Flocculation, in the field of
chemistryChemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
, is a process wherein colloids come out of
suspensionIn 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...
in the form of floc or flakes by the addition of a
clarifying agent-Process:Particles finer than 0.1 µm in water remain continuously in motion due to electrostatic charge which causes them to repel each other. Once their electrostatic charge is neutralized by the use of coagulant chemical, the finer particles start to collide and agglomerate under the...
. The action differs from
precipitationPrecipitation is the formation of a solid in a solution or inside anothersolid during a chemical reaction or by diffusion in a solid. When the reaction occurs in a liquid, the solid formed is called the precipitate, or when compacted by a centrifuge, a pellet. The liquid remaining above the solid...
in that, prior to flocculation, colloids are merely suspended in a liquid and not actually dissolved in a
solutionIn chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...
. In the flocculated system, there is no formation of a cake, since all the flocs are in the suspension.
Term definition
According to the IUPAC definition, flocculation is "a process of contact and adhesion whereby the particles of a dispersion form larger-size clusters." Flocculation is synonymous with
agglomerationParticle aggregation in materials science is direct mutual attraction between particles via van der Waals forces or chemical bonding....
, aggregation, and
coagulationCoagulation may refer to:* Coagulation, in colloid chemistry, a process in which dispersed colloidal particles agglomerate. See flocculation* Coagulation of blood* Coagulation , the coagulation of milk into curd by rennet or acid...
/
coalescenceIn chemistry, coalescence is a process in which two phase domains of the same composition come together and form a larger phase domain.-References:*...
.
Surface chemistry
In colloid chemistry, flocculation refers to the process by which fine particulates are caused to clump together into a floc. The floc may then float to the top of the liquid,
settleSettling is the process by which particulates settle to the bottom of a liquid and form a sediment. Particles that experience a force, either due to gravity or due to centrifugal motion will tend to move in a uniform manner in the direction exerted by that force...
to the bottom of the liquid, or be readily
filteredFiltration is commonly the mechanical or physical operation which is used for the separation of solids from fluids by interposing a medium through which only the fluid can pass...
from the liquid.
Physical chemistry
For
emulsionAn emulsion is a mixture of two or more liquids that are normally immiscible . Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion is used when both the dispersed and the...
s, flocculation describes clustering of individual dispersed droplets together, whereby the individual droplets do not lose their identity. Flocculation is thus the initial step leading to further aging of the emulsion (droplet coalescence and the ultimate separation of the phases).
Civil engineering/earth sciences
In
civil engineeringCivil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including works like roads, bridges, canals, dams, and buildings...
, and in the earth sciences, flocculation is a condition in which clays, polymers or other small charged particles become attached and form a fragile
structureStructure is a fundamental, tangible or intangible notion referring to the recognition, observation, nature, and permanence of patterns and relationships of entities. This notion may itself be an object, such as a built structure, or an attribute, such as the structure of society...
, a floc. In dispersed
clayClay 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...
slurriesA slurry is, in general, a thick suspension of solids in a liquid.-Examples of slurries:Examples of slurries include:* Lahars* A mixture of water and cement to form concrete* A mixture of water, gelling agent, and oxidizers used as an explosive...
, flocculation occurs after mechanical agitation ceases and the dispersed clay platelets spontaneously form flocs because of attractions between negative face charges and positive edge charges.
Biology
In
biologyBiology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
, the process is used to refer to the asexual aggregation of microorganisms.
Cheese production
Flocculation is widely employed to measure the progress of
curdCurds are a dairy product obtained by curdling milk with rennet or an edible acidic substance such as lemon juice or vinegar, and then draining off the liquid portion. The increased acidity causes the milk proteins to tangle into solid masses, or curds. The remaining liquid, which contains only...
formation while in the initial stages of making many
cheeseCheese is a generic term for a diverse group of milk-based food products. Cheese is produced throughout the world in wide-ranging flavors, textures, and forms....
s to determine how long the curds must set. The reaction involving the
rennetRennet is a complex of enzymes produced in any mammalian stomach to digest the mother's milk, and is often used in the production of cheese. Rennet contains many enzymes, including a proteolytic enzyme that coagulates the milk, causing it to separate into solids and liquid...
micelles are modeled by Smoluchowski Kinetics.
Brewing
Flocculation is used to measure the rate at which yeast settles to the bottom of the fermentation vessel. Yeast strains with higher flocculation will settle out of the beer faster once fermentation is complete.
Water treatment
Flocculation and sedimentation are widely employed in the
purificationWater purification is the process of removing undesirable chemicals, materials, and biological contaminants from contaminated water. The goal is to produce water fit for a specific purpose...
of
drinking waterDrinking water or potable water is water pure enough to be consumed or used with low risk of immediate or long term harm. In most developed countries, the water supplied to households, commerce and industry is all of drinking water standard, even though only a very small proportion is actually...
as well as
sewage treatmentSewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants...
, stormwater treatment and treatment of other industrial wastewater streams.
Deflocculation
A deflocculant is a chemical additive to prevent a colloid from coming out of suspension or to thin suspensions or slurries. It is used to reduce
viscosityViscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
or prevent flocculation and is sometimes incorrectly called a "
dispersantA dispersant or a dispersing agent or a plasticizer or a superplasticizer is either a non-surface active polymer or a surface-active substance added to a suspension, usually a colloid, to improve the separation of particles and to prevent settling or clumping...
." Most deflocculants are low-molecular-weight anionic polymers that neutralize positive charges on suspended particles, in particular
clayClay 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...
s and aryl-alkyl derivative of sulfonic acid. Examples include
polyphosphateTriphosphates are salts or esters of polymeric oxyanions formed from tetrahedral PO4 structural units linked together by sharing oxygen atoms. When two corners are shared the polyphosphate may have a linear chain structure or a cyclic ring structure. In biology the polyphosphate esters AMP, ADP...
s,
lignosulfonatesLignosulfonates, or sulfonated lignin, are water-soluble anionic polyelectrolyte polymers: they are byproducts from the production of wood pulp using sulfite pulping....
, quebracho tannins, and various water-soluble synthetic polymers.
Deflocculation is also used to describe the undesired effect in an
activated sludgeActivated sludge is a process for treating sewage and industrial wastewaters using air and a biological floc composed of bacteria and protozoans.-Purpose:...
basin if the sludge is subjected to high-speed mixing. In general, deflocculation can be prevented or reduced by applying gentle mixing (e.g., by using
submersible propeller mixersA submersible mixer is a mechanical device that is used to mix sludge tanks and other liquid volumes. Submersible mixers are often used in sewage treatment plants to keep solids in suspension in the various process tanks and/or sludge holding tanks....
that utilize large/wide propeller blades and operate at low rotational speed).
See also
- Aggregation (disambiguation)
- Algaculture
Algaculture is a form of aquaculture involving the farming of species of algae.The majority of algae that are intentionally cultivated fall into the category of microalgae...
- Clay-water interaction
Clay-water interaction is an all-inclusive term to describe various progressive interactions between clay minerals and water. In the dry state, clay packets exist in face-to-face stacks like a deck of playing cards, but clay packets begin to change when exposed to water...
- Coagulation (disambiguation)
Coagulation may refer to:* Coagulation, in colloid chemistry, a process in which dispersed colloidal particles agglomerate. See flocculation* Coagulation of blood* Coagulation , the coagulation of milk into curd by rennet or acid...
- Drilling mud
- Isoelectric point
The isoelectric point , sometimes abbreviated to IEP, is the pH at which a particular molecule or surface carries no net electrical charge....
- Lamella clarifier
A lamellaR clarifier is a water treatment process that features a rack of inclined metal plates, which cause flocculated material to precipitate from water that flows across the plates....
- Ostwald ripening
right|thumb|300px|Basic schematic of the Ostwald ripening process Ostwald ripening is an observed phenomenon in solid solutions or liquid sols which describes the change of an inhomogeneous structure over time...
- Seawater
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...
- Sedimentation
Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained, and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration...
- 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...
- Yeast flocculation
Yeast flocculation typically refers to the clumping together of brewing yeast once the sugar in a beer has been fermented into ethyl alcohol...
- Smoluchowski coagulation equation
The Smoluchowski coagulation equation is an integrodifferential equation introduced by Marian Smoluchowski in a seminal 1916 publication , describing the evolution of the number density of particles of size x at a time t...
- Einstein–Smoluchowski relation
In physics the Einstein relation is a previously unexpected connection revealed independently by Albert Einstein in 1905 and by Marian Smoluchowski in their papers on Brownian motion...
Further reading
- John Gregory (2006), Particles in water: properties and processes, Taylor & Francis, ISBN 1-58716-085-4