊中,胶体和水生生物可能是造成这一现象的主要原因。     

滨海地下水交互带中的胶体运移行为研究综述

在分析国内外已有研究的基础上,综述滨海地下水交互过程中的胶体运移规律,重点阐述咸淡水驱替作用下胶体的宏观运移规律和微观作用机理。胶体在滨海地下水交互中可成为联系海-陆相的物质传输纽带,其运移行为主要受地下水水化学参数波动影响,受控于胶体类型与数量、表面电位及地下水pH、离子强度等因素,具有水动力、水环境多因子联合作用的特征,并在含水层中具有空间堵塞和团聚体结构改变的不确定性。未来关于滨海地下水交互带中的胶体行为研究应重视基础勘察,考虑胶体群体效应,结合滨海含水层对水动力、水化学条件的敏感性,研究胶体在多相体系中胶体运移的不确定性及其对污染物的协同运移作用,为滨海资源化研究构建统一分析体系和预测机制。     

九龙江口水体中不同相态磷的环境化学行为研究

利用切向超滤技术分离和提取九龙江口水体中溶解相(粒径<0.45μm)、胶体相(分子量>1 kDa,粒径<0.45μm)和真溶解相(分子量<1 kDa)的活性磷酸盐(SRP)和溶解态总磷(DTP),初步探讨了不同相中各形态磷的环境化学行为.研究表明,切向超滤过程的SRP和DTP系统空白分别为ND～0.001 mg/dm3...     

Dispersion and immobilization of pollutants in Cretaceous sandstones where U ore was mined by sulfuric acid leaching

The uranium deposit Straz pod Ralskem in the northern part of the Czech Republic was exploited by underground acidic leaching between 1968 and 1996. More than 14000 tons of uranium were produced during this period. More than 4 million tons of H2SO4, 300 thousand tons of HNO3, 120 thousand tons of NH3 and other chemicals were injected in Cenomanian sandstones. The mining has resulted in a large contamination of ground waters. Lateral hydrodynamic dispersion of the pollutants and migration of pollutants across aquitard are a potential hazard to drinking water supply and to surface aquatic environment, Chemical leaching was done by forced circulation of a technological acid solution introduced to the sandstones through injection drill holes and withdrawal of the enriched resulting solution by production wells. The solution is reacting not only with uranium ore, but also with minerals of the rock environment. Hydrogen ions are replaced by uranium and other cations leached from the rock, especially Fe, Al, Be and As. Ammonia remaining after the precipitation of the yellow cake （ammonium diuranate） was rejected underground in spite of that it serves no purpose in the underground leaching. High concentrations of Al, Be, As and ammonium ions in ground water became the most serious ecological pollutant. Modelling of the hydrodynamic dispersion of the pollutants predicts the future risks to local water supplies in 200 to 500 years. A possible way to reduce the risk is an immobilization of the pollutants in deeper parts of the sandstone aquifer. We found that modeling of the geochemical reactions using classical hydrochemical models give unrealistic results because of formation of colloidal particles.     

Speciation of Trace Elements in Acidic PoreWaters from Waste Rock Dumps by Ultrafiltration andIon Exchange Combined with ICPMS and ICPOES

A speciation procedure developed on reactive acidicpore water samples from mining areas is presented.Methods with low consumption of solution are requiredthat allow rapid sample preparation to avoid equilibriumchanges as far as possible. The entire procedure includesonly three parallel separation steps. One aliquot is filteredthrough an 1 kd ultrafiltration membrane to separate traceelements adsorbed or complexed by colloids. One cationand one anion exchange are performed with two additionalaliquots to determine simple hydrated ions and smallinorganic complex ions. Commonly used procedures ofion exchange seem to be problematic. This new techniqueis based on a novel ion exchanger. Subsequently the threefractions obtained from the separation procedures and theoriginal pore water sample are analysed by ICPMS, ICPOES,ET-AAS, Flame-AAS, FES and IC to determine the concentrationsof the major ions and additionally up to 50 trace elements. Theinfluence of pH-values and several dissolved compounds iscontrolled in experiment series with synthetically preparedsolutions to reveal potential artifacts.     

Colloid transport and distribution in the hyporheic zone

Colloids moving from the stream into the hyporheic zone may have a negative impact on aquatic ecosystems as they are potential contaminants or carriers of contaminants. Moreover, retained colloids in the hyporheic zone could not only reduce the exchange flux between the stream and streambed but also change the conditions of the bed, affecting the habitats for aquatic organisms. Previous studies focused on the exchange flux across the sediment–water interface, but the colloid transport processes and distribution of retained colloids in the streambed have received little attention. We conducted experiments within a laboratory flume to examine these processes in a streambed driven by bedform‐induced hyporheic flow. Retained colloids measured in the bed at the end of the experiments revealed colloid retention mainly in the shallow layer of hyporheic zone (0–5 cm below the interface). The results demonstrated significant effects of particle trapping and settling on the colloid transport and distribution in the streambed. Retention leads to the formation of a colloid‐filled shallow layer in the bed. Particle paths based on model simulations showed that colloid settling in pore water modifies the direction of colloid transport and allows the colloid particles to move more deeply in the bed.