Colloid-facilitated transport
Encyclopedia
Colloid-facilitated transport designates a transport process by which colloid
al particles serve as transport vector
of diverse contaminants in the surface water (sea water, lakes, rivers, fresh water bodies) and in underground water circulating in fissured rocks
(limestone
, sandstone
, granite
, ...). The transport of colloidal particles in surface soil
s and in the ground
can also occur, depending on the soil structure
, soil compaction
, and the particles size
, but the importance of colloidal transport was only given sufficient attention during the '1980 years.
Radionuclides, heavy metals, and organic pollutants, easily sorb
onto colloids suspended in water and that can easily act as contaminant carrier.
Various types of colloids are recognised: inorganic colloids (clay
particles, silicates, iron oxy-hydroxide
s, ...), organic colloids (humic
and fulvic substances). When heavy metals or radionuclides form their own pure colloids, the term "Eigencolloid
" is used to designate pure phases, e.g., Tc(OH)4, Th(OH)4, U(OH)4, Am(OH)3. Colloids have been suspected for the long range transport of plutonium on the Nevada Nuclear Test Site
. They have been the subject of detailed studies for many years. However, the mobility of inorganic colloids is very low in compacted bentonite
s and in deep clay formations
because of the process of ultrafiltration
occurring in dense clay membrane.
The question is less clear for small organic colloids often mixed in porewater with truly dissolved organic molecules.
Colloid
A colloid is a substance microscopically dispersed evenly throughout another substance.A colloidal system consists of two separate phases: a dispersed phase and a continuous phase . A colloidal system may be solid, liquid, or gaseous.Many familiar substances are colloids, as shown in the chart below...
al particles serve as transport vector
of diverse contaminants in the surface water (sea water, lakes, rivers, fresh water bodies) and in underground water circulating in fissured rocks
(limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
, sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
, granite
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
, ...). The transport of colloidal particles in surface soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
s and in the ground
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
can also occur, depending on the soil structure
Soil structure
Soil structure is determined by how individual soil granules clump or bind together and aggregate, and therefore, the arrangement of soil pores between them...
, soil compaction
Soil compaction
In Geotechnical engineering, soil compaction is the process in which a stress applied to a soil causes densification as air is displaced from the pores between the soil grains. When stress is applied that causes densification due to water being displaced from between the soil grains then...
, and the particles size
Particle size (grain size)
Particle size, also called grain size, refers to the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. This is different from the crystallite size, which is the size of a single crystal inside the...
, but the importance of colloidal transport was only given sufficient attention during the '1980 years.
Radionuclides, heavy metals, and organic pollutants, easily sorb
Sorption
Sorption refers to the action of absorption* Absorption is the incorporation of a substance in one state into another of a different state ....
onto colloids suspended in water and that can easily act as contaminant carrier.
Various types of colloids are recognised: inorganic colloids (clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
particles, silicates, iron oxy-hydroxide
Ferrihydrite
Ferrihydrite is a widespread hydrous ferric oxyhydroxide mineral at the Earth's surface, and a likely constituent in extraterrestrial materials. It forms in several types of environments, from freshwater to marine systems, aquifers to hydrothermal hot springs and scales, soils, and areas affected...
s, ...), organic colloids (humic
Humic acid
Humic acid is a principal component of humic substances, which are the major organic constituents of soil , peat, coal, many upland streams, dystrophic lakes, and ocean water. It is produced by biodegradation of dead organic matter...
and fulvic substances). When heavy metals or radionuclides form their own pure colloids, the term "Eigencolloid
Eigencolloid
Eigencolloid is a term derived from the German language and used to designate colloids made of pure phases. Most often such colloids are formed by the hydrolysis of heavy metals cations or radionuclides, such as, e.g., Tc4, Th4, U4, Pu4, or Am3...
" is used to designate pure phases, e.g., Tc(OH)4, Th(OH)4, U(OH)4, Am(OH)3. Colloids have been suspected for the long range transport of plutonium on the Nevada Nuclear Test Site
Nevada Test Site
The Nevada National Security Site , previously the Nevada Test Site , is a United States Department of Energy reservation located in southeastern Nye County, Nevada, about northwest of the city of Las Vegas...
. They have been the subject of detailed studies for many years. However, the mobility of inorganic colloids is very low in compacted bentonite
Bentonite
Bentonite is an absorbent aluminium phyllosilicate, essentially impure clay consisting mostly of montmorillonite. There are different types of bentonite, each named after the respective dominant element, such as potassium , sodium , calcium , and aluminum . Experts debate a number of nomenclatorial...
s and in deep clay formations
because of the process of ultrafiltration
Ultrafiltration
Ultrafiltration is a variety of membrane filtration in which hydrostatic pressure forces a liquid against a semipermeable membrane. Suspended solids and solutes of high molecular weight are retained, while water and low molecular weight solutes pass through the membrane...
occurring in dense clay membrane.
The question is less clear for small organic colloids often mixed in porewater with truly dissolved organic molecules.
See also
- ColloidColloidA colloid is a substance microscopically dispersed evenly throughout another substance.A colloidal system consists of two separate phases: a dispersed phase and a continuous phase . A colloidal system may be solid, liquid, or gaseous.Many familiar substances are colloids, as shown in the chart below...
- DispersionDispersion (chemistry)A dispersion is a system in which particles are dispersed in a continuous phase of a different composition . See also emulsion. A dispersion is classified in a number of different ways, including how large the particles are in relation to the particles of the continuous phase, whether or not...
- EigencolloidEigencolloidEigencolloid is a term derived from the German language and used to designate colloids made of pure phases. Most often such colloids are formed by the hydrolysis of heavy metals cations or radionuclides, such as, e.g., Tc4, Th4, U4, Pu4, or Am3...
- FlocculationFlocculationFlocculation, in the field of chemistry, is a process wherein colloids come out of suspension in the form of floc or flakes by the addition of a clarifying agent. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended in a liquid and not actually...
- Hydrosol
- InterfaceInterface (chemistry)An interface is a surface forming a common boundary among two different phases, such as an insoluble solid and a liquid, two immiscible liquids or a liquid and an insoluble gas. The importance of the interface depends on which type of system is being treated: the bigger the quotient area/volume,...
- NanoparticleNanoparticleIn nanotechnology, a particle is defined as a small object that behaves as a whole unit in terms of its transport and properties. Particles are further classified according to size : in terms of diameter, coarse particles cover a range between 10,000 and 2,500 nanometers. Fine particles are sized...
- PeptizationPeptizationPeptization is the process responsible for the formation of stable dispersion of colloidal particles in water. This is particularly important in colloid chemistry or for precipitation reactions in an aqueous solution. When colloidal particles bear a same sign electric charge, they mutually repel...
- Sol (colloid)Sol (colloid)A sol is a colloidal suspension of very small solid particles in a continuous liquid medium. They are quite stable and show the Tyndall effect. Examples include blood, pigmented ink, and paint....
- Sol-gel
- SuspensionSuspension (chemistry)In chemistry, a suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometer. The internal phase is dispersed throughout the external phase through mechanical agitation, with the use of certain...
- Electrical double layer (EDL)
- Streaming potential
- Zeta potentialZeta potentialZeta potential is a scientific term for electrokinetic potential in colloidal systems. In the colloidal chemistry literature, it is usually denoted using the Greek letter zeta, hence ζ-potential...