Colloid-facilitated transport designates a transport process by which

colloid A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others exte ...

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 is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...

, ...). The transport of colloidal particles in surface

soil Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...

s and in the

ground Ground may refer to: Geology * Land, the solid terrestrial surface of the Earth * Soil, a mixture of clay, sand and organic matter present on the surface of the Earth Electricity * Ground (electricity), the reference point in an electrical circ ...

can also occur, depending on the

soil structure In geotechnical engineering, soil structure describes the arrangement of the solid parts of the soil and of the Pore space in soil, pore space located between them. It is determined by how individual soil granules clump, bind together, and Soil a ...

soil compaction In geotechnical engineering, soil compaction is the process in which 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 (or other ...

, 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 Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

particles, silicates, iron oxy-hydroxides, ...), organic colloids (

humic Humic substances (HS) are colored relatively recalcitrant organic compounds naturally formed during long-term decomposition and transformation of biomass residues. The color of humic substances varies from bright yellow to light or dark brown lead ...

and

fulvic Humic substances (HS) are colored relatively recalcitrant organic compounds naturally formed during long-term decomposition and transformation of biomass residues. The color of humic substances varies from bright yellow to light or dark brown lead ...

substances). When heavy metals or radionuclides form their own pure colloids, the term "''

Eigencolloid Eigencolloid is a term derived from the German language (''eigen'': own) and used to designate colloids made of pure phases, also known as intrinsic colloids. Eigencolloids are metal oxyhydroxide colloids on the nanometer scale formed by aggregatio ...

''" 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 Bentonite ( ) is an Absorption (chemistry), absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelli ...

s and in deep clay formations because of the process of

ultrafiltration Ultrafiltration (UF) is a variety of membrane filtration in which forces such as pressure or concentration gradients lead to a separation through a semipermeable membrane. Suspended solids and solutes of high molecular weight are retained in t ...

occurring in dense clay membrane. The question is less clear for small organic colloids often mixed in porewater with truly dissolved organic molecules.

References

External links

Colloidal transport in porous media

BELBar European project on the role of clay colloids in the transport of radionuclides for the deep geological disposal of radioactive waste

Software programs for modeling colloid-facilitated transport

The Geochemist's Workbench The Geochemist's Workbench (GWB) is an integrated set of interactive software tools for solving a range of problems in aqueous chemistry. The graphical user interface simplifies the use of the geochemical code. History The GWB package was ori ...

Hydrus Hydrus is a small constellation in the deep Southern Celestial Hemisphere, southern sky. It was one of twelve constellations created by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman and it first ap ...

Actinides Colloids Colloidal chemistry Transport by mode Physical chemistry {{chem-stub

See also

References

External links

Software programs for modeling colloid-facilitated transport