Editing Flocculation

{{short description|Process by which colloidal particles come out of suspension to precipitate as floc or flake}}
{{redirect|Flocculent|the galaxy type|Flocculent spiral galaxy}}
{{Quote box
 |title =[[International Union of Pure and Applied Chemistry|IUPAC]] definition<ref name="goldbook.iupac.org">{{cite journal|title=Terminology of polymers and polymerization processes in dispersed systems (IUPAC Recommendations 2011)|journal=[[Pure and Applied Chemistry]]|year=2011|volume=83|issue=12|pages=2229–2259|doi=10.1351/PAC-REC-10-06-03|url=http://pac.iupac.org/publications/pac/pdf/2011/pdf/8312x2229.pdf|last1=Slomkowski|first1=Stanislaw|last2=Alemán|first2=José V.|last3=Gilbert|first3=Robert G.|last4=Hess|first4=Michael|last5=Horie|first5=Kazuyuki|last6=Jones|first6=Richard G.|last7=Kubisa|first7=Przemyslaw|last8=Meisel|first8=Ingrid|last9=Mormann|first9=Werner|last10=Penczek|first10=Stanisław|last11=Stepto|first11=Robert F. T.|s2cid=96812603|access-date=2013-07-27|archive-date=2013-10-20|archive-url=https://web.archive.org/web/20131020164408/http://pac.iupac.org/publications/pac/pdf/2011/pdf/8312x2229.pdf|url-status=dead}}</ref>
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 |quote = '''Flocculation (in polymer science)''': Reversible formation of aggregates in which the particles are not in physical contact.
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'''Agglomeration (except in polymer science)'''<br />'''Coagulation (except in polymer science)'''<br />'''Flocculation (except in polymer science)'''<br />Process of contact and adhesion whereby dispersed molecules or particles are held together by weak physical interactions ultimately leading to phase separation by the formation of precipitates of larger than colloidal size.
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* In contrast to aggregation, agglomeration is a reversible process.
* The definition proposed here is recommended for distinguishing agglomeration from aggregation. The particles that comprise agglomerates can be dispersed again.
* This quotation is from [[Compendium of Macromolecular Nomenclature|the Purple Book]] (Compendium of Polymer Terminology and Nomenclature: IUPAC Recommendations, 2008).<ref>{{cite book|title=Compendium of Polymer Terminology and Nomenclature (IUPAC Recommendations 2008) "The Purple Book"|year=2009|publisher=RSC Publishing|isbn=978-0-85404-491-7|edition=2nd|editor1=Richard G. Jones |editor2=Edward S. Wilks |editor3=W. Val Metanomski |editor4=Jaroslav Kahovec |editor5=Michael Hess |editor6=Robert Stepto |editor7=Tatsuki Kitayama }}</ref>}}
[[File:Flocculation settling time edited 0.webm|thumb|4x speed video of floc settling after adding flocculant polymers during a [[jar test]].]]

In [[colloidal chemistry]], '''flocculation''' is a process by which [[colloid]]al particles come out of [[Suspension (chemistry)|suspension]] to sediment in the form of floc or flake, either spontaneously or due to the addition of a [[clarifying agent]]. The action differs from [[Precipitation (chemistry)|precipitation]] in that, prior to flocculation, colloids are merely suspended, under the form of a stable dispersion (where the internal phase (solid) is dispersed throughout the external phase (fluid) through mechanical agitation) and are not truly dissolved in [[Solution (chemistry)|solution]].

[[Coagulation (water treatment)|Coagulation]] and flocculation are important processes in fermentation and water treatment with coagulation aimed to destabilize and aggregate particles through chemical interactions between the coagulant and colloids, and flocculation to sediment the destabilized particles by causing their aggregation into floc.{{Clarify|date=November 2020}}

== 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 [[particle aggregation|agglomeration]] and coagulation/[[coalescence (chemistry)|coalescence]].<ref>{{GoldBookRef |title = flocculation|file = F02429}}</ref><ref>{{cite book
|last = Hubbard|first = Arthur T.|title = Encyclopedia of Surface and Colloid Science|publisher = CRC Press|year = 2004|url = https://books.google.com/books?id=vnb2X7Q8_cYC&q=ostwald+ripening+emulsion+polymerization&pg=PA4230|access-date = 2007-11-13|isbn = 978-0-8247-0759-0|page = 4230}}</ref>

Basically, coagulation is a process of addition of coagulant to destabilize a stabilized charged particle. Meanwhile, flocculation is a technique that promotes agglomeration and assists in the settling of particles. The most common used coagulant is [[alum]], Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>·14H<sub>2</sub>O.

The chemical reaction involved:

:Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> · 14 H<sub>2</sub>O → 2 Al(OH)<sub>3</sub>{{abbr|(s)|solid}} + 6 H<sup>+</sup> + 3 {{chem|SO|4|2-}} + 8 H<sub>2</sub>O

During flocculation, gentle mixing accelerates the rate of particle collision, and the destabilized particles are further aggregated and enmeshed into larger precipitates. Flocculation is affected by several parameters, including mixing shear and intensity, time and [[pH]]. The product of the mixing intensity and mixing time is used to describe flocculation processes.

=== Jar test ===
The process by which the dosage and choice of flocculant are selected is called a jar test. The equipment used for jar testing consists of one or more beakers, each equipped with a paddle mixer. After the addition of flocculants, rapid mixing takes place, followed by slow mixing and later the sedimentation process. Samples can then be taken from the aqueous phase in each beaker. <ref>{{cite book |author=<!--Staff writer(s); no by-line.--> |date=2011-06-01 |title=Operational Control of Coagulation and Filtration Processes (M37): AWWA Manual of Practice |url= https://engage.awwa.org/PersonifyEbusiness/Store/Product-Details/productId/6726|publisher= American Water Works Association|isbn=978-1583218013}}</ref>

== Mechanisms ==
One mechanism for flocculation is [[Coacervate|coacervation]].

== Applications ==
=== Surface chemistry ===
In [[colloid chemistry]], flocculation refers to the process by which fine [[particulate]]s are caused to clump together into a floc. The floc may then float to the top of the liquid (creaming), [[settling|settle]] to the bottom of the liquid ([[sedimentation]]), or be readily [[filtration|filtered]] from the liquid. Flocculation behavior of soil colloids is closely related to freshwater quality. High dispersibility of soil colloids not only directly causes turbidity of the surrounding water but it also induces [[eutrophication]] due to the adsorption of nutritional substances in rivers and lakes and even boats under the sea.

=== Physical chemistry ===
For [[emulsion]]s, flocculation describes clustering of individual dispersed droplets together, whereby the individual droplets do not lose their identity.<ref>Adamson A.W. and Gast A.P. (1997) "Physical Chemistry of Surfaces", John Wiley and Sons.</ref> Flocculation is thus the initial step leading to further ageing of the emulsion (droplet coalescence and the ultimate separation of the phases). Flocculation is used in mineral dressing,<ref>Investigation of laws of selective flocculation of coals with synthetic latexes / P. V. Sergeev, V. S. Biletskyy // ICCS’97. 7–12 September 1997, Essen, Germany. V. 1.  pp. 503–506.</ref> but can be also used in the design of physical properties of food and pharmaceutical products. <ref>{{Cite journal|last1=Fuhrmann|first1=Philipp L.|last2=Sala|first2=Guido|last3=Stieger|first3=Markus|last4=Scholten|first4=Elke|date=2019-08-01|title=Clustering of oil droplets in o/w emulsions: Controlling cluster size and interaction strength|journal=Food Research International|volume=122|pages=537–547|doi=10.1016/j.foodres.2019.04.027|pmid=31229109|issn=0963-9969|doi-access=free}}</ref>

=== Medical diagnostics ===
In a [[medical laboratory]], flocculation is the core principle used in various diagnostic tests, for example the [[rapid plasma reagin]] test.<ref>{{Cite journal |last1=Arora |first1=Satyam |last2=Doda |first2=Veena |last3=Rani |first3=Sunita |last4=Kotwal |first4=Urvershi |date=2015 |title=Rapid plasma reagin test: High false positivity or important marker of high risk behavior |journal=Asian Journal of Transfusion Science |volume=9 |issue=1 |pages=109 |doi=10.4103/0973-6247.150979 |issn=0973-6247 |pmc=4339923 |pmid=25722593 |doi-access=free }}</ref>
{{seealso|Porges-Meier reaction}}

=== Civil engineering/earth sciences ===
In [[civil engineering]], and in the [[earth sciences]], flocculation is a condition in which [[clay]]s, polymers or other small charged particles become attached and form a fragile [[structure]], a floc. In dispersed clay [[Slurry|slurries]],
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 ===
{{See also|Yeast flocculation#Process}}
Flocculation is used in [[biotechnology]] applications in conjunction with [[microfiltration]] to improve the efficiency of biological feeds. The addition of synthetic flocculants to the [[bioreactor]] can increase the average particle size making microfiltration more efficient. When flocculants are not added, cakes form and accumulate causing low cell viability. Positively charged flocculants work better than negatively charged ones since the cells are generally negatively charged.<ref>{{Cite journal|title = Flocculation of biological cells: Experiment vs. theory|journal = AIChE Journal|date = 2003-07-01|issn = 1547-5905|pages = 1687–1701|volume = 49|issue = 7|doi = 10.1002/aic.690490709|first1 = Binbing|last1 = Han|first2 = S.|last2 = Akeprathumchai|first3 = S. R.|last3 = Wickramasinghe|first4 = X.|last4 = Qian| bibcode=2003AIChE..49.1687H }}</ref>

=== Cheese industry ===
Flocculation is widely employed to measure the progress of [[curd]] formation in the initial stages of [[cheese]] making to determine how long the curds must set.<ref name="fox2" /> The reaction involving the [[rennet]] [[micelle]]s are modeled by [[Einstein relation (kinetic theory)|Smoluchowski kinetics]].<ref name="fox2">{{Cite book
|last = Fox |first = Patrick F. |title = Cheese Volume 1: Chemistry, Physics, and Microbiology |edition = 2nd |publisher = Aspen Publishers |year = 1999 |location = [[Gaithersburg, Maryland]]|pages = 144–150|isbn = 978-0-8342-1378-4}}</ref> During the renneting of milk the micelles can approach one another and flocculate, a process that involves [[hydrolysis]] of molecules and macropeptides.<ref>{{Cite book|title = Cheese - Chemistry, Physics and Microbiology|last = Fox|first = Patrick F.|publisher = Elsevier|year = 2004|isbn = 978-0-12-263653-0|pages = 72|edition = 3rd}}</ref>

Flocculation is also used during cheese [[wastewater treatment]]. Three different coagulants are mainly used:<ref>{{Cite journal |title = Treatment of Cheese Whey Wastewater: Combined Coagulation−Flocculation and Aerobic Biodegradation |journal = Journal of Agricultural and Food Chemistry |date = 2010-07-14 |issn = 0021-8561 |pages = 7871–7877 |volume = 58 |issue = 13 |doi = 10.1021/jf100602j |first1 = Javier|last1 = Rivas |first2 = Ana R. |last2 = Prazeres |first3 = Fatima |last3 = Carvalho |first4 = Fernando |last4 = Beltrán |pmid=20557068 |bibcode = 2010JAFC...58.7871R |hdl=20.500.12207/540 |hdl-access = free}}</ref>
* FeSO<sub>4</sub> ([[iron(II) sulfate]])
* Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> ([[aluminium sulfate]])
* FeCl<sub>3</sub> ([[iron(III) chloride]])

=== Brewing ===
{{main|Yeast flocculation}}
In the brewing industry flocculation has a different meaning. It is a very important process in [[fermentation]] during the production of beer where cells form macroscopic flocs. These flocs cause the yeast to sediment or rise to the top of a fermentation at the end of the fermentation. Subsequently, the yeast can be collected (cropped) from the top ([[ale]] fermentation) or the bottom ([[lager]] fermentation) of the fermenter in order to be reused for the next fermentation.

[[Yeast flocculation]] is partially determined by the calcium concentration, often in the 50-100ppm range.<ref>{{cite web|last1=Brungard |first1 =Martin|title=Water Knowledge|url=https://sites.google.com/site/brunwater/water-knowledge|website=Bru'n Water|date = 20 February 2018}}</ref>  Calcium salts can be added to cause flocculation, or the process can be reversed by removing calcium by adding [[phosphate]] to form insoluble calcium phosphate, adding excess [[sulfate]] to form insoluble calcium sulfate, or adding [[EDTA]] to [[chelate]] the calcium ions. While it appears similar to sedimentation in colloidal dispersions, the mechanisms are different.<ref>{{Cite journal|title = Flocculation in Saccharomyces cerevisiae |journal=Food Res. Int.|date = 1999|pages =421–440|volume = 31|first1 = Y-L.|last1 = Jin |first2 = R.A..|last2 = Speers|issue=6–7 |doi=10.1016/S0963-9969(99)00021-6 }}</ref>

=== Water treatment process ===
[[File:The coagulation and filtration processes at a drinking water treatment plant. (14868618507).jpg|thumb|Coagulation-flocculation process in a water treatment system]]
Flocculation and [[sedimentation (water treatment)|sedimentation]] are widely employed in the [[water purification|purification]] of [[drinking water]] as well as in [[sewage treatment]], storm-water treatment and treatment of industrial wastewater streams. 
For drinking water, typical treatment processes consist of grates, coagulation, flocculation, sedimentation, granular filtration and disinfection.<ref>{{Cite web |url = http://app.knovel.com/hotlink/toc/id:kpWTPME003/water-treatment-process/water-treatment-process |title=Water Treatment Process Monitoring and Evaluation |date=2014-04-17 |access-date=2015-10-14 |website = Knovel |publisher = American Water Works Association (AWWA) |last = Beverly |first = Richard P}}</ref> The coagulation and flocculation steps are similar, causing particles to aggregate and fall out of solution, but may use different chemicals or physical movement of water.<ref name="Engelhardt" /> A variety of salts may be added to adjust the pH and act as [[clarifying agent]]s, depending on the water chemistry. These include [[sodium hydroxide]], [[calcium hydroxide]], [[aluminum sulfate]], [[aluminum oxide]], [[ferric sulfate]], [[ferric chloride]], [[sodium aluminate]], with flocculant aids [[polyaluminum chloride]], [[polyferric chloride]].<ref name="Engelhardt" />  A variety of [[cationic]], [[anionic]], and [[non-ionic]] [[polymer]]s are also used, typically with a [[molecular weight]] below 500,000.<ref name="Engelhardt" /> [[Polydiallyldimethyl ammonium chloride]] (polyDADMAC) and epiDMA (a [[copolymer]] of [[epichlorohydrin]] and [[dimethylamine]]) are common choices, though these can produce carcinogenic [[nitrosamine]]s.<ref name="Engelhardt" /> Sand, powerdered [[activated carbon]], and clay may also be used as [[nucleating agents]]; in some cases, these are re-used after extraction.<ref name="Engelhardt">{{cite web |title=Coagulation, Flocculation and Clarification of Drinking Water |author=Terry L. Engelhardt |date=April 2010 |url=https://sswm.info/sites/default/files/reference_attachments/ENGELHARDT%202010%20Coagulation%20Flocculation%20and%20Clarification.pdf}}</ref>

Biopolymers, especially, [[chitosan]], are increasingly popular as environmentally friendly flocculants.<ref>{{Cite journal |last1=Lamanna |first1=Leonardo |last2=Giacoia |first2=Gabriele |last3=Friuli |first3=Marco |last4=Leone |first4=Gabriella |last5=Carlucci |first5=Nicola |last6=Russo |first6=Fabrizio |last7=Sannino |first7=Alessandro |last8=Demitri |first8=Christian |date=2023-06-13 |title=Oil–Water Emulsion Flocculation through Chitosan Desolubilization Driven by pH Variation |journal=ACS Omega |language=en |volume=8 |issue=23 |pages=20708–20713 |doi=10.1021/acsomega.3c01257 |issn=2470-1343 |pmc=10268613 |pmid=37332801}}</ref> Chitosan is not only biodegradable but also exhibits a unique ability to bind with a wide range of contaminants, including heavy metals and organic pollutants, effectively removing them from water sources.<ref>{{Cite journal |last1=Pal |first1=Preeti |last2=Pal |first2=Anjali |last3=Nakashima |first3=Kazunori |last4=Yadav |first4=Brijesh Kumar |date=2021-03-01 |title=Applications of chitosan in environmental remediation: A review |url=https://www.sciencedirect.com/science/article/pii/S0045653520331313 |journal=Chemosphere |volume=266 |pages=128934 |doi=10.1016/j.chemosphere.2020.128934 |pmid=33246700 |bibcode=2021Chmsp.26628934P |issn=0045-6535|url-access=subscription }}</ref> 

Flocculation provides promising results for removing fine particles and treating stormwater runoff from transportation construction projects, but are not used by most state departments of transportation in the U.S. This may be due to regulative restrictions or insufficient guidance for [[soil]] sampling requirements in light of changing soil characteristics. States that must achieve a numeric turbidity limit are more inclined to use flocculants to ensure the appropriate level of treatment.<ref>{{Cite journal |last=Kazaz |first=Billur |date=July 2021 |title=State-of-the-Practice Review on the Use of Flocculants for Construction Stormwater Management in the United States |url=https://journals.sagepub.com/doi/10.1177/0361198121995192 |journal=Transportation Research Record |volume=2675 |issue=7 |pages=248–258 |doi=10.1177/0361198121995192 |via=Sage|url-access=subscription }}</ref>

== Deflocculation ==
{{Main|Peptization}}
Deflocculation is the opposite of flocculation, sometimes known as [[peptization]]. [[Sodium silicate]] (Na<sub>2</sub>SiO<sub>3</sub>) is a typical example. Usually, in higher [[pH]] ranges, in addition to low [[ionic strength]] of solutions and domination of monovalent metal [[cation]]s, the [[colloid]]al particles can be dispersed.<ref name="Deflocculation">{{Cite book|publisher = Springer New York|date = 2007-01-01|isbn = 978-0-387-31021-3|pages = 265|doi = 10.1007/978-0-387-30160-0_3313|editor-first = Jan W.|editor-last = Gooch|title = Encyclopedic Dictionary of Polymers|chapter = Deflocculation }}</ref>
The additive that prevents the colloids from forming flocs is called a deflocculant. For deflocculation imparted through electrostatic barriers, the efficacy of a deflocculant can be gauged in terms of [[zeta potential]]. According to the Encyclopedic Dictionary of Polymers deflocculation is ''"''a state or condition of a dispersion of a solid in a liquid in which each solid particle remains independent and unassociated with adjacent particles (much like [[Emulsion|emulsifier]]). A deflocculated suspension shows zero or very low yield value".<ref name="Deflocculation"/>

Deflocculation can be a problem in wastewater treatment plants, as it commonly causes problems with [[sludge]] settling and deterioration of the [[effluent]] quality.

== See also ==
{{div col}}
* {{annotated link|Algaculture}}
* {{annotated link|Clay–water interaction}}
* {{annotated link|Deposition (geology)}}
* {{annotated link|Depletion force}}
* {{annotated link|DLVO theory}} (stability of colloids)
* {{annotated link|Drilling fluid|aka=drilling mud}}
* {{annotated link|Isoelectric point}}
* {{annotated link|Lamella clarifier}}
* {{annotated link|Particle aggregation}}
* {{annotated link|Ostwald ripening}}
* {{annotated link|Seawater}}
* {{annotated link|Smoluchowski coagulation equation}}
* {{annotated link|Soil structure}}
* {{annotated link|Syneresis (chemistry)}}
{{div col end}}

== References ==
{{Reflist}}

== Further reading ==
* John Gregory (2006), ''Particles in water: properties and processes'', Taylor & Francis, {{ISBN|1-58716-085-4}}
* John C. Crittenden, R. Rhodes Trussell, David W. Hand, Kerry J. Howe, George Tchobanoglous (2012), ''MWH's water treatment: principles and design, third edition'', John Wiley & Sons, {{ISBN|978-0-470-40539-0}}

{{Separation processes}}
{{Aerosol terminology|state=collapsed}}

[[Category:Metallurgy]]
[[Category:Chemical processes]]
[[Category:Separation processes]]
[[Category:Sewerage]]
[[Category:Water treatment]]

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