FLOCCULATION
In the field of chemistry, flocculation is the process by which colloidal particles emerge from a precipitate in flocculent or flake form from a suspension either spontaneously or by the addition of a clarifier. This process differs from precipitation in that the colloid is only suspended in the liquid as a stable dispersion before flocculation and is not actually dissolved in solution.
Coagulation and flocculation are important processes in water treatment. The coagulation action is to destabilize and aggregate particles by chemical interaction between coagulant and colloid, and flocculate and precipitate unstable particles by coagulating them into flocculation.
TERM DEFINITION
According to IUPAC, flocculation is “the process of contact and adhesion whereby particles of a dispersion form clusters of larger size”.
Basically, flocculation is the process of adding a flocculant to destabilize stable charged particles. At the same time, flocculation is a mixing technique that promotes agglomeration and contributes to particle settlement. The common coagulant is Al2 (SO4) 3• 14H2O.
Application field
WATER TREATMENT TECHNOLOGY
Flocculation and precipitation are widely used in the purification of drinking water and in the treatment of sewage, stormwater and industrial wastewater. Typical treatment processes include gratings, coagulation, flocculation, precipitation, particle filtration and disinfection.
SURFACE CHEMISTRY
In colloidal chemistry, flocculation is the process by which fine particles are clumped together. The floc may then float to the top of the liquid (opalescent), settle to the bottom of the liquid (precipitate) or easily filter out of the liquid. The flocculation behavior of soil colloid is closely related to freshwater quality. The high dispersion of soil colloid not only directly causes turbidity of surrounding water, but also causes eutrophication due to absorption of nutrients in rivers, lakes and even submarine hull.
PHYSICAL CHEMISTRY
For emulsions, flocculation describes the aggregation of single dispersed droplets so that the individual droplets do not lose their properties. Thus, flocculation is the initial step (droplet coalescence and final phase separation) that leads to further aging of the emulsion. Flocculants are used in mineral beneficiation, but can also be used in the design of physical properties of food and drugs.
DEFLOCCULATE
Reverse flocculation is the exact opposite of flocculation and is sometimes called gelling. Sodium silicate (Na2SiO3) is a typical example. Colloidal particles are usually dispersed at higher pH ranges, except for the low ionic strength of the solution and the dominance of monovalent metal cations. Additives that prevent colloid from forming flocculent are called antiflocculants. For reverse flocculation through electrostatic barriers, the effect of the reverse flocculant can be measured by zeta potential. According to the Encyclopedia Dictionary of Polymers, antiflocculation is “a state or state of dispersion of a solid in a liquid in which each solid particle remains independent and unconnected to its neighbors (much like an emulsifier). Non-flocculating suspensions have zero or very low yield values “.
Reverse flocculation can be a problem in sewage treatment plants as it often leads to sludge settling problems and deterioration of effluent quality.
Post time: Mar-03-2023