Bromine

Typical wastewaters

• coal power plant flue gas desulfurisation wastewater bromide Br⁻ in the scrubber water, limited to 0.2 mg/L daily under the voluntary incentives programme the only bromide effluent limit read
• oil and gas produced water and brines bromide Br⁻ as a conservative anion of the brine WHO names brine and oilfield water, road salt and industrial effluent as anthropogenic bromide sources
• chlor-alkali and hypochlorite production bromide impurity in the salt and caustic, oxidised to bromate BrO₃⁻ in the concentrated high pH hypochlorite; the same in on-site electrolytic hypochlorite from bromide bearing brine a bromate source without ozone
• textile dyeing and finishing organically bound bromine from brominated flame retardant finishing, counted in AOX (BAT-AEL 0.1 to 0.4 mg/L) bromate from sulfur dye dyeing is named by the element entry, not by this source

1 · Identity

Symbol, number

Br, 35

Oxidation states in water

-1 bromide, Br⁻, the natural form, conservative and unsorbed; +1 hypobromous acid and hypobromite (HOBr, OBr⁻) and bromamines, formed transiently when ozone or chlorine meets bromide; +5 bromate, BrO₃⁻, the stable end product of ozonation; organic bromine in brominated disinfection by-products and in brominated flame retardants; 0 as elemental bromine in the disinfectant chemicals themselves.

Note

The element entry covers brine extraction, flame retardants and the chlor-alkali route to bromate; this chapter is the disinfection chemistry.

2 · Occurrence in water

Natural sources

Bromide occurs with sodium chloride in smaller amounts: seawater 65 mg/L to well over 80 mg/L in confined seas, fresh water from trace amounts to about 0.5 mg/L, desalinated water up to 1 mg/L (WHO). Bromide in surface water and groundwater fluctuates seasonally and rises with saltwater intrusion in drought and with pollution (WHO brominated acetic acids sheet).

Anthropogenic sources

Bromide from brine and oilfield water, road salt and industrial effluent; bromide in flue gas desulfurisation wastewater, limited to 0.2 mg/L under the US voluntary incentives programme for power plants; bromate impurity in sodium hypochlorite made from bromide contaminated salt and caustic, and in on-site electrolytic hypochlorite from bromide bearing brine (WHO); bromate from sulfur dye textile dyeing and permanent wave neutralisers; brominated flame retardants leaching from finished textiles and plastics and bromine impurities in chlor-alkali and EDC production (element entry).

3 · Speciation

Bromide is conservative: it neither sorbs nor precipitates in fresh water and survives every conventional process. Ozone oxidises it to hypobromite and hypobromous acid; hypobromous acid brominates natural organic matter and reacts with ammonia to bromamines, while hypobromite is oxidised further by ozone and hydroxyl radicals to bromate. Low pH favours HOBr and the brominated organics, high pH favours OBr⁻ and bromate. Chlorine oxidises bromide to hypobromous acid too, which is why chlorinated bromide waters carry bromoform, bromodichloromethane, dibromochloromethane and brominated acetic acids. Chlorine dioxide does not oxidise bromide and makes no bromate under treatment conditions. Bromate, once formed, is stable, non volatile and only slightly sorbed; its long term fate is slow reduction by organic matter back to bromide (WHO).

Solubility

Bromide salts of the common cations are very soluble; potassium bromate dissolves at 133 g/L at 40 C and sodium bromate at 275 g/L at 8 C (WHO). Nothing precipitates bromide or bromate in water treatment.

Hydrolysis

Hypobromous acid is a weak acid and bromous and bromic acids are weaker than hydrobromic acid (WHO); the HOBr dissociation constant is not printed in the sources read, so none is quoted. Basic hypobromite solutions are stable at 0 C but disproportionate rapidly to bromide and bromate at about 50 C and above (WHO citing Cotton and Wilkinson).

Complexation

Bromide forms no complexes of consequence in fresh water; silver ions are sequestered by bromide among other anions (WHO silver document). Not otherwise addressed.

Precipitates

None in treatment; silver bromide in the analytical chloride removal cartridge.

4 · Role in treatment

5 · Removal and control

6 · Analytics

Sampling pitfalls

Bromate samples must not be exposed to residual ozone or hypochlorite after collection or bromate keeps forming; quench the oxidant at sampling (EPA 300.1 preservation was not read, so no reagent is named). High chloride and high carbonate mask bromate on the column (WHO). Bromide itself is stable and needs no preservation. Hypochlorite stock solutions should be assayed for bromate separately.

7 · Regulatory limits

Limits change, and many are set locally. Treat these as the published values to start from, not as your compliance target: check the standard in force at your site and the numbers written into your own permit.

8 · Health and environmental effects

Toxicity

Bromide: sedative at pharmacological doses; JMPR ADI 0 to 1 mg/kg body weight (1966, 1988) and a conservative human NOEL of 4 mg/kg per day giving 0 to 0.4 mg/kg; dietary intake 2 to 9 mg/day. Bromate: IARC Group 2B, mutagenic in vitro and in vivo, kidney tumours, mesotheliomas and thyroid tumours in rats; drinking water at 20, 2 and 0.2 µg/L corresponds to 10⁻4, 10⁻5 and 10⁻6 upper bound risks; if ozone is used, bromate intake could be 120 to 180 µg/day in early estimates (WHO).

Bioaccumulation

Not addressed for bromide or bromate in the sources read; brominated flame retardants bioaccumulate, which is why brominated diphenylethers carry an EU biota standard.

Ecotoxicity

Not addressed for bromide or bromate in the sources read; no US EPA aquatic criterion appears in the table for either.

Flags

• The bromate formation and bromamine equations are stoichiometries written from the EPA pathway figure and WHO text; neither source prints them.
• The HOBr dissociation constant is not printed in the sources read; the pH 8 branch point is stated qualitatively by the EPA manual.
• The 0.18 mg/L bromide threshold is one 1993 study cited by WHO, not a design rule.
• The bromate occurrence range up to 293 µg/L includes laboratory studies at unrealistic bromide.
• The US FGD bromide limit belongs to the voluntary incentives programme and carries compliance dates.
• The WHO supporting document on bromine, iodine and silver as alternative disinfectants was not read; the bromine disinfectant row rests on the element entry.
• No GCC discharge standard lists bromide or bromate; the row records the absence.

Gaps

• No bromide concentrations in municipal or industrial wastewater were read; only the FGD bromide limit.
• The HOBr pKa, the ozone and hydroxyl radical rate constants and the bromate formation models (von Gunten) were not read; the EPA manual cites them.
• No bromide removal process was read; reverse osmosis and anion exchange are named by analogy only.
• EPA 300.1 preservation and the bromate MDL table were not extracted from the method text read.
• The EU total THM parametric value and the US TTHM MCL were not transcribed here; they belong to the chlorine entry.
• The WHO bromine disinfectant document and the WHO reference numbers of the bromate and bromide background documents were read from the file headers only.
• Other GCC discharge standards were not read.
• The bromate, bromide and bromamine equations added here are electron balances written from the pathways the WHO background document describes in words; no rate constants or yields were read.
• No balanced equation is written for the bromination of natural organic matter to bromoform and the brominated acetic acids: natural organic matter has no formula and no source read prints a model compound stoichiometry.

Sources

Identity

Name and symbol

Bromine, Br

Atomic number

35 protons

Position

group 17 · period 4 · p-block · diatomic nonmetal

CAS number

7726-95-6

Atomic structure

Atomic mass

79.904 u

Electron configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵
[Ar] 4s²³d¹⁰⁴p⁵

Electrons per shell

2, 8, 18, 7

Valence electrons

7 outer shell

Physical properties

State at room temperature

Liquid

Melting point

265.95 K (-7.2 °C)

Boiling point

331.95 K (58.8 °C)

Density

3.11 g/cm3

Appearance

reddish-brown liquid

Thermal conductivity

0.122 W/(m·K)

Electrical resistivity

7.8×10¹⁰ Ω·m at 20 °C

Electrical conductivity

1.28e-11 S/m

Crystal structure

orthorhombic

Molar heat capacity

not in sources

Chemical properties

Oxidation states

+5, +1, -1

Electronegativity

2.96 (Pauling Scale)

Ionisation energy

11.814 eV
1st 1,139.9, 2nd 2,103, 3rd 3,470 kJ/mol

Electron affinity

3.365 eV

Atomic radius

empirical 120, covalent 120, van der Waals 183 pm

Ionic radius

Br⁻ 196; Br³⁺ 59 (4sq-coordinate); Br⁵⁺ 31 (3py-coordinate); Br⁷⁺ 39 pm

Reactivity

The only liquid non-metal, a halogen between chlorine and iodine in reactivity: a strong oxidising agent that combines readily with most elements, weaker than chlorine but stronger than iodine.

with water

Dissolves readily in water to a red solution and partly disproportionates to hypobromous acid and bromide: $\ce{Br2 + H2O -> HOBr + H+ + Br-}$, a reversible equilibrium.

with oxygen, air

Does not react with oxygen directly; the oxides and bromates are made by other routes and are strong oxidising agents.

with acids

No reaction with acids; in alkali it disproportionates to hypobromite and bromide: $\ce{Br2 + 2 OH- -> OBr- + Br- + H2O}$.

with halogens

Forms interhalogen compounds with the other halogens, for example bromine trifluoride: $\ce{Br2 + 3 F2 -> 2 BrF3}$, and bromine pentafluoride BrF5.

Typical compounds

• HBr hydrogen bromide hydrobromic acid; source of inorganic and alkyl bromides
• AgBr silver bromide light-sensitive salt of photographic film
• KBr potassium bromide historic sedative, infrared optics
• BrF₃ bromine trifluoride interhalogen fluorinating agent
• NaBrO₃ sodium bromate bromate oxidising agent
• C₂H₄Br₂ 1,2-dibromoethane organobromine; flame retardants use most bromine

Occurrence, production and use

Crustal abundance

2.4 milligrams per kilogram

Oceanic abundance

6.73×101 milligrams per liter

Occurrence and sources

A member of the halogen group, bromine is obtained from natural brines from wells in Michigan and Arkansas. Some bromine is extracted today from seawater, which contains only about 85 ppm.

• bromide in seawater about 65 parts per million, an estimated 100 trillion tonnes; recovered as a co product of solar salt
• bromide in evaporitic lakes and underground brines the Dead Sea (Israel, Jordan; about 1 billion tonnes of bromine), petroleum associated brines in Arkansas and Michigan, brines in China

Extraction, production

Chlorine displacement from bromide brine

$\ce{2 Br- + Cl2 -> Br2 + 2 Cl-}$

Balanced from the reactants and product stated by the RSC account of Balard's discovery (chlorine passed into concentrated brine liberates bromine), with chloride as the only possible co product; the same displacement, followed by steaming out and condensing the bromine, is the industrial route from Arkansas and Dead Sea brines. The RSC also describes extraction by electrolysis. World production about 400,000 tonnes in 2024 (estimate) excluding the United States.

Bromine recycling from hydrogen bromide

Hydrogen bromide emitted as a by product of organic brominations is recycled with virgin brine as a source of bromine; the OFC BREF lists recovery of bromine and HBr from exhaust gases as a technique. No reaction is stated.

Uses

Elemental bromine is a hazardous material. It causes severe burns when it comes in contact with the skin and its vapor irritates the eyes, nose and throat. Most of the bromine produced in the United States was used in the manufacture of ethylene dibromide(C2H4Br2), a chemical added to leaded gasolines that prevented the accumulation of lead compounds within the engine. With the discontinuation of leaded gasolines in favor of unleaded gasolines, the demand for bromine has been greatly reduced. Silver bromide (AgBr), a chemical used in photography, now accounts for the largest use of bromine. Other bromine compounds are used in fumigants, in flameproofing agents and in some compounds used to purify water. Tyrian purple, an expensive purple dye known to ancient civilizations, was produced from an organic bromine compound secreted from a sea mussel known as the murex.

Bromine is used in making fumigants, flameproofing agents, water purification compounds, dyes, medicines, sanitizers, inorganic bromides for photography, etc. Organic bromides are also important.

• Flame retardants and plastics: brominated flame retardants (tetrabromobisphenol A, decabromodiphenyl oxide and others) in electronics casings, furniture foam and construction plastics; bromine in recycled plastics tends to be carried into new products brominated flame retardants and clear brine fluids are the leading global applications (USGS, ranking only)
• Textiles: brominated flame retardants applied in flame retardant finishing of cotton, viscose, polyester and other fabrics for upholstery, carpets, curtains and transport; decaBDE and related brominated compounds are discharged from that process (Textiles BREF)
• Oil and gas: calcium, zinc and sodium bromide clear brine drilling and completion fluids, for which there is no comparable substitute in well completion and packer applications
• Chemicals: bromide in salt and brine is oxidised in chlor-alkali cells to bromate, a compound of the chlor-alkali chapter; bromine impurities in cell room chlorine give brominated by products in EDC direct chlorination unless purified liquid chlorine is used (LVOC BREF); brominated intermediates, dyestuffs and agricultural chemicals
• Pharmaceuticals and fine chemicals: bromine as a halogenating agent in fine chemical synthesis, used less than chlorine because of its price; recovery of bromine and hydrobromic acid from exhaust gases
• Food and beverage: brominated vegetable oil (E443), used since the 1920s to stabilise fruit flavour oils in beverages at up to 15 parts per million; the United States FDA revoked its authorisation in July 2024 because a safe dietary level could not be established
• Water treatment and batteries: bromine compounds for water treatment and sanitation, where chlorine and iodine can substitute; zinc bromine flow batteries, from which bromine is fully recoverable; silver bromide in photography

Safety, toxicity

not in sources

Discovery and name

Discovered by

Antoine Jérôme Balard and Carl Jacob Löwig

Discovered

1825

First isolated

not in sources

Named by

not in sources

Origin of the name

from Ancient Greek βρῶμος, 'stench', for its sharp and pungent smell

Bromine is the only nonmetallic liquid element. It is a heavy, mobile, reddish-brown liquid, volatilizing readily at room temperature to a red vapor with a strong disagreeable odor, resembling chlorine, and having a very irritating effect on the eyes and throat; it is readily soluble in water or carbon disulfide, forming a red solution, is less active than chlorine but more so than iodine; it unites readily with many elements and has a bleaching action; when spilled on the skin it produces painful sores. It presents a serious health hazard, and maximum safety precautions should be taken when handling it.