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Brine is a high-concentration
solution Solution may refer to: * Solution (chemistry), a mixture where one substance is dissolved in another * Solution (equation), in mathematics ** Numerical solution, in numerical analysis, approximate solutions within specified error bounds * Soluti ...
of salt (NaCl) in water (H2O). In diverse contexts, ''brine'' may refer to the salt solutions ranging from about 3.5% (a typical concentration of seawater, on the lower end of that of solutions used for brining foods) up to about 26% (a typical
saturated solution In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubil ...
, depending on temperature). Brine forms naturally due to
evaporation Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humidi ...
of ground saline water but it is also generated in the mining of sodium chloride. Brine is used for food processing and cooking ( pickling and brining), for de-icing of roads and other structures, and in a number of technological processes. It is also a by-product of many industrial processes, such as
desalination Desalination is a process that takes away mineral components from saline water. More generally, desalination refers to the removal of salts and minerals from a target substance, as in Soil salinity control, soil desalination, which is an issue f ...
, so it requires
wastewater treatment Wastewater treatment is a process used to remove contaminants from wastewater and convert it into an effluent that can be returned to the water cycle. Once returned to the water cycle, the effluent creates an acceptable impact on the environme ...
for proper disposal or further utilization (
fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...
recovery).


In nature

Brines are produced in multiple ways in nature. Modification of seawater via evaporation results in the concentration of salts in the residual fluid, a characteristic geologic deposit called an evaporite is formed as different dissolved ions reach the saturation states of minerals, typically gypsum and halite. Dissolution of such salt deposits into water can produce brines as well. As seawater freezes, dissolved ions tend to remain in solution resulting in a fluid termed a cryogenic brine. At the time of formation, these cryogenic brines are by definition cooler than the freezing temperature of seawater and can produce a feature called a brinicle where cool brines descend, freezing the surrounding seawater. The brine cropping out at the surface as saltwater springs are known as "licks" or "salines". The contents of dissolved solids in groundwater vary highly from one location to another on Earth, both in terms of specific constituents (e.g. halite, anhydrite, carbonates, gypsum,
fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an inorganic, monatomic anion of fluorine, with the chemical formula (also written ), whose salts are typically white or colorless. Fluoride salts typ ...
-salts,
organic halide Halocarbon compounds are chemicals in which one or more carbon atoms are linked by covalent bonds with one or more halogen atoms ( fluorine, chlorine, bromine or iodine – ) resulting in the formation of organofluorine compounds, organoch ...
s, and sulfate-salts) and regarding the concentration level. Using one of several classification of groundwater based on total dissolved solids (TDS), brine is water containing more than 100,000 mg/L TDS. Brine is commonly produced during well completion operations, particularly after the
hydraulic fracturing Fracking (also known as hydraulic fracturing, hydrofracturing, or hydrofracking) is a well stimulation technique involving the fracturing of bedrock formations by a pressurized liquid. The process involves the high-pressure injection of "frack ...
of a well.


Uses


Culinary

Brine is a common agent in
food processing Food processing is the transformation of agricultural products into food, or of one form of food into other forms. Food processing includes many forms of processing foods, from grinding grain to make raw flour to home cooking to complex industr ...
and cooking. Brining is used to
preserve The word preserve may refer to: Common uses * Fruit preserves, a type of sweet spread or condiment * Nature reserve, an area of importance for wildlife, flora, fauna or other special interest, usually protected Arts, entertainment, and media ...
or season the food. Brining can be applied to vegetables,
cheese Cheese is a dairy product produced in wide ranges of flavors, textures, and forms by coagulation of the milk protein casein. It comprises proteins and fat from milk, usually the milk of cows, buffalo, goats, or sheep. During production, ...
s and fruit in a process known as pickling.
Meat Meat is animal flesh that is eaten as food. Humans have hunted, farmed, and scavenged animals for meat since prehistoric times. The establishment of settlements in the Neolithic Revolution allowed the domestication of animals such as chic ...
and fish are typically
steeped Steeping is the soaking of an organic solid, such as leaves, in a liquid (usually water) to extract flavours or to soften it. The specific process of teas being prepared for drinking by leaving the leaves in heated water to release the flavour a ...
in brine for shorter periods of time, as a form of marination, enhancing its tenderness and
flavor Flavor or flavour is either the sensory perception of taste or smell, or a flavoring in food that produces such perception. Flavor or flavour may also refer to: Science *Flavors (programming language), an early object-oriented extension to Lis ...
, or to enhance shelf period.


Chlorine production

Elemental chlorine can be produced by
electrolysis In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...
of brine ( NaCl solution). This process also produces
sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and alkali ...
(NaOH) and Hydrogen gas (H2). The reaction equations are as follows: * Cathode: 2 H+ + 2 e- -> H2 (^) * Anode: 2 Cl- -> Cl2 (^) + 2 e- * Overall process: 2 NaCl + 2 H2O -> Cl2 + H2 + 2 NaOH


Refrigerating fluid

Brine is used as a secondary
fluid In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...
in large refrigeration installations for the transport of thermal energy. Most commonly used brines are based on inexpensive calcium chloride and
sodium chloride Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...
. It is used because the addition of salt to water lowers the freezing temperature of the solution and the heat transport efficiency can be greatly enhanced for the comparatively low cost of the material. The lowest freezing point obtainable for NaCl brine is at the concentration of 23.3% NaCl by weight. This is called the eutectic point. Because of their corrosive properties salt-based brines have been replaced by organic liquids such as ethylene glycol. Sodium chloride brine spray is used on some fishing vessels to freeze fish. The brine temperature is generally . Air blast freezing temperatures are or lower. Given the higher temperature of brine, the system efficiency over air blast freezing can be higher. High-value fish usually are frozen at much lower temperatures, below the practical temperature limit for brine.


Water softening and purification

Brine is an auxiliary agent in water softening and water purification systems involving ion exchange technology. The most common example are household dishwashers, utilizing sodium chloride in form of
dishwasher salt Dishwasher salt is a particular grade of granulated, crystalline sodium chloride intended for regenerating the water softener circuit of household or industrial dishwashers. Analogous to water softener salt, dishwasher salt regenerates ion exc ...
. Brine is not involved in the purification process itself, but used for regeneration of ion-exchange resin on cyclical basis. The water being treated flows through the resin container until the resin is considered exhausted and water is purified to a desired level. Resin is then regenerated by sequentially backwashing the resin bed to remove accumulated solids, flushing removed ions from the resin with a concentrated solution of replacement ions, and rinsing the flushing solution from the resin. After treatment, ion-exchange resin beads saturated with calcium and magnesium ions from the treated water, are regenerated by soaking in brine containing 6–12% NaCl. The sodium ions from brine replace the calcium and magnesium ions on the beads.


De-icing

In lower temperatures, a brine solution can be used to de-ice or reduce freezing temperatures on roads.


Wastewater

Brine is a byproduct of many industrial processes, such as
desalination Desalination is a process that takes away mineral components from saline water. More generally, desalination refers to the removal of salts and minerals from a target substance, as in Soil salinity control, soil desalination, which is an issue f ...
, power plant cooling towers, produced water from oil and natural gas extraction, acid mine or acid rock drainage,
reverse osmosis Reverse osmosis (RO) is a water purification process that uses a partially permeable membrane to separate ions, unwanted molecules and larger particles from drinking water. In reverse osmosis, an applied pressure is used to overcome osmotic pre ...
reject, chlor-alkali wastewater treatment, pulp and paper mill effluent, and waste streams from food and beverage processing. Along with diluted salts, it can contain residues of pretreatment and cleaning chemicals, their reaction byproducts and heavy metals due to corrosion. Wastewater brine can pose a significant environmental hazard, both due to corrosive and sediment-forming effects of salts and toxicity of other chemicals diluted in it. Unpolluted brine from desalination plants and cooling towers can be returned to the ocean. To limit the environmental impact, it can be diluted with another stream of water, such as the outfall of a
wastewater treatment Wastewater treatment is a process used to remove contaminants from wastewater and convert it into an effluent that can be returned to the water cycle. Once returned to the water cycle, the effluent creates an acceptable impact on the environme ...
or power plant. Since brine is heavier than seawater and would accumulate on the ocean bottom, it requires methods to ensure proper diffusion, such as installing underwater diffusers in the
sewerage Sewerage (or sewage system) is the infrastructure that conveys sewage or surface runoff (stormwater, meltwater, rainwater) using sewers. It encompasses components such as receiving drainage, drains, manholes, pumping stations, storm overflows, a ...
. Other methods include drying in evaporation ponds, injecting to deep wells, and storing and reusing the brine for irrigation, de-icing or dust control purposes. Technologies for treatment of polluted brine include: membrane filtration processes, such as
reverse osmosis Reverse osmosis (RO) is a water purification process that uses a partially permeable membrane to separate ions, unwanted molecules and larger particles from drinking water. In reverse osmosis, an applied pressure is used to overcome osmotic pre ...
and
forward osmosis Forward osmosis (FO) is an osmotic process that, like reverse osmosis (RO), uses a semi-permeable membrane to effect separation of water from dissolved solutes. The driving force for this separation is an osmotic pressure gradient, such that a "d ...
; ion exchange processes such as electrodialysis or weak acid cation exchange; or evaporation processes, such as thermal brine concentrators and crystallizers employing
mechanical vapour recompression Mechanical vapor recompression (MVR) is an energy recovery process which can be used to recycle waste heat to improve efficiency. Typically, the compressed vapor is fed back to help heat the mother liquor in order to produce more vapor or steam. Ap ...
and steam. New methods for membrane brine concentration, employing osmotically assisted reverse osmosis and related processes, are beginning to gain ground as part of zero liquid discharge systems (ZLD).


Composition and purification

Brine consists of concentrated solution of Na+ and Cl ions. Sodium chloride per se does not exist in water: it is fully ionized. Other cations found in various brines include K+, Mg2+, Ca2+, and Sr2+. The latter three are problematic because they form scale and they react with soaps. Aside from chloride, brines sometimes contain Br and I and, most problematically, . Purification steps often include the addition of calcium oxide to precipitate solid magnesium hydroxide together with gypsum (CaSO4), which can be removed by filtration. Further purification is achieved by
fractional crystallization Fractional crystallization may refer to: * Fractional crystallization (chemistry), a process to separate different solutes from a solution * Fractional crystallization (geology) Fractional crystallization, or crystal fractionation, is one of the ...
. The resulting purified salt is called evaporated salt or vacuum salt.


See also

* * * Brine pools – Anoxic pockets of high salinity on the
ocean bottom The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as 'seabeds'. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...


References

{{Authority control Salts Coolants Refrigerants Hydrology Industrial minerals