Brine (or briny water) is a high-concentration solution of salt (typically sodium chloride or calcium chloride) in water. 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, depending on temperature). Brine forms naturally due to evaporation 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, so it requires wastewater treatment for proper disposal or further utilization (fresh water 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".
Uses
Iodine and bromine mining
Iodine, essential for human health, is obtained on a commercial scale from iodide-rich brines. The purification begins by converting iodide to hydroiodic acid, which is then oxidized to iodine using chlorine. The iodine is then separated by evaporation or adsorption.
Lithium and magnesium mining
Major deposits of lithium are in the form of brines.
Chlorine production
Elemental chlorine can be produced by electrolysis of brine (NaCl solution). This process also produces sodium hydroxide (NaOH) and hydrogen gas (H2). The reaction equations are as follows:
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Cathode:
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Anode:
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Overall process:
Refrigerating fluid
Brine (primarily cheap brines based on calcium chloride and sodium chloride
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.
Water softening and purification
Brine is used for regeneration of ion-exchange resins.
Culinary
Brine is a common agent in food processing and cooking. Brining is used to preserve or seasoning the food. Brining can be applied to , , fruit and some fish in a process known as pickling. Meat and fish are typically steeping in brine for shorter periods of time, as a form of marination, enhancing its meat tenderness and Flavoring, or to enhance shelf period.
De-icing
In lower temperatures, a brine solution can be used to De-icing or reduce freezing temperatures on roads.
Quenching
Quenching is a heat-treatment process when forging metals such as steel. A brine solution, along with oil and other substances, is commonly used to harden steel. When brine is used, there is an enhanced uniformity of the cooling process and heat transfer.[3. Luís H. Pizetta Zordão, Vinícius A. Oliveira, George E. Totten, Lauralice C.F. Canale, "Quenching power of aqueous salt solution", International Journal of Heat and Mass Transfer, Volume 140, 2019, pp. 807–818.]
Desalination
The desalination process consists of the separation of salts from an aqueous solution to obtain fresh water from a source of seawater or brackish water; and in turn, a discharge is generated, commonly called brine.
Characteristics
The characteristics of the discharge depend on different factors, such as the desalination technology used, salinity and Water quality of the water used, environmental and Oceanography characteristics, desalination process carried out, among others.
Dissolved chemicals
The discharge could contain Trace element used during the industrial treatments applies,such as Antiscalant,
Heavy metals
The materials used in SWRO plants are dominated by Nonmetal components and , since lower operating temperatures allow the construction of desalination plants with more Corrosion .
Discharge
The discharge is generally dumped back into the sea, through an underwater outfall or coastal release, due to its lower energy and economic cost compared to other discharge methods.
Marine environment
Brine discharge might lead to an increase in salinity above certain threshold levels that has the potential to affect Benthic zone, especially those more sensitive to osmotic pressure, finally having an effect on their abundance and diversity.
However, if appropriate mitigation measures are applied, the potential environmental impacts of discharges from SWRO plants can be correctly minimized.
Mitigation measures
The mitigation measures that are typically employed to prevent negatively impacting sensitive marine environments are listed below:
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A well-designed discharge mechanism, employing the use of efficient diffusers or pre-dilution of discharges with seawater
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An environmental evaluation study, which assesses the correct location of the discharge point, considering Geomorphology and oceanographic variables, such as Ocean current, bathymetry, and type of bottom, which favor a rapid mixing process of the discharges;
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The implementation of an adequate environmental surveillance program, which guarantees the correct operation of the desalination plants during their operational phase, allowing an accurate and early Diagnosis of potential environmental threats
Regulation
Currently, in many countries, such as Spain, Israel, Chile and Australia, the development of a rigorous environmental impact assessment process is required, both for the construction and operational phases.
Under the context of this environmental assessment process, numerous countries require compliance with an Environmental Monitoring Program (PVA), in order to evaluate the effectiveness of the preventive and corrective measures established during the environmental assessment process, and thus guarantee the operation of desalination plants without producing significant environmental impacts.
Wastewater
Brine is a byproduct of many industrial processes, such as desalination, power plant , produced water from oil and natural gas extraction, acid mine or acid rock drainage, reverse osmosis 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. From the desalination process, reject brine is produced, which proposes potential damages to the marine life and habitats.[5. A. Giwa, V. Dufour, F. Al Marzooqi, M. Al Kaabi, S.W. Hasan, "Brine management methods: Recent innovations and current status", Desalination, Volume 407, 2017, pp. 1–23] To limit the environmental impact, it can be diluted with another stream of water, such as the outfall of a Sewage treatment 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.[
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Technologies for treatment of polluted brine include: membrane filtration processes, such as reverse osmosis and forward osmosis; 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 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. 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, sulfate . 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. The resulting purified salt is called evaporated salt or vacuum salt.
See also
